The engineering conflict: Flexibility vs. migration
To achieve low Shore A hardness, traditional TPU formulations typically rely on external plasticizers or reduced hard segment content. However, these methods introduce significant long-term risks:
- Material hardening: External plasticizers are thermodynamically unstable and migrate—or “bleed”—to the surface over time. This causes the TPU to lose its original flexibility and become brittle.
- Adhesion and surface failure: Migrated plasticizers act as a release agent, leading to delamination in multi-material assemblies (e.g., footwear) and preventing successful bonding to other substrates.
- Mechanical degradation: Reducing hard segment content to achieve softness often compromises essential properties like chemical resistance and compression set.
The Kuraray’s solution: Softness by design, not by addition
Intrinsic softness. Permanent integrity.
KURARAY POLYOL (specifically high molecular weight grades like P-3010 and P-3050) enables the production of soft TPU without hazardous additives. This is achieved through the unique MPD-based methyl-branched architecture, which disrupts chain symmetry and prevents the crystallization typical of high-molecular-weight linear diols.
By engineering "free volume" directly into the polymer backbone, KURARAY POLYOL ensures the material remains permanently soft and amorphous.
Strategic advantages
- High molecular weight stability: Maintain superior mechanical strength and chemical resistance while achieving a low Shore A hardness.
- Zero migration risk: Eliminate "bleeding" to ensure consistent surface aesthetics and permanent adhesion in critical applications like conveyor belts and high-performance footwear.
- Intrinsic purity: Formulate safe, plasticizer-free elastomers that simplify regulatory compliance (REACH/RoHS) and eliminate the risk of toxic leaching.
Performance validation: Hardness stability over time
The following data demonstrates how KURARAY POLYOL maintains stable Shore A hardness, whereas standard linear alternatives undergo significant hardening due to crystallization and additive loss.
Figure 1: Hardness retention analysis of KURARAY POLYOL TPU applications (Hs A)
Long-term comparison of KURARAY POLYOL (P-3010/P-3050) against poly (1,4-butylene adipate) -diol (PBA3000). While the standard linear backbone undergoes rapid hardening due to post-crystallization, the MPD-based architecture ensures stable Shore A hardness, validating the intrinsic softness of the molecular design.
