Polyester and PVC are used for some specialty applications (Figure 6.1).
Figure 6.1 Types of filmic facestocks
Polyethylene. Polyethylene has a non-oriented structure – the molecules do not line up in either a longitudinal or transverse direction. This gives PE great flexibility and conformability (the ability to adapt to a container’s shape), making PE films suitable for squeezable containers such as tubes but also complex container shapes.
Polypropylene. Polypropylene films can be stretched in one direction (OPP) or two directions (BOPP), usually in three layers. This makes the film very rigid, and suitable for labeling of rigid containers such as glass or polyester bottles. Excellent clarity makes PP ideal for ‘no label’ look (clear-on-clear) labels. The material offers good film flatness, excellent dispensability even for thin films, and good die-cutting and printing characteristics.
Co-extruded. Semi-conformable co-extruded facestocks are multilayer films that can be a mix of polyethylene and polypropylene, depending on the properties required. These are suitable for semi-squeezable containers and bottles, often used for shampoo or sauces.
Polyester. Polyester films are very rigid films with high durability and clarity, and also high temperature resistance. Their rigidity allows these materials to be used for label-grade facestocks as thin as 12 microns. Some polyester films are flame retardant, and are used for applications such as electric cable labeling.
PVC (polyvinyl chloride). PVC films are highly conformable and flexible, and one key application is graphic wraps for automobiles. These materials also have very good outdoor resistance and ageing properties, along with high durability and resistance to UV light, temperature and chemicals.
PVC-based labels are suitable for applications such as drum labeling, farm applications, and durable indoor/outdoor graphics.
Choosing the right labeling material grade depends on container type, required film appearance and end-use performance requirements.
As we have seen, containers can be anything from very rigid to fully conformable. Polypropylene suits rigid containers, because of its clarity, dimensional stability and rigidity. Polyethylene is flexible, and is therefore the main industry choice for conformable films.
The appearance of a film – opaque, colored or clear – depends not only on the material chosen, but also the production process employed (Figure 6.2).
Figure 6.2 Filmic facestock appearance
A filmic face label has three layers: a core, a print ‘skin’ and an adhesive ‘skin’. When all of these layers are clear, the final facestock is also clear. An opaque white film can be made by adding titanium dioxide to the core layer.
Another type of PP is a ‘cavitated’ white. Air is entrapped in the middle white layer, adding a pearlescent effect to the white color.
As well as white and clear filmic facestocks, silver filmic facestocks are available. The silver layer is applied either to the print skin or to the adhesive skin when the facestock is made. When it is applied on the print skin, the absence of an intermediate material makes the film appear high gloss.
When applied on the adhesive skin, the material has a more moderate gloss look.
After manufacture, uncoated filmic facestocks require a surface treatment (corona, plasma or topcoating) to ensure proper ink anchorage and good printability.
During corona treatment, the film manufacturer increases the surface energy of the film by exposing the surface to a high voltage discharge.
Because the effect wears off over time, it is recommended that converters boost the corona effect using an inline treater on the press infeed press, to guarantee good ink anchorage.
Topcoating is a different form of surface treatment by adding a chemical top layer to the print skin, a coating designed to improve ink and toner anchorage (Figure 6.3). Universal topcoats, suitable for any printing technique, have been unavailable in the past, but are now coming to the market. This avoids the need to warehouse different topcoated materials for different print processes.
Topcoated films have some advantages over corona-treated films, such as a more premium look (improved inch anchorage), compatibility with high speed printing, and in some cases suitability for both conventional and digital (UV Inkjet) print technologies.
Figure 6.3 Ink anchorage tape test
PAPER OR FILM?
When are filmic labels generally preferred over paper labels?
One material type is not generally ‘better’ than the other. Instead, the requirements of a specific application will point the way towards paper or film.
One benefit of using film rather than paper is that it allows for the premium ‘no label’ look, often used in craft beer, spirits or personal care applications.
Film is also the preferred choice where flexibility, conformability, weather, moisture and tear resistance are required. Polyester provides extreme durability, for example coping with high levels of UV, heat, chemical or abrasion resistance.
The principal advantages of paper are lower cost, a wider variety of facestock options and higher performance with printing technologies that suit porous material structures. Film is a smooth material, and ink cannot anchor without either a topcoating or corona treatment. Paper has a structure that means it can more readily absorb inks such as water-based inks.
