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1. Heat Resistance: PA6 Modified engineering plastics is the King
This is the most fundamental difference between the two.
- Melting Point: PA66 is approx. 260°C, while PA6 is approx. 220°C.
- Heat Deflection Temperature (HDT): Under high load (1.8 MPa), the HDT of PA66 is typically 20°C ~ 40°C higher than that of PA6.
- Conclusion: If your product needs to be exposed to environments above 150°C long-term, or requires short-term high-temperature processes (like SMT reflow soldering), PA66 is the mandatory choice.
2. Surface Appearance: PA6’s “Aesthetic” Advantage
Many engineers notice that with the same percentage of glass fiber, PA6 products have a glossy, smooth surface, while PA66 tends to show “floating fiber” (surface roughness with visible white fiber marks).
- The Reason: PA6 has a slower crystallization speed. This gives the resin more time to flow and encapsulate the glass fibers while cooling in the mold.
- Conclusion: For exposed parts, handles, and housings where high aesthetic quality is required, PA6 is the preferred choice.
3. Toughness vs. Stiffness: Spear vs. Shield
- Stiffness (Hardness): PA66 has a higher modulus; it is harder and has better creep resistance.
- Toughness (Elasticity): PA6 molecular chains are more flexible, making its impact resistance (especially at low temperatures) superior to PA66.
- Conclusion: Worried about the product shattering when dropped? Choose PA6. Worried about deformation under long-term load? Choose PA66.
III. Decision Tool: Detailed PA6 vs. PA66 Comparison Table
To help you compare visually, the key metrics are organized below:
| Dimension | Metric | PA6 (Modified) | PA66 (Modified) | Winner / Verdict |
|---|---|---|---|---|
| Thermal | Melting Point ($T_m$) | $\approx 220^\circ\text{C}$ | $\approx 260^\circ\text{C}$ | PA66 (Stronger heat resistance) |
| Thermal | Long-term Heat Aging | Medium | Excellent | PA66 (Essential for engine parts) |
| Mechanical | Stiffness & Modulus | High | Very High | PA66 (Harder) |
| Mechanical | Toughness & Impact | Excellent | Medium/Good | PA6 (More shatter-resistant) |
| Aesthetics | Surface Gloss | Excellent (Low fiber exposure) | Average (Prone to floating fiber) | PA6 (Better looking) |
| Processing | Flowability | Excellent (Fills thin walls) | Good | PA6 (Easier for complex parts) |
| Processing | Crystallization Speed | Slower | Very Fast | PA66 (Cools fast but prone to warp) |
| Physical | Water Absorption | Higher (Dimensions vary) | Slightly Lower | PA66 (Slightly more stable) |
| Commercial | Raw Material Cost | Lower | Higher | PA6 (Better Value) |
IV. Processing & Cost: The Hidden Bill
Beyond the unit price of the material itself (PA6 is usually cheaper than PA66), we need to calculate the “processing bill”:
- Process Window: PA6 has a wider processing temperature range, which usually means lower scrap rates and easier machine tuning.
- Mold Filling: Because PA6 has better flowability, injection pressure can be lower for thin-walled, long-flow complex structures, resulting in less wear on the mold.
- Shrinkage Control: PA66 crystallizes too fast, making shrinkage rates hard to control precisely, often leading to warpage; PA6 shrinkage is relatively milder, making it easier to maintain dimensional accuracy.
V. Application Scenarios: finding the Right Fit
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Typical Scenarios for PA66:
- Under the Car Hood: Intake manifolds, radiator tanks, oil pans (requires heat and oil resistance).
- Electronics: Circuit breaker housings, connectors (requires resistance to soldering heat).
- Industrial Parts: High-load gears, bearing cages (requires high stiffness and wear resistance).
-
Typical Scenarios for PA6:
- Automotive Interior/Exterior: Door handles, mirror brackets, wheel covers (requires good looks, toughness, and paintability).
- Power Tools: Power drill housings, lawnmower bodies (requires high impact resistance and aesthetics).
- Office Furniture: Office chair bases, armrests (requires load-bearing without breaking, plus a smooth surface).
