Conductive thermoplastic sheath/core filaments having a reflectivity greater than 8 percent in the undelustered filament and fiber blends containing at least some of said conductive filaments. The sheath/core filament employs as a core a thermoplastic polymer having dispersed therein a material selected from the group consisting of zinc oxide, cuprous iodide, colloidal silver and colloidal graphite. The conductive filament when blended with nonconductive filaments is found to have utility as face yarns in pile fabrics.

This invention relates to conductive filaments and more specifically to 
conductive thermoplastic continuous filaments having a color suitable for 
use in textile applications. 
Small percentages of conductive fibers in a blend with organic fibers have 
the propensity of dissipating electrostatic charges. In general, these 
fibers must have a resistance of less than 10.sup.9 ohms/inch at a 
potential of 2 kilovolts direct current. The electrostatic dissipating 
capability of the fibers is achieved even when these fibers fail to 
provide a continuous electrical path, either as the result of 
insufficiency in amount or as the result of being highly dispersed in the 
blend. It is theorized that the conductive fibers dissipate the static 
fields by charge delocalization through a smearing of the fields. 
Conductive thermoplastic continuous filaments are known to the art, such 
filaments usually employing conductive surface coatings bonded to a 
filament substrate. While the carbon black and elemental metals employed 
in such surface coatings produce a high degree of conductivity in 
thermoplastic filaments, the intense coloration of these materials 
detracts from their use in textile applications. Representative of surface 
coated conductive thermoplastic filaments employing carbon black or 
elemental metals as the conductive element is U.S. Pat. No. 3,582,445. 
An alternative to surface coatings has been set forth in British Pat. No. 
1,393,234, wherein a sheath/core filament is set forth, the core of which 
comprises electrically conductive carbon black dispersed in a 
thermoplastic synthetic polymer. The coloration of the conductive material 
may thereby be reduced by the sheath itself as well as by delustrants 
added to the polymeric material comprising the sheath. Despite the 
improvements obtained in a sheath/core structure, the coloration of a 
product employing carbon black as the conductive material is still such as 
to exhibit a reflectivity of less than 8 percent in the undelustered and 
heavily sheathed filament. 
The dark coloration of the conductive filaments of the prior art 
necessitates the presence of at least one conductive filament in each yarn 
filament bundle in the visible yarns of most fabric constructions. In 
order to achieve antistatic effects, not every filament yarn bundle of a 
fabric need contain a conductive filament. However, if identical yarns are 
not employed, undesirable patterns are visable in the fabric when 
employing the dark colored conductive filaments of the prior art. 
It is therefore an object of this invention to provide a conductive 
sheath/core filament having a resistance of less than 10.sup.9 ohms/inch 
at a potential of 2 kilovolts D.C. and an undelustered reflectivity 
greater than 8 percent. 
It is a further object of this invention to provide a conductive 
sheath/core filament having a resistance of less than 10.sup.9 ohms/inch 
at a potential of 2 kilovolts D.C. and an undelustered reflectivity 
greater than 8 percent wherein the core comprises the major portion of the 
sheath/core cross section. 
It is another object of this invention to provide a filament bundle of 
conductive and nonconductive filaments and fabric constructions employing 
said filament bundle wherein the conductive filament does not detract from 
the aesthetics of the nonconductive filaments. 
It is still another object of this invention to provide a process for the 
preparation of a conductive sheath/core filament having a resistance of 
less than 10.sup.9 ohms/inch at a potential of 2 kilovolts D.C. and an 
undelustered reflectivity greater than 8 percent. 
These and other objects of the invention will become more apparent from the 
following detailed description. 
In accordance with this invention, it has now been discovered that a 
sheath/core conductive filament having a resistance of less than 10.sup.9 
ohms/inch at a potential of 2 kilovolts and a reflectivity greater than 8 
percent may be obtained by employing as the core a thermoplastic polymer 
having dispersed therein a material selected from the group consisting of 
zinc oxide, cuprous iodide, colloidal silver and colloidal graphite. The 
conductive filament of this invention employs as a sheath material a 
compatable fiber forming thermoplastic polymer. preferably, the sheath 
material is a polymer selected from the group consisting of polyamides, 
polyesters, and polyolefins. Preferably, the thermoplastic core material 
is a polyolefin such as polyethylene. The sheath material, which makes up 
a major percentage of the sheath/core cross sectional area, is most 
preferably a sheath material selected from the group consisting of nylon 
6, nylon 66 and poly(ethylene terephthalate), and polypropylene. 
