Short answer
A colorant is not inert. It carries moisture, carrier and pigment that can interact with surfactant and catalysts. Moisture above about 0.2 % adds blowing water, an incompatible carrier upsets the silicone surfactant, and some pigments adsorb amine catalyst. Test any new colorant at its working dose against a carrier-only blank before scaling up.
Likely causes
Moisture in the colorant
Water reacts with isocyanate to make CO₂, raising gas, heat and lowering density.
Carrier incompatible with the surfactant
Leads to coarse, uneven cells or splits.
Pigment adsorbing catalyst
Notably some carbon black grades and fine inorganics, giving slower cream or gel time.
Overdosing
Every extra part of colorant multiplies the above effects.
How to diagnose it
- Run the same formulation with a carrier-only blank in place of the colorant.
- Karl Fischer moisture test on the colorant.
- Compare cream, gel and rise times with and without colour.
How to fix it
- Keep dosing within the recommended range for the grade.
- Re-trim catalyst after a colour change.
- Ask for a lower-moisture or system-matched grade.
How to stop it coming back
- Trial every new shade on your own system before scale-up.
- Check moisture content on the certificate of analysis. Chemie PU colorants typically run below 0.2 %.
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.
