Heat-resistant seal material, endless seal member using heat-resistant seal material, and downhole apparatus including endless seal member

1. A heat-resistant seal material comprising:

100 parts by weight of a ternary fluoroelastomer;

1 to 30 parts by weight of vapor-grown carbon fibers having an average diameter of more than 30 nm and 200 nm or less; and

carbon black having an average particle diameter of 25 to 500 nm,

the heat-resistant seal material containing the vapor-grown carbon fibers and the carbon black in an amount of 20 to 40 parts by weight in total, and having a compression set when subjected to a compression set test at a compression rate of 25% and a temperature of 200° C. for 70 hours of 0 to 15% and a dynamic modulus of elasticity at 200° C. (E′/200° C.) of 30 to 100 MPa.

2. The heat-resistant seal material as defined in claim 1 , wherein the vapor-grown carbon fibers have an average diameter of 67 to 176 nm.

3. The heat-resistant seal material as defined in claim 1 ,

wherein the vapor-grown carbon fibers are rigid fibers having an average bending index of 5 to 15, the bending index being defined by the following expression (1),

Bending index= Lx÷D   (1)

Lx: length of linear portion of the vapor-grown carbon fiber, and

D: diameter of the vapor-grown carbon fiber.

4. The heat-resistant seal material as defined in claim 1 , having a creep instantaneous strain determined by a creep test at a temperature of 260° C. and a load of 1 MPa of 0 to 5%, and having a creep rate per hour during a steady-state creep period of 20,000 ppm or less.

5. The heat-resistant seal material as defined in claim 4 , wherein the heat-resistant seal material does not break for 15 hours when subjected to the creep test.

6. The heat-resistant seal material as defined in claim 1 , comprising the vapor-grown carbon fibers in an amount of 3 to 20 parts by weight, and having a compression set when subjected to a compression set test at a compression rate of 25% and a temperature of 230° C. for 70 hours of 0 to 18% and a dynamic modulus of elasticity at 230° C. (E′/230° C.) of 29 to 70 MPa.

7. An endless seal member formed by using the heat-resistant seal material as defined in claim 1 and having an external shape without ends.

8. The endless seal member as defined in claim 7 , the endless seal member being an O-ring having a circular horizontal cross-sectional shape.

9. A downhole apparatus comprising the endless seal member as defined in claim 7 .