by Eric Dean, Manager, Global Business Development and Marketing Strategy at LORD Corporation
Liquid silicone rubber (LSR) is used for a wide range of parts for many different markets. Some notable segments include medical devices, cookware, electronics, automotive components and personal electronic devices.
Silicone polymers exhibit numerous unique properties that other materials are not able to achieve, combining rubbery flexibility with excellent thermal stability, durability, low-surface energy, biocompatibility, and a soft feel. As the market need for LSR expands, product designs are becoming more sophisticated and require bonding of silicone to other substrates.
Primers for bonding silicones do exist on the market today. The majority are based on alkoxy silanes that contain functional groups which are appropriate for the curing mechanism used in the silicone. These options need to be applied very thin to surfaces that are exceptionally clean with pre-treatments such as corona or plasma.
Expensive self-bonding liquid silicone rubber often requires a similarly complicated process of pre-treatments, tightly controlled environments, curing kinetics and post-cure procedures. Self-bonding silicones don’t perform well when the thickness of LSR varies throughout the part design. Self-bonding silicones also struggle with many substrates.
The limitations with silane primers and self-bonding silicones have created a market need for silicone adhesives that are easier to use and more effective on various substrates.
LORD Corporation recently introduced two new in-mold bonding (IMB) adhesives for bonding platinum-cured silicones to multiple substrates including plastics. These LORD IMB adhesives enable assemblies between LSR and plastic or metal substrate to be made during the molding process.
Unlike silane primers, IMB adhesives are not sensitive to moisture or atmosphere. LORD IMB Adhesives can be applied to a substrate and then stored on a shelf for weeks before molding. IMB adhesives insensitivity to moisture also eliminate the need for precise molding facility environments.These new adhesive solutions effectively bond LSR to various substrates directly in an injection- or compression-molding process. These new adhesives are simple and effective on a huge variety of substrates like aluminum, glass, stainless steel, and even a variety of plastics. They don’t even require surface pre-treatments, maybe just a simple wipe with IPA.
Primers on the market today typically must be applied as a very thin coating, sometimes less than one micron. This is difficult to control and nearly impossible measure in a manufacturing/production environment. LORD IMB adhesives provide robust bonding when applied at a range of thicknesses that you can measure with standard tools.
Applications for these IMB adhesives include consumer electronics, automotive components and medical devices. Compatible substrates for IMB adhesives include aluminum, anodized aluminum, glass, steel/stainless steel, polycarbonate, select polyamides, and select thermoplastic elastomers.
Learn more about IMB adhesives in this video.