US3548059A - 9,10-disubstituted anthracenes for use as photoconductors - Google Patents

Description

3,548,059 9,10-DISUBSTITUTED ANTHRACENES FOR USE AS PHOTOCONDUCTORS Eisuke Ishida, Moriguchi-shi, and Kazuhisa Morimoto,

Osaka-shi, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Osaka, Japan N Drawing. Filed Dec. 15, 1966, Ser. No. 601,875

Claims priority, application Japan, Dec. 16, 1965, 40/79,!)03, 40/79,004; Dec. 29, 1965, 41/226; June 9, 1966, 41/37,603

Int. Cl. G03g 5/00 US. CI. 96-15 2 Claims ABSTRACT OF THE DISCLOSURE The present invention is directed to novel electrophotographic materials having the formula wherein R represents a member selected from the group consisting of phenyl, naphthyl and benzanthryl and R represents a member selected from the group consisting of hydrogen and CH R The invention relates to electrophotographic materials adapted for electrostatic printing, and more particularly to photoconductive organic substances which can be laminated on a conductive support layer.

Electrostatic processes for graphic reproduction and photography have been developed by many investigators for a long period of time, their goals being mainly limited to graphic reproduction on opaque papers.

After the best-known system called Xerography had been disclosed in the Journal of the Optical Society of America, vol. 38, No. 12, December 1948, there appeared in the literature various modifications in the materials and process. Conventional materials for the photoconductive layer adherent to a conductive support layer include selenium, sulphur, zinc oxide and also organic substances such as anthracene, anthraquinone, poly-N-vinylcarbazole, polyacenaphthylene or polyvinyltriphenylpyrazoline.

However, transparent photography by an electrostatic process has not been achieved successfully because transparent photographs are usually projected in large magnification onto a screen and require high resolution, less fog and an exact reproduction covering half tone. It is important for obtaining excellent pictures on the screen that the photoconductive layer is flexible, colorless and transparent as Well as photoconductive.

Prior inorganic substances such as zinc oxide and selenium are not sufiiciently transparent. Organic substances mentioned above are not entirely satisfactory for transparent photography, because some of them have an excellent photoconductivity, but a poor adhesion to the conductive layer and others have a high transparency and a high adherence but a poor photoconductivity. According to a conventional method, a photoconductive organic substance is required to be admixed with a resin binder which decreases the photoconductivity thereof for applying to the conductive support.

It is an object of this invention to provide an electrophotographic material which comprises a photoconductive and transparent organic substance.

A further object of this invention is to provide a photoconductive and transparent organic substance which i United States Patent 0 ice can be applied uniformly to a conductive support layer with or without employing any organic colloid.

A further object of this invention is to provide a transparent electrophotographic material which comprises a photoconductive and transparent organic substance applied to a transparent conductive support layer.

Another object of this invention is to provide a method for making a photoconductive organic substance which is characterized by a high transparency adapted for preparation of a transparent electrophotographic material.

These and other objects of this invention will become apparent upon consideration of the following descriptl'on.

It has been discovered according to the invention that a photoconductive material adapted for an electrophotographic process can be prepared with the aid of condensation compounds having a methylene linkage illustrated by the following general formula in which each of R and R is an aryl, or heterocyclic radical.

A condensation compound adapted for electrophotographic material according to the invention can be prepared by the following chemical reaction equation:

wherein A represents an aromatic compound or a heterocyclic compound and B represents an aromatic compound substituted by a halomethyl group or a heterocyclic compound substituted by a halomethyl group.

Various compounds A and B, as listed in Table I, are known.

TABLE I A-compounds Benzene Naphthalene Anthracene Acenaphthene 1,2-benzanthracene N-ethylcarbazole 9-ethylanthracene 9,10-dimethylanthracene 9,10-dimethoxyanthracene Carbazole Acridine Polystyrene Poly-l -vinylnaphthalene Poly-9-vinylanthracene Polyacenaphthylene Poly-N-vinylcarbazole Polyvinylcaridine B-compounds Benzyl chloride Benzyl bromide 1-chloromethylnaphthalene l-bromomethylnaphthalene 2-chloromethylnaphthalene 2-bromomethylnaphthalene 9, lO-dichloromethylanthracene 9,10-dibromomethylanthracene 7-chloromethyl-1,2-benzanthracene 2-chloromethyll-imidazole Z-chloromethyltetrahydrofuran 3 -brornomethylquinoline Among these compounds there exist numerous combinations of A and B. According to the invention it has been discovered that the combinations listed in Table II are operable for producing the condensation compounds defined in the above general formula.

