WO2013076658A2

WO2013076658A2 - Apparatus and process for folding a web in two

Info

Publication number: WO2013076658A2
Application number: PCT/IB2012/056584
Authority: WO
Inventors: Armando DE LUCA
Original assignee: Fameccanica.Data S.P.A.
Priority date: 2011-11-24
Filing date: 2012-11-21
Publication date: 2013-05-30
Also published as: ITTO20111085A1; WO2013076658A3

Abstract

An apparatus for folding in two a composite continuous web (10) with anisotropic mechanical characteristics advancing in a longitudinal direction of feed (A) along a longitudinal-folding line (B) parallel to said direction (A), said web (10) having opposite longitudinal edges (14, 15) and having an original transverse dimension subject to variation during said advance, so as to bring said longitudinal edges (14, 15) into a predetermined relative position as a result of said folding, said apparatus comprising: - a station for transverse laying-out of the web (40) designed to restore said original transverse dimension of said web (10); - an alignment station (50) designed to align the centre line of said web (10) with respect to said longitudinal-folding line (B) parallel to said direction of feed (A); and - a folding station (60) designed to fold said continuous web along said longitudinal-folding line (B) parallel to said longitudinal direction (A).

Description

"Apparatus and process for folding a web in two"

-k -k -k -k

TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to an apparatus and a process for folding in two a web that advances in a continuous way in a longitudinal direction.

The invention has been developed in particular for the production of absorbent sanitary products that can be worn like pants. A typical example of absorbent sanitary products of this type is represented by the so-called training pants.

Description of the relevant art

A common technique for the production of sanitary products that can be worn like pants consists in providing a continuous composite web formed by a continuous chain of blanks arranged in a transverse direction with respect to the direction of feed of the web. The continuous composite web is folded in two about a longitudinal axis so as to set the opposite longitudinal edges of the web on top of one another. The opposite longitudinal edges are then connected together in transverse connection areas set at a distance apart in the longitudinal direction by a pitch equal to the width of the products. The continuous chain of blanks is then subjected to an operation of cutting in a transverse direction to form the finished products .

An example of a process for manufacturing absorbent sanitary products of this type is described in the documents Nos. EP-A-1523968 and EP-A-2025311 filed in the name of the present applicant.

In processes of this type it is necessary to ensure a mutual alignment between the opposite longitudinal edges of the continuous web during the folding step. To obtain a precise alignment of the edges, it is necessary to detect the position of the longitudinal edges of the web by means of sensors and correct the relative position of the web and, consequently, of the edges if the edges are not aligned to one another as required.

The document No. EP-A-1607357 describes a device for correcting the position of the opposite longitudinal edges of the continuous web during the folding operation. The document No. EP-A-1607357 describes an apparatus and a method for folding a web, which carries out alignment of the edges causing variation of the path followed by each edge of said web and, consequently, causing variation of the state of tension of the entire composite web. Said process is certainly effective with webs with constant and homogeneous mechanical characteristics throughout its length .

Neither in the aforesaid document nor in others are the effects caused by the marked anisotropy present in a continuous composite web formed by a continuous chain of blanks arranged in a transverse direction taken into due consideration.

In fact, it is known that, since said web is obtained by setting on top of one another a number of layers of different materials with elastic elements set between the various layers, during its advance along the production line its original transverse dimension (corresponding to the effective width of the web in a completely splayed-out configuration) with respect to the longitudinal direction of feed varies easily and in an unforeseeable way, precisely on account of the aforesaid anisotropy and variability.

Said phenomenon is aggravated by the fact that the variations in dimension are not symmetrical and homogeneous along the two longitudinal edges; namely, it is normal for one longitudinal edge of the web to present different variations with respect to the variations present on the other edge, thus causing relative displacement of the longitudinal axis of the composite web itself.

Object and summary of the invention

The object of the present invention is to improve the technique for folding a composite web in such a way that the opposite longitudinal edges of the composite web can be easily controlled to maintain the condition of mutual alignment.

According to the present invention, this object is achieved by an apparatus and a process that form the subject of Claims 1 and 8.

The claims form an integral part of the teaching provided herein in relation to the invention.

