Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/06—Developers the developer being electrolytic
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G17/00—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process
  • G03G17/02—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process with electrolytic development

Definitions

• This invention relates to the formation of permanent visible reproductions of light-images on photoconductive surfaces by methods involving electrolysis at the exposed light-sensitive surface. It has particular reference to improved electrolytic developer solutions employed in such method.
• a recommended form of light-sensitive copy-paper for use with the apparatus and method hereinabove identi fied consists of a strongly photoconductive zinc oxide surface coating on a metallized or metallic conductive backing or sheet material.
• a sheet having an 0.8 mil coating of four parts by weight of zinc oxide and one part of polymeric insulating binder on a laminate of paper and aluminum foil, typically has a conductivity value, measured as hereinafter described, of at least about mho/cm. and preferably not less than about 10* mho/crn. Under equilibrium dark conditions the conductivity value is not higher than about one-twentieth of the conductivity value under illumination, and ordinarily is much lower.
• the conductivity value is measured as follows: A small sample of the sheet material is insulated at back and edge areas with a nonconductive waterproof covering, e.g., of plastic adhesive tape, an electrical connection to the conductive metallic substrate being provided. The sample is suspended in a transparent glass cell containing 200 ml. of a solution of tenth-molar ammonium sulfate and facing an open frame electrode serving as the anode. Current flow per unit area through the measured thickness of the coating under an applied voltage is measured both with the sample under equilibrium dark conditions and when illuminated. A potential of 10 volts is convenient but not critical. Values at several thicknesses of coatings may be determined and the value at a standard thickness of 0.8 mil obtained by interpolation. Illumination is provided from a 500 watt incandescent-filament lamp, i.e. at an intensity of about 1300 foot-candles. The photoconductivity value is calculated from the values thus obtained.
• a nonconductive waterproof covering e.g., of plastic adhesive tape
• the image areas obtained are in most cases grayish rather than the desired dense black, and the copy lacks contrast.
• the noble metals produced no better, or even less effective images.
• Silver nitrate, for example, produces a yellowish-brown image and a darkened background.
• Gold salts likewise produce images of low density. Solutions of gold and platinum salts are highly corrosive to metallic structural components and prohibitively expensive for most copying purposes.
• Electrodeposition of metals from corresponding salt solutions is frequently improved in one respect or another by the inclusion of variout additives in the plating solution.
• variout additives for example, soluble cyanides are normally added in small amounts to silver-plating baths to improve the brightness and permanence of the plate. It might therefore be expected that the substitution of typical metal-plating solutions for the simple salt solutions would likewise improved the quality of the image obtainable in the electrolytic reproduction process hereinabove identified. It has been found, however, that electroplating formulations in general offer inadequate improvement over the less complicated simple salt solution in such process. Formulations employing base metals provide image areas of somewhat improved initial density and contrast, but the images are not permanent and fade or disappear rapidly when the sheet is held at high humidities.
• the cyanides are additionally highly undesirable because of their poisonous nature, since the residual unreacted salts, or residues resulting from the electrolytic decomposition of such salts, in all instances remain on the copy-paper rather than being removed, as in normal metal plating operations, by subsequent washmg.
• additives which are employed to provide increased brightness of the metallic plate might appear likely to be disadvantageous in the electrolytic development of light-images on a white base, where a dense black rather than a bright metallic deposit is normally desired.
• the several components are mixed together at room temperature, forming a clear solution, which is placed in the metal reservoir of an electrolytic printing device.
• a thin strip of cellulosic sponge is partly submerged in the solution.
• a sheet of photoconductive zinc oxide coated copypaper as described hereinbefore is exposed to a lightimage, and the exposed surface then drawn slowly across the strip of sponge while the conductive backing of .the sheet and the metal reservoir are connected to the poles of a battery. The sheet is thereby made the cathode of an electrolytic cell.
