EP0785478A2 - Verfahren um Tonerbilder aus zwei unterschiedlichen Tonermaterialen zu erstellen - Google Patents

Verfahren um Tonerbilder aus zwei unterschiedlichen Tonermaterialen zu erstellen Download PDF

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Publication number
EP0785478A2
EP0785478A2 EP97200016A EP97200016A EP0785478A2 EP 0785478 A2 EP0785478 A2 EP 0785478A2 EP 97200016 A EP97200016 A EP 97200016A EP 97200016 A EP97200016 A EP 97200016A EP 0785478 A2 EP0785478 A2 EP 0785478A2
Authority
EP
European Patent Office
Prior art keywords
image
toner
polarity
electrostatic
applying
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.)
Granted
Application number
EP97200016A
Other languages
English (en)
French (fr)
Other versions
EP0785478A3 (de
EP0785478B1 (de
Inventor
Eric C. c/o Eastman Kodak Company Stelter
Joseph E. c/o Eastman Kodak Company Guth
Charles W. c/o Eastman Kodak Company Kasiske
Edward M. c/o Eastman Kodak Company Eck
Garold F. c/o Eastman Kodak Company Fritz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NexPress Solutions LLC
Original Assignee
Eastman Kodak Co
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
Priority claimed from US08/583,732 external-priority patent/US5748218A/en
Priority claimed from US08/583,731 external-priority patent/US5713064A/en
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0785478A2 publication Critical patent/EP0785478A2/de
Publication of EP0785478A3 publication Critical patent/EP0785478A3/de
Application granted granted Critical
Publication of EP0785478B1 publication Critical patent/EP0785478B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • G03G13/22—Processes involving a combination of more than one step according to groups G03G13/02 - G03G13/20
    • 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
    • G03G13/01—Electrographic processes using a charge pattern for multicoloured copies
    • G03G13/013—Electrographic processes using a charge pattern for multicoloured copies characterised by the developing step, e.g. the properties of the colour developers
    • 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
    • G03G13/08—Developing using a solid developer, e.g. powder developer
    • G03G13/09—Developing using a solid developer, e.g. powder developer using magnetic brush
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/04—Arrangements for exposing and producing an image
    • G03G2215/0497—Exposure from behind the image carrying surface

