Patent Publication Number: US-7214174-B2

Title: Apparatus for folding a nonbonded nonwoven web

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 10/699,549, filed Oct. 31, 2003, now U.S. Pat. No. 7,008,363, and the disclosure of which is hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The invention relates generally to nonwoven webs and, in particular, to apparatus and methods for folding nonbonded nonwoven webs. 
   BACKGROUND OF THE INVENTION 
   Nonwoven webs made from overlapped or entangled filaments or fibers of melt-processable thermoplastic polymers are commonly produced using spunbond and meltblown processes. Nonwoven webs are incorporated into many consumer and industrial products, such as single-use or short-life hygienic products, disposable protective apparel, fluid filtration media, and durables like bedding and carpeting. Nonwoven webs are fashioned by the operation of a meltspinning apparatus in either a spunbond process or a meltblown process. 
   A spunbond process generally involves extruding a curtain of fine diameter, semi-solid filaments of one or more thermoplastic polymers from multiple rows of fine orifices in a spinneret. A voluminous flow of relatively cool process air is directed at the curtain of extruded filaments to quench the molten thermoplastic polymer. The filaments are attenuated or drawn to a specified diameter and oriented on a molecular scale by drag forces created by a high-velocity flow of process air. The drawn filaments are propelled by the high-velocity air flow in a filament/air mixture toward a forming zone and collected on a moving collector to form a continuous length spunbond nonwoven web. 
   A meltblown process also involves pumping a thermoplastic polymer from an extruder through a die to form a curtain of filaments. However, converging layers of heated air, typically discharged from slots or holes on opposite sides of the curtain of filaments, contact the filaments immediately after extrusion and, through concomitant drag forces, stretch and attenuate the filaments. The filaments are collected on a moving collector forming a continuous length meltblown nonwoven web. Generally, meltblown filaments are finer than spunbond filaments and meltblown nonwoven webs are more fragile than spunbond nonwoven webs. Nonetheless, spunbond and meltblown nonwoven webs are susceptible to damage arising from mechanical contact, particularly before consolidation by a process such as calendaring. After consolidation, the nonwoven web is wound into a roll and removed from the meltspinning apparatus to another location for forming a consumer or industrial product. 
   The consolidated nonwoven web may be unwound from the roll and then folded with a fold line extending longitudinally along its continuous length to form a finished product. One type of folding device is a stationary folding board or skid plates that defines a chute that mechanically contacts and guides portions of a moving nonwoven web in a curving manner effective to create a longitudinal fold. Other conventional folding devices include a convoluted folding belt that contacts and moves with a moving nonwoven web. The folding belt directs a portion of the nonwoven web in a twisting path that ultimately produces a longitudinal fold. However, such guides, chutes, formers and additional moving belts of conventional web folding apparatus cannot be used in an in-line process with a meltspinning apparatus to longitudinally fold an unconsolidated nonwoven web, as the mechanical contact would damage the nonwoven web in this fragile state. 
   In view of the deficiencies in conventional web folding apparatus discussed above, it would be desirable to provide an apparatus capable of creating a longitudinal fold in an unconsolidated nonwoven web either absent mechanical contact or, at the least, with a minimal level of mechanical contact. 
   SUMMARY 
   The invention provides an apparatus for folding a nonwoven web that includes a first vacuum device and a second vacuum device downstream in a machine direction from the first vacuum device. The first vacuum device is capable of applying a vacuum effective to attract a first portion and a second portion of a nonwoven web to a collector moving in the machine direction. The second vacuum device includes at least one air inlet opening positioned to underlie the collector. The vacuum device is capable of applying a vacuum through the at least one air inlet opening to the first portion effective to attract the first portion to the collector. The vacuum also aspirates air through the second portion effective to move the second portion relative to the first portion along a fold line extending in the machine direction and thereby establishes an overlapping relationship with the first portion. 
