Electret and electrostatic induction conversion device

1 . An electret containing a fluoropolymer which comprises at least one repeating unit selected from the group consisting of a repeating unit represented by the following formula (a), a repeating unit represented by the following formula (b) and a repeating unit represented by the following formula (c), in a total amount of at least 80 mol % based on all repeating units, and which has a glass transition temperature of from 110 to 350° C.:

wherein each of X 1 to X 4 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group; one of a and b is 0 and the other is 1, and a+b=1; and c is an integer of from 0 to 3; provided that when X 1 and X 2 are, respectively, present in plurality, such a plurality of X 1 and a plurality of X 2 may, respectively, be the same or different;

wherein each of Y 1 to Y 3 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group, provided that Y 2 and Y 3 may be bonded to each other to form a fluorinated alicyclic ring;

wherein each of Z 1 to Z 4 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group.

2 . An electret containing a fluoropolymer which comprises at least one repeating unit selected from the group consisting of a repeating unit represented by the following formula (a1), a repeating unit represented by the following formula (b) and a repeating unit represented by the following formula (c), in a total amount of at least 80 mol % based on all repeating units:

wherein each of X 11 to X 14 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group, provided that at least one of X 11 to X 14 is a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group; one of d and e is 0 and the other is 1; and f is an integer of from 0 to 3; provided that when X 11 and X 12 are, respectively, present in plurality, such a plurality of X 11 and a plurality of X 12 may, respectively, be the same or different;

wherein each of Y 1 to Y 3 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group, provided that Y 2 and Y 3 may be bonded to each other to form a fluorinated alicyclic ring;

wherein each of Z 1 to Z 4 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group.

3 . An electret containing a fluoropolymer which comprises a repeating unit represented by the following formula (a2), and a repeating unit represented by the following formula (b) and/or a repeating unit represented by the following formula (c), wherein the total amount of the repeating unit represented by the formula (b) and the repeating unit represented by the formula (c) is at least 2 mol % based on all repeating units:

wherein one of g and h is 0 and the other is 1; and i is an integer of from 0 to 3;

wherein each of Y 1 to Y 3 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group, provided that Y 2 and Y 3 may be bonded to each other to form a fluorinated alicyclic ring;

wherein each of Z 1 to Z 4 which are independent of one another, is a fluorine atom, a chlorine atom, a fluorinated alkyl group or a fluorinated alkoxy group.

4 . The electret according to claim 1 , wherein the fluoropolymer is a copolymer comprising the repeating unit (a) and the repeating unit (b), wherein in the unit (a), each of X 1 to X 4 is a fluorine atom, and in the unit (b), Y 1 is a fluorine atom and each of Y 2 and Y 3 is a trifluoromethyl group.

5 . The electret according to claim 2 , wherein the fluoropolymer is a polymer containing only the repeating unit represented by the formula (a1).

6 . The electret according to claim 5 , wherein the fluoropolymer is such that in the formula (a1), each of X 11 and X 12 is a fluorine atom, and each of X 13 and X 14 is a chlorine atom, or each of X 11 , X 12 and X 13 is a fluorine atom and X 14 is a chlorine atom.

7 . The electret according to claim 5 , wherein the fluoropolymer is such that in the formula (a1), X 11 is a fluorine atom, X 12 is a trifluoromethyl group and each of X 13 and X 14 is a fluorine atom, or each of X 11 , X 12 and X 13 is a fluorine atom and X 14 is a trifluoromethyl group.

8 . The electret according to claim 3 , wherein the fluoropolymer is a copolymer comprising the repeating unit represented by the formula (a2) and the repeating unit represented by the formula (b).

9 . The electret according to claim 1 , which is a coating film.

10 . The electret according to claim 2 , which is a coating film.

11 . The electret according to claim 3 , which is a coating film.

12 . An electrostatic induction conversion device comprising the electret as defined in claim 1 .

13 . An electrostatic induction conversion device comprising the electret as defined in claim 2 .

14 . An electrostatic induction conversion device comprising the electret as defined in claim 3 .