U.S. patent application number 13/113848 was filed with the patent office on 2012-01-26 for process for making a monofilament-like product.
This patent application is currently assigned to DSM IP Assets B.V.. Invention is credited to Christiaan Henri Peter Dirks, Cyril David VEILLAT.
Application Number | 20120021216 13/113848 |
Document ID | / |
Family ID | 32088022 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120021216 |
Kind Code |
A1 |
VEILLAT; Cyril David ; et
al. |
January 26, 2012 |
PROCESS FOR MAKING A MONOFILAMENT-LIKE PRODUCT
Abstract
The invention relates to a process for making a
monofilament-like product from a precursor containing at least one
strand of a spun yarn made from polyolefin staple fibres,
comprising the steps of a) exposing the precursor to a temperature
within the melting point range of the polyolefin for a time
sufficient to at least partly fuse adjacent fibres and b)
simultaneously stretching the precursor at a draw ratio of at least
1.0. The invention further relates to a monofilament-like product
obtainable by said process showing improved abrasion resistance,
and to the use of said monofilament-like product for making various
semi-finished and end-use products.
Inventors: |
VEILLAT; Cyril David;
(Maastricht, NL) ; Dirks; Christiaan Henri Peter;
(Dilsen, BE) |
Assignee: |
DSM IP Assets B.V.
Heerlen
NL
|
Family ID: |
32088022 |
Appl. No.: |
13/113848 |
Filed: |
May 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10530435 |
Sep 28, 2005 |
|
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|
PCT/NL2003/000687 |
Oct 10, 2003 |
|
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13113848 |
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Current U.S.
Class: |
428/360 ;
156/180 |
Current CPC
Class: |
D02G 3/22 20130101; D02G
3/402 20130101; D02G 3/444 20130101; D02G 3/442 20130101; Y10T
428/2905 20150115; Y10T 428/2913 20150115 |
Class at
Publication: |
428/360 ;
156/180 |
International
Class: |
D02G 3/22 20060101
D02G003/22; D01D 5/12 20060101 D01D005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2002 |
EP |
02079204.0 |
Claims
1. Process for making a monofilament-like product comprising the
steps of: a) exposing a precursor of indefinite length containing
at least one strand comprised of a spun yarn of polyolefin staple
fibres to a temperature within the melting point range of the
polyolefin fibres for a time sufficient to soften the staple fibers
without partial melting and allow adjacent staple fibers to at
least partly fuse to one another, and b) simultaneously with step
a) stretching the precursor at a draw ratio of at least 1.0.
2. Process according to claim 1, wherein the draw ratio is from 1.2
to 25.
3. Process according to claim 1, wherein the polyolefin is
ultra-high molar mass polyethylene.
4. Process according to claim 1, wherein the staple fibres have
been obtained by stretch-breaking of a polyolefin multifilament
yarn.
5. Process according to claim 1, wherein the precursor contains
plied and twisted strands.
6. Process according to claim 1, further comprising a step
preceding step a) of pretreating the precursor in order to enhance
inter fibre bonding.
7. Process according to claim 6, wherein pretreating comprises
applying an oil to the precursor.
8. Process according to claim 6, wherein pretreating comprises
applying a polyurethane composition to the precursor.
9. Process according to claim 1, further comprising a step of
applying a coating composition to the product after steps a) and
b).
10. Monofilament-like product comprising an at least partly fused
spun yarn made from polyolefin staple fibres made by the process
according to claim 1.
11. A fishing line which comprises a monofilament-like product
according to claim 10.
12. A cut-resistant article which comprises a monofilament-like
product according to claim 10.
13. Monofilament-like product according to claim 10, comprising an
outer surface layer in which the polyolefin staple fibers are at
least partly fused to one another.
14. Monofilament-like product according to claim 13, wherein the
polyolefin staple fibers are at least partly fused to one another
in both the outer surface layer and an inner layer of the
product.
15. Monofilament-like product comprising a spun yarn made from
polyolefin staple fibers, wherein adjacent ones of the staple
fibers are at least partly fused without being partially
melted.
16. Process according to claim 1, wherein step a) is practiced such
that adjacent polyolefin staple fibers in at least an outer surface
layer of the monofilament-like product are at least partly fused to
one another without partial melting.
17. Process according to claim 16, wherein step a) is practiced to
at least partly fuse staple fibers to one another without melting
in both the outer layer and an inner layer of the monofilament-like
product.
Description
[0001] This application is a continuation of commonly owned
co-pending U.S. application Ser. No. 10/530,435, filed Apr. 6,
2005, which in turn is the national phase application under 35 USC
.sctn.371 of PCT/NL2003/000687, filed Oct. 10, 2003, which
designated the U.S. and claims priority to EP 02079204.0 filed Oct.
10, 2002, the entire contents of each of which are hereby
incorporated by reference.
[0002] The invention relates to a process for making a
monofilament-like product from a precursor containing at least one
strand of polyolefin fibres, comprising the steps of a) exposing
the precursor to a temperature within the melting point range of
the polyolefin for a time sufficient to at least partly fuse
adjacent fibres and b) simultaneously stretching the precursor at a
draw ratio of at least 1.0. The invention further relates to a
monofilament-like product for making various semi-finished and
end-use products.
