U.S. patent application number 14/762212 was filed with the patent office on 2015-12-17 for method of manufacturing a drawn multifilament yarn.
The applicant listed for this patent is DSM IP ASSETS B.V.. Invention is credited to Evert Florentinus Florimondus DE DANSCHUTTER, Andreas Oliver MITTENZWEI.
Application Number | 20150361588 14/762212 |
Document ID | / |
Family ID | 47603462 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361588 |
Kind Code |
A1 |
DE DANSCHUTTER; Evert Florentinus
Florimondus ; et al. |
December 17, 2015 |
METHOD OF MANUFACTURING A DRAWN MULTIFILAMENT YARN
Abstract
The invention relates to a method of manufacturing a polyolefin
multifilament yarn comprising twisting a partially drawn
multifilament yarn and post-twist-drawing the twisted partially
drawn multifilament yarn.
Inventors: |
DE DANSCHUTTER; Evert Florentinus
Florimondus; (Echt, NL) ; MITTENZWEI; Andreas
Oliver; (Echt, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DSM IP ASSETS B.V. |
TE Heerlen |
|
NL |
|
|
Family ID: |
47603462 |
Appl. No.: |
14/762212 |
Filed: |
January 27, 2014 |
PCT Filed: |
January 27, 2014 |
PCT NO: |
PCT/EP2014/051534 |
371 Date: |
July 21, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61756577 |
Jan 25, 2013 |
|
|
|
Current U.S.
Class: |
264/103 |
Current CPC
Class: |
D02G 3/26 20130101; D01D
5/12 20130101; D01F 6/04 20130101; D10B 2321/0211 20130101 |
International
Class: |
D01D 5/12 20060101
D01D005/12; D01F 6/04 20060101 D01F006/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2013 |
EP |
13152764.0 |
Claims
1. A method of manufacturing a multifilament yarn comprising the
steps of providing a partially drawn multifilament yarn comprising
partially drawn filaments, twisting the partially drawn
multifilament yarn to a partially-drawn-twist-level of 4 turns per
meter to 600 turns per meter to form a twisted partially drawn
multifilament yarn, preferably twisting the partially drawn yarn to
a partially-drawn-twist-level of 10 turns per meter to 500 turns
per meter, more preferably twisting the partially drawn yarn to a
partially-drawn-twist-level of 12 to 200 turns per meter, and
post-twist-drawing the twisted partially drawn multifilament yarn
by a draw ratio DR.sub.pt of at least 1.1, preferably
post-twist-drawing by DR.sub.pt of at least 1.5, more preferably
post-twist-drawing by DR.sub.pt of at least 2, and most preferably
post-twist-drawing by DR.sub.pt of at least 3.
2. Method according to claim 1, wherein the
partially-drawn-twist-level/DR.sub.pt is between 2-250 turns per
meter, preferably the partially-drawn-twist-level/DR.sub.pt is
between 2-120 turns per meter.
3. Method according to claim 1, wherein at least one of the
filaments of the partially drawn multifilament yarn is selected
from the group consisting of (coloured) polyester filaments, HD
polyethylene filaments, UHMWPE filaments, polypropylene filaments;
preferably the partially drawn multifilament yarn comprises at
least 75 number-% UHMWPE filaments; more preferably the partially
drawn multifilament yarn comprises at least 90 number-% UHMWPE
filaments; and most preferably the filaments of the partially drawn
multifilament yarn consist of UHMWPE filaments.
4. Method according to claim 1, wherein twisting of the partially
drawn multifilament yarn is realized inline with a drawing
step.
5. Method according to claim 1, wherein the steps of twisting the
partially drawn multifilament yarn and post-twist-drawing are
conducted inline.
6. Method according to claim 1, wherein twisting the partially
drawn yarn is conducted by an Uster twister system.
7. Method according to claim 1, wherein twisting the partially
drawn yarn is conducted by first winding an untwisted partially
drawn multifilament yarn followed by twisting of the partially
drawn multifilament yarn by unwinding the partially drawn
multifilament yarn using a twisting creel system, preferably the
twisting creel system is arranged to conduct the unwinding and
twisting inline with the post-twist-drawing process wherein
unwinding speed and rotation speed of the twisting creel system is
adjusted to the inline post-twist-drawing process.
8. Method according to claim 6, further comprising the step of
tensioning the multifilament yarn in a tensioning station after
twisting the partially drawn yarn and before post-twist-drawing of
the partially drawn yarn.
9. Method according to claim 1, wherein the partially drawn
multifilament yarn is post-twist-drawn by a draw ratio DR.sub.pt of
at most 100 to form a HPPE multifilament yarn, preferably by a
DR.sub.pt of at most 25, and more preferably by a DR.sub.pt of at
most 10.
10. A method of removing a spin solvent from a gelspun
multifilament polyolefin yarn comprising the steps of providing a
multifilament yarn comprising polyolefin filaments and a spin
solvent, twisting the yarn to a twist level of 10 to 600 turns per
meter, and removing at least a part of the spin solvent from the
multifilament yarn after twisting the yarn.
