US3561961A

US3561961A - Photosensitive lithographic printing master and process for preparation of a lithographic plate

Info

Publication number: US3561961A
Application number: US617078A
Authority: US
Inventors: Ralph Kingsley Blake
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1967-02-20
Filing date: 1967-02-20
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09
Also published as: NL7017453A; DE2057934A1; DE2057934C3; BE759629A; DE2057934B2; GB1309304A

Abstract

A PHOTOSENSITIVE LITHOGRAPHIC PRINTING MASTER IS PREPARED FROM A SUPPORT SUCH AS A POLYETHYLENE TEREPHTHALATE FILM COATED WITH A HYDROPHILIC PHOTOSENSITIVE SILVER HALIDE EMULSION THE OUTER SURFACE OF SAID WMULSION BEING OLEPHILIC AND WATER-PERMEABLE. THE SURFACE OF THE SUPPORT IN CONTACT WITH THE EMULSION CAN BE COATED WITH A HYDROPHILIC LAYER SUCH AS A GELATIN LAYER CONTAINING SILICA PARTICLES.

Description

United States Patent O 3,561,961 PHOTOSENSII lVL LITHOGRAPHTC PRINTING MASTER AND PROCESS FOR PREPARATHON OF A LITHOGRAPHIC PLATE Ralph Kingsiey Blake, Westfield, Ni, assignor to E. I. du Pont de Near-ours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Feb. 20, 1967, Ser. No. 617,078 Int. Cl. Gillie 1/78, 5/00; G03f 7/02 US. Cl. 96-33 17 Claims ABSTRACT OF THE DISCLOSURE DESCRIPTION OF THE PRIOR ART Various photographic methods are employed in the lithographic industry for the formation of a positive oleophilic image on a hydrophilic surface of a lithographic printing plate from a high contrast line or halftone original. Within the meaning of this invention, oleophilic means a surface which accepts greasy ink and hydrophilic means a surface which accepts water. A positive oleophilic image is one in which the oleophilic areas correspond to the black areas of the original and the areas corresponding to the clear areas of the original are hydrophilic and oleophobic. A lithographic plate having a positive oleophilic image is defined as a positive-working plate. A positive copy is a copy obtained from a positive working plate. A plate having a negative oleophilic surface will produce a negative copy. Such plates may be mounted on a roller of an oifset printing press and passed in contact with an aqueous fountain solution and a printing ink. The inked image is applied to a rubber printing blanket and then transferred to the sheet to be printed. The method of producing plates often requires complicated procedures as well as special films.

SUMMARY OF THE INVENTION The product of this invention in its broadest aspects comprises (a) a support such as a polyester film, (b) a light-sensitive hydrophilic gelatino-silver halide emulsion layer coated on the support, and (c) an oleophilic waterpermeable surface on said emulsion layer.

The support itself can have a hydrophilic surface. A support having a hydrophilic surface is defined as a (1) hydrophilic support which would naturally have a hydrophilic surface, or (2) a support having a hydrophilic layer between the emulsion and the support.

This invention also encompasses the process of converting these novel film elements into a printing plate. The process comprises imagewise exposing the novel element, developing the exposed silver image, treating said silver image with an etch-bleach bath which degrades the gelatin in the exposed areas, and in said areas, removing the oleophilic layer covering the exposed silver image and the degraded emulsion layer thereby forming a hydrophilic surface in the etched areas. The resultant element of this process produces an oleophilic/hydrophilic printing plate.

The oleophilic Water permeable surface on the emulsion can be obtained in several ways. The following are methods, within the scope of this invention, of obtaining such oleophilic coatings:

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(a) Coating the emulsion surface with an oleophilic Werner-type chromium complex having a hydrophobic group, e.g., complexes of myristic acid, stearic acid, etc.;

(h) Coating the emulsion surface with polyacrolein;

(c) Coating the emulsion surface with a mixture of and (d) Coating the emulsion surface with a solution of a polymeric dialdehyde;

(e) Coating the emulsion surface with elements of (a), (b), (c) or (d) mixed with a compatible binder such as gelatin;

f) Coating the emulsion surface with elements of (a), (b), (c), (d), either independently or mixed in any arrangement, and a surfactant such as sodium dodecyl sulfate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The amount of oleophilic coating will vary depending on the composition of the coating. Consequently, a simple empirical determination with a particular coating will give the desired coating for any given element. The oleophilic surface should be oleophilic enough to readily accept a conventional quick-drying printing ink and yet the coating should still be Water-permeable. Too much of an oleophilic coating will prevent processing of the exposed element with the standard aqueous developing systems. When a hydrophilic layer is coated over the support, it is preferably a gelatin coating containing colloidal SiO particles in amounts of 0 to 20 parts by weight, generally l to 12 parts by weight; a hardener usually a polymeric dialdehyde starch produced by the oxidation of of the anhydroglucose units of starch, in amounts of 0.4 to 10 parts by Weight, generally 1 to 4 parts by weight; and a surface wetting agent usually saponin and alcohol in amounts of 0.5 to 10 parts by weight, usually 1 to 3 parts by weight. The light-sensitive layer which covers the SiO layer is preferably a gelatino-silver halide emulsion containing silver bromide, silver chloride or mixtures thereof, usually containing at least 50 mole percent silver chloride. The polymeric dialdehyde may also be present in the emulsion in the same limits of about 0.4 to 10 parts by weight. The oleophilic overcoating for this particular element is preferably comprised of a Werner chromium complex of stearic or myristic acid in amounts of 30 to 70 parts by weight, a hardener such as formaldehyde in amounts of 0 to 40 parts by weight, usually 10 to 25 parts by weight, and a surfactant, usually sodium dodecyl sulfate, in amounts of 5 to 40 parts by weight and preferably 10 to 33 parts by weight. All parts by weight in this particular preferred element are the final dry, photosensitive product.

