DEVICE FOR IMPREGNATING A FIBROUS SUPPORT WITH POWDER

Abstract

The invention relates to a device (100) for impregnating a fibrous or porous support (S) with a powdery material (P), comprising: - means for setting the support (S) in motion (1), - means for depositing (5) the powdery material (P) on one side of the support (S), - transverse electrodes (4), connected to terminals of alternating voltage generators (G1, G2, G3), generating an electric field applied to the path of the support (S) set in motion, characterized in that the generators (G1, G2, G3) generate alternating potentials (u, v, w) phase-shifted two by two by 10 to 180°, the neighboring electrodes (4) being alternately connected to a different potential (u, v, w) in the direction of progression of the support (S). Figure for the abstract: [Fig. 1]

Description

Title of the invention: DEVICE FOR IMPREGNATING A FIBROUS SUPPORT WITH POWDER Technical field

[0001] The present invention relates to the field of impregnation of porous supports with powdery materials. The supports are, for example, textiles or non-woven and / or agglomerated porous materials.

[0002] The supports are to be treated by impregnation with powders having physicochemical properties, for example thermoplastic, thermosetting, retardant or flame-retardant powders, disinfectant, hydrophobic powders, etc. Previous Art

[0003] Document FR3114261 describes an installation for impregnating powder into a fibrous or porous support. The installation described comprises means for moving the support, on which the powder is deposited.

[0004] The support with the powder is then transported in a longitudinal direction between electrodes connected to an alternating voltage generator, the electrodes on each side of the support being connected to one of the terminals of a voltage generator.

[0005] The electrically charged powder will be driven by the electric field, perpendicular to the two electrodes, in particular towards the center of the support. The powder then impregnates the support.

[0006] By means of this process, the poorly polarizable powders are impregnated in a relatively homogeneous manner, with however in places an agglomeration of powder grains by electrostatic effect, which results in almost point inhomogeneities distributed randomly, which can degrade the performance of the product obtained.

[0007] On the other hand, in the case of conductive or polarizable powders, the electrostatic forces have a strong tendency to create large agglomerates, which makes the inhomogeneities very significant, by concentrating the particles in the form of point groupings which can in particular remain mainly outside the substrate.

[0008] There is therefore a need for a device allowing better impregnation of powders by homogenizing the distribution of said powder, and in particular when the powder is polarizable or has a certain electrical conductivity. Presentation of the invention

[0009] In order to address this technical problem, the invention proposes a device for impregnating a fibrous or porous support with a powdery material, comprising: - means of moving the support, - means for depositing the powdered material on one side of the support, - transverse electrodes, connected to terminals of alternating voltage generators, generating an electric field applied to the path of the moving support.

[0010] The device according to the invention is characterized in that the generators generate alternating potentials phase-shifted two by two by 10 to 180°, the neighboring electrodes being alternately connected to a different potential in the direction of progression of the support.

[0011] By generating a longitudinal component of electric field, the phase-shifted potentials set the agglomerates of powdery material in longitudinal motion, which disperses them

[0012] The device according to the invention may further have one or more of the following characteristics.

[0013] The phase shift of the electrode potentials can be between 10 and 45°, more particularly between 15 and 30°.

[0014] This smaller phase shift makes it possible to avoid breakdown between two neighboring electrodes.

[0015] The device may comprise one or more generators generating three potentials and the neighboring electrodes are then each connected to a different potential of said one or more generators.

[0016] Devices with three potentials with different phases make it possible in particular to generate an electric field with complex shapes allowing significant agitation of the particles of powdered material.

[0017] The device may comprise one or more generators generating two potentials and the neighboring electrodes are then each connected to a different potential of said one or more generators.

[0018] The electrodes connected to the different potentials can be located on the same side of the support, and, on the other side of the support, no electrode is present opposite or a plate electrode with floating potential is present.

[0019] The electrodes connected to the different potentials can be located on the same side of the support, and, on the other side of the support, a single plate electrode connected to ground is present.

[0020] The electrodes may comprise a succession of pairs of electrodes each connected to one of two potentials, located on the same side of the support, and, on the other side of the support, a plate electrode connected to ground.

[0021] The electrodes may comprise electrodes on each side of the support, with facing electrodes connected to the same potential among the three or facing electrodes connected to potentials that are out of phase two by two.

[0022] In practice and generally, the different potentials can be generated by several separate and synchronized generators, or by a single generator having several output terminals. Combinations of these two options are possible.