Brief description of the drawings

The present invention will now be described in detail with reference to the attached drawings, which are provided purely by way of non-limiting example and in which:

- Figure 1 is a schematic perspective view that represents the step of folding of a composite web in a process for the production of absorbent sanitary products that can be worn like pants;

Figure 2A is a schematic side view of an apparatus for folding a composite web;

Figure 2B is a schematic side view that illustrates a second embodiment of the apparatus according to the invention;

- Figure 2C is a schematic cross section according to the line II-II of Figure 2B;

- Figure 3 is a schematic perspective view that illustrates a station for transverse laying-out of the web according to the invention;

- Figure 4 is a schematic perspective view of an absorbent product obtained with an apparatus and a process according to the present invention;

- Figure 5 is a schematic top plan view of the product of Figure 4 prior to formation of the transverse welds; and

- Figure 6 is a schematic perspective view that illustrates a variant of the product of Figure 4.

Detailed description of embodiments

In the ensuing description various specific details are illustrated aimed at an in-depth understanding of the embodiments. The embodiments may be provided without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not shown or described in detail so that various aspects of the embodiments will not be obscured .

Reference to "an embodiment" or "one embodiment" in the framework of this description is meant to indicate that a particular configuration, structure or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as "in an embodiment" or "in one embodiment" that may be present in various points of this description do not necessarily refer to one and the same embodiment. Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.

The references used herein are only provided for convenience and hence do not define the sphere of protection or the scope of the embodiments.

With reference to Figure 4, designated by 100 is a disposable absorbent product of the so-called "pull-on" or "training pant" type obtained with a method and an apparatus according to the teachings provided by the present invention.

In basic terms, the product 100 is made up of a central body or absorbent insert 12, which is to come into contact with the body of the user and is able to assume the general U conformation suitable for absorbing and withholding exudates. The absorbent insert 12 is moreover positioned on a chassis 114 that sets itself in contact with the garments of the user and is characterized in that it is able to keep the absorbent insert 12 in the correct working position, even when it becomes heavier on account of the liquids absorbed .

The absorbent insert 12 has a structure in which there may be recognized (in addition to various other accessory elements) :

a top layer or topsheet 13, permeable to body liquids evacuated, which is to face the body of the user;

a bottom layer or backsheet 115, impermeable to body liquids, that is to face the outside, i.e., the chassis 114; and

an absorbent core 116, which is set between the topsheet 13 and the backsheet 115 and has the function of absorbing and withholding exudates.

Present on the absorbent insert 12 are other characteristic elements that contribute to increasing the characteristics of wearability and absorbance of the insert 12 itself, such as for example the elastic elements for the legs 117 that contribute to adherence of the absorbent product 100 to the body of the end user and likewise the so-called cuffs or elasticated sides 119 arranged at the sides of the absorbent core 116 with a function of lateral containment of the body fluids .

For a more detailed description of the characteristic elements listed above and of others still, that are well known to persons skilled in the sector, reference may be made to the extensive literature existing on the subject, such as for example U.S. 4,704,116 granted on November 3, 1987 granted to Enloe .

The chassis 114 is constituted by at least one sheet of non-woven fabric 118, or some other adequate material, on which there are made to adhere elastic materials in threads and/or strips 19, such as, for example, Lycra threads produced by Invista and/or synthetic-rubber strips produced by Fulflex.

Said elastic materials are rendered fixed with respect to the sheet of non-woven fabric 118 of the chassis 114 by means of adhesives or thanks to welds made with heated rollers or ultrasound systems. Normally, set on top of the elastic materials is a further sheet of non-woven fabric 17, which can come from another sheet or can be the same material 118 appropriately chosen wider than necessary and then folded inwards to cover the elastic elements 19.

Made on the chassis 114 is a shaped cut 113 that outlines the border of the openings for the user' s legs .

As is evident to a person skilled in the branch, the representations of Figures 4 and 5 are schematic and have the purpose of highlighting that the process and apparatus forming the subject of the present invention can be applied to a wide range of possible types of embodiment of the product 100.

