Electrically-conductive textile filaments

Abstract

 Electrically-conductive filaments containing an inner portion comprising a synthetic polymer which is coated on the surface with a substantially transparent electrically-conductive metal powder having specific average particle sizes and comprising antimony oxide and tin oxide. The filaments can have a circular cross-sectional profile or an asymmetrical cross-sectional profile. Procedures for preparing the electrically-conductive filaments are disclosed therein.

Description

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0001] This invention relates to electrically-conductive textile fibers which find particular application in the construction of antistatic fabrics of various kinds.

B. Description of the Prior Art

[0002] The accumulation of static electricity as a result of the utilization of fabrics is a phenomenon which has commanded the attention of the textile industry for some time. The presence of static is a cause not only of annoyance -- (e.g., items of apparel cling to the body and are attracted to other garments; fine particles of lint and dust are attracted to upholstery fabrics, thereby increasing the frequency of required cleaning; one experiences a jolt or shock upon touching a metal doorknob after walking across a carpet) -- but also fo danger (e.g., the discharge of static electricity can result in sparks capable of igniting flammable mixtures such as ether/air, which are commonly found in hospitals, especially in operating rooms). All of these effects are accentuated in atmospheres of low relative humidity.

[0003] The term "fiber" as used herein includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple). The term "yarn" as used herein means a continuous strand of fibers.

[0004] One procedure for preventing the undesirable buildup of static electricity involves the utilization of conductive filaments which have been coated on the surface with electrically conductive carbon black particles in combination with natural fibers or fibers made from synthetic polymers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, which readily dissipates the static charges as they are generated. Representative of such a procedure is disclosed in United States Patent Nos. 3,823,035 and 4,255,487, which are owned by the assignee of the present invention and are hereby incorporated by reference.

[0005] Although the above-described procedure has been successful in a number of applications, certain problems remain. For instance, fibers coated with carbon black have a dark color, i.e., black or grey, which impairs the color tone of the fibers. When they are combined with fibers having a color lighter, the appearance of the resulting fabricated structure is impaired.

[0006] Another procedure for preventing the buildup of static electricity involves the use of conductive filaments having an integral sheath and core wherein the core contains electrically conductive carbon black particles. Although the color of the base tone of these filaments is somewhat lighter than carbon coated filaments, fabricated structures containing these filaments can still be aesthetically unacceptable in many applications. Furthermore, the filaments are somewhat limited in their utility; vis, they are not suitable in applications requiring very low resistance and are more expensive and difficult to manufacture than carbon coated filaments.

[0007] Thus, a need exists for electrically-conductive textile filament which are economical, easy to manufacture, and have aesthetically pleasing qualities.

SUMMARY OF THE INVENTION

[0008] The present invention relates to electrically-conductive filaments containing an inner portion comprising a synthetic polymer which is coated on the surface with a substantially transparent electrically-conductive metal oxide powder comprising antimony oxide (Sb₂O₃, Sb₂O₅, or mixtures thereof), and tin oxide (SnO, SnO₂ or mixtures thereof).

[0009] Electrically-conductive filaments coated with the transparent, conductive metal oxide powder are economical, easy to manufacture, have excellent antistatic properties, and have aesthetically pleasing properties, in that the color of the synthetic polymer is not impaired. In addition, the filaments can have either a circular or asymmetrical cross-sectional profile.

[0010] The electrically conductive filaments of the present invention are preferably prepared using either orifice or roller coating procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

FIGURE 1 represents a cross-section of a fiber having one-sided asymmetry.

FIGURE 2 represents a cross-section of a fiber having two-sided asymmetry.

FIGURE 3 represents a cross-section of a fiber which comprises an outer polymeric coating surrounding the conductive coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The electrically-conductive, transparent composition of the present invention comprises the following ingredients:

(A) a first powder containing at least 25 weight percent based on the total weight of the composition, having an average particle size in the range of from about at least 0.5µm to les than 2.0µm, and comprising antimony oxide and tin oxide; and,

(B) a second powder containing less than 75 weight percent based on the total weight of the composition, having an average particle size of less than 0.5µm, and comprising antimony oxide and tin oxide.

