Murray, Frank C. (Marietta, GA, US)
Wendt, Greg A. (Neenah, WI, US)
Edwards, Steven L. (Fremont, WI, US)
Mccullough, Stephen J. (Mount Calvary, WI, US)
Super, Guy H. (Menasha, WI, US)

Plaque It!

11/108458

10/28/2008

04/18/2005

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Georgia-Pacific Consumer Products LP (Atlanta, GA, US)

162/111

156/183, 162/123, 264/282, 162/117

B31F1/16; B31F1/07

162/115-117, 156/183, 162/123-133, 162/111-113, 162/109, 264/282-283

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Fortuna, José A.

Ferrell, Michael W.

CLAIM FOR PRIORITY AND TECHNICAL FIELD

This application is based upon and claims priority of U.S. Provisional Patent Application Ser. No. 60/563,519, filed Apr. 19, 2004. This application is also a continuation-in-part of copending U.S. patent application Ser. No. 10/679,862 entitled “Fabric Crepe Process for Making Absorbent Sheet”, filed on Oct. 6, 2003, the priority of which is claimed. Further, this application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/416,666, filed Oct. 7, 2002. This application is directed, in part, to a process wherein a web is compactively dewatered, creped into a creping fabric and dried in situ in that fabric.

What is claimed is:

1. A method of making a fabric-creped absorbent cellulosic sheet comprising: a) forming a nascent web from a papermaking furnish, the nascent web having a generally random distribution of papermaking fiber; b) transferring the web having a generally random distribution of papermaking fiber to a translating transfer surface moving at a transfer surface speed; c) drying the web to a consistency of from about 30 to about 60 percent including compactively dewatering the web prior to or concurrently with transfer to the transfer surface; d) fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent utilizing a creping fabric with a patterned creping surface, the fabric creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a fabric speed slower than the speed of said transfer surface, the fabric pattern, nip parameters, velocity delta and web consistency being selected such that the web is creped from the transfer surface and redistributed on the creping fabric such that the web has a plurality of fiber-enriched regions of high local basis weight arranged in a pattern corresponding to the patterned creping surface of the fabric, e) retaining the wet web in the creping fabric; f) drying the wet web while it is held in the creping fabric to a consistency of at least about 90 percent; and g) drawing the dried web, the step of drawing the dried web being effective to increase the void volume thereof by at least 5%.

2. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is dried with a plurality of can dryers while it is held in the creping fabric.

3. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is dried with an impingement-air dryer while it is held in the creping fabric.

4. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn on-line.

5. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn between a first roll operated at a machine direction velocity greater than the creping fabric velocity and a second roll operated at a machine direction velocity greater than the first roll.

6. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the dried web is calendered on-line.

7. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn at least about 10% after fabric-creping.

8. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn at least about 15% after fabric-creping.

9. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn at least about 30% after fabric-creping.

10. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn at least about 45% after fabric-creping.

11. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the web is drawn up to about 75% after fabric-creping.

12. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a fabric crepe of from about 10% to about 300% and a crepe recovery of from about 10% to about 100%.

13. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 20%.

14. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 30%.

15. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 40%.

16. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 50%.

17. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 60%.

18. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 80%.

19. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a crepe recovery of at least about 100%.

20. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a fabric crepe of from about 10 to about 100%.

21. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a fabric crepe of at least about 40%.

22. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a fabric crepe of at least about 60%.

23. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, operated at a fabric crepe of at least about 80%.

24. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web until it achieves a void volume of at least about 6 gm/gm.

25. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web until it achieves a void volume of at least about 7 gm/gm.

26. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web until it achieves a void volume of at least about 8 gm/gm.

27. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web until it achieves a void volume of at least about 9 gm/gm.

28. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web until it achieves a void volume of at least about 10 gm/gm.

29. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the dried web and increasing its void volume by at least about 10%.

30. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the dried web and increasing its void volume by at least about 25%.

31. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the dried web and increasing its void volume by at least about 50%.

32. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web and preferentially attenuating the fiber-enriched regions of the web.

33. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the orientation of fibers in the fiber-enriched regions is biased in the CD.

34. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, wherein the fiber-enriched regions have a plurality of microfolds with fold lines extending transverse to the machine direction, and wherein drawing the web in the machine direction expands the microfolds.

35. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web and increasing its bulk.

36. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web and reducing the sidedness of the web.

37. The method of making a fabric-creped absorbent cellulosic sheet according to claim 1, including drawing the web and reducing the TMI Friction value of the fabric side of the web.

38. A method of making a fabric-creped absorbent cellulosic sheet comprising: a) compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; b) applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a transfer surface speed; c) fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a fabric speed slower than the speed of said transfer surface, the fabric pattern, nip parameters, velocity delta and web consistency being selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions; d) drying the web; and e) drawing the web, wherein the web is can-dried in a two-tier can drying section such that both the fabric side of the web and the opposite side of the web contact the surface of at least one dryer can and wherein the void volume is increased by at least by at least 5%.

BACKGROUND

Methods of making paper tissue, towel, and the like are well known, including various features such as Yankee drying, through drying, fabric creping, dry creping, wet creping and so forth. Conventional wet pressing (CWP) processes have certain advantages over conventional through-air drying processes including: (1) lower energy costs associated with the mechanical removal of water rather than transpiration drying with hot air; and (2) higher production speeds which are more readily achieved with processes which utilize wet pressing to form a web. On the other hand, through-air drying processing has been adopted for new capital investment, particularly for the production of soft, bulky, premium quality tissue and towel products.

Fabric creping has been employed in connection with papermaking processes which include mechanical or compactive dewatering of the paper web as a means to influence product properties. See U.S. Pat. Nos. 4,689,119 and 4,551,199 of Weldon; U.S. Pat. Nos. 4,849,054 and 4,834,838 of Klowak; and U.S. Pat. No. 6,287,426 of Edwards et al. Operation of fabric creping processes has been hampered by the difficulty of effectively transfering a web of high or intermediate consistency to a dryer. Note also U.S. Pat. No. 6,350,349 to Hermans et al. which discloses wet transfer of a web from a rotating transfer surface to a fabric. Further patents relating to fabric creping more generally include the following: U.S. Pat. Nos. 4,834,838; 4,482,429 4,445,638 as well as U.S. Pat. No. 4,440,597 to Wells et al.

In connection with papermaking processes, fabric molding has also been employed as a means to provide texture and bulk. In this respect, there is seen in U.S. Pat. No. 6,610,173 to Lindsay et al. a method for imprinting a paper web during a wet pressing event which results in asymmetrical protrusions corresponding to the deflection conduits of a deflection member. The '173 patent reports that a differential velocity transfer during a pressing event serves to improve the molding and imprinting of a web with a deflection member. The tissue webs produced are reported as having particular sets of physical and geometrical properties, such as a pattern densified network and a repeating pattern of protrusions having asymmetrical structures. With respect to wet-molding of a web using textured fabrics, see, also, the following U.S. Pat. Nos. 6,017,417 and 5,672,248 both to Wendt et al.; U.S. Pat. Nos. 5,508,818 and 5,510,002 to Hermans et al. and U.S. Pat. No. 4,637,859 to Trokhan. With respect to the use of fabrics used to impart texture to a mostly dry sheet, see U.S. Pat. No. 6,585,855 to Drew et al., as well as United States Publication No. US 2003/000064.

