There are many differences between LSR and traditional thermoplastic material processing, which increases the difficulty of processing. LSR has significant differences from traditional thermoplastic material processing in terms of shrinkage rate, demolding, mold materials, cold runner system, temperature control, etc., making LSR more difficult to process than ordinary thermoplastic adhesives.

The waterproof silicone ring of smartphones is mostly formed by secondary molding on existing metal or plastic accessories, and its volume is smaller than that of commonly used silicone rings, requiring higher compatibility with the casing and accessories, and requiring more precise (micro) injection molding technology.

The key points for LSR to achieve precision injection molding are as follows:
(1) Adequate mixing of liquid silicone gel
Accurate mixing ratio: LSR is a two-component raw material consisting of A and B. Before injection molding, it must be thoroughly mixed in a precise 1:1 ratio. If it is a colored liquid silicone product, the color paste ratio must also be accurately controlled.
Mixer: The static mixer is a key component in injection molding. Only after the static mixer is fully and uniformly mixed, can the liquid silicone gel injected into the mold be fully vulcanized and molded.

(2) Sealing and temperature control of injection molding machine components
Due to the low viscosity of LSR, material reflux and leakage must be considered, and the screw must be sealed;
Due to the heating of the mold during the LSR molding process, a water-cooled nozzle structure can be used to prevent solidification of the LSR and ensure a sufficiently low temperature.

(3) Finished product control during injection molding process
Splitting line: Pre considering the position and accuracy of the splitting line can help avoid air entrainment and welding, and prevent burrs
Shrinkage: Although LSR does not shrink during injection molding, due to its extremely high coefficient of thermal expansion, it typically shrinks by 2% to 3% after demolding and cooling;
The position of the injection port: actual product shrinkage rate needs to be considered;
Vacuuming: When designing the parting line, ensure that the mold is sealed, and the vacuum pump will evacuate all cavities through the fixture under the mold switch;
Demoulding: Generally, the demoulding techniques of distillation column tray, push top pin, and air push top are used, or manual demoulding is employed.
Mold temperature: LSR is formed by vulcanization during heating, and the temperature distribution inside the mold must be controlled uniformly. The temperature difference is controlled within+/-10 ℃.

Regarding liquid silicone rubber, please refer to our website for details: IOTA Liquid Silicone Rubber