Polymer thickened grease compositions and their use

Abstract

The invention provides a grease composition comprising: (a) a polymer thickened grease; (b) an acid having a pKa in the range of 2-7 wherein the pKa is measured in water at 25° C.; and (c) a metal salt. The invention further provides a mechanical component having a metal surface onto which a layer of the grease composition according to the invention has been applied. In addition, the invention relates to the use of the present grease composition for reconditioning the lubrication of a mechanical component having a metal surface; and the use of the present grease composition for protecting a mechanical component having a metal surface against corrosion, wear or anti-fretting. The invention also relates to a method for preparing the present grease composition.

1 . A grease composition comprising:
 (a) a polymer thickened grease;   (b) an acid having a pKa in the range of 2 7 with the pKa being measured in water at 25° C.; and   (c) a metal salt.   
     
     
         2 . The grease composition according to  claim 1 , further comprising the step of applying the grease composition to a metal surface of a mechanical component, the metal salt reacting with the acid and the acid or the acid so obtained etches the metal surface, thereby forming on the metal surface a layer including the metal of the metal salt. 
     
     
         3 . The grease composition according to  claim 2 , wherein the metal of the metal salt is selected from the group consisting of Group 1A, 1B, 2A, 2B, 4A, 5A, 7B and 8B elements of the Periodic Table. 
     
     
         4 . The grease composition according to  claim 3  comprising:
 (a) 1-99 wt % of the lubricating base oil; 
 (b) 1-20 wt % of the polymeric thickener; 
 (c) 0.01-10 wt % of the acid; and 
 (d) 0.01-40 wt % of the metal containing compound, wherein 
 
       all weight percentages are based on the total weight of the grease composition. 
     
     
         5 . The grease composition according to  claim 4  further comprising a polymeric ester in an amount in the range of from 0.1-40 wt %, based on the total weight of the grease composition. 
     
     
         6 . The grease composition according to  claim 5 , wherein
 the acid is a polyprotic acid having two pKa values in the range of from 2-10.   
     
     
         7 . The grease composition according to  claim 6 , wherein the acid is phosphoric acid. 
     
     
         8 . The grease composition according to  claim 7 , wherein the polymeric thickener includes at least one component selected from the group consisting of natural rubber, polypropylene, polyisoprene, polybutadiene, poly(styrene-butadiene), poly(ethylene-propylene-diene), polyurethane, polymethacrylate, polyisobutylene, poly(isobutylene-succinic acid), poly(isobutylene-succinic acid-polyacrylamide), polyurea and polyethylene. 
     
     
         9 . The grease composition according to  claim 8 , wherein the polymeric thickener comprises a first component and a second component, with the first component having a higher weight average molecular weight than the second component. 
     
     
         10 . The grease composition according to  claim 9 , wherein the polymeric thickener includes a high molecular weight component and a low molecular weight component, and wherein
 the thickener further comprises a mixture of (1) a (co- or homo-)polymer of propylene with a weight average molecular weight of more than 200.000 and (2) a (co- or homo-)polymer of propylene with a weight average molecular weight of less than 200.000.   
     
     
         11 . The grease composition according to  claim 10 , wherein the weight ratio between the high molecular weight component and the low molecular weight component is 1:40-1:5, preferably 1:25-1:15, more preferably 1:18-1:20. 
     
     
         12 . The grease composition according to  claim 11 , wherein the low molecular weight component is a polypropylene homopolymer. 
     
     
         13 . The grease composition according to  claim 12 , wherein the low molecular weight component has an average molecular weight between 20.000 and 100.000 and a melt flow rate of 500-1500, preferably 750-1250. 
     
     
         14 . The grease composition according to  claim 13 , wherein the high molecular weight component is a polypropylene homopolymer or a propylene/ethylene-copolymer. 
     
     
         15 . The grease composition according to  claim 14 , wherein the high molecular weight component has an average molecular weight of 200.000-350.000 and a melt flow rate of 1.5-15, preferably 1.5-7. 
     
     
         16 . The grease composition according to  claim 15 , wherein the metal salt is selected from the group consisting of naphtenates, octoate, carbamate, carboxamides, sulfonamides, stearates, hydroxystearates and any mixture thereof. 
     
     
         17 . The grease composition according to  claim 16 , wherein the metal salt is a stearate, a hydroxystearate or a mixture thereof. 
     
     
         18 . The grease composition according to  claim 17 , wherein the metal in the metal salt is selected from the group consisting of bismuth, zinc, sodium, calcium, magnesium, antimony, barium, manganese, silver, gold, copper and lead. 
     
     
         19 . The grease composition according to  claim 18 , wherein the metal in the metal salt is bismuth or zinc. 
     
     
         20 . The grease composition according to  claim 19 , further comprising an ester oil in an amount in the range of from 1-40 wt %, based on the total weight of the grease composition. 
     
     
         21 . The grease composition according to  claim 20  further comprising an inert powder in an amount in the range of from 1-10 wt %, based on the total weight of the grease composition. 
     
     
         22 . The grease composition according to  claim 21  further comprising at least one additive component which is selected from the group consisting of antioxidants, corrosion inhibitors, anti-wear agents and pressure tolerance-increasing additives, and
 wherein the total content of the additive component(s) is in the range between 0.2 and 15% by weight, and preferably between 1 and 8% by weight, based on the total weight of the grease composition. 
 
     
     
         23 . A mechanical component having a metal surface onto which a layer of a grease composition has been applied, the grease composition comprising:
 (a) a polymer thickened grease;   (b) an acid having a pKa in the range of 2-7 with the pKa being measured in water at 25° C.; and   (c) a metal salt.   
     
     
         24 . The mechanical component according to  claim 23 , further comprising providing a metal surface onto which a layer has formed comprising the metal of the metal salt. 
     
     
         25 . The mechanical component according to  claim 23  further comprising a bearing, bearing component or bearing application system. 
     
     
         26 . Use of a grease composition for reconditioning the lubrication of a mechanical component having a metal surface, the grease composition comprising:
 (a) a polymer thickened grease;   (b) an acid having a pKa in the range of 2 7 with the pKa being measured in water at 25° C.; and   (c) a metal salt.   
     
     
         27 . Use of the grease composition according to  claim 26 , further comprising for protecting a mechanical component having a metal surface against corrosion. 
     
     
         28 . Use of the grease composition according to  claim 26 , further comprising for protecting a mechanical component having a metal surface against wear. 
     
     
         29 . Use of the grease composition according to  claim 26 , further comprising for protecting a mechanical component having a metal surface against fretting. 
     
     
         30 . Use of the grease composition according to  claim 29 , wherein the mechanical component comprises a bearing, bearing component or bearing application system. 
     
     
         31 . A method for preparing a grease composition having a polymer thickened grease; an acid having a pKa in the range of 2-7 with the pKa is measured in water at 25° C.; and a metal salt, the method comprising the following steps:
 a) mixing the polymer thickened grease with the metal salt; and 
 b) adding to the mixture obtained in step (a) the acid. 
 
     
     
         32 . The method for preparing a grease composition according to  claim 31 , wherein in step (a) the metal salt is heated above its melting point. 
     
     
         33 . The method according to  claim 31 , further comprising additionally mixing during step (a) one or more anti-wear additives, anti-corrosion additives, anti-oxidants, inert powder(s) and/or other additives. 
     
     
         34 . The method according to  claim 33 , wherein a final mixing in step (a) is carried out using a three-roll mill or ball-mill.