US3219452A

US3219452A - Photographic media and process for producing same

Info

Publication number: US3219452A
Application number: US243740A
Authority: US
Inventors: Hartouni Edward
Original assignee: Technical Operations Inc
Current assignee: Technical Operations Inc
Priority date: 1962-12-11
Filing date: 1962-12-11
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23
Also published as: GB1075159A; NL301544A; BE641007A

Description

United States Patent 3,219,452 PHOTOGRAPl-HC MEDLA AND PROCESS FOR PRODUCING SAME Edward Hartouni, Westwood, Mass, assignor, by mesne assignments, to Technical Operations, Incorporated, a corporation of Delaware No Drawing. Filed Dec. 11, 1962, Ser. No. 243,740 23 Claims. '(Cl. 96108) This invention relates to photography, and more particularly to novel sensitized photographic media and processes for producing same.

Photographic media formed of a layer of microcrystalline, substantially binder-free silver halide on a suitable substrate, and a process for manufacturing such media by vacuum evaporation techniques are disclosed in French Patent No. 1,267,623, granted June 12, 1961, to Technical Operations, Incorporated. Media of this type can be distinguished from conventional emulsion type photographic film and other photographic media not only by their structure and method of manufacture, but also for some purposes by their high acutance, high resolution, and quick developability.

Such media may be photographically sensitized by treatment of the surface of the microcrystalline binder-free silver halide layer.

Media of this type are especially useful, for example, in image transfer processes, because the image developed therein is not masked by binder and can be transferred by adhesion of the surface of a developed silver image to the surface of a receiving sheet. In transfer processes, it is often desirable to have the transferred image in positive form i.e. having image densities which are approximately inversely proportional to the intensity of the radi ation which formed the latent image. With a surface sensitized medium, transfer usually removes substantially all of the image, hence but only one transfer of that image can generally be made.

The present invention is directed to improvements in the sensitization of microcrystalline binder-free silver halide photographic media, and has for its principal object to provide novel bulk sensitized photographic media of this type and methods for making the same.

More specific objects of the present invention are to provide such a method in which both the photosensitive silver halide and the sensitizing material are codeposited on a substrate such as by vacuum deposition; to provide a method of producing a substantially binder-free layer of particulate silver halide having sensitizing material substantially homogeneously distributed therein; to provide novel sensitized photographic media; to provide a medium which is sensitized to produce a direct positive image upon short exposures and normal development; to provide a medium which is sensitized to produce a print-out effect; to provide a direct positive-image producing medium wherein the sensitizer is selected from the group consisting of iron, tin, indium and tellurium; and to provide a method of forming in a simple evaporation process, a sensitized photographic medium.

Other objects of the present invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products and compositions possessing the features, properties and relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed 3,219,452 iatented Nov. 23, 1965 description of the invention and certain exemplary embodiments thereof.

The present invention is intended to form in one process microcrystalline binder-free silver halide photographic media which are bulk sensitized. Certain media of this type are developable to form direct positive images following brief exposure, hence are termed direct positive media. Other media of this type, upon exposure, exhibit a print-out effect i.e. the formation of a visible silver image without development.

While not being limited to any particular theory, it is believed that the sensitization phenomena of the present invention are due, not primarily to surface effects as appears to be true in surface sensitization (of microcrystals in either binder-free form or emulsion suspension) but probably largely to distortions introduced into the crystalline lattices of the silver halide microcrystals themselves by the sensitizer or to internal chemical reactions between the sensitizer and the silver halide photolysis products.

Photographic media according to the present invention may be prepared by vacuum evaporation techniques similar to those described in the aforesaid French Patent No. 1,267,623. A basic machine of the kind useful to form such media by vacuum evaporation is illustrated and de scribed in the book, Vacuum Deposition of Thin Films by L. Holland, published by John Wiley & Sons, New York City, 1948, pp. 7-8. Vacuum coating apparatus of this type is well known and usually comprises an evacuatable container, such as a bell jar, and means for evacuating the latter to an ambient pressure which is preferably less than approximately 1 l0- mm. of Hg. The latter appears to be the maximum pressure at which reasonably desirable layer formation can be achieved. Included within the bell jar is a crucible or boat which is intended to carry the material which is to be evaporated. Means for heating the boat are usually included, and in one form of the apparatus the boat is made of, for instance, tungsten provided with leads to a source of electrical power so that the filament can be heated electrically. By this method the temperature of the evaporating material can be readily controlled. In other known forms of vacuum evaporation apparatus, the starting material may be heated by electrical induction, for example. The apparatus also includes means for holding substrate material, such as a support sheet, at a predetermined location within the bell jar wherein preferably one surface of the substrate faces the boat, thus insuring that the stream of vapor from the evaporating material in the boat will strike the substrate surface and condense thereon to form a film or layer according to the well known principles of evaporation techniques. It is desired to keep the silver-halide layer thus formed within a thickness range of about 0.1 to 0.5 micron inasmuch as optimum photographic param eters such as gamma, density, and speed are found within this range.

