Note: Descriptions are shown in the official language in which they were submitted.
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SPINNING DOPE AND FIBRES SPUN THEREFROM
The invention relates to the field of making synthetic yarns, in
particular to synthetic yarns spun from sulphuric acid anisotropic
solutions of rigid chain aromatic polyamides blended with aliphatic:
polyamides.
Spinning dopes of sulphuric acid and aromatic and aliphatic
polyamides, and fibres made thereof, are known from Japanese laid open
No. 59163418-A, in which a spinning dope composed of 80-99 wt.~,
poly(p-phenylene terephthalamide) and 1-20 wt.% aliphatic polyamide is
described. The fibres prepared from said dope are particularly
suitable for making paper.
In EP 392558 a biphasic solution (dope) of para-aramid polymer and a
polymer that can be thermally consolidated, like polyhexamethylene
adipamide or poly(~-caproamide), is mentioned. The fibres made thereof
are considered suitable for the preparation of thermally shaped
objects (prepregs).
Although poly(p-phenylene terephthalamide) fibres are known to have
very high thermal stability and very high strength, there is a need to
improve their other characteristics. In the prior art, such other
characteristics were enhanced by the use of blends. However, this, in
its turn, was found to result in a reduction of other beneficial
properties of the fibres, such as their strength and/or abrasio~
resistance.
It was found that by the use of a spinning dope according to the
present invention, improved physical properties could be obtained
without a significant loss of other beneficial properties. Such
improvement was obtained by the use of a spinning dope composition
comprising an aromatic and an aliphatic polyamide and concentrated
=
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sulphuric acid, and is characterized in that at least one of the
aromatic and aliphatic polyamides is a copQlymer built up of two
aromatic and two aliphatic homopolymer units, respectively, the
aromatic copolymer having the formula
(formula I):
[~HN-c6H4-NHco-c6H4-co~u ~HN-c6H4-coNH-c6H4-NHco-c6H4 co~W]
wherein u = 75-95 wt.%, preferably 80-90 wt.% and w = 5-25 wt.%,
preferably 10-20 wt.%.
and the aliphatic copolymer having the formula
(formula II):
[~HN-(CH2)6-NHCO-(cH2)4-cO~n ~HN-(CH2)5-CO~m]
wherein n = 95-50 wt.%, preferably 93-60 wt.%, and m = 5-50 wt.%,
preferably 7-40 wt.%.
Very good results are obtained if use is made of a spinning dope
according to the above invention in which about 16-19.4 wt.% of the
aromatic polyamide, 0.6-4.0 wt.% of the aliphatic polyamide, and up to
100 wt% of concentrated sulphuric acid are present.
Such a spinning dope can be prepared by the method described in
European Patent No. 021484, which is incorporated by reference.
In order to avoid a solution of aliphatic and aromatic (co)polyamides
being separated into two phases, i.e. an anisotropic and an isotropic
phase, thorough agitation of the solution prior to processing is
considered necessary, in particular if the polymer blend in the
solution comprises more than 12 wt.% of aliphatic polyamides based on
the total amount of polymer in the solution.
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In Japanese patent application JP 59/116411-A it is described that
adhesion to rubber and other materials, usually a finish coating is
applied. By adding an aliphatic polyamide polymer to the spinning dope
of poly(p-phenylene terephthalamide), an increase in adhesion is
obtained. However, such an addition is attended with a significant
drop in strength. By using a spinning dope of poly(p-phenylene
terephthalamide), an aliphatic polymer of formula II, and sulphuric
acid it is possible to make fibres or yarns which are very suitable
for making reinforced and self-reinforced plastics and reinforced
rubber technical articles, in particular cord for reinforcing
automobile tyres.
By spinning a spinning dope of sulphuric acid, poly(p-phenylene
terephthalamide) and more than 5 wt.% of a common aliphatic polymer
based on the total polymer amount present, fibres are obtained which
show a considerable drop of (up to 28%) or even more in fibre strength
as compared with the poly(p-phenylene terephthalamide) fibre strength.
