US3408187A - Electrophotographic materials and methods employing photoconductive resinous charge transfer complexes - Google Patents

Description

United States Patent Office 3,408,187 Patented Oct. 29, 1968 3,408,187 ELECTROPHOTOGRAPHIC MATERIALS AND METHGDS EMPLOYING PHOTOCONDUC- TIVE RESINOUS CHARGE TRANSFER COMPLEXES Joseph Mammino, Penr'ield, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed Jan. 24, 1966, Ser. No. 522,393 24 Claims. (Cl. 961.5)

ABSTRACT OF THE DISCLOSURE Photoconductive materials are prepared from aromatic silicone resins and Lewis acids. The materials are charge transfer complexes. The photoconductive materials are used to make electrophotographic plates. Methods of using the plates are also disclosed.

This invention relates to photoconductive materials, and more particularly, to their use in electrophotography.

It is known that images may be formed and developed on the surface of certain photoconductive materials by electrostatic means. The basic xerographic process, as taught by Carlson in US. Patent 2,297,691, involves uniformly charging a photoconductive insulating layer and then exposing the layer to a light-and-shadow image which dissipates the charge on the areas of the layer which are exposed to light. The electrostatic latent image formed on the layer corresponds to the configuration of the light-and-shadow image. This image is rendered visible by depositing on the image layer a finely divided developing material comprising an electroscopic marking material called a toner. The powder developing material will normally be attracted to those portions of the layer which retain a charge, thereby forming a powder image corresponding to the latent electrostatic image. This powder image may be transferred to paper or other receiving surfaces. The paper then will bear the powder image which may subsequently be made permanent by heating or other suitable fixing means. The above general process is also described in US. Patents, 2,357,809; 2,891,011 and 3,079,342. i

That various photoconductive insulating materials ma be used in making electrophotographic plates is known. Suitable photoconductive insulating materials such as anthracene, sulfur, selenium or mixtures thereof, have been disclosed by Carlson in US. Patent 2,297,691. These materials generally have sensitivity in the blue or near ultraviolet range, and all but selenium have a further limitation of being only slightly light sensitive. For this reason, selenium has been the most commercially accepted material for use in electrophotographic plates.

Vitreous selenium however, while desirable in most aspects, suffers from serious limitations in that its spectral response is somewhat limited to the'ultraviolet, blue and green regions of the spectrum and the preparation of vitreous selenium plates requires costly and complex procedures, such as vacuum evaporation. Also, selenium plates require the use of a separate conductive substrate layer, preferably with an additional barrier layer deposited thereon before deposition of the selenium photoconductor. Because of these economic and commercial considerations, there have been many recent efforts towards developing photoconductive insulating materials other than selenium for use in electrographic plates.

It has been proposed that various two-component materials be used in photoconductive insulating layers used in electrophotographic plates. For example, the use of inorganic photoconductive pigments dispersed in suitable binder materials to form photoconductive insulating layers is known. It has further been demonstrated that organic photoconductive dyes and a wide variety of polycyclic compounds may be used together with suitable resin materials to form photoconductive insulating layers useful in binder-type plates. In each of these two systems, it is necessary that at least one original component used to prepare the photoconductive insulating layer be, itself, a photoconductive material.

In a third type plate, inherently photoconductive polymers are used; frequently in combination with sensitizing dyes or Lewis acids to form photoconductive insulating layers. Again, in these plates at least one photoconductive component is necessary in the formation of the layer. While the concept of sensitizing photoconductors is, itself, commercially useful, it does have the drawback of being limited to only those materials already having substantial photoconductivity.

The above discussed three types of known plates are further described in US. Patents 3,097,095; 3,113,022; 3,041,165; 3,126,281; 3,073,861; 3,072,479; 2,999,750; Canadian Patent 644,167 and German Patent 1,068,115.

The polymeric and binder-type organic photoconductor plates of the prior art generally have the inherent disadvantages of high cost of manufacture, brittleness, and poor adhesion to supporting substrates. A number of these photoconductive insulating layers have low temperature distortion properties which make them undesirable in an automatic electrophotographic apparatus which often includes powerful lamps and thermal fusing devices which tend to heat the xerographic plate. Also, the choice of physical properties has been limited by the necessity of using only inherently photoconductive materials.

