US2868642A - Electrophotographic method - Google Patents

Electrophotographic method Download PDF

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Publication number
US2868642A
US2868642A US479268A US47926855A US2868642A US 2868642 A US2868642 A US 2868642A US 479268 A US479268 A US 479268A US 47926855 A US47926855 A US 47926855A US 2868642 A US2868642 A US 2868642A
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United States
Prior art keywords
image
light
pattern
electrostatic
shadow
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US479268A
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English (en)
Inventor
Richard E Hayford
Carl B Kaiser
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Xerox Corp
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Xerox Corp
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Publication date
Priority to DENDAT1050189D priority Critical patent/DE1050189B/de
Application filed by Xerox Corp filed Critical Xerox Corp
Priority to US479268A priority patent/US2868642A/en
Priority to FR1146633D priority patent/FR1146633A/fr
Priority to GB143/56A priority patent/GB812419A/en
Application granted granted Critical
Publication of US2868642A publication Critical patent/US2868642A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G13/00—Electrographic processes using a charge pattern
    • G03G13/06—Developing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S101/00—Printing
    • Y10S101/37—Printing employing electrostatic force

Definitions

  • the present invention relates, in general, to the art of electrophotography, and more particularly to methods of enhancing the range of photographic density over which a xerographic reproduction conforms substantially to an original copy.
  • the electrophotographic process sequentially involves (a) the sensitization of a xerographic plate, (b) the exposure of the sensitized plate to an original image to be reproduced, (c) the development of the exposed plate to produce a powder image, (d) the transfer of a powder image from the plate to a final support, and (e) the fiX ing of the transferred image to form the final print.
  • a standard xerographic plate is constituted by a thin layer of selenium on a backing plate of polished brass, the selenium being deposited thereon in a vitreous form.
  • the selenium layer In the dark state, the selenium layer has an extremely high resistivity, but when exposed to light the resistivity is reduced many orders of magnitude, depending on the intensity of the light. By reason of its high electrical resistance in darkness, the selenium layer can be charged electrostatically, which charge is retained for a prolonged period should no light impinge thereon. However, when light strikes the xerographic plate, the resistivity decreases and the charge is lost to the hacking plate.
  • the xerographic plate In the basic electrophotographic process the xerographic plate must be sensitized before use by impressing an electrical charge on the selenium surface. This is customarily accomplished by means of a corona discharge device. After sensitization the plate is exposed to a light image in a camera. Where light strikes the plate the selenium is rendered conductive and the electrical charge on its surface leaks through to the metal backing plate in proportion to the intensity of illumination. The retained electrical image then present on the plate is developed by subjecting the plate to a cloud of charged powder particles. These particles are attracted to the electrical image and they deposit on the plate in a quantity depending on the potential of the electric image.
  • the powder image is transferred and fixed to a white plastic sheet which is coated with an adhesive.
  • the powder image adheres to the adhesive and is thus removed from the selenium surface.
  • the transferred image is covered with a transparent adhesive tape.
  • the light-fidelity or naturalness of the reproduction thus formed is a function of the brightness range of the picture, this range extending from white through progressively darker shades of grey to black.
  • the resultant picture will exhibit a high order of atent o 2 light-fidelity.
  • the density range is limited in scope and the picture contrast is relatively poor. Consequently, if the light areas on the picture are truly light, then the dark areas are only a moderately dark grey. On the other hand, if the dark areas are decidedly dark, then the light areas are not particularly bright.
  • Fig. 1 shows the density curve of a xerographic reproduction with respect to the density of the original, which curve is typical of the conventional electrophotographic method.
  • Fig. 2 shows the density curve of a xerographic repro duction with respect to the original density, which curve characterizes a cyclic xerographic process in accordancewith the present invention.
