Patent Publication Number: US-7914648-B2

Title: Device for web control having a plurality of surface features

Description:
CROSS-REFERENCE TO RELATION APPLICATION 
     This application claims the benefit of provisional U.S. Application No. 61/014,490, filed Dec. 18, 2007. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a foil for use in a papermaking apparatus wherein the foil provides stabilization, while providing a relative low amount of drag, to a paper web as the paper web passes the foil. 
     BACKGROUND OF THE INVENTION 
     During the manufacturing of a paper web, the moving web, such as one that may be used as the substrate for a paper towel or tissue towel, is transported at very high velocities. In many instances, the web is transported without support and this may result in the web ‘fluttering’ or otherwise losing control. 
     Those of skill in the art may appreciate that flutter is undesirable because flutter is thought to be a contributing cause of tearing that may occur in the paper web. Further, flutter in the web often forces producers to reduce the velocity at which the paper web is transported, causing decreases in efficiency and incurring additional costs. 
     One method available in the prior art to address the problem of sheet flutter is through the use of stabilizing devices, such as a foil. The foils described in the prior art may be used either in converting processes/apparatus or in papermaking processes/apparatus. The foil may be used to act as a guide for the traveling web in order to reduce or eliminate flutter. However, a problem that those of skill in the art will appreciate exists with many of the prior art foils is that the foil, while stabilizing the web, may cause drag on the surface of the web. Drag may be detrimental to a traveling paper web, especially a relatively light paper web, because it is thought that drag may cause tearing or other mechanical failures in the paper web. In some instances, the velocity of a paper web in a papermaking operation may require special design considerations due to the relatively high velocity that a paper web in the paper making operation. 
     As a result, there exists the need for a web stabilizing device that exerts a relatively low amount of drag on a moving paper web. It was surprisingly discovered that by providing a plurality of discrete features in the surface of a foil, the amount of drag caused by the foil was reduced relative to the drag caused by a foil of the prior art. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention is directed to a papermaking apparatus comprising a machine direction, cross machine direction, and a z-direction, the apparatus further comprising: a web stabilization device, wherein the web stabilization device comprises a plurality of surface features; wherein the surface features have a feature depth of greater than about 0.020″. 
     In another embodiment, the present invention is directed to a web stabilization device wherein the web stabilization device comprises a first surface and a second surface, and wherein the web stabilization device further comprises a plurality of surface features having a feature depth of greater than about 0.020″. 
     In another embodiment still, the present invention is directed to a web stabilization device wherein the web stabilization device provides a test system wall shear stress (lb/in 2 ) of less than about:
 