When using an element containing the hydrophilic support surface, the photosensitive element is fully exposed to actinic radiation to form a latent image throughout the thickness of the silver halide emulsion. The image is completely developed in a conventional high contrast lithographic developer such as hydroquinone and sodium bisulfite. After development, the photosensitive element is bathed in an acid peroxide, etch-bleach solution containing a halide in amounts of 0.1 g./l. to 1'0 g./l., a conventional bleaching salt, e.g., cupric nitrate in amounts of 0.5 g./l. to 70 g./l., an acid activator, e.g., lactic acid in amounts of 1 rnl./l. to rnl./l. and hydrogen peroxide in concentrations of 0.1% to 3.0%. The etch-bleach treatment oxidizes the developed silver image causing degradation of the binder in the presence of the developed silver thus destroying the developed regions of the emulsion layer. The softened binder in the exposed area may be removed by rubbing, down to the hydrophilic surface of the support, or the support itself if the latter is hydrophilic, leaving an oleophilic positive image surrounded by hydrophilic areas. This printing plate may then be mounted on a conventional offset printing press and using a fountain solution, preferably containing gum arabic and asphaltum and a conventional quick-drying ink, many copies can be produced. It has been noted that slightly improved printing plates were obtained from elements of this invention which were conditioned in an oven at about 120 F. and 65% relative humidity for several days before exposure and processing.

If a light-sensitive element is used as previously defined where said element has no hydrophilic support surface, the following modified process can be used to form the plates. This process comprises exposing and developing the photosensitive element, and then completely removing the oleophilic overcoating in the exposed areas, and plurality removing the developed silver image in the exposed areas. The removal of the exposed areas can be achieved by l) restricting the bleaching and etching of a fully developed silver image to the upper part of the emulsion layer by controlling the contact time, (2) restricting development to limit the silver image to the upper part of the emulsion layer followed by complete bleaching and etching of the developed image by controlling the contact time, and (3) by limiting the exposure time to restrict the image to the surface when developed. In the exposed areas, the oleophilic overcoating and the gelatin, degraded by the etching and bleaching, can be removed by rubbing, leaving an oleophilic positive image surrounded by hydrophilic gelatin of the emulsion as the background area. The control over partial development or partial etching is easily deter-mined empirically, depending on the thickness of the gelatinosilver halide layer. A variation of this invention is obtained by overcoating the emulsion layer with the oleophilic overcoating after exposure and development but before bleaching and etching.

A preferred photosensitive element for use in the process which partially removes the silver halide emulsion layer is prepared by coating on a resin subbed polyethylene terephthalate film base, an orthochromatically, sensitized, lithographic, gelatino-silver halide emulsion generally containing at least 50 mol percent silver chloride, and an oleophilic surface overcoating coated from: (1) an ethanol solution containing 0.1 g. to 1.0 g. of a Werner chrome complex of stearic or myristic acid per 100 ml. of ethanol, or (2) a 75%25% ethanolwater solution, containing 0.05 g. to 0.5 g. of a sodium bisulfite adduct of polyacrolein (average molecular weight:400,000) per 100 ml. of solution. The weights of the Werner chrome complex are given as a solution of 27% of the complex in isopropanol.

Since the polyacrolein coating has a tendency to harden when aged, it is possible to use greater amounts of polyacrolein if the plate is used within a short period of time after coating of the polyacrolein.

The preferred process of this aspect of the invention comprises exposing the photosensitive element and then restricting the development of the negative latent image to the surface of the emulsion. This can be accomplished by using a developer which restricts development to the surface of the emulsion. A preferred developer is a high pH developer, i.e., pH above 12.0 containing p-methylaminophenol sulfate in amounts of 1 g. to 10 g. per liter of developer, sodium sulfite in amounts of 10 g. to 100 g. per liter, and sodium hydroxide in amounts of 1 g. to 50 g. per liter as well as other conventional developer additives. The emulsion surface developed negative image is generally immersed in a stop bath of 5% acetic acid and then placed in an acid-peroxide bath generally containing a halide in amounts of 0.1 g./l. to g./l., a heavy metal salt, e.g., cupric nitrate in amounts of 0.5 g./l. to 70 g./l., an acid activator, e.g., lactic acid (85%) in amounts of 1 ml./l. to 100 ml./l., and hydrogen peroxide in concentrations of 0.1% to 3.0%. During the bleaching and etching, usually 1 to 2 minutes, the silver image and gelatin in the exposed areas bleaches and becomes A polyethylene terephthalate film base was prepared with a resin sub stratum as disclosed in Example 4, Alles, US. Pat. 2,779,864. Over this subbed base there was coated to a weight of 35 mg/dm. (AgBr equivalent) an orthochromatically sensitized emulsion containing mole percent AgCl, 20 mole percent AgBr and 110 gm. of gelatin per mole of silver halide. An antiabrasion layer of clear gelatin was then coated over the emulsion layer. The following oleophilic water-permeable overcoating was prepared:

