WO2004031463A2

WO2004031463A2 - Method and device for stabilizing the edges of a nonwoven web

Info

Publication number: WO2004031463A2
Application number: PCT/IB2003/004343
Authority: WO
Inventors: Giancarlo Appiani; Bruno Cometa; Nicola Maglia
Original assignee: Tenotex Spa
Priority date: 2002-10-01
Filing date: 2003-10-01
Publication date: 2004-04-15
Also published as: ES2262025T3; AU2003265072A8; ATE321906T1; AU2003265072A1; EP1556536B1; WO2004031463A3; EP1556536A2; DE60304367D1; DE60304367T2; ITVI20020209A1

Abstract

A method for stabilizing the edges (B, B') of a nonwoven web (V) on a movable support surface (3), wherein the web is obtained by continuous carding and spinning (A) of long fibers (Fl) and by subsequently laying short fibers (Fc) on the web (V) which is driven on the movable support surface. As the short fibers (Fc) are laid thereon, the side edges (B, B') of the web (V) are at least partly covered and compressed against the movable support surface (3), so that in such area short fibers (Fc) are prevented from being laid along the edges, whose stability is thereby increased, by preventing rolling or folding thereof. The covering and compressing action is exerted on the longitudinal edges of the web over a length corresponding at least to the short fiber laying area, and over a transverse width which is predetermined by using a pair of plates (10, 10') which are designed to cover the edges (B, B') and are at least partly in contact with the movable support surface (3).

Description

METHOD AND DEVICE FOR STABILIZING THE EDGES OF A NONWOVEN WEB

Technical field

The present invention relates to a method for stabilizing the edges of a nonwoven web in accordance with the preamble of claim 1.

The invention also relates to a device for implementing the method, as well as the nonwoven fabric obtained by using said method and apparatus.

Background art

Nonwoven fabric production methods and plants are known, which include at least one step of preparing a support web, formed by a long fiber layer or mat, at least one step of laying short staple fibers or wood pulp thereon and at least one step of bonding the short fibers together and to the preformed web on which they are laid, to provide the nonwoven fabric so obtained with the desired consistency.

The preformed mat or web is composed of long fibers and may be obtained by carding operation, i.e. by using carding machines, or by continuous spinning, i.e. by using so called spinning machines.

The wood pulp or the short fibers are generally conveyed and laid on the preformed long fiber web by the pneumatic action of machines that are known in the art as "airlaid machines".

Fiber bonding may be obtained by a thermal process, i.e. partial melting and welding at fiber contact points, or by a chemical process, i.e. partial melting and welding by means of a solvent, that is later evaporated, or yet by a mechanical process, i.e. weaving of fibers by using high pressure liquid jets. Typically, water is used for the latter operation, which is generally known by those skilled in the art as "hydro-entangling".

In a known method and plant, a long fiber web, prepared by carding or spinning is overlaid first with a short fiber layer and then with another carded or spun long fiber web. The assembly is later bonded by a thermal treatment or by hydro- entangling.

According to other methods, the short fiber layer is spread over an already bonded long fiber layer and is further bonded by another hydro-entangling operation.

Depending on the desired type of nonwoven fabric, such operations are combined and/or repeated.

One drawback of such prior art methods consists in the difficulty of controlling web edges when short fibers are laid, due to the aerodynamic turbulences generated close to the edges of the belt conveyor, by the pneumatic laying unit, which turbulences cause the web to be folded and curled, thereby generating irregular edges and defects in the final product.

This drawback increases with the web feeding speed and accordingly reduces the productivity of the plant.

A further drawback lies in the presence of wood pulp at the web edges, which pulp has to be removed before bonding, for instance by local suction. Such suction is not easily controlled, as the long fibers of the preformed web or mat also tend to be sucked in.

Such fibers, different in nature and length from the pulp laid thereon, tend to clog and soil the short fiber conveying and laying system, whereto the sucked fibers are fed, and this negatively affects proper operation of such system. Also, the wood pulp at the edge of the web causes faster soiling of the hydro- entangling machine, and consequent defects in the finished product, as well as the need for more frequent cleaning and maintenance operations on the machine.

Disclosure of the invention

A general object of this invention is to obviate the above drawbacks by providing a method for manufacturing nonwoven fabric, which allows to obtain a uniform nonwoven fabric, as described before, in a reliable and cost-effective manner, even at high feed and production speeds.

A further object is to conceive a short fiber laying method which reduces nonwoven fabric defects especially at the edges thereof.

Yet another object is to provide a short fiber laying method which allows to easily adjust suction of excess short fibers laid at the web edges.

