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 · 10 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.
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