EP0027777A1 - Process and device for the simultaneous production of a plurality of filaments by electrostatic means, and application of the process to produce non-woven products or coverings - Google Patents

Abstract

The device comprises an inclined conducting plate (1) defining, in cooperation with a vertical conducting plate (8) arranged plumb with the central portion of the plate (1), a V-shaped longitudinal space (12) comprising at the lower part thereof a longitudinal opening (13). A hopper (15) arranged plumb with the plates (1 and 8) supplies the space (12) with thermoplastic material, which material is maintained at a molten state at the plates (1 and 8) by heating these plates by Joule effect. The molten bath thus provided in the space (12) gives rise to the formation of an even molten layer (25) flowing continuously by gravity along the lower portion (1b) of the plate (1). The flowing portion (25) arriving at the level of the lower edge (2) of the plate (1) is then subjected to a strong electrostatic field sufficiently concentrated on that lower edge (field provided by application, on a counter electrode 18 located at a distance from the edge 2, of D.C. high voltage by means of an HT source, the edge 2 being earthed) to drive the electrostatic drawing of that portion in the form of filaments (26). Application particularly to the production of non woven product.

Description

Technical area

The subject of the present invention is a method and a device for simultaneously manufacturing a plurality of filaments electrostatically, as well as products which can be obtained using such a method.

Prior art

The formation of fibers or filaments by electrostatic pulling has been a technique developed for a long time. The various methods proposed so far for such a formation of fibers or filaments are however not without presenting a certain number of drawbacks.

It has thus already been proposed, by way of example, to form fibers by electrostatic pulling from a molten thermoplastic substance disposed on the surface of a filiform substrate serving as a supply electrode (as described in English patent 1,484 .584). The major advantage of this process lies in its ability to be able to form a large number of fibers simultaneously, so that it is particularly suitable for the manufacture of nonwoven products. However, such a method has the great disadvantage of only giving rise to fibers of limited length, due to the finite mass of molten thermoplastic material deposited on the filiform electrode (the residual thermoplastic material remaining on the electrode in end of draw must also be eliminated from this electrode by burning, before being able to pro yield to a new supply of material, which constitutes an additional disadvantage for the process). The choice of materials which can be spun according to this process is also reduced to those of thermoplastic materials capable of being ground in the pulverulent state (the most suitable means for forming a regular layer of molten thermoplastic material on the filiform electrode consisting in fact coating this electrode with powdered material and then melting this powdered material), so that this choice remains relatively limited (all the materials cannot in fact be ground to the powder state).

It has also already been proposed to form fibers or filaments by electrostatic drawing from solutions sprayed in the electrostatic field (ccmne described for example in US Patent 1,975,5o4). As such a process generally requires the use of nozzles to spray the solution, it follows that the simultaneous production of a plurality of fibers or filaments requires the use of an equivalent number of nozzles, which doesn 'is not without causing a certain complication of the apparatus in the case where it is desired to simultaneously produce a large number of filaments. Such a process is moreover strictly limited to the electrostatic drawing of soluble substances.

Statement of the invention

The object of the present invention is precisely to at least partially remedy the aforementioned drawbacks, by proposing a particularly simple method making it possible to simultaneously produce a large number of fibers or filaments, this production being able, moreover, to be carried out from materials having very diverse initial forms.

• - former en continu sur au moins une surface inclinée une couche d'un matériau normalement diélectrique maintenue, au moins dans la partie inférieure de cette surface inclinée, dans un état suffisamment fluide pour pouvoir s'écouler en continu par gravité jusqu'au bord inférieur de cette surface inclinée, ledit matériau étant par ailleurs capable de solidification relativement rapide après cessation dudit maintien à l'état fluide et,
• - soumettre au moins la portion de ladite couche fluide arrivant sur ledit bord inférieur à l'action d'un champ électrostatique intense suffisamment concentré au voisinage de cette portion de couche fluide pour entraîner le tirage, à partir de cette portion de couche fluide de groupes de molécules progressant alors le long des lignes de forces électrostatiques en donnant lieu à la formation de filaments, lesquels se solidifient ensuite progressivement en s'éloignant dudit bord inférieur de ladite surface inclinée.

To this end, the subject of the present invention is a method for simultaneously manufacturing a plurality of filaments by electrostatic means, characterized in that it consists in:

• - Continuously forming on at least one inclined surface a layer of a normally dielectric material maintained, at least in the lower part of this inclined surface, in a state sufficiently fluid to be able to flow continuously by gravity to the lower edge of this inclined surface, said material being also capable of relatively rapid solidification after cessation of said maintenance in the fluid state and,
• subjecting at least the portion of said fluid layer arriving on said lower edge to the action of an intense electrostatic field sufficiently concentrated in the vicinity of this portion of fluid layer to cause the drawing, from this portion of fluid layer of groups molecules then progressing along the lines of electrostatic forces giving rise to the formation of filaments, which then solidify progressively away from said lower edge of said inclined surface.