Definitions

  • This invention relates to the formation of toner images and, more specifically, to the formation of toner images of two distinct toners, for example, toners of two different colors.
  • the second and subsequent images are toned with a particular toning process using high coercivity carrier and a rotating magnetic core.
  • This process provides a very soft magnetic brush which disturbs the earlier toner images less than an ordinary magnetic brush, even though the brush strands may be allowed to contact the image member.
  • European Patent Application 94-107101.1 published November 23, 1994 (Publication No. 0 625 730), describes a problem with a DAD-DAD system in which toner on the edges of areas of the first image, which abut second images, have a tendency to move into the second image as a result of the second exposure. Overlapping of the first image with the second image corrects this problem in this process. The image overlapping is facilitated by exposing the second image through the base.
  • an image member is charged to a first polarity and exposed to create an electrostatic image.
  • the electrostatic image is developed with toner also charged to the first polarity (DAD).
  • DAD first polarity
  • the image member is preferably not recharged, but is exposed to create a second electrostatic image, still of the first polarity.
  • This image is toned with a toner of a second polarity opposite the first polarity (CAD).
  • the second toning step uses contact development with a magnetic brush of the Mosehauer type. That is, it has "hard” magnetic carrier and a rapidly rotating magnetic core with the developer moving into direct contact with the image member during the development process.
  • high resolution two color toner images are produced with little scavenging using a DAD-CAD process with contact developing of the second image with a brush having "hard” magnetic carrier and a rotating magnetic core and with a second exposure through the side of the image member opposite the first toner image.
  • FIGS. 1-7 show seven steps in a method for forming a two color image.
  • FIGS. 8-14 show a submethod variation on the method shown in FIGS. 1-7.
  • FIGS. 15-18 show a four step submethod which is a variation to the submethod shown in FIGS. 8-14.
  • FIG. 19 is a side schematic of an image forming apparatus.
  • FIG. 20 is a side schematic of a development station.
  • FIGS. 1-7 illustrate a DAD-CAD method (sometimes herein called a "submethod") of forming a two color toner image.
  • an image member 1 includes an image side 2 and an opposite or base side 4.
  • the image member 1 is transparent.
  • it can be a belt or web image member having a polyester or other suitable transparent support well known and used in the art.
  • Such image members include a transparent conductive layer on the image side 2 upon which is coated suitable photoconductive layers to make the image member 1 photoconductive.
  • the conductive layer and photoconductive layers are extremely thin and are not shown in the FIGS.
  • the image member could also be a glass drum with similar layers coated thereon.
  • the image member is uniformly charged to a negative potential. It is imagewise exposed to create a negative electrostatic image and, as shown in FIG. 1, a negative toner is applied to it in the presence of an electric field which encourages deposition of the negative toner according to the amount of discharge of the electrostatic image. That is, the toner shown in FIG. 1 adheres to areas of lowest potential in the electrostatic image, creating a first toner image, as shown in FIG. 2, created by a DAD process.
  • the image member is exposed through its base 4 (preferably without recharging) to create a second electrostatic image. It is important that this exposure be conducted through the base in order to discharge the charge underneath the first toner image below that of exposed areas surrounding the first toner image. If this charge is not dissipated, the negatively charged first toner has a tendency to be pushed by that charge into the areas adjacent it that have been equally or more discharged, thereby reducing the sharpness and resolution of the first toner image. With exposure through the base, we have been able to reduce the charge underneath the first toner image to 50-100 volts below that of areas surrounding the image that are also exposed. This allows the adjacent negative charge to hold the negative toner of the first image in place.
  • the second electrostatic image is toned using a CAD toning process. More specifically, a magnetic brush 11 containing positive toner applies toner to image member 1 in the presence of an electric field that encourages deposition of toner on the high potential portions of the second electrostatic image.
  • the electric field is biased so that magnetic brush 11 is slightly more negative than the exposed portion of the second electrostatic image to inhibit development of the nonimage areas in the second electrostatic image. This bias also inhibits pickup of negative toner from the first image.
  • the two color toner image shown in FIG. 4, contains both negatively charged and positively charged toner.
  • the image is treated so that it responds more uniformly in an electrical field.
  • FIG. 5 this is accomplished by using a negatively biased corona charger 15 which sprays negative charges on the image side of the image member 1.
  • the charger 15 can be assisted by an erase lamp 17 which, with a transparent image member 1, can be positioned on the opposite or base side of the image member 1.
  • the two color image is transferred to a receiving sheet 30 in the presence of an electric field created by a bias supplied from a source of potential 19 to a transfer backing member or roller 23.
