Atomization in electrostatic coating

Abstract

A method of atomizing liquid paint using a rotating atomizing device and electrostatically coating an article with a smooth homogeneous film of paint and without the generation of foam or other surface irregularities on the article being coated, wherein an electrostatic field is established between the peripheral edge of the rotating atomizing device and the article to be coated and the liquid paint flows toward the edge of the atomizing device as a continuous thin film, which film is formed into a circumferential series of branch flows of narrow width flowing in the peripheral direction of the atomizing edge, and the liquid paint is atomized from the series of branch flows as they are projected beyond the edge of the atomizing device. The rotary atomizing device may be in the form of a bell or disk and includes a plurality of shallow grooves near its periphery preferably extending radially and of increasing depth in the direction of paint flow and terminating at the discharge edge.

We claim: 
     
       1. A method of atomizing a liquid paint using a rotating atomizing device and electrostatically coating an article with a smooth homogeneous film of liquid paint, wherein an electrostatic field is established between the peripheral edge of the rotating atomizing device and the article to be coated and the liquid paint flows toward the edge of the atomizing device as a continuous thin film, characterized in substantially reducing the thickness of the paint film as it reaches the peripheral edge by flowing the film over a series of circumferentially spaced recessed grooves which run substantially in the direction of paint flow and terminate at the discharge edge, where said grooves extend into the peripheral edge of the device, and atomizing the liquid paint film as it is projected beyond the peripheral edge. 
     
     
       2. A method of atomizing liquid paint according to claim 1 wherein the thickness of the paint film reaching the peripheral edge does not exceed 100 microns. 
     
     
       3. A method of atomizing a liquid paint using a rotating atomizing device and electrostatically coating an article with a smooth homogeneous film of liquid paint, wherein an electrostatic field is established between the peripheral edge of the rotating atomizing device and the article to be coated and the liquid paint flows toward the edge of the atomizing device as a continuous thin film, characterized by providing adjacent the peripheral edge circumferentially spaced, recessed grooves which extend into the peripheral edge of the device to form the thin flowing film of liquid paint into a series of branch flows of narrow width flowing in the peripheral direction of the edge of the atomizing device, and atomizing the liquid paint from the series of branch flows as the paint is projected beyond the edge of the atomizing device. 
     
     
       4. A method of atomizing liquid paint according to claim 3 wherein the thickness of the branch flows reaching the peripheral edge does not exceed 100 microns. .Iadd. 5. A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising: feeding liquid at a controlled rate from a source to an atomizing means having a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge edge adjacent the liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a substantially uniform film of liquid on the liquid film support surface;   flowing the film of liquid through a plurality of grooves in the liquid film support surface aligned generally in the direction of liquid flow and extending into the discharge edge such that a series of independent streams of the liquid are formed by said grooves, said streams being uniformly spaced circumferentially adjacent the discharge edge, and terminating in strands of liquid that extend beyond the discharge edge and produce a spray of finely divided discrete particles; and   establishing between said discharge edge and the article an electric field of sufficient strength to draw the particles away from the atomizing means   
     
