Why does filler masterbatch break film? 6 causes and fixes

Film breaks during blown-film production are usually traced back to the CaCO3 filler masterbatch rather than the resin itself. Each cause leaves a different trace — here is how to read it.

Updated 29 October 2026 · Masterbatch Co. technical notes

1. Overdosing — the most common cause

Above roughly 30% addition in film, elongation at break drops steeply. A bubble that was stable at 18% can flutter and tear at 24% on the same day, because the line was moved slightly faster. The symptom is: breaks happen at the bubble neck, look like a tear, and occur more often as speed increases.

Fix: Run a trial ladder at 15%, 20%, 25% and 30%. Stop at the highest rate where elongation at break (measured with a tensile tester) stays above your specification, not where the bubble looks fine.

2. Wet masterbatch — bubbles, not tears

Moisture above about 0.2% flashes into steam in the barrel, producing tiny voids that weaken the film. The symptom is: breaks show a cloudy, frothy edge, and the problem disappears after drying the masterbatch for 2–4 hours at 80 °C.

Fix: Specify moisture ≤ 0.15% on the TDS. If you do not have a dryer, cut the rate by 5–10% on humid days rather than guessing.

3. Poor dispersion — multiple parallel breaks

Undispersed agglomerates act as stress concentrations. The symptom is: multiple breaks running in roughly the same direction across the film at the same machine position. The agglomerates themselves are visible as specks if you hold the film up to a light.

Fix: Switch from 1250 mesh to 2000–2500 mesh, or ask the supplier for a coated grade. If you run a twin-screw, add one kneading block section rather than changing the masterbatch first.

4. Carrier resin mismatch — gels and weak welds

If the masterbatch carrier is PP-based and your virgin resin is PE (or vice versa), the two do not blend cleanly. The symptom is: small, round gel-like spots appearing in a steady stream, and weld-line strength dropping below specification.

Fix: Match the carrier to your virgin resin. PE film lines need LDPE/LLDPE carrier masterbatch; PP injection lines need PP carrier.

5. Screen pack blinding — breaks move around

Masterbatch with a broad particle-size distribution (large particles mixed with fines) plugs the screen pack unevenly. The symptom is: breaks appear at random positions, melt pressure rises gradually over a shift, and the problem stops after changing the screen pack.

Fix: Ask the supplier for a particle-size top cut ("99% below X µm" on the TDS), or add a finer mesh screen to the pack if your line tolerates it.

6. Low-temperature embrittlement — breaks on rewinder

Some film producers find the bubble stable but the web breaks on the rewinder or during slitting. This is usually low-temperature embrittlement: breaks happen after the film has cooled, at slitting or rewinding, not at the bubble.

Fix: Reduce filler content by 5%, or switch to a lower-density CaCO3 grade (1250 mesh rather than 2500 mesh — finer particles increase stiffness more than coarser ones).

The five-minute diagnostic test

Before you change anything, run this test on your next shift:

1. Drop the filler addition rate by 10% and run 20 minutes.
2. If breaks stop, the problem is overdosing or dispersion — go back to cause 1 or 3.
3. If breaks continue, dry the masterbatch 2 hours and re-run.
4. If breaks stop after drying, the problem is moisture — cause 2.
5. If breaks still continue, check whether the masterbatch carrier matches your virgin resin — cause 4.

This simple test separates the most common four causes in about an hour. Skip it and you risk changing the wrong parameter.

Common questions

Related: addition rate by process · how to choose a CaCO3 grade · CaCO3 filler masterbatch specifications