Conductive fiber and method for producing the same

Abstract

To provide a conductive fiber enabling improvement in wash durability, and a method for producing the same.SOLUTION: A conductive fiber has a base material having a conductive polymer deposited thereon. The base material includes a chemical fiber. The conductive polymer is poly(3,4-ethylenedioxythiophene) with an iron salt of p-toluenesulfonic acid added as an oxidant and a dopant. The conductive polymer also penetrates into the interior of the base material. The penetration ratio of the conductive polymer into the base material is 1% or more and 100% or less on a cross section orthogonal to the longitudinal direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a conductive fiber having a conductive polymer adhered to a substrate, and a method for producing the same.

Background Art

[0002] In recent years, conductive fibers in which a conductive polymer such as PEDOT-PSS {poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid)} is adhered to a substrate made of silk have been known (see, for example, Patent Document 1). Since this conductive fiber has conductivity, hydrophilicity, tensile strength, and water resistance, it can be particularly used as a material for a bioelectrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventional conductive fibers have a problem that their conductivity decreases when washing is repeated.

[0005] The present invention has been made based on such problems, and an object thereof is to provide a conductive fiber capable of improving washing durability and a method for producing the same.

Means for Solving the Problems

[0006] The conductive fiber of the present invention has a conductive polymer adhered to a base material. The base material includes synthetic fibers, and the conductive polymer is poly(3,4-ethylenedioxythiophene) with an iron salt of p-toluenesulfonic acid added as an oxidizing agent and a dopant. Moreover, it has penetrated into the interior of the base material, and the penetration ratio of the conductive polymer into the base material is 1% or more and 100% or less in a cross section orthogonal to the longitudinal direction.

[0007] The method for manufacturing the conductive fiber of the present invention is for manufacturing the conductive fiber of the present invention. The conductive polymer is polymerized using a reaction solution containing an iron salt of p-toluenesulfonic acid, a monomer of poly(3,4-ethylenedioxythiophene), and a solvent. The solvent is water, and by adjusting at least one of the temperature and humidity during polymerization to control the polymerization rate, the conductive polymer is allowed to penetrate into the interior of the base material.

Advantages of the Invention

[0008] According to the conductive fiber of the present invention, since the conductive polymer has penetrated into the interior of the base material, an anchor effect can be obtained in which the conductive polymer strongly adheres to the base material, improving the conductivity between the conductive fibers and enhancing the sheet resistance and washing durability.

[0009] According to the method for manufacturing the conductor of the present invention, since the solvent of the reaction solution is water and at least one of the temperature and humidity during polymerization is adjusted to control the polymerization rate, the conductor of the present invention can be easily obtained.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] A conductor according to an embodiment of the present invention includes a plurality of conductive fibers having a conductive polymer adhered to a base material. The shape of the conductor is preferably, for example, filamentous, cloth-like, or sheet-like. In the case of cloth-like or sheet-like, it may be any of woven fabric, knitted fabric, or non-woven fabric. A non-woven fabric is a sheet-like material in which fibers are intertwined without being woven, and the fibers are adhered or intertwined by heat, mechanical, or chemical action. This conductor can be used, for example, as a conductive polymer electrode.

[0013] The base material preferably includes, for example, chemical fibers such as synthetic fibers because of excellent productivity and stretchability. Examples of chemical fibers include synthetic fibers such as polyester, nylon, and urethane, and it is preferable to include at least one of these. Further, if synthetic fibers having a deformed cross-section (i.e., deformed cross-section yarns) are included, the conductive polymer can also adhere between the fibers, which is preferable because the washing resistance can be enhanced.

[0014] As the conductive polymer, poly(3,4-ethylenedioxythiophene) (hereinafter referred to as PEDOT) added with an iron salt of p-toluenesulfonic acid (hereinafter referred to as pTS) is preferable. That is, the conductive polymer contains pTS and PEDOT. pTS functions as an oxidizing agent when polymerizing the monomer of PEDOT, that is, 3,4-ethylenedioxythiophene (hereinafter referred to as EDOT), and also functions as a dopant for causing PEDOT to exhibit conductivity.

[0015] It is preferable that the crystallinity of PEDOT is low. For example, being amorphous is preferable because the adhesiveness to the substrate can be improved and the washing resistance can be enhanced. Regarding the crystallinity of PEDOT, for example, since a crystalline peak appears at around 2θ = 5° to 7° in X-ray diffraction, it can be judged by measuring the intensity of this crystalline peak. Also, the proportion of PEDOT in which pTS is coordinated in PEDOT is preferably 10% or more and 50% or less because the conductivity and the washing resistance can be further improved. The proportion of PEDOT in which pTS is coordinated in PEDOT can be determined, for example, from the area ratio between the peak of PEDOT obtained by XPS (X-ray Photoelectron Spectroscopy) and the peak of PEDOT in which pTS is coordinated.

