Polycarbonate (PC) Injection Moulding: Properties & Design Guide
Polycarbonate (PC) is the highest-impact amorphous engineering thermoplastic available as a standard injection-moulding material. It combines near-glass optical clarity with exceptional toughness — an Izod impact strength of 600–900 J/m notched — and a continuous service temperature up to 125°C. Nordmould uses PC for optical components, protective enclosures, medical housings, and any application where structural failure is not an option.
What are the mechanical and thermal properties of polycarbonate?
PC is an amorphous polymer based on bisphenol-A carbonate repeat units. Amorphous structure means low and uniform shrinkage, optical transparency, and freedom from the warp patterns common in semi-crystalline materials. The trade-off is sensitivity to notches, solvents, and hydrolytic degradation at elevated temperatures.
| 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 | 0.5–0.7% | ISO 294-4 |
| Light Transmittance | 88–90% | ASTM D1003 |
| Water Absorption (24 h) | 0.15–0.35% | ISO 62 |
PC's shrinkage (0.5–0.7%) is low and nearly isotropic, which makes it reliable for precise enclosures and optical components where dimensional drift would be unacceptable.
Where is polycarbonate injection moulding used?
PC's combination of transparency, impact resistance, and elevated temperature capability places it in demanding applications across multiple sectors.
Optical and lighting components: Headlamp lenses, light diffusers, light-pipe assemblies, safety visors, and optical instruments. PC is the dominant material for automotive exterior optical applications due to its formability and UV-coatability.
Electronic and electrical enclosures: Electrical junction boxes, power supply housings, and portable device shells where high impact from drops is a primary requirement. Flame-retardant grades (UL 94 V-0) are standard for IEC-compliant enclosures.
Medical devices: Blood oxygenator chambers, filter housings, dialysis equipment, ventilator components, and surgical instrument handles. BPA-free and ISO 10993-compliant grades are available.
Safety equipment: Face shields, ballistic-resistant glazing, motorcycle helmet visors, and riot shields. PC sheet and moulded parts are both used in personal protective equipment.
Consumer electronics: Smartphone internals, laptop screen bezels, protective covers, and display light guides.
Aerospace and defence: Cabin interior components, transparent covers for avionics, and structural light-duty brackets subject to impact loading.
What are the moulding characteristics of polycarbonate?
PC is considered a moderately difficult material to injection mould. It demands careful control of moisture, temperature, and fill rate to achieve the combination of optical quality, impact performance, and surface finish that the material is capable of.
Melt temperature: 280–320°C. Temperature must be held consistently; localised overheating above 340°C causes thermal degradation (yellowing, loss of molecular weight, reduced impact). Hot runners require careful zone control.
Mould temperature: 80–120°C. High mould temperature is essential for optical parts and for managing internal stress. Low mould temperatures produce cloudy, stressed parts and poor surface replication.
Injection speed: Moderate. PC is shear-thinning but also shear-degradable; very high injection rates produce jetting and surface defects in thick optical sections. A controlled fill profile with a gradual acceleration phase is recommended.
Drying: Critical. PC must be dried to below 0.02% moisture (0.005% for optical applications) before processing. Standard: 4–6 hours at 110–120°C in a dehumidifying dryer. Hot-air dryers are insufficient; only dehumidifying or desiccant systems are acceptable.
Shrinkage: 0.5–0.7%, essentially isotropic due to amorphous structure. Predictable and consistent, which is why PC is chosen for mating assemblies with tight dimensional requirements.
Draft angles: Minimum 1° on all vertical walls; 1.5–2° on textured surfaces. High mould temperatures allow lower draft than with PP or POM, but draft should not be reduced below 0.5° even on polished optical surfaces.
Sink and warp: PC warps less than semi-crystalline materials. Sink marks at ribs or bosses are the primary concern. Rib width should not exceed 50–60% of the nominal wall; boss walls should be 50–70% of the connecting wall thickness.
Gate design: For optical parts, fan gates or film gates spread the melt more uniformly and reduce gate stress. Pinpoint gates on visible surfaces require careful positioning to avoid visible blush or halos in transparent PC.
Which PC grades and variants should you consider?
| Grade / Variant | Key Modification | Typical Use |
|---|---|---|
| Standard PC | Baseline | General enclosures, optical parts |
| High-flow PC | Lower MW, easier processing | Thin-wall electronics |
| Flame-retardant PC (V-0) | Phosphate or brominated FR | Electrical enclosures |
| UV-stabilised PC | UV absorber + HALS | Outdoor lenses, headlamps |
| Medical/BPA-free PC | Low extractables, ISO 10993 | Medical devices |
| PC + GF (10–30%) | Glass fibre | Structural housings, stiff brackets |
| PC + ABS blend | ABS toughening | Automotive trim, mid-cost housings |
| Optical-grade PC | Ultra-low haze, tight refractive index | Precision optics, lenses |
GF-PC offers very high stiffness (flexural modulus up to 8,000 MPa at 30% GF) but becomes opaque and has an anisotropic shrinkage that requires careful gate design to avoid warp.
