Patent Application
20070040301
The present invention relates to the field of webs, web processing methods, and web processing apparatus. More particularly, the present invention provides apparatus and methods for stretching one or more zones of a web in the cross-web direction and webs so stretched.
It is desirable in many instances to stretch a web in the cross-web direction (it is noted that cross direction, cross-web direction and cross machine direction are used interchangeably) during processing. For example, webs including layers of inelastic materials, e.g., nonwoven webs, laminated or otherwise attached to elastic layers while the elastic is not extended typically require stretching to impart elasticity to the web. The web is stretched so that the inelastic layers, or bonds within the inelastic layer or layers, are broken or otherwise disrupted allowing the elastic to freely stretch which leaves the stretched web laminate elastic. Such stretching to impart elasticity to a web is commonly referred to as “activation” of the web (with the elasticity of the web being “activated” by the stretching). Activation can be done in the machine direction of the web or the cross direction of the web or both. Cross direction stretching or activation can be performed by a variety of known methods including, for example, tentering and ring rolling.
Tentering typically involves grasping the edges of a web and stretching the web in the cross-web direction while advancing the web in the downweb direction (i.e., along the length of the web). Although tentering does provide the ability to vary the amount of strain induced in the web, it also suffers from a number of disadvantages. For example, the edges of the web must often be discarded after tentering due to damage or inconsistent strain in the web at the edges. Another potential disadvantage is that it may be difficult or impossible to induce strain into selected portions or zones of a web using tentering. Further, tentering equipment can be both costly, complex, and may require significant amounts of floor space to operate as the web expands in the cross direction during the process.
Ring rolling is an alternative to tentering for stretching a web in the cross direction. Various ring rolling apparatus are described in, e.g., U.S. Pat. No. 4,223,059 (Schwarz); U.S. Pat. No. 4,968,313 (Sabee); U.S. Pat. No. 5,143,679 (Weber et al.); U.S. Pat. No. 5,156,793 (Buell et al.); and U.S. Pat. No. 5,167,897 (Weber). Ring rolling or incremental stretching refers generally to placing the web between rolls having interengaging teeth. The engaging teeth stretch the web based generally on the size, number and pitch of the teeth. Ring rolling can be used to stretch selected zones in a web and stretch only in the cross direction. However ring rolling teeth grip the web and this contact of the web by the ring rolling apparatus can tear the web and undesirably affect the web's appearance. The amount of strain that can be induced in a web using ring rolling is limited by the specific ring rolls used. Adjustment or change in the degree of stretch requires new ring rolls to be machined. This is of course costly and inflexible.
The present invention provides apparatus and methods for stretching one or more zones of a web and webs including one or more stretched zones. Each of the stretched zones in the web is stretched in the cross-web direction, i.e., the direction transverse to the downweb direction. The stretching can be performed continuously on the web as the web is advancing through the apparatus in the down-web direction.
The method for stretching an extensible web in the cross direction generally is practiced on a substantially continuous cross-directional extensible web. The web is traveling in a first downweb direction at a first speed. The extensible web has a width and substantially continuous length in the first downweb direction. The crossweb stretching occurs in an orientation zone established between at least two moving nip points. The nip points are in a plane of the web with a leading nip downweb of a trailing nip with the at least two nips offset in the cross direction. The leading nip moves at a faster speed than the trailing nip, where the degree of crossweb orientation in the orientation zone is proportional at least to a ratio of the leading nip speed to the trailing nip speed.
a is a top view of the wheels used in the apparatus of
As shown in
Two orientation zones 26, 27 are shown diagrammatically in
There can be one or more orientation zones formed relative to the web in the crossweb direction, each formed by similar pairs of nips. Each of these orientation zones could be the same or different. Different orientation zones could be created by different speeds of the nips, different spacings of nips or the like. Multiple orientation zones could be arranged using a continuous series of nips forming a large composite orientation zone. Alternatively the nips forming the orientation zones could be spaced apart, leaving discrete areas of the web unoriented between discrete orientation zones. Orientation zones could also be arranged downweb of each other in either an overlapping or nonoverlapping relationship. By overlapping it is meant the two orientation zones activate to some extent the same crossweb zone or region of the web sequentially. Overlapping orientation zones would allow additional orientation to be imparted to specific regions, for example at steadily increasing orientation levels to provide for a gentler incremental stretching of a specific zone or region in the web.
