Cool bit of info there, but I've stuck plenty of sheets of spartec, plaskolite, shefield, and others, and never have I ever cooked a sheet at 250F for an hour. How do you manage that without a purpose built oven?
At any rate this recently happened to me. We printed a set of faces on our hp 560, some in color, some just black/white. Within a week we also did a full coverage black background with white letters next door, out of black cast vinyl. 2 weeks later, the black on white prints are bubbling, everything else is fine. The faces were double layered clear. I stripped the faces and found that the bubbles were between the first layer of black on the poly and the first layer of laminate. Bubbles only appeared in the black region. My heart sank when I thought about the full coverage face next door. It was perfectly fine. Both the cast vinyl and the clear print were laid with rapid tac.
I couldn't say why this location had an issue, I've done the same dual layered prints all over the place, other than the fact it was minimal coverage black ink with a healthy white background. My theory is the ink is actually acting as a barrier, preventing any gasses from permeating outward, but when an unprinted region begins to outgas, it will find the area with the most give and collect, like black lettering being heated by the sun to a more pliable state than the white region surrounding it, giving it the appearance that the black ink is failing.
Long story short I plotted the black and replaced it free. Black cast > Printed black.
