U.S. patent application number 10/680284 was filed with the patent office on 2004-04-29 for conductive soil-repellent core-sheath fiber of high chemical resistance, its preparation and use.
This patent application is currently assigned to Teijin Monofilament Germany GmbH. Invention is credited to Bruning, Hans-Joachim, Hofmann, Herbert.
Application Number | 20040078903 10/680284 |
Document ID | / |
Family ID | 32049587 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040078903 |
Kind Code |
A1 |
Bruning, Hans-Joachim ; et
al. |
April 29, 2004 |
Conductive soil-repellent core-sheath fiber of high chemical
resistance, its preparation and use
Abstract
Conductive soil-repellent core-sheath fiber of high chemical
resistance, its preparation and use Described is a melt-spun fiber
having a core-sheath structure and a high tensile strength whose
core contains a synthetic thermoplastic polymer which is not a
fluoropolymer and whose sheath contains at least one melt-spinnable
fluoropolymer and particles comprising electroconductive material.
The fibers of the invention are useful especially in the form of
monofilaments for producing textile fabrics for industrial
applications
Inventors: |
Bruning, Hans-Joachim;
(Augsburg, DE) ; Hofmann, Herbert; (Konigsbrunn,
DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
Teijin Monofilament Germany
GmbH
|
Family ID: |
32049587 |
Appl. No.: |
10/680284 |
Filed: |
October 7, 2003 |
Current U.S.
Class: |
8/181 |
Current CPC
Class: |
D01F 8/14 20130101; D01F
1/09 20130101; D01F 8/12 20130101 |
Class at
Publication: |
008/181 |
International
Class: |
D06M 013/322 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2002 |
DE |
DE 102 49 585.8 |
Claims
What is claimed is:
1. A melt-spun fiber having a core-sheath structure and a tensile
strength of at least 15 cN/tex whose core contains a synthetic
thermoplastic polymer which is not a fluoropolymer and whose sheath
contains at least one melt-spinnable fluoropolymer and particles
comprising electroconductive material.
2. The melt-spun fiber of claim 1, wherein the synthetic
thermoplastic polymer of the core is a polyamide and especially a
polyester.
3. The melt-spun fiber of claim 2, wherein the polyester is a
polyethylene terephthalate.
4. The melt-spun fiber of claim 2, wherein the polyester is a
liquid-crystalline polyester.
5. The melt-spun fiber of claim 1, wherein the melt-spinnable
fluoropolymer is a copolymer of tetrafluoroethylene with at least
one alpha-olefin, preferably ethylene.
6. The melt-spun fiber of claim 1, wherein the melt-spinnable
fluoropolymer is a polyvinylidene fluoride.
7. The melt-spun fiber of claim 1, wherein the sheath contains up
to 50% by weight and preferably 2 to 15% by weight of
electroconductive particles.
8. The melt-spun fiber of claim 6, wherein the sheath contains
between 2% by weight and 15% by weight and especially between 4% by
weight and 9% by weight of electroconductive particles.
9. The melt-spun fiber of claim 1, wherein the particles comprising
electroconductive material consist of carbon, metals or metal
alloys and are especially carbon black or graphite.
10. The melt-spun fiber of claim 1 which is a filament, especially
a monofilament.
11. A process for preparing the melt-spun core-sheath fiber of
claim 1, comprising the measures of: i) selecting a first polymer
which is a synthetic thermoplastic polymer and not a fluoropolymer
and which has a first melting point, ii) selecting a second polymer
which contains particles comprising electroconductive material and
which is a melt-spinnable fluoropolymer which has a second melting
point at least 20.degree. C. below the first melting point, iii)
coextruding the first polymer and the second polymer through a
heterofilament spinneret at a spinning temperature above the first
melting point to form a bicomponent fiber having a core comprising
the first polymer and a sheath comprising the second polymer and
iv) drawing the produced core-sheath filament to increase the
tensile strength.
12. The use of melt-spun core-sheath fibers of claim 1 for
producing industrial wovens.
13. The use of claim 12, wherein the industrial woven is a paper
machine wire, a filter cloth, a screen printing cloth, a conveyor
belt or a reinforcing ply.
Description
[0001] The present invention relates to conductive soil-repellent
core-sheath fibers, especially monofilaments, which are useful in
industrial fabrics in particular.
