Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-01-13
2001-10-30
Cameron, Erma (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
Reexamination Certificate
active
06309710
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an aqueous coating material comprising a multicomponent aqueous dispersion consisting of at least one aqueous dispersion of a hydroxyl-containing binder and of an aqueous dispersion of a hydrophobicized amino resin, which latter dispersion is prepared using hydroxyl-containing emulsifiers.
PRIOR ART
Water based clearcoats are acquiring increasing importance in the sector of automotive OEM finishing and refinishing since they permit a marked reduction in the emission of organic solvents during the coating operation.
In general, the water based clearcoats comprise an aqueous dispersion or solution of a crosslinkable polymer as binder and one or more crosslinking agents, such as water miscible blocked isocyanates or water miscible melamine resins, and also further customary coating auxiliaries or additives, such as light stabilizers, thickeners or leveling agents, for example. DE-A-43 42 551, for example, describes aqueous polymer dispersions and aqueous coatings based on these polymer dispersions and comprising hydroxyl-containing polyacrylates as a binder component, which are particularly suitable for producing transparent coating films, especially topcoat films, which have high acid and scratch resistances.
DE-A-43 22 242 comprises aqueous two-component coating compositions comprising aqueous dispersions of polyacrylates as binder and polyisocyanates as crosslinking agent, which are likewise used, in particular, as topcoats, preferably in automotive refinishing, and which, in addition to the requirements imposed on an automotive refinish, exhibit good leveling, good mechanical properties, and high weathering stability.
DE-A-43 32 015 describes, finally, aqueous coating materials comprising mixtures of aqueous dispersions of polyurethane acrylate resins and aqueous dispersions of polyacrylate, polyurethane and/or polyester resins and also, if desired, crosslinking agents, such as amino resins and blocked polyisocyanates. Coating materials of this kind are suitable for producing topcoat films which, despite low baking temperatures, are distinguished by good properties of the resulting coating film.
DE-A-38 03 522 describes an aqueous coating composition comprising a water-dispersible acrylic polymer and a melamine resin, but which contains pigments as a mandatory component. The hydrophobic melamine resin is dispersed in water in the presence of a water soluble resin. The coating composition cannot be used as a clearcoat.
The water based clearcoat formulations of the prior art, however, have the problem of inadequate popping resistance and of the insufficient evaporation rate of the coating film, for which reason the use of such water based clearcoat formulations in OEM finishing necessitates special measures for gentle evaporation, which in turn reduce the cycle rate of production-line manufacture and, furthermore, necessitate high levels of capital investment.
Furthermore, two-component water based clearcoats consisting of a binder component and a crosslinker component often lack the necessary processing stability, something which is manifested, for example, in an unwanted increase in viscosity in the coating material, after the binder component and the crosslinker component have been mixed, as a result of reaction between the two components.
Problem and Solution
On the basis of the difficulties set out above, the resulting problem was to provide processing-stable aqueous coating materials which lead to coating films having excellent properties, such as, in particular, acid and scratch resistance, and also weathering stability, in conjunction with a rapid evaporation rate and a high level of popping resistance in the course of drying. This problem can surprisingly be solved with the multicomponent aqueous dispersion of the invention as a coating constituent.
The multicomponent aqueous dispersion of the invention, as a constituent of aqueous coating materials, comprises
A) at least one aqueous dispersion of a hydroxyl-containing binder, and
B) a stable aqueous dispersion of a hydrophobic amino resin, said dispersion being prepared using hydroxyl-containing emulsifiers.
In one preferred embodiment of the invention, the emulsifier used to prepare the stable aqueous dispersion of the hydrophobic amino resin is a diol and/or polyol having a molecular weight of at least 500 daltons, selected with particular preference from the group consisting of the polyacrylate-diols and/or -polyols, polyester-diols and/or -polyols and polyether-diols and/or -polyols, and also, with very particular preference, polyurethane-diols and/or -polyols, polycarbonate-diols and/or -polyols, and polyether-diols and/or -polyols.
In the case of the polyether-diols and/or -polyols, these can also be attached to the amino resin. For this purpose it is preferred to use block copolyether radicals consisting of ethylene oxide and propylene oxide units.
Preference is given as hydrophobic amino resin, furthermore, to a hydrophobic melamine resin, with particular preference obtained by etherification of a melamine-formaldehyde condensation product with C3 to C12 alcohols.
In addition to the crosslinker component B), the multicomponent aqueous dispersions of the invention preferably include at least one further crosslinking agent in aqueous dispersion, with particular preference a trisalkoxycarbonylaminotriazine in aqueous dispersion.
The hydroxyl-containing binder present in aqueous dispersion in component A) is preferably a polymer selected from the group of hydroxyl-containing polyesters, polyethers, alkyd resins and cellulose derivatives, and also, with particular preference, polyurethanes, polyacrylates and polyurethane acrylates.
The invention further provides a method of applying a multilayer coating to a substrate surface, in which the topcoat applied is an aqueous coating material comprising the multicomponent aqueous dispersion of the invention, and provides substrates coated with such multilayer coatings.
IMPLEMENTATION OF THE INVENTION
Components A) and B) of the Multicomponent Aqueous Dispersion
Component A) consists of at least one aqueous dispersion of a hydroxyl-containing binder, preferably a polyester, polyether, alkyd resin and/or cellulose derivative, with particular preference a hydroxyl-containing polyacrylate, polyurethane and/or polyurethane acrylate.
The particularly preferred polyacrylates, polyurethanes and polyurethane acrylates can be prepared, for example, in accordance with the above-cited Laid-Open Specifications DE-A-43 22 242 , DE-A-43 32 015 , and DE-A-43 42 551.
In accordance with the invention, the aqueous multicomponent dispersion comprises as component B) a stable aqueous dispersion of a hydrophobic amino resin, this dispersion being prepared by means of hydroxyl-containing emulsifiers.
The hydrophobic amino resins which are known per se are preferably condensation products of aldehydes, especially formaldehyde, and, for example, urea, guanamine, benzoguanamine, and preferably melamine. The hydrophobic amino resins contain alcohol groups, preferably methylol groups, which are etherified preferably with C3 to C12 alcohols, such as isopropanol, n-butanol, isobutanol, tert-butanol, amyl alcohol, 1-hexanol, 1-octanol, 2-ethylhexanol, 1-decanol, isodecanol, 1-dodecanol or isododecanol, for example.
Butanol-etherified melamine-formaldehyde resins are used in particular as hydrophobic amino resins.
The hydroxyl-containing emulsifiers used for the hydrophobic amino resins are preferably diols and/or polyols having emulsifying properties, with particular preference diols and/or polyols having a molecular weight of between 500 and 50,000 daltons; with very particular preference, having a molecular weight of between 500 and 10,000 daltons and, in particular, from 500 to 5000 daltons. The emulsifying diols and/or polyols are preferably selected from the group of the polyacrylate-diols and/or -polyols, polyester-diols and/or -polyols and polyether-diols and/or -polyols, and, with very particular preference, from the group of the polyurethane-dio
BASF Coatings AG
Cameron Erma
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