JPH10310974A - Production of electrically conductive fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain electrically conductive fiber that has low electric resistance on the fiber surface and low inner electric resistivity between cross sections, shows excellent uniformity of conductivity in the fiber length direction and is useful for woven or knit fabrics by subjecting specific sheath-core conjugated fibers to the discharge treatment between high-voltage electrodes. SOLUTION: The core component containing an electrically conductive substance as stannic oxide or zinc oxide is completely covered with the sheath component comprising a fiber-forming polymer as a polyester with a moisture absorption of >=1.0% and the resultant sheath-core conjugated fiber is discharge- treated between the high-voltage electrodes thereby preparing the objective electrically conductive fiber. The core cross section perpendicularly crossing the fiber axis is a modified cross section having 2 or more keen projections and at least one of the minimum thick parts Vi formed by the keen projection and the outer periphery of the sheath component is <=5.0 μm. In a preferred embodiment, the sheath-core conjugated fiber is previously moistened on its surface and subjected to discharge treatment between the high-voltage electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a core-sheath type conductive fiber containing a conductive substance in a core component. More specifically, the present invention relates to a method for stably producing conductive fibers having a core-in-sheath structure having excellent quality with uniform conductivity in the length direction of the fibers.

[0002]

2. Description of the Related Art Thermoplastic resins such as polyethylene, polyamide, and polyester are used for many purposes as textile products, but have a drawback that they are poor in antistatic properties and are easily charged, so that they have conductivity. Much research has been done to do this.

For example, there is a method in which a powder of a conductive substance is dispersed in a thermoplastic resin to form a core component, and a fiber-forming polymer is used as a sheath component to form a core-sheath composite fiber.
The conductivity between the cores of the fiber cross section is good and there is no problem, but since the sheath component is formed of a polymer with excellent fiber forming properties but poor conductivity, the electric resistance of the surface is high. ,
There is a problem that the conductivity becomes substantially poor. Therefore, even with such a core-sheath type composite fiber containing a conductive substance in the core, discomfort due to static electricity of the fabric using the fiber (the wrapping of the worn clothes on the body, discharge noise when undressing, air (Dust adhesion in the inside) still remained.

In order to solve this problem, Japanese Patent Laid-Open Publication No. Sho 62
Japanese Patent Application Publication No. 53416 proposes a method of subjecting a core-sheath composite fiber containing a conductive substance to a core component to electric discharge machining between high-voltage electrodes. However, this method is insufficient in terms of quality stability (in terms of stability of conductive performance in the fiber length direction) as a conductive fiber that requires recent high performance.

Japanese Unexamined Patent Publication (Kokai) No. 63-219624 proposes a method for electrical discharge machining of a sheath-core composite fiber having a sharp projection with a core component containing a conductive substance having a cross section of 2 or more. . Certainly, according to this method, although the electrical resistance of the fiber surface can be reduced and the dispersion of the conductive performance can be reduced, the quality stability is insufficient in the field where high performance is still required.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a core component containing a conductive substance and a fiber-forming polymer covering the core component. In the method of reducing the electric resistance of the fiber surface by subjecting the core-sheath type composite fiber composed of the sheath component to electric discharge machining between high-voltage electrodes, the uniformity of the conductive performance in the yarn length direction of the fiber is significantly improved. It is to provide a method that does not make it.

[0007]

The present invention adopts the following constitution to achieve the above object. That is, the present invention provides a method of discharging a core-in-sheath composite fiber composed of a core component containing a conductive substance and a sheath component made of a fiber-forming polymer that completely covers the core component between high-voltage electrodes. A method for producing a conductive fiber to be processed, wherein the fiber-forming polymer is a polyester having a moisture absorption of 1.0% or more. "

