ESD ABS vs ESD POM: choosing antistatic plastic for fixtures and handling

Antistatic sheet is one of those categories where two materials with the same printed surface resistivity behave completely differently in a production cell. ESD ABS and ESD POM both sit in the dissipative range, both are stocked in black, and both are machined into fixtures, trays, nests and guide rails. After a year on the line one of them is covered in fine dust and the other still looks new — and it is not always the same one.

What the resistivity number does and does not tell you

ESD plastics are usually specified between 10^6 and 10^9 ohms surface resistivity, which is the dissipative band: slow enough to avoid a discharge that damages a device, fast enough to bleed charge away before it accumulates. Conductive grades sit at 10^3 to 10^5 ohms. The number is a property of the compound and the filler loading, not of the polymer, so a 10^6 ohm ABS and a 10^6 ohm POM are electrically equivalent. Everything that decides the case happens elsewhere.

Wear debris is the hidden failure

In a cleanroom or a semiconductor line the enemy is not the discharge, it is the particle. ABS is amorphous and relatively soft; machined edges and sliding contacts shed fine debris that lands on the product. POM is semi-crystalline, harder, and has a low coefficient of friction, so a POM guide rail wears far more slowly against a moving part. Where the ESD part is a wear surface — rails, end stops, gripper jaws, chain guides — POM is usually the right answer and ABS is a false economy.

Solvents, cleaning agents and stress cracking

ABS is the weaker of the two chemically. Isopropyl alcohol is fine, but ketones, esters, chlorinated solvents and many label adhesives will attack it, and a machined ABS part carrying residual stress will craze along the tool marks. POM resists alcohols, fuels, oils and mild alkalis well, is attacked by strong acids, and is generally the safer choice in a plant that wipes fixtures down with solvent several times a shift.

Side-by-side

Where each one wins

ABS wins on housings, covers, carrier frames and anything large and thin. It is easier to machine without chipping, it takes inserts and bonded joints more readily, and it is the cheaper sheet. If the part does not slide against anything and is cleaned with IPA only, ABS does the job.

POM wins on anything that touches moving product: nests, rails, locating pins, gripper jaws, tray dividers. It holds tolerance better after machining, resists creep under a clamp load, and produces far less debris. The cost premium is small against the cost of a contaminated lot.

There is a third case worth naming: carbon-fibre filled grades reach the conductive band at 10^3 to 10^5 ohms and are much stiffer, but they are abrasive, they wear tooling, and the fibre dust is unwelcome in a cleanroom. Use them when the specification demands conductive rather than dissipative, not as a default upgrade.

Three questions that settle it

• Does the part slide, rub or clamp against product? If yes, ESD POM.
• Is the part cleaned with anything other than alcohol? If yes, ESD POM.
• Is it a large cover, housing or frame with no wear contact and IPA-only cleaning? ESD ABS is cheaper and easier to machine.

Questions we are asked most

Will the resistivity drift over time?

Carbon-loaded compounds are stable in service; the drift people see is usually surface contamination — release agents, tape residue, skin oils — sitting on top of the filler network. Wipe with IPA and re-measure before condemning the sheet.

Can I glue ESD ABS and ESD POM?

ABS bonds readily with solvent cements and structural acrylics. POM is notoriously difficult: it needs surface treatment or a mechanical joint. If the assembly is bonded, that alone can decide the material.

Do these grades need annealing after machining?

POM benefits from an anneal when the part is thick or must hold a tight tolerance at temperature. ABS rarely needs it unless the part is heavily machined from thick sheet.