TABLE II Reaction temper- Reaction Color of Formula Cataature time resultant Number A-compound B-oompound lyst Solvent 0.) (hr.) product 1 Benzene Benzyl chloride Zn Tetraehloroethano 60-70 6 White.

Anthraeene d d 70-80 4 Yellow. 3 1,2-benzanthracene "(10. 60-70 7 Do. 4- N-ethyloarbazole. 70-75 7 Do.

Anthracene 60-65 6 Pale yellow.

1,2-benzanthracene. 70-80 2.5 Do.

N-ethylcarbazole.. 60-70 2. White.

Benzene 60-70 5 Yellow.

Naphthalene. 70-80 5 Greenish yellow.

Anthraeene 60-65 1. 5 Brown. 1,2-benzanthracene 60-65 1. 5 Greenish yellow.

N-ethylcarbazole... 50-60 2 Pale yellow.

Benzene 60-70 1 White.

Naphthalene. 60-65 1 Green.

Anthracene. 60-65 1 Pale pink. 1,2-benzanthracene. 60-65 1 White. N-ethyloarbazole- 55-60 1. 5 Pale yellow. Polystyrene 60-70 4 Do.

19 Poly-l-vinylnaphthalene Dichloroethanm 60-70 4 Do.

Formula 8 The resultant condensation compounds corresponding to the combinations of Table II are represented by the following chemical formulae designated by the corresponding numbers of Table II:

Formula 1 Q Formula 2 Formula 3 Formula 4 Formula 5 3OII2-i Z Formula 6 Formula 7 Formula 9 F0 rm ula 1 0 Formula 11 Formula 12 Formula 13 Formula 14 Formula 17 Formula 19 CHz (I) H It is also requisite to a high production yield that the mixing ratio of A-compound and B-compound be controlled. The best ratio is 1.0 mole of A-compound and 0.7 to 3.0 moles of B-compound.

A combination of A-compound and B-compound is dissolved in a solvent. Operable solvent for the combinations listed in Table II is a halogenated hydrocarbon solvent, e.g. tetrachloroethane, dichloroethane and/or chlorobenzene. A solution so produced is admixed with a catalyst selected from the group consisting of zine powder, iron powder, tin powder, cobalt powder, nickel powder and their combinations, and then is heated at a temperature of to 120 C. for 1 to 24 hours. Optimal catalyst, heating temperature and time are described in Table II in connection with the combination of A-compound and B-compound.

The aforesaid reaction for producing the novel photoconductive compounds resembles the FriedelCraft catalyst reaction, but has many excellent merits as follows in addition to producing superior photoconductive compounds for electrophotography.

It is the first merit that the separation of catalyst from the reaction mixture is easy. In the Friedel-Craft catalyst reaction, the catalyst in the resultant mixtures of reaction is required to be dissolved in an acid solution or an alkali solution for separation of resultant product and the resultant mixture must be washed out with Water. in the method of the invention, the metallic powder catalyst can be filtered off easily and be re-used. If a part of the aimed resultant product exists as a precipitate, it is suitable to filter the catalyst after dissolving the precipitate in an appropriate solvent which is added to the resultant mixture.

The second merit is that the said filtered-off catalyst retains its catalytic activity for further uses.

The third merit is that the solvent used can be recovered by distillation and be re-used.

The fourth merit is that the condensation compounds by the method in accordance with the invention are free from any by-products and have solubility in a solvent higher than that of the Friedel-Craft product.

As mentioned above, the condensation compounds in accordance with the invention have superior properties as photoconductive materials in comparison with the condensation compounds produced by the Friedel-Craft reaction. Especially, a condensation compound according to Formula 12, i.e. a condensation compound of N-ethylcarbazole and 9,10-dichloromethylanthracene, gives best results. The compound of Formula 12 has high photoconductivity, high solubility and high transparency, and it is easily applied to a transparent photoconductive insulating layer for electrophotography.

Following description will explain the preparation of novel condensation compounds in connection with exemplary compounds. The details of the preparation of other compounds of the invention will be clear to the skilled in the art upon consideration of preceding and following descriptions, since only analogy procedure will be required.