• - au moins une surface inclinée,
• - des moyens pour former en continu sur ladite surface inclinée une couche dudit matériau normalement diélectrique, et pour maintenir cette couche, au moins dans la partie inférieure de cette surface inclinée, dans un état suffisamment fluide pour permettre son écoulement continu par gravité jusqu'au bord inférieur de ladite surface inclinée, et,
• - des moyens pour _'x'umettre au moins la portion de cette couche fluide arrivant sur ledit bord inférieur à l'action d'un champ électrostatique intense suffisamment concentré sur cette portion de couche fluide pour entraîner son tirage sous la forme de filaments.

The present invention also relates to a device for the implementation of such a method, characterized in that it comprises:

• - at least one inclined surface,
• - Means for continuously forming on said inclined surface a layer of said normally dielectric material, and for maintaining this layer, at least in the lower part of this inclined surface, in a sufficiently fluid state to allow its continuous flow by gravity until lower edge of said inclined surface, and,
• - Means for _'x' umitting at least the portion of this fluid layer arriving on said lower edge to the action of an intense electrostatic field sufficiently concentrated on this portion of fluid layer to cause its drawing in the form of filaments.

The present invention finally relates to the various products which can be obtained using such a method and / or device.

It can thus be seen that one of the essential characteristics of the process and / or device described above resides in the continuous formation on at least one inclined surface of a layer of a normally dielectric material maintained, at least in the lower part of this inclined surface, in a sufficiently fluid state to be able to flow continuously by gravity to the lower edge of this inclined surface, the simultaneous formation of a plurality of filaments then being obtained by electrostatic drawing. tick of at least the portion of this fluid layer arriving continuously on this lower edge. The realization of such a continuous flow of the spinnable material _'along a inclined surface has the major advantage of allowing a continuous flow of material at the lower edge of the inclined surface, and consequently the constant renewal of this material at this lower edge, as it is removed to give rise to the formation of filaments. The constant renewal of material in the electrostatic drawing zone (moreover assured, as can be seen, in a particularly simple manner) can in particular be used to ensure the formation of filaments of indefinite length.

The normally dielectric materials capable of being thus spun by the process according to the invention can be of very diverse nature, the essential thing being that they can be temporarily maintained in a sufficiently fluid state to allow their continuous flow in the form of a regular layer along an inclined surface, at the same time as their electrostatic drawing in the form of filaments (any dielectric material can indeed be electrostatically spun only if its viscosity can be lowered enough to allow the electrostatic forces of the '' prevail over the reaction forces developed by viscosity), while nevertheless being capable of relatively rapid solidification after cessation of their maintenance in this fluid state (in order to allow the filaments obtained present, when arriving on their receiving surface, a degree solidification sufficiently pronounced not to be forced to automatically give back t instead of a continuous fluid layer).
As materials capable of meeting the abovementioned requirements, we may thus in particular consider, in a particularly advantageous manner, the use of thermoplastic or hot-melt materials, namely materials capable of being brought into a sufficiently fluid state by heating, and of then be re-solidified sufficiently quickly (all the more quickly since it is a question of filaments of relatively small section) by simple cooling (in principle natural cooling, nevertheless capable of being reinforced by any suitable means, such as for example circulation of gas against the current of the direction of progression of the filaments). Rod thermoplastic or hot-melt materials possible (the expression "thermoplastic materials" should here be understood in a much broader sense than that normally used in the field of plastics), it will thus be possible to envisage spinning plastics such as polypropylene, polyethylene, etc ..., inorganic materials such as glasses, etc ... or other very diverse materials such as coal or petroleum pitch, chocolate, etc. The layer intended to be formed continuously on the inclined surface according to the invention by means of such thermoplastic or hot-melt materials can advantageously be maintained in a sufficiently fluid state (to allow its continuous flow along this inclined surface) by adequate heating of this inclined surface, such heating of this inclined surface may, in a particularly advantageous manner, be achieved by the Joule effect, while providing for using r an inclined surface made of an electrically conductive material (such an electrically conductive material should however be chosen so as to have a sufficiently high resistivity to allow good energy dissipation, as well as a sufficiently strong oxidation resistance to prevent any risk of oxidation during its heating, so that it may advantageously consist of one of the types of materials normally used as a resistive heating element in electric heaters). The actual formation of the layer of thermoplastic or hot-melt material on the inclined surface can, for its part, be carried out in very different ways (which will be described later), the thermoplastic or hot-melt material being able in particular to be poured onto the inclined surface under a still solid form (and brought into a sufficiently fluid state only after contacting the inclined surface) or on the contrary in an already fluid form or even completely melted. It can therefore be seen that the above-described formation process of the continuous flow of material along the inclined surface allows the use of thermoplastic or hot-melt materials likely to be presented in the most diverse initial forms such as powder, granules, flakes, mass pays, melt, etc ...

