EP1936016B1 - Method for adjusting the local characteristics of a non-woven fabric and corresponding installation - Google Patents

Description

The present invention relates to a process for producing a nonwoven fabric having locally determined characteristics, in particular in terms of mechanical strength. The invention also relates to an installation for implementing this method.

Technical area

It is known to produce a continuous web in a spreader-lapper supplied with one or more webs of topping produced in a card.

In the spreader-lapper, the web is folded alternately in one direction and the other on an exit belt, thus giving a web composed of overlapping web segments, tilted alternately in one direction and the other relatively to the direction of the web width. The folds between successive segments are aligned along the side edges of the web produced. The sheet of fibers obtained is generally intended for a subsequent consolidation treatment, for example by needling, by coating, and / or etc. to give the desired nonwoven fabric, endowed with a certain consistency and having a certain number of characteristics of mechanical strength, particularly in tensile strength.

The patent FR-A-2 234 395 teaches the speed relationships that must be observed in the spreader-lapper to control the surface weight of the web at all points of its width.

The needling machine consolidates the web by entangling the fibers with one another and interpenetrating the different layers. Planks lined with a large number of needles perpendicular to the plane of the web regularly strike the web of fibers passing through the needling machine. Fibers of the different layers are thus drawn from one layer to the other, and a felting effect follows which gives the web a certain resistance.

During its consolidation, the web undergoes changes in the distribution of fibers. Due to the interpenetration and the entanglement of the fibers, the web is compacted mainly by reducing its thickness. However, it is also observed that the width of the web decreases slightly. In addition, the surface weight of the water table is often affected by the consolidation process, typically being increased at the edges of the web.

A drawback of these alterations to the web is that the overall quantity of fibers must be increased so that the lightest point of the consolidated web meets the criteria of weight per unit area requested by the purchaser. The heaviest areas of the web, i.e. the edges, then correspond to unnecessary consumption of fibers which is not profitable on sale, as well as an unnecessary increase in the total weight of the web with subsequent drawbacks resulting therefrom, for example during handling or implementation.

Up to now, attempts have been made to overcome this drawback by producing a web having, before needling, a greater surface weight at its center than at its edges.

Thus, the patent EP-B-0 371 948 describes a process intended to precompensate the defects occurring during the subsequent consolidation, in particular the needling, by locally varying the weight of the topping web introduced into the spreader-lapper. This is achieved by automatically adjusting the speed of a card comber relative to the speed of the card drum. The faster the comb turns relative to the drum, the lighter the haze formed by the comb. The lightest areas of the web are those intended to form the edges of the web.

The patent EP-A-1 036 227 describes a process making it possible to produce a web whose surface weight has a determined profile over the width of the web, again by locally varying the surface weight of the web of lapping introduced into the spreader-lapper. This is obtained by varying at the level of the card a dynamic adjustment influencing the weight of the web, for example by modifying the spacing between the combing device and the carding drum to modify the quantity of fibers taken up by the combing device, or again by “Condensing” the fibers in a variable manner downstream of the comb. It is said that we “condense” a card web when, in particular in a device called a “condenser”, the web is compressed longitudinally to increase its surface weight and at the same time to cause the web to pass from an initial state where the fibers are oriented longitudinally in a condensed state where the fibers exhibit a less unidirectional distribution of orientations, i.e. with at at least a portion of the fibers having over at least a portion of their length an orientation forming an angle with the longitudinal direction of the web.

According to WO 00/73547 A1 , the dynamic weight adjustment means form part of a control loop comprising means for detecting the surface weight profile of the consolidated sheet. Typically, the speed of rotation of the card comber is readjusted according to the difference between the result of this detection and a set point. The detection detects at the same time the width of the consolidated web and the regulation corrects the length of the stroke of the lapper carriage of the lapper-lapper as a function of the difference between the detected width and a nominal width setpoint, so as to giving the web an actual width as close as possible to the desired nominal width. In an improved version, the longitudinal profile of the surface weights of the web is also regulated. The consolidated sheet obtained thus has a width and a surface weight that are very uniform and very close to the respective nominal values targeted. The EP 1 057 906 B1 describes another method of dynamically adjusting the weight profile of a web.

However, more and more, buyers take into account certain criteria, in particular tensile strength values, measured in particular according to different directions of the nonwoven, for example according to the direction of the width of the nonwoven ("Cross Direction") and in the longitudinal direction of the nonwoven ("Machine Direction").

• la résistance à la rupture en traction dans le sens longitudinal du textile (ou de la nappe), qualifiée de "Machine Direction";
• la résistance à la rupture en traction dans le sens de la largeur du textile (ou de la nappe), qualifiée de "Cross Direction";
• le rapport entre ces deux valeurs de résistance, noté MD/CD, c'est à dire la résistance "Machine Direction" divisée par la résistance "Cross Direction".

For example, a criterion commonly required for nonwovens, in particular in the field of geotextiles, is expressed in the form of the following quantities:

• the tensile strength in the longitudinal direction of the textile (or of the web), referred to as "Machine Direction";
• the tensile strength in the direction of the width of the textile (or of the web), referred to as "Cross Direction";
• the ratio between these two resistance values, denoted MD / CD, ie the "Machine Direction" resistance divided by the "Cross Direction" resistance.

When the mechanical characteristics obtained in the consolidated web do not correspond to the requirements, the current practice consists in reinforcing the entire web by increasing the quantity of fibers, locally or in general. To satisfy one of these characteristics, it often comes to use more fiber than required by the other characteristic, which goes against an optimization of the amount of fiber consumed.

