Abstract:
Complex sulfides of antimony combined with either molybdenum disulfide or graphite are used as mixtures to impart synergistic effects in imparting extreme pressure and antiwear properties to lubricants.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to lubricant compositions containing a mixture of antimony thioantimonate (SbSbS 4 ) and molybdenum disulfide (MoS 2 ) or graphite with lubricating materials for imparting extreme pressure and antiwear properties to the lubricant composition. 
     Antimony thioantimonate (SbSbS 4 ) is known as a lubricant additive in oils and greases wherein the additive concentration is 1-60% of the composition (U.S. Pat. No. 3,965,016). 
     It is known that certain materials of lamellar crystal structure such as molybdenum disulfide and graphite can impart lubricating properties to greases, solid films, and other configurations in which they are employed. U.S. Pat. No. 3,935,114 discloses the use of molybdenum disulfide and a selected class of metallic oxides such as antimony trioxide in effective and synergistic amounts for use as lubricant additives. 
     The synergistic mixture of the instant invention has not been found in the prior art. 
     SUMMARY OF THE INVENTION 
     This invention is directed to a lubricating composition consisting essentially of, based on the weight of the composition, from about 60 to about 99.8% of a lubricant selected from the group consisting of a grease, a mineral oil of lubricating viscosity, and a synthetic fluid of lubricating viscosity, and a synergistic mixture of from about 0.1 to about 20% of SbSbS 4  and from about 0.1 to about 20% of MoS 2  or graphite or mixtures thereof, wherein said SbSbS 4  and MoS 2  or graphite are mixed in a synergistic ratio in the range of 1 to 9 to 9 to 1, preferably 1 to 3 to 3 to 1. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The extreme pressure (EP) and antiwear additives embodied in the synergistic mixture of the present invention generally are incorporated in lubricant compositions in a particulate form, i.e., as a finely divided powder having a particle size in general, within the range from about 0.01 microns to about 100 microns, and preferably within the range of from about 0.1 to about 10 microns. 
     The composition of this invention is useful for lubricating the contacting surfaces of a wide variety of materials, for example, metals such as steel, molybdenum, zinc, copper, bronze, brass, Monel and other metals and metal alloys, plastics, ceramics, graphite, and other materials, wherein the contacting surfaces may be of the same or different materials. The most important of these compositions are oil and grease compositions having improved extreme pressure and load-carrying ability which are prepared by incorporating in a conventional oil or grease from about 0.2 to about 40% by weight of the synergistic mixture of this invention, preferably from about 1.0% to about 20% by weight of the composition. 
     The conventional grease can be a natural petroleum grease (which may contain small amounts of antioxidants, anticorrosives, or other additives) or a synthetic grease. The synthetic grease is comprised of a synthetic fluid (such as dioctyl sebacate, dioctyl adipate, tributyl phosphate, di-2-ethylhexyl sebacate, ditridecyl phthalate, ditridecyl adipate, dioctyl dimerate, trimethylolpropane tripelargonate, pentaerythritol tetravalerate, triaryl phosphate, polyalkylene ethers, polyalphaolefins, and the like), from about 5% to about 45% of a thickener) such as lithium stearate, aluminum stearate, lithium hydroxy stearate, calcium stearate, silica, clay, hydroxyaluminum benzoate stearate, polyureas, and the like), and small amounts of other additives (such as antioxidants and anticorrosion agents). Other greases which are improved by the synergistic mixture of this invention are silicone greases comprised of a silicone oil containing a thickening agent such as tetrafluoroethylene polymers and copolymers, other fluoropolymers, or fumed silica. 
     The synergistic mixture also finds use as a component for the lubricating dispersion comprising a liquid oil carrier having lubricating viscosity such as a hydrocarbon oil, synthetic ester oil, synthetic polyether oil, or silicone oil containing therein from about 0.2% to about 40% by weight of the solid synergistic mixture particles, preferably from about 1.0% to about 20% by weight based on a total weight of dispersion. 
     Antimony thioantimonate complex may be prepared by the method described in U.S. Pat. No. 3,965,016 which is herein incorporated by reference. 
     The following examples are provided to further illustrate the present invention in which the antimony thioantimonate and molybdenum disulfide or graphite synergistic mixtures were prepared and tested as lubricant mixtures with greases and oils of lubricating viscosity. 
    
    
     EXAMPLES 1 THROUGH 7 
     A silica grease derived from a synthetic polyalphaolefin base fluid thickened with silica was separately blended with different mixtures of SbSbS 4  and MoS 2  as shown in Table I below. The blended greases were evaluated by means of Shell Four-Ball EP and Wear testers. The experimental results are recorded in Table I. The wear scar diameters, load wear indexes and weld points of the greases containing different ratios of SbSbS 4  and MoS 2  are superior to those of the greases containing either SbSbS 4  or MoS 2  alone. 
     
