Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a yarn made from
wholly aromatic polyamides, which yarn is impregnated with a
dispersion containing solid, lubricating particles, such as
particles of fluorine-containing polymers and/or graphite. The
invention also relates to a process for the manufacture of such
yarn, and packing material, for instance stuffing box packing,
containing said yarn.
A yarn of the type indicated above is disclosed in V.S.
Patent No., 4,371,180, which describes packing composed of ~rai-
ded inorganic yarns, preferably of glass, and of braided organic
yarns, preferable of polytetrafluoroethylene or wholly aromatic
polyamide~. Before or after being bra1ded, the yarn may be imp-
regnated with a dispersion of solid particles of a fluorine-con-
taining polymer and starch. The dispersion containing a poly-
tetrafluoroethylene (PTFE) particles contributes considerably to
the sealing properties of the end product in the form of packing
material. Although the results obtained with the packing mate-
rial disclosed in U.S. Patent 4,371,180 are reasonable, the pre~
sent invention makes lt possible to improve on these results.
According to the present invention a yarn of the above
type from wholly aromatic polyamides has been developed in the
first place for use in packing material, which yarn is built up
of a great many endless filaments on which the solid particles
are present and over which the solid particles are distributed by
sub~ecting the yarn to a blowing treatment in the wet state in
particular in fluid jet process. In that process the filaments
are generally entangled and interlaced. According to the inven-
tion the solid particles may consist of a fluorine-containing
polymer, such as polytetrafluoroethylene or of graphite. Alter-
natively, however, use may be made of a mixture of solid par-
ticles of a fluorine-containing polymer and of graphite. The wet
yarn sub~ected to a blowing treatment according to the invention
has a voluminous character, which renders the yarn accordlng to
the invention particularly suitable for taking up a lubricant.
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Owing to its voluminous character the yarn will readily absorb a
large amount of lubricant, which makes the yarn according to the
invention partlcularly suitable to be formed into a packing mate-
rial. AS lubricants commonly used in the
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- pressure and, possibly, a chemically agressive medium. Further, as a result
of the uniform distrlbution of the PTFE particleg over practically all the
filaments of the yarn only a relatively small amount of PTFE particles is
needed for this yarn of the present invention to be made into a satisfac-
torily sealing packing material. Another advantage of the uniform distrlbu-
tion of the PTFE particles in the yarn according to the invention consists
in that the packing into which the yarn is braided need not be additional-
ly impregnated with a PTFE particles-containing dispersion.
The yarn according to the invention has been especially developed and made
suitable to be worked up into a packing material, such as stuffing box
packing, which is widely used in machine construction for the sealing of
rotating shafts and reciprocating parts. In the manufacture of packing
material a number of yarns of the invention impregnated with PTFE and/or
graphite particles can be braided together on a packing braiding machine to
form a packing material which may for instance have a rectangular cross-
section. The braided packing material is generally impregnated with a
lubricating agent, such as a special oil, fat or other substances required
in view of the use of the packing material. In the completed packing mate-
rial according to the invention the proport:on by weight of solid parti-
cles, calculated on the dry weight of the aramid yarn without solid par-
ticles, may be lower than 60%, and is preferably 10 to 45%. The invention
particularly comprises a packing material of aromatic polyamide yarn im
pregnated with solid PTFE and/or graphite particles, which packing mate-
rial is characterized in that it contains a fairly large amount of said
lubricating agent, viz. an amount of 20 to 50% by weight, preferably about
2570 by weight, calculated on the weight of the dry yarn provided with solid
particles.
A simple and effective method of manufacturing the yarn according to the
invention,compri~ing the application to the yarn of a dispersion of solid
particles of a fluorine-containing polymer and/or graphite,is characterized
in that whilst in the wet state the yarn is subJected to a blowing process
using a fluid under pressure, such as air, as a result of which the solid
particles are distributed over the filaments and the filaments are general-
ly inter-entangled and braided. According to a preferred embodiment of the
process according to the invention the yarn is subjected to a blowing pro-
cess after the dispersion of solid particles of a fluorine-containing
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polymer and/or graphite particles-containing dispersion has been applied to
the yarn. Alternatively, according to the invention, the dispersion of
particles of a fluorine-containing polymer and/or graphite may be direct-
ly blown onto the yarn whlle belng fed to lt under pressure. In the blow-
S ing process air i5 used at an absolute pressure of 3 to lO bar.
According to a preferred embodiment of the process of the present invention
the, preferably positively charged, PTFE are applied to the yarn from an
aqueous dispersion whose composition may substantially be as follows:
~ 45 to 75% by weight of PTFE particles, preferably about 58% by weight;
. 50 to ~0% by weight of water, preferably about 40% by weight;
not more than 5% by weight of a wetting agent based on alkylphenoxyetha-
nol, preferably about 3,5% by weight.
