US 3600166 A
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Aug. 17, 1971 15 ETAL 3,600,166
LITHOGRAPHIC PLATE AND PROCESS OF MAKING Filed July 5, 1967 POL YACRYLA/M/DE /0 W suPP0/?r /4 4 w //A V/ A r//7 MUL5/0/v *POLYACRYLAM/DE SUPPORT ALBERT L. S/EG ROBE)? T N. W 000 WARD IN VENTORS A TTOR/VE Y "United States Patent Ofice 3,600,166 LITHOGRAPHIC PLATE AND PROCESS OF MAKING Albert L. Sieg and Robert N. Woodward, Rochester,
N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.
Filed July 3, 1967, Ser. No. 650,864 Int. Cl. G03f 7/02 US. CI. 96-36;: 17 Claims ABSTRACT OF THE DISCLOSURE A photographic element comprising a support such as paper, aluminum, etc., a gelatin photographic silver halide emulsion layer having a melting point above about 180 F. and adjacent to said layer and between the emulsion layer and the support a non-porous hydrophilic layer such as polyacrylamide, etc., having a contact angle of less than about 65 is used to provide a lithographic printing plate by the etch-bleach process.
This invention is concerned with photographic elements, their preparation and use. In one aspect, this invention relates to an element comprising a support having thereon a hydrophilic layer over which is coated a photographic silver halide emulsion. In another aspect, this invention relates to the formation of a lithographic plate using an etch-bleach process.
It is known that lithographic printing plates can be prepared directly from photographic elements comprising light sensitive silver halide layers. In the past, photographic elements of this type have employed an unhardened silver halide gelatin emulsion layer which is exposed and developed using a hardening developer. This hardening developer hardens the photographic silver halide emulsion in the exposed areas and unhardened areas can then be removed by washing with warm water. The re sulting plate can then be used on a lithographic printing press. However, such printing plates are often subject to extensive abrasion and wear when used on a lithographic press and, therefore, exhibit a relatively short press life. Furthermore, photographic elements in which an un hardened gelatin layer is removed to obtain the printing surface often have a residual gelatin layer on the unexposed areas which accepts ink and causes scumming on the lithographic press. In addition, it has been desired to use metal supports such as aluminum in photographic elements intended for use as printing plates. However, silver halide emulsion layers, particularly unhardened silver halide emulsion layers, often react with metal supports such as aluminum to form a hardened layer at the interface between the metal support and the silver halide emulsion. Accordingly, it has been extremely difficult to obtain a lithographic printing plate in which a photo graphic silver halide emulsion is coated over a metal support such as aluminum.
It is evident, therefore, that a photographic element comprising a silver halide emulsion layer which will form a lithographic printing plate which is not subject to the aforementioned deficiencies would represent a substantial advance in the art. Likewise, a process for the preparation of a lithographic printing plate directly from such a'photographic element would substantially enhance the art.
Accordingly, it is an object of this invention to provide a novel photographic element which is particularly adapted to the preparation of a lithographic printing plate. Another object of this invention is to provide a means for obtaining good quality lithographic printing plates in a Patented Aug. 17, 1971 convenient, economical and rapid manner. It is another object of this invention to provide photographic elements in which a light sensitive silver halide layer is coated over a metal support such as aluminum which elements give good -quality lithographic printing plates.
Another object of this invention is to provide a photographic element which can be processed using an etchbleach solution to obtain a surface exhibiting excellent ink-water differential suitable for inking and printing on a lithographic press. Still another object of this invention is to provide a process for obtaining a surface exhibiting excellent ink-water differential by subjecting a novel photographic element to an etch-bleach process. A further object of this invention is to provide a lithographic printing plate which is particularly adapted to processing by automation. Other objects of this invention will become apparent from an examination of the specification and claims which follow.
In accordance with this invention, it has been found that a photographic element comprising a unique combination of layers having particular properties, as described hereinafter, can be employed as a lithographic printing plate having long press life and exhibiting excellent printing characteristics. In practicing this invention, such elements can be subjected to an etch-bleach solution to obtain a printing surface exhibiting excellent ink-water dilferential.
- One embodiment of this invention relates to a photo graphic element comprising a support, a gelatin photographic silver halide emulsion layer having a melting point above about 180 F. and adjacent to said layer and between said layer and said support, a non-porous hydro philic layer having a contact angle of less than about Another embodiment of this invention relates to a pro cess which comprises imbibing an etch-bleach solution into an exposed photographic element as described herein, whereby there is obtained a surface exhibiting excellent ink-water differential.
The drawing shows one embodiment of our invention.
