The technology and product designs are in constant development and it is, therefore, impossible to maintain a continuous up-date of every current innovation by this rapidly evolving industry. The body of work presented is intended to provide a comprehensive insight to extrusion coaters, laminators and converters of the various options that are available to produce tailor-made products and how to best exploit the available fabrication technologies. For the demanding process of extrusion coating this study focuses on aspects of extruder and die design, chill roll cooling and the critical optimization of adhesion to all substrates and films. Film lamination, which is the complimentary process, is discussed with the emphasis on the preparation of film surfaces, adhesives, and web handling. Finally, coextrusion which, enables the production of multi-layered structures in a single extrusion process is reviewed in detail with the emphasis on interlayer adhesion, inter-layer melt stability, thickness distribution, and properties.
The study offers the film processor and convertor additional insights on how to select, prepare and formulate materials to maximize synergies. The wide palette of polymers, plastic films, metal foils and pulp and paper products available are summarized. All the adhesive materials and adhesion promotion methods are compared and will be of invaluable benefit to engineers and technologists employed in this industry.
In summary for the producer of plastic based packaging materials particularly, in the sensitive perishable food sector, a number of attributes have to be embodied in the product according to the demands of the application.
Some are listed:
•Interlayer adhesion in multilayered structures.
•Heat sealability: no leakers from the package.
•Machinability: enables high speed packaging rates.
•Surface properties: easily printable to emphasize logos and product information.
•High strength and abuse resistance in-use.
•Balanced properties in the machine and transverse directions of the film.
•Controlled moisture vapour transmission rate (MVTR).
•Controlled oxygen transmission rate (OTR).
•Product resistance: to acids, alcohols, vegetable oils.
•No loss of nutrients, aroma and moisture.
•Opaqueness to UV light to reduce rancidity (food spoilage).
These characteristics when specified must be manufactured on high productivity machines with the most efficient use of materials to reduce waste and minimize carbon footprint. Dimensional control and overall product integrity must be perfectly matched to meet end-use regulations and the specified shelf-life.
The processes that can integrate these properties either individually or in combination are:
The extrusion coating process is an excellent method to combine a thin polymer layer, typically polyethylene with paper based materials and aluminum foil.
Adhesive lamination, with reactive polyurethane adhesives, is very versatile since it can combine all flexible roll fed webs made from the above processes with others such as, biaxially-oriented and metallized films in order to achieve the maximum benefits.
Coextrusion is used to combine a variety of different polymers, in a single step, that can be embodied in all multilayered structures produced by both of the above techniques.