Inorganic pigment-binder plates are limited in usefulness because they are often opaque and are thus limited to use in systems where light transmission is not required. Inorganic pigment-binder plates have the further disadvantage of being nonreusable due to high fatigue and rough surfaces which make cleaning difiicult. Still another disadvantage is that the materials used have been limited to those having inherent photoconductive insulating properties.

It is, therefore, an object of this invention to provide a photoconductive insulating material suitable for use in electrophotographic plates devoid of the above-noted disadvantages.

Another object of this invention is to provide an economical method for the preparation of photoconductive insulating materials wherein none of the required components is by itself substantially photoconductive.

Another object of this invention is to provide a photoconductive insulating material suitable for use in electrophotographic plates in both single use and reusable systems.

Yet still another object is to provide a photoconductive insulating layer for an electrophotographic plate which is substantially resistant to abrasion and has a relatively high distortion temperature.

Yet, a further object of this invention is to provide an electrophotographic plate having a wide range of useful physical properties.

A still further object of this invention is to provide photoconductive insulating layers which may be cast into the photoconductive insulating layer of xerographic plate which are easily coated on a desired substrate or combined with a conductive layer. 1 I

(A) A suitable Lewis Acid with (B) An aromatic silicon resin having the general forwherein each R is selected from the group consisting of aryl and alkyl radicals; at least one R being aryl; and n is a positive integer, at least 2.

It should be noted that neither of the above two components, (A) and (B) used to make the photoconductor of this invention is by itself photoconductive; rather, they are each nonphotoconductive.

After the above substantially nonphotoconductive Lewis acid is mixed or otherwise complexed with said substantially nonphotoconductive resinous material, a highly desirable photoconductive insulating material is obtained which may be either cast as a self-supporting layer or may be deposited on a suitable supporting substrate. Any other suitable method of preparing a photoconductive plate from the above photoconductive material may be used.

It has been found by the present invention that electron acceptor complexing may be used to render inherently nonphotoconductive electron donor type insulators photoconductive. This greatly increases the range of useful materials for electrophotography.

A Lewis Acid is any electron acceptor relative to other materials present in the system. A Lewis Acid will tend to accept electrons furnished by an electron donor (or Lewis base) in the process of forming a chemical compound or, in the present invention, a charge transfer complex.

A Lewis Acid is defined for the purposes of this invention as any electron accepting material relative to the polymer to which it is complexed.

A charge-transfer complex may be defined as a molecular complex between substantially neutral electron donor and acceptor molecules, characterized by the fact that photoexcitation produces internal electron transfer to yield a temporary excited state in which the donor is more positive and the acceptor more negative than in the ground state.

It is believed that the donor-type insulating resins of the present invention are rendered photoconductive by the formation of charge transfer complexes with electron acceptors or Lewis Acids and that these complexes, once formed, constitute the photoconductive elements of the plates.

Broadly speaking, charge transfer complexes are loose associations containing electron donors and acceptors, frequently in stoichiometric ratios, which are characterized as follows:

(A) Donor-acceptor interaction is weak in the neutral ground state, i.e. neither donor nor acceptor is appreciably perturbed by the other in the absence of photoexcitation.

(B) Donor-acceptor interaction is relatively strong in the photoexcited state, i.e. the components are at least partially ionized by photoexcitation.

(C) When the complex is formed, one or more new absorption bands appear in the near ultraviolet or visible region (wave lengths between 3200-7500 angstrom units) which are present in neither donor alone nor acceptor alone, but which are instead a property of the donoracceptor complex.

Both the intrinsic absorption bands of the donor and the charge transfer bands of the complex may be used to excite photoconductivity.

Photoconductive insulator for the purposes of this invention is defined with reference to the practical application in electrophotographic imaging. It is generally considered that any insulator may be rendered photoconductive through excitation by sutficiently intense radiation of sufficiently short wave-lengths. This statement applies generally to inorganic as well as to organic materials, including the inert binder resins used in binder plates, and the electron acceptor type activators and aromatic resins used in the present invention. However, the short wavelength radiation sensitivity is not useful in practical imaging systems because sufficiently intense sources of wavelengths below 3200 angstrom units are not available, because such radiation is damaging to the human eye and because this radiation is absorbed by glass optical systems. Accordingly, for the purposes of this application, the term photoconductive insulator includes only those materials which may be characterized as follows:

(1) They may be formed into continuous films which are capable of retaining an electrostatic charge in the absence of actinic radiation.