Solution A p 1% aqueous sodium bisulfite adduct of polyacrolein,

(av. mol. wt. 400,000) 50 Water 25 Ethanol 25 Solution A was coated over the antiabrasion layer at room temperature at 8 f.p.rn. and allowed to air dry.

The photosensitive element was then exposed through the base in contact with a halftone positive image to a high intensity-tungsten filament incandescent lamp, e.g., General Electric No. 2 Photofiood lamp, for 10 seconds at a distance of two feet and operating at 20 volts.

The following developer solution was prepared:

Solution B Water800 m1. Na SO (anhydrous)80 g. p-Methylamino phenol sulfate1 g. Boric acid-5 .5 g. KBr-2 g. NaOH-24 g. Water to make 1000 ml.

The exposed photosensitive element was developed for one minute in Solution B at 68 F. followed by short stopping for 15 seconds in a 5% acetic acid bath. Because of the high pH, 13.9, of Solution B and the use of a developing agent whose oxidation product inhibits subsequent development, the developed image was restricted to the emulsion surface.

A bleach-etch solution was then prepared as follows:

Solution C Water200 ml. Cupric nitrate18.8 g. Potassium bromide1 g. Lactic acid )15.6 ml. Hydrogen peroxide (3 )250 ml. Water to make 1000 ml.

The photosensitive element was bleached and etched in Solution C for 2 minutes. In the exposed areas, the silver image was bleached and the gelatin binder degraded to such an extent that the degraded areas could be rubbed away to the hydrophilic surface of the gelatin binder of the emulsion, leaving a positive, oleophilic image in the unexposed areas. This prepared plate was then mounted on a conventional offset printing press and using 5% acetic acid as the fountain solution and conventional ink, 1600 positive copies were obtained.

EXAMPLE 2 A film base was prepared as in Example 1 and then coated with the emulsion of Example 1, followed by an overcoating of a clear gelatin antiabrasion layer as in Example 1. An oleophilic overcoating was coated from an alcohol solution, containing 1 gm. of the Werner chrome complex of myristic acid (27% of the complex in isopropanol) per 200 ml. of ethanol, at room temperature and 8 f.p.m. Exposure was the same as in Example 1 except that the photoflood lamp was operating at 30 volts.

After exposure, the film was developed in Solution B for one minute followed by short stopping in 5% acetic acid for seconds. Development of the photosensitive element in Solution B restricted the development of the latent image to the surface of the emulsion. The restricted image was then bleached and etched in Solution C for 2 /2 minutes. The bleaching and etching caused the gelatin in the exposed areas to become degraded and softened. The softened exposed areas were then rubbed away with 5% acetic acid down to the hydrophilic gelatin binder found below the developed silver leaving a positive oleophilic image with a gelatin hydrophilic background suitable for printing copies thereof. The printing plate was then mounted on an offset printing press as in Example 1 and 22,600 positive copies were produced.

EXAMPLE 3 A film base of polyethylene terephthalate was prepared as in Example 1. A direct positive emulsion, as disclosed in assignees application Ser. No. 392,625, filed Aug. 27, 1964, US. Pat. 3,361,564, Jan. 2, 1968, containing 15 mole percent silver chloride, 85 mole percent silver bromide, 0.0017 gram of morpholine borane per mole of silver halide and having a gelatin to silver ratio of 0.68 was coated over the oleophilic film base. An oleophilic overcoating containing 10 ml. of 1 percent polyacrolein resin as described in Example 1, 65 ml. of water, and ml. of ethanol was then coated over the hydrophilic direct positive emulsion at 8 ft./min. The photosensitive element was then given an image exposure using a General Electric No. 2 Photofiood at a distance of 24 inches for 20 seconds at 115 volts.

The following developer was prepared:

Solution D Component 1:

Water-500 ml.

Hydroquinone45 g.

Sodium sulfiteg.

Sulfuric acid, C.P. grade4 ml.

Water to make 1000 ml. Component 2:

Water500 ml.

Sodium carbonate-30 g.

Potassium carbonate90 g.

Potassium bromide8.3 g.

Sodium sulfite-90 g.

Water to make 1000 ml.

To make Solution D, equal parts of Component 1 and Component 2 were used. Normally, ex osed elements are developed in Solution D for 45 minutes, but the exposed element of this example was developed in Solution D for 2 minutes thereby restricting the development to the surface of the emulsion. After development, the element was water washed for /2 minute and then bleached and etched in Solution C for 2 minutes. Since the emulsion used in this example was a direct positive emulsion, the gelatin in the unexposed surface areas became degraded and was removed by rubbing. Etching in the unexposed areas was not complete thereby leaving hydrophilic gelatin in the unexposed areas and an oleophilic image in the exposed areas. The element was rubbed with water and a conventional black lithographic offset ink, the ink adhering only to the oleophilic exposed areas. The inked surface was then rolled in contact with a piece of white paper giving a direct negative inked image on the paper. This process could be repeated to give many copies.

