JP6168912B2 - Elastic electrode and sensor sheet - Google Patents

Description

The present invention relates to a stretchable electrode and a sensor sheet provided with the stretchable electrode.

In recent years, stretchable and flexible electrodes have been demanded in the field of medical materials such as artificial muscles and artificial skins that require stretchability, in addition to electronic devices such as soft sensors, various actuators, and flexible display devices.

As such a stretchable and flexible electrode, for example, in Patent Document 1, a wiring formed by drying a conductive paste made of a polyurethane dispersion and metal particles such as silver particles, and a flexible substrate are used. Proposed conductive members have been proposed.

Moreover, in patent document 2, as a flexible electrode excellent in flexibility and conductivity, a carbon composed of carbon fibers having a diameter of 0.5 to 80 nm and three-dimensionally extending from the central portion in an elastomer. A flexible electrode has been proposed in which a continuous conductive path is formed of nanotubes.

JP 2012-54192 A JP 2008-198425 A

However, in the conductive member described in Patent Document 1, the stretchability as the conductive member is ensured, but the wiring portion responsible for the conductivity is formed using a conductive paste containing silver particles, so that the conductive member is stretched. Sometimes the conductive path is cut and the electrical resistance is greatly increased, and further, the variation in electrical resistance is increased when the expansion and contraction is repeated.
Moreover, in the flexible electrode described in Patent Document 2, although flexibility is ensured, it is inferior in stretchability, and the electrical resistance increases at the time of high elongation, or the electrical resistance varies when repeatedly stretched. was there.

The present invention has been made in view of such circumstances, and the object thereof is excellent in flexibility and stretchability, and it is possible to suppress an increase in electrical resistance and variations when repeatedly stretched. An object of the present invention is to provide a stretchable electrode.

As a result of intensive studies to achieve the above object, the present inventors can achieve the above object by forming an electrode body using a mixture of carbon nanotubes obtained by blending single-walled carbon nanotubes and multi-walled carbon nanotubes. The present invention has been completed by finding out what can be done.

The stretchable electrode of the present invention comprises a base material made of an elastomer composition and an electrode body made of carbon nanotubes integrated with the base material.
The carbon nanotube is a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes,
The content of the single-walled carbon nanotube with respect to the total amount of the single-walled carbon nanotube and the multi-walled carbon nanotube is 20 to 70% by weight.

In the stretchable electrode, the single-walled carbon nanotube is preferably a single-walled carbon nanotube having an average length of 100 to 700 μm. The multi-walled carbon nanotube is preferably a multi-walled carbon nanotube having a fiber diameter of 5 to 15 nm.
Moreover, the said elastic electrode can be used suitably for a sensor sheet.

The sensor sheet of the present invention includes the stretchable electrode of the present invention.

The stretchable electrode of the present invention includes an electrode body made of a mixture of carbon nanotubes in which single-walled carbon nanotubes and multi-walled carbon nanotubes are blended at a specific ratio, so that conductivity, particularly initial conductivity (no stretch) (Conductivity in the state of elongation rate = 0%)) and excellent variation in that there is little variation in conductivity (electric resistance) during repeated expansion and contraction.

Since the sensor sheet of the present invention includes the stretchable electrode of the present invention having the above-described characteristics, a sensor having excellent long-term reliability can be provided.

(A) is a perspective view which shows typically an example of the elastic electrode of this invention, (b) is the sectional view on the AA line of (a). (A)-(c) is sectional drawing which shows typically another example of the elastic electrode of this invention, respectively. It is a schematic diagram for demonstrating an example of the shaping | molding apparatus used for preparation of a sheet-like base material. (A) is a top view which shows typically an example of the sensor sheet provided with the elastic electrode of this invention, (b) is the sectional view on the AA line of the sensor sheet shown to (a). . It is a schematic diagram which shows an example of the electrostatic capacitance type sensor using the sensor sheet | seat shown in FIG. It is a schematic diagram for demonstrating the measuring method of the electrical resistance at the time of repeated expansion-contraction in an Example and a comparative example. In Comparative example 1, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. In Comparative example 2, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. In Example 1, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. In Example 2, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. In Example 3, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. In Comparative example 3, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to repeated expansion and contraction. In Comparative example 4, it is a graph which shows the measurement result which measured the change of the electrical resistance with respect to expansion and contraction repeatedly. It is the graph which put together the result of the Example and the comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The stretchable electrode of the present invention comprises a base material made of an elastomer composition and an electrode body made of carbon nanotubes integrated with the base material.
The carbon nanotube is a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes,
The content of the single-walled carbon nanotube with respect to the total amount of the single-walled carbon nanotube and the multi-walled carbon nanotube is 20 to 70% by weight.

Fig.1 (a) is a perspective view which shows typically an example of the elastic electrode of this invention, (b) is the sectional view on the AA line of (a).
In the stretchable electrode 100 shown in FIGS. 1A and 1B, an electrode body 102 made of carbon nanotubes is laminated and integrated on the entire upper surface of a sheet-like substrate 101 made of an elastomer composition.

The said base material consists of an elastomer composition, and can ensure a stretching property by this.
As said elastomer composition, what contains an elastomer and another arbitrary component as needed is mentioned.
Examples of the elastomer include natural rubber, isoprene rubber, nitrile rubber (NBR), ethylene propylene rubber (EPDM), styrene / butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), silicone rubber, and fluorine. Examples thereof include rubber, acrylic rubber, hydrogenated nitrile rubber, and urethane rubber. These may be used alone or in combination of two or more.
Among these, urethane rubber or silicone rubber is preferable. This is because the permanent set (or permanent elongation) is small.
Furthermore, urethane rubber is particularly preferable because it has excellent adhesion to carbon nanotubes compared to silicone rubber.

