METHOD FOR PRODUCING A TEXTILE OBJECT HAVING ELECTROSTATICALLY CHARGED FIBRES, AND TEXTILE OBJECT

Abstract

The invention relates to a method for the production of a textile object having electrostatically charged fibres and to a textile object. A die arrangement comprising at least two separate dies or a multipolymer die is used for the production of fibres from different polymers, whereby the polymers are spaced sufficiently apart in a triboelectric series. During the process, the fibres produced from the polymers are co-mingled, at least in sections, and charged triboelectrically. Alternatively or in addition, the fibres are charged triboelectrically by means of an uncomplicated finishing process. Filters with quality factors greater than 0.2 can be produced with the textile object.

Claims

1. A method for producing a textile object having electrostatically charged fibres, comprising: spinning a first polymer to fibres of a first fibre type using a first die and at least one second polymer to fibres of a second fibre type using at least one second die, wherein the fibres are spun using a melt spinning process and/or using a solvent spinning process, or spinning a first polymer to fibres of a first fibre type and at least one second polymer to fibres of a second fibre type using at least one multipolymer die, wherein the fibres are spun using a melt spinning process and/or using a solvent spinning process, selecting the first polymer and the at least one second polymer such that the fibres produced from the first polymer can be so strongly charged triboelectrically by frictional interaction with the fibres produced from the at least one second polymer that a filter with a quality factor in excess of 0.2 can be manufactured with the textile object, shaping the textile object, wherein the frictional interaction occurs before and/or during shaping of the textile object, and/or inducing the frictional interaction during a finishing process, wherein, the first polymer and/or the at least one second polymer, contains at least one additive capable of binding free radicals and/or acting as internal slip agent.

2. The method according to claim 1, further comprising spinning the fibres of one fibre type and the fibres of at least one other fibre type such that the fibres of the one fibre type have a larger average fibre diameter than the fibres of the at least one other fibre type.

3. The method according to claim 1, wherein, one fibre type has a smaller average fibre diameter than at least one other fibre type, and the first or at least one second polymer used to form the one fibre type contains the at least one additive capable of binding free radicals and/or the additive capable of acting as an internal slip agent.

4. The method according to claim 1, further comprising spinning the fibres of the first fibre type and the fibres of the at least one second fibre type such that the fibres of the first fibre type have a larger average fibre diameter than the fibres of the at least one second fibre type.

5. The method according to claim 1, wherein at least the first die has concentric orifices.

6. The method according to claim 1 further comprising mechanically treating the textile object after it has been shaped such that the fibres of the textile object rub against one another.

7. The method according to claim 1, further comprising charging the textile object triboelectrically after it has been shaped using sonic or ultrasonic irradiation.

8. The method according to claim 7, wherein, the sonic or ultrasonic irradiation contains at least one frequency within the range from 1 kHz to 100 kHz.

9. The method according to claim 1, further comprising triboelectrically charging the textile object after it has been shaped by passing gases or vapours through it.

10. The method according to claim 2, further comprising mixing, before and/or during shaping of the textile object, the fibres of the one fibre type with the fibres of the at least one other fibre type such that, at least in a partial volume of the textile object, the proportions of the fibres of the one fibre type and of the fibres of the at least one other fibre type exhibit a gradient over a cross section of the textile object.

11. The method according to claim 2, wherein the first or at least one second polymer used to form fibres of the one fibre type has a melt flow index of less than 800.

12. The method according to claim 2, wherein the first or the at least one second die used for the production of fibres of the at least one other fibre type has concentric orifices, and the first or the at least one second polymer used to form the at least one other fibre type has a melt flow index of less than 2000, or further comprising spinning a polymer solution.

13. The method according to claim 2, wherein the first or the at least one second die used for the production of fibres of the at least one other fibre type has Exxon-type orifices, and the first or the at least one second polymer used to form the at least one other fibre type has a melt flow index of greater than 300.

14. The method according to claim 1, wherein at least one of the first and the at least one second polymers comprise polypropylene, polyactide, polyamide, polystyrene, polyvinyl chloride or a blend of these polymers.

15. The method according to any claim 1, wherein at least one of the first and the at least one second polymers comprise nylon, polyurethane, cellulose, polycarbonate, an artificial resin, polybutylene terephthalate, polyethylene terephthalate, PVDF POM, PEEK, PAN, PMMA, melamine or a blend of these polymers.

16. The method according to claim 1, further comprising adding super-fine fibres having an average fibre diameter of less than 1 μm to the fibres of the first fibre type and to the fibres of the second fibre type before and/or during shaping of the textile object using a collecting device.

17. A textile object comprising: first fibres of a first fibre type, which are formed from a first polymer, and second fibres of at least one second fibre type, which the are formed from at least one second polymer, which differs from the first polymer, wherein the first and second fibres are spun by a melt spinning process and/or by a solvent spinning process, wherein the first fibres produced from the first polymer and/or the second fibres produced from the at least one second polymer are so strongly charged triboelectrically by frictional interaction occurring before and/or during shaping of the textile object and/or by frictional interaction occurring during a finishing process that the textile object can be used to manufacture filters with quality factors in excess of 0.2, wherein the first polymer and/or the at least one second polymer contains at least one additive capable of binding free radicals and/or contains an additive capable of acting as an internal slip agent.