11. Method according to claim 10, wherein during the twisting of
the multifilament yarn, the spin solvent content of the
multifilament yarn is 10 ppm to 1000 ppm based on the weight of
polyethylene and spin solvent, preferably the spin solvent content
of the multifilament yarn is 20 ppm to 500 ppm based on the weight
of polyethylene and spin solvent.
12. Method according to claim 10, wherein during the twisting of
the multifilament yarn, the spin solvent content of the
multifilament yarn is at least 0.1 wt-% based on the weight of
polyethylene and spin solvent, preferably the spin solvent content
of the multifilament yarn is at least 0.5 wt-%, more preferably the
spin solvent content of the multifilament yarn is at least 2 wt-%,
more preferably the spin solvent content of the multifilament yarn
is at least 10 wt-%.
13. Method according to claim 10, wherein at least 10 wt-% of the
spin solvent present during the twisting is removed after twisting
the multifilament yarn, preferably at least 90 wt-% of the spin
solvent present during the twisting is removed after twisting the
multifilament yarn, most preferably at least 99 wt-% based on
solvent content during twisting of the spin solvent present during
the twisting is removed after twisting the multifilament yarn.
14. Method according to claim 10, further comprising the step of
post-twist-drawing the multifilament yarn by a draw ratio DR.sub.pt
of at least 1.1 to form a HPPE multifilament yarn, preferably by a
DR.sub.pt of at least 1.5, more preferably by a DR.sub.pt of at
least 2, and most preferably by a DR.sub.pt of at least 3.
15. A method of manufacturing a gelspun HPPE multifilament yarn
comprising the steps of providing a solution of 3-25 wt-% UHMWPE in
a spin solvent (based on UHMWPE and spin solvent in the solution),
spinning the solution through a spinneret having at least two spin
holes, quenching the solution in a quench bath to form a solid
multifilament yarn comprising partially drawn UHMWPE filaments,
removing of at least a part of the spin solvent from the solid
multifilament yarn, twisting the solid multifilament yarn to a
twist level of 10 to 600 turns per meter to form a twisted
partially drawn multifilament yarn, post-twist-drawing the twisted
partially drawn multifilament yarn by a draw ratio DR.sub.pt of at
least 1.1 to form a HPPE multifilament yarn, wherein twisting,
removing of the spin solvent and post-twist-drawing are conducted
without adding a spin finish to the multifilament yarn.
16. Method according to claim 15 further comprising the step of
removing at least 99.5 wt-% of the spin solvent (based on spin
solvent in the solution), preferably removing at least 99.9 wt-% of
the spin solvent, more preferably removing at least 99.95 wt-% of
the spin solvent.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The invention relates to a method of manufacturing a
multifilament yarn, such as a high performance polyethylene (HPPE)
multifilament yarn. More particularly, the invention relates to a
method of manufacturing and/or cleaning a multifilament yarn, where
no organic spin finish is required.
BACKGROUND OF THE INVENTION
[0002] Multifilament polyolefin yarn is typically manufactured by
spinning of a fluid, such as molten polyethylene or a solution
(sometimes also referred to as a gel) of polyethylene in a spin
solvent, through a spinneret with a multiplicity of spinholes to
form filaments. Thereafter, the filaments are cooled and drawn. If
a spin solvent is used, then at least some of this solvent is
removed by for example evaporation or extraction. Examples of
manufacturing processes are meltspinning process (as for example
disclosed in EP1445356), solid state process (as for example
disclosed in EP1627719) or gelspinning (as for example disclosed in
WO 2005/066401). A general description is also presented in
"Advanced Fibre Spinning Technology", Ed. T. Nakajima, Woodhead
Publ. Ltd (1994), ISBN 185573 182 7, all incorporated herein by
reference.
[0003] One problem when manufacturing multifilament yarn of
polyethylene is that polyethylene is an electrical isolator and
hence tend to build up electro static charge during manufacturing
and since the individual filaments of the multifilament yarn is
charged similarly (plus or minus), then individual filaments will
electro statically repel each other. This means that the
multifilament yarn will tend to loosen up instead of forming a
unity. Furthermore, in case of filament breakage, the filament ends
will tend to move as far away as possible from the main body of the
multifilament yarn reducing the quality of the manufactured
multifilament yarn by fluff formation or even risk of a loose
filament (end) being caught in the manufacturing equipment and
hence even requiring production stop to releasing the broken
filament.
[0004] Traditionally, this has been solved by adding an organic
spin finish to the multifilament yarn during the drawing process.
However, organic spin finish is a surface active product and should
be avoided for environmental reasons.
[0005] One route to reduce influence of the spin finish has been
suggested in WO2004/053212 where use of a volatile spin finish is
suggested.
OBJECTS OF THE INVENTION
[0006] It is the object of the invention to provide an improved
method of manufacturing a multifilament yarn.
[0007] It is another object of the invention to provide an improved
multifilament yarn or yarn construction.
DISCLOSURE OF THE INVENTION
[0008] The improvement may for example be one or more of a
reduction of the environmental impact, better logistics, reduced
handling or another improvement provided by the present invention
as discussed below.