The urethane rubber is not particularly limited, and is an olefin urethane rubber having an olefin polyol as a polyol component, an ester urethane rubber having an ester polyol as a polyol component, an ether urethane rubber having an ether polyol as a polyol component, and a carbonate. Examples thereof include carbonate-based urethane rubber using a polyol as a polyol component and castor oil-based urethane rubber using a castor oil-based polyol as a polyol component. These may be used alone or in combination of two or more.
The urethane rubber may be a combination of two or more polyol components.

Examples of the olefin-based polyol include Epol (made by Idemitsu Kosan Co., Ltd.) and the like.
Examples of the ester-based polyol include Polylite 8651 (manufactured by DIC).
Examples of the ether polyol include polyoxytetramethylene glycol, PTG-2000SN (Hodogaya Chemical Co., Ltd.), polypropylene glycol, and Preminol S3003 (Asahi Glass Co., Ltd.).

In addition to the elastomer, the elastomer composition may contain additives such as a dielectric filler, a plasticizer, a chain extender, a crosslinking agent, a catalyst, a vulcanization accelerator, an antioxidant, an antioxidant, and a colorant. Good.

Moreover, the said elastomer composition may contain another component further according to the use of a stretchable electrode.
Specifically, for example, when the stretchable electrode of the present invention is used as a capacitive sensor sheet, it may contain a dielectric filler such as barium titanate. Thereby, the capacitance C can be increased, and as a result, the detection sensitivity of the capacitance type sensor sheet can be increased.
When the dielectric filler is contained, its content in the elastomer composition is usually more than 0% by volume and about 25% by volume or less.
When the content of the dielectric filler exceeds 25% by volume, the hardness of the base material may increase or permanent set may increase. Moreover, since the liquid viscosity before hardening becomes high at the time of shaping | molding the base material made from urethane rubber, highly accurate thin film formation may become difficult.

The electrode body is made of carbon nanotubes, and a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes is used as the carbon nanotubes.
By using such a mixture of two types of carbon nanotubes, the conductivity of the electrode body, particularly the initial conductivity, is increased (lowering the electrical resistance), and the conductivity (electrical resistance) variation during repeated expansion and contraction is reduced. Can be suppressed.
More specifically, the use of single-walled carbon nanotubes can suppress variations in electrical resistance during expansion and contraction, and the use of multi-walled carbon nanotubes can reduce electrical resistance (particularly the initial electrical resistance). .
In the present specification, when only “carbon nanotube” is described, it means a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

The single-walled carbon nanotube (SWCNT) is preferably a single-walled carbon nanotube having a smaller diameter (fiber diameter) and a larger aspect ratio.
The lower limit of the average length of the single-walled carbon nanotube is preferably 10 μm, more preferably 100 μm, further preferably 300 μm, and particularly preferably 600 μm. On the other hand, the upper limit of the average length is preferably 700 μm.
In particular, by using single-walled carbon nanotubes having an average length of 100 to 700 μm, variation in electrical resistance during expansion and contraction can be remarkably suppressed.

The aspect ratio of the single-walled carbon nanotube is preferably 100 or more, more preferably 1000 or more, still more preferably 10,000 or more, and particularly preferably 30000 or more.
By including such a long single-walled carbon nanotube, when the electrode body is repeatedly expanded and contracted, fluctuation (variation) in electric resistance is reduced. As a result, long-term reliability is also excellent. The reason for this is considered to be that, in the case of a long single-walled carbon nanotube, the carbon nanotube itself easily expands and contracts, and the conductive path is less likely to be cut when the electrode body extends following the base material. Moreover, when an electrode main body is formed using carbon nanotubes, the conductivity is manifested when the carbon nanotubes come into contact with each other (form electrical contacts). Here, when long carbon nanotubes are used, a higher-dimensional electrical network can be formed because the number of electrode contacts with other carbon nanotubes in one carbon nanotube is increased. This is considered to be the reason why the path becomes difficult to cut.
In the present invention, the shape (average length and aspect ratio) of the carbon nanotube to be used as the single-walled carbon nanotube is comprehensively determined based on the use of the stretchable electrode, required characteristics, cost, and the like. May be selected as appropriate.

The single-walled carbon nanotube preferably has a purity of 99% by weight or more.
Carbon nanotubes may contain catalytic metals, non-nanotube carbon materials (amorphous carbon, graphite, etc.), dispersants, etc. in the production process, and a large amount of components (impurities) other than such carbon nanotubes. This is because when the single-walled carbon nanotube contained in is used, the effect of containing the single-walled carbon nanotube, that is, the effect of suppressing variation in electric resistance during repeated expansion and contraction may be inferior.

The multi-walled carbon nanotube may be a double-walled carbon nanotube (DWNT), or may be a multi-walled carbon nanotube (MWNT) of three or more layers (in this specification, a combination of both is simply a multi-walled carbon nanotube and However, among these, multi-walled carbon nanotubes having three or more layers are preferable.

The fiber diameter of the multi-walled carbon nanotube is preferably 5 to 15 nm.
When the fiber diameter is less than 5 nm, the dispersion of the multi-walled carbon nanotubes is deteriorated. As a result, the conductive path may not be widened and the conductivity may be insufficient. On the other hand, when the fiber diameter exceeds 15 nm, the number of carbon nanotubes is the same even with the same weight. May decrease and the conductivity may be insufficient.