                       TABLE I______________________________________Shell Four-Ball Lubricating Properties ofSilica Grease.sup.1 Containing Various AdditivesExample No. 1      2      3    4    5    6    7______________________________________Sb.sub.2 S.sub.4        0      10    7.5  6.7  5.0  3.3   0MoS.sub.2.sup.3        0      0     2.5  3.3  5.0  6.7  10Scar Dia., mm.sup.2       0.81   0.72    0.56                           0.52                                0.53                                     0.52                                         0.63Weld Pt., kg       126    400    500  500  500  400  250Load Wear Index       33     100    111  111  113  107  35______________________________________ .sup.1 Polyalphaolefin oil thickened with silica. .sup.2 1200 rpm, 40 kg and 167° F. for one hour (AISI 52100 steel balls). .sup.3 Technical fine grade. 
    
     EXAMPLE 8 THROUGH 12 
     Using the same procedure as described in Example 1-7, silica grease was separately blended with different mixtures of SbSbS 4  and graphite as shown in Table II below. The performance data of scar diameters, load wear indexes and weld points are listed in Table II. The greases containing mixtures of Sb 2  S 4  and graphite show superior performance to those of greases containing either SbSbS 4  or graphite alone. 
     
                       TABLE II______________________________________Shell Four-Ball Lubricating Properties ofSilica Grease.sup.1 Containing Various AdditivesExample No.  8       9       10    11    12______________________________________Sb.sub.2 S.sub.4         10     7.5     6.7   5.0    0Graphite.sup.3         0      2.5     3.3   5.0   10Scar Diameter, mm.sup.2        0.72     0.52    0.47  0.74 0.86Weld Pt., kg 400     400     500   400   200Load Wear Index        100      87      86    80   39______________________________________ .sup.1 Polyalphaolefin thickened with silica. .sup.2 1200 rpm, 40 kg, and 167° F. for one hour (AISI 52100 steel balls). .sup.3 Graphite powder with an average particle size of 50μ. 
    
     EXAMPLES 13 THROUGH 15 
     A bright stock mineral oil of 2600 SUS viscosity at 100° F. was separately blended with 0.5% Sb 2  S 4 , 0.25% Sb 2  S 4  /0.25% MoS 2 , and 0.5% MoS 2  using a high speed mechanical stirrer. The Shell Four-Ball wear scar diameters of the blends were determined at 1800 rpm and 40 kg for five minutes. The wear data are recorded in Table III. The scar diameter of the oil containing a mixture of 0.25% Sb 2  S 4  and 0.25% MoS 2  is smaller than that of the oil samples containing either 0.5% Sb 2  S 4  or 0.5% MoS 2  alone. 
     
                       TABLE III______________________________________Shell Four-Ball Wear Scar Diameters.sup.1of a Mineral Oil Containing AdditivesExample Oil Composition    Scar Diameter______________________________________13      0.5% Sb.sub.2 S.sub.4 in base oil.sup.2                      0.5414      0.25% Sb.sub.2 S.sub.4 and 0.25% MoS.sub.2                      0.43   in base oil15      0.5% MoS.sub.2 in base oil                      0.53______________________________________ .sup.1 1800 rpm and 40 kg for five minutes (AISI 52100 steel balls). .sup.2 The base oil is bright stock mineral oil with 2600 SUS viscosity a 100° F. 
    
     EXAMPLES 16 THROUGH 18 
     In addition to the EP and antiwear properties, another desirable characteristic of a lubricant additive is to provide low coefficient of friction. This series of experiments is to determine whether a mixture of Sb 2  S 4  and MoS 2  in a mineral oil can produce coefficient of friction lower than that of the single components. A paraffinic mineral oil having a viscosity of 155 SUS at 100° F. was separately blended with different amounts of SbSbS 4  and MoS 2  as indicated in Table IV in the presence of a succinimide type suspending agent. The coefficients of friction of these blends were obtained on a Shell Four-Ball Wear Tester with a torque measuring attachment. The results are recorded in Table IV. It is interesting to note that the oil blend containing the mixture of Sb 2  S 4  and MoS 2  produced the lowest coefficient of friction among the three blends. 
     
                       TABLE IV______________________________________Coefficients of Frictionof a Mineral Oil Containing Additives.sup.1Example  Oil Composition    Coefficient of Friction______________________________________16     0.5% Sb.sub.2 S.sub.4 in base oil                     0.0417     0.25% Sb.sub.2 S.sub.4 and 0.25% MoS.sub.2                     0.01  in base oil18     0.5% MoS.sub.2 in base oil                     0.04______________________________________ .sup.1 Coefficients of friction were obtained at 1200 rpm and 40 kg for five minutes (AISI 52100 steel balls).