US3554745A

US3554745A - Electrophotographic composition and element

Info

Publication number: US3554745A
Application number: US717373A
Authority: US
Inventors: James A Van Allan
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1968-03-29
Filing date: 1968-03-29
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: DE1912589A1; FR2005060A1; GB1227938A; DE1912589C3; DE1912589B2; BE730717A

Abstract

4-AMINO BENZO(B)PYRYLIUM AND 4-AMINO BENZO(B)THIAPYRLIUM SALTS ARE SENSITIZERS FOR PHOTOCONDUCTORS. PHOTOCONDUCTIVE COMPOSITIONS SENSITIZED WITH THESE COMPOUNDS HAVE INCREASED ELECTROPHOTOGRAPHIC SPEED AND ARE SENSITIVE IN THE ULTRAVIOLET REGION OF THE SPECTRUM.

Description

United States Patent 3,554,745 ELECTROPHOTOGRAPHIC COMPOSITION AND ELEMENT James A. Van Allan, Rochester, -N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 29, 1968, Ser. No. 717,373 Int. Cl. G03g 5/00 US. Cl. 961.6 7 Claims ABSTRACT OF THE DISCLOSURE 4amino benzo(b)pyrylium and 4-amino benzo (b)thiapyrylium salts are sensitizers for photoconductors. Photoconductive compositions sensitized with these compounds have increased electrophotographic speed and are sensitive in the ultraviolet region of the spectrum.

This invention relates to the novel use of a class of organic compounds as sensitizers in electrophotographic elements.

The process of xerography, as disclosed by Carlson in US. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident actinic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge after a suitable period of dark adaptation. The element is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of the surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with 21 suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or in the absence of charge pattern as desired. The deposited marking material may then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor and the like or transferred to a second element to which it may similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

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 present-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. Optically clear organic photoconductor-containing elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements may be exposed 3,554,745 Patented Jan. 12, 1971 through a transparent base, if desired, thereby providing unusual 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 a used to form subsequent images after residual toner from prior images has been removed by transfer and/or clean- Although some of the organic photocond-uctor materials referred to above are inherently light sensitive, their degree of sensitivity is usually low and not always in a desired wavelength portion of the spectrum so that it is common practice to add materials to increase the speed and to shift the spectral sensitivity.

Increasing the speed and shifting the sensitivity of such systems has several advantages in that it reduces exposure time, allows projection printing through various optical systems etc. By increasing the speed through the use of sensitizers, photoconductors which would otherwise have been unsatisfactory are useful in processes Where higher speeds are required. However, a major disadvantage of many prior sensitized organic photoconductor systems has been the highly colored nature of such systems.

It is, therefore, an object of this invention to provide a novel class of sensitizers for use in combination With organic photoconductors.

Another object of this invention is to sensitized photoconductive elements.

A further object of this invention is to provide novel photoconductive compositions which are colorless and are sensitive to ultraviolet radiation.

These and other objects are accomplished by the use of 4-amino benzo(b)pyrylium and 4-amino benzo(b) thiapyrylium salts as sensitizers in organic photoconductor-containing systems. Typical sensitizers of the present invention include those having the following structural formula:

provide novel wherein X is a sulfur atom or an oxygen atom;

Z is an anionic function including such acid anions as perchlorate, fluoroborate, sulfonate, periodate, p-toluenesulfonate etc.;

R is an alkyl radical of from 1 to 10 carbon atoms, such as methyl, ethyl, isopropyl, n-butyl, pentyl, octyl, decyl etc. including cycloalkyl such as cyclopentyl, cyclohexyl etc., as Well as such substituted alkyl radicals as aralkyl radicals having from 1 to 4 carbon atoms in the alkyl moiety such as benzyl, phenylethyl, phenylpropyl and phenylbutyl, an aryl radical as phenyl and naphthyl radicals, and the like;

R is a hydrogen atom, a lower alkyl radical of from 1 to 4 carbon atoms such as methyl, ethyl, isopropyl, butyl etc. and a lower alkoxy radical having from 1 to 4 carbon atoms in the alkyl moiety such as methoxy, ethoxy, propoxy, butoxy etc.; and

R and R when taken separately each represents a hydrogen atom and When taken together are attached to adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring such as a benzo ring and including substituted fused aromatic rings.

