Patent Grant
10934665
Our invention relates to paper products such as absorbent sheets. Our invention also relates to methods of making paper products such as absorbent sheets, as well as to structuring fabrics for making paper products such as absorbent sheets.
The use of fabrics is well known in the papermaking industry for imparting structure to paper products. More specifically, it is well known that a shape can be provided to paper products by pressing a malleable web of cellulosic fibers against a fabric and then subsequently drying the web. The resulting paper products are thereby formed with a molded shape corresponding to the surface of the fabric. The resulting paper products also thereby have characteristics resulting from the molded shape, such as a particular caliper and absorbency. As such, a myriad of structuring fabrics has been developed for use in papermaking processes to provide products with different shapes and characteristics. And, fabrics can be woven into a near limitless number of patterns for potential use in papermaking processes.
One important characteristic of many absorbent paper products is softness—consumers want, for example, soft paper towels. Many techniques for increasing the softness of paper products, however, have the effect of reducing other desirable properties of the paper products. For example, calendering basesheets as part of a process for producing paper towels can increase the softness of the resulting paper towels, but calendering also has the effect of reducing the caliper and absorbency of the paper towels. On the other hand, many techniques for improving other important properties of paper products have the effect of reducing the softness of the paper products. For example, using wet and dry strength resins in a papermaking process can improve the underlying strength of paper products, but wet and dry strength resins also reduce the perceived softness of the products.
For these reasons, it is desirable to make softer paper products, such as absorbent sheets. And, it is desirable to be able to make such softer absorbent sheets through manipulation of a structuring fabric used in the process of making the absorbent sheets.
According to one aspect, our invention provides an absorbent sheet of cellulosic fibers. The absorbent cellulosic sheet includes a plurality of projected regions projecting from the absorbent sheet, wherein the projected regions include folds that are curved relative to the machine direction of the absorbent sheet. Ends of the curved folds are on opposite sides of the projected regions and such that one of the ends of each of the curved folds is positioned downstream from the other end of the curved folds in the machine direction of the absorbent sheet. Apexes of the curved folds are positioned downstream in the machine direction of the absorbent sheet. Further, connecting regions connecting the projected regions of the absorbent sheet.
According to another aspect, our invention provides an absorbent cellulosic sheet. A plurality of projected regions project from the absorbent sheet, wherein the projected regions include folds that are curved relative to the machine direction of the absorbent sheet. Ends of the curved folds are on opposite sides of the projected regions, and the curved folds have a radius of curvature of about 0.5 mm to about 2.0 mm. Further, connecting regions connecting the projected regions of the absorbent sheet.
According to a further aspect, our invention provides a papermaking web. The papermaking web comprises a plurality of projected regions projecting from the papermaking web, wherein the projected regions include folds that are curved relative to a machine direction of the absorbent sheet, with ends of the curved folds being on opposite sides of the projected regions and such that one of the ends of each of the curved folds is positioned downstream from the other end of the curved folds in the machine direction of the papermaking web. Apexes of the curved folds are positioned downstream in the machine direction of the papermaking web. Connecting regions form a network connecting the projected regions of the papermaking web.
According to yet another aspect, our invention provides a method of making a fabric-creped absorbent cellulosic sheet. The method includes compactively dewatering a papermaking furnish to form a web. The method also includes creping the web under pressure in a creping nip between a transfer surface and a structuring fabric. The structuring fabric includes knuckles formed on warp yarns of the structuring fabric, with the knuckles being positioned along lines that are angled relative to the machine direction of the fabric, wherein the angle of lines relative to the machine direction is between about 10° and about 30°. Further, the method includes a step of drying the web to form the absorbent cellulosic sheet.
According to yet another aspect, our invention provides an absorbent cellulosic sheet that includes a plurality of projected regions projecting from the absorbent sheet, with the projected regions including folds that are curved in the machine direction of the absorbent sheet, and with ends of the curved folds being on opposite sides of the projected regions. The absorbent sheet has a normalized fold curvature ratio that is less than about 4. The absorbent sheet also includes connecting regions forming a network connecting the projected regions of the absorbent sheet.