For example, if the two resistors MD and CD must have the same minimum value, to optimize the consumption of fibers by ensuring sufficient resistance in both directions, the MD / CD ratio should be as close as possible to the value 1: 1

In addition, it is often observed that the MD / CD ratio has a fairly different value on the edges of the web compared to the central part. Even if the surface weight of the nonwoven is uniform over its entire width, thanks in particular to the weight compensations carried out according to the prior art, the MD / CD ratio of a nonwoven according to the prior art is generally not uniform, because the orientation distribution of the fibers is not the same at all points of the width of the nonwoven. For example, consolidation by needling tends to favor the transverse orientation of the fibers near the center of the web rather than near the edges of the web.

If the distribution of the resistance values observed does not correspond to the required characteristics, and in particular if the required values are the same over the entire width of the web, then the web will have to be reinforced over its entire width so that the lowest value is sufficient.

Furthermore, it may be useful to be able to choose a distribution of these resistance values within the width of the web according to a non-uniform profile meeting the needs of a particular specification. It may for example be a matter of obtaining a profile exhibiting one or more resistance values which are specifically higher, or lower, in one or more zones of such a profile.

• une ou plusieurs caractéristiques mécaniques locales maîtrisées en une ou plusieurs régions;
• une répartition uniforme de ses valeurs de résistance longitudinale (résistance MD), ou transversale (résistance CD), ou du rapport de ces valeurs;
• une répartition non-uniforme de ces valeurs, de façon distribuée selon un profil déterminé;
• une combinaison de telles répartitions des valeurs de résistance avec une répartition de poids surfacique distribuée selon un profil déterminé.

An aim of the invention is thus to make it possible to obtain a nonwoven fabric having in its width at least one of the following characteristics:

• one or more local mechanical characteristics controlled in one or more regions;
• a uniform distribution of its longitudinal resistance values (MD resistance), or transverse (CD resistance), or the ratio of these values;
• a non-uniform distribution of these values, in a distributed manner according to a determined profile;
• a combination of such distributions of resistance values with a distribution of surface weight distributed according to a determined profile.

The invention also seeks to optimize the quantity of fibers necessary to obtain a nonwoven fabric of which all the parts have certain minimum characteristics, as well as to optimize the weight or the volume of such a nonwoven fabric.

For this purpose, the invention provides a method for manufacturing nonwoven web textiles according to claim 1.

This comprises at least one dynamic adjustment. The distribution of orientation of the fibers is influenced in a targeted manner as a function of the position of said fibers in the direction of the width of the strip.

By "dynamic adjustment" is meant an adjustment which is revised and if necessary modified continuously or repetitively (for example at regular time intervals) while the installation is operating in production.

The invention is based on the idea of differentiating the orientations of fibers as a function of the location of the fibers along the width of the web, either to obtain different mechanical characteristics in different areas of the width of the web, or to precompensate for uniformity defects introduced into the mechanical characteristics of the web during subsequent steps of the manufacturing process, in particular during consolidation and more particularly during needling. In the case of precompensation, knowing that needling tends to “longitudinalize” the fibers close to the edges, the invention can be used to give the fibers close to the edges of the web before needling a distribution of orientations favoring more the transverse orientation than for the fibers forming the central zone of the web.

In certain cases, for example for textiles intended to be easily cut, separated or torn, the desired control may aim to provide one or more zones of lower resistance, or a sufficiently low resistance at all points of the textile.

Relevant mechanical characteristics, especially in the field of geotextiles, include resistance characteristics to traction in the plane of the textile, for example elongation before breakage and above all resistance to breakage. For a given category of textile, these characteristics must be of sufficient value in all regions of the textile, and in particular over its entire width. In the case of characteristics such as tensile strength, this sufficient value will generally correspond to a minimum value, and the present description will concentrate essentially on this type of characteristic. However, for other characteristics such as elongations, this sufficient value may in fact correspond to a maximum value, without departing from the scope of the invention.

In the context of the present invention, the notion of “distribution of orientations” is used. This notion takes into account the different orientations present in a given zone, and the greater or lesser abundance of each orientation in this zone. We can illustrate a distribution by a closed curve with a center. The distance between each point of the curve and the center indicates the percentage of fibers having the orientation indicated by the vector going from the center to that point. In the simplest case of an uncondensed carded web, the fibers are typically all parallel to the length of the web (orientation distribution curve flattened to give a single segment). If this web is then layered in successive segments which overlap in zig-zag as will be described later, the distribution in the web obtained has a preponderance parallel to the width of the web, however with a longitudinal dimension resulting from the obliquity web segments relative to the width of the web. We could speak of bidirectional distribution represented by a more or less flattened "X".

In the more complex case of a condensed card web, the initially longitudinal fibers of the non-condensed web have been folded back on themselves and / or “transversalized” by the condensation so that the orientation distribution is no longer unidirectional but omnidirectional, represented by an oval.

In a first embodiment or preferred embodiment, the orientation of the fibers in the web is influenced. Such a dynamic adjustment relating to the web is carried out before folding the web back on itself to form the web. For example, it is possible to influence the orientation distribution of the fibers in the web within the assembly forming the card, but also during transport to the spreader-lapper or in the input circuit of the spreader-lapper. The orientation distribution of the fibers is adjusted in the successive zones of the length of the web as a function of the position that these zones will take along the width of the web.

In particular, the orientation of the fibers can be influenced by means of adjustable condensation of the web. Such condensation of the veil can itself be obtained in several ways which can be used as desired or even be combined with one another.

Typically the dynamically adjustable condensation according to the invention is obtained at least in part by varying the speeds of at least two rotary members of the card which contribute to the manufacture or transport of the web with respect to each other.