6 EXAMPLE 4 This is an example of total development and a partial bleach to produce a printing plate. A photosensitlve element including the Werner complex, oleophilic overcoating of Example 2 was prepared. The element was exposed as in Example 2. A developer was prepared as follows:

Solution E Water800 ml. p-Methylaminophenol sulfate3 g. Sodium sulfite (anhydrous)50 g. Hydroquinone--9 g. Potassium carbonate-50 g. Potassium bromide4.5 g. Water to make 1000 ml.

The exposed element was developed in Solution E for one minute and then immersed in a 5% acetic acid bath for 15 seconds. The developed element was bleached for 45 seconds in Solution C and immersed in the acetic acid solution for 15 seconds. The element was rubbed with a conventional lithographic ink. The ink held only to the unexposed, positive image areas and not to the negative, exposed areas which were bleached and etched by Solution C to such an extent that the oleophilic surface softened and rubbed away to leave some unoxidized negative silver image below in the hydrophilic gelatin binder. This printing plate was tested as in Example 3 and many high quality copies produced.

EXAMPLE 5 A photosensitive element including the overcoated oleophilic polyacrolein resin was pr pared as in Example 1. The element was exposed as in Example 1 and then r the silver image was surface developed for one minute in the following developer:

Solution F Solution F, of pH 13.4, was prepared by mixing 100 ml. of a solution containing 800 ml. of water, g. of Na SO 20 g. of p-methylaminophenol sulfate, 5.5 g. of boric acid, 2 g. of KBr and water to make 1 liter; ml. of a solution containing 800 ml. of water, 200 g. of Na SO 13.75 g. of boric acid, 5 g. of KBr, 60 g. of NaOH, and water to make 1 liter; and 800 ml. of water.

Following development, the element was water washed for /2 minute and then bleached and etched in the following solution:

Solution G Solution G is the same as Solution C of Example 1 except that the copper nitrate, potassium bromide, lactic acid, and hydrogen peroxide concentration were doubled prior to dilution to one liter.

The etching and bleaching treatment degraded the gelatin in the exposed areas to such an extent that the silver surface image could be rubbed away leaving a positive, oleophilic image in the unexposed areas surrounded by hydrophilic gelatin of the emulsion in the exposed areas. The printing plate was then inked and successfully tested as in Example 4.

EXAMPLE 6 This example describes a process of obtaining a negative working plate from the polyacrolein overcoated plate described in Example 1.

A photosensitive printing plate including the overcoating of sodium bisulfite adduct of polyacrolein was prepared as in Example 1. The photosensitive element was exposed through its support to a negative transparency as in Example. The exposed element was developed for one minute in Solution E of Example 4 except that prior to dilution to 1 liter with water, 2 grams of Na SO was added to Solution E. The original exposed areas were developed to give a tough, tanned negative image. The

developed element was then water washed for A minute and bleached in the following:

Solution H Potassium dichromate9.6 g. Sulfuric acid (conc.)10.7 ml. Water to make 1 1.

Following the bleaching in Solution H, the photosensitive element was water washed for one minute and then subjected to white light. Following exposure to white light, the image in the original unexposed areas was developed in Solution F of Example 5 for one minute, water washed for V: minute and then bleached and etched in the cupric nitrate, acid-peroxide bath, Solution C, Example 1 for 1% minutes. The second exposed image etches much more rapidly than the first chrometreated negative image. In this manner the original unexposed areas can be rubbed away leaving a negative oleophilic image surrounded by hydrophilic gelatin. This negative plate was inked and used to produce many high quality negative copies.

EXAMPLE 7 Example 7 is an example of full developement in a conventional lithographic developer followed by a partial bleach and etch. After the element of Example 5 was exposed as in Example 5, it was developed in Solution E of Example 4 for one minute. The developed element was water washed for one minute and then bleached and etched in the following solution for one minute.

Solution I M1. 3 M sodium chloride 100 1 M ferric nitrate 50 3 M phosphoric acid 50 Water 300 3% hydrogen peroxide 500 Solution I is a rapid acting, stable, surface bleaching and etching solution. The exposed areas were degraded on the surface to such an extent that the surface could be rubbed away leaving a positive, oleophilic image surrounded by hydrophilic gelatin in the exposed areas. The printing plate produced by the partial etching was tested as in Example 4 and was found to produce good quality copies.

EXAMPLE 8 A polyethylene terephthalate film base was subbed on both sides with a vinylidene chloride resin as disclosed in Example 4, U.S. Pat. 2,779,864 and then overcoated on one side with a clear gelatin backing.

A hydrophilic coating, layer 1, was prepared as follows:

Solution I Gelatin200 .g.

Distilled water-4000 ml.

1% aqueous dioctyl sodium sulfosuccinate5 3.5 g.

2% aqueous mucochloric acid-50 ml.

Distilled water97 ml.

The gelatin and water in Solution 1 were digested for minute at 125 F. prior to the addition of the other components.

Solution K, in the amount of 43.5 grams and comprising a mixture of 76% water, 16% silica gel (Si0 of average particle size of 7p), 7% gelatin, and 1% of a mixture of thymol and ethanol (160 g./l.), was then added to Solution I and the resulting mixture coated over the support on the side which was not gelatin backed to a weight of mg./dm. An orthochromatically sensitized emulsion containing 20 mol percent silver bromide, 80 mol percent silver chloride, 110 gm. of gelatin per mol of silver halide, and 0.43 percent of a polymeric dialdehyde hardener produced by the oxidation of of the anhydroglucose units of starch, was coated over layer 1 at a coating weight of 35 mg./dm. (calculated as AgBr).

An oleophilic overcoating, coated over the emulsion at F., was prepared as follows:

Solution L Werner chrome complex of stearic and myrisic acids (40 ml. of complex/8 liters of 40% ethanol) 8 20% aqueous solution of sodium bisulfite adduct of polyacrolein (av. mol. wt. 400,000) 2.4 10% aqueous solution of sodium dodecyl sulfate 3.2 Distilled water 112 areas to soften. The softened areas were rubbed away with a cotton cloth leaving a positive oleophilic image with a hydrophilic background. The prepared printing plate was mounted on a conventional offset printing press using one ounce of 14 Baum gum arabic per gallon of water buffered at pH 3.5 with H PO and NaH PO as the fountain solution and a quick drying ink. Two thousand good quality copies were obtained.

EXAMPLE 9 A polyethylene terephthalate film base was prepared as in Example 8 except that it was backed on one side with an aqueous gelatin solution containing C.I. Acid Violet (C.I. refers to Color Index, 2nd ed., Society of Dyes and Colorists) A gelatin sublayer was prepared and coated on the side of the base which was not backed. The sublayer was prepared by mixing gelatin, silica gel of average particle size of 7 microns, water, as in Example 8, and

adding 50 ml./200 gm. of gelatin of a 2% aqueous mucochloric acid hardener.

The silver halide emulsion of Example 8 was coated to a weight of 26.5 rng./dm. except that it did not contain any polymeric dialdehyde but did contain 7.0 gm. of the polyacrolein adduct described in Example 8 and 45 ml. of 2% aqueous mucochloric acid.

An oleophilic overcoating was prepared by mixing 1.92% of the polyacrolein adduct described in Example 8, 1% of an ethanol solution containing 37% formaldehyde, 0.34% of a mixture of saturated monocarboxylic acids having a C C or C chain length, 1% of a 10% aqueous solution of cetyl betaine, and water. The oleophilic coating was coated over the emulsion in a conventional manner.

The photosensitive element was exposed, developed, bleached, and mounted on an offset printing press as in Example 8. Some wear was evident after short runs, but such wear was not present if the element were aged for four days in a tropical oven at F. and 65% relative humidity before exposure and processing.

EXAMPLE 10 The following coating solution was prepared:

Solution M Gm. Gelatin 864 10% saponin-ethanol solution 200 Solution K (from Example 8) 182 Water to make 12,000 gm.

The gelatin and 10 liters of water were digested at 125 F. for minutes and allowed to cool to 100 F. prior to the addition of the remaining components. Solution M was then chilled prior to use. Prior to coating, Solution M was heated to 145 F. for 15 minutes and allowed to cool to 100 F. at which time 100 ml. of 12.5% aqueous solution of dialdehyde starch as described in Example 8 was added to Solution M. The polyethylene terephthalate subbed base of Example 8 was then coated with Solution M.

An orthochromatically sensitized emulsion in an amount of 6,000 grams and containing 20 mol percent silver bromide, 80 mol percent silver chloride and 110 gm. of gelatin per mole of silver halide was diluted with 5,000 ml. of water and melted at 120 F. After cooling to 100 F., 120 ml. of a 10% aqueous sodium dodecyl sulfate solution was added to the emulsion with 120 ml. of a 12.5% aqueous dialdehyde starch as described in Example 8. This emulsion mixture was coated at 70 ft./min. over the prepared sublayer.

An oleophilic overcoating was then coated over the emulsion. The overcoating, Solution N, was prepared as follows:

Solution N Werner-type chromium complex of stearic acid1 10 gm. 37% formaldehyde37 ml.

10% aqueous sodium dodecyl sulfate220 ml.

Water to make 12,000 gm.

Solution N was warmed to 85 F. and then coated over the emulsion. The photosensitive element was then aged for three days in a tropical oven as in Example 9. After aging, the element was exposed through the base to a line and continuous tone copy for 40 seconds at f/ 22, as in Example 8. Exposure was followed by development in a conventional developer for 75 seconds at 75 F. Development was followed by immersion of the element for seconds in a 2% aqueous acetic acid bath. An etching solution was prepared as follows:

Solution 0 Lactic acid, 85%1.5 .0 ml.

Water to make 1000 ml.

