US3586500A

US3586500A - Electrophotographic composition and element

Info

Publication number: US3586500A
Application number: US772863A
Authority: US
Inventors: Lawrence E Contois; Donald P Specht
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1968-11-01
Filing date: 1968-11-01
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22
Also published as: GB1234706A; DE1954538B2; FR2022355A1; BE741045A; DE1954538A1

Abstract

PYRYLIUM, BENZO(B)PYRYLIUM AND BENZO(B)THIAPYRYLIUM SALTS CAN BE USED AS INFRARED SENSITIZERS OF PHOTOCONDUCTORS. THESE SALTS INTERACT WITH CERTAIN ORGANIC PHOTOCONDUCTORS, SUCH AS ARYLAMINE-CONTAINING COMPOUNDS, TO EXTEND THE SPECTRAL SENSITIVITY OF THE PHOTO CONDUCTOR INTO THE FAR RED AND NEAR INFRARED REGION OF THE SPECTRUM.

Description

United States Patent 3,586,500 ELECTROPHOTOGRAPHIC COMPOSITION AND ELEMENT Lawrence E. Contois, Webster, and Donald P. Specht,

Spencerport, N.Y., assignors to Eastman Kodak Company, Rochester, NY. No Drawing. Filed Nov. 1, 1968, Ser. No. 772,863

Int. Cl. G03g 5/06 US. Cl. 961.6 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to novel sensitized electrophotographic compositions and electrophotographic elements prepared therewith.

, The processof 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 a 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 introductions of electrophotography, many organic compounds have been found to possess some degree of photoconductivity 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 can be exposed through a transparent base, if desired, thereby providing unusual flexibility in equipment design. Such compgsitions when coated as a film or layer on a suitable support also yield an element which is reusable; that is, it canbe used to form subsequent images after residual toner from prior images has been removed by transfer and/ or cleaning.

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Although some of the organic photoconductor materials referred to above are inherently light sensitive, their degree of sensitivity is usually low. In addition, the spectral response of organic photoconductor materials is generally limited to the ultraviolet or blue region of the spectrum. Often the spectral response of such materials can be extended into the visible region of the spectrum by the use of sensitizers. Such sensitization can be advantageous in that common tungsten light sources can then be used for exposure. The spectral response for such a sensitized system is usually directly related to the absorbance spectra of the individual components of the system.

Often it is desirable to extend the spectral response of an organic photoconductor material even beyond the visible region and into the far red or infrared region of the spectrum. However, sensitization of a photoconductive composition to the infrared region requires the use of sensitizers having an absorbance maximum in this region. It has generally been found that such a means for sensitization is an inefficient one. Additionally, the sensitizers which have an infrared absorbance maximum are often compounds having very complex structures which render them either unstable or extremely difficult to synthesize economically.

It is, therefore, an object of this invention to provide novel photoconductive compositions-which are sensitive to far red and near infrared radiation.

Another object of this invention is to provide novel sensitized photoconductive elements having a spectral response in the far red and near infrared region.

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

s l I s- [R2 [R7 V 2 1 Ro- 6 Re I. II.

wherein:

X is a sulfur atom or an oxygen atom;

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

R is a hydrogen atom, a halogen atom such as chlorine, bromine, etc.; an alkyl radical having from 1 to 12 carbon atoms such as methyl, ethyl, isopropyl, n-butyl, pentyl, octyl, decyl, dodecyl, etc., including cycloalkyl such as cyclopentyl, cyclohexyl, etc.; an alkoxy radical having from 1 to 4 carbon atoms in the alkyl moiety such as methoxy, ethoxy, propoxy, butoxy, etc.; an aryl radical such as phenyl, naphthyl, etc., including substituted aryl radicals; an aralkenyl radical having from 2 to 6 carbon atoms in the alkenyl moiety such as ethenyl, propenyl, hexenyl, etc.; and a monoor polycyclic, heterocyclic radical typically having 5 or 6 atoms in the hetero ring and including at least one hetero atom selected from oxygen or sulfur such as thienyl, coumaryl, etc.;

R is a hydrogen atom; a halogen atom as above; an alkyl radical as above including halogen substituted alkyl radical such as chloromethyl, dichloropropyl, bromopentyl, etc.; an alkoxy radicalas above; an aryl radical as above; an aroyl radical such as benzoyl, naphthoyl, etc.; and an alkoxycarbonyl radical having from 1 to 4 carbon atoms in the alkoxy moiety such as methoxy, ethoxy,

propoxy, butoxy, etc.;

