CONDUCTIVE CLOTH

Abstract

Provided is a conductive cloth having excellent stretchability and conduction stability. A conductive cloth 1a, 1b comprises a base cloth 10 and conductive yarns 100 stitched into the base cloth 10, wherein the constant load elongation ratio (S0) of the base cloth 10 is at least 24%, the conductive yarns 100 are stitched in at least two directions, and each conductive yarn 100 is exposed from at least one side of the base cloth 10, and the ratio (S1/S2) of the constant load elongation ratio (S1) of the conductive cloth 1a, 1b in a region in which the conductive yarns 100 are stitched and the constant load elongation ratio (S2) of the conductive cloth 1a, 1b in a region in which the conductive yarns are not stitched is 0.55 to 0.90.

Description

TECHNICAL FIELD

The present invention relates to conductive cloths obtained by stitching conductive yarns into a base cloth.

BACKGROUND ART

Conductive cloths are widely used as an electrode cloth for a sensor in, for example, interior articles for vehicles, clothes, health, nursing care, and medical products, furniture, and the like. As to interior articles for vehicles, for example, a conductive cloth is used as an electrical circuit of a sensor (touch sensor) that is included in a steering wheel, and that detects a pressure applied by a driver to the steering wheel. That sensor is for detecting a state of the driver holding the steering wheel (e.g., whether or not the driver is holding the steering wheel with their both hands, and what portion of the steering wheel is being held). Therefore, the sensor needs to accurately detect the pressure applied by the driver to the steering wheel. To this end, it is necessary for the conductive cloth to have stable conductivity.

As the above type of conductive cloth, for example, one in which a metal film layer produced by electroless metal plating is provided on a surface of a base cloth made of a woven fabric constituted by insulating yarns has conventionally been proposed (see, for example, Patent Document 1).

As another conductive cloth, for example, one in which a conductive pattern (conductive layer) made of a conductive material is layered on a surface of a cloth made of insulating fibers with an adhesive agent interposed therebetween has been proposed (see, for example, Patent Document 2).

As still another conductive cloth, for example, one in which both sides of a mesh base cloth that is an insulating woven fabric are covered with a conductive composition has been proposed (see, for example, Patent Document 3).

As still another conductive cloth, one in which metal wires are machine-stitched into a base cloth has been proposed (see, for example, Patent Document 4).

CITATION LIST

Patent Literature

• • Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-11035
  • Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-124497
  • Patent Document 3: Japanese Unexamined Patent Application Publication No. 2020-75422
  • Patent Document 4: Japanese Unexamined Patent Application Publication No. 2017-99837

SUMMARY OF INVENTION

Technical Problem

For the conductive cloths described in Patent Documents 1 to 3 in which a conductive layer is put on top of an insulating base cloth, the conductive layer is likely to peel off the base cloth or the conductive cloth is likely to break (crack) or the like when the cloth stretches or contracts. The occurrence of such peeling off or break increases a change in resistance value between before and after the cloth stretches or contracts and thereby causes unstable conductivity, leading to a reduction in electrical reliability. In addition, if the conductive layer partially peels off or breaks, the peeling off or break spreads in the in-plane direction, resulting in a further increase in a change in resistance value.

Incidentally, in the case in which a conductive cloth is included in a sensor or the like, it is necessary to satisfactorily tightly attach the conductive cloth to an object to be measured, following the shape of the object, in order to improve the sensitivity of the sensor. Therefore, it is necessary for conductive cloths to have stretchability. If the stretchability of a conductive cloth is insufficient, conductive yarns are likely to break due to stress, so that a resistance change ratio increases, and therefore, conduction stability decreases.

In this regard, the stretchability of the conductive cloth described in Patent Document 4 is insufficient. Therefore, it cannot be said that the conductivity of the conductive cloth described in Patent Document 4 is stable.

With the above problems in mind, the present invention has been made. It is an object of the present invention to provide a conductive cloth having excellent stretchability and conduction stability.

Solution to Problem

A characteristic feature of a conductive cloth according to the present invention for solving the above problems is a conductive cloth comprising a base cloth and conductive yarns stitched into the base cloth, wherein

• • the constant load elongation ratio (S0) of the base cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 24%,
  • the conductive yarns are stitched in at least two directions, and each conductive yarn is exposed from at least one side of the base cloth, and
  • the ratio (S1/S2) of the constant load elongation ratio (S1) of the conductive cloth in a region in which the conductive yarns are stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto, and the constant load elongation ratio (S2) of the conductive cloth in a region in which the conductive yarns are not stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto, is 0.55 to 0.90.

In the conductive cloth thus configured, the conductive yarns are stitched into the base cloth, and therefore, conductivity is imparted to the conductive cloth. Here, the constant load elongation ratio (S0) of the base cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto (hereinafter also referred to as a “5 N constant load elongation ratio”) is at least 24%, and therefore, the conductive cloth has sufficient stretchability. In addition, the conductive yarns are stitched in at least two directions, and therefore, can be arranged in a wide range of the conductive cloth. In addition, each conductive yarn is exposed from at least one side of the base cloth, and therefore, conductivity is imparted to and concentrated on the at least one side of the conductive cloth. Therefore, the conductivity is increased, leading to an increase in the conduction stability. In addition, for example, in the case in which the conductive cloth is used in a sensor, the sensitivity of the sensor can be improved. Here, the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth in a region in which the conductive yarns are stitched (hereinafter also referred to as a “stitched region”) and the 5 N constant load elongation ratio (S2) of the conductive cloth in a region in which the conductive yarns are not stitched (hereinafter also referred to as a “non-stitched region”) is 0.55 to 0.90, and therefore, the difference in 5 N constant load elongation ratio between the stitched region and the non-stitched region is reduced. As a result, when the conductive cloth stretches, a break in the conductive yarns is inhibited, resulting in an increase in the conduction stability.

In the conductive cloth of the present invention,

• • the constant load elongation ratio (S3) of the entire conductive cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is preferably at least 20%.

In the conductive cloth thus configured, the constant load elongation ratio (S3) of the entire conductive cloth is at least 20%, and therefore, the stretchability of the conductive cloth is further increased.

Next, a characteristic feature of a conductive cloth according to the present invention for solving the above problems is a conductive cloth comprising a base cloth and conductive yarns stitched into the base cloth, wherein

• • the constant load elongation ratio (S0) of the base cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 24%,
  • the conductive yarns are stitched in at least two directions, and each conductive yarn is exposed from at least one side of the base cloth, and
  • the constant load elongation ratio (S3) of the entire conductive cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is preferably at least 20%.

In the conductive cloth thus configured, the conductive yarns are stitched into the base cloth, and therefore, conductivity is imparted to the conductive cloth. Here, the constant load elongation ratio (S0) of the base cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 24%, and the 5 N constant load elongation ratio (S3) of the entire conductive cloth is at least 20%, and therefore, a decrease in the stretchability is reduced even in the state in which the conductive yarns are stitched into the base cloth, resulting in sufficient stretchability of the conductive cloth. In addition, the conductive yarns are stitched in at least two directions, and therefore, can be arranged in a wide range of the conductive cloth. In addition, each conductive yarn is exposed from at least one side of the base cloth, and therefore, conductivity is imparted to and concentrated on the at least one side of the conductive cloth. Therefore, the conductivity is increased, leading to an increase in the conduction stability. In addition, for example, in the case in which the conductive cloth is used in a sensor, the sensitivity of the sensor can be improved.

In the conductive cloth according to the present invention,

• • the constant load elongation ratio (S1) of the conductive cloth in a region in which the conductive yarns are stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is preferably at least 18%.