  • Photographic density is closely allied with the darkness of the picture deposit.
  • Photographic density is measured by determining the light transmission or reflection properties of the picture deposit. More specifically, the density figure is the log of the ratio between the light incident to the deposit and the light reflected therefrom. The exposure is plotted on a logarithmic scale, for the range covered (frequently as high as 10,000 to 1 in intensity) is too great to plot conveniently in any other manner, and also because the logarithm scale more nearly approaches the scale of brightness involved in vision.
  • a density of 1.0 means that only 10% of the light is reflected
  • a density of 2.0 means that only 1% is reflected.
  • Fig. 1 there is shown a typical density curve of a xerographic reproduction of the prior art type with respect to the original density.
  • the photographic density values of the original appear along the abscissa and the values of the reproduction appear along the ordinate, the same scale of units being used on both axes. If the response curve is a straight line with a slope of l (at a proper exposure pro prises an exact reproduction of any brightness scale.
  • the xerographic process is carried out in the following cyclical manner.
  • the xerographic plate is sensitized by an electrostatic charge and exposed to the light image emanating from a positive photographic transparency in the usual way.
  • the sensitized plate is then developed by the powder cloud technique for a period lasting about one half the normal time required for complete development.
  • the xerographic plate bearing the under-developed image is recharged, then placed in the camera in keyed position in register and re-exposed.
  • the re-exposure operation makes use of an exposure exceeding the normal time limits, preferably about eight times the normal exposure. It will be noted that in the reexposure, in the dark image areas the light must pass through both the dark portions of the photographic transparency and the heavy image areas of the xerographic developer. Thus the light is masked both by the dark portions of the transparency and the heavy image areas of the developer. Next, the image is again developed, this time to completion. The remaining steps of transfer and fixing are along conventional lines.
  • Fig. 2 the results attained by th repetitive cycles of exposure and development is made evident.
  • the long exposure effects a substantially complete discharge, so that the development in the second cycle does not deposit additional developer in the high-light areas on the picture.
  • the combination of the light-absorbing action of the photographic positive transparency and the light-absorbing action of the previously developed xerographic powder image leaves a substantial charge on the plate, whereby the second development cycle causes additional deposition or density more or less as indicated by the upper curve.
  • the point of intersection between the upper and lower curve and the flatness of the upper curve will be controlled principally by the duration of the second exposure. What occurs in the second exposure is that the highlight portions, and progressively the next portions are discharged. In consequence, the greater the exposure, the more this point of intersection moves out on this curve and the flatter the upper curve becomes. Ideally this point of intersection should be brought roughly to the shoulder of the first curve.
  • the first cycle a normal exposure was made followed by a development of two seconds, i. e. about /2 of the normal period, so that the good results in density fell off very close to 1.0, and generally at about 1.1.
  • the exposure was for approximately eight times the normal period and the development (two seconds) again about one-half the normal time. This caused the second density results to level off at about 1.4 or 1.5.
  • the third cycle repeated the conditions of the second cycle, with the result that this time the final density leveled off at about 1.8, which, as pointed out earlier, is far superior to the results heretofore obtained.
