PRODUCTION OF BINDER-FREE SILVER HALIDE ELEMENTS UTILIZING ELEMENTAL HALOGEN OR PLATINUM HALIDE
United States Patent 3660098
Binder-free silver halide photosensitive strata are prepared by solution halogenation of binder-free silver strata. Mixed silver halides may be prepared by contacting the binder-free silver strata successively with different solutions of halogenating agents.
US Patent References:
Incandescent lamp and its manufacture
Birdseye - January 1939 - 2144673
Metal coating
Lukens - January 1952 - 2583581
Incandescent lamp and its manufacture
Birdseye - January 1939 - 2144673
Metal coating
Lukens - January 1952 - 2583581
Application Number:
04/789588
Publication Date:
05/02/1972
Filing Date:
01/07/1969
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Export Citation:
Assignee:
Polaroid Corporation (Cambridge, MA)
Primary Class:
Other Classes:
430/932
International Classes:
G03C1/496; G03C1/494; G03C1/02
Field of Search:
96/94BF 95/3 117/62
Primary Examiner:
Torchin, Norman G.
Assistant Examiner:
Hightower J. R.
Parent Case Data:
This application is a continuation in part of Ser. No. 615,962 filed Feb. 14, 1967 (now abandoned).
Claims:
What is claimed is
1. The process of preparing a photosensitive silver halide element comprising contacting a binder-free silver stratum with a halogenating solution, having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides, for a period of time sufficient to halogenate at least a portion of said silver by said dissolved halogenating agent.
2. The process of claim 1 wherein said silver stratum comprises vacuum deposited silver.
3. The process of claim 1 wherein said silver stratum also contains gold.
4. The process of claim 1 wherein said halogenating agent is taken from the group consisting of elemental chlorine, bromine and iodine.
5. The process of claim 1 wherein said halogenating solution has dissolved therein an elemental halogen and an alkali metal halide of the same halogen.
6. The process of claim 1 wherein said halogenating agent is platinic chloride.
7. The process of claim 1 including the step of continuously feeding a binder-free silver stratum into said halogenating solution and removing the resulting halogenated binder-free silver stratum from said solution.
8. The process of claim 1 including the steps of removing said binder-free silver stratum from said halogenating solution, washing said stratum to remove the halogenating agent, and contacting said halogenated silver stratum with a second halogenating solution containing a different halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides to thus form a silver halide of a second halogen.
9. The process of claim 8 wherein the first halogenation treatment partially halogenates said silver stratum whereby the second halogenation treatment results in the formation of a mixed silver halide.
10. A photosensitive silver halide element comprising a support carrying a binder-free stratum of silver halide formed by halogenation of a binder-free silver stratum with a solution having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides.
11. A light-sensitive element as defined in claim 10 wherein said halogenated silver stratum contains silver and halogen in approximately a stoichiometric ratio.
12. The process of preparing a photosensitive silver halide element comprising contacting a binder-free silver halide stratum with a halogenating solution, having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides and comprises a different halogen from that originally present in the silver halide stratum, for a period of time sufficient to form a silver halide containing said different halogen.
1. The process of preparing a photosensitive silver halide element comprising contacting a binder-free silver stratum with a halogenating solution, having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides, for a period of time sufficient to halogenate at least a portion of said silver by said dissolved halogenating agent.
2. The process of claim 1 wherein said silver stratum comprises vacuum deposited silver.
3. The process of claim 1 wherein said silver stratum also contains gold.
4. The process of claim 1 wherein said halogenating agent is taken from the group consisting of elemental chlorine, bromine and iodine.
5. The process of claim 1 wherein said halogenating solution has dissolved therein an elemental halogen and an alkali metal halide of the same halogen.
6. The process of claim 1 wherein said halogenating agent is platinic chloride.
7. The process of claim 1 including the step of continuously feeding a binder-free silver stratum into said halogenating solution and removing the resulting halogenated binder-free silver stratum from said solution.
8. The process of claim 1 including the steps of removing said binder-free silver stratum from said halogenating solution, washing said stratum to remove the halogenating agent, and contacting said halogenated silver stratum with a second halogenating solution containing a different halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides to thus form a silver halide of a second halogen.
9. The process of claim 8 wherein the first halogenation treatment partially halogenates said silver stratum whereby the second halogenation treatment results in the formation of a mixed silver halide.
10. A photosensitive silver halide element comprising a support carrying a binder-free stratum of silver halide formed by halogenation of a binder-free silver stratum with a solution having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides.
11. A light-sensitive element as defined in claim 10 wherein said halogenated silver stratum contains silver and halogen in approximately a stoichiometric ratio.
12. The process of preparing a photosensitive silver halide element comprising contacting a binder-free silver halide stratum with a halogenating solution, having a halogenating agent dissolved therein which is taken from the group consisting of elemental halogens and platinum halides and comprises a different halogen from that originally present in the silver halide stratum, for a period of time sufficient to form a silver halide containing said different halogen.
Description:
The present invention relates to novel photographic processes and products and more particularly to novel processes and products for the preparation of photosensitive elements.
The most common method of preparing photographic silver halide emulsions is to react a water-soluble silver salt, such as silver nitrate, with at least one water-soluble alkali or ammonium halide in the presence of an aqueous solution of an emulsifying agent such as gelatin. The mode of reaction of these materials, including such factors as the sequence of addition, rate of addition, the temperature and pressure and the concentration of the various reactants can be varied in accordance with the technical knowhow of the producer. The dispersion of silver halide thus formed contains numerous water-soluble salts as by-products of the primary reaction as well as unreacted initial reagents. It is considered desirable to remove most of these unwanted materials by processes known in the art.
