JP7835704B2 - Flexible sheet electrodes, wearable bioelectrodes, and biosensors - Google Patents

Description

This invention relates to a flexible sheet electrode, a wearable bioelectrode, and a biosensor.

Various developments have been made regarding sheet electrodes. As an example of this type of technology, the technology described in Patent Document 1 is known. Patent Document 1 describes an electrode member characterized in that a conductive polymer is supported on the surface of the single fibers constituting the fibrous structure and/or in the gaps between the single fibers (Claim 1 of Patent Document 1, etc.). In the examples of the same document, a method for supporting the conductive polymer on the fibrous structure is described, which involves gravure coating the fibrous structure with a dispersion of a conductive polymer such as PEDOT/PSS and a binder dispersed in a solvent, so that the coating amount is approximately 15 g/ ^m² (approximately 1.5 mg/ ^cm² ).

International Publication No. 2015/115440

However, the electrode member described in Patent Document 1 does not adequately consider a configuration using a conductive elastomer layer as the sheet-like electrode portion.

The inventors' investigations revealed that there is room for improvement in measurement stability in sheet electrodes having a conductive elastomer layer.

Further investigation by the inventors revealed that the stability of measurements using flexible sheet electrodes can be evaluated by using the arithmetic mean height and maximum height on the surface of the conductive elastomer layer when stretched by 20% as indicators. Based on this finding, further intensive research revealed that by setting the arithmetic mean height (Sa ₂₀ ) and/or maximum height (Sz ₂₀ ) on the surface of the conductive elastomer layer when stretched by 20% to below a predetermined value, noise during biopotential measurement is suppressed, and the measurement stability of flexible sheet electrodes can be improved, thus completing the present invention.

According to the present invention,
Flexible substrate and
A conductive elastomer layer provided on the flexible substrate,
A flexible sheet electrode comprising,
When the arithmetic mean height of the conductive elastomer layer at 20% elongation, measured with a laser microscope whose laser light wavelength is 404 nm, is defined as Sa ₂₀ and the maximum height as Sz ₂₀ ,
Sa ₂₀ ≤ 21.0 μm and/or Sz ₂₀ ≤ 250 μm,
Flexible sheet electrodes are provided.

Furthermore, according to the present invention,
A wearable bioelectrode is provided, which includes the flexible sheet electrode described above.

Furthermore, according to the present invention,
A biosensor equipped with the above-mentioned wearable bioelectrode is provided.

According to the present invention, a flexible sheet electrode with excellent measurement stability, a wearable bioelectrode, and a biosensor using the same are provided.

This figure shows an example of the configuration of the flexible sheet electrode of this embodiment. This figure shows an example of a modified flexible sheet electrode. This figure shows an example of the configuration of a wearable bioelectrode according to this embodiment. This is a cross-sectional view taken along line B-B in Figure 3. This figure illustrates an example of the configuration of the biosensor in this embodiment.

The embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted where appropriate. Furthermore, the drawings are schematic diagrams and do not necessarily correspond to actual dimensional proportions.

The following describes the outline of the flexible sheet electrode of this embodiment.

The flexible sheet electrode of this embodiment comprises a flexible substrate and a conductive elastomer layer provided on the flexible substrate, and is configured such that when the arithmetic mean height on the surface of the conductive elastomer layer at 20% elongation, measured with a laser microscope with a laser light wavelength of 404 nm, is defined as Sa ₂₀ and the maximum height as Sz ₂₀ , Sa ₂₀ ≤ 21.0 μm and/or Sz ₂₀ ≤ 250 μm.

The arithmetic mean height Sa represents the average of the absolute differences in height between each store relative to the average plane of a two-dimensional surface.
The maximum height Sz represents the distance from the highest point to the lowest point on a two-dimensional surface.

According to the inventors' findings, by setting the arithmetic mean height (Sa ₂₀ ) and/or maximum height (Sz ₂₀ ) on the surface of a conductive elastomer layer functioning as an electrode to be below the above upper limit when stretched by 20%, noise when measuring biopotential can be suppressed, and the measurement stability of the flexible sheet electrode can be improved.
Although the detailed mechanism is not clear, it is thought that by moderately smoothing the surface of the conductive elastomer layer in its extended state, noise can be suppressed when measuring biopotential in actual measurement scenarios where a flexible sheet electrode is made to follow the surface of the object being measured.

Flexible sheet electrodes can be applied to various uses, one of which is wearable bioelectrodes. The wearable bioelectrode of this embodiment is equipped with the flexible sheet electrode described above.

According to this embodiment, a wearable bioelectrode can be realized in which noise in the electrocardiogram waveform is suppressed and the S-T region is clearly visible. The height of the S-T region is an important factor in determining cardiac abnormalities. For example, a lower S-T region may indicate angina pectoris, while a higher S-T region may indicate myocardial infarction.

Wearable bioelectrodes can detect electrical potential fluctuations from living organisms, such as heart rate, muscle activity, and nervous system activity. For example, a wearable bioelectrode may be configured to measure at least one of the following bioelectric potentials: electrocardiogram, electromyogram, and skin potential.

According to this embodiment, a stretchable and/or bendable wearable bioelectrode can be realized.
Such wearable bioelectrodes suppress wire breakage in the flexible sheet electrode even when the substrate is deformed, such as by stretching or bending, enabling stable measurement of biopotential. Furthermore, even when the substrate is deformed, delamination of the flexible sheet electrode from the flexible substrate is suppressed, and mutual adhesion is maintained.

Wearable bioelectrodes can be used as wearable devices that can be attached to either the body or clothing. Due to their elasticity, such wearable bioelectrodes can conform to the surface shape and movements of the body. In this case, the wearable bioelectrode may be attached directly to the body or to the body via a body-mounting component (clothing). Clothing with wearable bioelectrodes may, for example, have the wearable bioelectrode sewn into the clothing, or have the wearable bioelectrode used as part of the clothing.

Wearable bioelectrodes can be further equipped with connectors and electronic components to form biosensors that can connect to external devices. These biosensors are wearable. By analyzing bioelectric potentials such as electrocardiograms detected by these biosensors, biosignal measurement systems tailored to various applications can be constructed.

Such wearable bioelectrodes, biosensors using them, and biosignal measurement systems are expected to be usable in a variety of settings, including physical diagnosis, health management, fitness, rehabilitation, and elderly care.

The configuration of the flexible sheet electrode and the wearable bioelectrode of this embodiment will be described in detail below.

<Flexible Sheet Electrode>
Figure 1 is a top view showing an example of the configuration of the flexible sheet electrode 1. Figure 1(a) is a cross-sectional view of the flexible sheet electrode 1 along line A-A in (b), and (b) is a top view of the flexible sheet electrode 1.

The flexible sheet electrode 1 comprises a flexible substrate 10 and a conductive elastomer layer 20 provided on the flexible substrate 10.

In the conductive elastomer layer 20 shown in Figure 1(a), the arithmetic mean height when unstretched is Sa ₀ and the maximum height is Sz ₀ , while the arithmetic mean height when the surface is stretched by 20% is Sa ₂₀ and the maximum height is Sz ₂₀ .

The upper limit of Sa ₂₀ is, for example, 19.5 μm or less, preferably 18.5 μm or less, and more preferably 12.0 μm or less. This improves the measurement stability of the flexible sheet electrode 1.
On the other hand, the lower limit of Sa ₂₀ is not particularly limited, but may be 0.5 μm or larger, or 1 μm or larger.

The upper limit of Sz ₂₀ is, for example, 200 μm or less, preferably 190 μm or less, and more preferably 80 μm or less. This improves the measurement stability of the flexible sheet electrode 1.
On the other hand, the lower limit of Sz ₂₀ is not particularly limited, but may be 1 μm or more, or 5 μm or more.

The flexible sheet electrode 1 may be configured to satisfy 0 μm ≤ |Sa ₂₀ - Sa ₀ | ≤ 10 μm and/or 0 μm ≤ |Sz ₂₀ - Sz ₀ | ≤ 80 μm.

The upper limit of |Sa ₂₀ - Sa ₀ | is, for example, 10 μm or less, preferably 8 μm or less, and more preferably 5 μm or less. This improves the measurement stability of the flexible sheet electrode 1.

The upper limit of |Sz ₂₀ - Sz ₀ | is, for example, 80 μm or less, preferably 60 μm or less, and more preferably 50 μm or less. This improves the measurement stability of the flexible sheet electrode 1.

After repeatedly performing the washing process 20 times according to the following procedures (1) to (4), the arithmetic mean height of the unstretched conductive elastomer layer 20, measured with a laser microscope with a laser light wavelength of 404 nm, is defined as Sa _W0 , and the maximum height as Sz _W0 .
(Laundry procedure)
1. The flexible sheet electrode is stretched and contracted 300 times in both the vertical and horizontal directions by 50%.
2. Put neutral detergent and water into a beaker, immerse the flexible sheet electrode that has been treated in step 1, and stir for 24 hours.
3. Pour water into a beaker, immerse the flexible sheet electrode that has been treated in step 2, stir for 10 minutes, and then rinse off the detergent.
4. Dry in a 90°C oven for 30 minutes.

The flexible sheet electrode 1 may be configured to satisfy Sa _W0 ≤ 16.0 μm and/or Sz _W0 ≤ 250 μm.

The upper limit of Sa _w0 is, for example, 16.0 μm or less, preferably 14.0 μm or less, and more preferably 7 μm or less. This improves the measurement stability of the flexible sheet electrode 1.
On the other hand, the lower limit of Sa _w0 is not particularly limited, but it may be 0.5 μm or larger, or 1 μm or larger.

The upper limit of Sz _w0 is, for example, 250 μm or less, preferably 200 μm or less, and more preferably 80 μm or less. This improves the measurement stability of the flexible sheet electrode 1.
On the other hand, the lower limit of Sz _w0 is not particularly limited, but it may be 1 μm or more, or 5 μm or more.

The lower limit of the amount of conductive elastomer layer 20 attached is, for example, 15 mg/ ^cm² or more, preferably 30 mg/ ^cm² or more, and more preferably 40 mg/ ^cm² or more. This enhances conductivity.
The upper limit of the amount of conductive elastomer layer 20 attached is, for example, 300 mg/ ^cm² or less, preferably 250 mg/ ^cm² or less, and more preferably 200 mg/ ^cm² or less. This suppresses a decrease in the flexibility of the flexible sheet electrode.

The conductive elastomer layer 20 is stretchable.

