Injection Molding Silicone
Polycarbonate – Amorphous Thermoplastic
Polycarbonate (PC), first introduced in 1958, is an amorphous engineering thermoplastic with exceptionally high impact strength, transparency, high temperature resistance, and dimensional stability. It has a high surface gloss and is available in many colors and color intensities. Additionally, it is impact resistant and maintains high strength and stiffness in a temperature range from -150 to +135˚C.
Maximal service temperature short-term is at 150˚C, with long-term at 130˚C. PC’s electrical properties are not affected by moisture, and it shows good resistance to high-energy radiation; however, its chemical resistance is limited. PC is also susceptible to stress cracking. Permeability of CO2 is relatively high; therefore bottles for CO2-containing liquids should have a barrier layer, e.g., PET or PBT. PC is sterilizable, and it self-extinguishes once the source of ignition is removed. Free flowing grades are available for the production of large-sized parts, such as covers for light fixtures, and smaller parts, such as compact disks. Grades with 10-40% short-strand glass fiber reinforcement are available to increase stiffness (especially at elevated temperatures) and to reduce stress cracking tendencies.
PC can be processed and post-treated using all standard thermoplastic processing methods. Its high melt viscosity requires either high injection pressures or relatively low ratios of flow length to wall thickness. To achieve stress-free parts when processing injection molding silicone, low injection speeds should be used to fill the cavities, and long cooling times should be set. Melt temperatures for injection molding silicone range from 280-320˚C, and mold temperatures range between 80 and 120˚C in order to control surface finish.
Drying for 4-24 hours at 120˚C is required to reduce residual moisture to below 0.01-0.02%. The possibility of shrinkage during processing is minimal, ranging from 0.6-0.8%. PC is well suited for precision injection molding silicone parts, such as those used in both optical and electrical applications. Extremely thin films can be cast with solutions of PC in methylene chloride. PC can be adhesively bonded with glues and has very good chemical adhesion to Liquid Silicone Rubber (LSR).
Some of the benefits of employing PC in Injection Molding Silicone are:
- High impact strength
- High precision due to good dimensional stability
- Low flammability
- High heat deflection temperatures
- Electrical shielding ability
- Gamma sterilizable
- Wear resistance
- Good electrical properties
Selected applications of PC in Injection Molding Silicone:
- Appliances: food processors and refrigerator drawers
- Media: CDs, DVDs and Blue-ray discs
- Transportation: tail and head lights, instrument panels, bullet-proof car windows
- Safety and sports: sports helmets and sunglass lenses
- Medical: dialysis components and devices, blood oxygenator and gamma sterilization appliances
- Construction: panels for roofing of sports arenas
At SIMTEC Silicone Parts, a leader in the production of LSR/Thermoplastic components, has experience molding LSR/PC components employing two shot technology.
 Campo, E. A.: Industrial Polymers; Hanser Gardner Publications, Cincinatti, 2007
 Osswald, T. A.; Baur, E.; Brinkmann, S.; Oberbach, K.; Schmachtenberg, E.: International Plastics Handbook; 4th edition, Hanser Gardner Pubilcations, Cincinatti, 2006
At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts, components, and injection molding silicone, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.
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