Papermaking belt with offset openings, papermaking process using a belt with offset openings, and paper products made therefrom

Abstract

A belt for creping a web during a papermaking process is disclosed. The belt includes a surface onto which the web is transferred during the papermaking process. A plurality of openings extend through the surface, wherein the openings are arranged in lines offset from lines in the machine direction (MD) and cross-machine direction (CD) of the belt. A paper product, such as an absorbent sheet, formed from the belt has hollow dome regions and connecting regions between the domes, wherein the domes are arranged in lines offset from lines in the MD and CD of the paper product.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on U.S. non-provisional patent application No. 17 / 010,538, filed on September 2, 2020, which is based on U.S. provisional patent application No. 62 / 905,058, filed on September 24, 2019. Priority is hereby claimed to the foregoing applications, and the disclosures of which are incorporated herein by reference in their entireties. Background Art Technical Field

[0004] The present invention relates to a belt that can be used in a papermaking process. The present invention also relates to a papermaking process that includes the use of such a belt. The present invention also relates to a paper product having excellent properties. Background Art

[0006] Belts are sometimes used in papermaking machines as part of the papermaking process. Examples of belts and paper products made from such belts are described in U.S. Patent No. 9,863,095 B2, which is incorporated herein by reference in its entirety. As discussed in that patent, a belt acts as a creping structure during an operation under pressure in a nip, where a nascent web of cellulosic fibers is forced into openings in the belt's top surface. After the creping operation, a vacuum may be applied to further draw the web into the openings in the creping structure. After the forming operation is complete and the web is fully dried, the resulting paper product has a structure that includes hollow domes formed in the belt's openings and connecting areas between the domes, where the connecting areas have been formed on the belt's top surface. Thus, the openings in the creping belt have a demonstrable effect on the paper structure resulting from the papermaking process.

[0007] It is apparent from the pictures of the paper product disclosed in the aforementioned U.S. Patent No. 9,863,095 B2 that the openings in the belt used to make the product are aligned in at least one of the machine direction (MD) and the cross-machine direction (CD) of the belt. A similar example of a belt with aligned openings known in the art is shown in U.S. Patent No. 4,529,480. This patent describes a deflection member in the form of an endless belt that can be used in a papermaking machine. The patent indicates that the endless belt includes deflection conduits in the form of hexagonal openings, and the patent asserts that these deflection conduits are arranged in a double transverse staggered array. In the patent Figure 2 In the array of conduits shown, each conduit is not aligned with the immediately adjacent conduit. However, the conduits are arranged in lines extending along the MD direction of the belt, and the conduits are also arranged along lines extending in the CD direction of the belt.

[0008] One of the more challenging parts of the papermaking process is transferring the nascent web to the creping structure (e.g., belt) in the creping nip. At this point in the papermaking process, the web is unstable due to its high moisture content, making it difficult to consistently move the web to the creping structure. However, to produce a high-quality product, the transfer operation needs to be consistent so that the web formation performed in the creping nip effectively achieves the desired properties in the product. Therefore, it is necessary to design a creping belt that facilitates the transfer operation as much as possible. Summary of the Invention

[0009] According to one aspect, the present invention relates to a belt for creping a web in a papermaking process. The belt comprises a first layer formed of a polymeric material, the first layer providing a first surface of the belt on which the web is deposited, and the first layer having a plurality of openings extending therethrough. The openings are arranged in lines offset from lines in both the machine direction (MD) and the cross-machine direction (CD) of the belt such that (i) for each line along the MD, the length of the line across an opening is different from the length of the line across adjacent openings on either side of the opening, and (ii) for each line along the CD, the length of the line across an opening is different from the length of the line across adjacent openings on either side of the opening. The belt further comprises a second layer attached to the first layer, the second layer providing a second surface of the belt.