Particular types of pre-closed absorbent product are extensively described in EP 1 523 968 Al and EP 2 057 975 Bl . In particular, in Figure 6 designated by 120 is an absorbent product provided according to the teachings of EP 2 057 975 Bl .

Figure 1 is a schematic representation of the process of production of an absorbent sanitary product 120. In Figure 1 designated by 10 is a composite web, formed by a chain of blanks of absorbent sanitary products 120, which advances in a continuous way in a longitudinal direction A. The composite web 10 has two opposite longitudinal ends 14 and 15, which on the product provide, respectively, the front waist edge and the rear waist edge. Said edges, during the process of production of the absorbent sanitary product, are set on top of one another following upon folding along a longitudinal-folding line B parallel to the direction of longitudinal advance of the web A. The arrow C indicates schematically the movement of folding that leads to obtaining superposition of the longitudinal edges 14 and 15. After folding about the longitudinal axis B , the longitudinal edges 14 and 15 set on top of one another are connected together at regular intervals. As represented in the embodiment of Figure 4 said connection can be obtained by means of two welds 110 or else, in the embodiment illustrated in Figure 6, by closing elements that can be opened and closed 16 and 18, as described in greater detail in the document No. EP 2 057 975 Bl filed in the name of the present applicant. After the folding and closing operations, the continuous composite web is subjected to operations of cutting along transverse lines P to form individual products 120. In the embodiments illustrated in Figures 4 and 6, the respective products 100 and 120 are training pants that may be of the type closed in a permanent way on the sides, as illustrated in Figure 4, or else with side panels that can be opened and closed, as represented in Figure 6. The composition, structure, and process of formation of the continuous composite web 10 are not described in detail in so far as they lie outside the scope of the present invention.

From Figure 1, it will be appreciated what may be the complexity of the web that is generated in a process of production in which the blanks 120 extend in a direction transverse to the direction of movement and likewise there will be appreciated the need to ensure that, during the operation of folding about the longitudinal axis B, the opposite longitudinal edges 14 and 15 are properly aligned to one another. The present invention regards the way in which the alignment of the longitudinal edges 14 and 15 is carried out within the operation of folding the composite web 10 about the axis B.

Figure 2A is a schematic illustration of an apparatus 20 according to the present invention that carries out longitudinal folding of the composite web 10 and mutual alignment of the opposite longitudinal edges 14 and 15. The apparatus 20 comprises a station for transverse laying-out of the composite web 10, an alignment station 50 and a folding station 60, which is set downstream of said station 40 for transverse laying-out and station 50 for alignment of the composite web 10.

In a preferred embodiment, the folding station 60 comprises a transverse return roller 61 and a folding wheel 62, which turns about an axis transverse to the longitudinal direction A. The folding wheel 62 has a front face 63 contained in a plane orthogonal to the composite web 10 formed by the chain of blanks of absorbent sanitary products 120, and hence positioned at the middle line of the composite web 10, i.e., the folding line B, in so far as said lines, in addition to being always parallel to one another, in the majority of cases also coincide. The folding wheel 62 makes a preliminary fold on the continuous web 10 in two sections 32, 34 set on opposite sides with respect to the longitudinal-folding line B. In the embodiment schematically illustrated in Figure 2A, a first section of web 32 is wound on the circumference of the folding wheel 62, and a second section 34 passes in contact with the front face 63 of the folding wheel 62. The folding section 60 further comprises a longitudinal- folding bar 64, which extends along the folding line B, i.e., along the middle of the web formed by the blanks of the products 120. The two sections of web 32 and 34 are folded on top of one another around the folding bar 64. The folding section 60 terminates with a pair of transverse conveying rollers 70 between which the two sections of web 32, 34 folded on top of one another are made to pass.

It is evident to a person skilled in the branch that the folding section 60 is not able to ensure that the opposite longitudinal edges 14 and 15 of the continuous web 10 are aligned with one another at the end of the folding operation. For this reason, provided upstream of the folding section 60 are the station for transverse laying-out 40 and the alignment station 50. The station for transverse laying-out 40 of the composite web 10 is able to bring the composite web 10 back to its original transverse dimension, i.e., to the effective width of the web in the completely splayed- out configuration. In fact, the composite web 10 formed by the blanks 120, during advance along the production line in the longitudinal direction A may typically vary its width, narrowing, both on account of the creases that are generated as a result of the pulling force necessary to cause advance of said web 10 along the production line and as a result of the internal stresses due to coupling of the various materials, each of which with it own internal state of stress.