The extrusion technique employed is a conventional sheath/core extrusion 
technique such as is set forth in U.S. Pat. Nos. 2,936,482 and 2,989,798, 
wherein a multicomponent filament is formed by jetting one or more 
core-forming components into radially converging flow of sheath-forming 
component and extruding the combination with the sheath-forming component 
surrounding the core-forming component. 
The core component may be compounded by blending the conductive ingredient 
with a thermoplastic polymer having a lower melting point than the sheath 
polymer so as to permit drawing of the composite structure without 
destroying the continuity and hence the conductivity of the core. The 
conductive component of the core preferably has a particle size small 
enough to effect a thorough dispersion in the core polymer, the particle 
surface characteristics being irregular or porous so as to expose maximum 
surface area. Adequate dispersion of the conductive component in the host 
polymer is required in order to achieve maximum conductivity. The 
dispersing of the conductive material may be accomplished by mixing a 
blend of conductive material and molten polymer. For the textile 
application contemplated herein, the conductive filament may be provided 
in the form of continuous filaments, staple yarn, blended or plied yarns 
utilizing either continuous or staple length conductive filaments. The 
fiber is preferably of such diameter as to provide the desired simulation 
of conventional textile fiber characteristics, such as flexibility, 
crimpability, abrasion resistance, etc., range in size from 2 to 20 
denier. 
The following specific examples are given for purposes of illustration and 
should not be considered as limiting the spirit or scope of this invention 
.

EXAMPLE I 
A core material for a sheath/core conductive filament is prepared by 
charging a mixer such as a Braybender plasticorder marketed by Braybender 
Instruments, Incorporated of South Hackensack, New Jersey, with 1000 grams 
of polyethylene having a melt index of 12. 430 grams of carbon black is 
then added, employing a mixing time of 15 minutes at a temperature of 190 
degrees centigrade and a speed of 60 RPM. The graphite and polyethylene 
core material is then dried under vacuum for 24 hours at 70 degrees 
centigrade. Standard sheath/core spinning equipment is then employed to 
extrude circular cross-section sheath/core filaments, with the sheath 
material being polyethylene terephthalate having an intrinsic viscosity of 
0.67. The sheath/core filamentary material which is extruded under a 
nitrogen blanket is taken up at a speed of 1000 feet per minute (f.p.m.) 
so as to produce a filament bundle having a total denier of 210. 
EXAMPLE II 
The process of Example 1 is repeated except that a 40% by weight dispersion 
of graphite in polyethylene having a melt index of 12 is employed as a 
core material. 
EXAMPLE III 
A 240 mililiter Braybender plasticorder is charged with 1000 grams of 
polyethylene having a melt index of 12 and sufficient cuprous iodide to 
result in a dispersion of 83% by weight cuprous iodide. The dispersion is 
mixed in the Braybender plasticorder for a mixing time of 15 minutes at a 
speed of 60 RPM and a temperature of 190 degrees centigrade. The core 
material is then extruded through standard sheath/core extrusion equipment 
employing, as the sheath material, polyethylene terephthalate having an 
intrinsic viscosity of 0.67. The product is extruded under a nitrogen 
blanket and taken up at a speed of 2100 f.p.m. so as to produce a product 
having a total denier of 200. 
EXAMPLE IV 
The process of Example III is repeated except that zinc oxide is 
substituted for cuprous iodide. 
EXAMPLE V 
The process of Example III is repeated except that colloidal silver is 
substituted for cuprous iodide. 
The light reflectance which is a measure of whiteness of each of the 
examples is measured with a standard photoelectric reflection meter 
employing a barium sulfate ceramic tile as a reference. Monofilament 
samples are wound on a black mirror card using 8 to 10 layers of fiber. 
