Polycarbonate (PC) is a high-performance engineering thermoplastic that has cemented its position as one of the “big five” general-purpose engineering polymers. This article provides a comprehensive overview of polycarbonate’s properties, machining processes and applications.
What is Polycarbonate?
Polycarbonate, abbreviated as PC, is a high-molecular-weight polymer material whose molecular chains contain carbonate groups, and it is one of the five general-purpose engineering plastics. The name Polycarbonate is derived from the carbonate linkages in its molecular structure. PC material overcomes the fragility of traditional transparent materials like glass. As a transparent engineering polymer, it also boasts outstanding impact resistance, creep resistance, heat resistance, and low water absorption, enabling PC to excel in high-demand applications.
Polycarbonate Properties
Polycarbonate is an amorphous, transparent thermoplastic polymer. It is odorless, tasteless, and non-toxic, possessing a balanced combination of mechanical, thermal, and dielectric properties, making it an excellent engineering plastic.
Mechanical Properties
Polycarbonate exhibits excellent mechanical properties. Its most notable feature is its high impact strength, ranking among the best of thermoplastic resins. It demonstrates low creep and good dimensional stability, retaining high mechanical strength even at low temperatures. Its drawbacks include lower fatigue strength, a tendency for stress cracking, and poor abrasion resistance. The table below shows the mechanical properties of polycarbonate.
| Property | Value | Property | Value |
| Tensile Strength, MPa | 60–70 | Notched Izod Impact Strength, kJ/m2 | 50–70 |
| Elongation, % | 60–130 | Brinell Hardness, MPa | 150–160 |
| Flexural Strength, MPa | 100–120 | Fatigue Strength, MPa | 10.5 |
| Flexural Modulus of Elasticity, GPa | 2.0–2.5 | ||
| Compressive Strength, MPa | 80–90 |
The creep resistance of polycarbonate is superior to that of engineering thermoplastics like nylon and polyoxymethylene (POM), which is a key indicator of PC’s good dimensional stability.
Compared to most other engineering plastics, polycarbonate has relatively poor abrasion resistance and a higher coefficient of friction.
Internal stress and stress cracking in polycarbonate products are significant issues. Internal stress primarily arises from the interaction of macromolecules due to forced orientation.
If a bent polycarbonate test specimen is flexed and held for a certain period, micro-tearing will occur when the stress exceeds its limit. When the average molecular weight of polycarbonate is above 2.4 x 104, it can withstand a stress greater than 30 MPa; for an average molecular weight of 2.2 x 104, the limit is about 20 MPa. Stress cracking generally does not occur if the residual stress or the stress borne by the product is below these values. However, if the polycarbonate product undergoes decomposition or aging due to reasons like excessive temperature during the molding process, or if the product has notches or weld lines, or is used in a chemical gas environment, the time to micro-tearing will be significantly shortened, and the limiting stress value will drop drastically.
Thermal Properties
Polycarbonate has good heat resistance, with a long-term service temperature of up to 120 °C. It also possesses excellent cold resistance, with a brittle temperature of −100 °C.
| Property | Value | Property | Value |
| Glass Transition Temperature, ℃ | 150 | Coefficient of Linear Thermal Expansion, x 10-5/℃ | 5–7 |
| Melting Temperature, ℃ | 220–230 | Heat Deflection Temperature （1.82MPa），℃ | 130–140 |
| Specific Heat Capacity, J/(g · ℃) | 1.17 | Thermal Decomposition Temperature, ℃ | ≥ 340 |
| Thermal Conductivity, W/（m · ℃） | 0.24 | Brittle Temperature, ℃ | -100 |
Polycarbonate does not have a distinct melting point, becoming molten in the range of 220～230℃. Due to the high rigidity of its molecular chains, its melt viscosity is relatively high.
