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Publication numberUS3543291 A
Publication typeGrant
Publication dateNov 24, 1970
Filing dateFeb 17, 1967
Priority dateFeb 17, 1967
Publication numberUS 3543291 A, US 3543291A, US-A-3543291, US3543291 A, US3543291A
InventorsJack Z Gilfert
Original AssigneeBolls & King
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Photolithography
US 3543291 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

Nov. 24, 1 970 WANSM/Tm/VCE z. GILFERT 3,543,291

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WAVE LENGTH '//V M/LL/M/(POA/S' INVENTOR. JACK z. G/L FEET POM l m; /(/V0.8BE a Mnleravs United States Patent 3,543,291 PHOTOLITHOGRAPHY Jack Z. Gilfert, Carmichael, Califi, assignor to Bolls & King, a limited partnership Filed Feb. 17, 1967, Ser. No. 616,970 Int. Cl. G03f 7/02 US. Cl. 96-33 10 Claims ABSTRACT OF THE DISCLOSURE A planographic, single emulsion, monochromatic, fine silver halide grain, high contrast, non-ultraviolet transmitting photographic film for use when color developed and fixed in exposing ultraviolet sensitive photomechanical reproduction plates, and a method of preparing such films by color coupler development of azomethine dyes in silver salt grain gelatin emulsions.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to photographic films and to methods of preparing and using high contrast, graphic arts, photographic films in the preparation of plates for photomechanical reproduction.

DESCRIPTION OF THE PRIOR ART In lithographic and gravure processes of printing, an exposed and developed photographic film is utilized to prepare a printing surface to receive ink that is mechanically transferred directly or indirectly to a paper surface.

Printing plates are composed of a base material which may be metal such as aluminum or zinc, or paper or other supports, depending upon the final use, and contain coatings which are sensitive to light mainly in the ultraviolet (300 to 400 m and somewhat in the blue visible (400 to 500 mg) ranges of the spectrum. Typical coatings are bichromated albumin or gum arabic or diazo-sensitized coatings such as a water soluble resin formed by the reaction of diazo-diphenylamine and formaldehyde. When these plates are exposed to a lamp which emits a substantial amount of ultraviolet light such as an arc lamp, the exposed portions are activated and can then be hardened by development.

Portions of the surface of the printing plate when properly treated either absorb greasy inks or repel them and the plate has no ability to distinguish or print gradation of tone. The ink goes down on the paper following the same all-or-nothing principle. Therefore, reproduction is limited to copy having no intermediate tones. In line copy, lines, spots, type and other high density deposits form images by contrast between the paper and the printed copy. A uniform amount of ink is deposited on the paper by the printing surface wherever the plate bears an image, and the paper remains'clear wherever there is no image.

This same principle is adapted to produce images appearing to have tonal gradations from white to black. Continuous tone copy having intermediate tones of gray can be photographically transformed into a series of dots in which the dot pattern creates the impression of an intermediate tone. Each dot is not discernible to the naked eye and is surrounded by a clear area. When the image is printed, the dots and white paper between the dots fuse visually and the eye sees intermediate tones. These dots accept ink according to the same all-or-nothing principle. Thus, the cameraman can break up a continuous tone original into a half-tone interpretation that can be printed.

Many special effects can be obtained. In the tone-line process a registered negative and a positive of nearly equal contrast of a continuous tone image are combined with the positive as a mask and a print is made on a high contrast film. A line positive is produced which simulates a pen-and-ink drawing. Shadow and detail such as stippling or hand painted dots can be added to the positive.

In printing, a copy is translated to a form which will permit the press to reproduce the original as closely as possible. In the translation of the original copy to its final printed form, numerous intermediate steps are necessary, each contributing to the progress of the work. The five steps are generally (1) camera work, (2) art work, (3) stripping, (4) plate making, and (5) press work.

The camera work depends on the copy received. It can be single color copy or multi-color copy and these may be subdivided into line or half tone. When there is a definite black and white or its equivalent of solid contrasting elements making up a copy similar to that found in type, lettering or any other copy that is produced in full strength ink strokes of whatever ink, that copy is said to be line work, whether or not it contains half tone dots. Any copy that can be reproduced without the aid of a half tone screen, can be called line copy.

Each surface that makes up the image, whether minute or large, Whether pinpoint dot or solid area, carries the same strength of ink. The illusion of the various tones present in a regular continuous tone photograph, is accomplished by breaking up the image into dots of varying size but of equal true density. The size of a particular dot depends among other things upon two main factors: (1) amount of light reflected from the copy, and (2) the kind of screen used between the light source and the photographic plate or film. The ratio of the dot size to the white surrounding it determines the value of the apparent tone. The equal true density is effected by use of high contrast film that is processed to an even density of gray in all exposed areas.

There are many types of screens such as circular, irregular design, lenticular and grain. The most widely used, however, is the half tone screen consisting of a series of parallel opaque lines. The lines are usually exactly as wide as the spaces between them and come in series of 60 lines to 300 or more lines per inch. As the dots become more numerous and the spaces between them smaller, it becomes harder to print because the white portions are harder to keep on the press. Consequently, and 133 lines screen are most popular in lithography. They give the best rendition with the least trouble.