Throughdried, creped products are disclosed in the following patents: U.S. Pat. No. 3,994,771 to Morgan, Jr. et al.; U.S. Pat No. 4,102,737 to Morton; and U.S. Pat No. 4,529,480 to Trokhan. The processes described in these patents comprise, very generally, forming a web on a foraminous support, thermally pre-drying the web, applying the web to a Yankee dryer with a nip defined, in part, by an impression fabric, and creping the product from the Yankee dryer. A relatively permeable web is typically required, making it difficult to employ recycle furnish at levels which may be desired. Transfer to the Yankee typically takes place at web consistencies of from about 60% to about 70%.

As noted in the above, throughdried products tend to exhibit enhanced bulk and softness; however, thermal dewatering with hot air tends to be energy intensive. Wet-press operations wherein the webs are mechanically dewatered are preferable from an energy perspective and are more readily applied to furnishes containing recycle fiber which tends to form webs with less permeability than virgin fiber. Many improvements relate to increasing the bulk and absorbency of compactively dewatered products which are typically dewatered, in part, with a papermaking felt.

U.S. Pat. No. 5,851,353 to Fiscus et al. teaches a method for can drying wet webs for tissue products wherein a partially dewatered wet web is restrained between a pair of molding fabrics. The restrained wet web is processed over a plurality of can dryers, for example, from a consistency of about 40 percent to a consistency of at least about 70 percent. The sheet molding fabrics protect the web from direct contact with the can dryers and impart an impression on the web. See also U.S. Pat. No. 5,336,373 to Scattolino et al.

Despite advances in the art, existing wet press processes have not produced the highly absorbent webs with preferred physical properties especially elevated CD stretch at relatively low MD/CD tensile ratios as are sought after for use in premium tissue and towel products.

In accordance with the present invention, the absorbency, bulk and stretch of a wet-pressed web can be vastly improved by wet fabric creping a web and rearranging the fiber on a creping fabric, while preserving the high speed, thermal efficiency, and furnish tolerance to recycle fiber of conventional wet press processes. The inventive process has the further advantage that existing equipment and facilities can readily be modified to practice the inventive process, using for example, can dryers which are particularly amenable to recycle energy sources and/or lower grade, less expensive fuels which may be available.

SUMMARY OF INVENTION

Fabric-creped products of the present invention typically include fiber-enriched regions of relatively elevated basis weight linked together with regions of lower basis weight. Especially preferred products have a drawable reticulum which is capable of expanding, that is, increasing in void volume and bulk when drawn to greater length. This highly unusual and surprising property is further appreciated by considering the photomicrographs of FIGS. 1 through 6 and the physical property data of FIGS. 7 through 12, as well as the other data discussed in the Detailed Description section hereinafter.

A photomicrograph of the fiber-enriched region of an undrawn, fabric-creped web is shown in FIG. 1 which is in section along the MD (left to right in the photo). It is seen that the web has microfolds transverse to the machine direction, i.e., the ridges or creases extend in the CD (into the photograph). FIG. 2 is a photomicrograph of a web similar to FIG. 1, wherein the web has been drawn 45%. Here it is seen that the microfolds have been expanded, dispersing fiber from the fiber-enriched regions along the machine direction. Without intending to be bound by any theory, it is believed this feature of the invention, rearrangement or unfolding of the material in the fiber-enriched regions, gives rise to the unique macroscopic properties exhibited by the material.

There is thus provided in accordance with the present invention, a method of making fabric-creped absorbent cellulosic sheet including: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying the web; and drawing the web; wherein the drawable reticulum of the web is characterized in that it comprises a cohesive fiber matrix which exhibits elevated void volume upon drawing. The web may be drawn after fabric-creping and before the web is air-dry; preferably, the web is dried to a consistency of at least about 90 percent prior to drawing thereof.

The web may be drawn at least about 10%, 15%, 30% or 45% after fabric-creping. Typically, the web is drawn up to about 75% after fabric-creping.

The inventive process may be operated at a fabric crepe of from about 10% to about 300% and a crepe recovery of from about 10% to about 100%. Crepe recovery may be at least about 20%; least about 30%; at least about 40%; at least about 50%; at least about 60%; at least about 80% or at least about 100%. Likewise, fabric crepe may be at least about 40%; at least about 60% or at least about 80% or more.

The method preferably includes drawing the web until it achieves a void volume of at least about 6 gm/gm. Drawing the web until it achieves a void volume of at least about 7 gm/gm, 8 gm/gm, 9 gm/gm, 10 gm/gm or more might be desirable in some embodiments. Preferred methods include drawing the dried web to increase its void volume by at least about 5%; at least about 10%; at least about 25%; at least about 50% or more.

Typically the inventive method of making a fabric-creped absorbent cellulosic sheet includes drawing the web to preferentially attenuate the fiber-enriched regions of the web which generally include fibers with orientation which is biased in the CD. The fiber-enriched regions most preferably have a plurality of microfolds with fold lines extending transverse to the machine direction, such that drawing the web in the machine direction expands the microfolds. Surprisingly, drawing the web increases its bulk and reduces the sidedness of the web. The step of drawing the web is especially effective to reduce the TMI friction value of the fabric side of the web.

Another aspect of the invention includes a method of making a fabric-creped absorbent cellulosic sheet including: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying; the web and drawing the web; wherein the drawable reticulum of the web is characterized in that it comprises a cohesive fiber matrix which exhibits increased bulk upon drawing. The method preferably includes drawing the dried web to increase the bulk of the web by at least about 5% or 10%.

Another method of making a fabric-creped absorbent cellulosic sheet according to the invention includes: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying the web; and drawing the web, wherein the step of drawing the dried web is effective to decrease the sidedness of the web. Drawing the web may decrease the sidedness of the web by at least about 10%; at least about 20% or at least about 40% or more.

Still yet another aspect of the invention is a method of making a fabric-creped absorbent cellulosic sheet including the steps of: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying the web; and drawing the web, wherein the step of drawing the web is effective to preferentially attenuate the fiber-enriched regions of the web.

In still yet another aspect of the invention there is provided a method of making a fabric-creped absorbent cellulosic sheet comprising: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying the web; and drawing the web,wherein the web has a stretch at break of at least 20% prior to drawing. Preferably, the web so produced has a stretch at break of at least 30% or 45% prior to drawing. In some preferred embodiments, the web has a stretch at break of at least 60% prior to drawing.

A yet further method of making a cellulosic web in accordance with the present invention includes: forming a nascent web from a papermaking furnish, the nascent web having a generally random distribution of papermaking fiber; transferring the web having a generally random distribution of papermaking fiber to a translating transfer surface moving at a first speed; drying the web to a consistency of from about 30 to about 60 percent including compactively dewatering the web prior to or concurrently with transfer to the transfer surface; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent utilizing a creping fabric with a patterned creping surface, the fabric creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency are selected such that the web is creped from the transfer surface and redistributed on the creping fabric such that the web has a plurality of fiber-enriched regions arranged in a pattern corresponding to the patterned creping surface of the fabric. The process further includes: retaining the wet web in the creping fabric; drying the wet web while it is held in the creping fabric to a consistency of at least about 90 percent; and drawing the dried web, the step of drawing the dried web being effective to increase the void volume thereof. In some cases the web is dried with a plurality of can dryers while it is held in the creping fabric; while in other cases the web is dried with an impingement-air dryer while it is held in the creping fabric.

