Polycarbonate was first synthesized by Alfred Einhorn in 1898, but it was not widely recognized. In 1955, Hermann Schnell of Bayer AG synthesized and patented polycarbonate again, using trade name "Makrolon." Around the same time, Daniel Fox of GE also independently synthesized and patented it. SABIC is one of the world's leading PC manufacturers, currently ranking second globally. In recent years, SABIC's PC business in China has grown rapidly.
Polycarbonate, abbreviated as PC, is a polymer containing carbonate groups in its molecular chain. It can be classified into aliphatic, aromatic, and aliphatic-aromatic types. Due to relatively low mechanical properties of aliphatic and aliphatic-aromatic polycarbonates, their application in engineering plastics has been limited. However, aromatic polycarbonates, due to their excellent performance, have achieved industrial production, have become the fastest-growing general-purpose engineering plastic among top five engineering plastics.

 

Physical properties

Polycarbonate is colorless and transparent, heat-resistant, impact-resistant, and flame-retardant (Class B1). It maintains excellent mechanical properties within normal operating temperatures. Compared to polymethyl methacrylate (PMMA), which has similar properties, polycarbonate offers superior impact resistance, a high refractive index, and excellent processability. It also achieves UL94 V-2 flame retardancy without need for additives. However, PMMA is less expensive than polycarbonate and can be produced in bulk for large devices.
Wear resistance of a material is relative. Comparing ABS with PC, PC has better wear resistance. However, compared to most plastics, polycarbonate's wear resistance is relatively poor, ranking below average. Therefore, some polycarbonate devices used in applications subject to wear require special surface treatment.
Chemical Properties
Polycarbonate (PC) is a polyester of carbonic acid. Carbonic acid itself is unstable, but its derivatives (such as phosgene, urea, carbonates, and carbonate esters) have a certain degree of stability.
Based on alcohol structure, polycarbonates can be divided into two categories: aliphatic and aromatic. Aliphatic polycarbonates, such as polyethylene carbonate, polytrimethylene carbonate, and their copolymers, have low melting points and glass transition temperatures, poor strength, and are therefore unsuitable for use as structural materials. However, their biocompatibility and biodegradability have led to their application in drug delivery systems, surgical sutures, and bone support materials.
Polycarbonate is resistant to weak acids, weak bases, and neutral oils.
Polycarbonate is not resistant to UV light or strong bases.
PC is a linear carbonate polyester in which carbonate groups alternate with other groups, which can be aromatic, aliphatic, or a combination. Bisphenol A-based PC is the most important industrial product.
PC is a nearly colorless, glassy, amorphous polymer with excellent optical properties. High-molecular-weight PC resins offer high toughness, with notched Izod impact strengths ranging from 600 to 900 J/m. Unfilled grades have a heat deflection temperature of approximately 130℃, a value that can be increased by 10℃ with glass fiber reinforcement. PC has a flexural modulus exceeding 2400 MPa, allowing the resin to be processed into large, rigid products. Below 100℃, its creep rate under load is very low. PC also has poor hydrolysis resistance and cannot be used in products subjected to repeated high-pressure steam exposure.
PC's main performance drawbacks include insufficient hydrolytic stability, notch sensitivity, poor resistance to organic chemicals and scratches, and yellowing with long-term UV exposure. Like other resins, PC is susceptible to corrosion by certain organic solvents.
PC is flame retardant and oxidatively resistant.
Advantages:
Mechanical Properties: Polycarbonate offers a unique combination of rigidity and toughness. While highly rigid materials are typically brittle and break upon impact, polycarbonate combines strength and toughness with excellent toughness.
Thermal Stability: PC offers excellent thermal stability and a wide melting temperature range, typically between 220℃ and 230℃. Furthermore, PC has a decomposition temperature exceeding 300℃ and can operate at temperatures up to 120℃ for extended periods, demonstrating excellent heat resistance.
Flowability: Polycarbonate has high melt viscosity and poor flowability, resulting in poor injection molding processability. Increased molecular weight increases melt viscosity. During molding process, adjusting temperature is more effective than changing shear rate.
Dimensional Stability: Polycarbonate exhibits excellent creep resistance, surpassing PA and POM among engineering thermoplastics. Minimal dimensional change and cold flow deformation due to water absorption, combined with low shrinkage, ensure excellent dimensional stability.
Optical Properties: Polycarbonate's macromolecular chains are difficult to orient and crystallize, maintaining an amorphous polymer state and resulting in excellent transparency.
Electrical Properties: Polycarbonate molecules have low polarity, a high glass transition temperature, and low water absorption, resulting in excellent electrical insulation properties comparable to or exceeding those of PET, traditionally considered an excellent electrical insulator.
Flame Retardancy: Polycarbonate natively possesses UL94 V-2 flame retardancy, eliminating need for flame retardants. By adding a small amount of flame retardants, PC can achieve higher fire protection standards while maintaining excellent optical and mechanical properties unmatched by other plastics.
Main Advantages

