In recent years, the coatings industry has become increasingly interested in high solids coatings, i.e., coatings which can be applied by conventional techniques without the necessity of high amounts of organic solvents. The use of high solids coatings presents several advantages, including high film build per application, economy of materials since organic solvents will normally be lost to the ambient surroundings, and the diminution of environmental control problems such as treatment of plant effluents to capture or destroy volatile pollutants.
The environmental requirements presently being placed on coating systems have further spurred much research activity in the area of water-based coating systems. It is known to produce water-dilutable polymer systems by preparing polymers which have free carboxylic acid groups which are reacted with amines to form water-dilutable systems. However, the presence of the amine salts creates environmental problems. Additionally, these systems have the disadvantage of requiring a large amount of solvent, including organic cosolvents, again creating ecological problems. Finally the presence of the amine generally causes an undesirable film yellowing and solution instability.
It is also known to provide polymer systems with oxyalkylene groups, as by reacting with an ethylene oxide, in order to enhance the water solubility of the polymer system. These systems form films which contain a large number of water sensitive ether groups, tend to weather badly and are easily swollen by water.
It would thus be highly desirable to combine the two types of coating systems, i.e., high-solids and water-thinnable, to form useful coating compositions. Such a combined system would reduce the total amount of organic solvent needed in the system, and at the same time, would reduce costs and increase ease of handling (e.g., cleaning of application and production equipment and thinning of the coating composition.)
To be a useful coating material, the composition after application must produce under conventional curing conditions a film having at least several of those properties required of coatings, such as adhesion, flexibility, hardness, stain resistance, detergent resistance, solvent resistance, water and humidity resistance, and the like.