[0013] The amount of antimony oxide present in the electrically-conductive transparent composition will generally be an amount in the range of from about 1 to aout 6 weight percent and, more preferably, from about 1 to about 2 weight percent based on the total weight of antimony oxide and tin oxide in the composition.

[0014] Surprisingly, the particle size of the powder is such that conductive filaments coated therewith have a resistance which is preferably not more than about 10⁹ ohms/cm, while at the same time the filaments exhibit sufficient transparency such that their base color and dyeability are not substantially impaired. Furthermore, the powder exhibits excellent dispersibility in suitable carrier fluids used to coat and produce the electrically-­conductive filaments.

[0015] A preferred first powder comprises at least 94% by weight of particles having a particle size of less than 2.0µm.

[0016] Preferably, the first powder has an average particle size in the range of from about 0.5 to about 0.7µm and, more preferably, an average particle size of 0.5µm. The term "particle size" as used herein means the average particle diameter of the individual particles as measured by Fisher Sub Sieve size.

[0017] Preferably, the electrically-conductive, transparent composition of the present invention comprises a powder consisting essentially of antimony oxide and tin oxide a particle size of about 0.5µm, and the antimony oxide is present in an amount of about 1 percent based on the total weight of antimony oxide and tin oxide in the composition.

[0018] The electrically-conductive, transparent composition of the invention can be prepared using various procedures known to persons skilled in the art. One such procedure comprises forming a powdery mixture containing desired amounts of antimony oxide and tin oxide, firing the resulting mixture to form the conductive composition, and grinding the conductive to the desired particle size. Another procedure involves precipitating an admixture of antimony oxide and tin oxide from solution.

[0019] Examples of synthetic polymers which are suitable for use in the invention include those polymers which are capable of being processed into shaped articles, i.e., fibers, filaments, yarns, and various textile products. For example, homopolymers of olefins such as low density polyethylene, high-density polyethylene, polypropylene, copolymers of olefins with other ethylenically unsaturated monomers such as ethylene-propylene copolymer, ethylenebutene copolymer, ethylene-vinyl acetate copolymer, styrene-butadiene copolymer, acrylonitrile-styrene-­butadiene copolymer and the like find application in the present invention.

[0020] Polyamides find particular application in the present invention. Examples of such polyamides include homopolyamides and copolyamides which are obtained by the polymerization of lactam or aminocarboxylic acid or a copolymerization product of diamine and dicarboxylic acid.

[0021] Typical polyamides include nylon 6, nylon 66, nylon 6,10, nylon 6,12, nylon 11, nylon 12, and copolymers thereof or mixtures thereof. Polyamides can be also copolymers of nylon 6 or nylon 66 and a nylon salt obtained by reacting a dicarboxylic acid component such as terephthalic acid, isophthalic acid, adipic acid and sebacic acid with a diamine such as hexamethylenediamine, methaxylenediamine, and 1,4-bisaminomethylcyclohexane.

[0022] Polyester fibers also find particular application in the present invention. The preferred polyesters are the linear terephthalate polyesters, i.e., polyesters of a glycol containing from 2 to 20 carbon atoms and a dicarboxylic acid component comprising at least about 75% terephthalic acid. The remainder, if any, of the dicarboxylic acid component may be any suitable dicarboxylic acid such as sebacic acid, adipic acid, isophthalic acid, sulfonyl-4,4-dibenzoic acid, or 2,8-di-benzofurandicarboxyl­ic acid. Examples of linear terephthalate polyesters which may be employed include poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene terephthalate/5-chloroisophthalate)-­(85/15), poly(ethyleneterephthalate/5-[sodium sulfo]-­isophthalate) (97/3), poly(cyclohexane-1,4,-dimethylene terephthalate/hexahydroterephthalate) (75/25).

[0023] Polyacrylonitrile homopolymers and copolymers can be utilized in the present invention. The term "polyacrylonitrile" as used herein means a synthetic polymer composed of at least 85 percent by weight acrylonitrile monomer units (-CH₂-

-).

