Headbox for forming a non-woven web or sheet of paper, and corresponding method

Abstract

The invention relates to a headbox for forming, on a running forming fabric (110), a non-woven web or a sheet of paper comprising fibres of at least one material, the headbox comprising: a feed (102) delivering an aqueous single-phase or two-phase (air / water foam) flow containing fibres of one or more materials in suspension, a first portion (P1) receiving said flow delivered by the feed and comprising a lower wall (103I) and an upper wall (103S) between which walls the flow circulates, the upper wall and the lower wall converging towards each other or diverging from each other, the first portion leading into a second portion (P2) of the headbox, the second portion comprising an upper wall (104S), and a lower opening (OP) through which the flow is in contact with the running forming fabric, and, beneath at least part of the lower opening of the second portion and beneath the running forming fabric, at least one dewatering box (105A, 105B).

Description

Description Title of the invention: Head box for forming non-woven fabric or paper sheet, and corresponding method Technical Field This presentation relates to the manufacture of a non-woven fabric or paper sheet, and the headboxes used for this manufacture. The invention finds application in the manufacture of fabrics or sheets with high basis weights and, for example, comprising fibers of materials such as aramid or polyethylene terephthalate. Previous technique

[0002] The continuous production of non-woven fabric or paper is carried out in a manner known per se by means of headboxes.

[0003] The head boxes are configured to deliver onto a moving screen an aqueous phase flow comprising suspended material fibers.

[0004] For example, in the papermaking industry, the headbox distributes a suspension of cellulose fibers onto the continuously moving forming cloth of the paper machine. The headbox is specifically configured to distribute the fibers uniformly in width and thickness across the cloth.

[0005] Head boxes are also used for the formation of non-woven fabric veils.

[0006] The term non-woven, well known to those in the trade, is for example defined in ISO 9092 in its 2019 version and refers, according to this standard, to "a pre-engineered fibrous assembly, essentially planar, possessing a nominal level of structural integrity conferred by means of physical and / or chemical processes, excluding weaving, knitting or papermaking".

[0007] In this document, the term "non-woven material" is used for both the finished product and the material in the process of being manufactured.

[0008] One application of nonwoven materials is the manufacture of electrical insulating materials that can be used, for example, as separators in Li-ion batteries or other devices, as insulation in electrical capacitors, or as high-voltage electrical insulation. For electrical applications, it is necessary to obtain a uniform, hole-free web to prevent any risk of electrical short circuits. The fibrous material used for these applications can be aramid or a combination of fibers including aramid fibers.

[0009] Reverse osmosis membranes, and in particular reverse osmosis membranes based on polyethylene terephthalate fibers, are also products that require an absence of holes to function as expected.

[0010] Obtaining sheets of paper or non-woven fabric such as those described above remains difficult to achieve, particularly for sheets and fabrics with a high basis weight, for example above 150g / m² 2 or even greater than 250g / m 2 .

[0011] At least three types of headbox are known from the earlier technique.

[0012] The so-called flat-table headboxes distribute a suspension of fibers in the form of a coherent jet deposited onto a horizontally moving screen. A downstream opening of a given height determines the quantity of fibers that must be deposited.

[0013] Inclined headboxes distribute a suspension of fibers onto a moving, inclined screen. The quantity of fibers deposited is determined, in particular, by a suction system implemented by lower chambers located under the terminal portion of the headbox.

[0014] The cylinder-mounted headboxes distribute a fiber suspension onto a fabric circulating around a cylinder, inside which suction boxes are arranged.

[0015] These three types of headboxes do not currently give satisfactory results for the manufacture of all types of paper and non-wovens, particularly when high basis weights are sought or when an absence of holes is sought. Description of the invention

[0016] The invention aims to remedy at least some of the aforementioned drawbacks.