   The invention also provides an apparatus for folding a nonwoven web moving on a collector in which the apparatus features a vacuum device including at least one air inlet opening positioned to underlie the collector and a positive pressure device including at least one air outlet opening positioned to underlie the collector proximate to the at least one air inlet opening. The vacuum device is capable of applying a vacuum to a first portion of a nonwoven web through the at least one air inlet opening effective to attract the first portion to the collector. The positive pressure device is capable of applying a forced air flow through the at least one air outlet opening to a second portion of the nonwoven web effective to move the second portion relative to the first portion along a fold line extending in the machine direction and thereby establish an overlapping relationship with the first portion after folding. The apparatus is used in conjunction with a melt-spinning device capable of discharging a stream of filaments collected by the collector to form the nonwoven web. 
   In accordance with the principles of the invention, an apparatus for forming a nonwoven web includes a melt-spinning device capable of discharging a stream of filaments and a collector moving in a machine direction. The collector collects the stream of filaments discharged by the melt-spinning device to form a nonwoven web. The apparatus further includes a transfer zone downstream in the machine direction from the melt-spinning device in which vacuum is applied through the collector to a first portion and a second portion of the nonwoven web and an initial folding zone downstream in the machine direction from the transfer zone in which vacuum is applied through the collector to the first portion. A folding zone downstream in the machine direction from the initial folding zone applies vacuum through the collector to the first portion and a positive pressure differential through the collector to the second portion. The positive pressure differential transfers momentum to the second portion causing the second portion to move relative to a fold line, past the perpendicular axis along the fold line. The vacuum subsequently attracts the second portion toward the first portion to establish an overlapping relationship in which the second portion of the nonwoven web lays flat over the first portion of the nonwoven web. 
   In accordance with the principles of the invention, a method is provided for folding a nonwoven web. The method includes forming the nonwoven web on a collector in a forming zone, moving the collector in a machine direction for transporting the nonwoven web away from the forming zone, applying a negative pressure differential or vacuum to a first region of the nonwoven web and applying a positive pressure differential, preferably simultaneously with the vacuum, to a second region of the nonwoven web. The vacuum attracts the first region to the collector. The positive pressure differential causes the second region to fold toward the first region about a fold line extending in the machine direction. 
   In accordance with an alternative embodiment, a method for folding a moving nonwoven web includes forming the nonwoven web on a collector in a forming zone and moving the collector in a machine direction for transporting the nonwoven web away from the forming zone in a machine direction. A first negative pressure differential to the first portion and the second portion of the nonwoven web thereby attracting the first portion and the second portion to the collector. A second negative pressure differential is applied to the first portion of the nonwoven web downstream in the machine direction from the first negative pressure differential. The second negative pressure differential attracts the first portion to the collector and aspirates air through the second portion effective to fold toward the first portion about a fold line extending in the machine direction. 
   In accordance with principles of the invention, nonwoven webs may be folded with high degree of accuracy and at line speeds characteristic of web-forming process lines by a non-contact folding procedure. The web folding apparatus of the invention is easily incorporated into the process line as a passive in-line component downstream from a melt-spinning device. The web folding apparatus of the invention is simple, compact and may be installed as a retrofit unit in association with an existing melt-spinning device. 
   These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention. 
