Selection of the best heatseal band for any given application involves several considerations. The band must be of the correct width and configuration to produce the desired seal or cut/seal. In addition, the band must be thick enough (have sufficient mass) to store the heat required for delivery to the material when being sealed. If needed, heat will be continually delivered to the material for the duration of the heating cycle. When impulse sealing it is desirable to terminate the heating cycle as soon as possible. And remember, the seal is not finally made until the seal area is cool enough to be dimensionally stabile. If the heatseal band is too thick or heat energy delivered is too great, the cooling time will be prolonged thus prolonging the total cycle and limiting production rate.
Ideal heatseal band selection is a function of many variables including material composition, material thickness, heat absorption of the jaw and the nature of the cover strip used over the heatseal band. In general, the thicker the material to be sealed, the thicker the heatseal band. Most materials, 1 mil to 6 mil can be sealed efficiently with heatseal bands in the thickness range of .1mm to .25mm. With very thick seals (multi-layers to totals of 15 mils or more) it may be well to use thicker bands or consider the possibility of applying heat from both sides.
Sealing through unequal thicknesses as in the case of closing a gussetted pouch can be accomplished even when the material is thick. Two layers of 6 mil material equals 12 mils, whereas four layers would be 24 mils. This is a very significant difference. Seals of this kind can be made with heat from one side providing that the sealing temperature range of the film is not exceeded and sufficient time is allowed for the heat to penetrate through the multi-layers to effect a bond. The two layer portion of the seal will not be damaged or burned through as long as the heatseal band temperature does not exceed the optimum sealing temperature of the material. Sealing time can be reduced by applying heat simultaneously from both sides. When heated from both sides, cooling will be slower, but cooling can be accelerated by the use of water-cooled jaws or air blown on the seal and/or the jaw.