Like other materials capable of being spun by the process according to the invention, it is also possible to envisage using materials temporarily maintained in solution in easily evaporable solvents, these materials in the form of solutions then being poured directly onto the inclined surface of so as to form a film of liquid flowing continuously by gravity to the lower edge of this inclined surface, the filaments drawn electrostatically from this edge then gradually solidify under the effect of the evaporation of the solvent (in principle natural evaporation, nevertheless capable of being reinforced by any appropriate means).

The above-described formation of a flow of spinnable material along the inclined surface will advantageously be implemented so as to provide a flow of material at the lower edge of this inclined surface which is adapted to the production rate of the filaments ( too high flow rate that could indeed _of on- ner in the formation of a film or web instead wish filaments, and a low output inversely risk of giving rise to the simple formation of droplets). This continuous flow of spinnable material along the inclined surface will moreover preferably be adjusted so as to give a flow of material at the lower edge of this inclined surface which is regular over the entire extent of the lower edge as well as constant over time, so as to allow the formation of regular filaments with constant characteristics and reproducible over time (the diameter of the filaments obtained depends in particular directly on this flow of material at the lower edge of the inclined surface). This adjustment of the material flow rate can be carried out in various ways, which will be explained later.

The establishment of an intense electrostatic field, sufficiently concentrated in the vicinity of the portion of fluid material arriving on the lower edge of the inclined surface to allow the electrostatic drawing of this portion in the form of filaments, can in turn be used, in a well known manner through the use of two suitable electrodes connected to one and the other terminals of an adequate direct high voltage source, namely, a first electrode provided a relatively sharp edge extending in the immediate vicinity of the portion of material to be electrostatically drawn, and a second electrode (or counter-electrode) of relatively large extension extending opposite and at a distance from this first electrode. This first electrode provided with a relatively sharp edge can, in a particularly advantageous manner, be precisely constituted by the lower edge of the inclined surface supporting the fluid layer of spinnable material, in the case where this inclined surface is made of an electrically conductive material (this lower edge then having to be shaped according to a profile which is sufficiently "sharp" to give rise to the required field concentration). This first electrode provided with a relatively sharp edge can nevertheless, in certain application cases, be constituted by an annex electrode entirely distinct from this lower edge (the inclined surface then being able in particular in such a case to be made of a material not electrically driver).

The filaments thus obtained by electrostatic drawing can be collected directly on the counter-electrode placed at a distance from the field concentrating electrode, or alternatively on any other suitable receiving surface interposed in front of this counter-electrode (for example receiving surface constituted by tissue , paper, or other suitable material). The filaments thus obtained by electrostatic drawing can also (taking into account the ability of the method according to the invention to be able to produce filaments of indefinite length) be advantageously subjected to a drawing operation before reaching their receiving surface, this drawing operation which can be carried out by all the appropriate cores (such as for example drawing trains arranged on the path of the filaments upstream of their receiving surface).
The filaments thus collected on an entire suitable receiving surface can then be the subject of very diverse applications such as production of non-woven products, formation of a continuous coating on an appropriate surface by subsequent melting of the filaments thus collected on this surface, etc.

In the method and / or device according to the invention, the inclined surface intended to allow a continuous supply of a spinnable material into the electrostatic drawing zone can finally take very diverse forms, depending on the type of applications envisaged. This inclined surface can thus take the form of a flat plate (inclined with respect to the vertical) of relatively large longitudinal extension, in the case where it is desired, for example, to collect the filaments on flat receiving surfaces (the counter-electrode can then in this case advantageously be constituted by a flat conductive plate of longitudinal extension substantially equivalent to that of the drawing zone, arranged horizontally below and at a distance from the rectilinear lower edge of this flat inclined plate). This inclined surface can also take the form of a frustoconical surface, in the case where it is desired for example to collect the filaments on tubular receiving surfaces (the counter-electrode can then in this case advantageously be constituted by a conductive plate annular disposed concentrically to the axis of revolution of the frustoconical inclined surface, at height and at a distance from the circular lower edge of the latter.