The reaction of benzene and benzyl chloride, corresponding to Formula 1 is as follows: In a 100 ml. (milliliter) round-bottomed flask equipped with a stirrer, a thermometer, a gas-inlet tube and a reflux condenser, are placed 2.4 g. (grams) of benzene, 2 g. of benzyl chloride, 50 ml. of tetrachloroethane and 1.2 g. of zinc powder. The mixture is stirred for 6 hrs. at to C. under a slight stream of nitrogen and is cooled to room temperature (20 to 30 C.). The zinc powder is filtered off with suction and then the filtrate is distilled to 7 ml. by a reduced pressure distillation. The resultant solution is poured into 50 ml. of n-hexane to yield a White precipitate which is filtered off and is dried to 1.2 g. of a white powder free from halogen.

Formula 4: Analogously, a mixture of 3.8 g. of 1,2- benzanthracene, 1.89 g. of benzylchloride, 50 ml. of tetrachloroethane and 1.0 g. of zinc powder is stirred for 7 hrs. at 70 C. under a slight stream of nitrogen. After the reaction is completed, the catalyst is filtered 01f and the filtrate is distilled at a reduced pressure of 7 ml. The resultant solution is added to 70 ml. of n-hexane. A pale yellow precipitate is obtained and is filtered off and is dried to 1.3 g. of pale yellow substance free from halogen.

Formula 7: Analogously, a mixture of 4.3 g. of N- ethylcarbazole, 3.5 g. of l-cliloromethylnaphthalene, 60 ml. of tetrachloroethane and 1.0 g. of zinc powder is stirred for 2.5 hrs. at 60 C. under a slight stream of nitrogen. After the filtration of the catalyst, tetrachloroethane is distilled. According to the said procedure a white powder (2.9 g.) is obtained.

Formula 12: Analogously, a mixture of 18.8 g. of N- ethylcarbazole, 11 g. of 9,10-dichloromethylanthracene, 1.5 g. of zinc powder and 240 ml. of tetrachloroethane is stirred for 2 hours. at 51 C. under a slight stream of nitrogen. After the filtration of the catalyst, tetrachloroethane is distilled. According to the said procedure a pale yellow powder (15.6 g.) is obtained.

The compounds to be used in accordance with the invention have very good photoconductivity and are particularly suitable for the preparation of homogeneous coatings of unlimited shelf-life.

If transparent supports are used, the electrophotographic images can also be used as masters for the production of further copies of any sort of light-sensitive sheets and specially as reproduction in movie pictures. In this respect, the photoconductive compounds used according to the invention are superior to the prior substances such as selenium and zinc oxide, because such materials do not form a solid solution with a binder material and exist in a suspension form which results in a cloudy layer.

For the preparation of the photoconductive insulating layers it is advantageous that said compounds according to the invention be a solution in organic solvent, e.g. chlorobenzene, methylene chloride, dichloroethane, tetrachloroethane, dioxane and their combinations. The photoconductive compounds according to the invention may be mixed with other organic photoconductive substances.

The photoconductive compounds according to the invention may be in suspension form for applying the supporting material.

When the novel photoconductive compounds are used in association with organic colloid, the proportion of organic colloid to photoconductive compound can be changed advantageously in a wide range. For example, a mixture of 30 to 120 parts of resin and 100 parts of photoconductive compound can be employed.

The novel compounds form satisfactory photoconductive insulating layers without any organic colloids. However, addition of suitable organic colloid can improve the resultant photoconductive insulating layer. Operable organic colloids are as follows: natural and synthetic resins, e.g. phenol resins modified with rosin, coumarone resin, indene resins, polyvinyl acetal, polyvinyl butyral, polystyrene, polyvinyl acetate, polyvinyl cinnamate, polycarbonate, ketone resins and vinyl chloridevinyl acetate copolymers. A mixture of the photoconductive compound and one of the said operable organic colloids can produce a homogeneous and transparent layer on a support, said layer being considered to be a solid solution of said photoconductive compound and said organic colloid when dried.

The addition of plasticizer can be aimed at the further improvement in the property of the photoconductive insulating layers.

Operable plasticizers are as follows: chlorinated diphenyl, dimethyl phthalate, diethyl phthalate and dioctyl phthalate.

It has further been known that the spectral sensitivity of the photoconductive layer can be extended into the visible part of the spectrum by adding dyestufi? sensitizers or chemical sensitizers.

