Process for the spray application of aqueous paints by controlling the temperature of the air in the paint spray zone

Claim 1

In a process for applying an aqueous dispersion or solution paint to a substrate by air-spraying the paint with a spray gun utilizing atomizing air at a flow rate of 5-40 cubic feet per minute and at an air pressure of 30-95 pounds per square inch at the spray gun and a paint flow rate of 5-30 ounces per minute which forms an air atomized paint spray which is applied to the substrate and baked at about 75° to 200°C. to form a uniform finish on the substrate, the improvement in use therewith comprising: spraying the atomized paint in an air atmosphere that is controlled by the addition of steam or water at a temperature of 15°-40°C. and at such a relative humidity that the air has a driving force value in the range of 0.002 to 0.004 humidity units which is constantly maintained at a set value within this range, thereby providing an atmosphere for initally drying the aqueous paint during the spraying at a uniform rate to provide a finish that has a uniform appearance after being baked; wherein the paint is an aqueous thermosetting acrylic enamel in which the film-forming constituents of the enamel comprise: 1. an acrylic polymer of styrene, methyl methacrylate or a mixture thereof, an alkyl acrylate or an alkyl methacrylate having 2-12 carbon atoms in the alkyl group, optionally a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate and an α,β-unsaturated carboxylic acid; and 2. a water soluble or water-dispersible cross-linking agent.