The graphite particles are also applied from an aqueous dispersion, which
may contain, for instance, about 18% by weight of graphite and 82% by
weight of water and a nonionic wetting agent.
Particularly favourable results may be obtained when the PTFE and/or gra-
phite particles are applied to the yarn from said dispersion with the aid
of a kiss roll. Optionally, the PTFE and/or graphite particles may be ap-
plied to the yarn by passing it through a bath of said dispersion.
According to the invention the yarn is fed to the blowing process at a rate
in excess of that at which it is withdrawn therefrom of at least 1%, pre-
ferably about 3% to 6%. According to the invention, however, a satisfac-
tory distribution of the solid particles over practically all the filaments
of the yarn also may be obtained when the yarn is subjected to the blowing
process without using an excess feed rate. In the process in which no ex-
cess feed rate is used the yarn may be passed through the blowing zone
practically without any tension. Furthermore, the yarn according to the
invention is particularly suitable to be used in the manufacture of rope
having an outer diameter of, for example 3 to 100 mm, such as marine rope,
hoisting rope and the like,which rope is built up of two or more strands by
laying or braiding. According to the invention the yarn to be incorporated
in such rope contains less than 10% by weight, preferably about 5% by
weight of solid particles.
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- The invention will be illustrated with reference to the accompanying sche- matic drawing.
Figure 1 shows an apparatus for applying PTFE particles to the yarn before
the blowing process.
Fig. 2 shows a somewha~ modified apparatus for carrying out the process of
the invention.
In the embodiment shown in Figure 1 the process is started from 5 packages
1 of non-twisted aramid filament yarn. The aramid yarn 2 of each of the
packages has 1000 filaments and a linear density of tex 168 and contains
about 0,8% of a finish applied to the yarn during spinning. The five ara-
mid filament yarns 2 are assembled by the schematically indicated yarn
guide 3 and drawn off from the starting packages 1 by the driven rolls
4,5. The assembled yarn is subsequently run over the kissing roll 7 rotat-
ing in an aqueous dispersion 8. The assembled filament yarn thus wetted
and provided with PTFE and/or graphite particles i3 fed to a blow box 9
containing an air nozzle 10 at a rate in excess of the rate at which it is
withdrawn from the blow box. The nozzle 10 may be of the type as indicated
in US 3 302 386. The blown and impregnated yarn is discharged from the
blow box 9 over a pair of driven pulling-off rolls 11,12 which have such a
lower circumferential speed than the feed rolls 415 as to ensure that the
yarn is fed to the air nozzle 10 at a sufficiently high excess feed rate.
After leaving the heated pulling-off rolls 11,12 the dried yarn may still
be lubricated, if desired, and subsequently wound into a package.
In the blow box 9 the assembled yarn 5x168 composed of 5 basic yarns 2 is
treated with air at an absolute pressure of 5 bar, the yarn being fed at an
excess rate of 3%. Alternatively, the assembled yarn may be made up of 10
basic yarns. Such assembled lOx168 tex yarn is treated in the blow box 9
with air fed at an absolute pressure of 10 bar, the excess feed rate of the
yarn being 60%. When the yarn is treated without applying an excess feed
rate, it may be fed to and discharged from the blowing zone at a speed of
60 min/min.
Fig. 2 shows a somewhat modified embodiment of the apparatus for carrying
out the process according to the invention. The untreated aramid yarn 13 is
fed by a pair of rolls 14 at a particular speed desired. After leaving the
rolls 14 the yarn is passed through a bath 15 containing an aqueous disper-
sion of PTFE and/or graphite particles. In the bath the yarn is passed over
two or more guide rolls (not shown in the drawing). After leaving the bath
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- 15 the yarn passes upwards through a feed pipe 17 ending in a blow box 18.In the blow box 18 there is again a noz~le (not ghown) of the type describ-
ed in US 3 302 386. The advantage of ~he feed pipe 17 i9 that excess dis-
persion not entralned by the yarn and blown off from the yarn flows back
into the bath through said pipe 17. After having been subjected to the
blowing treatment, the impregnated yarn 19 leaves the blow box 18 through
the outlet opening 20. The yarn is withdrawn from the blow box 18 by the
driven roll 24 with separator roll 21. The roll 24 may be heated for drying
the yarn. The yarn thus impregnated and dried may be formed into a package
via a traverse mechanism 22. The circumferentlal speed of the roll 24 is
0 lower than that of the rolls 14~ so that the yarn is passed through the
blow bo~ at the particular excess feed rate desired.
