Analysis of the reasons for the decrease of heat s

Analysis of the reasons for the decline of heat sealing strength of composite soft film

food. With the rapid development of cosmetics, medicine and other industries, their demand for plastic composite packaging products is increasing day by day. At the same uniform value, higher quality of plastic composite packaging products are also put forward. 12. Longitudinal shrinkage rate: gb/t 6671 ⑵ 001 requirements for the determination of longitudinal shrinkage rate of thermoplastic pipes. Although packaging users attach great importance to the beauty and physical properties of packaging products, in actual use, they pay more attention to the heat sealing strength of packaging products, because it directly affects the packaging speed. Transportation, storage and sales of contents

in the actual production, all manufacturers take the heat sealing strength as the most important quality index in the quality monitoring of both bag making products and coil products used in the automatic packaging production line. Now I will make a simple analysis of the factors that affect the heat sealing strength in production based on my experience in practical work

first, heat sealing temperature

heat sealing temperature directly affects the heat sealing strength of plastic composite packaging products. In the process of packaging or bag making, if the heat sealing temperature is set improperly or adjusted improperly, the following two situations will occur

1. when the heat sealing temperature is too high, which exceeds the heat shrinkage temperature of the composite film surface material, it will cause the shrinkage deformation of the composite film, resulting in adhesion between the composite film and the heat sealing knife, melting and extrusion of the heat sealing edge material, resulting in undercutting

2, when the heat sealing temperature is too low, poor heat sealing will occur

therefore, the following two points should be paid attention to in actual production

1. In the selected composite structure, the combination of surface material and its thickness and heat seal material and its thickness should be reasonable

2. the heat sealing temperature should be set according to the material, structure, thickness, heat sealing position (longitudinal or horizontal seal), machine speed, pressure and other data of plastic composite flexible packaging, and the set operation data should be slightly adjusted according to the actual heat sealing effect until they match each other. For example, when the thickness and heat resistance of the composite film surface material limit the heat sealing bag making temperature, so that it can no longer rise and poor heat sealing occurs, the method of increasing the heat sealing pressure and prolonging the heat sealing time can be used to make up for it

II. Heat sealing time

the heat sealing time of the automatic halogen containing installation machine or the old bag making machine is determined by the machine speed. When the heat sealing temperature and pressure remain unchanged, the longer the heat sealing time is, the stronger the bonding between the heat sealing layers is. However, if the heat sealing time is too long, the heat sealing part of the composite film will be wrinkled and uneven, which will cause serious fatigue. The installation of the testing machine is simple and affect the appearance quality of the product

in recent years, some major bag making machine manufacturers in Japan have produced internationally advanced bag making machines, which have solved the above problems in the old bag making machines. For example, the 8h-60hvl three side sealing high-speed automatic bag making machine produced by HuGu Jiyan Industry Co., Ltd. uses a servo motor to separately control the up and down movement and feeding of the heat sealing knife. The machine sets a waiting time for heat sealing (the adjustment time for bag making) in a complete motion cycle, that is, the time for heat sealing a packaging bag is equal to the feeding time. Sum of heat sealing waiting time and heat sealing time. When the bag making machine is adjusted to produce genuine bags, the waiting time for heat sealing can be set to 0 to enter normal production. In this way, when adjusting the running speed of the bag making machine, the heat sealing time can remain unchanged, and there is no need to change the set heat sealing temperature, which greatly facilitates the adjustment of the machine and the quality control of bag making. At the same time, it also improves the production efficiency.

Third, heat sealing pressure

in order to ensure the heat sealing strength of plastic composite flexible packaging, a certain heat sealing pressure is essential. Therefore, in the process of heat sealing, the heat sealing pressure is required to be moderate and uniform. If the heat sealing pressure is insufficient or uneven, bubbles will be generated at the heat sealing part, resulting in poor heat sealing. If the heat sealing pressure is too large, the sealing deformation will occur at the heat sealing part. When the heat sealing temperature is high, some composite materials will be squeezed away, resulting in brittle heat sealing edges, easy to crack, and a decrease in heat sealing strength

there are several factors causing uneven heat sealing pressure

1. deformation of the heat sealing knife

the heat sealing knife is generally made of aluminum or copper with good heat transfer performance, both of which are relatively soft. Therefore, when installing the heat sealing knife, if the method of tightening the fixing screws is wrong, the force on the heat sealing knife will be uneven, and after frequent tool replacement, the heat sealing knife will be deformed. Therefore, the correct installation method should be used when installing the heat sealing knife

2. Low machining accuracy of the heat sealing knife machine

low machining accuracy of the heat sealing knife machine will cause uneven surface of the heat sealing knife, which will cause uneven heat sealing pressure during the heat sealing process, thus affecting the heat sealing strength of the composite packaging bag. (to be continued)