JP7388412B2 - Strain sensor element manufacturing method and strain sensor element - Google Patents

Description

The present invention relates to a method of manufacturing a strain sensor element and a strain sensor element.

A laminate including a thin film-like conductive elastomer layer and insulating elastomer layers laminated on both sides of the conductive elastomer layer is formed into a band shape, and a change in resistance of the conductive elastomer layer due to longitudinal expansion and contraction is detected. Strain sensor elements are known (see, for example, Japanese Patent Laid-Open No. 2000-258112).

The strain sensor element described in the above publication has a pair of electrodes inserted between a conductive elastomer layer and an insulating elastomer layer and protruding from the conductive elastomer layer and the insulating elastomer layer in the longitudinal direction at both longitudinal ends. By providing the conductor, it is possible to detect a change in resistance of the conductive elastomer layer.

In such a strain sensor element, it is necessary to arrange electrode conductors in advance when laminating the conductive elastomer layer and the insulating elastomer layer, which complicates the manufacturing process and makes it difficult to change the design. .

Furthermore, a strain sensor element using carbon nanotubes (CNT) as a resistor has also been proposed (see Japanese Patent Laid-Open No. 2011-47702). This strain sensor element has a CNT film made of a plurality of carbon nanotubes oriented in a predetermined direction. This strain sensor element is said to be able to cope with large strains because the CNT film can expand and contract relatively largely in the orientation direction of the carbon nanotubes or in the direction perpendicular to the orientation direction.

In this strain sensor element using a CNT film, a CNT film is formed on the surface of a stretchable sheet-like base material, and after patterning this CNT film, electrodes are connected to both ends of the CNT film pattern using conductive paste. It is manufactured by In other words, this strain sensor element also has a complicated manufacturing process, and it is not easy to change the design.

Japanese Patent Application Publication No. 2000-258112 Japanese Patent Application Publication No. 2011-47702

The present invention has been made based on such circumstances, and an object of the present invention is to provide a method for manufacturing a strain sensor element and a strain sensor element that can be relatively easily manufactured and can be relatively easily modified in design.

The invention made in order to solve the above problems includes: a CNT membrane or CNT yarn including a plurality of CNT fibers aligned in one direction; a resin layer coated on the front and back of the CNT membrane or the outer periphery of the CNT yarn; A method for manufacturing a strain sensor element comprising a pair of electrodes laminated on both end regions of a resin layer covering of a CNT film or CNT thread and electrically connected to the CNT film or CNT thread, the method comprising: A strain sensor element comprising the steps of: irradiating at least part of the surface of both end regions of the body with a laser; and filling holes formed in the resin layer in the laser irradiation step with a conductive material. This is a manufacturing method.

Before the laser irradiation step, it further includes a step of applying a laser absorbing material to the surfaces of both end regions of the resin layer covering, and in the laser irradiation step, the laser is applied to at least a portion of the coating film obtained in the application step. It is recommended to irradiate.

It is preferable that the laser-absorbing material is an ink in which fine carbon black particles are dispersed in a volatile solvent.

The average diameter of the holes formed in the resin layer is preferably 0.5 mm or more and 2.0 mm or less.

Preferably, a plurality of holes are formed in each end region of the resin layer covering in the laser irradiation step, and a conductive material is applied across the plurality of holes in each end region in the conductive material filling step.

Another invention made to solve the above problem includes a CNT membrane or CNT yarn including a plurality of CNT fibers aligned in one direction, and a resin coated on the front and back of the CNT membrane or on the outer periphery of the CNT yarn. layer, and a pair of electrodes laminated on both end regions of the resin layer covering of the CNT membrane or CNT yarn and electrically connected to the CNT membrane or CNT yarn, the strain sensor element comprising: A strain sensor element characterized in that the layer has a connection hole leading to a CNT membrane or CNT thread, and the electrode includes a conductive material filled in the connection hole.

The strain sensor element may further include a laser absorbing material layer existing between the surface of the resin layer surrounding the connection hole and the electrode.

In the method for manufacturing the strain sensor element, holes exposing the CNTs can be easily and accurately formed in the resin layer by irradiating both end regions of the CNT film or the resin layer covering of the CNT thread with a laser. By filling the pores of this resin layer with a conductive material, electrical connection to the CNT membrane or CNT thread can be made relatively easily, so the strain sensor element can be manufactured relatively easily. Furthermore, since the laser irradiation position can be easily changed, the strain sensor element manufacturing method allows relatively easy design changes of the strain sensor element. For the same reason, the strain sensor element has a configuration in which the electrodes include a conductive material filled in the connection hole of the resin layer, so that the design can be changed relatively easily and the strain sensor element can be manufactured relatively easily.

FIG. 1 is a schematic cross-sectional view of a strain sensor element according to an embodiment of the present invention. 2 is a schematic plan view of the strain sensor element of FIG. 1. FIG. 2 is a flowchart showing the steps of a method for manufacturing the strain sensor element of FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view of a strain sensor element different from FIG. 1. FIG. FIG. 2 is a schematic plan view showing a reference form of a strain sensor element. 6 is a schematic cross-sectional view of the strain sensor element of FIG. 5. FIG. 6 is a schematic plan view of a plate-shaped electrode for a strain sensor element different from that in FIG. 5. FIG. 7 is a schematic cross-sectional view of a strain sensor element different from FIG. 6. FIG. 9 is a schematic cross-sectional view of a strain sensor element different from FIGS. 6 and 8. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
The strain sensor element of the first embodiment of the present invention shown in FIGS. 1 and 2 includes a CNT film 11 formed in a band shape and including a plurality of CNT fibers aligned in the longitudinal direction, and a coating on the front and back of this CNT film 11. The resin layers 12 and 13 are laminated on both end regions in the CNT fiber alignment direction on the front side of the resin layer covering made of the CNT film 11 and the resin layers 12 and 13, and are electrically connected to the CNT film 11. A laser absorbing material layer 15 partially exists between the resin layer 12 on the front side and the electrodes 14. Note that the "front" refers to the side on which the pair of electrodes 14 are disposed, and the "back" refers to the opposite side, and does not necessarily mean the front and back when the strain sensor element is in use.

<CNT film>
The CNT film 11 consists of a layer formed from a plurality of CNT fibers aligned in one direction, and the front and back layers are made of a material whose main component is an insulating elastomer (hereinafter simply referred to as "insulating elastomer"), which will become a resin layer to be described later. ) are laminated, and the insulating elastomer is impregnated into the front and back layers of the CNT membrane 11 (at least from the surface side of the CNT membrane 11), so that the CNT fibers and the insulating elastomer are composited and formed into a membrane. has been done. The CNT film 11 has elasticity due to the elastic force of the insulating elastomer, and can be expanded and contracted at least in the longitudinal direction. When this CNT film 11 is stretched at least in the longitudinal direction, the CNT fibers are separated from each other and the electrical resistance increases, and when the CNT film 11 contracts due to elastic force, the CNT fibers come into contact with each other again and the electrical resistance is reduced. Note that the CNT film 11 may include insulating fibers made of, for example, synthetic resin in order to suppress the contact rate between the CNT fibers and adjust the electrical resistance.

Since the CNT membrane 11 is laminated with at least the surface layer impregnated with an insulating elastomer, the insulating elastomer covers the CNT fiber bundles described later, and this insulating elastomer guides the expansion and contraction direction of the plurality of CNT fiber bundles. It also functions as a guide member. As a result, in the strain sensor, the CNT fibers separated during stretching can be brought into contact again at the same location during contraction, and it is possible to prevent a decrease in the detection accuracy of stretching strain due to repeated use. Furthermore, according to such a configuration, the contact relationship between the plurality of CNT fibers can be easily maintained, and the elasticity of the plurality of CNT fibers can be easily adjusted. Therefore, the expansion/contraction strain of the CNT film 11 can be detected with higher accuracy. Further, in order to further facilitate the maintenance of such a contact relationship and the adjustment of elasticity, it is preferable that the back layer (region near the back surface) of the CNT film 11 is also impregnated with an insulating elastomer. At this time, since at least a portion of the surface layer of the CNT fiber bundle is impregnated with the insulating elastomer, the bonding strength between the CNT fiber bundle and the insulating elastomer is also increased.

(CNT fiber)
Each of the CNT fibers constituting the CNT membrane 11 can be formed from a plurality of CNT single fibers. Here, the CNT single fiber refers to one long carbon nanotube. Moreover, the CNT fiber has a connection part where the ends of the CNT single fibers are connected to each other. The CNT single fibers are connected to each other in the longitudinal direction of these CNT single fibers. In this way, in the CNT film 11, the CNT single fibers are connected to each other in the longitudinal direction, so that the CNT film 11 with a large orientation length of the CNT fibers can be formed, and the longitudinal length of the strain sensor can be Sensitivity can be improved by increasing the size.