It is known that conventional silver halide photosensitive materials present several inadequacies. For example, the resolution is lower than that theoretically available from the silver halide grain due to light scattering caused by the presence of the gelatin binder, as well as physical distortion which occurs during the processing of the matrix, i.e., swelling, hardening, etc. Another problem that exists with the conventional emulsions is the fact that when gelatin is present there is incomplete utilization of silver in both the exposed and unexposed forms. The preparation of conventional photographic emulsions is a highly empirical art in view of the infinite number of variables present in the gelatin material. The most basic variable is the structure of the gelatin, which is a complex compound(s) which has as yet not been completely analyzed. Furthermore, the presence of various polypeptides and other compounds renders the control of the emulsion preparation quite difficult.
Thus it is seen that the investigation and preparation of photosensitive elements which do not possess the problems set forth above would indeed be useful. Such products are prepared in the process of the present invention which employs a binder-free system.
The term binder-free is utilized to signify the fact that the photosensitive elements of the present invention are prepared without gelatin or an equivalent binder as is used in conventional photographic materials. In certain instances, however, it may be desirable to apply a stratum of a polymeric material over the surface of the binder-free photosensitive element, in which event the silver halide will still be substantially binder-free.
Accordingly, it is a primary object of this invention to prepare photosensitive silver halide elements by solution halogenation of silver coated strata.
Still another object is the preparation of photosensitive elements utilizing solution halogenation techniques which elements can be tray developed.
Yet another object of this invention is the preparation of novel photosensitive elements which can be utilized in diffusion transfer processes.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The process of the present invention in general entails the depositing of silver and optionally other metals such as gold, tellurium, indium, iron, tin, and lead, by vacuum deposition or other conventional techniques upon the base material and then subjecting the metal coated stratum to a solution halogenation treatment. A convenient method of adding the optional metal is by doping during the silver deposition.
Among the metal depositing techniques are sputtering, electroplating, and vapor deposition under vacuum. For a more thorough understanding of a process involving vacuum deposition of a silver coating upon a support material, reference is made to U.S. Pat. No. 3,142,566, issued July 28, 1964 to Edwin H. Land.
In the Land U.S. Pat. No. 3,142,566, there is disclosed a method of forming a photosensitive element by the vacuum deposition of silver, and/or silver with a substratum of gold and a subsequent treatment of this metal coating with the vapor of elemental halogen, e.g., chlorine, bromine, iodine or combinations thereof, or with vapors of volatile halogen salts, e.g., hydrogen bromide, hydrogen iodide or combinations thereof at a suitable temperature, for example, room temperature.
In the present invention the novel photosensitive elements are prepared by vacuum depositing silver alone or in combination with another metal, e.g., gold, upon a suitable support, followed by the subjection of the metal coated support or base to a solution halogenation process, as opposed to the vapor halogenation treatment of the aforementioned patent. Solution halogenation of the metal coated substrate can be carried out by any suitable means including dipping, brushing, coating, spraying, doctoring and continually passing the substrate through the appropriate solution.
The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application 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 description.
Support materials utilizable herein include any suitable base to which silver will adhere and which will not be adversely affected by the solution halogenation step. Typical examples are materials such as baryta paper; plastics such as polyethylene terephthalate, polyvinyl acetate, and polycarbonate; metals such as aluminum and lead; as well as glass. All of these can be coated with silver and optionally with other metals by known techniques.
Good quality results have been obtained wherein the metal coated upon the support material comprises silver or silver in combination with gold, wherein the gold and silver are deposited in either sequence or together.
Halogenation is effected by subjecting the metallic stratum to a solution containing dissolved therein at least one halogenating agent, preferably an elemental halogen or, in certain instances, a halide ion, e.g., platinum chloride, platinum iodide, or platinum bromide. Accordingly, this can be done by spraying, dipping, brushing, coating or any other suitable technique. The halogenation treatments are done at atmospheric pressure at a suitable temperature, for instance, room temperature. The effective time required for halogenation of the metallic stratum ranges from instantaneous, i.e., less than 1 second up to several minutes. The duration of the treatment is dependent upon the thickness of the metallic layer, the concentration of the halogen substance, and the amount of halogenation desired.
Elemental halogens such as chlorine, bromine and iodine dissolved in a suitable solvent such as water can be used as the halogenation solution. Organic solvents may also be used, e.g., iodine dissolved in ethylene glycol has provided a useful non-flammable halogenating solution. Excellent results have been obtained when iodine is dissolved in an alkyl alcoholic solvent such as methanol, butanol, isopropanol, and octanol. The addition of an alkali metal halide to a solution of an elemental halogen appears to aid the growth of the silver halide crystals, possibly because the alkali metal halide can act as a solvent for the silver halide formed. In a particularly useful embodiment, bromine is dissolved in an aqueous or alcoholic solution of sodium or potassium bromide.
The process of the present invention can be utilized with metal strata containing varying amounts of silver. The silver coverage may range from 20 milligrams per square foot to the vicinity of 150 milligrams per square foot. The process set forth hereinabove can be utilized with silver strata that have been chemically sensitized, such as by the deposition of gold either in sequence or together with silver; or with non-sensitized silver strata.
