Method for producing a pleatable textile fabric with electrostatically charged fibers

Abstract

A method for producing a pleatable textile object having electrostatically charged fibres, and to a pleatable textile object is described. At least two separate dies are used, one for the production of finer fibres and one for the production of coarser fibres, using a melt spinning process. At least the first die, which is used to produce the coarser fibres, has concentric orifices. The finer and coarser fibres are mixed at least in sections during the process and are also charged electrostatically with the aid of a polar liquid. The textile object can be used to make filters with a quality factor in excess of 0.2.

Claims

1. A method for producing a pleatable textile object having electrostatically charged fibres, comprising: using a die arrangement comprising at least separate first and second dies, wherein at least the first die has concentric orifices, extruding a first polymer to fibres of a first fibre type using the first die with a meltblown spinning process, extruding a second polymer to fibres of a second fibre type using the second die with a meltblown spinning process, spinning the fibres of the first and of the second fibre type such that the average of the fibre diameter of the first fibre type is larger than 10 microns, whereas the fibres of the first fibre type have a larger average fibre diameter than the fibres of the second fibre type, mixing the fibres of the first fibre type with the fibres of the second fibre type, at least in sections, at least one of before and during shaping of the textile object with the aid of a collecting device, treating at least one of the fibres of the first fibre type and the fibres of the second fibre type with a polar liquid during at least one of fibre formation and drawing, thereby charging the fibres electrostatically; one of before and during shaping of the textile object, mixing the fibres of the first fibre type with the fibres of the second fibre type in such a way that, at least in a partial volume of the textile object, the proportion of fibres of the first fibre type and of fibres of the second fibre type show a gradient over a cross section of the textile object; and orienting the gradient such that the proportion of fibres of the first fibre type relative to the fibres of the second fibre type is higher at an upstream flow side of the textile object and the proportion of fibres of the second fibre type relative to the fibres of the first fibre type is higher at a downstream flow side thereof.

2. The method according to claim 1, further comprising charging both the fibres of the first fibre type and the fibres of the second fibre type electrostatically using the polar liquid.

3. The method according to claim 1, further comprising using water as the polar liquid for electrostatic charging.

4. The method according to claim 1, further comprising at least one of before and during shaping of the textile object, mixing the fibres of the first fibre type with the fibres of the second fibre type in such a way that, in at least 50% of the volume of the textile object, the proportions of fibres of the first fibre type and of fibres of the second fibre type show a gradient.

5. The method according to claim 1, further comprising using the first polymer for producing fibres of the first fibre type having a melt flow index of less than 800.

6. The method according to claim 1, further comprising using the second die having concentric orifices for the production of fibres of the second fibre type and using the second polymer having a melt flow index of less than 2000.

7. The method according to claim 1, wherein the second die used for the production of fibres of the second fibre type has Exxon-type orifices, and the second polymer has a melt flow index greater than 300.

8. The method according to claim 1, wherein the first polymer comprises at least one of polypropylene, polyethylene, polycarbonate, polylactide, polyamide, polybutylene terephthalate, polyethylene terephthalate, or polyvinylidene fluoride.

9. The method according to claim 1, wherein at least one of the first polymer and the second polymer contains at least one additive able to bind free radicals.

10. The method according to claim 1, wherein at least one of the first polymer and the second polymer contains at least one additive able to act as an internal slip agent.

11. The method according to claim 1, further comprising adding super-fine fibres having an average fibre diameter of less than 1 m to the fibres of the first fibre type and to the fibres of the second fibre type at least one of before and during shaping of the textile object using the collecting device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail below on the basis of embodiments. The drawing in

(2) FIG. 1 is a schematic view showing the structure of a melt-blowing facility having a Biax die of single-row configuration.

(3) FIG. 2 is a schematic view showing the structure of a melt-blowing facility having a Biax die of multi-row configuration.

(4) FIG. 3 is a schematic view showing the structure of a melt-blowing facility with a die arrangement consisting of one Exxon and one Biax die.

(5) FIG. 4 is a schematic view showing the structure of a melt-blowing facility with a die arrangement consisting of two Biax dies.

(6) FIG. 5 is a schematic view showing the structure of a facility having a Biax die and a solution-blowing spinning unit.

(7) FIG. 6 shows a Biax die having one kind of concentric orifices, which have identical capillary diameters.

(8) FIG. 7 shows a Biax die having two different kinds of concentric orifices, which have different capillary and/or orifice duct and/or air outlet diameters.

(9) FIG. 8 is a schematic view showing the geometry of a melt-blowing facility having two dies.

(10) FIG. 9 shows a SEM image and the corresponding fibre distributions of the top side of a layered fibrous fleece.

(11) FIG. 10 shows a SEM image and the corresponding fibre distributions of the bottom side of a layered fibrous fleece.

(12) FIG. 11 shows a SEM image and the corresponding fibre distributions of the top side of a fibrous fleece having partial co-mingling.

(13) FIG. 12 shows a SEM image and the corresponding fibre distributions of the bottom side of a fibrous nonwoven having partial co-mingling.

(14) FIG. 13 shows a SEM image and the corresponding fibre distributions of the top side of a fibrous fleece having thorough co-mingling.

(15) FIG. 14 shows a SEM image and the corresponding fibre distributions of the bottom side of a fibrous nonwoven having thorough co-mingling.

DETAILED DESCRIPTION

(16) FIG. 1 shows a schematic view of a melt-blowing facility having a single-row Biax die 1, i.e. the Biax-type orifices are arranged in a row across the width of the die. FIG. 2 shows an analogous arrangement having a multirow Biax die 2.

