EP0601277B1 - Method and apparatus for making a non woven spunbonded - Google Patents

Description

The invention relates to a method for producing a textile fabric, in which the melt of a polymeric material is converted into the form of threads with the aid of a spinning rotor, the threads emerging from the spinning rotor being stretched and combined to form a common fabric.

Such a method is known from DE-OS 38 01 080. First, a polymer granulate is melted and fed to a rotating nozzle head with a large number of outlet bores. The melted granules are spun out of the rotating nozzle head to form fibers and the fibers formed are deposited as a fleece on a tray. The melted polymer granulate is introduced into the nozzle head with an overpressure of up to 230 bar. The fibers are deflected in a radial distance of 10 mm to 200 mm from the outlet bores in the axial direction by a high-speed gas stream, and at the same time are stretched and stretched. Before the fibers are caught by the axial deflection flow, they are stretched in the radial direction immediately when they have emerged from the outlet bores on the nozzle head.

Another method is known from DE-OS 15 60 800. This process uses two melts of two polymeric materials that are suitable for the production of mixed nonwovens, with different polymers being alternately spun out in the melt spinning process. It should be noted, however, that the filter properties of the previously known nonwoven are not very satisfactory.

The invention has for its object to further develop a method of the known type such that filter elements made of nonwoven fabrics have good performance characteristics over a long period of use.

This object is achieved with the characterizing features of claim 1. Subclaims 2 to 5 relate to advantageous embodiments.

In the method according to the invention, it is provided that at least two melts of at least second polymeric materials with an electrical differential potential of at least ten charge units are melted separately from one another, that each melt is supplied unmixed to and passed through only a portion of outlet openings of the spinning rotor and that this solidified fabrics are triboelectrically charged by an aftertreatment.

The advantage here is that the different polymeric materials have as large a potential difference as possible, which is retained, for example, by needling the spun-out sheet even during a very long period of use. As a result, the filter effect is almost consistently good over the entire service life of the filter material. Polypropylene and polyacrylic 6, for example, are used as preferred polymeric material pairs. After the two polymeric materials have been deposited to form a homogeneous nonwoven and the nonwoven has been subjected to a mechanical aftertreatment, e.g. B. needling, was charged triboelectrically, the different charge and the good filtering effect are retained for a long time. The frictional forces during needling generate electrostatic charges in the filter fleece. The spinning rotor offers various options for producing triboelectric filter nonwovens. In addition to the material combination already mentioned, materials made of glass and polypropylene can also be produced, for example. The use of glass balls is easily possible. In such a process, it is important that the nonwoven be free of finishing agents, since these would encourage the charges to flow away. In addition to needling the nonwoven web, for example, hydroentangling is also possible, in which the finish is removed at the same time.

According to an advantageous embodiment, the melt can be fed through two separate distributor segments of a distributor device within the spinning rotor only to the outlet openings adjacent in the radial direction, so that only threads of one material emerge from the outlet openings in the region of each distributor segment. A reliable separation of the melted, different polymeric materials is thereby guaranteed and premature mixing of the materials before they emerge and solidify is reliably prevented.

Immediately after they emerge from the outlet openings in the still sticky state, the threads can be subjected to an air flow into which solid dipole particles are sprinkled before they hit the still sticky threads, the threads then being able to be exposed to ionizing radiation. The dipole particles can consist, for example, of barium titanate, which form agglomerates at room temperature and thus neutralize their charge. If the particles are heated to temperatures above 120 ° C by means of the air flow, they lose their charge. In this state, the particles reach the still plastic fiber surface facing the air flow in a uniform distribution and stick to it. This pretzel stick effect has the advantage that no separate adhesive is used which negatively influences the filter effect of the fabric. As the size of the applied particles increases, the filter effect of the nonwoven fabric is further improved. A further improvement in the filter effect results if the threads are exposed to ionizing radiation immediately after they have been exposed to the particles. The ionizing radiation creates filter-effective charges that remain effective even after long filter use.

After their shaping and consolidation, the threads can be continuously deposited on a carrier fleece. The fabric sheets processed in this way can subsequently be laminated, for example, with a covering material and rolled up on a winding station.

Furthermore, the invention relates to a device for use in a method as described above, comprising a spinning rotor which can be rotated about its axis and has outlet openings in the region of its circumferential surface and first auxiliary means which can be moved transversely to the axis to continuously catch the threads emerging from the outlet openings.

Such a device is known from DE-OS 38 01 080. However, it should be noted that only a polymeric material is melted and introduced into the spinning rotor under a pre-pressure. The melt streams emerging from the outlet openings are deflected by a blower, stretched and brought to rest on a first aid, a carrier fleece. In addition to the disadvantage that the fleece formed by this device is not very suitable as a filter fleece, since it does not ensure a sufficiently high filtering effect over a long period of use, the reliability of the device during the intended use is not very satisfactory. With increasing service life, the known device tends to leak when the melt is introduced under pressure into the spinning rotor.