The average length of the multi-walled carbon nanotube is preferably 1 to 10 μm. If the average length of the multi-walled carbon nanotube is less than 1 μm, the contact between the carbon nanotubes in the conductive path increases, and as a result, the contact resistance may increase and the conductivity may decrease, whereas it exceeds 10 μm. As a result, the dispersion of the carbon nanotubes deteriorates, and as a result, the conductive path may not spread and the conductivity may be lowered.
More preferably, it is 1-5 micrometers, More preferably, it is 1-3 micrometers.
The aspect ratio of the multi-walled carbon nanotube is preferably 50 to 2000.

In the mixture of the single-walled carbon nanotube and the multi-walled carbon nanotube, the content of the single-walled carbon nanotube is 20 to 70% by weight with respect to the total amount of the single-walled carbon nanotube and the multi-walled carbon nanotube.
When the content of the single-walled carbon nanotube is less than 20% by weight, the variation in conductivity (electric resistance) when the stretchable electrode is repeatedly expanded and contracted becomes large, while the content of the single-walled carbon nanotube is 70% by weight. This is because the electrical resistance (particularly, the initial electrical resistance) increases when the percentage exceeds 50%.
The lower limit of the content of the single-walled carbon nanotube is preferably 30% by weight from the viewpoint of more reliably suppressing variation in electrical resistance.

In addition to the carbon nanotube, the electrode body may contain a binder component as a connecting material for the carbon nanotube.
By containing the binder component, it is possible to improve the adhesion to the substrate and the strength of the electrode body itself, and further suppress the scattering of carbon nanotubes when forming the electrode body by the method described later. Therefore, the safety at the time of forming the electrode body can be improved.

Examples of the binder component include butyl rubber, ethylene propylene rubber, polyethylene, chlorosulfonated polyethylene, natural rubber, isoprene rubber, butadiene rubber, styrene / butadiene rubber, polystyrene, chloroprene rubber, nitrile rubber, polymethyl methacrylate, polyacetic acid. Examples thereof include vinyl, polyvinyl chloride, acrylic rubber, styrene-ethylene-butylene-styrene block copolymer (SEBS), and the like. These may be used alone or in combination of two or more.
In addition, as the binder component, raw rubber (in a state where natural rubber and synthetic rubber are not vulcanized) can be used. By using a material having relatively low elasticity as described above, The followability of the electrode body with respect to deformation of the material can also be improved.

The binder component preferably has a solubility parameter (SP value [cal / cm ³ ) ^1/2 ] that is close to that of the elastomer constituting the substrate, and the absolute value of the difference between the solubility parameters (SP value) of the binder component is 1. The following are more preferable. This is because the closer the solubility parameter, the better the adhesion between the substrate and the electrode body.
In the present invention, the SP value is a value calculated by Fedors' estimation method.
The binder component is particularly preferably the same type as the elastomer constituting the substrate. This is because the adhesion between the substrate and the electrode body can be significantly improved.

The electrode body may contain various additives in addition to the carbon nanotube and the binder component. Examples of the additive include a crosslinking agent for the binder component, a vulcanization accelerator, a vulcanization aid, an anti-aging agent, a plasticizer, a softening agent, and a colorant.
Here, when the said electrode main body contains a plasticizer and the said base material also contains a plasticizer, it is preferable that both plasticizer density | concentrations are the same. This is because the migration of the plasticizer between the base material and the electrode main body can be prevented, thereby suppressing the occurrence of warpage and wrinkles in the stretchable electrode.

In the stretchable electrode of the present invention, the electrode body may be formed substantially only from carbon nanotubes. This is also because sufficient adhesion between the substrate and the substrate can be ensured. In this case, the carbon nanotube and the base material are firmly adhered by van der Waals force.
The content of carbon nanotubes in the electrode body is not particularly limited as long as it is a concentration at which conductivity is expressed. When the binder component is contained, it varies depending on the type of the binder component, but the total solid component of the electrode body It is preferably 0.1 to 100% by weight.
By increasing the content of carbon nanotubes, it is possible to suppress a decrease in conductivity (increase in electric resistance) of the electrode body when it is repeatedly expanded and contracted, and durability can be improved.

When the shape of the electrode body is layered as shown in FIG. 1, the average thickness is preferably 0.1 to 10 μm. This is because when the average thickness of the electrode main body is within the above range, the electrode main body can exhibit excellent followability to the expansion and contraction of the substrate during expansion and contraction.
On the other hand, if the average thickness is less than 0.1 μm, the conductivity may be insufficient. On the other hand, if it exceeds 10 μm, the stretchable electrode itself becomes hard due to the reinforcing effect of the carbon nanotubes, and the stretchability is insufficient. There is a risk of becoming.
In addition, when the shape of an electrode main body is layered, the average thickness of an electrode main body can be measured using a laser microscope (for example, Keyence Corporation make, VK-9510).
Specifically, for example, when the electrode main body is laminated on a part of the surface of the base material, the thickness direction of the electrode main body laminated on the surface of the base material is scanned in increments of 0.01 μm, and its 3D shape After measuring the average height of the rectangular area of 200 × 200 μm in the area where the electrode layer is laminated on the surface of the dielectric layer and the area where the electrode layer is not laminated, the step of the average height is measured. The average thickness of the electrode body may be used.

