Overview of Fluoropolymer Foam Technology

Wire New England ’07

WAI New England Chapter

October, 2007

Robert T. Young, DuPont Fluoroproducts

2

OutlineOutline

• Resin Structure and Properties

• General aspects of Foaming

• Equipment requirements for Foaming

• Resin, Construction & Processing Considerations

• Summary/Conclusion

3

Tefzel® ETFETefzel® ETFE -- CFCF22 -- CFCF22 -- CHCH22 -- CHCH22 -- nn-- 59% F59% F

Teflon® PTFETeflon® PTFE -- CFCF22 -- CFCF22 -- nn-- 76% F76% F

Teflon® FEPTeflon® FEP -- -- CFCF22 -- CFCF22 m CFm CF22 -- CFCF-- nn-- 76% F76% F

CFCF33

Teflon® PFATeflon® PFA -- -- CFCF22 -- CFCF22 m CFm CF22 -- CFCF-- nn-- 76% F76% F

OCOC33FF77

Tefzel® ETFETefzel® ETFE -- CFCF22 -- CFCF22 -- CHCH22 -- CHCH22 -- nn-- 59% F59% F

Teflon® PTFETeflon® PTFE -- CFCF22 -- CFCF22 -- nn-- 76% F76% F

Teflon® FEPTeflon® FEP -- -- CFCF22 -- CFCF22 m CFm CF22 -- CFCF-- nn-- 76% F76% F

CFCF33

Teflon® PFATeflon® PFA -- -- CFCF22 -- CFCF22 m CFm CF22 -- CFCF-- nn-- 76% F76% F

OCOC33FF77

Structure & Properties of Structure & Properties of FluoropolymersFluoropolymers

• PTFE discovered in the 1930s but could not be melt extruded

• Modifications to polymer architecture led to the development of melt processable fluoropolymers such as FEP, PFA, FEP, PVDF

• Ability to be melt extruded coupled with properties such as a low dielectric constant and low flammability has made materials such as FEP and PFA well suited for wire and cable applications

PropertyProperty PTFEPTFE FEPFEP ETFEETFE PFAPFA

Specific GravitySpecific Gravity 2.152.15 2.152.15 1.701.70 2.152.15

Melting Point (2nd),°CMelting Point (2nd),°C 327327 260260 270270 310310

Tensile Strength, MPaTensile Strength, MPa 2020 2020 4040 2828

Elongation, %Elongation, % 300300 300300 300300 300300

Flexural Modulus, MPa Flexural Modulus, MPa 560560 650650 1,1001,100 650650

Temperature Rating,°CTemperature Rating,°C 260260 200200 150150 260260

Dielectric ConstantDielectric Constant 2.12.1 2.12.1 2.62.6 2.12.1

Coefficient of FrictionCoefficient of Friction 0.10.1 0.20.2 0.40.4 0.20.2

CutCut--Through, kgThrough, kg 4.54.5 4.5 4.5 1818 4.54.5

Chemical ResistanceChemical Resistance ExcellentExcellent ExcellentExcellent Very goodVery good ExcellentExcellent

* Nominal values* Nominal values

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Foaming, Why do it?Foaming, Why do it?

- DIELECTRIC CONSTANT

- DISSIPATION FACTOR

- CAPACITANCE

- ATTENUATION

- RELATIVE VELOCITY

- WEIGHT

- WALL THICKNESS

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VOID CONTENT, %

DIE

LEC

TR

IC C

ON

ST

AN

T2.6

2.5

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.00 10 20 30 40 50 60 70 80 90 100

FEP/PFA

POLYETHYLENE

ETFE

DIELECTRIC CONSTANT DIELECTRIC CONSTANT VERSUS VOID CONTENTVERSUS VOID CONTENT

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Technology Implemented For FoamingTechnology Implemented For Foaming

1980

1985

1990

2000

Low PressureFreon ® Injection

Liquid Freon ®

Injection

High PressureNitrogen Injection

Low PressureNitrogen Injection

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• Polymer is melted and conveyed ( Extruder )

• Gas is introduced into melt, forms solution

(Injector and High Pressure Pump )

• Ratio of polymer to N2 controls final product void Content

• Polymer/N2 solution exits Crosshead under

pressure

• Gas comes out of solution, forming bubbles

• Nucleating agents assist bubble formation

• Polymer cools on wire, freezing in structure

Mechanisms and Equipment for Mechanisms and Equipment for Foaming Foaming FluoropolymersFluoropolymers

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Extruder ConfigurationExtruder Configuration

A traditional 3 to 4 stage screw is typically used

• Feed, Compression,Metering, and Mixing

• Typical compression ratio of around 3

A gentle mixing elements are recommended

• Low shear, divide & recombine elements beneficial in distributing the N2

Corrosion resistant materials of construction are needed

Extruder and screw design needs to be sized properly

• Too large (slow rpm) results in poor mixing and melting

• Too small (high rpm) can result in excessive shear and heat

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Flow versus Pressure for Injector with 0.118 mil Nozzle

y = 0.0145x

R2 = 0.9989

40

60

80

100

120

140

2000 3000 4000 5000 6000 7000 8000 9000 10000

Pressure (psig)

