Combining PC And LSR Silicone Injection Mold

Combining PC (Polycarbonate) and LSR (Liquid Silicone Rubber) in injection molding is a common technique used to create parts that require both the strength of plastic and the flexibility or sealing properties of silicone. This process is often referred to as two-component (2K) or multi-shot molding, or overmolding.

Key Considerations When Combining PC and LSR silicone Injection Mold:

1. Material Compatibility

• Bonding: PC and LSR don’t naturally bond very well. To achieve good adhesion:

  • Use adhesion-promoting primers on the PC surface.

  • Choose self-bonding grades of LSR specifically formulated to adhere to PC.

• Some surface treatments (e.g. plasma, flame, or corona) may be used on PC to enhance bonding.

2. LSR silicone Injection Mold Tooling Design

• A specialized 2K injection mold is required, capable of:

  • First injecting the PC.

  • Then transferring the part (manually or via rotating or sliding mold inserts) to the LSR cavity.

  • Injecting LSR into/onto the PC substrate.

• Temperature control is crucial: PC is processed at ~280–320°C; LSR is vulcanized at ~150–180°C. The mold must accommodate both.

3. Injection Molding Process

• PC Injection: Done first because it requires higher temperature and pressure.

• LSR Injection: Done second in a cold runner system after PC cools enough to prevent deformation.

• Curing: LSR is heat-cured (via platinum-catalyzed addition cure) during or after the injection cycle.

4. Applications

• Medical devices (e.g., seals, buttons on devices)

• Baby products (e.g., pacifiers, bottle parts)

• Automotive and electronics (e.g., waterproof buttons, gaskets)

5. Advantages

• Combines rigidity and transparency of PC with soft-touch, flexible, or sealing qualities of LSR.

• Eliminates need for adhesives or secondary assembly.

• Enables miniaturization and improved part performance.