To provide a charge retention medium having a surface potential at a practical level, although it is obtained from a composition containing a fluorinated copolymer having repeating units based on tetrafluoroethylene and repeating units based on ethylene.
A charge retention medium (electret 30) which is obtained from a composition containing a fluorinated copolymer (A) having repeating units based on tetrafluoroethylene and repeating units based on ethylene; and at least one charge aid (B) selected from the group consisting of a compound having at least one amino group and at least one reactive functional group (excluding an amino group) and a compound having at least two amino groups and having no reactive functional group (excluding an amino group).
To provide a process for producing a charge retention medium, with which a coating film (precursor of a charge retention medium) containing a fluorinated copolymer having repeating units based on tetrafluoroethylene and repeating units based on ethylene can easily be formed on the surface of a substrate, even in a case where the surface of the substrate has a complicated shape.
A process for producing a charge retention medium (electret 30), which comprises a step of applying a coating composition containing a fluorinated copolymer (A) having repeating units based on tetrafluoroethylene and repeating units based on ethylene, and an organic solvent (C), to a substrate (first substrate 10) to form a coating film.