Absorbent paper made by process that includes creping step on multilayer belt having connected openings

Abstract

To provide an absorbent sheet with superior characteristics.SOLUTION: An absorbent sheet has a machine direction corresponding to a direction where the absorbent sheet moves on a paper-making machine during formation, and a machine cross direction perpendicular to the machine direction. The absorbent sheet includes plural domes that protrude from one face thereof, and each of the plural domes overlaps at least one of other domes. Each of the plural domes has a sectional area of 1.0 mm2 to 15 mm2 and a volume of 0.5 mm3 to 23 mm3. A ratio of a diameter in the machine cross direction to a diameter in the machine direction of each dome is 1.0 to 1.8.SELECTED DRAWING: None

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 897,842, filed Sep. 9, 2019, and U.S. Provisional Patent Application No. 17 / 004,906, filed Aug. 27, 2020. The priority of the aforementioned applications is claimed herein, and their disclosures are incorporated herein by reference in their entirety.

[0002] (Field of the Invention) The present invention relates to a multi - layer belt for creping a cellulose web in a papermaking process. The multi - layer creping belt has connected openings. The present invention also relates to a method of manufacturing a paper product using such a multi - layer belt. Still further, the present invention relates to a paper product having excellent properties and manufactured using such a multi - layer belt.

Background Art

[0003] Processes for manufacturing paper products such as tissues and towels are well - known. In such processes, first, an aqueous initial web is formed from a papermaking furnish. The initial web is dewatered, for example, using a belt structure made from a polymeric material, usually in the form of a press cloth. In some papermaking processes, after dewatering, a shape or three - dimensional texture is imparted to the web, and thus the web is referred to as a structured sheet. One way to impart a shape to the web involves using a creping operation while the web is still in a semi - solid, moldable state. Such an operation typically uses a creping structure in the form of a structured cloth or belt. The creping operation is performed at a creping nip under pressure, and the web is pushed into the openings of the creping structure of the nip. After the creping operation, a vacuum can also be used to further draw the web into the openings of the creping structure. After the forming operation is complete, the web is dried using well - known equipment, such as a Yankee dryer, to substantially remove residual water.

[0004] In the art, there are known structured fabrics and belts of various configurations. Specific examples of structured fabrics and belts that can be used for creping in the papermaking process can be found in U.S. Patent No. 8,152,957, as well as U.S. Patent Application Publication Nos. 2010 / 0186913, 2016 / 0090692, 2016 / 0009063, and 2016 / 0090698, all of which are hereby incorporated by reference in their entirety. In particular, U.S. Patent Application Publication Nos. 2016 / 0090692, 2016 / 0009063, and 2016 / 0090698 disclose a creping belt having a multilayer structure with a plurality of openings in the upper layer of the belt. During a creping operation using the multilayer belt, the web is drawn into the openings to impart structure to the final product of the papermaking process. The openings in the upper layer of the belt are formed, for example, by laser perforation or mechanical punching. As disclosed in U.S. Patent Application Publication No. 2016 / 0090698, in particular, the multilayer belt disclosed therein can produce paper products having a combination of excellent properties.

[0005] However, all of the belts disclosed in U.S. Patent Application Publication Nos. 2016 / 0090692, 2016 / 009063, and 2016 / 0090698 have the openings in the upper layer separated from each other by a certain distance along the surface of the upper layer that contacts the web. That is, there is a space between the outer perimeters of each of the openings along the surface of the upper layer, and each opening is separated from all of the other openings by a portion having the full thickness of the upper layer. Such a distance between the openings ensures that even after the openings are formed, a large amount of the material of the upper layer remains, thereby providing a sufficient surface area for securely attaching the upper layer and the bottom layer using an adhesive structure to the side of the upper layer disposed adjacent to the bottom layer. However, the distance between the openings along the contact surface also results in a separated dome structure in the paper product formed using the multilayer belt. This separated dome affects the properties of the paper product manufactured using the multilayer belt.

Summary of the Invention

Means for Solving the Problems

[0006] According to one aspect, the present invention provides a creping belt having connected openings that can be used in a papermaking process. In another aspect, the present invention relates to a papermaking process using a belt having a multilayer structure with connected openings.

[0007] The present invention further relates to a paper product having excellent properties formed using a multilayer creping belt having connected openings.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] In one aspect, the present invention relates to a creping belt having connected openings that can be used in a papermaking process. In another aspect, the present invention relates to a papermaking process using a belt having a multilayer structure with connected openings. The present invention further relates to a paper product having excellent properties formed using a multilayer creping belt having connected openings.

[0010] As used herein, the term "paper product" includes any product incorporating papermaking fibers having cellulose as a main component. This includes, for example, products sold as paper towels, toilet paper, facial tissues, etc. Examples of papermaking fibers include virgin pulp or recycled (secondary) cellulose fibers, or fiber mixtures containing cellulose fibers. Examples of wood fibers include softwood fibers such as northern and southern softwood kraft fibers, and those obtained from deciduous and coniferous trees including hardwood fibers such as eucalyptus, maple, oak, poplar, etc. Examples of fibers suitable for making the web of the present invention include non-wood fibers such as cotton fibers or cotton derivatives, abaca, kenaf, sabai grass, linen, esparto grass, straw, jute, bagasse, corn husk fiber, and pineapple leaf fiber. "Finished furnish" and similar terms refer to an aqueous composition containing papermaking fibers and optionally wet strength resins, release agents, etc. for making paper products.

[0011] As used herein, the initial fiber and liquid mixture that is dried in the papermaking process to become the final product is referred to as a "web" and / or an "initial web". The dried single-ply product obtained by the papermaking process is called a "base sheet". Further, the product of the papermaking process may be referred to as an "absorbent sheet". In this regard, the absorbent sheet may be the same as a single base sheet. Alternatively, the absorbent sheet may include a plurality of base sheets, such as in a multi-ply structure. Further, the absorbent sheet may have been subjected to additional processing, such as embossing, after being dried in the first base sheet forming process.

