TROUBLESHOOTING EXTRUSION COATING

     The following identification of problems, probable causes, and suggested corrections should be helpful to readers, but cannot be considered complete in any way. Extrusion coating is very much an art as well as a science, and no listing of advice can approach the value of experience and know-how in achieving and maintaining efficient economical extrusion coating practices.

 

ADHESION APPLESAUCE DRAW RESONANCE
EDGE TEAR GAUGE BANDS GELS
MOLTEN CURTAIN BREAKS ODOR OXIDATION
HEAT SEALABILITY SURGING VOIDS

 

Problem

CAUSE (REASON)

SUGGESTED CORRECTIONS


ADHESION
  A Melt temperature too low (polymer viscosity too high)

1 Increase temp. settings.

2 Check for heater and/or   controller malfunctions.

3 Increase back pressure.

  B Melt temp. too high (polymer viscosity too high or polymer thermally degraded

1 Decrease temp. settings.

2 Check for heater/controller malfunctions.

3 Decrease back pressure.

  C Inadequate oxidation

1 Increase air gap.

2 Lower line speed.

3 Increase flame or corona treatment.

  D Premature cooling

1 Decrease air gap.

2 Increase chill roll temp.

  E Chill roll tack

1 Decrease chill roll temp.

  F Non-optimum substrate surface

1 Pre-treat substrate.

2 Change substrate.

  G Additive effects

1 Confirm that proper type and level of additive are used.

APPLESAUCE   A Resin incompatibility

1 Check on resin compatibility (chemical and rheological).

2 Make sure previous resin is completely purged.

  B Temperature too high (degradation

1 Decrease temperature.

  C Temperature too low (increased viscosity)  
DRAW RESONANCE   A Draw ratio too high

1 (See Edge Tear).

  B Temperature too high

1 Decrease polymer temp.

2 Repair runaway heaters.

EDGE TEAR   A Draw ratio too high

1 Decrease die gap.

2 Increase coating weight

  B Die end temperature too low

1 Increase temperature of die ends.

  C Incorrect polymer temp.

1 Adjust temp. to optimum.



GAUGE BANDS
  A Unclean die

1 Clean die interior periodically.

2 Scrape the inside of die lips to dislodge foreign material.

  B Improperly adjusted die

1 Adjust die bolts

2 Measure die gap periodically.

  C Temperature variations

1 Repair heater malfunctions.

2 Keep adapter, transfer pipe, and die temps. close to the extruder melt temp.

  D Temperature too high

1 Lower temp. settings.

2 Repair malfunctioning heaters or controllers.

GELS   A Resin contamination

1 Keep extruder and storage areas clean

  B Incorrect melt temp.

1 Adjust to optimum.

  C Poor purging

1 Use proper purging techniques.

  D Poor mixing

1 Increase back pressure

2 Increase number or density of screen packs.

3 Assure compatibility of blends.

MOLTEN CURTAIN BREAKS   A Draw ratio too high

1 Decrease die gap.

2 Increase coating weight.

  B Incorrect melt temp.

1 Adjust to optimum.

ODOR   A Over-Oxidation

1 Decrease melt temp.

2 Decrease air gap.

OXIDATION   A Degradation

1 Decrease temperature.

2 Increase screw speed.

3 Clean non-streamlined areas often.

  B Poor purging

1 Use proper techniques, usually lower temp.

2 Do not stop extruder when still above 400? F.

3 Always purge out copolymer with a homopolymer before turning off extruder.

HEAT SEALABILITY   A Over-oxidation

1 Decrease melt temperature.

2 Decrease air gap.

3 Check corona treatment.

  B Contamination

1 Check on additives used.

2 Keep handling of sealant surface to minimum and keep stock in clean dry area.

SURGING   A Hopper bridging (improper feeding)

1 Reduce feed zone temp

  B Improper screw design

1 Use appropriately designed screw for the resin(s) employed.

VOIDS   A Moisture

1 Avoid abrupt temperature changes in product storage.
2 Check for leaks in resin handling system.
3 Protect hygroscopic resins from humidity.
4 Condensate in feed throat

  B Polymer degradation

1 Do not exceed recommended maximum melt temperatures.
2 Oxidation

  C Gels