CN113186749A - Soft absorbent sheet and method for producing soft absorbent sheet - Google Patents

Abstract

A soft absorbent sheet and a method of making a soft absorbent sheet. The flexible absorbent sheet has a plurality of extended regions and a connecting region connecting the extended regions. The protruding region includes folded portions that are bent with respect to the machine direction of the absorbent sheet, ends of the bent folded portions are located on opposite sides of the protruding region and apexes of the bent folded portions are located downstream in the machine direction of the absorbent sheet. The absorbent sheet may be formed from a structured fabric having angled warp knuckle threads.

Description

Soft absorbent sheet and method for producing soft absorbent sheet

The present application is a divisional application of chinese patent application No. 201780034686.8 entitled "soft absorbent sheet, structured fabric for making soft absorbent sheet and method of making soft absorbent sheet", international application PCT/US2017/026509 filed 2017, 4, 7, into the chinese national phase.

Priority requirement

This application is based on U.S. non-provisional application No.15/175,949 filed on 7/6/2016 and is also based on U.S. non-provisional application No.15/371,773 filed on 7/12/2016. The priority of the aforementioned application is claimed herein, and the disclosure thereof is incorporated herein by reference.

Technical Field

The present invention relates to paper products such as absorbent sheets. The present invention also relates to methods of making paper products such as absorbent sheets and structured fabrics for use in making paper products such as absorbent sheets.

Background

It is well known in the paper industry to use fabrics to impart structure to paper products. More particularly, it is well known to be able to impart shape to paper products by pressing a malleable web of cellulosic fibers against a fabric and then drying the web. The formed paper product is thus formed to have a molded shape corresponding to the surface of the fabric. The formed paper product thus also has properties resulting from the molded shape, such as a particular thickness and absorbency. As a result, numerous structured fabrics have been developed for use in the papermaking process to provide different shapes and characteristics to the article. Moreover, fabrics can be woven in a nearly unlimited number of patterns for potential applications in the papermaking process.

An important characteristic of many absorbent paper articles is softness (consumer demand), e.g., soft tissue. However, many techniques for increasing the softness of paper products have the effect of reducing other desirable properties of the paper product. For example, calendering a base sheet as part of the process of making a tissue can increase the softness of the formed tissue, but the calendering operation also has the effect of reducing the caliper and absorbency of the tissue. On the other hand, many techniques for improving other important properties of paper products have the effect of reducing the softness of the paper product. For example, the use of wet and dry strength resins in the papermaking process can increase the base strength of the paper product, but wet and dry strength resins reduce the perceived softness of the product.

For these reasons, it is desirable to make softer paper products, such as absorbent sheets. Moreover, it would be desirable to be able to make such softer absorbent sheets by manipulating the structured fabric used in the process of making the absorbent sheet.

Disclosure of Invention

According to one aspect, the present invention provides an absorbent sheet made from cellulosic fibers. The absorbent cellulosic sheet comprises a plurality of extended regions extending from the absorbent sheet, wherein the extended regions comprise folds that are curved relative to the machine direction of the absorbent sheet. The ends of the curved folds are located on opposite sides of the projection area such that one end of each curved fold is located downstream of the other end of the curved fold in the machine direction of the absorbent sheet. The apex of the curved fold is located downstream in the machine direction of the absorbent sheet. Further, the attachment region attaches the extended region of the absorbent sheet.

According to another aspect, the present invention provides an absorbent cellulosic sheet. A plurality of extension regions extend from the absorbent sheet, wherein the extension regions include folds that are curved relative to a machine direction of the absorbent sheet. The ends of the curved fold are on opposite sides of the overhang region, and the curved fold has a radius of curvature of about 0.5mm to about 2.0 mm. Further, the attachment region attaches the extended region of the absorbent sheet.

According to yet another aspect, the present invention provides a papermaking web. The papermaking web comprises a plurality of extension regions extending from the papermaking web, wherein the extension regions comprise folds that are curved relative to the machine direction of the absorbent sheet, the ends of the curved folds being located on opposite sides of the extension regions, and such that one end of each curved fold is located downstream, in the machine direction of the papermaking web, of the other end of the curved fold. The apex of the curved fold is located downstream in the machine direction of the papermaking web. The attachment areas form a network that connects the extended areas of the papermaking web.

According to yet another aspect, the present invention provides a method of making a creped fabric absorbent cellulosic sheet. The method includes compressively dewatering a papermaking furnish to form a web. The method further includes creping the web under pressure in a creping nip between the transfer surface and the structured fabric. The structured fabric comprises knuckles formed on the warp yarns of the structured fabric, wherein the knuckles are positioned along lines that are angled with respect to the machine direction of the fabric, wherein the lines are angled with respect to the machine direction from about 10 ° to about 30 °. Further, the method comprises the step of drying the web to form the absorbent cellulosic sheet.

According to yet another aspect, the present invention provides an absorbent cellulosic sheet comprising a plurality of extension regions extending from the absorbent sheet, wherein the extension regions comprise folds that are curved in the machine direction of the absorbent sheet, the ends of the curved folds being located on opposite sides of the extension regions. The fold normalized curvature ratio of the absorbent sheet is less than about 4. The absorbent sheet further comprises a connection region forming a network connecting the extended regions of the absorbent sheet.

Drawings

FIG. 1 is a schematic illustration of a paper machine configuration that can be used in conjunction with the present invention.

FIG. 2 is a top view of a structured fabric for use in manufacturing paper products according to an embodiment of the present invention.

Fig. 3A to 3F show properties of a structured fabric according to an embodiment of the invention and properties of a comparative structured fabric.

Fig. 4A to 4E are photographs of an absorbent sheet according to an embodiment of the present invention.

Fig. 5 is an annotated version of the photograph shown in fig. 4E.

Fig. 6A and 6B are cross-sectional views of a portion of an absorbent sheet and a portion of a comparative absorbent sheet, respectively, according to an embodiment of the present invention.

Fig. 7A and 7B illustrate laser scans for determining the profile of portions of an absorbent sheet according to embodiments of the present invention.

Fig. 8 shows properties of a structured fabric according to an embodiment of the invention and a comparative structured fabric.

Fig. 9 illustrates properties of a base sheet made using a structured fabric having the properties illustrated in fig. 8.

Fig. 10A to 10D show properties of further structured fabrics according to embodiments of the present invention.

Fig. 11A to 11E are photographs of an absorbent sheet according to an embodiment of the present invention.

Fig. 12A to 12E are photographs of additional absorbent sheets according to embodiments of the present invention.

Fig. 13 shows properties of a structured fabric according to an embodiment of the invention and a comparative structured fabric.

Figure 14 shows a contour measurement along one of the warp yarns of a structured fabric according to an embodiment of the invention.

Fig. 15 is a graph showing the percent fabric wrinkles versus thickness for base sheets made with fabrics according to embodiments of the invention and a comparative fabric.

FIG. 16 is a graph showing fabric wrinkle percentage versus SAT capacity for base sheets made with fabrics in accordance with embodiments of the invention and a comparative fabric.

Fig. 17 is a graph showing fabric wrinkle percentage versus thickness for base sheets made with different furnishes and fabrics according to embodiments of the invention.

FIG. 18 is a graph showing fabric wrinkle percentage versus SAT capacity for base sheets made with different formulations and fabrics according to embodiments of the invention.

FIG. 19 is a graph showing the percent fabric wrinkling versus void volume for base sheets made with fabrics according to the present invention and comparative fabrics.

Fig. 20A and 20B are soft x-ray images of an absorbent sheet according to an embodiment of the invention.

Fig. 21A and 21B are soft x-ray images of an absorbent sheet according to another embodiment of the invention.

Fig. 22A to 22E are photographs of an absorbent sheet according to further embodiments of the present invention.

Fig. 23A and 23B are photographs of an absorbent sheet according to an embodiment of the present invention and a comparative absorbent sheet.

Fig. 24A and 24B are photographs of a section of the absorbent sheet illustrated in fig. 23A and 23B, respectively.

Fig. 25A and 25B illustrate characteristics of additional structured fabrics according to embodiments of the present invention.

FIG. 26 is an embossed detail view of one of the structured fabrics having the characteristics shown in FIG. 25B.

Figures 27A-27C illustrate a fold configuration around a knuckle in a structured fabric according to an embodiment of the present invention and a fold configuration around a knuckle in a comparative structured fabric.

Fig. 28A to 28E are photographs of additional absorbent sheets according to embodiments of the present invention.

FIG. 29 is a photograph of an absorbent sheet having annotation lines for determining aspects of the fabric according to an embodiment of the invention.