(2) These films are sufficiently sensitive to illumination of wavelengths longer than 3200 angstrom units to be discharged by at least one half by a total flux of at most 10 quanta/cm. of absorbed radiation.

This definition excludes the resins and Lewis Acids of our disclosure when used individually from the class of photoconductive insulators.

The aromatic silicone resins used in the present invention may be prepared in any conventional manner. For example, any of the synthesis described in Silicones by R. N. Meals and F. M. Lewis, Reinhold Publishing Corp, New York (1959), may be used.

Any suitable aromatic silicone resin may be used in the present invention. Optimum sensitivity is obtained when using phenyltrichlorosilane, diphenyldimethoxy sil'ane, methylphenyldiethoxysilane and dimethylphenyldichlorosilane in the preparation of the resin, therefore, these silane compounds are preferred. Other typical aromatic silicone resins include those prepared from diphenyltrichlorosilane, dinaphthylsilanediol, anthracenetrichlorosilane, biphenylenetrichlorosilane, fluorenetrichlorosilane and 9,9-dicarbazalolyldichlorosilane. The resin may be cross-linked for greater durability, if desired.

Any suitable Lewis Acid can be complexed withthe above-noted silicone resins to form the desired photoconductive material. While the mechanism of the complex chemical interaction involved in the present process is not completely understood, it is believed that a charge transfer complex is formed having absorption band characteristics of neither of the two components considered individually. The mixture of the two nonphotoconductive components seems tohave a synergistic effect which is much greater than additive.

Best results are obtained when using these preferred Lewis Acids: 2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a) anthracene- 7, 12-dione, 1,3,5-Jtrinitroben2ene; and 9-dicyanomethylene-2,4,7-trinitrofiuorene.

Other typical Lewis Acids include quinones, such as p-benzo-quinone, 2,5-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, chloranil, naphthoquinone-( 1,4), 2,3-dichloronaphthoquinone-(1,4), anthraquinone, Z-methylanthraquinone, l,4-dimethyl-anthraquinone, l-chloroanthraquinone, anthraquinoneZ-carboxylic acid, 1,5-dichloroanthraquinone, 1 chloro 4 nitro-anthraquinone, phenanthrenequinone, acenaphthenequinone, pyranthrenequinone. chrystenequinone, thio-naphthene-quinone, anthraquinone- 1,8-disulfonic acid and anthraquinOne-Z-aldehyde, triphthaloyl-benzene-aldehydes such as bromal, 4-nitrobenzaldehyde, 2,6-dichlorobenzaledehyde-2, ethoxy-l-naphthaldehyde, anthracene-9-aldehyde, pyr'ene-B-aldehyde, oxindole-3-aldehyde, pyridine+2,6-dialdehyde, biphenyl-4-aldehyde; organic phosphonic acids such as 4-chloro-3-nitrobenzene-phosphonic acid; nitrophenols, such as 4-nitrophenol, and picric acid; acid anhydrides, for example, acetic-anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, perylene-3,4,9,lO-tetracarboxylic acid and chrysene-2,3,S,9-tetracarboxylic anhydride, di-bromo maleic acid anhydride; metal-halides of the metals and metalloids of the groups 18, II through to group VIII of the periodical system, for example: aluminum chloride, zinc chloride, ferric chloride, tin tetrachloride (stannic chloride), arsenic trichloride, stannous chloride, antimony pentachloride, magnesium chloride, magnesium bromide, calcium bromide, calcium iodide, strontium bromide, chromic bromide, manganous chloride, cobaltous chloride, cobaltic chloride, cupric bromide, ceric chloride, thorium chloride, arsenic triiodide; boron halide compounds for example: boron trifiuoride, and boron trichloride, and ketones, such as acetophenone, benzophenone, 2-acetyl-naphthalene, benzil, benzoin, 5- benzoyl acenaphthene, biacene-dione, S-acetyI-anthracene, 9-benzoyl-anthracene, 4-(4-dimethylamino-cinnamoyl) -1- acetylbenzene, acetoacetic acid anilide, indandione-(l,3), (l-3-diketo-hydrindene), acenaphthene quinone-dichloride, anisil, 2,2-pyridil and furil.

