In the realm of modern high-end manufacturing, from baby bottle nipples to heart valve replacements, and from waterproof seals for smartphones to lenses for autonomous vehicle LiDAR systems, an increasing number of complex silicone products are being mass-produced through a highly efficient, clean, and automated process known as Liquid Silicone Rubber Injection Molding (LSR Molding). This technology not only breaks free from the mold and labor dependencies associated with traditional millable silicone rubber but also pushes the boundaries of silicone application towards miniaturization, high precision, and medical-grade cleanliness—a true "flexible revolution" in elastomer processing.

The Fundamental Difference Between LSR and Millable Silicone Rubber

Liquid Silicone Rubber (LSR) fundamentally differs from millable silicone rubber (HCR) due to its extremely low initial viscosity. LSR consists of two components: Component A includes vinyl-containing polysiloxane and reinforcing fillers, while Component B contains hydrogen-containing siloxane crosslinkers and platinum catalysts. At room temperature, both components are milky white liquids with viscosities ranging from about 1,000 to 100,000 mPa·s, allowing them to be precisely metered, mixed, and injected into molds much like thermoplastics via injection molding machines.

Core Advantage One: High Precision and Complex Structures in One Shot

During injection, LSR can perfectly fill intricate details down to micrometer scales, such as walls as thin as 0.1 mm, deep cavities, thin ribs, micro-holes, or even composite structures embedded with metal or plastic frames. Post-curing shrinkage is minimal (<0.3%), ensuring excellent dimensional stability with tolerances reaching ±0.025 mm. This makes it the material of choice for producing medical connectors, miniature sensor seals, optical lenses, and more. For example, subcutaneous sensing pads used in continuous glucose monitors require one-shot formation of internal microfluidic channels and biocompatible surfaces, a task uniquely suited to LSR processes.

Core Advantage Two: Additive Curing Without Byproducts Ensures Biocompatibility

LSR employs a platinum-catalyzed addition reaction curing mechanism where vinyl groups directly crosslink with Si-H bonds to form stable C-Si bonds without releasing any small molecule byproducts. In contrast, peroxide-cured HCR produces volatile organic compounds that need secondary baking to remove. LSR parts are ready for use upon demolding, requiring no post-processing, thus naturally meeting stringent biocompatibility standards like ISO 10993 and USP Class VI. This makes LSR widely applicable in long-term implant devices such as brain shunts and artificial sphincters.

Core Advantage Three: Full Automation and High Efficiency

LSR injection systems typically integrate dual-barrel metering pumps, static mixers, cold runner molds, and automatic demolding robots, enabling "unmanned" continuous production from raw materials to finished products. An eight-cavity mold can produce a batch every 30 to 60 seconds, achieving daily outputs of tens of thousands of pieces. Moreover, cold runner designs allow uncured LSR to be recycled, keeping material waste below 1%, far superior to hot runner thermoplastic processes.

Key Process Considerations: Poison Prevention and Temperature Control

Platinum catalysts are easily deactivated ("poisoned") by substances containing elements like nitrogen, phosphorus, sulfur, or tin. Therefore, LSR production environments must strictly isolate common rubbers, epoxy resins, certain release agents, and even human sweat. Mold steels should be selected from highly polished stainless steel grades (such as S136) to prevent catalytic impurities from leaching out. Additionally, mold temperatures are usually controlled between 120°C and 180°C to ensure rapid and uniform curing without localized overheating leading to scorching.

Expanding Application Scenarios

Consumer Electronics: Waterproof seals for TWS earbuds, straps for smartwatches.

New Energy Vehicles: Thermal interface materials for battery packs, insulating sleeves for electrical connectors.

Optical Devices: Lenses for LEDs, flexible waveguides for AR/VR devices.

Microfluidic Chips: 3D microchannels for lab-on-a-chip applications.

Of course, LSR processes face challenges such as high equipment investment, expensive mold costs, and extreme requirements for raw material purity. However, as technologies like multi-component co-injection, insert molding, and in-mold labeling mature, their overall benefits become increasingly apparent.

Conclusion

Liquid silicone rubber injection molding represents not just an upgrade in manufacturing methods but also a liberation in product design philosophy. It endows soft silicones with the precision of metals, the efficiency of plastics, and the purity required for life-related applications—bridging the gap between the microscopic and macroscopic worlds, paving the way toward a future of flexible intelligent products.



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