Suitable sensitizers would include the following representative compounds:

TABLE A 4-benzylamino-2-phenylbenzo [b] pyrylium perchlorate 4-anilino-2- 4-rnethoxyphenyl naphtho 1,2-b] pyrylium perchlorate 1- [N-butylamino] -3-phenylnaphtho [2, 1-b] pyryliurn perchlorate 4- (N-butylamino -2- (4-methoxyphenyl) naphtho- 1,2-b]pyryl1um perchlorate 1-anilino-3-phenylnaphtho[2,1 b]pyrylium perchlorate 4-[N-butylamino] -2-phenylbenzo [b] thiapyrylium perchlorate 4-anilino fiavylium perchlorate 4-cyclohexylamino-2-phenylbenzo [b] thiapyrylium perchlorate 4- ['N-octylamino] -2-phe'nylbenzo [b] thiapyrylium perchlorate 4-phenylamino-2-phenylbenzo [b] thiapyrylium perchlorate 2-phenyl-4-phenethylaminobenzeno [b] thiapyrylium perchlorate 4- [N-butylamino] -2(p-methoxyphenyl)benzo [b] pyrylium fluoroborate 4- [N-butylamino] -2(p-methoxyphenyl)benzo [b] pyrylium perchlorate Electrophotographic elements of the invention can be prepared with a variety of organic photoconductive compound and the sensitizing compounds of this invention in the usual manner, i.e., by blending a dispersion or solution of the photoconductive compound together With an electrically insulating, film-forming resin binder when necessary or desirable and coating or forming a selfsupporting layer with the photoconductive composition. Generally, a suitable amount of the sensitizing compound is mixed with the photoconductive coating composition so that after thorough mixing the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. The amount of sensitizer that can be added to a photoconductor containing 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 from about 0.005 to about 5.0 percent by weight of the total coating composition.

The sensitizers of this invention are effective for enhancing the electrophotosensitivity of a wide variety of photoconductors. The preferred photoconductors are those organic compounds which exhibit an electrophotosensitivity to light and are capable of forming transparent elements. A useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising 1) diarylamines such as diphenylamine, dinaphthylamine, N,N'- diphenylbenzidine, N-phenyl-l-naphthylamine, N-phenyl- Z-naphthylamine, N,N diphenyl p phenylenediamine, 2-carboxy 5 chloro-4'-methoxydiphenylamine, 6-anilinophenol, N,N' di 2 naphthyl-p-phenylenediamine, the materials described in Fox US. Pat. 3,240,597, is sued Mar. 15, 1966, and the like, and (2) triarylamines including (a) nonpolymeric triarylamines, such as triphenylamine, N,N,N',N-tetraphenyl m phenylenediamine; 4 acetyltriphenylamine, 4 hexanoyltriphenylamine; 4 lauroyltriphenylamine, 4 hexyltriphenylamine, 4-dodecyltriphenylamine, 4,4 bis(diphenylamino)benzyl, 4,4 bis(diphenylamino) benzophenone and the like and (b) polymeric triarylamines such as poly[N,4"-(N, N,N' triphenylbenzidine)], polyadipyltriphenylamine, polysebacyltriphenylamine, polydecamethylene triphenylamine; poly N (4-vinylphenyl)diphenylamine, poly- N-(vinylphenyl) a,a' dinaphthylamine and the like. Other useful amine-type photoconductors are disclosed in US. Pat. 3,180,730, issued Apr. 27, 1965. In addition, photoconductive substances capable of being spectrally sensitized in accordance with this invention are disclosed in Fox US. Pat. 3,265,496, issued Aug. 9, 1966, and include those represented by the following general formula:

wherein A represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.) or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.) or 2. nitro group; A represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.) or a substituted monovalent aromatic radical wherein said substituent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.) or a nitro group; Q can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as A'NH; b represents an integer from 1 to about 12; and G represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, a nitro group or a poly- (4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group.

