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
  • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
  • G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
  • B41J2/447—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources
  • B41J2/4476—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources using cathode ray or electron beam tubes
• • 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
  • G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
  • G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
  • G03G15/1625—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer on a base other than paper
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G2215/00—Apparatus for electrophotographic processes
  • G03G2215/06—Developing structures, details
  • G03G2215/0602—Developer
  • G03G2215/0626—Developer liquid type (at developing position)
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2217/00—Gas-filled discharge tubes
  • H01J2217/38—Cold-cathode tubes
  • H01J2217/49—Display panels, e.g. not making use of alternating current
  • H01J2217/492—Details
  • H01J2217/49207—Electrodes

Definitions

• the invention concerns a process for the electrostatic printing of functional materials configured as liquid toners on relatively thick glass plates for various manufacturing applications.
• Field emission displays are a relatively new technology. They consist of an array of field emission points in a vacuum, spraying electrons onto a phosphor screen. With three color dots on the screen and addressibility of the emitting points, one has a full color display.
• the Plasma displays have been produced for about 25 years, mostly as a single color orange neon "glow discharge". In the last 10 years, UN light from this discharge has been "harnessed” to excite three color phosphors to produce a color plasma displays. 40" diagonal displays have been recently announced, but their cost is about $10,000.
• the reason for the small size/high cost of production are the currently used manufacturing techniques. These include: a. photolithography or the patterning of photo sensitive resists and the "washing" and etching processes that are attendant to them. b. the silk screen printing of relatively large area features (30 ⁇ or more) c. the low pressure sputtering processes for coating glasses with metals like aluminum or indium / tin oxide (ITO), a transparent electrode or dielectrics like SiO 2 . In all cases the process has many steps, many in which the glass has to be heated and then cooled back to room temperature before the next step. Each of these steps requires a large piece of capital equipment in a class 100 clean room whose capital cost is $500 per square foot for the room itself. The capital equipment runs the gamut from a $40,000 liquid etcher, or developer, to a $2.5M stepper to a $4M sputtering cluster (six to eight vacuum chambers that accept lm x lm glass).
• Electrostatic printing has been used for color proofing in Du Ponts EMP process during the late 1980's.
• Du Pont used the electrostatic printing which is described by Reisenfield in US No. 4,732,831. It used liquid toners that were transferred directly to a smooth, coated sheet of paper.
• the transfer of liquid toner, which is important to this invention, was disclosed by Bujese in US No. 4,879,184 and US No. 4,786,576. These documents teach the transfer of liquid toners across a finite mechanical gap, typically 50 ⁇ to 150 ⁇ . This technology has been applied where toner, with etch resist properties, was transferred to copper clad glass epoxy boards.
• the present invention teaches a technique for the electrostatic printing of functional materials on glass to produce various "microstructures" like ribs or electrodes, spacers, filters etc. by a copy machine type of device at rates from 0.1 to 1.0 m/sec. In some cases there is a later step of sintering or electroless plating, but this is "after the fact" in that dimensional accuracy was previously determined by the printing step done at room temperature.
• the functional materials include metals, dielectrics, phosphors, catalytic seed materials, etc. configured as liquid toners. Since the substrate material is glass it presents special requirements:
• liquid toners dispensers of solid particles; metal, glass, etc.
• Fig. 1 illustrates an overall mechanical schematic of the invention.
• Fig. 2 illustrates a detailed view of the nip between drum and glass.
• Figs. 3a-d illustrate the electrostatic printing plate and the four steps in the imaging process.
• Figs. 4a-c illustrate the progressive exposure of the electrostatic printing plate.
• Fig. 4d illustrates a plate exposed one quarter of its thickness.
• Figs. 5a-b illustrates the ideal and typical charge decay cures for the electrostatic printing plate.
• Figs. 6a-d illustrates the four typical corona devices used in copy machine and electrostatic printers.
• Figs. 7a-b illustrates the printing plate current versus voltage for smooth wire and pin array corona units respectively.
• Figs. 8a-b illustrates the printing plate current versus the voltage on the plate for dicorotrons and scorotons respectively.
• Fig. 9 illustrates the plate/glass layout with its equivalent circuit.
• Figs. lOa-b illustrate electrical changes induced in printing plate during the transfer step.
