Microlayer injection process for license.

At last month's SPE ANTEC meeting in New Orleans, Dow Plastics, Midland, Mich., presented three papers on a patented process that the company is offering to license for injection or injection blow molding. This microlayer or "lamellar" molding process injects two or more independent melt streams simultaneously to produce hundreds or thousands of alternating layers on a micron scale of thickness throughout the part. It can be practiced on any multi-barrel injection system capable of simultaneous injection, and requires only the addition of a feedblock and layer multiplier modules between the screw and nozzle. These feedblock modules subdivide and recombine the melt streams in exponentially increasing numbers of layers.

This process is an outgrowth of continuous coextrusion technology (not presently available for license), which Dow uses to produce its Polymeric Reflective Material (PRM) sheet (see PT, Dec. '92, p. 39). Dow discovered that the microlayer structure survives not only the higher shear of injection molding, but also the stop/go nature of the process (with intermittent hold-up of layered material in the nozzle), as well as narrow runner and gate restrictions and obstructions and changes of flow direction within a mold. Dow says the lamellar morphology can be maintained in complex multi-cavity parts, even with a minor component in a proportion below 10%.

Dow thinks the process has exciting and varied potential. Producing barrier food containers is an obvious possibility. Automotive fuel-line components with hydrocarbon barrier is another.

More intriguing is the evident ability to provide a more cost-effective alternative to some polymer blends and alloys. For example, a microlayer automotive exterior part of PBT and polycarbonate achieves the desired chemical resistance with only half as much of the more expensive PBT component as would be required in a blend-- and also without the cost of compounding. What's more, the PC/PBT microlayer structure exhibits 50[degrees] F higher HDT.

Likewise, microlayer moldings of filled and unfilled resin achieve reduction in thermal-expansion coefficient with less filler than would be required in a blend. Potential for similarly cost-effective toughening with interleaved flexible and rigid layers has yet to be explored. (CIRCLE 34)