Polyarylalkane photoconductors are particularly useful in accordance with the present invention. Such photoconductors are described in US. Pat. 3,274,000; French Pat. 1,383,461 and in copending application of Seus and Goldman entitled Photoconductive Elements Containing Organic Photoconductors filed Apr. 3, 1967. These photoconductors include leuco bases of diaryl or triarylmethane dye salts, 1,1,1-triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are non-leuco base materials.

Preferred polyaryl alkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group,

wherein each L can be an alkyl group typically having 1 to 8 carbon atoms, a hydrogen atom, an aryl group or together the necessary atoms to form a heterocyclic amino group typically having to 6 atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E and G is preferably p-dialkylaminophenyl group. When I is an alkyl group, such an alkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylalkane photoconductors include the compounds listed below:

TABLE B Wherein R and R are each phenyl radicals including substituted phenyl radicals and particularly when R is a phenyl radical having the formula:

where R and R are each aryl radicals, aliphatic residues of 1 to 12 carbon atoms such as alkyl radicals preferably having 1 to 4 carbon atoms or hydrogen. Particularly advantageous results are obtained when R is a phenyl radical including substituted phenyl radicals and where R is diphenylaminophenyl, dimethylaminophenyl or phenyl.

Preferred binders for use in preparing the present photoconductive layers comprise polymers having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soya-alkyd resins; poly (vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(viny1 acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly (n-butylmethacrylate), poly(isobutyl methacrylate), etc.;

Compound name Compound No.:

4,4'benzylidine-bis(N,N-dietl1yl-m-toluidine) 4' ,4"-diamino-4-dimethy1amino-2',2"-dimethyltriphenylmethane.

4 ,4"-bis (diethylamino) -4-dimethylamino-2,2"-dimethyltriphenylmethane.

(7) 4 ,4-bis (diethylamino)-2-chloro-2,2"-dimethyl-4-dimethylaminotriphenylrnethane. (8) 4,4"-bis(diethylamino)-4-dimethylarnino 2,2,2"-trimethyltriphenylmethane. (9) 4 ,4"-bis(dimethylamino) ,2-chloro-2 ,2"-din1ethyltriphenylmethane. (10) 4' ,4"-bis(dimethylamino) -2' ,2-dimethyl4-methoxytriphenylmethane. (11) Bis(4-diethylamino)-1,1,1-triphenylethane. (12). Bis(4-diethylamino)tetraphenylmethane. (13)- 4,4"-bis(benzylethylamino)-2,2"-dimethyltriphenylmethane. (14). 4,4"-bis(diethylamino)2',2-diethoxytriphenylmethane.

(15)- 4,4-bis(d.imethylamino)-1,1,1-triphenylethane. (16)- 1-(4-N,N-dimethylaminophenyl)-1,l-dipheny1ethane. gflguu 4-dinfiethylaminotetraphenylmethane.

Additional organic photoconductors which can be employed with the sensitizing compounds described herein are non-ionic cycloheptenyl compounds such as those described in copending application Ser. No. 654,091, filed July 1-8, 1967; the N,N-bicarbazyls and tetra-substituted hydrazines; the 3,3 bis 1,5-diarylpyrazolines; triarylamines having at least one of the aryl radicals substituted by either a vinyl radical, or a vinylene radical having at least one active hydrogen-containing group such as pdiphenylaminocinnamic acid; triarylamines substituted by an active hydrogen-containing group, e.g., 4-carboxytriphgtylamine; and those described in Australian Pat.'No. 248,402.

