Electrostatic Printing, a Versatile Manufacturing Process for the Electronics Industries
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EXPOSWE
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Figure 1. Plate Making The plate is sensitized by corona charging it. The resulting surface potential for a typical 37p thick plate is from 500 to 1000 volts. After a short period of time the unexposed regions of the plate self discharge due to their relatively low electrical resistivity. We now have a
151 Mat. Res. Soc. Symp. Proc. Vol. 625 © 2000 Materials Research Society
traditional latent electrostatic image. The latent image is processed by development with an electrophoretic liquid toner Figure 2 shows the transfer step wherein the toner is transferred across a finite mechanical gap to a receiving glass plate by an electrical field created by the electric field plate ELECThi F1KWPLAT!
GLASS
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Figure 2:Toner Transfer Across a Gap on the other side of the glass driven to a suitable potential. An alternate scheme not shown in Figure 3 is to corona charge the other side of the glass with a charge of polarity opposite that of the toner. Figure 3 shows a highly irregular surface, not an exaggeration. This is a particular advantage of electrostatic printing over other printing or deposition techniques. The toner travels across the gap following the parallel electric field lines and it does not disperse as a function of distance between glass and plate. Therefore high resolution images, true to their design, can be deposited on the glass substrate, even if it has imperfections or a relief structure already on it. We have also printed on metal plates, polymeric films and paper. An example of printing on steeply relieved metal surfaces is the printing of images on U.S. coins. The Plate While a photo addressable drum or plate could be used. Electrox chose an electrostatic plate for the following reasons: 1. The electrostatic plate offers a superior latent image over that of the photo receptor plate. 2. Small features like 10 micronss or even smaller are possible. 3. The electrostatic plate offers reasonable process speeds of 250 mm/sec for high through put. The Toner In this area, our toner technology, is far removed from traditional liquid electrographic toners. The following table shows these differences Metals Glasses, Ceramics Catalysts Composites
Materials Aluminum Silver Glass flits Phosphors Palladium Tin Conductor-Silver filled resin Resistors-Carbon filled resin Capacitor Barium Titanate filled resin
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Particle 30 micron 0.2 micron 0.5 to 7 micron 0.6 to 80 microns 0.33 micron 0.8 mircons
Capabilities of Functional liquid Toners: High densities, up to 10 gm/cm3 Board range of Electrical resistivity Silver 1.63x10"6 ohm cm
Glass
10+15
Board range of particle sizes 0.05 micron to 100 micron Broad range of mechanical properties, soft resins to very hard materials Resinless or very little unwanted materials Virtually any material not swelled nor dissolved by the Isopar diluent liquid can be made into a liquid toner. There are few "process burden" materials required to make the liquid toner. Our solid silver particle toner is 96% silver with no resin to interfere with e
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