  • the process of producing an electrophotographic reproduction of a pattern of light and shadow to be recorded comprising the steps of applying a uniform electrostatic charge to a photoconductive insulating surface overlying a conductive backing, exposing said surface to a pattern of light and shadow to be reproduced, whereby there is produced on said surface a pattern of electrostatic charges corresponding to the pattern of light and shadow to be reproduced, repeating cyclically at least once the steps of contacting said surface bearing the electrostatic latent image with finely-divided electrostatically-charged powder particles whereby said particles begin to deposit on said surface in accordance with said electrostatic image, removing said particles from contact with said surface while deposition is still substantially incomplete leaving on said surface a lightly visible powder image corresponding to said electrostatic image, applying a uniform electrostatic charge to said surface, exposing said surface to the original pattern of light and shadow, the exposure being made in register with said powder image and for a length of time substantially greater than that necessary for the brightest portion of the original scene to reduce the electrostatic potential of the corresponding portions of said
  • the method of producing a xerographic reproduction of a pattern of light and shadow to be recorded comprising electrically charging a photoconductive insulating surface overlying an electrically conductive backing, exposing said surface to a pattern of light and shadow to be reproduced whereby there is produced on said surface a pattern of electrostatic charges corresponding to the pattern of light and shadow to be reproduced, contacting said surface with a supply of finely-divided electrostatically-charged powder particles whereby said particles begin to deposit on said surface in accordance with said electrostatic image, removing said supply from contact with said surface while deposition is still substantially incomplete leaving on said surface a lightlyvisible powder image corresponding to said electrostatic image, applying a uniform electrostatic charge to said.
  • the method of producing a xerographic reproduction of a pattern of light and shadow to be recorded comprising electrically charging a photoconductive insulating surface overlying an electrically conductive backing, exposing said surface to a pattern of light and shadow to be reproduced whereby there is produced on said surface a pattern of electrostatic charges corresponding to the pattern of light and shadow to be reproduced, contacting said surface with a supply of finely-divided electrostatically-charged powder particles whereby said particles begin to deposit on said surface in accordance with said electrostatic image, removing said supply from contact with said surface while deposition is only about half complete leaving on said surface a lightlyvisible powder image corresponding to said electrostatic image, applying a uniform electrostatic charge to said surface, exposing said surface to the original scene corresponding to said powder image, the exposure being made in register with said powder image and for a length of time about eight times greater than that necessary for the brightest portions of the original scene to reduce the electrostatic potential of the corresponding portions of said surface to their lowest value, then contacting said surface again with a
  • the method of producing a xerographic reproduction of a pattern of light and shadow to be recorded comprising electrically charging a photoconductive insulating surface overlying an electrically conductive backing, exposing said surface to a pattern of light and shadow to be reproduced whereby there is produced on said surface a pattern of electrostatic charges corresponding to the pattern of light and shadow to be reproduced, repeating cyclically at least once the steps of contacting said surface with a supply of finely-divided electrostatically-charged powder particles whereby said particles begin to deposit on said surface in accordance with said electrostatic image.
  • the method of producing a xerographic reproduction of a pattern of light and shadow to be recorded comprising electrically charging a photoconductive insulating surface overlying an electrically conductive backing, exposing said surface to a pattern of light and shadow to be reproduced whereby there is produced on said surface a pattern of electrostatic charges corresponding to the pattern of light and shadow to be reproduced, contacting said surface with a powder cloud of finely-divided electrostatically-charged powder particles wherebysaid particles begin to deposit on said surface in accordance with said electrostatic image, removing said powder cloud from contact with said surface while deposition is still substantially incomplete leaving on said surface a lightlyvisible powder image corresponding to said electrostatic image, applying a uniform electrostatic charge to said surface, exposing said surface to the original scene corresponding to said powder image, the exposure being made in register with said powder image and for a length of time substantially greater than that necessary for the brightest portions of the original scene to reduce the electrostatic potential of the corresponding portions of said surface to their lowest value, and then contacting said surface again with

