EP3690088A1

EP3690088A1 - Conductive composite fiber

Info

Publication number: EP3690088A1
Application number: EP18859995.5A
Authority: EP
Inventors: Sumio Yamaguchi; Sho MURATA; Yasunori KANEMORI
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2017-09-28
Filing date: 2018-09-26
Publication date: 2020-08-05
Anticipated expiration: 2038-09-26
Also published as: EP3690088B1; JP7107226B2; JPWO2019065681A1; KR20200058378A; US20200216984A1; CN110945167A; EP3690088A4; WO2019065681A1

Abstract

Provided is a conductive composite fiber formed from a polymer containing conductive carbon black in a polyamide resin as a conductive layer and thermoplastic resin as a nonconductive layer, wherein the conductive layer is exposed in three or more locations on the outside surface of the fiber in a cross section, the coefficient of variation (CV %) in the surface area of each conductive layer in a fiber cross section is 10% or less, and the average value of the area specific resistance is 4 log (Ω·cm). It is possible to provide a conductive composite fiber wherein the variation in the fiber surface specific resistance is suppressed and the variation in the exposed surface area of each conductive layer polymer in a fiber cross section is suppressed by exposure of the conductive layer in three or more locations on the fiber surface, crimping of the original yarn is suppressed by equal disposition, and antistatic performance for woven and knitted fabrics and carpets is improved.

Description

TECHNICAL FIELD

The present invention relates to a conductive composite fiber having excellent static elimination performance. More specifically, the present invention relates to a conductive composite fiber in which the variation in the fiber surface specific resistance and the variation in areas of conductive layers in a fiber cross section is suppressed by exposure of the conductive layers at three or more locations on the fiber surface, crimping of the original yarn is suppressed by equal disposition, and antistatic performance for woven and knitted fabrics is improved.

BACKGROUND ART

Conventionally, various proposals have been made for conductive fibers as fibers having excellent static elimination performance. Examples of the proposals include plating the surface of nonconductive fibers with a metal to provide conductivity, and dispersing a conductive carbon black in a resin or rubber and then coating the fiber surface with the resin or the rubber to form a conductive coating layer. However, there is a problem that the conductive fibers are of no practical use because the methods to obtain the conductive fibers are technically difficult due to the complicated manufacturing process, and because the conductivity is easily deteriorated in the preparation stage for practical use of the conductive fibers, for example, in the chemical treatment in the scouring process for weaving and knitting, or by external actions of wear, repeated washing, and the like in actual use.
As other conductive fibers, metal fibers such as steel fibers are known to have excellent static elimination performance. Metal fibers are, however, expensive and difficult to match with general organic materials, so that metal fibers easily have poor spinning performance, cause problems in processes of weaving, and dyeing and finishing, cause breaking and falling due to washing when worn, and also cause problems of electric shock and sparking due to electrical conductivity, a trouble in fabric melting, and the like.
In addition, a method of fiberizing a polymer in which a conductive carbon black is uniformly dispersed to obtain another type of conductive fiber has been proposed. However, because the conductive fiber contains a large amount of carbon black, manufacturing the conductive fiber is difficult, the cost is high, and the physical properties of the fiber are remarkably deteriorated, so that there is a problem that it is difficult to manufacture products unless special processes are used. As a proposal to solve the problems, for example, in Patent Document 1, a fiber in which a conductive polymer layer containing conductive carbon and a nonconductive polymer layer containing the same polymer and no conductive carbon are laminated together in a multilayer shape is proposed for the purpose of improving durability, mainly for the purpose of improving static elimination performance and preventing exfoliation between the component layers. Also in the fiber, however, the layer containing a conductive carbon black is exposed too much on the surface, so that improvement in chemical resistance and durability is not recognized.
Furthermore, proposals have been recently made in Patent Documents 2 to 4 to improve conductive performance by exposure of a conductive layer on the outside surface of the fiber in a fiber cross section. For example, Patent Document 2 provides a conductive fiber having an excellent static elimination effect and static elimination durability obtained by exposure of conductive layers at four or more locations on the outside surface of the fiber in a fiber cross section and by substantially equal disposition of conductive layers.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Japanese Patent Laid-open Publication No. 52-152513
Patent Document 2: Japanese Patent Laid-open Publication No. 2003-278031
Patent Document 3: Japanese Patent Laid-open Publication No. 2004-36040
Patent Document 4: International Publication No. 2007/046296

