罐头涂料 化学品

BPA non-intent (BPA-NI) can coatings use polyester resins (terephthalate or isophthalate-based), acrylic-based systems, or epoxy resins from non-bisphenol A sources. Acrylic organosols are widely adopted for beverage can ends and easy-open lids. Polyester-based systems are prevalent in two-piece drawn and ironed (DWI) can interiors.

Can coatings are cured at high temperatures (180–215°C) for very short dwell times (10–60 seconds) on high-speed coil or sheet coating lines. This requires resins with fast crosslink kinetics and good flow at elevated temperatures. Melamine-formaldehyde and phenolic crosslinkers are common. Low-temperature and UV-cure systems are being developed to reduce energy consumption.

In the US, FDA 21 CFR 175.300 governs food contact coatings. In the EU, Regulation 10/2011 on plastic food contact materials applies. In China, GB 4806.10 covers food contact coatings. Each region has specific positive lists and migration test protocols that formulations must pass before commercialization.

Two-piece (DWI/DRD) cans are formed by deep drawing — the interior coating must withstand mechanical stretching with strong adhesion; polyester-based or acrylic systems are used. Three-piece cans are made from rolled and welded sheet — the interior coating is applied to flat sheet then formed; epoxy organosols and water-based epoxy systems remain widespread. Both must pass extraction tests for the intended food product.

Acidic and salty foods (tomato, fish in brine) demand coatings with very low water and oxygen permeability. Epoxy phenolic resins with phenolic hardeners provide the toughest barrier. White pigmented coatings include zinc oxide for sulfide-stain resistance with high-sulfur foods. Coating defects (porosity, fractures from forming) are detected by enamel-rater electrical conductivity tests at <50 mA threshold.

Can coatings undergo extraction testing per FDA 21 CFR 175.300 (and EU 10/2011) using food simulants — overall migration < 60 mg/kg food, specific migration limits per substance. Adhesion is tested after retort processing (121°C/60 min in distilled water). Flexibility and corrosion resistance are evaluated by enamel-rater electrical conductivity testing on actual cans before commercial qualification.