What are the UV Resistant Inks Used on Food Labels?
Product labels must be durable and hardwearing as you cannot control how your products will be handled once they leave the factory.
Products may get wet or exposed to condensation, be left out on display in windows where they might fade, or just get knocked around and scuffed. The more durable the labels are, the better.
What Makes a Good Ink?
UV resistant inks have a lot of positive properties. They have good physical and chemical resistance, which means that you don't need to use protective varnish to keep the label looking good.
In addition, they tend to have vibrant colours, so you don't need to use a lot of ink to get a powerful colour, unlike inks that are made from water or solvents.
UV resistant inks can be cured using very powerful UV lights.
Where normal inks will dry on the plate, UV ink is ready to print instantly. The inks are solid and will not evaporate, so they have a long shelf-life.
Waste is reduced because the ink won't dry out if you need to stop and start a print run.
This is done by printing the label and exposing it to a burst of intense UV light to cure it, and then the ink is stable and won't fade, smudge or run.
UV Ink and Modern Safety Regulations
There are several international safety regulations that relate to UV resistant inks.
The EU Regulation 1935/2004 EC, the FDA, and the EFSA procedures all have their own tests that relate to food packaging and big brands.
So far there is not a single international regulator that determines the rules for inks, and UV resistant inks are in the awkward position of being a new and relatively untested product.
However, when used properly UF resistant inks have a lot of promise.
By using a small amount of photoinitiator in the ink it should be possible to eliminate the presence of non-cured free radicals (ink that did not cure from UV exposure).
This will help to reduce the presence of free radicals that are a cause for concern in the food industry.
Another option is to laminate the inside of the package with a solventless laminate to act as a barrier against ink migration.
Low-Migration UV Flexo Inks
One fear is that inks could migrate to the back of the reel where they would come into contact with food. This is something that the label printing and inks industries are trying to get around.
Cationic UV inks are an interesting option since you can wait longer periods before starting polymerisation.
It takes longer to cure cationic inks, but once the curing is completed the ink will not migrate.
Some companies have successfully employed cationic inks as a method of producing short-run food packaging, since the inks have good adhesion, do not produce a lot of waste, and have good print quality.
One challenge, however, is that oxygen can interfere with the curing process.
To get around this, printers must use sophisticated equipment with nitrogen reservoirs, feeders and pipes to prevent oxygen from interfering with the chain of polymerisation within the ink.
There are some new inks that have migration results less than 10ppb, which puts them within the requirements for the international safety legislation for food packaging.
However, these low migration results occur only when the ink is cured in perfect circumstances.
This means that if you are a food manufacturer that is looking for a reliable printing company to make food packaging, you should vet their practices thoroughly to ensure any cartons or packets that they produce are indeed food-safe, especially if they promise to use UV flexo printing.
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