Polymer resin producers have been developing new plastics from which converters can manufacture films with surfaces with a higher level of printability or offering more scope for eye-catching graphics than before.
Still, further improvements are needed to make full use of flexible packaging for presentation and promotional purposes. Sometimes these can be provided by additives, but many are having to come from the ink makers themselves.
Flexible packaging, particular plastic, is gaining a growing share of the European packaging market, as retailers and consumer product companies try to cut down costs by using less or lighter packaging.
More products are appearing on the supermarket shelves in new forms of flexible packaging such as stand-up pouches. Bottles and other forms of flexible packaging are being given greater appeal by being wrapped in plastic shrink sleeves.
But the increase is not just confined to packaging within stores. In their endeavors to achieve greater efficiencies in the logistics of their supply chains, European retailers have been making less use of secondary packaging materials such as board and more of shrink and stretch film for products during transit.
With some products like multipacks of beverages or alcoholic drinks, they often want the shrink or stretch film to provide the in-store packaging as well, with a printability to maximize branding and promotional possibilities.
"Packaging is fast becoming the in-store, silent salesperson," said Kurt Aerts, ExxonMobil Chemical's manager of global polyethylene films.
As a result of the emphasis on the shelf appeal of products, flexible packaging is having to provide an extra visual attraction. This demand for higher quality graphics is coming at a time when consumer product companies are reducing expenditures on advertising in the conventional media. Instead, they are spending more on marketing at the retail level.
Research by top brand owners like Procter & Gamble has shown that shoppers make up their minds to buy a product when they see it on the supermarket shelf. Hence, companies want highly distinctive packaging of their products, backed if possible by in-store promotional initiatives.
Packaging not only has to give a product an individualized identity but also show its usefulness to consumers. The colors in the packaging of some products have to be visually striking because they are often linked to an overall image which is immediately recognizable by shoppers.
As a result, brand owners and retailers want high print standards from flexible packaging materials, some of which, particularly polymers, have previously presented considerable technical problems in achieving quality graphics.
Among the major difficulties with some polymer substrates and printing processes in flexible packaging have been the transfer of the ink from the plates, the adhesion of the ink to the plastic, lightfastness, maintaining print quality on quick-moving packaging lines and general lack of consistency.
Dealing with the complexities of printing on polymers used for retort and shrink sleeve packaging has been technically tough.
The inks and the laminated films on the lids of modified atmosphere packaging (MAP) systems, which are used in a lot for retort applications for food processing and cooking of ready-meals in microwave ovens, have to be highly temperature resistant.
With shrink sleeves, which in Europe are one of the fastest growing segments of packaging, the inks must shrink at the same rate as the material during the packaging process.
"Shrink sleeves are becoming particularly popular with brand owners in segments like dairy products, alcoholic drinks and beverages, household cleaners and cosmetics because they offer the opportunity to decorate the whole bottle or containers with graphics," said a marketing executive in one ink company. "But this can pose printing problems, particular with contoured bottles."
Most printing of sleeves in Europe is done on gravure presses. But there has been increasing pressure from retailers and consumer product companies for more printing to be done on flexo presses due of their ability to handle shorter runs and because they are less expensive.
"For a short-run job, the startup costs with flexo printing on sleeves can be as much as five times cheaper than those for printing by gravure," said a UK-based printing consultant. "If the inks and substrates are right, flexo has the same print quality as gravure. But with certain inks, like waterborne, there can be big problems with adhesion."
Solving the technical difficulties posed by flexible packaging can require a lot of cooperation between makers of presses, plates, inks, polymers, additives and auxiliaries.
"The ink producer has to understand the whole packaging supply chain," said Felipe Mellado, corporate vice president, marketing and technology, at Sun Chemical Europe. "That means knowing about the film and other flexible packaging materials, about packaging lines, the printing processes and the requirements of the food industry and retailers."
Polymer makers have been developing new grades of plastic with improved printability for applications like stretch and shrink packaging film. ExxonMobil Chemical launched in the European market for flexible packaging films this year a range of co-extrusion polyethylene resins, some produced through a metallacene catalyst process which helps to give more clarity and better print quality.
BASF has introduced a bi-oriented polyamide (BOPA) with an antiblock additive which improves the adhesion of inks to the surface of the polymer in films.
"The additive give the BOPA film a slightly rougher surface than normal, providing opportunities for improved presentation of products in supermarkets," said Rolf-Egbert Gruetzner, BASF's business manager for polyamide and intermediates. "It enables quality printing to be done on the packaging of food products like sausage casings. It also offers scope for printing on the tops of lids of MAP packaging, in which BOPA forms the upper layer."
Ink producers have been endeavoring to develop inks for flexible packaging which do not require primers or use of other pre-treatment auxiliaries to achieve an acceptable print quality.
"The ideal is to have inks which have all the necessary properties for adhesion to the substrate," said Niklas Olsson, global brand manager for narrow-web inks at XSYS Print Solutions. "In this way the inks are more cost effective because the use of primers and other pre-treatment products only adds to the overall expense of the printing."
To obtain an optimal level of ink transfer and adhesion, ink companies have created formulations and systems using a variety of ingredients.
Ink producers best placed to solve some of the major difficulties with flexible packaging printing seem to be those whose operations are horizontally or vertically integrated.
XSYS has been strengthening its presence in flexible packaging by utilizing its capabilities in both inks and plates for the sector.
The company has just launched a new plate for flexo printing on flexible packaging which minimizes dot gain in halftone areas while ensuring a consistent ink lay-down on a variety of substrates, including shrink sleeves.
"We have the advantage of having experts in both plates and inks to develop and test new products like this," said Eva Freudenthaler, XSYS' marketing manager for printing plates. "In flexible packaging the key first step is to have an efficient transfer of the ink from the plate to the substrate. Everyone wants simplicity so customers are tending to use the same plate for different applications. It is the same with the inks as well."
XSYS now has UV narrow web inks which can be applied to virtually the full range of shrinkages of polymers like PET in sleeve packaging.
"With free-radical UV technologies like we use, there used to be a limitation on shrinkages of around 40 percent," said Mr. Olsson. "But now there is hardly any limitation since the inks adhere well to a wide range of substrates with shrinkages as high as 75 percent. The problem of UV cross-linking causing brittleness has also been eliminated."
Sun Chemical launched at Labelexpo in Brussels in September an advanced cationic UV flexo ink which it claims cures twice as fast as other products, while having a high level of adhesion and resistance on almost all film and metallized materials.
The company's technological strategy in flexible packaging applications has been to capitalize on the expertise of its resins operation in polymer chemistry so it can provide inks which stick effectively to all substrates.
"Our R&D in this area is focused on polymer science so that we are able to develop our own polymers to enable inks to achieve not only a high level of adhesion but also to enhance the properties of the film itself," said Mr. Mellado.
"The polymers in our inks are particularly important with MAP applications because their temperature resistance ensures that they remain intact during the retort process without affecting the structure of the laminated film of the MAP package," he said.
Sun Chemical works closely with polymer producers like ExxonMobil and converters in the development of its flexible packaging inks. It also has a technical backup service which includes the placing of its technical staff on the premises of packaging companies so that they can provide on-the-spot advice and tests.
Ink makers are likely to be confronted with problems in flexible packaging printing for some time. They will have to be sorted out in partnership not only with customers but other players in the packaging supply chain.