Food packaging: an inky issue

There are several types of ink migration, and they all apply to varnishes and coatings as well. One is penetration through a porous material, or straightforward set-off in the stack of material or on the reel. This is usually a result of inadequate drying. But migration can also occur by vapour phase transfer, or by distillation.

It is the transference of one substance to another that makes it a major problem with food packaging, because it cannot always be detected by smell or change of colour, taste, or touch. These are called the organoleptic properties, and can often be detected only by highly sensitive chemical tests, carried out under strict laboratory conditions, using spectroscopy or chromatography equipment.

Owing to the fact that food varies in its consistency, simulants, which mimic the behaviour of the product, are used to create a more stable test sample. Foods with large surface areas are more prone than others, as are those with a high fat content, which has the capacity to absorb the migrating chemical.

The size of the printed image, the weight of the food, the time spent in contact, and the temperature at which the product and packaging are stored together, are all contributory factors, as is the quality of the substrate.

A raft of EU legislation covers the subject, and for many involved in trying to meet the latest requirements there is a feeling that the target is constantly moving. In general terms, materials that come into contact with food should not pose a health problem, nor bring about an unacceptable change in the composition or organoleptic characteristic of the food.

One potential problem area is the photoinitiator, and the well-documented case of a Nestlé product in a Tetra Pak container, which was never conclusively proven, was sufficient for IsopropilThioXantone (ITX), to be permanently damaged as a brand. The problem revolved around ink set-off in the reel, and the fact that the PE inner packaging was able to absorb chemicals used in ITX.

Subsequently, 4-Methyl Benzophenone (4-MBP), often used for cereal packaging, was banned. Although tests proved it to be unharmful, it had the effect of developing a whole new range of ‘safe’ photo-initiators which, not surprisingly, are more expensive!

Conventional oil-based inks and varnishes, which emit aldehydes during oxidation, cannot be used for chocolate packaging because of their ability to absorb fat. High fat content foods also have the ability to soften ‘fully dry’ inks and varnishes, leading to possible contamination where there is direct contact. And the longer the period of contact the greater the problem.

The secret is knowing what you are using and what it will be used for. Cereal packaging, for example, has a low risk of contamination through migration, unless it’s a chocolate variety, when the higher fat content changes the equation, while straight chocolate poses one of the biggest risks.

Another problem product is tea, where the paper used for the tea bags is porous, so susceptible to absorbing chemicals migrating from the packaging.

All this has led to the development of low migration inks and varnishes over the past decade or so, but even then, the slow setting and lack of oxidative drying of conventional inks requires a WB coating to be used, and similarly with low migration UV inks, either a WB or appropriate UV lacquer is needed to ‘seal’ the ink surface.

So, who bears the responsibility for this potential hazard? Technically speaking, it is the producer of the finished package who takes the rap but, of course, with so many constituent parts making up that carton or wrapper or pouch, the buck is normally passed to the converter.

Good Manufacturing Practice (GMP) is vital, so careful monitoring of items such as solvents, washes, cleaning chemicals, oils and greases on the production floor is essential. Less easy but of no less importance is an awareness of monomers from plastics substances or coatings, hydrocarbon distillates or minerals from inks, low molecular weight components from board or adhesives, and any byproducts associated with drying or curing.

With pressure today on the need to reduce the amount of secondary and tertiary packaging for environmental reasons, the risk of potential contamination caused by the removal of inner packaging layers is great.

But for many in the industry, this is just a smokescreen used for political gain. The real problem is that less packaging increases the risk of damaged goods that cannot be sold. The resulting increase in landfill waste poses a greater problem of greenhouse gases than that created by the additional packaging that is, in many cases, recycled.

Solutions

So, what are ink manufacturers doing to deal with the problem, whether it is potential or actual? Stehlin Hostag (Huber Group) refers to GMP Regulation 2023/2006, relating to flexible and fibre-based packaging for food and covers substrates, all materials used including inks, coatings, and adhesives and production methods. To cater for this, the company created a dedicated production facility in the UK at which it can mix UV and conventional inks in separate controlled environments that are 100% GMP standard.

