Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-04-03
2002-11-12
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S273500, C156S275500, C156S275700
Reexamination Certificate
active
06478915
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods of edge fold sealing at the edges of body parts.
For edge fold sealing in motor vehicle construction, a hardenable material is commonly laid over the outwardly open part of the fold, usually in the form of a bead. The hardenable material is gelled in a first hardening operation, for example by inductive heating of the sheet metal in the region of the hardenable composition, and is then completely cured in a following hardening operation, which may take place, for example, in a KTL, i.e., “cathodic dip coating”) kiln. As the hardenable composition, polyvinyl chloride (PVC) is often employed.
This method presents problems when the hardenable material encloses pockets of air or absorbs liquids or gases before final hardening that will expand during subsequent kiln hardening and form outwardly visible blisters. These blisters in the first place impair the visual appearance of the sealed edge and in the second place form weak spots permitting corrosive attack in the seal.
In an alternative conventional finishing step in the production of vehicle parts, for example doors, hatch and hood flaps, sliding roof panels and the like, two sheet metal parts are connected by folding the edge of an outer part over the edge of an inner part. Thus, in building the unfinished rough body part, an adhesive is first applied to the oiled metal sheet, generally consisting of steel, hot-galvanized or electrically galvanized steel or aluminum, along the edge of the outer part, generally by “swirl” processes in a layer having a thickness of about 0.2 mm and, after insertion of the inner part, the outer edge of the outer part is rolled over the periphery of the inner part. Only then is the corrosion-sensitive edge of the outer part sealed by coating, usually by hand, with a sealant such as PVC plastisols for example. For reasons of production technology, quality and economy, it would be desirable to eliminate such edge fold sealing from the coating process and relegate it to construction of the rough body part, i.e. to employ the first method described above. In other words, there should be no material applications in the coating process that might impair the coating surface in any way. Hitherto, this objective has not been satisfactorily achieved, since as yet no dependable and economical procedure is available for the purpose.
German Offenlegungsschift No. 33 14 896 describes an adhesive for edge fold sealing that is pre-cross-linked by ultraviolet (UV) irradiation and is later finish-hardened in the kiln after passing through the cleaning baths at temperatures of around 180° C. together with the KTL priming. Apart from the relative simplicity of UV irradiation, it also has the disadvantage that the resulting hardening, and hence the cross-linking as well, takes place only from the outside in. For layer thicknesses greater than 0.3 mm, adequate pre-cross-linking can not be assured even with increased irradiation time, and the underlying layers remain un-cross-linked in a pasty condition. This pasty layer, beneath the pre-cross-linked surface has significant negative effects on the visual appearance of the seal. First, since the parts are at times transported manually, one consequence is that the adhesive, while not tacky, is not solid, resulting in fingerprints which may constitute a visual drawback. Second, there is danger that this uncross-linked material may be forced out of the seal upon thermal hardening in the KTL kiln as a result of expansion of the air enclosed between the edge fold bond and the seal. Third, upon subsequent cooling, the pasty seal material may be drawn back in the edge fold. Fourth, adhesives tend, especially in un-cross-linked condition, to absorb moisture, leading to formation of blisters upon thermal exposure in the KTL kiln.
The conditions described above are significant in the sense that it is desirable for reasons of economy to produce the parts in a finished form, that is, including the seal, at a central station and ship them from the central station to production lines which may be located in different parts of the world where they go directly into the cleaning bath which is the first step in the coating process. This procedure involves a substantial potential saving since the rough body parts and the sealing steps, which are in any event unwelcome in the coating process, can be avoided on the production line. Moreover, any new sealing process should be capable of integration in existing finishing operations on the rough body parts satisfactorily and without major financial outlay. In this respect, the requirement for an additional kiln would be absolutely unacceptable.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of edge fold sealing which overcomes disadvantages of the prior art.
Another object of the invention is to provide a method of edge fold sealing in which blister formation due to enclosed gases or liquids is suppressed in the subsequent kiln treatment, and/or good “handling” of the sealed parts is assured throughout process.
These and other objects of the invention are attained by providing a method of edge fold sealing which includes pre-hardening of a seal in a plurality of steps which may include ultraviolet radiation hardening and/or thermal hardening by infrared radiation, inductive heating and hot air impingement and/or reactive hardening without any external application of energy.
In accordance with the invention, a special process for the production of vehicle components, and particularly a new method of edge fold sealing, is provided in which fabrication is greatly simplified and quality enhanced.
Thus, by the method of the present invention, the disadvantages of the prior art are overcome, and edge fold sealing is carried out that satisfies all requirements for secure production of attachments and, in particular, for worldwide transport of “rough” or oiled parts, otherwise known as “parts tourism.” In such cases, it is important for the visual quality of the edge fold seal to remain perfect even after prolonged transport of the parts through various climate zones and to ensure a smooth surface without pits, cracks, etc. Furthermore, the method may be applied to the rough body parts without any major fixed investment, and substantial manufacturing advantages can be gained by the new method.
According to a preferred embodiment of the invention, hardening of the seal takes place by a photochemical reaction, induced by light, in particular UV light, combined with a multi-step hardening procedure. Depending on the kind of seal, the UV light has a depth of penetration from about 0.01 to 1 mm, so that a surface hardening of the seal is achieved but deeper penetration of the UV radiation is also possible. The seal surface thus hardened protects against the entry of gases or liquids into the seal so that, upon later thermal hardening, no blisters will be raised. In addition, with such a surface hardening, emergence of any gases already contained in the seal is suppressed or prevented during thermal hardening.
Advantageously, the photochemical hardening is accomplished in such manner that, upon subsequent thermal hardening, the region of the composition that has already been photochemically hardened will be further hardened by the thermal hardening, i.e. so that functional groups which are already present for the photochemical as well as the thermal hardening will also be thermally cross-linked to enhance the hardening. In this way, an especially stable surface of the sealing composition is created.
For all embodiments of the method, a sealing procedure may be employed in which hardening is an exothermal process, so that once initiated, the hardening process continues at least in part, and correspondingly a more complete hardening is achieved. For this purpose, the sealing may combine reactive sealing components so as to be capable of initiating the hardening process without application of external energy.
In a further embodiment according to th
Beckord Volker
Bucher Patricia
Merz Peter W.
Schmalbruch Jörg
Sonnenberg Karl-Heinz
Baker & Botts LLP
Ball Michael W.
Kilkenny Todd J.
Volkswagen AG
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