Common Troubleshooting in Film-Blowing Processes

Low yield

z The output of the extrusion production line has not reached the expected level.

z Possible solutions

– Increase the amount of air in the air loop

– Reduce back pressure in the extruder

• Replace the dirty filter or use a filter with larger mesh openings.

• Increase the die gap

• Use a larger-sized mouthpiece

– Eliminate water cooling of the screw ( If using )

– Install air-cooling equipment or an in-mold cooling system

– Select different resin grades

Melt fracture ( Sharkskin )

z The rough film surface is caused by excessive shear.

z Possible solutions

– Increase the die gap

– Increase the extrusion melt temperature

– Increase the temperature of the last heating zone ( Heated die lip )

– Use processing aids (PPA)

– Use a resin with a higher melt index

– Blending 5-10% LDPE

– Reduced yield

z Membrane vesicle movement is primarily driven by changes in membrane thickness and surface-related factors.

z Possible solutions

– Reduce the extrudate melt temperature

– Use cooling air

– Install a foam stabilization device ,  Check the excessive drag effect of the stabilizing device.

– Check whether the air ring is blocked.

– Lower the height of the cooling line

– Replace the wind ring

– Reduce BUR Or use a larger mouthpiece.

– Join 10-20% LDPE

– Reduced yield

Wide-range thickness variation

z Excessive variations in film thickness can affect both the appearance of the film roll and the mechanical properties of the film.

z Possible solutions

– Check the die gap and clean the die head.

– Inspect the wind ring

• Adjust the air ring

• Check for obstructions

• Check for uneven airflow and air leaks in the supply lines.

• Suitable die size

– Check whether the molten resin flows evenly into the die.

– Inspection of screw designs used in resin processing

Effects caused by improper die adjustment

-  Improper placement of the die center can result in noticeable thickness variations.

Contamination of the air ring leads to variations in film thickness.

-  Contaminated air rings can cause uneven airflow, leading to significant variations in film thickness.

by Tipped Membrane thickness variation caused by the air ring

- Tipped The air ring can cause the height of the freeze line ( FLH ) non-uniformity, thereby leading to variations in membrane thickness.

Insufficient thinning

z The produced film did not meet the expected thickness.

z Possible solutions

– Reduce the die gap ( If the pressure permits )

– Adjust the extruder’s process parameters to ensure a more uniform flow of molten resin into the die.

– Check for impurities in the resin

– Switch to a resin with a higher melt index.

The film has poor transparency.

z For terminal applications, the film is either too opaque or not transparent enough.

z Possible solutions

– Increase BUR

– Reduce the height of the freezing line

– Use cooling air

– Reduce the die gap

– Blending 5-20% LDPE

– Reduce the dosage of the opening agent

– Use a lower-density resin

– Improved wind ring design

The Influence of the Die Lip (Die Defect?) on Thin Films

-  The die lip line can significantly reduce the film’s toughness.

The Influence of Die Line (Defect?) on the Film

-  The die lip line can also cause thinning of the film along the length of the web.

Gel, fish eyes, and bubbles in the film

z The poor visual quality of the film is caused by defects within the film.

z Possible measures to prevent gel formation and corns

– Check for impurities in the resin ( Exogenous particles, such as wood dust and metal shavings )

– Check if the temperature is too high – Causes resin degradation

– Check whether the temperature is too low – Causes incomplete resin melting.

– Replace the filter or filter cartridge

– Replace with a resin that offers superior antioxidant performance

– Clean the die head

– Eliminate dead spots in the system (where molten resin flow is zero or very slow)

z Possible solutions for preventing bubbles

– Use dry resin

z Film wrinkling can affect both the winding process and the film’s appearance.

z Possible solutions

– Eliminate thickness variations

• Non-uniform thickness can cause the film to wind unevenly onto the reel.

– Adjust the winding tension

• Both excessively high and excessively low winding tension can cause the film to wrinkle.

– Adjust the content of slip agents

• Increase the amount of slip agent to minimize film adhesion.

– Check the machine settings

• Improper setting of the nip rollers and take-up reel can cause wrinkling of the film.

Membrane adhesion

z Film adhesion to the nip rollers can lead to winding difficulties and issues in bag‑making production.

z Possible solutions

– Reduce the film temperature -  Overheated films are prone to sticking together.

• Reduce the extrusion melt temperature

• Increase the air volume inside the air ring

• Increase cooling air and/or the internal cooling system of the bubble film

• Add an additional cooling air ring above the freeze line.

• Increase the height of the nip rollers

• Reduce the speed of the machine production line

– Reduce nip pressure

– Use resins with a high content of release agents.

Printing issue

z The ink adhesion of the film is poor.

z Possible solutions

– Regarding corona treatment

• Perform corona treatment while the film is still warm; the film is more receptive to corona treatment when it has just passed through the nip rollers.

Easy to process, with minimal migration of slip agents.

• Reduce the power of the corona treatment unit to achieve higher…? dyne level

• Reduce the gap between the electrode and the thin film

• Check the uniformity of the clearance

• Check the electrode length - Is it the same as the film width?

– Use resins with lower levels of slip agents

• Excessive slip agents can reduce the ink’s adhesion.

Heat-sealing issues

z The thermal sealing performance of the film is poor.

z May resolve

– Reduce the extrusion melt temperature

• Excessively high melt temperatures can cause resin oxidation at the die lip, thereby degrading heat-seal performance.

– Reduce the degree of corona treatment applied to the film

• Excessive corona treatment or back-side treatment can degrade heat-sealing performance.

– Select resin – Low slip agent content, low density, and high copolymer content.

• An excessively high concentration of slip agent can degrade heat-sealing performance.

• Lower-density resins can enhance heat-sealing performance.

• High copolymer content ( Such as VA) Can improve heat-sealing performance.

Summary

z Resins encounter numerous issues during use.

z Most problems have solutions.

z The proposed solution may be effective for certain resin grades, but it may not necessarily be applicable to others.

Grade

z When addressing extrusion issues, accurate production records are extremely helpful.

z When troubleshooting, change only one parameter at a time to determine its effect.

z When dealing with processing issues, please contact the resin supplier for assistance.