US3341472A

US3341472A - Photoconductors and method of making the same

Info

Publication number: US3341472A
Application number: US304687A
Authority: US
Inventors: William A Hewett; Alfred H Sporer
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1963-08-26
Filing date: 1963-08-26
Publication date: 1967-09-12
Anticipated expiration: 1984-09-12

Description

United States Patent 3,341,472 PHOTOCONDUCTORS AND METHOD OF MAKING THE SAME William A. Hewett, Saratoga, and Alfred H. Sporer, San

Jose, Calif., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Aug. 26, 1963, Ser. No. 304,687 19 Claims. (Cl. 252-501) The present invention generally relates to photoconductors and more particularly relates to new organic polymeric photoconductors and method of making the same.

Photoconductors exhibit changes in electrical conductivity upon exposure to radiation of a given wavelength. The usual photoconductors are inorganic semiconductors, However, a few of the newer photoconductors are organic in nature. Photoconductors have a number of actual and potential uses, for example as components in various types of photoelectric cells and similar instruments, variable resistor components and the like.

Photoconductors have particular application in electrophotographic processes, that is, processes where an electrostatic latent image or charge pattern is formed. Such latent image is then developed to a visible image in a suitable manner, after which the visible image is then fixed or made permanent.

The electrostatic latent image is usually formed on the surface of a photoconductive insulating layer which, in turn, may be disposed on a suitable substrate or support. For example, photoconductive material can be dispersed or dissolved in a suitable medium in admixture with a binding agent. The dispersion or solution can then be coated on a suitable support material and, when dried, the resulting film can be used as the photoconductive insulating layer. The surface of this layer can then be charged in the dark, for example, by means of a corona discharge. The resulting charge on the surface of the layer is substantially retained because of the low electrical conductivity of the layer in the dark. However, upon exposure of the layer to a pattern of light, for example a lens-projected light image, the photoconductivity of those portions of the layer which are exposed to the light increases so that the surface charge in those exposed areas leaks away, leaving the charge only on the unexposed, that is the unilluminated, surface areas of the photoconductive layer. This charge pattern constitutes the electrostatic latent image.

The latent image can be developed by any suitable means, for example by coating the layer with an electros copic powder which adheres only to the charged areas of the layer. Such powder may contain, for example, a pigment and a heat-softenable resin, so that the image can then be made permanent merely by heating the powder to above the softening point of the resin, causing the resin to permanently adhere to the underlying material. Such underlying material may be a part of the original photoconductive layer or the original support for that layer or a second support to which the powder image is first transferred before heating it up to above the softening point of the resin. Cooling of the powder image to below the softening point of the resin solidifies the image.

It is of considerable importance in electrophotographic processes to maximize conditions so as to obtain high quality images. One factor which affects the quality of the image is the nature of the binding material which is usually present with the photoconductive material or photoconductor in the photoconductive layer. Thus, the binding material must be carefully selected so that it does not materially interfere with the formation, development and fixation of the image. Moreover, ditficulties may 3,341,472 Patented Sept. 12, 1957 arise because of the particular distribution of particles of the photoconductive materials in the photoconductive layer and the spatial relationship of such photoconductive material to the binding material. The net result is that in many instances with such systems, it is relatively diflicult to obtain uniformly high quality, sharp, clear developed images.

A few of the newer types of photoconductive materials which are of an organic nature do not require admixture with binding agents in forming the photoconductive layer. Instead, certain of these photoconductors can be formed into films by heating the materials to above the melting points thereof, or by dissolving the same in organic solvents, forming the film and evaporating the solvents. The resulting films are continuous and strongly adhere to substrates. Moreover, in a few instances, the photoconductive materials can be effectively used without any substrate or support. At least one of these newer photoconductive materials with the indicated improved characteristics is in the form of a polymer. However, the polymer is characterized by having a relatively high melting point so that when it is desired to dissolve crystals of the polymer in a suitable solvent or to heat the polymer to above the softening point thereof in a film-forming operation, con-. siderable heat for a substantial period of time must be employed. Moreover, careful selection must be made with respect to the nature of other additives, for example solvents, thinners, etc. so that they can withstand the high temperatures to which the polymer must be subjected in order to convert this to a film. Moreover, such polymer is further characterized by having only a limited range of physical characteristics and being highly selective with respect to the materials with which this can be copolymerized. Accordingly, the possible polymeric compounds which can be prepared incorporating such polymer and the physical and chemical properties of such compounds are limited, so that such compounds are not adaptable to a wide variety of applications as photoconductive materials. Furthermore, such polymer is relatively difficult to provide in an ordered or tactic polymeric form which would tend to enhance its inherent photoconductivity.

Accordingly, it is a principal object of the present invention to provide improved crystallizable polymeric photoconductive materials.

It is also an object of the present invention to provide organic polymeric photoconductors which can be readily prepared in a crystallizable form and as thin films at relatively low temperatures, and method of making the same.

It is a further object of the present invention to provide new organic polymeric photoconductors which can be readily copolymerized with a wide variety of materials to prepare products having a wide range of physical characteristics.

It is a still further object of the present invention to provide new low melting point polymeric photoconductors which have improved film-forming characteristics, and method of making the same.

