METHOD FOR RECOVERING FILTERING PERFORMANCE OF ULTRAFILTER MEMBRANE IN ELECTRODEPOSITION PAINTING LINE

摘要

PURPOSE:To recover remarkably the filtering characteristic of an ultrafilter membrane in an electrodeposition line by washing said film by a washing liquid consisting essentially of an ord. acid, when the filtering performance of said membrane decreases, then washing the membrane with a dilute soln. of an inorg. acid or inorg. base. CONSTITUTION:Iron or steel parts are pretreated by a phosphate soln. to form a phosphate film thereon and are then subjected to electrodeposition painting, washing and electrodeposition painting using an electrodeposition paint. Since the electrodeposition paint is filtered by an ultrafilter membrane and is used for electrodeposition painting in this case, the filtering performance of the ultrafilter membrane decreases increasingly. Such filter membrane is first washed by a liquid contg. an org. acid such as acetic acid, formic acis, lactic acid, glycolic acid, malic acid or the like in 0.1-20% concn. in order to recover the filtering performance of said membrane. The membrane is then washed for 30min-24hr with 0.05-0.2N soln. of an inorg. acid such as hydrochloric acid, nitric acid or the like or an inorg. base such as caustic soda, ammonia or the like and is further washed with pure water, by which the filtering function of the ultrafilter membrane is recovered.