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Fluorinated Ethylene Propylene
Fluorocarbon Resin

TECHNICAL INFORMATION

Description:

Fluorinated Ethylene Propylene (FEP) fluorocarbon resin is a melt-processible fluorocarbon resin suitable for extrusion as a primary coating onto most gauge wires (AWG #12 and smaller) for twisted-pair constructions and for limited jacketing applications.

As shown on Table 1, this resin provides the electrical and mechanical properties needed for low - voltage applications. Fluorinated Ethylene Propylene has a melt flow rate of: 6.6 g/10 min. This permits a good combination of extrusion speed and stress crack resistance, making Fluorinated Ethylene Propylene the insulation of choice for most primary insulation that is more than 7 mils thick.

FEP possesses a balance of processing and performance properties which make it the preferred resin for many applications. Like all fluorocarbon resins, FEP offers an excellent combination of properties: chemical inertness, exceptional dielectric properties, heat resistance, toughness, flexibility, low coefficient of friction, nonstick characteristics, negligible moisture absorption, low flammability, performance at temperature extremes and weather resistance.

Applications:

FEP is used in many applications. One of the largest uses is in telecommunications/data cables where FEP not only provides excellent fire performance and physical properties but also superior electrical performance. In this role, it is ideal as an insulation for constructions meeting Article 725 and Article 800 of the National Electric Code (NEC) where FEP provides superior dielectric properties for rapid, clear signal transmission. Cables insulated with FEP have met the requirements oh Underwriter's Laboratory UL 910 Steiner Tunnel Test for installation in plenums without metal conduits.

FEP is not normally recommended as a jacket material, but it can be used as jacketing for small plenum cables that do not have a braided wire shielding.

Safe Handling:

Use of adequate ventilation system allows safe processing of FEP in extruders at high temperatures.

Packaging:

FEP is supplied as pellets and is available in 55 lb (24.9 kg) multi layer kraft bags with an integral polyethylene liner.

U.S. Freight Classification:

For rail shipments, FEP is classified as "Plastic, Synthetic, OTL, NOIBN;" for truck shipments as "Plastic Materials, Granules;"and for express shipments as "Plastic, Synthetic."

TABLE 1
Typical Properties of FEP Fluorocarbon Resin
Property
ASTM Method
Units
Value
Electrical
Dielectric Constant
D-1531
100 kHz (105 Hz)
-
2.06
1 MHz (106 HZ)
-
2.06
Dissipation Factor
D-1531
100 kHz (105 Hz)
-
0.0003
1 MHz (106 HZ)
-
0.0006
Dielectric Strength
D-149
10 mil Film
V/mil
2000
1/8 in Sheet
V/mil
510
Mechanical
Melt Flow Number
D-2116
g/10 min
6.6
Specific Gravity
D-762
-
2.15
Tensile Strength
D-1708
psi
MPa
4000
27
Elongation
D-1708
%
340
Thermal
Melting Point
DTA-E168
°C
°F
264
507

Processing Guidelines for Wire and Cable Use Extrusion Equipment:

FEP is fabricated using the same melt processing techniques as other thermoplastics.

Molten FEP resins are corrosive to many metals; therefore, special corrosion-resistant material must be used for all parts of extrusion equipment that comes in contact with the melt. Nickel-based alloys such as HASTELLOY®, INCONEL®, MONEL®, AND XALOY® are the materials of choice. Hardened electroless nickel plate can be used, but even small holes, chips or cracks in the plating can compromise its performance. Chrome-plated materials are not recommended. Corrosion is likely to occur if dead spots exist in the equipment, processing temperatures are too high or hold-up time is too long. In addition, resin degradation will accelerate corrosion.

A 1.5 to 2.5 inch (38 to 64 mm) extruder with a barrel length-to-diameter ratio of 20:1 - 30:1 is recommended for extruding FEP. Extruder Barrels should have 3 to 5 independently controlled heater zones with temperature controllers capable of accurate operation (±0.6 °C / ±1 °F) in the temperature range of 316 °C to 425 °C (600 °F to 800 °F). Heaters should be made of cast bronze or aluminum. Controllers with proportional-integral-derivatibe (PID) action are recommended.

A 3:1 compression ratio screw consisting of a relatively long feed zone, a 1 to 3 turn transition and a metering section that compromises approximately 1/4 of the length of the screw is recommended. The addition of a mixing section at the end of the screw can improve processibility.

