What is the reason for the high bag breaking rate of composite packaging bags?
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 are the influencing factors of the heat sealing process: 1. The type, thickness and quality of the heat sealing material have a decisive influence on the heat sealing strength.
Common heat sealing materials for composite packaging include CPE, CPP, EVA, Hot Melt Adhesive and other ionic resin Coextruded or blended modified films.
The thickness of the heat seal material is generally 20 ~ Between 80μm, it also reaches 100 ~ 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 pouch is generally required to reach 40 ~ 50 Newton, therefore, its heat sealing material thickness should be 60 ~ More than 80μm.
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 thickness of composite substrate, the actual heat sealing temperature is often higher than the melting temperature of heat sealing material.
The lower the heat sealing pressure, the higher the heat sealing temperature is required;
The faster the machine speed, the thicker the surface material of the composite film, and the higher the required heat sealing temperature.
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 to melt and extrude, resulting in a 'root cutting' phenomenon, which 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 essential.
For thin and light packaging bags, the Heat sealing pressure should reach at least 2 kg/cm22, and it will increase correspondingly with the increase of the total thickness of the composite film.
If the Heat sealing pressure is insufficient, it is difficult to achieve real fusion between the two layers of film, the local heat sealing is not good, or it is difficult to catch the bubbles sandwiched in the middle of the weld, resulting in virtual welding;
Of course, the Heat sealing pressure is not as high as possible, and it is advisable not to damage the welding edge, because at a higher heat sealing temperature, the Heat sealing material at the welding edge is already in a semi-molten state, too much pressure is easy to squeeze out part of the heat sealing material, so that the weld edge forms a semi-cut state, 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.
Heat sealing time is also a key factor affecting the sealing strength and appearance of welds.
With the same heat sealing temperature and pressure and long heat sealing time, the Heat sealing layer will fuse more fully and combine more firmly, but the Heat sealing time is too long, which will easily cause weld wrinkling and affect the appearance.
5. If the weld seam after heat sealing is not cooled well, it will not only affect the appearance flatness of the weld seam, but also have certain influence on the heat sealing strength.
The cooling process is a process of eliminating stress concentration by shaping the weld 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, warped hot sealing edges, and reduced heat sealing strength. 6. The more heat sealing times, the higher the heat sealing strength.
The number of longitudinal heat sealing depends on the ratio of the effective length of the longitudinal welding rod to the bag length;
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.
There are 2 groups of ironing knives for General bag making machines, and the higher the degree of overlap of ironing knife positions, the better the Heat sealing effect.
7. For composite films with the same structure and thickness, the higher the peel strength between composite layers, the greater the Heat sealing strength.
For products with low composite peel strength, the weld damage is often caused by the interlayer peeling of the composite film at the weld, resulting in the inner heat seal layer independently bearing the destructive tension, while the surface material loses the reinforcement effect, the heat sealing strength of the weld is thus greatly reduced.
If the composite peeling strength is large, interlayer peeling at the weld edge will not occur, and the measured actual heat sealing strength is much larger.
Through understanding, we believe that the reason for the high rate of bag breaking in this package bag is that the two groups of heat sealing hot knife parts do not completely overlap, virtual welding occurs near the hot sealing edge, the CP film becomes thinner, and some structures are damaged, when cooking, the thin CPP layer cannot withstand pressure and produce broken bags.