Fig. 30A and 30B are photographs of an absorbent sheet according to the present invention and a comparative absorbent sheet, respectively.

Detailed Description

The present invention relates to paper products such as absorbent sheets and methods of making paper products such as absorbent sheets. The absorbent paper article according to the invention has an outstanding combination of properties over other absorbent paper articles known in the art. In some particular embodiments, the absorbent paper articles according to the present disclosure have a combination of properties that are particularly suited for absorbent hand towels, facial tissues, or toilet tissues.

The term "paper product" as used herein includes any product comprising papermaking fibers having cellulose as a major component. This would include, for example, products sold as paper towels, toilet tissue, facial tissue, and the like. Papermaking fibers include virgin pulp or recycled (secondary) cellulosic fibers, or fiber blends including cellulosic fibers. The wood fiber includes: for example, fibers obtained from deciduous and coniferous trees include softwood fibers, such as northern and southern softwood kraft fibers, and hardwood fibers, such as eucalyptus, maple, birch, aspen, and the like. Examples of fibers suitable for making the articles of the present invention include non-wood materials such as cotton fibers or cotton derivatives, abaca, kenaf, indian grass, flax, thatch, straw, jute, bagasse, milkweed floss fibers, and pineapple leaf fibers.

"furnish" or similar term refers to an aqueous mix for making paper products comprising papermaking fibers and optionally including wet strength resins, debonders, and the like. Various ingredients may be used in embodiments of the invention and specific ingredients are disclosed in the examples discussed below. In some embodiments, the furnish is used in accordance with the specifications described in commonly assigned U.S. patent No.8,080,130 (the disclosure of which is incorporated herein by reference). The furnish of this patent includes, among other things, cellulosic long fibers having a coarseness of at least about 15.5mg/100 mm. Examples of ingredients are also recited in the examples discussed below.

As used herein, the initial fiber and liquid mixture that is dried into the final product during the papermaking process will be referred to as the "web" and/or the "nascent web". The dried single-ply product resulting from the papermaking process will be referred to as the "base sheet". Further, the articles of the papermaking process may be referred to as "absorbent sheets". In this regard, the absorbent sheet may be the same as the single base sheet. Alternatively, the absorbent sheet may also comprise a plurality of base sheets, as in a multilayer structure. In addition, the absorbent sheet may have undergone additional processing after being dried in the initial base sheet formation process in order to form a final paper product from the reformed base sheet. "absorbent sheet" includes articles sold as, for example, hand towels.

When describing the present invention herein, the terms "machine direction" (MD) and "cross-machine direction" (CD) will be used according to their well-known meaning in the art. That is, the MD of a fabric or other structure refers to the direction in which the structure moves on a papermaking machine during the papermaking process, and the CD refers to the direction that intersects the MD of the structure. Similarly, when referring to a paper product, the MD of the paper product refers to the direction of the product moving on the papermaking machine during the papermaking process, and the CD of the product refers to the direction that intersects the MD of the product. With respect to the MD of the paper product, "downstream" refers to the area formed prior to the "upstream" area.

FIG. 1 shows an example of a papermaking machine 200 that can be used to manufacture paper products according to the present invention. A detailed description of the construction and operation of paper machine 200 may be found in commonly assigned U.S. patent No.7,494,563 ("the' 563 patent"), the entire contents of which are incorporated herein by reference. Notably, the papermaking process described by the' 563 patent does not use through-air drying (TAD). The following is a brief summary of a process for forming an absorbent sheet using the paper machine 200.

The paper machine 200 is a three fabric loop machine that includes a press section 100 in which a creping operation is performed. Upstream of the pressing section 100 is a forming section 202. The forming section 202 includes a headbox 204 that lays an aqueous furnish on a forming wire 206 supported by rolls 208 and 210 to form an initial aqueous cellulosic web 116. The forming section 202 also includes forming rolls 212 that support the papermaking felt 102 such that the web 116 is formed directly on the felt 102. The felt path 214 extends around the suction turning roll 104 and then to the shoe press section 216 where the web 116 is laid down on the backing roll 108. The web 116 is wet-pressed while the web 116 is transferred to the backing roll 108, which carries the web 116 to the creping nip 120. However, in other embodiments, instead of being transferred onto the support roll 108, the web 116 may be transferred from the felt section 214 onto an endless belt in the dewatering nip, which then carries the web 116 to the creping nip 120. An example of such a configuration can be seen in U.S. patent No.8,871,060, which is incorporated herein by reference in its entirety.

The web 116 is transferred to the structured fabric 112 in the creping nip 120 and then evacuated by the vacuum box 114. After this creping operation, the web 116 is laid down on a Yankee dryer (Yankee dryer)218 in another press nip 217 using creping adhesive. The adhesive is applied to the surface of the yankee dryer 218. The web 116 is dried on a yankee dryer 218, which is a heated cylinder, and then the web 116 is also dried by high jet velocity impingement air in a hood around the yankee dryer 218. As the yankee dryer 218 rotates, the web 116 is stripped from the yankee dryer 218 at location 220. The web 116 may then be subsequently wound on a take-up spool (not shown). In steady state, the reel may operate slower than the yankee dryer 218 in order to further crepe the web. Alternatively, the creping doctor 222 may be used to perform conventional dry creping of the web 116 as it is removed from the yankee dryer 218.

In creping nip 120, web 116 is transferred to the top side of structured fabric 112. A creping nip 120 is defined between the anvil roll 108 and the structured fabric 112, wherein the structured fabric 112 is pressed against the anvil roll 108 by the creping roll 110. Because the web 116 still has a high moisture content when transferred to the structured fabric 112, the web can deform such that portions of the web can be drawn into pockets formed between the yarns making up the structured fabric 112. (the pockets of the structured fabric will be described in detail below). During a particular papermaking process, the structured fabric 112 moves more slowly than the papermaking felt 102. Thus, web 116 is creped as it is transferred to structured fabric 112.

The suction applied from the vacuum box 114 may also assist in drawing the web 116 into pockets in the surface of the structured fabric 112, as will be described below. As it travels along structured fabric 112, fabric 116 reaches a highly consistent state in which most of the moisture has been removed. The web 116 is thus more or less permanently imparted by the structured fabric 112 with a shape that includes a domed area where the web 116 is drawn into pockets of the structured fabric 112.

The base sheet made by the paper machine 200 may also be subjected to additional processing, as is known in the art, in order to convert the base sheet into a particular article. For example, embossing may be performed on a base sheet, and two base sheets may be combined into a multi-layer article. The details of such conversion processes are well known in the art.

Using the process described in the aforementioned' 563 patent, the web 116 is dewatered to a point where the web has a higher consistency when transferred onto the top side of the structured fabric 112 than similar operations in other papermaking processes, for example, as compared to TAD processing. That is, the web 116 is compressively dewatered to have a consistency (i.e., solids content) of from about 30% to about 60% prior to entering the creping nip 120. In the creping nip 120, the web 116 is subjected to a load of about 30 pounds Per Linear Inch (PLI) to about 200 PLI. In addition, there is a speed differential between the anvil roll 108 and the structured fabric 112. This speed difference is called the fabric crepe percentage and can be calculated as follows:

percent of fabric wrinkle ═ S₁/S₂-1

Wherein S is₁Is the speed of the back-up roll 108, and S₂Is the speed of the structured fabric 112. In particular embodiments, the fabric drape percentage or "drape ratio" may be any value from about 3% to about 100%. This combination of web consistency, speed differential occurring at creping nip 120, pressure applied at creping nip 120, and structured fabric 112 and creping nip 120 geometry serves to rearrange the cellulose fibers while web 116 is still sufficientFlexible to withstand structural changes. In particular, without being bound by theory, it is believed that the slower forming surface speed of structured fabric 112 will cause web 116 to be substantially molded into the openings in structured fabric 116 with the fibers being rearranged in proportion to the creping ratio.

Although a particular process has been described in connection with paper machine 200, those skilled in the art will appreciate that the invention disclosed herein is not limited to the paper-making process described above. For example, the present invention may relate to a TAD papermaking process, as opposed to the non-TAD process described above. An example of a TAD papermaking process can be seen in U.S. patent No.8,080,130, which is incorporated herein by reference in its entirety.

