CaCO3 filler masterbatch addition rate by process: film, injection, pipe, woven sacks
Most film producers should run 10–30% filler masterbatch. Injection molders can go to 20–40%. Pipe extruders rarely go above 15%. Here is the range per process, and what pushes you to the low end.
Typical addition rate by process
| Process | Typical addition rate | Practical ceiling | What usually limits you |
|---|---|---|---|
| Blown film, 30–80 µm | 10–25% | 30% | Bubble stability, dart impact |
| Blown film, below 25 µm | 5–15% | 20% | Specks, elongation at break |
| Cast film | 10–25% | 30% | Surface gloss, blocking |
| Injection molding | 20–40% | 45% | Impact strength, weld-line strength |
| Pipe and profile extrusion | 5–15% | 20% | Ring stiffness test, pressure rating |
| Woven sacks and raffia | 15–30% | 35% | Tape elongation, loom breaks |
| Blow molding | 10–20% | 25% | Parison sag, drop impact |
Mixed or let-down ratio: the part people get wrong
"Adding 20%" means 20 kg of masterbatch per 100 kg of virgin resin, then the total becomes 120 kg. Many factories instead quote a let-down ratio like 1:5, meaning 1 part masterbatch to 5 parts resin (about 16.7%). Ask which convention a supplier is using before you approve a trial quantity.
The three factors that force you below the usual range
1. Finished thickness
The thinner the wall or film, the lower the ceiling. In film below 25 µm, a particle or agglomerate that would be invisible in a 60 µm film becomes a pinhole or a visible speck. Reduce addition rate and increase mesh fineness together, rather than only reducing rate.
2. Mechanical property requirements
Calcium carbonate raises stiffness and reduces elongation and impact strength. If your specification includes a dart impact or elongation at break test, run a trial ladder at 10%, 15% and 20% and test each step. Do not approve the highest rate that passes visually.
3. Downstream process speed
Higher filler loading raises melt viscosity and lowers draw-down stability. On high-output lines running near the maximum bubble or line speed, a rate that works at low speed can cause bubble flutter or web breaks at full output.
How to run a trial properly
- Start at the low end of the range for your process.
- Run at least 30 minutes to reach steady state before sampling.
- Measure elongation at break and impact, not only visual appearance.
- Check screen pack pressure and die build-up after the run.
- Increase in 5% steps until a property fails, then step back one level.
Record the moisture content of the masterbatch before the trial. Wet masterbatch produces bubbles and voids that look exactly like overdosing, and that sends buyers chasing the wrong parameter.
Common questions
Can I run 40% filler masterbatch in blown film?
No, not on normal film lines. Above roughly 30% you lose bubble stability and elongation at break drops sharply. Film applications are limited to about 30% even in thick gauges.
Does addition rate affect colour?
Yes. Calcium carbonate is white and acts as an opacifier. Adding filler masterbatch lightens the base colour, so pigment loading must be re-tuned after any change in filler rate.
Should I add filler masterbatch before or after the colour masterbatch?
Both are normally fed through separate gravimetric feeders at the throat. Keep them on separate feeders so each rate can be adjusted independently during a trial.
What happens if the masterbatch is not dried?
Moisture above about 0.2% produces voids, silver streaking and bubble instability in film. Dry the masterbatch or specify a low-moisture grade rather than compensating with a lower addition rate.
Related: how to choose a CaCO3 grade · how to read a masterbatch TDS · CaCO3 filler masterbatch specifications