US3649262A - Simultaneous development-cleaning of the same area of an electrostatographic image support surface - Google Patents

Simultaneous development-cleaning of the same area of an electrostatographic image support surface Download PDF

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US3649262A
US3649262A US789031A US3649262DA US3649262A US 3649262 A US3649262 A US 3649262A US 789031 A US789031 A US 789031A US 3649262D A US3649262D A US 3649262DA US 3649262 A US3649262 A US 3649262A
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toner
electrostatic latent
range
support surface
developer
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Ronald L Cade
Stewart William Volkers
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Xerox Corp
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Xerox Corp
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    • 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
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/0801—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer for cascading
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G21/00—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
    • G03G21/0005—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge for removing solid developer or debris from the electrographic recording medium
    • G03G21/0047—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge for removing solid developer or debris from the electrographic recording medium using electrostatic or magnetic means; Details thereof, e.g. magnetic pole arrangement of magnetic devices
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2221/00—Processes not provided for by group G03G2215/00, e.g. cleaning or residual charge elimination
    • G03G2221/0005—Cleaning of residual toner

Definitions

  • ABSTRACT A system for removing residual toner images from electrostatographic image support surfaces and simultaneously developing an undeveloped electrostatic latent image on essentially the same area of said surface, including developmentcleaning a xerographic plate, for example, by cascading developer along the image support surface of the plate.
  • This invention relates to electrostatic imaging and more specifically to the development of electrostatic latent images and the removal of the residual toner images from a. support surface.
  • the most successful electrostatic imaging process and one preferred in the present invention is that of xerography.
  • the xerographic process is performed upon a xerographic plate comprising a layer of photoconductive insulating material upon a conductive backing.
  • the surface of the plate is uniformly charged and then exposed to a light and shadow image pattern.
  • the photoconductive plate discharges in the exposed areas proportionally to the intensity of the radiation reaching the exposed area, thereby creating an electrostatic latent image on the surface of the photocon ductive layer corresponding to the light and shadow image pattern projected upon the plate.
  • the electrostatic latent image is then developed by contact with an electroscopic marking material called toner.
  • the electrostatic latent image which has been developed by contact with toner is then referred to as the toner image or developed image".
  • This developed image may be fixed on the xerographic plate itself, or it may be transferred to paper or other material, and the transferred image may be fixed on said other material. However, after the developed image is transferred to another base material, there may still be and there typically is, a residual image of toner particles adhering to the surface of the photoconductive layer. if this residual image is not removed before the plate is reused, portions of the residual image may be transferred and fixed to any new copy which is made from the same plate.
  • the plate may take any suitable form including a web, foil, laminate or the like, metallic strip, sheet, coil, cylinder, drum, endless belt, endless mobius strip, circular disc or other shape.
  • the electrically conductive support may comprise two or more layers depending upon the desired characteristics of the support plate as a whole.
  • the words xerographic plate or plate are commonly used herein to designate any of these various configurations.
  • the form of the plate surface may control the manner in which the various xerographic process steps may be performed upon the plate.
  • electrostatic latent images may be formed by methods in addition to the preferred mode of charging and exposing a xerographic plate.
  • Other modes include charging or sensitizing in an image configuration through the use of a mask or stencil, or by first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic reproduction techniques and then transferring this charged pattern to the surface of another plate by bringing the two into very close proximity and utilizing breakdown techniques as described, for example, in Carlson U.S. Pat. No. 2,982,647, and Walkup U.S. Pat. Nos. 2,825,814 and 2,937,943.
  • charge patterns conforming to selected shaped electrodes or combinations of electrodes may be formed on a support surface by the 'lESl" discharge technique, as more fully described in Schwertz Pat. Nos. 3,023,731 and 2,919,967, or by techniques described in Walkup Pat. Nos. 3,001,848 and 3,001,849, as well as by electron beam recording techniques, as described in Glenn U.S. Pat. No. 3,113,179.
  • Electrostatography is defined as the formation and utilization of latent electrostatic charge patterns for the purpose of recording and reproducing patterns in viewable form (See Standard Definitions of Terms for Electrostatographic Devices, lEEE No. 224, Nov. 1965, published by The Institute of Electrical and Electronics Engineers, Inc., 345 East 47 Street, New York, N.Y. 10017.)
  • FIG. l' is a side view of an otherwise typical xerographic apparatus employing the advantageous system of this invention.
  • FIG. 2 is a side view of a preferred cascade developmentcleaning apparatus used in the embodiment of FIG. 1.
  • FIG. 3 is a graphic illustration of the preferred operating range of the present invention in one preferred mode of forming the electrostatic latent image, expressed in the variables Charging Voltage and Relative Exposure Illumination used to form said electrostatic latent image.
  • FIG. 1 discloses a xerographic apparatus showing the steps typically used in the xerographic process, but embodying the advantageous system of the present invention
  • 10 designates the rotating drum with photoconductor layer.
  • a corona discharge device 12 initially charges said surface.
  • the charged surface then advances through station 13 where the light and shadow image desired to be copied is projected onto the surface 1 l of the drum 10.
  • the advantageous and surprising development-cleaning system of the present invention is carried out by a cascade of developer comprising toner and carrier which develops electrostatic latent images and at the same time, as will be further described, removes residual images comprising toner particles, typically adhering to the surface of the drum in essentially the same area.
