ENAMELING AND COATING
The tin base must be treated to further protect the product and to protect from
adverse product reaction to the can. To further protect the steel base, enamels are
applied to the inside surface and coatings are applied to the outside surface of the can,
prior to can fabrication.
a. Enamels. Can enamels are the paint-like composition baked onto the interior
of cans to prevent the production of hydrogen gas and to prevent or inhibit unfavorable
reactions between the can and its content. They are inert, adhere tightly to the tin plate,
and will withstand stress. The type of enamel used is dependent upon the product to be
put into the can.
b. Coating. Coatings are the nontoxic, external paints, or enamels that are
applied for the purpose of preventing corrosion and providing camouflage. Coatings
must be nontoxic and must meet specification requirements, as required. The coatings
are precoated or postcoated. Precoated coating refers to a coating applied to the
exterior flat sheets of tin plate prior to fabricating the tin plate into cans. Postcoated
coating is applied to the exterior of food cans after they have been filled with food,
sealed, and processed.
1-9. CAN LABELING METHODS
Can labeling serves to identify the contents of the can as to contents, weight,
manufacturer, and processing plant. The labeling used on containers depends on the
product and its intended use.
a. Lithographing. Lithographing is printing which has been baked to the
surface of the tin by heat treatment. It is accomplished prior to coating the can. The
labeling is usually placed on the packer's end of the can but in some instances, it may
be on the can body. This process is often used for operational rations.
b. Stamping. Stamping is the application of marking with an inked stamp. It is
not bonded to the surface of the tin with heat, although it may be subjected to heat in
order to speed drying.
c. Embossing. In embossing, the markings are raised in the tin plate of the can
end or of the body. These markings must not be sharp or have well-defined edges.
The embossing procedure must be carefully controlled to ensure legible markings
without "harming" the can. Can codes are usually embossed on the packer's end of the
d. Paper Labels. Paper labels are permitted for domestic shipments on military
contracts. They are rarely used on products that are shipped overseas because the
glue tends to hold moisture in close contact with the can, resulting in corrosion.