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

In the conductive fiber proposed in Patent Document 2, it is difficult to expose locally without variation and dispose equally a minute amount of polymer having poor fluidity and containing conductive fine particles, and the static elimination performance is not at a satisfactory level. Similarly, in the conductive composite fibers proposed in Patent Documents 3 and 4 in which the conductive layer portion is partially exposed on the fiber surface, the coefficient of variation (CV%) in the area exposed on the surface of conductive layers in a fiber cross section is large, and the variation in the disposition of conductive layers is also caused, so that there is a problem that a stable static elimination effect cannot be obtained because wave-like crimping is caused in the longitudinal direction of the yarn.
An object of the present invention is to provide a conductive composite fiber, which cannot be sufficiently achieved by conventionally known conductive composite fibers, in which the variation in the area of the polymer in conductive layers in a fiber cross section is suppressed, and crimping of the original yarn is suppressed by accurate equal disposition, and antistatic performance for woven and knitted fabrics is improved.

SOLUTIONS TO THE PROBLEMS

The present invention adopts the following configuration in order to solve the above-described problems.

(1) A conductive composite fiber containing: a polymer as conductive layers, the polymer containing a polyamide resin containing a conductive carbon black; and a thermoplastic resin as a nonconductive layer, wherein the conductive layers are exposed at three or more locations on an outside surface of the conductive composite fiber in a fiber cross section, a coefficient of variation (CV%) of areas of the conductive layers in a fiber cross section is 10% or less, and the conductive composite fiber has an average value of a volume specific resistance of 4 log (Ω·cm) or less.
(2) The conductive composite fiber according to (1), wherein a CV% of angles formed by neighboring line segments each connecting a middle point of an exposed portion of each of the conductive layers on the outside surface of the conductive composite fiber in a fiber cross section and a center point of the fiber cross section is 5% or less.
(3) The conductive composite fiber according to (1) or (2), wherein the thermoplastic resin contains a polyamide or a polyester.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to provide a conductive composite fiber in which the variation in the fiber surface specific resistance is suppressed and the variation in area of the conductive layers in a fiber cross section is suppressed by exposure of the conductive layers at three or more locations on the fiber surface, crimping of the original yarn is suppressed by equal disposition, and antistatic performance for woven and knitted fabrics and carpets is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a front sectional view of a main part of the structure of an exemplary composite spinneret for illustrating a method for manufacturing the conductive composite fiber according to the present invention.
Fig. 2 is an exemplary schematic view showing a cross section of the conductive composite fiber according to the present invention.