In this specification, elasticity is expressed as the elongation rate when stretched in a predetermined direction. As the predetermined direction, for example, in the top view of Figure 1, the direction in which the conductive elastomer layer 20, specifically the conductive elastomer layer 20, has the maximum length may be adopted.
When the top view shape of the conductive elastomer layer 20 is rectangular, when measuring the arithmetic mean height (Sa ₂₀ ) and the maximum height (Sz ₂₀ ), the layer may be stretched in the planar direction by grasping two opposing sides, and when measuring the surface resistivity, it may be stretched in the diagonal direction.

When stretched in the direction described above, "stretchable" means that the material can be stretched to, for example, 10% or more, preferably 20% or more, and more preferably 50% or more, and that the conductive elastomer layer 20 does not break at that stretched rate.

Let R1 be the surface resistance of the conductive elastomer layer 20 at 25°C and before stretching, and R2 be the surface resistance of the conductive elastomer layer 20 at 25°C and after stretching by 20% in one of the in-plane directions of the surface. The structure is configured such that R1 and R2 satisfy 1.0 ≤ R2/R1 ≤ 7.0.

The upper limit of R2/R1 is, for example, 7.0 or less, preferably 6.5 or less, and more preferably 5.0 or less. This improves measurement stability.
On the other hand, the lower limit of R2/R1 is not particularly limited, but may be 1.0 or greater, and preferably 1.1 or greater.
Furthermore, the upper limit of R2 is, for example, 30 Ω or less, preferably 20 Ω or less, and more preferably 15 Ω or less. On the other hand, the lower limit of R2 may be, for example, 0.5 Ω or more.

Furthermore, while resistance measurements such as surface resistivity may be taken between any two points, if the top view shape of the conductive elastomer layer 20 is rectangular, the measurements may also be taken diagonally across the conductive elastomer layer 20.

The conductive elastomer layer 20 is constructed using a conductive elastomer described later.
Furthermore, the conductive elastomer layer 20 may be formed by a printing method using a conductive paste containing a conductive elastomer. That is, an example of the conductive elastomer layer 20 is composed of a printed layer of conductive paste. This makes it possible to provide a flexible sheet electrode with excellent design freedom for the sheet electrode design.

The flexible substrate 10 is not particularly limited as long as it is a substrate that can be stretched and/or bent, but for example, it may be composed of a fibrous substrate or an elastomer substrate.

Examples of fiber structural materials for fiber base materials include natural fibers such as plant fibers and animal fibers; and chemical fibers such as inorganic fibers, regenerated fibers, semi-synthetic fibers, and synthetic fibers. These may be used individually or in combination of two or more types. Among these, from the viewpoint of durability, chemical fibers may be used, as may synthetic fibers such as acrylic, polyester, nylon, and polyurethane.

The fibrous substrate can be any known fibrous substrate, but it may also be composed of either an insulating material or a conductive material, or both.

The lower limit of the basis weight of the fibrous base material is, for example, 10 g/ ^m² or more, preferably 20 g/ ^m² or more, and more preferably 30 g/ ^m² or more. This increases the mechanical strength.
On the other hand, the upper limit of the basis weight of the fiber base material is, for example, 500 g/ ^m² or less, preferably 400 g/ ^m² or less, and more preferably 350 g/ ^m² or less. This suppresses a decrease in flexibility. It also increases the degree of impregnation of the conductive elastomer layer.

The elastomer substrate may be composed of an insulating elastomer as described later. Furthermore, the elastomer substrate may be a porous elastomer substrate, or an elastomer substrate with surface irregularities, etc.

The structure of the fibrous base material is not limited, but from the viewpoint of flexibility, woven or knitted fabrics may be used.

The upper limit of the thickness of the flexible substrate 10 can be set according to the application, for example, it may be 10 mm or less, preferably 1 mm or less, but from the viewpoint of wearable device applications, it is more preferably 600 μm or less. By setting it to 600 μm or less, a thin film sheet-like wearable bioelectrode can be realized.
From the viewpoint of mechanical strength, the lower limit of the thickness of the flexible substrate 10 is, for example, 10 μm or more, preferably 50 μm or more, and more preferably 100 μm or more.

One example of a method for manufacturing the flexible sheet electrode 1 of this embodiment includes a step of impregnating a flexible substrate 10 with a conductive elastomer material.
The conductive elastomer material may be in the form of a paste or a film. The impregnation method can be selected from known methods depending on the form.
Impregnation methods include screen processing, dipping, coating, calendering, lamination, and vacuum impregnation. In these processes, it is possible to introduce the conductive elastomer material into the flexible substrate 10 using blades, rollers, presses, etc., and heating if necessary.

As a specific example of a manufacturing method for the flexible sheet electrode 1, we will describe an example of screen processing using a conductive paste as the conductive elastomer material and a squeegee.
First, a support is placed on the workbench, and the flexible base material 10 is placed on the support.
Next, a mask having a predetermined opening pattern shape is placed on the flexible substrate 10.
Next, a conductive paste is applied to the flexible sheet electrode 1 using a squeegee, via a mask.
Subsequently, the conductive paste is subjected to a curing treatment. For example, in the case of a conductive paste containing a silicone rubber-based curable composition, the curing temperature can be set to 160°C to 220°C and the curing time to 1 to 3 hours. The mask is removed after or before the curing treatment.
Subsequently, the flexible substrate 10 support is separated to obtain the flexible sheet electrode 1.

In this embodiment, for example, by appropriately selecting the method for manufacturing the flexible sheet electrode 1, it is possible to control the Sa ₂₀ , Sa ₀ , Sz ₂₀ , Sz ₀ , and adhesion amount of the conductive elastomer layer 20. Among these, for example, appropriately selecting the thickness of the mask, the number of mask layers, the number of coatings, and the solid content concentration of the conductive paste are examples of factors that can bring the Sa ₂₀ , Sa ₀ , Sz ₂₀ , Sz ₀ , and adhesion amount of the conductive elastomer layer 20 into a desired numerical range.

An example of deformation of the flexible sheet electrode 1 will be explained using Figure 2.

The flexible substrate 10 may be configured such that, in the thickness direction, a portion of it includes an impregnation layer 21 of the conductive elastomer layer 20, as shown in Figure 2(a), or the entire substrate may include an impregnation layer 21.
This makes it possible to realize a flexible sheet electrode 1 with excellent wash resistance.

Furthermore, as shown in Figure 2(b), the flexible substrate 10 may have an insulating elastomer layer 60 on the side opposite to the side with the conductive elastomer layer 20. The insulating elastomer layer 60 may be partially or entirely impregnated into the flexible substrate 10. The insulating elastomer layer 60 may be composed of an insulating elastomer as described later.

<Wearable Bioelectrodes>
Figure 3 is a top view showing an example of the configuration of the wearable bioelectrode 100. Figure 4 is a cross-sectional view taken along line B-B in Figure 3.
The wearable bioelectrode 100 comprises a flexible sheet electrode 1 having a flexible substrate 10 and a conductive elastomer layer 20.

The wearable bioelectrode 100 can detect bioelectrical signals generated from biological activities such as the heart, muscles, skin, and nerves by allowing one surface 22 of the conductive elastomer layer 20 to conform to the subject's body. When this wearable bioelectrode 100 has multiple conductive elastomer layers 20 in the in-plane direction of the flexible substrate 10, it can be suitably used as an electrode for measuring electrocardiogram waveforms.

Subjects include humans, non-human animals, etc.

The wearable bioelectrode 100 can be used as a simple and reusable dry sensor, rather than a wet sensor that requires gel application to the subject's measurement area.

The flexible substrate 10 has an electrode-forming region where a conductive elastomer layer 20 is formed, as seen from above. In this electrode-forming region, the flexible substrate 10 and the conductive elastomer layer 20 adhere closely together, both when non-stretched and when stretched, thereby increasing the overall mechanical strength of the wearable bioelectrode 100.

Furthermore, the flexible substrate 10 may have an electrode-free region around the electroforming area where the conductive elastomer layer 20 is not formed. Attachments such as sewing threads or snap buttons for mounting to clothing can be attached to this electrode-free region. Alternatively, when the wearable bioelectrode 100 is wrapped around the body, such as the wrist or ankle, the electrode-free region of the flexible substrate 10 may be overlapped in the thickness direction to secure it to the body.

As shown in Figure 1, an example of the flexible substrate 10 is that at least a portion of it, for example, the main body 12, has a band shape that can be wrapped around the body. Such a wearable bioelectrode 100 has a structure suitable for a band-type bioelectrode that can be wrapped around a part of the body, such as the wrist or ankle.

Furthermore, the band-type flexible substrate 10 in Figure 3 may have a main body 12 and an expansion portion 14 that protrudes in the in-plane direction of the main body 12. Even when the main body 12 is deformed into a ring structure or the like, deformation of the expansion portion 14 is suppressed. Therefore, connection failures at the external connection portion 30 attached to the expansion portion 14 can be suppressed.

The conductive elastomer layer 20 is configured in a sheet shape and has an exposed surface that comes into direct contact with the body.
In this specification, "sheet-like" means that when the thickness of the conductive elastomer layer 20 is D (mm) and the area of one surface 22 of the conductive elastomer layer 20 in a top view is S ( ^mm² ), S and D are, for example, 50 ≤ S/D, preferably 200 ≤ S/D, and more preferably 400 ≤ S/D. The upper limit of S/D can be set according to the measurement site of the subject and is not particularly limited, but for example, S/D ≤ ^10⁷ may be used.

The conductive elastomer layer 20 comes into contact with the body when the wearable bioelectrode 100 is used and can conform well to the contact surface, following the body's surface shape and deformation.

The wearable bioelectrode 100 may be configured to be connected to the outside via a conductive elastomer layer 20, or it may be configured to be connected via a connecting portion 26, which is a separate component electrically connected to the conductive elastomer layer 20. This connecting portion 26 may be configured to be electrically connected to the conductive elastomer layer 20 via a stretchable wiring 24, as shown in Figure 3.

The conductive elastomer layer 20, the stretchable wiring 24, and the connecting portion 26 are composed of the same/different conductive elastomer, preferably the same conductive elastomer.

Each component of the conductive elastomer layer 20 may be composed of a printed layer formed by a printing method using a conductive paste. In this case, each component, including the conductive elastomer layer 20, the stretchable wiring 24, and the connecting portion 26, may be seamlessly connected to one another.

The external connection section 30 can transmit bioelectric signals detected through the conductive elastomer layer 20 to external electronic components, etc.

The wearable bioelectrode 100 shown in Figure 3 includes an external connection part 30.
The external connection portion 30 is provided on the flexible substrate 10 opposite to the conductive elastomer layer 20. For example, the external connection portion 30 in Figure 2 is formed on the other surface 13 of the flexible substrate 10. This prevents the external connection portion 30 from coming into contact with the body together with the conductive elastomer layer 20 when the wearable bioelectrode 100 is in use, thereby suppressing interference with the detection of bioelectrical signals.

