U.S. patent application number 14/366469 was filed with the patent office on 2015-06-04 for rope comprising at least one fibrillated film tape.
The applicant listed for this patent is DSM IP Assets B.V.. Invention is credited to Rigobert Bosman, Kishor Darda, Christiaan Henri Peter Dirks.
Application Number | 20150152593 14/366469 |
Document ID | / |
Family ID | 47520046 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150152593 |
Kind Code |
A1 |
Darda; Kishor ; et
al. |
June 4, 2015 |
ROPE COMPRISING AT LEAST ONE FIBRILLATED FILM TAPE
Abstract
A process for producing a high strength rope comprising the step
of i) providing a uniaxially oriented tape (10) comprising
ultra-high molecular weight polyethylene, the tape (10) having a
tensile strength of at least 0.9 GPa, and ii) simultaneously
twisting and fibrillating the tape (10) into a twisted strand of
fibrillated tape with a coherent network of filaments and fibrils.
A rope obtainable by the process and products comprising the rope
are also disclosed.
Inventors: |
Darda; Kishor; (Mumbai,
IN) ; Bosman; Rigobert; (Echt, NL) ; Dirks;
Christiaan Henri Peter; (Echt, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DSM IP Assets B.V. |
Heerlen |
|
NL |
|
|
Family ID: |
47520046 |
Appl. No.: |
14/366469 |
Filed: |
December 18, 2012 |
PCT Filed: |
December 18, 2012 |
PCT NO: |
PCT/EP2012/076005 |
371 Date: |
June 18, 2014 |
Current U.S.
Class: |
87/3 ; 57/260;
57/31; 87/8 |
Current CPC
Class: |
D07B 2501/2061 20130101;
D07B 2205/2014 20130101; D07B 2201/1096 20130101; D07B 2201/2003
20130101; D07B 2207/405 20130101; D07B 1/025 20130101; D07B
2201/1004 20130101; D07B 2207/405 20130101; D07B 2201/1044
20130101; D07B 2501/2038 20130101; D07B 5/00 20130101; D07B
2205/2014 20130101; D07B 2205/502 20130101; D07B 2801/12 20130101;
D07B 2801/60 20130101; D07B 1/02 20130101; D07B 2801/10
20130101 |
International
Class: |
D07B 1/02 20060101
D07B001/02; D07B 5/00 20060101 D07B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2011 |
EP |
11194279.3 |
Claims
1. Process for production of a high tensile strength rope
comprising the step of providing an uniaxially oriented tape
comprising ultra-high molecular weight polyethylene, the tape
having a tensile strength of at least 0.9 GPa as measured in
accordance with ISO 1184(H), and simultaneously twisting and
fibrillating the tape into a twisted strand of fibrillated tape
with a coherent network of filaments and fibrils.
2. The process according to claim 1 characterized in that the twist
level of the twisted strand of fibrillated tape is in the range
from 1 to 100 turns per meter.
3. The process of claim 1 characterized in that the linear density
of the tape is between 400 and 200,000 dtex.
4. The process of claim 1 characterized in that the tape has an
areal density of between 2 and 200 g/m.sup.2.
5. The process of claim characterized in that the tape has a
tensile strength of at least 1.2 GPa, preferably 1.5 GPa.
6. The process of claim 1 further comprising the step of braiding,
laying, twisting or bundling into a rope at least one of said
twisted strands comprising the fibrillated tape.
7. The process according to claim 1 further characterized in that
the uniaxially oriented tape is provided from a package.
8. The process according to claim 7 characterized in that the
unwinding is performed by pulling off the tape over-head from a
stationary package.
9. A rope obtainable by a process according to claim 1.
10. The rope of claim 9 comprising at least one strand wherein said
strand comprises a fibrillated tape having a tensile strength
before fibrillation of at least 0.9 GPa as measured in accordance
with ISO 1184(H) wherein the fibrillated tape comprises a coherent
network of filaments and fibrils.
11. The rope of claim 9 characterized in that it comprises more
than one strand comprising a fibrillated tape.
12. The rope according to claim 9 characterized in that the rope is
of a braided construction.
13. The rope according to claim 9 characterized in that at least
one strand is a braided rope.
14. A product comprising any one of the ropes according to claim
9.
15. The product of claim 14, wherein the product is chosen from the
group consisting of mooring lines, towing lines, lifting ropes,
off-shore ropes, fishing lines, fishing nets, cargo nets, cargo
curtains, belts, woven fabrics, raschels and slings.