According to the process of the present invention it is possible not only to prepare silver halide crystals wherein a single halide is present, but it is similarly possible to prepare mixed silver halide crystals wherein two or even three halides are present. It should be realized that the compounds such as AgBrI and AgIClBr, are not pure stoichiometric compounds, but rather they comprise crystal lattices wherein a certain percentage of the second and/or third halide constitutes an impurity in the crystal lattice.
Mixed silver halide crystals may be prepared by the incomplete halogenation of the silver in a first halogenation treatment (e.g., by interrupting the halogenation via a washing operation) followed by a second halogenating treatment with a second halogen. This process can be repeated to introduce a third halide. Alternatively, mixed silver halides may be prepared by using a solution having two halogens dissolved therein, with the halogen of lower oxidation potential being present in great excess. In multistep preparation of "mixed" halides, a particular halogen may be used in two different steps, e.g., bromine may be used in the first and third steps of a multistep solution halogenation to obtain a mixed halide such as AgBrClBr.
It is also within the scope of this invention to use solution halogenation treatment to replace, in whole or in part, one halogen with another, e.g., silver bromide crystals can be formed by treatment of a silver iodide binderless film with a bromine solution. This procedure is particularly advantageous if large silver bromide crystals are desired, since prolonged contact with a bromine solution to grow large crystals may cause the crystals to fall off of the support; in contrast, silver may be left in contact with an iodine solution for the long times required to grow large crystals and then the crystals may be converted to silver bromide.
The advantages of the present invention include the fact that each step of the synthesis of the photosensitive element can be documented and controlled analytically. The photographic resolution can approach the theoretical resolution of the silver halide form, since a binder is not present. A major benefit to be derived from the process of the present invention is the fact that photosensitive elements can be prepared relatively easily and quite fast, when viewed in contrast to binder emulsion, as well as vapor deposition technology. When the photosensitive element prepared by the present invention is utilized in a diffusion transfer process, it is seen that substantially all unexposed silver can be utilized in a positive transfer since no binder is present to retard the silver from complexing with the transfer agent or to prevent it from transferring after complexing has taken place.
Photosensitive strata prepared in accordance with this invention may be developed utilizing conventional developing solutions which include Microdol, sold by Eastman Kodak Company, Rochester, New York; Cronex X-Ray Developer, sold by E. I. duPont de Nemours and Co., Wilmington, Delaware; as well as other commercially available developers.
The photosensitive products of the present process are particularly suited to prepare microfilm in view of the fact that these photosensitive elements have high resolution and may be readily formed on dimensionally stable supports. In view of the fact that these photosensitive elements contain no gelatin it is seen that it is not necessary to add microbial retarders to the formulation. Therefore, these photosensitive elements would find special utility in archival work.
The examples set forth hereinafter are meant to be illustrative only and are not to be construed as limiting.
EXAMPLE I
A glass plate was subjected to a vacuum deposition treatment with silver. This silver-coated glass was then dipped into a saturated solution of iodine crystals dissolved in methanol. The solution contained one per cent iodine by weight. The immersion time for the halogenation treatment was 30 seconds. It was conducted under atmospheric pressure at 25° C. The glass was washed three times with methanol to insure the removal of excess iodine. The coated substrate was dried in the air. Upon spectrophotometric inspection the coating was found to be silver iodide. This conclusion was substantiated by X-ray diffraction studies. After exposure and development, the resulting image exhibited negligible grain.
EXAMPLE II
A sheet of polyethylene terephthalate plastic with a subbing layer annexed thereon and available commercially as "subbed Cronar" from E. I. duPont de Nemours & Co., Wilmington, Delaware, was subjected to a vacuum deposition treatment to coat it with silver. The silver-coated polyester was dipped into a solution of bromine water for 5 minutes. The sheet which now contained a layer of silver bromide was washed in water to remove excess bromine and then air dried. This photosensitive element was photoexposed for one-thirtieth second to 1,620 meter candles of white light. It was developed in the conventional manner utilizing a liquid developer and it was subsequently fixed.
EXAMPLE III
A sheet of polyester was subjected to a silver vacuum deposition treatment to provide a coverage of approximately 60 mg. of silver per square foot of polyester. In complete darkness this silver coated substrate was submerged into a solution of platinic chloride, [H 2 PtCl 6 .6H 2 O] for 1 minute at room temperature and atmospheric pressure. It was then removed from the solution, washed for 30 seconds in methanol at the same temperature and air dried. The sheet was contact photoexposed for 15 seconds through a conventional step wedge. The light source was a number two flood light at a distance of 2 feet from the sheet. The exposed stratum was developed for 30 seconds in duPont X-ray developer, then rinsed, fixed and washed. An image was obtained.
EXAMPLE IV
A sheet of paper coated with 150 mg. of silver per square foot was sprayed for 15 seconds with a solution containing 17 percent iodine by weight dissolved in isopropanol. The halogenation was interrupted prior to completion by washing thrice in methanol. The sheet was inserted into an alcoholic solution which contained 15 percent sodium bromide and 1.5 percent bromine, both by weight for 2 minutes. The sheet was removed and washed in distilled water to remove the halogenating agent and was then dried. This sheet was exposed and developed substantially in the same manner as described in Example III.