[0023] The means for moving the support may comprise: - an endless conveyor with cyclic movement, which has an external face comprising asperities, the powder depositing means depositing the powder in the asperities of the external face, - means for compressing the support configured to press the support against the external face of the endless conveyor with the asperities filled with powder, - the endless conveyor passing at the level of the electrodes during its cyclic movement with the support pressed against the external face whose asperities contain powder.

[0024] If the support is a thin or narrow wire or strip, the device may comprise a tubular containment member, through which the support to be treated or impregnated passes and into which powder is also poured, the electrodes being located at the level of said containment member, between an inlet of the support and the powder and an outlet of the impregnated support.

[0025] The electrodes may in particular have potentials with offset phases with an increasing phase shift in the direction of progression of the support to drive the powdery material in the direction of progression of the support by variation of the electric field.

[0026] Alternatively, the electrodes may have potentials at offset phases with a decreasing phase shift in the direction of progression of the support to drive the powdery material in the opposite direction of progression of the support by variation of the electric field.

[0027] The invention also relates to the method of impregnating a fibrous or porous support with a powdery material by applying an electric field, comprising the steps: - movement of the support, - depositing powdered material against a surface of the moving support, characterized in that it further comprises the step: - conveying the support with the powdered material to the level of electrodes connected to generators generating alternating potentials phase-shifted two by two by 10 to 180°, the neighboring electrodes being alternately connected to a different potential in the direction of progression of the support. Brief description of the figures

[0028] The invention will be clearly understood on reading the following description, the details of which are given solely by way of example, and developed in relation to the appended figures, in which identical references refer to identical elements:

[0029] [Fig. 1] is a schematic representation in side view of an embodiment of an impregnation device according to the invention,

[0030] [Fig.2] is a longitudinal sectional view of the electrodes of the device of [Fig.l] and of the electric field vectors at different times of an oscillation period,

[0031] [Fig.3] is a schematic side view representation of an alternative embodiment of an impregnation device,

[0032] [Fig.4] is a partial perspective schematic representation of a third embodiment of an impregnation device for a narrow or wire support,

[0033] [Fig.5],

[0034] [Fig.6],

[0035] [Fig.7],

[0036] [Fig.8] and

[0037] [Fig.9] are schematic representations of different electrode arrangements for the impregnation devices of Figures 1, 3 and 4.

[0038] The particular embodiments shown are given for illustrative and non-limiting purposes. Certain elements are shown schematically, and with false proportions. In particular, the powder particles are shown visible separately for better understanding, but their actual size may be micrometric or even nanometric, making them invisible to the naked eye. Detailed description of the invention

[0039] [Fig.l] is a schematic representation in side view of a device 100 for impregnating a fibrous or porous support S according to a first embodiment of the invention.

[0040] The impregnation device 100 comprises means 1 for moving the support S, here a longitudinal conveyor, which moves the support along a longitudinal axis with a predetermined direction of progression, denoted by an arrow.

[0041] In particular, the support S may be an open-cell foam, a sheet or a fabric of braided or non-woven fibers. The conveyor may, for example, take the support S from a roll and, at the outlet, deliver it to a winder which reconditions it into a roll.

[0042] The impregnation device 100 comprises means 5 for depositing a pulverulent material or powder P, for example a sprinkler, a doser, a pourer or a grid through which the particles of powder P pass.

[0043] The deposition of powder P is done, in the example of [Fig.l], by gravity by means of a pourer 5 which pours powder P by gravity, with possibly mechanical agitation of the pourer 5 to set it in motion. The deposition is consequently done on the upper surface of the support S.

[0044] A deposition of powder P on the lower face is however possible, for example by means of a blower or by depositing the powder on the conveyor 1 then covered by the support S.

[0045] The support S coated with powder P then passes in the direction of progression under a containment conveyor 3, which covers the powder P and serves to confine it spatially.

[0046] The support S then passes under transverse electrodes 4, here three in number, and connected to alternating high voltage generators Gl, G2, G3, which generate three phase-shifted potentials u, v, w, each supplying one of the electrodes 4.

[0047] These electrodes 4 are for example produced in the form of a thin metal strip deposited on a dielectric support.

[0048] The generators Gl, G2, G3 generate in particular potentials of the order of several thousand or even tens of thousands of volts.

