Factors affecting the heat sealing quality of the

Factors affecting the heat sealing quality of cooking bag packaging

in November 2004, a customer in Guangdong reported that using our company's 300 cooking resistant ink and pu-1750 cooking resistant adhesive to process ny//cpp cooking packaging, the bag breaking rate was high (as high as 45%), and later the manufacturer switched to another brand of cooking resistant adhesive, which also produced the same phenomenon. The manufacturer sent packaging bags and some materials, please check what caused it

through the inspection of the packaging bag, it is found that there is a quality problem in the heat sealing of the packaging bag. Pulling the heat sealing edge of the packaging bag by hand, the heat sealing strength is not very good, and the fastness of the sealing edge 1 ~ 2mm close to the heat sealing is extremely poor. CPP and CPP heat sealing can be very light, and the automatic target identification technology can be loosened, but the composite strength of ny//cpp cannot be stripped. At the same time, stretch your hand into the bag and pick the heat sealing edge with your fingertips, It is found that in some places, the CPP and CPP are heat sealed by cutting 1 ~ 2mm. Therefore, we believe that there is a problem with the heat sealing process

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 layer material have a decisive impact on the heat sealing strength. Commonly used heat sealing materials for composite packaging include CPE, CPP, EVA, hot melt adhesive and some other ionic resin coextrusion or blending modified films. The thickness of heat seal material is generally 20 ~ 80 μ M, and 100 ~ 200 in special cases 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 bags is generally required to be 40 ~ 50N, so the thickness of heat sealing material should be 60 ~ 80 μ M above

2. The effect of heat sealing temperature on 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 composite substrate, the actual heat sealing temperature is often higher than the melting temperature of heat sealing material. The lower the pressure of heat sealing, the higher the temperature of heat sealing 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 really seal. However, if the heat sealing temperature is too high, it is very easy to damage the melting and extrusion of the heat sealing material at the welding edge, resulting in the phenomenon of "undercutting", 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 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 real fusion between the two films, resulting in poor local heat sealing, or it is difficult to drive out the bubbles sandwiched in the middle of the weld, resulting in false welding; Of course, the higher the heat sealing pressure is, the better. It is better not to damage the welding edge, because at a higher heat sealing structure: temperature, the heat sealing material of the welding edge has been 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, if the heat sealing time is long, the heat sealing layer will be fused more fully and bonded more firmly, but if the heat sealing time is too long, it is easy to cause the weld wrinkle 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 a process of eliminating stress concentration by shaping the weld just after melting and heat sealing with a lower temperature under a certain pressure. Therefore, the pressure of China's extruder industry in terms of foreign trade export 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, which will lead to poor cooling, warping of heat sealing edges, and reduction of 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 horizontal heat sealing is determined by the number of groups of horizontal heat sealing devices on the machine. Good heat sealing requires at least two times of heat sealing. The general bag making machine has two groups of scalding knives, and the higher the overlap of scalding 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, weld damage is often caused by the first interlayer peeling of the composite film at the weld, resulting in the internal heat sealing layer independently bearing the destructive tension, while the surface material loses its reinforcement effect, and the heat sealing strength of the weld is greatly reduced. If the composite peel strength is large, the interlayer peel 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 bag breaking rate of the packaging bag this time is that the positions of the two groups of hot sealing hot knives are not completely overlapped, and there is a false soldering near the hot sealing edge, the CPP film becomes thinner, and some structures are damaged. The action should be light and stable during loading, and the thinner CPP layer cannot withstand pressure during cooking, resulting in bag breaking

Author: Xiao Haiyi source: Guangdong packaging