18. The textile object according to claim 17, wherein the first fibres of the first fibre type have an average fibre diameter of greater than 7 μm.

19. The textile object according to claim 17, wherein the second fibres of the at least one second fibre type have an average fibre diameter of smaller than 7 μm.

20. A filter element constructed with a textile object produced with the method according to claim 1.

Description

[0063] The invention is explained in more detail below on the basis of embodiments.

[0064] FIG. 1 is a schematic view showing the structure of a melt-blowing facility with a die arrangement consisting of one Exxon and one Biax die.

[0065] FIG. 2 is a schematic view showing the structure of a melt-blowing facility with a die arrangement consisting of two Biax dies.

[0066] FIG. 3 is a schematic view showing the structure of a facility with a die arrangement consisting of one solution-blowing and one Biax die.

[0067] FIG. 4 is a schematic view showing the geometry of a melt-blowing facility having two dies.

[0068] FIG. 5 is a schematic view showing the structure of the facility used in the experiment on the production and ultrasound finishing of a fibrous web.

[0069] As is evident from FIG. 1, in the case of the multirow Biax die 1 (of concentric design), a molten first polymer 2 is supplied to the polymer feed line 4 and exits again at the end of the duct 5. In addition, hot compressed air 6 is supplied to the Biax-type orifices of the Biax die 1 and exits again as high-speed blowing air 8 at the outlet 7. The exiting first polymer 2 is caught up by the high-speed blowing air 8, which draws the polymer fibres formed from the exiting polymer 2. The polymer fibres of the polymer 2 are deposited on the collecting drum 9.

[0070] The Exxon die 10 is used to spin a second polymer 3, which typically has a charge affinity value that differs greatly from that of the first polymer 2, to polymer fibres. The spinning process carried out with the Exxon die 10 is very similar to the spinning process carried out with the Biax die 1. However, the Exxon die 10, unlike the Biax die 1, is of linear design.

[0071] The polymer fibres made of the first polymer 2 and of the second polymer 3 co-mingle for the first time, at least partially, at the co-mingling point 11 on their way to the collecting drum 9. The distance between the co-mingling point 11 and the two dies 1, 10 is not drawn to scale. In reality, it is usually closer to the two dies 1, 10 than shown in the drawings. The frictional interaction occurring during co-mingling causes the polymer fibres to acquire a certain amount of triboelectric charge already in situ. If this triboelectric charging is insufficient, the polymer fibres of the fibrous fleece generated may be subjected to additional triboelectric charging by a mechanical finishing process which causes intensive frictional activity between the polymer fibres (pairwise between the polymer fibres consisting of the first polymer 2 and the second polymer 3.

[0072] FIG. 2 shows a similar setup, in which, however, two Biax dies 1 are used. The first polymer 2 is spun to polymer fibres with the one Biax die 1 and a second polymer 3 with the other Biax die 1. FIG. 3 shows an analogous setup, in which a solution-blowing die 12 is used in combination with a Biax die.

[0073] FIG. 4 is a schematic illustration of how, in principle, the geometry of a melt-blowing facility having a first die 13 and a second die 14 may be adjusted. In order, firstly, to achieve intensive triboelectric charging of the fibres and, secondly, to selectively adjust the layered structure of the fibrous webs produced with the facility, the axis A, B or C of the second die 14 is first of all tilted by an angle θ relative to the axis D of the first die 13 and/or the distance between the first die 13 and the collecting drum 9 varied. The tilt angle is typically 15° to 60°. In addition, the length of the axis D, i.e. the distance between the first die 13 and the collecting drum 9, may be varied.

[0074] In order to obtain high-quality fibrous fleeces, the diameters of the orifice capillaries, the number of orifices, the polymer throughput in each case and the amount of high-speed blowing air must be selected such that a sufficient number of fibres, generally fine and coarse fibres, are spun and, simultaneously, a nonwoven object is produced which is as homogeneous as possible. In order to achieve intensive triboelectric charging of the polymer fibres, the co-mingling point 11 should, on the one hand, be as far as possible from the collecting drum 9. On the other hand, the co-mingling point 11 must not be too far away from the collecting drum 9 because otherwise the quality, in particular the uniformity, of the fibrous webs produced deteriorates.

[0075] Suitable parameter selection will generally enable the production of fibrous webs with triboelectrically charged fibres and with a layered structure, with partial co-mingling (gradient structure) of the two fibre types or with thorough co-mingling (largely homogeneous with only little gradient structure) of the two fibre types.

[0076] As described in more detail below, pursuit of the essence of the invention has already enabled the production of nonwovens with the help of whose triboelectric charge it was possible to manufacture filters with substantially higher filtration efficiencies and quality factors than filters made from electrically uncharged but otherwise structurally identical nonwovens. In particular, quality factors substantially in excess of 0.2 were achieved with the filters in question.