[0003] Such a process is known from EP 0740002 B1. In this patent
publication a process for making a fishing line from yarns of
filamentous materials is described, wherein a braided, twisted, or
twisted and plied fishing line made from yarns of gel spun
polyolefin filaments, is exposed to a temperature within the
melting point range of said polyolefin for a time sufficient to at
least partially fuse adjacent filaments while stretching said line
at a stretching ratio within the range from 1.01 to 2.5. The yarns
applied in this process are continuous multi-filament yarns, more
specifically such yarns made by so-called gel spinning of
ultra-high molar mass polyethylene (UHMwPE), for example yarns
commercially available under the names Spectra.RTM. of
Dyeema.RTM..
[0004] Fishing lines are generally monofilaments made from
synthetic polymers, having a round, firm structure that allows
convenient handling for bait casting, spinning, and spin casting.
Such monofilament lines generally have a still nature and smooth
surface, which combine to reduce drag during the case and enable
longer casts while providing better release from fishing reels.
Braided lines are less suited for fishing lines, because they have
a tendency to fray at the end of the line, may entrap water,
present an outer surface that is vulnerable to snags and
entanglement, and have an opaque white colour which is too visible
below water. The process known from EP 0740002 B1 allows making
monofilament-like fishing lines from braided or twisted lines made
from polyolefin multi-filaments yarns, which lines do not have the
said disadvantages of braided lines.
[0005] A disadvantage of the process described in EP 0740002 B1 is
that the product obtained therewith shows limited resistance to
break when exposed to abrasive conditions.
[0006] It is therefore an object of the present invention to
provide a process for making a monofilament-like product that does
not show said disadvantage.
[0007] This object is achieved according to the invention with a
process for making a monofilament-like product from a precursor
containing at least one strand of polyolefin fibres, comprising the
steps of a) exposing the precursor to a temperature within the
melting point range of the polyolefin for a time sufficient to at
least partly fuse adjacent fibres and b) simultaneously stretching
the precursor at a draw ratio of at least 1.0, wherein the strand
is a spun yarn made from polyolefin staple fibres.
[0008] With the process according to the invention a
monofilament-like product can be made from e.g. a plied or braided
polyolefin yarn construction, which product shows improved abrasion
resistance, as expressed in the number of cycles until break as
measured in a test described under Materials and Methods.
[0009] The monofilament-like product obtained by the process
according to the invention also shows surprisingly high tensile
strength, significantly higher than the initial spun yarn or the
plied yarn made from such spun yarn and used as the precursor. The
mono-filament-like product obtained further has a pleasant touch or
feel and can be easily handled and knotted; furthermore it shows
surprisingly high knot strength and knot strength efficiency.
Another advantage of the process according to the invention is that
the degree of fusion can be easily varied and controlled; resulting
in products with tailored property profiles. A still further
advantage is that the monofilament-like product obtained may be
effectively coated with a coating composition in an additional
process step.
[0010] With the process according to the invention a
monofilament-like product is made from a precursor containing at
least one strand of polyolefin fibres. A monofilament-like product
is understood to be a product that has an appearance and feel more
resembling that of a monofilament than that of multi-filament yarn
or cord, but which actually is made from at least one strand
containing a multitude of fibres, which fibres typically have a
diameter of less than about 50 micrometer.
[0011] The monofilament-like product may have a diameter that
varies within a wide range, e.g from about 0.1 up to 10 millimetre.
A precursor is herein understood to be an article of indefinite
length that contains at least one strand of polyolefin fibres, and
is used as feed or starting material. A suitable precursor can be
in the form of for example a braided cord, a plied and twisted
yarn, cord or rope comprising a number of strands, but also a
single-strand yarn. A strand of polyolefin fibres is understood to
be a fibrous article like a yarn containing predominantly, i.e. 50
or more mass % of polyolefin fibres.
[0012] The process according to the invention comprises the step of
exposing the precursor to a temperature within the melting point
range of the polyolefin for a time sufficient to at least partly
fuse adjacent fibres. The conditions of this fusion step are chosen
such, that the temperature and time of exposure are sufficient to
soften the polyolefin fibres and to allow them to fuse at least
partly within the specific structure applied. The melting point
range of the polyolefin is the temperature range between the peak
melting point of a non-oriented polyolefin and the peak melting
point of a constrained highly-oriented polyolefin fibre, as
determined by DSC analysis using a scan-rate of 20.degree. C./min.
For UHMwPE fibres, typically showing a melting point range of
138-162.degree. C., the temperature is preferably within the range
from about 150.degree. C. up to about 157.degree. C. Residence
times during which the precursor is exposed to the fusion
temperature may vary within a broad range, but are typically within
the range from about 5 seconds to about 1500 seconds. Although
higher temperatures tend to enhance the fusion process, care should
be taken not to apply too high a temperature as this may cause loss
in strength of the product, resulting from e.g. partial melting or
other molecular relaxation effects.
[0013] During the fusion process, the appearance of the precursor
changes from an initial, opaque white colour into a translucent,
milky, or even substantially transparent surface appearance of the
product, depending on the degree of fusion and type of precursor
material. The light transmission of the product increases with
increased degree of fusion between fibres. Such an increase in
translucency or light transmission is a definite advantage for
application as underwater fishing lines.
