US3488705A - Thermally unstable organic acid salts of triarylmethane dyes as sensitizers for organic photoconductors - Google Patents

Description

United States Patent US. Cl. 961.6 32 Claims ABSTRACT OF THE DISCLOSURE Organic acid salts of triarylmethane dyes are useful as sensitizers in electrophotographic elements. They are thermally unstable and thus readily bleachable. Accordingly, exposed and developed electrophotographic elements having colorless background areas are attainable.

This application is a continuation-inpart of Ser. No. 447,937, filed Mar. 16, 1965, now US. Patent 3,387,973, which in turn is a division of Ser. No. 163,092, filed Dec. 29, 1961, now US. Patent 3,234,280.

This invention relates to electrophotography, and in particular to novel sensitized photoconductive compositions and elements having coated thereon such compositions.

The process of Xerography, as disclosed by Carlson in Us. Patent 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, generally in the dark after a suitable period of dark adaptation. It 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 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, or 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 also been screened for their photoconductive properties. As a result, a very large number of organic compounds are known 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 3,488,705 Patented Jan. 6, 1970 ICC having desirable electrophotographic properties can be especially useful in elecetrophotography. Such electrophotographic elements may be exposed 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 used to form subsequent images after residual toner from prior images has been removed by transfer and/ or cleaning.

Although some of the organic photoconductors comprising the materials described are inherently light sensitive, their degree of sensitivity is usually low and in the short wavelength portion of the spectrum so that it is common practice to add materials to increase the speed and to shift the sensitivity toward the longer wavelength portion of the visible spectrum. Increasing the speed and shifting the sensitivity of such systems into the visible regon of the spectrum has several advantages: it makes available inexpensive and convenient light sources such as incandescent lamps; it reduces exposure time; it makes possible the recording of a wide range of colors in proper tonal relationship, and allows projection printing through various optical systems. By increasing the speed through the use of sensitizers, photoconductors which would otherwise have been unsatisfactory are useful in processes Where high speeds are required such as document copying. However, while some of the sensitizers have appreciably increased the speed of a photoconductive system, they have also produced a colored background in the finished print. This is particularly true of the triarylmethane dye sensitizers such as crystal violet, rhodamine B and hexaphenylpararosaniline. While these dyes are generally considered to be effective for sensitizing photocondutcive compounds, they also impart color to the initial photoconductive composition. The intense color of these dyes is maintained throughout the processing of the photoconductive coatings and thus appears in the final product.

It is, therefore, an object of this invention to provide a novel class of triarylmethane dye sensitizers for use in combination with photoconducting compounds so that colorless final reproductions are obtainable.

Another object of this invention is to provide novel sensitized photoconductive elements.

It is also an object to provide novel sensitized photoconductive compositions which can be positively and negatively charged.

These and other objects of this invention are accomplished with photoconductive compositions containing a photoconductor and a sensitizer which is an organic acid salt of a triarylmethane dye. In accordance with this invention, it has been found that the organic acid salts of these dyes have a range of thermal instability. The ad- Vantage of employing a thermally unstable sensitizing dye is that the intense color of the dye in the background areas of the image-bearing element may be eliminated simply by applying heat to the coating. The use of the organic acid salt does not alter the ability of the triarylmethane to effectively sensitize the photoconductive composition. While the chloride salts, the usual form in which the dyes exist, are relatively stable, the corresponding organic acid salt derivatives of these dyes are thermally unstable. Thus, upon heating an element after an image is obtained, the dye compound is decomposed and bleaching occurs. By this technique the background areas of the reproduction are rendered colorless.

The anion of the triarylmethane organic acid salts of this invention are derived from a wide variety of organic acids. The term organic acid salt includes mono-salt derivatives as well as di-salt derivatives obtained from monocarboxylic and polycarboxylic acids. Typical organic acid salt derivatives which form the anion of the sensitizers of this invention include the following:

Alkanoate derivatives having one to ten carbon atoms such as formate, acetate, propionate and butyrate radicals including substituted alkanoate derivatives such as haloacetate, cyanoacetate and oxalate radicals;

Aryloate derivatives such as benzoate and naphthoate radicals and including substituted aryloate derivatives such as a salicylate radical;

Alkenoate derivatives having one to ten carbon atoms such as acrylate, crotonate and vinylacetate radicals; and

Aryl and alkane sulfonate derivatives such as benzenesulfonate and methylsulfonate radicals.