[0002] It is known that fluoropolymers have good thermal stability,
good chemical resistance and soil-repellent properties. It has
already been attempted to process melt-spinnable fluoropolymers
into fibers, multi- and monofilaments in order that textile fabrics
for industrial applications that have the abovementioned properties
of fluoropolymers may be manufactured therefrom. The disadvantage
with melt-spinnable fluoropolymers is the high creep. Fibers and
filaments formed from this material therefore have only low tensile
strengths and are not shape stable.
[0003] It has also already been tried to combine fluoropolymers
with polymers having good mechanical performance characteristics,
for example with polyethylene terephthalate (hereinafter also
referred to as PET). However, it is to be noted in this context
that fluoropolymers are often incompatible with other polymers in
that they generally do not mix with them. The result is thus
frequently a two-phase mixture in which the fluoropolymers form
three-dimensional islands. The weight fraction of fluoropolymer
which can be added is thus frequently limited, since the boundary
layers of the polymers have only poor adhesion to each other. This
property manifests itself in fibers as a tendency to split.
[0004] Monofilaments composed of PET and random copolymers of
ethylene and tetrafluoroethylene (ETFE) have been commercially
available for years. Frequently, these fibers have a low carboxyl
end group content to stabilize them against hydrolysis and are
stabilized with carbodiimides to cap the carboxyl end groups. The
capping of carboxyl groups by means of carbodiimides is described
for example in EP-A417,717 and EP-A-503,421.
[0005] Industrial fabrics woven from these monofilaments do largely
have the mechanical properties of a PET filament, but combined with
increased hydrolysis resistance and improved soil repellency.
[0006] Because the fluoropolymer fraction is relatively low, the
thermal stability and chemical resistance of these fibers are
substantially equal to the data for pure PET. However, the
increased tendency to split can manifest itself under mechanical
stresses, for example at the beating up of the fell on the weaving
machine.
[0007] Fibers composed of synthetic polymers and woven fabrics
produced therefrom have the disadvantage, however, that they can
become charged up with static electricity as a result of friction.
Conductive fibers for producing textile fabrics, such as wovens for
industrial use, or for other applications, for example brushes,
have long been the goal of numerous developments.
[0008] DE-A-1 98 26 120 discloses a flame-retardant
electroconductive woven fabric which contains electroconductive and
flameproofed nonelectroconductive fibers. The electroconductive
fibers can contain electroconductive particles, such as carbon
black or metal particles, be coated with metal or consist of
electroconductive materials, such as polyanilines. The fiber
materials mentioned are polyester and polyolefins.
[0009] DE-U-86 238 79 discloses yarn for the manufacture of spiral
tapes which is sheathed with a layer of curable polymer. This layer
contains electroconductive carbon. Melamine resins, epoxides,
phenolic resins or polyurethanes are mentioned by way of example as
polymers for the sheath layer.
[0010] DE-A-39 38 414 describes high-strength woven fabric which is
formed from artificial fibers, these being incorporated in the form
of electroconductive fibers in the warp and the weft, and which
contains nonelectroconductive fibers as well. The electroconductive
fibers consist of polyolefins and contain graphite or carbon
black.
[0011] EP-A-160,320 describes hairbrush core-sheath monofilaments
composed of selected polymers. The core contains nylon or
polyesters which comprise at least 60% by weight of polybutylene
terephthalate units. The sheath contains specific nylon grades or
copolyetherester.
[0012] DE-U-86/06334 discloses core-sheath fibers whose core
consists of thermoplastic polymer, preferably of polyamide, and
whose sheath consists of electroconductive polymer, preferably of
polyamide, which contains embedded carbon black or metals.
[0013] JP-A-07/278,956 describes electroconductive copolyesters
which mainly contain polybutylene terephthalate units and which are
doped with carbon black. It also describes core-sheath fibers
composed of this material which have a core which consists of
aromatic polyester.
[0014] WO-A-98/14,647 discloses electroconductive heterofilaments
which can be configured as core-sheath fibers for example. Examples
described of core and sheath polymers are PET and other polyesters
or PET/nylon.
[0015] WO-A-01/20,076 discloses nonwovens having a high dielectric
constant. Mixtures of polyvinylidene fluoride and polypropylene are
proposed as fiber material. The products formed therefrom are
notable for a long half-life for electrostatic charges and can be
used as electrostatic filters.
[0016] U.S. Pat. No. 6,085,061 describes a brush for cleaning
electrostatically charged surfaces. The fiber materials used can be
core-sheath fibers whose core is electroconductive and whose sheath
consists of polyvinylidene fluoride.
