Water-based coating compositions include water-based copolymers and cross-linking agents as components. The water-based copolymers are desirable for use in coating systems in the automotive and industrial coatings industries because these copolymers enable formulation of waterborne coating systems, such as WBBC, WBCC, and waterborne primer systems. It is known in the art that waterborne coating systems are ideal as compared to solventborne coating systems because waterborne coating systems have lower content of volatile organic compounds (VOCs).
The water-based copolymers of the prior art have proven to be inadequate for use as a component in water-based coating compositions. The water-based copolymers of the prior art are ineffective because these copolymers are highly viscous, as secondary dispersions, and generally have poorly defined film forming characteristics, as primary dispersions. Furthermore, the cross-linking between the copolymers of the prior art and conventional cross-linking agents, such as aminoplasts, are often particularly susceptible to poor chip performance and environmental acid etch.
The water-based copolymers of the prior art are also deficient because these copolymers often incorporate additional components such as co-solvents and surfactants which are both undesirable components in waterborne coating systems. For instance, conventional water-based copolymers typically incorporate a co-solvent to promote dispersibility of the copolymer in water, and these co-solvents contribute to increased VOCs. Conventional water-based copolymers also typically incorporate surfactants into the copolymer to promote and maintain miscibility and incorporation of the copolymer in water, and as understood by those skilled in the art, the incorporation of surfactants into coating compositions frequently contributes to water sensitivity, humidity, and ‘cratering’ as well as other coating defects detrimental to the appearance of the waterborne coating system.
The free-radical polymerization methods of preparing the water-based copolymers of the prior art are also deficient. These conventional methods are typically highly exothermic and are therefore difficult to predict and control. The unpredictability of these methods leads to uncontrollable and inconsistent physical properties of the water-based copolymer and ultimately of the water-based coating composition which includes the copolymer as a component. More specifically, the unpredictability of these methods frequently leads to inconsistent molecular weight distribution of the copolymer, and to incomplete conversion of monomer components into the copolymer. Furthermore, in the preparation of conventional water-based copolymers, distribution of the monomer components is random and does not produce a ‘tailored’ polymeric architecture that is able to meet particular needs depending on whether the copolymer is utilized in a WBBC, WBCC, or waterborne primer system. It is understood in the art that inconsistent molecular weights, incomplete conversion of monomer components, and even random distribution of the monomer components affects, among other things, the stability of the viscosity of the copolymer and can even result in ‘gelling’ of the copolymer and of the water-based coating composition. Additionally, poor appearance characteristics of the WBBC, WBCC, or waterborne primer system, such as gloss and distinctness of image (DOI), can result from poor rheology, i.e., flow, of the coating composition upon application that is due to the inconsistencies in the water-based copolymer.
In sum, the prior art water-based copolymers which are components of the water-based coating composition, as detailed above, are characterized by one or more inadequacies. Due to the inadequacies identified in the prior art, it is desirable to provide a novel water-based copolymer and coating composition to be utilized in WBBC, WBCC, and waterborne primer systems as well as a novel method of preparing the coating composition and a cured film.