Non-woven material manufacturing machine including glass microfiber and corresponding process

Abstract

A machine for manufacturing nonwoven material comprising glass microfiber, comprising: a forming unit (110, 110') for nonwoven material comprising glass microfiber, on a lower web (120) driven in a forward direction; a smoothing unit (140) comprising an upper web (141) moving in the forward direction and extending so that the nonwoven material is held between the lower and upper webs at the level of the smoothing unit; and a plurality of portions (P1, P2), the plurality of portions defining a lower surface (SI) of the smoothing unit pressed against the upper web at a location where the upper web is in contact with the nonwoven material, wherein a stronger suction is applied to the last portion. [Fig. 1]

Description

Title of the invention: Machine for manufacturing non-woven material comprising glass microfiber and corresponding process. Technical field

[0001] The present disclosure relates to the wet manufacturing of nonwoven materials comprising glass microfiber and the corresponding manufacturing machines. Prior art

[0002] The expression non-woven materials, well known to those skilled in the art, 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, having a nominal level of structural integrity conferred by means of physical and / or chemical processes, excluding weaving, knitting or papermaking".

[0003] In this document, the expression "non-woven material" is used for both the finished product and the material being manufactured.

[0004] Conventionally, the manufacture of non-woven materials comprising glass microfiber involves the use of a forming unit equipped with a lower scrolling fabric on which a fibrous suspension (comprising, for example, a quantity of glass microfiber greater than 40% by dry weight) is deposited uniformly along the width of the lower fabric (the width being orthogonal to the direction of scrolling of the fabric).

[0005] A draining of the fibrous suspension is then implemented to remove the liquid phase of the suspension, typically water or foam, in which the fibers were initially suspended, to obtain a non-woven material.

[0006] It has been observed that the presence of glass microfibers leads to the formation of flocs in the upper part of the nonwoven material, which, during the draining phase, form clumps of microfibers. The surface of nonwoven materials containing glass microfibers obtained by current techniques is therefore generally very irregular, these clumps being considered defects that degrade the quality of the final product.

[0007] Techniques to prevent the formation of these clumps may slow down the draining process and therefore the productivity of the manufacturing machine. These techniques are unsatisfactory because they significantly impact the quantity of nonwoven material produced per minute.

[0008] There is therefore a real need for a non-woven material manufacturing machine comprising glass microfiber which is free, at least in part, from the disadvantages mentioned above. Description of the invention

[0009] The present invention relates to a machine for manufacturing non-woven material comprising glass microfiber, comprising: a non-woven material forming unit comprising glass microfiber, on a lower web driven in a direction of travel (this direction of travel is followed at least when the non-woven material is on the lower web), downstream of the forming unit and above the lower web, a smoothing unit comprising an upper web running in the direction of travel and extending so that the nonwoven material is held between the lower web (this is the same web on which the nonwoven material is formed by the forming unit) and the upper web at the level of the smoothing unit, and a plurality of portions arranged consecutively in the direction of travel, the plurality of portions defining a lower surface of the smoothing unit pressed against the upper web at a location where the upper web is in contact with the nonwoven material, wherein at least the last portion (i.e., the most downstream portion of the plurality of portions) is provided with a plurality of orifices and is controlled by a suction control system of the smoothing unit to apply suction through the orifices of the last portion,And if the first portion has a plurality of orifices, the suction is stronger through the orifices of the last portion than through the orifices of the first portion (i.e., the most upstream portion of the plurality of portions).

[0010] If the first portion does not have orifices (it is a solid surface), no suction can be applied to it, and the suction through the orifices of the last portion is non-zero.

[0011] The inventors of the present invention have observed that by using a smoothing unit comprising several sections, with lower or even zero suction at the beginning (for the first section) and higher or at least non-zero suction at the end (for the last section), a smoothed nonwoven material is obtained with a good reduction, after removal of the surface liquid phase, in the presence of the resulting bubble clusters. In fact, the first section of the lower surface of the smoothing unit (i.e., the lower surface of the first section) is in contact with the upper fabric at a location where the nonwoven material is saturated with liquid on its upper face.At this stage, the upper surface of the nonwoven material is more malleable than after vacuum draining, which facilitates the mechanical flattening of the nonwoven material, and in particular its upper surface (opposite to that supported by the lower fabric), by the first portion. The absence of vacuum or low vacuum (compared to the last portion) in the first portion. This allows the smoothing unit to shape the top surface of the non-woven material to make it smoother.

