Injection processing applications

Working with a solution is needed for polymers which above their melting point would degrade (example aromatic polyamide fibres such as Kevlar and Twaron). For fibres the removal of the solvent is not too problematic. In e.g. injection moulding applications solvents caimot be used here thermotropic LCP s have to be used. Since these would degrade during processing, they are diluted by copolymerisation (example poly-hydroxy-benzoic acid - co - PETP)... 

Depending on the application, different demands are placed on the melt viscosity of the polymer. For injection molding applications, lower melt viscosities are required than for extrusion applications. For a given comonomer composition and processing temperature, the melt viscosity of the cycloolefin copolymers increases with the mean molecular weight. 

Ion-exchange systems in process applications may be batch, semicontinuous, or continuous. Batch operations are not common but, where used, involve a ketde with mechanical agitation. Injecting with air or an inert gas is an alternative. A screened siphon or drain valve is required to prevent resin from leaving with the product stream. 

Today s vinyl moulding compounds are successfully meeting the combined challenges of physical properties, appearance, processability, and cost requirements in a variety of specialty injection moulding applications such as appliance parts, business equipment, and electrical enclosures. One of the major reasons why vinyl materials are so versatile is that the PVC resins on which they are based can be easily modified with a variety of additives to tailor the particular performance features of the compounds to their intended applications. Determination of an appropriate combination of PVC resin and additives to produce an effective and cost-competitive compound,... 

Temperature-dependent injection was attributed to a competitive population of low-lying state [thought to be a ligand field (LF) state] and the remote injection process. Regardless of the mechanism, the results demonstrate that sensitized electrodes can be fabricated for temperature-sensing applications. 

ICP s. The BCA hanopolyesters prepared with 1,4-butanediol or 1,6-hexanediol and their oopolyesters with ethylene glycol, 1,4-butanediol, or 1,6-hexanediol had suitable melting points and melt processing characteristics for injection-molding applications. 

A number of commercially significant PC copolymers are produced. In addition to the previously discussed branched PCs (for extrusion and blow-molding applications) and copolymers of BPA with tetrabromo-BPA for enhanced flame retardancy, high-Tg polyester carbonate copolymers have been produced for a number of years (Bayer Apec , GE LEXAN PPC Tg approximately 190°C). Polyester carbonate copolymers can be produced via copolymerization of BPA with diacyl chlorides. Aromatic diadds produce high-Tg copolymers, while aliphatic diadds yield lower-Tg copolymers. A lower-Tg PC aliphatic polyester copolymer (GE LEXAN SP resin) exhibits enhanced flow and ductility in comparison to standard PC and is useful for thin-wall injection molding applications requiring ductility and ease of melt processability, such as personal communication devices. GE has recently introduced two new PC copolymers, a PC-siloxane copolymer (LEXAN EXL) and a copolymer of... 

Recent work has included tests that examine the effects of shear rate and cure simultaneously (which will also be discussed below). The models derived from these tests are recombined to provide an overall chemoviscosity model to be used in processing applications. The effect of pressure on chemoviscosity has not been studied extensively however, system pressure may be relevant to high-pressure injection-moulding and transfer-moulding processes. 

R. A. Mowery, Jr., The Potential of Flow Injection Techniques for On-Stream Process Applications. Proc. Jt. Symp. Instrum. Control 80 s (1984) 51. 

---