Up to 15 percent of the polymer can be comprised of a vinyl monomer which is copolymerizable with acrylonitrile such as methyl acrylate, methyl methacrylate, vinyl acetate, and vinyl derivatives containing sulfo or carboxyl groups.

[0024] The electrically conductive powder is preferably applied to the surface of the filaments utilizing a binder. Preferred binders include the same synthetic polymers from which the filaments are prepared, i.e., polyolefins, polyamides, polyesters, and polyethers.

[0025] The filaments of the present invention can have either a circular cross-sectional profile or an asymmetrical cross-sectional profile.

[0026] The asymmetry of the filaments of the invention is determined by measuring their eccentricity (E). Eccentricity (E) is measured by the following equation:

wherein T_max is the maximum thickness of the filaments and T_min is the minimum thickness of the coating of the filaments. For filaments having one-sided asymmetry, T_min is a positive integer that is substantially less than T_max. For filaments having two-sided asymmetry, T_min will be a positive integer that is larger than the value of T_min for filaments having a one-sided asymmetrical profile.

[0027] When the filaments of the invention have an asymmetrical cross-sectional profile, both one-sided and two-sided, the eccentricity (E) of the filaments is preferably an amount in the range of from about 0.3 to about 0.99 and, more preferably, from about 0.6 to about 0.9.

[0028] Now referring to FIGURE 1, a preferred filament having a one-sided asymmetrical cross-sectional profile is shown. The filament comprises a polymeric substrate (2) surrounded by an electroconductive coating (4). T_max is determined by measuring in the filament at its portion of greatest thickness the distance from outside of the polymeric substrate (6) to inside of the electroconductive powder (8). T_min is determined in the same manner. The distance of T_min will be substantially less than T_max. In this filament, the asymmetry is due primarily to an uneven coating of the electrically-conductive powder (8) on one side of the filament.

[0029] Another preferred filament has a two-sided asymmetrical cross-sectional profile, as shown in FIGURE 2. The filament comprises a polymeric substrate (10) surrounded by an electrically-conductive coating(12). T_max is measured in the same way as the filament at its portion of greatest thickness, the distance from the outside of the polymeric substrate (14) to the inside of the electroconductive powder (16). T_min is determined in the same manner as the filament of FIGURE 1 by measuring the distance of minimum thickness from the outside of the polymeric substrate (18) to the inside of the electroconductive powder. T_min will generally have a greater value for filaments having a two-sided asymmetrical cross-sectional profile than filaments having a one-sided asymmetrical cross-sectional profile. In this filament, the asymmetry is due primarily to an uneven coating of the electroconductive powder (12) on two sides of the filament.

[0030] A particularly desirable feature of the filaments illustrated in FIGURES 1 and 2 is that they are self-crimping when heated, such as by contacting the filaments with steam.

[0031] The filaments of the invention can have a wide range of deniers. Filaments, particularly of polyamides such as nylon 6, having a denier/filament in the range of from about 5 and 50 find particular application in many apparel and floor covering applications.

[0032] The fibers preferably have an electrical resistance in the range of from about 10⁴ to about 10⁹ ohms/cm. Fibers having this amount of electrical resistance are particularly suitable for employment in a wide variety of fabrics for preventing the accumulation of high charges of static electricity while presenting no appreciable electrocution hazard.

[0033] The amount of electrically-conductive powder coated on the surface of the filament will vary over a wide range with no limitation. The greater the quantity, the higher the conductivity of the filaments. If too much is applied, however, the physical properties of the filaments can be adversely affected. If very small amounts are applied, satisfactory electrical conductivity properties will not be obtained. Generally, the filaments will contain from about 1 to about 30 weight percent of powder based on the weight of the synthetic polymer. Furthermore, the resulting electrically-conductive filaments will have a powder coating thickness of from about 0.5 to about 10µm.

