Likewise, the Swiss Ordinance: the definitive set of regulations determining materials deemed safe for use in food packaging. Among any number of global and local equivalents are guidelines issued by the US Food and Drug Administration (FDA); the British Retail Consortium (BRC) in the UK; and with especial reference to print, the European Printing Ink Association (EuPIA). Common to all are exclusion lists prohibiting the use of chemicals with known or suspected toxicity.

While we are ultimately what we eat, that outer packaging of much of our food-stuff is the delivery mechanism on which we depend to validate its sourcing and viability. Nothing compromises brand integrity more rapidly – and sometimes irreparably – than an inability to live up to its promise. 

Consumer protection may be the primary intention of all of these initiatives, but arguably undermining it are commercial realities that can be far more compelling spurs to compliance; not least fears of legislation resulting from an unfortunate food safety mishap. 

As a result, enactment can be a cumbersome and not wholly satisfactory process, viz the FDAs’ recent banning of three perfluorinated compounds (PFCs) used in grease-proof coatings for fast food paper packaging 10 years after the potential risks had first been identified. The more cynical observer might detect partiality in favour of a large US tax-paying corporation. There may, however, be a more straightforward explanation.

Inks have been relatively slow in showing up on the regulatory radar, says Pulse Print Products technical director David Morris. “There’s no very clear regulation about printing inks for food. It wasn’t really thought about as being an issue until it was realised that the printed material on the outside of food packaging isn’t necessarily isolated from the contents, and that there can be some transfer of constituents throughout the packaging.

“There are a lot of chemicals that can be found in ink, and if you’re going to start testing how safe they all are it’s going to take a long time and cost a lot of money. 

“Because that work hasn’t really been done, the limits that have been set by the Swiss Ordinance are very low indeed. It could well be that were those chemicals to be properly assessed they’d be a lot less potentially harmful than might currently be supposed.”

Bearing responsibility

In the meantime, though, better to be safe than sorry. The general consensus within the UK is that inks for food packaging should only contain raw materials that are listed on the Swiss Ordinance positive list. The underlying objective is to reduce or eliminate the risk of migration from the outer surface of the pack and coming into direct contact with its contents. 

Compliance, however, can be just as dependent upon competence as chemistry; indeed, while an accredited ink formulation may be low-migration-capable, there can never be any guarantee of its efficacy if used incorrectly. “It’s not good enough for a converter to just say ‘I’ve bought a low-migration ink, therefore job done’,” says Sun Chemicals’ global business director for digital, Peter Saunders. “In the event of there being an issue, they’re the one responsible for the brand integrity of their customers.”

While the financial buck might end up on the converter’s factory floor, the longer-term damage to the brand owner can be more wide-reaching. Selling over a billion products worldwide each day, Nestlé is acutely aware of the importance within its business model of consumer trust, and under no illusions about the negative fall-out if it’s breached. 

Having suffered the full force of consumer opprobrium in 2005 when the photo-initiator isopropyl thioxanthone (ITX) inadvertently found its way into their baby-milk product – the converter had failed to properly cure the UV offset ink used to print the cartons – it was one of the first to phase out Bisphenol A (BPA) five years later despite inconclusive scientific opinion.

“Obviously we have to follow the highest food safety initiatives, and consider every market with equal importance irrespective of size,” says Bruce Funnell, head of packaging at Nestlé’s UK product technology centre. 

“We have to think global and local. We demand full transparency and insist upon a declaration of regulatory compliance and a full disclosure of all chemicals used in producing our packaging. 

“If suppliers aren’t appropriately accredited we conduct our own GMP audits.”

Costs incurred are borne by Nestlé, although anecdotally other food manufacturers and retailers can be less forthcoming; a bone of contention with some converters, who may be faced with a bill of £2,000 for the privilege of being included on an official roster. 