These and other objects are accomplished in accordance with the present invention by providing new polymeric photoconductors which include selected 9-alkenyl substituted carbazole polymers, The polymers have alkenyl substituents with carbon chain length of 4 to 23 carbon atoms and are readily crystallizable. Moreover, the polymers can have relatively low melting points and can be readily prepared as homopolymers and as copolymers. The copolymers may be formed by copolymerizing two or more selected 9-alkenyl substituted carbazoles or by copolymerizing a 9-alkenyl substituted carbazole with a polymerizable material of a different type. Such polymerization reactions can be carried out effectively utilizing a wide variety of catalysts, and the extent of polymerization can be readily controlled so that the physical characteristics of the polymers and the photo-conductors prepared therefrom can be varied within wide limits.

The photoconductors of the invention can be made simply, efficiently and rapidly from such polymers in accordance with the present method. Such method includes sensitizing selected poly-9-alkenyl substituted carbazolecontaining material with selected sensitizing agents which increase the sensitivity of the product to radiation within the visible and/or ultraviolet regions of the photospectrum. As an example, an im roved photoconductor was prepared by, sensitizing poly-9-(4-pentenyl) carbazole having the following structural formula:

where m indicated the number average monomeric chain length and Was about 500. As a practical matter, the individual polymers in the polymeric mixture have monomeric chain lengths which can vary from a relatively low monomeric unit multiplication number to a relatively high monomeric unit multiplication number. The poly-9-(4- pentenyl) carbazole was sensitized by mixing it with about 3 percent, by weight, of 2,5-diphenyl quinone, after dissolving the polymer in a solvent, and then coating the resulting wet mixture on an aluminum plate and drying it. The dried and set film was then charged in the dark with 280 volts from a corona unit. The sensitizer conplexed with the aromatic units of the polymer so that the product exhibited a charge transfer absorption band in the visible region of the photospectrum. Accordingly, when the charged film was exposed to visible light radiation from a high pressure mercury arc lamp, the electrical conductivity of the product rapidly and substantially increased, resulting in a dissipation of about one-half of the 280 voltage potential (from the surface of the film) in 16.7 milliseconds.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.

It has now been discovered that the photoconductors of this invention can be easily prepared from selected crystallizable organic polymers, the physical characteristics of which can be readily controlled. The mechanism of action of the present organic photoconductors is not fully understood. However, it is believed, although the present invention is not limited to this belief, that in the polymeric photoconductors of the present invention, the change in electrical conductivity in response to exposure to radiation of a selected wavelength may be due to the presence of a specific absorption center in the photoconductive material. Thus, an electron donor layer comprising selected donor molecules may be in intimate contact with an electron acceptor layer comprising selected acceptor molecules, and electron transfer may occur from the donor molecules to the electron acceptor molecules. Irradiation in a particular absorption band of the photoconductor or in a band produced by the addition of sensitizer to the photoconductor results in the production of charge carriers.

In accordance with the present method, the aromatic units of the selected polymers are complexed with selected photosensitizers. The photosensitizer molecules act as acceptor molecules, while the aromatic units of the polymer molecules act as the donor molecules, the donoracoeptor interface occurring at the sites where the sensitizer molecules complex with the polymer aromatic units.

The positive charges can be passed between aromatic unit sites within and between respective polymer molecules, and negative charges can be passed between sensitizer or other trapping sites within and between the respective polymer molecules.

Although the described manner of operation of the polymeric photoconductors of the invention is considerably simplified and theoretical, the improved photoconductivity of the present organic photoconductors is substantial and reproducible.

Now referring more particularly to the present method, polymeric materials containing new selected 9-alkenyl substituted carbazole polymers are sensitized with selected sensitizing agents. These polymers have the following general structural formula:

where n: l-20 and m is the number average monomeric unit multiplication and where R, R, R", R'" and R-"' are substituents selected from the group consisting of hydrogen, alkyl, aryl, and substituted alkyl and aryl substituents. Usually, m will vary between about 70 and 1000. However, it is also within the scope of the present invention, and several examples are directed thereto, to provide a much lower number average monomeric unit multiplication, for example, as low as 10. All that is required is that m be sufficiently high so that it is possible to form a thin film from the polymer. The minimum m number Will therefore vary, depending upon the particular polymer employed, its molecular weight, etc.

The methods of preparation of this new class of polymers are more particularly set forth in copending United States Patent application Ser. No. 304,697, filed on Aug. 26, 1963, by William A. Hewett and entitled, Polymeric Materials and Methods of Making the Same, the said application having been assigned to the assignee of the present application. As set forth in that application, the polymers may be homopolymers, copolymers, block copolymers and the like, and such polymers can be in tactic or .atactic form. A distinct advantage of these polymers is that they can be readily prepared in crystallizable form and that they can be easily converted, in accordance with the present method, to film form for use in photoconductors in electrophotographic process. In accordance with the present method, the polymeric material which is sensitized must contain monomeric units having the following structural formula:

Lli 1 1 lm where n=1-20 and R, R, R", R', and R are substituents selected from the group consisting of alkyl, aryl, hydrogen and substituted alkyl and aryl substituents. Preferably all monomeric units of the polymeric material used in the photoconductors fall within the described structural formula. However, selected 9-alkenyl substituted monomers can be copolymerized with other polymeric-forming materials, such as propylene, ethylene or the like to provide copolymers having film-forming number average monomeric unit multiplications of, for example, 70-1000,

as previously indicated, and containing at least some monomeric units of the above structural formula.