The external connection portion 30 is not particularly limited as long as it is configured to be electrically connected to the conductive elastomer layer 20, but it is made of a conductive material such as a metal or a conductive elastomer.

The shape of the external connection part 30 is not particularly limited, but it may have a connector that can be connected to electronic components or a structure that facilitates wiring.

An example of the external connection part 30 may be a metal snap button.
The external connection part 30 in Figure 4 is a male snap button and is fixed to the flexible base material 10 using a metal mounting plate 32 and mounting pin 34. By fixing the flexible base material 10 by sandwiching it between the external connection part 30 and the mounting plate 32, misalignment of the fixing position of the external connection part 30 can be suppressed.
The mounting pin 34 contacts a part of the conductive elastomer layer 20, for example, the connection portion 26, thereby enabling electrical connection between the conductive elastomer layer 20 and the external connection portion 30.

Furthermore, a portion or the entire surface of the mounting plate 32 in Figure 4 is covered with an insulating protective layer 52. The insulating protective layer 52 prevents contact between the mounting plate 32 and the body. The insulating protective layer 52 may be made of any insulating material, such as an insulating elastomer like silicone rubber.

The biosensor of this embodiment will now be described.

The biosensor comprises one wearable bioelectrode 100, or two or more wearable bioelectrodes 100, depending on the application. The biosensor may be directly attached to the body, or it may be attached to a body-mounting component such as clothing.

The biosensor includes electronic components that can be electrically connected to the wearable bioelectrode 100 via an external connection unit 30.

Various known electronic components can be used depending on the application, but examples include amplifiers, AD converters, CPUs, memory, communication circuits, wireless communication units, analog filters, capacitors, resistors, and batteries. One or more of these may be modularized on a circuit board. This allows the biosensor to be used as a wearable device.
Furthermore, other sensors such as acceleration sensors, temperature sensors, and pressure sensors may be used in combination as electronic components.

Figure 5 illustrates an example of the configuration of the biosensor 200.
The biosensor 200 in Figure 5 comprises a wearable bioelectrode 100, a connector 210, a cable 220, a sensor module 230, and a computer 240.

The connector 210 has a structure that allows it to be electrically coupled to the external connection part 30 of the wearable bioelectrode 100, and may have, for example, a female snap button.
The cable 220 electrically connects the connector 210 to the electronic components, namely the sensor module 230 and the computer 240.
The sensor module 230 can be used with an ECG sensor module when measuring electrocardiogram waveforms. The sensor module 230 has an electrical circuit that suppresses interference from external RF sources, line frequencies, and electrical noise, and can suppress noise when measuring bioelectrical signals.
Computer 240 can acquire bioelectrical signals and generate and output waveforms of bioelectric potentials such as surface electromyography, electrocardiogram, skin potential, and electroencephalography. Computer 240 may use a single-board computer consisting of a printed circuit board equipped with a CPU, peripheral components, input/output interfaces, connectors, etc.

The biosignal measurement system of this embodiment will now be described.
The biosignal measurement system of this embodiment is equipped with a biosensor. The biosignal measurement system may be a system (measuring device) that displays, analyzes, or stores data received from the biosensor.

A modified example of the wearable bioelectrode 100 will be described.

As shown in Figure 1, the wearable bioelectrode 100 may include a protective layer 50 between the flexible substrate 10 and the external connection portion 30. This increases mechanical strength and prevents damage to the conductive elastomer layer 20 when an external terminal is connected to the external connection portion 30.

The protective layer 50 may be formed wider than the external connection portion 30 when viewed from the other side 13, and may also be formed to conform to the shape of the expanded portion 14 of the flexible base material 10. This increases the mechanical strength of the expanded portion 14.

The protective layer 50 may be made of an elastic material, such as an insulating elastomer like silicone rubber, or the same material as the flexible base material 10. This improves the adhesion between the flexible base material 10 and the protective layer 50.

The flexible base material 10 may be composed of a single layer or multiple layers laminated together.
The wearable bioelectrode 100 may have a multilayer wiring structure in which a flexible substrate 10 and a conductive elastomer layer 20 are alternately laminated.

The shape of the flexible substrate 10 in a top view is not particularly limited and can be appropriately deformed depending on the application.

The flexible substrate 10 may have one conductive elastomer layer 20 on the same surface 11, or it may have two or three or more conductive elastomer layers 20 independently.

The conductive elastomer layer 20, or the shape of the conductive elastomer layer 20 as viewed from above, is not particularly limited and can be appropriately deformed depending on the application. Examples include a square shape, a circular shape, an elliptical shape, and other polygonal shapes. This ensures a certain contact area with the body and improves measurement stability.

The conductive elastomer layer 20, or the corners of the conductive elastomer layer 20 in a top view, may have a rounded edge. This helps to prevent localized stress from occurring at the corners during use, thus suppressing damage to the conductive elastomer layer 20.

The external connection section 30 may be composed of a single component, or it may be composed of multiple components assembled together.
The external connection part 30 is installed on the flexible substrate 10 by mechanical means, but it may also be installed by chemical means using an adhesive or the like.

The snap button used in the external connection part 30 may be either a male or female snap button. The external connection part 30 is fixed to the flexible base material 10, but it may also be attached in a detachable manner.

The following describes the material of the conductive elastomer layer 20.

In one example of the flexible sheet electrode 1 of this embodiment, the conductive elastomer layer 20 is made of conductive elastomer. In addition, the insulating elastomer layer 60 is made of insulating elastomer.
The insulating elastomer and the conductive elastomer may be configured to contain the same elastomer material.

Insulating elastomers can include, for example, silicone rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber, styrene rubber, chloroprene rubber, ethylene propylene rubber, and the like. Among these, the elastomer includes one or more thermosetting elastomers (elastomer materials) selected from the group consisting of silicone rubber, urethane rubber, and fluororubber.
An insulating elastomer may consist of an elastomer material alone, or it may be composed of an elastomer material and a non-conductive filler. An example of an insulating elastomer includes silicone rubber, preferably silicone rubber and a non-conductive filler. Among elastomers, silicone rubber is chemically stable and also has excellent mechanical strength.
Among these, from a hygienic standpoint, it is preferable to use silicone rubber, which has high biocompatibility, as the elastomer material.

Conductive elastomers can include, for example, silicone rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber, styrene rubber, chloroprene rubber, ethylene propylene rubber, and the like. Among these, the elastomer comprises one or more thermosetting elastomers (elastomer materials) selected from the group consisting of silicone rubber, urethane rubber, and fluororubber, and a conductive filler.
A preferred example of a conductive elastomer includes silicone rubber and a conductive filler. This enhances the elasticity and conductivity of the conductive elastomer.

At least one, preferably both, of the insulating elastomer and the conductive elastomer may contain a non-conductive filler. Known materials can be used as the non-conductive filler; for example, silica particles, silicone rubber particles, talc, etc., may be used. Among these, silica particles may also be included.

The conductive filler may include, for example, one or more selected from the group consisting of powdered or fibrous metal-based fillers, carbon-based fillers, metal oxide fillers, and metal-plated fillers. Among these, a metal-based filler such as silver powder may be used as the conductive filler.

The conductive elastomer may further contain non-conductive fillers in addition to the conductive fillers. This can enhance the mechanical properties of the conductive elastomer.

A specific example is that the conductive elastomer layer 20 may contain silver powder as a conductive filler, preferably in the form of flake-shaped silver powder. This can improve conductivity and, moreover, stretch conductivity.
Furthermore, the conductive elastomer layer 20 may also contain silver powder and silica particles as a non-conductive filler. This improves the stretchability and durability of the conductive elastomer layer 20.

The conductive elastomer of the conductive elastomer layer 20, the insulating elastomer of the flexible substrate 10, and at least two or all of the insulating elastomers of the protective layer 50 and the insulating protective layer 52 may be configured to contain the same elastomer material.

In this specification, "containing the same elastomer material" means that each contains at least one of the same type of elastomer material from among the types of thermosetting elastomers exemplified above.
Furthermore, if the same silicone rubber is included, this silicone rubber may be composed of a cured product of a silicone rubber-based curable composition containing a vinyl group-containing organopolysiloxane.

The insulating elastomer may be composed of a cured product of a silicone rubber-based curable composition containing a vinyl group-containing organopolysiloxane. The conductive elastomer may also be composed of a conductive filler and a cured product of a silicone rubber-based curable composition containing a vinyl group-containing organopolysiloxane.

The following provides a detailed explanation of the components of the silicone rubber-based curable composition.

In this specification, "containing the same silicone rubber" means that the silicone rubber-based curable composition contains at least the same type of vinyl group-containing linear organopolysiloxane, and may further contain one or more selected from the group consisting of the same type of crosslinking agent, the same type of nonconductive filler, the same type of silane coupling agent, and the same type of catalyst.

A linear organopolysiloxane containing the same type of vinyl group is defined as one that contains at least the same vinyl group functional group and has a linear structure; however, the amount of vinyl groups in the molecule, the molecular weight distribution, or the amount added may differ.

Similar crosslinking agents only need to share a common structure, such as a linear or branched structure. They may have different molecular weight distributions, different functional groups, and different amounts added.

Non-conductive fillers of the same type only need to share at least common constituent materials; they may differ in particle size, specific surface area, surface treatment agent, or the amount of these additives.

Similar silane coupling agents only need to share at least one common functional group; other functional groups in the molecule and the amount added may differ.

Catalysts of the same type only need to have at least common constituent materials; they may contain different compositions, and the amounts of these compositions may differ.

A silicone rubber-based curable composition comprising the same silicone rubber may further contain one or more selected from the group consisting of different types of vinyl group-containing linear organopolysiloxanes, crosslinking agents, nonconductive fillers, silane coupling agents, and catalysts.

The silicone rubber-based curable composition of this embodiment may contain a vinyl group-containing organopolysiloxane (A). The vinyl group-containing organopolysiloxane (A) is a polymer that forms the main component of the silicone rubber-based curable composition of this embodiment.

The vinyl group-containing organopolysiloxane (A) described above may include a vinyl group-containing linear organopolysiloxane (A1) having a linear structure.

The above-mentioned vinyl group-containing linear organopolysiloxane (A1) has a linear structure and contains vinyl groups, which serve as crosslinking points during curing.

The vinyl group content of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but it is preferable that it contains two or more vinyl groups in the molecule and has a content of 15 mol% or less. This optimizes the amount of vinyl groups in the vinyl group-containing linear organopolysiloxane (A1), ensuring the formation of a network with the components described later.

In this specification, unless otherwise specified, "~" indicates that it includes both the upper and lower limits.

