GB1190316A - Electrostatic Printing Process - Google Patents

Abstract

1,190,316. Electrostatic printing. MONSANTO GRAPHIC SYSTEMS Inc. 5 Aug., 1968 [14 Aug., 1967], No. 37228/68. Heading B6C. In a printing system wherein electroscopic powder is transferred from a powder-image producing member to a receiving surface by an electric field, the image producing member comprises a spongy porous sheet pervious to the powder. As shown in Fig. 1, the porous sheet 20, which may be polyurethane foam, has a screen electrode 20 at one face and a mask 22 defining the required image on the other face. The surface 18 to be printed is supported on an electrode 16. In place of the screen electrode 10, a metal plate may be used or a metal coating may be deposited on the sheet 20. Alternatively. the sheet 20 may be made conductive by immersion in a plating solution. Powder is applied to the exposed image areas of the sheet 20 by direct application by means of a brush, by dipping the sheet into a powder box whilst a vacuum is applied to its other face (Fig. 12), or by blowing powder on to the face opposite the mask and removing excess powder from the masked face (Fig. 11). The porous material may be cut in the form of the desired image, such as the letters 32, 34, 36, Fig. 6, assembled on conductive rails 37, 39 or attached by glue or wire-staples to an electrode. Pressure may be applied to the back of the porous sheet by means of the electrode to supplement the action of the electric field in ejecting the particles (Fig. 13). As shown in Fig. 7, the porous sheet material is in the form of a belt 40 with the mask 46 on its outer face. Powder is applied by a brush 52, excess being removed by a blade 54. The belt passes between electrodes 56, 58, and a web 62 to be printed is fed between tho belt and the electrode 58, the belt and web being moved at the same speed by a motor 48. The porous material and mask may, however, be mounted on a cylinder (Fig. 8) for printing on a web. For printing on a curved article such as a bottle, the porous sheet material is shaded to conform to the surface of the article (Fig. 9).