In the conductive cloth thus configured, the constant load elongation ratio (S1) of the conductive cloth in a region in which the conductive yarns are stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 18%, and therefore, the conductive cloth has more sufficient stretchability.

In the conductive cloth according to the present invention,

• • the conductive cloth preferably has a resistance value change ratio during 40% elongation of at most 30%.

In the conductive cloth thus configured, the conductive cloth has a resistance value change ratio during 40% elongation of at most 30%, and therefore, a change in resistance value between before and after the conductive cloth stretches decreases (i.e., a change in resistance value due to stretching or contraction decreases), resulting in an increase in the conduction stability. For example, in the case in which the conductive cloth is used in a sensor, the sensitivity of the sensor can be improved.

In the conductive cloth of the present invention,

• • the base cloth preferably has a thickness of at most 1 mm.

In the conductive cloth thus configured, the base cloth has a thickness of at most 1 mm, and therefore, a level difference (step) can be inhibited from occurring when the conductive cloth is included in another member. For example, in the case in which the conductive cloth is included in a sensor, such as a steering wheel sensor, a level difference can be inhibited from occurring in the sensor, and therefore, the conductive cloth does not have an adverse influence on tactile sensations on the sensor.

In the conductive cloth of the present invention,

• • a space between each conductive yarn is preferably 1 to 10 mm.

In the conductive cloth thus configured, a space between each conductive yarn is 1 to 10 mm, and therefore, the number of conductive yarns per unit area is increased, resulting in an increase in the conductivity of the conductive cloth, which leads to an increase in the conduction stability. In addition, the stretchability of the conductive cloth can be sufficiently increased.

In the conductive cloth of the present invention,

• • the conductive cloth preferably further comprises insulating yarns directly stitched into the base cloth in a manner that allows the insulating yarns to freely stretch and contract, and
  • the conductive yarn is preferably passed through gaps between stitches of the insulating yarn and the base cloth to be indirectly stitched into the base cloth.

In the conductive cloth thus configured, the insulating yarn is directly stitched into the base cloth in a manner that allows the insulating yarn to freely stretch and contract, and therefore, can satisfactorily follow stretching and contraction of the base cloth. In addition, the conductive yarn is passed through gaps between stitches of the insulating yarn and the base cloth to be indirectly stitched into the base cloth, and therefore, a region in which the conductive yarn is allowed to move is increased, which significantly contributes to an improvement in the stretchability. Furthermore, the conductive yarns are exposed from one side of the base cloth, but not from the other one, and therefore, conductivity is imparted to and concentrated on one side of the conductive cloth, resulting in an increase in the conductivity compared to the case in which the conductive yarns are exposed from both sides of the conductive cloth, which leads to an increase in the conduction stability.

In the conductive cloth of the present invention,

• • the conductive yarns are preferably stitched into the base cloth in an undulating pattern and a grid pattern.

In the conductive cloth thus configured, the conductive yarns are stitched into the base cloth in an undulating pattern and a grid pattern, and therefore, the conductive yarns can be arranged in a wide range of the conductive cloth.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a steering wheel including a conductive cloth according to a first embodiment of the present invention, together with an enlarged view of a portion of the included conductive cloth.

FIG. 2 is an enlarged view of a portion of the conductive cloth according to the first embodiment of the present invention. FIG. 2(a) illustrates a state in which a load is not applied to the conductive cloth. FIG. 2(b) illustrates a state in which a load is applied to the conductive cloth. FIG. 2(c) illustrates a state in which conductive yarns are stitched into a base cloth through insulating yarns. FIG. 2(d) illustrates another method for stitching insulating yarns.

FIG. 3 is a schematic diagram of a base cloth used in the conductive cloth according to the first embodiment of the present invention. FIG. 3(a) illustrates a state in which a load is not applied to the conductive cloth. FIG. 3(b) illustrates a state in which a load is applied to the conductive cloth.

FIG. 4 is an enlarged view of a portion of a conductive cloth according to a second embodiment of the present invention. FIG. 4(a) illustrates a state in which a load is not applied to the conductive cloth. FIG. 4(b) illustrates a state in which a load is applied to the conductive cloth. FIG. 4(c) illustrates a state in which a conductive yarn is stitched together with an insulating yarn into a base cloth.

DESCRIPTION OF EMBODIMENTS

A conductive cloth according to the present invention according to the present invention will be described with reference to the accompanying drawings. It should be noted that in each figure, a configuration (structure) is exaggerated or simplified, as appropriate, for the sake of convenience, and yarns included in the structure are not exactly identical to those in actual conductive cloths in terms of size and scale relationships.

First Embodiment

<Conductive Cloth>

FIG. 1 is a plan view schematically illustrating a steering wheel 500 of a vehicle including a conductive cloth 1a according to a first embodiment of the present invention. In this example, the conductive cloth 1a is included in the steering wheel 500, and forms an electrical circuit in a steering wheel sensor. In the conductive cloth 1a, conductive yarns 100 are stitched into a base cloth 10 in at least two directions (here, an undulating pattern), and each conductive yarn 100 is exposed from at least one side of the base cloth 10. In this embodiment, it is assumed that the conductive yarns 100 are exposed from one side of the base cloth 10, but not from the other side. It should be noted that the stretchability of the base cloth 10 allows the conductive cloth 1a to satisfactorily deform and follow the shape of an outer surface portion (synthetic leather or the like) of the steering wheel 500. In the steering wheel 500, for example, an electrode is provided in each of two installation regions (not illustrated) separated from each other in the weft direction. As described below, the conductive yarn 100 includes a metal wire, and in the installation regions, the steering wheel sensor is configured to detect a pressure applied when a driver holds the steering wheel 500, with the passage of electrical current through the conductive cloth 1a by means of the electrodes. As the electrode, conventionally known electrodes may be used. In the steering wheel 500, for example, the conductive cloth 1a may be arranged such that the weft direction thereof extends along the direction of rotation of the steering wheel 500, and the warp direction thereof extends along the circumferential direction (holding direction) of the steering wheel 500. The arrangement of the conductive cloth 1a is not particularly limited.

FIG. 2 is an enlarged view of a portion of the conductive cloth 1a according to the first embodiment of the present invention. FIG. 2(a) illustrates a state in which a load is not applied to the conductive cloth 1a. In this embodiment, the conductive yarn 100 is not directly stitched into the base cloth 10, and is indirectly stitched into the base cloth 10 through an insulating yarn 400. As a result, the conductive yarn 100 is only exposed from one side of the base cloth 10. The conductive yarn 100 is also supported on the base cloth 10 by the insulating yarn 400 so as to undulate. As a result, the conductive yarns 100 are indirectly stitched into the base cloth 10 in at least two directions. The combination of the undulating conductive yarns and the stretchable base cloth 10 imparts stretchability to the conductive cloth 1a. In addition, since the conductive yarn 100 is formed in an undulating pattern, conductivity is imparted to one side of the base cloth 10 in the in-plane direction, resulting in the conductive cloth 1a. Although, in this embodiment, the conductive yarns 100 are thus exposed from one side of the base cloth 10, the base cloth 10 may alternatively be configured such that the conductive yarns 100 are exposed from both sides, i.e., one side and the other side. It should be noted that, in the present invention, the term “exposed from a side” of the base cloth 10 with respect to the conductive yarn 100 means that the conductive yarn 100 is “externally in contact with yarns constituting the side” of the base cloth 10. Therefore, an embodiment in which, when a load is applied to the conductive cloth 1a, which in turn stretches, a conductive yarn 100 that is located further inside than yarns constituting the side is simply seen externally is not included in the above embodiment in which a conductive yarn 100 is “exposed from the side.”