EMBODIMENTS OF THE INVENTION

The conductive composite fiber according to the present invention is a conductive composite fiber containing a polymer containing a polyamide resin containing a conductive carbon black as a conductive layer, and a thermoplastic resin as a nonconductive layer.
The polyamide resin used in the conductive layer is not particularly limited as long as it is a polymer including amide bonds produced by repeated polycondensation. The polyamide resin may be nylon 6, nylon 66, nylon 12, nylon 610, or the like, or may be a polyamide containing a small amount of a third component. The conductive carbon black may be furnace black, acetylene black, channel black, ketjen black, or the like, and is preferably furnace black having excellent dispersibility.
The thermoplastic resin used in the nonconductive layer is not particularly limited as long as it is a fiber-forming thermoplastic polymer, and is preferably a polyamide or a polyester because a polymer having poor spinnability has poor process passability. The polyamide is not particularly limited as long as it is a polymer including amide bonds produced by repeated polycondensation. The polyamide may be nylon 6, nylon 66, nylon 12, nylon 610, or the like, or may be a polyamide containing a small amount of a third component. Furthermore, the polyamide may contain a small amount of additive, matting agent, and the like. The polyester is preferably polyethylene terephthalate in which 80 mol% or more of repeating units are ethylene terephthalate, polybutylene terephthalate in which 80 mol% or more of repeating units are butylene terephthalate, or polytrimethylene terephthalate in which 80 mol% or more of repeating units are trimethylene terephthalate. Furthermore, the polyester may be copolymerized with aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene 2,6-dicarboxylic acid, phthalic acid, and 5-sodium sulfoisophthalic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and the like to such an extent that the fiber-forming property inherently possessed by the polyester homopolymer is not impaired. Furthermore, the polyester may contain a small amount of additive, matting agent, and the like.
In the conductive composite fiber according to the present invention, the conductive layers are exposed at three or more locations on the outside surface of the conductive composite fiber in a fiber cross section. By the exposure at three or more locations, the variation in the fiber surface specific resistance can be suppressed, and stable static elimination performance can be maintained. When the conductive layers are exposed at two or less locations, the variation in the fiber surface specific resistance increases, and it is difficult to obtain desired static elimination performance.
In the conductive composite fiber according to the present invention, the CV% in area of the conductive layers in a fiber cross section is 10% or less. By setting the CV% in such a range, the variation in the conductivity between the conductive layers can be suppressed, the wave-like fine crimping in the longitudinal direction of the yarn can be suppressed, and excellent static elimination performance can be obtained when the conductive composite fiber is used in a woven or knitted fabric. When the CV% in area of the conductive layers exceeds 10%, the variation in the conductivity between the conductive layers increases, missing occurs in the conductive layer portion when the conductive composite fiber is used continuously for a long period of time, and stable static elimination performance cannot be obtained. The CV% is preferably 8% or less.
The conductive composite fiber according to the present invention has an average value of the volume specific resistance of 4 log (Ω·cm) or less. By setting the average value of the volume specific resistance to 4 log (Ω·cm) or less, a desired static elimination effect can be obtained, and it is possible to expand applications of the conductive composite fiber to the field in which static elimination performance is strongly desired, such as carpets and work clothes. The average value of the volume specific resistance is preferably 2 to 3.5 log (Ω·cm).
The means for setting the average value of the volume specific resistance to 4 log (Ω·cm) or less may be any of a method of adjusting the concentration of the conductive carbon black contained in the polyamide resin, adjusting the occupancy rate of the conductive layers in the surface area in a fiber cross section, and the like. The conductive carbon black preferably has a specific electrical resistance of 10^-3 to 10² (Ω·cm). As is well known, when a carbon black is completely dispersed in particles, the conductivity is generally poor. When a carbon black assumes a chain structure called a structure, the conductivity is improved and the carbon black is called a conductive carbon black. Therefore, in making a polymer conductive with a conductive carbon black, it is important to disperse the carbon black without destroying the structure. As the electric conduction mechanism of the conductive carbon black-containing composite, a carbon black chain contact and a tunnel effect can be mentioned, and the former is mainly mentioned. Accordingly, the longer the carbon black chain is, and at the higher density the carbon black is present in the polymer, the higher the contact probability is, and the higher the conductivity is. As a result of the study made by the present inventors, when the conductive carbon black content is less than 15% by mass, there is almost no effect. When the content is 20% by mass, the conductivity is rapidly improved, and when the content exceeds 40% by mass, the effect is almost saturated. Furthermore, when the content exceeds 40% by mass, the fluidity of the polymer is poor, and therefore the concentration of the conductive carbon black is preferably 30 to 40% by mass. The occupancy rate of the conductive layers in the surface area in a fiber cross section is not particularly limited, but is preferably 3 to 10% from the viewpoints of spinnability, stretchability, and high-order passability. By setting the occupancy rate in such a range, the abrasion resistance with various guides in a yarn-making process and a high-order processing process can be suppressed, and stable spinnability, stretchability, and high-order passability can be obtained.
Furthermore, the CV% of the angle formed by neighboring line segments each connecting the middle point of the exposed portion of each of the conductive layers on the outside surface of the conductive composite fiber in a fiber cross section and the center point of the fiber cross section is preferably 5% or less. By setting the CV% in such a range, the wave-like fine crimping in the longitudinal direction of the yarn in the conductive composite fiber can be suppressed, more excellent static elimination performance can be obtained when the conductive composite fiber is used in a woven or knitted fabric, and it is possible to apply the conductive composite fiber to the field in which static elimination performance is strongly required, such as carpets and dust-proof clothes. The CV% is more preferably 3.5% or less.
Here, the crimping is represented by the crimping rate calculated from the difference between the fiber length without a load and the fiber length with a load of 0.04 cN/dtex of the conductive composite fiber as described below in EXAMPLES. For example, when the fiber length without a load is 400 mm, and the fiber length with a load of 0.04 cN/dtex is 415 mm, the crimping rate is 3.8%.
In the conductive composite fiber according to the present invention, it is preferable that the conductive layers be equally disposed in a fiber cross section in order to develop more excellent static elimination performance.
In order to form the cross section of an aspect shown in Fig. 2 in which the conductive layers are equally disposed in the fiber cross section, for example, it is preferable to use a composite spinneret implemented by the composite spinneret technology described in Japanese Patent Laid-open Publication No. 2011-174215 .
Since the conductive layer contains a conductive carbon black at a high concentration of 30 to 40% based on the polyamide resin depending on the static elimination performance, the polymer has reduced fluidity at the time of melting. When the conductive layer component containing such a polymer having the reduced fluidity is distributed, by using a composite spinneret having a structure in which distribution, merging, and measuring are repeated a plurality of times with a merging groove having a plurality of distribution holes, the conductive layers can be equally disposed, and the area CV% and the angle CV% can be controlled in such ranges.
The composite spinneret shown in Fig. 1 is incorporated into a spinning pack in a state where mainly three types of members, that is, a measuring plate 1, a distribution plate 2, and an ejecting plate 3 are stacked in this order from the top, and the pack is used for spinning.
In the spinneret member illustrated in Fig. 1, the measuring plate 1 has a role of measuring the amount of the polymer per each ejecting hole 6 and flowing the polymer into the distribution plate 2. The distribution plate 2 has a role of controlling the composite cross section and the cross-sectional shape in the single fiber cross section, and the ejecting plate 3 has a role of compressing and ejecting the composite polymer flow formed with the distribution plate 2.
Although not shown in Fig. 1 in order to avoid complicated illustration of the composite spinneret, as for the member stacked above the measuring plate 1, a member having a channel is required to be used in accordance with the spinning machine and the spinning pack. By designing the measuring plate 1 in accordance with the existing channel member, the existing spinning pack and members of the spinning pack can be used as they are. Therefore, it is not necessary to dedicate the spinning machine especially to the spinneret. In practice, a plurality of channel plates (not shown) is preferably stacked between the channel and the measuring plate or between the measuring plate 1 and the distribution plate 2. The purpose is to provide a structure with the channel through which the polymer is transferred and introduced into the distribution plate 2 efficiently in the cross-sectional direction of the spinneret and in the cross-sectional direction of the single fiber. The composite polymer flow ejected from the ejecting plate 3 is formed into a composite fiber using a method in which the composite polymer flow is cooled and solidified, an oil agent is applied to the composite polymer flow, and an undrawn yarn is wound up once and then heated and drawn in accordance with a conventional melt spinning method, or a direct spinning drawing method in which an undrawn yarn is heated and drawn without being wound up once.
In the manufacture of the conductive composite fiber according to the present invention, it is preferable to control the oxygen concentration immediately below the composite spinneret (ejecting plate 3) to 1% or less. The oxygen concentration (%) is measured using an oxygen concentration meter XP3180E manufactured by NEW COSMOS ELECTRIC CO., LTD. with the tip of a detection tube attached to the lower surface of the ejecting plate. The oxygen concentration was measured at the following three points, that is, the center of the lower surface of the ejecting plate, the position of the ejecting hole in the outermost layer within an area that is formed by quadrisecting the lower surface of the ejecting plate, and the midpoint between the center of the lower surface of the ejecting plate and the ejecting hole in the outermost layer, and the number average value was determined. By setting the oxygen concentration in such a range, the effect of suppressing contamination of the spinneret is exhibited, and as a result, formation of the composite cross section is stabilized. In particular, in the case of a polyamide fiber sensitive in terms of thermal stability and stability against oxygen, the effect is more remarkable. As a result, the formation stability of the composite cross section over time can be dramatically improved, and the conductive layers can be accurately equally disposed.