Wall Shear Stress=(5×10 −7 )(Web velocity)−5×10 −4  
 
to an adjacent web with a web velocity of from about 2000 FPM to about 6000 FPM.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims that particularly point out and distinctly claim the present invention, it is believed that the present invention will be understood better from the following description of embodiments, taken in conjunction with the accompanying drawings, in which like reference numerals identify identical elements. 
       Without intending to limit the invention, embodiments are described in more detail below: 
         FIG. 1  is a schematic view of an exemplary paper making apparatus according to the present invention. 
         FIG. 2  is a perspective view of an exemplary web stabilization device according to the present invention. 
         FIG. 3  is a schematic view of an exemplary web stabilization device according to the present invention juxtaposed adjacent to a moving paper web. 
         FIG. 4A  is a perspective view of an exemplary web stabilization device according to the present invention comprising a plurality of surface features. 
         FIG. 4B  is a cross-sectional view of the exemplary web stabilization device of  FIG. 4A  taken along the line  4 B- 4 B. 
         FIG. 5A  is a graphical representation of the wall shear stress exerted on a moving web using exemplary web stabilization devices. 
         FIG. 5B  is a graphical representation of the total drag/area exerted on a moving web using exemplary web stabilization devices. 
         FIG. 6  is a top view of a portion of an exemplary web stabilization device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
     As used herein, “fibrous structure” means an arrangement of fibers produced in any papermaking machine known in the art to create a ply of paper. “Fiber” means an elongate particulate having an apparent length exceeding its apparent width. More specifically, and as used herein, fiber refers to such fibers suitable for a papermaking process. 
     As used herein, “paper product” refers to any formed, fibrous structure products, traditionally, but not necessarily, comprising cellulose fibers. In one embodiment, the paper products of the present invention include bath tissue products. 
     As used herein, “conventional paper web” refers to a paper web which has not been textured by a papermaking belt, wire, fabric, and the like during the papermaking process. In one embodiment, conventional paper web refers to a paper web which has been dried only by contact with the Yankee dryer. In another embodiment, a conventional paper web does not have any texture imparted onto the surface, although it may be textured during a converting process. 
     As used herein, “ply” or “plies” means an individual fibrous structure or sheet of fibrous structure, optionally to be disposed in a substantially contiguous, face-to-face relationship with other plies, forming a multi-ply fibrous structure. It is also contemplated that a single fibrous structure can effectively form two “plies” or multiple “plies”, for example, by being folded on itself. In one embodiment, the ply has an end use as a tissue-towel paper product. A ply may comprise one or more wet-laid layers, air-laid layers, and/or combinations thereof. If more than one layer is used, it is not necessary for each layer to be made from the same fibrous structure. Further, the layers may or may not be homogenous within a layer. The actual makeup of a tissue paper ply is generally determined by the desired benefits of the final tissue-towel paper product, as would be known to one of skill in the art. The fibrous structure may comprise one or more plies of non-woven materials in addition to the wet-laid and/or air-laid plies. 
     As used herein, “basis weight” or “BW” is the weight per unit area of a sample reported in lbs/3000 ft 2  or g/m 2 . 
     As used herein, “caliper” or “sheet caliper” is the macroscopic thickness of a product sample under load. 
     As used herein, “machine direction” or “MD” refers to the direction parallel to the flow of the fibrous structure through the papermaking machine and/or product manufacturing equipment. 
     As used herein, “cross machine direction” or “CD” refers to the direction perpendicular to the machine direction in the same plane of the fibrous structure and/or fibrous structure product comprising the fibrous structure. 
     As used herein, “z-direction” refers to the direction normal to a plane formed by machine direction and cross machine directions. 
     As used herein, “paper-making apparatus” or “paper-making equipment” or “paper-making machinery” refers to the apparatus, equipment and/or machinery that may be used to provide a web of paper product from a slurry of fibers. An exemplary paper-making apparatus is described infra. In one embodiment, a papermaking apparatus runs at, or above, about 3200 FPM. In another embodiment, a papermaking apparatus runs from about 3200 FPM to about 8000 FPM. In another embodiment, a papermaking apparatus runs from about 3800 FPM to about 4500 FPM. 
     As used herein, “converting apparatus” or “converting equipment” or “converting machinery” refers to the apparatus, equipment, and/or machinery that may be used to perform a converting operation (i.e., embossing, printing, lamination, etc.) after the paper has been made by a paper-making apparatus/equipment/machinery. Those of skill in the art may appreciate that converting apparatus typically runs at, or below, about 2500 FPM which is relatively slow compared to a papermaking apparatus which typically runs at, or above, about 3200 FPM. Thus, without wishing to be limited by theory, one of skill in the art may appreciate that because of the speed differential, a web-stabilization device which may be used in a converting apparatus may not be suitable for a web-stabilization device which may be used in a papermaking apparatus due to the mechanical operations that a converting apparatus performs. However, one of skill in the art will appreciate that the ability of a single type of web-stabilization device in both the papermaking and converting apparatus will lead to improved efficiency (since only one interchangeable part will be required) and lower costs. 
