Marking plastics is a chemistry problem the moulder solved months earlier
Contrast depends on additives in the resin. By the time a part reaches the marking cell, the achievable result was already fixed at the compounding stage.
A marking engineer handed a bag of plastic parts and asked to produce a legible black code is working within limits set long before, by whoever specified the resin. Polymers do not mark by virtue of being polymers; they mark because of what is in them.
The mechanisms available
Carbonisation. Heat chars the polymer, producing dark marks on light material. Works well on some resins, produces a rough, sometimes foamed surface on others.
Foaming. Gas bubbles below the surface scatter light and produce a light mark on dark material. Useful for light-on-dark contrast, but the raised surface is a problem where cleanability matters.
Additive activation. Pigments designed to change colour under laser exposure produce high contrast with minimal surface disruption. This is the mechanism most industrial plastic marking now relies on.
Coating removal. Marking through a painted or plated layer to reveal the substrate, used extensively in backlit automotive and appliance controls.
Why additives dominate
Laser-markable additives, typically antimony or bismuth based, allow a resin that marks poorly to mark cleanly and consistently. They are added at compounding, at a loading of a fraction of a per cent.
Which means the decision belongs to material selection, not to manufacturing engineering. A part specified without a markable additive may be physically impossible to mark to the required contrast, regardless of the equipment.
The recurring project failure
The common pattern is a marking cell specified and purchased against sample parts, followed by a resin change for cost or supply reasons, followed by marking that no longer meets specification. The resin change looked like a purchasing decision; it was also a marking decision.
The practical fix
Manufacturers who avoid this write markability into the material specification and include a marking check in resin qualification. It costs almost nothing at that stage and removes an entire category of production problem — and it puts the decision with the people who can actually make it.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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