PC plastic What is PC plastic?

Polycarbonate (PC) is a thermoplastic containing carbonate group in the main chain of a molecule. according to the composition of the structural unit can be divided into aromatic, aliphatic, aliphatic aromatic three categories, the varieties used for engineering plastics are mainly bisphenol a type of aromatic PC. PC is one of the five general engineering plastics (PA, PC, POM, PBT, PPO), and the output and consumption is second only to PA.

Two, PC characteristics

1, Physical properties: PC is a tasteless, odorless, non-toxic, transparent amorphous thermoplastic polymer, density of 1.2g/cm3. Slow burning, self-extinguishing from the fire, melting and foaming when burning, accompanied by rotten fruit odor. can be made into transparent, translucent, opaque products.

2, Mechanical properties: hard and tough polymer (more sensitive to the notch, easier to produce internal stress and cause stress cracking), excellent mechanical properties, high impact (higher than the impact strength of PA 3 times), small creep value, fatigue resistance and wear resistance.

3, Thermal performance: tg is high (about 150℃), melting temperature is 220-230℃, td is above 320℃, long-term working temperature can reach 120℃, short-term use temperature can reach 140℃;

4, Chemical properties: PC at room temperature resistance to inorganic and organic dilute acid solution, salt solution, saturated potassium bromide solution, aliphatic hydrocarbons, cycloalkanes and most alcohols and oils. However, it is not resistant to lye, concentrated sulfuric acid, aqua regia and sugar aldehyde. PC is easy to interact (dissolve) with polar organic solvents

5, Electrical properties: dielectric constant (10^6Hz) is about 3.05, volume resistivity is 4x10^ 16ω.cm, dielectric strength is 15-22KV/mm

6, Optical performance: transmittance of 85%-90%, refractive index of 1.585-1.587, its transmittance is related to the wavelength of light and the thickness of the workpiece, 2mm thickness of the thin plate visible light transmittance can reach 90%

Three, injection molding process (precautions)

Raw material drying: PC is extremely sensitive to water (usually the water absorption rate of about 0.18%, but because it contains esters, trace water at the molding temperature is easy to cause high temperature hydrolysis, release co2 and other gases, so that the product produces discoloration, molecular weight drops sharply, the surface of the product appears silver wire, bubbles, etc.), so it must be fully dry before injection, so that its water content is reduced to less than 0.02%. General drying conditions: 110~120℃, time about 4 hours

Injection temperature: injection temperature (can not exceed 330 degrees celsius, otherwise the PC will decompose) must be integrated with the shape of the product, size, mold structure and other aspects of the situation, the general product selection temperature of 260~300℃, for complex shape or thin-walled products, the molding temperature is 285-310℃. The barrel temperature is high before and low after use, and the inlet temperature is controlled above 230℃ (to reduce material resistance and injection pressure loss)

Injection pressure: PC melt viscosity is high, poor fluidity, the molding process should use a higher injection pressure, generally controlled at 80-120MPa, for thin-walled, long process, complex shape, small gate products, injection pressure is usually controlled at 120-150MPa. To obtain complete and smooth surface products

Holding pressure and holding time: the holding pressure is too small, the feeding effect is small, and the vacuum bubble or the surface is prone to concave, the holding pressure is too large, and the internal stress around the gate is easy to produce (the actual production is set with high material temperature and low holding pressure). Generally, the pressure holding time of small and thin products is short, and the pressure holding time of large and thick products should be longer. The length of the pressure holding time can be determined by the test of the sealing time of the gate.

Injection speed: The injection speed should not be too slow, otherwise the melt is easy to condense and lead to insufficient filling mold, medium speed or multi-stage injection is generally used in production, and the multi-stage injection speed is generally set to slow-fast-slow

Mold temperature: generally controlled at 80-100℃, for complex shapes, thin, demanding products, can be increased to 100-120℃, but can not exceed its thermal deformation temperature (mold temperature is high to reduce the difference between mold temperature and PC material temperature, can reduce the internal stress of the parts)

Screw speed and back pressure: Due to the large viscosity of PC melt, in order to prevent excessive screw load, the screw speed is generally controlled at 30-60r/min, and the back pressure is 10-15% of the injection pressure

The use of release agent: PC molding should not use release agent, so as not to affect the transparency of the product, (indeed difficult products, can use stearic acid or silicone oil substances as release agent, but to strictly control the amount), while the use of recycled materials can not be more than three times, the use of less than 20%

Mold design requirements: the mold release inclination is about 1.0°, the cross section of the runner and gate is preferably circular (to reduce the flow resistance of the molten material), the design is thick and short, the flow channel with less turning, the mold should pay attention to heating and prevent local overheating. The injection gate can be any form of gate, but the inlet water level diameter is not less than 1.5mm.

Injection molding machine requirements: The maximum injection volume of the required product (including runner, gate, etc.) should not be greater than 60-80% of the nominal injection volume. The screw is usually a single head full thread, equal pitch, gradual compression screw with a check ring. The nozzle adopts ordinary open extended nozzle (with heating device)

Application of polycarbonate

PC polycarbonate application development is to high composite, high function, specialization, serialization direction, has launched the CD, automobile, office equipment, box, packaging, medicine, lighting, film and other products of their own special grade

Optical lighting: used to manufacture large lampshades, protective glass, left and right eyepiece tubes for optical instruments, etc., and can also be widely used in transparent materials on aircraft

Electrical and electronic appliances: polycarbonate is an excellent E(120℃) class insulation material, used in the manufacture of insulation connectors, coil frames, tube holders, insulating bushings, telephone shells and parts, mining lamp battery shells, etc. It can also be used to make parts with high dimensional accuracy, such as optical discs, telephones, electronic computers, video recorders, telephone switches, signal relays and other communication equipment. Polycarbonate film is also widely used as capacitors, insulating bags, audio tapes, color video tapes, etc.

Mechanical equipment: used to manufacture all kinds of gears, rack, worm gear, worm, bearing, CAM, bolt, lever, crankshaft, ratchet, can also be used for some mechanical equipment housing, cover cover and frame parts

Medical equipment: cups, canisters, bottles for medical purposes and dental instruments, medicine containers and surgical instruments, and even artificial organs such as artificial kidneys and lungs

Other aspects: the building is used as hollow rib double wall panel, conservatory glass, etc.; Used in the textile industry as textile yarn tube, textile machine bearing shell, etc. For daily use as baby bottles, tableware, toys, models, LED lamp shell and mobile phone shell.