[0010] According to another aspect, the present invention relates to a belt for creping a web in a papermaking process. The belt includes a first layer formed of a polymeric material, the first layer providing a first surface of the belt on which the web is deposited, and the first layer having a plurality of openings extending therethrough. The openings are arranged in (i) a repeating pattern of openings arranged around a central opening, (ii) such that the openings are not mirrored about a line extending along a diameter of the central opening in the machine direction (MD), and (iii) such that the openings are not mirrored about a line extending along a diameter of the central opening in the cross-machine direction (CD). The belt also includes a second layer attached to the first layer, wherein the second layer provides a second surface of the belt.

[0011] According to yet another aspect, the present invention relates to a belt for creping a web in a papermaking process. The belt includes a first layer formed of a polymeric material, the first layer providing a first surface of the belt on which the web is deposited, and the first layer having a plurality of openings extending therethrough. The openings are arranged in a pattern having an angle of rotational symmetry of sixty degrees and a degree of rotational symmetry of six. The belt also includes a second layer attached to the first layer, the second layer providing a second surface of the belt.

[0012] According to another aspect, the present invention relates to a belt for creping a web in a papermaking process. The belt includes a first layer formed of a polymeric material, the first layer providing a first surface of the belt on which the web is deposited, and the first layer having a plurality of openings extending therethrough, wherein the openings are arranged in a pattern such that a repetitive peak in the sum of the MD line contact profile occurs below about 0.55 mm in the CD. The belt also includes a second layer attached to the first layer, the second layer providing a second surface of the belt.

[0013] According to yet another aspect, the present invention relates to an absorbent sheet of cellulose fibers having an upper side and a lower side. The absorbent sheet includes a plurality of hollow dome-shaped regions having an elliptical shape and protruding from the upper side of the sheet, the plurality of domes being arranged along a line rotated by about 13 degrees to about 21 degrees relative to a line along the MD of the absorbent sheet, and the major axes of the plurality of domes being formed at a mean average angle of about 4 degrees to about 5 degrees in a clockwise direction relative to a line along the CD of the absorbent sheet. The sheet also includes connecting regions forming a network interconnected with the hollow dome-shaped regions of the sheet.

[0014] According to yet another aspect, the present invention relates to a method for making a creped absorbent cellulosic sheet. The method comprises: forming a nascent web from a papermaking furnish, the nascent web having a substantially random distribution of papermaking fibers; transferring the nascent web to a translating transfer surface moving at a transfer speed; drying the nascent web to form a web having a consistency of from about 30% to about 60%; and creping the web from the transfer surface using a creping belt provided with a plurality of openings, the plurality of openings being arranged in lines offset in the machine direction (MD) and in lines offset in the cross-machine direction (CD), wherein nip parameters, velocity delta, and web consistency are configured such that the line in which the web first contacts the creping belt extends substantially in the CD direction across the plurality of lines of openings offset in the MD direction and thereafter extends substantially in the MD direction. The method further comprises the step of drying the web to form the creped absorbent cellulosic sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of a papermaking machine configuration that may be used in conjunction with the present invention.

[0016] Figure 2 It shows Figure 1 Schematic diagram of the wet press transfer and belt creping sections of a paper machine is shown.

[0017] Figure 3 is a schematic diagram of an alternative papermaking machine configuration that may be used in conjunction with the present invention.

[0018] Figure 4A is a cross-sectional view of a portion of a creping belt according to an embodiment of the present invention.

[0019] Figure 4B yes Figure 4A Top view of the portion shown.

[0020] Figure 5A is a cross-sectional view of a portion of a multilayer creping belt according to another embodiment of the present invention.

[0021] Figure 5B yes Figure 5A Top view of the portion shown.

[0022] Figure 6 is a schematic diagram illustrating a pattern of offset openings of a creping belt according to an embodiment of the present invention.

[0023] Figure 7 is a table showing properties of creping belts according to embodiments of the present invention.

[0024] Figure 8 is a model illustrating the transfer of a papermaking web to a creping belt according to an embodiment of the present invention.

[0025] Figure 9 is a model showing the transfer of a paper web to a comparative creping belt.

[0026] Figure 10 is a schematic diagram illustrating the characteristics of openings in a creping belt according to an embodiment of the present invention.

[0027] Figure 11 is a model representation of an opening in a creping belt according to an embodiment of the present invention.

