The tear resistance of liquid silicone fresh-keeping boxes is a key indicator of their durability, directly impacting their lifespan under frequent opening and closing, squeezing, and alternating hot and cold conditions. The vulcanization process, a crucial step in transforming liquid silicone from a viscous fluid into a highly elastic solid, imparts tear resistance through molecular chain crosslinking and reconstruction. Optimizing this process requires a systematic approach encompassing crosslinking system design, process parameter control, and post-processing enhancement.
Crosslink density is a key factor determining the tear strength of liquid silicone fresh-keeping boxes. During the vulcanization process, the crosslinker reacts with the active groups in the silicone rubber molecular chains to form a three-dimensional network structure. Increasing the vinyl content or using trifunctional hydrogenated silicone oils can increase the crosslink density, creating tighter physical connections between the molecular chains. For example, in a platinum-catalyzed vulcanization system, adjusting the molar ratio of hydrogenated silicone oil to vinyl silicone oil allows for precise control of the crosslink density. This allows for more even distribution of stress within the network when subjected to external forces, preventing localized stress concentrations that can lead to tearing.
Coordinated control of vulcanization temperature and time is crucial for crosslinking quality. Liquid silicone fresh-keeping boxes are typically cured using a hot vulcanization process. Excessively low temperatures can lead to incomplete crosslinking, resulting in a loose structure between molecular chains and a significant reduction in tear strength. Excessively high temperatures can cause excessive molecular chain degradation, compromising the integrity of the network structure. In practice, a step-by-step curing profile is designed based on the silicone formulation's characteristics. For example, basic crosslinking can be achieved initially at a low temperature, followed by further crosslinking at a higher temperature to ensure a thorough and uniform crosslinking reaction. Furthermore, the curing time must be matched to the temperature to avoid insufficient crosslinking due to insufficient curing time, or material degradation due to excessive curing time.
Cure pressure management is key to eliminating bubbles and improving structural density. During compression or injection molding, applying appropriate pressure ensures that the liquid silicone fully fills the mold cavity and eliminates internal bubbles. Bubbles create stress concentration points, significantly reducing tear strength. By optimizing mold design and incorporating dynamic pressure control technology, higher pressure can be applied during the initial curing phase to ensure material density, while gradually reducing pressure to prevent molecular chain breakage caused by excessive compression. This ensures structural integrity while improving the material's tear resistance.
Post-treatment processes play a crucial role in consolidating the vulcanization effect. After vulcanization, liquid silicone fresh-keeping boxes require secondary vulcanization or heat treatment to eliminate residual stress and improve the crosslinking network. Secondary vulcanization, by extending the high-temperature treatment time, promotes the continued reaction of unreacted crosslinkers, increasing the degree of crosslinking. Heat treatment also relieves tension within the material's molecular chains, reducing microcracks caused by rapid cooling. Furthermore, rounding the edges of the fresh-keeping box can avoid stress concentration caused by right-angle structures under load, further reducing the risk of tearing.
Optimizing the material formulation requires a balance between tear strength and other properties. For example, increasing filler content improves hardness and tear resistance but may reduce flexibility. Adding plasticizers improves processability but may weaken crosslink density. Therefore, experimental screening is necessary to optimize the formulation. For example, using nano-silica as a reinforcing agent can enhance friction between molecular chains and improve tear strength without significantly affecting the material's transparency and flexibility.
Process monitoring and quality inspection are key to ensuring stable vulcanization results. An online monitoring system tracks changes in temperature, pressure, and crosslinking during the vulcanization process in real time, enabling timely detection and parameter adjustments. Finished products undergo rigorous testing, including tear strength and heat aging tests, to ensure they meet tear strength standards. For example, a tensile testing machine measures the tear force at the edge of the fresh-keeping box at a specific speed to assess its tear resistance in actual use.
Optimizing the tear strength of liquid silicone fresh-keeping boxes requires meticulous attention throughout the entire vulcanization process. From crosslinking system design to process parameter control, post-processing enhancements, and quality inspection, every step requires precise control. Through system optimization, the durability of fresh-keeping boxes can be significantly improved in complex environments, meeting consumer demand for high-quality food containers.
