Note: Descriptions are shown in the official language in which they were submitted.
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Combination twists for paper machine felts and process for the production
thereof
In machinery used for the production of paper, paperboard, pulp or similar
products,
the fibrous slurry is partially dewatered by being squeezed either between two
press
rolls or, in "shoe" presses, between a pressure roll and a press shoe. For
economic
reasons, it is generally desirable to remove the majority of the water from
the fibrous
slurry in this press section. In recent decades, intensive research has
resulted in the
development of entirely new types of felts or fabrics which are suitable for
dewatering in the press section of paper machines. It has been possible with
the
assistance of these new paper machine fabrics to satisfy increasingly
stringent
requirements far dewatering efficiency.
At the same time, it has also proved possible to achieve a major increase in
machine
running speeds with the consequence that the search for materials with a major
increase in speed after the installation of a new paper machine fabric has
intensified.
Other properties, such as running behaviour, resistance to vibration and
abrasion
resistance also had to be enhanced.
The invention relates to a novel (base) fabric for paper machine felts, in
particular
press felts with improved properties, in particular with improved elasticity
in the felt
thickness direction, greater compressibility and improved water absorption
capacity
during paper production from the beginning to the end of the felt's service
life.
The invention is achieved in that, during production of the supporting
fabric for the paper machine felt, combination yarns of polyamide and
thermoplastic
polyurethane filaments, in particular twisted yams of combination twists with
1
to 20 monofilaments of polyamide 6 and/or polyamide 4,6, polyamide 6,10,
polyamide 6,12, polyamide 11 or polyamide 12 and 20 to 1 monofilaments
produced
from thermoplastic polyurethane are used in the warp and/or weft direction
instead
of twist or individual monofilament yarns composed solely of polyaJnide
monofilaments.
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Processes for the production of monofilaments of thermoplastic polymers are
known
in principle from the prior art (c.f. Handbuch der Kunststofftechnik II
[manual of
plastics technology II], C. Hawser-Verlag, Munich 1986, pages 295-319).
The Lehrbuch der Papier- and Kartonerzeugung [textbook of paper and paperboard
production), VEB-Fachbuchverlag 1987, pages 190 et seq.) contains information
about paper production in modern paper machines, for example with regard to
sheet
formation (forming section), mechanical dewatering (press section) and thermal
dewatering (drying section) as well as to smoothing (calendering) and winding.
Fabrics for the sheet forming section mainly consist of polyester
monofilaments. In
order to increase abrasion resistance, monofilaments based on polyamide
monofilaments together with polyester filaments are used as alternating
threads in
the cross-machine direction of the paper machine.
Press felts in the press section consist of one or more base fabrics needle-
punched
with nonwoven fabric. These press felts are produced virhzally exclusively
from
polyamide fibres and polyamide monofilaments, primarily from pure polyamide 6
or
also polyamide 6,6 filaments.
Commercial press felts based on polyamide 6 monofilaments offer considerable
advantages relative to felts which are possibly also produced from other
materials,
for example polypropylene/polyester or wool, due to their good abrasion
resistance,
elevated compressibility and good recovery characteristics after passage
through the
press nip.
Fabrics for the drying section, which are used in the final section of the
paper
machine, conventionally consist of polyester monofilaments which are
stabilised
against hydrolytic degradation, for example by stabilisers such as Stabaxol~
(commercial product, produced by Rheinchemie; Mannheim).
Specifically, the following types of press felts axe known in principle from
the prior
art.
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Patent specification US-A-4,323,622 discloses a high-elasticity dewatering
felt for
use, for example, in papermaking or in cellulose machines, in which the
elastic
properties of the felt are achieved by incorporating molecular thermoplastic
elastomers. Alternatively, a high-molecular, branched urethane-based elastomer
material could here be incorporated in order to achieve the desired
elasticity. Tn this
structure, however, the elasticity is oriented in machine direction and the
elastomer
material is intended to be capable of extending to at least twice its original
length
and finally rapidly returning substantially to its original length once the
load has
been removed from the fabric.
The disadvantages of the prior art according to US-A-4,323,622 are, however,
serious. The elevated extension of the material in the paper machine may bring
about an unwanted extension of the fabric and likewise of the paper in the
machine
direction together with contraction thereof in the cross-machine direction.
Such
major dimensional changes in the fabric normally result in creasing of the
felt and of
the paper, which in tum causes breakage of the papex sheet. The term machine
direction (MD) is here taken to mean the direction parallel to the motion of
the felts
in the papermaking machine.
