US3549358A

US3549358A - Electrophotographic process using organic photoconductors having at least two chromophores

Info

Publication number: US3549358A
Application number: US786461A
Authority: US
Inventors: Nicholas J Clecak; Robert J Cox
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1968-12-23
Filing date: 1968-12-23
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22
Also published as: GB1296864A; DE1963197A1; FR2026846A1; GB1296863A; GB1296862A

Description

United States Patent Int. Cl. G03g 5/00 US. Cl. 96--1 2 Claims ABSTRACT OF THE DISCLOSURE The organic photoconductors are certain linear molecules having at least two chromophores such as a Schiffs base group or an azo group joined to one another through a benzene ring or series of benzene rings. These compounds have been found to be useful as photocondnctors in electrophotographic processes. Some of the compounds are novel.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a class of organic photoconductive materials and, more particularly, relates to their use as photocondnctors in electrophotographic processes, especially those utilizing contact reflex exposure.

Description of prior art A number of organic photocondnctors are known in the prior art, but most of them have not achieved commercial success because their sensitivity or exposure speed is too slow to compete favorably with the commercially used inorganic photocondnctors, such as selenium. However, aside from speed, most organic photoconductors offer many advantages over the commercially used selenium. That is, photoconductive elements fabricated from organic photocondnctors are easily manufactured, can be substantially translucent, and are sufficiently flexible to be used in belt configurations and the configurations of Us. patent application Ser. No. 649,162 filed June 22, 1967, now abandoned.

US. patent application Ser. No. 668,697, filed Sept. 18, 1967, describes a contact reflex reproduction method. The compounds of the present invention are particularly useful in such a process.

US. patent applications Ser. No. 668,703, filed Sept. 18, 1967, now US. Pat. 3,489,558 and Ser. No. 668,696, filed Sept. 18, 1967, now US. Pat. 3,501,293 both describe other compounds useful as organic photoconductors.

SUMMARY OF THE INVENTION It has now been found that a class of compounds offer the advantages of organic photocondnctors, discussed above, and, in addition, exhibit dichroism. The compounds of the present invention are those having the forwherein A is selected from the group consisting of X is selected from the group consisting of: CH==N), (N=CH) (N=N) (CH=CH-CH=N) and (N=CHCH=CH); and R is selected from the group consisting of hydrogen, nitro, lower dialkyl-amino, and lower dialkyl-aminophenylazo.

Of the compounds covered by the above general formula, the most preferred ones are those in which R is lower dialkyl-aminophenylazo while X is (CH=N-) and A is and also those in which R is lower dialkyl-amino while X is (CH=CHCH=N-) and A is Both of these two classes of most preferred compounds are novel.

For the preparation of photoconductive elements, it is advantageous for the compounds of the general formula to be dissolved in organic solvents, such as tetrahydrofuran, or any other solvent in which the compounds are at least partially soluble. Such solutions are applied to substrates suitable for electrophotography and the solvent is then removed. Mixtures of solvents can also be used.

Instead of the above preparation, the compounds of the general formula can be used in conjunction with a resinous binder. Suitable resins include both natural and synthetic resins, examples of which are balsam resins, phenol resins modified with colophony, coumarone resins, indene resins, cellulose ethers, polyvinylchlorides, polyvinylacetate, acrylic polymers, such as polymethyl acrylic esters, polystyrene, polyisobutylene, polyvinylnormal, polycondensates, such as phthalate resins, polyamides, and polyadducts, such as polyurethanes.

The proportion of resin to the photoconductive compound can vary greatly, but elements having a high proportion of resin and a low proportion of photoconductive compound are the less desired. Mixtures of at least equal parts resin and photoconductive compound are preferred.

The substrate material, if one is desired, may be any which satisfy the requirements of electrophotography such as metal, glass, paper, or plastic. Unless it is to be used in a device employing dual corona discharge, such as US. Pat. 2,922,883, the substrate should preferably have a conductivity greater than 10- ohm cm.-

Application of the solutions of the compounds of the general class, with or without resins, is in the usual manner, such as 'by spraying, doctor blade, meniscus coating, etc., followed by drying.

One type of electrophotographic process in which the compounds of the present invention are useful is known as xerography. The process comprises the laying down of the uniform electrostatic charge on a photoconductive and insulating element, exposing the electrostatic charge surinto contact with the developed image and transferred I thereto and fixed thereon. The residual toner remaining on the photoconductive insulating element is removed by cleaning and the element is then ready for the preparation of the next copy or the next cycle.

Because they have the additional advantage of being dichroic, the compounds of the present invention are suitable for use in that type of electrophotography known as contact reflex reproduction, which is an electrophotographic process for the production of related as a yellow crystalline solid as shown in Beil., 14, 35. It had the following analysis.

Calcd. for C H N (percent): C, 77.8; H, 7.1; N, 15.1. Found (percent): C, 77.9; H, 7.1; N, 15.1.

