Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1988-10-28
1991-12-24
Kight, III, John
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524840, 528 45, C08L 7506, C08G 1842, C08G 1880
Patent
active
050753720
DESCRIPTION:
BRIEF SUMMARY
The invention relates to dispersions of crosslinked polymer micro-particles in aqueous media.
It is an acknowledged objective of paint manufacturers to reduce, as far as possible, the proportion of organic solvents in coating compositions.
One route towards achieving this objective is the development of water-dilutable coating compositions.
Particularly in the field of the application of automobile paints, but also in other fields, there is considerable interest in aqueous paint systems.
In the application of automobile paints, multi-coat paint coatings of the "base coat/clear coat" type have made considerable headway, above all for metal effect paint coatings.
"Base coat/clear coat" paint coatings are produced by initially applying a pigmented base lacquer and exposing this to the air for a short period without a baking stage (wet-on-wet process) and then overlacquering with a clear lacquer, and finally baking the base lacquer and the clear lacquer together.
There has been no lack of attempts to prepare at least the base coats of these two-coat systems from aqueous coating compositions.
The coating agents for the production of these base coats must be processable by the streamlined "wet-on-wet" process which is nowadays customary, i.e. they must, after as short as possible a pre-drying time and no baking stage, be capable of being overlacquered with a (transparent) top coat without exhibiting troublesome partial solution and "strike in" phenomena.
Besides this, further problems also have to be solved in developing coating agents for base coats of metal effect paints. The metal effect depends crucially on the orientation of the metal pigment particles in the lacquer film. A metal effect base lacquer which can be processed by the "wet-on-wet" process must therefore produce lacquer films in which the metal pigments are present in an advantageous spatial orientation after application and in which this orientation is rapidly fixed in such a way that it cannot be disturbed in the course of the further lacquering process.
The replacement of the organic solvents employed in conventional paint systems involves a series of problems.
Thus, for example, the rheology (viscosity behavior during application, pseudoplasticity, thixotropy, leveling and run-off properties) of conventional paint systems can be selectively controlled by relatively simple means via the evaporation behavior of the organic solvents or solvent mixtures used. In the case of aqueous systems, it is only possible to utilize these possible means to a very limited extent or not at all.
However, it is precisely in the production of multi-coat paint coatings of high-grade quality, in particular metal effect paint coatings, that it is extremely important to control the rheological properties of the coating compositions employed.
Thus, for example, a rapid increase in viscosity after application has a very advantageous effect on the orientation and fixation of the metal pigment particles in metal effect base lacquers.
However, in the case of other coating processes--in particular in the case of coatings applied by spraying--the quality of the coatings obtained also depends to a great extent on the rheological properties of the coating compositions used.
It is known that the rheological properties of aqueous coating compositions can be affected by adding crosslinked polymer micro-particles.
It is also known that, in the production of multi-coat coatings of the base coat/clear coat type, the troublesome partial solution and strike in phenomena mentioned above are restrained if base coating compositions containing crosslinked polymer micro-particles are employed.
Thus EP 38,127 discloses a process for the production of multi-coat coatings of the base coat/clear coat type, in which aqueous base coating compositions which contain a stable dispersion of crosslinked polymer micro-particles and have a pseudoplastic or thixotropic character are used.
The incorporation of crosslinked polymer micro-particles into coating compositions can give rise to problems due to
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Dobbelstein Arnold
Hille Hans-Dieter
Mayenfels Peter
Muller Horst
BASF Lacke+Farben Aktiengesellschaft
Kight III John
Sergent Rabon
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