Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-09-16
1999-12-14
Buttner, David
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524456, 524591, 525454, 525455, 4284231, C09D15106, C09D17504
Patent
active
060019158
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a polyurethane-modifed polyacrylate which is suitable for producing aqueous pigmented coating materials.
Coating materials of this kind are suitable for the basecoat/clearcoat techniques known from the prior art which are employed in particular in the automotive industry for producing high-quality finishes, especially metallic finishes (cf. EP-A-38127, EP-A-89497 and DE-A-3628124). In these techniques the predominant proportion of the basecoats employed comprise exclusively organic solvents as diluents and/or solvents.
For some years, therefore, the coatings industry has developed aqueous basecoats suitable for basecoat/clearcoat techniques. An essential feature of these basecoat/clearcoat techniques is that the transparent topcoat is applied to the unstoved basecoat and only then are the basecoat and topcoat stoved together (wet-on-wet technique).
Coating materials suitable for this procedure are described, inter alia, in DE-A-4009858. There, special water-thinnable polyacrylate resins are employed for the coating materials.
Basecoats suitable for wet-on-wet techniques are additionally described in DE-A-4010176. They contain as binder a polymer which is obtainable by reacting ethylenically unsaturated monomers and polyurethane resins in an organic solvent or in a mixture of organic solvents. Essential in this process is the use of polymerizable double bonds in the preparation of the polyurethane resins.
Experience to date has indicated that the coating materials applied by the wet-on-wet technique still do not have sufficient stability on storage. This is particularly the case if storage takes place under the elevated temperatures encountered in practice.
Accordingly, the present invention has set itself the object of providing a polyurethane-modifed polyacrylate which is suitable for the production of aqueous basecoats and brings about, in these basecoats, an increased storage stability.
This object is achieved in that the polyurethane-modified polyacrylate is obtainable hydroxyl group per molecule and is essentially carboxyl-free or of a mixture of such monomers, and which is different from (a1) and (a2), or of a mixture of such monomers, bonds, carboxyl group per molecule, or of a mixture of such monomers, and of a mixture of such monomers, in water.
The proportions by weight of (a1) are 40-90, preferably 40-80% by weight, of (a2) 0-45, preferably 4-34% by weight, of (a3) 0-40, preferably 10-30% by weight, of (b1) 2.5-15, preferably 3-7% by weight, and of (b2) 0-60, preferably 0-28% by weight.
In accordance with the invention the polyurethane, which contains no copolymerizable double bonds, is dissolved in an organic solvent or a solvent mixture. The polymerization according to stage II is preferably not carried out until at least 80% of the monomers added in stage I have been reacted.
The water-thinnable polyacrylate resins employed in accordance with the invention make it possible to formulate basecoats which--especially in comparison with known basecoats containing polyacrylate resin--feature improved storage stability.
For the preparation of the polyacrylate resins to be employed in accordance with the invention it is possible to employ as component (a1) any essentially carboxyl-free esters of (meth)acrylic acid which are copolymerizable with (a2), (a3), (b1) and (b2), or a mixture of such (meth)acrylic esters. Examples are alkyl acrylates and alkyl methacrylates having up to 20 carbon atoms in the alkyl radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate and methacrylate, and cycloaliphatic (meth)acrylic esters, for example cyclohexyl (meth)acrylate. It is preferred to employ as component (a1) mixtures of alkyl acrylates and/or alkyl methacrylates which consist to the extent of at least 25% by weight of n-butyl and/or t-butyl acrylate and/or n-butyl and/or t-butyl methacrylate.
As component (a2) it is possible to employ all ethylenically unsaturated monomers which carry at least one hydroxyl group per molecule and are essen
REFERENCES:
patent: 5169719 (1992-12-01), Balatan
patent: 5494980 (1996-02-01), Buter
patent: 5552496 (1996-09-01), Vogt-Birnbrich
patent: 5569715 (1996-10-01), Grandhee
Petri-Huber Cornelia
Reusmann Gerhard
Schwarte Stephan
Wegner Egon
BASF Coating AG
Buttner David
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