A melt thermocouple and melt pressure probe should be installed in the adapter section of the extruder. To obtain an accurate measurement, the thermocouple should extend to the center line of the flow channel.

Degradation of the resin during processing greatly reduces the performance of FEP in stringent applications. Degradation is caused by excessively high melt temperatures, long residence time in the extruder, and/or excessive shear from the screw. In general, increases in the melt flow number (MFN) greater than 10% during extrusion should be avoided. This 10% rise in MFN will occur after only 5 minutes at 393 °C (740 °F) or approximately 45 minutes at 382 °C (720 °F), but it increases to only 5% after 60 minutes at 360 °C (680 °F). This indicates the importance of maintaining resin flow through the extruder while at operating temperature and shows why temperatures should be decreased if the extruder is down even for a short period of time.

Other processing conditions that can reduce the resin's performance include melt fracture, very low or uneven melt temperatures, and the presence of hydrocarbon or silicone oils which act as stress crack promoters.

Wire-Coating Techniques:

FEP is typically applied as a wire insulation using tubing techniques.Draw-down ratios (DDR) generally ranging from 50:1 to 200:1 are common, with higher DDRs usually allowing greater line speed. A draw-ratio balance (DRB) ranging from 0.9 to 1.1 is recommended.

A controlled vacuum is required at the rear of the crosshead to adjust the melt cone to the desired length. A melt cone that is too long results in excessive caliper variations while a melt cone that is too short result in excessive spark failures and cone breaks. Laboratory experience has shown that a cone length of 2.5 in to 3.0 in (64 to 76 mm) yields satisfactory results with a DRR of 156:1 and a DRB of 1.00. Control can be achieved at a shorter cone length if a higher DRB is used.

An electric wire preheater located as close to the crosshead as possible is recommended for preheating the wire. Although the amount of preheat will depend on the application, the preheater should be capable of heating the wire to 149 °C to 204 °C (300 °F to 400 °F) while operating at a typical line speed of 500 ft/min (152m/min).

Stationary pulleys should be located on both sides of the crosshead to reduce wire flutter. The wire should pass through the crosshead, without touching the crosshead or the extrusion tip. Sponges should not be used to reduce flutter downstream of the crosshead because they can produce insulation faults.

The coated wire should pass through a 1 to 5 ft (0.3 - 1.5 m) air gap followed by a warm-water quench at 38 °C to 66 °C (100 °F to 150 °F) to allow uniform cooling and prevent the formation of shrinkage voids in the insulation. The cooling is highly dependant on the thickness of the insulation.

Processing conditions depend on the equipment size and line speed. Tables 2 and 3 list the actual processing conditions for a 10-mil wall of FEP on a 24 AWG copper wire. Adjustments may be necessary for other equipment.

Color Concentrates:

FEP based on color concentrates are commercially available from several manufacturers. Only inorganic pigments should be used due to the high temperatures used to process FEP. Concentrate loading information is available from the manufacturer, and it will normally depend on the compositions of concentrate, wire size, insulation thickness, and intensity of color desired.

Band Marking:

Band marking inks for FEP are commercially available from several manufacturers. In-line band marking of FEP can be accomplished by positioning the band marking unit as close to the crosshead as possible and by using inks with high boiling solvents.

TABLE 2
Typical Temperature Profile for Extruding
FEP on AWG #24
Solid Copper Wire 1
Zone
°C
°F
Rear Zone 2
366
690
Rear Center 2
382
720
Center
388
730
Front Center
393
740
Front
396
745
Clamp
396
745
Adapter
396
745
Crosshead
396
745
Die Holder
416
780
Melt
393
740
1 Based on a 60 mm extruder with a 30:1 L/D; adjustments may be needed for other equipment.
2 For a smaller machine, it will be necessary to raise the temperature to ensure that the resin is completely melted before entry into the extruder's transition zone. A surging output at the idle could be caused by incomplete melting.

 

TABLE 3
Typical Operating Conditions for Extruding
FEP on AWG #24
Solid Copper Wire 1

Extruder Speed
rpm
8
Line Speed
ft/min
m/min
500
335
Wire Preheat
°C
°F
152
240
Pressure
MPa
psig
4.6
670
Die
in
mm
0.500
12.70
Tip
in
mm
0.250
6.35
DDR
-
156:1
DRB
-
1.00
1 Based on a 60 mm extruder with a 30:1 L/D; adjustments may be needed for other equipment.
 
   
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