In this specification, the vinyl group content refers to the mole percentage of vinyl group-containing siloxane units, where the total number of units constituting the vinyl group-containing linear organopolysiloxane (A1) is considered to be 100 mol%. However, it is assumed that there is one vinyl group per vinyl group-containing siloxane unit.

Furthermore, the degree of polymerization of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but is preferably in the range of approximately 1,000 to 10,000, and more preferably 2,000 to 5,000. The degree of polymerization can be determined, for example, by the number-average degree of polymerization (or number-average molecular weight) in polystyrene terms in GPC (gel permeation chromatography) using chloroform as the developing solvent.

Furthermore, the specific gravity of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but is preferably in the range of approximately 0.9 to 1.1.

By using a vinyl group-containing linear organopolysiloxane (A1) having a degree of polymerization and specific gravity within the above-mentioned range, the heat resistance, flame retardancy, and chemical stability of the resulting silicone rubber can be improved.

The vinyl group-containing linear organopolysiloxane (A1) is preferably one having the structure represented by the following formula (1).

In formula (1), ^R1 is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or a hydrocarbon group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl, allyl, and butenyl groups, with vinyl being preferred. Examples of aryl groups having 1 to 10 carbon atoms include phenyl.

Furthermore, ^R2 is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or a hydrocarbon group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl, allyl, and butenyl groups. An example of an aryl group having 1 to 10 carbon atoms is the phenyl group.

Furthermore, ^R3 is a substituted or unsubstituted alkyl group, aryl group, or hydrocarbon group having 1 to 8 carbon atoms. Examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. An example of an aryl group having 1 to 8 carbon atoms is the phenyl group.

Furthermore, examples of substituents for ^R1 and ^R2 in formula (1) include methyl groups and vinyl groups, and examples of substituents for ^R3 include methyl groups.

In equation (1), the multiple ^R1s are independent of each other and may be different from each other or the same. The same applies to ^R2 and ^R3 .

Furthermore, m and n are the number of repeating units constituting the vinyl group-containing linear organopolysiloxane (A1) represented by formula (1), where m is an integer from 0 to 2000 and n is an integer from 1000 to 10000. m is preferably from 0 to 1000, and n is preferably from 2000 to 5000.

Furthermore, a specific structure of the vinyl group-containing linear organopolysiloxane (A1) represented by formula (1) can be found, for example, in the structure represented by formula (1-1) below.

In formula (1-1), ^R1 and ^R2 are each independently a methyl group or a vinyl group, and at least one of them is a vinyl group.

The vinyl group-containing linear organopolysiloxane (A1) may include a first vinyl group-containing linear organopolysiloxane (A1-1) having two or more vinyl groups in the molecule and containing 0.4 mol% or less. The amount of vinyl groups in the first vinyl group-containing linear organopolysiloxane (A1-1) may be 0.1 mol% or less.

Furthermore, the vinyl group-containing linear organopolysiloxane (A1) may contain a first vinyl group-containing linear organopolysiloxane (A1-1) and a second vinyl group-containing linear organopolysiloxane (A1-2) having a vinyl group content of 0.5 to 15 mol%.

By combining a first vinyl group-containing linear organopolysiloxane (A1-1) and a second vinyl group-containing linear organopolysiloxane (A1-2), which has a high vinyl group content, as raw rubber raw materials for silicone rubber, the vinyl groups can be unevenly distributed, allowing for more effective formation of crosslink density variations within the crosslinking network of the silicone rubber. As a result, the tear strength of the silicone rubber can be more effectively increased.

Specifically, it is preferable to use, for example, a first vinyl group-containing linear organopolysiloxane (A1-1) having two or more units in the molecule where R1 is a vinyl group and/or R2 is a vinyl group in the above formula (1-1), and containing 0.4 mol% or less of these units, and a second vinyl group-containing linear organopolysiloxane (A1-2) containing 0.5 to 15 mol% of units where R1 is a vinyl group and/or R2 is a vinyl group.

Furthermore, the first vinyl group-containing linear organopolysiloxane (A1-1) preferably has a vinyl group content of 0.01 to 0.2 mol%. The second vinyl group-containing linear organopolysiloxane (A1-2) preferably has a vinyl group content of 0.8 to 12 mol%.

Furthermore, when combining the first vinyl group-containing linear organopolysiloxane (A1-1) and the second vinyl group-containing linear organopolysiloxane (A1-2), the ratio of (A1-1) to (A1-2) is not particularly limited, but for example, a weight ratio of (A1-1):(A1-2) of 50:50 to 95:5 is preferred, and a weight ratio of 80:20 to 90:10 is more preferred.

Furthermore, the first and second vinyl group-containing linear organopolysiloxanes (A1-1) and (A1-2) may be used individually or in combination of two or more types.

Furthermore, the vinyl group-containing organopolysiloxane (A) may also include a vinyl group-containing branched organopolysiloxane (A2) having a branched structure.

<<Organohydrogenpolysiloxane (B)>>
The silicone rubber-based curable composition of this embodiment may contain organohydrogenpolysiloxane (B).
Organohydrogenpolysiloxanes (B) are classified into linear organohydrogenpolysiloxanes (B1) having a linear structure and branched organohydrogenpolysiloxanes (B2) having a branched structure, and a compound may contain either one or both of these.

The linear organohydrogenpolysiloxane (B1) has a linear structure and a structure in which hydrogen is directly bonded to Si (≡Si-H). It is a polymer that undergoes a hydrosilylation reaction with the vinyl groups of vinyl group-containing organopolysiloxane (A), as well as vinyl groups of components incorporated into silicone rubber-based curable compositions, thereby crosslinking these components.

The molecular weight of the linear organohydrogenpolysiloxane (B1) is not particularly limited, but for example, a weight-average molecular weight of 20,000 or less is preferred, and a weight-average molecular weight of 1,000 or more and 10,000 or less is more preferred.

Furthermore, the weight-average molecular weight of linear organohydrogenpolysiloxane (B1) can be measured, for example, by converting it to polystyrene equivalent using GPC (gel permeation chromatography) with chloroform as the developing solvent.

Furthermore, it is preferable that the linear organohydrogenpolysiloxane (B1) does not typically contain vinyl groups. This effectively prevents the crosslinking reaction from proceeding within the linear organohydrogenpolysiloxane (B1) molecule.

As the linear organohydrogenpolysiloxane (B1) described above, one having the structure represented by the following formula (2) is preferably used.

In formula (2), ^R4 is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, hydrocarbon group, or hydride group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl, allyl, and butenyl groups. Examples of aryl groups having 1 to 10 carbon atoms include phenyl.

Furthermore, ^R5 is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, hydrocarbon group, or hydride group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl, allyl, and butenyl groups. An example of an aryl group having 1 to 10 carbon atoms is the phenyl group.

In formula (2), the multiple ^R4s are independent of each other and may be different from each other or the same. The same applies to ^R5 . However, at least two of the multiple ^R4s and ^R5s are hydride groups.

Furthermore, ^R6 is a substituted or unsubstituted alkyl group, aryl group, or hydrocarbon group having 1 to 8 carbon atoms. Examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. An example of an aryl group having 1 to 8 carbon atoms is the phenyl group. Multiple ^R6s are independent of each other and may be different from each other or the same.

In formula (2), examples of substituents ^R4 , ^R5 , and ^R6 include methyl groups and vinyl groups, and methyl groups are preferred from the viewpoint of preventing intramolecular crosslinking reactions.

Furthermore, m and n are the number of repeating units constituting the linear organohydrogenpolysiloxane (B1) represented by formula (2), where m is an integer from 2 to 150 and n is an integer from 2 to 150. Preferably, m is an integer from 2 to 100 and n is an integer from 2 to 100.

Furthermore, linear organohydrogenpolysiloxane (B1) may be used alone or in combination of two or more types.

The branched organohydrogenpolysiloxane (B2) has a branched structure, forming regions with high crosslink density, and is a component that greatly contributes to the formation of a dense-sparse crosslink structure within the silicone rubber system. Furthermore, similar to the linear organohydrogenpolysiloxane (B1) described above, it has a structure in which hydrogen is directly bonded to Si (≡Si-H), and is a polymer that undergoes hydrosilylation reactions with the vinyl groups of vinyl group-containing organopolysiloxane (A), as well as the vinyl groups of components blended into the silicone rubber curable composition, thereby crosslinking these components.

Furthermore, the specific gravity of branched organohydrogenpolysiloxane (B2) is in the range of 0.9 to 0.95.

Furthermore, it is preferable that the branched organohydrogenpolysiloxane (B2) typically does not contain vinyl groups. This effectively prevents the crosslinking reaction from proceeding within the branched organohydrogenpolysiloxane (B2) molecule.

Furthermore, the branched organohydrogenpolysiloxane (B2) is preferably the one shown in the following average composition formula (c).

Average composition formula (c)
(H _a (R ⁷ ) _3-a SiO _1/2 ) _m (SiO _4/2 ) _n
(In formula (c), R ⁷ is a monovalent organic group, a is an integer in the range of 1 to 3, m is the number of H _a (R ⁷ ) _3-a SiO _1/2 units, and n is the number of SiO _4/2 units.)

In formula (c), ^R7 is a monovalent organic group, preferably a substituted or unsubstituted alkyl group, aryl group, or hydrocarbon group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. An example of an aryl group having 1 to 10 carbon atoms is the phenyl group.

In formula (c), a is the number of hydride groups (hydrogen atoms directly bonded to Si), and is an integer in the range of 1 to 3, preferably 1.

Furthermore, in equation (c), m is the number of H _a (R ⁷ ) _3-a SiO _1/2 units, and n is the number of SiO _4/2 units.

Branched organohydrogenpolysiloxane (B2) has a branched structure. Linear organohydrogenpolysiloxane (B1) and branched organohydrogenpolysiloxane (B2) differ in their structure, specifically whether they are linear or branched. The number of alkyl groups R attached to Si (R/Si), where Si is considered as 1, ranges from 1.8 to 2.1 for linear organohydrogenpolysiloxane (B1) and from 0.8 to 1.7 for branched organohydrogenpolysiloxane (B2).

Furthermore, because branched organohydrogenpolysiloxane (B2) has a branched structure, the amount of residue when heated to 1000°C at a heating rate of 10°C/min under a nitrogen atmosphere is 5% or more. In contrast, linear organohydrogenpolysiloxane (B1), being linear, has virtually zero residue after heating under the above conditions.

Furthermore, a specific example of a branched organohydrogenpolysiloxane (B2) is one having the structure represented by the following formula (3).

In formula (3), ^R7 is a substituted or unsubstituted alkyl group, aryl group, or a hydrocarbon group combining these, or a hydrogen atom, having 1 to 8 carbon atoms. Examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. An example of an aryl group having 1 to 8 carbon atoms is the phenyl group. Examples of substituents on ^R7 include methyl groups.

