Grease composition and sliding member coated therewith

1. A grease composition comprising:

(A) a perfluoropolyether that has a kinematic viscosity of 2-110 mm 2 /sec at 40° C. and that is represented by general formula (1)

RfO(CF 2 CF 2 O) m (CF 2 O) n Rf  (1)

where Rf is a C 1-4 perfluoro lower alkyl group, m and n are each an integer ≥0, the sum of m and n is 30-190, and the CF 2 CF 2 O and CF 2 O groups are randomly bonded in the main chain;

(B) a perfluoropolyether that has a kinematic viscosity of 2-100 mm 2 /sec at 40° C. and that is represented by general formula (2)

RfO(CF(CF 3 )CF 2 O) p (CF 2 O) r Rf  (2)

where Rf is a C 1-4 perfluoro lower alkyl group, p is a positive number, r is a number ≥0, the sum of p and r is 5-50, and the CF(CF 3 )CF 2 O and CF 2 O groups are randomly bonded in the main chain; and

(C) a fluororesin powder having a primary particle size ≤1 μm,

wherein the fluororesin powder content is 25-40 wt % based on the weight of the grease composition, and the perfluoropolyether (A) to perfluoropolyether (B) weight ratio is 15:85 to 70:30.

2. The grease composition as claimed in claim 1 , furthermore comprising (D) polyethylene and/or polypropylene particles having a viscosity-average molecular weight of 500,000-7,000,000 and a particle size ranging from 10-200 μm in an amount of 1.5-10 wt % based on the weight of the grease composition.

3. The grease composition as claimed in claim 1 , wherein the m/n ratio in general formula (1) is ≥1, and the p/r ratio in general formula (2) is ≥10.

4. The grease composition as claimed in claim 1 , wherein the fluororesin powder is obtained by emulsion polymerization.

5. A sliding member, the sliding surface of which is coated with the grease composition as claimed in claim 1 , wherein the oil film formed by the grease composition is ≥0.2 μm thick.

6. The sliding member as claimed in claim 5 , which operates at temperatures ranging from −40° C. to 200° C.

7. The sliding member as claimed in claim 5 , which is included as a part in an automobile or industrial machinery.

8. The sliding member as claimed in claim 5 , wherein the sliding member is a rotary sliding member.

9. A rotary sliding member comprising a metal member, a resin member, or a combination thereof, the sliding surface of which is provided with a lubrication coating comprising the grease composition as claimed in claim 1 to an oil film thickness of 0.25-0.50 μm.

10. The sliding member as claimed in claim 5 , wherein the grease composition furthermore comprises (D) polyethylene and/or polypropylene particles having a viscosity-average molecular weight of 500,000-7,000,000 and a particle size ranging from 10-200 μm in an amount of 1.5-10 wt % based on the weight of the grease composition.

11. The sliding member as claimed in claim 5 , wherein the m/n ratio in general formula (1) is ≥1, and the p/r ratio in general formula (2) is ≥10.

12. The sliding member as claimed in claim 5 , wherein the fluororesin powder is obtained by emulsion polymerization.

13. The rotary sliding member as claimed in claim 9 , wherein the grease composition furthermore comprises (D) polyolefin particles having a viscosity-average molecular weight of 500,000-7,000,000 and a particle size ranging from 10-200 μm in an amount of 1.5-10 wt % based on the weight of the grease composition.

14. The rotary sliding member as claimed in claim 9 , wherein the m/n ratio in general formula (1) is ≥1, and the p/r ratio in general formula (2) is ≥10.

15. The rotary sliding member as claimed in claim 9 , wherein the fluororesin powder is obtained by emulsion polymerization.

16. A grease composition comprising:

(A) a perfluoropolyether that has a kinematic viscosity of 2-110 mm 2 /sec at 40° C. and that is represented by general formula (1)

RfO(CF 2 CF 2 O) m (CF 2 O) n Rf  (1)

where Rf is a C 1-4 perfluoro lower alkyl group, m and n are each an integer ≥0, the sum of m and n is 30-190, and the CF 2 CF 2 O and CF 2 O groups are randomly bonded in the main chain;

(B) a perfluoropolyether that has a kinematic viscosity of 2-100 mm 2 /sec at 40° C. and that is represented by general formula (2)

RfO(CF(CF 3 )CF 2 O) p (CF 2 O) r Rf  (2)

where Rf is a C 1-4 perfluoro lower alkyl group, p is a positive number, r is a number ≥0, the sum of p and r is 5-50, and the CF(CF 3 )CF 2 O and CF 2 O groups are randomly bonded in the main chain; and

(C) a fluororesin powder having a primary particle size ≤1 μm,

wherein the fluororesin powder content is 25-40 wt % based on the weight of the grease composition, and the perfluoropolyether (A) to perfluoropolyether (B) weight ratio is 15:85 to 70:30, and

furthermore comprising (D) polyethylene and/or polypropylene particles having a viscosity-average molecular weight of 500,000-7,000,000.

17. The grease composition of claim 16 wherein the (D) polyethylene and/or polypropylene particles have a particle size from 10-200 μm and have a viscosity-average molecular weight of 1,000,000-3,000,000 and are present in an amount of 1.5-10 wt % based on the weight of the grease composition.

18. A grease composition comprising:

(A) a perfluoropolyether that has a kinematic viscosity of 85 mm 2 /sec at 40° C. that is present in an amount of from 14-27 wt % based on a total weight of the grease composition and that is represented by general formula (1)

RfO(CF 2 CF 2 O) m (CF 2 O) n Rf  (1)

where Rf is a C 1-4 perfluoro lower alkyl group, m and n are each an integer ≥0, the sum of m and n is 30-190, and the CF 2 CF 2 O and CF 2 O groups are randomly bonded in the main chain;

(B) a perfluoropolyether that has a kinematic viscosity of 56-80 mm 2 /sec at 40° C. that is present in an amount of from 40-56 wt % based on a total weight of the grease composition and that is represented by general formula (2)

RfO(CF(CF 3 )CF 2 O) p (CF 2 O) r Rf  (2)

where Rf is a C 1-4 perfluoro lower alkyl group, p is a positive number, r is a number ≥0, the sum of p and r is 5-50, and the CF(CF 3 )CF 2 O and CF 2 O groups are randomly bonded in the main chain; and

(C) a fluororesin powder having a primary particle size of 0.1-0.4 μm and present in an amount of 30-35 wt % based on the weight of the grease composition.

19. The grease composition of claim 18 further comprising (D) polyethylene and/or polypropylene particles having a viscosity-average molecular weight of 2,000,000 and a particle size of 22 μm and present in an amount of 2 wt % based on a total weight of the grease composition.

20. The grease composition of claim 19 wherein the (D) particles are further defined as polyethylene particles.