Additional Lewis Acids are mineral acids such as the hydrogen halides, sulphuric acid and phosphoric acid; organic carboxylic acids, such as acetic acid and the substitution products thereof, monochloro-acetic acid, dichloroacetic acid, trichloro-acetic acid, phenylacetic acid, and 6-methyl-coumarinylacetic acid (4); maleic acid, cinnamic acid, benzoic acid, l-(4-diethyl-amino-benzoyl)benzene- Z-carboxylic acid, phthalic acid, and tetra-chlorophthalic acid, alpha-beta-dibromo-beta-formyl-acrylic acid (mucobromic acid), dibromo-maleic acid, 2-bromo-benzoic acid, gallic acid, 3-nitro-2-hydroxyl-l-benzoic acid, Z-nitro phenoxy-acetic acid, 2-nitro-benzoic acid, 3-nitro-benzoic acid, 4-nitro-benzoic acid, 3-nitro-4-ethoxy-benzoic acid, 2-chloro-4-nitro-1-benzoic acid, 2-chloro-4-nitro-l-benzoic acid,

3-nitro-4-'nethoxy-benzoic acid, 4-nitro-l-methyl-benzoic' acid, Z-chloro-S-nitro-l-benzoic acid, 3-chloro6-nitro-1- benzoic acid, 4-chloro-3-nitro-l-benzoic acid, 5-chloro-3- nitro-2-hydroxy-benzoic acid, 4-chloro-2-hydroxybenzoic acid, 2,4-dinitro-1-benzoic acid, 2-bromo-5-nitro-benzoic acid, 4-chlorophenyl-acetic acid, 2-chloro-cinnamic acid, Z-cyano-cinnamic acid, 2,4-dichlorobenzoic acid, 3,5-dinitro-benzoic, 3,5-dinitrosalicylic acid, malcnic acid, mucic acid, acetosalicylic acid, benzilic acid, butane-tetracarboxylic acid, citric acid, cyano-acetic acid, cyclo-hexane-dicarboxylic acid, cyclo-hexene-carboxylic acid, 9,10-dichloro-stearic acid, fumaric acid, itaconic acid, levulinic acid (levulic acid), malic acid, succinic acid, alpha-bromostearic acid, citraconic acid, dibromo-succinic acid, pyrene- 2,3,7,8-tetra-carboxylic acid, tartaric acid; organic sulphonic acids such as 4-toluene sulphonic acid, and benzene sulphonic acids, 2,4-dinitro l-methyl benzene dsulphonic acid 2,6-dinitro+l-hydroxy-benzene-4-sulphonic acid, 2- nitro-l-hydroxy-benzene-4-sulphonic acid, 4-nitro-1-hydroxy-benzene-5-sulphonic acid, 6-nitro-4-methyl-1-hydroxy-benzene-2-sulphonic acid, 4-chloro-l-hydroxy-benzene-3-sulphonic acid, 2-chloro-3-nitro-l-methyl-benzene- 5-sulph0nic acid and 2-chloro-l-methyl-benzenet-sulphonic acid.

The following examples will further define the present invention. Parts and percentages are by Weight unless otherwise indicated. The examples below should be considered to illustrate various preferred embodiments of the present invention.

In each example, the substance to be evaluated is coated from solution by suitable means onto a conductive substrate and dried. The coated plate is connected to ground and the layer is electrically charged in the dark by a corona discharge device (as described by Carlson in US. Patent 2,588,699) to saturation potential using a needlepoint scorotron powered by a high voltage power supply manufactured by High Volt Power Supply Company, Condenser Products Division, Model PS101M operat ing at 7 kilovolts while maintaining the grid potential at 0.9 kilovolt using a Kepco, Incorporated regulated D.C. supply (0.1500 volts). Charging time is seconds.