In equation (3), the multiple ^R7s are independent of each other and may be different from each other or the same.

Furthermore, in equation (3), "-O-Si≡" indicates that Si has a branched structure that extends in three dimensions.

Furthermore, branched organohydrogenpolysiloxane (B2) may be used alone or in combination of two or more types.

Furthermore, the amount of hydrogen atoms (hydride groups) directly bonded to Si in the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) is not particularly limited. However, in the silicone rubber-based curable composition, it is preferable that the total amount of hydride groups in the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) is 0.5 to 5 moles, and more preferably 1 to 3.5 moles, per mole of vinyl groups in the vinyl group-containing linear organohydrogenpolysiloxane (A1). This ensures the reliable formation of a crosslinking network between the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) and the vinyl group-containing linear organohydrogenpolysiloxane (A1).

<<Silica particles (C)>>
The silicone rubber-based curable composition of this embodiment may optionally contain silica particles (C) as a non-conductive filler.

The silica particles (C) are not particularly limited, but for example, fumed silica, calcined silica, precipitated silica, etc., can be used. These may be used individually or in combination of two or more types.

The silica particles (C) preferably have a specific surface area of, for example, 50 to 400 ^m² /g by the BET method, and more preferably 100 to 400 ^m² /g. The average primary particle size of the silica particles (C) is preferably 1 to 100 nm, and more preferably about 5 to 20 nm.

By using silica particles (C) within the specified range of specific surface area and average particle size, the hardness and mechanical strength of the resulting silicone rubber can be improved, particularly its tensile strength.

<<Silane coupling agent (D)>>
The silicone rubber-based curable composition of this embodiment may contain a silane coupling agent (D).
The silane coupling agent (D) may have a hydrolyzable group. The hydrolyzable group is hydrolyzed by water to form a hydroxyl group, and this hydroxyl group undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the silica particles (C), thereby modifying the surface of the silica particles (C).

Furthermore, this silane coupling agent (D) may include a silane coupling agent having hydrophobic groups. This imparts these hydrophobic groups to the surface of the silica particles (C), thereby reducing the cohesive force of the silica particles (C) in the silicone rubber curable composition and, consequently, in the silicone rubber itself (reducing aggregation due to hydrogen bonding by silanol groups). As a result, it is presumed that the dispersibility of the silica particles in the silicone rubber curable composition improves. This increases the interface between the silica particles and the rubber matrix, enhancing the reinforcing effect of the silica particles. Furthermore, it is presumed that the slipperiness of the silica particles within the matrix improves during deformation of the rubber matrix. Finally, the improved dispersibility and slipperiness of the silica particles (C) improve the mechanical strength of the silicone rubber due to the silica particles (C) (e.g., tensile strength and tear strength).

Furthermore, the silane coupling agent (D) may include a silane coupling agent having vinyl groups. This introduces vinyl groups to the surface of the silica particles (C). Therefore, during the curing of the silicone rubber-based curable composition—that is, when the vinyl groups of the vinyl group-containing organopolysiloxane (A) and the hydride groups of the organohydrogenpolysiloxane (B) undergo a hydrosilylation reaction to form a network (crosslinked structure)—the vinyl groups of the silica particles (C) also participate in the hydrosilylation reaction with the hydride groups of the organohydrogenpolysiloxane (B), thus incorporating the silica particles (C) into the network. This allows for lower hardness and higher modulus of the resulting silicone rubber.

As the silane coupling agent (D), a silane coupling agent having a hydrophobic group and a silane coupling agent having a vinyl group can be used in combination.

Examples of silane coupling agents (D) include those represented by the following formula (4).

Y _n -Si-(X) _4-n ...(4)
In formula (4) above, n represents an integer from 1 to 3. Y represents a functional group having a hydrophobic group, a hydrophilic group, or a vinyl group, and when n is 1, it is a hydrophobic group, and when n is 2 or 3, at least one of them is a hydrophobic group. X represents a hydrolyzable group.

Hydrophobic groups are alkyl groups, aryl groups, or hydrocarbon groups with 1 to 6 carbon atoms, such as methyl, ethyl, propyl, and phenyl groups. Among these, methyl groups are particularly preferred.

Furthermore, hydrophilic groups include, for example, hydroxyl groups, sulfonic acid groups, carboxyl groups, or carbonyl groups, with hydroxyl groups being particularly preferred. While hydrophilic groups may be included as functional groups, their absence is preferable from the viewpoint of imparting hydrophobicity to the silane coupling agent (D).

Furthermore, hydrolyzable groups include alkoxy groups such as methoxy groups and ethoxy groups, chloro groups, and silazane groups, among which silazane groups are preferred due to their high reactivity with silica particles (C). Note that those having a silazane group as a hydrolyzable group will have two (Y _n -Si-) structures in formula (4) above, due to their structural characteristics.

Specific examples of the silane coupling agent (D) represented by the above formula (4) include, for example, alkoxysilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, and decyltrimethoxysilane, which have a hydrophobic group as a functional group; chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and phenyltrichlorosilane; and hexamethyldisilazane, which have a hydrophobic group as a functional group. Examples of materials having a vinyl group include alkoxysilanes such as methacryloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropylmethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinylmethyldimethoxysilane; chlorosilanes such as vinyltrichlorosilane and vinylmethyldichlorosilane; and divinyltetramethyldisilazane. Among these, considering the above, hexamethyldisilazane is particularly preferred as the material having a hydrophobic group, and divinyltetramethyldisilazane as the material having a vinyl group.

In this embodiment, the lower limit of the silane coupling agent (D) content is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100 parts by weight of the total amount of vinyl group-containing organopolysiloxane (A). The upper limit of the silane coupling agent (D) content is preferably 100% by mass or less, more preferably 80% by mass or less, and even more preferably 40% by mass or less, based on 100 parts by weight of the total amount of vinyl group-containing organopolysiloxane (A).
By setting the content of the silane coupling agent (D) to above the lower limit, when silica particles (C) are used, it is possible to improve the overall mechanical strength of the silicone rubber. Furthermore, by setting the content of the silane coupling agent (D) to below the upper limit, the silicone rubber can be made to have appropriate mechanical properties.

<<Platinum or platinum compound (E)>>
The silicone rubber-based curable composition of this embodiment may contain platinum or a platinum compound (E).
Platinum or platinum compound (E) is a catalytic component that acts as a catalyst during hardening. The amount of platinum or platinum compound (E) added is the catalytic amount.

As platinum or a platinum compound (E), known materials can be used, such as platinum black, platinum supported on silica or carbon black, chloroplatinic acid or an alcoholic solution of chloroplatinic acid, a complex salt of chloroplatinic acid and an olefin, or a complex salt of chloroplatinic acid and a vinylsiloxane.

Furthermore, platinum or platinum compound (E) may be used alone or in combination of two or more types.

<<Water (F)>>
Furthermore, the silicone rubber-based curable composition of this embodiment may also contain water (F) in addition to the above components (A) to (E).

Water (F) functions as a dispersion medium that disperses the various components contained in the silicone rubber-based curable composition, and also contributes to the reaction between silica particles (C) and the silane coupling agent (D). Therefore, within the silicone rubber, the silica particles (C) and the silane coupling agent (D) can be more reliably linked to each other, resulting in uniform properties overall.

Furthermore, if water (F) is included, its content can be set as appropriate, but specifically, it is preferably in the range of 10 to 100 parts by weight, and more preferably in the range of 30 to 70 parts by weight, per 100 parts by weight of the silane coupling agent (D). This allows the reaction between the silane coupling agent (D) and the silica particles (C) to proceed more reliably.

(Other ingredients)
Furthermore, the silicone rubber-based curable composition of this embodiment may further contain other components in addition to the components (A) to (F) described above. Examples of these other components include inorganic fillers other than silica particles (C), such as diatomaceous earth, iron oxide, zinc oxide, titanium oxide, barium oxide, magnesium oxide, cerium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, glass wool, and mica; additives such as reaction inhibitors, dispersants, pigments, dyes, antistatic agents, antioxidants, flame retardants, and thermal conductivity enhancers.

In a silicone rubber-based curable composition, the proportions of each component are not particularly limited, but for example, they may be set as follows.

In this embodiment, the upper limit of the silica particle (C) content may be, for example, 60 parts by weight or less, preferably 50 parts by weight or less, and more preferably 40 parts by weight or less, relative to 100 parts by weight of the total amount of vinyl group-containing organopolysiloxane (A). This allows for a balance of mechanical strength, such as hardness and tensile strength. The lower limit of the silica particle (C) content is not particularly limited, but may be, for example, 10 parts by weight or more, relative to 100 parts by weight of the total amount of vinyl group-containing organopolysiloxane (A).

The silane coupling agent (D) is preferably present in an amount of 5 to 100 parts by weight, and more preferably 5 to 40 parts by weight, per 100 parts by weight of the vinyl group-containing organopolysiloxane (A). This ensures that the dispersibility of silica particles (C) in the silicone rubber-based curable composition is reliably improved.

The content of organohydrogenpolysiloxane (B) is preferably, for example, 0.5 parts by weight to 20 parts by weight, and more preferably 0.8 parts by weight to 15 parts by weight, based on 100 parts by weight of the total amount of vinyl group-containing organopolysiloxane (A), silica particles (C), and silane coupling agent (D). A content of (B) within this range may allow for a more effective curing reaction.

The content of platinum or platinum compound (E) represents the catalytic amount and can be set as appropriate. Specifically, it is the amount such that the platinum group metal in this component is 0.01 to 1000 ppm by weight relative to the total amount of vinyl group-containing organopolysiloxane (A), silica particles (C), and silane coupling agent (D), preferably 0.1 to 500 ppm. By setting the content of platinum or platinum compound (E) to above the lower limit, the resulting silicone rubber composition can be sufficiently cured. By setting the content of platinum or platinum compound (E) to below the upper limit, the curing speed of the resulting silicone rubber composition can be improved.

Furthermore, if water (F) is included, its content can be set as appropriate, but specifically, it is preferably in the range of 10 to 100 parts by weight, and more preferably in the range of 30 to 70 parts by weight, per 100 parts by weight of the silane coupling agent (D). This allows the reaction between the silane coupling agent (D) and the silica particles (C) to proceed more reliably.

In this embodiment, the hardness, tensile strength, elongation at break, and tear strength can be controlled by appropriately selecting, for example, the type and amount of each component contained in the silicone rubber curable composition, the method of preparing the silicone rubber curable composition, and so on. Among these, for example, appropriately controlling the type and blending ratio of the resin constituting the silicone rubber, the crosslinking density and crosslinking structure of the resin, improving the blending ratio of the inorganic filler and the bonding of the inorganic filler to the rubber, using a first vinyl group-containing linear organopolysiloxane (A1-1) with a vinyl group content of 0.4 mol% or less, using a silane coupling agent having vinyl groups, and appropriately adjusting the silica particle (C) content and silane coupling agent content are examples of factors that can bring the hardness, tensile strength, elongation at break, and tear strength within the desired numerical range.

