Introduction

Mercian Labels has been conducting long term experiments on the UV degredation of printed labels since 2006 to ensure that we, and the industry in general, gives accurate information on the UV degredation of various types of printing inks used in the label printing industry.

We are frequently approached by clients with queries about the potential effects of sunlight on print labels. 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.

We have 2 experiments running currently:

• Experiment 1, commenced in early 2006, is testing the effects of UV (ultraviolet) daylight from the sun on self adhesive labels printed by hotfoil, UV letterpress, water and solvent based flexography and thermal transfer methods, including laminated and non laminated labels.  You can read the experimental method, see the detailed imagery results, and our conclusions here.
• Experiment 2, commenced in early 2008, is testing the effects of UV (ultraviolet) daylight from the sun on self adhesive labels printed by a variety of digital printing methods including technology by Xeikon, HP (Indigo) QuickLabel VIVO!, Konica Minolta, Degrava, Nilpeter Caslon, Xaar inkjet (unknown ink), including laminated and non laminated labels.  You can read the experimental method, see the detailed imagery results, and our conclusions here.

If you want to comment on this experiment please do so on our Blog entry here.

(All results and images © Mercian Labels 2008 )

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Experiment 1 (Conventional inks) - started 15/2/2006

Introduction

The purpose of this experiment was 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 commenced in early 2006 and it is planned to record the results throughout the year. The experiment is 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.

Method

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 abbreviations used are as follows:

HF - hotfoil printed
FW - flexo printed with a water based pigment ink
FS - flexo printed with a solvent based dye ink
LPUV - letterpress printed with a UV curable ink
TT - thermal transfer printed with a wax resin ribbon
LAMI - laminated with a 23 micron clear polyester overlamination
VARN - varnished with a UV cured clear gloss varnish

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.

Note: Sheet 5 "FRAGILE" label is mislabelled as FS instead of FW and is water based..

Results

Week 2 - (14 days exposure)(15/2/06)

sheet 1 - sheet 2 - sheet 3 - sheet 4 -
sheet 5 - sheet 6 - sheet 7

 

week 4 - (28 days exposure)

sheet 1 - sheet 2 - sheet 3 - sheet 4 -
sheet 5 - sheet 6 - sheet 7

 

week 6 - (42 days exposure)

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6 - sheet 7

week 10 - (70 days exposure) (26/5/06)

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6 - sheet 7

week 16 - (112 days exposure) (7/6/06) 

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6 - sheet 7

 

week 22- (155 days exposure) (20/7/06)

sheet 1 - sheet 2 - sheet 3 - sheet 4 -
sheet 5 - sheet 6 - sheet 7

 

week 40- (280 days exposure) (15/11/06)

sheet 1 - sheet 2 - sheet 3 - sheet 4 -
sheet 5 - sheet 6 - sheet 7

week 132 - (2.5 years exposure)  (27/08/08)

sheet 1 - sheet 2 - sheet 3 - sheet 4 -
sheet 5 - sheet 6 - sheet 7 

Conclusion

 

Week 2 - (14 days exposure)

There is no visible change to any of the labels apart from a darkening of the blue/lightening of the orange label on sheet 5, a dye based solvent ink. Surprisingly the label exposed to light has got darker than the original unexposed version. Lamination of the label made not notable difference to this effect.

Week 4- (28 days exposure)

There is no visible change to any of the labels apart from a significant darkening of the blue/lightening of the orange label on sheet 5, a dye based solvent ink. Lamination of the label made no notable difference to this effect. All other inks are unaffected to date.

Week 6- (42 days exposure)

The dye based inks have changed colour to be completely different from the original after 6 weeks, whereas all other inks have no change.

Week 10- (70 days exposure)

The dye based inks have completely faded to a point of being almost white and unreadable. All other inks have no notable changes.

Week 16- (112 days exposure)

The dye based inks are now white and almost unreadable. Hotfoil and water based flexo inks show no change. The majority of UV letterpress inks show no change whatsoever, but 2 samples show some changes. It appears that dark UV letterpress inks are very resistant to UV, but a lighter 4 colour process image has started to change colour from pale pink to pale blue. The cause of this is not clear, but maybe a result of different degradation rates of the 4 process colours.

Week 22- (155 days exposure)

The dye based inks are now white and unreadable. Hotfoil and water based flexo inks show no change. The majority of UV letterpress inks show no change whatsoever, but 2 samples show some changes, especially those lighter inks with red and yellow pigments.

Week 40- (280 days exposure)

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 still scan perfectly after 40 weeks exposure.

 

Week 132- (2.5 Years exposure)

Very 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 the least discernable fading of all the inks
• 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 after 2.5 years exposure.

 

Discussion 

This is our opinion (to date) on the comparative effects of UV light on different printing inks 

resistance to UV light	low	medium	high
hotfoil foils (except metallics)			X
flexo-water based inks			X
flexo-solvent based inks	X
UV Letterpress inks		X(yellow)	X(other colours)
Thermal transfer ribbons			X
the effect of varnish	X
the effect of lamination	X

 

After 2.5 years solvent based flexo inks are very significantly affected and it can be concluded that they are unsuitable for prolonged exposure to UV. Lighter 4 colour process UV letterpress images can be affected, but to a much smaller degree. All other ink forms appear to be mostly unaffected.

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Experiment 2 (Digital inks) - started 15/2/2008

Introduction

The purpose of this experiment was to examine the effects of sunlight on digitally printed labels made using the following printing techniques:

• 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 from Degrava
• Injet images from Nilpeter using their Caslon technology with Xaar inkjet heads 
• Injet images from Xaar using their own inkjet heads (unknown ink)

The experiment commenced in early 2008. The experiment is 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.

Method

A selection of printed self adhesive labels collected as samples from trade shows and commercial samples over the previous 12 months (stored in UV light fast storage cabinets) was collated on 13 February 2008. These labels were stuck onto 6 A4 sheets of paper, along with an abbreviation of the labels origin.

1. Sheet 1 has only Xeikon labels
2. Sheet 2 has only Xeikon labels
3. Sheet 3 has only HP labels
4. Sheet 4 has only HP labels
5. Sheet 5 has VIVO, Konica Minolta and Degrava labels
6. Sheet 6 has Nilpeter Caslon and Xaar labels

The sheets were then cut in half, with half the label on each part of the sheet. The right half of each sheet were labeled as "EXPOSED TO UV" and permanently displayed in a window fully exposed to sunlight. The left half of each sheet was 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. 

 

Results

 

Week 2 - 28/2/08

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6

Week 4 - 11/3/08

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6

Week 6 - 27/3/08

sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6

Week 28 - 27/8/08

 sheet 1 - sheet 2 - sheet 3 - sheet 4 - sheet 5 - sheet 6

 

Conclusions

 

Week 2 

There is no visible change to any of the labels.

Week 4 

There is no visible change to any of the labels.

Week 6

There is no visible change to any of the labels.

Week 28

There is no visible change to any of the labels apart from a slight fading of the skin tones on bottom label on xeikon image 1.

 

Discussion 

After 6 months all the labels are showing excellent resistance to UV degredation, which compares favourably to the resuts from conventional UV, sovlent and water based inks.

 

resistance to UV light	low	medium	high
Xeikon			X
HP			X
VIVO!			X
Konica Minolta			X
Degrava			X
Nilpeter Caslon			X
Xaar			X