The cation of the sensitizing salts of this invention is formed from any of the triarylmethane dyes which exhibit a sensitizing effect when used with a photoconductive composition. Such cation furnishing dyes include malachite green; various dyes from the rosaniline series such as pararosaniline, hexaphenylpararosaniline, tri-para-tolylpararosaniline, methyl violet and crystal violet; various phthaleins such as phenol phthalein; and xanthenes such as fluorescein, rosamine and rhodamine B. The preferred triarylmethane dye derivatives are the triphenylmethane dyes having at least one phenyl radical substituted in the para position by an amino radical including substituted amino radicals such as an alkylamino radical.

Typical triarylmethane dye salts which belong to the herein described general class of sensitizing compounds include the following:

formate salt of hexaphenylpararosaniline diformate salt of hexaphenylpararosaniline acetate salt of hexaphenylpararosaniline chloroacetate salt of hexaphenylpararosaniline dichloroacetate salt of hexaphenylpararosaniline diacetate salt of hexaphenylparaosaniline di-(dichloroacetate) salt of hexaphenylpararosaniline di-(chloroacetate) salt of hexaphenylpararosaniline fiuoroacetate salt of hexaphenylpararosaniline difluoroacetate salt of hexaphenylpararosaniline trifluor'oacetate salt of hexaphenylpararosaniline di-(fiuoroacetate) salt of hexaphenylpararosaniline di-(trifluoroacetate) salt of hexaphenylpararosaniline cyanoacetate salt of hexaphenylpararosaniline di-(cyanoacetate) salt of hexaphenylpararosaniline salicylate salt of hexaphenylpararosaniline oxalate salt of hexaphenylpararosaniline benzenesulfonate salt of hexaphenylpararosaniline methylsulfonate salt of hexaphenylpararosaniline acetate salt of tri-p-tolylpararosaniline trifiuoroacetate salt of tri-p-tolylpararosaniline formate salt of tri-p-tolylpararosaniline trifluoroacetate salt of crystal violet di-(trifluoroacetate) salt of crystal violet formate salt of crystal violet diformate salt of crystal violet acetate salt of crystal violet diacetate salt crystal violet salicylate salt of crystal violet difluoroacetate salt of crystal violet diphenylanthranilate salt of crystal violet dichloroacetate salt of crystal violet trifiuoroacetate salt of rhodamine B salicylate salt of rhodamine B di-(trifluoroacetate) salt of rhodamine B diacetate salt of rhodamine B formate salt of rhodamine B acetate salt of rhodamine B trifiuoroacetate salt of poly-hexaphenylpararosaniline di-(trifluoroacetate) salt of poly-hexaphenylpararosaniline chloroacetate salt of poly-hexaphenylpararosaniline dichloroacetate salt of poly-hexaphenylpararosaniline cyanoacetate salt of poly-hexaphenylpararosaniline (ii-(chloroacetate) salt of po1y-hexaphenylpararosaniline di-(dichloroacetate) salt of poly-hexaphenylpararosaniline di-(cyanoacetate) salt of poly-hexaphenylpararosaniline The organic acid salts of the triarylmethane dyes of this invention are obtained by converting the chloride salt, the usual form in which the dye exists, to the carbinol base and subsequently treating the carbinol base with the desired acid. The di-salt is obtained by using twice the stoichiometric amount of acid required. The conversion to the carbinol base is accomplished by treating the chloride salt in solution with dilute alkali.

Electrophotographic elements of the invention can be prepared with any photoconductive compound and the sensitizers of this invention in the usual manner, i.e., by blending a dispersion or solution of the photoconductive compound together with a 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-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 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 photoconductors can be organic compounds including organo-metallic compounds, or inorganic compounds. Typical inorganic photoconducting compounds are zinc oxide and selenium while representative organo-metallic compounds are the organic derivatives of Group We and Va metals such as those having at least one aminoaryl group attached to the metal atom. Exemplary organometallic compounds are the triphenyl-pdialkylaminophenyl derivatives of silicon, germanium, tin, and lead and the tri-p-dialkylaminophenyl derivatives of arsenic, antimony, phosphorous and bismuth.

