Polycarbonate (PC) Injection Moulding: Properties & Design Guide
Polycarbonate (PC) is the go-to amorphous engineering thermoplastic when impact resistance cannot be compromised. It pairs near-glass transparency with a notched Izod impact strength typically in the range of 600–900 J/m, and holds its shape up to around 125°C continuous service. The material turns up in industrial light covers, protective enclosures, and medical device housings—often in place of glass or aluminium where weight or geometry rules those out.
Mechanical and Thermal Properties
As an amorphous polymer, PC has no sharp melting point—it softens over a range. That structure gives it low, predictable shrinkage and good dimensional stability, but it also makes PC sensitive to both moisture during processing and solvents in service.
| Property | Typical Value | Test Standard |
|---|---|---|
| Tensile Strength | 55–75 MPa | ISO 527 |
| Flexural Modulus | 2,300–2,500 MPa | ISO 178 |
| Izod Impact (notched, 23°C) | 600–900 J/m | ISO 180 |
| Izod Impact (notched, −30°C) | 500–800 J/m | ISO 180 |
| Heat Deflection Temp (0.45 MPa) | 130–145°C | ISO 75 |
| Vicat Softening Point | 147–150°C | ISO 306 |
| Density | 1.20–1.22 g/cm³ | ISO 1183 |
| Mould Shrinkage | 0.5–0.8% | ISO 294-4 |
| Light Transmittance | 88–90% | ASTM D1003 |
| Water Absorption (24 h) | 0.15–0.35% | ISO 62 |
PC shrinks isotropically—the same in all directions. That makes it easier to hit tight tolerances in complex assemblies compared to semi-crystalline materials like PP or Nylon, where flow-direction and cross-flow shrinkage differ.
Common Applications
Lighting and Optical: Automotive headlamp lenses, light pipes, and safety visors. PC takes a high-polish finish well enough for exterior optical components, provided the grade is UV-stabilised—standard grades will yellow within a few years outdoors.
Electrical Enclosures: Power supply housings and junction boxes. Flame-retardant grades (UL 94 V-0) are the standard specification for mains-powered devices.
Medical Hardware: Dialysis equipment, surgical handles, and fluid containers. ISO 10993-compliant and BPA-free grades are available—grade selection and certification documentation should be confirmed at the quoting stage.
Industrial Safety: Face shields, machine guards, and protective glazing. Where glass would shatter, PC deforms or absorbs the energy. At 1.2 g/cm³, it is about half the weight of glass.
Processing and Design Considerations
Moulding PC is more demanding than moulding ABS. It wants high temperatures, a dry barrel, and a warm mould.
- Melt Temperature (280–320°C): Overheating beyond 340°C causes yellowing and molecular-weight loss, both of which destroy impact resistance. General-purpose grades run best at 290–300°C.
- Mould Temperature (80–120°C): A cold mould freezes in stress. Parts ejected from a 40°C mould may look fine but crack in the field. Keep mould temps up.
- Moisture Control: PC must be dried to below 0.02% moisture content—typically 4–6 hours at 120°C in a dehumidifying dryer with a dew point at or below −30°C. Water in the melt triggers hydrolysis, which breaks polymer chains and makes the part brittle regardless of how well the rest of the process runs.
- Draft Angles: Aim for at least 1° on smooth walls. Heavy texture needs 2° or more to avoid drag marks on ejection.
- Gate Design: For transparent parts, tab or fan gates reduce shear stress at entry and prevent the cloudy "blush" often seen near pinpoint gates. Gate placement is reviewed during DFM.
Material Grades
| Grade / Variant | Modification | Typical Use |
|---|---|---|
| Standard PC | Baseline | General housings, covers |
| High-flow PC | Lower viscosity | Thin-walled electronics |
| Flame-retardant | UL 94 V-0 rated | Mains-powered devices |
| UV-stabilised | UV absorbers added | Outdoor lenses, signage |
| PC + GF (10–30%) | Glass fibre reinforced | High-stiffness structural parts |
| PC + ABS Blend | Improved processability | Automotive interior trim |
Glass-filled PC significantly increases stiffness—flexural modulus can reach 8,000 MPa at 30% GF—but the material becomes opaque and shows more anisotropic shrinkage.
Advantages and Trade-offs
Why choose PC:
- High impact strength that holds down to −30°C.
- Excellent clarity and light transmission for optical parts.
- Dimensionally stable across a wide temperature range.
- Available in regulated grades (medical, UL 94, food-safe).
What to watch for:
- Chemical sensitivity: PC crazes or cracks on contact with acetone, many alcohols, and some industrial lubricants. Check compatibility before specifying a cleaning or assembly process.
- Cost: Noticeably more expensive than ABS or PP.
- Processing overhead: Mandatory drying and high barrel temperatures increase cycle energy and production cost.
- Notch sensitivity: A sharp 90° internal corner can reduce impact strength by up to 80%. Radii of 0.5mm minimum on all internal edges are non-negotiable.
PC vs Alternatives
- PC vs PMMA: Use PC where the part could be dropped or struck; use PMMA where scratch resistance and marginal clarity gains (92–93% vs 88–90% transmittance) matter more than impact toughness.
- PC vs ABS: PC for heat resistance and impact; ABS for cost-effective opaque housings with easier processing.
- PC vs Nylon: PC stays dimensionally stable regardless of humidity; glass-filled Nylon rivals it on stiffness but absorbs moisture and changes dimension over time.
Sustainability
PC carries resin code 7. Industrial regrind is common for non-critical, opaque applications. Post-industrial recycled grades are available but are generally limited to non-optical, non-medical parts. For projects with formal environmental targets, confirm availability and documentation at the quoting stage.
Nordmould provides orders from 100 pieces with tooling starting at €3,000. Send us your STEP file for a free DFM review—we'll check wall thicknesses and radii to confirm your design is optimised for polycarbonate.