Canvera Can Coating2 November 2017
Canvera Can Coating
The tide is turning against epoxy-based can coatings, but what are the alternatives and how should the metal packaging industry respond?
When a law was introduced in France in 2015 prohibiting the use of Bisphenol A (BPA) in food packaging of any kind, it put the chemical, which has been shown to be an endocrine disrupter in some studies, firmly on the radar for can makers across the world.
Indeed, a few months after the French ban in 2015, BPA was put on California’s Proposition 65 list which means that businesses must provide warnings for products that expose Californians to significant amounts of BPA. Since then, the European Chemicals Agency (ECHA) has published the addition of Bisphenol-A (BPA) to the Candidate List of Substances of Very High Concern (SVHC).
BPA safety fears have also sparked a growing awareness among can makers about other chemicals of concern – i.e. any chemicals that can migrate from a can or other food and drink packaging into its contents, and also any chemicals thought to be hormone disruptors or carcinogenic. Some other coating options may include materials of concern to consumers such as other bisphenol epoxies, styrene, or phenol-formaldehyde cross-linkers.
There are now a number of potential alternatives to BPA for beverage cans. These include acrylic, BPA-NI (BPA not intentionally added) products that do not contain BPA but still can contain other potential materials of concern, such as styrene or phenol-formaldehydes.
Another option is an epoxy that is free of BPA but is derived from a bisphenol that is structurally similar to BPA, tetramethyl-Bisphenol-F. There are some safety concerns about bisphenols since they are closely related to BPA, (1) A research paper suggests they are non-estrogenic. However, in contrast, another screen has cast a broad brush at over 40 different bisphenols, as being potentially endocrine active (2) .
A new option, which has been trialled in France and is now beginning to appear on the shelves in the retail market, harnesses disruptive technology to achieve a feat that was once considered impossible – using thermoplastic coatings, applied in liquid form, to protect the contents of metal food and drink cans. Extraction studies have shown very low levels of migratables even at a level down to 10 parts-per-billion (ppb).
The BLUEWAVE Technology from Dow has facilitated enabled a new process to be invented that allows polyolefins used in flexible and rigid plastic packaging to be turned into a water-borne dispersion that can be applied to the inside of metal beverage cans.
The resulting product, known as CANVERA Polyolefin Dispersion (POD), uses a POD technology which can be formulated into a coating that offers a very thin, protective, thermoplastic lining that not only affords excellent food and flavour retention for the can’s contents, but also protects the can from corrosion and gives film flexibility.
As POD is a dispersion of thermoplastic polymers, the polymerization reaction has taken place well before the product goes into the can. No further polymerization reaction mechanism is needed to make the film inside the can. This results in an improved safety profile compared to the thermosetting options discussed above, which still rely on a chemical reaction to build molecular weight and form the coating. In the latter technology, there is always a higher risk that unreacted monomers or unknown by-products will form that can possibly migrate into the food and beverage.