<Base Cloth>

FIG. 3 is a schematic diagram of the base cloth 10 used in the conductive cloth 1a. FIG. 3(a) illustrates a state in which a load is not applied to the base cloth 10, and FIG. 3(b) illustrates a state in which a load is applied to the base cloth 10.

The base cloth 10 is stretchable. The base cloth 10 is not particularly limited, as long as the base cloth 10 is stretchable. Specific examples of the base cloth 10 include knitted fabrics, woven fabrics, and nonwoven fabrics. Of them, knitted fabrics are preferable in terms of stretchability. Weft-knitted fabrics are a preferable knitted fabric in terms of stretchability. Circular knitted fabrics kitted by smooth stitch, stockinette stitch, ribbing stitch, and the like are preferable in terms of productivity and cost. In the case in which the base cloth 10 is a knitted fabric, the base cloth 10 includes a single knitted fabric as illustrated in this embodiment, for example. Alternatively, the base cloth 10 may, for example, be a multi-knitted fabric including a front knitted fabric as a front base cloth and a back knitted fabric as a back base cloth, which are linked together using linking yarns. If the base cloth 10 includes a single knitted fabric, the base cloth 10 has relatively excellent stretchability, resulting in an increase in the stretchability of the conductive cloth 1a.

The 5 N constant load elongation ratio (S0) of the base cloth 10 is preferably at least 24%, more preferably at least 30%, and even more preferably at least 34%. If the 5 N constant load elongation ratio (S0) of the base cloth 10 is at least 24%, the conductive cloth 1a has sufficient stretchability. It should be noted that, in the case in which the base cloth 10 includes a front base cloth and a back base cloth as described above, the 5 N constant load elongation ratio (S0) of the base cloth 10 is assessed as the 5 N constant load elongation ratio (S0) of the front and back base cloths as a whole. The 5 N constant load elongation ratio (S0) of the base cloth 10 is calculated as the elongation ratio of the length L2 of the base cloth 10 in the presence of a constant load F of 5 N as illustrated in FIG. 3(b) to the length L1 of the base cloth 10 in the absence of an applied load as illustrated in FIG. 3(a), by expression (1). It should be noted that L1 may be a chuck spacing described below.

$\begin{array}{cc}S0=\left(L2-L1\right)/L1\times 100& \left(1\right)\end{array}$

In the case in which the base cloth 10 is a knitted fabric, base yarns constituting the fabric may, for example, be in the form of spun yarn (short fiber yarn), multifilament yarn, or monofilament yarn. The multifilament yarn may be optionally twisted, or may be subjected to a treatment such as false twisting, DDW, or fluid agitation. The fineness (total fineness) of the base yarn is preferably at most 330 dtex, more preferably at most 167 dtex, even more preferably at most 110 dtex, and particularly preferably at most 84 dtex. The fineness (total fineness) of the base yarn is preferably at least 33 dtex, more preferably at least 56 dtex. If the total fineness of a yarn used as the base yarn is at most 330 dtex, the base cloth 10 has a soft base structure, resulting in excellent bendability of the conductive cloth 1a. In addition, if the fineness (total fineness) of the base yarn is at least 33 dtex, the conductive cloth 1a has excellent durability.

A material for fibers constituting the base yarn is not particularly limited. Examples of such a material include natural fibers, regenerated fibers, semisynthetic fibers, and synthetic fibers. These may be used alone or in combination. Of them, synthetic fibers are preferable because of the excellent strength thereof. Polyester fibers, such as polyethylene terephthalate, are preferable. The shape of the fiber is not particularly limited. The fiber may be either a long fiber or a short fiber. In addition, the cross-sectional shape of the fiber is not particularly limited, and may be typically circular, or alternatively, different shapes, such as flat, elliptical, triangular, hollow, Y-shaped, T-shaped, and U-shaped.

The thickness of the base cloth 10 is preferably at most 1 mm. If the thickness of the base cloth 10 is at most 1 mm, then when the conductive cloth 1a is included in another member, a level difference (step) can be inhibited from occurring. For example, in the case in which the conductive cloth 1a is included in a sensor, such as the steering wheel sensor of the steering wheel 500, a level difference can be inhibited from occurring in the sensor, and therefore, the conductive cloth 1a does not have an adverse influence on tactile sensations on the sensor. The lower limit of the thickness of the base cloth 10 is not particularly limited, and can be set as appropriate. For example, the lower limit of the thickness of the base cloth 10 may be 0.1 mm.

<Insulating Yarn>

The insulating yarn 400 directly stitched into the base cloth 10 is not particularly limited, and can be set as appropriate. Examples of a material for the insulating yarn 400 include synthetic fibers such as fibers of polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, fibers of polyamides such as nylon 6 and nylon 66, acrylic fibers including polyacrylonitrile as the main component, fibers of polyolefins such as polyethylene and polypropylene, polyurethane fibers, and polyvinyl chloride fibers. Of them, polyethylene terephthalate is preferable in terms of durability. The fineness of the insulating yarn 400 is preferably 33 to 110 dtex, more preferably 33 to 84 dtex, and particularly preferably 56 to 84 dtex. If the fineness of the insulating yarn 400 is 33 to 110 dtex, the durability of the insulating yarn 400 can be improved while the insulating yarn 400 can be easily stitched into the base cloth 10.

The insulating yarns 400 are directly stitched into the base cloth 10 using a known stitching technique such that the insulating yarns 400 can follow stretching and contraction of the base cloth 10, and due to this following, the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth 1a in the non-stitched region is 0.55 to 0.90.

As illustrated in FIG. 2(a), in the conductive cloth 1a, the insulating yarns 400 are directly stitched into the base cloth 10 using a known stitching method in a manner that allows the insulating yarns 400 to freely stretch and contract in one direction (here, the weft direction). The insulating yarns 400 are stitched into the base cloth 10 in parallel with each other. FIG. 2(c) illustrates a state in which the conductive yarns 100 are stitched into the base cloth 10 through the insulating yarns 400. FIG. 2(d) illustrates another method for stitching the insulating yarns 400. For example, as illustrated in FIG. 2(c), the insulating yarns 400 are directly stitched into the base cloth 10, one for each row, in a manner that allows the insulating yarns to freely stretch and contract. As a result, in the conductive cloth 1a, the conductive yarns 100 are stitched into the base cloth 10 in at least two directions so as to pass through gaps between the insulating yarns 400 and the base cloth 10. In addition, each conductive yarn 100 is exposed from one side of the base cloth 10, but not from the other side.

Alternatively, for example, as illustrated in FIG. 2(d), two insulating yarns 400 and 410 may be directly stitched into the base cloth 10 for each row. In that case, the insulating yarns 400 and 410 are machine-stitched into one side of the base cloth 10 so as to form loops (rings) with the insulating yarn 400 used as the upper yarn and the insulating yarn 410 used as the lower yarn. As a result, the insulating yarns 400 and 410 are allowed to freely stretch and contract. In addition, although not illustrated, the conductive yarn 100 is passed through a gap between the insulating yarn 400 and the base cloth 10.

<Conductive Yarn>

The conductive yarn 100 includes a metal wire. The electrical resistivity of the conductive yarn 100 is preferably at most 5×10⁻⁵ Ω·m in order to impart sufficient conductivity to the conductive cloth 1a. Therefore, the conductive yarn 100 preferably does not include any insulating film and only includes a metal wire.

The diameter of the metal wire of the conductive yarn 100 is preferably 20 to 100 μm. If the diameter of the metal wire of the conductive yarn 100 is at least 20 μm, the conductive yarn 100 is less likely to break when the conductive yarn 100 stretches or contracts. Therefore, a change in the resistance value of the conductive cloth 1a that occurs when the conductive cloth 1a stretches or contracts is reduced. In addition, if the diameter of the metal wire of the conductive yarn 100 is at most 100 μm, the stiffness of the conductive yarn 100 is not too high, and therefore, the stretchability of the conductive cloth 1a is increased. The diameter of the metal wire of the conductive yarn 100 is the greatest diameter.

