Polycarbonate (PC) is an engineering thermoplastic chosen where a part needs high impact resistance, useful heat performance and, in transparent grades, optical clarity. Typical applications include machine guards, covers, lenses and instrument housings. Gemini moulds and finishes polycarbonate at its own UK facilities.
The Material
| Property | Typical value |
|---|---|
| Melt temperature | 280 to 320 °C |
| Mould temperature | 80 to 120 °C |
| Tensile strength | 55 to 75 MPa |
| Mould shrinkage | 0.5 to 0.8% |
| Impact resistance | Very high unfilled, but notch sensitive |
| Chemical resistance | Limited. Attacked by many solvents and alkalis |
| Heat performance | Grade dependent. Use the specific resin datasheet and the relevant HDT or long-term temperature rating for the application |
| Optical clarity | Transparent, roughly 88 to 90% light transmission |
| Drying before moulding | Required for hygroscopic grades. A representative general-purpose PC grade specifies 120 °C for 2 to 3 hours. Follow the chosen grade datasheet and its moisture limit |
The figures above describe unfilled polycarbonate. Glass-filled grades raise stiffness and strength and cut shrinkage, at the cost of the clarity that is usually the reason for choosing the material in the first place.
Where a clear part does not need PC-level impact resistance, PMMA can offer higher surface hardness and slightly higher light transmission. Cost should be checked against the actual grade and volume. Our guide to injection moulding materials sets polycarbonate against the alternatives in more detail.
Impact resistance and low weight are both design drivers in drones and autonomous systems, one of the sectors Gemini works in.
Why it is specified
Offers substantially higher impact resistance than PMMA and many general-purpose ABS grades, which is why PC is widely used for guards, covers and protective housings.
Transparent grades combine optical clarity with much higher toughness than PMMA, which is useful where a clear component also has a mechanical role.
Holds its shape at temperatures that soften ABS, useful near motors, lamps and electronics.
Unfilled PC has relatively low and fairly uniform mould shrinkage, which can help dimensional control. Final tolerance still depends on geometry, tooling and process control.
Know before you specify
The surface is soft compared with acrylic or glass. On a part that gets wiped, handled or cleaned regularly, it will haze over time. A hard coat solves it and adds a secondary operation and cost.
Notches, sharp internal corners and abrupt section changes can reduce PC impact performance by concentrating stress. Use generous radii and avoid unnecessary stress raisers.
Many solvents, alkalis and some cleaning products attack polycarbonate. A moulded-in stress plus the wrong cleaner is a common route to crazing in service, so it is worth naming the cleaning regime early.
PC is generally positioned above commodity polymers such as PP on material cost, but the actual difference depends on grade, supplier and volume. Standard grades can also lose colour and surface quality during prolonged UV exposure, so outdoor applications should use a suitable UV-stabilised grade or protective system.
Typical Applications
PC is generally specified where impact resistance matters, and often where the part also has to be seen through. Common uses include:
Machine guards and equipment covers, where an operator needs to see the process and the guard has to survive an impact.
Lamp covers, sight glasses and instrument windows that need clarity together with resistance to knocks and heat.
Electronics and instrument housings where impact resistance and heat tolerance are needed alongside a moulded finish.
On the machine
Drying. Polycarbonate is hygroscopic. Moisture during processing can cause hydrolytic degradation, lower molecular weight and visible splay. Dry the resin to the grade manufacturer's stated moisture limit before moulding. A representative general-purpose grade specifies 120 °C drying and a maximum moisture content of 0.02%.
Melt viscosity. PC has relatively high melt viscosity compared with easier-flowing commodity polymers. Thin sections and long flow paths therefore need suitable grade selection, gate sizing, melt temperature, mould temperature and injection pressure.
Residual stress. Residual moulding stress can increase the risk of crazing or stress cracking, particularly where the finished part contacts incompatible chemicals. Even wall sections, suitable mould temperature, sensible packing and generous radii all help control it.
Why Gemini
More than 26 years moulding engineering thermoplastics, polycarbonate among them, for UK manufacturers.
Tools cut and maintained in-house, so gate and venting changes for a high-viscosity material happen on site.
Polycarbonate degrades if moulded wet, so resin is dried to the grade datasheet before a run starts.
An ISO 9001 quality system, with parts inspected by hand before they are dispatched.
FAQ
No. Both are clear, but they behave differently. Polycarbonate is far tougher and survives impact that would shatter acrylic, while acrylic is harder, more scratch resistant and slightly clearer. Acrylic is also cheaper. The usual decision is whether the part will take knocks in service: if it will, polycarbonate; if it will not and appearance matters most, acrylic.
Polycarbonate absorbs moisture from the air, and moulding it wet can cause hydrolytic degradation, reducing molecular weight and causing visible splay. Drying conditions depend on the grade. A representative general-purpose PC grade specifies 120 °C for 2 to 3 hours, but the chosen resin datasheet should always govern.
Because it is notch sensitive. Unfilled polycarbonate absorbs a lot of energy in an impact, but a sharp internal corner, a moulded-in notch or a machining mark concentrates stress at one point and the material fails there. Generous radii on internal corners are the usual fix, along with avoiding sharp transitions in wall thickness.
For prolonged outdoor exposure, specify a UV-stabilised PC grade or a suitable protective coating where colour, clarity and surface appearance need to be retained. Outdoor performance is grade specific, so check the datasheet rather than assuming the polymer family behaves the same way.
Send Gemini a STEP file, a 2D drawing or details of the application. We can review the impact, temperature, optical and chemical requirements and advise whether PC, PMMA, ABS or another material is the better fit.