When taken together any two of R R R R and R attached to adjacent carbon atoms represent the atoms necessary to form a fused ring having from 5 to 8 carbon atoms and can be aromatic, alicyclic, unsaturated alicyclic radicals including the corresponding substituted radicals having such substituents as a halogen atom as above, an alkyl radical as above, an aryl radical as above and an aralkenyl as above;

R and R can be a hydrogen atom, an alkyl radical as above and an aryl radical as above;

R is a hydrogen atom, an alkoxycarbonyl radical as in R above and an aryl radical; and

R is a hydrogen atom, a hydroxy radical, an alkoxy radical as above or an aryl radical.

Typical useful sensitizers that can be used in the invention include the following representative compounds:

TABLE A 8-ethyl-2-(4-methoxyphenyl)benzo[b]pyrylium perchlorate.

2,3Fdipl1enylbenzo[b]pyryliu.rn perchlorate. Z-bromomethyl-3phenylnaphtho[2,l-b1pyrylinm perchlorate. 2,3diphenylbenzo[b]pyrylium perchlorate.

2-(4-methoxyphenyl)-4-methylmercaptobenzo[b]pyryl1um perchlorate.

Name

7 4-methoxy-2-( t-methoxyphenyl)benzo[b]pyrylium perchlorate. 8- 4-chloro-2-(4-methoxyphenyl)benzo[b]pyryliu m perchlorate.

9- Q-methylxanthylium perchlorate.

10 2-phenyl'4-styrylbenzo[b]pyryliurn perchlorate.

11- 4-1nethoxy-2-phenylbenzo[b]thiapyrylium perchlorate.

4-hydroxy-2,6-diphenylpyrylium perchlorate.

13 Q-methylthiaxanthylium perchlorate. 14 2-chloro-3-phenylnaphtho[2,l-b]pyryllum perchlorate. 15 IOH-indenotl,2-b]benzo[e]pyryliurn perchlorate.

3-methyl-2 4-n1ethoxypheny1)henzo[b]pyryllum fiuoroborate.

2,4,6-triphenyl-Zi-carboxypyrylium perchlorate.

2,4,6-triphenyl-3-carboxyethylpyrylinm perchlorate.

- 2-phenylrnethyl-3,4,6-triphenylpyrylium perchlorate.

. 2-phenylcarbonyl-B-phenylnaphtho[2,l-b1pyrylium perchlorate. 2-hydroxy-3-phenylnaphtho[2,1-b1pyrylium perchlorate.

22. Z-phenylbenzoIblpyrylium perchlorate.

Typical useful sensitizers that can be used in the invenductors used to form an interaction product which gives rise to a considerable extension of the absorption range of the photoconductors. The useful photoconductors alone do not exhibit any appreciable absorption in the red region of the spectrum. However, when the present sensitizers are combined with the useful photoconductors an interaction product results which in general has a long Wavelength radiation absorption maximum at wavelengths of greater than about 665 me. Not only is the absorption range of the photoconductor greatly extended, but more important is the fact that this increased absorption is electrophotographically useful. In particular, a sensitized photoconductive composition of this invention has a spectral distribution of sensitization that is substantially changed from that of the individual components such that the interaction product exhibits significant long wavelength spectral sensitvity to far red and infrared radiation. The term far red as used here refers to the portion of the spectrum including light having a Wavelength in the range of from about 650 to about 700 my, and the term near infrared refers to light having a wavelength of from about 700 to about 900 me. However, it should be noted that in general the sensitizers by themselves do not have any appreciable sensitivity in the red region of the spectrum.

The sensitizers used in the invention are effective for enhancing the sensitivity of a variety of photoconductors.

The preferred photoconductors are those organic arylamine-containing compounds which exhibit an electrophotosensitivity to light and which are capable of interacting with the sensitizer so as to produce a substantial extension of the spectral distribution of sensitization to include the far red and infrared portion ofthe spectrum. The useful photoconductors by themselves have very little absorption in the red region, for example, one useful photoconductor has a long wavelength absorption maximum at about 420 mp. Furthermore, any slight long wavelength absorption which the photoconductor alone may exhibit is not useful absorption in that it does not result in any long wavelength spectral sensitivity.

