An outodepositing coating process wherein a coating bath containing an acidic aqueous coating composition comprising as essential ingredients: (1) an acid; (2) an oxidizing agent; and (3) an aqueous dispersion of coating forming resin particles and surfactant, which surfactant is subject to being slowly altered by the acidic oxidizing environment in the metal coating bath resulting in the buildup of reaction products in the bath, which bath is maintained in continuous coating forming operability by replenishing in a manner which prevents the deterioration of the coating quality of the bath. The coating composition and replenishing composition may also contain as an optional ingredient an aqueous dispersion of pigment and surfactant and may also contain non-essential ingredients, which non-essential ingredients may increase in concentration as the bath is operated until a deleterious effect is asserted on the coating formation. The coating quality of the replenished bath is maintained by the addition of an aqueous surfactant composition and by operating the replenished bath at an elevated redox potential or by removal of the altered surfactant.
An effective electrically insulating film on the surface of a metal object, such as a common type of electric motor core assembly, in which the surface includes an interior comer on which insulation is desired, can be formed by autodeposition with an adequate thickness in the interior corner without need for excessive thickness on other parts of the surface that are more readily covered by prior art methods of applying an insulating coating. If the autodeposition composition used includes as its primary film-forming component a copolymer of certain acrylic monomers, a very high volume resistivity can be achieved.
A method to make volumetric additions of dilute aqueous acid solutions to a colloidal catalyst bath that will retard the salt crystallization. The process includes the steps of measuring the volumetric loss of water by physical measurements and adding dilute aqueous acid solution to the bath in the amount of the loss or by measuring the density or specific gravity of the solution and adding dilute aqueous acid solutions to maintain the specific gravity in the desired range.
A method for stabilizing the iron salt content of a PVDC latex autodeposition bath by: filtering a metered portion of the bath to separate it into a filtrate containing the iron salts and a retentate containing the latex and pigment particles; discarding the filtrate; recycling the retentate back into the bath; and adding D.I. water in a volume equal to that of the filtrate.
An autodeposition bath for coating steel and similar metals is operated initially with a low content of dissolved iron and at a high oxidizing potential. After the iron content has increased beyond a specific level, such as 1.5 g/l, the oxidizing potential is reduced. This permits continued satisfactory operation of the bath with lower rates of iron accumulation in the bath, so that the need for bath stabilization by removing dissolved iron is deferred.
Properties of cured autodeposited coatings are improved by contacting the uncured form of the autodeposited coating with an alkaline material, for example, with an aqueous solution of ammonium bicarbonate, or a hydroxide of an alkali metal or ammonia.