Fig. 2 is a detail showing a portion of a web-contacting side of a structured fabric 300 having a construction for forming a paper product, according to an embodiment of the present invention. Structured fabric 300 comprises: warp yarns 302 that extend in the Machine Direction (MD) when the fabric is used in a papermaking process; and weft yarns 304 extending in the cross-machine direction (CD). Warp yarns 302 and weft yarns 304 are woven together to form the body of structured fabric 300. The web-contacting surface of structured fabric 300 is formed by knuckles (two of which are shown in fig. 2 and labeled 306 and 310) that are formed on warp yarns 302, but not on weft yarns 304. It should be noted, however, that although structured fabric 300 is shown in fig. 2 as having knuckles only on warp yarns 302, the present invention is not limited to structured fabrics having only warp knuckles, but also encompasses fabrics having both warp knuckles and weft knuckles. Indeed, fabrics having only warp knuckles and fabrics having both warp and weft knuckles will be described in detail below.

The knuckles 306 and 310 in the structured fabric 300 lie in a plane that constitutes the surface that the web 116 contacts during a papermaking operation. Pockets 308 (one of which is shown in fig. 2 as a dashed outline) are defined in the area between the nodules 306 and 310.

The portions of the web 116 that do not contact the knuckles 306 and 310 are drawn into the pocket 308 as described above. It is the portion of the web 116 that is drawn into the pocket 308 that creates the domed area that occurs in the formed paper product.

Those skilled in the art will appreciate that a significant length of the warp yarn knuckles 306 and 310 is along the MD of the structured fabric 300, and that the fabric 300 is configured such that the long warp yarn knuckles 306 and 310 outline long pockets along the MD. In a particular embodiment of the present invention, the warp yarn knuckles 306 and 310 have a length of about 2mm to about 6 mm. Most structured fabrics known in the art have shorter warp knuckles (even if the fabric has any warp knuckles). As described below, the longer warp knuckles 306 and 310 provide a greater contact area for the web 116 during the papermaking process, and this is believed to be at least in part responsible for the increased softness of the absorbent sheet according to the present invention as compared to an absorbent sheet having shorter conventional warp knuckles.

To quantify the parameters of the structured fabrics described herein, the parameters described in commonly assigned U.S. patent application publication nos. 2014/0133734; 2014/0130996, respectively; 2014/0254885 and 2015/0129145 (hereinafter referred to as "fabric characterization publications"). The entire contents of these fabric characterization publications are incorporated herein by reference. This fabric characterization technique makes it easy to quantify the parameters of the structured fabric, including knuckle length and width, knuckle density, pocket area, pocket density, pocket depth, and pocket volume.

Fig. 3A-3E illustrate some of the characteristics of structured fabrics, labeled as fabrics 1-14, made according to embodiments of the present invention. Fig. 3F also shows the characteristics of a conventional structured fabric, labeled as fabrics 15 and 16. The structured fabric types shown in fig. 3A through 3F can be made by a number of manufacturers, including Albany International of rochester, new hampshire and Voith GmbH of heim, germany. Fabrics 1 through 14 have long warp knuckle fabrics such that the majority of the contact area in fabrics 1 through 14 is from the warp knuckles as opposed to the weft knuckles (even if the fabrics have any weft knuckles). Fabrics 15 and 16 are provided for comparison, and have shorter warp knuckles. All of the characteristics shown in fig. 3A to 3F are determined using the techniques in the fabric characterization publications described above, and in particular using the non-rectangular parallelogram calculation methods set forth in the fabric characterization publications. Note that the indication "N/C" in fig. 3A to 3F means that a specific characteristic is not determined.

The air permeability of the structured fabric is another characteristic that can affect the performance of paper products made with the structured fabric. Air permeability of structured fabrics is measured according to equipment and tests well known in the art, such as those manufactured by Frazier Precision Instrument Company of Black Grosston, Md

Pressure difference air permeability measuring instrument. In general, the long warp knuckle structured fabrics used to produce paper products according to the present invention have a high degree of air permeability. In particular embodiments of the present invention, the long warp yarn knuckle structured fabric has an air permeability of about 450CFM to about 1000 CFM.

Fig. 4A through 4E are photographs of absorbent sheets made from long warp yarn knuckle structured fabrics, such as the long warp yarn knuckle structured fabrics having those features in fig. 3A through 3E. More particularly, fig. 4A-4E illustrate the air side of the absorbent sheet, i.e., the side of the absorbent sheet that contacts the structured fabric during the process of forming the absorbent sheet. Thus, the unique shape imparted to the absorbent sheet by contact with the structured fabric, including the domed regions protruding from the illustrated sides of the absorbent sheet, can be seen in fig. 4A through 4E. Note that the MD of the absorbent sheet is vertically illustrated in these figures.

The specific features of the absorbent sheet 1000 are noted in fig. 5, which is based on a photograph as shown in fig. 4E. The absorbent sheet 1000 includes a plurality of generally rectangular shaped domed regions, some of which are delineated in fig. 5 and labeled 1010, 1020, 1030, 1040, 1050, 1060, 1070, and 1080. As explained above, the domed regions 1010, 1020, 1030, 1040, 1050, 1060, 1070, and 1080 correspond to portions of the web that are drawn into pockets of the structured fabric during the process of forming the absorbent sheet 1000. The connected areas form a network interconnecting the dome areas, some of which are labeled 1015, 1025, and 1035 in fig. 5. The connection regions substantially correspond to portions of the web that are formed in the plane of the knuckles of the structured fabric during the process of forming the absorbent sheet 1000.

Those skilled in the art will immediately recognize several features of the absorbent sheet shown in fig. 4A to 4E and fig. 5 that differ from conventional absorbent sheets. For example, all of the domed regions include a plurality of recessed strips formed into the tops of the domed regions, with the recessed strips extending across the domed regions in the CD of the absorbent sheet. Some of these recessed strips are outlined in fig. 5 and are labeled 1085. Note that almost all dome areas have three such recessed strips, with some of the dome areas having four, five, six, seven or even eight recessed strips. The number of recessed bars may be confirmed using laser scanning profiling techniques (described below). Using this laser scanning profiling technique, it was found that there were an average (mean) of about 6 depressed stripes per dome area in a particular absorbent sheet according to the present invention.

Without being limited by theory, we believe that the depression bars seen in the absorbent sheets shown in fig. 4A-4E and fig. 5 are formed during the manufacturing process described herein when the web is transferred onto a structured fabric having the construction described herein. In particular, when the web is creped with a speed differential as it is transferred to the structured fabric, the web "plows" onto the knuckles of the structured fabric and into the pockets between the knuckles. As a result, folds are created in the structure of the web, particularly in the regions of the web that move into the pockets of the structured fabric. A recessed strip is thus formed between two such folds in the web. Because of the long MD pockets in the long warp knuckle structured fabrics described herein, the plowing/folding action occurs multiple times across the pockets in the structured fabric in the web. Thus, a plurality of depressed strips are formed in each of the domed regions of an absorbent sheet made from the long warp yarn knuckle structured fabric described herein.

Again without being limited by theory, it is believed that the recessed strips in the domed regions may help to increase the softness perceived in the absorbent sheet according to the invention. In particular, the recessed strips provide a smoother, flat plane that is perceived when touching the absorbent sheet, as compared to absorbent sheets having conventional domed regions. Fig. 6A and 6B illustrate differences in the sensing planes, which are views illustrating sections of the absorbent sheet 2000 and the comparative sheet 3000 according to the present invention, respectively. In the absorbent sheet 2000, the domed regions 2010 and 2020 include depressed strips 2080 with ridges formed between the depressed strips 2080 (ridges/depressions corresponding to folds in the web during the papermaking process as described above). Due to the small recessed strip 2080 and the plurality of ridges around the recessed strip 2080, a flat, smooth sensing plane P1 (marked with dashed lines in fig. 6A) is formed. These flat, smooth planes P1 are perceived when touching the absorbent sheet 2000. We further consider that the user is not able to perceive a small discontinuity in the depressed strips 2080 in the surface of the dome areas 2010 and 2020, nor is the user able to perceive the short distance between the dome areas 2010 and 2020. Therefore, the absorbent sheet 2000 is perceived as having a smooth soft surface. On the other hand, the perceived plane P2 has a more rounded shape than the conventional domes 3010 and 3020 in the comparative sheet 3000, as shown in fig. 6B, and the conventional domes 3010 and 3020 are spaced apart. It is believed that because the perceived planes P2 of conventional domes 3010 and 3020 are spaced a significant distance from each other, comparative sheet 3000 is perceived as being less smooth and soft than the perceived plane P1 found in the dome areas 2010 and 2020 with recessed strips 2080.

One skilled in the art will appreciate that not every domed area in the absorbent sheet is the same due to the nature of the papermaking process. Indeed, as mentioned above, the domed regions of an absorbent sheet according to the invention may have a different number of depressed strips. Also, some of the domed regions observed in any particular absorbent sheet of the present invention may not include any depressed strips. However, as long as the majority of the domed regions comprise depressed strips, the overall performance of the absorbent sheet will not be affected. Thus, when we refer to an absorbent sheet having a domed area comprising a plurality of recessed strips, it should be understood that the absorbent sheet may have some domed areas without recessed strips.

