U.S. patent application number 15/318768 was filed with the patent office on 2017-06-01 for fibrous tape.
The applicant listed for this patent is DSM IP Assets B.V.. Invention is credited to Marina CALAZANS-BEHN, Roelof MARISSEN, Reinard Jozef Maria STEEMAN, Koen VAN PUTTEN, Antoon Maria VERSPAGEN, Christa WEBER.
Application Number | 20170153090 15/318768 |
Document ID | / |
Family ID | 50942158 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170153090 |
Kind Code |
A1 |
VAN PUTTEN; Koen ; et
al. |
June 1, 2017 |
FIBROUS TAPE
Abstract
The invention relates to a fibrous tape made from fibers
comprising highly oriented polymer, the tape having a tenacity of
at least 1.2 N/tex and an areal density of between 5 and 250
g/m.sup.2, wherein the tape has a transversal strength of at least
0.5 MPa. The invention also relates to sheets comprising the tape
of the invention and antiballistic articles comprising at least two
of said sheets. The invention further relates to a process for the
preparation of the tapes of the invention.
Inventors: |
VAN PUTTEN; Koen; (Echt,
NL) ; CALAZANS-BEHN; Marina; (Echt, NL) ;
MARISSEN; Roelof; (Echt, NL) ; VERSPAGEN; Antoon
Maria; (Echt, NL) ; WEBER; Christa; (Echt,
NL) ; STEEMAN; Reinard Jozef Maria; (Echt,
NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DSM IP Assets B.V. |
Heerlen |
|
NL |
|
|
Family ID: |
50942158 |
Appl. No.: |
15/318768 |
Filed: |
June 15, 2015 |
PCT Filed: |
June 15, 2015 |
PCT NO: |
PCT/EP2015/063270 |
371 Date: |
December 14, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D06C 3/00 20130101; F41H
5/0485 20130101 |
International
Class: |
F41H 5/04 20060101
F41H005/04; D06C 3/00 20060101 D06C003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2014 |
EP |
14172525.9 |
Claims
1. A fibrous tape made from fibers comprising highly oriented
polymer, the tape having a tenacity of at least 1.2 N/tex and an
areal density of between 5 and 250 g/m.sup.2, wherein the tape has
a transversal strength of at least 0.5 MPa.
2. The tape of claim 1, wherein the polymer is a polyolefin,
preferably a polyethylene and more preferably a high or ultrahigh
molecular weight polyethylene (UHMWPE).
3. The tape of claim 1 wherein the tape has a cross-sectional
aspect ratio thickness to width of at most 1:50, preferably at most
1:100, more preferably at most 1:500.
4. The tape of claim 1 wherein the tape has a tenacity of at least
1.5 N/tex, preferably at least 2.0 N/tex, more preferably at least
2.5 N/tex, even more preferably 3.0 N/tex and most preferably 3.5
N/tex.
5. The tape of claim 1 wherein the transversal strength is at least
0.6 MPa, more preferably at least 0.7 MPa, even more preferably at
least 0.8 MPa, and most preferably at least 0.9 MPa.
6. The tape of claim 1 wherein the fibers comprising the polymer
comprise at least 10 ppm of a solvent for the polymer.
7. A sheet comprising at least two monolayers comprising fibrous
tape or at least one layer of woven fibrous tapes, wherein the
fibrous tapes are selected from claim 1.
8. The sheet according to claim 7 wherein the direction of the
fibrous tape in a monolayer is at an angle .alpha. to the direction
of a fibrous tape in an adjacent monolayer or wherein the layer of
woven fibrous tapes comprises weft and warp woven tapes and the
direction of orientation of the weft and the warp woven tapes in
the layer of woven fibrous tapes are at an angle .beta. and wherein
.alpha. or .beta. are between 20 and 90.degree., more preferably
between 45 and 90.degree., most preferably between 75 and
90.degree..
9. An antiballistic article comprising at least 2, preferably at
least 4, more preferably at least 8 sheets according to claim
7.
10. The antiballistic article of claim 9 having an areal density
between 0.25 Kg/m.sup.2 and 250 Kg/m.sup.2, preferably between 0.5
Kg/m.sup.2 and 100 Kg/m.sup.2, more preferably between 1 Kg/m.sup.2
and 75 kg/m.sup.2 and most preferably between 2 Kg/m.sup.2 and 50
kg/m.sup.2.
11. The antiballistic article of claim 9, comprising a number of
contacts between two tapes separated by an intermediate tape,
wherein the number of contacts is less than 20 per unit of width of
1 meter of the intermediate tape, while a contact corresponds to a
tape-to-tape interaction of the two tapes separated by an
intermediate tape, occurring through a split of the intermediate
tape.
12. A process for the preparation of the fibrous tape of claim 1,
the process comprising: (a) providing fibers comprising a highly
oriented polymer, said fibers having a tenacity of at least 1.2
N/tex (b) forming a layer comprising the fibers; (c) applying a
longitudinal tensile force to the fibers in the layer, (d)
stretching the fiber layer at a draw ratio of at least 1.01 to form
a stretched layer; (e) providing the stretched layer at a
processing temperature T.sub.p to compression means; (f)
compressing the stretched layer of fibers by subjecting the layer
to a compression by the compression means having a temperature
T.sub.c to form a fibrous tape; (g) optionally stretching the
fibrous tape by a draw rate of at most 1.1 and, (h) cooling the
fibrous tape to a temperature of at most 80.degree. C. under a
tension sufficient to prevent loss of mechanical properties;
wherein T.sub.m is the melting temperature of the polymer, wherein
T.sub.m>T.sub.p.gtoreq.T.sub.m-30 K, and wherein
T.sub.c.ltoreq.T.sub.p-3 K.
13. The process according to claim 11 wherein
T.sub.m>T.sub.p.gtoreq.T.sub.m-15 K, and wherein
T.sub.c.ltoreq.T.sub.p-15 K.
14. The process according to claim 11 wherein the polymer is
UHMWPE, preferably the UHMWPE has an intrinsic viscosity of between
5 dL/g to 40 dL/g, more preferably between 8 and 30 dL/g.
15. The process of claim 11 wherein the filaments are stretched in
between the steps (a) and (f) to a draw ratio from 1.02 to 3.0,
preferably 1.03 to 2.0.