[0016] The conductive polymer is preferably adhered to the surface of the substrate in a thin film form because high conductivity can be obtained. Also, the conductive polymer not only adheres to the surface of the substrate but also penetrates into the interior of the substrate. FIG. 1 shows an SEM photograph of a cross section of the conductive fiber according to the present embodiment cut in a direction perpendicular to the longitudinal direction. In FIG. 1, the white part is the substrate, and the gray part covering the periphery thereof and the gray part irregularly present inside the substrate are the conductive polymer. As shown in FIG. 1, it can be seen that in this conductive fiber, the conductive polymer adheres to the outer peripheral surface of the substrate and also penetrates into the interior of the substrate. By having the conductive polymer penetrate into the interior of the substrate in this way, an anchor effect in which the conductive polymer strongly adheres to the substrate can be obtained.

[0017] The penetration ratio of the conductive polymer into the base material is 1% or more and 100% or less, preferably 10% or more and 100% or less, and more preferably 30% or more and 100% or less, in a cross-section obtained by cutting the conductive fiber in a direction perpendicular to the longitudinal direction. This is because a higher anchor effect can be expected. The penetration ratio of the conductive polymer into the base material can be determined, for example, by taking a cross-sectional photograph of the conductive fiber cut in a direction perpendicular to the longitudinal direction and performing image analysis. Specifically, for example, an SEM photograph of a cross-section cut in a direction perpendicular to the longitudinal direction of the conductive fiber is taken, and it can be determined from the area of the portion of the conductive polymer that has penetrated into the base material and the area of the entire base material including the portion of the conductive polymer that has penetrated into the base material.

[0018] This conductive fiber can be produced, for example, as follows. First, a first liquid containing pTS and a solvent and a second liquid containing EDOT and a solvent are mixed to prepare a mixed solution. At this time, it is preferable to adjust the ratio of pTS to EDOT (pTS:EDOT) to be within the range of 1:0.2 to 1:0.6 in terms of molar ratio. This is because the ratio of PEDOT in which pTS is coordinated can be within the range of 10% or more and 50% or less.

[0019] Next, a solvent is mixed into the mixed solution to prepare a reaction solution. The solvent in the mixed solution and the reaction solution is preferably water and does not contain an alcohol such as ethanol. This is because the polymerization rate of EDOT can be easily slowed down by using water as the solvent. In addition, it is preferable to adjust the ratio of water in the reaction solution (water / reaction solution) to be within the range of 1 volume% or more and 30 volume% or less.

[0020] Subsequently, the reaction solution is applied to the substrate, and EDOT is polymerized to attach the conductive polymer to the substrate. At this time, it is preferable to control the polymerization rate by adjusting at least one of the temperature and humidity during polymerization. This is because by reducing the polymerization rate, the reaction solution can penetrate into the interior of the substrate, allowing the conductive polymer to penetrate into the interior of the substrate. The heating temperature during polymerization is preferably, for example, from 20°C to 60°C, the heating time is preferably, for example, from 5 minutes to 60 minutes, and the reaction time is preferably from 10 minutes to 24 hours.

[0021] Thereafter, for example, it is washed with water and dried. Note that the steps of applying the reaction solution to the substrate, polymerizing it, and then washing with water and drying are preferably repeated a plurality of times, and more preferably repeated two or more times.

[0022] Thus, according to the conductive fiber of the present embodiment, since the conductive polymer penetrates into the interior of the substrate, an anchor effect in which the conductive polymer strongly adheres to the substrate can be obtained, improving the conductivity between the conductive fibers and enhancing the sheet resistance and washing durability.

[0023] According to the manufacturing method of the present embodiment, since the solvent of the reaction solution is water and the polymerization rate is controlled by adjusting at least one of the temperature and humidity during polymerization, the conductive fiber of the present embodiment can be easily obtained.

Example

[0024] (Example 1) First, a first liquid containing pTS and water as a solvent and a second liquid containing EDOT and water as a solvent were mixed to prepare a mixed solution. The ratio of pTS to EDOT (pTS:EDOT) was set to 1:0.2 to 1:0.6 in terms of molar ratio. Subsequently, water was mixed into this mixed solution as a solvent to prepare a reaction solution. That is, the solvent of the reaction solution was water. The ratio of water in the reaction solution (water / reaction solution) was set to 20% by volume.

[0025] Subsequently, the reaction solution was applied to the substrate, heated, and then kept in a room at 25°C and 60% humidity for 2 hours to polymerize EDOT, thereby attaching the conductive polymer to the substrate. A polyester cloth was used as the substrate. The heating temperature was 60°C and the heating time was 6 minutes. Note that the temperature and humidity during polymerization were adjusted so that the polymerization rate would be slow. Thereafter, it was washed with water and dried. Further, the steps of applying the reaction solution to the substrate, polymerizing it, washing with water, and drying were performed again in sequence. Thus, the conductor of Example 1 was obtained.

[0026] Regarding the obtained conductive fibers, as described above, SEM photographs of the cross-section cut in a direction perpendicular to the longitudinal direction were taken, and the penetration rate of the conductive polymer into the substrate was determined to be 31.25%. The SEM photograph of the cross-section cut in a direction perpendicular to the longitudinal direction of the conductive fibers of Example 1 is as shown in FIG. 1.