The length and depth of the recessed strips in the absorbent sheet and the length of the dome region may be determined from the surface profile of the dome region obtained using laser scanning techniques well known in the art. Fig. 7A and 7B show laser scanning profiles across a dome area in two absorbent sheets according to the present invention. The peaks of the laser scan profile are the areas adjacent to the domes of the recessed strip, while the valleys of the profile represent the bottoms of the recessed strip. By using this laser scanning profile, we find that the recessed strip extends to a depth of about 45 microns to about 160 microns below the top of the adjacent area of the dome region. In a particular embodiment, the recessed strips extend an average (mean) of about 90 microns below the top of the adjoining areas of the dome region. In some embodiments, the domed regions extend a total length of about 2.5mm to about 3mm along the general MD of the absorbent sheet. Those skilled in the art will appreciate that the length of the domed regions along the MD is greater than the length of the domed regions in conventional fabrics and that the long domed regions are at least partially a result of the long MD pockets in the structured fabrics used to create the absorbent sheets as described above. It can also be seen from the laser scanning profile that in an embodiment of the invention, the depressed strips are spaced apart by about 0.5mm along the length of the dome region.

Additional unique features that can be seen in the absorbent sheets shown in fig. 4A-4E and 5 include that the dome areas are bilaterally staggered along the MD such that a substantially continuous line of dome areas that is stepped extends along the MD of the sheet. For example, referring again to fig. 5, the dome area 1010 is located adjacent the dome area 1020, where the two dome areas overlap in the area 1090. Similarly, the dome area 1020 overlaps the dome area 1030 in the area 1095. The bilaterally staggered dome areas 1010, 1020, and 1030 form a continuous line of steps substantially along the MD of the absorbent sheet 1000. The other dome areas form a similar stepped continuous line along the MD.

It is believed that the configuration of elongate, bilaterally staggered domed regions in combination with recessed strips extending across the domed regions results in an absorbent sheet having a more stable configuration. For example, the bilaterally staggered dome areas provide a smooth planar surface on the yankee side of the absorbent sheet, which thus results in better distribution of the pressure points on the absorbent sheet. Note that the yankee side of the absorbent sheet is the side of the absorbent sheet opposite the air side of the absorbent sheet that is drawn into the structured fabric during the papermaking process. In effect, the bilaterally staggered dome areas act like long panels in the MD that lay the absorbent sheet structure flat. This effect, created by the combination of bilaterally staggered domed regions and recessed strips, will result, for example, in better laydown of the web on the surface of the yankee dryer during the papermaking process, resulting in better absorbent sheet formation.

Similar to the continuous line of the dome area, the substantially continuous line of the connection area extends in a stepwise manner along the MD of the absorbent sheet 1000. For example, the connecting region 1015 extending substantially along the CD is continuous with the connecting region 1025 extending substantially along the CD. The connecting region 1025 is also continuous with a connecting region 1035 that extends substantially along the MD. Similarly, the connecting region 1015 is continuous with the connecting region 1025 and the connecting region 1055. In summary, the MD connected areas are substantially longer than the CD connected areas so that a stepped continuous line of connected areas can be seen along the absorbent sheet.

As mentioned above, the dimensions of the domed and connected regions of the absorbent sheet substantially correspond to the pocket and knuckle dimensions in the structured fabric used to make the absorbent sheet. In this regard, it is believed that the relative sizing of the domes and the attachment areas contributes to the softness of the absorbent sheet made of fabric. It is also believed that softness is further enhanced by the substantially continuous lines of domed regions and lines of joined regions. In a particular embodiment of the invention, the distance across the dome area in CD is about 1.0mm, while the distance across the connection area oriented in CD in MD is about 0.5 mm. Furthermore, the overlap/reach area between adjacent dome areas in substantially consecutive rows is about 1.0mm in length along the MD. These dimensions can be determined by visual inspection of the absorbent sheet or by laser scanning profiles as described above. When these dimensions are combined with the other features of the invention described herein, a particularly soft absorbent sheet can be achieved.

To evaluate the performance of an article according to the present invention, an absorbent sheet was made using the fabric 14 shown in fig. 3E using the process described above in a papermaking machine having the general configuration shown in fig. 1. For comparison, an article was made using a shorter warp length knuckle fabric 16 (which is also shown in FIG. 3F) under the same processing conditions. The parameters for manufacturing the base sheet for these tests are shown in table 1.

TABLE 1

The base sheet was converted to make a double-ply taped tissue prototype. Table 2 shows the conversion specification for this test.

TABLE 2

The sheet formed with fabric 14 (i.e., the long warp knuckle fabric) in the test was found to be smoother and softer than the sheet formed with fabric 16 (i.e., the shorter warp knuckle fabric) in the test. Other important properties of the sheet made with fabric 14, such as thickness and volume, have also been found to be comparable to those of the sheet made with fabric 16. Thus, it is apparent that a base sheet made with long warp knuckle fabric 14 could potentially be used to make an absorbent product that is softer than an absorbent product made with shorter warp knuckle fabric 16 without detracting from other important properties of the absorbent product.

As described in the fabric characterization publications above, the Planar Volume Index (PVI) is a useful parameter for characterizing structured fabric features. The PVI of the structured fabric is calculated as the Contact Area Ratio (CAR) multiplied by the Effective Pocket Volume (EPV) multiplied by one hundred, where EPV is the product of the pocket area estimate (PA) and the measured pocket depth. Pocket depth is most accurately calculated by measuring the thickness of a handsheet formed on a structured fabric in the laboratory and then correlating the measured thickness to pocket depth. Also, this handsheet thickness measurement method was used to determine all PVI-related parameters described herein, unless explicitly stated otherwise. Further, the non-rectangular parallelogram PVI is calculated as Contact Area Ratio (CAR) multiplied by Effective Pocket Volume (EPV) multiplied by 100, where CAR and EPV are calculated using a non-rectangular parallelogram unit cell area calculation method. In an embodiment of the present invention, the contact area of the structured long warp knuckle fabric varies between about 25% to about 35% and the pocket depth varies between about 100 microns to about 600 microns, with a corresponding variation in PVI.

Another useful parameter for characterizing structured fabrics in relation to PVI is the planar bulk density index (PVDI) of the structured fabric. The PVDI of a structured fabric is defined as PVI multiplied by pocket density. Note that in the examples of the present invention, the pocket density was about 10cm^-2To about 47cm^-2To change between. Another useful parameter of the structured fabric can be developed by multiplying the PVDI by the length to width ratio of the knuckles of the fabric, thereby providing a PVDI-knuckle ratio (PVDI-KR). For example, the PVDI-KR for the long warp yarn knuckle structured fabric described herein would be the PVDI of the structured fabric multiplied by the ratio of the warp yarn knuckle length in the MD to the warp yarn knuckle width in the CD. As is apparent from the variables used to calculate PVDI and PVDI-KR, these parameters take into account important aspects of the structured fabric (including percent contact area, pocket density, and pocket depth) that affect the shape of the paper product made using the structured fabric, and thus PVDI and PVDI-KR can represent the properties of the paper product, such as softness and absorbency.

PVI, PVDI-KR and other characteristics were determined for a three long warp yarn knuckle structured fabric according to an embodiment of the present invention, the results of which are shown as fabrics 18-20 in figure 8. For comparison, PVI, PVDI-KR and other characteristics were also determined for the shorter warp knuckle structured fabric, as shown for fabric 21 in FIG. 8. Note that the PVDI-KR for the fabrics 18-20 was about 43 to about 50, significantly greater than the PVDI-KR for the fabric 21 of 16.7.

Fig. 18 to 21 are for producing an absorbent sheet, and the characteristics of the absorbent sheet are determined as shown in fig. 9. The characteristics shown in fig. 9 were determined using the same techniques described in the fabric characterization publications discussed above. In this regard, the determination of the interconnection area corresponds to a warp yarn knuckle on the structured fabric and the domed area corresponds to a pocket of the structured fabric. Also, it can again be seen that the sheet made from the long warp knuckle fabrics 18-20 has a plurality of depressed strips in each dome area. On the other hand, the domed regions of the absorbent sheet formed by the shorter warp knuckle fabric 21 have at most one depressed strip and many of the domed regions do not have any depressed strips at all.