[0014] For a monofilament-like product showing low end fraying it
suffices that the outer surface layer of fibres is at least partly
fused, as seen by increase in light transmission. A higher degree
of fusion, e.g. also binding fibres in more inner parts of a
precursor or strand, however, is preferred for making a product
with higher abrasion resistance, and a higher bending stiffness,
that is with more monofilament-like characteristics. The degree of
fusion can be adjusted by varying exposure temperature and/or time
of exposure in the process according to the invention.
[0015] The degree of fusion can be determined on the product
obtained, for example by visual evaluation, e.g. with the naked aye
or by using an optical or electron microscope; or by measuring
mechanical properties like strength or stiffness. Another
possibility is to determine the amount and rate of absorption of a
coloured liquid, e.g. from a marker, as described in EP 0740002 B1.
The degree of fusion can also be derived from a test, wherein the
loaded product is abraded over a metal rod and the number of
movements is determined after which the monofilament-like product
disintegrates into its constituting filaments.
[0016] In a special embodiment of the process, the degree of fusion
is only very low, or even hardly measurable on the product
obtained. Surprisingly, it has been found that such product that
has been stretched at elevated temperature does show markedly
improved tensile strength over its precursor, be it that the
abrasion resistance is only slightly better. The invention
therefore also relates to a process for stretching a braided or
plied construction containing at least one strand of spun yarn made
from polyolefin staple fibres at a draw ratio of at least 1.1,
while exposing it to a temperature within the melting point range
of the polyolefin. The product obtained with this process shows
improved tensile properties, but still has bending properties much
like the starting construction.
[0017] The process according to the invention also includes
simultaneously stretching the precursor at a draw ratio, also
called stretch ratio, of at least 1.0. Applying a draw ratio of at
least 1 to the precursor during the heat exposure prevents a
decrease in strength of the product. A draw ratio of 1.1 or higher
tends to improve especially the tensile strength. The strength of
the product is than surprisingly found to be significantly higher
than that of the precursor or of the strands contained therein.
Above a certain draw ratio this effect levels off, or strength may
even decrease as result of partly damaging or breaking of fibres.
In addition, the higher the draw ratio, the lower the titre of the
resulting product. The maximum draw ratio is thus dependent on the
type of precursor and its fibres, and is generally at most about
50. Preferably, the draw ratio is from 1.1 to 40, from 1.2 to 25,
more preferably from 1.3 to 10, or even from 1.4 to 5.
[0018] Preferably, the product obtained after step b) is cooled
while keeping it under tension. This has the advantage that the
orientation in the product obtained during fusing and stretching,
on a level of fibres and on molecular level within fibres, is
retained better. Such tension results from, for example, winding
the product into packages subsequent to preceding steps of the
process.
[0019] In the process according to the invention at least one
strand in the precursor is a spun yarn made from polyolefin staple
fibres, that is the spun yarn comprises at least 50 mass % of
polyolefin staple fibres. In general, yarns can be made of
continuous filaments, staple fibres or combinations thereof.
Natural fibres can be classified in two categories: short staple
fibres (cotton like, with typical staple or filament length 15-60
mm) and long staple fibres (wool like, typical staple length 40-200
mm). Synthetic fibres are first made as continuous filaments; they
can be subsequently converted into staple fibres by either cutting
or stretch breaking processes. Cutting generally leads to a square
filament distribution (all filaments having about the same length);
although modified systems allow obtaining some variation in the
filament length distribution. Stretch breaking generally results in
staple fibres having a more Gaussian-like distribution of filament
lengths. In a stretch breaking process, the filaments are stretched
between several sets of rollers operating at different speeds until
they break.
[0020] Staple fibres can be made into yarn via a process of pulling
and twisting strands of parallel fibres, generally referred to as
spinning. For this reason, yarn made from staple fibres is called
spun yarn.
[0021] Industrial yarn spinning processes include the following
basic process steps: loosening, carding, drawing and spinning.
Loosening refers to separating and optionally cleaning of e.g.
baled staple fibres. Carding is the further loosening and
separating of fibres, for example by passing them between rotating
drums covered with needles. This results in a thin web of partly
paralleled fibres, which is formed into a rope-like strand often
called a sliver. Combing may then be applied to enhance orientation
of fibres and to remove small fibres. During drawing, slivers are
drawn out in one or more steps. Several slivers, either of the same
or of different staple fibres, may be blended together in order to
obtain a uniform fibre density. Mixing staple fibres at the carding
stage can also make yarns comprising blends of different natural
and/or synthetic fibres. Before feeding to the spinning machine,
the sliver may be further drawn while a slight twist is added,
called roving. During spinning, the sliver or roving is further
drawn out and a twist is added to provide cohesion of the
overlapping fibres, and the yarn is winded onto bobbins. Such a
package of winded yarn may be of conical or cylindrical form, and
is normally simply referred to as package.
[0022] The described spinning process results in a twisted,
single-strand yarn, also called single yarn. Depending on the
twisting direction applied, such yarns are often referred to as
either S or Z yarns. A twisted single-strand yarn is generally
rather `lively`, meaning that it tends to twist, tangle, slant or
curl round itself when held with insufficient tension. In order to
reduce this liveliness, that is to obtain a calm or balanced yarn
that can be satisfactorily further processed into e.g. a fabric, it
has been generally accepted in industry that two or more strands of
single yarns need to be combined in an additional step. Such
combining step is normally called folding or plying. A two-fold
yarn, or two-plied yarn can, for example, be made by twisting
together two single-strand Z yarns with a S-twist, or by plying
together a Z and S type yarn. The thus obtained folded yarns may
also be stronger and more uniform than single-strand yarns.
