Glycol ether-free ink safeguards food packaging from migrating odours.

Because certain foods are susceptible to tainting by unpleasant odours, packaged goods marketers will be looking to formulators to provide them with inks that will not alter the delicate flavour of the foods they package. Thus, formulators may wish to explore a new polymer technology which

Carboset[R] glycol ether-free polymers for ink and coating formulations leave foodstuffs such as chocolate, confections, snacks, coffee, tea, and tobacco products free from chemical odours, so the intended taste and aroma of the foods remain intact. Properly formulated, these glycol ether-free polymers run well on most flexible film and paper substrates and print effectively on flexographic and rotogravure presses.

Why eliminate glycol

ethers?

Formulators examining glycol ether-free ink technology should have a working knowledge of how glycol ethers and residual monomers get into most water-based inks and coatings, and how they are now being eliminated or reduced. Most waterborne graphic arts polymers are either low-molecular-weight resins made in a solution polymerisation process, or emulsions which incorporate low-molecular-weight resins as raw materials. In either case, the chain of manufacturing processes leading to most waterborne inks begins with a process called solution polymerisation.

In solution polymerisation, a solvent is of course required to produce the `solution'. After polymerisation, most of the residual solvent is removed. However, because 100 per cent removal is impossible, all solution polymers contain some level of the residual solvent.

Glycol ethers

Most low-molecular weight graphic arts polymers are polymerised in a glycolether solvent, and therefore contain residual glycol ether. Analytical testing shows these products, as shipped to the inkmaker, generally contain glycol ethers at levels between 2 per cent and 7 per cent of the dry weight of the actual polymer. 'Glycol ethers' is a broad term used to describe a variety of highly odorous solvents which are based on either ethylene, propylene or diethylene glycols. Glycol ethers evaporate very slowly -- most much more slowly than water -- which means they are not fully detectable in an hour-long, 105 [degrees] C test for VOCs. (See Fig. 1). Over the shelf life of a consumer product, however, most of the glycol ethers may remain volatile and may migrate from printed inks and thus pose a threat to food taste and aroma. This migration may take place even if the ink is reverse-printed and sandwiched between film layers. For these reasons, many formulators are finding glycol ethers increasingly unacceptable to packaged-goods marketers.

Residual monomers

During polymerisation, monomers are reacted to form a polymer. However, because chemical reactions are not 100 per cent efficient, some monomers are not converted into polymers. These unconverted materials, known as residual monomers, are volatile organic compounds VOCs). These residual monomers not only add to converters' VOC emission levels, they also can then migrate into packaged products, tainting aroma and taste.

At the end of BF Goodrich's proprietary glycol ether-free polymerisation process, ultra-low VOCs are achieved by using a new technology to greatly reduce unreacted monomers. Through this process the level of residual monomers is reduced to produce polymers with virtually zero residual solvent and low VOC levels (See Fig. 2). The total VOC content for most of these polymers is generally less than 0.1 per cent, which makes them ideal for packaging applications where odour, flavor integrity and the total volatile levels are a priority. (See Fig. 3).

Formulators should be aware that, as with most waterborne polymers, glycol ether-free polymers are most often stabilised with a solution of ammonia hydroxide prior to ink formulation. Therefore, ink users will notice a modest, familiar odour of ammonia during printing. However, the fast-evaporating ammonia (which is carbon-free) is not a VOC and is completely driven-off as the ink dries, so no threat to product integrity is created.

Print quality

Formulators can assure their customers that glycol ether-free inks not only protect product integrity, they also deliver the same high print quality as traditional water-based systems. In addition to drying faster, many of these new inks show significantly higher gloss than their glycol ether-containing counterparts.

Higher gloss levels are possible because polymers produced without glycol ethers generally have a much smaller particle size than those produced by processes using glycol ethers. (See Fig. 4). This smaller size allows particles to get closer together, which can lead to improved coalescence. In turn, smoother film surfaces are possible and higher gloss can be achieved. (See Fig. 5).

These advanced polymers are comparable in price to those which contain glycol ethers, so the benefits of the cleaner technology can be offered with virtually no additional cost. In some cases, formulators might accurately tell customers that productivity is improved, as the absence of glycol ethers allows shorter drying time and increased press speeds.

In essence, glycol ether-free, low VOC polymers are taking waterborne inks into the next generation. They provide substantial benefits for product taste and aroma protection. And this allows formulators to assist packaged goods marketers to guarantee product integrity.