[0012] When describing the present invention herein, the terms "machine direction" (MD) and "cross machine direction" (CD) are used according to their well-understood meanings in the art. That is, the MD of a fabric or other structure refers to the direction in which the structure moves on a paper machine in the papermaking process, while the CD refers to the direction transverse to the MD of the structure. Similarly, when referring to a paper product, the MD of the paper product refers to the direction on the product in which the product moved on the paper machine in the papermaking process, and the CD of the product refers to the direction transverse to the MD of the product.

[0013] Paper machine The process of manufacturing the product of the present invention using the belt of the present invention may involve compressing and dewatering a papermaking furnish having a random fiber distribution to form a semi-solid web, and then creping the web with a belt to redistribute the fibers and form the web so as to achieve a paper product having desired properties. These steps of the papermaking process can be performed on paper machines having many different configurations. Two examples of such paper machines are described here.

[0014] Figure 1 shows a first example of a paper machine 200. The paper machine 200 includes a press section 100 where a creping operation is performed. Upstream of the press section 100 is a forming section 202, which in the case of the paper machine 200 is called a crescent former in the art. The forming section 202 includes a headbox 204 that deposits a finished furnish onto a forming wire 206 supported by rolls 208 and 210, thereby initially forming a paper web. The forming section 202 also includes a forming roll 212 that supports a paper felt 102 such that the web 116 is also formed directly onto the paper felt 102. The felt run 214 extends to a shoe press section 216 where the wet web is deposited onto a backing roll 108 and the web 116 is wet pressed as it is transferred to the backing roll 108.

[0015] An alternative example of the configuration of the paper machine 200 includes a twin-wire forming section instead of the crescent former 202. In such a configuration, the remaining components of such a paper machine downstream of the twin-wire forming section may be configured and arranged in a manner similar to those of the paper machine 200. An example of a paper machine having a twin-wire forming section can be found in the aforementioned U.S. Patent Application Publication No. 2010 / 0186913. Still further examples of alternative forming sections that can be used in a paper machine include a C-wrap twin-wire former, an S-wrap twin-wire former, or a suction breast roll former. One of ordinary skill in the art will recognize how these, or still further alternative forming sections, can be incorporated into a paper machine.

[0016] Web 116 is transferred onto the creping belt 112 at the belt crepe nip 120 and then is vacuumed by the vacuum box 114 as described in more detail below. After this creping operation, the web 116 is deposited onto the Yankee dryer 218 at another press nip 217 using a creping adhesive. The transfer to the Yankee dryer 218 can occur, for example, at a pressure of about 250 pounds per linear inch (PLI) to about 350 PLI (about 43.8 kN / m to about 61.3 kN / m) in a pressure contact area of about 4% to about 40% between the web 116 and the Yankee surface. The transfer at the press nip 217 can occur, for example, at a web consistency of about 25% to about 70%. As used herein, "consistency" refers to, for example, the percentage of solids of the initial web calculated on a completely dry basis. At a consistency of about 25% to about 70%, it may be difficult to firmly adhere the web 116 to the surface of the Yankee dryer 218 enough to completely remove the web from the creping belt 112. To increase the adhesion between the web 116 and the surface of the Yankee dryer 218, an adhesive may be applied to the surface of the Yankee dryer 218. The adhesive can enable high-speed operation of the system and collision air drying at high jet speeds, and can also enable subsequent peeling of the web 116 from the Yankee dryer 218. An example of such an adhesive is a poly(vinyl alcohol) / polyamide adhesive composition, and an exemplary application rate of this adhesive is less than about 40 mg per square meter of sheet. 2 However, one of ordinary skill in the art will recognize a wide variety of alternative adhesives and even the amount of adhesive that can be used to facilitate the transfer of the web 116 to the Yankee dryer 218.

[0017] Web 116 is dried by impinging air at a high injection velocity within the Yankee hood around the Yankee dryer 218, which is a heated cylinder. As the Yankee dryer 218 rotates, the web 116 is peeled off from the Yankee dryer 218 at position 220. The web 116 may then subsequently be wound onto a take-up reel (not shown). The reel may be operated at a higher speed than the Yankee dryer 218 in a steady state to impart further crepe to the web 116. Optionally, a creping doctor blade 222 may be used to dry crepe the web 116 in a conventional manner. In either case, a cleaning doctor may be mounted in an intermittent engagement and used to control the deposits.

[0018] Figure 2 shows details of the press section 100 where creping takes place. The press section 100 includes a paper-making felt 102, a suction roll 104, a press shoe 106, and a backing roll 108. The backing roll 108 may optionally be heated, for example, by steam. The press section 100 also includes a creping roll 110, a creping belt 112, and a vacuum box 114. The creping belt 112 may be configured as the multi-layer belt of the present invention described in detail below.

[0019] In the creping nip 120, the web 116 is transferred to the upper side of the creping belt 112. The creping nip 120 is defined between the backing roll 108 and the creping belt 112, and the creping belt 112 is pressed against the backing roll 108 by the surface 172 of the creping roll 110. In this transfer in the creping nip 120, the cellulose fibers of the web 116 are repositioned and oriented as described in detail below. After the web 116 is transferred onto the creping belt 112, a suction force may be applied to the web 116 using the vacuum box 114 to at least partially pull out the minute folds. The applied suction force also assists in drawing the web 116 into the openings of the creping belt 112, thereby further shaping the web 116. Further details of this shaping of the web 116 are described below.

