How can the tensile strength and resilience of silicone watch bands be optimized through the vulcanization process?
Release Time : 2025-12-09
Tensile strength and resilience are core performance indicators of silicone watch bands, directly affecting wearing comfort and lifespan. The vulcanization process, as a key manufacturing step, can systematically improve these two properties by controlling crosslinking density, vulcanization time and temperature, selecting the vulcanization system, and optimizing the process. The following analysis focuses on the core parameters and optimization strategies of the vulcanization process.
Crosslinking density is the core factor determining the degree of connection between silicone molecular chains, having a dual impact on tensile strength and resilience. During vulcanization, crosslinking agents (such as peroxides and vulcanizing agents) react with silicone molecular chains to form a three-dimensional network structure. If the crosslinking density is too low, the intermolecular forces are weak, making irreversible deformation more likely under stress, resulting in insufficient tensile strength and poor resilience. If the crosslinking density is too high, molecular chain movement is restricted; while tensile strength can be improved, resilience will be weakened due to decreased elastic recovery. Therefore, the optimal crosslinking density range needs to be determined experimentally. For example, in the production of silicone watch bands, a medium crosslinking density design ensures sufficient tensile strength to withstand daily pulling while maintaining good resilience to adapt to wrist movements.
The coordinated control of vulcanization time and temperature is crucial for performance optimization. Insufficient vulcanization time leads to incomplete cross-linking, preventing the formation of a stable molecular network and resulting in insufficient tensile strength and resilience. Excessive vulcanization time, on the other hand, can cause over-cross-linking, stiffening the molecular chains and reducing resilience. Vulcanization temperature also affects the reaction rate and cross-linking quality: too low a temperature results in a slow reaction, requiring a longer vulcanization time; too high a temperature, while accelerating the reaction, can easily lead to localized overheating, causing uneven cross-linking or molecular chain breakage. In actual production, a segmented vulcanization process needs to be developed based on the silicone formulation and equipment characteristics. For example, pre-vulcanization at a low temperature (e.g., 150℃) can be performed to uniformly initiate the cross-linking reaction, followed by raising the temperature to 180℃ for final vulcanization, ensuring sufficient cross-linking and structural stability of the molecular chains.
The choice of vulcanization system directly influences the direction of performance optimization. Peroxide vulcanization systems (such as DCP) are suitable for high-temperature vulcanization applications. Their high crosslinking bond energy improves the tensile strength and heat resistance of silicone watch bands, but the resilience may be slightly reduced due to the stronger rigidity of the crosslinking bonds. Disulfide vulcanization systems (such as TMTD) are suitable for low-temperature vulcanization. Their better crosslinking bond flexibility helps maintain resilience, but the tensile strength may be slightly lower. To balance these two properties, a composite vulcanization system can be used, combining the advantages of different vulcanizing agents. For example, adding both peroxide and disulfide to the silicone watch bands formulation and adjusting the ratio can synergistically improve tensile strength and resilience.
Process optimization is a practical path to improve performance. During the mixing process, it is necessary to ensure that the vulcanizing agent and the silicone matrix are uniformly dispersed, avoiding excessively high or low local crosslinking densities. For example, using a Banbury mixer for high-shear mixing can break down filler agglomerates, improve dispersibility, and thus optimize the uniformity of the crosslinking network. In terms of molding processes, injection molding injects liquid silicone into a mold under high pressure, reducing internal defects and improving tensile strength. Compression molding is suitable for solid silicone, promoting cross-linking reactions through high temperature and pressure, thus enhancing resilience. Furthermore, secondary vulcanization further removes residual volatiles, improving product stability and durability.
The synergistic effect of fillers and additives is also crucial. Nanofillers (such as nano-calcium carbonate and nano-silica) have a large specific surface area, forming a uniform network structure that improves tensile strength and resilience. For example, adding 2% nano-carbon black can increase resilience by approximately 12%. Dispersants (such as silane coupling agents) can reduce the surface energy of fillers, promoting dispersion and preventing performance degradation caused by agglomeration. The selection of softeners is equally critical. Light mineral oils (such as naphthenic oils) have less impact on resilience than aromatic hydrocarbon softeners, and their dosage should be controlled between 5% and 15%, using the lower limit for low-temperature environments and the upper limit for high-temperature environments.
The impact of environmental factors on the vulcanization process must be considered. At low temperatures, the movement of silicone molecular chains is hindered, reducing the vulcanization reaction rate. Therefore, it's necessary to appropriately extend the vulcanization time or increase the temperature. At high temperatures, the activity of the molecular chains increases, requiring prevention of excessive cross-linking. Regarding humidity, high humidity can cause silicone to absorb moisture, affecting vulcanization quality. Therefore, production workshops need to be equipped with dehumidification equipment to ensure that the ambient humidity is controlled between 40% and 60%.
Through cross-linking density control, synergistic effects of vulcanization time and temperature, selection of vulcanization systems, process optimization, synergistic effects of fillers and additives, and control of environmental factors, the tensile strength and resilience of silicone watch bands can be systematically improved. For example, one manufacturer, by optimizing the vulcanization process, increased the tensile strength of the watch band to over 10 MPa while maintaining a resilience of over 60%, meeting the needs of high-end wearable devices. In the future, with advancements in materials science and manufacturing technology, vulcanization processes will further develop towards precision and intelligence, providing stronger support for optimizing the performance of silicone watch bands.