As a professional in the soft bag industry, we must have encountered the faults caused by the heat sealing of composite bags. In order to better facilitate you to solve similar problems, small special finishing caused by soft packaging composite bag heat sealing failure analysis, I hope to help you!
1. The type, thickness and quality of heat sealing material have the most direct influence on the heat sealing strength.
Commonly used heat sealing materials for composite packaging are CEP, LPPE, CPP, OPP, EVA, hot melt adhesive and other ionic resin co extrusion or blending modified films. The thickness of the heat seal material is generally between 20-80 μ M. In special cases, the heat sealing strength of the same kind of heat sealing material is increased with the increase of heat sealing thickness. For example, the heat sealing strength of cooking bag is generally required to be 40-50 n, so the heat sealing thickness should be above 60-80 μ M. Temperature is involved in the process of heat sealing bag making, and the temperature control is displayed by the temperature meter. In the process of heat sealing composite bag processing, the more precise the thermometer is, the better. The error range and setting value should not be greater than ± 5 ℃. 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 actual production process, due to the influence of heat sealing pressure, bag making machine 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 prolong the heat sealing time, the heat sealing layer cannot be truly sealed. 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 during melting extrusion, which greatly reduces the heat sealing strength of the sealing and the impact resistance of the composite bag. In the actual process of bag making and heat sealing, the pressure of heat sealing tool is often adjusted by rotatable spring. The adjustment process is generally composed of two springs, which are divided into left and right sides. If the pressure affects the heat sealing strength, the detection method is as follows: take a composite bag being processed and observe the seam trace carefully. If the pressure is uniform, there will be no bubbles and other phenomena; Another method is to use the special smooth bamboo block with length of 500px, width of 75px and thickness of 5000px to carry out the test. Because the pressure is not enough and the strength is low, leakage often occurs. So uniform pressure and temperature is one of the basic factors to reduce the low strength and delamination phenomenon.
2. In order to achieve the ideal heat sealing strength, the heat sealing pressure is essential.

For light and thin packaging bags, the heat sealing pressure should be at least 2kg / cm2, and it should be increased 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 difficult to eliminate the air bubble sandwiched in the welding seam, resulting in false welding. However, the higher the heat sealing pressure is, the better is not to damage the welding edge, because the heat sealing material at the welding edge is in the semi melting state when the heat sealing temperature is higher, too much pressure will easily squeeze out part of the heat sealing material and form a semi cutting state at the edge of the weld. The weld is brittle and the heat sealing strength is reduced. So the adjustment of pressure is very important.

3. The heat sealing time is mainly determined by the speed of bag making machine.
If the speed is fast, the heat sealing time will be short; if the speed is slow, the heat sealing time will be long. Heat sealing time is also a key factor affecting the sealing strength and appearance of weld. Under the same heat sealing temperature and pressure, if the heat sealing time is long, the fusion of the heat sealing layer will be more sufficient and the bonding will be more firm; however, if the heat sealing time is too long, it will easily cause the welding seam wrinkling deformation and affect the flatness and appearance. If the weld after heat sealing is not cooled well, it will not only affect the appearance flatness of the welding suspect, but also have a certain impact on the strength of the heat seal. The cooling process is to shape the weld after just melting and heat sealing with a lower temperature under a certain pressure. Therefore, insufficient pressure, poor cooling and circulation, insufficient circulation, too high water temperature or untimely cooling will lead to poor cooling and reduced heat sealing strength.
4. The number of longitudinal heat sealing depends on the ratio of effective length of longitudinal welding rod and bag length.
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. For the products with low composite peel strength, the composite film at the weld joint is often peeled off first, which results in the inner thermal seal bearing the destructive tensile force independently, while the surface material loses the reinforcing effect, which leads to the decrease of heat sealing strength; If the delamination between the composite layers is strong, the delamination at the welding edge will not occur, and the actual heat sealing strength measured will be more; when the inner layer of heat sealing is PE or OPP, the heat sealing strength is much better than that of BOPP with the same thickness.
5. The influence of the contents of the composite bag.
Some products are powder packed and easy to contaminate and seal during filling. For example, when LDPE material is used as inner layer material, the sealing part is easy to crack. This is because LDPE is not very good for the heat sealing of inclusions, so the heat sealing strength can be improved by replacing the inner membrane material or increasing the thickness of the material.
6. The effect of additives on composite materials.
In the process of compounding polyethylene film, polyethylene will precipitate after being extruded by hot pressing roller. A layer of white is like powdery white. This phenomenon is that a certain amount of lubricant is added in the production process of polyethylene, which is some wax with low melting point, which is easy to precipitate to the surface of the film. The most direct harm of this layer of wax with low melting point after precipitation is that the composite strength is greatly weakened, and the heat sealing strength is also greatly weakened, especially at the edge sealing position, resulting in easy opening and separation.
The solutions are as follows: 1) pretreat the polyethylene again to achieve the ideal surface tension; 2) select the appropriate adhesive to enhance the composite fastness; 3) reduce the aging temperature to avoid the material precipitation, so as to increase the composite fastness and heat sealing strength.
7. The delamination of flexible packaging composite bag after heat sealing is related to the quality of printing ink layer and corona surface.
In the actual production process, in order to achieve the true reproduction of color, it is inevitable to mix printing ink and surface printing ink. From the theoretical analysis, the inner and outer printing inks are incompatible. If the printing film ink layer is mixed with the inner surface ink layer, the fastness between the ink layers is not good, and it is easy to layer. The lamination phenomenon is also easy to be caused at the heat sealing weld joint, and the heat sealing strength will be poor.
Solution: try to avoid the mixture of surface printing ink and inner printing ink, so as to improve the heat sealing strength and reduce the phenomenon of delamination.
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.
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