Liquid injection molding development

Liquid-Injection Molding. In Hquid-injection mol ding (LIM), monomers and oligomers are injected into a mold cavity where a rapid polymerization takes place to produce a thermoset article. Advantages of these processes are low cost, low pressure requirement, and flexibiHty in mold configuration. Conventional systems, such as isocyanate with polyol, release Htfle or no volatiles. The generation of substantial volatiles in the mold is obviously undesirable and has represented a significant obstacle to the development of a phenoHc-based LIM system. A phenoHc LIM system based on an... 

On account of their low viscosity, liquid silicone rubbers are processed chiefly by liquid injection molding (LM), a technique which resembles the injection molding of plastics and is combined with a meter/mix unit developed specifically for the process [7]. Additional homogenization is effected by a static mixer located between the mixing station and the feed screw of the injection molding machine (Fig. 5). 

More recently, this has led to the development of liquid injection molding (LIM), in which the reactive sdicone oligomer system is injection molded at 200 to 250°C and cures in a few seconds, a great advance over conventional vulcanization systems. 

Because PTFE melts at such a high temperature and the melt is very viscous, it is difficult to work by conventional plastics techniques such as injection molding or extrusion. It is usually formed into useful shapes by sintering at about 380 °C sometimes liquid alkanes are used as a carrier, but the product then tends to be porous (this emerges as a serious problem when thin-walled objects are machined out of PTFE stock). Accordingly, several fluorocarbon thermoplastics have been developed that have lower melt viscosities, at the expense of somewhat poorer thermal and mechanical properties than PTFE. For example, the thermoplastic FEP (fluori-nated ethylene propylene), made by copolymerization of F2C=CF2 and... 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

The lowest cost process for preparing all-arcmatic liquid crystalline polyesters involves the reaction of aromatic carboxylic acids with acetates of aromatic hydroxy ocnpounds a recent history (2) describes the development of these ICP s. Because aoetic acid is evolved in the process and reaction temperatures are above 300°C, expensive corrosion-resistant reactors must be installed for ccranercial production. In cur latest paper (2) of this ICP series, we described a number of aliphatic-aromatic ICP s which can be produced in conventional polyester reactors and injection molded to give plastics with very high mechanical properties, heat-deflection temperatures (HDT s), and solvent resistance. These ICP s (la) were prepared by the reaction of the dimethyl ester of... 

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