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Liquid Silicone Rubber (LSR) Molding Materials
Liquid Silicone Rubber (LSR) is a high-purity, platinum-cured thermoset elastomer known for its exceptional biocompatibility, thermal stability, and transparency. Unlike thermoplastic elastomers (TPE) that melt, LSR cures into a permanent shape via heat, offering superior compression set and chemical resistance. At JUCHENG, we utilize specialized Liquid Injection Molding (LIM) technology to process this advanced material. From Class 100,000 clean-room molding for medical devices to high-precision optical silicone for automotive lighting, our facility delivers flash-free, fully cured silicone parts that meet the highest industry standards.
Liquid Silicone Rubber (LSR) Molding Materials

Liquid Silicone Rubber (LSR) Molding Materials

Processing liquid silicone requires fundamentally different equipment than standard plastics. JUCHENG delivers:
  • Specialized LIM Units: We use dedicated injection machines with metered pumping systems to mix Part A and Part B silicone components precisely before injection.
  • Cold Deck / Cold Runner Technology: LSR cures with heat. We use cold runner systems to keep the material liquid until it enters the heated mold cavity, virtually eliminating material waste.
  • Flash-Free Tooling: LSR has extremely low viscosity (flows like water). Our molds are manufactured to micron-level tolerances to prevent "flash" (leakage) at the parting lines.
  • LSR Overmolding: We specialize in bonding LSR onto high-temperature thermoplastics (like PA, PBT) or metals to create integrated multi-material components.
Rubber (LSR) medical respiratory mask

Detailed Material Profiles

We offer a range of specialized LSR grades for specific performance needs:
1、General Purpose LSR
  • Description: The standard for durable, flexible parts. Available in a wide range of hardness (Durometer).
  • Key Characteristics: Excellent heat resistance (up to 200°C), good compression set (bounces back), water repellent.
  • Ideal Applications: Keypads, gaskets, O-rings, consumer electronic buttons, kitchenware.
2、Medical / Healthcare Grade LSR
  • Description: High-purity formulations designed for body contact.
  • Key Characteristics: Biocompatible (USP Class VI, ISO 10993 compliant), hypoallergenic, resistant to bacteria, sterilizable (Autoclave/Gamma).
  • Ideal Applications: Respiratory masks, catheter valves, syringe stoppers, implantable device components, menstrual cups.
3. Optical Grade LSR
  • Description: Highly transparent silicone that rivals glass and PMMA.
  • Key Characteristics: Non-yellowing UV stability, high light transmission (>94%), optically clear even in thick sections, flexible (won't shatter).
  • Ideal Applications: Automotive LED matrix lenses, street lighting optics, high-power light guides, magnifying lenses.
4. Self-Lubricating LSR
  • Description: LSR containing incompatible fluids (like phenyl oil) that bloom to the surface after curing.
  • Key Characteristics: Reduces coefficient of friction, prevents parts from sticking together (slit valves), aids assembly.
  • Ideal Applications: Wire harness seals (plug seals), connector membranes, dynamic valves.

Comparison: LSR vs. TPE (Why choose LSR?)

Many clients confuse LSR with TPE. Here is why LSR is superior for high-end applications:
Feature Liquid Silicone Rubber (LSR) Thermoplastic Elastomer (TPE)
Chemistry Thermoset (Cured by heat, permanent) Thermoplastic (Melted by heat, re-moldable)
Heat Resistance Excellent (Up to 200°C - 250°C) Moderate (Melts/Softens > 80°C - 100°C)
Compression Set Superior (Best for long-term sealing) Good (May deform under constant load over time)
Biocompatibility Best (Standard for implants/skin contact) Good (Medical grades available)
Chemical Resistance High Moderate
Cycle Time Longer (Curing time required) Faster (Cooling only)
Cost Higher (Material & Tooling) Lower

Design Guidelines for LSR

  • Venting: Air traps can cause "diesel effect" (burning). Molds must be vented meticulously (vent depth < 0.005mm).
  • Shrinkage: LSR has high shrinkage (2% - 3%). Tooling must be scaled accordingly.
  • Undercuts: Due to high elasticity, LSR parts can often be manually pulled out of molds with severe undercuts, simplifying tool design compared to plastics.
  • Surface Finish: High-polish finishes are recommended for optical parts; textured finishes are good for preventing surface tackiness.

Application Scenarios

  • Medical: CPR masks, anesthesia bellows, dialysis pump tubing, baby bottle nipples.
  • Automotive: Connector seals (wire seals), rain sensors, optical lenses for adaptive headlights.
  • Consumer Electronics: Waterproof seals for smartphones (IP67/IP68 rated), earbuds tips (soft touch).
  • Industrial: Vibration dampeners, high-temperature gaskets.

Physical Properties Table

Typical values for Standard LSR:
Property LSR (30 Shore A) LSR (50 Shore A) LSR (70 Shore A) Unit
Hardness 30 50 70 Shore A
Tensile Strength 8 - 10 9 - 11 8 - 10 MPa
Elongation at Break 500 - 600 400 - 500 300 - 400 %
Tear Strength 20 - 30 30 - 40 25 - 35 kN/m
Compression Set < 15 < 15 < 20 % (22h @ 175°C)
Service Temp -50 to +200 -50 to +200 -50 to +200 °C
 
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