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.
The chart below illustrates the working life values that can be achieved for select grades of systems with different fillers:
|System Type||Product||Working life after mixing, 75°F. 100 gram batch|
|Two part epoxy||EP29LPAO||5-7 hours|
|Two part epoxy||EP21LVSP6||3-5 hours|
|Two part epoxy||EP39MAOHT||120-150 minutes|
|Two part epoxy||EP29LPSP||>4-5 hours|
|Two part silicone||MasterSil 151AO||2-4 hours|
|Two part epoxy||EP37-3LV||>10 hours; 1 lb. >5 hours|
|Two part epoxy||EP29LP||>10 hours; 1 lb. >5 hours|
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
Low viscosity potting/encapsulation compound. Superior dielectric properties. Versatile cure schedules. Convenient one to one mix ratio weight or volume. Minimal shrinkage and stress development. Resists thermal cycling and mechanical shocks. Successfully tested for 1,000 hours 85°C/85% RH. Service temperature range -100°F to +400°F.
Thermally conductive/electrically insulative heat resistant epoxy compound. Requires oven curing. Meets NASA low outgassing specifications. Meets MIL-STD-883J Section 3.5.2 for thermal stability. Excellent dimensional stability. Withstands 1,000 hours 85°C/85% RH. Serviceable from -100°F to +550°F. Tg 215-220°C.
Clear, two component epoxy system has long pot life. Convenient one to one mix ratio. High bond strength. Superb chemical resistance properties. Used in bonding, sealing, potting and filament winding applications. Low viscosity compound. Exceptionally low exotherm. Cures rigid. Service operating temperature range from -60°F to +250°F.
Thermally conductive/electrically insulative epoxy for large potting/encapsulation applications. Low exotherm. Long working life. Excellent flow properties. Very low shrinkage upon cure. Impressive compressive strength. Shore D hardness 80-90. Serviceable from -60°F to +250°F.
Highly flexibilized, thermally conductive/electrically insulative epoxy adhesive. High elongation. Exhibits superior shear and peel strength properties. Serviceable from 4K to 250°F. Withstands thermal cycling, thermal shock and mechanical shock. Passes NASA low outgassing test. Cures at room temperature or more quickly at elevated temperatures.