Problems and solutions in the production process of LDPE blown film

1. Thin film transparency

cause of issue:

1 The extrusion temperature is low, and the resin is poorly plasticized, resulting in poor transparency of the film after blow molding;

2 the inflation ratio is too small;

3 The cooling effect is not good, which affects the transparency of the film;

4 The moisture content in the resin raw material is too large;

5 The pulling speed is too fast and the film cooling is insufficient.

Solution:

1 appropriately increase the extrusion temperature to enable the resin to be uniformly plasticized;

2 appropriately increase the inflation ratio;

3 increase the air volume and improve the cooling effect;

4 drying the raw materials;

5 Properly reduce the traction speed.

2. Wrinkles in the film

cause of issue:

1 film thickness is not uniform;

2 cooling effect is not enough;

3 The inflation ratio is too large, causing the bubble to be unstable, swinging back and forth, and wrinkles are easy to occur;

The angle between the 4 herringbone plates is too large, and the bubble is flattened in a short distance, so the film is also prone to wrinkles;

5 The pressure on both sides of the traction roller is inconsistent, 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, and wrinkles occur.

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 inflation ratio;

4 appropriately reduce the angle of the herringbone splint;

5 adjust the pressure of the traction roller to ensure uniform force on the film;

6 Check the axes of the guide shafts and make them parallel to each other.

3. The film is too sticky and has poor opening

cause of issue:

1 The resin material type is wrong, not the blown film grade low density polyethylene resin particles, which contain no opening agent or the content of the opening agent is low;

2 The temperature of the molten resin is too high and the fluidity is too large;

3 The inflation ratio is too large, resulting in poor opening of the film;

4 The cooling rate is too slow, the film is insufficiently cooled, and mutual adhesion occurs under the action of the traction roller pressure;

5 traction speed is too fast.

Solution:

1 replace the resin raw materials, or add a certain amount of opening agent to the department;

2 appropriately reduce the extrusion temperature and the temperature of the resin;

3 appropriately reduce the inflation ratio;

4 increase the air volume, improve the cooling effect, and accelerate the film cooling rate;

5 Properly reduce the traction speed.

4. The film has a foggy water pattern

cause of issue:

1 The extrusion temperature is low, and the resin is poorly plasticized;

2 The resin is damp and the moisture content is too high.

Solution:

1 Adjust the temperature setting of the extruder and increase the extrusion temperature appropriately.

2 Drying the resin raw material generally requires that the water content of the resin should not exceed 0.3%.

5. Uneven film thickness

cause of issue:

1 The uniformity of the die gap directly affects the uniformity of the film thickness. If the die gap is not uniform, the gap between the parts is large, and the gap between the parts is small, which results in more or less extrusion. Therefore, the thickness of the formed film is also inconsistent, some parts are thin, and some parts are thick;

2 The temperature distribution of the die is not uniform, and there are high and low, so that the film after blow molding is thin and uneven;

3 The air supply volume around the cooling air ring is inconsistent, resulting in uneven cooling effect, resulting in uneven thickness of the film;

4 The inflation ratio and the traction ratio are not suitable, so that the bubble thickness is not easy to control;

5 The traction speed is not constant and changes constantly, which of course affects the thickness of the film.

Solution:

1Adjust the gap between the die heads to ensure uniformity everywhere;

2 Adjust the temperature of the die head to make the temperature of the die part uniform;

3 Adjust the cooling device to ensure that the air outlet of the air outlet is even;

4 adjust the inflation ratio and the traction ratio;

5 Check the mechanical transmission to keep the traction speed constant.

6. The thickness of the film is thick

cause of issue:

1 The die gap and the extrusion amount are too large, so the film thickness is thick;

2 The air volume of the cooling air ring is too large, and the film cools too fast;

3 Traction speed is too slow.

Solution:

1 adjust the die gap;

