When carbon black is incorporated in a room temperature vulcanizable composition such as described in U.S. Pat. No. 4,111,890 to Getson et al, the resultant composition is thixotropic, but exhibits poor shelf-life. Moreover, when the composition is cured in atmospheric moisture, the surface cure appears to be incomplete and the carbon black can be easily transferred (rubbed-off) from the surface of the cured composition. However, it has been found that when the carbon black is treated with a hydrophobic agent, a thixotropic composition is obtained which upon curing to an elastomeric solid is resistant to the transfer (rub-off) of carbon black from the cured surface. Furthermore, it has been found that the resultant composition exhibits better shelf stability over longer periods of time.
Therefore it is an object of this invention to provide a room temperature vulcanizable composition which is thixotropic and has non-slump properties. Another object of this invention is to provide a room temperature vulcanizable composition containing carbon black which is substantially free of carbon black rub-off from the cured surface. A further object of this invention is to provide a method for incorporating carbon black into a room temperature vulcanizable composition without inhibiting the surface cure of the composition. A still further object of this invention is to provide a method of incorporating carbon black into a room temperature vulcanizable composition and eliminate rub-off of the carbon black from the cured surface.