Triboelectric chargeable coating powder

Details Triboelectric chargeable coating powder Triboelectric chargeable coating powder

1999-11-15

2001-06-05

Cameron, Erma (Department: 1762)

Coating processes

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

Electrostatic charge, field, or force utilized

C427S475000, C427S485000, C427S385500

Reexamination Certificate

active

06242052

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to powder coating materials which through the use of an additive are particularly suitable for triboelectric application equipment.
BACKGROUND ART
For some years now, powder coating materials, commonly known as powder coatings, have been finding an ever larger field of use. Powder coating materials are in the form of a dry powder which is applied in finely divided form to the surface of the article to be coated, generally with the aid of electrostatic charging, and is subsequently “dried”, i.e., baked. In the course of baking, which usually takes place at temperatures between 130 and 220° C., crosslinking reactions and film formation turn the powder into a solid coating on the workpiece. Powder coating materials of this kind offer a range of advantages. For instance, the pulverized consistency of the coating material removes the need to operate with solvents. Accordingly, all of the environmental problems commonly associated with the evaporation of the solvents disappear with powder coating materials. Furthermore, a saving is made in terms of the heating energy otherwise necessary for the evaporation of the solvents. A further advantage of powder coating materials is that material which has not remained adhering to the workpiece can be collected on the floor of the powder booth and simply used again. In this way, a degree of powder utilization of up to 98% can be achieved. In addition to cost advantages, this increased degree of utilization also brings with it a far lesser degree of environmental burden than in the case of customary coating materials. Powder coating materials are prepared from binders, hardeners, fillers, pigments and additives. In respect of the binders and hardeners used, modern-day powder coating materials are generally based on one of the following polymer classes: epoxies; epoxy-polyester mixtures; polyesters; polyesters/isocyanates (polyurethanes); polyacrylates.
SUMMARY OF THE INVENTION
In powder coating technology, the powder coating materials are applied either by way of high-voltage processes, e.g., via a corona electrode, or by way of the tribo process, which is based on the triboelectric charging of the powder coating materials.
The tribo process has a number of advantages over its high-voltage counterpart. On the one hand, there is no need for high-voltage equipment; on the other, no “Farady cages” are formed since there are no electrical field lines.
A key disadvantage of the triboelectric charging of current powder coating materials is the inadequate deposition rate of the powder coating materials on the workpiece. Powder particles having an average diameter <10 &mgr;m, in particular, frequently give rise to problems in coating practice, since they have a poor degree of deposition on the workpiece in the tribo process.
In order to improve the deposition rate of triboelectrically applied powder coating materials, the prior art has taken recourse to specific binders or has added to the powder coating materials additives, such as aluminum oxide in the so-called dry-blend process. The powder coating materials prepared in this way must, however, be specially adjusted in their particle size spectrum; i.e., the fraction of powder particles having an average particle diameter <10 &mgr;m must be reduced.


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