[0009] In a first aspect of the invention, the object of the
invention is achieved by a method of manufacturing a multifilament
yarn comprising the steps of providing a partially drawn
multifilament yarn comprising partially drawn filaments, twisting
the partially drawn multifilament yarn to a
partially-drawn-twist-level of 4 to 600 turns per meter to form a
twisted partially drawn multifilament yarn, and post-twist-drawing
the twisted partially drawn multifilament yarn by a draw ratio
DR.sub.pt of at least 1.1.
[0010] The partially drawn multifilament yarn may be provided
directly from the spinning process in the case where the spin holes
of the multifilament spinneret has a contraction zone shaped to
provide partially drawing or aligning of the filaments already in
the spin holes for example as disclosed in WO 2005/066401. The
partial draw multifilament yarn may also be a result of drawing in
an airgap after the spinneret. Preferably, the partially drawn
multifilament yarn is a solid stage yarn for example after cooling
in a quench bath after the spinning. If the partially drawn
multifilament yarn is a gelspun multifilament yarn, it is preferred
that at least a part of the solvent has been removed (as compared
to the solvent content during spinning through the spinneret) prior
to twisting of the partially drawn multifilament yarn.
[0011] Drawing of the multifilament yarn takes place in multiple
steps. The twisting of the partially drawn multifilament yarn may
be realized inline with a drawing step, or offline not connected
with a drawing step. By inline is herein meant that the partially
drawn yarn runs directly between a station where twisting of the
partially drawn multifilament yarn is conducted and a station where
the multifilament yarn is drawn. Offline typically means that a
winding step takes place between drawing and twisting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be explained more fully below with
reference to exemplary embodiments as well as the drawings, in
which
[0013] FIG. 1 shows schematic flowcharts of methods according to
the invention, and
[0014] FIG. 2 shows schematic flowcharts of a method of
manufacturing a HPPE multifilament yarn according to the
invention.
[0015] All figures show only steps which are necessary in order to
elucidate the invention, other parts being omitted or merely
suggested.
DETAILED DESCRIPTION
[0016] The drawing of the multifilament yarn may be conducted in
one or more of the following variations (see FIG. 1): a) inline
before twisting and followed by offline post-twist-drawing; b)
inline before and inline after twisting of the partially drawn
multifilament yarn; c) offline before twisting and inline after
twisting; d) offline before and offline after twisting, so twisting
of the partially drawn yarn takes place in a step separated (in
time and/or space) from drawing of the partially drawn
multifilament yarn before and after the twisting.
[0017] It is preferred that twisting the partially drawn
multifilament yarn and post-twist-drawing is conducted inline. The
method according to the invention may incorporate more than one
post-twist-drawing steps. If more than one post-twist-drawing steps
are conducted in the method according to the invention, then it is
preferred that twisting of the partially drawn multifilament yarn
is conducted inline with at least one of the post-twist-drawing
steps, and more preferably twisting of the partially drawn
multifilament yarn is conducted inline with all post-twist-drawing
steps. The method according to the invention may incorporate more
than one twisting steps. If more than one twisting steps are
conducted in the method according to the invention, then it is
preferred that at least one of the twisting steps is conducted
inline with a post-twist-drawing step.
[0018] Twisting of the partially drawn multifilament yarn may be
conducted on a dedicated (freestanding) equipment or may be
combined with into one piece of equipment with one or more of a
drawing oven, a quench bath, a winder, an unwinder, a spinning
plate. In one embodiment, twisting the partially drawn yarn is
conducted by an inline twister system for example as described in
U.S. Pat. No. 6,155,037. Inline twister systems described in U.S.
Pat. No. 6,155,037 is hereinafter referred to as an Uster twister
system. As this type of equipment allows for introducing a twist to
a partially drawn multifilament yarn without having access to the
ends of the yarn, this type of equipment is particularly
advantageous for retrofitting of existing equipment, such as an
existing drawing oven, or an existing winder or unwinder. One
aspect of the invention therefore concerns a combination of an
Uster twister system and a drawing oven, an Uster twister system
and a winder, or a Uster twister system and an unwinder.
[0019] In a particularly preferred embodiment, twisting the
partially drawn yarn is conducted by first winding an untwisted
partially drawn multifilament yarn followed by twisting the
partially drawn multifilament yarn by unwinding the untwisted
partially drawn multifilament yarn using a twisting creel system.
Preferably the twisting creel system is arranged to conduct the
unwinding and twisting inline with the post-twist-drawing process
wherein the unwinding speed and rotation speed of the twisting
creel system is adjusted to the inline post-twist-drawing
process.
[0020] The method according to the invention may further comprising
the step of tensioning the multifilament yarn in a tensioning
station after twisting the partially drawn multifilament yarn and
before post-twist-drawing of the partially drawn yarn. This allows
to keep the tension in the partially drawn multifilament yarn
relatively low during twisting while the tension during drawing may
be kept sufficiently high to ensure the required drawing. Examples
of suitable tensioning stations include a number of rolls, a break
system and a friction system.
[0021] For all aspects of the invention, drawing of the
multifilament yarn typically takes place at an elevated
temperature. It is preferred that at least one drawing step takes
place at a temperature of above 100.degree. C., and preferably at
least one drawing step takes place at a temperature above
120.degree. C. It is preferred that at least one drawing step takes
place below the melting point of the multifilament yarn. More
preferably, all drawing steps after the spinning takes place below
the melting point of the multifilament yarn. Yet more preferably,
all drawing steps after spinning takes place at a temperature of at
least 5.degree. C. below the melting point of the multifilament
yarn, and more preferably at a temperature of at least 10.degree.
