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How can we address bubbles and porosity in butyl rubber extrusion?

Time：

2026-04-01

How can bubbles and porosity in butyl rubber extrusion be addressed? Possible causes include: moisture absorption by the raw material; inadequate venting; improper temperature settings; uneven feeding that entrains air; an extruder screw and barrel design unsuitable for butyl rubber; issues with the die flow‑channel design; and problems with the compound formulation.

How can we address bubbles and porosity in butyl rubber extrusion?

How can we address bubbles and porosity in butyl rubber extrusion?

1. Moisture absorption by the raw materials (the most common cause)

Once butyl rubber and fillers absorb moisture, heating causes the water to vaporize, resulting in porosity.

Solution:

Store raw materials in sealed containers to prevent exposure to open-air and humid conditions.

Preheat and dry appropriately before production (at low temperature; avoid overheating).

Avoid using lumpy, damp rubber compounds.

2. Inadequate venting

Butyl adhesive has high viscosity, and air entrapped in the material cannot be expelled.

Solution:

Appropriately reduce the screw speed to allow the melt sufficient time to vent.

Check whether the nozzle is experiencing pressure buildup and whether the flow path is unobstructed.

Use an extrusion structure with venting functionality when necessary.

3. The temperature setting is inappropriate.

Excessive temperature leads to decomposition of the rubber compound and gas generation; insufficient temperature results in inadequate plasticization and entrapment of air.

Solution:

Butyl rubber is typically extruded at low temperatures: 50–90°C.

Segmented temperature control—avoid localized high temperatures.

The die temperature is slightly higher than the barrel temperature, which facilitates venting.

4. Uneven feeding and air entrainment

Manual feeding is often uneven—sometimes too fast, sometimes too slow—which most easily traps air.

Solution: Use a forced-feed roller or a forced-feeding device to ensure uniform, continuous material feeding; avoid abrupt feeding or material interruptions. Cut the rubber compound into uniform blocks to minimize voids.

5. The screw and barrel design is unsuitable for butyl rubber.

Conventional extruders generate high shear and are prone to entrapping air, so butyl rubber requires a dedicated extruder design.

Solution:

Use a low-shear, slow-pressure-type screw specifically designed for butyl.

The inner wall of the barrel is polished to reduce vortex-induced air entrainment.

Pressure is stable, preventing melt pulsation.

6. Mold Runner Design Issues

Air pockets can accumulate in flow‑channel dead zones and abrupt diameter changes.

Solution:

The mold runner features smooth transitions with no dead corners.

Appropriately increase the die pressure to compact the melt.

Regularly clean out accumulated resin and charred material from the mold.

7. Compound formulation issues

Excessive filler, insufficient oil content, and poor dispersion can all lead to porosity.

Solution:

Ensure the formulation is evenly dispersed.

Avoid using excessive volatile additives.

Thorough mixing ensures reduced internal porosity.