US 3615446 A
Description (OCR text may contain errors)
United States Patent  Inventor Hans K. Wong Arlington, Mas.
 App]. No. 697,948
 Filed Jan. 15, 1968  Patented Oct. 26, 197]  Assignee ltek Corporation Lexington, Mass.
 PHOTOGRAPI'IIC COPY MEDIUM COMPRISING A SEMICONDUCTOR LAYER WITH A PHOTOPOLYMERIZABLE LAYER THEREOVER 12 Claims, 4 Drawing Figs.
52 US. Cl 96/33, 96/351, 96/48 PD, 96/69, 96/29 R  Int. Cl 603i 7/02, G03c 5/00  Field oISeareh 96/33,480 P, 35.1, 36
 References Cited UNITED STATES PATENTS 2,704,254 3/1955 Gresham 96/33 3,143,414 8/1964 Yackeletal... 96/64 3.038300 6/1962 Luckey et al. 96/351 3,245,793 4/1966 Smith 96/351 Pho/asens/h've Semiconductor Layer Primary Examiner-Norman G. Torchin Assistant Examiner-1ohn Winkelman Atlorneys-Homer 0. Blair, Robert L. Nathans and W. Gary Goodson ABSTRACT: A photographic copy medium comprising a photosensitive semiconductor, e.g. ZnO or TiO, having a photopolymerizable coating thereover. Photographic images are produced by imagewise exposing such a medium to polymerize it in the exposed areas, and then rendering the image visible in the unexposed portions of the medium. These unexposed portions are made visible by, for example, contacting with a fogging developer; by exposing the medium to radiation which activates the semiconductor but does not polymerize the coating and then contacting the medium with image-forming materials reactive with the activated semiconductor areas; or by first removing the unexposed, unpolymerized portions of the coating, then uniformly exposing the medium to radiation capable of activating the semiconductor, and then contacting it with image-forming materials. A medium having a coating over the photopolymer coating comprising a heat-sensitive composition which forms oleophilic-hydrophilic images upon imagewise application of heat is also disclosed.
Phofoimpermeabhzab/e Coo/mg PHOTOGRAPIIIC COPY MEDIUM COMPRISING A SEMICONDUCTOR LAYER WITH A PHOTOPOLYMERIZABLE LAYER THEREOVER BACKGROUND OF THE INVENTION forming processes and photographic imaging media utilizing photosensitive semiconductors. As disclosed in said copending application, the contents of which are incorporated herein by reference, certain semiconductors, typically compounds of metals with elements of Group VI of the Periodic Table, can be activated by exposure to actinic radiation to render the materials capable of effecting chemical reactions at their surface. These chemical reactions can be employed to produce photographic images in photographic imaging media comprising these semiconductors.
For example, a photosensitive semiconductor such as titanium dioxide can be used to coat or fill a support layer such as paper, or can be applied as a thin layer on a transparent or translucent substrate such as cellulose acetate, to form a photographic imaging medium. lmagewise exposure of the medium to actinic radiation, such as visible or ultraviolet light, activates lighbstruck portions of the semiconductor rendering them capable of effecting chemical reactions in imageforming developing agents subsequently applied to the surface. These image-forming developing agents are generally easily reducible materials, commonly metal ions. n contact with the activated semiconductor, the image-forming materi als react, e.g. metal ions are reduced to form free metal deposits, to define a visible image in the photographic imaging medium.
It will be evident that the image so formed will be a negative of the original image because the imaging agent is caused to react (e.g. metal is deposited) in light-struck areas, i.e. those areas of the original image which are transparent to light.
SUMMARY OF THE INVENTION According to the present invention, a method is described for producing positive photographic images in imaging media comprising a photosensitive semiconductor, as well as a photographic imaging medium useful for producing such positive images. ln particular, the present invention pertains to a photographic imaging medium comprising a supported photosensitive semiconductor of a type known in the art and earlier described herein, which medium has a photoimperrneablizable coating thereover. When such an imaging medium is exposed to activating means such as actinic light, impermeablization of the photoimperrneablizable coating occurs in exposed portions of the imaging medium.
