PROCESS AND APPARATUS FOR PRODUCING A SPUNBOND NONWOVEN FABRIC

Abstract

 Process for producing a nonwoven fabric (150), comprising the steps of:
(a) extruding a plurality of filaments (100) by means of a spinneret (11);
(b) cooling said filaments (100) by means of one or more cooling elements (15,15') arranged below said spinneret (11);
(c) drawing said filaments (100) in a drawing duct (17) arranged below said one or more cooling elements (15,15');
(d) laying the filaments (100) on a movable support (28) arranged below said drawing duct (17), along a feed direction (D) in order to form a nonwoven fabric (150);
(e) suctioning gas with a first suction speed by means of a first suction device (31) in a first suction region (30) below said movable support (28);
(f) heating the nonwoven fabric (150) by means of a heated calender (11a,11b) arranged downstream of the first suction region (30) to consolidate the filaments of said nonwoven fabric (150) and to cause an increase in the volume of said nonwoven fabric (150);
(g) suctioning gas below said movable support (28) with a second suction speed higher than said first speed, in at least one second suction region (40) arranged downstream of the heated calender (11a, 11b), by means of a second suction device (41);
(h) suctioning gas below said movable support (28) in a third suction region (50) with a third suction speed lower than the second suction speed, and able to be controlled by means of a shutter (51) equipped with one or more adjustable openings (52).

Description

[0001] The present invention relates to the field of nonwoven fabrics, particularly that of voluminous nonwoven fabrics.

[0002] As a matter of fact, it is well known that voluminous and, in particular, very thick nonwoven fabrics can be made by thermally treating these fabrics. The filaments of these fabrics are configured to crimp when thermally treated, so that their bulkiness is increased.

[0003] Methods and apparatuses for making these fabrics are known and typically have thermal treatment devices such as ovens or the like. Therefore, these methods are complex and energy consuming.

[0004] In addition, the known apparatuses are bulky because they require a large number of components arranged in series in order to make a voluminous nonwoven fabric. Specifically, these apparatuses have a device dedicated to thermal treatment and typically a compacting device upstream of the thermal treatment, so that the nonwoven fabric is at least partially shaped before the thermal treatment.

[0005] Object of the present invention is to solve the above mentioned problems and to provide a simple apparatus and process for producing a voluminous nonwoven fabric by means of a compact apparatus.

[0006] These and other objects are solved by the present invention by means of a process and apparatus according to one or more of the appended claims.

[0007] In particular, an apparatus and process according to the independent claims are object of the present invention. Preferred aspects are set forth in the dependent claims.

[0008] According to an aspect of the present invention, a process for producing a nonwoven fabric comprises the steps of: (a) extruding a plurality of filaments by means of a spinneret; (b) cooling the filaments by means of one or more cooling elements arranged below the spinneret; (c) drawing the filaments in a drawing duct arranged below the one or more cooling elements; (d) laying the filaments on a movable support arranged below the drawing duct, that is movable along a feed direction, in order to form a nonwoven fabric; (e) suctioning gas with a first suction speed by means of a first suction device in a first suction region below the movable support; (f) heating the nonwoven fabric by means of a heated calender arranged downstream of the first suction region to consolidate the filaments of the nonwoven fabric and to cause an increase in the volume of the nonwoven fabric; (g) suctioning gas below the movable support with a second suction speed higher than the first speed, in at least one second suction region arranged downstream of the heated calender, by means of a second suction device; (h) suctioning gas below the movable support in a third suction region with a third suction speed lower than the second suction speed, and obtained by means of a shutter equipped with one or more openings which have a preferably adjustable opening degree.

[0009] The present method allows a voluminous nonwoven fabric to be formed by means of a simple and compact apparatus. In particular, the suction regions allow the nonwoven fabric to be effectively formed, while the heated calender allows the volume to be increased immediately after the filaments have been laid.