To obtain the dot formation in the negative or positive, the half tone screen can be introduced in the camera while making the exposure or in the vacuum frame while making a contact. In the camera the screen is placed just before and parallel to the light sensitive emulsion and between it and the lens. In the vacuum frame process the screen or a copy of it is placed between the continuous tone negative or positive and the photolithographical emulsion, with emulsion side of the screen copy down.

During exposure a reversal takes place in that the light rays alfect the sensitive emulsion in the clear areas of the 3 negative. This forms a latent image made visible by development. The portions unaffected by light dissolve away in the fixing process. These clear sections actually represent the work or image.

Color reproduction is made possible due to the ability of a plurality of superimposed monochromes to reproduce all colors. In the commonly used methods of color printing, color separation negatives are made by use of filters or mask and these are converted to half-tones which the press can print. It is possible to form the separation half-tone directly by a step known as direct screening.

The preparation of a printing plate from a single negative or positive film is a simple procedure which can be either by direct contact or projection exposure. However, when a plurality of films are layed out adjacent one another, such as different lined screened half-tones or superimposed such as during surprinting of detail or lettering or in color separation printing, it is extremely difiicult to assure perfect register of the dot patterns.

High contrast photographic film is transparent in the printing areas and contains opaque black silver in the nonprinting areas. The complete opacity of the latter areas and the inability to see through the dot areas on the layout table even with illumination has added substantial complexity and risks of error to layout procedures. In the case of color work where exact registration is essential in order to avoid blurred dot patterns or the moire effect, it has been found necessary to place color registration marks on the original art work which are reproduced on each of the color separation negatives and on the corresponding half-tones. Even so, if the registration marks have any breadth to them at all, the registration of the half-tones can be olf and the final printing plates burned from these half-tones would not produce a satisfactory print. Furthermore, in stripping a half-tone film to a line film in proper position, a considerably larger cutout has to be made in the line film, before the half-tone is entered and taped into position. The half-tone can easily shift position again ruining the final printing plate that is prepared from this layout.

SUMMARY OF THE INVENTION In accordance with the invention, the limitations of working with a film having opaque areas are substantially eliminated and the modified film of the invention, produced in an efiicient and controllable manner, allows much more flexibility in preparing plates for photomechanical reproduction. The opaque black silver nonprinting area, i.e. the completely opaque areas and the halftone dot areas of the high contrast film, are converted according to the invention into dyed transparent areas of a pronounced color which do not allow transmission of any significant amounts of the ultraviolet and blue wavelength light that exposes and initiates the hardening of the sensitive coatings of photon-rechanical reproduction plates. As compared to the irregular and fuzzy silver opaque areas, the corresponding dyed areas of the invention allow at least as good resolution since the dye molecules are more finite and give a more definite record facilitating alignment of the now pronounced colored dot patterns.

Perfect register in any close register work whether in abutting relation or in superposed relation, becomes much simplified since the operator can now see through the formerly opaque areas and with the aid of magnification can adjust the relationship of the films to the exact desired position. This is all done much more efiiciently and easily than with the former black images. Then by the use of a punch, mating holes are placed in all negatives in at least two positions and accurate registration on the plate is guaranteed by use of these mechanical registering means during exposure.

In the stripping of one film to another, the transparent high contrast film can be placed in its correct position on the line work initially, and the cutout can then be made to exact measurements eliminating shifting or other changes and allowing for a smaller cutout. Even in the layout of a single film to a masking sheet, the operation is much simplified since the operator can at all times view exactly what is being done since more light passes through the film to the masking sheet allowing easier viewrng.

With a transparent high contrast film, a design can be repeated on a plate by a step-off repeat process much more accurately than before since registration marks on the plate will be visible through the film and allow exact and speedy placement to be effected without expensive special equipment formerly required. Forgotten or correction detail or forgotten half-tones can be added to an exposed or finished plate that formerly would have to be discarded. The exposed and developed sensitized coating can be honed ofi in the error area and resensitized by means of a wipe-on sensitizing liquid, and then the transparent high contrast film can be visually placed in exact position on the plate and the plate exposed and developed in the usual manner, thus saving an otherwise useless plate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a series of graphs showing the percentage transmission of radiation as the ordinate versus the radiation wavelength as the abcissa for a typical yellow dye, magenta dye, and a combination of yellow and magenta dyes.

FIG. 2 is a vertical section of a film which forms part of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preparation of the colored, transparent, high contrast film according to the invention, makes use of materials and processing techniques familiar to the printing industry. The films are produced by photochemical processing of high contrast graphic arts photographic films. These films are special materials typically reserved for making line or screen negatives or positives. Line or litho-film is clearly distinguishable from continuous-tone film in several particulars. Litho-film has a steep low-to-high density characteristic sensitometric curve (i.e. density versus exposure) which is responsible for the clear black and white definition between line and half-tone dots versus clear background. These films are described, for example, on page 12 of Films and Plates for the Graphic Arts, Kodak Graphic Arts Data Book Q-2, Eastman Kodak Company, 4th Edition, 1961:

The angular slope of such almost vertical line-film sensitometric curves is of the order of about 75-85 degrees, more or less, on graphs plotting density units (ordinate) as a function of the logarithm of exposure (abcissa), with the units of density and exposure having the same scale. Typical curves of this character are presented, for example, on data sheet D4 of the said book.