A positive image of the original is then produced in the imaging medium by one of the following methods: (I) the copy medium is contacted with a fogging developer. The fogging developer is one which will permeate the nonexposed areas of the photoimperrneablizable layer but will not permeate the exposed areas and therefore a visible image is produced in these nonexposed areas. (2) uniformly irradiating the imagewise exposed imaging medium, to thereby activate the photosensitive semiconductor uniformly. The imaging medium is then developed by contacting with an image-forming material such as a redox developer in a solvent which will permeate the nonexposed portions of the imaging medium but will not permeate the exposed portions of such medium. (3) removing unimpermeablized material from the imaging material by chemical or mechanical means, such as by a solution or brushing to lay bare the underlying photosensitive semiconductor in the portions of the medium which are not protected by a imperrneablized layer. The medium is next uniformly exposed to activating means such as actinic radiation, thereby activating the photosensitive semiconductor uniformly. Finally, the imaging medium is developed by contacting with image-forming materials such as a redox developer, which will form a visible image on the activated portions of the copy medium which are exposed and not covered with the imperrneablized layer.
The positive image of the original is produced in this photographic process since the imperrneablized portions caused by the imagewise exposure prevents the image-forming materials from contacting the photosensitive semiconductor portions of the copy medium directly under such imperrneablized layer portions. Thus, only those portions of the imaging medium in which the semiconductor is not covered by a protective layer of imperrneablized material will be reached by the developing agent. Thus, imaging material will be deposited only in those portions of the imaging medium which were not exposed to radiation in the first, imaging exposure to which the medium was subjected. Hence, a positive photographic image is obtained.
The imaging medium of this invention may suitably be adapted for use as a planographic master. As described in US. Pat. application Ser. No. 675,798 entitled "Processes for Producing Images on a Photosensitive Printing Plate and Products Produced Thereby," filed in the name of E. Berman, and now abandoned a planographic printing plate is disclosed comprising a photoconductor which becomes reversibly activated and capable of being made heat producing upon exposure to activating radiation and a heat-sensitive composition which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat. Therefore, if the photoimperrneablizable coating of this invention is also one which, upon heating, will form an oleophilic-hydrophilic image pattern upon selective imagewise application of heat, then the imaging medium of this invention may suitably be used as a planographic master by first forming a visible positive image according to the above-described process of this invention, and then uniformly exposing the imaging medium containing this visible image to heat-producing activating radiation which causes selective heating in the image areas, thereby producing an oleophilic-hydrophilic image pattern. This oleophilic-hydrophilic image-bearing imaging medium may then be used with a polar solvent-based ink or a greasy or oil-based ink as a printing master.
DESCRIPTION OF PREFERRED EMBODIMENT( S) The supported semiconductor portions of the novel imaging media of this invention may be like those known in the art from the aforesaid copending patent applications. That is, the photosensitive semiconductor may be deposited, with or without a binder, onto a substrate which may be rigid or flexible, transparent, translucent, or opaque, and made of materials including wood, paper, cardboard, glass, metal, and plastic. The photosensitive material may also be dispersed through a substrate such as plastic or paper.
The photosensitive semiconductors used in this invention are those known in the art from the aforesaid patent applications. A preferred group of said semiconductor 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; metal sulfides such as cadmium sulfide (CdS), zinc sulfide (ZnS), and tin disulfide (Sn z); metal selenides such as cadmium selenide (CdSe).
Metal oxides are especially preferred photosensitive semiconductors of this inventlon. 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 photosensitive semiconductor materials are certain fluorescent materials. Such materials include, for example, compounds such as silver activated zinc sulfide and zinc activated zinc oxide.
Certain organic photosensitive semiconductors are suitable for use in this invention. Examples of these are the imidazolidinones, the imidazolidine-thiones, the tetraarylazacyclo-octatetraenes, and thiazines, such as l,3diphenyl-4,5- bis (p-methoxyphenyl)imidazolidinone-Z; 4,5-bis(paramethoxyphenyl) imidazolidinone-Z; 4-phenyl-5- (paradimethyl-aminophenyl) imidazolidinone-Z; 4,5-bis(para -methoxyphenyl)imidazolidenethione-2; 3,4,7,8-tetraphenyl- 1,2 5,6-tetraazacyclooctatetraene-2,4,6,8; and methylene blue.
