Antistatic synthetic bicomponent filaments of the core-sheath type have a core of increased electrical conductivity comprising a synthetic polymer in which solid, electrically conductive particles have been dispersed and a sheath of increased conductivity comprising a filament-forming polymer which contains one or more conventional antistats.

DESCRIPTION 
The present invention relates to antistatic, synthetic bicomponent 
filaments of the core-sheath type where not only the core but also the 
sheath shows increased electrical conductivity. 
Core-sheath filaments having an electrically conductive core are already 
known from DE-C-2 337 103. The conductive core of these filaments contains 
finely divided, electrically conducting carbon black in amounts of from 15 
to 50%. The sheath of these filaments is free of dispersed carbon black 
and other conductivity-increasing additions and therefore is electrically 
non-conducting. These known filaments develop an adequate electrical 
conductivity only when a relatively high electric voltage is applied to 
them. For this reason the antistatic effect of these known filaments does 
not meet the high requirements for use for example in clean room clothing. 
Filaments which contain dispersed carbon black over their entire 
cross-section are not only unattractive but also, owing to their low 
strength, difficult to process as textiles and also show inadequate wear 
properties. 
DE-A-1 908 173 discloses electrically conductive polyester filaments which 
contain an addition of paraffin-sulfonates as antistat. This addition and 
hence the electrostatic effect, however, prove to be insufficiently 
resistant to laundering to be used for example for manufacturing clean 
room clothing. The experience is similar with virtually any antistatic 
addition, so that the addition of carbon black or other conductive 
particles to the fiber-forming polymer continues to produce the best 
antistatic effect. 
There is therefore still an urgent need for synthetic filaments which show 
good, wash-resistant electrical conductivity and at the same time have 
good textile processing and wear properties. 
The antistatic, synthetic bicomponent filaments according to the present 
invention have a considerably improved property portfolio compared with 
the known antistatic filaments of the core-sheath type. The antistatic, 
synthetic bicomponent filaments according to the present invention are 
those of the core-filament type where the core shows increased electrical 
conductivity; however, they are distinguished from existing such filaments 
in that their sheath also shows increased electrical conductivity. 
The core and the sheath of the filaments according to the present invention 
contain different conductivity additions. Whereas the core consists of a 
synthetic polymer in which solid, electrically conductive, particles have 
been dispersed, the sheath consists of a filament-forming polymer which 
contains an addition of conventional antistats based on sulfonato- or 
carboxylato-containing organic compounds of low diffusivity in the 
polymer. 
The solid, electrically conductive particles of the core material consist 
preferably of conductive carbon modifications or of conventional 
semiconductor materials. 
Suitable conductive carbon modifications are conductive carbon black or 
graphite. The conductive carbon black used can be for example furnace 
black, oil furnace black or gas black acetylene black, in particular the 
specific, electrically superconductive grades thereof. 
Particular preference is of course given to specific high conductivity 
blacks such as the commercial high conductivity black .sup.(.RTM.) Printex 
XE2 from Degussa, Frankfurt (M). 
Semiconductor materials which are capable if finely divided of imparting 
the desired conductivity to the core material of the filaments according 
to the present invention are for example metal oxides which have been 
doped to be n- or p-conducting. 
Electrically conducting materials based on metal oxides consist of mixed 
oxides where the crystal lattice of the main component contains a small or 
minor amount of an oxide component of a metal having a valence or ionic 
radius which differs from that of the metal of the main lattice. Examples 
of such mixed oxides are nickel oxide, cobalt oxide, iron oxide and 
manganese oxide doped with lithium oxide; zinc oxide doped with aluminum 
oxide; titanium oxide doped with tantalum oxide; bismuth oxide doped with 
barium oxide; iron oxide (Fe.sub.2 O.sub.3) doped with titanium oxide; 
titanium-barium oxide (BaTiO.sub.3) doped with lanthanum oxide or tantalum 
oxide; chromium-lanthanum oxide (LaCrO.sub.3) or manganese-lanthanum oxide 
(LaMnO.sub.3) doped with strontium oxide; and chromium oxide doped with 
manganese oxide. This list is by no means exhaustive. There are many other 
suitable mixed oxides, but it is also possible to use other known 
compounds having electrical semiconductor properties, for example those 
which are based on metal sulfides. A preferred solid semiconductor 
material which in finely divided form is capable of conferring the desired 
electrical conductivity on the core material of the filaments according to 
the present invention is for example antimony- or iodine-doped tin oxide. 
The electrically conductive particles dispersed in the core of the 
electrically conductive filaments according to the present invention have 
an average particle size which for "textile" filament deniers is 
advantageously below 5 .mu.m. Preferably, the conductive particles have an 
average particle size of below 1 .mu.m, in particular below 0.3 .mu.m. 
The amount of conductive particles present in the core polymer depends on 
the conductivity requirements for the filament and on the nature of the 
conductivity addition. 
Conductive carbon modifications are dispersed in the core of the filaments 
according to the present invention in an amount of 5-60% by weight, 
preferably 5-30% by weight, in particular 8-15% by weight, in a finely 
divided form. 
