US3634083A

US3634083A - Photographic process for producing relief images by extended physical development

Info

Publication number: US3634083A
Application number: US699375A
Authority: US
Inventors: Elliot Berman; Robert H Maher; John R Manhardt
Original assignee: Itek Corp
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1968-01-22
Filing date: 1968-01-22
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11
Also published as: BE727190A; CH496967A; FR2000513A1; DE1903096A1; GB1256971A; NL6900929A

Abstract

A photographic process for producing relief images comprises (1) exposing a copy medium comprising a photosensitive photoconductor layer comprising photosensitive material incorporated in a binder capable of being physically developed in radiation-struck areas and wherein the photosensitive layer is deposited on a support, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) selectively removing the exposed areas of the photosensitive layer down to the support by prolonging the physical development step until the image becomes frangible. Removal may be speeded up by contacting the medium with a bleach bath, or by washing or brushing. The process of this invention may be used for producing positive or negative prints of an original, for producing diazomasters, or for producing lithographic plates.

Description

United States Patent Elliot Berman Quincy;

Robert H. Maher, North Adams, both of Mass.; John R. Manhardt, Nashua, NJ-l.

[72] Inventors [21] App]. No. 699,375

[22] Filed Jan. 22, 1968 [45] Patented Jan. 11, 1972 [73] Assignee ltek Corporation Lexington, Mass.

[54] PHOTOGRAPHIC PROCESS FOR PRODUCING RELIEF IMAGES BY EXTENDED PHYSICAL [5 6] References Cited UNITED STATES PATENTS 1,938,290 12/1933 Hurst et a1. 96/36.3

Primary Examiner-Norman G. Torchin Assistant Examiner-John Winkelman Attorneys-Homer 0. Blair, Robert L. Nathans and W. Gary Goodson ABSTRACT: A photographic process for producing relief images comprises (1) exposing a copy medium comprising a photosensitive photoconductor layer comprising photosensitive material incorporated in a binder capable of being physically developed in radiation-struck areas and wherein the photosensitive layer is deposited on a support, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) selectively removing the exposed areas of the photosensitive layer down to the support by prolonging the physical development step until the image becomes frangible. Removal may be speeded up by contacting the medium with a bleach bath, or by washing or brushing. The process of this invention may be used for producing positive or negative prints of an original, for producing diazomasters, or for producing lithographic plates.

PHOTOGRAPI-IIC PROCESS FOR PRODUCING RELIEF IMAGES BY EXTENDED PHYSICAL DEVELOPMENT BACKGROUND OF TH E INVENTION 1. Field of the Invention This invention relates to photographic processes and, more particularly, to photographic processes for producing relief images utilizing photosensitive materials which can be physically developed.

2. Description of the Prior Art In silver halide photography the ordinary type of development is the so-called chemical development. In chemical development a visible photographic image is obtained by the reduction of metal ions of the water-insoluble silver halide present in the latent image in the exposed portions of the copy medium. Initially, the developing solution employed in chemical development does not contain any image-forming material. Prolonged use of the chemical developer sometimes causes image-forming material to be deposited in the developer however.

Physical development, on the other hand, involves developers containing image-forming materials which are deposited on the latent image-exposed portions of the copy medium. These physical developers may be in the form of a unitary solution as, for example, where a reducible metal compound such as silver nitrate is combined with a photographic reducing agent such as p-methylaminophenol. Generally, to prevent such unitary solutions from decomposing rapidly, it is necessary to include in the developers stabilizers and other such additives.

Physical developers also include separate solutions as, for example, wherein the reducible metal compound is applied in one solution and the photographic reducing agent is applied in a separate solution. Such separate solution physical developers have the advantage of increased developing life. As the process of this invention is continued, however, these solutions become partially mixed with each other.

Physical developers have been used to increase the optical density of visible images produced by chemical development such as in silver halide photography. Physical developers are also used extensively for development of other photosensitive substrates comprising a photoconductor which becomes activated upon exposure to activating radiation and thereby capable of causing chemical reaction in these exposed areas. An example of such photoconductors is titanium dioxide which becomes reversibly activated upon exposure to suitable activating means.