[0010] It should be noted that, hereinafter, reference will be made to "first region," "second region" and "third region". These expressions are intended to mean the three suction regions. Similarly, to indicate the suction speed in one of the three suction regions, "first speed", "second speed" and "third speed" will also be simply referred to.

[0011] The calender is typically designed so that the pressure it exerts does not prevent the nonwoven fabric from increasing in volume. As the suction speed in the second region is higher than in the first region, the filaments downstream of the calender are prevented from being pulled back by the low pressure caused by the first suction region.

[0012] The third suction region allows the suction force to be decreased non-instantaneously and thus provides a region where suction is lower compared to the second suction region.

[0013] In particular, according to a preferred aspect, the third suction speed is progressively decreasing. In other words, in the third suction region, the suction speed has more values which decrease along the feed direction of the nonwoven fabric.

[0014] Therefore, it should be noted that reference will be generally made to the "third suction speed" even though the third region has multiple decreasing suction values.

[0015] Thus, the "third suction speed" is the set of these speeds. When a characteristic is applied to the "third suction speed", it is intended to be applied to each value of the third suction speed. Thus, when the third suction speed is described as lower than the second suction speed, this means that each of the values taken by the third speed is lower than the value of the second suction speed.

[0016] At the first and second suction regions, the suction speed is substantially uniform. "Substantially" means that it is uniform within the normal variability of a fluid flow within a tube (e.g., as known, the speed of a flow within a tube or channel is typically higher at the axis of the tube or channel and is slightly lower at the walls). The value of the first and second suction speeds is to be understood as the average value of this speed, taking into account the normal speed variations in a flow.

[0017] As discussed, the gas suction speed in the third suction region is lower than in the second suction region. This prevents the suction speed downstream of the second suction region from instantaneously decreasing to zero, which could cause deformations in the nonwoven fabric.

[0018] According to an aspect, the first and second suction speeds are between 10 m/s and 50 m/s. However, the second suction speed is always higher than the first suction speed. According to an aspect, the temperature of the heated calender is between 40°C and 180°C when it thermally treats the nonwoven fabric.

[0019] According to an aspect, the cooling elements provide gas having temperature between 10 °C and 50 °C and speed between 2 m/s and 60 m/s.

[0020] According to an aspect, the drawn filaments are laid at the first suction region. According to an aspect, the filaments are bicomponent filaments.

[0021] An aspect of the present invention further relates to an apparatus for producing a nonwoven fabric, comprising: a spinneret for extruding a plurality of filaments; one or more cooling elements to cool the filaments downstream of said spinneret, which are adapted to direct a gas, preferably air, against the filaments; a drawing channel arranged downstream of the one or more cooling elements and adapted to draw the filaments; a movable support, permeable to gases, adapted to collect the drawn filaments so as to form a nonwoven fabric and configured to move the nonwoven fabric along a feed direction; a heated calender adapted to heat the nonwoven fabric and cause an increase in the volume thereof; a first suction device adapted to define a first suction region upstream of the heated calender relative to the feed direction, a second suction device adapted to define at least one second suction region downstream of the heated calender, and a shutter equipped with one or more adjustable openings for the passage of gas, the shutter being adapted to define a third suction region arranged downstream of the second suction region.

[0022] Furthermore, it should be noted that the second suction device has been described as defining "at least" one second suction region downstream of the calender.

[0023] In possible embodiments, the second suction device can be fluidically connected to a seat into which one of the rollers of the heated calender is inserted. Thus, the second suction device can suction gas (by affecting the air around the calender roller), even at a region upstream of the heated calender. This region is not to be considered part of the second suction region, which is the region downstream of the calender where the suction of the second suction device acts.

[0024] Furthermore, as better discussed later, the shutter defining the third suction region can be connected to the same aspirator as the second suction device. In this case, the suction speed at the third suction region can be controlled by the opening degree of the adjustable openings.

