Coating metals by electrostatic powder- and electrodip lacquering - using compsn. contg. conductive metal or metalloid component

摘要

Coating of metal articles takes place by electrostatic powder lacquering, followed by electrodip lacquering of surfaces not reached in first lacquering step. A powder lacquering compsn. contg. =1 electrically highly conductive component (I) is used. (I) may consist of =1 metal, pref. Zn if substrate consists of or contains Fe, or of =1 metalloid. Deposition of electrodip lacquer film is constant. No transitional zone can be seen or felt between powder- and electrodip lacquer layers. Corrosion in transitional zone is prevented. In an example, powder lacquer was applied to steel from a 1:1 mixt. of (A) contg. 38.7 pts. wt. oil-free polyester having acid no. 70-110 and 38.6 pts. wt. epoxy resin with epoxide equiv. 730-840 and (B) contg. 77 pts. wt. Zn dust, 9 pts. wt. polyester and 10 pts. wt. epoxy resin. An electrodip layer was subsequently applied. Film withstood salt spray test for 200 hrs. In control, without Zn addn., transition zone of powder lacquer-electrodip withstood salt spray test for only 20 hrs.