SUMMARY OF THE INVENTION This invention relates to photographic processes for producing relief images comprising (1) forming a latent image in a copy medium by exposing this copy medium comprising a photosensitive layer comprising photosensitive material incorporated in a binder wherein the photosensitive layer is deposited on a support, (2) physically developing the latent image until the photosensitive layer can be selectively removed from the support, and (3) selectively removing the photosensitive layer from the exposed areas of the copy medium by washing, brushing, and like means known to the art. This process has the advantage of being very versatile in that the final produce can be used for a number of different purposes. By choosing a photosensitive layer and a support giving different visual effects, it is possible to obtain a print which is either a negative or positive of an original, depending upon the visual properties of the support and the photosensitive layer. For example, if the support is colored or black and the photosensitive layer is white, then a negative of an original is produced by this process. However, if the photosensitive layer is black or colored and the support is white or light colored, then the final print is a positive ofan original. Furthermore, by using a radiation-transmissive support and a photosensitive layer which is radiation absorbing, the final print becomes a very good diazomaster for use in a diazocopying machine. For

example, the photosensitive layer may be UV absorbing and the support is transparent or translucent to UV radiation. Additionally, the process of this invention is useful for producing lithographic plates. This may be done by choosing a support and photosensitive layer so that one of them is oleophilic and the other is hydrophilic with respect to each other. Thus, if the support is hydrophilic with respect to the photosensitive layer and the photosensitive layer is oleophilic with respect to the support, then the final print obtained by the process of this invention can be used as a master with an oil-based ink to form positive copies of the original. On the other hand, by using a polar solvent-based ink with this lithographic printing plate, a negative copy of the original is produced. By the same token, where the support is olephilic with respect to the photosensitive layer and the photosensitive layer is hydrophilic with respect to the support, the final print obtained by this process is a lithographic printing plate which can be used to form negative or positive copies of the original, depending upon whether a polar or nonpolar solvent-based ink is used.

Carrying out the physical development to the point where the image areas may be selectively removed is due to the prolonged physical development which causes these areas to become frangible and therefore removable as for example by washing, brushing, or just by flaking off when the copy medium is dried. It is believed that the image areas which are physically developed for prolonged periods become frangible due to the large buildup of metal or other image-forming material within the binder of the substrate, which ordinarily results in the rupture or failure of the binder. Therefore anything which will hasten or add to this buildup can be suitably used in this invention to aid in the removal of the photosensitive layer in the exposed areas of the copy medium. Thus, it is possible to contact the physically developed areas with a bleachwhich will react with the image-forming materials to expand the volume of these image-forming materials. Therefore if the silver images in the exposed areas of a copy medium which has undergone physical development are converted to silver bromide images, the volume of the image is considerably expanded, thereby increasing the frangibility of the photosensitive layer in the exposed areas. Softening bleaches which deteriorate the binder in the image areas of the copy medium may also be used to hasten the removal of the photosensitive layer in the exposed areas. Such softening bleaches are ones containing peroxides and are to be distinguished from bleaches of the type which do not deteriorate the binder but rather react with the silver image to form a buildup in the image areas and thereby increasing the frangible nature of the exposed physically developed areas of the copy medium.

DESCRIPTION OF PREFERRED EM BODIM ENT( S) Physical developers useful in this invention are image-forming materials which will cause image buildup in the exposed areas of a photosensitive copy medium. Physical developers which are useful in this invention are those such as described in US. Pat. No. 3,157,502 and in copending application Ser. No. 199,21 1, now abandoned, both of which are herein incorporated by reference. These physical developers include an oxidizing agent and a reducing agent. The oxidizing agent is generally the image-forming component of the image-forming material and is preferably a reducible metal compound. The reducing agent may in certain cases function as the imageforming component of the physical developer. Either organic or inorganic oxidizing agents may be employed as the oxidizing component of the image-forming material. Preferred oxidizing agents comprise the reducible metal ions having at least the oxidizing power of cupric ion. However, reducible metal ions useful in this invention include such metal ions as Ag+, Hg+2 Phi-4 A -t'l A +l!, Pt+2 Pt+4 lqi+2y s +2, Pb+2 C 'I-I, and Cu".