[0017] For this purpose, a headbox is proposed for forming, on a conveyed conveyor belt, a non-woven fabric or a sheet of paper comprising fibers of at least one material, the headbox comprising: a feed delivering a flow in single-phase aqueous or two-phase air-water (for example, an aqueous foam) comprising, in suspension, fibers of said at least one material, a first portion receiving said flow delivered by the feed and comprising a lower wall and an upper wall between which the flow circulates in the direction of conveyor belt movement, the upper wall and the lower wall converging towards each other or diverging from each other in the direction of conveyor belt movement, the first portion opening into a second portion of the headbox, the second portion comprising an upper wall contiguous with the upper wall of the first portion,and a lower opening through which the flow is in contact with the scrolling fabric, below at least part of the lower opening of the second portion and below the scrolling fabric, at least one drip box controlled by a drip control unit (for example, suction is applied to the drip box, this suction being controlled by the drip control unit, the suction may correspond to a pressure lower than that of the flow in the second portion), the upper wall of the second portion extending above the lower opening in the direction of the scrolling fabric to a distal end, located above or below the opening, at a given height of the scrolling canvas, the given height corresponding to 30 to 70% of the height of the upper wall of the second portion at the level of an upstream edge of the opening (for example measured between the canvas and the upper wall at the upstream edge).

[0018] The invention therefore proposes a particular headbox in that it comprises, on the one hand, a lower opening and drainage (or suction) chambers, and on the other hand, a downstream (or distal) opening arranged between the fabric and the distal end of the upper wall of the second portion, this opening being fixed by a given height. Consequently, the formation of the web or sheet is achieved through two techniques: one technique analogous to those implemented by inclined or cylindrical headboxes (using the drainage or suction chambers within the headbox), and a technique analogous to that implemented by headboxes on flat tables where the opening determines the quantity of fiber deposited on the fabric.Thus, the resulting veil or sheet comprises a lower portion resulting from formation through the opening using at least one dripping chamber, and an upper portion resulting from the dripping of the flow from the given height of the distal end downstream of this opening.

[0019] By forming a veil or a sheet with a lower portion and an upper portion formed by two different processes or two different techniques, the risk of the appearance of holes is limited since the appearance of a hole during the formation of the veil or the sheet according to one of the techniques is compensated by the formation of the veil or the sheet according to the other technique.

[0020] Also, by adjusting to a given height corresponding to 30 to 70% of the height of the upper wall of the second section at the level of an upstream edge of the opening, measured from the moving fabric, we obtain a contribution from the forming technique resulting from the opening and suction / draining by the chamber to the final surface mass of the veil or sheet (i.e., the veil once dried or the sheet once dried) which is 30% to 70% of the total surface mass. The remainder of the surface mass then results from the The formation technique involves opening and draining the fabric. This results in a veil or sheet with a lower and upper portion, thus preventing the formation of veils or sheets with holes.

[0021] Also, the headbox shown here facilitates the formation of high grammage veils or sheets, and the given height facilitates the use of fluxes with a low concentration of suspended fibers.

[0022] We can note that the first portion can be adapted to diverge (the upper and lower walls are closer to each other downstream than upstream) or converge (the upper and lower walls are further apart downstream than upstream), so that a flow velocity at the exit of the first portion is close to the scrolling speed of the canvas.

[0023] According to a particular embodiment, the given height is greater than or equal to 30mm.

[0024] This height of more than 30mm, which also corresponds to 30 to 70% of the height of the upper wall of the second portion at the level of an upstream edge of the opening, is well suited for a flow with a low concentration of suspended fibers.

[0025] According to a particular embodiment, the given height is chosen so that: on the one hand, 30% to 70% by mass of the veil obtained once dried or of the sheet obtained once dried results from a formation resulting from the draining at the level of said at least one draining box (or at the level of the draining boxes if there are several), and on the other hand, the remaining fraction by mass of the veil obtained once dried or of the sheet obtained once dried results from a formation downstream of the distal end of the upper wall of the second portion.

[0026] This particular embodiment specifies that the veil or sheet is indeed obtained through a formation process resulting from two techniques. The inventors observed that obtaining veils or sheets using two manufacturing methods results in a structure that can delaminate into two sub- veils or under-sheets, which allows for the implementation of a measurement of the grammage resulting from each manufacturing method.

[0027] It can be noted that within a single veil or sheet produced by this process, the two sub-veins or sub-sheets each have a different structure resulting from the two techniques. A skilled professional will be able to identify these two different structures, which can lead to delamination.