FIG. 1 discloses a support 10 having thereon a polyacrylamide layer 11 showing a latent image 14in the silver halide emulsion 12.
FIG. 2 shows the same photographic element of FIG. 7 after development with a silver halide developer.
FIG. 3 shows the image areas 14 which have been removed by the etch-bleach step with the unaffected colloid 12 remaining.
In practicing this invention, an exposed and developed photographic element, as described herein, is placed in an etch-bleach bath. A typical etch-bleach bath or solution contains an oxidizing agent such as hydrogen peroxide, an insoluble silver salt former such as chloride ion and a metal ion catalyst such as cupric ion. A gelatin softener such as citric acid and/ or urea is often used in an etch-bleach bath. The etch-bleach reaction takes place in areas where silver has been formed resulting in bleaching the silver image and at the same time degrading or etching gelatin in these same areas. After the image areas are etch-bleached, the undeveloped emulsion remains. If desired, the emulsion can then be re-exposed to regular roomlight and then redeveloped to provide an image in those areas which were not etched. This provides a darkened image area for proofing purposes on the plate. However, the plate can be dried immediately following the etch-bleach operation and inked to provide a darkened image area and run on the lithographic press.
In one embodiment of our invention, an anodized aluminum sheet is used as the support which has been coated with a layer of polyacrylamide in an amount of about milligrams of polyacrylamide per square foot. Over the polyacrylamide layer is coated a high contrast projection speed silver halide emulsion which is exposed to a light image and developed in a developer such as Kodak Developer D-19. Following development, the silver halide emulsion is immersed in an etch-bleach bath such as Kodak Etch Bleach Bath EB-4 containing cupric chloride, citric acid, urea and hydrogen peroxide. This results in bleaching silver grains and at the same time degrading or softening gelatin so that it is removed in the image areas. The resulting lithographic plate is then inked and placed on a lithographic press.
In another embodiment, a paper support is coated with polyvinyl alcohol which has been cross-linked with formaldehyde in combination with dihydroxydioxane in the presence of an acid catalyst. A typical such useful hydrophilic coating is disclosed in Perkins U.S. Pat. 3,055,295. Over the polyvinyl alcohol layer is coated a high contrast projection speed silver halide emulsion which is exposed to a light image and developed in a silver halide developer. Following development, the silver halide emulsion is immersed in an etch-bleach bath such as Kodak Etch Bleach Bath EB-4 containing cupric chloride, citric acid, urea and hydrogen peroxide. The silver is bleached and at the same time the gelatin is etched out and removed in the image areas. The resulting lithographic plate is wetted, inked and placed on a lithographic press.
It is a significant feature of the invention that the hydrophilic coating on the support is non-porous, i.e. substantially non-permeable to a gelatin solution in water at a concentration of 3% or above, by weight, gelatin. Thus, as illustrated by Example 1, which follows, an element comprising a porous hydrophilic layer gives poor ink-water differential and prints in the background areas. Another significant feature is the hydrophilic nature of the layer. This hydrophilicity is shown by a contact angle of less than about 65 measured with water. Contact angle is conveniently determined by placing a drop of water on a surface and drawing a line from the point of contact with the water and the surface tangent to the drop and measuring the angle formed between this line and the surface. On a hydrophilic coating, a Water drop tends to spread so that the angle measured as above is smaller than that in a hydrophobic coating wherein a drop of water will tend to remain in a spherical shape such that the angle contact would be substantially above 65 A still further significant feature of the invention is that the hydrophilic layer comprises a material different from the gelatin binder in the silver halide emulsion layer. This is important since gelatin layers are porous. Furthermore, it is conventional in a lithographic plate employing gelatin wherein the gelatin image is intended to be oleophilic, to treat the gelatin image area with an image conditioner which enhances its ability to be ink receptive to a greasy printing ink. It is evident, therefore, that the hydrophilic layer should be inert to an image conditioner which would be effective in treating the gelatin. Otherwise, the hydrophilic layer would also become ink receptive following the treatment with an image conditioner.
The photographic silver halide emulsions which can be used in this invention include silver halide emulsions such as silver chloride, silver bromide, silver iodide, silver chlorobromide, silver chloroiodide, silver bromoiodide, silver chlorobromoiodide, etc. A particularly useful emulsion is a high contrast chlorobromide emulsion in which the silver halide contains at least 60 mole percent silver chloride.
Although it is preferred to use gelatin as the sole binding agent for the silver halide, it will be appreciated that other hydrophilic colloids can be used with gelatin to give a layer which can be hardened to a point where it has a melting point above about 180 F., and generally below about 300 F. Suitable hydrophilic colloids include colloidal albumin, cellulose derivatives, synthetic resins, particularly polyvinyl compounds and the like. Water insoluble polymerized vinyl compounds, e.g., polymers of alkyl acrylates or methacrylates can also be included.
