Cary, North Carolina – 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% relative humidity for 14 days, according to Lord.
"The bond strength is greater than the silicone being molded and leaves 100% rubber on the substrate after peel tests," said Eric Dean, Lord's manager of global business development and marketing strategy.
Areas of focus
Lord is looking at personal electronic devices and automotive as the two main places where it believes it can gain traction with the IMB for LSRs, Zambanini said. For the electronic devices, there already is a lot of demand coming from such applications as smart phones, smart watches, fitness bands and even the plugs used to charge the devices.
"I have a colleague whose only job is to address the OEM designers," he said. "He goes back and forth to China to work with our manufacturing houses. The reason is they are already using thermoplastic to metal combinations and they just don't know how to provide a robust assembly or a robust seal."
Some of the LSRs typically are self-bonding, and Zambanini said those usually have poor adhesion. Lord always has prided itself on producing a 100% rubber tear with its Chemlok adhesives, where the substrate fails before the adhesive, and he doesn't think it's an unreasonable request when customers expect the same with LSR.
"But liquid silicone rubber is tricky," he said. "It's a different monster than natural rubber. So we have active programs right now for IMB and other technologies to improve the bonding of LSR to metal, and we've had a lot of success there in the personal electronic device space."
The second area of focus is in automotive, an area where Lord has a significant presence. The firm has a strong network of early adopters to test new technology, Zambanini said. Looking at something like a gasket seal, some customer might be using a fluoroelastomer, saying they'd like to use an LSR but can't get it to bond.
"People should be able to use the material combinations they want to use," he said. "It's our job as a company to find the adhesive that allows them to make those things."
Lord has aimed its automotive effort with IMB on connectors and flow control devices, applications where air or fluid passes through. "If you had it overmolded, you have a leak path," Zambanini said. "Providing that covalent bond eliminates that leak path. We've seen some early success there."
Rick Ziebell, vice president of technology at R.D. Abbott Co. Inc., one of Lord's original distributors, said the IMB adhesives for LSRs meet all current automotive specifications for fuel and oil sealing. R.D. Abbott also distributes silicones for Dow Performance Silicones, one of the leading producers of LSR materials.
"Other fluoro adhesive systems generally fall apart either in heat, fuel or steam," Ziebell said. "This particular system is good for all three, and all three are typically needed in automotive applications.
Working with both Lord and Dow has allowed R.D. Abbott to take the "synergies of our suppliers to build technical platforms that are useful for our customers," he said. "This is taking the best of Lord and Dow Performance Silicones and applying it in a way that's unusual, or unique, and we're showing valuable applications for automotive sealing."
On the front lines
Christopher Schneider is Lord's manager of application engineering and technical services for elastomers, adhesives and coatings. He is part of the product development group in Erie, Pa., that makes sure the firm's offerings are application friendly and work properly.
"We want to make sure our adhesives work in customer-oriented parts and applications, and not strictly R&D type testing. If they don't work for our customers, they won't work for our sales."
For the new IMB lines for LSR, the group has been working with customers from the OEM to Tier 1 level in automotive, medical and personal device markets.
"This is something we've had a lot of pull from the customers," Schneider said. "We can bond to steel, we can bond to polycarbonate. We can bond to a number of different substrates with the LSRs."
Most of his team's work is in the trenches with customers. "If we see a problem with performance, we're right there with the product developers," he said. "We then go back to the chemistry and the chemical labs to re-design and get that fixed."
With bonding the LSR and thermoplastics to metal, it's not something that's been done before, so Lord has to work to get the word out so the "designers can start looking at these and designing parts that have typically not been done before," he said. "These are for applications that have not even been thought of. You go to the university level and they didn't even realize these adhesives existed."
Zambanini said being able to bond polymers to substrates opens up new worlds of possibilities, and there's a good bit of education that is needed with regards to the capabilities. And he cautions that the technology isn't meant for every application.
For example, a kids' play set doesn't need IMB, but connectors for a self-parking car likely would be a good candidate.
"So part of it's application dependent and part of it is OEM dependent," he said. "Have they solved it a different way? And part of it is it's brand new, and anything brand new that has a functionality people haven't considered before is going to take time to evaluate and adopt."
In the time that Lord put out the first IMB formulations to bond LSR and thermoplastics to various substrates, they've looked at a number of areas. Some have panned out, while others haven't.
Zambanini said they looked at consumer durables early on, but with a few exceptions found that nobody cared. It was all about the cost. In that and some other areas, there was a sense of interest, but Lord found the firm wasn't solving a problem.
"The markets where Lord really excels is where somebody says, 'I want to do that,' " he said. "And whatever comes after that is something they typically can't do."
With automotive and personal electronics, they found two markets where the firm could make a difference. For instance, he said cell phones are to younger people today what cars were to the 20-year-olds in the 1950s.