As a variant in the context of this first embodiment of the invention, the condensation is obtained at least in part by adjusting a movement of at least one carriage of the spreader-lapper in a direction substantially transverse to the tablecloth, for example by giving this carriage a speed different from that which would ensure that the web leaves the lapper carriage with a travel speed equal to the displacement speed of the lapper carriage.

If at a given point in the stroke of the lapper carriage the displacement of the lapper carriage is slower than the movement of the web through the lapper carriage, the web condenses locally at the outlet of the lapper carriage.

If, on the contrary, at a given point in the stroke of the lapper carriage, the movement of the lapper carriage is faster than the movement of the web through the lapper carriage, the web is stretched at the exit of the lapper carriage. This can for example locally reduce the effect of a pre-existing condensation of the web and thus modify the local distribution of the orientations of the fibers to make it closer to a longitudinal unidirectional distribution relative to the web.

And if at a given point in the stroke of the lapper carriage the speed of movement of the lapper carriage is equal to the travel speed of the web through the lapper carriage, the web is deposited substantially unchanged on the output apron of the spreader. lapper.

In a second embodiment, possibly combinable with the first embodiment, the relationship between the deposit of the web on the output apron of the spreader-lapper and the travel speed of the output apron conveying the web in formation towards the output of the spreader lapper.

The direction in which the web is deposited on the web is thus modified, that is to say the angle formed by this direction with the axes of the web, and therefore the angle formed by the fibers deposited with the axes of the web. sheet, in particular when the fibers of the web are longitudinal relative to the web. In particular, the angle of inclination of the web segments in the web depends on the ratio between the speed of the outlet apron and the speed of movement of the lapper carriage. For example, if the speed of the exit apron is reduced not only in absolute terms but also in relation to the speed of the lapper carriage which is itself in the process of decreasing when the lapper carriage is in the vicinity of its ends of stroke, the fibers of the web are deposited with a less inclination with respect to the width of the web in the vicinity of the edges of the web; which precompensates the defect introduced later by a consolidation process by needling.

The invention is very advantageously combined with the methods known per se to achieve a predetermined distribution of surface weights over the width of the web.

In particular, the degree of condensation of the parts of the web intended to be located at the edge of the web can be reduced so that the fibers are “more transverse” in the web in the vicinity of the edges of the web before consolidation. In principle, this results in a variation in surface weight in the vicinity of the edges of the sheet. To obtain the desired surface weight profile, a second variation is added to this first variation which has substantially no effect on the orientation distribution of the fibers, for example a variation in the spacing between the comb and the card drum, or again a variation in the speed of the comb and a proportional variation of the fiber transport members located downstream of the comb. In principle, an accumulator means capable of absorbing the speed fluctuations is provided downstream of the scraper so that the speed of transport of the fibers downstream of the accumulator is not affected by these fluctuations. Such an accumulator may for example be constituted by an apparatus interposed between the card and the spreader, or alternatively by an accumulator placed at the outlet of the spreader lapper, or alternatively by the accumulator carriage of the spreader-lapper as described in EP-A-1 036 227 .

Preferably, the method according to the invention comprises a regulation of the dynamic adjustment of the orientation of the fibers as a function of a detection of at least one quantity representative of the orientation distribution of the fibers in the nonwoven, preferably the non-woven after consolidation.

The measured quantity may be the shrinkage undergone by the web during its consolidation by needling. Such a shrinkage can be interpreted in terms of modification of the orientation distribution of the fibers in the edge zones of the web. The dynamic adjustment consists in pre-compensating for this modification by one of the orientation means described above, namely the condensation in the card, between the card and the spreader, or at the exit of the lapper carriage, or else the adjustment of the speed of the spreader output apron relative to the speed of movement of the lapper carriage.

Alternatively, the measured quantity can be taken from an image of the web which is analyzed to determine the local distribution of orientations, or a numerical value or a set of numerical values which represents this distribution, for example its bidirectional spectrum such as it will be defined later.

According to a second aspect, the invention relates to an installation for the production of nonwovens according to claim 20.

This comprises a card providing at least one web of fibers, a spreader-lapper arranging the web in successive transverse segments on an output apron to form a web, and a consolidation machine such as a needling machine or a binding device. by water, thermal or chemical jet downstream of the outlet apron, characterized in that it further comprises orientation means for influencing the orientation distribution of the fibers according to their position along the width of the web, in a process according to one of claims 1 to 19.

• les figures la à 1c illustrent un exemple de variation des caractéristiques de résistance mécanique au sein d'une nappe selon l'art antérieur, en particulier :
• la figure la représente une coupe transversale de la nappe avant et après consolidation selon l'art antérieur, sans compensation de poids surfacique;
• la figure 1b est analogue à la figure la mais avec compensation de poids surfacique;
• la figure 1c représente le profil de variation du rapport MD/CD suivant la largeur de la nappe consolidée de la figure 1b, toujours selon l'art antérieur;
• la figure 2 est une vue de dessus de la nappe avant et après le traitement de consolidation, illustrant le procédé selon l'invention;
• les figures 3a et 3b représentent les distributions d'orientation d'une nappe non consolidée lorsque le voile est non-condensé (figure 3a) et lorsque le voile est condensé (figure 3b) ;
• les figures 4 à 6 illustrent l'invention dans son premier mode de réalisation, en particulier :
  • la figure 4 est une vue de côté de la carde et de l'étaleur-nappeur, illustrant certaines variantes du premier mode de réalisation de l'invention ;
  • la figure 5 est une vue schématique de dessus de l'étaleur-nappeur (partiellement éclaté) et de ses entrée et sortie, dans un exemple de mise en œuvre du premier mode de réalisation de l'invention;
  • la figure 6 est une vue de côté de la carde dans une autre configuration, illustrant certaines variantes du premier mode de réalisation de l'invention;
• la figure 7 est une vue de dessus de l'étaleur-nappeur (partiellement éclaté) et de ses entrée et sortie, dans un exemple de mise en œuvre du deuxième mode de réalisation de l'invention; et
• la figure 8 est une vue de côté des chariots de l'étaleur-nappeur, illustrant certaines variantes du deuxième mode de réalisation de l'invention.

