The surface coating process for touch displays is a core technology balancing scratch resistance and touch sensitivity. Its essence lies in constructing a functional layer on the surface of a glass or plastic substrate, combining mechanical strength and electrical properties, through material selection and process design. This process requires comprehensive consideration of the coating material's hardness, thickness, surface energy, and compatibility with the touch sensor to achieve synergistic optimization of durability and user experience.
Improved scratch resistance primarily depends on the hardness and structural strength of the coating material. Traditional chemically strengthened glass forms a surface compressive stress layer through ion exchange, which can resist scratches below a Mohs hardness of 6, but it can still be damaged by gravel or metal tools. To address this, modern processes introduce diamond-like carbon (DLC) coatings or alumina (Al₂O₃) coatings, whose hardness approaches that of diamond, effectively dispersing external impacts and preventing the substrate from being directly exposed to sharp objects. For example, DLC coatings, formed using plasma-enhanced chemical vapor deposition (PECVD) technology, are only 2-5 micrometers thick, yet can improve the screen's scratch resistance by more than 3 times while maintaining a coefficient of friction below 0.1, reducing resistance during touch. Maintaining touch sensitivity requires the coating layer to have low surface energy and high light transmittance. Materials with excessively high surface energy easily attract grease and dust, forming an insulating layer that interferes with the electric field distribution of capacitive touch, leading to operation delays or accidental touches. Therefore, coating processes often use fluoride or siloxane materials to reduce the surface energy to 20-30 mN/m, making it difficult for fingerprints and stains to adhere, allowing for easy cleaning with a gentle wipe. Furthermore, the light transmittance of the coating layer needs to exceed 90% to avoid light refraction or absorption affecting the display effect, while ensuring the touch sensor can accurately capture the minute movements of the finger. For example, multilayer composite coatings, by alternately depositing high-refractive-index (such as TiO₃) and low-refractive-index (such as SiO₂) materials, form a gradient refractive index structure, which can reduce reflectivity to below 0.3% while maintaining a surface hardness of 8H, balancing optical performance and wear resistance.
Precise control of process parameters is key to balancing these two aspects. The coating temperature needs to be adjusted according to the substrate characteristics: glass substrates can withstand high temperatures of 200-300℃ to promote grain growth and improve conductivity; while plastic substrates (such as PET) require low-temperature processes (<150℃), combined with magnetron sputtering or plasma enhancement technology to avoid thermal deformation. Furthermore, the coating thickness must be strictly controlled at the micrometer level; excessive thickness reduces light transmittance and increases touch resistance, while insufficient thickness fails to provide adequate protection. For example, the thickness of ITO (indium tin oxide) films is typically 0.2 mm, which meets the conductivity requirements of capacitive touch while maintaining smooth operation.
The introduction of surface micro/nano structures provides a new approach to performance balance. Through nanoimprinting technology, subwavelength conical structures (period <200 nm) can be imprinted on the coating surface, mimicking the hydrophobic properties of lotus leaves to achieve superhydrophobicity (contact angle >160°) and self-cleaning functions. This structure not only reduces stain adhesion but also lowers the coefficient of friction during touch, improving operational smoothness. Meanwhile, the light scattering effect of micro-nano structures enhances screen visibility under strong light, further optimizing the user experience.
Long-term performance maintenance relies on the self-healing capability of the coating. Some advanced processes add microencapsulated repair agents to the coating. When micro-cracks appear on the surface, the capsules rupture, releasing the repair agent to fill the cracks and restore protective performance. For example, after applying a self-healing coating, the light transmittance of a touchscreen in a smart factory still recovered to 95% of its initial value after 200 scratch tests, significantly extending its service life.
The differentiated needs of application scenarios have driven the diversified development of coating processes. Outdoor equipment needs to balance high light transmittance (≥90%) and abrasion resistance (Mohs hardness ≥7H), often using a combination of DLC coating + OCA full lamination + floating design; industrial control equipment prioritizes chemical corrosion resistance, favoring Al₂O₃ coating + LOCA lamination + self-healing coating. This tiered application strategy allows coating processes to adjust materials and structures according to specific needs, achieving the optimal balance between performance and cost.
Through material innovation, structural optimization, and process control, the surface coating process of touch displays has achieved a precise balance between scratch resistance and touch sensitivity. From the ultra-hard protection of DLC coatings to the self-cleaning properties of micro-nano structures, from low-temperature sputtering adaptation to plastic substrates to the long-term maintenance of self-healing coatings, each technological breakthrough is driving touch displays toward higher performance and lower maintenance costs, providing reliable assurance for the interactive experience of industrial digitalization and consumer electronics.
