CA1151461A

CA1151461A - Electrically activated recording material containing a dye-forming coupler and an oxidation-reduction combination

Info

Publication number: CA1151461A
Application number: CA000341975A
Authority: CA
Inventors: Mark Lelental
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1979-07-09
Filing date: 1979-12-14
Publication date: 1983-08-09
Also published as: JPS5625742A; DE3025839A1; GB2054884B; BE884244A; FR2461284A1; FR2461284B1; GB2054884A

Abstract

DYE FORMING ELECTRICALLY ACTIVATED
RECORDING MATERIAL AND PROCESS
Abstract of the Disclosure A dye-forming electrically activated recording element comprises an electrically conductive support having thereon (a) an electrically activated recording layer com-prising in an electrically conductive polymeric binder, an organic silver salt and a reducing agent, (b) a photo-conductive layer separated from (a) by an air gap of up to 20 microns and (c) an electrically conductive layer on (b), wherein the recording layer (a) comprises in reactive association, (A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which in its oxidized form forms a dye with the dye-forming coupler.
The recording element can be room light handleable and can provide a dye image and silver image by dry development processing.

Description

DYE FORMING ELECTRICALLY ACTIVATED
RECORDING MATERIAL AND PROCESS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to dye-forming charge-sensitive recording materials. One aspect of the invention relates to the use of (A) a dye-forming coupler and (B) an image-forming combination in a charge-sensitive recording material which is capable of producing a dye 10 image and silver image by dry development processes.
DESCRIPTION OF THE STATE OF THE ART
A variety of recording materials and processes have been proposed to provide image recording. The better known and commercially more successful of these recording 15 materials and processes can be classified as photographic, thermographic or electrographic or as a combination of two or more of these processes. For example, one known recording material is a photothermographic material which is a heat developable photosensitive material. Each of the known image 20 recording materials and processes have certain advantages for particular uses. However, the materials and processes also suffer from disadvantages which limit the usefulness in particular applications. For example, conventional photographic materials have the disadvantage that they 25 are not room light handleable prior to imagewise exposure and processing. Thermographic materials require imagewise heating to provide a visible image and are not capable of the degree of light sensitivity provided by conventional photographic materials. Electrographic materials including, 30 for example, xerographic materials require mechanical dust pattern transfer procedures to provide a desired image.
It has been desirable to provide an image recording material and process which enable the formation of a dye image and a silver image under daylight conditions, yet 35 avoid the need for conventional processing baths and solutions.

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115~1 Heat developable photographic materials which after imagewise exposure can be heated to produce a developed image in the absence of processing solutions or baths are known.
These photosensitive materials have the disadvantage that 5 they are not room light handleable prior to imagewise exposure for recording purposes.
Another means proposed for imaging involves a recording material which produces an image by passing an electric current through the recording materlal. Such 10 recording materials involve electrographic image recording techniques. One such recording material comprises a conventional light sensitive photographic material that is positioned contiguous to a photoconductive layer for image recording purposes. Upon applying a uniform electric field 15 across the photoconductive and photographic layers and simultaneously imagewise exposing the photoconductive layer to a light pattern, an imagewise current flow is produced in the photographic layer. This imagewise current flow in turn produces a developable latent image in the photographic 20 layer. The recording material, however, has the disadvantages associated with light sensitive photographic materials which require processing with conventional solutions and baths.
Moreover, the material requires a substantial current flow in the recording layer and therefore provides a relatively 25 lengthy exposure time with low current flow or a high current flow with a short exposure time.
Dry electrographic recording materials and processes which involve production of a visible image in a charge-sensitive recording element have been described in, 30 for example, French Patent 2,280,517 published February 27, 1976 and U.S. Patent 4,113,484. Such dry electrographic recording materials can be processed by dry development techniques. However, no suggestion is given of producing a dye image and silver image in such a recording material 35 and process.

~51461 Accordingly, a continuing need has existed to provide an electrically activated recording element that (a) avoids the need for conventional processing solutions and baths, (b) enables room light handling of the recording 5 material prior to imagewise exposure and processing, and (c) enables the formation of a dye image and silver image, preferably a dye image that enhances the silver image.
SUMMARY OF THE INVENTION
It has been found according to the invention that 10 the described advantages are provided in an electrically activated recording element comprising an electrically conductive support having thereon, in sequence, (a) an electrically activated recording layer comprising an organic silver salt and a reducing agent, and (b) a photoconductive 15 layer separated from (a) by an air gap of up to 20 microns and (c) an electrically conductive layer on (b), wherein the recording layer comprises, in reactive association, (A) a dye-forming coupler, and (B) an oxidation-reduction com-bination comprising (i) an organic silver salt oxidizing 20 agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with the dye-forming coupler. Such an electrically activated recording element enables formation of a dye image and silver image by heat processing after imagewise exposure. The electrically activated recording 25 element according to the invention preferably also comprises an electrically conductive subbing layer on the electrically conductive support.
It has also been found according to the invention that a dye image and silver image, especially a dye enhanced 30 silver image, can be produced by a dry, electrically activated recording process comprlsing the steps o~ (I) applying an electric potential lmagewise to an electrically activated recording layer of a charge-sensitive recording element of a magnitude and for a sufficient time to produce 35 in the image areas a charge density within the range of about 10 3 coulomb/cm to about 10 9 coulomb/cm2, said charge density forming a developable latent image in the charge-sensitive recording layer; and, then (II~ heating the element substantially uniformly at a temperature and for a time sufficient to produce a dye image and silver image, preferably a dye enhanced silver image, in the recording layer. In this process embodiment the electrically activated recording layer comprises the described components; however, other means than a photoconductor can be useful to produce the desired charge density in the recording layer, such as a contact or non-contact electrode.
A further process which has been found according to the invention which produces a dye image and silver image comprises ~I) imagewise altering the conductivity of the photoconductive layer of the described element in accord with an image to be recorded; (II) applying across the photo-conductive layer and recording layer an electrical potential of a magnitude and for a sufficient time to produce a developable latent image in the recording layer corresponding to the image to be recorded; and then (III) heating the recording layer substantially uniformly at a temperature and for a time sufficient to produce a dye image and a silver image, preferably a dye enhanced silver image, in the recording layer. The step (I) of imagewise altering the conductivity of the photoconductive layer is preferably carried out while simultaneously (II) applying the described electrical potential across the photoconductive layer and recording layer.
A further process which has been found according to the invention is a dry, electrically activated recording 3 process for producing a dye image and silver image, preferably a dye enhanced silver image, in an electrically activated recording element comprising the steps: (I? imagewise altering the conductivity of a photoconductive layer CZ) in accord with an image to be recorded; CII~ positioning the imagewise altered photoconductive layer CZ~ from ~I~ in face-to-face relationship with an electrically activated recording layer CY~ of the recording element, which element comprises (A) a dye-forming coupler and (B) an image-forming combination comprising (i) an organic silver salt oxidizing il51gt6 agent, with ~ii) a reducing agent which, in its oxidized form, forms a dye with the dye-forming coupler; ~III) applying across the photoconductive layer and recording layer an electrical potential of a magnitude and for a sufficient time to produce in the areas of the recording layer corresponding to the imagewise altered portions of the photoconductive layer a charge density within the range of about 10 3 coulomb/cm2 to about 10 9 coulomb/c~2, the charge density forming in the areas a developable latent image, and then ~IV) unifor~ly heating the recording element at a temperature and for a time sufficient to produce a dye image and silver image, especially a dye enhanced silver image, in the recording element.
Another process according to the invention is a dry electrically activated recording process for producing a dye image and silver image, preferably a dye enhanced silver image, in a charge-sensitive recording element, preferably having ohmic resistivity within the range of about 104 to about 1 x 1012 ohm-cm, containing at least one electrically activated recording material comprising in an electrically conductive binder, (A) a dye-forming coupler, and (B) an image-forming combination comprising (i) an organic silver salt oxi.dizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with the dye-forming coupler; comprising the steps: (I) positioning the recording material on an electrically conductive backing member; (II) modulating a corona ion current flow to the recording element by an electrostatic field established imagewise between an 3 image grid comprising an electroconductive core sequentially connectable to sources of different potential relative to the backing member and covered with a coating of a photo-conductive insulating material and a control grid that is electrically conductive and sequentially connectable to sources of different potential relative to the backing 115~