Flo

w (

cc/m

in)

Gas Injection and MeteringGas Injection and Metering

Example of Injector (Maillefer Extrusion)

Example of high pressure gas pump (Fine International Corporation)

• Injector needs to be sized to deliver therequired gas flow at the desired pressure

• Flow to extruder controlled by orifice size & gas pressure supplied to the injector

• For stability, desirable to run injector pressures 1.5X to 2X higher than the barrel pressure

Metering Orifice

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DieTip

WireFoaming

SlightMeltDraw

Melt Draw Extrusion Foamingfor Fluoropolymers

DieTip

WireFoaming

SlightMeltDraw

Melt Draw Extrusion Foamingfor Fluoropolymers

Profile Extrusion and DrawingProfile Extrusion and Drawing

• Ratio of the cross sectional areas of the annular tooling gap to that of the coating on the wire

• Lower DDR gives a more stable cone

• Higher DDR facilitates faster production rates

• DDR of 5:1 to 30:1 is typical

• Balance between the rates the outside and inside of the cone draw down

• R1 is die diameter divided by coated wire diameter

• R2 is tip diameter divided by bare wire diameter

• DRB = R1/R2

• DRB of 1.02 to 1.10 is typical

Drawdown Ratio (DDR)Draw Ratio Balance (DRB)

Optimum to have materialfoam once it is on the wire

Tooling calculations shouldbe based on the “pre-foamed”insulation diameter

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Increasing Shear Rate

Screw RPM

She

ar S

tres

s (M

Pa)

StickSlip

Die wallAdhesion

Slipping“Super Shear”

Melt Fracture

EXAMPLE OF FEP RHEOLOGICAL BEHAVIOR EXAMPLE OF FEP RHEOLOGICAL BEHAVIOR

Smooth Increasinglyrough

Smooth & Clear

Distorted extrudate

Draw Down

Temperature

Typical operating region for solid resins

Typical operating

region for foam

resins

Resin MFR

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Construction ConsiderationsConstruction Considerations

Twisted Pair

Spacer

Jacket

Cat 5e

Cat 6

10 Gig

Jacket Spacer

Twisted Pair

Spacer

Jacket

Cat 5e

Cat 6

10 Gig

Jacket Spacer

• Resin and processing requirements highly dependent on construction

• Thicker wall (> 20 mil), higher void content (> 45%) constructions typically utilize lower MFR (< 15) resins and lower draw down tooling(RG cable, etc.)

• Thinner wall (< 20 mil), lower void content (< 45%) often made with higher MFR resins (> 15) and higher draw down tooling (Cat 6, 10 Gig, etc.)

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Successful Foam = Good Return Loss/AdhesionSuccessful Foam = Good Return Loss/Adhesion

Return Loss measures the amount of signal that is l ost due to reflections along the length of the cable

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What is required for good Return Loss?What is required for good Return Loss?

Consistency, Consistency, Consistency !!!!!

- Small and uniform cell structure

- Consistent and good bond between the conductor & insulation (maintains spacing)

- Uniform material along the conductor(voids along conductor are detrimental)

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Processing & Formulation = PerformanceProcessing & Formulation = Performance

• Good return loss can be achieved by combining material and processing parameters

• Polymer and nucleant formulation are contributing factors to producing uniform cells and better adhesion to the conductor

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Variability in Diameter & Capacitance vs Nucleant P ackage

0.10%

0.15%

0.20%

0.25%

0.30%

0.35%

0.40%

0.45%

0.50%

0.55%

0.60%

Diameter Capacitance

CO

V %

(S

tand

ard

Dev

iatio

n/A

vera

ge)

Nucleant ANucleant B

Nucleant A

Nucleant B

Performance via FormulationPerformance via Formulation

• Nucleant type and loading can have an effect on processing and cell structure which impacts electrical performance

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Return Loss Adhesion CapacitanceCone Length

Wire Preheat TemperatureQuench Point

Processing Effects on Product AttributesProcessing Effects on Product Attributes

• Process variables typically used to control items such as diameter & capacitance can have large impact on performance of the cable

• Have to keep a good balance between finding a robust, stable process while maintaining desired electrical performance

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Alternative Methods for ProcessingAlternative Methods for Processing

Film / Foam / Skin

Film (Solid layer next to conductor)

• Provides void free uniform material next to the conductor• Serves to help improve return loss and adhesion

Skin (Solid layer on external Surface)

• Provide layer to help minimize blow through• Smoother surface for better contact for processes such

as shielding/braiding• Better processing control for items such as the cone

Foam / Skin

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Summary and ConclusionsSummary and Conclusions

• Foaming of fluoropolymer resins such as FEP/PFAwith gas injection provides a safe & economical way to produce plenum rated cables of reduced size with desirable electrical performance

• Implementation of foamed products being facilitated with improvements in material formulations and processing technology

Makes for exciting times in the Wire and Cable Indu stryMakes for exciting times in the Wire and Cable Indu stry