Description
[0001] The invention relates to a fibrous tape made from fibers
comprising highly oriented polymer, the tape having a tenacity of
at least 1.2 N/tex and an areal density of between 5 and 250
g/m.sup.2. The invention further relates to a process to
manufacture said fibrous tape from said fibers comprising highly
oriented polymer.
[0002] Such tape is known from WO2013/131996. WO2013/131996
discloses a fibrous tape having a tenacity of at 3.54 N/tex and an
areal density of about 35 g/m.sup.2 made from a plurality of fused
high tenacity UHMWPE filaments. The tape disclosed in WO2013/131996
is further in contact with a plastomer layer at an areal density of
between 0.2 and 15 g/m.sup.2.
[0003] Although the tapes according to WO2013/131996 show
satisfactory strength and performance in applications such as
antiballistic panels, they show a deficiency during handling of the
tapes and/or the sheets comprising the tapes which is expressed by
the occurrence of defects in the tape due to unwanted splitting of
the tape. Furthermore, the performance of the tape in ballistic
applications can be further improved.
[0004] The object of the present invention is to provide a fibrous
tape with optimized handling properties resulting in less defects
of the tape through splitting. A further objective of the invention
may be to provide a tape with improved antiballistic
performance.
[0005] This objective is achieved according to the invention by
providing a tape with a transversal strength of at least 0.5 MPa.
It was observed that tapes with such improved transversal strength
may provide improved handling properties. It appeared that tapes
according to the invention can be handled more easily and may be
processed into antiballistic sheets and antiballistic panels with
substantially less defects. It was further observed, that the tapes
according to the invention may provide antiballistic sheets and
panels with optimized antiballistic performance.
[0006] Fibrous tapes are also known from other patent applications
such as WO2012/080274 and WO2013/130160. Also the therein disclosed
fibrous tapes have high tenacity but also present the above
described deficiencies.
[0007] By the term "fibrous tape" is herein understood a tape
obtained by a process wherein fibers comprising polymer are used as
a precursor material. A fibrous tape is structurally different from
a non-fibrous tape, which is usually obtained by compressing
polymeric powders or spinning solutions or melts of polymers. The
cross-section of a fibrous tape according to the invention, if
observed with a microscope, possesses boundaries between the fibers
forming the tape. The observable boundaries of the precursor fibers
may be recognized as substantially straight limits between the
precursor fibers in the fibrous tape, which precursor fibers may
possess a mainly polygonal cross-section, for examples a hexagonal,
pentagonal or rectangular cross-section.
[0008] The fibrous tape comprises abutting polymeric fibers having
a fiber length, wherein the abutting fibers may be fused to each
other over an abutting length. Preferably a plurality of fibers,
i.e. more than one fiber, is used to make such tape, the plurality
of fibers may be provided by a single or more than one yarn
comprising the fibers. Preferably, the abutting length is at least
50% of the fibers' length, more preferably at least 70%, most
preferably at least 90%. More preferably, the abutting length of
the polymeric fibers is about the same with the fibers' length. The
abutting length over which abutting polymeric fibers may be fused
to each other is a measure of the degree of fibers' fusion. The
degree of fibers' fusion may be adjusted as it will be detailed
hereinafter and the abutting length may be measured with a
microscope preferably provided with an adjustable depth of field
and/or with a contrast enhancer device. The difference between two,
at least partially, fused fibers and two non-fused fibers is that
the fused fibers are hindered in moving one in respect to each
other over the fused part which keeps the fibers in contact.
Accordingly a fibrous tape in the context of the present invention
is structurally different from the monolayers known in the art
comprising fibers and an elastic resin or a polymeric matrix that
encapsulate and holds the fibers together. In contrast to said
monolayers known in the art, the fibers of the present tapes are
essentially held together by the above described interaction of
abutting fibers. The present fibrous tapes are substantially devoid
of resins or adhesives located in between the fibers forming the
tape. Preferably the fibrous tapes are substantially devoid of
resins or adhesives. By substantially devoid is understood that the
fibrous tapes comprise less than 5 wt %, preferably less than 3 wt
%, more preferably less than 2 wt % and most preferably less than 1
wt % of resin or adhesive.
[0009] By tape is herein understood an elongated body having a
longitudinal direction, a width, a thickness and a cross-sectional
aspect ratio, i.e. the ratio of thickness to width. Said
cross-section is defined as substantially perpendicular to the
longitudinal direction of the tape. The longitudinal direction or
machine direction of the tape essentially corresponds to the
orientation of the fused fibers. The length dimension of a tape of
the invention is not particularly limited. The length may exceed 10
km and mainly depends on the polymeric fibres and the process used
to produce the tape. Nevertheless said tape can for convenience
reasons be manufactured to smaller sizes, according to the
requirements of the envisioned applications.
[0010] In a preferred embodiment, the tape of the invention has an
average cross-sectional aspect ratio (thickness:width) of at most
1:50, preferably at most 1:100, more preferably at most 1:500, even
more preferably at most 1:1000. The width of the fibrous tape is
preferably between 2 mm and 3000 mm, more preferable between 10 mm
and 2500 mm, even more preferably between 20 mm and 2000 mm, yet
even more preferably between 50 mm and 1800 mm and most preferably
between 80 mm and 1600 mm. The fibrous tape preferably has a
thickness of between 1 .mu.m and 200 .mu.m, more preferably of
between 3 .mu.m and 120 .mu.m, even more preferably of between 5
.mu.m and 100 .mu.m, even more preferably of between 8 .mu.m and 80
.mu.m and most preferably of between 10 .mu.m and 50 .mu.m. By
width is herein understood the largest dimension between two points
on the perimeter of a cross-section of the tape, said cross-section
being orthogonal to the length of the tape. By thickness is herein
understood a distance between two points on the perimeter of said
cross-section, said distance being perpendicular on the width of
the tape. The width and the thickness of a tape can be measured
according to known methods in the art, e.g. with the help of a
ruler and a microscope or a micrometer, respectively. It was
observed that in contrast to the tapes of the prior art, the tapes
according to the invention can be produced within above preferred
widths and thicknesses while a low amount of defects of the tapes
once processed into antiballistic articles is maintained.
