The adhesion of the anti-fingerprint coating and the durability of anti-oil stain of PVC tempered film are the key performances that distinguish it from ordinary protective films, and also directly affect the daily use experience of users. Compared with glass film, there are essential differences in the surface characteristics of PVC material and the way the coating is combined. This difference is reflected not only in the process logic of coating adhesion, but also in the law of performance attenuation after long-term use.
The adhesion of the anti-fingerprint coating of PVC tempered film depends first on the pretreatment process of the substrate surface. The PVC substrate itself is a polymer material with weak polarity and low surface tension. If the anti-fingerprint coating is directly applied (mostly fluorine-containing hydrophobic materials), it is easy to have problems of weak adhesion and partial shedding. Therefore, in production, it is necessary to increase the roughness and polar groups of the PVC surface through "plasma etching" or "corona treatment": plasma etching can form nano-scale pits on the PVC surface to expand the contact area of the coating; corona treatment introduces polar groups such as hydroxyl and carboxyl groups, which are combined with the coating molecules through chemical bonds. After pretreatment, the adhesion between the coating and PVC can be increased by 3-5 times, laying the foundation for the durability of the anti-oil effect.
The material properties and coating process of the anti-fingerprint coating determine its initial anti-oil ability. The current mainstream anti-fingerprint coating is perfluoropolyether (PFPE) or fluorinated silane. This type of material has extremely low surface energy (usually less than 20mN/m) and can repel polar substances such as water and grease. During the coating process, PVC tempered film mostly uses "dip coating" or "magnetron sputtering" process: the dip coating process controls the concentration of the coating solution to form a uniform film of 50-100 nanometers on the surface of PVC, which is suitable for large-scale production; magnetron sputtering can attach fluorine-containing materials with atomic-level precision, with higher coating density and better scratch resistance. The coatings formed by both processes can achieve a hydrophobic effect of "water drop angle > 110°", and the initial anti-fingerprint ability is close to that of glass film.
The adhesion of the anti-fingerprint coating of the glass film relies on the physical and chemical properties of the glass itself. The glass surface is rich in silanol (-Si-OH), and its reactivity with the fluorinated coating is much higher than that of PVC. Before coating, the glass only needs a simple ultrasonic cleaning to remove impurities, and the coating molecules can be firmly bonded to the glass surface through the "silicon oxygen bond (-Si-O-)". The stability of this chemical bond is much higher than the physical adsorption and polar bonding of the PVC surface, so the coating adhesion of the glass film is naturally more advantageous, and even after high-frequency friction, the coating is not easy to peel off from the glass surface.
In terms of the durability of the anti-oil effect, the biggest challenge faced by PVC tempered film is the deformation of the substrate and the fatigue of the coating. PVC is a polymer material with a certain elasticity. In daily use, the bending and extrusion of the mobile phone will cause a slight deformation of the PVC substrate, which will be transmitted to the surface coating, causing stress concentration inside the coating. After long-term repeated deformation, the coating may have micro-cracks at the edge or local area, and oil (such as sebum secreted by fingers) will penetrate between the coating and PVC along the cracks, destroying the hydrophobic structure. Usually after 3-6 months of use, the hydrophobicity of PVC tempered film will decrease significantly, the water drop angle may drop below 90°, and fingerprint residues become difficult to wipe off.
The durability of glass film's anti-oil performance depends more on the wear resistance of the coating itself. The rigid nature of the glass substrate avoids coating fatigue caused by deformation, and its performance degradation mainly comes from the physical wear of the coating - repeated friction of fingers and scratches by sand and dust particles will gradually wear away the fluorine-containing coating on the surface. The coating thickness of high-quality glass film can reach more than 200 nanometers, and it adopts a multi-layer composite structure (such as bottom reinforcement and surface wear resistance). Under the same frequency of use, its hydrophobic performance can be maintained for 6-12 months. Even if local wear occurs, the unworn area can still maintain a good anti-oil effect.
Environmental factors have different effects on the durability of the two. In a high temperature and high humidity environment (such as the sweaty season in summer), the PVC substrate may expand slightly due to moisture absorption, exacerbating the peeling of the coating and the substrate; while the chemical stability of glass is not affected by temperature and humidity, and it only needs to deal with the slow erosion of the coating by the salt in sweat. In a low temperature environment, the brittleness of PVC increases, and the coating is prone to cracking due to the shrinkage of the substrate, while glass does not have this problem. In addition, PVC is more sensitive to organic solvents (such as alcohol). If it is wiped and cleaned with alcohol, it may accelerate the dissolution of the coating, while the coating of the glass film is more tolerant to alcohol and the cleaning method is more flexible.
The difference in coating repair ability further widens the durability gap between the two. Once the anti-fingerprint coating of the glass film is worn, it is basically unable to repair itself; but when the coating of the PVC tempered film is slightly damaged, it can be partially restored through the "thermal repair" mechanism-the molecular chain of the PVC substrate has a certain fluidity. Under the action of the weak heat (35-40℃) generated by the use of the mobile phone, the coating molecules can slowly migrate to fill the microcracks, so that the hydrophobic performance can be temporarily restored. This limited self-healing ability can extend the anti-oil effect of PVC tempered film by 1-2 months, but it cannot be compared with the long-term stability of glass film.
The anti-fingerprint coating of PVC tempered film achieves the initial anti-oil effect through pretreatment and process optimization, but its durability is still weaker than glass film due to the characteristics of the substrate. For users who pursue low cost and flexibility (such as curved screen adaptation), PVC tempered film needs to be replaced regularly to maintain the experience; although the glass film is more expensive, it has a greater advantage in the stability of anti-oil effect in long-term use of more than 6 months, which is also one of the core differences in the market positioning of the two.
