As more and more paper labels are replaced by film, most especially polypropylene, label printers are developing new skills and methods of production: ink manufacturers are developing inks purely for filmic materials and substrate producers are continuing to refine and develop their products to make them more user-friendly.

Previous caution about the use of polypropylene is being dispelled as increasing numbers of printers become accustomed to using the latest materials. The new generation top-coated films have been designed to accommodate both the increasing trend towards the use of water-based and UV inks and the move from rotary letterpress to flexo, especially UV flexo and combination printing.

The central issue remains film printability and the surface treatment required to ensure that inks stay in place under the standard industry scratch and tape tests.

There are two main choices facing label printers – buy a film which has a pre-treated surface for ink adhesive or install their own corona treatment equipment.

Corona treatment is necessary on un-coated film to prevent ink sliding off the material. Film has a lower surface energy than most inks and since ink cannot be absorbed there is little to bind film and ink together. Corona treatment activates the film surface to an electrical discharge generating ozone and free electrons leads to an oxidisation of the surface, an increase in polarity and, therefore, surface energy.

This is essentially a dedicated operation. Too little treatment will result in poor ink adhesion and over treatment may damage the surface of the film, destroying the molecular bonds to the bulk material.

Over the past decade, polypropylene film manufacturers have formulated products which allow easier corona treatment, and film converters now supply pre-treated films with performance guaranteed for several months.

However, the real developments remain with coated film which eliminate the need for corona treatment by providing the inks with a chemical surface for bonding. The resulting adhesion is much stronger and coated films tend to throw up far fewer problems for label printers than un-coated grades.

Coated films are of particular benefit when a range of different print processes are being used, specifically with water-based and ultra violet (UV) cured inks for letterpress, silkscreen and, more recently flexographic label printing, which are vastly different with respect to viscosity.

Top-coated films command a premium price but, given that the printer needs do no more than apply the ink, they provide a higher degree of security and confidence for the label producer and the end user.

Coatings have also been developed which improve the overall performance of the label with regard to resistance to water and extreme temperatures.

An example is the printed acrylic coated film developed by UCB Films which will withstand pasteurisation at 95ºC and immersion in ice for 24 hours and still pass the scratch resistance test on screen-applied inks.

A top-coated film of this type opens up a wide range of possibilities in markets such as those for bottled beers and wine where there is a demand for high quality, elaborate graphics with a no-label look which can stay with the bottle during its life-cycle.

Further recent development has seen the creation of a top coating for computer imprintable variable information printing (VIP).

The UCB Films’ development grade – RAYOFACE WI – features a top coating which has a high mineral filler making it computer imprintable. This is ideal for information printed via a dot matrix printer, such as batch codes and sell-by-dates.

The film is smooth and matt white for clear printing with all types of conventional inks. Its thickness makes it suitable for hand-applied labels.

The UCB Films development team is now working with metallised, top coated films which combine the barrier and presentation properties of metal with print-friendly coatings.

Coatings are, of course, an addition to the inherent qualities of plastic film as a labelling substrate, such as the ability to promote a ‘no label’ look by using clear film on clear containers, gloss and resistance to scuffing and tearing.

There are a number of reason which explain why biaxially oriented polypropylene (BOPP) is gaining market share.

A few years ago, PVC made up nearly 70 per cent of all plastic label films, now it is polypropylene and polyethylene which dominate the market.

The reason behind the growth of BOPP in the labels facestock market are numerous. Key, though, is the need to produce recyclable plastic bottles and containers. Polyethylene and polypropylene dominate the blow moulding industry and in small quantities such as a label, can be mixed with minimal effect on the recycled product.

The critical thickness for BOPP for high speed dispensing can be as low as 60 microns which, together with its low density, means far less raw material is required than PE or PVC.

UCB Films’ label facestock and release liners are produced using the bubble process, giving good rigidity and tensile strength for register control during die cutting. The films’ balanced orientation means sophisticated shapes can be die cut without feathering around the edges and corners of the label and matrix stripping is trouble-free.

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