Why does colour fade on packaging (light cardboard boxes) if not exposed to sunlight or any direct light/heat?

We designed the packaging for premium skincare boxes using light Pantone colours (two are pastels, one is just light soild) + soft touch matte coating.
After just two months of sitting on the shelves in retail the colours faded on the boxes. The client said they were never exposed to direct sunlight or under any lamps or similar – and I believe them because we have those same boxes in our office – so they went straight from the printers to the shelf in our office never exposed to anything but air, and the same thing happened.

The printers said that this just happens with these very light colours and there’s nothing to do about it but change colours.
Now they are arranging with our client that the boxes should be printed again but with darker colours, and they want me to choose new colours so this wouldnt happen..
Would that even solve the problem?

Why did this happen in the first place?
Is there a chance we would have the same problem with darker colours (how much darker would they have to be?)?
Is this about the type of coating or the type of cardboard (High Point 295g)? Would protective transparent foil over the products solve the problem?

Later today the printers also mentioned they will try to dry the colours a few more days before coating (they dried them all for a day before the matte soft touch coating)

Thank you

EDIT: I am attaching an illustration of what happened on one box :enter image description here

Answer

Gosh… I doubt this will be an objective answer, only assumptions. But I will post it for two reasons. You have a very specific issue that needs to be (solved) explored asap, and the question is very nice elaborated.

It is pretty obvious now that the problem is not the overall absorption of the ink to the paper or acidity of it, because they would affect all the printed area.

It looks that there are some environmental factors. Probably this is reduced to a few of them.

  • Light, as you pointed.

  • Some oxidation.

  • Reaction to the ambient (a contaminant?) But we can skip this one because your test sites were different.

  • I am not sure about the oxidation, because overall the other parts are not sealed and shielded from the air… which almost gives only one option. Light.


Assuming this, we could try to figure out what options we have.

  • Quality of the ink.

  • Quality of the coating.

  • Quality in the process, or the decision making.


I will skip 1 and 2, because not only I have no idea, and I can not make quality tests, neither you.

So, this leaves me… What kind of process could be made to make a pastel color in commercial printing? (Warning, more assumptions here)

  • One option is to use a dark ink and dilute it on a transparent base. This is the option that could produce too few pigments “floating on the air”.

  • A second option is to use white ink to dilute the pigmentation but can be applied on a thicker layer, which could help.

  • But probably the best option is to use a pastel ink from start, not a dark one. Let me explain.

If we start with a pure red, made of X chemical, and we add a lot of white, we can have a light pink.

But if we use Y chemical on which the intrinsic color of it is already pink, we need to dilute a lot less with white, so more Y pink particles are there.


And the other option is that the coating was not enough to protect the ink, I don’t know if it was absorbed by the paper, therefore not protecting it from normal light.


I would probably make some quality control tests, putting some pieces to direct sunlight in various conditions:

  • Some covered with transparent acrylic (to isolate them from air, but not the sun.

  • Some with some space between a cover and the pice, to let air pass but block the direct sun.

  • Some stay there for 1 day, some for 2, some for 4 days.

  • You could probably try some UV lamps to make indoors tests.

  • Some without the “coating”.

  • Etc.

Attribution
Source : Link , Question Author : Mjav , Answer Author : Rafael

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