In a preferred embodiment, the web is drawn on-line; perhaps most preferably in incremental amounts in a plurality of steps wherein the web is only partially drawn out in each step. The web may be drawn between a first roll operated at a machine direction velocity greater than the creping fabric velocity and a second roll operated at a machine direction velocity greater than the first roll or between a pair of nips or a nip and a roll operating at different speeds if so desired. Likewise, the dried web may be calendered on-line.

Another method of the invention of making a fabric-creped absorbent cellulosic sheet comprises: compactively dewatering a papermaking furnish to form a nascent web having an apparently random distribution of papermaking fiber; applying the dewatered web having the apparently random fiber distribution to a translating transfer surface moving at a first speed; fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface. The fabric pattern, nip parameters, velocity delta and web consistency being selected such that the web is creped from the transfer surface and redistributed on the creping fabric to form a web with a drawable reticulum having a plurality of interconnected regions of different local basis weights including at least (i) a plurality of fiber-enriched regions of high local basis weight, interconnected by way of (ii) a plurality of lower local basis weight linking regions. The process further includes: drying the web; and drawing the web, wherein the web is can-dried in a two-tier can drying section such that both the fabric side of the web and the opposite side of the web contact the surface of at least one dryer can. Two-tier can drying sections are illustrated schematically in FIGS. 31 and FIG. 33.

Cellulosic absorbent sheet of the invention may be made by way of: preparing a cellulosic web from an aqueous papermaking furnish, the web being provided with a plurality of fiber-enriched regions with a drawable reticulum having relatively high local basis weight interconnected by way of a plurality of lower basis weight linking regions, the reticulum being further characterized in that it comprises a cohesive fiber matrix capable of increase in void volume upon drawing; drying the web while substantially preserving the drawable fiber reticulum and thereafter drawing the web. In connection with this method, web may be dried to a consistency of at least about 90% or 92% prior to drawing. Drawing the web increases bulk and void volume; however drawing decreases sidedness. The results are both highly desirable and unexpected. Superior results are achieved with furnish comprising secondary fiber.

A particularly unusual feature of the invention is that drawing the web decreases the caliper of the web less than its basis weight. Generally, the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than 1 upon drawing the web; typically, the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.85 upon drawing the web; and preferably the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.7 upon drawing the web. In an especially preferred embodiment, the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.6 upon drawing the web.

Further aspects of the inventive process are: preparing a cellulosic web with a drawable reticulum provided with a plurality of microfolds with fold lines transverse to the machine direction; drying the web by way of contacting the web with a dryer surface wherein the drawable reticulum of the web is substantially preserved and wherein the dried web is characterized in that the microfolds may be expanded by drawing the web, whereby the void volume of the web is increased. The web may be provided to a single-tier or two-tier can-drying section at a consistency of less than about 70% and dried to a consistency of greater than about 90% in the single-tier drying section.

Methods of making cellulosic absorbent sheet of the invention include: preparing a cellulosic web from an aqueous papermaking furnish; the web being provided with an expandable reticulum having relatively high local basis weight fiber enriched regions interconnected by way of a plurality of lower basis weight linking regions; drying the web while substantially preserving the expandable fiber reticulum; and expanding the dried web to increase its void volume. The fiber enriched regions typically have fiber bias in the CD and the linking regions typically have fiber bias along a direction between fiber enriched regions. The dried web may be expanded to increase its void volume by at least about 1 g/g; at least bout 2 g/g; or at least about 3 g/g.

Products of the invention include an absorbent cellulosic web comprising a plurality of fiber-enriched regions of relatively high local basis weight interconnected by a plurality of lower local basis weight regions, characterized in that drawing the web increases the void volume thereof. In many cases, is capable of an increase in void volume of up to about 25%, 35%, 50% or more upon drawing. In one preferred embodiment, drawing the web by 30% increases the void volume by at least about 5% and in another, dry-drawing the web by 45% increases the void volume by at least about 20%.

Another product of the invention is an absorbent cellulosic web comprising a plurality of fiber-enriched regions of relatively high local basis weight interconnected by a plurality of lower local basis weight regions, characterized in that drawing the web increases the bulk thereof. Typically, drawing the web by 30% increases the bulk thereof by at least about 5% and drawing the web by 45% increases the bulk thereof by at least about 10%.

Yet other products are absorbent cellulosic webs comprising a plurality of fiber-enriched regions of relatively high local basis weight interconnected by a plurality of lower local basis weight regions, characterized in that drawing the web is effective to decrease the sidedness thereof and preferentially attenuate the fiber enriched regions. The absorbent cellulosic web products may incorporate secondary fiber, sometimes at least 50% or over 50% by weight secondary fiber.

As noted above, the products have the unusual and surprising feature that caliper of the web decreases more slowly than basis weight upon drawing the web such as wherein the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.85 upon drawing the web. Preferably, the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.7 upon drawing the web. In some especially preferred products, the ratio of percent decrease in caliper/percent decrease in basis weight of the web is less than about 0.6 upon drawing the web. Generally, the web products of the invention have a basis weight of from about 5 to about 30 lbs per 3000 square feet ream.

Another unique aspect of products of the invention is that they include recovered creped material as part of the product matrix. Typically, the web has a recovered crepe of at least about 10%. A recovered crepe of at least about 25%; at least about 50%; or at least about 100% is desirable in some products.

The invention provides an absorbent cellulosic web with an expandable reticulum of fiber enriched, relatively high basis weight regions interconnected by way of lower basis weight linking regions, characterized in that the void volume of the web may be increased by expanding the fiber enriched regions. In preferred embodiments, the fiber enriched regions have fiber bias in the CD and the linking regions have fiber bias along a direction between fiber enriched regions and the fiber enriched regions are provided with a plurality of microfolds with fold lines transverse to the machine direction. The absorbent cellulosic web may be expanded to increase its void volume from the as-dried condition (or with respect to a like web that is unexpanded) by at least about 1 g/g; at least about 2 g/g; at least about 3 g/g or more.

Still yet other features and advantages of the invention will become apparent from the following description and appended Figures.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to the drawings, wherein like numerals designate similar parts:

FIG. 1 is a photomicrograph (120×) in section along the machine direction of a fiber-enriched region of a fabric-creped sheet which has not been drawn subsequent to fabric creping;

FIG. 2 is a photomicrograph (120×) in section along the machine direction of a fiber-enriched region of a fabric-creped sheet of the invention which has been drawn 45% subsequent to fabric creping.