Examples of a material for the metal wire included in the conductive yarn 100 include single metals such as aluminum, nickel, copper, titanium, magnesium, tin, zinc, iron, silver, gold, platinum, vanadium, molybdenum, tungsten, chromium, manganese, silicon, lead, bismuth, boron, germanium, arsenic, antimony, tellurium, and cobalt, and alloys thereof. Of them, alloys of copper and tin and alloys of copper and silicon are preferable. It should be noted that the conductive yarn 100 may be made of carbon fibers, instead of a metal wire.

The electrical resistivity of the metal wire of the conductive yarn 100 is preferably at most 5×10⁻⁵ Ω·m, more preferably at most 1.5×10⁻⁶ Ω·m, and even more preferably at most 5.0×10⁻⁷ Ω·m. If the electrical resistivity of the metal wire of the conductive yarn 100 is at most 5×10⁻⁵ Ω·m, the conductivity of the conductive cloth 1a is increased, leading to an increase in the conduction stability. In addition, in the case in which the conductive cloth 1a is used in a sensor, the sensitivity of the sensor can be increased.

As illustrated in FIG. 2(a), the plurality of conductive yarns 100 are passed through gaps between the exposed portions (stitch) of the insulating yarns 400 and the base cloth 10 such that each conductive yarn 100 is arranged in an undulating pattern, extending in the weft direction while rising and falling in the warp direction, and adjacent conductive yarns 100 in the weft direction have a phase difference of 90°, and adjacent conductive yarns 100 in the warp direction have such a phase difference that the projecting end portions of the waveforms thereof cross. Each conductive yarn 100 is passed through two adjacent stitches in the weft direction (in FIG. 2(a), the horizontal direction) of a first insulating yarn 400, which causes the conductive yarn 100 to curve, and then passed through two adjacent stitches in the weft direction (in FIG. 2(a), the horizontal direction) of a second insulating yarn 400 adjacent to the first one in the warp direction (in FIG. 2(a), the vertical direction), which causes the conductive yarn 100 to curve. This is repeatedly performed, resulting in an undulating pattern.

Thus, the conductive yarns 100 are indirectly stitched into the base cloth 10 in an undulating pattern, which allows the conductive cloth 1a to stretch and contract as described below. In addition, the conductive yarns 100 are stitched in at least two directions (here, an undulating pattern), which allows the conductive yarns 100 to be arranged in a wide range of the conductive cloth 1a. Furthermore, each conductive yarn 100 is exposed from one side of the base cloth 10, but not from the other side, so that conductivity is imparted to and concentrated one side of the conductive cloth 1a. Therefore, the conductivity is increased compared to the case in which the conductive yarns 100 are exposed from both sides, leading to an increase in the conduction stability. For example, in the case in which the conductive cloth 1a is used in a sensor, the sensitivity of the sensor can be improved. In addition, since the conductive yarns 100 are exposed from one side of the base cloth 10, the stretchability of the conductive cloth 1a can be increased compared to the case in which the conductive yarns 100 are exposed from both sides of the base cloth 10.

A space S between each conductive yarn 100 is preferably 1 to 10 mm. If the space between each conductive yarn 100 is at most 10 mm, the number of conductive yarns 100 per unit area is increased, so that the conductivity of the conductive cloth 1a is leading increased, to an increase in the conduction stability. Meanwhile, if the space between each conductive yarn 100 is at least 1 mm, the stretchability of the conductive cloth 1a can be sufficiently increased. It should be noted that the space S between each conductive yarn 100 means the greatest distance between adjacent conductive yarns 100 in the weft direction, warp direction, or diagonal direction. Specifically, as illustrated in FIG. 2(a), in this embodiment, the space S between each conductive yarn 100 is the space between projecting end portions of the waveforms of adjacent conductive yarns 100 in the warp direction that are most distant from each other. In addition, the space S between each conductive yarn 100 can be adjusted by adjusting the space between each insulating yarn 400.

The amplitude and spatial period of the waveform of the conductive yarn 100 may be set, as appropriate, such that the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth 1a in the non-stitched region is 0.55 to 0.90.

The arrangement and pattern of the conductive yarns 100 are not particularly limited, and may be set, as appropriate, so as to obtain the ratio (S1/S2) of 0.55 to 0.90.

<Characteristics of Conductive Cloth>

FIG. 2(b) illustrates a state in which a load is applied to the conductive cloth 1a. When the conductive cloth 1a is in a load-free state as illustrated in FIG. 2(a), then if a load F is applied to the conductive cloth 1a, the base cloth 10 stretches, so that the amplitude of the waveform of the conductive yarn 100 decreases while the spatial period thereof increases (possible elongation is reduced), and therefore, the conductive yarn 100 proportionately becomes longer in the weft direction as illustrated in FIG. 2(b). Thus, the conductive yarn 100 elongates in the direction of the applied load (apparent length increases), following the elongation of the base cloth 10, so that the conductive cloth 1a elongates in the direction of the applied load. As a result, the length of the conductive cloth 1a increases from a length K1 in a load-free state (e.g., a length corresponding to a chuck spacing described below) (see FIG. 2(a)) to reach a length K2 (see FIG. 2(b)).

When the load F (FIG. 2(b)) applied to the conductive cloth 1a is removed, the base cloth 10 contracts. At that time, the reduced amplitude and elongated spatial period of the waveform of the conductive yarn 100 are restored (possible elongation is restored), so that the conductive yarn 100 proportionately becomes shorter in the weft direction. Thus, the conductive yarn 100 becomes shorter in the direction of the applied load (apparent length decreases), following the contraction of the base cloth 10, so that the conductive cloth 1a contracts in the direction of the applied load (see FIG. 2(a)). The length of the conductive cloth 1a decreases from the length K2 (see FIG. 2(b)), and returns to the length K1 (see FIG. 2(a)).

The ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth 1a in the non-stitched region is preferably 0.55 to 0.90. If the ratio (S1/S2) is 0.55 to 0.90, the difference in 5 N constant load elongation ratio between the stitched region and the non-stitched region is reduced. As a result, when the conductive cloth 1a stretches, the conductive yarns 100 are inhibited from breaking, resulting in an increase in the conduction stability. The 5 N constant load elongation ratio (S1) in the stitched region is calculated by expression (2), and the 5 N constant load elongation ratio (S2) in the non-stitched region is calculated by expression (3). It should be noted that, for both of the 5 N constant load elongation ratio (S2) in the non-stitched region and the 5 N constant load elongation ratio (S0) of the base cloth 10, an object to be measured has no conductive yarns 100. However, the 5 N constant load elongation ratio (S2) in the non-stitched region is affected by the stitched region adjacent thereto, and therefore, is not exactly same as the 5 N constant load elongation ratio (S0) of the base cloth 10.