[0012] A portion here is formed of one or more surface elements intended to be in contact with the upper fabric, the portion optionally having orifices (the last portion has orifices, the first portion optionally has them). The portions extend across the width of the nonwoven material (in a direction orthogonal to the direction of travel) and have a given length (in the direction of travel) which may be the same or different for different portions. The portions, in particular the last portion, may be in fluidic communication with the suction control system so that liquid is drawn through the portion's orifices if they have them. Here, there are at least two portions. The suction control system is configured to control portions independently of each other if both are equipped with orifices.

[0013] It can be noted that a portion has a length measured in the direction of the web's movement, ranging from 100 mm to 800 mm depending on the type of glass microfibers used

[0014] Also, an orifice can extend over the entire width of a portion (the orifice is located between surface elements which can be blades which extend on either side of orifices over the entire width of a portion).

[0015] Alternatively, an orifice can be completely surrounded by a surface element; for example, the portion comprises a single surface element and several orifices distributed over the width and length of the portion / single surface element (for example, in a uniform distribution). Orifices of this type can have any shape (cylinder with a circular base, cylinder with an oblong base, etc.).

[0016] The surface elements of all the portions define the lower surface of the smoothing unit. The upper fabric exerts pressure on the lower surface of the smoothing unit at a location where the upper fabric is in contact with the nonwoven material, which is also in contact with the lower fabric itself, exerting pressure on the nonwoven material. The nonwoven material is thus constrained by the lower surface of the smoothing unit, this constraint resulting from the arrangement of the lower surface of the smoothing unit, which itself depends on the arrangement of the portions.

[0017] According to a particular embodiment, the plurality of portions has a given radius of curvature with a center of curvature located above the lower surface.

[0018] As an indication, the radius of curvature can be between 2m and 100m, preferably between 5m and 30m, and for example equal to 15m.

[0019] It has been observed by the inventors that the radius of curvature contributes to the improvement of smoothing.

[0020] According to a particular embodiment, the machine includes a suction orifice arranged to allow recovery of supernatant liquid upstream of the first portion, the suction orifice being controlled by said suction control system.

[0021] It should be noted that the suction orifice differs from said portions in that it comprises a single orifice whereas the portions comprise a plurality of orifices.

[0022] The suction orifice can be defined by means of a blade extending across the width of the fabric from the first portion and configured to lightly touch the inner face of the upper fabric (i.e., the face of the upper fabric against which the lower surface is in contact) so that the movement of the fabric lifts liquid by means of the blade, which is then suctioned through the suction orifice. Since this supernatant liquid contributes little or nothing to the malleability of the nonwoven material, it can be removed by suction before smoothing.

[0023] According to a particular embodiment, the machine includes a draining roller arranged at the outlet of the forming unit and upstream of the smoothing unit, the draining roller being arranged to be in contact with the upper face of the non-woven material.

[0024] The draining roller may comprise a cylinder with a circular base extending in the direction orthogonal to the flow of the non-woven material. In a manner known per se for draining rollers.

[0025] The inventors of the present invention observed that using a drain roller at the outlet of the forming unit further improves the smoothing of the nonwoven material. The drain roller is in contact with the nonwoven material at a location that is not yet in contact with the upper fabric of the smoothing unit.

[0026] According to a particular embodiment, the draining roller is driven in rotation at a different speed than the speed at which the non-woven material is driven (by machine drive means, for example) in the direction of travel.

[0027] By using a different speed (higher or lower than that of the scrolling), a shear appears in the non-woven material, which facilitates a reorganization of the glass microfibers of the non-woven material and which contributes to the smoothing of the non-woven material.

[0028] According to a particular embodiment, the machine includes a unit for controlling the thickness of the non-woven material downstream of the location where the lower surface of the plurality of portions is in contact with the upper fabric.

[0029] According to a particular embodiment, the forming unit is configured to deliver a non-woven material comprising more than 40% by dry weight of glass microfiber.

[0030] A person skilled in the art will know how to choose the parameters of the fibrous suspension used in the forming unit as well as the speed of the lower web to obtain a non-woven material having, by dry weight, a quantity greater than 40% glass microfiber.

[0031] According to a particular embodiment, the machine comprises, on either side of the lower surface (i.e. upstream and downstream of the lower surface), lower curved support surfaces in contact with the inner face of the lower fabric (this inner face being the face of the lower fabric opposite to that supporting the non-woven material) and each having a center of curvature which is below the lower fabric.

