ABSTRACT
This chapter covers single layer, multi-layer and combination materials found as films, foils, laminations, coextrusions, coatings, etc.
Single ply materials Although a proportion of 'flexibles' are multi-layer materials, a number of flexible packaging materials are found as single plies. Single ply materials are found in the form of paper, and those plastics which either do not require an additional coating to achieve a heat seal or can be employed as a direct wrap. Examples of these include various grades of polyethylene and plasticised PVC, which have to be high-frequency welded. A few foils may be used uncoated. (Note that most foils are varnished, lacquered or wash coated to improve scuff resistance or to assist print key.) Other single (monolayer) plastics may also be found as wraps which are restrained by a secondary feature (such as a tie or tape) or rely on special properties, e.g. cling films, for their retention around a product. Cling films, skin wraps, etc. involve such materials as thin gauges of plasticised PVC, Surlyn ionomer, modified grades of low-density polyethylene and Saran (PVdC) copolymers. Thus the use of single ply materials should not be ignored, particularly as these are frequently seen as being more environmentally friendly (i.e. multilayer materials are always more difficult to recover or recycle). Of the single ply materials listed above, paper needs special mention since it was one of the earliest wrapping materials and still has significant use worldwide.
