Photosensitive Element Containing A Photoreducible Palladium Compound And The Use Thereof In Physical Development

Abstract

Light-sensitive palladium compounds are reduced on exposure to actinic light to nuclei which are catalytic centers for the deposition of metal from a physical developer. The palladium nuclei are catalysts for deposition of metal from stable physical developers, which developers do not respond to catalysts used in the physical development of silver latent images.

Description

This invention relates to photographic elements and processes. In a particular aspect it relates to processes and elements for the physical development of non-silver latent images.

Physical development of photographic images concerns the amplification of a latent image by the deposition of metal from a developer bath comprising a metal salt or complex and a reducing agent. The bath is formulated so that it is stable under conditions of storage, but in the presence of a catalyst, such as the latent image, it decomposes and deposits reduced metal on catalytic sites. Once a catalytic site is enveloped with metal deposited from the bath it is essential that the reduced metal be autocatalytic, that is, it too must catalyze the decomposition of the bath.

Physical development involving silver compounds is well known. However, such processes have not had any substantial application due to the fact that silver physical developer solutions are extremely unstable. Thus, shortly after a physical developer bath is prepared by mixing silver salts and reducing agents, reduced silver begins to deposit rapidly, so that in a few hours the bath is completely decomposed and is useless. This type of instability is inherent in silver physical developer baths because of the autocatalytic properties of silver metal.

Physical developer baths which are stable under storage conditions can be formulated from salts or complexes of some metals other than silver; however, these stable physical developer baths do not respond to the catalysts which are commonly used in silver physical development, such as colloidal silver, zinc sulfide, nickel sulfide, etc.

Therefore, it is an object of this invention to provide new and improved photographic elements and processes.

It is a further object of this invention to provide novel photographic processes wherein photographic images are developed with relatively stable physical developers.

It is a still further object of this invention to provide novel processes where the only steps necessary to produce stable photographic images are exposure and physical development.

It is another object of this invention to provide novel elements which can be used in physical development processes.

The above and other objects of this invention will become apparent to those skilled in the art from the further discussion of the invention which follows.

In accordance with the present invention there is provided a photographic element containing a light-sensitive palladium compound which on exposure to actinic light forms catalytic centers or sites for the deposition of metal from a physical developer. Catalytic centers or sites are formed by photoreduction of the palladium compound to elemental palladium, or to a compound which is readily reduced to elemental palladium. After exposure the element can be washed to remove unexposed palladium compound, or in some embodiments this washing is not required. The element is then contacted with a physical developer comprising a heavy metal salt, a complexing agent for the metal salt and a reducing agent. In a preferred embodiment the palladium nuclei formed by exposure act as catalytic centers or sites for the deposition of metal from a bath of the physical developer. They constitute a latent image which is formed by exposure and which is developed and given density by building up a deposit of metal thereon from the physical developer bath. In another embodiment the element is contacted with a receiving sheet containing the physical developer and the unexposed palladium compound migrates to the receiving sheet where it is reduced and developed.

A wide variety of light-sensitive palladium compounds such as salts and complexes of palladium are useful in the elements of this invention. Light-sensitive palladium compounds which are useful in the practice of the present invention include those having the general formula:

[Pd(L).sub.x ].sub.y M.sub.z (I)

where L is a ligand such as a halogen ligand such as bromine, chlorine, or iodine, a carboxylic acid ligand such as a malonate group, an oxalate group, etc., and aromatic ligand such as phenol, styrene, naphthol, etc., a nitrogen ligand such as ammonia, an amine such as methyl amine, ethyl amine, benzyl amine, propane diamine, tetraethylene pentamine, aminoethanol, methylaminoethanol, aminonaphthol, bipyridine, phenanthroline, ethylene diaminetetraacetic acid, etc., a nitrile such as nitrilotriethanol, benzonitrile, etc., an imine such as iminodiethanol, an oxime such as salicylaldoxime or an azide such as benzhydrazide, a phosphorous ligand such as triarylphosphine, trialkylphosphine, etc., an arsenic ligand such as triarylarsine, trialkylarsine, etc., an antimony ligand such as triarylantimony, trialkylantimony, etc., and the like; M is an ion such as a hydrogen ion, an inorganic acid ion such as a chloride ion, a bromide ion, an iodide ion, a sulfate ion, a nitrate ion, a phosphate ion, etc., an organic acid ion such as an acetate ion, an acrylate ion, an ion, a malonate ion, etc., a metal ion such as a sodium ion, a potassium ion, a calcium ion, a strontium ion, an aluminum ion, etc., an onium ion such as those containing nitrogen, phosphorus or sulfur like a quaternary ammonium ion, a quaternary phosphonium ion, a tertiary sulfonium ion, etc., and the like, or M can be a [Pd(L).sub.x ] group; x is an integer from 0 through 4; y is an integer from 1 through 4; z is an integer from 0 through 2, and x and z are not 0 at the same time.