[0032] These curved support surfaces facilitate the pressing of the lower surface of the smoothing unit against the lower canvas.

[0033] The invention also relates to a method for manufacturing a non-woven material comprising glass microfiber, comprising: a formation by a non-woven material forming unit comprising glass microfiber, on a lower fabric driven in a scrolling direction, a smoothing process implemented downstream of the forming unit and above the lower web, by means of a smoothing unit comprising an upper web running in the direction of travel and extending so that the non-woven material is held between the lower web and the upper web at the level of the smoothing unit, and a plurality of portions arranged consecutively in the direction of travel, the plurality of portions defining a lower surface pressed against the upper web at a location where the upper web is in contact with the non-woven material, in which at least the last portion is provided with a plurality of orifices and is controlled to apply suction through the orifices of the last portion, and if the first portion is provided with a plurality of orifices, the suction is stronger through the orifices of the last portion than through the orifices of the first portion.

[0034] This method can be adapted to implement each of the embodiments of the machine described above.

[0035] According to a particular embodiment, the non-woven material is conveyed at a speed greater than 5 m / min and preferably greater than 25 m / min.

[0036] The use of the smoothing unit makes it possible to obtain a non-woven material acceptable in terms of absence of clumps for these speeds. Brief description of the drawings

[0037] The attached drawings are schematic and are intended primarily to illustrate the principles of the exposition.

[0038] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols.

[0039] [Fig. 1] The [Fig. 1] is a schematic representation of a machine according to an example.

[0040] [Fig.2] Fig.2 is a schematic representation of a machine according to another example.

[0041] [Fig.3] Fig.3 shows in more detail a smoothing unit.

[0042] [Fig.4A] The [Fig.4A] is a photograph of a non-woven material obtained without a smoothing unit.

[0043] [Fig.4B] Fig.4B is a photograph of a non-woven material obtained using a drain roller.

[0044] [Fig.4C] Fig.4C is a photograph of a non-woven material obtained using a smoothing unit. Description of the implementation methods

[0045] We will now describe a machine for the manufacture of non-woven materials comprising glass microfiber.

[0046] The term “glass microfiber” refers to fibers having average diameters between 0.2 pm and 10 pm, and preferably between 0.26 pm and 5.5 pm.

[0047] The manufacturing process for this non-woven material will be described simultaneously.

[0048] The machine and process described herein make it possible to obtain a smooth nonwoven material, or at least a smoother nonwoven material than that obtained using prior art techniques, i.e., one in which the presence of glass microfiber clumps is limited. Furthermore, the machine and process described below make it possible to obtain this smooth nonwoven material at a production rate of several meters per minute (greater than 5 m / min and preferably greater than 25 m / min).

[0049] The nonwoven materials obtained using this machine and process can be used in AGM (Absorbent Glass Mat) type batteries. The invention thus makes it possible to obtain more desirable nonwoven materials for the manufacture of these batteries. In fact, lead-acid batteries designated by the English acronym "AGM" (Absorbent Glass Mat) comprise electrodes that are not immersed in acid but separated by porous separator layers made of nonwoven material comprising glass microfiber and in which an electrolyte / acid is stored.

[0050] The invention is not limited to nonwoven materials usable for AGM type storage batteries. For example, the nonwoven materials obtained using this machine and process can also be used in the manufacture of HVAC (Heating, Ventilation, and Air Conditioning) filters. which can be used for air filtration, and be pre-filters, fine filters, HEPA filters (High-Efficiency Particulate Air), ULPA filters (Ultra-Low Penetration Air), cryogenic insulation papers, or any other material that must contain at least 40% glass microfibers.

[0051] Figure 1 shows a first example of a nonwoven material manufacturing machine in side view. This machine 100 comprises a forming unit 110, known per se, configured for depositing a fibrous suspension, including glass microfiber, onto a lower, scrolling fabric 120. The forming unit of the type shown in Figure 1 comprises a cylinder 111 around which the lower fabric scrolls. The forming unit 110 further comprises a module 112 for depositing the fibrous suspension onto the lower fabric, which is located on the cylinder. By way of example, the forming unit may be of the type marketed by the French company ALLIMAND under the trade name ROTOFORMER. Although such means are not shown in the figure, the machine may include means for driving the cylinder 111.

[0052] For reasons of simplicity, the non-woven material is not visible in this figure.