Patent specification US-A-4,533,594 discloses a paper machine felt, in which
the
mesh layer is a fabric which is in turn formed from yam in the machine
direction in .
combination with yarn in cross-machine direction. The crosswise oriented yarns
axe
here multifilament yams based on nylon, polyester or polyacrylonitrile with a
polyurethane coating. The object of said patent specification is to provide a
paper
machine felt of the butt-on-mesh type in which the mesh fabric exhibits
improved
resilience. A similar fabric is described in patent specification US-A 4,731,2
1, in
which a fabric is obtained from totally encapsulated monofilament yarns. The
yarns
are coated prior to weaving in order to impart anti-stick characteristics to
the fabric.
The coating may be adjusted such that the thickness of the yarn in the machine
direction differs from the thickness of the yarn in the cross-machine
direction.
The disadvantages of the above-stated prior art according to US-A 4,533,594
are
also serious. The coating on the monofilarnents consists of another type of
polymer
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and is only physically bonded around the core filament. The coating is only
very
weakly chemically bonded. This means that the coating may be deformed or moved
on the core filament with a consequent decline in the originally desired
properties.
The needling process during production of the papex machine felts is typically
very
aggressive with regard to this type of coating, which in turn results in the
originally
desired properties not being retained. In addition to these disadvantages, the
coating
on the core yarn is only a proportion of the crass-section in the yarn. The
actual
elastic deformation accordingly occurs in only a small part of the shell,
resulting in a
smaller elastic effect. The tension/recovery characteristics of a fabric based
on this
type of yarn thus almost exclusively depend on the properties of the core
material.
Patent specification US-A 5,360,518 describes another press fabric with coated
yarn
which may be used in the press section of a paper machine. It comprises a
multilayer
structure with a thin paper-contacting surface and an ample underlying layer.
One of
two or more layers of woven yarns comprises multicomponent yarns with a
plurality
of load-bearing strands. The multicomponent yarns may be multifilament or
multistrand yarns which are composed of thin polyamide filaments. They may
also
be polyurethane-coated monofilament yarns and provide the press fabric with a
compressible, resilient structure. Die multifilament or multistrand yarns may
likewise be polyurethane-coated. The disadvantages of this prior art are
comparable
with the disadvantages of the fabric known from US-A 4,533,594. It is more
readily
feasible to achieve a strong coating bond with multifilarnent yarns. However,
such a
yarn suffers from the same limitations as the above-described monoflament-
coated
monofilament core yarn. During the frequently repeated pressure phases in the
press
nip (of the order of several million press operations), the coating is torn
off or
distorted on the core yam and the originally desired effect declines.
In patent specification US-A-5,194,121, it is attempted to produce a felt with
elevated elasticity, recovery and durability with an elastic component in the
fibre
layer of the felt. However, polyurethane is described as unusable for the
needling
process which is intended to fasten the fibres to the base fabric. As an
alternative
solution, it is proposed instead to use a polyamide block copolymer with hard
and
soft segments.
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Various attempts have been made to improve the properties of polyamide and
thermoplastic polyurethanes by mixing the polymers during the extrusion
process.
Published patent application DE 19 829 928 A2 describes a process for the
S production of filament material which comprises a mixture of polyamide and
thermoplastic polyurethane. However, the large disparity in melting points of
the
two polymers results in particular processing problems. The resultant
monofilament
is lower in strength than conventional polyamide. Moreover, only a slight
increase in
cross-sectional elasticity is observed. The thermal degradability of the
thermoplastic
polyurethane may also be very disadvantageous during extrusion if the
residence time
in the extruder is excessively long.
Patent specification US-A-6,514,386 describes a paper machine felt which is
asserted to exhibit excellent elasticity over an extended duration, and which
consists
of a base fabric and needled nonwoven layer together with a separate film
layer with
elongate ridges oriented in cross-machine direction. Such a film may be
provided in
the base fabric or between different layers of the felt. The paper machine
felt is
consequently capable of running smoothly through the winding section of the
paper
machine and is comparatively resistant to the fatigue which may occur due to
repeated pressing in the press nip.
From the standpoint of felt production, laminating an elastic layer onto a
strong base
fabric may be a very risky operation as ruckling and unevenness can easily be
produced. The edges of the film must be joined, these zones then always being
imperfect zones.
