Electrically conductive composition, sheet-form flexible electrode using same, and method for producing said electrode
This electrically conductive composition includes a thermoplastic elastomer and flaky graphite, the melt viscosity of the thermoplastic elastomer at 200° C. in a low-shear zone with a shear rate of 60 s −1 to 200 s −1 being 50 Pa·s to 1400 Pa·s, and the roundness of the flaky graphite being 0.5 or less. This method for producing a sheet-form flexible electrode has a kneading step for kneading expanded graphite and a thermoplastic elastomer having a melt viscosity of 50 Pa·s to 1400 Pa·s at 200° C. in a low-shear zone with a shear rate of 60 s −1 to 200 s− 1 to produce the electrically conductive composition, and a molding step for molding the electrically conductive composition into the form of a sheet by injection molding or extrusion molding.
1 . An electrically conductive composition, comprising a thermoplastic elastomer and flaky graphite, wherein
the thermoplastic elastomer is selected from the group consisting of styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS) and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), wherein a styrene content in the thermoplastic elastomer is 35% by mass or less,
a melt viscosity of the thermoplastic elastomer at 200° C. in a low shear zone with a shear rate of 60 s −1 or more and 200 s −1 or less is 50 Pa·s or more and 1400 Pa·s or less, and
the flaky graphite has a roundness of 0.5 or less, and a volume-based particle size distribution curve of the flaky graphite has one or more peaks, and a shoulder portion continuous on a small particle size side of a main peak defined by selecting one of the peaks as the main peak, and in the volume-based particle size distribution curve, a peak top of the main peak is present at a particle size of 50 μm or more to 300 μm, and at least one of a start point and an end point of the shoulder portion is present at a particle size of 10 μm or more to 100 μm,
wherein the electrically conductive composition is a solvent-free electrically conductive composition that is formed by kneading a raw material composition comprising the thermoplastic elastomer and expanded graphite, and the expanded graphite has a roundness of 0.5 or less before kneading, and wherein the flaky graphite is produced from the expanded graphite after kneading.
2 . The electrically conductive composition according to claim 1 , wherein
a content of the flaky graphite is 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the thermoplastic elastomer.
3 . The electrically conductive composition according to claim 1 , further comprising an electrically conductive filler having a particle size of 1 μm or less.
4 . The electrically conductive composition according to claim 3 , wherein
a content of the electrically conductive filler is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the thermoplastic elastomer.
5 . The electrically conductive composition according to claim 1 , further comprising one or more processing aids selected from an aliphatic compound and a silicone compound.
6 . A sheet-form flexible electrode, using the electrically conductive composition according to claim 1 .
7 . The sheet-form flexible electrode according to claim 6 , having a volume resistivity of 10 Ω·cm or less.
8 . A capacitance sensor, comprising the sheet-form flexible electrode according to claim 6 .
9 . A method for producing a sheet-form flexible electrode, producing the sheet-form flexible electrode according to claim 6 , comprising:
a kneading step in which the raw material composition comprising the thermoplastic elastomer and the expanded graphite is kneaded to produce the electrically conductive composition; and
a molding step in which the electrically conductive composition is injection molded or extrusion molded into a form of a sheet.
10 . The method for producing a sheet-form flexible electrode according to claim 9 , wherein,
in the volume-based particle size distribution curve of the expanded graphite before kneading, a peak top of a first peak is present at a particle size of 10 μm or more.