Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1998-02-06
2000-12-12
Parker, Fred J.
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427485, 523403, 525408, 525411, B05D 104
Patent
active
06159556&
DESCRIPTION:
BRIEF SUMMARY
The application also relates to a process for the preparation of the powder coating dispersion and to its use for car bodies.
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous powder coating dispersion which is particularly suitable as a coating for car bodies which have been coated with aqueous basecoat.
For the coating of car bodies, preference is currently given to the use of liquid coating materials. These cause numerous environmental problems owing to their solvent content. The same applies to cases where water-based coating materials are employed.
For this reason, increased efforts have been made in recent years to use powder coatings for the coating operation. The results so far, however, are not satisfactory; in particular, increased coat thicknesses are necessary in order to achieve a uniform appearance. On the other hand, the use of pulverulent coating materials entails a different application technology. Plants designed for liquid coating materials, therefore, cannot be used for the powders. The aim is therefore to develop powder coatings in the form of aqueous dispersions which can be processed with liquid coating technologies.
U.S. Pat. No. 4,268,542, for example, discloses a process in which a powder coating slurry is used which is suitable for the coating of cars. In this process, a conventional powder coat is first applied to the body, and the clearcoat slurry is applied as second coat. In this clearcoat slurry, which is based on acrylate resins, ionic thickeners are used. Furthermore, in one of the examples these thickeners contain from 0.5 to 30% of glycidyl-containing monomers. Moreover, high stoving temperatures (above 160.degree. C.) are necessary.
The present invention has now set itself the object of providing an aqueous powder coating dispersion which can be applied to car bodies by the existing liquid coating technology and which, in particular, can be stoved even at temperatures of 130.degree. C.
SUMMARY OF THE INVENTION
This object is achieved in that the aqueous powder coating dispersion can be prepared by subjecting an aqueous dispersion of a powder coating having a glass transition temperature of from 20 to 90.degree. C., preferably from 40 to 70.degree. C., a viscosity of from 10 to 1000 mPas, preferably from 50 to 300 mPas, at a shear rate of 500 s.sup.-1 and a solids content of from 10 to 50%, preferably from 20 to 40% by weight, to a grinding process while maintaining a temperature of from 0 to 60.degree. C., preferably from 5 to 35.degree. C. The specific energy input during the grinding process is preferably from 20 to 500 Wh/kg, in particular from 50 to 250 Wh/kg.
DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 provide an illustration of a grinding process for use in preparing the instant invention.
DETAILED DESCRIPTION OF THE INVENTION
An aqueous powder coating dispersion employed in accordance with the invention comprises a solid, pulverulent component A and an aqueous component B, in which by weight, preferably from 30 to 35%, of glycidyl-containing monomers and, if desired, with a content of aromatic vinyl compounds, preferably styrene, dicarboxylic acids and/or carboxy-functional polyesters, and such as degassing agents, levelling agents, UV absorbers, free-radical scavengers and antioxidants, auxiliaries, wetting agents, preferably carboxy-functional dispersants, antioxidants, UV absorbers, free-radical scavengers, small quantities of solvent, antioxidants, UV absorbers, free-radical scavengers, small quantities of solvent, levelling agents, biocides and/or hygroscopic agents.
Dispersions with such a composition are used in particular for powder clearcoats.
Suitable epoxy-functional binders for the solid powder coating used to prepare the dispersion are, for example, polyacrylate resins which contain epoxide groups and which can be prepared by copolymerization of at least one ethylenically unsaturated monomer containing at least one epoxide group in the molecule with at least one other ethylenically unsaturated monomer containing no epo
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Webster's Ninth New Collegiate Dictionary, A Merriam-Wester,cover page, & p. 365 Undated.
Chemical Dictionary Fifth Edition, Grant & Hach's, Roger Grant & Claire Grant, cover page & p. 192 Undated.
Paints, Coating and Solvents, Second, Completely Revised edition, Dieter Stoye, Werner Freitag (Editors), cover page, and pp. 37-38 Undated.
Moller Dietmar
Woltering Joachim
BASF Coatings AG
Parker Fred J.
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