[0011] By fiber is herein understood an elongated body having a
length much greater than its transverse dimensions. A fiber may
have a regular rounded cross-section, e.g. oval or circular; or an
irregular cross-section, e.g. lobed, C-shaped or U-shaped. The
fibers may have continuous lengths, known in the art as filaments,
or discontinuous lengths, known in the art as staple fibers. Staple
fibers are commonly obtained by cutting or stretch-breaking
filaments. A yarn for the purpose of the invention is an elongated
body containing many fibers. The fiber has a cross sectional aspect
ratio, i.e. the ratio of the largest dimension between two points
on the perimeter of a cross-section of the fiber to the lowest
dimension between two points on the same perimeter. Preferably the
cross-sectional aspect ratio of the fiber is at most 10:1, more
preferably of at most 5:1 and even more preferably 3:1.
[0012] Examples of fibers of polymer suitable for the present
invention include but are not limited to fibers manufactured from
polyamides and polyaramides, e.g. poly(p-phenyleneterephthalamide)
(known as Kevlar.RTM.); poly(tetrafluoroethylene) (PTFE);
poly{2,6-diimidazo-[4,5b-4',5'e]pyridinylene-1,4(2,5-dihydroxy)phenylene}
(known as M5); poly(p-phenylene-2, 6-benzobisoxazole) (PBO) (known
as Zylon.RTM.); poly(hexamethyleneadipamide) (known as nylon 6,6),
poly(4-aminobutyric acid) (known as nylon 6); polyesters, e.g.
poly(ethylene terephthalate), poly(butyleneterephthalate), and
poly(1,4 cyclohexylidenedimethyleneterephthalate); polyvinyl
alcohols; thermotropic liquid crystal polymers (LCP) as known from
e.g. U.S. Pat. No. 4,384,016; polyolefins e.g. homopolymers and
copolymers of polyethylene and/or polypropylene; and combinations
thereof.
[0013] Good results may be obtained when the polymer is a
polyolefin, preferably a polyethylene. Preferred polyethylenes are
high or ultrahigh molecular weight polyethylene (UHMWPE).
Polyethylene fibers may be manufactured by any technique known in
the art, preferably by a melt or a gel spinning process. Most
preferred fibers are gel spun UHMWPE fibers, e.g. those sold by DSM
Dyneema, NL trademarked as Dyneema.RTM.. If a melt spinning process
is used, the polyethylene starting material used for manufacturing
thereof is preferably a high molecular weight polyethylene with a
weight-average molecular weight between 20,000 and 600,000 g/mol,
more preferably between 60,000 and 200,000 g/mol. An example of a
melt spinning process is disclosed in EP 1,350,868 incorporated
herein by reference. If the gel spinning process is used to
manufacture said fibers, preferably an UHMWPE is used with an
intrinsic viscosity (IV) of preferably at least 5 dL/g, more
preferably at least 8 dL/g, most preferably at least 12 dL/g.
Preferably the IV is at most 40 dL/g, more preferably at most 30
dL/g, more preferably at most 25 dL/g. Preferably, the UHMWPE has
less than 1 side chain per 100 C atoms, more preferably less than 1
side chain per 300 C atoms. Preferably the UHMWPE fibers are
manufactured according to a gel spinning process as described in
numerous publications, including U.S. Pat. No. 4,413,110, GB
2042414 A, GB-A-2051667, WO 01/73173 A1.
[0014] The tenacity or tensile strength of the polymeric fibers is
preferably at least 1.2 N/tex, more preferably at least 2.5 N/tex,
most preferably at least 3.5 N/tex. Best results were obtained when
the fibers of polymer were UHMWPE fibers having a tenacity of at
least 2 N/tex, more preferably at least 3 N/tex.
[0015] The tenacity of the tape of the invention is preferably at
least 1.5 N/tex, preferably at least 2.0 N/tex, more preferably at
least 2.5 N/tex, even more preferably at least 3.0 N/tex and most
preferably at least 3.5 N/tex. It was observed that tapes with
increased tenacity, sheets and panels with further improved
ballistic properties can be obtained.
[0016] The fibrous tape of the invention has a transversal strength
of at least 0.5 MPa. Achieving such transversal strength came as a
surprise for the inventors as it is known in the art that increased
transversal strength of tapes usually come to the expense of other
mechanical properties such as tenacity. It is considered to be an
achievement of the inventors to have identified a process allowing
for the first time to produce fibrous tapes with transversal
strength exceeding 0.5 MPa while substantially maintaining the
tenacities of the employed fibers. Preferably the transversal
strength of the tape of the invention is at least 0.6 MPa, more
preferably at least 0.7 MPa, even more preferably at least 0.8 MPa
and most preferably at least 0.9 MPa. It was observed that
increasing the transversal strength to such preferred levels
further improved the handling properties of the tapes and may
further reduced the amount of defects in the antiballistic articles
made thereof. By transversal strength of a fibrous tape in the
context of the present invention is meant the force, in Newton (N),
required to rupture a tape along a cross-sectional area
perpendicular to its width direction divided by the surface (in
mm.sup.2) of said cross-sectional area. Said transversal strength
is thus expressed in MPa or alternatively in N/mm.sup.2. Further
details as to the measurement of the transversal strength can be
found in the Methods of Measuring.
[0017] It has further been found that the balance between
transversal strength and tenacity could be further improved if the
fibers from which the tape according to the invention are produced
contain between 10 ppm and 1 wt % of a solvent for the polymer from
which the fibers are made, wherein the weight percentage is
expressed as weight solvent per total weight of the fiber.
Accordingly a preferred embodiment of the tapes of the present
invention is that the fibers comprising polymer from which the
tapes have been made comprise at least 10 ppm, preferably 20 ppm
most preferably 50 ppm of a solvent for the polymer. Contents
higher than 1 wt % no longer essentially contribute to the
improvement, or even impair the transversal strength. For the above
reasons, the solvent content in the fibre is preferably from 10 ppm
to 1 wt %, more preferably 20 ppm to 0.5 wt %, even more preferably
between 50 ppm to 0.1 wt %, and most preferably between 0.01 wt %
to 0.1 wt %.