Another object is to provide a short fiber laying method, which allows to recover the short fibers or wood pulp that have been sucked in, with no presence of long fibers from the preformed mat or web.

A further object is to provide a nonwoven fabric producing method which can operate continuously and with a high productivity.

These and other objects, which will be more clearly understood hereinafter, are achieved by a method for stabilizing the edges of a nonwoven web, according to claim 1 , wherein the fabric is obtained by carding or continuously spinning long fibers and laying them over a movable support surface, having a predetermined advancement speed to form a web with substantially straight side edges, subsequently laying a short fiber layer on said web, bonding said short fiber layer with said web to form the nonwoven fabric, characterized in that, before laying the short fibers the side edges of the web are at least partly shielded and compressed against the movable support surface.

Thanks to such method, it is possible to prevent short fibers from being laid along the web edges, and to remove any aerodynamic turbulence, as well as to increase stability and to avoid edge curls or folds, regardless of the feed speed and of the length of the long fibers having been laid.

According to a further aspect of the invention, an edge stabilizing device for a nonwoven web is provided for implementation of the above method, suitable to be mounted on a short fiber laying unit placed downstream of a continuous long fiber web spinning station, which web is fed over a movable support surface, which device, according to claim 9, is characterized in that it comprises means for shielding and compressing the longitudinal edges of the web in the short fiber laying area, so as to prevent them from being laid along said edges and to increase the web stability, thus avoiding any curl or fold thereon.

The device of the invention allows to prevent wood pulp or short fibers from being laid on the web edges, thereby obviating the drawbacks of pollution and of wood pulp and short fiber accumulation on the downstream machine for mechanically bonding the web by high pressure water jets.

Brief Description of the Drawings

Further features and advantages of the invention will be more clearly understood from the detailed description of a method and a device for stabilizing the edges of a nonwoven fabric, which are described by way of non limiting example with the help of the annexed drawings, in which:

Fig. 1 shows a flowchart of the inventive method; Fig. 2 is a side schematic view of a device for implementing the inventive method;

Fig. 3 is a front schematic view of the device of Fig. 2; Fig. 4 is a top schematic view of the device of Fig. 2; Fig. 4a is a sectional view of an isolated and enlarged detail of Fig. 4, as taken along an axis IV-IV;

Fig. 5 is a side schematic view of the detail of the device for implementing the inventive method;

Fig. 6 is a front schematic view of the device of Fig. 5.

Detailed description of several exemplary embodiments

With reference to the above mentioned figures, a process for making a nonwoven fabric T generally comprises step A in which long fibers F| are carded or continuously spun, a step B in which said fibers are evenly laid to form a mat or web V, with a substantially uniform thickness and substantially straight longitudinal lateral edges B, B'.

This step is followed by step D in which a layer of short fibers F_c, possibly including wood pulp, is laid over web V.

Finally, step E is executed in which the short fibers F_c are bonded with the long fibers Fι of the web V to form the nonwoven fabric T.

Particularly, short fibers F_c may be laid by using air, according to a process known per se by those skilled in the art as "airlaid process", whereas the bonding step E may be performed by using high pressure jets of water according to the hydro- entangling technique.

Suitably, the long fibers F| which form the carded web V may be laid over a movable support surface, for instance a belt conveyor which is drive at a predetermined speed S.

According to the invention, before step D of laying the short fiber F_c , the longitudinal edges B, B' of the web V are subjected to step C in which the long fibers F| are shielded and compressed along the surface of the conveyor belt 3, to increase the stability and adherence of these web portions and prevent them from being folded or curled.

Suitably, the shielding and compressing action C is exerted on the longitudinal edges B, B' of the web over a length that corresponds at least to the short fiber laying area, and over a predetermined transverse width W.

The edges of the web V were experimentally found to be properly stabilized with a width W of the shielding and compression regions ranging from 10 to 100 mm.

Advantageously, the compression exerted on the edges B, B' may be adjusted according to typology of web W, in such a manner as to allow a free feed thereof.

Furthermore, the excess short fibers F_c on the conveyor are sucked, upon laying thereof on the web at a predetermined distance from the edges B, B', outside the edge covering and compression area, to prevent long fibers Fι of web V from being sucked along, and conveyed back to the fiber laying unit.

This prevents short fiber intakes, and the laying unit itself, from being soiled and clogged.

Referring now to the annexed figures, a device 1 for carding or spinning and laying long fibers Fι to form a web V is placed upstream of a unit 2 which lays short fibers F_c by using air, to prepare a nonwoven fabric T.

