PC has excellent performance, high transparency, good impact toughness, creep resistance and wide temperature range. The melt viscosity of PC is less sensitive to shear rate, and the sensitivity to temperature is large, there is no obvious melting point, the melt body viscosity is high, the resin is easy to hydrolysis at high temperature, and the product is easy to crack.

For these characteristics, we should pay special attention to different treatment:

(1) To increase the fluidity of the melt, it is not necessary to increase the injection pressure but to increase the injection temperature;

2, the flow channel and gate of the mold are required to be short and thick to reduce the pressure loss of the fluid, and at the same time, the injection pressure is higher;

3, the resin should be fully dried before forming and processing, so that its water content is controlled below 0.02%;

4, in addition, during the processing of the resin should also take insulation measures to prevent re-moisture absorption;

5, not only the need for reasonable product design, but also the correct grasp of the molding process, such as increasing the mold temperature, post-processing products can reduce or eliminate internal stress. Adjust the process parameters in time according to the different conditions of the product.

Molding process

Raw material drying: PC plastic, even in very low water will produce hydrolysis and broken bonds, molecular weight reduction and physical strength reduction phenomenon.

Therefore, before the molding process, the moisture of polycarbonate should be strictly controlled below 0.02% to avoid the mechanical strength of the molding product or the abnormal appearance of bubbles and silver lines on the surface. PC is extremely sensitive to water, so it must be fully dried before injection, so that its water content is reduced to less than 0.02%, PC general drying conditions: 100~120℃, time at least 4 hours or more.

Injection temperature: the shape, size and mold structure of the product must be integrated. Product performance, requirements and other aspects of the situation to be considered before making.

Generally in the molding selection temperature between 270~320℃, too high material temperature such as more than 340℃, PC will appear decomposition, product color darkening, surface silver wire, filaments, black spots, bubbles and other defects, while the physical and mechanical properties are also significantly reduced. PC is also very sensitive to temperature, melt viscosity decreases significantly with the increase of temperature, barrel temperature 250~320℃(preferably not more than 350℃), the appropriate increase in temperature barrel temperature is good for PC plasticization. If necessary, the internal stress is annealed, the oven temperature is 125~135℃, the time is 2 hours, and the natural cooling is normal temperature.

Injection pressure: too low or too high injection pressure will cause some defects in the product, the general injection pressure is controlled between 80-120MPa, for thin-walled, long process, complex shape, and small gate products, in order to overcome the resistance of melt flow, in order to fill the mold cavity in time, the higher injection pressure (120-145MPa) is selected. To obtain a complete and smooth surface of the product.

Holding pressure and holding time: the holding pressure is too small, the feeding effect is small, and the vacuum bubble or the surface is prone to concave, the holding pressure is too large, and the internal stress around the gate is easy to produce, which is often solved by high material temperature and low holding pressure in actual processing. The choice of pressure holding time should be based on the thickness of the product, the size of the gate, the mold temperature, etc. The length of the pressure holding time can be determined by the test of the gate sealing time.

Injection speed: there is no significant impact on the performance of PC products, in addition to thin-wall, small gate, deep hole, long process products, generally using medium or slow processing, preferably multi-stage injection, generally using slow-fast-slow multi-stage injection method.

Mold temperature control: 85~120 ° C, generally controlled at 80~100 ° C, for complex shapes, thin, demanding products, can also be increased to 100-120 ° C, but can not exceed the mold thermal deformation temperature. The mold temperature is high to reduce the difference between the mold temperature and the PC material temperature, which can reduce the internal stress of the parts.

Screw speed and back pressure: Due to the large viscosity of PC melt, from the favorable plasticization, favorable exhaust, favorable maintenance of the plastic machine, to prevent the screw load is too large, the speed requirements of the screw can not be too high, generally controlled at 30-60r/min is appropriate, and the back pressure control is appropriate between 10-15% of the injection pressure.

The use of additives: PC in the injection process to strictly control the use of release agents, while the use of recycled materials can not be more than three times, the amount of use should be about 20%.