Corrosion Protection of Self-Healing Coating Contained Fiber/Spherical Shaped Capsules Formed on Substrate Metal

Coating is one of the most useful techniques for corrosion protection of metallic materials, however, if coating is damaged, local corrosion will occur. It is important to repair the damaged area of coating soon, however it needs much cost. From these, our research group develop the coating with self-healing property, called by self-healing coating. In this coating capsules containing healing-agent of coating are dispersed. If the coating is damaged, capsules will be broken at the same time. The healing-agent containing in capsules will flow out. The healing-agent reacts with the water vapor in the air to form a healing-structure and cover the damaged area of coating. The capsules contained healing-agent are produced as follows. First, the prepolymer, this is precursor of shell of capsules, drip into the aqueous solution dissolved glycerol, it hardly dissolves in the aqueous solution since the prepolymer is the oil phase. A mixture of oil droplets dispersed in the aqueous solution is formed. When this mixture is agitated with high speed, the oil droplets become micro spheres and emulsion forms. Furthermore, the reaction between prepolymer and glycerol occurs only at this interface between oil phase and water phase, spherical shaped capsules contained a healing-agent in a polyurethane shell can be produced. From our previous study, the coating with these spherical capsules has a self-healing property, because healing-structure could be observed at the damaged area of coating, but this structure covered damaged area, incompletely. It is necessary to improve self-healing property of coating. From the self-healing mechanism of the coating, the self-healing property of the coating will be strongly depended on the amount of healing-agent flowing to the damaged area. Therefore, we start the development of the coating with capsules with other shape such as fiber shape are dispersed in order to develop an advanced self-healing coating with higher healing property. Considering the procedure of capsule formation, the shape of capsules can be controlled by the agitation speed and viscosity of prepolymer solution. The shape of capsules will be related to the amount of healing-agent flow from capsules to the damaged area of coating, when coating is damaged. e.g. more amount of healing-agent will flow from fiber shaped capsules than that from spherical shaped capsules, because fiber capsules will be arranged horizontally to the metal substrate due to the flow during the