Finally, the method and / or device according to the invention is not, of course, in any way limited to the use of a single inclined surface (although mention has hitherto been made of a single surface in the description), and on the contrary, it is quite possible to envisage the simultaneous use, in the same apparatus, of a plurality of inclined surfaces arranged one next to the other, so as to allow the simultaneous production of several pluralities of filaments. Such production can in particular be taken advantage of so as to allow the production of non-woven multilayer products of relatively large overall thickness (receiving surface then passing successively vertically below each of the inclined surfaces), the mn-woven products thus made which can also be optionally composite (by providing a supply of different materials on the different inclined surfaces).

Brief description of the drawings

• La fig.l est une vue en perspective schématique, illustrant une première forme d'exécution.
• La fig.2 est une vue en coupe longitudinale partielle aggran- die, selon l'axe II - II de la fig.l, illustrant un détail de cette première forme d'exécution.
• La fig.3 est une vue en coupe longitudinale, illustrant une variante de cette première forme d'exécution.
• La fig.4 est une vue en coupe longitudinale analogue à celle de la fig.3, illustrant une deuxième forme d'exécution.
• La fig.5 est une vue en coupe longitudinale analogue à celle de la fig.3 illustrant une première variante de cette deuxième forme d'exécution .
• La fig.6 est une vue en coupe longitudinale analogue à celle de la fig.3, illustrant une seconde variante de cette deuxième forme d'exécution.
• La fig.7 est une vue en coupe axiale, illustrant une troisié- me forme d'exécution.
• La fig.8 est une vue en coupe longitudinale, illustrant une quatrième forme d'exécution.

The attached drawing illustrates, schematically and by way of example, several embodiments as well as variant devices for implementing the method according to the present invention.

• Fig.l is a schematic perspective view, illustrating a first embodiment.
• Fig.2 is an enlarged partial longitudinal sectional view, along the axis II - II of Fig.l, illustrating a detail of this first embodiment.
• Fig.3 is a longitudinal sectional view, illustrating a variant of this first embodiment.
• Fig.4 is a longitudinal sectional view similar to that of Fig.3, illustrating a second embodiment.
• Fig.5 is a longitudinal sectional view similar to that of Fig.3 illustrating a first variant of this second embodiment.
• Fig.6 is a longitudinal sectional view similar to that of Fig.3, illustrating a second variant of this second embodiment.
• Fig.7 is an axial sectional view, illustrating a third embodiment.
• Fig.8 is a longitudinal sectional view, illustrating a fourth embodiment.

Best Ways to Carry Out the Invention

The first embodiment shown in FIGS. 1 and 2 can take an electrically conductive flat plate 1 of rectangular shape, the longitudinal extension of which is relatively high compared to its transverse extension (for example longitudinal extension of about 100 cm for a transverse extension of approximately 2cm). This flat conductive plate 1 is mounted by its respective ends to la and lb on two inclined insulating arms 3a and 3b (themselves connected to a frame 4), so as to be held in an inclined position relative to the vertical in its transverse direction (inclination of the plate 1 chosen of the order of 45 °) while extending substantially horizontally in its longitudinal direction. The conductive plate 1 is also my tee on the respective inclined arms 3a and 3b so that it can be put under mechanical tension in its longitudinal direction. To this end, one of the ends 1a of this plate 1 is held in a fixed position on the corresponding inclined arm 3a (for example by means of screws), while its other end 1b is connected to the other inclined arm. 3b by means of threaded rods sliding freely through this arm 3b, so as to allow the mechanical tensioning of the plate 1 by compression, by means of nuts 7, of springs 6 threaded on the free end of the rods 5 projecting from the rear face of the inclined arm 3b. The lower end of this inclined plate 1 is also curved backwards, so as to delimit a straight lower edge 2 having a rounded profile with a relatively small radius of curvature (for example radius of curvature of the order of 0, 4mm, the thickness of the plate 1 being also of the order of 0.3mm).

Plumb with the front face of this inclined plate 1 is also arranged an electrically conductive flat counter plate 8 of rectangular shape, whose longitudinal extension is equivalent to that of plate 1, and whose lower end is also advantageously bent backwards (namely towards its face opposite to that facing the plate 1) so as to delimit a straight lower edge 9 with a rounded profile. This conductive counter plate 8 is mounted by its respective ends 8a and 8b on two vertical insulating arms 10a and 10b (themselves connected to a frame 11), so as to be held in its transverse direction in a substantially vertical position, while extending by its lower rectilinear edge 9 above the substantially central part of the front face of the plate 1. The mounting of this counterplate 8 on its respective vertical arms 10a and 10b is also carried out so analogous to the mounting of the plate 1 on its respective inclined arms 3a and 3b, so as also to allow the mechanical tensioning of this counterplate 8.

