This invention relates to halo-functional silanes, their preparation, rubber compositions containing same and articles such as tires manufactured therefrom.
The use of the silica/silane-filler system to reduce the rolling resistance and improve the wet traction of passenger car tires is well known in the art. A reduction of rolling resistance, and therefore less fuel consumption, is also of strong interest for truck tires. However, the use of silica to replace carbon black filler in natural rubber (NR) containing formulations such as truck tread compounds is limited due to poor abrasion resistance. At the present time, truck tire treads use highly reinforcing carbon black for maximum reinforcement and excellent resistance to abrasion. The replacement of carbon black by silica in truck applications has been hampered by ineffective coupling of the silica to the polymer chains of natural rubber.
Polysulfurized alkoxysilanes such as bis(triethoxysilylpropyl)tetrasulfide (TESPT) and blocked mercapto-functional silanes such as 3-octanoylthio-1-propyltriethoxysilane are currently regarded as the most effective and the most widely used coupling agents in rubber compositions for tires, especially those compositions containing styrene-butadiene rubber or butadiene rubber. The reinforcing efficiency and abrasion resistance of vulcanizates filled with silica are not good enough to justify the replacement of carbon black in formulations containing high levels of natural rubber.
The use of non-sulfur silanes is focused on the use of activated double bonds to improve the coupling between fillers and polymer, notably natural rubber. But these non-sulfur coupling agents have shown inadequate coupling performance or performance inferior to that offered by polysulfurized silanes such as bis(triethoxysilylpropyl)tetrasulfide. In addition, the known non-sulfur silanes are very reactive with conventional fillers and elastomers and are therefore difficult to use. When known non-sulfur silanes are used at levels necessary to achieve optimum coupling of filler to the host elastomer, the uncured filled elastomer typically exhibits poorly dispersed filler and short scorch times during curing. Both good filler dispersion and good filler reinforcing efficiency are required to achieve satisfactory end-use properties.
Commonly assigned, copending U.S. patent application Ser. No. 11/703,969, filed Feb. 8, 2007, addresses the inadequate coupling performance of non-sulfur silanes by using halo-functional silane. This halo-functional silane is derived from mono-alcohols that generate volatile organic compound (VOC's) emissions during their use in filled elastomers. The mono-alcohols that are formed during use of the halo-functional silane have low flash points and therefore create potential hazards during fabrication and use. In addition, the mono-alcohol derived halo-functional silanes generate mono-alcohols during use that may impact adversely on the environment.
Glycol derivatives of organosilanes are known in the art. Commonly assigned, copending U.S. patent application Ser. Nos. 11/358,550, filed Feb. 21, 2006, 11/358,818, filed Feb. 21, 2006, 11/358,369, filed Feb. 21, 2006, and 11/358,861, filed Feb. 21, 2006, address the scorch, VOC emissions and coupling performance of filled elastomers by using organofunctional silanes or mixtures of organofunctional silanes that contain both blocked and free mercaptan groups. Commonly assigned, copending U.S. patent application Ser. Nos. 11/505,055, filed Aug. 14, 2006, 11/505,166, filed Aug. 14, 2006, and 11/505,178 filed Aug. 14, 2006, address the scorch, VOC emissions and coupling performance of filled elastomers using organofunctional silanes or mixtures of organofunctional silanes that contain both dispersing and free mercaptan groups. In addition, commonly assigned, copending U.S. patent application Ser. No. 11/104,103, filed Apr. 12, 2005, addresses the VOC emissions of organofunctional silanes containing alkanedioxysilyl groups. The entire contents of aforementioned U.S. patent application Ser. Nos. 11/358,550; 11/358,818; 11/358,681; 11/505,055; 11/505,166; 11/505,178; and 11/104,103 are incorporated by reference herein.
It would be desirable for various rubber applications to have a rubber composition that utilizes increased levels of silica and lower levels of carbon black while maintaining low VOC emissions from the filled elastomeric materials and elastomeric articles during their preparation and use and still exhibiting the properties of low scorch, good filler dispersion and improved abrasion resistance.