Polycarbonate, Polycarbonate, abbreviated as PC. PC is an amorphous, odorless, non-toxic, highly transparent colorless or yellowish thermoplastic engineering plastics, with excellent physical and mechanical properties, especially impact resistance, tensile strength, bending strength, compression strength; creep is small, dimensional stability; good heat resistance and low temperature resistance. In a wide range of temperatures with stable mechanical properties, dimensional stability, electrical properties and flame retardant, can be used for a long time at -60 ~ 120 ℃; no significant melting point, in 220-230 ℃ is molten; due to the rigidity of the molecular chain, the resin melt viscosity; small water absorption, small shrinkage, high dimensional accuracy, good dimensional stability, film permeability is small; is a self-extinguishing material; light stable, but not UV resistance, weathering. Not resistant to ultraviolet light, good weather resistance; oil, acid, not resistant to strong alkalis, oxidizing acids and amines, ketones, soluble in chlorinated hydrocarbons and aromatic solvents, long-term hydrolysis and cracking in the water, the disadvantage is that due to poor fatigue strength, prone to stress cracking, poor solvent resistance, poor abrasion resistance.
Physical and chemical properties
PC plastic process characteristics are as follows:
① is an amorphous plastic, Tg 149 ~ 150 ℃; Tf 215 ~ 225 ℃; molding temperature of 250 ~ 310 ℃; the relative average molecular mass of 2 ~ 40,000.
② Thermal stability is good, and with the increase in relative molecular mass.
③ Rheological properties close to Newtonian liquids, apparent viscosity is affected by the temperature, less affected by the shear rate, and increases with the increase in relative average molecular mass. There is no obvious melting point, melt viscosity is higher. pc molecular chain has a benzene ring, so, the rigidity of the molecular chain is large.
④ PC creep resistance is good, good dimensional stability; but the internal stress is not easy to eliminate.
⑤ PC is easy to degrade when it meets water at high temperature, and the water content is required to be below 0.02% when molding.
⑤ PC is easy to degrade in the presence of water at high temperature, and the moisture content is required to be less than 0.02% during molding.
Before molding, PC resin must be fully dried. Drying methods can be used boiling bed drying (temperature 120 ~ 130 ℃, time 1 ~ 2h), vacuum drying (temperature 110 ℃, vacuum degree of 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-hygroscopicity, it should be placed in a holding tank at 90℃, and should be taken as it is used, and should not be stored for a long time. Molding hopper must be closed, the hopper should be equipped with a heating device, the temperature is not less than 100 ℃, no insulation device for the hopper, a charging amount of the best less than half an hour's worth of dosage, and to be covered with a tight lid.
Judge the drying effect of the rapid test method, is used in the injection molding machine "to the empty injection". If the material slowly out of the nozzle is uniformly transparent, bright silver and bubble-free thin strip, it is qualified. This method is applicable to general plastics.
The melt viscosity of PC is much larger than PA, PS, PE, etc., and the fluidity is poor. The flow characteristics of the melt is close to the Newtonian fluid, melt viscosity is less affected by the shear rate, and very sensitive to changes in temperature, therefore, molding as long as the processing temperature is adjusted, you can effectively control the performance of PC viscosity.
The choice of molding temperature is related to the relative average molecular mass of the resin and its distribution, the shape and size of the product, the type of injection molding machine, etc., and is generally controlled in the range of 250 to 310 ℃. Injection molding materials, it is appropriate to use the relative average molecular mass of the resin is slightly lower, MFR for 5 ~ 7g/10min; for complex shapes or thin-walled products. Molding temperature should be high, 285 ~ 305 ℃; and thick-walled products, molding temperature is slightly lower, 250 ~ 280 ℃. Different injection molding machine, molding temperature is not the same. Screw type is 260～285℃, plunger type is 270～310℃. The barrel temperature is set in a front-high and back-low manner, and the back barrel temperature near the hopper end should be controlled above the softening temperature of PC, i.e., greater than 230°C, in order to reduce material resistance and injection pressure loss. Although increasing the molding temperature is beneficial to melt filling. But not more than 230 ℃, otherwise, PC will degrade, so that the product color becomes darker, the surface of the silver wire, dark bars, black spots, bubbles and other defects, at the same time, the physical and mechanical properties will be significantly reduced.
The nozzle temperature is 260 ~ 310 ℃, two types of injection molding machine nozzle temperature control is different.