Further, the plurality of CNT fibers constituting the CNT film 11 may form a network structure. Specifically, the plurality of CNT fibers may be connected or in contact with each other in the form of a network through connection parts where CNT single fibers are connected to each other. At this time, the ends of three or more CNT single fibers may be combined at this connection part, or the ends of two CNT single fibers and the intermediate part of another single fiber may be combined. When a plurality of CNT fibers form such a network structure, the CNT fibers are brought into close contact with each other, and the resistance of the CNT film 11 can be lowered.

Furthermore, the CNT film 11 may have a CNT fiber bundle consisting of a plurality of CNT fibers oriented in the longitudinal direction. When the CNT film 11 has a plurality of CNT fiber bundles oriented in the longitudinal direction, when strain is applied to stretch the CNT film 11 in the stretching direction, the CNT fibers are cut, separated, and the cutting space (gap) of the CNT fiber bundles is created. ), the resistance of the CNT film 11 changes more accurately.

More specifically, the CNT fiber bundle has a bundle structure consisting of a plurality of CNT fibers, and in any cross section of the CNT fiber bundle, there are CNT fibers that are not cut and CNT fibers that are cut and separated. Both gaps will exist. Furthermore, since the surface layer of the plurality of CNT fiber bundles is coated with an insulating elastomer, the pressure within this gap is considered to be lower than atmospheric pressure (negative pressure). (When the strain is released), the contraction force of this gap forces the strain sensor 1 to contract. Furthermore, since the friction between the CNT fibers is reduced within this gap, the movement of the CNT fibers is less likely to be restricted.

The CNT film 11 may have a single layer structure in which a plurality of CNT fibers or a plurality of CNT fiber bundles are arranged substantially parallel in a plane, or may have a multilayer structure. However, in order to ensure a certain degree of conductivity, it is preferable to have a multilayer structure.

As the CNT single fiber, either a single-wall nanotube (SWNT) or a multi-wall nanotube (MWNT) can be used, but from the viewpoint of electrical conductivity and heat capacity, MWNT is preferable and has a diameter of 1.5 mm. MWNTs with a diameter of 5 nm or more and 100 nm or less are more preferable.

The CNT single fibers can be manufactured by a known method, such as a CVD method, an arc method, a laser ablation method, a DIPS method, or a CoMoCAT method. Among these, it is preferable to manufacture by a CVD method using iron as a catalyst and ethylene gas, since carbon nanotubes (MWNT) of a desired size can be efficiently obtained. In this case, a thin film of iron or nickel as a catalyst is formed on a substrate such as a quartz glass substrate or a silicon substrate with an oxide film, and carbon nanotubes are grown in a vertical orientation to obtain carbon nanotube crystals of a desired length. I can do it.

The average length in the longitudinal direction of the CNT film 11 is not particularly limited, and can be freely selected depending on the object to be measured using the strain sensor element, and may be, for example, 1 cm or more and 20 cm or less.

The average length in the longitudinal direction of the region sandwiched between the pair of electrodes 14 in a plan view of the CNT film 11 can be freely selected depending on the object to be measured using the strain sensor element. The average length can be, for example, 2 mm or more and 18 cm or less.

The average length in the longitudinal direction of the region of the CNT film 11 that overlaps with the pair of electrodes 14 in a plan view is appropriately selected depending on the method of fixing to the measurement target, the method of wiring to the electrodes 14, etc., and is, for example, 3 mm or more. It can be 5 cm or less.

The average width of the CNT film 11 can be freely selected depending on the object to be measured using the strain sensor element. The lower limit of the average width between the electrodes 14 of the CNT film 11 is preferably 0.5 mm, more preferably 0.8 mm. On the other hand, the upper limit of the average width of the CNT film 11 is preferably 10 cm, more preferably 5 cm. If the average width of the CNT film 11 is less than the lower limit, the electrical resistance of the CNT film 11 may become excessively large or vary. On the other hand, if the average width of the CNT film 11 exceeds the upper limit, the strain sensor element becomes large, and there is a possibility that the applicable measurement object is excessively limited.

The lower limit of the average thickness of the CNT film 11 is preferably 1 μm, more preferably 10 μm. On the other hand, the upper limit of the average thickness of the CNT film 11 is preferably 5 mm, more preferably 1 mm. If the average thickness of the CNT film 11 is less than the lower limit, there is a risk that the formation of the CNT film 11 will be difficult or that the resistance will increase too much. Conversely, if the average thickness of the CNT film 11 exceeds the upper limit, the sensitivity to strain may decrease.

The lower limit of the electrical resistance (value measured between a pair of electrodes 14) in a state where there is no distortion of the CNT film 11 is preferably 10Ω, more preferably 100Ω. On the other hand, the upper limit of the electrical resistance of the CNT film 11 without distortion is preferably 100 kΩ, more preferably 10 kΩ. If the electrical resistance of the CNT film 11 in an unstrained state is less than the lower limit, the current for detecting the elongation strain increases, and the power consumption of the strain sensor element may increase. Conversely, if the electrical resistance of the CNT film 11 without strain exceeds the upper limit, the voltage of the detection circuit becomes high, making it difficult to downsize and save power of the device that processes the output of the strain sensor element. There is a risk that this may occur.

<Resin layer>
The pair of resin layers 12 and 13 are made of an insulating elastomer and are laminated on both surfaces (the above-mentioned front and back layers) of the CNT film 11, respectively. The resin layers 12 and 13 are made of the above-mentioned insulating elastomer, cover both sides of the CNT film 11, and protect the CNT film 11.

(Insulating elastomer)
As the insulating elastomer impregnated into at least the surface layer of the CNT film 11, a thermoplastic elastomer may be used. The thermoplastic elastomer can contain various synthetic resins.

Examples of the thermoplastic elastomer include styrene elastomer, olefin elastomer, polyester elastomer, and the like.

Examples of the thermoplastic elastomer include polyurethane (PUR), polyimide (PI), polyethylene (PE), high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), polypropylene (PP), and polyethylene. Vinyl chloride (PVC), polyvinylidene chloride, polystyrene (PS), polyvinyl acetate (PVAc), acrylonitrile butadiene styrene resin (ABS), acrylonitrile styrene resin (AS), polymethyl methacrylic (PMMA), polyamide (PA), Examples include polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and cyclic polyolefin (COP).

Further, as the insulating elastomer impregnated into at least the surface layer of the CNT film 11, rubber made of a synthetic thermosetting elastomer may be used.

Examples of the rubber include natural rubber (NR), butyl rubber (IIR), isoprene rubber (IR), ethylene propylene rubber (EPDM), butadiene rubber (BR), urethane rubber (U), and styrene butadiene rubber (SBR). , silicone rubber (Q), chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), acrylonitrile butadiene rubber (NBR), chlorinated polyethylene (CM), acrylic rubber (ACM), epichlorohydrin rubber (CO, ECO), Examples include fluororubber (FKM) and polydimethylsiloxane (PDMS). Among these, natural rubber is preferred from the viewpoint of strength and the like.

The insulating elastomer is preferably impregnated into at least the surface layer of the plurality of CNT fibers by coating with an aqueous emulsion. The aqueous emulsion refers to an emulsion in which the main component of the dispersion medium is water. Since carbon nanotubes are highly hydrophobic, when they are impregnated with an insulating elastomer by coating with an aqueous emulsion, the insulating elastomer does not completely penetrate between the plurality of CNT fibers. That is, although the surface layer of the plurality of CNT fiber layers is impregnated with the insulating elastomer, the insulating elastomer does not impregnate the entire area in the cross section of each CNT fiber in the thickness direction. This prevents the insulating elastomer from completely penetrating between the plurality of CNT fibers and affecting the resistance change of the CNT film 11, and reduces the sensitivity to distortion of the CNT film 11 due to the presence of the insulating elastomer. can be suppressed.

The main component of the dispersion medium of the aqueous emulsion is water, but other hydrophilic dispersion mediums such as alcohol may also be contained.

Further, the insulating elastomer preferably contains a coupling agent. When the material whose main component is an insulating elastomer contains a coupling agent, the insulating elastomer and the CNT fibers can be crosslinked, and the bonding force between the insulating elastomer and the CNT fibers can be improved.

As the coupling agent, for example, an amino coupling agent such as an aminosilane coupling agent, an aminotitanium coupling agent, an aminoaluminum coupling agent, or a silane coupling agent can be used.

