Silicone rubber wire cables are widely used in high-end fields such as aerospace, shipbuilding, and new energy due to their excellent high-temperature resistance, aging resistance, and electrical insulation properties. However, the non-polar nature of silicone rubber molecular chains results in low bonding strength with metal conductors and conventional reinforcing materials, easily leading to problems such as insulation layer detachment and uneven electric field distribution. Improving the bonding strength between the conductor and the insulation layer requires a comprehensive approach from three aspects: material modification, process optimization, and interface design. The following analysis focuses on key technical pathways.
Material modification is fundamental to improving bonding strength. Silicone rubber itself lacks polar groups in its molecular chains, resulting in poor wettability with metal conductors. Introducing tackifiers can significantly improve this defect. Tackifiers are mostly silane or siloxane oligomers containing alkoxy, silanol, or reactive organic groups. Their mechanism of action is to form chemical bonds with the conductor surface during vulcanization, while simultaneously undergoing a cross-linking reaction with the silicone rubber molecular chains to form "molecular bridges." For example, treating the conductor surface with an epoxy-containing silane coupling agent can simultaneously react with metal oxides and the hydroxyl groups in silicone rubber, enhancing interfacial bonding. Furthermore, adding a small amount of vinyl silicone rubber or fluorosilicone rubber blend to the silicone rubber formulation can enhance vulcanization activity, promote synergistic effects with tackifiers, and further improve bond strength.
Conductor surface pretreatment is a critical process. The cleanliness, roughness, and chemical state of the conductor surface directly affect the bonding effect. During production, multi-stage cleaning of the conductor is required, including mechanical grinding to remove the oxide layer, chemical cleaning to remove oil stains, and plasma treatment to activate the surface. Plasma treatment, by generating high-energy particles to bombard the conductor surface, introduces polar groups such as hydroxyl and carboxyl groups, significantly improving the wettability between the silicone rubber and the conductor. For copper conductors, tin plating or silver plating can also be used to form a dense metallic coating on the surface, preventing oxidation and providing active sites for reaction with silicone rubber. In addition, the conductor stranding process also needs to be optimized to avoid air penetration into the insulation layer due to excessive stranding gaps, which would reduce bond strength.
Controlling vulcanization process parameters affects the final performance. Vulcanization temperature, time, and pressure are the core factors determining the crosslinking density and interfacial bonding state of the silicone rubber. Too low a vulcanization temperature leads to incomplete cross-linking, preventing the tackifier from fully reacting; too high a temperature may cause thermal degradation of the silicone rubber, damaging the bonding interface. A staged vulcanization process is typically used, first allowing the tackifier to react initially with the conductor surface at a low temperature, then raising the temperature to complete the vulcanization of the silicone rubber body. The vulcanization pressure needs to be adjusted according to the conductor structure. For multi-core stranded conductors, vacuum vulcanization or high-pressure molding is required to ensure the insulation layer fully fills the strand gaps and avoids air bubble residue. Furthermore, the cooling rate after vulcanization must be controlled; excessively rapid cooling may lead to internal stress concentration, weakening the bonding strength.
Interfacial compatibilization design can improve long-term stability. By introducing a transition layer at the silicone rubber-conductor interface, stress concentration caused by differences in thermal expansion coefficients can be alleviated. For example, coating the conductor surface with a thin layer of ethylene-vinyl acetate copolymer (EVA) allows its polar groups to form physical entanglement with the silicone rubber, while its flexibility absorbs interfacial stress. Another strategy is to employ nanocomposite technology, adding a small amount of nano-silica or carbon nanotubes to silicone rubber. These nanoparticles can form a "pinning effect" at the interface, preventing crack propagation and improving bond durability.
Production environment control ensures process consistency. Silicone rubber is sensitive to impurities; production workshops must be kept clean to prevent dust, oil, and other contaminants from polluting the conductor or silicone rubber. The mixing process requires specialized equipment to prevent organic rubber impurities from entering the silicone rubber system. Furthermore, the storage conditions of silicone rubber must be strictly controlled to prevent performance degradation due to moisture absorption or aging, which would affect bond strength.
Quality testing and standard compliance ensure reliability. During production, the quality of conductor surface treatment, vulcanization parameters, and finished product bond strength must be rigorously tested. Methods such as peel tests and tensile tests can be used to quantify bond performance, while referring to standards such as IEC 60502 and GB/T 2951 to ensure that the product meets the insulation requirements of high-voltage cables. For special applications, such as the new energy field, additional performance indicators such as resistance to PID (potential-induced decay) must also be met.
Technological innovation drives upgrades in bond performance. With the development of materials science, new silicone rubber systems are constantly emerging. For example, self-adhesive silicone rubber achieves strong adhesion to conductors without additional treatment through built-in tackifying groups; liquid silicone rubber (LSR) uses injection molding technology, which can precisely control the insulation layer thickness and interface state, further improving the bonding quality. These technologies provide new directions for the high performance of silicone rubber wire cables.