Sensory softness was determined for the absorbent sheet shown in fig. 9. Sensory softness is the perceived softness of the paper product as determined by trained evaluators using standardized testing techniques. More particularly, sensory softness is measured by an evaluator having experience in determining softness, wherein the evaluator follows a particular technique to grasp the paper and determine the sensory softness of the paper. The higher the sensory softness number, the higher the sensory softness. In the case of the sheet made of the fabrics 18 to 20, it was found that the absorbent sheet made of the fabrics 18 to 20 was higher by 0.2 to 0.3 softness units than the absorbent sheet made of the fabric 21. This difference is more pronounced. Furthermore, sensory softness was found to correlate with the PVDI-KR of the fabric. That is, the higher the PVDI-KR of the structured fabric, the higher the degree of sensory softness achieved. Thus, we believe that PVDI-KR is a good indicator of the softness that can be achieved in a paper product made using a process of structured fabric, with structured fabrics of higher PVDI-KR yielding softer products.

Figures 10A to 10D illustrate characteristics of additional long warp knuckle fabrics 22 to 41 including PVI, PVDI, and PVDI-KR for each of the fabrics in accordance with various embodiments of the present invention. Note that these structured fabrics have a wider range of properties than the structured fabrics described above. For example, the warp yarn knuckles of fabrics 22-41 have a contact length ranging from about 2.2mm to about 5.6 mm. However, in further embodiments of the present invention, the contact length of the warp yarn knuckles may range from about 2.2mm to about 7.5 mm. Note that in the case of fabrics 22 to 37 and 41, the pocket depth is determined by forming a handsheet on the fabric and then determining the size of the dome portion on the handsheet (the size of the dome portion corresponds to the size of the pocket, as described above). The pocket depths for the webs 38-40 are determined using the techniques described in the web characterization patents described above.

Additional tests were performed to evaluate the performance of the absorbent sheets according to the examples of the present invention. In these tests, fabrics 27 and 38 were used. For these tests, a paper machine having the general configuration shown in fig. 1 was used using the procedure described above. The parameters used to produce the base sheet for these tests are shown in table 3. Note that an indication of the rate of change means that the process variable is changing in different test runs.

TABLE 3

The base sheet in these tests was converted into a single-ply roll without embossing.

Fig. 11A to 11E show photographs of the absorbent sheet made of the fabric 27, and fig. 12A to 12E show photographs of the absorbent sheet made of the fabric 38. As is apparent from fig. 11A to 11E and fig. 12A to 12E, the domed regions of the absorbent sheet include a plurality of recessed strips, similar to the absorbent sheet described above. Also, similar to the absorbent sheets described above, the absorbent sheets made with the webs 27 and 38 include bilaterally staggered dome areas resulting in the formation of a stepped substantially continuous line along the MD of the absorbent sheet and a substantially continuous stepped connecting area between the dome areas.

The contours of the domed regions in the base sheet made from webs 27 and 38 were determined using laser scanning in the same manner as the contours were determined in the absorbent sheet described above. The domed regions in the base sheet made from the fabric 27 were found to have 4 to 7 depressed stripes, with an average (mean) of 5.2 depressed stripes per domed region. The depressed strips of the dome region extend about 132 microns to about 274 microns below the top of the adjoining regions of the dome region, wherein the average (mean) depth is about 190 microns. Further, the dome area extends about 4.5mm in the MD of the base sheet.

The domed regions in the base sheet made from the web 38 have 4 to 8 depressed strips, with each domed region having an average (mean) of 6.29 depressed strips. The depressed strips of domed regions in the base sheet made from web 38 extend about 46 microns to about 159 microns below the top of the adjacent regions of domed regions, with an average (mean) depth of about 88 microns. Further, the dome area extends about 3mm in the MD of the base sheet.

Since the MD-direction dome regions extending in the base sheet made of the fabrics 27 and 38 include a plurality of recessed strips, the base sheet will have advantageous properties derived from the configuration of the dome regions similar to those of the absorbent sheet described above. For example, base sheets made with fabrics 27 and 38 are softer to the touch than base sheets made with fabrics that do not have long warp knuckles.

Other properties of the base sheet made with fabrics 27 and 38 were compared to those of the base sheet made with the shorter knuckle fabric. In particular, the thickness and pocket depth of uncalendered base sheets made with different fabrics were compared. The thickness is measured using standard techniques well known in the art. The base sheet made with fabric 27 was found to vary in thickness from about 80 mils (mils)/8 sheets to about 110 mils/8 sheets, while the base sheet made with fabric 38 varied from about 80 mils/8 sheets to about 90 mils/8 sheets. These two thickness ranges are comparable, if not better, than the thicknesses of about 60 mils/8 sheet to about 93 mils/8 sheet found in base sheets made with shorter warp knuckle fabrics under similar processing conditions.

The depth of the dome area is measured using a topographical profile scan of the air side of the base sheet (i.e., the side of the base sheet that contacts the structured fabric during the papermaking process) to determine the depth of the lowest point of the dome area below the yankee side surface. The depth of the dome areas in the base sheet made using fabric 27 ranged from about 500 microns to about 675 microns, while the depth of the dome areas in the base sheet made using fabric 38 ranged from about 400 microns to about 475 microns. These domed regions are comparable, if not deeper than the depth of the domed regions in a base sheet made from a structured fabric having shorter warp knuckles. The comparability of the depth of the dome area is consistent with the finding that a base sheet made with a long warp structured fabric has a comparable thickness to a base sheet made with a shorter warp structured fabric, since the depth of the dome area is directly related to the thickness of the absorbent sheet.

Additional long warp knuckle fabrics in accordance with the invention have characteristics labeled as fabrics 42 through 44 in figure 13. Figure 13 also shows a conventional fabric 45 that does not include long warp knuckles. An additional characteristic of the fabric 42 is given in figure 14, which shows the profile along one of the warp yarns of the fabric. As can be seen in these figures, fabric 42 includes several significant features in addition to long warp knuckles. One feature is that the pocket is long and deep, as reflected by the PVI-related parameters indicated in fig. 13. Another significant feature of this fabric, as can also be seen in the embossing of the fabric 42 shown in fig. 13, is that the CD yarns are all below the plane of the knuckles in the MD yarns, so that there are no CD knuckles at the top surface of the fabric. Because there are no CD knuckles, there is a gentle slope along the z-direction relative to the warp yarns, the details of which are shown in the profile scan of fig. 14. As shown in this figure, the warp yarns have a slope of about 200 μm/mm from the lowest point where the warp yarns pass under the CD yarns to the top of the adjacent warp yarn knuckles. More generally, the warp yarns are angled at about 11 degrees relative to the plane along which the fabric 42 moves during the creping operation. It is believed that this gentle slope of the warp yarns allows the fibers in the web to be pressed until the fabric 42 only slightly accumulates on the inclined portions of the warp yarns before some of the fibers slide over the tops of adjacent knuckles. The gradual slope of the warp yarns in fabric 42 thus produces less abrupt stops for the web fibers and less fiber densification than other fabrics in which the warp yarns have a steeper slope that is contacted by the web.

Both fabrics 42 and 43 have relatively high PVDI-KR values, and these values, along with the PVDI-KR values of the other structured fabrics described herein, represent a range of PVDI-KR values that can be found in embodiments of the present invention. Furthermore, structured fabrics having even higher PVDI-KR values, such as structured fabrics having PVDI-KR values up to about 250, may also be used.

To evaluate the performance of the fabric 42, a series of tests were performed with the fabric and the fabric 45 for comparison. In these tests, a papermaking machine having the general configuration shown in fig. 1 was used to form an absorbent tissue base sheet. The non-TAD process outlined above (and specifically described in the aforementioned' 563 patent) is used, wherein the web is dewatered to the point where it has a consistency of about 40% to about 43% when transferred onto the top side of the structured fabric (i.e., fabric 42 or 45) at the creping nip. Table 4 shows other specific parameters of these tests.

TABLE 4

Tables 5 to 9 show the properties of the base sheets made with fabrics 42 and 45 in these tests. Test protocols for determining the performance indicated in tables 5 to 9 may be found in U.S. Pat. Nos. 7,399,378 and 8,409,404, which are incorporated herein by reference in their entirety. The indication "N/C" indicates that performance was not calculated for a particular test.

The test results shown in tables 5 to 9 indicate that the fabric 42 can be used to make a base sheet having an outstanding combination of properties, in particular a combination of caliper and absorbency. Without being bound by theory, we believe that these results arise in part from the thickness and pocket configuration in the fabric 42. In particular, the construction of the fabric 42 provides an extremely efficient creping operation due to the aspect ratio of the pockets (i.e., the ratio of the length of the pockets in the MD to the width of the pockets in the CD), the pockets being deep and the pockets forming long, nearly continuous lines in the MD. These properties of the pockets allow for greater fiber "mobility", which is a condition where the wet-compressed web is subjected to mechanical forces that produce localized basis weight movement. Furthermore, during the creping process, the cellulosic fibers in the web are subjected to various local forces (e.g., pushing forces, pulling forces, bending forces, delaminating forces) and then become more separated from one another. In other words, the fibers debond and result in a lower modulus article. Thus, the web has better vacuum "plasticity" which results in greater thickness and a more open structure that provides greater absorbency.

