Reactive Labels: Better Not Turn Red
Labels can do much more than impart printed information -
they can now change color to let the consumer know about the
freshness of their fish or meal, for instance. Kishore Sarkar from
the Swiss label specialists, the Gallus Group, explains the
functions of reactive labels, how they work and the opportunities
they offer packaging specialists.
Mr. Sarkar, are reactive labels really useful or are they more
of a gimmick?
Kishore Sarkar: Labels with a so-called Time Temperature
Indicator (TTI) are particularly valuable, above all in the food
industry. They show deviations from the ideal cooling temperature
by changing color when the temperature changes. That allows the
consumer to see if the cold chain has been interrupted and how long
the product will remain edible. This is especially useful with
easily perishable goods like fresh fish, meat and prepared meals.
How does it work?
Sarkar: If fish, for example, needs a cooling
temperature of 41 degrees Fahrenheit (5 degrees centigrade), but
the actual temperature is 33.8 to 41 degrees Fahrenheit (1-5
degrees centigrade) higher, an originally yellow label turns orange
or red, or a dark blue one becomes light blue. This color change is
irreversible: even if the food reaches the "correct" temperature
again, the label retains the new color.
So cheating isn't possible…
Sarkar: No, and that's a good thing. It isn't only a
service for the end consumer, but much more a matter of consumer
protection and avoidance of possible liability claims. The labels
allow retail companies and logistics companies to be monitored. In
some countries, such as the United States, for example, retail and
logistics companies are legally required to make cooled foods
retraceable through the entire supply chain.
Labels with a so-called Time Temperature Indicator (TTI) are particularly valuable, above all in the food industry. They show deviations from the ideal cooling temperature by changing color when the temperature changes
How does the color change work?
Sarkar: The temperature range in which the printed color
changes can be individually set based on the combination of
printing inks. For this purpose, color pigments are calibrated so
that their chemical structure changes at specific temperatures and
thus reflects the light with a different color, either darker or
lighter. There are currently colors for two temperature ranges: one
for 32 to 39.2 degrees Fahrenheit (0-4 degrees centigrade) for
meat, dairy and convenience products which last for up to 14 days.
The other is for 41 degrees Fahrenheit (5 degrees centigrade) for
fish and meat products which can be stored for five days.
Which printing processes are used here?
Sarkar: The labels are usually produced using
water-based flexographic printing or UV flexoprinting. Conventional
offset printing is less suitable because the reactive labels
require more ink application. That's because the color
particles are enveloped by a protective microcapsule and are
therefore larger than "normal" color particles. I'm sure
that in a few years from now with the help of nanotechnology, we
will be able to print these kinds of inks using offset.
Are there any special demands placed on printers in terms of
room temperature during production and storage?
Sarkar: No. The color, or more specifically the
protective microcapsule layer is only activated during
packaging - with the help of a LED-UV light.
What do you estimate to be the market potential?
Sarkar: It is definitely growing because the retail
trade is pushing the use of reactive labels. In England,
Switzerland and the United States, consumers value this type of
packaging, which is widespread. In Germany and Australia, the
labels are already being used for several products. Demand will
continue to grow particularly in Europe, because sales for
convenience food are growing disproportionately here. Reactive
labels, however, don't yet work on frozen products. An
appropriate printing ink still has to be developed for this
temperature range. In the future, the pharmaceutical and healthcare
industry will increasingly look to reactive labels, for example for
transporting blood bottles or temperature-sensitive medications.
Where else can you use reactive labels?
Sarkar: People can use reactive labels on packaging
where the goods are stored and sold in a defined atmosphere.
Pigments like nano silver particles are used here. These react to
gases which are emitted during the spoilage process. Take fresh
fish for example. When it starts to spoil, hydrogen sulfide is
generated. The nano silver particles react with the hydrogen
sulfide to form silver sulfide, thus changing the color.
And in marketing?
Sarkar: Labels printed with thermochromatic inks are very
well-suited here. They show if a drink, for example wine or beer,
is at the right serving temperature. These labels are primarily
widespread in the United States on beer bottles. They are also used
on bottled drinks in discos or bars. At a certain cooling
temperature, the product logo glows noticeably. Thermochromatic
colors are reversible. That means they can change their color time
and again, for example from blue to red and back to blue again.
Their applications are diverse, which is why printers are urged to
inform and advise their customers.