Bubble stability in blown film

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Transcript of Bubble stability in blown film

Blown film & bubble stability Ted Brink

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WHATdetermines bubble stability?Bubble stability in blown film

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Overview of discussion topicsblown filmbubble coolingdie constructionmelt viscositymelt strengthtemperature influence

Bubble stability in blown film

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frost linebelow frost line:melt phaseabove frost line:solid phasethe bubble is:pulled up by nip rollssupported by melt strengthBubble stability in blown film

Page nr.Bubble stabilityBubble stability is a combination of:integrity of the molten filmmelt strengthmelt viscosityshear rateintegrity of the solid filmthicknessmaterial (stiffness)

melt phasesolid phase

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Integrity of the solid filmFilm characteristics:film thicknessmaterials used (stiffness, crystallization rate, Mw or MFI)

Machine characteristics:outputdie gapcooling efficiencybubble height

Bubble stability in blown film

Page nr.Polymer rheologyhigh zero shear viscosity positive for bubble stabilityfor multilayer extrusionflow simulation is useful toolmost layers consist of more than one component

Bubble stability in blown film

Page nr.Melt strengthmelt strength determinesbubble stabilitystretching behaviour

melt strength = resistance to drawingmelt strength is related to entanglementsMwMw/Mnbranching

Bubble stability in blown film

Page nr.Melt strengthMelt strength is influenced by:molecular weightmolecular weight distributionchain entanglementsmolecular branches

determined byresin supplier

Bubble stability in blown film

Page nr.Melt viscosityMelt viscosity is influenced by:molecular weightpolydispersity MWDpolymer temperaturebubble coolingshear rate

determined byresin supplier

determined byfilm producer

Bubble stability in blown film

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Melt strength and viscosity are influenced by:molecular weightmolecular weight distributionchain entanglementsmolecular branchespolymer temperaturebubble coolingshear rate

determined byresin supplier

determined byfilm producer

Bubble stability in blown film

Page nr.Extrusion temperature - 1A low polymer temperature:improves bubble stabilityreduces thermal polymer breakdown

But:increases shear risk of uncontrolled polymer temperaturepolymer temperature influenced by output

Bubble stability in blown film

Page nr.Extrusion temperature - 2Common practice:flat temperature profile on the extruder barrel

Why?adequate for low shear 3-zone screwsoperation simplicityreduce chance for mistakes

Bubble stability in blown film

Page nr.Example extrusion temperature control for PA6flat temperature profilereversed temperature profilepoor control of polymer temperaturegood control of polymer temperature

Bubble stability in blown film

Page nr.Bubble coolingexternal bubble coolingchilled airinternal bubble cooling (IBC)

Bubble stability in blown film

Page nr.Pancake dies versus spiral diesPancake diestemperature isolation of the layersnylon at 230 250 C, EVOH at 175 205 Crelative long residence timeSpiral diesshort residence times

Bubble stability in blown film

Page nr.Measurement of melt strengthGttfert Rheotens

oscillatory rheometer

Bubble stability in blown film

Page nr.SummaryImprovement of bubble stability can be realised by:high melt viscosity of the polymer in the bubblehigh Mwbranched polymerlow polymer temperatureefficient bubble coolinglower frost line

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Contact

Ted BrinkEmail: ted.brink@extrusionist.comInternet: www.extrusionist.comTel.: +31 651109899

Skype: ted.brink

Bubble stability in blown film

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