• Fig. 11 illustrates a mechanical schematic of a "flat” to "flat” printing apparatus.
• Fig. 12 illustrates a crossection of a typical AC plasma display panel.
• Figs. 13a-c illustrate detailed sequences of manufacturing steps in the production of critical features of the AC plasma display.
• Fig. 14a-c illustrates the "self-printing" of the black intermatrix of a color filter panel
• Fig. 14d illustrates the self-printing of a vacuum phosphor front panel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT During the course of this description, like numbers will be used to identify like elements according to the different views which illustrate the invention.
• Fig. 1 shows an overall mechanical schematic of the preferred embodiment.
• Drum 10 has a latent electrostatic image 13 on its surface 11. It is charged by sensitizing corona 12. If it is a photo sensitive surface it is exposed in an image wise fashion by LED/ strip lens assembly 14. Alternately it could compose an electrostatic printing plate as disclosed by Reisenfeld of US No. 4,732,831 where the image areas retain charge and the background areas discharge before the drum 10 rotates to the developer unit 16.
• the unit 16 is comprised of toner developer roller 18 that are splashed with liquid toner by pipe 20. They rotate in such a manner as to move in the same direction of the drum but typically at a relative velocity of 1.5 times.
• Reverse roller 22 rotates in a manner opposite the drum 10 and with a relative velocity of 3 times.
• this reverse roller 22 serves to scavenge excess toner liquid off the image surface 11 which also controls unwanted background.
• a corona unit 24 at roughly the 5 o'clock position serves to "compact” the toner image before transfer. This is also referred to as “depress” corona.
• Corona unit 30 charges the bottom surfaces of the glass 26.
• Wire 31 is raised to about 7 kilovolts grounded mechanical shutters 32 are adjustable to charge the glass 26 at the proper desired location to achieve optimum toner transfer.
• Corona unit 34 is an AC corona discharge to discharge the drum 10 before cleaning. Alternately this unit, or a second AC corona, may be located after cleaning unit 36. This first AC corona is not shown.
• Cleaning unit 36 typically consists of a squeegee roller 38 that does bulk, rough removal of residual toner, while wiper blade 40 does the final, complete cleaning of the drum surface 11. The drum 10 is now ready for the next image.
• Fig. 2 Here is shown an enlarged view of the drum 10, gap 42, glass structure 26 at the transfer point, nominally at 6 o'clock.
• the drum 10 is wet with liquid toner and residual diluent coming into the nip formed by drum 10 and glass 26.
• the glass is pre-wetted with clear diluent to ensure that the gap between drum and glass is filled with liquid. Metering of liquid on the drum and the pre-wetting liquid on the glass is not very precise so a wave of excessive liquid 44 builds up in the input to the nip. This is referred to, herein, as the Tsunami effect.
• the toner on the drum before transfer 50 needs to transfer to the glass in a location of low turbulence, about 6 o'clock.
• the amount of liquid between drum and glass is precisely determined by the gap which is between 50 ⁇ to 150 ⁇ and can be easily controlled to +/- 5 ⁇ with the "floating" techniques mentioned previously. Therefore a "film splitting" occurred as shown in Figure 2 not necessarily 50%/50% as suggested by this drawing. Actual values will depend on the surface energy of the drum surface (amorphous selenium or silicon or alternately a photopolymer) versus that of the glass.
• the film splitting point 46 is precisely defined and unchanging for particular materials and one gap setting while the wave front 44 is highly unstable and moves to the right from the beginning of the glass sheet to its end and can become quite violent and turbulent. Important features of the preferred embodiment are now evident:
• the actual transfer electric fields can be quite large as typical soda lime glass has substantial electrical conductivity (as much as 10 "10 mho/cm) so the corona charge migrates through the glass to near the transfer point. As the drum and glass surface start moving away for each other very high electric fields can be generated.
• these "image” forces are significantly smaller than the strong binding forces between surface toner and the nearby transfer charges.
• Other important features of this invention are the ability to print very large substrates, one meter by one meter or more with very small “features” (i.e. the dimensions of the image elements) and with very high levels of “overlay” accuracy (i.e. the registration of features) on one layer (or printing step) to overlay accurately the features on subsequent layers (or printing steps).