The preferred photoconductors are those organic compounds which exhibit an electrophotosensitivity to light and are capable of forming transparent elements. An especially 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; p-anilinophenol; N,N di 2- naphthyl-p-phenylenediamine; 4,4benzylidene-bis-(N,N- diethyl-m-toluidine), those described in Fox US. Patent 3,240,597 issued March 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-hexanoyltripheny1- amine; 4-laur0yltriphenylamine; 4-hexyltriphenylamine, 4-dodecyltn'phenylamine, 4,4'-bis(diphenylamino)benzil, 4,4'-bis(diphenylamino)benzophenone, and the like, and (b) polymeric triarylamines such as poly[N,4"- (N,N,N triphenylbenzidine)]; polyadipyltriphenylamine, polysebacyltriphenylamine; polydecamethylenetriphenylamine; poly N-(4-vinylphenyl)diphenylamine, poly-N-(vinylphenyl)-a,a'-dinaphthylamine and the like.

Other useful amine-type photoconductors are disclosed in US. Patent 3,180,730, issued Apr. 27, 1965.

Useful photoconductive substances capable of being spectrally sensitized in accordance with this invention are disclosed in Fox US. Patent 3,265,496 issued Aug. 9, 1966, and include those represented by the following wherein R 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 a 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,retc.), 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 polynucle-ar 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, or 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 producing the present invention. Such photoconductors are described in US. Patent 3,274,000; French Patent 1,383,461 and in copending application of Seus and Goldman Ser. No. 627,857 filed Apr. 3, 1967. These photoconductors include leuco bases of diaryl or triarylmethane dye salts, 1,1,1-triary1alkanes 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 polyarylalkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and I is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are pref era bly phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having 1 to 8 carbon atoms, hydroxy, halogen, etc. in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula 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 5 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 I Compound name Compound No.

4,4-diethylamino-2,2'-dimethyltriphenylmethane 1 4',4" diamino 4-dimethylamino-2,2"-dimethyltriphenylmethane 2 4',4" bis(diethylamino) 2,6 dichloro 2',2"-

dimethyltriphenylmethane 3 4,4"-bis(diethylamino) 2,2 dimethyldiphenylnaphthylmethane 4 2',2" dimethyl 4,4',4" tris(dimethylamino) triphenylmethane 5 4',4" bis(diethylamino) 4-dimethylamino-2',2"-

dimethyltriphenylmethane 6 4',4" bis(diethylamino)-2-chloro-2',2"-dimethyl- 4-dimethylaminotriphenylmethane 7 4',4 bis(diethylamino)-4-dimethylamino-2,2,2"-

trimethyltriphenylmethane 8 4,4" bis(dimethylamino)-2-chloro-2',2"-dimethyl- 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(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(ethylenealkaryloxyalkylene terephthalate); phenol-form aldehyde resins; ketone resins; polyarnides, polycarbonates; polythiocarbonates; poly(ethyleneglycolco-bishydroxyethoxyphenyl propane terephathalate); 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. Patents 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-lOl, 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 paraflin, 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, 2-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 was 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 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 or aluminum and the like. An especially useful conducting support can be prepared by coating a support material such as polyethylene terephthalate with a layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Patent 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 by the layer owing to 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 a latent image in the photoconducting layer. By exposure of the surface in this manner, a charge 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, e.g., powder, a pigment in a resinous carrier, i.e., toner, or a liquid developer may 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 Patent 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photo-conductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. The heating also causes the sensitizing dye to bleach thus rendering the background areas colorless. The heating is generally carried out in a temperature range of from about 25 C. to about 150 C. The preferred range is from about C. to about C.

The present invention is not limited to any particular mode of use of the new electrophotographic materials, and the exposure technique, the charging method, the transfer (if any), the developing method, and the fixing method as well as the material used in these methods can be selected and adapted to the requirements of any particular technique.

Electrophotographic materials according to the present invention can be applied to reproduction techniques wherein different kinds of radiations, i.e., electromag netic radiations as well as nuclear radiations can be used. For this reason, it is pointed out herein that although materials according to the invention are mainly intended for use in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, is to be interpreted broadly and understood to comprise both xerography and xeroradiography.

The invention is further illustrated by the following examples which include preferred embodiments thereof.

EXAMPLE 1 Preparation of the diformate salt of hexaphenylpararosaniline EXAMPLE 2 Preparation of the formate salt of hexaphenylpararosaniline The preparation is carried out in a manner similar to that set forth in Example 1 except that an equimolar amount of formic acid is added to form the formate.