The coverage of the silver halide emulsion can be varied depending upon the use intended. A useful range is about to 800 milligrams per square foot of gelatin, preferably 100 to 400 milligrams per square foot and about 50 to 200 milligrams per square foot of silver as silver halide, preferably 50 to milligrams per square foot. The photographic emulsions described herein can be chemically sensitized such as with compounds of the sulfur groups, noble metal salts such as gold salts, reduction sensitized with reducing agents, combinations of these, etc. Furthermore, emulsion layers can be hardened with any suitable hardener such as aldehyde hardeners, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides, such as oxystarch, oxy plant gums and the like.
The photographic silver halide emulsions can also contain additional additives particularly those known to be beneficial in photographic emulsions, including for example stabilizers or antifoggants, particularly the water soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in U.S. Pat. 2,839,405, substituted triazaindolines as disclosed in U.S. Pats. 2,444,605 and 2,444,607, speed increasing materials, plasticizers, absorbing dyes and the like. Sensitizers which give particularly good results in typical emulsions useful in our in vention are the alkylene oxide polymers which can be employed alone or in combination with other materials such as quaternary ammonium salts as disclosed in U.S. Pat. 2,886,437 or with mercury compounds and nitrogencontaining compounds, as disclosed in U.S. Pat. 2,751,299. The emulsions can be blue sensitized, orthochromatic, panchromatic, infrared sensitive, etc.
The silver halide emulsions used in practicing this invention include both negative and positive emulsions. Suitable positive emulsions which can be used include direct positive emulsions such as (1) hardened solarizing silver halide emulsions and (2) hardened internal latent image silver halide emulsions forming the latent image mostly inside the silver halide grains.
The solarizing direct positive silver halide emulsions are silver halide emulsions which have been effectively fogged either chemically or by radiation, to a point which corresponds approximately to the maximum density of the reversal curve as shown by Mees, The Theory of the Photographic Process, published by the Macmillan Company, New York, New York, 1942, pages 261-297.
Typical methods for the preparation of solarizing emulsions are shown by Groves British Pat. 443,245, Feb. 25, 1936 which describes subjecting an emulsion to roentgen rays until the emulsion layer, when developed without additional exposure, is blackened up to the apex of its gradation curve; Szaz British Pat. 462,730, Mar. 15, 1937, the use of either light or chemicals such as silver nitrate, organic sulfur compounds and dyes to convert ordinary silver halide emulsions to solarizing direct positive emulsions; Arens U.S. Pat. 2,005,837, June 25, 1935, the use of silver nitrate and other compounds in conjunction with heat to effect solarization of the silver halide and Leermakers U.S. Pat. 2,183,013, the use of large concentrations of non-acid optical sensitizing dyes and reducing agents to effect solarization.
Kendall and Hill U.S. Pat. 2,541,472, Feb. 13, 1951, shows useful solarizing emulsions particularly susceptible to an exposure with long wave-length light to produce a Herschel effect described by Mees above, produced by adding nitro substituted electron acceptors and other compounds to the emulsion which is fogged either chemically or with white light.
In using solarizing emulsions, a sufiicient reversal image exposure is employed using minus blue light of from about 500-700 millimicrons wave-lengths, preferably 520-540 millimicrons, to substantially destroy the latent image in the silver halide grains in the region of the image exposure.
Conventional silver halide developing solutions can be used to develop a direct positive image in a solarizing emulsion.
The internal latent image direct positive silver halide emulsions used in this invention include those well known in the art which upon exposure form the latent image mostly inside the silver halide grains, the direct positive properties of the emulsions being attributable to the crystalline structure of the silver halide grains. That is, a number of authorities in the field of photography have shown that there are imperfections or flaws, in the crystal structure (on the surface or internally) of silver halide which is used in photography, at which flaws the latent image forms by trapping photoelectrons to give development centers. Development, therefore, commences at the sites of these flaws. Journal of Photographic Science. Photographic Sensitivity, text of a lecture given on July 1, 1957, by J. W. Mitchell; vol. 6, No. 3 (1958).
Other photographic reversal emulsions may be used 'including those containing grains comprising a central core of a water insoluble silver salt containing centers which promote the deposition of photolytic silver and an outer shell or covering for such core of-a fogged or spontaneously developable water insoluble silver salt. The fogged shell of such grains is developed to silver without exposure. Emulsions of this type are described in Berriman U.S. Pat. application Ser. No. 448,467, filed Apr. 15, 1965, now U.S. Pat. No. 3,367,778.