  • the area of the surface just cleaned and developed by the advantageous system of the present invention, and now sup porting the developed image advances through the field of pretransfer electrode 15 which recharges the surface of the drum in preparation for the transfer step.
  • the surface carrying the developed image next advances into the transfer station 16 where the developed image is transferred to another backing 19.
  • the transfer station 16 As the paper 20 advances through the fixing process, the corresponding portion of the surface of the xerographic drum from which the image now supported on the paper was transferred, continues to advance through the cycle, but now supporting only the residual image of toner particles remaining after the transfer step.
  • the drum surface advances past a negative charging apparatus 21 wherein the charge on the drum is reversed in preparation for cleaning. 22 designates the position where cleaning apparatus would typically be located in prior xerographic systems.
  • the surface supporting the residual image continues to advance through discharge station 23 where the entire surface of the drum is flooded with light to discharge the photoconductive insulating layer.
  • the surface of the drum After discharge at 23 the surface of the drum is then ready to be charged and exposed again, although the residual image from the previous exposure typically still remains on the same area of said surface.
  • the surprising and advantageous system of the present invention is used in the illustrated embodiment.
  • the drum surface would typically require an additional cleaning step before the charging and exposing steps of the subsequent xerographic cycle are performed.
  • Cascading developer comprising toner and carrier, along the surface of the photoconductive layer supporting residual toner images
  • Cascading developer is a preferred mode of development-cleaning.
  • electrostatic latent images are developed, and, surprisingly, residual images of toner particles from the previous cycle are removed by combinations of mechanical, triboelectric and electrostatic actions of the cascading developer. It is believed that the developer particles physically knock and scrub residual toner particles from the surface of the photoconductor, and that the toner-free portions of carrier particles electrostatically attract and thereby scavenge the residual toner particles.
  • the surprising ability of the cascade system to simultaneously remove residual images while developing electrostatic latent images is most advantageous in achieving the objects of the present invention.
  • FIG. 2 A preferred embodiment of cascade development cleaning apparatus is illustrated in FIG. 2 wherein the developer 24 is shown cascading at 25 over the surface 11 of the drum within the development-cleaning zone.
  • Electrodes placed adjacent and parallel to the xerographic plate.
  • the electrode may comprise a solid sheet, a screen, a series of wires, or a series of points suspended or located over or near the plate surface, said electrode being connected by conductor with a suitable potential source creating the desired electric field between the electrode and the photoconductor.
  • the electrode is preferably biased to a voltage of the same polarity as the electrostatic image on the plate.
  • FIG. 2 shows an electrode 26 adjacent to the plate surface 11.
  • the apparatus depicted in FIG. 2 also illustrates an electroded developer control bafile 27 which is designed to control carrier flow and toner action, such as toner clouds, near the exit of the development-cleaning zone. While controlling extraneous toner, the control baffle 27 also assists development in the same manner as the primary development-cleaning electrode.
  • One of those variables is the angle at which the cascading developer advances relative to the surface of the photoconductor. It is observed in both FIGS. 1 and 2 that that portion of the xerographic drum over which developer is cascaded forms an are so that a tangent to the drum surface at any point along that arc forms a different angle with the horizontal. Hence, at any point on the surface of the drum, the developer is generally passing along the photoconductor at approximately a given angle. However, because the developer is a particulate mixture, at any point along the arc of drum surface or flat plate surface in other embodiments, individual carrier beads, toner particles and combinations thereof, typically will be traveling in directions and at angles somewhat different from that made by the plate and electrode at that point. However the mean developer path will generally follow the direction and angle of the plate and electrode at a given point.
  • the developer may be cascaded over a flat plate comprising the photoconductive insulating layer on a conductive backing, and the flat plate and the accompanying electrode may be oriented at any angle with the horizontal up to
  • the flat plate embodiment may be used in the conventional mode, that is, cascade across the surface of the photoconductor itself, or in the inverted mode, wherein the developer cascades along the electrode which is closely spaced adjacent and parallel to the surface of the photoconductor. It has been found that maximum development and cleaning occur when the xerographic plate or electrode angle is in the optimum range of about 70 conventional to about 70 inverted, from the horizontal. That is, optimum development-cleaning occurs when the plate and electrode are in a substantially vertical position.
  • a preferred range for the angle between the electrode and the horizontal is from about 60 to about 60 inverted. Electroded, cascade development-cleaning is performed satisfactorily when the angle between the electrode and horizontal is about 20 to about 20 inverted, the lower limit being about the angle of repose of the particular system.
  • the angle of repose is the angle formed with the horizontal by the xerographic plate or the accompanying electrode at which developer will start to flow down the surface of the uncharged plate or the surface of the electrode when operating in the inverted mode. Developer will flow over the surface which is placed at an angle somewhat less than the angle of repose if the developer is applied with an initial velocity. However, at such low angles developer flow tends to be unstable and the quality of development-cleaning is reduced.
  • Another variable is the voltage difference between voltages, development-cleaning electrode and the exposed (background) and unexposed (image) portions of the imaged plate.
  • V, and V are necessarily dependent upon the initial charging voltage placed on the plate at the beginning of a xerographic cycle.
  • the background voltage, V is the voltage potential remaining at exposed areas of the surface of the photoconductor after those areas have been partially discharged by light impinging upon said areas during the exposure step. This relationship is discussed at length later herein. It is found that a preferred range for the initial charging voltage is in the range of about ri-200 to about +700 volts. An optimum range of initial charging voltages is in the range of about +300 to about 500 volts.
