WO1987005720A1 - Procede et appareil utilisant un effacement a couronne pour ameliorer une image electrophotographique multicolore - Google Patents

Procede et appareil utilisant un effacement a couronne pour ameliorer une image electrophotographique multicolore Download PDF

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Publication number
WO1987005720A1
WO1987005720A1 PCT/US1987/000383 US8700383W WO8705720A1 WO 1987005720 A1 WO1987005720 A1 WO 1987005720A1 US 8700383 W US8700383 W US 8700383W WO 8705720 A1 WO8705720 A1 WO 8705720A1
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WO
WIPO (PCT)
Prior art keywords
medium
image
voltage
exposing
toning
Prior art date
Application number
PCT/US1987/000383
Other languages
English (en)
Inventor
Albert Valentine Buettner
Carl Edwin Cowan
Original Assignee
Eastman Kodak Company
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Company filed Critical Eastman Kodak Company
Priority to DE19873777173 priority Critical patent/DE3777173D1/de
Publication of WO1987005720A1 publication Critical patent/WO1987005720A1/fr

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/01—Apparatus for electrographic processes using a charge pattern for producing multicoloured copies
    • G03G15/0142—Structure of complete machines
    • G03G15/0147—Structure of complete machines using a single reusable electrographic recording member
    • G03G15/0152—Structure of complete machines using a single reusable electrographic recording member onto which the monocolour toner images are superposed before common transfer from the recording member
    • G03G15/0157—Structure of complete machines using a single reusable electrographic recording member onto which the monocolour toner images are superposed before common transfer from the recording member with special treatment between monocolour image formation
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/01—Apparatus for electrographic processes using a charge pattern for producing multicoloured copies
    • G03G15/0142—Structure of complete machines
    • G03G15/0147—Structure of complete machines using a single reusable electrographic recording member
    • G03G15/0152—Structure of complete machines using a single reusable electrographic recording member onto which the monocolour toner images are superposed before common transfer from the recording member
    • G03G15/0163—Structure of complete machines using a single reusable electrographic recording member onto which the monocolour toner images are superposed before common transfer from the recording member primary transfer to the final recording medium

