Automation, injection molding

Thermoplastic RPs (RTPs), even with their relatively lower properties when compared to thermoset RPs (RTSs), consume about 55wt% of all RP products. Practically all of the RTPs are injection molded with very fast cycles using short glass fiber producing highly automated and high performance products. 

For higher throughput applications, injection-molded plastic microtiter plates have served as the formats of choice for automated assay development. Thermoplastics such as polystyrene, polycarbonate, and polypropylene are used for a variety of purposes including storage and assay plates, lids, pipette tips, and Eppendorf PCR tubes. Polystyrene plates are used for cell culture and ELISAs. Polycarbonate reagent bottles are popular, while polypropylene storage plates and PCR tubes are standards. 

Thicker sections can be cross-linked by hydrosilylation addition. This is the same chemistry used to produce fluorosilicone monomers with the vinyl functionality present on silicon. The catalyst reaction occurs between a vinyl group and silicone hydride.66 The advantage of this system is that it does not produce volatile by-products. On the other hand, the disadvantage is that it is available only as a two-part system.67 Recently, however, one-part, platinum-catalyzed products have been developed.66 The reaction is very rapid and at room temperature it is completed in 10 to 30 minutes. It is accelerated with increasing temperature and at 150°C (302°F) it is completed within a few seconds. This makes the compounds ideal for fast automated injection molding operations.68 One-part systems use the chemical complexing of the catalyst, which is activated at elevated temperatures, or its encapsulation into an impermeable shell, which is solid at room temperature and melts at elevated temperatures68... 

Extrusion and injection molding are the two leading methods of converting plastic materials into solid products. Extrusion produces continuous products with a fixed cross-section injection molding produces discrete products with more complex shapes. Modern injection molding is a very fast, automated process for large-scale manufacture of complex products at minimum cost. An injection molding machine can be used for many different jobs and for many years, so the amortization per job can be very low. On the other hand, it requires a different mold to make each product, so the cost of the mold must be amortized over the life of its individual production run. 

Rucinski, P., Manufacturing Solutions for the Automation, Control, and Monitoring of the Injection Molding Process, SPE IMD Newsletter, Issue 59, Spring 2002. 

The capillary rheometer is a valuable tool for predicting the processability of thermoplastic resins. This is done by measuring melt viscosities at shear rates and temperatures commonly encountered in extrusion and injection molding. This procedure is difficult and time consuming due to the complex nature of rheological measurements and analyses. An automated system for acquisition and analyses of capillary rheometer data has been developed to speed up and simplify this important analytical technique. 

The elements can also be made by casting aqueous slurries. These two methods require prefiring at low temperatures so that they can be handled in an automated large scale process. Elements can also be injection molded similar to plastic parts, in which the ceramic powder is mixed into an organic matrix. This third method leads to a very robust green (unfired) stone that can be easily processed further without prefiring. 

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