[0049] The electrodes 4 are phase-shifted two by two by an angle generally of 10 to 180°. By passing under the electrodes 4, the powder is stirred by electrostatic forces, and penetrates into the support S, which then impregnates said support S with a controllable gradient in its thickness, or even with a homogeneous distribution of the powder P in the thickness of the support S.

[0050] The phase shift between the electrodes 4 induces a component of the electric field parallel to the support, which longitudinally displaces the powder P. This results in a disruption of the agglomerated powder P packets which could form by electrostatic attraction of the powder P particles when the latter is polarizable or sufficiently conductive. This phenomenon is linked to the generation of a progressive and not a stationary wave in the impregnation zone.

[0051] However, significant phase shifts, for example 120 or 180° for a three-phase or opposite-phase generator, will generate a transverse electric field between the electrodes that is higher than the vertical electric field allowing impregnation. The electric field elevation factor is possibly the square root of three or the square root of two, which can induce a breakdown between neighboring electrodes 4 by arcing, and therefore excessive horizontal scanning or even a failure of the impregnation device 100.

[0052] Also, the phase shift for two or three phase-shifted potentials u, v, w is advantageously maintained in the order of 10 to 45°, and in particular 15 to 30°.

[0053] The examples discussed here are with two or three phase-shifted potentials, however other embodiments with four or more mutually phase-shifted potentials are of course possible.

[0054] These lower phase shift ranges induce a longitudinal component sufficiently large to avoid the formation of agglomerates while reducing the transverse voltage, which makes it possible, at equal voltages, to reduce the gap between the electrodes 4.

[0055] The embodiment of [Fig.l] has, opposite the first set of three electrodes 4, a second set of identical electrodes 4, but connected differently to the potentials u, v, w. In particular, following the direction of progression of the support, the electrodes 4 located at the top are in particular connected in order to the first potential u, then to the second v, and finally to the third w.

[0056] The electrodes 4 located at the bottom are, following the same convention, connected in order to the third potential w, then to the first u and finally to the second v.

[0057] This assembly results in a complex electric field with longitudinal components resulting on the one hand from the phase shift between the electrodes 4 located on the same side, and on the other hand from the phase shift between the electrodes 4 facing each other.

[0058] [Fig.2] shows electrodes 4 for the impregnation device of [Fig.l] and the electric field as it is oriented at different times in the same period of the alternating potentials u, v, w between the electrodes 4.

[0059] The electrodes 4 (not all referenced) are shown to be of ovoid section, with six electrodes on either side of a central space through which the support S (not shown) passes.

[0060] The electric field is represented by arrows whose orientation corresponds to that of the field, and the length to its intensity.

[0061] It is noted that the electrodes 4 have, in pairs facing each other, electric fields that are alternately strong and weak, with, in the center of the space between the electrodes 4 facing each other, essentially transverse fields.

[0062] On the edges of this space between the facing electrodes, oblique fields, therefore with a non-zero longitudinal component, are observed.

[0063] These fields are induced between the neighboring electrodes 4 out of phase in the same plane, and the induced transverse field serves to disperse the agglomerated packets of powder P.

[0064] [Fig.3] shows an alternative embodiment of an impregnation device according to the invention.

[0065] In this embodiment, the means for moving the support S comprise an endless conveyor with cyclic movement, for example a hollow roller around which the support S is wound.

[0066] The surface of the conveyor 1 has small asperities (not visible in [Fig.3]), in which powder P is deposited by the deposition means 5.

[0067] The support S is pressed against the external face of the conveyor 1, by pressing means, which can be either a dedicated structure in which the support is inserted, or means for tensioning the support, for example by means of reels from which the support S comes and in which it is wound at the outlet of the impregnation device 100.

[0068] The conveyor 1 passes the support S pressed against its external face coated with powder P at the level of the electrodes 4 during its cycle.

[0069] The electrodes 4 are here represented as three in number, placed inside the cylinder forming the conveyor 1. They are each respectively connected to one of the potentials u, v, w and face a plate electrode 40 with floating potential.

[0070] [Fig.4] shows a third embodiment of impregnation device 100, suitable for a support S in the form of a ribbon or wire.

[0071] The means 1 for setting the support S in motion comprise, for example, two coils, forming a source of the untreated support S and conditioning the support S once impregnated.

[0072] Between the two coils 1, a straight, taut section of support wire or ribbon S is passed into a tubular containment member 7, into which the support S passes and into which the deposition means 5 also pour powder P.