[0017] DE-A44 12 396 discloses melt-spun undrawn
nonelectroconductive fibers having a core-sheath structure whose
sheath contains fluoropolymers. The core polymer used is
polycarbonate. This fiber is used as an optical fiber and is
unsuitable for industrial textiles, such as industrial wovens for
example, on account of its low strengths. Moreover, the critical
properties with an optical fiber are high reflection at the
boundary layer and very low attenuation of the electromagnetic
wave. Both these properties can only be achieved through use of a
high-purity coating.
[0018] JP-A-2001-127,218 describes a semiconducting fiber composed
of a fluoropolymer which contains carbon black. This fiber does not
have a core-sheath structure and is used for manufacturing
nonwovens, for example by the melt-blow process. The fiber has not
been drawn.
[0019] It is an object of the present invention to combine the
performance advantages of the materials known for fiber production
without having to incur the disadvantages associated with the use
of the individual materials.
[0020] A person skilled in the art knows that bonding problems are
normal at the boundary layer between two polymers. This holds
especially for the use of known poor-bonding fluoropolymers with
other polymers. It has been determined that, surprisingly, the use
of a fluoropolymer which is doped with electroconductive particles
provides very good bonding to the polymer core.
[0021] It is thus a further object of the present invention to
provide core-sheath fibers which possess good bonding between the
individual layers.
[0022] The present invention thus provides fibers, especially
monofilaments, which combine antistatic properties with high
chemical and thermal stability and good mechanical shape stability
and also high tensile strength.
[0023] This invention is a melt-spun fiber having a core-sheath
structure and a tensile strength of at least 15 cN/tex whose core
contains a synthetic thermoplastic polymer which is not a
fluoropolymer and whose sheath contains at least one melt-spinnable
fluoropolymer and particles comprising electroconductive
material.
[0024] The synthetic thermoplastic polymers forming the core are
freely chooseable, as long as they are melt spinnable and provide
the fiber with the properties desired for the particular intended
application. Fluoropolymers are not comprehended by synthetic
thermoplastic polymers, even though the core may contain
fluoropolymers as a blend component as well as synthetic
thermoplastic polymers.
[0025] Examples of synthetic thermoplastic materials are
polyolefins, such as polyethylene, polypropylene or copolymers
containing ethylene and/or propylene units combined with other
copolymerized alpha-olefin units, such as alpha-butylene,
alpha-pentylene, alpha-hexylene or alpha-octylene; polyesters, such
as polycarbonate, aliphatically aromatic polyesters or wholly
aromatic polyesters; polyamides, such as aliphatic or aliphatically
aromatic polyamides (nylons) or wholly aromatic polyamides
(aramids); or polyether ketones, ie polymers which have at least
ether and ketone groups and generally aromatic divalent radicals,
such as phenylene, in the recurring chain, many combinations of
these groups being possible, for example PEK, PEEK or PEKK; or
polyarylene sulfides, preferably polyphenylene sulfide; or
polyether esters, ie polymers which have at least ether and ester
groups and generally aromatic divalent radicals, such as phenylene,
in the recurring chain, for example TPE-E; or polyacrylonitrile or
polyacrylonitrile copolymers with other ethylenically unsaturated
comonomers, such as acrylic or methacrylic acid.
[0026] Preferably, the core of the core-sheath fibers of this
invention contains polyamides and especially polyesters.
[0027] The thermoplastic polyamides which are preferably used in
the compositions of the present invention are known per se.
[0028] Examples thereof are fiber-forming polyamides, such as
aliphatic or aliphatically aromatic polyamides, for example
polycaprolactam, poly(hexamethylene-1,6-diamineadipamide),
poly(hexamethylene-1,6-diamines- ebacamide),
poly(hexamethylene-1,6-diamineterephthalamide) or
poly(hexamethylene-1,6-diamineisophthalamide); or else wholly
aromatic polyamides, such as
poly(phenylene-1,4-diamineterephthalamide) or
poly(phenylene-1,4-diamineisophthalamide).
[0029] The polyamides used in this invention have DIN 53727
viscosity numbers which are customarily in the range from 120 to
350 and preferably from 150 to 320 cm.sup.3/g (measured at
25.degree. C. in sulfuric acid).
[0030] The thermoplastic polyesters and/or aromatic
liquid-crystalline polyesters which are more preferably used in the
compositions of the present invention are known per se.