[0028] According to a particular embodiment, said at least one drainage box comprises a drainage surface facing the moving fabric, the drainage surface comprising a succession of slots, for example slots extending in a direction substantially orthogonal to the direction of movement of the fabric, or inclined with respect to the direction of movement of the fabric.

[0029] For example, the drainage surface may have a grid structure due to the presence of slots.

[0030] According to a particular embodiment, said at least one drainage box comprises a drainage surface defining a flat or convex region against which the fabric passes.

[0031] This particular embodiment allows for a web to be moved along a plane, resulting in a structure analogous to a flat headbox (but with a drainage box) or an inclined headbox (but with an opening at a given height). Here, the web is in contact with the drainage surface of at least one drainage box.

[0032] According to a particular embodiment, said at least one drainage box comprises a drainage surface defining a curved region conforming to the shape of a rotating cylinder, said at least one box being fixedly arranged inside the cylinder, such that the cylinder is between the fabric and said drainage surface, the cylinder being a circular-based cylinder rotated about its axis and around which the canvas scrolls, and comprising a distribution of orifices passing through its surface.

[0033] This particular method of embodiment allows a canvas to be scrolled around a cylinder, to have a structure analogous to a cylindrical head box (but with a terminal opening at the given height).

[0034] The rotating cylinder can be driven into rotation by any suitable actuator.

[0035] According to a particular embodiment, the head box comprises two or more successive drainage boxes which follow each other in the direction of the web's movement, each drainage box being controlled by the drainage control unit.

[0036] By using several successive drainage chambers, the progressive nature of the drainage can be controlled by segmenting it. Indeed, if there is only one chamber, the drainage flux density (flux per unit area) will vary between the beginning and end of the chamber because the thickness of the fibrous mat that is gradually deposited on the fabric as it passes over the drainage chamber increases, thereby offering increasing resistance to drainage. The velocity of the flux F circulating between the upper wall 104S and the opening OP is then no longer constant, and the structure of the sheet would vary too much between the first and last layers of deposited fibers.

[0037] Thus, in this embodiment, the control (or suction) applied to the several drainage boxes can be different between two drainage boxes.

[0038] According to a particular embodiment, the feed is configured to deliver the stream comprising fibers of said at least one material at a concentration between 0.05% and 1%.

[0039] According to a particular embodiment, said at least one material is aramid or polyethylene terephthalate.

[0040] These materials are well suited, as mentioned above, for the manufacture of battery separators or for the manufacture of filtration membranes.

[0041] According to a particular embodiment, the veil obtained once dried or the sheet obtained once dried has a basis weight greater than 150g / m 2 or even greater than 250 g / m 2 .

[0042] The person in the trade will know how to adjust the parameters such as the given height, the suction by the drainage box, the concentration of fibers in the suspension, and the speed of the fabric's movement to obtain these weights. [0043JII is also proposed a method for forming, on a conveyed conveyor belt, a non-woven fabric or a sheet of paper comprising fibers of at least one material, the method being implemented by a headbox and comprising: delivering, by means of a feed, a single-phase aqueous or two-phase air-water flow comprising, in suspension, fibers of said at least one material, circulating the solution in a first portion receiving said flow delivered by the feed and comprising a lower wall and an upper wall between which the flow circulates in the direction of conveyor belt movement, the upper and lower walls converging towards each other or diverging from each other in the direction of conveyor belt movement, the first portion opening into a second portion of the headbox, circulating the solution in the second portion,the second portion comprising an upper wall contiguous with the upper wall of the first portion, and a lower opening through which the flow is in contact with the scrolling fabric, under at least a part of the lower opening of the second portion and under the scrolling fabric, at least one drip box controlled by a drip control unit, the upper wall of the second portion extending over the lower opening in the direction of the scrolling fabric to a distal end, located above or below the opening, at a given height of the scrolling canvas, the given height corresponding to 30 to 70% of the height of the upper wall of the second portion at the level of an upstream edge of the opening.

[0044] This process can be adapted to be implemented by any of the embodiments of the head box presented above.

[0045] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows, along with examples of headbox designs. This detailed description refers to the attached drawings. Brief description of the drawings

[0046] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0047] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols.

[0048] [Fig. 1] Figure 1 is a schematic representation of an installation including a head box according to an example.

[0049] [Fig. 2] Figure 2 is a schematic representation of an installation including a head box according to another example.

