MINERAL RUBBER - GENERAL DESCRIPTION
T-MR Hydrocarbon is the name of the product resulting from the controlled oxidation of selected and blended bituminous petroleum fractions. It is technically classified as a "Petroleum Hydrocarbon Plasticizer and Extender" and is compatible with all organic polymers (N.R., SBR, NBR, CR, etc.).
The low specific gravity (1.05) of T-MR leads to a low pound/volume cost in a rubber compound. Consequently, large volumes of T-MR have been used in rubber compounds for many years, as well as in compounds containing reclaimed rubber. Because of its wide-spread use, T-MR has acquired a number of popular names (i.e., Mineral Rubber, Hard Hydrocarbon and Ground Asphalt).
T-MR decreases the viscosity of uncured rubber compounds, thereby offering the compounder an inexpensive method of improving flow for injection molding, transfer molding and extruding. Concurrent with the improved plasticity, T-MR substantially aids in the dispersion of dry ingredients, such as fillers (clays, taics, CaCO3) and carbon black. The use of modest amounts (10-25 phr) of T-MR will show a little, if any, change in the ultimate physical properties of the rubber compound. High-volume use (35-80 phr) of T-MR will probably show a slight increase in Shore A hardness with other physical properties remaining unchanged.
The rubber compounder should find improvement in the oxygen and air aging of compounds highly loaded with T-MR. This, coupled with the low pound/volume cost of T-MR, makes it the logical choice for high loading in compounds not requiring the ultimate in physical properties. Such loadings may require a slight upward adjustment in accelerator or sulfur level.
INCORPORATION & GENERAL INFORMATION
The point of incorporating T-MR in a mixing sequence is important to ensure full realization of all the benefits it will bring to both the uncured and cured compound. As T-MR is an easily-handled, non-dusting fine grind, it should be added to the mill or internal mixer just after the polymer has been "broken down." This will permit the incorporated T-MR to help the dispersion of filler, etc.