The fiber mobility provided by the pocket configuration of the fabric 42 can be seen in the results shown in fig. 15 and 16. These figures compare the thickness, SAT capacity and void volume at various wrinkle levels used in the tests. Fig. 15 and 16 show that the caliper and SAT capacity increase with increasing fabric wrinkle level even in tests using fabric 42 without vacuum molding. Because there is no vacuum molding, the increase in caliper and SAT capacity is directly related to the fiber mobility in the fabric 42. Fig. 15 and 16 also demonstrate that higher caliper and SAT capacity is achieved with the fabric 42 — the caliper and SAT capacity of the base sheet made with the fabric 42 is much higher than the caliper and SAT capacity of the base sheet made with the fabric 45 at each pleat level in the test using vacuum molding.

The fiber plasticity provided by the fabric 42 can also be seen in the results shown in fig. 15 and 16. In particular, the difference between the caliper and SAT capacity in the test without vacuum molding and the caliper and SAT capacity in the test with vacuum molding indicates that the fibers in the web are highly plasticized on the fabric 42. As described below, vacuum molding draws fibers in the web area formed in the pockets of the fabric 42. Greater fiber mobility means that the fibers are pulled out significantly during the molding operation, which results in an increase in the thickness and SAT capacity of the formed article.

Fig. 19 also demonstrates that greater fiber mobility is achieved with the fabric 42 by comparing the void volume of the base sheet from the test at the fabric pleat level. The absorbency of the sheet is directly related to the void volume, which is essentially a measure of the space between the cellulose fibers. Void volume was measured by the procedure set forth in the above-mentioned U.S. patent No.7,399.378. As shown in fig. 19, in the test using the fabric 42 without vacuum molding, the void volume increased as the fabric wrinkles increased. This indicates that the cellulose fibers are further apart from each other at each fabric crepe level (i.e., debonding, which results in a lower modulus) in order to create additional vacuum volume. Fig. 19 further demonstrates that, when vacuum molding is used, at each fabric wrinkle level, fabric 42 produces a base sheet having a vacuum volume greater than that of conventional fabric 45.

Fiber activity with the use of the fabric 42 can also be seen in fig. 20A, 20B, 21A and 21B, which are soft x-ray images of a base sheet made using the fabric 42. As understood by those skilled in the art, soft x-ray imaging is a high resolution technique that can be used to measure lump homogeneity in paper. The base sheet in fig. 20A and 20B made 8% fabric gathers, while the base sheet in fig. 21A and 21B made 25% fabric gathers. Fig. 20A and 21A show fiber movement at a more "macroscopic" level, with the images showing an area of 26.5mm x 21.2 mm. Higher fabric wrinkles (fig. 21A) can see less lumpy wavy patterns (corresponding to brighter areas in the image), but lower fabric wrinkles (fig. 20A) do not easily see less lumpy areas. Fig. 20B and 21B show fiber movement at a more "microscopic" level, with the images showing an area of 13.2 x 10.6 mm. In the case of the higher fabric crepe (fig. 21B) the cellulose fibers can be clearly seen because they are spaced further apart and pulled away from each other than in the case of the lower fabric crepe (fig. 20B). In summary, the soft x-ray images also demonstrate that the fabric 42 provides greater fiber mobility, with higher local mass motion seen at higher fabric wrinkle levels than at lower fabric wrinkle levels.

Fig. 17 and 18 and fig. 19 show the results of the tests in terms of ingredients. In particular, these figures show that fabric 42 can produce comparable amounts of caliper, SAT capacity, and void volume when using non-premium furnishes, as well as using premium furnishes. This is advantageous because it demonstrates that fabric 42 can achieve outstanding results with low cost, non-premium furnishes.

Because fabric 42 has very long warp knuckles, as in the other very long warp knuckle fabrics discussed above, an article made with fabric 42 may have a plurality of depressed strips extending in the CD direction. The recessed strips also result in folds in the area of the web moving into the pockets of the structured fabric. In the case of fabric 42, it is believed that the length of the knuckles and the aspect ratio across the length of the pockets further enhances the formation of the fold/recess strips. This is because the web is semi-constrained to the long warp knuckles while having greater mobility within the pockets of the fabric 42. The result is that the web can buckle or fold at multiple locations along each pocket, which in turn results in a CD debossed strip seen in the article.

The recessed strips formed in the absorbent sheet made of the web 42 can be seen in fig. 22A to 22E. These figures are images of the air side of an article made with fabric 42 at different levels of fabric wrinkling, but without vacuum molding. MD is the vertical direction along all these figures. Note that instead of having sharply defined domed regions as in the above-described articles, the articles in fig. 22A-22E are characterized by parallel, nearly continuous lines of extended regions that extend substantially in the MD, with each extended region including a plurality of recessed strips that extend across the extended regions along substantially the CD of the absorbent sheet. These extended areas correspond to pocket lines extending along the MD of the fabric 42. The connecting regions are located between the extended regions, which also extend substantially along the MD. The connecting areas correspond to the long warp knuckles of the fabric 42.

The article in fig. 22A made 25% fabric wrinkles. In this article, the recessed strips are very unique. This pattern of depressed stripes is believed to be a result of the fiber network on the fabric 42 being subjected to a wide range of forces during the creping process, including in-plane compression, tension, bending and buckling. All of these forces will contribute to fiber mobility and fiber plasticity as described above. Moreover, due to the nearly continuous nature of the extended regions extending in the MD, fiber mobility and fiber plasticity can be enhanced in a nearly continuous manner in the MD.

Fig. 22B-22E illustrate a configuration of an article having less fabric wrinkling as compared to the article illustrated in fig. 22A. In fig. 22B, the fabric wrinkle level used to form the article shown is 15%, in fig. 22C the fabric wrinkle level is 10%, in fig. 22D the fabric wrinkle level is 8%, and in fig. 22E the fabric wrinkle level is 3%. As will be expected, it can be seen that the amplitude of the folds/debossments decreases as the fabric wrinkle level decreases. It should be noted, however, that the frequency of the recessed strips remains approximately the same at all fabric fold levels. This means that regardless of the fabric wrinkle level used, the web buckles/folds in the same position relative to the knuckles and pockets in the fabric 42. Thus, beneficial properties resulting from the formation of folds/debossments can be found even at lower fabric wrinkle levels.

In summary, fig. 22A through 22E show that pocket high aspect ratios of the fabric 42 have the ability to uniformly apply loose energy to the web, such that fiber mobility and fiber plasticity are promoted over a wide range of fabric crepe. Also, such fiber mobility and fiber plasticity are very important factors in outstanding properties found in absorbent sheets made with the fabric 42, such as thickness and SAT capacity.

Fig. 23A-24B are scanning electron microscope images of the air side of an article made with fabric 42 (fig. 23A and 24A) and a comparative article made with fabric 45 (fig. 23B and 24B). In these cases, the article was made with 30% fabric wrinkles and molded using maximum vacuum. The central area of the images in fig. 23A and 23B shows the area formed in the pocket of the respective fabrics, and the area surrounding the central area thereof corresponds to the area formed on the knuckle of the respective fabrics. The cross-sections shown in fig. 24A and 24B extend substantially along the MD, with extended overhanging regions of the fabric 42 visible in fig. 24A and multiple domes (formed in multiple pockets) visible in the fabric 45 article shown in fig. 24B. It can be seen very clearly that the fibres in the article made with the fabric 42 are packed with a much less degree of densification than the cellulose fibres in the article made with the fabric 45. That is, the central domed region in the fabric 45 article is highly densified, if not more densified than the connecting region surrounding the pocket region in the fabric 42 article. In addition, fig. 24A and 24B show that the fibers in the fabric 42 article are much looser, i.e., less dense, than the fabric 45 article, with the unique fibers jumping out of the fabric 42 article in fig. 24A. Fig. 23A-24B thus also confirm that the fabric 42 provides a greater amount of fiber mobility and fiber plasticity during the creping process, which in turn results in areas of significantly reduced density in the absorbent sheet product made with the fabric. This reduced density region provides greater absorbency in the article. In addition, the reduced density areas provide greater caliper as the sheet becomes more "lofty" in the reduced density areas. Moreover, the lofty, less dense areas will result in the article feeling softer to the touch.