The invention has for its object to develop a device of the type mentioned in such a way that it has better performance characteristics over a longer period of use has and is suitable for the production of filter fleeces, which ensure a high filtering effect over a long period of use.

This object is achieved according to the invention with the characterizing features of claim 6. Subclaims 7 to 11 relate to advantageous configurations.

In the context of the present invention, it is provided that the spinning rotor for feeding two melts made of differing, polymeric materials has two separate groups of outlet openings, as well as a distributor device assigned to the spinning rotor in the region of the axis for feeding the melts into the outlet openings which in different radial planes enclosing the axis are arranged and a needling device is assigned to the first aid. The advantage here is that the different polymer melts are supplied unmixed to the outlet openings of the spinning rotor and pass through them. The fibers subsequently consolidated to form a textile fabric and deposited on a carrier fleece can thus be charged particularly well triboelectrically. A needling system is assigned to the first aid, which is formed, for example, by a carrier fleece. Due to the needling of the nonwoven web, in which the fibers always consist of only one polymeric material, electrostatic charges can remain almost unchanged due to the friction of the needling system over a particularly long period of use. The filter effect of such nonwovens is particularly good.

According to an advantageous embodiment, it is provided that the distributor device is disc-shaped, consists of metallic material and is arranged concentrically and non-rotatably within the spinning rotor. In addition to good thermal resistance, such a distributor device can be produced economically in an economical manner.

The distributor device can have groove-shaped depressions in the region of its two axial boundary surfaces, which are opened axially and radially in the direction of the spinning rotor. The essentially channel-shaped depressions are sealed against one another, so that a reliable separation of the two melts is ensured. From a fluidic point of view, it is advantageous if the depressions are widened in a funnel shape in the radial direction from the axis of rotation.

According to a further advantageous embodiment, it is provided that the depressions are arranged substantially perpendicular to one another. When using two polymeric materials and essentially feeding the melts into the distributor device, the melts are alternately directed onto a 90 ° segment of the outlet openings during the intended use of the device, the segments being acted upon by the same melt in one another radial direction are arranged opposite.

According to another embodiment, the outlet openings of the spinning rotor can be arranged in different radial planes surrounding the axis, the outlet openings in a radial plane being able to be acted upon only by a melt. This embodiment of the device also causes non-mixed exits from the spinning rotor Fibers made from different polymeric starting materials so that a good triboelectric charging of the deposited nonwoven fabric can be carried out and the electrostatic charges on the fibers are retained over a very long period of use.

The method and the device are described in more detail below with the aid of the accompanying drawings.

Figure 1 shows an embodiment of the device according to the invention in a schematic representation, Figure 2 shows the spinning rotor with built-in distributor device, Figure 3 shows the distributor device as an individual part and Figure 4 shows the structure of the filter nonwoven fabric and the needling device shown schematically.

Figure 1 shows the device according to the invention in a schematic representation. For a better understanding, only the first carrier fleece 6 is shown, which encloses the spinning rotor 1 along a substantially semicircular circumferential surface with a radial distance. A second carrier fleece 7 used is assigned in parallel to the first carrier fleece 6 and encloses the other half of the spinning rotor 1 in the same way, but is not shown here. The second carrier fleece 7 is assigned the second half of the suction box 10, which is also not shown here.

A centrifugal force is exerted on the two polymer melts by the rotation of the spinning head. The melts accumulate only in the area of the inner circumference of the spinning rotor 1 assigned to them in front of the outlet openings 4 and become dependent on the speed of the spinning rotor 1 and the viscosity the melt is pushed through it. In this exemplary embodiment it is provided that two melts A, B are used, to which 90 ° of the outlet openings 4 on the circumference of the spinning rotor 1 are alternately assigned.

Through the distributor device 3 shown in FIGS. 2 and 3, threads 2 of a material emerge from the outlet openings 4 on the opposite sides of the circumference of the spinning rotor 1. The emerging, still plastic threads 2 are stretched by the braking effect of the air, the centrifugal force and their own inertia. The carrier webs 6, 7 move past the outlet openings 4 in the direction of the axis 8 of the spinning rotor 1, the spinning rotor 1 being encircled on the circumferential side by the carrier webs 6, 7 and a suction box 10. The carrier fleeces 6, 7 are arranged in the radial direction between the spinning rotor 1 and the two-part suction box 10. Due to the suction effect of the suction box 10, the threads 2 are continuously and progressively brought to rest on the carrier webs 6, 7 after they have solidified. The two coated material webs are laminated in the nip 12 and then needled. The needles 11 are shown schematically in FIG. 1. The mechanical after-treatment of needling and the polymer materials, which show a high potential difference even in their original state, give the filter fleece triboelectric properties, with the electrostatic charges having a good filter effect over a long period of use.