  • electrode voltages V which produce the desired and advantageous development-cleaning, are optimum in the range of about +150 to about +300 volts, and preferred in the range of about +150 to about +500 volts.
  • electrically negative initial charging voltages, electrostatic latent images, and development-cleaning electrode voltages may also be used. Satisfactory development-cleaning may occur at voltages above or below the indicated preferred range. However, at lower voltage magnitudes, the cleaning efi'rciency of the development-cleaning system is reduced almost linearly. While satisfactory development-cleaning is performed at voltages above the preferred range for various systems embodying the present invention, sticking of cascade carrier beads to the photoconductor may occur at such higher voltages.
  • Bead sticking is the adherance of carrier beads to the xerographic plate surface which results when the electrostatic attraction of the xerographic plate for the toner and the toner for the carrier bead are together greater than the mechanical forces, such as gravity, accelerating the carrier bead.
  • concentration of toner in the developer is lowered, carrier beads stick to the surface of the plate, and the surface of the xerographic plate is susceptible to being scratched and pitted by the sticking carrier beads as the plate passes through closely fitted apparatus during other steps in the xerographic process.
  • Another variable in the novel cascade development-cleaning system of this invention is the developer flow rate. Maximum cleaning results where the developer activity is greatest. So, the greatest active residence time of developer near the plate is desired. Development-cleaning efficiency per unit time increases with increasing flow rate. As a general rule, the greater the flow rate the better the cleaning efficiency, although the developer will perform development-cleaning insofar as possible at any flow rate. The charge density of the residual image will also affect the development-cleaning efficiency and can therefore influence the selection of developer flow rate. Charge density is the charge per unit area of plate surface and not to be confused with image density which is defined later herein. On an absolute basis, images developed from higher initial charge density latent images are preferably cleaned at higher developer flow rates.
  • Toner particle size is a significant factor in this invention. Toner particle size affects the efficiency of the electrostatic transfer of toner to latent electrostatic images and the transfer of residual toner from the xerographic plate back to the carrier. It has been found that both processes become more efficient with larger toner particle sizes. At a given toner concentration, smaller toner particles tend to cover more of the surface of the carrier beads thereby leaving less free bead surface available for developmentcleaning or scavenging. The smaller toner particles are also less susceptible to being physically knocked from the plate surface. It has therefore been found advantageous to use toners having a particle size distribution which contains minimal amounts of relatively small toner particles.
  • Toner particles may be classified as to particle size in a classifier for fine dry powders such as the Sharples K8 Super Classifier, manufactured by the Sharples Company, 424 West Fourth Street, Bridgeport, Pennsylvania. In the Sharples scale, toner particles are measured in microns. Toners with particles of average size by number in the range of about l0 to about 20 microns, with negligible numbers of particles of size less than 5 microns, give results preferred over those of average size in the range of about 4 to about 7 microns, with about 50 percent of the particles of a size less than 5 microns.
  • a classifier for fine dry powders such as the Sharples K8 Super Classifier, manufactured by the Sharples Company, 424 West Fourth Street, Bridgeport, Pennsylvania.
  • toner particles are measured in microns. Toners with particles of average size by number in the range of about l0 to about 20 microns, with negligible numbers of particles of size less than 5 microns, give results preferred over those of average size in the range of about 4 to about 7 micro
  • Toners in both of the above ranges give development-cleaning efficiencies which are preferred over those attainable with particles of average size in the range of about 2 to about 3 microns, with about percent of the particles less than 5 microns in diameter.
  • the smaller tone particles will still perform the development-cleaning, although the build up of toner-film on the apparatus typically is accelerated.
  • toner concentration in the developer mixture Another parameter is toner concentration in the developer mixture.
  • concentration of toner affects developmentcleaning primarily in the development part of the process. The cleaning will go on, but if the toner concentration is too high, the cleaned residual images will be redeveloped as quickly as they are cleaned.
  • the limiting concentration at one end is development capability (i.e., sufficient toner to develop electrostatic latent images) while the other end point is the limit of the cleaning ability of the system.
  • concentration limitations depend on the degree of quality of copy desired.
  • Toner concentration is conveniently expressed in terms of mass per unit surface area, said surface being the surface of the carrier particles or beads.
  • the advantageous cascade development-cleaning system of the present invention produces satisfactory results in toner concentration ranges of about 0.1 to about 0.4 mg. of toner per sq. cm.
  • a preferred range of toner concentration in the developer mixture is about 0.2 to about 0.3 mg/sq.cm. These concentrations indicate that it is most desirable to closely control the toner concentration, preferably by automatic means.
  • Such lubricants include metallic salts of fatty acids such as zinc searate, and other materials such as colloidal pyrogenic silica particles such as CabO-Sil", available from the Cabot Corporation, or various mixtures of such materials.
  • An extensive group of such lubricants is recited in copending application Ser. No. 702,306, filed Feb. 2, 1968, now U.S. Pat. No. 3,552,850.
  • a preferred range of concentrations for the lubricant is in the range of about 0.1 to about 1 percent by weight of toner.
  • the other component in the developer is a granular material called carrier which by mixing with the toner particles triboelectrically acquires charge of polarity opposite that acquired by the toner.
  • Carrier granules may be any shaped solid particle from flat platelets to cubes to spherical heads.
  • the carrier may be made of any suitable material such as glass, plastic, metal or other granular material.
  • Carrier granules of average size in the range of about 30 to about 1,000 microns perform satisfactorily.