As is further exemplified by the test results of spinning fibre blends
of poly(p-phenylene terephthalamide) and a formula II copolymer, the
drop in fibre strength is much less severe. On the other hand, when
using such a blend an increase in fibre adhesion can be obtained
compared with poly(p-phenylene terephthalamide) fibres.
According to this preferred embodiment, the aliphatic copolyamide is
preferably applied in amounts of between 3 and 20 wt.%, based on the
total amount of polymer present.
From UK Patent Application GB 2 160 878 it is known to dissolve a
mixture of a poly(p-phenylene terephthalamide) polymer and an
aromatic-aliphatic copolyamide in concentrated sulphuric acid to
obtain fibres of increased tenacity and modulus. The drawback to this
method is the necessity of incorporating into the blend up to 15 wt.%
of aromatic-aliphatic copolyamide, the production of which is very
difficult, at any rate more difficult than that of poly(p-phenylene
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terephthalamide). Furthermore, the fibre density is not lowered,
contrary to what has been found with the use of spinning dopes
according to the present invention.
Furthermore, the abrasion resistance of fibres made from the spinning
dopes described in the prior art is not always as high as desired. The
abrasion resistance of the fibres obtained from a spinning dope
comprising an aromatic copolyamide of formula I and an aliphatic
copolyamide of formula II was found to be superior to that of prior
art fibre compositions and fibres substantially comprising
poly(p-phenylene terephthalamide) polymer.
Unexpectedly, it was found that when introducing the above-mentioned
aliphatic copolyamide of formula II at a certain component ratio gives
a sharp increase in yarn strength and yarn abrasion resistance. The
mechanism for strengthening the yarns of the blends indicated above
apparently is different from that when mixing aromatic-aliphatic
additive with poly(p-phenylene terephthalamide) as in UK Patent
Application GB 2 160 878, since the aliphatic copolyamide cannot be
built into the crystal lattice of poly(p-phenylene terephthalamide),
and thus is not.
By use of the aliphatic copolyamide of formula II, up to 8 mass% with
the remaining polymer amount of 92 wt.% being poly(p-phenylene
terephthalamide), provides a yarn which has a strength of up to
2010-2059 mN/tex, whereas a comparable yarn of poly(p-phenylene
terephthalamide) polymer has a strength of about 2059 mN/tex. The yarn
strength is increased when, together with the aliphatic copolyamide of
formula II, an aromatic copolyamide of formula I is applied. Compared
with the same poly(p-phenylene terephthalamide) fibre strength of 2059
mN/tex, a yarn strength of 2255 up to 2450 mN/tex was found.
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At a higher concentration of aliphatic copolyamide in the polymer
blend (up to 20 wt.%), the decrease of the yarn strength as compared
with aliphatic polyamides such as polycaproamide or polyhexamethylene
adipamide or a blend thereof is lower.
The amount of incorporated aliphatic copolyamides is 3-20 wt.% of the
polymer blend.
The addition of less than 3 wt.% of aliphatic copolyamides does not
considerably affect the yarn properties. The addition of more than
20 wt.% of such an aliphatic polyamide, however, results in a reduced
tenacity, which is not considered acceptable for each and every
application of the fibres.
The fibre strength is found not to decrease when is use is made of a
blend of an aromatic copolyamide of the formula I and an aliphatic
polyamide such as polycaproamide or polyhexamethylene-adipamide (PA 6
and PA 66), contrary to what was found if a common PPDT
(poly[p-phenylene terephthalamide]) and such an aliphatic polyamide
were applied. Moreover, the fibres made of the now found composition
were found to have a low density, which is considered favourable in
applications where both a low density and a very high yarn strength
are required. This is in particular the case when the fibres are
used for making reinforced plastics, reinforced rubber articles, and
heat-insulation materials.