The polymerization reaction by which the selected 9- alkenyl substituted polymers are prepared is carried out in suitable reaction media, such as a solvent for the selected 9-alkenyl substituted carbazole monomer, for example, hexane, benzene, toluene, tetrahydrofuran or the like, and in the presence of a suitable polymerization catalyst, for example, of the ionic(cationic-anionic) or Friedel-Crafts, Ziegler or other type. Thus, for example, the catalyst may be of the Ziegler (Ziegler-Natta) type, such as a complex or titanium trichloride with another substance such as diethyl aluminum chloride or the like. Alternatively, a cationic catalyst such as ethyl aluminum chloride can be used.

The polymerization is usually carried out at relatively low temperature, for example, -70 0, and is terminated either automatically or when the desired monomeric unit multiplication has been eifected, for example, by the addition thereto of suitable concentrations of hydrogen. The product is then separated from the reaction medium, unreacted substituents and remaining catalyst to provide the desired polymer useful in the preparation of the photoconductors of the present invention.

As an example, hexenyl carbazole was reatced at 60 C. in benzene in the presence of a Ziegler catalyst comprising a complex of diethyl aluminum chloride and titanium trichloride (the diethyl aluminum chloride being in ,a mole ratio of about 2.5 to the titanium trichloride, i.e. 2.5 Et AlCl/lTiCl with the hexenyl carbazole being in a weight ratio to the catalyst of about 100:1. The polymerization reaction was instituted by contacting the hexenyl carbazole in the solvent with the catalyst at the polymerization temperature and at atmospheric pressure, under anhydrous, non-oxidizing conditions.

Selected 9-alkenyl substituted carbazoles for the manufacture of the 9-alkenyl substituted carbazole-containing polymers used in the preparation of the photoconductors of the present invention, can be prepared in any suitable manner. For example, those 9-alkenyl substituted carbazoles wherein the alkenyl substituents have carbon chain lentghs of to 23 carbon atoms can be prepared as particularly set forth in copending United States patent application Ser. No. 304,688, filed on Aug. 26, 1963 by William A. Hewett and entitled Organic Compounds and Method of Making Same, now U.S. Patent 3,252,993, said patent having been assigned to the assignee of the present application. As set forth in that patent application, such 9- alkenyl substituted carbazoles can be prepared by reaction of a 9-a1kali metal carbazole with a monohalogenated alkene having a carbon chain length corresponding to that desired for the alkenyl substituent of the carbazole at .any suitable temperature, for example 50 C.

As a typical example, carbazole in tetrahydrofuran is initially reacted under anhydrous, non-oxidizing conditions with sodium hydride in tetrahydrofuran at room temperature and at atmospheric pressure to prepare 9- sodium carbazole having the following structural formula:

The 9-sodium carbazole in the tetrahydrofuran is then reacted at 50 C. and ,at atmospheric pressure under anhydrous, non-oxidizing conditions with 5-bromopentene-1 in tetrahydrofuran. The S-bromopentene-l has the following structural formula:

The reaction is completed in 1 hour and the desired product, 9-(4-pentenyl) carbazole, is obtained in a yield of about 607 9 alkenyl substituted carbazoles having alkenyl substit-uents with a carbon chain length of four carbon atoms cannot be prepared by the indicated condensation procedure. Instead, those carbazoles must be prepared by a different route, such as that set forth in copending United States patent application Ser. No. 304,696, filed on Aug. 26, 1963, by Jorge Heller and entitled Organic Compounds and Method of Making Same, now U. S. Patent No. 3,268,550, said patent having been assigned to the assignee of the present application. As: more particularly set forth in that application, in order to prevent the formation of butadiene type products, it is necessary to prepare 9 (3 butenyl) carbazoles by first condensing under anhydrous, non-oxidizing conditions 9-a1kali metal substituted carbazole (sodium, potassium or lithium carbazole) with 1,4 dihalogenated butane, wherein the halogen atoms are selected from the group consisting of chlorine, bromine and iodine atoms. Such reaction may be carried out in the presence of a suitable catalyst, and the product is a 9 (4 monohalogenated butyl) carbazole. This product is then dehydrohalogenated under anhydrous, non-oxidizing conditions in the presence of a suitable catalyst, such as potassium tertiary butoxide, that is, potassium in tertiary butyl alcohol, at about refluxing temperature, that is, under rather severe dehydrohalogenating conditions, to produce 9 (3 butenyl) carbazole.

As an example, sodium carbazole has been reacted with 1,4 dichlorobutane under anhydrous, non-oxidizing conditions to produce 9 (4 chlorobutyl) carbazole, the reaction taking place in the presence of sodium iodide and while the constituents were disposed in anhydrous tetrahydrofuran. The resulting 9 (4 chlorobutyl) carbazole has been dehydrohalogenated under anhydrous, non-oxidizing conditions at refluxing temperature to 9- (3 butenyl) carbazole while in teriary butyl alcohol along with potassium. It has been found that similar carbazoles which, however, carry substituents (alkyl, aryl and/or alkylaryl) on the 3-butenyl substituent can be prepared by the same method. The 9 (3 butenyl) type carbazoles can also be made by other procedures.

