GB1120051A - Improvements in printing - Google Patents

Abstract

1,120,051. Electrostatic printing. CONTINENTAL CAN CO. Inc. 21 July, 1965 [14 Sept., 1964], No. 30921/65. Heading B6C. Apparatus for electrostatic printing upon a substrate 25 comprises a housing 29, a base electrode 30 (as shown, a continuously-moving conductive endless band 30), a stencil screen 16 disposed between the electrode and the substrate, means in the housing for supplying toner particles to the electrode, and means for establishing an electric field between the electrode and the stencil screen so as to cause the toner particles to be accelerated towards the stencil. The particles which pass through the openings in the stencil and are deposited on the substrate in the required pattern, are subsequently fixed to the substrate by heating or the use of a solvent. The particles used consist of large carrier particles of electrically conductive material e.g. iron filings and relatively small pigmented-resin 'toner particles, the smaller particles adhering to the larger particles by triboelectric forces. A magnetic drum 33 feeds the particles to the band electrode 30 from a supply 32 in the housing. A magnetic roller 36 over which the band 10 passes has a more intense magnetic field than the roller 33 so as to attract the particles to the band 30. A blade 30 distributes the particles on the band and forms part of a connection, through the particles, between the band and a source of power 52 which applies potentials of opposite signs to the electrode 30 and stencil 16 to create an electric field between them. The carrier particles receive a charge from the band and of the same polarity, and are thus expelled therefrom and carried with toner particles adhering thereto towards the stencil by the electric field. The mesh of the stencil screen is such that only the toner particles can pass through the stencil openings to the substrate 25, and the carrier particles oscillate between the stencil and electrode. Surplus particles pass to the supply 32 along an incline 31 where a brush and container 47, 45 supply fresh toner particles., If the substrate material is highly conducting, an electrical connection may be made thereto to neutralize the electric field formed thereon by the charged toner image which tends to repel toner particles. For substrate material, such as paper, a suitably connected electrode may be situated behind the substrate to neutralize this field. For non-conductive materials, this field is neutralized by supplying ions of suitable polarity to the surface of the substrate from a corona discharge apparatus 40, 51. A grid 41, connected to a source of power 50 controls the flow of ions from the corona discharge to the substrate. The stencil screen 16 may be cleaned when printing is completed by applying a potential difference from a power source 53 to the screen and electrode opposite in polarity to that used for printing, thus causing particles to be expelled from the stencil on to the board 30, and to be returned to the supply 32. To clean the rest of the machine, the stencil 16 is replaced by an electrode 60, Fig. 3 (not shown) having a continuous conductive surface, the electrode being maintained at the same potential as the stencil is during printing. The electric field thus created causes the carrier particles to oscillate back-and-forth between the electrodes 30, 60, and the toner particles are freed from the carrier particles by the collisions between the particles and are attracted to the electrode 60 from which they are collected in a bin 64 by means of a scaper 63. Cleaned carrier particles circulate through the machine and pick up toner particles which have collected on surfaces of the machine.