[0028] Figure 12 Shown Figure 11 The band shown represents the sum of the MD line contact profiles.

[0029] Figures 13 to 18 is a table showing characteristics of substrates and converted products made according to embodiments of the present invention.

[0030] Figure 19A and Figure 19B is a micrograph of a substrate according to an embodiment of the present invention.

[0031] Figure 20A is a photomicrograph of a paper product according to an embodiment of the present invention, and Figure 20B is a black and white image converted from this photomicrograph.

[0032] 21A to 21D XR-μCT analysis of paper products according to embodiments of the present invention and comparative paper products made with structured fabrics are shown. DETAILED DESCRIPTION

[0033] In one aspect, the present invention relates to a creping belt for use in a papermaking process. The present invention also relates to a papermaking process using a creping belt. The present invention also relates to paper products having superior properties. In certain embodiments, the creping belt has an offset opening that provides surprising improvements to the papermaking process and paper products.

[0034] As used herein, the term "paper product" encompasses any product incorporating papermaking fibers having cellulose as a primary component. This would include, for example, products sold as hand towels, toilet paper, facial tissue, and the like. Papermaking fibers include virgin pulp or recycled (secondary) cellulose fibers or fiber mixtures comprising cellulose 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, poplar, and the like). Examples of fibers suitable for preparing the webs of our invention include non-wood fibers such as cotton fibers or cotton derivatives, abaca, kenaf, Indian grass, flax, thatch, straw, jute, bagasse, milkweed fibers, and pineapple leaf fibers. "Furnish" and similar terms refer to an aqueous composition used to prepare a paper product, which includes papermaking fibers and optionally wet strength resins, peptizing agents, and the like.

[0035] As used herein, the initial fiber and liquid mixture that is dried into the finished product during the papermaking process will be referred to as a "web" and / or a "nascent web." The dried, single-ply product from the papermaking process will be referred to as a "basesheet." Additionally, the product of the 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 multiple basesheets, such as in a multi-layer structure. Additionally, the absorbent sheet may undergo additional processing (e.g., embossing) after being dried during the initial basesheet formation process.

[0036] When describing the present invention herein, the terms "machine direction" (MD) and "cross-machine direction" (CD) will be used according to their well-understood meanings in the art. That is, the MD of a belt or other creping structure refers to the direction in which the belt or other creping structure moves during the papermaking process, while the CD refers to the direction cross-machine direction of the belt or other creping structure. Similarly, when referring to a paper product, the MD of the paper product refers to the direction on the paper product in which the product moves during the papermaking process, and the CD refers to the direction on the paper product cross-machine direction of the product.

[0037] papermaking machine

[0038] The process of utilizing the belts of the present invention and making the products of the present invention can include compacting and dewatering a papermaking furnish having a random fiber distribution to form a semisolid web, and then belt-creping the web to redistribute the fibers and shape the web to achieve a paper product having desired properties. These steps of the papermaking process can be performed on papermaking machines having many different configurations. Two examples of such papermaking machines will now be described.

[0039] Figure 1 A first example of a papermaking machine 200 is shown. Papermaking machine 200 is a three-fabric loop machine that includes a press section 100 in which a creping operation is performed. Upstream of press section 100 is a forming section 202, which in the case of papermaking machine 200 is known in the art as a crescent former. Forming section 202 includes a headbox 204 that deposits a furnish onto a forming wire 206 supported by rolls 208 and 210, thereby initially forming a papermaking web. Forming section 202 also includes forming rolls 212 that support a papermaking felt 102, such that web 116 is also formed directly on the papermaking felt 102. Felt run 214 extends to a shoe-shaped press section 216, where the wet web is deposited onto a backing roll 108, where web 116 is wet-pressed while being transferred to backing roll 108.