[0020] The creping nip 120 generally extends over a belt creping nip distance or width of, for example, about 1 / 8 inch to about 2 inches (about 3.18 mm to about 50.8 mm), more specifically about 0.5 inch to about 2 inches (about 12.7 mm to about 50.8 mm). The nip pressure in the creping nip 120 is generated by the load between the creping roll 110 and the backing roll 108. The creping pressure is generally about 20 to about 100 PLI (about 3.5 kN / m to about 17.5 kN / m), more specifically about 40 PLI to about 70 PLI (about 7 kN / m to about 12.25 kN / m). Although a minimum pressure of 10 PLI (1.75 kN / m) or 20 PLI (3.5 kN / m) in the creping nip 120 is often required, those skilled in the art will understand that in commercially available machines, the maximum pressure can be as high as possible and is limited only by the specific machinery used. Thus, if practical, pressures exceeding 100 PLI (17.5 kN / m), exceeding 500 PLI (87.5 kN / m), or exceeding 1000 PLI (175 kN / m) or more can be used, provided that the speed differential can be maintained.

[0021] In some embodiments, it may be desirable to reconfigure the interfiber characteristics of the web 116, and in other cases, it may be desirable to affect the characteristics only within the plane of the web 116. The creping nip parameters can affect the distribution of fibers within the web 116 in various directions, including inducing changes in the z-direction (i.e., the bulk of the web 116), as well as in the MD and CD. In either case, the creping belt 112 moves slower than the web 116 moves away from the backing roll 108, and the transfer from the creping belt 112 is significantly affected in terms of significant speed changes. In this regard, the degree of creping is often referred to as the creping ratio, which is calculated as follows: Creping ratio (%) = (S1 / S2 - 1) In the formula, S1 is the speed of the backing roll 108, and S2 is the speed of the creping belt 112. Typically, the web 116 is creped at a ratio of about 5% to about 60%. In practice, a high degree of creping close to or even exceeding 100% can be used.

[0022] It should be noted again that the paper machine shown in FIG. 1 is only an example of a possible configuration that can be used in conjunction with the present invention described herein. As a further example, there is the one described in the aforementioned U.S. Patent Application Publication No. 2010 / 0186913.

[0023] Multi-layer creping belt The present invention is directed, in part, to multi-layer belts that can be used in creping operations in paper machines such as those described above. As described above, such multi-layer creping belts are described in U.S. Patent Application Publication Nos. 2016 / 0090692, 2016 / 009063, and 2016 / 0090698 (the "multi-layer belt applications"). As is apparent from the disclosures in these patent application publications, the structure of the multi-layer creping belt provides many advantageous features particularly suitable for creping operations. Specifically, the multi-layer creping belt provides all of the desirable aspects of a polymeric creping belt by providing different properties to the belt in different layers of the belt structure as a whole. Specifically, the multi-layer belt includes an upper layer made of a polymeric material that allows openings having various shapes and sizes to be formed in the layer. On the other hand, the bottom layer of the multi-layer belt is formed of a material that imparts strength and durability to the belt. By providing strength and durability to the bottom layer, the upper layer does not have to contribute to the strength and durability of the belt, so the upper polymeric layer can be provided with larger openings than could otherwise be provided in a polymeric belt.

[0024] The multilayer creping belt described in this specification includes at least two layers. As used herein, a "layer" is a continuous and distinct portion of the belt structure that is physically separated from another continuous and distinct layer in the belt structure. An example of two layers in a multilayer belt according to the present invention is a polymer layer adhered to a fabric layer with an adhesive. It should be noted that a layer as defined herein may include a structure in which another structure is substantially embedded therein. For example, U.S. Patent No. 7,118,647 describes a papermaking belt structure in which a layer made of a photosensitive resin has a reinforcing element embedded in the resin. The photosensitive resin having this reinforcing element is a layer from the perspective of the present invention. However, at the same time, since the photosensitive resin having the reinforcing element is not two continuous and distinct portions of the belt structure that are physically separated from each other, the photosensitive resin having the reinforcing element does not constitute what is referred to as a "multilayer" structure used in this application.

[0025] It should be noted that the "upper" or "sheet" or "yankee" side of the creping belt refers to the side of the belt on which the web is deposited for the creping operation. Thus, the "upper layer" is the portion of the multilayer belt that forms the surface on which the cellulose web is formed during the creping operation. As used herein, the "bottom" or "air" ("machine") side of the creping belt refers to the opposite side of the belt, i.e., the side that faces and contacts processing devices such as creping rolls and vacuum boxes. Thus, the "bottom layer" provides the bottom (air) side surface.

[0026] One of the functions of the upper layer of the multilayer belt according to the present invention is to provide a structure in which openings can be formed. The openings penetrate the layer from one side to the other side of the layer, and the openings impart a dome shape to the web in the papermaking process. The upper layer itself does not need to impart strength and durability to the belt structure, because, as described below, these properties are mainly provided by the bottom layer. Further, the openings in the upper layer do not need to be configured to prevent fibers from being drawn through the upper layer during the papermaking process, because this is also achieved by the bottom layer, as also described below.

[0027] In some embodiments of the present invention, the upper layer of the multilayer belt is made from a flexible thermoplastic material that is extruded. In this regard, there is no particular limitation on the type of thermoplastic material that can be used to form the upper layer, as long as the material generally imparts properties such as friction (e.g., between the paper-forming web and the belt), compressibility, and tensile strength to the upper layer described herein. Also, as will be apparent to those skilled in the art from the disclosure herein, there are many possible flexible thermoplastic materials that can be used that provide substantially the same properties as the thermoplastic materials specifically contemplated herein. It should also be noted that, as used herein, the term "thermoplastic material" is intended to include thermoplastic elastomers, such as rubber materials. It should be further noted that the thermoplastic material can include either non-plastic additives such as those found in fibrous forms of thermoplastic materials (e.g., chopped polyester fibers) or composite materials.

