US3711280A - Metallocene photoconductors used in electrophotography - Google Patents

Abstract

A CLASS OF METALLOCENE COMPOUNDS ARE DISCLOSED WHICH EXHIBIT PHOTOCONDUCTIVE PROPERTIES USEFUL IN ELECTROPHOTOGRAPHY.

Description

United States Patent 3,711,280 METALLOCENE PHOTOCONDUCTORS USED IN ELECTROPHOTOGRAPHY Arthur L. Johnson, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Feb. 17, 1971, Ser. No. 116,208 Int. Cl. G03g 5/06 U.S. Cl. 961.6 6 Claims ABSTRACT OF THE DISCLOSURE A class of metallocene compounds are disclosed which exhibit photoconductive properties useful in electrophotography.

This invention relates to electrophotography and more particularly to a novel compound and to a class of photoconductive materials and the compositions and elements produced therefrom.

Electrophotographic imaging processes and techniques are based on the discovery that certain materials which are normally insulating become conductive during exposure to electromagnetic radiation of certain wave lengths after being electrically charged. Such materials, which may be either organic or inorganic, are termed photoconductors. They are conveniently formed into usable imageforming elements by coating a layer of the photoconductive composition, together with an electrically insulating resinous binder where necessary or desirable, onto a suitable support. Such an element will accept and retain an electrostatic charge in the absence of actinic radiation. In use, the surface of the element is charged in the dark to a uniform potential and exposed to an imagewise pattern of actirnc radiation, which selectively reduces the surface potential to produce a charge pattern corresponding to the imagewise radiation pattern. The resultant charge pattern or electrostatic latent image may be developed by contacting it with suitable charged marking particles which adhere in accordance with the charge pattern, or it may be transferred to another insulating surface upon which it is developed. The particles may then be fused or fixed to the surface by known means such as heat or solvent vapor, or they may be transferred to another surface to which they may similarly be fixed, to produce a permanent reproduction of the original radiation pattern.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in pre'sent-day document copying applications.

Since the introduction of electrophotography, a great many organic compounds have been found to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions. As a result, a large number of organic compounds have been known to possess some degree of photoconductivity. Typical of these organic photoconductors are the triphenylamines and the triarylmethane leuco bases. Optically clear photoconductor-containing elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements can be exposed through a transparent base if desired, thereby providing flexibility in equipment design. Such compositions, when coated as a film or layer on a suitable support, also yield an element which is reusable;

that is, it can be used to form subsequent images after Patented Jan. 16, .1973

residual toner from prior images has been removed by transfer and/ or cleaning. Thus far, the selection of various compounds for incorporation into photoconductive compositions to form electrophotographic layers has proceeded on a compound-by-compound basis. Nothing as yet has been discovered from the la ge number of different photoconductive substances tested which permits effective prediction, and therefore selection of the particular compounds exhibiting the desired electrophotographic properties.

It is, therefore, an object of this invention to provide a novel class of photoconductive compounds.

It is another object of this invention to provide a novel class of photoconductors having useful photosensitivity when electrically charged.

It is yet another object of this invention to provide novel photoconductor-containing compositions which exhibit useful electrical speeds when positively or negatively charged.

It is still another object of this invention to provide novel transparent electrophotographic elements having useful electrophotographic speeds.

It is a further object of this invention to provide an improved process utilizing the novel photoconductors described herein.

These and other objects of this invention are accomplished with electrophotographic elements having coated thereon photoconductive compositions containing as photoconductors metallocenes derived from first row transition metals.

The metals from which these metallocenes are derived are those in the first row of Groups IVb, Vb, VII), VIII) and VIII in accordance with the Periodic Table of the Elements (Handbook of Chemistry and Physics, 38th edition, pp. 394-) and include titanium, vanadium, chromium, manganese, iron, cobalt and nickel. Similarly, vinyl polymers containing the metallocenes 3J8 side chains can be used. The metallocene can be substituted on one or both of its aromatic nuclei with a wide variety of substituents, such as those hereinafter set forth.