[0023] The spun yarn applied in the process according to the
invention comprises at least 50 mass % of polyolefin staple fibres.
The spun yarn may further comprise up to 50 mass % of one or more
other staple fibres, like natural fibres or synthetic fibres, to
make a blend yarn. Suitable examples of such secondary staple
fibres include wool, polyolefin, acrylic, polyester or polyarnide,
including aromatic polyarnide fibres.
[0024] In a special embodiment of the process according to the
invention, the spun yarn comprises an amount of a staple yarn made
from a thermoplastic polymer having a lower melting point range
than the polyolefin staple fibres. The advantage hereof is that
additional thermal bonding may take place during step a). Use of a
spun yarn in the process according to the invention enables this
possibility, since making a blended spun yarn is easier and more
economical than making a blended multi-filament yarn. Examples of
suitable thermoplastic polymers include copolymers of at least one
alpha-olefin with other monomers, like LLDPE, or ethylene-acrylic
copolymers. Effective amounts of such staple fibres can be
determined by experimentation, and are generally about 5 to 25 mass
%.
[0025] In a further special embodiment according to the invention,
the main component of the spun yarn is not a polyolefin staple
fibre, but a staple fibre made from a high strength, high modulus
filament yarn having a higher heat resistance than a polyolefin and
that cannot be thermally bonded per se; like an aromatic polyarnid
yarn such as Kevlar.RTM. or Twaron.RTM., a liquid crystalline
polyester yarn, or polybenzoxazole or polybenzothiazole based yarn.
Such spun yarn further comprises up to 50 mass % of a staple yarn
made from a thermoplastic polymer having a relatively low melting
point range, for example polyolefin staple fibres with a melting
point below 200.degree. C. Examples of suitable thermoplastic
polymers include copolymers of at least one alpha-olefin with other
monomers, like LLDPE, or ethylene-acrylic copolymers. The advantage
of this embodiment is that thermal bonding can take place during
step a), whereas without the presence of fibres with low melting
point no monofilament-like product can be made from such high
strength, high modulus filament yarns having a high heat resistance
by exposing it to heat while stretching. Effective amounts of such
thermoplastic heat fusable staple fibres can be determined by
experimentation, and are generally about 5 to 25 mass %. A
monofilament-like product based on a spun yarn comprising aromatic
polyarnid staple fibres and heat-fusable staple fibres made by said
process combines high strength, high abrasion resistance and high
thermal resistance.
[0026] The spun yarn, and the staple fibres, may further contain
the usual additives, like stabilizers, colorants, mineral
particles, sizing agents, and the like.
[0027] The choice of the other staple fibres, e.g. type, length,
titre (dpf), whether they can be fused under the applied
temperature and time conditions along with the polyolefin staple
fibres, and/or of additives, is mainly determined by the ultimate
properties that are desired, and can be made by the skilled person
using general knowledge or routine experimentation.
[0028] Preferably, the spun yarn that is applied in the process
according to the invention comprises at least 60, 70, 80 or even 90
mass % of polyolefin staple fibres, because this enables better
mechanical properties of products obtained. For this reason, the
spun yarn applied most preferably comprises essentially only said
staple fibres.
[0029] Staple fibres obtained from various polyolefin yarns can be
chosen as staple fibres for application in the process according to
the invention. Particularly suitable polyolefin yarns are made from
homo- and copolymers of ethylene or propylene. In addition, the
polyolefins used may contain small amounts of one or more other
monomers, in particular other alpha-olefins. Good results are
achieved if linear polyethylene (PE) is chosen as polyolefin.
Linear polyethylene is here understood to be polyethylene with less
than one side chain per 100 carbon atoms, and preferably less than
one side chain per 300 carbon atoms; a side chain or branch usually
containing at least 10 carbon atoms. The linear polyethylene may
further contain up to 5 mol % of one or more comonomers, such as
alkenes like propylene, butene, pentene, 4-methylpentene or octene.
Besides the polyolefin the fibre may contain small amounts of
solvents or additives that are customary for such fibres, such as
anti-oxidants, spin-finishes, thermal stabilizers, colorants,
etc.
[0030] Preferably, the polyolefin fibre, in particular the
polyethylene fibre, has an intrinsic viscosity (IV) of more than 5
dl/g. Because of their long molecule chains, polyolefin fibres with
such an IV have very good mechanical properties, such as a high
tensile strength, modulus, and energy absorption at break. This is
also the reason why even more preferably the polyolefin is a
polyethylene with an IV of more than 10 dl/g. The IV is determined
according to method PTC-179 (Hercules Inc. Rev. Apr. 29, 1982) at
135.degree. C. in decalin, the dissolution time being 16 hours, the
anti-oxidant is DBPC, in an amount of 2 g/l solution, and the
viscosity at different concentrations is extrapolated to zero
concentration. Polyethylene of such high viscosity is often called
UHMwPE. UHMwPE filament yarn can be prepared by spinning of a
solution of UHMwPE Into a gel fibre and drawing the fibre before,
during and/or after partial or complete removal of the solvent;
that is via a so-called gel-spinning process as for example
described in EP 0205960 A, in WO 01/73173 A1, in Advanced fiber
spinning technology, Ed. T. Nakajima, Woodhead Publ. Ltd (1994),
ISBN 185573 182 7, and in references cited therein.