The reducing agent component of the physical developers of this invention are inorganic compounds such as the oxalates, formates, and ethylenediaminetetraacetate complexes of metals having variable valence; and organic compounds such as dihydroxybenzenes, aminophenols, and aminoanilines. Also, tetracyanoethane and ascorbic acid may be used as reducing agents in this invention. Suitable specific reducing compounds include hydroquinone or derivatives thereof, and p-aminophenol, p-methylaminophenol sulfate, p-hydroxyphenyl glycine, oand p-phenylenediamine, l-phenyl-3- pyrazolidone, alkali and alkaline earth metal oxalates and formates.

Also useful as physical developers in this invention are electroplating baths such as disclosed in US. Pat. No. 3,010,883. In order to apply these electroplating solutions it is generally necessary to deposit the photosensitive layer of this invention upon an electrically conductive support. Examples of suitable electrolytic solutions are aqueous copper sulfate solutions, aqueous silver nitrate solutions, and aqueous nickelous chloride solutions having incorporated therein a small proportion of sodium thiosulfate.

Additionally, the physical developers may contain organic acids or alkali metal salts thereof, which can react with metal ions to form complex metal anions. Further, the developers may contain other complexing agents and the like to improve image formation, stability of the developer solution and other properties found to be desirable in this art.

Photosensitive material suitable for incorporation in the photosensitive layer of this invention includes any photosensitive materials which may be physically developed. Therefore included within this invention are photosensitive materials such as silver halide and photoconductors which become activated upon exposure to activating radiation and thereby capable of causing chemical reaction in the exposed areas. The photoconductor or photocatalyst preferred in this invention are metal containing photoconductors. A preferred group of such photosensitive materials are the inorganic materials such as compounds of a metal and a nonmetallic element of Group VIA of the periodic table such as oxides, such as zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide, tin oxide; metal sulfides such as cadmium sulfide, zinc sulfide, and tin disulfide; metal selenides such as cadmium selenide. Metal oxides are especially preferred photoconductors of this group. Titanium dioxide is a preferred metal oxide because of its unexpectedly good results. Titanium dioxide having an average particle size less than about 250 millimicrons and which has been treated in an oxidizing atmosphere at a temperature between about 200 C. and 950 C. for from about 0.5 hours to about 30 hours is especially preferred, and more especially, that titanium dioxide produced by high-temperature pyrolysis of titanium halide.

Also useful in this invention as photoconductors are certain fluorescent materials. Such materials include, for example, compounds such as silver-activated zinc sulfide, zinc-activated zinc oxide, manganese-activated zinc phosphate, an admixture of copper sulfide, antimony sulfide and magnesium oxide, and cadmium borate.

While the exact mechanism by which the photoconductors of this invention work is not known, it is believed that expo sure of photoconductors or photocatalysts of this invention to activating means causes an electron or electrons to be transferred from the valence band of the photoconductor or photocatalyst to the conductance band of the same or at least to some similar excited state whereby the electron is loosely held, thereby changing the photoconductor from an inactive form to an active form. If the active form of the photoconductor is in the presence of an electron accepting compound a transfer of electrons will take place between the photoconductor and the electron accepting compound, thereby reducing the electron accepting compound. Therefore a simple test which may be used to determine whetheror not materials have a photoconductor or photocatalytic effect is to mix the material in question with an aqueous solution of silver nitrate. Little, if any, reaction should take place in the absence of light. The mixture is then subjected to light. At the same time a control sample of an aqueous solution of silver nitrate alone is subjected to light, such as ultraviolet light. If the mixture darkens faster than the silver nitrate alone, that material is a photoconductor.

