Patent ID: 8277927

Claim:
An electret disposed on a substrate comprising a laminate of directly laminated layers of alternating layer types (A) and (B), wherein layer type (A) comprises a resin (a) and layer type (B) comprises a resin (b) other than the resin (a), wherein the resin (a) is an amorphous fluororesin having an alicyclic structure; wherein a layer of layer type (B) is disposed on a side of the electret opposite to the side where electric charge is injected at the time of injecting electric charge into the laminate to form the electret; wherein layer type (A) has a thickness in the range of 5 to 20 μm; wherein layer type (B) has a thickness in the range of 0.1 to 20 μm; wherein the electret, not including the substrate, has a total thickness in the range of 5.1 to 20 μm; wherein the laminate comprises a structure selected from the group consisting of (i) a layer of type (A) which overlays a layer of type (B) which, in turn, overlays the substrate; (ii) a first layer of type (B) which overlays a layer of type (A) which, in turn, overlays a second layer of type (B) which, in turn, overlays the substrate; and (iii) a first layer of type (A) which overlays a first layer of type (B), which, in turn, overlays a second layer of type (A), which, in turn, overlays a second layer of type (B), which, in turn, overlays the substrate; wherein the resin (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, a polyether sulfone, a polyether ketone, a polyether nitrile, a polyether imide, a polyarylenethioether, a polythioether sulfone, a polysulfone, nylon, a polyester, a polystyrene, a polyethylene, a polypropylene, a polyketone, an epoxy resin, an acrylic resin, a polyurethane and an aramid resin; and wherein the layers of alternating layer types (A) and (B) are separately applied layers.