The inclined plate 1 and the vertical plywood 8 are thus arranged one with respect to the other in such a way that the vertical plywood 8 delimits in cooperation with the par upper tie the one of the plate 1 a longitudinal space 12 in the form of a V, the lower rectilinear edge 9 of the counter plate 8 delimiting, moreover, with the corresponding portion of the plate 1 a longitudinal opening 13 of constant width (under which s 'extend the lower part Id of the plate 1 provided with its lower rectilinear edge 2). The width of this longitudinal opening 13 is moreover capable of being adjusted by vertical movement of the chassis 11, using appropriate means not shown in the drawing (vertical movement shown diagrammatically in the drawing by the arrow F).

Above the V-shaped longitudinal space 12 thus delimited by the plates 1 and 8 is disposed a hopper 15 made of an electrically insulating material, fixed to the respective arms 3a and 3b of the chassis 4 by means of lugs fastening 16. This hopper 15, which is intended to be filled with a thermoplastic material in the solid state capable of being in any suitable initial form, is arranged above the longitudinal space 12 so that its longitudinal walls just come flush with the respective upper edges of the plates 1 and 8 (fig. 2), in order to allow the thermoplastic material delivered by this hopper 15 to come freely to contact the walls opposite the respective plates 1 and 8 (this hopper 15 being furthermore designed so that its end walls, on the other hand, extend to the bottom of the V-shaped space 12, in order to prevent the material 12 from being able to escape laterally).

The electrically conductive plates 1 and 8 are also intended to be traversed by a longitudinal electric current in order to allow their heating by Joule effect, so as to cause a sufficient softening of the thermoplastic material thus brought into contact with them (the constituent electrically conductive material of these plates 1 and 8 must then be chosen so as to be sufficiently resistive to allow good dissipation of energy, as well as sufficiently resistant to oxidation to prevent any corrosion during its heating). For this purpose, the respective ends 1b and 8b of these plates are intended to be connected to one of the poles of a source of ten alternative Zion S (of the order of 10V), the other pole of which is connected to ground, the other ends 1a and 8a of these plates also being also connected to ground.

Below and at a distance from the lower rectilinear edge 2 of the conductive plate 1 is finally disposed a horizontal metal plate 18 of longitudinal extension substantially identical to that of the hopper 15, intended to be connected to one of the (positive poles or negative) from a high voltage direct current HV source (of the order of 20 to 40 kv), the other pole of which is connected to ground.

This metal plate 18 thus capable of being brought to a continuous high voltage is intended to allow the establishment in cooperation with the lower rectilinear edge 2 of the plate 1 connected to ground (apart from the low alternating voltage established in the direction longitudinal of the plate 1), of an intense electrostatic field coming to be concentrated on this lower edge 2 (this lower edge 2 thus playing the role of a field concentrating electrode in the device thus described, and the metal plate 18 that of 'a counter electrode). In front of the counter-electrode 18 is finally interposed a flexible receiving surface 19, capable of being drawn continuously from a supply roller 20 to be rewound continuously on a storage roller 21, by means of a motor drive 22 mounted on the roller shaft 21.

• La trémie 15 étant remplie de matériau thermoplastique 23 à l'état solide (l'ouverture 13 délimitée entre les plaques 1 et 8 étant au besoin fermée par abaissement de la plaque 8 en vue d'empêcher le passage de particules solides 23, au cas où ces dernières auraient une taille inférieure à la largeur de l'ouverture 13 désirée pour la suite du processus), la source de tension alternative S est alors branchée sur les plaques respectives 1 et 8 comme indiqué précédemment, de façon à permettre leur échauffement par effet Joule. Cet échauffement par effet Joule a alors pour effet d'entraîner la fusion des portions de matériau thermoplastique se trouvant au contact des plaques 1 et 8, puis de proche en proche, la fusion des portions de matériau thermoplastique plus éloignées de ces plaques, donnant ainsi rapidement lieu à la formation d'un bain fondu 24 occupant tout l'espace 12 délimité entre les plaques 1 et 8.

