According to a recent study, a transparent protective coating material has been developed that can heal itself in 30 minutes when exposed to sunlight. The research results were published in the journal ACS Applied Polymer Materials. The most important factor in protecting the vehicle’s surface is the excellent durability of automotive coatings. In order to preserve the original color of the product, protective coatings should also be transparent and colorless. However, all these requirements must be met to ensure a self-healing function. High hardness and excellent toughness are accompanied by remarkably poor self-healing performance for materials with free molecular motion, while the opposite is true for materials with high self-healing efficiency but low lifetime.
Researchers from the Korea Research Institute of Chemical Technology (KRICT) led by Drs. Jin Chul Kim, Young Il Park, and Ji-Eun Jeong have created a transparent coating material that meets all of the above requirements, functions similarly to commercial protective coating materials, and can self-heal using only sunlight (especially near-infrared light in sunlight, in the range wavelengths of 1,000 to 1,100 nm). Surface scratches can be repaired with the developed self-healing protective material in 30 minutes of exposure to sunlight. The research team used a spray paint machine to paint a lab-scale model car to demonstrate the self-healing capabilities of the developed paint material. The scratch completely disappeared and the paint surface was restored after the model car spent about 30 minutes in the midday sun.
The principle of the self-healing phenomenon is that the surface temperature of the developed material increases when sunlight is absorbed because the light energy is converted into heat energy. Repeated dissociation and recombination of chemical bonds in the polymer structure is then enabled by the increased surface temperature to self-heal the surface scratch. The research team mixes the currently available commercially available coating resin with transparent photothermal dye and dynamic chemical bonding (Hindered urea structure), which can repeat the decomposition and recombination of the polymer structure, so that dynamic chemical bonding can actively occur when exposed to sunlight.
Although photothermal dyes have been used to study self-healing properties, most previous research has focused on inorganic materials, which are challenging to use in industrial environments because the coating materials must be transparent. In addition, creating a photothermal effect in inorganic materials requires a significant amount of light energy. The research team used transparent organic photothermal dyes that absorb near-infrared light. Near-infrared light can prevent the vehicle’s surface temperature from rising excessively because it is a long-wavelength energy source that makes up less than 10% of midday sunlight.
In addition, organic photothermal dyes have a number of advantages for commercialization, including the fact that they are inexpensive, easily mixed with different dyes, and do not change the color of the product due to their colorless intrinsic color. Future applications for the self-healing material created include coatings for building materials, electronic devices such as computers and smartphones, and transportation applications. In addition, the use of less harmful organic solvents – which are produced in significant quantities during vehicle repainting – is expected to help the world achieve carbon neutrality. Research Director, Dr. Jin Chul Kim of KRICT, said: “The technology created is a platform technology that creates self-healing coating materials using both photothermal dyes and low-cost commercial polymer materials. It is expected to be widely used in many applications.” except automotive clearcoats.’
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