EP1177336B2 - Device for opening and distributing a bundle of filaments when producing a nonwoven textile web - Google Patents

Abstract

The invention concerns a device for opening and distributing a bundle of filaments when producing a nonwoven textile web by a technique which consists in: extruding melted organic polymer through a die perforated with holes, so as to form a bundle or curtain of filaments; then directing the extruded filaments by drawing by means of one or several fluid jets; and finally, receiving the bundle of filaments in the form of a web on a mobile conveyor belt. The invention is characterised in that it consists of an assembly arranged downstream of the outlet of the drawing assembly and separate therefrom, said assembly comprising, arranged in the proximity of the drawing slot outlet, a diffuser comprising an intake zone shaped as a convergent nozzle extending over the whole width of the installation opposite the drawing slot outlet producing the web, extended by a divergent nozzle, said assembly being associated with a ramp electrostatically charging the filaments before they are received on the receiving belt.

Description

Technical area

The present invention relates to an improvement made to the facilities for the manufacture of a nonwoven textile web, commonly known by the generic name "spunbond", which is formed by continuous synthetic filaments.

It relates more particularly to an improvement in the means for ensuring the distribution of the extruded filaments, after drawing, on a movable conveyor belt on which they are distributed at random to form a regular sheet, weight and thickness adjustable according to the applications.

Previous techniques

• à extruder un polymère organique fondu au travers d'une filière percée de trous, de manière à former un faisceau ou rideau de filaments ;
• puis, à orienter les filaments extrudés par étirage au moyen d'un ou plusieurs dispositifs à jets de fluide, notamment à air comprimé ;
• et enfin, à recevoir le faisceau de filaments sous la forme d'une nappe sur un tapis transporteur mobile, en général soumis à une source d'aspiration, et dont la vitesse est réglée en fonction des caractéristiques de la nappe, épaisseur notamment, que l'on souhaite obtenir.

The production of spunbond nonwoven webs goes back decades and consists, in a general way:

• extruding a molten organic polymer through a die pierced with holes to form a bundle or curtain of filaments;
• then, directing the extruded filaments by stretching by means of one or more fluid jet devices, in particular with compressed air;
• and finally, receiving the bundle of filaments in the form of a sheet on a moving conveyor belt, generally subjected to a suction source, and whose speed is adjusted according to the characteristics of the sheet, including thickness, that we want to get.

After completion, the web is consolidated, for example by performing a calibration or calendering, preferably hot, so that the filaments. Elementals are linked to each other.

Other consolidation treatments may optionally be carried out, such as for example a needling treatment (conventional or by fluid jets), and / or the deposition on the surface or inside the sheet of a binder material .

• au moins une extrudeuse pour un polymère organique fondu alimentant une filière permettant de produire un rideau de filaments ;
• une zone de refroidissement permettant d'obtenir la solidification au moins superficielle desdits filaments extrudés ;
• un dispositif d'aspiration se présentant sous la forme d'une chambre de section rectangulaire, de faible largeur, à l'intérieur de laquelle le rideau de filaments est soumis à l'action de veines d'air à grande vitesse provoquant l'étirage des filaments, ensemble qui dans la suite de la description, sera désigné par l'expression « fente d'étirage » et ;
• un moyen permettant, en sortie de ladite fente d'étirage, de dévier et ralentir le flux d'air et de répartir les filaments de manière aléatoire sur un tapis récepteur.

In general, the installations used to produce such products comprise:

• at least one extruder for a molten organic polymer feeding a die for producing a curtain of filaments;
• a cooling zone for at least superficial solidification of said extruded filaments;
• a suction device in the form of a rectangular section chamber, of small width, inside which the curtain of filaments is subjected to the action of air streams at high speed causing stretching filaments, together which in the following description, will be designated by the term "stretching slot"and;
• means allowing, at the outlet of said drawing slot, to deflect and slow down the flow of air and to distribute the filaments randomly on a receiving belt.

In such installations, the filaments appear at the outlet of the drawing slot in the form of a bundle of filaments grouped in the median plane of said slot.

These filaments are ejected at a very high speed from said drawing slot, a speed of up to 3000 m / min or more depending on the state.

In order to obtain a non-woven web that is as homogeneous as possible on the receiving carpet on which the filaments emerging from the drawing slot are projected, it is necessary not only to separate said filaments from one another, but also to slow down their speed. before their impact on said carpet, in order to limit uncontrollable rebound phenomena which generate a heterogeneous formation of the web.