Moreover, it is preferable that the insulating elastomer contains a dispersant that has adsorption properties to CNT fibers. Dispersants with such adsorption properties include those whose adsorption group has a salt structure (e.g., alkylammonium salts, etc.), and those with hydrophobic groups of CNT fibers (e.g., alkyl chains, aromatic rings, etc.). Those having a hydrophilic group (for example, polyether, etc.) that can interact in the molecule can be used.

The laminated structure of these resin layers 12 and 13 and the CNT film 11 may be formed by coating one of the layers (or films) with a material that will form another layer (or film), and each layer ( It may be formed by fusing or welding layers (or films), or by adhering each layer (or film) using a thermoplastic adhesive. Further, the resin layers 12 and 13 may be formed integrally with an insulating elastomer that is at least partially impregnated into the surface layer and back layer of the CNT film 11. That is, in the process of forming the CNT film 11, the insulating elastomer may be applied so as to remain on the front and back surfaces of the plurality of CNT fibers to form the resin layers 12 and 13, without impregnating the plurality of CNT fibers. Further, the resin layers 12 and 13 may have a multilayer structure consisting of a plurality of different layers. In that case, it is best to combine it with a material with high springiness. Specifically, it is preferable to use polyurethane as a material with high springiness.

The lower limit of the average thickness of each of the resin layers 12 and 13 is preferably 10 μm, more preferably 15 μm. On the other hand, the upper limit of the average thickness of the resin layers 12 and 13 is preferably 5 mm, more preferably 2 mm. If the average thickness of the resin layers 12 and 13 is less than the lower limit, the CNT film 11 may not be sufficiently protected. On the other hand, if the average thickness of the resin layers 12 and 13 exceeds the upper limit, the strain sensor 1 may become unnecessarily thick, or the elastic modulus of the CNT film 11 may increase, inhibiting the deformation of the measurement target. be. Note that the average thickness of the front and back resin layers 12 and 13 may be different from each other.

Furthermore, the resin layer 12 on the front side has a plurality of connection holes 16 that reach the CNT film 11 in the laminated region (both end regions) of the electrodes 14 . A plurality of connection holes 16 are preferably formed in each end region in order to improve the connection strength of the electrode 14 to the CNT film 11. Further, the plurality of connection holes 16 are preferably formed in regular arrays at a constant pitch in order to suppress a decrease in the strength of the resin layer 2 and to facilitate manufacturing. Note that the connection hole 16 may be formed in the shape of a notch that opens at the outer edge of the strain sensor element in plan view.

(Connection hole)
The lower limit of the average diameter of the connection holes 16 is preferably 0.5 mm, more preferably 0.7 mm. On the other hand, the upper limit of the average diameter of the connection holes 16 is preferably 2.0 mm, more preferably 1.5 mm. If the average diameter of the connection holes 16 is less than the lower limit, the connection of the electrode 14 to the CNT film 11 may become uncertain. Conversely, if the average diameter of the connection holes 16 exceeds the upper limit, the CNT film 11 may be easily damaged during formation of the connection holes 16.

The lower limit of the total area ratio of the connection holes 16 to the electrodes 14 is preferably 3%, more preferably 5%. On the other hand, the upper limit of the total area ratio of the connection holes 16 to the electrodes 14 is preferably 60%, more preferably 50%. If the total area ratio of the connection holes 16 to the electrode 14 is less than the lower limit, the connection strength of the electrode 14 to the CNT film 11 may be insufficient. Conversely, if the total area ratio of the connection holes 16 to the electrodes 14 exceeds the upper limit, the CNT film 11 may be easily damaged when the connection holes 16 are formed.

<Electrode>
The pair of electrodes 14 are formed from a conductive material that is filled in the connection hole 16. This conductive material is preferably laminated on the surfaces of the connection hole 16 and the surrounding resin layer 12 and laser absorption material layer 15 to increase the surface area and facilitate electrical connection.

The electrode 14 may have a further conductor, for example a copper foil, laminated to the surface side of the conductive material filling the connection hole 16. That is, the electrode 14 may include a conductive material that fills the connection hole 16 as a part thereof. By having copper foil or the like on the surface of the conductive material of the electrode 14, it becomes easy to solder the lead wire to the electrode 14.

(conductive material)
As the conductive material filled in the connection hole 16, for example, conductive paste, conductive paint, etc. can be used. That is, the electrode 14 can be formed by applying and curing a conductive paste or a conductive paint. As the conductive paste and conductive paint, commercially available ones containing conductive fine particles made of silver, copper, etc. can be used, for example.

The lower limit of the average thickness of the conductive material on the resin layer 12 is preferably 10 μm, more preferably 15 μm. On the other hand, the upper limit of the average thickness of the conductive material on the resin layer 12 is preferably 50 μm, more preferably 20 μm. If the average thickness of the conductive material on the resin layer 12 is less than the lower limit, it may be difficult to uniformly laminate the conductive material. Conversely, if the average thickness of the conductive material on the resin layer 12 exceeds the upper limit, manufacturing costs may increase unnecessarily.

<Laser absorbing material layer>
Laser absorbing material layer 15 is interposed between the surface of resin layer 12 around connection hole 16 and electrode 14 . The laser absorbing material layer 15 may be disposed only in the vicinity of the connection hole 16, or may be disposed over substantially the entire stacked region of the electrode 14 except for the inside of the connection hole 16.

The lower limit of the average thickness of the laser absorbing material layer 15 is preferably 1 μm, more preferably 2 μm. On the other hand, the upper limit of the average thickness of the laser absorbing material layer 15 is preferably 15 μm, more preferably 10 μm. If the average thickness of the laser-absorbing material layer 15 is less than the lower limit, the laser-absorbing material layer 15 may not be able to sufficiently promote the formation of the connection holes 16, and the manufacturing efficiency of the strain sensor element may be reduced. Conversely, if the average thickness of the laser absorbing material layer 15 exceeds the upper limit, the electrode 14 may easily peel off.

(laser absorbing material)
The laser absorbing material forming the laser absorbing material layer 15 can include fine particles made of a material with a relatively high laser absorption rate and a binder thereof.

As the fine particles, various pigments and the like can be used, depending on the wavelength of the laser used to form the connection hole 16. Among these, carbon black is particularly preferably used as the fine particles because it has a relatively high laser absorption rate and is electrically conductive so that the electrical connection between the CNT film 11 and the electrode 14 is not easily inhibited.

As the binder, various polymer binders can be used.

〔Production method〕
As shown in FIG. 3, the strain sensor element is manufactured by applying a laser absorbing material to the surface of both end regions of a resin layer covering body in which a CNT film 11 is covered with resin layers 12 and 13 <Step S1: Laser absorbing material coating step>, a step of irradiating at least part of the surface of both end regions of the resin layer covering with a laser <Step S2: Laser irradiation step>, and a step of applying a conductive material to the holes formed in the resin layer 12 in the laser irradiation step. It can be manufactured by a method comprising a step of filling a conductive material <Step S3: Conductive material filling step> and a step of cutting out the strain sensor element from the resin layer covering body <Step S4: Cutting out step>.

<Laser absorbing material coating process>
In the laser-absorbing material application step of step S1, a laser-absorbing material coating is applied to the surfaces of both end regions of the plurality of parts of the laminate of the large CNT film 11 and the pair of resin layers 12 and 13 used as the strain sensor elements. form. In other words, the strain sensor manufacturing method manufactures a plurality of strain sensors at once.

The laser-absorbing material can be applied using a printing technique such as screen printing, but may also be applied using a simpler method such as brush coating.

(laser absorbing material)
The laser-absorbing material can be applied using a laser-absorbing material-dispersed ink in which fine particles having a relatively high laser absorption rate are dispersed in a solvent. This laser-absorbing material-dispersed ink may contain arbitrary additives such as a dispersant for dispersing fine particles, a binder for retaining fine particles after the solvent has evaporated, and a surfactant for improving coating properties. Can be used.

As the solvent for this laser-absorbing material-dispersed ink, it is preferable to use a volatile organic solvent such as toluene, acetone, methanol, methyl ethyl ketone, isopropyl alcohol, etc. so that it can volatilize immediately after coating to form a stable coating film.

<Laser irradiation process>
In the laser irradiation step of step S2, at least a portion of the coating film obtained in the coating step is irradiated with a laser. As a result, the laser-absorbing material absorbs the laser and generates heat, thermally decomposing the resin layer 12 to form the connection hole 16.

