Thermal Mastic

Several of the newer refrigerators, freezers and other polyurethane foam insulated appliances have tubing rv fridge that is held in place by a high thermal conductivity mastic disposed between the tubing and the walls of the refrigeration system. This mastic may be a one-component product or a mix of mastic and filler in the form of a pumpable paste.

The mastic is typically a smooth, pumpable heat transfer compound having an elastomeric film which serves to fill the gaps between two adjacent metallic surfaces. The mastic is commonly used to promote heat transfer from the evaporator coils of an air conditioner or refrigerator, as well as to provide a seal for the temperature sensor, defrost thermostat and other components in a variety of appliances.

A typical mastic composition employs a low viscosity chlorinated paraffin vehicle along with powdered inorganic fillers such as aluminum silicate clay or calcium carbonate, and a small amount of a wetting agent such as oleic acid. The kinematic viscosity of the vehicle is usually between about 2600 and 6000 centistokes at 24 C. This formulation provides a mastic that is suited for all types of applications, including application by hand.

The kinematic viscosity can be controlled by controlling the proportion of the vehicle to the filler. This control is necessary to achieve the desired mastic properties such as a good adhesion and a high heat transfer coefficient of the mastic.

This invention is a novel and cost effective thermal mastic suitable for use in a wide range of refrigeration systems, which does not degrade the polyurethane foam insulation that is used as a cavity filler between the inner wall of the cooling compartment and the outer shell of the appliance. A low viscosity chlorinated paraffin as a vehicle in combination with the correct filler and a wetting agent is a formula that produces a thermal mastic of the highest quality and reliability for a low cost.

The mastic is most commonly applied to the evaporator coils of an HVAC or refrigeration unit. The mastic is also used to make a seal around the recessed portion of the foam block that surrounds the evaporator coils in an RV, marine or truck cooling unit.