[0031] Preferably, UHMwPE staple fibres are chosen, because they
combine high strength with a low relative density. More
specifically, the spun yarn that is applied in the process
according to the invention comprises UHMwPE staple fibres that have
been made via a stretch-breaking process from a multi-filament
UHMwPE yarn, since the broader fibre length distribution of such
staple results in a yarn with better mechanical properties.
[0032] In a special embodiment, the spun yarn applied is a
single-strand spun yarn. In a further embodiment, the single-strand
spun yarn as described in a co-pending application, which is not
yet published, is applied in the process according to the
invention. This single-strand spun yarn has been made from at least
50 mass % of staple fibres that have been obtained from a
continuous polyolefin multifilament yarn having a tensile strength
of at least 16 cN/dtex; a tensile modulus of at least 700 cN/dtex;
and a denier per filament of fibre of at most 18 dpf; which staple
fibres have an average fibre length of between 40 and 180 mm; and
show essentially no crimp; and which spun yarn has a twist level
characterized by an a twist coefficient of 40-100
t.m..sup.-1.(m/g).sup.-1/2. Preferably, the staple fibres have been
obtained from highly-oriented polyolefin fibres, such as those
based on ultra-high molar mass polyethylene (UHMwPE). The advantage
of this process is that translucent or semi-transparent
monofilament-like products having a relatively low titre, e.g. of
10-100, preferably 15-50 dTex, and a low relative density can be
made at higher overall production rate and lower overall costs
compared with the process known from EP 0740002 A1 starting from
multi-filament yarns. The products obtained by this process are
especially suited for medical applications, like surgical
sutures.
[0033] The a twist coefficient characterizes the twist level of a
yarn according to the Koechlin equation: T=.alpha.(Nm).sup.1/2,
wherein T is the twist level expressed as the number of turns per
meter (t.m..sup.-1) and Nm is the metric yarn count (1000/tex, or
m/g). This twist coefficient is also referred to as (metric) twist
factor, or twist multiplier; see for example at
http://www.fibre2fashion.com/GLOSSARY/glossary17.htm. Preferably,
the twist coefficient is between 60 and 100, 65 and 90, or even
between 70 and 85.
[0034] This single-strand spun yarn shows very little liveliness,
and is calm enough to enable further processing without the need of
first making a folded yarn. The staple fibres in the single-strand
spun yarn have been obtained from a filament yarn having a linear
density of at most 18 denier per filament (dpf), preferably at most
14, more preferably at most 10 dpf, and even more preferred at most
6, or at most 4 dpf. The lower the linear density of the fibres,
the thinner the spun yarn can be, since a certain minimum number of
fibres is needed in a cross-section to give a yarn of sufficient
integrity. Furthermore, a lower the linear density of the fibres
results in higher tensile strength of the spun yarn at a constant
yarn titre. In view of fibre production efficiency it is preferred
that the linear density is at least 0.2, 0.3 or at least 0.5 dpf.
Starting from thinner spun yarns has the advantage that thinner
monofilament-like products can be produced in a more economical
way.
[0035] The single-strand spun yarn applied in the process according
to the invention comprises polyolefin staple fibres that show
essentially no crimp; the fibres not being, or only slightly
textured. Crimp is a measure for the waviness of a fibre, and may
be expressed as the difference between the length of the
straightened or fully extended fibre and the crimped length, that
is the length of the fibre when substantially free from external
restraint. Showing essentially no crimp is herein understood to
mean that the length of the staple fibres in unstrained condition
is at least 80% of the straightened length. Preferably, the crimped
length is at least 90% of the straightened length, even better at
least 95%. Showing essentially no crimp is further understood to
include no permanent crimp. For example, UHMwPE staple fibres may
show some crimp that may have been introduced during staple making,
but this crimp is not permanent, since it will essentially
disappear upon exposing the fibres to elongational forces, which
may e.g. occur during spinning.
[0036] In the process according to the invention at least one
strand in the precursor is a spun yarn made from polyolefin staple
fibres. The precursor may also contain one or more strands made
from other staple fibres and/or from continuous filaments, to
arrive at a monofilament-like product of different degrees of
fusion between and within strands and at different mechanical
properties and appearance and feel. Such variations can be made by
a skilled person using general knowledge or routine
experimentation. Preferably, all strands In the precursor are spun
yarns based on polyolefin staple fibres, since this allows to vary
the degree of fusion, and thus of product properties to a great
extent.
[0037] The process according to the invention can be performed with
a precursor of various constructions, for example of a braided
construction, or a plied and twisted construction. Preferably, a
precursor with plied (or folded) and twisted strands is applied.
This has the advantage that the precursor can be made more easily
and more cost-effectively; and that the product obtained shows
better performance; especially surprisingly good resistance to
failure during abrasion tests.
[0038] The process according to the invention can further comprise
a step preceding step a) of pretreating the precursor, or one or
more of the strands therein, in order to enhance inter fibre
bonding during the fusion step. Such pre-treatment step may include
coating the precursor with a component or a composition; scouring
the precursor, that is washing-off surface components like spin
finishes etc.; or applying a high-voltage plasma or corona
treatment.