The laser output is selected depending on the diameter of the connection hole 16, the material of the resin layer 12, etc., but generally, the lower limit of the laser output is preferably 3W, more preferably 5W. On the other hand, the upper limit of the laser output is preferably 30W, more preferably 20W. If the laser output is less than the lower limit, there is a possibility that the connection hole 16 cannot be formed. Conversely, if the laser output exceeds the upper limit, there is a risk of damaging the surrounding resin layer 12 and CNT film 11 when forming the connection hole 16.

<Conductive material filling process>
In the conductive material filling step of step S3, the inside of the connection hole 16 is filled with the conductive material by applying the conductive material to the surface of both end regions of the resin layer covering in which the connection hole 16 is formed, and A coating film of a conductive material is formed on the surface of the resin layer 12 around the connection hole 16 . This coating of conductive material forms at least a portion of the electrode 14.

When a plurality of connection holes 16 in each end region are formed, it is preferable to apply the conductive material across the plurality of connection holes 16 in each end region in this conductive material filling step. In this way, by applying the conductive material across the plurality of connection holes 16 in each end region, the electrical connection between the CNT film 11 and the electrode 14 can be made more reliable.

The conductive material can be applied using a printing technique such as screen printing, but it may also be applied using a simpler method such as brush coating.

<Cutting process>
In the cutting step of step S4, a plurality of strain sensor elements are cut out from the resin layer covering on which the electrodes 14 are formed.

The strain sensor element may be cut out by punching using a die and a punch, or by sequentially cutting out the outline of the strain sensor element using a cutter or the like.

<Advantages>
In the strain sensor element, the electrodes 14 are formed by filling the connection holes 16 with a conductive material, so electrical connection between the CNT film 11 and the electrodes 14 is relatively easy. Furthermore, since the connection hole 16 of the strain sensor element is formed using a laser, design changes are relatively easy.

[Second embodiment]
The strain sensor element according to the second embodiment of the present invention, whose cross section at one end region is shown in FIG. A resin layer 22 to be covered, a pair of electrodes 23 laminated on both end regions of the resin layer 22 of the CNT thread 21 and electrically connected to the CNT thread 21, and a pair of electrodes 23 between the resin layer 22 and the electrode 23. and a layer of laser absorbing material 24 partially present therebetween.

<CNT thread>
The structure of the CNT thread 21 of the sensor element in FIG. 4 can be the same as the structure of the CNT film 11 of the sensor element in FIG. 1, except that the CNT fibers are arranged in a thread shape. Note that when arranging the CNT fibers into a thread, the CNT fibers may be twisted together.

<Resin layer>
The resin layer 22 has one or more connection holes 25 leading to the CNT threads 21 in each end region. When forming a plurality of connection holes 25, they may be formed so as to open in different directions around the central axis of the CNT thread 21, but they may be arranged in the axial direction so as to open in the same direction around the central axis of the CNT thread 21. Forming it facilitates processing.

The other structure of the resin layer 22 of the sensor element in FIG. 4 can be the same as the structure of the resin layers 12 and 13 of the sensor element in FIG. .

<Electrode>
The pair of electrodes 23 includes a conductive material that fills the connection hole 25 . Further, the electrode 23 may have an additional conductor such as a copper foil laminated on the surface side of the conductive material filling the connection hole 25.

(conductive material)
As the conductive material for the electrode 23 of the sensor element in FIG. 4, the same conductive material as the electrode 14 for the sensor element in FIG. 1 can be used.

〔Production method〕
The strain sensor element consists of a step of applying a laser absorbing material to the surface of both end regions of a resin layer covering body in which a CNT thread 21 is covered with a resin layer 22 to form a laser absorbing material layer 24, and a process of forming a laser absorbing material layer 24 of the resin layer covering body. A method comprising the steps of irradiating at least part of the surface of both end regions with a laser, and filling the connection hole 25 formed in the resin layer 22 in the laser irradiation step with a conductive material to form the electrode 23. It can be manufactured by

Since the strain sensor element is thread-like, it can be used as a thread constituting a woven fabric or a thread sewn onto a fabric, and can be used to form a fabric whose strain can be detected.

[Other embodiments]
The embodiments described above do not limit the configuration of the present invention. Therefore, in the embodiment, it is possible to omit, replace, or add components of each part of the embodiment based on the description in this specification and common general knowledge, and all of these are interpreted as falling within the scope of the present invention. Should.

The strain sensor element may not have a laser absorbing material layer if the resin layer has a relatively high laser absorption rate. Therefore, in the method for manufacturing the strain sensor element, the laser absorbing material coating step can be omitted.

Furthermore, in the method for manufacturing the strain sensor element, the resin layer covering of the CNT film may be cut out in the shape of the strain sensor element, and then connection holes may be formed in the resin layer and a conductive material may be applied.

Further, the strain sensor element including the CNT thread may be coated with a laser absorbing material and a conductive material over the entire circumference. Further, the planar shape of the connection hole opened by laser irradiation is not limited to a circular shape.

Hereinafter, reference embodiments of strain sensor elements related to the present invention will be described.

[First reference form]
The strain sensor element of the first reference embodiment of the present invention shown in FIGS. 5 and 6 includes a CNT film 1 formed in a band shape and including a plurality of CNT fibers aligned in the longitudinal direction, and a coating on the front and back surfaces of the CNT film 1. A pair of resin layers 2 and 3 are laminated on the surface of the resin layer covering consisting of the CNT film 1 and the resin layers 2 and 3 at both end regions in the direction in which the CNT fibers are aligned, and the CNT film 1 and the electrical It comprises a pair of plate-shaped electrodes 4 that are connected to each other, and a pair of sandwiching sheets 5 that are disposed opposite to the plate-shaped electrodes 4 at both end regions on the back side of the resin layer covering.

In the strain sensor element, at least a portion of the pair of plate-shaped electrodes 4 is embedded in the resin layer 2 on the front side. More specifically, the pair of plate-shaped electrodes 4 are implanted in the thickness direction from the surface side of the resin layer 2 on the front side. At least a portion of each of the pair of plate-shaped electrodes 4 is exposed from the resin layer 2, and each exposed portion is connected to external wiring (not shown).

<CNT film>
The CNT film 1 consists of a layer formed from a plurality of CNT fibers aligned in one direction, and the front and back layers are made of a material whose main component is an insulating elastomer (hereinafter simply referred to as "insulating elastomer"), which will become a resin layer to be described later. ) are laminated, and the front and back layers of the CNT membrane 1 are impregnated with an insulating elastomer (at least from the surface side of the CNT membrane 1), so that the CNT fibers and the insulating elastomer are composited and formed into a membrane. has been done. The CNT film 1 has elasticity due to the elastic force of the insulating elastomer, and can be expanded and contracted at least in the longitudinal direction. When this CNT film 1 is stretched at least in the longitudinal direction, the CNT fibers are separated from each other and the electrical resistance increases, and when the CNT film 1 contracts due to elastic force, the CNT fibers come into contact with each other again and the electrical resistance is reduced. Note that the CNT film 1 may include insulating fibers made of, for example, synthetic resin in order to suppress the contact rate between the CNT fibers and adjust the electrical resistance.

Since the CNT membrane 1 is laminated with at least the surface layer impregnated with an insulating elastomer, the insulating elastomer covers the CNT fiber bundles described below, and this insulating elastomer guides the expansion and contraction direction of the plurality of CNT fiber bundles. It also functions as a guide member. As a result, in the strain sensor, the CNT fibers separated during stretching can be brought into contact again at the same location during contraction, and it is possible to prevent a decrease in the detection accuracy of stretching strain due to repeated use. Furthermore, according to such a configuration, the contact relationship between the plurality of CNT fibers can be easily maintained, and the elasticity of the plurality of CNT fibers can be easily adjusted. Therefore, the expansion/contraction strain of the CNT film 1 can be detected with higher accuracy. Further, in order to further facilitate the maintenance of such a contact relationship and the adjustment of elasticity, it is preferable that the back layer (region near the back surface) of the CNT film 1 is also impregnated with an insulating elastomer. At this time, since at least a portion of the surface layer of the CNT fiber bundle is impregnated with the insulating elastomer, the bonding strength between the CNT fiber bundle and the insulating elastomer is also increased.

(CNT fiber)
Each of the CNT fibers constituting the CNT membrane 1 can be formed from a plurality of CNT single fibers. Here, the CNT single fiber refers to one long carbon nanotube. Moreover, the CNT fiber has a connection part where the ends of the CNT single fibers are connected to each other. The CNT single fibers are connected to each other in the longitudinal direction of these CNT single fibers. In this way, in the CNT film 1, the CNT single fibers are connected to each other in the longitudinal direction, so that the CNT film 1 with a large orientation length of the CNT fibers can be formed, and the longitudinal length of the strain sensor can be Sensitivity can be improved by increasing the size.

