US3178362A

US3178362A - Photoconductography employing quaternary salts

Info

Publication number: US3178362A
Application number: US45954A
Authority: US
Inventors: John J Sagura; James A Van Allan
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1960-07-28
Filing date: 1960-07-28
Publication date: 1965-04-13
Anticipated expiration: 1982-04-13
Also published as: DE1225492B; GB1006118A

Description

United States Patent 0 PHOTOCONDUCTOGRAPHY EMPLOYING QUATERNARY SALTS John J. Sagura and James A. Van Allan, Rochester, N. assignors to Eastman Kodak Company, Rochester, N.Y.,

a corporation of New Jersey Filed July 28, 1960, Ser. No. 45,954 8 Claims. (Cl. 204-18) The present invention relates to electrolytic recording and particularly to photoconductography.

Photoconductography forms a complete image at one time or at least a non-uniform part of an image as distinguished from facsimile which at any one moment produces only a uniform dot. The present invention relates particularly to the formation of a negative image on a photoconductive layer, although certai'n special embodiments form a direct positive image. I

7 Cross reference is made to the following series of cofiled applications:

Serial No. 45,940, John W. Castle, In, Photoconductography Employing Reducing Agents.

Serial No. 45,941, now abandoned, Raymond F. Reithel, "Photoconductolithography Employing Nickel Salts, continuation-in-part Serial No. 120,863, filed June 7, 1961, now Patent No. 3,106,157.

Serial No. 45,942, now Patent No. 3,053,179, Raymond F. Reithel, "Photoconductolithography Employing Magnesium Salts.

Serial No. 45,943, Raymond F. Reithel, Photoconductography Employing Spongy Hydroxide Images, now abandoned, continuation-in-part Serial No. 120,035, filed June 27, 1961, now Patent No. 3,106,518.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer Prints Using a Photoconductographic Process.

Serial No. 45,945, Raymond F. Reithel, Photoconductography Employing Manganese Compounds.

Serial No. 45,946, now abandoned, Raymond F. Reithel, Photoconductography Employing Molybdenum or Ferrous Oxide, continuation-in-part Serial No. 120,03 6, filed June 27, 1961, now Patent No. 3,106,156.

Serial No. 45,947, Raymond F. Reithel, Photoconductography Employing Cobaltous or Nickelous Hydroxide, now abandoned, continuation-impart 120,037, filed June 27, 1961, now Patent No. 3,057,788.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial No. 45,949, Donald R. Eastman, Photoconductolithography Employing Hydrophobic Images.

Serial No. 45,950, now'Patent No. 3,106,516, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Electrolytic Images-to Harden or Soften Films. 1

Serial No. 45,951, now abandoned, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Absorbed Metal Ions, continuation-in-part Serial No. 120,038, filed June 27, 1961.

Serial No. 45,952, now Patent No. 3,106,517, Donald R.

Eastman and Raymond F. Reithel, Photoconductography Employing Spongy Images Containing Gelatin Hardeners.

Serial No. 45,953, now Patent No. 3,057,787, John I. Sagura, Photoconductography Employing Alkaline Dye Formation.

Eastman and Raymond F. Reithel, Electrolytic Re- I cording with Organic Polymers. Serial No. 46,034, now abandoned, Franz Urbach and Donald Pearlman, Electrolytic Recording.

Electrolytic facsimile systems are well known; Electrophotoconductography is described in detail in British Patent 188,030, Von Bronk, and British Patent 464,112, Goldmann, modifications being described in British 709,309, Berchtold, and Belgian 461,403, Johnson et al.

The object of the present invention is to provide a reliable, inexpensive photoconductographic process which gives better contrast and better quality prints than heretofore available. In certain embodiments of the present invention the image which is electrolytically deposited is colorless or only faintly colored. It is not essential to the invention, except in the special direct positive case discussed separately below, that the photocon produced image be invisible, but the fact that it may be invisible widens the choice of recording materials. This permits the recording material to be chosen to give the highest resolution and highest speed of development without reference to the color of the material being deposited.

Certain features which are useful with the invention and with other forms of photoconductography are also described in detail below.

