Liquid Silicone Rubber

Liquid Silicone Rubber (LSR) is a high-purity platinum-cured silicone, for when it comes to precision and effectiveness.

What is a Liquid Silicone Rubber?

A Liquid silicone rubber is a high-purity, two-component platinum-cured silicone, ideally formulated for the production of technical parts, where strength, resistance and high quality are a must. LSRs are viscous, but pumpable materials, mostly processed through liquid injection molding (LIM).

Chemical structure

Liquid Silicone Rubber (LSR) is a two-component system, where long polysiloxane chains are reinforced with specially treated silica. Component A contains a platinum catalyst and Component B contains methylhydrogensiloxane as a cross-linker and an alcohol inhibitor. The primary differentiator between liquid silicone rubber (LSR) and high consistency rubber (HCR) is the “flowable” or “liquid” nature of LSR materials. While HCR can use either a peroxide or a platinum curing process, LSR uses only additive curing with platinum. Due to the thermosetting nature of the material, liquid silicone rubber injection molding requires special treatment, such as intensive distributive mixing, while maintaining the material at a low temperature before it is pushed into the heated cavity and vulcanized.

Liquid silicone rubber properties

Depending on the application or its industrial use, LSR offers several advantages. First, it is highly biocompatible, which means it can be used for parts that come into contact with humans, for such applications as organ parts or prostheses. Second, it is very durable and therefore ensures long-term stability and chemical resistance. Third, it is also compatible with a wide spectrum of temperatures, from -60°C to +250°C, maintaining its high-performance mechanical properties at all times. Fourth, its electrical properties makes it ideal for insulation and precise conductivity protection. Finally, it is transparent and can be pigmented to harmonize with all color needs, including human skin tones.

LSR are also considered as the material of choice for industries such as Automotive or Medical devices for which small and complex elastomeric parts needs to be produced at high speed and optimum productivity. In such cases, Liquid Injection Molding of LSRs becomes one of the most efficient process to fabricators.

Revision sheet

Technology ​LSR
Definition ​LSR (liquid silicone rubber) refers to a two-component compound which can be cured with Pt-catalyzed hydrosilylation reaction. Formulation: Base: silicone oil + filler + plasticizer; Component 1: base + catalyst; Component 2: base + crosslinker + inhibitor
General Information ​- Innocuous and biocompatible
- Good processability
- Service temperature ranges from -60°C to 250°C
- Good electrical properties
​Typical properties  ​- Hardness 5~70 ShA
- Mechanical strength 7~12 MPa
- Elongation 200~800%
- Tear strength 15~50 N/mm
Curing Mechanism (Polyaddition)RTV2 LSR curing mechanism.png
Processability ​Liquid Injection Molding system including a pump which mixes A and B parts and injects the LSR into a multicavity heated mold to make the final part.
​Application/final products Medical, Industrial or Automotive parts

 

Why use Liquid silicone rubber?

Liquid Silicone Rubber (LSR) are used in industries requiring precise results, lets see how LSR is used by automotive manufacturers. Thanks to LSR high tear strength, low compression set, good thermal resistance and continue stable self-oil bleeding, automotive harness connector has been using oil bleeding Liquid silicone rubber instead of other rubber (such as NBR and EPDM) for harness sealing. LSR formulation dosing system produce the precise material features that allows control on the cure kinetics, leading to improved productivity and flexibility to achieve precise results, from low temperature curing for over-molding applications to improved cycle times for serial production.
LSR is also perfectly adapted to new digital, intelligent and networked industrial processes for making products such as lighting primary and secondary optical systems and its innocuous and biocompatible features make it suitable for healthcare including Long Term Implantable applications.

Related applications

Unlike many thermoplastic elastomers such as TPEs and TPRs, LSR has performance characteristics and fast cure cycles, which makes it a perfectly adapted material for small molded components. The material maintains its flexibility and elasticity from extremely low temperatures down to -60°C and retains these features up to 250°C. LSR is often used in applications for products that require a high level of precision. Here are some notable examples:

  • Seals
  • Gaskets
  • Cushioning pads in mobile communication devices
  • Data acquisition instruments
  • Electronic devices used in rugged environments
  • Infant products (such as baby bottle nipples)
  • Kitchen utensils (spatulas)
  • Electrical connectors
  • Automotive parts
  • Self-bonding or self-bleeding parts
  • Medical applications, including catheters and hoses.

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