[0028] The thermoplastic upper layer can be made by any suitable technique, such as molding, extrusion, thermoforming, etc. It should be noted that the thermoplastic upper layer can be made, for example, from a plurality of parts whose sides are joined together spirally, as described in U.S. Patent No. 8,394,239, the disclosure of which is incorporated herein by reference in its entirety. Further, the thermoplastic upper layer can be made to any particular required length and can be adjusted to match the path length required for any particular papermaking configuration.

[0029] In certain embodiments, the material used to form the upper layer of the multi-layer belt is polyurethane. As an alternative to polyurethane, another thermoplastic material that may be used to form the upper layer in other embodiments of the present invention is sold by E.I. du Pont de Nemours and Company (Wilmington, Delaware) under the name HYTREL®. HYTREL® products are polyester thermoplastic elastomers having the friction, compressibility, and tensile properties useful for forming the upper layer of the multi-layer creping belt described herein.

[0030] Thermoplastic materials such as the above-described polyurethane are advantageous materials for forming the upper layer of the multi-layer belt of the present invention, considering the ability of the thermoplastic material to form openings of different sizes and configurations. The openings of the thermoplastic material used to form the upper layer can be easily formed using various techniques. Examples of such techniques include laser engraving, perforating, cutting, or mechanical punching. As will be understood by those skilled in the art, such techniques can be used to form large and consistent-sized openings. In fact, openings of almost any configuration (dimensions, shape, sidewall angle, etc.) can be formed in the thermoplastic upper layer using such techniques.

[0031] The bottom layer of the multi-layer creping belt functions to provide strength, MD elongation, and creep resistance, CD stability, and durability to the belt. As described above, flexible polymer materials such as polyurethane provide an attractive option for the upper layer of the belt. However, polyurethane is a relatively weak material that does not, by itself, provide the desirable properties to the belt. A homogeneous monolithic polyurethane belt cannot withstand the stresses and strains applied to the belt during the papermaking process. However, by joining the polyurethane upper layer to a second layer, the second layer can provide the required strength, elongation resistance, etc. to the belt. In essence, by using a separate bottom layer that is separated from the upper layer, the possible range of materials that can be used for the upper layer is expanded.

[0032] Similar to the upper layer, the bottom layer also includes a plurality of openings that extend through the thickness of the layer. Each opening in the bottom layer is aligned with at least one opening in the upper layer, and thus the openings are provided through the thickness of the multi-layer belt, i.e., through the upper layer and the bottom layer. However, the openings in the bottom layer are smaller than the openings in the upper layer. That is, the openings in the bottom layer have a cross-sectional area that is smaller than the cross-sectional area of the plurality of openings in the upper layer that are adjacent to the interface between the upper layer and the bottom layer, adjacent to the interface between the upper layer and the bottom layer. Thus, the openings in the bottom layer can prevent, for example, cellulose fibers from being completely drawn through the multi-layer belt structure when the belt and the paper web are exposed to a vacuum.

[0033] In some embodiments of the present invention, a woven fabric is provided as the bottom layer of the multi-layer creping belt. As described above, the structured woven fabric has the strength and durability to withstand the forces of the creping operation. Thus, the structured woven fabric itself is used as a creping structure in the papermaking process. Therefore, the structured woven fabric can provide the strength, durability, and other properties required for the multi-layer creping belt according to the present invention. In certain embodiments of the multi-layer creping belt, the woven fabric provided in the bottom layer has similar properties to the structured woven fabric that is itself used as a creping structure. Such a fabric has, in fact, a fabric structure having a plurality of "openings" formed between the yarns constituting the fabric structure. In this regard, the result of the openings in the fabric can be quantified as an air permeability that allows air flow to pass through the fabric. From the perspective of the present invention, the permeability of the fabric, together with the openings in the upper layer, allows air to be drawn through the belt. Such an air flow can be drawn through the belt in the vacuum box of the papermaking machine, as described above. Another aspect of the woven fabric layer is its ability to prevent fibers from being drawn completely through the multi-layer belt in the vacuum box. Generally, during the papermaking process, it is preferred that less than 1 percent of the fibers should pass completely through the creping belt or fabric.

[0034] As an alternative to the woven fabric, in other embodiments of the present invention, the bottom layer of the multi-layer creping belt can be formed from an extruded thermoplastic material. However, unlike the flexible thermoplastic material used to form the upper layer described above, the thermoplastic material used to form the bottom layer is provided to impart strength, stretch resistance, durability, etc. to the multi-layer creping belt. Examples of thermoplastic materials that can be used to form the bottom layer include polyester, copolyester, polyamide, and copolyamide.

[0035] Figure 3A is a cross-sectional view of a portion of a multi-layer creping belt 400 according to an embodiment of the present invention. The creping belt 400 includes a polymeric upper layer 402 and a woven bottom layer 404. The polymeric upper layer 402 provides the upper surface 408 of the creping belt 400 on which the web is creped during the creping operation of the papermaking process. As described above, the openings 406 are formed in the polymeric upper layer 402. It should be noted that the openings 406 extend from the upper surface 408 through the thickness of the polymeric upper layer 402 to the surface facing the woven bottom layer 404. Since the woven bottom layer 404 has a certain transmittance, a vacuum can be applied to the side of the creping belt 400 where the woven bottom layer 404 is located, and thus an air flow can be drawn out through the openings 406 and the woven bottom layer 404. During the creping operation using the creping belt 400, the cellulose fibers from the web are drawn into the openings 406 of the polymeric upper layer 402, thereby forming a dome structure on the web (described in more detail below). Further, a vacuum may be used to draw the web into the openings 406.