The shape of the stretchable electrode of the present invention is not limited to the shape shown in FIG. 1, and may have, for example, the shapes shown in FIGS. 2 (a) to (c).
2A to 2C are cross-sectional views schematically showing another example of the stretchable electrode of the present invention.
The stretchable electrode 110 shown in FIG. 2A has a shape in which the electrode main body 112 is sandwiched between two sheet-like substrates 111a and 111b. When the stretchable electrode has such a shape, the electrode body is less likely to be damaged by an external impact or the like.

The stretchable electrode 120 shown in FIG. 2 (b) has a shape in which two sheet-like base materials 121a and 121b and two layers of electrode bodies 122a and 122b are alternately stacked. The main body has a multilayer structure.
When the electrode main body has a multilayer structure, the total number is not limited to two layers as shown in FIG. 2B, and may be three or more layers. Moreover, the upper and lower surfaces of the layered electrode body may be protected by a base material.

A stretchable electrode 130 shown in FIG. 2C has a shape in which two electrode main bodies 132 a and 132 b are laminated on the upper surface of a sheet-like base material 131. When laminating an electrode body on one surface of a sheet-like base material, not only two but also a plurality of electrode bodies may be laminated, or a circuit pattern made of carbon nanotubes may be formed as an electrode body Good.
Of course, the shape of the stretchable electrode of the present invention is not limited to the shape shown so far, and various shapes according to the design of the stretchable electrode can be adopted.

Since the stretchable electrode of the present invention has the above-described configuration, it is excellent in conductivity (especially in the initial state (non-elongation (elongation rate = 0%) state)) (low electrical resistance) and repeatedly stretched. It has an excellent characteristic that there is little variation in electrical conductivity (electrical resistance) at the time.
Here, the stretchable electrode is stretched 100% in the uniaxial direction from the unstretched state, and then stretched 100% in the second cycle when the stretch to return to the unstretched state is repeated 1000 cycles. The difference between the resistance of the electrode body at the time of 100% and the resistance of the electrode body at the time of 100% elongation at the 1000th cycle is preferably 2 kΩ or less.
Here, the reason for comparing the 100% elongation at the second cycle and the 100% elongation at the 1000th cycle, not at the time of 100% elongation at the first cycle, is that the first ( This is because the behavior of the electrode body (how the electric resistance fluctuates) at the time of extension (the first cycle) is greatly different from that at the second and subsequent times (second cycle). It is presumed that the state of the carbon nanotubes constituting the electrode body is stabilized only after being produced and then stretched once.
Therefore, when using the stretchable electrode of the present invention, it is preferable to use it after being stretched and then stretched at least once.

When the stretchable electrode is stretched in a uniaxial direction from a non-stretched state, it is preferable that the stretch rate withstanding uniaxial tension is as large as possible, specifically 30% or more, and preferably 50% or more. Is more preferably 100% or more, and particularly preferably 200% or more.
It is because it becomes possible to use for various uses by enlarging the said expansion | extension rate.
The elongation that can withstand uniaxial tension refers to the elongation that is equal to or lower than the elongation at break in a tensile test in accordance with JIS K 6251, and that restores the original state after releasing the tensile load. When the elongation rate that can withstand uniaxial tension is 100% or more, it does not break when it is stretched 100% in the uniaxial direction, and is restored to its original state after releasing the tensile load (that is, It is in the range of elastic deformation.
The elongation ratio that can withstand the uniaxial tension can be controlled by the design (material, shape, etc.) of the substrate.

Next, the manufacturing method of the stretchable electrode of this invention is demonstrated.
The stretchable electrode of the present invention is, for example,
(1) A step of producing a substrate made of an elastomer composition (hereinafter also referred to as “step (1)”), and (2) a composition containing carbon nanotubes and a dispersion medium is applied and integrated with the substrate. Forming an electrode body (hereinafter also referred to as “process (2)”)
It can manufacture by going through.
Hereinafter, the manufacturing method of a stretchable electrode is demonstrated in order of a process for an example of the stretchable electrode provided with the sheet-like base material and the layered electrode main body.

[Step (1)]
In this step, a substrate made of the elastomer composition is formed. First, an elastomer (or a raw material thereof) as a raw material composition, if necessary, a dielectric filler, a plasticizer, a chain extender, a crosslinking agent, a vulcanization accelerator, a catalyst, an antioxidant, an anti-aging agent, a coloring agent, etc. A raw material composition containing the additive is prepared.
It does not specifically limit as a shaping | molding method of the said base material, After preparing the said raw material composition, a base material can be shape | molded by shape | molding by a conventionally well-known method.
Specifically, when molding a base material containing urethane rubber as a base material, for example, a polyol component, a plasticizer, and an antioxidant are weighed and stirred and mixed for a certain time under heating and reduced pressure. Prepare. Next, after measuring the mixed solution and adjusting the temperature, the catalyst is added and stirred with an agitator or the like. Thereafter, a predetermined amount of an isocyanate component is added, and after stirring with an agitator or the like, the mixed solution is immediately poured into the molding apparatus shown in FIG. A roll-wrapped sheet having a predetermined thickness is obtained. Then, a base material can be manufactured by carrying out a crosslinking reaction for a certain time in a furnace.

In addition, FIG. 3 is a schematic diagram for explaining an example of a molding apparatus used for producing a sheet-like base material. In the molding apparatus 30 shown in FIG. 3, the raw material composition 33 is poured into a gap between a protective film 31 made of polyethylene terephthalate (PET) continuously fed from a pair of spaced apart rolls 32 and 32 ′. The curing reaction (crosslinking reaction) is allowed to proceed while holding the raw material composition 33 in the gap, and is introduced into the heating device 34 to thermally cure the raw material composition 33 while being held between the pair of protective films 31. Then, the sheet-like base material 35 is formed.

