Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Anti-Static PTFE Tapes

Among the myriad properties of PTFE that make it such a sought-after material, electrical resistance rates as one of the more popular. Because of its extraordinary dielectric strength and high breakdown voltage, PTFE is an invaluable addition in heavy electrical applications. As such, the following products are used across industries:

1. Skived PTFE tapes for heavy insulation 

2. Expanded PTFE (ePTFE) Tapes for cable wrapping

3. PTFE Radomes

4. PTFE transducer covers

5. PTFE insulation blocks

6. PTFE battery separators

These are but a few products that are commonly used. We often find that applications where electrical discharge is likely to be high benefit from a component made from PTFE to ensure that the equipment remains safe and does not leak current, causing harm.

Anti-static PTFE

The downside to the extreme insulative properties of PTFE lie in the build-up of static charge. Most applications do not find the build-up of static electricity to affect their process. However, certain assemblies – especially those where the equipment is being used in environments where flammability is high – require the charge to dissipate through the insulation so that sparks or static bursts do not occur. In such a situation, pure PTFE can cause problems, as it is such a strong insulator, that it does not allow the static charge to run through it.

To mitigate this problem, anti-static PTFE materials can be made, which employ conductive materials such as carbon to give mild conductive properties to the PTFE and allow it to discharge static build-ups through the carbon mixed into it.

Anti-static PTFE Tapes

Increasingly, applications that require PTFE tapes have started using anti-static tapes in areas where static build up can be an issue. However, most applications are very specific about the resistivity of the tape. Too much resistivity and you risk static build up; too little and you end up with a material that is too conductive to insulate effectively.

The base property of PTFE gives a surface resistivity of 1014 ?. For most conductive applications, this value needs to be reduced to 104 ?. In order to achieve this, the base filler of carbon needs to be adjusted. A lot of this final property depends on both the base property of the virgin PTFE (different grades will vary from the base value mentioned above) and the conductive properties of the carbon additive itself. Various types of carbon will offer different levels of reduction in surface resistivity, implying the percentage of filler needs to be adjusted accordingly.

Another complication that arises due to the addition of carbon is that there can be a physical discharge of materials from the surface of the PTFE. Because PTFE and carbon are merely combined as a mixture, there is the likelihood that fine particles can come loose from the surface of the PTFE. For many high-purity applications, this can be a showstopper. Hence the quantity of the conductive filler needs to be minimized, while also allowing the conductive properties to be met. One material that has emerged as effective in this regard is Vulcan. While standard grades of conductive carbon need to be mixed to the extent of 10-15% into the PTFE (85% PTFE, 15% Carbon), with Vulcan, the same level of conductivity can be achieved with as little as 1-2%. However, as Vulcan is expensive, its incorporation is restricted to applications where there is a stringent need for no particle discharge to happen.

Electrical properties of pure virgin PTFE 

General properties

Density

ISO 1183

2,16

g/cm³

Transparency

 

Opaque

 

Mechanical properties

Stress at yield

ISO 527

10

MPa

Tensile strength

ISO 527

20-25

MPa

Elongation at break

ISO 527

350

%

Tensile modulus (Flexural Modulus)

ISO 527

420

MPa

Flexural strength @ 3.5% deflection

ISO 178

14

MPa

Ball pressure hardness

ISO 2039-1

28

MPa

The standard for ball pressure hardness

 

H358 / 30

 

Hardness Shore (A/D) or Rockwell (R/L/M)

ISO 868, ISO 2039-2

D55

-

Izod notched impact strength 23 °C

ISO 180/4A

185

J/m

Friction against steel without lubrication

 

<0.1

-

Abrasion relative to the pressure

 

420

(µm/km)/MPa

Electrical properties

Dielectric constant 50 Hz

IEC 60250

2,1

-

Dielectric constant 1 MHz

IEC 60250

2,1

-

Dissipation factor 50 Hz

IEC 60250

0,5

10-Apr

Dissipation factor 1 MHz

IEC 60250

0,7

10-Apr

Dielectric strength

IEC 60243-1

7.5-24

kV/mm

Thickness for electric strength

 

3

mm

Volume Resistivity

IEC 60093

1.00E+14

? · m

Surface resistivity

IEC 60093

1.00E+14

?

Creep Resistance (Comparative Tracking Index)

IEC 60112

600

-

Thermal properties

Thermal conductance

ISO 22007

0,24

W/K m

Specific heat

IEC 1006

0,96

J/g K

Linear thermal expansion along/cross to direction of flow

ISO 11359

130-200

10-6/K

Melting point

ISO 11357

327

°C

Heat distortion temperature A

ISO 75 HDT/A (1,8 MPa)

50

°C

Heat distortion temperature B

ISO 75 HDT/B (0,45 MPa)

121

°C

Short time use temperature

 

300

°C

Continuous use temperature

 

260

°C

Minimal use temperature

 

-200

°C

Other properties

Humidity absorption at 23°C/50%

ISO 62

<0,1

%

Water absorption

ISO 62

<0,1

%

Flammability UL 94

IEC 60695-11-10

V-0

-

Limiting oxygen index

ISO 4589

95

%



 

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