US3525612A - Electrophotographic reproduction process employing a light sensitive material and a photoconductive material - Google Patents

Description

United States Patent US. Cl. 961 9 Claims ABSTRACT OF THE DISCLOSURE A novel electrophotographic process is described wherein an element containing a light sensitive material and a photoconductive composition is imagewise exposed, charged, blanket exposed and developed. This process permits processing in room-light, provides for camera exposures of electrophotographic elements and is characterized by very rapid imagewise exposures.

This invention relates to photographic reproduction and more particularly to a novel method for employing a light sensitive material in electrophotography.

The electrophotographic production of images is presently based upon proportional changes in the conduc tivity of an electrically charged photoconductive element when that element is exposed in an imagewise manner to actinic radiation. Subsequent development of the charge pattern produced during exposure must then be accomplished by the deposition of electroscopic particles applied either dry or in liquid media to the original charge pattern or to a transferred pattern to achieve a visibile image. The principles applicable to most present electrophotographic applications remain the same as expressed in the Carlson US. Pat. No. 2,297,691.

It is therefore an object of this invention to provide a novel electrophotographic process.

It is a further object of this invention to provide photoconductive elements which are adapted for use in the herein described electrophotogra phic process.

The above and further objects and advantages are achieved in the present invention by the novel employment of a material in which a light sensitive or as referred to herein a photolysable compound is contained in a photoconductive layer containing an organic or an inorganic photoconductor. Initially the layer is constructed in a conventional manner to exhibit a uniform photoconductive sensitivity. By the further employment of photosensitive materials in this layer the photoconductive sensitivity of the layer may be altered by exposure to light in an imagewise manner. The change in photoconductive sensitivity of the photoconductive layer is brought about by imagewise change of the photolysable compound during the light exposure. The .photolysable compound may in its unaltered form be either a sensitizer or desensitizer for the photoconductor of the element. Upon imagewise exposure to light the compound can be altered to form a compound or compounds which have in the first instance little or no effect on the photoconductive sensitivity of the photoconductor or in the 3,525,612 Patented Aug. 25, 1970 second instance may be a relatively strong sensitize! for the photoconductor. Alternatively the photolysable compound may initially have little or no sensitizing or desensitizing action on the photoconductor but, on light exposure, produce a .photolytic product or products which have such action or which react with still more constituents in the photoconductive layer to form compounds having sensitizing or desensitizing action.

The sensitization or desensitization of the photoconductor may be termed as intrinsic, in which case the absolute photoconductive sensitivity of the photoconductor is affected, or the specific property may be spectral in which only the sensitivity of the photoconductor to certain regions of the spectrum is affected. In the latter case the measurable sensitivity of the photoconductive layer will of course depend upon the spectral region chosen for measurement. In the preferred practice of this invention the composition of the photoconductor is designed to provide a differential photoconductive sensitivity pattern upon exposure to actinic light. Such an imagewise pattern may subsequently be used in the formation of a visible image.

The invention in its preferred practice also provides a method of imparting to a layer a differential photoconductivity pattern by exposing the layer to a light image, the layer being comprised of a photoconductor containing composition and a light sensitive composition which can modify the electrophotographic sensitivity of the photoconductor differentially to a greater or lesser amount than its photolytic products. For example the photolytic compound can be decomposed or altered in an imagewise pattern and thereafter the layer can be given a second, uniform, exposure so as to form a difIerential photoconductivity pattern on the layer.

When desired the initially formed photoconductive sensitivity pattern may be either retained in the dark until it is desired to form a corresponding visible image or alternatively the exposed material may be stabilised to .prevent further light initiated change. Such stabilization treatment can be accomplished by simply removing or desensitizing any photolysable compound remaining in the layer after exposure. Where desired the photolysable compound can be rendered insensitive to light by either heat treatment or chemical treatment when feasible.

In the practice of this invention it may further be desired to form a visible image corresponding to the photoconductive sensitivity pattern by a wide number of procedures. For example a visible image may be formed from differential photoconductivity patterns in appropriate cases by a uniform print out exposure of the photoconductive layer with conductivity inducing radiation.

If it should be desired to form the pattern on the element by the electrostatic deposition process, the light exposed layer can be given a uniform electrostatic charge before a uniform exposure to the appropriate conductivity inducing radiation. If the material has not been generally stabilised against further light action, the uniform exposure can be made by using radiation which induces photoconduction in the layer but is selected so as to have no effect on the remaining photolysable or light sensitive compound in the layer.

