Coating processes – Solid particles or fibers applied – Uniting particles to form continuous coating with...
Patent
1998-04-28
2000-07-04
Parker, Fred J.
Coating processes
Solid particles or fibers applied
Uniting particles to form continuous coating with...
4272082, 427277, 427287, 427370, B05D 112
Patent
active
060835583
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process for coating the adhesive surfaces of structural or support elements and, in particular, of fastening elements.
This invention focuses specifically on the application of highly reactive hot melt adhesives which, on exposure to temperatures up to 50.degree. C., are wear-resistant and nonsticking and which can be reactivated on exposure to heat or some other kind of energy so as to produce a permanent adhesive joint. The adhesive coating applied to the surface must be totally nonsticky and adhesion-resistant until the fastening element is used, and the adhesive force inherent in the adhesive should be triggered only after the adhesive has been reactivated at the site of application.
It is known from German Patent No. DE 44 02 550 A1 that hot melt adhesive can be applied to the adhesive surface of a plate by lowering the fastening element with the adhesive surface face down into a hot melt adhesive bath and by lifting it again as soon as the entire adhesive surface has been wetted with a sufficient quantity of adhesive. The adhesive layer adhering to the lower surface has to be dried before the fastening elements can be packaged and transported to the application site to prevent the fastening element from sticking together.
This procedure, however, is relatively cumbersome and time-consuming since the fastening elements must be separately grasped, after which they are immersed into the hot melt adhesive bath with the adhesive surface facing down, which is followed by a drying step.
SUMMARY OF THE INVENTION
This invention is directed to simplifying the application of hot melt adhesive to the adhesive surfaces so as to not only lower the coating costs but also to increase the production.
This is accomplished by a process as follows: ready-mixed adhesive in solid form is applied to the adhesive bearing surface of the fastener and is heated while exerting a mild contact pressure. In one embodiment of the invention, the powdered adhesive is compressed to form a thin plate corresponding to the shape of the adhesive surface prior to applying it to the adhesive bearing surface.
The heat required to heat the structural or support elements and, in particular, the fastening elements can be generated using, for example, ultrasound, infrared lamps or other high-energy radiation, heating elements, hot air, or induction, with the induction method being preferred.
This method makes it possible not only to coat the adhesive surface more rapidly and cost-effectively with a hot melt adhesive but also offers another advantage in that the hot melt adhesive is subjected to the lowest possible thermal stress since only the boundary surface of the adhesive plate which is in contact with the metal surface is melted by an electromagnetic heater. This method makes it possible for the reactivation capacity of the adhesive to be substantially maintained until used on location.
By preheating the fastening elements in the range of 50.degree. C. to 90.degree. and subsequently to a temperature high enough to ensure the boundary surface is melted, the coating time is further shortened since the time required to melt the boundary surface of the adhesive plates can be shortened. This goal can be furthered by preheating the fastening elements to a temperature which will be sufficient to melt the adhesive when it is applied. The cooling time is even further shortened, and the coated fastening elements can be ready for use more rapidly for the intended purpose.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a diagrammatic representation of several embodiments of implementing the coating process according to this invention which are explained in greater detail below. As can be seen,
FIG. 1a) shows adhesive as it is applied in the form of a powder to the circular adhesive surface of a locking bolt,
FIG. 1b) shows adhesive as it is applied in the form of pellets to the circular adhesive surface of a locking bolt, and
FIG. 1c) shows adhesive as it is applied in the form of compr
REFERENCES:
patent: 4223632 (1980-09-01), Cadwallader
patent: 4262038 (1981-04-01), Wallace
patent: 4508759 (1985-04-01), Wallace
patent: 5262197 (1993-11-01), Pollizzi
A. Raymond & Cie
Parker Fred J.
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