Other features and advantages of the invention will emerge from the detailed description of embodiments which are in no way limiting, and from the accompanying drawings, in which:

• FIGS. la to 1c illustrate an example of variation of the mechanical strength characteristics within a web according to the prior art, in particular:
• FIG. la shows a cross section of the web before and after consolidation according to the prior art, without compensation for the surface weight;
• the figure 1b is similar to Figure 1a but with compensation for surface weight;
• the figure 1c represents the variation profile of the MD / CD ratio according to the width of the consolidated layer of the figure 1b , still according to the prior art;
• the figure 2 is a top view of the web before and after the consolidation treatment, illustrating the process according to the invention;
• the figures 3a and 3b represent the orientation distributions of an unconsolidated layer when the web is non-condensed ( figure 3a ) and when the veil is condensed ( figure 3b );
• the figures 4 to 6 illustrate the invention in its first embodiment, in particular:
  • the figure 4 is a side view of the card and the spreader-lapper, illustrating certain variants of the first embodiment of the invention;
  • the figure 5 is a schematic top view of the spreader-lapper (partially exploded) and its inlet and outlet, in an exemplary implementation of the first embodiment of the invention;
  • the figure 6 is a side view of the card in another configuration, illustrating certain variations of the first embodiment of the invention;
• the figure 7 is a top view of the spreader-lapper (partially exploded) and its inlet and outlet, in an exemplary implementation of the second embodiment of the invention; and
• the figure 8 is a side view of the carriages of the spreader-lapper, illustrating certain variants of the second embodiment of the invention.

As illustrated in figure 1a , in the known configurations where the fibers are deposited in a regular manner to form a sheet of substantially rectangular section 430a, the consolidation gives a nonwoven fabric having a profile 440a whose edges are significantly heavier, for example example with a surface weight of the order of 115 to 120 for the edges if the surface weight at the center is 100. This increase in the surface weight near the edges is fed by a lateral shrinkage dc of the consolidated sheet with respect to the sheet non-consolidated.

According to the prior art, compensation for variations in surface weight is typically obtained by depositing more fibers in the central part of the web. A domed profile 430b is thus produced as shown in dotted lines in figure 1b . Consolidation then gives a nonwoven fabric exhibiting a substantially uniform weight profile 440b.

Despite the surface weight uniformity thus obtained, the different tensile strengths obtained in the transverse direction CD and in the longitudinal direction MD exhibit a certain heterogeneity between the edges and the central part of the consolidated sheet of the prior art. As illustrated in figure 1c , the MD / CD ratio between these two breaking strengths can in some cases be 40% greater near the edges than in the central part. The tensile strength in the longitudinal direction of the web (MD strength) is higher near the edges of the web than in its central region, compared to the tensile strength in the width direction of the web (resistance CD). It is believed that this heterogeneity is due to the fact that the orientation of fibers near the edge of the web is altered by the needling process, together with the occurrence of dc shrinkage. According to this theory, the fibers of the edge of the consolidated web would tend to form, on average, a greater angle with the width of the web, than the fibers of the central region of the web.

Tablecloth 430 ( figure 2 ) is typically obtained by superimposing several segments of S430 sails overlapping each other. The segments are interconnected by folds extending along the edges of the web. The fibers of the web 430 have different orientations resulting from the orientation of the fibers within each of these segments, as well as from the angle A430 according to which these segments are deposited on the mobile apron carrying the web. Typically, a web made of non-condensed web, the fibers of which are therefore longitudinal in the web, exhibits a much greater tensile strength in the transverse direction of the web (CD) than in its longitudinal direction (MD) because the longitudinal direction of the web, and therefore the direction of the fibers, are almost transverse in the water table. If the web used is condensed, the orientation distribution in the web is more homogeneous, but the transverse or quasi-transverse orientations remain preferred. Therefore, the resistance CD remains higher than the resistance MD, although the ratio between the two is less than 1: 1 than when the web used is not condensed.

In a given zone of the web 430, the distribution of the orientation of all the fibers present can be represented by a closed curve C _F linked to this zone and having a center of symmetry Cs. The figure 3a represents an example of curve C _F for a sheet made of non-condensed veil and the figure 3b an example of curve C _F for a sheet made of condensed veil. Each point P of the curves C _F indicates by its distance from the center Cs the proportion of fibers having an orientation identical to that of the vector ray CsP connecting the center Cs to this point P.

From a curve C _{F it} is possible to establish a representation comprising an arrow FM parallel to the longitudinal direction and an arrow FC parallel to the width of the web. The two arrows then each have a length proportional to the sum of the longitudinal components and respectively to the sum of the transverse components of the vector rays CsP of a quadrant (chosen arbitrarily among the four possible ones) of the curve C _F. The ratio between the lengths of the arrows FM and FC gives an idea of the MD / CD ratio at the center Cs. The set formed by the two arrows FM and FC at a given point of a web or of a web will be called “bidirectional spectrum of orientations”.