     As used herein, “web-stabilization device” or “web-stabilizing device” refers to a web handling element that may be used to stabilize a moving web. In some embodiments, a web-stabilizing device may be used in either a papermaking and/or converting process. In other embodiments, a web-stabilizing device may be used in conjunction with any web product, described infra. A web stabilization device may be passive and operate by relying on local forces (i.e., the Bernoulli effect) to attract a moving web towards the web-stabilizing device and thereby reduce flutter in, and thus stabilize, the paper web. Alternatively, a web stabilizing device may be active in that it might use compressed air or a vacuum in addition to the device alone to stabilize the paper web. Exemplary prior art web stabilization devices are exemplified in U.S. Pat. Nos. 6,375,801 and 5,891,309 and U.S. Pat. App. Pub. No. 2005/0161185A1. In some embodiments, a “web-stabilization device” may be referred to as a “foil” or an “airfoil.” 
     As used herein, “surface feature” refers to a structured element on the surface of a web-stabilization device or foil. In one embodiment, a surface feature is a recessed area on the surface of the web-stabilization device or foil. In another embodiment, a surface feature is a raised element on the surface of the web-stabilization device or foil. A surface feature may be either discrete, continuous, or semicontinuous. A surface feature may be introduced on the surface of a web-stabilization device or foil by any means known in the art. Exemplary materials having surface features are described in U.S. Pat. Nos. 5,114,099 and 4,434,957. Further, materials that may be used to provide a web-stabilization device or foil of the present invention are commercially available from Rimex Metals Inc. (Edison, N.J.), Mechanical Metals Inc. (Newtown, Pa.), and Rigidized Metals (Buffalo, N.Y.). 
     Paper Product 
     The present invention contemplates the use of a variety of paper making fibers, such as natural fibers, synthetic fibers, as well as any other suitable fibers, starches, and combinations thereof. Paper making fibers useful in the present invention include cellulosic fibers commonly known as wood pulp fibers. Applicable wood pulps include chemical pulps, such as Kraft, sulfite and sulfate pulps, as well as mechanical pulps including, groundwood, thermomechanical pulp, chemically modified, and the like. Chemical pulps may be used in tissue towel embodiments since they are known to those of skill in the art to impart a superior tactical sense of softness to tissue sheets made therefrom. Pulps derived from deciduous trees (hardwood) and/or coniferous trees (softwood) can be utilized herein. Such hardwood and softwood fibers can be blended or deposited in layers to provide a stratified web. Exemplary layering embodiments and processes of layering are disclosed in U.S. Pat. Nos. 3,994,771 and 4,300,981. Additionally, fibers derived from wood pulp such as cotton linters, bagesse, and the like, can be used. Additionally, fibers derived from recycled paper, which may contain any of all of the categories as well as other non-fibrous materials such as fillers and adhesives used to manufacture the original paper product may be used in the present web. In addition, fibers and/or filaments made from polymers, specifically hydroxyl polymers, may be used in the present invention. Non-limiting examples of suitable hydroxyl polymers include polyvinyl alcohol, starch, starch derivatives, chitosan, chitosan derivatives, cellulose derivatives, gums, arabinans, galactans, and combinations thereof. Additionally, other synthetic fibers such as rayon, polyethylene, and polypropylene fibers can be used within the scope of the present invention. Further, such fibers may be latex bonded. 
     Other materials are also intended to be within the scope of the present invention as long as they do not interfere or counteract any advantage presented by the instant invention. 
     The paper product may comprise any tissue-towel paper product known in the industry. Embodiment of these substrates may be made according U.S. Pat. Nos. 4,191,609, 4,300,981, 4,514,345, 4,528,239, 4,529,480, 4,637,859, 5,245,025, 5,275,700, 5,328,565, 5,334,289, 5,364,504, 5,527,428, 5,556,509, 5,628,876, 5,629,052, 5,637,194, and 5,411,636; EP 677612, and U.S. Pat. App. No. 2004/0192136A1. 
     The substrates used to make the present invention paper product may be manufactured via a wet-laid making process where the resulting web is through-air-dried or conventionally dried. Optionally, the substrate may be foreshortened by creping or by wet microcontraction. Creping and/or wet microcontraction are disclosed in commonly assigned U.S. Pat. Nos. 6,048,938, 5,942,085, 5,865,950, 4,440,597, 4,191,756, and 6,187,138. 
     Conventionally pressed paper and a method for making such is described infra and is also exemplified in U.S. Pat. No. 6,547,928. Uncompacted, non pattern-densified paper products are also contemplated within the scope of the present invention and are described in U.S. Pat. Nos. 3,812,000 and 4,208,459. Uncreped paper products as defined in the art are also contemplated. The techniques to produce uncreped paper products in this manner are exemplified in European Pat. App. Nos. 0 677 612A2 and 0 617 164 A1; and in U.S. Pat. No. 5,656,132. 
     Uncreped paper product, in one embodiment, refers to a paper product which is non-compressively dried. In one embodiment, an uncreped paper product is dried by through air drying. Resultant through air dried paper products may be pattern densified such that zones of relatively high density are dispersed within a high bulk field, including pattern densified tissue wherein zones of relatively high density are continuous and the high bulk field is discrete. The techniques to produce uncreped paper product in this manner are taught in the prior art. For example, Wendt, et. al. in European Pat. App. Nos. 0 677 612A2 and 0 617 164 A1; and U.S. Pat. No. 5,656,132 