In a first embodiment orientation unit, shown in
In operation the web behind the faster leading nip is advanced unrestrained in the downweb direction relative to the slower trailing nips. The offset or spacing of the trailing nip points in the cross direction allows the opposing portion of the web, adjacent the slower upweb nip, and directly upweb of the first nip, to travel unrestrained toward the leading nip. Namely the web directly upweb of the faster leading nip 28 is allowed to advance unrestrained toward that nip 28 so that there is little or no machine direction (MD) orientation of the web. However, the web in the cross direction is subjected to an orientation force. This force is created by the speed differential between the two nip points 29 and 28 or 30 and 28, respectively, which is translated into a cross directional stretching force. This occurs as the web between the two nip points (29 and 28 or 30 and 28, respectively) is in essence rotated between the two nips creating a crossweb orientation force or draw. The rotated web is then drawn toward the faster nip creating the crossweb stretching as shown in
In the embodiment of
The operation of the orientation unit of
The degree of crossweb orientation is generally proportional to a ratio of the leading nip speed to the trailing nip speed and also the length of the orientation zone. The ratio of leading nip speed to a trailing nip speed is generally at least 1.1 or at least 1.2. This ensures at least some orientation between the two nips. Generally at least 10 percent orientation is desired, or at least 50 percent. The ratio of the leading nip speed to the trailing nip speed is generally less than 10 to 1 or less than 5 to 1. With large orientation zones, the ratio of the leading to trailing nip speed can be slower, lowering the chance of distortion while obtaining potentially higher levels of orientation. If the speed ratio is too high the web is subject to distortion and tearing.
The leading nip and trailing nip need not be separated in the downweb direction, but could be separated by at least 0.1 cm or 1 cm or 2 cm and separated in the crossweb direction by at least 0.5 cm or 1 cm or 2 cm, or are separated in the downweb direction by 0.1 to 20 cm and in the crossweb direction by 0.5 to 20 cm or 0.5 to 10 cm. The crossweb separation 16 or 17 spreads out the orientation over a larger area. The crossweb separation of the nips allows the orientation to occur preferentially in the cross direction. With greater crossweb separation, less residual downweb or machine direction orientation is likely to occur. Large crossweb separation of an individual orientation zone spreads the orientation over a larger portion of the web. Orientation over extended cross directional regions of the web can also be done by using multiple orientation zones placed side by side, such as shown partially in
Orientation of inelastic webs can be facilitated by heating the web within the orientation zone. This could be done by hot air, heated rolls, radiation heating or the like.
As discussed above there can be two or more orientation zones provided in the cross direction of the web and two or more orientation zones provided in the downweb direction where the two or more orientation zones provided in the downweb direction can overlap at least in part. Generally the two or more orientation zones are in the same plane, but if desired they could be in different planes. For example, the web could be driven in the form of a zigzag arrangement to save on space with alternating orientation zones in the downweb direction, forming legs of the zigs and the zags. However, the invention method does not rely on moving one portion of the web out of plane from another portion of the web to create orientation or stretch. Also the invention stretching occurs in the absence of physical contact within the orientation zone of the web. That lack of physical contact may prevent distortion or marking of the web during stretching. Another potential advantage of the apparatus and methods of the present invention is that strain induced on web layers in the oriented zones can be introduced gradually by use of multiple orientation zones arranged downweb of one another whereas rapid stretching of a zone could result in tearing or rupture of the web or web layers.
Another advantage of the apparatus and methods of the present invention is that the amount of orientation may be easily adjusted, even while the web is being processed, without requiring equipment changes. This ability to adjust orientation on the fly or dynamically may be especially useful if, e.g., coupled with a feedback control system that monitors the orientation or other characteristics to maintain desired properties in the stretched webs, related to a set of predetermined desired end properties and/or changes in the input or output web. It may also be useful in starting up the process because the web may be threaded through the apparatus with no stretch being induced, followed by gradually increasing the stretch amount as the web moves through the device.
The diversion device could be any shape or form and could be, for example, a ramp having a gradual increase to an apex. This ramp could be a solid stationary tool or be formed by one or more discrete elements, wheels, rollers or the like. The diversion device could also be provided as one or more adjacent units, which could be integral or mechanically isolated units.