The selected sensitizer utilized in the method of the present invention for the preparation of the new photoconductors, is any sensitizer which is capable of complexing with the aromatic units of the above-described polymer so that the product exhibits increased photosemiconductive capacity in the near ultra-violet and/or visible light portions of the photospectrum. The sensitizer renders the polymer photosensitive in the near ultraviolet and/or visible light portions of the photospectrum so that it becomes a suitable photoconductor for a variety of purposes. Also as previously described, the sensitizer acts to provide electron acceptors and cooperates with the polymer to provide donor-acceptor interfaces in the form of a charge-separating complex. Many types of commercially available sensitizers can be used in the present method. They include, but are not limited to, quinones, such as 2,5-diphenyl benzoquinone, benzoquinone, di-ter-tiary butylbenzoquinone, anthroquinone, duroquinone, and phenyl benzoquinone. They also include other materials such as unsaturated acid anhydrides, for example, pyromellitic dianhydride.

In addition, various types of polynitro compounds can be used. For example, polynitroethylene, polynitrobenzene, polynitrotoluene and polynitroxylene. Moreover, various polycyano compounds can be used, for example, tetracyanoethylene, polycyanobenzene, polycyanotoluene and polycyanoxylene. In addition, other photosensitizers such as iodine, O-chloranil, boron trifluoride, ferric chloride and diethyl aluminum chloride can be used.

In accordance with the present method, the sensitizer is complexed with the polymer. Any suitable amount of sensitizer can be used depending on the particular polymer and sensitizer.

In order to facilitate complexing of the sensitizer with the polymer, the sensitizer is intimately and uniformly dispersed throughout the polymeric material. The dispersal can be effected by any suitable procedure, for

example, ball milling the polymer and sensitizer in a suitable solvent for the polymer and the sensitizer until the sensitizer is dissolved. Such solvent may be, for example, toluene, benzene, xylene, methyl pyrrolidone, methyl ethyl ketone, methylene chloride or the like. The ball milling is carried out at solvent temperatures ranging up to the boiling point of the solvent. It will be noted that relatively low boiling point solvents can be used without difiiculty, particularly with those polymers which have low monomeric unit multiplications. This is in contrast to prior higher melting point, more difficultly soluble photoconductive polymers. Alternatively, the polymers can be heated to a relatively low temperature, in contrast to prior photoconductive polymers, to render them viscous, whereupon the dispersal is effected by stirring the sensitizers into the viscous polymers. For example, a powdered mixture of a selected polymer and sensitizer can be melted at, for example, about 190 C.

The resulting improved photoconductor can, if desired, then be directly applied as a thin film on a suitable support or substrate, such as an aluminum plate, and can then be allowed' to dry or solidify. Thus, for example, poly 9 (4 pentenyl) carbazole can be sensitized with 2,5 diphenyl benzoquinone (4% concentration, by weight), the mixture also containing methylene chloride, whereupon the mixture can be coated on an aluminum or other electrically conductive base plate. The desired film thickness will vary, depending on the particular photoconductive material, but usually is relatively thin, for example, from about 0.1 mil to about 5 mils in the dried state. The dried coating or film can then be charged in the dark with a corona unit to provide a suitable voltage potential, which upon subsequent exposure to suitable light radiation will decay or bleed off rapidly to a given value in a relatively few milliseconds.

Certain features of the present invention are illustrated in the following examples:

EXAMPLE I A novel photoconductor comprising poly 9 (4 pentenyl) carbazole complexed with 2,5 diphenyl benzoquinone is prepared according to the following procedure:

Approximately 8.5 gm. of sodium carbazole in 120 ml. of anhydrous tetrahydrofuran, previously prepared by reacting under anhydrous conditions and under a nitrogen blanket about 8.4 gm. of carbazole in the same solvent with about 1.3 gm. of sodium hydride at 35 C. for 1.5 hours, is reacted at refluxing temperature under anhydrous conditions and under a nitrogen blanket with 9 gm. of 5-bromo-pentene-1 in 20 ml. of anhydrous tetrahydrofuran for 20 hours under agitation to provide 6 gm. of 9- (4-pentenyl) carbazole. The 9-(4-pentenyl) carbazole in about 5 gm. amount is then disposed in 50 ml. of benzene which contains 1% benzoyl peroxide. The temperature of the reactants is then raised to and maintained at 70 C. for 24 hours under anhydrous conditions until the monomeric unit multiplication is approximately 10. A yield of about 3.5 gm. of the polymer is obtained. The polymer is separated from the catalyst and reaction medium by repeatedly washing it with large volumes of ethyl alcohol. This polymer has an intrinsic viscosity of about 0.03.