Light-sensitive compounds of Formula (I) which are useful in the present invention include: palladium diammine dichloride, palladium styrene dichloride, palladium di(tributylphosphine) dichloride, palladium di(benzonitrile) dichloride, palladium di(triphenylphosphine) dichloride, palladium di(triphenylarsine) dichloride, palladium di(triphenylantimony) dichloride, palladium di(1-naphthol) dichloride, palladium di( 2-naphthol) dichloride, palladium di( 5-amino-1-naphthol) dichloride, palladium di(benzylamine) dichloride, palladium o-phenylene-diamine dichloride, palladium 1,10-phenanthroline dichloride, palladium 2,2'-bipyridine dichloride, palladium di(benzyhydrazide) dichloride, palladium salicylaldoxime dichloride, palladium di-(N-phenyl-2-naphthylamine) dichloride, and potassium palladous chloride.

Certain palladium salts and complexes are preferred because they are not readily reduced by the reducing agent in the physical developer bath. Therefore, with these preferred compounds unexposed palladium compound need not be removed from the element between exposure and development. Use of these preferred compounds permit reduction in the number of processing steps and greater efficiency of operation since non-fogged images can be obtained without washing between development and exposure.

Compounds of Formula I useful in the present invention which are not readily reduced by the reducing agents of the present invention include: palladium tetrammine di(tetraphenylboride), palladium ethylenediamine dichloride, palladium di(1,3-propanediamine) dichloride, palladium tetra(methylamine) dichloride, palladium triethylenetetramine dichloride, palladium tetra-(tetraethylenepentamine) dichloride, palladium tetra(2-diethylaminoethanol) dichloride, palladium tetra(2-aminoethanol) dichloride, palladium tetra( 2-methylaminoethanol) dichloride, palladium tetra(nitrilotriethanol) dichloride, palladium tetra( 2,2'-iminodiethanol) dichloride, palladium tetra(triphenylphosphine) dichloride, palladium tetrammine dichloride, palladium tetrammine dibromide, palladium diammine oxalate, palladium triphenylarsine oxalate, palladium di(triphenylantimony) oxalate, palladium 2,2'-bipyridine oxalate, palladium 1,10-phenanthroline oxalate, palladium oxalate, potassium palladium oxalate, potassium palladium malonate, palladium tetrammine palladium dioxalate and palladium tetrammine palladium tetrachloride.

Light-sensitive palladium compounds useful in the practice of the present invention can be prepared by techniques known to those skilled in the art. Preparation of some of the palladium compounds useful in the present invention are shown in Examples 1, 3 and 6. Preparative methods for other palladium compounds can be found in such works as Encyclopedia of Chemical Reactions, C.A. Jacobson; Reinhold Publishing Corp. N.Y.; Vol. V, 1953, pp. 301-321; and Tretise on Inorganic and Theoretical Chemistry, G.W. Mellor; Longmans Green & Co., N.Y., Vol. XV, 1936, pp. 654-685.

The physical developer which is used to produce a visible image can comprise an aqueous bath in which is dissolved a salt of a heavy metal, a complexing agent for the metal ion, and reducing agent. The physical developer bath is chosen so that deposition of the heavy metal from the bath is catalyzed by palladium nuclei produced on exposure. The heavy metal deposited from the bath must itself be autocatalytic; that is, it must act as a catalyst for further deposition of metal from the developer. This is necessary in order that deposition and development will continue after palladium nuclei are enveloped with heavy metal. With respect to the Periodic Table, suitable heavy metals can be selected from Group VIII metals such as nickel, cobalt, iron, palladium and platinum, Group VIB metals such as chromium and Group IB metals such as copper, silver and gold. Almost any heavy metal salt which is a source of the desired heavy metal ions can be employed. Suitable heavy metal salts useful in the invention include heavy metal halides such as cobaltous bromide, cobaltous chloride, cobaltous iodide, ferrous bromide, ferrous chloride, chromium bromide, chromium chloride, chromium iodide, copper chloride, silver bromide, silver chloride, silver iodide, gold chloride, palladium chloride and platinum chloride, heavy metal sulfates such as nickel sulfate, ferrous sulfate, cobaltous sulfate, chromium sulfate, copper sulfate, palladium sulfate and platinum sulfate, heavy metal nitrates such as nickel nitrate, ferrous nitrate, cobaltous nitrate, chromium nitrate and copper nitrate, and heavy metal salts of organic acids such as ferrous acetate, cobaltous acetate, chromium acetate and copper formate. Baths can be formulated based on a single heavy metal or based on mixtures of heavy metals. When more than one heavy metal is employed in the bath, the image which is deposited will generally be an alloy of the two metals. Physical developers based on noble metals such as silver, gold and platinum are relatively unstable and cannot be stored for long periods of time. However, such physical developers are operative in the processes of this invention and can be employed if the developer bath is prepared shortly before use.