EXAMPLE 3 Preparation of organic acid mono-salts of triphenylmethane dyes Mono-salts of tri-para-tolylpararosaniline, hexaphenylpararosaniline, crystal violet and rhodamine B are prepared by the procedure of Example 1 from the following organic acids:

trifluoroacetic acid cyanoacetic acid salicyclic acid oxalic acid benzenesulfonic acid methylsulfonic acid formic acid acetic acid chloroacetic acid dichloroacetic acid fluoroacetic acid difiuoroacetic acid In each instance the mono-salt of the corresponding acid is obtained.

9 EXAMPLE 4 Preparation of organic acid di-salts of triphenylmethane dyes The preparation is carried out in the same manner as Example 3 by reacting the dyes of Example 3 with two 5 moles of organic acid for each mole of dye. In' each instance the di-salt of the corresponding acid is obtained.

EXAMPLE 5 Preparation of organic acid salts of polymers of hexaphenylpararosaniline EXAMPLE 6 25 Photoconductive compositions containing the triarylmethane salt sensitizers of the type described herein are separately incorporated into a coating dope having the following composition:

The following tables set forth the number of steps developed showing the eflectiveness of these materials as sensitizers. The polymeric binder used in the coating compositions is a polyester of terephthalic acid and a mixture of ethylene glycol (1 part by weight) and 2,2-bis(4- fl-hydroxyethoxyphenyl)propane (9 parts by weight). The photoconductors referred to in the following tables are:

Al ,3,S-triphenyl-Z-pyrazoline B-4,4'-diethylamino-2,2-dimethyltriphenylmethane C4,4'-bis (diethylamino benzophenone D-tetra-2-naphthyl hydrazine EN- [2-( 1,2,3,4-tetrahydro-2-methyll-quinolyl) ethyl] phthalimide F-2,3 ,4,5-tetraphenylpyrrole Gtriphenylamine The sensitizers referred to in the following tables are:

HPPR-hexaphenylpararosaniline TTPR-tri-para-tolylpararosaniline CV-crystal violet RBrhodamine B TABLE II The following data shows the sensitizing effect of various HPPR organic acid salts with a number of organic acid salts with a number of organic photoconductors.

No. of Color Change on Heating Photo- Image clear No. conductor HPPR salt used formed steps Before After Trifluoroacetate Yes 21 Blue Colorless. Di-(trifluoroacetate) Yes-.." Do. Cyanoaeetate-.. Yes-.. Do. Di-(eyanoacetate) Yes..." Do. Chloroacetate Yes... Do. Di-(ehloroacetate) Yes Do. Dichloroacetate Yes. Do, Di-(dichloroacetate) Yes. Do. Formate Yes. Do. Acetate Yes Do. Di-(trifiuoroacetate) Yes.. Do. do Yes"... Do. Yes-.." Do. Yes Do. Yes Do.

Organic photoconductor g 0.15 TABLE III P l meric ind r .5 sgngitizer b e t 2 2 The following data shows the sensitlzing elfect of r r 7""""""""-'""" various TTPR or anic a i s lts Methylene chlorlde or tetrahydrofuran ml 5 g c d a Wlth Photoconductor A These compositions are then separately coated at a wet thickness of 0.004 inch on an aluminum surface maintained at 100 F. to provide the coatings described in Table 1 below. In a darkened room, the surface of each of the Photoconductive layers so prepared is either positively or negatively charged to a potential of about 600 volts under a corona charger. The charged layer is exa powder toner comprising carbon black particles in a polystyrene binder having optical density according to the method described in US. Patent 2,297,691. After the latent image is developed, the coating is heated to a temperature of to about C. Heating bleaches the background and fixes the developer simultaneously. 75

Color Changes on No. of Heating Photo- Image clear N o. conductor TTPR Salt formed steps Before After a A Formate Yes 9 Blue Colorless. b A Chloride Yes do Blue.

TABLE IV The following data shows the sensitizing effect of various CV organic acid salts with a number of photoconductors.

Color Change on No. of Heating Photo Image clear No. conductor CV Salt formed steps Before After a A Diformate Yes 16 Blue Colorless. b A Chloride Yes 5 do Blue.

B Do. (1 C Do TABLE V The following data shows the sensitizing effect of various RB organic acid salts with a number of photoconductors.

No. Color Changes on of Heating Photo- Image clear No. conductor RB Salt formed step Before After a- G Chloride Yes 7 Pink Faint pink. b 6 do Colorless.

