Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1998-02-02
1999-10-12
Lovering, Richard D.
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427484, 516 77, 523410, 524902, 524904, 525934, 526932, B05D 104, C08K 5092, C08K 5205
Patent
active
059652136
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an aqueous dispersion of a transparent powder coating, which is particularly suitable as a coating for vehicle bodies coated with water-based basecoat.
Nowadays, for the purpose of coating vehicle bodies, liquid coating materials preferably are employed. Such materials cause numerous environmental problems due to their solvent content. This also applies to the use of water-based coating materials.
This is the reason why increased efforts have been made in recent years to employ powder coatings in the coating step. However, the results have not been satisfying up to now; in particular, it is necessary to provide coatings with an increased thickness in order to obtain a uniform appearance. On the other hand, the use of coating materials in powder form necessitates a different application technology. The plants designed for liquid coating materials cannot therefore be employed for the powders. Hence, an attempt is being made to develop aqueous dispersions of powder coatings, which may be processed by means of liquid-coating technologies.
U.S. Pat. No. 4,268,542, for example, discloses a process employing a powder coating slurry which is suitable for the coating of vehicles. In this process, a conventional powder coat is first applied to the bodywork, and the transparent coating slurry is applied as a second coat. In this transparent coating slurry based on acrylate resins, ionic thickeners are used which lead to a relatively high sensitivity of the applied coat to moisture, especially to condensation. Furthermore, in one of the examples these have a content of from 0.5 to 30% of glycidyl-containing monomers. Moreover, it is necessary to operate with high baking temperatures (over 160.degree. C.).
In the text which follows, the terms transparent powder coating dispersion and powder clearcoat are used synonymously.
It is an object of the present invention to provide an aqueous dispersion of a transparent powder coating, which may be applied to vehicle bodies by means of the conventional liquid-coating technology and which may particularly be baked even at temperatures of 130.degree. C.
This object is achieved by an aqueous dispersion of a transparent powder coating, consisting of a solid powder component A and an aqueous component B, wherein glycidyl-containing monomers of from 30 to 45%, preferably from 30 to 35%, and optionally having a content of vinylaromatic compounds, preferably styrene; dicarboxylic acids and/or carboxy-functional polyesters; and powder coatings, such as deaerating agents, levelling agents, UV absorbers, radical scavengers and antioxidants; and wetting agents, preferably carboxy-functional dispersants, antioxidants, UV absorbers, radical scavengers, small amounts of solvents, levelling agents, biocides and/or water retaining agents.
The epoxy functional binder for the solid transparent powder coating used for the preparation of the dispersion comprises, for example, epoxy group-containing polyacrylate resins which are preparable by copolymerisation of the least one ethylenically unsaturated monomer containing at least one epoxy group within the molecule and at least one further ethylenically unsaturated monomer containing no epoxy group within the molecule, at least one of the monomers being an ester of acrylic acid or methacrylic acid. Such epoxy group-containing polacrylate resins are, for example, known from EP-A-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 ethylenically unsaturated monomers containing no epoxy group within the molecule are alkyl esters of acrylic acid and methacrylic acid containing 1 to 20 carbon atoms in thealkyl radical, perticularly methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate. Further examples of ethylenically unsaturated monomers containing no epoxy groups within the molecule are acid amides, for example acrylamide and methacrylamide, vinylaromatic compo
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Clark Peter
Sacharski Lawrence
Woltering Joachim
Wonnemann Heinrich
BASF Coatings AG
Lovering Richard D.
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