The complexing agent employed in the physical developer bath should tie up the metal ions so that they show a lessened tendency to be reduced spontaneously. However, the complexing agent should not bind the metal ions so tightly that they will be unable to be reduced and deposited on the latent image sites in the presence of the catalyst. Suitable complexing agents include ammonium salts such as ammonium chloride, organic acids such as aspartic acid, malic acid, citric acid, glycolic acid, salts of organic acids such as sodium citrate, potassium citrate, sodium glycolate, potassium glycolate, sodium succinate, potassium succinate, potassium sodium tartrate, etc. A single complexing agent can be used or a combination of more than one complexing agent can be incorporated in the physical developer bath.

The reducing agent can be any compound which provides a ready source of electrons for the reduction of the metal ions and which does not otherwise interfer with development. A general criteria for a reducing agent useful in the physical developers of the present invention is that the potential of the chemical couple of the reducing agent, written as follows:

Reducing agent .revreaction. Products + electrons

must be more positive than that for the metal or metals which are to be deposited from the bath. For example, the potential for the nickel couple:

Ni.degree. .revreaction. Ni.sup.+.sup.+ + 2 electrons

is +0.277 volts for acidic solutions. It is necessary for the reducing agent to possess a potential that is greater, i.e., more positive, than +0.277 volts in order that it be capable of reducing nickel ions in the bath. Suitable reducing agents include hypophosphites such as sodium hypophosphite, manganous hypophosphite, potassium hypophosphite, etc., hydrosulfites such as sodium hydrosulfite, potassium hydrosulfite, calcium hydrosulfite, etc., borohydrides such as sodium borohydride, potassium borohydride, etc., hydrazines, and the like.

There can be added to the physical developer bath a variety of other materials such as buffering agents, acid or base to adjust the pH, preservatives, etc. in accordance with usual practices.

The proportions in which the various components of the physical developer are present in the bath can vary over a wide range. Suitable concentrations of metal salt in the developer bath are in the range of from about 0.01 to about 0.5 moles of metal salt per liter of bath. The upper limit of concentration is controlled by the solubility of the particular metal salt employed. Preferably, the bath is between about 0.05 molar and 0.25 molar with respect to metal salt. The relative proportions of metal salt and complexing agent are dependent upon the particular metal salt or salts and the particular complexing agent or agents which are employed. As a general rule sufficient complexing agent should be incorporated to bind the metal ions and lessen the tendency of the metal ions to be reduced prior to use of the developer. Depending upon the particular metal salt and complexing agent employed, the amount of complexing agent present can vary from about 4 mole to about 10 moles of complexing agent per mole of metal salt present. The reducing agent can be present in amounts of from about 0.1 moles to about 5 moles of reducing agent per mole of metal salt present.

In preparing photosensitive elements utilizing the palladium compounds of this invention, the palladium compound can be imbibed in or coated on a support, or it can be incorporated in a self-supporting binder.

When the palladium compound is imbibed in a support, an aqueous solution of the compound is prepared and a porous support is immersed in the solution. After drying a photosensitive element is obtained.

Suitable porous supports include paper, coated paper, porcelain, polymeric films, such as are described hereinafter, on which is coated such porous materials as gelatin, olefinic polymers such as polyvinyl alcohols, polyvinyl phthalates, etc., carboxyl containing polymers such as carboxymethyl cellulose, cellulose ether phthalates, cellulose ether succinates, cellulose ether maleates, copolymers of alkyl acrylates with acrylic acid, etc., and the like.

The amount of palladium compound that is taken up in the support generally varies from about 2 to about 25 mg. of palladium/ft..sup.2 The amount which is absorbed by a polymer coating on film base is dependent on the nature and coverage of the polymer, the degree to which it has been crosslinked, the temperature of the imbibing bath, and the pH of the bath. Coverages as low as 2 mg. of palladium/ft.sup.2 are adequate when using development conditions described herein. The photographic speed will increase with increasing concentration of the light-sensitive palladium compound. The preferred coverage is generally in the range of 10 to 25 mg. of palladium/ft..sup.2

When the palladium compound is coated on a support, it is generally coated with a hydrophilic binder. A solution or dispersion of the palladium compound and binder is formulated, and after thorough mixing it is coated on the support by any well-known coating process such as hopper coating, doctor-blade coating, dip coating, swirl coating, spray coating, etc.

Suitable binders in which the palladium compounds of the present invention can be incorporated include gelatin such as bone gelatin, pigskin gelatin, etc.; olefinic polymers such as polyvinyl alcohol, polyvinyl phthalates, etc., carboxyl containing polymers such as carboxymethyl cellulose, cellulose ether phthalates, cellulose ether succinates, cellulose ether maleates, copolymers of alkyl acrylates with acrylic acid, etc., and the like. Non-hydrophilic polymers such as ethyl cellulose can be used in procedures which do not involve imbibition and where the coating composition is a stable dispersion which gives a porous coating upon drying. Such a coating is described in Example 8.