FIG. 3 is a photomicrograph (10×) of the fabric side of a fabric-creped web which was dried in the fabric;

FIG. 4 is a photomicrograph (10×) of the fabric side of a fabric-creped web which was dried in-fabric then drawn 45%;

FIG. 5 is a photomicrograph (10×) of the dryer side of the web of FIG. 3;

FIG. 6 is a photomicrograph (10×) of the dryer side of the web of FIG. 4;

FIG. 7 is a plot of void volume versus draw for various absorbent products;

FIG. 8 is a plot of basis weight, caliper and bulk versus draw for a fabric-creped, can-dried web of the invention;

FIG. 9 is a plot of basis weight, caliper and bulk versus draw for a fabric-creped, Yankee-dried web;

FIG. 10 is a plot of TMI Friction values versus bulk for fabric-creped, can-dried webs of the invention;

FIGS. 11 and 12 are plots of TMI Friction values and void volume versus percent draw for a fabric-creped, in-fabric dried web of the invention;

FIG. 13 is a photomicrograph (8×) of an open mesh web including a plurality of high basis weight regions linked by lower basis weight regions extending therebetween;

FIG. 14 is a photomicrograph showing enlarged detail (32×) of the web of FIG. 13;

FIG. 15 is a photomicrograph (8×) showing the open mesh web of FIG. 13 placed on the creping fabric used to manufacture the web;

FIG. 16 is a photomicrograph showing a web having a basis weight of 19 lbs/ream produced with a 17% Fabric Crepe;

FIG. 17 is a photomicrograph showing a web having a basis weight of 19 lbs/ream produced with a 40% Fabric Crepe;

FIG. 18 is a photomicrograph showing a web having a basis weight of 27 lbs/ream produced with a 28% Fabric Crepe;

FIG. 19 is a surface image (10×) of an absorbent sheet, indicating areas where samples for surface and section SEMs were taken;

FIGS. 20-22 are surface SEMs of a sample of material taken from the sheet seen in FIG. 19;

FIGS. 23 and 24 are SEMs of the sheet shown in FIG. 19 in section across the MD;

FIGS. 25 and 26 are SEMs of the sheet shown in FIG. 19 in section along the MD;

FIGS. 27 and 28 are SEMs of the sheet shown in FIG. 19 in section also along the MD;

FIGS. 29 and 30 are SEMs of the sheet shown in FIG. 19 in section across the MD;

FIG. 31 is a schematic diagram of a papermachine for producing absorbent sheet in accordance with the present invention;

FIG. 32 is a schematic diagram showing a portion of another papermachine for making the products of the present invention;

FIG. 33 is a schematic diagram of a portion of yet another papermachine for making the products of the present invention;

FIG. 34 is a plot of void volume versus basis weight as webs are drawn;

FIG. 35 is a diagram showing the machine direction modulus of webs of the invention wherein the respective abscissas have been shifted for purposes of clarity;

FIG. 36 is a plot of machine direction modulus versus percent stretch for can dried products of the present invention;

FIG. 37 is a plot of caliper change versus basis weight for various products of the invention;

FIG. 38 is a plot of caliper change and void volume change versus basis weight change for various fabric-creped webs;

FIG. 39 is a plot of caliper versus applied vacuum for fabric-creped webs;

FIG. 40 is a plot of caliper versus applied vacuum for fabric-creped webs and various creping fabrics;

FIG. 41 is a plot of TMI Friction values versus draw for various webs of the invention;

FIG. 42 is a plot of void volume change versus basis weight change for various products; and

FIG. 43 is a diagram showing representative curves of MD/CD tensile ratio versus jet to wire velocity delta for the products of the invention and conventional wet press (CWP) absorbent sheet.

DETAILED DESCRIPTION

The invention is described in detail below with reference to several embodiments and numerous examples. Such discussion is for purposes of illustration only. Modifications to particular examples within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to one of skill in the art.

Terminology used herein is given its ordinary meaning consistent with the exemplary definitions set forth immediately below.

Throughout this specification and claims, when we refer to a nascent web having an apparently random distribution of fiber orientation (or use like terminology), we are referring to the distribution of fiber orientation that results when known forming techniques are used for depositing a furnish on the forming fabric. When examined microscopically, the fibers give the appearance of being randomly oriented even though, depending on the jet to wire speed, there may be a significant bias toward machine direction orientation making the machine direction tensile strength of the web exceed the cross-direction tensile strength.

Unless otherwise specified, “basis weight”, BWT, bwt and so forth refers to the weight of a 3000 square foot ream of product. Consistency refers to percent solids of a nascent web, for example, calculated on a bone dry basis. “Air dry” means including residual moisture, by convention up to about 10 percent moisture for pulp and up to about 6% for paper. A nascent web having 50 percent water and 50 percent bone dry pulp has a consistency of 50 percent.

The term “cellulosic”, “cellulosic sheet” and the like is meant to include any product incorporating papermaking fiber having cellulose as a major constituent. “Papermaking fibers” include virgin pulps or recycle (secondary) cellulosic fibers or fiber mixes comprising cellulosic fibers. Fibers suitable for making the webs of this invention include: nonwood fibers, such as cotton fibers or cotton derivatives, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and wood fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as eucalyptus, maple, birch, aspen, or the like. Papermaking fibers can be liberated from their source material by any one of a number of chemical pulping processes familiar to one experienced in the art including sulfate, sulfite, polysulfide, soda pulping, etc. The pulp can be bleached if desired by chemical means including the use of chlorine, chlorine dioxide, oxygen, alkaline peroxide and so forth. The products of the present invention may comprise a blend of conventional fibers (whether derived from virgin pulp or recycle sources) and high coarseness lignin-rich tubular fibers, such as bleached chemical thermomechanical pulp (BCTMP). “Furnishes” and like terminology refers to aqueous compositions including papermaking fibers, optionally wet strength resins, debonders and the like for making paper products.

“Can drying” refers to drying a web by contacting a web with a dryer drum while not adhering the web to the dryer surface, typically while the web is also in contact with a fabric. In a single-tier system, only one side of the web contacts the drums, while in a conventional two-tier system, both sides of the web contact dryer surfaces as will be appreciated from FIGS. 32 and 33, discussed hereafter.

As used herein, the term compactively dewatering the web or furnish refers to mechanical dewatering by wet pressing on a dewatering felt, for example, in some embodiments by use of mechanical pressure applied continuously over the web surface as in a nip between a press roll and a press shoe wherein the web is in contact with a papermaking felt. The terminology “compactively dewatering” is used to distinguish processes wherein the initial dewatering of the web is carried out largely by thermal means as is the case, for example, in U.S. Pat. Nos. 4,529,480 to Trokhan and 5,607,551 to Farrington et al. noted above. Compactively dewatering a web thus refers, for example, to removing water from a nascent web having a consistency of less than 30 percent or so by application of pressure thereto and/or increasing the consistency of the web by about 15 percent or more by application of pressure thereto.

Creping fabric and like terminology refers to a fabric or belt which bears a pattern suitable for practicing the process of the present invention and preferably is permeable enough such that the web may be dried while it is held in the creping fabric. In cases where the web is transferred to another fabric or surface (other than the creping fabric) for drying, the creping fabric may have lower permeability.

“Fabric side” and like terminology refers to the side of the web which is in contact with the creping and drying fabric. “Dryer side” or “can side” is the side of the web opposite the fabric side of the web.

Fpm refers to feet per minute while consistency refers to the weight percent fiber of the web.

MD means machine direction and CD means cross-machine direction.

Nip parameters include, without limitation, nip pressure, nip length, backing roll hardness, fabric approach angle, fabric takeaway angle, uniformity, and velocity delta between surfaces of the nip.

Nip length means the length over which the nip surfaces are in contact.

The drawable reticulum is “substantially preserved” when the web is capable of exhibiting a void volume increase upon drawing.

“On line” and like terminology refers to a process step performed without removing the web from the papermachine in which the web is produced. A web is drawn or calendered on line when it is drawn or calendered without being severed prior to wind-up.

A translating transfer surface refers to the surface from which the web is creped into the creping fabric. The translating transfer surface may be the surface of a rotating drum as described hereafter, or may be the surface of a continuous smooth moving belt or another moving fabric which may have surface texture and so forth. The translating transfer surface needs to support the web and facilitate the high solids creping as will be appreciated from the discussion which follows.