In the example shown in figure 2 , the orientation of the fibers in the web 430 has been influenced so as to obtain in the central part of the web not yet consolidated an orientation spectrum ON2 different from the orientation spectrum ON1 in the parts of the web close to its edges.

Compared to the prior art illustrated in figure 1c , we will often seek for the web before needling an orientation spectrum ON2 at the center of the web 430 in which the component FM ₂ parallel to the longitudinal axis A43 of displacement of this web is greater than the corresponding component FM ₁ of the spectrum orientation ON1 near the edges, so as to precompensate the variations in the MD / CD ratio observed in the prior art after needling, and to obtain, after needling, a spectrum of orientations which is substantially the same at all points of the width of the consolidated water table.

The orientation of the fibers in a given part of the web 430 is influenced by a dynamic adjustment made upstream of the consolidation treatment in the needling machine 3. More particularly, in this example, the adjustment affects each region of the length of the web. depending on the position that this region of the length of the web will take in the web.

The fibers of the regions of the web intended to come to be placed at the edges of the web are given an orientation spectrum having a greater longitudinal preponderance (relative to the web) than the fibers of the web intended to come to be placed in the central region of the web. the tablecloth.

A first embodiment will be described, with more particular reference to figures 4 to 6 .

The figure 4 illustrates a nonwoven production installation comprising a card 1 producing a web 421 feeding a spreader-lapper 2. The card comprises a feed roller 11 collecting fibers 411 directly or indirectly in a reserve, to feed a card drum 12. The periphery of the drum 12 is equipped with known means, not shown, for working the fibers carried by the drum. These fibers are taken from the drum 12 by a combing roller 13, then transferred successively to a first condensing roll 14 and a second condensing roll 15. The web 421 thus formed is detached by a stripping roller 16 rotating in the same direction as the last. condenser roller and depositing the web on a conveyor belt 17 leading to the inlet 20 of the spreader-lapper 2. The fibers are oriented circumferentially on the comb 13. In conventional machines, the condensers 14 and 15 are used to increase the surface weight of the veil, reduce the speed of the veil and give the fibers a more varied orientation than on the comb. The condensation effect is obtained by giving the second condensation roller 15 a peripheral speed less than that of the first condensation roller 14, the peripheral speed of which is itself lower than that of the comb 13.

The spreader-lapper 2 comprises an inlet mat or front mat 24 and a rear mat 25 each forming a closed loop. These loops are exterior to each other and bypass various rollers rotating around fixed axes, as well as rollers carried by an accumulator carriage 21 and others carried by a lapper carriage 22. Each of the two belts 24 and 25 is driven by one of the fixed-axis rollers which is associated with it and which is coupled to a respective electric servo motor.

At the inlet 20 of the spreader-lapper 2, the web 421 is brought to the accumulator carriage 21 by the inlet belt or front belt 24, one region of which may constitute the transport belt 17, as shown. The web passes downward through the first accumulator carriage 21, then the lapper carriage 22. The lapper carriage 22 is in reciprocating motion M22 in a direction perpendicular to the width of the web, and thus deposits the web 421 in successive segments on an apron of outlet 28 movable in a direction parallel to the width of the web. The successive accumulated and offset segments formed by the web 421 deposited on the outlet apron 28 form the web 431 ( Fig 5 ) which is routed to consolidation processing 3 ( figure 2 ). The accumulator carriage 21 is in reciprocating motion M21 in the same direction as the lapper carriage 22 with a displacement law calculated to adjust the distance to be traveled by the web between the inlet 20 of the lapper-lapper and the lapper carriage 22. Said distance is more particularly adjusted to combine with each other the speed of entry of the web 421 into the spreader-lapper with the speed at which the web passes through the lapper carriage 22. The entry speed 20 is equal. at the production speed of the card, as modified if necessary at each instant by the comb 13 which can be at variable speed and by the variable condensation which will be described. The speed at which the web passes through the lapper carriage 22 is either equal to the travel speed of the lapper carriage 22 if the web is to be deposited without adding condensation or stretching, or is different if the web is to be condensed or stretched when it is deposited on the output apron of the spreader-lapper.

In the first embodiment, the dynamic adjustment according to the invention affects the preparation or transport of the web 421, that is to say upstream of the deposition of the web on the outlet apron 28 by the lapper carriage 22.

In the embodiment illustrated in figure 5 , this adjustment modification produces in the web 421 entering the spreader-lapper 2 an alternating structure having, along the longitudinal direction of the web 421, an alternation of VC and VB zones which differ in their fiber orientation distributions.

The areas VB are intended to compose the edge areas B1 of the web 431, while the areas VC are intended to compose its central part. In the VB zones corresponding to the edges of the web, the fibers of the web have a certain OVB orientation spectrum, while in the VC zones corresponding to the center of the web, the fibers of the web have another OVC orientation spectrum.

When it is sought to increase the MD / CD ratio of the central zone of the web 431, the dynamic adjustment is made so as to increase the transverse component of the OVC orientation spectrum of the VC zones of the web 421. These VC zones produce then in the sheet a central zone where the fibers present an orientation spectrum ON2 ( figure 2 ) having a larger longitudinal component FM2. After consolidation, this same central zone presents an increased MD / CD ratio. As for its part the MD / CD ratio of the edge zones of the consolidated sheet has been increased by the effect of the needling described with reference to the figure 1c , the two MD / CD ratios can be made equal.

Similarly to what has just been explained for the standardization of the MD / CD ratio in the consolidated web, the method according to the invention can be used to produce other types of distribution profile of the orientation spectra of the fibers within the width of the web such as 431. The invention thus makes it possible to produce a nonwoven having, after consolidation, mechanical strengths distributed according to a chosen profile, preferably taking into account the variations directly induced by the consolidation in the edge areas as shown in figure 1c .

