Characteristics and applications of PC materials

PC (polycarbonate) is a high molecular polymer containing carbonate groups in the molecular chain. According to the structure of ester groups, it can be divided into aliphatic, aromatic, aliphatic-aromatic and other types. It is currently one of the five major engineering plastics. The fastest growing general engineering plastics.

　　 The advantages and disadvantages of PC materials

　　 Polycarbonate is colorless and transparent, heat-resistant, impact-resistant, flame-retardant, BI-level, and has good mechanical properties at ordinary temperatures. Polycarbonate has good impact resistance, high refractive index, and good processing performance. It has UL94 V-0 flame retardant performance without additives. The main performance defects of PC are that it is not sufficiently resistant to hydrolysis, is sensitive to notches, is resistant to organic chemicals, and has poor scratch resistance. It will turn yellow when exposed to ultraviolet light for a long time. PC, like other resins, is easily eroded by some organic solvents. Polycarbonate has poor abrasion resistance, and some polycarbonate devices used for wear-prone applications require special surface treatment.

　　PC (polycarbonate) processing conditions

　　 Polycarbonate has excellent comprehensive properties, and is especially suitable for the manufacture of small parts with precise dimensions, complex shapes, light load or less impact load. During the processing, the viscosity decreases with the increase of temperature. It is necessary to strictly control the three major conditions of raw material drying, injection temperature, and mold temperature.

　　(1) Drying of raw materials

　　 The most prominent feature of polycarbonate is its sensitivity to trace moisture at high temperatures. In addition, its high melting temperature and high melt viscosity often lead to cracking and other quality accidents due to improper handling. Therefore, it must be dried strictly and thoroughly before injection. After drying, the moisture content of the plastic should not be greater than 0.02%. The presence of trace moisture can cause destructive degradation of polycarbonate, decrease the viscosity, emit carbon dioxide and other gases, discolor the plastic, and deteriorate its performance. The injected optical disc products are easy to contain silver wire, bubbles, or even break. The higher the moisture content, the more severe the destructive degradation phenomenon.

　　(2) Injection temperature

　　 There are two thermal processing characteristics of polycarbonate: high thermal stability and a wide molding temperature range; the viscosity change caused by the temperature change is large, and the viscosity change caused by the shear rate change is small.

　　 That is, the melt fluidity of polycarbonate (PC) is greatly affected by temperature changes, while pressure has little effect. Therefore, the adjustment of the injection temperature has always been an effective means for smooth molding and controlling the quality of parts.

However, if the temperature is too low, the viscosity is large, and the supply is insufficient, it will cause the surface of the part to shrink, wrinkle, dull, and disorder the silver wire; if the temperature is too high or higher than 320℃ and the residence time is too long, it will cause serious degradation. As a result, the parts have flashing edges, are dark brown, have dark silver strips, spots and traces on the surface, and have bubbles inside, and their physical properties are greatly reduced.

　　(3) Mold temperature

　　 Polycarbonate has high viscosity, poor fluidity, is insensitive to shearing, and has a fast cooling rate. It is easy to cause defects on the surface of the part and form internal stress.

　　 If the mold temperature is too low, the part is difficult to fill the cavity, or has apparent defects such as large shrinkage, ripples, freckles, dark stripes, and voids, which will increase the residual of the part.

　　 If the mold temperature is too high, the parts will cool slowly, the molding cycle will be long, and the surface gloss will be poor. It will also cause mold sticking, difficult ejection and demolding, and parts bridges and warping deformation.

　　 PC (polycarbonate) injection pressure

　　The influence of injection pressure on the performance of parts is mainly manifested in the holding time. The pressure holding time is short, and the parts shrink, or shrink voids, vacuum bubbles; increase the pressure holding time, especially for large-area thick-walled parts, increase its density, eliminate vacuum holes, and improve dimensional stability; pressure holding time is too long , It will cause internal stress in the part, which is easy to crack.

　　 PC (polycarbonate) applications

　　PC is widely used in building materials, automobiles, medical, aviation, aerospace, electronic appliances, packaging and other fields.

　　Building materials industry: PC board has good light transmittance, impact resistance, dimensional stability, molding processability and UV resistance, and has obvious technical performance advantages over traditional inorganic glass.

Automobile field: Polycarbonate has good impact resistance, thermal distortion resistance, good weather resistance and high hardness, so it is suitable for the production of various parts of cars and light trucks. Its applications are mainly concentrated in lighting systems, instrument panels, Heating plate, defroster, bumper made of polycarbonate alloy, etc.

Medical equipment: Because PC products can withstand steam, cleaning agents, heating and high-dose radiation sterilization without yellowing and physical performance degradation, they are widely used in artificial kidney hemodialysis equipment and other operations that need to be transparent and intuitive. And in medical equipment that needs to be repeatedly sterilized. Such as the production of high-pressure syringes, surgical masks, disposable dental appliances, blood separators, etc.

　　Aerospace: With the rapid development of aviation and aerospace technology, the requirements for various components in aircraft and spacecraft continue to increase, making the application of PCs in this field increasing. According to statistics, there are 2,500 polycarbonate components used on a Boeing aircraft alone, and a single plane consumes about 2 tons of polycarbonate. On the spacecraft, hundreds of polycarbonate parts with different configurations and reinforced by glass fiber and astronaut protective equipment are used.

　　Packaging field: The new growth point in the packaging field is various types of water storage bottles that can be sterilized and used repeatedly. Because polycarbonate products have the advantages of light weight, good impact resistance and transparency, no deformation and transparency when washed with hot water and corrosive solutions, the use of PC bottles is very common.

　　Electronics: Because polycarbonate has good and constant electrical insulation in a wide range of temperature and humidity, it is an excellent insulating material. At the same time, due to its good flame resistance and dimensional stability, it is widely used in the electronic and electrical industry, including power tool housings, bodies, brackets, refrigerator freezer drawers and vacuum cleaner parts. In terms of important parts and components in computers, video recorders and color televisions, PC materials are also used in many applications.

　　 Optical lens: Polycarbonate occupies an extremely important position in this field due to its unique characteristics of high light transmittance, high refractive index, high impact resistance, dimensional stability and easy processing and molding. Optical lenses made of optical grade polycarbonate can be used not only for cameras, microscopes, telescopes and optical testing instruments, but also for film projector lenses, copier lenses, infrared auto-focusing projector lenses, laser beam printer lenses, and various Kinds of prisms, polygon mirrors and many other office equipment and home appliances. In the glasses industry, PC materials are also making great efforts to use in children's glasses, sunglasses and safety glasses and adult glasses.

　　 CD: The amount of PC materials consumed by the world's CD manufacturing industry has exceeded 20% of the total consumption of PCs, and it is developing rapidly.