EXAMPLES

Hereinafter, the present invention is described more specifically with reference to examples. The physical property values in the examples were measured by the methods described below.

(1) Fineness (dtex)

The fineness was measured in accordance with JIS L1013 (2010) 8.3.1, Fineness based on Corrected Weight (Method A). The official moisture regain of a polyamide was 4.5%, and the official moisture regain of a polyester was 0.4%.

(2) Volume Specific Resistance

The electrical resistance value (Ω/cm) was measured under conditions of a temperature of 20°C and a humidity of 30%RH using a super-insulation resistance meter (TERAOHMMETER R-503, manufactured by Kawaguchi Denki), and applying a voltage of 100 (V) to a fiber having a test length of 10 cm, and the volume specific resistance was calculated from the following formula. $RS = R \times D/ (L \times SG) \times 10^{- 6}$

RS:: Specific resistance (log (Ω·cm))
R:: Electrical resistance value (Ω)
D:: Yarn mass (g) per 10000 m
L:: Test length (cm)
SG:: Yarn density (g/cm³)

(3) Area CV (%) of Conductive Layers

The cross section of the conductive composite fiber was enlarged 100 to 300 times using a digital microscope (VHX-2000) manufactured by KEYENCE CORPORATION, the areas of conductive layer parts in a single yarn were measured, and the CV value was calculated.

