How to achieve uniform dispersion of additives in the production of anti-fog polyolefin film?

In the production and manufacturing of anti-fog polyolefin film, the stable performance of anti-fog performance depends on whether the anti-fog additives can be evenly dispersed inside the film, and the extrusion process, as a key link in production, plays a decisive role in the dispersion effect of the additives.

The anti-fog function of anti-fog polyolefin film depends on special anti-fog additives. These additives are mostly surfactants, and their molecular structure has both non-polar hydrocarbon chains compatible with polyolefin substrates and polar groups that interact with water. During the use of the film, it is the polar groups that reduce the surface tension of water, causing water vapor to form a transparent water film on the surface of the film to avoid atomization. However, to achieve a stable and long-lasting anti-fog effect, the premise is that the additives are evenly distributed in the film, which puts strict requirements on the extrusion process.

The extrusion process is the stage of fully mixing the polyolefin raw material with the anti-fog additive and melt-plasticizing it. Before the start of production, the ratio of polyolefin resin and anti-fog additive needs to be accurately controlled, and pre-mixed by a high-speed mixer to initially achieve uniform distribution of the additives between the resin particles. The premixed material enters the extruder barrel. Under the push of the screw, the material undergoes the process of conveying, compression, melting and homogenization in sequence. In this series of processes, the structural design and parameter setting of the screw are the key factors affecting the dispersion of additives.

The screw's parameters such as thread depth, pitch and compression ratio directly affect the residence time, shear strength and mixing effect of the material in the barrel. Deeper thread depth and larger pitch are conducive to rapid material conveying, but may weaken the shear mixing effect; while a smaller compression ratio makes it difficult to fully compact and melt the material, affecting the dispersion of additives. Therefore, it is necessary to reasonably design the screw structure according to the type of polyolefin resin, the characteristics of the anti-fog additive and the final performance requirements of the film. For example, for polyolefin resins with poor melt fluidity, it is necessary to appropriately reduce the thread depth, increase the compression ratio, and improve the shear strength, so that the anti-fog additive can fully break the agglomerates under high temperature, high pressure and strong shear force, and evenly disperse in the polyolefin melt.

The temperature control of the extruder should not be ignored either. When the temperature is too high, the viscosity of the polyolefin melt decreases and the fluidity increases. Although it helps the dispersion of additives, it may cause the additives to decompose or volatilize, affecting the anti-fog performance; when the temperature is too low, the material is not fully melted, the additives cannot be effectively dispersed, and it may also cause excessive screw torque and damage the equipment. Therefore, it is necessary to set a reasonable temperature gradient in different sections of the extruder. Generally speaking, the temperature of the barrel feeding section is relatively low, which is mainly used for material transportation; the temperature of the compression section gradually increases to achieve the compaction and partial melting of the material; the temperature of the homogenization section is the highest to ensure that the material is completely melted and the additives are fully dispersed. By precisely controlling the temperature of each section, the polyolefin resin can be fully mixed with the anti-fog additive at a suitable viscosity.

In addition to the screw structure and temperature control, the speed of the extruder will also affect the dispersion effect of the additive. A higher screw speed can increase the shear rate of the material and promote the dispersion of the additive, but too fast a speed will make the material stay in the barrel too short, resulting in insufficient mixing; too slow a speed may make the material stay at high temperature for too long, causing degradation. Therefore, it is necessary to optimize the screw speed according to the material characteristics and equipment parameters to achieve uniform dispersion of anti-fog additives while ensuring production efficiency.

After the material is fully mixed and melted in the extruder, it is extruded through the die head to enter the subsequent molding process. In this process, the flow channel design of the die head should ensure uniform extrusion of the melt to avoid uneven distribution of additives due to uneven local pressure or flow rate differences. Whether it is blow molding or cast molding, the control of parameters such as temperature and stretch ratio during the molding process will also affect the final distribution of additives. It is necessary to coordinate with the extrusion process to ensure the consistency of the overall performance of the anti-fog polyolefin film.

From raw material ratio to extrusion molding, each link is closely related and jointly affects the dispersion effect of anti-fog additives in polyolefin films. Only by fully understanding the mechanism of action of each process parameter and accurately controlling the key factors in the extrusion process can the uniform dispersion of anti-fog additives be achieved, thereby producing anti-fog polyolefin films with excellent performance and stable anti-fog effects to meet the application needs of food packaging, agricultural greenhouses and other fields.