The difference between liquid silicone rubber (LSR) and silicone rubber (HTV): in-depth analysis from molecular structure to application scenarios
In the field of silicone materials, liquid silicone rubber (LSR) and high-temperature vulcanizing silicone rubber (HTV) are two core materials. Although the main components of both are polysiloxane, there are significant differences in their molecular structure, processing technology and terminal applications. This article will systematically compare the differences between the two from the perspective of material science and provide selection recommendations.
One. Basic definition and chemical structure
1. Liquid silicone rubber (LSR)
Chemical form:
Two-component (A/B) low-viscosity liquid, containing vinyl-terminated polydimethylsiloxane (Vi-PDMS), hydrogen-containing silicone oil crosslinker and platinum catalyst.
Crosslinking mechanism:
Through platinum-catalyzed addition reaction (Hydrosilylation), a three-dimensional network structure is formed, reaction formula:
≡Si-CH=CH₂ + H-Si≡ → ≡Si-CH₂-CH₂-Si≡
Typical viscosity:
5,000-50,000 cP (close to honey fluidity when not cured).
2. High temperature vulcanized silicone rubber (HTV)
Chemical form:
High molecular weight solid raw rubber (molecular weight 400,000-800,000), which needs to be combined with additives such as white carbon black and peroxide (such as DCP).
Crosslinking mechanism:
Peroxide triggers free radical reaction, breaks Si-CH₃ bond to form Si-O-Si crosslinking.
Morphological characteristics:
When not vulcanized, it is a flake or block solid (Mooney viscosity 30-80).
Two. Core performance comparison
| Performance indicators | Liquid silicone rubber (LSR) | High temperature vulcanized silicone rubber (HTV) |
| Hardness range | Shore A 10-80 (easier to achieve super soft glue) | Shore A 20-90 (high hardness is more stable) |
| Tensile strength | 4-12 MPa (depends on filler) | 5-15 MPa (can be enhanced to 20MPa+) |
| Tear strength | 10-30 kN/m | 20-50 kN/m |
| Temperature resistance | -50℃~200℃ (short-term 250℃) | -60℃~250℃ (special formula up to 300℃) |
| Shrinkage | 0.1-0.3% (injection molding) | 1.5-3% (compression vulcanization) |
| Production efficiency | Fast curing (30s-3min) | Slow vulcanization (5-15min) |
Three. Processing technology differences
1. Liquid silicone rubber (LSR)
Molding technology:
Injection molding: Precisely mix A/B components through two-component metering equipment (such as ARBURG) and inject into 170-180℃ mold.
Advantages:
2. High temperature vulcanized silicone rubber (HTV)
Processing flow:
Raw rubber mixing → preforming → molding/calendering → vulcanization (first stage vulcanization 160℃×10min + second stage vulcanization 200℃×4h)
Process characteristics:
Open mixer/internal mixer mixing is required (high energy consumption)
Suitable for large-sized products (such as sealing strips, rollers)
Four. Application scenario selection
Typical applications of liquid silicone (LSR)
Medical grade:
Baby pacifier (FDA 21 CFR 177.2600)
Implantable catheter (biocompatibility ISO 10993)
Electronic grade:
5G base station seal (weather resistance UL94 V-0)
Keyboard keys (lifespan > 5 million presses)
✔ No mixing required, direct injection molding
✔ Can produce complex thin-walled parts (minimum wall thickness 0.2mm)
✔ High degree of automation (qualified rate > 99%)
Advantages of high temperature vulcanized silicone rubber (HTV)
Industrial products:
High voltage insulators (arc resistance > 20kV/mm)
Automobile turbocharger pipe (oil resistance ASTM D471)
Special materials:
Flame retardant silicone (UL94 V-0, containing aluminum hydroxide filler)
Conductive silicone (volume resistance 10³-10⁶Ω·cm, containing carbon black/silver powder)
Five. Cost and supply chain considerations
| Factors | Liquid silicone rubber (LSR) |
High temperature vulcanized silicone rubber (HTV) |
| Raw material cost | High (platinum catalyst price > 80 yuan/g) | Low (peroxide cost < 50 yuan/kg) |
| Equipment investment | Requires a dedicated injection molding machine (> 2 million yuan) | General mixing/molding equipment (< 1 million yuan) |
| Minimum order quantity | Suitable for small batches (1kg for trial production) | Requires large batches (usually > 50kg) |
Conclusion and Recommendations
Scenarios where LSR is preferred:
Fields requiring high precision and high cleanliness, such as medical implants and microelectronics.
Projects that require rapid automated production (such as mass production of daily necessities).
Scenario where HTV is preferred:
Industrial parts that are resistant to extreme environments (high temperature/strong oxidation).
Large products that are cost-sensitive and do not require high dimensional accuracy.
Future trends: LSR is moving towards lower viscosity (for micro-injection molding) and higher thermal conductivity (>1.5 W/mK), while HTV continues to innovate in the field of environmentally friendly odorless vulcanizers (replacing DCP). Enterprises should make comprehensive decisions based on product requirements, process capabilities and budget.