Such selected profiles can make it possible, for example, to produce a textile which will tear more easily along a selected longitudinal zone, for example to facilitate separation or cutting in such a zone.

In some cases, the orientation profile of the fibers in the web 431, such as that shown in figure 5 which is symmetrical with respect to the longitudinal axis of the web 431, the periodicity of variation of the settings influencing the orientation of the fibers corresponds to a half-period of work of the spreader-lapper 2, corresponding to a sequence of a VC zone and a zone VB on the web 421. In the general case such as that of a non-symmetrical profile, the adjustment variation period corresponds to a complete working period of the spreader-lapper.

In the embodiment illustrated in figures 4 to 6 , the orientation of the fibers of the web 421 is influenced by carrying out condensation in the VC parts of the web.

However, certain combinations of zones and settings give particularly advantageous results in the field of the orientation of the fibers, as well as the distribution of the mechanical strengths and elongations after consolidation.

Indeed, tests have shown that the reorientation of the fibers by condensation of the web, in particular upstream of the carriages of the spreader-lapper or within the card, had on the anisotropy of the mechanical resistance in the nonwoven. final a spectacular effect compared to the degree of condensation chosen.

Thus, a condensation of the order of 17% by surface weight can cause the value of MD / CD in the consolidated web to vary by approximately 40%, in the case of a geotextile based on polypropylene fibers.

Preferably, the variable condensation is carried out within the card, during the production or transport of the web, by varying the speeds of at least two rotary members of the card with respect to each other or transportation. One of these members rotates for example at a given speed and one or more subsequent members rotate at a lower speed when the condensation is to be effective.

For example if the combing roller 13 rotates at a circumferential speed of 130 m / min while the detacher 16 rotates at 100 m / min, the web produced will exhibit a condensation of 30%. This condensation could for example be carried out in several intermediate phases, with the first condenser roll 14 rotating at 80 m / min and the second condenser roll 15 rotating at 50 m / min.

In another configuration not shown, the card could include a single condenser roll. Such a condensation of 30% can then be obtained with a comb roller rotating at 130 m / min, the condenser roller rotating at 80 m / min, and the stripper rotating at 100 m / min.

In another configuration shown in figure 6 , a comb roller 13 is directly followed by a stripper roller 16. Such a condensation of 30% can then be carried out directly between the comber rotating at 130 m / min and the stripper rotating at 100 m / min.

Alternatively or in combination with the dynamic adjustment of the condensation in the card 1, a condensation can also be dynamically adjusted on the transport path or within the spreader-lapper 2.

The transport path can thus include one or more condensing devices. It may be, for example, one or more condenser rolls, the circumferential speed of which is dynamically adjusted. Dynamically adjustable condensation can be achieved with a stretching or compression device as described in WO 02/101130 A1 where the FR-A3-2 828 696 placed between the card itself and the spreader-lapper itself. These devices can for example, according to the invention, operate in variable stretching to cancel at least in part, and in a variable manner, a constant condensation at the exit of the card. Both an adjustment of the surface weight and an adjustment of the orientation spectrum are thus carried out, since the zones of the length of the web undergoing the strongest stretching, intended to be placed near the edges of the web, are at the same time. times lightened (reduced surface weight) and at the same time “longitudinalized” with regard to the orientation of the fibers, while the other areas, less stretched, retain the higher surface weight and the more homogeneous orientation spectrum which result from condensation at the end of the card.

A dynamic adjustment of the condensation of the web can also be carried out in the spreader-lapper 2, for example by modifying the law of displacement of one or two of its carriages 21 and 22 so as to adjust the speed at which the web passes through the web. lapper carriage 22 relative to the speed of movement of the lapper carriage 22. Instead of adjusting the condensation for each point in the stroke of the lapper carriage, and therefore for each point of the width of the web, it is also possible to make adjustments by zones, for example the two edge zones and the central zone.

A second embodiment, which will be described with reference to figures 7 and 8 , can be implemented as an alternative to the first embodiment or in combination with it.

In this second embodiment, a dynamic adjustment is carried out affecting the preparation or transport of the web 432, that is to say at the stage or downstream of the deposition of the web 422 on the outlet apron 28 in the spreader-lapper. 2.

As illustrated in figure 7 , this adjustment modification produces a modification of the web deposition pattern to form each of the transverse segments making up the web 432, by modifying the inclination of the segment relative to the width of the web. Within the web 432, the longitudinal direction DB or DC of each segment forms with the width of the web an angle AB or AC respectively.

In some conventional lapper spreaders, the exit apron such as 28 advances at a constant speed. The ratio between this constant speed and the speed of movement of the lapper carriage such as 22 defines the angle between the width of the web and the longitudinal direction of the web segments.

It is known practice to slow down the exit apron when the lapper carriage slows down in the vicinity of its reversal points, so as to maintain constant the ratio between the speed of the exit apron and the speed of the lapper carriage. Thus, the angle formed by a segment with the width of the web is constant from one edge to the other of the web according to the state of the art.

With the present invention, the exit apron is further slowed down, so that the angle AB in the edge areas B2 is less than the angle AC in the central region of the web, as shown. figure 7 .

From a dominant orientation OV2 of the fibers in the web 422, varying the direction of deposition of the web on the outlet apron thus produces a desired variation in the orientations of the fibers along the width of the web.

