LDPE films are generally made by both blow molding and casting processes. Cast polyethylene film has a uniform thickness, but is rarely used due to its high price. Blown polyethylene film is made from blow-molded grade PE pellets by blow-molding machines, which is the most widely used because of its lower cost.
Low-density polyethylene film is a semi-transparent, glossy, soft texture of the film, with excellent chemical stability, heat sealing, water resistance and moisture resistance, freezing resistance, can be boiled. Its main drawback is the poor barrier to oxygen, commonly used in composite flexible packaging materials, the inner layer of the film, but also is currently the most widely used, the largest amount of a plastic packaging film, accounting for more than 40% of the consumption of plastic packaging film.
Since the polyethylene molecule does not contain polar groups and has a high degree of crystallinity and low surface free energy, the film has poor printing properties and poor adhesion to inks and adhesives, so surface treatment is required before printing and laminating.
The following are common failures and solutions for LDPE blown film:
Film too sticky, poor openability
Cause analysis:
1. The resin raw material is not of the right type, not blown film grade LDPE resin, which does not contain an opening agent or the opening agent is of lower quality;
2. The temperature of the molten resin is too high, the fluidity is too big;
3. The blowing ratio is too large, resulting in poor film openings;
4. The cooling speed is too slow, the film is not cooled enough, and mutual bonding occurs under the action of the traction roller pressure;
5. The traction speed is too fast.
Solutions
① Replace the resin raw material, or add a certain amount of opening agent to the hopper;
② Appropriately reduce the extrusion temperature and the temperature of the resin;
③ Appropriately reduce the blowing ratio;
④ Increase the wind volume to improve the cooling effect and speed up the film cooling speed;
⑤ Appropriately reduce the haul-off speed.
Poor film transparency
Cause analysis:
1. low extrusion temperature, poor resin plasticization, resulting in poor transparency of the film after blow molding;
2. The blowing ratio is too small;
3. Poor cooling effect, thus affecting the transparency of the film;
4. The moisture content in the resin raw material is too large;
5. The traction speed is too fast and the film is not cooled enough.
Solution
① Appropriately increase the extrusion temperature, so that the resin can be uniformly plasticized;
② Appropriately increase the blowing ratio;
③Increase the wind volume to improve the cooling effect;
③ Increase the air volume to improve the cooling effect;
④ Dry the raw material;
⑤ Reduce the haul-off speed appropriately.
Film wrinkles
Cause analysis
1. Uneven film thickness;
2. Insufficient cooling effect;
3. The blowing ratio is too large, causing the film bubble to be unstable, swinging back and forth from side to side, so the film is prone to wrinkle;
4. The angle of the herringbone clamp is too large, the film bubble is flattened in a short distance, so the film is also prone to wrinkling;
5. The pressure on both sides of the traction roller is not consistent, one side is high and the other side is low;
6. The axes between the guide rollers are not parallel, which affects the stability and flatness of the film, thus wrinkling occurs.
Solution
① Adjust the thickness of the film to ensure uniform thickness;
② Improve the cooling effect to ensure that the film can be fully cooled;
③ Appropriately reduce the blowing ratio;
③ Reduce the blowing ratio appropriately;
④ Reduce the clamping angle of the herringbone clamp appropriately;
⑤ Adjust the pressure of the traction roller to ensure that the film is subjected to uniform force;
⑥ Check the axis of each guide shaft and make them parallel to each other.
Poor heat sealing performance of the film
Cause analysis
1. The frost line is too low, the polymer molecules undergo orientation, thus making the performance of the film close to that of an oriented film, resulting in lower heat sealing performance;
2. The blowing ratio and traction ratio are too large, and the film undergoes stretching orientation, thus affecting the heat sealing performance of the film.
Solution
① Adjust the size of the wind volume in the wind ring to make the dew point a little higher, as far as possible, under the melting point of the plastic blowing and traction, in order to reduce the molecules due to blowing and traction caused by stretching orientation;
② The blowing and traction ratios should be appropriately small. If the blowing ratio is too large and the traction speed is too fast, the film is overstretched in the transverse and longitudinal directions, then the performance of the film tends to be bi-directionally stretched, and the film’s heat sealing properties will become poor.
Film has an odor
Cause analysis
1. The resin raw material itself has an odor;
2. The extrusion temperature of the molten resin is too high, which causes the resin to decompose, thus producing an odor;
3. Insufficient cooling of the film bubble, the hot air inside the film bubble is not removed.
Solution
① Replace the resin raw material;
② Adjust the extrusion temperature;
③ Improve the cooling efficiency of the cooling air ring, so that the film bubble is sufficiently cooled.
White precipitates on the surface of the film
Reason: Is mainly additives in raw materials, low molecular weight resins and dust, etc., which condense on the mouth mold during processing, and after accumulating a certain amount are taken away by the film continuously, thus forming White precipitates on the film.
Solution
① After a certain period of time, increase the screw speed, increase the melt extrusion pressure, take away the precipitates.
② Regularly clean the mouth mold.
③ Increase the temperature of the melt appropriately to fully plasticize;
④ Use SILIEK PFAS-free PPA masterbatch can effectively improve the resin processing fluidity, improve internal and external lubrication performance, improve the dispersion between the components, reduce agglomeration, improve the mouth die accumulation, and at the same time can be brought out of the dead corner of the equipment, thus improving the surface quality of the film. SILIEK PFAS-free PPA masterbatch is a perfect alternative to fluorinated polymer PPA additives to meet the requirements of the current fluorine restriction. SILIEK PFAS-free PPA masterbatch is a perfect substitute for fluorinated polymer PPA additives, which meets the requirements of the current fluorine restriction.
⑤ The use of SILIKE SILIMER series of non-precipitating film smooth opening agent, solving the traditional smooth agent is easy to precipitate off the powder problem.
LDPE film solutions to improve product quality
SILIMER Series Non-Precipitation Film Slip Masterbatch is a kind of modified copolysiloxane containing active organic functional groups developed by Silicone. The long carbon chain is compatible with the resin to play the role of anchoring, and the silicon chain is polarized to the surface of the film to play the role of slipperiness, which can play the role of slipperiness without complete precipitation.
Adding small amount of SILIKE SILIMER 5064MB1, SILIMER 5064MB2 and other series of products can significantly improve the quality of the film, unlike the traditional film talc, SILIMER series of non-precipitated film talc does not precipitate, does not fall out of the powder, the coefficient of friction is stable, high-temperature talc does not stick. At the same time does not affect the subsequent processing of the film, does not affect the film heat sealing performance, does not affect the transparency of the film, does not affect the printing, laminating and so on.
Contact us Tel: +86-28-83625089 or via email: amy.wang@silike.cn
website: www.siliketech.com to learn more.
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