Reactive two-part polyurethane compositions and optionally self-

Details Reactive two-part polyurethane compositions and optionally self- Reactive two-part polyurethane compositions and optionally self-

1997-04-01

1998-08-25

Cameron, Erma

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...

524507, 524591, 524839, 524840, 560 25, 560 26, 560115, 560158, 560330, 560355, 560358, 556414, 528 28, 528 80, 528 71, 528 76, 528 8, 528 59, 528 45, 528 60, 528 65, 528 66, 528 70, 528 77, C08J 300

Patent

active

057984093

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to water-based and non-water based two-part reactive polyurethane compositions. The invention also relates to particular compositions that upon cure exhibit high damping character, excellent scratch-resistance, excellent mar-resistance, and self-healing characteristics. The invention also relates to a novel polyurethane prepolymer useful therein. The invention also relates to the cured coatings prepared from the novel compositions.


BACKGROUND OF THE INVENTION

Solvent-based two-part reactive polyurethane (PUR) compositions have been known for their excellent performance in industry for many years. However, the increasing demands on industry to reduce solvent emissions has limited the use of these solvent-based P PUR compositions significantly. Furthermore, these compositions essentially have no distinct self-healing characteristics at room temperature (no self-healing in 3-7 days at 25.degree.). There are no known water-based 2-part or 1-part polyurethane compositions. One of the alternatives that is being widely used to reduce volatile organic compounds (VOC) is a one-part water-based slightly crosslinked polyurethane-urea dispersion. This type of water-based polyurethane-urea dispersion can be further crosslinked by using a polyaziridine, a melamine, an epoxy, a metal complex (zinc or zirconium), or a multi-functional carbodiimide. The additional crosslinking, accomplished via carboxyl functional groups, is low. Coatings made from this type of dispersion, thus, typically demonstrate a lack of thermal stability. As a result, the outdoor durability and weatherability as well as solvent-, water-, and chemical-resistance of this insufficiently crosslinked water-based 1-part polyurethane-urea is inferior to the solvent-based 2-part reactive PUR systems. Moreover, the known large urea content has a great tendency to cause the resultant coating to yellow.
Investigators have attempted to overcome the short comings of conventional water-based polyurethane-urea dispersions in several ways (i.e., by increasing crosslinking and decreasing urea content). So far, the attempts have not been completely successful.
The following are methods of making 1-part water-based polyurethane-urea compositions, none of which are self-healing.
A first method is to prepare highly crosslinked (and thereby potentially thermally stable) NCO-terminated polyurethane prepolymers in a limited amount of organic solvent and then chain-extend the prepolymers with a diamine while dispersing into water. The disadvantage of this first method is that the solution viscosity of this type of dispersion increases very rapidly during the dispersing step and most of the time a poor dispersion (along with a tendency to form large micelles) results and gelation of the dispersion can occur.
A second method to develop a thermally stable water-based system involves the use of a poly-functional amine chain extender while dispersing an NCO-terminated polyurethane prepolymer into water. Again, the problems encountered are the same as those encountered in the first method.
A third method of obtaining thermally stable water-based polymer systems is described in European Patent Application No. 469389. This third method demonstrates the co-reaction of isocyanate functional materials with hydroxyl functional materials and water. The reaction product, though it demonstrates an increasing thermal stability, is, as indicated above, a polyurethane-urea system. Polyurethane-urea systems have a number of disadvantages, including a tendency to yellow over time.
Thus, although water-based polyurethane-ureas exist, there are no known water-based polyurethanes. Polyurethane-ureas are inferior to polyurethanes due to their poorer thermal stability, outdoor durability, and weatherability as well as their tendency to yellow.


SUMMARY OF THE INVENTION

A need thus exists for a water-based polyurethane composition. A need also exists for non-aqueous-based polyurethane compositions which can provide improved properties compar

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