Heat sealing is usually the last step in the manufacturing of stand up bags. Pouch bags are sealed after they have been filled. Most manufacturers use either of the two popular types of sealers - (1) impulse heat sealer, and (2) direct heat sealers.
Impulse heat sealers are mainly used on thermoplastics (polypropylene, polyethylene) whose seal temperatures are not very high. These sealers function by first warming a part of the pouch and then suddenly subjecting it to an intense ray of heat. This is followed by immediate cooling. Nylon, Mylar, bubble packs, and a range of other materials are sealed using impulse heat sealers.
In direct heat sealing, a constant temperature is maintained in two jaws that act as sealers. This kind of sealing functions as long as the machine is on. These sealers can be used to seal thicker packages and materials. They are primarily used to package pouches made from poly cello films, coated Kraft papers, cellophane, coated PP, and other materials.
In addition to these two, there are hand sealers and a range of other sealing methods.