[0027] (Comparative Example 1) As Comparative Example 1 for Example 1, a conductive fiber was produced in the same manner as in Example 1, except that a first liquid containing pTS and ethanol as a solvent and a second liquid containing EDOT and ethanol as a solvent were mixed to prepare a mixed solution. That is, in Comparative Example 1, the solvent of the mixed solution was ethanol, and the solvent of the reaction solution was a mixture of water and ethanol. That is, Example 1 and Comparative Example 1 differ in the composition of the solvent, and in Example 1, by using water as the solvent, the polymerization rate is made slower than in Comparative Example 1.

[0028] Regarding the obtained conductive fibers, the penetration rate of the conductive polymer into the substrate was determined in the same manner as in Example 1, and it was less than 1%. FIG. 2 shows an SEM photograph of the cross-section of the conductive fibers of Comparative Example 1 cut in a direction perpendicular to the longitudinal direction. In FIG. 2, the white portion is the substrate, and the gray portion covering it is the conductive polymer. Note that in FIG. 2, the gray portion seen inside the substrate is due to the shadow of the substrate or the conductive polymer attached around the substrate adhering during cutting.

[0029] (Performance Evaluation of Example 1 and Comparative Example 1) For the conductors of Example 1 and Comparative Example 1, washing was performed from 1 to 10 times, and the sheet resistance was measured before washing (i.e., 0 times of washing) and after each washing to examine the change in resistance due to washing. The washing method was JIS L 103 method. The sheet resistance was measured using Loresta-AX MCP-T370 manufactured by Mitsubishi Chemical Analytech, and the surface resistance between three points separated by 8 mm was measured. The obtained results are shown in Figure 3.

[0030] As shown in Figure 3, according to Example 1, the sheet resistance before washing could be made smaller compared to Comparative Example 1. Also, according to Example 1, the degree to which the sheet resistance increased due to repeated washing could be significantly reduced compared to Comparative Example 1. That is, it was found that by setting the penetration ratio of the conductive polymer into the base material to be 1% or more and 100% or less, further 10% or more and 100% or less, and further 30% or more and 100% or less in a cross-section orthogonal to the longitudinal direction, the sheet resistance and washing durability could be improved. It was also found that by using water as the solvent of the reaction solution to slow down the polymerization rate of EDOT, the conductive polymer could penetrate into the interior of the base material.

[0031] The present invention has been described above by way of embodiments, but the present invention is not limited to the above embodiments and can be variously modified. For example, in the above embodiments, each component has been specifically described, but not all components need to be provided, and other components may be provided.

Industrial Applicability

[0032] In recent years in Japan, with the aging population progressing, for the purpose of monitoring health conditions and extending healthy life spans, wearable devices have been developed to detect biological information such as electrocardiogram (the information that forms the basis of an electrocardiogram; the same applies hereinafter) and electromyogram through unobtrusive sensing, preventing diseases and injuries and enabling early detection of diseases. However, when measuring electrocardiogram and the like, conventionally, it has been necessary to attach a gel or a sticky seal for measurement or strongly press with a belt, making it difficult to wear for a long time. Also, although disposable seals and the like are used as substitutes, there may be a sense of discomfort during wearing and problems such as rough skin may occur. Also, conventionally, those mainly coated with Ag metal have been generally used, but there are concerns about adverse effects on the living body. Furthermore, there has also been a problem that the electrodes are oxidized by moisture and sweat, causing performance degradation. That is, it is desired that the electrodes do not have an adverse effect on the living body even when used continuously for a long time. According to the present invention, for example, a mixed solution containing a monomer of a conductive polymer, an oxidizing agent, and ethanol as a solvent is applied to the surface of commercially available underwear and polymerized by a chemical reaction, enabling the underwear to have a conductive function. The electrodes can be measured without strongly pressing against the living body, the underwear can be manufactured at a lower cost than conventional products, and biological information can be detected. If the price of the wear is reduced, it can be widely applied to healthcare and care support robots, work support robots, fitness, work clothes, etc.

Claims

1. A conductive fiber having a conductive polymer attached to a substrate, wherein the substrate includes chemical fibers, the conductive polymer is poly(3,4-ethylenedioxythiophene) with an iron salt of p-toluenesulfonic acid added as an oxidizing agent and a dopant, and also penetrates into the interior of the substrate, and the penetration ratio of the conductive polymer into the substrate is 1% or more and 100% or less in a cross-section perpendicular to the longitudinal direction. A conductive fiber characterized by the above.

2. The conductive fiber according to claim 1, wherein the substrate includes at least one of polyester, nylon, and urethane.

3. A method for manufacturing the conductive fiber according to claim 1, wherein the conductive polymer is polymerized using a reaction solution containing an iron salt of p-toluenesulfonic acid, a monomer of poly(3,4-ethylenedioxythiophene), and a solvent, the solvent is water, and the polymerization rate is controlled by adjusting at least one of the temperature and humidity during polymerization, thereby allowing the conductive polymer to penetrate into the interior of the substrate. A method for manufacturing a conductive fiber characterized by the above.

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