$\begin{array}{cc}S1=\left(K2\mathrm{in}\mathrm{the}\mathrm{stitched}\mathrm{region}-K1\mathrm{in}\mathrm{the}\mathrm{stitched}\mathrm{region}\right)/\left(K1\mathrm{in}\mathrm{the}\mathrm{stitched}\mathrm{region}\right)\times 100& \left(2\right)\end{array}$ $\begin{array}{cc}S2=\left(K2\mathrm{in}\mathrm{the}\mathrm{non}-\mathrm{stitched}\mathrm{region}-K1\mathrm{in}\mathrm{the}\mathrm{non}-\mathrm{stitched}\mathrm{region}\right)/\left(K1\mathrm{in}\mathrm{the}\mathrm{non}-\mathrm{stitched}\mathrm{region}\right)\times 100& \left(3\right)\end{array}$

The 5 N constant load elongation ratio (S3) of the entire conductive cloth 1a (including the stitched region and the non-stitched region) is preferably at least 20%. If the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1a is at least 20%, the stretchability of the conductive cloth 1a is further increased. The 5 N constant load elongation ratio (S3) of the entire conductive cloth 1a is calculated by expression (4). The upper limit of the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1a is not particularly limited, and can be set as appropriate. For example, the upper limit of the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1a may be 100%.

$\begin{array}{cc}S3=\left(K2\mathrm{of}\mathrm{the}\mathrm{entire}\mathrm{cloth}-K1\mathrm{of}\mathrm{the}\mathrm{entire}\mathrm{cloth}\right)/\left(K1\mathrm{of}\mathrm{the}\mathrm{entire}\mathrm{cloth}\right)\times 100& \left(4\right)\end{array}$

The 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region is preferably at least 18%. If the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region is at least 18%, the conductive 1a cloth has more sufficient stretchability. The upper limit of the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region is not particularly limited, and can be set as appropriate. For example, the upper limit of the 5 N constant load elongation ratio (S1) of the conductive cloth 1a in the stitched region may be 100%.

The resistance value change ratio during 40% elongation of the conductive cloth 1a is preferably at most 30%. If the resistance value change ratio during 40% elongation of the conductive cloth 1a is at most 30%, a change in the resistance value of the conductive cloth 1a between before and after the conductive cloth 1a stretches decreases (i.e., a change in the resistance value due to the stretching or contraction decreases), and therefore, the conduction stability is increased. For example, in the case in which the conductive cloth 1a is used in a sensor, the sensitivity of the sensor can be improved. The lower limit of the resistance value change ratio during 40% elongation of the conductive cloth 1a is not particularly limited, and is typically about 5%. The resistance value change ratio during 40% elongation is the change ratio (%) of the resistance value between before and after the conductive cloth 1a elongates by 40%, and is measured by a method described below.

Second Embodiment

<Conductive Cloth>

FIG. 4 is an enlarged view of a portion of a conductive cloth 1b according to a second embodiment of the present invention. FIG. 4(a) illustrates a state in which a load is not applied to the conductive cloth 1b. FIG. 4(b) illustrates a state in which a load is applied to the conductive cloth 1b. FIG. 4(c) illustrates a state in which a conductive yarn 100 is stitched together with an insulating yarn 400 into a base cloth 10. In the conductive cloth 1b according to the second embodiment of the present invention, conductive yarns 100 are stitched in a grid pattern, as is different from the conductive cloth 1a in which the conductive yarns 100 are indirectly stitched in an undulating pattern through the insulating yarns 400. Except for this, the conductive cloth 1b according to the second embodiment is the same as the conductive cloth 1a according to the first embodiment (electrodes and the like). In addition, the characteristics of the conductive cloth 1b according to the second embodiment are similar to those of the conductive cloth 1a according to the first embodiment.

In the conductive cloth 1b, the conductive yarns 100 are stitched into the base cloth 10 in at least two directions (here, a grid pattern), and each conductive yarn 100 is exposed from at least one side of the base cloth 10. In this embodiment, it is assumed that the conductive yarns 100 are exposed from one side of the base cloth 10, but not from the other side. The conductive cloth 1b can deform, satisfactorily following the shape of the outer surface (synthetic leather or the like) of the steering wheel 500 (see FIG. 1), due to the stretchability of the base cloth 10. In this embodiment, as illustrated in FIG. 4(c), an insulating yarn 400 is used for each row, and the conductive yarn 100 is machine-stitched into one side of the base cloth 10 so as to form loops (rings) with the conductive yarn 100 used as the upper yarn and the insulating yarn 400 used as the lower yarn. This allows the conductive yarn 100 to freely stretch and contract, and also allows the insulating yarn 400 to freely stretch and contract. The conductive yarn 100 is exposed from one side of the base cloth 10. Although, in this embodiment, the conductive yarn 100 is exposed from one side of the base cloth 10, the conductive yarn 100 may be alternatively exposed from one side, the other side, or both sides of the base cloth 10 as in the first embodiment.

<Base Cloth>

A base cloth similar to the base cloth 10 used in the first embodiment may be used as the base cloth 10 of the second embodiment. As in the first embodiment, the base cloth 10 preferably includes a single knitted fabric in terms of stretchability. It should be noted that, as in the first embodiment, the base cloth 10 may, for example, be configured as a multi-knitted fabric including a front knitted fabric as a front base cloth and a back knitted fabric as a back base cloth.

As in the first embodiment, the 5 N constant load elongation ratio (S0) of the base cloth 10 is preferably at least 24%, more preferably at least 30%, and even more preferably at least 34%. If the 5 N constant load elongation ratio (S0) is at least 24%, the conductive cloth 1b has sufficient stretchability. It should be noted that, if the base cloth 10 includes a front base cloth and a back base cloth as described above, the 5 N constant load elongation ratio (S0) of the base cloth 10 is assessed as the 5 N constant load elongation ratio (S0) of the front and back base cloths as a whole. The 5 N constant load elongation ratio (S0) of the base cloth 10 is also represented by an expression similar to expression (1) described in the first embodiment.

As in the first embodiment, the thickness of the base cloth 10 is preferably at most 1 mm. If the thickness of the base cloth 10 is at most 1 mm, then when the conductive cloth 1b is included in another member, a level difference (step) can be inhibited from occurring. For example, in the case in which the conductive cloth 1b is included in a sensor, such as the steering wheel sensor of the steering wheel 500, a level difference can be inhibited from occurring in the sensor, and therefore, the conductive cloth 1b does not have an adverse influence on tactile sensations on the sensor. The lower limit of the thickness of the base cloth 10 is not particularly limited, and can be set as appropriate. For example, the lower limit of the thickness of the base cloth 10 may be 0.1 mm.

<Conductive Yarn>

A conductive yarn similar to the conductive yarn 100 used in the first embodiment may be used as the conductive yarn 100 of the second embodiment.

In the conductive cloth 1b, the conductive yarns 100 are stitched into the base cloth 10 along the course direction (weft direction) and the wale direction (warp direction) in a grid pattern. As a result, the conductive yarns 100 are stitched in at least two directions (here, two directions in a grid pattern). In addition, as illustrated in FIG. 4(c), each conductive yarn 100 is stitched onto one side of the base cloth 10 so as to form loops. As a result, the conductive yarns 100 are exposed from one side of the base cloth 10, but not from the other side. The combination of the looped conductive yarn 100 and the stretchable base cloth 10 imparts stretchability to the conductive cloth 1b. In addition, since the conductive yarns 100 are formed in a grid pattern, conductivity is imparted in the in-plane direction on the surface of the front base cloth 200, resulting in the conductive cloth 1b.

The conductive yarns 100 are stitched in at least two directions (here, two directions in a grid pattern), which allows the conductive yarns 100 to be arranged in a wide range of the conductive cloth 1b. Furthermore, each conductive yarn 100 is exposed from one side of the base cloth 10, but not from the other side, so that conductivity is imparted to and concentrated on one side of the conductive cloth 1b. Therefore, the conductivity is increased compared to the case in which the conductive yarns 100 are exposed from both sides, leading to an increase in the conduction stability. In addition, for example, in the case in which the conductive cloth 1b is used in a sensor, the sensitivity of the sensor can be improved. In addition, since the conductive yarns 100 are exposed from side one of the base cloth 10, the stretchability of the conductive cloth 1b can be increased compared to the case in which the conductive yarns 100 are exposed from both sides of the base cloth 10.

