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Durable Coating Self-Heals in 30 Minutes Upon Sunlight Exposure

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DAEJEON, South Korea, Aug. 23, 2022 — Researchers at the Korea Research Institute of Chemical Technology (KRICT) developed a transparent protective coating material that can self-heal in 30 minutes when exposed to sunlight.

According to the researchers, excellent durability of automotive coatings is the most important issue in protecting a vehicle surface. In addition, protective coating materials should be colorless and transparent so that the original color of the product can be seen. However, it is difficult to provide a self-healing function while satisfying these conditions. Materials with free molecular movement have high self-healing efficiency, but have low durability, whereas materials with high hardness and excellent durability have remarkably poor self-healing performance.

The research team’s transparent coating material satisfied these conditions and showed similar performance to that of commercial protective coating materials, and could be self-healed with only sunlight — particularly near-infrared (NIR) light, in the wavelength range of 1000 to 1100 nm.

Using the developed self-healing protective material, surface scratches healed in 30 min when exposed to sunlight, the researchers said. To demonstrate the self-healing performance of the developed coating material, the research team coated a laboratory-scale model car using a spray-coating machine. When the model car was exposed to midday sunlight for about 30 min, a scratch completely disappeared and the surface of the coating material was restored.

When sunlight is absorbed by the developed material, the surface temperature rises as light energy is converted into thermal energy. Subsequently, the increased surface temperature makes it possible to self-heal a surface scratch by repeating the dissociation and recombination of chemical bonds in the polymer structure.

Self-healed surface of a model car after scratching when exposed to focused sunlight with a magnifying glass (top) or to direct sunlight. Courtesy of Korea Research Institute of Chemical Technology (KRICT).
Self-healed surface of a model car after scratching when exposed to focused sunlight with a magnifying glass (top) or to direct sunlight. Courtesy of Korea Research Institute of Chemical Technology (KRICT).

The researchers designed a self-healing automotive clearcoat with a reversible polymer network based on acryl polyol and dynamic hindered urea bonds and introduced N-butyl-substituted diammonium borate dye as a photothermal dye. The added dynamic chemical bond (hindered urea structure) can repeat the decomposition and recombination of the polymer structure. The researchers mixed it with the transparent photothermal dye to induce dynamic chemical bonding actively upon exposure to sunlight.

The team used transparent organic photothermal dyes that can absorb NIR light. NIR light accounts for less than 10% of midday sunlight, and can thus circumvent excessive increase of the vehicle surface temperature. In addition, organic photothermal dyes have several advantages for commercialization: They do not affect the product color due to inherent colorlessness, they easily blend with paints, and they are inexpensive.

In the future, the developed self-healing material could be used as a coating material for transportation applications, electronic devices such as smartphones and computers, and building materials. In addition, it is expected to contribute to the realization of carbon neutrality by reducing the use of harmful organic solvents, which are generated in large amounts when repainting vehicles.

Previous studies using photothermal dyes were mainly based on inorganic materials that are difficult to apply industrially as the coating material should be transparent. In addition, inorganic materials require a large amount of light energy to produce a photothermal effect.

The research was published in ACS Applied Polymer Materials (
Aug 2022
The attribute of visual experience that can be described as having quantitatively specifiable dimensions of hue, saturation, and brightness or lightness. The visual experience, not including aspects of extent (e.g., size, shape, texture, etc.) and duration (e.g., movement, flicker, etc.).
coatingsmaterialsMaterials & CoatingsMaterials & ChemicalspolymersResearch & TechnologyeducationAsia Pacificpolymer materialsphotothermalphotothermal dyeindustrialchemicalsKorea Institute of Chemical Technologycolorclearcoatlight exposure

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