Illustrative photoconductors of this invention are represented by the following structure:

M represents an atom of titanium, vanadium, chromium,

manganese, iron, cobalt or nickel;

R represents any of the following:

(1) An aliphatic group having 1 to 18 carbon atoms, e.g., methyl, ethyl, propyl, butyl, isobutyl, octyl, dodecyl, etc., including a substituted alkyl group having 1 to 18 carbon atoms, such as:

(h) nitroalkyl, e.g., nitrobutyl, nitroethyl,

nitropentyl, etc.,

(i) cyanoalkyl, e.g., cyanopropyl, cyanobutyl,

cyanoethyl, etc.,

(j) haloalkyl, e.g., chloromethyl, bromopentyl,

chlorooctyl, etc.,

' (k) alkyl substituted with an acyl group having the formula wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl, etc., lower alkyl having 1 to 8 carbon atoms, e.g., methyl, ethyl, propyl, etc., amino, including substituted amino, e.g., diloweralkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g., butoxy, methoxy, etc., aryloxy, e.g., phenoxy, naphthoxy, etc.;

(2) An aryl group, e.g., phenyl, naphthyl, anthryl, fiuorenyl, etc., including a substituted aryl group such as wherein R is hydroxy, halogen, e.g., chlorine, hydrogen, aryl, e.g., phenyl, naphthyl, etc., amino, including substituted amino, e.g., diloweralkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g., butoxy, methoxy, etc., aryloxy, e.g., phenoxy, naphthoxy, etc., lower alkyl having 1 to ,8 carbon atoms, e.g., methyl, ethyl, propyl, butyl, etc.,

(1) alkaryl, e.g., tolyl, ethylphenyl, propylnaththyl, etc.

(3) a cycloalkyl group having 4 to 8 carbon atoms in the cyclic nucleus, e.g., cyclobutyl, cyclohexyl, cyclopentyl, etc., including a substituted cycloalkyl group such (a) alkoxycycloalkyl, e.g., ethoxycyclohexyl, methoxycyclobutyl, propoxycyclohexyl, etc., (b) aryloxycycloalkyl, e.g., iphenoxycyclohexyl, naphthoxycyclohexyl, phenoxycyclopentyl, etc, (c) aminocycloalkyl, e.g., aminocyclobutyl, aminocyclohexyl, aminocyclopentyl, etc., (d) hydroxycycloalkyl, e.g., hydroxycyclohexyl, hy-

droxycyclopentyl, hydroxycyclobutyl, etc., (e) arylcycloalkyl, e.g., phenylcyclohexyl, phenylcyclobutyl, etc., (f) alkylaminocycloalkyl, e.g., rnethylaminocyclohcxyl, methylaminocyclopentyl, etc., and also including dialkyla-minocycloalkyl, e.g., diethylamiuocyclohexyl,

dimethylaminocyclobutyl, dipropylarninocyclooctyl, etc.,

(g) arylarninocycloalkyl, e.g., phenylarninocyclohexyl, diphenylaminocyclohexyl, N-pheuyl-N-ethylaminocyclopentyl, N-phenyl-N-methylaminocyclohexyl, naphthylarninocyclopentyl, etc.,

(h) nitrocycloalkyl, e.g., nitrocyclobutyl, nitrocyclohexyl, nitrocyclopentyl, etc.,

(i) cyanocycloalkyl, e.g., cyanocyclohexyl, cyanocyclobutyl, cyanocyclopentyl, etc.,

(j) halocycloalkyl, e.g., chlorocyclohexyl, bromocyclopentyl, chlorocyclooctyl, etc.,

(k) cycloalkyl-substituted with an acyl group having the formula:

wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naphthyl, etc., amino, including substituted amino, cg, diloweralkylamino, lower alkoxy having 1 to 8 carbon atoms, e.g., butoxy, methoxy, etc., aryloxy, e.g., phenoxy, naphthoxy, etc., lower alkyl having 1 to 8 carbon atoms, e.g., methyl, ethyl, propyl, butyl, etc.;

(4) a heterocyclic group including a substituted heterocyclic group containing 5 to 6 members in the hetero nucleus and including at least one sulfur, selenium, oxygen or nitrogen atom such as a thienyl group, e.g., a benzothienyl group, a pyrrolyl group, e.g., a nitropyrrolyl group, a pyrrolidinyl group, e.g., a prolyl group, a pyr rolinyl group, a benzopyrrolyl group, e.g., an indolyl group, a carbazolyl group, a furyl group, e.g., a furfuryl group, a benzofuryl group, etc., a pyridyl group, e.g., a halopyridyl group, an aminopyridyl group, a hydroxypyridyl group, an alkylpyridyl group, a nitropyridyl group, etc., a piperidyl group, a quinolyl group, an acridinyl group, a pyranyl group, a benzopyranyl group, a pyrazolyl group, an oxaz'olyl group, a thiazolyl group, etc.;