[0040] An example of an alternative configuration for papermaking machine 200 includes a twin-wire forming section instead of crescent forming section 202. In such a configuration, downstream of the twin-wire forming section, the remaining components of such a papermaking machine can be constructed and arranged in a manner similar to papermaking machine 200. An example of a papermaking machine having a twin-wire forming section can be found in U.S. Patent No. 8,293,072 B2, which is incorporated herein by reference in its entirety. Further examples of alternative forming sections that can be used in a papermaking machine include a C-turn twin-wire former, an S-turn twin-wire former, or a suction breast roll former. Those skilled in the art will recognize how to integrate these or even further alternative forming sections into a papermaking machine.

[0041] Web 116 is transferred to creping belt 112 in belt creping nip 120, and vacuum is then drawn by vacuum box 114, as described in greater detail below. Following this creping operation, web 116 is deposited onto Yankee dryer 218 using a creping adhesive in another press nip 224. Transfer to Yankee dryer 218 can be performed, for example, under 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), with a pressurized contact area of about 4% to about 40% between web 116 and the Yankee surface. Transfer at nip 224 can be performed at a web consistency (e.g., about 25% to about 70%). Note that, as used herein, "consistency" refers to the percentage of solids of the nascent web, for example, calculated on a bone-dry basis. At consistencies of about 25% to about 70%, it is sometimes difficult to adhere web 116 firmly enough to the surface of Yankee dryer 218 to allow for clean removal of the web from creping belt 112. To increase adhesion between web 116 and the surface of Yankee dryer 218, an adhesive may be applied to the surface of Yankee dryer 218. The adhesive may allow for high speed operation of the system and high jet velocity impingement air drying, and also allow for subsequent release of web 116 from Yankee dryer 218. An example of such an adhesive is a poly(vinyl alcohol) / polyamide adhesive composition, wherein an exemplary application rate for the adhesive is less than about 40 mg / m 2 However, those skilled in the art will recognize a variety of alternative adhesives that can be used to facilitate transfer of the web 116 to the Yankee dryer 218, and also various amounts of adhesive.

[0042] The web 116 is dried on a Yankee dryer 218 (which is a heated cylinder) and by high-velocity jets of impinging air in a Yankee hood surrounding the Yankee dryer 218. As the Yankee dryer 218 rotates, the web 116 is peeled from the Yankee dryer 218 at position 220. The web 116 can then be wound onto a take-up reel (not shown). The reel can operate faster than the Yankee dryer 218 in a steady state to further crepe the web 116. Optionally, a creping doctor blade 222 can be used to conventionally dry-crepe the web 116. In any case, a cleaning doctor blade can be installed for intermittent engagement and to control accumulation.

[0043] Figure 2 Details of press section 100, where creping occurs, are shown. Press section 100 includes a papermaking felt 102, a suction roll 104, a press shoe 106, and a backing roll 108. Backing roll 108 may optionally be heated, for example, by steam. Press section 100 also includes a creping roll 110, a creping belt 112, and a vacuum box 114. Creping belt 112 may be configured with offset openings, as will be described in detail below.

[0044] In creping nip 120, web 116 is transferred onto the top side of creping belt 112. Creping nip 120 is defined between backing roll 108 and creping belt 112, with creping belt 112 pressed against backing roll 108 by surface 172 of creping roll 110. During this transfer at creping nip 120, the cellulosic fibers of web 116 are repositioned and oriented, as described in detail below. After web 116 is transferred onto creping belt 112, vacuum boxes 114 may be used to apply suction to web 116 to at least partially extract microwrinkles. The applied suction may also help draw web 116 into openings in creping belt 112, thereby further shaping web 116. Additional details of shaping web 116 will be described below.

[0045] The creping nip 120 typically extends a distance or width across the belt creping nip of, for example, anywhere from 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 derived from the loading between the creping roll 110 and the backing roll 108. The creping pressure is typically from about 20 PLI to about 100 PLI (about 3.5 kN / m to about 17.5 kN / m), more specifically, from about 40 PLI to about 70 PLI (about 7 kN / m to about 12.25 kN / m). While a minimum pressure of 10 PLI (1.75 kN / m) or 20 PLI (3.5 kN / m) is typically desired in the creping nip 120, those skilled in the art will appreciate that in commercial machines, the maximum pressure can be as high as desired, limited only by the particular machine employed. Thus, pressures exceeding 100 PLI (17.5 kN / m), 500 PLI (87.5 kN / m), or 1000 PLI (175 kN / m), or greater, may be used if feasible, and provided that the velocity delta can be maintained.