Although it could in principle be conceivable to use TPU monofilaments and/or
twisted yarns based on TPU monofilaments in the base fabric of press felts,
the
person skilled in the art would probably initially anticipate severe
processing
problems as monofilaments based on thermoplastic polyurethanes are highly
elastic
and highly extensible and moreover exhibit an elevated coefficient of
friction. TPU
monofilarnents axe accordingly only processed in relatively large diameters
and
under tension. Yarns and fabric produced in this manner would exhibit defects
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unacceptable to the paper machine industry. Dimensional stability and tension
in
machine direction and cross-machine direction of the paper machine would not
be
tolerable. Since the elastic yarns are highly extensible, such a fabric would
exhibit
low modulus in machine direction and elevated contraction in cross-machine
direction. These disadvantages could in part be overcome by laminating such a
fabric onto another fabric of polyamide. However, problems would still remain
due
to the very different tension/recovery characteristics of such a twin base
fabric.
Rolling of the fabric edges is for example one result of the mismatch between
these
opposing base fabrics.
It has surprisingly now been found that the above-described disadvantages of
the
prior art may largely be avoided if TPU monofilaments are simultaneously
processed with one or more polyamide monofilaments and/or polyamide
multifilaments to yield industrial base fabrics, in particular if they are
first twisted
and then woven. It has furthermore surprisingly been found that these
combination
yarns (twists) based on thermoplastic polyurethane and polyamide monofilaments
may be converted into base fabrics or felts virtually in the same manner as
conventional pure polyamide yarns.
The present invention provides a base fabric, in particular for use as machine
clothing for paper machines or as a textile for other industrial processes,
which is
characterised in that the base fabric contains at least one combination yarn
of
polyamide and TPU monofilaments.
The thermoplastic polyurethane (TPU/polyamide (PA)) combination yarns may
consist either only of initial twists (with one direction of twist) or of
initial and final
twists (twists with different direction of twist). The TPU/PA combination
yarns may
preferably be arranged in the machine direction and/or cross-machine direction
of
the press felt of the paper machine.
A preferred base fabric is characterised in that the polyamide is selected
from the
range polyamide 4,6, polyamide 6, polyamide 6,6, polyamide 6,I2, polyamide
6,10,
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polyaxnide 1 l and polyamide 12, together with copolyaxnides of the stated
polymers
or selected mixtures of these polyamides.
In a preferred embodiment, the combination yarn is made from straight, i.e.
untwisted filaments of polyamide and thermoplastic polyurethanes.
In a preferred variant of the base fabric, the combination yaxn is produced
from at
least one part of twisted polyamide filaments and thermoplastic polyurethane
filaments.
In a further preferred embodiment of the base fabric, the above-stated
combination
yarn will comprise a combination of 1 to 10,000 monofilaments of polyamide and
to I monofilaments of thermoplastic polyurethanes.
I S Very particularly preferably, the combination yarn for the base fabric is
a
combination of 1 to 20 monofilaments of polyamide and 20 to 1 monofilaments of
thermoplastic polyurethanes.
A particularly preferred base fabric is also one which is characterised in
that the
20 monofilaments in the combination yarn (polyamide and/or TPU monofilaments)
exhibit a diameter in the range from 0.05 to 2 mm.
One particular advantage of the above-stated base fabric is that it may be
produced
straightforwardly using existing paper machine manufacturing technology,
including .
conventional twisting machines and looms.
Another advantage is that the modulus of elasticity of the polyamide is
retained in
machine direction and may be combined with the modulus of elasticity of the
thermoplastic polyurethane in the thickness direction of the fabric.
It has furthermore been found that press felts produced on the basis of the
base
fabric according to the invention not only have a greater paper dewatering
capacity
but also achieve a higher level of dewatering more quickly and retain their
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dewatering capacity over a longer period than press felts which have been
produced
without the stated combination yarns based on TPU/polyamide. It has moreover
also
been found that paper machine vibration may be further reduced if press felts
are
used which have been produced with the assistance of the above-stated base
fabric.
As a result, less energy is required for the drying step at the end of the
papermaking
process. Alternatively, the paper machine may be operated at higher speeds
with
otherwise identical energy consumption.
The TPU/PA polyfilament combination may also be processed in the untwisted
state. This may be achieved by simultaneously winding TPU and polyamide
monofilaments onto the bobbin after production. Thermoplastic polyurethanes
suitable for the production of TPU filaments are any extrusion grades of
thermoplastic polyurethane elastomers based both on polyester or polyether
grades,
preferably with a Shore hardness of 75 to 99 Shore A.