[0036] Figure 3B is a top view of the creping belt 400 looking down on the portion having the openings 406 shown in Figure 3A. As is apparent from Figures 3A and 3B, the woven bottom layer 404 allows a vacuum to be drawn through the creping belt 400, but the woven bottom layer 404 also effectively closes the openings 406 of the upper layer 402. That is, the woven bottom layer 404 provides a plurality of openings having a smaller cross-sectional area, substantially adjacent to the interface between the polymeric upper layer 402 and the woven bottom layer 404. Thus, the woven bottom layer 404 can substantially prevent cellulose fibers from passing through the creping belt 400. As described above, the woven bottom layer 404 also imparts strength, durability, and stability to the creping belt 400.

[0037] The layers of the multi-layer creping belt 400 according to the present invention may be joined together in any manner that provides a sufficiently durable connection between the layers so that the multi-layer creping belt 400 can be used in the papermaking process. In some embodiments, the layers are joined together by chemical means such as using an adhesive. A specific example of an adhesive structure that can be used to join the layers is a double-sided tape. In other embodiments, the layers may be joined together by mechanical means such as using a hook-and-loop fastener. In still other embodiments, the layers of the multi-layer belt may be joined by techniques such as heat welding and laser fusion. Those skilled in the art will understand the numerous lamination techniques that can be used to join the layers described herein to form the multi-layer creping belt 400.

[0038] Figures 4A - 4C show the arrangement of the openings 406 in the upper layer 402 of the multi - layer creping belt 400 according to an embodiment of the present invention. In these figures, the MD is shown towards the top of the page. As shown in the figures, the openings 406 are arranged in substantially parallel lines extending in the MD of the belt. The lines between the openings 406 are substantially parallel to the contact surface of the polymer upper layer 402. The openings 406 of each MD line are closely arranged to each other such that there is an "overlap" in each of the openings. When referring herein to "overlapping" openings, because the openings 406 are positioned close together, the area openings along the upper layer 402 that would have been formed if the openings were spaced apart from all other openings on the surface of the creping belt 400 actually overlap with the area of another opening due to the close positioning of the openings. For example, in the schematic view shown in Figure 4C, the area of the opening 450 formed by laser drilling in the upper layer 402 is shown by the solid line 452. The areas of the adjacent openings 460 and 470 on the upper layer 402 are shown by the solid lines 462 and 472 respectively. The areas of the openings 450, 460, and 470 along the bottom surface are shown by the dashed lines 454, 464, and 474 respectively. The area of the opening 450 in the upper layer 402 shown by the solid line 452 overlaps with the areas of the openings 460 and 470 shown by the solid lines 462 and 472 respectively. The overlap distance between the edges of the openings 480 and 490 is shown as OD in Figure 4C.

[0039] As can be seen in Figure 4B, as a result of the overlapping areas of the openings, the upper edge of each opening includes a portion that is common with the upper edge of the adjacent opening. For example, the upper edge of the opening 410 includes a portion 412 that is also part of the upper edge of the adjacent opening 420. The upper edge of the opening 410 also includes another portion 414 that is also part of the upper edge of the adjacent opening 430.

[0040] As can also be seen in FIG. 4B, the inner surface of the opening is angled from the upper edge on the upper layer 402 to the bottom edge of the opening on the bottom surface of the upper layer 402. That is, the inner surface of the opening is angled inward with respect to the upper edge. As a result, the area of the opening in the upper layer 402 is larger than the area of the opening on the bottom surface of the upper layer 402. Also, as a result of the combination of the shape of the opening, the overlap of the openings, and the angled inner surface of the opening, the portion of the upper edge of the opening that is common between the two openings is located below the surface of the upper layer 402. For example, the shared edge 412 of the openings 410 and 420 undulates downward from the separate edge portions of the openings 410 and 420 to the lowest point of the center of the shared edge 412. Due to the undulation in the common portion of the lower edge of the upper layer 402 of the creping belt 400, each of the openings is essentially "connected" to the other openings in that there is an open space between the openings below the surface of the upper layer 402. As will be described in more detail below, as a result of the connection between the openings, the domes formed in the paper product manufactured using such connected openings are also connected, whereby a paper product having surprisingly good properties is obtained as compared to a paper product made using a belt in which the openings in the upper layer are spaced apart from each other.

[0041] In the embodiments shown in FIGS. 4A and 4B, the openings are arranged in a substantially straight line extending in the MD of the belt. However, the present invention is not limited to such a configuration. For example, FIGS. 5A and 5B are schematic views of connected openings of a multi-layer belt according to a further embodiment of the present invention, and the openings do not extend linearly.

[0042] In the embodiment shown in FIG. 5A, the openings are staggered such that each opening is offset from two adjacent connected openings by CD. For example, opening 500 is positioned with respect to CD such that edge 502 of opening 500 on the upper surface of the upper layer of the belt is offset from edges 512 and 522 of adjacent connected openings 510 and 520 (edges 504, 514, and 524 of openings 500, 510, and 520 on the bottom surface of the upper layer are also offset from CD). Thus, the line of connected openings extends in the MD of the belt, but the line of openings is not straight. Although the schematic of FIG. 5A shows three lines of openings extending in the MD, it should be noted that the belt according to the present invention may include a number of additional lines along the CD length of the belt.

[0043] FIG. 5B is a schematic view of a further alternative arrangement of the openings in the upper layer of the creping belt according to an embodiment of the present invention. In this embodiment, there is a repeating pattern of five overlapping openings. For example, opening 550 overlaps (and thus is connected to) openings 560, 570, 580, and 590. This pattern of overlapping openings repeats such that a line of connected openings is formed in the MD. Although two such lines are shown in FIG. 5B, the belt according to the present invention may include a number of additional lines along the CD length of the belt.