Also used as photoconductors in this invention are the heteropolyacids such as phosphotungstic acid, phosphosilicic acid, and phosphomolybdic acid.
While the exact mechanism by which the photosensitive semiconductor materials of this invention work is not known, it is believed that exposure of photoconductors or photocatalysts of this invention to activating means causes an electron or electrons to be transferred from the valence band of the semiconductor materials to the conductance band of the same or at least to some similar excited state whereby the electron is loosely held, thereby changing the semiconductor from an inactive form to an active fonn. If the active form of the semiconductor is in the presence of an electron accepting compound a transfer of electrons will take place between the photographic and the electron accepting compound, thereby reducing the electron accepting compound. Therefore a simple test which may be used to determine whether or not materials have a photosensitive semiconductor or photoconductor 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 or a photosensitive semiconductor material.
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. On the other hand, excessive impurity content can interfere with a compound acting as a photoconductor, as above described.
The photosensitive semiconductors 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 in pages 371-429 in The Theory of Photographic Process by C. E. Kenneth Mees published by McMillan Company in 1951. 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. Sensitizing dyes disclosed in copending U.S. Pat. application Ser. No. 633,689 are especially preferred.
The photoimpermeablizable coating to be applied over the imaging media of this invention are those which are made impermeable by exposure to activating radiation so as to prevent image-forming materials from contacting the photosensitive semiconductor portions of the imaging media which are protected by the impermeablized coating. On the other hand, the photoimpermeablizable coating is one which will allow a solution of the imaging materials to penetrate this coating when it is in a nonimpermeablized state. Thus, the material used for this photoimpermeablizable coating will vary, depending upon the nature of the solvent used for the image-forming materials, whether or not the unimpermeablized portions of the photoimpermeablizable layer are removed prior to contacting with image-forming materials, the nature of the image-forming materials, and like factors. Preferred photoimpermeablizable materials are the photopolymerizable coatings which are well known to the art where they are employed in the preparation of the so-called photoresists. The materials include natural materials such as glue or gelatinlike materials sensitized with additives such as chromates. Synthetic polymerizable materials may also be employed, and commonly include olefinically unsaturated monomers having light-sensitive polymerization catalysts dispersed therethrough.
The photoimpermeablizable material is one which upon exposure will result in an impermeablized coating impermeable to the image-forming developing agent employed in the exposed portions. In a preferred system the nonexposed areas of this copy medium will remain permeable to the image-forming materials. In one embodiment the nonexposed portions of the photoimpermeablizable layer are removed prior to contacting with image-forming material; therefore, in this embodiment the nonexposed photoimpermeable layer may be impermeable to the image-forming materials.
Because the image-forming agents are generally in aqueous solution, preferred photoimpermeablizable materials will, on exposure, form polymers which are water-impermeable. However, image-forming agents incorporating an organic liquid are also contemplated according to this invention and photoimpermeablized coatings resistant to organic solvents are not to be excluded. Because of penetration of a polymer or like-impermeablized material by a developing solution is usually slow and because development times are, in most cases, extremely short, even materials which in their impermeablized state have some degree of permeability to water or organic solvents can be employed according to this invention.
The thickness of the photoimpermeablizable coatings on the imaging medium is not critical to this invention, providing only that the coating after impermeablization is sufiicient to prevent contact of the image-forming developing agent with the photosensitized semiconductor.
Examples of suitable photoimpermeablizable materials are those such as the N-vinyl-carbazole free radical materials described in U.S. Pat. No. 3,046,125, which comprise a photoresist composition comprising at least one arylamine such as N -vinyl-carbazole and at least one organic halogen-containing compound. This patent is incorporated herein by reference.
