Fluorinated greases having a low torque at low temperatures

Abstract

Fluorinated greases comprising: (A) from 1% to 50% by weight of a thickener; (B) from 99% to 50% by weight of a mixture of: (B1) from 0, 1 to 100% by weight of a compound of structure: X 1 —O(CF 2 O)n(CF 2 CF 2 O) m (CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q —X 2   (I) wherein: X 1 , X 2 have formula —(CF 2 ) Z CF 3 wherein z is an integer between 0 and 3; n is an integer between 1 and 200; m is an integer between 0 and 200; p, q are integers between 0 and 10; with the proviso that: the (p+q)/(p+q+m+n)≦0.05; m/n≦0.7; the number average molecular weight of (I) is between 1,000 and 10,000; the kinematic viscosity at 40° C. is lower than 20 cSt; and (B2) from 99.9% to 0% by weight of a perfluoropolyether oil having a kinematic viscosity at 40° C. higher than 15 cSt and comprising repeating units of the type (CFXO) wherein X is F or CF 3 ; —CF 2 CF 2 O—, —C 3 F 6 O, —CF(CF 3 ) CF 2 O, —CF 2 CF (CF 3 ) O—, statistically distributed along the chain.

1 . Fluorinated greases comprising  
     from (% by weight): 
 (A) 1% to 50%, preferably from 10% to 40%, of one or more thickeners;  
 (B) 99% to 50%, preferably from 90% to 60%, of a mixture of the following perfluoropolyethers: 
 (B1) 0.1% to 100%, preferably from 5% to 100%, of a perfluoropolyether having the following formula:  
   X 1 —O(CF 2 O) n (CF 2 CF 2 O) m (CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q —X 2   (I)  wherein: 
 the repeating units —CF 2 O—, —CF 2 CF 2 O—, —CF 2 CF 2 CF 2 O—, —CF 2 CF 2 CF 2 CF 2 O— are statistically distributed along the backbone;  
 —X 1  and —X 2  are perfluoroalkyl chain end groups equal to or different from each other, having formula —(CF 2 ) z CF 3  wherein z is an integer from 0 to 3;  
 n is an integer between 1 and 200,  
 m is an integer between 0 and 200,  
 p, q are integers between 0 and 10, preferably between 0 and 5, more preferably between 0 and 1;  
   with the proviso that: 
 the ratio (p+q)/(p+q+m+n) is lower than or equal to 0.05, or also 0;  
 the ratio m/n, (when n is different from 0), is lower than or equal to 0.7, preferably lower than 0.5, more preferably lower than 0.35;  
 the number average molecular weight of the compound of formula (I) is between 1,000 and 10,000, preferably between 2,000 and 8,000, more preferably between 2,400 and 5,000;  
 the kinematic viscosity, at 40° C., is lower than 20 cSt; and  
 the chlorine atoms, determined by  19 F NMR, are substantially absent;  
   
 (B2) 99.9% to 0%, preferably from 95% to 0%, of a perfluoropolyether oil having a kinematic viscosity at 40° C. higher than 15 cSt and comprising repeating units of the type (CFXO) wherein X is F or CF 3 ; —CF 2 CF 2 O—, —CF (CF 3 ) CF 2 O—, —CF 2 CF(CF 3 )O—, statistically distributed along the backbone;  
 and optionally  
 (C) 0% to 1.0% with respect to the total weight of (A)+(B), preferably from 1% to 3%, of one or more additives selected from anti-wear additives for high or low loads, anti-rust, antioxidant additives, stabilizers.  
 
 
   
   
       2 . Greases according to  claim 1 , wherein the thickener (A) is selected from the known thickeners of the prior art, for example talc, silica, polytetrafluoroethylene (PTFE), or their mixtures.  
   
   
       3 . Greases according to  claim 1 , wherein the thickener is silica, in amounts ranging from 1 to 10% by weight with respect to the total weight of (A)+(B).  
   
   
       4 . Greases according to  claim 1 , wherein the thickener is talc or PTFE, in amounts ranging from 5% to 40% by weight, more preferably from 5% to 35%, with respect to the total (A)+(B).  
   
   
       5 . Greases according to  claim 4 , wherein the thickener is PTFE, more preferably PTFE having an average particle size between 0.01 μm and 0.3 μm.  
   
