Most Thermoforming films shrink somewhat during the thermoforming process. Concern is placed particularly on those films which shrink in an erratic manner.

films shrink more than PVC in the trans-machine direction (TD). This shrinking both narrows the web and curls the film. Properly processed film may shrink 3-5% for copolymer and 1-3% for homopolymer PCTFE films.

Note: With all films, tension in the machine direction will result in loss of web width. Lessening the heat or increasing lines speeds will reduce the TD shrinkage in most films.

• Film curl occurs when two or more films have different shrinkage rates. This most commonly occurs with films that are laminated to PVC with a PE tie layer.

• Typical solutions to this difficulty are identical to reducing film shrinkage. Curl can also be reduced by duplex laminations and conversion to homopolymer materials.

• May occur between the heating platens and/or to the forming mold.
• Most common with PVdC/PVC materials (PVdC-coating relatively tacky).
• Cleanliness & condition of heating platen surfaces is important.
• Gap between platens should be uniform over entire area.
• Platens should be replaced or reconditioned periodically with a non-stick (e.g., Teflon) surface.
• Additional mold-cooling recommended for PVdC/PVC, but not for laminations.
• Sticking may cause MD (machine direction)-stretching and web shrinkage.

• Normally indicates insufficient heat to film.
• Is sometimes accompanied by milky-white areas within cavities.
• Is also seen with loss of forming air pressure (audible venting).
• Cavity formation may usually be improved by using more heat (higher temperatures and/or slower cycle speeds).
• Striations may be caused by excessive heat used on laminations.
• The actual temperature of the heating plates needs to be calibrated against the read-out on the controller.

Another cause of incomplete forming can be temporary or actual lack of air pressure to the line. In some cases it may be necessary to install a regulated air pressure booster at the line to provide continuous air pressure. (Especially if the unit is in a plant environment where there is heavy usage of air pressure and or long lines from the main compressor to the blister line, causing a drop in pressure).

• Sealing temperature indicates heat applied to coating on aluminum foil-based lidstock.
• Sealing temperature normally identical for PVC, PVdC/PVC and /(PE)/PVC (PVC is generally product & lidstock contact layer).
• Sealing to correct side?
• Minimum heat-seal activation temperature.
• Sealing pressure.
• Cleanliness, condition, and pattern of sealing platens is important.
• Alignment and flatness of platens is important.

• Most common with laminations (card curls toward PCTFE side).
• Same phenomenon as film curl.
• Same cause as TD web shrinkage: higher TD shrinkage rate of raw film compared to PVC and PE films.
• Curl normally may be decreased by using less heat at heating-platen station (lower temperatures and/or faster cycle speeds).
• Curl may also be decreased by utilizing duplex PVC/ construction.