The electrostatic potential due to the charge is then measured with a transparent electrometer probe Without touching the layer or affecting the charge. The signal generated in the probe by the charged layer is amplified and fed into a Mosely Autograf recorder, Model 680. The graph directly plotted by the recorder indicates the magnitude of the charge on the layer and rate of decay of the charge with time. After a period of about 15 seconds, the layer is illuminated by shining light onto the layer through the transparent probe using an American Optical Spence microscope illuminator having a GE. 1493 medical type incandescent lamp operating at 2800 K. color temperature. The illumination level is measured with a Weston Illumination Meter, Model No. 756, and is recorded in the table. The light discharge rate is measured for a period of 15 seconds or until a steady residual potential is reached. The illumination level in each example is about 60 foot-candles.

The numerical difference in the rate of discharge of the charge on the layer with time in the light minus the rate of discharge of the charge on the layer in the dark is considered to be a measure of the light sensitivity of the layer.

A practical test is also made on each material under study which shows photoconductivity. An electrophotographic image is produced by charging the material by corona discharge, exposing the material by projection to a light-and-shadow image and cascade developing the electrostatic latent image by the method described by Walkup in US. Patent 2,618,551. Details EXAMPLE I About 14 parts of an SR82 (a methylphenyl silicone resin available from General Electric) solution consisting of about 60% solids in xylene is mixed with about 40 parts toluene and about parts cyclohexanone. To this solution is added about 2 parts of 2,4,7-trinitro-9-fluorenone. The solution is coated to about 5 microns thickness onto a 5 mil aluminum plate (type 1145-Hl9 sold by Aluminum Company of America) by flow coating. The coating is dried, then cured for about minutes at about 200 C.

A portion of this plate is negatively charged to about 250 volts by means of a corona discharge in the manner described by Carlson in US. Patent 2,588,699. The charged plate is then exposed for about 15 seconds by projection using a Simmons Omega D3 Enlarger equipped with an f4.5 lens and a tungsten light source operating at 2950 K. color temperature. The light exposure is about 500 footcandle-seconds. The plate is then cascade developed. The developed image is electrostatically transferred to a receiving sheet in the manner described by Schaffert in US Patent 2,576,047. The image on the receiving sheet corresponds to the original projected image.

The plate is cleaned of residual toner and is reused as by the above-described process.

Another portion of the above plate is electrometered as previously described and the results are tabulated in Table 1.

EXAMPLE II A coating solution is prepared as described in Example I above, except that about 0.1 part of Brilliant Green Special Dye, a triphenyl methane type dye, Color Index 7 No. 662, available from Allied Chemical Corporation, is added to the solution. The solution is applied onto an aluminum plate as before and cured in an oven for about 30 minutes at about 200 C.

The plate is charged, exposed, and developed as in Example I and the image is fused onto the plate surface. The image developed on. the plate corresponds to the original.

Another portion of the above plate is electrometered as previously described and the results tabulated in Table I. As indicated in Table I, the spectral sensitivity and photosensitivity of the plate is improved by the addition of sensitizing dyes.

EXAMPLE HI A coating solution is prepared as described in Example I except that the 2,4,7-trinitrofluorenone is not included. The solution is applied onto an aluminum plate as be fore and cured in an oven for about 30 minutes at about 200 C. The plate is charged, exposed and developed as in Example I. No image is observed on the plate. Another portion of the plate is electrometered and the results are tabulated in Table I. As indicated by the table, the plate without the Lewis acid has no photosensitivity.

EXAMPLE IV About 8 parts of Dow R5061A, a diphenyl type silicone resin, available from Dow Corning, is dissolved in a mixture of about 40 parts toluene and about 20 parts cyclohexanone. To this solution is added about 2 parts 2,4,7-trinitrofiuorenone. The solution is applied onto an aluminum plate to a thickness of about 5 microns by flow coating. The coating is air-dried and then cured at about 200 C. for about 30 minutes.

Another portion of the above plate is electrometered as previously described and the results tabulated in Example I. As can be seen from the table, the plate without the Lewis acid has no photosensitivity.

EXAMPLE VII About 2 part of Lucite 2042, an ethyl methacrylate resin manufactured by E. I. du Pont de Nemours and 5 this resin, when used alone, has no photosensitivity.

A portion of the above plate is negatively charged to about 300 volts by means of corona discharge and exposed for about 15 seconds by projection using a Simmons Omega D3 Enlarger equipped with an f4.5 lens and a tungsten light source operating at about 2950 K. color temperature. The total exposure is about 500 foot-candle seconds. The plate is then cascade developed, the image is electrostatically transferred to a receiving sheet and is fused. The image on the receiving sheet corresponds to the original projected image. The plate is cleaned of residual toner and is reused by the above described process.