C. below the melting point of the multifilament yarn. Particularly,
it is preferred that post-twist-drawing takes place in a range
between the melting point of the multifilament yarn and 30.degree.
C. below the melting point of the multifilament yarn, more
preferably the post-twist drawing takes place at a temperature at
least 5.degree. C. below the melting point of the multifilament
yarn, such as 10.degree. C. below the melting point of the
multifilament yarn. For gelspun UHMWPE multifilament yarn, it is
preferred that drawing--and particularly post-twist-drawing--takes
place at a temperature below 138.degree. C., preferably at a
temperature below 135.degree. C. and more preferably at a
temperature below 132.degree. C. For gelspun UHMWPE multifilament
yarn, it is preferred that drawing--and particularly
post-twist-drawing--takes place at a temperature above 100.degree.
C., preferably at a temperature above 110.degree. C., more
preferably at a temperature above 120.degree. C., and more
preferably at a temperature above 130.degree. C.
[0022] Within the context of the present invention, monofilaments
are understood to mean elongated bodies of indefinite length and
with length dimension much greater than their transversal
dimensions, e.g. width, thickness or radius, and can have regular
or irregular cross-section. The monofilaments may have continuous
lengths, known in the art as filaments, or discontinuous lengths,
known in the art as staple fibers. A multifilament yarn according
to the present invention is an elongated body comprising a
plurality of monofilaments.
[0023] By a gel-spun multifilament yarn is herein understood a
multifilament yarn manufactured by spinning a solution (sometimes
also referred to as a gel) comprising a polymer and a solvent for
said polymer. The spinning of the solution may be conducted by
converting a suspension of polymer and solvent into a solution in
an extruder and extruding said solution through a spinneret
containing more than one spinning apertures. Particularly preferred
are gel-spun polyolefin multifilament yarns, which are spun from a
solution containing the polyolefin and a solvent for polyolefin,
which solvent can be removed from the multifilament yarn after
spinning of the yarn by evaporation, like for example naphthenes
such as decaline, tetralin or methylcyclohexane.
[0024] Preferably, the gel-spun multifilament yarns obtained
according to the invention are high performance gel-spun
multifilament yarns with a tenacity of at least 1.5 N/tex,
preferably at least 2.0 N/tex, more preferably at least 2.5 N/tex
or even at least 3.0 N/tex. There is no reason for an upper limit
of the tenacity of the multifilament yarns, but gel-spun
multifilament yarns typically having a tenacity of at most about 5
to 6 N/tex may be manufactured. Generally such high performance
gel-spun multifilament yarns also have a high tensile modulus (also
referred to as Young's modulus), of e.g. at least 50 N/tex,
preferably at least 75 N/tex, more preferably 100 N/tex, most
preferably at least 125 N/tex. There is no reason for an upper
limit of the tensile modulus, but gel-spun multifilament yarns
typically having a tenacity of at most about 180 N/tex.
[0025] Tensile strength (also simply referred to as strength)
tenacity and modulus of multifilament yarns are determined by known
methods, as based on ASTM D2256-97.
[0026] The multifilament yarns obtained according to the invention
have a titer of preferably at least 2 dtex, preferably at least 7
dtex and more preferably at least 8 dtex. For practical reasons,
the titer of the multifilament yarns of the invention are at most
several thousand dtex, preferably at most 2500 dtex, more
preferably at most 500 dtex. The multifilament yarns comprising a
plurality of filaments preferably have a titer per filament in the
0.2-5 dtex range, preferably 0.5-2 dtex. Partially drawn
multifilament yarns comprising a plurality of filaments preferably
have a titer per filament in the 0.5-25 dtex range.
[0027] The multifilament yarn is preferably selected from the group
consisting of polyolefin (such as polyethylene and polypropylene),
polyester (such as PET, vectran and PLA), polyamide (such as nylon
and aramide) and more preferably the multifilament yarn is
polyolefin. It is preferred that polyolefin used in accordance with
the present invention is polypropylene or polyethylene, more
preferably ultrahigh molecular weight polyethylene (UHMWPE).
[0028] By HPPE multifilament yarn is herein understood high
performance polyethylene, which is yarn comprising drawed
polyethylene with a Young's modulus of at least 30 GPa. A
particularly preferred type of HPPE is gelspun ultra high molecular
weight polyethylene (UHMWPE), where the UHMWPE has an intrinsic
viscosity (IV) as measured on a solution of UHMWPE in decalin at
135.degree. C., of at least 5 dl/g, preferably at least 10 dl/g,
more preferably at least 15 dl/g, most preferably at least 21 dl/g.
Preferably, the IV is at most 40 dl/g, more preferably at most 30
dl/g, even more preferably at most 25 dl/g. Gelspun UHMWPE
typically has a Young's modulus of at least 50 GPa. Preferably the
HPPE multifilament yarn has a tenacity of at least 1GPa. Preferably
the HPPE multifilament yarn comprises at least 90 wt-% UHMWPE
filaments and most preferably the HPPE multifilament yarn consists
of UHMWPE filaments.