[0050] [Fig. 3] Figure 3 is a photograph showing an example of a sail obtained.

[0051] [Fig. 4] Figure 4 is another photograph showing an example of a sail obtained. Description of the implementation methods

[0052] To make the explanation more concrete, an example of a non-woven fabric or paper sheet manufacturing installation using a headbox is described in detail below, with reference to Figure 1. The manufacturing process The corresponding example is also described. It is noted that the invention is not limited to this example.

[0053] Figure 1 shows a partial and schematic representation of a non-woven fabric or paper manufacturing installation. Figure 1 is a side view of the installation.

[0054] Although not shown for simplicity, installation 1 may, in a manner known per se, include a pressing and / or drying unit. Installation 1 comprises a headbox 100, which is connected to a fiber suspension inlet 101. The fiber suspension inlet may be provided by a manifold, a central distributor, or a linear distributor, with or without a basis weight profile controller by dilution.

[0055] The fiber suspension inlet 101 is configured to supply the headbox 100 with a single-phase aqueous or two-phase (air-water) flow comprising, in suspension, fibers of one or more materials.

[0056] For example, one of the materials could be aramid, for example to obtain separators usable in electric batteries to separate the anode from the cathode in these batteries.

[0057] For example, a material could be aramid, for example to obtain high voltage electrical insulators used for example in the manufacture of electric motors.

[0058]

[0059] Also, a material can be polyethylene terephthalate, for example to obtain reverse osmosis membranes.

[0060] Of course, the invention is not limited to these materials, and different fibrous materials can be used. In particular, mixtures of several different fibrous materials can be used.

[0061] The fiber suspension inlet is connected to a fiber suspension power supply 102. For reference, this power supply can also be configured to implement deflocculation of the received fibrous suspension. For example, the feed may include a deflocculating roller or a stepped diffuser for this purpose.

[0062] A flow F is delivered by the feed 102, at a given outlet pressure. In the figure, the flow F circulates from right to left. The flow F is an aqueous phase flow containing fibers of the aforementioned material(s) in suspension. It is delivered into a first portion PI of the headbox.

[0063] This first section comprises a lower wall 1031 and an upper wall 103S between which the flow circulates. Side walls defining the width of the headbox are also present, but are not shown in the figure for simplicity.

[0064] The lower wall 1031 extends substantially horizontally from the feed until it is flush above a passing training cloth 110, at the level of the headbox, from right to left. The training cloth 110 is kept in continuous motion by means of rollers 115, at least one of which is driven in rotation at a given rotational speed (which is also the speed at which the training cloth is passed).

[0065] The upper wall 103S is arranged so that, in the direction of web movement (here under the downstream end of the lower wall, where it meets the web), the upper and lower walls converge or diverge. While not limiting, the figure shows a configuration in which the walls converge.

[0066] In fact, the height between the upstream end of the upper wall and the upstream end of the lower wall is arranged relative to the height between the downstream end of the upper wall and the downstream end of the lower wall. This convergence or divergence allows for a certain velocity of the flow F exiting section PI. Advantageously, the flow F is brought to a velocity close to, or even equal to, the speed of the web 110 exiting the first section PI.

[0067] The flow originates from the first section PI and extends to a second section P2, which comprises an upper wall 104S contiguous with the upper wall 103S of the first section. By contiguous, we mean that there is a junction J between the upper walls of the first and second sections. The upper wall 104S is inclined downwards in the direction of the moving web, which flows beneath the second section P2.

[0068] The second section P2 does not have a bottom wall but it does have an opening OP through which the flow comes into contact with the moving fabric. Below the opening OP (either the entire opening or a portion of it), two drainage boxes are arranged: a first drainage box 105A followed, downstream, by a second box 105B. The opening OP extends across the entire width of the second section (a width close to that of the forming fabric), measured in the direction perpendicular to the direction of fabric movement, and between side walls (not shown) that define the width of the head box. The two boxes 105A and 105B also extend across the entire width of the opening OP.

[0069] Boxes 105A and 105B have successive slots F on their upper face, separated here by blades. The upper face defined by the slots (and the blades) is either flat or convex, here flat and horizontal (though this is not a limiting factor). The screen 110 moves horizontally above boxes 105A and 105B, with part of the flow F passing through the moving screen.

