Pseudoplastic powder lacquer slurry free of organic solvents, method for production and the use thereof

Abstract

A pseudoplastic powder clearcoat slurry which is free from organic solvents and comprises solid and / or highly viscous, particles which are dimensionally stable under storage and application conditions and have an average size of from 0.8 to 20 μm, at least 99% of the particles having a size ≦30 μm, which is preparable by 1) emulsifying an organic solution comprising binder and crosslinking agent to give an emulsion of the oil-in-water type, 2) removing the organic solvent or solvents, and 3) wet grinding the resulting slurry; and also the use of the powder clearcoat slurry to produce clearcoats for automotive OEM finishing and automotive refinish, for furniture coating and for industrial coating, including coil coating, container coating and the coating of electrical components.

Description

BACKGROUND The present invention relates to a novel powder clearcoat slurry, free from organic solvents, which possesses pseudoplasticity. The present invention also relates to a novel process for preparing this powder clearcoat slurry. The invention relates not least to the use of the novel powder clearcoat slurry for producing clearcoats for the automotive sector and for the industrial sector. For the coating of automobile bodies, preference is given today to the use of liquid coating materials, i.e., spray paints. These give rise to numerous environmental problems owing to their solvent content. The same applies to cases where waterborne clearcoat materials are used, since they still always contain certain amounts of organic solvents. Waterborne clearcoat materials of this kind are known from the German patent DE 196 23 371 A1. Directly after application, the conventional waterborne clearcoat materials do not dry to a powder but instead flow out to form a continuous film. They...

AI Technical Summary

Benefits of technology

"The present invention provides a novel powder clearcoat slurry that has improved application characteristics and can be prepared with fewer processing steps than conventional slurries. The slurry should have reliable application characteristics even without the assistance of organic solvents and should be able to be subjected to wet grinding without any problems. The slurry should also have a wider processing window in terms of wet grinding and should be filterable without problems. The invention also provides a novel process for preparing powder clearcoat slurries that ensures good homogeneity of the resulting particles."

Problems solved by technology

These give rise to numerous environmental problems owing to their solvent content.

The results to date, however, have not been satisfactory; in particular, powder clearcoat materials still show weaknesses with regard to chemical resistance and yellowing.

And yet it is not possible to do without wet grinding, since otherwise the coarse particle fraction of the powder clearcoat slurry is not reduced in size.

In the course of this filtering operation, even very small coarse particle fractions (particle size>10 μm) result in clogging of the filters, so that the production process has to be stopped—a disadvantage both technically and economically.

For stabilization, it is necessary, in addition to the ionic stabilization, to employ external emulsifiers as well—generally polyethylene oxide adducts, which decrease the resistance of the coating to water and moisture.

Moreover, these known powder clearcoat slurries still always include certain amounts of organic cosolvents or leveling agents, which cannot be removed since they are essential to the leveling properties of the partly dried film.

Furthermore, the patent does not give any teaching as to how the problem of filterability in connection with powder clearcoat slurries might be solved.

It has been found that even this powder clearcoat slurry must be filtered prior to its application and in the course of such filtration gives rise to problems similar to those encountered with the known powder clearcoat slurries.