Short answer
Specks are undispersed pigment agglomerates. Streaks and marbling are incomplete mixing of colorant into polyol. Check the colorant fineness of grind first, then the mixing and filtration on your machine, then colour changeover.
Likely causes
Coarse or agglomerated pigment
Poor dispersion or a batch that has hard-packed in storage.
Sediment pulled from the drum bottom
Unagitated stock delivers sediment at the end of the drum.
Too little mixing energy
Low-pressure mixing heads and day tanks without agitation.
Cross-contamination at colour change
Residual colour left in lines, filters and mixing heads.
Very low dosing
At a fraction of a part per 100 polyol the colorant may not blend evenly without pre-dilution.
How to diagnose it
- Grind gauge reading on the colorant.
- Glass drawdown to see specks directly.
- Cut the part: specks local to one spot or throughout?
- Review changeover and flushing procedure.
How to fix it
- Fit an in-line filter sized to the grind of your colorant.
- Stir or recirculate before use.
- Flush lines between colours.
- Pre-blend colorant into a portion of polyol for very low dosing.
- Reject and return any batch that fails its grind specification.
How to stop it coming back
- Incoming grind-gauge check on every batch.
- Dedicated lines and filters per colour family where practical.
Where this problem appears most
Send us your batch number, PU system and a photo of the defect and our technical team will help you trace the cause. Ask a technical question.
