Masterbatch dosage guidelines exist because colour and additive failures almost never trace back to the pigment itself. They trace back to how much masterbatch was dosed, how uniformly it mixed and whether the carrier was compatible with the base resin. The central number is the let-down ratio, the share of masterbatch blended into natural polymer at the machine. Get that number, the dosing accuracy and the dispersion right, and shade holds from the first shot to the ten-thousandth. This guide covers the ratios, the math and the controls that keep colour drift out of production.
Masterbatch Dosage Guidelines by Type
Start from the supplier technical data sheet, which is calibrated to the pigment or additive loading in that specific masterbatch. Typical starting points by family:
| Masterbatch type | Typical let-down ratio | Notes |
|---|---|---|
| Colour, opaque shades | 2-4% | Depends on shade depth and pigment strength |
| Colour, transparent or translucent | 3% and above | Higher dosing evens out distribution in clear polymers |
| White, titanium dioxide | 3-8% | Opacity targets in thin walls drive the upper end |
| Black | 1-3% | High-tint carbon black allows low dosing |
| Additive, UV, slip, antistatic | 1-5% | Set by the active level the finished part needs |
| Filler, calcium carbonate, talc | 10-40% | Loaded for stiffness and cost, not colour |
The Math Behind the Let-Down Ratio
Two formulas cover nearly every case. For a target let-down ratio, masterbatch required equals batch weight multiplied by the LDR, so a 100 kg batch at 3% takes 3 kg of masterbatch. For a target final pigment level, addition rate equals the target pigment percentage divided by the masterbatch pigment percentage, times 100. A 40% pigment masterbatch used to hit a 2% final loading therefore doses at 5%. Masterbatch pigment loading itself runs 20 to 50%, with 25 to 40% the practical sweet spot, because above roughly 50% dispersion quality collapses and agglomerates surface as specks on the finished part.
Dosing and Mixing Controls
Color masterbatch dosage accuracy decides shade consistency. Gravimetric loss-in-weight feeders hold tight control at low ratios, while volumetric feeders suffice above roughly 2% on stable, free-flowing pellets. Pre-blend masterbatch with natural resin in a tumble mixer for 5 to 8 minutes rather than dumping granules straight into the hopper throat, and verify dosing with a scale check every shift. In the press, back pressure of 10 to 20 bar and a screw with an L/D of at least 20:1 plus a dedicated mixing section break up agglomerates, while total residence time should stay between 2 and 5 minutes to avoid pigment degradation.
Compatibility, QC and Common Failures
Carrier compatibility comes first: a PE-carrier masterbatch runs fine in PP, but PET or PA carriers need matched drying and higher melt temperatures. Keep melt-flow-rate variance within about 30% and match pigment heat stability to the barrel temperature plus a 10 to 20 C margin, since a yellow rated to 200 C will char in a 280 C PP run. For quality control, measure total colour difference with a spectrophotometer, where a delta E below 2.0 is generally acceptable and below 1.0 for critical matched parts, with reputable suppliers holding batch-to-batch loading within plus or minus 0.5%. Streaks point to poor dispersion or worn screws, silver streaks to moisture in resin or masterbatch, and shade drift to dosing error or barrel overheating.
Buyer Checklist for Additive Masterbatch Programs
- Get the recommended let-down ratio and pigment loading in writing on the technical data sheet
- Confirm additive masterbatch dosage delivers the active level the part needs, not just a colour target
- Specify gravimetric dosing for low-ratio and transparent programs
- Run a trial batch and spectrophotometer check before scaling production
- Store masterbatch sealed in cool, dry conditions to prevent moisture pick-up
Additive selection interacts with material performance covered in our antistatic plastic material guide, and the plastic datasheet guide explains which numbers to demand. Masterbatch grades are listed in the plastic materials hub, and manufacturing partners appear in the company directory.
