Basic Properties of LSR Liquid Silicone Rubber
LSR (Liquid Silicone Rubber) is a two-component addition-curing thermosetting material with the following characteristics:
Low Viscosity: Before vulcanization, it exists in a low-viscosity liquid state (10-50 Pa·s), facilitating injection molding.
Rapid Curing: Elastomers are formed through the addition reaction of silicon-hydrogen bonds and vinyl groups catalyzed by a platinum catalyst.
Shear Thinning: Viscosity decreases under shear force, which is beneficial for filling complex molds.
High Transparency: High product transparency allows observation of the casting material within the mold.
Low Shrinkage: Linear shrinkage ≤0.1%, ensuring precise dimensional reproduction.
Excellent Properties: Including tear strength, resilience, resistance to yellowing, and thermal stability.

Definition of Thixotropy and Flowability
Thixotropy refers to the property of a material where viscosity decreases under shear force and recovers after shearing ceases. The thixotropic properties of LSR are primarily adjusted by adding fillers such as fumed silica. These fillers interact with liquid silicone rubber molecules to form a network structure, thereby increasing the system viscosity.

Flowability refers to the material's ability to fill a mold under pressure. LSR has excellent flowability (viscosity 10-50 Pa·s), making it easy to fill complex molds; however, excessive flow can lead to flash or dimensional deviations.

Analysis of Influencing Factors
Thixotropic Properties
* Filler Type and Ratio: The amount of fumed silica added directly affects the thixotropic index (TI), typically controlled between 2.5 and 3.5.
* Temperature: Increased temperature reduces the thixotropic effect.
* Vulcanization Process: Platinum vulcanization systems exhibit more stable thixotropy than traditional peroxide systems.
* Molecular Structure: The vinyl content in the base adhesive affects the crosslinking density, thus influencing thixotropic behavior.

Flowability Influencing Factors
* Viscosity: Base viscosity directly affects flowability.
* Mold Temperature: Too low a temperature reduces flowability.
* Injection Parameters: Speed, pressure, and temperature need to be optimized and balanced.
* Mold Design: Runner layout and venting structure affect flow resistance.
* Raw Material State: Refrigerated adhesives need to be warmed to room temperature before use.