  • the receiving sheet 30 is separated from the image member 1, as shown in FIG. 7, with the two color image attached.
  • CAD developing with opposite polarity toner for the second image greatly reduces the tendency of first toner to scavenge into the second station or for the second toner to overtone the first toner image. This permits the use of contact developing rather than projection developing with its increased density at high speed and greatly reduced sensitivity to spacing.
  • the reduced scavenging effect is optimized by the use of a brush similar to that shown in the Mosehauer patent.
  • This brush will be discussed in more detail with respect to FIG. 20. It has a very soft nap which reduces the tendency of the brush to scrape off the first image and also provides extremely high density development at high speed with a relatively small development station.
  • any toner from the first image that has a tendency to be scavenged into the second toning station is likely to be deposited in the background of subsequent images, assuming it has maintained its original charge.
  • the life of the developer in the second station is dependent upon the extent of this scavenging.
  • the point at which a noticeable amount of the first, negative toner from the first image appears in the background of the second image is the point at which the developer must be changed in the second station. Because of the polarities of the toners in the DAD-CAD process, shown in FIGS. 1-7, and the softness of the development brush, shown in FIG. 20, this effect is quite small, and the life of the developer is relatively long. However, we have found two submethods which can prolong the life of the second developer even further.
  • FIGS. 8-14 show a method in which there is a demand for second color only images. That is, if the color of the first toner image is black and the color of the second toner image is red in the process shown in FIGS. 1-7, the same apparatus will, from time to time, be asked to make only red images for one or more runs.
  • Image member 1 is shown in FIG. 8 without any charge on it as it enters the process. According to FIG. 9, it is charged to a negative polarity by the same charging device 9 used to form the first electrostatic image in FIG. 1. According to FIG. 10, the image member 1 is imagewise exposed to create a negative electrostatic image, and according to FIG. 11, that electrostatic image is toned by application of positive toner from magnetic brush 11.
  • Magnetic brush 11 has been operating for many images without changing the developer and contains some negatively charged toner that had been scavenged from first, black images in earlier two-color image forming runs. Some of these negatively charged black toner particles have a tendency to deposit in the background portions of the electrostatic image, as shown in FIG. 11.
  • the treatment step shown in FIG. 5 is eliminated and the red image with some black toner particles in its background is fed into the transfer station, as shown in FIG. 12.
  • the transfer field is reversed in FIG. 12 from that shown in FIG. 6 to encourage the transfer of untreated positively charged (red) toner particles while inhibiting the transfer of negatively charged (black) toner particles.
  • the receiving sheet 30 is separated from image member 1 with the red toner image adhering to receiving sheet 30 and the black toner adhering to image member 1.
  • the black toner is cleaned off image member 1 by a cleaning device 29 at a cleaning station so that the image member 1 can be reused.
  • FIGS. 8-14 provides background-free copy with an old developer while actually getting rid of some of the contamination of magnetic brush 11. An extended single color run of this nature would have a cleansing effect on the second development station, thereby prolonging the life of its developer.
  • FIGS. 15-18 illustrate use of a similar submethod to that shown in FIGS. 8-14 to clean the second development station without actually making images.
  • the image member is discharged by some means, for example, the same exposure means that forms the electrostatic image in FIGS. 3 and 10.
  • the magnetic brush 11 is allowed to attempt to tone the discharged image member 1 in the presence of a field urging the application of negative toner to image member 1 while discouraging the application of any positive toner.
  • This field is shown in FIG. 16 as having a somewhat stronger negative bias on toning station 11 than is used for development (FIGS. 4 and 11).
  • the treating step shown in FIG. 5 can be again eliminated.
  • the transfer step, shown in FIG. 6, is also eliminated. No receiving sheet need be fed.
  • transfer backing member 23 is articulated away from image member 1. Transfer to the backing member 23 can also be prevented by adjusting the bias on transfer backing member 23 as is done in FIG. 12. If electrostatic transfer is accomplished by a corona, the corona need only be turned off. The negative (black) toner on image member 1 is then cleaned off by cleaning device 29, as shown in FIG. 18.
  • the submethod shown in FIGS. 15-18 can be employed any time the apparatus is otherwise not in use, for example, it can be routinely used while the apparatus is warming up, since the routine does not require use of a fuser which may require the longest warmup time.
  • FIG. 19 shows an image forming apparatus 10 for carrying out all three submethods shown in FIGS. 1-18.
  • an image member 1 in the form of a transparent photoconductive belt is trained about a series of rollers for movement through a path past a series of stations.