Calipers and or bulk reported herein may be measured using 1, 4 or 8 sheet calipers as specified. The sheets are stacked and the caliper measurement taken about the central portion of the stack. Preferably, the test samples are conditioned in an atmosphere of 23°±1.0° C. (73.4°±1.8° F.) at 50% relative humidity for at least about 2 hours and then measured with a Thwing-Albert Model 89-II-JR or Progage Electronic Thickness Tester with 2-in (50.8-mm) diameter anvils, 539±10 grams dead weight load, and 0.231 in./sec descent rate. For finished product testing, each sheet of product to be tested must have the same number of plies as the product is sold. For testing in general, eight sheets are selected and stacked together. For napkin testing, napkins are unfolded prior to stacking. For basesheet testing off of winders, each sheet to be tested must have the same number of plies as produced off the winder. For basesheet testing off of the papermachine reel, single plies must be used. Sheets are stacked together aligned in the MD. On custom embossed or printed product, avoid measurements in these areas if at all possible. Bulk may also be expressed in units of volume/weight by dividing caliper by basis weight.

Absorbency of the inventive products is measured with a simple absorbency tester. The simple absorbency tester is a particularly useful apparatus for measuring the hydrophilicity and absorbency properties of a sample of tissue, napkins, or towel. In this test a sample of tissue, napkins, or towel 2.0 inches in diameter is mounted between a top flat plastic cover and a bottom grooved sample plate. The tissue, napkin, or towel sample disc is held in place by a ⅛ inch wide circumference flange area. The sample is not compressed by the holder. De-ionized water at 73° F. is introduced to the sample at the center of the bottom sample plate through a 1 mm. diameter conduit. This water is at a hydrostatic head of minus 5 mm. Flow is initiated by a pulse introduced at the start of the measurement by the instrument mechanism. Water is thus imbibed by the tissue, napkin, or towel sample from this central entrance point radially outward by capillary action. When the rate of water imbibation decreases below 0.005 gm water per 5 seconds, the test is terminated. The amount of water removed from the reservoir and absorbed by the sample is weighed and reported as grams of water per square meter of sample or grams of water per gram of sheet. In practice, an M/K Systems Inc. Gravimetric Absorbency Testing System is used. This is a commercial system obtainable from M/K Systems Inc., 12 Garden Street, Danvers, Mass., 01923. WAC or water absorbent capacity also referred to as SAT is actually determined by the instrument itself. WAC is defined as the point where the weight versus time graph has a “zero” slope, i.e., the sample has stopped absorbing. The termination criteria for a test are expressed in maximum change in water weight absorbed over a fixed time period. This is basically an estimate of zero slope on the weight versus time graph. The program uses a change of 0.005 g over a 5 second time interval as termination criteria; unless “Slow SAT” is specified in which case the cut off criteria is 1 mg in 20 seconds.

Dry tensile strengths (MD and CD), stretch, ratios thereof, modulus, break modulus, stress and strain are measured with a standard Instron test device or other suitable elongation tensile tester which may be configured in various ways, typically using 3 or 1 inch wide strips of tissue or towel, conditioned in an atmosphere of 23°±1° C. (73.4°±1° F.) at 50% relative humidity for 2 hours. The tensile test is run at a crosshead speed of 2 in/min. Modulus is expressed in lbs/inch per inch of elongation unless otherwise indicated.

Tensile ratios are simply ratios of the values determined by way of the foregoing methods. Unless otherwise specified, a tensile property is a dry sheet property.

“Fabric crepe ratio” is an expression of the speed differential between the creping fabric and the forming wire and typically calculated as the ratio of the web speed immediately before fabric creping and the web speed immediately following fabric creping, the forming wire and transfer surface being typically, but not necessarily, operated at the same speed:
Fabric crepe ratio=transfer cylinder speed÷creping fabric speed

Fabric crepe can also be expressed as a percentage calculated as:
Fabric crepe, percent,=[Fabric crepe ratio−1]×100%

A web creped from a transfer cylinder with a surface speed of 750 fpm to a fabric with a velocity of 500 fpm has a fabric crepe ratio of 1.5 and a fabric crepe of 50%.

The draw ratio is calculated similarly, typically as the ratio of winding speed to the creping fabric speed. Draw may be expressed as a percentage by subtracting 1 from the draw ratio and multiply by 100%. The “pullout” or “draw” applied to a test specimen is calculated from the ratio of final length divided by its length prior to elongation. Unless otherwise specified, draw refers to elongation with respect to the length of the as-dried web. This quantity may also be expressed as a percentage. For example a 4″ test specimen drawn to 5″ has a draw ratio of 5/4 or 1.25 and a draw of 25%.

The total crepe ratio is calculated as the ratio of the forming wire speed to the reel speed and a % total crepe is:
Total Crepe %=[Total Crepe Ratio−1]×100%

A process with a forming wire speed of 2000 fpm and a reel speed of 1000 fpm has a line or total crepe ratio of 2 and a total crepe of 100%.

The recovered crepe of a web is the amount of fabric crepe removed when the web is elongated or drawn. This quantity is calculated as follows and expressed as a percentage:

$\mathrm{Recovered}\mathrm{Crepe}\%=\left[1-\frac{\%\mathrm{Total}\mathrm{Crepe}}{\%\mathrm{Fabric}\mathrm{Crepe}}\right]\times 100\%$

A process with a total crepe of 25% and fabric crepe of 50% has a recovered crepe of 50%.

Recovered crepe is referred to as the crepe recovery when quantifying the amount of crepe and draw applied to a particular web. Sample calculations of the various quantities for a papermachine 40 of the type shown in FIG. 31 provided with a forming wire 52 a transfer cylinder 76 , a creping fabric 80 as well as a take up reel 106 are given in Table 1 below. Recovered fabric crepe is a product attribute which relates to bulk and void volume as is seen in the Figures and Examples below.

TABLE 1
Sample Calculations of Fabric Crepe, Draw and Recovered Crepe
Wire	Crepe Fabric	Reel		FabCrp %		Draw %	TotalCrp
fpm	fpm	fpm	FCRatio	%	DrawRatio	%	Ratio	ToCrptPct %	RecCrp %
1000	500	750	2.00	100%	1.5	50%	1.33	33%	67%
2000	1500	1600	1.33	33%	1.067	6.7%	1.25	25%	25%
2000	1500	2000	1.33	33%	1.33	33%	1.00	0%	100%
3000	1500	2625	2.00	100%	1.75	75%	1.14	14%	86%
3000	2000	2500	1.50	50%	1.25	25%	1.20	20%	60%

Friction values and sidedness are calculated by a modification to the TMI method discussed in U.S. Pat. No. 6,827,819 to Dwiggins et al., this modified method is described below. A percent change in friction value or sidedness upon drawing is based on the difference between the initial value without draw and the drawn value, divided by the initial value and expressed as a percentage.

Sidedness and friction deviation measurements can be accomplished using a Lab Master Slip & Friction tester, with special high-sensitivity load measuring option and custom top and sample support block, Model 32-90 available from:

Testing Machines Inc.

2910 Expressway Drive South

Islandia, N.Y. 11722

800-678-3221

www.testingmachines.com

• • adapted to accept a Friction Sensor, available from:

Noriyuki Uezumi

Kato Tech Co., Ltd.