Before the shell of water insoluble silver salt is added to the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described in the prior art. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 5765, are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as labile sulfur compound and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.
The core emulsions can be chemically sensitized by any method suitable for this purpose. For example, the core emulsions can be digested with naturally active gelatin, or sulfur compounds can be added to those described in Shepard U.S. Pat. 1,574,944, isued Mar. 2, 1926, Shepard et al. U.S. Pat. 1,623,499, issued Apr. 5, 1927 and Shepard et al. U.S. Pat. 2,410,689, issued Nov. 5, 1946.
The core emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Pat. 2,399,083, issued Apr. 23, 1946 and Damschroder et al. U.S. Pat. 2,642,361, issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, aurictrichloride and 2- aurosulfobenzothiazole methylchloride.
The core emulsions can also be chemically sensitized with reducing agent, such as stannous salts (Carroll U.S. Pat. 2,487,850, issued Nov. 15, 1949), polyamines such as diethylenetriamine (Lowe and Jones U.S. Pat. 2,618,598, issued Aug. 15, 1950), polyamines such as spermine (Lowe and Allen U.S. Pat. 2,521,925, issued Sept. 12, 1950) or bis(beta-aminoethyl)sulfide and its water soluble salts (Lowe and Jones U.S. Pat. 2,521,926, issued Sept. 12, 1950).
The shell of the grains comprising the emulsions used in practicing this invention is prepared by precipitating over the core grains a light sensitive water-insoluble silver salt that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufficiently fogged to produce a density of at least about 0.5 when developed for six minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of mg. per square foot.
DEVELOPER A Grams N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0
Potassium metaborate 35.0 Potassium bromide 1.0 Water to 1.0 liter.
pH of 9.6.
Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and like fogging means well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged, for example, reduction fogged with a reducing agent such as stannous chloride. Fogging by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.
Another direct positive silver halide emulsion which may be used is a fogged direct positive silver halide emulsion comprising fogged silver halide grains which have a uniform diameter frequency distribution, i.e. silver halide grains which have substantially uniform diameter. In one embodiment of this type of emulsion, the direct positive photographic emulsion comprises fogged silver halide grains, at least 95% by weight of said grains having a diameter which is within about 40% of the mean grain diameter. Preferably, photographic emulsions of this type comprises reduction and gold fogged silver halide grains and a compound which accepts electrons. The use of low concentrations of reduction and gold fogging agents, in preparing such emulsions give unique fogged silver halide grains which are characterized by a very high photographic speed in conventional photographic processing solutions.
To increase sharpness, it may be desirable to include an antihalation pigment or dye in the emulsion. Typical dyes and pigments used in antihalation layers may be used provided they are inert to the emulsion and do not affect the etch-bleach reaction. In a preferred embodiment, at carbon pigment is used. A useful amount of antihalation dye or pigment is 20 to 50 grams per silver mole.
It will be understood that the emulsion can be coated using methods known in the art. It must be sufficiently hardened so that it will have a melting temperature of at least about F., generally above about 200 F. and preferably above about 230 F.
It will be appreciated that any of the conventional silver halide developing agents can be used in the practice of this invention. Such developing agents can be incorporated into the element contiguous to silver halide, e.g. in the emulsion layer or in a contiguous layer. Typical developing agents include hydroquinone and substituted hydroquinone such as bromohydroquinone, chlorohydroquinone, toluhydroquinone, morpholinomethylhydroquinone, etc. It will also be appreciated that an auxiliary developing agent can be used in an amount of 0 to 20% of the hydroquinone or substituted hydroquinone in order to improve the speed without affecting the developing reaction.
Typical auxiliary agents include 3-pyrazolidone, developing agents known in the art as well as Elon (N- methyl-p-aminophenol sulfate), and the like. Particularly useful auxiliary agents are 1-phenyl-3-pyrazolidone and 1-pl1enyl-4,4-dimethyl-3-pyrazolidone.
Generally the hydrophilic colloid will be placed directly on the support, particularly if the support is a metal such as aluminum. However, various other structures may be used such as those which would include resin coated paper having a coating such as polyethylene on one or both sides of the paper over which is then coated the hydrophilic layer. The emulsion and hydrophilic layers are adjacent or contiguous layers, preferably abutting. For instance, a thin layer containing Carey Lea silver might be interposed between the emulsion layer and the hydrophilic layer for purposes of the antihalation or the like. Since this layer would contain colloidal silver, the etch-bleach solution would be able to etchbleach through the coating to the hydrophilic layer. In a typical structure, the emulsion layer would be the outermost layer of the support. However, it will be appreciated that a very thin layer of gelatin or a similar colloid might be coated over the emulsion layer in order to protect it from abrasion or the like. Such a layer would necessarily have to be thin in order to permit penetration by the oxidizing etch-bleach solution. In order to facilitate the processing of the element, Carey Lea silver might be dispersed in such an overcoat.
