Metal cans offer affordable long-term storage for a wide range of foodstuffs, and coatings play an intrinsic protective role, inside and out.

Protective internal coatings for beverages and solid foodstuffs have for decades been based on a relatively small number of basic chemistries for regulatory and performance reasons, according to Metal Packaging Manufacturers Association (MPMA) technical manager David Smith.

Smith says: “Epoxy-based internal coatings have been the mainstay for use in contact with both food and beverage products for decades because of their workability, substrate adhesion, product resistance and freedom from taint qualities.”

One way to improve the perception of coated metal packaging for the future could lie in the formulation of ‘cleaner’ coatings. Smith says this doesn’t mean coatings haven’t always been clean: “It has to be stressed that ‘traditional’ coatings have been ‘clean’ in the regulatory and consumer safety senses, but even cleaner coatings could raise the image of metal packaging onto a higher plane.”

The findings of a three-year Defra-funded study could point the way for the future development of coatings. The collaborative study, carried out by the Central Science Laboratory (CSL), Leeds University, coatings manufacturer Valspar, metal packaging specialist Impress and Heinz, which also acted as project manager, looked in detail at the issue of migration and how it can be minimised in future coating development.

The main focus of the study was on new formulations for epoxy phenolics and polyester polyurethane coatings. The project studied the way different coating formulations act as a protective barrier and the potential for new cleaner coatings.

According to project manager Julian Stocker from Heinz, coatings science and technology have historically been driven mainly by technological demands, such as faster manufacturing speeds, lightweighting, more user-friendly cans and lower solvent emissions in oven curing.

So why was it the right time to conduct the project? Stocker says: “The protection offered has been so successful that there has been little investment into fundamental research of the interactions between coatings and food. The time was right to do more basic research towards identifying and understanding the factors affecting levels of migration in order to accelerate the development of reduced migration coatings.”