Читать книгу Packaging Technology and Engineering - Dipak Kumar Sarker - Страница 24

Two materials, namely steel sheeting (or aluminium sheeting) and metallic ends, are used to make tinplate metal packaging. Higher grade iron, with less carbon, known as steel, forms the scaffold in the form of sheets that are electroplated with metallic tin to prevent oxidation. A further layer of organic or resinous lacquer is applied to the tin‐plated steel; therefore, any direct contact of steel with can contents (usually food) is removed. In this manner, corrosion‐resistant metal packages can be mass produced. Can bodies and ends are produced for various types of product such as high‐acid, low‐acid, and high‐sulfur‐resistant metal packaging. Other than food products, metal packaging is also used for the packaging of pigments, oils, waxes, paints, and chemical materials. The metal packaging forms a physical barrier, which is resistant to pests (insects and rodents) and also to humidity, light, and air. The thermal resistance of lacquered tin or aluminium cans favours sterilisation and is consequently used as a standard form of packaging. This is certainly the case for foods, where use is common because the can and contents can be heated and simultaneously cooled during retort sterilisation without contamination of the contents.

In the modern era, the important factors determining the preference of metal packaging are related to cost, metal abundance, environmental concerns, health concerns, and payments or levies. These have shaped modern production techniques and advances in the sophistication of manufacturing and handling machines used for various forms of container and formats of accessing the contents. As such, the development and wide‐scale use of easy‐to‐open lids, various surface designs, high structural robustness, and the tightness of seams assuring sterility are areas of considerable interest among manufacturers. Probably the most common form of making tin cans (tin‐plated steel; cans) is the drawn and redrawn process for steel or aluminium cans, with a ubiquitous example being the standard food can. The second most common form of making cans involves a DWI process for aluminium or steel cans, with a common example being the thin‐walled soft drink or beer can. Other processes include the drawn and ironed (DI) steel can; the shaped aluminium or steel can, e.g. the sardine or pilchard can; the stretch‐drawn ironed aluminium or steel can (Toyo ULtimate Can; TULC); and the welded side wall tin‐plated steel can. However, because of concerns over toxicity and lack of assurance in seam integrity, ‘soldered’ cans are rarely used in modern times. Additionally, combinations of the above forms of canning vessel may be used to create hybrid products. The frequency of use of the tin can as a routine form of preservation over the last 10–15 years for foods and beverages has seen an observable increase of roughly two times.