Kyoto Branch Office

Nihon-Seimei-Kyoto-Santetsu Bldg. 3F

Higashishiokoji-Agaru, Nishinotoin-Dori

Shimogyo-ku, Kyoto 600-8216

Japan 81-75-361-6360

katotech@mx1.alpha-web.ne.jp

The software for the Lab Master Slip and Friction tester is modified to allow it to: (1) retrieve and directly record instantaneous data on the force exerted on the friction sensor as it moves across the samples; (2) compute an average for that data; (3) calculate the deviation--absolute value of the difference between each of the instantaneous data points and the calculated mean; and (4) calculate a mean deviation over the scan to be reported in grams.

Prior to testing, the test samples should be conditioned in an atmosphere of 23.0°±1° C. (73.4°±1.8° F.) and 50% ±2% R.H. Testing should also be conducted at these conditions. The samples should be handled by edges and corners only and any touching of the area of the sample to be tested should be minimized as the samples are delicate, and physical properties may be easily changed by rough handling or transfer of oils from the hands of the tester.

The samples to be tested are prepared, using a paper cutter to get straight edges, as 3-inch wide (CD) by 5-inch long (MD) strips; any sheets with obvious imperfections being removed and replaced with acceptable sheets. These dimensions correspond to those of a standard tensile test, allowing the same specimen to be first elongated in the tensile tester, then tested for surface friction.

Each specimen is placed on the sample table of the tester and the edges of the specimen are aligned with the front edge of the sample table and the chucking device. A metal frame is placed on top of the specimen in the center of the sample table while ensuring that the specimen is flat beneath the frame by gently smoothing the outside edges of the sheet. The sensor is placed carefully on the specimen with the sensor arm in the middle of the sensor holder. Two MD-scans are run on each side of each specimen.

To compute the TMI Friction Value of a sample, two MD scans of the sensor head are run on each side of each sheet, where The Average Deviation value from the first MD scan of the fabric side of the sheet is recorded as MD _F1 ; the result obtained on the second scan on the fabric side of the sheet is recorded as MD _F2 . MD _D1 and MD _D2 are the results of the scans run on the Dryer side (Can or Yankee side) of the sheet.

The TMI Friction Value for the fabric side is calculated as follows:

${\mathrm{TMI\_FV}}_F=\frac{{\mathrm{MD}}_{F1}+{\mathrm{MD}}_{F2}}{2}$

Likewise, the TMI Friction Value for the dryer side is calculated as:

${\mathrm{TMI\_FV}}_D=\frac{{\mathrm{MD}}_{D1}+{\mathrm{MD}}_{D2}}{2}$

An overall Sheet Friction Value can be calculated as the average of the fabric side and the dryer side, as follows:

${\mathrm{TMI\_FV}}_{\mathrm{AVG}}=\frac{{\mathrm{TMI\_FV}}_F+{\mathrm{TMI\_FV}}_D}{2}$

Leading to Sidedness as an indication of how much the friction differs between the two sides of the sheet. The sidedness is defined as:

$\mathrm{Sidedness}=\frac{{\mathrm{TMI\_FV}}_U}{{\mathrm{TMI\_FV}}_L}*{\mathrm{TMI\_FV}}_{\mathrm{AVG}}$
here “U” and “L” subscripts refer to the upper and lower values of the friction deviation of the two sides (Fabric and Dryer)—that is the larger Friction value is always placed in the numerator.

For fabric-creped products, the fabric side friction value will be higher than the dryer side friction value. Sidedness takes into account not only the relative difference between the two sides of the sheet but the overall friction level. Accordingly, low sidedness values are normally preferred.

PLI or pli means pounds force per linear inch.

Pusey and Jones (P&J) hardness (indentation) is measured in accordance with ASTM D 531, and refers to the indentation number (standard specimen and conditions).

Velocity delta means a difference in linear speed.

The void volume and/or void volume ratio as referred to hereafter, are determined by saturating a sheet with a nonpolar POROFIL® liquid and measuring the amount of liquid absorbed. The volume of liquid absorbed is equivalent to the void volume within the sheet structure. The percent weight increase (PWI) is expressed as grams of liquid absorbed per gram of fiber in the sheet structure times 100, as noted hereinafter. More specifically, for each single-ply sheet sample to be tested, select 8 sheets and cut out a 1 inch by 1 inch square (1 inch in the machine direction and 1 inch in the cross-machine direction). For multi-ply product samples, each ply is measured as a separate entity. Multiple samples should be separated into individual single plies and 8 sheets from each ply position used for testing. To measure absorbency, weigh and record the dry weight of each test specimen to the nearest 0.0001 gram. Place the specimen in a dish containing POROFIL® liquid having a specific gravity of 1.875 grams per cubic centimeter, available from Coulter Electronics Ltd., Northwell Drive, Luton, Beds, England; Part No. 9902458.) After 10 seconds, grasp the specimen at the very edge (1-2 Millimeters in) of one corner with tweezers and remove from the liquid. Hold the specimen with that corner uppermost and allow excess liquid to drip for 30 seconds. Lightly dab (less than ½ second contact) the lower corner of the specimen on #4 filter paper (Whatman Lt., Maidstone, England) in order to remove any excess of the last partial drop. Immediately weigh the specimen, within 10 seconds, recording the weight to the nearest 0.0001 gram. The PWI for each specimen, expressed as grams of POROFIL® liquid per gram of fiber, is calculated as follows:
PWI =[( W ₂ −W ₁ )/ W ₁ ]×100%
wherein

“W ₁ ” is the dry weight of the specimen, in grams; and

“W ₂ ” is the wet weight of the specimen, in grams.

The PWI for all eight individual specimens is determined as described above and the average of the eight specimens is the PWI for the sample.

The void volume ratio is calculated by dividing the PWI by 1.9 (density of fluid) to express the ratio as a percentage, whereas the void volume (gms/gm) is simply the weight increase ratio; that is, PWI divided by 100.

During fabric creping in a pressure nip, the fiber is redistributed on the fabric, making the process tolerant of less than ideal forming conditions, as are sometimes seen with a Fourdrinier former. The forming section of a Fourdrinier machine includes two major parts, the headbox and the Fourdrinier Table. The latter consists of the wire run over the various drainage-controlling devices. The actual forming occurs along the Fourdrinier Table. The hydrodynamic effects of drainage, oriented shear, and turbulence generated along the table are generally the controlling factors in the forming process. Of course, the headbox also has an important influence in the process, usually on a scale that is much larger than the structural elements of the paper web. Thus the headbox may cause such large-scale effects as variations in distribution of flow rates, velocities, and concentrations across the full width of the machine; vortex streaks generated ahead of and aligned in the machine direction by the accelerating flow in the approach to the slice; and time-varying surges or pulsations of flow to the headbox. The existence of MD-aligned vortices in headbox discharges is common. Fourdrinier formers are further described in The Sheet Forming Process, Parker, J. D., Ed., TAPPI Press (1972, reissued 1994) Atlanta, Ga.