It is evident that the gap between the valence and the conducting band of a compound determines the energy needed to make electron transitions. The more energy needed, the higher the frequency to which the photoconductor will respond. It is known to the art that it is possible to reduce the band-gap for these compounds by adding a foreign compound as an activator which either by virtue of its atomic dimensions or by possessing a particular electronic forbidden zone structure or through the presence of traps as donor levels in the intermediate zone between the valence and the conduction band stresses the electronic configuration of the photoconductive compound, thereby reducing its band-gap and thus increasing its ability to release electrons to its conduction band. Phosphors almost necessarily imply the presence of such activating substances. The effect of such impurities may be such as to confer photoconductivity upon a compound which intrinsically is nonphotoconductive. The (CrSr)S phosphors are believed to be an example of this group. On the other hand, excessive impurity content can interfere with a compound acting as a photoconductor, as above described.

The photoconductors of this invention may be sensitized to visible and other wavelengths of light by foreign ion doping, addition of fluorescent materials, and/or by means of sensitizing dyes. Bleachable dyes useful for sensitizing the photoconductors of this invention include, for example, the cyanine dyes, the dicarbocyanine dyes, the carbocyanine dyes, and the hemicyanine dyes. Additional dyes which are useful for sensitizing the photosensitive medium of this invention are the cyanine dyes described on pages 371-429 in The Theory of Photographic Process by C. E. Kenneth Mees published by McMillan Company in 1952. Other useful dyes include those known to the art as triphenylmethane dyes such as crystal violet and basic Fuchsin, diphenylmethane dyes such as Auroamine O, and Xanthene dyes such as Rhodamine B.

Irradiation sources which are useful in this invention for producing the initial latent image include any activating electromagnetic radiation. Thus actinic light, X-rays or gamma rays are effective in exciting the photoconductor. Beams of electrons and other like particles may also be used in the place of the ordinary forms of electromagnetic radiation for forming an image according to this invention. These various activating means are designated by the term activating radiation."

The support of the photographic copy medium of this invention comprises any suitable backing of sufficient strength and durability to satisfactorily serve as a reproduction carrier. The base sheet may be in any form such as, for example, sheets, ribbons, rolls, etc. This sheet may be made of any suitable materials such as wood, rag content paper, pulp paper, plastics such as, for example, polyethylene terephthalate (Mylar) and cellulose-acetate, cloth, metal such as aluminum, and glass. When electrolytic physical development is employed then the support generally must be electrically conducting.

Useful binders for the photosensitive layer of this invention include materials such as gelatin and various synthetic materials such as resins. The binder is preferably solvent permeable but not soluble in the processing solvent used in the physical developer at the particular temperature employed. Examples of suitable resins are butadiene-styrene copolymer, poly(alkyl acrylates) such as poly(methyl methacrylate), polyamides, polyvinyl acetate, polyvinyl alcohol, and polyvinyl pyrrolidone. These binder materials may be transparent or translucent or may be opaque, depending upon the intended use of the copy medium. Also, the binder materials may be hydrophilic or oleophilic and such properties may be increased by the incorporation in the binder of a suitable hydrophilic or oleophilic filler.

The ratio of photosensitive material to binder in the photosensitive layer of the copy medium of this invention is very important in order to reduce the physical development time needed to produce a relief image. Preferably the ratio of photosensitive material to binder varies from about one part by weight to about 50 parts by weight of photosensitive material per part by weight of binder. It is desirable to increase the proportion of photosensitive material to binder until just before the photosensitive layer ceases to be a continuous film. Such a photosensitive layer having a high proportion of photosensitive material becomes frangible much more readily in the process of this invention. However, the ratio of photosensitive material to binder should not be so great that the photosensitive layer becomes so frangible that it will not adhere to the support. The particular ratio of photosensitive material to binder will depend upon such factors as the nature of the photosensitive material, the nature of the binder, the nature and length of physical development desired, and the use to be made ofthe final image.