Useful photoconductive compoundswhich exhibit such interaction with the sensitizers would include the following:

4.. 4(l-hydroxyethyl)triphenylamine.

carboxytriphenylamine.

- -acetylphenyl)-N,N-dimethylamine.

N-(4carboxyethenylphenyl)-N,N-tlirnethylarnine.

N (4methoxycarbonylet;henylphenyl)-N,N-diethylamine.

9 N(tearboxyethenylphenyl)-N-phenyl-N-rnethylamine.

10 N- (4-carboxyethenylphenyl) N,N-bis- (phenylmethyl) amine. l1 Bis-(4-diphcnylaminobenzal)acetone.

Electrophotographc elements of the invention can be prepared with organic photoconductive compounds 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 self-supporting 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, 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. Usually, 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.

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; styrenealkyd resins; silicone-alkyd resins; soya-alkyd resins; poly (vinyl chloride); poly(vinylidene chloride); 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(methylmethacrylate), poly(n-butylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(cthylene alkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycol-co-bishydroxyethoxyphenyl propane terephthalate); nuclear substituted poly-- vinyl 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 tradenames as Vitel PE-101, Cymac, Piccopale 100, Saran F-220 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 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 theamount 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 fromabout 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 weight percent to about 60weight 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 sufficiently 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(ethylene terephthalat'e) 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 beprepared 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 U.S. 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 processof this-type theelectrophotographic 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 selectiively dissipated from the surface of the layer byexposure to light through an imagebearing 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 developing 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 U8. and foreign patents such as US. Pats. 2,297,691 and 2,551,- 582 and in RCA Review, vol. 15 (1954), pp. 469-484.

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

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

Poly[ethyleneglycol co 2,2 bis(hydroxyethoxyphenyl) propane terephthalate] (binder) 1.0 4,4'-bis(diphenylaminochalcone) (photoconductor) 0.25 Dichloromethane (solvent) 9.6

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 US. Pat. No. 3,260,706. The coating block temperature is maintained at F. The resultant element is called Element 1 (control). The above procedure is repeated with the addition of 0.01 g. of 2-chloro-3- phenylnapl1tho[2,1 b]pyryliurn perchlorate as the sensitizer prior to coating. The resultant element is called Element 2. 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 the 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 expressionof 10 divided by the exposure in meter-candleseconds required to reduce the 600 volt charged surface potential to a value of 500 volts 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.

7 8 TABLE I.ELECTROPHOTO GRAPHIC SPEEDS TABLE IIL-ELECTROPHDTO GRAPHIC SPEED 100 volt 100 volt 100 volt 100 volt shoulder speed toe speed shoulder speed toe speed Element N; Element N0.

1 (control) 101 0 32 0 5 (control) 21 36 0 0 2 710 120 40 2 s 710 120 7 4o- 12 Element 5 exhibits an absorption maximum only in the These elements can then be charged, eXpOSed and devel' ultraviolet region of the spectrum; whereas, Element 6 p with liquid developers Of the yp described in U- 10 has a long Wavelength absorption peak at about 700 my Pat. NO- 2,907,674 to form visible images. The optical toned wedge pectrograms howing ensitivity e absorption of the above two transparent coatings is then tending i h i f d i measured by a commercially available spectrophotom- EXAMPLE 4 eter such as a Beckman Model B spectrophotometer. The coating of Element 1 (control) has an absorption Two series of electrophotographic elements are prerange extending through the visible light region to 570 m with no absorption being observed at 700 m Element 2 shows an additional unexpected long wavelength absorption peak at 700 m with absorption extending well into the infrared region of the spectrum. Next the spectral sensitivity of the elements is measured by electrostatically charging the elements under a corona source and exposing in a standard spectrograph. After exposure the elements are toned with a developer of the type described in US. Pat. 2,907,674 to form wedge spectro grams. The spectrograms show Element No. 2 to have significant sensitivity in the far red and infrared portion of the spectrum.

EXAMPLE 2 Two electrophotographic elements are prepared as in Example 1. The first element (No. 3) carries a photoconductive layer prepared from the following ingredients:

Binder of Example 1 1.0

Triphenylamine (photoconductor) 0.25 10H indeno[l,2 b]benzo[e]pyrylium perchlorate (sensitizer) 0.01

Dichloromethane (solvent) 9.6

Element No. 3 is a control which contains a non-interacting photoconductor. Element 4 is similar to No. 3 with the exception that 4,4'-bis(diphenylaminochalcone) is used as the photoconductor. These elements are then measured for electrophotographic speed as in Example 1. The speeds are shown in Table II below.

