Composition for gas seal member and method of producing same, gas seal member for high-pressure hydrogen device, and high-pressure hydrogen device

A method of producing a composition for a gas seal member used in a high-pressure hydrogen environment, the method comprising:

• a slurry preparation step of preparing a slurry containing an elastomer, fibrous carbon nano structures, and a solvent or dispersion medium;
• a removal step of removing the solvent or dispersion medium from the slurry to obtain a mixture of elastomer and fibrous carbon nanostructures;
• and
• a kneading step including two or more and seven or fewer kneading operations of adding and kneading additional elastomer with the mixture of elastomer and fibrous carbon nanostructures after the removal step to obtain the composition for a gas seal member, wherein the kneading step includes two or more and seven or fewer kneading operations in which mass (A) of a mixture prior to elastomer addition and mass (B) of elastomer added to the mixture satisfy a relationship 0.45≤A/(A+B)<1, wherein
• the fibrous carbon nanostructures are contained in the composition for a gas seal member in a proportion of not less than 1 part by mass and not more than 10 parts by mass per 100 parts by mass of the elastomer, and
• an area fraction S, in units of %, of aggregates of the fibrous carbon nanostructures in a cross-section of the composition for a gas seal member and a volume percentage V, in units of volume %, of the fibrous carbon nanostructures in the composition for a gas seal member satisfy a relationship 0≤S/V≤2.0.