Direct Answer: A colour masterbatch is a concentrated formulation of organic or inorganic pigments encapsulated into a specific polymer carrier resin during melt compounding. It allows plastic converters to add precise, mess-free, and homogeneously dispersed colour to virgin resin during extrusion or injection moulding.
1. Composition of a Masterbatch
A high-performance colour masterbatch contains three vital components:
- Pigments / Colorants: Organic pigments (for bright chromatic hues) or inorganic pigments (such as metal oxides for superior thermal and UV resistance).
- Carrier Resin: A compatible base polymer (such as LDPE, LLDPE, HDPE, PP, or PS) with a melt flow index (MFI) formulated to match or exceed the host resin.
- Dispersing Agents & Additives: Low-molecular-weight waxes and processing aids that wet the pigment particles, break agglomerates, and prevent re-flocculation during extrusion.
2. Why Not Use Raw Pigment Powder?
Directly introducing dry pigment powder into conversion machinery causes dusting, equipment contamination, uneven shade streaks, and inconsistent let-down ratios. Masterbatches pelletize the concentrated colorant, ensuring safe handling, precise dosing via gravimetric or volumetric feeders, and complete thermal homogeneity.
3. The Let-Down Ratio (LDR)
The Let-Down Ratio (LDR) is the percentage of masterbatch blended into the virgin polymer resin, typically ranging from 1% to 5% depending on wall thickness, pigment opacity, and final shade requirements.