GB1335195A - Treatment of electrodeposition baths - Google Patents

Abstract

1335195 Electro-deposition, ultra filtration and ion exchange P P G INDUSTRIES Inc 24 Nov 1970 [25 Nov 1969] 55769/70 Heading C7B At least a portion of an electro-deposition bath comprising a synthetic resin ionically solubilized in an aqueous medium is subjected to ultrafiltration and the ultrafiltrate is contacted with an ion-exchange resin to raise or lower the pH of said ultrafiltrate depending on whether the ultrafiltrate is acid-containing or base-containing respectively. The ultrafilter may be microporous, a diffusive gel membrane, or preferably an anisotropic membrane and is designed for example to retain the vehicle resin and pass water and solutes of low molecular size. The process is batch or continuous, at a pressure of 10-150 p.s.i., the bath at the face of the filter being kept in motion by mechanical stirring or a force vector parallel to the filter surface to avoid clogging the filter. Retained matter from the ultrafiltration may be returned to the bath, optionally after reconstitution with water. The bath may comprise a synthetic polyacid resin solubilized with base; in this case the ion-exchange resin is a cation-exchange resin, e.g. of the carboxylic acid type or sulphonic acid type, or may comprise an acid-solubilized polybasic resin; the ion-exchange resin is then an anion-exchange resin of the polyamine or quaternary ammonium type. The ion-exchange process is batch or continuous, performed concurrently or intermittently with the ultrafiltration, a suitable apparatus being described.