Removal of acid from cathodic electrocoating baths by electrodialysis
AssigneeBASF SE
InventorsHartwig Voss, Thomas Bruecken
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Abstract
Acid is removed from cathodic electrocoating baths in which electroconductive substrates are being coated with cationic resins present in the form of aqueous dispersions, at least a portion of the coating bath being subjected to an ultrafiltration where the ultrafiltration membrane retains the cationic resin to form an ultrafiltrate which contains water, solvent, low molecular weight substances and ions and is at least partly recycled into the coating bath, by subjecting at least a portion of the ultrafiltrate to a specific electrodialysis treatment before returning it into the electrocoating bath.
Claims10
A process for removing acid from a cathodic electrocoating bath in which an electroconductive substrate is being coated with a cationic resin in the form of an aqueous dispersion by separation of the dispersion by ultrafiltration into a resin dispersion and an ultrafiltrate and deacidification of the ultrafiltrate by passing the ultrafiltrate through the chambers K.sub.1 of a direct current operated electrodialysis cell comprising the characteristic sequence
- -(K.sub.2 -M.sub.1 -K.sub.1 -M.sub.1).sub.n -,
- where M.sub.1 is an anion exchange membrane and n is from 1 to about 500, and passing and aqueous base through the chambers K.sub.2, which comprises reversing the polarity of the electric field responsible for ion transport through the membrane.
Dependencies are inferred from the claim text.