INJECTION DEFECT ANALYSIS
Color Defects in Injection Molding and Masterbatch Solutions
Color defects in molded parts rarely have one cause; dosing, mixing, melt temperature, residence time, mold flow, and contamination from the previous run must be assessed together.
Color Masterbatch Technical Team · 2026-08-13 · 4 min
Most Common Color Errors
The shape of the color defect gives the first clue about the root cause. It should be noted whether the error is continuous throughout the part, only around the runner, in the initial cycles, or occurs as random points.
Flow and coalescence traces
The tone difference seen in the mold filling direction; may be related to pigment orientation, inadequate mixing, differential cooling or surface gloss. Color measurement should be done on the same surface and from the same angle.
Burnt tone and black spots
Excessive temperature, long residence time, dead zones or the previous color remaining in the machine can cause darkening and spots. Cleaning recording and separation of initial cycles speeds up diagnosis.
How to Separate Masterbatch and Process?
Trying to fix the problem by simply changing the masterbatch may hide the true root cause. Raw material lot, actual dosage and machine parameters are verified one by one by comparison with the approved production.
Controlled comparison
A small reference trial is made with the same masterbatch and raw materials. Then, by changing only one variable, such as temperature, back pressure, screw speed or dosage, the result is recorded.
Feeding and mixing
Volumetric dosator calibration, granule size difference and separation in the hopper may cause color fluctuation within the batch. Gravimetric recording or weighing control verifies the actual dosage.
How to Build a Reproducible Solution?
The permanent solution is not just to capture the good part; is to standardize the materials and process conditions that produce that part.
Store error instance
Good and faulty parts; Raw material and masterbatch lot should be stored with date, machine, mold compartment and cycle information. This record embodies the technical review.
Production standard
The approved formulation, tolerance, drying condition, cleaning step and initial waste limit are added to the work instruction. Changes are confirmed with a new sample.
Short Technical Answers
Why does the color fluctuate on the injection part?
Actual dosage variation, separation in the hopper, temperature and cycle fluctuation, raw material lot or insufficient mixing may cause color difference.
Is blackhead always caused by masterbatch?
No. Burnt material, dead zone, inadequate cleaning and previous production residue in the machine can also cause black spots.
Does the flow trace affect color measurement?
Yes. Flow direction and brightness difference may affect visual perception and device measurement. Comparisons should be made at the same location, angle and surface.
Share good and defective part samples, formulation and machine parameters; Let's plan a controlled error analysis.
Related guides
- MasterARM product page
- MasterMIC product page
- MasterKEM product page
- What Causes Color Variation in Plastics? Troubleshooting Guide
- Masterbatch Dosage Rate and Calculation Guide
- How to Select a Masterbatch Supplier: Sample and Quality Checklist
Sources
Investigating colour defects in injection moulding
Information to provide
Record polymer grade, regrind proportion, colour reference, wall thickness and dosage. Identify whether streaks, specks, colour variation or burn marks occur across the part or in specific areas. Follow the raw-material data sheet for drying requirements.
A controlled production trial
Check dosing consistency, contamination from the previous colour and mixing first. Trial one change at a time using the same mould and raw material; record temperature and residence time. Compare samples of equal thickness. Increasing dosage is not a universal fix; share samples and process records with the technical team if the defect persists.
Related technical guides
What should you record during a trial?
These checks help distinguish possible causes; they are not a diagnosis or an approval of product suitability. Change one variable at a time and keep records.
| Observation | Possible cause | Check | Record |
|---|---|---|---|
| Streaks or colour variation | Mixing, dosing or residue from the previous colour | Check feeding and cleanliness; compare samples of equal thickness. | Polymer grade, dosage, mould and wall thickness |
| Specks or burn marks | Contamination or effects of heat and residence time | Review raw-material and process records with the technical team. | Batch, temperature, residence time and defect location |
Keep a record of your own trial
Download a blank worksheet. It is not a test result or compliance document; complete it for your own sample and process.