The heat sealing quality of composite packaging bag is always one of the most important items for packaging manufacturers to control product quality. The following are the influencing factors of heat sealing process:
1. The type, thickness and quality of heat sealing material have a decisive influence on the heat sealing strength. Common heat sealing materials used in composite packaging are CPE, CPP, EVA, hot melt adhesive and some other ionic resin coextrusion or blending modified films. The thickness of the heat seal material is generally between 20 μ m and 80 μ m, and in some special cases, it is up to 100-200 μ M. The heat sealing strength of the same heat sealing material increases with the increase of heat sealing thickness. The heat sealing strength of cooking bag is generally required to be 40-50 n, so the thickness of heat sealing material should be more than 60-80 μ M.
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 composite substrate, the actual heat sealing temperature is often higher than the melting temperature of 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, 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 seal the heat seal layer. However, if the heat sealing temperature is too high, it is easy to damage the heat sealing material at the welding edge, resulting in "undercutting" 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 light and thin packaging bags, the heat sealing pressure should be at least 2kg / cm22, 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 the true fusion between the two films, and the local heat sealing is not good, or it is difficult to catch up the bubbles sandwiched in the welding seam, resulting in false welding; of course, the heat sealing pressure is not the better, so it is better not to damage the welding edge, because at a higher heat sealing temperature, the heat sealing material at the welding edge is in the semi melting state, and too much pressure is easy to squeeze out the part The heat sealing material can make the weld edge form semi cutting state, make the weld brittle and reduce the heat sealing strength.
4. The heat sealing time is mainly determined by the speed of bag making machine. Heat sealing time is also a key factor affecting the sealing strength and appearance of weld. With the same heat sealing temperature and pressure and long heat sealing time, the fusion of the heat sealing layer is more sufficient and the bonding is more firm. However, if the heat sealing time is too long, it is easy to cause weld wrinkling and affect the appearance.
5. If the weld after heat sealing is not cooled well, it will not only affect the appearance flatness of the weld, but also have a certain impact on the heat sealing strength. The cooling process is to set the shape of the weld just after melting and heat sealing with a lower temperature under a certain pressure to eliminate the stress concentration. Therefore, insufficient pressure, poor circulation of cooling water, insufficient circulating quantity, too high water temperature or untimely cooling will lead to poor cooling, warping of hot sealing edge and reduction of 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 of the effective length of the longitudinal welding rod to the length of the bag, and the number of transverse heat sealing devices is determined by the number of transverse heat sealing devices. Good heat sealing requires at least two times of heat sealing. There are two groups of ironing knife in general bag making machine, and the higher the overlapping degree of ironing knife position is, the better the heat sealing effect is.
7. With the same structure and thickness of the composite film, the higher the peel strength is, the greater the heat sealing strength is. For the products with low composite peel strength, the weld failure is usually that the composite film at the weld joint is peeled off first, which results in the inner thermal seal bearing the failure tension independently, while the surface material loses the reinforcement effect, thus the heat sealing strength of the weld is greatly reduced. If the composite peeling strength is larger, the interlayer peeling at the welding edge will not occur, and the measured actual heat sealing strength is much greater.
Through understanding, we think that the reason for the high bag breakage rate is that the parts of the two groups of hot sealing ironing knives are not completely overlapped, there is a false welding near the hot sealing edge, the CPP film becomes thin, and part of the structure is damaged, and the thinner CPP layer is unable to bear the pressure during cooking, resulting in bag breakage.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service. The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries. We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.