Description
[0001] The invention relates to a process for production of a high
tensile strength rope comprising at least one strand wherein said
strand comprises a uniaxially oriented elongated body comprising
ultra-high molecular weight polyethylene.
[0002] Such a rope is known from U.S. Pat. No. 5,901,632. In this
patent publication a large-diameter braided rope is described,
which rope contains primary strands, preferably from secondary
strands containing high tensile strength uniaxially oriented
ultra-high molecular weight polyethylene filaments. In the most
preferred embodiments indicated, the rope is a 12-strand,
two-over/two-under circular braid, wherein each strand is itself a
12-strand braid made from high-modulus polyethylene (HMPE)
filaments (12.times.12 construction).
[0003] Such ropes, especially if produced from high tenacity
fibers, will show a high resistance to longitudinal deformation
even when high extensional forces are applied, making them
especially suited for load bearing applications.
[0004] Nevertheless it was observed that such ropes may undergo
substantial deformation when non-extensional forces are applied in
other directions, such as axial compression, bending forces or a
transversal or rolling force applied crosswise to its length
direction. When exposed to frequent non-extensional forces, ropes
may fail due to rope and filament damage resulting from e.g.
external and internal abrasion, frictional heat, or fatigue.
Additionally, when ropes are subjected to an excessive number of
axial compressions, e.g. cycles at low tension, axial compression
fatigue caused by buckling and kinking within the strands is
observed. No solution other than avoiding conditions of rope cycles
at low tension has been proposed to improve axial compression
fatigue; see for example at p.171ff and 353 of the Handbook of
fibre rope technology (eds McKenna, Hearle and O'Hear, Woodhead
Publishing Ltd, ISBN 1 85573 606 3).
[0005] It is an aim of the present invention to provide a process
for a rope with optimized properties with respect to above
mentioned deficits.
[0006] This aim is achieved according to the invention by a process
for producing a rope comprising the step of providing a uniaxially
oriented ultra-high molecular weight polyethylene tape having a
tensile strength of at least 0.9 GPa as measured in accordance with
ISO 1184(H), and simultaneously twisting and fibrillating the tape
into a twisted strand of fibrillated tape with a coherent network
of filaments and fibrils.
[0007] It was surprisingly observed that the process of the
invention provides ropes which may have an optimized stability
against the non-extensional deformational forces.
[0008] The invention further relates to a rope obtainable by the
process according to the invention.
[0009] The rope according to the invention can have a round
cross-section, e.g. a cross-section that is about circular or one
that is oblong. By oblong-cross-section is herein meant that the
cross-section of the rope shows a flattened, oval, or even an
almost rectangular form. Such oblong cross-section preferably has
an aspect ratio, i.e. the ratio of width to height of the
cross-section, in the range from 1.2 to 4.0. Methods to determine
the aspect ratio are known to the skilled person; an example
includes measuring the outside dimensions of the rope, while
keeping the rope taut, or after tightly winding an adhesive tape
around it. The advantage of an oblong cross-section with said
aspect ratio is that during cyclic bending where the width
direction of the cross section is parallel to the width direction
of the sheave, less stress differences might occur between the
fibres in the rope. Also for certain applications, less abrasion
and frictional heat may occur, which may result in enhanced bend
fatigue life. The cross-section preferably has an aspect ratio of
about 1.3-3.0, more preferably about 1.4-2.0.
[0010] Preferably, the rope and/or the fibrillated tape in the rope
are coated with a coating for improving various properties such as
abrasion resistance or bending fatigue. Such coatings, which can be
applied to the fibrillated tape before construction of the rope, or
onto the rope after it is constructed, are known and examples
include coatings comprising silicone oil, bitumen and both.
Polyurethane-based coating is also known, possibly mixed with
silicone oil. The rope preferably contains a coating in an amount
of 2.5-35 wt %, expressed as weight of coating per total weight of
the rope. More preferably, the rope contains an amount of 5-15 wt %
of the coating.
[0011] By rope is herein understood a long assembly of at least one
strand. Strands may also comprise more than one sub-strands,
commonly called secondary strands. Each strand or secondary strand
may comprise at least one fibrillated tape as the one used in
accordance with the invention.
[0012] In a preferred embodiment, the rope of the invention
comprises more than one strand comprising the fibrillated tape.
