Polymerization of an epoxy is an exothermic reaction resulting in heat release. Master Bond offers special two component epoxy systems that generate low exotherm even in thick sections. These products avoid premature cures, have lower shrinkage and create less stress than conventional high exothermic systems. This is important in potting/encapsulation and conformal coating applications. Low heat buildup prevents mechanical stresses that can damage electronic devices. Additionally, high viscosity systems are available for gap filling and bonding vertical surfaces, especially for heat sensitive substrates.
Liquid epoxy resins are converted to a solid after being mixed with a hardener/curing agent. Depending on the specific combination of epoxy, curing agent and fillers that is being used for formulating an epoxy system, the exotherm can vary significantly. Polymerization results from the build up of heat. Generally the thinner the layer being applied the less heat being generated the slower the cure. Also, fast cure epoxy systems shorten fixture times while low exotherm releasing epoxies are essential when processing a large mass of material.
Low Exothermic Epoxies for Large Volume Casting and Potting
Low exothermic epoxies with low mixed viscosity excel in moderate to large volume casting and potting applications. These systems generate low heat even in deep cross section thicknesses. These formulations are 100% solid, avoid air entrapment, can flow into tight crevices around complex shapes and contain no solvents or diluents.
Casting/potting epoxy systems are engineered to have convenient mix ratios, and are easily dispensed with automatic meter mix dispense equipment, semi-automatic or manual applications. These compounds feature superior electrical insulation characteristics, enhancing components’ reliability and longevity.
Epoxy Systems with Long Working/Pot Life and Low Exotherm
The working life (or pot life) for two part epoxy systems is the amount of time available to apply the product after both components have been mixed together. It can be anywhere from minutes to hours depending on the formulation. It is very difficult to work with a mixed system beyond its pot life, as the system gels and starts to harden at that point. The pot life depends on the amount of material mixed and the temperature of the system. It considerably decreases with an increase in temperature; therefore, open time is much shorter at higher temperatures.
In many applications, a long pot life is desired due to application requirements. Some of the applications where a long pot life is necessary include large volume potting applications and coating or bonding very large surface areas. In such cases, a long open time is preferred to make the application process easier. Another important factor to be considered is the amount of heat generated during curing reaction.
Master Bond formulates various epoxies with different chemistries that offer a long pot life (ranging from an hour to 24 hours) coupled with low exotherm properties. These products help to avoid excessive heat build up and damage to thermally sensitive components.
Other Properties of Low Exotherm Epoxies
Available in a range of viscosities, hardnesses and colors including transparency for light emission, these systems feature minimal shrinkage, dimensional stability, excellent physical strength properties. They guard against humidity/water, shock, vibration, thermal cycling, chemicals, abrasion, UV and high/low temperature exposure. Specific grades offer superb thermal conductivity for outstanding heat dissipation. Products can be customized to meet unique requirements such as stress relief for sensitive electronic components, thermal shock exposure and cryogenic serviceability.
Master Bond’s Most Popular Low Exotherm Epoxy Systems
- Exceptionally tough. Low viscosity compound with a one to one mix ratio by weight or volume. Can cure at ambient or elevated temperatures. Serviceable up to 400°F. Minimal shrinkage and stress development. Superior resistance to chemicals, mechanical shock/vibration. Can be used for complex geometrical configurations.
- Unrivaled dimensional stability. Excellent thermal conductivity/electrical insulation properties. Resists -100°F to +550°F (-73°C to +288°C). High bond strength to metals, glass, ceramics, composites and most plastics. Tg 215 – 220°C. Volume resistivity >1016 ohm-cm.
- Superb optical clarity and light transmission properties. Extraordinary long open time. Room temperature curing system. Low exotherm. 100% reactive formulation. Top notch electrical insulator. Formidable impact resistance.
- Impressive compressive strength and tensile modulus. Reliable electrical insulation values. Heat dissipative. Shore D hardness 80 – 90. Excellent flow properties. Low linear and volumetric shrinkage. Mix ratio 100 to 50 by weight.
- Highly flexibilized two component epoxy system. Features thermal conductivity combined with electrical insulation. Passes NASA low outgassing test and can be serviceable at cryogenic temperatures. High peel strength and elongation.