Printing inks
You shall choose printing inks, which obtain in combination with the substrate a sufficient highly surface tension. This is a pre-condition for good wetting by the blister varnish and therefore a pre-condition for good adhesion between the printing ink and blister varnish, i.e. a pre-condition for a good blister result.
The usage of “overnight” i.e. “fresh” inks can also lead to adhesion problems. It is recommended to use solvent resistant printing inks, because they are more resistant to heat than non-resistant printing inks.
Please inform your ink supplier and point out that the printing inks should be suitable for blister application.