Heat laminating a cover foil to a base foil

An apparatus for sealing a cover sheet to a base sheet, the apparatus comprising:

• means including a lower roller over which the base sheet is spanned for advancing the base sheet;
• means including an upper roller for pulling the cover sheet along a path and pressing it against the base sheet at the lower roller;
• a preheater housing along the path upstream of the rollers formed with a chamber open toward the path and the cover sheet extending along the path;
• a radiant heater in the chamber directed therefrom transversely at the path, whereby the heater heats the cover sheet passing along the path;
• sensor means along the path adjacent the chamber for detecting atmosphere in and around the chamber and for generating an output when the detected atmosphere indicates an unsafe hot condition of the cover sheet;
• a shutter shiftable between a retracted position offset from the chamber and an advanced position closing the chamber;
• and
• control means connected to the sensor means for shifting the shutter from the retracted position to the advanced position when the output is generated by the sensor means.