Another class of photoconductors useful in this invention are the 4-diarylamino-substit-uted chalcones. Typical compounds of this type are low molecular weight nonpolymeric ketones having the general formula:

polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylene alkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketoneresins; polyamides; polycarbonates; polythiocarbonates; poly (ethyleneglycol co bishydroxyethoxyphenyl propane terephthalate); nuclear substituted polyvinyl haloarylates; 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 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names as Vitel PE-101, Cymac, Piccopale 100, Saran F-220 and Lexan 105. Other types of binders which can be used in the photoconductive layers of the invention include such materials as parafi'in, mineral waxes etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, Z-butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained where the photoconductor 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 photoconductor substance present can be widely varied in accordance with usual practice. In those cases where a binder is employed, it is normally required that the photoconductor substance be present in an amount from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductor substance 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 coating in the range of about 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thickness is found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 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, aluminum and the like coated on paper or conventional photographic film bases such as cellulose acetate, polystyrene, etc. Such conducting materials as nickel can be coated by vacuum deposition on transparent film supports in sufiiciently thin layers to allow electrophotographic elements prepared therewith to be exposed from either side of such elements. An especially useful conducting support can be prepared by coating a support material such as poly(e'thylene terephthalate) with a conducting layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Pat. 3,245,833. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in US. 3,007,901 and 3,267,807.

The elements of the present invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the aforementioned xerographic process. As explained previously, in a process of this type the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained on the layer by virtue of the substantial 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 photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form an electrostatic latent image in the photoconducting layer. By exposure of the surface in this manner, a charged pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust or a pigment in a resinous carrier or a liquid developer can be used in which the devel- 8 oping particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature in such patents, for example, as US. 2,297,691 and in Australian Pat. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has a low-melting resin as one of its components, it is possible to treat the developed photoconductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the image formed on the photoconductive layer can be made to a second support which would then become the final print. Techniques of the type indicated are well known in the art and have been described in a number of US. and foreign patents such as U.S. Pats. 2,297,691 and 2,551,582 and in RCA Review, vol. 15 (1954), pages 469-484.

An increasing use of electrophotographic elements has occurred in the field of recording data displayed on a cathode-ray tube. Advantages gained through such use include attractively high photographic speed, desirable spectral response, and short time of access to a visible recorded image.

It is frequently desirable to employ the image-bearing electrophotographic element having a transparent film base as a master from which further prints can be generated. Such elements can be used as masters in many types of reproduction processes. Typical of these processes are the rerographic process, thermographic process, direct electrostatic process, stabilization process, gelatin transfer process, diifusion transfer process, etc. A particularly advantageous process by which such a print can be made is the diazo process. In this process, a diazonium saltcontaining element is exposed through a transparent electrophotographic original bearing a developed or toned image to activating radiation from an ultraviolet source. The exposure causes decomposition of the salt in those areas which are struck by activating radiation. Subsequently, the exposed diazo element is passed through an atmosphere of a suitable alkaline material, such as ammonia vapor. In the presence of the alkaline material and a dye-forming coupler, which can be either incorporated in the diazonium-containing layer or introduced during the development step, the diazonium salt which is not 0 decomposed by exposure is converted to an azo dye. A

positive reproduction of the original is formed.

A difliculty commonly encountered in the production of copies from sensitized photoconductor-containing coated elements is that the photoconductive element possesses a relatively high optical opacity resulting from coloration imparted by the sensitized photoconductor-containing composition. As a result the element does not transmit sufficient radiation in that portion of the electromagnetic spectrum to which the copy element is sensitive. Therefore, reprints are very difiicult to obtain. Also, if the image-bearing elements are to be used for direct reading, the image portions of the elements are often almost indiscernible due to the lack of contrast. One solution proposed for this problem has been to bleach the highly colored photoconductive elements. However, with the present class of sensitizers a colorless photoconductive layer results which eliminates the need for an extra bleaching step.

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

EXAMPLE 1 A control coating is prepared from the following ingredients:

wPoly[ethyleneglycol-co-bis (hydroxyethoxyphenyl) propane terephthalate] (binder)1.5 g.

(Triphenylamine (photoconductor)0.5 g.