EXAMPLE V
A piece of "subbed" polyethylene terephthalate coated with 60 mg. per square foot of silver was submerged into a solution which contained methanol as a solvent and sodium bromide and bromine as solutes for 5 minutes. The solution contained 1.52 percent bromine and 15.65 percent sodium bromide and 82.83 percent methanol by weight. The polyethylene terephthalate was then washed thrice in fresh methanol, dipped into acetone and air dried. These steps were performed in the dark at room temperature and atmospheric pressure. The photosensitive element was exposed by projecting light through a step wedge. The light source, which measured 1,620 meter candles at the film plane, comprised a 2,800° Kelvin, 500 watt projection lamp. Exposure time was one-half second at an aperture of f/4.7. Two similarly exposed photosensitive elements were processed according to diffusion transfer methods. The first was processed utilizing a processing pod similar to those found with Type 42 Land film; while the second used a pod similar to the pod of Type 47 Land film. Transfer was made in both instances onto a receiving sheet similar to that of Type 47 Land film. In both instances a positive-transfer image was obtained and a negative image remained in the negative. The equivalent ASA exposure index for the transfer image was calculated to be in the vicinity of 0.4. The negative obtained using either of the above processing systems was found to exhibit a transmission density D max of 1.1 and a D min of 0.03. The positive was found to have a reflection density, D max of 1.9 and a D min of 0.03. The transparent negative was light-stable without fixing or other after treatments, and reusable to produce further prints, enlargements or projection images.
EXAMPLE VI
The procedure of Example V was repreated except that the silver was submerged for only 15 seconds. Substantially the same photographic results were obtained.
EXAMPLE VII
A sheet of polyethylene terephthalate coated with 60 mg. of silver per square foot was immersed into an aqueous bath of sodium bromide and bromine water. Halogenation was interrupted by removing the sheet after 5 minutes. It was washed thrice in methanol and immersed into a bath of KI and I 2 in methanol. The sheet was then washed in methanol, followed by an acetone bath and was allowed to air dry. This photosensitive element was exposed in the conventional manner and developed utilizing conventional tray liquid development agents.
EXAMPLE VIII
The two-step halogenation procedure described in Example VII was repeated using various combinations of solution halogenating agents, each halogenation step being interrupted before completion to avoid the possibility of a mono-halide product. The halogenating agent/solvent combinations and the resulting mixed halide (the last listed anion representing the halogen used in the greatest proportion) were:
First Second Mixed Halogenation Halogenation Silver Halide ____________________________________________________________ ______________ iodine/methanol bromine/methanol AgIBr chlorine/methanol iodine/methanol AgClI platinum chloride/water bromine/water AgClBr iodine/water chlorine/isopropanol AgIcl bromine/methanol chlorine/water AgBrCl ____________________________________________________________ ______________
EXAMPLE IX
Because of the observed differences in photographic properties of solution halogenated and vapor halogenated silver halide films, a series of comparison samples were prepared and studied by several analytical techniques. Samples of polyethylene terephthalate were vacuum coated with silver at a plurality of coverages (as set forth in Table A) and each sample was then divided into two pairs one of which was solution halogenated while the other was vapor halogenated to provide silver iodide photosensitive films. Visual examination of the resulting pairs of silver iodide films indicated the solution halogenated film to be more translucent and less transparent than the corresponding vapor halogenated film. ------------------------------------------------------------ --------------- TABLE A
Milligrams of Silver per Square Foot of Polyester as Determined by Atomic Absorption Prior to Halogenation Treatment
Silver Coverage Per Square Foot of Polyester Sample Number Prior to Halogenation ____________________________________________________________ ______________ 1 22 2 38 3 62 4 80 5 100 6 115 7 140 ____________________________________________________________ ______________
Spectrophotometric analysis of several pairs of such halogenated films showed that, for the same silver coverage, the percentage of transmission in the range of 450-600 millimicrons was always higher for the vapor halogenated specimen than for the solution halogenated specimen. As the weight of silver in the specimen increased, the difference in percent transmission between the vapor halogenated and solution halogenated specimens also increased, with the vapor halogenated specimen always having the greater transmission. Since the silver coverages were the same, the differences in percent transmission are due to differences in the light scattering characteristics of the respective silver halide crystals, e.g., to differences in crystal size. As shown in Table B, chemical quantitative analysis determined that all samples after halogenation by vapor or solution halogenation techniques contained substantially the same amount of silver as prior to halogenation. ##SPC1##
The halogen content of all solution halogenated specimens in this example was found to be that of a stoichiometric balance with the silver. There was no excess of either halide or silver as determined by wet chemical analysis, whereas the vapor halogenated samples had an excess of silver.
Upon electron microscopic examination, a textural difference was observed on the 111 face of the several silver halide crystals. It appears to be more characteristic of the vapor halogenated crystals that they have a rigid or stepwise surface instead of a smooth planar surface on the crystal face. This is not to say, however, that the crystals obtained by solution halogenation have no stepwise texture whatsoever, but rather that the predominance of such an appearance lies with the crystals obtained by vapor halogenation.
A still further difference between the silver halide crystals obtained by solution and vapor halogenation processes is observed by X-ray diffraction examination. If two specimens are cut from the same sample of silvered polyester or other support and one is subjected to vapor halogenation and one to solution halogenation utilizing the same halogenation agent under conditions such that there is a minimum of possible interceding variables, the resultant silver halide crystals from the vapor halogenated specimen exhibit a preferential growth in the 112 hexagonal or the 311 cubic habit, whereas the solution halogenated specimens exhibit a different preferential growth, namely, the 111 cubic or 002 hexagonal habits.