<Method of manufacturing silicone rubber>
Next, the method for manufacturing the silicone rubber of this embodiment will be described.
The method for producing silicone rubber according to this embodiment involves preparing a silicone rubber-based curable composition and curing this silicone rubber-based curable composition to obtain silicone rubber.
The details are explained below.

First, the components of the silicone rubber-based curable composition are uniformly mixed using any mixing device to prepare the silicone rubber-based curable composition.

[1] For example, predetermined amounts of a vinyl group-containing organopolysiloxane (A), silica particles (C), and a silane coupling agent (D) are weighed, and then kneaded using any kneading device to obtain a kneaded product containing these components (A), (C), and (D).

Furthermore, it is preferable to obtain this compound by first kneading a vinyl group-containing organopolysiloxane (A) and a silane coupling agent (D), and then kneading (mixing) silica particles (C). This further improves the dispersibility of the silica particles (C) within the vinyl group-containing organopolysiloxane (A).

Furthermore, when obtaining this mixture, water (F) may be added to the mixture of components (A), (C), and (D) as needed. This allows the reaction between the silane coupling agent (D) and the silica particles (C) to proceed more reliably.

Furthermore, it is preferable that the kneading of each component (A), (C), and (D) proceeds through a first step of heating at a first temperature and a second step of heating at a second temperature. This allows the surface of the silica particles (C) to be surface-treated with the coupling agent (D) in the first step, and ensures the removal of by-products generated by the reaction between the silica particles (C) and the coupling agent (D) from the kneaded mixture in the second step. Subsequently, if necessary, component (A) may be added to the resulting kneaded mixture and kneaded further. This improves the compatibility of the components in the kneaded mixture.

The first temperature is preferably, for example, around 40 to 120°C, and more preferably, around 60 to 90°C. The second temperature is preferably, for example, around 130 to 210°C, and more preferably, around 160 to 180°C.

Furthermore, the atmosphere in the first step is preferably an inert atmosphere such as a nitrogen atmosphere, and the atmosphere in the second step is preferably a reduced-pressure atmosphere.

Furthermore, the duration of the first step is preferably about 0.3 to 1.5 hours, and more preferably about 0.5 to 1.2 hours. The duration of the second step is preferably about 0.7 to 3.0 hours, and more preferably about 1.0 to 2.0 hours.

By setting the conditions for the first and second steps as described above, the aforementioned effects can be obtained more significantly.

[2] Next, predetermined amounts of organohydrogenpolysiloxane (B) and platinum or a platinum compound (E) are weighed, and then, using any kneading apparatus, components (B) and (E) are kneaded into the mixture prepared in step [1] to obtain a silicone rubber-based curable composition. The obtained silicone rubber-based curable composition may be a paste containing a solvent.

Furthermore, when kneading components (B) and (E), it is preferable to first knead the mixture prepared in step [1] with organohydrogenpolysiloxane (B), and the mixture prepared in step [1] with platinum or a platinum compound (E), and then knead each of these mixtures. This ensures that components (A) to (E) are reliably dispersed in the silicone rubber-based curable composition without allowing the reaction between the vinyl group-containing organopolysiloxane (A) and organohydrogenpolysiloxane (B) to proceed.

The temperature during the mixing of components (B) and (E) is preferably, as the roll setting temperature, around 10 to 70°C, and more preferably around 25 to 30°C.

Furthermore, the mixing time is preferably, for example, 5 minutes to 1 hour, and more preferably 10 to 40 minutes.

In steps [1] and [2] described above, by keeping the temperature within the above range, the reaction between the vinyl group-containing organopolysiloxane (A) and the organohydrogenpolysiloxane (B) can be more effectively prevented or suppressed. Furthermore, by keeping the kneading time within the above range in steps [1] and [2] described above, each component (A) to (E) can be more reliably dispersed in the silicone rubber-based curable composition.

The kneading equipment used in each of the processes [1] and [2] is not particularly limited, but for example, a kneader, a two-roll mixer, a Banbury mixer (continuous kneader), a pressure kneader, etc., can be used.

Furthermore, in step [2], a reaction inhibitor such as 1-ethynylcyclohexanol may be added to the kneaded mixture. This allows for more effective prevention or suppression of the reaction between the vinyl group-containing organopolysiloxane (A) and the organohydrogenpolysiloxane (B), even when the temperature of the kneaded mixture is set to a relatively high temperature.

[3] Next, silicone rubber is formed by curing the silicone rubber-based curable composition.

In this embodiment, the curing process of the silicone rubber-based curable resin composition is carried out, for example, by heating at 100 to 250°C for 1 to 30 minutes (primary curing), followed by post-baking at 200°C for 1 to 4 hours (secondary curing).

Through the above process, a silicone rubber is obtained, consisting of a cured product of a silicone rubber-based curable resin composition.

[3] Next, an insulating paste can be obtained by dissolving the silicone rubber-based curable composition obtained in step [2] in a solvent.
Furthermore, [3] Next, a conductive paste can be obtained by dissolving the silicone rubber-based curable composition obtained in step [2] in a solvent and adding a conductive filler.

(solvent)
Conductive pastes and insulating pastes contain solvents.
Various known solvents can be used as the solvent, but for example, high-boiling point solvents may be included. These may be used individually or in combination of two or more.

The lower limit of the boiling point of the high-boiling-point solvent is, for example, 100°C or higher, preferably 130°C or higher, and more preferably 150°C or higher. This improves the printing stability, such as in screen printing. On the other hand, the upper limit of the boiling point of the high-boiling-point solvent is not particularly limited, but may be, for example, 300°C or lower, 290°C or lower, or 280°C or lower. This suppresses excessive thermal history during wiring formation, thereby preventing damage to the substrate and maintaining the shape of the wiring formed with conductive paste in good condition.

Furthermore, while the solvent can be appropriately selected from the viewpoint of its solubility and boiling point for the silicone rubber-based curable resin composition, it may include, for example, aliphatic hydrocarbons having 5 to 20 carbon atoms, preferably aliphatic hydrocarbons having 8 to 18 carbon atoms, and more preferably aliphatic hydrocarbons having 10 to 15 carbon atoms.

Examples of solvents include aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, methylcyclohexane, ethylcyclohexane, octane, decane, dodecane, and tetradecane; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene, mesitylene, trifluoromethylbenzene, and benzotrifluoride; and diethyl ether, diisopropyl ether, dibutyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. Examples include ethers such as chol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl-n-propyl ether, 1,4-dioxane, 1,3-dioxane, and tetrahydrofuran; haloalkanes such as dichloromethane, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, and 1,1,2-trichloroethane; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and esters such as diethyl carbonate. These may be used individually or in combination of two or more.
The solvent used here should be appropriately selected from among solvents that can uniformly dissolve or disperse the components of the conductive paste described above.

The above solvent may include a first solvent in which the upper limit of the polarity term (δ _p ) of the Hansen solubility parameter is, for example, 10 MPa ^1/2 or less, preferably 7 MPa ^1/2 or less, and more preferably 5.5 MPa ^1/2 or less. This makes it possible to improve the dispersibility and solubility of the silicone rubber-based curable resin composition in the paste. The lower limit of the above polarity term (δ _p ) of this first solvent is not particularly limited, but may be, for example, 0 Pa ^1/2 or more.

The upper limit of the hydrogen bonding term ( _δh ) of the Hansen solubility parameter in the first solvent described above is, for example, 20 MPa ^1/2 or less, preferably 10 MPa ^1/2 or less, and more preferably 7 MPa ^1/2 or less. This allows for good dispersibility and solubility of the silicone rubber-based curable resin composition in the paste. The lower limit of the hydrogen bonding term ( _δh ) in this first solvent is not particularly limited, but may be, for example, 0 Pa ^1/2 or more.

Hansen's solubility parameter (HSP) is an index that represents the solubility of one substance in another. HSP represents solubility as a three-dimensional vector. This three-dimensional vector can typically be represented by a dispersion term (δ _d ), a polarity term (δ _p ), and a hydrogen bonding term (δ _h ). Substances with similar vectors are judged to have high solubility. The similarity of the vectors can be judged by the distance between Hansen solubility parameters (HSP distance).

The Hansen solubility parameter (HSP value) used in this specification can be calculated using software called HSPiP (Hansen Solubility Parameters in Practice). HSPiP, developed by Hansen and Abbott, includes a function for calculating HSP distance and a database listing Hansen parameters for various resins and solvents or non-solvents.
The solubility of each resin in pure solvents and mixed solvents of good and poor solvents is investigated, and the results are entered into HSPiP software to calculate D: dispersion term, P: polarity term, H: hydrogen bonding term, and R0: solubility sphere radius.

As the solvent in this embodiment, for example, one can be selected that has a small difference in HSP distance, polarity, and hydrogen bonding terms between the elastomer or the constituent units of the elastomer and the solvent.

The lower limit of the viscosity of conductive paste and/or insulating paste, measured at room temperature (25°C) with a shear rate of 20 ¹/s, is, for example, 1 Pa·s or more, preferably 5 Pa·s or more, and more preferably 10 Pa·s or more. This improves film formation and enhances shape retention even during thick film formation. On the other hand, the upper limit of the viscosity of conductive paste and/or insulating paste at room temperature (25°C) is, for example, 100 Pa·s or less, preferably 90 Pa·s or less, and more preferably 80 Pa·s or less. This improves the printability of the paste.

At room temperature of 25°C, the viscosity measured at a shear rate of 1 [1/s] is defined as η1, and the viscosity measured at a shear rate of 5 [1/s] is defined as η5. The thixotropy index is defined as the viscosity ratio (η1/η5).
In this case, the lower limit of the thixotropy of the conductive paste and/or insulating paste is, for example, 1.0 or higher, preferably 1.1 or higher, and more preferably 1.2 or higher. This allows the shape of the wiring obtained by the printing method to be stably maintained. On the other hand, the upper limit of the thixotropy of the conductive paste and/or insulating paste is, for example, 3.0 or lower, preferably 2.5 or lower, and more preferably 2.0 or lower. This improves the printability of the paste.

The content of the silicone rubber-based curable composition in the insulating paste is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on 100% by mass of the insulating paste. Furthermore, the content of the silicone rubber-based curable composition in the insulating paste is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, based on 100% by mass of the insulating paste.

