Properties of Silicone Rubber Raw Materials for Wires and Cables

1. Thermal Properties (Core Advantage, Far Superior to Ordinary Plastics & Rubbers)

1. Stable elasticity over an ultra-wide temperature range
   • Conventional VMQ cable grade silicone rubber: Continuous long-term service temperature -60℃ ~ +180℃ (Class H insulation); modified high-grade versions withstand -60℃ to 250℃.
   • Short-term peak resistance: No melting or dripping under transient exposure to 300~350℃; tolerates temperatures above 250℃ for 5 seconds under short-circuit conditions.
   • Excellent low-temperature performance: Remains flexible without cracking at -60℃, while ordinary PVC hardens and cracks below -10℃. Ideal for outdoor wiring in frigid northern regions and low-temperature equipment cables.
2. Superior thermal aging resistance
   Hardening, pulverization and cracking rarely occur under prolonged high-temperature exposure; tensile and insulation properties retain high residual rates after thermal aging, with a service life 3–5 times longer than PVC.
3. Combustion performance
   Decomposes into inorganic silicon dioxide (SiO₂) under heat, forming a heat-insulating barrier to block heat transfer; no molten dripping that may ignite surrounding combustibles.

2. Electrical Insulation Properties (Critical for Cable Applications)

1. High insulation stability across wide temperature and frequency ranges
   Volume resistivity ≥ 10¹⁴ Ω·cm, dielectric breakdown strength ≥ 20kV/mm. Insulation resistance barely declines under high temperature, high humidity or varying frequencies, unlike PVC whose insulation deteriorates severely at high temperatures.
2. Outstanding corona and arc resistance
   The inorganic Si-O molecular backbone resists ablation by high-voltage electric arcs; the residual SiO₂ layer maintains insulation even after arc exposure. Suitable for motors, high-voltage furnaces and new energy wiring harnesses.
3. Low dielectric loss
   Dielectric constant ranging from 3.0 to 3.5, minimizing signal attenuation at high frequencies for sensor, aerospace control and RF cables.

3. Mechanical Elasticity & Processing Characteristics

1. Ultra-flexible with high resilience
   Extremely flexible molecular chains allow cables to bend at a radius only 4 times the cable outer diameter, resisting cracking after repeated flexing. Perfect for cable chains, robotic equipment and frequently moving flexible wires.
2. Compatible with wire extrusion manufacturing
   Cable-grade silicone rubber reinforced with fumed silica delivers smooth extruded surfaces and anti-sticking performance on molds, enabling stable high-speed extrusion for insulation and sheathing layers.
3. Basic mechanical indicators (standard 60–70 Shore A cable grade)
   Tensile strength: 6–10 MPa; elongation at break ≥ 300%; high rebound rate.
   Drawback: Tear strength and wear resistance at room temperature are inferior to EPDM and PU; prone to damage under sharp friction. Glass fiber braiding reinforcement is required for heavy-duty abrasion-prone applications.

4. Weather, Chemical & Waterproof Resistance

1. Exceptional anti-aging performance (premier choice for outdoor use)
   Fully resistant to UV radiation, ozone and oxidative aging; remains intact without pulverization or cracking after 10 years of outdoor exposure, while ordinary rubber embrittles and discolors over time outdoors.
2. Hydrophobic, waterproof and mildew-proof
   Non-polar hydrophobic molecular structure preserves insulation performance almost completely after water immersion; inhibits mold growth, applicable to underwater wiring, high-humidity kilns and kitchen & bathroom equipment cables.
3. Selective chemical resistance
   Resistant to: weak acids, weak alkalis, water, ethanol, lubricating oil, high-temperature steam and most inorganic corrosive media.
   Not resistant to: non-polar organic solvents such as gasoline and toluene (causes swelling), concentrated strong acids & alkalis, and long-term immersion under high-pressure high-temperature oil.

5. Flame Retardant, Eco-Friendly & Safety Properties

1. Inherent self-extinguishing capability, halogen-free low-smoke formulation available
   Virgin silicone rubber self-extinguishes once removed from flame. Formulations filled with ATH or platinum flame retardant systems achieve UL94 V-0 and IEC bundled flame retardancy standards. Halogen-free grades produce low smoke, low toxicity and non-corrosive halogen-free gas during combustion, mandatory for fire protection, new energy and rail transit industries.
2. Physiologically inert, non-toxic and odorless
   Free of heavy metals and plasticizer precipitation; food-grade and medical-grade silicone rubber can be used for wiring inside food machinery and medical devices, complying with FDA and RoHS environmental standards.
3. Radiation resistance
   Phenyl-modified silicone rubber (PVMQ) withstands gamma rays and high-energy radiation, adopted for special cables in nuclear power and aerospace industries.

6. Major Drawbacks of Cable-Grade Silicone Rubber (Key Selection Notes)

1. Relatively low mechanical strength at room temperature, poor tear and abrasion resistance, susceptible to skin damage under sharp contact;
2. Poor resistance to mineral oil and organic solvents, not recommended as standalone sheathing for oil bath environments;
3. Raw material and processing costs far exceed PVC, PE and conventional rubber;
4. Long-term exposure to high-pressure steam above 150℃ gradually degrades mechanical properties;
5. Conventional bis-2,4 vulcanized silicone rubber contains trace chlorine; platinum vulcanized raw materials are required for high-end halogen-free wiring harnesses.

7. Basic Composition of HTV Compound Silicone Rubber for Wires

1. Base polymer: Methyl vinyl silicone rubber (MVQ, general grade for 180℃ cables); Phenyl silicone rubber (PVMQ, for 200–250℃ high-temperature and radiation-resistant applications).
2. Reinforcing filler: Fumed silica (core filler to boost tensile and tear resistance for cable materials).
3. Functional additives: Flame retardants, heat stabilizers, release agents, color masterbatches, anti-mildew agents.
4. Vulcanization systems: Bis-2,4 vulcanization (low-cost general grade); platinum vulcanization (high-end halogen-free low-smoke wiring harnesses).

8. Typical Application Scenarios