Since early 2006 we at Mercian Labels have been conducting extended experiments on the effects of daylight on self adhesive labels printed using a variety of label printing methods, and we have regularly updated the results of these experiments on a dedicated webpage.
This can be a serious problem in our industry, as labels are often used for warnings and often exposed to daylight for extended periods.Â The fact that UV energy in daylight causes fading in many printed media is well accepted, but beyond rumour and “conventional wisdom”, I’ve never actually seen any hard evidence that shows how different types of inks and printing techniques perform when faced with extended periods of exposure to daylight.
We have had experiments going since early 2006Â and early 2008 on the following printing ink technologies:
- flexography – solvent based ink – dye based
- flexography – water based ink – pigmented
- letterpress – UV cured ink
- hotfoil - heat and pressure cured ink
- thermal transfer – wax resin based foil image
- Electrostatic toner based technology (v3) from Xeikon (Punch Graphix) from a Xeikon 330
- Digital offset technology from HP (Indigo) from a HP WS 4xxx press
- Electrostatic toner based technology from QuickLabel VIVO!
- UV cured inkjet imagery from Konica Minolta
- Electrostatic toner based technology fromÂ Degrava
- Inkjet images from Nilpeter using their Caslon technology with Xaar inkjet heads
- Inkjet images from Xaar using their own inkjet heads (unknown ink)
To give you an idea of what happens when labels fade badly, this is how much a label can fade if its made using inappropriate techniques for its end use application.
This image shows the difference between 2 halves of 4 different labels before and after 2.5 years of daylight exposure behind a south facing glass window.Â The top 2 labels were printed with solvent based flexographic inks in a cream colour and a blue colour, and as you can see, the colour has faded to being almost no existent.Â Areas with a clear lamination have given no protection to UV rays.
The middle red FRAGILE label was printed with water based flexo inks, and has noticeably faded but is still very clear.Â The bottom barcode labels have hardly faded, although the lamination has yellowed.
Looking at a totally different technology, UV cured letterpress inks also fade quite noticeably, especially the lighter colours (yellow being particularly poor)
Best of all, hotfoil printed labels have shown almost no difference, apart from a colour change on the metallic blue foil on the middle gold label.
Looking at digital ink technology, our current test has been running for over 6 months, and there is hardly any changes in any of the many different ink technologies we have been trying.Â See the detailed results here.
These (above) are from a Xeikon 330 digital label press.
and these (above) are from a HP Indigo digital label press
and (above) from a Vivo (above top), a Konica Minolta UV inkjet (above middle), and a Degrava (above right bottom “castelhino”)
And the final ones above are from the Xaar printhead used on a Nilpeter Caslon machine and from Xaar themselves.
I guess these observations and opinions will be of serious interest to those involved in specifying labels, and will probably destroy a few myths:
- UV cured ink technology is not resistant to UV light!
- solvent based inks have been a mainstay of the industry for decades, and whilst they are easy to use, they fade easily and have limited long term performance.Â In line with our Corporate Social Responsibility policy, we at Mercian Labels do not routinely use solvent based inks on any of our labels any more.
- cheap and simple thermal transfer labels are very resistant to UV, probably due to the high carbon content in the ribbon
- All the established and emerging digital label printing technologies have a good resistance to UV (so far), but one will emerge as the winner, so watch this space!
I would positively welcome comments from customers, label users, suppliers, manufactuers or others in the industry on this subject – are the results of this experiment what you would expect?Â Would anyone wish to predict which if the digital label technologies will do best?