Present day techniques for the spray application of coatings are generally categorized in one of three basic spray application techniques. The first of these techniques is air atomization wherein the coating particles ride on an air stream from the spray gun to the product being coated. The second of these techniques is airless atomization wherein the coating material is atomized and propelled by hydraulic pressure. The third is electrostatic spraying wherein the coating material is atomized by air or airless techniques and the deposition of coating on the product being sprayed is by electrical attraction of the coating particles. With each of these spray techniques spray booths are commonly employed and usually required by federal or state regulatory agencies.
Present day spray booths are designed with the objectives of providing a safe working place, preventing pollution of the atmosphere and enhancing the quality of the product being sprayed. The rapid and thorough removal of volatile solvents and vehicle fumes from the premises is essential in many spray applications to meet the requirements of the Occupational Safety and Health Administration and insurance carriers. The air moving through the spray booth carries coating over-spray away from the product, avoiding the finish marring consequences of semi-dry coating particles settling on already coated surfaces. By effectively removing coating particles from the air being discharged to the outside, the spray booth eliminates a common cause of air pollution and thus helps the user avoid risking violations of legal requirements, particularly those of the Environmental Protection Agency, and prevents staining and dirtying of immediately adjacent property.
Numerous filter designs have been proposed for spray booth applications, but in each case these designs have been found to be inadequate due to the fact that they have either clogged too rapidly or have been cumbersome and costly in design. There exists a need for a replaceable filter for use with spray booths that is simple in construction and suitable for allowing large volumes of air to pass through with a minimal loss of efficiency.
U.S. Pat. No. 2,909,237 discloses a collapsible filter for separating particulate matter from a fluid stream. U.S. Pat. No. 3,075,337 discloses a replaceable filter medium that is particularly suited for use in spray booths. The filters disclosed in each of these patents, however, are complex in design and construction and do not offer the advantages of the present invention.