(4) Angle CV (%)

The cross section of the conductive composite fiber was enlarged 100 to 300 times using a digital microscope (VHX-2000) manufactured by KEYENCE CORPORATION, angles formed by neighboring line segments each connecting a middle point of an exposed portion of each of the conductive layers on the outside surface of the fiber in the fiber cross section and the center point of the fiber cross section in a single yarn (two-dot chain lines in Fig. 2) were measured, and the CV value was calculated.

(5) Variation in Surface Specific Resistance

A sample to be measured at medium temperature and medium humidity (25°C, relative humidity 60%) was kept in the atmosphere for at least 48 hours and then measured. When the yarn was run with a pair of mirror rollers including a yarn feeding roller and a take-up roller, the resistance value for a length of 10 m was measured with a device in which the running yarn was applied to a probe including two rod terminals connected to an insulation resistance meter SM-8220 manufactured by HIOKI E.E. CORPORATION between the rollers under the conditions of a rod diameter of 2 mm, a distance of the applied yarn between the rod terminals of 2.0 cm, an applied voltage of 100 V, a yarn feeding speed of 1 m/min, a yarn tension between the rollers of 0.5 cN/dtex, and a sampling rate in the insulation resistance system of 1 second, and the average [Ω] of the resulting resistance values was divided by the distance of the applied yarn between the rod terminals (2.0cm) to obtain the average resistivity P [Ω/cm]. Furthermore, the standard deviation Q of all the resistance values obtained at the same time was calculated and then the coefficient of variation in the average resistivity CV (CV = Q/P) was calculated from the ratio of P to Q.

(6) Crimping Rate

The fiber length without a load and the fiber length with a load of 0.04 cN/dtex of the conductive composite fiber were measured, and the crimping rate was calculated from the formula below. The resulting value is rounded off to the first decimal place. $CR = (F 2 - F 1) / F 1 \times 100$

CR:: Crimping rate (%)
F1:: Fiber length (mm) without a load
F2:: Fiber length with a load of 0.04 cN/dtex

(7) Carpet evaluation

The conductive composite fiber was mixed with a nylon 6 crimped yarn having a total fineness of 2800 dtex with an air nozzle, the resulting crimped yarn containing the conductive composite fiber was mixed at a rate of 1 to 12, the mixture of the resulting crimped yarn and the nylon 6 crimped yarn was formed into a tuft having a fabric weight of 400 g/m² and a pile height of 4.0 m, the tuft was cut into a size of 30 cm x 30 cm in width, the charging potential was measured 5 times at each level in accordance with JIS A 1455 (floor rubbing type charging test), and the average charging potential of the resulting three charging potential values excluding the maximum and minimum values was determined and evaluated.

S:: Charging potential of -40 V or less
A:: Charging potential of -41 V to -50 V
B:: Charging potential of -51 to -60 V
C:: Charging potential of -61 V or more

[Example 1]

A nylon-based chip (trade name "CARBOREX NYRON YT-01" manufactured by DIC Corporation) containing 35% by mass of a conductive carbon black was used as a conductive layer polymer, and a nylon 6 chip was used as a nonconductive layer polymer. The chips were melted at a melting temperature of 280°C in individual pressure melters at a ratio of 5% by mass of the conductive layer polymer to 95% by mass of the nonconductive layer polymer, the melted chips were merged into a spinning pack and a spinneret to form a composite, and the composite was ejected from the spinneret so that the conductive layer polymer was equally disposed and exposed at three locations on the fiber surface. In the spinneret used, three types of members, that is, a measuring plate 1, a distribution plate 2, and an ejecting plate 3 were stacked in this order from the top, and a plurality of distribution plates were stacked to form a fine channel as shown in Fig. 1. Then, with the oxygen concentration immediately below the spinneret controlled to 1.0% or less, the polymer ejected from the spinneret was cooled with cold air at 18°C and fed with an emulsion oil agent, and then an undrawn yarn was obtained at a speed of 900 m/min. Subsequently, the undrawn yarn was aged for 24 hours in an environment of a temperature of 25°C and a humidity of 70% and then was wound with a drawing machine at a feed roller speed of 150 m/min, at a hot plate temperature of 160°C, and at a drawing roller speed of 450 m/min to obtain a conductive composite fiber of 20 dtex-2 filament having conductive layers exposed at three locations. The obtained conductive composite fiber had a volume specific resistance value of 3.3 log (Ω·cm), an area CV value of conductive layers of 3.0%, and an angle CV value of 2.0%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.30σ, the crimping rate was 2.3%, and the charging potential was also suppressed to -45 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was A and at an acceptable level.

