Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-06-06
2002-07-16
Beck, Shrive P. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S386000, C427S388100, C427S409000, C427S410000
Reexamination Certificate
active
06419989
ABSTRACT:
This application claims priority under 35 USC § 120 upon International PCT Application PCT/EP 99/06607 filed Sep. 8, 1999, now WO 00/16912 and German Patent Application DE 198 43 581.9, filed Sep. 23, 1998.
The present invention relates to a process for producing coated substrates, especially coated automobile bodies, in which first of all a powder slurry clearcoat material and then a sol-gel clearcoat material are applied to an optionally precoated substrate and are then cured conjointly.
Automobile bodies are for the most part provided with a multicoat coating system. As the final coat, it is common to apply clearcoat materials. For this purpose it has recently been possible to use what are known as powder slurry clearcoat materials as well.
Powder slurry coating materials comprise powder coating materials in the form of aqueous dispersions. Slurries of this kind are described, for example, in the U.S. patent U.S. Pat. No. 4,268,542 and in the German applications DE-A-195 18 392.4 and 198 14 471.7, which were unpublished at the priority date of the present specification.
Recently, materials known as sol-gel clearcoats and based on siloxane-containing coating formulations have been developed which are obtained by hydrolysis and condensation of silane compounds. These coating materials, which are used as coating compositions on plastics, are described, for example, in the German patents DE-A-43 03 570, 34 07 087, 40 11 045, 40 25 215, 38 28 098, 40 20 316, and 41 22 743.
Sol-gel clearcoats impart very good scratch resistance to substrates made of plastic, such as spectacle lenses or motorcycle helmet visors, for example. This scratch resistance is not achieved by the known OEM (original equipment manufacturing) clearcoat materials normally used for the original finishing of vehicles. The automobile industry is now demanding that this improved scratch resistance be transferred to the clearcoats used in the finishing of automobiles as well.
Replacing the OEM clearcoat materials or OEM powder slurry clearcoat materials commonly used in automotive finishing by sol-gel clearcoat materials is not possible, since the sol-gel clearcoats are too brittle for this purpose, for example, and have poor optical properties (appearance). Above all, the sol-gel clearcoat materials are too expensive. The economically more favorable use of the sol-gel clearcoat materials as an additional coat over the clearcoats or powder slurry clearcoats used to date gives rise to adhesion problems between the clearcoat and the sol-gel coat, these problems arising in particular after stone chipping and on exposure to condensation.
It is therefore an object of the present invention to provide a coating system which comprises a clearcoat and which at the same time has very good scratch resistance and adhesion, and a process for producing said coating system.
This object is surprisingly achieved by the process of the invention for producing a coated substrate, in which a powder slurry clearcoat material and, subsequently, a sol-gel clearcoat material are applied to a substrate to which, if desired, one or more coating compositions are applied first of all, where
A) following application at a temperature above the film formation temperature of the powder slurry clearcoat material and below the temperature at which the crosslinking of this powder slurry clearcoat material is complete, the powder slurry clearcoat material is predried and induced to form a film,
B) subsequently the sol-gel clearcoat material is applied, and
C) finally both coatings are cured conjointly,
the powder slurry clearcoat material being only partly cured in step A) and the powder slurry clearcoat material and the sol-gel clearcoat material being chosen such that a chemical bond between them is possible.
It is found that automobile finishes produced by the process of the invention have a very good scratch resistance which cannot be attained using the clearcoat systems that are commonly employed. Furthermore, relative to the prior art clearcoat/sol-gel clearcoat systems, outstanding adhesion of the coats was found, even on stone chipping or following exposure to condensation, i.e., ten days' exposure of the coats in an atmosphere of 40° C. and 100% relative humidity. The optical properties of the coating systems thus produced are also good, and no cracks are found in the scratch-resistant coating.
The process of the invention is elucidated in more detail below.
For the process of the invention it is possible to use any conceivable substrate. By way of example, mention may be made of substrates of metal, plastic, glass or ceramic. The substrate used with preference is a substrate of plastic or, in particular, of metal. The substrate used in accordance with the invention may have any conceivable form, such as the form of a vehicle body, especially an auto body. Furthermore, the substrate may also have been subjected to a surface treatment, such as galvanizing or phosphating, for example.
In accordance with the process of the invention, the substrate may if desired be provided with one or more coats. The coating compositions used for this purpose may comprise any coating compositions used in accordance with the prior art. They may comprise, for example, liquid coating compositions which are aqueous or contain organic solvents, or coating compositions in powder form or in the form of a powder slurry. They may be applied by the processes known from the prior art, such as rolling, spraying, dipping, scattering, or by means of electrodeposition coating, for example.
The process of the invention is preferably used in the context of the multicoat system customary for the finishing of automobiles. In this customary multicoat system, for example, a primer, a surfacer coat, and also basecoats, topcoats and clearcoats are applied to the automobile body. The coating compositions used for the respective coats are known to the skilled worker. The coats may be applied to the body in such a way that, following the application of one coating film, it is dried and/or cured before the next film is applied, or two or more films are applied by the technique known as wet-on-wet, in which these films are dried and/or cured conjointly.
In the context of the preferred use of the process of the invention, therefore, a multicoat system customary for automobile finishing is effected, the clearcoat being formed from the powder slurry clearcoat/sol-gel clearcoat material used in accordance with the invention.
The powder slurry clearcoat/sol-gel clearcoat system is preferably used as a coating over basecoats, which are preferably part of a multicoat system, especially in the automobile industry. Particularly suitable as the basecoat are aqueous basecoat materials based on a polyester, polyurethane resin and an amino resin. In this case the basecoat materials are normally subjected to partial drying, without being crosslinked, after which the powder slurry clearcoat film is applied wet- on-wet.
The process of the invention is further used with preference for the continuous coating of metal sheets or metal strips by the coil coating process. In this case, the powder slurry clearcoat/sol-gel clearcoat system may be applied directly to the metal surface or to a customary and known primer coat that is present thereon. Not least, the process of the invention is also suitable for coating film-coated metal sheets and substrates of wood or glass. Accordingly, the process of the invention may be employed with advantage not only in the automobile sector but also in the fields of industrial coating and of furniture coating.
Powder slurry coating materials are powder coating materials in the form of aqueous dispersions. Powder coating materials, i.e., coating materials in powder form, were developed in order to replace the liquid coating materials which are presently employed with preference for the coating of automobile bodies which cause numerous environmental problems. The use of powder coating materials necessitates a different application technology than the use of liquid coatin
Betz Peter
Ehlig Christel
Hintze-Büning Horst
BASF Coatings AG
Beck Shrive P.
Blanton Rebecca A.
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