PC is commonly known as polycarbonate, which is commonly known as bulletproof glue due to its excellent mechanical properties. PC has the characteristics of high mechanical strength, wide operating temperature range, good electrical insulation performance (but unchanged arc resistance), good dimensional stability and transparency. It is widely used in electrical products, electrical instrument shells, and electronic product structural parts. There are many modified products of PC, usually adding glass fiber, mineral fillers, chemical flame retardants, other plastics, etc. PC has poor fluidity and high processing temperatures, so the processing of many grades of modified materials requires specialized plasticized injection structures.
1. Treatment of plastics
PC water absorption rate is large, must be preheated and dried before processing, pure PC drying 120 °C, modified PC generally with 110 °C temperature drying for more than 4 hours. The drying time should not exceed 10 hours. Generally, the empty extrusion method can be used to determine whether the drying is sufficient.
The proportion of recycled material can be up to 20%. In some cases, 100% recycled material can be used, depending on the quality requirements of the product. The recycled material cannot be mixed with different masterbatches at the same time, otherwise the properties of the finished product will be seriously damaged.
2. Selection of injection molding machine
Now PC products due to cost and other reasons, more use of modified materials, especially electrical products, but also to increase fire performance, in flame retardant PC and other plastic alloy products molding, the requirements for injection molding machine plasticizing system is good mixing, corrosion resistance, conventional plasticizing screw is difficult to do, in the purchase, must be explained in advance. Ramada has dedicated PC screws for customers to choose.
3. Mold and gate design
Common mold temperature is 80-100 °C, glass fiber is 100-130 °C, small products can be needle gate, gate depth should have 70% of the thickest part, other gates have ring and rectangular.
The larger the gate, the better to reduce defects caused by excessive shearing of the plastic.
The depth of the exhaust hole should be less than 0.03-0.06mm, and the flow channel should be as short and round as possible.
The demolding slope is generally about 30′-1°.
4. Melting temperature
The air injection method can be used to determine the processing temperature. The general PC processing temperature is 270-320 °C, and some modified or low molecular weight PC is 230-270 °C.
5. Injection speed
It is more common to use fast injection speed molding, such as electrical switches. Slow → rapid prototyping is common.
6. Back pressure
The back pressure of about 10 bar can be appropriately reduced in the absence of air lines and color mixing.
7. Residence time
If the residence time is too long at high temperature, the material will deteriorate, release CO2, and turn yellow. Do not clean the barrel with LDPE, POM, ABS, or PA. Apply PS Cleanup.
8. Precautions
Some modified PCs are prone to dark brown liquid bubbles due to too many times of recovery (reduced molecular weight) or uneven mixing of various components.
