Process for coating substrates with aqueous polymer dispersions

Abstract

A process for providing a substrate such as a polyethylene terephthalate container with a gas barrier coating of a copolymer of vinylidene chloride is disclosed. The process includes locating the container to be coated in close proximity to one or more airless spray nozzles and impacting the outside surface of the container with a stream of a stabilized aqueous polymer dispersion such as an aqueous polyvinylidene chloride dispersion. The impacting force of the stable polyvinylidene chloride dispersion on the surface of the container is sufficient to cause selective destabilization of the dispersion at the surface interface to form a gel layer containing the polymer in the continuous phase. This gel layer serves as an adhesive layer for an overlying layer of the aqueous polymer dispersion as a continuous uniform coating. The resulting wet coating does not sag or run off. The coating on the container is then dried in a controlled atmosphere to complete the gel formation throughout its thickness whereupon it is further dried to remove the water from the coating and to collapse the gel to form a film without distoring the container. The dried coating is smooth, uniform and uniformly transparent. In operation, the overspray can be collected and returned to achieve greater than 95% material efficiency. The process can be carried out in a continuous manner to provide a continuously moving series of containers with a uniformly transparent, gas barrier polyvinylidene chloride coating at production rates suitable for commercial applications.