[0044] One of ordinary skill in the art will recognize a number of alternative arrangements of the openings that, while different from the exact patterns shown in FIGS. 4A - 5B, will similarly result in a line of connected openings extending in the MD. Therefore, the present invention should not be construed as being limited to any of the specific patterns of openings shown herein.

[0045] FIG. 6 is a view of a portion of the upper surface 602 of a multi-layer creping belt 600 according to yet another embodiment of the present invention. In this case, the openings in the upper layer do not overlap, but the openings are connected in any case. For example, the opening 604 includes the edge 606 of the upper surface 602 of the upper layer and the edge 608 of the bottom surface. Adjacent to the opening 604, there is a groove 610 formed in the upper surface 602 of the creping belt 600. The groove 610 extends in depth into the upper layer, but not completely from the upper layer to the bottom surface. The groove 610 extends from the edge 606 of the opening 604 to the edge of another opening 616 that is generally aligned with the opening 604 in the CD. Thus, the opening 604 and the opening 616 are connected by the groove 610, and the groove 610 forms an open space between the openings 604 and 616 under the surface of the upper surface 602 of the creping belt 600. The groove 610 has edges 612 and 614. With the configuration of the openings shown in FIG. 6, even when the openings do not overlap, a line of connected openings is formed in the MD.

[0046] As will be understood by those skilled in the art, the portions of the upper layer of the belts shown in FIGS. 4A-6 may form most of the pattern of openings in the upper layer, but the belts according to the present invention may include other portions different from the illustrated portions. For example, the openings in the upper layer of the multi-layer belt may be formed using a "stamp" having a pattern as shown in FIGS. 5A and 5B. Such a stamp is repeated over the area of the belt, but there may be break points where no openings are formed between each stamp. Alternatively, as another example, different patterns of openings formed in the upper layer may exist between each stamp. Despite such break points in the stamp pattern, the results of the present invention (described in detail below) are still achieved.

[0047] Considering different configurations of the openings that may be formed in the upper layer, it is important to note that the openings do not have to be shaped identically to any of the shapes shown herein. That is, some of the openings formed in the upper layer may have a different configuration than other openings formed in the upper layer. In fact, different openings may be provided in the upper layer to provide different functions in the papermaking process. For example, some of the openings in the upper layer can be sized and shaped to provide the formation of a dome structure in the papermaking web during the creping operation (described in detail below). At the same time, other openings in the upper layer may be of much larger sizes and various shapes so as to provide a pattern in the papermaking web that is equivalent to the pattern achieved by the embossing operation. The ability to provide the embossing effect using a belt is highly advantageous because it can reduce or eliminate the undesirable effects of the actual embossing process, such as loss of sheet bulk and other desired properties.

[0048] Considering the size of the openings for forming a dome structure in the papermaking web in the creping operation, the upper layer of the multi-layer belt of the present invention allows for much larger sizes than alternative structures such as structured woven fabrics and monolithic polymer belt structures. The size of the openings can be quantified in terms of the cross-sectional area of the openings in the plane of the surface of the multi-layer belt provided by the upper layer. In some embodiments, the openings in the upper layer of the multi-layer belt have an average cross-sectional area of at least about 1.0 mm 2 on the forming (upper) surface. More specifically, the openings are from about 1.0 mm 2 to about 15 mm 2 , or even more specifically from about 1.5 mm 2 to about 8.0 mm 2 , or even more specifically from about 2.1 mm 2 to about 7.1 mm 2has an average cross-sectional area. As will be readily understood by those skilled in the art, forming a monolithic belt having openings with the cross-sectional area of the multi-layer belt according to the present invention would be extremely difficult, if not impossible or impractical. For example, openings of these sizes would require the removal of large amounts of the material forming the monolithic belt, and as a result, the belt would be less likely to have sufficient durability to withstand the severity and stresses of the creping process of a paper-making belt. As will be readily understood by those skilled in the art, it is unlikely that a structured woven fabric could provide openings of these sizes, as the yarns of the fabric cannot be woven (spaced apart or to such sizes) to provide openings equivalent to these and still provide sufficient structural integrity to function in a paper-making process.

[0049] The size of the openings may also be quantified in terms of volume. As used herein, the volume of the openings refers to the space occupied by the openings through the thickness of the belt. The openings in the upper layer of the multi-layer belt according to the present invention can have a volume of at least about 0.2 mm 3 or more specifically, the volume of the openings can be in the range of about 0.5 mm 3 to about 23 mm 3 or more specifically, the volume of the openings can be in the range of 0.5 mm 3 to about 11 mm 3 of the multi-layer belt according to the present invention.

[0050] Tables 1 and 2 show the specific configurations and characteristics of a multilayer belt having connected openings in the upper layer according to embodiments of the present invention. These belts include a polymeric upper layer and a fabric or polymeric bottom layer as described above. Tables 1 and 2 describe the characteristics of the openings in the upper layer (i.e., the "sheet side") of the respective belts, such as cross-sectional area, volume of the openings, and the angle of the sidewalls of the openings. Tables 1 and 2 also describe the characteristics of the openings in the bottom layer (i.e., the "air side"). The openings in the belt embodiments described in Tables 1 and 2 are aligned substantially linearly in the MD as shown in FIGS. 4A - 4C. The overlap of the openings can be seen from the MD land distance characteristics described in Tables 1 and 2. That is, the MD land distance ("MDLD") indicates the distance between the edges of two adjacent openings in the MD direction on the upper surface of the upper layer. Thus, a negative value for the MD land distance in Tables 1 and 2 indicates the overlap distance at the edges in the manner in which the edges of openings 480 and 490 in FIG. 4C overlap by a distance MDLD. Also, the CD land distance ("CDLD") indicates the distance between the edges of two parallel lines on the upper surface, as shown as CDLD in FIG. 4C for example.