• the electrostatic printing plate is shown in Fig. 3a is a photopolymer layer 52 bonded to an electrically grounded substrate 54.
• a photopolymer layer 54 is heat and pressure laminated to a grounded substrate, typically an aluminized polyester film (PET). It is then exposed through a contact photo tool to actinic radiation (350nm to 440nm wavelength) to cross link the exposed areas.
• Fig. 3b the plate is charged by a corona unit 56.
• the cross linked areas are much higher in electrical resistivity than normal photopolymer so they store charge for significant periods of time. After a suitable delay to allow the normal photopolymer to discharge, we have a latent image on the printing plate as in Fig. 3c.
• Fig. 3a is a photopolymer layer 52 bonded to an electrically grounded substrate 54.
• a photopolymer layer 54 is heat and pressure laminated to a grounded substrate, typically an aluminized polyester film (PET). It is then exposed through a contact photo tool to
• a "reversal" development is effected with a liquid toner 58, i.e. development of the discharged areas of the plate (those referred to as normal photopolymer or not cross linked). Note the process can be a "normal" image, where the charged areas are developed or reversed as previously mentioned.
• the Electrostatic Printing Plate can be film coated from a liquid solution which can be dried and partially hardened by a gentle bake. Coating methods include roller coating, spray coating, spin coating, dip coating or meniscus coating.
• Useful liquid photopolymers are usually negatively acting ones, those that cross link and that are insoluble in hydrocarbons or at least not significantly swelled by them. Typical examples of commercially available liquid materials are: Hoechst AZ-5200 IR, and MacDermid HDI-1, 2 or 3, also Mac Dermid. MT-1400.
• the dry film photopolymers are precast films than can be heat and pressure laminated to suitable substrates. They include these materials:
• the liquid resists can range in thickness from a fraction of a micron to about
• An important feature of this invention is the partial exposure of the photo resist.
• Data has shown that the photopolymer 52 is exposed in ever increasing thickness of a layer starting at its surface, as shown in Fig. 4a through 4c.
• Increasingly by longer exposure to actinic radiation 60 cross-links ever deeper layer of the photo polymer. Therefore if one is using photopolymer at 38 micron thick but wants to make 5 ⁇ features, one might expose only one quarter of it in thickness as shown in Fig. 4b.
• One now has highly resistive image in a "sea" of less resistive background areas. Since we never remove the unexposed background areas (an indeed their presence is a critical element in the success of the process, as discussed next), the partially exposed (or unexposed layers under the image) present no problems.
• One determines the proper level of exposure for the "partial exposure" condition by a series of increasing exposure levels and measuring the charge voltage in large solid areas.
• Such photopolymers can be used if one gives them a broad pre-exposed of the unexposed plate to bring it up to the proper electrical resistivity so that the initial voltage in the background areas is adequate. Then the pre-exposed plate is imaged with a photo-tool to produce a proper image above the pre-exposed level. This has been done is silver halide for years and is called "pre-fogging" of the plate. Pre- exposure of an electrostatic printing plate is discussed in prior art literature such as Bujese in US No. 4,968,570. Other photopolymers have just the proper level of resistivity in the unexposed regions and require no pre-exposure or "pre-fogging".
• the machine design shown in the invention includes an AC erase discharge corona located just in front of the charge or sensitizing corona. By careful attention to design the AC corona will "reset” or discharge all areas of the plate after the last print cycle. Now the plate is ready to be charged. Ideally the charging cornea will charge all areas of the plate to the same voltage whether they be large solid areas of image, large areas of background (the unexposed regions) and the fine image structure.
• the unit "a” with an electrically biased metal screen or grid between it and the plate or drum (the Xerox trademark for this is a scorotron).
• the above approaches have different voltage versus corona current densities that will show which one is optimum for this situation.
• the electrostatic printing plate poses new problems for corona design.
• the plate has areas of two different electrical resistivities, the high resistivity charge retaining layer and the lower resistivity background regions. It has already been discussed how a plate could be pre- fogged to raise the background area resistivity to a point where its charge voltage would decay to a negligible value (typically 10% of the initial voltage) within the process time between charging and development. Given that this has been accomplished, the initial charge voltage in the non-exposed or background areas are a fraction of the initial voltage in the exposed areas can be maximized by the choice of charge corona type and its design details. Procedures to accomplish this will now be described.