Continuous-tone film, on the other hand (page 10 of the said Data Book), generally has an angular slope in its sensitometric curve that is much less steep, of the order of about 30 to 45 degrees, more or less, in the initial portion thereof. Reference may be made, for example, to data page D-19 of the said book. Other well-known characteristic difference between line and continuous-tone film are the following:

Line film: Continuous-tone film: Generally orthochromat- Generally panchromatic ic.

Maximumgamma generally about 1 to 2. Maximum density generally about 1.5 to 2.

High-speed emulsion.

The sharp cutoff high contrast charcteristics are provided in these films by the nature of the silver halide grains. The grains in a high contrast film are very small, typically averaging less than 0.3 micron and usually averaging about 0.1 micron in a very small size distribution. The silver halide grains in continuous tone films are much larger, of the order of an average of 3 to 5 microns, and are distributed over a large size range. The smaller grain emulsions are slower speed and are not sensitive to low intensity light. These emulsions are developed with energetic developers. An important characteristic being that the high contrast films develop to an image of even tonal density. That is, each dot or line will be of even blackness or density and will absorb light equally. There is an absence of tonal gradation in the final exposed and developed film.

Several present day commercial examples of line film are those sold under the trademark Kodalith Ortho- Ester Base (Eastman Kodakdata pages D-9 through 9-17 of the said book); under the trade name Reprolith (Ansco); under the mark Photolith (Du Font); and under the name Process Extra Ortho (Gevaert).

The plate developing wavelengths that should not be transmitted substantially are those from just below visible to slightly above visible from about less than 500 millimicrons to about 300 millimicrons with more extreme sensitivity in the range of 350450 millimicrons. On exposure of the sensitized plate to ultraviolet light, only the film areas absent opaque silver transmit this light and are hardened by photochemical action. The black opaque areas prevent the transmission of light by absorption. The present invention is based on providing materials that prevent transmission of light capable of activating development of presensitized printing plates but yet allow transmission of the remaining visible light.

According to the invention, the reduced black silver in metal form is converted to organic stable dyes having the characteristic of preventing transmission of light that would expose the plate.

By reference to FIG. 1 which is a series of graphs of the percentage transmission of radiation as ordinate versus radiation wavelength as abscissa for a typical yellow and magenta dye and their combination, it can be seen from Curve A, which relates to the transmission of a typical yellow organic dye, that this dye substantially prevents transmission of more than 10 per cent of the short wavelength ultraviolet and blue light of concern. Curve B illustrates the transmission characteristics of a magenta dye, and Curve C is a combined characteristic of the two which would in essence be an orange-red to red dye. This is in reality of subtractive method of color mixing and Curves A and B represent the transmission curves of a yellow and magenta filter respectively. When these two filters are inserted in a beam of white light from a projection lantern, a fraction of the incident light is absorbed or reflected as the light passes through the first filter and the remaining light then passes through the second filter where this fraction is again filtered and the fraction of the fraction is what is transmitted. Thus, at 500 m percent of the incident light is transmitted by the yellow filter, and 11 percent of this fraction is transmitted by the magenta filter. Hence, Curve C, the transmittance of the combination, is found by multiplying the transmittance curves of the filters together at each wavelength. The final result is the same whether the filters are in adjacent relationship or color bodies which act as the filters are intimately mixed in a transparent support such as the photographic emulsion of the present invention.

The suspended particles of dye behave like tiny filters in the path of the light rays entering the support or vehicle. Since the light rays pass through both yellow and magenta filters before being reflected from the top surface or penetrating and leaving the bottom surface, the effect is the same as that produced when the yellow and magenta filters are placed in series in the path of a light beam. Nonprinting areas of the plate are not exposed and hardened if less than 20 percent of the projected radiation in the 300 to 500 m range is transmitted, and preferably less than 10 percent of this radiation is transmitted in the 350 to 450 m range.

The yellow dye alone sufiiciently inhibits transmission of substantial ultraviolet and blue light. However, by reference to Curve C, it is apparent that the combined characteristics of the two dyes are much more etfective in transmitting less light in the desired range and the redorange dot patterns are much more pronounced and evident against a clear background as compared to the corresponding yellow dot patterns. However, substantial light above 500 millimicrons is still transmitted so that dots and lines of distinct color are still sufficiently trans parent to allow superimposed viewing during alignment and registration.