[0018] Solvent is here understood to be a substance that is capable
of dissolving the polymer in question. Suitable solvents for
polymers are known to one skilled in the art. They can, for
example, be chosen from the `Polymer Handbook` by J. Brandrup and
E. H. Immergut, third edition, chapter VII, pages 379-402. Examples
of suitable solvents for polyolefins, in particular for
polyethylene, are, separately or in combination: decalin, tetralin,
toluene, lower n-alkanes such as hexane, (para-)xylene, paraffin
oil, squalane, mineral oil, paraffin wax, cyclooctane. For the
reasons cited above, the solvent is most preferably paraffin oil,
paraffin wax or decalin.
[0019] Preferably, the solvent is a high boiling solvent, such as
paraffin oil. It was observed that such solvents provide fibrous
tapes with further improved transversal strength. Preferably, these
are solvents having a boiling temperature that is substantially
higher, preferably at least 50 K, more preferably at least 100 K
higher, than the melting temperature of the polymer. The melting
temperature of the fibers can be determined by DSC using a
methodology as described at pg. 13 of WO 2009/056286.
[0020] The presence of the solvent in the fiber may have multiple
origins. For example the solvent present in the fibre may be a
remainder of solvent used during the spinning process of the fibre
or it may have been purposely added before, during or after the
spinning process of the fibre or the manufacturing of the fibrous
tape.
[0021] In the context of the present invention fibres of highly
oriented polymer is defined as that the polymer chains run
substantially parallel with the direction of fiber. It is preferred
for the degree of orientation F to be at least 0.95, more
preferably at least 0.97 and even more preferably at least 0.98.
The degree of orientation is defined by the formula
F=(90.degree.-H.degree./2)90.degree., where H.degree. is the width
at half the height of the scattering intensity along the Debye ring
of the strongest reflection on the equator.
[0022] The fibrous tape, or the therefrom produced sheets and/or
the antiballistic articles of the invention may also comprise a
binder or a matrix material. Said binder or matrix material may be
present in between the polymeric fibers or in between the fibrous
tapes. Various binders or matrices may be used, examples thereof
including thermosetting and thermoplastic materials. A wide variety
of thermosetting materials are available, however, epoxy resins or
polyester resins are most common. Suitable thermosetting and
thermoplastic materials are enumerated in, for example, WO 91/12136
A1 (pages 15-21) included herein by reference. From the group of
thermosetting materials, vinyl esters, unsaturated polyesters,
epoxides or phenol resins are preferred. From the group of
thermoplastic materials, polyurethanes, polyvinyls, polyacrylics,
polybutyleneterephthalate (PBT), polyolefins or thermoplastic
elastomeric block copolymers such as
polyisopropene-polyethylene-butylene-polystyrene or
polystyrene-polyisoprene-polystyrene block copolymers are
preferred.
[0023] More preferred, however, is that the fibrous tape is
substantially free of any binder or matrix material between the
polymeric fibers. It was observed that in the absence of binders or
matrix materials, the ballistic properties of the material of the
invention may be improved.
[0024] Yet in a preferred embodiment, the binder or matrix material
is present on and in between the fibrous tapes as for example
disclosed in WO2013/131996, especially on pages 9, 11 and 12,
included herein by reference.
[0025] The invention further relates to a process for the
manufacturing of the tapes of the invention, comprising the steps
of: [0026] (a) providing fibers comprising highly a oriented
polymer, said fibers having a tenacity of at least 1.2 N/tex;
[0027] (b) forming a layer comprising the fibers; [0028] (c)
applying a longitudinal tensile force to the fibers in the layer,
[0029] (d) stretching the fiber layer at a draw ratio of at least
1.01 to form a stretched layer; [0030] (e) providing the stretched
layer at a processing temperature T.sub.p to compression means;
[0031] (f) compressing the stretched layer of fibers by subjecting
the layer to a compression by the compression means, the
compression means having a temperature T.sub.c, to form a fibrous
tape; [0032] (g) optionally stretching the fibrous tape by a draw
rate of at most 1.1 and, [0033] (h) cooling the fibrous tape to a
temperature of at most 80.degree. C. under a tension sufficient to
prevent loss of mechanical properties; wherein T.sub.m is the
melting temperature of the polymer, wherein
T.sub.m>T.sub.p.gtoreq.T.sub.m-30 K, and wherein
T.sub.c.ltoreq.T.sub.p-3 K.
[0034] It was observed that with the process of the invention, a
tape having increased transversal strength as compared with known
fibrous tapes may be obtained.
[0035] It was further observed that the mechanical properties of
the fibrous tape made according to the process according to the
invention are similar to the mechanical properties of the fibers
utilized to manufacture the tape thereof. This came also as a
surprise since hitherto the mechanical properties of tapes
manufactured from polymeric fibers were usually much lower than
those of the polymeric fibers. Accordingly the present invention
also relates to a fibrous tape obtainable by the process of the
invention. Preferably the fibrous tape obtainable by the process of
the invention has a tenacity which is at most 20% lower than the
tenacity of the polymeric fibers used to manufacture said fibrous
tape, more preferably at most 10%, most preferably with at most 5%
lower tenacity than the polymeric fibers used to manufacture the
fibrous tape. If polymeric fibers with various tenacities and
moduli are used to manufacture the tape of the invention, the
tenacity or modulus of the polymeric fibers to be considered are an
average tenacity and modulus of the various polymeric fibers.
[0036] Preferably, at step (a) of the process of the invention, the
plurality of highly oriented polymer fibers is provided as at least
one yarn, more preferably more than one yarn, that may be twisted
or untwisted. Preferably the yarns have a twist of less than 1 per
100 cm yarn, more preferably less than 1 twist per 200 cm yarn and
even more preferably less than 1 twist per 400 cm. Most preferably
the yarns are substantially untwisted. In case a twisted yarn is
provided to the process, the skilled person will be aware of means
to remove the twist from the provided yarns before or during the
formation into a layer comprising the fibers, step (b).