Disadvantages:
Poor fatigue resistance: Polycarbonate has poor fatigue resistance and is not easily subjected to cyclic stress.
Poor wear resistance: PC is easily affected by external forces, resulting in surface scratches and wear. Low crystallinity and disordered molecular chain arrangement reduce scratch resistance. Adding powdered polytetrafluoroethylene can enhance self-lubrication, while adding glass fiber can increase hardness and improve wear resistance.
Poor stress cracking resistance: Polycarbonate's macromolecular chains are difficult to relax under external forces, making it difficult to naturally eliminate internal stress after molding.
Poor hydrolysis resistance: Due to ester groups in its molecular chains, PC easily hydrolyzes in acidic and alkaline conditions, producing acids or alcohols. Its hydrolysis stability is low, making it unsuitable for products subjected to repeated high-pressure steam exposure.
Chemical resistance: PC has excellent chemical resistance and can withstand corrosion from a variety of chemicals, but its alkali resistance is relatively poor.
Notch sensitivity: Notch sensitivity means that if a part has a notch on its edge, it is prone to cracking along notch when subjected to stress. Because internal stress in PC is difficult to eliminate, parts with notches are more likely to crack.
Weather resistance: Long-term UV exposure causes PC to yellow, requiring addition of UV absorbers to improve aging resistance.

▶ Formability
PC materials are easy to process and can be processed by injection molding, extrusion, blow molding and other processes. However, PC has poor fluidity. Mold casting system should be thick and short. Wall of plastic part should not be too thick and should be uniform to avoid sharp corners and gaps. Since PC materials are sensitive to water, they need to be dried before molding. Moisture content should be less than 0.02%. At the same time, molding conditions need to be strictly controlled to avoid problems such as melt cracking and stress concentration.
(1) Fluidity
Melt viscosity of polycarbonate increases with increase of relative molecular weight. At lower molding temperatures, viscosity increases rapidly; at higher temperatures, viscosity decreases. When cooling, viscosity rises rapidly, which shortens molding time. At high shear rates, viscosity decreases slightly, but change is small. Adjusting temperature is more effective in improving flow state than changing shear rate.
(2) Water absorption
Polycarbonate absorbs water due to polar groups and surface adsorption. When heated, water-containing PC is prone to hydrolysis, resulting in molecular chain breakage, reduced mechanical properties and crack resistance, and affected appearance quality. Water content of PC should be paid attention to during molding.
(3) Molding shrinkage
Molding shrinkage of polycarbonate is 0.4% to 0.8%, which is affected by factors such as melt temperature, mold temperature, injection speed and holding pressure. Thickness of product also affects shrinkage: shrinkage is the smallest when it is 4.2mm, increases with increasing thickness when it is greater than 4.2mm, and increases sharply with decreasing thickness when it is less than 4.2mm.

 

Properties

Following is a table of selected physical properties for Class A PC plastics for low-temperature injection molding for IMD/IML processes.

