A multicolor paint is a composition which, when coated on a surface and dried, results in a coating that is characterized by dispersed discrete visibly discernible spots (or dots). Water-in-water multicolor paints have been proposed (see, for example, Sellars et al. U.S. Pat. No. 3,950,283, Grasko U.S. Pat. No. 3,852,076 and Zola U.S Pat. No. 4,376,654) and are of commercial interest particularly in view of the developing governmental interest in establishing regulations limiting the quantity of organic volatiles emitted into the environment by a paint during application and subsequent air drying. The states of Calif., N.J. and N.Y., for example, have adopted regulations limiting paint emissions and many other states reportedly will be adopting similar regulations.
It is difficult to prepare a commercially acceptable water-in-water multicolor paint because of various problems. One problem is the fact that the discrete color bodies comprising the disperse phase in such a paint need to contain a relatively high concentration of a water soluble, film-forming polymer in order to achieve commercially acceptable characteristics in the resulting coating. Another problem is that such polymers should be in a highly water insoluble state after the paint has been coated and dried; otherwise, the coated and dried paint provides little or no water resistance. Another problem is to prepare and utilize a disperse phase composition which can be formed into discrete color bodies that have sufficient structural integrity in the continuous phase of the paint for practical commercial purposes. Structurally weak, discrete color bodies would break up easily and become part of this continuous phase.
Prior art multicolor paints commonly contain a solution or dispersion of a film-forming polymer in an organic liquid carrier with the polymer being, for example, nitrocellulose or styrene butadiene, and the carrier liquid being mineral spirits or the like. However, the solubility and dispersibility of the polymers in water is so limited as to make it impossible to use the polymers in making a water-based paint of commercially acceptable quality. It is also not practical to "fortify" the water with a water-miscible organic cosolvent to enhance polymer solubility or dispersibility because the maximum amount of the organic cosolvent which can be present should be kept below about 7-8 weight percent on a total product paint composition basis in order to comply with the foregoing proposed regulatory standards.
So far as now known, no one has previously succeeded in preparing a water-in-water multicolor paint wherein the aqueous disperse phase color bodies are characterized by having:
(a) a relatively high content of water dispersible, film-forming, crosslinkable polymer in association with a crosslinking agent, PA0 (b) a relatively high structural integrity, and PA0 (c) a capacity to form highly crosslinked, water insoluble, chemical resistant, mar resistant and thermally stable coatings with a high degree of hardness after paint application and drying. PA0 (a) water dispersed, film-forming, crosslinkable polyurethane polymer system selected from the group consisting of a polyurethane polymer system, a carboxylated polymer system, and mixtures thereof, and PA0 (b) hydroxy (lower alkyl) cellulose and/or alkali metal carboxyl (lower alkyl) cellulose. PA0 (a) having polyfunctionality in their molecular chains, PA0 (b) being in combination with a water dispersed reactive curative, or PA0 (c) having initially blocked isocyanate groups in their molecular chains wherein the blocking agent is released at a predetermined elevated temperature.
Previously, in the above-referenced parent patent applications, water-in-water multicolor paints based upon crosslinkable carboxylated polymers were provided which overcame the prior art problems and which had the foregoing characteristics. However, it has been further discovered that improved water-in-water multicolor paints can also be made based upon crosslinkable polyurethane polymers.