[0070] During operation, suction is applied to boxes 105A and 105B to allow drainage.

[0071] This is achieved by means of a drip control unit 106A for controlling the suction in the chamber 105A and by means of a drip control unit 106B for controlling the suction in the chamber 105B. It should be noted that the drip control units can, for example, control a flow rate (or a suction pressure). In the head chamber shown in the figure, a suction system 107 common to both drip control units is also shown, to apply a Suction is controlled by each drainage control unit. Alternatively, several suction systems can be used.

[0072] It can be noted that the suction control units are configured so that the pressure in the drip boxes is lower than the pressure in the second portion.

[0073] The OP opening and the drainage boxes contribute to the formation of a veil or sheet on the forming fabric according to a first mode of formation (or a first formation technique).

[0074] The height of the upper wall of the second portion at its distal end 104E, measured from the scrolling canvas, is noted Hl.

[0075] The height of the upper wall of the second portion at the upstream edge of the opening OP is noted H2.

[0076] Here, Hl is chosen so that Hl is equal to 30 to 70% of the height H2, which corresponds to a large opening, for example greater than or equal to 30 mm. The height Hl thus chosen allows for the formation of a veil or sheet on the forming fabric (or more precisely on a veil or sheet partially obtained using the first forming method) according to a second forming method (or a second forming technique).

[0077] Here, the chosen height and the use of an opening with a drainage box are such that, once dried, the resulting veils or sheets comprise a mass of 30 to 70% fiber resulting from the first mode of formation and a remaining mass resulting from the second mode of formation.

[0078] This is particularly advantageous for avoiding the presence of through holes in sails or sheets.

[0079] Downstream of the distal end 104E, the fabric continues to move horizontally so that the second forming mode can contribute to the formation of the sheet or veil. In effect, this allows for conventional forming on a forming table familiar to those skilled in the art. The head box in Figure 1 is therefore partly analogous to a box it has a flat table head, but it differs from it due to the presence of the OP opening and the suction boxes.

[0080] The resulting sheet or veil is then transferred to a pressing or drying unit, towards the left in the figure.

[0081] The invention is not limited to headboxes analogous to flat headboxes like the one in Figure 1. The headbox in Figure 1 can also be configured in an inclined version. The headbox in Figure 1 is therefore also partly analogous to a headbox on an inclined table, but it differs from it due to the significant height H1 compared to H2.

[0082] Also, as can be seen in Figure 2, a cylindrical headbox can also be used. This example is well suited to producing sheets or banners with a high basis weight.

[0083] Figure 2 shows an example of an installation including a 100' head box. Elements bearing the same references are analogous at least in function but their shape can be adapted for a "cylindrical" geometry.

[0084] Here, the flow F and the lower wall 1031 of the first portion are flush with the fabric 110 at the level of the opening OP in a more or less tangential manner with respect to a cylinder CY around which the forming fabric 110 circulates. The cylinder CY has a perforated surface.

[0085] The upper wall 104S of the second portion P2 is curved and is configured to obtain a relationship between H1 and H2 analogous to that described above.

[0086] The 105A and 105B drainage boxes are also curved so that their upper face follows the shape of the CY cylinder.

[0087] The training fabric is here driven in scrolling by means of the cylinder CY and / or at least one of the cylinders 115.

[0088] Figures 3 and 4 show sheets of paper obtained through the two formation methods using a headbox such as that in Figure 1 or that in Figure 2. [0089JII] The inventors observed that the resulting sheet is such that its lower portion results from the first formation method (30 to 70% by mass per unit area after drying) and its upper portion results from the second formation method (30 to 70% by mass per unit area after drying). Although strongly bonded together, the two portions are distinct and differentiable, as can be seen in the photographs in Figures 3 and 4 after delamination of the sheet.

[0090] The possibility of delaminating the sheet shows that the two layers have different structures and result from two distinct modes of formation, which effectively prevents through holes.

[0091] The head boxes shown above can also be used to produce veils or sheets with high basis weights, for example above 150g / m² 2 or even higher than 250g / m 2 possibly with fibers from the materials presented above.