The polymer is an intrinsic photoconductor in the ultraviolet region but is further sensitized to the near ultraviolet and visible regions of the photospectrum by complexing the aromatic units thereof with, as previously indicated, 2,S-diphenyl-p-benzoquinone, the latter in a concentration of 4% by weight. Such sensitization is effected by first dissolving the poly-pentenyl carbazole in methylene chloride and then adding the indicated concen- 8 tration of the 2,S-diphenyl-p-benzoquinone. The resulting product has a charge transfer absorption band in the blue region of the photospectrum with a dark conductivity of about 0.8% that of its light conductivity, i.e., conductivity when exposed to light from a high pressure mercury arc lamp.

The resulting photoconductor is disposed in the dark while dissolved in the methylene chloride as a thin film approximately 0.5 mils thick (when dried) on an aluminum plate. It is then dried and is then subjected in the dark to a voltage of about 300 volts positive. When the charged film is subsequently exposed to a high pressure mercury arc lamp radiation, the voltage decreases in approximately 6 milliseconds to about volts, indicating a large increase in the electrical conductivity thereof. Accordingly, the novel photoconductor is suitable for use in electrophotographic processes requiring a photoconductive material upon which can be disposed an electrostatic latent image which can be developed to a visible image and fixed.

EXAMPLE II A novel photoconductor comprising poly 9-(4-pentenyl) carbazole having a number average monomeric unit multiplication of about 200 is prepared in the following manner:

The 9-(4-pentenyl) carbazole monomer is prepared in accordance with the method set forth in Example I. The polymer is prepared therefrom by reacting about 4.7 gm. of the monomer while disposed in 40 ml. of benzene with a Ziegler catalyst comprising 2 millimoles of titanium trichloride and 5 millimoles of diethyl aluminum chloride. The reaction temperature is maintained at 50 C. for 72 hours under non-oxidizing anhydrous conditions until the desired monomeric unit multiplication of about 200 is obtained. Approximately 2.5 gm. of the polymer is obtained by this method. The so-produced polymer is separated from the catalyst and reaction medium by adding the product to a mixture of 20 ml. of hydrochloric acid in methanol (10% by volume of the product) and stirring the mixture for 15 minutes, after which the product is poured into a large volume of methanol and filtered. Such purified product upon drying is found to be in tactic form and have an intrinsic viscosity of about 0.40. It is a white powder with a softening point of about C.

In preparing the photoconductor from the poly 9-(4- pentenyl) carbazole having a monomeric unit multiplication number of 200, the polymer in powderform is melted at C. and to it is added about 4% by weight of phenanthrenequinone. The phenanthrenequinone is uniformly distributed throughout the melted powder. Upon testing, the resulting photoconductor is found to have a charge transfer absorption band in the blue region of the photospectrum. This product in melted form is disposed as a thin film approximately 1 mil thick (when dried) on an aluminum plate and when the film is solidified, it is subjected in the dark to a voltage of about 650 volts positive from a corona unit. The charged film is then exposed to the radiation from a high pressure mercury arc lamp and it is found that the voltage decreases in about 29 milliseconds to approximately 325 volts, indicating an increase in the electrical conductivity of the film of about 8,000 times. Accordingly, the novel photoconductor is suitable for use in electrophotographic processes which require a photoconductive material capable of carrying an electrostatic latent image and having the image developed in a suitable manner and fixed.

EXAMPLE III A novel photoconductor comprising poly 9-(4-pentenyl) carbazole having a number average monomeric unit multiplication of about 10 and complexed with orthochloranil is prepared in the following manner:

The monomer and the polymer are prepared according to the method set forth in Example I. The polymer is then dissolved in methylene chloride in a concentration of about gm. of polymer per 100 ml. of the chloride, after which about 20 mg. of the sensitizer is added thereto. The resulting photoconductor while still dissolved in the methylene chloride is coated on an aluminum plate to a coating thickness (dry state) of about 0.5 mil. After the coating is dried, it is subjected in the dark to a charge of about 240 volts positive. When the charged film is then exposed to the radiation from a high pressure mercury arc lamp, the voltage decreases in about 2.5 milliseconds to about 120 volts, indicating an increase in the electrical conductivity of the fihn of about 7,200 times. Accordingly, the novel photoconductor is suitable for use in electrophotographic processes and the like.

EXAMPLE IV A novel photoconductor comprising poly 9-(4-pentenyl) carbazole complexed with pyromellitic dianhydride sensitizer is prepared in the following manner:

The monomer and polymer are prepared in accordance with the method set forth in Example II, the polymer having a number average monomeric unit multiplication of about 200. The polymer is converted into an improved photoconductor by melting the polymer at 190 C. and adding thereto about 4% by weight of pyromellitic dianhydride sensitizer. The resulting molten photoconductor is then disposed on an aluminum plate to a film thickness of about 1 mil (when solidified) and is cooled to below the solidification point thereof. When the solidified film is subjected to a charge of about 630 volts positive in the dark from a corona unit, and then subsequently exposed to radiation from a high pressure mercury arc lamp, it is found that the voltage decreases in about 70 milliseconds to about 315 volts, indicating an increase in the electrical conductivity of about 1,300 times. Accordingly, the novel photoconductor is suitable for use in electrophotographic processes and the like which re quire a photoconductive material which is capable of readily forming into a film at relatively 'low temperature and which is also capable of retaining an electrostatic latent image, which image can be developed and fixed.

