Fluorinated copolymer composition, crosslinked rubber and method for its production

A fluorinated copolymer composition, comprising:

• a crosslinking agent;
• a crosslinking co-agent;
• and
• a fluorinated copolymer having units based on tetrafluoroethylene, units based on a perfluoro (alkyl vinyl ether), and units based on formula (2), (CR1R2═CR3)aR4 where each of R1, R2 and R3 independently is a hydrogen atom, a fluorine atom or a methyl group, a represents an integer of from 2 to 6, and R4 is an a-valent C1-10 perfluorohydrocarbon group or a group having an etheric oxygen atom at a terminal or between carbon-carbon atoms of the perfluorohydrocarbon group,
• wherein in the fluorinated copolymer, a content of the units based on tetrafluoroethylene is from 69 to 90 mol % based on a total number of moles of units of the fluorinated copolymer, a content of the crosslinking agent is from 0.03 to 0.7 part by mass to 100 parts by mass of the fluorinated copolymer, a content of the crosslinking co-agent is from 0.1 to 2.5 parts by mass to 100 parts by mass of the fluorinated copolymer, and a content of the units based on the formula (2) is from 0.03 to 0.5 mol % based on a total number of moles of units of the fluorinated copolymer.