Claims

Demands

1. Head box for forming, on a conveyed conveying fabric (110), a non-woven veil or a sheet of paper comprising fibers of at least one material, the head box comprising: a feed (102) delivering a single-phase aqueous or two-phase air-water flow comprising, in suspension, fibers of said at least one material, a first portion (PI) receiving said flow delivered by the feed and comprising a lower wall (1031) and an upper wall (103S) between which the flow circulates in the direction of conveying the fabric, the upper wall and the lower wall converging towards each other or diverging from each other in the direction of conveying the fabric, the first portion opening into a second portion (P2) of the head box, the second portion comprising an upper wall (104S) contiguous with the upper wall of the first portion,and a lower opening (OP) through which the flow is in contact with the scrolling fabric, under at least a portion of the lower opening of the second portion and under the scrolling fabric, at least one drip box (105A, 105B) controlled by a drip control unit (106A, 106B), the upper wall of the second portion extending above the lower opening in the direction of the scrolling fabric to a distal end located above or downstream of the opening, at a given height (H1) of the scrolling fabric, the given height corresponding to 30 to 70% of the height (H2) of the upper wall of the second portion at an upstream edge of the opening.

2. Head box according to claim 1, wherein the given height is greater than or equal to 30mm.

3. Head box according to claim 1 or 2, wherein the given height is chosen such that: on the one hand, 30% to 70% by mass of the veil obtained once dried or of the sheet obtained once dried results from a formation resulting from the draining at the level of said at least one draining box, and on the other hand, the remaining mass fraction of the veil obtained once dried or of the sheet obtained once dried results from a formation downstream of the distal end of the upper wall of the second portion.

4. Head box according to any one of claims 1 to 4, wherein said at least one drainage box comprises a drainage surface facing the moving fabric, the drainage surface comprising a succession of slots, for example slots extending in a direction substantially orthogonal to the direction of movement of the fabric.

5. Head box according to any one of claims 1 to 4, wherein said at least one drainage box comprises a drainage surface defining a flat or convex region against which the fabric passes.

6. Head box according to any one of claims 1 to 3, wherein said at least one drainage box comprises a drainage surface defining a curved region conforming to the shape of a rotating cylinder, said at least one box being fixedly arranged inside the cylinder, such that the cylinder is between the fabric and said drainage surface, the cylinder being a circular-based cylinder driven in rotation about its axis and around which the fabric passes, and comprising a distribution of through-holes in its surface.

7. Head box according to any one of claims 1 to 6, comprising two or more successive drain boxes following one another in the direction of the web's movement, each drain box being controlled by the drain control unit.

8. Headbox according to any one of claims 1 to 7, wherein the feed is configured to deliver the stream comprising fibers of said at least one material at a concentration between 0.05% and 1%.

9. Head box according to any one of the claims 1 to 8, in which said at least one material is aramid or polyethylene terephthalate.

10. Head box according to any one of the claims 1 to 9, in which the veil obtained once dried or the sheet obtained once dried has a basis weight greater than 150g / m 2 or even greater than 250 g / m 2 .

11. A method for forming, on a conveyed conveyor belt, a non-woven fabric or a sheet of paper comprising fibers of at least one material, the method being implemented by a headbox and comprising: delivering, by means of a feed (102) a single-phase aqueous or two-phase (air-water foam) flow comprising, in suspension, fibers of said at least one material, circulating the flow in a first portion (PI) receiving said flow delivered by the feed and comprising a lower wall (1031) and an upper wall (103S) between which the flow circulates in the direction of conveyor belt movement, the upper and lower walls converging towards or diverging from each other in the direction of conveyor belt movement, the first portion opening into a second portion (P2) of the headbox, circulating the flow in the second portion,the second portion comprising an upper wall (104S) contiguous with the upper wall of the first portion, and a lower opening (OP) through which the flow is in contact with the moving fabric, under at least a part of the lower opening of the second portion and under the moving fabric, at least one drip box controlled by a drip control unit, the upper wall of the second portion extending above the lower opening in the direction of the fabric's movement to a distal end located above or downstream of the opening, at a given height (Hl) of the moving fabric, the given height corresponding to 30 to 70% of the height (H2) of the upper wall of the second portion at the level of an upstream edge of the opening.

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