The conversion of the silver image whether in latent or exposed form is accomplished according to the invention by dye coupling color development of silver salts. Certain difunctional aromatic amines when present during the development of silver will couple with the reduced silver to simultaneously form an insoluble dye image which remains when the silver is removed from the emulsion to leave a transparent dyed area. As the production of dye is directly connected with the reduction of silver, the dye will form a positive image, the intensity of which is related to the concentration of reduced silver.

There are two basic types of coupling developers, derivatives of p-phenylenediamine and derivatives of paminophenol both coupling at the amino group so that the amino group in the aminophenol developers and one of the amino groups in the p-phenylenediamine developers must be unsubstituted.

There are also two general types of couplers, hydroxyaromatics such as phenols or naphthols and materials containing an active methylene group (O=CCH C=O). A phenylenediamine couples with the phenol to form an indoaniline dye, a p-aminophenol derivative couples with the phenol to form an indophenol dye and the dyes formed when either developer couples with an active methylene group are called azomethine dyes. The phenol or naphthol couplers form dyes which generally absorb light in the red end of the spectrum, thus reflecting and transmitting cyan or blue wavelength lights, the opposite of the intended eflect of the invention. Couplers which are pyrazolones, cyanoacetyl compounds and derivatives of p-nitrobenzylcyanide when coupled with diethyl-p-phenylenediamine form dyes with the major absorption of radiant energy in the green region of the spectrum, thus leading to magenta or orange dyes. A few of the better known couplers are shown in the following table.

TABLE I 1-p-nitrophenyl-3-methyl-5-pyrazolone 1-phenyl-3-methyl-5-pyrazolone p-Nitrobenzylcyanide Benzoylacetonitrile Napthoylacetonitrile Couplers with the active methylene group between two C=O groups give dyes mainly absorbing blue wavelength light and thus are yellow or orange. A few of the better known couplers are shown in the following table.

TABLE II Ethylacetoacetate Ethyl benzoylacetate Acetoacetanilide p-Napthoylacetone Diethyl malonate Thus, the yellow, orange or magenta dyes are of the azomethine type.

The p-aminophenols developers and the substituted dcrivatives thereof have not been used much in practice because of solubility and instability the dyes formed from these developers. The most important developers used for coupling are the substituted p-phenylenediamines. These may have one or both of the hydrogen atoms on one of the nitrogens substituted by lower alkyl, aryl or substituted lower alkyl such as the groups:

where R is alkylene or arylene, R is hydrogen or lower alkyl and n is 1-5. The benzene ring may also carry similar substituents such as lower alkyl. Typical p-phenylenediamine derivatives useful as the color developers of this invention are p-toluenediamine, di-methyl-p-phenylenediamine, diethyl-p-phenylenediamine and 2-amino-5- diethylaminotoluene. These developers are sometimes marketed as an acid addition salt such as the hydrochloride.

The invention may be practiced with the silver salts of the emulsion in an exposed latent image form or in an exposed and developed form. In the latter case, it is required that the silver be returned to a salt which is reduceable by color developing reducing agents. The color developing agents may be in a processing solution or may form a part of the photographic emulsion.

In the instance where the silver is in a reduced, developed form, the material to be processed is a previously exposed high contrast material discussed above, such as a half-tone or line film made by any of the multitude of graphic art processes whether of the one, two, three or four multiple step procedures for preparing a line or half-tone image in a high contrast film in a form suitable for exposure of a presensitized printing plate. For example, a line positive can be made on a suitable commercial film such as Kodalith Orthofilm Type 3, according to the procedure set forth in the pamphlet entitled Kodak Tone-Line Process, Kodak Pamphlet No. Ql8 (1963), or a half-tone can be made on the same film according to the procedure disclosed in Kodak Publication Q1 entitled Basic Photography for the Graphic Arts. The film could be made with many of the other materials available on the market, and it could also be made with self-masking or autoscreen type of films. The manner of exposing and developing the high contrast film follows procedures Wellknown in the art, that are not important to the invention except that recommended procedures should be observed in order to prepare a high quality, high contrast developed film of good rendition and resolution. The black and white high contrast developer can be any of the high energy solutions normally utilized, such as hydroquinone, hydroquinone-paraformaldehyde, hydroquinone-metol or the metol type.

In order to practice the rebleach process, the silver in metallic form must be converted to a reducible salt form. The silver salt in the film is then subjected to color development in presence of a color developer and dye coupler and finally the silver is removed without affecting the stable and insoluble dye images that have been formed. The product will have evenly colored areas of equal density, hue and saturation in the areas formerly occupied by the completely opaque silver. If the density of the dye image is not believed sufficient, the image can be intensified by a repeat of the process.

The oxidation of the metallic silver can be by any of the oxidation agents known to be useful in the photographic art such as those containing cupric ion, ferric ion or ferricyanide ion such as cupric halides, e.g. cupric bromide chloride, cupric sulphate or nitrate, ferric chloride, bromide or sulphate, ammonium citrate or an alkali metal ferricyanide such as sodium, potassium or ammonium ferricyanide and the like. Since dye is not present in the initial stage of the process, fairly vigorous oxidizing agents such as acidified potassium bichromate, or potassium permanganate can be utilized. The latter two oxidizing agents are not preferred because of the tendency to stain or weaken the physical characteristics of the emulsion.

