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Blown film & bubble stability
Ted Brink
Page  2
WHAT
determines
bubble stability?
Bubble stability in blown film
Page  3 Bubble stability in blown film
Overview of discussion topics
• blown film
• bubble cooling
• die construction
• m...
Page  4
frost line
below frost line:
melt phase
above frost line:
solid phase
the bubble is:
• pulled up by nip rolls
• s...
Page  5 Bubble stability in blown film
Bubble stability
Bubble stability is a combination of:
• integrity of the molten f...
Page  6 Bubble stability in blown film
Integrity of the solid film
Film characteristics:
• film thickness
• materials use...
Page  7 Bubble stability in blown film
Polymer rheology
• high zero shear viscosity positive for bubble stability
• for m...
Page  8 Bubble stability in blown film
Melt strength
• melt strength determines
- bubble stability
- stretching behaviour...
Page  9 Bubble stability in blown film
Melt strength
Melt strength is influenced by:
• molecular weight
• molecular weigh...
Page  10 Bubble stability in blown film
Melt viscosity
Melt viscosity is influenced by:
• molecular weight
• polydispersi...
Page  11 Bubble stability in blown film
Melt strength and viscosity are influenced by:
• molecular weight
• molecular wei...
Page  12 Bubble stability in blown film
Extrusion temperature - 1
A low polymer temperature:
• improves bubble stability
...
Page  13 Bubble stability in blown film
Extrusion temperature - 2
Common practice:
• flat temperature profile on the extr...
Page  14 Bubble stability in blown film
Example extrusion temperature control for PA6
230
250
270
290
1 2 3 4 Tpol
temper...
Page  15 Bubble stability in blown film
Bubble cooling
• external bubble cooling
- chilled air
• internal bubble cooling ...
Page  16 Bubble stability in blown film
Pancake dies versus spiral dies
Pancake dies
• temperature isolation of the layer...
Page  17 Bubble stability in blown film
Measurement of melt strength
• Göttfert Rheotens
• oscillatory rheometer
Page  18 Bubble stability in blown film
Summary
Improvement of bubble stability can be realised by:
• high melt viscosity...
Page  19
Contact
Ted Brink
Email: ted.brink@extrusionist.com
Internet: www.extrusionist.com
Tel.: +31 651109899
Skype: te...
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Bubble stability in blown film

  1. 1. Blown film & bubble stability Ted Brink
  2. 2. Page  2 WHAT determines bubble stability? Bubble stability in blown film
  3. 3. Page  3 Bubble stability in blown film Overview of discussion topics • blown film • bubble cooling • die construction • melt viscosity • melt strength • temperature influence
  4. 4. Page  4 frost line below frost line: melt phase above frost line: solid phase the bubble is: • pulled up by nip rolls • supported by melt strength Bubble stability in blown film
  5. 5. Page  5 Bubble stability in blown film Bubble stability Bubble stability is a combination of: • integrity of the molten film - melt strength - melt viscosity - shear rate • integrity of the solid film - thickness - material (stiffness) melt phase solid phase
  6. 6. Page  6 Bubble stability in blown film Integrity of the solid film Film characteristics: • film thickness • materials used (stiffness, crystallization rate, Mw or MFI) Machine characteristics: • output • die gap • cooling efficiency • bubble height
  7. 7. Page  7 Bubble stability in blown film Polymer rheology • high zero shear viscosity positive for bubble stability • for multilayer extrusion - flow simulation is useful tool - most layers consist of more than one component
  8. 8. Page  8 Bubble stability in blown film Melt strength • melt strength determines - bubble stability - stretching behaviour • melt strength = resistance to drawing • melt strength is related to entanglements - Mw - Mw/Mn - branching
  9. 9. Page  9 Bubble stability in blown film Melt strength Melt strength is influenced by: • molecular weight • molecular weight distribution • chain entanglements • molecular branches determined by resin supplier
  10. 10. Page  10 Bubble stability in blown film Melt viscosity Melt viscosity is influenced by: • molecular weight • polydispersity MWD • polymer temperature • bubble cooling • shear rate determined by resin supplier determined by film producer
  11. 11. Page  11 Bubble stability in blown film Melt strength and viscosity are influenced by: • molecular weight • molecular weight distribution • chain entanglements • molecular branches • polymer temperature • bubble cooling • shear rate determined by resin supplier determined by film producer
  12. 12. Page  12 Bubble stability in blown film Extrusion temperature - 1 A low polymer temperature: • improves bubble stability • reduces thermal polymer breakdown But: • increases shear - risk of uncontrolled polymer temperature - polymer temperature influenced by output
  13. 13. Page  13 Bubble stability in blown film Extrusion temperature - 2 Common practice: • flat temperature profile on the extruder barrel Why? • adequate for low shear 3-zone screws • operation simplicity • reduce chance for mistakes
  14. 14. Page  14 Bubble stability in blown film Example extrusion temperature control for PA6 230 250 270 290 1 2 3 4 Tpol temperature[°C] barrel zone set actual 230 250 270 290 1 2 3 4 5 temperature[°C] barrel zone set actual flat temperature profile reversed temperature profile poor control of polymer temperature good control of polymer temperature
  15. 15. Page  15 Bubble stability in blown film Bubble cooling • external bubble cooling - chilled air • internal bubble cooling (IBC)
  16. 16. Page  16 Bubble stability in blown film Pancake dies versus spiral dies Pancake dies • temperature isolation of the layers - nylon at 230 – 250 °C, EVOH at 175 – 205 °C • relative long residence time Spiral dies • short residence times
  17. 17. Page  17 Bubble stability in blown film Measurement of melt strength • Göttfert Rheotens • oscillatory rheometer
  18. 18. Page  18 Bubble stability in blown film Summary Improvement of bubble stability can be realised by: • high melt viscosity of the polymer in the bubble - high Mw - branched polymer - low polymer temperature - efficient bubble cooling - lower frost line
  19. 19. Page  19 Contact Ted Brink Email: ted.brink@extrusionist.com Internet: www.extrusionist.com Tel.: +31 651109899 Skype: ted.brink Bubble stability in blown film
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Understanding bubble stability in blown film extrusion

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