Additional tests were performed using web 42 to evaluate converted tissue articles according to embodiments of the present invention. For these tests, the same conditions as the tests described in connection with tables 4 and 5 were used. The base sheet was then converted into a two-ply tissue. Table 10 shows the conversion specifications for these tests. The properties of the articles made in these tests are shown in tables 11 to 13.

Watch 10

It should be noted that test 22 formed only one layer of the article, but other transformations were performed in the same manner as the other tests.

The results shown in tables 11 to 13 demonstrate that excellent performance can be achieved using long warp knuckle fabrics according to the present invention. For example, the final article made with fabric 42 has a higher caliper and higher SAT capacity than the comparative article made with fabric 45. Furthermore, the results in tables 11-13 demonstrate that comparable articles can be made with fabric 42, regardless of whether a premium furnish or a non-premium furnish is used.

Performance based on articles manufactured in the tests described hereinIt should be clear that the long warp yarn knuckle structured fabrics described herein can be used in methods that provide articles with a combination of outstanding properties. For example, the long warp yarn knuckle structured fabric described herein can be used in conjunction with the non-TAD process outlined above and specifically set forth in the above-referenced' 563 patent to form a fabric having (wherein the papermaking furnish is compressively dewatered prior to creping) at least about 9.5g/g and at least about 500g/m²The SAT capacity absorbent sheet of (1). Further, the absorbent sheet can be formed in this process while using a creping ratio of less than about 25%. Even further, the method and long warp knuckle structured fabric can be used to produce an absorbent sheet having at least about 10.0g/g and at least about 500g/m²Has a basis weight of less than about 30 lbs/ream (ream) and has a thickness of 220 mils/8 sheets. We believe that this type of process has never before produced such absorbent sheets.

Additional absorbent tissue base sheets were also made in the tests using the fabrics 42 and 45. These tests were conducted on a paper machine having the configuration shown in FIG. 1, using the non-TAD process outlined above (and described in detail in the aforementioned' 563 patent), and the parameters of these tests were the same as shown and described in Table 4 above. The results of these tests are shown in tables 14 to 16 below.

As with the previous tests, the absorbent sheets made using the fabric 42 in the tests shown in tables 14 to 16 have an outstanding combination of properties, in particular outstanding caliper and absorbency.

Fig. 25A and 25B may represent characteristics of additional structured fabrics according to embodiments of the present invention. Like the fabrics discussed above, the fabrics 46-52 shown in FIGS. 25A and 25B have long warp knuckles in the range of about 2.4mm to about 5.7 mm. Also as with the fabrics discussed above, the fabrics 46 through 52 have high PVDI-KR values, ranging from about 41 to about 123.

Fabrics 46 through 52 illustrate yet another aspect of the present invention relating to the positioning of knuckles on the web-contacting surface of a structured fabric. As can be seen from the imprinted photographs, the knuckles in the fabrics 46-52 are positioned relative to each other such that a straight line can be drawn through the centers of the plurality of knuckles. One such line L1 is shown in fig. 26, which is a detailed view of the embossing of the web 50. The angle α of line L1 with respect to line MDL extending along the MD of the fabric is about 15 °. In other structured fabrics according to embodiments of the present invention, the warp yarn knuckles may be at an angle of about 10 ° to about 30 ° with respect to the MD line, and in more specific embodiments, the warp yarn knuckles may be at an angle of about 10 ° to about 20 ° with respect to the MD line. The angles of the warp knuckle lines for the fabrics 46-52 are given in figures 25A and 25B. It should also be noted that some of these other structured fabrics described herein include similar angled warp yarn knuckles, including, for example, fabric 42 shown in FIG. 13.

We have found that paper products made with structured fabrics having angled warp knuckle lines (e.g., those shown in fabrics 42 and 46-52) have superior performance. Without being bound by theory, we believe that these superior properties result from the large amount of fiber mobility provided by the structured fabric with angled warp knuckle threads.

This fiber mobility of the structured fabric with angled warp knuckle lines is shown in fig. 27A and can be compared to other structured fabric configurations as shown in fig. 27B and 27C. The fibers are moved to the fold structures 4002 and 5002 shown in these figures, for example, during a creping operation, such as when the web 116 is transferred from the anvil roll 108 to the structured fabric 112 in the creping nip 120, as shown in fig. 1 and described above. Fig. 27B shows an example of MD knuckles 4000 in a structured fabric. During creping, the cellulosic fibers of the web are stacked in the densified fold 4002 against the edge 4004 of the knuckles 4000, forming localized densified regions 4006 adjacent to the knuckles 4000. This localized densification of the fibers may also occur at other MD knuckles in the structured fabric. Fig. 27C shows how CD knuckles 5000 of the structured fabric also have locally densified regions due to the layering of web folds 5002 on the edges 5004 of the knuckles 5000.

In contrast, the knuckles 6000 in the angled warp yarns shown in fig. 27A produce a fold structure that is very different from the fold structures shown in fig. 27B and 27C. With angled warp yarn knuckle lines, a strain field is created by a combination of the movement of the knuckles 6000 and the adhesion of the web 116 to the support roll 108. The strain field is localized in the pocket regions between the nodules 6000. Due to the creping ratio, the strain field causes a speed difference during transfer from the web to the structured fabric from the transfer surface: in the creping nip, a portion of the web is pulled in the downstream direction by the faster moving transfer surface, while the other portion of the web is effectively retained by the slower moving knuckles 6000. During the creping operation, the web is, for example, 40% to 45% solids, which means that the web will behave in a substantially viscous manner. Thus, the fibers of the web in the strain field may always be repositioned relative to each other — after exiting the creping operation, the fibers do not return to their relative positions prior to entering the strain field. This fiber mobility in the strain field increases the fiber-to-fiber distance, weakening the bonds between fibers, making it easier to mold the web. As a result, the fibers are distributed in the pockets between the nodes 6000 in curved folds. The curved fold is an indication that fibre activity has occurred in the pocket. Also, as shown by the results of the above tests, when fiber movement leading to curved folds is achieved, absorbency and softness are significantly improved, as evidenced, for example, by the SAT and void volume of the absorbent sheet made from the web 42.

The curved fold is shaped such that the apex 6003 of the curved fold is located downstream in the MD and the end of the curved fold is offset in the MD, with the end 6007 of the curved fold being located upstream in the MD relative to the other end 6009 of the curved fold. In contrast, the curved folds shown in fig. 27A are significantly less dense than the fiber lay-ups formed at the edges of the MD knuckles and CD knuckles in the structured fabrics without angled warp yarns shown in fig. 27B and 27C. Also, it is believed that the absorbent sheet has greatly improved softness and absorbency due to the reduced densification of the curved folds, which in turn is related to the fiber mobility discussed above.

The shape of the curved fold is also related to the distance D1 between the nodules 6000. As will be appreciated by those skilled in the art, if the nodes 6000 are too close together, there will not be enough room in the pockets between the nodes 6000 for the fibers to move into the less dense curved folds. On the other hand, if the knuckles are too far apart, many of the fibers will not be subjected to the strain fields of the faster moving transfer surface and the slower moving knuckles, and therefore fewer, less pronounced curved folds may form in the web and the absorbent sheet formed therefrom. In view of these factors, in embodiments of the invention, the distance D1 between the centers of two adjacent knuckles 6000 in different warp yarn knuckle lines may be about 1.5mm to about 4.0 mm. In a particular embodiment, the distance D1 is about 2.0 mm. In the case of a distance of 2.0mm between the nodes 6000, there is a space of about 1.5mm in the pocket region between two adjacent nodes 6000.

Fig. 28A through 28E are photographs of an absorbent base sheet made with a structured fabric having angled warp knuckle threads, wherein the papermaking machine has the general configuration shown in fig. 1, uses the non-TAD process outlined above (and specifically set forth in the aforementioned' 563 patent), and has the parameters shown in table 4 above. Different creping ratios (i.e., fabric crepe%) and different mold box vacuum were used for each base sheet shown in fig. 28A through 28E. In particular, the base sheet in fig. 28A was made with a creping ratio of 25% and a die box vacuum of 2in.hg, the base sheet in fig. 28B was made with a creping ratio of 25% and a die box vacuum of 8in.hg, the base sheet in fig. 28C was made with a creping ratio of 30% and a die box vacuum of 10in.hg, and the base sheet in fig. 28D was made with a creping ratio of 25% and a die box vacuum of 8 in.hg. The base sheet shown in FIG. 28E was made with a creping ratio of 20% but without the mold box vacuum. Note that since vacuum molding is not used in the manufacture of the base sheet shown in fig. 28E, the base sheet also exhibits a web structure after the creping operation in the paper-making process. That is, the web in the papermaking process will have a substantially curved fold configuration identical to the base sheet product shown in fig. 28E. It should also be noted that in other embodiments of the present invention, different creping ratios may be used in conjunction with structured fabrics having angled warp knuckle lines. In some embodiments, the creping ratios used with fabrics having angled warp knuckle threads are from about 3% to about 100%, in more particular embodiments from about 3% to about 50%, and in even more particular embodiments from about 5% to 30%.