  • a preferred range of carrier particle size is in the range of about to about 600 microns.
  • Another variable effecting development-cleaning in the inventive system, where the electrostatic latent image is formed by the preferred mode of charging and exposing a xerographic plate, is the charging voltage initially charging the photoconductor.
  • Initial charging voltage is often also referred to as the initial potential on the photoconductor or as the initial surface potential. It is found, surprisingly, that the cleaning efficiency may be affected in portions of the plate carrying residual images by the magnitude of the initial charge.
  • the rate of decay of charge in plate areas which are masked by residual toner images may be less than the rate of decay in unmasked areas. In the masked areas the residual toner particles may prevent light from reaching and therefore discharging those areas of 'the photoconductor during the exposure and discharge steps of subsequent xerographic cycles.
  • Such charged residual image areas may then be redeveloped thereby increasing the amount of residual image on the plate.
  • the initial charging voltage is kept below about +700 volts, or below about .-l-500 volts for optimum results, residual transferred images on subsequent copies are eliminated.
  • the initial charging voltage in the development-cleaning system is also of importance when taken in conjunction with the relative exposure illumination used during the exposure step of the xerographic process.
  • relative exposure illumination is a unit of measure of the amount of light which reaches and then discharges exposed areas of the xerographic plate.
  • the relative exposure illumination is expressed in terms of f-number.
  • the f-number is a number indicating the relative aperture of a particular lens or diaphragm opening in conventional projection apparatus, where relative aperture equals F/D, where F is the focal length of the lens and D the effective diameter of the aperture.
  • FIG. 3 illustrates the relationship of Charging Voltage and Relative Exposure Illumination.
  • line 30 represents approximate maximum charging voltages corresponding to relative exposure illuminations for a particular set of parameters, at which the system will still adequately clean residual image areas. It has also been mentioned above that the initial charging voltage put on the photoconductor must be so sufficient that the dark image areas of the electrostatic latent image as projected onto the photoconductor will be fully developed by the particular development system.
  • Line 31 in FIG. 3 represents charging voltages corresponding to various relative exposure illumination values which are approximately minimum values of the charging voltage which will result in images which may be adequately developed to produce satisfactory quality in copies made by that particular system.
  • a preferred range for the initial charging voltage on the surface of the photoconductor is in the range of about +200 to about +700 volts.
  • An optimum range of initial charging voltages is in the range of about +300 to about +500 volts.
  • a preferred range relative exposure illumination to which the surface of the photoconductor is exposed is in the range of about f/8 to about f/5.6.
  • background voltages resulting from charging and exposing at values outside these ranges may produce satisfactory development-cleaning and good copy quality depending upon the particular set of parameter values which define the operating range for the given system.
  • lines 30 and 31 define an envelope 32 which contains most points corresponding to particular values of the charging voltage and relative exposure illumination at which development cleaning is satisfactorily operable and copy quality is good. It is also noted that broken line 33 closes the lower portion of the envelope in FIG. 3, illustrating that when the charge on the xerographic plate is low and the relative exposure illumination projected onto the charged xerographic plate is also low, the electrostatic latent image on the plate is not sufficiently distinct to give acceptable copy quality.
  • FIG. 3 is a representative example of the approximate operating range of one development-cleaning system and that the data shown on the particular drawing of FIG. 3 are applicable only to a given set of parameters. Changes in any one or any combination of the various parameters in the development-cleaning system may vary the values which would be shown in the plot of charging voltage against relative exposure illumination.
  • an optimum embodiment of the present invention is an embodiment comprising parameter settings within the optimum ranges of each of the independent variables in the inventive system.
  • an optimum embodiment is a xerographic process including an electroded, cascade development-cleaning system wherein the photoconductor and electrode are substantially vertical to the horizontal plane, the electrode voltage is in the range of about to about +300 volts, toner size is in the range of about 10 to about 20 microns with negligible numbers of toner particles of size less than 5 microns, toner concentration in the range of about 0.2 to about 0.3 mg/sq.cm., carrier size in the range of about 250-300 microns, initial charging voltage in the range of about +300 to about +500 volts, and relative exposure illumination in the range of about f/8 to about f/5.6.
  • various preferred embodiments may be constructed using parameter settings in any and all possible combinations of the various preferred ranges of the individual parameters in the inventive system.
  • Another preferred embodiment of the advantageous development-cleaning system of the present invention comprises passing the electrostatic latent image support surface having said image thereon, in contact with a magnetic brush.
  • the brush is formed from magnetic carrier particles to which toner particles are electrostatically attached.
  • the toner particles are attached to the magnetic carrier and are then electrostatically transferred to the imaged areas of the support surface.
  • residual toner images in background areas on the support surface are removed by the electrostatic and mechanical action of the magnetic bristles of the brush.
  • the magnetic brush system easily removes such residual toner particles and is a suitable specific embodiment for the advantageous development-cleaning system of the present invention.
  • Magnetic brush systems which have previously been used only for development of electrostatic latent images, are disclosed in Wilson U.S. Pat. No. 2,846,333, and Thompson U.S. Pat. No. 3,064,622. It is noted that the supply of toner particles in a magnetic brush system may be either a mass consisting essentially of magnetic or nonmagnetic toner particles, or a liquid suspension of magnetic or nonmagnetic toner particles.
