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
  • G03G15/22—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20
  • G03G15/32—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the charge pattern is formed dotwise, e.g. by a thermal head
  • G03G15/321—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the charge pattern is formed dotwise, e.g. by a thermal head by charge transfer onto the recording material in accordance with the image
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/02—Charge-receiving layers
  • G03G5/0202—Dielectric layers for electrography

Definitions

• This invention relates to electrographic printing and, more specifically, to a novel process for electrographic printing on a plurality of substrates.
• This application is a Continuation-In-Part application of Parent Application Serial No. 08/014,744 filed in the U.S. Patent and Trademark Office on February 8, 1993.
• xerographic or xerography which involves placing a uniform charge on a photoconductive element, selectively exposing this charge to light in image configuration to form a latent image, applying a marking material to the latent image and subsequently transferring the developed image to a receiving sheet such as bond paper or the like, and the image fixed by heat or pressure.
• This basic xerographic process is disclosed in U.S. Patents to Carlson 2,297,691; Middleton 2,663,636; Bixby 2,970,906; Schaffert 2,576,047 and Middleton and Reynolds 3,121,006.
• This xerographic process is limited to functional photoconductive materials that will hold a charge in the dark and have the ability to have charge dissipation upon exposure. Only a limited number of materials having desirable photoconductive properties have been found commercially acceptable such as selenium, zinc oxide, cadmium sulfate and a few other inorganic and organic materials.
• electrography Another electrostatic imaging system heretofore used is called electrography.
• a dielectric material is charged in image configuration by various means such as print heads, electron beams, electronic stencils or shaped masks. While photoconductive insulators will only hold an electrical charge in the dark, dielectrics can hold an electrical charge in the presence of visible light which makes them more practical for various commercial uses such as in manufacturing processes.
• There are various patents and publications which specifically define the parameters of electrography such as Principles of Non-Impact Printing by Jerome S. Johnson, Palatino Press, 18792 Via Palatino, Irvine, CA 92715 and U.S. Patent Nos. 5,025,273; 5,124,730; 5,126,769 and 5,162,179.
• the electrographic process also has some inherent drawbacks.
• One such drawback is that the dielectric surface layer must have a capacitance per unit area of at least 200 picofarad (PF) per cm squared and a resistivity of at least 10 14 ohms centimeters bulk resistivity in order to properly function.
• PF picofarad
• a further disadvantage of prior art electrographic systems is that the dielectric paper structure used comprises a conducting layer having a resistivity of about 10' ohms centimeters having coated thereon an insulating dielectric layer of about 10 14 ohms centimeters resistivity. The manufacture of this dielectric paper is a relative complex
• Another object of this invention is to provide an electrographic imaging process which enables the use of a multitude of charge retentive substrates not heretofore available in electrography.
• Still another object of this invention is to provide a process for electrographic imaging using specific process parameters for successful operation and results.
• Yet another object of this invention is to provide an electrographic process which does not require a two layer substrate consisting of a dielectric layer of limited resistivity and a conducting layer also of restricted resistivity.
• Another still further object of this invention is to provide a process with novel process parameters that will allow substrates heretofore not usable in electrography to be now used with good results.
• D is equal to the distance between latent image deposition and completion of development in arbitrary units
• TC is the time constant of the charge retentive substrate in seconds
• S is the speed in the system of the substrate in the same units as D per second;
• QF is equal to the number of time constants of the substrate used in the process.
• process parameters are used to provide a means of depositing a latent electrostatic image on a charge retentive substrate (such as plain paper) and developing or toning the latent charge created within a time which is less than that to substantially discharge a significant portion of the latent electrostatic image through any resistive paths in the substrate.
• Plain paper is one of the charge retentive substrates usable in the process of this invention.
• the term "plain paper” is meant to include any paper or paper equivalent which is of substantially uniform composition and particularly devoid of a layered structure; i.e. a dielectric layer and a conducting layer.
• An example of such a plain paper is xerographic bond paper used in
• paper we mean any thin, flexible material that may be made into paper-like sheets which exists, at least, to serve the function of conveying printed or written information.
• the paper is temporarily in contact with a conductive carrier.
• the "plain paper” could have permanent metalized backing if desirable. This metalized backing would act as the conductive carrier for the plain paper charge retentive surface.
• a paper substrate containing one or more thin layers of polymeric films such as those prepared by extrusion coating and/or by film lamination are useful in this invention.