Trifluoroacetate Yes .1. 13 do Do. Di-(trifluoroacetate) Yes. do Do. Diacetate Y Do. Fonnate Do. Acetate. Do. Chloride. Faint pink. Salicylate. Colorless. 'Irifluoroacetate Do. Di-(trifiuoroacetate) Yes. Do. Diacetate Y Do. Do. Do. Faint; pink. Colorless. Trifluoroacetate D o. Di-(trifluoroacetate) Diacetate Formats Acetate.

Chloride Trifluoroaeetate Yes- Di-(trifluoroaeetate) Yes- Dlacetate Y Acetate Pink. Colorless.

It is to be noted in the above tables that when the triarylmethane dyes are used in their usual form, the chloride salt, little or no bleaching occurs. Also to be noted is that there is no appreciable loss in the sensitizing efiect of the triarylmethane compounds when an organic acid salt is used instead of the chloride.

EXAMPLE 7 The procedure of Example VI is repeated except that the triarylmethane sensitizing dyes used are polymers of the various organic acid salts of hexaphenylpararosaniline set forth in Table I. In each case the exposed element is bleachable upon application of heat and also in each instance an image is obtained.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

We claim:

1. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising (a) an organic photoconductor, (b) a sensitizer comprising an organic acid salt of a triphenylmethane dye having at least one of said phenyl radicals substituted in the para position by an amino radical, the anion of said salt being selected from the group consisting of an alkanoate radical, an aryloate radical, an alkenoate radical, an aryl sulfonate radical and an alkane sulfonate radical and (c) a polymeric binder, said sensitizer comprising from about 0.0001 to about percent by weight of said photoconductive composition.

2. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising (a) an organic photoconductor, (b) a sensitizer comprising an organic acid salt of a triphenylmethane dye having at least one of said phenyl radicals substituted in the para position by an amino radical, the anion of said salt being selected from the group consisting of a formate radical, an acetate radical, a salicylate radical, an oxalate radical, an aryl sulfonate radical, an alkane sulfonate radical and a malonate radical and (c) a polymeric binder, said sensitizer comprising from about 0.0001 to about 30 percent by weight of said photoconductive composition.

3. The electrophotographic element of claim 2 wherein the anion of said sensitizer salt is an acetate radical selected from the group consisting of a haloacetate radical and a cyano acetate radical.

4. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising (a) an organic photoconductor, (b) a sensitizer comprising an organic acid salt of a triphenylmethane dye selected from the group consisting of a hexaphenylpararosaniline, a polymer of hexaphenylpararosaniline, a tri-p-tolylpararosaniline, crystal violet and rhodamine B, the anion of said salt being selected from the group consisting of a formate radical, an acetate radical, a salicylate radical, an oxalate radical, an aryl sulfonate radical, an alkane sulfonate radical and a malonate radical and (c) a polymeric binder, said sensitizer comprising from about 0.0001 to about 30 percent by weight of said photoconductive composition.

5. The electrophotographic element of claim 4 wherein the sensitizer comprises the monoformate salt of said triphenylmethane dye.

6. The electrophotographic element of claim 4 wherein the sensitizer comprises the diformate salt of said triphenylmethane dye.

7. The electrophotographic element of claim 4 wherein the sensitizer comprises the acetate salt of said triphenylmethane dye.

8. The electrophotographic element of claim 4 wherein the sensitizer comprises the diacetate salt of said triphenylmethane dye.

9. The electrophotographic element of claim 4 wherein the sensitizer comprises the chloroacetate salt of said triphenylmethane dye.

10. The electrophotographic element of claim 4 wherein the sensitizer comprises the di-(chloroacetate) salt of said tri-phenylmethane dye.

11. The electrophotographic element of claim 4 wherein the sensitizer comprises the dichloroacetate salt of said triphenylmethane dye.

12. The electrophotographic element of claim 4 wherein the sensitizer comprises the di-(dichloroacetate) salt of said triphenylmethane dye.

13. The electrophotographic element of claim 4 wherein the sensitizer comprises the fluoroacetate salt of said triphenylmethane dye.

14. The electrophotographic element of claim 4 wherein the senstiizer comprises the di-(fluoroacetate) salt of said triphenylmethane dye.

15. The electrophotographic element of claim 4 wherein the sensitizer comprises the difluoroacetate salt of said triphenylmethane dye.

