Internal Mold Release (Zinc Stearate)
Key Features
- Internal release eliminates need for external mold release application
- Zinc stearate migrates to resin–mold interface during cure
- Suitable for SMC, BMC, RTM, and closed mold production
- 0.5–2.0 phr dosage with minimal effect on resin properties
- Reduces mold cleaning frequency in high-cycle production
This zinc stearate-based internal mold release agent is added directly to polyester, vinyl ester, or epoxy resin systems before lamination, providing release from the mold without the need for external mold surface treatment. Zinc stearate (CAS 557-05-1) migrates to the resin–mold interface during cure, forming a thin, low-friction boundary layer that enables demolding. Particularly effective in closed mold processes (SMC compression molding, RTM, and BMC molding) where external re-coating of molds between cycles is impractical. Supplied as a fine white powder or resin-dispersed paste. Dosage is typically 0.5–2.0 phr (parts per hundred resin) depending on the resin system and molding conditions. The internal release reduces mold cleaning frequency and enables faster production cycles in SMC and BMC compression molding. At recommended dosage, the internal release does not significantly affect resin mechanical properties or gelation time.
Specifications
| Parameter | Value |
|---|---|
| Form | White powder or resin paste |
| Dosage | 0.5–2.0 phr |
| Chemical | Zinc stearate |
| CAS Number | 557-05-1 |
| Shelf Life | 24 months |
| Compatible Resins | Polyester, vinyl ester, epoxy |
| Melting Point (powder) | 120–130°C |
Applications
FAQ
Zinc stearate powder should be pre-dispersed in a small quantity of resin (styrene or reactive diluent for polyester) using a high-shear mixer until a uniform, lump-free dispersion is obtained. Add this master batch to the main resin batch at the required ratio and mix thoroughly. Undispersed zinc stearate lumps will cause surface defects and inconsistent release. Alternatively, use the supplied resin paste grade which is pre-dispersed and ready to add directly at the required dosage.
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