主权项 |
1. A modified polytetrafluoroethylene fine powder constituting a particle core and a particle shell,
wherein said particle core comprises a modified polytetrafluoroethylene (i) resulting from copolymerization with at least one modifier selected from the group consisting of a fluoro(alkyl vinyl ether) represented by the general formula (I):
F2C═CFO(CF2)n1X1 (I) (wherein X1 represents hydrogen atom or fluorine atom and n1 represents an integer of 1 to 6), and a fluoroolefin represented by the general formula (III):
CX4X5═CX6(CF2)n2F (III) (wherein X4, X5 and X6 each represents hydrogen atom or fluorine atom provided that at least one of them represents fluorine atom; and n2 represents an integer of 1 to 5) and the modifier-derived modifier unit content in the particle core is 0.01 to 0.5% by mass based on all the primary particles constituting the modified PTFE fine powder, said particle shell comprises a modified polytetrafluoroethylene (ii), wherein the modification in the modified polytetrafluoroethylene (ii) is carried out by using a chain transfer agent and by copolymerizing a fluoro (alkyl vinyl ether) represented by the general formula (I):
F2C═CFO(CF2)n1X1 (I) (wherein X1 represents hydrogen atom or fluorine atom and n1 represents an integer of 1 to 6) or a fluoroolefin represented by the general formula (III):
CX4X5═CX6(CF2)nF (III) (wherein X4, X5 and X6 each represents hydrogen atom of fluorine atom provided that at least one of them represents fluorine atom; and n2 represents an integer of 1 to 5) as a modifier, the chain transfer agent comprises at least one member selected from the group consisting of water-soluble alcohols containing 1 to 4 carbon atoms, hydrocarbons containing 1 to 4 carbon atoms and fluorinated hydrocarbons containing 1 to 4 carbon atoms, wherein the content of a modifier unit derived from the modifier in the particle shell is 0.005 to 0.5% by mass based on all primary particles constituting the modified PTFE fine powder, and said modified polytetrafluoroethylene fine powder has the cylinder extrusion pressure at a reduction ratio of 1600, using an extruder according to ASTM D 4895, of not higher than 50 MPa. |