[0037] According to the process of the invention, at step (b) the
polymeric fibers are formed into a layer comprising the fibers,
preferably a layer of fibers. Said layer may be fibers arranged in
configurations of various types which may comprise random or
ordered oriented fibers such as arranged in parallel arrays. Most
preferred the layer of fibers is an unidirectional network wherein
a majority of fibers, e.g. at least 50 mass %, more preferably at
least 75 mass %, even more preferably at least 95 mass %, most
preferably about 100 mass % of the total mass of fibers forming the
layer, is arranged to run substantially in parallel along a common
direction. The unidirectional alignment of polymeric fibers may be
achieved through various standard techniques known in the art that
are able to produce substantially straight rows of unidirectionally
aligned fibers, such that adjacent fibers overlap and preferably
there is substantially no gap between them. An example of such a
technique is described in WO 2009/0056286 included herein by
reference, wherein a layer comprising abutting and unidirectionally
aligned polymeric fibers may suitably be formed by feeding a
polymer fiber from an unwinding station under tension, through an
alignment means, e.g. a reel followed by a plurality of spreader
bars. It was observed that such substantial parallel alignment of
the fibers in the layer provides tapes with further improved
transversal strength.
[0038] The thickness of the layer comprising the polymeric fibers
is preferably chosen to yield after the stretching of steps (d) and
compression step (f) the desired thickness of the tape. The layer
may have a minimum thickness of about the diameter of the fibers.
Preferably the thickness of the layer will be at least twice the
thickness of the fibers.
[0039] Preferably, the process of the invention comprises an
additional step (b1) wherein the fibers are preheated to a
temperature below T.sub.m, before or while stretching the layer in
step (d). Preheating of the layer may be carried out by keeping the
layer for a dwell time in an oven set at a preheating temperature,
subjecting the layer to heat radiation or contacting the layer with
a heating medium such as a heating fluid or a heated surface.
Preferably, the preheating temperature is between T.sub.m-2 K and
T.sub.m-30 K, more preferably between T.sub.m-3 K and T.sub.m-20 K,
most preferably between T.sub.m-5 K and T.sub.m-15 K. The dwell
time is preferably between 2 and 100 seconds, more preferably
between 3 and 60 seconds, most preferably between 4 and 30
seconds.
[0040] During the process of the invention, in step (d) the layer
is stretched at a draw ratio of at least 1.01. More preferably the
draw ratio is at least 1.03, even more preferably at least 1.05 and
most preferably at least 1.08. The maximum draw rate that may be
applied on the layer may essentially be limited by the drawability
of the fibers employed in the process. Nevertheless it was observed
that too high draw rates applied to the layer before the compaction
step (f) may result in unwanted deficiencies of the produced tapes,
such as fibrillation or splitting of the tapes during or after the
processing of the fibrous tape. Accordingly, the stretching in step
(d) is preferably limited to a draw ratio of less than 2.0,
preferably less than 1.8, more preferably less than 1.5 and most
preferred less than 1.3. In a yet preferred embodiment the draw
ratio of the layer may be between 1.01 and 2.0, preferably between
1.03 and 1.8, more preferably between 1.05 and 1.5 and most
preferably between 1.08 and 1.3. It was observed that at such
limited draw ratio fibrous tapes having further improved properties
may be obtained.
[0041] In an alternative process of the invention, the process may
form an integral part of the manufacturing process of high tenacity
fibers and wherein the stretching step (b) is the last stretching
step of the drawing operation to which the fibers are subjected.
Depending on the number of drawing steps and the respective drawing
ratios in said drawing steps the draw ratio of step (d) may be
between 2.0 and 10, preferably between 2.5 and 9.0, more preferably
between 3.0 and 8.0, and most preferably between 4.0 and 7.0. It
was observed that combination of the drawing step (d) with the
production of high tenacity fibers has a substantial efficiency
advantage while the transversal strength of the produced tape
remains substantially unaffected.
[0042] In step (e) the layer is provided at a temperature T.sub.p
to compression means. The temperature T.sub.p may be achieved by
heating or cooling the layer with means known to the skilled
person. Preferably the temperature T.sub.p is between T.sub.m-1 K
and T.sub.m-30 K, more preferably between T.sub.m-1 K and
T.sub.m-15 K, most preferably between T.sub.m-1 K and T.sub.m-5
K.
[0043] At step (f) of the process of the invention, the layer
comprising the polymeric fibers is compressed by the compression
means. Preferably the compression means may be a calender, a
smoothing unit, a double belt press, an alternating press. The
compression means form a gap through which the layer will be
processed. Preferably, said layer is introduced into said gap with
an inline speed of at least 1 m/min, more preferably of at least 2
m/min, most preferably of at least 3 m/min. The transversal
pressure to which the layer is subjected may be expressed in N/mm
or N/mm.sup.2 depending on the geometry of the compression means.
In the case the compression means is a calender or a comparable
compression means applying a compression to a narrow surface area,
the line pressure is at least 100 N/mm, more preferably at least
200 N/mm, even more preferably at least 300 N/mm, most preferably
at least 500 N/mm. In case the compression means is a press, i.e.
applying a compression to a broad surface, the surface pressure is
at least 1 N/mm.sup.2, more preferably at least 5 N/mm.sup.2, even
more preferably at least 10 N/mm.sup.2, most preferably at least 20
N/mm.sup.2. It was observed that the higher the respective
pressure, the higher the transversal strength of the fibrous tapes
is. It is commonly known in the art that a calender comprises at
least two counter-rotating calendering rolls which form a nip, e.g.
where the rolls abut each other, by applying a, preferably
constant, closing force on said rolls. The closing force is usually
measured by a force gauge. The calendering line pressure can
therefore be easily determined by dividing the closing force as
measured by the force gauge to the width of the layer comprising
the network of fibers. It is further commonly known in the art that
a press comprises at least 2 counteracting compression surfaces by
applying a, preferably constant, closing force on said compression
surfaces and hence applying a pressure in N per mm.sup.2 onto the
material in between the at least 2 compression surfaces.
[0044] The compression step (f) of the process is carried out with
a temperature T.sub.c of the compression means, wherein T.sub.c is
below the temperature T.sub.p at which the layer comprising the
polymer fibers is fed to the compression means. Preferably the
temperature of the compression means is at least 3 K below T.sub.p,
preferably at least 5 K, more preferably at least 10 K, more
preferably at least 20 K, even more preferably at least 30 K and
most preferably at least 50 K below the T.sub.p of the layer. The
inventors surprisingly found out, that by applying lower
temperatures of the compression means may provide tapes with an
optimized balance of mechanical properties. It was observed that
operating the process according to the invention may provide
fibrous tapes with optimized tenacity and transversal strength. The
temperature of the compression means may be set by using internally
heated or cooled compression means. Said temperature is influenced
amongst others by the dimensions of the compression means (for
example the diameter of the calendering rolls), the temperature
(T.sub.p) at which the layer is provided, the inline speed and
optionally the temperature applied to the space beyond the
compression means, such as a forced cooling of the produced fibrous
tape exciting the compression means. By temperature of the
compression means (T.sub.a) is herein understood the temperature of
the surface of the compression means in contact with the compressed
layer. In case said surface temperature is different for different
positions of the compression means, the T.sub.c is measured at the
position where the fibrous tape is released from the compression
means. In case the compression means is a calender, the calendering
rolls preferably have a diameter of between 100 mm and 1000 mm,
more preferably between 200 mm and 700 mm, most preferably between
300 mm and 600 mm.
