Currently, the main types of coatings used for canned goods include epoxy phenolic coatings, epoxy amine coatings, organic solvent coatings, ethylene-based coatings, polyester coatings, acrylic coatings, and epoxy ester coatings. The characteristics of various resins, as well as the performance and applications of coatings produced from them, are briefly outlined below.
Epoxy Amine Coatings:
Epoxy amine coatings are formulated with epoxy resin and amine resin as the primary components in specific proportions. Widely used as protective coatings for the external surfaces of can lids, can bodies, twist-off caps, and sealing caps, these coatings exhibit the following key properties and advantages:
(1) Colorless Coating:
The coating is transparent, providing a colorless appearance.
(2) Excellent Chemical Resistance and Processability:
Demonstrates good resistance to chemical agents and is easily processed.
(3) High Boil Resistance:
Exhibits strong resistance to boiling conditions.
(4) Good Color Fastness Upon Re-Baking:
Maintains good color stability when subjected to additional baking.
Epoxy amine coatings are highly sterilization-resistant, particularly in strongly alkaline water with a pH range of 9 to 10, making them the preferred choice for protecting the external surfaces of can lids. This property is also utilized in packaging latex paint. The resistance to water absorption and resistance to whitening during the cooking process are significantly better than other modified epoxy products. Their excellent heat resistance prevents mechanical abrasions during heat treatment.
The color fastness and resistance to yellowing of epoxy amine coatings during re-baking are noteworthy, making them widely applied as protective coatings for the external surfaces of three-piece beverage and food cans, including can bodies, can lids, twist-off caps, and crown caps. They are especially useful when the final baking of internal coatings may affect the performance of external coatings.
Epoxy amine coatings maintain their performance well even when exposed to contents that may spill and corrode the external coating of the can. Due to their excellent adhesion, they are also used as base coatings for printing.
Curing for epoxy amine coatings is achieved through thermal polymerization. For mixed-can products, they are typically heated to a peak temperature of 170-180°C for up to 10 minutes. When higher boil resistance and chemical resistance are required, a peak temperature of 200°C is recommended.
Epoxy amine coatings are also frequently used as internal coatings, especially in beverage cans with low corrosive contents such as dairy products and fruit juice beverages.