Examples of suitable photoimpermeablizable materials are those containing ethylenically-unsaturated monomers having a light-sensitive or photopolymerizable -Cl-l=C group. These photopolymerizable materials are wellknown in the art and have been described in a number of domestic and foreign patents, for example, U.S. Pat. No. 3,236,644, herein incorporated by reference. Accordingly, suitable polymerizable compositions for use in preparing the photopolymerizable receiving layers of the invention include as the essential polymerizable component thereof, at least one polymerizable ethylenically unsaturated vinyl or vinylidene compound, for example, water-soluble acrylic monomers, such as acrylic lOl007 0159 acid, and derivatives of acrylic acid, e.g., methacrylic acid, methyl, ethyl, or propyl acrylate, etc., acrylamide, and derivatives of acrylamide, e.g., methacrylamide, methylene bisacrylamide, gamma dimethylamino-propylacrylamide, etc., metal acrylates, e.g., calcium acrylate; acrylonitrile, etc., vinylpyrrolidone; vinylpyridines; quaternary salts of vinylpyridines, e.g., 1,2-dimethyl-4-vinylpyridinium methyl sulfate; etc. Of these monomers, acrylamide and metal acrylates, and derivatives of these monomers are particularly preferable for producing homogenous mixture with nonlight sensitive, binding and vehicular substances, such as, for example, gelatin, zein, nylon, monostearin (glycerol monostearate), ethyl cellu lose, polyvinyl pyrrolidone, maleopimaric acid, methylmethacrylate-methacrylic acid copolymer, polymethacrylic acid, polyvinyl hydrogen phthalate, cellulose acetate phthalate, polyethylene glycols, such as Carbowax 4000 to Car bowax 20,000, etc. The numbers given the Carbowax materials indicate the approximate molecular weight.
The photoimpermeablizable materials useful in this invention also include heat-sensitive compositions which form an oleophilic -hydrophilic image pattern upon selected imagewise application of heat. Therefore, for example, a hydrophilic continuous phase which is photopolymerizable having incorporated therein an oleophilic disperse phase is suitable for producing a lithographic master which will produce positive copies when using an oil-base ink on the lithographic master produced. Thus, for example, a paper sub strate coated with a photosensitive semiconductor such as titanium dioxide, when coated with such a photopolymerizable hydrophilic continuous phase having incorporated therein an oleophilic disperse phase is first exposed imagewise to activating radiation which polymerizes the photopolymerizable layer in the exposed areas. This thus-exposed photographic substrate is then exposed uniformly to activating radiation which will not photopolymerize the unpolymerized portions of the top photopolymerizable layer but which will activate the photosensitive semiconductor layer uniformly. The thus-activated photographic substrate is then contacted with imageforming materials such as an aqueous solution of silver nitrate and then a separate solution of reducing agent such as P- methylaminophenol, to thereby produce a visible image which is a positive of the original and which corresponds to the unpolymerized portions of the top layer. This photographic substrate containing the visible image is then exposed to heat-producing radiation such as infrared radiation which causes heating in the visible image areas of the photographic copy medium and thus causes the top hydrophilic layer to be coverted to an oleophilic layer in the areas which correspond to the visible image portions of this copy medium.
Thus by using a photoimpermeablizable material as the continuous phase of the planographic printing plate disclosed in copending application U. 8. Pat. Ser. No. 675,798, now abandoned tiled in the name of E. Herman, a planographic printing plate can be produced having a new flexibility in that the visible image is a positive of the original. The disclosure from U.S. Pat. Ser. No. 675,798 is herein incorporated by reference.
While the photosensitive semiconductor material preferably comprises a separate layer from the photoimpermeablizable layer of this invention, it will be understood that these layers can be mixed so long as they do not interfere with the function of each layer as it acts separately. Thus, for example, where you have a photopolymerizable layer containing a zinc oxide photocatalyst, the zinc oxide may serve as a catalyst to catalyze the photopolymerization on the initial imaging exposure and then on the second exposure by properly choosing the wave length of light and the length of exposure serve merely as a photosensitive semiconductor which will cause formation of a visible image when contacted with image-forming materials and will not cause the photopolymerization of these areas in this second exposure.
When this photosensitive semiconductor is in a separate layer, it may be desirable to incorporate it in a binder. In general, these binders are translucent or transparent so as not to interfere with the transmission of light therethrough. Preferred binder materials are organic materials such as resins or gelatin. Examples of suitable resins are butadiene-styrene copolymer, poly(alkyl acrylatesl such as poly(methylmethacrylate), polyamides, polyvinyl acetate, polyvinyl alcohol, and polyvinyl pyrrolidone.