The electrostatic image formed by the uniform exposure of the charge layer may likewise be rendered visible by conventional electrostatic developement methods such as by deposition of charged particles in either the charge bearing or discharged areas. The charged particles may be electroscopic powders, smoke or aerosol clouds or dispersions of solid charged particles in insulating liquid carriers. The deposited image may be subsequently transferred to a receiving sheet if so desired. Likewise the charge pattern may be transferred to a suitable receiving sheet and developed there when that is desired.

As an alternative procedure the photoconductive sensitivity pattern may be uniformly exposed to a photoconductivity inducing radiation while one side is in contact with an electrically conductive layer and the other in contact with an electrolyte containing an electrode. In this embodiment an image is deposited electrolytically on the conductive areas of the photoconductive layer when an optimum value of current is passed between the conductive layer and the electrode.

In the case of photoconductive layers containing photoconductors such as zinc oxide whose photoconductivity persists after exposure it is possible to uniformly expose the layer prior to the electrolytic deposition of an image thereon.

In the practice of the present invention the preferred light sensitive materials should of course be selected from among groups of compounds or compositions which will perform the desired function. For example if the method practiced specifically involved a light induced imagewise increase in photoconduction the light reaction products of the photolysable compound or composition must be a sensitizer for the photoconductor selected for use in a particular element.

Conversely the starting light sensitive material must be compatible with the selected photoconductor but exert little or no sensitizing effect on the photoconductor relative to the activity of its light reaction product. The reverse of these properties would, of course, by desired when the light reaction products were intended to exert little or no sensitization of the photoconductor relative to the sensitization of the unaltered photolysable compound or composition.

Specific light sensitive compounds that are useful in the practice of this invention include thiapyrylium, pyrylium and selenapyrylium dye salts, organo halides such as carbon tetrabromide, pentabromoethane and iodoform, light sensitive azides such as 2,6-di (4-azidobenzylidene)- 4-methylcyclohexanone, and compositions containing combinations of these classes of compounds. Photoconductive compounds which are useful will include both organic and inorganic photoconductor compositions which can be effected by changes in the light sensitive material. Compositions having the desired characteristics can be selected without undue experimentation.

The following examples illustrate the preparation of light sensitive materials and their use in the formation of photographic images.

EXAMPLE 1 The following composition was prepared:

Vitel 101 (Goodyear polyester)2.0 grams Triphenylamine--0.5 grams 2,6-bis(4-ethyl phenyl)-4-(4-amyloxyphenyl) thiapyrylium perchlorate-0.0005 gram Allylthiourea-0.05 gram Dichloromethane-l5 mls.

Vitel 101 is a mixed polyester of ethylene glycol and isophthalic and terephthalic acid.

The resulting clear dope was coated at 0.004 inch thickness on paper-backed aluminium foil. The resulting colourless coating was dark conditioned at 47 C. for 15 hours, followed by 2 hours at room temperature and 50% R.H. The material was then exposed for 60 seconds through an original to a high intensity tungsten light source having a brightness of about 7,000 lumens per square foot in order to obtain a latent dye image. One 7 week later the material was charged negatively under a corona discharge unit and then given a uniform overall second exposure of 8 seconds to a medium intensity tungsten light source having a brightness of about 750 lumens per square foot. After the second exposure the sample was toned with a positive toner by the magnetic brush method to give a negative working copy of the original. Alternatively, when a negative fringe toner was used (e.g., a styrene and n-butyl methacrylate carrier with cellulosic marking material such as Xerox 914 Toner), a positive working copy of the original was obtained. When using the negative fringe toner, it was found that the 60 seconds original exposure could be reduced to 5 seconds without causing any loss of image quality. The second overall light exposure is made in order to discharge the material in accordance with the photoconductive sensitivity pattern formed by the initial exposure. Thus, if the second overall exposure is not given then no toned image results.

EXAMPLE 2.

A material was prepared as described in Example 1, but the amount of 2,6-bis(4-ethyl phenyl)-4-(4-amyloxyphenyl) thiapyrylium perchlorate was increased to 0.025 gram. In this case it was necessary to increase the initial exposure to 8 minutes using the high intensity light source when a positive dye image of the original was clearly visible. One week later the material was charged negative under a corona discharge unit and then given an overall second exposure of 60 seconds to the medium intensity light source. After exposure the sample was toned with a positive toner on iron filings to give a negative working copy of the original.

EXAMPLE 3 The following composition was prepared:

Vitel l012.0 grams Triphenylamine0.15 gram Carbon tetrabromide0.1 gram Dichloromethane-IS mls.