• FIG. 6 The various corona devices in use are shown in Fig. 6.
• the top figure shows the oldest design dating to the late 1950's, the corona unit 74 or a bare wire usually gold plated tungsten of 50 ⁇ to 75 ⁇ in diameter in a grounded metal shroud.
• the front aperture was constricted inward to serve as a self extinguishing function in that the surface to be charged would not exceed a certain value. This was important otherwise the drum voltage, if excessive, could puncture the photo conductive surface of the drums used at that time, causing permanent damage.
• This invention uses an ac neutralizing corona unit to discharge the printing plate at the end of the printing cycle. Either the bare wire or pin corona are adequate for this job.
• the charging corona is located just after the neutralizing corona. Here a V-i curve is desired that will best charge the exposed and unexposed regions of the printing plate to the same voltage.
• the ideal voltage- current characteristic from the corona unit would be one in which the corona current density (in microamps/cm 2 ) would be independent of printing plate voltage, or a flat straight line in Fig. 7 and 8. Then if the plate is charged quickly, both exposed and unexposed plate areas would charge to the same value, after a suitable delay the unexposed regions would decay to a negligible value yielding an excellent electrostatic "contrast" (the difference between image and background).
• the best corotron design for this invention is the DC bare wire or pin corotron whose V-i curve is shown on Fig. 7a. It's V-i curves are the "flattest" of the four types of corona units and will yield the high ratio of unexposed to exposed initial charge voltage.
• toner images are transferred to relatively thick layer of glass, 0.5 to 3.0 mm thick (500 to 3,000 micron) spaced away from the image by a fluid filled mechanical gap of 50 to 150 microns.
• Relative conductivities of the glass versus the gap filling liquid (toner plus added diluent), capacitances, applied voltages and the time over which they are applied etc. are important.
• Figure 9 shows a mechanical schematic of the transfer process and a electrical equivalent circuit which allows one to calculate the voltage division across the three elements (glass, gap, and printing plate) during the transfer process.
• A. Electrical conductivity of the glass versus the conductivity of the gap liquid The most critical issues are the conductivities of the liquids in the gap versus the glass as this determines the voltage division between glass and gap. If most of the voltage appears across the glass and very little across the gap between plate and glass, all of toner will transfer. This is best illustrated by some examples:
• Printing plate 400 consists of a photopolymer 402 of 10 to 50 micron thickness connected to electrical ground. Receiving glass plate 404 of typical thickness 0.5 to 3.0 mm thickness is backed by a field electrode 406 connected to transfer voltage 408. It is separated by mechanical gap 430 from printing plate 400. The equivalent circuit for this structure 412 is shown to the right.
• A-l. A Glass of Interest is Electro allocatede ELC- 7401 made in Switzerland. If charged and then the voltage decay measured it shows a decay time constant of 1 second which calculates to a resistivity of 2 X 10 +12 ohm • cm. Typical ranges of toner bath conductivities are of the order 10 to 100 pico mho/cm (10 +n to 10 +1 ° ⁇ • cm resistivity).
• the charging test with the glass is a dc test and measures the flow of electronic charges through the glass, while the measure of toner conductivity is an 18 hertz test that measures back and forth flow of electrons, ions, and charged toner particles.
• the voltages divide capacities between the elements, glass, gap, and plate. Since the imaged areas of the plate 400 are highly resistive they can be disregarded for short periods of time. Since the glass is thicker than the gap, typically 10 to 100 times, and it's dielectric constant is 5 verses 2.1 of the liquids in the gap, the voltages divided preferentially across the glass with little across the gap. If the conductivity of the gap fluids is higher than the glass this situation will worsen the time and transfer will be inhibited. With time, the voltages divide resistively between glass and gap. If the conductivity of the gap fluids is higher than that of the glass, practically all of the voltage is across the glass and none across the gap. If toner had transferred, it will back transfer due to the image charges on the printing plate. This, in fact has been observed.