       FIG. 1  is a schematic perspective view of a melt-spinning device capable of forming a nonwoven web and a folding apparatus in accordance with the principles of the invention; 
       FIG. 2  is a top view of a portion of  FIG. 1  detailing the folding apparatus; 
       FIG. 3  is a cross-sectional view taken generally along line  3 — 3  of  FIG. 2 ; 
       FIG. 3A  is a cross-sectional view similar to  FIG. 3  of a folding apparatus in accordance with an alternative embodiment of the invention; 
       FIG. 4  is a top view similar to  FIG. 2  of a folding apparatus in accordance with an alternative embodiment of the invention; 
       FIG. 5A  is a cross-sectional view taken generally along line  5 A— 5 A of  FIG. 4 ; and 
       FIG. 5B  is a cross-sectional view similar to  FIG. 5A . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention is directed to an apparatus and methods for forming a longitudinal fold in a continuous length nonbonded, nonwoven web moving on a collector. To that end, impingement of a stream of a gas, such as air, transfers momentum to one portion of the nonwoven web for folding that portion over another portion of the web secured to the collector by vacuum. Although the invention will be described herein in terms of an exemplary system used for folding nonwoven webs, it should be understood that modifications to the exemplary system described herein could be made so as to conform any portion or the entire system to a particular need without departing from the intended spirit and scope of the invention. 
   With reference to  FIGS. 1 and 2 , a melt-spinning device  10  is equipped with an extruder  12  that converts solid thermoplastic polymer into a molten or semi-solid state. Gear pumps  14  pump the semi-solid thermoplastic polymer from the extruder  12  to an extrusion die or spinneret  16 , which discharges a curtain of filaments  18 . A second thermoplastic polymer may be supplied to the spinneret  16  for forming multi-component filaments  18 . A cross-flow of cooling air from a quench blower  20  accelerates solidification of the airborne curtain of filaments  18 . The filaments  18  are directed into a filament-drawing device  22 , which envelops the filaments  18  with a tangential high velocity flow of process air to thereby apply a drag force in a direction substantially parallel to the length of the filaments  18 . Because the filaments  18  are extensible, the drag force attenuates and molecularly orients the filaments  18 . The curtain of attenuated filaments  18  exiting the filament-drawing device  22  is deposited or laid down in a substantially random and preferably uniform manner in the form of a nonwoven web  28  on a horizontally and linearly moving perforated collector  26 . The collector  26  spans the width of the spinneret  16  and moves in a machine direction, represented by the arrow labeled MD, extending along the length of the nonwoven web  28  in the direction in which it is produced. 
   The collector  26  mechanically supports the nonwoven web  28  as web  28  is transported in the machine direction. Generally, the nonwoven web  28  is a flexible continuous sheet layer having a structure of individual filaments  18  interlaid in a random manner to have an open, porous structure. The porous structure of the nonwoven web  28  presents a resistance to gas flow therethrough sufficient to apply an unbalanced force to the web  28  if a positive or negative pressure differential is applied to a surface of the nonwoven web  28  confronting the collector  26 . The invention contemplates that the nonwoven web  28  may be formed from fibers or filaments originating from a meltblowing process, in addition to or instead of the illustrated spunbond process. In certain embodiments of the invention, the nonwoven web  28  may constitute a laminate of two or more layers such as, for example, a spunbond/meltblown/spunbond (SMS) laminate. The invention contemplates that the principles of the invention are applicable for use with any suitable meltspinning apparatus including, but not limited to, meltspinning apparatus  10 , that is capable of forming a nonwoven web on a collector. 
   With continued reference to  FIGS. 1 and 2 , the nonwoven web  28  includes a central portion  30 , a left peripheral portion  30 , and a right peripheral portion  34 . The peripheral portions  32 ,  34  flank the central portion  30  and extend inwardly from one of the opposite side edges of the nonwoven web  28  in a cross-machine direction, represented by the double-headed arrow labeled CD, generally perpendicular to the machine direction. The center region  30  interconnects the peripheral portions  32 ,  34  to define an integral and continuous structure. 