(5) hydrogen;

(6) alkoxy having 1 to 18 carbon atoms, e.g,, methoxy, ethoxy, propoxy, butoxy, etc.',

(7) aryloxy, e.g., phenoxy, naphthoxy, etc.;

(8) vinyl;

(9) amino having the formula:

wherein R and R are the same or difierent including lower alkyl having 1 to about 8 carbon atoms such as methyl, isopropyl, hexyl, octyl, etc., and aryl such as phenyl, naphthyl, etc.;

(10) nitro; and

(11) halogen such as chlorine, bromine, fluorine or iodine; and Z represents any of the following:

is an integer having a value equal to the valence of. the metal M minus 1;

(7) a group corresponding to the formula:

(8) a group corresponding to the formula:

(9) a group corresponding to the formula:

(10) a group corresponding to the formula:

and

and

wherein M and Z have the same meanings hereinabove set forth, A is a nitrogen atom or a carbon atom, X represents the atoms required to complete a monoor polycyclic aromatic nucleus which may be carbocyclic or heterocyclic having such hetero atoms as oxygen, sulfur, nitrogen, etc., and containing up to 19 atoms. The symbol n is a positive integer having a value of about 3 to 1000 and n and n are positive integers each having a value of about 1 to 999 with 3n +n 1000 Typical of such aromatic nuclei are carbazole, indole, quinoline, quinoxaline, benzofuran, dibenzofuran, benzothiophene, dibenzothiophene, pyrazole, fluorene, anthracene and the like. Additional aromatic nuclei are those derived from organometallic compounds having at least one aminoaryl substituent attached to a Group IIIa, Group IVa or Group Va metal atom, as described in copending Goldman and Johnson U.S. Ser. No. 650,664, filed July 3, 1967 now U.S. Pat. No. 3,647,429, issued Mar. 7, 1972; and Johnson U.S. Ser. No. 755,711, filed Aug. 28, 1968 now U.S. Pat. No. 3,607,257, issued Sept. 21, 1971.

The preferred substituents for R include hydrogen atoms, halogen atoms, lower alkyl groups having from 1 to about 8 carbon atoms, aryl groups and amino groups, while the preferred substituents for Z include diarylamino, dialkylaminopheuyl, diarylaminophenyl, and bis- (dialkylaminophenyl)methylene.

Preferred metallocene photoconductors according to the invention are ferrocenes corresponding to the general structure:

wherein R and R are amino substituted aryl groups, said aryl grups preferably being substituted in the para position. The particularly preferred photoconductor is ferrocenylbis(2-methyl 4 diethylaminophenyl)methane, corresponding to the formula:

I Me

Some typical metallocene photoconductors according to the invention include the following:

( l l,l-bis(p-diphenylaminophenyl)ferrocene (2) p-diphenylaminophenylferrocene (3 p-diethylaminophenyltitanocene (4) 1- [tris (p-diethylaminophenyl) germyl] cobaltocene (5) diethylaminonickelocene (6) poly(vinylferrocene-co-3-bromo-N-vinylcarbazole) (7) poly (vinylferrocene-co-4-vinyl-4',4"-dimethyltri'phenylamine) The monomeric photoconductors of this invention are generally prepared by reacting in an inert atmosphere the aldehyde of the ferrocene or analogous metallocene with the desired aromatic compound in solution. Separation and purification are accomplished by conventional methods. The polymeric photoconductors of the invention are prepared by first making the vinyl monomers containing the photoconductive groups and then polymerizing in a conventional manner.

Electrophotographic elements of the invention can be prepared with the photoconducting compounds of the invention in the usual manner, i.e., by blending a dispersion or solution of a photoconductive compound together with a. binder, when necessary or desirable, and coating or forming a self-supporting layer with the photoconductorcontaining material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art can be combined with the present photoconductors. In addition, supplemental matcrials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials.

