Why Your Colour Keeps Drifting Between Batches // Geiger Handling UK Blog

Last week, the colour was spot on. This week, it’s slightly off. Nothing has changed on the machine and the masterbatch is the same one. Yet the parts don’t quite match. In this blog, Geiger Handling UK discusses colour drift, and how it is one of the most common quality complaints in injection moulding. Here are the usual causes, and where to look first.

Colour is affected by several things at once. Dosing accuracy, material condition, processing temperature, and residence time all play a part. A small change in any one of them can shift the final shade, often by an amount that’s hard to see until two parts sit side by side.

That’s why colour problems tend to be blamed on the masterbatch first. In Geiger’s experience, the masterbatch is rarely the real culprit.

Common Causes Seen on Site

1. Dosing Inaccuracy
   This is the most frequent cause. If the amount of colourant added varies, even slightly, the colour will vary with it. Worn dosing screws, a feeder that’s drifted out of calibration, or masterbatch that bridges in the hopper can all cause the dose to wander over a long run.
2. Poor Mixing
   Colourant and base material need to blend evenly before they reach the screw. If they separate on the way, you get streaking or patchy colour. Material of different pellet sizes is particularly prone to this, since the smaller pellets settle out of the mix.
3. Inconsistent Base Material
   If the base resin isn’t consistent, the colour won’t be either. Moisture is a common offender. A dryer that isn’t hitting spec can change how the material processes, and that can shift the shade. See Geiger’s article on common causes of inconsistent moulded parts for more on this.
4. Regrind Variation
   Regrind carries the colour of its previous life. If the regrind ratio changes, or the regrind comes from a slightly different colour batch, the final colour moves with it. Keeping regrind traceable matters as much for colour as it does for contamination.
5. Processing Temperature and Residence Time
   Some pigments change shade when they’re overheated or held in the barrel for too long. If cycle times stretch, or the barrel runs hotter than planned, the colour can shift even though the dosing hasn’t changed.

How to Track It Down

Work through the likely causes in order, starting with the simplest checks:

• Check the dosing rate against the set point, not just whether the doser is running
• Look for bridging or blockages in the masterbatch hopper
• Confirm the base material is within moisture spec
• Check the regrind ratio and where the regrind came from
• Compare barrel temperatures and cycle time against a known good batch

Keeping Colour Consistent

The most reliable fix is accurate, repeatable dosing. A well-specified doser, kept calibrated, removes the biggest single source of colour variation. Geiger’s range of colour dosers is chosen to suit your material, throughput and colour change frequency.

It also helps to log dosing rates and regrind ratios against each batch. When colour does drift, a record makes it much quicker to find out why.

Get in Touch

If colour consistency has become a problem on your line, Geiger Handling UK is happy to talk it through. Sometimes it’s a quick calibration check. Sometimes it’s worth looking at the dosing equipment itself.

Read more news from Geiger Handling UK.

Geiger Handling UK
01782 630555
Website
Email