AIST Stories No2

9Leading the way AIST!substances from waste treatment facilities.Various types of clays exist. Clays widely produced in Japan’s Tohoku region possess better water retention properties compared to clays from Aichi Prefecture that are commonly employed in pottery*3. These Tohoku clays are commonly employed in the reinforcement of foundations at construction sites, soil improvement in agricultural land, and water-impermeable layers at the base of dams. In 2003, Ebina started investigating this clay property of not readily allowing water to pass through; in other words focusing on the water permeability of clay in an attempt to apply water barrier characteristics in barrier materials for toxic substances. Ebina formed a layer of clay and poured water on it. However, the water did not seep through the clay layer. This meant that the clay was suitable as a barrier material but as the water did not seep through, actual data could not be collected. Thereupon, Ebina decided to gradually reduce the thickness of the clay layer and measure the time required for water to seep through. Here, an unexpected fact became clear.“The thinner the clay layer, the slower the rate that water passed through it. In other words, barrier properties improved the thinner the layer was: the thinnest film actually possessed the highest barrier properties.”20,000 stacked crystals prevent leakage of water and gasHow does such a thing occur? Air and water are present in the gaps between individual clay particles. If the air and water are removed, clay crystals normally sediment randomly. Under these conditions, gaps exist between individual crystals and water is able to permeate through. However, it was found that the thinner the clay layer, the easier it was for all the individual crystals to become oriented in a single direction. Furthermore, clay that is usually brittle becomes flexible when fabricated into a film and it can be folded and bent.A material with such high barrier properties that is also flexible and moreover, possesses the high heat resistance of clay surely must have some uses. The first practical use idea that came to mind was the potential for high performance sealing materials in chemical plants.“When the gas barrier properties and heat resistance of this thin film were tested, a high heat resistance of 600°C was discovered as well as compression properties that could respond to variations in the joint gap between piping that results from temperature variations in metals. In other words, the film performs extremely well as a sealant.”In fact, it has been known for some time that gas barrier properties increase dramatically when a small quantity of clay is added to plastic. Adding 5% clay results in a three-fold increase in gas barrier properties compared with a material that does not incorporate clay. In the case of Claist, if conversely clay constitutes 95% and the additive 5%, gas barrier properties are calculated to increase 2,400-fold. In fact, there are cases where this improvement reaches more than 10,000-fold. This is a key property of Claist.Principle of ClaistClaist manufacturing processCrumpling up paper and spreading it over a deep colanderresults in water leaking. Leakage!Precisely and neatly spreading the paper to form multiplelayers keeps the water from leakingNo leakage!▼‌‌In the solvent cast method, a clay dispersion is poured into a flat vessel to form a dry film. In principle, the process is the same as paper making.*1 Plasticity: The property whereby applying force to an object results in its deformation and the object does not return to its original shape even if the force is removed.*2 Gas barrier properties: A gas-shielding property. Particularly important when the objective is retaining quality, preventing oxidative degradation, retaining flavor, and preventing gas leakage in fields such as food and pharmaceutical packaging, electronic materials, and gas sealing material.*3 Firing clay: The humidity-regulating tiles introduced in AIST Stories 2013 No.1 were developed by R&D on firing clay produced in Aichi Prefecture. Impact in the following fields! Community life◦Food ◦Residential◦Information technology◦Eco products◦‌‌Medical treatment, welfare, caregiving◦Electronics◦Motor vehicles◦Aerospace◦‌Building & construction◦Materials◦‌‌Medical treatment, chemistry, biotechnology◦Food productsIndustry