[0034] The coating of the electrically-conductive powder on the surface of the filamentary polymer substrate is preferably characterized by the existence of a discrete, independent phase of electrically conductive particles suffused into a non-conductive filamentary polymer substrate. When the polymer substrate is of substantially circular configuration, it has been found of especial advantage if the annular region of suffused electrically-­conductive particles extends perpendicularly inwardly from the periphery of the filament up to a distance equal to about 1/10 the radius of the filament. Under such conditions, the physical properties of the suffused filamentary substrate still closely approximate those of the unmodified filamentary substrate while the conductivity thereof has been strikingly increased. For cross-sectional configurations other than circular (e.g., trilobal, square, rectangular, etc.), the annular region most advantageously extends perpendicularly inwardly from the periphery of the filament up to a distance equal to about 1/10 the radius of a circle inscribed within the cross-sectional perimeter of the filament.

[0035] The electrically-conductive textile fiber of the present invention may be prepared for the filamentary polymer substrates using special techniques, the most satisfactory of which comprehend applying to the filamentary polymer substrate a disperson of the finely divided, electrically-conductive material in a liquid, preferably containing a binder, which is a good solvent for the substrate, but does not react with or dissolve the electrically-conductive material.

[0036] A combination of such liquids may be used if desired. The chosen concentration of electrically-conductive material in the solvent system is dependent upon the desired fiber conductivity and is limited by the viscosity of the dispersion. (Dispersions which are either too viscous or not viscous enough are difficultly applied when certain methods of application are expedient.)

[0037] Application of this dispersion to the filamentary substrate may be by padding, painting, spraying, dipping, rolling, printing, or the like. If desired for viscosity or other purposes, the dispersion may contain dissolved polymer (binder) of the same nature as that of the substrate, under which conditions the annular suffusion terminates imperceptibly in an integral coating of the same composition. In any event, solvent removal from the substrate must be effected before the structural integrity thereof is appreciably destroyed. This is conveniently accomplished by vaporization (for volatile solvents) and/or washing with a non-solvent (for non-volatile solvents) after the desired degree of solvent penetration has taken place (esp. up to about 1/10 of the radius of substantially cylindrical filamentary substrates). By way of example, when filamentary substrates of polyamides such as nylon 6 are employed, the applicable dispersion usually contains from about 15 to about 45 percent by weight conductive powder based on the total weight of the dispersion in a mixture comprising a solvent of formic acid and acetic acid or water. The solvent may be advantageously removed by continuously passing the dispersion-treated filament through a chamber in which the air is continually exchanged, e.g., by means of air jets and/or means for evacuation.

[0038] The preferred methods of preparing the conductive filaments of the present invention are roller or orifice coating procedures. A preferred roller coating procedure is disclosed in United States Patent 4,704,311, which is assigned to the assignee of the present invention and is hereby incorporated by reference. The use of the roller coating procedure disclosed therein results in a conductive filament having the profile shown in FIGURE 2. The two-sided asymmetry of the filament is due to the grooved, roll-type mix applicator disclosed therein, in which the grooves have a "V" cross section. Furthermore, utilizing the roller coating technique, a coating comprising polymeric material can be subsequently applied to the filament coated with the electrically conductive powder to enhance the durability of the electrically conductive powder on the filament. For instance, in FIGURE 3, a symmetrical filament is illustrated containing a polymeric substrate (22), conductive coating (24) and an outer polymeric coating (26). Asymmetrical filaments, such as those illustrated in FIGURES 1 and 2 can also contain an outer polymeric coating. The outer polymeric coating can comprise the same or different synthetic polymers from which the filaments are prepared.

[0039] Orifice coating techniques find particular application in preparing conductive filaments represented by FIGURE 1 wherein the coating is applied uniformly to the filament to produce a filament having two-sided asymmetry. Other techniques of preparing the conductive filaments are known to persons skilled in the art.

[0040] In certain instances, it is desirable that the electrically-conductive filaments be subjected to heat treatment in order to increase the adhesion of the coating on the filaments. The treatment is referred to as heatsetting. Preferably, the heatsetting operation is accomplished using either Superba equipment, in which case the filaments are subjected to steam at about 130°C-140°C, or Suessen equipment, in which case the filaments are subject to hot air at about 195°C-205°C.

