Film & Foil
GETTING ON IN PLASTIC FILMS By Tom Kerchiss - RK Print Coat Instruments
woven fabrics, accounted for a major proportion of packaging materials up until the end of the 1960s and the beginning of the 1970s. Although a limited range of plastic filmic materials was around during this time, the cost was prohibitive and application potential was considered to be too small and specialised. However, nothing remains the same and resin formulators and film manufacturers began to unveil new products that were more price competitive and which could be used either as a replacement for existing materials, or could serve as a material foundation for an exciting new category of products - termed flexible packaging.
P But first, mention must be made of
polyolefin. These films provided niche opportunities for the converter, packaging printer and end users. As with everything else there needed to be a market for these products. Fortuitously this coincided with a time when consumers were looking for low cost products that were brightly coloured, attractive and that were more in keeping with a growing optimism about life in general. Plastics were among a whole host of developments and innovations that were seen as finally ending the era of austerity that had previously dominated so much of
aperboard, corrugated material, glass bottles, wooden packing crates, and to some extent hessian, jute and
life after the Second World War. Polyolefin is a collective term for polyethylene and polypropylene (PP). Polyethylene was the simplest and most inexpensive plastic film to develop and manufacture at the time and initially was available as either high density or low density. Polypropylene, a harder, denser and more transparent material became commercially available much later. To begin with, Polyolefin films were used
as a replacement for cellophane. Not only did the new materials provide better physical properties and moisture resistance, they did so at a much lower cost. As cellophane lost market share to polyolefin, manufacturers and investors gained confidence and further investment in film product development took place, notably in areas such as polypropylene, for items such as snack food packaging. PP offered good tensile strength and modulus values. Most importantly from a converter’s perspective, PP is readily convertible, even when variants such as bi-axially orientated polypropylene (BOPP) are taken into account. BOPP itself provides the stiffness and stand up properties that are needed for modern day heavy- duty plastic bag and sack applications. Another evolutionary step in the manufacture and converting of filmic materials was the use of coatings, first for the heat sealing of bags and as a way of
enhancing the look of a product, and most importantly for extending product shelf life and minimising spoilage caused by gases, contaminants, moisture and light. Package food scientists and others also turned their attention to developing the means to improve oxygen transmission resistance. Polyvinyl Dichloride and Ethylene Vinyl Alcohol (EVA) material compounds proved effective. The former, known as PvDC was often applied using in-line systems on packaging presses by the converter. Bringing us up-to-date both commercial and industrial demands place greater pressure on film producers, technologists and converters to process new and often unfamiliar materials, often for products that are themselves at the cutting edge of technology. Convertibility is a critical consideration; many of the products, materials and consumables involved are new. Failure in any area, whether processing a multi-web structure, lamination technique, ink or a coating material that is contaminated or out of spec, may jeopardise the look and performance. The same is also true of press and converting machine performance. The colour must be right, but so too must rub and chemical resistance, durability and flexibility. Product development tools and quality control systems have an increasingly prominent role in processing, both in terms of commercial and product viability. Many of the materials now on the processing scene are specialist in that they are engineered for specific purposes. More often than not they have a thin profile, frequently less than 0.25mm in thickness. Made in small quantities for applications that include electronics, automotive, aerospace, medical, security, packaging, civil engineering and thermal/light regulatory devices, these specialist films tend to be at the high end of the price spectrum. Consequently converting is generally conducted with care in order to minimise waste. Coating films to improve anti-static
resistance and abrasion resistance, as well as optimise adhesion and provide for barrier resistance continues. Films are often coated to provide be-spoke properties. Films are sometimes metallised to alter their electrical properties or reduce moisture permeability. Films can be mono-layered, multi-layered, laminated or co-extruded. Lets briefly consider some of the materials that the converter may come across. Polyester associated films and materials such as PET or polyethylene terephthalate are employed in a variety of applications, including flexible packaging. Good printability, machinability and properties, such as a resistance to extremes of temperature, puncture resistance, strength and barrier resistance, make materials like
20 April 2018
www.convertermag.co.uk
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