[0029] By yarn construction is herein meant a collection of at
least two multifilament yarns connected for example by braiding,
weaving, knitting, twisting, heat treatment involving partial
melting, air entanglement and gluing.
[0030] By post-twist-drawing is herein meant the process of drawing
a yarn by a factor of at least 1.1 after twisting of the yarn by at
least 4 turns per meter and before optionally converting the yarn
into a yarn construction. It should be observed that drawing of a
yarn construction (such as drawing of a rope construction as
described in EP 0 398 434) is a fundamentally different process
than post-twist-drawing since drawing of a yarn construction
realize the fundamentally different effect of realigning filaments
of the construction by creep and does not improve the coherence
between the filaments of an individual yarn between the individual
filaments in one multifilament yarn of the yarn construction.
Furthermore, in addition to a more coherent filament bundle
twisting of the partially drawn multifilament yarn before
post-twist-drawing appeared to providing for a better heat and
stress distribution in the multifilament yarn during
post-twist-drawing which again allowed for a more uniform drawing
on filament level. A more uniform drawing leads to improved
processability of the obtained multifilament yarn as well as
improved yield of the manufacturing process since more uniform
drawing appeared to lead to reduced filament breakage.
Post-twist-drawing also results in a higher reduction of the titer
as compared to drawing a yarn construction.
[0031] In a preferred embodiment, the partially drawn multifilament
yarn is twisted to a partially-drawn-twist-level of 10 to 500, and
more preferably the partially drawn yarn is twisted to a
partially-drawn-twist-level of 12 to 200 turns per meter. The
optimum partially-drawn-twist-level depends on the titer of the
multifilament yarn, the post-twist-drawing ratio, the desired twist
level of the multifilament yarn and the optional twist level to be
applied to the multifilament yarn after post-twist-drawing.
[0032] In another preferred embodiment, the twisted partially drawn
multifilament yarn is post-twist-drawing by DR.sub.pt of at least
1.5, and more preferably post-twist-drawing by DR.sub.pt of at
least 2, and most preferably post-twist-drawing by DR.sub.pt of at
least 3. The upper limit of the post-twist-drawing ratio DR.sub.pt,
depends on the condition of the yarn prior to the twisting of the
partially drawn yarn, such as for example, the type of polymer, and
the draw ratio prior to twisting of the partially drawn yarn, the
temperature of the post-twist-drawing. Typically, the
post-twist-drawing ratio is less than 1000; preferably DR.sub.pt is
at most 100; more preferably DR.sub.pt is less than 50; more
preferably DR.sub.pt is at most 25; more preferably DR.sub.pt is at
most 10 or less than 10.
[0033] The partially-drawn-twist-level is the number of turns per
meter that the partially drawn multifilament yarn has directly
after the twisting of the partially drawn multifilament yarn. In a
preferred embodiment of the invention, the partially drawn
multifilament yarn is twisted to a level where the factor between
the partially-drawn-twist-level and the draw ratio, DR.sub.pt, of
the post-twist-drawing is between 2-250 turns per meter, preferably
the partially-drawn-twist-level/DR.sub.pt is between 2-120 turns
per meter, more preferably the
partially-drawn-twist-level/DR.sub.pt is between 2-20 turns per
meter, such as 5 to 20 turns per meter. In one embodiment, the
twist level of the partially drawn multifilament yarn is
sufficiently high that no further twisting of the multifilament
yarn is required after post-twist-drawing.
[0034] The partially drawn multifilament yarn may be a homo-yarn or
a hetero-yarn. By homo-yarn is meant that the multifilament yarn
consist of filaments having the same composition. By hetero-yarn is
meant that at least one of the filaments of the multifilament yarn
has a different composition that other of the filaments of the
multifilament yarn. In one embodiment, at least one of the
filaments of the partially drawn multifilament yarn is selected
from the group consisting of (coloured or uncoloured) polyester
filaments, HD polyethylene filaments, UHMWPE filaments,
polypropylene filaments. Preferably, the partially drawn
multifilament yarn comprises at least 75 number-% UHMWPE filaments
and more preferably the partially drawn multifilament yarn
comprises at least 90 number-% UHMWPE filaments. Most preferably,
the filaments of the partially drawn multifilament yarn consist of
UHMWPE filaments, as this provides the strongest and most
homogeneous performance of the multifilament yarn.