Methylene chloride (s0lvent)l 1.7 ml.

The above homogeneous photoconductive composition is coated at a wet thickness of 0.004 inch onto a poly(ethylene terephthalate) film support carrying a conductive layer of the sodium salt of a polymeric lactone as described in U.S. Pat. No. 3,260,706. The coating block temperature is maintained at 90 F. The resulting element is called Element I (control). The above procedure is repeated with the addition of 0.2 g. of 4N-butylamino-2- (4-methoxyphenyl)benzo(b)pyrylium perchlorate as the sensitizer prior to coating. The resultant element is called Element H. Next, an element similar to Element I is prepared using 0.5 g. of 4,4'-benzylidene-bis(N,N-diethyl-mtoluidine) in place of the previous photoconductor. The resultant element is called Element III (control). Finally, Element IV is prepared using the photoconductive composition of Element III plus 0.02 g. of 4-N-butylamino-2- (4-methoxyphenyl)benzo(b) pyrilium perchlorate as the sensitizer. The resultant electrophotographic elements are then electrostatically charged under a corona source until the surface potential, as measured by ,an electrometer probe, reaches about 600 volts. The charged elements are then exposed to a 3000 K. tungsten light source through a stepped density gray scale. The exposure causes reduction of the surface potential of the elements 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 in meter-candle-seconds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step. The actual positive or negative speed of the photoconductive composition used can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed arbitrarily selected value. Herein, unless otherwise stated, the actual positive or negative speed is the numerical expression of 10 divided by the exposure in meter-candleseconds required to reduce the 600 volt charged surface potential to a value of 500 volts (100 volt shoulder speed) or to a value of 100 volts (100 volt toe speed). The speeds of the elements are recorded in Table I below.

TABLE I.ELECTROPHOTO GRAPHIC SPEEDS These elements can be charged, exposed and developed with liquid developers of the type described in US. Pat. No. 2,907,674 to form visible images.

EXAMPLE 2 Another element (5) similar to Element II of Example 1 is prepared. The element is then charged to a positive polarity of 610 v. and exposed to a zenon light source through a 1.9 neutral density filter in combination with a set of filters simulating the wavelength distribution of P-16 phosphor emission. P-16 phosphors are standard materials used in cathode ray tubes, have a fluorescent color of ultraviolet to blue, have a typical wavelength peak at 3800 A. and comprise calcium magnesium silicate doped with cesium. Upon exposure the element photodecays to a 50 v. surface potential in only 13.5 seconds. An element (6) similar to Element IV is prepared by using polyvinyl-m-bromobenzoate-co-vinylacetate as the binder. This element gives a similar response to the P16 phosphor simulation photodecay test. These elements can then bechargcd, exposed and developed with a liquid developer of the type described in US. Pat. No. 2,907,674 to form visible images.

EXAMPLE 3 Four electrophotographic elements are prepared as above using 1.5 g. of binder, 0.5 g. of photoconductor, 11.7 ml. of solvent and 0.01 to 0.02 g. of sensitizer where used. The binders used are (a) poly(vinyl-m-bromobenzoate-co-vinyl-acetate) and (b) a polycarbonate resin formed from the reaction between phosgene and a dihydroxydiarylalkane or from the ester exchange reaction between diphenylcarbonate and 2,2-bis-4-hydroxyphenylpropane (Lexan 145 resin, General Electric Company). The photoconductor used is 4,4'-benzylidene-bis(N,N-diethyl-m-toluidine). The sensitizer used is 4-N-butylamino- 2-(4-methoxy-phenyl) benzo (b)pyrylium perchlorate. The elements are then subjected to an ultraviolet (365 m photodecay test as in Example 2 by charging to a positive and/or a negative 600 v. surface charge and exposing until the potential decays to v. The results of these tests are shown in Table 11 below.

TABLE II 100 v. photodecay time, see. Amounts of Binder sensitizer, g.