The photoconductive layers of the invention can also be sensitized by the addition of effective amounts of sensitizing compounds to exhibit improved electrophotosensitivity. Sensitizing compounds useful with the photoconductive compounds of the present invention can be selected from a wide variety of materials, including such materials as pyrylium dye salts including thiapyrylium dye salts and selenapyrylium dye salts disclosed in Vanv Allan et al. U.S. Pat. 3,250,615, issued May 10, 1966; fluorenes, such as 7,12-dioxo 13 dibenzo(a,h)fiuorene, 5,10 dioxo 4a,1l diabenzo(b)fluorene, 3,13-dioxo-7- oxadibenzo(b,g)fluorene, and the like; aromatic nitro compounds of the kinds described in U.S. Pat. 2,610,120 by Minsk, issued Sept. 9, 1952; anthrones like those disclosed in US. Pat. 2,670,284 by Zvanut, issued Feb. 23, 1954; quinones, U.S. Pat. 2,670,286 by Minsk, issued Feb. 23, 1954; benzophenones, U.S. Pat. 2,670,287 by Minsk, issued Feb. 23, 1954; thiazoles, U.S. Pat. 2,732,- 301 by Robertson, issued Jan. 24, 1956; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid,

and salicylic acid; sulfoinic and phosphoric acids; and various dyes, such as cyanine (including carbocyanine), merocyanine, diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes and the like and mixtures thereof. The sensitizers preferred for use with the compounds of this invention are selected from pyrylium salts including selenapyrylium salts and thiapyrylium salts, and cyanine dyes including carbocyanine dyes.

Where a sensitizing compound is employed with the binder and organic photoconductor to form a sensitized electrophotographic element, it is the normal practice to mix a suitable amount of the sensitizing compound with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed in the coated element. Other methods of incorporating the sensitizer or the effect of the sensitizer may, however, be employed consistent with the practice of this invention. In preparing the photoconductive layers, no sensitizing compound is required to give photoconductivity in the layers which contain the photoconducting substances, therefore, no sensitizer is required in a particular photoconductive layer. However, since relatively minor amounts of sensitizing compound give substantial improvement in speed of such layers, the use of a sensitizer is preferred. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the Weight of the film-forming coating composition. Normally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.

Preferred binders for use in preparing the present photoconductive layers are film-forming, hydrophobic polymeric binders having fairly high dielectric strength which are good electrically insulating, film-forming vehicles. Materials of this type comprise styrene-butadiene compolymers; silicone resins; styrene-alkyd resins; siliconealkyd resins; soya-alkyd resins; poly(vinyl chloride); poly- (vinylidene chloride); vinylidene chloride-vinyl chloride copolymers; vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(rnethylmethacrylate), poly(n-butylmethacrylate), poly(isobutylmethacrylate), etc; polystyrene; nitrated polystyrene; polymethylstyrene; polyvinyl toluene-styrene copolymers; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenolformaldehyde resins; ketone resins; polyamides; polycarbonate; polythiocarbonates; poly(ethyleneglycol co bis hydroxyethoxyphenyl) propane terephthalate; copolyrners of vinyl haloarylates and vinyl acetate such as poly(vinyl-mbromobenzoate-co-vinylacetate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in US. Pats. 2,361,019 by Gerhart, issued Oct. 24, 1944 and 2,258,423 by Rust, issued Oct. 7, 1941. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trademarks as Geon 222, Vitel PE-101, Cymac, Piccopale 100, Saran F-220, Lexan 105 and Lexan 145. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents useful for preparing coating compositions with the photoconductors of the present invention can include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; Z-butanone; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, and the like; ethers, such as tetrahydrofuran and the like, or mixtures of such solvents can advantageously be employed in the practice of this invention.

In preparing the coating compositions utilizing the 'photoconductors disclosed herein, useful results are obtained where the photoconductive substance is present in an amount equal to at least about 1 weight percent of the coating composition. The upper limit in the amount of photoconductive material present can be Widely varied in accordance with usual practice. It is normally required that the photoconductive material be present in an amount ranging from about 1 Weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred Weight range for the photoconductive material in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a wet coating thickness in the range of about 25 microns to about 500 microns is useful in the practice of the invention A preferred range of coating thickness is from about 50 microns to about microns before drying although such thicknesses can vary Widely depending on the particular application desired for the electrophotographic element.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of the electrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates; metal foils, such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, Zinc, brass, and galvanized plates; vapor deposited metal layers such as silver, nickel or aluminum on conventional film supports such as cellulose acetate, poly- (ethylene terephthalate), polystyrene and the like conducting supports.

