As is well known, the heat sealing of plastic films relies on the control and adjustment of three quantities:
- time
- pressure
- temperature
Of these three, temperature has been the most critical factor in achieving efficient and effective control and regulation. Historically, the sealing of plastic films first relied on hot bar systems: simple metal masses heated by cartridge resistors.
While the hot bar was a starting point, it quickly became a limitation greater effciency. What was its primary flaw? The temperature not completely under control, the thermal drift, the inability to cool the fillm with closed bars. The result: a lot of waste and potentially unstable processes.
Time-based systems: from the inertia of the hot bar to the first rudimentary “heat pulse”
To address this obstacle, early 50s of the last century, systems using the heating element (resistive heater), consisting of a thin metal strip with reduced thermal mass, were introduced. These systems, controlled by a simple timer and a rheostat
to control the power, partially eliminate the problems of the hot bar: the cooling of the film with closed bars allows it to stabilize the plastic film, avoiding elongation, defects in tightness and optical quality.
However, the control is still approximate and is based on an estimate of the temperature/time combination and not on the actual temperature, always leaving inaccuracies at the mercy of inaccuracies and making commissioning time-consuming and expensive. The use of temperature sensors, PID and artifcial intelligence to reduce weaknesses are a palliative, but they do not solve the underlying problem: process control and regulation are not dynamic and precise enough in the presence of high speeds, critical films and are difficult to set up.
These systems are commonly referred to as “impulse sealing” or “pulse sealing”,referring to the fact that they can be switched on and off in much faster intervals than the hot bar.
To be completely right, the most correct definition is time-based sealing systems