The developed element was then etched in Solution 0 at 75 F. for 35 seconds. The etched element was placed under running water and the softened areas corresponding to the exposed areas were rubbed away to the hydrophilic subbing layer leaving an oleophilic image on a hydrophilic background.

The printing plate was then rubbed with a commercially available asphaltum-gum etch as prepared by Western Litho Plate and Supply Co., St. Louis, Mo. This treatment increased the difference in the oleophilic/hydrophilic properties of the element. After air drying, the printing plate was mounted on an oifset printing press using con ventional ink and a gum arabic-phosphoric acid fountain solution and 500 good quality copies produced. There was no unwanted inking or wear of the printing plate. Similar results were obtained when Solution N contained a complex of myristic acid.

EXAMPLE 11 A polyethylene terephthalate base was subbed as in Example 8 and then coated on one side with the following hydrophilic gelatin coating.

Solution P Gelatin-1500 gm.

Thymol (16 gm./ 100 ml. ethanol-l50 gm. 10% saponin-ethanol150 gm.

Water15 l.

Solution P was prepared by heating the water and gelatin to 125 F. for 20 minutes, cooling to 100 F., and then adding the remaining components. The coating was then coated at two different weights, mg./dm. and 60 mg./dm.

The emulsion of Example 8, without the polymeric dialdehyde hardener was then coated over each of the samples at a coating weight of 48 mg./dm. (AgBr equiv.) and at a temperature of 100 F.

A /2% Werner chromium complex of stearic acid (1 gnu/200 ml. of ethanol) wa coated in a 25%/75% ethanol/water solution at 9 f.p.m. and room temperature over the emulsion layer. Samples were also coated with a 1% Werner complex of stearic acid.

The samples were then exposed through the base to a halftone image for 10 seconds to a General Electric No. 2 Photoflood lamp at a 2ft. maximum distance. The film was developed as in Example 8, immersed in a 5% acetic acid stop bath for 15 seconds, etched as in Example 8 for seconds, and finally immersed in the stop bath for 15 seconds. The etching bleached the exposed silver image and softened the adjacent gelatin so that the oleophilic surface coating rubbed away during inking to provide a fresh hydrophilic surface which would not accept any ink in the presence of water. When inked with a water, benzene, lithographic ink mixture, the oleophilic surface held the ink providing a planographic printing surface from which many positive copies could be produced.

EXAMPLE 12 Example 10 was repeated except that the dialdehyde starch in the sublayer was replaced with 200 ml. of 10% aqueous chrome alum. The dialdehyde starch in the emulsion was also replaced with chrome alum. The photo- 7 sensitive element was processed as in Example 10 producing similar results.

EXAMPLE 13 Solution Q Ml. Werner chromium complex of stearic acid 27.5 37% formaldehyde 9.25 10% aqueous sodium dodecyl sulfate Water to make 3000 ml.

This photosensitive element was exposed and developed as in Example 8 except that the element was immersed in the developer for 2 minutes. The developed element wa short stopped as in Example 8 and etched in Solution 0 for 45 seconds. After etching, the softened exposed areas were rubbed away as in Example 8 leaving an oleophilic positive image on a hydrophilic background. The paper base printing element was mounted on an offset press as in Example 10 and many good quality copies were obtained. Similar results were obtained when Solution Q contained a complex of myristic acid.

When a hydrophilic coating is used between the support and the emulsion layer, it usually contains silica in average particle size of 312 microns and gelatin. However, other adjuvants may be used including clay, polyacrylic acid, or any adjuvarit containing a hydrophilic group. Various other additives can be incorporated in the coating. These include hardeners, e.g., chrome alum, formaldehyde, mucochloric acid, dimethylolurea, polymeric dialdehyde starch produced by the oxidation of of the anhydroglucose units of starch, other polymeric aldehydes, 2,5-dimethoxytetrahydrofuran, and other hardeners used in photographic emulsions; gelatin or other suitable binders; and wetting agents such as dioctylsodiurn sulfosuccinate, saponin, etc. It is the purpose of this overcoating to insure that the difference in the oleophobic/ oleophilic properties will be sufficiently great such that no ink will adhere to the oleophobic background causing a spotted background on the printed copies.

The film supports useful in this invention are not limited to polyethylene terephthalate. If etching is complete to the support surface, the support surface must be hydrophilic but if partial etching or restricted development is used, the support surface need not be hydrophilic. These include metals, papers, cellulosic supports and all other bases such as those disclosed in US. Pats. 2,760,863; 2,779,864; 3,052,543; and Canadian Pat. 562,672.

The film supports may contain gelatin sublayers as well as resin sublayers as disclosed in Alles, U.S. Pats. 2,779,864 and 2,627,088. Suitable antihalation coatings may be coated over the support. Such coatings are disclosed in US. Pats. 1,523,485; 2,085,736; 2,274,782; and 2,282,890.

The emulsion layer may be any developable lightsensitive silver salt which may be processed by conventional means. These include the silver chloride, silver bromide, emulsions or mixtures thereof. The preferred emulsion contains silver halide grains of bromochloride containing at least 50 mol percent silver chloride. In addition, direct positive emulsions containing at least 50 mol percent silver bromide may also be satisfactorily used.

