How to Run a Masterbatch Trial Before You Switch Supplier

Most masterbatch trials prove nothing. Not because the product was bad, but because the trial was run with three variables moving at once, on a day the line was already struggling, and nobody wrote down what a pass would look like before they started.

A trial that proves something is not much more work. Here is the protocol.

Before the trial: define the pass

Write down, before any material is ordered, what result would make you switch. If you cannot write it, you are not ready to trial.

A usable pass definition covers:

• Colour: the tolerance, formula, illuminant and geometry. For example ΔE*00 ≤ 1.5, D65/10°, specular included, measured on moulded plaques not on pellets.
• Dispersion: the filter pressure value you will accept, or the screen-pack life you need.
• Process: no increase in cycle time, no increase in melt temperature, no additional screen changes.
• Function, if additive: surface resistivity at your real ambient humidity, property retention after a stated kLy, fog performance under your storage conditions.
• Appearance: no visible specks, streaks or gels at your normal inspection standard.

Send this to the supplier. A good one will tell you in advance whether it is achievable, which saves everybody a trial.

Change one thing

The single most common reason a trial is uninterpretable: the new masterbatch arrives, and it gets run on a different resin lot, at a different regrind percentage, after a tooling change, on the night shift.

Control everything you can:

• Same base resin grade and lot if possible
• Same regrind percentage, from the same source
• Same machine, same tool, same operator if you can arrange it
• Same process settings — do not let anyone “optimise” mid-trial
• Same ambient conditions where they matter

If something has to change, change it in a separate run.

Run the incumbent alongside

This is the step most often skipped, and it is what turns opinion into evidence.

Run your current masterbatch immediately before or after the trial material, under identical conditions, and measure both. Now you have a controlled comparison rather than a measurement against a remembered standard.

It also protects you from a trap: sometimes the trial material measures slightly worse than your specification and so does your incumbent. That tells you the specification is wrong, not the supplier.

Size the trial properly

Too small and you are measuring start-up transients. Too large and you are committing before you know.

A sensible trial runs long enough to get past purge and reach steady state, then produces enough parts to sample across the run rather than at one point. For most processes this means a meaningful fraction of a normal production shift, not a handful of shots.

Sample across the run, not just at the start. Early samples carry residue from the previous material. Late samples tell you whether anything drifts as the barrel heats and the hopper empties.

What to measure, and how

Colour

Measure moulded plaques or actual parts, never pellets. Pellet colour correlates poorly with part colour.

Measure at several points across the run. Record the conditions. If the supplier measured too, compare conditions before comparing numbers — a disagreement about ΔE is usually a disagreement about geometry.

Check under every illuminant the part will be seen under, not just the one you matched under.

Dispersion

Filter pressure value is the quantitative check. On your own line, screen-pack pressure rise over the run is the practical one — watch it and record it rather than relying on an impression.

For black, and for pipe applications under IS 4984, a microscope dispersion rating may be required. See carbon black content in HDPE pipe.

Process behaviour

Record melt temperature, back pressure, cycle time and any screen change during the run. A masterbatch that needs five degrees more melt to run is costing you something, even if the parts look right.

Function, for additive grades

Test the function, not the presence. See additive masterbatch for what each one needs:

• UV packages: accelerated weathering against a kLy target, measuring property retention
• Antistatic: surface resistivity at your actual ambient humidity, after the conditioning period
• Anti-fog: hot and cold fog, matching your real storage conditions
• Slip and anti-block: coefficient of friction and seal strength together

Appearance

Inspect against your normal standard, with your normal lighting, by the people who normally inspect. A trial judged by the technical team under lab light is not a trial of what your inspectors will accept.

Test more than one batch

This is the part that actually matters and the part almost everyone skips.

Any supplier can make one good batch. What you are buying is consistency. A trial of a single batch tells you the supplier can make the product once.

Ask for material from at least three separate production batches, ideally produced weeks apart, and measure the variation between them. That variation — not the absolute value of batch one — is what you will live with.

If a supplier is reluctant to provide material from separate batches, that is itself information.

Common mistakes that waste a trial

• No written pass criteria. The result becomes a matter of opinion, and the loudest opinion wins.
• Changing resin lot at the same time. Now you cannot attribute anything.
• No incumbent control run. You are comparing against memory.
• Measuring pellets. They do not predict part colour.
• Sampling only at the start. You measure the previous material’s residue.
• One batch only. You prove capability, not consistency.
• Running it on your worst day. A trial on a line that is already fighting a problem will blame the new material.
• Letting the process be optimised mid-run. Then you cannot compare anything.

After the trial

Whatever the result, write it down with the conditions. A trial record that says “ΔE*00 1.2 average across six samples, D65/10° SCI, filter pressure value X, no screen change, no process adjustment, three batches within 0.4 ΔE of each other” is a document you can act on in six months.

“It was fine” is not.

If you are switching, do it deliberately — see switching masterbatch suppliers without stopping the line.

Talk to us

We would rather be trialled properly than win on a sample that looked right.

We will tell you in advance whether your pass criteria are achievable, we will supply material from separate production batches so you can measure consistency rather than capability, and we will match in your resin so the trial is testing the product rather than a resin difference.

Send us your polymer and grade, your process, your colour standard and your pass criteria and we will propose a trial — including what to measure and what a pass should look like. Related: colour masterbatches, white masterbatches, black masterbatches, additive masterbatches, about us.

Frequently asked questions

How do I run a masterbatch trial properly?

Write the pass criteria before you start, control everything except the masterbatch, run your incumbent alongside under identical conditions, sample across the run rather than at one point, measure rather than judge visually, and test material from at least three separate production batches.

How much material do I need for a masterbatch trial?

Enough to get past purge and reach steady state, then enough to sample across the run rather than at a single point. For most processes that means a meaningful part of a normal shift rather than a handful of shots.

Should I measure colour on pellets or on parts?

On moulded plaques or actual parts. Pellet colour correlates poorly with finished part colour, because thickness, surface texture and processing history all affect the result.

Why should I run my existing masterbatch alongside the trial material?

It converts opinion into a controlled comparison. It also protects you from discovering that the trial material misses your specification while your incumbent misses it too, which means the specification is wrong rather than the supplier.

How many batches should I test before switching masterbatch supplier?

At least three separate production batches, ideally made weeks apart. One batch proves the supplier can make the product once. The variation between batches is what you will actually live with.

What should I measure in a masterbatch trial?

Colour on parts under every illuminant the part will be seen under, dispersion by filter pressure value and screen-pack behaviour, process impact including melt temperature and cycle time, appearance against your normal inspection standard, and for additive grades the function itself rather than its presence.

What makes a masterbatch trial invalid?

Changing the resin lot or regrind percentage at the same time, having no written pass criteria, no control run, sampling only at the start, testing a single batch, or allowing the process to be adjusted mid-run.

What should I do with the trial results afterwards?

Record the numbers with the conditions they were measured under – tolerance achieved, filter pressure value, process impact and batch-to-batch variation. A documented trial record is usable six months later; an impression that it went well is not.