     The substrate which comprises the paper product of the present invention may be cellulosic, or a combination of both cellulose and non-cellulose. The substrate may be conventionally dried using one or more press felts. If the substrate which comprises the paper product according to the present invention is conventionally dried, it may be conventionally dried using a felt which applies a pattern to the paper as taught by commonly assigned U.S. Pat. No. 5,556,509; and PCT App. No. WO 96/00812. Other exemplary paper products may be made according to U.S. Pat. Nos. 4,528,239, 4,529,480, 5,275,700, 5,364,504, 5,527,428, 5,609,725, 5,679,222, 5,709,775, 5,795,440, 5,900,122, 5,906,710, 5,935,381, and 5,938,893. 
     Web Product 
     In some embodiments, a web material can be produced from a papermaking machine or the like. Nonlimiting exemplary web materials may be selected from the group consisting of: polymeric films, fabric, cloth, metal films, nonwovens, airlaid products, the like, and combinations thereof. 
     As described supra, in some embodiments, the web material may be made of polymeric materials. For example, flexible films, particularly those made of comparatively polymeric materials, have been widely employed for the protection and preservation and containment of various items and materials. Additionally, web materials having modified properties to provide a desired resistive force to an applied elongation force on the web are generally known. Such web materials are described in U.S. Pat. Nos. 5,518,801; 6,394,651; and 6,394,652. 
     In some other embodiments, the web material may be a laminate web. Laminate webs formed by the joining of discrete webs in a layered relationship are well known in the art. For example, often laminate nonwoven webs are utilized in disposable absorbent articles such as diapers and adult incontinence products. Such laminated webs can be used as a topsheet, backsheet, or side panels. One example of a laminate web is a film/nonwoven laminate useful for a stretch side panel of a disposable diaper. Nonwoven/nonwoven laminates are also utilized to provide additional bulk or softness to a web component. Likewise, film/film laminate webs can provide benefits by combining the characteristics of various films in a layered relationship. Laminate webs can also be called composite webs. 
     Less common examples of laminate webs include laminates of dissimilar materials. The materials may be dissimilar in mechanical tensile properties, thermal properties, or visual/tactile properties. For example, a nonwoven web may be joined to a relatively stiff fabric to provide for a soft surface feel to the fabric. The dissimilar materials may be joined by melt bonding, adhesive bonding, ultrasonic bonding, and the like. Bonding methods are often determined by the materials themselves, but often require adhesive bonding. For example, a laminate or composite of materials having widely differing melt properties may require an adhesive layer between laminate layers. Even materials having similar melt properties, such as nonwoven and thermoplastic film materials are often joined by adhesive for adequate bonding to prevent unwanted delamination. Such processing methods can be expensive due to the addition of adhesive, and the resulting laminate is often relatively stiff, depending on the level of adhesive added. 
     Apertured laminate webs can be made by methods in the art. One beneficial method of aperturing a nonwoven web, for example, is disclosed in commonly-assigned U.S. Pat. No. 5,916,661. 
     Paper Making Apparatus 
       FIG. 1  shows a schematic view of an exemplary paper making apparatus  21  in which the web-stabilization device of the present invention may be used. The papermaking machine  21  comprises a transfer zone  20  and a forming section  41 , an intermediate carrier section  42 , a pre-dryer/imprinting section  43 , a drying/creping section  44 , a calendar assembly  45 , and reel  46 . 
     The forming section  41  of the paper machine  21  comprises a headbox  50 ; a loop of fine mesh backing wire or fabric  51  which is looped about a vacuum breast roll  52 , over vacuum box  70 , about rolls  55  through  59 , and under showers  60 . Intermediate rolls  56  and  57 , backing wire/fabric  51  is deflected from a straight run by a separation roll  62 . Biasing means not shown are provided for moving roll  58  as indicated by the adjacent arrow to maintain fabric/wire  51  in a slack obviating tensioned state. 
     The intermediate carrier section  42  comprises a loop of forming and carrier fabric  26  which is looped about rolls  62  through  69  and about a portion of roll  56 . The forming and carrier fabric  26  also passes over vacuum boxes  70  and  53 , and transfer head  25 ; and under showers  71 . Biasing means are also provided to move roll  65  to obviate slack in fabric  26 . Juxtaposed portions of fabrics  51  and  26  extend about an arcuate portion of roll  56 , across vacuum box  70 , and separate after passing over an arcuate portion of separation roll  62 . In one embodiment, forming and carrier fabric  26  is identical to backing wire/fabric  51  except for the lengths. 
     The pre-dryer/imprinting section  43  of paper machine  21  comprises a loop of transfer fabric or imprinting fabric  28 . Transfer/imprinting fabric  28  is looped about rolls  77  through  86 ; passes across transfer head  25  and vacuum box  29 ; through a blow-through pre-dryer  88 ; and under showers  89 . Additionally, not shown is a biasing mechanism for biasing roll  79  towards the adjacent Yankee dryer  91  with a predetermined force per lineal inch to effect imprinting the knuckle pattern of fabric  28  in web  30  in the manner of, and for the purpose disclosed in, U.S. Pat. No. 3,301,746. Not shown is a biasing mechanism for moving roll  85  as indicated by the adjacent arrow to obviate slack in fabric  28 . 
     The drying/creping section  44  of paper machine  21  comprises Yankee dryer  91 , adhesive applicator  92 , creping blade  93 , and reel roll  94 . A web stabilizing device  100  according to the present invention may be installed between the creping blade  93  and the calendar assembly  45 . In some embodiments, the web stabilizing device  100  may be juxtaposed adjacent to the web  30 . In other embodiments, the web stabilizing device  100  may be juxtaposed adjacent to, and above (in the Z-direction), the web  30 . One of skill in the art may appreciate that a web stabilization device  100  does not necessarily have to be positioned between the creping blade  93  and the calendar assembly, but may be positioned anywhere in the papermaking apparatus where the user may require web stabilization. 