• multi-layered paper composites consisting of cellulosic layers, polymeric films including metalized films and/or metallic foils can be used.
• substrates which consist of combinations of natural and man-made fibers, including organic and inorganic fibers, coated and uncoated, are likely alternates to plain paper as long as they meet the guidelines for forming an image in an electrographic system according to the formula and description and claims of this invention.
• the function of the conductive carrier is to provide an electrical return path and to set the absolute electrical
• any prior art dielectric paper used in prior art electrographic processes or any conventional printable substrate with a dielectric surface including polymeric substrates with or without metalized backings may also be used in this invention provided the process parameters of this invention are followed. In this invention, all of these above-described substrates function as the dielectric capable of retaining an electrostatic latent image or function as the "charge retentive substrate".
• the latent electrostatic image may be formed by any number of conventional means such as with an ionographic print head of the type manufactured by Delphax, an ion pin array such as that manufactured by KCR, an electron beam, electronic stencils or shaped masks, indirect charge transfer means, and any other means which are capable of depositing electronic charge at a rate sufficiently high to charge the paper to potentials that enable good development of the latent image with the desired toners.
• Development or toning of the latent electrostatic image may be accomplished with any of the conventional powder or liquid toners presently used in electrographic or electrophotographic printing or copying or any toner developed for a specific implementation of this invention.
• the required properties such as with an ionographic print head of the type manufactured by Delphax, an ion pin array such as that manufactured by KCR, an electron beam, electronic stencils or shaped masks, indirect charge transfer means, and any other means which are capable of depositing electronic charge at a rate sufficiently high to charge the paper to potentials that enable good development of the latent image with
• toner are only that is have a charge opposite to that deposited on the substrate, having a charge to mass ratio that will cause the required optical density to be developed according to the charge deposited and adhere to the paper in such a way as to give the imaged paper the required performance characteristics for its end application.
• Other toner parameters will be required according to the specific implementation of the invention depending upon, for example, whether a single component or two component powder developer system is used.
• the fixing process may be performed by any of the conventional approaches such as thermal fixing using a heated roller or flash fusing with a flash lamp; pressure fusing by applying pressure across the paper in a nip between two rollers; chemical fusing by exposing the toner to a solvent vapor or designing the toner to chemically bond to the paper; and/or by any other means by which the toner is made to be permanently attached to the paper.
• the fixing process is not a necessary step in this invention although it is likely to be included in most implementations of it.
• TC electrical time constant of the paper.
• the definition of the electrical time constant, TC is the time for which the voltage applied to a dielectric will discharge to a
• the time constant can be calculated as follows:
• QF determines the percentage of the charge (or voltage) that is desired to have remaining in the dielectric due to self discharge prior to completing development of the latent electrostatic image.
• the paper has both electrical dielectric and resistive properties.
• the dielectric properties enable a latent electrostatic image to be deposited and retained on the paper.
• the resistance properties determine the rate that the charge of the latent electrostatic image is bled away from the original location of its deposition.
• a high resistivity is preferable to minimize the rate of charge bleed of the latent electrostatic image.
• the product of the dielectric constant of the paper and its resistivity determines the time constant of the paper.
• a large time constant is preferred to allow longer periods and/or larger distances to be used in the charge deposition and development process. Actually, there are two time constants that apply; the bulk time constant associated with the diffusion of charge through the bulk of the paper and the surface time constant associated with the diffusion of charge on the surface of the paper.
• the time constant can be either or both of the bulk time constant and surface time constant.
• the time constant should be sufficiently long such that minimal discharge of the electrostatic image occurs between the time the charge is deposited and the image is fully developed. This may range from one time constant for black/white images to one-sixth or less time constant for the highest quality continuous color images.
• the relationship between the time the paper is charged and fully developed sets the dimensions and specific relationships of the printer. For example, for a one second time constant paper and a distance between the head and end of the development station of one foot, a 60 feet per minute speed is required for one time constant black/white or binary printing. For the same parameters but for the very highest quality gray-scale image where minimal charge leakage can be tolerated (0.17 time constants), a higher speed of 360 feet
• Typical 3 mil thick paper with a dielectric constant of approximately 5 will have a capacitance of approximately 58 picofarads (PF) per square centimeter.
• PF picofarads
• a bulk resistivity of 2 x 10 12 ohms centimeters will be required.
