2. Varnish composition and characteristics

2.1 Definition and functions

A varnish can be defined as a macromolecular material deposited on the metal surface to form an adherent, inert, thin film (3 to 15 µm thick).

Its essential functions are to protect the metal of the packaging on its inner and outer surfaces, and also to protect the contents themselves from the potentially adverse effects of contact with metals. The varnish can also be used to facilitate the shaping of the metal (in the case of chromed iron or aluminum); it also often has an aesthetic function, helping to give a regular, attractive appearance to the inside and outside of the can.