Photoconductography involves exposure of a photoconductive layer to produce an image pattern of variations in conductivity, within the layer. According to the present invention, this photoconductographic image is electrolytically developed by placing the layer in contact with an electrolyte containing a heterocyclic quaternary ammonium salt and then passing current through the layer, distributed in accordance with the conductivity pattern, to deposit the anhydro base of the quaternary salt on the layer imagewise. Quaternary ammonium salts behave somewhat like inorganic salts to the extent that they are ionized or dis-associated in water solution. This is perhaps one of their best known properties. When a solution of a quaternary salt is used in an electrolytic bath thematerial which deposits on the cathode is termed the methylene base or more accurately the anhydro base of the quaternary salt. The present invention employs this anhydro base.

Strictly speaking quaternary ammonium salts include some of the simple salts of ammonia although it is not usual to use the term thus. Also the various embodiments of the present invention requirefor practical reasons the use of heterocyclic quaternary salts. All such salts are useful in photoconductography but the preferred embodiments of the present invention (whether for colored images or color forming images or electrical resistance stencils, all as discussed below) employ the heterocyclic quaternary salts which have an active methyl or methylene 3 group in the number 2 position, i.e. on the carbon atom adjacent to the nitrogen atom. With the latter type of salts the anhydro base is either colored or a color precursor which reacts to form a dye.

Thus in the preferred embodiments, the developer electrolyte contains a heterocyclic quaternary salt with an active methyl or methylene group. Such electrolytes are highly ionized. The salt is soluble in water. The cathodic deposit (the anhydro base) is substantially insoluble, relatively hydrophobic and has high electrical resistance. Furthermore, the deposit is either colored or is a known color precursor. The insolubility prevents the deposit from going back into solution and thus smearing or losing the image. All of these desirable properties are obtained with heterocyclic quaternary salts, having an active methyl or methylene group.

The heterocyclic quaternary salts which do not have the active methyl or methylene group (including those which have an active methinyl group in this number 2 position) are not useful in depositing dyes or dye precursors, but do deposit the base from which they were derived and this base is hydrophobic with'relatively high electrical resistance compared to that of the photoconducto r. This base is useful in resistance stencil processes discussed below.

. In those embodiments of the invention in which the anhydro base itself is highly colored, i.e. has a high optical density, the electro deposited image itself may constitute the final image on the photoconductive layer. High quality, high resolution, prints have been obtained by this method.

In the case where the anhydro base is colorless or only faintly colored it constitutes a dye former. This is true of all such anhydro bases of heterocyclic quaternary salts with an active methyl or methylene group although the preferred material with which the anhydro base is reacted to form a dye depends on which anhydro base is selected. Various reactions are given in the examples below including reacting with aldehydes, with diazonium salts, with pnitrozodimethylaniline, with quinones, with oxidized color developers or with additional quaternary salts to form dyes. The particular dye forming reaction and reagent selected is not a novel part of the present invention. Any of the known dye forming reactions involving the anhydro base of such quaternary salts may be used and such reactions are known for each such anhydro base.

. Photoconductography employing such salts, such deposited bases and such dye formation, gives results far superior to prior photoconductographic processes.

The anhydro (methylene) bases electrodeposited from the quaternary salt solutions tend to be hydrophobic, nonelectrolytic and electrically resistant. They may thus act as a stencil in a second or subsequent electrolytic bath, in which a metal or other colored material is deposited on the areas of the photoconductor not already covered by the anhydro base. This gives a direct positive image if the anhydro base is colorless or lighter in color than the material deposited by the second electrolytic bath. This process works whether or not the quaternary salt has an active methyl or methylene group.

In addition to the main features of the invention as described above the following alternative arrangements, somewhat similar but inferior to the invention, should be noted. The deposition of an invisible image fo later development or redevelopment is also obtained when salts of basic azo couplers are used in the electrolyte which deposits the free couplers on the photoconductive layer and these free couplers are subsequently treated with diazo compounds to yield azo dyes. The similarity of this process to the diazo treatment of methylene (anhydro) bases is noteworthy but the images by the latter process are superior. Similarly the electro deposition of colorless reducing agents which are then treated with salts of noble metals so that the deposited metal images constitute the result of electro deposition of an invisible image and later converting to a visible one but again the present invention is superior. An aqueous solution of l-ethylquinaldinium iodide when used as the electrolyte for developing a photocon image, produces a colorless image but when later treated with silver nitrate (no electric potential being applied) produces a positive brownish toned silver image or if treated with potassium chloroaurate solution in place of the silver nitrate, blue black images are obtained.

