In a process wherein a resinous coating is formed on a ferriferous surface by immersing the surface in an acidic aqueous coating composition prepared from dispersed particles of resin, HF and FeF.sub.3, wherein said composition forms on said surface a resinous coating which increases in thickness the longer the surface is immersed in the composition and wherein as the composition is used to coat additional surfaces, it begins to form thinner coatings or it destabilizes, the improvement comprising maintaining the effectiveness of said composition by adding thereto an oxidizing agent which is effective in oxidizing ferrous iron.
A method of improving the anticorrosion properties of an autodeposited resin coating by including in the post-bath rinse (a) a metal dichromate, (b) a metal hypophosphite, or (c) a combination of either of the foregoing with a metal hydrogenphosphate, followed by curing.
A process for increasing the anticorrosive properties of an autodeposited coating wherein after the bath but before the curing, metallic chromate salts are formed in situ by first rinsing with metallic non-chromate water soluble salts and then rinsing with a chromium compound.
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 autodepositing coating composition of the ferric iron-containing type wherein ferrous iron tends to build up in concentration in the composition and affect adversely the coating capabilities of the composition as it is used continuously to autodeposit coatings on iron-containing surfaces, the improvement comprising adding to said composition, in an amount effective to decrease the amount of ferrous iron which tends to adversely affect the coating capabilities of the composition, a carboxylic acid which is effective in forming a complex with said ferrous iron.
Autodeposition unsaturated latex baths which are hydrogen peroxide-free (using iodine or certain iodine salts or free acids as the oxidizer) and which are hydrofluoric acid-free (using, preferably, acetic acid) afford coatings which can incorporate silicate-containing pigments, fillers, and other ingredients.