[0051]

Table 1

[0052]

Table 2

[0053] Process Another aspect of the present invention is directed to a process for manufacturing a paper product. The process may utilize the multi-layer belt described herein in a creping operation. In such a process, any of the general types of paper machines described above can be used. Of course, one of ordinary skill in the art will recognize numerous variations and alternative configurations of paper machines that can be utilized to carry out the process of the present invention described herein. Further, one of ordinary skill in the art can readily determine well-known variables and parameters that are part of any papermaking process and can be used in conjunction with the process of the present invention, for example, that a particular type of furnish for forming a web in a papermaking process can be selected based on the desired properties of the product.

[0054] In some processes according to the present invention, the web has a consistency (i.e., solids content) of about 15 to about 25 percent when deposited on the creping belt. In other processes according to the present invention, belt creping is performed under pressure in the creping nip while the web is at a consistency of about 30 to about 60 percent. In such processes, the paper machine may have the configuration shown and described above in, for example, FIG. 1. Details of such processes can be found in the aforementioned U.S. Patent Application Publication No. 2010 / 0186913. In this process, the web consistency, the velocity differential that occurs in the belt-creping nip, the pressure used in the creping nip, and the geometry of the belt and nip act to reposition the fibers while maintaining sufficient flexibility for the web to undergo structural changes. Without intending to be bound by theory, it is believed that the slower the forming surface velocity of the creping belt, the more substantially the web is formed into the openings in the creping belt and the fibers are realigned in proportion to the creping ratio. Some of the fibers are moved into the CD orientation while other fibers are folded into MD ribbons. As a result of this creping operation, a high caliper sheet can be formed. The multi-layer belts described herein are suitable for these processes. Specifically, as described above, the multi-layer belts may be configured to have a wide range of sizes of openings and can thus be used effectively with these processes.

[0055] A further aspect of the process according to the invention is to apply a vacuum to the multi-layer creping belt. As described above, the vacuum may be applied when the web is deposited on the creping belt in the papermaking process. The vacuum acts to draw the web into the openings of the creping belt, i.e., the openings of the upper layer of the multi-layer belt according to the invention. In particular, in any process, whether with or without the use of vacuum, the web is drawn into the plurality of openings of the upper layer of the multi-layer belt structure, but the web is not drawn into the bottom layer of the multi-layer belt structure. In some of the embodiments of the invention, the applied vacuum is from about 5 inches of mercury to about 30 inches of mercury. As detailed above, the bottom layer of the multi-layer belt functions as a screen to prevent fibers from being drawn out through the belt structure. This screening function of the bottom layer is particularly important when a vacuum is applied because it prevents fibers from being drawn into the structure that creates the vacuum, i.e., the vacuum box.

[0056] Paper products Another aspect of the invention is a novel paper product that cannot be manufactured using known papermaking machines and processes known in the art. In particular, the multi-layer belt having connected openings described herein enables the formation of paper products that exhibit excellent properties and characteristics not previously found in paper products manufactured with known papermaking machines and papermaking processes.

[0057] It should be noted that the paper products referred to herein include products of all grades. That is, some embodiments of the invention generally target tissue grade products having a basis weight of less than about 27 pounds per ream and a caliper of less than about 180 mils / 8 sheets. Other embodiments of the invention generally target towel grade products having a basis weight of more than about 35 pounds per ream and a caliper of more than about 225 mils / 8 sheets.

[0058] Tactile softness is a measure of the perceived softness of a paper product determined by trained evaluators using standardized test techniques. That is, tactile softness is measured by having evaluators experienced in softness determination squeeze the paper and judge the softness according to specific techniques for determining the perceived softness of the paper. The higher the number for tactile softness, the higher the perceived softness.

[0059] To demonstrate this combination of properties, products were made using belts having the constructions of Belts 1 - 3 shown in Table 1. In these tests, as shown below, a two - ply tissue grade product was ultimately formed.

[0060] For Belt 1, tests were conducted on a paper machine similar to the machine shown in FIG. 1 using the indicated operating conditions. In these tests, a finished paper furnish for papermaking was used in a homogeneous mode. A caliper of 75 mils / 8 sheets was targeted. A total of 1.25 pounds / ton of release agent was added to the air - side stock and no release agent was added to the Yankee - side stock. KL506 PVOH was used as part of the Yankee coating adhesive to ensure proper Yankee adhesion. The target base - sheet caliper was achieved by generating the highest possible uncalendered caliper and then calendering the resulting product to 125 mils / 8 plies. By balancing refining with the addition of wet strength and carboxymethyl cellulose (CMC), 550 g / in 3 of CD wet tensile was achieved. The initial refining settings were 45 HP with initial usage amounts of 25 and 5 pounds / ton of wet strength resin and CMC, respectively. Note that northern softwood kraft (NSWK), softwood kraft (SWK), wet strength resin (WSR), carboxymethyl cellulose (CMC), and polyvinyl alcohol (PVOH) may be omitted as shown.

[0061] The calipers of the base sheets produced in four test runs using Belt 1 are shown in Table 3. Note that each of the test runs was collected on two reels, as shown.

[0062] [Table 3]

[0063] Next, the base sheets obtained from the tests in Table 3 were converted. Table 4 shows the properties of the converted base sheets.

[0064] [Table 4]

[0065] Next, the converted base sheets shown in Table 4 were made into the final two-ply product. Table 5 shows the driver burst properties of the final product.