Thus, thanks to the dynamic adjustment of the direction of web deposition so as to increase the deposition angle AC in the central zone relative to the deposition angle AB in the edge zones B2, the orientation spectrum ON2 at the center of the web is less elongated in the direction of the width of the web than the ON1 orientation spectrum in the edge zones. After consolidation, the edge zones have an MD / CD ratio close to that of the central zone.

In the same way as specified for the first embodiment, this second embodiment can also be used to obtain a selected non-uniform profile, with regard to the distribution of resistances within the textile obtained, and not simply a uniform profile.

Preferably, the installation according to the invention combines the means described so far aimed at controlling the orientation distributions of the fibers over the width of the web, with means such as according to EP-1 036 227 to control the profile of the surface weights over the width of the web.

For this, once the adjustments have been made to provide the desired distribution of the orientation distributions over the width of the web and / or the desired distribution, over the width of the web, of the quantities, such as the ratio MD / CD, relating to the mechanical strength of the web, a second dynamic adjustment is carried out affecting the surface weight of the web but having substantially no effect on the orientation of the fibers. The second adjustment may be an adjustment varying the quantity of fibers taken by the comber from the carding drum. More specifically, the second adjustment can for example consist in varying the speed of rotation of the comb (the faster the comb turns the less fibers it collects at each turn, and the lighter the haze it produces) or the spacing of the comber relative to the carding drum (the farther away the comber is from the drum, the less fibers it withdraws at each turn, and the lighter the haze it produces).

In a concrete example, the speed of the comber is dynamically adjusted to produce a web whose weight is non-uniform along its longitudinal direction as for example described in EP-A-1036 227 , and the orientation distribution of the fibers in the web is adjusted by dynamically varying the rate of condensation of this web, that is to say for example the ratio between the speed of a detacher and the speed of the comber. Therefore, if at any point in time the speed of the comb is changing and the rate of condensation is to remain constant, typically the speed of the stripper should vary in the same proportion as the speed of the comb.

It is provided according to the invention to regulate the dynamic adjustment affecting the orientation of the fibers in the web. In a preferred version, this regulation is combined with a regulation of the surface weight profile such as according to the WO A 00/73547 where the EP 1 057 906 B1 .

For this, as shown in figure 2 , a transverse detector 41 of the type of that described in section 3 is placed above the web exiting the needling machine 3. WO A 00/73547 comprising a series of sensors aligned parallel to the width of the web or, as a variant, a single so-called "traveling" sensor making back and forth movements above the web. The transverse detector 41 detects the width of the consolidated web 440 and the surface weight at different points of the width of the web. The detection of the width of the web allows a computer 42 to calculate the lateral shrinkage dc undergone by the web during consolidation, either by difference with a detection of width (not shown) upstream of the needling machine 3, either by difference with the stroke length of the lapper carriage of the lapper-lapper 2. This stroke length is known to the computer 42 because the lapper carriage is actuated precisely by a servo-motor (not shown) also controlled by this calculator.

The width of the edge zone of the sheet which is altered in connection with the phenomenon of shrinkage dc is known from experience or from prior tests. A simple arithmetic calculation and / or preliminary tests make it possible to evaluate the impact of this shrinkage on the orientation distribution of the fibers in the edge zone affected by the shrinkage. As a function of this evaluation, the computer 42 controls an adjustment of the orientation means.

For example, as a function of said evaluation, the computer 42 calculates a rate of condensation which must be applied to the parts of the web intended to form the central zone of the sheet so that this central zone presents in the consolidated sheet an orientation distribution. , or in any case a bidirectional orientation spectrum, which is substantially equal to that of the edge zones. Simultaneously or alternately in time with this regulation of the orientation distributions, the computer 42 receives from the detector 41 measurements of the surface weight at different points of the width of the consolidated sheet 440 and regulates the surface weight profile of the consolidated sheet and the width of the consolidated sheet as described in WO A 00/73547 , by influencing parameters, such as those described previously (speed of the comb, distance of the comb), little or no affecting the orientation of the fibers in the web. The figure 4 schematically illustrates the computer 42 sending orders 43 to the condensers 14, 15 and to the detacher 16 for the dynamic adjustment of the condensation, orders 44 to the comb 13 for the dynamic adjustment of the weight without affecting the orientation of the fibers, and orders 46 to the lapper spreader 2 to adjust and define at any time the position of the two lapper carriages 21, 22 in their reciprocating movements M21, M22 as well as the speed of circulation of the belts 24, 25. The lines 43, 44, 46 are bidirectional for transmitting in return, to the computer 42, information on the real values of the operating parameters of the card and of the spreader-lapper in particular.

In another embodiment of the regulation, it is envisaged to use at the output of the needling machine 3, in addition to the detector 41, at least one image sensor (not shown) in one of the edge zones , and preferably at least three image sensors for the two edge zones and the central zone respectively. The images produced by these sensors are analyzed to determine the orientation distribution of the fibers in the images obtained. The computer 42 then calculates, for example, the bidirectional orientation spectra corresponding to the observed distributions, and controls the orientation means in a direction tending to equalize or keep these bidirectional spectra equal.

In particular, the regulation based on a detection of the transverse shrinkage of the web could be carried out without being combined with a regulation of the surface weight profile.

The orientation means controlled within the framework of the regulation of the distributions or orientation spectra can be any of those described, for example the drive motor of the output apron of the spreader-lapper 2 as described in reference to figure 7 .