• Bulk resistivity of typical electrographic paper is 10 12 ohms centimeters at a nominal relative humidity of 50%.
• An increase in the bulk resistivity can be accomplished by heating the paper to reduce its water content.
• the paper can be loaded with a hydrophobic polymer or a surfactant which causes the paper to be hydrophobic.
• a paper which uses either of these latter approaches or others to increase the resistivity should be relatively easy to obtain from a paper manufacturer at prices which are substantially the same as standard paper prices.
• high quality continuous tone color images (0.33 time constants) can be achieved at 250 feet per minute with approximately 7.5 inches between deposition of the charge and completion of development.
• Papers with bulk resistivity of 10 14 ohms centimeters are achievable when loaded and/or coated with polymers and/or pigments.
• Commercially available papers with these resistivities in the dielectric layer of a two layer paper are typically used in electrostatic printers and plotters. Using paper with this resistivity, the highest
• quality continuous tone color images (0.17 time constant) can be achieved at 60 feet per minute with approximately 9 inches between deposition of the charge and completion of development.
• D TC x S x QF
• D is equal to the distance between latent image charge deposition and development in arbitrary units
• TC is the time constant of the paper in seconds
• S is the speed of the paper web in the same units as D per second
• QF is equal to the number of time constants of the paper used in the process.
• One time constant yields a loss of 37% of the charge during the process, adequate for binary printing processes.
• One third time constant yields a loss of 5% of the charge during the process, adequate for continuous tone color printing processes where absolute color rendition is not important.
• One sixth time constant yields a loss of 0.25% of the charge during the process, adequate for continuous tone color printing processes where absolute color rendition is essential.
• the non-impact printer apparatus of this invention comprises a system having in combination a substrate supply station, an imaging station having means to deposit a latent electrostatic image upon a charge retentive substrate, a developing station, a separation station, and means for controlling image development of said substrate with a distance in said system. This distance is determined from the formula:
• D is equal to the distance between latent electrostatic image deposition and completion of development in arbitrary units
• TC is the time constant of the charge retentive substrate in seconds
• S is the speed in the system of the substrate in the same units as D per second;
• QF is equal to the number of time constants of the substrate used in the process.
• the distance D can be adjusted by conventional means including mechanical means according to the needs of the process, for example, to compensate for the speed S of the system or the resistivity or capacitance of the printable substrate.
• the means for controlling the image development can be any suitable means such as a motor controlled positioner or adjuster including optically or servo controlled positioners.
• Figure 1 is a description of the electrographic printing process of this invention in block diagram form.
• Figure 2 is a schematic diagram of a print engine which implements the printing process of this invention.
• Figure 3 is an expansion of the schematic diagram of the print engine which shows the variable distance between the position of charge deposition and the position of development of the resulting latent electrostatic image to make it visible.
• Figure 4 is a schematic diagram of the charge associated with the latent electrostatic image on the paper and the charge leakage paths.
• the first stage 1 is that of having an image in some electronic form.
• the image may be stored as a series of bytes in semiconductor memory.
• Conversion of the electronically stored information to a latent electrostatic image stored on the paper occurs by the step 2 of selectively depositing charge on the paper according to the electronically stored image. This may be accomplished by any suitable means including the means previously discussed.
• the requirements of the charge deposition process are that it be capable of delivering charge to the paper at a sufficiently high rate so as to be able to form electrostatic latent images which can be developed with suitable toners.
• the charge deposition means must be capable of depositing 9.525 microCoulombs of charge per second per square centimeter.
• This process has many variations which are applicable and well known in the art. Having completed the second step and reached the third stage 5, where the developed visible image has been created on paper, no further stages or processing steps are required in the process. However, an optional fixing step may be included if it is desired to permanently affix the visible image to the paper.
• This two step process is very simple, much more so than for electrophotographic printing which requires, with plain paper, at least the additional steps of conversion of electrical information into optical information and transferring of the developed image to the paper.
• the advantage of such a simple electronic printing process is that it can easily be made highly reliable thereby enabling the use of it in operations where reliability of the process is of high importance such as in manufacturing or volume printing.
• FIG. 2 a printing system is shown which is indicative of one possible implementation of the invention.
• Supply roll 6 provides plain paper 7 to the entrainment roller 8 which temporarily attaches the paper 7 to the conductive drum 9.
• An optional erasure station 10 discharges or pre-charges the exposed surface of the paper 7 to a known uniform potential.