[0053] A parameter of the forming unit can be the quantity of glass microfibers contained in the fiber suspension that feeds it. As an example, the quantity of glass microfibers in the fiber suspension can be chosen so that the resulting nonwoven material comprises more than 40% glass microfibers by dry weight.

[0054] In [Fig. 1], the lower web 120 moves from left to right along the side supporting the nonwoven material being formed. For illustrative purposes, the speed of movement of the lower web (and therefore of the nonwoven material) can be greater than 5 m / min, as indicated above, and preferably greater than 25 m / min. The lower web and the nonwoven material supported by this web are driven by rollers 130 on which the lower web is mounted to circulate continuously in a clockwise direction, allowing continuous movement from left to right where the nonwoven material is supported by the lower web. Some of these rollers can be driven in rotation by motors, which are not shown for the sake of simplicity.

[0055] Downstream of the forming unit 110, a smoothing unit 140 is shown partially above the lower web. The smoothing unit comprises an upper web 141 which runs in the same direction as the lower web where it is in contact with the nonwoven material (more precisely, with the upper surface of the nonwoven material). For this purpose, the upper web is mounted to run continuously counterclockwise on rollers 142 and allow continuous running from left to right. The right side is where the top fabric is in contact with the non-woven material. Some of these rollers can be driven in rotation by motors, not shown for simplicity.

[0056] It is understood that in one area, the non-woven material is held between the lower fabric 120 and the upper fabric 141. This holding will be described in more detail below with reference to [Fig.3].

[0057] To smooth the non-woven material, the smoothing unit comprises a plurality of portions arranged consecutively in the direction of travel. Here, a first portion PI is shown, followed by a second portion P2. Portion PI is upstream of portion P2. The invention is not limited to the presence of only two portions and also applies to machines comprising, for example, three or four portions.

[0058] The first portion PI here comprises a plurality of orifices 144 which are openings allowing the water to be drawn in to pass through (in the case where a suction is applied; at the very least, they allow the suction). Alternatively, the first portion may have no orifices or only one orifice (this is not the case for the second portion, which has several orifices).

[0059] The openings are delimited by surface elements 143, which are solid portions serving as a support surface for the upper fabric. For a first portion without openings, the first portion comprises only one solid surface element.

[0060] It can be noted that a portion may have a plateau structure with solid areas and possibly empty areas.

[0061] The second portion P2 is here analogous to the portion PI provided with several orifices.

[0062] The lower surfaces of portions PI and P2 define a lower surface of The smoothing unit, referenced SI in the figure, is typically composed of perforated plates or a series of spaced blades, as shown in [Fig. 1], extending in a direction orthogonal to the direction of travel of the nonwoven material / fabrics. Between these blades, referenced 143, are openings 144.

[0063] The lower surface SI of the smoothing unit is pressed against the upper fabric of the smoothing unit due to its arrangement, at a location where the upper fabric is in contact with the non-woven material, as will be seen in [Fig. 3]. This pressing leads to a deformation of the lower fabric (and of the non-woven material) visible in [Fig. 1].

[0064] Within the smoothing unit, at least the second portion is controlled by a machine suction system, not shown in [Fig. 1] for simplicity. That being said, in the illustrated example, each portion P1 or P2 is connected to a 145 conduit which is its own and in fluidic communication with the machine's suction control system.

[0065] When suction is applied to a portion, a vacuum is obtained at the level of the portion to suction in particular liquid through the orifices 144.

[0066] Here, the suction control system is configured to apply stronger suction through the orifices of the second portion P2 than through the orifices of the first portion PI. In [Fig. 1], this is represented by an arrow extending from the line 145 associated with the second portion P2 that is longer than the arrow extending from the line 145 associated with the first portion PI.

[0067] The inventors observed that the nonwoven material obtained at the outlet of the forming unit 110, which always circulates on the lower fabric 120 of the forming unit, is particularly malleable when saturated with water. Therefore, it is advantageous to apply little or no suction through the orifices of the first portion PI. This allows for mechanical smoothing of the upper surface of the nonwoven material, even though the nonwoven material is then easily deformable.

[0068] Through the second portion P2 and its orifices, a stronger suction is applied to remove liquid from the non-woven material. The non-woven material remains in contact with the lower surface SI under the second portion, which also contributes to its smoothing by fixing the effect obtained in the portion PL

[0069] As an indication, the suction pressure of the first portion can be between 0 and -5 kPa. The suction pressure of the second portion can be on the order of several tens of kPa, preferably between -20 kPa and -40 kPa.