Since the purpose of the oxidation is to return the silver to a reducible salt form, and not necessarily to a photosensitive form, it is not essential that a halide be present in the bleach bath, though typical commercial photographic bleaches are a combination oxidation-rehalogenation type of compositions containing an alkali metal halide such as a combination of potassium ferricyanide and potassium bromide. Conversion of silver to a halide form is preferred since it is compatible with the color developing compositions utilized in the process and formation of insoluble silver bromide propels the bleaching reaction to completion.

The color developer as previously discussed, is a combination of a developer and coupler portion. Because of instability of this developer, it is normally prepared within a short time before use by combining separate solutions of the developer and coupler. This solution usually contains additional ingredients such as an alkali to dissolve the coupler and to activate the developer and a buffer to preserve alkalinity. A small amount of sulphite acts as a preservative and bromide ion restrains development. Frequently an additional organic antifoggant such as benzotriazole is present. In some cases an organic solvent is used instead of or in addition to alkali to dissolve the coupler. Temperature during development should be kept constant, usually about 68 F., and more uniform contrast is obtained in a shorter time when the bath is agitated.

The removal of the reduced silver and any residual halides remaining after color development requires two operations: (1) fixing, the conversion of the silver into water soluble compounds such as halides, and (2) washing to remove these compounds. Although there are a number of solvents for silver halides such as lithium or guanidine thiosulfate, potassium cyanide, thiourea, potassium or ammonium thiocyanate, only sodium and ammonium thiosulfate are in widespread use. The life of the fixing bath is sometimes diminished by carry over of developing solution. This may be prevented by use of a stop bath between developing and fixing or by addition of a developer stopping agent to the fixing bath.

The following is an example of a preferred procedure to be followed in the rebleach process of color developing a previously developed black and white high contrast film.

Example I (1) Softening of emulsion.The black and white developed and fixed film if dry is placed in water in a tray or under running water for about two minutes.

(2) Bleach of silver.-The film is then bleached from black to white in the opaque areas represented by silver dots or lines by a bleach bath consisting of equal amounts of potassium bromide and potassium ferricyanide dissolved in water. Within approximately one to two minutes, the silver is converted to silver bromide. Care is taken that the silver is completely bleached by inspection of both sides of the film.

(3) Wash film in running water for 15 seconds.

(4) Color development.Place film in color developing bath and agitate during the first one to two minutes. Allow the film to completely redevelop for approximately 57 minutes, inspecting the nonemulsion side of the film to assure it is practically as dark as the original black and white film. Developing time must be extended with developer that has been mixed and used for over one hour. The composition of this developing bath will be described later.

(5) Rinse film in running water for approximately 15 seconds.

(6) Rebleach of film.Return film to bleach bath of step 2 for approximately 15-40 seconds to again oxidize the silver to silver bromide. If the color intensity is not sufficient, steps 3-6 are repeated at this time to intensify the color.

(7) Rinse film in running water for about 5 seconds.

(8) Fixing of film.Place film in fixing bath consisting of sodium thiosulfate solution in water until all visible traces of residual silver have been eliminated and a clear dye image remains. If residual traces of silver remain after one minute, rinse and return to the bleach bath for a short time and rinse and refix.

(9) Rinse film in running water for one to three minutes.

(l) Drying of film.-Dry film in air and optionally with the use of mild heat.

The color developing solution is made in several parts as the keeping qualities are not good and activity decreases after the components are combined. The first part of the color developing solution contains sodium sulfite as an antioxidant, sodium carbonate as an alkali and potassium bromide as a restrainer in the following proportions:

Working solution A:

Water (distilled)-32 oz. Sodium sulfite3 oz. Sodium carbonate3 oz. Potassium bromide-1 gram The second part contains a color developing portion, and two separate color forming solutions, a yellow color former and a magenta color former.

Developer solution B:

Iisopropyl alcohol (70% v.)l.5 oz. 2 amino diethyl aminotoluenemonohydrochloride1.75 g. Acetone-0.5 oz.

Magenta color former solution C:

P-nitrophenyl acetonitrile-0.4 g. Acetone-.1 oz.

Isopropyl alcohol (70% v.).1 02.

Yellow color former solution D:

Acetoacetanilide4.2 g. Isopropyl alcohol 70% v.)-1 oz. Acetone-1 oz.

The dry chemicals in Solutions B, C and D are dissolved in the first organic solvent with mixing and the second listed solvent is then added. The color former Solutions C and D are first mixed together with vigorous shaking and then are combined with Solution B. Six parts of Solution A and 48 parts of water by volume are then combined with one part of combined Solutions B, C and D. The mixture is mixed Well and aged 1-2 minutes before use.

An alternative procedure would be to bleach-rehalogenize according to steps 1-3 and then color develop with developer solution and one coupler, and then rebleachrehalogenize, color develop With the second coupler and complete the bleach-fix silver removal. This would double the amount of dye formed. The preferred color is obtained in either case with a weight ratio of yellow to magenta of about 10 to 12 to 1.