Various hydrophilic layers are useful in this invention, particularly those which will not become hydrophobic when treated with an image conditioner such as, for example, with tannic acid, i.e. the contact angle will not increase above 65 when treated with an aqueous solution containing a tannic acid. Tannic acid is a particularly efficacious component in an image conditioner which is used to treat gelatin to further emphasize the ink-water differential of the printing plate. Cross-linked polyvinyl alcohol provides a very useful hydrophilic coating. For instance, polyvinyl alcohol combined with mineral pigments may be cross-linked with formaldehyde in combination with dihydroxydioxane in the presence of an acid catalyst. A particularly useful hydrophilic coating is disclosed in Perkins US. Pat. 3,055,295. Other methods of cross-linking polyvinyl alcohol may be used. For instance, a polyvinyl alcohol coating may be applied and then heated to a temperature above 175 C. (320 F.) for a sufficient length of time to render the coating water insoluble.
In addition to polyvinyl alcohol, various other hydrophilic colloidal materials may be used to provide a satis factory non-porous hydrophilic layer including for example modified urea formaldehyde and melamine formaldehyde, modified urea formaldehyde and melamine formaldehyde resins treated with a water dispersable member of a class consisting of polycarboxy compounds, combined polyhydroxy, polycarboxy compounds and alkali metal silicates.
The hydrophilic layer present in the element of this invention is advantageously a synthetic, hydrophilic vinyl polymer such as an acrylamide polymer, typically coated in a concentration of about 25 to about 250 mg. per square foot. A particularly advantageous range is from about 75 to about 100 mg. per square foot. Polyacrylamide is a preferred polymer but derivatives of polyacrylic acid amide may also be used provided that they are hydrophilic. For example, acrylamide polymer comprising I II CHZCHCNR2 groups in which each R is alkyl having from 1-4 carbon atoms can be used. Moreover, mixtures of vinyl polymers can be used in the same manner. Suitable acrylamide polymers include copolymers of acrylamide with other ethylenically unsaturated monomers such as acrylic acid, vinyl acetate and the like. Polymeric materials useful in our invention include those prepared from a monomeric mixture containing 20100% by weight acrylamide and which can be coated to form a hydrophilic layer having a contact angle measured with water of less than 65.
Any convenient polymer can be used to provide the hydrophilic layer which is nonporous, sufficiently hydrophilic and results in a substantially water insoluble layer. Particularly useful polymers include vinyl polymers such as copoly(acrylamide-methacryloxyethyl acetoacetate), -10% by weight, copoly(acrylamide-N-methylacryloyl- N-cyanoacetyl hydrazine), 90l0% by weight, copoly (acrylamide-acrylic acid), 60-10% by Weight and the like.
For most purposes, it is desirable that the polymer be water soluble for ease in coating, although solvent soluble polymers may be used, provided the hydrophilic characteristics are satisfactory. The coatings may also be latexes, if desired. Since the hydrophilic coating is substantially insoluble in water, water soluble polymers such as polyvinyl alcohol are crosslinked to insolubilize the coating.
The hydrophilic layers are applied to the support in any convenient solvent or dispersion. For this purpose, organic solvents may be used as well as water. It Will be appreciated that the advantageous solvents or solvent mixture includes those which are volatile such as benzene, toluene and xylene; also solvents such as acetone and the chlorinated hydrocarbons may be employed. Additional solvents include the humectants or hydroscopic solvents such as for example, the alcohols, such as methyl, ethyl, propyl, isopropyl, butyl and isobutyl alcohol, ethylene glycol, diethylene glycol, glycerol, Cellosolve, Cellosolve acetate, Cellosolve butylate, methyl Cellosolve, butyl Cellosolve, Carbitol, butyl Carbitol, and the like. The content of the solid material in the solvent or dispersion vehicle is a matter of choice. However, a single application of the solvent or vehicle containing about 0.1% to about 10.0% by weight of solid may be used.