Our invention relates to paper products such as absorbent sheets and methods of making paper products such as absorbent sheets. Absorbent paper products according to our invention have outstanding combinations of properties that are superior to other absorbent paper products that are known in the art. In some specific embodiments, the absorbent paper products according to our invention have combinations of properties particularly well suited for absorbent hand towels, facial tissues, or toilet paper.
The term “paper product,” as used herein, encompasses any product incorporating papermaking fibers having cellulose as a major constituent. This would include, for example, products marketed as paper towels, toilet paper, facial tissue, etc. Papermaking fibers include virgin pulps or recycled (secondary) cellulosic fibers, or fiber mixes comprising cellulosic fibers. Wood fibers include, for example, those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers, and hardwood fibers, such as eucalyptus, maple, birch, aspen, or the like. Examples of fibers suitable for making the products of our invention include non-wood 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.
“Furnishes” and like terminology refers to aqueous compositions including papermaking fibers, and, optionally, wet strength resins, debonders, and the like, for making paper products. A variety of furnishes can be used in embodiments of our invention, and specific furnishes are disclosed in the examples discussed below. In some embodiments, furnishes are used according to the specifications described in commonly-assigned U.S. Pat. No. 8,080,130 (the disclosure of which is incorporated by reference in its entirety). The furnishes in this patent include, among other things, cellulosic long fibers having a coarseness of at least about 15.5 mg/100 mm. Examples of furnishes are also specified in the examples discussed below.
As used herein, the initial fiber and liquid mixture that is dried to a finished product in a papermaking process will be referred to as a “web” and/or a “nascent web.” The dried, single-ply product from a papermaking process will be referred to as a “basesheet.” Further, the product of a papermaking process may be referred to as an “absorbent sheet.” In this regard, an absorbent sheet may be the same as a single basesheet. Alternatively, an absorbent sheet may include a plurality of basesheets, as in a multi-ply structure. Further, an absorbent sheet may have undergone additional processing after being dried in the initial basesheet forming process in order to form a final paper product from a converted basesheet. An “absorbent sheet” includes commercial products marketed as, for example, hand towels.
When describing our invention herein, the terms “machine direction” (MD) and “cross machine direction” (CD) will be used in accordance with their well-understood meaning in the art. That is, the MD of a fabric or other structure refers to the direction that the structure moves on a papermaking machine in a papermaking process, while CD refers to a direction crossing the MD of the structure. Similarly, when referencing paper products, the MD of the paper product refers to the direction on the product that the product moved on the papermaking machine in the papermaking process, and the CD of the product refers to the direction crossing the MD of the product. In terms of the MD of the paper product, “downstream” refers to an area that is formed before an “upstream” area.
The papermaking machine 200 is a three-fabric loop machine that includes a press section 100 in which a creping operation is conducted. Upstream of the press section 100 is a forming section 202. The forming section 202 includes headbox 204 that deposits an aqueous furnish on a forming wire 206 supported by rolls 208 and 210, thereby forming an initial aqueous cellulosic web 116. The forming section 202 also includes a forming roll 212 that supports a papermaking felt 102 such that web 116 is also formed directly on the felt 102. A felt run 214 extends about a suction turning roll 104 and then to a shoe press section 216 wherein the web 116 is deposited on a backing roll 108. The web 116 is wet-pressed concurrently with the transfer of the web 116 to the backing roll 108, which carries the web 116 to a creping nip 120. In other embodiments, however, instead of being transferred on the backing roll 108, the web 116 by be transferred from the felt run 214 onto an endless belt in a dewatering nip, with the endless belt then carrying the web 116 to the creping nip 120. An example of such a configuration can be seen in U.S. Pat. No. 8,871,060, which is incorporated by reference herein in its entirety.
