Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2002-10-17
2004-08-03
Beck, Shrive P. (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S386000, C427S487000, C524S417000, C524S422000, C524S321000, C525S161000, C525S176000, C525S519000
Reexamination Certificate
active
06770329
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preventing the yellowing of single-coat or multicoat paint systems produced using powder coating dispersions, especially powder clearcoat slurries.
BACKGROUND OF THE INVENTION
Powder clearcoat materials and also aqueous powder clearcoat dispersions are part of a trend for automobile coatings and, owing to their environmental compatibility, are displacing those materials which have been used to date in finishing, namely solventborne one-component clearcoat materials based on melamine resins and also the likewise solvent-based two-component clearcoat materials comprising polyacrylate resins with polyisocyanates as crosslinkers.
Aqueous powder clearcoat dispersions, also referred to by those in the art as powder clearcoat slurries, have the advantage over the powder clearcoat materials that they can be processed using conventional liquid paint technology. Furthermore, they can be applied at low film thickness and hence they contribute to the sparing use of resources. Processes of this kind are prior art. For example, the U.S. Pat. No. 4,268,542 describes a process in which a multicoat system comprising two or more coats is applied to a substrate. The surface of the substrate is first of all coated fully or partly with a powder coating material. Thereafter a powder coating dispersion, consisting of synthetic resin particles dispersed in an aqueous medium, is applied and the substrate thus treated is dried in a single step by the action of heat.
DE 196 13 547 discloses an aqueous powder clearcoat dispersion which, through the use epoxy-carboxy systems, permits crosslinking at temperatures below 160° C. However, this system exhibits a relatively strong tendency to yellow in comparison to the conventional clearcoat materials based on melamine resin or on polyisocyanate.
The German patent applications 197 41 555.5 and 197 44 561.6 describe a powder clearcoat material in which a glycidyl-containing addition polymer is crosslinked with tris(alkoxycarbonylamino)triazine and polycarboxylic acids and/or carboxy-functional poly-esters. This powder clearcoat material may likewise be formulated as an aqueous powder clearcoat material, which in relation to the prior art has advantages in respect of etchability by environmental chemicals, and also exhibits improvements in terms of yellowing. Particularly with the clearcoating of white shades, however, the yellowing resistance is still critical and requires particular care at the production stage. When selecting the raw materials and intermediates that are used for this purpose it is necessary to ensure particularly high purity and very low intrinsic yellowing, which is a disadvantage. Especially when preparing powder coating dispersions in the production plant, in batch sizes which exceed the laboratory scale, such batches may occasionally be found to be particularly critical in terms of yellowing, following application to a white undercoat.
It was therefore an object of the present invention to provide a process for producing single-coat or multicoat paint systems using powder clearcoat slurries that no longer has the disadvantages of the prior art but instead provides paint systems which in particular no longer show any yellowing, without detracting from the other, positive qualities of these paint systems.
BRIEF SUMMARY OF THE INVENTION
What has been found, accordingly, is a process for producing single-coat or multicoat clearcoat finishes on primed or unprimed substrates by applying at least one powder coating dispersion, in particular a powder clearcoat slurry, to the substrate and then curing the resulting film(s) thermally and/or with actinic radiation, in which at least one polyvalent inorganic acid and/or oxalic acid are or is added to at least one powder coating dispersion, in particular to a powder clearcoat slurry.
DETAILED DESCRIPTION OF THE INVENTION
In the text below, the novel process is referred to as the process of the invention.
The present invention additionally relates to powder clearcoat slurries to which at least one polyvalent acid and/or oxalic acid have or has been added and also to the single-coat or multicoat clearcoat finishes, and coated articles, produced by applying these powder coating dispersions, particularly powder clearcoat slurries.
In one variant of the process of the invention, the polyvalent acids and/or the oxalic acid are also added to the aqueous basecoat dispersion, leading to a further suppression of yellowing.
The novel powder coating dispersions or powder clearcoat slurries are referred to below as powder clearcoat slurries of the invention and the novel single-coat or multicoat powder clearcoat finishes are referred to as coatings of the invention.
In the light of the prior art it was surprising, and unforeseeable for the skilled worker, that as a result of the process of the invention the powder clearcoat slurries of the invention and the coatings of the invention would no longer have the disadvantages of the prior art, while suffering no impairment of their other, positive qualities.
Furthermore, it is an advantage of the present invention that the absence of color-falsifying yellow hues in the coating of the invention results in better reproducibility of the shade of the color-imparting coat.
The essential constituent of the powder clearcoat slurry of the invention is at least one polyvalent inorganic acid and/or oxalic acid.
As polyvalent acids it is possible to use, with preference, phosphoric acid and its derivatives, sulfuric acid and its derivatives, and boric acid, with particular preference phosphoric acid and its derivatives, with very particular preference phosphoric acid. Instead of or in addition to these acids it is possible to use oxalic acid.
In the context of the process of the invention, the acids are added to the powder clearcoat slurries of the invention in effective amounts. By “effective amounts” here are meant amounts which on the one hand reliably prevent yellowing without destabilizing the powder clearcoat slurry and/or harming the performance application profile of the paint systems. The skilled worker is therefore able to determine the appropriate amounts by means of simple preliminary tests.
Of particular advantage are amounts from 0.1 to 2 000 ppm, preferably from 1 to 1 500 ppm, with particular preference from 100 to 1 200 ppm, and in particular from 800 to 1 100 ppm, based in each case on the overall amount of the powder clearcoat slurry of the invention. They are therefore employed with preference.
In accordance with the invention, the acids are added to the starting products or to the intermediates at any step in the process of preparing the powder clearcoat slurry of the invention, or to the finished powder clearcoat slurry of the invention, the last-mentioned variant being of advantage and therefore being employed with preference.
To produce the coatings of the invention, the powder clearcoat slurry of the invention is applied in accordance with the process of the invention to the primed or unprimed substrate to be coated. Viewed in terms of its method, the application has no special features, but instead takes place with the aid of the customary and known methods such as spraying, knife coating, brushing, dipping, flow coating or rolling, but especially spraying. The process of the invention starts from the substrate to be coated. The substrate may be of metal, wood, plastic, glass, ceramic or paper or may comprise these materials in the form of composites. Preferably, the substrates in question comprise automobile body parts or industrial components, including containers, made of metal, or furniture.
The substrate may have been provided with a primer. In the case of plastics, the primer in question is what is known as a hydroprimer, which is cured prior to the application of the coating material of the invention, particularly of the aqueous basecoat material or of the clearcoat material. In the case of metals, especially automobile body parts, the primer comprises customary and known, cure
Bendix Maximilian
Berg Jan
Kalck Ulrich
Ott Günther
Röckrath Ulrike
BASF Coatings AG
Beck Shrive P.
Fletcher, III William Phillip
LandOfFree
Low-yellowing aqueous clear powder coating dispersions,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low-yellowing aqueous clear powder coating dispersions,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-yellowing aqueous clear powder coating dispersions,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3272912