Element No.:

Element 7 has only a 27.5% absorption at 365 m whereas Element 8 has an 84.5% absorption at 365 mg. After testing Elements 8 and 10 can be charged, exposed and developed as above.

EXAMPLE 4 Five elements are prepared in accordance with Example 1 using 1.5 g. of the binder of Element I, 0.5 g. of one of the following photoconductors (1) triphenylamine, (2) 1-(p-diphenyl-aminophenyl)ethanol, (3) 4-hydroxymethyl triphenylamine, and (4) B-(N,N-diphenylamino)propionic acid and 0.06 or 0.02 g. of the sensitizer 4-N-butylamino-2-(4-methoxyphenyl) benzo(b)-pyrylium perchlorate. The elements are then measured for the 100 volt shoulder speeds as in Example 1. The results of these measurements are shown in Table III below.

A variety of electrophotographic elements are prepared in accordance with Example 1. The photoconductive compositions contain the binder of Element I with 20% by weight of one of the following photoconductors (A) triphenylamine, (B) 4,4-benzylidene-bis(N,N-diethyl-m-toluidine) or (C) 4,4'-bis(diphenylaminochalcone) and 0.8% by weight of a sensitizer as listed below. The resultant elements are then measured for positive and negative 100 v. shoulder speed as before. The results of these measurements are shown in Table IV below:

ing binder material and having dispersed therein a sensitizing amount of a member selected from the group con- TABLE IV 100 v. shoulder Photospeed conductor Sensitizer Element No 17 -benzylamino-2-phenylbenzo[b]pyrylium perchlorate A 140 112 do B 110 8 C 450 280 A 250 100 B 63 d0 t a C 320 160 l-[N-butylamin0]-3-phenylnaptho[2,1-b]pyrylium perchlorate A 220 .do t B 105 C 300 250 A. 250 100 B 160 130 C 180 100 A 100 0 B 50 11 31 C 400 100 32 A 100 B 120 63 C 360 100 A 63 50 B 32 36 d0 C 500 200 4-cyclohexylamino-2-phenylbcnzo[b]thia-pyrylium perchlorate. A 120 l o B 120 140 l.d0 C 560 200 4[N-octy1amino]-2-phenylbenzo-[b]thiapyrylium perchlorate. A 180 110 o B 180 80 C 320 200 A 100 50 B 16 9. 0 C 400 80 A 280 90 B 220 200 C 450 250 A 160 B 160 63 C 250 110 A 250 200 B 140 200 C 160 63 The absorption maximum is measured for each of Elements 17-21 and is found to be in the ultraviolet region in all instances.

EXAMPLE 6 Several electrophotographic elements are prepared in accordance with Example 1 using poly(vinyl-m-bromo benzoate-co-vinylacetate) as the binder with 25% by weight of 4,4'-benzylidene-bis(N,N-diethyl-m-toluidine) as the photoconductor and l to 3% by weight of the sensitizer 4-N-butylan1ino-2-(4-methoxyphenyl) benzo(b) pyrylium perchlorate. The various elements are then subjected to a Pl6 phosphor simulation photodecay test as in Example 2. The elements are charged to a positive polarity of about 600 v. and exposed. The elements are allowed to photodecay to 100 and to 50 v., respectively, and the time is measured. The results are shown below.

TABLE V Photodecay time, sec. Amount of sensitizcr (percent by weight) 100 v. 50 v.

sisting of 4-aminobenzo(b)pyrylium and 4-aminobenzo (b)thiapyrylium salts having the formula:

X is selected from the group consisting of a sulfur atom and an oxygen atom;

Z is an anion;

R is selected from the group consisting of an alkyl radical and an aryl radical;

R is selected from the group consisting of a hydrogen atom, a lower alkyl radical and a lower alkoxy radical; and

R and R when taken separately, each represents a hydrogen atom, and when taken together, are attached 0 adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring.

