Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1993-12-13
1995-02-28
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
2041802, 204300EC, C25F 500
Patent
active
053933907
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates generally to a process for spray coating an object with a waterborne coating and, more particularly, to a process for the treatment and recycling of overspray resulting from such spray coating. The present process is applicable in industry in general and, especially, in the automotive industry where car bodies and a wide variety of other larger objects are spray coated.
Efficient coating of automobiles and other larger objects with liquid coatings normally requires spray application. Current spray application techniques generate a significant amount of overspray and, in order to isolate this overspray from the immediate surrounding environment, the spraying operation is normally conducted in a spray booth.
The overspray occurring, for example, during automobile coating with waterborne coatings is normally removed from the spray booth by an exhaust air stream and/or absorbed in water (water curtains or cascades) circulated from a catchment tank. When it is considered that in one automobile spray booth alone approximately 1-1.5 tons of paints are applied daily and approximately 20-30% of this is overspray, the magnitude of the resulting waste problem is apparent.
There exist essentially two options with respect to handling this waste product--disposal and/or recycling. Because of the large volumes generated, and because of the environmental consequences involved, disposal is a burdensome and very expensive option. Recycling, therefore, becomes the desirable alternative.
Waterborne coatings utilized in general industry, and particularly in the automotive field, can include a large number of solid and/or liquid components. These components can generally be broken down into three primary categories with subcategories as set forth below: compounds) including one or more of water-insoluble, water-dispersible and/or water-soluble components; and water-insoluble (e.g. pigments), water-dispersible (e.g., emulsifiers, stabilizers and rheological additives) and/or water-soluble (e.g. lower molecular weight polar organic co-solvents, acids and amines) components.
The sheer variety of components makes effective treatment and recycling a difficult task.
The currently practiced recycling procedures for waterborne coatings require the addition of coagulating agents and/or detackifiers to the collected overspray. The resulting coagulate is extracted by sedimentation, flotation, filtration and/or similar separation processes, and subsequently removed from the spraying area. Due to the presence of the added chemicals, and due to the coagulated form of the recovered product, recycling is a costly and complex process. In addition, the chemical additives often affect the properties of any reclaimed product, and separation of many water-soluble materials, such as low molecular weight organic cosolvents, acids and amines, remains a problem.
Various other recycling methods have also been proposed, but none have been totally successful. For example, WO82/02543 describes a method for recovery and recycling of waterborne coating overspray, whereby the overspray is collected and separated (e.g. by a traveling screen filter or a settling tank) into a low and high solids (e.g. 10-50% solids) fraction. The solids content of the high solids fraction is preferably adjusted to fall within the range of 5-30% solids (e.g. by the addition of water), then passed in the form of a slurry to a decanter centrifuge, of a type well-known in the art, which further separates the liquid from the solids. The solid component is said to comprise about 75 wt % solids, which can be utilized as a base for a reclaimed paint product, or can be further dried for disposal at a landfill. The liquid component, which can be recycled back to the spray booth, is said to typically comprise less than 1 wt % solids. As is clear, the separation methods described in the reference are generally ineffective for separating water-soluble components and, especially, the aforementioned lower molecular weight water-soluble
REFERENCES:
patent: 3748244 (1973-07-01), Gilchrist
patent: 4607592 (1986-08-01), Richter
Freese Karl-Heinz
Gunter Gerhard
Akzo Nobel nv
Mancini Ralph J.
Mayekar Kishor
Morris Louis A.
Niebling John
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