The equipment of biaxial tensile mesh production line is generally multi-layer Masonic film, which is made of polypropylene particles through co extrusion to form a sheet, and then stretched in both vertical and horizontal directions. Due to stretching molecular orientation, the film has good physical stability, mechanical strength, air tightness, high transparency and gloss, toughness and wear resistance. It is a widely used printing film at present, with a thickness of 20 ~ 40 μ m. Widely used is 20 μ m 。 The main disadvantage of biaxially oriented polypropylene film is poor heat sealing, so it is generally used as the outer film of composite film. For example, after compounding with polyethylene film, the moisture resistance, transparency, strength, stiffness and printability are ideal, which is suitable for holding dry food. As the surface of biaxially oriented polypropylene film is non-polar, with high crystallinity and low surface free energy, its printing performance is poor and its adhesion to ink and adhesive is poor. Surface treatment is required before printing and compounding.

Transverse stripe

(1) The main causes of large spacing transverse stripes are unstable extrusion melt pressure, uneven speed or temperature of quench roll, and excessive fluctuation of air flow of air knife. Point 1 is common. There are many factors causing pressure instability. On the one hand, the production line speed is increased too fast, resulting in the rapid increase of metering pump speed. On the other hand, the screw speed of the main extruder is increased relatively slowly, resulting in insufficient discharge of die head and unstable pressure. In such cases, it is better to extend the acceleration time appropriately. After the linear speed is stable, the transverse stripes will disappear naturally. Another common situation is the raw material factor. When the process conditions are well controlled and there is no obvious improvement after many adjustments, it is necessary to consider replacing raw materials.

(2) Small spacing transverse stripe small spacing transverse stripe is not common in the actual production process. There are four reasons: inappropriate angle of the machine head, inappropriate angle of the air knife or air volume, influence of air flow near the machine head, and unstable speed of the quench roll. These four aspects can be solved.

Longitudinal stripe

During the casting process, it is sometimes seen that there are continuous longitudinal stripes at the local and fixed positions of the extruded slab. If BOPP film is produced with this cast sheet, the transverse thickness of the film will be uneven; There are obvious protrusions (ribs) or longitudinal stripes on the appearance of the rolled and slitted films. The measures usually taken to eliminate the longitudinal stripes are as follows: ① select the die head with reasonable structure and good quality to ensure that the lip is clean and free of any mechanical damage. ② Strengthen melt filtration. ③ Timely remove the sundries on the lip and do a good job in the maintenance of the machine head. ④ Improve the uniformity of air blowing of air knife. ⑤ Reasonably control the temperature of each extrusion section. ⑥ Adjust the position of the head relative to the quench roll.

Warping on both sides

This phenomenon is mainly caused by poor attachment effect and excessive temperature difference on both sides during casting. The warping of the cast sheet will affect the flatness of the film. For PP, the uneven cooling and crystallization of the cast sheet will directly affect the film-forming property of the film. The edge of the casting sheet is usually warped to the side with lower temperature, so the temperature of the cooling water on the quench roll surface and in the water tank can be judged according to the warpage of the casting sheet in the production process, and then the solution can be considered

Bubbles appear

If the melt contains impurities, the moisture content of raw materials is too high, the extrusion temperature is too high, the material heating time is too long, or there is air or degradation products in the extruder and filter, bubbles may appear in the cast sheet. If bubbles appear in the normal production process, carefully observe the bubble shape, color, etc., analyze the causes and solve them. If the air screw is started to extrude or a new melt filter is replaced, there may be air or degradation products in the extruder or filter, and bubbles will generally appear in the cast sheet. This problem can usually be solved by fully discharging.