Are you upset that the composite bag you make tends to break down? Do you know the reasons why the complex bag you ordered is likely to rupture?Next, let Guangdong Lebei Packaging Co., Ltd. answer for you.
There are seven major reasons.
The one is thermal sealing temperature has the most direct influence on the thermal sealing strength.
The melting temperature of the various materials directly determines the minimum thermal sealing temperature of the composite bag. In the production process, due to the thermal sealing pressure, the bag making speed and the thickness of the composite substrate, the actual thermal sealing temperature is often higher than the melting temperature of the hot sealing material. The lower the thermal sealing pressure, the higher the thermal sealing temperature; the faster the speed, the thicker the material of the composite film, the higher the required thermal sealing temperature. If the thermal sealing temperature is lower than the softening point of the thermal sealing material, it is impossible to truly seal the thermal sealing layer no matter how to increase the pressure or extend the thermal sealing time. However, if the hot sealing temperature is too high, it is easy to damage the molten extrusion of the hot sealing material at the welding edge, resulting in the phenomenon of “root cutting”, which greatly reduces the hot sealing strength of the seal and the impact resistance of the bag.
The second, the type, thickness and quality of the thermal sealing layer material have a decisive influence on the thermal sealing strength.
The commonly used hot sealing materials for composite packaging are CPE, CPP, EVA, hot melt adhesive and some other ionic resin co-extrusion or mixed modified film. The thickness of thermal sealing layer material is generally between 20 and 80 μ m, and in special cases, up to 100~200 μ m. The same thermal sealing material, its thermal sealing strength increases with the increase of the thermal sealing thickness. The hot sealing strength of the cooking bag is generally required to reach 40~50 Newton, so the thickness of the hot sealing material should be more than 60~80 μ m.
Third, to achieve the ideal thermal seal strength, a certain pressure is essential.
For the light and light packaging bags, the thermal sealing pressure should reach at least 2kg / cm2, and increase accordingly with the increase of the total thickness of the composite film. If the heat sealing pressure is insufficient, it is difficult to achieve the real fusion between the two films, causing the local heat sealing is not good, or it is difficult to catch the bubbles sandwiched in the middle of the weld, causing virtual welding; of course, the greater the heat sealing pressure is not the better, the heat should be appropriate not to damage the welding edge, because the heat sealing material on the welding edge is in a semi-molten state, too much pressure is easy to squeeze away part of the heat sealing material, so that the weld edge form a semi-cut state, the weld seam is brittle, and the heat sealing strength is reduced.
Fourth, if the weld after hot sealing is not cooled well, it will not only affect the appearance and flatness of the weld, but also have a certain impact on the heat sealing strength.
The cooling process is to eliminate the stress concentration process by shaping the just molten hot sealing weld seam at a lower temperature under a certain pressure. Therefore, the pressure is not enough, the cooling water circulation is not smooth, the circulation amount is not enough, the water temperature is too high, or the cooling is not timely will lead to poor cooling, the heat sealing edge is warping, and the heat sealing strength is reduced.
Fifth, the hot sealing time is mainly determined by the speed of the bag-making machine.
Thermal sealing time is also a key factor affecting the strength and appearance of weld sealing. The same hot sealing temperature and pressure, the hot sealing time is long, the hot sealing layer fusion is more fully, the combination is more firm, but the hot sealing time is too long, easy to cause the weld wrinkle, affect the appearance.
Sixth, the more heat sealing times, the higher the heat sealing strength.
The number of longitudinal thermal sealing depends on the ratio of the effective length and the bag length, and the longitudinal thermal sealing length is determined by the number of sets of the transverse thermal sealing unit. Good hot sealing, requiring the number of hot sealing times at least twice. There are two groups of hot knife in general bag making machine, and the higher the overlap of the hot knife, the better the hot sealing effect.
Finally, the composite film with the same structure and thickness, the higher the stripping strength of the composite layer, the greater the thermal sealing strength.
For products with low composite stripping strength, the failure of the weld is often the first stripping of the composite film at the weld seam, resulting in the inner thermal sealing layer independently bearing the destructive tensile force, and the surface layer material loses the reinforcing effect, so the thermal sealing strength of the weld is greatly reduced. If the composite stripping strength is large, the inter layer stripping will not occur, and the actual thermal sealing strength measured is much greater.
