Core Requirements of High-Quality Silicone Insoles for Liquid Silicone Rubber (LSR)
The core requirements for liquid silicone rubber (LSR) used in premium silicone insoles focus on five key dimensions: safety & compliance, mechanical durability, comfort & resilience, processability, and long-term stability. Below are specific indicators and selection criteria, balancing performance and mass production feasibility.
I. Safety & Compliance (Mandatory)
System & Certifications:Prioritize platinum-catalyzed addition-cure LSR with a 1:1 A/B component ratio, free of peroxide residues. Compliance with FDA 21 CFR §177.2600, EU 10/2011 (food contact), and ISO 10993-5/-10 (cytotoxicity, sensitization) is required.
Hazardous Substances:Heavy metals (Pb≤90mg/kg, Cd≤75mg/kg), VOC≤100μg/m³, and migratable substances (e.g., D4/D5) must meet REACH restrictions. The material should be odorless and non-leaching.
Yellowing Resistance:Adopt non-migratory UV stabilizers and antioxidants (addition level: 0.3%–0.8%). Avoid peroxide curing agents. For transparent/light-colored products, high-purity LSR (impurity≤0.1%) is preferred.
II. Mechanical Durability (Core Performance)
| Performance Indicator | Recommended Range | Explanation |
|---|---|---|
| Hardness (Shore A) | 25–40 (daily use); 40–50 (supportive type) | 25–30 for complex textures, 30–40 for simple structures (balances softness and anti-collapse) |
| Tensile Strength | ≥6.0 MPa | Ensures no tearing during long-term wear; ≥7.0 MPa is preferred. |
| Tear Strength | ≥20 kN/m | Prevents edge cracking; ≥25 kN/m required for complex shapes. |
| Elongation at Break | ≥450% | Enhances bending durability and reduces fracture risk. |
| Compression Set | ≤10% (70℃×22 h) | Maintains long-term resilience and avoids permanent deformation after compression. |
| Rebound Resilience | Elastic recovery rate ≥70% | Energy loss rate ≤15% (balances shock absorption and comfort). |
III. Comfort & User Experience
Softness & Resilience:Low hardness (25–35 Shore A) combined with low compression set (≤8%) provides a snug fit and long-lasting support. For supportive insoles, local reinforcement (e.g., arch area) can be 40–50 Shore A.
Breathability & Moisture Wicking:Formula optimization reduces hygroscopicity. Mold design with air vents/grooves minimizes stuffiness and slipperiness.
Temperature & Weather Resistance:Stable performance from -50℃ to 200℃, with UV and ozone aging resistance for extended service life.