[0031] Examples thereof are fiber-forming polyesters, such as
polycarbonate or aliphatically aromatic polyesters, for example
polybutylene terephthalate, polycyclohexanedimethyl terephthalate,
polyethylene naphthalate or especially polyethylene terephthalate,
or else wholly aromatic, liquid-crystalline polyesters, such as
polyoxybenzonaphthoate. Building blocks of fiber-forming polyesters
are preferably diols and dicarboxylic acids or appropriately
constructed hydroxy carboxylic acids. The main acid constituent of
the polyesters is terephthalic acid or cyclohexanedicarboxylic
acid, but other aromatic and/or aliphatic or cycloaliphatic
dicarboxylic acids may be suitable as well, preferably para- or
trans-disposed aromatic compounds, such as for example
2,6-naphthalenedicarboxylic acid or 4,4'-biphenyldicarboxylic acid,
or else p-hydroxybenzoic acid. Aliphatic dicarboxylic acids, such
as adipic acid or sebacic acid for example, are preferably used in
combination with aromatic dicarboxylic acids.
[0032] Typical suitable dihydric alcohols are aliphatic and/or
cycloaliphatic and/or aromatic diols, for example ethylene glycol,
propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol or else
hydroquinone. Preference is given to aliphatic diols which have 2
to 4 carbon atoms, especially ethylene glycol; preference is
further given to cycloaliphatic diols, such as
1,4-cyclohexanedimethanol.
[0033] Preferred thermoplastic polyesters are especially selected
from the group consisting of polyethylene terephthalate,
polyethylene naphthalate, polybutylene naphthalate, polypropylene
terephthalate, polybutylene terephthalate,
polycyclohexanedimethanol terephthalate, polycarbonate or a
copolycondensate containing polybutylene glycol, terephthalic acid
and naphthalenedicarboxylic acid units.
[0034] Further preferred thermoplastic polyesters are aromatic,
liquid-crystalline polyesters, especially polyesters containing
p-hydroxybenzoate units.
[0035] Especially in the case of fibers which are to be used in hot
moist environments, such as monofilaments for use in paper
machines, and which contain polyesters as a core component, these
polyesters are preferably stabilized against hydrolytic degradation
by addition of polyester stabilizers.
[0036] Such stabilized fibers exhibit a significant reduction in
the degradation tendency of the polyester, so that monofilament
lifetimes can be achieved which are equivalent to those of
monofilaments based on extremely stable fiber materials, such as
polyarylene sulfides or oxides.
[0037] Particular preference is given to fibers containing
stabilized polyesters and particularly preferably carbodiimides in
the core.
[0038] The polyesters used in the present invention typically have
solution viscosities (IV values) of at least 0.60 dl/g, preferably
of 0.60 to 1.05 dl/g, more preferably of 0.62-0.93 dl/g, (measured
at 25.degree. C. in dichloroacetic acid).
[0039] The fluoropolymers forming the sheath are likewise freely
chooseable, as long as they are melt spinnable.
[0040] The fluoropolymers used in the present invention are
poly(fluoroolefin) homopolymers and/or copolymers derived from
ethylenically unsaturated fluorous olefin monomers and other
monomers which are copolymerizable therewith. Such polymers are
likewise known per se.
[0041] Examples thereof are melt-spinnable copolymers of
tetrafluoroethylene with other alpha-olefins, such as ethylene,
propylene, butylene, hexylene or octylene.
[0042] But it is also possible to use homo- or copolymers which are
derived from other fluorous monomers, for example from mono-, di-,
trifluoroethylene, from vinyl fluoride or especially from
vinylidene fluoride.
[0043] Particular preference is given to using melt-spinnable
copolymers of tetrafluoroethylene with at least one alpha-olefin,
preferably with ethylene.
[0044] Very particular preference is given to using polyvinylidene
fluoride (PVDF) as a sheath component.
[0045] When spinning polyesters, especially PET, with PVDF to form
a bicomponent monofilament in a core-sheath structure there is a
surprise in that very good core-sheath bonding is obtained.
[0046] The invention therefore also includes a heterofilament fiber
containing at least two components, the first component being an
electric insulator and comprising a thermoplastic polymer which is
not a fluoropolymer and the second component comprising
polyvinylidene fluoride.
[0047] The particles composed of electroconductive material which
are present in the sheath of the melt-spun fiber of the present
invention are freely chooseable, as long as they provide the sheath
with an increased electroconductivity.