Nestlé also binds itself to non-disclosure agreements to protect supplier IP and that of their suppliers. It’s indicative of a commitment towards developing more equitable working relationships with greater probability of delivering safer outcomes. 

“While the inks we use do not contain any materials listed on the EuPIA exclusion list they are generally designed for ambient or chilled storage and use. 

“However, special care is required when the end-product requires either direct food contact inks or the packaging is used in an elevated temperature environment such as microwave, retort, boil or cook in the pack,” says Parkside Flexibles new product development manager Mark Shaw. 

“An understanding of the final product application is crucial to selecting the safest ink system.”

Taking the cure

Irrespective of whether they are thermal-based (solvent or water) or energy-curable (UV) based – the regulation-approved ink chemistries – the performance of low-migration inks is governed by the drying or curing process they undergo. “Whilst there are a lot of good reasons to use energy-curable inks, there’s also space for other formulations,” explains Saunders. “Water-based tends to be cheaper with fewer environmental concerns to address; solvent-based inks give excellent print quality when used for flexible packaging.”

While UV inks provide a high-quality printed effect, concerns over their use centre on their inclusion of potentially harmful monomers and photo-initiators. These, however, are mitigated by continuing advances in the curing process; for example, Flint’s newly introduced EkoCure Ancora UV LED-curable low-migration ink for narrow-web flexo food packaging applications that contrasts positively with the downtime associated with mercury lamp inefficiencies, and can run at 150m/min.

Targeting the same market sector as LED is the newer electron beam curing (EB). It can be a real alternative to UV, says Ebeam Technologies business development manager Elsa Callini. “Electrons are particles, so the physics behind the curing process it facilitates is intrinsically different. There is enough energy to achieve polymerisation without recourse to triggers such as photo-initiators, which it seems will eventually be banned. It’s my opinion that brands won’t wait for the legislation to take effect now that there’s a more secure option.”

Ebeam Technologies has partnered with ink manufacturers such as Collins Inkjet to develop and test EB-curable inks that are ready for immediate use. Whereas the process was initially offline, Ebeam has developed an electron beam with a life expectancy of at least 10,000 hours that’s sited at the end of the line and can easily keep pace with presses running at 300m/min, according to Callini. 

Meanwhile, the company has linked up with Edale and AB Graphic to incorporate EB into the Digicon 3000 mid-web finishing solution for digitally printed flexible packaging and labels on systems such as the HP Indigo 20000.

Jetting into a water-based future

Although inkjet accounts for less than 1% of the food packaging market the consensus view is that, in its ability to provide short-run, personalised capability at speed, it’s time is nigh. 

That latter attribute in conjunction with the low-viscosity droplet size of inkjet inks has hitherto posed particular challenges in terms of controlling migration – albeit efficiently addressed by UV curable formulations developed notably by Agfa Graphics.

But while UV curable is the de facto standard for digital inkjet devices such as Screen’s increasingly adopted 50m/min Truepress L350, other solutions are lining up. On track for commercialisation sometime in 2017, the high-speed Landa W10 flexible packaging offset press outputting at a top speed of 200m/min will use a hot-air dried water-based solvent-free ink, which although containing some pigments can claim the lowest migration values.

The direction of travel, however, could be via hybrid ink technologies; for example, Sunjets’ Aquacure that combines UV for adhesion and printability with an 80% proportion of water to deliver an odour-free lightweight film, and with a significantly wider colour gamut. 

According to Saunders, majoring on the formulation’s low-migration properties weren’t originally the main focus. “While there’ll always be an area for 100% solid UV curable ink, one of the concerns is that can put down too thick a layer.

“Water-based gives the opportunity to reduce the cost of these higher-grade inkjet specific materials, while additionally lowering the risk of migration. 

“We know that as inkjet is increasingly adopted there will be more water-based solutions. However, there’ll also be a need to supplement it with other materials, not only to protect that coating but simply you because an ink that’s just water and pigment won’t stick to anything.”