Electrographic Organic Photoconductor Comprising Of N,n,n',n', Tetrabenzyl 4,4'oxydianaline

Abstract

The present invention relates to the composition of N,N,N', N,' tetrabenzyl 4,4' oxydianaline represented by the formula ##SPC1## And its use as an organic photoconductor for preparing photoconductive layers.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to electrographics and, particularly, it is directed to a novel organic photoconductor and its use in preparing photoconductive elements for use in electrographic imaging processes. More specifically, this invention is directed to the novel composition of N,N,N',N' tetrabenzyl 4,4' oxydianaline and its use as a photoconductor.

The term electrophotography, as generally understood in the art, means a reproduction or copying process which utilizes a combination of the electrostatics and the photoconductive phenomena of substances. Electrophotographic processes which depend on photoconductive layers are well known in the art. The most widely used processes are xerography, which employs a selenium coated drum as the photoconductive element, and "Electrofax," which uses zinc oxide as the photoconductor. However, many other photoconductographic processes are well known and reported in the literature.

In an electrophotographic process the electrophotographic element consists essentially of a layer of the photoconductive compound coated on a relatively more conductive support such as electroconductive paper, aluminum foil and the like. When in use, the photoconductive layer is electrically charged in the dark with a corona discharge or the like so that the coating has a uniform positive or negative charge density on its surface. The element is then exposed to a light image which activates the photoconductive compound and an invisible charge pattern is developed on the element. The invisible charge image is subsequently developed with an electrostatically charged toner as is known by those in the art.

In recent years much research has been expended trying to develop suitable photoconductive materials. In the past, most photoconductive layers used in the electrophotographic processes have been based on the use of such inorganic materials as selenium, zinc oxide, cadmium sulfide and the like as the photosensitive element. However, much time has been spent investigating organic photoconductors. Most notable among the organic photoconductors which have heretofore been used are anthracene, anthraquinone, carbazole and perylene. Recently much work has been done on the use of organic photoconductors such as polyvinylcarbazole, N,N,N',N' tetrasubstituted-p-phenylenediamines, and the disubstituted benzylideneazines and the like. For example, see U.S. Pat. No. 3,421,891 which is directed to polyvinylcarbazoles and U.S. Pat. No. 3,314,788 directed to the use of the N,N,N',N' tetrasubstituted-p-phenylenediamines (TSPD) and U.S. Pat. No. 3,290,147 directed to the use of the N-disubstituted benzylideneazines.

However, many of these organic photoconductors suffer from various drawbacks. For instance, some of the compounds are not as photosensitive as desired. Another serious drawback which is especially associated with the TSPD compounds is their limited solubility. The solubility of these compounds in the systems preferred by the industry is very limited and the compounds tend to crystallize rather than form a uniform coating. Therefore, it is an object of this invention to provide a novel organic photoconductive compound which is useful in preparing photoconductive elements.

SUMMARY OF THE INVENTION

We have found that N,N,N',N' tetrabenzyl 4,4' oxydianaline ##SPC2##

is a good photoconductor compound and is very useful in preparing photoconductive elements. Our novel photoconductor is compatible with most of the common resin binders systems used in preparing electrophotographic plates. Moreover, our novel compound is also readily soluble in most of the common solvents preferred by the industry.

We do not wish to be bound by any theories but we believe that the ether functional group enhances the utility of our compound. First, the unshared electrons on the ether oxygen atom improve the photoconductivity of our compound. In addition, the presence of the ether oxygen also modifies the solubility properties. For example, our compound is soluble in solvents such Tetrabenzyl cyclohexanone and the like whereas the TSPD type compounds are not as readily soluble. Our compound is therefore an improvement over the prior art compounds.