Similarly a metal together with a metal mercaptan may be electrolytically deposited from an electrolyte containing an aqueous solution of both the metal salt and some material such as isothiouronium salts or disulfides which generate a mercaptan by the reaction at the cathode interface, and give an excellent image.

In all photoconductographic processes, the overall contrast of the final print can be increased if the so-called toe of the characteristic reproduction curve is eliminated or reduced. That is, the very light areas of the print should reproduce as white or clear and there should be no density until one reaches the middle tones or dark areas of the image. One method of obtaining this improved result is to have an electrolyte with a relatively low pH. For example contrast is improved when acid is added to the electrolyte containing the heterocyclic quaternary salt according to the invention.

Also, in certain photoconductographic processes, for example those in which the electrolyte contains a hydroquinone and the heterocyclic quaternary salt, higher density images are obtained in the presence of cobalt chelate of ethylene bis salicyaldamine which is prepared by condensing one mole of ethylene diamine with two moles of salicyaldehyde in the presence of a cobalt salt. During the cathodic reaction, the oxygen combined with this cobalt compound is released and oxidizes the hydroquinone-leuco dye, formed from the reaction of a hydroquinone and the heterocyclic base, to yield a colored image.

Examples of the invention and of these special features are given below. The invention will be more fully understood when read in connection with these examples and with the accompanying drawings in which:

FIG. 1 constitutes a flow chart schematically illustrating the formation of a photoconductographic image according to one embodiment of the invention.

FIG. 2 similarly illustrates an alternative arrangement in which the electrolytic deposition is simultaneous with the exposure.

FIG. 3 illustrates the ultimate step in certain embodiments of the invention in which the electro-deposited image is intensified or colored.

FIG. 4 similarly illustrates the ultimate step in an embodiment of the invention from which either direct positives or negatives are obatined. In FIG. 1 the image of a negative transparency 10 illuminated by a lamp 11 is focused on a photoconductrve layer 15, for example of zinc oxide in suitable resin binder, carried on an electrically conducting support 16 which may be highly conducting paper or which preferably includes a metal foil layer. In this particular arrangernent, the transparency 10 is moved to the left as indicated by the arrow 17 while the photoconductive layer 15 is moved to the right as indicated by the arrow 18 so that the image and photoconductive layer move synchronously to expose the layer part at a time.

The exposed photoconductive layer 15 is then passed between

electrodes

20 and 21 so that the photoconductive layer acts as a cathode in an electrolytic bath, the electrolyte being contained in the brush electrode 20. Thus an image 23 is formed on the photoconductive layer 15 in those areas which have been exposed and which transmit electric current.

According to the invention the brush 20 contains a solution of a heterocyclic quaternary ammonium salt preferably with an active methyl or methylene group V v and the image 23 is the anhydro, preferably methylene, base of this salt.

Photoconductographic processes in which the electro depositing and the exposure takes place simultaneously,

may also employ the present invention. Such an arrangement is shown in FIG. 2 in which the transparency is illuminated by a lamp 25 and a diffusing sheet 26; in this case the lens 27 focuses an image of the whole transparency 10 onto the photoconductive layer 15. There is no motion of the transparency in or the layer 15 during exposure. A transparent electrode such as metal oxide coated on glass constitutes the anode 28. The electrolyte 29 containing the quaternary ammonium salt or salts, is placed between the layer 15 and the electrode 28. When the switch shown schematically at 24 is closed, electric potential from the source 34 causes the anhydro base of the quaternary salt to deposit in the exposed'areas of the photoconductive layer 15. Either FIG. 1 or FIG. 2 results in an anhydro base image 23 on the photoconductive layer 15.

This anhydro base image 23 in FIG. 3 may be invisible, barely visible or colored, but in FIG. 3 it is treated with a color forming reagent in a second brush to produce the final high density image 36. All anhydro bases of such salts are colored or are dye precursors of known idye forming processes.