The operation of the above-described device is then as follows:

• The hopper 15 being filled with thermoplastic material 23 in the solid state (the opening 13 delimited between the plates 1 and 8 being closed if necessary by lowering the plate 8 in order to prevent the passage of solid particles 23, in the case where the latter would have a size less than the width of the opening 13 desired for the rest of the process), the alternating voltage source S is then connected to the respective plates 1 and 8 as indicated above, so as to allow them to heat up by Joule effect. This heating by Joule effect then has the effect of causing the melting of the portions of thermoplastic material being in contact with the plates 1 and 8, then from close nearby, the melting of the portions of thermoplastic material more distant from these plates, thus quickly giving rise to the formation of a molten bath 24 occupying all the space 12 delimited between the plates 1 and 8.

The opening 13 is then restored to the desired width for the rest of the process, thus giving rise to the formation of a regular molten layer 25 flowing continuously by gravity along the lower part ld of the plate 1, according to a perfectly constant flow over time. The perfectly constant nature of this flow is explained by the fact that it only depends on the height of the molten bath 24, which is precisely fixed by the free height of the heated plates 1 and 8 above the opening. 13, as well as the width of the opening 13, which is also precisely fixed by the rigorous arrangement of the plates 1 and 8 relative to each other (any risk of deviation in the width of this opening 13, likely to occur due to the heating of the plates 1 and 8, being precisely suppressed by the mechanical tensioning of these plates 1 and 8).

The continuous flow 25 having progressed by gravity to the lower edge 2 of the plate 1, the continuous high voltage source HT is then connected to the counter-electrode 18 as indicated above, so as to ensure the establishment of a field intense electrostatic, the lines of electrostatic forces of which concentrate sufficiently on the lower edge 2 to cause the electrostatic pulling, from the flow portion 25 arriving on this lower edge 2, of groups of molecules then progressing along the lines of forces in the form of filaments 26 propelled in the direction of the counter-electrode 18 (these filaments 26 still fluid near the electrostatic pulling zone solidifying progressively further away from this pulling zone). The filaments 26 thus propelled towards the counter-electrode 18 are then collected on the flexible receiving surface 19, the distance between this receiving surface 19 and the field concentrating electrode 2 being moreover chosen large enough for the filaments 26 to arrive on this receiving surface with a degree of solidification sufficient to allow them to keep their filament shape. The filaments 26 thus obtained are moreover capable of being drawn according to indefinite lengths, taking into account the constant renewal of the portion of material 25 fed continuously on the field concentrating electrode 2.

The electrostatic drawdown described above is of course made possible only by the fact that the material to be spun is undoubtedly electrostatically charged when arriving at the electrode 2 (an electrostatic field applied to a non-electrically charged particle remaining in effect obviously without action on this particle). It is nevertheless difficult to give a rigorously exact scientific explanation of the mechanism by which this thermoplastic material is effectively charged upon its arrival on the electrode 2. One can always try to explain such a charging mechanism by the fact that the concentration of field at the level of the electrode 2 must probably prove to be sufficient to ionize the ambient atmosphere prevailing around this electrode, so that this ionized atmosphere can then in turn charge the flow portion 25 arriving at the level of the electrode 2 ("corona" effect). Such a charging mechanism attributable to the "corona" effect could possibly be reinforced by another charge recanism, attributable to a certain displacement of charges inside the molten thermoplastic material arriving at the electrode. (displacement of charges made possible by the fact that certain thermoplastic materials are capable, while they are normally dielectric in the solid state, of exhibiting seyi = conductive properties in the molten state). The rigorously exact explanation of such a charging mechanism is however absolutely not essential for a good understanding of the process according to the invention, the teaching given elsewhere as to this process appear indeed amply sufficient to allow its reproduction by those skilled in the art, even without precise knowledge of this charging mechanism.

The device shown in fig.l and 2 could thus, by way of example, be used to ensure the formation of polypropylene filaments of indefinite length. To do this, the parties polypropylene cules introduced in the solid state into the hopper 15 were heated using the plates 1 and 8 to a temperature of about 250 ° C, so as to give rise (the length of the opening 13 being fixed at approximately 1 mm, and the height of the molten bath 24 at approximately 10 mm) to the production of a continuous flow 25 along the lower part of the inclined plate 1 which has a viscosity of the order of 100 Newtons x sec / m ² , as well as a mass flow rate of the order of 5 mg / sec per unit length (meter) of the inclined plate 1. The application to the counter-electrode 18 (disposed about 10 cm below the concentrator electrode 2) with a high continuous voltage of the order of 20 KV then makes it possible to obtain the production of polypropylene filaments of indefinite length, having a relatively regular cylindrical shape (in particular without any presence of drops) of approximately 5 microns in diameter.

In the example described above, it is also possible to choose to form “multi-branch” filaments instead of forming monofilaments as previously, while then providing to apply to the counter-electrode 18 a high continuous voltage which is greater than 40 KV.