Further, the plurality of CNT fibers constituting the CNT film 1 may form a network structure. Specifically, the plurality of CNT fibers may be connected or in contact with each other in the form of a network through connection parts where CNT single fibers are connected to each other. At this time, the ends of three or more CNT single fibers may be combined at this connection part, or the ends of two CNT single fibers and the intermediate part of another single fiber may be combined. When a plurality of CNT fibers form such a network structure, the CNT fibers are brought into close contact with each other, and the resistance of the CNT film 1 can be lowered.

Furthermore, the CNT film 1 may have a CNT fiber bundle consisting of a plurality of CNT fibers oriented in the longitudinal direction. When the CNT film 1 has a plurality of CNT fiber bundles oriented in the longitudinal direction, when strain is applied to the CNT film 1 to stretch in the stretching direction, the CNT fibers are cut, separated, and the cutting space (gap) of the CNT fiber bundles is created. ), the resistance of the CNT film 1 changes more accurately.

More specifically, the CNT fiber bundle has a bundle structure consisting of a plurality of CNT fibers, and in any cross section of the CNT fiber bundle, there are CNT fibers that are not cut and CNT fibers that are cut and separated. Both gaps will exist. Furthermore, since the surface layer of the plurality of CNT fiber bundles is coated with an insulating elastomer, the pressure within this gap is considered to be lower than atmospheric pressure (negative pressure). (When the strain is released), the contraction force of this gap forces the strain sensor 1 to contract. Furthermore, since the friction between the CNT fibers is reduced within this gap, the movement of the CNT fibers is less likely to be restricted.

Note that the CNT film 1 may have a single layer structure in which a plurality of CNT fibers or a plurality of CNT fiber bundles are arranged substantially parallel in a plane, or may have a multilayer structure. However, in order to ensure a certain degree of conductivity, it is preferable to have a multilayer structure.

As the CNT single fiber, either a single-wall nanotube (SWNT) or a multi-wall nanotube (MWNT) can be used, but from the viewpoint of electrical conductivity and heat capacity, MWNT is preferable and has a diameter of 1.5 mm. MWNTs with a diameter of 5 nm or more and 100 nm or less are more preferable.

The CNT single fibers can be manufactured by a known method, such as a CVD method, an arc method, a laser ablation method, a DIPS method, or a CoMoCAT method. Among these, it is preferable to manufacture by a CVD method using iron as a catalyst and ethylene gas, since carbon nanotubes (MWNT) of a desired size can be efficiently obtained. In this case, a thin film of iron or nickel as a catalyst is formed on a substrate such as a quartz glass substrate or a silicon substrate with an oxide film, and carbon nanotubes are grown in a vertical orientation to obtain carbon nanotube crystals of a desired length. I can do it.

The average length in the longitudinal direction of the CNT film 1 is not particularly limited, and can be freely selected depending on the object to be measured using the strain sensor element, and may be, for example, 1 cm or more and 20 cm or less.

The average length in the longitudinal direction of the region sandwiched between the pair of plate-shaped electrodes 4 in a plan view of the CNT film 1 can be freely selected depending on the object to be measured using the strain sensor element. The average length can be, for example, 2 mm or more and 18 cm or less.

The average length in the longitudinal direction of the region of the CNT film 1 that overlaps with the pair of plate-shaped electrodes 4 in a plan view is appropriately selected depending on the method of fixing to the measurement target, the wiring method to the plate-shaped electrodes 4, etc. , for example, 3 mm or more and 5 cm or less.

The average width of the CNT film 1 can be freely selected depending on the object to be measured using the strain sensor element. The lower limit of the average width of the CNT film 1 is preferably 1 mm, more preferably 2 mm. On the other hand, the upper limit of the average width of the CNT film 1 is preferably 10 cm, more preferably 5 cm. If the average width of the CNT film 1 is less than the lower limit, the electrical resistance of the CNT film 1 may become excessively large or vary. On the other hand, if the average width of the CNT film 1 exceeds the upper limit, the strain sensor element becomes large, and there is a possibility that the applicable measurement object is excessively limited.

The lower limit of the average thickness of the CNT film 1 is preferably 1 μm, more preferably 10 μm. On the other hand, the upper limit of the average thickness of the CNT film 1 is preferably 5 mm, more preferably 1 mm. If the average thickness of the CNT film 1 is less than the lower limit, the formation of the CNT film 1 may be difficult or the resistance may increase too much. Conversely, if the average thickness of the CNT film 1 exceeds the upper limit, the sensitivity to strain may decrease.

The lower limit of the electrical resistance (value measured between a pair of plate-like electrodes 4) in a state where the CNT film 1 is not strained is preferably 10Ω, more preferably 100Ω. On the other hand, the upper limit of the electrical resistance of the CNT film 1 without distortion is preferably 100 kΩ, more preferably 10 kΩ. If the electrical resistance of the CNT film 1 in an unstrained state is less than the lower limit, the current for detecting the elongation strain increases, and the power consumption of the strain sensor element may increase. Conversely, if the electrical resistance of the CNT film 1 without strain exceeds the upper limit, the voltage of the detection circuit will increase, making it difficult to downsize and save power of the device that processes the output of the strain sensor element. There is a risk that this may occur.

<Resin layer>
The pair of resin layers 2 and 3 are made of an insulating elastomer and are laminated on both surfaces (the above-mentioned front and back layers) of the CNT film 1, respectively. The resin layers 2 and 3 are made of the above-mentioned insulating elastomer, cover both sides of the CNT film 1, and protect the CNT film 1.

(Insulating elastomer)
As the insulating elastomer impregnated into at least the surface layer of the CNT film 1, a thermoplastic elastomer may be used. The thermoplastic elastomer can contain various synthetic resins.

Examples of the thermoplastic elastomer include styrene elastomer, olefin elastomer, polyester elastomer, and the like.

Examples of the thermoplastic elastomer include polyurethane (PUR), polyimide (PI), polyethylene (PE), high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), polypropylene (PP), and polyethylene. Vinyl chloride (PVC), polyvinylidene chloride, polystyrene (PS), polyvinyl acetate (PVAc), acrylonitrile butadiene styrene resin (ABS), acrylonitrile styrene resin (AS), polymethyl methacrylic (PMMA), polyamide (PA), Examples include polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (m-PPE), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and cyclic polyolefin (COP).

Further, as the insulating elastomer impregnated into at least the surface layer of the CNT film 1, rubber made of a synthetic thermosetting elastomer may be used.

Examples of the rubber include natural rubber (NR), butyl rubber (IIR), isoprene rubber (IR), ethylene propylene rubber (EPDM), butadiene rubber (BR), urethane rubber (U), and styrene butadiene rubber (SBR). , silicone rubber (Q), chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), acrylonitrile butadiene rubber (NBR), chlorinated polyethylene (CM), acrylic rubber (ACM), epichlorohydrin rubber (CO, ECO), Examples include fluororubber (FKM) and polydimethylsiloxane (PDMS). Among these, natural rubber is preferred from the viewpoint of strength and the like.

The insulating elastomer is preferably impregnated into at least the surface layer of the plurality of CNT fibers by coating with an aqueous emulsion. The aqueous emulsion refers to an emulsion in which the main component of the dispersion medium is water. Since carbon nanotubes are highly hydrophobic, when they are impregnated with an insulating elastomer by coating with an aqueous emulsion, the insulating elastomer does not completely penetrate between the plurality of CNT fibers. That is, although the surface layer of the plurality of CNT fiber layers is impregnated with the insulating elastomer, the insulating elastomer does not impregnate the entire area in the cross section of each CNT fiber in the thickness direction. This prevents the insulating elastomer from completely penetrating between the plurality of CNT fibers and affecting the resistance change of the CNT film 1, and reduces the sensitivity of the CNT film 1 to strain caused by the presence of the insulating elastomer. can be suppressed.

The main component of the dispersion medium of the aqueous emulsion is water, but other hydrophilic dispersion mediums such as alcohol may also be contained.

Further, the insulating elastomer preferably contains a coupling agent. When the material whose main component is an insulating elastomer contains a coupling agent, the insulating elastomer and the CNT fibers can be crosslinked, and the bonding force between the insulating elastomer and the CNT fibers can be improved.

As the coupling agent, for example, an amino coupling agent such as an aminosilane coupling agent, an aminotitanium coupling agent, an aminoaluminum coupling agent, or a silane coupling agent can be used.