Thermoplastic polyurethane elastomers {TPU) are industrially significant
because
they exhibit excellent mechanical properties and can be processed by low-cost
melt-
processing methods. The mechanical properties may be varied over a wide range
by
using different chemical synthesis components. ~verviews of TPU, their
properties
and applications may be found in Kunststoffe 68 {1978), pages 819-825 and
Kautschuk, Gummi, Kunststoffe 35 (1982), pages 568-584.
TPU are synthesised from linear polyols, usually polyester or polyether
polyols,
organic diisocyanates and short-chain diols (chain extenders). Catalysts may
additionally be added to accelerate the formation reaction. The molar ratios
of the
synthesis components may be varied over a wide range, by which means it is
possible to adjust product properties. Molar ratios of polyols to chain
extenders of
1:1 to 1:12 have proved effective, yielding products in the range from 70
Shore A to
75 Shore D. Synthesis of the melt-processable polyurethane elastomers may
proceed
either stepwise (prepolymer process) or by the simultaneous reaction of all
components in a single stage {one-shot process). In the prepolyrner process, a
prepolyrner containing isocyanate is formed from the polyol and diisocyanate,
the
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prepolymer being reacted with the chain extender in a second step. TPU may be
produced continuously or discontinuously. The best known industrial production
processes are the belt process and the extruder process.
Melt-processable polyurethanes usable according to the invention may be
obtained
by reacting the polyurethane-forming components
A) organic diisocyanate,
B) linear hydroxyl-terminated polyol with a molecular weight of 500 to 5000,
C) diol or diamine chain extenders with a molecular weight of 60 to 500,
wherein the molar ratio of NCO-groups in A) to the isocyanate-reactive groups
in B)
andC)is0.9to1.2.
Organic diisocyanates A) which may, for example, be considered are aliphatic,
cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as are
described
in Justus Liebigs Anna.len der Chemie, 562, pages 75-136.
The following may specifically be stated by way of example: aliphatic
diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic
diisocyanates,
such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-
cyclohexane diisocyanate and 1-methyl-2,6-cyclohexane diisocyanate and the
corresponding isomer mixtures, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-
dicyclohexylmethane diisocyanate and 2,2'-dicyclohexylmethane diisocyanate and
the corresponding isomer mixtures, aromatic diisocyanates, such as 2,4-
tolylene
diisocyanate, mixtures of 2,4-tolylene diisocyanate and, 2,6-tolylene
diisocyanate,
4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 2,2'-
diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate
and
4,4'-diphenylmethane diisocyanate, urethane-modified, liquid 4,4'-
diphenylmethane
diisocyanates and 2,4'-diphenylmethane diisocyanates, 4,4'-diisocyanato-1,2-
diphenylethane and 1,5-naphthylene diisocyanate. Preferably used compounds are
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1,6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane
diisocyanate, diphenylmethane diisocyanate isomer mixtures with a 4,4'-
diphenylmethane diisocyanate content of >96 wt.% and in particular 4,4°-
diphenylinethane diisocyanate and 1,5-naphthylene diisocyanate. The stated
diisocyanates may be used individually or in the form of mixtures with one
another.
They may also be used together with up to 15 wt.% (calculated relative to the
total
quantity of diisocyanate) of a polyisocyanate, for example triphenylmethane
4,4',4"-
triisocyanate or polyphenyl-polymethylene polyisocyanates.
Linear hydroxyl-terminated polyols with a molecular weight of 500 to 5000 are
used
as component B). As a result of their production process, these often contain
small
quantities of nonlinear compounds and they are consequently often referred to
as
"substantially linear polyols". Polyester, polyether, polycarbonate diols or
mixtures
of these are preferred.
Suitable polyether diols may be produced by reacting one or more alkylene
oxides
having 2 to 4 carbon atoms in the alkylene residue with a starter molecule
which
contains two active hydrogen atoms in bound form. Alkylene oxides which may be
mentioned by way of example are: ethylene oxide, 1,2-propylene oxide,
epichlorohydrin and 1,2-butylene oxide and 2,3-butylene oxide. Ethylene oxide,
propylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide are
preferably used. The alkylene oxides may be used individually, alternately in
succession or as mixtures. Starter molecules which may, for example, be
considered
are: water, aminoalcohols, such as N-alkyldiethanolamines, for example N-
methyldiethanolamine, and diols, such as ethylene glycol, 1,3-propylene
glycol, 1,4-
butanediol and 1,6-hexanediol. Mixtures of starter molecule may optionally
also be
used. Suitable polyether diols are furthermore the hydroxyl group-containing
polymerisation products of tetrahydrofuran. Trifunctional polyethers may also
be
used in proportions of 0 to 30 wt.%, relative to the difunctional polyether,
but at
most in such a quantity that a melt-processable product is obtained. The
substantially linear polyether diols have molecular weights of 500 to $000.
