PC plastic is known as polycarbonate, because of its excellent mechanical properties, commonly known as bulletproof plastic. PC plastics have high mechanical strength, wide temperature range, good electrical insulation performance (but no anti-arcing performance), good dimensional stability, and transparency.
It is widely used in electrical products, electrical instrument casings, electronic product structural parts. There are many modified PC products, usually adding glass fiber, mineral fillers, chemical flame retardants, and other plastics. PC plastics have poor fluidity and high processing temperatures, so the processing of many grades of modified materials requires specialized plastic injection structures.
1, plastic processing
PC water absorption rate is large, must be preheated and dried before processing, pure PC drying 120 °C, modified PC is generally used 110 °C temperature drying more than 4 hours. Drying time cannot exceed 10 hours. Dry extrusion methods are generally used to determine if drying is adequate.
The proportion of recycled materials can reach 20%. In some cases, renewable materials can be used 100%. The actual amount depends on the quality requirements of the product. Recycled material cannot mix different masterbatch at the same time, otherwise it will seriously damage the properties of the finished product.
2, the choice of injection molding machine
Nowadays, due to the cost and other reasons, PC products use more modified materials, especially electrical products, and must also increase the fire performance. When the flame-retardant PC and other plastic alloy products are molded, the requirements for the injection molding machine plasticization system are: Good mixing and corrosion resistance. The conventional plasticizing screw is difficult to do. When purchasing, it must be stated in advance. Ramada has a dedicated PC screw for customers to choose.
3, mold and gate design
Common mold temperature 80-100 °C, plus glass fiber is 100-130 °C, small products available needle-shaped gate, gate depth should be 70% of the thickest parts, other gates have a ring and rectangular.
The bigger the gate, the better, to reduce the defects caused by excessive shearing of the plastic. The depth of the vent hole should be less than 0.03-0.06mm, and the flow path should be as short and round as possible. The draft angle is generally about 30'-1.
4, melt temperature
Can use the air injection method to determine the processing temperature level. Typical PC processing temperatures are 270-320°C, and some modified or low molecular weight PCs are 230-270°C.
5, injection speed
More common with the injection molding speed faster, such as electrical switch parts. Commonly slow → rapid prototyping.
6, back pressure
The back pressure of about 10 bar can be properly reduced without gas lines and color mixing.
7, stay time
If the residence time is too long at high temperature, the material will be degraded and CO2 will be released to become yellow. Do not clean the barrel with LDPE, POM, ABS, or PA. Apply PS cleanup.
8, matters needing attention
Some modified PCs, due to too many recycling (decrease in molecular weight) or uneven mixing of various ingredients, easy to produce dark brown liquid bubbles.
