For many bonding applications viscosity is a key criteria in the selection process. Master Bond liquid epoxy adhesives are formulated in low, medium and non-drip viscosities. Low viscosity systems excel in many kinds of adhesive applications, including potting, impregnation and sealing. Moderate viscosity products have easy flowability for convenient dispensing and possess good wetting characteristics. High viscosity pastes are noted for their gap filling capability as well as non-drip and non-sagging properties.
Viscosity and modes of flow
Viscosity may be simply defined as the resistance to flow of a solid or a liquid. Physicists describe two different modes of flow: Newtonian and non-Newtonian. Newtonian flow is dependent on the amount of applied shear or pressure while non-Newtonian flow is related to the amount of applied force. Epoxy resin compounds, like the great majority of other polymer systems, fall into the non-Newtonian category.
There are many test methods for measuring the viscosity, especially for liquids. They include Brookfield, Cannon Fenske and Gartner Bubble, to list only a few. Viscosity is widely measured in poises or antipoises. One readily available instrument for viscosity tests is the Brookfield viscometer which determines viscosity as a function of shear rates and temperatures.
Viscosity of common materials
The table below lists the viscosities of common fluids and solids at 75°F in cps:
|Viscosities of Typical Fluids & Solids|
|Liquid or Solid Name||Viscosity, cps, at 75°F|
|Ethylene glycol antifreeze||15|
|SAE 30 motor oil||250|
|Ketchup or french mustard||30,000-50,000|
An epoxy’s viscosity limits the applications it can be used for, as well as the means by which it can be applied. In general, a low viscosity epoxy formulation is preferred for applications where a very thin gap has to be filled with an adhesive or when space available for a potting compound is limited. Master Bond epoxy compounds are available in a very wide range of viscosities from as low as 200 cps to in excess of 1,500,000 cps for bonding, sealing and casting. Some of our systems include EP30, EP21LV and EP62-1 with service ranges up to 300°F and products including EP121CL and EP112 for thermal stability up to 500°F. Additionally, for applications when a high viscosity (no flow upon application when placed in a vertical position) is desired, compounds such as EP21TCHT-1, EP33ND and Supreme 10HT are available for service over the temperature range of -60°F to +450°F.
Our technical support team will analyze customer requirements to help select the most desirable viscosity to meet production needs. Viscosity of an existing formulation can often be adjusted to satisfy specific needs.