Moreover, it is preferable that the insulating elastomer contains a dispersant that has adsorption properties to CNT fibers. Dispersants with such adsorption properties include those whose adsorption group has a salt structure (e.g., alkylammonium salts, etc.), and those with hydrophobic groups of CNT fibers (e.g., alkyl chains, aromatic rings, etc.). Those having a hydrophilic group (for example, polyether, etc.) that can interact in the molecule can be used.

The laminated structure of these resin layers 2 and 3 and the CNT film 1 may be formed by coating one of the layers (or films) with a material that will form another layer (or film), and each layer ( It may be formed by fusing or welding layers (or films), or by adhering each layer (or film) using a thermoplastic adhesive. Furthermore, the resin layers 2 and 3 may be formed integrally with an insulating elastomer that is at least partially impregnated into the surface and back layers of the CNT film 1. That is, in the process of forming the CNT film 1, the insulating elastomer may be applied so as to remain on the front and back surfaces of the plurality of CNT fibers to form the resin layers 2 and 3, without impregnating the plurality of CNT fibers. Further, the resin layers 2 and 3 may have a multilayer structure consisting of a plurality of different layers. In that case, it is best to combine it with a material with high springiness. Specifically, it is preferable to use polyurethane as a material with high springiness.

The lower limit of the average thickness of each of the resin layers 2 and 3 is preferably 10 μm, more preferably 15 μm. On the other hand, the upper limit of the average thickness of the resin layers 2 and 3 is preferably 5 mm, more preferably 2 mm. If the average thickness of the resin layers 2 and 3 is less than the lower limit, there is a risk that the CNT film 1 may not be sufficiently protected, and the buried plate-shaped electrode 4 may easily fall off. On the other hand, if the average thickness of the resin layers 2 and 3 exceeds the upper limit, the strain sensor 1 may become unnecessarily thick, or the elastic modulus of the CNT film 1 may increase, inhibiting the deformation of the measurement target. Therefore, it may not be easy to embed the plate electrode 4. Note that the average thickness of the front and back resin layers 2 and 3 may be different from each other.

<Plate electrode>
As the plate electrode 4, a generally plate-shaped conductor is used. As such a conductor, for example, a sheet-like material, a net-like material, etc. are used. Further, examples of the material of the plate electrode 4 include metals such as copper, aluminum, nickel, and stainless steel, and carbon. This plate-shaped electrode 4 may have, for example, a protrusion penetrating the CNT film 1, a protrusion for connecting to external wiring, or the like.

It is preferable that the plate-shaped electrode 4 has a plurality of through holes 4a as shown in the figure. The through-hole 4a of the plate-shaped electrode 4 is formed, for example, by a hole formed in a sheet-shaped material, an opening between strands of a net-shaped material, or the like. Further, the through holes 4a of the plate electrode 4 are not limited to those that are independent from each other, but may be slit-shaped or cut-out holes that open at the periphery of the plate electrode 4, as illustrated in FIG. 7, for example. Good too.

As described above, since the plate electrode 4 has a plurality of through holes 4a, when the plate electrode 4 is buried in the resin layer 2 on the front side, the material constituting the resin layer 2 is formed in the through holes 4a of the plate electrode 4. The plate-shaped electrode 4 can be embedded in the resin layer 2 relatively easily. Further, the material forming the resin layer 2 that has flowed into the through hole 4a increases the contact area between the plate electrode 4 and the resin layer 2, thereby making the plate electrode 4 more securely held.

The plate-shaped electrode 4 is heated and pressed against the resin layer 2 on the front side to fluidize the resin layer 2 and embed the plate-shaped electrode 4 in the resin layer 2. It is preferable that the portion buried in layer 2 has high thermal conductivity.

The lower limit of the thermal conductivity of the buried portion of the plate electrode 4 is preferably 5 W/(m·K), more preferably 10 W/(m·K). If the thermal conductivity of the buried portion of the plate electrode 4 is less than the lower limit, it will be difficult to transfer heat to the resin layer 2 on the front side and make it flow, and there is a risk that it will not be easy to bury the plate electrode 4. be.

It is preferable that the plate-shaped electrode 4 has flexibility so that it can bend when buried and smoothly push out the resin layer 2 on the front side outward in a plan view. Further, by fixing the flexible plate-shaped electrode 4 in a bent state, a resin layer 2 having a wedge-shaped cross section is left between the plate-shaped electrode 4 and the CNT film 1, and the plate-shaped electrode 4 is fixed in a bent state. The contact area between the electrode 4 and the resin layer 2 increases, and the effect of preventing the plate-shaped electrode 4 from detaching can also be obtained.

In order to increase the contact area with the resin layer 2 in this way, the flexible plate-shaped electrode 4 has its central part pushed into the resin layer 2 on the front side, so that the outer peripheral part in plan view is the surface of the resin layer 2. It is preferable to bury it so that it protrudes from the surface. Further, in order to facilitate such embedding, the plate-shaped electrode 4 may be formed by combining a plurality of types of materials so that the thermal conductivity of the central portion is increased in plan view. Furthermore, in order to increase the contact area between the plate-shaped electrode 4 and the CNT film 1, the flexibility of the peripheral portion of the plate-shaped electrode 4 may be made greater than that of the central portion that is brought into contact with the CNT film 1. The flexibility of the plate electrode 4 may be adjusted by, for example, the size, shape, arrangement density, etc. of the through hole 4a.

Moreover, it is preferable that the plate electrode 4 has a convex shape that bulges toward the CNT film 1 side while being fixed so as to be connected to the CNT film 1 . More preferably, this convex shape is formed by curving the plate electrode 4. Since the plate-shaped electrode 4 has such a convex shape, the resin layer 2 can be smoothly pushed outward in a plan view when the plate-shaped electrode 4 is buried. Further, since the plate electrode 4 has a convex shape, the contact area between the plate electrode 4 and the CNT film 1 can be increased, and the electrical connection can be further improved. Furthermore, the convex plate-shaped electrode 4 can sandwich not only the CNT film 1 and the resin layer 3 on the back side but also the resin layer 2 on the front side between its peripheral portion and the sandwiching sheet 5. It is difficult to break because the tension is dispersed.

The plate-shaped electrode 4 having such a convex portion is buried so that at least the tip of the convex portion in the thickness direction reaches the surface of the CNT film 1. More preferably, the plate-like electrode 4 is arranged in the thickness direction of the convex portion so as to contact the CNT fibers at different positions in the thickness direction of the CNT film 1 to obtain a more reliable electrical connection with the CNT film 1. It is buried so that the tip reaches the back surface of the CNT film 1.

Moreover, it is preferable that the plate-shaped electrode 4 does not substantially expand or contract during use of the strain sensor element. Note that "not substantially expanding or contracting" refers to the region (hereinafter also referred to as "stretching region") disposed between the pair of plate electrodes 4 in plan view during measurement using the strain sensor element. This means that the ratio of the expansion/contraction rate in the longitudinal direction of the plate electrode 4 to the expansion/contraction rate in the longitudinal direction is 1/100 or less, preferably 1/1000 or less.

Further, the number of digits of the ratio of the expansion/contraction rate of the stretchable region to the expansion/contraction rate of the plate-shaped electrode 4 during measurement using the strain sensor element is preferably larger than the number of digits of the effective numerical value in the measurement, and is two or more digits larger. It is more preferable.

The lower limit of the average thickness (or average wire diameter in the case of a mesh) of the plate electrode 4 is preferably 10 μm, more preferably 50 μm. On the other hand, the upper limit of the average thickness of the plate electrode 4 is preferably 1 mm, more preferably 0.5 mm. If the average thickness of the plate electrode 4 is less than the lower limit, the plate electrode 4 may break due to bending or the like. On the other hand, if the average thickness of the plate electrode 4 exceeds the upper limit, the strain sensor element may become unnecessarily thick, or the non-stretchable region may lack flexibility and cannot be properly attached to the measurement target. There is a risk.

The planar shape of the plate electrode 4 can be substantially the same as the planar shape of the end region of the CNT film 1. As shown in FIG. 5, the plate electrode 4 may be formed to be slightly smaller than the end region of the CNT film 1 so as not to protrude from the CNT film 1 in plan view. By leaving the resin layer 2 on the surface side around the plate electrode 4 whose thickness has not been reduced by embedding the plate electrode 4, it is possible to suppress a decrease in the strength of the resin layer 2.

As the plate-shaped electrode 4 that satisfies the above conditions, it is possible to use, for example, a wire mesh made of stainless steel and having a nominal opening of 5 μm or more and 100 μm or less and formed from strands with an average wire diameter of 3 μm or more and 100 μm or less.

