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. Below is a brief introduction to the characteristics of various resins and the performance and applications of coatings made from them.
Epoxy Ester Coatings
Epoxy ester resin is a product obtained through the esterification process of plant oil reacting with epoxy resin. This resin imparts flexibility and color to coatings.
Epoxy ester coatings are primarily used for post-printing varnish, suitable for both mixed-can products and products resistant to boiling. Therefore, it is suitable for metal can bodies, deep-drawn cans, twist-off caps, crown caps, and all types of mixed-can products.
Most epoxy ester coatings are colorless, but the addition of dyes can produce golden epoxy ester coatings used for decorating the external surfaces of twist-off caps and crown caps. The key properties and advantages include:
(1) Excellent Gloss:
Exhibits a high level of gloss.
(2) Good Color Fastness:
Maintains good color stability, crucial for external designs.
(3) Combination of Flexibility and Hardness:
Combines flexibility with good hardness.
(4) Excellent Ink Compatibility:
Exceptionally compatible with inks, especially suitable for the “wet-on-wet” production process.
Compared to other synthetic coatings, epoxy ester coatings are one of the most versatile varieties. They can achieve the same level of gloss as oil resin varnish while overcoming the drawbacks of poor color fastness and susceptibility to yellowing.
Curing for epoxy ester coatings is achieved through oxidation and thermal polymerization. For mixed-can production, a peak temperature of 160-180°C is typically used, heated for up to 10 minutes when high ink color fastness is required. The difference in dry film color is minimal within this temperature range. When used for products resistant to boiling, heating with a peak temperature of up to 190°C for a maximum of 10 minutes is needed to maximize water and steam resistance performance.