[0046] In some embodiments, it may be desirable to reshape the inter-fiber properties of web 116, while in other cases, it may be desirable to affect only the properties in the plane of web 116. The creping nip parameters can affect the distribution of fibers in web 116 in various directions, including causing changes in the z-direction (i.e., the body of web 116) as well as in the MD and CD. In any case, the transfer from creping belt 112 is at high impact because the travel speed of creping belt 112 is slower than the travel speed of web 116 away from backing roll 108, and a significant change in speed occurs. In this regard, the degree of creping is often referred to as the creping ratio, where the ratio is calculated as:

[0047] Crepe ratio (%) = S1 / S2 – 1

[0048] Where 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 rate of about 5% to about 60%. In fact, a high degree of creping can be used, which approaches or even exceeds 100%.

[0049] Figure 3 Shown can be used as Figure 2 An example of an alternative paper machine to the one depicted is a paper machine 300. The paper machine 300 is configured for through air drying (TAD), in which water is substantially removed from the web by moving high temperature air through the web. Figure 3 As shown, a furnish is initially supplied to a paper machine 300 via a headbox 302. As the furnish passes between a forming roll 308 and a breast roll 310, it is directed in jets into the nip formed between a forming fabric 304 and a transfer fabric 306. Forming fabric 304 and transfer fabric 306 translate in a continuous loop that diverges after passing between forming roll 308 and breast roll 310. After separation from forming fabric 304, transfer fabric 306 passes through a dewatering zone 312, where suction boxes 314 remove water from the web and transfer fabric 306, thereby increasing the web's consistency from approximately 10% to approximately 25%. The web is then transferred to a throughdrying surface 316, which, in embodiments of the present invention, is a creping belt. In some embodiments, vacuum is applied to assist in transferring the web to belt 316, as indicated by vacuum-assist boxes 318 in transfer zone 320.

[0050] Next, the web-carrying belt 316 passes around through-drying cylinders 322 and 324, where the web's consistency is increased from approximately 60% to approximately 90%. After passing through drying cylinders 322 and 324, the web is more or less permanently imparted with a creped structure. The web is then transferred to a Yankee cylinder 326 without significant degradation of its properties, where adhesive is sometimes sprayed onto the Yankee cylinder 326 just prior to contact with the translating web to facilitate transfer. After the web reaches a consistency of approximately 96% or greater, it is removed from the Yankee cylinder 326 using further creping and taken up by reel 328. The reel speed can be controlled relative to the speed of the Yankee cylinder 326 to adjust the further creping applied to the web as it is removed from the Yankee cylinder 326.

[0051] It should be pointed out that Figures 1 to 3 The papermaking machine depicted is merely an example of a possible configuration that may be used with the invention described herein. Additional examples include those described in the aforementioned US Patent No. 8,293,072 B2.

[0052] Crepe belt

[0053] The present invention relates, in part, to a belt that can be used in a creping operation, such as those described above, in a papermaking machine. As will be apparent from the disclosure herein, the belt structure provides a number of advantageous properties particularly suited for creping operations. However, it should be noted that, since the belt is structurally as described herein, the belt structure can be used in applications other than creping operations, such as molding processes that strictly impart shape to a papermaking web.

[0054] Creping belts according to embodiments of the present invention may have a multilayer structure, as described in U.S. Patent No. 9,863,095 B2, which is incorporated herein by reference in its entirety. Such multilayer creping belts according to the present invention include at least two layers. As used herein, a "layer" is a continuous, distinct portion of a belt structure that is physically separate from another continuous, distinct layer in the belt structure. As discussed below, an example of two layers in a multilayer belt according to the present invention is a polymer layer bonded to a fabric layer via an adhesive.

