Polycarbonate (PC) is one of the core materials in the engineering plastic field due to its excellent mechanical properties, light transmittance and weather resistance. However, the limitations of its inherent heat resistance once restricted its application in high-temperature working conditions. With the continuous upgrading of modification technologies and molding processes, high temperature resistant PC products have broken through the traditional application boundaries, and are widely used in automotive, electronic and electrical, aerospace and other fields with strict requirements for heat resistance. They have become indispensable key materials in high-end manufacturing, and their technological development directly promotes the transformation of related industries towards lightweight and high performance.
The glass transition temperature of PC is about 150℃, the long-term service temperature of unmodified PC is about 80-100℃, and the short-term heat resistance temperature can reach 130℃. This characteristic makes it stable in conventional environments, but it cannot meet the needs of high-temperature working conditions. Its heat resistance bottleneck mainly comes from the carbonate groups in the molecular chain structure, which are prone to segment movement at high temperatures, leading to the decline of material mechanical properties. Therefore, it is necessary to optimize the molecular structure or aggregate structure through modification technologies to improve thermal stability.
At present, the mainstream high temperature resistant modification paths in the industry include copolymerization modification, filling modification and blending modification. Copolymerization modification enhances the rigidity of molecular chains by introducing rigid aromatic ring structure monomers, and the long-term service temperature of modified PC can be increased to 120-130℃; filling modification uses heat-resistant fillers such as glass fiber and carbon fiber, which not only increases the heat distortion temperature, but also improves the dimensional stability of materials; blending modification blends with high temperature resistant polymers such as polyphenylene oxide (PPO) and polyimide (PI), taking into account heat resistance and processing fluidity to meet the molding needs of complex products.
The injection molding of high temperature resistant PC needs to focus on controlling temperature and pressure parameters: the barrel temperature should be set at 280-320℃ to ensure the material is fully melted without thermal degradation; the mold temperature is controlled at 80-120℃ to reduce internal stress of products and avoid cracking during high-temperature use; the injection pressure needs to be higher than that of conventional PC injection molding, generally 80-120MPa, to ensure complete melt filling. In addition, annealing treatment is required after molding, holding at 120℃ for 2-4 hours to further release internal stress and improve the heat resistance stability of products.
For extruded products such as high temperature resistant PC sheets and pipes, single-screw or twin-screw extruders with a screw length-diameter ratio of not less than 25:1 should be used to ensure uniform mixing of materials. The extrusion temperature is controlled in sections, from the feeding section to the die head, which are 250℃, 270℃, 290℃ and 300℃ in turn, and the die head temperature is slightly lower than the melt temperature to prevent material degradation. In the cooling and shaping stage, gradient cooling should be adopted to avoid warpage of products due to excessive temperature difference, which affects the structural stability at high temperatures.
The secondary processing of high temperature resistant PC products needs to match its heat resistance characteristics. For example, thermoforming needs to control the molding temperature at 140-160℃, lower than the heat distortion temperature of the material; hot melt bonding or epoxy adhesive bonding is preferred for bonding process to avoid material swelling caused by solvent-based adhesives; sharp tools should be used for mechanical processing to reduce frictional heat generation during processing and prevent local overheating from causing material softening.
Components around automobile engines are the core application scenarios of high temperature resistant PC products, such as engine hood inner guards and intake manifold covers. These components are in a high-temperature environment of 100-120℃ for a long time. Modified high temperature resistant PC can replace traditional metal materials to achieve lightweight, and has excellent aging resistance. In addition, the shell of new energy vehicle charging piles adopts high temperature resistant PC, which can withstand continuous high temperatures generated during charging and ensure electrical safety.
In the electronic and electrical field, high temperature resistant PC products are used for LED lamp heat dissipation shells, electrical switch panels, server chassis components, etc. LED lamp shells need to withstand long-term high temperatures during lamp operation, and high temperature resistant PC not only has heat resistance, but also has light transmittance and flame retardancy; the heat generated by server chassis components during continuous operation can reach 110℃, and modified PC products can maintain structural stability and have good electromagnetic shielding adaptability.
The aerospace field has extremely high requirements for material heat resistance and lightweight. High temperature resistant PC products are used for aircraft interior parts, cabin control panels, etc. The temperature in some areas inside the cabin can reach 120℃, and modified PC can meet the long-term use needs. At the same time, it is more than 30% lighter than metal materials, which helps reduce the overall energy consumption of the aircraft. In addition, insulating brackets in satellite components also use high temperature resistant PC to adapt to temperature fluctuations in the space environment.
Current high temperature resistant PC modification technologies are developing towards multi-functional integration, that is, while improving heat resistance, integrating flame retardancy, antistatic, scratch resistance and other characteristics to meet the comprehensive needs of complex scenarios. For example, introducing nano-scale heat-resistant fillers can significantly improve the thermal stability of materials with a small amount of addition, while maintaining good processing fluidity.
With the penetration of Industry 4.0 technology, the molding process of high temperature resistant PC products has gradually realized intelligent control. Sensors are used to collect real-time data such as melt temperature and mold pressure, and AI algorithms are used to dynamically adjust process parameters, reducing human errors and improving product consistency. Some enterprises have realized the full-process automation of injection molding, from raw material ratio to product inspection without manual intervention.
Driven by the concept of green manufacturing, breakthroughs have been made in the R&D of bio-based high temperature resistant PC materials, using biomass raw materials to replace part of petrochemical raw materials and reduce carbon emissions. At the same time, the recycling and reuse technology of waste high temperature resistant PC products is constantly maturing, and circular use is realized through chemical depolymerization or physical modification, which conforms to the low-carbon development trend of the industry.