[0048] The particles can be composed of carbon, being for example
carbon fibers, carbon black or graphite; of metals, for example of
copper, silver, aluminum or iron; of metal alloys, for example
bronze; or of conductive plastics, for example of polyanilines or
of polypyrrole.
[0049] The particles can be present in any desired form, for
example in fiber form or in the form of round or irregular
particles.
[0050] The level of electroconductive particles in the sheath is to
be chosen such that a distinct increase in the electroconductivity
of the polymeric material results. Typical amounts vary in the
range of up to 50% by weight and preferably 2 to 15% by weight,
based on the amount of the sheath material.
[0051] Particular preference is given to melt-spun fibers wherein
the sheath contains between 2% by weight and 15% by weight and
especially between 4% by weight and 9% by weight of
electroconductive particles.
[0052] The core-sheath fibers of the present invention can be
present in any desired form, for example as multifilaments, as
staple fibers or especially as monofilaments.
[0053] The linear density of the core-sheath fibers of the present
invention can likewise vary within wide limits. Examples thereof
are 100 to 45,000 dtex and especially 400 to 7,000 dtex.
[0054] Particular preference is given to monofilaments.
[0055] Particular preference is given to monofilaments whose
cross-sectional shape is round, oval or n-gonal, where n is not
less than 3.
[0056] The staple lengths in the case of staple fibers can likewise
vary within wide limits, for example between 30 to 70 mm.
[0057] The core of the core-sheath fiber of the present invention
forms the mechanical, load-bearing component of the fiber, whereas
the sheath determines mainly the performance characteristics, such
as antistatic performance and lubricity. The core can preferably
utilize a commercially available PET raw material.
[0058] The sheath more preferably utilizes a fluoropolymer based on
PVDF which was previously processed with carbon black in particular
into a spinnable mixture.
[0059] The weight fraction of the core-forming component A) to the
sheath-forming component B) is, based on the total amount of these
components, 50 to 95% by weight and preferably 60 to 80% by weight
for component A) and 50 to 5% by weight and preferably 40 to 20% by
weight for component B).
[0060] The core-sheath fibers of the present invention can be
prepared according to processes known per se.
[0061] These processes comprise the measures of:
[0062] i) selecting a first polymer which is a synthetic
thermoplastic polymer and not a fluoropolymer and which has a first
melting point,
[0063] ii) selecting a second polymer which contains particles
comprising electroconductive material and which is a melt-spinnable
fluoropolymer which has a second melting point at least 20.degree.
C. below the first melting point,
[0064] iii) coextruding the first polymer and the second polymer
through a heterofilament spinneret at a spinning temperature above
the first melting point to form a bicomponent fiber having a core
comprising the first polymer and a sheath comprising the second
polymer and
[0065] iv) drawing the produced core-sheath filament to increase
the tensile strength.
[0066] The two polymers or mixtures containing these polymers are
preferably dried directly before being fed into the extruder,
melted in the extruder and filtered through a spin pack. The
fluoropolymer is provided with the electroconductive particles.
This is typically accomplished before the fluoropolymer is fed to
the extruder, but can also take place directly upstream of the spin
pack. It is similarly possible to use masterbatches containing the
fluoropolymer and electroconductive particles.
[0067] After the polymer melts have been pressed through a
heterofilament spinneret, the molten polymer thread is quenched in
a spin bath, for example a water bath, and subsequently wound up or
taken off. The takeoff speed is greater than the ejection speed of
the polymer melt and thus causes stretching or drawing of the
extruded thread.
[0068] The as-spun heterofilament thread thus produced is
subsequently preferably subjected to an afterdrawing operation,
more preferably in plural stages, especially to a two- or
three-stage afterdrawing operation, to an overall draw ratio of 1:3
to 1:8 and preferably 1:4 to 1:6.
[0069] Drawing is preferably followed by heat setting, for which
temperatures of 130 to 280.degree. C. are employed; the length is
maintained constant or shrinkage of up to 30% is allowed.
[0070] It has been determined to be particularly advantageous for
the monofilaments of the present invention to operate at a melt
temperature in the range from 285 to 315.degree. C. and at a jet
stretch ratio of 1:2 to 1:6.
[0071] The spinning takeoff speed is customarily 10-40 m per
minute.
[0072] When the thermoplastic polymer of the core and the
fluoropolymer of the sheath are spun into a bicomponent
monofilament in core-sheath structure there is a surprise in that
very good core-sheath bonding is obtained.