Claims (26)

1. A method for the production of a non-woven strip (440), wherein by a dynamic control influence is exerted in a targeted manner on the distribution of orientations (OVB, OVC) of the fibres according to the position of said fibres in the widthwise direction of the strip (430, 440); characterized in that different distributions of orientation (OVB, OVC) are established at different points of the width of the strip at an intermediate production stage (430) so that the non-woven textile obtained at a subsequent production stage (440) exhibits at different points of the width of the textile sought respective distributions with regard to mechanical strength and/or elongation, the distributions of orientation of the fibres being chosen so as to promote the uniformity at all points of the width of the non-woven textile of a variable (MD/CD) representative of the mechanical strength or of the elongation of the non-woven textile.
2. A method according to claim 1, in which a fiber lap is produced and this fiber lap is consolidated, in particular, by needle-punching, characterized in that in the spectrum of orientation of the fibres (430, 431, 432), a component parallel to the width of the lap before needle-punching is greater, compared with a longitudinal component, in two edge regions of the lap than in a central region of the lap.
3. A method according to claim 1 or 2, in which a carding machine (1) provides at least one web (421, 422) which is superimposed in successive substantially transversal segments which overlap one another in order to form in a crosslapper (2) a lap (430, 431, 432), which subsequently undergoes a consolidation treatment (3), characterized in that said dynamic control exerts an influence on the orientation of the fibres in successive regions (VB, VC) of the length of the web (421).
4. A method according to claim 3, characterized in that said dynamic control exerts an influence on a degree of condensation of the web (421).
5. A method according to claim 4, characterized in that the dynamic control exerting an influence on the condensation is at least in part an adjustment of the relative speeds, in relation to each other, of at least two rotating members (12-17) of the carding machine contributing to the manufacture or the transportation of the web (421).
6. A method according to claim 5, characterized in that said relative speeds are those of a stripping roll (16) and respectively of a doffer (13) of the carding machine.
7. A method according to claim 5, characterized in that said relative speeds are those of a condenser (15; 14) and respectively of another condenser (14) or of a doffer (13) of the carding machine.
8. A method according to claim 5, characterized in that said relative speeds are those of a stripping roll (16) and respectively of a condenser (15, 15) of the carding machine.
9. A method according to claim 3, characterized in that the dynamic control affects the displacement (M21, M22) of at least one carriage (21, 22) of the crosslapper (2) in a direction substantially transversal to the lap.
10. A method according to claim 9, characterized in that the dynamic control exerts an influence on the ratio of a speed at which the lap exits the crosslapper and of the speed at which a point of deposition of the web (422) on the lap being formed within the crosslapper (2) moves along the width of the lap.
11. A method according to one of claims 3 to 10, characterized in that said at least one dynamic control exerts an influence on a run-off speed of an exit (28) apron of the crosslaper (2) fed with a web of fibres having an anisotropic distribution of orientations, preferably preponderantly longitudinal relative to the web.
12. A method according to one of claims 2 to 11, characterized in that the consolidation stage comprises a mechanical needle-punching and/or by water jet, thermal or chemical bonding.
13. A method according to one of claims 1 to 12, characterized in that the dynamic control forms part of a control loop also comprising means of measuring (31) at least one physical variable relating to the strip, and control means for modifying said dynamic control in function of the measured physical variable.
14. A method according to claim 13, characterized in that the measured physical variable is the widthwise (dc) shrinkage experienced by the strip during the consolidation procedure.
15. A method according to claim 13 or 14, characterized in that the physical variable relative to the distribution of orientations.
16. A method according to claim 15, characterized in that the physical variable relative to the distribution of orientations is determined by image analysis.
17. A method according to one of claims 13 to 16, characterized in that a double adjustment is carried out, on the one hand said adjustment exerting an influence on the distributions of orientations of the fibres, and on the other hand an adjustment of the surface weight of the strip at different points of its width by exerting an influence on a second dynamic control which substantially has no effect on the orientations of the fibres.
18. A method according to one of claims 1 to 17, characterized in that influence is exerted on the surface weight of the strip at different points of its width by a second dynamic control which substantially has no effect on the orientation of the fibres.
19. A method according to claim 17 or 18, characterized in that the second dynamic control affects the quantity of fibres collected by a carding machine doffer.
20. An installation for the production of non-wovens comprising:

    - a carding machine (1) providing at least one web (421, 422) of fibres;

    - a crosslapper (2) depositing the web in successive transversal segments on an exit (28) apron in order to form a lap (431, 432);

    - a consolidation machine such as a needle loom (3), or a water jet, thermal or chemical bonding device, downstream of the exit (28) apron;

    characterized in that it also comprises orientation means for exerting an influence on the distribution of orientations of the fibres according to their position along the width of the lap, in a method according to one of claims 1 to 19.
21. An installation according to claim 20, characterized in that the orientation means comprise means for adjusting a degree of condensation upstream of the crosslapper.
22. An installation according to claim 20 or 21, characterized by also comprising weight adjustment means for exerting an influence in a targeted manner on the local surface weight of the lap at different points of its width, the weight adjustment means having substantially no effect on the orientation of the fibres.
23. An installation according to claim 22, characterized in that the weight adjustment means comprise means for adjusting the quantity of fibres removed by a doffer (13) of the carding machine (1) on a cylinder (12) of the carding machine.
24. An installation according to claim 22 or 23, characterized by detection means (41) for detecting at least indirectly the surface weights of the lap at different sites of its width and for controlling the weight adjustment means according to the result of this detection.
25. An installation according to one of claims 20 to 24, characterized in that detection means, in particular those of claim 25, detect at least indirectly the width of the consolidated lap, and the installation comprises means for controlling the orientation means according to the detected width.
26. An installation according to one of claims 20 to 24, characterized by comprising images analysis means for detecting the orientation distribution of the fibres of the lap, the orientation means being controlled according to the result of this analysis.

Images