• Printing plates 430 and 432 in Figs. 10a and b respectively are "negative" images of each other. 430 is cross linked in the image area and developed with toner 434. 432 is cross - linked in the non-image areas and developed with toner 434. Both plates are sensitized with charges 433. Field plates 436 and driven by voltages 438 and 440 respectively. Receiving glass 442 accepts the transferred image. Mechanical gap 444 is filled with transfer fluid (not shown). High resistivity regions 446 are the cross - linked regions of the plate. Induced charges 448 occur when the transfer voltage is applied and are restricted to the non-cross linked regions of the plate. B. Mounting Techniques for the Printing Plate and Glass
• the transfer electric field must be everywhere normal to the plane of the plate and undistorted on the edges. And since we are transferring to glass with a resistivity of the order of 10 +12 to 10 +16 ohm • cm the mounting and holding of the plate must be consistent with these resistivities, i.e. these fixtures must be of materials substantially higher in resistivity. Even with the most conductive glass (lowest resistivity of 10 +12 ohm • cm) some typical engineering materials, like cotton filled phenolics or poly acetals (Delrin of DuPont) may not be adequate for the job. For instance, Corning 7059 or 1737 glass is typically used for liquid crystal display panels for lap top computers.
• An important feature of using the fixed resistivity configuration electrostatic printing plate is a phenomenon that helps to "focus" or direct the toner particles during transfer IF the plate is used in the normal imaging mode. By this it is meant that the toner development of the charged areas of the plate as opposed to the "reversal" mode where the discharged areas of the plate are developed with toner particles.
• the former is used in a typical office copier while the latter is used in a laser or LED printer.
• Figure 10a and b Figure 10a shows the normal imaging mode, positive sensitizing charges developed with negative toner particles and transferred with a positive electric field.
• Figure 10b shows reversal with again positive sensitizing charges, positive toner particles transferred with a negative electric field. Note the charge retaining areas of the printing plate, they are highly resistive necessarily to retain the sensitizing charges. The other areas of the plate (areas not cross-linked in the plate exposure step) are much lower in resistivity.
• the transfer field "induces” electrical charges in these lower resistivity areas of the plate, which produces a significant result.
• the sensitizing charges are positive while the induced background area charges are negative. These background area negative charges enhance the strength of the imaging fields and help to control the direction of the toner particles during the transfer step.
• charges induced in the lower resistivity regions of the plate are of the same polarity as the imaging fields and tend to reduce the fields. Indeed if the induced charge density equals that of the sensitizing charges there is no longer an imaging field and toner particles are free to move laterally during the transfer step. This will cause significant "de-focusing" of the transferred toner image. For this reason, normal imaging is preferred when using the electrostatic printing plate for highest resolution images.
• electrostatic printing process for printing functional materials on glass plates is a simple one with few process step. It has these advantages over current technologies:
• the process is a room temperature process until sintering so critical to large geometries due to thermal glass .
• the four filter colors are printed at room temperature, then baked at once.
• FIG. 11 shows this embodiment.
• Chuck 100 carrying electrostatic printing plate 102 is transported on linear bearings 104 by belt drive 106, canted at roughly a 45° angle to the horizontal.
• chuck 100 starts at the top near pulley 108. Moving at uniform speed it passes corona unit 110 which charges the printing plate, 102 with a uniform electrostatic charge. After a short period of time, the low resistivity areas of the plate with discharge to a negligible charge level; the high resistivity areas of the plate retain the charge to near original levels.
• This latent electrostatic image is now developed by liquid toner which floods the gap between developer roll 112 and plate 102. Valve 114 floods this gap with a measured quantity of liquid toner 116. Developer roll 112 has an electrical bias voltage 118 which controls the accumulation of unwanted toner particles in background areas of the image. After passing between the developer roll plate 102 is stripped of excess liquids by reverse roll 120. After this the liquid toner is compacted by "depress" corona 122. The image is now finally developed and ready for transfer to the receiving substrate.
• Receiving substrate 130 rests on its chuck 132 which rides on linear drive 134 driven by belts 136 and pulleys 138. It moves right past valve 140 which wets it with a thin layer of clear Isopar diluent. It moves to transfer position 142 and stops.
• Chuck 100 carrying printing plate 102 rotates approximately 135° counter clock wise to a position in obverse relation to receiving substrate 130. Spacing means not shown, accurately position plate 102 from receiving substrate 130 by a precisely controlled mechanical gap, typically of the order of 50 ⁇ to 150 ⁇ .
• a voltage is applied to chuck 132 to create a transfer electric field which transfers the toner image on plate 102 to receiving substrate 130.