[0070] It can be noted that the portions and their associated conduits can be implemented by means of suction boxes known per se in non-woven material manufacturing machines.

[0071] As indicated above, the invention applies to smoothing units comprising more than two portions. That being said, the last portion, i.e., the most downstream portion, must have a stronger suction than that applied to the first portion. Also, and preferably, the suction level should increase from upstream to downstream between each consecutive portion.

[0072] To facilitate the pressing of the lower surface SI against the upper fabric, the non-woven material, and the lower fabric, the machine further comprises, on either side of the lower surface SI (i.e., upstream and downstream), a curved lower support surface 146 upstream of the lower surface SI, and a curved lower support surface 147 downstream of the lower surface SL

[0073] Preferably the lower curved support surface 147, the one located downstream, is controlled by the machine's suction control system to apply a aspiration. This can help to hold the webs and the non-woven material together well. The two curved lower support surfaces have centers of curvature located under the lower web (where it supports the non-woven material).

[0074] Also, in the example of [Fig. 1], a drip roller 150 (also known as a "dandy roll") is shown, arranged at the outlet of the forming unit and upstream of the smoothing unit. This drip roller is arranged to be in contact with the upper surface of the nonwoven material. This drip roller can be driven in rotation by drive means not shown in [Fig. 1]. Preferably, the drip roller is driven in rotation at a different speed than the speed at which the nonwoven material is driven in the direction of travel. The inventors have observed that this creates shear and reorganizes the fibers of the nonwoven material, which further prevents the formation of clumps and results in a smoother nonwoven material.

[0075] The machine of [Fig. 1], and more specifically the smoothing unit 140, includes another optional element, a non-woven material thickness control unit 160 arranged downstream of the location where the lower surface SL is located. The non-woven material thickness control unit 160 here includes a roller. Other units known per se may be used, for example, using several rollers in a rolling mill configuration.

[0076] Figure 2 shows another example of a manufacturing machine 100' which differs from that of Figure 1, notably in that its forming unit 110' does not deposit a fibrous suspension onto a fabric mounted on a cylinder, but rather an inclined table-type forming unit. The forming unit 110' also includes a module 112' for depositing the fibrous suspension onto the lower fabric, which moves along an inclined table 111'. In the inclined table 111', a set of suction chambers 113' draws the liquid from the nonwoven material that has just been deposited. As an example, the forming unit could be of the type marketed by the French company ALLIMAND under the trade name HYDROFIBER.

[0077] In the same way as for [Fig.1] and although it has not been shown, the machine shown in [Fig.2] may include a thickness control unit downstream of the surface SI and upstream of the curved surface 147.

[0078] It is understood that the invention applies to any type of forming unit capable of forming a non-woven material comprising glass microfiber onto a lower fabric. For example, the forming unit may also be of the round type, also called a "vat former" in English. By way of example, the forming unit may be of the type marketed by the French company ALLIMAND under the trade name CAISSE DE TÊTE FP, SFP, S4, or E-BOX.

[0079] It should be noted that the lower canvas of the forming unit on which is The fibrous suspension deposited is the same as that on which the nonwoven material is at the point of passage through the smoothing unit. Indeed, the smoothing unit preferentially processes a liquid-saturated nonwoven material, which is not yet transferable to another screen, and which is therefore on the same lower screen as that on which the forming unit forms the nonwoven material.

[0080] Figure 3 shows in more detail the smoothing unit, which can be that of machine 100 of Figure 1, machine 100' of Figure 2, or any other machine equipped with a forming unit. In Figure 3, the lower fabric 120, the non-woven material 200, and the upper fabric 141 are shown spaced apart, these three elements actually being in contact at least along a portion, contrary to what is shown. As can be seen, this portion extends between the two lowest drive rollers 142 of the smoothing unit.

[0081] To achieve good smoothing and prevent deterioration of the non-woven material 200, the lower surface SI has a radius of curvature R, with a center of curvature C located above the lower surface SI. As an indication, a suitable radius of curvature for smoothing the non-woven material can be between 2 m and 100 m, preferably between 5 m and 30 m, for example, 15 m. This radius of curvature is obtained by the relative position of each of the surface elements 144 of the portions PI and P2, to define a curve.

[0082] Within the smoothing unit of [Fig.3], a suction orifice 180 was formed arranged to allow recovery of supernatant liquid upstream of the first portion PI.