The invention above described is exemplified as follows:

EXAMPLE 1 A black cellulose triacetate support subbed with a mixture of gelatin and cellulose triacetate is coated on the subbed side with a white photosensitive layer comprising a finely divided titanium dioxide dispersed in a gelatin binder, which gelatin binder is hardened by incorporation of formaldehyde therein. 8.5 grams of titanium dioxide are used with 2.8 grams of gelatin. The photosensitive layer is coated so that 3.8Xl grams of titanium dioxide are present per square cm. of substrate. This thus-coated copy medium is soaked in aqueous 1N silver nitrate solution, dried, exposed behind a step wedge* The step wedge is a transparent film with 21 different density patches graduated in increments of 0. l density units. Step 21 possesses the minimum optical density of about 0.05 density units and allows the greatest exposure of the copy medium. Step 1 possesses a maximum optical density of about 3.05 density units and therefore allows the minimum exposure of the copy medium.) to a cold cathode mercury lamp spaced about 3 inches from the copy medium for 60 seconds to give a total light intensity of about 1,500 foot candles, and developed for 4 days in a developer having the following composition:

ferrous ammonium sulfaurfil-l o 3.39 grams ferric nitrate-9l l O 6.09 grams citric acid monohydrate 1.73 grams silver nitrate 2.88 grams Armac 12D (a distilled mixture of dodecyl amine acetate-95% by weight; dccylamine acetate-2%; and tetra dccylamine acetate-3%) 0.034 grams Synthrapol N (an alkylztted phenolethylcne oxide condensate) 0.034 grams Distilled water to 125 milliliters Upon removing the film strip from the physical developer, it is noted that the photosensitive layer in the most exposed steps (steps 14 through 21 of the wedge) has sloughed off the support whereas the photosensitive layer still adheres to the support in the surrounding unexposed or less exposed regions of the copy medium.

This thus-processed copy medium provides a negative print of an original since the black support is exposed when the exposed portions of the photosensitive layer are removed from the support. A white or light-colored support is used in combination with a black or colored photosensitive layer in the above-described procedure to obtain a positive print of the original and a translucent or transparent support is used in the above-described procedure to obtain a master suitable for making copies on a diazocopying machine. Because the photosensitive layer is UV absorbing and the support is UV transmitting, the processed print provides a very efficient diazomaster when used with a UV light source. The processed copy medium is also used with a greasy ink on a printing press to produce positive copies of the original. The watery fountain solution of the printing press adheres to the exposed hydrophilic support whereas the greasy ink adheres to the more oleophilic photosensitive layer in the unexposed areas of the copy medium.

EXAMPLE 2 A transparent cellulose triacetate support is coated with a titanium dioxide-gelatin photosensitive layer, immersed in silver nitrate solution, exposed and physically developed according to the procedure of example I. In addition, the copy medium is immersed in a bleaching bath containing 10 milliliters of concentrated sulfuric acid, milliliters of water, and saturated with potassium dichromate. The photosensitive layer is removed from the support in the exposed areas of the step wedge, i.e., steps 14 through 21, as in example I, and in addition in steps 11 through 13. Therefore a bleaching bath can also be used in addition to the physical development to hasten removal of the photosensitive layer from the support or to increase the effieiency of the removal of the photosensitive layer from the support in the exposed areas of the copy medium.

EXAMPLE 3 The procedure of example 1 is repeated except that the copy medium is soaked in aqueous 10 N silver nitrate solution before exposure instead of the aqueous l N silver nitrate solution. The entire photosensitive layer is intact upon the support upon removal from the physical developer. The copy medium is then immersed in a water bath. The photosensitive layer in steps 16-21 of the step wedge sloughs off from the support in the water bath. Exposure of the copy medium prior to contacting with the silver nitrate solution gives similar results.

EXAMPLE 4 A photosensitive copy medium is prepared, exposed and developed as in example 1 except that after removal from the physical developer the copy medium is dried and then brushed with an ordinary bristle brush to remove the photosensitive layer from the support in steps l6-2l of the step wedge.

The thus-processed copy medium is contacted with an oilbase ink and used as a master for producing positive copies of the original. The cellulose acetate support being more hydrophilic attracts water from the fountain solution whereas the gelatin containing titanium dioxide is more oleophilic and therefore attracts the oil-based ink. A second copy medium prepared as described above is used with a polar solvent-based ink for producing negative copies of the original. The polar solvent-based ink is attracted to the more hydrophilic cellulose acetate surface which is exposed upon removal of the photosensitive layer from the most exposed areas of the copy medium. An oil-base fountain solution is alternately used with the polar solvent-based ink to prevent this ink from adhering to the gelatin-based photosensitive layer.

