Separator for solid polymer fuel cells, and production process thereof

1. A solid polymer fuel cell separator that is molded or formed of a resin composition comprising (A) 25 to 65% by mass of a thermoplastic resin, (B) 25 to 65% by mass of a conductive carbon black having a bulk density of at least 0.3 g/ml and a DBP oil absorption of up to 100 ml/100 g, and (C) 2 to 35% by mass of at least one conductive filler selected from the group consisting of carbon fiber and graphite and having a volume resistivity of less than 1 Ω·cm, wherein said solid polymer fuel cell separator has a volume resistivity of 0.001 to 1 Ω·cm and a bending strength of at least 40 MPa.

2. The solid polymer fuel cell separator according to claim 1 , wherein said thermoplastic resin (A) is at least one thermoplastic resin selected from the group consisting of a polyolefin, a poly (arylene sulfide), a liquid crystal polymer, a poly (vinylidene fluoride), a thermoplastic polyester, a polyamide, a polyacetal, a polycarbonate, a poly (vinyl chloride) and a poly (ether ether ketone).

3. The solid polymer fuel cell separator according to claim 1 , wherein said thermoplastic resin (A) is at least one thermoplastic resin selected from the group consisting of a polypropylene, a poly (phenylene sulfide), a liquid crystal polymer and a poly (vinylidene fluoride).

4. The solid polymer fuel cell separator according to claim 1 , wherein said conductive carbon black (B) has a bulk density of at least 0.4 g/ml.

5. The solid polymer fuel cell separator according to claim 1 , wherein said conductive carbon black (B) has a bulk density of at least 0.45 g/ml.

6. The solid polymer fuel cell separator according to claim 1 , wherein said resin composition contains an additive having solid lubricating properties in a proportion of up to 10% by mass.

7. The solid polymer fuel cell separator according to claim 1 , wherein said thermoplastic resin (A) is used in a proportion of 30 to 55% by mass.

8. The solid polymer fuel cell separator according to claim 1 , wherein said conductive carbon black (B) is used in a proportion of 30 to 63% by mass.

9. The solid polymer fuel cell separator according to claim 1 , wherein said conductive filler (C) is used in a proportion of 3 to 30% by mass.

10. The solid polymer fuel cell separator according to claim 1 , wherein said solid polymer fuel cell separator has a volume resistivity of 0.01 to 0.3 Ω·cm and a bending strength of at least 50 MPa.

11. A process for producing a solid polymer fuel cell separator by injection molding of a resin composition comprising (A) 25 to 65% by mass of a thermoplastic resin, (B) 25 to 65% by mass of a conductive carbon black having a bulk density of at least 0.3 g/ml and a DBP oil absorption of up to 100 ml/100 g, and (C) 2 to 35% by mass of at least one conductive filler selected from the group consisting of carbon fiber and graphite and having a volume resistivity of less than 1 Ω·cm. wherein a solid polymer fuel cell separator having a volume resistivity of 0.001 to 1 Ω·cm and a bending strength of at least 40 MPa is obtained.

12. The production process according to claim 11 , wherein upon injection molding of said resin composition, a mixture of 1 to 900 parts by weight of a fluid having a boiling point of up to 250° C. with 100 parts by weight of said resin composition is injection molded, while said fluid is discharged out of a mold in an injection molding machine.

13. The production process according to claim 12 , wherein a mixture of a pellet of said resin composition with said fluid is injected into said mold in said injection molding machine, wherein said fluid is discharged through a gas vent in said mold.

14. The production process according to claim 12 , wherein said fluid is an amide compound, an N-alkylpyrrolidone compound, an N-cycloalkylpyrrolidone compound, an N,N-dialkylimidazolidinone compound, a tetraalkylurea compound or a hexaalkylphosphoric triamde compound.

15. The production process according to claim 14 , wherein said N-alkylpyrrolidone compound is N-methyl-2-pyrrolidone.

16. The production process according to claim 11 , wherein said thermoplastic resin (A) is at least one thermoplastic resin selected from the group consisting of a polyolefin, a poly (arylene sulfide), a liquid crystal polymer, a poly (vinylidene fluoride), a thermoplastic polyester, a polyamide, a polyacetal, a polycarbonate, a poly (vinyl chloride) and a poly (ether ether ketone).

17. The production process according to claim 16 , wherein said thermoplastic resin (A) is at least one thermoplastic resin selected from the group consisting of a polypropylene, a poly (phenylene sulfide), a liquid crystal polymer and a poly (vinylidene fluoride).

18. The production process according to claim 11 , wherein said conductive carbon black (B) has a bulk density of at least 0.4 g/ml.

19. The production process according to claim 11 , wherein said conductive carbon black (B) has a bulk density of at least 0.45 g/ml.

20. The production process according to claim 11 , wherein said thermoplastic resin (A) is used in a proportion of 30 to 55% by mass.

21. The production process according to claim 11 , wherein said conductive carbon black (B) is used in a proportion of 30 to 63% by mass.

22. The production process according to claim 11 , wherein said conductive filler (C) is used in a proportion of 3 to 30% by mass.

23. The production process according to claim 11 , wherein said resin composition contains an additive having solid lubricating properties in a proportion of upto 10% by mass.

24. The production process according to claim 11 , wherein a solid polymer fuel cell separator having a volume resistivity of 0.01 to 0.3 Ω·cm and a bending strength of at least 50 MPa is obtained.