What are the precautions for processing PC raw materials into finished products?
Which products meet the needs of customers and highlight our product competitiveness? We conducted research on online platforms and found that PC processed products are very popular, such as sun visors, basketball boards, lampshades, shields, and so on.
The production of a product mainly depends on the mold. As long as the mold is designed, the desired style of product is sufficient. But the most headache in the production process is that processing requires attention to many details, otherwise the products produced will either be deformed or not meet the standards we want. So, what details do we need to pay attention to in the production process? We have summarized the top ten considerations.
First note: Dry raw materials
PC plastics, even when exposed to very low levels of moisture, can undergo hydrolysis to break bonds, reduce molecular weight, and decrease physical strength. Therefore, before the molding process, the moisture content of polycarbonate should be strictly controlled to be below 0.02%.
Second note: Injection temperature
Generally, the temperature between 270~320 ℃ is selected for molding. If the material temperature exceeds 340 ℃, PC will decompose, the color of the product will darken, and defects such as silver wires, dark stripes, black spots, and bubbles will appear on the surface. At the same time, the physical and mechanical properties will also significantly decrease.
Third note: Injection pressure
The physical and mechanical properties, internal stress, and molding shrinkage of PC products have a certain impact on their appearance and demolding properties. Too low or too high injection pressure can cause certain defects in the products. Generally, the injection pressure is controlled between 80-120MPa.
Fourth note: Holding pressure and holding time
The magnitude of the holding pressure and the duration of the holding time have a significant impact on the internal stress of PC products. If the pressure is too low and the shrinkage effect is small, vacuum bubbles or surface indentations may occur. If the pressure is too high, significant internal stress may be generated around the sprue. In practical processing, high material temperature and low holding pressure are often used to solve this problem.
Fifth note: Injection speed
There is no significant impact on the performance of PC products, except for thin-walled, small gate, deep hole, and long process products. Generally, medium or slow speed processing is used, and multi-stage injection is preferred, usually using a slow fast slow multi-stage injection method.
Sixth note: Mold temperature
85~120 ℃, generally controlled at 80-100 ℃. For products with complex shapes, thin thickness, and high requirements, it can also be increased to 100-120 ℃, but it cannot exceed the hot deformation temperature of the mold.
Seventh note: Screw speed and back pressure
Due to the high viscosity of PC melt, it is beneficial for plasticization, exhaust, and maintenance of the plasticizing machine to prevent excessive screw load. The requirement for screw speed should not be too high, generally controlled at 30-60r/min, and the back pressure should be controlled between 10-15% of the injection pressure.
Eighth note: Use of additives
During the injection molding process of PC, the use of release agents should be strictly controlled, and the use of recycled materials should not exceed three times, with a usage rate of about 20%.
Ninth note: PC injection molding has high requirements for molds:
Design channels that are as thick and short as possible, with minimal bending, and use circular cross-section diversion channels and channel grinding and polishing to reduce the flow resistance of the molten material. The injection gate can use any form of gate, but the diameter of the inlet water level should not be less than 1.5mm.
Tenth note: Requirements for plastic machines used in the production of PC products:
The maximum injection volume of the product should not exceed 70-80% of the nominal injection volume; The clamping pressure ranges from 0.47 to 0.78 tons per square centimeter of the projected area of the finished product; The optimal size of the machine is about 40 to 60% of the capacity of the injection molding machine based on the weight of the finished product. The minimum length of the screw should be 15 diameters long, with an L/D ratio of 20:1 being optimal.
Reasonable and effective processing is necessary to maximize the effectiveness of the finished product. Provide customers with more choices.