Mold temperature has a great impact on the mechanical properties of products. With the increase in mold temperature. The temperature difference between the material temperature and mold temperature becomes smaller, the shear stress is reduced, the melt can be slowly cooled in the mold cavity, the molecular chain can be relaxed, the degree of orientation is reduced, thus reducing the internal stress of the product, but the impact strength of the product, the elongation of the product decreased significantly, and at the same time, there will be a product demolding difficulties. Easy to deform when demolding, and prolong the molding cycle, reducing productivity; and lower mold temperature, but will make the products of the internal stress increases. Therefore, the mold temperature must be controlled. Usually, the mold temperature of PC is 80 to 120 ℃. Ordinary products are controlled at 80 ~ 100 ℃, while for complex shapes, thin-walled and demanding products, it is controlled at 100 ~ 120 ℃, not allowed to exceed its heat deformation temperature.
Molding PC thick-walled products, mold temperature control is particularly important. For example, in the molding of simply supported beam impact test samples (thickness of 10mm), if the mold does not control the temperature, the molded samples of the internal shrinkage of many holes, but also very large. At this time, if the mold is not equipped with a heating device, a simple method can be used to heat the main flow channel of the mold. The simple method is in a wire tied to a cotton ball, dipped in industrial alcohol, heating the main stream, so that, although it can not eliminate shrinkage, but the number of shrinkage is greatly reduced. The degree is greatly reduced. Of course. This is a way out of the way, is a way of the earth, do not recommend the use of. Because of this, it is easy to make the mold main stream deformation and oxidation.
Although the injection pressure during injection molding of the melt strength and fluidity of the impact is small, but due to the high viscosity of the PC melt, fluidity is poor, therefore, the injection pressure can not be too low, generally controlled at 80 ~ 120MPa, the use of plunger-type injection molding machine, the injection pressure should be 100 ~ 150MPa; for the thin-walled, long-flowing distance, the shape of complexity, the gate size of the product is small, in order to make the melt For thin-walled, long-flow distance, complex shape, small gate size products, in order to make the melt smooth, timely filling of the mold, the injection pressure should be appropriately increased to 120 ~ 150MPa. PC injection molding process control of the general principle is: high material temperature, low pressure.
The size of the holding pressure and the length of the holding time directly affects the quality of the product. Holding pressure is too small, the shrinkage effect is small, the product will be formed inside the contraction of air bubbles, the product surface will also appear dents; Holding pressure is too large. If the holding pressure is too high, it is easy to produce large internal stress around the gate. Holding time is long, high dimensional accuracy, low shrinkage, good surface quality, but increased internal stress in the product, prolonging the molding cycle. Holding pressure of 80 ~ 100 MPa. As previously mentioned methods - heating the main flow channel with fire to extend the solidification time of the melt in the gate to increase the role of complementary shrinkage. pc injection molding, you can increase the back pressure.
The injection rate has little effect on the performance of the product. However, from the molding point of view, the injection rate should not be too slow, otherwise the melt into the mold cavity is easy to condense and lead to insufficient mold filling, even if full, the surface of the product package is prone to ripples, material flow marks and other defects; the injection rate should not be too fast, to prevent the wrapping into the air and the melt rupture phenomenon. Production, generally using medium or slow speed, it is best to use multi-stage injection molding. Injection, the speed is not set as slow → fast → slow, which can greatly improve product quality.
Screw speed should not be too high, generally 30 ~ 60 r/min. Inserts need to be preheated to 200 ℃, at least 120 ℃, generally 110 ~ 130 ℃. The number of times of regeneration of the regenerated material is not more than 3 times, and the dosage is about 20%.
PC is a transparent plastic, molding is generally not recommended to use mold release agent, so as not to affect the transparency of the product. For products that are difficult to demold, stearic acid or silicone oil can be used as a mold release agent, but the dosage should be strictly controlled.
PC products should try to avoid the use of metal inserts. If you do need to use metal inserts, you must first preheat the metal inserts to about 200 ℃, and then placed in the mold cavity for injection molding, so as to avoid the coefficient of expansion of the disparity between the difference between the cooling of the contraction of inconsistent and strict birth of a larger internal stress, so that the product cracking.
The method of reducing internal stress, in addition to the product modeling design to avoid gaps, sharp corners, thickness disparity and the use of correct molding process parameters, it is best to heat treatment of products, heat treatment temperature control in 125 ~ 135 ℃ (resin Tg below 10 ~ 20 ℃), processing time of 2h or so, the thicker the product the longer the processing time. General wall thickness of less than 5mm products, time for 8h; greater than 20mm products, time for 24h.