The web 116 is transferred onto the structuring fabric 112 in the creping nip 120, and then vacuum drawn by vacuum molding box 114. After this creping operation, the web 116 is deposited on a Yankee dryer 218 in another press nip 217 using a creping adhesive that is applied to the surface of the Yankee dryer 218. The web 116 is dried on Yankee dryer 218, which is a heated cylinder, and the web 116 is also dried by high jet velocity impingement air in the hood around the Yankee dryer 218. As the Yankee dryer 218 rotates, the web 116 is peeled from the dryer 218 at position 220. The web 116 may then be subsequently wound on a take-up reel (not shown). The reel may be operated slower than the Yankee dryer 218 at steady-state in order to impart a further crepe to the web. Optionally, a creping doctor blade 222 may be used to conventionally dry-crepe the web 116 as it is removed from the Yankee dryer 218.
In the creping nip 120, the web 116 is transferred onto the top side of the structuring fabric 112. The creping nip 120 is defined between the backing roll 108 and the structuring fabric 112, with the structuring fabric 112 being pressed against the backing roll 108 by a creping roll 110. Because the web 116 still has a high moisture content when it is transferred to the structuring fabric 112, the web is deformable such that portions of the web can be drawn into pockets formed between the yarns that make up the structuring fabric 112. (The pockets of structuring fabrics will be described in detail below.) In particular papermaking processes, the structuring fabric 112 moves more slowly than does the papermaking felt 102. Thus, the web 116 is creped as it is transferred onto the structuring fabric 112.
An applied suction from vacuum molding box 114 may also aid in drawing the web 116 into pockets in the surface of the structuring fabric 112, as will be described below. When traveling along the structuring fabric 112, the web 116 reaches a highly consistent state with most of the moisture having been removed. The web 116 is thereby more or less permanently imparted with a shape by the structuring fabric 112, with the shape including domed regions where the web 116 is drawn into the pockets of the structuring fabric 112.
Basesheets made with papermaking machine 200 may also be subjected to further processing, as is known in the art, in order to convert the basesheets into specific products. For example, the basesheets may be embossed, and two basesheets can be combined into multi-ply products. The specifics of such converting processes are well known in the art.
Using the process described in the aforementioned '563 patent, the web 116 is dewatered to the point that it has a higher consistency when transferred onto the top side of the structuring fabric 112 as compared to an analogous operation in other papermaking processes, such as a TAD process. That is, the web 116 is compactively dewatered so as to have from about 30 percent to about 60 percent consistency (i.e., solids content) before 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. Further, there is a speed differential between the backing roll 108 and the structuring fabric 112. This speed differential is referred to as the fabric creping percentage, and may be calculated as:
Fabric Crepe %=S1/S2−1
where S1 is the speed of the backing roll 108 and S2 is the speed of the structuring fabric 112. In particular embodiments, the fabric crepe percentage, or “creping ratio,” can be anywhere from about 3% to about 100%. This combination of web consistency, speed differential occurring at the creping nip 120, the pressure employed at the creping nip 120, and the structuring fabric 112 and creping nip 120 geometry act to rearrange the cellulose fibers while the web 116 is still pliable enough to undergo structural change. In particular, without intending to be bound by theory, it is believed that the slower forming surface speed of the structuring fabric 112 causes the web 116 to be substantially molded into openings in the structuring fabric 116, with the fibers being realigned in proportion to the creping ratio.
While a specific process has been described in conjunction with the papermaking machine 200, those skilled in the art will appreciate that our invention disclosed herein is not limited to the above-described papermaking process. For example, as opposed to the non-TAD process described above, our invention could be related to a TAD papermaking process. An example of a TAD papermaking process can be seen in U.S. Pat. No. 8,080,130, the disclosure of which is incorporated by reference in its entirety.
The knuckles 306 and 310 in the structuring fabric 300 are in a plane that makes up the surface that the web 116 contacts during a papermaking operation. Pockets 308 (one of which is shown as the dotted outlined area in
Those skilled in the art will appreciate the significant length of warp yarn knuckles 306 and 310 in the MD of structuring fabric 300, and will further appreciate that the fabric 300 is configured such that the long warp yarn knuckles 306 and 310 delineate long pockets in the MD. In particular embodiments of our invention, the warp yarn knuckles 306 and 310 have a length of about 2 mm to about 6 mm. Most structuring fabrics known in the art have shorter warp yarn knuckles (if the fabrics have any warp yarn knuckles at all). As will be described below, the longer warp yarn knuckles 306 and 310 provide for a larger contact area for the web 116 during the papermaking process, and, it is believed, might be at least partially responsible for the increased softness seen in absorbent sheets according to our invention, as compared to absorbent sheets with conventional, shorter warp yarn knuckles.