[0077] Use was made of a melt-blowing facility of the kind shown in FIG. 1, i.e. a facility with a die arrangement consisting of one Exxon die 10 and one Biax die 1. The exact geometry of the die arrangement used is shown in FIG. 5. Each of the dies has a separate polymer-melt supply means, in which pellets of the respective polymer are melted in an extruder. The polymer melt was then conveyed to the associated die. Table 3 shows the configuration of the experimental facility used and the processing parameters used.

[0078] As is usual with meltblown spinning processes, the fibres produced followed an air stream (aligned in the spinning direction) towards a collecting belt that was equipped with a collecting device. There, the collected fibres formed a nonwoven that was removed and wound up in the direction of the belt's movement. Care was taken that the nonwovens produced possessed only just enough structural integrity, thereby ensuring that as many of the fibres as possible did not adhere, or at least not firmly, to one another but remained mobile or were only so weakly bonded that the bonds were easy to break under the influence of ultrasonic waves. The intention here was to achieve a high level of triboelectric chargeability. During blending of the coarse and fine fibres care was taken, moreover, to obtain a structure with a favourable relation between efficiency and differential pressure. Table 4 lists the basic properties of the nonwovens produced in this way.

TABLE-US-00003 TABLE 3 No. 1: EXXON No. 2 Concentric Die type type type (BIAX) Width 500 500 mm Holes/inch 7.16 25.4 Capillary-Ø 0.4 mm  0.2 mm Capillary rows across 1 2 the width Polymer Polyamide PA 6 Polypropylene Ultramid B24 N03 PP HL504FB (BASF) (Borealis) Viscosity in RV RV 2.43 ± 0.03 MFR 400 (ISO 307)/MFR (ISO 1133) [g/10 min] Additive 1 — Chimassorb ® 944 (BASF) Amount in the polymer — 1.6% Additive 2 — Crodamide ™ EBS (Croda) Amount in the polymer — 1.6% Temperature spinning 270 230 head [° C.] Blowing air 300 250 temperature [° C.] Air volume 200 730 [Nm.sup.3/h]

TABLE-US-00004 TABLE 4 Die type No. 1: EXXON type No. 2: Concentric type Mass per unit area/die 14.4 10.5 [g/m.sup.2] Fibre diameter 12 1.5 (median) [μm] Mass per unit area 24.9 ± 0.9  [g/m.sup.2] ISO 9073-1 Thickness [mm] 0.28 ± 0.04 ISO 9073-2

[0079] No significant triboelectric charging of the nonwovens produced was achieved by way of the spinning process on its own, at least not with the selected process parameters. However, it is probably possible to select the process parameters in such a way that significant triboelectric charging is already achieved during the spinning process (i.e. inline). Alternatively, or in addition, a sound energy treatment (with optimized sound intensity and duration of acoustic irradiation) may be carried out during the spinning and deposition process in order to achieve triboelectric charging already at the spinning stage.

[0080] In the present embodiment of the invention, the nonwovens were not subjected to sound energy treatment until after their production. For this purpose, the nonwovens were irradiated with sound waves having a frequency of 20 kHz for one minute by means of a Visaton G20SC dome tweeter. The dome tweeter was controlled with a Grundig TG4 audio generator. It is also conceivable to use acoustic irradiation of this kind directly during production of the nonwoven as well as for purposes of regenerating filters comprising the nonwovens of the invention if their efficiency has dropped during service. The differential pressure and the filtration efficiency was measured with a Palas MFP 3000 test rig at a flow-through speed of 0.1 m/s. The measuring surface was 100 cm.sup.2; DEHS was used as aerosol. The quality factor was calculated according to the formula

Quality factor=−ln(DEHS penetration/100))/differential pressure in mm H.sub.2O.

Each of the measurements was performed on the same nonwovens with and without ultrasound finishing (sonication). Ultrasound finishing increased the quality factors of all the nonwovens tested by a factor of 50 to 100.

TABLE-US-00005 TABLE 5 Filtration Filtration Quality efficiency efficiency factor** Differential (@0.4 μm) Quality (@0.4 μm) after Sample pressure [%] factor** [%] after sonica- no. [mm H.sub.2O] untreated untreated sonication tion 1 4.4 50.1 0.009 94.5 0.66 2 5.1 62.5 0.007 96.1 0.64 3 4.9 59.2 0.008 96.8 0.70 4 4.2 48.0 0.009 91.7 0.59 5 4.8 65.1 0.007 87.0 0.43 6 5.0 63.7 0.007 97.4 0.73 Average 4.7 58.1 0.008 93.4 0.62

TABLE-US-00006 List of reference numerals 1 Biax multirow die 2 First polymer 3 Second polymer 4 Polymer feed line 5 Duct with capillaries 6 Hot compressed air 7 Outlet for high-speed blowing air 8 High-speed blowing air (coaxial) 9 Collecting drum 10 Exxon die 11 Co-mingling point 12 Solution-blow die 13 First die 14 Second die A, B, C Axes of the second die D Axis of the first die q Tilt angle between the axis of the first die and the axes of the second die