As in the first embodiment, the space S between each conductive yarn 100 is preferably 1 to 10 mm. If the space between each conductive yarn 100 is at most 10 mm, the number of conductive yarns 100 per unit area is increased, so that the conductivity of the conductive cloth 1b is increased, leading to an increase in the conduction stability. Meanwhile, if the space between each conductive yarn 100 is at least 1 mm, the stretchability of the conductive cloth 1b can be sufficiently increased. It should be noted that the space between each conductive yarn 100 means the greatest distance between adjacent conductive yarns 100 in the weft direction, warp direction, or diagonal direction. Specifically, as illustrated in FIG. 4(a), in this embodiment, the space S between each conductive yarn 100 is the greatest distance between lines constituting the grid pattern of adjacent conductive yarns 100 in the warp direction.

The arrangement and pattern of the conductive yarns 100 are not particularly limited, and may be set, as appropriate, such that ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth 1b in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth 1b in the non-stitched region is 0.55 to 0.90.

<Insulating Yarn>

An insulating yarn similar to the insulating yarn 400 used in the first embodiment may be used as the insulating yarn 400 that is directly stitched into the base cloth 10.

<Characteristics of Conductive Cloth>

When the conductive cloth 1b is in a load-free state as illustrated in FIG. 4(a), then if a load F is applied to the conductive cloth 1b, the base cloth 10 stretches, so that the loops (possible elongation) of the conductive yarn 100 become smaller on one side of the base cloth 10, and therefore, the conductive yarn 100 proportionately becomes longer (apparent length increases) in the direction of the applied load as illustrated in FIG. 4(b). Thus, the conductive yarn 100 becomes longer in the direction of the applied load, following the elongation of the base cloth 10, so that the conductive cloth 1b stretches in the direction of the applied load (from the state of FIG. 4(a) to the state of FIG. 4(b)).

Meanwhile, when the load applied to the conductive cloth 1b is removed, the base cloth 10 contracts, so that the reduced loops of the conductive yarn 100 on one side of the base cloth 10 are restored, and therefore, the conductive yarn 100 proportionately becomes shorter in the weft direction (apparent length decreases). Thus, the conductive yarn 100 becomes shorter in the direction of the applied load, following the contraction of the base cloth 10, so that the conductive cloth 1b contracts in the weft direction (returns from the state of FIG. 4(b) to the state of FIG. 4(a)).

Thus, the conductive yarns 100 are stitched into the base cloth 10 so as to form loops on one side of the base cloth 10, which allows the conductive cloth 1b to stretch and contract.

As in the first embodiment, the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth 1b in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth 1b in the non-stitched region is preferably 0.55 to 0.90. If the ratio (S1/S2) is 0.55 to 0.90, the difference in 5 N constant load elongation ratio between the stitched region and the non-stitched region is reduced. As a result, when the conductive cloth 1b stretches, the conductive yarns 100 are inhibited from in breaking, resulting an increase in the conduction stability. The 5 N constant load elongation ratio (S1) in the stitched region and the 5 N constant load elongation ratio (S2) in the non-stitched region are represented by expressions similar to expressions (2) and (3) described in the first embodiment.

As in the first embodiment, the 5 N constant elongation ratio (S3) of the entire conductive cloth 1b (entirety including the stitched region and the non-stitched region) is preferably at least 20%. If the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1b is at least 20%, the stretchability of the conductive cloth 1b is further increased. It should be noted that the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1b is represented by an expression similar to expression (4) described in the first embodiment. The upper limit of the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1b is not particularly limited, and can be set as appropriate. For example, the upper limit of the 5 N constant load elongation ratio (S3) of the entire conductive cloth 1b may be 100%.

As in the first embodiment, the 5 N constant load elongation ratio (S1) of a region of the conductive cloth 1b in which conductive yarns are stitched is preferably at least 18%. If the 5 N constant load elongation ratio (S1) of a region of the conductive cloth 1b in which conductive yarns are stitched is at least 18%, the stretchability of the conductive cloth 1b is further increased. The upper limit of the 5 N constant load elongation ratio (S1) of a region of the conductive cloth 1b in which conductive yarns are stitched is not particularly limited, and can be set as appropriate. For example, the 5 N constant load elongation ratio (S1) of a region of the conductive cloth 1b in which conductive yarns are stitched may be 100%.

As in the first embodiment, the resistance value change ratio during 40% elongation of the conductive cloth 1b is preferably at most 30%. If the resistance value change ratio during 40% elongation of the conductive cloth 1b is at most 30%, a change in the resistance value of the conductive cloth 1b between before and after the conductive cloth 1b stretches decreases (i.e., a change in the resistance value due to the stretching or contraction decreases), and therefore, the conduction stability is increased. For example, in the case in which the conductive cloth 1b is used in a sensor, the sensitivity of the sensor can be improved. The lower limit of the resistance value change ratio during 40% elongation of the conductive cloth 1b is not particularly limited, and is typically about 5%. The resistance value change ratio during 40% elongation is measured by a method described below.

EXAMPLES

Conductive cloths having a characteristic feature of the present invention (Examples 1 to 15) were prepared and subjected to various measurements and assessments. For comparison, conductive cloths that do not have any characteristic feature of the present invention (Comparative Examples 1 to 3) were prepared and subjected to similar measurements and assessments. Measurement and assessment items were the 5 N constant load elongation ratio (S0) of a base cloth, the 5 N constant load elongation ratio (S1) of a conductive cloth in the stitched region, the 5 N constant load elongation ratio (S2) of a conductive cloth in the non-stitched region, the ratio (S1/S2), the 5 N constant load elongation ratio (S3) of an entire conductive cloth, the stretchability, and the resistance value change ratio during 40% elongation. Each item is described below.

[5 N Constant Load Elongation Ratio (S0) of Base Cloth]

The 5 N constant load elongation ratio of each conductive cloth was measured in accordance with the D-method (constant load method for knitted fabric) in “8.16.1 Elongation ratio” of “JIS L1096 Method for testing cloths of woven fabric and knitted fabric.” Specifically, a test piece of 150 mm in the warp direction×25 mm in the weft direction was taken from the base cloth. The chuck spacing of a tensile tester (Autograph AG-I/20 kN-50 kN, manufactured by Shimadzu Corporation) was set to 100 mm. The test piece (width: 25 mm) was fixed with the upper and lower end thereof held by a clamp. Thereafter, the chuck spacing (elongation length) (mm) was measured when the test piece was elongated until a load of 5 N was applied thereto. The 5 N constant load elongation ratio (S0) was calculated based on expression (5).

$\begin{array}{cc}S0\left(\%\right)=\left(\mathrm{chuck}\mathrm{distance}\mathrm{during}\mathrm{application}\mathrm{of}a\mathrm{load}\mathrm{of}5N\right)/100\times 100& \left(5\right)\end{array}$

[5 N Constant Load Elongation Ratio (S1) in Stitched Region]

The 5 N constant load elongation ratio (S1) of each conductive cloth in the stitched region was measured in the same manner as that described above in “5 N constant load elongation ratio (S0) of base cloth,” except that a test piece of 150 mm in the warp direction×25 mm in the weft direction was taken from a region of the conductive cloth in which conductive yarns are stitched.

[5 N Constant Load Elongation Ratio (S2) in Non-Stitched Region]

The 5 N constant load elongation ratio (S2) of each conductive cloth in the non-stitched region was measured in the same manner as that described above in “5 N constant load elongation ratio (S0) of base cloth,” except that a test piece of 150 mm in the warp direction×25 mm in the weft direction was taken from a region of the conductive cloth in which conductive yarns are not stitched.