The resulting clear dope was coated at 0.004 inch thickness on the paper-backed aluminium foil and allowed to dry. The material was then exposed for 60 seconds through an original to a medium intensity tungsten light source without any filter. The latent image may then be developed up at a later time. One day later the material was charged negative under a corona discharge unit and then given an overall exposure of 60 seconds to the same tungsten light source using a No. 8 (yellow) Wratten filter. After exposure, the sample was toned with a positive toner using the magnetic brush method to give a positive working copy of the original. Either a liquid dispersion or a fringe toner may be used in place of the above toner and in this case the original exposure may be reduced to 15 seconds. Using a liquid toner 1% blue printing ink dispersed in a solvent comprising a mixture of liquid aliphatic hydrocarbons) a positive copy of the original was obtained and using Xerox 914 fringe toner a negative copy of the original was obtained. The copies may be stabilized to further print out by heating for a few minutes at C.

The triphenylamine, carbon tetrabromide print out systern used in Example 3 is sensitive in the ultraviolet and blue regions of the spectrum.

The carbon tetrabromide in Example 3 may be replaced by other light sensitive organo-halides e.g., pentabromoethane or iodoform.

EXAMPLE 4 The following composition was prepared:

Vitel 101-2.0 grams Triphenylamine--0.5 gram Diphenylamine-0.05 gram Carbon tetrabromide-0.1 gram Dichloromethane-15 mls.

The resulting dope was coated at 0.004 inch thickness on paper-backed aluminium foil and allowed to dry. The material was then exposed for seconds through an original to a medium intensity tungsten light source without any filter. One day later the material was charged negatively under a corona discharge unit and then given an overall exposure of 60 seconds to the medium intensity tungsten light source using a No. 8 (yellow) Wratten filter. On toning with a liquid toner (1% blue printing ink dispersed in the aforesaid solvent) a positive copy of the original was obtained. Alternatively Xerox 914 fringe toner was used when a negative copy was obtained. An image was not obtained if the second overall exposure was not given. The copies may be stabilized to further print out by heating at 100 C. for a few minutes.

The carbon tetrabromide in Example 4 may be replaced by other oragno-halides e.g., iodoform or pentabromoethane. If iodoform is used then the original exposure may be reduced to 2 seconds on the medium intensity light source.

EXAMPLE 5 The following composition was prepared:

Polyvinylcarbazole3.0 g. Diphenylamine-0.05 g. Iodoform-0.l g. Dichloromethane15 mls.

The resulting clear dope was coated at 0.004 inch thickness on baryta coated paper and allowed to dry. The material was then exposed for 60 seconds through an original to a medium intensity tungsten source (750 lumens per sq. ft.) Without any filter. Three days later, the material was charged negatively under a corona discharge unit and then given an overall exposure of 60 seconds to the same tungsten source using a No. (red) Wratten filter. After exposure, the sample was toned with a positive toner (1% blue printing ink dispersed in the aforesaid solvent) to give a positive Working copy of the original.

The iodoform in Example 5 may be replaced by other light-sensitive oragno-halides, such as carbon tetrabromide.

EXAMPLE 6 The same composition as Example 5 was prepared but the diphenylamine was replaced by 0.05 g. of Z-p-dimethylaminostyrylbenzothiazole.

The No. 25 (red) filter was replacedby a No. 58 green) Wratten filter and the original was reduced to 15 seconds.

EXAMPLE 7 The following composition was prepared:

Vitel 10l-2.0 g.

Zinc oxide (New Jersey Zinc Co.)--7.0 g. Diphenylamine0.07 g. Iodoform0.l5 g. Trimethylchlorosilane0.l g. Dichloromethane25 mls.

The suspension was ball milled for several hours and then coated at 0.004 inch thickness onto paper-backed aluminium foil and allowed to dry. The material was then exposed for 10 seconds through an original to a medium intensity tungsten source 750 lumens/ sq. ft.) without any filter. One day later, the material was charged negatively under a corona discharge unit and then given an overall exposure of 60 seconds to a low intensity tungsten source (44 lumens/sq. ft.) using a N0. 25 (red) Wratten filter. After exposure, the sample was toned with a positive toner (1% blue printing ink dispersed in the aforesaid solvent) to give a positive copy of the original.

The iodoform in Example 7 may be replaced by other light-sensitive oragno-halides such as carbon tetrabromide.

A coating composition as in Example 7 but without trimethylchlorosilane gave no copy after the final toning operation.