[0013] In a further preferred embodiment all strands of the rope of
the invention comprise a fibrillated tape.
[0014] In a yet another preferred embodiment, the at least one
strand of the rope of the invention comprises secondary strands,
wherein the secondary strands comprise the fibrillated tape.
[0015] The rope according to the invention may be of various
constructions, including laid, braided, plaited, parallel, with or
without a core. The number of strands in the rope may also vary
widely. A parallel rope may be constructed with at least a single
strand. The number of strands in more complex rope constructions
may be at least 3 and preferably at most 50, more preferable at
most 25, to arrive at a combination of good performance and ease of
manufacture.
[0016] In a preferred embodiment the rope according to the
invention is of a braided construction. Braiding provides a robust
and torque-balanced rope that retains its coherency during use.
There is a variety of braid types known, each generally
distinguished by the method of braiding. Suitable constructions
include soutache braids, tubular braids, and flat braids. Tubular
or circular braids are the most preferred braids for rope
applications and generally consist of two sets of strands that are
intertwined, with different patterns possible. The number of
strands in a tubular braid may vary widely. Especially if the
number of strands is high, and/or if the strands are relatively
thin, the tubular braid may have a hollow core; and the braid may
collapse into an oblong shape. The number of strands in a braided
rope according to the invention is preferably at least 4. There is
no upper limit to the number of strands, although in practice ropes
will generally have no more than 48 strands. Particularly suitable
are ropes of an 8- or 12-strand braided construction. Such ropes
provide a favourable combination of tenacity and resistance to bend
fatigue, and can be made economically on relatively simple
machines.
[0017] The rope according to the invention can also be of a laid
construction having a lay length, wherein the lay length, i.e. the
length of one turn of a strand in a laid construction, or of a
braided construction having a braiding period, i.e. the pitch
length of the braided rope, which is in the range of from 4 to 20
times the diameter of the rope. A higher lay length or braiding
period may result in a rope having higher strength efficiency.
Preferably, the lay length or braiding period is about 5-15 times
the diameter of the rope, more preferably 6-10 times the diameter
of the rope.
[0018] The construction of the strands of the rope according to the
invention may also be laid, braided or twisted strands.
[0019] In one embodiment of the invention, at least one strand is a
braided rope, more preferably all strands are braided ropes.
Preferably said strands are circular braids made from an even
number of secondary strands, wherein the secondary strands comprise
the fibrillated tape. The number of secondary strands forming the
braided rope strand is not limited, and may for example range from
4 to 32; with 8, 12 or 16 being preferred in view of available
machinery for making such braids.
[0020] The uniaxially oriented ultra-high molecular weight
polyethylene tapes suitable to manufacture the fibrillated tape may
be prepared by drawing films. Films may be prepared by feeding an
ultra-high molecular weight polyethylene (UHMWPE) powder between a
combination of endless belts, compression-molding the UHMWPE powder
at a temperature below the melting point thereof and rolling the
resultant compression-molded polymer thereby forming a film.
Another preferred process for the formation of films comprises
feeding UHMWPE powder to an extruder, extruding a film at a
temperature above the melting point thereof and drawing the
extruded polymer film. If desired, prior to feeding the polymer to
the extruder, the polymer may be mixed with a suitable liquid
organic compound, for instance to form a gel, such as is preferably
the case when using ultra high molecular weight polyethylene.
[0021] Drawing, preferably uniaxial drawing, of the films to
produce tapes may be carried out by means known in the art. Such
means comprise extrusion stretching and tensile stretching on
suitable drawing units. To attain increased mechanical strength and
stiffness, drawing may be carried out in multiple steps.
[0022] The tapes used in the present invention are oriented by
drawing, for instance at a suitable temperature, to obtain a
uniaxially oriented material. With uniaxially oriented tapes is
meant in the context of this application that the tapes exhibit a
preferred orientation of the polymer chains in one direction, i.e.
in the direction of drawing. Such tapes will exhibit anisotropic
mechanical properties.
[0023] The resulting drawn tapes may be used as such in the rope
production process, or they may be cut or split to a desired width.
Preferably the split is carried out along the direction of
drawing.
