Stock material or miscellaneous articles – Composite
Reexamination Certificate
2002-11-19
2004-11-16
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Composite
C427S385500, C524S377000, C524S800000, C524S804000, C524S832000, C524S904000
Reexamination Certificate
active
06818303
ABSTRACT:
The present invention relates to powder clearcoat dispersions (powder slurry clearcoats). The present invention further relates to a novel process for preventing surface defects in clearcoat finishes. The present invention relates, moreover, to the use of the novel powder slurry clearcoats in automotive finishing, in the interior and exterior coating of constructions, in furniture, door and window coating and in industrial coating, including coil coating and container coating.
Color and/or effect finishes on motor vehicle bodies, especially automobile bodies, nowadays consist preferably of two or more coats which are applied on top of one another and have different properties.
For example, a substrate has applied to it, in succession, an electrodeposition coating (EDC) as primer, a surfacer coat or antistonechip primer, a basecoat, and a clearcoat. The particular purpose of the EDC is to protect the metal panel against corrosion. In the art it is also commonly referred to as the primer. The surfacer coat serves to cover over unevennesses in the substrate and, by its elasticity, to ensure stone-chip resistance. If desired, the surfacer coat may also act to reinforce the hiding power and to deepen the color of the coating system.
The base coat contributes the colors and/or optical effects. The clearcoat is used to intensify the optical effects and to protect the coating system against mechanical and chemical damage. Basecoat and clearcoat are often also referred to collectively as the topcoat. For further details, reference is made to Römpp Lexikon Lacke und Druckfarben, George Thieme Verlag, Stuttgart, New York, 1998, pages 49 and 51, “Automotive finishes”.
An important objective in modern automotive finishing is significantly to reduce, or do away altogether with, the amount of organic solvents released in the course of the coating operation. Appropriate coating materials, such as EDCs, aqueous surfacers or aqueous clearcoats, powder coating materials or powder slurry clearcoats, are available.
Of these, the powder slurry clearcoats, which are known, for example, from U.S. Pat. Nos. 4,268,542 A1 and 5,379,947 A1 and from the Patent Applications EP 0 714 958 A2, DE 195 40 977 A1, DE 195 18 392 A1, DE 196 17 086 A1, DE-A-196 13 547, EP 0 652 264 A1, DE 196 18 657 A1, DE 196 52 813 A1, DE 196 17 086 A1, DE 198 14 471 A1 and DE 198 35 206 A1, offer particular advantages: firstly, they can be prepared and applied without solvent, like the powder coating materials; secondly, the customary and known spraying techniques for liquid coating materials may be employed for their application.
A disadvantage of the powder slurry clearcoats known to date is that the clearcoat finishes produced therefrom in some cases have surface defects such as depressions, craters and agglomerates, which detract from the otherwise excellent overall visual impression. Nor has it been possible to date entirely to eliminate this problem by adding additives such as wetting agents, emulsifiers, dispersing auxiliaries or defoamers during the preparation of the powder slurry clearcoats.
It is an object of the present invention to find new powder clearcoat dispersions (powder slurry clearcoats) which, like the powder slurry clearcoats known to date, provide clearcoat finishes with an excellent overall visual impression and high scratch, chemical and weathering resistance but without surface defects such as depressions, craters or agglomerates.
Accordingly, the novel powder clearcoat dispersions (powder slurry clearcoats) have been found, which may be prepared by dispersing a powder clearcoat in an aqueous medium and wet milling the resulting powder slurry, at least one adduct of ethylene oxide and/or propylene oxide with at least one glycol being added to the powder slurry prior to wet milling.
In the text below, the novel powder clearcoat dispersions or powder slurry clearcoats are referred to as “powder slurry clearcoats of the invention”. Further subject matter of the invention will emerge from the following description.
In the light of the prior art it was surprising and unforeseeable by the skilled worker that the use, in accordance with the invention, of adducts of ethylene oxide and/or propylene oxide with glycols would result in powder slurry clearcoats which provide clearcoat finishes with an excellent overall visual impression and high scratch, chemical and weathering resistance but without surface defects such as depressions, craters or agglomerates.
The powder slurry clearcoats of the invention comprise at least one finely divided dimensionally stable constituent, i.e., a powder coating material, as the disperse phase, and an aqueous medium as the continuous phase.
The finely divided, dimensionally stable constituent or powder coating material may be solid and/or highly viscous. In the context of the present invention, “highly viscous” means that the particles behave essentially as solid particles under the customary and known conditions of the preparation, storage and use of powder slurry clearcoats or powder coatings. The powder coating material is preferably solid.
Furthermore, the individual particles of the finely divided constituent or powder coating material are dimensionally stable. In the context of the present invention, “dimensionally stable” means that under the customary and known conditions of the storage and use of powder slurry clearcoats and powder coatings the particles agglomerate and/or break down into smaller particles only to a small extent, if at all, but essentially retain their original form even under the influence of shear forces.
The solids content of the powder slurry clearcoat of the invention is preferably from 10 to 80, more preferably from 15 to 75, with particular preference from 20 to 70, with very particular preference from 25 to 70, and in particular from 30 to 65% by weight, based in each case on the powder slurry of the invention.
The average particle size of the finely divided dimensionally stable constituents of the powder slurry clearcoat of the invention is preferably from 0.8 to 40 &mgr;m, more preferably from 0.8 to 20 &mgr;m, and with particular preference from 2 to 6 &mgr;m. By average particle size is meant the 50% median value determined by the laser diffraction method, i.e., 50% of the particles have a particle diameter≦the median value and 50% of the particles have a particle diameter≧the median value. In general, the particle size of the finely divided dimensionally stable constituents reaches its upper limit when owing to their size the particles are no longer able to flow out completely on baking, with the consequence of an adverse effect on film leveling. 40 &mgr;m is considered a sensible upper limit, since above this particle size blockage of the rinsing tubes of the highly sensitive application apparatus is to be expected.
Powder slurry clearcoats with average particle sizes of this kind possess better application properties and, at the applied film thicknesses of >30 &mgr;m as currently practiced in the automotive industry for the OEM finishing of automobiles, surprisingly exhibit a significantly reduced tendency toward popping and mudcracking than conventional combinations of surfacer, basecoat, and clearcoat.
The powder slurry clearcoat of the invention is essentially free from organic solvents (cosolvents). In the context of the present invention, this means that the clearcoats have a residual volatile solvent content of <5% by weight, preferably <3% by weight and with particular preference <2% by weight, based on the overall weight of the powder slurry clearcoat.
The constituent of the powder slurry clearcoats of the invention that is essential to the invention is at least one adduct of ethylene oxide and/or propylene oxide with at least one glycol, especially ethylene glycol, 1,3- and/or 1,2-propylene glycol or 1,2-1,3- and/or 1,4-butylene glycol.
Examples of highly suitable adducts are polyethylene glycols, polypropylene glycols, block copolymers of ethylene oxide and propylene oxide (Pluronics®) or polytetramethylene gl
Bremser Wolfgang
Hintze-Brüning Horst
Lassmann Walter
Röckrath Ulrike
BASF Coatings AG
Zacharia Ramsey
LandOfFree
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