  • Another specific embodiment of the advantageous development-cleaning system of the present invention comprises a fur, applicator-cleaner brush, which is located adjacent to and in contact with the electrostatic latent image supportsurface, and also adjacently contacting a supply of toner particles for the development of electrostatic latent images.
  • the toner particles and material from which the bristles of said brush are made triboelectrically interact so that toner particles adhere to the brush bristles, which in turn apply said toner particles to the electrostatic latent image support surface, thereby viewably developing said image.
  • the fur bristles triboelectrically and mechanically remove residual toner particles from essentially the same area of the support surface.
  • a fur brush development system suitable for use as a specific embodiment of the advantageous development-cleaning system of the present invention is disclosed in Greaves U.S. Pat. No. 2,902,974.
  • a mass of developer is supported in contact with the electrostatic latent image support surface, and the surface supporting said image is passed through the mass of developer.
  • the toner carrying a charge opposite to the charge in the imaged areas on the support surface, adheres to said images areas thereby producing a viewable image pattern.
  • residual toner images remaining on said surface from previous electrostatographic cycles are removed by the combination of electrostatic attraction of residual toner to the carrier particles in the developer, and by the scrubbing action of the developer on the residual toner particles.
  • Yet another specific embodiment of the advantageous development-cleaning system of the present invention comprises passing the electrostatic latent image support surface having said image thereon, through a fluidized bed of developer.
  • a mass of developer particles may be fluidized by passing a stream of gas upwardly through the mass of developer particles thereby suspending the particles in the flowing gas stream.
  • a mass of developer particles may be fluidized by mechanically vibrating the entire mass, thereby suspending some of the moving particles.
  • a fluidized bed of developer particles is disclosed in Mott U.S. Pat. No. 3,008,826,and in Donalies U.S. Pat. No. 3,393,663, and used therein solely for development, but not heretofore used for cleaning residual images from an electrostatographic surface, nor from the advantageous simultaneous development-cleaning system of the present invention.
  • the advantageous system of the present invention is useful in any electrostatographic process having an electrostatic latent image support surface.
  • the electrostatic latent image support surface is the surface of a photoconductive insulating layer.
  • Selenium in its amorphous form is found to be a preferred photoconductive insulating material for use in xerography because of its extremely high quality image making capability, relatively high light response, and capability to receive and retain charged areas at different potentials and of different polarity.
  • Any suitable photoconductive insulating layer may similarly be used in the practice of the invention. However, it is found that the inventive system performs more satisfactorily if the electrostatic latent image support surface is quite smooth.
  • Typical photoconductive insulating layers include: amorphous selenium, alloys of sulfur arsenic or tellurium with selenium, selenium doped with materials such as thallium, cadmium sulfide, cadmium selenide, etc., particulate photoconductive materials such as zinc sulfide, zinc cadmium sulfide, French process zinc oxide, phthalocyanine, cadmium sulfide, cadmium selenide, zinc silicate, cadmium sulfoselenide, linear quinacridones, etc., dispersed in an insulating inorganic film forming binder such as a glass or an insulating organic film forming binder such as an epoxy resin, a silicone resin, an alkyd resin, a styrene-butadiene resin, a wax or the like.
  • photoconductive insulating materials include: blends, copolymer, terpolymers, etc., of photoconductors and nonphotoconductive materials which are either copolymerizable or miscible together to form solid solutions and organic photoconductive materials of this type include: anthracene, polyvinylanthracene, anthra-quinone, oxadiazole derivatives such as 2,5-bis-(p-amino-phenyl-l 1,3,4-oxadiazole; 2-phenylbenzoxazole; and charge transfer complexes made by complexing resins such as polyvinylcarbazole, phenolaldehydes, epoxies, phenoxies, polycarbonates, etc., with Lewis acid such as tetrachlorophthalic anhydride; 2,4,7-trinitro-fiuorenone; metallic chlorides such as aluminum, zinc or ferric chlorides; 4,4-bis(dimethylamino) benzophenone; chloranil; pic
  • the system of the present invention may also be used as a separate cleaning system.
  • the use of such a system for the sole purpose of cleaning would fail to achieve some of the objectives of the simultaneous development-cleaning system, such as reduction in machine size, improvement of machine cleanliness, and improvement in the life of the electrostatic latent image support surface.
  • the use of the advantageous system of the present invention solely as a cleaning system is in itself novel since no previous cleaning system using developer as the functional cleaning mechanism, has heretofore been successful in a one-pass operation.
  • a one-pass cleaning system using developer as the functional cleaning medium also shows that the advantageous development-cleaning system of the present invention can be used as both a development system and a cleaning system, in any two-cycle electrostatographic process.
  • the development occurs during the first cycle and the cleaning occurs during the second cycle, which cycle is solely for the purpose of removing residual toner images from the electrostatic latent image support surface.
  • the twocycle system achieves all of the objects of the preferred inventive system, except that the recycling may involve slightly more complicated mechanisms and electrical circuits.
  • charge density in electrostatic latent images has previously been mentioned as a factor affecting development-cleaning.
  • charge density on the photoconductor is not easily measured, especially in automatically recycling xerographic apparatus.
  • Standard image densities are illustrated in the Examples. For instance, in a very dense area of an original where only one-tenth of the incident light is reflected back to the eye of the viewer, R would equal onetenth and the log of HR, i.e., image density, would be I.
  • a density of 1.3 is where about one-twentieth of the incident light is reflected back to the viewer. Densities in the range of about 1.2-1.5 or above appear to the unaided eye as a very dense black. Image densities therefore provide a convenient basis for comparing the quality of xerographic or other copies to the original from which said copies are made.