To quantify the parameters of the structuring fabrics described herein, the fabric characterization techniques described in the commonly-assigned U.S. Patent Application Publication Nos. 2014/0133734; 2014/0130996; 2014/0254885, and 2015/0129145 (hereafter referred to as the “fabric characterization publications”) can be used. The disclosures of the fabric characterization publications are incorporated by reference in their entirety. Such fabric characterization techniques allow for parameters of a structuring fabric to be easily quantified, including knuckle lengths and widths, knuckle densities, pocket areas, pocket densities, pocket depths, and pocket volumes.
The air permeability of a structuring fabric is another characteristic that can influence the properties of paper products made with the structuring fabric. The air permeability of a structuring fabric is measured according to well-known equipment and tests in the art, such as Frazier® Differential Pressure Air Permeability Measuring Instruments by Frazier Precision Instrument Company of Hagerstown, Md. Generally speaking, the long warp knuckle structuring fabrics used to produce paper products according to our invention have a high amount of air permeability. In a particular embodiment of our invention, the long warp knuckle structuring fabric has an air permeability of about 450 CFM to about 1000 CFM.
Specific features of the absorbent sheet 1000 are annotated in
Those skilled in the art will immediately recognize several features of the absorbent sheets shown in
Without being limited by theory, we believe that the indented bars seen in the absorbent sheets shown in
Again, without being limited by theory, we believe that the indented bars in the domed regions may contribute to an increased softness that is perceived in the absorbent sheets according to our invention. Specifically, the indented bars provide a more smooth, flat plane being perceived when the absorbent sheet is touched, as compared to absorbent sheets having conventional domed regions. The difference in perceptional planes is illustrated in
Those skilled in the art will appreciate that, due to the nature of a papermaking process, not every domed region in an absorbent sheet will be identical. Indeed, as noted above, domed regions of an absorbent sheet according to our invention might have different numbers of indented bars. At the same time, a few of the domed regions observed in any particular absorbent sheet of our invention might not include any indented bars. This will not affect the overall properties of the absorbent sheet, however, as long as a majority of the domed regions includes the indented bars. Thus, when we refer to an absorbent sheet as having domed regions that include a plurality of indented bars, it will be understood that that absorbent sheet might have a few domed regions with no indented bars.
The lengths and depths of the indented bars in absorbent sheets, as well as the lengths of the domed regions, can be determined from a surface profile of a domed region that is made using laser scanning techniques, which are well known in the art.
Further distinct features that can be seen in the absorbent sheets shown in
We believe that the configuration of the elongated, bilaterally staggered domed regions, in combination with the indented bars extending across the domed regions, results in the absorbent sheets having a more stable configuration. For example, the bilaterally staggered domed regions provide for a smooth planar surface on the Yankee side of the absorbent sheets, which thereby results in a better distribution of pressure points on the absorbent sheet. Note, the Yankee side of an absorbent sheet is the side of the absorbent sheets that is opposite to the air side of the absorbent sheets that is drawn into the structuring fabric during the papermaking process. In effect, the bilaterally staggered domed regions act like long boards in the MD direction that cause the absorbent sheet structure to lay flat. This effect, resulting from the combination of bilaterally staggered domed regions and indented bars will, for example, cause a web to better lay down on the surface of a Yankee dryer during a papermaking process, which results in better absorbent sheets.
Similar to the continuous lines of domed regions, substantially continuous lines of connecting regions extend in a stepped manner along the MD of the absorbent sheet 1000. For example, connection region 1015, which runs substantially in the CD, is contiguous with connecting region 1025, which runs substantially in the CD. Connecting region 1025 is also contiguous with connecting region 1035, which runs substantially in the MD. Similarly, connecting region 1015 is contiguous with connecting region 1025 and connecting region 1055. In sum, the MD connecting regions are substantially longer than the CD connecting regions, such that lines of stepped, continuous connecting regions can be seen along the absorbent sheet.
