EP1177336B1 - 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 installations allowing the manufacture of a nonwoven textile web, commonly referred to as the generic name of "spunbond", which is formed by synthetic filaments continuous.

It relates more particularly to an improvement brought to the means ensuring the distribution of the extruded filaments, after stretching, on a carpet mobile transporter on which they are distributed randomly so as to form a regular tablecloth, 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 type nonwoven tablecloths dates back decades and generally consists of:

• extruding a molten organic polymer through a die pierced with holes, so as to form a bundle or curtain of filaments;
• then orienting the extruded filaments by drawing by means of one or more fluid jets devices, in particular with compressed air;
• and finally, to receive the bundle of filaments in the form of a sheet on a movable conveyor belt, generally subjected to a suction source, and the speed of which is adjusted according to the characteristics of the sheet, thickness in particular, that one wishes to obtain.

After completion, the sheet is consolidated, for example by carrying out a sizing or calendering, preferably hot, so that the filaments. are linked to each other.

Other consolidation treatments can possibly be carried out, such as for example a needling treatment (conventional or by jets of fluid), and / or the deposition on the surface or inside of 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 make such products include:

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

In such installations, the filaments come out of the slot drawing in the form of a bundle of filaments grouped in the median plane of said slot.

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

In order to obtain a non-woven sheet as homogeneous as possible on the carpet receiver on which the filaments coming out of the drawing slot are projected, it is necessary not only to separate said filaments from each other, but also to slow down their speed before their impact on said mat, in order to limit uncontrollable rebound phenomena that generate heterogeneous formation veil.

To ensure such bursting and distribution of the curtain of extruded filaments, various techniques have been proposed to date.

The oldest technique, which emerges in particular from patent GB-A-932 482, of patent US-A-3,967,118, consists in electrostatically charging the filaments, which tends to repel them relative to each other (Corona effect).

This technology improves the formation of the veil when the filaments are ejected at relatively low speed from the drawing slot and that, by Consequently, the so-called “regrouping” phenomena of the filaments are preponderant compared to those of the rebound of the filaments on the carpet.

This is particularly the case when the veil consists of filaments relatively coarse, i.e. with a titer greater than or equal to 2.2 dtex per filament, filaments which are generally produced with velocities out of stretching slot less than 3000 ni / min.

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

This device is not entirely satisfactory, since no control of the speed is not possible and the filaments are also subject to all currents outside air, which disturbs the veil and creates defects.

Finally, the simple friction of the filaments in the air over a distance also short does not allow a sufficient slowdown of their speed which allows to sufficiently reduce the rebound phenomena of the filaments on the carpet.

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

Since this solution was not entirely satisfactory, it was proposed, as is apparent from US-A-3,325,906, to associate with the divergent disposed at the outlet of the stretching slot, an assembly for blowing air on each side of this divergent, which creates a negative pressure in the vicinity of walls, thereby attracting fibers to the walls, which tends to open the bundle of filaments and also to slow the speed of the latter.

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

Statement of the invention

Now we have found, and this is what is the subject of the invention, that it was possible not only to obtain a perfect opening of the bundle of extruded filaments at the outlet of the stretching slot, but also a very homogeneous distribution on the receiving mat, on the one hand by dissociating the opening assembly of the beam from filaments of the drawing slot proper, and secondly and above all, in realizing this opening set in such a way that it combines both advantages of electrostatic filament charging techniques and techniques beam opening by slowing the air speed at the outlet of the slit drawing, and therefore the speed of the filaments before reception on the receiving belt.

• à extrader 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 ;
• et enfin, à recevoir le faisceau de filaments sous la forme d'une nappe sur un tapis transporteur mobile en dessous duquel est disposée une source d'aspiration.

In general, the invention therefore relates to a device making it possible to ensure the opening and the distribution of a bundle of filaments during the production of a nonwoven textile web, according to the technique which consists:

• extruding a molten organic polymer through a die pierced with holes, so as to form a bundle or curtain of filaments;
• then orienting the extruded filaments by drawing by means of one or more fluid jets;
• and finally, to receive the bundle of filaments in the form of a sheet on a movable conveyor belt below which a suction source is arranged.

The device for opening and distributing the bundle of filaments in accordance to the invention, is constituted by an assembly arranged downstream of the outlet of the drawing assembly and dissociated from the latter, this assembly comprising, arranged at near the exit of the stretching slot, a diffuser comprising an area Convergent inlet extending over the entire width of the installation at look at the exit from the web production stretch, extended by a divergent, said assembly being associated with a ramp charging electrostatically the filaments before reception on the receiving belt.