EXAMPLE V A novel photoconductor comprising poly 9-(5-hexenyl) carbazole, sensitized with phenyl p-benzoquinone sensitizer, is prepared in accordance with the following procedure:

9-(5-hexenyl) carbazole is prepared by reacting 55 gm. of 9-sodium carbazole in 800 ml. of anhydrous tetrahydrofuran at about 70 C. under anhydrous conditions and under a nitrogen blanket with 65 gm. of 6-bromo-1- hexene disposed in 100 ml. of anhydrous tetrahydrofuran for 20 hours under agitation. The product comprises 36 gm. of the 9-(5-hexeny-l) carbazole. The 9-sodium carbazole was previously prepared by reacting about 55 gm. of anhydrous carbazole in anhydrous tetrahydrofuran with about 9 gm. of anhydrous sodium hydride at 25 C. for 3 hours and under anhydrous conditions under a nitrogen blanket.

About 5 gm. of the 9-(5-hexenyl) carbazole is dispersed in 40 ml. of benzene containing 2 millimoles of titanium trichloride, 5 millimoles of diethyl aluminum chloride. The reactants are maintained at 70 C. for 2 hours under non-oxidizing anhydrous conditions until a polymer is formed which has the number average monomeric unit multiplication of about 200. Approximately 26 gm. of the polymer are obtained. On purification the polymer has a viscosity of about 0.46 and is in the form of a white powder with a softening point of about 180 C.

The polymer is converted into improved photoconductor by the following procedure:

The improved photoconductor is disposed as a thin film of about 1.5 ml. thickness on an aluminum plate by the following procedure:

The mixture of polymer and 4% by weight phenyl pbenzoquinone was compression molded into a thin film (approximately 1 mil) on an aluminum substrate at 170 C. and 20,000 psi. pressure.

The dry film is charged to a positive voltage of about 860 volts in the dark and upon subsequent exposure of the film to radiation from a high pressure mercury arc lamp, the voltage decreases in about 18 milliseconds to about 430 volts, indicating an increase of electrical conductivity of the film of about 1,800 times. Accordingly, the novel photoconductor is suitable for use in a wide variety of applications including use as a photoconductive layer in an electrophotographic process.

EXAMPLE VI A novel photoconductor is prepared, which photoconductor comprises poly-9-(22-tricosenyl) carbazole complexed with a nitrophenylquinone sensitizer. The method of preparation of the improved photoconductor is as follows:

About 8.5 gm. of 9-sodium carbazole in 120 ml. of anhydrous tetrahydrofuran, previously prepared by reacting under anhydrous non-oxidizing conditions about 8.4 gm. of carbazole in the same solvent with about 1.3 gm. of sodium hydride at 23 C. for 1.5 hours, is reacted under, anhydrous non-oxidizing conditions at about 70C. with 24 gm. of 23-bromo-l-tricosene disposed in 40 ml. of anhydrous tetrahydrofuran for 20 hours under agitation to provide 10 gm. of 9-(22-tricosenyl) carbazole. This product in 10 gm. amount is disposed in ml. of benzene which also contains 2 millimoles of titanium trichloride and 5 millimoles of diethyl aluminum chloride. The temperature of the reactant is maintained at 70 C. for 72 hours under anhydrous nonoxidizing conditions until a polymer is produced which has a number average monomeric unit multiplication of about 100. This polymer is produced in about 6 gm. amount. Upon purification, the product is identifiable as poly-9-(22-tricosenyl) carbazole and is converted to an improved photoconductor by the following procedure:

This product is mixed with 4% by weight of 4-nitrophenyl-quinone and then melted at 130 C. and in the molten condition is coated on an aluminum plate and then cooled to below the solidification point thereof to provide a 1 mil thick film in the solid state on the aluminum plate. This film is then subjected to a voltage of about 1,000 volts positive in the dark and when subsequently exposed to radiation from a high pressure mercury arc lamp, this voltage decreases to about 500 volts in about milliseconds, indicating an increase in the electrical conductivity of the film of about 300 times.

Accordingly, the novel photoconductor has improved properties and is suitable for use in electrophotographic processes and the like. In this connection, the novel photoconductor can be disposed as a film, as previously indicated, on a suitable substrate and then can be charged in the dark to a suitable voltage and then exposed to image-wise radiation to which it is sensitive, for example in the ultra-violet region or the visible light region of the photospectrum. The electrostatic latent image pattern remaining on the photoconductor film after the imagewise radiation can be developed by various techniques, such as a conventional toning technique and the like. Moreover, the latent image can be developed and rendered visible by a heating technique, such as is used in thermoplastic recording of electronic beam images. Thus, upon rapid heating of the photoconductor containing the electrostatic latent image pattern to the melting point of the photoconductor, the electrostatic latent image remaining on the surface of the photoconductor film causes deformation of the polymer of the film in the charged areas, resulting in a deformation image which can be detected by a suitable technique.

Accordingly, with this and others of the improved photoconductors of the present invention, there is no necessity to employ conventional time-consuming toning techniques in order to develop and fix images. Instead, the electrostatic latent image can be used directly to modify the physical condition of the polymer in the area immediately associated therewith so that the desired developing and fixing of the latent image occurs in a simple improved manner. Accordingly, the improved photoconductors of the present invention have improved versatility in applications to electrophotographic processes and other systems requiring sensitized photoconductive materials.

