US3281240A

US3281240A - Electrophotographic material

Info

Publication number: US3281240A
Application number: US144579A
Authority: US
Inventors: Cassiers Paul Maria; Noe Robert Joseph
Original assignee: Gevaert Photo Producten NV
Current assignee: Gevaert Photo Producten NV
Priority date: 1960-10-12
Filing date: 1961-10-12
Publication date: 1966-10-25
Anticipated expiration: 1983-10-25
Also published as: FR1314416A; DE1215523B; GB1007349A; NL256772A; BE609056A

Description

United States Patent F 3,281,240 ELECTROPHOTOGRAPHIC MATERIAL Paul Maria Cassiers, Mortsel-Antwerp, and Robert Joseph Noe, Berchem-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel, Belgium, a Belgian company No Drawing. Filed Oct. 12, 1961, Ser. No. 144,579 Claims priority, application Netherlands, Oct. 12, 1960, 256,772 7 Claims. (Cl. 96-1) This invention relates to clectrophotographic material and more especially to the photoconductive layer of this electrophotographic material.

Electrophotographic materials are known consisting of a support and a photoconductive layer which contains an inorganic substance as a photoconductor e.g. selenium, zinc oxide or an organic substance such as anthracene, benzidine or a heterocyclic compound. Further, photoconductive polymers are employed in the manufacture of photoconductive layers such as described in the Belgian patent specifications 588,048, 588,049, 588,050, 599,627 and 604,127.

Most of the known elec-trophotographic materials show the characteristic disadvantage of having an insufiiciently homogeneous reproduction of large black image areas in the original. These large black image areas are only reproduced on their edges by black lines. This effect is called fringing effect and is described e.g. by Dessauer, Mott and Bogdonoff in Phot. Eng. 6 (1955), pp. 250269. According to these authors the fringing effect on selenium plates can be eliminated by the use of an auxiliary or development electrode.

Homogeneously covered image areas may also be obtained e.g. by charging the electrophotographic material through an intermittent contact with macromolecular substances instead of charging the electrophotographic material by an ionisation effect in an air layer, as occurs in the corona discharge. This method is described in the Belgian patent specification 568,659.

In another method which aims at the same result, viz. the elimination of the fringing elfect, a specific composition of the photoconductive layer is used, containing besides the photoconductive component: zinc oxide, other organic or mineral substances with a grain size and in a weight ratio based upon that of the photoconductor. This process is described in Belgian patent specification 576,367.

It has now been found that for obtaining a visible reproduction of an electrostatic image by using an electrophot-ographic material comprising a photoconductive layer containing two different high-molecular compounds, one of which being discontinuously present in the other, which in its turn is present in the layer in a continuous way and which consists of a photoconductive polymer, the product of the dielectric constant e and the specific resistivity p of said photoconductive polymer being at least two times greater or smaller than the product of the dielectric constant e and the specific resistivity p of the high-molecular compound which is discontinuously present in the photoconductive layer, the quality of the formed image and especially the uniformity of the image and the density of the black par-ts are markedly improved.

By specific resistivity p of the photoconductive highmolecular compound is pure understood the specific resistivi-ty measured in the dark, for which reason it is also called dark-resistivity.

The determination of the resistivity in the dark of photoconductive polymers is carried out according to Standard Method of Test for Electrical Resistance of Insulating Materials, A.S.T.M. designations: D 257-58 ((41) Volume Resistivity), p. 612, and also D 1371-55 T, p.

3,281,240 Patented Oct. 25, 1966 703, 1958 Book of A.S.T.M. Standards, Part g. The measuring of the specific resistivity of powdery macromolecular substances takes place according to the method described in Chemie-Ingenieur-Technik, 31, 1959, pp. 43- 45. The measuring of the dielectric constant takes place by means of the same measuring cell as for the specific resistivity, but with the help of a Schering-bridge. Although the measurings on powdery substances give only approximative values, they suflice for the purpose of this invention, since only the ratio of the values and not the absolute values are of importance. The reproducibility of these measurings improves by vibrating the above cited measuring cell until an optimal volume concentration of the powder is reached. In respect of the examples below, the measuring results on the photoconductive polymers and the macromolecular compounds dispersed therein are now given:

e p in eXp ohm.cm.

(1) Hostalit CAM (registered trademark) 3. 43 2. 2X10 7. 4X10 (2) Starch 7.5 2.6X10 2x10 (3) Polyvinylcarbazole 3.05 5.8)(10 1.8 10 (4) Methylene starch 9. 15 6.2)(10 5.7)(10 See preparation 1Methylene urea starch.