EXAMPLE X
A mixed halide photosensitive element was prepared as follows: a polyester support was vacuum coated with metallic silver to provide a silver coverage of 60 mg./ft 2 . This element was then immersed in a methanol solution of chlorine for 3 minutes and then washed. The thus-prepared silver chloride element was then immersed for 3 minutes in a solution composed, by weight, of 98.55 percent methanol and 1.45 % elemental bromine. After washing the resulting silver bromochloride element had a Br - : Cl - ratio of 5.9 to 1. This element was then immersed for 20 minutes in a solution composed, by weight, of 98.73 percent methanol and 1.27 percent elemental iodine. After washing the element had a Br - : I - : Cl - ratio of 1.00 : 0.25 : 0.15. Immersion for 20 minutes in this methanol/iodine solution of the first described silver chloride element gave, after washing, a mixed halide element having a Cl - : I - ratio of 1.00 : 0.314. (The halogen ratios were obtained by wet chemical analysis.)
It will be understood that the solution halogenation process may be used to replace a halogen in a binder-free silver halide stratum previously introduced by other techniques, e.g., vapor halogenation or vacuum deposition of a preformed silver halide.
The photosensitive silver halide elements prepared by solution halogenation in accordance with this invention differ in kind from those prepared by vapor halogenation in accordance with the prior art teachings. Solution halogenated silver strata exhibit higher film speed and higher contrast, particularly when used in silver transfer processes, than the corresponding vapor halogenated silver strata. The ratio of halogen to silver in vapor halogenated silver strata is less, and frequently much less, than a stoichiometric ratio of 1 which ratio may readily be obtained by solution halogenation. This lack of a stoichiometric ratio of halogen to silver is particularly pronounced in vapor brominated silver strata and is believed to be due to the formation of a protective silver bromide "skin" at the surface of the silver stratum preventing or limiting growth of silver bromide crystals and bromination of silver deeper in the stratum (cf. "The Relationship Between The Nucleation And Growth Of Chemically Formed Surface Films And Those Deposited By The Vacuum Evaporation Technique" by D. W. Pashley, Memoires Scientifiques Rev. Metallurg, LXII, pp. 93-104, May, 1965, at p. 103). It is also possible to have halogen in excess of the stoichiometric ratio by solution halogenation. Vapor halogenation of silver on various film bases, e.g., cellulose acetate or polyester, may result in attack upon the base or penetration into the base to provide a residue of halogen which could adversely affect a subsequently formed image. These problems are avoided or at least minimized by solution halogenation for the halogen remains in the solution. Solution halogenation is markedly faster than vapor halogenation, thus facilitating manufacture and further minimizing possible adverse chemical reactions e.g., between the halogenating agent and the base. Solution halogenated silver iodide and silver bromide binderless films have given resolution in excess of 100-200 lines per mm. and greater resolution is possible.
Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter containing the above description shall be interpreted as illustrative and not in a limiting sense.
The most common method of preparing photographic silver halide emulsions is to react a water-soluble silver salt, such as silver nitrate, with at least one water-soluble alkali or ammonium halide in the presence of an aqueous solution of an emulsifying agent such as gelatin. The mode of reaction of these materials, including such factors as the sequence of addition, rate of addition, the temperature and pressure and the concentration of the various reactants can be varied in accordance with the technical knowhow of the producer. The dispersion of silver halide thus formed contains numerous water-soluble salts as by-products of the primary reaction as well as unreacted initial reagents. It is considered desirable to remove most of these unwanted materials by processes known in the art.
It is known that conventional silver halide photosensitive materials present several inadequacies. For example, the resolution is lower than that theoretically available from the silver halide grain due to light scattering caused by the presence of the gelatin binder, as well as physical distortion which occurs during the processing of the matrix, i.e., swelling, hardening, etc. Another problem that exists with the conventional emulsions is the fact that when gelatin is present there is incomplete utilization of silver in both the exposed and unexposed forms. The preparation of conventional photographic emulsions is a highly empirical art in view of the infinite number of variables present in the gelatin material. The most basic variable is the structure of the gelatin, which is a complex compound(s) which has as yet not been completely analyzed. Furthermore, the presence of various polypeptides and other compounds renders the control of the emulsion preparation quite difficult.
Thus it is seen that the investigation and preparation of photosensitive elements which do not possess the problems set forth above would indeed be useful. Such products are prepared in the process of the present invention which employs a binder-free system.
The term binder-free is utilized to signify the fact that the photosensitive elements of the present invention are prepared without gelatin or an equivalent binder as is used in conventional photographic materials. In certain instances, however, it may be desirable to apply a stratum of a polymeric material over the surface of the binder-free photosensitive element, in which event the silver halide will still be substantially binder-free.
Accordingly, it is a primary object of this invention to prepare photosensitive silver halide elements by solution halogenation of silver coated strata.
Still another object is the preparation of photosensitive elements utilizing solution halogenation techniques which elements can be tray developed.
Yet another object of this invention is the preparation of novel photosensitive elements which can be utilized in diffusion transfer processes.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The process of the present invention in general entails the depositing of silver and optionally other metals such as gold, tellurium, indium, iron, tin, and lead, by vacuum deposition or other conventional techniques upon the base material and then subjecting the metal coated stratum to a solution halogenation treatment. A convenient method of adding the optional metal is by doping during the silver deposition.
Among the metal depositing techniques are sputtering, electroplating, and vapor deposition under vacuum. For a more thorough understanding of a process involving vacuum deposition of a silver coating upon a support material, reference is made to U.S. Pat. No. 3,142,566, issued July 28, 1964 to Edwin H. Land.
In the Land U.S. Pat. No. 3,142,566, there is disclosed a method of forming a photosensitive element by the vacuum deposition of silver, and/or silver with a substratum of gold and a subsequent treatment of this metal coating with the vapor of elemental halogen, e.g., chlorine, bromine, iodine or combinations thereof, or with vapors of volatile halogen salts, e.g., hydrogen bromide, hydrogen iodide or combinations thereof at a suitable temperature, for example, room temperature.
