Can coatings

Your Content Go Due to toxicological data, public debate, and recent regulatory rulings, alternatives to epoxy-based can coatings are now in use. Background information on the specifications, components, and characteristics of can coatings is provided in the FPF article.

Why do cans have coatings?

Food and beverage cans preserve the taste and nutritional values of their filling for up to several years. As a consequence of such long storage times, the interactions between the packaging and the food need to be minimized. Cans are typically coated with an organic layer that protects the integrity of the can from effects of the food and prevents chemical reactions between the can’s metal and the food. To fulfill the technical and legal requirements, can coatings should withstand the production and sterilization processes (1, 3), be universally applicable for all food and beverage types (2), prevent chemical migration into food in quantities that endanger human health (4), adhere to the can even after non-intentional deformation (5), resist aggressive food types and protect the metal of the cans (6), and preserve the food and maintain its organoleptic properties over several years (7).es Here

Can data on the market and production

The three materials used to create cans are aluminum, tin-coated steel (tinplate), and electrolytic steel coated with chromium (ECCS). There are three main methods for creating can bodies: 3-piece welded cans (3PC), 2-piece drawn and redrawn (DRD) cans, or 2-piece drawn and ironed (D&I) cans. Regardless of the substance or the production process, the majority of cans are coated both inside and externally with films that range in thickness from 1 to 10 m. Roller coating is often used to cover both sides of planar metal sheets or coils before the cans are made. Cans that have already been produced instead have coatings sprayed on them. Tin is utilized in cans without an inner coating for light-colored, acidic juices and fruits because it oxidizes more quickly than food (such as pineapple, pears, and peaches).

Characteristics and alternatives for coatings

There are many different types of commercially available can coatings, but the majority of them are based on just a few chemical processes (Table). A wide range of additives are used in coatings, including lubricants, anti-foaming agents, adhesives, hydrochloric acid scavengers, pigments, and compounds that improve surface sliding and container coating abrasion and scratch resistance.

Epoxy-based coatings have the largest market share, accounting for more than 90%. However, can manufacturers and food firms have started to substitute epoxy coatings based on BPA with alternatives as a result of toxicological evidence, public discussion, and recent regulatory decisions. Acrylic and polyester are now used as first-generation alternatives to epoxy coatings. Epoxy coatings made of polyolefin and without BPA have also been developed more recently. There are also BPA capturing methods and

Epoxy coatings

Epoxy resins were first used to cover steel and aluminum cans in the 1950s. They became the most widely utilized coating material because of their stability, protective function, and technological characteristics. The majority of epoxy coatings are created by mixing bisphenol A (BPA, CAS 80-05-7) with epichlorohydrin to create epoxy resins with bisphenol A-diglycidyl ether. Epoxy-phenolic coatings are the most significant subgroup of the several various epoxy mixes that have been created. Epoxy amines, acrylates, and anhydrides are some examples of other mixed resins.

Oleoresins

Oleoresins, which are blends of oil and resin produced from plants, were the first materials used to coat cans. Oleoresins are quite flexible and simple to apply, but they do not stick well to metal surfaces, have a poor resistance to corrosion, and take a long time to cure. Additionally, they could alter the food’s organoleptic characteristics.

Vinyl

Vinyl chloride and vinyl acetate are used to create vinyl coatings. Although they attach poorly to metal and cannot resist high temperatures, they are very flexible and robust in acidic and alkaline environments. Vinyl coatings frequently combine different resins with plasticizers and stabilizers. Resin suspensions in organic solvent are used to make vinyl organosols. Compared to vinyl coatings, organosols have comparable improvements in chemical resistance, thermal stability, and adhesion.

Phenolic

Aldehydes and phenols make up phenolic resins. They shield cans from sulfide discoloration and exhibit good corrosion resistance. Phenolics can alter the flavor and aroma of food, are not very flexible, and stick poorly to metal. Unblended phenolic resins are utilized as coatings for drums and pails but not in food and beverage cans. However, phenolics are frequent crosslinkers that boost resistance (for instance, in epoxide resins).

