ELECTROSTATICALLY ASSISTED PRINTING SYSTEM

摘要

A printing system and printing method are provided having an electric circuit supplying an output potential to assist the transfer of ink to a printable substrate. The printing apparatus includes (a) a printing cylinder; (b) an impression roller positioned with respect to the printing cylinder; (c) an ink supply positioned to provide ink to the printing cylinder; (d) a web having one surface contacting the printing cylinder and the other surface contacting the impression roller and passing therebetween during operation of the apparatus; (e) means for moving the web through the apparatus; (f) means for inducing an electrostatic charge onto the web so that the surface contacting the printing cylinder has a given polarity which the ink supply has opposite polarity; (g) a high voltage power supply connected to supply a high voltage to the chargeinducing means to produce an electrostatic field only between the web and the printing cylinder for aiding the transfer of ink from the printing cylinder to the web, wherein the charge-inducing means is positioned so as to induce the charge onto the web prior to entry of the web into the nip between the printing cylinder and the impression roller; (h) a conductive roller positioned to roll in contact with the impression roller; and (i) a low voltage power supply providing a voltage ranging from 1 to 10 percent of the high voltage potential provided by the high voltage power supply, the low voltage power supply being connected to the conductive roller to supply a low voltage thereto of a polarity the same as the polarity of the high voltage connected to the charge inducing means. Thus, the potential is applied to the substrate prior to entry of the substrate into the nip of the printing apparatus. The potential may be applied by a roller, or by a plate, a knife-edge, a series of points or a corona discharge. The substrate may be neutralised before and after charging and printing. Plates may be provided to pre-charge the substrate prior to application of potential. The impression roller can carry a lower potential than that imposed on the substrate, or may have no potential imposed thereon. This method and system provides an improvement on the indrodution of an electrostatic field into the impression roller since the problem of clean up shut-down in the event that the web tears or has holes therein is obviated. continued.