[0041] The electrically-conductive textile fiber of the instant invention finds special utility in the production of fabrics, the use of which avoids the accumulation of high charges of static electricity while presenting no appreciable electrocution hazard. By way of illustration, woven fabrics are produced by standard interweaving of the electrically-conductive fiber of the instant invention with ordinary threads made from natural fibers such as cotton or wool, and/or man-made fibers such as nylon, rayon, acrylic or polyester. The electrically-conductive fiber is preferably present in an amount equal to about 0.05-10.0, and preferably 0.1-5.0 percent by weight of the woven fabric. By way of further illustrating the special utility of the electrically-­conductive filaments of the present invention, pile fabrics can be produced comprising a backing material having pile loops anchored therein. The backing material comprises chain yarns interwoven with filler yarns, as is very well-known in the art. Moreover, the backing material may be constructed from any of the materials commonly employed in the art, such as jute or hemp, among many others. The pile loops comprise a yarn made of a plurality of strands twisted together by standard techniques. At least one such strand comprises the electrically-conductive fiber of the present invention. The balance of the yarn comprises any commonly-employed natural or man-made fibers. As will be understood by one of skill in the art, it may not be necessary that every end of yarn in the pile contain a strand of the electrically-conductive fiber of the present invention. Moreover, more than one strand of the electrically-conductive fiber per end of yarn in the pile may be advantageous, especially under conditions of very low relative humidity. In any event, the electrically-conductive fiber of the present invention is generally present in an amount equal to about 0.05-10.0, and, preferably, 0.1-5.0 percent by weight of the pile fabric.

[0042] Fabrics such as those of the preparation of which is outlined above, when employed in an atmosphere having a relative humidity of 20%, will not generate a static charge above about 3000 volts, which is in proximity to the threshold level of human sensitivity. These fabrics, moreover, when containing an especially-preferred embodiment of the electrically-conductive fiber of the present invention, do not present an electrocution hazard to those contacting them in the event of an accidental and simultaneous contact of such fabrics with a source of essentially unlimited electrical current, as is available from an ordinary electrical outlet, or an electrical appliance short-circuited by insulation failure.

[0043] The following examples will serve to more comprehensively illustrate the principles of the invention, but are not intended to limit the bounds of the invention. All percentages in the Examples are expressed in weight percent unless otherwise specified.

Example I

[0044] An electrically conductive filament was prepared utilizing an electrically conductive coating composition containing the following ingredients:

Coating Composition
Tin Oxide/Antimony Oxide Powder	25%
Nylon 6 Chips	5%
Dispersing Agent	1%
Formic Acid	48%
Water	21%

[0045] The tin oxide/antimony oxide powder contained 99 percent by weight tin oxide and 1% by weight antimony oxide. At least 25.0 weight percent of the powder based on the total weight of the antimony oxide and tin oxide has an average particle size of at least 0.5µm, but less than 1.0µm. The remainder had an average particle size of less than 0.5µm.

[0046] The coating composition was prepared by dispersing the tin oxide/antimony oxide powder, formic acid, water, and dispersing agent using a suitable mill (sandmill, ballmill, etc.). Next, the nylon 6 chips were dissolved in the dispersion. The coating composition was then applied to a 20 denier nylon monofilament using a kissroll or low pressure (-2 PSIG) die with an internal diameter of 75 microns. The formic acid and water was then removed from the monofilament by evaporation using a dryer. The dry, coated, electrically-conductive filament, which had a denier of 24.5, was then wound on a tube. Using a FLUKE 8020 Electrometer, the electrical resistance of the filament was determined to be 1 x 10⁸ ohms/cm.

Example II

[0047] An electrically conductive filament was prepared utilizing a coating composition containing the following ingredients:

Coating Composition
Tin/Antimony Oxide Powder	35.0%
Nylon 6 Chips	4.0%
Dispersing Agent	0.4%
Formic Acid	18.0%
Acetic Acid	40.6%
Water	2.0%

[0048] The tin oxide/antimony oxide powder had the same proportions and particle size as set forth in Example I.