The size of the internal stress of the product can be tested by polarized light and solvent impregnation method. Polarized light test method applies to a variety of transparent products, it is the use of PC transparency, the products are placed in the polarized light between the lenses, from the mirror on the surface of the products to observe the colored light band area, to determine the size of the products to the size of the colored light band area to the size of the product internal stress, if the observed color packet light band area is large, the products of the internal stress is large; solvent impregnation method is a means of detection commonly used in factories, the method is the PC products are dipped into the PC products. Some solvents (such as benzene, carbon tetrachloride, cyclohexane, ethanol, methanol, etc.), to the product cracking and destruction of the time required to determine the size of the stress, the longer the stress is smaller. If the impregnation of 5 ~ 15 s on the crack, indicating that the internal stress is very large; if the impregnation of 1 ~ 2min does not appear cracks, indicating that the internal stress is very small, the use of such products in the process of general will not be cracked.
Injection molding process
Drying treatment: PC material has hygroscopicity, drying before processing is very important. Suggested drying conditions are 100C to 200C, 3~4 hours. The humidity must be less than 0.02% before processing.
Melting temperature: 260~340C.
Mold temperature: 70~120C.
Injection pressure: Use high injection pressure as much as possible.
Injection speed: Use low speed injection for smaller gates and high speed injection for other types of gates.
Applications
PC can be injection molded, extruded, molded, blow molded, thermoformed, printed, bonded, coated, and machined, with the most important process being injection molding. Before molding must be pre-dried, the moisture content should be less than 0.02%, trace moisture processing at high temperatures will make the products produce a whitish color, silver wire and bubbles, PC at room temperature has a considerable forced high elastic deformation capacity. The impact toughness is high, so it can be cold pressed, cold drawn, cold rolled and other cold molding process. Extrusion with PC molecular weight should be greater than 30,000, to use gradual compression type screw, L/D ratio 1:18~24, compression ratio 1:2.5, can be used for extrusion blow molding, injection - blowing, injection - pulling - blowing method of molding high-quality, high-transparent bottles. a wide range of PC alloys, to improve the PC melt viscosity (processability) and the products are prone to stress cracking and other defects, PC and different polymers to form alloys or **** blends that Improve material properties. Specifically PC / ABS alloy, PC / ASA alloy, PC / PBT alloy, PC / PET alloy, PC / PET / elastomer **** blend, PC / MBS **** blend, PC / PTFE alloy, PC / PA alloy, etc., Lee has two material performance advantages, and reduce costs, such as the PC / ABS alloy, PC mainly contributes to high heat resistance, better toughness and impact strength, high strength, flame retardant, ABS can improve moldability, apparent quality, reduce density.PC's three major applications are the glass assembly industry, the automotive industry and the electronics, electrical appliances industry, followed by industrial machinery parts, CD-ROMs, packaging, computers, and other office equipment, medical and health care, film, recreation, and protective equipment.PC can be used as glass for windows and doors, and PC laminates are widely used in Protective windows in banks, embassies, detention centers and public **** places, used in aircraft cabin covers, lighting equipment, industrial safety stalls and bulletproof glass. PC boards can be used for various signs, such as gasoline pump dials, automobile instrument panels, cargo and open-air commercial signs, point sliding indicators, PC resin used in automobile camera systems, dashboard systems and interior decorative systems, used as headlamp covers, front and rear automobile gear boards with reinforcing ribbing, reflective mirror frames, door frames, operating rod sheathing, flow blocking boards, PC is used as a junction box, sockets, plugs and bushings, spacers, TV conversion devices, telephone line brackets under the communication cables, PC is applied as a junction box, receptacles, plugs and sleeves, gaskets, television conversion PC is used as junction boxes, sockets, plugs and bushings, gaskets, TV converters, connectors for communication cables under telephone line brackets, electric switch boxes, telephone switchboards, switchboard components, relay housings, PC can be used as low load parts for household appliance motors, vacuum cleaners, shampooers, coffee makers, toasters, handles for power tools, various gears, worm gears, bushings, guide gauges, shelves in refrigerators, etc. PC is an ideal material for optical disc storage media. PC bottles (containers) are lightweight, good impact resistance, resistant to certain high temperatures and corrosive solution washing, as recyclable bottles (containers). pc and pc alloy can be used to make computer racks, shells and auxiliary machines, printer parts. Modified PC is resistant to high-energy radiation sterilization, boiling and baking disinfection, can be used for blood specimen collection instruments, blood oxygenator, surgical instruments, kidney dialyzer, etc. PC can be made into helmets and helmets, protective masks, sunglasses and sports eye protection. PC film is widely used in printing charts, pharmaceutical packaging, membrane commutator.