▶ Injection Molding
Polycarbonate (PC) injection molding is suitable for producing small and medium-sized parts that require precise dimensions and are impact-resistant. This process primarily utilizes a screw injection molding machine equipped with a single-start, full-thread, constant-pitch, compression-grade screw. To reduce backflow, use a conical tip or a screw with a check valve. High melt viscosity of PC requires a large-channel closed nozzle and an extended open nozzle to improve product quality.
Dry PC loses its effectiveness after 15 minutes in room-temperature air. Hopper must be insulated to maintain material temperature at least 100℃, and material must be used up within 0.5 to 1 hour. Average molecular weight of PC for injection molding should be between 2.7 and 3.4 × 10⁴, and moisture content should be kept below 0.03%.
Polycarbonate Injection Molding Process Conditions

Injection molding temperature should be controlled between 240℃ (flow temperature) and 340℃ (decomposition temperature). High molding pressure and injection speed increase melt shear and internal stress, while too slow a speed can easily produce weld lines and waviness. PC's impact strength is highest at an injection speed of 12 g/s.
Upper limit of temperature at which part cools and sets in mold is determined by PC's glass transition temperature (130℃). Increasing mold temperature facilitates demolding and uniform cooling, reducing internal stress. Internal stress is typically measured using polarized light method and solvent immersion method.
Polycarbonate Properties and Molding Parameters

1. Raw Material Drying: Ordinary drying oven temperature 110-130℃ for 2-4 hours; top hopper drying oven temperature 100-120℃. Moisture content must be less than 0.03%.
2. Determining Moisture Content: Observe material strands during empty injection process. After plasticization, strands flowing out of nozzle should be uniform, colorless, and free of silver streaks and bubbles. Otherwise, drying is incomplete.

1. Adjust molding parameters of injection molding machine (depending on molecular weight of raw material):

1. Injection temperature should be adjusted accordingly based on molecular weight of raw material, shape and size of product, and type of injection molding machine.
2. It is best to use a multi-stage injection process, employing a slow-fast-slow injection method.
3. Injection pressure depends on shape and size of product. For plunger-type injection molding machines, it is generally 100-160 MPa, and for screw-type injection molding machines, it is 70-140 MPa.
4. Molding cycle depends on product wall thickness and injection volume. Generally, filling time is short and holding time is long. Cooling time should be sufficient to prevent deformation during demolding.
5. Mold temperature depends on shape and thickness of product. Appropriately increasing mold temperature facilitates demolding and improves product quality.
6. Product Post-Processing: For products with complex shapes, metal inserts, or extremely high operating temperatures, post-processing is necessary to eliminate or reduce internal stress.
Method: Place product in a drying oven and begin heating it. When temperature rises from room temperature to 100-105℃, hold it for 10-20 minutes. Continue heating it to 120-125℃ and hold it for 30-40 minutes. Then, slowly cool it to below 60℃ before removing it.

▶ Extrusion Molding
Polycarbonate extrusion molding can produce sheets, tubes, rods, and films. A single-screw extruder is used, and screw design adapts to viscosity of PC.
Reference Dimensions of Polycarbonate Extrusion Screws

Polycarbonate extrusion screws have an aspect ratio of 18-20, resulting in good plasticization but are susceptible to degradation. Extrusion temperature is lower than that of injection molding, with a temperature difference of 10-20℃ between front and rear sections. Shear rate has little effect on melt viscosity, and rotational speed should be <100 rpm. For small aspect ratios, use a low speed to ensure plasticization.
Polycarbonate Tube Extrusion Molding Process Conditions

Three major application areas for PC engineering plastics are glazing industry, automotive industry, electronics and electrical appliance industries. Other applications include industrial machinery parts, optical discs, packaging, computers and other office equipment, medical and healthcare equipment, films, leisure and protective equipment, etc. PC can be used for door and window glass. PC laminates are widely used for protective windows in banks, embassies, detention centers, and public places, as well as in aircraft canopies, lighting equipment, industrial safety panels, and bulletproof glass.

 

PC Classifications: Antistatic PC, Conductive PC, Fiber-Reinforced Fireproof PC, UV-Resistant and Weather-Resistant PC, Food-Grade PC, and Chemical-Resistant PC.
Polycarbonate (PC) is a rapidly growing engineering plastic, with major producers in United States, Western Europe, and Japan. Despite its late start, China's PC industry has achieved independent research and development, and its production capacity is rapidly increasing.
Environmentally friendly non-phosgene PC production processes are future direction of development, requiring development of efficient catalysts and reactors to reduce costs. Currently, most Chinese PC products are based on basic materials, with high-end products relying on foreign companies. As production capacity increases and industry competition intensifies, companies need to improve product performance, develop high-performance products, reduce costs, improve competitiveness, and strengthen independent research and development.