Depending on the application, paper has its own disadvantages. These include lower durability, no (or less) water resistance, lower tear resistance, and a possible tendency to wrinkle in the presence of moisture.
FILMS STRENGTHS AND WEAKNESSES:
Transparency – ‘no label’ look
Gloss with additional lamination
Good barrier/product resistance
Compatibility with plastic containers
Suited to high speed application
POLYETHYLENE VERSUS POLYPROPYLENE
As noted earlier, the two main types of filmic materials used in facestocks are PE and PP. We now look in more detail at their performance characteristics and how this affects application choice.
Polyethylene (Figure 6.4)
Figure 6.4 Properties of PE
Standard PE, typically used for labeling home & personal care products, comes in a standard thickness of 80-85 microns.
Semi-conformable films (co-extruded) are used for squeezable packaging, typically in the food and personal care sectors (e.g. shampoos and ketchups). They are available in the 50-65 micron range.
Thinner grades of PE (from 30-60 microns) can be used for direct labeling of food products such as kiwi fruit.
For industrial applications where increased durability is required – such as petrochemicals, lubricant packaging or drum labeling – thicker PE facestocks in the range 100-120 microns are used.
Polypropylene (Figure 6.5)
Figure 6.5 Properties of PP
Standard PP (between 50-60 microns) is used mainly on rigid surfaces such as glass and polyester containers (bottles, jars, trays), for beer & beverages, wine & spirits and food applications.
Thin PP (between 20-40 microns) is typically used for small diameter pharmaceutical devices such as syringes and injectors. It can also be used as an overlaminating film to protect print from scratching – a common practice for glass bottles.
Thick PPs in the range 100-120 microns are, for example, used in wine and spirits applications where requirements such as high opacity and ice-bucket performance play an important role.
PP films with a direct thermal coating are available for variable information labels in food and retail, creating opportunities for a premium ‘no label’ look in these segments as well.
As the environmental debate around the place of plastics in the packaging supply chain continues, what is the likely future for filmic labels?
Globally, government legislation and controls around plastics are increasing. In 2018, the European Commission announced the EU’s plastics strategy, stating that by 2030 all plastics packaging put into the EU market must be reusable, or able to be recycled ‘in a cost-effective manner.’
Plastic waste recycling targets were set at 55 percent of plastic packaging waste by 2030.
Single-use plastics are also being targeted in developing economies. India, for example, banned all single-trip plastics from October 2019, while ruling out the use of any plastics films below 50 microns.
This will directly impact polyester liner suppliers, because using a polyester liner above 50 microns is considered economically unviable, as well as going against the trend of light-weighting.
Alongside this legislative trend, younger consumers in particular have started to focus more on products available in what is perceived to be sustainable packaging. The major global brands have responded with their own sustainability pledges.
For example, Unilever has pledged that by 2025 all its plastic packaging will be designed to be fully reusable, recyclable or compostable.
Coca-Cola has pledged that by 2025 all its packaging will be fully recyclable globally.
What does all of this mean for the label industry? Suppliers of filmic PSA labelstocks are clearly focused on sustainability issues, including:
Increasing the recycled content of plastic label materials. It is estimated that PET liners with 30 per cent recycled content save 14 percent of greenhouse gases, up to 5 percent of water usage and up to 11 percent of energy consumption.
Reducing the amount of material used in face stocks and liners (down-gauging). Note that there are limits to what can be achieved with face materials, due to the bulk performance requirements noted above.
Improving PET recycling. For single-use PET bottles, new ‘switch off’ adhesives deactivate in the presence of liquids used in the recycling process, so that PP label materials can be separated from PET flakes in a flotation tank.
Label solutions that enable reuse of returnable glass bottles in the beer & beverage market. These labels detache easily and clean from the bottle in a conventional bottle washer.
Switching to renewables. Filmic labels can be made from renewable and bio-based sources.
In summary, the overwhelming majority of the filmic label market consists of PP (for rigid containers), PE (for conformable) and PE/PP co-extrusions (for semi-conformable). Polyester and PVC facestocks are used for specialist applications.
Surface treatment is always required for film stocks. This can be either a corona treatment or a topcoat. In performance terms, filmic facestocks give better flexibility, conformability, tear resistance, water resistance and durability when compared with paper labels. Paper has its own advantages, as discussed above, principally cost savings and ease-of-use with some printing technologies.