TABLE IL-ELECTROPHOTO GRAPHIC SPEED 100 volt 100 volt shoulder speed toe speed Element N0.

3 (control) 320 22 4 900 630 50 25 Electrophotographic Elements 5 and 6 are prepared similar to Elements 3 and 4, respectively, only using 2- chloro 3 phenylnaphtho[2,l-b]pyrylium perchlorate as the sensitizer in order to compare the results of using this sensitizer with a non-interacting and an interacting photoconductor, respectively. These elements are tested for electrophotographic speed as previously and the results are shown in Table III below.

pared as previously described using the sensitizers listed below. The first series contains 4,4-bis(diphenylaminochalcone) as the photoconductor and the control series contains triphenylamine as the photoconductor. The various elements are then measured for absorption at different Wavelengths as in Example 1. The region of maximum long wavelength interaction absorption for each element of the invention is shown in Table IV below. For comparative purposes the absorption maximum is also shown for each corresponding element containing the non-interacting triphenylamine photoconductor (control).

Absorption (m Element Inter- No. Sensitizer Control action 7 3-ethyl-2-(4-rnethoxyphenyl) benzo[b]- UV 750 pyrylium perchlorate. 8 2,3-diphenylbenzo[b]pyrylium perchlorate- 450 710 9 2-bromomcthyl-3-phenylnaphtho[2,1-b] 430 680 pyrylium perchlorate. 10 2,3-diphcnylbenzo[blpyrylium perchlorate- UV 670 11 2-styrylbenzolb1pyryllum perchlorate. 460 690 12 4-111ethoxy-2-(-i-methoxyphenyl)benzo[b] UV 765 pyrylium perchlorate. 13 4-chloro-2-(4-methoxyphenyDbenzo[b]- UV 770 pyrylium perchlorate. 14 Q-methylxanthylium perchlorate UV l5 2-phenyl-4-styrylbenzo[b1pyrylium 480 perchlorate. l6 4-1nethoxy-2phenylbenzolb1thiapyrylium UV 750 perchlorate. l7 4-hydr'oxy-2,6-diphenylpyrylium UV 680 perchlorate. 18 Q-methylthiaxanthylium perchlorate G70 1 Increasing absorption from 580 into IR. Increasing absorption from 610 into IR.

Similar results are also obtained using the following sensitizers to prepare photoconductive coatings:

2,6-dimethyl-4-phenylpyrylium perchlorate; 2,4,6-triphenyl-3-carboxypyrylium perchlorate; 2,4,6-triphenyl-3-carboxyethylpyrylium perchlorate; 2-phenylmethy1-3,4,6-triphenylpyrylium perchlorate; 2-phenylcarbonyl-3 -phenylnaphtho [2,1-b]pyrylium perchlorate; and

2-hydroxy-3-phenylnaphtho [2,l-b1pyry1ium perchlorate.

EXAMPLE 5 An electrophotographic element is prepared as described in the previous examples using the following coating composition:

Binder of Example l1.0 g.

Bis(4-diphenylaminobenzal)acetone (photoconductor)- Sensitizer of Example 30.01 g.

Dichloromethane -6.2 ml.

Methyl alcohol --1.0 ml.

1 Solvent.

Absorption measurements made as in the previous examples show this element to exhibit an unexpected long wavelength absorption peak at 740 mp. Next, a wedge spectrogram is made as in the previous examples. This spectrogram shows that Element No. 18 exhibits a spectral distribution of sensitization extending well into the infrared region of the spectrum.

9. EXAMPLE 3 j 'An electrophotographic element prepared as infExjample using 4-acetyltriphenylamine as the photoconductor. The elementis then measured for absorption as in Example 1 and found to have a long wavelength absorption peak at 720 mp. Next, the element is charged, exposed and developed as in the preceding examples to produce a wedge spectrogram. The spectrogram shows that the long wavelength absorption of this element is useful in that the sensitivity extends well into the infrared region. I As previously mentioned, the present sensitized electrically insulating photoconductive compositions have a usefnl sensitivity to light in the far red and near infrared portion of the spectrum. Consequently, the instant 'compositions and elements are particularly suited for use in, for example, infrared recording applications; I

The invention has been described in detail with particular reference to certain preferredembodiments thereof, but it will be understood that variations and modifications Lean be effected withinthe spirit andscope of the invention.

