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Cast versus blown film

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Cast versus blown film

  1. 1. Cast versus blown film Ted Brink polyamide-based
  2. 2. Page  2 Contents • film requirements • polyamide characteristics • blown versus cast film technology • conclusions cast versus blown film
  3. 3. Page  3 Main applications PA-based films cast versus blown film
  4. 4. Page  4 Food packaging - film requirements • oxygen barrier • moisture barrier • grease and fat resistant • shrink performance • puncture resistance • sealability • printability • transparency cast versus blown film
  5. 5. Page  5 Main reasons to use polyamide O2 mechanical strength barrier properties cast versus blown film
  6. 6. Page  6 Polyamide properties PA-type Melting point [°C] H2O permeability [cc/m2/atm/day] O2 permeability [cc/m2/atm/day] PA66 255 8 12 PA6 220 15 12 PA6.12 215 5 45 PA6.66 195 16 14 PA11 190 4 120 PA12 180 5 190 cast versus blown film
  7. 7. Page  7 film production cast versus blown film
  8. 8. Page  8 In spite of significant differences, both technologies are used for similar applications blown cast cast versus blown film
  9. 9. Page  9 cast film cast versus blown film
  10. 10. Page  10 1. Plasticising unit 2. Die 3. Casting station 4. Winder 5. Automation system Cast film line cast versus blown film
  11. 11. Page  11 Cast film basics cast versus blown film
  12. 12. Page  12 Chill roll cooling • efficient cooling - temperature controlled water or oil • chill roll surface structure - high gloss or embossed - influences quenching rate and film surface cast versus blown film
  13. 13. Page  13 Chill roll temperature • 20 – 40 °C for optimum thermoforming • > 80 °C for optimum dimensional stability • uniform temperature gradient across the roll - prevent morphological differences cast versus blown film
  14. 14. Page  14 blown film cast versus blown film
  15. 15. Page  15 cast versus blown film
  16. 16. Page  16 Bubble cooling • cooling medium: air • cooling technologies - external bubble cooling - internal bubble cooling • cooling influences: - output - film morphology ambient air or chilled air cast versus blown film
  17. 17. Page  17 External bubble cooling cooling from the outside • commonly ambient air cast versus blown film
  18. 18. Page  18 Internal bubble cooling (IBC) IBC cools the bubble from the inside • cool air injected (5 – 15 °C) • warm air removed (± 75 °C) • increased output cast versus blown film
  19. 19. Page  19 cast ↔ blown cast versus blown film
  20. 20. Page  20 Blown versus cast film – polymer viscosity • blown film: - requires melt strength → high viscosity • cast film: - less critical → medium to even low viscosity cast versus blown film
  21. 21. Page  21 Blown versus cast film – cooling efficiency • cooling medium blown film: air - air not very efficient cooling medium - outer bubble cooling - inner bubble cooling • cooling medium cast film: chill roll - cooling by water or oil - chill roll temperature between 25 and 125 °C cooling efficiency determines output cast versus blown film
  22. 22. Page  22 Blown versus cast film – film morphology • cooling rate determines morphology - slow cooling → large crystals - fast cooling → smaller crystals (crystals frozen-in) - high quenching rate → film remains (almost) amorphous cast versus blown film
  23. 23. Page  23 Blown versus cast film – film transparency • transparency related to morphology - slow cooling → large crystals → more haze - fast cooling → crystals less time to grow → higher transparency - very fast cooling → low crystallinity → highest transparency films with low crystallinity may show postcrystallization cast versus blown film
  24. 24. Page  24 Blown versus cast film – film stiffness • stiffness related to morphology - slow cooling → higher crystallinity → higher stiffness - fast cooling → low crystallinity → lower stiffness films with low crystallinity may show postcrystallization cast versus blown film
  25. 25. Page  25 Blown versus cast film – thermoforming • cast films perform better than blown films - lower crystallinity → easier drawing at lower stress film morphology determines thermoforming cast versus blown film
  26. 26. Page  26 Blown versus cast film – curling • curling may occur in nonsymmetrical films • nonsymmetrical films have different polymers • different polymers have different crystallization rate A layer A and B liquid B layer B crystallizes layer A follows A B layer A crystallizes layer B cannot follow B A cause for curling cast versus blown film
  27. 27. Page  27 Blown versus cast film – orientation • difference in MD and TD stretching determines orientation • cast film: - fixed width - uniaxial drawdown • blown film: - more balanced MD – TD orientation - tools: BUR and DDR cast versus blown film
  28. 28. Page  28 Blown versus cast film – process flexibility • cast film: - die has fixed width - neck-in - side trim • blown film: - adjustable bubble size cast versus blown film
  29. 29. Page  29 Blown versus cast film – gauge uniformity • cast film: - ± 2 % independent on film thickness • blown film: - ± 10 % for thin films (< 20 µm) - ± 5 % for thicker films (> 20 µm) cast versus blown film
  30. 30. Page  30 Blown versus cast film – waste • cast film: - start-up ad shut-down waste - change-over waste - waste due to side trims • blown film: - start-up ad shut-down waste - change-over waste waste: • cast film: 5 – 8 % • blown film: < 5 % cast versus blown film
  31. 31. Page  31 Blown versus cast film – costs • cast film: - floor space needed - higher investment costs • blown film: - height needed - lower investment cost cast film requires higher investment than blown film cast versus blown film
  32. 32. Page  32 Blown versus cast film – PA6 versus PA6.66 • cast film: - only PA6 is used • blown film: - PA6.66 used more than PA6 - PA6.66 more transparent than PA6 - PA6.66 shows less curling than PA6 - PA6 blended with PA6I/6T cast film: PA6 blown film: PA6.66 cast versus blown film
  33. 33. Page  33 Cast versus blown film - overview Polymer related: • required viscosity • morphology • transparency • stiffness • thermoform performance • curling Machine related: • cooling efficiency • process flexibility • gauge uniformity • orientation • waste • costs some grey areas cast versus blown film
  34. 34. Page  34 Cast versus blown film – overview contd Property Cast Blown Cooling efficiency +++ + Viscosity required Medium/low High Transparency +++ + Thermoforming performance +++ + Curling in non-symmetrical films Less More Film orientation More Less Trim/scrap More Less Gauge variation Good Medium cast versus blown film
  35. 35. Page  35 Cast versus blown film - summary • process: - cast film: higher output - cast film: better gauge control - blown film: less floor space and investment • films: - morphology difference  film crystallinity  crystal size - optical properties - thermoforming due to cooling rate cast versus blown film
  36. 36. Page  36 More information and contact Ted Brink Email: ted.brink@extrusionist.com Internet: www.extrusionist.com Tel.: +31 651109899 Skype: ted.brink cast versus blown film

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