(Conductive filler)
As the conductive filler, known conductive materials may be used, but metal powder (G) may also be used.
The metals that make up the metal powder (G) are not particularly limited, but for example, it may include at least one of copper, silver, gold, nickel, tin, lead, zinc, bismuth, antimony, or alloys thereof, or two or more of these.
Of these, the metal powder (G) is preferably silver or copper, that is, silver powder or copper powder, due to its high conductivity and ease of availability.
Furthermore, these metal powders (G) can also be used if they are coated with other types of metals.

In this embodiment, there are no restrictions on the shape of the metal powder (G), but conventionally used shapes such as dendritic, spherical, or flake-shaped powders can be used. Among these, flake-shaped metal powder (G) may also be used.

Furthermore, the particle size of the metal powder (G) is not limited, but it is preferably 0.001 μm or larger, more preferably 0.01 μm or larger, and even more preferably 0.1 μm or larger, with an average particle size D ₅₀ of 0.00 μm or larger. The particle size of the metal powder (G) is preferably 1,000 μm or smaller, more preferably 100 μm or smaller, and even more preferably 20 μm or smaller, with an average particle size D ₅₀ of 1,000 μm or smaller.
By setting the average particle size D ₅₀ within this range, the silicone rubber can exhibit appropriate conductivity.
The particle size of the metal powder (G) can be defined, for example, by observing conductive paste or silicone rubber molded using conductive paste with a transmission electron microscope, performing image analysis, and taking the average value of 200 arbitrarily selected metal powders.

The content of conductive filler in the conductive paste is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total content of the conductive paste. Furthermore, the content of conductive filler in the conductive paste is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 65% by mass or less, based on the total content of the conductive paste.
By setting the conductive filler content above the lower limit, the silicone rubber can acquire appropriate conductivity. Furthermore, by setting the conductive filler content below the upper limit, the silicone rubber can acquire appropriate flexibility.

The content of the silicone rubber-based curable composition in the conductive paste is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the conductive paste. Furthermore, the content of the silicone rubber-based curable composition in the conductive paste is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on 100% by mass of the conductive paste.
By setting the content of the silicone rubber-based curable composition to be above the lower limit, the silicone rubber can have appropriate flexibility. Furthermore, by setting the content of the silicone rubber-based curable composition to be below the upper limit, the mechanical strength of the silicone rubber can be improved.

The lower limit of the silica particle (C) content in the conductive paste is, for example, 1% by mass or more, preferably 3% by mass or more, and more preferably 4% by mass or more, based on 100% by mass of the total amount of silica particles (C) and conductive filler. This improves the mechanical strength of the silicone rubber. On the other hand, the upper limit of the silica particle (C) content in the conductive paste is, for example, 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the total amount of silica particles (C) and conductive filler. This allows for a balance between the stretch-electrical properties and mechanical strength of the silicone rubber.

The lower limit of the conductive filler content in the conductive cured product obtained by curing the conductive paste constituting the conductive elastomer layer 20 is, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more, based on 100% by mass of the conductive cured product. This enhances the stretch-electric properties. On the other hand, the upper limit of the conductive filler content in the conductive cured product is, for example, 90% by mass or less, preferably 88% by mass or less, and more preferably 85% by mass or less, based on 100% by mass of the conductive elastomer layer 20. This suppresses the deterioration of rubber properties such as stretchability.

The lower limit of the silica particle (C) content in the conductive cured product obtained by curing the conductive paste constituting the conductive elastomer layer 20 is, for example, 1% by mass or more, preferably 3% by mass or more, and more preferably 4% by mass or more, based on 100% by mass of the total amount of silica particles (C) and conductive filler. This improves the mechanical strength of the silicone rubber. On the other hand, the upper limit of the silica particle (C) content in the conductive cured product is, for example, 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the total amount of silica particles (C) and conductive filler. This allows for a balance between the stretch-electrical properties and mechanical strength of the silicone rubber.

Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.
Examples of reference formats are provided below.
1. Flexible base material and
A conductive elastomer layer provided on the flexible substrate,
A flexible sheet electrode comprising,
When the arithmetic mean height of the conductive elastomer layer at 20% elongation, measured with a laser microscope whose laser light wavelength is 404 nm, is defined as Sa ₂₀ and the maximum height as Sz ₂₀ ,
Sa ₂₀ ≤ 19.5 μm and/or Sz ₂₀ ≤ 200 μm,
Flexible sheet electrode.
2. The flexible sheet electrode described in 1.
When the arithmetic mean height of the unextended conductive elastomer layer on its surface, measured with a laser microscope whose laser light wavelength is 404 nm, is defined as Sa ₀ and the maximum height as Sz ₀ ,
A flexible sheet electrode satisfying 0 μm ≤ |Sa ₂₀ - Sa ₀ | ≤ 10 μm and/or 0 μm ≤ |Sz ₂₀ - Sz ₀ | ≤ 80 μm.
3. A flexible sheet electrode as described in 1. or 2.,
After repeating the washing process 20 times according to the following steps (1) to (4), the wavelength of the laser light is
When the arithmetic mean height of the unextended conductive elastomer layer on its surface, measured with a 404 nm laser microscope, is denoted as Sa _W0 , and the maximum height as Sz _W0 ,
A flexible sheet electrode satisfying Sa _W0 ≤ 16.0 μm and/or Sz _W0 ≤ 250 μm.
(procedure)
1. The flexible sheet electrode is stretched and contracted 300 times by 50% in both the vertical and horizontal directions.
2. Put neutral detergent and water into a beaker, immerse the flexible sheet electrode that has been treated in step 1, and stir for 24 hours.
3. Pour water into a beaker, immerse the flexible sheet electrode that has been treated in step 2, stir for 10 minutes, and then rinse off the detergent.
4. Dry in a 90°C oven for 30 minutes.
4. A flexible sheet electrode as described in any one of 1 to 3,
A flexible sheet electrode wherein the conductive elastomer layer includes a conductive filler and a non-conductive filler.
5. The flexible sheet electrode described in 4.
A flexible sheet electrode wherein the conductive filler comprises one or more selected from the group consisting of metal-based fillers, carbon-based fillers, metal oxide fillers, and metal-plated fillers.
6. A flexible sheet electrode as described in 4. or 5.
A flexible sheet electrode in which the conductive filler contains flake-shaped silver powder.
7. A flexible sheet electrode as described in any one of 4. to 6.
A flexible sheet electrode in which the nonconductive filler contains silica particles.
8. A flexible sheet electrode as described in any one of 4. to 7.
A flexible sheet electrode wherein the content of the conductive filler in the conductive elastomer layer is 50% by mass or more and 90% by mass or less.
9. A flexible sheet electrode as described in any one of 1 to 8,
A flexible sheet electrode wherein the conductive elastomer layer comprises one or more elastomer materials selected from the group consisting of silicone rubber, urethane rubber, and fluororubber.
A flexible sheet electrode as described in any one of 10.1 to 9.
A flexible sheet electrode in which, in the conductive elastomer layer, when the surface resistance value when unstretched is R1 and the surface resistance value when stretched by 20% in one of the in-plane directions of the surface is R2, R1 and R2 are configured to satisfy 1.0 ≤ R2/R1 ≤ 7.0.
A flexible sheet electrode as described in any one of 11.1 to 10.
A flexible sheet electrode, wherein the flexible substrate is composed of a fibrous substrate.
12. The flexible sheet electrode described in 11.
A flexible sheet electrode wherein the fibrous base material is a woven or knitted fabric.
13. A wearable bioelectrode comprising a flexible sheet electrode as described in any one of items 1 to 12.
14. A biosensor equipped with the wearable bioelectrode described in 13.

The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to the descriptions of these examples.
The raw material components shown in Table 1 are listed below.
(A1-1): First vinyl group-containing linear organopolysiloxane: Vinyl group-containing dimethylpolysiloxane synthesized by the following synthesis scheme 1 (structure represented by formula (1-1) above)
(A1-2): Second vinyl group-containing linear organopolysiloxane: Vinyl group-containing dimethylpolysiloxane synthesized by the following synthesis scheme 2 (structure represented by formula (1-1) above, in which ^R1 and ^R2 are vinyl groups)

(Organohydrogenpolysiloxane (B))
(B-1): Organohydrogenpolysiloxane: Momentive Corporation, "TC-25D"

(Silica particles (C))
(C): Silica microparticles (particle size 7 nm, specific surface area 300 ^m² /g), manufactured by Nippon Aerosil Co., Ltd., "AEROSIL300"

(Silane coupling agent (D))
(D-1): Hexamethyldisilazane (HMDZ), manufactured by Gelest, "HEXAMETHYLDISILAZANE (SIH6110.1)"
(D-2) Divinyltetramethyldisilazane, manufactured by Gelest, "1,3-DIVINYLTETRAMETHYLDISILAZANE (SID4612.0)"

(Platinum or platinum compound (E))
(E-1): Platinum compound (manufactured by Momentive, trade name "TC-25A")

(Water (F))
(F): Pure water

(Metal powder (G))
(G1): Silver powder, manufactured by Tokuriki Chemical Research Institute, product name "TC-101", median diameter d ₅₀ : 8.0 μm, aspect ratio 16.4, average major diameter 4.6 μm

(Synthesis of vinyl group-containing organopolysiloxane (A))
[Synthesis Scheme 1: Synthesis of the first vinyl group-containing linear organopolysiloxane (A1-1)]
A first vinyl group-containing linear organopolysiloxane (A1-1) was synthesized according to the following formula (5).
Specifically, 74.7 g (252 mmol) of octamethylcyclotetrasiloxane and 0.1 g of potassium silicate were placed in a 300 mL separable flask equipped with a condenser and stirring blades, which had been purged with Ar gas. The mixture was then heated and stirred at 120°C for 30 minutes. An increase in viscosity was observed during this process.
The temperature was then raised to 155°C, and stirring was continued for 3 hours. After 3 hours, 0.1 g (0.6 mmol) of 1,3-divinyltetramethyldisiloxane was added, and the mixture was stirred again at 155°C for 4 hours.
Furthermore, after 4 hours, the mixture was diluted with 250 mL of toluene and washed three times with water. The organic layer after washing was reprecipitated and purified by washing several times with 1.5 L of methanol to separate the oligomer and polymer. The obtained polymer was dried under reduced pressure at 60°C overnight to obtain the first vinyl group-containing linear organopolysiloxane (A1-1) (Mn = 2.2 × ^10⁵ , Mw = 4.8 × ^10⁵ ). The vinyl group content, calculated by 1H-NMR spectroscopy, was 0.04 mol%.

