Liquid Silicone Overmolding on Glass Lids
Our expertise in integrating liquid silicone rubber (LSR) with substrates such as metal, plastic, and glass enables us to deliver components that combine the rigidity of structural materials with the flexibility, safety, and sealing properties of silicone.
This case study analyzes our liquid silicone overmolding process on glass lids—a critical component in food storage containers, premium cookware, and baby feeding systems. By chemically bonding LSR to glass, we create products that are hermetically sealed, thermally stable, and safe for food contact.
The Challenge: Bonding Silicone to Glass
Glass is a challenging substrate for overmolding due to its:
- Low surface energy: Silicone does not naturally adhere to smooth glass surfaces.
- Thermal sensitivity: Glass can fracture under rapid temperature changes during molding.
- Dimensional precision: Glass components have inherent tolerances that must be accommodated without cracking.
Our proprietary process overcomes these challenges through a combination of surface activation, precision tooling, and controlled molding parameters.
Liquid Silicone Rubber (LSR) Overmolding
This is the core of Kingod’s manufacturing capability. We utilize fully automated vertical injection molding machines equipped with precision tooling designed specifically for glass insert molding.
Mold Design
Our tooling incorporates:
- Cavity inserts that precisely cradle the glass lid, compensating for minor dimensional variations.
- Pinch-off edges that create clean, flash-free silicone sealing lips.
- Temperature-controlled zones to maintain uniform heating of the glass before injection, preventing thermal shock.
Injection Parameters
LSR Material: Platinum-cured, food-grade LSR (FDA, LFGB, and EU 10/2011 compliant).
Injection Temperature: 150°C–190°C—sufficient to cure the silicone while remaining below the thermal stress threshold of the glass.
Clamping Force: Precisely controlled to secure the glass without inducing fracture.
During injection, the heat activates the silane primer, forming a covalent chemical bond between the silicone and glass. Unlike mechanically attached gaskets or slip-on seals, this bond is permanent—the silicone will not rotate, loosen, or trap moisture underneath.