Hence, the invention also encompasses a spinning dope of an aromatic
copolyamide of one of the formulae I, an aliphatic polyamide
comprising a component chosen from PA 6, PA 66, or a copolymer
thereof, and concentrated sulphuric acid.
A very beneficial spinning dope and fibres spun therefrom result when
~ a spinning solution of an aromatic copolyamide according to one of the
formulae I is used together with an aliphatic copolyamide according to
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formula II and concentrated sulphuric acid. The spinning dope
preferably comprises 16-18.5 wt.% of the aromatic copolyamide,
1.5-4.0 wt.% of aliphatic copolyamide, and a balance amount of
sulphuric acid.
The invention is further illustrated by the examples given below. In
these examples, the inherent viscosity IV which is defined as
IV = ln (~rel)/c~ in which c is the concentration, was
determined by a viscometric method on solutions containing 0,5 9 of
polymer in 100 ml of 96% sulphuric acid at 25~C.
Complex yarn strength having optimum twist were determined by clamping
a length of 500 mm yarn on an Instron tensile tester according to
standard procedures known in the art for such tensile testers.
1~ Example 1
A 20%-dope was prepared in reactor with a capacity of 63 litres. To
this end, 9.5 kg (19 wt.%) of aromatic copolyamide of formula I
wherein u=90 and w=10 wt.% and with an inherent viscosity IV of 5.5
dl/g, 0.5 kg (1 wt.%) of aliphatic copolyamide of formula II wherein
n=80 and m=20 wt.% and with an inherent viscosity IV of 1.2 dl/g, and
21.9 l (80 wt.%) of 99.9%-sulphuric acid solution were fed, under
vacuum, to a filtration step while being mixed at a temperature of
75~C, and then to the spinning machine. Spinning was carried out by a
dry-wet method through an air gap of about 10 mm, into a 10%-sulphuric
acid spinning bath having a temperature of 8~C. The take-up yarn rate
was 85 m/min, and the cup spinnerets of precious metal had a cup
diameter of 28 mm, the number of holes being 1000 and the hole
diameter being 0,07 mm. The draw ratio of the dope stream in the air
gap was 8.1,
At the spinning machine the yarn was subjected to a washing step under
a tension of 20-60 mN/tex. Further acid neutralization took place
using an 0.02% solution of sodium hydroxide. Next, the yarn was dried
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- at about 120-150~C and taken up by a take-up device without any twist
being applied after the spinning. The IV viscosity of the polymer
blend in the yarn was 4.8 dl/g. The yarn was subjected to a twist of
up to 80 twists per meter. The yarn's linear density was 167 tex, the
tensile strength 2255 mN/tex, and the elongation at break 4.3%. The
abrasion resistance was found to amount to 23 thousand cycles.
Example lA
The tensile strength of yarn being spun, under similar conditions to
those indicated in Example 1, from a 20% solution of the same aromatic
copolyamide as used in Example 1, and in the same way as indicated in
Example 1, but this time without the addition of an aliphatic
copolyamide to the solution was 2010 mN/tex. The abrasion resistance
was 14 thousand cycles.
Example 1B
A yarn was spun by the same procedure as indicated in Example 1, with
the same amount of the aromatic copolyamide of formula I being
applied. Instead of the aliphatic polyamide of formula II, this time a
similar amount of polycaproamide with an inherent viscosity IV of 1.2
dl/g was incorporated into the blend in the same way, and the yarn was
spun under conditions similar to those of Example 1. The yarn obtained
showed a tensile strength of 1990 mN/tex and an abrasion resistance ol
12 thousand cycles. The adhesion was found to be superior to that ol
the yarns obtained in Example lA.
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Examples 2-7
Several spinning dopes were prepared, use being made of different dope
compositions and polymers of a different structure. The 20 wt.%
polymer-containing spinning dopes were prepared by mixing the polymer
components with a 99.8%-sulphuric acid solution. After 4 hours of
stirring in a mixer at 75~C the obtained anisotropic solution was fed,
under vacuum, to a filter and subsequently to the spinning machine.
