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Reactive, neutral cure RTV polysiloxane compositions consists of a base, curative and catalyst, which are combined to yield a mixture that cures to form solid rubber.  To yield a foamed rubber composition on cure, blowing agents or pore-formers are added to the reactive mixture.  Injection molding is ideal for consistent, affordable production of a wide range of high-quality complex parts that can withstand any environment in a variety of industries, especially in the medical and electronics industries.  The properties of silicone, especially liquid silicone rubber, provide a key advantage in injection moldings.  Its shear-thinning property helps silicone to improve its flow into the thin walls of the mold, making it ideal material when the mold has small and intricate details.  However, for closed cavity injection molding operations, blowing agents and sacrificial pore formers are not typically suitable as additives to yield low density foamed rubber composition on cure.  Instead non-reactive pore formers such as microballoons/microspheres are more promising as they can be uniformly distributed and do not adversely react to other components in the composition.


LLNL researchers have developed a custom formulated extreme low viscosity reactive silicone resin base modified with a temperature dependent thixotrope along with a modified catalyst package.  The uncatalyzed composition is capable of accepting loadings of polymer microspheres sufficient to produce a cured bulk rubber that has a density as low as 0.3 g/cc, thus compatible with high-resolution injection molding processes.  Depending on the application, the catalyst package can be optimized for a given work, gel and cure time.  The final composition is highly processable post catalysis, allowing for complex features to be properly filled with minimal void entrapment and high fidelity.

  • Improved performance of low-density silicone for injection molding
  • Complex geometries can be created
Potential Applications
  • Electronics capsulation
  • Gap-filling, potting of components
  • Thermal insulation
Development Status

Current stage of technology development:  TRL 4

LLNL has filed for patent protection on this invention.

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