[0039] In one embodiment the precursor is pretreated by applying;
e.g. by dipping or wetting, an effective amount of a mineral oil
(e.g. heat transfer grade mineral oil with an average molar mass of
about 250-700), vegetable oil (e.g. coconut oil), or a, preferably
non-volatile, solvent for polyolefin, like paraffin. This
pre-treatment step may be performed at ambient conditions, or at
elevated temperature up to below the melting temperature range of
the polyolefin fibre.
[0040] In another embodiment, pretreating comprises applying a
coating composition to the precursor, which composition may be a
solution or dispersion of a polymer that enhances fibre to fibre
bonding during exposure to higher temperature at the fusing step,
or otherwise improves performance. In a preferred embodiment, the
precursor is coated with a polyurethane composition, like a
dispersion of film-forming polyurethane. Such a composition may
further comprise components that contribute to improving the
abrasion- or cut-resistance of the monofilament-like product.
Examples of components that improve cut-resistant are small
particulate particles of high surface hardness, like mineral
particles, ceramic particles, glass, metals and the like. The
coating composition may further comprise other additives, like
colorants or stabilisers.
[0041] The process according to the invention can further comprise
a step wherein a coating composition is applied to the product
after steps a) and b) to form a coating layer. Such coating
composition may comprise a typical spin finish to allow easier
handling and processing of the product in subsequent operations; a
compound or composition to control adhesion during subsequent
making of composite articles comprising the product; or a binder
composition that further enhances integrity and strength of the
product. Typical examples of the latter include polyurethane or
polyolefin-based, like ethylene-acrylic copolymers, binder
compositions. The coating composition may be applied as a solution
or dispersion. Such a composition may further comprise components
that further improve the abrasion- or cut-resistance of the
monofilament-like product. Examples of components that improve
cut-resistant are small particulate particles of high surface
hardness, like various mineral or ceramic particles. The coating
composition may further comprise other additives, like colorants,
stabilisers, etc.
[0042] Application of a coating composition in the process
according to the invention is found to be relatively easy and
effective compared with a process wherein continuous filament yarn
is applied as precursor. Apparently the product obtained after
steps a) and b) is more receptive towards such coatings, especially
if the fibres at the surface of the product have been only partly
fused.
[0043] The invention also relates to a monofilament-like product
comprising an at least partly fused spun yarn made from polyolefin
staple fibres, which product is obtainable by the process according
to the invention. This product has a unique structure and combines
several advantageous properties; it has the translucent appearance
of a monofilament, yet its touch and feel are different from
polyolefin monofilaments or monofilament-like products as known
from, for example, EP 0740002 B1. The monofilament-like product
according to the invention shows surprisingly high resistance to
break during abrasive testing; can be easily knotted, and the
knotted product shows high retention of strength. The
monofilament-like product also shows surprisingly high tensile
strength; even significantly higher than the strength of the
starting spun yarn in the precursor. Typically, the
monofilament-like product has a tensile strength of at least 10
cN/dtex, preferably at least 15, 20 or even 25 cN/dTex. Such a high
strength is typically found for a product based on a precursor that
comprises a relatively high amount of spun yarn based on UHMwPE
staple fibres.
[0044] The monofilament-like product obtainable by the process
according to the invention has a linear density, also referred to
as titre, which may vary within wide limits, e.g. from 10 to 15000
dTex. Generally, the product has a titre of from 30 to 2500 dtex.
The lower titre products are suitable for use as sutures and the
like. In view of applications like fishing lines, or protective
garments and clothing, the titre is preferably from 100 to 1600
dTex, even more preferably from 200 to 1200 dTex.
[0045] The invention further relates to the use of the
monofilament-like product according to invention for making various
semi-finished and end-use products, like fishing-lines; sutures,
fabrics; cords and ropes; composite yarns; and their use in for
example cut-resistant articles.
[0046] The invention also concerns semi-finished and end-use
products comprising the monofilament-like product according to the
invention.
[0047] The invention will now be further illustrated by the
following examples and comparative experiments.
Materials and Methods
[0048] Multi-filament UHMwPE yarn, Dyneema.RTM. 1760SK60 (DSM High
Performance Fibres, NL), having a titre of 1760 dTex, a tensile
strength of 28 cN/dTex, a tensile modulus of 910 cN/dTex, and a
denier per filament of fibre of about 1 dpf was made into staple
fibres by a stretch-breaking process, as for example described in
EP 0445872 A1. The average length of the staple fibres was about 80
mm. The staple fibres were subsequently spun into a single-strand
yarn using NSC equipment of the long staple fibre type. The yarn
obtained had a yarn count of about Nm 44 (about 225 dTex), the
twist level applied corresponded to at coefficient of about 80
Koechlin law). The spun yarn showed little liveliness, as was
demonstrated by cutting a length of 100 cm, holding it vertically
fixed at only one end, and observing hardly any tendency to twist.
Its tensile strength was about 15.0 cN/dTex, tensile modulus about
153 cN/dTex, and elongation at break about 4.3%. This material is
referred to as SSSY hereafter.
[0049] The tensile strength (or strength) (and the tensile modulus)
are defined and determined on multifilament and spun yarns, and on
monofilament-like products as specified in ASTM D885M, using a
nominal gauge length of the fibre of 500 mm, a crosshead speed of
50%/min and Instron 2714 clamps. For calculation of the strength,
the tensile forces measured are divided by the titre, as determined
by weighing 10 metres (or another length) of fibre. Elongation is
the measured elongation at break, expressed in % of the original
length after clamping the specimen.
