Comparison of Hardness Between Liquid(LSR) and Solid Silicone Rubber (HTV)
Abstract
Silicone rubber is available in two primary forms: Liquid Silicone Rubber (LSR) and Solid (High-Temperature Vulcanizing, HTV) Silicone Rubber. While both exhibit excellent elasticity and durability, their hardness properties differ significantly due to variations in molecular structure, curing mechanisms, and filler content. This article compares the hardness characteristics of LSR and HTV, their influencing factors, and typical applications based on hardness requirements.
1. Introduction
Hardness is a critical mechanical property of silicone rubber, measured using the Shore A or Shore 00 scale (for very soft materials). LSR and HTV silicones differ in their base polymers, curing processes, and reinforcement methods, leading to distinct hardness ranges and performance in applications.
2. Hardness of Liquid Silicone Rubber (LSR)
Typical Hardness Range: Shore A 10 to 80
Soft Grades (Shore A 10-30):
Used in medical devices (e.g., baby bottle nipples, soft seals).
High flexibility, excellent compression set resistance.
Medium Grades (Shore A 30-60):
Common in consumer goods (e.g., kitchenware, wearable devices).
Balanced elasticity and durability.
Firm Grades (Shore A 60-80):
Used in automotive gaskets and industrial components.
Factors Affecting LSR Hardness
Filler Content: More silica fillers increase hardness.
Crosslinking Density: Higher curing temperatures can slightly increase hardness.
Platinum Catalyst System: Provides uniform curing but limits ultra-high hardness.
3. Hardness of Solid Silicone Rubber (HTV)
Typical Hardness Range: Shore A 20 to 90
Soft to Medium (Shore A 20-50):
Used in seals, gaskets, and flexible tubing.
Firm to Hard (Shore A 50-90):
Industrial applications (e.g., high-pressure seals, automotive parts).
Can be reinforced with peroxide curing for extreme durability.
Factors Affecting HTV Hardness
Filler Type & Content: Carbon black, silica, and alumina trihydrate increase hardness.
Curing Method: Peroxide vulcanization allows higher hardness than LSR.
Post-Curing: Additional heat treatment can enhance hardness stability.
4. Key Differences in Hardness Performance
| Property | Liquid Silicone (LSR) | Solid Silicone (HTV) |
|---|---|---|
| Hardness Range (Shore A) | 10 - 80 | 20 - 90 |
| Ultra-Soft Options | Yes (Shore 00 available) | Limited (rarely below Shore 20) |
| Ultra-Hard Options | Rarely exceeds Shore 80 | Can reach Shore 90+ |
| Curing Influence | Platinum catalyst limits hardness | Peroxide allows higher hardness |
| Elasticity Retention | Excellent at low hardness | Better at high hardness |
5. Application-Based Hardness Selection
When to Choose LSR?
Medical & Food-Grade Products (soft, biocompatible).
Precision Molding (complex shapes with consistent hardness).
Wearable Devices (needs flexibility and comfort).
When to Choose HTV?
High-Stress Industrial Parts (harder, more durable).
Automotive & Aerospace (extreme temperature and pressure resistance).
Electrical Insulation (requires firm, stable hardness).
6. Conclusion
LSR excels in low-to-medium hardness applications requiring precision and biocompatibility.
HTV is better suited for medium-to-high hardness demands, especially in harsh environments.
The choice depends on required hardness, curing method, and end-use conditions.