member, said current flow being of a magnitude sufficient to produce a charge density within the range of about 10 3 to about 10 9 coulomb/cm2 imagewise in said recording-element, which charge density forms a developable latent image in the electrically activated recording material; and, (III) substantially uniformly heating the recording element at a temperature and for a time sufficient to produce a dye enhanced silver image in the recording element.
The heating step in each of the described process embodiments can be carried out at a temperature within the range of about 80C to about 200~C, typically at a temperature within the range of about 100C to about 180C, until the desired silver image and dye image are formed.
BRIEF DESCRIPTION OF THE DRAWINGS
~igures 1 and 2 illustrate schematically an image recording material and process according to one illustrative embodiment of the invention; and Figures 3 and 4 illustrate schematically an electrically activated recording process embodying the described invention.
Figure 5 illustrates schematically an image recording material that is especially useful according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
. _ _ .. . . .. _ _ Many dye-forming couplers, organic silver salt oxidizing agents and reducing agents which in their oxidized form form a dye with the dye-forming coupler may be used in the described electrically activated recording materials according to the invention. The exact mechanism by which the latent image is formed in the recording material is not fully understood. It is postulated that the in~ection of an electron due to the electric field into the comblnation of components results in the formation of a developable latent image. It is believed that the development of the latent image is accomplished by a reaction in which the latent image catalyzes the reaction of the described image-forming combination. In such a reaction the organic silver salt 1~51~161 oxidizing agent reacts with the described reducing agent.
Then, the oxidized form of the reducing agent resulting from this reaction in turn reacts with the dye-forming coupler to produce a dye in the image areas. It is not entirely clear, however, what part, if any, the dye-forming coupler and the other described components play in latent image formation.
While a variety of image recording combinations containing the described components can be useful, the optimum image recording combination and image recording element will depend upon such factors as the desired image, the particular image-forming combination, the source of exposing energy, processing condition ranges and the like.
The term "charge-sensitive recording material"
as used herein is intended to mean a material which when subjected to an electrical current undergoes a chemical and/or electrical change which provides a developable latent image.
The term "latent image" as used herein is intended to mean an image that is not visible to the unaided eye or is faintly visible to the unaided eye and that is capable of amplification in a subsequent processing step, especially in a subsequent heat development step.
The term "resistive recording material" as used herein is intended to mean a material that has an ohmic resistivity of at least about 104 ohm-cm.
The term "electrically conductive" such as in "electrically conductive support" or "electrically conductive subbing layer" is intended herein to mean a support and subbing layer that have a resistivity less than about 1012 ohm-cm.
Many photoconductors may be used in an element according to the invention. Selection of an optimum photo-conductor will depend upon such factors as the particular electrically activated recording layer, the charge sensitivity of the element, the desired image, the ohmic resistivity ~5 desired, exposure means, processing conditions and the like.
It is advantageous to select a photoconductor which has the property of being the most useful with the operative voltages to be used for imaging. The photoconductor can be either an organic photoconductor or an inorganic photoconductor.
Combinations of photoconductors can be useful. The resistivity of the photoconductor can change rapidly in the operating voltage ranges which can be useful according to the invention. In some cases, it is desirable that the photoconductive layer have what is known in the art as persistent conductivity. Examples of useful photoconductors include lead oxide, cadmium sulfide, cadmium selenide, cadmium telluride, selenium and lanthanum oxide. Useful organic photoconductors include, for instance, polyvinyl carbazole/trinitrofluorenone photoconductors and aggregate type organic photoconductors described in, for example, U.S.
3,615,414. These photoconductors are known in the image recording art and are described in, for example, U.S. Patent 3,577,272; Research Disclosure, August 1973, Item 1120 of Reithel, published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, PO9 lEF, UK; "Electrography" by R. M.
Schaffert (1975) and "Xerography and Related Processes" by Dessauer and Clark (1965) both published by Focal Press Limited, and U.S. 3,615,414.
An especially useful photoconductive layer comprises a dispersion of lead oxide in an insulating binder, such as a binder comprising a polycarbonate (for example, LEXAN, a trademark of General Electric Company, U.S.A., consisting of a Bisphenol A polycarbonate~, polystyrene or polytvinyl butyral~.
A recording element according to the invention is especially useful wherein the photoconductive layer is X-ray sensitive and the conductivity of the photoconductor layer can be imagewise altered by imagewise exposing the 35 photoconductive layer to X-ray radiation.

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Many dye-forming couplers may be used in the element and process as described. The exact mechanism by which the dye image and silver image are produced is not fully understood. However, it is believed that the dye-forming coupler reacts with the described oxidized form of the reducing agent to form a desired dye. The dye-forming coupler herein is accordingly intended to mean a compound or combination of compounds which with other of the described components produces a desired dye image upon heating the recording layer after exposure.
These are designated as dye-forming couplers because it is believed that the compounds couple with the oxidized developer to produce the desired dye. The dye-forming couplers described herein are also known in the photographic art as color-forming couplers. Selection of a suitable dye-forming coupler will be influenced by such factors as the desired dye image, other components of the recording layer, processing conditions, particular reducing agent in the recording layer and the like. An example of a useful magenta dye-forming coupler is 1-(2,4,6-trichlorophenol)-3-[3-]-(3-pentadecylphenoxy)butyramido [benzamido]-5-pyrazolone. A useful cyan dye-forming coupler is the described 2,4-dichloro-1-naphthol. A useful yellow dye-forming coupler is ~-[3-]-(2,4-di-tertiary-amylphenoxy~
acetamido]-benzoyl]-2-fluoroacetanilide. Useful cyan, magenta and yellow dye-forming couplers can be selected from those described in, for example, "Neblette's Handbook of Photography and Reprography", edited by John M. Sturge, 7th Edition, 1977, pages 120-121 and Research Disclosure, December 1978, Item 17643, Paragraphs VII C-G.
An especially useful dye-forming coupler is a resorcinol dye-forming coupler. The resorcinol dye-forming coupler is preferably one that produces a neutral (black~ or nearly neutral appearing dye with the oxidized form of the described reducing agent. Mono-substituted resorcinol dye-forming couplers containing a substituent in the two position are especially useful.

1~5~61 The resorcinol dye-forming coupler and other components in the recording layer should be sufficiently stable to avoid any significant adverse interaction in the recording layer prior to imagewise exposure and processing. A variety of resorcinol dye-forming couplers can be useful. A useful resorcinol dye-forming coupler is typically one represented by the formula:

H O~ ~O H
IoI
R4/ \t/ \R2 wherein O O O
Rl is hydrogen, COH, NHCR5, CR6, or NHSo2R7;

O O

2 ~ "
R is hydrogen, COH, CNHCH2CH20H, or o CNH~C6H5~0C5Hlln;
O O
R3 is hydrogen, NHCR5, or CR6;
O O
Jl ,. ..
R' is hydrogen, COH, CNHCH2CH20H or o CNH~C6H5~C5Hlln;
R5 is haloalkyl containing 1 to 3 carbon atoms, such as CC13, CF3, and C3H~IBr3, CH20CH3, CH2SR , C2H4COOH, CH=CH2, NHC2H4Cl, alkyl containing 1 to 20 carbon atoms, such as 1 to 10 carbon atoms, including methyl, ethyl, propyl~ and decyl, or phenyl;

-` ~i51~61 R6 is OH, NH2, NHCH2CH20H, and NH~C6H5~0C5Hlln;
R7 is alkyl containing 1 to 5 carbon atoms, such as methyl, ethyl, propyl or pentyl, or phenyl; and R8 is hydrogen, haloalkyl containing 1 to 3 carbon atoms, such as CC13, CF3 and C3H4Br, CH20CH3, or C2H4COOH .
o The letter n, such as in CNH~C6H5~0C5Hlln, means normal-Alkyl and phenyl, as described, are intended to include alkyl and phenyl that are unsubstituted alkyl and phenyl as well as alkyl and phenyl that contain substituent groups that do not adversely effect the desired image. An example of a suitable substituent group is alkyl containing 1 to 3 carbon atoms, such as methyl or ethyl.
Examples of useful resorcinol dye-forming couplers are described ln, for example, Research Disclosure, September 1978, Item 17326. Especially useful resorcinol dye-forming couplers include 2l,6'-dihydroxyacetanilide and 2',6'-dihydroxytrifluoroacetanilide. Another useful resorçinol dye-forming coupler is 2',6'-dihydroxy-2,5-dimethylbenzanilide (2',6'-dihydroxyacetanilide has also been known as 2,6-dihydroxyacetanilide and 2',6'-dihydroxy-2,5-dimethylbenzanilide has also been known as 2,6-dihydroxy-2',5'-dimethylbenzanilide).
Resorcinol dye-forming couplers as described can be prepared by procedures known in the chemical art. For example, resorcinol couplers as described can be prepared from amino resorcinols or dihydroxybenzoic acids.
The dye-forming coupler can be used in a range of concentrations in the descrlbed recording layer.
Typically, the recording layer contains a concentration of dye-forming coupler that is within the range of about 0.1 to about 1.0 mole of the dye-forming coupler per mole of total silver in the recording layer. An especially useful concentration of dye-forming coupler is within the .