[0050] Knot strength is determined by measuring the strength of a
specimen comprising a Palomar-knot. The Palomar-knot is a
general-purpose connection recommended for joining a fishing line
to a swivel, a snap or a hook. The doubled end of the specimen is
passed through the eye of a hook and a simple overhand knot is
made. The hook is then passed through the loop and the knot is
tightened.
[0051] Knot strength efficiency is calculated as the relative value
(%) of the measured knot strength to measured tensile strength.
[0052] Abrasion resistance was measured following a procedure based
on the test described by ASTM D 3108 for determining yarn friction.
For this purpose the Yarn Friction Measuring Apparatus described in
ASTM D 3108 has been adapted, such that one end of the sample to be
tested is fixed to an eccentric crank or cam rotated by a motor,
the other end is loaded with a weight. During the test the sample
is abraded against a ceramic eye and the number of cycles is
determined until the sample fails (breaks). The number given is the
average of at least 5 tests.
Comparative Experiment A
[0053] As precursor (feed) material a braided construction made
from a multi-filament gel-spun UHMwPE yarn having a titre of 224
dTex, a tensile strength of 39 cN/dTex, a tensile modulus of 1250
cN/dTex, and a denier per filament of fibre of about 1 dpf was
applied. This braid contained 8 strands of said yarn braided with a
medium tightness, expressed as picks per centimetre, of 7.5
(presented as 8.times.224/7.5; see Table 1).
[0054] This braid was passed through a bath of liquid paraffin as
pretreatment step, and excess oil was wiped off by passing between
non-woven fabrics. The paraffin content was calculated to be about
11 mass % by determining the mass increase upon this step. The
braid was then guided over first driven rolls into an oven, kept at
a constant temperature of 153.5.degree. C., with a constant speed
of 10 m/min. At the exit of the oven, the braid was guided over
second driven rolls. The speed of the second rolls was adjusted
such that a draw ratio of 1.9 and a stretch rate of 0.7 m/min was
applied. In case a different draw ratio is to be applied, as in
some other experiments, the stretch rate in the oven is kept about
constant by varying the pathlength of the sample in the oven and
the speed of the second rolls. The oven is equipped with a number
of rolls, such that the sample pathlength in the oven can be from
2.8 up to 58.8 meter.
[0055] The product appearance changed from initially opaque white
to almost translucent; its surface was still rather smooth,
although definitely less smooth and shiny than of the starting
product. Also the product felt more rough and stiffer, and retained
at an angle after bending.
[0056] Results of further testing are compiled in Table 1. It
should be noted that the knot strength efficiency found is markedly
lower than reported for similar products in EP 0740002 B1; this may
be related to the type of knot that is used.
Comparative Experiment B
[0057] The experiment was performed largely analogous to Comp. Exp.
A, be it that a twisted and plied construction was made from 6
strands of the same multifilament yarn, applying a clockwise twist
of 120 turns/cm (indicated as 6/224; 120Z). Measured paraffin
content was about 12 mass %; the draw ratio was 1.8. Results of
further testing are compiled in Table 1.
EXAMPLE 1
[0058] A braided construction containing 8 strands of the SSSY
material described above, with 12 picks/cm (indicated as
8.times.Nm44/12 in Table 1) was used as precursor. Analogously to
Comp. Exp. A this braid was passed through the oven, but without
any pre-treatment step and applying a draw ratio of 1.0. The
resulting product had similar appearance as its starting material;
it was found to have a lower tensile strength than the spun yarn
originally applied as strands. The product showed high strength
retention after a knot was made.
EXAMPLES 2-3
[0059] Example 1 was repeated, but now about 12 mass % paraffin was
added before step a) and a draw ratio of 1.8, respectively 1.7, was
applied. The more translucent appearance of the products indicates
more fusion to have taken place. The surface touch was less smooth
than for Comp. Exp. A. Both resulting products have a higher
tensile strength than the spun yarn applied as strands, show a
higher resistance to bending (stiffer) and retain at an angle after
bending. The number of cycles until break during abrasion testing
was found to be more than 5 times higher for Ex. 2 than for Comp.
Exp. A.
EXAMPLES 4-6
[0060] Braided constructions made from the SSSY material described
above, containing 8 strands with 9.5 picks/cm were used as
precursor. Analogously to Comp. Exp. A, this braid was passed
through the oven, but without any pre-treatment step and applying a
draw ratio of 1.0. The resulting product appeared to have a lower
tensile strength than the spun yarn applied as strands; but a knot
could but made with high strength retention (Ex. 4). If a draw
ratio of 1.6 or 1.7 was applied, the tensile strength again
increased, as with Ex. 2-3; but the abrasion resistance was only
slightly better. Apparently under the temperature and time
conditions applied, the degree of fusion of the fibres was not high
enough to result in high abrasion resistance, without a
pre-treatment.
EXAMPLES 7-9
[0061] Examples 4-6 were repeated, but now about 13 mass % of
paraffin was added to the precursor. A strength increase vs. the
original spun yarn was observed for all samples; example 7 confirms
the positive effects of a higher degree of fusion on abrasion
resistance.