[0073] The conductivity of the sheath can be lost at drawing, but
can be restored by a heat treatment and the thereby induced
shrinkage, preferably above the melting point of the sheath
material but below the melting temperature of the core.
[0074] The conductively doped fluoropolymer determines mainly the
surface properties. The fibers of the present invention are notable
for very good soil repellency, good chemical resistance and
electroconductivity.
[0075] The combination with the fluoropolymer leads to fibers
having improved lubricity properties compared with fibers composed
of straight thermoplastic polymer. These fibers exhibit enhanced
soil repellency compared with fibers composed of straight
thermoplastic polymer.
[0076] The fibers of the present invention can contain assistants
as well as components A) and B). Examples of assistants are
processing assistants, stabilizers, antioxidants, plasticizers,
lubricants, pigments, delusterants, viscosity modifiers or
crystallization accelerants.
[0077] Examples of processing assistants are siloxanes, waxes or
long-chain carboxylic acids or their salts, aliphatic, aromatic
esters or ethers.
[0078] Examples of stabilizers and antioxidants are the
abovementioned polyester stabilizers, phosphorus compounds, such as
phosphoric esters or carbodiimides.
[0079] Examples of pigments or delusterants are organic dye
pigments or titanium dioxide.
[0080] Examples of viscosity modifiers are polybasic carboxylic
acids and their esters or polyhydric alcohols.
[0081] The fibers of the present invention, especially the
monofilaments, are preferably used for producing textile fabrics,
such as wovens, formed-loop knits, drawn-loop knits, non crimp
fabrics and nonwovens.
[0082] Textile fabrics containing monofilaments of the present
invention are especially useful for industrial applications, as for
filters, as screen printing materials or especially as paper
machine wires.
[0083] The monofilaments of the present invention have good
textile-physical properties and are easy to process by weaving. The
wovens have the usual shape stability of the thermoplastic polymers
which form the core.
[0084] Wovens formed from these monofilaments are very useful for
industrial cloths, especially in the filtration of aggressive media
where there is also a risk of an electrostatic charge buildup; that
is, especially in solid-gaseous and solid-liquid filtration.
[0085] The invention also includes the use of the fibers for
producing textile fabrics which are used in environments featuring
severe chemical and/or physical stress, especially as paper machine
wires or industrial wovens, as for example in filtration, for
producing conveyor belts or as reinforcing plies. Here the fibers
are used as monofilaments and especially as weft threads in the
woven fabric.
[0086] The use of the monofilaments of the present invention as
paper machine wires can take place in the forming section, the
pressing section or in particular the drying section. When used in
the drying section, the monofilaments of the present invention are
used as spiral wires in particular.
[0087] For these applications, the fibers used according to the
present invention, especially in the form of monofilaments,
typically have a linear density range from 10 to 4,500 tex, an
elasticity modulus of 2.0 to 8.0 N/tex, a tenacity of 15 to 50
cN/tex, a breaking extension of 15 to 45% and a 180.degree. C. hot
air shrinkage of 1.0 to 20.0%.
[0088] The example which follows illustrates the invention without
limiting it.
[0089] Core-sheath fibers composed of polyethylene terephthalate
and polyvinylidene fluoride containing carbon black.
[0090] Polyethylene terephthalate (PET) (70% by weight) and
polyvinylidene fluoride (as a masterbatch containing 9% by weight
of conductivity carbon black; Palmarole EXP 184/14; 30% by weight)
were melted in two extruders featuring separate temperature control
(PET at 282.degree. C. melting temperature (core material) and PVDF
at 240.degree. C. melting temperature (sheath material) and spun
through a 20 hole spinneret having a hole diameter of 1.40 mm and a
hauloff speed of 15 m/min to form a core-sheath monofilament,
doubly drawn (first drawing in water bath at 80.degree. C.; second
drawing in hot air duct at 150.degree. C.) and also heat set in the
hot air duct at 205.degree. C. The overall draw ratio was 4.1:1.
The final diameter of the core-sheath monofilament was 0.500
mm.
[0091] The core-sheath monofilament obtained had the following
properties:
1 Linear density: 2890 dtex Tenacity: 24 cN/tex 160.degree. C. hot
air shrinkage 10': 2.5% Loop tenacity: >20 cN/tex Breaking
extension: 44% 12 cN/tex EASL: 8.5% 15 cN/tex EASL: 13% El.
resistance (10 mm clamped length): 8 * 10.sup.5 (ohm) El.
resistance (150 mm clamped length): 9 * 10.sup.6 (ohm)
* * * * *