     V 1  is the velocity of the papermaking fabrics  51  and  26 . V 2  is the velocity about the transfer/printing rolls  77  through  86 . V 3  is the velocity of the calendar assembly  45 . V 4  is the reel velocity of the reel roll  94 . 
     Web Stabilization Device 
     The web stabilization device of the present invention can be made from any material or materials suitable for the particular purpose of the device, whether the material(s) is now known or later becomes known. For example, a web stabilization device may be made from a material selected from the group consisting of: stainless steel, carbon steel, alloy metals, aluminum, aluminum alloys, composite materials, fiberglass, epoxy based, multi-bonded materials, carbon fibers, woven and/or bonded materials, cured and/or baked materials, plastics, and combinations thereof. 
       FIG. 2  shows a perspective view of an exemplary embodiment of the present invention web-stabilization device. In the exemplary embodiment, the web-stabilization device  100  comprises a first surface  110  and a second surface  120 . In the exemplary embodiment, the first surface and second surface are juxtaposed such that the first surface  110  and second surface  120  are in a substantially axially parallel configuration. One of skill in the art may appreciate that a web-stabilization device  100  may be provided with any dimensions that are suitable for the specific application or apparatus with which the web stabilization device is to be used. In particular, because it is thought that only a surface having a plurality of surface features is required to provide suitable stabilization to a moving web, the web stabilization device may comprise a single panel wherein the first surface  110  and second surface  120  are the opposite faces of the same panel. The web stabilization device  100  may have any thickness T that may be practical or suitable for the intended purpose. In one embodiment, the thickness is from about ½″ to about 15″. In one embodiment, the web stabilization device  100  has a length, L, of from about 2″ to about 600″. In another embodiment, the length is from about 24″ to about 120″. In one embodiment, the web stabilization device has a width of from about 4″ to about 250″ inches. 
     In the exemplary embodiment shown in  FIG. 2 , the web stabilization device  100  comprises a plurality of support frame elements  112  on which sheets of solid material (for example, a textured metal, fiberglass, carbon fiber, and the like) may be mounted using any means known in the art. The web stabilization device  100  further comprises a plurality of surface features  127 . In one embodiment, the surface features  127  are on the outward-facing sides of the first surface  110  and/or the second surface  120 . In another embodiment, the surface features  127  are on the face of the web stabilization element  100  that is adjacent to the moving paper web during operation in a paper making apparatus. In some embodiments, the first surface  110  of the web stabilization device is not flat, but may have a slight curvature. In one embodiment, the first surface  110  is concave. In another embodiment, the first surface  110  is convex. In one embodiment, the maximum offset distance, D offset , for a curved surface is from about 1/16″ to about 4″. The maximum offset distance is the furthest distance (positive or negative z-direction) out of the MD-CD plane which the first surface may extend. 
     Web Stabilization Device: Textured Surface 
     It is thought that drag may be caused by actual contact with the surface and from other forces. Without wishing to be limited by theory, it is thought that flow between a moving web and a web stabilization device may be described as Couette flow. One of skill in the art may appreciate that Couette flow may be described as having a linear velocity profile for a relatively small space S between two objects (i.e., moving web  30  and web stabilization device  100  comprising a first surface  110 ) as is shown in  FIG. 3 . In some embodiments, the average space, or gap height, h, between the moving web  30  and the web stabilization device  100  is from about 0.001″ to about 0.04″. 
     Surprisingly, it was discovered that when a web stabilization device  100  comprising a plurality of surface features  127  is used instead of a web stabilization device having no surface features (i.e., is smooth), there was a reduction in drag on the moving web  30 . Without wishing to be limited by theory, it is thought that a web stabilization device  100  with surface features provides a controlled space between the device  100  and a moving web  30  which controls the aerodynamic elements of drag force. Those of skill in the art may appreciate that depending on gap height a boundary layer may form and form a free stream flow between the web stabilization device  100  and the moving web  30  at relatively large gaps. 
     It is thought that when the surface of a web stabilization device  100  is used to support an adjacent moving web  30  there is always a certain amount of spacing or some amount of fluid (i.e., air) that is between the web stabilization device  100  and the moving web  30 , despite a high level of smoothness and planarity of the web stabilization device  100 . Further, one of skill in the art may appreciate that a combination of the mechanical frictional force and the direct aerodynamic shear on the web surface create the total drag force on the web. 
     Further, one of skill in the art may appreciate that drag force increases with velocity. Without wishing to be limited by theory, it is thought that the relationship between the suction force (of which mechanical drag force is a function) exerted on a moving web and an adjacent object, such as a web-stabilization device, is directly proportional to the velocity of the moving web.
 
