In ultra-thin foldable mobile phone holder designs, preventing cracking and maintaining the sealing performance of the silicone layer requires comprehensive optimization from four aspects: material properties, structural design, process control, and adaptability to the intended use case. Silicone, due to its high elasticity, wear resistance, and skin-friendliness, is an ideal cushioning and sealing component for aluminum alloy holders. However, the risk of cracking primarily stems from stress concentration during folding, material fatigue, and environmental factors. Targeted improvements can significantly enhance the reliability and sealing performance of the silicone layer in ultra-thin foldable applications.
The selection of silicone materials must balance elasticity and tear resistance. Ordinary silicone is prone to cracking due to molecular chain breakage during repeated folding. However, high-strength silicone or modified silicone with nano-reinforced phases can significantly improve tear resistance. These materials optimize their molecular structure to more evenly distribute stress during stretching, reducing localized stress concentrations. For example, the three-dimensional network structure formed by curing a two-component addition-type silicone enhances the crosslinking density between molecular chains, thereby improving fatigue resistance and extending the life of the silicone layer in the folded state.
The bonding process between the silicone layer and the aluminum alloy substrate is critical for preventing cracking. If the bonding is weak, relative displacement between the silicone and aluminum alloy can occur during folding, leading to tearing at the silicone edges. Specially modified silicone structural adhesives or hard structural adhesives are required for bonding. These adhesives penetrate the micropores of the aluminum alloy surface, forming a mechanical interlocking structure and enhancing adhesion. Furthermore, the aluminum alloy surface should be degreased, sandblasted, or chemically etched to increase surface roughness and improve the adhesive's adhesion area. After bonding, a constant temperature and humidity curing process is required to ensure full adhesive reaction and avoid bond strength loss due to incomplete curing.
The silicone layer's structural design must be adapted to the requirements of ultra-thin folding devices. Traditional flat silicone layers are prone to cracking during folding due to a small bend radius. Silicone layers with a textured or wavy surface design can disperse stress by increasing the contact area. For example, a fine texture can be pressed onto the silicone layer's surface to distribute stress along the grooves during folding, avoiding localized stress concentration. Furthermore, the silicone layer's thickness must be uniform. Too thin can lead to insufficient tear resistance, while too thick increases folding resistance, compromising the stand's portability. Typically, the thickness of the silicone layer in an ultra-thin foldable stent is controlled between 0.5 and 1.5 mm, ensuring both sealing and folding flexibility.
The folding structure design of the aluminum alloy stent needs to be optimized in tandem with the silicone layer. For example, rounded corners can be used at the folding joints to reduce bending stress on the silicone layer during folding; or the stretch ratio of the silicone layer can be reduced by increasing the folding radius of the aluminum alloy. Furthermore, the folding mechanism of the aluminum alloy stent must have precise limiters to prevent excessive folding, which could lead to the silicone layer being stretched to its limit. For example, a biaxial limiter can be used to limit the maximum folding angle of the stent, preventing cracking of the silicone layer due to excessive stretching.
Improving environmental adaptability can enhance the long-term stability of the silicone layer. Silicone materials are prone to hardening or softening in high or low temperature environments, resulting in a decrease in sealing performance. Weathering agents should be added to ensure that the silicone layer maintains stable elasticity within a temperature range of -20°C to 80°C. Furthermore, a hydrophobic coating can be applied to the silicone layer to reduce the penetration of moisture and dust, thus preventing aging and cracking caused by environmental factors. For example, treating the silicone surface with a fluorinated hydrophobic agent creates a low-surface-energy coating, causing water droplets to roll spherically on the surface and reducing moisture retention.
Adaptive design for specific usage scenarios can further reduce the risk of silicone cracking. For example, for in-vehicle use, mobile phone holders need to be vibration-resistant. Microporous structures can be embedded in the silicone layer to absorb vibration energy and reduce fatigue damage to the silicone layer. For outdoor use, the silicone layer needs to be UV-resistant. UV absorbers can be added to prevent photooxidation-induced breakage of the silicone molecular chains.
Preventing cracking and maintaining the sealing properties of the silicone layer in mobile phone holders requires coordinated optimization of materials, structure, process, and environmental adaptability. By selecting highly tear-resistant silicone materials, improving the bonding process, optimizing the structural design, and enhancing environmental adaptability, the reliability and sealing properties of the silicone layer in ultra-thin foldable devices can be significantly improved, meeting the dual needs of portability and durability.