A wheel type diversion device, as is the wheel 21, can rotate in a preferred embodiment, but could also be stationary if it is a separate unit other than nip wheel 21. The wheel could have flat faces, or could have a profile in the X direction. The edge of the wheel in contact with the web preferably is rounded to avoid sharp edges tearing the web. With a wheel type diversion device, the web material will wrap around the wheel over some area. This wrap is determined by the direction of the web being fed onto the wheel, which is determined by the position of the rolls 20 and 22 or other device from which the web is fed into the diversion device as well as the leading nip 28 into which the web is fed. This wrap could be from 5 to 300 degrees or 10 to 90 degrees. The height (H) of the apex 40 of the diversion device over the web path could be any value as long as it allows for diversion of the web but generally would be from 1 to 100 cm, or from 5 to 20 cm, which determines the degree of diversion.
The extensible web is in a preferred embodiment a laminate of an elastically extensible web and one or more relatively inelastic webs. In this case the orientation apparatus and methods of the present invention can be used to “activate” zones in a web such that the activated zones exhibit preferential cross direction elasticity after activation. Activation is stretching a web such that inelastic layers, or bonds within the inelastic layer or layers, are broken or otherwise disrupted, thereby leaving the stretched portion of the web elastic due to, e.g., the elastic materials or layers located within the laminate, which recover after the activation stretching. The inelastic layer or layers which are now broken or otherwise disrupted do not provide significant resistance to subsequent elastic extensions of the web. As used herein, an inelastic zone in a web is “activated” if it has been stretched such that, after stretching, the stretched zone of the web exhibits at least some elastic behavior. By elastic behavior, it is meant that, after stretching of an activated zone, the activated zone returns at least in part to its relaxed dimension in the absence of any constraining forces.
An orientation device used to stretch portions of a web in accordance with the invention can be used in-line with other web processing equipment or can easily be placed in an existing multifunctional line such as a diaper line. For example, the web processing apparatus may be located downstream of an apparatus that may, for example, process a pre-existing web by, e.g., heating, cooling, calendering, applying materials to an existing web (e.g., laminating a material by heat, ultrasonics, hot melt or pressure sensitive adhesives), etc. In some instances, the apparatus may manufacture a web (by, e.g., extrusion, spun-bonding, carding, melt blowing, weaving, laminating a nonwoven or other inelastic web to an elastic web, etc.) that is then directed as is or in a laminated form into a web processing apparatus according to the present invention.
The web processing apparatus according to the present invention may also be located upstream of another processing apparatus that acts on the web after portions of the web have been stretched according to the principles of the present invention. For example, apparatus for slitting, perforating, and/or aperturing the web at one or more locations or apparatus for laminating materials to the web (e.g., such as attaching fastener materials such as hooks), die cutting, etc. An orientation device, in accordance with the invention could easily be placed in an assembly line, such as a diaper assembly line, to specifically orient or activate certain predetermined cross direction zones.
As briefly addressed above, the present invention can be used to process any suitable extensible web, including homogenous webs, monolayer webs, multilayer webs, composite webs. This would include assembled articles which had specific zones or regions that were extensible.
The preceding specific embodiments are illustrative of the practice of the invention. This invention may be suitably practiced in the absence of any element or item not specifically described in this document. The complete disclosures of all patents, patent applications, and publications are incorporated into this document by reference as if individually incorporated in total.
The following examples are provided to enhance understanding of the present invention. The examples are not intended to limit the scope of the invention.
Hysteresis:
The hysteresis properties of the elastic/nonwoven laminates were measured. A 50 mm wide by 100 mm long piece of laminate was mounted in a tensile testing machine (INSTRON Model 55R1122, available from the Instron Corp.) with the upper and lower jaws 40 mm apart. Line contact jaws were used to minimize slip and breakage in the jaws. The jaws were then separated at a rate of 51 cm/minute until a load of 15 Newtons was recorded. The jaws were then held stationary for 1 second after which they returned to the zero elongation position. The jaws were again held stationary for 1 second and then separated at the same rate until a load of 16 Newtons was recorded. The cycle was repeated twice more for a total of 3 cycles. Two (2) replicates were tested with the results shown in
An elastic/nonwoven laminate web was prepared using the method disclosed in PCT publication WO 2004/082918.