MGA, as the inks are branded, are low migration but cost substantially more than standard formulations. This cost often cannot be passed on to the brand owner, which poses a problem. Much of the primary packaging still uses standard inks because of cost, pack design, and lack of awareness. To overcome this, the company believes in working closely with converters and their customers to learn more about the technology that is being developed to overcome the potential health hazard.

The company admits that it’s a difficult subject, but that in order to stay ahead of the legislators, a full, frank, and free forum is necessary. MGA inks already meet the EuPIA standards due to be implemented in 2015, but they come at a price. In addition to inks, Stehlin Hostag also supplies low odour and low migration water-based and UV varnishes that meet MGA standards.

ICE Arets confirmed the dilemma that faces converters. The company cites an example of two official bodies that offer contradictory advice, with the EuPIA recommending the use of tailor-made low migration and low odour inks and varnishes as laid down in their own guidelines, while ECMA’s view is that other inks and varnishes should be substituted for UV where primary food packaging is involved.

The problem is not simply related to UV, nor to certain elements within the inks and varnishes. The key is whether there is direct contact between the print and the foodstuff, and this includes items such as window patch substrate and the adhesive.

The industry suffered scares with photo-initiators, which although largely unproven, raised awareness all round. This led to a rethink on ink and varnish formulations, and the latest UV polymeric inks have been tested and approved across a range of substrates from board to film, and meet with the latest legal criteria of less than 10 parts per billion of unknown substances.

An essential part in developing this new ink technology was a detailed analysis of the elements used to carry the colour of the ink. Traditionally these include the pigment itself and in varying proportions, monomers, oligomers, prepolymers, additives, and the photo-initiator. Monomers proved to be the main culprit in migration, owing to their low molecular weight and small particle size, and as a consequence the company re-formulated its products.

The problem was two-fold: monomers lower the ink viscosity; and they are cheap. The key is using a polymeric photo-initiator, which has allowed the level of monomers to be eliminated. The latest UV formulations have large particles with high molecular weights, and therefore low odour and migration capability. With low migration conventional inks becoming available, tests are under way to establish whether they can meet the standards already being achieved by their UV counterparts.

But the problem is not straightforward to identify. As the Flint Group explains, the same printing ink system can be safe or unsafe for use on food packaging, according to the material it is printed on, the printing conditions, the food that is packed with the printed packaging, the conditions during the packaging manufacturing and filling (for example applied temperatures), and the way the food packaging is intended to be used (deep freeze, ovenable, microwavable).

For this reason, Flint believes the ink supplier alone cannot assume full responsibility for an ink being safe for any specific application.

Zeller & Gmelin, which claims to have pioneered certifiable low migration inks, makes extensive use of its own in-house R&D facility. This allows the company to develop and test its technology across a variety of substrates, some new, others of variable quality, to ensure compliance of its inks. Migration security is carried out by gas-chromatography and liquid-chromatography with mass spectrogram. All tested samples are sent to independent laboratories for double verification. This technique has allowed Zeller & Gmelin to undercut the legal 10ppb migration limit with 95% ethanol.

New facility

At Sun Chemical, a new manufacturing facility in Frankfurt, Germany, gives it enhanced capacity to supply low migration inks for all types of packaging substrate across all its conventional technology. The facility, which cost €4 million, exceeds the current requirements for cleanroom production environment, and features modern mixers and mills, process control computers and two blending stations – one specifically for low migration, and the other, housed in a separate location to avoid any risk of contamination, for conventional ink.

The final word on the subject is with an official body: The UK Food Standards Agency, which monitors and advises on the current and upcoming legislation to ensure compliance on all sides. While its fundamental role is to protect the customer who buys and consumes the product, the agency is supportive of regulations that are ‘sensible, workable, and proportionate’.

The responsibility for safety lies with the company that places the product on the market, and that can be interpreted as the converter, the packer, the retailer, the substrate manufacturer, the ink manufacturer, or the brand owner – none is allowed to shirk its duty of care.

In an industry sector that is large and rapidly growing larger on a global basis, as developed markets become more sophisticated, and emerging countries jump on the consumer bandwagon, the issue of safety in food packaging is clearly here to stay. What the industry and legislators have to do is decide on a realistic meeting point where commercial interests and consumer safety can be accommodated without either being compromised.

Now, that will be a tough nut to crack!