Fig.3 illustrates a variant of the form of execution of Figs. 1 and 2, which differs essentially from the latter (the identical elements remaining assigned the same reference signs of the drawing) by the fact that the lower part ld of the inclined plate 1 is here curved towards the rear face of the upper part lc of this plate 1, instead of extending in the extension of this upper part (as before), in order to allow the production of a regular layer 25 which flows continuously under this lower part ld, instead of flowing over this lower part as before (the flow 25 remaining here nevertheless pressed against the lower part ld thanks to the surface tension). This variant has the advantage of allowing the entire extent of the flow 25 to be located opposite the counter-electrode 18, instead of the only lower portion of this flow as previously, which ensures better electric charge of the material to be electrostatically drawn (the electrostatic field being located effect here applied to the entire extent of the flow 25, instead of being applied to the sole lower portion of this flow as previously).

Fig.4 illustrates a second embodiment of the device according to the invention, which differs from the first embodiment of Fig.l and 2 essentially by the means used to form the continuous flow of thermoplastic material 25 on the inclined plate 1. (The elements of this second embodiment identical to those of the first embodiment remaining assigned the same signs of reference to the drawing). In this second embodiment represented in FIG. 4, the means making it possible to produce a reservoir of molten material above the inclined plate 1 (namely, use of a hopper 15 in combination with a vertical counterplate 8) are here simply deleted, and replaced by a simple hopper 31 disposed directly above the upper part of the inclined plate 1. This hopper 31 is responsible for discharging, via an adjustable valve 32, particles of thermoplastic material in the solid state directly on the upper part of the plate 1. The heating of this plate 1 by Joule effect then has the effect of causing the adhesion of the solid particles arriving in contact, these particles adhering to the plate 1 then gradually softening under the effect of the heating of this plate to give rise to the formation of a regular layer quickly brought into a sufficiently fluid state to cause its continuous flow u 25 along the plate 1. The flow rate of this continuous flow 25 can for its part be adjusted to the desired value by appropriate actuation of the control valve 32. The continuous flow 25 thus produced can then be electrostatically drawn in the form of filaments 26, as it arrives at the electrode 2, in the manner already described above.

Fig.5 illustrates a first variant of the embodiment shown in Fig.4 (identical elements remaining assigned the same signs of reference to the drawing), which differs essentially from the latter by the complementary use of a wire additional electrically conductive 41 extending below the lower edge of the inclined plate 1. This wire 41 is also connected to ground so that it serves as a field concentrator electrode in place of the lower edge 2 (the 3rd field lines coming to concentrate on this wire 41 instead of concentrating on the lower edge as before ). The electrostatic field no longer acting at the lower edge 2, the layer 25 maintained in continuous flow along the inclined plate 1 by the heating of this plate then simply spills onto the wire 41 also heated by Joule effect , so that the filaments 26 are now drawn continuously from this thread 41.

This variant has the major advantage of allowing the thermoplastic material to be heated in two successive stages of unequal duration, namely a first stage of relatively long duration at the inclined plate 1, during which the material is heated to a sufficient temperature. weak to avoid its degradation (but nevertheless sufficient to allow its flow along this plate), and a second short-term step at the level of the wire 41, during which the material is rapidly heated to a temperature sufficient to allow it to be drawn electrostatic (temperature allowing its viscosity to be lowered to a sufficiently low value for the electrostatic forces to prevail over the viscosity forces).

Fig.6 illustrates a second variant of the embodiment shown in Fig.4. (the identical elements remaining assigned the same signs of reference to the drawing), according to which the filaments are drawn from a material in solution instead of a thermoplastic or hot-melt material as previously. In this second variant, the hopper 31 is replaced by a tube 51 provided with a longitudinal slot 52, placed directly above the upper part of the inclined plate 1. This tube 51, which is connected by means of an adjustment valve 53 to a reservoir 54 filled with material in solution, is responsible for pouring onto the inclined plate 1 a film of solution 25 continuously flowing by gravity along this plate 1 (the flow of this continuous flow 25 being moreover capable of being adjusted by means of the valve 53). Plate 1 having in this va laughing no need to be heated by Joule effect in order to ensure the continuous flow of the material to be spun, the latter can then very well be made of a dielectric material instead of a conductive material as before. The field concentration necessary to ensure the electrostatic pulling of the filaments can then in this case be advantageously ensured by an annex electrode in the form of a blade 55 connected to ground, arranged so that its sharp edge 55a points towards the portion of solution 25 arriving at the lower edge 2 of the plate 1. In the device of this FIG. 6, the receiving surface 19 is also, as a complementary variant, made of an electrically conductive material (for example a metallic mesh), so that one can then consider purely and simply suppressing the counter-electrode 18, and connecting the high voltage source HT directly to this conductive surface 19, by means of a sliding contact 56.

