Coating apparatus – With vacuum or fluid pressure chamber
Reexamination Certificate
1999-10-29
2001-07-24
Beck, Shrive (Department: 1762)
Coating apparatus
With vacuum or fluid pressure chamber
C118S319000, C118S325000, C118S326000
Reexamination Certificate
active
06264743
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the application of coatings to substrates and more particularly to an apparatus and method for controlling airborne overspray incident to the non-contact spraying of a coating material onto a moving, porous substrate.
BACKGROUND OF THE INVENTION
Many industrial processes rely upon a technique that can apply a uniform layer of coating material onto a discrete surface area of a moving, porous substrate. Applications include the manufacture of diapers, incontinence pads, and other hygienic products, as well as many other products. Among the various techniques, non-contact dispensers can apply a layer of coating material without physically touching the moving substrate surface. Typically, a non-contact dispenser sprays a stream of coating material from an outlet nozzle of a dispenser located adjacent to the substrate surface. Particles of coating material must cross an air gap between the outlet nozzle of the dispenser and the substrate surface.
In many industrial processes that apply a non-contact coating, the substrate moves quickly and this displaces air in and around the air gap between the dispenser and the substrate. The turbulent air flow induced by the moving substrate captures stray particles of coating material that rebound from the substrate surface. In addition, the speeding air deflects particles of coating material having low kinetic energy from the spray stream. These misdirected particles of coating material constitute airborne overspray and are transported by the turbulent air flow to various undesired locations within the production machinery.
As a consequence of the randomly misdirected overspray, maintenance personnel must periodically clean the machinery of accumulated coating material. If the buildup is not periodically removed, components may eventually become coated with enough material to create various problems in the machinery. For example, moving components of the machinery may prematurely wear, or otherwise be adversely affected, and require replacement. This decreases productivity, due to machine down-time during maintenance, and raises production costs. If the coating material is an adhesive, simple overspray collection methods, such as those used in powder coating processes, are inadequate since adhesives significantly coagulate and bind to collection heads, conduits, collection vessels and similar structures. In addition, simple overspray collection methods generate a waste stream for either disposal or recycling.
The prior art has failed to provide a suitable solution for reducing or eliminating non-contact coating overspray, especially with regard to non-contact coating of porous substrates. Thus, the coating industry continues to need an apparatus for capturing airborne particles of coating material not received or retained by the surface of the moving substrate.
SUMMARY OF THE INVENTION
The present invention addresses these and other problems associated with the prior art by providing an apparatus and method for the non-contact dispensing of a coating material onto a first surface of a moving substrate and for controlling overspray incident to non-contact dispensing. An apparatus and method for dispensing coating material and controlling the overspray therefrom comprises a non-contact dispenser dispensing a coating material onto a first surface of a relatively moving porous substrate and a vacuum member having a hollow interior attached to a source of vacuum pressure. As used herein, the terms “vacuum pressure” or “vacuum” are not meant to imply any specific amount of pressure other than a pressure that performs the functions stated and claimed herein. At least one orifice in the peripheral surface of the vacuum member further communicates the vacuum pressure to the second surface of the porous substrate in at least substantially the same plane as the dispensed material. In a typical case, this will be a vertical plane. Due to the porosity, the vacuum is further communicated through the thickness of the porous substrate to the first surface. As a result, airborne particles of the coating material are attracted to the first surface of the porous substrate.
Airborne particles of coating material dispensed by the non-contact dispenser will experience the vacuum pressure and accelerate towards the first surface. Particles of coating material formerly having low energy will be less susceptible to the influence of the air flowing about the moving substrate due to the influence of the vacuum pressure. In addition, a particle of coating material is less likely to rebound and be transported away by the moving air flow. When a particle strikes the surface of the porous substrate, the vacuum pressure adds to the normal binding force at the instant the coating material impacts the substrate. These physical phenomena reduce the probability that any single particle of coating material will contribute to airborne overspray.
A secondary benefit of the applied vacuum pressure is that the moving substrate itself will be attracted to the surface of the vacuum member. This attractive force will aid in registering the moving substrate surface with the nozzle outlet of the liquid dispenser so that the dispenser more precisely applies the coating material.
In a preferred embodiment, the vacuum member freely rotates about a longitudinal axis thereof and supports the moving substrate as it passes the non-contact dispenser. Preferably, the vacuum member is cylindrical. In one aspect, the vacuum member rotates about the axis of a stationary shaft.
In another aspect, the stationary shaft is hollow and is connected to the source of vacuum pressure. The surface of the shaft has one or more orifices that communicate the vacuum pressure to the interior of the vacuum member.
Another feature of the invention controls the surface area of the vacuum member that is actively communicating vacuum pressure to the substrate. More specifically, the rotating vacuum member may be housed inside a stationary cradle which has a longitudinal opening in its surface to expose only a portion of the surface of the vacuum member. Only orifices in the exposed portion of the vacuum member can act upon the substrate.
One advantage of the vacuum assisted overspray controller is that the airborne overspray of adhesive particles can be controlled in an industrial process that dispenses a stream of coating material through an air space onto a porous substrate.
Another advantage of the vacuum assisted overspray controller is that the airborne overspray of coating material for a non-contact coating dispenser is deposited on the intended porous substrate, rather than collected for disposal as a waste stream or recycled for respraying.
Another advantage of the vacuum assisted overspray controller is that it can be readily incorporated into a conveying system for transporting a porous substrate past a non-contact coating dispenser.
Another advantage of the vacuum assisted overspray controller is that the vacuum pressure aids in the proper registration of the porous substrate for receiving the stream of particles or beads from a non-contact coating dispenser.
Another advantage of the vacuum assisted overspray controller is that the present invention can be easily retrofitted to existing production machinery.
Additional features, advantages and objectives of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.
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Beck Shrive
Crockford Kirsten A.
Nordson Corporation
Wood Herron & Evans L.L.P.
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