Another portion of the above plate is electrometered as previously described and the results are given in Table I. As indicated by the table, this plate has good photosensitivity, with especially high photosensitivity with negative charging.

EXAMPLE V A coating solution is prepared as described in Example IV 'above, except that about 0.1 part of Brilliant Green Special Dye, CI. No. 662, is added to this solution. The mixture is stirred until a solution is achieved and is coated onto an aluminum plate and cured.

The plate is charged, exposed, and developed as in Example IV above and the image is fused onto the plate surface. The irnage developed on the plate corresponds to the original projected image.

Another portion of the above plate is electrometered as previously described and the results tabulated in Table I. As can be seen from the table, the addition of the sensitizing dye produces a very significant increase in the photosensitivity of the plate.

EXAMPLE VI A coating solution is prepared as in Example IV above, except that the 2,4,7-trinitrofluorenone is omitted from thecoating solution. The mixture is coated onto an aluminum substrate and cured. The plate is charged, exposed, and developed as in Example IV above. No image is produced on this plate.

EXAMPLE VIII About 0.2 part of 2,4,7-trinitrofluorenone is added to the resin coating solution prepared as described in Example VII above. This solution is applied onto an aluminum sheet to a thickness of about 5 microns and dried. The plate is electrometered and the results are tabulated. See Table I.

This plate indicates that the addition of a Lewis acid to an inert resin does not result in photosensitive response. This indicates thatLewis acids alone are not photosensitive.

EXAMPLE IX A coating solution is prepared as described in Example IV except that about 2 parts of 9-dicyanomethylene-2,4,7- trinitrofluorene is added in place of the 2,4,7-trinitrofluorenone. The mixture is stirred until solution is achieved. The solution is applied onto an aluminum plate as before and cured.

The plate is charged, exposed, and developed and the image is fused onto the plate surface. The image developed on the plate corresponds to the original projected image.

Another portion of the above plate is electrometered as previously described and the results tabulated in Table I. As seen from the table, the plate has comparable sensitivity when used with a different Lewis Acid.

TABLE I Light Dark Residual Sensitivity Imtral d1sehar e discharge potential (volts/ Example (volts) (volts; (volts! after 15 f. 0. sec.)

sec.) sec.) sec. (v.)

III 3. 6 3. 6 90 0 4. 7 4. 7 I10 0 V +240 58. 8 2. 3 115 94. 2 210 64. 0 Trace 100 106. 7

VII +460 4. 4 4. 4 394 0 -500 5. 3 5. 3 420 0 VIII +420 0. 0 0.0 420 0 450 0. 0 0. 0 450 0 Although specific materials and conditions were set forth in the above examples, these were merely illustrative of the present invention. Various other compositions, such as the typical materials listed above and various conditions, where suitable, may be substituted for those given in the examples with similar results. For example, the aromatic silicone resin may be in the form of a continuous coating, as in the above examples, or in the form of a sponge or foam-like layer. The photoconductive composition of this invention may have other materials mixed therewith to enhance, sensitize, synergize' or otherwise modify the photoconductive properties of the composition.

Many other modifications of the present invention will occur to those skilled in the art upon a reading of this disclosure. These are intended to be encompassed within the spirit of this invention.

What is claimed is:

1. A photoconductive charge transfer complex material comprising a mixture of a Lewis acid and an aromatic silicone resin, said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

2. The photoconductive material of claim 1 comprising from about 1 to about 100 parts of said resin for one part Lewis acid.

3. The photoconductive charge transfer complex material of claim 1 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fiuorenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a)anthracene-ZlZ-diOne, 1,3,5-trinitrobenzene, and 9-dicyanomethylene-2,4,7-trinitrofluor ene.

4. The photoconductive charge transfer complex material of claim 3 wherein said Lewis acid is 2,4,7-trinitro- 9-fluorenone.

5. A photoconductive charge transfer complex material comprising a mixture of a Lewis acid and an aromatic silicone resin having the general formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals, at least one R being an aryl radical; and n is a positive integer having a value of at least two; said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

6. The photoconductive material of claim 5 comprising from about 1 to 100 parts by weight of said resin for every one part Lewis acid.