[Ratio (S1/S2)]

The ratio (S1/S2) of the 5 N constant load elongation ratio (S1) in the stitched region and the 5 N constant load elongation ratio (S2) in the non-stitched region that are obtained as described above was calculated.

[5 N Constant Load Elongation Ratio (S3) of Entire Conductive Cloth]

The 5 N constant load elongation ratio (S3) of each entire conductive cloth was measured in the same manner as that described above in “5 N constant load elongation ratio (S0) of base cloth,” except that a test piece of 150 mm in the warp direction×25 mm in the weft direction was taken from the entirety of the conductive cloth with the test piece containing conductive yarns.

[Stretchability]

The stretchability of each conductive cloth was assessed using the 5 N constant load elongation ratio (S3) of the entire conductive cloth, in accordance with the following assessment criteria.

The 5 N constant load elongation ratio (S3) of the entire conductive cloth is at least 20%: + (good)

The 5 N constant load elongation ratio (S3) of the entire conductive cloth is less than 20%:− (bad)

[Resistance Value Change Ratio During 40% Elongation]

A test piece of 150 mm in the warp direction×25 mm in the weft direction was taken from each conductive cloth.

Copper foil tapes were attached to the center of the test piece and spaced by a distance of 50 mm for marking. The chuck spacing of a tensile tester (Autograph AG-I/20 kN-50 kN, manufactured by Shimadzu Corporation) was set to 100 mm. The test piece (width: 25 mm) was fixed with the upper and lower end thereof held by a clamp. After the fixation, an mΩ tester was attached to the copper foil tapes. A resistance value (Ω) between the markings (an initial resistance value, i.e., a resistance value before elongation or contraction) was measured. Thereafter, the sample was elongated at a rate of elongation of 40 mm per minute. The elongation was stopped when the elongation ratio was 40%. After the elongation was stopped, the resistance value (Ω) between the markings was measured again using the mΩ tester (a resistance value during 40% elongation). The resistance change ratio during 40% elongation was calculated based on expression (6).

$\begin{array}{cc}\mathrm{Resistance}\mathrm{value}\mathrm{change}\mathrm{ratio}\left(\%\right)\mathrm{during}40\%\mathrm{elongation}=\left(\mathrm{initial}\mathrm{resistance}\mathrm{value}-\mathrm{resistance}\mathrm{value}\mathrm{during}40\%\mathrm{elongation}\right)/\mathrm{initial}\mathrm{resistance}\mathrm{value}\times 100& \left(6\right)\end{array}$

The resistance value change ratio during 40% elongation thus obtained was assessed using the following assessment criteria.

• • At most 30%: + (good)
  • More than 30%:− (bad)

Example 1

Conductive cloths configured as shown in Table 1 were prepared by indirectly stitching conductive yarns (Cu/Sn alloy (indicated by “Cu/Sn” in Tables 1 to 4)) into a circular-knitted (stockinette) base cloth constituted by polyethylene terephthalate yarns (thickness: 0.86 mm, yarn density: 75/48, insulating yarn (yarn used): PET 84 dtex/36 f) through insulating yarns (PET 56 dtex/36 f, manufactured by Nanya) in an undulating pattern as illustrated in FIG. 2(a).

Example 2

A conductive cloth configured as shown in Table 1 was prepared using a base cloth similar to that of Example 1 in the same manner as that of Example 1, except that conductive yarns were stitched into the base cloth in a grid pattern as illustrated in FIG. 4(a).

Examples 3 to 15 and Comparative Examples 1 to 3

Conductive cloths were prepared in the same manner as that of Example 1, except that the conductive cloths have configurations shown in Tables 1 to 4. It should be noted that, in Example 10, conductive yarns were stitched into both sides of the base cloth in a grid pattern as illustrated in FIG. 4(a). In Example 11, “Cu/Si” indicates a Cu/Si alloy. In Example 12, “Ny” indicates nylon (78 T/24). In Example 13, a double-layer structure including a front base cloth and a back base cloth was used as the base cloth.

The configurations, measurement results, and assessment results of the conductive cloths of Examples 1 to 15 and Comparative Examples 1 to 3 are shown in Tables 1 to 4.

	TABLE 1
	Example 1	Example 2	Example 3	Example 4	Example 5
Base cloth	Fineness of insulating yarn (yarn used) (dtex)	84	84	84	84	33
	Material for insulating yarn (yarn used)	PET	PET	PET	PET	PET
	Thickness (mm)	0.86	0.85	0.72	0.96	0.76
	5N constant load elongation ratio: SO (%)	34.0	34.0	34.0	34.0	26.0
Insulating yarn	Fineness of insulating yarn (dtex)	56	56	56	56	56
Conductive yarn	Diameter of metal wire (μm)	80	80	20	100	80
	Material for metal wire	Cu/Sn	Cu/Sn	Cu/Sn	Cu/Sn	Cu/Sn
Conductive cloth	5N constant load elongation ratio	24.0	22.8	26.5	22.5	18.5
	in stitched region: S1 (%)
	5N constant load elongation ratio	33.9	34.2	34.0	33.9	26.1
	in non-stitched region: S2 (%)
	S1/S2	0.71	0.67	0.78	0.66	0.71
	5N constant load elongation ratio of entire	27.0	25.9	29.5	25.5	20.2
	cloth: S3 (%)
	Space S between each conductive yarn (mm)	5	5	5	5	5
	Stitching pattern	Undulating	Grid	Undulating	Undulating	Undulating
		pattern	pattern	pattern	pattern	pattern
Stretchability	+	+	+	+	+
Resistance change ratio during 40% elongation (%)	25.0	26.5	25.3	24.6	25.8
	+	+	+	+	+

	TABLE 2
	Example 6	Example 7	Example 8	Example 9	Example 10
Base cloth	Fineness of insulating yarn (yarn used) (dtex)	110	84	84	84	84
	Material for insulating yarn (yarn used)	PET	PET	PET	PET	PET
	Thickness (mm)	0.91	0.86	0.86	0.86	0.86
	5N constant load elongation ratio: SO (%)	40.0	34.0	34.0	25.0	34.0
Insulating yarn	Fineness of insulating yarn (dtex)	56	56	56	56	56
Conductive yarn	Diameter of metal wire (μm)	80	80	80	50	80
	Material for metal wire	Cu/Sn	Cu/Sn	Cu/Sn	Cu/Sn	Cu/Sn
Conductive cloth	5N constant load elongation ratio	26.7	19.0	28.5	18.3	22.1
	in stitched region: S1 (%)
	5N constant load elongation ratio	40.1	34.0	33.8	25.1	33.9
	in non-stitched region: S2 (%)
	S1/S2	0.67	0.56	0.84	0.73	0.65
	5N constant load elongation ratio of entire	28.7	23.1	31.3	20.3	22.5
	cloth: S3 (%)
	Space S between each conductive yarn (mm)	5	1	10	10	5
	Stitching pattern	Undulating	Undulating	Undulating	Undulating	Grid
		pattern	pattern	pattern	pattern	pattern
Stretchability	+	+	+	+	+
Resistance change ratio during 40% elongation (%)	24.6	21.6	29.6	26.7	28.5
	+	+	+	+	+