[Example 2]

A conductive composite fiber was obtained under the same conditions as in Example 1, except that the ratio of the conductive layer polymer was changed to 3% by mass, the ratio of the nonconductive layer polymer was changed to 97% by mass, and the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 3.5 log (Ω·cm), an area CV value of conductive layers of 6.1%, and an angle CV value of 3.1%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance can be suppressed to 0.10σ because the number of locations of the exposed conductive layers was changed to six. The crimping rate was at a level of 2.8%, and the charging potential was also suppressed to -38 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was S and at an acceptable level.

[Example 3]

A conductive composite fiber was obtained under the same conditions as in Example 1, except that the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 3.2 log (Ω·cm), an area CV value of conductive layers of 6.0%, and an angle CV value of 3.0%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance can be suppressed to 0.10σ because the number of locations of the exposed conductive layers was changed to six. The crimping rate was at a level of 2.9%, and the charging potential was suppressed to -30 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was S and at an acceptable level.

[Example 4]

A conductive composite fiber was obtained under the same conditions as in Example 1, except that a nylon-based chip containing 45% by mass of a conductive carbon black was used as a conductive layer polymer, and the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 1.9 log (Ω·cm), an area CV value of conductive layers of 6.1%, and an angle CV value of 4.9%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance can be suppressed to 0.12σ because the number of locations of the exposed conductive layers was changed to six. The crimping rate was at a level of 4.7% because the melt viscosity of the conductive layer polymer was high, however, the charging potential was -45 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was A and at an acceptable level.

[Example 5]

A conductive composite fiber was obtained under the same conditions as in Example 1, except that the ratio of the conductive layer polymer was changed to 7% by mass, the ratio of the nonconductive layer polymer was changed to 93% by mass, and the number of locations of the exposed conductive layers was changed to nine. The obtained conductive composite fiber had a volume specific resistance value of 2.8 log (Ω·cm), an area CV value of conductive layers of 6.7%, and an angle CV value of 3.3%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was a favorable result of 0.08σ because the number of locations of the exposed conductive layers was changed to nine. The crimping rate was at a level of 3.3%, and the charging potential was suppressed to -28 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was S and at an acceptable level.

[Example 6]

A conductive composite fiber was obtained under the same conditions as in Example 1, except that the ratio of the conductive layer polymer was changed to 10% by mass, the ratio of the nonconductive layer polymer was changed to 90% by mass, and the number of locations of the exposed conductive layers was changed to 12. The obtained conductive composite fiber had a volume specific resistance value of 2.5 log (Ω·cm), an area CV value of conductive layers of 8.2%, and an angle CV value of 3.5%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was a favorable result of 0.06σ because the number of locations of the exposed conductive layers was changed to 12. The crimping rate was at a level of 4.9%, and the charging potential was suppressed to -46 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was A and at an acceptable level.

[Example 7]

A nylon-based chip (trade name "CARBOREX NYRON YT-01" manufactured by DIC Corporation) containing 35% by mass of a conductive carbon black was used as a conductive layer polymer, and a polyester chip was used as a nonconductive layer polymer. The chips were melted at a melting temperature of 285°C in individual pressure melters at a ratio of 5% by mass of the conductive layer polymer to 95% by mass of the nonconductive layer polymer, the melted chips were merged into a spinning pack and a spinneret to form a composite, and the composite was ejected from the spinneret so that the conductive layer polymer was equally disposed and exposed at three locations on the fiber surface. In the spinneret used, three types of members, that is, a measuring plate 1, a distribution plate 2, and an ejecting plate 3 were stacked in this order from the top, and a fine channel was formed as shown in Fig. 1. Then, with the oxygen concentration immediately below the spinneret controlled to 1.0% or less, the polymer ejected from the spinneret was cooled with cold air at 18°C and fed with an emulsion oil agent, and then an undrawn yarn was obtained at a speed of 900 m/min. Subsequently, the undrawn yarn was aged for 24 hours in an environment of a temperature of 25°C and a humidity of 70% and then was wound with a drawing machine at a feed roller speed of 135 m/min, at a hot plate temperature of 170°C, and at a drawing roller speed of 400 m/min to obtain a conductive composite fiber of 20 dtex-2 filament having conductive layers exposed at three locations. The obtained conductive composite fiber had a volume specific resistance value of 3.3 log (Ω·cm), an area CV value of conductive layers of 3.1%, and an angle CV value of 2.1%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.31σ, the crimping rate was 2.4%, and the charging potential was also suppressed to -44 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was A and at an acceptable level.