  • EXAMPLE I Using a 4 inches by 4 inches flat plate with selenium as the photoconductor; the plate is charged to a surface potential of about +500 volts, exposed, developed and the developed image is transferred to paper so that the average solid area image density of such transferred images is about 1.3. The plate carrying the residual image is then exposed to a 300 watt photoflood source at about l inches for about 30 seconds after each development and transfer sequence. The exposure by the photoflood source discharges the photoconductor. This cycle is then repeated many times.
  • the developer is composed of a glass bead carrier, about 250 microns in average diameter, Xerox 914 toner, at a toner concentration of about 0.3 mg/sq.cm., a developer flow rate of about 2 g./inc. width of plate/sec. and total flows of 25, 50 and 100 g. respectively.
  • a development electrode a 4 inches by 4 inches stainless steel flat plate is biased at about +100 volts and placed parallel to and about 0.06 inch from the selenium surface.
  • Developmentcleaning runs are made at various electrode angles in both the conventional and inverted modes. Data from the development-cleaning runs shown that optimum development-cleaning occurs at electrode angles near the vertical (90) with preferred cleaning in the range of about 60 conventional to about 60 inverted.
  • Example II A xerographic plate and developer mix as in Example I are used. The plate is charged as in Example I and exposed to produce images with a transferred developed image density of about 1.3.
  • a developer flow rate of about g./in.-sec., 100 grams total flow of developer is used in an inverted electroded cascade development-cleaning apparatus with the same electrode and electrode-plate spacing as in Example I at an electrode angle of 75 inverted; the electrode voltage is varied from 0 to about +1 ,200 volts.
  • Preferred development-cleaning occurs in the range of about +200 to about +700 volts. For this particular set of parameter settings, some bead sticking is found to occur at electrode bias values above about +l,200 volts.
  • EXAMPLE III A standard 914 copier manufactured by the Xerox Corporation, Rochester New York, is fitted with apparatus embodying the present invention.
  • the development-cleaning housing includes an electrode assembly having a development-cleaning electrode about 2.5 inches long (from entrance to exit measured along its are as it parallels the drum surface) and spaced about 0.08 inches from the drum surface.
  • the drum carries an amorphous selenium photoconductor.
  • the electrode assembly rides against the edges of the drum thereby minimizing adjustment problems.
  • an electroded battle is introduced immediately following the developmentcleaning electrode to control excessive developer losses occuring at the exit of the development-cleaning zone.
  • a pretransfer corotron is installed after the development-cleaning zone, before the transfer corotron, to increase transfer effi ciency.
  • the developer mix is composed of uncoated leaded glass beads of average diameter of about 250 microns, with Xerox 914 toner, of average size in the range of about 12 to about 15 microns, and one-eighth of 1 percent by weight of the toner of zinc stearate lubricant.
  • the electrode voltage is about +200 volts.
  • This embodiment of the developmentcleaning system continually produces high-quality solids, halftones and lined images with low background over extended machine runs of more than 50,000 prints. Such image quality is enhanced by maintaining toner concentration at approximately 0.28 mg./sq.cm. of carrier bead surface. Toner consumption and toner efficiency for this embodiment are excellent, often greater than 15,000 8-% by 11-inch copies per pound of toner.
  • EXAMPLE IV Using the copier embodying the present invention described in Example III, with an initial charging voltage of about +400 volts; relative exposure illumination of about f/6.3; toner concentration of about 0.28 mg./sq.cm. by weight; leaded glass bead carrier of average size of about 250 microns; an electrode voltage of about volts, the development-cleaning system of the present invention operates satisfactorily enabling the xerographic apparatus to produce high numbers of copies of excellent quality.
  • EXAMPLE V Using the apparatus embodying the present invention as described in Example III, with a transfer corotron current of about 16 microamperes, various test copies are made at different charging potentials and exposure levels. Standards are adopted for acceptable operation and copy quality: the system must clean the residual image when input image density is about 1.3 and develop that input image density to a trans ferred image density of about L2, and the system must also develop an input image density of about 0.3 to the density of a prepared test standard of density of about 0.2 Data from various runs defines an operating range approximately as shown in FIG. 3.
  • the envelope 32 is enclosed by curve 30 representing the maximum charging potential which allows cleaning meeting the standards imposed in this Example and in the range of exposures shown, and curve 31 which represents the maximum exposure which allows development meeting the standards and in the range of charging potential shown.
  • curve 30 representing the maximum charging potential which allows cleaning meeting the standards imposed in this Example and in the range of exposures shown
  • curve 31 which represents the maximum exposure which allows development meeting the standards and in the range of charging potential shown.
  • the operating area is bounded by the condition that satisfactory maximum density cannot be obtained; that is, the standard of producing a transferred image density of about 1.2 from an input image density of about 1.3 cannot be met.
  • broken line 33 represents this limitation.
  • the envelope 32 defines an approximate operating range including those values of charging voltage and relative exposure illumination at which this apparatus and particular set of parameter values operate satisfactorily to produce copies of image density meeting the standards.
  • a method of simultaneously developing and cleaning an electrostatic latent image support surface comprising:
  • said developer comprising a mixture of carrier granules and toner particles, contiguous the electrostatic latent image support surface between said surface and said electrode, whereby, simultaneously, the second electrostatic latent image is developed into a toner image corresponding to said second electrostatic latent image, and said residual toner image corresponding to said first electrostatic latent image is removed from said electrostatic latent image support surface.