Excellent sensitizing effects can be produced by addition of 0.02 to 0.5 weight part of the said dyestuffs to 100 weight parts of photoconductive compound.

Particularly preferable as dyestutf sensitizers are triarylmethane dyestuffs such as brillian green, victoria blue B, methyl violet, crystal violet; xanthene dyestuffs, such as rhodamine B, rhodamine 6G, rhodamine G extra; thi- 8 azine dyestuffs such as methylene blue and their combinatlons.

Particularly preferable as chemical sensitizers are picric acid, tetrachlorophthalic anhydride, naphthalic anhydride, 3,6-dinitronaphthalic anhydride, Z-methylanthraquinone, 1,2-benzanthraquinone. Preferable amounts thereof are from 0.2 to 20 weight parts with respect to 100 weight parts of the said photoconductive compounds.

The operable materials for electroconductive supports may be made of any materials which satisfy the requirement of electrophotography, e.g. metal plate or glass plate having NESA coating plates or foils made of electrically conductive resins or coated with evaporated thin metal layer, or paper. The solutions of the compounds of the photoconductive materials, with or without the resins, are applied to the supports in the usual manner, for example by spraying, by direct application, by means of rollers, etc., and then dried so as to produce a homogeneous photoconductive layer on the electroconductive support. The transparent support can produce a transparent electrophotographic plate or foil. After an electrostatic charge has been applied, i.e. after the layer has been charged positively or negatively by means of a corona discharge, the layer becomes light sensitive.

The reproduction of images by electrophotographic methods is carried out as follows; when the photoconductive layer has been charged, by means of corona discharge with a charging apparatus maintained at 6000-7000 volts, the support with the sensitized layer is exposed to light under a master and is then dusted over in known manner with a resin powder colored with carbon black. The image that now becomes visible can easily be wiped off. It can also be fixed by heating at about 120 C. From positive masters, positive images characterized by good contrast are produced.

The invention will be further illustrated by reference to the following specific examples:

(1) 1 g. of the compound of Formula 1, and 0.5 g. of polyvinylcinnamate and 0.1 g. of Z-methylanthraquinone are dissolved in 7 ml. of monochlorobenzene. The solution is applied to an aluminum plate by means of whirler coating and is dried to form a layer of 4 in thickness. After the said aluminum plate provided with the layer is charged positively by means of corona discharge with a charging device maintained at approximately 6000 volts in the dark, it is placed under a positive master and is exposed for 20 seconds to a 100 w. tungsten lamp at an illumination of 1000 luxes, and the said plate is powdered over with a developer in a per se known manner. This developer consists of toner and carrier. The toner is composed of a low melting-point polystyrene, colophony and carbon-black. The toner is mixed with a carrier substance having such nature that the toner becomes triboelectrically charged with a charge that is the opposite of that produced on the plate, e.g. glass balls or iron filings. A positive image is produced which is fixed by slight heating.

(2) 1 g. of the compound of Formula 3, 0.5 g. of polycarbonate resin and 1 mg. of crystal violet are dissolved in 7 ml. of methylene chloride. The solution is applied to an aluminum plate and is dried. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 2 second to light of 250 luxes.

(3) 1 g. of the compound of Formula 5, and 0.5 g. of vinyl chloride-vinyl acetate copolymer are dissolved in 7 ml. of monochlorobenzene. The solution is applied to an aluminum plate and is dried to form a layer of 4 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 10 second to light of 400 luxes.

(4) 1 g. of the compound of Formula 5, 0.5 g. of polyvinyl acetate, 0.1 g. of tetrachlorophthalic anhydride and 1 mg. (milligram) of methylene blue are dissolved in 7 ml. of methylene chloride. The solution is applied to an aluminum plate and dried to form a layer of 4 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 6 seconds to light of 250 luxes.

(5) 3 g. of the compound of Formula 7, and 1.5 g. of polystyrene are dissolved in 9 ml. of monochlorobenzene. The solution is applied to a cellulose diacetate film sheet which surface is in advance vacuum-evaporated with cuprous iodide by means of a blade coating and is dried to form a layer of 8p. in thickness. On this transparent sheet an electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 25 seconds to light of 1000 luxes. It can then be used as intermediate originals for further duplication, e.g. for copying on diazo paper.

(6) 3 g. of the compound of Formula 7, 1.5 g. of polystyrene and 3 mg. of crystal violet are dissolved in a mixture of 2 ml. of methylene chloride and 7 ml. of monochlorobenzene. The solution is applied to a transparent support and is dried to form a layer of 8 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 4 seconds to light of 200 luxes.