In one embodiment, the composite web 10, formed by the blanks 120, is fed along the entire line thanks to motor means such as, for example, pairs of drawing rollers 90, as highlighted in Figures 2A and 2B.

Immediately after the station 40 for transverse laying-out of the web and immediately before the longitudinal-folding section 60, the alignment station 50 is installed, which is able to align the centre line of said composite web 10 with respect to the longitudinal-folding line (B) parallel to the direction of feed and, obviously, to the longitudinal axis of the web, which in the specific CcL S Θ cL S highlighted by Figure 1, coincide. The aforesaid configuration constituted by a station for transverse laying-out 40 of the web and by a station for alignment 50 of said web with the centre line, always delivering in a correct way the composite web 10 itself to the longitudinal-folding section 60 causes the edges 14 and 15 to be aligned properly with respect to one another or to present, at the very least, the required precision of alignment.

In a preferred embodiment, as may be appreciated in the view of Figure 3, the station for transverse laying-out 40 of the web comprises two gripping devices 41 set alongside the composite web 10, each of which is able to grip the respective longitudinal edge 14 and 15.

In a preferred embodiment, as illustrated in Figure 3, each gripping device is provided with two rollers for engagement of the edges 42 and 43, arranged in such a way that they present the respective axes of rotation parallel to one another and parallel to the plane of advance of the composite web 10. The two pairs of engagement rollers 42 and 43 are set in front of one another specularly so that the composite web 10, to pass beyond them, is forced to carry out an S-shaped path. In this way, each of the two longitudinal edges 14 and 15 of the composite web 10 engages the respective pair of engagement rollers in such a way that the first roller 42 comes into contact with the top surface of the web 10, whilst the second engagement roller 43 engages the bottom surface thereof.

Thanks to the configuration just described the engagement rollers 42 and 43 of each gripping device are able to grip the respective edge 14, 15 of the composite web 10 in a stable way. To render gripping of the longitudinal edges 14 and 15 on the surfaces of the engagement rollers 42 and 43 still more effective there can be carried out a surface treatment capable of enhancing the coefficient of friction of said surfaces with the material of the composite web 10. An example of a convenient surface treatment may be Plasma Coating PC 936 manufactured by the company Smaltiriva of Valdaro - Mantova - Italy.

In a preferred embodiment, as may be better appreciated in the view of Figure 3, the engagement rollers 42 and 43 are connected with appropriate mechanical means 44 to the end of the arm 45, which, in turn, is hinged at the opposite end to the pin 46, which guarantees rotation of said arm 45 about the axis of rotation XI orthogonal to the plane of advance of the web 10.

Rotation of the arm 45 about the axis XI causes movement of the engagement rollers 42 and 43 in a direction substantially transverse to the direction of advance A of the composite web 10.

Each gripping device 41 is provided with an actuator means 47 designed to govern rotation of said arm 41 about the axis XI.

An actuator suitable for this type of use may be the linear motor identified as: Linear Digital Actuator model D-LAB-3A-5-050.1-ISCT manufactured by Fife- Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany .

Each gripping device 41 further comprises a device 48 designed to detect the position of the respective longitudinal edge 14, 15 of the composite web 10.

Detection devices 48 adequate for this type of control may be the linear-matrix sensors model DAC 005 manufactured by Fife-Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany.

In order to process the signals coming from the sensors 48, present in the gripping device 41 is a processor or control system 140, which carries out the measurement of the error of alignment of the respective longitudinal edge 14, 15 by comparing the measurement of position detected by the respective control device 48 with the theoretical position that the corresponding longitudinal edge should occupy, and as a function of said error corrects the position of the respective edge by actuating the actuator 47.

A control system suitable for this type of task may be the Digital Processor model D-MAX-2 designed and manufactured by Fife-Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany.

