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1. Associations, M. P. (2016, December 6). mpma. Retrieved from www.mpma.org.uk: http://www.mpma.org.uk/pages/pv.asp?p=mpma27

2. Nehring, P. K. (2007). Packaging Materials For Food Stuffs. International life science institute.

3. Association, M. P. (n.d.). How a three-piece welded food can is made. Workingham: mpma. Retrieved from www.mpma.org.uk

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1.  internal protective coatings, generally termed ‘lacquers’ in UK, these are designed firstly to withstand can/component manufacturing and subsequent use,

2.To minimise interaction between product and can substrate over the full shelf life of the filled can  which may be up to three years.

The required properties include, inertness, flexibility, freedom from taint and processibility at high temperatures (most food cans are in-can heat sterilised).

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For all coatings an epoxy phenolic basecoat may be used, e.g. for a food can easy-open end. Vegetables, meat, soups and fish are slightly corrosive and, where sulphur staining could be a problem, can ends are normally coated with zinc oxide-modified epoxy phenolic lacquers. Aluminiumised epoxy phenolics are increasingly used for solid meat packs.

The use of epoxy phenolics has some advantages over oleoresinous lacquers (which tend to soften during retorting), such as the promotion of meat release properties, an important factor in meat packs. Content release is also assisted by incorporation of waxes and silicones in order to help, e.g. solid meat or fish to slide more easily from the can by preventing the contents from sticking to the sides of the can. In these cases, the wax is known as a “meat release agent” and lacquers using these waxes are widely used for luncheon meat, pâté and fish roe.

Cans do not always need an internal coating. Some packs of vegetable oils, particularly large catering
tins (5 l), may not be coated, but their ends may be. Uncoated ETP cans are used for specific food types,
including tomatoes and other tomato-based products, white fruits and some vegetables (e.g. mushrooms,
asparagus). Uncoated cans are preferred to lacquered cans in situations where a small lacquer discontinuity
(e.g. scratch) would result in a concentrated attack of the base steel (the small area of tin would quickly
disappear) and could potentially lead to pin holing and microbiological contamination. For many acidic
products, the presence of tin is desirable because it eliminates oxygen, which would otherwise cause
discolouration of the contents.

Additionally, for many tomato-based products, the presence of a bare tin surface inside the can leads to protection of the natural flavour and appearance of the food, through oxidation of the tin surface in preference to oxidative degradation of the food. This process retains the quality attributes that consumers expect from these products throughout their long shelf life. Fully lacquered cans do not allow this flavour to develop. It should be noted that whilst the ETP body may bencoated, if TFS ends are used they would always be coated.

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Many canned foods are thermally processed in the can after filling, canned foods are the most demanding product that require coatings. A more diverse range of coatings is found in comparison to all other forms of foodstuffs in metal packaging.

1. The biggest variation in coating properties relates to the type of food, due to the large number of different foodstuffs packed and their individual requirements and processing conditions.

For example: The most demanding foods are meat, fish, high-sulphur vegetables (peas and sweet corn), highly acidic foods (sauerkraut and rhubarb) and highly coloured foods (red fruits and curry).2. Both internal and external coating must withstand the conditions. The internal lacquers must be resistant to the contents of the can during processing and any by-products, such as hydrogen sulphide, formed in the food during the processing. In addition, migration of components of the coating layer should meet the restrictions of the applicable legislation

The bulk of the food can coatings are based upon epoxy resins, primarily epoxy phenolics (internal gold lacquers for food cans) and to a lesser extent epoxy anhydride (white internals for food cans), with PVC-based organosols being the next most-used category (organosols finding larger usage in North America than in Europe).