PC — Polycarbonate
Polycarbonate
PC (polycarbonate) is a transparent amorphous thermoplastic known for its very high impact resistance and good heat resistance. It is essential for optical parts, technical glazing and demanding housings, but requires rigorous drying and remains sensitive to stress cracking.
- Mold temperature: 80-120°C
- Melt temperature: 280-320°C
- Shrinkage: 0.5-0.7%
- Density: 1.20
- Manufacturer grades: Makrolon 2405 (Covestro), Lexan 141R (SABIC), Tarflon A2200 (Idemitsu)
Processing
PC is hygroscopic and drying is critical: dry for 2 to 4 h at 120 °C before molding, otherwise moisture causes irreversible hydrolysis (brittleness, silver streaks). Its high viscosity calls for melt temperatures of 290 to 310 °C and a mold regulated between 90 and 110 °C to limit internal stresses. Design generous radii and avoid contact with solvents, which trigger stress cracking.
Advantages
- Very high impact resistance, even in thin walls
- Optical transparency and good dimensional stability (amorphous)
- Good heat resistance (high continuous service temperature)
- Low shrinkage: precision parts and tight tolerances
Limitations
- Hygroscopic: critical drying at 120 °C to prevent hydrolysis
- Sensitive to stress cracking and to solvents
- High viscosity requiring high temperatures and pressures
- Notch-sensitive and prone to thermal degradation at high temperature
Common injection molding defects
- Silver streaks — Residual moisture: dry PC for 2 to 4 h at 120 °C before molding
- Burn marks (dieseling) — High-temperature degradation or trapped air: lower melt temperature and improve venting
- Stress cracking — Internal stresses or solvent contact: raise mold temperature and avoid chemical agents
Typical applications
Optics, automotive headlights, glazing, screens, safety helmets