We claim:

1. A far red and near infrared sensitive photoconductive composition comprising an electrically insulating filmforming resin binder, an organic arylamine-containing photoconductor and a sensitizer material selected from the group of compounds having the formula:

wherein: p

Z is an anion;

X isselected from the group consisting of oxygen and sulfur; R is selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 12 carbon atoms, an alkoxy radical having from 1 to 4 carbon atoms in the alkyl moiety, an aryl radical, an aralk enyl radical having from 2 to 6 carbon atoms in the alkenyl moiety and a heterocyclic radical having 5 to 6 atoms in the hetero ring including at least one hetero atom selected from the group consisting of oxygen and sulfur;

R is selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 12 carbon atoms, an alkoxy radical as above, an aryl radical, an aroyl radical and an alkoxycarbonyl radical having from 1 to 4 carbon atoms in the alkoxy moiety;

R is selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy radical, an alkyl radical having from 1 to 12 carbon atoms, an alkoxy radical as in R a vinyl radical and an aryl radical;

R and R are each selected from the group consisting of a hydrogen atom and an alkyl radical of from 1 to 12 carbon atoms; when taken together, any two of R R R R and R attached to adjacent carbon atoms represent the atoms necessary to form a fused ring structure selected from the group consisting of aromatic, alicyclic and unsaturated alicyclic radicals having from 5 to 8 carbon atoms;

said photoconductor being present in an amount of at least about 1% by weight of the composition and said sensitizer material being present in an amount of about 0.0001 to about 30% by weight of the composition,

each of said photoconductor and said sensitizer material having substantially no sensitivity to radiation of a wavelength greater than about 650 m and said composition being characterized in that said photoconductor and sensitizer interact to give a long wavelength radiation absorption maximum at wavelengths of greater than about 665 Ill/L- 2. Ayphotoconductive composition as in claim 1 wherein the sensitizer material is selected from the group consisting of; 7 'i p "i 3-ethyl-2-(4 methoxyphenyl)benzo[b]-pyrylium per- 2,3-diphenylbe nzo[b]pyryliurn perchlorate,

2-bromornet hyl-3-phenylnaphtho[-2,I-b]-pyry1ium perchlorate, v v 2,3-diphenylbenzo[b]pyrylium perchlorate,

2-styrylbenzo [-b]pyry1ium-perch1orat e, p 2-(4-methoxyphenyl)-4-methylmercaptobenzo[b] pyrylium perchlorate, 4-methoxy-2-(4-methoxyphenyl)benzo [b]pyry1ium I perchlorate, v

4-chloro-2- (4-rnethoxyphenyl) benzo [b] pyrylium perchlorate, 1 .Y 9-methylxanthylium perchlorate, 2-phenyl-4-styrylbenzo[b]pyrylium perchlorate, 4 methoxy-2-phenylbenzo [b] thiapyrylium perchlorate, 9-methylthiaxanthylium perchlorate, 2-chloro-3-phenylnaphtho[2,1-b] pyrylium perchlorate, 10H-indeno[ 1,2-b] benzo [e] pyrylium perchlorate, 3-methyl-2- (4-methoxyphenyl) benzo [b] pyrylium perchlorate,

2-phenylcarbonyl-3 -phenylnaphtho[2,1-b] pyrylium,

2-hydroxy-3-phenylnaphtho[2,1-b]pyrylium perchlorate and 2-phenylbenzo [b] pyrylium perchlorate.

3. An electrophotographic element comprising a support having coated thereon a layer of a photoconductive composition of claim 2.

4. A photoconductive composition as in claim 1 wherein the photoconductor is selected from the group consisting of: 4,4-bis(diphenylaminochalcone),

4-acetyltriphenylamine, 4-(B-carboxyisopropenyl)triphenylamine,

4-( l-hydroxyethyl) triphenylamine, 4-carboxytriphenylamine,

N- 4-acetylphenyl) -N,N-dimethylamine, N-(4 carboxyethenylphenyl)-N,N-dimethylamine, N-(4-methoxycarbonylethenylphenyl)-N,N-diethy1- N- (4-carb0xyethenylphenyl) -N-phenyl-N-methylamlne,

N-(4-carboxyethenylphenyl)-N,N-bis (phenylmethyl) amine, and

bis- (4-diphenylaminobenzal) acetone 5. An electrophotographic element comprising a support having coated thereon a layer of a photoconductive composition of claim 4.