Although anodized aluminum is a particularly useful support in the practice of our invention, it will be appreciated that other supports can be used including metals such as copper, zinc, steel and the like. In addition, other supports including paper, glass, various polymeric materials such as polyesters, polyamides, polyolefins and the like may be used. Since the hydrophilic layer, e.g. polyacrylamide layer or similar non-porous coating provides the hydrophilic areas in a lithographic plate, various supports may be substituted under the polyacrylamide without affecting the lithographic characteristic of resulting plate. Therefore, the choice of support will depend upon the durability, availability and cost of the support material.
The developed silver halide emulsion is processed to a lithographic plate with an etch-bleach solution. Such solutions typically contain an oxidizing agent such as hydrogen peroxide, an insoluble silver salt former such as chloride ion and a metal ion catalyst such as cupric ion. A gelatin softener such as citric acid and/or urea may also be incorporated in the etch-bleach bath. The etch-bleach solution can be applied by spraying, dipping, immersing, swabbing, etc. in the areas where silver has been formed resulting in bleaching silver image and at the same time degrading or etching gelatin in these same areas. The etchble-ach application normally removes the gelatin in the image area. However, the emulsion may be washed to remove the etch-bleach solution and any remaining softened colloid. If desired, the emulsion can then be re-exposed to regular roomlight and then redeveloped to provide an image in those areas which were not etched. This provides a darkened image area for proofiing purposes on the plate. Of course, the emulsion can be hardened after the etch-bleach, if desired, to compensate for any surface softening due to the etch bleach. However, this is not necessary. The plate can be dried immediately following the etch-bleach operation and inked to provide a darkened image area and run on the lithographic press.
The etch-bleach solution may be one of those containing cupric chloride, citric acid, and hydrogen peroxide, such as Kodak Etch-Bleach Bath EB-3 or EB-4, as follows:
KODAK ETCH-BLEACH BATH EB-3 Water, at 125 F.--750 cc. Cupric chloride-10 g.
Citric acid10 g.
Water to make 1 liter Hydrogen peroxide 3%1 liter KODAK ETCH BLEACH BATH EB-4 Water, at 125 F.600 cc. Cupric chloride-10 g.
Citric acid150 g.
Water to make 1 liter Hydrogen peroxide 3%-1 liter Another suitable etch-bleach bath containing copper sulfate, citric acid, potassium bromide and hydrogen peroxide is known as Kodak Etch-Bleach Bath EB-2. However, an etch-bleach bath containing cupric chloride, citric acid, urea and hydrogen peroxide in which there is at least 20 grams per liter of cupric chloride is particularly suitable in producing a clean removal of the gelatin in the image areas in the period of time as short as 20 seconds. Such etch-bleach solutions are described in application Ser. No. 650,616, filed concurrently herewith and now abandoned. Various other oxidizing compounds may be used in place of hydrogen peroxide such as hydrogen peroxide precursors and the like. However, X1- dizing agents which are used in place of hydrogen peroxide must be those which act selectively on the image area-where the silver image is located rather than attacking the complete emulsion layer which would be the case, for example, if nitric acid was utilized.
The following examples are intended to illustrate our invention but not to limit it in any way.
EXAMPLE 1 As previously pointed out, when the hydrophilic layer under the hardened silver halide emulsion layer is a porous gelatin-containing layer, undesirable printing n background areas occurs. To illustrate, a porous gelatin layer is coated under the silver halide emulsion layer. Thus, an aluminum support anodized in a phosphoric acid bath is coated with a hardened gelatin layer containing a titanium dioxide pigment at a 1:2 ratio by weight, dry basis, and is finally overcoated with a hardened high-contrast' silver chlorobromide negative emulsion having a melting point of 250 F. coated to yield a silver coverage of 165 mg. of silver per square foot.
The element is exposed in a standard copy camera fitted with an image-reversing prism. It is processed in a hydroquinone type silver halide developer for two minutes at 68 F. After development, the plate is etch-bleached in a solution of the following composition for 60 seconds:
G. Cupric chloride 5 Citric acid 75 Urea 75 EXAMPLE 2 In contrast to Example 1, a plate is prepared wherein a non-porous hydrophilic layer coated at 68 mg. of polyacrylamide per square foothaving a contact angle of 51 is substituted for the pigmented gelatin layer present in 10 the element described in Example 1. When this plate is run as described in Example 1, its lithographic latitude is judged to be very wide. There is no background gelatin present from the emulsion and the polyacrylamide layer accepts no greasy printing ink resulting in a very sharp ink-water difierential.
EXAMPLE 3 A plate is prepared as in Example 2 but differs in that the non-porous hydrophilic layer is coated at 135 mg. of polyacrylamide per square foot. When exposed and processed as described in Example 1, this plate is judged to have extremely wide lithographic latitude. The contact angle is 51 on the polyacrylamide.