In one method of using this apparatus, a quantity of silver halide, e.g. of purity of 99.99% or better, and a quantity of the sensi'tizer material or dopant are placed within the container, for example at a first location, and a suitable substrate sheet is placed within the container at a second location displaced from the first location. The container is pumped down to achieve an operating pressure, and the silver halide and the dopant are brought to a temperature at which evaporation, at least of the silver halide, will occur. The resulting vapor in which dopant is commingled, as by evaporation thereof or by entrapment, is a sensitizer-doped silver halide which is then condensed upon the substrate surface to form the product.

In another form of the foregoing process, the silver halide is first prepared in high purity form, brought to 'to the support, and other reasons. such subbing layers on base materials are well known I and need not be described here.

a molten state, and the desired quantity of sensitizerdopant is introduced into the molten .silver halide, as by mixing or reacting directly with the latter. The doped silver halide is then cooled and is ready for use in the vacuum evaporator by, for example, reheating to a molten state in a single crucible. This, provides a precisely known pre-evaporation composition for the doped silver halide.

.In yet another form of the method of the invention, the high purity silver halide is placed in a single crucible, rendered molten under the requisite reduced pressure, and the dopant, for instance in the form of an elemental metal or a salt is placed directly into the molten silver 'salt at the beginning of or during the evaporation process. Alternatively it has been foundthat suspending a dopant metal in the vapor stream from molten silver halide being evaporated under reduced pressure will also result in introducing the dopant, probably as a halide due to reaction of the metal with the silver halide vapor, into the final evaporated film.

Yet another method of achieving the doped product is to employ apparatus of the type disclosed in US. Patent No. 2,938,816, Karl George Gunther, for simultaneous vacuum evaporation or coevaporation, of two or more materials from a corresponding number of crucibles, each of which may then be separately temperature controlled, to provide a commingled vapor from which is deposited a thin layer of doped photographic material of the type 'hereinbefore described.

Among the silver halides which are useful in evaporation processes to form the media of the present invention are silver bromide, silver chloride and silver iodobromide.

Exemplary support or substrate materials upon which the "doped film is deposited include many diverse materials,

other polyesters, polyamides and the like; and cellulose esters such as cellulose'acetate, cellulose propionate and the like.

.In any of the above methods, the thickness of the doped silver halide layer is readily controlled as by adjustment of the evaporation temperature, the evaporation time and the distance between the silver halide source and the substrate, or any of them. The layer thus provided exhibits a density which appears quite close, i.e.

within approximately to that of a solid silver halide macrocrystal.

The base or substrate materials may be transparent, translucent or opaque to radiation actinic to the silver halide, and may be used directly to provide a condensation surface or may be coated with a subbing layer. The subbing layer may be provided for several purposes, eg

to alter support opacity, to change support reflectivity, to modify adherence of the silver-halide-sensitized layer Methods for coating As materials for sensitization doping of microcrystalline binder-free silver halide photographic media during formation of the latter by evaporation we have found many metallic substances and salts thereof which are useful.

For example, it appears that iron, tin, indium, tellurium,

ferred for various reasons.

For example, the use of dopants such as iron, tin,

indium or tellurium will provide a sensitized photographic medium which, upon relatively brief exposure to ordinary light intensities, and ordinary development, is found to yield a direct positive image. It is believed that these are but some of the elements which are useful as materials for sensitization doping during vacuum evaporation of silver halides to provide direct-positive media.

The use of a dopant such as lead, for example in the form of the halide salt, will provide a photographic medium which, upon relatively brief exposure to actinic radiation, is found to yield a strong print-out effect.

The methods of the present invention, and the products achieved thereby, may be illustrated in the following examples.

Example 1 A support sheet of polyethylene terephthalate having a subbing layer thereon for the purpose of improving adhesion characteristics, such as material suitable for the application thereto of a photographic emulsion and sold under the trade name of Cronar by E. I. du Pont de Nemours Co., is placed in the evacuatable container of a vacuum deposition apparatus of the type described above. Six grams of high purity AgBr is placed in a tungsten boat also located in the container and spaced 'several inches, for instance about 3 /2 inches, from the subbed surface of the support sheet. A sample, about 4 inches long of approximately #18 gauge, of very pure iron is suspended about inch above the tungsten boat. The container is evacuated to a pressure of about 5 X l0 mm. of Hg and the boat heated electrically to a temperature of approximately 600:20 C. to bring the silver halide to a molten state and cause evaporation thereof for a sufiicient time to form a layer of photosensitive material about 0.25 micron thick on the subbed surface of the support sheet. The latter, being essentially vacuuminsulated from the boat is maintained at an equilibrium temperature of approximately 5060 C. The iron wire, being suspended in the stream of silver halide vapor between the boat to the support sheet, will be corroded apparently by reaction with the vapor thereby providing a mixed vapor which forms a photosensitive layer doped with iron in some form, probably as the bromide.

