Process for preparing lubricating greases based on polytetrafluoroethylene and perfluoropolyethers

Claim 1

A process for preparing a lubricating grease based on polytetrafluoroethylene and on a liquid dispersant selected from the group consisting of the oligomers of trifluorochloroethylene and the perfluoropolyethers, comprising the following working steps: (a) heating, under reduced pressure, a polytetrafluoroethylene having a molecular weight of from 500,000 to 1,000,000, consisting of particles of the aggregated type, to remove air and volatile products; (b) heating, under reduced pressure, a compound selected from the group consisting of oligomers of trifluorochloroethylene having a viscosity, at 20° C., of from 100 to 1,000 cst and perfluoropolyethers belonging to the classes of general formulae: X--O--(C.sub.3 F.sub.6 O).sub.M (CF.sub.2 O).sub.n --Y (I) A--O--(C.sub.2 F.sub.4 O).sub.p (CF.sub.2 O).sub.q --B (II) A--O--(C.sub.2 F.sub.4 O).sub.r (CF.sub.2 O).sub.s (C.sub.t F.sub.2t O).sub.u --B (III) wherein: X and Y are a terminal group --CF 3 or --C 2 F 5 , m and n are integers, m+n=10-100, m/n=10-50, A and B are terminal groups --CF 3 , --C 2 F 5 , --CF 2 Cl, --CF 2 CF 2 Cl, p and q are integers, p+q=10-200, p/q=0.1-10, r+s+u=10-3,000, ##EQU2## r/s=0.1-10, t≅3, and having a viscosity, at 20° C., ranging from 20 to 4,000 cs if belonging to class (I) from 50 to 6,000 cs if belonging to class (II) and from 40 to 30,000 cs if belonging to class (III), and with a perfluorinated surfactant of the anionic type, characterized by a perfluoroalkylene chain or by a perfluorooxyalkylene chain, (c) mixing, under reduced pressure, the polytetrafluoroethylene coming from step (a) with the oligomer of trifluorochloroethylene or the perfluoropolyether containing the perfluorinated surfactant, coming from step (b), to obtain a mix containing from 15 to 40% by weight of polytetrafluoroethylene, from 60% to 85% by weight of oligomer of trifluorochloroethylene or perfluoropolyether, and from 0.1% to 0.4% by weight of surfactant.