We have prepared the N,N,N',N' tetrabenzyl 4,4' oxydianaline of out invention in the following manner:

EXAMPLE 1

Preparation of N,N,N',N' Tetrabanzyl 4,4' Oxydianaline

Into a four-necked, one-liter flask equipped with a mechanical stirrer, reflux condenser, thermometer and addition funnel was charged 0.2 moles of 4,4' oxydianaline dissolved in 300 ml. of Fischer's Reagent Alcohol (ethanol denatured with methanol and isopropanol). Then 0.8 moles of benzyl chloride was added to the reaction flask and the mixture brought to reflux temperature. Then 0.8 moles of potassium hydroxide dissolved in 150 ml. of reagent alcohol was added dropwise over a period of one-half hour. After the potassium hydroxide addition was completed, the reaction mixture was refluxed for 1 hour. The reaction mixture was poured into 1,000 ml. of hot water to dissolve the potassium chloride which had precipitated. The resultant mixture was filtered and the precipitate washed several times with hot water. The precipitate was dissolved in chloroform and decolorized with Nuchar activated carbon. The tetrabenzyloxydianaline was crystallized from the chloroform solution by the addition of reagent alcohol. The result was a 74 percent yield of N,N,N',N' tetrabenzyl 4,4' oxydianaline which had a melting point of 114.degree. to 118.degree. C.

EXAMPLE 2

Preparation of N,N,N',N' Tetrabenzyl 4,4' Oxydianaline

Into a four-necked, one-liter flask equipped with a mechanical stirrer, reflux condenser and thermometer was charged the following reaction mixture: (a) 20 grams (0.1 moles) of purified 4,4' oxydianaline; (b) 50.4 grams (0.4 moles) of benzyl chloride; (c) 33.6 grams (0.4 moles) sodium bicarbonate; (d) a solvent system comprised of 300 ml. of ethanol and 100 ml. of distilled water. The reaction mixture was brought to reflux temperature and refluxed for about 5 hours. The reflux was discontinued when no more CO.sub.2 evolved from the reaction mixture. The reaction mixture was then cooled and the heavy oily phase was dissolved in chloroform, filtered and charcoal treated. The tetrabenzyloxydianaline was crystallized from the chloroform solution by the addition of reagent alcohol. The result was 45.4 grams (80 percent yield) of N,N,N',N' tetrabenzyl 4,4' oxydianaline which had a melting point of 114.degree. to 118.degree. C. The product obtained from this procedure was considerably less colored and crystallized more readily than the product obtained in example 1.

The novel photoconductor of our invention was evaluated in the following manner. The tetrabenzyl oxydianaline (TBODA) was formulated with a solvent and binder and then filmed onto a sheet of aluminum foil. The TBODA film was charged with a high voltage corona in the dark and the charge acceptance measured. The charged film was then exposed to an ultraviolet light source and the charge dissipation measured and recorded. The formulation used consisted of 15 grams of polystyrene resin (Kopper's KTPL-7), 5 grams of the TBODA and 100 grams of chloroform. The insensitized photoconductive formulation was filmed onto filmed foil, air dried and then dark adapted for 24 hours prior to evaluation. The charge acceptance value (C.A.) was measured by placing an electrode on the charged film immediately after discontinuing the corona. The ultraviolet light source was turned on after the charge acceptance was measured. The residual charge (R.C.) was measured by the voltage level 15 seconds after the ultraviolet source was activated. The light source used was an U.V. fluorescent apparatus with a peak output at 3,660 A. The results of this test illustrated that TBODA had photoconductive properties. The above experiment was repeated using different known photoconductors in place of the TBODA. The other photoconductors which were evaluated using this procedure were N,N,N',N' tetrabenzyl paraphenylenediamine (TBPDA), and zinc oxide. A comparison of the results as shown in table I clearly illustrated that TBODA was a good photoconductor.

TABLE I

Compound Charge Acceptance (Volts) Residual Charge (Volts) __________________________________________________________________________ TBPDA 400 150 ZnO* 600 0 TBODA 400 200 --------------------------------------------------------------------------- *a commercial "Electrofax" sheet with sensitizers included.