• Chuck 100 with printing plate 102 is now lifted vertically by means not shown or simply rotated clock wise by approximately 135° to its original position.
• Receiving substrate 130 is now dried before removing it from its chuck 132.
• Plate 102 is now moved up the 45° ramp and cleaned by suitable means, not shown, to repeat the next printing step.
• the manifestation of the invention has advantages over the rotating process of the preferred embodiment in that is a ascychronous, i.e. variable time intervals can be introduced between each step of the process; and transfer occurs in the flat to flat situation when hydrodynamic events and forces have subsided.
• the flat receiving substrate which may be of the order lm x 1.2m must be on the bottom so it can be flooded by the diluent to fill the gap between the plate 102 and receiving substrate 130.
• the "overlay" accuracy of one flat plate, the printing plate; to a receiving sheet is much better, flat to flat, then in the dynamic situation of a moving flat sheet that needs to be accurately "phased” to a rotating print drum. Achieving very uniform linear and rotary drives are not trivial but phasing them "on the fly” to levels of their individual variations is a major task, all of which does not apply here. Second Alternate Embodiment
• Fig. 12 shows a cross section of the cathode plate 200 of an AC Plasma Color Display Panel. It consists of a glass back plate 200 with black glass spacer ribs 202 that optically and electrically isolated image cells from one another. These ribs are typically lOO ⁇ high and 30 ⁇ to 40 ⁇ in nominal width. At the bottom of the "wells" are the address electrode lines of copper 204 or nickel metal. Covering the walls and bottom of the "canyons" is the phosphor 206 that converts the UV radiation from the plasma discharge to visible radiation, RG&B in the case of a color display. Alternate canyons are coated with red, then green then blue phosphor.
• One advantage of the electrostatic printing technique is the non-contact or gap transfer aspect of it; i.e. the ability to transfer functional materials across relatively large mechanical gaps.
• Fig. 13 is a greatly magnified picture of the mechanical gap 220 between the print drum and glass surface 200 of the invention.
• the gap here is set to a value of 150 ⁇ .
• glass toner is printed to make the spacer/isolator ribs 202.
• Four layers of toner 203 is shown, each about 25 ⁇ high, one printed on top of the other.
• the manufacturing sequence is as follows: Step 1 Print first layer of glass ribs Step 2 Dry the toner by blowing warm air on it to partially set the resinous material that coats the glass particles. Note it is desired to maintain this as a constant temperature process so warm air is needed to compensate for the natural cooling that occurs with the evaporation of the diluent liquid Step 3 Reprint and dry the second layer of glass toner
• Step 4 Reprint and dry subsequent layers of glass toner until the desired height is achieved.
• Step 5 Fire the glass panel at high temperature to burn off the resin in the toner and reflow the glass particles to make a solid rib
• Step 6 The rib manufacture process is now complete.
• Figure 13 shows the process for the printing of the metallic address electrodes 204 in the base of the canyons formed by the ribs.
• a palladium catalytic toner 224 is image on the drum and transferred across the 150 ⁇ gap to the base of the canyons.
• the toner is dried leaving a very thin layer of palladium seeds in a line that runs the length of the canyons.
• the plate is removed from the printing machine of the invention and immersed in an "electroless" plating bath. Metal grows from solution is on the palladium seeds, then on previously plated metal. Electroless processes have advanced to a point where one can plate up to one micron of metal per minute. After the growth of about 25 ⁇ of metal 226, usually nickel, the cathode electrodes are complete.
• Figure 13 shows the deposition of phosphor toner 230 in the canyons. Phosphor toner 230 is imaged on the plate and transferred across the 150 ⁇ gap.
• the transferred toner moves in straight lines but can coat relief images like coins.
• the toner image is sized to cover the walls of the canyons as well as the base where the electrodes are located.
• Note one phosphor color is imaged at a time so the printing plate has an image of every third canyon on it.
• the toner is dried with warm air to set it; then the second color is imaged; then the third color.
• the same printing plate can be used for all three colors; all that is needed is to mechanically index the glass with respect to the printing drum.
• An alternate method to produce conductors is to print metal toners themselves, to burn off the resin that coats the metal particles; then reflow the metal into a smooth conductor pattern.
