Carbon fiber composite material and method of producing the same

1. A method of producing a carbon fiber composite material comprising:

(a) masticating an elastomer, the elastomer in uncrosslinked form having a first spin-spin relaxation time (T 2 n ), measured at 30° C. by a Hahn-echo method using a pulsed NMR technique with 1 H as an observing nucleus, of 100 to 3000 microseconds, to reduce the molecular weight of the elastomer to obtain a liquid elastomer;

(b) mixing the elastomer obtained in the step (a) and carbon nanofibers having an average diameter of 0.5 to 500 nm to obtain a mixture;

(c) increasing the molecular weight of the elastomer in the mixture obtained in the step (b) to obtain a rubbery elastic mixture; and

(d) mixing the rubbery elastic mixture obtained in the step (c) to disperse the carbon nanofibers in the elastomer by a shear force to obtain a carbon fiber composite material.

2. The method of producing a carbon fiber composite material as defined in claim 1 ,

wherein the liquid elastomer obtained in the step (a) in uncrosslinked form has a first spin-spin relaxation time (T 2 n ), measured at 30° C. by the Hahn-echo method using the pulsed NMR technique with 1 H as an observing nucleus, of greater than 3000 microseconds; and

wherein the rubbery elastic mixture obtained in the step (c) has a first spin-spin relaxation time (T 2 n ), measured at 30° C. by the Hahn-echo method using the pulsed NMR technique with 1 H as an observing nucleus, of 3000 microseconds or less.

3. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the first spin-spin relaxation time (T 2 n ) of the liquid elastomer obtained in the step (a) is 5 to 30 times the first spin-spin relaxation time (T 2 n ) of the elastomer before mastication in the step (a).

4. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the first spin-spin relaxation time (T 2 n ) of the rubbery elastic mixture obtained in the step (c) is 0.5 to 10 times the first spin-spin relaxation time (T 2 n ) of the elastomer before mastication in the step (a).

5. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the first spin-spin relaxation time (T 2 n ) of the carbon fiber composite material obtained in the step (d) is shorter than the first spin-spin relaxation time (T 2 n ) of the rubbery elastic mixture obtained in the step (c).

6. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the carbon fiber composite material in uncrosslinked form has a first spin-spin relaxation time (T 2 n ), measured at 150° C. by the Hahn-echo method using the pulsed NMR technique with 1 H as an observing nucleus, of 100 to 3000 microseconds, and a fraction (fnn) of components having a second spin-spin relaxation time (T 2 nn ) of less than 0.2.

7. The method of producing a carbon fiber composite material as defined in claim 1 , the method further comprising: (e) crosslinking the carbon fiber composite material obtained in the step (d).

8. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the molecular weight of the elastomer is increased in the step (c) by heating the mixture obtained in the step (b).

9. The method of producing a carbon fiber composite material as defined in claim 1 , wherein the step (d) is performed by an open-roll method with a roll distance of 0.5 mm or less.

10. The method of producing a carbon fiber composite material as defined in claim 9 , wherein a roll temperature is set at 0 to 50° C. in the step (d).