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range of about 0.25 to about 0.75 mole of dye-forming coupler per mole of total silver in the recording layer.
Selection of an optimum concentration of dye-forming coupler will depend upon such factors as the particular coupler, the desired image; processing conditions, other components in the recording layer and the like.
Many organic silver salt oxidizing agents may be used in the described image-forming combination in the recording layer. The organic silver salt oxidizing agent is typically resistant to darkening upon illumination which helps reduce undesired deterioration of the developed image. One class of useful silver salt oxidlzing agents is represented by the silver salts of long-chain fatty acids which are stable to light. The term "long-chain"
as used herein is intended to mean a chain of carbon atoms containing 10 to 30 carbon atoms. Compounds within this class which are useful include silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxy-stearate, silver caprate, silver myristate and silverpalmitate.
Another useful class of organic silver salt oxidizing agents include silver salts of certain heterocyclic thione compounds. Useful silver salts of heterocyclic thione compounds include, for example, those represented by the formula:
-R-~
~N - C=S
(Z'~COOH
wherein Z' is alkylene containing 1 to 10 carbon atoms, such as methylene, ethylene and propylene; R represents the atoms necessary to complete a heterocyclic nucleus selected from carbon, oxygen, sulfur and nitrogen atoms, such as a thiazoline or imidazoline nucleus. Useful silver salts of the described thione compounds include, for example, the silver salts of the following compounds:

;

iiS~9~61

3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione;
3-(2-carboxyethyl~benzothiazoline-2-thione;
3-(2-carboxyethyl)-5-phenyl-1,3,4-oxadiazoline-2-thione;
3-(2-carboxyethyl)-5-phenyl-1,3,4-thiadiazoline-2-thione;
3-carboxymethyl-4-methyl-4-thiazoline-2-thione;
3-(2-carboxyethyl~ phenyl-1,3,4-triazoline-2-thione;
1,3-bis~2-carboxyethyl~imidazoline-2-thione;
1,3-bis(2-carboxyethyl~benzimidazoline-2-thione;
3-~2-carboxyethyl)-1-methylimidazoline-2-thione;
3-~2-carboxyethyl~benzoxazoline-2-thione; and 3-(1-carboxyethyl~-4-methyl-4-thiazoline-2-thione.
Another useful class of organic silver salt oxidizing agents is represented by the complexes of silver with nitrogen acids, such as nitrogen acids selected from the group consisting of imidazole, pyrazole, urazole, 1,2,4-triazole and lH-tetrazole nitrogen acids or combinations of these acids. These silver salts of nitrogen acids are described in, for example, Research Disclosure, Volume 150, October 1976, Item 15026. Examples of useful silver salts of nitrogen acids are the silver salts of the following compounds: lH-tetrazole; 5-dodecyltetrazole; 5-n-butyl-lH-tetrazole; 1,2,4-triazole; urazole; pyrazole; imidazole and benzimidazole.
Another useful class of silver salt oxidizing agent is represented by the silver salts of 1,2,4-mercapto-triazole derivatives represented by the formula:

N NH
3 (I~
Z N S (CH2 )mY

wherein Y is aryl containing 6 to 12 carbon atoms, such as phenyl, naphthyl and para-chlorophenyl; m is O to 2; and .
.

Z is hydrogen, hydroxyl or amine (-NH2~. Especially useful organic silver salt oxidizing agents within this class are those silver salts of the described 1,2,4-mercaptotriazole derivatives wherein Y is phenyl, naphthyl or para-chloro-5 phenyl and Z is amine (-NH2) in the above formula (I').
An example of such a compound is the silver salt of 3-amino-5-benzylthio-1,2,4-triazole (referred to herein as ABT). Such organic silver salt oxidizing agents are described in, for instance, U.S. Patent 4,123,274 and U.S. Patent 10 4,128,557.
Combinations of silver salt oxidizing agents can also be useful. An example of a combination of silver salt oxidizing agents is the combination of the silver salts of ABT with the silver salt of l-methyl-4-imidazoline-15 2-thione.
Selection of an optimum silver salt oxidizing agent or combination of silver salt oxidizing agents will depend upon the described factors, such as the desired image, the particular reducing agent, the particular dye-forming 20 coupler, processing conditions, the particular binder and the like. An especially useful silver salt oxidizing agent is the silver salt of ABT, as described.
The silver salt oxidizing agent or combination of silver salt oxidizing agents can be useful in a range of 25 concentrations in the described recording layer. Selection of an optimum concentration of silver salt oxidizing agent or combination of silver salt oxidizing agents will depend upon the described factors, such as the desired image, the particular reducing agent, the particular dye-~orming 30 coupler, processing condltions and the llke. A typically useful concentration of silver salt oxidizing agent or combination of silver salt oxidizing agents is within the range of about 0.1 mole to about 2.0 moles of silver salt oxidizing agent per mole of reducing agent in the recording 35 layer. For example, when the silver salt oxidizing agent is the silver salt of ABT, a typically useful concentration of the silver salt oxidizing agent is within the range of about 0.1 to about 2.0 moles of silver salt oxidizing agent per mole of reducing agent in the recording layer.

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Preparation of the described organic silver salt oxidizing agent is typically not carried out in situ~ that is not in combination with other components of the recording layer as described. Rather, the preparation of the oxidiæing agent is typically carried out ex situ, that is separate from other components of the recording layer.
In most instances, the preparation of the silver salt oxidizing agent will be separate from the other components based on the ease of control of preparation and storage capability.
The term "salt" as used herein, such as in organic silver salt, is intended to include any type of bonding or complexing mechanism which enables the resulting material to produce desired imaging properties in the described recording layer. In some instances the exact bonding of the described silver salt with the organic compound is not fully understood. Accordingly, the term "salt" is intended to include what are known in the chemical art as "complexes".
The term "salt" is intended to include, for example, neutral complexes and non-neutral complexes. The term is also intended to include compounds which contain any form of bonding which enables the desired image-forming combination to provide the desired image.
Many reducing agents which, in their oxidized form, form a dye with the described dye-forming coupler may be used in the recording element according to the invention. The reducing agent is typically an organic silver halide color developing agent. Combinations of reducing agents can be useful. It is important that the reducing agent produces an oxidized form upon reaction with the organic silver salt oxidizing agent which can react at processing temperature with the described dye-forming coupler to produce a desired dye. Especially useful reducing agents are primary aromatic amines including, for example~ para-phenylenediamines. Examples of useful reducing agents whichare primary aromatic amines include 4-amino-N,N-dimethylaniline;

~51~

4-amino-N,N-diethylaniline; 4-amino-3-methyl-N,N-diethylaniline (also krown as N,N-diethyl-3-methyl-paraphenylenediamine~;
4-amino-N-ethyl-N-~-hydroxyethylaniline; 4-amino-3-methyl-N-ethyl-N-~-hydroxyethylaniline; 4-amino-3-methoxy-N-ethyl-N-~-hydroxyethylaniline; 4-amino-N-butyl-N-gamma-sulfobutyl-aniline; 4-amino-3-methyl-N-ethyl-N-~-sulfoethylaniline; 4-amino-3~ methanesulfonamido~ethyl-N,N-diethylaniline; 4-amino-3-methyl-N-ethyl-N-~-~methanesulfonamido)ethylaniline;
4-amino-3-methyl-N-ethyl-N-~-methoxyethylaniline and the like.
The term "reducing agent" as used herein is intended to include compounds which are reducing agent precursors in the described recording layer. That is, those compounds are intended to be included which are not reducing agents in the recording layer until a condition occurs such as heating of the recording layer.
An especially useful reducing agent is one that consists essentially of a paraphenylenediamine silver halide developing agent that exhibits an E 1/2 value in aqueous solution at pH 10 within the range of -25 to +175 millivolts versus SCE. The term "E 1/2 value" herein means half wave potential. The term "SCE" herein means saturated calomel electrode. These values are determined by analytical procedures known in the photographic art and described in, for example, the text "The Theory of the Photographic Process", 4th Edition, Mees and James, 1977, pages 318-319.
The described reducing agent can be useful in a range of concentrations in the described element according to the invention. Selection of an optimum concentration of reducing agent or combination of reducing agents will 3 depend upon the described factors including the desired image, the particular silver salt oxidizing agent, the particular dye-forming coupler, processing conditions and the like. A typically useful concentration of reducing agent or combination of reducing agents is within the range of about 0.1 to about 5.0 moles of reducing agent per mole of organic silver salt in the recording layer as ~LS14t~J

described. An especially useful concentratlon Or reduclng agent is wi*hln the range or about 0.2 to about 2 moles Or reduclng agent per mole Or organlc silver salt ln the recordlng layer.
The tone Or the combined sllver lmage and dye ~mage produced accordlng to the inventlon wlll vary dependlng upon such factors as the sllver morphology Or the developed silver image, the coverlng power Or the sllver materlals, the particular dye-formlng coupler, the partlcular developlng lO agent, processlng condltlons and the llke. In recordlng layers that produce a brown sllver lmage, the hue Or the dye lmage produced is preferably compllmentary to the hue Or the silver image. An lmage hue of the comblned dye image and sllver lmage ls preferably "neutral".
The term "neutral" as employed hereln ls lntended to include hues whlch occaslonally are descrlbed ln the photographic art as blue-black, grayj purple-black, black and the llke. Whether or not a glven lmage ls "neutral" can be readily determlned by vlsual lnspectlon wlth the unalded 20 eye.
Procedures for determlning whether or not an image is "neutral" are known ln the photographlc art, such as described ln Research Dlsclosure, September 1978, Item 17326.
Silica can be userul in an lmage recording layer Or a recording element according to the lnventlon. Slllca ln the recording layer can help produce lncreased denslty ln a developed lmage upon lmagewlse exposure and heatlng the recordlng layer. A varlety Or rOrms Or slllca can 30 be useful. However, colloldal slllca can be especlally userul because lt has a large surrace area. The optlmum concentratlon Or slllca ln the recordlng layer wlll depend upon such factors as the deslred lmage, other components ln the recordlng layer, processlng condltlons, layer 1~51 3L~;1 thickness and the like. Typically, the concentration of silica is within the range of about 1 to about 1,000 milligrams per 500 square centimeters of support. The silica can be a disadvantage in some cases, such as in

5 preparation of a high resolution transparency, because the silica may reduce resolution of the developed image and cause undesired light scattering.
The average particle size and particle size range of silica in the recording layer can vary. The 10 optimum average particle size and particle size range of silica will depend upon the described factors regarding silica concentration. Typically, the average particle size and particle size range of colloidal silica are most useful.
Colloidal silica that is useful includes such commercially 15 available colloidal silica products as "Cab-0-Sil", a trademark of and available from the Cabot Corporation, U.S.A. and "Aerosil", a trademark of and available from DEGUSSA, West Germany. It is important that the average particle size and particle size range of the silica or 20 any other equivalent particles not adversely affect the desired properties of the electrically activated recording element of the invention or the desired image produced upon imagewise exposure and heating of the recording layer.
For instance, the silica selected should not decrease 25 sensitivity of the recording layer or produce undesired fogging of the developed image.
The mechanism and properties which cause colloidal silica to produce increased density in a recording layer according to the invention is not fully understood. It is 30 believed that the large surface area of colloidal sillca contributes to the desired results. In any case, an especially useful embodiment of the invention, as described, is one containing colloidal silica in the recording layer of a charge-sensitive recording paper according to the 35 invention.

