PBT — Polybutylene Terephthalate
Polybutylene Terephthalate
PBT (polybutylene terephthalate) is a semi-crystalline technical polyester with fast crystallization. It is valued for its excellent electrical properties, dimensional stability and chemical resistance, making it the reference for electrical connectors and automotive parts.
- Mold temperature: 60-80°C
- Melt temperature: 240-270°C
- Shrinkage: 1.5-2.0%
- Density: 1.30-1.32
- Manufacturer grades: Ultradur B4520 (BASF), Crastin S600F20 (DuPont), Pocan B1505 (Lanxess)
Processing
PBT is hygroscopic: drying of about 2 to 4 h at 120 °C is required before molding to avoid hydrolysis and a viscosity drop. Run the melt between 240 and 270 °C with a mold regulated between 60 and 80 °C. Its fast crystallization shortens cycles but demands uniform cooling, especially on glass-fiber filled grades prone to warpage.
Advantages
- Excellent insulating electrical properties: connectors and electronics
- Good dimensional stability and low water absorption
- Fast crystallization: short cycles and easy demolding
- Good chemical resistance to fuels, oils and solvents
Limitations
- Hygroscopic: drying at 120 °C required to avoid hydrolysis
- Marked warpage on glass-fiber filled grades
- High shrinkage (1.5 to 2.0 %) to offset with holding
- Notch sensitivity: moderate impact resistance unfilled
Common injection molding defects
- Warpage — Anisotropic shrinkage of glass-fiber grades: balance the fill and homogenize cooling
- Sink marks — High crystallization shrinkage: increase holding pressure and time
- Weld lines — Cooled melt front: raise melt temperature and injection speed
Typical applications
Electrical connectors, housings, under-hood automotive parts