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a fiber to be subjected to electric discharge machining is a core composed of a core component containing a conductive substance and a sheath component made of a fiber-forming polymer that completely covers the core component. It is a sheath type composite fiber. Here, as the conductive substance contained in the core component, known substances such as conductive carbon black and conductive metal compounds can be used. As types of carbon black, acetylene black,
Examples thereof include oil furnace black, thermal black, channel black, Ketjen black and the like. On the other hand, as the conductive metal compound, a conductive metal oxide is mainly used, and stannic oxide and zinc oxide which are particularly excellent in whiteness are preferable. The stannic oxide mentioned here includes stannic oxide containing a small amount of an antimony compound, and a conductive metal complex obtained by coating the surface of titanium oxide particles with stannic oxide containing a small amount of an antimony compound. It is. Zinc oxide also includes conductive zinc oxide in which a small amount of aluminum oxide, lithium oxide, indium oxide, or the like is dissolved.
These can be usually used as fine powders dispersed in a matrix polymer.

Examples of the matrix polymer include polyesters, polyolefins, and polyamides. The matrix polymer has an adhesive property with a fiber-forming polyester used as a sheath component described later, an affinity with a dispersed conductive material, and the like. From the viewpoint of handleability and the like, an optimum one may be appropriately selected.

Next, it is important that the sheath component completely surrounding the core component is a fiber-forming polyester and has a moisture absorption of 1.0% or more. When the sheath component is a polymer other than polyester or a polymer having a moisture absorption of less than 1.0%, the feeling of the obtained conductive fiber and the stability of electric discharge machining (in the yarn length direction of the fiber). (Uniformity of conductivity) cannot be achieved. Here, the moisture absorption means that the sheath component alone is a single fiber fineness 2
5 denier fiber was prepared, and the fiber was allowed to stand in a desiccator (relative humidity: 65% RH) containing a saturated aqueous solution of sodium nitrite (relative humidity: 65% RH) for 48 hours at 25 ° C. Is a value calculated from the following formula from the weight (fiber weight at the time of absolute drying) measured after drying in a vacuum dryer at 105 ° C. for 24 hours. Moisture absorption = [(weight of fiber when absorbed-weight of fiber when dried) / weight of fiber when dried] x 100

The polyester having such hygroscopicity is, for example, a polyester obtained by copolymerizing a component having a sulfonic acid metal base such as 5-sodium sulfoisophthalic acid or a polyalkylene glycol such as polyoxyethylene glycol. And the like. Further, it may be one obtained by graft copolymerization of acrylic acid and / or methacrylic acid in order to increase the moisture absorption. In addition, when the main repeating unit of the polyester is ethylene terephthalate in particular, it is preferable because a conductive fiber obtained having both excellent feeling and stability of electric discharge machining can be obtained.

It is preferable that the core-sheath type conjugate fiber composed of such a component has an irregular cross-sectional shape having two or more, preferably 2 to 8, sharp projections in the cross section of the fiber. Here, the cross-sectional shape having a sharp protrusion refers to a cross-sectional shape having a convex or a protruding convex portion, and the main ones are those shown in FIGS. 1 (a) to 1 (d). Can be. When the number of the sharp protrusions is less than 2, the stability of the electric discharge machining described below decreases, and the uniformity of the conductive performance in the length direction decreases.

Further, as illustrated in FIG. 1 (b), at least one of a minimum thickness of V _i between the sharp peaks and the sheath component periphery is more preferably less 5.0 .mu.m. If all V _i exceeds 5μm, discharge machining process to obtain a sufficient conductivity performance becomes difficult difficult. When the minimum thickness V _i is too thin, and one of them is less than 0.5 μm, it becomes difficult to completely cover the core component with the sheath component, and the core and the sheath may peel off or become conductive. since the conductive performance sexual component to fall off is likely to occur problems such as causing contamination lowered, all V _i is desirably 0.5μm or more.

In the present invention, the core-sheath type conjugate fiber having the above-mentioned shape has a high surface electric resistance value and insufficient conductivity, and is still easily charged. There is a feature,
As a result, the electric resistance value of the fiber surface becomes 10 ¹⁰ Ω / c.
m order or less, and the internal electrical resistance between the fiber cross sections (measured in Ω / cm) and the surface electrical resistance (Ω / cm)
Is less than or equal to 10 ³ , and a conductive fiber whose conductivity is uniform and stable in the length direction of the fiber can be obtained.