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The described element according to the invention can comprise a variety of colloids and polymers alone or in combination as vehicles and binding agents. These vehicles and binding agents can be in various layers of the 5 element, especially in the recording layer. Suitable materials can be hydrophobic or hydrophilic. It is necessary, however, that the vehicle or binder in the element not adversely affect the charge sensitivity or ohmic resistivity of the element of the invention. Accordingly, the selection 10 of an optimum colloid or polymer, or combination of colloids or polymers, will depend upon such factors as the desired charge sensitivity, desired ohmic resistivity, particular polymer, desired image, particular processing conditions and the like. Useful colloids and polymers can be transparent 15 or translucent and include both naturally occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides, such as dextran, gum arabic and the like. Synthetic polymers, however, are preferred due to their desired charge 20 sensitivity properties and ohmic resistivity properties.
Useful polymeric materials for this purpose include polyvinyl compounds, such as poly~vinyl pyrrolidone), acrylamide polymers and dispersed vinyl compounds such as in latex form. Effective polymers include water insoluble polymers 25 of alkylacrylates and methacrylates, acrylic acid, sulfo-alkylacrylates, methacrylates and those which have crosslinking sites which facilitate hardening or curing.
Especially useful polymers are high molecular weight materials and resins which are compatible with the described 3 components of the element according to the invention. These include, for example, poly(vinyl butyral), cellulose acetate butyrate, poly(methyl methacrylate), poly(vinyl pyrrolidone), ethyl cellulose, polystyrene, poly(vinyl chloride), poly(isobutylene), butadiene-styrene copolymers, vinyl 35 chloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and maleic acid and poly(vinyl , ~5~46~
-, ;1'' alcohol~. Combinations of colloids and polymers can also be useful depending upon the described factors. Highly preferred binders include polyacrylamide, as well as copolymers of acrylamide and other vinyl addition monomers such as copolymers of acrylamide and vinyl imidazole or copolymers of acrylamide and N-methyl acrylamide.
An overcoat layer can be useful on the recording layer according to the invention. It is important that the overcoat layer not adversely affect the desired charge sensitivity and ohmic resistivity properties of the element according to the invention. Such an overcoat layer can reduce fingerprinting and abrasion marks before and after exposure and processing. The overcoat layer can be one or more of the described polymers which are useful as binders.
These materials must be compatible with other components of the described element according to the invention and must be able to tolerate the processing temperatures which are useful for developing the described images.
While it is in most cases unnecessary and undesirable, a photosensitive component can be present in the electrically activated recording layer, as described, if desired. The photosensitive component can be any photo-sensitive metal salt or complex which produces developable nuclei upon charge exposure according to the invention. If a photosensitive component is present in the recording layer, an especially useful photosensitive metal salt is photo-sensitive silver halide due to its desired properties in forming developable nuclei upon charge exposure. A typical concentration of photosensitive metal salt is within the range of about 0.0001 to about 10.0 moles of photosensitive metal salt per mole of organic silver salt in the described element according to the invention. For example, a typical concentration range of photosensitive silver halide is within the range of about 0.001 to about 2.0 moles of silver halide per mole of organic silver salt in the recording element. A preferred photosensitive silver halide '' '' ~ ' ~

: 1~514~1 is silver chloride, silver bromide, silver bromoiodide or mixtures thereof. For purposes of the invention, silver iodide is also considered to be a photosensitive silver halide. Very fine grain photographic silver halide can be 5 useful, although a range of grain size from fine grain to coarse grain photographic silver halide can be included in the recording layer if desired. The photographic silver halide can be prepared by any of the procedures known in the photographic art. Such procedures and forms of photographic silver halide are described in, for example, the Product Licensing Index, Volume 92, December 1971, Publication 9232.
The photographic silver halide can be washed or unwashed, can be chemically sensitized by means of chemical sensitiza-tion procedures known in the art, can be protected against 15 the production of fog and stabilized against loss of sensitivity during keeping as described in the above Product Licensing Index publication.
If a photosensitive component is present in the described electrically activated recording layer, the 20 described image-forming combination enables the concentration of the photosensitive component to be lower than normally would be expected in a photosensitive element. This lower concentration is enabled by the amplification affect of the image-forming combination, as described, as well as the 25 formation of developable nuclei according to the invention in addition to the dye enhancement of the silver image formed. In some instances the concentration of photosensitive metal salt can be sufficiently low that after imagewise exposure and development of the photosensitive metal salt 30 alone, in the absence of other of the described component, the developed image is not visible to the unaided eye.
The elements according to the invention can contain addenda which aid in producing a desired image. These addenda can include, for example, development modifiers that function :

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as speed-increasing compounds, hardeners, plasticizers and lubricants, coating aids, brighteners, spectral sensitizing dyes, absorbing and filter dyes. These addenda are described in, for example, the Product Licensing Index, Volume 92, December 1971, Publication 9232, and Research Disclosure, December 1978, Item 17643.
While it is in many cases unnecessary and undesirable, a post-processing stabilizer or stabilizer precursor to increase post-processing stability of the developed image can be included in the described recording layer. In many cases the recording layer following processing is sufficiently stable to avoid the need for incorporation of a stabilizer or stabilizer precursor in the recording layer. However, in the case of recording materials which contain photosensitive silver halide, it can be desirable to include such a stabilizer or post-processing stabilizer precursor to provide increased post-processing stability. A variety of stabilizer or stabilizer precursors can be useful in the elements according to the invention.
These stabilizers or stabilizer precursors can be useful alone or in combination if desired. Typically useful stabilizers or stabilizer precursors include, for instance, photolytically active polybrominated organic compounds.
Thioethers or blocked azolinethione stabilizer precursors or other organic thione stabilizer precursors known to be useful in photothermographic materials can be useful if desired.
When a stabilizer or stabilizer precursor is present in the recording layer of an element accordlng to the invention, a range of concentrations of stabillzer or stabilizer precursor can be useful. The optimum concen-tration of stabilizer or stabilizer precursor will depend upon such factors as the particular element, processing conditions, particular stabilizer or stabilizer precursor, desired stability of the developed image and the like.

A typically useful concentration of stabilizer or stabilizer precursor is within the range of about 1 to about 10 moles of stabilizer or stabilizer precursor per mole of photo-sensitive component in the element according to the invention.
It is often advantageous to include a heat sensitive base-release agent or base precursor in the recording element according to the invention to produce improved and more effective image development. A base-release agent or base precursor herein is intended to include compounds which upon heating in the recording layer produce a more effective reaction between the described components of the image-forming combination and in addition produce improved reaction between the oxidized form of the described reducing agent and the dye-forming coupler. Examples of useful heat sensitive base-release agents or base precursors are aminimide base-release agents, such as described in Research Disclosure, ~olume 157, May 1977, Items 15733, 15732, 15776 and 15734; guanidinium compounds, such as guanidinium trichloroacetate; and other compounds which are known in the photothermographic art to release a base moiety upon heating, but do not adversely affect the desired properties of the recording element. Combinations of heat sensitive base-release agents can be useful if desired.
A heat sensitive base-release agent or base precursor, or combinations of such compounds, can be useful in a range of concentrations in the described elements according to the invention. The optimum concentration of heat sensitive base-release agent or base precursor will 3 depend upon such factors as the desired lmage, particular dye-forming coupler, particular reducing agent, other components of the imaging element, processing conditions and the like. A useful concentration of described base-release -agent is typically within the range of about 0.25 to 2.5 '` ' , ': ~ ~, ,~ . ~. - .. ,.:
.
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moles of base-release agent or base precursor per mole of reducing agent in the recording layer according to the invention.
The charge-sensitive element according to the invention can comprise a variety of supports. The term "electrically conductive support" is intended herein to include (a) supports that are electrically conductive without the need for separate addenda in the support or on the support to produce the desired degree of electrical conductivity and (b) supports that comprise addenda or separate electrically conductive layers that enable the desired degree of electrical conductivity. Typical supports include cellulose ester, polytvinyl acetal), poly(ethylene terephthalate), polycarbonate and polyester film supports and related films and resinous materials. Other supports are useful, such as glass, paper, metal and the like which can withstand the processing temperatures described and do not adversely affect the charge-sensitive properties and ohmic resistivity which is desired. Typically, a flexible support is most useful.
The recording element according to the invention can include an electrically conductive layer positioned between the support and the described electrically conductive subbing layer. This is illustrated by subbing layer 55 in Figure 5 for example. The electrically conductive layers, as described, such as layers 62 and 55 in Figure 5, can comprise a variety of electrically conducting compounds which do not adversely effect the charge sensitivity and ohmic resistivity properties of an element according to the invention. Examples of useful electrically conductive layers include layers comprising electrically conductive chromium compositions and nickel.
An especially useful embodiment of the invention is an electrically activated recording element, as described, , .
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wherein the electrlcally conductlve support has an electrlcally conductlve subblng layer between the electrlcally conductlve support and the electrlcally actlvated recording layer. The electrlcally conductive subbing layer can comprlse a sultable electrlcally conductive polymer. ExampleS Or suitable subbing layers lnclude poly(alkyl acrylate-co-vlnylldene chlorlde-co-ltaconlc acld) layers. Sultable polymers for the subbing layer are descrlbed in, for example, U.S. Patent 3,271,345.
In some embodlments the photoconductlve layer can be a self-supportlng layer, such as a photoconductor ln a sultable blnder. In such embodlments an electrlcally conductlve layer, such as an electrlcally conductlve nlckel or chromium composition layer, can be coated on the photo-conductive layer. This is lllustrated ln, ror instance, Flgure 3 ln the drawings ln which electrlcally conductlve layer 2B ls on photoconductlve layer 30 whlch ls selr supportlng. Alternatlvely, the photoconductlve layer can be coated on an electrlcally conductlve support, such as lllustrated ln Figure 5 of the drawlngs.
The descrlbed layers accordlng to the lnvention can be coated by coatlng procedures known ln the photo-graphic art lncludlng dlp coatlng, alrknlfe coatlng, curtaln coatlng or extruslon coatlng uslng hoppers known ln the photographic art. I~ deslred, two or more layers can be coated slmultaneously.
The various components of the charge-sensitlve materlals accordlng to the inventlon can be prepared ror coatlng by mlxlng the components wlth sultable solutlons or mlxtures lncludlng sultable organlc solvents dependlng on the partlcular charge-sensltlve materlal and the components. The components can be added by means of procedures known ln the photographlc art.