  • Image member 1 is uniformly charged by a charging station 9 and imagewise exposed at a first exposure station, for example, an LED printhead 5, a laser, or the like, to form a first electrostatic image.
  • the first electrostatic image is of a first polarity as determined by the charge from charging station 9.
  • a first toner of a first color and a first polarity (for example, negative black toner) is applied to the first electrostatic image by a suitable toning station 7 to form a first toner image. Because the toner is negative in polarity, it adheres most densely to the most discharged portions of the first electrostatic image (DAD development).
  • a first polarity for example, negative black toner
  • the image member with the first toner image can be recharged by a charging station 6, again, to a negative potential (a step that may well not be necessary). Whether recharged or not, it is imagewise exposed by a second exposure station, for example, an LED printhead 12, laser, or the like, positioned behind image member 1 to create a second electrostatic image.
  • This electrostatic image is toned by the application of positively charged toner of a second color (for example, red) from the previously shown second toning station 11.
  • the second electrostatic image can be toned by application of positively charged toner of a third color, for example, yellow, from a third toning station 13.
  • both toning stations 11 and 13 are constructed, as will be described with respect to FIG. 20, to provide a soft magnetic brush having a tendency to cause little disturbance to the first toner image and providing extremely high density at high speed with a relatively small station.
  • image member 1 now has a two color image.
  • the toners in stations 7 and 11 could be of the same color but different characteristics.
  • one of the two toners could be a black magnetic toner and the other a black non-magnetic toner, which arrangement would have certain advantages in certain processes.
  • such a combination of non-magnetic and magnetic black toners is essentially the same as a two color toner image.
  • the two color toner image proceeds to a treatment station made up of a corona charger 15 and an erase lamp 17.
  • Corona charger 15 is biased to change the polarity of one of the toners making up the two color toner image. For example, it may apply a negative charge to the two color image, thereby changing the charge on the positive toner particles applied at either toning station 11 or toning station 13.
  • this process can be assisted by use of an erase lamp 17 positioned at and/or before the corona charger 15 which further reduces the affinity of the toner for image member 1.
  • the treated two color image proceeds to the transfer station, including a transfer backing roller 23, where a potential is applied from a reversible potential source 19, encouraging transfer of the toner from a receiving sheet fed from a receiving sheet supply 21.
  • the receiving sheet is separated from image member 1 as image member 1 passes around a small roller and is transported to a fuser 25 and eventually into an output tray 27.
  • Cleaning station 29 cleans the image member 1 so that it can continue to be used in the process.
  • the submethod described with respect to FIGS. 15-18 is carried out by the image forming apparatus 10, for example, during cycle-up of the apparatus 10 when it is initially turned on for the day.
  • the image member 1 is driven through its endless path.
  • LED printhead 12 and either or both of toning stations 11 and 13 are turned on.
  • LED printhead 12 fully erases any charge on image member 1 and bias is applied to stations 11 and 13 which encourages the deposition of any black toner remaining in those stations onto image member 1.
  • the black toner being negative in polarity, is repelled by a strong negative bias on toning stations 11 and 13.
  • corona 15 and erase lamp 17 are turned off and transfer backing member 23 is articulated away from image member 1 to allow the black toner on image member 1 to continue to the cleaning device 29. Obviously, no sheet is fed from receiving sheet supply 21 for this portion of the operation. As mentioned above, backing member 23 can be maintained in place but biased to prevent the transfer of toner to it.
  • Operation of the image forming apparatus 10 is controlled by logic and control 100 which turns on and off all of the subsystems in appropriate timing, as is well known in the art. As shown in FIG. 19, it especially controls the bias applied to transfer backing roller 23 and the actuation of corona 15 and erase lamp 17 for working of the submethods shown in FIGS. 8-18. It also controls the bias on the development stations, including the bias applied to stations 11 and 13 during the subprocess shown in FIGS. 15-18.
  • station 22 is shown in FIG. 19. This station could be used to provide a second primary color alternative to that supplied by station 7 for the DAD image. However, it can be used for a different purpose to further prevent scavenging of toner applied by station 7. More specifically, for this purpose, station 22 contains clear toner of the same polarity as the toner in station 7 (negative, in the example). This station 22 is biased to apply a light topping of clear toner to the first toner image created by stations 9, 5 and 7. This toner does not affect the density of the image because it is clear. However, if any toner is scavenged from the image by stations 11 or 13, it is likely to be the toner on top, i.e., the clear toner supplied by station 22. Eventually, some toner from station 7, for example, black toner, will be scavenged by station 22 since they are of both the same polarity.
  • the use of the clear toning station 22 greatly prolongs the life of the developers in stations 11 and 13.
