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
1997-09-11
1999-08-24
Michl, Paul R.
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...
C08L 3300
Patent
active
059425709
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a water-based paint composition which contains a water-dispersible acrylic graft copolymer and internally non-crosslinked acrylic fine particles, and especially to a water-based paint composition suited to metallic paint for automobiles.
As the problem of pollution of the global environment has deepened in recent years, international regulations regarding the discharge of organic solvents have become more and more stringent. Against this background water-based paint using water as a medium has stepped into the spotlight. In this context, the development of water-based metallic undercoats for industrial painting and especially automobile painting has been regarded as advantageous, not only because it has the effect of decreasing the use of organic solvents but also from the point of view of finished appearance and cost-performance, and to date various water-based undercoats have been developed.
When one looks at the history of the art of making water-based undercoats, the trend has been to adopt water-dispersible resins as base resins. This is because water-based paints in the form of an aqueous dispersion have the advantage of giving the water-based undercoat the rheological properties it requires.
Water-based paints in the form of aqueous dispersions are characterized in that the basic resin is present in the water as particles. These can be classified broadly into direct emulsions or indirect emulsions according to the method for preparing the basic emulsion. In the direct emulsion method particles are formed directly in water by emulsion polymerization or suspension polymerization; in the indirect emulsion method the base resin is first prepared in a solvent phase and then transferred to an aqueous phase.
Of these the direct emulsion method is very much more efficacious in eliminating solvents from water-based paint since no organic solvent is needed at the preparation stage, and the preparation of the base resin is also easy. However, because of the limitations imposed by preparing the base resin in water, it has the problems that the suitability of the starting materials employed for polymerization has a considerable effect, and scope for resin design is narrowed.
On the other hand, with the indirect emulsion method there is a large degree of freedom as to the starting materials which can be employed and wide scope for resin design, but on the other hand there are problems in that it is difficult to remove the organic solvent employed when preparing the base resin, and this hinders the production of low-solvent water-based undercoats.
In this connection, water-based paints using polymer fine particles obtained by emulsion polymerization are recorded in EP00387 A1 and EP0401565 A1.
However, although such water-based paints do not give rise to painting faults such as sagging or bittiness, etc., since the particles confer pseudoplastic or thixotropic properties, there is the problem that the viscosity of the paint is prone to rise after application to the object to be painted and rheological properties become inadequate, and consequently smoothness is inferior. They also have the problem that dispersibility of pigments is inferior and it is difficult to obtain paint films with an outstanding gloss. Moreover, because the emulsifier is present in the aqueous dispersion after obtaining the resin by emulsion polymerization, inferior water-resistance is a problem.
In Japanese Examined Patent HS-30867 a water-based paint composition is recorded which contains water-insoluble vinyl resin fine particles of mean particle size 0.3-6 .mu.m obtained by polymerizing at least one type of water-soluble resin selected from polyester resins, alkyd resins, vinyl resins, vinyl-modified polyester resins and vinyl-modified alkyd resins, with a polymerizable unsaturated monomer in water by two-stage emulsion polymerization in the presence of a seeded emulsion.
However, this water-based paint composition has the problem that because it is formed by dispersing a water-insoluble resin storage sta
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Kawamura Yoshiaki
Matsukura Yoshiaki
Sakai Atsuhiro
Taniguchi Hitoshi
BASF Coatings AG
Michl Paul R.
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