[0045] In an optional embodiment the fibrous tape is stretched in
step (g) at a draw rate of at most 1.1. Preferably the draw rate of
the fibrous tape is at most 1.05, more preferably at most 1.03 and
most preferably at most 1.01. It was surprisingly observed that
such a limitation of the draw rate after the compression of the
polymer fibers into a tape may provide a fibrous tape with further
increased transversal strength.
[0046] The inventive process employs highly oriented polymer
fibers. Such fibers may be fully drawn fibers, meaning that the
fibers have been drawn as much as chosen for the manufacturing of
the fiber product. Since a fiber manufacturer typically designs the
product to have safety margin, a fully drawn fiber may be drawn
further, though excessive further drawing typically will lead to
fiber failure. A preferred embodiment of the inventive process is
that the layer comprising the polymeric fibers are stretched in
between the steps (a) and (f) to a total draw ratio from 1.02 to
3.0, preferably 1.03 to 2.0, more preferably 1.05 to 1.5 and most
preferably 1.08 to 1.3. It was observed that these preferred ranges
of drawing during the manufacture of the tape will optimize the
balance of tape strength and transversal strength. While higher
draw rates may result in increases of the tape tenacity, they may
negatively affect the transversal strength. If too low draw rates
are applied, both transversal strength and tenacity of the tape may
be negatively affected.
[0047] In the mentioned step (h) here above, the fibrous tape is
cooled such that the temperature of the tape is reduced with at
least 25.degree. C., preferably the tapes are cooled to room
temperature.
[0048] Accordingly, in a preferred embodiment of the process of the
invention T.sub.p and T.sub.c are chosen to respect the conditions
of T.sub.m>T.sub.p.gtoreq.T.sub.m-15 K, and wherein
T.sub.c.ltoreq.T.sub.p-15 K. In a further preferred embodiment
T.sub.p and T.sub.c are chosen to respect the condition of
T.sub.m>T.sub.p.gtoreq.T.sub.m-5 K, and wherein
T.sub.c.ltoreq.T.sub.p-30 K. It was observed that if the process of
the invention is operated within the above boundaries, the obtained
fibrous tapes have optimized balance of tenacity and transversal
strength and will provide antiballistic articles with substantially
reduced number of defects.
[0049] In a preferred process according to the invention the fibers
comprise as a polymer UHMWPE, preferably the UHMWPE has an IV
(measured at @135.degree. C. in decalin) of between 5 dL/g to 40
dL/g, more preferably between 8 and 30 dL/g and more preferably
between 10 dL/g and 25 dL/g. It was observed that such ranges of
intrinsic viscosities of UHMWPE provide further improved
antiballistic performance of the therefrom manufactured fibrous
tapes.
[0050] The process of the present invention furthermore enables
tapes to be made that were never made available before, i.e. tapes
with a unique combination of mechanical properties, i.e. a balance
between ballistic properties and handling defects. More
specifically the present invention enables fibrous tapes with a
tenacity (TS) of at least 1.2 N/tex and a transversal strength
(S.sub.tr) of at least 0.5 MPa. In a preferred embodiment, the
tenacity and the transversal strength of the tape respect the
relation of formula 1;
S.sub.tr=2 MPa-a*.rho.*TS Formula (1)
wherein S.sub.tr is expressed in MPa, .rho. is the density of the
fibers in g/mm.sup.3, TS is expressed in N/tex and the factor a is
at most 6.5.times.10.sup.-3, more preferably a is at most
5.0.times.10.sup.-3, even more preferably a is at most
4.0.times.10.sup.-3 and most preferably at most
3.0.times.10.sup.-3. Surprisingly such tapes yield excellent
performance when used in the manufacture of antiballistic products.
Such high performance is unexpected in the field of antiballistic
products.
[0051] The invention further relates to products such as sheets and
antiballistic articles comprising the fibrous tapes of the
invention. In particular, the invention relates to a sheet
comprising at least two monolayers comprising fibrous tapes
according to the invention or at least one layer of woven fibrous
tapes according to the invention. Preferably the monolayers
comprise unidirectional aligned fibrous tapes.
[0052] The sheets may also contain a binder in between the tapes
forming said sheet. The purpose of the binder may be to hold said
fibrous tapes in place in order to improve the ease of operation of
the monolayers or sheets comprising thereof. Suitable binders are
described in e.g. EP 0191306 B1, EP 1170925 A1, EP 0683374 B1 and
EP 1144740 A1. It was observed that good results may be obtained
when the sheets or the therefrom manufactured panel is
substantially free of any binder or any other material the purpose
of which being to hold the fibrous tapes together.
[0053] By a monolayer of unidirectional aligned fibrous tapes is
herein understood that a majority of the fibrous tapes in the
sheet, e.g. at least 70 mass % of the total mass of fibrous tapes
in said monolayer, more preferably at least 90 mass %, most
preferably about 100 mass %, run along a common direction. In a
sheet comprising at least two monolayers, the direction of the
fibrous tapes in a monolayer is at an angle .alpha. to the
direction of a fibrous tape in an adjacent monolayer. In a layer of
woven fibrous tapes comprising weft and warp woven tapes the
directions of orientation of the weft and the warp woven fibrous
tapes are at an angle .beta., whereby respectively .alpha. and
.beta. are preferably between 20 and 90.degree., more preferably
between 45 and 90.degree. and most preferably between 75 and
90.degree. most preferably the angles .alpha. and .beta. are about
90.degree..