The ordinary conductive core-sheath type composite fiber has a very high surface electric resistance value, for example, on the order of 10 ¹³ Ω / cm, because the sheath made of the fiber-forming polymer has a large electric resistance. Internal electrical resistance between end faces is 10 ⁷
Even if it is as low as Ω / cm, the ratio of the electric resistance of the surface to the internal electric resistance between the end faces is as large as about 10 ^6, and there is a problem that almost no conductivity is exhibited on the fiber surface.

On the other hand, the surface resistance of the conductive fiber according to the method of the present invention is as low as 10 ¹⁰ Ω / cm or less even if the sheath component is composed of a non-conductive fiber-forming polyester. In addition, since the sheath component is subjected to a special electric discharge machining treatment described later using polyester having a high moisture absorption rate, the conductive performance is stabilized in the length direction of the fiber.

Here, the electric resistance value (Ω / cm) is measured as follows. (A) Internal electric resistance value between fiber end faces Ag doutite (a silver particle-containing conductive resin paint, Fujikura Co., Ltd.) The sample having the above-mentioned method was applied on an electrically insulating polyethylene terephthalate film at a temperature of 20 ° C. and a relative humidity of 30% at 1 kV.
Is applied using the Ag-doutite-attached surface to determine the value of the current flowing between the two sections, and the electrical resistance (Ω / cm) is calculated according to Ohm's law.

(B) Surface electric resistance value A sample prepared by attaching the above-mentioned Ag doutite to the surface (fiber side surface) near both ends of a fiber cut to a length of about 2.0 cm in the fiber axis direction. Was applied on the electrically insulating polyethylene terephthalate film under the conditions of a temperature of 20 ° C. and a relative humidity of 30% to apply a DC voltage of 1 kV between the Ag doughites to obtain a current value flowing between the Ag doughites. The distance between them is measured, and the surface electric resistance Ω / cm is calculated according to Ohm's law.

The electric discharge machining method of the present invention includes an energization method of applying the high voltage by bringing the core-in-sheath composite fiber thus constituted into contact with a high-voltage electrode, a corona discharge having a different discharge shape, and a spark discharge. High voltage electric discharge machining methods such as glow discharge and arc discharge can be adopted. The applied voltage of the electric discharge machining is a high voltage exceeding 1 kV,
The range up to 0 kV is suitable, preferably between 2 and 50 kV. The polarity of the electrodes may be positive or negative (DC) or AC. The distance between the electrodes is 0-1
The range of 00 cm is appropriate, and the distance between the electrodes can be appropriately set according to the discharge mode, the processing speed, and the target conductivity. In addition, a method in which a core component containing a conductive substance is used as one electrode and the other electrode is separately provided, a high voltage is applied to both electrodes, and a discharge treatment is performed between the high-voltage electrodes is exemplified as an optimal method. However, the method is not limited to this method, and a method of applying a high voltage to two separately provided poles and performing a discharge treatment may be used.

Further, such a machining discharge treatment can be performed in a state of a yarn or a state of a fabric such as a woven or knitted fabric or a nonwoven fabric. Furthermore, in the case of a yarn state, it may be applied to a drawn yarn or an undrawn yarn. By such electric discharge machining, not only the surface electric resistance can be reduced to the order of 10 ¹⁰ Ω / cm or less, but also the ratio of the surface electric resistance to the electric resistance between the cross sections is 10 ³ or less, preferably 10 ² or less. In particular, when used under severe conditions, it can be set to 10 or less.

Further, when performing the electric discharge machining treatment, it is more preferable to apply moisture to the surface of the core-sheath composite fiber before the electric discharge machining, and more preferably to attach the moisture so as to cover the entire surface. By doing so, there is no unevenness in the electric resistance on the fiber surface, the stability of the electric discharge machining is significantly improved, and it is possible to obtain a conductive fiber whose conductive performance is extremely stable in the length direction of the fiber.

The method for adhering moisture to the fiber (original yarn) before the electric discharge machining is not particularly limited, but an oiling method (oiling roller,
MO nozzle, etc.), or the raw yarn may be directly immersed in a water bath. The amount of adhered moisture is not particularly limited as long as the fiber surface is covered with moisture.