   With continued reference to  FIGS. 1 and 2 , located beneath the collector  26  and generally underneath the filament-drawing device  22  is a forming zone  36  in which a negative pressure differential or vacuum is applied so that the filaments  18  lay down on the collector  26  to form nonwoven web  28 . The collector  26  is porous and gas-permeable for effectively transferring a vacuum through the collector thickness with a nominal pressure drop. The forming zone  36  includes a collecting duct  38  situated below the collector  26  and an air-moving device  40 , such as a blower, a fan or a vacuum pump, communicating with the collecting duct  38 . The air-moving device  40  actively draws process air discharged from the filament-drawing device  22  and secondary air entrained by the process air into air inlet openings  42  formed in the collecting duct  38  beneath the collector  26 . The air inlet openings  42  are distributed in an arrangement effective for applying a substantially uniform vacuum in the cross-machine direction across the width of the forming zone  36 , which promotes uniform filament laydown and uniform basis weight of the nonwoven web  28  by reducing extraneous air currents. 
   A transfer zone  44  downstream from the forming zone  36  secures the nonwoven web  28  to the collector  26  with vacuum or suction for transport or transfer away from the forming zone  36 . The transfer zone  44  includes a collecting duct  46  incorporating multiple air inlet openings  48  located vertically below the collector  26 . An air-moving device  50 , such as a blower, a fan or a vacuum pump, coupled in communication with the collecting duct  46  actively draws air from the ambient environment successively through the air inlet openings  48 , the nonwoven web  28  and the collector  26  into the collecting duct  46 . A negative pressure differential applied to the nonwoven web  28  within the transfer zone  44  attracts the nonwoven web  28  to the collector  26  for the length of its travel path in the machine direction overlying the collecting duct  46 . The air inlet openings  48  span the cross-machine dimension of the collector  26  and, therefore, the nonwoven web  28  for securing the central portion  30  and peripheral portions  32 ,  34  of the nonwoven web  28  to the collector  26 . The nonwoven web  28  is transferred or transported on the collector  26  away from the forming zone  36  over an arbitrary distance in the transfer zone  44  while vacuum is applied across the entire cross-machine dimension. 
   With continued reference to  FIGS. 1 and 2 , downstream from the transfer zone  44  is an initial folding zone  52  including a collecting duct  54  and multiple air inlet openings  56  in the collecting duct  54  positioned beneath the collector  26 . An air-moving device  58 , such as a blower, a fan or a vacuum pump, coupled in communication with the collecting duct  54  actively draws air from the ambient environment successively through the nonwoven web  28 , the collector  26  and the air inlet openings  56  into the collecting duct  54 . Initial folding zone  52  applies a negative pressure differential that attracts the central portion  30  of nonwoven web  28  to the collector  26  for the segment of its travel path in the machine direction overlying the collecting duct  54 . However, the air inlet openings  56  span less than the full cross-machine dimension of the collector  26 . As a result, the vacuum applied to the central portion  30  is maintained as the nonwoven web  28  moves from the transfer zone  44  to the initial folding zone  52  and the peripheral portions  32 ,  34  of the nonwoven web  28  are no longer attracted to the collector  26  by a negative pressure differential. 
   With reference to  FIGS. 1–3 , a folding zone  60  downstream from initial folding zone  52  includes a collecting duct  62  enclosing an air plenum  61  having multiple air inlet openings  64  arranged to underlie the collector  26 . The air plenum  61  of collecting duct  62  communicates with, and is evacuated by, an air-moving device  66 , such as a blower, a fan or a vacuum pump. The vacuum actively draws or aspirates air from the ambient environment above the nonwoven web  28 , which successively permeates through the nonwoven web  28 , the collector  26  and the air inlet openings  64  into the air plenum  61 , as is depicted by arrows  67  representing the flow of air. The aspiration applies a negative pressure differential to the central portion  30  of the nonwoven web  28 , which attracts central portion  30  to the collector  26  for the portion of its travel path in the machine direction that overlies the collecting duct  62 . As a result, vacuum across the central portion  30  is maintained in the folding zone  60 , as present in the initial folding zone  52 . 
   The folding zone  60  further includes positive pressure regions  68 ,  70  that flank the air inlet openings  64  in the cross-machine direction. Positive pressure region  68  includes an exhaust duct  72  coupled in communication with an air-moving device  76 , such as a blower, a fan, or a source of pressurized air like an air compressor. Similarly, positive pressure region  70  includes an exhaust duct  74  coupled in communication with air-moving device  76 . Each exhaust duct  72 ,  74  includes a corresponding set of air outlet openings  78 ,  80 , respectively, positioned laterally on opposite sides of air inlet openings  64  and vertically beneath the collector  26 . 
   An upward forced flow of air exhausted from the exhaust ducts  72 ,  74  successively permeates through the air outlet openings  78 ,  80 , the nonwoven web  28  and the collector  26 , as is depicted by arrows  82  representing the substantially columnar air flow. The upward forced air flow applies an unbalanced lifting force directed away from the collector  26  to each successive length or section of the peripheral portions  32 ,  34  as those sections consecutively enter and overlie the corresponding set of air outlet openings  78 ,  80 . The unbalanced lifting force applied to the peripheral portions  32 ,  34  is generally opposite, at least when the peripheral portions  32 ,  34  begin to overlie the air outlet openings  78 ,  80 , to the unbalanced force applied in the folding zone  60  to the central portion  30 . The peripheral portions  32 ,  34  move upward in response to the lifting force and the positive pressure differential applied to the downwardly-facing surfaces of peripheral portions  32 ,  34 . The center region  30  of the nonwoven web  28  is attracted toward the collector  26  by the vacuum applied from air inlet openings  64 . Vacuum applied through air inlet openings  48  of upstream transfer zone  44  ( FIG. 2 ) across the entire width of the nonwoven web  28  anchors upstream lengths of the peripheral portions  32 ,  34  for the folding induced within folding zone  60 . 
   With continued reference to  FIGS. 1–3 , the angular momentum applied to peripheral portion  32  by the lifting force causes peripheral portion  32  to lift from contact with the collector  26  and pivot or revolve, as represented by arrows  83 , about a longitudinal fold line  84  defined adjacent to one lateral edge of air inlet openings  64 . Similarly, the angular momentum applied to peripheral portion  34  by the lifting force causes peripheral portion  34  to lift from contact with the collector  26  and pivot or revolve, as represented by arrows  83 , about a longitudinal fold line  86  defined adjacent to an opposite lateral edge of air inlet openings  64 . The longitudinal fold lines  84 ,  86  are oriented substantially parallel to the machine direction. 
   The dwell time of the peripheral portions  32 ,  34  over the corresponding set of air outlet openings  78 ,  80 , considered in conjunction with the velocity at which the web  28  is moved in the machine direction, is effective to create a lifting force effective to propel the peripheral portions  32 ,  34  toward the air inlet openings  64 . The peripheral portions  32 ,  34  experience a continuous rotation or twisting over the extent of the folding from a first position having a contacting relationship with the collector  26  (0° rotation angle) to a second position having a contacting relationship with the center region  30  (180° rotation angle). At a 90° rotation angle, the peripheral portions  32 ,  34  are perpendicular to the central portion  30  and the upward lifting force is no longer applied by the air exhausted by air outlet openings  78 ,  80  to the corresponding one of the peripheral portions  32 ,  34 . As the rotation angle exceeds 90°, each of the peripheral portions  32 ,  34  begins to overlie the central portion  30  and the negative pressure differential applied by the air inlet openings  64  attracts the peripheral portions  32 ,  34  toward the secured central portion  30  of the nonwoven web  28 . Due to the attraction of the central portion  30  to the collector  26  in the initial folding zone  52  and the air inlet openings  64  of folding zone  60 , the positive pressure differential causes the peripheral portions  32 ,  34  of the nonwoven web  28  to fold in a rolling manner upward and inward to assume a substantially flat, overlapping relationship with the central portion  30  of the nonwoven web  28 . 
