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Polyamide extrusion

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Basic guidelines to facilitate extrusion of polyamide

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Polyamide extrusion

  1. 1. Polyamide extrusion Processing guidelines Ted Brink
  2. 2. Page  2
  3. 3. Page  3 Moisture
  4. 4. Page  4 How to deal with moisture • reliable resin manufacturers supply nylon dry and ready-to-use • avoid moisture absorption • use packaging size according to consumption • shield hopper from atmosphere • maximum allowable moisture content 0.1 %
  5. 5. Page  5 Too high moisture • too high moisture content results in: • bubbles/foaming of the melt • holes in the film • bubble collapses • hydrolytic breakdown
  6. 6. Page  6 Screws for polyamide extrusion General Purpose screws can be used, provided: • the barrel is not grooved (unless .....) • the heating capacity is sufficient • the compression ratio is < 4.0 • the L/D ratio is > 24 • barrier screws suitable
  7. 7. Page  7 Mixing or dispersing elements • mixing sections on standard 3-zone screws may be needed • dispersing antiblock agent • pigments • not needed for standard additives • mixing elements: • pineapple (distributive mixing) • pin (distributive mixing) • Maddock (dispersive mixing)
  8. 8. Page  8 Screen pack Function: • build-up pressure • filtration
  9. 9. Page  9 Extruder output PA6 extrusion 0 200 400 600 800 30 60 90 120 150 180 output[kg/hr] screw diameter [mm] • single screw • 3-zone • Tcil 250 C
  10. 10. Page  10 Thermal properties of PA6 0 50 100 150 200 250 300 processing range crystal growth melting point glass transition temperature temperature[°C]
  11. 11. Page  11 Communicate with the machine • listen to what the machine is telling you • watch energy demand of band heaters – shows where energy is needed – shows where no energy is needed • avoid adiabatic extrusion – the machine is in control, not you! – Tpol will show large variations
  12. 12. Page  12 Temperature settings • too low settings may result in too high polymer temperature • nylons with higher crystallinity require different approach
  13. 13. Page  13 Melt stability • polyamide is a condensation polymer • consequence for extrusion: • when dry: polymerization occurs • when wet: depolymerization occurs • reactivity depends on: • moisture content • residence time • temperature • end groups
  14. 14. Page  14 Miscelleneous Blown film: • BUR 1:1 – 1:3 • lay flat when film is stil warm to prevent wrinkles General: • die gap 1 – 1.2 mm Cast film: Chill roll temperature: • 20 – 40 C for optimum thermoforming behavior • 80 – 130 C for optimum dimensional stability • chill roll as close to the die to avoid neck-in
  15. 15. Page  15 Film post treatment • Corona treatment • Plasma treatment • Flame surface treatment • Purpose of these treatments: • increase surface energy so that inks “wet-out” • improve adhesion during lamination However, polyamide has intrinsically good printing and lamination performance and thus no real need for Corona treatment untreated film treated film
  16. 16. Page  16 Polyamide film properties • films are (near to) isotropic • films are transparent • high puncture resistance
  17. 17. Page  17 Influence of moisture on film properties • when dry: • very high oxygen barrier • high modulus • when conditioned • high oxygen barrier • increased flexibility • postcrystallization possible • dimensional fluctuations
  18. 18. Page  18 Coextrusion • polyamide mostly used in multilayer structures • polyamide function: • mechanical protection • barrier properties • tie resin required for adhesion to nonpolar polymers like PE and PP • coectruded polymers should rheologically match
  19. 19. Page  19 Applications Food packaging • cheese • meat • fish Non food • agricultural films • medical films • release films for smc
  20. 20. Page  20 Contact Ted Brink Email: ted.brink@extrusionist.com Internet: www.extrusionist.com Tel.: +31 651109899 More information
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Basic guidelines to facilitate extrusion of polyamide

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