EXAMPLE 4 A plate is prepared as described in Example 2 but differs in that it contains 204 mg. of polyacrylamide per square foot. The lithographic latitude is again judged to be very wide and the contact angle is 51.
EXAMPLE 5 A control plate is prepared in the manner of the plates described in Examples 24 but differs in that the silver halide emulsion layer is coated directly on the aluminum support without the benefit of the non-porous hydrophilic interlayer. The contact angle on the aluminum is 69. When exposed and processed as described in Example 1, this plate is judged to have very poor lithographic latitude in that heavy, oleophilic deposits of background gelatin are obtained from the emulsion layer.
Metals are employed as supports according to the present invention including aluminum, copper, lead, zinc, tin chromium, magnesium, tantalum and titanium. Still other metal or metallized surfaces are used in our invention as long as strongly adherent water insoluble, non-porous layers can be applied thereto to obtain a contact angle of less than 65 C.
EXAMPLE 6 Projection negative on paper lithographic support A projection speed negative gelatin emulsion having a melting point of 250 F. is coated on a hydrophilic lithographic surface on a support consisting of a paper stock that is laminated on both sides with polyethylene. A nonporous lithographic layer having a contact angle of about 20, essentially comprising polyvinyl alcohol, colloidal silica and a cross-linking agent is coated on this support. The layer is then wash-coated with an inorganic hardening system to form the lithographic surface.
Exposure of this product is carried out in a standard copy camera fitted with an image-reversing prism.
This exposed plate is then processed in a silver halide developer (D19) for 20 seconds. After sqneegeeing, it is placed in an etch-bleach bath of the following composition for 20 to 60 seconds:
Gms. Cupric chloride 5 Citric acid Urea 75 all dissolved in one liter of 1% percent hydrogen peroxide. This plate is treated with an aqueous image conditioner containing tannic acid, thus rendering the gelatin ink-receptive. The background lithographic layer is waterreceptive. This plate is then put on a standard lithographic duplicator, and right-reading, positive copies of the original are obtained.
EXAMPLE 7 An alternate processing procedure to that described in Example 6 can be used. Thus, after exposure of the material, the following processing cycle is used:
Develop in Eastman Kodak D-19 developer for 20 seconds Etch-bleach for 2060 seconds 1 1 Rinse in water Re-expose and redevelop in D19 for 5 to seconds Rinse The plate is then treated with image conditioner as in Example 6 and then is placed on a lithographic duplicator. Very good quality is obtained using this procedure, and blinding and/or toning are minimized.
EXAMPLE 8 High contrast emulsion on paper lithographic support A high contrast silver halide emulsion having a melting point of 250 F. is coated on a hydrophilic, lithographic support. This support is identical to that described in Example 6. Following exposure to a positive original in a standard copy camera equipped with an image-reversing prism, the exposed matrix is processed in the following sequence:
Develop for 2 minutes Etch-bleach in the solution described in Example 1 for 20 to 60 seconds Rinse and re-expose Redevelop for 5 to 10 seconds Rinse in water The plate is then treated with an image conditioner as in Example 6 to render the gelatin areas ink-receptive. The plate is then put on a standard lithographic duplicator and positive, right-reading copies of the original document are obtained.
EXAMPLE 9 High contrast emulsion on aluminum A high contrast emulsion is coated on an aluminum support. This aluminum support has a hydrophilic, nonporous, lithographic coating having a contact angle of about 52. This material, when exposed and processed in the manner described in Example 8, gives a plate capable of being used on a lithographic press. Positive, right-reading copies of the original document exhibiting high quality are obtained, including good half-tones and good fine line retention.
EXAMPLE 10 Satisfactory lithographic plates similar to those described in Examples 6 and 7 are made using other materials for the hydrophilic, lithographic surface. A lithographic surface is utilized, which is in all respects similar to that described in Example 6 except that no colloidal silica is used and no wash coat is employed. This product is sensitized with an emulsion and operated as described in Example 6. Other aluminum supports are also used, such as an anodized aluminum coated with a non-porous acrylate type agent having a contact angle of 35. Also, emulsions are used containing incorporated developers. A negative working plate is used employing an autopositive emulsion in place of the projection negative emulsion.
EXAMPLE 1 1 Elements described in Example 2 are. prepared using emulsions having melting points of 230 F. and 250 F. The exposed elements are developed and etch-bleached as in Example 1 except that following the etch-bleach, they are reexposed and redeveloped to produce darkened image areas. The developer solution contains 2 /2% glutaraldehyde by weight. The elements are immersed in the developer solution for 2 minutes, sufficient time to obtain maximum hardness. The plates were placed on a lithographic press and used for printing. During the printing run, the image areas were observed to determine wear. The first perceptible loss of gelatin determined the length of press run. The 250 F. emulsion produced an average of 7324 copies while the 230 F. emulsion produced an average of 1612 copies.