EXAMPLE VII An improved photoconductor comprising poly-9(10- phenyl-lO-undecenyl) carbazole complexed and sensitized with p-chlorophenylquinone sensitizer, is prepared in the following manner:

The 9-(10-phenyl-10-undecenyl) carbazole is prepared by reacting about 8.5 gm. of 9-sodium carbazole in 120 ml. of anhydrous tetrahydrofuran, previously prepared by reacting under anhydrous non-oxidizing conditions about 8.4 gm. of carbazole in the same solvent with about 1.3 gm. of sodium hydride at 23 C. for 1.5 hours, with 18.5 gm. of 2-phenyl-1l-bromo-undecene-l in 60 ml. of tetrahydrofuran at about 70 C. under anhydrous non-oxidizing conditions for 20 hours under agitation. About 12 gm. of 9-(10-phenyl-10-undecenyl) carbazole is provided. About 5 gm. of this product is then disposed in 60 ml. of methylene chloride containing about 0.2 gm. of boron trifluoride etherate catalyst. The reactants are maintained at 78 C. for 6 hours under anhydrous non-oxidizing conditions until a polymer is produced which has a number average monomeric unit multiplication of about 12. Thereupon, the polymerization is discontinued by the addition to the reaction medium of ammonium hydroxide. The produced polymer is then separated from the catalyst, monomer and reaction medium by repeatedly washing it with methanol until it is neutral in pH. The polymer is then filtered and dried and is converted into the improved photoconductor by melting it at 190 C. and adding thereto about 4% by weight of p-chlorophenylquinone sensitizer and distributing the sensitizer throughout the melted polymer.

The resulting improved photoconductor has an absorption band in the ultra-violet region of the photospectrum and a dark conductivity of about 5% that of its light conductivity when exposed to a high pressure mercury arc lamp light. Such product in the molten state is then coated as a thin film on an aluminum plate (to a film thickness, when dry, of about 1 mil), solidified, and then charged in the dark to a voltage of about 900 volts positive. When the charged film is then exposed to a high pressure are lamp radiation, the voltage decreases in about 30 milliseconds to about 450 volts, indicating a substantial increase in the electrical conductivity of the film. Accordingly, the improved photoconductor is suitable for use for a wide variety of applications including electrophotographic processes.

EXAMPLE VIII An improved photoconductor comprising poly-9-(4- methyl-4-pentenyl) carbazole sensitized with 2,4,6 trinitrobenzoic acid is prepared in the following manner: Approximately 8.5 gm. of 9-sodium carbazole, in 120 ml. of anhydrous tetrahydrofuran solvent, previously prepared by reacting under a nitrogen blanket 8.4 gm. of anhydrous carbazole in the same solvent with about 1.3 gm. of anhydrous sodium hydride at 23 C. for 1.5 hours, is reacted under anhydrous non-oxidizing conditions at about 70 C. with 10 gm. of 2-methyl-5-bromopentene- 1 disposed in 60 ml. of tetrahydrofuran for 20 hours under agitation to provide 5 gm. of 9-(4-methyl-4-pentenyl) carbazole.

This product, upon separation from the catalyst, reaction medium and unreacted constituents, is disposed in 60 ml. of methylene chloride solvent which also contains 0.2 gm. of boron trifluoride etherate polymerization catalyst. The temperature of the reactants is maintained at 78 C. for 6 hours under anhydrous non-oxidizing conditions, until the number average monomeric unit multiplication is approximately 12. A yield of about 3.5 gm. of poly-9-(4-methyl-4-pentenyl) carbazole is obtained. Thereupon the so-produced polymer is separated from the catalyst and reaction medium by the following procedure: Repeatedly working it with large volumes of methyl alcohol. The purified polymer has an intrinsic viscosity of about 0.03, and is a white powder.

The poly-9-(4-methyl-4-pentenyl) carbazole is converted to an improved photoconductor by complexing the aromatic units of the polymer with, as previously indicated, 2,4,6 trinitrobenzoic acid sensitizer, the latter being in a 4% by weight concentration, with respect to the product. The sensitization reaction is effected by the following procedure: The polymer is compression molded at C. and 20,000 psi. on an aluminum substrate. The polymer is then swelled with a 4% solution of 2,4,6 trinitrobenzoic acid in benzene. The resulting improved photoconduction product has a charge-transfer absorption band in the ultra-violet region of the photospectrum, with a dark conductivity approximately 4% that of its light conductivity, e.g. conductivity when exposed to mercury are light. Such product is disposed in a thin film approximately 1.5 mils thick on an aluminum plate. The'film is then charged to a voltage of approximately 850 volts positive in the dark. When the charged film is subsequently exposed to radiation from a high pressure mercury arc lamp, the voltage decreases in approximately 20 milliseconds to approximately 425 volts, indicating an increase in the electrical conductivity of the exposed film of approximately 1,700 times. Accordingly, the improved photoconductor is suitable for use in electrophotographic processes and the like.