   The invention contemplates that, by eliminating one of the two positive pressure regions  68 ,  70 , only one of the two peripheral portions  32 ,  34  of the nonwoven web  28  is folded. In accordance with this alternative embodiment of the invention, the width of the remaining one of the peripheral portions  32 ,  34  in the cross-machine direction may be less than, equal to or greater than the width of the central portion  30 . For example, the remaining set of air outlet openings, for example, air openings  78 , and air inlet openings  64  may be arranged such that fold line the nonwoven web  28  is folded in half along a central longitudinal fold line (not shown) extending parallel to the longitudinal centerline of web  28 . 
   The invention further contemplates that the set of air inlet openings  64  may be omitted in its entirety such that the central portion  30  of the nonwoven web  28  is not attracted by a negative pressure differential toward the collector  26  in the folding zone  60 . According to this embodiment of the invention, the upstream initial folding zone  52  and a downstream final or overlap zone  94  are effective to secure the central portion  30  of the nonwoven web  28  to the collector  26 , and the downstream overlap zone  94  attracts and secures the peripheral portions  32 ,  34  against the central portion  30  during and after folding. The upstream initial folding zone  52  and downstream final or overlap zone  94  define the transverse location of the longitudinal fold lines  84 ,  86 . 
   With continued reference to  FIGS. 1–3 , intersections between a set of partitioning walls  87 ,  88  in each of the exhaust ducts  72 ,  74  define the corresponding air outlet openings  78 ,  80 . The partitioning walls  87 ,  88  are oriented such that the individual air streams from air outlet openings  78 ,  80  are substantially columnar and impinge the plane of the nonwoven web  28  initially at approximately 90° relative to the machine direction and at approximately 90° relative to the cross-machine direction. As the peripheral portions  32 ,  34  fold inwardly, the inclination between the individual air streams and the peripheral portions  32 ,  34  decreases until the air flow is tangential and the peripheral portions  32 ,  34  begin to experience the negative pressure differential applied by the air inlet openings  64  in folding zone  60 . The invention contemplates that the geometry and inclination of the partitioning walls  87 ,  88  may be adjusted to direct or distribute some or all of the individual air streams in the machine direction, counter to the machine direction, and/or in the cross-machine direction. It is believed that inclining the individual air streams inwardly in the cross-machine direction will increase the angular momentum imparted to the peripheral portions  32 ,  34 . As such, the partitioning walls  87 ,  88  effectively operate as an air baffle capable of profiling air flow from the air outlet openings  78 ,  80  in the machine and cross-machine directions. 
   The air-moving device  76  may be configured to adjust the velocity of the air streams emitted from the air outlet openings  78 ,  80 . For example, the air-moving device  76  may be a variable-speed blower or an air compressor with a pressure-regulated output. The air velocity is selected such that the nonwoven web  28 , which is nonbonded and fragile, is not damaged or degraded. The invention contemplates that each of the positive pressure regions  68 ,  70  may communicate with separate and distinct air-moving devices like air-moving device  76 . 
   With continued reference to  FIGS. 1–3 , the nonwoven web  28  is transported, after folding, downstream in the machine direction to a calender  90  and passes through the nip of a pair of nip rollers  91 ,  92  constituting the calender  90 . The overlap zone  94 , similar to transfer zone  44 , downstream from the folding zone  60  and the positive pressure regions  68 ,  70 , applies a negative pressure differential from an air-moving device  95  to outlet openings  97  that secures the central portion  30  of the nonwoven web  28  to the collector  26 . The nip rollers  91 ,  92  apply heat and pressure to flatten and consolidate the nonwoven web  28  in a direction normal to the plane of the web  28 , which reduces the web thickness, bonds its filaments, and sets the longitudinal fold(s) at the location of the longitudinal fold lines  84 ,  86 . The calendered nonwoven web  28  has a tensile strength sufficient such that it may be rolled up by a winder  96  for storage, transportation and unwinding to be cut into various shapes depending on the ultimate application form. For example, the nonwoven web  28  may be shaped to manufacture single-use or short-life hygienic products, disposable protective apparel, fluid filtration media, and durables like bedding and carpeting. 