7. A process for producing a photoconductive charge transfer complex material which comprises mixing an arcmatic silicone resin and a Lewis acid, said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

8. The process as disclosed in claim 7 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fiuorenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a)anthracene-7,l2-di0ne, 1,3,5-trinitrobenzene, and 9-dicyanomethylene2,4,7-trinitrofluorene.

9. The process as disclosed in claim 8 wherein said Lewis acid is 2,4,7-trinitro-9-fluorenone.

10. A process for the preparation of a photoconductive charge transfer complex material comprising mixing a Lewis acid and an aromatic silicone resin having the general formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals, at least one R being an aryl radical; and n is a positive integer having a value of at least 2; said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

11. The process of claim 10 wherein from about 1 to about parts by weight of resin are mixed with every one part of Lewis acid.

12. An electrophotographic plate comprising a support substrate having fixed to the surface thereof a photoconductive charge transfer complex material comprising a mixture of a Lewis acid and an aromatic silicone resin, said photoconductive charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units.

13. The electrophotographic plate of claim 12 wherein said aromatic silicone resin has the general formula:

[0SiO-Sii-] wherein:

each R is selected from the group consisting of aryl and alkyl radicals, at least one R being an aryl radical; and n is a positive integer having a value of at least 2.

14. The electrophotographic plate of claim 13 wherein said charge transfer complex material comprises from about 1 to about 100 parts by weight of said resin for every one part of Lewis acid.

15. The electrophotographic plate of claim 12 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a)- anthracene-7,12-dione, 1,3,5-trinitrobenzene, and 9-dicyanomethylene-Z,4,7-trinitrofluorene.

16. The plate as disclosed in claim 15 wherein said Lewis acid comprises 2,4,7-trinitro-9-flu0renone.

17. A process for forming a latent electrostatic charge pattern which comprises uniformly electrostatically charging a photoconductive layer, said layer comprising a photoconductive charge transfer complex material comprising a mixture of a Lewis acid and an aromatic silicone resin, said charge transfer complex material having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units, and exposing said photoconductive layer to a pattern of activating electromagnetic radiation to produce said charge pattern.

18. The process as disclosed in claim 17 wherein said aromatic silicone resin comprises the general formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals, at least one R being an aryl radical; and n is a positive integer having a value of at least 2.

19. The process as disclosed in claim 18 wherein said Lewis acid is selected from at least one member of the group consisting of 2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil, picric acid, benz(a)anthracene-7,l2-dione, 1,3,5-trinitrobenzene, and 9-dicyanomethylene-2,4,7-trinitrofiuorene.

20. The process as disclosed in claim 19 wherein said Lewis acid comprises 2,4,7-trinitro-9-fiuorenone.

21. An electrophotographic imaging process which comprises forming an electrostatic latent image on the surface of a photoconductive layer, said layer comprising a photoconductive charge transfer complex which comprises a mixture of a Lewis acid and an aromatic silicone resin, said photoconductive charge transfer complex having at least one new absorption band within a range of from about 3200 to about 7500 angstrom units and developing said image with electroscopic marking particles.

22. The process as disclosed in claim 21 whereby the steps of forming an electrostatic latent image and developing said image are repeated at least more than one time.

11 w .12 23. The process as disclosed in claim-21 wherein said Lewis acid i s selected from at least one member of the aromatic'silicone resin has the general formula: group consisting of 2,4,7-trinitrofluorenone, tetrachloro- I phthalic anhydride, chloranil, picrie acid, benz(a)anthra- R R I cene-7,l2-dione, 1,3,5-trinitrobenzene and 9-dicyanometh- [O O l 1 U 5 ylene-Z,4,7-trinitrofiuorene..

I I References Cited UNITED STATES PATENTS wherein:

ch R is selected from the group consisting of r l 3,287,120 11/1966 Hoegl 96-1.5

and alkyl radicals, at least one R being an aryl radical; 10 JOSEPH R LIBERM AN Primary Examiner and n is a positive integer having a value of-at least 2. 24. The process as disclosed in claim 23 wherein said E-VAN HORN, Assistant Examiner-