In FIG. 4 on the other hand, the electric resistance of the anhydro base 23 is utilized. The photoconductive layer with the anhydro base stencil 23 thereon, is passed through a second electrolytic bath applied between a brush so and roller 41, potential being supplied by a source 42. In this case the layer 15 is conducting since the step is performed in the light (not in the dark) except where covered by the base 23. Metal or other material having optical density is electro deposited to form the image material 43 which constitutes a direct positive image. In those cases where the anhydro or methylene base is itself colored or is coupled to form a dye, it may still act as an electrically resistant stencil permitting the deposition of a light colored material in the non-image area to enhance the contrast of the negative image.

It is noted that the electrolyte in the above examples, is compatible with the zinc oxide and upon reaction at the zinc oxide cathode yields (and deposits) a nonelectrolyte which is also compatible. If the developer itself were a non-electrolyte, it would function very poorly and if the product formed at the cathode from the electrolyte salt were an electrolyte itself, it would have little tendency to separate from the solution and adhere to the photoconductive layer. This constitutes some of the advantages of the heterocyclic quaternary salts of nitrogen compounds.

Examples of the invention are as follows:

Example 1 Colorless tetrazolium salts will react at the zinc oxide cat-hodeto yield colored formazans, e.g.,

where Ar refers to an aromatic group. This Example 1 shows a heterocyclic quaternary ammonium salt (tetrazolium) which does not (necessarily) have the active methyl or methylene group in the adjacent position on the aromatic ring. It does give a dye image directly however. The X is simple chlorine in this case. A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with a one-half a capable of subsequent color forming reactions.

6 percent aqueous solution of 2,3,5-triphenyl-2H-tetrazolium chloride to obtain a red (formazan) positive image.

Example '2 Similarly certain salts which are unstable in the presence of hydroxyl ions are capable of depositing colored images.

Blue non-electrolyte (probable structure); the active group is now methtnyl A sensitized zinc oxide layer on aluminum foil'was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with a one-and-onehalf percent aqueous solution of 1-methyl- 2-(2,4--dinitrobenzyl)-pyridinium-p-toluenesulfonate to obtain a blue positive image. The X is p-toluenesulfonate in this case.

Example 3 9 N CH X N -CHz 6B CH CH Note active methyl group Magenta (probable structure) A sensitizedzinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with a one-half percent aqueous solution of 4-chloroquinaldine methosulfate to obtain a magenta positive image. The X is methosulfate but the p-toluenesulfonate could have been used instead.

Example 4 Note active methyl group CH \N/ Yellow (proabble structure) A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with a one-tenth percent aqueous solution of 1,2dimethylbenzothiazolium p-toluenesulfonate to obtain a yellow positive image.

Examples 2, 3 and 4- have the active group on the heterocyclic salt and deposit a color directly.

Example 5 While the Examples 3 and 4 produce colord deposits directly, these deposits are relatively low density but are For example the yellow image of Example 4 may be treated as 7 in FIG. 3 above with an aldehyde to give a darker color; that is, Example consists of Example 4 plus the following step:

A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with a dilute aqueous methanol solution of 1,2-dimethylbenzothiazoliurn p-toluene-sulfonate (i.e. Example 4) and p-dimethylaminobenzaldehyde to obtain a pink positive image that intensified on exposure to light.

Example 6 A dyes can be made to adhere to the zinc oxide layer by coupling the deposited methylene base with diazonium salt, e.g., Example 6 consists of the deposit of a methylene base, the same as or similar to Example 3 plus the following step:

\N CHM-Xe canon CziHdOH Example 7 The methylene base (for example from Example 3) is reacted with p-nitrosodimethylaniline (or other oxldized color developer) \N cal CH CH A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with an aqueous solution of quinaldine methiodide and p-nitrosodimethylaniline. The print was then exposed to an RS Sunlamp at 10 inches for seconds to obtain a violet-brown image.

The specific Example 8 The methylene base is reacted with a different heterocyclic quaternary ammonium salt.

Example 9 The methylene base (for example from Example 4) is reacted with a quinone to form a dye.

O S H i l s OH- N i (in A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for 5 seconds at 400 foot candles. The conductive image was then developed in the manner described above with an aqueous methanol solution of 1,Z-dimethylbenzothiazolium p-toluenesulfonate (as in Example 4), p-quinone, and sodium chloride to obtain a blue-violet image.

