Understanding viscosity is vital to the proper use of epoxies and urethanes. In many polymer systems, temperature is used to control the viscosity of the material. At lower temperatures, viscosities increase or the material gets thicker. At higher temperatures, the viscosity decreases, or the material gets thinner, and flows more easily. The viscosity of epoxies, in particular, is extremely sensitive to temperature. For example, let’s look at this chart showing the viscosity of our material, 20206, at different temperatures.
The viscosity of the material is important for several reasons. Most obviously, it affects how the material flows. The lower the viscosity, the more easily the material flows into tight cracks and spaces. For example, if you are potting a tightly wound coil, or a tightly packaged electronic device, you will want an extremely low viscosity material that will enable the material to fully penetrate any void.
The viscosity of the material is also critical for storing a material with mineral filler, such as 20206. When the material is stored at room temperature, the high viscosity helps to hold the solid mineral filler particles in suspension. As that viscosity drops, mineral filler can more easily fall out of suspension, and settle to the bottom of the container. One way around this problem, is to mix the material as it is heated, keeping the filler in suspension. This is typically seen in meter-mix dispense machines.
Another reason viscosity is important, is for mixing the material. We know that in order for materials to reach full cure, they need to be fully mixed. The more similar the viscosity of the two materials, the easier they are to mix together.