(7) l g. of the compound of Formula 8, and 0.5 g. of polystyrene are dissolved in ml. of tetrachloroethane. The solution is applied to an aluminum plate and is dried to form a layer of 4 in thickness. An electrophotographic image is produced in a similar Way to that descriebd in Example 1. It is exposed for 2 seconds to light of 60 luxes.

(8) 1 g. of the compound of Formula 9, and 0.5 g. of polyvinyl butyral resin are dissolved in 10 ml. of monochlorobenzene. The solution is applied to an aluminum foil and is dried to form a layer of 4a in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 4 seconds to light of 500 luxes.

(9) 3 g. of the compound of Formula 12, and 1.5 g. of vinyl chloride-vinyl acetate copolymer are dissolved in a mixture of 8 ml. of toluene and 2 ml. of methyl ethyl ketone. The solution is applied to an electroconductive plastic film of a surface conductivity of 10 t'l-cm. and is dried to form a layer of 8a in thickness. After the film is charged negatively by means of corona discharge in the dark, the said film is placed under a positive master and is exposed for seconds to a tungsten lamp at an illumination of 500 luxes, and the said film is powdered over With a developer in known manner. A positive image is produced which is fixed by slight heating.

(10) 3 g. of the compound of Formula 12, 1.2 g. of

polycarbonate resin and 0.2 g. of 3,6-dinitronanphthalic anhydride are dissolved in a mixture of 3 ml. of dichloroethane and 12 ml. of monochlorobenzene. The solution is applied to a transparent support as described in Example 5 and is dried to form a layer of 10 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1 on the said transparent support. It is exposed for 2 seconds to light of 50 luxes.

(ll) 3 g. of the compound of Formula 12, 1.5 g. of polyvinylcinnamate and 3 mg. of crystal violet are dis solved in 12 ml. of monochlorobenzene. The solution is applied to a transparent support as described in Example 5 and is dried to form a layer of 10 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 2 seconds to light of 50 luxes.

(l2) 3 g. of the compound of Formula 13, 1.5 g. of polyvinylcinnamate and 0.15 g. of 1,2-benzanthraquinone are dissolved in 12 ml. of monochlorobenzene. The solution is applied to a transparent plastic film having an electroconducting layer of 10 SZ-cm. and is dried to form a layer of 10a in thickness. The said film is provided with a negative charge by the corona discharge. After the film has been exposed for 2 seconds to light of 50 luxes under a master, the image produced thereon is developed by powdering over with a developer, in a similar way to that described in Example 1. The resultant positive image of master shows excellent contrast likewise.

(l3) 1 g. of the compound of Formula 14, 0.5 g. of polystyrene and 10 mg. of naphthalic anhydride are dissolved in 7 ml. of monochlorobenzene. The solution is applied to an aluminum plate and is dried to form a layer of 4 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 2 seconds to light of luxes.

(14) 1 g. of the compound of Formula 16 and 0.5 g. of polystyrene are dissolved in 7 ml. of monochlorobenzene. The solution is applied to an aluminum plate and is dried to form a layer of 4 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 4 seconds to light of 100 luxes.

(15) 1 g. of the compound of Formula 16, 0.5 g. of polystyrene and 10 mg. of picric acid are dissolved in 7 m1. of monochlorobenzene. The solution is applied to an aluminum plate and is dried to form a layer of 4,u in thickness. The said plate is provided with a negative charge by the corona discharge. After the plate has been exposed for 2 seconds at light of 100 luxes under a master, the image produced thereon is developed by powdering over a developer, in a similar way to that described in Example 1. The resultant positive image of master, shows excellent contrast likewise.

(l6) 1 g. of the compound of Formula 18, 0.1 g. of 2-methylanthraquinone, 0.5 mg. of Rhodamine G and chlorinated diphenyl are dissolved in 15 ml. of tetrahydrofuran. The solution is applied to an aluminum plate and dried to form a layer of 4 1 in thickness. An electrophotographic image is produced in a similar way to that described in Example 1. It is exposed for 2 seconds to light of 100 luxes.

What is claimed is:

1. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising compounds having the for- References Cited UNITED STATES PATENTS 9/1966 Noe et al. 96l.5 11/1966 Hoegl 96-1.5

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R.