[0055] As used herein, the "top," or "sheet," or "Yankee" side of a multilayer creping belt refers to the side of the belt onto which the web is deposited for the creping operation. Thus, the "top layer" is the portion of the multilayer belt that forms the surface onto which the cellulosic web is formed during the creping operation. As used herein, the "bottom," or "air" ("machine") side of a creping belt refers to the opposite side of the belt, i.e., the side that faces and contacts processing equipment such as creping rolls and vacuum boxes. And, thus, the "bottom layer" provides the bottom (air) side surface.

[0056] It should be noted that while a two-layer belt is described in detail herein, creping belts according to embodiments of the present invention may alternatively be made using a single-layer belt. Indeed, one skilled in the art will recognize, for example, different materials for constructing a single-layer belt in which the opening patterns described herein are formed.

[0057] Top layer of multi-layer creping belt

[0058] One of the functions of the top layer of a multilayer belt according to the present invention is to provide a structure in which openings can be formed, wherein the openings pass through the layers from one side to the other, and wherein the openings impart a domed shape to the web during the papermaking process. The top layer itself need not impart any strength or durability to the belt structure, as these properties are primarily provided by the bottom layer, as described below. Furthermore, the openings in the top layer need not be configured to prevent fibers from being pulled through the top layer during the papermaking process, as this is also provided by the bottom layer, as also described below. As will be described below, in embodiments of the present invention, the openings in the top layer of a multilayer creping belt are arranged in a pattern in which the openings are offset in the MD and CD of the belt.

[0059] In some embodiments of the present invention, the top layer of the multilayer belt of the present invention is made of extruded flexible thermoplastic material. In this regard, there is no specific limitation on the type of thermoplastic material that can be used to form the top layer, as long as the material generally imparts the properties of the top layer described herein, such as friction (e.g., between the paper forming web and the belt), compressibility, and tensile strength. Moreover, it will be apparent to those skilled in the art, based on the disclosure herein, that there are many possible flexible thermoplastic materials that can be used that will provide properties substantially similar to the thermoplastics specifically discussed herein. It should also be noted that, as used herein, the term "thermoplastic material" is intended to include thermoplastic elastomers (e.g., rubber materials). It should also be noted that the thermoplastic material may include thermoplastic materials in the form of fibers (e.g., short-cut polyester fibers) or non-plastic additives, such as those present in composite materials.

[0060] The thermoplastic top layer can be made by any suitable technique (e.g., molding, extrusion, thermoforming, etc.). Notably, the thermoplastic top layer can be made from multiple segments joined together, for example, in a spiral fashion from side to side, as described in U.S. Pat. No. 8,394,239 B2, the disclosure of which is incorporated by reference in its entirety. Furthermore, the thermoplastic top layer can be made to any specific desired length and can be customized to the path length required for any specific papermaking machine configuration.

[0061] In a specific embodiment, the material used to form the top layer of the multilayer tape is polyurethane. As an alternative to polyurethane, examples of specific thermoplastics that can be used to form the top layer in other embodiments of the present invention are available from EI du Pont de Nemours and Company of Wilmington, Delaware under the name sell. is a polyester thermoplastic elastomer having friction, compressibility, and stretch properties favorable for forming the top layer of the multilayer creping belt described herein.

[0062] When considering the ability to form openings of varying sizes and configurations in thermoplastics, thermoplastics such as the aforementioned polyurethanes are advantageous materials for forming the top layer of the multilayer tape of the present invention. The openings in the thermoplastic used to form the top layer can be easily formed using a variety of techniques. Examples of such techniques include laser engraving, drilling, cutting, or mechanical stamping. As will be appreciated by those skilled in the art, such techniques can be used to form relatively large, uniformly sized openings. In fact, such techniques can be used to form openings of most any configuration (size, shape, sidewall angle, etc.) in the thermoplastic top layer.

