With the gradual phase-out of HCFC-141b, pentane has gradually become a mainstream blowing agent in the continuous panel industry.What problems will be encountered during the production of continuous PUR panel using pentane as the blowing agent?Let us take a look at the common defects and corresponding solutions.

1. Insufficient Foaming / High Density

Phenomenon：Heavy panels, brittle and hard foam, incomplete foam filling.

Causes：Rapid volatilization of pentane, low material temperature, insufficient catalyst activity, excessively high isocyanate index.

Solutions：

· Maintain temperature of polyol and isocyanate at 20–25℃, ambient temperature above 18℃.

· Verify catalyst dosage, especially gel catalysts.

· Control isocyanate index (1.05–1.10 recommended for common flame-retardant panels).

2. Excessive Foaming / Low Density

Phenomenon：Overly soft foam, poor mechanical strength, reduced closed-cell ratio.

Causes：Excessive pentane or water content, high ambient temperature, slow reaction rate.

Solutions：

· Keep pentane dosage within reasonable range (normally 10–14%).

· Improve catalyst activity or reduce material temperature in summer.

3. Bubbles & Pinholes

Phenomenon：Small pores appear inside or on the foam surface.

Causes：Excessive moisture content, insufficient mixing, contamination from mold release agent and other impurities.

Solutions：

· Control moisture content in polyol component.

· Check for clogging in static mixer.

· Avoid contamination, especially silicone oil impurities.

4. Surface Bulging

Phenomenon：Local protrusions on panel surface.

Causes：Mismatched foaming rate and curing rate, localized overheating, concentrated gas release.

Solutions：

· Adjust catalytic system to balance cream time and tack-free time.

· Check over-high temperature of upper and lower facing materials.

5. Dimensional Shrinkage

Phenomenon：Panel length and width shrink obviously after cooling.

Causes：Excessive foaming, insufficient post-curing, rapid cooling.

Solutions：

· Reduce pentane and water dosage, or increase isocyanate index.

· Raise post-curing temperature (50–60℃ insulation recommended).

6. Poor Adhesion (Delamination between Foam and Facings)

Phenomenon:Debonding between foam and glass fiber cloth / color steel sheet.

Causes: Oil contamination or oxidation on facing surface, poor wettability of composite material, insufficient foaming pressure.

Solutions:

· Clean or conduct corona treatment on metal facings.

· Add 1–2% tackifying resin (e.g. terpene phenolic resin).

· Increase material injection volume to elevate internal pressure.

7. Foam Shrinkage (Edge Collapse)

Phenomenon: Inward depression at panel edges.

Causes: Low closed-cell ratio, pentane leakage, insufficient post-curing.

Solutions:

· Increase silicone surfactant dosage (1.5–2.5% recommended).

· Extend thermal insulation in post-curing section.

8. Internal Layer Separation

Phenomenon: Layered cracking inside foam along thickness direction.

Causes: Pressure fluctuation at mixing head, excessively short cream time.

Solutions:

· Stabilize mixing head pressure at 120–150 bar.

· Control cream time within optimal range of 15–25 seconds.

9. Core Burning (Yellowing & Brittle Core)

Phenomenon: Central area of thick panels yellows and becomes brittle.

Causes: Excessively high internal temperature, over-active catalysts, concentrated exothermic reaction of pentane.

Solutions:

· Reduce catalyst dosage.

· Adopt low-exothermic formula for thick panels (>150 mm).