Within the silicone rubber family, Liquid Silicone Rubber (LSR) and High-Temperature Vulcanizing Silicone Rubber (HTV) are two mainstream products. Despite their similar chemical nature (both being polydimethylsiloxane), significant differences in molecular weight, processing methods, and vulcanization mechanisms lead to distinct performance characteristics, application scenarios, and manufacturing principles. Understanding the boundaries between LSR and HTV is crucial for material selection and process design.

I. Basic Characteristics Comparison

Feature  Liquid Silicone Rubber (LSR)     High-Temperature Vulcanizing Silicone Rubber (HTV)

Physical form Low viscosity liquid (A/B components)   High molecular weight raw rubber (solid blocks or granules)

Molecular weight 50,000–100,000   500,000–800,000

Vulcanization method Platinum-catalyzed addition reaction (100–150°C)     Peroxide or platinum vulcanization (160–200°C)

Processing technology      Liquid injection molding (LIM)  Compression molding, extrusion, calendering

Production efficiency  Cures within seconds, highly automated Minutes-long curing, requires preforming

Product precision ±0.05 mm, suitable for micro parts ±0.2 mm, suitable for large parts

Transparency Extremely high (>95%) Medium (often contains fillers)

Cost       Higher raw material cost but lower labor/energy costs      Lower raw material cost but higher labor/energy costs

II. Typical Application Divergence

LSR Dominant Fields:

Medical: Baby bottle nipples, catheter connectors, implantable sensor housings (high purity, no flash);

Electronics: Mobile phone buttons, LED lenses, connector seals (high precision, high light transmission);

Automotive: Turbocharger hose seals, sensor encapsulation (heat resistance, consistency);

Consumer Goods: Baking molds, electric toothbrush handles (complex structures, smooth surfaces).

Advantages: Capable of forming fine structures with wall thicknesses of 0.3 mm and length-to-diameter ratios >20:1; no flash, eliminating post-processing.

HTV Dominant Fields:

Industrial: Large diameter seals, rubber rolls, vibration damping pads (large sizes, high strength);

Construction: Curtain wall sealing strips, bridge bearings (requires continuous extrusion molding);

Power: High-voltage insulators, cable accessories (high mechanical strength, arc resistance);

DIY/Small Batch: Custom molded parts by manual compression (no need for expensive injection molding equipment).

Advantages: Can incorporate a high proportion of reinforcing fillers (such as fumed silica), tensile strength reaches 8–12 MPa, superior to LSR (6–9 MPa).

III. Performance Boundary Analysis

Heat Resistance: HTV has a slightly higher long-term use temperature due to its higher crosslink density (250°C vs. 230°C).

Compression Set: LSR typically performs better (<15% vs. 20–30%) because addition cure produces no byproducts.

Biocompatibility: LSR more easily achieves implant grade due to no risk of peroxide residue.

Recyclability: HTV scrap can be crushed and reused (about 10–20%), whereas LSR waste is generally non-recyclable.

IV. Process Selection Decision Tree

Choosing between LSR and HTV depends on four factors:

Production Volume: >100,000 units/year → LSR; <10,000 units/year → HTV compression molding;

Precision Requirements: Micrometer-level tolerances → LSR;

Complexity of Structure: Multi-cavity, thin walls, inserts → LSR;

Cost Structure: High labor costs, strong automation capability → LSR; Limited equipment investment → HTV.

V. Convergence Trends: Blurring Boundaries

High Flowability HTV: Developing low Mooney viscosity HTV for small injection machines;

Functionalized LSR: Conductive, thermally conductive, magnetic LSR expands electronic applications;

3D Printing HTV/LSR: Liquid deposition or powder sintering breaks traditional process limitations.

Conclusion

LSR and HTV, like precision watches and heavy machinery, each have their irreplaceable roles. LSR achieves micron-level accuracy with "liquid flexibility," while HTV supports ton-scale reliability with "solid toughness." In the eyes of materials engineers, there's no "better," only "more suitable." Understanding their molecular language and process logic enables finding the optimal engineering path among softness and strength, speed and cost, precision and scale—because true manufacturing wisdom begins with profound respect for material properties.



Low compression set fluorosilicone rubber MY FHTV 3961 series