Semiconductor materials, for example the above-mentioned ones based on 
doped metal oxides, are present in the core in an amount of 60-80% by 
weight, preferably 65-75% by weight. 
The antistat present in the sheath of the filaments according to the 
present invention has sulfonate or carboxylate groups, i.e. salts of sulfo 
or carboxyl groups. The nature of the salt-forming metal is in principle 
of minor importance. However, preference is given to sulfonates or 
carboxylates formed with a monovalent or divalent metal, preferably an 
alkali or alkaline earth metal. Of the two salt-forming groups mentioned, 
the sulfonic acid group and hence the sulfonates are preferred. The 
sulfonato- or carboxylato-containing organic compounds should migrate as 
little as possible within the sheath polymer of the filaments according to 
the present invention. One way of minimizing the migration of these 
antistatic additions is to use compounds having a long-chain polyether or 
alkyl moiety of from 8 to 30 carbon atoms in the chain. 
Particular preference is given here to compounds which contain an alkyl 
chain of from 8 to 30, preferably from 12 to 18, carbon atoms. 
Particularly preferred antistats for the sheath polymer of the filaments 
according to the present invention are alkanesulfonates of the 
above-mentioned chain lengths, in particular their sodium or potassium 
salts. 
The polymers used for the core and the sheath of the bicomponent filaments 
according to the present invention can be identical or different. Having 
regard to the functions of core and sheath, it has proved to be 
advantageous to use different materials which can be optimized to the 
desired function Advantageously, the sheath is made of a polymer which 
confers on the bicomponent filament according to the present invention the 
desired textile property, in particular strength and processibility, while 
the core must guarantee the permanent electrical conductivity of the 
material; that is, the core must retain its continuity throughout all 
further processing operations on the filament and it must possess optimal 
carrying capacity for the dispersed solid semiconductor material. It is 
not essential for the core that the polymer be spinnable into filaments on 
its own and therefore this polymer need not be a filament-forming polymer. 
On the other hand, the use of filament-forming polymers for the core 
material is in general advantageous. 
However, it has proved to be very advantageous to use for the core of the 
bicomponent filaments according to the present invention a polymer which 
has a lower melting point than the polymer of the sheath. The melting 
point difference should be at least 20.degree. C., preferably at least 
40.degree. C. 
In a preferred filament material according to the present invention, the 
polymer of the core consists of polyethylene or nylon 6 or of a 
copolyamide or a copolyester whose cocomponents have been selected in a 
conventional manner in such a way that the desired melting point 
difference obtains. Further suitable polymers for the core of the 
filaments according to the present invention are block copolymers having 
rigid and soft segments, e.g. block polyether-esters or other 
polyalkylenes, e.g. relatively low molecular weight polypropylene. 
A suitably material for the sheath of the bicomponent filaments according 
to the present invention, which preferably determines the textile 
properties of the filament material, is in particular a high molecular 
weight polymer, in particular a polyester or polyamide. Particularly 
advantageous properties are possessed by bicomponent filaments according 
to the present invention whose sheath consists of polyesters, preferably 
polyethylene terephthalate. 
The proportion of the volume of the whole filament according to the present 
invention accounted for by the core is from 2 to 50%, preferably from 5 to 
20%. 
The sheath of the antistatic filaments according to the present invention 
may, in addition to the antistat, contain customary amounts of further 
additives which are customary in synthetic fibers, for example 
delusterants or pigments. 
In a preferred embodiment, the sheath cf the filaments according to the 
present invention contains a delusterant whereby the shining through the 
sheath of the core, which may be colored owing to its conductivity 
addition, is prevented or reduced; which is determined by the amount of 
delusterant chosen. 
A preferred delusterant is titanium dioxide, which may ordinarily be 
present in the filament sheath in amounts of from 0.5 to 3% by weight. 
The electrically conductive bicomponent filaments according to the present 
invention are produced by first producing a core material by homogeneously 
mixing a finely divided form or formulation, for example a powder or a 
user-friendly powder formulation in granule or bead form, of one of the 
abovementioned electrically conductive materials into a first polymer 
material, producing a sheath material by homogeneously mixing one of the 
abovementioned antistats based on a sulfonato- or carboxylato-containing 
organic compound with or without further customary additives into a second 
polymer material, which may be identical to the first polymer material, 
and spinning the so pretreated core and sheath materials from a 
conventional spinning arrangement into core-sheath filaments at a volume 
ratio of core to sheath material extruded per unit time of from 2:98 to 
1:1. 
Depending on the jet take-off speed chosen, which today depending on the 
equipment may in general be within the range from a few 100 m/min to about 
8000 m/min, the filaments obtained differ in orientation and hence in 
mechanical properties, for example tensile strength, extensibility and 
initial modulus. At very high spin speeds the filaments as spun already 
have a high degree of orientation and hence good mechanical and textile 
properties. 
Lower spin speeds produce initially less highly oriented, i.e. less strong, 
more extensible filaments which are drawable in a conventional manner in 
order that the mechanical properties required may be instilled. 
