Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/14—Inert intermediate or cover layers for charge-receiving layers
  • G03G5/147—Cover layers
  • G03G5/14708—Cover layers comprising organic material
  • G03G5/14713—Macromolecular material
  • G03G5/14747—Macromolecular material obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G5/14769—Other polycondensates comprising nitrogen atoms with or without oxygen atoms in the main chain

Definitions

• This invention relates to xerography and electrophotography and more particularly to a method and composition for protecting and stabilizing the photoconductive insulating materials employed in connection therewith.
• an electrostatic latent image on a member or plate which comprises a substantially electrically conductive backing member such as, for example,*a paper or metallic memher having a photoconductive insulating material applied to the surface thereof.
• a suitable electrostatic image forming member for xerographic purposes is an electrically conductive backing member, for example, metal, which may be employed in the form of a sheet, drum or belt, having applied to the surface thereof, a photoconductive material, for example, selenium, inorganic materials, such as cadmium sulfo-selenide, cadmium sulfide, zinc oxide and mixtures thereof; organic materials such as complexed poly-N-vinyl carbazole, and other like photoconductive materials useful for such purpose.
• These electrostatic image forming members are characterized by being capable of receiving electrostatic charge and selectively dissipating such charge when exposed to a light pattern.
• our invention comprises the application to the photoconductive surface of an electrostatic image forming member, of a thin uniform coating of polyurethane to provide positive protection against abrasion and contamination.
• the photoconductive surface of electrostatic image fonning members can' be protected from abrasion and contamination by the application thereto of a thin, uniform coating of a polyurethane.
• the polyurethane coating which may be satisfactorily employed in the practice of this invention must have'a very high resistance to abrasion.
• the polyurethane must have low surface leakage properties as indicated by a high dielectric strength and surface resis- 1 tance, so that the applied electrical charges will not be I dissipated by bypassing of the underlying photoconductive material.
• the total surface leakage of the polyure thanes which are useful in the practice of this invention may be determined in the same manner as is done for photoconductors, i.e., a thin coating of the polyure-' thane, about 1 mil or less, is tested for charge acceptance.
• the polyurethane when the polyurethane is tested by being charged in a Victoreen Electrostatic Paper Analyzer the polyurethane must accept a charge equivalent to at least 1,000 volts/mil of thickness and preferably at least 1,500 volts/mil, to yield satisfactory results hereunder.
• the polyurethane coating must be inert to the photoconductive material upon which it is to be applied and must have good adhesion properties which will permit its permanent bonding to the photoconductive surface on which it is applied.
• the adhesion properties of the polyurethane must provide a uniform coating and help prevent air pockets or other surface irregularities which could interfere with the photoconductive properties of the image forming member.
• the polyurethane coating must have fast air drying properties to permit facile coating thereof on the photoconductive surface. In the practice of this invention we have found that a polyurethane capable of being cured by solvent evaporation provides satisfactory results. I
• the electrically conductive backing member which may be employed in the electrostatic latent image forming member useful in the practice of the instant invention may be comprised of any material that has been previously found. to be satisfactory in the practice of xerography. Included among the electrically conductive materials whichmay be employed in the practice of this invention are metals, for example, aluminum or brass, conductive paper, graphitized Mylar, metallized Mylar and other like material.
• the photoconductive insulating materials which may be satisfactorily employed in the practice of this invention are those photoconductive materials which have heretofore been so employed in the practice of xerography and which may be satisfactorily applied on the electrically conductive backing materials.
• the photoconductive materials which may be employed in the practice of the instant invention are such materials as selenium, cadmium sulfo-selenide, cadmium sulfide, zinc oxide, poly-N-vinyl carbazole and other like materials.
• a mixture of cadmium sulfo-selenide/zinc oxide is both protected and electrically stabilized by a thin, uniform coating of polyurethane.
• the polyurethane protective coating employed in the practice of this invention must have the physical properties set forth hereinabove. In addition, we have found that satisfactory results are obtained when the polyurethane coating employed is possessed of a charge acceptance of at least 1,000 volts/mil of thickness. In the preferred practice of the instant invention, we have found that most satisfactory results are obtained when a polyurethane having a charge acceptance of at least 1,500 volts/mil is employed. The successful practice of this invention is dependent upon the characteristics and properties of the polyurethane employed and although many polyurethanes were tested it was unexpectedly found that only the polyurethanes possessing the specific properties set forth hereinabove provided satisfactory results.
