November 30, 2023

Thermal Mastic

Thermal Mastic

The term “thermal mastic” is used in the appliance industry to describe a pumpable heat transfer compound which acts as a gap filler. These compounds are applied to a variety of applications including freezers, rv fridge, air conditioners and motor vehicles to improve the performance of these systems or components.

A typical thermal mastic consists of a vehicle such as chlorinated paraffin, a filler such as powdered aluminum silicate clay and calcium carbonate, and a wetting agent such as oleic acid. A small amount of a resin such as polybutene may also be included in the formulation to improve adhesion.

Using a low viscosity chlorinated paraffin as a vehicle has been shown to produce a thermal mastic that can be applied in a variety of ways while providing a good quality seal that will not degrade polyurethane foam insulation in refrigeration applications such as chest freezers. However, the most effective mastic may be comprised of a more complex and expensive mix of ingredients.

In one test, a chlorinated paraffin containing paste was applied as a thermal mastic in the interior of a large metal container which was then filled with a polyetherurethane foam. The mastic was in direct contact with the frothed foam and the resultant mastic-foam interface showed no deleterious effect on the cellular structure of the foam.

Other tests were conducted to determine if the same type of thermal mastic could be made with a non-paraffin vehicle. These tests showed that the same types of compositions as described above can be produced with a non-paraffin vehicle that has the same performance as the chlorinated paraffin vehicle.

Alternatively, the same type of thermal mastic can be prepared with a paraffin vehicle in a smaller amount, to achieve the same performance as the larger volume, more expensive mixture. The resulting mastic has the same performance as the more expensive vehicle, but is much easier to apply and does not require as much of the mastic.

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