In addition, the emulsion may be either panchromatically sensitized or contain no optical sensitizer.

The preferred hydrophilic organic colloid binder for the silver halide emulsion is gelatin; however, any natural or synthetic water-permeable hydrophilic colloid binder may be used with the proviso that the binder is susceptible to the bleaching and etching of the acid-peroxide type bleaching solutions. The emulsions may also contain other standard emulsion ingredients such as hardeners, surfactants such as sodium dodecyl sulfate and sensitizers, etc. as well as other conventional emulsion additlves.

The water-permeable oleophilic overcoating can be obtained in many ways. One of the oleophilic substances which can be coated onto the outer emulsion surface is a metallo-organic Werner complex, which is a coordina tion complex compound of the type in which a trivalent metal is coordinated with an organic acid through its carboxylic oxygen atoms.

Trivalent chromium is the most common metal used in forming such complex compounds. The properties of the Werner-type complexes vary with the coordinated acid-groups. The long chain acid groups, e.g., stearato groups, myristo groups, and other hydrophobic groups make the complexes useful for providing a high degree of oleophilicity. Chromium complexes are generally acidic solutions of the chromium complex in 2-propanol, water, and sometimes acetone. The complex content will vary between about and 35%, depending on the molecular weight of the carboxylic acid. The amount of water varies from about 5% to depending upon the complex in question; the acetone, if any is present, is 'less than 3%; and usually the remainder of the commodity is 2-propanol.

Several methods of preparing the Werner-type chromium complexes useful in this invention are described in Chromium Complexes, F. B. Hauserman, Advances in Chemistry Series No. 23, American Chemical Society, pp. 338-356, (1959). The nomenclature of Werner complexes is also fully described in US. Pats. 2,273,040 and 2,356,161.

Polyacroiein is also suitable as an oleophilic coating. The preferred polyacrolein is a sodium bisulfite adduct of polyacroleirr having an average molecular weight of 400,000. Several methods of polymerizing polyacrolein are described in Acrolein, C. W. Smith, editor, John Wiley & Sons, Inc., New York, pp. 225233, (1962). Processes for production are available in British Pats. 990,263 and 948,669.

The emulsion, subbing layers, and oleophilic overcoating may be coated in any conventional manner such as those described in US. Pats. 3,038,441 and 3,063,868.

The radiation source used for exposing the films of this invention must furnish an effective amount of radiation. Such sources include carbon arcs, mercury arcs, electronic flash units, and photographic flood lamps.

When using an element without a hydrophilic support surface, the degree and time of exposure significantly influences the amount of reduced silver in the image and the depth of formation of the silver image. Of course, the results obtained with these elements are modified by the type of developer used but generally, a developer which restricts development of the image to the surface of the emulsion is preferred since then the image develops more rapidly and does not penetrate as deeply toward the base. A suitable surface developer contains p-methylamino phenol sulfate, sodium hydroxide and sodium sulfite. Restricted surface development will generally require complete etching and bleaching of the surface image when treated in the acid-peroxide bath.

Other suitable developers include the conventional lithographic developers, e.g., hydroquinone and sodium sulfite, etc. The conventional developers containing sodium carbonate, potassium bromide, boric acid, etc., may also be satisfactorily used. When development of the image is complete with the conventional developers on an element without the hydrophilic support surface, bleaching and etching is restricted to the surface of the developed image as shown in Examples 4 and 7.

The etch-bleach solutions are generally of the acid peroxide type such as those disclosed in British Pat. 793,550 published Apr. 16, 1958. Acid persulfate baths may also be used to etch the film. The etch-bleach process includes at least two reactions; (1) oxidation of the developed silver, (bleaching) and (2) degradation of the gelatin (etching). The rates of these reactions depend on the halide, heavy metal, hydrogen peroxide concentrations, and pH, the latter generally in the range of 1 to 3. The most effective pH range was 1.5-1.6. With exposure through the base followed by development, a negative silver image is obtained. The developed film is then placed in an etch-bleach bath until the etching destroys the developed regions of the emulsion.

The reaction of the light is the opposite when direct positive emulsions are used causing bleaching and etching to occur in the unexposed areas leaving an oleophilic negative image on a hydrophilic background. The stronger acid peroxide bleaches referred to above usually bleach and etch the entire image when the silver image is formed near the surface as previously described. However, surface bleaching of an image may also be effected by shorter bleach times as demonstrated by the previous examples. When bleaching is not complete, the surface bleached area may be removed by rubbing, leaving hydrophilic gelatin of the emulsion below and a positive oleophilic surface image in the background. This gives a partially recessed printing plate having the raised oleophilic surface and partially recessed hydrophilic surface.

It has been found that a bleach solution containing ferric ions is excellent for preparing the partially etched plates of this invention. Such surface bleach contains hydrogen peroxide, a citrate, citric acid, or phosphoric acid, and a salt containing a ferric ion along with a halide such as chloride, bromide, etc. This surface bleach reacts only on the surface to such an extent that the degraded gelatin may be removed leaving the hydrophilic gelatin of the emulsion as the background area for the positive olephilic surface image.