[0054] In a preferred embodiment, the sheets of the invention are
compacted by mechanical fusing of the fibrous tapes. Said
mechanical fusing is preferably achieved under a combination of
pressure, temperature and time which results in substantially no
melt bonding. Preferably, there is no detectable melt bonding as
detected by DSC (10 K/min). No detectable melt bonding means that
no visible endothermic effect consistent with partially melt
recrystallized fibers is detected, when the sample is analyzed in
triplicate. It has been found that the application of high
pressures at a temperature suitably below the melting point of the
fiber results in no detectable amount of melt recrystallized fibers
being present, which is consistent with the substantial absence of
melt bonding.
[0055] Accordingly the invention also relates to compressed sheets
comprising the fibrous tape of the invention. It was observed that
said compressed sheet will have a more homogeneous appearance if
compared to compressed sheets made from fibrous tapes known in the
art. As presented above, the fibrous tapes known in the art are
prone to longitudinal splitting upon handling. In sheets
manufactured from said prior art fibrous tapes imperfections in the
form of splits may be observed. The presence of splits in the tapes
may result in local defects due to overlaps or gaps in the tape.
Hence the invention also relates to sheets comprising the fibrous
tape, wherein the split length in the tape is less than 5 m/m.sup.2
of sheet, preferably less than 2 m/m.sup.2 of sheet, even more
preferably less than 1 m/m.sup.2 of sheet, and most preferably less
than 50 cm/m.sup.2 of sheet. It was observed that such low split
length in a sheet comprising the tape improves the antiballistic
performance of articles made from said sheets.
[0056] The invention also relates to antiballistic articles
comprising the sheet according to the invention. Preferably the
antiballistic article comprising at least 2, preferably at least 4,
more preferably at least 8 sheets. It was observed that
antiballistic articles comprising such number of sheets have
improved antiballistic properties when compare to sheets comprising
the fibrous tapes known in the art.
[0057] In a preferred embodiment, the antiballistic article has an
areal density between 0.25 Kg/m.sup.2 and 250 Kg/m.sup.2,
preferably between 0.5 Kg/m.sup.2 and 100 Kg/m.sup.2, more
preferably between 1 Kg/m.sup.2 and 75 kg/m.sup.2 and most
preferably between 2 Kg/m.sup.2 and 50 Kg/m.sup.2.
[0058] In a yet preferred embodiment, the antiballistic article of
the invention is a panel. By panel is understood herein that the
individual sheets have been compressed, optionally under elevated
temperature to form a single monolithic structure. Preferably, the
panel of the invention is compressed at a temperature of below the
T.sub.m of the polymeric fibers, more preferably at a temperature
of between said T.sub.m and T.sub.m-100 K and with a pressure of at
least 100 bars, more preferably at least 150 bars, to obtain a
panel.
[0059] It was observed that the panels comprising the tapes
according to the invention have increased structural homogeneity
and hence provide a panel with less fluctuation in the
antiballistic properties compared to panels comprising fibrous
tapes known from the prior art. The inventors observed that tapes
with splits may lead to local fiber and/or tape displacements by
portions of adjacent tapes being squeezed under moulding conditions
into said splits of the intermediate tape. Such migration of
portions of tape result in reduced structural homogeneity of the
antiballistic panel. Structural inhomogeneity can for example be
observed by microscopy of a cross-section of a compacted panel
whereby the cross-section is perpendicular to the common direction
of unidirectional aligned fibrous tape. In such cross-section (FIG.
1 and FIG. 2) unidirectional aligned fibrous tapes may be observed
as distinct, substantially parallel bands (1). A displacement due
to a split tape of a monolayer (2) may appear as a location in said
cross-section where the tapes of the 2 adjacent monolayers (3 and
4) originally separated by the tape of intermediate monolayer (2),
contact each other (5). It is the purpose of the present invention
to provide a panel with an increased structural homogeneity, i.e.
with a reduced number of such tape contacts. The invention thus
also relates to an antiballistic article comprising a number of
contacts between 2 tapes separated by at least one intermediate
tape, alternatively called separating tape, wherein the number of
contacts is less than 20 per unit of width of 1 meter of
intermediate tape, while a contact corresponds to a tape-to-tape
interaction of two tapes separated by an intermediate tape,
occurring through a split of the intermediate tape. Such contacts
can easily be counted by the skilled person when analysing a
cross-section of said panel as depicted in FIG. 1 and FIG. 2.
[0060] The invention further relates to an armor comprising the
panel of the invention. Examples of armors include but are not
limited to helmets, breast plates, vehicle hulls and vehicle
doors.
[0061] The present invention further relates to a product for
automotive applications such as car parts, etc.; marine
applications such as ships, boats, panels, etc.; aerospace
applications such as planes, helicopters, panels, etc.;
defense/life-protection applications such as ballistic protection,
body armor, ballistic vests, shields, ballistic helmets, ballistic
vehicle protection, etc.; architectural applications such as
windows, doors, walls, pseudowalls, cargo doors, cargo walls,
radomes, shields, etc. wherein said product contains the tapes, the
sheets or the panel of the invention.
[0062] FIGS. 1 and 2 show a light microscopy picture at 2 different
scales showing a portion of a cross-section (1) through a panel
comprising monolayers the fibrous tapes according to the invention.
The monolayers of which the fibers run substantially in parallel to
the cross section are of a lighter shade (3 and 4) than the
monolayers of which the fibers run substantially perpendicular to
the cross-section (2). The position (5) in the figures indicates a
split of the tape of monolayer (2), which split has been filled
with the tapes of the respective adjacent monolayers (3) and
(4).
[0063] The invention will be further explained with the help of the
following examples without however being limited thereto.
