Lubricating greases

Abstract

Lubricating greases comprising: A) from 65.1 to 95% by weight of a (per)fluoropolyether oil having a viscosity at 20° C. in the range 20-2,000 cSt; B) from 5 to 34.9% by weight of powder of polytetrafluoroethylene or of a tetrafluoroethylene copolymer with another monomer having an ethylene type unsaturation, said powder obtainable by coagulation with an electrolyte of an aqueous latex containing polymeric particles having sizes comprised between 5 and 100 nm, wherein the grease has a surfactant content lower than 20 ppm and a water content lower than 100 ppm.

1 . (Per)fluoropolyether lubricating greases comprising: 
 A) from 65.1 to 95% by weight of a (per)fluoropolyether oil having a viscosity at 20° C. in the range 20-2,000 cSt;    B) from 5 to 34.9% by weight of polytetrafluoroethylene or of a tetrafluoroethylene copolymer powder with another monomer having an ethylene type unsaturation, said polymers having a number average molecular weight in the range 20,000-1,000,000, preferably 40,000-800,000, said powder obtainable by coagulation with an electrolyte of an aqueous latex containing polymeric particles having sizes in the range 5-100 nm, preferably 10-60 nm formed of polytetrafluoroethylene or of a tetrafluoroethylene copolymer with another monomer having an ethylene type unsaturation, having a number average molecular weight in the range 20,000-1,000,000, preferably 40,000-800,000, and subsequent drying,    wherein the grease has a surfactant content lower than 20 ppm and a water content lower than 100 ppm, preferably lower than 60 ppm.    
     
     
         2 . Greases according to  claim 1 , wherein the drying to obtain component B) is carried out at a temperature in the range 105° C.-190° C., preferably 110-140° C.  
     
     
         3 . Greases according to  claim 1 , wherein component B) is in the form of powder particle aggregates having an average size between 10 and 30 micron.  
     
     
         4 . Greases according to  claim 1 , wherein the perfluoropolyether oils of component A) are selected from the following classes: 
         E—O—(CF(CF 3 )CF 2 O) m′ (CFXO) n′ —E′  (1) 
       wherein: 
 X is equal to F or CF 3 ;  
 E and E′, equal to or different from each other, are selected from CF 3 , C 2 F 5  or C 3 F 7 , one fluorine atom of one or of both end groups can be substituted by Cl and/or H;  
 m′ and n′ are integers such that the m′/n′ ratio is in the range 20-1,000 and the product viscosity be between 10 and 4,000 cSt; the various units are statistically distributed along the chain; 
   C 3 F 7 O(CF(CF 3 )CF 2 O) o′ —D  (2) 
 wherein:  
 D is equal to —C 2 F 5  or —C 3 F 7 , one fluorine atom of one or of both end groups can be substituted by Cl and/or H;  
 o′ is an integer such that the product viscosity is within the above range; 
   {C 3 F 7 O—(CF(CF 3 )CF 2 O) p′ —CF(CF 3 )—} 2   (3) 
 wherein:  
 p′ is an integer such that the compound viscosity is within the above range, one F atom of one or of both end groups C 3 F 7  can be substituted by Cl and/or H. 
   E—O—(CF(CF 3 )CF 2 O) q′ (C 2 F 4 O) r′ (CFX) s′ —E′  (4) 
 wherein:  
 X is equal to F or CF 3 ;  
 E and E′, equal to or different from each other, are as above defined;  
 q′, r′ and s′ are integers and can also have the 0 value, and such that the product viscosity is within the above range. 
   E—O—(C 2 F 4 O) t′ (CF 2 O) u′ —E′  (5) 
 wherein:  
 E and E′, equal to or different from each other, are as above;  
 t′ and u′ are integers such that the t′/u′ ratio is between 0.1 and 5 and the product viscosity is within the above range. 
   E—O—(CF 2 CF 2 CF 2 O) v′ —E′  (6) 
 wherein:  
 E and E′, equal to or different from each other, are as above;  
 v′ is a number such that the product viscosity is within the above range. 
   D—O—(CF 2 CF 2 O) z′ —D′  (7) 
 wherein:  
 D and D′, equal to or different from each other, are selected from C 2 F 5  or C 3 F 7 , one fluorine atom of one or of both end groups can be substituted by Cl and/or H;  
 z′ is an integer such that the product viscosity is within the above range.  
 
