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...
Reexamination Certificate
2000-09-29
2002-08-20
Michl, Paul R. (Department: 1714)
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...
C524S507000
Reexamination Certificate
active
06437041
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention provides aqueous coating agents which contain aqueous binder dispersions based on hybrid polymers which are prepared by radical copolymerisation of olefinically unsaturated monomers in the presence of aqueous dispersed polyurethane resins which contain siloxane bridges and/or silanol groups but do not contain double bonds. It also provides a process for preparing the aqueous coating agents and a process for multi-layer finishing using these coating agents, in particular as a water-based base-coat lacquer in a process for preparing decorative multi-layer finishes of the water-based base-coat lacquer/clear lacquer type.
Polyurethane/poly(meth)acrylate hybrid polymers are known as binders for aqueous coating agents.
EP-A-0 297 576 describes the polymerisation of (meth)acrylic monomers in the presence of previously prepared polyurethane dispersions. After the completion of polymerisation, aqueous base-coat lacquers can be prepared from the dispersions obtained.
EP-A-0 353 797 describes the preparation of a hydroxy-functional polyurethane resin in an olefinically unsaturated monomer as solvent, wherein the unsaturated monomer may be reactive towards isocyanate. After converting the polyurethane solution into the aqueous phase, emulsion polymerisation is performed. The hybrid polymer dispersion obtained may be used as a water-based base-coat lacquer binder.
WO 95 28 429 discloses aqueous polyurethane dispersions suitable for use as binders for water-based base-coat lacquers which are stabilised by ionic and/or hydrophilic groups and are based on polyurethane resins chain-lengthened via siloxane bridges.
WO 95 28 428 discloses a process for preparing a multi-layered finish by using a self-cross-linking water-based base-coat lacquer which contains, as binder, an aqueous polyurethane resin dispersion based on a polyurethane resin with hydroxyl groups and/or R′O groups which are bonded to silicon in lateral and/or terminal positions.
In order to avoid the appearance of sagging, it is desirable that aqueous coating agents have high run limits. Otherwise, the layers can be applied in only limited thicknesses and, in particular in the case of colours with low covering power, application in several spray passes with intermediate drying, or intermediate evaporation is required.
The applicant suggested, in patent applications PCT/EP 97/04821 and P 197 46 327 which do not have priority over this document, coating agents which can be used as water-based base-coat lacquers which contain aqueous binder dispersions based on hybrid polymers which are prepared by the radical copolymerisation of polyurethane resins which contain siloxane bridges and/or silanol groups and also olefinic double bonds with olefinically unsaturated comonomers.
The object of the present invention is the provision of aqueous coating agents with high sagging limits which are suitable in particular for multi-layered finishes, in particular for the provision of colour and/or effect-providing layers. They are intended to be applicable in only a single spray pass in a thick layer to give an opaque surface coating.
SUMMARY OF THE INVENTION
The invention provides aqueous coating agents containing an aqueous binder dispersion and also optionally one or more organic solvents, cross-linking agents, pigments, fillers, conventional lacquer additives and/or one or more further binders, which are characterised in that the aqueous binder dispersion is based on polyurethane/polymer hybrid polymers with a ratio by weight of polyurethane fraction to polymer fraction of 0.1:1 to 50:1, wherein the polyurethane fraction of the polyurethane/polymer hybrid polymer does not contain any olefinic double bonds and has a hydroxyl value of 0 to 150, with respect to the solid resin, wherein hydroxyl groups bonded to silicon do not enter into the calculation for the OH value, and an acid value of 1.5 to 60 mg KOH/g, with respect to solid resin, and a concentration of 0.5 to 300 mmol of silicon per 100 g of solid resin in the form of siloxane bridges (—Si—O—Si—) incorporated into the polyurethane fraction and/or in the form of silanol groups bonded to the polyurethane fraction. The polyurethane/polymer hybrid polymers are obtainable by polymerisation of olefinically unsaturated monomers in the presence of polyurethane prepolymers which do not contain olefinic double bonds.
The hybrid polymers consist of polyurethane fractions and polymer fractions. The polyurethane fraction and the polymer fraction may be present as an interpenetrating network and/or the polymer fraction may be grafted onto the polyurethane fraction. The olefinic double bonds in the olefinically unsaturated monomers which participate in building up the polymer fraction in the polyurethane/polymer hybrid polymer are allylic and/or vinylic double bonds and/or alpha/beta-unsaturated carbonyl groups, for example preferably (meth)acrylic double bonds. The proportion of allylic double bonds is preferably less than 10%, whereas the proportion of (meth)acryloyl groups is at least 50%, preferably more than 70%. If more than 50% of the olefinic double bonds contributing to polymerisation are from (meth)acryloyl groups, then the hybrid polymers are polyurethane/poly(meth)acrylate hybrid polymers.
DETAILED DESCRIPTION OF THE INVENTION
The binder dispersion based on polyurethane/polymer hybrid polymers used in aqueous coating agents according to the invention has an acid value of 1.5 to 60 mg KOH/g, preferably 3 to 40 mg KOH/g, with respect to solid resin. At least 70% of the acid groups are preferably exclusively constituents of the polyurethane fraction. The acid groups stabilise the hybrid polymer particles in the aqueous phase. The polyurethane/polymer hybrid polymers may contain additional stabilising hydrophilic non-ionic groups, for example polyalkylene oxide groups, e.g. polyethylene oxide groups.
The binder dispersion based on polyurethane/polymer hybrid polymers used in aqueous coating agents according to the invention have a hydroxyl value of 0 to 150, preferably less than 100 mg KOH/g, with respect to solid resin. The optional hydroxyl value of the binder may arise from the polyurethane fraction and/or from the polymer fraction.
The aqueous binder dispersions which can be used in aqueous coating agents according to the invention are based on hybrid polymers which can be prepared by radical polymerisation of olefinically unsaturated monomers in the presence of polyurethane resins which contain siloxane bridges and/or silanol groups but which do not contain olefinic double bonds.
The aqueous binder dispersions based on polyurethane/polymer hybrid polymers can be prepared, for example, by converting a polyurethane prepolymer which contains acid groups and does not contain olefinic double bonds, which has, on average, 0.7 to 9 R′—O groups bonded to silicon per molecule, in which
R′=C1 to C8 alkyl or C(O)R′″, and
R′″=C1 to C10 alkyl
and which may be present dissolved in a solvent which is inert towards isocyanate, optionally after previous neutralisation of the acid groups, into an aqueous dispersion by adding water, and then subjecting the prepolymer, together with olefinically unsaturated monomers, to radical polymerisation. The olefinically unsaturated monomers may be added before and/or after preparation of the aqueous dispersion. For example, the olefinically unsaturated monomers, or some of them, may take on the function of a solvent which is inert towards isocyanate prior to preparing the aqueous dispersion, and these do not have to be removed at a later stage.
Polyurethane prepolymers which contain acid groups but do not contain olefinic double bonds and with, on average, 0.7 to 9, preferably lateral and/or terminal silicon-bonded R′O groups per molecule may be prepared, for example, by preparing a linear or branched, non-gelled, polyurethane prepolymer which does not contain olefinic double bonds but does contain acid groups and is hydroxy-functional in an inert organic solvent (mix
Bosch Werner
Göbel Armin
Schmidt Holger
Vogt-Birnbrich Bettina
E. I. du Pont de Nemours & Company
Michl Paul R.
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