In Figure 2, the spinning rotor 1 is shown schematically, which has a ring with outlet openings 4 along its outer circumferential boundary. The distributor device 3 is formed in one piece and consists of a metallic material and is fixed concentrically and non-rotatably within the spinning rotor 1. The channel-like depressions 9 are arranged in different radial planes, the two melts also being fed into the respective radial plane. In this exemplary embodiment, the polymer flows of the melts A and B are assigned to one another perpendicularly and extend essentially along the axes of symmetry. The melts A and B alternately act on 1/4 of the outer circumference of the spinning rotor 1. It is important to ensure that only melt of a polymeric material is fed to the respective outlet openings 4 and that mixing within the spinning rotor 1 is reliably avoided.

In Figure 3, the distribution device 3 is shown as a single part. The channel-like recess 9 can be seen, into which the melt of the polymeric materials A and B is fed and are conveyed in the radial direction with the spinning rotor 1 when the distributor device 3 rotates. Perpendicular to the melt flow of melt A, the melt flow of material B is conveyed in the direction of the outlet openings 4 in a lower radial plane. In this exemplary embodiment, it is provided that two melts A, B are used, each of which is assigned to two peripheral segments of the spinning rotor 1 according to FIG. Different configurations are also possible.

Figure 4 shows the structure of the filter material according to the invention. Embedded between the carrier nonwovens 6, 7 is a layer of very fine nonwoven fabric 13 which can be triboelectrically charged by the needles 11 of a needling device shown schematically here. The needles 11 of the needling device alternately move into and out of the filter material in the direction shown by the double arrow.

Claims (11)

1. A method for making a textile surface covering, in which the melt of a polymeric material is transformed into filaments (2) with the aid of a spinning rotor, the filaments (2) emerging from the spinning rotor (1) being stretched and bonded together to form a fabric, characterized in that at least two melts of at least two polymeric materials having an electrical differential potential of at least ten units of charge are melted separately from each other, in that each melt is fed unmixed to in each case only a partial region of outlet openings (4) of the spinning rotor (1) and is passed through these, and in that the consolidated fabric is triboelectrically charged by a subsequent treatment.
2. A method according to claim 1, characterized in that the melts are fed through two manifold segments (3.1, 3.2), separate from each other, of the manifold device (3) within the spinning rotor (1) only to the respective outlet openings (4) which are adjacent in the radial direction and in that only filaments (2) of one material emerge from the outlet openings (4) in the region of each manifold segment (3.1, 3.2).
3. A method according to either of claims 1 and 2, characterized in that, immediately after they emerge from the outlet openings (4) and while they are still in a tacky state, the filaments (2) are subjected to an air flow into which solid dipole particles (5) are scattered before it comes into contact with the filaments (2), and in that the filaments (2) are subsequently subjected to an ionizing irradiation.
4. A method according to any of claims 1 to 3, characterised in that, after their forming and bonding, the filaments (2) are deposited in continuous progression on a supporting nonwoven (6, 7).
5. A method according to any of claims 1 to 4, characterized in that a needling of the nonwoven fabric is performed as a subsequent treatment.
6. An apparatus for use in a method according to either of claims 1 and 2, comprising a spinning rotor which can be set in rotary motion about its axis and has outlet openings in the region of its circumferential surface, and first auxiliary means, movable parallel to the axis, for continuously intercepting the filaments emerging from the outlet openings, characterized in that the spinning rotor (1) has, for feeding in two melts of polymeric materials which differ from each other, two groups of outlet openings (4.1, 4.2) which are separate from each other, and, associated with the spinning rotor (1) in the region of the axis (8), a manifold device (3) for feeding the melts into the outlet openings (4), which are arranged in radial planes which are different from each other and surround the axis (8), and in that a needling device is associated with the first auxiliary means.
7. An apparatus according to claim 6, characterized in that the manifold device (3) is designed in the form of a disc and is in one piece, is composed of a metallic material and is arranged concentrically and relatively unrotatably within the spinning rotor (1).
8. An apparatus according to either of claims 6 and 7, characterized in that the manifold device (3) has in the region of its axial bonding surfaces groove-shaped depressions (9), which are open axially and radially in the direction of the spinning rotor (1).
9. An apparatus according to claim 8, characterized in that the depressions (9) are widened radially from the axis (8) in a funnel-shaped manner.
10. An apparatus according to either of claims 8 and 9, characterized in that the depressions (9) are arranged substantially perpendicularly with respect to each other.
11. An apparatus according to any of claims 6 to 10, characterized in that the outlet openings (4) of the spinning rotor (1) are arranged in radial planes which are different from each other and surround the axis (8), and in that the outlet openings (4) of one radial plane are associated with only one depression (9) of the manifold device (3).

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