With aggressive products such as pickles, marinades and some beverages, the tin protection on the tinplate of the cans was damaged and even perforated before the product expired. For this reason, extra protection began to be added to the inside.
The metal packaging used for both food and non-food products has an inner and outer coating that acts as a protective layer. In the case of the external coat, it is also used to make the packaging more attractive. This protection is achieved by applying varnishes such as thermosetting acrylic resins.
What are thermosetting acrylic resins and what are they used for?
This type of resins are copolymers of different acrylic and methacrylic esters to which an internal crosslinker, also acrylic, is added, which also polymerises. These resins are subjected to high temperatures of 170-180ºC to produce products with very different properties to the initial ones. The cross-linking allows the change from a linear structure to a three-dimensional one by cross-linking the polymer chains, giving coatings with excellent chemical and mechanical properties.
The result is materials suitable for the outer coating of cans and jars and for general industrial coatings.
What other materials are used for can coatings?
Organosols and epoxy resins are still used for the inner lining of food and beverage cans, but the presence of bisphenol A (BPA) has put epoxy resins in the spotlight because of their potential health consequences for humans.
Currently, polyester resins are being introduced as an alternative.
Advantages of using thermosetting resins for can coatings
Acrylic thermosetting resins have a multitude of applications thanks to their good adhesion to aluminium and tinplate, resistance to water, cracking and alkaline cleaners. They also possess good flexibility, high gloss, extensibility, and extraordinary hardness.
Functions of thermosetting acrylic resins
Synthesia's Synthacril specialties for can coatings are recommended for several formulations: coatings, varnishes, and paints for roller application in the metalworking industry. Also, for exterior coatings of drums and cans.