A 40 mm diameter twin screw extruder fitted with a gear pump was used to deliver 75 grams/meter2 of a molten elastomeric polymer blend consisting of a styrene-ethylenebutylene-styrene block copolymer (70%, KRATON G-1657, Kraton Polymers Inc., Houston, Tex.) and ultra low density polyethylene (30%, Engage 8452, Exxon Polymers Inc., Houston, Tex.) at a melt temperature of approximately 246° C. to a die. The die was positioned such that a film of molten polymer was extruded vertically downward into the interface region of a heated doctor blade and a cooled forming roll. The doctor blade was maintained at a temperature of 246° C. and the forming roll was maintained at a temperature of 30° C. by circulating chilled water through the interior of the roll. The doctor blade was held against the forming roll with a pressure of 450 pounds per lineal inch (788 Newtons/lineal cm).
Approximately 15 cm in width of the exterior surface of the forming roll was chemically etched so as to have a series of elliptically shaped posts arranged around the periphery of the roll. The posts were 1.6 mm wide and spaced 3.2 mm apart circumferentially (downweb) around the roll and 5 mm apart axially (crossweb) along the roll. The height of the posts was 63 microns. The tops (or lands) of the posts were the same height as the non-machined outermost areas of the roll such that when the doctor blade wiped extrudate from the roll, no extrudate was left on the lands of the posts resulting in an apertured polymeric film 15 cm in width. The extrudate was transferred from the forming roll to a lightly bonded high extension carded (HEC) nonwoven polypropylene substrate (Product FPN 332D) with a basis weight of 27 grams/meter2 and a width of 22 cm from BBA Nonwovens (Simpsonville, S.C.) at a nip formed with a conformable backup roll (a steel core with a rubber cover having a durometer of 75 Shore A). The core of the backup roll was chilled by circulating water at a temperature of 5° C. The pressure exerted on the nip between the forming roll and the backup roll was 14 pounds per lineal inch (25 Newtons/lineal cm). To enhance the bond between the extrudate and the nonwoven, the nonwoven was sprayed in a swirl pattern with a hot melt adhesive (4.5 grams/meter2, H9388, Bostik, Wauwatosa, Wis.) across the full width (22 cm) of the nonwoven. The 15 cm of extrudate was centered onto the 22 cm wide nonwoven, resulting in approximately 6 cm of outermost edge zones without elastomer. A second layer (22 cm width) of the same type of nonwoven, also sprayed with adhesive, was then laminated to the elastomer side of the previously created laminate using a rubber roll/steel roll nip, resulting in a 3 layer laminate in the middle 15 cm of the web and a 2 layer laminate in the outermost 6 cm of the web.
The laminate was then stretched in the cross-direction using an apparatus similar to that shown in
An elastic/nonwoven laminate web was prepared using the method disclosed in PCT publication WO 2004/082918 as described in Example 1 above.
The laminate was then stretched in the cross-direction using an apparatus similar to that shown in
Sixty (60) centimeter long sheets of the elastic/nonwoven laminate described above were hand fed at 5 meters/min into the nip zones of the apparatus created by the belts and the drive roll 48. The second set of gears 46′, in cooperation with the corresponding set of belts, being driven at a faster speed than the underlying drive roll 48, advanced the laminate in the machine direction in a leading nip lane having the same width (5 mm) as the belt used to form the nip zone. This advancement of the web was possible due to the underlying wheels 50 being free to rotate at the same speed as the gears 46′ and corresponding belts. The trailing nip lanes of material adjacent to the leading nip lanes, created by the first set of gears 46 and the corresponding belts, remained at the same speed as the slower drive roll 48 because the gears and belts were free to rotate and thus driven by the underlying wheels 49 that were fixed to the same shaft as slower roll 48. The 50% overspeed of gears 46′ created the orientation zone due to a machine direction tension on the laminate in the leading nip lane which in cooperation with the trailing nip lane translated into a cross-direction force or shear resulting in stretching of the web in the cross direction in approximately 5 mm wide alternating bands across the laminate. After passing through the apparatus the oriented regions retracted back to approximately the original dimensions due to the laminate having been activated, and recovering elastically. The activated sheet of laminate was then passed through the apparatus a second and third time, with a 3 mm offset each time to further activate the laminate. The activated laminates were then tested for their hysteresis or elastic properties as shown in
As briefly addressed above, the present invention can be used to process any suitable extensible web, including homogenous webs, monolayer webs, multilayer webs and composite webs. This would include assembled articles, which had specific zones or regions that were extensible.
The preceding specific embodiments are illustrative of the practice of the invention. This invention may be suitably practiced in the absence of any element or item not specifically described in this document. The complete disclosures of all patents, patent applications, and publications are incorporated into this document by reference as if individually incorporated in total.