According to one embodiment, the divergent zone of the diffuser comprises two walls and two side slots located at the top of said diffuser, of each side of it and allowing either a call for air from the outside by effect Venturi, possibly an injection of air, under a pressure below one bar and advantageously between 0.4 and 0.8 bar, causing a flow of the air against the walls of said diffuser.

The above diffuser allows precise adjustment of the beam width of fibers as well as the impact speed of the filaments on the receiving mat, the whole electrostatic charge possibly located downstream of the assembly diffuser, but preferably being integrated inside the latter, which allows 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 has a convergent entry zone connected to the two walls of the diverging zone by a rectilinear slot, the ramp electrostatically charging the filaments being mounted at the rectilinear slot immediately upstream of the diverging zone;
• the distance of the diffuser from the receiving belt is adjustable, in order to minimize the influence of 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 as a function of the speed filaments at the outlet of the stretching slot, which makes such a device particularly suitable for forming a veil consisting of low denier filaments, as well as for production installations working at high speed;
• finally, the separation of the actual stretching and distribution systems of the curtain of filaments, 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:

• FIG. 1 is an overall view of an installation making it possible to produce a “spunbond” type nonwoven web;
• Figure 2 is a detail view schematically showing the structure and operation of an assembly allowing the opening of the bundle of filaments formed and its deposit on the receiving belt;
• FIG. 3 illustrates an alternative embodiment according to the invention in which the electrostatic charge of the filaments is obtained by means of a ramp integrated inside the diffuser, the flow of air inside the latter against the walls can be achieved either by natural call of the outside air, or by an injection system under low pressure less than a bar.

Way of realizing the invention

Referring to the appended figures, the device according to the invention is therefore intended to be used on a production line for a non-woven textile woven fabric consisting of continuous synthetic filaments.

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

From a practical point of view, as an indication, the sector consists of a plate each comprising a multitude of holes, for example the number of 5000 per meter of width and having a diameter depending on the extruded filaments, by example of 0.5 mm. These holes are distributed over a plurality of parallel rows, for example eighteen rows and this, over a width at the outlet of the die of 140 mm.

At the outlet of this die, is arranged a cooling assembly (4) allowing the regulation of the temperature of the filaments as a function of the polymers and composed for example of a plurality of successive zones (4a, 4b, 4c) making it possible to subject the curtain of filaments (3) to through air flows 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 speed of each zone decreases by first zone (4a) to the third zone (4c).

Downstream of this cooling zone, a stretching assembly is arranged. proper (5) which is in the form of a closed enclosure comprising a slot (F) inside which air is injected 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 speed air streams to ensure the draw.

At the outlet of the drawing assembly (5), the bundle of filaments (3) is projected on the receiving mat (7) by means of an assembly (6), an assembly which makes the subject of the invention and two embodiments of which emerge from Figures 2 and 3, and which causes a deflection of the air flow leaving the slot (5), a slowing down 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 drawing slot (F) of the assembly (5), a part, a diffuser, designated by the general reference (10) consisting essentially by a divergent which extends over the entire width of the production of the aquifer and, on the other hand, downstream of this opening assembly, a ramp (11) allowing electrostatically charge the filaments at the outlet of the assembly (10) an opening at the heart of said bundle of filaments before depositing them on the carpet receiver (7).

In this embodiment, the diffuser assembly (10) is composed essentially a chamber (12) having an internal slot (13) in the form of converging / diverging extending over the entire width of the installation opposite the exit from the stretching slot (F) of the assembly (5).

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

The divergent 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) allowing to electrostatically charge the filaments thus making it possible to accentuate beam opening. Such a ramp (11) is a conventional ramp, for example of the type described in US-A-3,967,118.

Figure 3 illustrates a second embodiment of an assembly opening and distributing a bundle of filaments in the form of a sheet produced in accordance with the invention.

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

In this embodiment, it also includes an entry area (13) in the form of a convergent extending opposite the outlet from the drawing slot (F). This convergent entry 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 inside the diffuser, at the end of the rectilinear slot (20) immediately upstream of the diverging zone (15).

A call for air from outside by Venturi effect is made through two contiguous lateral slits formed by the underside of the assembly drawing (5) and the upper face of the opening and distribution assembly (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 injection of air, at low pressure, less than 1 bar, could be made at the two lateral slots formed between the drawing assembly (5) and the opening and distribution assembly (6).

It has been found that with such a device, not only does one obtain a perfect opening of the bundle of filaments, but that, moreover, reception on the carpet (7) was done very regularly and led to obtaining a very homogeneous non-woven tablecloth.

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 consists:

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

   then, in orienting 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,

   characterised in that it consists of 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), the said assembly being associated with a rail (11) electrostatically charging the filaments before they are received on the receiving belt (7).
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 an indraught of 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) of 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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