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(11) | EP 0 327 736 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for the manufacture of packing yarn |
| (57) A process for the manufacture of packing yarn, comprising the deposition on an aromatic
polyamide filament yarn, via a dispersion, of solid particles of polyfluorocarbon,
and/or graphite, the yarn provided with particles being subjected to an after-blowing
treatment with a fluid under pressure. Before the solid particles are deposited on
the yarn, the yarn is subjected to a pre-blowing treatment with a fluid at a higher
pressure, as a result of which the filaments of the yarn are interentangled and interlaced.
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[0001] A process for the manufacture of packing yarn, comprising the deposition on an aromatic polyamide filament yarn, via a dispersion, of solid particles of polyfluorocarbon, such as polytetrafluoroethylene (PTFE), and/or graphite, the yarn provided with particles being subjected to an after-blowing treatment with a fluid under pressure.
[0002] A process of the type indicated above is know from EP 0 136 727-B₁. In this known process the after-blowing treatment serves a great many purposes, viz. pulling along the starting yarn fed at an excess rate, intertwining/interentangling/interlacing/bulking, displacing solid particles through the yarn by blowing, and metering and determining to some extent the final amount of solid particles which is to be deposited on and introduced into the yarn.
[0003] Although this known process is very effective, it has been found that the results obtained with it may still be improved by reducing the functions of the after-blowing treatment. The process of the type indicated in the opening paragraph is characterized according to the invention in that before the solid particles are deposited on the yarn, the yarn is subjected to a pre-blowing treatment with a fluid under pressure, as a result of which the filaments of the yarn are interentangled and interlaced, and during the pre-blowing treatment the yarn is subjected to a higher fluid pressure than during the after-blowing treatment.
According to the invention it is preferred that the pre-blowing treatment should be carried out at a superatmospheric pressure of 400 to 800 kPa, more particularly 500-600 kPa and the after-blowing treatment at a superatmospheric pressure of 50 to 200 kPa, more particularly about 100 kPa. Further, the process according to the invention is advantageously character ized in that the yarn is fed to the pre-blowing zone at such an excess rate, viz. 0,5 to 10%, more particularly 1,5 to 6%, as will result in the formation of a yarn which is made up of interentangled and interlaced filaments and which, depending on the overfeed rate applied, as is known in itself, is to a greater or lesser extent bulky and looped.
The use according to the invention of a few blowing treatments permits dividing the various functions of the one blowing treatment used in the known manufacturing process between a few blowing treatments. Each of the two blowing treatments used in the process according to the invention will then be more capable of fulfilling the functions allocated to each treatment. The use of a relatively high fluid pressure in the pre-blowing zone makes it possible to apply a sufficiently high tensile force to the yarns fed at an excess rate.
Further, in the pre-blowing zone the yarn is intertwined/interlaced/interentangled and at a sufficiently high excess feed rate it is rendered voluminous and provided with loops. In the process according to the invention the after-blowing zone is entirely available for distributing the solid particles over all or practically all the filaments of the yarn, as well as for the accurate metering of the account of solid particles to be deposited on the packing yarn.
The use of the process according to the invention permits an even better and particularly a more uniform distribution of the solid lubricating PTFE and/or graphite particles over and in the packing yarn. The great advantage thereof is that it permits using a particular amount of solid, lubricating particles to attain optimum results, i.e. a packing yarn which can be braided into a packing having optimum sealing properties. It has also been found that the process according to the invention is less affected by deviations in the starting yarns, such as variations in the amount of finish present on the starting yarn.
[0004] After the packing yarn impregnated with solid particles of PTFE and/or graphite has passed through the after-blowing zone, it must still be dried and subsequently be impregnated with a lubricating agent, use being made of an immersion bath or a kissing roll system. The interlaced or voluminous structure of the yarn makes it possible for it readily to absorb a relatively large amount of lubricant, which makes the yarn according to the invention, after it has been dried, particularly suitable to be formed into a packing material. As lubricants commonly used in the packing industry for impregnating yarns may be mentioned: paraffin oil, silicone oil or molybdenum disulphide or some other suitable lubricant, depending on the field of application of the packing to be manufactured.