F suction ∝½AρV b  
 
Where F suction  is the suction force, A is the area of the web, V is the web velocity, and ρ is the density of the fluid medium, and b=2 for second order velocity.
 
The aerodynamic drag force also is proportional to velocity for Couette flow
 
 D=Aμu/h.  
 
Where D is the aerodynamic drag force, A is the area of the web, μ is the dynamic viscosity of air, u is the velocity of the web and h is the gap height.
 
     The use and design of non-smooth surfaces to reduce the drag forces exerted on a moving object in a fluid medium is known in the art. Exemplary non-smooth surfaces are described in U.S. Pat. Nos. 5,114,099 and 4,434,957. It was surprisingly discovered that by providing surface features to the face of the web stabilization device in the papermaking section of a paper machine, the amount of drag exerted onto the moving web is dramatically reduced, in both the converting apparatus and in the relatively high velocities of a papermaking apparatus. 
       FIG. 4A  shows a perspective view of an exemplary web stabilization device  100  comprising a plurality of surface features  127 . In some embodiments, the surface features  127  may be selected from the group consisting of: round, oblong, curved, circular, the like, and combinations thereof. In another embodiment, the surface features  127  may be recessed into (i.e., have a local minima in the −z direction) the surface of the web stabilization device  100 . In another embodiment, the surface features  127  may extend from (i.e., have a local maxima in the +z direction) the surface of the web stabilization device  100 . Such extension or recession may be referred to as the feature depth (D feature ). It is surprisingly discovered that feature depth (extension or recession) has a significant impact on the forces exerted on the web. In one embodiment, the feature depth is greater than about 0.020″. In another embodiment, the feature depth is from about 0.020″ to about 0.040″. In another embodiment, the feature depth is from about 0.020″ to about 0.032″. 
     One of skill in the art will appreciate that the surface features  127  of the present invention may be any shape that is suitable for the intended purpose. In one embodiment, the shape of the surface features  127  may be selected from the group consisting of: circles, ovals, diamonds, honeycomb, curved, square, rectangular, triangular, and combinations thereof. 
     The surface features may be any size that is suitable for the intended application. In the exemplary embodiment, a surface feature  127  may have a major axis, A maj , of from about 1/16″ to about 1″. In another embodiment, the major axis is from about 0.18″ to about 0.72″. In some embodiments, a surface feature  127  may have a minor axis, A min , of from about 1/16″ to about 1″. In another embodiment, the minor axis is from about 0.18″ to about 0.72″. A surface feature may be incorporated onto either the first surface  110  or the second surface  120  of the web stabilization device. 
     In some embodiments, the surface features  127  may be arranged in repeating, or non-repeating, patterns, such that the pattern may be reduced to a repeating unit. In one embodiment, the repeating unit may be described by a grid formation wherein a first surface feature  127   a  is offset from an adjacent surface feature  127   c  in the machine direction (i.e., has an MD offset ) of from about 0.5 A maj  to about 2 A maj . In another embodiment, the MD offset  is from about 0.2″ to about 0.9″. In some other embodiments, the surface features  127  may be arranged wherein a first surface feature  127   a  is offset from an adjacent surface feature  127   b  in the cross-machine direction (i.e., has a CD offset ) of from about 0.5 A min  to about 2 A min . In one embodiment, the CD offset  is from about 0.18″ to about 0.72″. The surface features  127  may be arranged in a repeating, or a non-repeating, pattern and may occupy the entire first surface  110 , or only a portion of the entire first surface  110 . 
     Additional surface features  127  may be positioned in any area between and/or around the surface features arranged described supra. For example, additional surface features  127   d  may be spaced in the halfway between the MD offset  and CD offset  of the surface features arranged in a grid  127   a,b,c.    
       FIG. 4B  is a cross-sectional view of the web stabilization device  100  of  FIG. 3A  taken along line  4 B- 4 B. As described supra, the surface features  127  may extend from, or be recessed into, the surface of the web stabilization device  100 . In the exemplary embodiment shown in  FIGS. 3A-B , the surface features  127  are recessed into the surface of the web stabilization device  100 . In some embodiments, a surface feature  127  may have a feature depth (i.e., D feature , or the longest distance in either the +z-direction or −z-direction from the surface feature  127  to the MD-CD plane of the web-stabilization device) of from about 1/1000″ to about ⅕″. Surface features  127  may have the same, or different, feature depths/feature heights. 
     Web Stabilization Device: Positioning Considerations 
     In addition to velocity, the suction and the aerodynamic drag forces exerted on a moving web and an adjacent object may also be affected by the proximity of the adjacent object (i.e., web stabilization device) to the moving web. Without wishing to be limited by theory, it is thought that the suction and aerodynamic drag forces exerted are inversely proportional to the gap height between the adjacent object and the moving web:
 