An especially useful conducting support can be repared by coating a transparent film support material such as poly(ethylene terephthalate) with a layer containing a semiconductor. A suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of a maleic anhydride-vinyl acetate copolyrner, cuprous iodide and the like. Such conductive layers and methods for their optimum preparation and use are disclosed in US. 3,007,901 by Minsk, issued Nov. 11, 1961, 3,245,833 by Trevoy, issued Apr. 12, 1966 and 3,262,807 by Sterman at al., issued July 26, 1966.

The compositions of the present invention can be employed in photocond-uctive elements useful in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element held in the dark, is given a blanket electrostatic charge by placing it under a corona discharge to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as, for example, by a contact-printing technique, or by lens projection of an image, or reflex or bireflex technique and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the light-struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area.

The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charge or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density. The developing electrostatically responsive particles can be in the form of a dust, or powder and generally comprise a pigment in a resinous carrier called a toner. A preferred method of applying such a toner to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S. patents: 2,786,439 by Young, issued Mar. 26, 1957; 2,786,440 by Giairno, issued Mar. 26, 1957; 2,786,441 by Young, issued Mar. 26, 1957; and 2,874,063 by Greig, issued Feb. 17, 1959. Liquid development of the latent electrostatic image may also be used. In liquid development, the developing particles are carried to the imagebearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. 2,907,674 by Metcalfe et al., issued Oct. 6, 1959. In dry developing processes, the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the charge image or powder image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after developing and fusing or fusing, respectively. Techniques of the type indicated are well known in the art and have been described in the literature such as in RCA 'Review, volume (1954), pages 469- 484.

The compositions of the present invention can be used in electrophotographic elements having many structural variations. For example, the photoconductive composition can be coated in the form of single layers or multiple layers on a suitable opaque or transparent conducting support. Likewise, the layers can be contiguous or spaced having layers of insulating material or other photoconductive material between layers or overcoated or interposed between the photoconductive layer or sensitizing layer and the conducting layer. It is also possible to adjust the position of the support and the conducting layer by placing a photoconductor layer over a support and coating the exposed face of the support or the exposed or overcoated face of the photoconductor with a conducting layer. Configurations differing from those contained in the example can be useful or even preferred for the same or different application for the electrophotographic element.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 Preparation of ferrocenyl-bis(2-methyl- 4-diethylaminophenyl methane A solution of 10.7 grams (0.05 mole) of ferrocene aldehyde, 16.3 grams (0.10 mole) of N,N-diethyl-m-toluidine, 3 grams (0.05 mole) of urea and 4.15 ml. (0.05 mole) of concentrated hydrochloric acid in ml. of methanol is heated under reflux in a nitrogen atmosphere for 18 hours. The mixture is allowed to cool to room temperature (25 C.), after which the solution is stirred in 2.5 l. of ice water. The resulting solid is filtered, washed with water, and dried in air at room temperature. There results a 14. 6 gram yield of yellow solid product having a M.P. of 130'136.5 C. The material is recrystallized from 700 ml. of absolute alcohol to obtain 8.8 grams of reddish-brown crystalline solid having a M.P. 148-15 1 C. The structure of the compound is confirmed by mass spectroscopy.

Analysis.--Calcd for C H FeN (percent): C, 75.8; H, 8.0; Fe, 10.7; N, 5.4. Found (percent): C, 75.9; H, 8.0; Fe, 10.3; N, 5.5.

10 EXAMPLE 2 The ferrocene compound prepared as in Example 1 is incorporated into a coating dope having the following composition.