The photographic medium thus formed i removed from the vacuum deposition apparatus and exposed in a moving wedge sensitometer (using a standard step wedge made by Eastman Kodak Co., and a light source corrected to 5600K) over 0.1 second intervals between 0.1 and 0.4 second. The exposed medium is then developed by immersion for 30 seconds at 25 C. in a solution made up as follows:

Gelatin, 1.25 g. Water to make 250 cc.

These are mixed by adding equal quantities of solution B to solution A and then of solution C to the mixture of solutions A and B.

Sensit-ometric results indicate that the average speed of this sensitized medium is increased by about one and a half orders of magnitude over unsensitized evaporated AgBr film made in the same apparatus with similar parameters. Also, all of the images achieved upon development are direct positive images, the maximum den sity being about 2.

Example 2 0.032 g. of high purity iron, in wire form, laid directly on the surface of the silver halide; after the latter is raised to a temperature of approximately 625 C. under an ambient pressure of approximately 5 X" mm. of Hg, a reaction will be observed between the wire and molten silver bromide. Evaporation is continued until a doped silver halide layer having a thickness of between 0.1 and 0.5 micron is substantially uniformly deposited upon a substrate. The resulting sensitized medium yields sensitometric results quite similar to those of Example 1.

Example 3 The experiment described in Example 1 is repeated, however, using baryta-coated paper as the support material. Again the results indicate substantial increase in film speed and the production of a positive image upon similar exposure and development.

Example 4 A sample of 6 g. of high purity AgBr is placed in the boat of the apparatus of Example 1, and 0.1 g. of indium metal is dropped into the AgBr when the latter is approximately at 575 C. under the same reduced pressure as in Example 1. The resulting evaporated layer of microcrystalline silver bromide doped in this manner with indium in some form, also yields, upon similar exposure and development, a direct positive image.

Example 5 The experiment of Example 4 is repeated employing metallic tin instead of indium metal. Substantially the same results are obtained. In both Example 4 and Example 5, a boiling reaction between the molten silver bromide and the dopant will be observed. Since both reactions are exothermic, the exact local temperature conditions at the surface of silver bromide are uncertain.

Example 6 In the apparatus of Example 1, a pre-evaporation mix of 0.05 gram of lead bromide and 5 grams of AgBr is placed in the tungsten boat. The latter is spaced about 2 /2 inches from the surface of a baryta-coated, paper support sheet. The mix is raised to a temperature of approximately 625 C. at an ambient pressure of about 5X 10- mm. of Hg, and allowed to evaporate for a time sufficient to form a photographic medium comprising a doped silver halide layer of about 0.3 micron in thickness deposited on the baryta surface.

The sensitized medium is then surface treated by immersion in a solution formed of 10 milligrams of ammonium chloroiridite and 10 milligrams of sodium aurous thiosulfate per liter of water, in order to increase the surface speed of the medium. The treated medium is then shaken and allowed to air dry.

Sensitized media, treated with the gold iridite solution or untreated, upon exposure in the sensitometer of Example 1 for 0.1 sec. will both show marked print-out effects. The print-out effect in both instances may be preserved simply by fixing the media in known fixes.

Since certain changes may be made in the above processes and products without departing from the scope of the invention herein involved it is intended that all matter contained in the above description shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. A method of producing a bulk sensitized photographic medium comprising the steps of placing in an evacuatable region a quantity of silver halide, placing a support surface at a predetermined distance from said halide in said region, locating between said halide and said support surface a quantity of a material which is reactable with vapors of said silver halide to form a sensitizing material, evacuating said region, heating said halide to above its melting point, and condensing the vapor passing from said halide and including that passing across and reacting with said material to form on said support surface a microcrystalline binder-free layer of silver halide substantially uniformly doped with said material.

2. A method as set forth in claim 1, wherein said material is selected from the group consisting of iron, indium, tellurium, tin and lead.

3. A method as set forth in claim 1, wherein said region is evacuated to a pressure below approximately 1 10'- mm.'of Hg.