In addition to the above described evaluation, TBODA photoconductor was evaluated by way of an actual electrophotographic printing process. The TBODA photoconductor was formulated into a resin binder system comprising of 10 grams of a polystrene resin (Kopper's KTPL-7), 100 ml. of chloroform, and 5 grams of the TBODA photoconductor. An electrophotographic plate was then prepared by coating a conductive substrate with the TBODA formulation using a number 40 draw rod. The conductive substrate was on aluminum foil, polyethylene, paper laminate (Thilmany Paper Co. -83600). Prior to coating, the aluminum foil laminated substrate was roughed up with steel wool and scrubbed with chloroform. The resulting electroconductive plate was dark conditioned for 24 hours before using. The print was then made by taping the photoconductive plate onto a grounded base and subjecting the plate to a 5.0 K.V. positive corona for 30 seconds. An IRE facsimile test chart photographic transparency was then quickly placed on the charged plate and the plate then exposed for 5 seconds to ultraviolet light from the fluorescent source. The latent charged image was then developed by dusting the sheets with a mixture of Bruning type D toner mixed with iron filings and removing the excess iron and toner with a magnet. The plate was then permanentized by placing in a 105.degree. C. oven for about 90 seconds. The quality of the print was rated as fair. This rating was a subjective rating and was assigned by paying particular attention to contrast, resolution, and cleanliness of background. Two additional electrophotographic plates were prepared and tested in the same manner using the TBODA formulation which had been enhanced by the incorporation of 0.005 grams of a sensitizer. The two sensitizers which were utilized are 1-chloroanthraquinone and 2-methyl anthraquinone. The quality of the print obtained from the sensitized plates was rated as good. Both sensitized plates produced reproductions that had good contrast and resolution and a very clean background. In addition, electrophotographic plates were prepared and tested in the same manner using a sensitized TBPDA formulation in place of the TBODA. A comparison of the reproductions clearly showed that TBODA was equal to or slightly superior to TBPDA.

The electrophotographic elements of this invention are comprised of an electrically conductive support which carries a photoconductive layer. The photoconductive layer consists essentially of suitable high dielectric film forming resinous binder which contains at least about 10 percent by weight of TBODA. In addition, the photoconductive layer may optionally contain a sensitizer.

The TBODA compound of our invention is also compatible with other clear resinous dielectric binders in addition to polystyrene. It may be used with other natural or synthetic polymeric binders such as polyvinyl chloride, polyvinyl acetate, polyvinyl ether, styrene-butadiene copolymers, polyvinylidene chloride, polyamides, polyacrylates and methacrylates, phenol-formaldehyde resins, paraffin, mineral waxes and the like. In addition, the binder system may optionally contain a plasticizer as is recognized by one skilled in the art. The plasticizer may be used to improve the film strength and film forming ability of the photoconductive layer of the electrophotographic element.

The TBODA compound is also readily soluble in such solvents as chloroform, toluene, methyl ethyl ketone, acetone, cyclohexanone and tetrahydrofuran.

The sensitizer constituent used in our invention may be either of the dye sensitizer type or the chemical sensitizer type or a combination of both types. The chemical type sensitizer is simply a chemical compound which increases the photosensitivity of the photoconductor. Many different theories have been advanced to explain the mechanism of chemical sensitization, but generally speaking, aromatic quinones and cyano compounds have been found to increase the photosensitivity of photoconductors. Some examples of these types of compounds are tetracyanoethylene, tetracyanoquinone-dimethane (TCNQ), anthraquinone and the substituted anthraquinones such as 2-methyl anthraquinone, 1-chloroanthraquinone, 1-nitroanthraquinone and the like. A dye type sensitizer is a compound which increases the sensitivity of the photoconductive compound by increasing or shifting the wavelength range to which the photoconductor is photosensitive. Examples of dye sensitizers are crystal violet, methylene blue, rhodamine B, rose bengal and the like.

Claims

We claim:

1. An improved photoconductive layer comprising a high dielectric resinous binder and a photoconductive compound wherein the improvement comprises N,N,N',N' tetrabenzyl 4,4' oxydianaline as the photoconductive compound.

2. An improved photoconductive layer as in claim 1 further including a sensitizer.

3. An improved electrophotographic element comprising a photoconductive layer coated onto a conductive support wherein the improvement comprises N,N,N',N' tetrabenzyl 4,4' oxydianaline as the photoconductive compound of the photoconductive layer.

4. An improved process of electrophotographic reproduction comprising (a) charging an electrographic element comprising a photoconductive layer coated onto a conductive support, (b) exposing the element to a light image to produce an invisible charge pattern, and (c) developing the invisible charge pattern with an electrostatically charged toner wherein the improvement comprises N,N,N',N' tetrabenzyl 4,4' oxydianaline as the photoconductive compound of the photoconductive layer.