F areo ∝1/h
 
Where F aero  represents the suction and aerodynamic drag forces and h is the gap height. Surprisingly, it was discovered that by providing surface features on the exterior of a web-stabilization device, the F aero  that is exerted onto the moving web is relatively lower when compared to the F aero  exerted by a similar web stabilization device having no surface features.
 
Present Invention Web Stabilization Device versus Prior Art Web Stabilization Device
 
     As discussed supra, the web stabilization devices comprising surface features of the present invention provide a relatively low amount of drag on an adjacent moving web when compared to a web stabilization device having no surface features. 
       FIGS. 5A and 5B  show a graphical representation of web velocity versus wall shear and total drag/area, respectively, for one prior art (i.e., having no surface features) web stabilization device, a friction-reducing foil (Perini), and two exemplary web stabilization devices having surface features. The drag and shear stress were obtained by a computer model of the exemplary web stabilization devices and a moving web. The method for calculating shear and total drag/area are described in the Drag Modeling Section infra. 
     The web stabilization devices modeled in  FIG. 5  may be described as follows: (1) a web stabilization device having no surface features (“flat plate”); (2) a web stabilization device having surface features which protrude from the MD-CD plane with a D feature  of about 0.0145″, an A major  of about 0.361″, an A minor  of about 0.190″, an MD offset  of about 0.450″, a CD offset  of about 0.360″, and with an additional surface feature in the center of the features of a repeating grid (“6-OM”); (3) a commercially available (Fabio Perini S.p.A., Italy) web stabilization device having surface features which protrude from the MD-CD plane with a D feature  of about 0.01968″, an A major  of about 0.393″, an A minor  of about 0.1181″, an MD offset  of about 0.4724″, a CD offset  of about 0.1752″, and with an additional surface feature in the center of the features of a repeating grid (“Perini”); (4) and an exemplary present invention web stabilization device having surface features which protrude from the MD-CD plane with a D feature  of about 0.032″, an A major  of about 0.361″, an A minor  of about 0.180″, an MD offset  of about 0.450″ and a CD offset  of about 0.360″, and with an additional surface feature in the center of the features of a repeating grid (“6-WL”). One of skill in the art will appreciate that depth may me calculated using a digital caliper, such as those made by Mitutoyo USA (Aurora, Ill.) 
     The resultant wall shear is described in terms of lb/in 2  for velocities of from about 2000 FPM to about 6000 FPM. For the purposes of simulation, the average gap width above the highest point on the web stabilization device is assumed to be 0.001″. It is also assumed that there is no direct mechanical friction when aerodynamic drag and suction pressure are computed by the CFD model. However, a mechanical drag force/area is estimated from the computed suction pressure in the web/foil gap and an assumed coefficient of friction. Further, the surface of the web stabilization device is assumed to comprise a repeating pattern of a grid as described supra, and the smallest repeat unit  200  comprising surface features  127  is illustrated in  FIG. 6 . A constant level of tension in the moving paper web is assumed and the pressure at the MD boundaries (i.e., front and back of the web stabilization device) is assumed to be zero. Symmetry in the CD is also assumed. A coefficient of friction of 0.3 is assumed. The conditions described supra are described as “test system.” The test system results are described as an average/web surface area. 
     The ideal drag and shear are calculated by assuming a situation in which a sheet may be placed at a fixed distance away from the web stabilization device, but without the actual surface features being there. This is used to calculate the lower limit of the wall shear stress. 
     In one embodiment, the web stabilization device of the present invention provides a test system wall shear stress/area (lb/in 2 ) of less than about the test system wall shear stress calculated by the following relationship (Eq. 1) at velocities of from about 2000 FPM to about 6000 FPM.
 