Acrylic

Ethylacrylate is the main raw material used to make acrylic resins. They are fragile and might alter the flavor and odor of food, but they have a clean look and have corrosion and sulfide stain resistance.

Polyester

The two primary carboxylic acids used in polyester coatings are isophthalic acid (IPA) and terephthalic acid (TPA). Polyester resins are simple to work with throughout the manufacturing process and stick to metal surfaces effectively, but they often aren’t stable in acidic environments and have little corrosion resistance. Beverage cans can also be laminated using polyethylene terephthalate (PET) coatings, although adhesives are required to attach the PET to the metal.

Polyolefins

Recently, coatings based on polyolefin dispersions have hit the market. The firm claims that the finished polyolefin coating demonstrates flexibility, adhesion, and corrosion resistance without altering the taste of the food.

Regulation U.S.

Under 21 CFR 175.300, polymeric and resinous coatings are covered. This code outlines test requirements, migration restrictions, and a list of approved starting materials. Can coatings that adhere to these requirements are legal. BPA was added to the list of substances known to be harmful to the development of fetuses and embryos under Proposition 65 by California’s Office of Environmental Health Hazard Assessment (OEHHA) in May 2015. A clear and fair warning about the chemical dangers must now be provided to consumers of BPA-containing items by manufacturers, distributors, and retailers (FPF reported).

Europe

Although there is no EU-wide law governing can coatings, the Netherlands, Belgium, the Czech Republic, Greece, Italy, Slovakia, France, and Spain have national regulations in place. Bisphenol A Diglycidyl Ether (BADGE) and its derivatives have unified rules (Commission Regulation EC 1895/2005) and inorganic tin has unified restrictions (Commission Regulation EC 242/2004) for certain compounds known to migrate from can coatings. The current recommended migration limit for BPA in varnishes and coatings is 0.05 mg/kg of food, according to a proposed Commission Regulation on the subject (FPF reported). The use of BPA in FCMs, including all packaging, containers, and utensils meant for direct contact with food, is forbidden in France (LOI n° 2010-729) (FPF reported).

Biomonitoring, exposure, and migration

BPA, BADGE, and their derivatives were the main subjects of the majority of investigations looking into chemical migration from food cans. Exposure estimations have a robust foundation thanks in particular to the volume of BPA data. However, oligomers, catalysts, reaction promoters, epoxidized food oils, amino resins, acrylic resins, different esters, waxes, lubricants, and metals may also be included in the total migrates from cans. Additionally, the migrate often includes non-intentionally added substances (NIAS) such contaminants, reaction byproducts, and degradation products. Because many NIAS are unnamed or unknown compounds, it is far more difficult or even impossible to compute exposure estimates for these frequently complicated mixes.

There is a link between eating canned food and, to a much lesser extent, drinking canned drinks and human exposure to BPA. According to a 2012 research, BADGE and its derivatives were found in all test samples from the U.S. and China, and urine concentrations were 3–4 times higher than those of BPA.

Effects on health

In general, can coatings emit a complicated chemical combination into the food, and only a small number of migrants have undergone extensive testing. There are several distinct endpoints covered by extensive toxicity evidence for BPA, including neurological, immune-modulatory, cardiovascular, and metabolic impacts as well as reproductive and developmental consequences. BADGE was determined not not be genotoxic, carcinogenic, reprotoxic, or developmental toxic in 2004. However, more recent research found some impacts on developmental and reprotoxic endpoints.

Although a large number of migrating compounds are entirely unknown, they may significantly increase the toxicity of the migration. A number of tests were used in 2006 to examine the cytotoxic effects of migrates from epoxy- and polyester-based coatings. According to one of these tests’ findings, only 0.5% of the cytotoxic effects seen in epoxy coating migration could be attributed to the presence of BPA, BADGE, and BADGE-H2O. This example highlights the value of doing tests during risk assessment that focus on the final migration rather than just a single drug.