Apparatus and methods for application of coatings with supercritical fluids as diluents by spraying from an orifice

A method for spraying a coating mixture comprising coating material and supercritical fluid in a feathered spray pattern at a temperature effective to provide such a feathered spray pattern which comprises supplying coating mixture to a feeding means, which feeding means supplies the coating mixture to a spray gun from which the coating mixture is sprayed in a feathered spray pattern, and which spray gun comprises a housing, an inlet means within said housing through which the coating mixture is passed into said gun, a first passageway for the flow of coating mixture communicating between said inlet means and a valve means through which the coating mixture is passed to a spray orifice means from which the coating mixture leaves said gun as a feathered spray, and a second passageway for the flow of coating mixture communicating between the valve means and the spray orifice means, wherein the temperature of the coating mixture is maintained effective to provide the feathered spray pattern by:

• a) including a plurality of conduits within said feeding means which are juxtaposed to one another and contained within an overall conduit, at least one or more of the plurality of conduits containing coating mixture and at least one or more of the plurality of conduits containing circulating heat transfer fluid for providing indirect heat exchange to the coating mixture;
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• b) indirectly heating the coating mixture while in said housing of the spray gun by providing passages in the housing for the circulation of a heat transfer fluid;
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• c) heating the coating mixture as it passes through a spray orifice tip in a nozzle assembly contained within the spray orifice means by providing the nozzle assembly with a heating means located in or on said nozzle assembly;
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• d) placing an insert having a channel to accommodate the flow of coating mixture as it passes from the valve means to the spray orifice means within said second passageway to effectively reduce the volume of said second passageway thereby helping to at least maintain the temperature in the coating mixture;
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• e) providing said valve means with a valve seat to be in juxtaposition with a spray orifice tip located in the spray orifice means to thereby reduce the volume of said second passageway and help maintain the temperature in the coating mixture;
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• f) providing said first passageway with a static mixer through which the coating mixture passes to help maintain the temperature in the coating mixture;
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• g) a combination thereof.