What Is Addition-Cure Liquid Fluorosilicone Rubber?
Addition-cure liquid fluorosilicone rubber, abbreviated as F-LSR, is a two-component liquid elastomer prepared from vinyl fluorosilicone oil as the base polymer, together with fillers, additives and a platinum catalytic system. Its curing mechanism is hydrosilylation: Part A typically contains a platinum catalyst, and Part B contains a hydrogen-functional crosslinker. After mixing at a 1:1 ratio, the material rapidly vulcanizes under heat.
Compared with ordinary liquid silicone rubber LSR, F-LSR introduces trifluoropropyl groups on the siloxane backbone, combining the wide-temperature elasticity of silicone rubber with the oil, solvent and chemical resistance of fluoroelastomers. No low-molecular by-products are released during curing, and shrinkage is low, making it suitable for high-precision, flash-free complex seals.
Key Technical Indicators
Hardness and Viscosity
According to the group standard T/FSI 071-2021
Addition Liquid Fluorosilicone Rubber, F-LSR is classified into 30, 40, 50 and 60 Shore A hardness grades. Different hardness levels correspond to different viscosity ranges; for example, 30 Shore A products have a viscosity of about 60±10 Pa·s, while 60 Shore A products are around 100±10 Pa·s at 25°C and 10 s⁻¹.
Higher hardness grades such as 70 Shore A are also available on the market for applications requiring greater rigidity and sealing pressure.
Mechanical Properties
Cured F-LSR exhibits good tensile and tear strength. For common grades, tensile strength is typically no less than 8.0 MPa, while elongation at break decreases as hardness increases—above 400% for 30 Shore A and above 150% for 60 Shore A. Tear strength is generally above 10-15 kN/m, depending on formulation and vulcanization conditions.
Oil and Chemical Resistance
A key advantage of F-LSR is its resistance to fuels, oils, hydraulic fluids and non-polar solvents. Under standard testing, volume change in IRM903 standard oil at 23°C for 24h can be controlled within 3%; volume change in reference fluids B and C is typically no more than 30%. This performance is significantly better than ordinary silicone rubber, making F-LSR a preferred sealing material for fuel systems, lubrication systems and chemical environments.
Compression Set
F-LSR typically achieves a compression set of ≤30% after 177°C for 22h, with optimized formulations achieving even lower values. Low compression set ensures that seals maintain resilience and sealing reliability under long-term compression and elevated temperatures.
Service Temperature Range
The typical service temperature range of F-LSR is about -63°C to 175°C under immersed conditions, and it can withstand up to 225°C in dry heat for short periods. This wide temperature range makes it suitable for severe thermal cycling conditions.
Curing Characteristics
F-LSR cures via platinum-catalyzed hydrosilylation, releasing no by-products and exhibiting low shrinkage. Curing begins within seconds at 150°C, with injection molding cycles typically ranging from 20 to 90 seconds depending on part size and mold temperature. Note that amines, sulfur compounds, tin compounds and some peroxides can inhibit the platinum catalyst, so contact with such substances should be avoided during production.
Main Performance Features
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Excellent oil and solvent resistance: outstanding resistance to aviation fuel, gasoline, engine oil, hydraulic fluid and non-polar solvents.
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Wide-temperature elasticity: remains flexible at low temperatures and retains strength and resilience at high temperatures.
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Platinum addition cure: no by-products, low shrinkage, high dimensional accuracy, suitable for automated production.
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Low compression set: reliable long-term sealing for both static and dynamic applications.
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Good electrical insulation: low dielectric loss, suitable for electrical connectors and insulation protection.
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Suitable for LIM and extrusion coating: ideal for complex precision parts and for extrusion coating onto wires, fabrics and metal surfaces.
Typical Application Scenarios
Automotive Fuel and Lubrication System Seals
F-LSR can be used to manufacture fuel pump diaphragms, injector O-rings, fuel line connector seals, turbocharger hose liners and engine-area seals, resisting fuel, oil and high temperatures.
Aerospace Fuel System Components
In aerospace, F-LSR is used for aircraft fuel system seals, hydraulic bellows, tank diaphragms and sensor seals, performing reliably in sub-zero and high-temperature fuel environments.
Electrical Connectors and Insulation Parts
Used for chemical-resistant electrical connectors, insulation boots, sensor encapsulation and wire harness seals, combining electrical insulation with oil resistance.
Petrochemical Equipment Seals
Suitable for pump and valve seals, tank seals, downhole tool seals and chemical pipeline gaskets, resisting various solvents and corrosive media.
Precision Injection-Molded Parts
F-LSR is well suited for liquid injection molding LIM, enabling flash-free, tight-tolerance seals, diaphragms and gaskets with high automation and short cycle times.
Selection and Usage Recommendations
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Select by hardness: 30-40 Shore A for flexible seals and diaphragms; 50-70 Shore A for pressure-bearing seals and structural parts.
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Confirm media compatibility: F-LSR performs best against non-polar solvents and fuels; resistance to strong polar solvents is relatively lower, so actual media should be verified.
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Match curing process: Use dedicated meter-mix equipment for injection molding to avoid air entrapment; mold temperature is typically 150-200°C, optimizable by part thickness.
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Avoid catalyst poisons: Keep away from amines, sulfur compounds, tin compounds and certain peroxides to prevent platinum catalyst inhibition.
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Consider post-cure: For parts requiring low compression set and high-temperature performance, post-cure at around 200°C for 4h is recommended.
IOTA FLSR3400 addition-type liquid fluorosilicone rubber
