The heat sealing quality of composite packaging bags has always been one of the most important items for packaging manufacturers to control product quality. The following factors affect the heat sealing process, I hope to help you! The heat-sealing quality of food packaging bags and composite packaging bags has always been one of the most important items for packaging manufacturers to control product quality. The following are the influencing factors of the heat sealing process: 1. The type, thickness and quality of the heat sealing layer material have a decisive influence on the heat sealing strength. Commonly used heat sealing materials for composite food packaging include CPE, CPP, EVA, hot melt adhesive and other ionic resin co-extruded or blended modified films. The thickness of the heat sealing layer material is generally between 20 and 80 μm, and in special cases, it is also 100 to 200 μm. For the same heat-sealing material, its heat-sealing strength increases with the increase of heat-sealing thickness. The heat sealing strength of the retort bag is generally requi to be 40-50 Newtons. Therefore, the thickness of the heat-sealing material should be above 60-80 μm. 2. The heat sealing temperature has the most direct influence on the heat sealing strength. The melting temperature of various materials directly determines the minimum heat sealing temperature of the composite bag. In the production process, due to the influence of heat sealing pressure, bag making speed and the thickness of the composite substrate, the actual heat sealing temperature is often higher than the melting temperature of the heat sealing material. The smaller the heat sealing pressure, the higher the heat sealing temperature; the faster the machine speed, the thicker the surface layer material of the composite film, and the higher the heat sealing temperature requi. If the heat-sealing temperature is lower than the softening point of the heat-sealing material, no matter how to increase the pressure or prolong the heat-sealing time, it is impossible to make the heat-sealing layer truly seal. However, if the heat sealing temperature is too high, it is very easy to damage the heat sealing material at the welding edge and melt extrusion, resulting in the phenomenon of “root cutting”, which greatly uces the heat sealing strength of the seal and the impact resistance of the bag. 3. To achieve the ideal heat sealing strength, a certain pressure is essential. For thin and light packaging bags, the heat sealing pressure should be at least 2kg/cm22, and it will increase with the increase of the total thickness of the composite film. If the heat sealing pressure is insufficient, it is difficult to achieve true fusion between the two films, resulting in poor local heat sealing, or it is difficult to remove the air bubbles sandwiched in the middle of the weld, resulting in virtual welding; of course, the heat sealing pressure is not as high as possible Well, it is advisable not to damage the welding edge, because at a higher heat sealing temperature, the heat sealing material of the welding edge is in a semi-molten state, and too much pressure will easily squeeze out part of the heat sealing material, causing the weld edge to form. In the half-cut state, the weld seam becomes brittle and the heat sealing strength decreases. 4. The heat sealing time is mainly determined by the speed of the bag making machine. Heat sealing time is also a key factor affecting the strength and appearance of the weld seal. At the same heat sealing temperature and pressure, if the heat sealing time is long, the heat sealing layer will be more fully fused and combined more firmly, but if the heat sealing time is too long, it is easy to cause wrinkling of the weld and affect the appearance. 5. If the welding seam after heat sealing is not cooled well, it will not only affect the appearance flatness of the welding seam, but also have a certain influence on the heat sealing strength. The cooling process is a process of eliminating stress concentration by shaping the welded seam just after melting and heat sealing at a lower temperature under a certain pressure. Therefore, insufficient pressure, poor circulation of cooling water, insufficient circulation, too high water temperature, or untimely cooling will result in poor cooling, warping of heat sealing edges, and uction in heat sealing strength. 6. The more times of heat sealing, the higher the heat sealing strength. The number of longitudinal heat sealing depends on the ratio between the effective length of the longitudinal welding rod and the length of the bag; the number of transverse heat sealing is determined by the number of sets of transverse heat sealing devices on the machine. Good heat sealing requires at least two times of heat sealing. The general bag making machine has two sets of hot knives, and the higher the overlapping degree of the hot knives, the better the heat sealing effect. 7. For the composite film of the same structure and thickness, the higher the peel strength between the composite layers, the greater the heat sealing strength. For products with low composite peel strength, the weld damage is often the first interlayer peeling of the composite film at the weld, resulting in the inner heat-sealing layer independently bearing the tensile force, while the surface layer material loses its reinforcing effect, and the heat-sealing of the weld The strength is thus greatly uced. If the composite peel strength is large, the interlayer peeling at the welding edge will not occur, and the measu actual heat seal strength is much larger. Through understanding, we believe that the reason for the high breakage rate of composite food bags is that the parts of the two sets of heat sealing and scalding knives are not completely overlapped, and virtual welding occurs near the heat sealing edge, the CPP film becomes thinner, and part of the structure is destroyed. The CPP layer cannot withstand the pressure and produces a broken bag.
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