Why does the surface of blister packaging wrinkle?

Several possible causes and solutions for wrinkles on the surface of blister packaging:
       The main reason may be that during production, the sheet is heated for too long, causing the sheet to sag, and the temperature adjusted by the heater is too high. When we find that such a problem occurs, we need to shorten the heating time or lower the heater temperature. ;
       It is also possible that it is too late to vacuum, and we need to vacuum at the right time;
       There may be too much pre-blow volume and the pre-blow volume needs to be reduced;
       It is also possible that the sheet comes into contact with the mold during heating, so we need to improve or adjust the machine to keep a considerable distance between the mold and the sheet;
       The last possibility is that there is no upper support equipment. If the machine structure allows, we can install additional support equipment.