The following is an example of the use of electrolytes containing heterocyclic quaternary salts not having the active methyl or methylene group and hence not useful in the main form of the present invention but still useful in producing a stencil for subsequent electrolytic plating (e.g. of a direct positive image).

Example 10 The anhydro base (for example from a benzothiazole) forms an insulating image:

thiouronium chloride to obtain a black negative image. Any plating material could be so plated.

Process 11 The following process is of interest since a stencil can be obtained thereby but it is inferior to those of the present invention. Example 11 so as to avoid confusion with the use of heterocyclic quaternary salts.

A sensitized zinc oxide layer on aluminum foil was exposedthrough a negative pattern for 5 seconds at 400 foot candles. The conductive image was then developed electrolytically in the manner described above with an aqueous solution of a,a'-tetramethyldiamino-di-p-tolylmethane dihydrochloride to obtain a colorless insulating image. The print was then given an overall exposure to light and then developed electrolytically with an aqueous solution of lead acetate and 2,5-dihydroxyphenylisothiouronium chloride to obtain a black negative image.

Example 12 A sensitized zinc oxide layer on aluminum foil was exposed through a negative pattern for two seconds at 400 foot candles. The conductive image was then electrolytically developed in the manner described above with an aqueous solution of l-ethylquinaldinium iodide (this is a heterocyclic quaternary without the active methyl or methylene group) to obtain a colorless image. This image is an anhydro base, but the pertinent property in this example is the fact it is a reducing agent. The zinc oxide surface was then treated with silver nitrate solution (with no potential applied) to obtain a positive brownish toned silver image. Blue-black images were obtained in the same manner by using potassium chloroaurate solution in place of the silver nitrate solution. To completely stabilize the prints obtained, it is necessary only to wash oil the excess of metal salt or to swab the print with a solution of a fixer such as hypo or thiourea.

Process 13 The possibility of producing similar results by the generating of a mercaptan at the cathode interface as discussed above is illustrated by Processes 13, 14 and 15. A metal salt plus isothiouronium salt or disulfide or other sulfur containing compound (including heterocyclic ones) may be used.

A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) was exposed through a negative pattern for five seconds at 400' foot candles. The image was then developed in the manner described above with an aqueous solution of lead acetate /2 percent) containing 2,5 -dihydroxyphenylisothiouroniuin chloride. A black positive image resulted.

Process 14 A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) was exposed through a negative pattern for five seconds at 400 foot candles. The image was then developed in the manner described above with an aqueous methanol solution of lead acetate /2 percent) containing S-thioctic acid. A black positive image resulted.

' Process 15 A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) was exposed through a negative pattern for five seconds at 400 foot candles.

It is identified as Process 11 rather than V The image was then developed in the manner described above with an aqueous methanol solution of lead acetate /2 percent) imidazoline. A black positive image resulted. Processes 13, 14 and 15 produce metal sulfide images-rather than dye images. The latter are preferable and hence heterocyclic quaternary salts are preferred in the electrolyte.

Examples of increasing the contrast of photoconductographic materials by use of lower pH in the electrolyte are illustrated in Examples 16 and 17 (employing the heterocyclic quaternary) and Process 18.

Example 16 To a solution containing 1 gram 1-methyl-2-(2,4-dinitro)benzyl pyridinium sulfonate, having a pH of 5.5, was added sufiicient acetic acid to bring the pH to 4.0. This solution was used in a viscose sponge as the electrolyte to develop an image on a previously exposed zinc oxide layer, with volts potential applied between the sponge and the conductive backing of the recording material. The resulting print formed on the anhydro base deposited had much higher contrast than did a print made similarly but developed with a solution whose pH ha not been adjusted by the addition of acid.

Example 17 A similar solution was brought to pH 3.5 by the addition of maleic acid. Again the print made with this solution showed much higher contrast than did one made similarly but developed with a solution Whose pH had not been adiusted by the addition of acid. The eifect is one of dropping out the highlights.

