Thermal Mastic
A mastic, or paste if it is applied as a sealant, camper refrigerator is a smooth, pumpable compound that acts as a gap filler to accomplish various tasks. A mastic can be used to seal a crack or hole in concrete, asphalt and other porous materials or to fill an air gap between two surfaces such as a plastic tube.
Among the many applications for thermal mastic is as a gap filler or a heat transfer compound in various refrigeration systems including refrigerators, freezers and air conditioners. In the case of a refrigerator, mastic is usually applied to the evaporator coils in order to enhance heat transfer to the freezer plate and fins. It can also be used to seal around the foam block of a cooling unit in order to prevent air leaks or to make a better bond between the box and the back side of the cooling unit.
The thermal mastic of the invention is comprised of a low viscosity chlorinated paraffin, a filler, and a wetting agent. The mastic has a K-factor of about.65 B.t.u./in./hr./ft. F and is not likely to cause degradation of polyurethane insulating foam in refrigeration systems.
In one test, a pumpable thermal mastic made from a chlorinated paraffin vehicle, a powdered aluminum silicate clay and a finely divided calcium carbonate had a kinematic viscosity of about 2600 centistokes at 24 C. This was achieved by combining the mastic with a small amount of oleic acid as a wetting agent.
Several standard chest freezer cabinets were filled with the mastic and subjected to performance tests. The mastic lasted for about six days before it was removed and the cellular structure of the polyurethane foam insulation was not degraded.
In general, the invention demonstrates the effectiveness of a thermal mastic that does not degrade polyurethane insulating foam and is of low cost. In particular, the novelty resides in the fact that the thermal mastic of the present invention combines low viscosity chlorinated paraffin as a vehicle with an ooh lala powdered aluminum silicate clay and finely divided calcium carbonate as a filler. A small amount of a wetting agent may be used to assist the dispersion of the mastic and to facilitate the naming of the thermal mastic.