They
may be used both individually and in the form of mixtures with one another.
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Suitable polyester diols may, for example, be produced from dicarboxylic acids
having 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric
alcohols. Dicarboxylic acids which may for example be considered are:
aliphatic
dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic
acid,
azelaic acid and sebacic acid and aromatic dicarboxyhc acids, such as phthalic
acid,
isophthalic acid and terephthalio acid. The dicarboxylic acids may be used
individually or as mixtures, for example in the form of a mixture of succinic,
glutamic and adipic acids. For the production of polyester diols, it may
optionally be
advantageous, instead of using dicarboxylic acids, to use the corresponding
dicarboxylic acid derivatives, such as carboxylic acid diesters having 1 to 4
carbon
atoms in the alcohol residue, carboxylic anhydrides or carboxylic acid
chlorides.
Examples of polyhydric alcohols are glycols having 2 to 10, preferably 2 to 6
carbon
atoms, such as ethylene glycol, diethyiene glycol, 1,4-butanediol, 1,5-
pentanediol,
1,6-hexanediol, 1,10-decanediol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol
and
dipropylene glycol. Depending upon the desired properties, the polyhydric
alcohols
may be used alone or optionally as a mixture. Esters of carbonic acid with the
stated
diols, in particular those having 4 to 6 carbon atoms, such as 1,4-butanediol
or 1,6-
hexanediol, condensation products of hydroxycarboxylic acids, for example
hydroxycaproic acid and polymerisation products of lactones, for example
optionally substituted caprolactones, are furthermore suitable. Preferably
used
polyester diols are ethanediol polyadipates, 1,4-butanediol polyadipates,
ethanediol/1,4-butanediol polyadipates, 1,6-hexanediol/neopentyl glycol
polyadipates, 1,6-hexanediol/1,4-butanediol polyadipates and
polycaproplactones.
The polyester diols have molecular weights of 500 to 5000 and may be used
individually or in the form of mixtures with one another.
Diols or diamines with a molecular weight of 60 to 500, preferably aliphatic
diols
having 2 to 14 carbon atoms, such as for example ethanediol, 1,6-hexanediol,
diethylene glycol, dipropylene glycol and in particular 1,4-butanediol are
used as the
chain extenders C). Diesters of terephthalic acid with glycols having 2 to 4
carbon
atoms are, however also suitable, such as for example texephthalic acid bis-
ethylene
glycol or terephthalic acid bis-1,4-butanediol, hydroxyalkylene ethers of
hydroquinone, such as for example 1,4-di(hydroxyethyl)hydroquinone,
ethoxylated
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bisphenols, (cyclo)aliphatic diamines, such as for example isophoronediamine,
ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, N-methylpropylene-
1,3-diaxnine, N,N'-dimethyl-ethylenediamine and aromatic diamines, such as for
example 2,4-tolylenediamine and 2,6-tolylenediamine, 3,5-diethyl-2,4-
tolylenediamine and 3,5-diethyl-2,6-tolylenediamine and primary mono-, di-,
tri- or
tetraalkyl-substituted 4,4'-diaminodiphenylmethane. ?Mixtures of the above-
stated
chain extenders may also be used. Smaller quantities of triols may
additionally be
used.
Conventional monofunctional compounds may furthermore be used in small
quantities, for example as chain terminators or mould release agents. Alcohols
such
as octanol and stearyl alcohol or amines such as butylamine and stearylamine
may
be mentioned by way of example.
In order to produce the TPU, the synthesis components, optionally in the
presence of
catalysts, auxiliaries and additives, are reacted in quantities such that the
equivalent
ratio of NCO groups to the total of the NCO-reactive groups, in particular the
OH
groups of the low molecular weight diols/triols and polyols is 0.9:1.0 to
1.2:1.0,
preferably 0.95:1.0 to 1.10:1Ø
Suitable catalysts according to the invention are known prior art and
conventional
tertiary amines, such as for example triethylamine, dimethylcyclohexylamine, N-
methylinorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol,
diazabicyclo(2.2.2)octane and similar and in particular organic metal
compounds
such as titanic acid esters, iron compounds, tin compounds, for example tin
diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic
carboxylic
acids such as dibutyltin diacetate, dibutyltin dilaurate or the like.