The film of Example I is now a deep orange-red of the same hue, brightness and saturation in all the former black opaque silver areas. A set of four color separation black and white high contrast transparencies are processed according to the procedure of Example I to deep orange-red transparencies, and are registered, a

series of holes are punched into the perfectly registered set. The separation films are separated and three registered printing plates are prepared therefrom by placing them in contact to a presensitized diazo plate and exposure to a high intensity carbon arc at a distance of about twenty inches for 1-3 minutes. The plates when developed and worked up with water and gum are completely unexposed in the corresponding red-orange areas of the film and print a perfectly registered image.

Two different fine screen half-tones are processed according to Example I and are registered on a stripping table by superimposing and overlapping the dot patterns of a portion of the films. The registered layout when utilized to expose and develop a plate exhibits perfect register and blending of the dot patterns on printing.

A surprint film with added shadow detail and the base image half-tone film are each processed according to Example I. The surprint is superimposed and registered to the base film on a stripping table by observing the transparent red-orange image of the base film. The surprint film is then taped to the base film and the ultraviolet opaque area of the base film corresponding to the surprint is cut out. The plate prepared from the assembled registered layout is perfect. The plate could have been prepared from the base film alone and before developing the plate it could have been re-exposed to the surprint or to the assembled registered combination to add the forgotten or later desired detail of the surprint.

With respect to the alternative process in which the latent silver halide image areas of the exposed high contrast film are directly color developed, it must be realized that the emulsion itself is slow speed and the aromatic diamine developer is a Weak developer. For this reason, the exposure is increased to approximately twice normal when this process is utilized. With such an exposure to a half-tone or line image, the high contrast film can be developed according to the procedure of Example I to a red-orange negative transparency of the same characteristics. The softening, bleaching and washing steps 1-3 are not necessary in this procedure, and this process eliminates the necessity of prior black and white development. When a stronger caustic such as sodium hydroxide is added to the color developer or substituted for at least part or all of the sodium carbonate, the developing action is more intensified and vigorous.

The process can be further simpliled by incorporating some of the color developing ingredients directly into the emulsion. This avoids the storage of some of the unstable chemicals and the requirement to mix them immediately before use and discard after a short usage. Furthermore, with a direct color developing film the procedure can be standardized and the technician will become educated and familiar with the capabilities and the uses of a single, versatile material, rather than to have to work with separate materials that are processed in different manners with dilferent reagent solutions.

By reference to FIG. 2, it is observed that the film of the invention comprises a transparent support 3 on which is coated a photographic emulsion 4 containing an intimate dispersion of a color coupler and intimately dispersed, finely and evenly divided grains 5 of silver halide. The transparent support may be polystyrene, a polyester such as polyethylene terephthalate or a cellulose ester.

A coupler can be immobilized in the emulsion by the attachment of large organic groups to the basic coupler structure or the coupler can be dispersed throughout the emulsion in an oily, organic material. The large organic group should not interfere with the color coupling capacity of the coupler. A typical immobilized yellow coupler is m-stearoyl-aminobenzoylacetanilide p carboxylic acid and a typical magenta coupler is 1-(5'-sulfo- 3-stearoylaminophenyl)-pyrazolone sodium. The coupler solvent employed for dispersing a coupler in the emulsion is not especially critical and can be selected from substantially water-insoluble low molecular weight organic crystalloidal materials having a boiling point above about 175 C. disclosed for example in US. Pat. No. 2,322,027. There are other coupler solvents known in the art. Suitable specific solvents are the lower dialkyl phthalates such as dibutyl phthalate.

The following is a typical procedure for forming a non-relieved i.e. planographic, single emulsion, monochromatic, transparent film of the invention capable on color development of transmitting radiation other than radiation of wavelengths of from 300 to 500 millicicrons, and especially of from 350 to 450 millicrons. To a high contrast gelatin emulsion containing a dispersion of substantially even grain silver halide of less than about 0.3 micron average diameter, is added a dispersion of a water immiscible organic solvent solution of at least one coupler capable of color development in the presence of silver halide to an ultraviolet absorbing, but otherwise transparent dye image. The high contrast emulsions contain from 40 mol percent chloride and 60 mol percent bromide to 90 mol percent chloride and 10 mol percent bromide. The emulsion can also contain small amounts of from 1 to 2 mol percent silver iodide. Alternatively, the color coupler can be in the form of a layer adjacent the silver halide emulsion layer.

The following is a disclosure of an embodiment of the novel film of the invention.

Example H A high contrast 0.1 micron average fine and even grain silver chloro-bromide emulsion in gelatin is prepared according to the procedure of the examples of U.S. Pat. No. 2,756,148. A molar equivalent amount with respect to silver of the color couplers of Example I of this disclosure in dibutyl phthalate is intimately dispersed throughout the emulsion. The emulsion is coated on a transparent support and when dry is exposed to a transparency at double the normal exposure for the corre sponding black and white high contrast film. The exposed film is then processed With a mixture of Solutions A and B of Example I diluted with the proper amount of water, and developed for 4 to 6 minutes. The film is then processed according to steps 4-10 of Example I to yield a red-orange transparent film of even density saturation and hue which is of the same quality as the high contrast films made by Example I or the direct color development procedure of the present disclosure.