2 appropriately reduce the air volume of the wind ring, so that the film is further inflated, so that the thickness thereof is thinner;

3 Appropriately increase the traction speed.

7. The thickness of the film is thin

cause of issue:

1 The die gap is small and the resistance is too large, so the film thickness is thin;

2 The air volume of the cooling air ring is too small, and the film cooling is too slow;

3 The pulling speed is too fast, and the film is stretched excessively, so that the thickness is thinned.

Solution:

1 adjust the die gap;

2 Appropriately increase the air volume of the wind ring to accelerate the cooling of the film;

3 Appropriately reduce the traction speed.

8. The film has poor heat sealability

cause of issue:

1 The dew point is too low, the polymer molecules are oriented, so that the performance of the film is close to the oriented film, resulting in a decrease in heat sealing performance;

2 The inflation ratio and the traction ratio are not appropriate (too large), and the film is stretched and oriented, thereby affecting the heat sealing performance of the film.

Solution:

1 Adjust the amount of wind in the wind ring to make the dew point higher, as much as possible to inflate and pull at the melting point of the plastic to reduce the molecular stretching orientation caused by inflation and traction;

2 The inflation ratio and the traction ratio should be appropriately small. If the inflation ratio is too large and the traction speed is too fast, the transverse and longitudinal stretching of the film is excessive, then the performance of the film tends to be biaxially stretched. Heat sealability will deteriorate.

9. Film longitudinal tensile strength difference

cause of issue:

1 The temperature of the molten resin is too high, which causes the longitudinal tensile strength of the film to decrease;

2 The pulling speed is slow, and the longitudinal orientation of the film is insufficient, so that the tensile strength in the longitudinal direction is deteriorated;

3 The inflation ratio is too large, and the traction ratio is not matched, so that the transverse orientation and tensile strength of the film are improved, and the tensile strength in the longitudinal direction is deteriorated;

4 The film is cooled too fast.

Solution:

1 appropriately lowering the temperature of the molten resin;

2 appropriately increase the traction speed;

3 adjust the inflation ratio to match the traction ratio;

4 Properly reduce the cooling rate.

10. Film transverse tensile strength difference

cause of issue:

1 The pulling speed is too fast, and the difference between the inflation ratio is too large, so that the longitudinal direction is fibrillated, and the transverse strength is deteriorated;

2 The cooling rate of the cooling air ring is too slow.

Solution:

1 appropriately reduce the traction speed to match the inflation ratio;

2 increase the amount of wind ring air, so that the inflation film is cooled quickly, avoiding higher

The temperature is stretched and oriented in a high elastic state.

11. Bubble instability

cause of issue:

1 Extrusion temperature is too high, the fluidity of the molten resin is too large, the viscosity is too small, and fluctuations are easily generated;

2 The extrusion temperature is too low, and the discharge amount is small;

3 The air volume of the cooling air ring is unstable, and the bubble cooling is uneven;

4 was affected by the interference and influence of strong external airflow.

Solution:

1 adjust the extrusion temperature;

2 adjust the extrusion temperature;

3 Check the cooling air ring to ensure that the air supply volume around is uniform;

4 Prevent and reduce interference from outside airflow.

12. The surface of the film is rough and uneven

cause of issue:

1 The extrusion temperature is too low, and the resin is poorly plasticized;

2 extrusion speed is too fast.

Solution:

1Adjust the extrusion temperature setting and increase the extrusion temperature appropriately to ensure good plasticization of the resin;

2 Properly reduce the extrusion speed.

13. The film has odor

cause of issue:

1 The resin raw material itself has an odor;

2 The extrusion temperature of the molten resin is too high, causing the resin to decompose, thereby generating an odor;

3 The bubble cooling is insufficient, and the hot air in the bubble is not removed.

Solution:

1 replacement of resin raw materials;

2 adjust the extrusion temperature;

3 Improve the cooling efficiency of the cooling air ring to fully cool the bubble.