Moreover, after preparing a raw material composition, you may produce the said base material using general purpose film-forming apparatuses and film-forming methods, such as various coating apparatuses, a bar coat, and a doctor blade.

[Step (2)]
In this step, an electrode body composed of carbon nanotubes integrated with the substrate is formed by applying a composition containing carbon nanotubes and a dispersion medium (carbon nanotube dispersion).

Specifically, first, carbon nanotubes are added to the dispersion medium. At this time, if necessary, a binder component (or a raw material for the binder component), a dispersant, and other various additives may be added.
Next, a coating liquid is prepared by dispersing (or dissolving) each component including carbon nanotubes in a dispersion medium using a wet disperser. Here, for example, an existing disperser such as an ultrasonic disperser, a jet mill, or a bead mill may be used for dispersion.

At this time, after (a) single-walled carbon nanotubes and multi-walled carbon nanotubes are added to separate dispersion media and dispersed (or dissolved) in the respective dispersion media using a wet disperser, The dispersion liquid and the multi-wall carbon nanotube dispersion liquid may be mixed to form a coating liquid. (B) Single-wall carbon nanotubes and multi-wall carbon nanotubes are simultaneously added to one dispersion medium and dispersed using a wet disperser. A coating solution may be dispersed (or dissolved) in a medium.

Examples of the dispersion medium include toluene, methyl isobutyl ketone (MIBK), alcohols, water, and the like. These dispersion media may be used independently and may be used together 2 or more types.

In the coating solution, the concentration of the carbon nanotube is preferably 0.01 to 10% by weight.
If it is less than 0.01% by weight, the concentration of the carbon nanotubes may be too thin to be repeatedly applied. On the other hand, if it exceeds 10% by weight, the viscosity of the coating solution becomes too high, and the carbon nanotubes are re-aggregated. In some cases, it is difficult to form a uniform electrode body.

Subsequently, the coating liquid is applied to a predetermined position on the surface of the substrate using an air brush or the like and dried. At this time, if necessary, the coating liquid may be applied after masking a position on the substrate surface where the electrode body is not formed.
The drying conditions for the coating solution are not particularly limited, and may be appropriately selected according to the type of the dispersion medium.

Further, the method of applying the coating liquid is not limited to the method using an air brush, and other methods such as a screen printing method and an ink jet printing method can also be employed.

In some cases, before the electrode body is formed on the surface of the base material, the surface of the base material may be pretreated in order to improve the adhesion between the two. Has extremely excellent adhesion, so that sufficient adhesion can be secured between the substrate and the electrode body without any pretreatment.

By undergoing such a process, a stretchable electrode having a shape as shown in FIGS. 1 and 2C can be manufactured.
In the case of manufacturing a stretchable electrode having a shape as shown in FIG. 2A, for example, after forming an electrode body on one surface of the substrate by the above-described method, various coating apparatuses, bar coaters, doctors, etc. The raw material composition can be applied by using a general-purpose film forming apparatus such as a blade or a film forming method, and then thermally cured. In addition, a sheet (base material) obtained by cross-linking or semi-cross-linking the raw material composition for preparing the base material is separately prepared, and manufactured by laminating the base material having the electrode body formed on one surface. In the case of semi-crosslinking, it may be completely crosslinked after lamination.

In the case where a base material such as the stretchable electrode shown in FIG. 2B and a stretchable electrode having a multilayer structure are manufactured, the base body is first prepared, and then the electrode body is formed thereon. And another base material are sequentially laminated by the method described above to produce a stretchable electrode having a multilayer structure.

Such a stretchable electrode of the present invention can be suitably used as a sensor sheet, for example. Of course, the use of the stretchable electrode according to the present invention is not limited to the sensor sheet, and other various signals such as actuators and generators as well as actuators and generators, as well as conductive wiring materials. It can be used for various purposes such as power lines and low-power power lines.

Next, the sensor sheet of the present invention having the stretchable electrode will be described with reference to the drawings.
Fig.4 (a) is a top view which shows typically an example of the sensor sheet provided with the elastic electrode of this invention, (b) is the sectional view on the AA line of the sensor sheet shown to (a). It is.

A sensor sheet 1 shown in FIGS. 4A and 4B is a capacitive sensor sheet, and has a sheet-like dielectric layer 2 and a belt-like shape laminated on the surface (front surface) of the dielectric layer 2. Front-side electrode layers 01A to 16A, strip-like back-side electrode layers 01B to 16B laminated on the back surface of dielectric layer 2, and front-side connection portion 01A1 for connection to external wiring provided at one end of front-side electrode layers 01A to 16A 16A1 and back side connection portions 01B1 to 16B1 for connecting to external wiring provided at one end of the back side electrode layers 01B to 16B.
The portions where the front-side electrode layer and the back-side electrode layer intersect in the front-back direction (thickness direction of the dielectric layer) are detection units C0101 to C1616. In the detection unit code “CXXΔΔ”, the upper two digits “XX” correspond to the front electrode layers 01A to 16A, and the lower two digits “ΔΔ” indicate the back electrode layers 01B to 01B. Corresponding to 16B.