The curved folds can be clearly seen in the protruding areas of the base sheet shown in fig. 28A to 28E. In these figures, the MD of the paper is in a vertical (i.e., up-down) direction, with the upstream side of the sheet at the top of the photograph and the downstream side of the sheet at the bottom of the figure. In fig. 28A, some of the curved folds have been marked with dashed lines. The ends of the curved shape are asymmetric due to the angled warp yarn knuckles: one end of the curved fold is located further downstream than the other end of the curved fold. The curved fold extends between the two ends to an apex located at a further downstream portion of the curved fold. And, the ends of the curved folds are positioned near the connection areas corresponding to the knuckles of the fabric.

The curved folded portion can also be seen in the absorbent sheet shown in fig. 22A and 22E. As previously mentioned, the absorbent sheet in these figures is formed using a fabric 42 comprising angled warp yarn knot lines. In addition, the curved folds can also be seen in the soft x-ray images shown in fig. 21A and 21B.

Fig. 28A to 28E also show that a plurality of curved folds are formed in each protruding region. The multiple curved folds are the result of the elongated length in the MD direction of the pocket in which the domed area is formed, and therefore the curved folds are also related to the length of the warp knuckles. When the web is transferred to a structured fabric during the manufacture of absorbent sheets using a creping operation (as described above), a plurality of folds are created in the web structure within the pockets. Therefore, in the same manner as in the above-described embodiment in which the plurality of concave stripes are formed in each protruding region of the absorbent sheet, the plurality of concave stripes are formed between the plurality of curved folded portions in the protruding regions of the absorbent sheet shown in fig. 28A to 28E. Such recessed strips can be seen between curved folds in the absorbent sheet shown in fig. 28A to 28E.

The connection region connecting the protruding regions with the curved folds can also be seen in the photographs of the base sheet shown in fig. 28A to 28E. These connection regions correspond to a large extent to the sheet portions formed on the knuckles of the fabrics used to make these sheets, and to the sheet portions formed in the areas adjacent to the knuckles and pockets. One aspect of the attachment area of the base sheet according to the invention is highlighted in fig. 28A, where the area adjacent to the upstream end of the protruding area is encircled. It can be seen that the sheet has folds in these rounded areas. As mentioned above, these folds are due to the z-direction skew in the warp yarns and the lack of CD knuckles. In particular, during the papermaking process, the web may slide into these portions of the connecting zone, creating folds. The folds in the attachment zones serve to further reduce the degree of densification of the fibers and thereby further improve the performance of the absorbent sheet.

The radius of curvature of the curved fold may be calculated based on photographs, such as those shown in fig. 28A to 28E. In particular, a circle may be drawn such that the arc of the circle is aligned with the curved fold. As is evident from the photographs shown in fig. 28A to 28E, the leading (downstream) edge of the curved fold is most prominent and, therefore, it is easiest to draw a circle so that the arc of a circle is aligned with the leading edge. Fig. 29 is the same photograph as fig. 28A, additionally showing a circle having a circular arc aligned with the leading edge of some of the curved folds. From these circles, and using the scale of the photograph, the average radius of curvature of the curved fold can be easily calculated. In an embodiment of the present invention, we have found that the radius of curvature of the curved fold averages about 1.2mm, with a radius ranging from about 0.5mm to about 2.0 mm.

As mentioned above, the curved fold is formed due to the local strain field that is generated when performing a creping operation with a fabric according to the invention having angled warp knuckles. For a given absorbent sheet, the fold normalized curvature ratio may be calculated as the radius of curvature of the curved fold divided by the radius of the circle drawn in the extended region. The lower the fold normalized curvature ratio, the more effectively the strain field bends the folds. Also, we believe that by forming the fold curvature more effectively, the absorbency and softness of the absorbent sheet are improved.

An example of calculating the fold normalized curvature ratio of the absorbent sheet will now be described with reference to fig. 30A and 30B. An absorbent sheet according to the present invention is shown in fig. 30A, and a comparative commercially available absorbent sheet is shown in fig. 30B. In fig. 30A, a circular arc is drawn to match one of the curved folds. From this arc and other similarly drawn arcs, the average radius of curvature of the curved fold may be calculated, as described above. Similarly, a circular arc is plotted in fig. 30B to match the slight curvature that can be seen in the fold structure, and thus the average radius of the absorbent sheet can be calculated from the circular arc and similar circular arcs. The complete circle in fig. 30A and 30B has been drawn within the extended region, with the opposite points of the circle aligned with the points on the opposite side of the extended region where the curved fold structure occurs. Circles are the largest dimension that can fit the extended regions, and thus the radius of these circles is half the distance across the extended regions in the CD of the absorbent sheet. The fold normalized curvature ratio of the absorbent sheet shown in fig. 30A and 30B may then be calculated as the ratio of the calculated average radius of curvature to the radius of curvature of the maximum circular dimension of the extended region. For the absorbent sheet according to the present invention shown in fig. 30A, the calculated average radius of curvature was about 1.2mm and the fold normalized curvature ratio was about 1.9. On the other hand, for the comparative absorbent sheet shown in fig. 30B, the calculated average radius of curvature is about 4.55 and the fold normalized curvature ratio is about 4.5. It is therefore apparent that the absorbent sheet according to the present invention has a greater curvature in its fold structure than the comparative sheet, and the curvature is closer to the maximum curvature possible in the formation of the absorbent sheet.

In embodiments of the invention, the fold normalized curvature ratio is less than about 4, more particularly, the fold normalized curvature ratio is about 0.5 to about 4. In a more particular embodiment, the fold normalized curvature ratio is from about 1 to about 3. As evidenced by the absorbent sheet shown in fig. 30A, embodiments of the present invention can have a specific fold normalized curvature ratio of about 2. When the fold normalized curvature ratio is within these ranges, we believe that a significant amount of fiber mobility has occurred for a given fabric. Thus, as mentioned above, the fibre mobility results in a paper product with better properties, for example with good absorbency.

Although the present invention has been described in certain specific exemplary embodiments, many other modifications and variations will be apparent to those skilled in the art in light of the present disclosure. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described. The present exemplary embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and the scope of the invention is to be determined by any claims that may be supported by the application and their equivalents rather than by the foregoing description.

Industrial applicability

The present invention can be used to produce a desired paper product, such as a hand towel or toilet tissue. Thus, the present invention is applicable to the paper product industry.

Claims (7)

1. A method of making a creped fabric absorbent cellulosic sheet, the method comprising:

subjecting a papermaking furnish to compressive dewatering to form a web;

creping the web under pressure in a creping nip between a transfer surface and a structured fabric, the structured fabric comprising knuckles formed on warp yarns of the structured fabric, wherein the knuckles are positioned along lines that are angled with respect to the machine direction of the structured fabric, wherein the lines are angled from 10 ° to 30 ° with respect to the machine direction; and

drying the web to form the absorbent cellulosic sheet.

2. The method of claim 1, wherein a creping ratio is defined by the speed of the transfer surface relative to the speed of the structured fabric, the creping ratio being from 3% to 25%.

3. The method of claim 1, wherein the angle of the line relative to the machine direction is about 15 °.

4. The method of claim 1, wherein the warp yarns of the structured fabric are inclined downwardly at a location adjacent the downstream end of the knuckle and the web is folded at a location adjacent the downwardly inclined portion of the warp yarns.

5. The method of claim 1, wherein the nodule has a length in the machine direction of 2.4mm to 5.7 mm.

6. The method of claim 1, wherein the planar bulk density index of the structured fabric multiplied by the aspect ratio of the knuckles formed on the warp yarns is from 41 to 123.

7. An absorbent cellulosic sheet made by the method of claim 1, comprising:

a plurality of projecting regions projecting from the absorbent cellulosic sheet, wherein the projecting regions are formed in curved folded portions that are curved with respect to a machine direction of the absorbent cellulosic sheet, ends of the curved folded portions are located on opposite sides of the projecting regions, and apexes of the curved folded portions are located downstream in the machine direction of the absorbent cellulosic sheet.

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