   With reference to  FIG. 3A  in which like reference numerals refer to like features in  FIG. 3  and in accordance with an alternative embodiment of the invention, a folding zone  60   a  includes collecting duct  62  enclosing an air plenum  61  evacuated by an air-moving device  66  and multiple air inlet openings  64 . The central portion  30  of the nonwoven web  28  is attracted to the collector  26  by vacuum applied through air inlet openings  64 , as present in the initial folding zone  52 . However, folding zone  60   a  lacks positive pressure regions, such as positive pressure regions  68 ,  70  ( FIGS. 2 and 3 ), that direct a forced flow of air at the peripheral portions  32 ,  34 . 
   The vacuum applied through air inlet openings  56  of initial folding zone  52  ( FIGS. 1 and 2 ) and air inlet openings  64  of folding zone  60   a  aspirates air from the ambient environment. Some of the aspirated air originates from beneath the peripheral portions  32 ,  34  of nonwoven web  28  and is drawn through peripheral portions  32 ,  34  and the corresponding underlying edges of the collector  26  into air inlet openings  56 ,  64 . The concomitant flow of air, indicated diagrammatically by reference numeral  99  through the peripheral portions  32 ,  34 , creates a negative pressure differential on the upper surface of the peripheral portions  32 ,  34  that causes the peripheral portions  32 ,  34  to move upward and pivot or revolve about longitudinal fold lines  84 ,  86 , respectively, and eventually overlie the central portion  30 . 
   Upstream from initial folding zone  52  and folding zone  60   a , vacuum is applied through air inlet openings  48  of transfer zone  44  ( FIG. 2 ) across the entire width of the nonwoven web  28  and, in particular, vacuum is applied to the peripheral portions  32 ,  34  as well as central portion  30 . The vacuum attracts upstream lengths of the peripheral portions  32 ,  34  to the collector  26  and provides an anchor for the folding induced within initial folding zone  52  and folding zone  60   a . The invention contemplates that the initial folding zone  52  and folding zone  60   a  may be combined to share a single collecting duct enclosing one air plenum evacuated by a common air-moving device. 
   With reference to  FIG. 4  and in accordance with an alternative embodiment of the invention, stationary inclined ramps  110 ,  112  may be provided that contact and alter the direction of motion of the peripheral portions  32 ,  34  as the nonwoven web  28  is conveyed past inclined ramps  110 ,  112  by collector  26 . The directional change imparts angular momentum to the peripheral portions  32 ,  34  that assists or supplements the pneumatic folding action of positive pressure regions  98 ,  100 . Specifically, each of the inclined ramps  110 , 112  contacts an underside of a corresponding one of the peripheral portions  32 ,  34  as the nonwoven web  28  is conveyed past the inclined ramps  110 , 112  in the machine direction on collector  26 . Each of the inclined ramps  110 , 112  is contoured with a surface that causes the corresponding contacting one of the peripheral portions  32 ,  34  to be directed in a curved path relative to the flat central portion  30 . Although mechanical contact is not required for folding nonwoven web  28 , inclined ramps  110 , 112 , or other types of conventional web folding apparatus, may be used in conjunction with positive pressure regions  98 ,  100  or with positive pressure regions  68 ,  70  ( FIGS. 1–3 ) for folding the peripheral portions  32 ,  34  along longitudinal fold lines  84 ,  86 . 
