Heat sealing roller having a temperature self-controlled PTC heating resistor for welding thermoplastic foils

DETAILED DESCRIPTION It is an object of the invention to provide a welding device for welding superimposed foils with improved and simplified heating and temperature controls.
Another object of the present invention is to provide a welding device for welding superimposed foils with a sealing roller having a small amount of thermal inertia, so that the sealing roller has small dimensions, enabling welding equipment provided with such sealing rollers to find application as household appliances.
With the foregoing and other objects in view, there is provided in accordance with the invention a welding device, especially for sealing at least two superimposed foils of thermosplastic synthetic material, having at least one electrically heated temperature-controlled sealing roller and a counterpressure organ cooperating with the sealing roller.
Between the sealing roller and counterpressure organ is a heated zone in which the foils are tightly welded while pressure is being applied.
The sealing roller is equipped with a PTC (positive temperature coefficient) resistor which serves as the heating element and the temperature control.
The PTC resistor has a resistance characteristic which rises steeply in the range of the operating temperature of the sealing roller.
The PTC resistor serving as the heating element is the effective part of the sealing roller which acts directly on the foils to be welded together.
The PTC resistor has axially opposite end faces, each provided with electrically conductive means rotatable with the resistor and providing a contact surface.
The welding device includes means for supplying electric current for heating to the PTC resistor via the electrically conductive means.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a welding device, especially for sealing of at least two superimposed foils of thermoplastic synthetic material, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims