There are 13 common faults when blown film: film too viscous, poor opening;Poor film transparency;Film with wrinkle;The film has water mist pattern;Film thickness uneven;Thickness of the film is too thick;Film thickness too thin;Poor thermal sealing of the film;Film longitudinal tensile strength difference;Film transverse tensile strength difference;Film bubble instability;Rough and uneven film surface;Film has peculiar smell etc.
1. Film too viscous, poor opening
Failure reason:
① Wrong Resin raw material model, not low density polyethylene resin particles, which do not contain opening agent or the low content opening agent;
②Molten resin temperature is too high and large fluidity;
③Blowing ratio is too large, resulting film with poor opening;
④Cooling speed is too slow, film cooling is insufficient, and mutual adhesion occurs under the action of traction roller pressure;
⑤Traction speed is too fast.
Solutions:
① Replace resin raw materials, or add a certain amount of opening agent to the bucket
②Appropriately reduce the extrusion temperature and resin temperature;
③Appropriately reduce the inflation ratio;
④Increase the air volume, improve the cooling effect, and accelerate the film cooling speed;
⑤Appropriately reduce the traction speed.
2.Poor film transparency
Failure reason:
① Low extrusion temperature and poor plasticization of resin cause poor transparency of film after blow molding;
② Too small blow ratio;
③ Poor cooling effect, thus affecting the transparency of film;
④ Too much moisture in resin raw materials;
⑤ Too fast traction speed, insufficient film cooling;
Solutions:
① Increase the extrusion temperature to make the resin uniformly plasticized;
② Increase the blowing ratio;
③ Increase the air volume to improve cooling effect;
④Dry the raw materials;
⑤Reduce the traction speed.
3. Film with wrinkle
Failure reason:
① Film thickness is uneven;
② The cooling effect is not enough;
③ The blow-up ratio is too large, causing the bubble to be unstable, swinging back and forth, and easy to wrinkle;
④ The angle of the lambdoidal board is too large, the film is flattened within short distance, so film also easy to wrinkle;
⑤ The pressure on the two sides of the traction roller is inconsistent, one side is high and the other side is low;
⑥ The axis between the guide rollers is not parallel, which affects film’s stability and flatness and then rise wrinkle.
Solutions:
① Adjust film thickness to ensure that the thickness is uniform;
② Improve the cooling effect to ensure that the film can be fully cooled;
③ Appropriately reduce the inflation ratio;
④ Appropriately reduce the angle of the lambdoidal board;
⑤ Adjust the pressure of the traction roller to ensure that the film is evenly stressed;
⑥ Check the axis of each guide shaft and make it parallel to each other.
4.The film has water mist pattern
Failure reasons as follows:
① Extrusion temperature is low, the resin plasticization is poor;
② Resin is damp, and the moisture content is too high.
Solutions:
① Adjust the temperature setting of extruder and increase the extrusion temperature properly.
② When drying the resin raw materials, the water content of the resin shall not exceed 0.3%.
5. Film thickness uneven
Failure reason:
①Uniformity of die gap directly affects the uniformity of film thickness. If the die gap is not uniform, some parts have larger gap and some parts have smaller gap, resulting in extrusion different. Therefore, the film thickness formed is not consistent, some parts are thin and some parts are thick;
② Die temperature distribution is not uniform, some are high and some are low ,so film thickness is uneven;
③ Air supply around the cooling air ring is inconsistent, resulting in uneven cooling effect, resulting in uneven thickness of the film;
④ Inflation ratio and traction ratio are not appropriate, making the thickness of the film bubble difficult to control;
⑤ Traction speed is not constant, constantly changing, which will certainly affect the thickness of the film.
Solutions:
① Adjust the die head gap to ensure uniform everywhere;
② Aadjust the head die temperature to make the die part temperature uniform;
③ Adjust the cooling device to ensure uniform air volume at the air outlet;
④ Adjust the inflation ratio and traction ratio;
⑤ Check the mechanical transmission device to keep the traction speed constant.
6. Thickness of the film is too thick
Failure reson:
① Die gap and extrusion amount are too large, so the film thickness is too thick;
② Athe air volume of the cooling air ring is too large, and film cooling is too fast;
③ Traction speed is too slow.
Solutions:
① Adjust the die gap;
② Reduce the air volume of the air ring properly to further expand the film, so that its thickness becomes thinner;
③ Increase the traction speed properly.
7. Film thickness too thin
Failure reason:
① Die gap is too small and the resistance is too large, so the film thickness is thin;
② Air volume of the cooling air ring is too small and the film cooling is too slow;
③ Traction speed is too fast and the film is stretched too much, so the thickness becomes thin.
Solutions:
① Aadjust the die clearance;
② Increase the air volume of the air ring properly to speed up the film cooling;
③ Rreduce the traction speed properly.
8.Poor thermal sealing of the film
Failure reason as follows:
① the dew point is too low, the polymer molecules are oriented, so that the film performance is close to the directional film, resulting in the decrease of the thermal sealing performance;
② the inappropriate blowing ratio and traction ratio (too large), the film is stretched, so that the thermal sealing performance of the film is affected.
Solutions:
① adjust the air volume in the air ring to make the dew point higher, and blow and pull under the melting point of the plastic as much as possible to reduce the molecular stretch orientation caused by blow and pull;
② The blowing ratio and traction ratio should be a little smaller. If the blowing ratio is too large, and the traction speed is too fast, and the transverse and longitudinal stretching of the film is excessive, then the performance of the film will tend to biaxial stretching, and the thermal sealing property of the film will be poor.
9.Poor longitudinal tensile strength of the film
Failure reason :
① too high temperature of the melt resin will reduce the longitudinal tensile strength of the film;
② slow traction speed, insufficient longitudinal directional effect of the film, so as to make the longitudinal tensile strength worse;
③ too large blowing expansion ratio, mismatching with the traction ratio, so that the transverse directional effect and tensile strength of the film increase, and the longitudinal tensile strength will be worse;
④ The film cools too fast.
Solutions:
① properly reduce the temperature of molten resin;
② properly increase the traction speed;
③ adjust the inflation ratio to make it adapt to the traction ratio; ④ properly reduce the cooling speed.
10.Film transverse tensile strength difference
Fault reasons:
① the traction speed is too fast, and the difference with the inflation ratio is too large, which causes fibrosis in the longitudinal direction, and the transverse strength becomes poor;
② the cooling speed of the cooling air ring is too slow.
Solutions:
① properly reduce the traction speed to match the blowing ratio;
② increase the air volume of the air ring to make the blown film cool quickly to avoid being stretched and oriented under the high elastic state of high temperature.
11. Film bubble instability
Failure reason:
① the extrusion temperature is too high, the fluidity of the melt resin is too large, the viscosity is too small, and it is easy to fluctuate;
② the extrusion temperature is too low, and the discharge quantity is small;
③ the air volume of the cooling air ring is not stable, and the film bubble cooling is not uniform;
④ it is interfered and affected by the strong external air flow.
Solutions:
① adjust the extrusion temperature;
② adjust the extrusion temperature;
③ check the cooling air ring to ensure that the air supply around is uniform;
④ prevent and reduce the interference of external air flow.
12.Rough and uneven film surface
Failure reason:
① Extrusion temperature is too low, the resin plasticization is poor;
② Extrusion speed is too fast.
Solutions:
① adjust the temperature setting of extrusion, and increase the extrusion temperature to ensure good plasticization of resin;
② reduce the extrusion speed properly.
13. Film has peculiar smell
Failure reason:
① Resin raw material has peculiar smell;
② Extrusion temperature of the molten resin is too high, resulting in resin decomposition, resulting in peculiar smell;
③ the cooling of the membrane bubble is insufficient, and the hot air in the membrane bubble is not removed completely.
Solutions:
① replace resin raw materials;
② adjust extrusion temperature;
③ improve cooling efficiency of cooling air ring to make the film bubble fully cooled.
Post time: Jun-09-2015