• the polyurethane protective coating must be applied to the photoconductive surface in such a manner as to avoid adversely affecting the photoconductive properties thereof.
• the thickness of the polyurethane coating must be controlled to avoid masking the photoconductive response to the underlying photoconductive material, while at the same time providing a coating which is thick enough to provide the required protection.
• satisfactory results are obtained when the coating is applied in a uniform thickness of from about 0.02 to about 01 mils; and preferably when the coating was applied uniformly in a thickness of from about 0.04 to about 0.08 mils.
• the polyurethane coating may be applied in any manner which is known and convenient to the skilled worker, for example, spraying, painting, Mayer rod, doctor blade or reverse roller applicators, which will provide a uniform coating of the polyurethane in the required thickness.
• solvents employed in the application of the polyurethane coating to the photoconductive surface so as to avoid interaction of the solvents with the underlying photoconductive materials or binders which may have been employed in connection therewith.
• Satisfactory solvents which we have found to be employable in connection with the polyurethane coating material of this invention include such solvents as isopropanol, cellosolve acetate and methyl ethyl ketone. although other solvents may be employed as may be de-, termined by the worker skilled in the art.
• the photoconductor composition should comprise a binder having a mixed pigment therein of from 20 percent to percent of cadmium sulfo-selenide and from 30 percent to percent zinc oxide by weight of total pigment.
• the mole fraction ratio of selenium to selenium plus sulfur in the cadmium sulfo-selenide should be from 0.05 to 0.7 e.g. where n equals the number of atoms of sulfur and selenium the ratio (n(Se)/n(S)+n(Se)) is from 0.05 to 0.7.
• Table A shows the necessity for particularly protecting the surface of a cadmium sulfo-selenide/zinc oxide photoconductor from bumishing.
• the effects of burnishing were simulated by rubbing the surfaces with cotton.
• Table A indicates that the mixed CdSSe/ZnO photoconductor shows a significant reduction in acceptance voltage as compared to either of the constituents when CdSSe and ZnO Crushed Together and ZnO particles interact when the surface is abraded.
• Table B below illustrates the effects of changing the pigmentto binder ratio (P/B) and CdSSe/ZnO ratio.
• EXAMPLE 1 A polyurethane resin having a charge acceptance of in excess of 1,500 volts/mil of thickness (commercially available from Cargill Co. as a percent solution under the designation Cargill-X-l 5 I 3-30" an aliphatic type urethane having a molecular weight of from 23,000 to 25,000) was-applied to the surface of a cadmium sulfo-selenide/zinc oxide mixed pigment photoconductor in different thicknesses of from 0.04 to 0.08 mils by diluting the polyurethane to various solid concentrations before coating. The higher the percentage of solids, the thicker the coating. The control had no top coating at all.
• the respective photoconductor propv erties were measured by employment of a modified Victoreen Electrostatic Paper Analyzer and the results thereof are set forth in TableD below:
• the pigment to binder ratio was 6:1 with a solvent t binder ratio of 7:1 for a total solids content of about 50 percent, of which the pigments were in the ratio of percent CdSSe and 75 percent ZnO by weight.
• the photoconductive belt was installed in a commercial xerographic copier and'run for 2,500 copies with no'change in copy quality.
• Example 1V The procedure of Example 1 was followed except that the photoconductive underlying material was poly-nvinyl carbazole/trinitrofluorenone complexed organic photoconductor.
• Example v The procedure of Example I was followed except that the underlying photoconductor material employed was amorphous selenium. Equivalent results to those obtained in Example IV were experienced with the amorphous selenium photoconductor.
• EXAMPLE 111 Another photoconductive belt was made using the same method as in Example 11 with the following changes.
• a protective top coat both protects and stabilizes xerographic photoconductors, and particularly the mixture of cadmium sulfo-selenide and photoconductive zinc oxide as a photoconductor. It will also be seen that the top coating should have a charge acceptance of at least 1,000 volts per mil of top coat thickness and preferably 1,500 volts per mil.
• the viscosity of the dispersion was The invention may be variously otherwise embodied.
• composition defined in claim 1 wherein the polyurethane coating has a charge acceptance of at least 1,000 volts/mil of thickness.
• composition defined in claim 1 wherein the polyurethane coating has a charge acceptance of at least 1,500 volts/mil of thickness.
• said polyurethane coating having a charge acceptance of at least 1000 volts per mil of thickness.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Photoreceptors In Electrophotography (AREA)

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Publications (1)

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Cited By (9)

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Citations (5)

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• 1973
  • 1973-03-08 US US00339084A patent/US3847606A/en not_active Expired - Lifetime
• 1974
  • 1974-03-07 CA CA194,290A patent/CA1027000A/en not_active Expired
  • 1974-03-07 AU AU66388/74A patent/AU474532B2/en not_active Expired
  • 1974-03-08 DE DE2411178A patent/DE2411178A1/de not_active Withdrawn
  • 1974-03-08 GB GB1058474A patent/GB1458617A/en not_active Expired
  • 1974-03-08 JP JP2641274A patent/JPS5724541B2/ja not_active Expired

Patent Citations (5)

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