  • toner particles in the developer are in the range of about 10 to about 20 microns with about 1 percent or less by number of particles of size less than 5 microns.
  • concentration of toner in the developer is in the range of about 0.2 to about 0.3 milligrams per square centimeter of carrier surface.
  • said photoconductive insulating layer comprises amorphous selenium.
  • said electrostatic latent image support surface is a surface of a photoconductive insulating layer comprising amorphous selenium
  • said electrostatic latent images are provided by electrostatically charging said support surface to a potential in the range between about .-l-200 and about +700 volts, and exposing said support surface with an image pattern of activating electromagnetic radiation thereby substantially reducing said potential in the imagewise exposed areas of said support surface,
  • said developer comprises carrier granules of average size in the range between about 100 and about 300 microns, toner particles of average particle size in the range between about 10 and about 20 microns with about 1 percent or less by number of said toner particles of size less than about 5 microns, and wherein the concentration of toner in said developer is in the range between about 0.2 and about 0.3 milligrams per square centimeter of carrier surface, and
  • said electrode is biased to a potential in the range between about +150 and about +300 volts.

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  • General Physics & Mathematics (AREA)
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US789031A 1968-12-31 1968-12-31 Simultaneous development-cleaning of the same area of an electrostatographic image support surface Expired - Lifetime US3649262A (en)

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Cited By (23)

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Publication number Priority date Publication date Assignee Title
US3783818A (en) * 1970-12-26 1974-01-08 Fuji Xerox Co Ltd Electrophotographic developing process
US3851962A (en) * 1973-08-29 1974-12-03 Savin Business Machines Corp Electrostatic hold down apparatus
US3865080A (en) * 1973-01-17 1975-02-11 Xerox Corp Toner pickoff apparatus
US3921577A (en) * 1974-05-28 1975-11-25 Xerox Corp Magnetic development units
US4063811A (en) * 1975-04-11 1977-12-20 Minolta Camera Kabushiki Kaisha Electrophotographic copier
US4265998A (en) * 1979-11-13 1981-05-05 International Business Machines Corporation Electrophotographic photoreceptive background areas cleaned by backcharge process
US4330199A (en) * 1972-04-13 1982-05-18 Canon Kabushiki Kaisha Electrophotographic device
US4470693A (en) * 1982-01-11 1984-09-11 Pitney Bowes Inc. Self-cleaning xerographic apparatus
US4500198A (en) * 1982-12-10 1985-02-19 International Business Machines Corporation Multiple roller magnetic brush developer having development electrode voltage switching
US4534641A (en) * 1983-10-31 1985-08-13 Xerox Corporation Charge erase device for copying or reproduction machines and printers
US4538900A (en) * 1983-11-09 1985-09-03 Ricoh Company, Ltd. Electrophotographic copying apparatus including drum conditioning apparatus and method
US4540274A (en) * 1982-01-18 1985-09-10 Toshiba Corporation Image forming apparatus
US4551005A (en) * 1982-04-16 1985-11-05 Ricoh Company Ltd. Method of forming images of sensor patterns in effecting image density control of electrophotographic copying apparatus
US4609280A (en) * 1983-10-31 1986-09-02 International Business Machines Corporation Xerographic apparatus and process with backside photoconductor imaging
US4652114A (en) * 1985-04-05 1987-03-24 Minnesota Mining And Manufacturing Company Electrophotographic copying apparatus and process
US4664504A (en) * 1983-01-20 1987-05-12 Tokyo Shibaura Denki Kabushiki Kaisha Image forming apparatus
US4769676A (en) * 1986-03-04 1988-09-06 Kabushiki Kaisha Toshiba Image forming apparatus including means for removing residual toner
US4800147A (en) * 1987-08-03 1989-01-24 Xerox Corporation Xerographic process without conventional cleaner
US4945388A (en) * 1988-09-20 1990-07-31 Minolta Camera Kabushiki Kaisha Method and apparatus for cleaning a color image forming apparatus by sticking developer on the photoconductor without forming an image
US5122838A (en) * 1989-05-31 1992-06-16 Kabushiki Kaisha Toshiba Image forming apparatus for developing a latent image on an image carrying body with a one component developing agent and simultaneously removing residual developing agent from the image carrying body
DE4204470A1 (de) * 1991-02-15 1992-08-20 Toshiba Kawasaki Kk Elektrostatographisches geraet
US5148219A (en) * 1989-05-31 1992-09-15 Kabushiki Kaisha Toshiba Image forming apparatus with developing and cleaning system
US5396317A (en) * 1990-02-07 1995-03-07 Minolta Camera Kabushiki Kaisha Magnetic particle-containing member for use in copying machine

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US3472657A (en) * 1965-04-30 1969-10-14 Xerox Corp Xerographic development method and apparatus
US3484265A (en) * 1966-07-21 1969-12-16 Xerox Corp Transversely reciprocating fluidized bed development method
