Sealing material for polymer electrolyte fuel-cell separator

Abstract

A sealing material comprising (A) an organopolysiloxane containing at least two alkenyl groups in a molecule, (B) a resinous copolymer composed mainly of R 3 SiO 1/2 and SiO 2 units in a molar ratio of 0.5-1.5:1, wherein R is a monovalent hydrocarbon group, and containing 5×10 −3 to 1×10 −4 mol/g of vinyl groups, (C) an organohydrogenpolysiloxane containing at least two Si—H groups in a molecule, (D) fumed silica having a specific surface area of 150-400 m 2 /g, and (E) an addition reaction catalyst is suited for sealing one side edge of a polymer electrolyte fuel-cell separator since it has excellent acid resistance and improved compression set in acidic solutions, and exerts satisfactory seal effects.

claims:  
     
         1 . A sealing material for sealing at least one side edge of a polymer electrolyte fuel-cell separator, comprising in parts by weight as essential components: 
 (A) 100 parts of an organopolysiloxane containing at least two alkenyl groups each attached to a silicon atom in a molecule,    (B) 5 to 50 parts of a resinous copolymer composed mainly of R 3 SiO 1/2  units and SiO 2  units in a molar ratio of 0.5:1 to 1.5:1, wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and containing 5×10 −3  to 1×10 −4  mol/g of vinyl groups,    (C) 0.5 to 20 parts, per 100 parts of components (A) and (B) combined, of an organohydrogenpolysiloxane containing at least two hydrogen atoms each attached to a silicon atom in a molecule,    (D) 10 to 30 parts, per 100 parts of components (A) and (B) combined, of fumed silica having a specific surface area of 150 to 400 m 2 /g, and    (E) a catalytic amount of an addition reaction catalyst.    
     
     
         2 . The sealing material of  claim 1  wherein a molar ratio of Si—H groups in component (C) to the total of silicon atom-bonded alkenyl groups in components (A) and (B) is 0.8:1 to 5.0:1.  
     
     
         3 . The sealing material of  claim 1  wherein the organopolysiloxane (A) has an average degree of polymerization of 100 to 2,000 and at least 90% of the entire organic groups attached to silicon atoms therein are methyl.