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Cast versus blown film
Ted Brink
polyamide-based
Page  2
Contents
• film requirements
• polyamide characteristics
• blown versus cast film technology
• conclusions
cast v...
Page  3
Main applications PA-based films
cast versus blown film
Page  4
Food packaging - film requirements
• oxygen barrier
• moisture barrier
• grease and fat resistant
• shrink perfor...
Page  5
Main reasons to use polyamide
O2
mechanical strength barrier properties
cast versus blown film
Page  6
Polyamide properties
PA-type
Melting point
[°C]
H2O permeability
[cc/m2/atm/day]
O2 permeability
[cc/m2/atm/day]
...
Page  7
film production
cast versus blown film
Page  8
In spite of significant differences, both
technologies are used for similar applications
blown cast
cast versus b...
Page  9
cast film
cast versus blown film
Page  10
1. Plasticising unit
2. Die
3. Casting station
4. Winder
5. Automation system
Cast film line
cast versus blown f...
Page  11
Cast film basics
cast versus blown film
Page  12
Chill roll cooling
• efficient cooling
- temperature controlled water or oil
• chill roll surface structure
- hi...
Page  13
Chill roll temperature
• 20 – 40 °C for optimum thermoforming
• > 80 °C for optimum dimensional stability
• unif...
Page  14
blown film
cast versus blown film
Page  15 cast versus blown film
Page  16
Bubble cooling
• cooling medium: air
• cooling technologies
- external bubble cooling
- internal bubble cooling
...
Page  17
External bubble cooling
cooling from the outside
• commonly ambient air
cast versus blown film
Page  18
Internal bubble cooling (IBC)
IBC cools the bubble from the inside
• cool air injected (5 – 15 °C)
• warm air re...
Page  19
cast ↔ blown
cast versus blown film
Page  20
Blown versus cast film – polymer viscosity
• blown film:
- requires melt strength → high viscosity
• cast film:
...
Page  21
Blown versus cast film – cooling efficiency
• cooling medium blown film: air
- air not very efficient cooling me...
Page  22
Blown versus cast film – film morphology
• cooling rate determines morphology
- slow cooling → large crystals
- ...
Page  23
Blown versus cast film – film transparency
• transparency related to morphology
- slow cooling → large crystals ...
Page  24
Blown versus cast film – film stiffness
• stiffness related to morphology
- slow cooling → higher crystallinity ...
Page  25
Blown versus cast film – thermoforming
• cast films perform better than blown films
- lower crystallinity → easi...
Page  26
Blown versus cast film – curling
• curling may occur in nonsymmetrical films
• nonsymmetrical films have differe...
Page  27
Blown versus cast film – orientation
• difference in MD and TD stretching determines orientation
• cast film:
- ...
Page  28
Blown versus cast film – process flexibility
• cast film:
- die has fixed width
- neck-in
- side trim
• blown fi...
Page  29
Blown versus cast film – gauge uniformity
• cast film:
- ± 2 % independent on film thickness
• blown film:
- ± 1...
Page  30
Blown versus cast film – waste
• cast film:
- start-up ad shut-down waste
- change-over waste
- waste due to sid...
Page  31
Blown versus cast film – costs
• cast film:
- floor space needed
- higher investment costs
• blown film:
- heigh...
Page  32
Blown versus cast film – PA6 versus PA6.66
• cast film:
- only PA6 is used
• blown film:
- PA6.66 used more than...
Page  33
Cast versus blown film - overview
Polymer related:
• required viscosity
• morphology
• transparency
• stiffness
...
Page  34
Cast versus blown film – overview contd
Property Cast Blown
Cooling efficiency +++ +
Viscosity required Medium/l...
Page  35
Cast versus blown film - summary
• process:
- cast film: higher output
- cast film: better gauge control
- blown...
Page  36
More information and contact
Ted Brink
Email: ted.brink@extrusionist.com
Internet: www.extrusionist.com
Tel.: +3...
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Cast versus blown film

Main differences between cast and blown film with respect to process and film characteristics

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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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