To ensure such a burst and distribution of the extruded filament curtain, various techniques have been proposed to date.

The oldest technique, which comes from the patent GB-A-932,482 , of U.S. Patent No. 3,967,118 consists of electrostatically charging the filaments, which tends to push them back relative to each other (corona effect).

This technology makes it possible to improve the formation of the haze when the filaments are ejected at relatively low speed from the drawing slot and that, therefore, the so-called "bundling" phenomena of the filaments are preponderant compared with those of the bounce of the filaments on the carpet.

This is the case in particular when the web consists of relatively coarse filaments, that is to say of a title greater than or equal to 2.2 dtex per filament, filaments which are generally produced with velocities at the output of stretching slot less than 3000 N / min.

In order to reduce the speed without adding additional member, it is necessary in this case that the end of the stretching slot on which the electrostatic device is fixed is located at a relatively large distance from the receiving belt, of the order 500 mm or more, so that the friction forces of the filaments in the air slow down their speed, which limits the rebound phenomena and thus improves the formation of the web.

This device is not entirely satisfactory because no speed control is possible and the filaments are also subjected to all external air currents, which disturbs the haze and creates defects.

Finally, the simple friction of the filaments in the air over such a short distance does not allow a sufficient slowdown in their speed which sufficiently mitigates the bounce phenomena of the filaments on the carpet.

As a result, it has been proposed, as US Patent 3,286,896 , to adapt to the end of the drawing slot (see Figures 7 and 8), a deflector system to ensure a better distribution and opening bundles of filaments produced.

However, this solution is not entirely satisfactory, it has been proposed, as US-A-3,325,906 , to associate with the divergent disposed at the output of the drawing slot, an assembly for blowing air on each side of this divergent, which creates a negative pressure in the vicinity of the walls, thus attracting the fibers to the walls, which tends to open the bundle of filaments and also slow down the speed of the latter.

Such a device, satisfactory in theory, however, has a limited efficiency, because it is mainly the fibers located on each side of the beam that are thus "spaced", those grouped in the center of said beam being extremely difficult to separate from each other.

At DE 4312419A1 an apparatus for producing a nonwoven filament web comprising, from top to bottom, successively an extrudense of a molten polymer through a die pierced with holes so as to form a filament curtain, a device for fluid jet slit stretching and a diffuser having a contiguous shaped inlet zone extended from a divergent exit zone. An opening is provided in the wall of the diffuser inlet which is connected with the bottom of the drawing device. The filaments emerging from the diffuser are deposited on a mobile receiver mat. The document represents the closest state of the art.

Presentation of the invention

It has been found, and this is the object of the invention, that it was possible to obtain not only a perfect opening of the bundle of extruded filaments at the outlet of the drawing slot, but also a very homogeneous distribution on the receiving belt, firstly by dissociating the opening assembly of the bundle of filaments of the actual drawing slot, and secondly and above all, by realizing this set of opening of such so that it combines both the advantages of the electrostatic charging techniques of the filaments and beam opening techniques by slowing down the air velocity at the outlet of the drawing slot, and therefore the speed of the front filaments reception on the receiving carpet.

In general, the invention therefore relates to a device according to claim 1.

According to one embodiment, the divergent zone of the diffuser comprises two walls and two lateral slots located at the top of said diffuser, on each side thereof and allowing either a call from outside air by Venturi effect, or possibly a injection of air at a pressure less than one bar and preferably between 0.4 and 0.8 bar, causing a flow of air against the walls of said diffuser.

The above diffuser makes it possible to precisely adjust the width of the fiber bundle as well as the speed of impact of the filaments on the conveyor belt, the electrostatic charge assembly being possibly located downstream of the diffuser assembly, but being of preferably integrated within the latter, which makes it possible to accentuate the opening of the bundle of filaments.

• le diffuseur comporte une zone d'entrée en forme de convergent reliée aux deux parois de la zone divergeante par une fente rectiligne, la rampe chargeant électrostatiquement les filaments étant montés au niveau de la fente rectiligne immédiatement en amont de la zone divergente ;
• la distance du diffuseur par rapport au tapis récepteur est réglable, et ce afin de minimiser l'influence des courants d'air extérieurs sur le faisceau de fibres ;
• la pression de l'air qui s'écoule dans le diffuseur contre les parois de ce dernier et l'ajustement de la tension appliquée dans la rampe électrostatique, permet d'adapter très précisément les conditions de la formation du voile en fonction de la vitesse des filaments en sortie de la fente d'étirage, ce qui rend particulièrement un tel dispositif adapté à la formation de voile constitué de filaments de faibles deniers, ainsi qu'aux installations de production travaillant à haute vitesse ;
• enfin, la séparation des systèmes d'étirage proprement dits et de répartition du rideau de filaments, autorise une possibilité de réglage du titrage desdits filaments sans changer l'aspect du voile et inversement.