   
       6 . Greases according to  claim 1 , wherein component (B2) is selected from the following classes 
 (1) E-O— (CF 2 CF(CF 3 )O) m′ (CFXO) n′ -E′   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 both the end groups being replaceable with Cl and/or H;    m′ and n′ are integers such that the m′/n′ ratio is between 20 and 1,000, n′ being different from zero; the units being statistically distributed along the backbone, the viscosity of the product being as above;    (2) C 3 F 7 O(CF (CF 3 ) CF 2 O) o′ -D    wherein:    D is equal to —C 2 F 5  or —C 3 F 7 , one fluorine atom of one or both the end groups being replaceable with C1 and/or H;    o′ is an integer such that the viscosity of the product is as above;    (3) {C 3 F 7 O—(CF(CF 3 ) CF 2 O) p′ —CF(CF 3 )—} 2      wherein:    p′ is an integer such that the viscosity of the product is as above, one F atom of one or both the end groups C 3 F 7  being replaceable with Cl and/or H;    (4) E-O— (CF 2 CF(CF 3 )O) q , (C 2 F 4 O) r , (CFX) s , -E′   wherein:    X is equal to F or CF 3 ;    E and E′, equal to or different from each other, are as above;    q′, r′ and s′ are integers including 0, and such that the viscosity of the product is as above;    (5) E-O—(C 2 F 4 O) t′ (CF 2 O) u′ -E′   wherein:    E and E′, equal to or different from each other, are as above;    t′ and u′ are integers such that the ratio t′/u′ is between 0.1 and 5, u′ being different from 0, and the viscosity of the product is as above;    (6) E-O—(CF 2 CF 2 CF 2 O) v′ -E′   wherein:    E and E′, equal to or different from each other, are as above;    v′ is a number such that the viscosity of the product is as above;    (7) D-O—(CF 2 CF 2 O) z , -D′   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 both the end groups being replaceable with C1 and/or H;    z′ is an integer such that the viscosity of the product is as above;    (8) E 1 -O(CF 2 O) n (CF 2 CF 2 O) m —(CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q -E 2      wherein:    E 1  and E 2  are perfluoroalkyl end groups, equal to or different from each other, having formula —(CF 2 ) z CF 3  wherein z is an integer from 0 to 3;    n, m, p, q are integers equal to or different from each other between 0 and 100 and selected so that the viscosity of the oil is as above and such that the ratio m/n is between 2 and 20, n being different from 0;    (p+q)/(n+m+p+q) is between 0.05 and 0.2, (n+m+p+q) being different from 0;    n/(n+m+p+q) is between 0.05 and 0.40, (n+m+p+q) being different from 0.    
   
   
       7 . Greases according to  claim 6 , wherein component (B2) is selected from the classes (1), (4), (5), (8) or their mixtures, more preferably from the classes (5) and (8) or their mixtures.  
   
   
       8 . Greases according to  claim 1  comprising additives commonly used in the lubrication field, preferably anti-wear additives for high and low loads, anti-rust, antioxidant additives and/or stabilizers, in an amount not higher than 10% by weight with respect to the total composition.  
   
   
       9 . Greases according to  claim 8 , wherein the stabilizing additives are selected from the perfluoropolyether dinitro derivative compounds and the perfluoropolyether pyridine derivatives.  
   
   
       10 . Greases according to  claim 8 , wherein the anti-wear additives are selected from molybdenum sulphide, molybdenum organic compounds, boron nitride, graphite, phosphazene derivatives, preferably phosphazene derivatives containing perfluoropolyether chains.  
   
   
       11 . Greases according to  claim 8 , wherein the anti-rust additives are selected from disodic sebacate, sodium carbonate, functionalized derivatives of carboxylic acids containing perfluoro-polyether chains.  
   
   
       12 . A process for preparing the greases of  claim 1 , comprising the following steps: 
 feeding of the oil and/or mixture of lubricating oils (B1), (B2), in a mixer and degassing under vacuum at 60° C. for 2 hours at 0.1 mbar;    gradual addition of component (A) (thickener) until reaching the desired composition;    optional addition of component (C) (additive): when the additive is liquid it is premixed with the basic oil or in the mixture before adding the thickener; when the additive is solid, it is premixed with the thickener powder before the gradual addition to the basic oil or to the mixture;    constant stirring for at least 8 hours under vacuum;    discharge of the obtained grease and its refining by passage on tri-roller refiner.    
   
   
       13 . Use of the greases of  claim 1  for the lubrication at temperatures lower than −40° C., preferably lower than −60° C., for applications in the aerospace and refrigeration industry.  
   
   
       14 . Use according to  claim 13  at temperatures from −40° C. to −80° C., wherein component B) is formed of an oil mixture, wherein the oil (B1) is present up to at most 50% by weight with respect to the oil (B2), preferably up to 30%, and the kinematic viscosity of the mixture is preferably lower than 40 cSt, more preferably lower than 35 cSt.  
   
   
       15 . Use according to  claim 13  at temperatures lower than −80° C. wherein component (B) of the grease is formed of the oil (B 1 ).  
   
   
       16 . Use of the greases of  claim 6  for the lubrication in applications having temperature ranges between −100 and +180° C. wherein the oil (B2) is that of the class (8).