Fig.7 illustrates a third embodiment of the device according to the invention, intended to allow the drawing of filaments from a circular drawing area, in order to obtain that these filaments can be collected on a receiving surface tubular. This embodiment comprises an inclined electrically conductive surface 61 of frustoconical shape, provided with a circular lower edge 62. This frustoconical surface 61 is electrically interrupted in the circumferential direction by an insulating strip 63 extending along a of its generators, so as to allow it to heat up by the Joule effect by means of an alternating current source S suitably connected by its two poles to this surface 61 (ie on either side of the insulating strip 63, one poles of this source S being also grounded). In line with the top of the frustoconical surface 61 is also arranged a hopper 64, responsible for discharging a pulverulent thermoplastic material on the upper part of the external face of this frustoconical surface 61. The heating by Joule effect of this surface 61 then gives rise to the formation of a regular layer 65 continuously flowing over the entire periphery of the truncated surface 61, until it reaches the circular lower edge 62 of this surface 61. Con centrally at the surface 61, and at the edge 62, is also arranged an annular counter-electrode 68, connected to one of the poles of a high voltage direct current source HV whose other pole is connected to ground . The portion of material 65 arriving continuously on the circular lower edge 62 is thus subjected to an intense electrostatic field sufficiently concentrated on this portion to allow the electrostatic drawing of the latter in the form of filaments 26, which are then likely to be collected on a tubular receiving surface 69 in axial movement in front of the counter-electrode 68.

Fig.8 illustrates a fourth embodiment of the device according to the invention, which differs from the first embodiment of Fig.l and 2 essentially in that it comprises a plurality of rectilinear stretching zones arranged one beside the other instead of having only one as in this first embodiment (the identical elements remaining assigned the same signs of reference to the drawing). This embodiment thus comprises a plurality of inclined plates 1 extending one beside the other on the same horizontal level, with each of which there is associated a counter plate 8 as described previously in FIGS. 1 and 2. The different longitudinal spaces 12 in shape (the V delimited between these pluralities of plates 1 and 8 are capable of being supplied with thermoplastic material in the pulverulent state by a single hopper 75, the heating by Joule effect of these pluralities of plate 1 and 8 then giving rise to the formation of continuous flows 25 progressing along the lower part of each of the plates 1 until reaching their straight edges 2. The different pluralities of filaments 26 drawn electrostatically from each of these edges rectilinear 2 (by means of a single counter-electrode 18 extending below the different concentrating electrodes 2) can then be collected successively on a recessed surface single appropriate eptrice 19 parading in front of the counter electrode 18, in order to allow for example the production of non-woven multilayer products of relatively high overall thickness. The non-woven products thus obtained are moreover capable of being composite, while planning to carry out contributions of different materials on the different inclined plates 1 (then providing for example to use a compartmentalized hopper 75, as sketched in dotted lines in the drawing, so as to allow the filling of the different compartments with different materials).

Claims (4)

1. Method for simultaneously manufacturing a plurality of filaments by electrostatic means, characterized in that it consists in: - continuously forming on at least one inclined surface a roll of a normally dielectric material maintained, at least in the lower part of this inclined surface, in a sufficiently fluid state to be able to flow continuously by gravity to lower edge of this inclined surface, said material being moreover capable of relatively rapid solidification after cessation of said maintenance in the fluid state, and, subjecting at least the portion of said fluid layer arriving on said lower edge to the action of an intense electrostatic field sufficiently concentrated in the vicinity of this portion of fluid layer to cause the drawing, from this portion of fluid layer, of groups of molecules then progressing along the lines of electrostatic forces giving rise to the formation of filaments, which then solidify progressively away from said lower edge of said inclined surface. 2. Device for implementing the method according to claim 1, characterized in that it comprises: - at least one inclined surface - Means for continuously forming on said inclined surface a layer of said normally dielectric material, and for maintaining this layer, at least in the lower part of this inclined surface, in a sufficiently fluid state to allow its continuous flow by gravity until lower edge of said inclined surface, and, - Means for subjecting at least the portion of this fluid layer arriving on said lower edge to the action of an intense electrostatic field sufficiently concentrated on this portion of fluid layer to cause its draft in the form of filaments. 3. Application of the method according to claim 1 for the production of non-woven products. 4. Application of the method according to claim 1 for the production of continuous coatings on a suitable substrate.

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