The front-side electrode layers 01A to 16A each have a strip shape, and a total of 16 layers are laminated on the surface of the dielectric layer 2. The front side electrode layers 01A to 16A each extend in the X direction (the left-right direction in FIG. 4A). The front side electrode layers 01A to 16A are spaced apart from each other at predetermined intervals in the Y direction (the vertical direction in FIG. 4A), and are arranged so as to be substantially parallel to each other.

The back electrode layers 01 </ b> B to 16 </ b> B each have a band shape, and a total of 16 layers are stacked on the back surface of the dielectric layer 2. The back-side electrode layers 01B to 16B are arranged so as to intersect the front-side electrode layers 01A to 16A at a substantially right angle when viewed from the front and back directions, respectively. That is, the back side electrode layers 01B to 16B each extend in the Y direction. Further, the back-side electrode layers 01B to 16B are arranged so as to be substantially parallel to each other at a predetermined interval in the X direction.

By arranging each of the front side electrode layers 01A to 16A and the back side electrode layers 01B to 16B in this way, the number of electrode layers and the number of electrode wirings are reduced when measuring the position and size of deformation of the measurement object. can do. That is, in the case of the said aspect, the detection part will be arrange | positioned efficiently.

More specifically, in the example shown in FIG. 4, there are 256 detection units in which the front electrode layer and the back electrode layer intersect in the thickness direction at 16 × 16 = 256. In the case where they are formed independently, there are a front side electrode and a back side electrode for each detection unit, and thus 256 wires of 256 × 2 are required to detect the capacitance of the detection unit. On the other hand, as in the example shown in FIG. 4, the front-side electrode layer and the back-side electrode layer are each composed of a plurality of strips arranged in parallel, and the front-side electrode layer and the back-side electrode layer are viewed from the front-back direction. In the case where they are arranged so as to intersect at substantially right angles, only 32 wires of 16 + 16 are required for detecting the electrostatic capacitance of the detection unit. For this reason, the detection units are efficiently arranged as described above.

And in the sensor sheet 1 shown to Fig.4 (a), (b), the dielectric layer 2 is corresponded to the base material in the elastic electrode of this invention, and front side electrode layer 01A-16A and back side electrode layer 01B-16B Each corresponds to an electrode body in the stretchable electrode of the present invention.

As will be described later, the sensor sheet 1 having such a configuration is connected to a measuring unit to form a capacitive sensor, and each of the 16 wires is switched by an external switching circuit, thereby detecting 256 detection units. The capacitance of each detection unit can be measured while switching one by one.
Based on the capacitance of each detection unit, information such as strain distribution, strain position, and surface pressure distribution in the capacitive sensor sheet can be detected.

In the capacitance type sensor sheet, the average thickness of the dielectric layer is 10 from the viewpoint of increasing the capacitance C and improving the detection sensitivity and improving the followability to the measurement object. It is preferable that it is -1000 micrometers, and it is more preferable that it is 30-200 micrometers.
Moreover, the dielectric constant at normal temperature of the dielectric layer is preferably 2 or more, and more preferably 5 or more. If the relative dielectric constant of the dielectric layer is less than 2, the capacitance C becomes small, and there is a possibility that sufficient sensitivity cannot be obtained when used as a capacitance type sensor.

In the sensor sheet, the outer shape such as the average thickness, width, and length of the dielectric layer (base material), the front electrode layer, and the back electrode layer (electrode body) is appropriately determined depending on the application of the sensor sheet used. The design can be changed.

Moreover, when using the elastic electrode of this invention as an electrostatic capacitance type sensor sheet, it is preferable that the Young's modulus of the said base material is 0.1-1 Mpa. If the Young's modulus is less than 0.1 MPa, the substrate is too soft, high quality processing is difficult, and sufficient measurement accuracy may not be obtained. On the other hand, if the Young's modulus exceeds 1 MPa, the base material is too hard, and when the deformation load of the measurement object is small, the deformation operation of the measurement object is hindered, and the measurement result may not match the measurement purpose. .

Moreover, when using the said stretchable electrode as a capacitance-type sensor sheet, the hardness of the said base material is the hardness (JIS A hardness) using the type A durometer based on JISK6253, and is 0. It is 30 °, or 10 to 55 ° is preferable in terms of hardness (JIS C hardness) using a type C durometer based on JIS K 7321.
If the C hardness is less than 10 °, the base material is too soft, making high-quality processing difficult, and sufficient measurement accuracy may not be ensured. On the other hand, if it exceeds 55 °, the base material is too hard. Therefore, when the deformation load of the measurement object is small, the deformation operation of the measurement object is hindered, and the measurement result may not match the measurement purpose.

As will be described later, the capacitive sensor sheet having such a configuration becomes a capacitive sensor by connecting each of the front electrode layer and the back electrode layer to a measuring means via an external wiring.

As a capacitive sensor using the sensor sheet (stretchable electrode) 1 shown in FIG. 4, for example, a sensor having a configuration as shown in FIG.
FIG. 5 is a schematic diagram illustrating an example of a capacitive sensor using the sensor sheet (stretchable electrode) illustrated in FIG. 4.

A capacitive sensor 201 shown in FIG. 5 includes the sensor sheet 1 shown in FIG. 4, external wirings 202 and 203, and measuring means 204.
Each of the front side connection portions 01A1 to 16A1 of the sensor sheet 1 is connected to the measuring means 204 via an external wiring 203 in which a plurality of (16) wires are bundled, and each of the back side connection portions 01B1 to 16B1. Are connected to the measuring means 204 via an external wiring 202 in which a plurality (16) of wirings are bundled.
As shown in FIG. 5, the external wiring only needs to be connected to one end of the front electrode layer and the back electrode layer, but may be connected to both ends depending on circumstances.