The palladium compound-binder composition can be coated from aqueous solution, or it can be coated from an organic solvent. In some instances, where an organic solvent is employed, the palladium compound-binder composition will form a water-in-oil type dispersion with the organic solvent. Suitable solvents include water immissible hydrocarbon solvents such as benzene, toluene, etc.; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, etc.; and the like. Mixtures of such solvents can be employed advantageously in the practice of this invention.

In preparing the coating compositions utilizing the palladium compounds disclosed herein useful elements are obtained where palladium is present in an amount equal to at least about 0.5 weight percent of the coating composition. The upper limit in the amount of palladium present can be varied widely. When a binder is employed, palladium is normally present in an amount from about 0.5 weight percent of the coating composition to about 20 weight percent of the coating composition. A preferred weight range for palladium in the coating composition is from about 1 weight percent to about 10 weight percent.

Coating thicknesses of the palladium compound-binder compositions on a support can vary widely. Normally, a wet coating thickness in the range of about 0.001 inch to about 0.01 inch is useful in the practice of the invention. A preferred range of coating thickness is from about 0.002 inch to about 0.007 inch before drying, although such thicknesses can vary depending upon the particular application contemplated for the element.

Suitable supports for coating the palladium compound-binder compositions of the present invention include paper, polyethylene-coated paper, glassine, vegetable parchment, polymeric films such as polystyrene film, cellulose nitrate film, cellulose acetate film, cellulose acetate-butyrate film, cellulose acetate-propionate film, polyethylene-terephthalate film, polyethylene-sebacate film, polyethylene-adipate film, etc., and the like. In some embodiments of this invention, a separate support need not be utilized, the binder acting as the support material.

Elements prepared according to the present invention can be exposed by techniques well known to those skilled in the art of photography. Since the compounds of this invention exhibit their greatest sensitivity in the blue and near ultraviolet regions, light sources rich in such radiation are preferably employed. Exposure to actinic light causes the reduction of the palladium compound to nuclei of elemental palladium which act as catalytic centers or sites for the deposition of metal from the physical developer. Depending upon the light source and the particular palladium compounds, exposure times of from several seconds to several minutes give satisfactory latent images.

Development of exposed elements can be effected by contacting the element with a physical developer bath, for example by immersion, for a period of time sufficient to produce an image of the desired density. The time required to deposit a satisfactory heavy metal image from the physical developer bath on the element can vary from 1 second to several hours depending upon the composition of the particular bath being employed, the density of heavy metal image desired, and the temperature of the bath. Satisfactory images can be produced from baths at room temperature (20.degree. C.) or at elevated temperatures. Bath temperature of from 20.degree. C. to 100.degree. C. are preferred.

Development can also be effected using a diffusion transfer process. In such a process the photosensitive element is exposed in the usual manner and is then contacted with a receiving sheet into which has been imbibed one of the physical developer solutions described above. When the element and the receiving sheet are in contact, heat is applied to promote diffusion of unexposed palladium compound from the element to the receiving sheet. Contact temperatures of from 45.degree. C. to 100.degree. C. are suitable. In the unexposed areas of the element the palladium compound migrates from the element to the receiving sheet where it is reduced and catalyzes the reduction of heavy metal salt in the sheet to form a positive image on the receiving sheet. In the exposed areas the palladium compound does not migrate as rapidly because of the smaller differential in concentration of palladium compound between the exposed areas of the element and the receiving sheet which results from the formation of palladium nuclei on exposure and the reduction of palladium compound in the vicinity of these nuclei. Thus, the difference in concentration of the palladium compound in exposed and unexposed areas of the element permits the transfer of sufficient palladium compound to the receiving sheet from unexposed areas of the element before a significant amount of palladium compound has been transferred from exposed areas of the element. Although the image formed on the receiving sheet can be used as such, in some instances it is preferred that the image be darkened further by immersing the receiving sheet in one of the physical developer baths described herein.

The physical developer solutions which are imbibed into the receiving sheet differ somewhat from the physical developer baths used for immersion development in that they contain a greater proportion of heavy metal salt and reducing agent and a lesser proportion of complexing agent. The additional reducing agent is required to effect reduction of the unexposed palladium compound. The ratio of reducing agent to metal salt can be the same as described above, although ratios of from about 1 to about 5 moles of reducing agent per mole of metal salt are preferred. The ratio of complexing agent to metal salt is lower than the range indicated above. Ratios of complexing agent to heavy metal salt of from about 0.5 moles to about 2.0 moles of complexing agent per mole of heavy metal salt are preferred. As in the case of the baths discussed above, these ratios will vary depending upon the particular metal salt and complexing agent employed.

The photosensitive compositions and elements of this invention find use in a wide variety of applications. Elements containing the photosensitive palladium compounds of this invention can be exposed to actinic radiation through a subject to be copied such as a transparency, and can then be developed with an appropriate physical developer bath. In this manner the processes and elements of this invention can be used to produce positive or negative copies from originals and continuous tone and line negatives for a variety of use for which systems based on silver are employed. Properties of certain of the heavy metal images can be utilized for specialized applications. For example, ink receptive metals can be used to produce lithographic printing masters, electrical conducting metals can be used to prepare printed circuits, and magnetic metals can be used to prepare magnetic images or records.