In a preferred embodiment, as may be better appreciated in the view of Figure 2A, the station for transverse laying-out 40 of the web is followed by a station 50 for alignment of the centre line of the composite web 10, which is able to centre the longitudinal axis of the composite web 10 with respect to the longitudinal-folding line B parallel to the direction of feed A. The alignment station 50 is made up of a guide system generally constituted by a structure comprising a fixed frame 51 and a mobile (or steering) frame 52 mounted on which are the guide rollers 53 and 54, which, according to how the web 10 traverses the alignment station 50, are also defined as input roller 53 and output roller 54. In fact, the web 10 enters the guide system engaging the roller 53 and exits therefrom from the roller 54. The mobile frame 52 is connected to the fixed frame 51 by means of the device 55 that enables it to turn about the axis X2 perpendicular to the axis of the guide rollers and tangential to the external edge of the input roller 53 in its middle.

The guide system is moreover provided with an actuator means 57 designed to carry out rotation of the mobile or steering frame 52 about the axis X2.

Devices that are adequate for this guide system may be the electromechanical web-guides of the series Fife Symat model 70B or 120A, to be chosen according to the width of the composite web 10, manufactured and marketed by Fife-Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany.

The alignment station 50 further comprises one or more sensors 56 designed to detect the position of each of the longitudinal edges 14 and 15. In the examples illustrated in Figures 2A and 2B, two sensors 56 are provided, each of which detects the position of the respective longitudinal edge 14 or 15 of the composite web 10, then determining, by comparison of the relative positions of the side edges 14 and 15, the width of the composite web 10 identifying the position of the middle line (or centre line) of the web 10 itself.

Detection devices adequate for this type of control may be ultrasound sensors with 25.4-mm proportional band model SE-37 produced by the Fife- Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany .

In the alignment station 50 a processor or control system 150 is moreover present, which processes the signals coming from the sensors 56 and determines instantaneously the measurement of the error of alignment of the middle line of the composite web 10 with respect to the desired/predetermined position.

A control system suitable for this type of task may be the Digital Processor model D-MAX-2 designed and marketed by Fife-Titland GmbH, Fifestrasse 1, (D) 65779 Kelkheim, Germany.

As soon as the composite web 10, on account of the internal stresses generated by its anisotropy deriving from its composite nature, or for external causes, abandons the correct working position, the sensors 56 detect the fact, in so far as they no longer read the predetermined position of the side edges 14 and 15 of the web, corresponding to a displacement of the centre line with respect to the predetermined position. Consequently, each of them sends a signal of a different value to the processor 150, which actuates instantaneously the actuator 57 of the guide system, which in turn moves appropriately the steering frame 52, correcting the transverse position of the composite web 10 with respect to the longitudinal direction of feed A so as to restore in the sensors 56 two readings that are the same as one another, i.e., two signals of the same value. In this way, the centre line of the web is brought back into the desired position with respect to the axis of longitudinal folding B . For example, in the embodiment illustrated, the centre line or longitudinal axis of the web 10 is brought back in to the centre, i.e., to coincide with the axis of longitudinal folding B .

The composite web 10, thus controlled, is transferred to the longitudinal-folding unit 60 previously described. In this way, even though the folding unit 60 is unable in itself to make a correction of the web and hence of the fold, said folding unit 60, by receiving the material always in an adequate way, i.e., always with the centre line of the web aligned as desired, for example coinciding, with the longitudinal-folding line B and always in a state of complete transverse laying-out, which eliminates any possible misalignment of the side edges thereof, manages to make said longitudinal fold in a correct and reliable way and above all with a constant quality over time.

It will not escape the notice of a person skilled in the sector that systems for longitudinal folding that do not envisage application of a station for transverse laying-out 40 of the web upstream of the stations for alignment 50 and longitudinal folding 60 of the web may not achieve comparable results from the standpoint of precision of the fold and above all of stability of the folding process itself as compared to the system described in the present document. In fact, in the absence of the system for transverse laying-out 40 of the web, non-homogeneous transverse dimensional variations in the two halves of the composite web 10 would lead to intervention of the alignment system 50, which would cause variation of the position of the longitudinal axis of the composite web 10 with respect to the axis of folding ( B ) , in so far as the alignment system 50 would find itself correcting, as position errors, internal deformations of the composite web 10 that have varied the position of the respective longitudinal edges 14 and/or 15 thereof, obtaining as a result a longitudinal fold of the web 10 that is erroneous .