  • the use of the clear toner also has another advantage. Gradual scavenging of black toner into the clear station is quite obvious and can be readily measured by either measuring light reflected or transmitted through toner in station 22. This allows a monitor of the scavenging effect of the system which, properly calibrated, can give the operator an indication when the developers in stations 11, 13 and 22 should be changed.
  • This feature associated with the use of clear toner in station 22 is shown with respect to a DAD-CAD process. In fact, it is particularly useful in any process in which an electrostatic image is toned in the presence of an unfixed toner image of any polarity. Note that, because the station 22 involves DAD development, scavenging into it is more likely than it is into stations 11 and 13, both of which are shown to be CAD stations in FIG. 19. Thus, projection toning is preferred in station 22.
  • FIG. 20 shows in detail a preferred embodiment of toning station 11 (and also station 13).
  • Toning station 11 as shown in FIG. 20, embodies technology first disclosed in U.S. Patent No. 4,546,060, Miskinis et al, issued October 8, 1985, and further described in U.S. Patent No. 5,001,028 to Mosehauer et al (cited above).
  • Toning station 11 includes a housing which defines a sump 39 in which a supply of developer is mixed by suitable mixing augers 51.
  • the developer includes "hard" magnetic carrier having a coercivity of at least 300 gauss, preferably in excess of 800 gauss, when magnetically saturated.
  • the carrier exhibits an induced magnetic moment of at least 20 EMU per gram of carrier when in an applied field of 1,000 gauss.
  • the toner is a typical insulative toner and is mixed thoroughly with the carrier (the combination generally being termed a "developer").
  • the developer is transported from sump 39 by a suitable transport device 53 to an applicator 41 for application to an electrostatic image carried by image member 1.
  • Transport device 53 can include a valving feature, well known in the art, which can turn off the station by cutting off the supply of developer to applicator 41.
  • Applicator 41 includes a rotatable magnetic core 43 positioned inside an also rotatable non-magnetic sleeve or shell 45. Although the core and shell can be rotated in either direction, most commercial embodiments rotate the core 43 at speeds of 1,000 revolutions per minute or higher in a clockwise direction to move the developer in a counter-clockwise direction around shell 45. If shell 45 is moved in a counter-clockwise direction, it also assists in the flow of developer.
  • the developer can be driven in its counter-clockwise direction primarily by rotation of sleeve 45, and core 43 can also be rotated in a counter-clockwise direction.
  • the rotation of the core has primarily a mixing function as it actually encourages movement of the developer against the counter-clockwise direction that the developer is driven by the shell 45.
  • the rapidly rotating core causes rapid pole transitions on the surface of shell 45 which cause the high coercivity carrier to flip rapidly, usually in strings of carrier, as the developer moves through a development zone 55 between applicator 41 and image member 1.
  • the flipping action moves the carrier from the shell to the image member and back rapidly, replacing lost charge and toner.
  • This device and process have been in use for some years and provide highest quality development with a very soft magnetic brush. The softness of this brush was pointed out in the Mosehauer patent as useful in developing an electrostatic image on an image already carrying an unfixed toner image of a different color.
  • the height of the developer nap is controlled, in part, by a skive 47, and the developer itself is skived off the sleeve 45 by another skive 49 so it can fall back into the sump 39 where it is mixed.
  • the developer station itself is mounted opposite a pair of skis 60 which control the position of image member 1 with respect to applicator 41.
  • printhead 12 also includes one or two skis 62 which control the location of image member 1 with respect to it.
  • core 43 and shell 45 are shown to have the same axis of rotation, some high quality commercial embodiments offset the core and shell axes. This strengthens the magnetic field in the development zone 55 and weakens it opposite the development zone where developer is returned to the sump 39. This construction works especially well when the developer is being moved entirely by shell movement and the core is only mixing, since the skive 49 is relatively ineffective in such an embodiment.
  • the development station 11 provides the highest quality of development available and accomplishes this with very high density at a very high toning speed. Because of the pole transitions and flipping of the strings of carrier themselves, this density and speed can be accomplished with a station of extremely modest size. When the softness of this brush is combined with the scavenging suppressing field associated with CAD developing, remarkably little scavenging occurs.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Color Electrophotography (AREA)
  • Magnetic Brush Developing In Electrophotography (AREA)
  • Cleaning In Electrography (AREA)
EP97200016A 1996-01-17 1997-01-06 Verfahren um Tonerbilder aus zwei unterschiedlichen Tonermaterialen zu erstellen Expired - Lifetime EP0785478B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US583732 1996-01-17
US583731 1996-01-17
US08/583,732 US5748218A (en) 1996-01-17 1996-01-17 Method for forming toner images with two distinct toners
US08/583,731 US5713064A (en) 1996-01-17 1996-01-17 Method and apparatus for forming toner images with two distinct toners