[0025] In a broad sense, therefore, the second suction device also provides the suction force to the third suction region. However, "second suction region" is intended to mean the suction region treated by the second suction device, downstream of the calender and upstream of the shutter.

[0026] According to an aspect, the shutter is fluidically connected to the second suction device.

[0027] According to an aspect, the adjustable openings are adjusted by an anemometer or Pitot tube.

[0028] With reference to the accompanying figures, exemplary and non-limiting embodiments of the present invention are now described, in which:

• figure 1 is a schematic view of an apparatus for producing a spunbond nonwoven fabric according to an embodiment of the present invention;
• figure 2 is a schematic view of a portion of the apparatus in figure 1 which shows the suction regions below the movable support.

[0029] An apparatus 1 for producing a nonwoven fabric 150 according to the present invention comprises a spinneret 11 for extruding a plurality of filaments 100 by means of extrusion holes (not shown in detail) and having one or more extruders (not shown) connected thereto for extruding or co-extruding single-, bi- or multi-component filaments 100, as known in the art and as for example described and claimed in documents EP1126055 and EP0786543, both in the name of Farè.

[0030] The polymer is distributed to the spinneret holes by known methods, such as by one or more planetary gear pumps, which can feed a single polymer (for single-component filaments) or multiple polymers (for multi-component filaments) to the extrusion holes. In the case of multiple components of different materials, the materials are typically fed to the extrusion holes through independent circuits. Typically, the distribution channels of the polymer (or polymers) from the pump to the extrusion holes of the spinneret 11 are sized (length and section) so as to have uniform pressure loss at every hole, in a manner known in the art, such as for example having all the same length and section.

[0031] The apparatus 10 further comprises cooling elements adapted to direct a gas, preferably air, against the filaments 100.

[0032] The cooling elements 15, 15' direct gas (typically air) against the filaments 100, so as to lower their temperature.

[0033] The cooling elements 15, 15' can be configured to direct air flows at different temperatures and/or speeds to different regions.

[0034] For example, in the embodiment shown, there are first cooling elements 15 arranged below the spinneret 11 and second cooling elements 15' arranged below the first cooling elements 15, or in any case configured to eject a gas flow from a position below that from which gas is ejected from the first cooling elements.

[0035] It should be noted that the position "below" is considered under the condition of use of the apparatus 10.

[0036] The cooling elements 15, 15' can be configured to eject gas along a substantially horizontal direction (in use condition), that is, substantially parallel to the plane of the spinneret surface from which the filaments 100 are extruded. However, e.g. via diverters or by tilting the channel of the cooling elements that directs gas flow against the filaments 100, at least part of the gas flow ejected by the cooling elements can be oblique (at an angle greater than 20°) relative to the plane of the spinneret surface from which the filaments 100 are extruded (i.e., relative to a horizontal plane, considering a use condition of the apparatus 10).

[0037] Typically, the cooling elements 15,15' provide gas having temperature between 10 °C and 50 °C and speed between 2 m/s and 60 m/s. As discussed, in case of different cooling elements, the gas speed and/or temperature are different between the different cooling elements.

[0038] According to a preferred aspect, the apparatus has suction elements 12, 13 adapted to suction gases and, in particular, for removing harmful elements formed during filament extrusion, such as oligomers, from the region arranged below the spinneret 11. These harmful gases may be harmful to the health of operators placed in close proximity to the apparatus and/or may adhere to the outer surface of the filaments, thus impairing their characteristics, such as their mechanical properties.

[0039] The suction elements may comprise one or more of side suction elements 13 and center suction elements 12.

[0040] Center suction elements 12 are typically configured to suction gas from an opening on the spinneret arranged between the filaments, i.e., from a region without extrusion holes but at least partially surrounded by extrusion holes for filaments 100 (or at least having them on its sides). These center suction elements 12 typically comprise a channel formed in the spinneret 11.

[0041] Center suction elements, on the other hand, are typically arranged below the spinneret 11 (typically above the cooling elements 15, 15') and they suction gases from a region external, or lateral, to the filaments 100.

