Blackplate for packaging

Blackplate is low carbon mild steel, not tincoated and normally not oil or otherwise treated. In other words, after the final cold rolling treatment – whether temper rolling or double reduction or no further treatment is given to it.

Blackplate can be used for container manufacture, using the techniques of welding or cementing for the production of the sod seam. Both its surface have to be protected by applying synthetic lacquer, otherwise rusting easily occurs.

Blackplate is no longer black. When new and clean, it is almost indistinguishable from tin plate to a passing observer.

It is called blackplate because in the days when it was rolled by hand, it acquiring a thin coating of black oxide which was left on the surface and not dissolved away in acid.

Blackplate is not used widely because of its tendency to rust rapidly, its spoor chemical resistance and its poor reflectivity, which creates decoration difficulties.
Blackplate for packaging

Lacquer

Various lacquers have been developed for lining cans, especially for preventing food discoloration that could occur as a result of interactions between the food and the can.

Internal coating eliminates the food-metal interaction during storage while the external protects the can from abrasion and corrosion.

Three-piece food cans are made from lacquered tinsheets. The lacquer is roller-coated the sheet at a rate of 3000 – 5000 sheet per hour.

The cured lacquer shows a film thickness of 3-6 microns – in other words a very thin film.

It also aids in forming of cup and provides base for decoration.
Lacquer

Epoxy in food packaging

Epoxy resins are characterized by the presence of at least two epoxy (or oxirane) groups within their molecular structure.

The group is composed of a planar, three-membered ring comprising two carbon atoms and one oxygen atom.

Epoxy resins containing Bisphenol-A or BPA are used as the inside coating of almost all food and beverage cans. The function of epoxy resins are to provide a protective lining on the interior surface of food and beverage cans to prevent the cans’ contents from contacting and reacting with the metal walls, ensuring sterility.

Many types of internal enamel coatings are available for food containers including epoxy-phenolic, epoxy-amino, epoxy-acrylate, epoxy-anhydrite, vinyl organosol, thermoset polyester, thermoset polymer coated, phenolic, and oleoresinous.

The original can coatings were based on oleoresinous products that include all those materials made by fusing material gums and rosins and blending them with drying oils such as linseed or tung (Chinese wood oil).

Epoxy-phenolic are the commonly used lacquer. They are epoxy resins based on epichlorohydrin and bisphenol.

They are combined with phenolic resins, which re produced by the reaction of phenol with formaldehyde.

This combination gives a gold lacquer with good flexibility, adhesion and chemical resistance.
Epoxy in food packaging