In a preferred embodiment, the two stations for transverse laying-out 40 and alignment 50 of the web may be integrated in a single station by housing the gripping devices of the station for transverse laying- out on the mobile frame of the guide system of the alignment station.

In a further preferred embodiment, as may be appreciated more clearly in the view of Figure 2B, the station for transverse laying-out of the web 40 may be housed on the mobile frame 52 of the guide system 50 in the space between the input roller 53 and the output roller 54.

In fact, as is well known to persons skilled in the sector, the guide systems of the Fife Symat type, and their equivalents, to be able to obtain an effective control of the alignment of the web, preferably require respect of appropriate internal dimensional ratios. In particular, the distance between the centres of the input roller 53 and output roller 54 should preferably be at least the same as the width (or transverse dimension) of the web 10 that is to be aligned. In any case, precisely to prevent stresses on the material constituting the web 10 itself, the greater said distance between centres, the smaller the deformation that is induced on the material of the web that is to undergo alignment, and the better the alignment system 50 works. Consequently, thanks to said geometrical needs of the alignment system 50 and in order to optimize the spaces on the production line and finally to optimize the process also eliminating any possible deformations and/or imperfections on the web that might be generated by the action of alignment carried out by oscillation about the axis X2 of the mobile frame 52 of the alignment station 50, the station for transverse laying-out 40 of the web may be conveniently installed on the alignment station 50, preferably between the input roller 53 and the output roller 54, with the control devices 48 of each gripping device 41 preferably set in the proximity of the output roller 54.

Clearly, it is evident that a configuration such as the one just described and highlighted in Figure 2B can render still more stable and reliable the folding process in so far as it delivers the web to the folding station 60 in ideal conditions without there possibly intervening further phenomena that might generate new errors on the composite web 10 itself.

In a further embodiment, as is highlighted more clearly in Figure 2B, in the folding station, in the proximity of its output section, i.e., immediately before the two sections 32, 34 of the composite web 10 are set on top of one another, there may be installed a further control device 80 designed to detect the position of each of the longitudinal edges 14 and 15.

In the embodiment illustrated in Figure 2B, two edge-detection devices 81 are provided, each of which detects the position of a respective longitudinal edge 14, 15.

Detection devices 81 adequate for this type of control may be the linear-matrix sensors model DAC 005 manufactured by Fife-Titland GmbH.

In the control device 80, a processor or control system 180 is moreover present, which processes the signals coming from the sensors 81 and determines instantaneously the measurement of the error of alignment of the middle line of the composite web 10 with respect to a desired position.

Also for this application a control system suitable for this type of task may be the Digital Processor model D-MAX-2 manufactured by Fife-Titland GmbH.

A measurement of the error of alignment between the longitudinal edges 14 and 15 is obtained by comparing the measurements of position of the respective longitudinal edges 14 and 15 thanks to the signals that each sensor 81 sends to the processor or control system 180.

In the case where an error in the position of the longitudinal edges is detected, and hence the system is making the longitudinal fold not along the theoretical folding axis B , but along another axis parallel thereto, the control device 180, through the processor 150, can carry out a new adjustment on the sensors 56 displacing the reference position thereof; namely, in other words, in the case where on the equipment two detection systems or sensors are provided, one for each longitudinal edge, the processor or control system varies for each sensor the theoretical position of where the edge should be located, virtually displacing said theoretical position of each sensor by one and the same length, but in an opposite direction, hence obtaining displacement of the centre line of the composite web 10 to obtain once again the desired alignment with the longitudinal-folding axis B , for example, as in the embodiments illustrated, bringing said centre line to coincide with said axis.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to is what described and illustrated herein, without thereby departing from the scope of the invention as defined in the ensuing claims.