The draw ratio employed here is within the range from 5% above the natural 
draw ratio to 95% of the maximum draw ration, preferably within the range 
from 3:1 to 5:1, in particular from 3:1 to 4:1. 
After drawing, the filaments may, if desired, be subjected to a customary 
heat setting treatment, in general a shrinkage of from 0 to 8%, 
preferably, from 0 to 4%, being allowed during heat setting or immediately 
thereafter. 
The drawing and heat setting temperatures are adapted to the processed 
fiber material in a conventional manner. Customarily, the drawing 
temperature is within the range from 40.degree. to 200.degree. C., 
preferably from 40.degree. to 160.degree. C., while the heat setting 
treatment is carried out within the temperature range from 100.degree. to 
240.degree. C. 
Thereafter the filaments thus produced can be further processed into 
textile products in any known manner. For example, the filaments can be 
bundled together to form continuous filament yarns and if desired be 
textured in a conventional manner, for example by air jet texturing, a 
false twist process or by a further draw-texturing operation, or the spun 
filaments can be subjected before or after a texturing operation to, for 
example, a stuffer box crimping operation and be cut into staple fibers, 
which are then spun into yarns. Preference is given to the further 
processing of the electrically conductive filaments according to the 
present invention into continuous filament yarns which are then converted 
into the desired textile products in a conventional manner. The textile 
products formed from the electrically conductive bicomponent filaments 
according to the present invention, for example continuous filament yarns 
in textured or nontextured form and staple fiber yarns but also 
intermediate forms such as filament tows or tundles and also the textile 
sheet materials produced from the filamentary materials, also form part of 
the subject-matter of the present invention. 
The electrically conductive filaments according to the present invention 
surprisingly show good electrical conductivity even at low applied 
voltages, as a consequence of which only significantly smaller electrical 
charge buildups can result than in the case of conventional filaments 
having an electrically conductive core. In addition, the electrical 
conductivity of the filaments according to the present invention is 
significantly more resistant to laundering than that of known filaments 
which have been modified with antistats in a conventional manner The 
particularly advantageous conductivity characteristics of the filaments 
according to the present invention are complemented by excellent textile 
properties. 
The Examples which follow illustrate the production of the electrically 
conductive filaments according to the present invention and demonstrate 
the surprising effect of the basically only slightly electrically 
conductive filament sheath on the antistatic effect of the filament as a 
whole and the very high resistance of this effect to intensive washing.

EXAMPLE 1 
(Filament According to the Present Invention) 
To produce the core material, 10 parts by weight of carbon black 
(.sup.(.RTM.) Printex XE 2 from Degussa) were incorporated at 170.degree. 
C. in a kneader into 100 parts by weight of a low-viscosity polyethylene 
(.sup.(.RTM.) Riblene 1800 V from Enichem). 
To produce the sheath material, 100 parts by weight of polyethylene 
terephthalate, 2 parts by weight of titanium dioxide and 2 parts by weight 
of sodium paraffinsulfonate (.sup.(.RTM.) Hostastat HS 1 from Hoechst AG) 
were mixed at 275.degree. C. in a twin-screw extruder. 
These two components were spun at 265.degree. C. from a 32-hole jet on a 
bicomponent melt spinning unit into core-sheath filaments which were wound 
up at 700 m/min. The core accounted for 10% of the volume. 
The filament was drawn over a 3-godet drawing unit, subjected to a heat 
treatment and wound up: 
1st godet 95.degree. C., 55 m/min 
2nd godet 180.degree. C., 181.5 m/min 
3rd godet 30.degree. C., 176 m/min 
The specific resistance of the filament is listed in the table. 
EXAMPLE 2 
(Conductive Core, Nonconductive Sheath) 
To produce the core material the procedure of Example 1 was followed. 
To produce the sheath material, 100 parts by weight of polyethylene 
terephthalate and 2 parts by weight of titanium dioxide were mixed at 
275.degree. C. in a twin-screw extruder. No antistat was added. 
These two components were used as described in Example 1 to produce a 
core-sheath filament. 
The specific resistance of the filament is listed in the table. 
EXAMPLE 3 
(Monocomponent Filament with Antistatic Finish) 
The antistatically finished sheath material of Example 1 was spun out on 
the same bicomponent unit, but no core material was added, producing a 
monocomponent filament which was drawn as described in Examples 1 and 2. 
The specific resistance of the filament is shown in the table. 
TABLE 
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Specific resistance of filaments pretreated by three 
washes with methanol, three washes with petroleum ether 
and a two-hour extraction with distilled water. The 
measurements were carried out after 24 hours' 
conditioning. 
Specific resistance in megaohm.cm 
65% relative 
20% relative 
humidity humidity 
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Example 1 (filament 
3 1,750 
according to the 
present invention) 
Example 2 (conductive 
2,800 35,000 
core, nonconductive 
sheath) 
Example 3 (anti- 
70,000 105,000 
statically finished 
monocomponent 
filament) 
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