Two Japanese firms have developed a microsphere additive technology for expanding PVC, SBS, and EVA resins, providing improved part densities, heat insulation, and sound insulation. Kaneka Corp. (Osaka) and Dainichiseika Color & Chemicals Mfg. Co. (Tokyo) join two other suppliers of similar technologies, but as Dainichiseika supplies its products in the form of masterbatches, the technology is applicable to a wider range of processes, including injection, extrusion, and calendering, used on conventional machinery.
Daifoam V masterbatches comprise gas-tight thermoplastic shells that encapsulate hydrocarbon liquid (pentane or hexane) blended into an EVA carrier. Kaneka developed the microspheres and Dainichiseika the masterbatch compounding technology. Dainichiseika is targeting sales of ¥1 billion ($8.5 million) in 2005. During processing, the hydrocarbon is gasified and increases its pressure while the thermoplastic shell softens, resulting in an increase in the volume of the microspheres by a factor of up to 70. Expansion starts at about 125C; commonly used blowing agents—azodicarbonamide (ADCA)—for example, expand at more than 150C. Dainichiseika says lower temperatures provide milder processing conditions.
When the part is cooled, the microspheres solidify and remain expanded. In testing of the technology, Dainichiseika has reduced the density of a PVC shoe sole from 1.4 to .6 with addition of 2.5 percent masterbatch.
Other suppliers of expandable microspheres include Sekisui Chemical Co. (Osaka) whose Advancell acrylonitrile-based spheres expand from 15 to 40, to 40 to 120 µm to form a closed-cell structure during processing at temperatures between 110 and 150C. They can be used with PVC and EVA. Applications include structural foam.
The third supplier is Expancel (Sundsvall, Sweden). Expancel says microspheres in PVC-plastisols offer advantages over chemical blowing agents, such as controlled foaming at low temperatures and homogeneous closed-cell structure. In some polyurethane applications, Expancel microspheres are added to compensate for normal shrinkage.