   With reference to  FIGS. 4 and 5A  in which like reference numerals refer to like features in  FIGS. 1–3  and in an alternative embodiment of the invention, a pair of positive pressure regions  98 ,  100  flanking folding zone  60  may each include a single elongate slot  102 ,  104  respectively, having a major axis extending in the machine direction. Air emitted from each slot  102 ,  104  applies an upward force that progressively folds the peripheral portions  32 ,  34  of the nonwoven web  28  along the corresponding longitudinal fold lines  84 ,  86  without mechanical contact to create an overlapping relationship with the central portion  30 , as described herein. The side wall of the slots  102 ,  104  may be inclined to direct some or all of the air stream in the machine direction, counter to the machine direction, and/or in the cross-machine direction. In addition, the major axis of each slot  102 ,  104  may be angled or inclined relative to the machine direction so that the air flow better corresponds with the progressively rolled profile of the peripheral portions  32 ,  34 . Alternatively, the length or major axis of each slot  102 ,  104  may also be lengthened or shortened for adjusting the extent of the air stream in the machine direction. Alternatively, the width of each slot  102 ,  104  in the cross-machine direction may be tapered for adjusting the air flows at different positions along the length. 
   Longitudinally-extending strands or bands  106 , 108 , which may be elastic or non-elastic, are each positioned a distance inward from each peripheral portion  32 ,  34  of the nonwoven web  28 . The bands  106 ,  108  may be unwound from a spool or reel (not shown) and, if elastic, are provided in a stretched or tensioned condition. The bands  106 ,  108  are positioned either vertically a short distance above a plane containing the nonwoven web  28  or in a contacting relationship with the nonwoven web  28 . The bands  106 ,  108  provide corresponding guide axes for defining longitudinal fold lines  84 ,  86  along which the peripheral portions  32 ,  34  of the nonwoven web  28  fold in response to the positive pressure differential applied by the positive pressure regions  98 ,  100 . Locating the bands  106 ,  108  axially coincident with the longitudinal fold lines  84 ,  86  may permit elimination of the set of air inlet openings  64  as the bands  106 ,  108  each provide a distinct physical axis of rotation. 
   The bands  106 ,  108  are secured with the constituent filaments  18  of nonwoven web  28  by use of adhesive bonds, heat bonds, pressure bonds, ultrasonic bonds, dynamic mechanical bonds, mechanical locking or intertwining, or any other suitable technique as recognized in the art. For example, calendering the nonwoven web  28  in calendar  90  may suffice to secure the bands  106 ,  108  with nonwoven web  28 . Alternatively, the bands  106 ,  108  may be ultrasonically bonded with the nonwoven web  28  using an ultrasonic bonder, adhesively bonded to the nonwoven web  28  with dots or beads of adhesive, or heatless mechanical bonded to the nonwoven web  28  by applying pressure in the nip between a smooth roller and an embossed roller. 
   If the bands  106 ,  108  are elastic, the peripheral portions  32 ,  34  of the nonwoven web  28  may be elasticized. For example, the elastic bands  106 ,  108  may be used to produce elasticized waist areas and leg cuffs for a disposable hygienic article. Such elastic bands and elastic strands suitable for use in the invention are commercially available, for example, from E.I. Dupont de Nemours and Company (Wilmington, Del.). 
   With reference to  FIG. 5B  in which like reference numerals refer to like features in  FIG. 5A , band  106  may be displaced inwardly toward a centerline of the central portion  30  so that, after folding, band  106  is positioned in the space between the central portion  30  and the folded peripheral portion  32  but not collinear with the longitudinal fold line  84 . Band  108  may have a similar non-aligned relationship with longitudinal fold line  86 . In accordance with this alternative embodiment of the invention, one or both bands  106 ,  108  do not coincide axially with the longitudinal fold lines  84 ,  86 . The invention further contemplates that additional bands, similar or identical to bands  106 ,  108 , may be positioned relative to the central portion  30  such that, after folding, the additional bands are likewise located in the space between the folded peripheral portions  32 ,  34  and the central portion  30 . 
   While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, longitudinal folds in accordance with the principles of the invention may be formed in other types of continuous length webs such as plastic films, foams, tissues, rubbers, metal foils and other materials, either separately or in combination, and in single-layer or multiple-layer arrangements. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.