Again, in this procedure, the stain of the background can be reduced and the development power of the developer boosted by substituting sodium hydroxide for at least part of the sodium carbonate. The exposed film may be subjected to non-color developing black and white high contrast development before color development. In the latter case, the emulsion is fixed and bleached before color development and the exposure time can be the normal exposure for the corresponding black and white high contrast film of equal characteristics. An anti-halation layer behind the emulsion and an outer anti-abrasion layer may be provided according to procedures well known in the art.

In the exposure and processing of deep-etch type of photomechanical sensitized reproduction plates such as the S series of the 3M Company, the plate is exposed to a positive rather than a negative high contrast film. In making this positive according to prior procedures, it is necessary to expose the original copy to a sheet of film in the camera, develop the film to a negative. A positive is then prepared by placing the negative in contact with another sheet of film, exposing through the base of the negative to effect lateral reversal and then developing the positive. The negative could be exposed through the base to obtain lateral reversal, developed and then placed in contact with another sheet of film, emulsion to emulsion, exposed and developed to obtain a correctly reading positive. In the lateral reversal technique a slight degree of sharpness of 12 the overall printing positive is lost unless an additional generation of reversal is carried out.

The present invention includes within its scope a method of preparing such positives in which a generation of photographic processing is eliminated, thus making for a more convenient procedure and further assuring a higher resolution, quality product. In such a process direct reversal of camera speed film during processing reverses the negative latent image of an exposed high contrast film to an orange-red high contrast positive eliminating at least one generation of reproduction processing.

In one procedure the color coupler containing single emulsion film of Example II is exposed to a half-tone positive and the negative light-sensitized areas are developed in a non-color developing black and white high contrast developer until development is complete and the action of the developer is then terminated by means of an acid short stop bath. The black and white developed film is then completely exposed to white light which activates the remaining light sensitive non-developed silver halide grains and these grains are then color developed and all the silver is fixed and removed according to the method of Example II. A reversed red-organge half-tone transparency results which is identical in properties to the films produced by the other procedures of the invention.

A reversed film can also be prepared with a black and white high contrast film by exposure of the film to a positive. The exposed film is processed by non-color developing, acid-fixing, re-exposure of the complete film and then color developing and removing all the silver by fixing according to steps 4-10 of Example I.

It is to be understood that the foregoing only relates to preferred embodiments of the invention, and that numerous modifications or alterations are possible without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. The process for preparing a photomechanical plate comprising the steps of: 7

developing with a color coupling dye the silver bearing image areas of an exposed high contrast photographic emulsion to form a color coupled dye associated with the reduced silver;

removing the silver from said emulsion without affecting said dye to form a photographic transparency consisting of clear areas and dye colored areas, the dye colored areas being substantially transparent to visible radiation and substantially opaque to ultraviolet radiation;

placing a plurality of said transparencies in proper registry by superimposing said transparencies, simultaneously viewing the images of said transparencies by visible light and positioning said transparencies in proper relationship;

exposing an ultraviolet sensitive plate through said transparencies individually to a source of sensitizing radiation, said transparencies being placed in rela tive registry during exposure of said plate, whereby the images on said plate are exposed in proper relationship.

2. The process as defined in claim 1 wherein the dye colored areas are a pronounced red-orange of even hue and saturation allowing substantial transmission of radiation of a wavelength above 500 millimicrons, and of a minimum brightness or density to prevent transmission of more than about 10 percent of radiation within the range of 350 milli-microns to 450 millimicrons.

3. The process as defined in claim 1 comprising the additional step of intensifying the dye image by repeatedly bleaching and color developing said image before removing the silver salt from the emulsion.

4. A method of forming an image on a mechanical reproduction plate sensitive to radiation in the range of 13 from 300 millimicrons to 500 millimicrons, comprising the steps of:

superimposing a plurality of high contrast photographic films in which the radiation absorbing areas are silver free and contain a dye which has a substantial transmission above said radiation range and less than 20 percent transmission within said range;

viewing through said plurality of films by means of a source of radiation having substantial emission above said radiation range;

aligning while viewing through said plurality of films to establish the dye patterns in an exact registered relationship;

providing mechanical means for reestablishing said registry between said films; and

interposing said films individually in relative registry between said plate and a source of radiation having substantial emission in the given range, thereby exposing said plate to a plurality of registered images.

5. The method as defined in claim 4 wherein two of said films comprise difierent half-tone image bearing films; said films are overlapped, the dot patterns placed in registry by viewing under illumination the distinct and pronounced colored, partially transparent, dots; the films are attached together before exposing the plate; and the attached films are exposed as an individual film.

