Cary, N.C. — Lord Corp. has been bonding rubber to metal and other substrates for more than six decades.
But bonding liquid silicone rubber and thermoplastics to other substrates wasn't quite so simple. To mate thermoplastics to other substrates, traditionally it had to be accomplished using a fastener or structural adhesive. Or you put a hole through the material and overmolded it.
These systems come with inherent shortcomings, according to Ross Zambanini, Lord's senior strategy and business development manager. There either isn't a robust covalent bond, or there are stress points at the hole with mechanical fasteners or overmolding. In addition, there are potential leak points across the whole assembly.
Lord, though, developed its In-Mold Bonding adhesive technology that allows plastic and silicone components to be assembled more like the firm's Chemlok adhesive, rather than the older methods. The firm said its IMB adhesives are non-tacky, polymer-based materials that, when applied to a rigid substrate, provide a structural bond to a thermoplastic or silicone that is formed under heat and pressure. This allows assemblies between plastics, silicones and metals to be made during the molding process.
The impetus behind IMB, Zambanini said, was that customers wanted to use those material combinations, whether it was for mounts, weatherstripping or personal electronic interfaces. "Having a more predictable manufacturing method that costs less and provides that sort of robustness that we do for Chemlok for a new material combination is something we're really excited about," he said.
One of the issues for LSR is the short cure time. Lord has bonded heat-cured silicone with Chemlok for decades, but those have a lot longer cure time, Zambanini said. But LSRs cure in a matter of seconds in the mold, so the challenge is having an adhesive that matches those cure kinetics.
To facilitate further development of LSR in IMB, the Cary-based firm recently launched two new adhesives systems—Lord IMB 3020 and IMB 3030—for bonding addition-cured silicone rubber to a variety of metal and compatible plastic substrates.
Both two-component adhesives allow for easy application, don't require extreme temperatures for curing, and generate bonds that withstand 85°C at 85 percent relative humidity for 14 days, according to Lord.
"The bond strength is greater than the silicone being molded and leaves 100 percent rubber on the substrate after peel tests," said Eric Dean, Lord's manager of global business development and marketing strategy.