Device 1 for treating long fibers Fι comprises a carding or spinning unit (not shown) and a unit for laying long fibers Fι on a movable support surface. The latter is, for example, a conveyor belt 3 extending between end rollers 4, 5.

The short fiber F_c laying unit 2 is placed downstream of the device 1 and may use the same conveyor belt 3. According to the invention, the laying device 2 comprises means for shielding and compressing the longitudinal edges of the web, overall designated as 6, 6', located in the short fiber F_c laying area, to prevent short fibers from being laid along the edges B, B' and to increase the stability of the web V, thus avoiding any curling or folding thereof in these areas.

Particularly, the shielding and compressing means 6, 6' are arranged over belt 3 along the short fiber laying unit 2 to shield and compress the edges of said web against the surface of belt 3.

Preferably, the shielding and compressing means 6, 6' are removably secured to the short fiber laying unit 2 by appropriate connection means 7, which may be adjusted at a variable transverse distance to fit the width of the web V.

Particularly, connection means 7 include adjustment means 8, 9 to control the pressure over said edges.

In the embodiment shown in the figures, the shielding and compressing means 6, 6' comprise a pair of longitudinal plates 10, 10' having curved end portions 11 , 12, 11', 12' which define torsion springs secured to the adjustment means 8, 9.

Adjustment means 8, 9 may include pins 14, 14', 15, 15' for the torsion of the end portions 11 , 12, 11 ', 12' of plates sheets 10, 10'. Pins 14, 14', 15, 15' may be rotated from the outside by any means, not shown, to impart bending moments acting on substantially vertical planes to the end portions 11 , 12, 11', 12' of the plates 10, 10'.

Suitably, plates 10, 10' are made of an elastic metallic material, particularly steel, or of a reinforced or composite plastic material. The device also includes means 16, 16' for suction of excess short fibers laid on the movable support surface, which suction means may consist of intakes 16 located at the opposite sides of the movable support surface 3, outside the edge B, B' covering and compression area.

Suction means 16, 16' may be connected by suitable pipes, not shown in the drawings, to the short fiber laying unit 2 to recirculate in this area the exceeding pulp or short fibers F_c .

Advantageously, plates 10, 10' have such a width as to cover the edges B, B' by a minimum transverse width W of 10 to 100 mm, thereby preventing short fibers from being laid thereon.

Appropriately, the sheets have a transverse width (H) of more than at least 10 mm. This allows to use intakes 16, 16' in such a manner as to avoid the risk of taking in carding fibers or continuous filaments together with short fibers, which fibers and filaments could also be sent to the short fiber laying unit 2 and cause such unit and the wood pulp grinding mills to be clogged, thereby creating serious mechanical problems and plant shutdown for servicing.

Appropriately, according to the invention, the machine for making the nonwoven fabric T with stabilized edges comprises a continuous long fiber web spinning station 1 , followed by a short fiber laying unit 2 comprising a web edge stabilization device.

This provides an increased web stability, prevents wrinkles and folds at the edges and counters any motion generated by the turbulence which is caused by the airlaid unit.

This plant matches a high manufacturing speed with a high quality of the manufactured fabric. As a result, the nonwoven fabric T with stabilized edges which is obtained by a device as described above comprises a web V of carded or spun long fibers Fι , which is overlaid with a layer of short fibers F_c , interwoven with the long fibers of the web V, whose edges B, B' are cleared of short fibers F_c , and are continuos, straight, have no folds and curls and no processing scraps.

For the foregoing description, it appears that the nonwoven fabric edge stabilizing method and device according to the invention, and as claimed in the annexed claims allow to achieve the intended objects and particularly to obtain a uniform nonwoven fabric in a cost-effective and reliable manner, even at high feed speeds and high production rates, thereby minimizing the defects of the final product, especially at the edges thereof.

Moreover, this method and device allow to prevent short fibers from being laid at the web edges, and to avoid clogging of the units for recycling them.

The method and device of this invention are susceptible to a numerous modification and changes, all falling within the inventive concept disclosed in the claims. All the details thereof may be replaced by other technically equivalents, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the object if the invention has been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.

The instant application is based upon and claims priority of patent application no. VI2002A000209 filed on 01.10.2002 in Italy, the disclosure of which is hereby expressly incorporated have in reference thereto.

