Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-02
2003-01-28
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S410000, C523S456000, C525S327300, C525S375000, C525S386000, C528S405000, C528S418000
Reexamination Certificate
active
06512026
ABSTRACT:
The present invention relates to a novel powder clearcoat material and to a novel aqueous powder clearcoat dispersion particularly suitable as a coating for automobile bodies coated with aqueous basecoat materials.
For the coating of automobile bodies, preference is currently given to the use of liquid coating materials, i.e., spray paints. These cause numerous environmental problems owing to their solvent content. The same applies to cases where aqueous coating materials are employed, since these still always include certain amounts of organic solvents.
For this reason, increased efforts have been made in recent years to use powder coating materials for the coating operation. The results so far, however, have not been satisfactory; in particular, powder clearcoat materials still exhibit weaknesses with regard to chemical resistance and yellowing. Epoxy/carboxy-crosslinked powder clearcoat materials exhibit a markedly poorer resistance to incipient etching by water, tree resin, and sulfuric acid.
In the meantime, many developments have had as their aim to develop powder coating materials in the form of aqueous dispersions which may be processed using liquid coating technologies.
The patent U.S. Pat. No. 4,268,542, for example, discloses a process using a powder coating dispersion based on acrylic resins which is suitable for coating automobiles. In this process, a conventional powder coat is first applied to the body, and then the powder coating dispersion is applied as the clearcoat. With this powder clearcoat dispersion, also referred to by those in the art as a powder slurry or powder clearcoat slurry, ionic thickeners are used, which lead to a relatively high sensitivity of the applied clearcoat film to moisture, especially to condensation. Moreover, it is necessary to operate at high baking temperatures of more than 160° C.
DE-A-196 13 547 discloses an aqueous powder clearcoat slurry which meets the specified requirements. However, following application and crosslinking, slurry, like the solid powder clearcoat materials known to date, exhibits poor stability with respect to incipient etching by water, tree resin, and sulfuric acid. Moreover, the clearcoat produced therewith displays a tendency to yellow.
A further disadvantage of clearcoats produced from the conventional powder clearcoat slurries is their tendency toward delamination if certain aqueous basecoat materials are used. This delamination may be manifested as early as in a change in the color of the aqueous basecoats.
It is an object of the present invention to provide a novel powder clearcoat material and a novel powder clearcoat slurry which no longer have the disadvantages of the prior art but which instead exhibit a much better incipient etch stability and a reduced tendency to yellow after crosslinking. Moreover, the clearcoat produced with the aid of the novel powder clearcoat slurry should adhere firmly to all common aqueous basecoat materials, and should not display any tendency toward delamination.
Accordingly we have found the novel powder clearcoat material and the novel powder clearcoat slurry, comprising
a) at least one epoxide-containing binder containing from 0.5 to 40% by weight, based on the binder, of copolymerized glycidyl-containing monomers, and
b) at least one tris(alkoxycarbonylamino)triazine and at least one polycarboxylic acid, in particular a straight-chain dicarboxylic acid, and/or a carboxy-functional polyester as crosslinking agent
or alternatively
a) at least one tris(alkoxycarbonylamino)triazine and at least one oligomeric or polymeric, epoxide-containing crosslinking agent containing from 0.5 to 40% by weight, based on the crosslinking agent, of copolymerized glycidyl-containing monomers, and/or a low molecular mass, epoxide-containing crosslinking agent, and
b) at least one carboxyl-containing polymer as binder,
both variants comprising
c) at least one polyol.
In the text below, the novel powder clearcoat material and the novel powder clearcoat slurry are referred to as the powder clearcoat material of the invention and as the slurry of the invention.
In the light of the prior art it was surprising and unforeseeable for the skilled worker that the powder clearcoat material of the invention and the slurry of the invention would no longer have the disadvantages of the prior art. A particular surprise was that the clearcoats produced with the aid of the slurry of the invention adhere firmly to all kinds of aqueous basecoat materials and no longer exhibit delamination even when the recipes are changed.
The composition of the powder clearcoat material of the invention and of the powder slurry of the invention may vary widely and may be optimized to the particular end use. In accordance with the invention it is of advantage if the powder clearcoat material of the invention and the powder slurry of the invention, based on the respective solids, contain the invention's key constituents a), b) and c) in the following amounts:
a) from 55 to 80, with particular preference from 60 to 78, and in particular from 62 to 75% by weight,
b) from 14 to 30, with particular preference from 17 to 25, and in particular from 18 to 23% by weight, and
c) from 2 to 22, with particular preference from 4 to 20, and in particular from 6 to 18% by weight.
Suitable epoxy-functional binders a) for the powder clearcoat material of the invention or the slurry of the invention are, for example, polyacrylate resins which contain epoxide groups and are preparable by copolymerizing at least one ethylenically unsaturated monomer containing at least one epoxide group in the molecule with at least one further ethylenically unsaturated monomer containing no epoxide group in the molecule, at least one of the monomers being an ester of acrylic acid or methacrylic acid. Polyacrylate resins of this kind containing epoxide groups are known, for example, from the patents EP-A-0 299 420, DE-B-22 14 650, DE-B-27 49 576, U.S. Pat. No. 4,091,048 and U.S. Pat. No. 3,781,379.
Examples of suitable monomers for inventive use which contain no epoxide group in the molecule are alkyl esters of acrylic and methacrylic acid, especially methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl meth-acrylate, secondary-butyl acrylate, secondary-butyl methacrylate, tert-butyl acrylate, tert-butyl meth-acrylate, neopentyl acrylate, neopentyl methacrylate, 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate; amides of acrylic acid and methacrylic acid, especially acrylamide and methacrylamide; vinylaromatic compounds, especially styrene, methylstyrene or vinyltoluene; the nitriles of acrylic acid and methacrylic acid; vinyl halides and vinylidene halides, especially vinyl chloride or vinylidene fluoride; vinyl esters, especially vinyl acetate and vinyl propionate; vinyl ethers, especially n-butyl vinyl ether; or hydroxyl-containing monomers, especially hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 4-hydroxybutyl acrylate or 4-hydroxybutyl methacrylate.
Examples of suitable epoxy-functional monomers for inventive use are glycidyl acrylate, glycidyl meth-acrylate, or allyl glycidyl ether.
The polyacrylate resin containing epoxide groups normally has an epoxide equivalent weight of from 400 to 2500, preferably from 420 to 700, a number-average molecular weight Mn (determined by gel permeation chromatography using a polystyrene standard) of from 2000 to 20,000, preferably from 3000 to 10,000, and a glass transition temperature Tg of from 30 to 80, preferably from 40 to 70, with particular preference from 40 to 60, and in particular from 48 to 52° C. (measured by means of differential scanning calorimetry (DSC)).
The preparation of the polyacrylate resin containing epoxide groups has no special features but instead takes place in accordance with the customary and known polymerization methods.
The further key constituent of the powder coating material of the invention and of the slurry of the invention is the crosslinking agent a) or b).
In accordance
Ott Günther
Röckrath Ulrike
Schwarte Stephan
Woltering Joachim
Wonnemann Heinrich
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