Electrically insulative epoxy from Master Bond 30 April 2021

Master Bond EP21NS is a two part epoxy that may be used for bonding, coating, sealing and potting/encapsulating. It has a nanosilica filler that imparts dimensional stability and abrasion resistance.

When measured according to ASTM D4060 with CS-17 wheel for 1,000 cycles, EP21NS exhibits a very low weight loss of 25mg. This formulation is a reliable electrical insulation with a volume resistivity greater than 1,015 ohm-cm; an outstanding dielectric constant of 2.6 at 16.4 GHz; and a dielectric strength of 450 volts/mil at 23.9°C (75°F) for a ⅛th inch thick specimen. It is serviceable over the temperature range of -62.2°C to +121°C (-80°F to +250°F).

This system has a long working life and good flow properties with a moderate mixed viscosity of 50,000 cps – 90,000 cps. The mix ratio of EP21NS is 1 to 1 by weight – and its optimal cure schedule is overnight at room temperature – followed by 4 to 5 hours at 65°C (150°F). It features very low shrinkage upon curing; a low coefficient of thermal expansion of 30 – 35 x 10-6 x in/in/°C; and a compressive strength of 16,000 psi – 18,000 psi.

This compound bonds well to a variety of substrates including metals, composites, glass, ceramics, rubbers and many plastics. EP21NS is resistant to water and salts and can be packaged in ounce, ½ pint, pint and quart kits. The colour of Part A is translucent and Part B is amber. EP21NS does not contain solvents and is RoHS compliant. 

Deputy Editor

Claire Aldridge Deputy Editor t: +44 (0) 1727 743 889


Having joined the magazine in 2012, Claire developed her knowledge of the industry through the numerous company visits, exhibitions and conferences she attended both in the UK and abroad.

Claire prides herself on keeping readers well informed and up to date with the latest industry news.