EXAMPLE 8 The following composition was prepared:

Vitel l0l2.0 g. Triphenylamine0.5 g. Leuco Crystal Violet0.05 g. Iodoform0.10 g. Dichloromethane15 mls.

The resulting dope was coated at 0.004 inch thickness onto paper-backed aluminium foil and allowed to dry. The material was then exposed for 5 seconds through an original to a low intensity tungsten source (44 lumens/ sq. ft.) without any filter. One day later, the material was charged negatively under a corona discharge unit and then given an overall exposure of 5 seconds to the same light source, using a No. 25 (red) Wratten filter. On toning with a positive toner (1% blue printing ink dispersed in the aforesaid solvent) :1 positive copy of the original was obtained.

The iodoform in Example 8 may be replaced by other light-sensitive oragno-halides such as carbon tetrabromide or with certain light-sensitive azides such as 2,6-di- 4-azidobenzylidene -4-methylcyclohexan one.

EXAMPLE 9 As Example 8 but the Leuco Crystal Violet was replaced by 0.05 g. of 2-phenyl-4(p-dimethylamin-ophenyl)-1,4-benzopyran (prepared by the method of Shriner and Shotton, J. Am. Chem. Soc. 74 3622 (1952) A positive copy of the original was obtained.

EXAMPLE 10 The following composition was prepared:

Vitel 1012.0 g.

Triphenylamine0.5 g.

Leuco Crystal Violet0.05 g.

2,6-bis- (4-ethylphenyl -4- (4-amyloxyphenyl thiapyrylium perchlorate0.005 g.

Dichloromethane15 mls.

The resulting dope was coated at 0.004 inch thickness onto paper backed aluminum foil and allowed to dry. The material was then exposed for 10 seconds to a low intensity tungsten source (44 lumens/ sq. ft.) without any filter. Three days later, the material was charged negatively under a corona discharge unit and then given an overall exposure of 30 seconds to the same low intensity source using a No. 25 (red) Wratten filter. On toning with a positive toner (1% blue printing ink dispersed in the aforesaid solvent) a positive copy of the original was obtained.

In all the examples given, only one copy of the original was obtained. It is, however, possible to obtain multicopies from one master. Thus, the final toned image may be transferred onto a receiving sheet. The process of charging, exposure to filtered light, toning and transfer may then be repeated indefinitely to give multi-copies.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it Will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A xerographic process com-prising the steps of (a) providing a xerographic element comprising a support having coated thereon a photoconductive composition comprising a photoconductor, a film-forming polymeric binder and a sensitizing compound for said photoconductor selected from the group consisting of a pyrylium dye salt, a thiapyrylium dye salt and a selenapyrylium dye salt, said sensitizing compound having the property of losing its sensitizing effect upon said photoconductor when exposed to visible light which is actinic with respect to said its sensitizing effect on said photoconductor in areas sensitizing compound, not struck by light, (b) imagewise exposing said element to a pattern of (c) imparting a positive surface potential to said visible light which is actinic with respect to said element,

((1) blanket exposing said element to visible light which is not actinic to said sensitizer thereby producing an electrostatic charge pattern in those areas where the sensitizing compound has lost its sensitizing effect on said photoconductor and an electrostatic discharge pattern in those areas where the sensitizing compound has retained its sensitizing effect on said photoconductor and (e) developing said electrostatic discharge pattern with a positive polarity toner to produce a positive re production.

6. The process of claim 5 wherein the electrostatic charge pattern is developed with a negative polarity toner to produce a negative reproduction.

7. A xerographic process comprising the steps of (a) providing a xerographic element comprising a supsensitizing compound, thereby causing said sensitizing compound to lose its sensitizing effect upon said photoconductor in the light struck areas to retain its sensitizing effect on said photoconductor in areas not struck by light,

(0) imparting a negative surface potential to said element,

(d) blanket exposing said element to visible light which is not actinic to said sensitizer thereby producing an electrostatic charge pattern in those areas where the sensitizing compound has lost its sensitizing effect on said photoconductor and an electrostatic discharge pattern in those areas where the sensitizing compound has retained its sensitizing effect on said photoconductor and (e) developing said electrostatic discharge pattern with a negative polarity toner to produce a positive reproduction.