For the application of the process of this invention are considered e.g. the photoconductive polymers described in the Belgian patent specifications 588,048, 588,049, 58 8,050, 570,790, 599,627 and 604,126, and also the photoconductive material from this last mentioned specification.

The following macromolecular additives are considered.

CELLULOSE DERIVATIVES acetate cinnamate, and cellulose acetate phthalate.

POLYSACCHARIDES AND PROTEINS Polyethylene, polytetrafiuoroethylene, polyamides of the adipic acid-hexamethylene diamine type, polyamides of the caprolactam type, rubber, phenol-formaldehyde resins, and urea-formaldehyde resins.

VINYL POLYMERS The chlorine containing polymers and copolymers cited in Belgian patent specification 604,126, and more especially the following polymers and copolymers of vinyl chloride: Geon Resin 100, Geon Resin 101, Geon Resin 202, Geon Resin 203, Geon =Resin 204, Geon Resin 205 and Geon Resin 404 (trade-names of British Geon Ltd., London).

Aluminum polysilicates e.g. porcelain powder and kaolin.

The following are preparations of some of the above cited products.

1. Preparation of a reaction product of formaldehyde, ureum, maleic anhydride and starch called methylene urea starch.

110 g. of undried starch, which corresponds to 100 g. of dry product, are Suspended in a solution of 11.5 g. of urea and 110 cm. of water. After staying for 1 /2 h., 400 cm. of acetone, 33.5 cm. of 40% aqueous formaldehyde, 1 g. of maleic anhydride and 12 cm. of water are added thereto. This reaction mixture is stirred for 2 h. at 40 C., whereupon the temperature is raised to 60 C. The mixture is stirred at this temperature for 4 h. Then the reaction mixture is cooled and the solid product is sucked off. The filter cake is washed with water until the washings are free of formaldehyde. The water in the filter cake is eliminated by acetone. The obtained product is dried under ventilation.

2. Preparation of starch-N-phenylcarbamate 55 g. of undried rice starch are dehydrated with benzene by an azeotropic distillation during which care is taken that the volume is kept constant by regular addition of water-free benzene.

After drying by distillation, 20 cm. of phenyl isocyanate are added. After refluxing for 6 h., the formed solid product is sucked off. This product is Washed with ethanol, sucked off again and dried.

Polymeric compounds which are used as additives for the elimination of the fringing effect, areinsoluble or are made insoluble in the usual solvents. This insol'ubiliz'ation can take place during the polycondensation if a synthetic product is concerned e.g. by cross-linking or hardening, or by an after-treatment after the formation of the polymer, e.g. photopolymerization, heat treatment, chemical hardening or vulcanization.

The size of the particles of the added macromolecular compounds preferably varies between 1 and a. The particles can occur in the form of grains, fibres or scales, without excluding, however, other particle forms.

In practice, the polymeric photoconductive substance used While Wet is ground with other additives as is described more specifically hereinafter in a solvent for the photoconductive components, until the required dispersion and grain size of the macromolecular insoluble compounds are obtained.

The solvent is chosen in such a way, that the particles to be dispersed of the high-molecular compound remain in their undissolved state whereas the photoconductive polymer can dissolve.

The obtained dispersion is uniformly spread over the surface of a support e.g. by centrifugation, spraying, brushing or coating, whereupon the formed layer is dried in such a way, that a uniform photoconductive layer is obtained.

Preferably the amount of macromolecular dispersed particles amounts to 5 to 50% based on the weight of the photoconductor.

The thickness of the photoconductive layers is not critical, but is open to choice within a wider range according to requirements. Good results are obtained with photoconductive layers having a thickness of between 1 and 20 but preferably of between 3 and 10;. Layers which are too thin have an insuificiently insulating power and layers which are too thick require extensive exposure times.

It is well understood that the invention is not limited by the use of dispersions of the above mentioned macromolecular compounds in solutions of previously polymerized compounds, but that e.g. dispersions in mixtures of monomeric and polymeric substances can be applied onto the surface of the support to be coated, and that these may be polymerized in situ, condensed or cross-linked according to one of the known methods in polymer chemistry.

The photoconductiv'e layers manufactured according to this invention, besides one or more photoconductive polymeric substances, may still contain one or more photoconductive monomeric compounds.

As monomeric photo'conductors are considered e.g. the photoconductive compounds mentioned in the U.S. patent specifications 2,599,542 (anthracine) and 2,663,636 (anthraquinone, acenaphthene, fluoranthene, naphthalene, chrysoquinone, pyrogallic acid and microcrystalline Waxes), the French patent specification 1,176,381 and the published German patent specification 1,060,712, the Belgian patent specifications 558,078, 558,630, 562,336, 562,426, 563,045 and 570,790, and the Austrian patent specification 205,516 (p-diphenyl benzene, benzanthrone and aromatic nitriles).