In the present invention the novel photosensitive elements are prepared by vacuum depositing silver alone or in combination with another metal, e.g., gold, upon a suitable support, followed by the subjection of the metal coated support or base to a solution halogenation process, as opposed to the vapor halogenation treatment of the aforementioned patent. Solution halogenation of the metal coated substrate can be carried out by any suitable means including dipping, brushing, coating, spraying, doctoring and continually passing the substrate through the appropriate solution.
The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application 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 description.
Support materials utilizable herein include any suitable base to which silver will adhere and which will not be adversely affected by the solution halogenation step. Typical examples are materials such as baryta paper; plastics such as polyethylene terephthalate, polyvinyl acetate, and polycarbonate; metals such as aluminum and lead; as well as glass. All of these can be coated with silver and optionally with other metals by known techniques.
Good quality results have been obtained wherein the metal coated upon the support material comprises silver or silver in combination with gold, wherein the gold and silver are deposited in either sequence or together.
Halogenation is effected by subjecting the metallic stratum to a solution containing dissolved therein at least one halogenating agent, preferably an elemental halogen or, in certain instances, a halide ion, e.g., platinum chloride, platinum iodide, or platinum bromide. Accordingly, this can be done by spraying, dipping, brushing, coating or any other suitable technique. The halogenation treatments are done at atmospheric pressure at a suitable temperature, for instance, room temperature. The effective time required for halogenation of the metallic stratum ranges from instantaneous, i.e., less than 1 second up to several minutes. The duration of the treatment is dependent upon the thickness of the metallic layer, the concentration of the halogen substance, and the amount of halogenation desired.
Elemental halogens such as chlorine, bromine and iodine dissolved in a suitable solvent such as water can be used as the halogenation solution. Organic solvents may also be used, e.g., iodine dissolved in ethylene glycol has provided a useful non-flammable halogenating solution. Excellent results have been obtained when iodine is dissolved in an alkyl alcoholic solvent such as methanol, butanol, isopropanol, and octanol. The addition of an alkali metal halide to a solution of an elemental halogen appears to aid the growth of the silver halide crystals, possibly because the alkali metal halide can act as a solvent for the silver halide formed. In a particularly useful embodiment, bromine is dissolved in an aqueous or alcoholic solution of sodium or potassium bromide.
The process of the present invention can be utilized with metal strata containing varying amounts of silver. The silver coverage may range from 20 milligrams per square foot to the vicinity of 150 milligrams per square foot. The process set forth hereinabove can be utilized with silver strata that have been chemically sensitized, such as by the deposition of gold either in sequence or together with silver; or with non-sensitized silver strata.
According to the process of the present invention it is possible not only to prepare silver halide crystals wherein a single halide is present, but it is similarly possible to prepare mixed silver halide crystals wherein two or even three halides are present. It should be realized that the compounds such as AgBrI and AgIClBr, are not pure stoichiometric compounds, but rather they comprise crystal lattices wherein a certain percentage of the second and/or third halide constitutes an impurity in the crystal lattice.
Mixed silver halide crystals may be prepared by the incomplete halogenation of the silver in a first halogenation treatment (e.g., by interrupting the halogenation via a washing operation) followed by a second halogenating treatment with a second halogen. This process can be repeated to introduce a third halide. Alternatively, mixed silver halides may be prepared by using a solution having two halogens dissolved therein, with the halogen of lower oxidation potential being present in great excess. In multistep preparation of "mixed" halides, a particular halogen may be used in two different steps, e.g., bromine may be used in the first and third steps of a multistep solution halogenation to obtain a mixed halide such as AgBrClBr.
It is also within the scope of this invention to use solution halogenation treatment to replace, in whole or in part, one halogen with another, e.g., silver bromide crystals can be formed by treatment of a silver iodide binderless film with a bromine solution. This procedure is particularly advantageous if large silver bromide crystals are desired, since prolonged contact with a bromine solution to grow large crystals may cause the crystals to fall off of the support; in contrast, silver may be left in contact with an iodine solution for the long times required to grow large crystals and then the crystals may be converted to silver bromide.
The advantages of the present invention include the fact that each step of the synthesis of the photosensitive element can be documented and controlled analytically. The photographic resolution can approach the theoretical resolution of the silver halide form, since a binder is not present. A major benefit to be derived from the process of the present invention is the fact that photosensitive elements can be prepared relatively easily and quite fast, when viewed in contrast to binder emulsion, as well as vapor deposition technology. When the photosensitive element prepared by the present invention is utilized in a diffusion transfer process, it is seen that substantially all unexposed silver can be utilized in a positive transfer since no binder is present to retard the silver from complexing with the transfer agent or to prevent it from transferring after complexing has taken place.
Photosensitive strata prepared in accordance with this invention may be developed utilizing conventional developing solutions which include Microdol, sold by Eastman Kodak Company, Rochester, New York; Cronex X-Ray Developer, sold by E. I. duPont de Nemours and Co., Wilmington, Delaware; as well as other commercially available developers.
The photosensitive products of the present process are particularly suited to prepare microfilm in view of the fact that these photosensitive elements have high resolution and may be readily formed on dimensionally stable supports. In view of the fact that these photosensitive elements contain no gelatin it is seen that it is not necessary to add microbial retarders to the formulation. Therefore, these photosensitive elements would find special utility in archival work.
