Polycarbonate, English name Polycarbonate, referred to as PC.
PC is an amorphous, odorless, non-toxic, highly transparent colorless or yellowish thermoplastic engineering plastic with excellent physical and mechanical properties, especially excellent impact resistance, high tensile strength, bending strength, and compressive strength; small creep and dimensional stability;
It has good heat resistance and low temperature resistance, stable mechanical properties, dimensional stability, electrical properties and flame retardancy over a wide temperature range, and can be used for a long time at -60~ 120 ° C; no obvious melting point, in a molten state at 220-230 ° C; due to the high rigidity of the molecular chain, the resin melt viscosity is large; the water absorption rate is small, the shrinkage rate is small, the dimensional accuracy is high, the dimensional stability is good, and the film air permeability is small; it is a self-extinguishing material; stable to light, but not resistant to ultraviolet light, good weather resistance;
Resistant to oil, acid, alkali, oxidizing acids, amines, ketones, soluble in chlorinated hydrocarbons and aromatic solvents, prone to hydrolysis and cracking in water for a long time. The disadvantage is that due to poor fatigue strength, it is prone to stress cracking, poor solvent resistance, and poor wear resistance.
Before molding, PC resin must be fully dried. The drying method can be boiling bed drying (temperature 120~ 130 ℃, time 1~ 2h), vacuum drying (temperature 110 ℃, vacuum degree 96kPa or more, time 10~ 25h), hot air circulation drying (temperature 120~ 130 ℃, time 6h or more).
In order to prevent the dried resin from re-absorbing moisture, it should be placed in an incubator at 90 ° C, and it should not be stored for a long time. When forming, the hopper must be airtight, and a heating device should be installed in the hopper, and the temperature should not be lower than 100 ° C. For hoppers without insulation devices, the amount of material added at one time should be less than half an hour, and the lid should be tightly closed.
The quick test method to judge the drying effect is to use "air injection" on the injection molding machine. If the material slowly flowing out of the nozzle is a thin strip that is uniform and transparent, bright without silver wires and bubbles, it is qualified. This method is applicable to general plastics.
The melt viscosity of PC is much larger than that of PA, PS, PE, etc., and the fluidity is poor. The flow characteristics of the melt are similar to those of Newtonian fluids. The melt viscosity is less affected by the shear rate and is very sensitive to temperature changes. Therefore, as long as the processing temperature is adjusted during molding, the apparent viscosity of PC can be effectively controlled.
The choice of molding temperature is related to the relative average molecular weight of the resin and its distribution, the shape and size of the product, the type of injection molding machine, etc., and is generally controlled within the range of 250~ 310 ° C. For injection molding materials, resins with a slightly lower relative average molecular weight should be selected, with an MFR of 5~ 7g/10min; for complex or thin-walled products. The molding temperature should be higher, 285~ 305 ° C; while for thick-walled products, the molding temperature is slightly lower, 250~ 280 ° C. Different injection molding machines have different molding temperatures.
The screw type is 260~ 285 ° C, and the plunger type is 270~ 310 ° C. The temperature of the barrel is set in the way of high front and low back. The temperature of the rear barrel near the end of the hopper should be controlled above the softening temperature of the PC, that is, greater than 230 ° C, to reduce material resistance and injection pressure loss.
Although increasing the molding temperature is conducive to melt filling. But it cannot exceed 230 ° C, otherwise, the PC will degrade, causing the color of the product to darken, and defects such as silver wires, dark strips, black spots, and bubbles will appear on the surface. At the same time, the physical and mechanical properties will also decrease significantly.
The nozzle temperature is 260~ 310 ° C, and the temperature control of the nozzles of the two types of injection molding machines is different.
The mold temperature has a great influence on the mechanical properties of the product. As the mold temperature increases