As discussed above, the sizes of the domed regions and the connecting regions of an absorbent sheet generally correspond to the pocket and knuckle sizes in the structuring fabric used to produce the absorbent sheet. In this regard, we believe that the relative sizing of the domed and connecting regions contributes to the softness of absorbent sheets made with the fabric. We also believe that the softness is further improved as a result of the substantially continuous lines of domed regions and connecting regions. In a particular embodiment of our invention, a distance in the CD across the domed regions is about 1.0 mm, and a distance in the CD across the MD oriented connecting regions is about 0.5 mm. Further, the overlap/touching regions between adjacent domed regions in the substantially continuous lines are about 1.0 mm in length along the MD. Such dimensions can be determined from a visual inspection of the absorbent sheets, or from a laser scan profile as described above. An exceptionally soft absorbent sheet can be achieved when these dimensions are combined with the other features of our invention described herein.
In order to evaluate the properties of products according to our invention, absorbent sheets were made using Fabric 15 as shown
The basesheets were converted to produce two-ply glued tissue prototypes. TABLE 2 shows the converting specifications for the trials.
Sheets formed in the trials with Fabric 15 (i.e., a long warp knuckle fabric) were found to be smoother and softer than the sheets formed in the trials with Fabric 17 (i.e., a shorter warp knuckle fabric). Other important properties of the sheets made with Fabric 15, such as caliper and bulk, were found to be very comparable to those properties of the sheets made with Fabric 17. Thus, it is clear that the basesheets made with the long warp knuckle Fabric 15 could potentially be used to make absorbent products that are softer than absorbent products with the shorter warp knuckle Fabric 17 without the reduction of other important properties of the absorbent products.
As described in the aforementioned fabric characterization publications, the planar volumetric index (PVI) is a useful parameter for characterizing a structuring fabric. The PVI for a structuring fabric is calculated as the contact area ratio (CAR) multiplied by the effective pocket volume (EPV) multiplied by one hundred, where the EPV is the product of the pocket area estimate (PA) and the measured pocket depth. The pocket depth is most accurately calculated by measuring the caliper of a handsheet formed on the structuring fabric in a laboratory, and then correlating the measured caliper to the pocket depth. And, unless otherwise noted, all of the PVI-related parameters described herein were determined using this handsheet caliper measuring method. Further, a non-rectangular, parallelogram PVI is calculated as the contact area ratio (CAR) multiplied by the effective pocket volume (EPV) multiplied by one hundred, where the CAR and EPV are calculated using a non-rectangular, parallelogram unit cell area calculation. In embodiments of our invention, the contact area of the structuring 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 the PVI thereby varying accordingly.
Another useful parameter for characterizing a structuring fabric related to the PVI is a planar volumetric density index (PVDI) of the structuring fabric. The PVDI of a structuring fabric is defined as the PVI multiplied by pocket density. Note that in embodiments of our invention, the pocket density varies between about 10 cm−2 to about 47 cm−2. Yet another useful parameter of a structuring fabric can be developed by multiplying the PVDI by the ratio of the length and width of the knuckles of the fabric, thereby providing a PVDI-knuckle ratio (PVDI-KR). For example, a PVDI-KR for a long warp knuckle structuring fabric as described herein would be the PVDI of the structuring fabric multiplied by the ratio of warp knuckles length in the MD to the warp knuckles width in the CD. As is apparent from the variables used to calculate the PVDI and PVDI-KR, these parameters take into account important aspects of a structuring fabric (including percentage of contact area, pocket density, and pocket depth) that affect shapes of paper products made using the structuring fabric, and, hence, the PVDI and PVDI-KR may be indicative of the properties of the paper products such as softness and absorbency.