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrophotography Using Other Than Carlson'S Method (AREA)
  • Photoreceptors In Electrophotography (AREA)
US479268A 1955-01-03 1955-01-03 Electrophotographic method Expired - Lifetime US2868642A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
DENDAT1050189D DE1050189B (US07122603-20061017-C00045.png) 1955-01-03
US479268A US2868642A (en) 1955-01-03 1955-01-03 Electrophotographic method
FR1146633D FR1146633A (fr) 1955-01-03 1956-01-03 Procédé électrophotographique
GB143/56A GB812419A (en) 1955-01-03 1956-01-03 Improved electrophotographic method

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US479268A US2868642A (en) 1955-01-03 1955-01-03 Electrophotographic method

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US2868642A true US2868642A (en) 1959-01-13

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US (1) US2868642A (US07122603-20061017-C00045.png)
DE (1) DE1050189B (US07122603-20061017-C00045.png)
FR (1) FR1146633A (US07122603-20061017-C00045.png)
GB (1) GB812419A (US07122603-20061017-C00045.png)

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3038799A (en) * 1958-01-13 1962-06-12 Commw Of Australia Method of reversing the image in xerography
US3051568A (en) * 1955-12-06 1962-08-28 Edward K Kaprelian Offset electrophotography
US3052155A (en) * 1958-09-11 1962-09-04 Bruning Charles Co Inc Apparatus for exposing light sensitive sheets and/or webs
US3060020A (en) * 1958-03-20 1962-10-23 Rca Corp Method of electrophotographically producing a multicolor image
US3178281A (en) * 1956-07-16 1965-04-13 Eastman Kodak Co Electrostatic color printing
US3212889A (en) * 1961-06-12 1965-10-19 Xerox Corp Xerographic contrast control
US3251688A (en) * 1962-07-02 1966-05-17 Xerox Corp Liquid transfer development
US3589290A (en) * 1966-05-20 1971-06-29 Xerox Corp Relief imaging plates made by repetitive xerographic processes
US3941592A (en) * 1972-09-01 1976-03-02 Minolta Camera Kabushiki Kaisha Electrophotographic method of transferring toner image
US4030106A (en) * 1974-09-24 1977-06-14 Agfa-Gevaert, A.G. Method and arrangement for eliminating undesired density variations in electrostatically created copies of an original
US4088481A (en) * 1974-10-10 1978-05-09 Xerox Corporation Extended range color electrophotographic method by superimposing a half-tone image on a low density continuous tone image
US4101320A (en) * 1974-12-30 1978-07-18 Xerox Corporation Magnetic imaging method
DE3628853A1 (de) * 1985-08-31 1987-03-19 Ricoh Kk Bildaufzeichnungsgeraet
US4927725A (en) * 1987-12-14 1990-05-22 Fuji Xerox Co., Ltd. Electrophotographic method
US5930567A (en) * 1996-10-29 1999-07-27 Fuji Photo Film Co., Ltd. Image recording method for forming toner images of the same color

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB241636A (en) * 1924-07-26 1925-10-26 Andres Steiner Improved method and apparatus for exhibiting images, visible by daylight
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2703280A (en) * 1950-05-17 1955-03-01 Western Electric Co Counting circuit control for electrophotographic printers
US2756676A (en) * 1953-05-04 1956-07-31 Haloid Co Method for the production of electrophotographic prints

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB241636A (en) * 1924-07-26 1925-10-26 Andres Steiner Improved method and apparatus for exhibiting images, visible by daylight
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2703280A (en) * 1950-05-17 1955-03-01 Western Electric Co Counting circuit control for electrophotographic printers
US2756676A (en) * 1953-05-04 1956-07-31 Haloid Co Method for the production of electrophotographic prints

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3051568A (en) * 1955-12-06 1962-08-28 Edward K Kaprelian Offset electrophotography
US3178281A (en) * 1956-07-16 1965-04-13 Eastman Kodak Co Electrostatic color printing
US3038799A (en) * 1958-01-13 1962-06-12 Commw Of Australia Method of reversing the image in xerography
US3060020A (en) * 1958-03-20 1962-10-23 Rca Corp Method of electrophotographically producing a multicolor image
US3052155A (en) * 1958-09-11 1962-09-04 Bruning Charles Co Inc Apparatus for exposing light sensitive sheets and/or webs
US3212889A (en) * 1961-06-12 1965-10-19 Xerox Corp Xerographic contrast control
US3251688A (en) * 1962-07-02 1966-05-17 Xerox Corp Liquid transfer development
US3589290A (en) * 1966-05-20 1971-06-29 Xerox Corp Relief imaging plates made by repetitive xerographic processes
US3941592A (en) * 1972-09-01 1976-03-02 Minolta Camera Kabushiki Kaisha Electrophotographic method of transferring toner image
US4030106A (en) * 1974-09-24 1977-06-14 Agfa-Gevaert, A.G. Method and arrangement for eliminating undesired density variations in electrostatically created copies of an original
US4088481A (en) * 1974-10-10 1978-05-09 Xerox Corporation Extended range color electrophotographic method by superimposing a half-tone image on a low density continuous tone image
US4101320A (en) * 1974-12-30 1978-07-18 Xerox Corporation Magnetic imaging method
DE3628853A1 (de) * 1985-08-31 1987-03-19 Ricoh Kk Bildaufzeichnungsgeraet
US4927725A (en) * 1987-12-14 1990-05-22 Fuji Xerox Co., Ltd. Electrophotographic method
US5930567A (en) * 1996-10-29 1999-07-27 Fuji Photo Film Co., Ltd. Image recording method for forming toner images of the same color

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Publication number Publication date
DE1050189B (US07122603-20061017-C00045.png)
GB812419A (en) 1959-04-22
FR1146633A (fr) 1957-11-13

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