LSR Liquid Silicone Rubber

What Is LSR Liquid Silicone Rubber?

LSR (Liquid Silicone Rubber) is a two-component, platinum-catalyzed addition-cure silicone system supplied as a pumpable liquid. Component A contains the vinyl-functional PDMS polymer and platinum catalyst; Component B contains the crosslinker (methylhydrosiloxane) and inhibitor. When the two components are combined — typically at a 1:1 weight ratio — and exposed to heat (150–200 °C), the platinum catalyst drives a hydrosilylation reaction that rapidly converts the liquid into a cross-linked elastomer.

LSR is processed by Liquid Injection Molding (LIM), a clean-room-compatible, fully automated process that delivers flash-free, dimensionally accurate parts in cycle times of 30–90 seconds. It is the dominant technology for high-volume precision silicone parts in medical, baby, wearable, and automotive applications.

How the LIM Process Works

In LIM processing, the two-component LSR is stored in sealed pails or drums and pumped through a static mixer at a precisely controlled 1:1 ratio into a cold runner (typically at 5–10 °C to prevent premature cure). The mixed material is injected into a heated steel mold (150–200 °C) where it cures in seconds. Because LSR is a liquid before cure, it fills complex cavities, undercuts, and thin walls that would be impossible with compression-molded HTV. The cold runner prevents material waste, and the flash-free cure eliminates the trimming step required in HTV compression molding.

Key Advantages of LSR

Precision and complexity: LSR injection molding achieves tolerances of ±0.05 mm and enables complex geometries — undercuts, thin walls as low as 0.3 mm, overmolding onto plastic substrates — that solid silicone cannot match.

Cleanliness and biocompatibility: Platinum addition cure produces no volatile by-products and leaves no amine or peroxide residues. This gives LSR an inherently clean extractable profile, enabling straightforward compliance with USP Class VI and FDA 21 CFR 177.2600.

High throughput: Cycle times of 30–90 seconds with multi-cavity tooling enable outputs of thousands of parts per hour, reducing per-part cost at volumes above ~50,000 pieces per year.

Self-adhesive grades: Selected LSR grades bond directly to engineering plastics (PC, PA, PBT) without primer, enabling two-shot and overmolding applications for wearables and medical device assemblies.

Clean-room compatibility: Fully enclosed LIM processing is compatible with ISO Class 7/8 clean-room environments, making LSR the standard for medical device and pharmaceutical components.

Medical and Baby Product Applications

Medical tubing: Platinum-cured LSR tubing (Shore 30A–50A) for peristaltic pumps, IV sets, and drainage systems. Transparent grades allow flow visualization. Compatible with autoclave, EtO, gamma, and e-beam sterilization.

Baby nipples and pacifiers: Transparent LSR Shore 30A–40A with FDA 21 CFR and LFGB certification. BPA-free, phthalate-free, latex-free. Withstands repeated steam sterilization (121 °C autoclave, dishwasher up to 80 °C).

Implant-adjacent components: USP Class VI-certified LSR grades for catheter tips, cochlear implant components, and drug delivery system closures. For true implant applications, ISO 10993 testing is additionally required.

Wearable device seals: Hypoallergenic LSR skin-contact surfaces for smartwatches, continuous glucose monitors (CGM), and fitness trackers. RoHS and REACH compliant.

LSR Hardness, Viscosity, and Grade Selection

LSR viscosity before cure ranges from 20,000 mPa·s (flowable, suitable for micro-injection) to 300,000 mPa·s (high-viscosity for compression overmolding). Shore hardness after cure spans Shore 10A (gel-like, cushioning) to Shore 70A (firm, structural). The grade selection depends on the required durometer, tear strength, transparency, and certification tier.

How to Specify LSR in an RFQ

Key specification parameters: Shore hardness ±3, tensile strength (MPa), elongation at break (%), tear strength (kN/m), transparency or color, certification requirements (FDA/USP/LFGB/RoHS), and processing method (LIM, compression, overmolding). Request test reports, Declaration of Conformity, and a 200 g sample.

Contact us to verify certification documents and request application-matched LSR samples. Inquiries are routed to specialist suppliers in the silicon materials network.