• the toner is then dried to temporarily fix it for reasons of safe handling.
• a rapid thermal processing of the metal is effected, where the toner and glass is raised to a temperature of 50° to 100°C below the softening point of the glass (approximately 500°C for soda lime glass). This effectively burns off the resin that coats the metallic particles.
• the aluminum is heated to its melting point while the glass absorbs little UV energy.
• Aluminum which melts at 659°C is a good choice of materials to be used with soda lime glass. Note this is not done in air but in a "reducing" atmosphere like one used in aluminum welding work.
• the glass 300 in Fig. 14a is first coated with a thin, transparent layer 301 that is electrically conductive. This very thin layer is not shown.
• Indium Tin Oxide (ITO) is a possibility except it absorbs about 5 to 10% of the transmitted light and ITO processing is expensive, of the order of $5 per square foot.
• the ITO conductivity of 50 to 100 ohms per square for a typical 2 ⁇ thick layer is higher than needed for this electrostatic process.
• a conducting polymer as resistive as 10 +5 ohms per square is adequate for this electrostatic process, all that is needed is to establish an electrostatic ground plane 302 as shown in Fig. 14a.
• the coated glass 300 is imaged with the RGB color mosaics 304 which are then reflowed by final heating.
• the plate is now complete except for the black intermatrix which has yet to be produced.
• Transparent conductive layer is electrically grounded through edge contact 306 as shown in Fig. 14a.
• the entire plate is corona charged with a suitable corona generator 308 as in Fig. 14a.
• the conductive under layer discharges immediately, while the color mosaics retain their charge 310 for considerable periods of time, as much as thousands of a second depending on the resins used in the mosaics.
• the partially finished color filter plate is now its own electrostatic printing plate, as seen in Fig. 14b. It can be developed in the reversal mode (i.e. develop the discharged [or uncharged] areas of the image) as is done in virtually all desk top laser printers.
• the mosaics are charged positively so a toner with a positive charge 312 will develop the non-charged areas as in Fig. 14c.
• This black toner will produce the intermatrix between the mosaics.
• One of the principal advantages of this embodiment is that the final printing operation of the black intermatrix is self-correcting of "self-healing". Any image defects in the mosaics will be over printed with black toner automatically.
• This glass plate #330 is typical of the face plate of a field emission display (FED).
• the glass is first coated with black chrome oxide #332 to enhance optical contrast and with a metallic chrome layer #334 to conduct away to ground the electrons that hit the phosphor. It is desired to coat phosphor in the bare spaces on the glass surface between the chrome fingers which are all connected together.
• To "self- print” the phosphor toner the glass panel is placed on an electrically ground plate #336, chrome side up. Using a wire or metallic probe #338 the chrome layer is made to act as an electrode by connecting it to a high voltage power supply, as high as possible before electrical breakdown occurs.
• Liquid toner is now poured over the plate and it is noted that toner #340 "develops" on the bare glass areas by means of the fringing electrical fields. If the toner particles have a positive charge on them, a positive voltage must be connected to the chrome layer; with negative toner conversely a negative voltage with respect to ground is needed. As before open area defects in the chrome layer will have toner deposited on them in a "self-healing" manner.
• Example 1 of the Preferred Embodiment An electrostatic printing plate was made by laminating DynaChem 5038, product of DynaChem Inc., Tustin California, photopolymer dry film resist material to 0.003 inches thick black anodized aluminum foil from Lawrence and Frederick of Des Plaines, Illinois (the part number is 1145-003-1419-SB). The laminating was done on an industry standard dry film laminator made by Western Magnum. After cooling from the lamination process, the plate was exposed by a negative photo tool to nominal exposure level 100 milli joules/cm 2 . The plate was charged to a nominal image voltage of -800V by a corona discharge unit.
• the glass toner of example 1 was prepared by the "organosol" process as taught by Kosel in US# 3,900,412.
• An organosol resin was polymerize in Isopar H diluent following the methods of Kosel.
• the resin had a Tg of -1 °C and a core to shell ratio of 4. It was designated the nomenclature of JB8-1 (Aveka Inc., Woodbury, Mn.)
