A masterbatch is only as good as its fit with the polymer it goes into. The pigment sets the colour, but the carrier decides whether that colour disperses evenly, whether the part keeps its strength and whether the batch feeds smoothly at the throat.
Match the carrier to the base polymer
The safest choice is a carrier of the same polymer family: polyethylene carriers for PE film and moulding, polypropylene for PP, PVC-compatible carriers for rigid and flexible PVC. Universal carriers are convenient when one batch must serve several polymers, but each new polymer should be confirmed by trial, because a carrier that is perfect in polystyrene can cause haze or weak weld lines in a polyolefin.
Melt flow and melting point
The carrier should melt at or slightly before the base polymer. A carrier that melts too late leaves streaks and specks; one that is far more fluid than the base can reduce melt strength in film blowing. For PVC, a fine, low-melting micro-granulate distributes early in the hot mixer or extruder, which is why it gives streak-free colour at low dosing and high line speed.
Pigment load and let-down
Higher pigment loads mean less carrier enters the part, which helps mechanical properties, but very high loads need excellent dispersion to avoid specks. Typical colour batches are used at 1 to 4 percent, white batches carry 50 to 75 percent titanium dioxide and black batches 30 to 50 percent carbon black.
Moisture and additives
Keep moisture at or below 0.1 percent for most processes, and dry hygroscopic carriers before use. If the part also needs UV protection, slip, antistatic or flame retardancy, combining colour and additives in one batch simplifies dosing; separate additive batches give more flexibility when one colour serves several end uses.
Checklist for a new masterbatch
- Base polymer, grade and melt flow
- Process: film, injection, blow moulding, pipe, profile or sheet
- Target dosing and the shade standard with tolerance
- End use: food contact, toys, outdoor exposure, pipe standards
- Additive functions needed in the same part
