GB736590A - Improvements relating to the manufacture of paint - Google Patents

Abstract

<PICT:0736590/III/1> Paint is made by suspending a finely-divided pigment in a current of gas, removing from the suspension particles exceeding a limit of size suitable for pigmentary purposes, subjecting the suspension containing the remaining particles to an atomized spray or curtain of a wetting liquid miscible with the body medium or vehicle to be employed, causing collision of the wetted particles so that they will cohere as aggregates of increased diameter, treating the suspension to collect the wetted aggregates composed of particles close to the optimum pigmentary size, and mixing them with a body medium or other paint vehicle. The gas, which is preferably an inert gas such as nitrogen or carbon dioxide, but may be air, may be circulated in a closed system, and substantially saturated with the wetting liquid. As shown, pigment falls in finely divided form from a hopper 10, provided with an isolating valve 11, into a hopper 12 from which it passes, through an isolating valve 13, having an automatic gas seal, into a screw conveyer 14, which is driven at variable speed and controls the rate of delivery of the pigment to a pulverizer 19. The latter disperses the pigment in a stream of gas supplied by a blower or fan 20; it passes thus suspended to a cyclone or other (e.g. wet or electrostatic) separator 15, which removes the oversize particles e.g. those exceeding 10 microns in diameter, and returns them, through an isolating valve 16, to the hopper 12. The remaining particles are then carried through a pipe 22 into a wetting device 23, which may comprise an aero-jet generator 25 such as described in Specification 686,779, [Group II], feeding a venturi, whereby a liquid spray or curtain is projected coaxially with the gas current, and the particles of pigment caused to undergo violent acceleration therewith in the narrow part of the venturi. The liquid may consist of white spirit, xylol or other solvent of the vehicle to be employed, or a drying oil, varnish, lacquer or the like, or a solution or mixture thereof. Wetting of, and coherence between, the pigment particles occurs, to form aggregates of increased mean diameter which are separated from the gaseous medium by a cyclone or separator 27, and mixed with a body medium or other vehicle, which may be supplied through a spraying device fed by a pipe 28, or mixed therewith in a separate chamber. The gaseous current, including unseparated fine particles, may be recirculated through pipes 29 and the fan 20.