Canning and Fish Packaging Technology

Unit 10 - Manufacture of plastic packages

10.1.2.6.Dispersion and lacquer coating
Coatings may be done on films by using volatile liquid to carry the coating. Dispersion coating uses water as the volatile medium and this dispersion contains about 50% of the solid polymer dispersed in it giving a milky appearance similar to rubber latex. In lacquer coating resins are dissolved in a solvent or combination of solvents to prepare a more viscous free flowing clear liquid. Usually fairly low viscosity, dispersion or lacquer solutions are used for coating.
In dispersion coating, the liquid is roller coated usually on to one side of the film and the excess is metered off by a controlled air jet called air knife or a wire wound roll called Meyer rod. Excess dispersion falls back into a reservoir and is re-circulated. Finally the wet film is dried by hot air. Solvent coating or lacquer coating is done in a similar manner.
Polypropylene, polyester and Nylon films are usually coated with PVDL and used in packaging. Low viscosity waxes and later high viscosity modified waxes (hot melts) are widely used as coating in flexible packaging, paper and paper board.