韩三星PC SC-1100R---Process characteristics of PC Resin
1. The aggregation property belongs to amorphous and noncrystalline plastics, with no obvious melting point and high meltviscosity. Glass transition temperature 140 °～ 150 ℃, meltingtemperature 215 ℃～ 225 ℃, molding temperature 250 ℃～ 320 ℃.
2. It has good thermal stability in the range of normalprocessing temperature. It does not decompose for a long time at300 ℃ and begins to decompose above 340 ℃.
3. The rheological property of the liquid is close to that ofNewtonian liquid, and the apparent viscosity is greatly affected bytemperature, less by shear rate, and increases with the increase ofmolecular weight. There is benzene ring in PC molecular chain, sothe molecular chain is rigid.
4. PC has good creep resistance and dimensional stability; Butthe internal stress is not easy to eliminate.
5. PC is easy to degrade when it meets with water at hightemperature, and the moisture content is required to be less than0.02% during molding.
6. The product is easy to crack.
The molding process of PC resin is controlled in the moldingprocess. The moisture control and the selection of moldingprocessing conditions are the two most important factors affectingthe molding quality
A. Moisture control PC plastics will hydrolyze and break bonds,reduce molecular weight and physical strength when using very lowmoisture. Therefore, the moisture content of PC resin should bestrictly controlled below 0.02% before molding, so as to avoid thereduction of mechanical strength or abnormal appearance such asbubbles and craze on the surface of molding products. In order toavoid the abnormal situation caused by moisture, polycarbonateshould be dried by hot air for more than 3 ~ 5h before processing,and the temperature should be set at 120 ℃, or the moisture shouldbe treated by dehumidification dryer.
B. Raw material selection in order to meet the needs of variousmolding processes, PC resin has different melt flow ratespecifications. Generally, the melt flow rate between 5 ~ 25g /10min is suitable for injection molding. However, the optimalprocessing conditions are quite different due to the types ofinjection molding machines, the shapes of products and thespecifications of PC resin, which should be adjusted according tothe actual situation.
C. Key points of injection molding machine selection: clampingpressure: 0.47 ~ 0.48t per cm2 (or 3 ~ 5T per square inch) machinesize: the weight of the finished product is about 40 ~ 60% of thecapacity of the injection molding machine. For example, when thecapacity of the machine is expressed by PS (ounces), it needs toreduce 10% to use PC (1 ounces = 28.3 grams). Screw: the length ofscrew should be at least 15 diameters, the L / D ratio should be20:1, and the compression ratio should be 1.5:1 to 30:1. The stopvalve at the front end of screw shall be of sliding ring type, andthe resin flow clearance shall be at least 3.2mm. Nozzle: the tipopening shall be at least 4.5mm in diameter. If the finishedproduct weight is more than 5.5kg, the nozzle diameter should bemore than 9.5mm. In addition, the tip opening should be 0.5 ~ 1mmless than the gate diameter, and the shorter the segment, thebetter, about 5mm.
D. Key points of molding conditions: melting temperature andmold temperature: the optimal molding temperature setting isrelated to many factors, such as injection molding machine size,screw configuration, mold and molding product design and moldingcycle, etc. Generally speaking, in order to make the plastic meltgradually, set a lower temperature in the break / feed zone behindthe tube and a higher temperature in the front of the tube.