According to the present invention, an absorbent paper web is made by dispersing papermaking fibers into aqueous furnish (slurry) and depositing the aqueous furnish onto the forming wire of a papermaking machine. Any suitable forming scheme might be used. For example, an extensive but non-exhaustive list in addition to Fourdrinier formers includes a crescent former, a C-wrap twin wire former, an S-wrap twin wire former, or a suction breast roll former. The forming fabric can be any suitable foraminous member including single layer fabrics, double layer fabrics, triple layer fabrics, photopolymer fabrics, and the like. Non-exhaustive background art in the forming fabric area includes U.S. Pat. Nos. 4,157,276; 4,605,585; 4,161,195; 3,545,705; 3,549,742; 3,858,623; 4,041,989; 4,071,050; 4,112,982; 4,149,571; 4,182,381; 4,184,519; 4,314,589; 4,359,069; 4,376,455; 4,379,735; 4,453,573; 4,564,052; 4,592,395; 4,611,639; 4,640,741; 4,709,732; 4,759,391; 4,759,976; 4,942,077; 4,967,085; 4,998,568; 5,016,678; 5,054,525; 5,066,532; 5,098,519; 5,103,874; 5,114,777; 5,167,261; 5,199,261; 5,199,467; 5,211,815; 5,219,004; 5,245,025; 5,277,761; 5,328,565; and 5,379,808 all of which are incorporated herein by reference in their entirety. One forming fabric particularly useful with the present invention is Voith Fabrics Forming Fabric 2164 made by Voith Fabrics Corporation, Shreveport, La.

Foam-forming of the aqueous furnish on a forming wire or fabric may be employed as a means for controlling the permeability or void volume of the sheet upon fabric-creping. Foam-forming techniques are disclosed in U.S. Pat. No. 4,543,156 and Canadian Patent No. 2,053,505, the disclosures of which are incorporated herein by reference. The foamed fiber furnish is made up from an aqueous slurry of fibers mixed with a foamed liquid carrier just prior to its introduction to the headbox. The pulp slurry supplied to the system has a consistency in the range of from about 0.5 to about 7 weight percent fibers, preferably in the range of from about 2.5 to about 4.5 weight percent. The pulp slurry is added to a foamed liquid comprising water, air and surfactant containing 50 to 80 percent air by volume forming a foamed fiber furnish having a consistency in the range of from about 0.1 to about 3 weight percent fiber by simple mixing from natural turbulence and mixing inherent in the process elements. The addition of the pulp as a low consistency slurry results in excess foamed liquid recovered from the forming wires. The excess foamed liquid is discharged from the system and may be used elsewhere or treated for recovery of surfactant therefrom.

The furnish may contain chemical additives to alter the physical properties of the paper produced. These chemistries are well understood by the skilled artisan and may be used in any known combination. Such additives may be surface modifiers, softeners, debonders, strength aids, latexes, opacifiers, optical brighteners, dyes, pigments, sizing agents, barrier chemicals, retention aids, insolubilizers, organic or inorganic crosslinkers, or combinations thereof; said chemicals optionally comprising polyols, starches, PPG esters, PEG esters, phospholipids, surfactants, polyamines, HMCP (Hydrophobically Modified Cationic Polymers), HMAP (Hydrophobically Modified Anionic Polymers) or the like.

The pulp can be mixed with strength adjusting agents such as wet strength agents, dry strength agents and debonders/softeners and so forth. Suitable wet strength agents are known to the skilled artisan. A comprehensive but non-exhaustive list of useful strength aids include urea-formaldehyde resins, melamine formaldehyde resins, glyoxylated polyacrylamide resins, polyamide-epichlorohydrin resins and the like. Thermosetting polyacrylamides are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Pat. No. 3,556,932 to Coscia et al. and U.S. Pat. No. 3,556,933 to Williams et al., both of which are incorporated herein by reference in their entirety. Resins of this type are commercially available under the trade name of PAREZ 631NC by Bayer Corporation. Different mole ratios of acrylamide/-DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce thermosetting wet strength characteristics. Of particular utility are the polyamide-epichlorohydrin wet strength resins, an example of which is sold under the trade names Kymene 557LX and Kymene 557H by Hercules Incorporated of Wilmington, Del. and Amres® from Georgia-Pacific Resins, Inc. These resins and the process for making the resins are described in U.S. Pat. Nos. 3,700,623 and 3,772,076 each of which is incorporated herein by reference in its entirety. An extensive description of polymeric-epihalohydrin resins is given in Chapter 2: Alkaline - Curing Polymeric Amine - Epichlorohydrin by Espy in Wet Strength Resins and Their Application (L. Chan, Editor, 1994), herein incorporated by reference in its entirety. A reasonably comprehensive list of wet strength resins is described by Westfelt in Cellulose Chemistry and Technology Volume 13, p. 813, 1979, which is incorporated herein by reference.

Suitable temporary wet strength agents may likewise be included. A comprehensive but non-exhaustive list of useful temporary wet strength agents includes aliphatic and aromatic aldehydes including glyoxal, malonic dialdehyde, succinic dialdehyde, glutaraldehyde and dialdehyde starches, as well as substituted or reacted starches, disaccharides, polysaccharides, chitosan, or other reacted polymeric reaction products of monomers or polymers having aldehyde groups, and optionally, nitrogen groups. Representative nitrogen containing polymers, which can suitably be reacted with the aldehyde containing monomers or polymers, includes vinyl-amides, acrylamides and related nitrogen containing polymers. These polymers impart a positive charge to the aldehyde containing reaction product. In addition, other commercially available temporary wet strength agents, such as, PAREZ 745, manufactured by Bayer can be used, along with those disclosed, for example in U.S. Pat. No. 4,605,702.

The temporary wet strength resin may be any one of a variety of water-soluble organic polymers comprising aldehydic units and cationic units used to increase dry and wet tensile strength of a paper product. Such resins are described in U.S. Pat. Nos. 4,675,394; 5,240,562; 5,138,002; 5,085,736; 4,981,557; 5,008,344; 4,603,176; 4,983,748; 4,866,151; 4,804,769 and 5,217,576. Modified starches sold under the trademarks CO-BOND® 1000 and CO-BOND® 1000 Plus, by National Starch and Chemical Company of Bridgewater, N.J. may be used. Prior to use, the cationic aldehydic water soluble polymer can be prepared by preheating an aqueous slurry of approximately 5% solids maintained at a temperature of approximately 240 degrees Fahrenheit and a pH of about 2.7 for approximately 3.5 minutes. Finally, the slurry can be quenched and diluted by adding water to produce a mixture of approximately 1.0% solids at less than about 130 degrees Fahrenheit.

Other temporary wet strength agents, also available from National Starch and Chemical Company are sold under the trademarks CO-BOND® 1600 and CO-BOND® 2300. These starches are supplied as aqueous colloidal dispersions and do not require preheating prior to use.

Temporary wet strength agents such as glyoxylated polyacrylamide can be used. Temporary wet strength agents such glyoxylated polyacrylamide resins are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking temporary or semi-permanent wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Pat. No. 3,556,932 to Coscia et al. and U.S. Pat. No. 3,556,933 to Williams et al., both of which are incorporated herein by reference. Resins of this type are commercially available under the trade name of PAREZ 631NC, by Bayer Industries. Different mole ratios of acrylamide/DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce wet strength characteristics.

Suitable dry strength agents include starch, guar gum, polyacrylamides, carboxymethyl cellulose and the like. Of particular utility is carboxymethyl cellulose, an example of which is sold under the trade name Hercules CMC, by Hercules Incorporated of Wilmington, Del. According to one embodiment, the pulp may contain from about 0 to about 15 lb/ton of dry strength agent. According to another embodiment, the pulp may contain from about 1 to about 5 lbs/ton of dry strength agent.