Advantageously and in practice:

• the diffuser comprises a convergent-shaped input zone connected to the two walls of the diverging zone by a rectilinear slot, the ramp electrostatically charging the filaments being mounted at the straight slot immediately upstream of the diverging zone;
• the distance of the diffuser relative to the receiving belt is adjustable, in order to minimize the influence of the external air currents on the fiber bundle;
• the pressure of the air flowing in the diffuser against the walls of the latter and the adjustment of the voltage applied in the electrostatic ramp makes it possible to very precisely adapt the conditions of the formation of the veil according to the speed filaments at the output of the drawing slot, which makes particularly such a device suitable for forming a veil made of filaments of low denier, as well as production facilities working at high speed;
• finally, the separation of the actual drawing systems and distribution of the filament curtain, allows a possibility of adjusting the titration of said filaments without changing the appearance of the web and vice versa.

Brief description of the drawings

• . la figure 1 est une vue d'ensemble d'une installation permettant de réaliser une nappe non tissée de type « spunbond » ;
• . la figure 2 est une vue de détail montrant de manière schématique la structure et le fonctionnement d'un ensemble permettant l'ouverture du faisceau de filaments formé et sa dépose sur le tapis récepteur ;
• . la figure 3 illustre une variante de réalisation conforme à l'invention dans laquelle la charge électrostatique des filaments est obtenue par l'intermédiaire d'une rampe intégrée à l'intérieur du diffuseur, l'écoulement de l'air à l'intérieur de ce dernier contre les parois pouvant être réalisé soit par appel naturel de l'air extérieur, soit par un système d'injection sous faible pression inférieure à un bar.

The invention and the advantages which emerge from it will be better understood thanks to the concrete example of embodiment which is given by way of indication but not limitation, and which is illustrated by the appended diagrams in which:

• . the figure 1 is an overview of an installation for producing a spunbond nonwoven web;
• . the figure 2 is a detailed view schematically showing the structure and operation of an assembly allowing the opening of the formed filament bundle and its removal on the receiving carpet;
• . the figure 3 illustrates an alternative embodiment according to the invention in which the electrostatic charge of the filaments is obtained via an integrated ramp inside the diffuser, the flow of air inside the latter against the walls can be realized either by natural call of the outside air, or by a system of injection under low pressure lower than a bar.

Way of realizing the invention

Referring to the accompanying figures, the device according to the invention is therefore intended to be used on a production line of a nonwoven textile web constituted by continuous synthetic filaments.

In general, as is apparent from the figure 1 , such a production line therefore consists essentially of at least one extruder, designated by the general reference (1) supplying synthetic polymer such as polyamide, polyethylene, polyester ..., a die (2) allowing the formation of a curtain of filaments (3).

From a practical point of view, as an indication, the die consists of a plate each comprising a multitude of holes, for example at the number of 5000 per meter of width and having a diameter function of the extruded filaments, for example 0 , 5 mm. These holes are distributed over a plurality of parallel rows, for example eighteen rows and this, over a die exit width of 140 mm.

At the exit of this die, is disposed a cooling assembly (4) for adjusting the temperature of the filaments according to the polymers and composed for example of a plurality of successive zones (4a, 4b, 4c) for submitting the curtain of filaments (3) to through air streams whose speed and temperature can be adjusted.

As an indication, the length of this cooling zone is of the order of 1200 mm and the temperature and the speed of each of the zones is decreasing from the first zone (4a) to the third zone (4c).

Downstream of this cooling zone, there is arranged a stretching assembly proper (5) which is in the form of a closed chamber having a slot (F) inside which is injected air under pressure, for example of the order of 0.5 bar.

Such a stretching system makes it possible to obtain the suction of the curtain of filaments and its entrainment by high velocity air streams to ensure stretching.

At the outlet of the drawing assembly (5), the bundle of filaments (3) is projected onto the conveyor belt (7) via a set (6), which assembly is the subject of the invention and two embodiments of which emerge from figures 2 and 3 , and which causes a deviation of the air flow leaving the slot (5), a slowing of this air flow thus causing the opening of the bundle of filaments.

