GB679814A - Apparatus and method of coating - Google Patents

Abstract

Surfaces are provided with thin, liquid coatings by subjecting the surface carrying spaced dielectric liquid particles to the action of an electrostatic field to cause the particles to spread upon the surface, the <PICT:0679814/III/1> <PICT:0679814/III/2> quantity of liquid being so small that the particles would not spread to form a continuous film in the absence of the flattening effect of the electrostatic forces within each particle. Preferably the coating is precipitated on the surface in an electrostatic ionizing field which also serves to spread the particles. In the apparatus shown in Fig. 1, a web 26 passes between two induction nozzles 35 and 36 situated in a electric field produced by electrodes 11 and 12 supported on frames 8 and 9. Streams of liquid dispersed in air at a low rate of flow are deflected by the field on to the web which passes on through the field when the coating flattens out to cover the surface. The dispersion unit 37, Fig. 3, contains one or more vertical tubes 42 having a narrow aperture 44 and a lower end extending into a trough 46 containing liquid to be atomized. A heating element 51 may be located below the trough. A jet of air from pipe 48 atomizes the liquid from the nozzle 44 and the spray hits a baffle 58 which disrupts the larger particles. As a result, the nozzle 35 issues a slow moving fine mist. The flow in the electrostatic field is aided by the exhaust duct 19, Fig. 1. Means for automatically regulating the rate of flow of the spray with the speed of the web to ensure uniform deposition are also illustrated and described. Surfaces which may be coated include conducting and non-conducting material but, in the latter case, a conducting backing should be provided. Specified liquids which may be applied are mineral, vegetable and animal oils, molten or dissolved natural or artificial waxes, resins, asphalts, tars and certain organic solvents. Specification 550,391 is referred to.