Organic photoconductor g 0.25 Polymeric binder g 1.0 Sensitizer g 0.0 1 Dichloromethane ml 7.2

Po1y[4,4' isopropylidenebis(phenyleneoxyethylene) coethylene terephthalate]. The resulting composition is coated at a wet thickness of microns onto a poly(ethylene terephthalate) film support bearing a conducting layer comprising metallic nickel vacuum deposited to an optical density of 0.04. The resultant electrophotographic element is charged under a positive or negative corona source until the surface potential, as measured by an electrometer probe reaches about 600 volts. It is then subjected to exposure from behind a stepped density gray scale to a 3000' K. tungsten source. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V to some lower potential, V, whose exact value depends on the actual amount of exposure received by the areas. The results of the measurements are plotted on a graph of surface potential V vs. log exposure for each step. The speed is the numerical expression of 10 multiplied by the reciprocal of the exposure required to reduce the 600 volt charged surface potential by 100 volts. The speed of the element thus produced is 34 when charged positively and 57 when charged negatively. The speed of a control element containing no photoconductor is 22 when charged positively and 40 when charged negatively. The sensitizer in each case is 2,6-bis(4-ethylphenyl) 4 (4-n-amyloxyphenyl) thiapyrylium perchlorate. Similar improvements in speed are obtained when the sensitizer is Rhodamine B (CI. 45170) or 4-(n-butylamino)-2(4-methoxyphenyl)-benzo [b] pyrylium perchlorate.

v EXAMPLE 3 A photoconductor-containing coating composition is made which contains the photoconductor of Example 1 together with other components as listed below:

Polymeric binder poly(4,4-isopropylidenediphenyl ene carbonate) 0.25 Organic photoconductor 0.25 Sensitizer -D solution 4.5 Aggregate solution 7.7

Sensitizer D solution contains 0.0029 gram of the dye 4 (4 dimethylaminophenyl)-2, fi-diphenylthiapyrylium perchlorate per milliliter of dichloromethane. The aggregate solution is made by combining 3.92 grams of the polycarbonate listed in the table above with 0.08 gram of Sensitizer D in 26.8 ml. of dichloromethane and subjecting the solution to high-speed shearing for several hours according to the procedure of copending Gramza application U.S. Ser. No. 821,513, filed May 2, 1969, entitled Method for the Preparation of Photoconductive Compositions, now U.S. Pat. No. 3,615,413, issued Oct. 26, 1971. The coating composition is then made by mixing the ingredients with moderate stirring for about one-half hour at room temperature. The resultant composition is coated at a wet thickness of 150 microns onto a piece of the support employed in Example 2 in the manner described there, and similarly dried to form a usable electrophotographic element. The element is tested as described in Example 2, except that the speed is measured at a point at 100 volts above the zero volt base line with both positive and negative charging. The element of this example has a speed as thus determined of when charged positively, compared to a speed of 25 for a control element identically prepared except that the photoconductor of the invention is omitted. When charged negatively, the

wherein R and R are amino substituted aryl groups.

2. An electrophotographic element as described in claim 1 wherein the ferrocene has the structure:

3. An electrophotographic element as described in claim 1 additionally comprising a sensitizer selected from the group consisting of pyryliurn and thiapyrylium dye salts and wherein said binder is a carbonate polymer.

4. A photoconductive element as described in claim 5 wherein said binder is a carbonate polymer.

5. A photoconductive element for use in electrophotography comprising a conductive support bearing a photoconductive layer comprising ferrocenylbis(2-methyl-4- diethylaminophenyDmethane, a pyrylium dye sensitizer and a polymeric film-forming electrically insulating binder.

6. In an electrophotographic process wherein an electrostatic charge pattern is formed on an electrophotographic element, the improvement characterized in that said photoconductive element has a photoconductive layer comprising a ferrocenylbis(2-methyl-4-diethylaminophenyDmethane photoconductor and an electrically insulating film-forming polymeric binder.

2 References Cited UNITED STATES PATENTS 3,098,864 7/1963 Rausch 260-439 CY 3,352,888 11/1967 Matsunaga 260439 CY 3,379,740 4/1968 Matsunaga 260439 CY X 3,577 ,235 5/ 1971 Contois. 3,335,008 8/1967 Dubose .260439' CY X 3,490,907 1/ 1970 Schenck et a1. 260439' CY X OTHER REFERENCES Metallo-Organic Polymers Open New Field, C & EN News, Sept. 27, 1971, pp. 37-38.

GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner US. Cl. X.R.

96-1 PC, 1.5; 252-501; 260-429 CY, 429.5, 438.5 R, 439 CY