The PVI, PVDI, PVDI-KR, and other characteristics were determined for three long warp knuckle structuring fabrics according to embodiments of our invention, with the results being shown as Fabrics 18-20 in
Fabrics 18-21 were used to produce absorbent sheets, and characteristics of the absorbent sheets were determined, as shown in
The sensory softness was determined for the absorbent sheets shown in
Further trials were conducted to evaluate properties of absorbent sheets according to embodiments of our invention. In these trials, the Fabrics 27 and 38 were used. For these trials, a papermaking machine having the general configuration shown in
The basesheets in these trials were converted into unembossed, single-ply rolls.
Pictures of the absorbent sheets made with Fabric 27 are shown in
The profiles of the domed regions in the basesheets made from Fabrics 27 and 38 were determined using laser scanning, in the same manner that the profiles were determined in the absorbent sheets described above. It was found that the domed regions in the basesheets made with Fabric 27 had 4 to 7 indented bars, with there being an average (mean) of 5.2 indented bars per domed region. The indented bars of domed regions extended from about 132 to about 274 microns below the tops of adjacent areas of the domed regions, with an average (mean) depth of about 190 microns. Further, the domed regions extended about 4.5 mm in the MD of the basesheets.
The domed regions in the basesheets made with Fabric 38 had 4 to 8 indented bars, with there being an average (mean) of 6.29 indented bars per domed region. The indented bars of domed regions in the basesheets made with Fabric 38 extended from about 46 to about 159 microns below the tops of adjacent areas of the domed regions, with an average (mean) depth of about 88 microns. Further, the domed regions extended about 3 mm in the MD of the basesheets.
Because the extended MD direction domed regions in the basesheets made with Fabrics 27 and 38 include a plurality of indented bars, it follows that the basesheets will have similar beneficial properties stemming from the configuration of the domed regions as the absorbent sheets described above. For example, the basesheets made with Fabrics 27 and 38 will be softer to the touch compared to basesheets made with fabrics not having long warp knuckles.
Other properties of the basesheets made with Fabrics 27 and 38 were compared to the properties of basesheets made with shorter knuckle fabrics. Specifically, the caliper and pocket depth were compared for uncalendered basesheets made with the different fabrics. The caliper was measured using standard techniques that are well known in the art. It was found that the caliper of the basesheets made with Fabric 27 varied from about 80 mils/8 sheets to about 110 mils/8 sheets, while the basesheets made with Fabric 38 varied from about 80 mils/8 sheets to about 90 mils/8 sheets. Both of these ranges of caliper are very comparable, if not better than, the about 60 to about 93 mils/8 sheets caliper that was found in the basesheets made with shorter warp yarn knuckle fabrics under similar process conditions.
The depths of the domed regions were measured using a topographical profile scan of the air side (i.e, the side of the basesheets that contacts the structuring fabric during the papermaking process) of the basesheets to determine the depths of the lowest points of domed regions below the Yankee side surface. The depths of the domed regions in the basesheets made using Fabric 27 ranged from about 500 microns to about 675 microns, while the depths of the domed regions in the basesheets made using Fabric 38 ranged from about 400 microns to about 475 microns. These domed regions were comparable to, if not greater than, the depths of the domed regions in basesheets made from the structuring fabrics having shorter warp yarn knuckles. This comparability of the depths of domed regions is consistent with the finding that the basesheets made with the long warp yarn structuring fabrics have comparable caliper to the basesheets made with the shorter warp yarn structuring fabrics inasmuch as the depth of domed regions is directly related to the caliper of an absorbent sheet.
The characteristics of further long warp yarn knuckle fabrics according to our invention are labeled as Fabrics 42-44 in
Fabrics 42 and 43 both have higher PVDI-KR values, and these values in conjunction with the PVDI-KR values of the other structuring fabrics described herein are generally indicative of the range of PVDI-KR values that can be found in embodiments of our invention. Further, structuring fabrics with even higher PVDI-KR values, for example, up to about 250, could also be used.
