PC is commonly known as polycarbonate. Due to its excellent mechanical properties, it is commonly known as bulletproof glue. PC has characteristics of high mechanical strength, wide operating temperature range, good electrical insulation performance (but arc protection performance remains unchanged), good dimensional stability, and transparency.
Process characteristics of PC: melt viscosity is less sensitive to shear rate, but more sensitive to temperature, no obvious melting point, high melt viscosity, resin is easy to hydrolyze at high temperature, and products are easy to crack.
In view of these characteristics, we should pay special attention to different treatments:
To increase fluidity of melt, it is not necessary to increase injection pressure but to increase injection temperature; mold runner and gate are required to be short and thick to reduce pressure loss of fluid, and at the same time, a higher injection pressure is required; resin needs to be fully dried before molding to control its water content below 0.02%;
In addition, insulation measures should be taken for resin during processing to prevent re-absorption of moisture;
Not only reasonable product design is required, but also molding process should be correctly mastered, such as increasing mold temperature and post-processing product to reduce or eliminate internal stress, and process parameters should be adjusted in time according to different conditions of product.

 

PC plastics will hydrolyze and break bonds, reduce molecular weight and reduce physical strength even when encountering very low moisture. Therefore, before molding, moisture content of polycarbonate should be strictly controlled below 0.02% to avoid reduced mechanical strength of molded product or 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 molding to reduce its water content to below 0.02%. General drying conditions for PC are: 100~120℃, and time is at least 4 hours;

Injection temperature must be determined after considering shape, size, mold structure, product performance, requirements and other aspects of product.
Generally, temperature used in molding is between 270~320℃. If material temperature is too high, such as exceeding 340℃, PC will decompose, product color will become darker, and defects such as silver wire, dark stripes, black spots, and bubbles will appear on the surface. At the same time, physical and mechanical properties will also decrease significantly.
PC temperature is very sensitive, and melt viscosity decreases significantly with increase of temperature. Barrel temperature is 250~320℃. (It is best not to exceed 350℃). Properly increasing barrel temperature is good for PC plasticization. If necessary, internal stress annealing, oven temperature is 125~135℃, time is 2 hours, and it is naturally cooled to room temperature.

 

It has a certain influence on physical and mechanical properties, internal stress, molding shrinkage, etc. of PC products. It has a great influence on appearance and demolding of products. Too low or too high injection pressure will cause certain defects in products.
Generally, injection pressure is controlled between 80-120MPa. For products with thin walls, long processes, complex shapes, and small gates, in order to overcome resistance of melt flow and fill mold cavity in time, a higher injection pressure (120-145MPa) is selected to obtain complete and smooth products.
Poor fluidity requires high-pressure injection, but large residual internal stress of plastic parts must be taken into account (which may cause cracking)
Injection speed: medium speed for thick walls and high speed for thin walls.

Size of holding pressure and length of holding time have a great influence on internal stress of PC products. If holding pressure is too small, shrinkage compensation effect is small, and vacuum bubbles or shrinkage concavities on the surface are prone to occur. If holding pressure is too large, large internal stress is easily generated around gate. In actual processing, high material temperature and low holding pressure are often used to solve problem.
Choice of holding time should depend on thickness of product, size of gate, mold temperature, etc. Generally, small and thin products do not need a long holding time. On the contrary, large and thick products should have a longer holding time.
Length of holding time can be determined by test of gate sealing time.

It has no obvious effect on performance of PC products. Except for thin-walled, small gates, deep holes, and long-flow products, medium or slow processing is generally adopted. Multi-stage injection is best, and slow-fast-slow multi-stage injection is generally adopted.

Mold temperature control: 85~120℃, generally controlled at 80-100℃, for complex, thin, and high-requirement products, it can also be increased to 100-120℃, but it cannot exceed mold thermal deformation temperature. High mold temperature can reduce difference between mold temperature and PC material temperature, which can reduce internal stress of product.

Since PC melt has a high viscosity, from perspective of plasticization, exhaust and maintenance of molding machine, in order to prevent excessive screw load, screw speed requirement should not be too high. It is generally controlled at 30-60r/min, and back pressure should be controlled between 10-15% of injection pressure.

Use of release agent should be strictly controlled during PC injection molding. At the same time, use of recycled materials should not exceed three times, and amount used should be about 20%.

 

1) Design a runner that is as thick and short as possible with few bends, use circular cross-section runners and runner grinding and polishing to reduce flow resistance of molten material.
2) Injection gate can use any form of gate, but water entry diameter should not be less than 1.5mm.

Maximum injection volume of product (including runners, gates, etc.) should not exceed 70-80% of nominal injection volume;
Clamping pressure: 0.47 to 0.78 tons per square centimeter of finished product projection area (or 3 to 5 tons per square inch);
Machine size: Weight of finished product is about 40 to 60% of injection molding machine capacity, which is the best. If machine uses polystyrene to express its capacity (ounces), it needs to be reduced by 10% to use capacity of GUANGDA. 1 ounce = 28.3 grams.
Screw: Screw length should be at least 15 diameters long, and its L/D is 20:1. Compression ratio should be 1.5:1 to 30:1. Stop valve at the front end of screw should be a sliding ring type, and resin flow gap should be at least 3.2MM.

Use PE material to pass machine.