[0024] The width of the tapes is only limited by the width of the
film from which they are produced. The width of the tapes used to
produce the ropes is preferably more than 2 mm, more preferably
more than 5 mm and most preferably more than 30 mm. The areal
density of said tapes can be varied over a large range, for
instance between 2 and 200 g/m.sup.2. Preferred areal density is
between 10 and 170 g/m.sup.2, more preferred between 10 and 100
g/m.sup.2 and most preferred between 20 and 60 g/m.sup.2. Further
increased stability against non-extensional deformation forces may
be achieved by tapes within the described preferred ranges.
[0025] The linear density of the strand of fibrillated tape of the
invention may vary within wide ranges and may be selected depending
upon the number of fibrillated tapes in the strand as well as the
final linear density of the rope. The linear density is measured by
determining the weight in mg of 10 meters of material and is
conveniently expressed in dtex (g/10 km) or denier (den, g/9 km).
The linear density of the fibrillated tape may depend upon the
areal density of the tape, the width of the tape and the twist
level of the fibrillated tape. Accordingly a reduced width of the
tape used to manufacture the fibrillated tape, a reduced areal
density of said tape, or a higher twist level of the fibrillated
tape may provide a lower linear density of the fibrillated tape,
whereas increased width of said tape, areal density of said tape or
reduced twist level of the fibrillated tape may provide a higher
linear density of the fibrillated tape. Preferably the linear
density of the fibrillated tape of the rope in the present
invention will be in the range from 400 dtex (360 den) to 200.000
dtex (180000 den). More preferably the linear density of the
fibrillated tape will be in the range from 1000 dtex (900 den) to
100000 dtex (90000 den), even more preferably from 2000 dtex (1800
den) to 50000 dtex (45000 den) and most preferably from 5000 dtex
(4500 den) to 20000 dtex (18000 den). Stability against
non-extensional deformation forces may be further optimized by
tapes with linear density within the described preferred
ranges.
[0026] The tape provided to the process of the invention comprises
ultra-high molecular weight polyethylene (UHMWPE). The ultra-high
molecular weight polyethylene may be linear or branched, although
preferably linear polyethylene is used. Linear polyethylene is
herein understood to mean polyethylene with less than 1 side chain
per 100 carbon atoms, and preferably with less than 1 side chain
per 300 carbon atoms; a side chain or branch generally containing
at least 10 carbon atoms. Side chains may suitably be measured by
FTIR on a 2 mm thick compression moulded film, as mentioned in e.g.
EP 0269151. The linear polyethylene may further contain up to 5 mol
% of one or more other alkenes that are copolymerisable therewith,
such as propene, butene, pentene, 4-methylpentene, octene.
Preferably, the linear polyethylene is of high molar mass with an
intrinsic viscosity (IV, as determined on solutions in decalin at
135.degree. C.) of at least 4 dl/g; more preferably of at least 8
dl/g, most preferably of at least 10 dl/g. Such polyethylene is
also referred to as ultra high molecular weight polyethylene
(UHMWPE). Intrinsic viscosity is a measure for molecular weight
that can more easily be determined than actual molar mass
parameters like Mn and Mw.
[0027] The rope according to the invention may comprise further
elongated bodies such as tapes, yarns and/or filaments. Such
further elongated bodies may comprise polymers selected from the
group consisting of polyolefins, polyesters, polyvinyl alcohols,
polyacrylonitriles, polyamides, especially poly(p-phenylene
teraphthalamide), liquid crystalline polymers and ladder-like
polymers, such as polybenzimidazole or polybenzoxazole, especially
poly(1,4-phenylene-2,6-benzobisoxazole), or
poly(2,6-diimidazo[4,5-b-4',5'-e]pyridinylene-1,4-(2,5-dihydroxy)pheny-
lene). Preferably the further elongated bodies comprise UHMWPE
according to the one of the tapes used in the present
invention.
[0028] The tensile strength of the tapes prior to the fibrillation
process depends on the UHMWPE from which they are produced, and on
their (uniaxial) stretch ratio. The tensile strength of said tapes
is at least 0.9 GPa, preferably at least 1.2 GPa, more preferably
at least 1.5 GPa, even more preferably at least 1.8 GPa, and even
more preferably at least 2.1 GPa, and most preferably at least 3
GPa.
[0029] The rope according to the invention is particularly useful
in various applications such as mooring, towing, lifting, offshore
installation.
[0030] It was also observed hat the ropes according to the
invention are also suitable for use in other applications like for
example fishing lines, fishing nets, cargo nets, cargo curtains,
belts, woven fabrics, raschels and slings. Therefore, the invention
also relates to the applications enumerated above containing the
ropes of the invention.
