Polyolefin Elastomer for Injection Molding: Processing Guidelines and Best Practices
How to successfully mold POE and POE-modified compounds — parameters, tooling, and troubleshooting for consistent parts
Injection molding with polyolefin elastomer — whether neat or as a modifier in PP compounds — requires understanding how this material differs from standard polyolefins. POE's rubber-like nature affects flow behavior, cooling rates, and part ejection. Get the parameters right and you'll produce consistent, high-quality parts. Get them wrong and you'll struggle with sink marks, warpage, or sticking.
We supply POE grades optimized for injection molding applications, with technical support for processing optimization. Here's what you need to know to mold POE successfully.
Material Behavior in Injection Molding
POE behaves differently than rigid PP or PE during injection molding. Understanding these differences helps explain the parameter choices:
- Lower melt viscosity: POE flows more easily than PP at equivalent melt temperatures. This allows faster injection and better flow into thin sections — but also requires attention to flash control.
- Higher elasticity: The rubber phase recovers elastically after shear. This affects packing pressure requirements and can cause die swell at the gate.
- Slower crystallization: POE crystallizes more slowly than PP, which affects cooling time and cycle time calculations.
- Different shrinkage: POE shrinks less than PP — typically 1.0–1.5% vs. 1.5–2.0% for homopolymer PP.
Key insight: When molding POE-modified PP, the behavior falls between the two extremes. Higher POE content moves behavior toward pure POE; lower content behaves more like standard PP.
Recommended Processing Parameters
Here are typical parameter ranges for injection molding POE and POE-rich compounds:
| Parameter | Pure POE | POE-PP Blend (30% POE) | Notes |
|---|---|---|---|
| Melt temperature | 170–200°C | 180–220°C | Lower end for flow; higher for surface finish |
| Mold temperature | 20–40°C | 30–50°C | Higher for gloss; lower for faster cycle |
| Injection speed | Moderate to fast | Moderate to fast | Fast speeds improve weld line strength |
| Injection pressure | 50–100 MPa | 70–120 MPa | Lower viscosity allows reduced pressure |
| Packing pressure | 30–60 MPa | 40–70 MPa | Critical for dimensional stability |
| Cooling time | Longer than PP | Slightly longer than PP | Allow for slower crystallization |
Tooling Considerations
Tool design for POE molding has some specific requirements:
Mold Design for POE
- Gate design: Submarine or edge gates work well. Avoid restricted gates that create excessive shear heating. Gate land length of 0.5–1.0 mm is typical.
- Venting: POE's lower viscosity means it can flash more easily into vents. Vent depths of 0.01–0.02 mm are typical — shallower than for rigid PP.
- Draft angles: Use 1–2° minimum draft for easy ejection. POE's elasticity helps with ejection, but parts can stick if undercuts are excessive.
- Surface finish: SPI-C3 to B2 finish typical. POE reproduces mold surface detail well. Textured surfaces may require slightly more draft.
- Ejection: Blade or sleeve ejection preferred for thin-walled parts. Ejector pin marks may be more visible due to material softness.
Common Issues and Troubleshooting
Even with good parameters, issues can arise. Here's how to address common problems:
- Sink marks: Increase packing pressure or time. POE's thermal expansion is higher than PP, making packing more critical. Ensure adequate hold pressure until gate freeze.
- Flash: Reduce injection pressure or clamp tonnage. Check vent depths — may need to be shallower. Ensure mold is properly aligned and clamped.
- Short shots: Increase melt temperature or injection speed. Check for restricted flow paths. Ensure adequate venting to allow air escape.
- Sticking in mold: Increase draft angles. Reduce packing pressure slightly. Ensure adequate cooling before ejection. Check for undercuts or damaged mold surfaces.
- Weld lines: Increase melt or mold temperature. Raise injection speed. Consider moving gates to improve flow pattern. Add venting at weld line location.
Processing tip: Start with the lower end of temperature ranges and increase only if needed for flow or surface finish. Excessive heat can cause degradation and odor issues, especially with high-POE compounds.
Recycling and Regrind
One of POE's advantages is its thermoplastic nature — scrap and regrind can be reused. Guidelines for regrind usage:
- Regrind level: Up to 20% regrind is typically acceptable without significant property loss. Higher levels may reduce impact performance.
- Regrind quality: Keep regrind clean and dry. Contamination from other materials or excessive heat history can cause defects.
- Blending: Blend regrind with virgin material uniformly. Segregation can cause property variations across parts.
- Color matching: Regrind may have slightly different color due to heat history. Monitor color consistency, especially for light colors.
POE for Injection Molding
Our Betopp-G POE grades are optimized for injection molding — consistent melt flow, predictable shrinkage, and excellent part quality. Technical support for processing optimization and troubleshooting.
Or contact our technical team for molding parameter recommendations.