EMMPLE II 1,4 bis benzylidene bis N,N dimethyl-p-phenylenediamine flex copies in which a document is positioned adjacent a photoconductive element which exhibits photoconductive dichroism and has a preferred absorption axis, and in which the photoconductive element is uniformly exposed through the photoconductive element with polarized light whose vector, relative to the absorption axis, is such that the light is not absorbed. The polarized light in striking the document is absorbed in some areas, nor- CHa and, hence, permits the formation of an electrostatic charge pattern corresponding to the document.

The general nature of the invention having been set forth, the following examples are now presented as to the specific preparation of compounds falling within the above general class and the specific preparation of these compounds into photoconductive elements which are then used in electrophotographic processes. The specific details presented are for purposes of illustration and not limitation.

A general method for the preparation of the Schitfs base type of condensation product is as follows:

The difunctional aldehyde or diamine is dissolved in an alcohol such as n-butanol with a slight excess of the mono functional aldehyde or amine and heated to reflux for 6-2 hours. The resultant condensation products precipitate out of the hot reaction solvent and are hot filtered. They are subsequently washed with acetone, ether, 55

and dried.

Prepared according to the general procedure by refluxing terephthaldehyde and N,N-dimethyl-p-phenylenediamine in ethanol for one hour. Isolated as an orange solid.

Calcd. for C H N (percent): C, 77.8; H, 7.1; N, p

15.1. Found (percent): C, 78.3; H, 7.1; N, 14.5.

EXAMPLE III 4,4 bis(p-dimethylaminobenzylideneamino) stilbene Prepared following the general procedure by reflexing 4,4 diaminostilbene and p dimethylaminobenzaldehyde for one hour in n-butanol. It was isolated as orange crystals as shown in Beil., 14 (I), 361.

Calcd. for C H N (percent): C, 81.3; H, 6.8; N, 11.8. Found (percent): C, 81.2; H, 6.8; N, 11.7.

EXAMPLE IV 4,4 bis(p-dimethylaminobenzylideneamino) bibenzyl Prepared by the general procedure using n-butanol and refluxing 4,4' diaminobibenzyl and p-dimethylaminobenz- 40 aldehyde for two hours. Isolated as yellow solids,

Calcd. for C H N, (percent): C, 81.0; H, 7.2; N, 11.8. Found (percent): C, 81.1; H, 7.3; N, 11.7.

EXAMPLE V N,N bis(benzylidene) benzidine Prepared by the general procedure by refluxing benzidine 5 and benzaldehyde in ethanol for 1 hour as referenced EXAMPLE VI N,N' bis (p-dimethylaminobenzylidene) benzidine EXAMPLE I N,N' bis(p-dimethylaminobenzylidene) p-phenylenediamine This compound was prepared by the above general method by refluxing in ethanol for one hour. It was iso- 70 Prepared by the general procedure by heating benzidine and p-dimethylaminobenzaldehyde in ethanol for one hour. Isolated as a yellow solid as shown in CA., 52:5197

Calcd. for C H N (percent): C, 80.7; H, 6.8; N, 12.5. Found (percent): C, 80.8; H, 6.9; N, 12.4.

EXAMPLE VII N,N' bis (9-julolidinidene) benzidine CHzCHzCHz CHaCHz (EH3 Prepared by the general procedure refluxing 9-formyl- '1 g. 4,4 diaminostilbene and 3 g. p-N,N-dimethylaminojulolidene and benzidine in n-butanol for two hours. Isocinnamaldehyde in 150 ml. n-butanol were refluxed for lated as yellow solids. 45 minutes. The resulting precipitate was hot filtered and Calcd. for C H N (percent): C, 82.8; H, 6.9; N, washed with acetone, ether and dried. Recovered 0.75 g.

10.2. Found (percent): C, 82.7; H, 6.9; N, 10.3. brown solids. The product had the following analysis.

This compound fits into the general formula given 5 Calcd. for C H N (percent): C, 82.4; H, 6.9; N, above when the lower dialkyl-amino group R is consid- 107. Found (percent): C, 81.6; H, 6.8; N, 10.9.

ered to be linked at both ends to the phenyl ring. d 'g q Bowl Compound was found to be y highly 1 or EXAMPLE VH1 c 0 EXAMPLE XIV N,N' bis (p-dimethylaminophenylazobenzilidine) A photoconductive element was prepared by dispersing benzidine N,N bis(p dimethylaminobenzylidene)p phenylenedi- CH; CH:

01 13 cHa Prepared by the general procedure by refluxing benzidine amine (the compound prepared in Example I above) in and p-dimethylaminophenylazobenzaldehyde in ethanol an equal weight of polystyrene dissolved in 1,2-dichlorofor A hour. Isolated as red crystals. ethane and coating the solution on an aluminum slide Calcd. for C H N (percent): C, 77.0; H, 5.8; N, with a doctor blade set at a 5 mil wet gap. The thus 17.1.Found (percent): C, 76.1; H, 5.9; N, 16.9. prepared photoconductive element was uniformly elec- This novel compound was found to be dichroic to an trostatically charged using a Xerox Model D Processor at outstanding degree. a potential of +7000 volts. After charging, the element EXAMPLE IX was exposed to a 375 watt GE Photo EBR lamp at a distance of 12 inches for 2 seconds and using positive trans- (p-dimethylaminocinflamalidene) benzidine parency as a document to be copied. The formed elec- Prepared y the general Procedure y refluxing bfinzidine trostatic image was developed with negatively charged and P-dimetPY1amininnama1dehde in ethanol for toner (Xerox 914) across the photoconductive element. hour. It was lsolated as a brown sohd.

