Silicones Enhance Mold Design, Improve Performance

Silicones have been developed that provide primer-less adhesion to a variety of thermoplastic resins and are optimal for multi-component silicone-to-plastic molding as they adhere to the thermoplastic substrate (plastic inserts), but not to the metal surface of the mold. For the mold manufacturer, this means no mold release coating or re-coating is required—saving time and money.

Shin-Etsu Silicones of America, Inc.’s KE2090 and KE2095 series Select-Hesive™ LIMS (Liquid Injection Molding System) are engineered for both silicone and plastic molders using either insert over-molding or co-injection (two-shot) molding. The short curing time yields a chemical bond which produces a firmly integrated composite part (rigid and elastomeric). Whereas no primer or pre-treatment of the substrate is required, adhesion tests proved that the silicone tore before the adhesive bond broke; resulting in 100 percent cohesive failure.

“These silicones provide mold designers and molders the means to manufacture a bi-material component in a fully automated manner by eliminating the need for hazardous priming, inconvenient pre-treatments and costly secondary assembly operations,” notes Shin-Etsu Silicones Marketing Manager Eric Bishop. “This technology enhances product design, improves performance and increases productivity.”

Bishop notes that cost efficiencies yielded from eliminating the intermediate operations are enhanced by the new LIMS outstanding bond strength performance under extreme conditions of high temperature (120°C), high humidity (85°C/85% RH) and thermal cycling (-40°C to 120°C). “While both products deliver the best of these properties, each has optimal adhesion applications: KE2090 series for adhesion to PC, PBT and PPO compounds, while the KE2095 series functions with PA (6,6 nylon and 6-nylon) and PPA resins,” Bishop states. “Both LIMS series products were tested by an independent laboratory and are found to comply with USP Class VI regulatory standards for biocompatibility.”

The new Select-Hesive™ LIMS product line offers hardness ranges from 30 to 70, Shore-A. Applications include automotive, consumer goods, healthcare and electronics.