The spinning of the yarns was carried out in the manner described in
Example 1. The tensile strength of the yarns and their abrasionresistance were measured and are indicated in Table I. The
specification and the amount of each of the polymers used are also
indicated in Table I.
The aromatic copolyamide is the copolyamide according to formula I.
The inherent viscosity IV of the aromatic polyamide used was between
5.4 and 5.5 dl/g, the viscosity of the different aliphatic polyamides
used was 1.2 dl/g.
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Table
Example Aromatic Aliphatic Dope Composi- Yarn Abrasion
Nos copoly- (co)poly- tion aromatic tensile resistance
amide amide copolyamide/ strength [thousand
aliphatic cycles]
[u/w] [n/m] copolyamide/ [mN/tex]
H204 [wt.%]
2A 90/10 85/15 19/1/80 2451 25
2B 90/10 polycapro- 19/1/80 2059 12
amide
3A 90/10 85/15 18/2/80 2255 22
3B 90/10 polyhexa- 18/2/80 2010 10
methylene
adipamide
4A 90/10 85/15 16/4/80 1863 18
4B 90/10 polycapro- 16/4/80 1716 12
amide
4C 90/10 50/50 16/4/80 1765 15
5A 85/15 85/15 19/1/80 2451 25
5B 85/15 polycapro- 19/1/80 2059 12
amide
5C 85/15 without 20/-/80 2059 14
aliphatic
PA
6A 75/25 93/7 19.4/0.6/80 2157 20
6B 75/25 polycapro- 19.4/0.6/80 2108 10
amide
6C 75/25 without 20/-/80 2108 14
aliphatic
PA
7A 75/25 50/50 16/4/80 1863 16
7B 75/25 polycapro- 16/4/80 1814 8
amide
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For the polymer compositions not comprising an aliphatic copolyamide
according to formula II but an aliphatic polyamide homopolymer like
polycaproamide or polyhexamethylene adipamide instead, a comparable
tensile strength of the yarns produced therefrom was found. The fibres
produced from these polymer compositions had a significantly increased
adhesion compared with the compositions comprising no aliphatic
polyamide at all. The superiority in characteristics of the fibres
obtained from polymer compositions comprising both a formula
aromatic copolyamide and a formula II aliphatic copolyamide is clear
from the above results.
Example 8
38 9 (19 wt.%) of poly(p-phenylene terephthalamide) with a viscosity
of 5.8 dl/g and 2 9 (1 wt.%) of an aliphatic copolyamide of formula II
wherein n=85 and m=15 and with an inherent viscosity IV of 1.2 dl/g
were incorporated as a blend into 87.4 ml (80 wt.%) of 99.8%-sulphuric
acid, stirred in a mixer for 3 hours at 82~C, filtered, and deaerated
within one hour at dissolution temperature. The spinning of the yarn
was carried out in a process similar to the one described for
Examples 2-7.
The viscosity of the polymer blend in the yarn was 4.8 dl/g, the yarn
tensile strength was 2059 mN/tex, the elongation at break of the yarn
3.4%, and the abrasion resistance of the yarn 22 thousand cycles.
Example 8A (comparative)
The strength of a yarn spun from a 20% poly(p-phenylene terephthalami-
de) polymer-comprising solution without any aliphatic (co)polyamide
was 1961 mN/tex, the abrasion resistance 10 thousand cycles.
