Water-reduced urethane coating compositions

An aqueous coating composition comprising:

• (A) a non-sedimenting aqueous dispersion which is emulsifiable in the absence of added emulsifier of an ungelled NCO-free polyurethane having a finely particulated dispersed phase of less than 10 microns which requires only mild agitation for dispersion formed by reacting in aqueous medium in which water is the principal ingredient:
• (1) an NCO-containing polymer containing anionic salt groups having a salt group equivalent weight of 200 to 5000 and having monovalent counter ions being substantially free of reactive active hydrogens and having a viscosity of 50 to 10,000 centipoises, said polymer formed from:
• (i). an organic polyisocyanate and
• (ii). an organic material containing at least two active hydrogens
• said organic polyisocyanate and said organic active hydrogen-containing material containing a total of not more than one gram-mole of compounds having a functionality of 3 or more per 500 grams of organic polyisocyanate and organic material containing at least 2 active hydrogens;
• said NCO-containing polymer containing an equivalent ratio of NCO in (i) to active hydrogen in (ii) of at least about 4/3, the anionic salt groups introduced into said NCO-containing polymer through (ii),
• (2) an active hydrogen-containing compound having at least one hydrogen more reactive with NCO groups than water having an average functionality of 2 or less to form a polyurethane having an intrinsic viscosity lower than 2.0 deciliters per gram;
• said aqueous dispersion containing at least 15 percent by weight aqueous medium based on total weight of polyurethane and aqueous medium of which at least 30 percent by weight of the aqueous medium is water with co-solvent constituting the remainder of the aqueous medium;
• (B) a curing agent.

A method of forming a non-sedimenting aqueous dispersion of an ungelled polyurethane which is emulsifiable in the absence of added emulsifier comprising:

• (A) preparing an NCO-containing polymer containing anionic salt groups or groups which are readily converted to anionic salt groups in aqueous medium, said salt groups having monovalent counter ions, said NCO-containing polymer being formed from
• (1) an organic polyisocyanate and
• (2) an active hydrogen-containing material containing at least two active hydrogens per molecule,
• said organic polyisocyanate and said active hydrogen-containing material containing a total of not more than one gram-mole of compounds having a functionality of 3 or more per 500 grams of organic polyisocyanate and active hydrogen-containing material;
• the equivalent ratio of NCO in (1) to active hydrogens in (2) being at least about 4/3;
• the anionic salt groups or groups which are readily converted to anionic salt groups introduced into said NCO-containing polymer through the active hydrogen-containing material (2);
• said NCO-containing polymer being substantially free of highly active hydrogens and having a viscosity of 50 to 10,000 centipoises;
• (B) dispersing said NCO-containing prepolymer in aqueous medium in which water is the principal ingredient, said NCO-containing polymer having an anionic salt group equivalent weight of from 200 to 5000 in said aqueous medium;
• (C) chain extending the dispersed NCO-containing prepolymer with an active hydrogen-containing material in which the active hydrogens are more reactive with the NCO groups than water to form a polyurethane having an intrinsic of less than 4.0 deciliters per gram;
• said chain extension occurring to form an ungelled polyurethane dispersion having a finely particulated dispersed phase of less than 10 microns and in which the dispersion contains at least 15 percent by weight aqueous medium based on total weight of the ungelled polyurethane and aqueous medium of which at least 30 percent by weight of the aqueous medium is water, the co-solvent constituting the remainder of the aqueous medium.