Electret and electrostatic induction conversion device

1. An electret comprising a laminate wherein a layer (A) containing a polymer compound (a) having a relative dielectric constant of from 1.8 to 3.0 and a layer (B) containing a polymer compound (b) having a relative dielectric constant higher than the polymer compound (a) are directly laminated, wherein the difference between the relative dielectric constant of the polymer compound (b) and the relative dielectric constant of the polymer compound (a) is at least 0.3; the layer (A) is disposed on the outermost surface on a side opposite to the side where electric charge is injected at the time of injecting electric charge into the laminate to form the electret; and the layer (B) has a thickness of at least 1 μm;

wherein the polymer compound (a) is a fluorinated polymer having an alicyclic structure, wherein the fluorinated polymer is at least one member selected from the list consisting of: (i) a polymer having a unit based on a cyclic fluorinated monomer, and (ii) a polymer having a unit formed by cyclopolymerization of a diene type fluorinated monomer;

wherein the layer (A) consists essentially of the polymer compound (a) and a silane coupling agent; and

wherein the polymer compound (b) is at least one member selected from the group consisting of: a polyimide, a polyparaxylylene resin, a polycarbonate, a polyarylene, a polyarylene ether, a polyether sulfone, and a polysulfone.

2. The electret according to claim 1 , wherein the polymer compound (b) has a glass transition temperature or melting point of at least 80° C.

3. The electret according to claim 1 , wherein the laminate is a (n A +n B ) layered laminate wherein n A layers of layer A and n B layers of layer B are alternately laminated, wherein n A is an integer of from 1 to 5, n B is an integer of from 1 to 5, and the value of n A −n B is 0 or 1.

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

5. The electret according to claim 1 , wherein the laminate is selected from the group consisting of:

a laminate comprising a substrate, a layer (A) disposed on and in direct contact with the substrate, and layer (B) disposed on and in direct contact with layer (A);

a laminate comprising a substrate, with layer (A) disposed on and in direct contact with the substrate, and layer (B) disposed on and in direct contact with layer (A), and a layer (A′) physically separated from and made of the same material as layer (A) and disposed on and in direct contact with layer (B); and

a laminate comprising a substrate, with layer (A) disposed on and in direct contact with the substrate, and layer (B) disposed on and in direct contact with layer (A), a layer (A′) physically separated from and made of the same material as later (A) and disposed on and in direct contact with layer (B), and a layer (B′) physically separated from and made of the same material as layer (B) and disposed on and in direct contact with layer (A′).

6. The electret according to claim 5 , wherein the laminate comprises at least one member selected from the group consisting of gold, platinum, copper, aluminum, chromium, nickel, glass, polyethylene terephthalate, polyimide, polycarbonate, an acrylic resin and silicon.

7. The electret according to claim 1 , wherein the polymer compound (a) is a fluorinated polymer that is (i) a polymer having a unit based on a cyclic fluorinated monomer, and wherein the cyclic fluorinated monomer is at least one member selected from the list consisting of:

a monomer having a polymerizable double bond between carbon atoms constituting a fluorinated alicyclic ring, and

a monomer having a polymerizable double bond between a carbon atom, constituting a fluorinated alicyclic ring and a carbon atom of other than a fluorinated alicyclic ring.

8. The electret according to claim 7 , wherein the cyclic fluorinated monomer comprises a compound of the formula:

wherein X 11 , X 12 , X 13 , X 14 , are independent of one another, and each is at least one member selected from the group consisting of: a fluorine atom, a perfluoroalkyl group, and a perfluoroalkoxy group.

9. The electret according to claim 7 , wherein the cyclic fluorinated monomer comprises a compound of the formula:

wherein Y 11 and Y 12 are independent of one another, and each is at least one member selected from the group consisting of: a fluorine atom, a perfluoroalkyl group, and a perfluoroalkoxy group.

10. The electret according to claim 1 , wherein the polymer compound (a) is a fluorinated polymer that is (ii) a polymer having a unit formed by cyclopolymerization of a diene type fluorinated monomer, wherein the diene type fluorinated monomer comprises a compound of the formula:

CF 2 ═CF-Q-CF═CF 2

wherein Q is a C 1-3 perfluoroalkylene group.

11. The electret according to claim 10 , wherein Q is a C 1-3 perfluoroalkylene group having an etheric oxygen atom.

12. The electret according to claim 10 , wherein Q is a C 1-3 perfluoroalkylene group wherein one or more fluorine atoms are substituted by halogen atoms other than fluorine atoms.

13. The electret according to claim 1 , wherein the polymer compound (a) has a carboxyl group at a terminal of a main chain or at a side chain.