Permanent antistatic TPU masterbatch: surface resistance without migration
Conventional antistatic additives migrate, bloom and stop working once they are gone. A polymer-type antistatic masterbatch builds a permanent conductive network in the matrix instead — 10^8 Ω/sq, stable, and 10–20% let-down.
What static actually ruins
Static is charge accumulating on a surface smaller than a centimetre and then discharging into whatever is nearby. For a polymer part that shows up in three ways.
- Surface contamination — a charged surface attracts dust, which degrades appearance and light transmission, and in a cleanroom degrades the cleanliness class itself.
- Processing interference — film and fibre wind onto rollers, printability falls and ink adhesion drops.
- End-use risk — ESD damage to semiconductor devices, spark ignition of flammable material, and contamination of parts that must stay clean.
Why conventional antistatic agents fail
The traditional route is a surfactant additive that migrates to the surface and holds a thin layer of moisture. It works at first, then stops: the additive is consumed, washed or wiped away, and the surface resistance climbs back to insulating. Humidity dependence is the second problem — in a dry environment there is no moisture layer to hold, and performance drops exactly where ESD protection matters most.
A migrating additive also contaminates what it touches. For medical, electronic and cleanroom applications that is disqualifying on its own.
The permanent route
A polymer-type antistatic system is compounded into the matrix and forms a conductive network through the material rather than on its surface. It does not depend on migration, so it does not deplete, and it does not depend on ambient moisture, so it keeps working in dry air.
In masterbatch form it is let down at 10%–20% into the base polymer, which keeps the base grade's mechanics intact while bringing surface resistance into the dissipative band.
Reading the surface-resistance ladder
Surface resistance is the specification that decides whether a material solves the problem or not. The bands are not arbitrary — each decade corresponds to a different physical behaviour.
| Surface resistance (Ω/sq) | Behaviour | What it is used for |
|---|---|---|
| Above 10^13 | Charge accumulates | Insulator — unusable where ESD is a risk |
| 10^12 – 10^13 | Very slow decay | Anti-dust only |
| 10^10 – 10^12 | Slow decay | General antistatic, explosion protection |
| 10^6 – 10^10 | Static dissipative | Protecting electronic components and circuits |
| Below 10^5 | Conductive | Grounded parts, conductive tooling |
Typical properties of the masterbatch
| Property | Test method | Typical value | Unit |
|---|---|---|---|
| Hardness | ASTM D2240 | 73 | Shore A |
| Density | ASTM D792 | 1.2 | g/cm³ |
| Tear strength | ASTM D624 | 62 | kN/m |
| Surface resistance | — | 1.00 × 10^8 | Ω/sq |
| Let-down ratio | — | 10 – 20 | % |
How those numbers were measured
The values are typical values on a 2 mm injection-moulded plaque. Before testing, every sample is conditioned for at least 48 hours at 23 °C and 50% relative humidity.
That conditioning step is not a formality. Surface resistance on a polymer is sensitive to moisture history, so a reading taken on a freshly moulded part is not comparable with a conditioned one. Any specification written between supplier and customer should state the conditioning regime alongside the resistance band, or the two sides will be measuring different things.
Applications
- Electronics — IC trays, carrier tape, packaging film, electronic assembly cleanroom curtains.
- Medical — surgical instrument housings, dialysis equipment components, medical tubing where static attracts particulate.
- Automotive — interior parts and fuel-system components where spark discharge is the design case.
- Construction and cleanroom — antistatic flooring, cleanroom wall panels, PVC-based antistatic products.
- Safety — containers and tools for handling flammable materials.
A note on scope
The masterbatch is a let-down product, not a catalogue grade: final surface resistance depends on the base polymer, the loading and the part geometry, so the 10^8 Ω/sq figure should be treated as a target to be confirmed on the actual compound.
For medical applications the biological status of the antistatic system has to be established separately from that of the base TPU — an additive that is acceptable in an IC tray is not automatically acceptable in a device that touches a patient.