Engineers sometimes ask us whether they can use an adhesive as a potting compound, or whether a potting material could double as an adhesive. The answer lies in the chemistry and in the way these materials are tested and profiled. The question typically revolves around epoxy and polyurethane products.
Head of Learning and Development Kevin gives us some things to think about.
Intent and data
Adhesives are designed for bonding. Their properties are optimised and validated to deliver strong adhesion between substrates. Potting compounds and encapsulants are formulated to encapsulate and protect. They are tested for properties that matter in bulk applications such as thermal management, electrical insulation, and environmental resistance. The TDS or PDS (technical or product data sheet) reflects this. Adhesives are rarely tested for electrical properties such as volume resistivity, dielectric strength, or permittivity. Potting materials often are, as these properties and the material insulating performance can be significant to reliability and safety.
The TDS should provide the information you need to decide whether a material is worth testing. When the datasheet includes the properties most relevant to your application, you can make that decision quickly and confidently. Having pertinent data available reduces your risk of choosing the wrong material and avoids wasted time in evaluation.
Viscosity
It is important for potting compounds to have a low viscosity so they can flow easily into and around components, filling voids and ensuring complete encapsulation without trapping air. It is important for adhesives to have a higher viscosity, so they stay in place after application, preventing flow or sagging and maintaining bond line thickness for reliable adhesion.
Exotherm
When a two-part resin cures, it gives off heat. Watch our JoinedUpMinute video which explains this. In principle, a larger mass (or volume) generates more exothermic heat, and this heat can be damaging to components and substrates. Also in principle, potting is a higher volume application than bonding. So potting compounds are formulated to cure more slowly and predictably in larger volumes, keeping the exotherm at manageable levels for encapsulation applications. In bonding applications, this is less likely but possible to be problematic due to the lower mass involved, even though adhesives that cure quickly at room temperature often generate high exothermic temperatures.
Flame retardancy, thermal conductivity and other properties
Potting compounds easier to make flame retardant or thermally conductive, since the appropriate fillers can usually be added without compromising their primary, protective function.
IRS 3078 Polyurethane Potting Compound can also be used as a low viscosity adhesive – an exception!
Our key takeaway: adhesives and potting compounds share chemistry, but they are not interchangeable. If you are considering one in place of the other, match the material to the application requirements, and validate it in real-world conditions.