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US2573881A (en) * 1948-11-02 1951-11-06 Battelle Development Corp Method and apparatus for developing electrostatic images with electroscopic powder
US2756676A (en) * 1953-05-04 1956-07-31 Haloid Co Method for the production of electrophotographic prints
US2911944A (en) * 1954-09-16 1959-11-10 Haloid Xerox Inc Xerographic development apparatus
US2956487A (en) * 1955-03-23 1960-10-18 Rca Corp Electrostatic printing
US2874064A (en) * 1955-05-16 1959-02-17 Haloid Xerox Inc Xerographic cleaner
US2959153A (en) * 1955-12-21 1960-11-08 Ibm Xerographic image developing apparatus
US2880699A (en) * 1957-10-21 1959-04-07 Haloid Xerox Inc Xerographic development
US3008826A (en) * 1958-03-06 1961-11-14 Xerox Corp Xerographic development
US3157546A (en) * 1960-04-19 1964-11-17 Xerox Corp Image transfer
US3257223A (en) * 1962-11-01 1966-06-21 Xerox Corp Electrostatic powder cloud xerographic development method and apparatus
US3424131A (en) * 1964-09-30 1969-01-28 Xerox Corp Electroded cascade development system
US3472657A (en) * 1965-04-30 1969-10-14 Xerox Corp Xerographic development method and apparatus
US3424615A (en) * 1966-01-03 1969-01-28 Xerox Corp Method and apparatus for cleaning xerographic plates
US3503776A (en) * 1966-02-21 1970-03-31 Xerox Corp Xerographic development
US3484265A (en) * 1966-07-21 1969-12-16 Xerox Corp Transversely reciprocating fluidized bed development method
US3412710A (en) * 1966-10-11 1968-11-26 Xerox Corp Cleanup electrode
US3520604A (en) * 1967-10-16 1970-07-14 Addressograph Multigraph Photoelectrostatic copier

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783818A (en) * 1970-12-26 1974-01-08 Fuji Xerox Co Ltd Electrophotographic developing process
US4330199A (en) * 1972-04-13 1982-05-18 Canon Kabushiki Kaisha Electrophotographic device
US3865080A (en) * 1973-01-17 1975-02-11 Xerox Corp Toner pickoff apparatus
US3851962A (en) * 1973-08-29 1974-12-03 Savin Business Machines Corp Electrostatic hold down apparatus
US3921577A (en) * 1974-05-28 1975-11-25 Xerox Corp Magnetic development units
US4063811A (en) * 1975-04-11 1977-12-20 Minolta Camera Kabushiki Kaisha Electrophotographic copier
US4265998A (en) * 1979-11-13 1981-05-05 International Business Machines Corporation Electrophotographic photoreceptive background areas cleaned by backcharge process
US4470693A (en) * 1982-01-11 1984-09-11 Pitney Bowes Inc. Self-cleaning xerographic apparatus
US4540274A (en) * 1982-01-18 1985-09-10 Toshiba Corporation Image forming apparatus
US4551005A (en) * 1982-04-16 1985-11-05 Ricoh Company Ltd. Method of forming images of sensor patterns in effecting image density control of electrophotographic copying apparatus
US4500198A (en) * 1982-12-10 1985-02-19 International Business Machines Corporation Multiple roller magnetic brush developer having development electrode voltage switching
US4843424A (en) * 1983-01-20 1989-06-27 Tokyo Shibaura Denki Kabushiki Kaisha Reverse developing image forming apparatus with disturbing means
US4664504A (en) * 1983-01-20 1987-05-12 Tokyo Shibaura Denki Kabushiki Kaisha Image forming apparatus
US4727395A (en) * 1983-01-20 1988-02-23 Tokyo Shibaura Denki Kabushiki Kaisha Reverse developing image forming apparatus with small drum
US4534641A (en) * 1983-10-31 1985-08-13 Xerox Corporation Charge erase device for copying or reproduction machines and printers
US4609280A (en) * 1983-10-31 1986-09-02 International Business Machines Corporation Xerographic apparatus and process with backside photoconductor imaging
US4538900A (en) * 1983-11-09 1985-09-03 Ricoh Company, Ltd. Electrophotographic copying apparatus including drum conditioning apparatus and method
US4652114A (en) * 1985-04-05 1987-03-24 Minnesota Mining And Manufacturing Company Electrophotographic copying apparatus and process
US4769676A (en) * 1986-03-04 1988-09-06 Kabushiki Kaisha Toshiba Image forming apparatus including means for removing residual toner
US4800147A (en) * 1987-08-03 1989-01-24 Xerox Corporation Xerographic process without conventional cleaner
US4945388A (en) * 1988-09-20 1990-07-31 Minolta Camera Kabushiki Kaisha Method and apparatus for cleaning a color image forming apparatus by sticking developer on the photoconductor without forming an image
US5122838A (en) * 1989-05-31 1992-06-16 Kabushiki Kaisha Toshiba Image forming apparatus for developing a latent image on an image carrying body with a one component developing agent and simultaneously removing residual developing agent from the image carrying body
US5148219A (en) * 1989-05-31 1992-09-15 Kabushiki Kaisha Toshiba Image forming apparatus with developing and cleaning system
US5396317A (en) * 1990-02-07 1995-03-07 Minolta Camera Kabushiki Kaisha Magnetic particle-containing member for use in copying machine
DE4204470A1 (de) * 1991-02-15 1992-08-20 Toshiba Kawasaki Kk Elektrostatographisches geraet
US5253023A (en) * 1991-02-15 1993-10-12 Kabushiki Kaisha Toshiba Electrostatographic apparatus without cleaner

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BE743661A (es) 1970-06-24
FR2027431A1 (es) 1970-09-25
GB1296997A (es) 1972-11-22
DE1965293A1 (de) 1970-09-17

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