The yarn according to the invention may be so voluminous that the absorption capacity for a lubricant of the polyfluorocarbon particles-containing yarn is in the range of 20 to 50 per cent by weight, preferably in the order of 25 per cent by weight, calculated on the weight of the dry yarn provided with solid PTFE particles. The lubricant contributes considerably to the gas and/or liquid tightness and the frictional behaviour of a packing material. After being successively impregnated with PTFE particles and/or graphite particles, and braided to form a packing material, and impregnated with a lubricating agent, the aromatic polyamide yarn according to the invention is capable of ensuring a long service life as far as high gas and/or liquid tightness and lubricating effects are concerned. According to the invention the yarn contains 1000 to 15 000 filaments, and the linear density of the non-impregnated starting yarn is in the range of decitex 1500 to 20 000. According to the invention the yarn need contain PTFE particles in an amount of as little as less than 60 per cent by weight, preferably 10-45% by weight, and more particularly about 20% by weight, calculated on the dry weight of the yarn with PTFE particles. The thickness of the PTFE particles is preferably in the range of about 0,1 to 1 µm.
[0005] 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 particles can be braided together on a packing braiding machine to form a packing materials which may for instance have a rectangular cross-section.
[0006] According to a preferred embodiment of the process of the present invention the, preferably positively charged, PTFE particles are deposited on 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 20% by weight of water, preferably about 40% by weight;
· not more than 5% by weight of a wetting agent based on alkylphenoxyethanol, preferably about 3,5% by weight.
[0007] The PTFE and/or graphite particles may be deposited on the yarn by passing it through a bath of said dispersion. Alternatively, however, the PTFE particles may be deposited on the yarn with the aid of a kiss roll system.
[0008] The invention will be illustrated with reference to the accompanying schematic drawing.
The drawing shows an embodiment for carrying out the process according to the invention.
In the embodiment shown in the drawing the process is started from five yarn packages 2 mounted in a frame 1, each package consisting of a non-twisted and non-tangled smooth multifilament yarn 3 of aromatic polyamide, preferably polyparaphenylene terephthalamide (PPDT). The PPDT yarn 3 of each of the packages 2 has 1000 filaments and a linear density of decitex 1680, and contains about 0,8% by weight of a finish applied to the yarn during spinning. The five PPDT filament yarns 3 are assembled by the yarn guide schematically indicated by the reference numeral 4 and drawn off from the starting packages 2 by the driven feed rolls 5, 6 at a constant rate. The assembled yarn subsequently passes through the pre-blowing zone 7, the immersion bath 9 with the PTFE-particles-containing dispersion 10 and equipped with guide rolls 8, the after-blowing zone 11 and via the pulling off rolls 12, 13 driven at a constant speed.
After the packing yarn has passed the pulling off rolls 12, 13, it is dried at elevated temperature in a manner not shown in the drawing, after which it is impregnated with one or more of said lubricating agents and subsequently wound into a driven package 14, which is positioned in a frame 15. The circumferential speed of the feed rolls V 5, 6 is always chosen higher than the circumferential speed of the pulling off rolls V 12, 13. Consequently, the assembled yarn is fed to the pre-blowing zone 7 at an excess feed rate. By excess feed rate expressed on a percentage basis is to be understood here:
[0009] Both in the pre-blowing zone 7 and in the after-blowing zone 11 use is made of blowers of the type known in itself from US 3 302 386. In the pre-blowing zone 7 use is made of a superatmospheric pressure of 500 kPa for the fluid in the form of air. As a result, the yarn is vigorously pulled off from the driven feed rolls 5, 6 and in the blower of the said type the filaments of the yarn are tangled and interlaced. If said excess feed rate is relatively low, for instance 0,5-1,5%, then the yarn in the pre-blowing zone 7 will only be tangled or interlaced and the yarn will practically not become voluminous and will contain hardly any loops. Using a higher excess feed rate of, for instance, about 3% will result in a tangled yarn of interlaced filaments which is also voluminous. Such a voluminous yarn is also referred to as a textured yarn. Using a sufficiently high excess feed rate of, say, 4-5% will result in a voluminous yarn which also contains a large number of internal and external loops.
