How can we prevent silicone sealing rings from releasing silicone oil over long-term use, potentially contaminating optical devices or electronic components?
Publish Time: 2025-09-16
In precision instruments, optical systems, and high-end electronic devices, seals do more than simply block fluids or gases; they must also ensure they do not become a source of contamination themselves. Silicone is widely used in these highly sensitive environments due to its excellent temperature resistance, elasticity, and chemical inertness. However, its potential for "oil release"—particularly the migration of low-molecular-weight siloxanes, commonly known as "silicone oil release"—can severely impact delicate surfaces. When these volatile or semi-volatile substances slowly release and deposit on lenses, sensors, circuit boards, or laser components, they can form a difficult-to-remove oil film, leading to optical attenuation, signal interference, or decreased electrical performance. Therefore, preventing silicone oil release from silicone sealing rings over long-term use becomes a core challenge in material design and process control.The root cause of silicone oil release lies in the molecular structure and manufacturing process of silicone. Silicone rubber is made from cross-linked long-chain polysiloxane molecules. However, during the polymerization and vulcanization process, a certain amount of low-molecular-weight cyclic siloxanes (such as D3, D4, and D5) that are not part of the network will always remain. These small molecules are highly mobile and, under prolonged heat or stress, can slowly migrate from the three-dimensional cross-linked network to the surface and volatilize. Furthermore, incomplete vulcanization or uneven filler dispersion can leave more mobile components, increasing the risk of precipitation.To fundamentally mitigate this phenomenon, optimizing the material formulation is paramount. Using a high-molecular-weight base polymer can reduce the oligomer content, thereby reducing the total amount of migratable substances at the source. Furthermore, selecting an efficient cross-linking system ensures a thorough vulcanization reaction and maximizes the conversion of linear molecules into a stable three-dimensional network. While peroxide vulcanization may produce a small amount of byproducts compared to addition-type (platinum-catalyzed) systems, its denser cross-linking structure provides greater binding capacity for low-molecular-weight substances, making it commonly used in applications where precipitation control is crucial.The use of reinforcing fillers is also crucial. Surface-treated fumed silica not only enhances mechanical strength, but its surface hydroxyl groups also form hydrogen bonds or chemical bonds with silicone rubber molecular chains, further anchoring the polymer network and restricting the free movement of small molecules. The uniformity of filler dispersion also directly impacts precipitation behavior. Agglomerated areas can become channels for the accumulation of low-molecular-weight substances. Therefore, high-shear mixing is essential to ensure the filler is fully dispersed within the matrix.Control of the production process is also crucial. High-temperature secondary vulcanization (post-baking) is a key step in eliminating residual low-molecular-weight substances. Under a specific temperature profile, the seal ring is heated for an extended period under no load, accelerating the volatilization and expulsion of residual small molecules. This process requires precise temperature control to prevent excessive aging and ensure uniform heat penetration, effectively releasing any residual matter. Some high-end applications even employ vacuum degassing or solvent extraction pretreatment to further reduce extractables.At the application level, seal structure design also plays a role in contamination control. Preventing the seal ring from being subjected to prolonged high compression can reduce the internal stress-driven migration of small molecules. At the same time, properly arranged ventilation or exhaust channels can help direct trace releases out of the system, rather than accumulating in sensitive areas. For extremely clean environments, consider adding an oil retainer ring or adsorption layer to the seal as a final physical barrier.When a microscope maintains continuous focus or a satellite's sensors orbit, every component within must remain absolutely clean. While soft and invisible, silicone sealing rings carry a significant responsibility—they must not only seal against the outside world but also maintain internal integrity. Through precise molecular-level control and meticulous manufacturing processes, modern high-performance silicones can maintain zero leakage over long periods of service, ensuring a truly silent and traceless seal.
