What is PTFE K25?
PTFE K25 consists of a PTFE matrix (polytetrafluoroethylene) with 25 percent by weight of carbon or graphite filler and is the most widely used, market-standard carbon/graphite PTFE grade. PTFE is a semi-crystalline fluoropolymer that is not melt-flowable and, like virgin PTFE, is therefore only machined, not welded. The high carbon/graphite content significantly stiffens the PTFE matrix, raises wear and compressive resistance to the maximum of the range, and makes the material electrically conductive – a clear difference from virgin PTFE, which is otherwise an excellent insulator. The colour is consistently black.
At this filler level, a continuous conductive network forms in the compound (percolation), so K25 is reliably antistatic or electrically dissipative – unlike the lower-filled PTFE K15, where conductivity is not yet reliable enough for ESD requirements. Compared with glass-fibre-filled grades such as PTFE GF15 and PTFE GF25, K25 has the advantage that carbon/graphite barely affects chemical resistance – resistance to hydrofluoric acid is largely retained – and is significantly less abrasive to soft counter-surfaces (e.g. bronze, aluminium) than glass fibre; glass-fibre compounds, in turn, offer higher compressive strength and dimensional stability but remain electrically insulating.
Electrically, K25 is reliably conductive/antistatic (volume resistivity 10³–10⁴ Ω·cm) – dielectric strength drops significantly as a result, compared with virgin PTFE or glass-fibre-filled grades. Chemically, K25 is near-universally resistant, including largely resistant to hydrofluoric acid; limits exist with fluorine and molten alkali metals.
Typical applications include heavily loaded plain bearings and slide strips, ESD/antistatic components in semiconductor and electronics manufacturing, seals and piston rings requiring minimal cold flow, and chemically loaded sliding and sealing parts up to 260 °C, including hydrofluoric acid contact. Typical industries are sealing technology, chemical process and plant engineering, pump and valve technology, compressor and drive technology, and semiconductor and electronics manufacturing (ESD).
Technical Data
| Property | Value | Test Standard |
|---|---|---|
| Physical Properties | ||
| Density | 2.10 g/cm³ | ISO 1183 |
| Water absorption | < 0.05 % | ISO 62 |
| Color | black | – |
| Mechanical Properties | ||
| Tensile strength | ≥ 13 MPa | ISO 527 |
| Elongation at break | ≥ 100 % | ISO 527 |
| Hardness | 62–67 Shore D | ISO 868 |
| Ball indentation hardness | ≥ 30 MPa | ISO 2039-1 |
| Coefficient of friction (vs. steel) | ~ 0.13 | DIN 53375 |
| Thermal Properties | ||
| Service temperature | -200 to +260 °C | – |
| Coefficient of linear expansion (25–100 °C) | ≈ 9.5 · 10⁻⁵/K | DIN 52612 |
| Thermal conductivity | ≈ 0.65 W/(m·K) | DIN 52612 |
| Electrical Properties | ||
| Dielectric strength | ~ 2.8 kV/mm | IEC 60243-1 |
| Volume resistivity | ~ 10³ … 10⁴ Ω·cm | IEC 60093 |
| Fire Behaviour | ||
| Flammability | V-0 (non-flammable) | UL 94 |
PTFE K25 in detail
1What is PTFE K25?+
PTFE K25 is the standard grade of carbon/graphite-filled PTFE compounds: a PTFE (polytetrafluoroethylene) filled with 25 % carbon/graphite. The high filler content provides the highest wear and compressive resistance and the lowest friction within the carbon/graphite PTFE range, and reliably makes the material electrically conductive, while chemical resistance remains almost unchanged compared with virgin PTFE.
2How does Liedtke machine PTFE K25?+
PTFE K25 machines well – turning, milling, drilling and sawing all give clean results. Because the carbon/graphite dust is electrically conductive, we consistently ensure dust extraction and avoid deposits in the machine and plant area; overheating is avoided throughout, since PTFE is not meltable or weldable.
3When should I choose PTFE K25?+
PTFE K25 is worthwhile when maximum wear resistance, lowest friction and reliable electrical dissipation come together:
- Heavily loaded plain bearings and slide strips
- ESD/antistatic components in semiconductor and electronics manufacturing
- Seals and piston rings requiring minimal cold flow
- Chemically loaded sliding and sealing parts up to 260 °C, including hydrofluoric acid contact
- Components where lower abrasiveness to the counter-surface is needed compared with glass-fibre compounds
4What determines the price of a PTFE K25 part?+
PTFE materials are among the higher-priced engineering plastics; carbon/graphite-filled standard grades such as K25 are in the range of virgin PTFE or slightly below. The component price is mainly determined by the semi-finished form and dimensions, material utilisation, machining effort and batch size. We are happy to provide binding prices on request based on your drawing.
5When is PTFE K25 not the right choice?+
Where electrical insulation is required, virgin PTFE or PTFE GF25 is the right choice, since K25's high carbon/graphite content makes it electrically conductive. For the highest requirements on elongation and toughness, K15 or virgin PTFE is better suited, and for unambiguous food contact without evidence, virgin/FDA-compliant PTFE is the better option.
6Advantages and disadvantages of PTFE K25+
An honest assessment:
- Advantage: Highest wear and compressive resistance in the carbon/graphite PTFE range
- Advantage: Very low creep (cold flow) under sustained load
- Advantage: Lowest friction coefficient, self-lubricating
- Advantage: Reliably electrically conductive/antistatic
- Advantage: Near-universal chemical resistance including hydrofluoric acid retained
- Disadvantage: Lower elongation/toughness than virgin PTFE or K15
- Disadvantage: Electrically conductive, unsuitable where insulation is required
- Disadvantage: Filled grade, food contact only with evidence
- Disadvantage: Not meltable/weldable (machining only)
- Disadvantage: Higher price than standard plastics
Typical Properties
- Highest wear and compressive resistance in the carbon/graphite PTFE range
- Very low creep (cold flow)
- -200 to +260 °C, non-flammable (UL 94 V-0)
- Near-universal chemical resistance, including hydrofluoric acid
- Lowest friction coefficient, self-lubricating
- Electrically conductive / antistatic
- Colour black
- Machining only (not weldable)
Typical Industries
- Sealing technology
- Chemical process and plant engineering
- Pump and valve technology
- Compressor and drive technology
- Mechanical engineering (plain bearings)
- Semiconductor and electronics manufacturing (ESD)
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