Coating processes – Flame contact
Reexamination Certificate
2001-02-13
2002-06-18
Beck, Shrive P. (Department: 1762)
Coating processes
Flame contact
C427S322000, C427S409000, C427S412100, C427S419200, C427S430100, C427S435000
Reexamination Certificate
active
06406748
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to processes useful in the assembly line manufacture of articles including organic surfaces and involving the repeated contacting of aqueous compositions with said surfaces at various points during a multi-step polymeric coating operation. This invention is particularly related to the field of coating plastic parts during the assembly of automobile bodies.
BACKGROUND OF THE INVENTION
Historically, automobiles have been constructed of metal parts the outer surfaces of which have been coated to provide a smooth showroom finish. The materials used to coat the metal comprise predominantly organic polymeric materials, or paints, such as lacquers, polyurethanes, acrylics and such, all of which provide a durable and attractive finish. More recently, automobile manufacturers have incorporated plastic parts into the automobile assembly process to reduce weight and improve rustproofing properties. The introduction of plastic parts into automotive assemblies has presented the automotive industry with challenges including the ability to maintain a uniform, constant color showroom finish on the different substrate materials. Various methods have been adopted to achieve this goal.
Many of the parts making up a typical automotive assembly are not manufactured by the original equipment manufacturer (“OEM”) but are produced by specialty suppliers at sites distant from where the final automobile assembly takes place. The plastic parts included in the assembly are normally molded and assembled at supplier facilities where their production and priming (in most cases) is also complex. In the case where plastic parts and sheet metal parts are not subjected to a common coating or painting operation, differences in color tone and/or “look” of the coating films between the two types of materials may remain after the finish coating. Furthermore, the parts are more likely to experience contamination, due to handling during assembly after such individual treatment. It may therefore be difficult to color match both types of parts in this type of operation and more difficult to ensure the quality of the finish due to handling contamination. Therefore, many automobile manufacturers choose to precondition the entire assembly of parts, and paint the completed assembly that includes the plastic parts and the sheet metal parts, referred to as the “body-in-white”.
The assembly plant receives the finished plastic component, where it is included in the automotive assembly, after which such components may be subjected to a variety of processes at the same time as the metal parts. These processes include steps leading up to the application of the finish coating of paint to the plastic and metal parts. More specifically, the manufacturing facility assembles the metal parts and plastic body parts into the automotive body-in-white, sends the body-in-white through several pretreatment steps and corrosion resistance processes, and lastly applies the final finish using a series of coating steps. These basic steps encompass the spraying, or dipping, of the assembly with a sequence of aqueous compositions that are recycled in a continuous manner and thereby contact newly assembled plastic and coated metal parts with aqueous compositions that have been in contact with previously treated assemblies of parts. In particular, the pretreatment operation typically comprises the steps of a power wash, a phosphate treatment, and an electrocoating process, each of which may employ an aqueous spray and/or aqueous bath dip process.
The assembly line coating of sheet metal-plastic hybrid assemblies presents problems relating to the actual coating processes and conditions. Since the physical and chemical properties of the plastic parts differ significantly from those of the sheet metal parts, each step in the coating operation must be designed to be compatible with each type of surface. Furthermore, the end result, a showroom quality paint finish, must be practically identical for both the plastic and sheet metal parts. The final properties of color matching, color depth, smoothness, luster, reflectivity, among others, must be uniform through all visible surfaces of the finish coat assembly.
While manufacturers have been successful in designing a series of coating process steps applicable to both plastic and sheet metal parts to achieve the aforementioned goals, the automation of this process has not been altogether successful. One of the daunting problems in coating the plastic and metal parts-containing assembly has been the appearance of defects in the surface quality of the plastic parts and/or metal parts that are pretreated with one or more coatings of organic primer material. These defects manifest as surface irregularities in the final painted surfaces that detract from the acceptability of the end product. To achieve the desired factory fresh showroom finish, manufacturers find it necessary to employ time consuming manual labor to prevent these defects from appearing or to repair such defects after they appear. This of course increases the cost of the overall coating operation.
Reported Developments
Automobile manufacturers have addressed the problem of organic surface defects by incorporating into the automated coating process a labor intensive hand wiping of the plastic and/or coated metal surfaces prior to the final coating operation. Automobile technical bulletins [Brouder, E. “The Problem Recognized: Surface Treatment of Plastics Before Painting” Ind. Anz. 108 (37-38, May 13, 1986) recognized that dust and dirt, fingerprints and parting agents contaminated the surfaces of plastic automobile parts and prescribed a regimen of cleaning solutions containing surfactants and/or antistatic coatings to remove and/or avoid the contamination. This bulletin appears to refer to the treatment of plastic parts separately from sheet metal parts and the removal of contamination resulting from handling the parts during parts manufacture per se and subsequent assembly. The surface contamination problems arising during whole assembly coating are not addressable economically using the cleaning solution method, in view of the recycling of the cleaning solutions which themselves appear to be the source of the problem as discussed below. To this day, hand wiping of the assembly at various stages prior to final coating is the only way, inelegant, as it may seem, by which the industry has addressed the surface defect problem.
Although many sources of contamination resulting in the organic surface defects are possible, the present invention recognizes that the major source of contamination arises from the physical removal of uncured resin particles from the metal surfaces of assemblies undergoing the coating operation The inventors have found that these particles originate with the sealers, sound deadeners, mastics and/or adhesives applied to selected portions of parts, predominately the metal parts, used in the automobile body construction, are removed therefrom by the physical forces present during the aqueous pretreatment steps, and become suspended in the recycling aqueous compositions. The present inventors also believe that on application of the aqueous composition to the sheet metal-plastic assemblies, these particles are redeposited on the organic surfaces, or in other words are transferred from the resin-treated metal surfaces to the organic surfaces. Upon curing of the final coating, the redeposited particles cause surface irregularities or defects in the finish coat.
SUMMARY OF THE INVENTION
The present invention relates to a method for maintaining in aqueous suspension hydrophobic particles contacted with organic surfaces, comprising oxidizing said organic surfaces, contacting said aqueous suspension of hydrophobic particles with said oxidized surfaces, and removing said aqueous suspension from said surfaces.
Another aspect of the present invention is a method of preventing the formation of coating defects in polymeric coated surfaces in a coating process comprising a plurality of steps
Fristad William E.
Held, III Theodore D.
Beck Shrive P.
Crockford Kirsten A.
Harper Stephen D.
Henkel Corporation
LandOfFree
Prevention of particle redeposition onto organic surfaces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Prevention of particle redeposition onto organic surfaces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Prevention of particle redeposition onto organic surfaces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2906343