[0035] Another aspect of the invention concerns a method of
removing a spin solvent from a gelspun multifilament polyolefin
yarn. The method comprising the steps of providing a multifilament
yarn comprising polyolefin filaments and a spin solvent, twisting
the yarn to a twist level of 10 to 600 turns per meter, and
removing at least a part of the spin solvent from the multifilament
yarn after twisting the yarn. The multifilament yarn provided in
the first step may be an undrawn, a partially drawn or
post-twist-drawn gelspun multifilament yarn, however, it is
preferred that the multifilament yarn is partially drawn or
post-twist-drawn. The removing of spin solvent is preferably by
evaporation or extraction. Evaporation is particularly relevant
when the spin solvent is a naphthene such as decaline, tetralin
and/or methylcyclohexane. Extraction is particularly relevant when
the spin solvent comprises paraffin. Twisting of the multifilament
yarn before removing at least a part of the solvent from the
multifilament yarn allows conducting the conversion into a yarn
construction without addition of spin finish to the multifilament
yarn. In other words, this aspect of the invention allows removal
of the spin solvent from a multifilament yarn in a more
environmentally friendly way without jeopardizing the handlabiilty
of the yarn, since a spin finish is not required or a smaller
amount of spin finish is required. In this embodiment of the
invention, it is also preferred to post-twist-drawing the
multifilament yarn, however, this is not a requirement. Preferred
twisting levels and optional post-twist-drawing levels correspond
to the levels as described herein for other aspects of the
invention.
[0036] In one embodiment of the invention, the spin solvent content
of the multifilament yarn is already very low before twisting of
the partially drawn multifilament yarn. In this embodiment, it is
preferred that the spin solvent of the multifilament yarn during
twisting is 10 ppm to 1000 ppm based on the weight of polyethylene
and spin solvent. Preferably, the spin solvent of the partially
drawn multifilament yarn during twisting is 20 ppm to 500 ppm.
[0037] In another embodiment of the invention, the spin solvent
content of the multifilament yarn during twisting of the
multifilament yarn is at least 0.1 wt-% based on the weight of
polyethylene and spin solvent, preferably the spin solvent content
of the multifilament yarn is at least 0.5 wt-%, more preferably the
spin solvent content of the multifilament yarn is at least 2 wt-%,
more preferably the spin solvent content of the multifilament yarn
is at least 5 wt-%, such as for example at least 10 wt-%.
Typically, the spin solvent content of the multifilament yarn
during twisting of the multifilament yarn is below 90 wt-%.
[0038] The amount of solvent removed after twisting of the
multifilament yarn depends to a large extent on the content before
twisting. Furthermore, the lower the solvent content of the
post-twist-drawn multifilament yarn, the higher the effect on
coherency of the twisting before removing the solvent from the
yarn. In one embodiment, at least 10 wt-% of the spin solvent
present during the twisting is removed after twisting the
multifilament yarn and preferably at least 90 wt-% of the spin
solvent present during the twisting is removed after twisting the
multifilament yarn. Most preferably at least 99 wt-% of the spin
solvent present during the twisting is removed after twisting the
multifilament yarn. It should be observed that if more twisting
steps are utilized, then the solvent content during twisting is the
solvent content during the first twisting step. The fraction of
solvent removed from the multifilament yarn after twisting depends
to some extent on the amount present before twisting. It is
preferred that 100% of the solvent is removed, but since traces of
solvent may stay in the multifilament yarn, in one embodiment at
most 99.999% of the solvent is removed. The removed spin solvent is
preferably collected and recycled by known means.
[0039] In the cleaning process according to this aspect of the
invention, it is highly preferred that the process further
comprises a post-twist-drawing step. Particularly, it was found to
be advantageous to post-twist-drawing the multifilament yarn by a
draw ratio DR.sub.pt of at least 1.1 to form a HPPE multifilament
yarn. More preferably the post-twist drawing draw ratio is at least
1.5, and even more preferably DR.sub.pt is at least 2, and most
preferably by a DR.sub.pt of at least 3. The upper limit of the
post-twist-drawing ratio DR.sub.PT, depends on the condition of the
yarn prior to the twisting of the partially drawn yarn, such as for
example, the type of polymer, and the draw ratio prior to twisting
of the partially drawn yarn, the temperature of the
post-twist-drawing. Typically, the post-twist-drawing ratio,
DR.sub.PT, is less than 1000; preferably DR.sub.pt is at most 100;
more preferably DR.sub.PT is less than 50; more preferably
DR.sub.pt is at most 25; more preferably DR.sub.PT is at most 10 or
less than 10.
[0040] Manufacturing of Gelspun multifilament HPPE traditionally
requires addition of spin finish during removal of the spin solvent
as the filaments would otherwise repulse each other due to
electrostatic charging effects of the electrically isolating
polymer. Unfortunately, being a surface active agent, spin finish
is not a desired additive for environmental perspective and
particularly for medical applications, spin finish should be
avoided. One aspect of the invention therefore concerns a method of
manufacturing a gelspun HPPE multifilament yarn without adding a
spin finish. The flowchart in FIG. 2 indicates this method. The
method comprising the steps of providing (2) a solution of 3-25
wt-% UHMWPE in a spin solvent (based on UHMWPE and spin solvent in
the solution). The solution may for example be provided by
converting a suspension of UHMWPE and spin solvent in an extruder,
spinning (4) the solution through a spinneret having at least two
spin holes, quenching (6) the solution in a quench bath, and
drawing (7) to form a solid multifilament yarn comprising partially
drawn UHMWPE filaments. Thereafter, twisting (12), the partially
drawn multifilament yarn to a twist level of 2 to 600 turns per
meter to form a twisted partially drawn multifilament yarn, and
post-twist-drawing (13) the twisted partially drawn multifilament
yarn by a draw ratio DR.sub.pt of at least 1.1 to form a HPPE
multifilament yarn, where twisting, removal of spin solvent and
post-twist-drawing are conducted without adding a spin finish to
the multifilament yarn. At least a part of the spin solvent is
removed during the process by evaporation or extraction. Twisting
of the partially drawn multifilament yarn may be conducted inline,
offline or a combination of inline and offline with drawing
conducted prior to twisting. Twisting of the partially drawn
multifilament yarn may be conducted inline, offline or a
combination of inline and offline with post-twist-drawing. It was
found to be highly advantageous to conduct drawing prior to
twisting offline with the twisting and to conduct twisting inline
with at least a part of the post-twist-drawing as this allows for
good traceability and compact process equipment.