[0010] After the yarn has passed through the pre-blowing zone in which it has somewhat been opened, it is passed through the bath 9 of the aqueous dispersion of PTFE particles. Because of its opened state the pre-blown yarn can take up a large amount of PTFE particles.
[0011] After the wet yarn impregnated with PTFE particles has left the immersion bath 9, it passes into the blower of the after-blowing zone 11, in which the blowing air is applied to the yarn at a far lower superatmospheric pressure of, say, 100 kPa. In the after-blower the PTFE particles present on and inside the yarn are uniformly distributed internally and externally. Further, the surplus of PTFE particles is blown off the yarn and returned to the immersion bath 9, which can be realized conveniently by positioning the after-blowing zone 11 over the immersion bath 9 in a similar way as indicated in Figure 2 of EP 0 136 727-B₁.
[0012] The afore-mentioned absorption capacity of the yarn mentioned hereinbefore with regard to lubricants, such as 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 PPDT filament yarn impregnated 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 absorption capacity, is determined by 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 determine the oil absorption capacity the first weighing is carried out on said 1 m long piece of yarn while still dry and impregnated with PTFE particles.
Assume the result of the first weighing to be A units of weight (= dry yarn + PTFE particles).
Assume the result of the second weighing to the B units of weight (= dry yarn + PTFE particles + paraffin oil). The oil absorption capacity C envisaged in accordance with the invention can be calculated then from the formula
[0013] If the results A and B of the first and the second weighings are, for instance, 1000 and 1350 weight units, respectively, then
[0014] It should be added that by dry aromatic polyamide yarn mentioned in various places in the description is to be understood a yarn which is dried at 100°C to a moisture content of 6% by weight. Said moisture content is defined at 20°C and 65% relative humidity.
The term wholly aromatic polyamides as used with regard to the present invention refers to polyamides which are entirely or substantially built up of recurrent units of the general formula
wherein A₁, 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. Examples of these radicals include 1,4-phenylene, 4,4′-biphenylene, 1,5-naphthylene and 2,6-naphthylene.
They may contain substituents or not, e.g. halogen atoms or alkyl groups. As regards the composition of the aromatic polyamides 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 ether groups, urea groups or ester groups. As examples of aromatic polyamides 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 solid particles of polyfluorocarbon compounds that may advantageously be used for applying the invention may be mentioned: polytetrafluoroethylene (PTFE), polyhexafluoropropylene, polychlorotrifluoroethene, polyvinylidene fluoride, tetrafluoroethene hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, fluorosilicone elastomers, polyfluoroaniline, tetrafluoroethene trifluoronitrosomethane copolymer, graphite fluoride, etc.
[0015] It should be added that DE 23 26 836 describes a blended yarn of different types of filament yarns 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 PTFE particles, they must be assembled, which may optionally be effected by the blowing processes described in US 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.
1. A process for the manufacture of packing yarn, comprising the deposition on an
aromatic polyamide filament yarn, via a dispersion, of solid particles of polyfluorocarbon,
and/or graphite, the yarn provided with particles being subjected to an after-blowing
treatment with a fluid under pressure, characterized in that before the solid particles
are deposited on the yarn, the yarn is subjected to a pre-blowing treatment with
a fluid under pressure, as a result of which the filaments of the yarn are interentangled
and interlaced.
2. A process according to claim 1, characterized in that during the pre-blowing treatment
the yarn is subjected to a higher fluid pressure than during the after-blowing treatment.
3. A process according to claim 2, characterized in that the pre-blowing treatment
is carried out at a superatmospheric pressure of 500 to 800 kPa, more particularly
500-600 kPa and the after-blowing treatment at a superatmospheric pressure of 50
to 200 kPa, more particularly 100 kPa.
4. A process according to claim 1, characterized in that the yarn is fed to the pre-blowing
zone at such an excess feed rate as will result in the formation of a voluminous yarn.
5. A process according claim 4, characterized in that the yarn is fed to the pre-blowing
zone at such an excess feed rate as will result in the formation of a looped yarn.
6. A process according to claim 1, characterized in that the yarn is fed to the pre-blowing
zone at an excess feed rate of 0,5 to 10%, more particularly 1,5 to 6%.