[0042] Below the cooling elements there is a drawing duct 17 adapted to draw the filaments 100, which are then laid on a movable support 28.

[0043] In this region, the filaments are typically aerodynamically drawn by injecting gas (usually air) towards the movable support 28. This injection can take place, for example, through channels 60, preferably with gas speeds between 20 and 110 m/s within the drawing channel. The size of the channels 60 can be changed by means of special movable elements, so that the speed at which gases flow into the drawing channel 17 can be adjusted.

[0044] The movable support, typically made of nonwoven fabric, is movable by means of known elements, typically along a closed path, and is configured to be gas permeable, or at least air permeable. The movable support 28 is configured to move, in use, the filaments 100 (i.e., the nonwoven fabric 150 formed by the laid filaments) along a feed direction D, which is typically substantially horizontal in use condition.

[0045] A first suction region 30 (as discussed, henceforth also referred to as "first region 30") is defined by first suction device 31 below the movable support 28.

[0046] The first region 30 is typically arranged at the region where the filaments 100 come into contact with the movable support 28.

[0047] The first suction device 31 typically comprises a first channel 32 and a first aspirator 33.

[0048] The first suction device is configured so that, in use, the gas suction speed (referred to from now on as "first speed") is preferably between 10 and 50 m/s, at least near the nonwoven fabric 150.

[0049] As discussed, this value is to be understood as the average value of the suction speed. This value is substantially uniform, within the normal variability caused, for example, by a channel 32 (as discussed, the value of a flow speed in a tube/channel is typically higher in the center of the same tube/channel than near its walls).

[0050] Downstream (considering the feed direction D) of the first region 30, there is a heated calender 11a, 11b.

[0051] The calender 11a, 11b typically comprises a pair of rollers 11a, 11b arranged above and below the movable support 28.

[0052] The calender 11a, 11b specifically comprises at least one roller 11a that is heated typically to a temperature between 40 and 180°C, and in any case such as to cause the filaments 100 of the nonwoven fabric 150 to crimp, so as to increase the thickness H. The thickness H of the nonwoven fabric 150 downstream of the calender 11a, 11b is therefore greater than the thickness of the nonwoven fabric 150 upstream of the calender 11a, 11b.

[0053] The calender can be heated by means of a heating liquid, such as oil, circulating inside the calender, that is to say inside at least one of the rollers of the calender 11a, 11b.

[0054] The surfaces of the rollers 11a, 11b are preferably smooth, although the use of rollers equipped with protrusions (typically the roller 11a above the movable support 28) is not excluded.

[0055] The apparatus 10 also has a second suction device 41.

[0056] The second suction device 41 typically comprises a suction channel and an aspirator, which for convenience's sake (so as to distinguish them from the similar elements of the first suction device) will be referred to here and in the following as the second channel 42 and the second aspirator 43, respectively.

[0057] The second suction device 41 defines at least one second suction region 40 arranged downstream of the calender 11a, 11b.

[0058] The suction speed of the second suction device (the "second speed", as named herein) is lower than the first speed. The second speed is typically considered at the moving support 28.

[0059] As with the first speed, the second speed is considered as an average value in the second region 40.

[0060] As previously discussed, the second suction device 41 can also be fluidically connected to a region located between the calender 11a, 11b and the first suction region 30. This region is not part of the second region 40 and the characteristics discussed hereafter do not necessarily apply to this region upstream of the calender 11a, 11b, too.

[0061] In particular, as in the embodiment shown in the figures, this possibility may occur if a roller 11b of the calender, arranged below the movable support 28, is rotatably arranged within a seat 44 which is fluidically connected to the second aspirator 43 by an opening 45.

[0062] The second region 40 is thus located within this seat 44, downstream of the calender 11a, 11b.

[0063] Typically, the section of the opening 45 is comparable to the size of the second region 40. Therefore, the second speed can be measured at this opening 45 or slightly upstream of this opening 45.