Although not shown, the measuring unit 204 includes a power supply circuit, an arithmetic circuit, a capacitance, a measurement circuit, a pixel switching circuit, a display device, and the like as necessary. Specific examples thereof include, for example, an LCR meter. Can be mentioned.

In such a capacitance type sensor 201, the change amount ΔC of the capacitance is detected from the capacitance C before placing the measurement object and the capacitance C after placing the measurement object. The deformation strain amount, the deformation strain distribution, and the surface pressure distribution can be obtained based on the change amount ΔC.
In addition, the sensor sheet (stretchable electrode) has a high elongation rate and can be repeatedly stretched by 30% or more in one axial direction, and can follow the deformation and operation of a flexible measurement object. In addition, since it has excellent durability against expansion and contraction deformation and repeated deformation, the capacitance type sensor provided with the sensor sheet can, for example, trace the shape of the measurement object or directly detect the movement of the measurement object. Etc.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Preparation of carbon nanotube dispersion>
(1) Preparation of Single-Walled Carbon Nanotube Dispersion Solution As single-walled carbon nanotubes, Super Growth CNT (median fiber diameter is about 3 nm, growth length is 500 μm to 700 μm, aspect ratio is about 100,000, carbon purity is 99.9%. (Provided by National Institute of Advanced Industrial Science and Technology, also referred to as SGCNT) 50 mg is added to 24.95 g of methyl isobutyl ketone, wet dispersion treatment is performed using a jet mill (Nanojet PAL JN10-SP003, manufactured by Joko), and methyl 25 g of isobutyl ketone was added to obtain a single-walled carbon nanotube dispersion having a concentration of 0.1% by weight.
The growth length of the carbon nanotubes refers to the height of the forest grown on the growth substrate when producing the carbon nanotubes, and substantially corresponds to the average length of the carbon nanotubes.

(2) Preparation of multi-walled carbon nanotube dispersion As multi-walled carbon nanotubes, 50 mg of NC7000 (fiber diameter 9.5 nm, average length 1.5 μm, aspect ratio 158, carbon purity 90%) manufactured by Nanosil Co., Ltd. 95 g, wet dispersion using a jet mill (NanoJet Pal JN10-SP003, manufactured by Joko), and further adding 25 g of methyl isobutyl ketone to obtain a 0.1 wt% multi-walled carbon nanotube dispersion. Obtained.

(Comparative Example 1)
(1) Hydrogenated hydroxyl group-terminated liquid polyolefin polyol (Epol, manufactured by Idemitsu Kosan Co., Ltd.) 100 parts by mass, high-temperature lubricating oil mainly composed of alkyl-substituted diphenyl ether (Molesco High Lube LB-100, manufactured by MORESCO) 100 parts by mass Were weighed and mixed by stirring at 2000 rpm for 3 minutes using a rotation and revolution mixer (manufactured by THINKY). Next, 0.07 part by mass of a catalyst (Fomrez catalyst UL-28, manufactured by Momentive) was added to the obtained mixture, and the mixture was stirred for 1.5 minutes with a rotation and revolution mixer. Thereafter, 11 parts by mass of isophorone diisocyanate (Desmodur I, manufactured by Sumika Bayer Urethane Co., Ltd.) was added, stirred for 3 minutes with a rotating / revolving mixer and defoamed for 1.5 minutes to prepare a raw material composition for a substrate. Thereafter, this was poured into the molding apparatus 30 shown in FIG. 3 and transferred in a sandwich form with a protective film, while being crosslinked and cured under conditions of a furnace temperature of 110 ° C. and a furnace time of 30 minutes. A roll roll sheet having a thickness was obtained. Then, after cross-linking in a furnace adjusted to 80 ° C. for 12 hours, a base sheet having a layer thickness of 50 μm was obtained.
Next, the obtained base material sheet was cut to prepare a 90 mm × 90 mm × 50 μm base material and a 90 mm × 60 mm × 50 μm base material one by one.

(2) Next, 8 g of the multi-walled carbon nanotube dispersion liquid is applied in a band shape with an airbrush to the central portion of one side of a single substrate (90 mm × 90 mm × 50 μm), and dried at 100 ° C. for 30 minutes, so that the width is 20 mm. An electrode body having a length of 80 mm and a thickness of 1 μm was formed.
Further, a 0.1 wt% toluene solution prepared by dissolving the same composition as the raw material composition for the base material in toluene was prepared, and a strip of air using an air brush on the electrode body using 8 g of this 0.1 wt% toluene solution as a primer. And dried at 100 ° C. for 30 minutes.
Thereafter, the base material on which the electrode main body was formed was bonded to another base material (90 mm × 60 mm × 50 μm) so as to sandwich the electrode main body to obtain a stretchable electrode.

(Evaluation: Measurement of electrical resistance change due to repeated expansion and contraction)
A cycle in which the stretchable electrode obtained in Comparative Example 1 is stretched 100% in the uniaxial direction (longitudinal direction of the electrode body) from the unstretched state using the evaluation device shown in FIG. Stretching was repeated 1000 cycles, and the electrical resistance of the electrode body at the 2nd, 3rd, 10th, 100th, 500th and 1000th cycles was measured.

