01Uneven lateral thickness of the film
The root cause is the uneven discharge of the mold mouth. The specific influencing factors and some solutions are as follows:
① Improper adjustment of the lip gap requires partial adjustment or complete re adjustment;
② Uneven temperature distribution in the transverse direction of the mold head, it is necessary to check whether the heater is faulty;
③ There are impurities in the mold cavity, which can cause logistics disorder and uneven discharge. It needs to be cleaned several times a year;
④ Excessive or fluctuating melt pressure can cause unstable extrusion and affect the uniformity of thickness. This can be improved by adjusting temperature, extrusion speed, and adjusting raw materials;
⑤ Inappropriate position and direction of the air knife or uneven air outlet result in uneven cooling and uneven thickness;
⑥ If there is too much or uneven addition of recycled material, the amount of recycled material should generally be less than 15-20% and added evenly.
02Thin film with multiple crystal points
Crystal dots are caused by a small amount of resin with high molecular weight in the raw material not being able to plasticize. Static mixers and other methods to increase shear and melt pressure can be added to the equipment, but the following situations are prone to producing crystal points:
① Insufficient or excessive barrel temperature, low temperature, and incomplete plasticization of raw materials; Excessive temperature, low melting pressure, and low shear force are actually detrimental to the plasticization of polyolefin plastics;
② If the melt pressure is low, resulting in low shear and poor plasticization, the number of filter layers and mesh can be appropriately increased;
③ Slow extrusion speed and insufficient shearing;
④ The raw materials used are of poor quality, so it is necessary to choose suitable grades of raw materials and pay attention to whether there are materials with significant differences mixed in.
03The film roll has exposed ribs
The fundamental reason lies in the uneven thickness, even if it is very small, it may cause obvious bulging after accumulation, affecting the appearance and use.
We can analyze and solve it from the following aspects:
① Uneven film thickness, identify influencing factors, and carefully adjust;
② The winding tension is too high, and the film roll is too tight;
③ Unstable melt pressure leads to uneven thickness;
④ Improper position and direction of the air knife or uneven air outlet, resulting in uneven thickness;
⑤ The shrinkage rate of the film after placement is high, and adjustments need to be made in terms of raw material production process and film roll storage.
04Poor transparency of thin film
Polyolefin is a crystalline polymer, and the key to improving transparency is to reduce crystallinity and make spherulites smaller. The main influencing factor is the resin raw material. The adjustment of the production process of cast film can only improve the transparency of the film to a certain extent.
The measures are as follows:
① Reduce the temperature of the rapid cooling roller to achieve better rapid cooling effect of the molten film;
② Shorten the distance between the die and the chill roll to reduce crystallization;
③ Slow down the extrusion speed to allow the molten film to cool sufficiently on the rapid cooling roller.
The XHD Xinhuida casting film production line has upgraded its temperature control system, equipped with a static mixer and optimized temperature online monitoring. The upgrade can lift and lower the water flow, effectively solving problems such as uneven film thickness, multiple crystal points, transparency, and poor brightness. The film quality has been significantly improved.
The XHD Xinhuida casting film production line adopts a variable frequency electromagnetic heating system and energy-saving motors, which are more energy-efficient, have stronger material adaptability, support non-stop order changing, reduce losses, and have precise extrusion control.