It has been found that with the process given in Figure 1 favourable re-
sults may be obtained, i.e., viewed in cross-section of the yarn the PTFE
particles are very uniformly distributed over practically all the fila-
ments mainly under the following process conditions:circumferential speed of the kissing roll: 42 m/min;
circumferential speed of the rolls 4,5: 59,5 m/min (yarn feed rate);
circumferential speed of the rolls 11,12: 58 m/min (yarn discharge rate);
overfeed of the yarn at the nozzle: 59~5-58.100% = 2,5%
58
absolute pressure of the blow air: 3 to 4 bar;
composition of dispersion : 56,5% by weight of PTFE particles, 40% by
weight of water and 3,5% by weight of wetting
agent of the Triton X 100 type, which is a
commercially available wetting agent based on
alkylphenoxy ethanol.
The dispersion used is of the type marketed by ICI under the name Fluon;
the PTFE particles in it carry a negative electric charge. In the process
of the invention, however, also other dispersions may be appliet. Use may
advantageously be made of dispersions in which the particles of the fluoro-
carbon compound, more particularly polytetrafluoroethylene (PTFE), carry apositive electric charge. These last-mentioned dispersions are elaborately
_ 7 _ ~2~ 5 AXU 190o R
~ ~ described in DE 26 ~4 152. Vse of a dispersion containing posltively
charged PTFE particles is expected to lead to an even better adhesion of
these particles to the filaments of the yarn.
It should be added that the excess feed rate used in the wet-blowing pro-
cess of the present invention is of great influence on the structure of
the yarn. Particularly the interentanglement or interlacement of the fila-
ments is very much dependent on the excess feed rate. At an the excess
feed rate of as low as 1% the non-twist2d yarn loses its smooth appear-
ance and becomes somewhat bulky or textured as a result of the interen-
tanglement and/or interlacement of the filaments and the formation of
0 loops in one or more filaments. The interentanglement and interlacement of
the filaments of a yarn and the manufacture of a yarn having a multitude
of loops are known in themselves from the textile art and are described in
US 3 302 386 and US 2 783 609. The interentanglement and interlacement of
the filaments of a yarn with the aid of a blowing process and using an
excess feed rate of the yarn imparts a voluminous character to the yarn. A
high excess feed rate renders the yarn very bulky. The yarn wetted with a
PTFE and/or graphite dispersion and subjected to a blowing treatment has a
voluminous character, which is influenced by the degree of impregnation
with solid particles. Impregnation of the yarn with a higher percentage of
PTFE partlcles is attended with a lower voluminous character as a result
of the adhesion of the PTFE particles to the yarn; in other words, the
degree of impregnation to be chosen depends on the voluminous character
desired.
In the manufacture of the yarn according to the invention the preferred ex-
cess feed rate is in the range of 3% to 6%, which results in a yarn having
a more or less loopy character. The presence of internal and/or external
loops formed in one or more filaments of the yarn and the resulting bulky
appearance is characteristic of a particular embodiment of the yarn accord-
ing to the invention. Particularly surprising is that already a fairly low
excess feed rate of 3% results in a sufficiently voluminous yarn which is
excellently suitable to be further proces~ed into a packing material. How-
ever, even in the case of a yarn subjected to a blowing process without
using an excess feed rate a particularly uniform distribution of the PTFE
and/or graphite particles over practically all the filaments of the yarn is
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- obtained. The blowing process constitutes an essential element of the ln-
vention with a view to obtaining a very good distribution of the solid
particles over the filaments of the yarn.
Also a smooth, non-air blown aramid filament yarn can be treated with a
PTFE particles-containing dispersion, use being made of an applicator roll
or impregnation. Experiments, however, have demonstrated that in that case
the PTFE particles will stick to the outer circumference of the yarn in
the form of variously sized lumps, as can be seen on a highly enlarged
photograph of a cross-section of the yarn. Such a photograph also shows
that hardly any PTFE particles at all are stuck to the filaments that are
within the circumference of the yarn. Therefore, a non-air treated aramid
filament yarn cannot be evenly impregnated with PTFE particles and is less
suitable to be worked up into a packing maeerial.
The afore-mentioned absorption capacity of the yarn mentioned hereinbefore
with regard to lubricants, such a paraffin oil, silicone oil, molybdenum
disulphide or the like is referred to as oil absorption capacity and is
determined as follows: An one metre long piece of aramid filament yarn im-
pregnated beforehand with PTFE particles is impregnated with paraffin oil
having a viscosity of 72 centipoises (measured by the Brookfield method) by
dipping the yarn in a tray with paraffin oil at room temperature, after
which the tray is kept in a vacuum chamber for 15 minutes. The yarn thus
impregnated is suspended by its one end in such a way that the paraffin oil
which cannot be retained by the yarn can drip off at its other, free end.