4. A method as set forth in claim 1, wherein said material is in the form of a wire.

5. A bulk sensitized direct positive photographic medium comprising a substrate supporting a substantially homogeneous binder-free microcrystalline layer of vapor deposited silver halide having a material uniformly incorporated therein selected from the group consisting of halides of iron, indium, tellurium, and tin.

6. A medium as defined in claim 5 wherein said layer is of predetermined thickness within the range of approximately 0.1 to 0.5 micron.

7. A medium as set forth in claim 5, material is iron halide.

8. A medium as set forth in claim 5, material is indium halide.

9. A medium as set forth in claim 5, material is tellurium halide.

10. A medium as set forth in claim 5, material is tin halide.

11. A medium as set forth in claim 5, wherein said silver halide includes silver bromide.

12. Method of producing a bulk sensitized direct positive photographic medium comprising vaporizing a silver halide and a sensitizer material in an ambient atmosphere of less than approximately 1 l0 mm. of Hg to form a silver halide vapor doped with said sensitizer material, said sensitizer material being chosen from the group con sisting of iron, indium, tellurium, tin, and compounds thereof, and condensing the doped vapor onto a support to form a thin layer of binder-free microcrystalline doped silver halide.

13. A method as set forth in claim 12, wherein said sensitizer material contains iron.

14. A method as set forth in claim 12, wherein said sensitizer material contains indium.

15. A method as set forth in claim 12, wherein said sensitizer material contains tellurium.

16. A method as set forth in claim 12, wherein said sensitizer material contains tin.

17. A method as set forth in claim 12, wherein said silver halide and sensitizer material are vaporized by being heated in separate vessels.

18. A method as set forth in claim 12, wherein said silver halide includes silver bromide.

19. A method of producing a bulk sensitized print-out photographic medium comprising vaporizing a silver halide and a sensitizer material in an ambient atmosphere of less than approximately 1 10 mm. of Hg to form a silver halide vapor doped with said sensitizer material, said sensitizer material being chosen from the group consisting of lead and compounds thereof, and condensing the doped vapor onto a support to form a thin layer of binder-free microcrystalline doped silver halide.

20. A method as set forth in claim 19, wherein the silver halide includes silver bromide.

21. A method as set forth in claim 19, wherein said silver halide and sensitizer material are vaporized by being heated in separate vessels.

22. A bulk sensitized print-out photographic medium comprising a substrate supporting a substantially homogeneous binder-free microcrystalline layer of vapor deposited silver halide having lead halide uniformly incorporated therein.

wherein said wherein said wherein said wherein said 7 '8 23. A mediurn'as set forth in claim 22, wherein said Goldberg et al.: A.D. No; 264,061 (Report No. TOB silver halide includes silver bromide. 61-37), August 1961. Luckey: Journal Physical Chemistry, vol. 57, pp. 79 1- References Cited by the Examiner 9% %1- 1 A N 2 7 O uVa e et a.: .D. 0.2 O, 28 Report No. T -B FOREIGN PATENTS 5 5941) July 1959 1 2 7 23 19 1 France. Moser et al.: Journal Physics and Chemistry of Solids,

vol. 9, pp. 217-234, 1959. OTHER REFERENCES Tutihasi: Physical Review, vol. 105, .pp. 882-884, 1957.

1O p g ri eg 211l9g6liournal V Photographic Science, vol. 4, NORMAN G. TORCHIN Primary Examiner.

Evans et 211.: Journal Photographic Science, Vol. 3, ALVIN E. TANENHOLTZ, J. T. BROWN, pp. 73-87, 1955. Assistant Examiners.

Claims

1. A METHOD OF PRODUCING A BULK SENSITIZED PHOTOGRAPHIC MEDIUM COMPRISING THE STEPS OF PLACING IN AN EVACUATABLE REGION A QUANTITY OF SILVER HALIDE, PLACING A SUPPORT SURFACE AT A PREDETERMINED DISTANCE FROM SAID HALIDE IN SAID REGION, LOCATING BETWEEN SAID HALIDE AND SAID SUPPORT SURFACE A QUANTITY OF A MATERIAL WHICH IS REACTABLE WITH VAPORS OF SAID SILVER HALIDE TO FORM A SENSITIZING MATERIAL, EVACUATING SAID REGION, HEATING SAID HALIDE TO ABOVE ITS MELTING POINT, AND CONDENSING THE VAPOR PASSING FROM SAID HALIDE AND INCLUDING THAT PASSING ACROSS AND REACTING WITH SAID MATERIAL TO FORM ON SAID SUPPORT SURFACE A MICROCRYSTALLING BINDER-FREE LAYER OF SILVER HALIDE SUBSTANTAILLY UNIFORMLY DOPED WITH SAID MATERIAL.