Electrical Properties
Polycarbonate has low polarity, a high glass transition temperature, and low water absorption, thus exhibiting excellent electrical properties.
| Property | 20℃ | 125℃ |
| Volume Resistivity, Ω・cm | 4.0×1016 | 4.0×1014 |
| Dielectric Strength, Ω・cm (Thin Film) | ≥ 100 | / |
| Dielectric Strength, kV/mm (2 mm Thick Disc) | 20–22 | / |
| Dielectric Constant (60 Hz) | 3.1 | 3.1 |
| Dielectric Constant (10³ Hz) | 3.1 | 3.0 |
| Dissipation Factor (60 Hz) | 6–7×10-4 | 7×10-4 |
| Dissipation Factor (10³ Hz) | ≤ 2×10⁻-3 | ≤ 2×10-2 |
Chemical Resistance
Polycarbonate is stable in acidic and oil-based media but is not resistant to alkalis and dissolves in chlorinated hydrocarbons. Prolonged immersion in boiling water can easily cause hydrolysis and cracking.
Optical Properties
Polycarbonate is colorless and transparent, with good visible light transmittance, reaching 85%−90%. Transmittance is related to the surface roughness of the product. PC has low surface hardness and poor abrasion resistance, so the surface is prone to scratching or hazing, which affects its light transmittance. Like other transparent polymers, when subjected to uniaxial stretching, the forced orientation of molecules in PC creates anisotropy and internal stress, leading to birefringence. This property allows polarized light to be used to inspect the magnitude of internal stress in polycarbonate products.
The refractive index of polycarbonate for visible light is 1.5872 at 20℃, ranging from 1.5914 at -20℃ to 1.5745 at 140℃, showing a linear relationship with temperature. Its refractive index is higher than that of other transparent polymers like acrylates, making it more suitable for optical lens materials.
Processes of PC Machining
Polycarbonate has excellent molding and processing characteristics. In the viscous flow state, it can be shaped by methods such as injection molding and extrusion.
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Injection Molding
PC injection molding is suitable for producing small to medium-sized parts that require precise dimensions and impact resistance. This process primarily uses screw-type injection machines equipped with a single-head, full-flight, equal-pitch, gradual-compression screw. To minimize backflow, a conical, sharp-tip or anti-return structure screw is used. PC’s high melt viscosity necessitates a sealed nozzle with a large-channel structure or an extended open nozzle to improve quality.
Dried PC material can become compromised by room-temperature air exposure within 15 minutes. The hopper must be insulated to maintain the material temperature at no less than 100 ℃, and the material should be used up within 0.5 to 1 hour.
Extrusion
Polycarbonate extrusion is used to manufacture products such as sheets, tubes, rods, and films. A single-screw extruder is used, with the screw designed to accommodate PC’s viscosity changes. PC extrusion screws typically have an L/D ratio of 18 ~ 20; while this provides good plasticization, it also increases the risk of degradation. Extrusion temperatures are lower than those for injection molding, with a 10 ~ 20 °C temperature difference between the front and rear zones. Shear rate has little effect on melt viscosity, and the screw speed should generally be less than 100 r/min. Low speeds are used for smaller L/D ratios to ensure proper plasticization.
CNC Machining
PC can withstand certain processing temperatures during CNC machining, however, its high viscosity and poor flowability require precise control of cutting speed and feed rate to prevent thermal degradation from excessive heat or molding difficulties due to insufficient flow. Additionally, the surface of the PC after machining often exhibits stress whitening, which can be mitigated by optimizing tool paths, adjusting machining parameters, and applying appropriate heat treatment to improve surface quality and overall performance.
Applications of PC Plastics
Polycarbonate combines good mechanical and electrical properties with features such as transparency, heat resistance, and dimensional stability, leading to its widespread use in fields including machinery, electronics and electrical appliances, transportation, lighting equipment, and medical devices.