2. The process of claim 1 wherein the electrostatic charge pattern is developed with a positive polarity toner port having coated thereon a photoconductive composition comprising a photoconductor, a film-forming polymeric binder and an inert compound which is an organo-halide selected from the group consistto produce anegative reproduction. ing of carbon tetrabromide, pentabromoethane and 3. Axerographic process comprising the steps of iodoform, said inert compound having a sensitizing (a) providing a xerographic element comprising a supeffect on said photoconductor when exposed to visible port having coated thereon a photoconductive c mlight which is actinic with respect to the inert composition comprising a photoconductor, a film-forming Pound, polymeric binder and an inert compound which is (b) g se exposing said element to a pattern of an organo-halide selected from the group consisting visible light which is actinic with respect to said of carbon tetrabromide, pentabromoethane and iodoinert compound, thereby causing said inert compound form, said inert compound having a sensitizing effect o ave a sensitizing effect on said photoconductor on said photoconductor when exposed to visible light in the light struck areas and to have no sensitizing which is actinic with respect to the inert compound, effect 011 Said PhC'toconduclor in areas not Struck y (b) imagewise exposing said element to a pattern of g visible light which is actinic with respect to said inert (C) imparting a positive surface potential to said elecompound, thereby causing said inert compound to ment, have a sensitizing effect on said photoconductor in the anket exposing said element to visible light light struck areas and to have no sensitizing effect 40 which is not actinic to Said inert compound, thereby on said photoconductor in areas not struck by light, producing an electrostatic discharge pattern in those (c) imparting a negative surface potential to said eleareas Where the inert Compound haS a sensitizing merit, effect on said photoconductor and an electrostatic (d) blanket exposing said element to visible light which charge P r in those areas Where the inert is not actinic to said inert compound, thereby pro- POund has 110 sensitizing effect 011 Said photoconducing an electrostatic discharge pattern in those areas where the inert compound has a sensitizing effect on said photoconductor and an electrostatic charge pattern in those areas where the inert comductor and (e) developing said electrostatic discharge pattern with a positive polarity toner to produce a negative reproduction.

8. The process of claim 7 wherein the electrostatic charge pattern is developed with a negative polarity toner to produce a positive reproduction.

9. A xerographic process comprising the steps of (a) providing a xerographic element comprising a suppound has no sensitizing effect on said photoconductor and (e) developing said electrostatic discharge pattern with a negative polarity toner to produce a negative reproduction.

4. The process of claim 3 wherein the electrostatic P having coated thfifcoh a photoconductive charge pattern is developed with a positive polarity toner Position Comprising a photoconductor, a film-forming to produce a positive reproduction polymeric binder and an inert compound which is 5. A xerographic process comprising the steps of Eli-(tazidobenzylidenfl'4-msthxleyhohexanone,

(a) providing a xerographic element comprising a supi Inert compound havmg sensmzmg on port having coated thereon a photoconductive comi pi q when exposeid to vlslble hght position comprising a photoconductor, a film-forming i 1S aimmc Wltli respept to the Inert compound polymeric binder and a sensitizing compound for g i i i i el.ement to a i p of said photoconductor selected from the group con- V151 e is acm-nc i r-espect to sand mart sisting of a pyrylium dye salt, a thiapyrylium dye iompoun Heie y Causing Sal-d mart compound i0 1 d 1 d It d ave a sensitizing effect on said photoconductor in 53 t an a Se napyry mm ye sa l i i i the light struck areas and to have no sensitizing effect compound having the Property of 105mg lts sensitizing on said photoconductor in areas not struck by light, i h p salci phhiocohducioh when exposed to (c) imparting a negative surface potential to said visible light which is actinic with respect to said element, sensitizing compound, (d) blanket exposing said element to visible light which (b) imagewise exposing said element to a pattern of is not actinic to said inert compound, thereby provisible light which is actinic with respect to said ducing an electrostatic discharge pattern in those sensitizing compound, thereby causing said sensitizareas where the inert compound has a sensitizing ing compound to lose its sensitizing effect upon said effect on said photoconductor and an electrostatic photoconductor in the light struck areas and to retain charge pattern in those areas where the inert comduction.

References Cited UNITED STATES PATENTS Kallman 961 Ebert 961 Cassier et a1. 96-1 10 Davis et a1. 961

1 0 3,148,276 9/ 1964 Rothstein 25065 3,180,730 4/1967 Klupfel et a1 961 3,310,401 3/1967 Grieg 96---1.5 3,316088 4/1967 Schaffert 9'6-1.5 3,287,123 11/1966 Hoegl 96l.5

DONALD LEVY, Primary Examiner J. C. COOPER, Assistant Examiner U.S. Cl. X.R. 96l.5; 11717.5