• the erasure station 10 is used if the electronically controlled latent image charge deposition station 11 has electrical characteristics of a current source or very high impedance. If, however, the electronically controlled latent image charge station 11 has electrical characteristics of a voltage source or very low impedance, the erase station 10 may not be necessary.
• Image deposition 11 and development station 12 can be movable in relationship to each other to accommodate different line speeds or other substrates 7.
• the paper 7 is advanced through the electronically controlled latent image charge deposition station 11 which deposits the latent electrostatic image on the paper.
• the paper is further advanced through the development station 12 which develops the latent electrostatic image with toner and turns it into a visible image.
• the paper is still further advanced through entrainment roller 13 which, in conjunction with entrainment roller 8, maintains attachment of the paper to the conductive drum 9.
• Entrainment roller 13 may also optionally fix the developed or toned image to the paper, for example by providing a high pressure nip between it and
• conductive drum 9 and/or by heating the image thereby fusing it with the paper.
• the imaged paper 14 is advanced to take-up roll 15 upon which it is stored for later use.
• the supply and take-up rolls, entrainment rollers and conductive drum are operatively advanced in conjunction with the paper by any suitable means at a speed which will prevent substantial discharge of the latent electrostatic image between the charge deposition station 11 and the development station 12.
• the printing system shown in Figure 2 is representative of only one possible implementation of the invention. Substantial modifications of the printing system shown in Figure 2 are possible without departing from the spirit or scope of the invention.
• a conductive belt or other carrier may be used in order to optimize the utilization of space and/or energy in the system.
• Figure 3 shows a conductive drum 16, electronically controlled latent image charge deposition station 17 and development station 18 which are identical to conductive drum 9, electronically controlled latent image deposition station 11 and development station 12 in Figure 2.
• the distance “D” shown between the latent image deposition station and the development station may be variable and is the distance between the deposition of the charge which forms the latent image and the development of the latent image. This distance “D” is determined by the electrical time constant of the paper and the speed at which the paper is advanced between the latent image charge deposition station and the development station. In this invention, a requirement is that the latent electrostatic image remains substantially undischarged as the paper is advanced from the deposition station to the development station.
• substantially undischarged is meant that the amount of charge in the latent image remaining at the development station is a significant percentage of the charge that was originally deposited at the charge deposition station. Important to this definition is the expectation that non-uniform discharging will take place; that is, some areas of the paper will discharge faster than other areas and, depending upon the application, this will show up as a reduction in the quality of the image. The degree to which this can be tolerated is dependent upon the final application. In general, it is believed that a discharging
• the maximum distance “D” that can be used in this invention is that distance for which during the movement of paper from the charge deposition station to the development station, the latent image remains substantially undischarged.
• Figure 4 shows charge comprising the latent image stored on the paper which is used as a dielectric.
• the solid circular lines above the paper are equipotential lines or points at which the potential is constant. These are similar to the lines of a contour map which indicate the areas of constant height.
• the dotted vertical lines are
• a plain paper of the type used in this invention is of substantially uniform composition and will tend to have resistivities that are of equal value in the horizontal and vertical directions. Near the surface of the paper the resistances may be different as a result of contamination that occurs during handling or surface treatments used to aid in handling. However, paper with surface treatments designed to equalize and/or increase the bulk and surface resistances are included in this invention.
• the paper used in this invention does not require a construction which is designed to cause it to have substantially higher resistivity on one surface as opposed to the other or a substantially higher surface resistivity than bulk resistivity in order to cause a multiple layer electrical structure to exist where part of the structure is for purposes of acting as a dielectric and a separate part of the structure is for purposes of acting as a conductor.
• Xerographic bond paper with a thickness of 0.003 inches and resistivity of 10 12 ohms centimeters is supplied from a feed roll to an electrically conductive stainless steel belt which is maintained at ground potential (zero volts) .
• the paper is attached to the belt in a nip created by a roller beneath the conductive belt and a second roller above the belt and paper.
• the second roller is heated to a temperature to increase the surface resistivity of the paper to a value similar to the bulk resistivity.
• the second roller is also held at an electrical potential of zero volts to maintain as little charge on the paper as possible.
• the belt with the paper attached is advanced to electrostatic latent image formation station which consists of a Delphax S3000 ionographic print cartridge and supporting drive electronics.
• the electrostatic imaging station is located at a third roller around which the belt and attached paper are made to go around.