[0063] When considering the different configurations of openings that can be formed in the top layer, it is important to note that the shapes of the openings do not need to be identical. That is, some openings formed in the top layer may have a different configuration than other openings formed in the top layer. In fact, different openings can be provided in the top layer to serve different functions in the papermaking process. For example, some openings in the top layer may be sized and shaped to provide for the formation of dome structures in the papermaking web during the creping operation (described in detail below). At the same time, other openings in the top layer may have much larger sizes and varying shapes to provide a pattern in the papermaking web that is equivalent to that achieved through an embossing operation. However, the pattern is achieved without undesirable embossing effects (such as loss of sheet bulk and other desirable properties).

[0064] When considering materials for forming the top layer of the multi-layer belt of the present invention, polyurethane is a very suitable material, as discussed above. Polyurethane is a relatively soft material for creping belts, especially when compared to materials that can be used to form single-piece creping belts. At the same time, polyurethane can provide a relatively high friction surface. Polyurethane is known to have a coefficient of friction ranging from about 0.5 to about 2, depending on its formulation. In embodiments of the present invention, the polyurethane top surface of the multi-layer belt has a coefficient of friction of about 0.6. Notably, Thermoplastics (also discussed above as a very suitable material for forming the top layer) have a coefficient of friction of about 0.5. Thus, the multilayer belts of the present invention can provide a soft and high friction top surface, thereby achieving a "soft" sheet creping operation.

[0065] The friction of the top surface of the top layer, as well as other surface properties of the top surface, can be modified by applying a coating to the top surface. In this regard, the coating can be added to the top surface to increase or decrease the friction of the top surface. Additionally or alternatively, the coating can be added to the top surface to modify the release properties of the top surface. Examples of such coatings include both hydrophobic and hydrophilic compositions, depending on the specific papermaking process in which the multi-layer creping belt is to be used. These coatings can be sprayed onto the belt during the papermaking process, or the coating can be formed as a permanent coating attached to the top surface of the multi-layer belt.

[0066] bottom layer

[0067] The bottom layer of a multi-layer creped belt serves to provide the belt with strength, MD stretch and creep resistance, CD stability, and durability. As discussed above, flexible polymer materials such as polyurethane offer an attractive option for the top layer of the belt. However, polyurethane is a relatively weak material that, by itself, would not provide the desired properties to the belt. A homogenous, single-piece polyurethane belt would not be able to withstand the stresses and strains imparted to the belt during the papermaking process. However, by bonding the polyurethane top layer to a second layer, the second layer can provide the belt with the required strength, stretch resistance, and other properties. Essentially, the use of a distinct bottom layer, separate from the top layer, expands the potential range of materials that can be used for the top layer.

[0068] Like the top layer, the bottom layer also includes a plurality of openings extending through the thickness of the multilayer belt. Each opening in the bottom layer is aligned with at least one opening in the top layer, and thus, the openings are arranged to extend through the thickness of the multilayer belt, i.e., through both the top layer and the bottom layer. However, the openings in the bottom layer are smaller than the openings in the top layer. That is, the cross-sectional area of the openings in the bottom layer adjacent to the interface between the top layer and the bottom layer is smaller than the cross-sectional area of the plurality of openings in the top layer adjacent to the interface between the top layer and the bottom layer. Thus, the openings in the bottom layer prevent cellulose fibers from being completely drawn through the multilayer belt structure, for example, when the belt and papermaking web are exposed to a vacuum. As discussed generally above, fibers drawn through the belt are detrimental to the papermaking process because, over time, fibers accumulate in the papermaking machine, for example, on the outer edges of the vacuum box. This accumulation of fibers requires machine downtime to clear the accumulation. Therefore, the openings in the bottom layer can be configured to substantially prevent fibers from being drawn through the belt. However, because the bottom layer does not provide a creping surface and is therefore not used to form the web during the creping operation, configuring the openings in the bottom layer to prevent fibers from being drawn through does not substantially affect the creping operation of the belt.

[0069] In some embodiments of the present invention, a woven fabric is provided as the bottom layer of a multi-layer creping belt. As discussed above, woven structured fabrics possess the strength and durability to withstand the forces of the creping operation. Consequently, woven structured fabrics themselves have been used as creping structures in papermaking processes. Thus, woven structured fabrics can provide the necessary strength, durability, and other properties for multi-layer creping belts according to the present invention.

