Expansion of polymeric twin screw extruder
The present twin screw extruder relates to a process for producing a dispersion of polymeric microspheres in a polyol comprising expanding 1 to 70% by weight of polymeric beads in a polyol with a single screw extruder to simultaneously mix and expand the beads to create a uniform dispersion of the microspheres in the polyol such that the wetting of the microspheres by the polyol is maximized.
In the process of the present sheet production extruder, an extruder is used to mix and expand the polymeric beads in a polyol into microspheres wherein a uniform dispersion of microspheres in the polyol is produced. The dispersion is subsequently mixed with other ingredients such as an isocyanate to produce a PUR/PIR foam. Preferably, a twin screw extruder is used. Such technology, for example, is disclosed in U.S. Pat. No. 5,424,014.
High loadings of inert and/or inorganic fillers pose several limitations on convention flexible and rigid foam processing methods: 1) high intrinsic viscosity; 2) difficult to completely wet-out particles; and 3) unstable dispersion leads to agglomeration and/or settling. High loadings of fillers, however, offer some very interesting potential benefits: 1) inexpensive; 2) offer ability to encapsulate additives; 3) improve compressive strength; and 4) alter energy absorbing capability.
The use of hollow polymeric microspheres as a filler in rigid boardstock polyol is disclosed in U.S. Ser. No. 08/909,447. Because of the extremely high viscosities in using fillers, polyol levels containing significant levels of these fillers cannot be processed on conventional boardstock mixing and metering equipment.
The following examples were processed using a ZSK30 twin- screw extruder from Werner-Pfleiderer GmbH. The screw design was selected based on the viscosity and throughput of the following examples.
Whereas, particular embodiments of this single screw extruder have been described herein for purposes of illustration, it will be evident to those skilled in the art that numerous variations in the details may be made without departing from the twin screw extruder as described in the claims appended hereto.