~ ~ t ~i Useful charge-sensitive elements according to the invention can comprise an electrically conductive support having thereon an electrically activated recording layer which has a thickness within the range of about l to about 30 microns, typically within the range of about 2 to about 15 microns. The optimum layer thickness of each of the layers of an element according to the invention will depend upon such factors as the particular ohmic resistivity desired, charge sensitivity, particular components of the layers, desired image and the like.
A "melt-forming compound" can be useful in the recording layer according to the invention to produce an improved developed image. A "melt-forming compound" can be especially useful with recording materials containing silver salts of nitrogen acids. The term "melt-forming compound" herein is intended to mean a compound which upon heating to the described processing temperature produces an improved reaction medium, typically a molten medium, wherein the described image-forming combination can produce a desired image upon development. The exact nature of the reaction medium at processing temperature described is not fully understood. It is believed that at the reaction temperature, as described, a melt occurs which permits the reaction components to better interact. If desired, a melt-forming compound can be included with other components of the recording layer prior to coating on the described support. Examples of useful melt-forming compounds include succinimide, dimethyl urea, sulfamide and acetamide.
The optimum concentration of the described components of the element according to the invention will depend upon a variety of factors as described. An especially useful recording element according to the invention comprises about l to about 5 moles of the described dye-forming coupler for each l to 5 moles o~ the described reducing agent and ` ~1514~1 ~

about 3 to about 20 moles of the described organic silver salt oxidizing agent.
The described organic silver salt oxidizing agent can contain a range of ratios of the organic moiety to the silver ion. The optimum ratio of the organic moiety to silver ion in the organic silver salt oxidizing agent will depend upon such factors as the particular organic moiety, the particular concentration of silver ion desired, processing conditions, the particular dye-forming coupler and the like. The molar ratio of organic moiety to silver as silver ion in the salt is typically within the range of about 0.5:1 to about 3:1.
The image recording layer of the invention can have a range of pAg. The pAg can be measured using conventional calomel and silver-silver chloride electrodes, connected to a commercial digital pH meter. Typically, the pAg in a dispersion containing the described components for the recording layer is within the range of about 2.5 to about 7.5. The optimum pAg will depend upon the described factors~ such as the desired image, processing conditions and the like.
A recording material containing the described organic silver salt oxidizing agent typically has a pH
that is within the range of about 1.5 to about 7Ø An especially useful pH for the described recording layer is within the range of about 2.0 to about 6.o.
The desired resistivity characteristics of a recording material according to the invention can be obtained by separately measuring the current-voltage characteristic of each sample coating at room temperature by means of a mercury contact sample holder to make a mercury contact to the surface of the coating. To eliminate the possibility that a micro thickness surface air gap might affect the measured resistivity, exposures can be made with evaporated metal (typically gold or aluminum~

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1~1461 electrode on the surface of a charge sensitive and photoconductor coating to be tested. The resistivity can be measured at various ambient temperatures. The data can be measured at a voltage of, for example, 20 volts 5 or 4 x 10 volts per centimeter, which is within the ohmic response range of the layer to be tested. It can be expected that the resistivity of the charge-sensitive layer will vary widely with temperature. It can also be expected that the dielectric strength of the layer will vary with 10 temperature. The selection of an optimum temperature for exposure can be determined based on the dielectric strength of the layer.
An especially useful embodiment of the invention having the desired characteristics comprises a charge-sensitive recording element, preferably having an ohmicresistivity of at least about 104 ohm-cm, comprising, in sequence: (a~ a first electrical conducting layer, (b) a photoconductive layer, (c~ an electrically activated recording layer separated from (b~ by an air gap of up to about 10 20 microns and comprising, in reactive association: (A) a dye-forming coupler consisting essentially of 2',6'-dihydroxy-trifluoroacetanilide, (B) an image-forming combination consisting essentially of (i) an organic silver salt oxidizing agent consisting essentially of a silver salt of 25 3-amino-5-benzylthio-1,2,4-triazole, with (ii~ a reducing agent consisting essentially of 4-amino-2-methoxy-N,N,5-trimethylaniline sulfate, and (C) a polyacrylamide binder, (d) an electrically conductive subbing layer comprising a poly(alkyl acrylate-co-vinylidene chloride~ on (e) a 3 second electrical conducting layer, on (f~ a support.
A variety of energy sources can be useful for imagewise exposure of a recording element accordlng to the invention. Selection of an optimum energy source for imagewise exposure will depend upon the described factors, 35 such as the sensitivity of the photoconductor layer, the particular image recording combination in the electrically activated recording layer, desired image and the llke.