	TABLE 3
	Example 11	Example 12	Example 13	Example 14	Example 15
Base cloth	Fineness of insulating yarn (yarn used) (dtex)	84	78	110	84	84
	Material for insulating yarn (yarn used)	PET	Ny	PET	PET	PET
	Thickness (mm)	0.86	0.82	0.92	0.86	0.86
	5N constant load elongation ratio: SO (%)	34.0	30.5	24.0	34.0	34.0
Insulating yarn	Fineness of insulating yarn (dtex)	56	56	56	84	33
Conductive yarn	Diameter of metal wire (μm)	80	80	80	80	80
	Material for metal wire	Cu/Si	Cu/Sn	Cu/Sn	Cu/Sn	Cu/Sn
Conductive cloth	5N constant load elongation ratio	25.1	20.9	20.2	24.6	23.4
	in stitched region: S1 (%)
	5N constant load elongation ratio	34.0	30.8	24.2	34.5	32.6
	in non-stitched region: S2 (%)
	S1/S2	0.74	0.68	0.83	0.71	0.72
	5N constant load elongation ratio of entire	25.9	22.1	20.6	26.5	26.5
	cloth: S3 (%)
	Space S between each conductive yarn (mm)	5	5	5	5	5
	Stitching pattern	Undulating	Undulating	Undulating	Undulating	Undulating
		pattern	pattern	pattern	pattern	pattern
Stretchability	+	+	+	+	+
Resistance change ratio during 40% elongation (%)	20.7	27.1	28.9	25.3	24.8
	+	+	+	+	+

	TABLE 4
	Comparative	Comparative	Comparative
	example 1	example 2	example 3
Base cloth	Fineness of insulating yarn (yarn used) (dtex)	84	84	84
	Material for insulating yarn (yarn used)	PET	PET	PET
	Thickness (mm)	0.86	0.86	0.86
	5N constant load elongation ratio: SO (%)	34.0	15.0	15.0
Insulating yarn	Fineness of insulating yarn (dtex)	56	56	56
Conductive yarn	Diameter of metal wire (μm)	80	80	80
	Material for metal wire	Cu/Sn	Cu/Sn	Cu/Sn
Conductive cloth	5N constant load elongation ratio	15.6	7.5	9.8
	in stitched region: S1 (%)
	5N constant load elongation ratio	34.1	15.1	15.1
	in non-stitched region: S2 (%)
	S1/S2	0.46	0.50	0.65
	5N constant load elongation ratio of entire	17.9	10.6	12.8
	cloth: S3 (%)
	Space S between each conductive yarn (mm)	0.5	5	5
	Stitching pattern	Undulating pattern	Undulating pattern	Undulating pattern
Stretchability	−	−	−
Resistance change ratio during 40% elongation (%)	20.8	38.5	28.5
	+	−	+

As shown in Tables 1 to 3, the conductive cloths of Examples 1 to 15 in which the 5 N constant load elongation ratio (S0) of the base cloth is at least 24%, and the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth in the non-stitched region is 0.55 to 0.90 all had a resistance value change ratio during 40% elongation of at most 30%, and therefore, a change in the resistance value thereof due to stretching or contraction was reduced (excellent conduction stability). In addition, the results of Examples 1 to 15 demonstrated that the diameter of the metal wire of the conductive yarn is preferably 20 to 100 μm, and that the space between each conductive yarn is preferably 1 to 10 mm. Furthermore, the results of Examples 1 to 15 demonstrated that, in all of the conductive cloths in which conductive yarns are indirectly stitched into a base cloth in an undulating pattern and the conductive cloths in which conductive yarns are stitched into a base cloth in a grid pattern, the 5 N constant load elongation ratio (S0) of the base cloth was at least 24%, and the ratio (S1/S2) was 0.55 to 0.90, and therefore, the resistance value change ratio during 40% elongation was at most 30%, resulting in excellent conduction stability. In addition, excellent stretchability was demonstrated. As indicated by Example 10, it was demonstrated that even in the case in which conductive yarns are stitched into both sides of a base cloth, a similar effect is obtained. As indicated by Examples 11 and 12, it was demonstrated that a similar effect is obtained even in the case in which a material for conductive yarns and a material for a base cloth are changed. As illustrated by Example 13, it was demonstrated that even in the case in which a base cloth having a double-layer structure is used, a similar effect is obtained. In addition, comparison between Example 6 and Example 13 demonstrated that stretchability is more excellent in the case in which a base cloth includes a single knitted fabric than in the case in which a base cloth includes two knitted fabrics (double-layer structure). Furthermore, it was demonstrated that even in the case in which the fineness of the insulating yarn is increased to 84 as illustrated in Example 14, or decreased to 33 as illustrated in Example 15, the stretchability and resistance value change ratio during 40% elongation do not significantly change (decrease), and are stable, compared to Examples 1 to 13.

In contrast to this, as shown in Table 4, in Comparative Example 1 in which the 5 N constant load elongation ratio (S0) of the base cloth is at least 24%, and the ratio (S1/S2) of the 5 N constant load elongation ratio (S1) of the conductive cloth in the stitched region and the 5 N constant load elongation ratio (S2) of the conductive cloth in the non-stitched region is out of the range of 0.55 to 0.90, the resistance value change ratio during 40% elongation was at most 30%, and a change in the resistance value due to stretching or contraction was reduced, but the stretchability was low. In Comparative Example 2 in which the 5 N constant load elongation ratio (S0) of the base cloth is less than 24% and the ratio (S1/S2) is out of the range of 0.55 to 0.90, the resistance value change ratio during 40% elongation was more than 30%, and a change in the resistance value due to stretching or contraction was not reduced, and the stretchability was low. In Comparative Example 3 in which the ratio (S1/S2) is 0.55 to 0.90 and the 5 N constant load elongation ratio (S0) of the base cloth is less than 24%, the resistance value change ratio during 40% elongation was at most 30%, and a change in the resistance value due to stretching or contraction was reduced, but the stretchability was low.

INDUSTRIAL APPLICABILITY

The conductive cloth according to the present invention is applicable as a sensor in, for example, interior articles for vehicles such as a steering wheel, clothing articles such as jackets, trousers, and globes, health and medical devices such as massage chairs and nursing care beds, furniture such as chairs and couches, and the like.

REFERENCE SIGNS LIST

• • 1 a, 1b CONDUCTIVE CLOTH
  • 10 BASE CLOTH
  • 100 CONDUCTIVE YARN
  • 400 INSULATING YARN
  • K1 LENGTH OF CONDUCTIVE CLOTH IN ABSENCE OF APPLIED LOAD
  • K2 LENGTH OF CONDUCTIVE CLOTH IN PRESENCE OF APPLIED LOAD
  • L1 LENGTH OF BASE CLOTH IN ABSENCE OF APPLIED LOAD
  • L2 LENGTH OF BASE CLOTH IN PRESENCE OF APPLIED LOAD LOAD
  • F
  • S SPACE BETWEEN EACH CONDUCTIVE YARN

Claims

1. A conductive cloth comprising a base cloth and conductive yarns stitched into the base cloth, wherein the constant load elongation ratio (S0) of the base cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 24%,the conductive yarns are stitched in at least two directions, and each conductive yarn is exposed from at least one side of the base cloth, andthe ratio (S1/S2) of the constant load elongation ratio (S1) of the conductive cloth in a region in which the conductive yarns are stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto, and the constant load elongation ratio (S2) of the conductive cloth in a region in which the conductive yarns are not stitched as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto, is 0.55 to 0.90.

2. The conductive cloth according to claim 1, wherein the constant load elongation ratio (S3) of the entire conductive cloth as measured in accordance with the elongation ratio (D-method) of JIS L1096 in the presence of a load of 5 N applied thereto is at least 20%.

3. The conductive cloth according to claim 1, wherein the conductive cloth has a resistance value change ratio during 40% elongation of at most 30%.

4. The conductive cloth according to claim 1, wherein the base cloth has a thickness of at most 1 mm.

5. The conductive cloth according to claim 1, wherein a space between each conductive yarn is 1 to 10 mm.