The present invention generally relates to methods and apparatus"" for treating plastic substrate parts to accept paint and, more particularly, to a method and apparatus for treating plastic substrate parts to accept paint without using adhesion promoters that allows plastic substrate parts having flat regions, undulations, and recesses to be properly treated.
In the art and science of painting, it is a practice to prepare a surface that is to be painted to receive paint. A surface properly prepared is more likely to produce a desirable result and remain properly painted for a long term. Preparation techniques vary depending on the material to be painted, the type of primer, stain and/or paint which will be used, the manner of application of the paint and the conditions to which the painted item will be subjected, among others.
In the past, with respect to automobiles and automobile parts, plastic played a minor role and typically could be prepared such that the plastic part was molded in the desired color. As plastic has become a more important product in the automobile industry, such items as interior and exterior door, dashboard and other body panels and protective equipment, such as bumpers and door guards, have been made of a plastic material. Typically, exterior plastic parts, especially in modern vehicles, are painted to match or aesthetically contrast, with the body of the automobile.
In order to speed production of parts, and reduce costs, plastic parts are now typically molded in one color (such that only a single run of molding is needed for all colors offered a vehicle model) and then painted to match the desired vehicle color. This allows for less planning and more availability of parts for all colors of a vehicle model, and typically greater numbers of color combinations to appeal to the tastes of purchasers. Further, this manner of producing parts allows an adequate supply of replacement parts for subsequent body repair needs on any color vehicle.
A problem arises, however, in producing painted parts, in that plastic material, used body parts, typically must have a smooth surface in order to be acceptable. Smooth surfaces are typically not amenable to painting. Paint sprayed, or otherwise placed, on smooth surfaces, especially those with low surface energies, generally does not stick to the surface and may be peeled or chipped off, which is a highly commercially undesirable result. While various means have been provided to stem this problem, such as abrading the surface prior to painting or adding adhesives, such as epoxy, to paint, in or to get the paint to stick to the item being painted, these has proved effective.
It has been found that the use of a grafting material, such as those in a family of multifuntional amine-containing organic compounds, on plastic parts, which have been oxidized, allows paint to better adhere to the plastic. See, for example, U.S. Pat. No. 5,922,161 to Wu et al. (the xe2x80x9c""161 patentxe2x80x9d) that discloses a method of modifying or tailoring the surface of polymers and or polymer-based materials to control surface and interface chemistry and molecular structure. The ""161 patent discloses a method for oxidizing the surface of a polymer and treating the surface with a grafting chemical. The content of the ""161 patent is incorporated by reference into this application as if fully set forth herein.
It has been found, however, procedures which employ the use of grafting chemicals added to plastic parts which have been oxidized are typically only generally applicable to sheets of plastic Further, the devices and methods used to oxidize the plastic and apply the chemical to sheets of plastic typically do so in such manner as to cause areas of the plastic sheet to be treated more than once, because of inadvertent overlapping, wasting chemicals, causing the loss of production time and weakening the over treated areas.
In one plastic sheet treating operation, a gas/air burner, having a large area with many burner ports, and comprising means to spray grafting chemicals onto areas of plastic with have been flame treated by the burner, is used. The burner and grafting chemical sprayer device is moved over the plastic sheet, overlapping some sections of the sheet in movement. In the operation of such a system, the burner oxidizes the plastic sheet and the grafting chemical is sprayed onto the oxidized plastic, to prepare the plastic for further processing, such as with paint, adhesives or other coatings. The sheet is thereby made amenable to adhesion by other chemicals, including paint.
However, plastic parts typically are not made in the form of plastic sheets, especially in automobile applications. Plastic parts are generally constructed in all shapes and with undulation, indentations, openings, crevices and other contours. The use of such treatment devices and methods, as described above, are ineffective to treat the variations in modern plastic parts. Further, treatments such as dipping or spraying have been found to be ineffective as the oxidation process cannot pre-treat the non-linear sections of the plastic part, causing the sprayed grafted material to be wasted.
Further, it has been found that the use of prior treating apparatus often cause large number of toxic chemicals to be released into the atmosphere as a result of the shot-gun approach to the treatment of plastics. This is especially the case when adhesion promoters are utilized to prepare a plastic substrate part to accept paint.
Another problem that exists in present plastic part treatment methods is that once the part is treated it is typically difficult, without sophisticated tests, to discern a difference between the treated part and an untreated part. In many instances, items that have been treated have been confused with items which have not been treated, causing a waste of materials and time in retreating, and generally, an over weakening of the surface of the part which is re-treated.
I have discovered and invented a method and apparatus for treating plastic substrate part to accept paint without using adhesion promoters that allows all undulations, indentation, openings, crevices and other contours in the plastic substrate parts to be effectively treated. In accordance with one aspect of my invention, I have designed a unique burner device that allows a desired portion of a substrate plastic part to be flame treated and sprayed with a graft chemical at substantially the same time thereby allowing adhesion of paint, or other coatings, to the part.
Such a method and apparatus has a number of distinct advantages. First, plastic substrate parts of all shapes and sizes can be prepared to accept paint. Second, the method disclosed herein is practiced in an environmentally friendly manner. For example, all of the environmentally deleterious effects associated with utilizing adhesion promoters such as, for example, the discharge of the active solvent utilized in typical adhesion promoters are completely eliminated. This allows, for example, the manufacturer""s capital costs to be reduced because, for example, there is reduced need for abatement systems that reduce the discharge of solvents to the atmosphere.
Third, this method and apparatus is suitable for use in large, commercial scale applications. For example, in accordance with one embodiment of the present invention, a plastic bumper beam can be treated to accept paint in approximately forty (40) seconds per part. Fourth, the use of this method and apparatus significantly reduces over-spray so that smaller amounts of graft chemicals can be utilized.
Other objects and advantages of the present invention will become apparent as the description proceeds.