10 kg Marked Well, 1 Tonne Started to Blur

In November 2017 we received a complaint from a customer in Tianjin: the laser marking on our flame retardant ABS was not performing well.

The complaint was not unexpected. What was unexpected was the sequence behind it.

The customer told us the 10 kg sample we first supplied marked well.

We then produced a 400 kg trial batch. The customer tracked both the performance and the marking. Both were fine.

Then came 1 tonne, 3 tonnes, 5 tonnes. On 20 November the customer reported that the marking quality had deteriorated.

10 kg was fine. 400 kg was fine. 1 tonne was not.

Same formulation. Why does the result change with scale?

The investigation started with the laser marking powder

We checked the laser marking powder first.

The powder used for the first 400 kg was not from the same batch as the powder used afterwards. We verified the later batch on its own and found nothing wrong with it.

So we went further into the formulation details, and that is where the answer was.

We make the laser marking powder into a masterbatch first and then add it into the final formulation. The final addition rate was 0.0125% by weight.

According to the powder supplier, that rate was already close to the limit.

Close to the limit means no margin. Any variation in process and the powder does not disperse evenly. Poor dispersion means fuzzy characters.

The 10 kg sample was mixed by hand. The mixing state of a 400 kg trial and of a 1 tonne production run is different, and feed rate, mixing time and temperature all shift the dispersion. With the same formulation, dispersion at production scale is simply less uniform than at trial scale.

Corrective action: move the addition rate away from the limit

Once the cause was identified, the corrective action ran in three stages.

First, we produced laser marking masterbatch urgently and sent it to the customer, to be added on top of the existing rate so production could recover immediately.

Second, we optimised the process for the flame retardant ABS and continued production on the revised formulation.

Third, we produced colour boards with increased marking powder and compared the marking results side by side.

The permanent actions were two.

One, a full review of all system BOMs and process cards against each other to remove any remaining risk. The review found no other issues.

Two, a BOM change raising the laser marking masterbatch addition rate by 28%, confirmed by repeated trials.

We also increased the frequency of our own laser marking checks and started retaining samples after every BOM change.

Three conclusions worth keeping

First, alongside the fixed formulation, the production process is equally decisive for marking performance. A correct formulation does not mean every batch comes out the same.

Second, the marking powder addition rate should sit above the limit rate. The margin is what absorbs normal process variation. Working at the limit leaves nothing to absorb it.

Third, production and trial batches are not the same thing. A hand-mixed sample that marks well does not prove that a tonne will. Scale the batch up a hundredfold and mixing and dispersion stability become a different question.

This is now a principle we apply when designing laser marking grades: the formulation is designed for production conditions, not laboratory conditions.

For a laser marking grade recommendation, send the base colour, the wall thickness, the laser power and speed you are running, and we will come back with a proposed grade.

If you are already marking and the result is poor, send a photograph of the characters. From the image it is usually possible to tell whether the cause is insufficient energy, excessive energy, or uneven dispersion.

Reply with the grade name and we will send the complete catalogue.

Qingdao Yunsu Polymer Material Technology Co., Ltd.