Anti-Fingerprint
Fluororesins, represented by polytetrafluoroethylene (PTFE), possess low surface energy and exhibit unique properties such as stain resistance, non-stick characteristics, acid resistance, heat resistance, and low friction. These features make them highly useful and widely recognized in industrial applications. However, due to the resin's inability to form a transparent coating and the requirement of high temperatures to create a film, it cannot be used for anti-staining applications on transparent resins.
In recent years, leveraging the unique advantages of these fluororesins, various coating agents capable of forming transparent thin films at room temperature have been developed and applied in practical use. In the following section, we will introduce fluorine-based coating agents that can be applied to plastic films or transparent resins for anti-staining or fingerprint-reducing purposes.
Stains on resin surfaces, such as fingerprints, sebum smudges, and watermarks, originate from wet contaminants. These attach to the resin surface due to intermolecular forces—specifically surface tension—created by the attraction between the molecules of the contaminants and those of the resin surface. Although resins generally have lower surface tension than inorganic compounds, their surface tension is not low enough to prevent oily contaminants from adhering, especially given the oleophilic nature of resins. By using fluorine-based coating agents, the surface tension of the resin surface can be significantly reduced, thereby minimizing the adhesion of these contaminants. This effect is especially apparent in the ease with which such stains can be wiped away using a cloth.
For hydrophilic fibrous materials like cotton or artificial suede made from polyvinyl alcohol (PVA), hydroxyl groups in the structure result in high surface tension in the fiber molecules. These molecules attract water, oil, and other substances via intermolecular forces and draw them upward through the material—a phenomenon also known as capillary action.
Fluorine-based coating agents used to reduce fingerprint adhesion and provide stain resistance can be broadly classified into two main types, as outlined below:
- Silane Coupling-Type Anti-Stain Coating Agents
These use fluorinated silane coupling agents as coating ingredients. After application, they bond to substrates such as glass and metal via silane coupling reactions, forming a monomolecular layer of fluororesin on the surface.
This type of coating features excellent adhesion and abrasion resistance. Furthermore, because the monomolecular layer is only about 10–20 nm thick, it is invisible to the naked eye and does not affect the appearance or optical properties of the coated material. Even if the coating gradually wears away or deteriorates over time, the degradation occurs on a molecular level and is not visible, thus preserving the aesthetic quality of the coated object.
- UV-Curable Anti-Stain Coating Agents
This system consists of two main types: additive types that are added to UV-curable resins, and ready-to-use coatings that already contain UV-curable resin and photoinitiators. UV curing is characterized by its rapid hardening speed, making it suitable for high-speed, continuous roll-to-roll coating processes on plastic films.
The curing reaction involves a crosslinking process triggered by radical polymerization, which is inhibited by oxygen. Therefore, exposure needs to occur in a nitrogen environment to isolate oxygen, or a thicker film must be used under normal conditions. In addition, the coated surface typically has a glossy appearance. Figure 4 shows the coating process and compound structure. During air-drying, the PFPE groups in the structure migrate to the surface, and even a small amount (about 1% solid content) is sufficient to deliver effective performance.
