The datasheet says surface resistivity in the antistatic range and everyone relaxes. Two years later the same boxes are protecting populated boards, nobody has measured anything since purchase, and the question of whether they still work is being decided by whether production has had static failures recently – which is the worst possible detection method.
Two different mechanisms
Antistatic polypropylene generally works one of two ways. Migrating additives are blended into the polymer and continuously bloom to the surface; they work well and they get consumed, washed off, or stop blooming after a couple of years. The other approach is a conductive coating or a filled compound.
Coatings give lower numbers initially and are far more vulnerable to abrasion and washing, because the functional layer is exactly the layer being cleaned. Filled compounds are stable but achieve their performance through loading that affects cost and sometimes physical properties. Ask which one you bought, because the maintenance answer differs completely. The definitions matter here, as set out in what surface resistivity means in practice.
What washing actually does
Every wash removes some migrating additive along with the soil. Hot water and aggressive detergent remove more. Dry wiping removes least. In practice that means crates washed weekly will decay measurably faster than the same crates wiped monthly, and the gap is large enough to matter over a service life.
Abrasion matters as much as chemistry. Boxes dragged over conveyor or stacked by machines lose surface material mechanically, which strips both coatings and additive-rich surface layers.
How to check for very little money
A handheld surface resistance meter with the standard two-probe electrode costs a modest amount and takes a few seconds per reading. Take readings at several points, including high-wear areas, on the same day every quarter, and record them.
You are looking for the trend, not a single value. A steady climb across a year tells you when to plan replacement. A sudden jump usually means somebody changed the cleaning product.
Environment changes the reading
Migrating additives depend on humidity to work. In a dry winter building, readings drift upward and sometimes cross the specification line without anything having changed permanently. Record humidity with the reading, or you will chase a phantom failure every January – and replace boxes you did not need to replace.
When to retire
Set an action level rather than waiting for out-of-specification results. If you intervene when readings are an order of magnitude inside the limit, you can plan purchases. Waiting until they fail means every failure is an emergency, and boards get moved in whatever is to hand.
Where we disagree with standard practice
Reapplying a topical antistatic spray restores surface readings and it is a legitimate stopgap. It is not a repair of the material, does not last, and can contaminate sensitive assembly processes. Use it to get through a week, not to extend a service life by a year.
The honest part
No permanent antistatic treatment exists for PP at a sensible price. Everything decays. Any supplier – us included – who quotes a resistivity figure without also telling you how long it survives your cleaning regime is giving you half an answer.
Storage between uses
How boxes are stored matters as much as how they are cleaned. Nested stacks of empty ESD boxes rub against each other in transit, which wears exactly the surface that carries the antistatic function. Separators or lower stack heights reduce this noticeably.
Keep them away from silicone, untreated paper dust and anything that leaves a transfer film, because a contaminated surface gives misleading readings and poor contact performance regardless of what the bulk material is doing. A covered store also stabilises humidity, which keeps your quarterly readings comparable and stops the January panic.
What we can do
We supply ESD corrugated boxes in both mechanisms and will tell you which one suits your cleaning regime. Send the wash temperature and detergent type and we will give you an expected service interval – with the caveat that you need your own readings to trust any number we give you.