In order to evaluate the properties of Fabric 42, a series of trials was conducted with this fabric and with Fabric 45 for comparison. In these trials, a papermaking machine having the general configuration shown in
The properties of the basesheets made in these trials with Fabrics 42 and 45 are shown in TABLES 5-9. The testing protocols used to determine the properties indicated in TABLES 5-9 can be found in U.S. Pat. Nos. 7,399,378 and 8,409,404, which are incorporated herein by reference in their entirety. An indication of “N/C” indicates that a property was not calculated for a particular trial.
The results of the trials shown in TABLES 5-9 demonstrate that Fabric 42 can be used to produce basesheets having an outstanding combination of properties, particularly caliper and absorbency. Without being bound by theory, we believe that these results stem, in part, from the configuration of knuckles and pockets in Fabric 42. Specifically, the configuration of Fabric 42 provides for a highly efficient creping operation due to the aspect ratio of the pockets (i.e., the length of the pockets in the MD versus the width of the pockets in the CD), the pockets being deep, and the pockets being formed in long, near continuous lines in the MD. These properties of the pockets allow for great fiber “mobility,” which is a condition where the wet compressed web is subjected to mechanical forces that create localized basis weight movement. Moreover, during the creping process, the cellulose fibers in the web are subjected to various localized forces (e.g., pushed, pulled, bent, delaminated), and subsequently become more separated from each other. In other words, the fibers become de-bonded and result in a lower modulus for the product. The web therefore has better vacuum “moldability,” which leads to greater caliper and a more open structure that provides for greater absorption.
The fiber mobility provided for with the pocket configuration of Fabric 42 can be seen in the results shown in
The fiber moldability provided by Fabric 42 can also be seen in the results shown in
The fiber mobility when using Fabric 42 can also be seen in
Because Fabric 42 has extra-long warp yarn knuckles, as with the other extra-long warp yarn knuckle fabrics described above, the products made with Fabric 42 may have multiple indented bars extending in a CD direction. The indented bars are again the result of folds being created in the areas of the web that are moved into the pockets of the structuring fabric. In the case of Fabric 42, it is believed that the aspect ratio of the length of the knuckles and the length across the pocket even further enhances the formation of the folds/indented bars. This is because the web is semi-restrained on the long warp knuckles while being more mobile within the pockets of Fabric 42. The result is that the web can buckle or fold at multiple places along each pocket, which in turn leads to the CD indented bars seen in the products.
The indented bars formed in absorbent sheets made from Fabric 42 can be seen in
The product in
In sum,
Further trials were conducted using Fabric 42 to evaluate properties of converted towel products according to embodiments of our invention. For these trials, the same conditions were used as in the trials described in conjunction with TABLES 4 and 5. The basesheets were then converted to two-ply paper towel. TABLE 10 shows the converting specifications for these trials. Properties of products made in these trials are shown in TABLES 11-13.
Note that Trial 22 only formed a one-ply product, but was otherwise converted in the same manner as the other trials.
The results shown in TABLES 11-13 demonstrate the excellent properties that can be achieved using a long warp warn knuckle fabric according to our invention. For example, the final products made with Fabric 42 had higher caliper and higher SAT capacity than the comparison products made with Fabric 45. Further, the results in TABLES 11-13 demonstrate that very comparable products can be made with Fabric 42 regardless of whether a premium or a non-premium furnish is used.
Based on properties of the products made in the trials described herein, it is clear that the long warp yarn knuckle structuring fabrics described herein can be used in methods that provide products having outstanding combinations of properties. For example, the long warp yarn knuckle structuring fabrics described herein can be used in conjunction with the non-TAD process described generally above and specifically set forth in the aforementioned '563 patent, (wherein the papermaking furnish is compactively dewatered before creping) to form an absorbent sheet that has SAT capacities of at least about 9.5 g/g and at least about 500 g/m2. Further, this absorbent sheet can be formed in the method while using a creping ratio of less than about 25%. Even further, the method and long warp yarn knuckle structuring fabrics can be used to produce an absorbent sheet that has SAT capacities of at least about at least about 10.0 g/g and at least about 500 g/m2, has a basis weight of less than about 30 lbs/ream, and a caliper 220 mils/8 sheets. We believe that this type of method has never created such an absorbent sheet before.
