THERMAL IMPULSE SEALING
Thermal impulse sealing is an advanced sealing method that was used in aseptic pouch sealing. This sealing technology has been proven to be the best method in the contrast of reliability, seal quality and energy efficiency
In impulse sealing Technic
Two film layers (1) are placed between two jaws, a seal bar (2) and a counter jaw (3), which press them together. The heating element (4) is provided with a thermal and electrical insulation on the support’s side and a non-stick coating (5) on the film’s side. The counter jaw is also thermally and electrically insulated. An impulse of electrical current is passed through the heating element causing it and the film layers beneath it to heat. The heat causes the film layers to plastify, fusing them firmly together (= sealing).
The most important influencing variables for this process are:
- pressure,
- temperature and
- time
The sealing process is generally followed by a cooling time during which the plastified material is allowed to cure to its full strength.The pressure applied to the sealing jaws also forces the material out of the seal area. The softer the transition the stronger the seal.
This displacement effect, which in the strict sense is an unfavorable effect, is turned to account in the cutting seal method. The heating element is given a profile which forces the film material out of the seal area until the material is completely separated.This enables the process of cutting and sealing simultaneously during the closing of the jaw. In short, the impulse sealing method offers the widest range of possibilities which can be varied to achieve the desired results. However, this may not be necessary for all applications, or not possible due to high machine speeds.In most cases the heating elements have a straight-lined design. But also even contours may be possible (form sealing bands). The resistance along the contour is constant to achieve the necessary heating.Adherence to the sealing parameters is decisive for the final result. While this is relatively easy as regards pressure and time, keeping the necessary temperature of the heating element poses a problem. When using low-cost installations or working at low speeds a time control is still used today. A defined flow of current is passed through the heating element for a set time. However, the actual temperature is not measured. Even so, this method provides satisfactory results.Today, nearly all modern machines are equipped with an electronic temperature control. This control uses the heat conductor’s characteristic of changing its electrical resistance in accordance with the temperature. This configuration eliminates the need for an additional sensor.
Advantages of thermal Impulse sealing involves,
- Longer band life
- Optimum energy utilization
- Strong and high quality seals
The application of impulse sealing technic had opened a wide scope in the packaging industry.
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