Conductive film, and transducer and flexible wiring board using the same

1. A conductive film containing an elastomer and metallic filler particles filled in the elastomer, the metallic filler particles including anisotropic filler particles oriented in the film expansion direction having a flake-like or needle-like shape with a thickness of 1 μm or less, the conductive film satisfying the following conditions (A) and (B):

(A) In a case where three straight lines extending in a film thickness direction are drawn on a film-thickness-direction cross-section photograph taken by using a scanning electron microscope with spacings at 3 μm each between the three straight lines in a film expansion direction; where, with respect to each of the straight lines, a count is made of the number of metallic filler particles that intersect the straight line and that each have a longest portion in the cross-section photograph with a length of 2 μm or more; and where, by dividing that number by the length of the straight line, a reference number per 1 μm of the straight line is calculated, an average value of the reference numbers of the three straight lines is 0.8 (1/μm) or more; or, the metallic filler particles include flake-like filler particles having a thickness of 1 μm or less and an aspect ratio of 26 or more, and the average value of the reference numbers is 0.4 (1/μm) or more; and

(B) In a case where a measurement area formed by connecting 100 four-sided unit areas each with 2 μm per side is provided on the film-thickness-direction cross-section photograph taken by using the scanning electron microscope, and an area occupied by the elastomer in each of the unit areas is measured, a number of unit areas for which an area percentage of the elastomer is 60% or more is 20 unit areas or more.

2. The conductive film according to claim 1 , wherein a filling amount of the metallic filling particles is less than 45% by volume when a volume of the conductive film is 100% by volume.

3. The conductive film according to claim 1 , wherein the metallic filler particles further include block-shaped filler particles having an average particle size of 0.1 μm or more and 1.5 μm or less.

4. The conductive film according to claim 3 , wherein a content ratio between the anisotropic filler particles and the block-shaped filler particles is from 2:1 to 50:1 in mass ratio.

5. The conductive film according to claim 1 , wherein the elastomer has a functional group capable of hydrogen bonding, and has a glass transition temperature (Tg) of −10° C. or lower.

6. The conductive film according to claim 5 , wherein the elastomer is of at least one kind selected from an acrylic rubber, a urethane rubber, a hydrin rubber, and a silicone rubber.

7. The conductive film according to claim 6 , wherein the acrylic rubber contains 50% by mole or more of an acrylic acid ester monomer unit having an alkyl group of four or more carbon atoms.

8. The conductive film according to claim 1 , wherein a compound containing sulfur is not used for cross-liking of the elastomer.

9. The conductive film according to claim 1 being formed on a surface of an elastic member made of an elastomer.

10. A transducer comprising:

a dielectric film made of an elastomer;

a plurality of electrodes arranged across the dielectric film; and

wirings connected to each of the plurality of electrodes, wherein

of the electrodes and the wirings, at least one is formed from the conductive film according to claim 1 .

11. A flexible wiring board wherein at least a portion of a wiring is formed from the conductive film according to claim 1 .