Further absorbent towel basesheets were made in trials with Fabrics 42 and 45. These trials were conducted on a papermaking machine having a configuration as shown in
As with the previously-described trials, the absorbent sheets made using Fabric 42 in the trials shown in TABLES 14-16 have an outstanding combination of properties, in particular, outstanding caliper and absorbency.
The Fabrics 46-52 also demonstrate another aspect of our invention related to positioning of the knuckles on the web-contacting surface of structuring fabrics. As can be seen from the pressure imprint pictures, the knuckles in Fabrics 46-52 are positioned relative to each other such that straight lines can be drawn through the centers of a plurality of the knuckles. One such line L1 is shown in
We have found that paper products made with structuring fabrics having angled warp yarn knuckle lines, such as those shown in Fabrics 42 and 46-52, have exceptional properties. Without being bound by theory, we believe that these exceptional properties stem from a large amount of fiber mobility that is provided for by structuring fabrics having angled warp yarn knuckle lines.
This fiber mobility of a structuring fabric that has angled warp yarn knuckle lines is demonstrated in
In contrast, the knuckles 6000 in the angled warp yarn lines shown in
The curved folds are shaped such that apexes 6003 of the curved folds are positioned downstream in the MD, and ends of the curved folds are offset in the MD, with ends 6007 of the curved folds being positioned upstream in the MD relative to the other ends 6009 of the curved folds. In comparison, the curved folds shown in
The shapes of the curved folds are also related to the distances D1 between the knuckles 6000. As will be appreciated by those skilled in the art, if the knuckles 6000 are too close, there will not be enough room in the pocket between the knuckles 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 field action of the faster moving transfer surface and the slower moving knuckles, and thus, fewer, less pronounced, curved folds may be formed in the web and the resultant absorbent sheet. With these considerations in mind, in embodiments of our invention the distances D1 between the centers of two adjacent knuckles 6000 in different warp yarn knuckle lines can be about 1.5 mm to about 4.0 mm. In a specific embodiment, the distances D1 are about 2.0 mm. With the 2.0 mm distance between the knuckles 6000, there is about 1.5 mm of room in the pocket region between the two adjacent knuckles 6000.
Curved folds can clearly be seen in the projected regions of the basesheets shown in
Curved folds can also be seen in the absorbent sheets shown in
The connecting regions connect the projected regions having the curved folds can also be seen in the photographs of the basesheets shown in
Based on photographs such as those shown in
As discussed above, the curved folds are formed as a result of a localized strain field that arises when a creping operation is performed with an angled warp yarn knuckle fabric according to our invention. For a given absorbent sheet, a normalized fold curvature ratio can be calculated as the radius of curvature for a curved fold divided by a radius of a circle drawn within the projected regions. The lower the normalized fold curvature ratio, the more effective the strain field has been to curve the folds. And, we believe that with a more effectively formed fold curvature, the absorbency and softness of the absorbent sheet are improved.
An example of calculating the normalized fold curvature ratio for absorbent sheet will now be described with reference to
In embodiments of our invention, the normalized fold curvature ratio is less than about 4, and more particularly, from about 0.5 to about 4. In more specific embodiments, the normalized fold curvature ratio is from about 1 to about 3. As evidence by the absorbent sheet shown in
Although this invention has been described in certain specific exemplary embodiments, many additional modifications and variations would be apparent to those skilled in the art in light of this disclosure. It is, therefore, to be understood that this invention may be practiced otherwise than as specifically described. Thus, the exemplary embodiments of the invention should be considered in all respects to be illustrative and not restrictive, and the scope of the invention to be determined by any claims supportable by this application and the equivalents thereof, rather than by the foregoing description.
The invention can be used to produce desirable paper products such as hand towels or toilet paper. Thus, the invention is applicable to the paper products industry.
This application is a divisional of U.S. patent application Ser. No. 15/371,773, filed Dec. 7, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 15/175,949, filed Jun. 7, 2016, now U.S. Pat. No. 9,963,831, which is based on U.S. Provisional Patent Application No. 62/172,659, filed Jun. 8, 2015, each of which is incorporated by reference herein in their entirety.
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