Aqueous dispersion of polyurethanes containing siloxane linkages

Details Aqueous dispersion of polyurethanes containing siloxane linkages Aqueous dispersion of polyurethanes containing siloxane linkages

1996-02-13

1998-06-02

Niland, Patrick D.

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...

524588, 524591, 524839, 524840, 528 28, C08J 300, C08K 320, C08L 7500, C08G 7704

Patent

active

057601232

DESCRIPTION:

BRIEF SUMMARY
This invention relates to aqueous polyurethane dispersions (PU dispersions), to a process for the production thereof, to water-borne coating compositions containing the polyurethane dispersions, and to the use thereof for the production of multilayer lacquer coatings.
A multitude of differently chain-extended polyurethane dispersions has become known. Due to their outstanding properties they have in particular found industrial applications as binders in aqueous base lacquers.
Thus, for example, EP-A-0 089 497, EP-A-0 228 003, DE-A-36 28 124 and EP-A-0 512 524 describe aqueous base lacquers which contain aqueous polyurethane dispersions as the binder, which may be produced by chain extension of isocyanate-functional prepolymers with polyamine and/or polyol.
DE-A-39 15 459 provides examples of aqueous base lacquers which contain aqueous polyurethane dispersions as the binder, which may be produced by chain extension of isocyanate-functional prepolymers with water.
Examples of aqueous base lacquers based on aqueous polyurethane dispersions, which may be produced by chain extension with polyisocyanates of polyisocyanate-reactive PU prepolymers containing active hydrogen, may be found in DE-A-39 03 804 and DE-A 40 01 841.
Multilayer lacquer coatings produced using water-based lacquers formulated on the basis of known polyurethane dispersions require improvement with regard to their resistance to condensed water. If known polyurethane dispersions are used as the sole binder in aqueous effect base lacquers, the resultant effect development is less favourable in comparison with aqueous effect base lacquers containing at least one further co-binder.
EP-A-0 163 214 describes aqueous self-crosslinking polyurethane dispersions with preferably lateral siliconate groups. The PU dispersions are produced and stored under conditions which deliberately prevent the siliconate groups from reacting together. After application, the binders crosslink by condensation of the siliconate groups to form siloxane linkages.
Further aqueous solutions or dispersions of polyurethanes with reactive siliconate groups suitable for crosslinking are known from EP-A-0 315 006. The binders described therein are synthesised by the reaction of the isocyanate groups of isocyanate prepolymers with amino groups, i.e. chain extension proceeds via amino groups. A large quantity of water is added during production of the binders, such that, in accordance with the law of mass action, virtually no siloxane linkages are produced.
The object of the present invention is to provide novel aqueous polyurethane dispersions which, when used as binders in aqueous coating compositions, in particular in aqueous base lacquers, allow the production of multilayer lacquer coatings with improved condensed water resistance. When aqueous effect base lacquers are used which contain as the sole binder the PU dispersion to be provided, the resultant effect development within multilayer lacquer coatings should satisfy present requirements in automotive lacquer coating.
This object is achieved by the provision of aqueous polyurethane dispersions based on a polyurethane resin with a number average molecular weight (Mn) of 2500 to 1000000, a content of 2 to 150 mmol, preferably of 3 to 100 mmol, particularly preferably of 7 to 70 mmol of siloxane linkages (--Si--O--Si--) per 100 g of solid resin, a hydroxyl value of 0 to 100, preferably of above 1 and below 60 mg KOH/g relative to the solid resin and a content of ionic groups, groups convertible into ionic groups and/or hydrophilic groups of 5 to 200 mEq per 100 g of solid resin. The polyurethane resins according to the invention are of a linear or branched structure or are in the form of microgels.
In the PU dispersion according to the invention, 5 to 200 mEq (milliequivalents) of ionic groups, groups convertible into ionic groups and/or hydrophilic groups are present per 100 g of solid resin.
If the groups convertible into ionic groups are acidic groups, or if the ionic groups are anionic, then above 15 and below 100, particula

REFERENCES:
patent: 3941733 (1976-03-01), Chang

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