[0049] The coating composition was prepared by predispensing the tin oxide/antimony oxide powder, a dispersing agent, acetic acid, formic acid and water in a high speed disc mixer such as a Cowles mixer. Next the nylon chips were added to the mixture and dissolved. This premix was then pumped through a sandmill to affect total disperson of the tin oxide/antimony oxide particles. A nylon monofilament having a denier of 15 was coated using the coating composition in the same manner as described in Example 1. The resulting filament, which had a denier of 19.5, was measured for electrical resistance. The resistance was determined to be 8 x 10⁷ ohm/cm.

Example III

[0050] An electrically conductive filament was prepared utilizing a coating composition containing the following ingredients:

Coating Composition
Tin/Antimony Oxide	20.0%
Nylon 6 Chips	8.0%
Dispersing Agent	0.2%
Formic Acid	16.0%
Acetic Acid	54.0%
Water	1.8%

[0051] The tin oxide/antimony oxide powder had the same proportions and particle size as set forth in Example I.

[0052] The coating composition was prepared in the same manner as Example II except that one half of the total amount of acetic acid utilized therewith was added to the mixture after the nylon 6 chips were added rather than during the predispersion step as in Example II. The predispersion was then sandmilled in the same manner as Example II. The coating mixture is not a particularly good solvent for nylon 6 and, therefore, is particularly suitable for coating nylon 6 monofilaments having a denier of 7 using the roller coating procedure.

Example IV

[0053] An electrically conductive filament was prepared utilizing a coating composition containing the following ingredients:

Coating Composition
Tin/Antimony Oxide	40.0%
Nylon 6 Chips	0.2%
Dispersing Agent	0.1%
Formic Acid	18.0%
Acetic Acid	39.7%
Water	2.0%

[0054] The coating composition was prepared in the same manner as Example III. A monofilament having a denier of 20 was coated with the composition, which resulted in a monofilament having a denier of 27. The coated monofilament was then overcoated, by means of a kiss roll on dye, using a coating solution having the following ingredients:

Nylon 6 Chips	7%
Formic Acid	28%
Acetic Acid	62%
Water	3%

[0055] The solvent was then removed by drying. The resulting monofilament had a 0.5µm thick overcoat. The monofilament was measured for electrical resistance which was determined to be 5 x 10⁷ ohm/cm.

[0056] This invention is not limited to the above described specific embodiments thereof; it must be understood, therefore, that the detail involved in the descriptions of the specific embodiments is presented for the purpose of illustration only, and reasonable variations and modifications, which will be apparent to those skilled in the art, can be made in this invention without departing from the spirit and scope thereof.

Claims

1. An electrically-conductive filament containing:
(a) a filamentary polymer substrate; and,
(b) an electrically-conductive composition coating the surface of said filament, said composition comprising
(i) a first powder present in an amount of at least 25 weight percent based on the total weight of the composition, having an average particle size in the range of from about at least 0.5µm to least than 2.0µm, and comprising antimony oxide and tin oxide; and,
(ii) a second powder present in an amount of less than 75 weight percent based on the total weight of the composition, having an average particle size of less than 0.5µm, and comprising antimony oxide and tin oxide;
wherein said first and second powders comprise from about 1 to about 6 weight percent antimony oxide based on the total weight of said antimony oxide and tin oxide in said electrically conductive composition.

2. The electrically-conductive filament of Claim 1 wherein said first powder has an average particle size in the range of from about 0.5 to about 0.7µm.

3. The electrically conductive filament of Claim 1 wherein said electrically conductive composition further comprises a binder.

4. The electrically-conductive filament of Claim 1 wherein said first and second powders comprise from about 1 to about 2 percent by weight of said antimony oxide based on the total weight of said antimony oxide and tin oxide percent in said composition.

5. The electrically-conductive filament of Claim 4 wherein said filamentary polymer substrate is selected from the group consisting of polyolefins, polyamides, polyester, polyacrylonitrile, and mixtures thereof.