• the toner contents were as follows:
• the resulting toner had the following characteristic: mean particle size 1.27 ⁇ toner conductivity 9.9 pico mho/cm particle mobility 3.06 x 10 "6 m 2 /v • s
• the glass particles have a true mass density of 5.2 while the Isopar L® has a density of 0.8 so the toner settles out substantially in 15 to 30 minutes. It can be successfully re-dispersed by moderately shaking of the toner containers by hand.
• Example #1 was repeated with the toner of example #2 but the toner was transferred to Cr coated glass.
• 75mm x 75mm x 1.2mm Corning 7059® glass were sputter coated with lOOnm to 150nm of pure chrome. The resulting surface had a brilliant shine to it.
• the Cr surface on the glass was wetted with Isopar and this wetted glass placed on the PET on a developed printing plate. The Cr surface was connected to a lab supply producing -1600V. Good glass toner images were transferred on the Cr coated glass.
• the PET spacers were 125 ⁇ thick.
• Example 4 of the Preferred Embodiment A catalytic toner was prepared with the following ingredients:
• the resulting toner had these measured characteristics: mean particle size 0.333 ⁇ conductivity 169 p mho/cm
• An aluminum powder toner was prepared by the following formulas: 75 gm of Alex Al, Argonide Corp.
• the toner was imaged on the plate of example 1 and transferred to the same type to soda lime glass. After drying it was subjected to rapid thermal processing in the model CP-3545 RTP machine of Intevac of Rocklin, California. The toner and glass were pre-heated to 550°C in a non-oxidizing atmosphere. It was then exposed to intense UV radiation that heated the aluminum toner but not the glass.
• a 1.1mm thick plate of soda lime glass was patterned with black chrome oxide, then metallic chrome with phosphor openings of 60 ⁇ by 130 ⁇ in a solid pattern of 75mm x 100mm.
• the plate was placed, chrome side up on a grounded copper plate. Electrical contact was made with the chrome surface and the power supply was turned on to +6,000 volts. No break down occurred.
• the chrome surface was flooded with the phosphor containing toner Similar to Example #2, the difference was equal amounts of phosphor and resin, 50g of phosphor, 50g of JB8-1. Unwanted background was washed away with clear Isopar G.
• the plate was allowed to air dry at room temperature. Good phosphor toner images were noted in the clear spaces between the chrome fingers.
• the phosphor toner NP-1053A was obtained from Nichia Kagaku Kogyo, K.K., Tokashima-ken, Japan.
• a printing plate from 38 micron thick DynaChem 5038 photopolymer was charged and imaged with Indigo E-1000 toner with a concentration of 1.5% by weight and a conductivity of 25 pico mhos/cm.
• Corning 7059 glass 1mm thick was placed on PET film, 25 microns thick spacers, above the plate. The gap between glass and plate was filled with pure Isopar G whose conductivity is less than 0.15 pico mho/cm.
• An electrode was placed on top of the 7059 glass and excited to +10kv with respect to the grounded base of the printing plate. The transfer voltage was held for 10 minutes.
• Example 2 of the First Alternate Embodiment The plate of Example 1 of the First Alternate Embodiment was imaged and developed. Electroveere glass ELC-7401 with a resistivity of 2 x 10 +12 ohm • cm was placed on 50 micron thick PET spacers.
• Example 1 of the First Alternate Embodiment using that toner An image was created on the plate of Example 1 of the First Alternate Embodiment using that toner.
• 2.25mm thick soda lime float glass i.e. common window glass
• Isopar G conductivity treated with Indigo Imaging Agent to a conductivity of 25 pico mho/cm was used to fill the gap between glass and plate.
• An electrode connected to 5kv of voltage was placed on top of the plate, which was reduced to 3kv in 5 seconds.
• the glass plate was lifted and an image of low density was found on the glass. A significant amount of toner remained untransferred on the printing plate.
• the conductivity of the gap liquid reduced the effective voltage across the gap causing poor transfer.
• this invention comprises a relatively uncomplicated high yield manufacturing process in which functional materials are configured as liquid electrographic toners that can be printed at commercially interesting rates of production in a non-contact mode.
• This non-contact feature allows one to print on non-flat surfaces or even relief surfaces such as ribbed surfaces.

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• Combination Of More Than One Step In Electrophotography (AREA)
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• 1999
  • 1999-10-12 DE DE69939596T patent/DE69939596D1/de not_active Expired - Lifetime
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