Heat-seal system

A heat-seal system (10) for sealing together two juxtaposed film plies (82a, 82b) via a continuous longitudinal seal, comprising: a. a heat-seal device (12), comprising 1) a heat source capable of producing heat, 2) a thermal conductor, which encapsulates at least a portion of said heat source and is capable of assuming a temperature that corresponds, at least in part, to the heat produced by said heat source, and 3) a thermal insulator, which substantially surrounds said thermal conductor but leaves a portion thereof exposed, said exposed portion of said thermal conductor providing a heat-seal contact surface, which is adapted to be brought into sliding contact with the juxtaposed film plies (82a, 82b) ; b. a conveyance mechanism (88a, 88b) for conveying the film plies against and in sliding contact with said heat-seal contact surface such that the film plies (82a, 82b) are sealed together at a continuous longitudinal seal, said conveyance mechanism being adapted to convey the film plies (82a, 82b) at varying speeds; c. a temperature-measuring device, at least a portion of which is encapsulated with said heat source; and d. a controller (16) in operative communication with said heat source and with said temperature-measuring device, said controller adapted to 1) receive input from said temperature-measuring device, and 2) send output to said heat source, which causes said heat source to produce more heat, less heat, or an unchanged amount of heat, whereby said controller determines the temperature of said thermal conductor, and is adapted to change said temperature based on changes in the speed at which the film plies (82a, 82b) are conveyed.