[0083] The suction orifice allows suction controlled by the machine's suction control system. The suction orifice is defined by a conduit 181 (in fluidic communication with the machine's suction control system) and, at the orifice, by a blade 182 that is flush with the surface of the upper screen to lift the supernatant liquid. The blade 182 extends upstream from the first portion PL.

[0084] The suction port 180 is optional.

[0085] Figure 4A is a photograph of a nonwoven material obtained without the use of a smoothing unit. This photograph shows raised areas indicating the presence of glass microfiber clumps, resulting from the presence of fiber flocs directly exiting the forming unit.

[0086] Figure 4B is a photograph of a non-woven material manufactured by a machine which also does not have a smoothing unit, but which has a drain roller similar to the drain roller 150 described, for example, with reference to Figure 1. This non-woven material still has raised areas and its appearance is not satisfactory for use in a battery.

[0087] Figure 4C is a photograph of a non-woven material manufactured by a machine that includes a smoothing unit of the type shown in Figures 1 to 3 described above. As can be seen, the non-woven material has a smoother appearance and does not contain lumps that exhibit significant relief, as seen in the non-woven materials of Figures 4A and 4B.

[0088] From Figures 4B and 4C, it can be understood that the draining roller alone is not sufficient to prevent defects in non-woven materials. On the other hand, it has been observed that the draining roller combined with a smoothing unit improves smoothness.

[0089] The invention is not limited to the examples described and represented because various modifications can be made to them without going out of its scope.

Claims

Demands

1. Machine for manufacturing non-woven material (200) comprising glass microfiber, comprising: a forming unit (110, 110') of a non-woven material comprising glass microfiber, on a lower web (120) driven in a direction of travel, downstream of the forming unit and above the lower web, a smoothing unit (140) comprising an upper web (141) traveling in the direction of travel and extending so that the non-woven material is held between the lower web and the upper web at the level of the smoothing unit, and a plurality of portions (PI, P2) arranged consecutively in the direction of travel, the plurality of portions defining a lower surface (SI) of the smoothing unit pressed against the upper web at a location where the upper web is in contact with the non-woven material,wherein at least the last portion is provided with a plurality of orifices and is controlled by a suction control system of the smoothing unit to apply suction through the orifices of the last portion, and if the first portion is provided with a plurality of orifices, the suction is stronger through the orifices of the last portion than through the orifices of the first portion.

2. Machine according to claim 1, wherein the lower surface of the plurality of portions has a given radius of curvature (R) with a center of curvature (C) located above the lower surface.

3. Machine according to claim 1 or 2, comprising a suction orifice (180) arranged to permit recovery of supernatant liquid upstream of the first portion, the suction orifice being controlled by said suction control system.

4. Machine according to any one of claims 1 to 3, comprising a drain roller (150) arranged at the outlet of the forming unit and upstream of the smoothing unit, the drain roller being arranged to be in contact with the upper face of the non-woven material.

5. Machine according to claim 4, wherein the draining roller is driven in rotation at a different speed than the speed at which the non-woven material is driven in the direction of travel.

6. A machine according to any one of claims 1 to 5, comprising a downstream nonwoven material thickness control unit (160). of the location where the lower surface of the plurality of portions is in contact with the upper canvas.

7. Machine according to any one of claims 1 to 6, wherein the forming unit is configured to deliver a non-woven material comprising more than 40% by dry weight of glass microfiber.

8. Machine according to any one of claims 1 to 7, comprising, on either side of the lower surface, curved lower support surfaces (146, 147) in contact with the lower web and each having a center of curvature which is below the lower web.

9. A method for manufacturing a nonwoven material (200) comprising glass microfiber, comprising: a forming by a forming unit (110, 110') of a nonwoven material comprising glass microfiber, on a lower web (120) conveyed in a direction of travel, a smoothing carried out downstream of the forming unit and above the lower web, by means of a smoothing unit (140) comprising an upper web (142) conveying in the direction of travel and extending so that the nonwoven material is held between the lower web and the upper web at the level of the smoothing unit, and a plurality of portions (PI, P2) arranged consecutively in the direction of travel, the plurality of portions defining a lower surface (SI) pressed against the upper web at a location where the upper web is in contact with the nonwoven material,in which at least the last portion is provided with a plurality of orifices and is controlled to apply suction through the orifices of the last portion, and if the first portion is provided with a plurality of orifices, the suction is stronger through the orifices of the last portion than through the orifices of the first portion.

10. A method according to claim 9, wherein the non-woven material is conveyed at a speed greater than 5 m / min and preferably greater than 25 m / min.