     
     
         5 . Greases according to  claim 4 , wherein the perfluoropolyether oils of component A) are selected from the classes (1), (4), (5) or their mixtures.  
     
     
         6 . Greases according to  claim 1 , wherein component B) is a TFE copolymer with 0.01-1% by weight of a comonomer having an ethylene type unsaturation.  
     
     
         7 . Greases according to  claim 6 , wherein the comonomer having an ethylene type unsaturation is selected from the olefinic, acrylic and styrene comonomers, preferably ethylene, propylene, methylmethacrylate, (metha)acrylic acid, butylacrylate, hydroxyethylhexylacrylate, styrene; C 3 -C 8  pefluoroolefins, preferably hexafluoropropene (HFP); C 2 -C 8  fluoroolefins containing hydrogen, preferably vinyl fluoride (VF), vinylidene fluoride (VDF), trifluoroethylene, hexafluoroisobutene, perfluoroalkylethylene CH 2 ═CH—R f , wherein R f  is a C 1 -C 6  perfluoroalkyl; C 2 -C 8  chloro- and/or bromo- and/or iodo-fluoroolefins, preferably chlorotrifluoroethylene (CTFE); (per)fluoroalkylvinylethers (PAVE) CF 2 ═CFOR f , wherein R f  is a C 1 -C 6  (per)fluoroalkyl, for example CF 3 , C 2 F 5 , C 3 F 7 , preferably perfluoropropyl-vinylether (PVE); (per)fluorooxyalkylvinylethers CF 2 ═CFOX, wherein X is: a C 1 -C 12  alkyl, or a C 1 -C 12  oxyalkyl, or a C 1 -C 12  (per)fluorooxy-alkyl having one or more ether groups, preferably perfluoro-2-propoxy-propyl; fluorodioxoles, preferably perfluorodioxoles; fluorovinylethers CFX═CXOCF 2 OR (MOVE) wherein X═F, H, and R is a C 2 -C 6  (per)fluoroalkyl or C 5 -C 6  cyclic group, or a C 2 -C 6  (per)fluorooxyalkyl group containing from one to three oxygen atoms, preferably perfluoro-3,5-dioxa-1-heptene CF 2 ═CF—O—CF 2 —O—CF 2 CF 3  (MOVE 1) and perfluoro-3,5,8-trioxa-1-nonene CF 3 OCF 2 CF 2 OCF 2 OCF═CF 2  (MOVE 2).  
     
     
         8 . Greases according to  claim 7 , wherein the comonomer is selected from perfluoropropyl-vinylether (PVE) and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD).  
     
     
         9 . Greases according to  claim 1 , wherein the coagulation electrolyte to obtain component B) is an inorganic acid or an inorganic salt selected from nitric acid, hydrochloric acid, sulphuric acid, potassium nitrate, ammonium carbonate, magnesium sulphate, aluminum sulphate, potassium carbonate, calcium nitrate, sodium chloride, preferably nitric acid or ammonium carbonate.  
     
     
         10 . A process for the preparation of the (per)fluoropolyether greases of  claim 1 , comprising the following steps: 
 a) introduction of the lubricating oil A) in a mixer;    b) gradual addition in a continuous way or by step of the powder of component B) to the oil;    c) slurry stirring;    d) discharge and refining of the obtained grease.    
     
     
         11 . A process according to  claim 10 , wherein in step a), after the introduction of the (per)fluoropolyether oil A) in the mixer, a degassing under vacuum at 60° C. for 2 hours at 0.1 mbar is carried out.  
     
     
         12 . A process according to  claim 10 , wherein in step b), in the addition of the powder of component B) to the oil is carried out in at least 3 hours.  
     
     
         13 . A process according to  claim 10 , wherein in step c), in the stirring is carried out in a constant way, for about 8 hours, under vacuum.  
     
     
         14 . A process according to  claim 10 , wherein the refining of step d) is carried out in a three cylinder refiner.  
     
     
         15 . Use of the greases according to  claim 1  in the lubrication of mechanical parts.  
     
     
         16 . Use of the greases according to  claim 15 , in the lubrication of bearings working at high speed and in a large temperature range.  
     
     
         17 . Use of the greases according to  claim 15  in the lubrication of microbearings, microgears, in plastic, preferably mechanical actuators.