Process for producing electret, and electrostatic induction conversion device

1. A process for producing an electret, which comprises a step of thermally treating a composition comprising a fluorinated polymer and a silane coupling agent, wherein the fluorinated polymer has an alicyclic structure in its main chain and has a carboxy group or an alkoxycarbonyl group as its terminal group; the silane coupling agent has an amino group; and the temperature for the thermal treatment is from 250° C. to 330° C.

2. The process for producing an electret according to claim 1 , wherein the fluorinated polymer has, as the alicyclic structure, a fluorinated alicyclic structure in its main chain.

3. The process for producing an electret according to claim 1 , wherein the fluorinated polymer has, as the alicyclic structure, a cyclic structure containing an etheric oxygen atom, in its main chain.

4. The process for producing an electret according to claim 1 , wherein the fluorinated polymer has, as the alicyclic structure, a fluorinated alicyclic structure containing an etheric oxygen atom, in its main chain.

5. The process for producing an electret according to claim 1 , wherein the weight average molecular weight of the fluorinated polymer is from 150,000 to 650,000.

6. The process for producing an electret according to claim 1 , wherein the silane coupling agent is at least one member selected from the group consisting of γ-aminopropylmethyldiethoxysilane, γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane and aminophenyltrimethoxysilane.

7. The process for producing an electret according to claim 1 , wherein the content of the silane coupling agent is from 0.1 to 20 mass %, based on the total amount of the fluorinated polymer and the silane coupling agent.

8. The process for producing an electret according to claim 1 , which includes the following (1) to (4) in the order of (1), (2), (3) and (4):

(1) a step of obtaining a coating fluid having the fluorinated polymer and the silane coupling agent dissolved in a solvent (a coating fluid-preparation step),

(2) a step of coating a substrate with the coating fluid to form a coating layer comprising the fluorinated polymer and the silane coupling agent (a coating step),

(3) a step of thermally treating the coating layer to obtain a coating film (a thermal treatment step), and

(4) a step of injecting an electric charge to the coating film after the thermal treatment.

9. The process for producing an electret according to claim 8 , wherein the solvent is a fluorinated organic solvent.

10. An electrostatic induction conversion device comprising the electret obtained by the process as defined in claim 1 .