The period of exposure both to photoimpermeablize imagewise and to form the latent image will depend upon the intensity of the light source, particular photoimpermeablizable material, particular photoconductor, the type and amount of catalyst, if any, and like factors known to the art. In general, however, the period of both exposures will vary from about 0.00l seconds to several minutes.
Image-forming materials which are useful in this invention are those such as described in U.S. Pat. 3,152,903 and in copending application Ser. No. 199,2l I. These image forming materials include preferably an oxidizing agent and a reducing agent. Such image-forming materials are often referred to in the art as physical developers. The oxidizing agent is generally the image-forming component of the image-forming material. However, this is not necessarily true. 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. The oxidizing agent may include such metal ions as Ag, Hg", Pb'" Au Au3, Pt Pt Ni, Sn"Pb", Cu, and Cu. Other suitable oxidizing agents useful in this invention as components of an image-forming material are permanganate (Mn0,"ion, various leuco dye materials such as disclosed in application Serial No. 623,534 filed Mar. 19, 1967, now U.S. Pat. No. 3,462,259, in the name of L. Case, and the like. Organic oxidizing agents include tetrazolium salts, such as tetrazolium blue and red, and diphenyl carbazole, and genarcyl red 68 (methine dye).
The reducing agent component of the image-forming materials 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, polyvinylpyrrolidones, hydrazine, and ascorbic acid may be used as reducing agents in this invention. Suitable specific reducing compounds include hydroquinone or derivatives thereof, oand p-aminophenol, p methylaminophenol sulfate, p-hydroxyphenyl glycine, oand p-phenylenediamine, l-phenyl-3-pyrazolidone, alkali and alkaline earth metal oxalates and formates.
Liquid redox systems are preferred for use as im age-forming materials because of the excellent results obtained therewith. However, when the photoimpermeablizable layer is removed from the imaging medium prior to contacting with imageforming materials of this invention may include electrical toners such as described in British Pat. No. 935,621, colored resins, and the like.
Additionally, the image-forming materials or 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 and other properties found to be desirable in this art.
it will be understood that part of the image-forming materials may be present on the imaging medium prior to exposure to photoimpermeablize imagewise the top layer of the imaging medium. Thus, for example, the oxidizing component of the redox developer could be present prior to the first photoimpermeablizing activating radiation. Then, upon exposing uniformly to activate the semiconductor and contacting with reducing agent, a positive of the original would be formed in the imaging medium. Alternatively, of course, the reducing agent component of the redox developer could also be present prior to exposure to photoimpermeablize the top layer of the imaging medium. Additionally, all of the image-forming material may be present in the imaging medium in an inactive state. The image-forming material in this embodiment is then converted to a visible image in the portions not covered by the photoimpermeablized layer portions by contacting with an activator solution.
The fogging developer useful in this invention comprises a redox system which will cause visible image formation in the presence of a photosensitive semiconductor whether or not it is activated by activating radiation. Thus, an ordinary redox developer system may be converted to a fogging developer by increasing the reducing power of the reducing agent component of this developer, by changing the pH of the solution, or by like factors known to 'the art.
DESCRIPTION OF THE DRAWING A better understanding of this invention and of its many advantages will be had by reference to the accompanying drawings and the following specific examples, given by way of illustration.
In the accompanying drawing, FIG. I is a perspective view, partly in section, of a photographic imaging medium according to this invention, having a photoimpermeablizable coating thereon;
FIG. 2 schematically represents the imagewise exposure of such a photographic imaging medium;
FIG. 3 schematically depicts the finished positive print; and
FIG. 4 schematically represents the finished positive print wherein the unimpermeablized portions of the top layer have been removed.
FIG. 1 shows a photographic imaging medium according to this invention comprising a support, a layer of photosensitive semiconductor thereon, and a photoimpermeablizable coating thereover.
FIG. 2 shows exposure of photographic imaging medium 11 according to this invention to source 12 of activating means such as actinic radiation through image 13 to be copied. Image 13 comprises relatively transparent areas 14 and relatively opaque areas 15. Imaging medium 11 comprises support 20 and photosensitive semiconductor l6 thereon, having thereover a photoimpermeablizable layer hardened in those portions l7 exposed to radiation through transparent portions 14 of image 13 and remaining unimpermeablized in portions [8 shielded from radiation source 12 by opaque portions 15 of the image.
