Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1998-02-03
1999-11-30
Dudash, Diana
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427409, 4273884, 524501, 524502, 524504, 524507, 524508, 524591, 524839, 523501, B05D 136, B05D 138, C08J 303
Patent
active
059939117
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a heat curable aqueous coating composition which is in particular suitable for the production of lacquer coatings, in particular for multi-layer lacquer coatings, for example as an aqueous surfacer, water-borne base lacquer and preferably as a water-borne clear or topcoat lacquer.
Aqueous lacquers, in particular clear lacquers are described in the literature. DE-A-28 06 497 describes a multi-layer lacquer coating with a clear lacquer coating as the topcoat, wherein this clear lacquer is also intended to be water-borne. Water-borne clear lacquers are, however, not defined. The base lacquer coating composition which is used comprises elevated molecular weight, high viscosity polyesters dissolved in xylene which are mixed with acrylic resins. Such lacquers require large quantities of neutralising agents. DE-A-35 32 617 describes aqueous coating compounds based on high performance resins, for example polyester resins, in which resin particles, which may be acrylic resins, are dispersed. The compounds obtained are unstable and are subject to rapid phase separation.
DE-A-35 37 855 describes the used of acidic polycondensation products based on acrylic resins and polyether polyols which, once neutralised, may be used as water-dilutable binders for the production of water-borne stoving surfacers, topcoat lacquers or clear lacquers. It has, however, been found that even after stoving these systems exhibit inadequate resistance to humidity and sulphuric acid.
EP-A-0 365 775 also describes acidic polyacrylates which, once neutralised and diluted, are used for the production of water-borne topcoat lacquers. Melamine resin is used as the crosslinking agent. These coating compositions have an unsatisfactory high solids value, i.e. they require an elevated content of organic solvents of the order of 27 g and above relative to 100 g of resin solids content (corresponding to a high solids value of 73 and below). DE-A-42 23 183 describes aqueous emulsions based on acrylic copolymers which are synthesised as a graft on one or more low molecular weight polyesters and are then crosslinked with a mixture of melamine resins and capped polyisocyanates. DE-A-38 32 826 describes a process for the production of a coating composition based on a water-dilutable polyacrylate resin and an aminoplastic resin. DE-A-39 10 829 describes a water soluble clear lacquer which is substantially composed of an oligoester acrylate resin and a melamine resin.
In practice, monoalkyl and dialkyl ethers of ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol have been used as solvents in aqueous lacquer systems. This is, however, associated with disadvantages. A strong tendency to sag and a pronounced tendency to pinholing at low film thicknesses must be accepted.
EP-A-0 051 483 describes epoxy dispersions which contain epoxy resins containing glycidyl groups, dihydric phenols and diglycidyl ethers of polyoxyalkylene glycols. Glycols or glycol ethers may be present as solvents.
The object of the invention is to provide an aqueous coating composition which is in particular suitable for chemical-resistant and non-yellowing coatings having very good topcoat lacquer qualities, a very slight tendency to sag and in particular very high resistance to pinholing, wherein the coating composition should have elevated storage stability. The coating composition should have an elevated processing solids content.
It has been found that this object may be achieved by the provision of an aqueous coating composition which contains poly(C.sub.2 -C.sub.3)alkylene glycol di(C.sub.1 -C.sub.4)alkyl ethers as the lacquer solvent. Such polyalkylene glycol dialkyl ethers are commercially available, for example polyethylene glycol di-n-butyl ether, a commercial product which is described, for example, in the company literature "Polyglycol BB 300" from Hoechst and has hitherto been used as an absorbent, for example for scrubbing exhaust air.
The present invention accordingly provides the use of poly(C.sub.2 -C.sub.3)alkylene glycol
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Brenke Stephan
Doebler Klaus-Peter
Duecoffre Volker
Lieverz Frank
Schubert Walter
Dudash Diana
Herberts GmbH
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