Abstract A process for electrostatically applying a multilayered coating on a substrate in one operation or step is disclosed, wherein a mixture of powders of at least two different coating materials is used as the coating composition, each powder, in the case of nonconducting powders, differing from the others in dielectric constant by a factor of at least 0.1, and the powders being of substantially different specific gravities, with the components having the lowest dielectric constant value having the lowest specific gravity value. At least one of the powders will be a powder of a film-forming non-conductive organic or inorganic polymer. Upon electrostatically applying a coating of this powdered composition to a conductive substrate which has a neutral charge or a charge opposite from that of the coating composition powder particles, the powders stratify into distinct layers of different compositions. The powders adhere to the substrate because of contact or static electrification for a reasonable length of time and until at least one of the powders can be cured or fused to form the final coating. Thus, for instance, in only one pass with an electrostatic spray gun, a protective coating of superimposed layers of zinc, epoxy, and polyethylene can be applied to a conductive substrate.
The process as claimed in claim 1 wherein said mixture contains at least one conductive metal and at least one film-forming non-conductive organic polymer.
Claim 2
Dependent Claim
56 words
The process as claimed in claim 2, wherein said conductive metal has an average particle size of less than about 50 microns, and is present in said mixture in the amount of about 4 to about 30 percent by weight, and said organic polymer has an average particle size of about 10 to about 300 microns.
Claim 3
Dependent Claim
27 words
The process as claimed in claim 3, wherein said film-forming organic polymer is a mixture of at least one thermoplastic polymer and at least one thermosetting polymer.
Claim 4
Dependent Claim
49 words
The process as claimed in claim 4 wherein said powder mixture contains about 5 to about 12 percent by weight of said conductive metal, about 55 to about 75 percent by weight of said thermosetting polymer and about 20 to about 40 percent by weight of said thermoplastic polymer.
Claim 5
Dependent Claim
23 words
The process as claimed in claim 5 wherein said thermosetting polymer is an epoxy polymer, and said thermoplastic polymer is an ethylene polymer.
Claim 6
Dependent Claim
13 words
The process as claimed in claim 6 wherein said conductive metal is zinc.
Claim 7
Dependent Claim
29 words
The process as claimed in claim 6, wherein less than 7 1/2 percent by weight of zinc is in said mixture, based on the total weight of said mixture.
Claim 8
Dependent Claim
22 words
The process as claimed in claim 8 wherein the average particle size of the zinc is about 4 to about 10 microns.