The effects of concentration of the various components in the etch-bleach solutions are described in Centa, J. M., PSA Journal, 11, p. 22, (1945); Marriage, A., Brit. Journal of Phot., 91, p. 142, (1944); Luckey, James, and Vanselow, Photo. Sci. Tech., 2, p. 130, (1955).

The product of this invention may be immersed in the developer and the etching solutions but other satisfactory methods of application, such as spraying, rolling, etc., may be used.

Prior to etching, the film element is usually treated in a stop bath, generally acetic acid or equivalent stop baths.

The printing plates of this invention may be mounted on conventional printing presses and many good quality copies produced therefrom.

This invention offers a simple process for obtaining lithographic printing plates. Printing plates of this invention produce tough, high quality copies and have long plate life. The printing plates of this invention are also inexpensive to produce since low silver content emulsions may be used in the process of this invention. The process used to produce the photographic plates of this invention offers the further advantage of a wide latitude in processing the exposed elements.

When making conventional printing plates, an ordinary negative is made and this is used for making a positive oleophilic image on the printing plate by contact exposure. The step of producing a negative is eliminated by this invention since the making of the negative is replaced by the direct preparation of the printing plate as described above.

A further advantage of this invention results from the relief image being ink receptive decreasing the possibillty of ink spots in the hydrophilic recessed areas.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A photographic element for the formation of a lithographic printing plate which comprises, in order,

(a) a support having a hydrophilic surface,

(b) an unexposed light-sensitive, hydrophilic waterpermeable organic colloid silver halide emulsion layer, and

(c) a relatively thin, oleophilic, water-permeable surface coating on the emulsion layer, said coating consisting of a member selected from the group consisting of (1) an oleophilic Werner-type chromium complex,

(2) a polymeric dialdehyde,

(3) mixtures of (1) and (2),

(4) mixtures of (l), (2), or (3) with a compatible binder, and

(5) mixtures of (l), (2), (3), or (4) with a surfactant.

2. A photographic element for the formation of a lithographic printing plate which comprises, in order,

(a) a support having a hydrophilic surface,

(c) a relatively thin, olephilic, water-permeable surface coating on the emulsion layer, said coating consisting of a member selected from the group consisting of (1) an oleophilic Werner-type chromium complex,

(2) polyacrolein,

(3) a polymeric dialdehyde,

(4) mixtures of (1), (2), and (3),

(5) mixtures of (1), (2), (3), or (4) with a surfactant.

3. An element as in claim 1 where said support is a film of polyethylene terephthalate and said hydrophilic surface contains clay, silica particles of 3 to 12 microns in size or polyacrylic acid polymer.

4. An element as in claim 1 where said Werner complex is a complex of trivalent chromium and myristic acid or stearic acid.

5. An element according to claim 1 wherein said colloid and binder are gelatin.

6. An element as in claim 1 where said coating comprises 30 to 70 parts of said Werner complex, up to 40 parts of formaldehyde and 5 to 40 parts of a surfactant.

7. A process for preparing a lithographic printing plate from a photosensitive element having a support bearing in order an unexposed, hydrophilic water-permeable organic colloid silver halide emulsion layer and a relatively thin, oleophilic water-permeable surface, said process comprising:

( 1) exposing said element to an image, by actinic radiation;

(2) developing said exposed element;

(3) treating the developed element in a silver etchbleach solution, and

(4) removing the etched portion of the developed silver image, including the oleophilic surface continuous therewith by rubbing to leave a recessed hydrophilic area and an oleophilic image in the unexposed areas.

8. A process according to claim 7 wherein said oleophilic surface is a member selected from the group consisting of (1) an oleophilic Werner-type chromium complex;

(2) polyacrolein;

(3) a polymeric dialdehyde;

(4) mixtures of (l), (2) and (3);

(5) mixtures of (l), (2), (3) or (4) with a compatible binder, and

(6) mixtures of (1), (2), (3), (4) or (5) with a surfactant.

9. A process according to claim 7 wherein said colloid and binding agent are gelatin.

10. A process according to claim 7 wherein the treating with the etch-bleach solution is of a duration to allow only partial removal of the gelatin layer in the developed area.

11. A process as in claim 9 Where said etch'bleach solutions are of the acid-peroxide type or acid-persulfate type having apH of 1 to 3.

12. A process as in claim 11 where said etch-bleach solution comprises a copper salt, a water-soluble bromide, hydrogen peroxide and an acid.

13. A process as in claim 9 where the support of said element has a hydrophilic surface and said developed image is removed down to said hydrophilic support.

14. A process as in claim 10 Where said development is controlled to reduce only the exposed silver halide in the upper portion of the silver halide emulsion layer.

15. A process as in claim 10 where said developed element is immersed in a dilute acid stop bath solution immediately after development.

16. A process as in claim 10 where said bleach-etch solution contains citric or phosphoric acid, hydrogen peroxide and a ferric salt.

17. A process as in claim 10 where said development is controlled by developing the emulsion surface in a high alkaline p-methylamino phenol sulfate developer of pH 12.0 or greater.

References Cited UNITED STATES PATENTS 4/1922 Schlecht 101-466 6/1964 Torstenson 101-466 US. Cl. X.R. 9636.3, 87