of UV-curable ink coating (case 03)
What is my curing depth profile?
A manufacturer of UV-curable inks wanted to know the depth profile of curing in the coating.
Insufficient curing at the interface with the substrate was considered a potential cause for occasional adhesion problems with some substrates.
Tests with the UV-curable ink
A test coating with two layers was provided. The first layer was fully cured under standard UV curing conditions, then a second layer was coated on top and deliberately cured incompletely.
Then, a cross-section was prepared for investigation in a Transmission Electron Microscope (TEM). Before starting the TEM acquisition, the sectioned sample was exposed to OsO4 as staining agent. The Os binds specifically to the unreacted acrylates, and therefore provides a means of assessing the curing degree.
Different cause of adhesion problem
The Os-profile across the sample clearly showed the difference in curing degree between the two layers. This proves the viability of the staining method.
Within the first layer that was cured under standard curing conditions, no significant depth profile or decrease in curing degree towards the substrate could be found. Therefore, insufficient curing could be ruled out as possible cause for occasional adhesion problems.
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