An element having an unhardened emulsion cannot withstand the etch-bleach process. Therefore, an element prepared by colloid transfer using an emulsion hardened enough to have a melting point of 110 F. is used to determine press life. Without any after treatment, the gelatin image shows wear at an average of 100 copies.
This example shows that hardening gelatin in the manufacture of the emulsion provides a plate having a longer press life than a plate having an emulsion of less original hardness which has had a subsequent hardening. It also shows that a simple inexpensive etch-bleach process provides a plate having superior press life to previously known plates.
It will be appreciated that, if desired, dyes and/or pigments may be incorporated in the emulsion to provide a color image area. These may also be conveniently added in an after bath following the etch bleach step.
A particularly useful image conditioner has the following composition:
ONE LITER FORMULA Resorcinol30.4 g.
50% sodium hydroxide solution1.74 ml. Sodium bisulfite4.0 g. 1,3-diethylthiourea61.7 g.
Tannic acid26.0 g.
Ethyl alcohol )84.0 g.
Acetic acid (glacial)10.5 g.
In accordance with the practice of this invention, excellent lithographic printing plates are obtained from silver images in gelatin layers. As indicated herein, the silver image, subjected to etch bleaching according to the process of this invention, can be obtained in any desired manner. Suitable means include, for example, physical or chemical development of gelatin layers comprising silver image-forming materials such as silver salts, for example, silver halides including mixed silver halides, silver soaps, etc., silver complexes such as, for example, silver dye complexes, etc. Silver images may be etch bleached according to the practice of this invention which are formed by chemical transfer, physical development of light sensitive nuclei, etc. Negative, particularly high contrast negative or positive silver halide emulsions may be used to obtain silver images including systems employing two superimposed emulsion layers e.g. as described in Kendall U.S. Pat. 2,725,296 to obtain direct positive images, systems involving reversal processing, etc.
This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
1. A photographic element comprising a support, a gelatin photographic silver halide emulsion layer having a melting point above about 180 F. and adjacent to said layer and between said layer and said support, a nonporous non-gelatin hydrophilic layer having a contact angle of less than about 65, said hydrophilic layer comprising a polymer and being substantially impermeable to a gelatin solution in water having a concentration of at least about 3% by weight gelatin.
2. A photographic element of claim 1 in which said hydrophilic layer comprises a vinyl polymer.
3. A photographic element of claim 1 in which said hydrophilic layer comprises an acrylamide polymer.
4. A photographic element of claim 3 in which said acrylamide polymer comprises 20 to about percent by weight acrylamide.
13 5. A photographic element of claim 1 in which said non-porous layer comprises an acrylamide polymer comprising groups in which said R is alkyl having from 1-4 carbon atoms.
6. A photographic element of claim 1 in which said support is aluminum.
7. A photographic element of claim 1 in which said support is paper.
8. A photographic element of claim 1 in which said support comprises paper having thereon a polyethylene coating.
9. A photographic element of claim 4 in which said acrylamide polymer is coated at a coverage in the range of about 25 to 250 milligrams per square foot.
10. A photographic element of claim 1 in which said hydrophilic layer is cross-linked polyvinyl alcohol.
11. A photographic element of claim 4 in which said support is aluminum.
12. A photographic element of claim 1 comprising a developing agent contiguous to said silver halide.
13. A photographic element of claim 1 in which said photographic silver halide emulsion is a direct positive emulsion.
14. A photographic element of claim 1 in which said non-porous layer comprises copoly(acrylamide-methacryloyloxyethyl acetoacetate).
15. A process which comprises imbibing an etch-bleach solution comprising an oxidizing agent, an insoluble silver salt former and a metal ion catalyst into an exposed and developed photographic element of claim 1 whereby there is obtained a surface exhibiting ink-water differential.
16. A process of claim 15 in which said metal ion catalyst comprises cupric chloride.
17. A process of claim 15 in which said etch-bleach solution contains a gelatin softener.
References Cited UNITED STATES PATENTS 2,013,116 9/1935 Troland 96-33 2,058,396 10/1936 Baker 96 33 3,003,413 10/1961 Taylor etal. 96-33 3,085,008 4/1963 Case 96-33 3,342,601 8/1967 Horele etal 96-33 GEORGE F. LESMES, Primary Examiner I. P. BRAMMER, Assistant Examiner US. Cl. X.R.