[0073] The electrodes 4 are located at the level of said tubular confinement member 7, and here comprise in particular on one side of the confinement member 7 three electrodes 4 connected, from bottom to top, respectively to the first u, second v and third w potentials.

[0074] With this configuration of electrodes 4 and phase-shifted potentials with an increasing phase from the first u to the third w, a contrary movement of the powder particles P to the direction of progression of the support S is obtained. In the case of pouring the powder into the confinement member 7, this movement of the powder P is oriented upwards, and it is then possible to reduce the quantity of lost powder falling at the level of the lower outlet of the confinement member 7.

[0075] Conversely, if it is necessary to avoid the accumulation of powder P at the level of the deposition means 5 or at the entrance of the device, the confinement member 7, the electrodes 4 and their connections to the different potentials u, v, w can be reversed so that the phase shift contributes to advancing the powder P in the direction of progression of the support S.

[0076] The phase shift between the potentials u, v, w thus makes it possible to move the powder P backward or forward relative to the support S.

[0077] Opposite these electrodes 4 in [Fig.4] is located a single plate electrode 40 connected to ground.

[0078] The different configurations of electrodes 4 and plate electrode 40 presented in each of the preceding figures are interchangeable.

[0079] Figures 5 to 9 schematically illustrate different possible configurations of electrodes 4, and of plate electrode 40 where appropriate.

[0080] In [Fig.5], the electrodes 4 are produced in the form of metal plates embedded in a mass of dielectric 4L. There are three of them, located at the top in [Fig.5] and each connected to one of the potentials u, v, w.

[0081] Opposite the three electrodes 4 is located a plate electrode 40 connected to no potential, including ground, and is therefore at floating potential.

[0082] Considering a deposition of powder P from above on the support S, the electrodes 4 are then located on the side of said deposition of powder P.

[0083] The floating potential of the plate electrode 40 reduces the electric field as it approaches said plate electrode 40. This results in an electric field gradient across the thickness of the support S which can, in a controlled manner, limit the deep penetration of the powder P into the support S.

[0084] This assembly corresponds to the case of [Fig.3].

[0085] An inverted assembly, with the plate electrode 40 on the upper side and the three electrodes 4 on the lower side (or a deposit of powder P under the support S) is also possible.

[0086] [Fig.6] is substantially identical to [Fig.5], but differs in that the plate electrode 40 is connected to ground.

[0087] By connecting the plate electrode 40 to ground, the electric fields remain relatively homogeneous and therefore of high norm up to the part close to the plate electrode 40, where they quickly cancel out on approaching said plate electrode 40.

[0088] A relatively homogeneous and strong electric field is thus obtained over potentially the entire thickness of the support S, especially if it is of small thickness, without having to arrange and connect a plurality of electrodes facing each other.

[0089] This assembly corresponds to that of [Fig.4].

[0090] Again, a reversed assembly, with the plate electrode 40 on the upper side and the three electrodes 4 on the lower side (or a deposit of powder P under the support S) is also possible.

[0091] [Fig.7] shows an assembly with two sets of electrodes 4, located on either side of the passage for the support S.

[0092] The electrodes 4 opposite each other are connected to the same potential, from left to right the first u, the second v and the third w.

[0093] [Fig.8] is a variant of the assembly of that of [Fig.7], in particular, the electrodes 4 opposite each other are not connected to the same potential. The electrodes 4 of the set located at the top in [Fig.8] are connected, from left to right to the first u, to the second v and to the third w respectively.

[0094] The electrodes 4 of the set located at the bottom in [Fig.8] are connected, from left to right, to the third w, to the first u and to the second v respectively.

[0095] This assembly corresponds to the case of [Fig.l] in particular. It makes it possible to obtain the complex electric field detailed in [Fig.2], and which makes it possible to disperse the powder agglomerates P.

[0096] [Fig.9] shows another embodiment with two potentials u, v. The electrodes 4 comprise a succession of pairs of electrodes 4 each connected to one of the two potentials u, v, all located on the same side of the support S. On the other side of the support S is arranged a plate electrode 40 connected to ground.

[0097] This succession of phase shifts at two potentials u, v creates significant agitation of the powder particles P during the passage of the support S covered with powder P.

[0098] An embodiment having a succession of pairs of electrodes 4 on each side of the support S is also possible, the electrodes 4 facing each other being able to be connected to the same potential u, v or to a phase-shifted potential u, v.

