Classic car on grass

Scratches to car paint disappear with self-healing coating material

Image credit: Derektenhue/Dreamstime

A transparent protective coating material that can be self-healed in 30 minutes when exposed to sunlight has been developed by scientists in South Korea.

Excellent durability of automotive coatings is the most important issue in protecting a vehicle surface. In addition, protective coating materials should be colourless and transparent so that the original colour of the product can be seen. However, it is difficult to provide a self-healing function while satisfying all of 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.

A research team of Dr. Jin Chul Kim, Dr. Young il Park and Dr. Ji-Eun Jeong, from the Korea Research Institute of Chemical Technology (KRICT), has developed a transparent coating material that satisfies all of the above conditions and has similar performance to that of commercial protective coating materials and which can be self-healed with only sunlight (particularly near-infrared light in sunlight, in the wavelength range of 1,000 to 1,100nm).

Using the developed self-healing protective material, surface scratches can be healed in 30 minutes when exposed to sunlight. 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 minutes, the scratch completely disappeared and the surface of the coating material was restored.

Self-healed surface of a model car after scratching when exposed to focused sunlight with a magnifying glass (upper) or to sunlight directly (down)

Image credit: Korea Research Institute of Chemical Technology (KRICT)

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.

To the existing commercial coating resin, the research team added a dynamic chemical bond that can repeat the decomposition and recombination of the polymer structure, mixing this with a transparent photothermal dye so that dynamic chemical bonding occurs actively upon exposure to sunlight.

Self-healing mechanism of eco-friendly protective coating material for vehicles including dynamic polymer network and photothermal dye

Image credit: Korea Research Institute of Chemical Technology (KRICT)

Although self-healing functions using photothermal dyes have been studied previously, those studies 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 Korean research team used transparent organic photothermal dyes that can absorb near-infrared light. Near-infrared light is a long-wavelength energy source that accounts for less than 10 per cent of midday sunlight and thus it can circumvent an excessive increase of the vehicle surface temperature. In addition, organic photothermal dyes have several advantages for commercialisation: they do not affect the product colour due to being inherently colourless; they easily blend with various paints, and they are inexpensive.

Dr. Jin Chul Kim, the research director, said: “The developed technology is a platform technology that synthesises self-healing coating materials using both inexpensive commercial polymer materials and photothermal dyes. It is expected to be widely used not only in automotive clearcoats but also in various applications.”

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

The research paper - 'Fast, Localised, and Low-Energy Consumption Self-Healing of Automotive Clearcoats Using a Photothermal Effect Triggered by NIR Radiation' - has been published in the journal ACS Applied Polymer Materials.

Sign up to the E&T News e-mail to get great stories like this delivered to your inbox every day.

Recent articles