(17) As is evident from FIGS. 1 and 2, a molten polymer 3 is supplied to the die by means of a 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 and exits again as high-speed blowing air 8 at the outlet 7. The exiting polymer 3 is caught up by the high-speed blowing air 8, causing the polymer threads formed from the exiting polymer 3 to be attenuated. Directly after the polymer threads have exited from the ducts 5, they are sprayed by means of spraying means 9 with a sufficient amount of water to cause electrostatic charging (hydrocharging). The polymer fibres are subsequently deposited on the collecting belt 10.

(18) FIG. 3 shows a melt-blowing facility having a die arrangement consisting of a multirow Biax die 2 and an Exxon die 11. Here, the two fibre types produced are deposited on a collecting drum 12. FIG. 4 shows a similar melt-blowing facility but with two multirow Biax dies 2. The facility also includes a Rando Webber 13, with which short-cut fibres 14 may be added to the produced fibres prior to deposition on the transport belt. Instead of the Rando Webber 13, it is also possible to blend in particles via a strewing trough or chute.

(19) FIG. 5 shows a facility in which the finer fibres are produced by means of a solution-blowing process. In this case, a polymer solution 15 is used instead of a polymer melt 3 to produce the fibres.

(20) FIG. 6 shows a multirow Biax die 2 from the side from which the polymer exits. The die has equal-sized Biax orifice ducts 16 with capillaries, whereas FIG. 7 shows a multirow Biax die 2 which has smaller Biax orifice ducts 16 with capillaries and larger Biax orifice ducts 17 (with capillaries).

(21) FIG. 8 is a schematic illustration of how the geometry of a melt-blowing facility having a first die 18 and a second die 19 may be adjusted. In the experiments described below, in order to selectively adjust the layered structure of the fibrous webs produced with the facility, the first step was to tilt the axis A, B or C of the second die 19 by an angle relative to the axis D of the first die 18 and/or to vary the distance between the first die 18 and the collecting drum 12. The tilt angle is typically 15 to 60. In a second step, the length of the axis D, i.e. the distance between the first die 18 and the collecting drum 12, was varied. In order to obtain high-quality fibrous fleeces, the diameters of the orifice capillaries as well as 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 fine and coarse fibres are spun and, simultaneously, a nonwoven web is produced which is as homogeneous as possible.

(22) Suitable parameter selection will generally enable the production of a fibrous web 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. FIGS. 9 to 14 each show a SEM image and the corresponding fibre distributions. FIG. 9 shows the top side of a web with a layered structure and FIG. 10 the bottom side. FIG. 11 shows the top side of a web having partial co-mingling and FIG. 12 the bottom side. FIG. 13 shows the top side of a web having thorough co-mingling and FIG. 14 the bottom side.

(23) Experiment: A series of tests was performed to investigate the influence both of the structure of the fibrous web and of the electrostatically charged fibres in the particular fibrous web on the filtration properties. To start with, the additives Crodamide EBS and Chimasorb 944 were melted on a 1:1 basis and added in sufficient quantities, preferably by way of co-extrusion, to the polymer melt. The melt was then mixed well.

(24) During the production of the web having electrostatically charged fibres and each weighing approx. 50 g/m.sup.2, the two fibre jets produced by the respective dies were sprayed from both sides with a sufficient amount of water before the two jets met, thereby intensively charging the fibres contained in the fibre jets.

(25) The fibrous fleeces produced in this way were subsequently measured using a TSI Model 8130 filter tester at a flow-through speed of 0.1 m/s, using a 2% NaCl solution. The results are shown in the following two tables.

(26) TABLE-US-00002 Temp. of high- Process speed blowing Orifice Extruder DCD Sample parameter air C. temp. Polymer temp. mm Layered 1. Biax die 240 C. 230 C. LyondellBasell Metocene 220 C. 300 (64) MF650W Layered 2. Biax dies 290 C. 250 C. LyondellBasell Metocene 250 C. 200 (62) MF650X Partial 1. Biax die 240 C. 230 C. LyondellBasell Metocene 220 C. 280 mixing (64) MF650W Partial 2. Biax dies 290 C. 250 C. LyondellBasell Metocene 250 C. 380 mixing (62) MF650X Thorough 1. Biax die 235 C. 230 C. LyondellBasell Metocene 220 C. 300 mixing (64) MF650W Thorough 2. Biax dies 290 C. 250 C. LyondellBasell Metocene 250 C. 380 mixing (62) MF650X

(27) TABLE-US-00003 Pressure drop Penetration Efficiency QF [mmH.sub.2O] [%] [%] [1/mmH.sub.2O] Layered Untreated 3.1 77.3 22.7 0.08 Layered With additive and water 2.5 23.2 76.8 0.58 quench Partial mixing Untreated 3.2 69.4 30.6 0.11 Partial mixing With additive and water 2.5 5.4 94.6 1.19 quench Thorough Untreated 2.9 79.2 20.8 0.08 mixing Thorough With additive and water 2.3 15.3 84.7 0.82 mixing quench

(28) Surprisingly, it was found that the fibrous web with partial co-mingling and electrostatically charged fibres showed much higher quality factors QF.

(29) TABLE-US-00004 List of reference numerals 1 Biax single-row die 2 Biax multirow die 3 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 9 Spraying device 10 Collecting belt 11 Exxon die 12 Collecting drum 13 Rando Webber 14 Short-cut fibres 15 Polymer solution 16 Smaller Biax orifice ducts with capillaries 17 Larger Biax orifice ducts with capillaries 18 First die 19 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