Preferred catalysts
are organic metal compounds, in particular titanic acid esters, iron or tin
compounds.
Apart from the TPU components and the catalysts, other auxiliaries and
additives
may also be added. The following may be mentioned by way of example:
lubricants
such as fatty acid esters, the metal soaps thereof, fatty acid amides and
silicone
compounds, antiblocking agents, inhibitors, stabilisers to counter hydrolysis,
the
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action of light or heat and discoloration, flame retardants, dyes, pigments,
inorganic
or organic fillers. Further details regarding the stated auxiliaries and
additives may
be found in the specialist literature, for example J.H. Saunders, K.C. Frisch:
"High
Polymers", volume XVI, Polyurethane, parts 1 and 2, Interscience Publishers
1962
and 1964, R. Gachter, H. IoiLiiller (eds.): Taschenbuch der Kunststoff
Additive
[plastics additive handbook], 3rd edition, Hanser Verlag, Munich 1989,
or DE-A 29 Ol 774.
Further additives which may be incorporated into the TPU are thermoplastics,
for
example polycarbonates and acrylonitrile/butadiene/styrene terpolymers, in
particular ABS. Other elastomers such as rubber, ethylene/vinyl acetate
copolymers,
styrene/butadiene copolymers and other TPU may likewise be used. Conventional
commercial plasticisers such as phosphates, phthalates, adipates, sebacates
and
alkylsulfonic acid esters are fiufihermore suitable for incorporation.
The TPU usable according to the invention may be produced continuously by the
"extruder" process, for example in a multi-screw extruder. The TPU components
A),
B) and C) may be apportioned simultaneously, i.e. by the one-shot process, or
in
succession, i.e. in accordance with a prepolyrner process. The prepolymer may
here
both be initially introduced batchwise and be continuously produced in one
section
of the extruder or in a separate, upstream prepolymer unit.
The TPU and polyamide monofilaments are produced as such using production
processes which are generally known from the prior art.
The present invention also provides a process for the production of a
combination
yarn of filaments produced from polyamide and such filaments produced from
thermoplastic polyurethanes, in which polyamide and thermoplastic polyurethane
monofilaments are delivered to a twisting machine at speeds of 5 to 50 m/min
and
then twisted at a tension of at Least 0.1 cN/tex, preferably of 0.2 to 4
cN/tex,
particularly preferably 0.3 to 0.8 cN/tex, wherein the tension relates to the
TPU
monofilaments.
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In a preferred process, the polyamide monofilaments consist of polyamide 4,6,
polyamide 6, polyamide 6,6, polyamide 6,12, polyamide 6, I 0, polyamide 11 and
polyamide 12 or selected copolymers or mixtures of these polyamides.
In a further, particularly preferred process, the TPU monofilaments are fed at
a
defined feed tension to the delivery unit of a twisting machine and then
twisted with
the polyamide filaments.
A further preferred process is characterised in that the defined feed tension
of the
TPU monofilaments is produced by means of an additional TPU delivery unit,
wherein the TPU delivery unit has a lower delivery speed than the PA
monofilament
delivery unit.
The following Examples illustrate the advantages of the invention with regard
to the
combination yarns without limiting the invention as such.
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Examples
Description of the twisting operation
Twist characteristics:
The initial twist of the monofilaments consists of at least one TPU
monofilament
and at least one polyamide monofilament and/or a polyamide multifilament. At
least
two of these initial twists are twisted together in order to form the twisted
yarn (final
twisting), which is processed by weaving.
Production of a twisted PA/TPU combination yarn:
The TPU monofilaments must be fed with a defined delivery tension to the
delivery
unit of the twisting machine and are then delivered into the twisting machine
with
the polyamide monofilaments and twisted. TPU monofilament is produced and PA
monofilament is taken from a yarn reel.
Both monofilaments are fed to a common bobbin, wherein the winding speed is
2Q determined by the delivery speed of the PA monofilament. Since the TPU
monofilament is delivered at a lower speed, it receives a certain feed tension
relative
to the PA monofilament.
An Alma Saurer model AZB-T twisting machine was used to produce the initial
twist and for the subsequent twisting steps.