Definitions

  • This invention relates to electrographlc development and more particularly to an improved method of plural stage development. While the following disclosure refers to a preferred embodiment employing liquid development, it will be understood that the invention is equally applicable to systems using dry developers.
  • liquid development of electrostatic charge latent images as in electrophotography and in other processes that form and develop electrostatic charge patterns, a substrate having a charge pattern on its surface is contacted with a liquid developer which is essentially a suspension of colloidal toner particles in an insulating liquid.
  • Liquid developers normally contain also a stabilizer or charge control agent. Liquid developers can be used in single stage or plural stage development processes. Examples of the latter may include the sequential development on a photoconductor of two or more color-separation images, the annotation of a previously developed image, or the repeated re-exposure and development of images on a reusable photoconductor, with transfer of images after each development.
  • the toe rise is unpredictably variable so that it is difficult, if not impossible, to control the entire process to provide satisfactory film performance. If provisions are not made to maintain the useable voltage range in systems utilizing a photoconductor having the foregoing phenomena of toe voltage rise with successive charge-expose cycles, the resulting Images will have an undesirable susceptibility to image variation with variations in work place humidity. A variation in image quality across the area of the image can also occur under such operating conditions. More importantly, it has been found that with increases in the toe voltage noted above, it is impossible to achieve high image density with succeeding stages or colors. All of these factors are detrimental to obtaining graphic arts quality images.
  • the electrophotographic method in which the present invention operates generally comprises uniformly charging a photoconductive element, exposing the photoconductive element to a pattern of actinic radiation to form a latent electrostatic image, developing the latent image with, for example, a liquid developer composition comprising a carrier liquid, a toner and charge control agent, rinsing the developed surface of the photoconductive element with a rinse solution, and drying the image. Thereafter, the surface of the photoconductive element is recharged and exposed to a pattern of actinic radiation tQ form a second latent electrostatic image which is developed with a liquid developer.
  • the method of the present invention is useful in any electrostatic imaging process wherein a charge pattern is formed and developed with a developer on a surface which has previously been developed.
  • the present invention provides a method and apparatus for producing a multi-color electrophotographic image that enhances the final image by the reduction or elimination of toe rise with successive charge-expose cycles of the photoconductor.
  • the Improvement provided by the present invention is simple and relatively easy to Implement at a nominal cost, it does not have any significant negative effects on the resulting image.
  • a method and apparatus for producing a multi-stage electrophotographic image wherein the medium is charged to a first voltage v , is exposed to discharge the exposed portion of the medium to a second voltage v , and is then toned to produce a first visible image.
  • the medium is reverse charged with a voltage having a polarity opposite to (v Q - v w ), and trapped charges are neutralized by recombination of the trapped charges with mobile charges of a polarity opposite to that of the trapped charges, to substantially eliminate toe voltage Increases with successive charge-expose cycles of the medium.
  • the medium is reverse charged with a voltage that has an absolute value equal to or greater than (v - v ) and having a polarity opposite to that of (vo_. - v speciw).
  • the neutralization of trapped charges includes the step of exposing the medium to actinic radiation to facilitate the recombination of trapped and mobile charges in the medium.
  • means for exposing the medium to radiation to facilitate the recombination of trapped and mobile charges therein after reverse charging only when the medium contains a charge barrier layer.
  • Yet another aspect of the present invention provides means for preventing toe rise in boti ⁇ p-type and n-type photoconductors, with and without charge barriers and regardless of whether the tonal reproductlon is positive or negative.
  • apparatus for producing a multi-color electrophotographic image on a p-type electrophotographic medium having a low optical density and being provided with a generally non-conductive overcoat and a charge barrier.
  • the apparatus Includes a substantially transparent carrier platen arranged for movement over a predetermined path with means for mounting the medium and a first image-bearing transparency in register on the carrier platen at a first position.
  • Means is provided for translating the platen, transparency and medium together over the predetermined path, past means for charging the medium to a first voltage v at a second position.
  • Means for exposing the medium through the transparency to a first light source is provided at a third position to discharge the exposed portion of the medium to a second voltage v .
  • a first toning element is arranged to engage the overcoat of the medium at a fourth position for selectively toning the image-bearing charged region of the medium to produce a first color visible image.
  • Means is provided for reverse charging the toned medium with a voltage the absolute value of which is equal to or greater than (v - v ) and having a polarity opposite to (v - v ). Trapped electrons are then neutralized by exposing the medium to radiation from a second light source to recombine trapped electrons with mobile holes.
  • the apparatus further includes means for returning the platen, transparency and neutralized medium to the first position whereby the first transparency is replaced with a second image-bearing transparency in register with the medium and for repeating the charging and exposing steps to expose the medium to the first light source to generate a second image and to tone the second image with a second toning element to produce a second color visible image in register with said first color visible image.
  • FIG. 1 is a graphic representation of the phenomenon of toe rise with successive charge-expose cycles solved by the present invention.
  • FIG. 2 is a schematic illustration of electrophotographic apparatus incorporating means for preventing toe rise.
  • FIG. 2 A schematic Illustration of a multi-color electrophotographic image processor is Illustrated in FIG. 2 and consists of a carrier or platen 12 which is movable along the processing path, represented by dotted line 14, past the respective processing stations of the apparatus, to be described hereinafter.
  • the path 14 may be determined by guide rails or other structure of the apparatus in a manner well-known in the art whereby the platen may move from a first position, illustrated, to the right-most position and then returned to the left to the starting position.
  • the platen 12 is preferably transparent and is provided with means, not shown, for retaining an electrophotographic medium 16 on the lower surface thereof with an image-bearing transparency 18 disposed therebetween which is used to generate the image in the electrophotograpic medium 16, in a manner more thoroughly described hereinbelow.
  • the electrophotographic medium comprises a photoconductive layer on an electrically conducting substrate which is capable of transmitting actinic radiation to which the photoconductive layer is responsive.
  • a dielectric support is releasably adhered to the substrate and either comprises the photoconductive layer or an overcoat thereof which forms an outer surface of the element capable of holding an electrostatic charge.