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Example 9
36 9 (18 wt.%) of poly(p-phenylene terephthalamide) and 4 g (2 wt.%)
of an aliphatic copolyamide of formula II wherein n=85 and m=15
(viscosity IV =1.2 dl/g) were incorporated as a blend into 87.4 ml
(80 wt.%) of a 99.8%-sulphuric acid solution, stirred in a mixer at
82~C for 3 hours, filtered, and deaerated at dissolution temperature
within 1 hour. The spinning of the yarn was carried out as described
in Example 10. The inherent viscosity IV of the polymer blend in the
yarn is 4.8 dl/g. The tensile strength was 1961 mN/tex, the elongation
at break 3.3%, and the abrasion resistance 20 thousand cycles.
Example 9A (comparative)
On repeating Example 9, except that polycaproamide and
polyhexamethylene adipamide, both with an inherent viscosity IV of
1.2 dl/g, were used instead of an aliphatic copolyamide according to
formula II, the resulting yarns showed a tensile strength of about
1441 mN/tex and an abrasion resistance of 8 thousand cycles. The
solution from which these yarns were made had the following
composition: 18.4/1.6/80 wt.% (poly(p-phenylene terephthalamide)/PA 6
or PA 6.6/sulphuric acid).
Example 10
18.5 wt.% of an aromatic copolyamide according to formula I wherein
u=90 and w=10 and with an inherent viscosity IV of 5.5 dl/g and 1.5
wt.% of polyhexamethylene adipamide with an inherent viscosity IV of
1.0 dl/g (7.5 wt.% of alipha-tic polyamide in the polymer blend) were
dissolved in 43.7 ml (80 wt.%) of 99.8%-sulphuric acid solution,
stirred in a mixer at 74-78~C for 3 hours, filtered, and deaerated at
dissolution temperature within 1,5-2 hours. From the thus obtained
anisotropic 20% polymer comprising spinning dope yarns were spun
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through a 5 mm air gap by the dry-wet spinning process for aramid
fibres well-known per se in the art, into water of 10~C and at a yarn
take-up speed of 120 m/min. The stream draw ratio in the air gap was
6Ø The spinnerets used had about 100 holes and a hole diameter of
0.08 mm. The wet yarn was taken up on a bobbin and the acid washed
off. Next the yarn was dried at room tem-perature and twisted up to
150 twists/meter. The viscosity IV of the polymer blend in the yarn
was 5.1 dl/g. The yarn's linear density was 29.4 tex, the density
1.35 g/cm3. The tensile strength of the yarn found, 2010 mN/tex,
corresponds to the tensile strength of a yarn not comprising any
flexible chain polymer but spun, under the same conditions, from a 20%
polymer comprising solution of rigid-chain polyamide. The bending
resistance of the yarn prepared was found to be 14000-16000 cycles,
whereas the bending resistance of the yarn not comprising the
aliphatic polyamide was 2000 cycles.
Example 11
A 20% polymer comprising spinning dope was prepared in reactor with a
capacity of 60 l. To this end were used 18 wt.% of an aromatic copo-
lyamide according to formula I wherein u=85 and w-15 and IV = 5.5,
2 wt.% of polycaproamide with an inherent viscosity IY of 1.33 dl/g
(10% of aliphatic polyamide in the polymer blend), and 22 l (80 wt.%)
of a 99.8%-sulphuric acid solution. After 4 hours of preparation in a
mixer the obtained anisotropic solution was fed under vacuum and at
75~C, to a filter and then to the spinning machine. Spinning was
carried out through an air gap of 7 mm into a 10%-sulphuric acid
spinning bath of 60~C, at a yarn take-up speed of 70 m/min and through
a spinneret comprising 1000 holes, the hole diameter being 0.07 mm,
and the stream draw ratio in the air gap being 8.1. The yarn on the
spinning machine was kept under a tension of 2.5 cN/tex and the acid
was washed off, the acid residue being further neutralized. Finally,
the yarn was dried at 100-150~C.