[0031] One embodiment of the invention relates to a process for the
production of a rope comprising the step of providing an uniaxially
oriented tape comprising ultra-high molecular weight polyethylene
having a tensile strength of at least 0.9 GPa as measured in
accordance with ISO 1184(H), and simultaneously twisting and
fibrillating the tape into a twisted strand of fibrillated tape
with a coherent network of filaments and fibrils. In the context of
the invention the term fibrillation refers to providing the tape
with a multitude of confined slits in the machine direction of the
tape, with rows of slits displaced laterally with respect to one
another. The fibrillation occurs during the twisting of the
uniaxially oriented tape and as a consequence of the mechanical
treatment of the tape. Fibrillation may partly occur also before
the twisting step such as during handling and supply of the
uniaxially oriented tape to the twisting equipment as well as after
the twisting step during for example transportation, winding and/or
compaction. Suitable twisting equipments are the ones commonly used
for the processing of continuous filament or staples into yarns and
will be well known to the person skilled in the art.
[0032] The process according to the invention may also further
comprise a step of post-stretching the twisted strand of
fibrillated tape and/or the rope comprising the twisted strand of
fibrillated tape. Such a post-stretching step is preferably
performed at elevated temperature but below the melting point of
the (lowest melting) fibrillated tape in the stands
(heat-stretching). For a rope containing fibrillated tape
comprising UHMWPE, a preferred temperature lies in the range
100-120.degree. C. Such a heat-stretching step is described in a.o.
EP 398843 B1 or U.S. Pat. No. 5,901,632.
[0033] The invention will be described referring to the figures in
the drawings.
[0034] FIG. 1 diagrammatically illustrates a top view of the
fibrillated tape upon spreading the twisted fibrillated tape to a
flat fibrillated tape. According to the invention the fibrillated
tape 10 comprises a multitude of longitudinal slits 20. The slits
20 may be of irregular length and number. The respective distances
in the width direction of the tape between adjacent slits may also
be of irregular size.
[0035] The fibrillated tape upon spreading may show a net-like
structure comprising filaments 12 and fibrils 14. The filaments 12
and fibrils 14 may be interconnected without however being
continuous. The fibrillated tape may have the appearance of a
loosely cohered continuous filament yarn or the appearance of an
interconnected web having randomly connected filaments further
interconnected with fibrils to form a yarn-like product with a high
degree of coherency.
[0036] In the context of the invention, the term filament and
fibril are both understood to indicate an elongated body being a
segment of the tape. Said elongated body (filament or fibril) is
delimited in it width direction by either two adjacent slits 22 or
by one slit and one edge of the tape 24.
[0037] Filaments 12 are such elongated bodies interconnected with
the net-like structure of the fibrillated tape by both their two
ends 16. Fibrils 14 are such elongated bodies interconnected with
the net like structure by one of their ends 16. Simply, a fibril is
a dangling filament.
[0038] The dimensions, e.g. width and length, of the filaments and
fibrils will be strongly dependant upon the dimensions of the
employed tape as well as the fibrillation process. The length of a
filament is defined by the distance between two consecutive ends
where the filament is interconnected with the net-like structure
and may vary broadly in the range from 1 to 1000 mm. Preferably the
fibrillation process is adjusted to provide filaments having
lengths of from 2 to 500 mm, more preferably from 4 to 200 mm and
most preferably from 10 to 100 mm. The length of a fibril is
defined as the distance between the end where the fibril it is
interconnected with the net-like structure and the opposite end
thereof and may vary broadly in the range from 1 to 1000 mm.
Preferably the fibrillation process is adjusted to provide fibrils
having a length of from 2 to 500 mm, more preferably from 4 to 200
mm and most preferably from 10 to 100 mm.
[0039] The thickness of the filaments or the fibrils may be
substantially equal to the thickness of the employed tape. The
width of a filament or a fibril as being defined by the distance
between the 2 adjacent slits forming the filament or fibrils may
vary widely, preferably between 20 .mu.m an 20 mm. Preferably the
width of a fibril or a filament is from 40 .mu.m to 5 mm, more
preferably from 80 .mu.m to 2 mm and most preferably from 100 .mu.m
to 1 mm. In a preferred embodiment of the invention, the filaments
and fibrils may have a substantially rectangular cross-section.