The ink receptive properties of the heavy metal deposited from the physical developer bath can be employed advantageously to make lithographic plates. Elements used to prepare such lithographic plates and masters require that the support and binder used be hydrophilic. Thus, after exposure and development, the heavy metal image areas will readily receive ink while in background areas, where heavy metal has not been deposited, ink will be repelled by the hydrophilic support or binder. These elements should be developed for a period of time sufficient to deposit from the developer bath enough heavy metal to mask the hydrophilic properties of the substrate in image areas. While the density of heavy metal required will vary depending upon the particular substrate and heavy metal employed, and the conditions under which it has been deposited, a heavy metal image density of about 1 gram/square foot or greater is generally sufficient to mask the hydrophilic properties of the substrate.

The electrical conductive properties of images of such heavy metals as copper, iron, nickel, etc., can be employed to produce printed circuits using the elements and process of this invention. For such applications, the supports and binders used should be non-conductive.

The invention is further illustrated by the following examples which include preferred embodiments thereof.

EXAMPLE 1

Four grams of potassium chloride were dissolved in 150 ml of water and 2.5 gm. of palladium chloride (PdCl.sub.2) were added to this solution. The mixture was stirred until all of the palladium chloride was dissolved. The solution was evaporated on a steam bath to a volume of 50 ml. and cooled in an ice bath. The resulting crystals were washed twice with cold water, then washed with ethanol and then ether. They were dried at room temperature. The yield of potassium palladous chloride (K.sub.2 PdCl.sub.4) was approximately 75 percent based on the palladium chloride. A strip of water-leaf paper stock was impregnated with a dilute (one-half percent) solution of potassium palladous chloride. After drying, the impregnated strip was exposed to a 350 watt mercury arc at a distance of 14-inches for one minute. The strip was then washed for several minutes in running water to remove unexposed palladium compound. It was then immersed in the following cobalt-type physical developer at 80.degree. C.

cobaltous chloride -- CoCl.sub.2.sup.. 6H.sub.2 O 7.5 g. Aspartic acid -- HOCOCHNH.sub.2 CH.sub.2 COOH 20.0 g. Sodium hypophosphite -- NaH.sub.2 PO.sub.2.sup.. H.sub.2 O 7.5 g. Water to make 1 liter

After a one-minute immersion, the exposed areas of the strip had a density of 0.8 and the unexposed areas remained essentially unchanged.

EXAMPLE 2

A strip of paper stock was prepared, exposed and washed as in Example 1. The strip was then immersed into a physical developer containing nickel ions as the source of heavy metal ions and sodium hypophosphite as the reducing agent (sold as "Enplate NI-410" by Enthone, Inc., New Haven, Connecticut.). After three seconds' immersion at 90.degree. C. the exposed portion of the strip developed to a density of from 0.6 to 1.0 and the unexposed area remained essentially unchanged.

EXAMPLE 3

Palladium tetrammine chloride (Pd(NH.sub.3).sub.4 Cl.sub.2) was prepared by dissolving palladous chloride in concentrated ammonium hydroxide, then lowering the pH of the solution to 6.0 with hydrochloric acid. A paper strip was impregnated with a dilute solution (0.5 percent) of this complex and dried. After drying, the strip was exposed as described in Example 1. The strip was developed by immersion for two seconds in the following nickel-type physical developer at 90.degree. C.

nickel chloride -- NiCl.sub.2.sup.. 6H.sub.2 O 30 g. Sodium hypophosphite -- NaH.sub.2 PO.sub.2.sup.. H.sub.2 O 10 g. Ammonium chloride 50 g.

Water was added to make one liter of solution and the pH was adjusted to 9.0 with ammonium hydroxide. The exposed areas of the strip developed to a density of 1.5 whereas the unexposed area remained unchanged.

EXAMPLE 4

A paper strip was impregnated with palladium tetrammine chloride as in Example 3 and dried. The strip was exposed with a mercury arc as described in Example 1, and was developed by immersion for five seconds in the following iron-type physical developer at 75.degree. C.

ferrous sulfate -- FeSO.sub.4.sup.. 7H.sub.2 O 30 g. Rochelle salt (KNa Tartrate) 50 g. Sodium hypophosphite -- NaH.sub.2 PO.sub.2.sup.. H.sub.2 O 10 g.

Water was added to make one liter of solution and the pH was adjusted to 9.1 with concentrated ammonium hydroxide. The exposed areas of the strip developed to a density of 0.5 whereas the unexposed area remained essentially unchanged.