  • the surface of the dielectric support is charged and the photoconductive layer is image-wise exposed to the actinic radiation, thereby forming a developable electrostatic image on the dielectric surface.
  • the electrostatic image in turn is developed with a toner to form a first color image.
  • a composite color image can be formed on the element by repeating the sequence one or more times with successive image-wise exposure of the photoconductive layer to actinic radiation transmitted through the transparent support and an image-bearing transparency, and developing over each preceding image with a different color toner.
  • the composite toned image is then transferred with the dielectric support to a receiving element to form a color copy which may be a color proof closely simulating the color print expected from a color print press.
  • the electrophotographic medium 16 is mounted onto the platen 12 with the transparency original 18, which may be a color separation representing a color to be printed, sandwiched therebetween.
  • the electrophotographic medium 16 and the transparency original 18 may be held to the platen 12 by any suitable means known in the art such as a vacuum clamp such that they are maintained in close proximity to assure satisfactory exposure, processing and registration.
  • the electrophotographic medium must also be suitably grounded to the apparatus to enable the charging process to be satisfactorily carried out. A number of grounding means are known in the art and will not be described herein.
  • the dielectric support of the electrophotographic medium is given an overall charge via a charging means 20, such as a corona charger, to form a uniform potential, v . on the surface of the o dielectric support.
  • a charging means 20 such as a corona charger
  • the electrophotographic medium is image-wise exposed by passing beneath an exposure lamp apparatus 22 which projects light through the transparent platen 12, the transparency original 18, and through the- transparent conductive substrate .of the electrophotographic medium.
  • mobile charge carriers in this case positively charged holes, are formed in the photoconductive layer and migrate away from the conducting layer as described in the above-identified application (or toward the conducting layer to give a negative image).
  • the platen continues its movement, to the right in FIG. 2, passing over a pre-rinse head 24 which is fixed in position whereby the fluid head provided thereat, when activated, contacts the lower surface of the electrophotographic medium as It passes in the processing direction, i.e., to the right, but does not contact the medium when the fluid head is inactivated, as when the platen is moved to the left in FIG. 2, to the original position.
  • the pre-rinse head prewets the medium with a dispersant dielectric liquid prior to the liquid toning step.
  • the platen moves past a raised first liquid toning station 26 which is raised into operating position whereby the lower surface of the electrophotographic medium is contacted and a toner Image is imparted thereto, in a manner well-known in the art.
  • the liquid toner is deposited in the unexposed, still charged area of the electrophotographic medium thereby forming an image which is a duplicate of the image carried by the transparency' 18.
  • negative images can also be produced with similar electrophotographic processes wherein the charges imparted to the electrophotographic medium and the toners are appropriately adjusted to give a negative image.
  • the platen continues movement to the right in the illustration, past appropriate rinse heads and dryers, not shown.
  • the last station 28 at the right end of the apparatus is an erase lamp that exposes the electrophotographic medium after the toning operation to expose those parts of the photoconductor layer that were not exposed by the original image exposure so that the entire electrophotographic medium has substantially the same exposure history.
  • Platen 12 is then reversed and is returned to the left towards the first position Illustrated in FIG. 2. As the platen reaches the charging means "0, it is activated as a corona erase apparatus in -;cordance with the present invention. However, the charge imparted by the corona erase mode of the charging means 20 is opposite in polarity to the charge initially given the photoconductor medium and of a magnitude substantially equal to the absolute value of (v - v ).
  • the platen, transparency and medium have then reached the first position and the first original transparency or color separation 18 is removed and replaced by a second transparency or color separation and registered with the electrophotographic medium 16 preparatory for the next pass through the apparatus to generate the second color image.
  • the electrophotographic medium 16 and the next original sheet 18 are re-registered on the platen 12
  • the platen is again moved to the right to the charging station 20 where the electrophotographic medium is again charged and then to the exposure position 22 where light again is projected through the platen and the second color separation 18 to selectively charge the photoconductive layer in accordance with the transparency or color separation then in contact with the electrophotographic medium.
  • the platen moves the electrophotographic medium to the pre-rinse station 24 and then to a second toning station 34 which is in operative position to tone the surface of the electrophotographic medium with a second color toner to produce a second color visible image overlying the first image.
  • the platen subsequently moves past the aforementioned rinse and drying stations and again past the erase exposure station 28 before being returned to the first position at the left end of the apparatus.
  • the charging, exposing, and toning steps will be repeated for two more color separation originals with the platen and electrophotographic medium being moved into operative contact with an additional two toning stations 36 and 38, one for each of the additional colors.
  • the toning order may not necessarily be represented by the physical order of the toning stations in the apparatus, and the order given above is by way of example only.
  • the corona erase cycle will be used after each exposure which is to be followed by a toning cycle after the corona erase.
  • corona erase will not be necessary after the final charge-expose-tone cycle, but will be after an Initial charge and expose only calibration cycle. It has been found that toe rise, or an increase in the final voltage obtainable with extended exposures, after multiple charge-expose cycles results from a build-up of trapped charges, within the thickness or the bulk of the photoconductor or near the surface thereof having a potential opposite to that of the trapped charge. Thus with p-type photoconductors, the trapped charges are electrons, while with n-type photoconductors the trapped charges are "holes'*. The problems associated with the build-up of such trapped charges have been found to increase when a charge barrier layer is also incorporated.
  • the present invention provides a method and apparatus for regenerating a photoconductor to substantially revitalize the medium to a condition closely resembling its unused condition, substantially eliminating the rise in toe voltage associated with prior systems.
  • the method and apparatus are simply and economically achieved and produce a high quality image suitable for use in graphic arts quality reproduction.
  • the re-erase lamp must be arranged to expose both sides of the medium, as in a negative/positive mode wherein the medium is exposed through a negative, with a positive being formed by the toned image. In other situations it is possible to satisfactorily employ the present invention by only exposing one side of the medium to the re-erase lamp. While the present invention has been described with an electrophotographic system wherein the exposure is through a transparency and a transparent platen and photoconductor, it will be appreciated that it is also applicable in systems where other means are utilized to expose the medium without the requirement that all of these elements be transparent.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Color Electrophotography (AREA)

