The heat sealing quality of composite packaging bag
s has always been one of the most important factors for packaging bag manufacturers to control product quality. Today, professional flexible packaging manufacturers will analyze the factors affecting the heat sealing process of composite packaging bags: 1. The type, thickness and quality of heat sealing layer materials have a decisive impact on the heat sealing strength. Generally, the heat sealing materials commonly used in composite packaging are: CPE, CPP, EVA, hot melt adhesive and some other ionic resins are co-extruded or blended modified films. The thickness of the heat sealing layer material is generally 20 to 80μm between 100 and 200 under special circumstances.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 cooking bag is generally required to be 40-50 Newtons, so the thickness of the heat-sealing material should be 60-80 Newtons.μm or more. 2. The influence of heat-sealing temperature on the heat-sealing strength is the most direct. 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 required. If the heat-sealing temperature is lower than the softening point of the heat-sealing material, no matter how to increase the pressure or extend the heat-sealing time, it is impossible to seal the heat-sealing layer. However, if the heat sealing temperature is too high, it is very easy to damage the melt extrusion of the heat sealing material at the welding edge, resulting in“undercut”This phenomenon greatly reduces 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 necessary. For thin and light packaging bags, the heat-sealing pressure must reach at least 2kg/cm22, and it will follow the increase of the total thickness of the composite film. If the heat sealing pressure is lacking, it is difficult to achieve the actual fusion between the two films, the heat sealing of the joint part is not good, or it is difficult to remove the air bubbles trapped in the center of the weld, resulting in a virtual welding; of course, the heat sealing pressure is not too high. The bigger the better, it should not damage the welding edge, because at a higher heat sealing temperature, the heat sealing material of the welding edge is already in a semi-molten state, and too much pressure will easily squeeze out part of the heat sealing material, making the edge of the welding seam. The semi-blocking state is formed, the weld is brittle, and the heat sealing strength is reduced. 4. The heat sealing time is mainly determined by the speed of the bag making machine. The heat sealing time is also an important factor affecting the sealing strength and appearance of the weld. The same heat-sealing temperature and pressure, long heat-sealing time, the heat-sealing layer will be more fully fused, and the bonding will be stronger, but the heat-sealing time is too long, which will easily cause the welding seam to wrinkle and affect the appearance. 5. If the welding seam after heat sealing is not well cooled, 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 to use a lower temperature under a certain pressure. The welded seam after melting and heat sealing is shaped to eliminate the process of stress concentration. Therefore, if the pressure is not enough, the cooling water circulation is not smooth, the circulation volume is not enough, the water temperature is too high, or the cooling is not timely, the cooling will be poor, the heat sealing edge will be warped, and the heat sealing strength will be reduced. 6. The more times of heat sealing, the higher the strength of heat sealing. The number of longitudinal heat sealing depends on the ratio of the useful length of the longitudinal welding rod to 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 composite films of the same structure and thickness, the higher the composite interlayer peel strength, the greater the heat sealing strength. For products with low composite peel strength, the damage to the weld often causes the composite film at the weld to peel off between layers first, resulting in The inner heat-sealing layer independently receives the damage tensile force, while the surface layer material loses the reinforcing effect, and the heat-sealing strength of the weld is greatly reduced. If the composite peel strength is large, the interlayer peeling at the welding edge will not occur, and the measured actual heat sealing strength is much larger. After understanding, we believe that the reason for the high bag breakage rate 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 damaged. The CPP layer can't bear the pressure and breaks the bag.
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