Suitable debonders are likewise known to the skilled artisan. Debonders or softeners may also be incorporated into the pulp or sprayed upon the web after its formation. The present invention may also be used with softener materials including but not limited to the class of amido amine salts derived from partially acid neutralized amines. Such materials are disclosed in U.S. Pat. No. 4,720,383. Evans, Chemistry and Industry, 5 Jul. 1969, pp. 893-903; Egan, J. Am. Oil Chemist's Soc., Vol. 55 (1978), pp. 118-121; and Trivedi et al., J. Am. Oil Chemist's Soc., June 1981, pp. 754-756, incorporated by reference in their entirety, indicate that softeners are often available commercially only as complex mixtures rather than as single compounds. While the following discussion will focus on the predominant species, it should be understood that commercially available mixtures would generally be used in practice.

Quasoft 202-JR is a suitable softener material, which may be derived by alkylating a condensation product of oleic acid and diethylenetriamine. Synthesis conditions using a deficiency of alkylation agent (e.g., diethyl sulfate) and only one alkylating step, followed by pH adjustment to protonate the non-ethylated species, result in a mixture consisting of cationic ethylated and cationic non-ethylated species. A minor proportion (e.g., about 10%) of the resulting amido amine cyclize to imidazoline compounds. Since only the imidazoline portions of these materials are quaternary ammonium compounds, the compositions as a whole are pH-sensitive. Therefore, in the practice of the present invention with this class of chemicals, the pH in the head box should be approximately 6 to 8, more preferably 6 to 7 and most preferably 6.5 to 7.

Quaternary ammonium compounds, such as dialkyl dimethyl quaternary ammonium salts are also suitable particularly when the alkyl groups contain from about 10 to 24 carbon atoms. These compounds have the advantage of being relatively insensitive to pH.

Biodegradable softeners can be utilized. Representative biodegradable cationic softeners/debonders are disclosed in U.S. Pat. Nos. 5,312,522; 5,415,737; 5,262,007; 5,264,082; and 5,223,096, all of which are incorporated herein by reference in their entirety. The compounds are biodegradable diesters of quaternary ammonia compounds, quaternized amine-esters, and biodegradable vegetable oil based esters functional with quaternary ammonium chloride and diester dierucyldimethyl ammonium chloride and are representative biodegradable softeners.

In some embodiments, a particularly preferred debonder composition includes a quaternary amine component as well as a nonionic surfactant.

The nascent web is typically dewatered on a papermaking felt. Any suitable felt may be used. For example, felts can have double-layer base weaves, triple-layer base weaves, or laminated base weaves. Preferred felts are those having the laminated base weave design. A wet-press-felt which may be particularly useful with the present invention is Vector 3 made by Voith Fabric. Background art in the press felt area includes U.S. Pat. Nos. 5,657,797; 5,368,696; 4,973,512; 5,023,132; 5,225,269; 5,182,164; 5,372,876; and 5,618,612. A differential pressing felt as is disclosed in U.S. Pat. No. 4,533,437 to Curran et al. may likewise be utilized.

Suitable creping fabrics include single layer, multi-layer, or composite preferably open meshed structures. Fabrics may have at least one of the following characteristics: (1) on the side of the creping fabric that is in contact with the wet web (the “top” side), the number of machine direction (MD) strands per inch (mesh) is from 10 to 200 and the number of cross-direction (CD) strands per inch (count) is also from 10 to 200; (2) The strand diameter is typically smaller than 0.050 inch; (3) on the top side, the distance between the highest point of the MD knuckles and the highest point on the CD knuckles is from about 0.001 to about 0.02 or 0.03 inch; (4) In between these two levels there can be knuckles formed either by MD or CD strands that give the topography a three dimensional hill/valley appearance which is imparted to the sheet; (5) The fabric may be oriented in any suitable way so as to achieve the desired effect on processing and on properties in the product; the long warp knuckles may be on the top side to increase MD ridges in the product, or the long shute knuckles may be on the top side if more CD ridges are desired to influence creping characteristics as the web is transferred from the transfer cylinder to the creping fabric; and (6) the fabric may be made to show certain geometric patterns that are pleasing to the eye, which is typically repeated between every two to 50 warp yarns. Suitable commercially available coarse fabrics include a number of fabrics made by Voith Fabrics.

The creping fabric may thus be of the class described in U.S. Pat. No. 5,607,551 to Farrington et al, Cols. 7-8 thereof, as well as the fabrics described in U.S. Pat. No. 4,239,065 to Trokhan and U.S. Pat. No. 3,974,025 to Ayers. Such fabrics may have about 20 to about 60 filaments per inch and are formed from monofilament polymeric fibers having diameters typically ranging from about 0.008 to about 0.025 inches. Both warp and weft monofilaments may, but need not necessarily be of the same diameter.

In some cases the filaments are so woven and complimentarily serpentinely configured in at least the Z-direction (the thickness of the fabric) to provide a first grouping or array of coplanar top-surface-plane crossovers of both sets of filaments; and a predetermined second grouping or array of sub-top-surface crossovers. The arrays are interspersed so that portions of the top-surface-plane crossovers define an array of wicker-basket-like cavities in the top surface of the fabric which cavities are disposed in staggered relation in both the machine direction (MD) and the cross-machine direction (CD), and so that each cavity spans at least one sub-top-surface crossover. The cavities are discretely perimetrically enclosed in the plan view by a picket-like-lineament comprising portions of a plurality of the top-surface plane crossovers. The loop of fabric may comprise heat set monofilaments of thermoplastic material; the top surfaces of the coplanar top-surface-plane crossovers may be monoplanar flat surfaces. Specific embodiments of the invention include satin weaves as well as hybrid weaves of three or greater sheds, and mesh counts of from about 10×10 to about 120×120 filaments per inch (4×4 to about 47×47 per centimeter), although the preferred range of mesh counts is from about 18 by 16 to about 55 by 48 filaments per inch (9×8 to about 22×19 per centimeter).

Instead of an impression fabric, a dryer fabric may be used as the creping fabric if so desired. Suitable fabrics are described in U.S. Pat. No. 5,449,026 (woven style) and U.S. Pat. No. 5,690,149 (stacked MD tape yarn style) to Lee as well as U.S. Pat. No. 4,490,925 to Smith (spiral style).

If a Fourdrinier former or other gap former is used as is shown in FIG. 31, the nascent web may be conditioned with vacuum boxes and a steam shroud until it reaches a solids content suitable for transferring to a dewatering felt. The nascent web may be transferred with vacuum assistance to the felt. In a crescent former, use of vacuum assist is unnecessary as the nascent web is formed between the forming fabric and the felt.

A preferred way of practicing the invention includes can-drying the web while it is in contact with the creping fabric which also serves as the drying fabric. Can drying can be used alone or in combination with impingement air drying, the combination being especially convenient if a two tier drying section layout is available as hereinafter described. Impingement air drying may also be used as the only means of drying the web as it is held in the fabric if so desired or either may be used in combination with can dryers. Suitable rotary impingement air drying equipment is described in U.S. Pat. No. 6,432,267 to Watson and U.S. Pat. No. 6,447,640 to Watson et al. Inasmuch as the process of the invention can readily be practiced on existing equipment with reasonable modifications, any existing flat dryers can be advantageously employed so as to conserve capital as well.

Alternatively, the web may be through-dried after fabric creping as is well known in the art. Representative references include: U