POWDER-IMPREGNATING DEVICE FOR A FIBROUS SUPPORT

Abstract

The invention relates to a device for impregnating (100) a fibrous or porous support (S) with a powdered material (P), comprising: - means for setting the support (S) in motion, - means for depositing (5) the powdered material (P) on one side of the support (S), - transverse electrodes (4) connected to the terminals of alternating voltage generators (G1, G2, G3), generating an electric field applied along the path of the moving support (S), characterized in that the generators (G1, G2, G3) generate alternating potentials (u, v, w) phase-shifted in pairs by 10 to 180°, the adjacent 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 POWDER-IMPREGNATING A FIBROUS SUPPORT technical field

[0001] The present invention relates to the field of impregnation of porous substrates by powdered materials. The substrates 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 substrate. The described installation includes means for moving the substrate onto 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 carried by the electric field, perpendicular to the two electrodes, specifically towards the center of the support. The powder then impregnates the support.

[0006] By means of this process, the weakly polarizable powders are impregnated in a relatively homogeneous way, with however in some 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, electrostatic forces have a strong tendency to create large agglomerates, which makes the inhomogeneities very important, concentrating the particles in the form of point groupings which can in particular remain mostly outside the substrate.

[0008] There is therefore a need for a device that allows for better impregnation of powders by homogenizing the distribution of said powder, and in particular when the powder is polarizable or exhibits a certain electrical conductivity. Description 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 powdered material, comprising: - means of setting the support in motion, - means of depositing the powdered material on one side of the support, - transverse electrodes, connected to the terminals of alternating voltage generators, generating an electric field applied along the path of the moving support.

[0010] The device according to the invention is characterized in that the generators generate alternating potentials that are two-by-two out of phase 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 the electric field, the phase-shifted potentials set the agglomerates of powdered material in longitudinal motion, thereby dispersing 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 helps to avoid breakdown between two neighboring electrodes.

[0015] The device may include 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 in 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 include 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 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 different potentials can be located on the same side of the support, and, on the other side of the support, only one 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 include electrodes on each side of the support, with opposite electrodes connected to the same potential among the three or opposite electrodes connected to potentials that are two-by-two out of phase.

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

[0023] The means for setting the support in motion may include: - an endless conveyor with cyclic motion, which has an external face with asperities, the powder deposition means depositing the powder in the asperities of the external face, - compression means for the support configured to press the support against the outer 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 outer face whose asperities contain powder.

[0024] If the support is a wire or a thin or narrow strip, the device may include a tubular containment element, 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 element, between an inlet of the support and the powder and an outlet of the impregnated support.

[0025] The electrodes may in particular have potentials at phase-shifted 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 can have phase-shifted potentials with a decreasing phase shift in the direction of support progression to drive the powdery material in the opposite direction of support progression by variation of the electric field.

[0027] The invention also relates to the process of impregnating a fibrous or porous support with a powdered material by applying an electric field, comprising the steps: - setting the support in motion, - deposition of 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 electrodes connected to generators generating alternating potentials phase-shifted two-to-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 better understood upon reading the following description, the details of which are given solely by way of example, and developed in relation to the accompanying figures, in which identical references refer to identical elements:

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

[0030] [Fig.2] is a longitudinal cross-sectional view of the electrodes of the device in [Fig.1] and of the electric field vectors at different times during 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 schematic partial perspective 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 specific embodiments shown are given by way of illustration and are not intended to be limiting. Some elements are shown schematically and with incorrect proportions. In particular, the powder particles are shown 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] The [Fig.1] is a schematic side view representation of an impregnation device 100 of a fibrous or porous support S according to a first embodiment of the invention.

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

[0041] In particular, the support S can be an open-cell foam, a sheet, or a fabric of braided or non-woven fibers. The conveyor can, for example, pick up the support S from a roll and, at the output, deliver it to a winder which re-rolls it.

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

[0043] In the example of [Fig. 1], the powder P is deposited by gravity using a dispenser 5 which dispenses the powder P by gravity, possibly with mechanical agitation of the dispenser 5 to set it in motion. The deposit is thus made on the upper surface of the support S.

[0044] A deposit 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 high voltage alternating 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 made in the form of a thin metallic strip deposited on a dielectric support.

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

[0049] The electrodes 4 are phase-shifted in pairs by an angle generally of 10 to 180°. As it passes under the electrodes 4, the powder is agitated by electrostatic forces and penetrates the support S, thereby impregnating 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 clumps that could form through electrostatic attraction of the powder P particles when the latter is polarizable or sufficiently conductive. This phenomenon is linked to the generation of a traveling, rather than stationary, wave in the impregnation zone.

[0051] However, significant phase shifts, for example of 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 required for impregnation. The electric field rise factor is possibly the square root of three or the square root of two, which can induce breakdown between neighboring electrodes 4 by arc, and therefore excessive horizontal sweep or even 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 from 15 to 30°.