Furthermore, if a small amount of a surfactant is contained in the water to be adhered, the friction between the raw yarn and the electric discharge machining electrode and the friction between the single yarns of the raw yarn can be reduced, so that the electric discharge machining with the single yarn can be performed. This is preferable because an increase in the area of contact with the electrode increases the EDM efficiency. Further, the fiber surface can be completely covered with a smaller amount of attached moisture. The type and concentration of the surfactant may be appropriately set as needed.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In addition, the variation in the length direction of the surface electric resistance value of the conductive fiber was represented by the difference between the maximum value and the minimum value by measuring the surface electric resistance value at 10 points every 1 m.

Example 1 A conductive resin composition composed of 30 parts by weight of conductive carbon black and 70 parts by weight of polyester as a conductive substance was used as a core component, and 7% by weight of polyethylene glycol having a number average molecular weight of 1000 was used. The copolymerized polyethylene terephthalate was used as a sheath component and melt-spun using an ordinary composite spinning apparatus to obtain a core-sheath composite fiber having a cross-sectional shape as shown in FIG.
It was drawn twice to obtain a multifilament having 25 deniers and 5 single yarns. After immersing this core-sheath type composite fiber in a water bath, discharge treatment was performed at a speed of 300 m / min. Table 1 shows the moisture absorption of the sheath component, the average value of the electric resistance value of the obtained conductive fibers, and the variation in the length direction.

[Examples 2 to 6, Comparative Example 1] In Example 1, the moisture absorption of the sheath component (copolymerization amount of polyethylene glycol having a number average molecular weight of 1,000), the water content and the Vi attached to the raw yarn before the discharge treatment were shown. A conductive fiber was obtained in the same manner as in Example 1 except for changing as in Example 1. The results are summarized in Table 1.

Example 7 240 parts by weight of conductive powder having titanium oxide particles coated with conductive stannic oxide and 75 parts by weight of polyethylene were charged into a kneader.
After kneading at 80 ° C. for 30 minutes, 18 parts by weight of liquid paraffin and 4 parts by weight of stearic acid as an oleophilic agent were added, and the mixture was further kneaded for 5 hours. A core-sheath type composite fiber (core / sheath weight ratio = 1) in which the obtained conductive resin composition is used as a core component and the same copolymerized polyethylene terephthalate as in Example 1 is used as a sheath component.
/ 6) was spun and stretched four times to obtain a multifilament of three 30-denier single yarns. After immersing this core-sheath type composite fiber in a water bath, discharge treatment was performed at a speed of 300 m / min. Table 1 shows the average value of the electric resistance value and the variation in the length direction of the obtained conductive fibers.

[0028]

[Table 1]

[0029]

As described above, according to the method for producing a conductive fiber of the present invention, the electric resistance value of the fiber surface and the internal electric resistance value between the cross sections are low, and the conductive performance is reduced in the longitudinal direction. The conductive fibers can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a cross-sectional shape of a conductive core-sheath composite fiber of the present invention.

[Explanation of symbols]

Vi Minimum thickness of the sheath component formed by the sharp projection and the outer periphery of the sheath component

Claims (3)

[Claims] An electric discharge machining process between a high-voltage electrode and a core-sheath composite fiber comprising a core component containing a conductive substance and a sheath component made of a fiber-forming polymer that completely covers the core component. The method for producing a conductive fiber, wherein the fiber-forming polymer is a polyester having a moisture absorption of 1.0% or more. 2. A shape of a core component in a cross section orthogonal to a fiber axis is an irregular cross-sectional shape having two or more sharp protrusions,
And該鋭peaks and at least one method for producing a conductive fiber according to claim 1, wherein less than 5.0μm among the sheath component minimum thickness V _i which is formed by the sheath component periphery. 3. The method for producing a conductive fiber according to claim 1, wherein water is previously attached to the surface of the core-sheath composite fiber, and then electrical discharge machining is performed between the high-voltage electrodes.