• the mounting of the imaging station is such that a spacing between the top surface of the paper and the screen of the cartridge is maintained accurately at 0.010 inches.
• the screen electrode is maintained at -650 volts relative to the belt thereby maintaining a field to accelerate the charge from the ionographic print cartridge.
• the RF lines of the cartridge are driven with an AC waveform of 2500 volts peak to peak as is normal practice for this type of cartridge and at a frequency of 1.25 MHz. However, only four RF cycles are used for each pixel as opposed to
• Charge is deposited imagewise on the paper creating a binary electrostatic image on the paper with a maximum apparent surface voltage of -250 volts.
• the electrostatically imaged paper and belt are advanced to a development station, the operative portion of which is ten inches from the ionographic cartridge.
• the development station comprises a toner reservoir in which single component toner of the type used by Delphax printers is stored, a rotating magnetic brush and a doctor blade used to set the height of the toner on the magnetic brush.
• the magnetic brush is made to be at zero volts relative to the belt and in close proximity to the electrostatically imaged paper such that toner particles are selectively removed from it by the electrostatic forces of the latent electrostatic image.
• the belt and the attached visibly imaged paper is next advanced to a fixing station.
• the fixing station comprises a xenon bulk and power supply.
• the xenon bulb is flashed with sufficient power and time to supply the energy required to melt the toner into the paper but at low enough power to ensure that the paper is not scorched.
• the belt and permanently imaged paper are advanced to a fourth roller. At this roller the paper is separated from the belt and wound onto a take-up roll.
• the belt moves back to the first roller.
• the belt is always taut because of the tension supplied by the rollers
• the paper is tightly attached to the belt as described because it is always under tension applied between the feed and take-up rolls.
• the belt and paper are advanced together at a continuous speed of 125 feet per minute. All rollers move at the same speed as the belt and paper. This speed and the distance between the ionographic printing cartridge and development station ensures that the latent electrostatic image created on the paper is developed prior to the decay of the electrostatic image associated with one time constant of the paper. High quality black/white binary images are created under these conditions.
• a magazine quality paper with a width of 9.5 inches and thickness of 0.003 inches, a smooth finish and high clay content is used.
• the clay used in the paper is calcined clay in order to achieve a bulk resistivity of 10 13 ohms centimeters and a bulk time constant of at least 4.5 seconds. It is supplied from a feed roll to an electrically conductive drum which is maintained at ground potential (zero volts) .
• the paper is attached to the drum in a nip created by the drum and a first roller above the drum and paper. The first roller is heated to a temperature which increases the surface resistivity of the paper to a value similar to its bulk resistivity.
• the first roller is also held at an electrical potential of zero volts to maintain as little charge on the paper as possible.
• the drum with the paper attached is advanced to an erasure station which removes any residual charge remaining on the paper.
• the erasure station is an AC corotron similar to that used in the erasure station of Delphax printers. After complete discharge of the paper the paper and drum are together advanced to the electrostatic latent image formation station. This consists of a cathode ray tube with a very thin metallic film window which allows a portion of the electron beam created in the tube to be projected beyond the tube.
• cathode ray tube and electrostatic latent image creation system is described in an article titled "A Novel Electron-Beam Printing Technique” written by Guillemot, Poussier and Roche and published by the SPSE in the advanced printing of paper summaries for the Fourth International Congress on Advances in Non-Impact Printing Technologies” which was held in New La, Louisiana on March 20-25, 1988 and is incorporated into this example by reference.
• the electrical potential of the window of the CRT (cathode ray tube) is made to be at -650 volts relative to the drum and the distance between the window and the drum is made to be 0.010 inches.
• the electron beam current created by the CRT is set to be a maximum of -22 microAmperes , thus generating a maximum apparent surface potential on the paper of -250 volts at the operative paper
• the electron beam current from the cathode ray tube is linearly modulated according to the desired optical density of the developed image such that maximum current corresponds to maximum optical density.
• the electrostatically imaged paper and drum are advanced to a development station, the end of the operative portion of which is within 18 inches of the window of the CRT.
• the development station comprises a toner reservoir in which liquid toner is stored; a series of six closely spaced rollers of 0.75 inches diameter, the surfaces of which are made to be parallel to and at a distance of 0.010 inches from the paper on the drum and held at an electrical potential of zero volts; a pump which pumps toner from the reservoir to the interfaces between the rollers and the paper; a catch basin which catches excess toner from the rollers and returns it to the reservoir; and a last reverse roller parallel to the paper and as close as possible to it which skims off the excess liquid on the paper.