[0064] The apparatus 10 further comprises a shutter 51 adapted to define a third suction region 50 located downstream of the second region 40, considering the feed direction D.

[0065] The shutter 51 is typically made with walls that are substantially impermeable, or at least not very permeable, to air and that have one or more openings 52 arranged thereon. For the sake of simplicity, reference will be made to embodiments with multiple openings 52. Where not specified, the following characteristics also apply to embodiments with a single opening 52. Therefore, the shutter 51 typically defines a chamber below the movable support device 28, made with walls of substantially impermeable material but equipped with openings to allow gas to flow through locally (i.e., at the openings themselves).

[0066] The openings 52 allow a reduced gas flow to be suctioned at the third region 50. The suction speed at the third region (measured in the shutter 51), that is, the "third speed", is lower than the second speed.

[0067] As discussed, the third speed preferably has a progressively decreasing value as a function of the feed direction D of the nonwoven fabric 150. This can be accomplished, for example, by means of openings having progressively decreasing size.

[0068] Thus, the suction speed decreases even more gradually downstream of the second suction region.

[0069] Movable elements, not shown in detail, are preferably arranged at the openings 52 so as to define at least one minimum size (possibly null) and one maximum size of the openings 52.

[0070] In general, the movable elements are controlled so that the opening degree (i.e., the useful size for gas passage) of the openings 52 can be finely adjusted.

[0071] According to a possible solution, the openings are controlled according to an anemometer or Pitot tube, so that the opening degree of the openings 52 is adjusted according to the gas speed in the third suction region, or "third speed". In particular, the anemometer or Pitot tube can be used to measure the value of the third speed and this value can be used to vary the opening degree (increasing or decreasing it) as needed.

[0072] In general, the movable elements can be made in various ways (e.g. a linearly movable shutter or hinged to resemble a door, etc.). Similarly, the control of the movable elements can be achieved in different ways. For example, movable elements of different openings can be controlled independently from each other. Alternatively, multiple movable elements can be controlled by a single control for all the movable elements, for example, a control configured to define different opening degrees between the various openings (so that, for example, the fully closed position of the most downstream opening may correspond to a position only partially closed of the opening 52 arranged further upstream).

[0073] Preferably, the openings are fluidically connected to the second aspirator 43.

[0074] Therefore, the suction of the second aspirator 43 causes gases to be suctioned at the third suction region as well. This action is reduced due to the presence of the openings 52.

[0075] In particular, in the case of openings 52 with adjustable opening degree, the third speed can be adjusted compared to the second speed, so that a given value of second speed can correspond to multiple values of third speed, depending on the opening degree of the openings 52.

[0076] A simpler embodiment, but with less adjustment degree, provides openings whose width cannot be changed. In this case, a second speed value substantially corresponds to a single third speed value.

[0077] In use, the spinneret 11 extrudes a plurality of filaments 100.

[0078] The filaments are cooled by the cooling elements 15, 15' preferably by means of gas flows having temperature between 10 °C and 50 °C and/or speed between 2 m/s and 60 m/s.

[0079] Possibly, harmful gases are removed from the region below the spinneret by means of suction devices 12, 13.

[0080] The filaments are then drawn in the drawing channel 7 and laid onto the movable support 28.

[0081] The formation of a nonwoven fabric 150 on the movable support 28 is assisted by the suction provided by the first suction means 31.

[0082] Next, the nonwoven fabric 150 formed by the filaments 100 is calendered by a heated calender 11a, 11b. Since the filaments 100 crimp, the volume, and in particular the thickness H, of the nonwoven fabric 150 increases.

[0083] Downstream of the calender, the second suction device 41 suctions air below the nonwoven fabric through the movable support 28 at a speed higher than the first speed, so as to prevent the nonwoven fabric from being pulled back to the first suction region 30.