EXAMPLE 5

A paper strip was impregnated with potassium palladous chloride as in Example 1 and dried. The strip was exposed to a mercury arc as described in Example 1. The exposed strip was then washed for several minutes in running water to remove unreacted palladium compound. It was then developed by immersion in the following chromium-type physical developer for 20 seconds at 99.degree. C.

chromium acetate -- CrAc.sub.3 30 g. Sodium acetate -- NaAc.sup.. 3H.sub.2 O 20 g. Sodium glycolate 40 g. Sodium citrate .sup.. 5-1/2 H.sub.2 O 40 g. Sodium hypophosphite .sup.. H.sub.2 O 10 g.

Water was added to make one liter of solution. The pH of the solution was 5.7. After development the exposed area of the strip had a density of 0.8.

EXAMPLE 6

Potassium palladium oxalate (K.sub.2 PdOx.sub.2) was prepared as follows. Two grams of potassium palladous chloride were dissolved in 20 ml. of water. Another solution was prepared consisting of 10 grams of potassium oxalate (K.sub.2 Ox.sup.. H.sub.2 O) in 40 ml. of water. The two solutions were mixed together and stirred for 10 minutes at room temperature. The precipitate which formed was filtered and washed with ethanol until the filtrate was free of chloride ion. It was then washed briefly with ethyl ether and dried at room temperature. The yield of potassium palladium oxalate was approximately 60 percent based on potassium palladous chloride. Two paper strips were impregnated with a dilute solution (0.5 percent) of this complex and dried. One of the strips was then exposed behind a negative to a 350 watt mercury arc at 14-inches distance for one minute. The second strip was exposed through a line copy negative to a 250 watt photo-flood lamp (GE No. 2) at 12-inches distance for one minute. Both samples were developed by immersion for five minutes in the following nickel-type physical developer at 60.degree. C.

nickel sulfate -- NiSO.sub.4.sup.. 6H.sub.2 O 23.7 g. Sodium hypophosphite -- NaH.sub.2 PO.sub.2.sup.. H.sub.2 O 23.9 g. Malic acid (DL) -- HOCOCHOHCH.sub.2 COOH 48.2 g. Sodium succinate -- (CH.sub.2 COO).sub.2 Na.sub.2.sup.. 6H.sub.2 O 16.2 g.

Water was added to make one liter of solution. The pH of the solution was 6.0. The exposed areas of both strips showed densities above 1.0. The unexposed areas had densities less then 0.01.

EXAMPLE 7

The following solution was prepared:

Poly(vinyl alcohol) (sold as "71-30" by E.I. DuPont De Nemours & Co.), 5 percent aqueous solution 10 g.

Palladium tetrammine chloride (0.5 percent solution) 10 ml.

Boric acid (1 percent solution) 1 ml.

The above solution was coated on a poly(vinyl alcohol) subbed polyester film base using an 0.005 inch coating knife. After drying it was exposed behind a negative to a 350 watt mercury arc at a distance of 14 inches for one minute. It was developed by immersion for 15 seconds in the cobalt-type physical developing bath described in Example 1. The exposed area of the film strip had a density of over 1.0 whereas the unexposed area remained transparent.

EXAMPLE 8

Ten ml. of the coating solution described in Example 7 was dispersed in 20 ml. of a 3.5 percent solution of ethyl cellulose (sold as "T-10," by the Hercules Chemical Co.) in toluene by means of a blender. A stable water-in-oil dispersion was obtained. A coating of the dispersion was made on paper using a 0.005 inch knife and dried. The coated element thus obtained was exposed and developed as in Example 7. The exposed area of the strip had a density exceeding 1.0 whereas the unexposed area had a density of less than 0.01.

EXAMPLE 9

A strip of poly(ethylene terephthalate) support coated with gelatin at a coverage of 350 mg. of gelatin/ft.sup.2 was immersed into a 0.5 percent solution of potassium palladium oxalate (K.sub.2 PdOx.sub.2) whose pH had been lowered to 2.0 by the addition of p-toluenesulfonic acid. After 10 minutes immersion, the film was wiped, dried, and exposed for 30 seconds through a line copy negative to an exposure unit drawing 1000 watts distributed among a small fan and 28 tungsten bulbs. The bulbs are 2-1/2 inches from the negative during exposure. The film was then developed for 3 seconds in the nickel-type physical developer of Example 3. The areas of film which had been exposed to light developed to a density greater than 2, whereas the unexposed areas of the film remained clear, thus resulting in a good quality positive copy of the original negative. A sample of the film which had been imbibed with a potassium palladium oxalate solution whose pH had not been lowered required a 2-1/2 minute exposure in order to obtain a good image using the same development procedure.

EXAMPLE 10

A strip of paper was immersed into a 0.5 percent solution of potassium palladium oxalate whose pH had been lowered to 2.8 by the addition of oxalic acid. After 10 minutes immersion, the paper was dried and exposed for 7 seconds through a line copy negative to the exposure unit described in Example 9. It was then developed for 3 seconds in the nickel physical developer of Example 3. A good quality positive print was obtained. A sample of the film which had been imbibed with a potassium palladium oxalate solution whose pH had not been lowered from its original value (5.8) required an exposure of 30 seconds in order to obtain a good image using the development conditions described above.

