Aqueous coatings, the production thereof and the use thereof in

Details Aqueous coatings, the production thereof and the use thereof in Aqueous coatings, the production thereof and the use thereof in

1999-03-08

2000-05-30

Gorr, Rachel

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

522 91, 522 96, 524838, 525455, 528 28, 528 49, 528 75, C08G 1804

Patent

active

060692189

DESCRIPTION:

BRIEF SUMMARY
The invention relates to aqueous coatings which contain aqueous binder dispersions based on hybrid polymers produced by radical copolymerisation of siloxane bridges and/or silanol groups containing polyurethane resins as well as olefinic double bonds together with olefinically unsaturated monomers. It also relates to processes for producing the aqueous coatings and processes for multi-layer painting using these coatings, in particular as waterborne basecoat in processes for producing decorative multi-layer paint coatings of the water-borne basecoat/clear lacquer type.
Polyurethane/poly(meth)acrylate polymer hybrids are known as binders for aqueous coatings.
EP-A-0 297 576 describes the polymerisation of (meth)acrylic monomers in the presence of previously produced polyurethane dispersions. On completion of polymerisation, it is possible to produce aqueous basecoats from the dispersions obtained.
EP-A-0 353 797 describes the production of a hydroxyfunctional polyurethane resin in an unsaturated monomer as solvent, wherein the unsaturated monomer can be reactive toward isocyanate. Emulsion polymerisation is carried out after conversion of the polyurethane solution into the aqueous phase. The hybrid polymer dispersion obtained can be used as paint binder for water-borne basecoats.
EP-A-0 401 565 describes water-borne basecoats of which the binders are produced by emulsion polymerisation of aqueous emulsions, produced by addition of external emulsifiers, of polyurethane macromonomers which are dissolved in unsaturated monomers and are functionalised in an unsaturated manner.
EP-A-0 424 705, EP-A-0 521 928, EP-A-0 522 419, EP-A-0 522 420, EP-A-0 662 992 and WO 95/14721 describe water-borne basecoats based on polyurethane/poly(meth)acrylate polymer hybrids, the polymer hybrids having been synthesised by graft or block polymerisation of unsaturated monomers with polyurethane macromers which are functionalised in an unsaturated manner. The unsaturated groups of polyurethane macromers can be arranged laterally or terminally. The unsaturated polyurethane macromers can be produced when dissolved in organic solvent, for example in the unsaturated monomer itself, or in the absence of solvents. Copolymerisation can take place in the aqueous or non-aqueous phase, in other words before or after conversion into the aqueous dispersion.
WO 95 28 429 discloses aqueous polyurethane dispersions which are suitable as binders for water-borne basecoats and are based on polyurethane resins stabilised by ionic and/or hydrophilic groups and chain-extended via siloxane bridges.
WO 95 28 428 discloses a process for producing a multi-layer paint coating using a self-crosslinking water-borne basecoat containing, as binder, an aqueous polyurethane resin dispersion based on a polyurethane resin with lateral and/or terminal hydroxyl and/or R'O-groups bound to silicon.
Aqueous coatings formulated on the basis of known polyurethane/poly(meth)acrylate hybrid binders, in particular water-borne basecoats, as well as the water-borne basecoats known from WO 95/28428 and WO 95/28429 require improvement with respect to their run limit, i.e. they can be applied only in a limited layer thickness, if curtaining is to be avoided.
In the case of shades having a low covering capacity, in particular, this necessitates application in several spraying operations with intermediate drying or intermediate exposure to air.
An object of the present invention is to provide novel aqueous coatings, in particular water-borne basecoats, which allow the production of layers of paint within a multi-layer paint coating with a higher curtaining limit. In particular, it should also be possible to apply the water-borne basecoats in a single spraying operation in the case of shades having a poor covering capacity.
The object is achieved by providing aqueous coatings containing binder dispersions based on polyurethane/polymer hybrid polymers with a numerical average of the molar mass (Mn) of 8000 to 1500000, a ratio by weight of polyurethane to polymer content of 0.05:1 to 50

REFERENCES:
patent: 4369300 (1983-01-01), Carter et al.
patent: 5230962 (1993-07-01), Stephenson
Derwent Abstract, re EP297576 Jan., 1992.
Derwent Abstract, re EP521928 Jan., 1993.
Derwent Abstract, re EP522419 Jan., 1993.
Derwent Abstract, re EP522420 Jan., 1993.
Derwent Abstract, re EP662992 Jul., 1995.
Derwent Abstract, re WO9514721 Jun., 1995.
Derwent Abstract, re WO9528429 Oct., 1995.

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