The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, wherein like reference numerals denote like elements and parts, in which:
The instant invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The instant invention relates to multi-layer woven creping fabrics used in the production of soft, absorbent, disposable paper products, such as facial tissue, bath tissue and paper toweling. The instant fabrics may minimize or even prevent rewetting of a paper product or sheet/web produced thereon.
The present invention provides for a multi-layer woven creping fabric for use in the apparatus shown in
In addition, fabrics constructed according to the instant invention improve performance on the papermaking machine because sheet holes are minimized or even prevented, which in turn allows it to operate at higher draw levels or at lower basis weights without sheet holes. Also, higher recycled fiber contents can also be used and still obtain the desired paper web property.
In addition, fabrics constructed in accordance with the instant invention will result in deeper pocket resulting in a paper web with higher bulk absorbency.
As used herein, lobed or grooved weft yarns are terms used to describe the yarns included in certain embodiments of the instant invention. As depicted in
Preferred embodiments of the invention will now be described in the context of full width, full length fabric structures for use as a creping fabric in the transfer/drying section of a papermaking machine.
In developing creping fabric options for a papermaking process used to make absorbent paper products such as those previously described, a unique and unexpected result was obtained. A relevant process is disclosed in PCT Publication No. WO 2004/033793 and U.S. Patent Application Publication No. 2005/0241786, the entire contents of which are incorporated herein by reference. As depicted in
The papermaking machine 10 has a conventional twin wire forming section 12, a fabric run 14, a shoe press section 16, a creping fabric 18 and a Yankee dryer 20. Forming section 12 includes a pair of forming fabrics 22, 24 supported by a plurality of rolls 26, 28, 30, 32, 34, 36 and a forming roll 38. A headbox 40 provides papermaking furnish to a nip 42 between forming roll 38 and roll 26 and the fabrics. The furnish forms a web 44 which is dewatered on the fabrics with the assistance of a vacuum, for example, by way of vacuum box 46.
The web 44 is advanced to a papermaking press fabric 48, which is supported by a plurality of rolls 50, 52, 54, 55, the fabric being in contact with a shoe press roll 56. The web 44 is of a low consistency as it is transferred to the fabric 48. Transfer may be assisted by vacuum, for example, roll 50 may be a vacuum roll if so desired or a pickup or vacuum shoe as is known in the art. As the web reaches the shoe press roll 56, it may have a consistency of 10 to 25 percent, preferably 20 to 25 percent or so as it enters nip 58 between shoe press roll 56 and transfer roll 60. Transfer roll 60 may be a heated roll if so desired. Instead of a shoe press roll, roll 56 could be a conventional suction pressure roll. If a shoe press is employed it is desirable and preferred that roll 54 is a vacuum roll to more effectively remove water form the fabric prior to the fabric entering the shoe press nip since water from the furnish will be pressed into the fabric in the shoe press nip. In any case, using a vacuum roll 54 is typically desirable to ensure the web remains in contact with the fabric during the direction change as one of skill in the art will appreciate from the diagram.
Web 44 is wet-pressed on the fabric 48 in nip 58 with the assistance of pressure shoe 62. The web is thus compactively dewatered at nip 58 typically by increasing the consistency by 15 or more percentage solids at this stage of the process. The configuration shown at nip 58 is generally termed a shoe press. In connection with the present invention, cylinder 60 is operative as a transfer cylinder which operates to convey web 44 at high speed, typically 1000 fpm to 6000 fpm to the creping fabric 18.
Cylinder 60 has a smooth surface 64 which may be provided with an adhesive and/or release agents if needed. Web 44 is adhered to transfer surface 64 of cylinder 60 which is rotating at a high angular velocity as the web 44 continues to advance in the machine-direction indicated by arrows 66. On the cylinder 60, web 44 has a generally random apparent distribution of fiber. Direction 66 is referred to as the machine-direction (MD) of the web as well as that of papermaking machine 10, whereas the cross-machine-direction (CD) is the direction in the plane of the web perpendicular to the MD.
Web 44 enters nip 58 typically at consistencies of 10 to 25 percent or so and is dewatered and dried to consistencies of from about 25 to about 70 percent by the time it is transferred to creping fabric 18 as shown in the diagram.
Creping fabric 18 is supported on a plurality of rolls 68, 70, 72 and a press nip roll 74 and forms a fabric crepe nip 76 with transfer cylinder 60 as shown. The creping fabric 18 defines a creping nip over the distance in which creping fabric 18 is adapted to contact roll 60, that is, applies significant pressure to the web 44 against the transfer cylinder 60. To this end, backing (or creping) roll 70 may be provided with a soft deformable surface which will increase the length of the creping nip and increase the fabric creping angle between the fabric and the sheet and the point of contact. Alternatively, a shoe press roll could be used as roll 70 to increase effective contact with the web in high impact fabric creping nip 76 where web 44 is transferred to creping fabric 18 and advanced in the machine-direction. By using different equipment at the creping nip 76, it is possible to adjust the fabric creping angle or the takeaway angle from the creping nip. Thus, it is possible to influence the nature and amount of redistribution of fiber, delamination/debonding which may occur at fabric creping nip 76 by adjusting these nip parameters.