Claims

1. An apparatus for folding in two a continuous composite web (10) with anisotropic mechanical characteristics advancing in a longitudinal direction of feed (A) along a longitudinal-folding line (B) parallel to said direction (A) , said web (10) having opposite longitudinal edges (14, 15) and having an original transverse dimension subject to variation during said advance, so as to bring said longitudinal edges (14, 15) into a predetermined relative position as a result of said folding, said apparatus comprising:

- a station for transverse laying-out (40) of the web designed to restore said original transverse dimension of said web (10) ;

- an alignment station (50) designed to align the centre line of said web (10) with respect to said longitudinal-folding line (B) parallel to said direction of feed (A) ; and

- a folding station (60) designed to fold said continuous web along said longitudinal-folding line (B) parallel to said longitudinal direction (A) .

2. The apparatus according to Claim 1, wherein said station for transverse laying-out (40) comprises at least one gripping device (41) for each longitudinal edge (14, 15) of said web (10), said at least one gripping device (41) comprising at least two engagement rollers (42, 43), which have axes of rotation parallel to one another and to the plane of advance of the web (10) , are able to engage both of the surfaces of the web at said respective longitudinal edges (14, 15), and are mobile in a transverse direction (D) with respect to the longitudinal direction (A) of advance of said web (10) .

3. The apparatus according to Claim 2, wherein the at least one gripping device (41) of said station for transverse laying-out (40) comprises an arm (45) carrying said at least two rollers (42, 43) at one of its ends and hinged at the other end about an axis (XI) perpendicular to the axis of said two rollers (42, 43), said arm (45) being driven in rotation about the axis of rotation (XI) by a respective actuator (47) controlled by a respective sensor (48) designed to detect the position of the respective longitudinal edge (14, 15) .

4. The apparatus according to any one of the preceding claims, wherein said alignment station (50) comprises a mobile structure (52) carrying an input roller (53) set at entry of the web (10) and an output roller (54) set at exit of said web (10) , said mobile structure (52) being rotatable about an axis (X2) perpendicular to the mobile structure (52) and tangential to the external edge of the input roller

(53) at its middle, said mobile structure (52) being driven by an actuator (57) governed through a processor (150) by first sensor means (56) designed to detect the position of the centre line of said web (10) .

5. The apparatus according to Claim 4, wherein said station for transverse laying-out (40) of the web (10) is positioned on said mobile structure (52) .

6. The apparatus according to Claim 5, wherein said station for transverse laying-out (40) of the web (10) is positioned on said mobile structure (52) between the input roller (53) and the output roller

(54) .

7. The apparatus according to any one of the preceding claims, comprising second sensor means (81) designed for detection of the relative position of the longitudinal edges (14, 15) of the web (10), positioned immediately before complete superposition of the sections (32, 34) of said web (10) formed upon said folding, and designed for correcting the information detected by the first sensor means (56) for detection of the longitudinal edges (14, 15) and of the centre line of the web (10) of the alignment station (50) .

8. A process for folding in two a continuous composite web (10) with anisotropic mechanical characteristics, which advances in a longitudinal direction (A) and has an original transverse dimension subject to variation during said advance, said process comprising the steps of:

- feeding said continuous web in said longitudinal direction (A) by conveyor means (90) ;

- laying out (40) said web (10) in a direction transverse to the direction of feed (A) , so as to restore said original transverse dimension;

- aligning (50) the centre line of the web (10) with respect to a longitudinal-folding line (B) parallel to said direction of feed (A) , according to the relative position of the longitudinal edges (14, 15) of said web (10) , detected following upon said laying-out step; and

folding (60) the web (10) in a direction transverse to the direction of feed (A) to form respective sections (32, 34) of said web (10), along the longitudinal-folding line (B) .

9. The process according to Claim 8, wherein the step (60) of folding the web (10) comprises the steps of:

controlling (80) the position of the longitudinal edges (14, 15) of said web (10) immediately before said complete superposition;

- generating information on the relative position of the longitudinal edges (14, 15); and

- correcting (180, 150) the position of the centre line of the web (10) with respect to the line (B) of folding of said web (10) according to the information on the relative position of the longitudinal edges (14, 15) of said web (10) .