Performance requirements of polyethylene film for

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Performance requirements of polyethylene film for milk packaging

in order to meet the filling requirements of high-speed automatic filling machine, polyethylene film for milk packaging must meet the following performance requirements:

1 It has good smoothness. To ensure 3 The experimental error meets the national standard. The milk packaging film can be filled successfully on the high-speed automatic filling machine. The dynamic and static friction coefficient of the film surface should be relatively low, generally between 0.2 and 0.4. The smoothness of the film is mainly achieved by adding a smooth agent. After the film is formed, the smooth agent migrates from the film to the surface and accumulates into a uniform thin layer, which can significantly reduce the friction coefficient of the film and make the film have a good smooth effect. Lubricant is usually an oil symptom: it is a mechanical mixture of caprolactam or erucic acid amide, which is not well compatible with high molecular polyethylene. The molecular thermal movement makes it gradually migrate to the low free energy interface, forming a weak interface. Therefore, if the content of lubricant is too high, it will affect the printability of the film

2. It has strong tensile strength. As the plastic film will be subjected to the mechanical tension from the automatic filling machine during the filling process, it is required that the film must have sufficient tensile strength to prevent it from being broken under the tension of the automatic filling machine. Choosing LDPE or HDPE particles with low melt index during film blowing is very beneficial to improve the tensile strength of polyethylene film

3. The surface wetting tension value should meet the requirements. In order to make the printing ink spread, wet and adhere smoothly on the surface of polyethylene plastic film, the surface tension of the film should reach a certain standard, otherwise it will affect the adhesion and firmness of the ink on its surface. Generally, the surface tension of polyethylene film should be above 38 dyne. Because polyethylene is a typical non-polar polymer material, its molecular structure does not contain polar groups, its crystallinity is high, its surface free energy is low, and its chemical properties are stable. Therefore, the printability of this film material is poor, and its adhesion to ink is not ideal; In addition, the additives in the film (smooth agent, plasticizer, etc.) continue to migrate and precipitate to the surface, forming a weak surface layer, which also affects the printing fastness of the printing ink. The experimental space can be adjusted. Therefore, before printing, the plastic film should be surface treated to change the chemical structure of the film surface and improve the film surface tension, so as to improve the printing suitability of polyethylene film and improve the adhesion to the ink, Ensure smooth production

4. It has excellent heat sealing performance. The film should have good heat sealing bag making fixture. The tensile property of plastic and rubber is one of the most important and basic mechanical properties, and it should also have good sealing property. Adding a certain proportion of LLDPE in the film blowing process can improve the low-temperature heat sealing performance and inclusion heat sealing performance of the milk film, but the addition of LLDPE should not be too large, otherwise the viscosity of the polyethylene milk film will be too high, making it prone to stick knife failure during heat sealing

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