PP-TD20 Versus TD30, and Why PA6 Warpage Is Harder to Cure

Where TD20 and TD30 separate

Flexural modulus: TD20 about 2,200-2,600 MPa versus TD30 around 2,800-3,400 MPa. Heat: TD20 HDT at 0.45 MPa near 115 °C, TD30 reaching 125-130 °C.

Costs: TD30 notched impact at room temperature is usually 60-70% of TD20 with steeper loss at low temperature; higher density adds piece weight; welding and painting degrade.

Rule of thumb: use TD30 when the part must resist deflection; use TD20 with ribs when there are snap-fits or drop requirements.

Why PA6 warpage is harder

PP-TD shrinkage is largely physical — large in magnitude but fairly predictable and correctable over a wide range through hold pressure and mould temperature.

PA6 GF30 warpage stems from anisotropy: flow-direction shrinkage of 0.1-0.3% against 0.8-1.2% across flow, a three-to-fivefold gap. That is inherent to the material; processing mitigates but cannot remove it.

PA also crystallises, so dimensions continue to drift 24-72 hours after ejection, complicating process set-up.

Countermeasures compared

PP-TD: adjusting hold pressure, balancing mould temperature and lowering injection speed usually resolves most issues.

PA-GF: design must be involved — uniform walls, optimised gate number and position, partial substitution of glass with mineral filler to reduce anisotropy, plus mould-flow analysis before production.