6. A method of forming and using a high contrast film containing pronounced red-orange colored, finite and distinct dyed areas of even hue and saturation allowing substantial transmission of radiation of a wavelength above 500 millimicrons, each dyed area being of a minimum brightness or density to prevent transmission of more than about 10 percent of radiation within the range of 350 millimicrons to 450 millimicrons, comprising the steps of:

converting the black opaque silver areas of an exposed, developed and fixed high contrast photographic filmhaving a maximum gamma of 4 to 5 and an angular slope of 75-85 degrees of the sensitometric curve to a reduced silver halide by a bleaching-rehalogenation of said film;

developing the finite silver bromide image areas by means of a yellow color coupler and a magenta color former to form pronounced red-orange image areas in association with reduced silver;

rebleaching and rehalogenating the silver;

converting said silver to a water soluble salt;

removing the water soluble silver salt from the emulsion leaving red-orange image dye areas which allow substantial transmission of radiation of a wavelength above 500 millimicrons and prevent transmission of more than about percent of radiation Within the range of 350 millimicrons to 450 millimicrons;

superimposing a plurality of said films;

viewing said films by means of a source of radiation having substantial emission of a Wavelength above 500 millimicrons;

aligning while viewing through said plurality of films to establish the dye patterns in exact registered relationship;

providing mechanical means for reestablishing said registry between said films; and

interposing said films individually in mechanically fixed relative registry between a mechanical reproduction plate which is sensitive to radiation in the range of 350 millimicrons to 450 millimicrons and a source of radiation having substantial emissions in said range for thereby exposing said plate to form a plurality of images which are in registry on the exposed plate.

7. A method of forming and using a high contrast reversal film containing pronounced red-orange colored, finite and distinct dyed areas of even hue and saturation allowing substantial transmission of radiation of a wavelength above 500 millimicrons, each dyed area being of a minimum brightness or density to prevent transmission of more than 'about110 percent of radiation within the range of 350 millimicrons to 450 millimicrons, comprising the steps of:

1, developing an exposed high contrast black on white film'to form an image of reduced silver; exposing the developed film to white light to form a latent reversal image; developing the reversal image areas by means of a yellow color coupler and a magenta color former to form pronounced red-orange reversal image areas in association with reduced silver;

bleaching the reduced silver image;

converting the silver to a water soluble salt;

removing the water soluble silver salt from the emulsion leaving red-orange reversal image dye areas which allow substantial transmission of radiation of I a wavelength above 500 millimicrons and prevent transmission of more than about 10 percent of radiation within the range of 350 millimicrons to 450 millimicrons; superimposing a plurality of films having image areas which have said transmission characteristics; viewing said films by means of a source of radiation having substantial emission of a wavelength above 500 millimicrons; aligning while viewing through said plurality of films to establish the dye patterns in exact registered relationship;

providing mechanical means for reestablishing said registry between said films; and

in'terposing said films individually in mechanically fixed relative registry between a mechanical reproduction plate which is sensitive to radiation in the range of 350 millimicrons to 450 millimicrons and a source of radiation having substantial emissions in said range for thereby exposing said plate to form a plurality of images which are in registry on the exposed plate. 8. A method according to claim 1, in which the silver in metal form is oxidized and color-developed by a colorcoupling reducing developer and the silver is dissolved and removed by bleaching and fixing.

9. A method according to claim 1, in which latent image areas of an exposed silver halide containing high contrast emulsion are directly color-developed.

10. A method according to claim 1, in which the silver halide emulsion contains one of the color forming reactants.

References Cited UNITED STATES PATENTS 2,312,875 3/1943 Bunting et al. 96-54 2,884,325 4/ 1959 Burgardl et al. 96-54 3,291,603 12/1966 Bryan 96-73 OTHER REFERENCES E. latte, E. Brody, F. Preucil, J. White, Color. Separation Photography, For Offset Lithography, Lithographic Technical Foundation, Inc., 131 E. 38th St, New York, N.Y., 1959, PP. 30-32.

NORMAN G. TORCHIN, Primary Examiner J. E. CALLAGHAN, Assistant Examiner U.S. Cl. X.R. 9631

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2312875 *Apr 27, 1940Mar 2, 1943Union Res CorpColor photography
US2884325 *Mar 3, 1955Apr 28, 1959Agfa AgProcess for the production of a yellow mask image in magenta-colored photographic images
US3291603 *Nov 29, 1963Dec 13, 1966Minnesota Mining & MfgColor proofing constructions and their use
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3772022 *Mar 31, 1972Nov 13, 1973Fuji Photo Film Co LtdDeveloping composition for use with photographic materials for the graphic arts
US3973953 *Dec 28, 1973Aug 10, 1976Xerox CorporationImaging method including exposure of photoconductive imaging member through lenticular lens element
US3973954 *Dec 28, 1973Aug 10, 1976Xerox CorporationImaging method including exposure of photoconductive imaging member through lenticular lens element
Classifications
U.S. Classification430/22, 430/302
International ClassificationG03F1/12, G03F3/10
Cooperative ClassificationG03F3/101, G03F1/54
European ClassificationG03F1/54, G03F3/10A