We claim:

1. A photographic process for producing relief images comprising (l) exposing to an image pattern of activating radiation a copy medium comprising a photosensitive layer comprising photosensitive photoconductor material capable upon exposure of producing a physically developable image incorporated in a binder and capable of being physically developed in the radiation-struck areas and wherein the photosensitive layer is deposited on a support, to form a latent image, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) selectively removing the photosensitive layer from exposed areas of the copy medium down to the support in these exposed areas by the step comprising prolonging the physical development step until the image becomes frangible.

2. A process as in claim 1 wherein at least one component of the physical developer is present on the copy medium at the time of exposure.

3. A process as in claim 1 wherein the removal of the visible image is assisted by means of at least one of the group consisting of washing, contacting with a bleach bath and brushing.

4. A process as in claim 1 wherein the photosensitive material is selected from at least one of the group consisting of silver halide and a photoconductor which becomes reversibly activated upon exposure to activating radiation and wherein the photosensitive material is capable of being physically developed in the radiation-struck areas.

5. A process as in claim 4 wherein the photoconductor is a metal-containing photoconductor.

6. A process as in claim 5 wherein the metal-containing photoconductor is an inorganic compound formed between a metal and a nonmetallic element of Group VIA of the Periodic Table.

7. A process as in claim 5 wherein the metal-containing photoconductor is at least one compound selected from the group consisting of metal oxides and metal sulfides.

8. A process as in claim 1 wherein the ratio of photosensitive material to binder varies from about one part by weight to about 50 parts by weight of photosensitive material per part by weight of binder.

9. A process as in claim 1 wherein the support is an electrically conducting support and wherein the physical developer is an electroplating bath.

10. A process as in claim 1 wherein the physical developer comprises a solution of reducible metal ions.

11. A process as in claim 1 wherein the physical developer comprises a reducible metal ion which is at least as easily reduced as cupric ion and a reducing agent for said reducible metal ion.

12. A process as in claim wherein the photosensitive material is titanium dioxide and the reducible metal ion-containing solution is a silver nitrate solution.

13. A photographic process for producing relief images comprising (1) exposing to an image pattern of activating radiation a copy medium comprising a photosensitive layer comprising photosensitive photoconductor material capable upon exposure of producing a physically developable image incorporated in a binder and capable of being physically developed in the radiation-struck areas and wherein the photosensitive layer is deposited on a support, to form a latent image, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) selectively removing the photosensitive layer from the exposed areas of the copy medium down to the support in these exposed areas by the step comprising prolonging the physical development step until the image becomes frangible, and contacting the copy medium with a peroxide bleaching agent to increase the speed of the selective removal of the photosensitive layer.

14. A process for producing a lithographic printing plate comprising l) exposing to an image pattern of activating radiation a copy medium comprising a photosensitive layer comprising photosensitive photoconductor material capable upon exposure of producing a physically developable image incorporated in a binder and capable of being physically developed in the light-struck areas and wherein the photosensitive layer is deposited on a support and wherein one of the support and the photosensitive layer is oleophilic and the other is hydrophilic with respect to each other and are therefore capable of forming a lithographic printing plate upon selective removal of part of the photosensitive layer, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) removing the photosensitive layer from the exposed areas of the copy medium down to the support in these exposed areas by the step comprising prolonging the physical development step until the image becomes frangible.

15. A process as in claim 14 wherein said photosensitivematerial is selected from at least one of the group consisting of silver halide and a photoconductor which becomes reversibly activated upon exposure to activating radiation and wherein the photosensitive material is capable of being physically developed in the radiation-struck areas.

16. A process as in claim 15 wherein the metal-containing photoconductor is an inorganic compound formed between a metal and a nonmetallic element of Group VIA of the Periodic Table.

17. A process as in claim 15 wherein the metal-containing photoconductor is at least one compound selected from the group consisting of metal oxides and metal sulfides.