Publications (3)

Publication Number Publication Date
EP0785478A2 true EP0785478A2 (de) 1997-07-23
EP0785478A3 EP0785478A3 (de) 2001-01-03
EP0785478B1 EP0785478B1 (de) 2002-12-11

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Application Number Title Priority Date Filing Date
EP97200016A Expired - Lifetime EP0785478B1 (de) 1996-01-17 1997-01-06 Verfahren um Tonerbilder aus zwei unterschiedlichen Tonermaterialen zu erstellen

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EP (1) EP0785478B1 (de)
JP (1) JPH09230667A (de)
DE (1) DE69717688T2 (de)

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4546060A (en) 1982-11-08 1985-10-08 Eastman Kodak Company Two-component, dry electrographic developer compositions containing hard magnetic carrier particles and method for using the same
US5001028A (en) 1988-08-15 1991-03-19 Eastman Kodak Company Electrophotographic method using hard magnetic carrier particles
US5045893A (en) 1990-07-02 1991-09-03 Xerox Corporation Highlight printing apparatus
US5049949A (en) 1989-06-29 1991-09-17 Xerox Corporation Extension of tri-level xerography to black plus 2 colors
US5208636A (en) 1992-03-23 1993-05-04 Xerox Corporation Highlight color printing machine
US5241356A (en) 1992-07-29 1993-08-31 Xerox Corporation Method and apparatus for minimizing the voltage difference between a developed electrostatic image area and a latent electrostaic non-developed image
US5258820A (en) 1992-07-29 1993-11-02 Xerox Corporation Pre-recharge device for voltage uniformity in read color systems
EP0625730A2 (de) 1993-05-20 1994-11-23 Eastman Kodak Company Verfahren und Vorrichtung zum zwei Tonerbilder in einem Abbildungsdurchlauf zu Erzeugen
US5409791A (en) 1993-05-20 1995-04-25 Eastman Kodak Company Image forming method and apparatus

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4205322A (en) * 1976-04-27 1980-05-27 Nippon Electric Co., Ltd. Electrostatic method of simultaneously transferring to a recording medium a toner image having different polarities
US5450189A (en) * 1994-02-15 1995-09-12 Hewlett-Packard Company Electrophotographic imaging with toners of opposite sign electrical charge

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4546060A (en) 1982-11-08 1985-10-08 Eastman Kodak Company Two-component, dry electrographic developer compositions containing hard magnetic carrier particles and method for using the same
US5001028A (en) 1988-08-15 1991-03-19 Eastman Kodak Company Electrophotographic method using hard magnetic carrier particles
US5049949A (en) 1989-06-29 1991-09-17 Xerox Corporation Extension of tri-level xerography to black plus 2 colors
US5045893A (en) 1990-07-02 1991-09-03 Xerox Corporation Highlight printing apparatus
US5208636A (en) 1992-03-23 1993-05-04 Xerox Corporation Highlight color printing machine
US5241356A (en) 1992-07-29 1993-08-31 Xerox Corporation Method and apparatus for minimizing the voltage difference between a developed electrostatic image area and a latent electrostaic non-developed image
US5258820A (en) 1992-07-29 1993-11-02 Xerox Corporation Pre-recharge device for voltage uniformity in read color systems
EP0625730A2 (de) 1993-05-20 1994-11-23 Eastman Kodak Company Verfahren und Vorrichtung zum zwei Tonerbilder in einem Abbildungsdurchlauf zu Erzeugen
US5409791A (en) 1993-05-20 1995-04-25 Eastman Kodak Company Image forming method and apparatus

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DE69717688T2 (de) 2003-09-18
EP0785478A3 (de) 2001-01-03
JPH09230667A (ja) 1997-09-05
DE69717688D1 (de) 2003-01-23
EP0785478B1 (de) 2002-12-11

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