(Pinching sheet)
The sandwiching sheet 5 is laminated on the other surface of the resin layers 2 and 3 so as to cover the other surface of the non-stretchable region. The sandwiching sheets 5 can be laminated using adhesive, for example. As this adhesive, for example, an adhesive, a curable adhesive, a thermoplastic adhesive, etc. can be used. Examples of the adhesive include acrylic adhesives. Examples of the curable adhesive include epoxy adhesives and the like.

Like the plate-shaped electrode 4, this sandwiching sheet 5 does not substantially expand or contract during use of the strain sensor element, and prevents expansion or contraction in the non-stretchable region. That is, by sandwiching the non-stretchable regions of the resin layers 2 and 3 and the CNT film 1 between the sandwiching sheet 5 and the plate-like electrode 4, expansion and contraction of the non-stretchable regions can be more reliably prevented. Therefore, by providing the sandwiching sheet 5, in the strain sensor element, the non-stretchable region and the stretchable region of the resin layers 2, 3 and the CNT film 1 are more clearly divided. Therefore, the strain sensor element has a high correlation between the amount of expansion and contraction and the electrical resistance of the CNT film 1, and has excellent strain detection accuracy.

The material of the sandwiching sheet 5 may be any material that has sufficient non-stretchability, and may be conductive or insulating. Specifically, as the sandwiching sheet 5, for example, a resin sheet whose main component is polyimide, polyethylene terephthalate, etc., a woven cloth such as glass cloth, etc. can be used. Further, as the sandwiching sheet 5, a commercially available adhesive tape on which an adhesive is laminated in advance may be used.

The lower limit of the average thickness of the sandwiching sheet 5 is preferably 20 μm, more preferably 50 μm. On the other hand, the upper limit of the average thickness of the sandwiching sheet 5 is preferably 1 mm, more preferably 0.5 mm. If the average thickness of the sandwiching sheet 5 is less than the lower limit, there is a risk that the sandwiching sheet 5 will break due to bending or the like. On the other hand, if the average thickness of the sandwiching sheet 5 exceeds the upper limit, the strain sensor element may become unnecessarily thick, or the non-stretchable region may lack flexibility and may not be properly attached to the measurement target. There is.

<Manufacturing method>
The strain sensor element consists of a process of forming a sheet body having a laminated structure of a CNT film 1 and resin layers 2 and 3, and a process of forming a CNT film 1 and resin layers 2 and 3 having a desired planar shape by cutting this sheet body. a step of forming a laminate (covering body), a step of embedding plate-like electrodes 4 in the resin layer 2 on the front side of both ends of the laminate, and a pair of sandwiching sheets on the back side of both ends of the laminate. It can be manufactured by a method comprising a step of adhering 5.

In the embedding step, the plate-shaped electrode 4 is pushed into the resin layer 2 on the surface side by pressing a relatively high-temperature heating member against the surface of the plate-shaped electrode 4. That is, by transmitting the heat of the heating member through the plate-shaped electrode 4 to the contact area of the resin layer 2 with the plate-shaped electrode 4, the material forming the resin layer 2 is fluidized, and this fluidized material is pushed away. Then, the plate-shaped electrode 4 is inserted into the resin layer 2. Therefore, the temperature of the heating member is preferably higher than the softening point of the resin layer 2 on the front side by 10° C. or more and 50° C. or less. For simplicity, a soldering iron or the like can be used as the heating member.

<Advantages>
The strain sensor element is manufactured by cutting a sheet body in which a CNT film 1 is covered with resin layers 2 and 3 into arbitrary dimensions, and then embedding a plate-shaped electrode 4 in the resin layer 2, thereby forming electrodes for wiring on the CNT film 1. can be connected, making it relatively easy to manufacture. Furthermore, as described above, in the strain sensor element, the plate-shaped electrode 4 is later embedded in the covering body cut out to any size from the sheet body, so the shape of the covering body cut out from the sheet body can be arbitrarily changed. design changes are relatively easy.

[Second reference form]
A strain sensor element according to a second embodiment of the present invention shown in FIG. The resin layers 2 and 3 are laminated on the front side of the resin layer covering consisting of the CNT film 1 and the resin layers 2 and 3 at both end regions in the alignment direction of the CNT fibers, and are electrically connected to the CNT film 1. a pair of plate-shaped electrodes 4, a pair of sandwiching sheets 5 disposed opposite to the plate-shaped electrodes 4 on both end areas of the back side of the resin layer covering, and a pair of sandwiching sheets 5 disposed on the opposite side of the plate-shaped electrodes 4 on the CNT film 1 side of the plate-shaped electrode 4. A pair of intervening conductive fabrics 6 are provided.

The CNT film 1, resin layers 2, 3, plate-like electrodes 4, and sandwiching sheet 5 in the strain sensor element of FIG. Since it is the same as sheet 5, duplicate explanation will be omitted.

<Conductive fabric>
The conductive fabric 6 is formed from a woven or knitted fabric or a nonwoven fabric of conductive fibers. This conductive fabric 6 is interposed between the CNT film 1 and the plate-shaped electrode 4 and comes into contact with both the CNT film 1 and the plate-shaped electrode 4. The conductive fabric 6 has fine irregularities formed by conductive fibers on its front and back surfaces, and these fine irregularities come into contact with the CNT film 1 and the plate-shaped electrode 4 at many locations. Thereby, the conductive fabric 6 improves the conductivity between the CNT film 1 and the plate-shaped electrode 4.

In order to hold the plate-shaped electrode 4 by the material forming the resin layer 2, the conductive fabric 6 is designed to have enough material to allow the material forming the resin layer 2 on the front side to penetrate in a molten state and pass through in the thickness direction. A coarse one is used.

The lower limit of the average thickness of the conductive fabric 6 is preferably 10 μm, more preferably 15 μm. On the other hand, the upper limit of the average thickness of the conductive fabric 6 is preferably 3 mm, more preferably 1 mm. If the average thickness of the conductive fabric 6 is less than the lower limit, the conductive fabric 6 may be torn due to insufficient strength when the plate electrode 4 is buried. Conversely, if the average thickness of the conductive fabric 6 exceeds the upper limit, the material forming the resin layer 3 will not be able to penetrate the conductive fabric 6 when the plate electrode 4 is buried, and the plate electrode 4 will be held. There is a possibility that it cannot be done.

The conductive fabric 6 is preferably larger than the plate electrode 4 in plan view so that it can reliably cover the entire back surface of the plate electrode 4 after being buried.

As the conductive fabric 6, a commercially available conductive adhesive tape having one surface of the conductive cloth coated with a conductive adhesive may be used. The conductive fabric 6 made of conductive adhesive tape is attached to the surface of the resin layer 2 on the front side or the back surface of the plate electrode 4 before embedding the plate electrode 4 to prevent positional shift. 4. Makes the burial work easier. Note that the conductive adhesive of the conductive adhesive tape can assist in electrical contact between the conductive fabric 6 and the CNT film 1 or the plate-shaped electrode 4; Since it is pushed away by the electrode 4, it does not hinder the embedding of the plate-shaped electrode 4.

[Third reference form]
A strain sensor element according to a third embodiment of the present invention shown in FIG. 9 includes a CNT film 1 formed in a band shape and including a plurality of CNT fibers aligned in the longitudinal direction, and a resin coated on the front and back surfaces of the CNT film 1. A pair of layers 2 and 3, which are laminated on both end regions in the CNT fiber alignment direction on the front side of the resin layer covering made of the CNT film 1 and the resin layers 2 and 3, and are electrically connected to the CNT film 1. A plate-shaped electrode 4, a pair of sandwiching sheets 5 disposed on both end regions of the back side of the resin layer covering so as to face the plate-shaped electrode 4, and a conductive sheet impregnated into at least a portion of the plate-shaped electrode 4. and a sexual paste 7.

The CNT film 1, resin layers 2, 3, plate-like electrodes 4, and sandwiching sheet 5 in the strain sensor element of FIG. Since it is the same as sheet 5, duplicate explanation will be omitted.

When the plate-shaped electrode 4 is heated and pressurized and embedded in the resin layer 2 on the front side so as to be in contact with the CNT film 1, the forming material of the resin layer 2 enters the plurality of through holes 4a of the plate-shaped electrode 4. However, the plurality of through holes 4a of the plate electrode 4 are not necessarily completely filled with the material forming the resin layer 2. In particular, when a wire mesh or the like is used as the plate-shaped electrode 4 in which the shape of the through-hole 4a is complicated, a space is likely to be left inside the through-hole 4a of the plate-shaped electrode 4, for example, at the intersection of metal wires. Therefore, by filling the space left in the through hole 4a of the plate electrode 4 with the conductive paste 7, the reliability of the electrical connection between the plate electrode 4 and the CNT film 1 can be further improved.