[0066] [Table 5]

[0067] As will be understood by those skilled in the art, the properties of the base sheets and final products shown in Tables 3 - 5 are exceptional for tissue grade products. Of particular note, the CD elongation was in the range of about 11.7 to about 13.9 for the converted base sheets, the elongation ratio was in the range of about 2.2 to about 2.6 for the converted base sheets, and the breaking coefficient was in the range of about 16.49 to about 24.58 for the converted base sheets. The combination of high CD elongation, high MD / CD elongation ratio, and low breaking coefficient results in a soft cloth-like product. That is, the combination of properties provides a highly desirable product that feels soft to the touch and drapes in the user's hand. Along with this cloth-like property, the caliper of the product ensures that the product has good absorbency.

[0068] In addition, the base sheet shown in Table 4 had a relatively low GM tensile strength in the range of about 341 to about 470. Since the lower the GM tensile strength, the easier it is to manufacture the base sheet, this is advantageous from the manufacturing perspective. The two-ply configuration provides sufficient GM tensile strength, and since the final product is still soft, the low GM tensile strength in the base sheet does not pose a problem in the final product.

[0069] Also notable is the driver burst test in the final product shown in Table 5. As would be understood by those skilled in the art, driver burst is a measure of the strength of the product. Values in the range of about 0.45 to about 0.55 lbf indicate the strength of the tissue grade of the final product.

[0070] The excellent characteristics found in the base sheet and the product shown in Tables 3 to 5 are considered to result from the configuration of the openings in Belt 1. As described above, the openings formed in the upper layer of the multi-layer creping belt impart a dome shape to the web during the papermaking process using the belt. Also, these dome shapes can be seen in the resulting product. For example, FIGS. 7 to 9 are micrographs of the base sheet formed in a test using Belt 1. FIGS. 7 and 9 show the air side (i.e., the side of the base sheet formed against the belt), while FIG. 8 shows the Yankee side (i.e., the side of the base sheet that is not formed against the belt and is transferred onto the surface of the Yankee dryer). In all the figures, MD is shown in the vertical direction. The domes formed by the openings in the belt are clearly visible as brighter regions in the figure, and four domes are labeled 702, 704, 706, and 708 in FIG. 9. Due to the connection (overlap) in the openings of the belt used to form the base sheet, domes 702 and 704 are effectively connected to each other in connection region 710, and domes 706 and 708 are effectively connected to each other in connection region 712. There is an interconnected region between the MD lines of the domes, and one of them is labeled 714. The interconnected region corresponds to the portion of the base sheet formed on the contact surface of the upper layer of the belt. Overall, the base sheet has parallel lines of connected domes extending in the MD, and the interconnected regions are formed between the MD lines of the connected domes. Without being bound by theory, the inventors believe that due to the parallel lines of connected domes extending in the MD, the base sheet has springiness in the CD, i.e., the structure of the base sheet in the CD is similar to that of an accordion. At the same time, the interconnected lines between the MD lines of the connected domes are considered to provide strength in the MD. As a result of the combination of springiness in the CD and strength in the MD, the base sheet and the resulting product made from the base sheet exhibit significant CD elongation while still having a high elongation ratio (i.e., the ratio of MD elongation to CD elongation).

[0071] Although the present invention has been described in certain specific exemplary embodiments, many additional modifications and variations will be apparent to those skilled in the art upon consideration of the present disclosure. Accordingly, it is to be understood that the invention can be practiced otherwise than as specifically described. Therefore, the exemplary embodiments of the present invention are to be considered in all respects as illustrative and not restrictive, and the scope of the invention is to be determined by the claims supported by this application and its equivalents rather than by the foregoing description. Industrial Applicability

[0072] The apparatus, process, and product described herein can be used in the manufacture of commercial paper products such as toilet paper and paper towels. Accordingly, the apparatus, process, and product have numerous applications related to the paper product industry.

Claims

1. An absorbent sheet comprising: a machine direction corresponding to the direction in which the absorbent sheet moved on the papermaking machine during formation, and a cross-machine direction perpendicular to the machine direction; a plurality of domes protruding from one side of the absorbent sheet; each dome of the plurality of domes overlaps at least one other dome; Each dome of the plurality of domes is 1.0 mm ２ ~15mm ２ and a cross-sectional area of ​​0.5 mm ３ ~23mm ３ and the ratio of said cross-machine direction diameter to said machine direction diameter of each dome is from 1.0 to 1.

8.

2. The absorbent sheet of claim 1 , wherein each of said plurality of domes overlaps at least one other dome in the machine direction.

3. 2. The absorbent sheet of claim 1, wherein said domes are arranged in parallel lines extending in said machine direction, with interconnected regions extending in said machine direction between said parallel lines of domes.

4. 4. The absorbent sheet of claim 3, wherein each dome of the plurality of domes located in one parallel line overlaps an adjacent dome in the machine direction to form an overlapping connection region between adjacent domes in each parallel line.

5. 10. The absorbent sheet of claim 1, wherein the absorbent sheet has a dry strength of from 0.45 lbf to 0.55 lbf as measured by TAPPI T-570.

6. 10. The absorbent sheet of claim 1, wherein the absorbent sheet is a tissue grade product having a basis weight of less than 27 lbs / ream and a caliper of less than 180 mils / 8 sheets.

7. 10. The absorbent sheet of claim 1, wherein the absorbent sheet is a towel grade product having a basis weight greater than 35 lbs / ream and a caliper greater than 225 mils / 8 sheets.

8. The absorbent sheet of claim 1, wherein the absorbent sheet has a CD stretch in the range of 11.7 to 13.

9.

9. The absorbent sheet according to claim 1, wherein the absorbent sheet has a ratio of MD stretch to CD stretch (stretch ratio) in the range of 2.2 to 2.

6.

10. The absorbent sheet of claim 1, wherein the absorbent sheet has a modulus of rupture in the range of 16.49 to 24.

58.

11. 10. The absorbent sheet of claim 1, wherein the absorbent sheet has a geometric mean (GM) tensile strength in the range of 341-470.

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