Abstract:
A lubricant composition containing both a dialkyl fumarate-vinyl acetate low temperature flow improver and sorbitan fatty acid ester or a polyoxyalkylene sorbitan fatty acid ester has reduced Gel Index.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to lubricating oils having improved low temperature performance and more specifically to crankcase engine lubricants containing an additive combination to reduce Scanning Brookfield Gel Index. 
     BACKGROUND OF INVENTION 
     Lubricating oils, such as those used in the crankcase of internal combustion engines, are designed to reduce friction, minimize deposit formation, prevent corrosion and wear, and to ensure adequate engine lubrication over a wide temperature range. The American Petroleum Institute (&#34;API&#34;), Society of Automotive Engineers (&#34;SAE&#34;), American Society for Testing and Materials (&#34;ASTM&#34;) and the International Lubricants Standardization and Approval Committee (&#34;ILSAC&#34;) are the key bodies that define industry requirements for engine lubricant quality, establish classifications and develop test methods to certify that lubricants meet performance requirements. Individual original equipment manufacturers (&#34;OEM&#39;s&#34;) often establish their own performance requirements that may be more stringent than those of API, SAE, ASTM or ILSAC requirements. 
     To insure that a lubricant has the appropriate low temperature properties generally three tests must be met. It must meet the requirements for pour point (ASTM D97), TP1 Mini Rotary Viscometer, &#34;TP1MRV&#34;, (ASTM D 4648) and Scanning Brookfield Gel Index, &#34;Gel Index&#34;, (ASTM D 5133). The pour point is an indication of dispensability at low temperatures while the TP1 MRV and Gel Index are measurements of lubricant pumpability at low temperatures. 
     Additives are used to formulate oil compositions that will meet the foregoing low temperature requirements. Unfortunately experience has shown that the TP1 MRV and Gel Index can vary independently of each other and that adjusting a lubricant composition to meet one of these properties often imposes a negative or undesirable effect on the other property. 
     Currently the industry requirements for a lubricant Gel Index is a maximum of 12 while the requirements for a lubricant TP1 MRV is a maximum of 60,000 cP at test temperature ranging from -10° C. to -40° C. depending upon the SAE grade. For example, a 5W-30 oil is tested at -35° C., 10W-30 at -30° C., and the like. 
     OEM&#39;s and lubricant formulators, of course, are continually seeking lubricant compositions that have properties that are better than the present standards. Thus, there remains a need for lubricating oils having reduced Gel Index values which still meet TP1 MRV and pour point requirements. 
     SUMMARY OF INVENTION 
     Surprisingly, it now has been found that the combination of a dialkylfumarate-vinyl acetate (&#34;DFVA&#34;) copolymer flow improver and an ester selected from the group consisting of sorbitan fatty acid esters and polyoxyalkylene sorbitan fatty acid esters is effective in reducing the Gel Index of a lubricant below 12 without substantially increasing the TP1 MRV and pour point of the lubricant. 
     Accordingly, in one embodiment of the present invention there is provided a lubricating composition comprising a major amount of an oil of lubricating viscosity, a minor amount of a dialkylfumarate-vinyl acetate copolymer flow improver and an ester selected from the group consisting of sorbitan fatty acid esters or polyoxyalkylene sorbitan fatty acid esters, the DFVA and ester being present in an amount sufficient to lower the Gel Index of the composition to below about 12. 
     In another embodiment a method is provided to lower the Gel Index of a lubricating composition containing a major amount of a lubricating oil, the method comprising adding to the composition the combination of a DFVA copolymer flow improver and an ester selected from the group consisting of sorbitan fatty acid esters and polyoxyalkylene fatty acid ester in an amount sufficient to lower the Gel Index of the composition. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The lubricating compositions of the present invention include a major amount of a base oil of lubricating viscosity, for example, in the range of about 13 to about 35 centistokes at 40° C. Indeed, any natural mineral base oil, hydrocracked and dewaxed base oils, wax isomerates, synthetic hydrocarbon oils such as polyalpha olefins or mixtures of these used in crankcase lubricating oils for spark ignited and compression ignited engines are suitable in the practice of the invention. Thus oils of API Groups I, II, III and IV or mixtures of these are suitable basestocks. 
     A lubricating composition of the present invention also includes a dialkylfumarate-vinyl acetate copolymer low temperature flow improver. In general the alkyl group in the DFVA will be in the range of 6 to 24 carbons and preferably 8 to 18 carbon atoms. The typical number average molecular weight of the DFVA useful is in the range of about 5,000 Mn to about 70,000 Mn. The DFVA flow improver generally is added to the lubricating composition in the form of a solution containing about 50% active ingredient. Typically the actual amount of DFVA present in the lubricant is in the range of from about 0.20 wt % to about 0.40 wt % based on the total weight of the lubricating composition. 
     The composition of the invention also includes a sorbitan fatty acid ester or a polyoxyalkylene sorbitan fatty acid ester including mono, di and triesters and mixtures thereof. In such esters the fatty acid typically will have alkyl chains of from about 10 to about 30 carbon atoms. The preferred fatty acid, however, is stearic acid and a preferred sorbitan ester is sorbitan tristearate. In the case where the ester is a polyoxyalkylene sorbitan ester the alkylene group in such esters typically is a C 2  to C 25  group and especially ethylene and the number of oxyalkylene units range from about 1 to about 20. Preferably the ester is a polyoxyethylene (20) sorbitan tristearate, especially when the base oil is a 150 N base oil. 
     The amount of sorbitan ester used in the lubricating compositions of the present invention is from about 0.20 wt % to 0.50 wt % based on the total weight of the composition. 
     The oil composition of the present invention may contain multi-functional additives of the types contained in modern oil formulations. These additives are usually not added independently, but are precombined in detergent-dispersant-inhibitor (DI) packages which can be obtained commercially from suppliers of lube oil additives. DI packages with a variety of ingredients, proportions and characteristics are available. 
     Optionally the oil composition may contain minor but effective amounts of antioxidants such as those used in contemporary motor oil formulations. 
     As will be readily appreciated the Gel Index of other fully formulated engine oils containing dialkylfumarate-vinyl acetate copolymer flow improvers can be lowered by adding sufficient polyoxyalkylene stearic acid esters to such oils. 
    
