The rate of broken composite packaging bags remains high, and the seven "culprits" have finally been found!

1. 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 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 is, the higher the heat sealing temperature is required; The faster the machine speed is, the thicker the surface material of the composite film is, and the higher the required heat sealing temperature is. 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 make the heat sealing layer truly sealed. However, if the heat sealing temperature is too high, it is easy to damage the heat sealing material at the welding edge by melting and extruding, resulting in "undercutting", which greatly reduces the heat sealing strength of the seal and the impact resistance of the bag.
2. The type, thickness and quality of the heat sealing material have a decisive influence on the heat sealing strength.
The commonly used heat sealing materials for composite packaging include CPE, CPP, EVA, hot melt adhesive and other ionic resin coextrusion or blending modified films. The thickness of heat seal material is generally 20~80 μ M, or 100-200 in special cases μ M. 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 reach 40~50 N, so the thickness of the heat sealing material should be 60~80 N μ M above.
3. To achieve the ideal heat sealing strength, a certain pressure is necessary.
For light and thin packaging bags, the heat sealing pressure should reach at least 2kg/cm2, and 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, the local heat sealing is not good, or it is difficult to drive out the bubbles sandwiched in the middle of the weld, causing false welding; Of course, the higher the heat sealing pressure is, the better it is. It is better not to damage the welding edge, because at a higher heat sealing temperature, the heat sealing material of the welding edge has been in a semi molten state. Too much pressure is easy to squeeze out some heat sealing materials, so that the weld edge forms a semi cut state, the weld is brittle, and the heat sealing strength decreases.
4. If the weld after heat sealing is not cooled well, not only the appearance flatness of the weld will be affected, but also the heat sealing strength will be affected.
The cooling process is a process to eliminate stress concentration by shaping the weld just after melting and heat sealing at a lower temperature under a certain pressure. Therefore, insufficient pressure, poor circulation of cooling water, insufficient circulating volume, too high water temperature, or untimely cooling will lead to poor cooling, warping of hot seal edges, and reduction of heat seal strength.
5. The heat sealing time is mainly determined by the speed of the bag making machine.
The heat sealing time is also a key factor affecting the sealing strength and appearance of the weld. With the same heat sealing temperature and pressure, if the heat sealing time is long, the heat sealing layer will be more fully fused and firmly combined. However, if the heat sealing time is too long, it is easy to cause wrinkling of the weld and affect the appearance.
6. The more times of heat sealing, the higher the heat sealing strength.
The number of longitudinal heat seals depends on the ratio of the effective length of the longitudinal welding rod to the bag length; The number of transverse heat sealing times is determined by the number of sets of transverse heat sealing devices of the machine. Good heat sealing requires at least two times of heat sealing. There are two groups of ironing knives for ordinary bag making machines, and the higher the overlapping degree of ironing knife positions, the better the heat sealing effect.
7. With the same structure and thickness of the composite film, the higher the peeling strength between the composite layers, the greater the heat sealing strength.
For products with low composite peel strength, the weld failure is often caused by the interlayer peeling of the composite film at the weld joint, which causes the internal heat seal layer to bear the failure tension independently, while the surface material loses the reinforcement effect, thus the heat seal strength of the weld joint is greatly reduced. If the composite peeling strength is large, the interlayer peeling at the weld edge will not occur, and the measured actual heat sealing strength will be much larger.