After fabric creping, the web 44 continues to advance along machine direction 66 where it is pressed onto Yankee cylinder 80 at transfer nip 82. Transfer at nip 82 occurs at a web consistency of generally from about 25 to about 70 percent. At these consistencies, it is difficult to adhere the web 44 to surface 84 of Yankee cylinder 80 firmly enough to thoroughly remove the web 44 from the fabric. This aspect of the process is important, particularly when it is desired to use a high velocity drying hood as well as maintain high impact creping conditions. In this connection, it is noted that conventional through-air-drying (TAD) processes do not employ high velocity hoods since sufficient adhesion to the Yankee cylinder 80 is not achieved. In accordance with the process, the use of particular adhesives cooperates with a moderately moist web (25 to 70 percent consistency) to adhere it to the Yankee cylinder 80 sufficiently to allow for high velocity operation of the system and high jet velocity impingement air drying.
The web 44 is dried on Yankee cylinder 80 which is a heated cylinder and by high jet velocity impingement air in Yankee hood 88. As the cylinder 80 rotates, web 44 is creped from the cylinder by creping doctor 89 and wound on a take-up roll 90.
One embodiment of a fabric design for use as creping fabric 18 in the above described process as depicted
Generally, a creping fabric has two sides: a sheet contacting side and a machine or roll side. The former is so-called because it is the side of the fabric that faces the newly formed paper web. The latter is so-called because it is the side of the fabric that passes over and is in contact with the rolls on the papermaking machine. In the process, the creping fabric is installed on the papermaking machine in the manner that is shown in
As previously discussed, in the manufacturing process, after the web 44 is transferred to the backing roll 60, the web 44 is picked up on the creping fabric 18 running at a much slower rate of speed. After pickup, there is a vacuum box (not shown) to pull the web deeper into the creping fabric 18 and to remove additional residual water from the paper web by pulling the residual water into (and through) the interior of the creping fabric 18. Conventional logic would indicate that any residual water left in the creping fabric 18 after showering would rewet the web 44 after pickup. In this embodiment, however, it does not appear to be the case with the creping fabric 18 installed on the papermaking machine such that the lobed or grooved weft yarns are disposed on the roll side. Moisture samples suggest that rewet is minimal if not totally eliminated. It has been observed that the fabric itself is running wet on the inside, which again is inconsistent with no rewetting. Additionally, drips falling on the inside of the fabric do not create sheet holes, which is usually the case with single layer fabric designs. Consequently, no rewetting of the web 44, is an unexpected result. Thus, this unexpected result may be a function of the woven multi-layer creping fabric 18 being installed on the papermaking machine with the lobed or grooved weft yarns facing the roll side.
It is believed that the multi-layer design having lobed or grooved weft yarns on the machine side may be the reason why residual fabric water reentering the web after it is removed is minimal or altogether prevented or eliminated. The reasons for this may be as follows. One reason may be due to the lobed or grooved yarns having an increased surface area over round yarns. Because of this increased surface area, surface tension between the fabric and the residual water may be greater, thus reducing the ability of the residual water to exit the fabric and reenter the paper web. Another reason may be because the use of the lobed or grooved weft yarns may change the relationship between the yarns at the crossover points. For example, if the yarns are both circular, the distance between the yarns at the crossovers continues to get smaller and smaller (approaching microns) and this small distance may create capillary forces that hold the water in the fabric. Thus, using lobed or grooved weft yarns on the machine side changes the geometry at the crossover points of the yarns, which may reduce capillary forces. Another possibility may be that the geometry created at the crossovers due to the lobed yarn can trap water or the geometry creates the pockets which prevents them from holding or retaining water or both.
Therefore, it is believed that the instant invention is not limited to the specific 8-shed multi-layer woven creping fabric design disclosed above. Instead, any multi-layer woven creping fabric having lobed or grooved weft yarns on its machine side, may also minimize or even prevent rewetting of a paper product produced thereon.
A fabric in accordance with one aspect of the instant invention may be constructed using an 8-shed multi-layer weave pattern as depicted in
The weave pattern shown in
In
Another embodiment of a multi-layer woven creping fabric design for use as, for example, a creping fabric 18 in the above-described process is depicted in
Note that the smaller diameter weft yarns or shutes may comprise or be used in addition to the lobed or grooved yarns aforementioned.
The use of a fabric as described herein may result with a web with much higher caliper and much lower density, an unexpected result. The higher caliper and lower density results in a softer paper product having an increased absorbency, both of which are very desired characteristics.
Lastly, the instant fabric may allow the process to be run at a wider array of percent of fabric crepe, basis weight and/or increased recycled fiber content and may produce significant value by increasing the range of operating process parameters.
Although a preferred embodiment of the present invention and modifications thereof have been described in detail herein, it is to be understood that this invention is not limited to this precise embodiment and modifications, and that other modifications and variations may be effected by one skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
This application claims priority benefits from U.S. Provisional Patent Application Ser. No. 60/793,049 filed Apr. 19, 2006, entitled “Multi-Layer Process Fabrics Having Lobed or Grooved Machine Side Weft Yarns to Prevent Rewet”; and U.S. Provisional Patent Application Ser. No. 60/794,614 filed Apr. 25, 2006 entitled “Multi-Layer Process Fabrics Having Lobed or Grooved Machine Side Weft Yams to Prevent Rewet”; and U.S. Provisional Patent Application Ser. No. 60/808,633 filed May 26, 2006 entitled “Impression or Creping Fabric”; and U.S. Provisional Patent Application Ser. No. 60/808,682 filed May 26, 2006 entitled “Multi-Layer Process Fabrics Having Lobed or Grooved Machine Side Weft Yarns to Prevent Rewet”; and U.S. Provisional Patent Application Ser. No. 60/809,042 filed May 26, 2006 entitled “Impression or Creping Fabric”.
Number | Date | Country | |
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60793049 | Apr 2006 | US | |
60794614 | Apr 2006 | US | |
60808633 | May 2006 | US | |
60808682 | May 2006 | US | |
60809042 | May 2006 | US |