The amount of paraffin oil absorbed, which is a measure of said oil absorp-
tion capacity, is determined ~y weighing. The second weighing of the oil-
impregnated yarn is carried out as soon as there can no longer be observed
any dripping at the free end of the yarn after at least 24 hours. To de-
termine the oil absorption capacity the first weighing i9 carried out on
said l m long piece of yarn while still dry and impregnated with PTFE
and/or graphite particles.
Assume the result of the first weighing to be A units of weight (- dry yarn
~ PTFE and/or graphite particle~).
Assume the result of the second weighing to be B units of weight (= dry
yarn + PTFE and/or graphite particles + paraffin oil). The oil absorption
capacity C envisaged in accordance with the invention can be calculated
then from the formula
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., 7
C% ~ ~-A 100%.
If the re3ults A snd B of the flrst and the gecond weighlngs ara, for in-
stanc~, 1000 and 1350 weight units, re~pectively, then
C ~ 1350-1000 .100% - 35 weight%.
1 000
It should be added that by dry aromatic polyamide yarn mentioned in vari-
OU9 places in the description is to be understood an aramid yarn which i9
dried at 100C to a moisture content of 6% by weight. Said moisture con-
tent is defined at 20C and 65% relativ~ humidity.
The term wholly aromatic polyamides as u3ed with legard to the present in-
vention refers to polyamides which are entirely or substantially built up
of recurrent units of the general formula
- 7 - A~ 2 ~ ~ - I - and/or - C - A3- N -
0 0 H H O H
wherein Al, A2 and A3 represent different or the same divalent, one or
more aromatic rings-containing rigid radicals which may also contain a
heterocyclic ring, of which radicals the chain extending bonds are in the
position para to each other or are parallel and oppositely directed. Exam-
ples of these radicalY include 1,4-phenylene, 4,4'-biphenylene, 1,5-naph-
thylene and 2,6-naphthylene.
They may contain substituent3 or not, e.g. halogen atoms or alkyl groups.
As regards the composition of the aramids it should be added that they may
optionally contain up to 35 mole % of other groups, such as m-phenylene
groups, non-rigid groups, such as alkyl groups, or ather groups, urea
groups or ester groups. As examples,of aramids may be mentioned poly-p-
benzamide, poly-p-phenylene terephthalamide and their copolymers. According
to the invention it is preferred that use should be made of yarns of poly-
p-phenylene terephthalamide (PPDT).
Of the fluorine-containing compounds that may advantageously be used for
the yarn according to the invention may be mentioned: polytetrafluoroethyl-
ene (PTFE), polyhexafluoropropylene, polychlorotrifluoroethene, polyvinyl-
idene fluoride, tetrafluoroethene hexafluoropropylene copolymer, vinylidene
~Z~ 7~75
fluoride-hexafluoropropylene copolymer, fluorosllicone elasto-
mers, polyfluoroaniline, tetrafluoroethene trifluoronitrosome-
thane copolymer, graphite fluoride, etc.
It should be added that DE 23 26 826 describes a blen-
ded yarn consisting of 50-80% by weight of PTFE filaments and 50-
20% by weight of aromatic polyamide filaments. Said blended yarn
is coated with fine PTFE particles and may in the braided form be
used as packing material. Before these two yarns are coated with
10 PTFE particles, they must be assembled, which may opt1Onally be
effected by the blowing process described in U.S. Patent No.
3,110 151. This blowing process results in a smooth yarn free of
loops and therefore not bulky or textured. Coating such a yarn
with PTFE particles will consequently result in these particles
being practically entirely present on the outside of the yarn.
Further~ considering that the yarn according to DE 23 26 826 is a
blend of two yarns having widely different properties, it is less
homogeneous than a yarn of one and the same material.
Reference is also made to EP 0 032 744, which discloses
a wholly aromatic polyamide yarn provided with a fluoro com-
pounds-containing polymer~ In that case the fluoro compound is
not present on the fibres ~n the form of separate particles, but
in the form of a continuous coating. As the PTFE is not present
then on the fibres in the form of separate particles, this known
yarn is not suitable to be used as packing yarn.
Further reference is made to Canadlan Patent No, 995
288 issued 17 August 1976 to Deering Milliken Research Corpora-
tion described a hovercraft skirt containing an elastomer coated
fabric composed of looped yarn textured by air under pressure,
which yarns preferably consist of wholly aromatic polyamides.
Therefore, looped yarns of aramids textured under air pressure
are known in themselves from Canadian Patent No. 955 288, but
their field of application is entirely different and they are not
at all meant to be used in combination with PTFE particles.
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Within the scope of the invention various modifications
may be made.
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