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

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

[0055] The embodiment of [Fig.1] presents, 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 connected in particular 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 opposite each other.

[0058] Fig. 2 represents electrodes 4 for the impregnation device of Fig. 1 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 have an ovoid cross-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 whose length corresponds to its intensity.

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

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

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

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

[0065] In this embodiment, the means for moving the support S include an endless conveyor with cyclic motion, for example a hollow roller around which the support S wraps.

[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 means of pressing, which can be either a dedicated structure in which the support is inserted, or means of tensioning the support, for example by means of reels from which the support S comes and in which it is wound at the exit of the impregnation device 100.

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

[0069] The electrodes 4 are represented here as three in number, placed inside the cylinder forming the conveyor 1. They are 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 the impregnation device 100, adapted for a support S in the form of a ribbon or wire.

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

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

[0073] The electrodes 4 are located at the level of said tubular confinement member 7, and here in particular comprise 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 electrode configuration 4 and phase-shifted potentials with increasing phase from the first u to the third w, a movement of the powder particles P in the opposite direction to the progression of the support S is obtained. In the case of powder being poured into the containment element 7, this movement of the powder P is directed upwards, and it is then possible to reduce the amount of powder lost falling at the lower outlet of the containment element 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 containment member 7, the electrodes 4 and their connections to the different potentials u, v, w can be reversed so that the phase shift helps to advance the powder P in the direction of progression of the support S.

[0076] The phase shift between the potentials u, v, w thus allows the powder P to move back 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 electrode 4 and plate electrode 40 shown 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 applicable.

[0080] In [Fig.5], the electrodes 4 are made 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 powder deposit P from above on the support S, the electrodes 4 are then located on the side of said powder deposit 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 over the thickness of the support S which can, in a controlled manner, limit the depth penetration of the powder P into the support S.

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

[0085] An inverted mounting, with the plate electrode 40 on the upper side and the three electrodes 4 on the lower side (or a powder deposit 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 significant magnitude up to the part close to the plate electrode 40, where they quickly cancel each other out as they approach said plate electrode 40.

[0088] This gives us a relatively homogeneous and strong electric field 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 opposite each other.

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

[0090] Again, an inverted mounting, with the plate electrode 40 on the upper side and the three electrodes 4 on the lower side (or a powder deposit 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 4 opposite electrodes are connected to the same potential, from left to right the first u, the second v and the third w.

[0093] Figure 8 is a variant of the setup shown in Figure 7; in particular, the opposite electrodes 4 are not connected to the same potential. The electrodes 4 of the set located at the top in Figure 8 are connected, from left to right, to the first u, the second v, and 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, the first u and the second v respectively.

[0095] This setup corresponds to the case of [Fig. 1] in particular. It makes it possible to obtain the complex electric field detailed in [Fig. 2], which allows the agglomerates of powder P to be dispersed.

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

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

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

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

Claims

Demands

1. Device for impregnating (100) a fibrous or porous support (S) with a powdery material (P), comprising: - means for moving (1) the support (S), - 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 along the path of the moving support (S), characterized in that the generators (G1, G2, G3) generate alternating potentials (u, v, w) that are two-to-two out of phase 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 (G1, 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 (G1, 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 opposite electrode (4) 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 any one of claims 1 to 4, characterized in that the electrodes (4) are arranged on each side of the support (S), with opposite electrodes (4) connected to the same potential (u, v, w) or opposite electrodes (4) connected to potentials (u, v, w) that are two-by-two out of phase.

9. Device according to any one of claims 1 to 8, characterized in that the means for moving the support (S) (1) comprise: - an endless conveyor (1) with cyclic motion, which has an external face having asperities, the means for depositing 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 electrodes (4) during its cyclic motion with the support (S) pressed against the external face whose asperities contain powdery material (P).

10. Device according to any 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 containment element (7), through which the support (S) to be impregnated passes and into which powdery material (P) is also poured, the electrodes (4) being located at the level of said containment element (7), between an inlet of the support and of the powdery material (P) and an outlet of the impregnated support (S).

11. Device according to any one of claims 1 to 10, characterized in that the electrodes (4) have potentials (u, v, w) at phase-shifted levels 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 any one of claims 1 to 10, characterized in that the electrodes (4) have potentials (u, v, w) at phase-shifted with a phase shift decreasing 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. A method for impregnating a fibrous or porous support (S) with a powdery material (P) by applying an electric field, comprising the steps: - moving the support (S), - depositing powdery material (P) against a surface of the moving support (S), characterized in that it further comprises the step: - moving the support (S) with the powdery material (P) to electrodes (4) connected to generators (G1, G2, G3) generating alternating potentials (u, v, w) phase-shifted two-to-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).

Images