[0099] Generally speaking, the use of pluralities of electrodes 4 with phase-shifted potentials makes it possible to significantly reduce the inhomogeneities linked to the agglomerates of powder P when said powder P is polarizable or sufficiently conductive.

Claims

Claims

1. Device (100) for impregnating a fibrous or porous support (S) with a powdery material (P), comprising: - means (1) for setting the support (S) in motion, - means (5) for depositing the powdery material (P) on one side of the support (S), - transverse electrodes (4), connected to terminals of alternating voltage generators (G1, G2, G3), generating an electric field applied to the path of the support (S) set in motion, characterized in that the generators (G1, G2, G3) generate alternating potentials (u, v, w) phase-shifted two by two by 10 to 180°, the neighboring electrodes (4) being alternately connected to a different potential (u, v, w) in the direction of progression of the support (S).

2. Device according to claim 1, characterized in that the phase shift between the potentials (u, v, w) of the electrodes (4) is between 10 and 45°, more particularly between 15 and 30°.

3. Device according to claim 1 or 2, characterized in that it comprises one or more generators (G1, G2, G3) generating three potentials (u, v, w) and in that the neighboring electrodes (4) are each connected to a different potential of said one or more generators.

4. Device according to claim 1 or 2, characterized in that it comprises one or more generators (Gl, G2, G3) generating two potentials (u, v) and in that the neighboring electrodes (4) are each connected to a different potential of said one or more generators (Gl, G2, G3).

5. Device according to claim 1 to 4, characterized in that the electrodes (4) connected to the different potentials (u, v, w) are located on the same side of the support (S) and in that it comprises, on the other side of the support (S), no electrode (4) opposite or a plate electrode (40) with floating potential.

6. Device according to claim 1 to 4, characterized in that the electrodes (4) connected to the potentials (u, v, w) are located on the same side of the support (S), and in that it comprises, on the other side of the support (S), a single plate electrode (40) connected to ground.

7. Device according to claim 1 or 2, characterized in that the electrodes (4) comprise a succession of pairs of electrodes (4) each connected to one of two potentials (u, v), located on the same side of the support (S).

8. Device according to one of claims 1 to 4, characterized in that the electrodes (4) are arranged on each side of the support (S), with facing electrodes (4) connected to the same potential (u, v, w) or facing electrodes (4) connected to potentials (u, v, w) phase-shifted two by two.

9. Device according to one of claims 1 to 8, characterized in that the means for setting in motion (1) the support (S) comprise: - an endless conveyor (1) with cyclic movement, which has an external face comprising asperities, the means for depositing (5) the powdery material (P) depositing the powdery material (P) in the asperities of the external face, - means for compressing the support configured to press the support (S) against the external face of the endless conveyor (1) with the asperities filled with powdery material (P), - the endless conveyor (1) passing at the level of the electrodes (4) during its cyclic movement with the support (S) pressed against the external face whose asperities contain powdery material (P).

10. Device according to one of claims 1 to 8, characterized in that the support (S) is a wire or a thin strip, and in that the device comprises a tubular confinement member (7), in which the support (S) to be impregnated passes and in which powdery material (P) is also poured, the electrodes (4) being located at the level of said confinement member (7), between an inlet of the support and the powdery material (P) and an outlet of the impregnated support (S).

11. Device according to one of claims 1 to 10, characterized in that the electrodes (4) have potentials (u, v, w) at offset phases with an increasing phase shift in the direction of progression of the support (S) to drive powdery material (P) in the direction of progression of the support (S) by variation of the electric field.

12. Device according to one of claims 1 to 10, characterized in that the electrodes (4) have potentials (u, v, w) at offset phases with a decreasing phase shift in the direction of progression of the support (S) to drive powdery material (P) in the opposite direction of progression of the support (S) by variation of the electric field.

13. Method for impregnating a fibrous or porous support (S) with a powdery material (P) by applying an electric field, comprising the steps: - setting the support (S) in motion, - depositing powdery material (P) against a surface of the support (S) in motion, characterized in that it further comprises the step: - conveying the support (S) with the powdery material (P) to the level of electrodes (4) connected to generators (G1, G2, G3) generating alternating potentials (u, v, w) phase-shifted two by two by 10 to 180°, the neighboring electrodes (4) being alternately connected to a different potential (u, v, w) in the direction of progression of the support (S).

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