6. The electrically-conductive filament of Claim 1 wherein said first powder consists essentially of particles having a particle size of 0.5µm.

7. The electrically-conductive filament of Claim 1 wherein said filament is asymmetrical and the eccentricity of said filament is an amount in the range of from about 0.3 to about 0.99.

8. The electrically-conductive filament of Claim 1 wherein said filament has a one-sided asymmetrical cross-sectional profile, and the eccentricity of said filament is an amount in the range of from about 0.6 to about 0.9 and said filament is self crimping.

9. The electrically-conductive filament of Claim 5 wherein said filament has an electrical resistance in the range of from about 10⁴ to about 10⁹ ohms/cm.

10. The electrically-conductive filament of Claim 8 wherein used filament contains from about 1 to about 30% by weight of said conductive composition based on the weight of the synthetic polymer.

11. The electrically-conductive filament of Claim 10 wherein said coating thickness is in the range of from about 0.5µm to about 10µm.

12. The electrically-conductive filament of Claim 1 wherein said powder is suffused as a phase independent of said polymer substrate in an annular region located at the periphery of said filament.

13. The electrically-conductive filament of Claim 10 wherein said coating of said powder extends perpendicularly inwardly from the periphery of said filament up to a distance equal to about 1/10 of the radius of said filament.

14. The electrically-conductive filament of Claim 1 further comprising an outer polymeric coating surrounding said coating of said powder.

15. A carpet containing the electrically conductive filaments of Claim 1.

16. A method of preparing an electrically-conductive filament comprising:
coating the surface of a filamentary polymer substrate with an electrically-conductive composition comprising
(i) a first powder present in an amount of at least 25 weight percent based on the total weight of the composition, having an average particle size in the range of from about at least 0.5µm to less than 2.0µm, and comprising antimony oxide and tine oxide; and,
(ii) a second powder present in an amount of less than 75 weight percent based on the total weight of the composition, having an average particle size of less than 0.5µm, and comprising antimony oxide and tin oxide;
wherein said first and second powders comprise from about 1 to about 6 weight percent antimony oxide based on the total weight of said antimony oxide and tin oxide in said electrically conductive composition.

17. The method recited in Claim 16 wherein said first powder has an average particle size in the range of from about 0.5 to about 0.7µm.

18. The method of Claim 16 wherein said coating is carried out by applying a dispersion of said electrically conductive composition to the surface of the filamentary polymer substrate.

19. The method of Claim 18 wherein said dispersion comprises said electrically-conductive composition, a resin, formic acid, acetic acid and water or acetic acid.

20. The method of Claim 19 wherein said first and second powders are suffused as a phase independent of said polymer substrate in an annular region located at the periphery of said filament.

21. The method of Claim 20 wherein said resin and said filamentary polymer substrate are independently selected from the group consisting of polyolefins, polyamides, polyester, polyacrylonitrile, and mixtures thereof.

22. The method of Claim 16 wherein said first powder consists essentially of particles having a particle size of about 0.5µm.

23. The method of Claim 17 wherein said electrically conductive composition contains from about 1 to 2 percent by weight of said antimony oxide based on the total weight of said antimony oxide and tin oxide percent in said composition.

24. The method of Claim 23 wherein said filament has an electrical resistance in the range of from about 10⁴ to about 10⁹ ohms/cm.

25. The method of Claim 24 wherein said filament contains from about 1 to about 30% by weight of said electrically conductive composition based on the weight of the synthetic polymer.

26. The method of Claim 25 further comprising the step of applying an outer polymeric coating to said filament coated with said electrically conductive composition.

27. The method of Claim 25 further comprising the step of heating the coated filament, having said outer polymeric coating and being coated with said electrically conductive composition.

28. The method recited in Claim 25 wherein said filament is prepared using an orifice coating procedure and said filament has two-sided asymmetry.

29. The method recited in Claim 25 wherein said filament is prepared using a roller coating procedure and said filament has one-sided asymmetry.

Drawing