How Is LSR (Liquid Silicone Rubber) Processed/Produced?

LSR is a high-performance elastomer known for its flexibility

Liquid silicone rubber (LSR) is a high-performance elastomer known for its flexibility, thermal stability, chemical resistance, and biocompatibility. It is widely used in medical devices, automotive components, electronics, baby care products, and kitchenware. Unlike traditional solid silicone rubber, LSR is a two-part liquid system that is processed through specialized injection molding equipment. Understanding how LSR is produced helps manufacturers and product developers appreciate its unique advantages and production requirements.

1. Raw Material Preparation

LSR production begins with two liquid components, commonly referred to as Part A and Part B. Part A typically contains the base silicone polymer, fillers, and other additives. Part B contains the platinum catalyst and crosslinking agents. When the two parts are mixed, a platinum-catalyzed addition reaction begins, which eventually cures the silicone into a solid elastic material.

The two components must be stored separately and kept cool to prevent premature curing. Before production, they are precisely metered and mixed in a specific ratio, usually 1:1 or 10:1, depending on the formulation. Accurate mixing is critical because an incorrect ratio can lead to incomplete curing, poor mechanical properties, or surface defects.

2. Metering and Mixing

In a typical LSR injection molding system, Part A and Part B are fed from separate containers into a metering unit. This unit uses precise pumps to deliver the correct amount of each component. The two streams are then combined in a static mixer or a dynamic mixing head.

After mixing, the liquid silicone is ready for injection. The mixed material has a low viscosity, which allows it to flow into very fine mold details. However, this low viscosity also means the material can leak easily, so the entire system must be well sealed and carefully controlled.

3. Injection Molding

The mixed LSR is injected into a heated mold cavity. Unlike thermoplastic injection molding, where the material is melted and then cooled to solidify, LSR cures through a chemical reaction triggered by heat. The mold is typically heated to around 150°C to 200°C, depending on the formulation and part geometry.

When the liquid silicone enters the hot mold, the platinum catalyst initiates crosslinking. The material transforms from a liquid into a solid rubber within seconds to minutes. This curing process gives LSR its elastic properties and dimensional stability.

4. Mold Design and Temperature Control

Mold design is a critical part of LSR processing. Because LSR is highly fluid, the mold must be precisely machined and well sealed to prevent flash. The mold also needs uniform heating to ensure consistent curing throughout the part. Temperature variations can cause incomplete curing, warping, or dimensional inconsistencies.

Cold runner systems are often used in LSR molding. In a cold runner system, the mixed silicone remains cool in the runner until it enters the heated mold cavity. This helps reduce material waste and prevents premature curing in the feed system.

5. Curing

Curing is the chemical process that turns liquid silicone into solid rubber. It occurs when the mixed LSR is exposed to heat in the mold. The platinum-catalyzed addition reaction forms crosslinks between polymer chains, creating a three-dimensional network.

Curing time depends on several factors, including mold temperature, part thickness, and silicone formulation. A shorter cure time improves production efficiency, but if the part is not fully cured, it may have weak mechanical properties or surface tackiness. A longer cure time ensures better properties but reduces output.

6. Demolding and Post-Processing

After curing, the LSR part is removed from the mold. Because silicone is soft and flexible, demolding must be done carefully to avoid tearing or deformation. In high-volume production, automated demolding systems are often used.

Post-processing may include deflashing, trimming, inspection, and secondary operations such as bonding, printing, or assembly. For medical or cleanroom applications, parts may also undergo cleaning, sterilization, or packaging under controlled conditions.

7. Quality Control

Quality control is essential throughout LSR production. Manufacturers monitor mixing ratios, injection pressure, mold temperature, curing time, and part dimensions. Common defects include flash, air bubbles, incomplete curing, and dimensional deviations. Inspections may include visual checks, dimensional measurements, hardness testing, and functional testing.

For regulated industries such as medical and automotive, additional testing and documentation may be required to meet industry standards and customer specifications.

8. Advantages of LSR Processing

LSR injection molding offers several advantages. It allows for high-precision parts with complex geometries, short cycle times, and consistent quality in high-volume production. LSR parts are also durable, heat-resistant, and biocompatible, making them suitable for demanding applications.

In addition, LSR can be molded into very small or thin-walled parts, which is difficult with many other materials. Its low viscosity allows it to fill fine details and reproduce intricate mold features accurately.

Conclusion

LSR processing is a precision-driven manufacturing method that involves material preparation, metering, mixing, injection molding, curing, demolding, and quality control. Each stage requires careful control because LSR is sensitive to mixing ratios, temperature, contamination, and mold design. For OEMs and product developers, understanding the LSR production process is essential for designing successful products and choosing the right manufacturing partner. With the right equipment and experience, LSR injection molding can deliver high-quality silicone parts at scale for a wide range of industries.