EXAMPLE 11

A paper strip was impregnated with palladium tetrammine chloride and dried. It was exposed as described in Example 7 and developed for 1 minute at 25.degree. C. in a physical developer containing copper ions and a reducing agent (sold as "Enplate CU-400" by Enthone, Inc.) The exposed areas of the strip had a dark image whereas the unexposed areas had a very faint image.

EXAMPLE 12

A strip of polyethylene terephthalate support coated with gelatin at a coverage of 350 mg. of gelatin/ft.sup.2 was immersed into a 0.5 percent solution of potassium palladium oxalate whose pH had been adjusted to 2.8 by means of oxalic acid. After 10 minutes immersion the coating was wiped, dried, and exposed through a line copy negative to a fluorescent light source [8-watt black light tube (GE)] for 30 seconds at a distance of 2 inches. Next, a sheet of baryta paper was impregnated with the following physical developer to form a processing web and receiver.

Nickel chloride 0.6 molar Malic acid 0.6 molar Sodium hypophosphite 0.6 molar Water to make 1 liter Concentrated ammonium hydroxide added to raise the pH to 7.0

The web was placed against the exposed film, and heated at 135.degree. F. for 3 seconds. A dark image appeared on the receiver sheet in the areas which were in contact with the unexposed areas of the gelatin film. After separating the negative and the receiver sheet, the image on the latter could be darkened by immersing it in a physical developer of the type used in Example 3.

EXAMPLE 13

A subbed polyethylene-coated paper support on which is coated a heavy layer of a titanium dioxide-gelatin mixture was soaked in a 0.5 percent potassium palladium oxalate (K.sub.2 PdOx.sub.2) solution at pH 2.8. The sheet was exposed through a negative line image by means of a bank of eight 8-watt black-light tubes (GE F8T5-BL) for 30 seconds at a distance of 2 inches. It was then developed for approximately 2 minutes in the nickel physical developer solution of Example 3 at 95.degree. C. A heavy metallic nickel image appeared on the sheet in the exposed areas, whereas the unexposed areas remained free of metal. The developed sheet was put on an offset printing press, wet with fountain solution (a dilute acid) and then inked with an oil-based ink. The plate took up ink in the nickel image areas and the background remained ink free. Several impressions were made using this printing master. The adhesion of the metal image to the support was excellent.

EXAMPLE 14

A sheet of baryta coated paper was soaked in a 0.5 percent solution of potassium palladium oxalate adjusted to pH 2.8. The treated sheet was exposed through a negative line image as in Example 13. It was then developed for approximately 2 hours in the nickel physical developer of Example 6 at room temperature. A heavy metallic nickel image appeared on the sheet in the exposed areas whereas the unexposed areas remained free of metal. The developed sheet was soaked in water and inked with lithographers' ink. The sheet was then pressed against a sheet of bond paper and gave an excellent ink transfer. The sheet was re-inked and the procedure carried out for several impressions. There was no change in the wettability characteristics of the master with extended use.

EXAMPLE 15

A sheet of polyethylene-coated paper on which had been coated a mixture of titanium dioxide and polyvinyl alcohol was soaked in a 0.5 percent solution of potassium palladium oxalate adjusted to pH 2.8. The sheet was exposed through a negative line image by means of a bank of eight 8-watt black-light tubes for 30 seconds at a distance of 2 inches. It was then developed for approximately 1 minute in a copper physical developer solution at room temperature. The physical developer was prepared by mixing five parts of the following solution with one part of a 37 percent formaldehyde solution.

Copper sulfate (CuSO.sub.4.sup.. 5H.sub.2 O) 35 gm. Rochelle salt (KNaC.sub.4 H.sub.4 O.sub.6.sup.. 4H.sub.2 O) 170 gm. Triethanolamine (HOC.sub.2 H.sub.4).sub.3 N 13 gm. Disodium ethylene diaminetetraacetic acid 6.5 gm. Sodium hydroxide 50 gm. Sodium carbonate 17 gm. Water to make 1 liter

The developed sheet showed an excellent copper image in the exposed areas. It was put on an offset printing press, wet with fountain solution, and inked with an oil-based ink. The plate showed good inking differentiation and several prints were made with this printing master.

EXAMPLE 16

A sheet of light weight water-leaf paper was impregnated with a 0.5 percent solution of palladium tetrammine chloride and dried. It was then exposed to a 350 watt mercury arc at a distance of 14 inches for one minute behind a negative which contained a line pattern. The exposed sheet was then immersed for five seconds at 90.degree. C. in the following nickel type physical developer:

Nickel chloride (NiCl.sub.2.sup.. 6H.sub.2 O) 30 gms. Sodium hypophosphite (NaH.sub.2 PO.sub.2.sup.. H.sub.2 O) 10 gms. Ammonium chloride (NH.sub.4 Cl) 50 gms.