• the design of this development station is similar to the design of the Savin 7450 photocopier and embodies the same principles of design.
• the use of liquid toners and this configuration of development station allows for nearly complete cancellation of the latent electrostatic image by the toner particles resulting in very high quality continuous tone development characteristics.
• the drum and attached visibly imaged paper is next advanced to a fixing station.
• the fixing station
• This type of fixing roller is similar to that used in a number of existing photocopiers and laser printers.
• the temperature of the roller is high enough to transfer sufficient energy into the toner to cause it to melt and stick on the surface of the paper.
• the drum and permanently imaged paper are advanced to a third separation roller. At this roller the paper is separated from the drum and wound on to a take-up roll. The paper is tightly attached to the drum because it is always under tension applied between the feed and take-up rolls.
• the drum and paper are advanced together at a continuous speed of 125 feet per minute. All rollers move at the same speed as the drum and paper.
• a photographic quality color printer is made by cascading four drums and associated stations using magenta, yellow, cyan and black toners.
• a magazine quality paper (clay coated paper) with a width of 9.5 inches and thickness of 0.003 inches, a smooth finish and high clay content is used.
• the clay used in the paper is calcined clay in order to achieve a bulk resistivity of 10 13 ohms centimeters and a bulk time constant of at least 4.5 seconds. It is supplied from a feed roll to an electrically conductive drum which is maintained at ground potential (zero volts).
• the paper is attached to the drum in a nip created by the drum and a first roller above the drum and paper. The first roller is heated to a temperature which increases the surface resistivity of the paper to a value similar to its bulk resistivity.
• the second roller is also held at an electrical potential of zero volts to maintain as little charge on the paper as possible.
• the drum with the paper attached is advanced to an erasure station which removes any residual charge remaining on the paper.
• the erasure station is an AC corotron similar to that used in the erasure station of Delphax printers. After complete discharge of the paper the paper and drum are together advanced to the electrostatic latent image formation station.
• This consists of a special purpose ionographic print cartridge and supporting electronics.
• the ionographic print cartridge is essentially of the same design as other Delphax ionographic print cartridges but has been designed to have 16 RF lines and optimized for high frequency operation with an RF
• a binary weighting factor for the charge packets allow the binary number representing the desired density to be used directly in modulating the state of the finger drive waveform. 20 RF cycles at 10 MHz are used per RF line where two cycles are used for each of the eight bits representing the desired density and four cycles are used for ensuring the envelope amplitude of the RF drive signal.
• the sequencing of the RF lines is such that an operative paper velocity of 500 feet per minute is maintained. Charge is deposited imagewise on the paper creating an essentially continuous tone electrostatic image on the paper with a maximum apparent surface voltage of -250
• the electrostatically imaged paper and drum are advanced to a development station, the end of the operative portion of which is within 145 inches of the special purpose ionographic print cartridge.
• the development station comprises a toner reservoir in which liquid toner is stored; a fine pitch screen made to be essentially parallel to and a distance of 0.020 inches from the paper and entrained around two rollers which move it at a velocity somewhat slower than the velocity of the paper, all of which are held at an electrical potential of zero volts; a pump which pumps toner from the reservoir to the interfaces between the screen and the paper a continuous supply of fresh toner between the screen and paper; a catch basin which catches excess toner from the screen and returns it to the reservoir; and a reverse roller parallel to the paper and as close as possible to it which skims off the excess liquid on the paper.
• this development station ensures the maximum availability of undepleted toner and highest field strength over an area to motivate development thereby providing for high speed development in a development station of small size.
• the use of liquid toners and this configuration of development station allows for nearly complete cancellation of the latent electrostatic image by the toner particles resulting in very high quality continuous tone development characteristics.
• the drum and attached visibly imaged paper is next advanced to a fixing
• the fixing station comprises a xenon bulb and power supply.
• the xenon bulb is flashed with sufficient power and time to supply the energy required to melt the toner onto the paper but at low enough power to ensure that the paper is not scorched.
• the drum and permanently imaged paper are advanced to a second separation roller. At this roller the paper is separated from the drum and wound onto a take-up roll. The paper is tightly attached to the drum because it is always under tension applied between the feed and take-up rolls. As previously described, the drum and paper are advanced together at a continuous speed of 500 feet per minute. The rollers move at the same speed as the drum and paper.
