to Watson Signs
If you applied vinyl to polycarbonate (Lexan), you are asking for trouble. Especially if you used a liquid to apply it.
Polycarbonate is hygroscopic, i.e. it absorbs moisture. If you apply vinyl over poly that has been exposed to air for while, it will absorb moisture. When the sun hits it, it will turn to vapor and separate the vinyl from the surface. Avery and 3M and others have commented on this on their web sites. Problems generally start in the summer, when it is hot.
Most translucent sign paints allow the moisture to escape and don't have this problem.
Acrylic doesn't do this - it is not hygroscopic. If vinyl is applied to a poly pan face that has just been baked in a vacuum mold, the moisture is baked out and the vinyl will generally be fine. However, after being out a day or so, it re-absorbs moisture and then trouble begins.
Your experience probably was not due to a problem in the vinyl.