FIG. 3 shows an imaging medium as in FIG. 2 wherein image-forming materials have been contacted with portion 19 which was below the unimpermeablized portions of the top layer and therefore allowed the solution of image-forming materials to penetrate in this portion of the imaging medium.
FIG. 4 shows imaging medium 11 after uniform exposure to source 12 of actinic radiation or other activating means, followed by development of those portions of photosensitive semiconductor conductor 16 not protected from the developing agent by impermeablized segments 17. Developed portion 19 of medium 11 thus is relatively opaque, corresponding with opaque portions 15 of image 13. The unimpermeablized portions 18 of the medium of FIGS. 2 and 3 have been removed by chemical or mechanical means, such as by solutions or by brushing to produce the medium of FIG. 4.
EXAMPLE I A supported photosensitive semiconductor imaging medium is prepared by coating paper with finely divided titanium dioxide dispersed in a polymethylmethacrylate binder. The coated paper is coated with a photoimpermeablizable layer by dipping in a commercially available photoresist solution comprising polyvinyl cinnamate and then drying.
The finished imaging medium is exposed in a Besseler box to the image to be copied with an 8-watt bulb producing blue light which is about 2 inches away from the imaging medium for about 1 minute and is subsequently developed with a commercially available developer complementary to the photoresist coating employed. The developer, essentially, washes off or dissolves unpolymerized portions of the photoresist coating without attacking the polymer formed in exposed areas.
After drying, the imaging medium is uniformly exposed to a 60'watt tungsten lamp 2 inches away for 5 seconds to activate the semiconductor. Development is effected by contacting the uniformly exposed sample with a 0.1M aqueous solution of silver nitrate, whereupon metallic silver is deposited in the imaging medium on those portions of the medium not protected by the polymer coating. The image formed is intensified by subsequent dipping in an aqueous p-methylamino-phenol developer for a few seconds. This treatment effects image intensification by physical development, that is, by deposition of additional silver from the silver nitrate solution remaining on the surface onto those portions of the print in which metallic silver is already present.
The print is subsequently fixed in a standard fixing bath for silver halide photographs and then washed.
Substituting zinc oxide for the titanium dioxide of this example gives similar results when following the same procedure.
EXAMPLE 2 Finely divided titanium dioxide dispersed in a polymethyl methacrylate binder is coated on a paper support. The thuscoated paper is then coated with a photopolymerizable layer by dipping in a methacrylic acid solution and then drying.
The final copy medium is then exposed in a Besseler box to selectively polymerize the photopolymerizable monomer in the exposed areas. The thus-imaged copy medium is then contacted with a solution of silver nitrate, followed by contacting with a solution of hydroquinone fogging developer for a time sufficient to cause the formation of a visible image in the areas of the copy medium not covered by a polymer layer. A visible positive image of the original is produced.
EXAMPLE 3 A titanium dioxide coated photographic substrate is coated with a methacrylic acid photopolymerizable layer, and finally with a hydrophilic layer of a continuous phase of gelatin having incorporated therein polyethylene as a discontinuous phase.
The thus-prepared imaging medium is then exposed in a Besseler box to selectively polymerize the photopolymerizable monomer in the exposed areas. A visible image is produced in the titanium dioxide layer by contacting with a silver nitrate and p-methylamino-phenol fogging developer.
This thus-imaged printing plate is then irradiated with an infrared radiation source in a thermographic copying machine. The visible image areas of the imaging medium are heated and thereby converted from an hydrophilic to an oleophilic surface in these heated areas. The nonimage areas of the printing plate remain hydrophilic. An oil base ink is used with this imaging medium to produce multiple positive copies of the original. A polar, solvent-based ink is used with this imaging medium as a master for producing negative copies of the original.
After the copy medium of this invention has been exposed and contacted with image forming materials the medium containing the visible image may be contacted with a receptor sheet and the image transferred by diffusion transfer from the photographic imaging medium to the receptor sheet.