EXAMPLES 10-16
[0062] Braided constructions made from the SSSY material described
above, containing 8 strands with 7.5 picks/cm were used as
precursor. Ex. 10 confirmed that at draw ratio 1.0 no increase in
tensile strength is found; and that without pre-treatment and under
the chosen conditions only little fusing occurs. Adding paraffin
and increasing exposure temperature increases degree of fusion, as
judged from appearance change. Improved fusion was also apparent
from testing resistance to desintegration of the product upon
abrading it over a metal rod; Ex. 11 could withstand 18, Ex. 12 and
13 about 33 movements. A 4-5 fold increase was observed in the
number of cycles until break in the abrasion resistance test. A
higher temperature or draw ratio did not result in further
improvement in tensile properties for the present precursor
construction.
EXAMPLE 17
[0063] The single-strand spun yarn SSSY was used as precursor.
Pretreatment consisted of applying an aqueous polyurethane
dispersion, L9010 ex GOVI (BE), via dipping. The polyurethane
content was determined (on the resulting product) to be about 15
mass %. The combination of pre-treatment, heat exposure and
stretching with draw ratio 1.6 markedly increased tensile strength
of the product. The product also had higher stiffness, more
translucent appearance, and a knot could be made easily with high
strength retention.
EXAMPLES 18-22
[0064] As precursor a 6-fold yarn based on SSSY, having a clockwise
twist of 120 turns/cm (indicated as 6/Nm44; 120Z) was applied. In
Ex. 19 about 13.5 mass % of paraffin was added as pre-treatment,
combined with a draw ratio of 1.8. This fused product showed very
good resistance to break during abrasion testing; about 15 fold
increase vs. Comp. Exp. B. The samples made with a polyurethane
pre-treatment (Ex. 20-22; PUR content about 16 mass %) showed very
good tensile properties and knot strength (efficiency), and
improved abrasion resistance.
EXAMPLES 23-24
[0065] The products were based on an 18-fold, twisted yarn
(starting strands were SSSY), with about 12.5 mass % paraffin and
were made under analogous conditions as before. The results
obtained for these thicker products, with titres of about 4100 and
2500 dTex, respectively, are in line with the other results.
TABLE-US-00001 TABLE 1 Product properties Abrasion Knot resistance
Process characteristics Tensile Knot strength (cycles Precursor
material Temp. Draw strength Elongation strength efficiency until
Type construction Pre-treatment (.degree. C.) ratio (cN/dTex) (%)
(cN/dTex) (%) break) Comp. Braided; 8 .times. 224/7.5 paraffin
153.5 1.9 27.9 3.8 15.2 54 5998 Exp. A cont. filament yarn Ex. 1
Braided 8 .times. Nm44/12 none 153.5 1.0 10.8 6.0 8.1 75 Ex. 2
Braided 8 .times. Nm44/12 paraffin 153.5 1.8 17.2 2.1 9.2 54 32998
Ex. 3 Braided 8 .times. Nm44/12 paraffin 153.5 1.7 16.5 2.1 Ex. 4
braided 8 .times. Nm44/9.5 none 153.5 1.0 12.9 4.5 10.5 81 Ex. 5
braided 8 .times. Nm44/9.5 none 153.5 1.6 22.4 2.8 14.9 67 7828 Ex.
6 braided 8 .times. Nm44/9.5 none 153.5 1.7 22.2 2.5 Ex. 7 braided
8 .times. Nm44/9.5 paraffin 153.5 1.6 20.2 2.5 25171 Ex. 8 braided
8 .times. Nm44/9.5 paraffin 153.5 1.7 16.7 2.0 Ex. 9 braided 8
.times. Nm44/9.5 paraffin 153.5 1.8 18.5 2.0 Ex. 10 braided 8
.times. Nm44/7.5 none 153.5 1.0 11.5 4.4 Ex. 11 braided 8 .times.
Nm44/7.5 paraffin 153.5 1.6 20.1 2.5 11.9 59 26234 Ex. 12 braided 8
.times. Nm44/7.5 paraffin 154.0 1.6 18.1 2.7 Ex. 13 braided 8
.times. Nm44/7.5 paraffin 154.5 1.6 17.1 2.4 30620 Ex. 14 braided 8
.times. Nm44/7.5 paraffin 155.0 1.6 16.8 2.7 Ex. 15 braided 8
.times. Nm44/7.5 paraffin 153.5 1.7 19.8 2.2 Ex. 16 braided 8
.times. Nm44/7.5 paraffin 153.5 1.8 18.6 2.1 Comp. Plied and
twisted 6/224-.120Z paraffin 153.5 1.8 29.4 3.9 17.5 60 6868 Exp B
cont. filament yarn Ex. 17 Single spun yarn Nm44 PUR 153.5 1.6 21.4
2.1 17.1 80 Ex. 18 Plied; twisted 6/Nm44; 120Z none 153.5 1.0 14.8
4.0 Ex 19 Plied; twisted 6/Nm44; 120Z paraffin 153.5 1.8 18.5 2.2
15.2 82 >100000 Ex. 20 Plied; twisted 6/Nm44; 120Z PUR 153.5 1.6
23.8 2.5 Ex. 21 Plied; twisted 6/Nm44; 120Z PUR 153.5 1.7 27.3 2.9
21.5 79 24580 Ex. 22 Plied; twisted 6/Nm44; 120Z PUR 153.5 1.8 24.1
2.5 Ex. 23 Plied; twisted 18/Nm44; 120Z none 153.5 1.0 14.5 4.8 Ex.
24 Plied; twisted 18/Nm44; 120Z paraffin 153.5 1.6 19.1 2.8
* * * * *
References