Specifically, as shown in FIG. 6, two sides perpendicular to the electrode body 52 of the stretchable electrode 50 including the base material 51 and the electrode body 52 are restrained by a resin frame 53, and the end of the electrode body 52 is Each is connected to a multimeter 55 (made by ADVANTEST, R6441C) 55 via a lead 54, and after extending between the frames in one axial direction (the direction of the arrow in the figure), it is repeatedly expanded and contracted to return to the non-extended state. The change in electrical resistance was measured.
The measurement results are shown in FIG. 7 as a graph in which the electrode resistance is plotted on the vertical axis and the elongation rate is plotted on the horizontal axis.

(Comparative Example 2)
The same as Comparative Example 1 except that instead of the multi-walled carbon nanotube dispersion, a carbon nanotube mixed liquid obtained by mixing the multi-walled carbon nanotube dispersion and the single-walled carbon nanotube dispersion at 90:10 (weight ratio) was applied. Thus, an elastic electrode was obtained.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

Example 1
The same as Comparative Example 1 except that instead of the multi-walled carbon nanotube dispersion, a carbon nanotube mixed liquid obtained by mixing the multi-walled carbon nanotube dispersion and the single-walled carbon nanotube dispersion at 70:30 (weight ratio) was applied. Thus, an elastic electrode was obtained.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

(Example 2)
The same as Comparative Example 1 except that instead of the multi-walled carbon nanotube dispersion, a carbon nanotube mixed liquid obtained by mixing the multi-walled carbon nanotube dispersion and the single-walled carbon nanotube dispersion at 50:50 (weight ratio) was applied. Thus, an elastic electrode was obtained.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

(Example 3)
The same as Comparative Example 1 except that instead of the multi-walled carbon nanotube dispersion, a carbon nanotube mixed liquid obtained by mixing the multi-walled carbon nanotube dispersion and the single-walled carbon nanotube dispersion at 30:70 (weight ratio) was applied. Thus, an elastic electrode was obtained.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

(Comparative Example 3)
The same as Comparative Example 1 except that instead of the multi-walled carbon nanotube dispersion, a carbon nanotube mixed liquid obtained by mixing the multi-walled carbon nanotube dispersion and the single-walled carbon nanotube dispersion at 10:90 (weight ratio) was applied. Thus, an elastic electrode was obtained.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

(Comparative Example 4)
A stretchable electrode was obtained in the same manner as in Comparative Example 1 except that the single-walled carbon nanotube dispersion was applied instead of the multi-walled carbon nanotube dispersion.
About the obtained elastic electrode, it carried out similarly to the comparative example 1, and measured the change of the electrical resistance with respect to repeated expansion / contraction. The results are shown in FIG.

The results of Examples and Comparative Examples are summarized in FIG.
FIG. 14 is a graph summarizing the results of Examples and Comparative Examples. The horizontal axis represents the ratio (weight) of SGCNT to the total amount (total CNT amount) of single-walled carbon nanotubes (SGCNT) and multi-walled carbon nanotubes (NC7000). %), And the vertical axis represents the initial resistance (R ₀ ) of the stretchable electrode and the difference (ΔR) in the electrical resistance at 100% elongation between the second and 1000th cycles.

As is apparent from the results shown in FIGS. 7 to 14, the stretchable electrodes of Comparative Examples 1 and 2 have a large content of multi-walled carbon nanotubes. The difference (ΔR) exceeded 2 kΩ, and the variation in electrical resistance during expansion and contraction increased.
Further, in the stretchable electrodes of Comparative Examples 3 and 4, since the content of the single-walled carbon nanotube was large, the initial resistance (R ₀ ) was increased.
In contrast, by setting the content of the single-walled carbon nanotubes to 20 to 70% by weight with respect to the total amount of the single-walled carbon nanotubes and the multi-walled carbon nanotubes, the initial resistance (R ₀ ) and the second and 1000th cycles The difference in electrical resistance (ΔR) when the eye stretched 100% could be kept low.

The stretchable electrode of the present invention can be used in various applications such as sensor sheets, conductive wiring materials, actuators, generators, and various signal lines and low-power power lines in places where stretch flexibility is required. It can be suitably used as a sensor sheet for a soft sensor that requires stretchability and flexibility, such as a capacitive sensor.

DESCRIPTION OF SYMBOLS 1 Capacitance type sensor sheet 2 Dielectric layer 01A1-16A1 Front side connection part 01A-16A, 01D-16D Front side electrode layer 01B1-16B1 Back side connection part 01B-16B, 01E-16E Back side electrode layer C0101-C1616, F0101-F1616 Detection Part 50, 100, 110, 120, 130 Stretchable electrode 51, 101, 111a, 111b, 121a, 121b, 131 Base material 52, 102, 112, 122a, 122b, 132a, 132b Electrode body 201 Capacitive sensor 202 203 External wiring 204 Measuring means

Claims (5)

A base material comprising an elastomer composition;
An electrode body made of carbon nanotubes integrated with the base material,
The carbon nanotube is a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes,
The stretchable electrode, wherein a content of the single-walled carbon nanotube is 20 to 70% by weight with respect to a total amount of the single-walled carbon nanotube and the multi-walled carbon nanotube. The stretchable electrode according to claim 1, wherein the single-walled carbon nanotube has an average length of 100 to 700 μm. The stretchable electrode according to claim 1 or 2, wherein the multi-walled carbon nanotube has a fiber diameter of 5 to 15 nm. The stretchable electrode according to any one of claims 1 to 3, which is used for a sensor sheet. A sensor sheet comprising the stretchable electrode according to claim 1.

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