To the composition of the photoconductive layer, which contains one or more polymeric photoconductors and one or more monomeric photocondu-ctors, a binding agent may be added for obtaining a mechanically suificiently strong subbing layer, such as described in the Belgian patent specification 585,555. If desired, plasticizers may be added which are also described in that same patent specification.

In the photoconductive layers according to this invention there can further be present compounds which occasionally possess photoconductive properties and which cause an increase of the general sensitivity and/ or of the sensitivity for electromagnetic rays from a defined part of the spectrum. Such compounds are described for instance in Belgium patent specification 588,050, p. 12-22, classes A to T inclusive. These compounds are pref- 'er'ably employed in amounts ranging from 0.1 to 5% based upon the weight of the used polymeric photo'conductive substances.

Other additives, well known in the art of coating, which may be used, include agents controlling ageing, oxidation, gloss, thermal stability, electric conductivity, mechanical resistance, viscosity or other physical properties. In selecting such additives, preference is given to those substances which do not markedly decrease the dark-resistivity of the photoconductive layer.

Suitable supports for the electrophoto'graphic layer are described in Belgian patent specification 588,050.

For charging and exposing of the electrophotographic material, developing and fixing of the image, this same patent specification and the article of Dessauer, Mott and Bo'gdonoff, Phot. Eng. 6 (1955), pp. 250-269, may be cited.

As a matter of fact this new invention should by no means be limited to one or other special embodiment, in regard to the use of the new electrophotographic materials, the method of charging, the exposure technique, the transfer (if any), the developing method, and the fixing method as well as the materials used in these steps can be chosen according to requirements.

Electrophotographic materials according to the present invention can be applied in reproducing techniques using different kinds of radiations, not only electromagnetic radiations as hereinbefore referred to but also nuclear radiations. For this reason, it should be pointed out that although materials according to the invention are mainly intended for application in processes involving an exposure, the term electrophotograp-hy wherever appearing in the description and the claims is used broadly, and includes both xerogra-phy and xeroradiography.

The following examples illustrate the present invention without limiting, however, the scope thereof.

EXAMPLE 1 A baryta-coated paper of 90 g./sq. m. bearing g. of baryta per sq. m., is coated with a layer from a 12% solution of Hostalit CAM (trademark of Farbwerke Hoechst A.G., Frankfurt am main-Hochst for a ter polymer of vinyl chloride, vinyl acetate and maleic anhydride) in acetone. The thickness of the dried layer is 5 This support is then coated with a layer from the following composition:

10% solution of Hostalit CAM (trademark) in acetone cm 50 10% solution of leuco malachite green in methylene chloride -cm 50 Starch (grain size of about 1 g 0.4

After completely drying, this material is negatively charged with a corona device. This material is exposed for 20 sec. through a diapositlve with a 100 Watt lamp placed at a distance of 10 cm. The latent electrophotographic image is then developed with a mixture consisting of 5 g. of Graph-O-Fax Toner No. 3 (trade-name of Philip A. Hunt Company, Palisades Park, N.J., for a xerographic developing dyestufi?) as a toner, and 100 g. of iron powder as a carrier.

By fixing according to one of the known methods, a strong and sharp print having especially well covered black areas, is obtained.

EXAMPLE 2 A mixture of the following composition is ground for 12 h. in a ball-mill:

Polyvinylcarbazole (prepared according to the method described in Belgian patent specification 589,995) cm 100 l-chloroanthraquinone g 0.1 Methylene ureum starch (prepared according to preparation 1) g l Methylene chloride cm 100 A mixture of the following composition is ground for 12 h. in a ball-mill:

Copolymer of vinylcarbazole and ethyl acrylate (prepared according to the method described in Belgian patent specification 589,995) g 7.5 Basic blue 3 (Cl. 51,005) mg 4 Starch-N-phenyl carbamate (prepared according to preparation 2) g 1 Methylene chloride cm 100 A baryta-coated paper of 90 g. per sq. m. bearing 10 g. of baryta per sq. m., is coated with a layer from this composition.

After drying the thickness of this photoconductive layer amounts to 10 The material is then charged with a corona device and exposed in an enlarger with a lamp of 75 watts. A linear enlargement of 10 times of a dia positive requires an exposure of 2 min. The obtained material is developed with a tribo-electric powder as described in Example 1. A vigorous image is obtained having a clear background and well covered black parts.