[0041] The methods according to the present invention are
particularly advantageous in relation to preparation of
polyethylene yarn to be used in medical applications, medical
repair products, implants and medical devices, as the methods
allows for preparation of polyethylene yarn without the use of a
spin finish and particularly an organic spin finish, which organic
spin finish typically is not desired inside the body or in contact
with the body. Example of medical applications are medical
components, like for example vascular prostheses, joint
arthroplasty, orthopedic and spine implants, for example meniscus
implants, surgical sutures, meshes for example hernia meshes,
fabrics, woven or non-woven, textiles, sheets, tapes, ribbons,
bands, artificial joints, cables such as trauma fixation cables,
sternum closure cables, prophylactic or per prosthetic cables, long
bone fracture fixation cables, small bone fracture fixation cables,
tube-like products for example ligament replacement, endless loop
products, bag-like, balloon-like products), tube-like products for
example ligament replacement, endless loop products, bag-like
products, balloon-like products, grafts, stent grafts, artificial
veins, Y-shaped hollow structures, skirts for valve structures,
such as heart valves and periphery valves and other medical
components.
[0042] Since use of spin finish is also not desired from an
environmental point of view, the methods according to the present
invention are also advantageous in relation to preparation of
polyethylene yarn to be used in other end-use products and
applications like ropes, cables and cords, mooring lines, fishing
lines and fishing nets, sports equipment, impact and abrasion
resistant products and ballistic-resistant products.
EXAMPLES
Example 1
Preparation of HPPE Yarn with Drawing Inline Before Twisting
[0043] FIG. 1a) shows a flow diagram of a method of preparation of
a polyolefin multifilament yarn where drawing inline with twisting
is conducted before twisting. After twisting, the partially drawn
multifilament yarn is wound on a bobbin before (at a later time)
conducting offline post-twist-drawing. The twisting may be
conducted in conjunction with winding of the partially drawn
multifilament yarn in a combined twisting and winding unit, such as
for example available from the companies Alma-Sauer, Dietze &
Schell, Galan, and Barmag. The twisting and winding may also be
conducted in two separate steps in which case the twisting for
example may be conducted in a process and equipment as disclosed in
U.S. Pat. No. 6,155,037 and the winding for example may be
conducted on a precision cross winder, for example from SSM, Dietze
& Schell, Comoli, Leesona, Georg Sahm GmbH, Oerlikon, and
Barmag. The winded and twisted partially drawn yarn is later (i.e.
offline) post-twist-drawing. This corresponds to the process
indicated in FIG. 1a, where in addition to the drawing (8)
conducted inline before twisting (12), further offline drawing (10)
may be conducted prior to the inline drawing (8).
Example 2
Preparation of HPPE Yarn with Drawing Inline Before and After
Twisting
[0044] FIG. 1b) shows a flow diagram of a method of preparation of
a polyolefin multifilament yarn where drawing inline with twisting
is conducted before as well as after twisting. The twisting may be
conducted with a twisting unit of the type for example disclosed in
U.S. Pat. No. 6,155,037 where a running yarn is twisted inline
during transfer through the twisting unit. In one embodiment of
drawing variation b), one large twisting step is utilized to
achieve the desired twist level. In another embodiment of drawing
variation c), multiple smaller steps of twisting (such as 2, 3, 4,
5, 6, 7, 8, 9 or 10 twisting steps) are utilized to achieve the
desired twist level. The multiple smaller drawing steps may be
arranged in between multiple smaller drawing steps or in groups of
drawing steps between drawing steps. As indicated in FIG. 1b), in
addition to the inline drawing before (8) and after (14) the
twisting (12), one or more offline drawing steps may optionally be
utilized before (10) or after (16) the inline drawing and twisting
steps (8, 12, 14).
Example 3
Preparation of HPPE Yarn with Drawing Inline After Twisting
[0045] FIG. 1c) shows a flow diagram of a method of preparation of
a polyolefin multifilament yarn where drawing inline with twisting
is conducted after twisting. In this case, a partially drawn
multifilament yarn is prepared by drawing (10) for example in a
first drawing oven the as-spun multifilament yarn and thereafter
winding the partially drawn multifilament yarn on bobbin for
example on a Twinstar precision cross winder from Georg Sahm GmbH.