What are polycarbonate's advantages and limitations?
Advantages:
- Exceptional impact strength — among the highest of any standard thermoplastic
- Optical transparency and low haze when properly processed
- Low, isotropic shrinkage enables precise dimensional control
- High continuous use temperature (up to 125°C for standard grades)
- Broad range of compliant grades for medical, electrical, and automotive sectors
- Good dimensional stability over a wide temperature range
Limitations:
- Hygroscopic: requires rigorous pre-drying or part quality degrades
- Notch-sensitive: sharp internal corners reduce impact strength disproportionately; all internal radii should be minimum 0.5 mm
- Poor solvent resistance: alcohols, ketones, and esters cause stress cracking, especially under residual moulding stress
- Higher processing temperatures than ABS or PP increase energy and tool wear
- Higher material cost than ABS, PP, or POM
- UV degradation without UV stabilisation; outdoor parts require coated or UV-grade material
When should you choose PC over alternative materials?
PC vs ABS: Choose PC when the part must survive impact loading, operate above 90°C, or require optical clarity. ABS is the more economical choice for opaque housings without extreme impact or temperature requirements.
PC vs PMMA: Choose PC when impact resistance is critical; PMMA is brittle by comparison. Choose PMMA when you need superior optical clarity, scratch resistance, or a lower material cost for non-impact-critical transparent parts.
PC vs POM: Choose PC for structural, transparent, or high-impact applications. Choose POM for precision sliding mechanisms, wear surfaces, and high fatigue-cycle parts.
PC vs Nylon: Choose PC when moisture absorption must be controlled (nylon absorbs significantly more water and changes dimensions). Choose nylon for high-temperature continuous loading where PC's creep resistance is insufficient.
Is polycarbonate recyclable?
PC carries resin code 7 and is not collected in most municipal recycling streams. Industrial recycling of clean, sorted PC regrind is established and produces acceptable mechanical-grade material for non-optical applications. Optical-grade and FR-grade PC regrind is more restricted. The material's high bisphenol-A content has driven formulation shifts toward BPA-free variants; end-of-life regulatory pressure on BPA-containing plastics is increasing in the EU.
For parts with sustainability requirements, Nordmould can discuss post-industrial recycled PC grades or alternative materials where performance allows.
Frequently asked questions
Is polycarbonate injection moulding optically clear?
Yes — unfilled PC has a light transmittance of approximately 88–90% and a refractive index of 1.586, comparable to glass. Optical clarity requires polished tooling, careful melt temperature control, and thorough pre-drying. Nordmould's DFM review covers gate placement and cooling for optical parts.
What is the impact strength of polycarbonate compared to ABS?
PC has roughly 10–15 times the notched Izod impact strength of standard ABS. It resists brittle fracture even at sub-zero temperatures, making it the preferred choice for protective covers, safety equipment, and aerospace components that must survive drop or ballistic loads.
Does polycarbonate need to be dried before injection moulding?
Yes — PC is hygroscopic and absorbs moisture rapidly. Insufficient drying causes hydrolytic degradation at melt temperature, producing surface splay, reduced impact strength, and molecular weight loss. Standard drying is 4–6 hours at 110–120°C in a dehumidifying dryer to reach below 0.02% moisture.
What are the processing temperatures for polycarbonate injection moulding?
PC melt temperature is typically 280–320°C, and mould temperature 80–120°C. PC requires significantly higher processing temperatures than ABS or PP, which increases energy consumption per cycle and demands higher-spec tooling with controlled cooling circuits.
What are the limitations of polycarbonate in injection moulding?
PC is susceptible to stress cracking when exposed to solvents, particularly alcohols and ketones. It is notch-sensitive: sharp internal corners dramatically reduce impact resistance. Standard PC also suffers UV degradation outdoors without UV-stabilised grades or hard coating.
Can polycarbonate be injection moulded for medical applications?
Yes — medical-grade PC grades meet ISO 10993 biocompatibility requirements and are used in blood oxygenators, dialysis equipment, and surgical instrument housings. These grades are formulated without bisphenol-A (BPA-free) where regulatory requirements demand it. Nordmould can source medical-grade PC on request.
How thick can polycarbonate walls be in injection moulding?
PC is best processed at 1.5–4.0 mm wall thickness. Very thick walls (above 6 mm) develop significant internal stress and optical distortion during cooling. For thick optical elements, staged mould temperatures and extended cooling times are required; Nordmould discusses these constraints during DFM review.
Send your STEP file to Nordmould for a free DFM review — our team will confirm whether PC is the correct material and flag any notch, gate, or drying risks in your design.