EXPERIMENTAL
Methods of Measuring
[0064] Areal density (AD) of a panel or sheet was determined by
measuring the weight of a sample of preferably 0.4 m.times.0.4 m
with an error of 0.1 g. The areal density of a tape was determined
by measuring the weight of a sample of preferably 1.0 m.times.0.03
m with an error of 0.1 g. [0065] Intrinsic Viscosity (IV) is
determined according to ASTM-D1601/2004 at 135.degree. C. in
decalin, the dissolution time being 16 hours, with DBPC as
anti-oxidant in an amount of 2 g/l solution, by extrapolating the
viscosity as measured at different concentrations to zero
concentration. There are several empirical relations between IV and
Mw, but such relation is highly dependent on molar mass
distribution. Based on the equation M.sub.w=5.37*10.sup.4
[IV].sup.1.37 (see EP 0504954 A1) an IV of 4.5 dl/g would be
equivalent to a M.sub.w of about 422 kg/mol. [0066] Side chains in
a polyethylene or UHMWPE sample is determined by FTIR on a 2 mm
thick compression molded film by quantifying the absorption at 1375
cm.sup.-1 using a calibration curve based on NMR measurements (as
in e.g. EP 0 269 151) [0067] Tensile properties, i.e. strength and
modulus, of fibers were determined on multifilament yarns 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, of
type Fibre Grip D5618C. For calculation of the strength, the
tensile forces measured are divided by the titre, as determined by
weighing 10 meter of fibre; values in GPa for are calculated
assuming the natural density of the polymer (.rho.), e.g. for
UHMWPE is 0.97 g/cm.sup.3. [0068] The tensile properties of tapes
and films are determined accordingly on tapes of a width of 2 mm
twisted 40 turns per meter. [0069] The transversal strength of
tapes is measured on a Zwick Z005 tensile tester with a 1 kN force
cell and manual G13T and G13B tape clamps. The test samples are
prepared by manually cutting the tapes to 250 mm strips. During
preparation of the test samples care should be paid to avoid
unintentional partial splitting of the tape. Samples which prove
impossible to be cut into coherent 250 mm strips are assigned a
transverse strength of 0 MPa. The clamping length of the samples is
60 mm and distance between clamps is 20 mm. Pre-load is 0.1 N, and
test occurs at a speed of 50 mm/min. The maximum force determines
the transversal strength. The strength in MPa is calculated by
dividing that maximum force in Newton by the width and the
thickness of the sample in mm. Thus a breaking stress in N/mm.sup.2
is achieved, being identical to breaking stress in MPa. The average
of 5 samples is reported. [0070] The melting temperature (T.sub.m)
of a filament is determined by DSC on a power-compensation Perkin
Elmer DSC-7 instrument which is calibrated with indium and tin with
a heating rate of 10 K/min on a 5 mg sample. For calibration (two
point temperature calibration) of the DSC-7 instrument about 5 mg
of indium and about 5 mg of tin are used, both weighed in at least
two decimal places. Indium is used for both temperature and heat
flow calibration; tin is used for temperature calibration only.
[0071] Ballistic performance was measured by subjecting the panels
to shooting tests performed with the further indicated ammunition.
The first shot was fired at a projectile speed (V.sub.50) at which
it is anticipated that 50% of the shots would be stopped. The
actual bullet speed was measured at a short distance before impact.
If a stop was obtained, the next shot was fired at an anticipated
speed being 10% higher than the previous speed. If a perforation
occurred, the next shot was fired at an anticipated speed 10% lower
than the previous speed. The result for the experimentally obtained
V50 value was the average of the two highest stops and the two
lowest perforations. The kinetic energy of the bullet at V.sub.50
(E.sub.kin=1/2mV.sub.50.sup.2) wherein m is the mass of the
projectile, was divided by the areal density of the armor to obtain
a so-called E.sub.abs value. E.sub.abs reflects the stopping power
of the armor relative to its weight/thickness thereof. The higher
the E.sub.abs the better the armor is. [0072] The speed of the
projectile was measured with a pair of Drello Infrared (IR) light
screen Type LS19i3 positioned perpendicular on the path of the
projectile. At the instant when a projectile passes through the
first light screen a first electric pulse will be produced due to
the disturbance of the IR beam. A second electric pulse will be
produced when the projectile passes through the second light
screen. Recording the moments in time when the first and the second
electric pulses occur, and knowing the distance between the light
screed the speed of the projectile can be immediately determined.
[0073] Tape-to-tape contacts in a panel are determined by light
microscopy of polished cross-sections of a panel. The number of
contacts is counted on a cross-section of at least 1 by 5 mm.sup.2.
The total width of cross-sectioned tape (in m) present in said
cross-section of 1 by 5 mm.sup.2 is calculated multiplying 0.005 m
cross-section length by the number of visible cross-sectioned tape,
i.e. by dividing the height by the tape thickness.
General Experimental Setup
[0074] 8 multifilament UHMWPE yarns were spread to form a
homogeneous layer of filaments with a total thickness of about 50
micron and a width of approximately 3 cm. The filament layer was
run through a set of two counter rotating calender rolls of a
diameter of 40 cm and a width of 4 cm each. The temperature
controlled rolls were set at a speed of 530 cm/min and applied a
pressure of 1750 N/mm to the filament layer. A further roller stand
placed after the calender rolls applied a tensile force of about 80
N to the tape exiting the nip of the calender rolls and optionally
perform a post draw to the formed fibrous tape before being air
cooled to a temperature below 80.degree. C. and wound on a
bobbin.
Comparative Experiment A
[0075] A multifilament UHMWPE yarn with a tenacity of 3.1 N/tex and
a paraffinic solvent level of about 50 ppm was subjected to above
general experimental setup. The calender rolls were heated to
161.degree. C. The obtained fibrous tape A had an average thickness
of 47.2 micrometer, a width of 28 mm, a titre of 957 dtex and a
tenacity of 3.01 N/tex. The transversal strength of the tape was
0.39 MPa.
Comparative Experiment B
[0076] Comparative Experiment A was repeated with the difference
that a forced air convection oven at a temperature of 143.degree.
C. in between two roller stands applying an tensile force to the
filaments was placed before the calender rolls. The tensile force
was adjusted to apply a draw rate of 1.12 to the filament layer
before entering the calender rolls set at a temperature of
160.degree. C. The obtained fibrous tape B had an average thickness
of 47 micrometer, a width of 29 mm, a titre of 968 dtex and a
tenacity of 2.83 N/tex. The transversal strength of the tape was
0.41 MPa.
Example 1
[0077] Comparative Experiment B was repeated with the addition that
the drawn filament layer was passed over a heated surface of
157.degree. C., the contact path with the heated surface having a
length of about 3 cm before entering the calendering rolls set at a
temperature of 139.degree. C. The obtained fibrous tape 1 had an
average thickness of 39.6 micrometer, a width of 30 mm, a titre of
751 dtex and a tenacity of 3.19 N/tex. The transversal strength of
the tape was 0.60 MPa representing about a 50% improvement over the
transversal strength of tape B.
* * * * *