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After the application of a spin finish, the yarn was placed on a take-
up device without being twisted. Next, the yarn was twisted to
80 twists/meter. The inherent viscosity IV of the polymer blend in the
yarn is 4.8 dl/g. The yarn's linear density was 167 tex, the density
1.35 g/cm3. The tensile strength was 2010 mN/tex, which corresponds to
the tensile strength of a yarn prepared under the same conditions,
from poly(p-phenylene terephthalamide) alone, i.e. not comprising any
flexible chain polymers (aliphatic polyamide). The yarn's dynamic
modulus of elasticity was 98066 N/mm2, the elongation at break 3.5%.
Example 12
The preparation of a spinning dope was carried out as described in
Example 11, except that use was made of 17 wt.% of an aromatic
copolyamide of formula I wherein u=80, w=20, and IV=5.5 dl/g together
with 3 wt.% of polycaproamide with an inherent viscosity IV of
1.33 dl/g. The polymer blend thus comprised 15 wt.% of aliphatic
polyamide. The inherent viscosity IV of the polymer blend in the yarn
was 4.7 dl/g. The linear density was 167 tex, the density 1.26 g/cm3,
and the tensile strength 1765-1863 mN/tex. The dynamic modulus of
elasticity was found to be 107866 N/mm2, the elongation at break
3.2-3.6%. The drop in yarn strength as compared with a yarn not
comprising flexible chains was found to be 7-12%.
Example 13
A spinning dope was prepared according to the process described in
Example 11, except that use was made of 16 wt.% of an aromatic copo-
lyamide of formula I wherein u=75 and w=25 and with an inherent
viscosity IV of 5.5 together with 4 wt.% of polycaproamide with
IV=1.33. Thus, the polymer blend consisted of 20 wt.% of aliphatic
7 polyamide. After some time the solution separated into an anisotropic
and an isotropic phase.
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14
The preparation of the yarns was carried out as described in
Example 11. The drying of the yarn on the spinning machine was carried
out at 100-270~C. The inherent viscosity IV of the polymer blend in
the yarn was 4. 65 dl/g. The yarn density was 1.17 g/cm3, the yarn
tensile strength 1617-1716 mN/tex. The dynamic modulus of elasticity
was 93157-118000 N/mm2, the elongation at break 3.3-3.7%. Compared
with a yarn not comprising an aliphatic polyamide (2010 mN/tex), the
drop in yarn strength was about 15-20%.
Example 14 (comparative)
A spinning dope comprising 20 wt.% of polymer in the solution was pre-
pared in a manner similar to that described in Example 10, except that
use was made of 18.4 wt.% of poly(p-phenylene terephthalamide)
(viscosity IV = 5.8 dl/g) together with 1.6 wt.% of polycaproamide (IV
= 1.33 dl/g) and 43.7 ml (80 wt.%) of a 99.8%-sulphuric acid solution.
The dope was prepared at 80-85~C, so an anisotropic was obtained. The
viscosity IV of the polymer blend in the yarn was 4.8 dl/g. The yarn's
density was 1.34 g/cm3, the tensile strength 1441 mN/tex (compared
with a yarn strength for poly(p-phenylene terephthalamide) alone of
2010 mN/tex). The tenacity drop therefore was 30%. The yarn's bending
resistance was 6000 cycles. For yarns of poly(p-phenylene
terephthalamide) without any aliphatic polyamide this was found to be
1000 cycles.
Example 15 (comparative)
A spinning dope comprising 20 wt.% of polymer in the solution was pre-
pared in a manner similar to that described in Example 10, except that
use was made of 18.6 wt.% of poly(p-phenylene terephtalamide)
(viscosity IV = 5.8 dl/g) together with 1,4 wt.% of polyhexamethylene
adipamide with an inherent viscosity IV of 1.33 dl/g and 43.7 ml (80
wt.%) of a 99.8%-sulphuric acid solution. The yarn density of 1.42
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l~i
g/cm3 was unchanged compared with the density of a poly(p-phenylene
terephthala-mide) yarn not comprising an aliphatic polyamide. The
-. tensile strength was 1441 mN/tex. The tenacity drop therefore was 30%.