At a later time, the partially drawn multifilament yarn is twisted
and post-twist-drawing. The twisting preferably takes place on a
combined twist and unwinder apparatus such as for example a
twisting creel available from for example Alma-Sauer, Dietze &
Schell, Galan, and Barmag. Alternatively, a separate unwinder may
be combined with a twisting unit of the type for example disclosed
in U.S. Pat. No. 6,155,037. After the inline post-twist-drawing
(14), the yarn may optionally be further drawn offline (16). The
advantage of this embodiment is, that the unwinding and twisting
can be finely tuned with the drawing process and allow for rapid
start and stop in relation to yarn breakage. Furthermore,
traceability is easier to handle as compared to the drawing
variation of Example 4 since less offline processes are
involved.
Example 4
Preparation of HPPE Yarn with Drawing Offline Before and After
Twisting
[0046] FIG. 1d) shows a flow diagram of a method of preparation of
a polyolefin multifilament yarn where drawing is conducted offline
before and after twisting. The partially drawn multifilament yarn
is prepared as described in Example 3 by drawing (10) for example
in a first drawing oven the as-spun multifilament yarn and
thereafter winding the partially drawn multifilament yarn on bobbin
for example on a Twinstar precision cross winder from Georg Sahm
GmbH. The partially drawn multifilament yarn is thereafter at a
later time twisted on a twist and rewind equipment for example
available from SSM, Dietze & Schell, Comoli, Leesona, Georg
Sahm GmbH, Oerlikon, and Barmag. Finally, post-twist-drawing is
conducted at a later time for example in a further drawing oven.
The advantage of this embodiment is that it allows for realizing
the improved coherence of the multifilament yarn in a simple
constellation and does not require alignment of twisting equipment
with one or more drawing stations. However, due to the process
steps being conducted offline, traceability needs to be handled
carefully.
Example 5
Preparation of Partially Drawn HPPE Yarn
[0047] Bobbins of partially drawn UHMWPE yarn were prepared by
preparing a solution of UHMWPE in decalin in an extruder, spinning
the solution through a spinneret having 200 spin holes, quenching
in a quench bath, partially drawing the as-spun yarn and removing
more than 99% of the spin solvent from the yarn as compared to spin
solvent content of the solution. No spin finish was provided during
the process. Finally, the yarn was wound on bobbins each holding
about 9000 m.
Example 6
Preparation of HPPE Yarn Utilizing Drawing Inline After
Twisting
[0048] Bobbins of partially drawn UHMWPE yarn prepared in Example 5
were subjected to the inline drawing process as described in FIG.
1c) using inline post-twist-drawing ratio of 4 by feeding the
drawing oven via a twisting creel unwinder. Twist levels of 9 and
12 turns per meter were used. No offline post-twist-drawing was
used and no spin finish was provided during the processes.
TABLE-US-00001 Twist level 9 turns 12 turns per meter per meter
Total number of bobbins 75 17 Minimum number of defects per bobbin
0 0 Maximum number of defects per bobbin 16 10 Average number of
defects per bobbin 3 1.5
[0049] It was therefore observed that the maximum number of defects
per bobbin as well as the average number of defects per bobbin
decreased when the twist level was increased.
Comparative Example 1
Preparation of HPPE Yarn Utilizing no Twisting
[0050] Experiment 6 was repeated using 0 turns per meter inline
twist. The resulting yarn showed very low coherency and no stable
bobbins could be prepared after final drawing.
Example 7
Preparation of HPPE Yarn Utilizing Drawing Offline Before and After
Twisting
[0051] Bobbins of partially drawn UHMWPE yarn prepared in Example 5
were subjected to the offline drawing process as described in FIG.
1d). A twist level of 16 turns per meter was provided by unwinding
using a ring-twister, parallel winding and a separate step of
rewinding using cross winding. The bobbins of partially drawn and
twisted UHMWPE yarn were hereafter drawn using an offline
post-twist-drawing ratio of 4. No spin finish was provided during
the twisting or post-twist-drawing processes.
[0052] Two batches of bobbins (each about 400 g) were prepared.
[0053] Batch 1: 50 bobbins of which 16 bobbins had one or more
defects [0054] Batch 2: 75 bobbins of which 24 bobbins had one or
more defects It was therefore observed that a very high quality
level and high consistency was realized utilizing a process
involving twisting of the yarn and post-twist-drawing despite no
spin finish was added during the process
Comparative Example 2
Preparation of HPPE Yarn Utilizing no Twisting
[0055] Experiment 7 was repeated using rewinding without twisting.
The resulting yarn showed very low coherency and no stable bobbins
could be prepared after final drawing.
[0056] An individual feature or combination of features from an
embodiment of the invention described herein, as well as obvious
variations thereof, are combinable with or exchangeable for
features of the other embodiments described herein, unless the
person skilled in the art would immediately realize that the
resulting embodiment is not physically feasible.
REFERENCE NUMBERS IN FIGURES
[0057] 2: Mixing [0058] 4: Spinning [0059] 6: Quenching and
removing part of solvent [0060] 7: Drawing [0061] 8: Inline drawing
[0062] 10: Offline drawing [0063] 12: Twisting [0064] 13:
Post-twist-drawing [0065] 14: Inline post-twist-drawing [0066] 16:
Offline post-twist-drawing [0067] 18: Un-drawn yarn [0068] 20:
Multifilament yarn
* * * * *