2. A photoconductive composition as in claim 1 wherein the sensitizing salt is selected from the group consisting of:

wherein 4-benzylamino-2-pheny1ben2o [b] pyrylium perchlorate,

4-anilino-2- (4-methoxyphenyl naphtho[ 1,2-b pyrylium perchlorate,

1-[N-butylamino1-3 -phenylnaphtho [2,1-b]pyrylium perchlorate,

4-(N-butylarnino)-2-(4-methoxyphenyl)naphtho[1,2-b]

pyrylium perchlorate,

l-anilino-3-phenylnaphtho [2,1-b]pyrylium perchlorate,

4-[N-octylamino]-2-phenylbenzo [bjthiapyrylium perchlorate,

triphenylamine,

4,4'-benzylidene-bis (N,N-diethyl-m-toluidine) 1- (p-dip henylaminophenyl) ethanol, 4-hydroxymethyl triphenylamine,

;8- (N,N'-diphenylamino propionic acid, and 4,4'-bis(diphenylaminochalcone) 4. An electrophotographic element comprising a support having coated thereon a layer of an electrically insulating binder material having dispersed therein an organic photoconductor and a sensitizing amount of a member selected from the group consisting of 4-aminobenzo(b)pyrylium and 4 aminobenzo(b)thiapyrylium salts having the formula:

wherein:

X is selected from the group consisting of a sulfur atom and an oxygen atom;

Z is an anion;

R and R when taken separately, each represents a hydrogen atom, and when taken together, are attached to adjacent carbon atoms and represent the atoms necessary to form a fused aromatic ring.

5. An electrophotographic element as in claim 4 wherein the senstizing salt is selected from the group consisting of:

4-benzylamino-2-phenylbenzo [b]pyrylium perchlorate,

4-ani1ino-2- (4-methoxyphenyl naphtho 1,2-b1pyrylium perchlorate,

1-[N-butylamino]-3-phenylnaphtho[2,1-b1pyrylium perchlorate,

4- N-butylamino) -2- (4-methoxyphenyl naphtho-[ 1,2-b]

pyrylium perchlorate,

1-anilino-3-phenylnaphtho[2,1-b]pyrylium perchlorate,

4-[N-butylamin0] -2-phenylbenzo [b] thiapyrylium perchlorate,

4-anilino flavylium perchlorate,

4-cyclohexylamino-2-phenylbenzo [b] thiapyrylium perchlorate,

4- [N-octylamino] -2-phenylbenzo [b] thiapyrylium perchlorate,

4-phenylamino-Z-phenylbenzo [b]thiapyry1ium perchlorate,

2-phenyl-4-phenethylaminobenzo [b] thiapyrylium perchlorate,

4- [N-butylamino] -2-(p-methoxyphenyl)benzo [b] pyrylium fluoroborate, and

4- [N-butylamino] -2- (p-methoxyphenyl) benzo [b pyrylium perchlorate.

6. An electrophotographic element as in claim 4 wherein the organic photoconductor is selected from the gr up consisting of: triphenylamine, 4,4'-benzylidene-bis (N,N-diethylm-toluidine) 1- (p-diphenylaminophenyl) ethanol, 4-hydroxymethyl triphenylamine,

r ,8-(N,N'-diphenylamino)propionic acid, and

4,4-bis (diphenylaminochalcone) 7. An electrophotographic element as in claim 4 wherein the support is electrically conducting.

References Cited UNITED STATES PATENTS 3,250,615 5/1966 Van Allan et a1. 961 3,397,086 8/1968 Bartfai 961.5X

GEORGE F. LESMES, Primary Examiner M. B. WITI'ENBERG, Assistant Examiner U.S. Cl. X.R.

@2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,55 +,7 +5 Dated January 12. 1971 Inventor) James A. VanAllan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 13, line 1]., "h-Ebutylaming? should read "h-[fi-butylamingT'; and

Column 14, line 2, "senstizing" should read "sensitizing".

Signed and sealed this 21 th day of August 1971.

(SEAL) Attest:

EDWARD M.FLET0HER,JR.

WILLIAM E. son LE Attesting Officer W Commissioner of Patents