In the first embodiment illustrated in figure 2 , such an assembly comprises, near the outlet of the stretching slot (F) of the assembly (5), on the one hand, a diffuser, designated by the general reference (10) consisting essentially of a divergent which extends over the entire width of the production of the sheet and, secondly, downstream of this opening assembly, a ramp (11) for electrostatically charging the filaments at the outlet of the assembly (10) causing said bundle of filaments to be fully open before being deposited on the receiving mat (7).

In this embodiment, the diffuser assembly (10) essentially consists of a chamber (12) having an internal convergent / divergent slot (13) extending over the entire width of the installation facing the output of the stretching slot (F) of the assembly (5).

In this slot (13) open, near the lower part of the diverging zone, two symmetrical slots (14) arranged laterally. These symmetrical slots (14) can be either connected to a source of compressed air injected at a pressure of less than 1 bar and advantageously of the order of 0.4 bar, or simply be open to the open air.

The diverging zone is, in this embodiment, extended by two walls (15) also divergent.

Immediately downstream of this diffuser assembly, or possibly integrated inside the latter, is arranged a conventional ramp (11) for electrostatically charging the filaments thus making it possible to accentuate the opening of the beam. Such a ramp (11) is a conventional ramp, for example of the type described in FIG. US-A-3,967,118 .

The figure 3 illustrates a second embodiment of a set of opening and distribution of a bundle of filaments in the form of a web made according to the invention.

In this variant, using the same references as those used to describe the example illustrated by the figure 2 , the opening and distribution device the bundle of filaments (6) is, as before, dissociated from the drawing assembly (5).

In this embodiment, it also comprises a convergent-shaped input zone (13) extending opposite the exit of the drawing slot (F). This convergent-shaped entrance zone (13) is connected to the two walls (15) of the divergent zone by a rectilinear slot (20).

The ramp (11) for electrostatically charging the filaments is, in this embodiment, integrated within the diffuser, at the end of the straight slot (20) immediately upstream of the diverging region (15).

A venturi air intake is achieved through the two adjacent contiguous slits formed by the lower face of the draw assembly (5) and the upper face of the opening and closing assembly. distribution (6).

There is therefore an air flow along the walls (20,15) on the opening and distribution assembly.

Optionally, as in the embodiment described in support of the figure 2 , an air injection, under low pressure, less than 1 bar, could be performed at the two lateral slots formed between the drawing assembly (5) and the opening and distribution assembly (6).

It was found that with such a device, not only was a perfect opening of the bundle of filaments, but that, moreover, the reception on the carpet (7) was done very regularly and led to the obtaining of a very homogeneous nonwoven web.

Claims (4)

1. Device for opening and distributing a bundle of filaments during the production of a nonwoven textile web, according to the technique which consist :

   - in extruding a melted organic polymer through a spinneret perforated with holes, so as to form a bundle or curtain of filaments ;

   - then in orientating the extruded filaments by drawing by means of one or more fluid-jet devices (5) ;

   - and finally, in receiving the bundle of filaments in the form of a web on a movable receiving belt below which is arranged a suction source,

   which comprises an assembly (6) arranged downstream of the outlet of the drawing assembly (5) and separated therefrom, the said assembly comprising, arranged close to the outlet of the drawing slot (F), a diffuser (10) comprising an inlet zone (13) in the form of a convergent nozzle extending over the entire width of the installation opposite the outlet of the drawing slot (F) for producing the web, extended by a divergent nozzle (15), in which a rail (11) electrostatically charging the filaments before they are received on the receiving belt (7) is integrated inside the diffuser (10) or is arranged immediately downstream of the diffuser (10).
2. Device according to Claim 1, characterised in that the diffuser (10) comprises an inlet zone (13) in the form of a convergent nozzle connected to the two walls (15) of the divergent zone by a rectilinear slot (20), the rail (11) electrostatically charging the filaments being mounted at the level of the rectilinear slot immediately upstream of the divergent zone (15).
3. Device according to one of Claims 1 and 2, characterised in that en indraught or air owing to the venturi effect is produced between the faces opposite the outlet of the drawing slot ( 5) and the inlet of the diffuser assembly (6), creating a an air flow against the walls (15) if the divergent zone.
4. Device according to Claim 3, characterised in that an injection of air under a pressure less than 1 bar is produced between the faces opposite the outlet of the drawing slot (5) and the inlet of the diffuser assembly (6).

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