The preceding examples clearly illustrate that novel organic polymeric photoconductors which are readily crystallizable and which can be readily converted into films at relatively low temperatures can be prepared easily, efiiciently and inexpensively in a wide variety of forms and with a wide variety of physical characteristics in accordance with the present method. The Examples also indicate that various reaction conditions and techniques can be employed in carrying out the present method. The polymers forming a part of the photoconductors can be homopolymers, copolymers, block copolymers and the like, in tactic or atactic form and having a wide range of monomeric unit multiplication. The sensitizers are those substances which increase the sensitivity or response of the photoconductive materials over that of the untreated photoconductive materials to radiation in the ultra-violet and/or visible portions of the photospectrurn. The sensitizers complex with the aromatic units of the carbazolecontaining portions of the polymers so that the net result is a product which exhibits increased photo-semiconductor capacity or sensitivity over that of the untreated polymers with respect to near ultra-violet and/ or visible light.

The new and improved photoconductors have particular utility in electrophotographic processes. However, due to the wide variety of physical characteristics which they exhibit, the photoconductors are suitable for use in other processes and as components of various types of mechanical and electronic equipment. Various other advantages of the present invention are as set forth in the foregoing.

While the invention has been particularly shown and described with reference to preferred embodiments there of, it will be understood 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. An organic polymeric photoconductor which consists essentially of:

' a'polymer which has the structural formula:

stituents, and

an electron acceptor complexed with aromatic units of said polymer, in a concentration which effectively increases the photo-semiconductive sensitivity of said polymer to radiation.

2. The photoconductor of claim 1 wherein the polymer is in tactic form.

3. The photoconductor of claim 1 wherein the polymer is in atactic form.

carbazole.

where n=l19, m=l-lO00, and R, R, R", R'" and R"" are substituents selected from the group consisting of hydrogen, alkyl, aryl and alkylaryl suba 9-(4-pentenyl) carbazole polymer having the structural formula:

6. An organic polymer photoconductor which consists essentially of:

a copolymer, a major amount of the monomeric units of which has the structural formula:

H I H H-C--H 10 H( 1N l 1n L H H J wherein m=1000, and an electron acceptor complexed therewith in a concentration sufficient to substantially increase the photo semiconductive sensitivity of the polymer to radiation.

11. A polymeric photoconductor consisting essentially of:

a 9-(5-hexenyl) carbazole polymer having the structural formula:

H|-H H-C-H H- -11 /H I L H H 1 wherein m=701000, and an electron accept-or compleXed therewith in a concentration suflicient to substantially increase the photosemiconductive sensitivity of the polymer to radiation. 12. The method of making an organic photoconductor, which method comprises:

complexing aromatic units of polymeric material containing monomeric units having the structural forwherein n=1-19, wherein m=l0l000, and wherein R, R, R, R" and R"" are substituents selected from the group consisting of hydrogen, alkyl, aryl and substituted alkyl and aryl groups, said copolymer being crystallizable and,

meric units to radiation.

7. The photoconductor of claim 6 wherein each of the monomeric units of said :copolymer have said structural formula 8. The photoconductor of claim 7 wherein said c0- polymer is in tactic form.

9. The photoconductor of claim 7 wherein said copolymer is in atactic form.

10. A polymeric photoconductor consisting essentially mula:

wherein n: l-19, m1=-101000, and wherein R, R, R", R and R"" are substituents selected from the group consisting of hydrogen, alkyl, aryl and alkylaryl substituents, with an electron acceptor in a concentration which effectively increases the photo-semiconductive sensitivity of the monomeric units to radiation.

13. The method of claim 12 wherein said polymeric material is a homopolymer containing said monomeric units.

14. The method of claim 12 wherein said homopolymer is poly-9-(5-hexenyl) carbazole in tactic form.

15. The method of claim 12 wherein said homopolymer is poly-9-(10-phenyl-10-undecenyl) carbazole in tactic form.

16. The method of claim 12 wherein said homopolymer is poly-9-(22-tricosenyl) carhazole in tactic form.

15 17. The method of making an organic photoconductor, which method comprises:

complexing polymeric aromatic units having the structural formula:

16 photo-semiconductive sensitivity of the polymer to radiation.

18. The method of claim 17 wherein each of the monomeric units of said copolymer has said structural formula.

19. The method of making an organic photoconductor comprising complexing aromatic units of a homopolymer of poly-9-(4-pentenyl) carbazole in tactic form and having 10-1000 monomeric units, by dissolving said polymer in methylene chloride and dispersing about 4%, 'by weight, of 2,S-diphenyl-p benzoquinone therethrough.

References Cited UNITED STATES PATENTS 3,037,861 6/1962 Hoegl et al 96-1 3,155,503 11/1964 Cassiers et al 961 3,232,755 2/1966 Hoegl et a1 961 LEON D. ROSDOL, Primary Examiner.

R. D. LOVERING, Examiner.

Claims

1. AN ORGANIC POLYMERIC PHOTOCONDUCTOR WHICH CONSISTS ESSENTIALLY OF: A POLYMER WHICH HAS THE STRUCTURAL FORMULA:

12. THE METHOD OF MAKING AN ORGANIC PHOTOCONDUCTOR, WHICH METHOD COMPRISES: COMPLEXING AROMATIC UNITS OF POLYMERIC MATERIAL CONTAINING MONOMERIC UNITS HAVING THE STRUCTURAL FORMULA: