Problems related to packaging inks

Johns et al have published a report on benzophenone in printed cardboard for food stored frozen. This substance was found at 0.4-3.0 mg/dm in four board samples out of seven. The authors suggest that UV-cured inks had been used with benzophenone as an initiator in the printing of these boards. Three of the corresponding foodstuffs contained benzophenone at a level of 0.6-2.9 mg/kg, though there was a polyethylene layer applied to the board. Model ink substances were added to the carton, which then was in direct contact with foodstuffs stored at -20 °C for a year. It was found that transfer of the volatile substances could be considerable even at low temperatures. 

Aurela et al studied migration of alkylbenzenes used as solvents in offset inks. Alkylbenzenes migrated from a hamburger collar into a roll at the level of 2 mg/kg of food. In a risk assessment report published by the European Commission, a NOAL (no observed adverse effect level) value of 50 mg/kg body weight per day was used. Thus, the migration from the printed hamburger collar is quite acceptable. 

Set-off can be avoided by the use of anti-set-off compoimds. These are spray powders that reduce the frictional contact between the sheets. Materials like silica and starch, which have a particle diameter slightly greater than the printed ink film thickness, can be used. Slow setting problems may be reduced by the use of less solvent or by a higher ratio of resin to oil. Varnishing with a formula that utilises polymerisation induced by radiation is another way to avoid set-off. The varnish covers the printed surface and direct contact between the layer of print and the iimer food contact surface of the substrate is avoided. 

UV-radiation is used to achieve rapid curing and to avoid set-off effects in offset printing. The binders in UV-inks are highly reactive acrylate monomers and oligomers to which photoinitiators are added. These initiators start the cross-linking reaction in response to UV-radiation. Photoinitiators are low 

Low-odour inks for food packaging are based on odour and taint-free substances, for example, aromatic free solvents and maleic resins. So called semi-drying oils are also used. These are slow to oxidise and therefore do not develop malodorous aldehydes as they dry. However, some smell may be noticed after a long period of time as oxidation proceeds. Other solvents, such as tung oil, develop quite some odour during drying but if properly 

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