16. The electrophotographic element of claim 4 wherein the sensitizer comprises the di-(difiuoroacetate) salt of said triphenylmethane dye.

17. The electrophotographic element of claim 4 wherein the sensitizer comprises the trifluoroacetate salt of said triphenylme-thane dye.

18. The electrophotographic element of claim 4 wherein the sensitizer comprises the di-(trifiuoroacetate) salt of said triphenylmethane dye.

19. The electrophotographic element of claim 4 wherein the sensitizer comprises the cyanoacetate salt of said triphenylmethane dye.

20. The electrophotogra-phic element of claim 4 wherein the sensitizer comprises the di-(cyanoacetate) salt of said triphenylmethane dye.

21. The electrophotographic element of claim 4 Wherein the sensitizer comprises the salicylate salt of said triphenylmethane dye.

22. The electrophotographic element of claim 4 wherein the sensitizer comprises the oxalate salt of said triphenylmethane dye.

23. The electrophotographic element of claim 4 wherein the sensitizer comprises the benzenesulfonate salt of said triphenylmethane dye.

24. The electrophotographic element of claim 4 wherein the sensitizer comprises the methylsulfonate salt of said tri-phenylmethane dye.

25. The electrophotographic element of claim 4 wherein the sensitizer comprises an organic acid salt of a polymer of hexaphenylpararosaniline.

26. A photoconductive element for use in electro photography comprising a support having coated thereon a photoconductive composition comprising:

(a) about 10 to 60% by Weight based on said photoconductive composition of an organic photoconductor,

(b) a film-forming polymeric binder for said photoconductor and (c) 0.005 to 5% of the diformate salt of hexaphenylpararosaniline.

27. A photoconductive element for use in electrophotography comprising a support having coated thereon a photoconductive composition comprising:

(a) about to 60% by weight based on said photoconductive composition of an organic photoconductor,

(b) a film-forming polymeric binder for said photoconductor, and

(c) 0.005 to 5% of the dichloroacetate salt of hexaphenylpararosaniline.

28. A photoconductive element for use in electrophotography comprising a support having coated thereon a photoconductive composition comprising:

(a) about 10 to 60% by weight based on said photoconductive composition of an organic photoconductor,

(b) a film-forming polymeric binder for said photoconductor, and

(c) 0.005 to 5% of the di-(dichloroacetate) salt of hexaphenylpararosaniline.

29. A photoconductive element for use in electrophotography comprising a support having coated thereon a photoconductive composition comprising:

(a) about 10 to 60% by weight based on said photoconductive composition of an organic photoconductor,

(b) a film-forming polymeric binder for said photoconductor, and

(c) 0.005 to 5% of the trifluoroacetate salt of hexaphenylpararosaniline.

30. A photoconductive element for use in electrophotography comprising a support having coated thereon a photoconductive composition comprising:

(a) about 10 to 60% by weight based on said photoconductive composition of an organic photoconduct'or,

(b) a film-forming polymeric binder for said photoconductor and (c) 0.005 to 5% of the di-(trifiuoroacetate) salt of hexaphenylpararosaniline.

31. A photoconductive element for use in electrophotography comprising a support having coated thereon a photoconductive composition comprising:

(a) about 10 to 60% by weight based on said photoconductive composition of an organic photoconductor,

(b) a film-forming polymeric binder for said photoconductor, and

(c) 0.005 to 5% of the di-(cyanoacetate) salt of hexaphenylpararosaniline.

32. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising (a) an organic photoconductor, (b) a sensitizer comprising an organic acid salt of a triphenylmethane dye, the cation of said salt being formed from a triphenylmethane dye selected from the group consisting of a rosaniline dye, a malachite green dye, a phthalein dye and a xanthene dye, and the anion of said salt being selected from the group consisting of an alkanoate radical, an aryloate radical, an alkenoate radical, an aryl sulfonate radical and an alkane sulfonate radical and (c) a polymeric binder, said sensitizer comprising from about 0.0001 to about 30 percent by weight of said photoconductive composition.

References Cited UNITED STATES PATENTS 3,140,948 7/1964 Stewart et al. 96-48 3,180,730 4/1965 Klupfel et al. 961 3,274,000 9/1966 Noe et al. 96-1.5 3,279,918 10/1966 Cassiers et al. 96-1 GEORGE F. LESMES, Primary Examiner J. C. COOPER III, Assistant Examiner U.S. Cl. X.R.