Wall Shear Stress=(5×10 −7 )(Web velocity)−5×10 −4   Eq. 1
 
In another embodiment, the test system wall shear stress is from about the test system wall shear stress calculated by Eq. 1 to the test system wall shear stress calculated by Eq. 2 at velocities of from about 2000 FPM to about 6000 FPM.
 
Wall Shear Stress=(3×10 −7 )(Web velocity)−3×10 −4   Eq. 2
 
     In one embodiment, the web stabilization device of the present invention provides a test system total drag/area (lb/in 2 ) of less than about the test system total drag/area calculated by the following relationship (Eq. 3) at velocities of from about 2000 FPM to about 6000 FPM.
 
Total Drag=(7.075×10 −7 )(Web velocity)−7.45×10 −4   Eq. 3
 
In another embodiment, the test system total drag/area (lb/in 2 ) is from about the web total drag/area calculated by Eq. 3 to the test system total drag/area calculated by Eq. 4 at velocities of from about 2000 FPM to about 6000 FPM.
 
Total Drag=(4.9975×10 −8 )(Web velocity)  Eq. 4
 
Test Methods
 
     The following describe the test methods utilized herein to determine the values consistent with those presented herein. 
     Drag Modeling Section 
     One of skill in the art may appreciate that the mechanism of interaction between the web stabilization device and a moving web having a surface structure is complex. Since there is a strong influence by the aerodynamics of this interaction, a computational fluid dynamics (CFD) analysis of the geometries of interest is performed using the Fluent™ CFD software package (Fluent, Inc., Lebanon, N.H.). The following assumptions are made in the analysis:
     1. The moving web is perfectly flat and non-porous. Further, it is assumed to be rigid and does not deflect into the recesses of the dimples.   2. There is no mechanical contact and there is about a 0.001″ gap between the web stabilization device and the moving web. In a scenario where the surface features protrude from the MD-CD plane of the web stabilization device, the 0.001″ gap is measured from the highest points of the surface features.   3. For comparison purposes, a small section of the plates is modeled and inlet and exit flows are assumed to have zero pressure. It requires an extremely large model to consider the actual plate lengths to be included in the model together with the very small dimple geometries that will be many.   4. Symmetric boundary conditions for repeat patterns in the CD.   5. The mesh density is such that the minimum mesh size is about 0.001″ for the patterned geometries. For the base flat plate model, the minimum mesh size is assumed to be 0.0001″.   6. Moving web has a constant tension.   7. Coefficient of friction is 0.3.   8. Mechanical drag is predicted from the coefficient of friction and suction pressure.   

     The geometry of the web stabilization foil is first generated in a CAD program and output as a *.sat file. The *.sat file is imported into GAMBIT (Fluent, Inc., Lebanon, N.H.) to generate a 3-D mesh and apply boundary conditions. 
     The 3-D mesh file is then exported to the Fluent CFD software. An isothermal flow is assumed. The Fluent CFD software is used to iteratively solve the Navier Stokes equations until the solution converges. Using the above parameters, one of skill in the art may use the Fluent CFD software package to solve the Navier-Srokes Equations to provide the wall shear and total drag results. 
     All measurements referred to herein are made at 25° C. unless otherwise specified. Herein, “comprising” means the term “comprising” and can include “consisting of” and “consisting essentially of.” 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”. 
     All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this written document conflicts with any meaning or definition of the term in a document incorporated by reference, the meaning or definition assigned to the term in this written document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.