Process 18 0.5 gram of an indicator, 3',3 dibromothymolsulfonephthalein was added to 50 cc. of a 3% gelatin solution containing 0.5 cc. glycerol, 0.5 cc. wetting agent and 0.6 cc. tormalin. The pH of this solution was 5.6. This solution was filtered through a balloon silk filter bag and overcoated 0.005 of an inch on a dyed zinc oxide photoconductive coating on aluminum foil support. The pH of the solution was adjusted in one case to 4.5 and in another to 3.5 with acetic-acid, and overcoated, at each pH, 0.005 of an inch on dyed zinc oxide coatings on aluminum foil supports. The above three coatings were exposed to 400 ft.-c. illumination through a 0.3 increment step wedge and developed with a brush electrode held at 80 volts potential between the brush and the conductive backing of the recording material using a 50% water solution of formalin containing 1% potassium chloride. The prints made from the recording layers having the lower pH values had more contrast than those made from the recording layers having the higher pH values.

As further examples of the two-step electrolytic development giving a direct positive by electroplating through a stencil formed of methylene base, various processes warrant mention. When the photoconductive layer is of a light color for example white zinc oxide and the second image formed is of a dark color, a positive print results. However, when the photoconductive layer is of a dark color, for example selenium, lead sulfide, antimony trisulfide or cadmium sulfide containing a high percentage of copper, the second image preferably is formed of a light color, so that a negative print results. If the second image formed has a hydrophilicity very different from that of the control image (the methylene or other anhydro base) the combination of images may be used as a lithographic printing matrix by wetting the sheet and printing With greasy ink from the less hydrophilic of the two images.

Further examples of the two-step electrolytic development are shown in

Processes

19, 20 and 21.

containing 2-carboxymethylmercapto-- Process 19 This process uses a heterocyclic quaternary in the second electrolytic bath but not in the first. A dye-sensitized zinc oxide layer on conducting support was exposed to an image for seconds using 400 ft.-c. illumination. The conducting image was then developed electrolytically with a solution containing 2% aluminum sulfate octodecahydrate and 1% sodium chloride. An insulating image presumably of aluminum hydroxide, was formed. The zinc oxide was then uniformly exposed to light and the layer was developed electrolytically using a 2% solution of l-ethylquinaldinium iodide, the anhydro base of which,

when oxidized aerially to form a brown color, formed a positive image of the original.

Process 20 A dye-sensitized zinc oxide layer on conducting support was exposed to an image for 5 seconds using 400 ft.-c. illumination. The conductive image was then developed electrolytically using a solution consisting of 0.3% aluminum sulfate octodecahydrate and 3% sodium chloride. An insulating image presumably of aluminum hydroxide was formed. The zinc oxide layer was then uniformly exposed to light for 5 seconds and developed electrolytically using a 1% solution of l methyl 2 (2,4-dinitrobenzyl) pyridinium paratoluene sulfonate. A colored positive image of the original was formed in the areas not previously coated with the insulating aluminum hydroxide image. Again the heterocyclic quaternary salt is used as the second electrolyte rather than the first.

Example 21 This example employs the heterocyclic quaternary as the first electrolyte. A dye-sensitized zinc oxide layer on conducting support Was exposed as above for 30 seconds and developed electrolytically with a 2% solution of 1- ethylquinaldinium iodide to form an insulating image. The zinc oxide layer was then uniformly exposed for 5 seconds as above and the areas not containing the insulatl ing image were developed electrolytically, with a solution containing 1% hypo and saturated with silver chloride. A direct positive image was formed.

To illustrate the improved effect improved D by the presence of cobalt chelate of ethylene bis salicylaldimine, hereinafter referred to by the trivial name Cosal we note the following Examples 22, 23 and 24, in which heterocyclic quaternary salts with the preferred active groups of methyl or methylene are used with all of the advantages of the preferred forms of the present invention.

Example 22 A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) then overcoated with a polyvinyl acetate layer containing Cosal was exposed through a negative pattern for five seconds at 400 foot-candles. The image Was then developed in the manner described above with an aqueous solution of 2-methyl benzothiazole-metho-p-toluene sulfonate and hydroquinone. A blue image of good quality and high density resulted.

Example 23 A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) then overcoated with a polyvinyl acetate layer containing Cosal was exposed through a negative pattern for five seconds at 400 foot-candles. The image was then developed in the manner described above with an aqueous solution of 2-methylbenzothiazole-metho-p-toluene sulfonate and t-butyl hydroquinone. A blue image of good quality resulted.