• a dense black deposit is formed at the conductive light-struck areas.
• the print shows no visible decrease in contrast or image density after several weeks in a high humidity test chamber at normal room temperature.
• the image areas are yellowish-brown in color and the background areas are noticeably darkened.
• the resulting reproduction is essentially stable, showing no obseivable change or prolonged storage at high humidity, but has low contrast and is not a desirable print.
• silver nitrate and thiourea When combined as described in Example 1, silver nitrate and thiourea form a normally stable, soluble, electrolyzable complex which can be separated from the solution in crystalline form by cooling to somewhat below C. The washed and dried crystals are found to melt at about 156 C. and to be substantially free of acetamide. Dissolved in appropriate ionizable solvent, the pure crystalline complex likewise provides a stable liquid electrolytic developer solution useful in forming permanent dense dark-colored image-forming deposits on photoconductive copy-paper.
• Example 1 In the absence of thiourea, the acetamide shown in Example 1 is itself instrumental in increasing the density and improving the appearance of the image-forming deposits obtained with the silver nitrate developer solution. However the complexes formed with this compound are relatively less stable and presumably are not present in the solution of the example, although such complexes may be present when less than three mols of thiourea are employed. The acetamide is in any event helpful in forming the stable complex from silver nitrate and thiourea and, since it imparts no harmful efiiects, is ordinarily retained in the developer solution.
• the image-forming deposits obtained with the thioureasilver nitrate complex have been observed to be composed primarily of metallic silver (or its oxide) and silver sulfide.
• the image areas therefore have much in common with images produced by silver halide photography; and the appearance of the finished prints furthers this comparison.
• stable soluble electrolyzable complexes of silver salts and sulfur-containing complexing agents are ordinarily preferred.
• Complexes of other platable metals with these and other complexing agents, and which are stable in solution form and on electrolysis produce permanent dark-colored dense image-forming deposits are also useful.
• Aqueous systems will ordinarily be found preferable, but other ionizing solvents are known with which effective solutions of many of these various complexes may be prepared.
• glycerine and formamide may be used where the amount applied is so small in relation to the thickness and absorbency of the copy-paper as to avoid any necessity of subsequent solvent evaporation.
• Example 2 A 2% solution of (HAuC1 -3H O) is applied in a thin coating on a sheet of photoconductive zinc oxide coated copy-paper which has been exposed to a lightimage.
• the solution is applied by wiping with a cellulosic sponge dampened with the solution and in conductive contact with a gold electrode through which contact is made to a suitable source of potential and to the conductive backing of the copy-paper.
• Plating occurs at the cathodic light-exposed areas, which are thereby rendered visible.
• the proportion of the incident light normally reflected by the untreated copy-paper which is absorbed by the thus developed image areas is found to be 37%. Although the image is stable, remaining unchanged in density after one week at high humidity, the density is undesirably low for effective readability.
• aqueous olution prepared with 2% of gold chloride in conjunction with 4% of acetamide is similarly tested.
• the image areas have a density of 68% as first prepared, and 67% after one week at high (98%) humidity.
• Addition of 2% thiourea to the solution results in the formation of developed image areas having a density of 81% and likewise dropping only to after one week at high humidity. In both instances excellent reproductions are obtained, and the image areas remain dark-colored and distinct in the presence of substantial residues of develo-per materials and at high humidities.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Molecular Biology (AREA)
• Photoreceptors In Electrophotography (AREA)
• Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)

Priority Applications (8)

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Cited By (4)

Citations (9)

• 0
  • NL NL242849D patent/NL242849A/xx unknown
  • BE BE582508D patent/BE582508A/xx unknown
  • NL NL130596D patent/NL130596C/xx active
• 1958
  • 1958-10-17 US US767788A patent/US3072541A/en not_active Expired - Lifetime
• 1959
  • 1959-09-11 CH CH7810159A patent/CH414350A/de unknown
  • 1959-09-11 FR FR804909A patent/FR1235105A/fr not_active Expired
  • 1959-09-15 GB GB31441/59A patent/GB927793A/en not_active Expired
  • 1959-09-25 DE DEM42859A patent/DE1131989B/de active Pending

Patent Citations (9)

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