Processing via the Elastoviscous State

In sandwich injection molding, two polymerizates in separate injection units are successively injected into a mold such that the second shot is fully enclosed in the first. The process is suitable, for example, for the enclosing 

Extrusion with wide exit slits is a special case. Planar films of 20-100 m in thickness, for example, are produced with wide exit slits. The film is then chilled by cold rolling or in water baths (melt-molding or chill-rolling method). Wide exit slits are also used in what is called extrusion coating of paper or cardboard with poly(ethylene). Papers thus treated can then be heat-sealed. 

In the extrusion of thermosets, it is really the monomer or a prepolymer which is extruded, whereupon the production of polymer and molding occur simultaneously. In theory, extrusion with simultaneous molding is also possible with thermoplasts, but is only used to a very limited extent, e.g., with methyl methacrylate. 

Internal mixing (Banbury mixing) serves to produce intermediate products from elastomers and is used in particular to work in fillers, mix elastomers, etc. 

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Figure 36-3. Processing via the elastoviscous state, (I) injection molding, (II) extrusion, (III) roll milling. The torpedo system shown for injection molding and previously exclusively used has more recently been replaced by screws or double screws.

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