[Example 8]

A conductive composite fiber was obtained under the same conditions as in Example 7, except that the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 3.2 log (Ω·cm), an area CV value of conductive layers of 6.1%, and an angle CV value of 3.1%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance can be suppressed to 0.11σ because the number of locations of the exposed conductive layers was changed to six. The crimping rate was at a level of 2.9%, and the charging potential was suppressed to -31 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was S and at an acceptable level.

[Comparative Example 1]

A nylon-based chip (trade name "CARBOREX NYRON YT-01" manufactured by DIC Corporation) containing 35% by mass of a conductive carbon black was used as a conductive layer polymer, and a nylon 6 chip was used as a nonconductive layer polymer. The chips were melted at a melting temperature of 280°C in individual pressure melters at a ratio of 5% by mass of the conductive layer polymer to 95% by mass of the nonconductive layer polymer, the melted chips were merged into a spinning pack and a spinneret to form a composite, and the composite was ejected from the spinneret so that the conductive layer polymer was equally disposed and exposed at two locations on the fiber surface. In the spinneret used, three types of members, that is, a measuring plate 1, a distribution plate 2, and an ejecting plate 3 were stacked in this order from the top, and a fine channel was formed as shown in Fig. 1. Then, with the oxygen concentration immediately below the spinneret controlled to 1.0% or less, the polymer ejected from the spinneret was cooled with cold air at 18°C and fed with an emulsion oil agent, and then an undrawn yarn was obtained at a speed of 900 m/min. Subsequently, the undrawn yarn was aged for 24 hours in an environment of a temperature of 25°C and a humidity of 70% and then was wound with a drawing machine at a feed roller speed of 150 m/min, at a hot plate temperature of 160°C, and at a drawing roller speed of 450 m/min to obtain a conductive composite fiber of 20 dtex-2 filament having conductive layers exposed at two locations. The obtained conductive composite fiber had a volume specific resistance value of 3.3 log (Ω·cm), an area CV value of conductive layers of 3.1%, and an angle CV value of 2.2%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.42σ, the crimping rate was 2.4%, and the charging potential was as high as -56 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was B and at an unacceptable level.

[Comparative Example 2]

A conductive composite fiber was obtained under the same conditions as in Comparative Example 1, except that a nylon-based chip containing 20% by mass of a conductive carbon black was used as a conductive layer polymer, and the number of locations of the exposed conductive layers was changed to three. The obtained conductive composite fiber had a volume specific resistance value of 4.5 log (Ω·cm), an area CV value of conductive layers of 2.8%, and an angle CV value of 2.0%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.29σ, and the crimping rate was 2.3%. The charging potential was, however, as high as -65 V in the conductive performance evaluation on a carpet because the volume specific resistance was high. The result of the overall evaluation was B and at an unacceptable level.

[Comparative Example 3]

A conductive composite fiber was obtained under the same conditions as in Comparative Example 1, except that the oxygen concentration immediately below the spinneret was changed to 2.0%, and the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 3.2 log (Ω·cm), an area CV value of conductive layers of 11.0%, and an angle CV value of 6.0%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.30σ, the crimping rate was 5.8%, and the charging potential was as high as -57 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was B and at an unacceptable level.

[Comparative Example 4]

A conductive composite fiber was obtained under the same conditions as in Comparative Example 1, except that in the spinneret used, three members, that is, a measuring plate, a distribution plate (no stacked distribution), and an ejecting plate were stacked, and the number of locations of the exposed conductive layers was changed to six. The obtained conductive composite fiber had a volume specific resistance value of 3.2 log (Ω·cm), an area CV value of conductive layers of 13.0%, and an angle CV value of 7.0%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.41σ, the crimping rate was 8.1%, and the charging potential was as high as -70 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was C and at an unacceptable level.