The examples set forth hereinafter are meant to be illustrative only and are not to be construed as limiting.
EXAMPLE I
A glass plate was subjected to a vacuum deposition treatment with silver. This silver-coated glass was then dipped into a saturated solution of iodine crystals dissolved in methanol. The solution contained one per cent iodine by weight. The immersion time for the halogenation treatment was 30 seconds. It was conducted under atmospheric pressure at 25° C. The glass was washed three times with methanol to insure the removal of excess iodine. The coated substrate was dried in the air. Upon spectrophotometric inspection the coating was found to be silver iodide. This conclusion was substantiated by X-ray diffraction studies. After exposure and development, the resulting image exhibited negligible grain.
EXAMPLE II
A sheet of polyethylene terephthalate plastic with a subbing layer annexed thereon and available commercially as "subbed Cronar" from E. I. duPont de Nemours & Co., Wilmington, Delaware, was subjected to a vacuum deposition treatment to coat it with silver. The silver-coated polyester was dipped into a solution of bromine water for 5 minutes. The sheet which now contained a layer of silver bromide was washed in water to remove excess bromine and then air dried. This photosensitive element was photoexposed for one-thirtieth second to 1,620 meter candles of white light. It was developed in the conventional manner utilizing a liquid developer and it was subsequently fixed.
EXAMPLE III
A sheet of polyester was subjected to a silver vacuum deposition treatment to provide a coverage of approximately 60 mg. of silver per square foot of polyester. In complete darkness this silver coated substrate was submerged into a solution of platinic chloride, [H 2 PtCl 6 .6H 2 O] for 1 minute at room temperature and atmospheric pressure. It was then removed from the solution, washed for 30 seconds in methanol at the same temperature and air dried. The sheet was contact photoexposed for 15 seconds through a conventional step wedge. The light source was a number two flood light at a distance of 2 feet from the sheet. The exposed stratum was developed for 30 seconds in duPont X-ray developer, then rinsed, fixed and washed. An image was obtained.
EXAMPLE IV
A sheet of paper coated with 150 mg. of silver per square foot was sprayed for 15 seconds with a solution containing 17 percent iodine by weight dissolved in isopropanol. The halogenation was interrupted prior to completion by washing thrice in methanol. The sheet was inserted into an alcoholic solution which contained 15 percent sodium bromide and 1.5 percent bromine, both by weight for 2 minutes. The sheet was removed and washed in distilled water to remove the halogenating agent and was then dried. This sheet was exposed and developed substantially in the same manner as described in Example III.
EXAMPLE V
A piece of "subbed" polyethylene terephthalate coated with 60 mg. per square foot of silver was submerged into a solution which contained methanol as a solvent and sodium bromide and bromine as solutes for 5 minutes. The solution contained 1.52 percent bromine and 15.65 percent sodium bromide and 82.83 percent methanol by weight. The polyethylene terephthalate was then washed thrice in fresh methanol, dipped into acetone and air dried. These steps were performed in the dark at room temperature and atmospheric pressure. The photosensitive element was exposed by projecting light through a step wedge. The light source, which measured 1,620 meter candles at the film plane, comprised a 2,800° Kelvin, 500 watt projection lamp. Exposure time was one-half second at an aperture of f/4.7. Two similarly exposed photosensitive elements were processed according to diffusion transfer methods. The first was processed utilizing a processing pod similar to those found with Type 42 Land film; while the second used a pod similar to the pod of Type 47 Land film. Transfer was made in both instances onto a receiving sheet similar to that of Type 47 Land film. In both instances a positive-transfer image was obtained and a negative image remained in the negative. The equivalent ASA exposure index for the transfer image was calculated to be in the vicinity of 0.4. The negative obtained using either of the above processing systems was found to exhibit a transmission density D max of 1.1 and a D min of 0.03. The positive was found to have a reflection density, D max of 1.9 and a D min of 0.03. The transparent negative was light-stable without fixing or other after treatments, and reusable to produce further prints, enlargements or projection images.
EXAMPLE VI
The procedure of Example V was repreated except that the silver was submerged for only 15 seconds. Substantially the same photographic results were obtained.
EXAMPLE VII
A sheet of polyethylene terephthalate coated with 60 mg. of silver per square foot was immersed into an aqueous bath of sodium bromide and bromine water. Halogenation was interrupted by removing the sheet after 5 minutes. It was washed thrice in methanol and immersed into a bath of KI and I 2 in methanol. The sheet was then washed in methanol, followed by an acetone bath and was allowed to air dry. This photosensitive element was exposed in the conventional manner and developed utilizing conventional tray liquid development agents.
