Method of coating heat sensitive materials with powder paint

Details Method of coating heat sensitive materials with powder paint Method of coating heat sensitive materials with powder paint

1993-01-15

1995-02-07

Pianalto, Bernard

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

427195, 4273743, 4273744, 427375, 427379, 4273855, 4273981, 427559, B05D 306

Patent

active

053874420

DESCRIPTION:

BRIEF SUMMARY
The present invention refers to a method by which it is possible to coat heat sensitive materials with powder paints. In the context of this report the term "heat sensitive materials" means materials which undergo physical and/or chemical modifications when treated at temperatures and times currently used in timing processes and possibly curing of paints in powder form, while "heat resistant materials" are those which do not undergo these modifications.
Powder paints are assuming an always greater importance for coating metallic or heat resistant objects of any type, given that these have eliminated numerous problems of environmental pollution and danger to the health of workers employed in painting, other than forming coatings with excellent qualities.
Powder paints, after having been applied to the objects by means off various systems, and today principally electrostatically, they must however be subject to melting, filmation and possibly curing to adhere permanently to the objects, and this generally takes place in kilns of various structure according to the objects to be coated, and always at rather high temperatures, made necessary by the melting temperatures of the paint components and maintaining these temperatures for continuous set times.
However until today it has been considered impossible to coat heat sensitive materials with powder paints, such as plastic materials, wood, paper and cardboard, leathers, textiles and so on, because these materials absolutely cannot resist the temperatures necessary for powder paint treatment for a continuous time. On the other hand it would be highly desirable to be able to coat these materials with powder paints too, to eliminate the abovementioned dangers and risks also in these industrial sectors due to the use made, currently necessary, of solvent-containing paints to coat the above mentioned heat sensitive materials.
The structures and methods carried out until now for the treatment of objects coated with powder paints do not however allow the treatment to be extended to heat sensitive materials which would be irremediably damaged. All the existing structures and methods are only suitable for metallic or heat resistent objects. In particular treatments by means of inffrared radiation exist, but the temperatures and times of the treatment are prohibitive for heat sensitive materials. From German patent DE-34 06 789 C1 (Berkmann) a process is known for filming and curing objects coated with powder paints by infrared radiation, in which an intermediate neutral area is provided between two heating areas which allows a certain cooling of the objects during treatment, but PG,4 also here the treatment temperatures and times in the areas are such as to exclude any utilization for heat sensitive materials.
In particular according to the details of the description of the above mentioned patent the temperature of the object is lowered only slightly, so that one can compensate for the temperature differences between thicknesses of different entity in the object. As a whole however, also in this case the temperature of the object remains excessive. Furthermore, Ebb whole object is heated by means of air circulation, something to be avoided in the presence of heat sensitive materials.
In the Japanese application A 59-87135 (Inoue et al.) a process is described for coating the surface of a polyurethane foam molded product with a thermoplastic synthetic resin, which is heated to be melted and then caused to solidify. No evidence is given of using thermosetting powders, nor means are specified to overcome problems of melting, spreading and curing such materials.
EP-A-O 330 237 (Hormann KG) discloses a process for coating hollow metal panels filled with heat-sensitive plastic material. In this case the substrate is heated only by conduction through a metal wall, which provides protection to some extent. The performance of this process may be objectionable when no shield is present and either heat is transmitted through the thin paint coating to the substrate, or even reaches

REFERENCES:
patent: 4665626 (1987-05-01), Berkmann et al.
Patent Abstracts of Japan, vol. 8, No. 197 (M-324) (1634), Sep. 11, 1984.

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