[0040] In a preferred embodiment the process of the present
invention provides a twisted strand comprising the fibrillated
tape, the strand having a twist level in the range from 1 to 100
turns per meter (tpm). Preferably said twist level is from 2 to 80
tpm, more preferably from 5 to 50 tpm and most preferably from 10
to 35 tpm.
[0041] In a yet preferred embodiment, the process of the present
invention further comprises the step of braiding, laying, twisting
or bundling into a rope at least one of said twisted strands
comprising the fibrillated tape.
[0042] In an alternative embodiment of the process of the present
invention the uniaxially oriented tape is provided from a package.
In the context of the invention a package may comprise any adequate
form of storage of uniaxially oriented tape such as a bobbin, a
roll, a continuous ribbon container or alike. In the instance that
the uniaxially oriented tape is provided by unwinding the tape from
a package, such unwinding is preferably performed by pulling off
the tape over-head from a stationary package. Stationary in the
context of the present invention means that the package is not
rotating substantially around its winding axis. Optionally the
package may move along a predetermined pathway such as typical for
braiding equipment.
[0043] The present invention will now be further elucidated by
examples and comparative experiment, without being limited
thereto.
Equipment
[0044] A Roblon Tornado 300 (TT83) is used to twist and fibrillate
the tape into a strand [0045] Roblon Strander RS2-12--winding unit
(TT99) is used to wind the fibrillated tape onto 12 carriers for a
Herzog equipment [0046] Herzog SE 1/12-266 (TT57) is used for
braiding strands comprising the fibrillated tape [0047] Zwick 1474
Winding grip/800 kN horizontal tensile tester Mennens b.v. is used
for tensile measurement of the braided ropes.
Material
[0048] An ultra high molecular weight polyethylene tape was
manufactured according to the process described in U.S. Pat. No.
5,091,133. A tape with the following properties was obtained:
Linear density of 43300 dtex; Tenacity: 16.5 cN/dtex; Modulus: 1125
cN/dtex; Width: 100 mm; Areal density: 42 g/m.sup.2
Production Steps
[0049] A bobbin of UHMWPE tape was mounted on a regular (un)winding
frame (rolling takeoff).
[0050] A Roblon Tornado 300 twister was used to twist the tape into
strands of fibrillated tape. The twist level was chosen to be 18
tpm. 200 m of fibrillated tape Z-strands and 200 m of fibrillated
tape S-strands were produced. Portions of the fibrillated tapes
were untwisted for visual inspection. A net-like coherent structure
of filaments and fibrils could be observed for both strands of
fibrillated tape.
[0051] The extent of fibrillation of the tape was determined by
cutting from the fibrillated tapes 3 lengths of 5 mm each. The
number of individual fragments present in each length was counted.
The Z-strand had an average number of 53 fragments and the S-strand
had an average number of 51 fragments. The fragments showed random
distribution of widths in the range of 0.1 to 5 mm. Such random
distribution was considered to be a replication of the widths of
the filaments and fibrils of the fibrillated tape.
[0052] Bobbins with the Z- and the S-strands of fibrillated tape
were mounted on the winding unit of a Roblon Strander RS2-12. With
this equipment the strands were winded onto the Herzog carriers.
Finally the carriers were mounted onto a Herzog SE 1/12-266
braiding machine and 3 ropes with different braiding periods have
been produced.
[0053] Rope construction: 12.times.1.times.43300 dtex; Strand twist
18 tpm; Braiding pitch 64 mm, 70 mm and 76 mm. Rope diameter of all
3 ropes was 12 mm.
Test methods as referred to in the present application, are as
follows [0054] Intrinsic Viscosity (IV) is determined according to
ASTM-D1601/2004 or alternatively method PTC-179 (Hercules Inc. Rev.
Apr. 29, 1982) at 135.degree. C. in decalin, the dissolution time
being 16 hours, with DBPC as anti-oxidant in an amount of 2 g/I
solution, by extrapolating the viscosity as measured at different
concentrations to zero concentration; [0055] Tensile properties of
tapes were measured in accordance with ISO 1184(H). For calculation
of the modulus and strength, the tensile forces measured are
divided by the linear density of the tape (dtex); the linear
density is determined by weighing in mg 10 meters of tape; values
in GPa are calculated assuming a density of 0.97 g/cm.sup.3.
* * * * *