EXAMPLE VIII
The two-step halogenation procedure described in Example VII was repeated using various combinations of solution halogenating agents, each halogenation step being interrupted before completion to avoid the possibility of a mono-halide product. The halogenating agent/solvent combinations and the resulting mixed halide (the last listed anion representing the halogen used in the greatest proportion) were:
First Second Mixed Halogenation Halogenation Silver Halide ____________________________________________________________ ______________ iodine/methanol bromine/methanol AgIBr chlorine/methanol iodine/methanol AgClI platinum chloride/water bromine/water AgClBr iodine/water chlorine/isopropanol AgIcl bromine/methanol chlorine/water AgBrCl ____________________________________________________________ ______________
EXAMPLE IX
Because of the observed differences in photographic properties of solution halogenated and vapor halogenated silver halide films, a series of comparison samples were prepared and studied by several analytical techniques. Samples of polyethylene terephthalate were vacuum coated with silver at a plurality of coverages (as set forth in Table A) and each sample was then divided into two pairs one of which was solution halogenated while the other was vapor halogenated to provide silver iodide photosensitive films. Visual examination of the resulting pairs of silver iodide films indicated the solution halogenated film to be more translucent and less transparent than the corresponding vapor halogenated film. ------------------------------------------------------------ --------------- TABLE A
Milligrams of Silver per Square Foot of Polyester as Determined by Atomic Absorption Prior to Halogenation Treatment
Silver Coverage Per Square Foot of Polyester Sample Number Prior to Halogenation ____________________________________________________________ ______________ 1 22 2 38 3 62 4 80 5 100 6 115 7 140 ____________________________________________________________ ______________
Spectrophotometric analysis of several pairs of such halogenated films showed that, for the same silver coverage, the percentage of transmission in the range of 450-600 millimicrons was always higher for the vapor halogenated specimen than for the solution halogenated specimen. As the weight of silver in the specimen increased, the difference in percent transmission between the vapor halogenated and solution halogenated specimens also increased, with the vapor halogenated specimen always having the greater transmission. Since the silver coverages were the same, the differences in percent transmission are due to differences in the light scattering characteristics of the respective silver halide crystals, e.g., to differences in crystal size. As shown in Table B, chemical quantitative analysis determined that all samples after halogenation by vapor or solution halogenation techniques contained substantially the same amount of silver as prior to halogenation. ##SPC1##
The halogen content of all solution halogenated specimens in this example was found to be that of a stoichiometric balance with the silver. There was no excess of either halide or silver as determined by wet chemical analysis, whereas the vapor halogenated samples had an excess of silver.
Upon electron microscopic examination, a textural difference was observed on the 111 face of the several silver halide crystals. It appears to be more characteristic of the vapor halogenated crystals that they have a rigid or stepwise surface instead of a smooth planar surface on the crystal face. This is not to say, however, that the crystals obtained by solution halogenation have no stepwise texture whatsoever, but rather that the predominance of such an appearance lies with the crystals obtained by vapor halogenation.
A still further difference between the silver halide crystals obtained by solution and vapor halogenation processes is observed by X-ray diffraction examination. If two specimens are cut from the same sample of silvered polyester or other support and one is subjected to vapor halogenation and one to solution halogenation utilizing the same halogenation agent under conditions such that there is a minimum of possible interceding variables, the resultant silver halide crystals from the vapor halogenated specimen exhibit a preferential growth in the 112 hexagonal or the 311 cubic habit, whereas the solution halogenated specimens exhibit a different preferential growth, namely, the 111 cubic or 002 hexagonal habits.
EXAMPLE X
A mixed halide photosensitive element was prepared as follows: a polyester support was vacuum coated with metallic silver to provide a silver coverage of 60 mg./ft 2 . This element was then immersed in a methanol solution of chlorine for 3 minutes and then washed. The thus-prepared silver chloride element was then immersed for 3 minutes in a solution composed, by weight, of 98.55 percent methanol and 1.45 % elemental bromine. After washing the resulting silver bromochloride element had a Br - : Cl - ratio of 5.9 to 1. This element was then immersed for 20 minutes in a solution composed, by weight, of 98.73 percent methanol and 1.27 percent elemental iodine. After washing the element had a Br - : I - : Cl - ratio of 1.00 : 0.25 : 0.15. Immersion for 20 minutes in this methanol/iodine solution of the first described silver chloride element gave, after washing, a mixed halide element having a Cl - : I - ratio of 1.00 : 0.314. (The halogen ratios were obtained by wet chemical analysis.)
It will be understood that the solution halogenation process may be used to replace a halogen in a binder-free silver halide stratum previously introduced by other techniques, e.g., vapor halogenation or vacuum deposition of a preformed silver halide.
The photosensitive silver halide elements prepared by solution halogenation in accordance with this invention differ in kind from those prepared by vapor halogenation in accordance with the prior art teachings. Solution halogenated silver strata exhibit higher film speed and higher contrast, particularly when used in silver transfer processes, than the corresponding vapor halogenated silver strata. The ratio of halogen to silver in vapor halogenated silver strata is less, and frequently much less, than a stoichiometric ratio of 1 which ratio may readily be obtained by solution halogenation. This lack of a stoichiometric ratio of halogen to silver is particularly pronounced in vapor brominated silver strata and is believed to be due to the formation of a protective silver bromide "skin" at the surface of the silver stratum preventing or limiting growth of silver bromide crystals and bromination of silver deeper in the stratum (cf. "The Relationship Between The Nucleation And Growth Of Chemically Formed Surface Films And Those Deposited By The Vacuum Evaporation Technique" by D. W. Pashley, Memoires Scientifiques Rev. Metallurg, LXII, pp. 93-104, May, 1965, at p. 103). It is also possible to have halogen in excess of the stoichiometric ratio by solution halogenation. Vapor halogenation of silver on various film bases, e.g., cellulose acetate or polyester, may result in attack upon the base or penetration into the base to provide a residue of halogen which could adversely affect a subsequently formed image. These problems are avoided or at least minimized by solution halogenation for the halogen remains in the solution. Solution halogenation is markedly faster than vapor halogenation, thus facilitating manufacture and further minimizing possible adverse chemical reactions e.g., between the halogenating agent and the base. Solution halogenated silver iodide and silver bromide binderless films have given resolution in excess of 100-200 lines per mm. and greater resolution is possible.
Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter containing the above description shall be interpreted as illustrative and not in a limiting sense.