The mirror card is then inserted into a 3 centimeter slot opening in the 
photoelectric reflection meter. Ten measurements are then taken from each 
of the cards and an average value recorded. 
To determine the resistance of each of the samples, the sheath is dissolved 
away and the resistivity determined with a low voltage ohm meter. The 
filament bundle sample, usually about 3 filaments, 2 inches in length, is 
provided with silver paint electrodes at either extremity and a free 
filament bundle is clamped between the electrodes of the test equipment. 
The volume resistivity is then determined according to the formula, volume 
resistivity=r(A/L) wherein r is the resistance in ohms, A is the 
cross-sectional area of the sample and L is the length of the sample 
bundle. 
Values for density of the sheath/core fiber, conductivity of the dry powder 
conductive material, conductivity of the conductive material in 
polyethylne, reflectivity and static protection in carpet are given for 
each of the examples in the following table: 
__________________________________________________________________________ 
Density in 
Conductive Core grams per 
Conductivity 
Conductivity of Com- 
Reflec- 
Example No. 
Material Classification 
c.c. Dry Powder 
pounded mat'l in 
tivity 
__________________________________________________________________________ 
I Control Carbon 
Semi-conductor 
1.0 10.sup.-1 ohm-cm 
50 ohm-cm 7% 
Black at 30% conc. 
II Graphite Semi-conductor 
1.56 10.sup.-2 ohm-cm 
70 ohm-cm 11% 
at 40% 
III Cuprous Iodide 
Conductivity de- 
Dependent on 
pendent on 1.sub.2 conc. 
5.6 1.sub.2 concentra- 
200 ohm-cm 31% 
tion at 80% 
IV Electrically 
Semi-conductor 
5.62 200 ohm-cm 
2000 ohm-cm 
57% 
Conductive at 83% 
Zinc oxide 
V Colloidal Silver 
Conductor 10.0 Below .01 
.01 ohm-cm 24% 
ohm-cm at 65% 
__________________________________________________________________________ 
In order to evaluate visability and conductivity of conductive sheath/core 
filaments in textile applications, the following specific carpet 
structures are set forth: 
EXAMPLE VI 
A level loop carpet is prepared by tufting 1300 denier nylon yarn into a 10 
ounce per square yard jute backing with a 5/32 gauge level loop machine 
wherein every eighth feed yarn contains one end of the conductive filament 
of Example I. The tufted product has a 5/32 inch pile height and a pile 
weight of 20 ounces per square yard. The tufted product is then dyed with 
the following dye bath: 
0.33 grams per liter of Irgasol DA dispersing agent 
0.08 grams per liter of aqueous ammonia, and 
1% by weight, based on the weight of the fiber being dyed, of Irgalan Gray 
BL 
The gray dyed carpet is then oven dried at temperatures not in excess of 
240.degree. F. 
The product is found to have an unacceptable appearance, the conductive 
ends in every eighth row being clearly visible giving the appearance of 
warp streaks. 
EXAMPLE VII 
The process of Example VI was repeated except that the conductive filament 
of Example II was employed. The dyed end product was found to be 
acceptable due to the reduced visibility of the conductive filaments 
providing an acceptable color merger with the dyed face yarns. 
Each of the carpet samples were tested for static electricity control in an 
atmosphere control room having a temperature maintained at approximately 
70 degrees Fahrenheit and a relative humidity of approximately 20 percent. 
The tests are conducted to simulate a person walking across the carpet and 
the electrostatic potential generated was measured. In all cases, static 
protection was found to be achieved. 
Several theories have been advanced by various investigators on the source 
and nature of electrostatic phenomenon. One of the earliest and still 
supported by some investigators is that the phenomenon is capacitative in 
nature whereby the material serves as a storage medium for electrical 
charges induced or generated within the material by external stimuli. In 
this sense, the charge densities developed within the fibrous material 
would be related to the specific inductive capacity or dielectric constant 
of the material which in turn would relate to the mass specific resistance 
of the material and to the degree of electrical breakdown at the 
material-air interface.