| 摘要 |
Improved coal tar compositions are described which are prepared from a blend comprising: (A) based on the combined weight of coal tar and coal tar pitch, from about 80 parts to about 98 parts by weight of coal tar having an overall float test of from about 50 seconds to about 220 seconds, (B) based on the combined weight of coal tar and coal tar pitch, from about 2 parts to about 20 parts by weight of coal tar pitch having a softening point of from about 140 DEG C. to about 160 DEG C., and (C) from about 1% to about 20% by weight, based on the total weight of the composition, of an acrylonitrile-butadiene copolymer. In one embodiment up to 35 parts by weight of the coal tar (A) is replaced with a coal tar selected from coal tars having softening points of from about 52 DEG C.-60 DEG C., and from about 56 DEG C.-64 DEG C. The coal tar compositions are not emulsions, and generally will not contain any significant amount of water (e.g., less than 0.5% by weight). The invention also relates to a process for preparing the coal tar compositions which comprises the steps of: (A) preparing at an elevated temperature, a first mixture comprising (A-1) from about 80 parts to about 98 parts by weight of coal tar having an overall float test of from about 50 seconds to about 220 seconds, and (A-2) from about 2 parts to about 20 parts by weight of coal tar pitch having a softening point of from about 140 DEG C. to about 160 DEG C., (B) maintaining the first mixture at a temperature of at least about 170 DEG C., (C) adding to the first mixture, from about 1% to about 20% by weight, based on the total weight of the composition, of an acrylonitrile-butadiene copolymer to form a second mixture and (D) mixing the copolymer into the second mixture. The coal tar compositions of the present invention are useful particularly as roofing, waterproofing and maintenance materials. More particularly, the coal tar compositions are useful in built-up roofing (BUR) applications. The coatings formed from the coal tar compositions of the invention exhibit improved tensile, elongation and recovery characteristics, improved fatigue resistance, improved adhesive qualities, and improved cold temperature performance.
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