Patent Application
20070293610
Sulfur vulcanizable rubber mixtures containing silica reinforcement and coupling agent were prepared as rubber Samples A through J. Samples A and B were Control Samples. Samples C through J contained an inclusion of ionic compounds individually comprised of an organic cation moiety and an anion moiety.
The rubber compositions were prepared by mixing the elastomers(s) together with compounding ingredients in a first non-productive mixing stage (NP-1) in an internal rubber mixer for about 5 minutes to a temperature of about 160° C. The rubber mixture is then mixed in a second non-productive mixing stage (NP-2) in an internal rubber mixer for about 3 minutes to a temperature of about 160° C. where one or more ingredients may be optionally added, if desired. The resulting rubber mixture is then mixed in a productive mixing stage (PR) in an internal rubber mixer with sulfur curatives for about 3 minutes to a temperature of about 110° C. The rubber composition is sheeted out and cooled to below 40° C. between each of the non-productive mixing steps and prior to the productive mixing step.
The basic rubber composition formulation for the respective Samples is presented in Table I and the ingredients are expressed in terms of weight, namely parts by weight (phr) unless otherwise indicated.
1Natural cis 1,4-polyisoprene rubber as TSR20
2N120 rubber reinforcing carbon black, an ASTM designation
3Precipitated silica as 1165MP ™ from Rhodia
4Coupling agent composite as X266S ™ from Degussa blended with carbon black in a 50/50 weight ratio, with the coupling agent comprised of a bis(3-triethoxysilylpropyl) polysulfide having a average in a range of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge and reported in Table 1 in terms of the composite.
5Fatty acid comprised primarily (at least 50 weight percent) of stearic acid and a minor amount of other fatty acids including palmitic and oleic acids
6Various ionic liquids from Sigma-Aldrich
7Sulfenamide and guanidine based sulfur cure accelerators
The following Table 2 (divided into Table 2 and Table 2 Cont.) reports cure behavior and various physical properties of rubber Samples A through J, of which Samples C through J contain the various ionic liquids, expressed in terms of weight (phr) and weight percent unless otherwise indicated. Where a cured rubber sample was evaluated, such as for the stress-strain, rebound, hardness, tear strength and abrasion measurements, the rubber sample was cured for about 32 minutes at a temperature of about 150° C.
1Data according to Rubber Process Analyzer as RPA 2000 ™ instrument by Alpha Technologies, formerly the Flexsys Company and formerly the Monsanto Company. References to an RPA-2000 instrument may be found in the following publications: H. A. Palowski, et al, Rubber World, June 1992 and January 1997, as well as Rubber & Plastics News, Apr. 26 and May 10, 1993.
2Data according to Automated Testing System (ATS) instrument by the Instron Corporation which incorporates six tests in one system. Such instrument may determine ultimate tensile, ultimate elongation, modulii, etc. Data reported in the Table is generated by running the ring tensile test station which is an Instron 4201 load frame.
3Volume resistivity (ohm/cm) as a measure of electrical resistivity, (and considered herein to be a measure of electrical resistance of a rubber composition, or a consideration of its electrical conductivity) according to ASTM D257.
From Table 2 it can be seen that the volume resistivity of Samples C through J was reduced significantly as compared to Control Samples A and B having volume resistivities of 9.2×105 and 4.5×1014 ohm/cm, respectively.
This is considered herein to be significant in the sense of enabling the volume resistivity of the high volume resistivity rubber compositions to be substantially reduced for the silica-reinforced rubber compounds containing the relatively minor rubber reinforcing carbon black content of less than 25 phr thereof (therefore containing a significant amount of precipitated silica reinforcement). It is considered herein that a tire tread composed of the rubber compositions C through J would have an improved electrical conductivity (sufficiently low, or reduced, electrical volume resistivity in a sense of sufficiently low electrical resistance) to provide a path of suitable electrical conductivity through the tire tread to its running surface (e.g. to the ground).
While, as hereinbefore discussed, the mechanism may not be completely understood, it is envisioned that the ionic compounds in Samples C through J are ionically conductive ionic compounds which permit a migration of electrical potential generated ions within the ionic compound from one electrical potential to the other electrical potential for the respective Sample.
From Table 2 it can also be seen that the tan delta physical property values of the Samples C through J, used the inclusion of the ionic liquids, were lower than those of the Control Samples A and B at the 10 percent or lower strain level and were higher than those of the Control Samples A and B at higher strain values.
This is considered herein to be significant in a sense of showing an improvement in such dynamic physical property which is apparently promoted by the inclusion of the ionic compound in the respective Sample, namely, the lower strain tan delta values promoting predictive lower rolling resistance for a tire having a tread of the rubber compositions of Samples C through J and the higher strain tan delta values promoting predictive better traction and handling (e.g. cornering or braking) for a tire having a tread of such rubber compositions.
From Table 2 it can further be seen that higher ultimate tensile strength and higher hardness (Shore A hardness) values were observed for the ionic liquid-containing Samples C through J which is further considered herein to be an additional significant result of the inclusion of the ionic liquids in the rubber compositions. This is considered herein to be significant in a sense of showing an improvement in such mechanical (physical) property, namely a better predictive durability, by the inclusion of the ionic compound in the respective rubber Sample.
From Table 2 it can additionally be seen that the hot rebound values (100° C.) Samples C through J were higher which is considered herein to be significant in a sense that it indicated that the rubber compositions of Samples C through J were less hysteretic (lower energy loss) and are predictive promoting lower rolling resistance for a tire having a tread of such rubber compositions and hence a better fuel economy for an associated vehicles with such tires, apparently as a result of inclusion of the ionic compound in the respective rubber Sample.
While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.