6. An electrophotographic element comprising a support having coated thereon a layer of a photoconductive composition of claim 1.

7. An electrophotographic element as in claim 6 wherein the support is electrically conducting.

8. An electroplhotographie element as in claim 6 wherein the organic photoconductor is selected from the group consisting of 4,4'-bis(diphenylaminochalcone), bis(4-diphenylaminobenzal)acetone and 4 acetyltriphenylamine and the sensitizer material is selected from the group consisting of:

3-ethyl-2- (4-methoxyphenyl) benzo [b] pyrylium perchlorate,

2,3-diphenylbenzo [b] pyrylium perchlorate,

2-bromomethyl-3-phenylnaphtho[2,l-b]pyrylium perchlorate,

2,3-diphenylbenzo[b]pyrylium perchlorate,

2-styrylbenzo[b] pyrylium perchlorate,

2- (4-methoxyphenyl) -4-methylmercapt0benzo [b] pyrylium perchlorate,

4-methoxy-2- 4-methoxyphenyl benzo [b] pyrylium perchlorate,

9-methylxanthylium perchlorate, I

2-phenyl- 4 styrylbenzo [b]pyrylium perchlorate,

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

9-methylthiaxanthylium perchlorate, I

2-cl 11oro-3phenylnaphtho[2,l-b] pyrylium perchlorate,

10Hi ndeno 1,2-b] benzo [e] pyrylium' perchlorate, and 3-methyl-2,-(4-methoxyphenyl) benzo [b] pyrylium fluoroborate I 9. A far red and near infraredsensitive photoconductive composition comprising an electrically" insulating filmforming resin binder and organic photoconductor selected from the group consisting of 4,4 bis(diphenpylaminochalcone), bis(4-diphenylaminobenzo)acetone and'4-acetyltriphenylamine and a sensitizer material selected from the group of compounds having the formula:

R4 R; I. l

wherein:

Z- is an anion;

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

R is selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 12 carbon atoms, an alkoxy radical having from 1 to 4 carbon atomsin the alkyl moiety, an aryl radical, an aralkenyl radical having from 2 to 6 carbon atoms in the alkenyl moiety and a heterocyclic radical havingS to 6 atoms in the hetero ring including at least one hetero atom selected from the group consisting of oxygen and sulfur;

R is selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 12 carbon atoms, an 'alkoxy radical as above, an aryl radical, an aroyl radical, and an alkoxycarbonyl radical having from'l to 4 carbon atoms in the alkoxy moiety;

12 R is selected from the groupconsisting of a hydrogen atom, a,ha1ogen. atom, a hydroxy. radical, analkyltradical having from 1 'to 112 carbon atoms, an alkoxyradicalas in R a vinyl radical and an arylradical; n n I R and R 'a're each selected from the groupcons'isting of a hydrogenatom andan alkyl radical of from 1 to 12 carbon atoms; i. 1 whenvtakentogether, any two of R R R R and R5 attached to adjacent carbon atoms represent the atoms necessaryto forma fused ring structure selected from thegroup consisting of aromatic, alicyclic and unsaturated alicyclic radicals having from 5 to 8 carbon atoms; f t "I said photoconductor being present in an amount of at least about 1% by weight of the composition and said sensitizer beingpresent in an amount of about 0.0001 to about 30%. by weight of the composition, each of said photoconductor. and said sensitizer'material having'sub: stantially no sensitivity to radiation of a wavelength greater than. about 650 my, s'aidscomposition characterized in that said photoconductor and sensitizer interact to exhibit a combined long Wavelength spectral sensitivity in the range of radiation having a wavelength of about 650 to about 900 m.

10. An electrophotographic element comprising a conductive support having coated thereon a. layer of a photoconductive composition of claim 9.

11. In an electrophotographic process wherein an electrostatic charge pattern is formed on a photoconductive element, the improvement wherein said photoconductive element has a photoconductive layer of a composition of claim 9. 7

References Cited UNITED STATES PATENTS