18. A process as in claim 14 wherein the ratio of photosensitive material to binder varies from about one part by weight to about 50 parts by weight of photosensitive material to one part of binder.

19. A process as in claim 14 wherein the photosensitive layer comprises titanium dioxide in a gelatin binder and the support is more hydrophilic than the photosensitive layer.

Claims

2. A process as in claim 1 wherein at least one component of the physical developer is present on the copy medium at the time of exposure.
3. A process as in claim 1 wherein the removal of the visible image is assisted by means of at least one of the group consisting of washing, contacting with a bleach bath and brushing.
4. A process as in claim 1 wherein the photosensitive material is selected from at least one of the group consisting of silver halide and a photoconductor which becomes reversibly activated upon exposure to activating radiation and wherein the photosensitive material is capable of being physically developed in the radiation-struck areas.
5. A process as in claim 4 wherein the photoconductor is a metal-containing photoconductor.
6. A process as in claim 5 wherein the metal-containing photoconductor is an inorganic compound formed between a metal and a nonmetallic element of Group VIA of the Periodic Table.
7. A process as in claim 5 wherein the metal-containing photoconductor is at least one compound selected from the group consisting of metal oxides and metal sulfides.
8. A process as in claim 1 wherein the ratio of photosensitive material to binder varies from about one part by weight to about 50 parts by weight of photosensitive material per part by weight of binder.
9. A process as in claim 1 wherein the support is an electrically conducting support and wherein the physical developer is an electroplating bath.
10. A process as in claim 1 wherein the physical developer comprises a solution oF reducible metal ions.
11. A process as in claim 1 wherein the physical developer comprises a reducible metal ion which is at least as easily reduced as cupric ion and a reducing agent for said reducible metal ion.
12. A process as in claim 10 wherein the photosensitive material is titanium dioxide and the reducible metal ion-containing solution is a silver nitrate solution.
13. A photographic process for producing relief images comprising (1) exposing to an image pattern of activating radiation a copy medium comprising a photosensitive layer comprising photosensitive photoconductor material capable upon exposure of producing a physically developable image incorporated in a binder and capable of being physically developed in the radiation-struck areas and wherein the photosensitive layer is deposited on a support, to form a latent image, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) selectively removing the photosensitive layer from the exposed areas of the copy medium down to the support in these exposed areas by the step comprising prolonging the physical development step until the image becomes frangible, and contacting the copy medium with a peroxide bleaching agent to increase the speed of the selective removal of the photosensitive layer.
14. A process for producing a lithographic printing plate comprising (1) exposing to an image pattern of activating radiation a copy medium comprising a photosensitive layer comprising photosensitive photoconductor material capable upon exposure of producing a physically developable image incorporated in a binder and capable of being physically developed in the light-struck areas and wherein the photosensitive layer is deposited on a support and wherein one of the support and the photosensitive layer is oleophilic and the other is hydrophilic with respect to each other and are therefore capable of forming a lithographic printing plate upon selective removal of part of the photosensitive layer, (2) forming a visible image in the copy medium by contacting the medium with a physical developer, and (3) removing the photosensitive layer from the exposed areas of the copy medium down to the support in these exposed areas by the step comprising prolonging the physical development step until the image becomes frangible.
15. A process as in claim 14 wherein said photosensitive material is selected from at least one of the group consisting of silver halide and a photoconductor which becomes reversibly activated upon exposure to activating radiation and wherein the photosensitive material is capable of being physically developed in the radiation-struck areas.
16. A process as in claim 15 wherein the metal-containing photoconductor is an inorganic compound formed between a metal and a nonmetallic element of Group VIA of the Periodic Table.
17. A process as in claim 15 wherein the metal-containing photoconductor is at least one compound selected from the group consisting of metal oxides and metal sulfides.
18. A process as in claim 14 wherein the ratio of photosensitive material to binder varies from about one part by weight to about 50 parts by weight of photosensitive material to one part of binder.
19. A process as in claim 14 wherein the photosensitive layer comprises titanium dioxide in a gelatin binder and the support is more hydrophilic than the photosensitive layer.