ANTIFRICTION COATING FOR MAINSPRING MADE OF COMPOSITE MATERIAL

1 - 24 . (canceled)

25 . A mainspring for a driving element for a timepiece movement, said mainspring being made of a material comprising a polymer matrix containing fibers, wherein said mainspring comprises a coating comprising a resin of epoxy type having a gel time which is greater than 20 min at 90° C.

26 . The mainspring according to claim 25 , wherein said thermosetting polymer of said polymer matrix comprises a resin of epoxy type.

27 . The mainspring according to claim 25 , wherein the fraction by volume of fibers in the polymer matrix is between 30% and 75% and preferably between 45% and 55%.

28 . The mainspring according to claim 25 , wherein the fibers are oriented unidirectionally in the polymer matrix.

29 . The mainspring according to claim 25 , wherein the fibers have an axial elasticity modulus of between 80 GPa and 600 GPa.

30 . The mainspring according to claim 25 , wherein the fibers comprise type S or type S2 glass fibers.

31 . The mainspring according to claim 25 , wherein the angle between the axis of each fiber and the axis of the spring is between 0° and 5°.

32 . The mainspring according to claim 25 , wherein the fibers have a diameter of between 1 μm and 35 μm.

33 . The mainspring according to claim 25 , wherein the matrix additionally comprises nanoparticles.

34 . The mainspring according to claim 33 , wherein said nanoparticles comprise silica or fullerenes.

35 . The mainspring according to claim 25 , wherein the coating has a thickness of between 3 μm and 20 μm.

36 . A driving element for a timepiece movement comprising a mainspring being made of a material comprising a polymer matrix containing fibers, said mainspring comprising a coating containing a resin of epoxy type having a gel time which is greater than 20 min at 90° C.

37 . A timepiece comprising a driving element comprising a mainspring being made of a material comprising a polymer matrix containing fibers, said mainspring comprising a coating containing a resin of epoxy type having a gel time which is greater than 20 min at 90° C.

38 . A process for producing a mainspring being made of a material comprising a polymer matrix containing fibers, said mainspring comprising a coating containing a resin of epoxy type having a gel time which is greater than 20 min at 90° C., the process comprising:

providing the mainspring made of a material comprising a polymer matrix comprising fibers;

coating the mainspring with a composition comprising a polymer;

homogenizing the thickness of the composition coating the mainspring; and

polymerizing the composition in order to form the coating.

39 . The process according to claim 38 , wherein the homogenization step comprises the rotation of the mainspring coated with the composition along axes of rotation oriented in the three orthogonal dimensions X, Y and Z.

40 . The process according to claim 38 , wherein the homogenization step comprises the rotation of the mainspring coated with the composition along an axis of rotation oriented with an angle of between 10° and 80° from the plane of winding of the mainspring.

41 . The process according to claim 38 , wherein the step of polymerization of the composition comprises the heating of the mainspring coated with the composition.

42 . The process according to claim 38 , wherein coating the mainspring comprises a step of immersion of the spring in the composition, or a step of spray coating, or a step of vapor-phase deposition.

43 . The process according to claim 38 , further comprising a step of polishing the coating so as to leave the coating with a thickness at least equal to a quarter of the width of a fiber of said fibers.

44 . The process according to claim 43 , the polishing step leaves the coating with a thickness of between 3 μm and 20 μm.