The composition has a corrosion inhibiting powdered metal, a black pigment of manganese dioxide and a primary bonding titanate polymer which when heated, undergoes a hydrolysis reaction producing an inorganic titanium dioxide bonding of the coating to the substrate. Improved film integrity and adhesion of the wet coating prior to the hydrolysis reaction is provided by a secondary organic resin. Preferably the coating composition also has thixotropic, metal suspension and hygroscopic agents. All the constituents are dispersed in a vehicle of active and inactive solvents.
Many processes and coatings have been developed for protecting metal stampings, and particularly plain carbon steel substrates, from both direct and electrochemical corrosion. Previously, metal stampings have been protected in varying degreesby applying organic and metal coatings such as phosphate, paint, plastic resins, zinc, lead, stainless steel, aluminum and the like.
Geeck U.S. Pat. No. 4,391,855 discloses a particularly effective corrosion resistant coating for a metal stamping. This coating has a corrosion inhibiting finely powdered metal dispersed in a phenoxy resin organic bonding material and avehicle of solvents. In this coating powdered zinc, cadmium, stainless steel and aluminum are all suitable corrosion inhibitors although zinc is preferred for steel substrates.
Corrosion resistant coatings are used in a variety of applications, many of which require specific colorings. While pigments are readily available for most colors, a satisfactory black corrosion resistant coating previously has not beenproduced. The two pigments often used to produce a black color, carbon black and iron oxide, increase the rate of oxidation and galvanic action of the powdered metal, thereby destroying corrosion resistance, and hence require an overlay of oil to retardthis oxidation and galvanic action. In many applications, such as on the underside of automobiles, this oil overlay is quickly washed or worn off which destroys the corrosion resistance of the black coating.
In the black coating of this invention a pigment of manganese dioxide and a primary corrosion inhibitor of finely divided metal are dispersed in a primary bonding material of a titanate resin and a vehicle of solvents. Preferably, the coating isadhered to a metal stamping by a secondary resin until the primary resin is cured to bond the coating to the substrate. Preferably, in the coating a thin and uniform film is produced on a substrate by including a thixotropic agent, premature curing ofthe primary bonding material is prevented by a hygroscopic agent, and the finely divided metal is prevented from settling out by a suspension agent.
Objects, features and advantages of this invention are to provide a corrosion resistant coating and method which has a black color, improved corrosion resistance, improved adhesion to a metal stamping, improved abrasion resistance, permitscoated substrates to be welded together, can be readily, easily and economically applied in one coat, readily and easily cured at a relatively low elevated temperature in a relatively short period of time, and is rugged, durable, economical and has a lowcoefficient of friction.
These and other objects, features and advantages of this invention will be apparent from the following detailed description and appended claims.
In this invention, a thin layer of a corosion resistant coating in a liquid form is applied to a metal stamping such as by dipping, rolling, brushing, spraying or the like. To convert the liquid layer to a solid dry film and to bond the film toa metal stamping, the liquid layer is heated to an elevated temperature for a relatively short period of time. The heating evaporates solvents in the liquid layer and initiates curing of a primary binding material to provide a dry, thin and uniformprotective film or coating permanently adhered to the substrate.
In the composition of the coating, the primary corrosion inhibitor is believed to be a finely divided metal stamping. To provide cathodic protection against galvanic corrosion of the metallic substrate, the finely divided metal is sufficiently anodic orhigh enough in the galvanic series to act as an anode in a couple with the substrate. For a substrate of iron or steel suitable anodic finely divided metal stampings are magnesium, zinc, aluminum, stainless steel and the like.