In operating conditions involving exposure to oils or chemical solvents—such as petrochemical processing, automotive fuel systems, and aviation hydraulic equipment—the swelling problem of conventional silicone rubber limits its sealing applications. By introducing fluorine substituents into the main chain, fluorosilicone rubber significantly enhances oil and solvent resistance while maintaining the broad-temperature-range elasticity of silicone rubber.

Performance Differences Arising from Molecular Structure

Conventional methyl vinyl silicone rubber (VMQ) has methyl side groups and relatively low molecular polarity, making it susceptible to swelling in non-polar mineral oils and fuels, with volume change rates potentially exceeding 50%. Fluorosilicone rubber (FVMQ) introduces trifluoropropyl groups into the side chains, increasing molecular polarity and steric hindrance, thereby reducing the permeation rate of oil molecules into the rubber. After 70 hours of immersion in ASTM No. 1 reference oil (IRM 901), the volume change rate of FVMQ is typically controlled between 5% and 15%, while VMQ exceeds 40%. The gap is even more significant in No. 3 oil (IRM 903, with higher aromatic hydrocarbon content).

Broad-Temperature-Range Elasticity Retention

Fluorosilicone rubber typically has a service temperature range of -60°C to 200°C, with some special formulations capable of short-term resistance up to 250°C. Its low-temperature performance surpasses most fluorocarbon rubbers (FKM), maintaining elasticity below -40°C—a characteristic critical for aviation hydraulic systems operating in low-temperature environments at high altitudes. While its high-temperature limit is slightly lower than some high-performance FKM grades, in long-term aging tests below 200°C, FVMQ exhibits slower growth in compression set, with better retention of sealing resilience.

Typical Application Scenarios

Automotive fuel system sealing is a traditional strength of fluorosilicone rubber. With the implementation of China's National VI emission standards and increasingly stringent limits on fuel vapor permeation, higher demands are placed on fuel resistance and low permeability of sealing materials. FVMQ demonstrates better stability in alcohol-blended fuels (E10, E85 ethanol gasoline) than most hydrocarbon rubbers, making it the mainstream material for fuel injection system seals.

Aviation hydraulic systems use phosphate ester-based hydraulic fluids (such as Skydrol), which are highly corrosive to ordinary rubbers. FVMQ exhibits a volume change rate of less than 10% in such media, meeting the reliability requirements of aviation seals. In semiconductor wet process equipment, FVMQ seals must withstand alternating exposure to multiple chemical solvents (isopropanol, acetone, NMP, etc.), where its chemical stability ensures process chamber cleanliness and seal service life.

Curing Systems and Application Methods

Fluorosilicone seal products are divided into two categories: one-component moisture-cure and two-component addition-cure systems. One-component products cure through dealcoholization or deketoximation, with tack-free time of 30–60 minutes and full cure in 24–72 hours, suitable for on-site application and repair. Two-component products have a pot life of 2–4 hours after mixing, and heat curing (80–150°C) can shorten the process to 30–60 minutes, suitable for batch production. The choice of adhesion primer must match the substrate type—silane coupling agent primers are commonly used for metal substrates, while plastic substrates require targeted selection.

Performance Testing and Quality Control

Oil resistance testing is performed according to GB/T 1690 or ASTM D471 standards, with test conditions typically at 100°C × 70 hours. In addition to volume change rate, attention should also be paid to hardness change, tensile strength retention rate, and elongation at break change. Compression set testing (GB/T 7759, 175°C × 22 hours) reflects the sealing resilience after long-term compression; high-quality FVMG can achieve compression set rates below 20%.

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