• a magazine quality color printer is made by cascading four drums and associated stations using magenta, yellow, cyan and black toners.
• a high quality grade of cellulosic paper having a width of 6.0 inches and a nominal thickness of 0.005 inches was used.
• the surfaces of both sides of the paper contain a high concentration of polyethylene resin which can be either applied "on-machine" during sizing of
• the resulting surfaces of both sides of the web of paper were smooth and comparable to some of the highest quality printing papers available.
• the surface coating contained mainly Ti02 (rutile) and barium sulfate as fillers in the range of 5.0%.
• the opposite side of the paper can be identical in filler content, however, the polyethylene coating on this side contained no filler.
• the coating on both sides measured between 0.5 to 1.0 mils in thickness.
• the dual-sized cellulosic paper was dispensed from an unwind stand and conveyed by a stainless steel belt.
• the tension of the paper against the positively driven belt insured intimate contact between the backside of the paper containing the unfilled polyethylene surface coating and the moving belt which was at ground potential.
• the paper plus belt were conveyed beneath an ac discharge corona which neutralized the surface of the paper plus applied a slight positive charge to eliminate background in the non-image areas.
• a novel ionographic print head manufactured by Delphax Systems Inc. was used to apply charge in an image-like pattern to the coated side of the paper containing the fillers. It was operated by an electronics package comprising an rf drive circuit described in Bowers,
• the ionographic print head was spaced 10 mils above the surface of the moving paper and belt. Data was supplied to the print head from an image buffer which contained a digital representation of the pattern to be electronically imaged on the coated paper surface. Using pulse width modulation techniques, bursts of negative charge were deposited in the form of the original pattern with 127 levels of charge control. Pulse width modulation of the ionographic head resulted in negative charge being deposited on the surface of the paper in the form of the original pattern.
• the paper was then conveyed through a platen-like developer with black liquid toner DDB-42 as supplied by Hilord Chemical Corporation.
• the toner was at approximately 1% concentration in Isopar G carrier.
• Full development of the multi-shade latent image was accomplished in black color where the optical density ranged from a value of zero (0) to 1.4 as measured with an X-Rite Densitometer, Model 404, manufactured by X-Rite, Grandville, Michigan.
• the Isopar G was evaporated from the toned surface and the image fused using conventional toner fusing techniques. The toned image was then re-rolled. Alternately, multiple colors can be applied on top of the first image and sequential images to produce a
• the second pass through the printer consisted of dispensing the previously imaged and toned paper containing the black pattern from an unwind stand and putting this side against the moving stainless steel belt. The same steps were repeated for the non-imaged side of the paper. There was sufficient tension between the previously imaged and toned side of the paper and the moving belt to provide an excellent ground plane for application of the second latent image to the backside of the paper containing the unfilled polyethylene surface coating.
• This example demonstrates the printing on both sides of a paper web using two separate passes using the same printing apparatus having a stainless steel belt. Each pass through the printer could apply multiple images to both sides of the paper and could involve one or more stations
• Both sides of the paper can be imaged and toned with two in-line printing presses containing stainless steel belts, one press printing each side of the paper. Also, a sheet of paper could be imaged and developed using one or more stations where a suction roll is the conductive substrate.
• the invention is not limited to this sequence of steps and the stainless steel belt can be replaced with any suitable conductive means which provides an appropriate ground beneath the latent image formation station.
• a latent image formation station, developer and Isopar G removal system for each color can be arranged alternately on each side of the moving web to produce images simultaneously on both sides of the paper web.
• the ground plane beneath the image formation unit could be conductive rollers.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Combination Of More Than One Step In Electrophotography (AREA)
• Photoreceptors In Electrophotography (AREA)
• Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
• Electrostatic Charge, Transfer And Separation In Electrography (AREA)

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• 1996
  • 1996-08-12 WO PCT/IB1996/000892 patent/WO1998007074A1/en not_active Application Discontinuation
  • 1996-08-12 AU AU67514/96A patent/AU6751496A/en not_active Abandoned
  • 1996-08-12 EP EP96927821A patent/EP0919016A4/de not_active Withdrawn
  • 1996-08-12 CA CA002263159A patent/CA2263159A1/en not_active Abandoned
  • 1996-08-12 JP JP51531997A patent/JP2001509906A/ja active Pending

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