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Many self adhesive labels are used in outside
environments, and can potentially fade and damage
when exposed to UV daylight. This is most often
a result of the degrading effects of UV light
in sunlight when exposed to labels used outside
or on view from the outside. The "bleaching"
or fading effects of sunlight are commonly accepted
as occurring on many coloured surfaces. Mercian
Labels therefore conducted an experiment in 2006
to examine the effects of sunlight on printed
labels, manufactured using the following printing
techniques:
- 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
The experiment was only designed to test the
effect of UV light on the printed labels. The
effect of UV on the adhesives and materials was
not tested.
A selection of recently printed self adhesive
labels manufactured by Mercian Labels was collated
on 15 February 2006. These labels were stuck onto
7 A4 sheets of paper, along with a tick box description
of the printing method and any varnish or lamination.
The sheets were then cut in half, with half the
label on each part of the sheet. The left half
of all 7 sheets were labeled as "EXPOSED
TO UV" and permanently displayed in window
fully exposed to sunlight. The right half of all
7 sheets were labeled as "NOT EXPOSED TO
UV" and stored in a draw away from all forms
of light.
At approximately 2 week intervals the exposed
halves were removed from the window and photographed
by a digital camera in indoor light conditions
adjacent to their unexposed counterpart. The purpose
of this was to allow a direct comparison with
an undamaged version of the label over time.
The same digital camera and lighting conditions
were used throughout, and the images were not
manipulated in any way apart from cropping and
rotating using basic image manipulation software.
The detailed results are available at http://www.selfadhesivelabels.com/uv_light_test_labels.html
Long term conclusions:
- Hotfoil labels are very resistant to UV degradation,
with no discernable changes in any labels apart
from some fading on metallic blue foils.
- Holographic and solid colours are unaffected
- Polyester lamination makes no difference to
fading due to UV
- water based flexo inks are very resilient
to UV degradation with no discernable fading
- Solvent based flexo inks have poor UV resistant.
- UV cured letterpress inks are resilient to
UV, but not as good as water based flexo inks.
Black, blue and red are very resistant, but
yellow UV letterpress ink is prone to fading
in the long term. Varnish has no effect.
- Thermal transfer ribbons are very resistant
to UV degradation and have shown no degradation,
and barcodes still scan perfectly after 40 weeks
exposure.
Our conclusions therefore are for
label printers and self adhesive label users
to be wary when specifying printing methods for
self adhesive labels being used outside. Go for
water based flexo inks first, with thermal transfer
ribbons for variable information. Hotfoil and
darker UV letterpress inks are good, but lighter
UV inks can fade over longer time scales.
Note: This article is provided for information
purposes only and the accuracy of the information
is not guaranteed. This article is Copyright of
Mercian Labels Ltd who are a label
printer.
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