    
     EXAMPLES 
     The invention will now be illustrated by reference to the following examples and comparative examples. 
     Examples 1 to 3 and Comparative Examples 1 and 2 
     In these examples a formulated 5W-30 motor oil, hereinafter referred to as Oil A, was prepared by blending a solvent dewaxed 100N-150N mineral oil mix with 9.22 wt % of a DI package and 10.16 wt % of Paratone 8458 which is a trademark for a viscosity index improver and low temperature flow improver sold by Oronite Company, Richmond, Calif. Paratone 8458 consists of a copolymer VI improver and 3.5 wt % of a dialkylfumarate-vinyl acetate low temperature flow improver. As formulated Oil A contained 0.36 wt % DFVA. 
     To each of four samples of Oil A was added from 0.2 to 0.8 wt % of different sorbitan esters. The resulting mixtures were heated at 55° C. to 60° C. for about 30 minutes to dissolve the esters and then cooled to room temperature. The Gel Index and other inspections for each sample were performed. The results are given in Table 1 along with the inspections for Oil A (Comparative Example 1). 
     Comparative Examples 3 to 4 
     Following the procedure of Examples 1 to 3, Oil A was combined with 0.5 wt % of sorbitan monooleate and sorbitan sesquioleate. The inspections are given in Table 1. 
     
                                           TABLE 1__________________________________________________________________________        Comparative               Example                    Example                         Example                              Comparative                                    Comparative                                          Comparative        Example 1               1    2    3    Example 2                                    Example 3                                          Example 4__________________________________________________________________________Oil A, wt %  100.00 99.80                    99.50                         99.80                              99.20 99.50 99.50Tween ® 610.sup.1, wt %        --     0.20 0.50 --   0.80  --    --Tween ® 65.sup.2, wt %        --     --   --   0.20 --Arlacel ® 83N.sup.3, wt %        --     --   --   --   --    0.50  --Span ® 80.sup.4, wt %        --     --   --   --   --    --    0.50InspectionsAppearance   Bright &amp; Clear               Bright &amp;                    Bright &amp;                         Bright &amp;                              Cloudy                                    Bright &amp;                                          Bright &amp;               Clear                    Clear                         Clear      Clear ClearGel Index (ASTM D5133)        15.2   8.7  9.1  6.5  6.5   14.4  15.3MRV TP1 (-35° C.) Visc. cP        26,000 29,300                    39,200                         26,700                              88,152                                    26,200                                          25,000MRV TP1 Yield Stress Pa        Pass   Pass Pass Pass Fail  Pass  PassPour Point   -39° C.   -36° C.__________________________________________________________________________ .sup.1 Tween ® 61 is a trade mark for a polyoxyethylene (4) sorbitan monostearate sold by ICI Americas Inc., Wilmington, Delaware. .sup.2 Tween ® 65 is a trademark for a polyoxyethylene (20)sorbitan tristearate sold by ICI Americas Inc. .sup.3 Arlacel ® 83N is a trademark for a sorbitan sesquioleate sold by ICI America Inc. .sup.4 Span ® 80 is a trademark for a sorbitan monooleate sold by ICI Americas Inc. 
    
     Examples 4 to 5 and Comparative Examples 5 and 6 
     The procedure of Example 1 was followed except that a formulated 10W-30, hereinafter Oil B, was prepared by blending a 150N mineral oil with 9.22 wt % of the same DI package as Oil A but with 7.71 wt % of Paratone 8458. As formulated Oil B contained 0.27 wt % of DFVA. The inspections made are given in Table 2 and are compared to Oil B (Comparative Example 5). 
     
                       TABLE 2______________________________________    Comparative            Example  Example  Comparative    Example 5                                       Example 6______________________________________Oil B, wt %      100.00    99.80    99.80  99.80Tween ® 61.sup.1, wt %                --                      --       --                                              0.20Tween ® 65.sup.2, wt %                      0.20                                   --Span ® 65.sup.3, wt %                      --       0.20                                          --InspectionsAppearance           Bright &amp;                      Bright &amp;                           Bright &amp;                                          Bright &amp;                         Clear                                             ClearGel Index            13.4                       6.4                                7.9                                          13.9(ASTMD 5133)MRV TP1 (-30° C.)                         27200                                             29700CP ASTM D4684Yield Stress, Pa                Pass                      Pass                                          Pass______________________________________ .sup.1, .sup.2  and .sup.3  are all trademarks of ICI Americas. .sup.1, .sup.2  See Table 1. .sup.3  Span ® 65 is the trademark for a sorbitan tristearate sold by ICI Americas.