We claim:

1. In a method of reproducing an original by the creation of a pattern of electrostatically charged and uncharged areas according to said original on a supported normally insulating layer becoming conductive upon exposure to electromagnetic radiation, which method includes the steps of electrostatically charging said layer and exposing said layer to an image of said radiation according to said original to create said pattern and developing said charged areas of said pattern with finely-divided electrostatically attractable material attracted by the charges therein but not attracted to the uncharged areas thereof, the improvement wherein said supported layer is comprised essentially of an insulating organic polymer becoming conductive upon said exposure and having at least substantially uniformly distributed therethrough discrete finely divided particles of a polymeric substance less conductive upon exposure to said radiation than said insulating organic polymer, the arithmetic product of the dielectric constant and the specific electric resistance of said insulating organic polymer measured in the dark differing by a factor of at least two from that of said polymeric substance, said polymeric substance being present in said layer in the amount of about 5-50% by weight of said insulating organic polymer.

2. A method according to claim 1 wherein electrophotographic material is subjected to a substantially uniform electrical field to produce electrostatic charge completely thereover and is thereafter exposed to said electromagnetic radiation image to create said pattern of electrostatic charges.

3. An electrophotographic material for use in the method of claim 1 comprising a supported layer comprised essentially of a continuous phase of an insulating organic polymer becoming conductive upon exposure to electromagnetic radiation, said polymer phase having at least substantially uniformly distributed therethrough a separate dispersed phase of discrete finely divided particles of a polymeric substance less conductive upon exposure to said radiation than said insulating organic polymer, the arithmetic product of the dielectric constant and the specific electric resistance of said insulating polymer measured in the dark differing by a factor of at least two from that of said polymeric substance, the amount of said polymeric substance in said layer being about 550% by weight of said insulating organic polymer.

4. The material of claim 3 wherein the finely divided particles of said polymeric substance are of a size of about 1-5 microns.

5. The material of claim 3 wherein said layer contains in addition to said organic polymer and said polymeric substance, at least one monomeric compound becoming conductive upon said radiation.

6. The material of claim 3 wherein said layer containsin addition to said organic polymer and said polymeric substance, an agent increasing the radiation sensitivity of said polymer.

7. The material of claim 3 wherein said layer has a thickness of about 1-20 microns.

References Cited by the Examiner UNITED STATES PATENTS 3,011,918 12/1961 Silvernail et al 96-1 3,037,861 6/1962 Hoegl 961 3,159,483 12/ 1964 Behmenberg et al. 96-1 NORMAN G. TORCHIN, Primary Examiner.

C. E. VAN HORN, Assistant Examiner.

Claims

1. IN A METHOD OF REPRODUCING AN ORIGINAL BY THE CREATION OF A PATTERN OF ELECTROSTATICALLY CHARGED AND UNCHARGED AREAS ACCORDING TO SAID ORIGINAL ON A SUPPORTED NORMALLY INSULATING LAYER BECOMING CONDUCTIVE UPON EXPOSURE TO ELECTROMAGNETIC RADIATION, WHICH METHOD INCLUDES THE STEPS OF ELECTROSTATICALLY CHARGING SAID LAYER AND EXPOSING SAID LAYER TO AN IMAGE OF SAID RADIATION ACCORDING TO SAID ORIGINAL TO CREATE SAID PATTERN AND DEVELOPING SAID CHARGED AREAS OF SAID PATTERN WITH FINELY-DIVIDED ELECTROSTATICALLY ATTRACTABLE MATERIAL ATTRACTED BY THE CHARGES THEREIN BUT NOT ATTRACTED TO THE UNCHARGED AREAS THEREOF, THE IMPROVEMENT WHEREIN SAID SUPPORTED LAYER IS COMPRISED ESSENTIALLY OF AN INSULATING ORGANIC POLYMER BECOMING CONDUCTIVE UPON SAID EXPOSURE AND HAVING AT LEAST SUBSTANTIALLY UNIFORMLY DISTRIBUTED THERETHROUGH DISCRETE FINELY DIVIDED PARTICLES OF A POLYMERIC SUBSTANCE LESS CONDUCTIVE UPON EXPOSURE TO SAID RADIATION THAN SAID INSULATING ORGANIC POLYMER, THE ARITHMETIC PRODUCT OF THE DIELECTRIC CONSTAND AND THE SPECIFIC ELECTRIC RESISTANCE OF SAID INSULATING ORGANIC POLYMER MEASURED IN THE DARK DIFFERING BY A FACTOR OF AT LEAST TWO FROM THAT OF SAID POLYMERIC SUBSTANCE, SAID POLYMERIC SUBSTANCE BEING PRESENT IN SAID LAYER IN THE AMOUNT OF ABOUT 5-50% BY WEIGHT OF SAID INSULATING ORGANIC POLYMER.