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-2~-Useful energy sources for imagewise exposure include, for example, visible light, X-rays, lasers, electron beams, ultraviolet radiation, infrared radiation and gamma rays.
A variety of processing steps and means can be useful for producing a dye image and silver image in the described recording layer after imagewise exposure. In one embodiment of the invention a dry electrically activated recording process for producing a dye image and silver image, preferably a dye enhanced silver image, in a charge-sensitive recording element, preferably having an ohmic resistivity of at least about 104 ohm-cm, containing at least one electrically activated recording image-forming combination consisting essentially of ~A~ a dye-forming coupler, and (B) an image-forming combination as described, which process can comprise the steps: ~I) applying an electric potential imagewise to the recording element of a magnitude and for a sufficient time to produce in the image areas a charge density within the range of about 10 3 coulomb/cm2 to about 10 9 coulomb/cm , the charge density forming a developable latent image in the image-forming combination;
and then (II) heating the recording element substantially uniformly at a temperature and for a time sufficient to produce a dye image and silver image, preferably a dye enhanced silver image.
An especially useful process embodiment of the invention is a dry electrically activated recording process for producing a dye enhanced silver image in a charge-sensitive recording element, preferably having an ohmic resistivity of at least about 104 ohm-cm, comprising, in sequence, a 3 support having thereon (a~ a first electrically conductive layer, (b~ an organic photoconductive layer, (c~ an electrically activated recording layer separated from ~b~
by an air gap of up to 20 microns and comprising ~A~ a dye-forming coupler consisting essentially of a compound selected from the group consisting of 2,6-dihydroxy-acetanilide and 2',6'-dihydroxytrifluoroacetanilide and ~5 combinations thereof, (B? an image-forming combination comprising (i) an organic silver salt oxidizing agent consisting essentially of a silver salt of 3-amino-5-benzyl-thio-1,2,4-triazole, with tii~ a reducing agent consisting essentially of 4-amino-2-methoxy-N,N,5-trimethylanilinesulfate, and (iii) a polyacrylamide binder, (d~ an electrically conductive polymer subbing layer and te) a second electrically conductive layer; said process comprising the steps: (I) imagewise altering the conductivity of the photoconductor layer in accord with an image (X') to be recorded while simultaneously (II~ applying across the photoconductor layer and recording layer an electrical potential of a magnitude and for a sufficient time to produce a developable latent image in the recording layer corresponding to the image ~X'); and then (III~ heating the recording layer substantially uniformly at a temperature and for a time sufficient to produce a dye enhanced silver image corresponding to image (X') in the recording layer.
An imagewise current flow is produced through the described electrically activated recording layer. Although a particular technique to produce an imagewise current flow has been described for use in a variety of recording apparatus, the especially useful techniques are those which include use of a photoconductive layer as an image to current converter. The imagewise current flow can be provided, however, by contacting the recording element with a suitable electrostatically charged means such as an electrostatically charged stencil or scanning the recording element with a beam of electrons.
Heating the recording element after latent image formation can be carrled out by technlques and by means known in the photothermographic art. For example, the heating can be carried out by passing the imagewise exposed recording element over a heated platen or through heated rolls, by heating the element by means of microwaves, by means of dielectric heating or by means of heated air and the like. A visible image can be produced in the described exposed material within a short time, that is within about l to about 90 seconds, by the described uniform heating step. An image having a maximum transmission density of at least 1.8 and typically at least 2.2 can be produced according to the invention. For example, the recording element can be uniformly heated to a temperature within the range of about 100C to about 200C until a desired image is developed, typically within about l to about gO seconds.
The imagewise exposed material according to the invention is preferably heated to a temperature within the range of about 120C to about 180C. The optimum temperature and time for processing will depend upon such factors as the desired image, the particular recording element, heating means and the like.
The described electrically activated recording process can be useful for producing multiple copies.
According to this embodiment of the invention, multiple copies can be prepared by a dry electrically activated recording process for producing a dye image and silver image, preferably a dye enhanced silver image, in an electrically activated recording element comprising the steps: (I) imagewise altering the conductivity of a photoconductive layer (Z) in accord with an image that is to be recorded; (II) positioning the imagewise altered photoconductive layer (Z) from (I) adjacent an electrically activated recording layer of the recording element comprising (A) a dye-forming coupler, and (B) an image-3 forming combination comprising ~i~ an organic silver saltoxidizing agent, with ~ii) a reducing agent which, in its oxidized form, forms a dye with the dye-forming coupler, wherein the photoconductive layer ls separated from the recording layer by an air gap of up to 20 microns, (III) , !
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applying an electrical potential across the photoconductor layer and recording layer of a magnltude and for a sufficient time to produce in the areas of the recording layer corresponding to the imagewise altered portions of the photoconductor layer a charge density within the range of about lO 3 coulomb/cm2 to about lQ 9 coulomb/cm2, the charge density forming in the areas a developable latent image;
then (IV~ uniformly heating the recording element at a temperature and for a time sufficient to produce a dye image and silver image, preferably a dye enhanced silver image, in the recording element; followed by (V) positioning the imagewise altered photoconductor layer ad~acent a second electrically activated recording layer, preferably having an ohmic resistivity of at least about 104 ohm-cm, wherein said photoconductor layer is separated from said second recording layer by an air gap of up to 20 microns; (VI) applying an electrical potential across the photoconductor layer and the second recording layer of a magnitude and for a sufficient time to produce in the areas of the image of said photoconductive layer a charge density within the range of about lO 3 coulomb/cm2 to about lO 9 coulomb/cm2, the charge density forming a developable latent image; and then (VII? uniformly heating the second recording layer at a temperature and for a time sufficient to produce a developed image in the second recording layer.
While the exact mechanism of image formation upon heating is not fully understood, it is believed that the imagewise exposure to charge provides nuclei in the image areas. It is believed that the nuclei formed in the image areas increase the reaction rate and act as catalysts for the reaction between the organic silver salt oxidizing agent and the reducing agent. It is believed that the nuclei enable a form of amplification which would not otherwise be possible. -The described organic silver salt oxidizing agent and reducing agent must be in a location with respect ,,, ` .
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llS1461 to each other which enables the nuclei formed to provide thedesired catalytic effect. The described organlc silver salt oxidizing agent and reducing agent as well as the dye-forming coupler are in reactive association in the electrically activated recording layer. The term "in reactive association"
is intended to mean that the nuclei resulting from the imagewise exposure are in a location with respect to the described components which enables desired catalytic activity, desired processing temperature and capability for a more useful dye image and silver image.
Referring to the drawings, embodiments of the invention are depicted schematically in Figures 1 and 2.
According to the embodiment illustrated in Figures 1 and 2, a charge-sensitive recording layer 10 is placed upon a grounded electrically conductive backing or support 12.
A current is selectively applied to the recording layer 10 by the point of a metal stylus 14 which is raised to a sufficiently high voltage relative to the support 12 by a voltage source 16, and brought into moving contact with the exposed surface of the recording layer 10 containing the described image-forming combination and dye-forming coupler.
Upon contacting the recording layer 10 with the stylus 14, a current flow is produced in the areas of the recording layer contacted by the stylus and a developable latent image forms, i.e. a pattern of nuclei sites, in the pattern desired. The charge density produced by the stylus in the contacted areas of the recording layer need not be sufficient to produce a visible image in the recording layer 10, however, the charge density must be sufficient to produce a latent image in the recording layer in those areas contacted by the stylus. Although a particular technlque to produce an imagewise current flow through the recording layer 10 has been described, techniques for producing imagewise current flow generally known in the art of recording can be useful and are intended to be encompassed .. A~
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5~4~1 by the description. The area of the recording layer 10 designated as 18 is intended to be illustrative of an area of nuclei sites formed upon contact of the stylus 14 with the recording layer 10. Other techniques for producing a nuclei pattern include, for example, contacting the recording layer 10 with an electrostatically charged stencil or scanning the layer 10 with a beam of electrons in an image pattern.
Figure 2 illustrates development of the latent image formed in the recording element in Figure 1 by, for example, moving the element from Figure 1 into contact with a heated metal platen 24. The heat from platen 24 passes through the support 22 to the layer 20 containing the latent image to cause the desired reaction in the latent image area.
The reaction in the latent image area causes development to produce a visible image 26 consisting essentially of a dye image and silver image, preferably a dye enhanced silver image, in the recording layer 20. Upon development the recording element is~removed from the platen 24. No processing solutions or baths are required in this heat development step.
Another illustrative embodiment of the invention is schematically shown in Figures 3 and 4. In this embodiment, in Figure 3, the developable sites 40 and 42, that is the latent image sites, are formed by sandwiching a charge-sensitive recording layer 32 and an image-to-current converter layer 30, preferably a photoconductive layer, between a pair of electrically conductive layers 28 and 34.
Layers 28 and 34 can comprise suitable supports for layers 30 and 32 or layers 28 and 34 can be on separate suitable supports, not shown, such as film supports. A high potential electric field is established across the photoconductive layer 30 and recording layer 32 by connecting the conductive layers 28 and-34 by connecting means 35 containing power 1~15~
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source 36. The electric field across the layers is con-trolled by switch 38. The latent image formation at latent image sites 40 and 42 is caused by imagewise exposing the photoconductive layer 30 through the conductor 28 to exposure means 44, typically actinic radiation, preferably X-ray.
The layer 28 and any support for layer 28 must be ~ufficiently transparent to the energy 44 to enable the energy to pass to a desired degree to photoconductive layer 30. The exposure selectively increases the conductivity Or the conductive layer in those regions exposed to actinic radiation. When switch 38 is closed thereby establishing an electric field across the layers, an imagewise current flow is produced through the recording layer 32. The current flow occurs in those regions of the recording layer 32 only in position with the exposed portions of the photoconductive layer 30. An air gap 46 of up to 20 microns is provided between layers 30 and 32. The air gap 46 can be, for example, 1 to 10 microns. After a sufficient charge density, typically less than 1 millicoulomb per square centimeter, preferably about 1.0 microcoulomb/cm2, has been produced in the current exposed portions of the recording layer 32, switch 38 is opened, thereby disrupting the current flow.
The described technique for application of voltage across the photoconductive and recording layers is illustrative. A variety of techniques known in the recording art can be useful and are intended to be included in this description. For example, a grid control corona discharge means, not shown, can be substituted for the voltage source and conducting layer 28.
To develop the dye image and silver image in latent image sites 40 and 42, the recording element containing layers 32 and 34 is moved away from the photoconductive layer. Connecting means 35 is also disconnected. The recording element illustrated in Figure 4 is then contacted with a heated platen 52 illustrated in Figure 4. The heat , : ' liS1~6~

from the platen 52 passes through the support 50 to the layer 48 containing a latent image to produce a visible dye image and silver image 54. The heating is preferably carried out substantially uniformly by merely positioning the recording element in heat transfer relationship with the heated platen 52. After the development of the silver image and the dye image, the recording element is removed from the platen.
An especially useful embodiment of the invention is illustrated in Figure 5 in the drawings. In Figure 5 the charge-sensitive recording arrangement consists of a support 54 having thereon an electrically conductive layer 55, typically consisting of a ~ermet composition, having thereon an electrically conductive subbing layer 56, such as an alkyl acrylate polymer layer. On the subbing layer 56 is coated a recording layer 57 containing the image-forming combination and dye-forming coupler. An air gap 59, typically about 1 micron thick, is present between overcoat layer 58 on recording layer 57 and a lead monoxide photo-conductive layer 60. The layer 60 has a nickel electricallyconductive layer 62 which is on a transparent film support 64. Developable nuclei are formed in recording layer 57 by imagewise exposure with a suitable radiation source, such as a tungsten light source or X-ray source, not shown, through step tablet 66. At the time of imagewise exposure with the energy source, a high potential electric field is established across the photoconductive and image-recording layers by connecting the conductive layer 62 and the electrically conductive layer 55 by connecting means 6~ through a power source 68. The electric field across the layers is controlled by switch 70. After the necessary charge density is established, switch 70 can be opened, thereby disrupting the current flow. Imagewise exposure for about 1 second at about 50 footcandles produces a developable image in recording layer 57. A 0.3 density step wedge can be used for imagewise exposure purposes if desired. To develop the resulting latent image, layer 57 is disconnected from connecting means , ~