[0084] Possibly, the second suction device can also suction air at a further region located between the calender 11a, 11b and the first suction region 30.

[0085] Typically, at this region upstream of the calender 11a, 11b, the suction speed is reduced by the presence of the calender 11a, 11b.

[0086] The shutter 51 equipped with openings 52 and arranged downstream of the second region 40, forms a third suction region 50 with suction speed lower than the second speed. Preferably, the opening degree of the openings 52 is adjusted in order to achieve the desired value of the third speed, or otherwise a value of the third speed decreasing according to desired values.

Claims

1. Process for producing a nonwoven fabric (150), comprising the steps of:

(a) extruding a plurality of filaments (100) by means of a spinneret (11);

(b) cooling said filaments (100) by means of one or more cooling elements (15,15') arranged below said spinneret (11);

(c) drawing said filaments (100) in a drawing duct (17) arranged below said one or more cooling elements (15,15');

(d) laying the filaments (100) on a movable support (28) arranged below said drawing duct (17), along a feed direction (D) in order to form a nonwoven fabric (150);

(e) suctioning gas with a first suction speed by means of a first suction device (31) in a first suction region (30) below said movable support (28);

(f) heating the nonwoven fabric (150) by means of a heated calender (11a,11b) arranged downstream of the first suction region (30) to consolidate the filaments of said nonwoven fabric (150) and to cause an increase in the volume of said nonwoven fabric (150);

(g) suctioning gas below said movable support (28) with a second suction speed higher than said first speed, in a second suction region (40) arranged downstream of the heated calender (11a, 11b), by means of a second suction device (41);

(h) suctioning gas below said movable support (28) in a third suction region (50) with a third suction speed lower than the second suction speed, and obtained by means of a shutter (51) equipped with one or more openings (52), the opening degree of said one or more openings being preferably adjustable.

2. Process according to claim 1, wherein the third suction speed is progressively decreasing.

3. Process according to claim 1 or 2, wherein the first and second suction speeds are between 10 m/s and 50 m/s.

4. Process according to one of the preceding claims, wherein during step (f) the temperature of the heated calender (11a, 11b) is between 40 °C and 180 °C.

5. Process according to any one of the preceding claims, wherein during step (b), said one or more cooling elements (15,15') provide gas having a temperature between 10 °C and 50 °C and/or a speed between 2 m/s and 60 m/s.

6. Process according to any one of the preceding claims, wherein in said step (d) the drawn filaments are laid at the first suction region (30).

7. Process according to any one of the preceding claims, wherein the filaments are bicomponent filaments.

8. Apparatus (10) for producing a nonwoven fabric (150), comprising:

- a spinneret (11) adapted to extrude a plurality of filaments (100) and comprising an extrusion surface (2a);

- one or more cooling elements (15, 15') to cool said filaments downstream of the spinneret (11), which are adapted to direct a gas, preferably air, against said filaments;

- a drawing channel (17) arranged downstream of said one or more cooling elements (15,15') and adapted to draw said filaments (100);

- a movable support (28), permeable to gases, adapted to collect said drawn filaments so as to form a nonwoven fabric and configured to move said nonwoven fabric along a feed direction (D).

- a heated calender (11a,11b) adapted to heat said nonwoven fabric (150) and cause an increase in the volume of said nonwoven fabric (150),

- a first suction device (31) adapted to define a first suction region (30) upstream of said heated calender with respect to the feed direction (D), a second suction device (41) adapted to define at least one second suction region (40) downstream of the heated calender, and a shutter (51) equipped with one or more openings (52)

- for the passage of gas, the shutter being adapted to define a third suction region (50) arranged downstream of said second suction region (40).

9. Apparatus according to claim 8, wherein the shutter (51) is fluidically connected to said second suction device (41).

10. Apparatus according to claim 9, wherein the openings (52) have adjustable opening degree, the adjustment of said adjustable openings (52) being preferably controlled by means of an anemometer or Pitot tube.

Drawing