PROCESS AND APPARATUS FOR THE PRODUCTION OF A BULKY SPUNBOND NONWOVEN FABRIC

Abstract

A process for producing a nonwoven fabric comprises the steps of a spinneret extruding a plurality of filaments, cooling the filaments with one or more cooling elements arranged below the spinneret, drawing the filaments in a drawing duct and laying the filaments on a movable support to form a nonwoven fabric. The process further comprises suctioning gas in a first suction device, heating the nonwoven fabric using a heated calender downstream of the first suction device to consolidate the filaments of the nonwoven fabric and to cause an increase in volume of the nonwoven fabric, suctioning gas below the movable support with a higher second suction speed, in a second suction device downstream of the heated calender, and suctioning gas below the movable support in a third suction region with a third suction speed lower than the second suction speed, by a shutter with one or more adjustable openings.

Claims

1. A process for producing a nonwoven fabric (150), comprising the steps of: (a) extruding a plurality of filaments (100) using a spinneret (11); (b) cooling said filaments (100) using 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 said 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 using a first suction device (31) in a first suction region (30) below said movable support (28); (f) heating the nonwoven fabric (150) using a heated calender (11a, 11b) arranged downstream of the first suction region (30) to consolidate the said filaments of said nonwoven fabric (150) and to cause a volume increase in said nonwoven fabric (150); (g) suctioning gas below said movable support (28) with a second suction speed higher than said first suction speed, in a second suction region (40) arranged downstream of the heated calender (11a, 11b), using a second suction device (41); and (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 using a shutter (51) equipped with one or more openings (52), the opening degree of said one or more openings being adjustable.

2. The process according to claim 1, wherein the third suction speed progressively decreases.

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

4. The process according to claim 1, wherein during said step (f), the temperature of the heated calender (11a, 11b) is between 40 C. and 180 C.

5. The process according to claim 1, wherein during said step (b), said one or more cooling elements (15,15) provide gas having a temperature between 10 C. and 50 C.

6. The process according to claim 1, wherein in said step (d) the drawn filaments are laid at the first suction region (30).

7. The process according to claim 1, wherein the filaments are bicomponent filaments.

8. An apparatus (10) for producing a nonwoven fabric (150), said apparatus 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) adapted to cool said plurality of filaments downstream of the spinneret (11), said one or more cooling elements adapted to direct a gas against said plurality of filaments; a drawing channel (17) arranged downstream of said one or more cooling elements (15,15) and adapted to draw said plurality of filaments (100); a movable support (28), permeable to gases and adapted to collect said drawn plurality of 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. The apparatus according to claim 8, wherein the shutter (51) is fluidically connected to said second suction device (41).

10. The apparatus according to claim 9, wherein the openings (52) are adjustable to different opening degrees.

11. The apparatus as in claim 10, wherein the openings are adjustable using an anemometer or Pitot tube.

12. The apparatus as in claim 8, wherein the gas is air.

13. The apparatus as in claim 9, wherein the gas is air and the openings are adjustable using an anemometer.

14. The process according to claim 2, wherein the first and second suction speeds are between 10 m/s and 50 m/s.

15. The process according to claim 14, wherein during said step (f), the temperature of the heated calender (11a, 11b) is between 40 C. and 180 C.

16. The process according to claim 2, wherein during said 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.

17. The process according to claim 5, wherein during said step (b), said one or more cooling elements (15,15) provide gas having a speed between 2 m/s and 60 m/s.

18. The process according to claim 2, wherein in said step (d) the drawn filaments are laid at the first suction region (30) and the filaments are bicomponent filaments.

Description

[0029] With reference to the accompanying figures, exemplary and non-limiting embodiments of the present invention are now described, in which:

[0030] FIG. 1 is a schematic view of an apparatus for producing a spunbond nonwoven fabric according to an embodiment of the present invention;

[0031] FIG. 2 is a schematic view of a portion of the apparatus in FIG. 1 which shows the suction regions below the movable support.

[0032] 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 Far.

[0033] 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.

[0034] The apparatus 10 further comprises cooling elements adapted to direct a gas, preferably air, against the filaments 100.

[0035] The cooling elements 15, 15 direct gas (typically air) against the filaments 100, so as to lower their temperature.

[0036] The cooling elements 15, 15 can be configured to direct air flows at different temperatures and/or speeds to different regions.

[0037] 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.

[0038] It should be noted that the position below is considered under the condition of use of the apparatus 10.

[0039] 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).

[0040] 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.

[0041] 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.

[0042] The suction elements may comprise one or more of side suction elements 13 and center suction elements 12.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The first region 30 is typically arranged at the region where the filaments 100 come into contact with the movable support 28.

[0050] The first suction device 31 typically comprises a first channel 32 and a first aspirator 33.

[0051] 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.

[0052] 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).

[0053] Downstream (considering the feed direction D) of the first region 30, there is a heated calender 11a, 11b.

[0054] The calender 11a, 11b typically comprises a pair of rollers 11a, 11b arranged above and below the movable support 28.

[0055] The calender 11a, 11b specifically comprises at least one roller 11a that is heated typically to a temperature between 4 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.

[0056] 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. 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.

[0057] The apparatus 10 also has a second suction device 41.

[0058] 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.

[0059] The second suction device 41 defines at least one second suction region 40 arranged downstream of the calender 11a, 11b.

[0060] 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.

[0061] As with the first speed, the second speed is considered as an average value in the second region 40.

[0062] 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.

[0063] 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.

[0064] The second region 40 is thus located within this seat 44, downstream of the calender 11a, 11b.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] Thus, the suction speed decreases even more gradually downstream of the second suction region.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] Preferably, the openings are fluidically connected to the second aspirator 43.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] In use, the spinneret 11 extrudes a plurality of filaments 100.

[0080] 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.

[0081] Possibly, harmful gases are removed from the region below the spinneret by means of suction devices 12, 13.

[0082] The filaments are then drawn in the drawing channel 7 and laid onto the movable support 28.

[0083] The formation of a nonwoven fabric 150 on the movable support 28 is assisted by the suction provided by the first suction means 31.

[0084] 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.

[0085] 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 suctio region 30.

[0086] 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.

[0087] Typically, at this region upstream of the calender 11a, 11b, the suction speed is reduced by the presence of the calender 11a, 11b.

[0088] 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.