Abstract

Perfectionnement du procédé et appareil de production d'une image électrophotographique multicolore où un support électrophotographique (16) peut être utilisé pour des cycles d'exposition-charges multiples sans l'accumulation de charges emprisonnées qui peuvent être le résultat d'une augmentation de la tension de base. Après la charge, l'exposition et le virage du support (16) pour produire une première image visible en couleur, on fait revenir le porteur (12) à la première position pour répéter les étapes précédentes de charge, d'exposition et de virage pour produire une seconde image visible en couleur. Avant la seconde étape de charge, le support (16) est inversement chargé et les charges emprisonnées sont neutralisées pour revitaliser sensiblement le support vers un état ressemblant étroitement à son état non utilisé de manière à éliminer l'augmentation de la tension de base.
PCT/US1987/000383 1986-03-12 1987-02-26 Procede et appareil utilisant un effacement a couronne pour ameliorer une image electrophotographique multicolore WO1987005720A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE19873777173 DE3777173D1 (de) 1986-03-12 1987-02-26 Verfahren und geraet mit coronaentladung zum verbessern eines elektrophotographischen mehrfarbigen bildes.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US83900986A 1986-03-12 1986-03-12
US839,009 1986-03-12

Publications (1)

Publication Number Publication Date
WO1987005720A1 true WO1987005720A1 (fr) 1987-09-24

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Application Number Title Priority Date Filing Date
PCT/US1987/000383 WO1987005720A1 (fr) 1986-03-12 1987-02-26 Procede et appareil utilisant un effacement a couronne pour ameliorer une image electrophotographique multicolore

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EP (1) EP0296169B1 (fr)
JP (1) JPS63503329A (fr)
WO (1) WO1987005720A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0717324A3 (fr) * 1994-12-12 1997-05-14 Xerox Corp Méthode et appareil de rechargement par effet corona pour la formation d'images en couleur

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2073750A5 (fr) * 1969-12-08 1971-10-01 Rank Xerox Ltd
US3687661A (en) * 1969-12-01 1972-08-29 Xerox Corp Color electrophotographic process
US4157219A (en) * 1976-07-10 1979-06-05 Konishiroku Photo Industry Co., Ltd. Multi-color electro-static image liquid development apparatus
US4510223A (en) * 1983-02-07 1985-04-09 Coulter Systems Corporation Multicolor electrophotographic imaging process

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5522789B2 (fr) * 1973-08-27 1980-06-19
JPS5814854A (ja) * 1981-07-20 1983-01-27 Matsushita Graphic Commun Syst Inc 多色静電記録装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3687661A (en) * 1969-12-01 1972-08-29 Xerox Corp Color electrophotographic process
FR2073750A5 (fr) * 1969-12-08 1971-10-01 Rank Xerox Ltd
US4157219A (en) * 1976-07-10 1979-06-05 Konishiroku Photo Industry Co., Ltd. Multi-color electro-static image liquid development apparatus
US4510223A (en) * 1983-02-07 1985-04-09 Coulter Systems Corporation Multicolor electrophotographic imaging process

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Volume 7, No. 176 (P-214)(1321), 4 August 1983, see the whole Abstract & JP, A, 5880653 (Canon K.K.) 14 May 1983 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0717324A3 (fr) * 1994-12-12 1997-05-14 Xerox Corp Méthode et appareil de rechargement par effet corona pour la formation d'images en couleur

Also Published As

Publication number Publication date
JPS63503329A (ja) 1988-12-02
EP0296169A1 (fr) 1988-12-28
EP0296169B1 (fr) 1992-03-04

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