[Comparative Example 5]

A nylon-based chip (trade name "CARBOREX NYRON YT-01" manufactured by DIC Corporation) containing 35% by mass of a conductive carbon black was used as a conductive layer polymer, and a polyester chip was used as a nonconductive layer polymer. The chips were melted at a melting temperature of 285°C in individual pressure melters at a ratio of 5% by mass of the conductive layer polymer to 95% by mass of the nonconductive layer polymer, the melted chips were merged into a spinning pack and a spinneret to form a composite, and the composite was ejected from the spinneret so that the conductive layer polymer was equally disposed and exposed at six locations on the fiber surface. In the spinneret used, three members, that is, a measuring plate, a distribution plate (no stacked distribution), and an ejecting plate were stacked. Then, with the oxygen concentration immediately below the spinneret controlled to 1.0% or less, the polymer ejected from the spinneret was cooled with cold air at 18°C and fed with an emulsion oil agent, and then an undrawn yarn was obtained at a speed of 900 m/min. Subsequently, the undrawn yarn was aged for 24 hours in an environment of a temperature of 25°C and a humidity of 70% and then was wound with a drawing machine at a feed roller speed of 135 m/min, at a hot plate temperature of 170°C, and at a drawing roller speed of 400 m/min to obtain a conductive composite fiber of 20 dtex-2 filament having conductive layers exposed at six locations. The obtained conductive composite fiber had a volume specific resistance value of 3.3 log (Ω·cm), an area CV value of conductive layers of 12.9%, and an angle CV value of 6.9%. As a result of the evaluation using the obtained conductive composite fiber, the variation in the surface specific resistance was 0.37σ, the crimping rate was 7.9%, and the charging potential was as high as -66 V in the conductive performance evaluation on a carpet. The result of the overall evaluation was C and at an unacceptable level.

[Table 1-1]

	Unit	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Example 8
Conductive layer polymer		Polyamide	Polyamide	Polyamide	Polyamide	Polyamide	Polyamide	Polyamide	Polyamide
Nonconductive layer polymer		Polyamide	Polyamide	Polyamide	Polyamide	Polyamide	Polyamide	Polyester	Polyester
Number of locations of exposed conductive layers	(Location)	3	6	6	6	9	12	3	6
Average of volume specific resistance	(log(Ω·cm))	3.3	3.5	3.2	1.9	2.8	2.5	3.3	3.2
Area CV of conductive layers	(%)	3.0	6.1	6.0	6.1	6.7	8.2	3.1	6.1
Angle CV	(%)	2.0	3.1	3.0	4.9	3.3	3.5	2.1	3.1
Occupancy rate of conductive layers	(%)	5	3	5	5	7	10	5	5
Variation in surface specific resistance	(σ)	0.30	0.10	0.10	0.12	0.08	0.06	0.31	0.11
Crimping rate	(%)	2.3	2.8	2.9	4.7	3.3	4.9	2.4	2.9
Carpet performance		A	S	S	A	S	A	A	S
Overall evaluation		A	S	S	A	S	A	A	S

[Table 1-2]

	Unit	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5
Conductive layer polymer	-	Polyamide	Polyamide	Polyamide	Polyamide	Polyamide
Nonconductive layer polymer	-	Polyamide	Polyamide	Polyamide	Polyamide	Polyester
Number of locations of exposed conductive layers	(Location)	2	3	6	6	6
Average of volume specific resistance	(log(Ω·cm))	3.3	4.5	3.2	3.2	3.3
Area CV of conductive layers	(%)	3.1	2.8	11.0	13.0	12.9
Angle CV	(%)	2.2	2.0	6.0	7.0	6.9
Occupancy rate of conductive layers	(%)	5	5	5	5	5
Variation in surface specific resistance	(σ)	0.42	0.29	0.30	0.41	0.37
Crimping rate	(%)	2.4	2.3	5.8	8.1	7.9
Carpet performance	-	B	C	B	C	C
Overall evaluation	-	B	B	B	C	C

DESCRIPTION OF REFERENCE SIGNS

1:: Measuring plate
2:: Distribution plate
3:: Ejecting plate
4:: Measuring groove A
5:: Measuring groove B
6:: Ejecting hole
7:: Conductive layer
8:: Nonconductive layer

Claims

A conductive composite fiber comprising:
a polymer as conductive layers, the polymer containing a polyamide resin containing a conductive carbon black; and

a thermoplastic resin as a nonconductive layer,

wherein the conductive layers are exposed at three or more locations on an outside surface of the conductive composite fiber in a fiber cross section, a coefficient of variation (CV%) in area of the conductive layers in a fiber cross section is 10% or less, and the conductive composite fiber has an average value of a volume specific resistance of 4 log (Ω·cm) or less.
The conductive composite fiber according to claim 1, wherein a CV% of angles formed by neighboring line segments each connecting a middle point of an exposed portion of each of the conductive layers on the outside surface of the conductive composite fiber in a fiber cross section and a center point of the fiber cross section is 5% or less.
The conductive composite fiber according to claim 1 or 2, wherein the thermoplastic resin contains a polyamide or a polyester.