[Synthesis Scheme 2: Synthesis of the second vinyl group-containing linear organopolysiloxane (A1-2)]
In the synthesis step of (A1-1) described above, 0.86 g (2.5 mmol) of 2,4,6,8-tetramethyl2,4,6,8-tetravinylcyclotetrasiloxane was added in addition to 74.7 g (252 mmol) of octamethylcyclotetrasiloxane. Except for this difference, the second vinyl group-containing linear organopolysiloxane (A1-2) was synthesized in the same manner as the synthesis step of (A1-1), as shown in formula (6) below (Mn = 2.3 × ^10⁵ , Mw = 5.0 × ^10⁵ ). Furthermore, the vinyl group content, calculated by 1H-NMR spectroscopy, was 0.93 mol%.

(Preparation of silicone rubber-based curable compositions)
The silicone rubber-based curable composition for Sample 1 was prepared according to the following procedure.
First, a mixture of 90% vinyl group-containing organopolysiloxane (A), silane coupling agent (D), and water (F) was pre-kneaded in the proportions shown in Table 1 below. Then, silica particles (C) were added to the mixture and kneaded further to obtain a compound (silicone rubber compound).
Here, the kneading after the addition of silica particles (C) was carried out in two steps: the first step of kneading under a nitrogen atmosphere at 60-90°C for 1 hour for the coupling reaction, and the second step of kneading under a reduced pressure atmosphere at 160-180°C for 2 hours to remove the by-product (ammonia). After that, it was cooled, and the remaining 10% vinyl group-containing organopolysiloxane (A) was added in two parts and kneaded for 20 minutes.
Next, organohydrogenpolysiloxane (B), platinum, or a platinum compound (E) were added to 100 parts by weight of the obtained mixture (silicone rubber compound) in the proportions shown in Table 2 below, and the mixture was kneaded with a roll to obtain a silicone rubber-based curable composition.

(Preparation of conductive paste 1)
The obtained 15.3 parts by weight of the silicone rubber-based curable composition of Sample 1 was immersed in 34.8 parts by weight of decane (solvent), then stirred with a rotating/revolving mixer, and after adding 65.2 parts by weight of metal powder (G1), the mixture was further kneaded with the rotating/revolving mixer to obtain a conductive paste 1 in which the total content of the silicone rubber-based curable composition and metal powder (G1) was 69.8% by weight.

(Fabrication of flexible sheet electrodes)
A flexible substrate (polyester knitted fabric, basis weight 130 g/ ^m² ) measuring 7 cm x 7 cm x 0.4 mm thick was placed on the flat surface of a SUS substrate, and then a mask (made of polyethylene terephthalate) with one 5 cm x 5 cm opening and a thickness of 125 μm was placed on the surface of the flexible substrate.
Next, the conductive paste described above was applied to the opening of the mask, and squeegee printing was performed using a glass plate in a printing direction perpendicular to the grain of the fibers, based on the printing conditions shown in Table 2.
Next, the mask was removed, and the printed conductive paste 1 was dried at 140°C for 20 minutes and cured at 180°C for 2 hours to produce a flexible sheet electrode having a conductive elastomer layer provided on a flexible substrate.

In Table 2, the arithmetic mean height (Sa ₀ ) and maximum height (Sz ₀ ) were measured using a shape analysis laser microscope (Keyence Corporation, product number: VK-X1000) at a laser wavelength of 404 nm over three regions (1 mm × 1 mm) on the surface of the conductive elastomer layer in an unextended state in the planar direction, and the average of the three values was used.
However, the arithmetic mean height (Sa ₂₀ ) and maximum height (Sz ₂₀ ) at 20% elongation were measured within the elongated region of a rectangular electrode (conductive elastomer layer) that was stretched 20% in the planar direction by grasping two opposing sides.
For reference, the Sa ₀ on the surface of the flexible substrate to which the conductive paste was applied was 3705.9 μm, and the Sz ₀ was 4.57.
Furthermore, the amount of conductive elastomer layer attached in Table 2 was calculated by subtracting the weight of the flexible substrate, which was measured in advance, from the weight of the flexible sheet electrode.

The following items were evaluated for the obtained flexible sheet electrodes. The results are shown in Table 2.
In Table 2, "-" indicates that the action was not taken.

(Surface resistance value)
A 5 cm x 5 cm printed section of the obtained flexible sheet electrode was cut to prepare a sample. Using this sample, the surface resistance (Ω) of the square-shaped flexible sheet electrode was measured at 25°C, either in its unstretched state or when stretched 20% diagonally.

(Wash resistance)
The obtained flexible sheet electrodes were subjected to a washing tolerance test by repeating the following washing procedure (1) to (4) 20 times.
(1) The flexible sheet electrode was stretched and contracted 300 times by 50% in both the vertical and horizontal directions.
(2) Put neutral detergent and water into a beaker, immerse the flexible sheet electrode that has been treated in (1), and stir for 24 hours.
(3) Water was placed in a beaker, the flexible sheet electrode treated in (2) was immersed in the water, stirred for 10 minutes, and the detergent was rinsed off.
(4) The flexible sheet electrodes from (3) were dried in a 90°C oven for 30 minutes.

In each example, it was confirmed that the conductive elastomer layer did not crack or delamination occurred between it and the flexible substrate, maintaining its initial state. On the other hand, in Comparative Example 1, cracks in the conductive elastomer layer and delamination between it and the flexible substrate were observed.
Furthermore, after the washing resistance test described above, the arithmetic mean height (Sa _w0 ) and maximum height (Sz _w0 ) on the surface of the unstretched conductive elastomer layer were measured using the same method as described above. The results are shown in Table 2.

(Bioelectric potential measurement)
In the resulting flexible sheet electrode, an external connector (a metal male snap button) was attached to the other side of the flexible substrate opposite to the side where the conductive elastomer layer was formed, and the external connector and the conductive elastomer layer were electrically connected to obtain a wearable bioelectrode.
Three wearable bioelectrodes were prepared, and the external connection points of each of the three wearable bioelectrodes were connected to a BITalino (manufactured by Plux) via electrode cables with connectors (female snap buttons) and ECG sensors (manufactured by Plux), thereby creating an electrocardiogram measurement device (biosensor).
Flexible sheet electrodes, each attached to one side of three wearable bioelectrodes, were placed directly on the subject's skin, and the subject's electrocardiogram was measured using a three-lead system (measurement point, reference, and body ground).

The results above confirm that electrocardiogram waveforms can be monitored by using wearable bioelectrodes equipped with flexible sheet electrodes as described in each embodiment.
Furthermore, the wearable bioelectrodes equipped with flexible sheet electrodes in Examples 1 to 3 showed suppressed noise in the electrocardiogram waveform and clear identification of the S-T region compared to Comparative Example 1.
Therefore, the biopotential stability of the flexible sheet electrodes in Examples 1 to 3 was evaluated as good (○), while that of Comparative Example 1 was evaluated as poor (×). The results are shown in Table 2.

The flexible sheet electrodes in each embodiment showed superior measurement stability in biopotential measurements such as electrocardiogram waveforms compared to Comparative Example 1.
Such flexible sheet electrodes can be suitably used in wearable bioelectrodes.

1 Flexible sheet electrode 10 Flexible base material 11 One side 12 Main body 13 Other side 14 Expansion part 20 Conductive elastomer layer 21 Impregnation layer 22 One side 24 Stretchable wiring 26 Connection part 30 External connection part 32 Mounting plate 34 Mounting pin 50 Protective layer 52 Insulating protective layer 60 Insulating elastomer layer 100 Wearable bioelectrode 200 Biosensor 210 Connector 220 Cable 230 Sensor module 240 Computer

Claims (14)

A flexible sheet electrode used to measure bioelectric potential,
A flexible substrate having insulating properties,
A sheet-like conductive elastomer layer is provided on the flexible substrate,
A flexible sheet electrode comprising,
The conductive elastomer layer comprises a conductive filler and a non-conductive filler,
The flexible substrate and the conductive elastomer layer are in close contact,
When the arithmetic mean height of the conductive elastomer layer at 20% elongation, measured with a laser microscope whose laser light wavelength is 404 nm, is defined as Sa ₂₀ and the maximum height as Sz ₂₀ ,
Sa ₂₀ ≤ 19.5 μm and Sz ₂₀ ≤ 250 μm satisfying,
Flexible sheet electrode. A flexible sheet electrode according to claim 1,
When the arithmetic mean height of the unextended conductive elastomer layer on its surface, measured with a laser microscope whose laser light wavelength is 404 nm, is defined as Sa ₀ and the maximum height as Sz ₀ ,
A flexible sheet electrode satisfying 0 μm ≤ |Sa ₂₀ - Sa ₀ | ≤ 10 μm and/or 0 μm ≤ |Sz ₂₀ - Sz ₀ | ≤ 80 μm. A flexible sheet electrode according to claim 1 or 2,
A flexible sheet electrode wherein the conductive filler comprises one or more selected from the group consisting of metal-based fillers, carbon-based fillers, metal oxide fillers, and metal-plated fillers. A flexible sheet electrode according to any one of claims 1 to 3,
A flexible sheet electrode in which the conductive filler contains flake-shaped silver powder. A flexible sheet electrode according to any one of claims 1 to 4,
A flexible sheet electrode in which the nonconductive filler contains silica particles. A flexible sheet electrode according to any one of claims 1 to 5,
A flexible sheet electrode wherein the content of the conductive filler in the conductive elastomer layer is 50% by mass or more and 90% by mass or less. A flexible sheet electrode according to any one of claims 1 to 6,
A flexible sheet electrode wherein the conductive elastomer layer comprises one or more elastomer materials selected from the group consisting of silicone rubber, urethane rubber, and fluororubber. A flexible sheet electrode according to any one of claims 1 to 7,
A flexible sheet electrode in which, in the conductive elastomer layer, when the surface resistance value when unstretched is R1 and the surface resistance value when stretched by 20% in one of the in-plane directions of the surface is R2, R1 and R2 are configured to satisfy 1.0 ≤ R2/R1 ≤ 7.0. A flexible sheet electrode according to any one of claims 1 to 8,
A flexible sheet electrode, wherein the flexible substrate is composed of a fibrous substrate. A flexible sheet electrode according to claim 9,
A flexible sheet electrode wherein the fibrous base material is a woven or knitted fabric. A flexible sheet electrode according to any one of claims 1 to 10,
A flexible sheet electrode wherein the bioelectric potential is at least one of the electrocardiogram, electromyogram, and electrocutaneous potential. A flexible sheet electrode according to any one of claims 1 to 11,
A flexible sheet electrode in which, when the thickness of the sheet-like conductive elastomer layer is D (mm) and the area of one surface of the conductive elastomer layer when viewed from above is S ( ^mm² ), S and D satisfy 50 ≤ S/D ≤ ^10⁷ . A wearable bioelectrode comprising a flexible sheet electrode according to any one of claims 1 to 12. A biosensor comprising a wearable bioelectrode as described in claim 13.