     
        toward the article. .Iaddend. .Iadd. 6.  A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising: feeding liquid at a controlled rate from a source to an atomizing means having a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge edge adjacent the liquid film support-surface having a flat surface generally perpendicular to said liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a substantially uniform film of liquid on the liquid film support surface;   flowing the film of liquid through a series of grooves in the liquid film support surface aligned generally in the direction of liquid flow, terminating at the discharge edge, and opening into the perpendicular surface, such that a series of independent streams of the liquid are formed by said grooves, said streams being uniformly spaced circumferentially adjacent the discharge edge, and producing a spray of finely divided discrete particles; and   establishing between said discharge edge and the article an electric field of sufficient strength to draw the particles away from the atomizing means toward the article. .Iaddend. .Iadd. 7. The method of claims 5 or 6 wherein said atomizing means is a generally bell-shaped atomizing device having a diameter of between about 4 and about 10 centimeters, the discharge edge has a thickness at between about 0.2 and about 1.0 millimeters, each of said grooves has a maximum depth of between about 0.1 and about 0.4 millimeters, each of said grooves has a length of between about 1.0 and about 10 millimeters, and said grooves have a pitch between about 0.2 and about 1.0 millimeters. .Iaddend..Iadd. 8. The method of claims 5 or 6 wherein said atomizing means is a generally disk-shaped atomizing device having a diameter of between about 10 and about 64 centimeters, the discharge edge has a thickness of between about 0.2 and about 4 millimeters, each of said grooves has a maximum depth of between about 0.1 and about 3 millimeters, each of said grooves has a length of between about 1.0 and about 15 millimeters, and said grooves have a pitch of between about 0.2 and about 3 millimeters. .Iaddend. .Iadd. 9. The method of claim 6, wherein said atomizing means has a diameter of between about 4 and about 64 centimeters, the discharge edge has a thickness of between about 0.2 and about 4 millimeters, said grooves have a pitch of between about 0.2 and about 3 millimeters, and each of said grooves has a maximum depth of between about 0.1 and about 3 millimeters and a length of between about 1.0 and about 15 millimeters. .Iaddend. .Iadd. 10. A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising:   feeding liquid at a controlled rate from a source to an atomizing means havng a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge edge adjacent the liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a substantially uniform film of liquid on the liquid film support surface;   flowing the film of liquid through a plurality of grooves in the liquid film support surface aligned generally in the direction of liquid flow and having increasing depth in the direction of liquid flow towards the discharge edge such that a series of independent streams of the liquid are formed by said grooves, said streams being uniformly spaced circumferentially adjacent the discharge edge, and terminating in strands of liquid that extend beyond the discharge edge and produce a spray of finely divided discrete particles; and   establishing between said discharge edge and the article an electric field of sufficient strength to draw the particles away from the atomizing means   
     
     
        toward the article. .Iaddend..Iadd. 11.  A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising: feeding liquid at a controlled rate from a source to an atomizing means having a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge end adjacent the liquid film support surface having a surface inclined with respect to said liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a film of liquid on the liquid film support surface;   flowing the film of liquid through a series of grooves in the liquid film support surface extending into the discharge end surface, such that a series of independent streams of the liquid are formed by said grooves, said streams being spaced along the discharge end surface at positions corresponding to the positions of said grooves and producing a spray of finely divided discrete particles; and   establishing between said discharge end and the article an electric field of sufficient strength to draw the particles away from the atomizing means toward the article. .Iaddend..Iadd. 12. A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising:   feeding liquid at a controlled rate from a source to an atomizing means having a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge end adjacent the liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a film of liquid on the liquid film support surface;   flowing the film of liquid through a plurality of grooves in the liquid film support surface extending into the discharge end such that a series of independent streams of the liquid are formed by said grooves, said streams being spaced along the discharge end at positions corresponding to the positions of said grooves, and terminating in strands of liquid that extend beyond the discharge end and produce a spray of finely divided discrete particles; and   establishing between said discharge end and the article an electric field of sufficient strength to draw the particles away from the atomizing means   
     
     
        toward the article. .Iaddend..Iadd. 13.  A method of atomizing a liquid and electrostatically spray coating the surface of an article with the atomized liquid comprising: feeding liquid at a controlled rate from a source to an atomizing means having a surface effective during rotation of said atomizing means for supporting a film of liquid to be atomized, and a circular discharge end adjacent the liquid film support surface having a surface inclined with respect to said liquid film support surface;   rotating said atomizing means such that the liquid fed to said atomizing means is formed into a film of liquid on the liquid film support surface;   flowing the film of liquid through a series of grooves in the liquid film support surface extending into the discharge end surface, such that a series of independent streams of the liquid are formed by said grooves, said streams being spaced along the discharge end surface at positions corresponding to the positions of said grooves, and producing a spray of finely divided discrete particles, each of said grooves producing one of said liquid streams; and   establishing between said discharge end and the article an electric field of sufficient strength to draw the particles away from the atomizing means toward the article. .Iaddend.