A variation of applicant's invention is to coat the copy medium comprising a supported photosensitive semiconductor having a photopolymerizable coating thereover with a coating comprising a heat-sensitive composition which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat. This top layer is that mentioned previously as being described in U.S. Pat. Ser. No. 675,798 which has been incorporated herein by reference. A process for making a printing plate according to this invention comprises (l) exposing imagewise a planographic printing plate comprising a photoconductor, a photopolymerizable coating,
101cm om and a heatsensitive coating composition coated thereover which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat to cause photopolymerization in the photopolymerizable layer in the exposed areas, (2) contacting the planographic printing plate with image forming materials to form a visible image in the areas not covered by the photopolymerized portions of the photopolymerizable layer, and (3) applying heat in areas of the printing plate corresponding with the visible image portions to produce a planographic printing master having an oleophilic-hydrophilic image pattern thereon.
What is claimed is:
l. A photographic imaging medium consisting essentially of a supported photosensitive semiconductor having a photopolymerizable coating thereover, and wherein said semiconductor comprises a metal oxide or metal sulfide.
2. An imaging medium as in claim 1 wherein the photosensitive semiconductor is zinc oxide or titanium dioxide.
3. An imaging medium as in claim 1 comprising titanium dioxide as the photosensitive semiconductor, dispersed in a binder and coated onto a flexible support.
4. A photographic imaging medium as in claim 1 having a coating on top of the photopolymerizable coating comprising a heat-sensitive composition which forms an oleophilic-hydrophilic image pattern upon selective imagewise application of heat wherein the heat-sensitive composition forms a normally hydrophilic planographic surface and comprises low-melting oleophilic, water-repellent particles dispersed within a continuous phase of a high-melting hydrophilic binder, and forms an oleophilic image on the planographic surface at areas subjected to the imagewise application of heat.
5. A process for preparing images in a photographic imaging medium comprising a supported photosensitive semiconductor having a photopolymerizable coating thereover, which process comprises imagewise exposing the photographic imaging medium, whereby photopolymerization takes place in exposed areas and contacting the imaging medium with imforming materials comprising a solution of metal ions.
6. A process as in claim 5 wherein the photosensitive semiconductor is a compound formed between a metal and a nonmetal element of Group VIA of the Periodic Table.
7. A process as in claim 6 wherein the nonexposed areas are rendered visible by contacting at least these nonexposed areas with a fogging developer.
8. A process for recording an image pattern in a photographic imaging medium comprising a photosensitive semiconductor having a photopolymerizable coating thereover, which process comprises imagewise exposing the photographic imaging medium, whereby photopolymerization takes place in exposed areas of the medium, exposing uniformly to radiation which activates the photosensitive semiconductor but which does not photopolymerize the photopolymerizable layer and then rendering unprotected un polymerized portions of the imaging medium visible by contacting with image-forming materials which undergo an oxidation-reduction type reaction and which fonn irreversible images on contact with activated portions of the copy medi- 9. A process as in claim 8 wherein the image-forming materials comprise a solution of metal ions at least as reducible to free metal as are cupric ions.
10. A process as in claim 9 wherein the image-fanning materials comprise a solution of silver ions.
11. A process for recording image patterns of activating radiation in a photographic imaging medium comprising a photosensitive semiconductor having a photopolymerizable coating thereover, which process comprises imagewise exposing the photographic imaging medium, whereby photopolymerization takes place in the exposed areas, removing unexposed unpolymerized material from the medium, uniformly exposing the medium to activate the photosensitive semiconductor, and then developing unprotected portions of the semiconductor by contacting these rtions with imageformlng materials which undergo an on anon-reduction type reaction and which fonn irreversible images on contact with activated portions of the copy medium.
12. A planographic printing plate comprising l) exposing imagewise a planographic printing plate comprising a photoconductor, a photopolymerizable coating coated thereover, and a heat-sensitive coating composition coated thereover which forms an oleophilic-hydrophilic image pat tern upon selective imagewise application of heat to cause photopolymerization in the photopolymerizable layer in the exposed areas, (2) contacting the planographic printing plate with image-forming materials which undergo an oxidationreduction type reaction and which form irreversible images on contact with activated portions of the copy medium to form a visible image in the areas not covered by the photopolymerized portions of the photopolymerizable layer, and (3) applying heat in areas of the printing plate corresponding with the visible image portions to produce planographic printing master having an oleophilic-hydrophilic image pattern thereon.