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69 and power source 68 and moved away from the photoconductive layer 60. The recording layer 57 can then be heated uniformly by contacting it with a heated metal platen, not shown, until the desired dye image and silver image are produced.
Interlayers can be useful in certain instances in the charge-sensitive recording element as desired, to help avoid undesired transfer of components of the described layers. Useful interlayers are described in, for example, U.S. Patent 3,978,335 of Gibbons.
The photoconductive layer, such as the layer 60 in Figure 5, can include a variety of binders and/or sensitizers known in the electrophotographic art. Useful binders are described in, for example, U.S. Patent 2,361,019 of Gerhart 1~ and U.S. Patent 2,258,423 of Rust. Sensitizing compounds useful in the photoconductive layer are described in, for example, U.S. Patent 3,978,335 of Gibbons.
In the embodiments illustrated which use an air gap between the photoconductor and image recording layers, the air gap distances can be controlled by methods known in the art, such as by the roughness of the surface of the photoconductor layer as well as the roughness of the surface of the image recording layer. The air gap need not be uniform. However, best results are often observed with a uniform air gap. The air gap can be, for example, up to about 2~ microns thick, preferably within the range of about 1 to about 10 microns thick. For example, the distances shown in Figure 3 between photoconductor layers 30 and 32 can be up to 20 microns, such as within the range of about 1 to about 10 microns, as illustrated by air gap 46.
The resistivity of a useful recording layer according to the invention can be effected by such factors as exposure history, the direction of the applied field and, when sandwiched with a photoconductor, by air gap affects and photoconductor affects. The number of variables affecting the resistance of the recording layer coupled with non-ohmic behavior of the layer at higher applied fields, can affect the choice of an optimum recording material and imaging ~A~

means. The reslstlvlty values as descrlbed hereln rOr particular recordlng materlals are thereror values measured under temperature and voltage condltlons whlch produce deslred ohmic behavlor.
If deslred, the recordlng element and lmaglng means accordlng to the lnventlon can be readlly modlrled to provlde a contlnuous lmage recordlng operatlon. This can be carrled out by means Or deslred control clrcultry and contlnuous transport apparatus, not shown.
The ~ollowlng examples are lncluded ror a rurther understanding of the lnventlon.
Example 1 This lllustrates a negatlve-worklng electrlcally activated recordlng element and process accordlng to the lnventlon for produclng a dye lmage and sllver lmage.
The element and layers for thls e~ample are slmllar to those descrlbed ln Flgure 5.
The followlng composltlon was coated on a poly(ethylene terephthalate) fllm support contalnlng a poly(methyl acrylate-co-vlnylldene chlorlde-co-ltaconlc acld) subbing layer on a Cermet conductlng layer:
sllver 3-amino-5-benzylthlo-1,2,4-8.0 ml trlazole (1.5:1 llgand to sllver lon ratlo) (dlspersed ln 1% gelatln) methyl mercaptotrlazole (1~ solutlon 0.3 ml ln ethanol) (antlroggant) 4-phenyl-3-lmino-5-thlourazole (1%0.3 ml solutlon ln ethanol~ (development accelerator~
surfactant (Surractant lOG whlch0.2 ml ls a polyglycldol ether avallable rrom the Olln Corporatlon, U.S.A.) tlO% solutlon ln water~
4-amlno-methoxy-N,N,5-trlmethyl-75 mg ~dlssolved 3~ anlllne sulfate ~reduclng agent~ ln 1 ml Or water~
2'~6'-dlhydroxytri~luoroacet-180 mg tdlssolved anlllde tdye-rormlng coupler)ln 1 ml Or water) ~, . .
'~ ' ~.

, ... . . ~ ... . ..

~i5 The composition after mixing was coated at a 5 mil wet coating thickness to produce a recording layer (57 in Figure 5) containing 90 to 100 milligrams of sllver per 929 cm2 of support.
The layer 60 consisted of a 17 micron thick coating of a composite type organic photoconductor con-sisting essentially of an aggregate organic photoconductor as described in U.S. 3,615,414 as the photoconductive compound. The photoconductor was coated on conducting layer 10 62 consisting of copper iodide on a poly(ethylene terephthalate) film support 64 shown in Figure 5. An air gap of about 1 to about 7 microns separated the photoconductive layer 60 from recording layer 57. ~isible light exposure imagewise was made with simultaneous application of a voltage Or positive 15 4, ooo volts to the resulting so-called sandwich shown in Figure 5. The intensity and duration of light exposure were sufficient to produce a developable latent image in the recording layer 57. A charge exposure of 100 microcoulombs/cm2 was used for forming a latent image in the recording layer The photoconductive layer and the recording layerwere separated after imagewise exposure and the recording layer was uniformly heated for 10 seconds at 160C. This produced a silver image and dye image in the exposed 25 areas of the recording layer. A 1.0 transmission density image was observed in the area exposed to charge.
Example 2 A recording element as described in Example 1 was prepared with the exception that the described accelerator 30 was not included in the recording layer. Visible light exposure imagewise was made with several silver film test obJects by means of the photoconductor described in Example 1 with simultaneous application of 1,800 volts to the described so-called sandwich. A positive polarity 35 was applied to the photoconductor. The 15 seconds exposure to visible light was made by means of a 55 footcandle yellow fluorescent illumination source ~about 500 to 700 nanometers).

1~519Lg~

The resulting exposed recording layer was separated from the photoconductive layer. The recording layer was then uniformly heated for 20 seconds at 180C. This produced a developed silver image and dye image in the exposed areas. The resulting negative image had a maximum transmission density of about 1.0 and a minimum transmission density of about 0.20.
Example 3 A charge recording element was prepared as described in Example 1.
X-ray exposures were made imagewise of several metallic test objects by means of a 90 micron thick coating of a photoconductor containing tetragonal lead oxide photo-conductor and photoconductive layer 60 as shown in Figure 5.
The photoconductive layer was coated on a conducting layer consisting essentially of nickel which was coated on a poly(ethylene terephthalate) film support. The photo-conductive layer served as a current transducer for the X-ray imaging. Exposures were made for 20 seconds using 110 kVp X-rays from a commercially available X-ray energy source. A voltage of 3,200 volts was applied to the so-called sandwich during the imagewise exposure with X-rays.
A positive polarity was applied to the photoconductor.
After imagewise exposure, the recording layer was separated from the photoconductive layer. The exposed recording layer was then heated for 10 seconds uniformly at 180C. A developed silver image and dye image was produced in the recording layer.
The resulting developed negative image had a maximum transmission density of about 1.2 to 1.1 and a minimum transmission density of 0.20. The tone o~ the developed image was neutral ~black).
Example 4 A charge recording element was prepared as described in Example 1 with the exception that the silver salt oxidizIng agent contained no gelatin binder. The sllver salt oxidizing agent consisted of a binderless 1.5:1 - liSl~

ligand to silver ion dispersion of a silver salt of 3-amino-5-benzylthio-1,2,4-triazole. Charge exposures were made by means of a grid controlled corona exposure device, not shown in the drawings, applying a positive 1,000 volt grid potential. The exposure device is described in, for example, U.S. 3,370,212.
The exposed recording layer was subsequentially processed by uniformly heating for 12 seconds at 160C.
A developed dye enhanced silver image was produced. The developed image had a maximum transmission density of 1.9. It was found that such an image could be produced with a charge of about 100 microcoulombs/cm2.
The procedure was repeated with the exception that the charge exposure was 4 microcoulombs/cm2. This produced a developed image having a maximum transmission density of 1.0 and a minimum transmission density of 0.20.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. In an electrically activated recording element comprising an electrically conductive support having thereon, in sequence:
(a) an electrically activated recording layer comprising an organic silver salt and a reducing agent, (b) a photoconductive layer separated from (a) by an air gap of up to 20 microns, and (c) an electrically conductive layer on (b), the improvement comprising, as said recording layer, the following, in reactive association:
(I) (A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with said dye-forming coupler; and (II) an electrically active conductive subbing layer as said electrically conductive support.

2. An electrically activated recording element as in Claim 1 wherein said dye-forming coupler is a resorcinol, dye-forming coupler.

3. An electrically activated recording element as in Claim 1 wherein said dye-forming coupler is a resorcinol, dye-forming coupler represented by the formula:

wherein R is hydroxy, phenyl, alkyl containing 1 to 20 carbon atoms, or haloalkyl.

4. An electrically activated recording element as in Claim 1 wherein said dye-forming coupler is a compound selected from the group consisting of 2',6'-dihydroxyacetanilide and 2',6'-dihydroxytrifluoroacetanilide and combinations thereof.

5. An electrically activated recording element as in Claim 1 wherein said organic silver salt oxidizing agent is a silver salt of a 1,2,4-mercaptotriazole derivative represented by the formula wherein Y is aryl containing 6 to 12 carbon atoms, m is 0 to 2; and Z is hydrogen, hydroxyl, or amine.

6. An electrically activated recording element as in Claim 1 wherein said organic silver salt oxidizing agent consists essentially of a silver salt of 3-amino-5-benzylthio-1,2,4-triazole.

7. An electrically activated recording element as in Claim 1 also comprising an electrically conductive binder in said electrically activated recording layer.

8. An electrically activated recording element as in Claim 1 also comprising an electrically conductive binder consisting essentially of a copolymer of acrylamide and vinyl imidazole.