Example 24 A zinc oxide coated aluminum foil (prepared and sensitized in the usual manner) and overcoated with a polyvinyl acetate layer containing Cosal was exposed through a negative pattern for five seconds at 400 foot-candles. The image was then developed in the manner described above with an aqueous solution of 2-ethyl quinaldinium iodide and t-butyl hydroquinone. A bluish-green image of good quality resulted. In each case the Cosal caused a slightly higher D Having given various examples of the invention and preferred arrangements thereof, it is pointed out that the invention is not limited to these specific examples but is of the scope of the appended claims.

We claim:

1. In a photoconductographic process in which an image pattern of variations in electrical conductivity is produced in a photoconductive layer, the steps comprising placing the layer as a cathode in contact with an electrolyte containing a heterocyclic quaternary ammonium salt containing an active group on the carbon adjacent to the nitrogen selected from the groups consisting of methyl and methylene, and with an anode also in contact with the electrolyte passing current through the layer distributed in accordance with said pattern to deposit the anhydro base of said salt cathodically on the layer similarly distributed.

2. The process according to claim 1 in which the quaternary ammonium salt is one Whose anhydro base has a high optical density.

3. The process according to claim 1 in which the quaternary ammonium salt is one whose anhydro base is colorless and including the step of treating the deposited anhydro base with a reagent selected from the group consisting of aldehydes, diazonium salts, p-nitrosodimethylaniline, quinones, oxidized color developers and additional quaternary salts which reacts with said base to form a dye. 4. The process according to claim 1 in which the quaternary ammonium salt is one whose anhydro base has a low optical density and has higher electrical resistance than the area of the photoconductor not covered by said base and which includes the additional step of electrolytically depositing material having high optical density on the area of the photoconducting layer not covered by the anhydro base.

5. The process according to claim 1 in which the heterocyclic quaternary ammonium salt is 1-methyl-2-(2,4- dinitrobenzyl)-pyridinium p-toluene sulfonate.

6. The process according to claim 1 in which the quaternary ammonium salt has an active methylene group and the anhydro base is a methylene base and including the additional step of treating the deposited methylene base with a reagent which reacts therewith to form a dye.

7. In a photoconductographic process in which an image pattern of variations in electrical conductivity is produced in a photoconductive layer, the steps comprising placing the layer in contact with an electrolyte containing a heterocyclic quaternary ammonium salt, passing current through the layer distributed in accordance with said pattern to deposit the anhydro base of said salt on the layer similarly distributed and with a higher electrical resistance than the areas of the photoconductor not covered by said base and electrolytically depositing material having an optical density different from that of said base on the areas of the photoconducting layer not covered by said base.

8. In a photoconductographic process in which an image pattern of variations in electrical conductivity is produced in a photoconductive layer, the steps comprising placing the layer in contact with an electrolyte containing a heterocyclic quaternary ammonium salt, passing current through the layer distributed in accordance with said pattern to deposit the anhydro base of said salt on the layer similarly distributed.

(References on following page) 13 14 References Cited by the Examiner OTHER REFERENCES UNITED STATES PATENTS Hickinbottom: Reactions of Organic Compounds, Third 2,30 471 12 Solomon 204,4 Edition, 1957, Pages 2363587 11/44 Bock 5 JOHN H. MACK, Primary Examiner.

FOREIGN PATENTS JOSEPH REBOLD, JOHN R. SPECK, Examiners.

215,754 6/58 Australia.

Claims

8. IN A PHOTOCONDUCTOGRAPHIC PROCESS IN WHICH AN IMAGE PATTEN OF VARIATIONS IN ELECTICAL CONDUCTIVITY IS PRODUCED IN A PHOTOCONDUCTIVE LYAER, THE STEPS COMPRISING PLACING THE LYAER IN CONTACT WITH AN ELECTROLYTE CONTAINING A HETEROCYCLIC QUATERNARY AMMONIUM SALT, PASSING CURRENT THROUGH THE LAYER DISTRUBUTED IN ACCORDANCE WITH SAID PATTERN TO DEPOSIT THE ANHYDRO BASE OF SAID SALT ON THE LYAER SIMILARYLY DISTRIBUTED.