<Conductive paste>
The conductive paste 7 can be one in which conductive fine particles are dispersed in a resin matrix, and specifically, for example, a commercially available silver paste or the like can be used. This conductive paste 7 is preferably applied from the surface side of the plate electrode 4 to impregnate it into the plate electrode 4 after the plate electrode 4 is buried therein.

<Advantages>
The strain sensor element is manufactured by cutting a sheet body in which a CNT film 1 is covered with resin layers 2 and 3 into arbitrary dimensions, forming an opening in the resin layer 2 by laser irradiation, and filling this opening with material. Since the electrode 8 is embedded, the shape of the covering body cut out from the sheet body can be arbitrarily changed, and design changes are relatively easy.

In addition, the strain sensor element thermally decomposes the insulating elastomer on the surface layer of the resin layer 2 and the CNT film 1 by laser irradiation to expose the CNT fibers, thereby establishing an electrical connection between the CNT fibers and the electrodes 8. is relatively certain.

The strain sensor element may be provided with one or more CNT threads including a plurality of CNT fibers aligned in a direction connecting a pair of plate-shaped electrodes, instead of the CNT film in each of the above-described embodiments. In this case, the CNT yarn is impregnated with an insulating elastomer in the vicinity of the outer peripheral surface. Further, the resin layer is integrally formed on the front and back sides and covers the outer periphery of the CNT thread. When a plurality of CNT threads are provided, the plate electrode is preferably curved in a convex manner so as to have a substantially equal cross section in the width direction perpendicular to the direction in which the CNT fibers are aligned so as to contact each CNT thread.

[Transformation of reference form]
In the above-mentioned reference form, components of each part can be omitted, replaced, or added based on the description of this specification and common general technical knowledge.

In the strain sensor element, at least a portion of the plate-shaped electrode only needs to be exposed so that it can be wired. Therefore, even if the entire plate-shaped electrode is buried so as to be located on the back side of the resin layer from the front surface, it is sufficient that an opening through which the plate-shaped electrode can be accessed remains in the resin layer.

In the strain sensor element, the CNT film may have a planar shape in which the stretchable region is smaller in width than both end regions.

The strain sensor element includes a conductive paste that is applied to the plate electrode from the surface side and impregnated into the plate electrode even when a conductive fabric is interposed on the CNT film or CNT thread side of the plate electrode. Good too.

In manufacturing the strain sensor element, heating when embedding the plate-shaped electrode in the resin layer may be performed by applying electricity or a high-frequency magnetic field to the plate-shaped electrode to generate heat in the plate-shaped electrode itself.

In the strain sensor element, the CNT film becomes a conductive elastomer by being impregnated with the resin layer laminated on the surface thereof, but it is also possible to impregnate the CNT film with the resin before laminating the resin layer.

In the strain sensor element of the fifth embodiment, the region where the resin layer is thermally decomposed by the laser is filled with an electrode forming material, but an electrode made of a solid may be arranged in that region. In that case, the electrode forming material and the conductive adhesive described above may also be filled.

Further, in the case of a strain sensor element having a plurality of CNT films or CNT threads, the CNTs of the plurality of CNT films or CNT threads can be brought into direct contact with each other and electrically connected by laser irradiation.

In addition, this method of electrically connecting CNT films or CNT threads by laser irradiation is applicable not only to sensor elements having CNT films or CNT threads, but also to electrically connecting conductive threads made by covering metal wires or conductive fibers with a resin layer. can also be applied. Therefore, an electrode can be formed by irradiating a laser onto a cloth woven with conductive threads or a cloth sewn with conductive threads and filling the cloth with an electrode forming material, thereby making it possible to make an electrical connection with an external circuit or the like. In this case as well, it is preferable to apply a paint that increases the laser absorption rate in advance to the position to be irradiated with the laser. It is also possible to form a fabric using a conductive thread coated with a resin layer, and a user can optionally form wiring in the fabric. Specifically, all or part of the threads constituting the fabric are conductive threads coated with a resin layer. By laser irradiation, the resin layer of any conductive thread can be opened and used as wiring. Furthermore, by opening the resin layer and electrically connecting the conductive threads to each other at a portion, it is also possible to form bent wiring or multilayer wiring. The resistance value of the wiring can also be lowered by connecting multiple wirings arranged in parallel.

The strain sensor element according to the present invention can be suitably used as a sensor for wearable devices and the like.

1 CNT films 2, 3 Resin layer 4 Plate electrode 4a Through hole 5 Sandwiching sheet 6 Conductive fabric 7 Conductive paste 11 CNT films 12, 13 Resin layer 14 Electrode 15 Laser absorbing material layer 16 Connection hole 21 CNT thread 22 Resin layer 23 Electrode 24 Laser absorbing material layer 25 Connection hole S1 Laser absorbing material coating process S2 Laser irradiation process S3 Conductive material filling process S4 Cutting process

Claims (14)

A CNT membrane or CNT thread that includes a plurality of CNT fibers that are aligned in one direction and has elasticity ;
A resin layer made of an insulating elastomer and coated on the front and back surfaces of the CNT membrane or the outer periphery of the CNT thread;
a pair of electrodes laminated on both end regions of the resin layer covering of the CNT membrane or CNT yarn and electrically connected to the CNT membrane or CNT yarn;
The insulating elastomer is impregnated into the CNT fibers in the surface layer of the CNT membrane or CNT yarn so as not to impregnate the entire area in the cross section of the CNT fibers in the thickness direction, thereby forming a bond between the CNT fibers in the surface layer and the insulation. A method for manufacturing a strain sensor element which is composited with a elastomer, the method comprising:
The insulating elastomer composited with the resin layer and the CNT fibers is irradiated with a laser on at least a portion of the surface of both end regions of the resin layer covering while suppressing damage to the CNT fibers. A laser irradiation step of forming a connection hole leading to the CNT film or CNT thread by thermal decomposition;
A method for manufacturing a strain sensor element, comprising: filling the connection hole with a conductive material. Before the laser irradiation step, further comprising a step of applying a laser absorbing material to the surface of both end regions of the resin layer covering,
The method for manufacturing a strain sensor element according to claim 1, wherein in the laser irradiation step, at least a portion of the coating film obtained in the coating step is irradiated with a laser. 3. The method of manufacturing a strain sensor element according to claim 2, wherein the laser-absorbing material is an ink in which fine carbon black particles are dispersed in a volatile solvent. 4. The method for manufacturing a strain sensor element according to claim 1, wherein the average diameter of the connection holes formed in the resin layer is 0.5 mm or more and 2.0 mm or less. The method for manufacturing a strain sensor element according to any one of claims 1 to 4, comprising the CNT film having a thickness of 5 mm or less. The method for manufacturing a strain sensor element according to any one of claims 1 to 5, wherein the upper limit of the output of the laser is 30W. 7. The method for manufacturing a strain sensor element according to claim 1, wherein the conductive material is applied across the plurality of connection holes in each end region in the conductive material filling step. A CNT membrane or CNT thread that includes a plurality of CNT fibers that are aligned in one direction and has elasticity ;
A resin layer made of an insulating elastomer and coated on the front and back surfaces of the CNT membrane or the outer periphery of the CNT thread;
a pair of electrodes laminated on both end regions of the resin layer covering of the CNT membrane or CNT yarn and electrically connected to the CNT membrane or CNT yarn;
The insulating elastomer is impregnated into the CNT fibers in the surface layer of the CNT membrane or CNT yarn so as not to impregnate the entire area in the cross section of the CNT fibers in the thickness direction, thereby forming a bond between the CNT fibers in the surface layer and the insulation. A strain sensor element comprising a composite elastomer,
having a bottomed connection hole extending from at least part of the surface of the both end regions of the resin layer covering to the CNT membrane or CNT thread that is not composited with the insulating elastomer;
A strain sensor element, wherein the electrode includes a conductive material filled in the connection hole. The strain sensor element according to claim 8, further comprising a laser absorbing material layer existing between the electrode and the surface of the resin layer surrounding the connection hole. 10. The strain sensor element according to claim 9, wherein the laser absorbing material is an ink in which fine carbon black particles are dispersed in a volatile solvent. The strain sensor element according to claim 8, 9, or 10, wherein the average diameter of the connection hole is 0.5 mm or more and 2.0 mm or less. The strain sensor element according to any one of claims 8 to 11, comprising the CNT film having a thickness of 5 mm or less. The strain sensor element according to any one of claims 8 to 12, wherein the connection hole is formed by a laser with an output of 30 W or less. The strain sensor element according to any one of claims 8 to 13, wherein the conductive material is arranged across the plurality of connection holes in each end region.

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