9. An electrically activated recording element comprising, in sequence:
(a) a first support having thereon (b) a first electrical conducting layer, and (c) a photoconductive layer, having thereover (d) an electrically activated recording layer separated from (c) by an air gap of up to 20 microns, and comprising, in an electrically conductive poly-acrylamide binder, in reactive association:
(A) a dye-forming coupler consisting essentially of 2',6'-dihydroxytrifluoroacetanilide, (B) an oxidation-reduction combination consist-ing essentially of (i) an organic silver salt oxidizing agent consisting essentially of a silver salt of 3-amino-5-benzylthio-1,2,4-triazole, with (ii) a reducing agent consisting essentially of 4-amino-2-methozy-N,N,5-trimethyl-aniline sulfate, (e) an electrically conductive subbing layer comprising a poly(alkyl acrylate-co-vinylidene chloride), and (f) a second electrically conductive layer, on (g) a second support.

10. A dry, electrically activated recording process for producing a dye enhanced silver image in an electrically activated charge-sensitive recording element comprising at least one electrically acti-vated recording, image-forming combination compris-ing, in an electrically conductive binder, in reactive association:
(A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with said dye-forming coupler, said processing comprising the steps:
(I) applying an electric potential imagewise to said recording element of a magnitude and for a sufficient time to produce in the image areas a charge density within the range of about 10-3 coulomb per cm2 to about 10-9 coulomb per cm2, said charge density forming a developable latent image in the image-forming combination; and, (II) heating said recording element substantially uniformly at a temperature within the range of 80° to 200°C and for a time sufficient to develop a dye enhanced silver image.

11. A dry, electrically activated recording process for producing a dye enhanced silver image in an electrically activated charge-sensitive recording element comprising, in sequence:
(a) a first electrically conductive layer, (b) a photoconductive layer, (c) an electrically activated recording layer separated from (b) by an air gap of up to 20 microns and comprising, in an electrically conductive binder, in reactive association:
(A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with said dye-forming coupler, and (d) an electrically active conductive subbing layer on (e) an electrically conductive support;
said process comprising (I) imagewise altering the conductivity of said photoconductive layer in accord with an image to be recorded while simultaneously (II) applying an electrical potential across said photoconductive layer and said recording layer of a magnitude and for a sufficient time to produce in the image areas a charge density within the range of about 10-3 coulomb per cm2 to about 10-9 coulomb per cm2, said charge density forming a developable latent image in said recording layer corresponding to the image to be recorded; and, (III) heating said recording layer substantially uniformly at a temperature within the range of 80° to 200°C and for a time sufficient to produce a dye enhanced silver image in said recording layer.

12. A process as in Claim 11 wherein said recording layer is heated in (III) to a temperature within the range of about 100°C to about 180°C until a dye enhanced silver image is produced in said recording layer.

13. A dry, electrically activated recording process for producing a dye enhanced silver image in a charge-sensitive recording element comprising, in sequence:
(a) a first support having thereon (b) a first electrically conductive layer, and (c) a photoconductive layer, having thereover (d) an electrically activated recording layer separated from (c) by an air gap of about up to 20 microns, and comprising, in an electrically conduc-tive polyacrylamide binder, (A) a dye-forming coupler consisting essentially of a compound selected from the group consisting of 2',6'-dihydroxyacetanilide and 2',6'-dihydroxytri-fluoroacetanilide and combinations thereof, (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent consisting essentially of a silver salt of 3-amino-5-benzylthio-1,2,4-triazole, with (ii) a reducing agent consisting essentially of 4-amino-2-methoxy-N,N,5-trimethyl-aniline sulfate, (e) an electrically active conductive subbing layer, and (f) a second electrically conductive layer on (g) a second support, said process comprising (I) imagewise altering the conductivity of said photoconductive layer in accord with an image to be recorded while simultaneously (II) applying an electrical potential across said photoconductor layer and recording layer of a magni-tude and for a sufficient time to produce in the image areas a charge density within the range of about 10-3 coulomb per cm2 to about 10-9 coulomb per cm2, said charge density forming a developable latent image in said recording layer corresponding to said image to be recorded; and, (III) heating said recording layer substantially uniformly at a temperature within the range of 80° to 200°C and for a time sufficient to produce a dye enhanced silver image in said recording layer.

14. A process as in Claim 13 wherein said recording layer is heated in (III) to a temperature within the range of about 100°C to about 180°C until a dye enhanced silver image is produced in said recording layer.

15. A dry, electrically activated record-ing process for producing a dye enhanced silver image in an electrically activated charge-sensitive record-i ing element comprising an electrically conductive support having thereon, in sequence, an electrically active conductive subbing layer, and, contiguous to said electrically active conductive subbing layer, an electrically activatable recording layer; said process comprising the steps:
(I) imagewise altering the conductivity of a photoconductive layer (Z) in accord with an image that is to be recorded;
(II) positioning the imagewise altered photo-conductive layer (Z) from (I) within 20 microns adjacent an electrically activated recording layer of said recording element comprising, in an electrically conductive binder, in reactive association:
(A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidizing form, forms a dye with said dye-forming coupler;
(III) applying an electrical potential across said photoconductive layer and recording layer of a magnitude and for a sufficient time to produce in the areas of said recording layer corresponding to the imagewise altered portions of said photoconductive layer a charge density within the range of about 10-3 coulomb/cm2 to about 10-9 coulomb/cm2, said charge density forming in said areas a develop-able latent image; and, (IV) uniformly heating the recording element at a temperature within the range of 80° to 200°C and for a time sufficient to produce a dye enhanced silver image in said recording element.

16. A dry, electrically activated recording process as in Claim 15 also comprising the steps:
(V) positioning said imagewise altered photo-conductive layer within 20 microns adjacent a second electrically activated recording layer;

(VI) applying an electrical potential across said photoconductive layer and said second recording layer of a magnitude and for a sufficient time to produce in the areas of said image of said photo-conductive layer a charge density within the range of about 10-3 coulomb/cm2 to about 10-9 coulomb/-cm2, said charge density forming a developable latent image; and, (VII) uniformly heating said second recording layer at a temperature within the range of 80° to 200°C and for a time sufficient to produce a developed image in said second recording layer.

17. A dry, electrically activated recording process for producing a dye enhanced silver image in an electrically activated charge-sensitive recording element comprising an electrically conductive support having thereon, in sequence, an electrically active conductive subbing layer, and, contiguous to said electrically active conductive subbing layer an electrically activatable recording layer comprising, in an electrically conductive binder, in reactive association:
(A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with said dye-forming coupler, said process comprising the steps:
(I) positioning said recording element in face-to-face relationship with a photoconductive element wherein said recording element is separated from said photoconductive element by an air gap of up to 20 microns;
(II) exposing said photoconductive element to an imagewise pattern of actinic radiation while simultaneously applying an electrical potential having a field strength of at least about 1 X 104 volts/cm across said photoconductive element and said recording element for a time sufficient to provide a developable latent image in the areas of said record-ing element corresponding to the exposed areas of said photoconductive element; and (III) substantially uniformly heating the recording element at a temperature within the range of 80° to 200°C and for a time sufficient to produce a dye enhanced silver image in said recording element.

18. A process as in Claim 17 wherein the impedance of said recording element differs from the impedance of said photoconductive element by no more than about 105 ohm-cm when said electrical potential is applied across said photoconductive element and said recording element.

19. A process as in Claim 17 wherein said electrical potential produces a charge flow within the range of about 10-3 coulomb/cm2 to about 10-9 coulomb/cm2 in the areas of said recording element corresponding to the exposed areas of said photoconductive element.

20. A process as in Claim 17 wherein said recording element in (III) is substantially uniformly heated to a temperature within the range of about 100°C to about 180°C until a dye enhanced silver image is produced.

21. A process as in Claim 17 wherein said photoconductive element is X-ray sensitive and the conductivity of said element is imagewise altered by exposing said photoconductive element to X-ray radiation in accord with an image to be recorded.

22. A process as in Claim 17 wherein said dye-forming coupler is a compound selected from the group consisting of 2,6'-dihydroxyacetanilide and 2',6'-dihydroxytrifluoroacetanilide and combinations thereof; said organic silver salt oxidizing agent consists essentially of a silver salt of 3-amino-5-benzylthio-1,2,4-triazole; and said reducing agent consists essentially of 4-amino-2-methoxy-N,N,5-tri-methylaniline sulfate.

23. A dry, electrically activated record-ing process for producing a dye enhanced silver image in an electrically activated recording element comprising an electrically active conductive layer, and contiguous to said electrically active conduc-tive layer, an electrically activatable recording layer comprising, in an electrically conductive binder, in reactive association:
(A) a dye-forming coupler, and (B) an oxidation-reduction combination comprising (i) an organic silver salt oxidizing agent, with (ii) a reducing agent which, in its oxidized form, forms a dye with said dye-forming coupler;
said process comprising the steps:
(I) positioning said recording element on an electrically conductive backing member;
(II) modulating a corona ion current flow to the recording element by an electrostatic field estab-lished imagewise between an image grid comprising an electroconductive core sequentially connectable to sources of different potential relative to said backing member and covered with a coating of a photoconductive insulating material and a control grid that is electrically conductive and sequentially connectable to sources of different potential rela-tive to said backing member, said current flow being of a magnitude sufficient to produce a charge density within the range of about 10-3 to about 10-9 coulomb/cm2 imagewise in said recording element, which charge density forms a developable latent image in said electreically activated recording material;
and (III) substantially uniformly heating said recording element at a temperature within the range of 80° to 200°C and for a time sufficient to produce a dye enhanced silver image in said recording element.