粘土を主成分とするガスバリアフィルムの開発と国際標準化

抄録

Since the 1970s, polymer-clay composite materials have been actively studied for the purpose of improving gas barrier properties, heat resistance, and flame retardancy of polymers. However, in most cases, a small amount of clay was added to the polymer, and its improving effect was limited. It was estimated that if clay could be used as the main component of the composite material, drastic improvement of its gas barrier properties, heat resistance, and flame retardancy were expected. Based on this concept, we have developed clay-based film (CBF) using smectite which has excellent film-forming properties. Specifically, using smectite as a clay component, the platelet crystals with a high aspect ratio are oriented parallel to the film surface and multi-layered at the nano level in CBF using an organic polymer as a binder to realize the simultaneous possession of the above three properties. Specifically, we developed a transparent clay film using synthetic smectite and water-soluble polymer. Furthermore, it was discovered that when the interlayer ions of montmorillonite were exchanged for small ions such as lithium, the film became water resistant due to the heat-induced fixation of the ions into the smectite crystal structure known as the Hofmann–Klemen effect. Using the process, we have developed a CBF with high water vapor barrier properties consisting of lithium-type natural smectite and polyimide. Furthermore, by applying CBF onto various materials, non-asbestos gaskets and transparent non-combustible plastic materials and so on were commercialized. On the other hand, the international standardization of raw clay materials has been conducted, and a technical specification ISO/TS 21236-2 Clay nanoplates for gas barrier films was published in May 2021. Its content is based on the above research. This standard document is expected to be used for the selection of appropriate clays that contribute to the improvement of gas barrier properties of polymer clay nanocomposite films including CBF.