Aqueous Polyurea Dispersions and Their Use for Preparing Coatings With Excellent Hydrolytic and Thermal Stability

In the following examples all parts and percentages are by weight unless otherwise specified.

The bis-aspartates set forth in the following table were prepared by adding dropwise 1 mole of a diamine with stirring to 2 moles of maleic acid dibutylester that was previously charged at ambient temperature to a 3-neck flask equipped with a stirrer, thermometer, nitrogen bubbler and an addition funnel. The amine was added at a rate such that the exotherm did not increase the temperature of the reaction mixture above 50.degree. C. Upon complete addition, the contents of the reaction flask were maintained at 50.degree. C. for a period of 12 hours.

The following table sets for the amounts of the reactants and the properties of the resulting bis-aspartates.

The bis-aspartate was charged into a 3-neck flask under a nitrogen atmosphere and then 1,6-hexamethylene diisocyanate (HDI) was added dropwise to the bis-aspartate while maintaining the temperature below 70.degree. C. for 2 hours or until the isocyanate band disappeared from the IR spectrum, whichever is longer. For the preparation of Hydantoin Prepolymer 6, 34.56 parts of dimethylol propionic acid was mixed with the bis-aspartate. After completion of urea formation, acetic acid was added as a catalyst in the amount of 5000 ppm. The reaction mixture was then heated to 120.degree. C. for 2-3 hours or until IR spectrum showed the disappearance of amide I and II bands and appearance of a split ester carbonyl peak as an indication of a planar hydantoin ring, whichever is longer. After hydantoin formation was complete, the alcohol was distilled off under vacuum. The following table sets forth the amounts of the reactants and the properties of the resulting aspartate-functional polyhydantoin prepolymers.

Step 1--Preparation of NCO Prepolymer

Dimethylolpropionic acid (DMPA), a polyether monohydric alcohol prepared from n-butanol, ethylene oxide, and propylene oxide (in a molar ratio ethylene oxide to propylene oxide of 83:17), N-methyl-pyrrolidone (NMP), isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI) and bis-(4-isocyanatocyclohexyl)-methane (H.sub.12 MDI) in the amounts specified in the following table were added to a 1000 ml three neck flask equipped with stirrer, thermometer, and condenser and reacted at 90.degree. C. to 100.degree. C. for two hours until the NCO content was constant 19.2%. The reaction mixture was then cooled to 40.degree. C., and triethylamine was added and reacted at 50.degree. C. for 10 minutes. The hydantoin prepolymer was then added and reacted for 10 minutes. The exothermic reaction resulted in a temperature increase from 40.degree. C. to about 80.degree. C.

Step 2--Dispersion and Chain Extension

The neutralized prepolymer was added slowly to the demineralized dispersing water at 50.degree. C. under rapid agitation in a second flask (2000 ml resin flask). After the dispersion step was complete, the dispersed prepolymer was chain extended by the slow addition of one or more of the following amine chain extenders in water: hydrazine hydrate, diethylenetriamine, an amine-terminated polyether (available from Huntsman as Jeffamine D400), 2-methyl-1,5-pentanediamine (MPDA) and ethylene diamine.

The dispersions were post reacted for 1 hour at 60.degree.-70.degree. C. The resulting aqueous polyurea dispersions had the properties listed in the following table. Films were prepared from the aqueous polyurethane dispersions by blending them with 0.5% by weight of a levelling agent (Fluorad FC 430, available from 3M) and drawing them down onto glass at a wet film thickness of 10 mil. The coatings were cured for 24 hours at room temperature, then for 1 hour at 60.degree. C., and finally for 4 more days at room temperature before they were removed tested. The tensile and elongation properties are set forth in the following table.

The film used in the comparison example was prepared from a commercial aqueous polyurethane dispersion, i.e., Bayhydrol 110, available from Bayer Corp. This polyurethane dispersion corresponds to those prepared in accordance with the present invention except that it is based on a polyester polyol instead of an aspartate-functional prepolymer and, thus, does not contain hydantoin groups.

Examples 2, 3, 4 and 6 demonstrate outstanding hydrolytic stability when compared to an aqueous polyurethane dispersion based on a polyester polyol.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.