Machinery
Due to its excellent impact toughness, high mechanical strength, and good dimensional accuracy and stability, polycarbonate is widely used to manufacture components for transmitting low to medium loads, such as gears, racks, worm gears, worms, cams, straight shafts, crankshafts, and levers; fasteners under low stress, such as screws, nuts, and rivets; low-wear, low-speed components, such as shaft sleeves, pipe sleeves, cages, and guide rails; as well as equipment housings, covers, and frames.
PC can be used to manufacture components for still and motion-picture cameras. For cameras, this includes toothed take-up spools, film spools, rewind knobs, eyepiece frames, display windows, viewfinders, distance adjustment rings, and light locks for apertures. For movie cameras, applications include housings, handles, switches, knobs, zoom rings, display windows, and aperture rings.
Electronics and Electrical Appliances
Polycarbonate is an excellent Class E (120 °C) insulating material, with extremely broad applications in the electronics and electrical fields. Injection molding is used to mass-produce insulated connectors, coil bobbins, terminal blocks, various switches, tube sockets, insulating sleeves, power tool casings, and battery housings for miners’ lamps.
PC’s low molding shrinkage, high dimensional accuracy, and good dimensional stability make it highly valuable for high-precision components in computers, video recorders, and color televisions. Its use in televisions primarily capitalizes on its excellent electrical insulation and self-extinguishing properties. Components such as the winding tube for the flyback transformer coil and parts of the deflection system, like the color purity transverse adjustment magnet cover and the deflection yoke cap, can all be made from polycarbonate.
Polycarbonate film has a light transmittance of 84% ~ 90%, excellent electrical insulation, dimensional stability, good abrasion resistance, high mechanical strength, UV stability, tear resistance, and is easy to bond. It can be used across a wide temperature range from – 25 ℃ to 125℃, making it widely used as an insulating film for electronics and electrical appliances, electrode bodies, capacitors, and for audio and color video magnetic tapes. In office automation, PC is used for the frames and housings of fax machines and photocopiers, mobile phone casings, and battery compartments for mobile phones.
Medical
Polycarbonate is tasteless, non-toxic, non-contaminating, and can be sterilized by high-pressure steam, making it suitable for manufacturing medical containers such as cups, bottles, and tubes, as well as syringes, plasma separators, artificial dialyzers, three-way stopcocks, and surgical instruments. In recent years, PC has also been used to manufacture artificial internal organs, such as artificial kidneys and artificial lungs.
Optics
Polycarbonate’s light transmittance of 85%−90% approaches that of acrylic glass. It has good heat resistance, with a long-term service temperature up to 120 °C. Adding UV absorbers to PC provides good weather resistance. Consequently, PC’s application in optical and lighting equipment is rapidly expanding, increasingly being used to manufacture various lamps and large lamp covers, such as signal light covers, explosion-proof lamp covers, and general lighting covers.
PC has seen rapid development as a substrate material for optical discs, being widely used to manufacture CD-ROMs. Key performance characteristics for optical disc grade polycarbonate are:
- High Purity: Requiring exceptionally high light transmittance, which is 91.9% at a wavelength of 550 ~ 800nm (for a 6.2mm thickness).
- Good Melt Flowability: The melt flow rate (MFR) should generally be greater than 65 g/min.
Transportation
Polycarbonate can be used to manufacture car dashboards, telephones, door handles, inner lenses of headlights, and windshields for cars and motorcycles. PC is also used for hanging handles and adjustable air conditioning nozzles in buses and subway trains. In the aerospace industry, PC is used for aircraft windshields, cockpit canopies, and other components; for instance, a single Boeing 747 aircraft uses approximately 2,500 polycarbonate components, totaling nearly 2 tons of PC per aircraft.
About Getzshape
At Getzshape, we are experienced manufacturers of CNC plastic parts. We have produced lots of plastic machined parts, including PC parts, and we are experts in minimizing distortion and other related challenges during PC CNC machining. If you are looking for quality PC parts screws, nuts, and rivets or other custom components, feel free to contact us.