Calcd. for C34H34N4 (percent): C, 80.2; H 69; N Again using the Xerox Model D Processor, the toner 11.2. Found (percent): C, 80.3; H, 6.9; N, 11.6. 35 image Was transferred to p p y spraying positive EXAMPLE X charges on the back of the paper. After transfer of the 4,4-bis (p-dimethylaminophenylazo) biphenyl toner image, the toner was fused to the paper on a hot CH: CE; a This was prepared by diazotizing benzidine and coupling plate to yield a high quality copy of the document with with dimethyl amiline as outlined in Aust. J. Chem., 1455 high contrast, high image density, and faint background.

(1967). EXAMPLE XV EXAMPLE XI A photoconductive element was prepared by dispers- 4,4 (bis p-nitrocinnamylidene) benzidine ing N,N' bis(p-dimethylaminophenylazobenzilidine)ben- 0.45 g. benzidine and 1.5 g. p-nitrocinnamaldehyde in zidine (the compound of Example VIII above) in an 100 ml. n-butanol were refluxed for 1 hour. The resultequal weight of polystyrene dissolved in 1,2-dichloroething precipitate was hot filtered and washed with acetone, ane and coating the solution on an aluminum slide with ether and dried. Recovered 1.05 g. red colored solids. a doctor blade set at a 5 mil Wet gap. The thus prepared Calcd. for C H N O (percent): C, 71.7; H, 4.4; N, photoconductive element was uniformly electrostatically 11.2. Found (percent): C, 71.8; H, 4.5; N, 11.4. charged using a Xerox Model D Processor at a potential EXAMPLE XII of +7000 volts. After charging, the element was exposed to a 375 watt GE Photo EBR lamp at a distance of 12 inches for 0.1 second and using positive transparency Bis (p-dimethylaminophenylimino) bis 1,4-phenylene-2- propeneylidene as a document to be copied. The formed electrostatic H3O CH3 N N=HC-HC=HC -CH=CH-CH=N N 1130 CHa Bis 1,4-phenylenepropenal and N,N-dimethyl-p-phenylimage was developed with negatively charged toner f i are refluxed 1I1 ethanol- The resultant P (Xerox 914) across the photoconductive element. Again ciprtate is hot filtered and the product worked up 1n a using the Xerox Model D Precassor the toner image manner analogous to the above examples was transferred to paper by spraying positive charges EXAMPLE XIII on the back of the paper. After transfer of the toner 4,4 -bis (p-dimethylaminocinnamylideneamino) stilbene image, the toner was fused to the paper on a hot plate CH3 CH3 CH3 CH3 7 to yield a high quality copy of the document with high contrast, high image density, and faint background.

EXAMPLE XVI 10% polyvinyl carbazole in benzene 40 Benzene a 20 Chloroform 30 Toluene 10 1,3-dinitronaphthalene 0.04

1% benzene solution of a plasticizer consisting of a combination of polymers of esters of acrylic acid and methacrylic acid 8 This formulation is coated at 3 feet per minute on a meniscus coater and cured for 1 hour at 90 C. Electrometer results show a charge acceptance of about 600 v. The film is used to make robot copies in the contact reflex mode. 7

While the invention has been shown and described with reference to preferred embodiments thereof, it will be appreciated by those skilled in the art that variations in form may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an electrophotographic reproduction process which comprises selectively rendering portions of a photoconductor electrically conductive by selective exposure to light, the improvement according to which the photoconductive element comprises a compound selected from the group consisting of compounds having the formula:

wherein A is selected from the group consisting of CH2CH2 X is selected from the group consisting of:

-cH=N-) (-N= H) N=N) (CH =CHCH=N) and (N=CH-CH=CH-); and R is selected from the group consisting of hydrogen, nitro, lower dialkylamino, and lower dialkyl-aminophenylazo.

2. A step of exposing the photoconductive element as claimed in claim 1 wherein the process is carried out in the contact reflex mode.

References Cited UNITED STATES PATENTS 3,066,023 11/1962 Schlesinger 96-1 3,163,532 12/1964 Schlesinger 96-1 3,335,003 8/1967 Snelling 96-1 3,489,558 1/1970 Clecak 96-1 GEORGE F. LESMES, Primary Examiner M. B. W'ITTENBERG, Assistant Examiner U.S. Cl. X.'R.