Water was added to make one liter and the solution was adjusted to pH 9 with ammonium hydroxide. An excellent image appeared which showed a resistance of 50 ohms/square.

EXAMPLE 17

An absorbent porcelain plate ("Streak Plate" sold by the Will Corporation) was dipped briefly in a 0.5 percent solution of potassium palladium oxalate and dried. It was exposed as in Example 16 behind a negative which contained a line pattern. The plate was then immersed for three minutes at 95.degree. C. in the following nickel physical developer:

Nickel chloride (NiCl.sub.2.sup.. 6H.sub.2 O) 30 gms. Sodium hypophosphite (NaH.sub.2 PO.sub.2.sup.. H.sub.2 O) 10 gms. Sodium citrate (Na.sub.3 C.sub.6 H.sub.5 O.sub.7.sup.. 5-1/2H.sub.2 O) 100 gms. Ammonium chloride (NH.sub.4 Cl) 50 gms.

Water was added to make one liter of solution and it was adjusted to pH 9 with ammonium hydroxide. An excellent image was formed which showed a resistance of 40 ohms/square.

EXAMPLE 18

A sheet of poly(ethylene terephthalate) film base coated with gelatin at a coverage of 350 mg. of gelatin/ft.sup.2 was imbibed with a 0.5 percent solution of potassium palladium oxalate for ten minutes and dried. It was exposed behind a line negative to a bank of eight 8-watt fluorescent tubes (BL type, GE) for thirty seconds and immersed in the physical developer solution used in Example 16 for 5 minutes. An excellent image was formed which had a resistance of approximately 500 ohms/square.

Although this invention has been described in considerable detail with particular reference to preferred embodiments thereof, modifications and variations can be effected within the spirit and scope of the invention as described above and as defined in the following claims.

Claims

We claim:

1. A photosensitive element comprising a support and a light-sensitive compound which on exposure to actinic light forms catalytic centers for the deposition of metal from a physical developer, said compound having the formula [Pd(L).sub.x ].sub.y Mz, wherein

L is a ligand, selected from the group consisting of

halogen ligands,

carboxylic acid ligands,

aromatic ligands,

nitrogen ligands,

phosphorous ligands,

arsenic ligands, and

antimony ligands;

M is selected from the group consisting of ions selected from the group consisting of

hydrogen ions,

inorganic acid ions,

organic acid ions,

metal ions selected from the group consisting of sodium ions, potassium ions, calcium ions, strontium ions, and aluminum ions, and

onium ions, and [Pd(L).sub.x ] groups;

x is an integer from 0 through 4;

y is an integer from 1 through 4;

z is an integer from 0 through 2;

and x and z are not 0 at the same time.

2. A photosensitive element as defined in claim 1, wherein at least a part of the support is porous and the light-sensitive palladium compound is imbibed therein.

3. A photosensitive element as defined in claim 1, wherein the light-sensitive palladium compound is coated on the support in a hydrophilic binder.

4. A photosensitive element as defined in claim 1, wherein the light-sensitive palladium compound is selected from the group consisting of potassium palladium oxalate, palladium oxalate, palladium tetrammine chloride, palladium tetrammine bromide, and potassium palladous chloride.

5. A photosensitive element comprising a support and a light-sensitive composition comprising potassium palladium oxalate.

6. A method of producing photographic images comprising the steps of

1. imagewise exposing to actinic light a photosensitive element comprising a support and a light-sensitive palladium compound, wherein the light-sensitive palladium compound has the formula [Pd(L).sub.x ].sub.y Mz, wherein

L is a ligand, selected from the group consisting of

halogen ligands,

carboxylic acid ligands,

aromatic ligands,

nitrogen ligands,

phosphorous ligands,

arsenic ligands, and

antimony ligands;

M is selected from the group consisting of ions selected from the group consisting of

hydrogen ions,

inorganic acid ions,

organic acid ions,

metal ions selected from the group consisting of sodium ions, potassium ions, calcium ions, strontium ions, and aluminum ions, and [Pd(L).sub.x ] groups;

x is an integer from 0 through 4;

y is an integer from 1 through 4;

z is an integer from 0 through 2;

and x and z are not 0 at the same time, and

2. developing the latent image thus formed with a physical developer comprising a reducible heavy metal salt selected from the group consisting of nicket salts, cobalt salts, iron salts, chromium salts, copper salts, and mixtures thereof, a complexing agent for heavy metal ions from said salt and a reducing agent for heavy metal ions from said salt.

7. A method of producing photographic images as defined in claim 6, further comprising the step of washing the element between exposure and development to remove unexposed palladium compound.

8. A method of producing photographic images as defined in claim 6, wherein development is accomplished by immersing the exposed element in a bath of the physical developer.

9. A method of producing photographic images as defined in claim 6, wherein development is accomplished by contacting the exposed element with a receiving sheet containing the physical developer and heating the element to cause migration of unexposed light-sensitive palladium compound from the element to the receiving sheet, where it is reduced and developed.