The document provides guidance on producing polycarbonate (PC) products through injection molding. Key points include: 1) Drying raw PC material thoroughly before molding to reduce moisture content below 0.02% and avoid strength reductions. 2) Use an injection temperature of 270-320°C to properly melt the material while avoiding decomposition. 3) Consider injection pressure, holding pressure and time, and mold temperature to reduce internal stresses and defects in the molded parts.

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PC polycarbonate products producing
Translated By Jasmine HL
What issues need to be paid attention to when producing PC polycarbonate products?
Raw material drying
PC-based plastics, even when encountering very low moisture content, will undergo hydrolysis
and bond breakage, decrease in molecular weight, and decrease in physical strength. Therefore,
before molding, the moisture of polycarbonate should be strictly controlled below 0.02% to avoid
the decrease of the mechanical strength of the molded product or the appearance of abnormal
appearance such as bubbles and silver streaks on the surface.
PC is extremely sensitive to water, so it must be fully dried before injection to reduce its water
content to below 0.02%. The general drying conditions of PC: 100 ~ 120 ℃, the time is at least 4
hours;
Injection temperature
The injection temperature must be integrated with the shape, size and mold structure of the
product. Product performance, requirements and other aspects of the situation can be
formulated after consideration.
Generally, the temperature is selected between 270 ~ 320 ℃ during molding. If the material
temperature is too high, the PC will decompose, the product color will become darker, and the
surface will have silver wires, dark stripes, black spots, bubbles, and other defects At the same
time, physical and mechanical properties have also decreased significantly.
PC is also very sensitive to temperature. The melt viscosity decreases significantly with increasing
temperature. The barrel temperature is 250 ~ 320 ℃ (preferably not more than 350 ℃).
Properly increasing the temperature of the barrel temperature is good for PC plasticization.

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Internal stress annealing if necessary, oven temperature 125 ~ 135 ℃, time 2 hours, natural
cooling to normal temperature.
Injection pressure
It has a certain effect on the physical and mechanical properties, internal stress, and molding
shrinkage of PC products. It has a greater impact on the appearance and mold release of the
product. Too low or too high injection pressure will cause some defects in the product. Generally,
the injection pressure is controlled between 80-120MPa. For products with thin walls, long
processes, complicated shapes, and small gates, in order to overcome the resistance of the melt
flow and fill the mold cavity in time, a higher injection pressure (120 -145MPa). Thereby, a
complete and smooth product is obtained.
Poor fluidity, high-pressure injection is required, but large internal stress (which may cause
cracking) of the rubber parts must be taken into account. Injection speed: medium thickness for
wall thickness, high speed for a thin wall.
Holding pressure and holding time
The size of the holding pressure and the length of the holding pressure have a greater impact on
the internal stress of the PC product. If the holding pressure is too small, the shrinkage effect is
small, and vacuum bubbles or surface dents are likely to occur. If the holding pressure is too large,
the Large internal stress easily occurs around the mouth. In actual processing, it is often solved
by high material temperature and low holding pressure.
The selection of the dwell time should depend on the thickness of the product, the size of the
gate, and the mold temperature. Generally, small and thin products do not require a longer dwell
time. On the contrary, the dwell time of large and thick products should be longer. The length of
the dwell time can be determined by testing the gate sealing time.
Injection speed
It has no significant effect on the performance of PC products. Except for thin-walled, small gates,
deep holes, and long-flow products, medium or slow processing is generally used, preferably
multi-stage injection, and slow-fast-slow is generally used. Multi-stage injection.
Mold temperature
Mold temperature control: 85 ~ 120 ℃, generally can be controlled at 80-100 ℃, for complex
shapes, thinner, more demanding products, it can also be increased to 100-120 ℃, 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 part.
Screw speed and backpressure
Due to the higher melt viscosity of the PC, it is beneficial to plasticize, to facilitate exhaustion, to
facilitate the maintenance of the plastic machine, to prevent the screw load from being too large,
and the speed of the screw should not be too high. Generally, it is appropriate to control it at
30-60r / min. The backpressure is preferably controlled between 10-15% of the injection
pressure.
Use of additives

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In the injection molding process of PC, the use of release agents should be strictly controlled, and
the use of recycled materials should not be more than three times, and the use amount should
be about 20%.
PC injection requires higher molds:
1) Design the flow channel which is as thick and short as possible with less bending position. Use
circular cross-section flow channel and flow channel grinding and polishing to reduce the flow
resistance of the molten material.
2) The injection gate can use any type of gate, but the diameter of the water level is not less than
1.5mm.
Requirements for presses for the production of PC products:
The maximum injection volume of the product (including runners, gates, etc.) should not be
greater than 70-80% of the nominal injection volume;
Clamping pressure: 0.47 to 0.78 tons per square centimeter of the projected area of the finished
product (or 3 to 5 tons per square inch);
Machine size: The weight of the finished product is about 40 to 60% of the capacity of the
injection molding machine. For example, when the machine uses polystyrene to indicate its
capacity (oz), it needs to be reduced by 10%, 1 oz = 28.3 grams.
Screw: The screw length should be at least 15 diameters long, and its L / D is 20: 1. The
compression ratio should be 1.5: 1 to 30: 1. The stop valve at the front end of the screw should
adopt a sliding ring type, and the resin flowable gap should be at least 3.2MM.