Claims

1. A method for stabilizing the edges of a nonwoven web, wherein the fabric is obtained (A) by continuously carding or spinning long fibers (Fι ), laying (B) said long fibers (Fι ) over a movable support surface (3), having a predetermined advancement speed (S) to form a web (V) having substantially straight side edges (B, B'), laying (C) a short fiber layer (F_c ) on said web (V), bonding (E) said short fiber layer (F_c ) with said web (V) to form the nonwoven fabric, characterized in that, before laying (C) the short fibers, the side edges (B, B') of the web (V) are at least partly shielded and compressed against the movable support surface (3) to prevent short fibers from being laid in said areas, and to remove any aerodynamic turbulence, as well as to increase stability and to prevent curls or folds in the fabric along its edges (B, B'), regardless of the feed speed and of the length of the long fibers that have been laid.

2. Method as claimed in claim 1 , characterized in that the shielding and compressing action is exerted along the longitudinal edges (B, B') of the web (V) over a length that corresponds to at least the short fiber laying area.

3. Method as claimed in claim 1 , characterized in that the shielding and compressing action is exerted along the longitudinal edges (B, B') of the web over a predetermined minimum transverse width (W).

4. Method as claimed in claim 1 , characterized in that the shielding and compressing action on the edges (B, B') is exerted by a pair of longitudinal plates

(10, 10') laying over said edges (B, B') in contact with the conveyor belt, without preventing the free feed of the web (V).

5. Method as claimed in claim 3, characterized in that said predetermined minimum shielding and compressing transverse width (W) is of 10 to 100 mm.

6. Method as claimed in claim 4, characterized in that the pressure of said plates (10, 10') against the movable support surface (3) may be adjusted by changing the pressure exerted along said edges, according to the web type.

7. Method as claimed in claim 4, characterized in that the excess short fibers on said movable support surface (3) are removed by suction, downstream of said short fiber laying area, outside the web edges (B, B'), substantially in line with said shielding and compressing plates (10, 10') to prevent the long fibers of the web (V) from being also taken in.

8. Method as claimed in one or more of the preceding claims, characterized in that said short fibers include wood pulp.

9. An device for stabilizing the edges (B, B') of a nonwoven web, is for carrying out the method according to one or more of the preceding claims, which device is applicable to a short fiber laying unit (2), arranged downstream of a station for continuously spinning a long fiber web (V) driven on a movable support surface (3), the device being characterized by comprising means (6, 6') for shielding and compressing the longitudinal edges of the web in the short fiber laying area, so as to prevent them from being laid along said edges and to increase the web stability, thus avoiding any curl or fold thereon.

10. Device as claimed in claim 9, characterized in that said shielding and compressing means (6, 6') are arranged over said belt along said unit to compress the fibers of said web against said movable support surface (3).

11. Device as claimed in claim 10, characterized in that said shielding and compressing means (6, 6') are removably secured to said short fiber laying unit (2) by appropriate connection means (7).

12. Device as claimed in claim 11 , characterized in that said connection means (7) are positioned at an adjustable transverse distance to fit the width of the web (V).

13. Device as claimed in claim 11 , characterized in that said connection means (7) include adjustment means to control the pressure exerted on said edges.

14. Device as claimed in claim 11 , characterized in that said shielding and compressing means (6, 6') comprise at least one pair of longitudinal plates (10,

10') having curved end portions which define torsion springs, with a terminal secured to said adjustment means.

15. Device as claimed in claim 14, characterized in that said plates have a transverse width (H) of more than at least 10 mm.

16. Device as claimed in claim 14, characterized in that said adjustment means comprise pins (8, 9) for rotating the end portions (11 , 12) of said plates (10, 10'), said pins (8, 9) being adapted to impart bending moments acting on substantially vertical planes to said portions.

17. Device as claimed in claim 14, characterized in that said sheets (10, 10') are made of a resilient metallic material, such as steel, or of an elastic synthetic material, such as reinforced plastic.

18. Device as claimed in claim 9, characterized by comprising means (16) for the suction of excess short fibers on said movable support surface (3), said suction means consisting of at least one pair of intakes (16) located on opposite sides relative to said movable support surface (3) at a predetermined distance from said edges (B, B') substantially in line with said shielding and compressing sheets (6, 6') to prevent the long fibers of the web from being also taken in and from clogging said intakes.

19. A machine for making a nonwoven web with stabilized edges, comprising a continuous long fiber web spinning station, a unit for laying short fibers on the web, a station for bonding said short fibers with said web to form the fabric, characterized in that it comprises a web edge stabilizing device according to one or more of claims 9 to 18.

20. A nonwoven fabric, comprising a web of carded or spun long fibers overlaid with a layer of short fibers, which are interwoven with said long fiber web, characterized in that it has longitudinal lateral edges (B, B') stabilized by the method and device according to one or more of claims 1 to 18 and by using a machine according to claim 19.