[0070] In a specific embodiment of a multi-layer creping belt, the woven fabric provided for the bottom layer has properties similar to those of a woven structured fabric used as the creping structure itself. Such fabrics have a woven structure that, in effect, has a plurality of "openings" formed between the yarns that comprise the fabric structure. In this regard, the resulting openings in the fabric can be quantified as air permeability, which allows airflow through the fabric. According to our invention, the permeability of the fabric, combined with the openings in the top layer, allows air to be drawn through the belt. This airflow can be drawn through the belt at the vacuum box in a papermaking machine, as described above. Another aspect of the woven fabric layer is its ability to prevent fibers from being completely drawn through the multi-layer belt at the vacuum box. Generally speaking, it is preferred that less than 1% of the fibers completely pass through the creping belt or fabric during the papermaking process.

[0071] As an alternative to woven fabrics, in other embodiments of the present invention, the bottom layer of the multilayer creping belt may be formed from an extruded thermoplastic material. However, unlike the flexible thermoplastic material used to form the top layer discussed above, the thermoplastic material used to form the bottom layer is provided to impart strength, stretch resistance, durability, and the like to the multilayer creping belt. Examples of thermoplastic materials that can be used to form the bottom layer include polyesters, copolyesters, polyamides, and copolyamides. Specific examples of polyesters, copolyesters, polyamides, and copolyamides that can be used to form the bottom layer can be found in the aforementioned U.S. Patent No. 8,394,239 B2.

[0072] In a specific embodiment of the present invention, PET can be used to form the extruded bottom layer of the multilayer tape. PET is a well-known durable and flexible polyester. In other embodiments, (which is discussed above) can be used to form the extruded bottom layer of the multilayer tape. Those skilled in the art will recognize similar alternative materials that can be used to form the bottom layer.

[0073] When an extruded polymer material is used for the bottom layer, openings can be provided through the polymer material in the same manner as openings are provided in the top layer (e.g., by laser drilling, cutting, or mechanical perforation). At least some of the openings in the bottom layer are aligned with openings in the top layer, thereby allowing air flow through the multilayer tape structure in the same manner as a woven fabric bottom layer allows air flow through a multilayer tape structure. However, the size of the openings in the bottom layer need not be the same as the size of the openings in the top layer. In fact, to reduce fiber pull-through in a manner similar to a fabric bottom layer, the openings in the extruded polymer bottom layer can be substantially smaller than the openings in the top layer. Generally speaking, the size of the openings in the bottom layer can be adjusted to allow a specific amount of air flow through the tape. In addition, multiple openings in the bottom layer can be aligned with openings in the top layer. If multiple openings are provided in the bottom layer to provide a larger total open area in the bottom layer relative to the area of the openings in the top layer, a larger air flow can be drawn through the tape at the vacuum box. At the same time, the use of multiple openings with smaller cross-sectional areas reduces fiber pull-through compared to a single, larger opening in the bottom layer. In a specific embodiment of the present invention, the openings in the second layer have a maximum cross-sectional area of 350 square microns near the interface with the first layer.

[0074] There are other materials that can be used to form the bottom layer in alternatives to the above-mentioned woven fabric and extruded polymer layer. For example, in an embodiment of the present invention, the bottom layer can be formed of a metal material, and in particular, a metal screen-like structure. The metal screen provides strength and flexibility properties to the multilayer belt in the same manner as the above-mentioned woven fabric and extruded polymer layer. In addition, the metal screen is used to prevent the cellulose fibers from being pulled through the belt structure in the same manner as the above-mentioned woven fabric and extruded polymer material. Another alternative material that can be used to form the bottom layer is a super fiber material, such as a material formed of para-aramid synthetic fibers. Super fibers may differ from the above-mentioned fabrics in that they are not woven together, but are still able to form a strong and flexible bottom layer. Those skilled in the art will recognize some other alternative materials that can provide the properties of the bottom layer of the multilayer belt described herein.

[0075] Multi-layer structure

[0076] The multilayer tape according to the present invention is formed by connecting the top and bottom layers described above. As will be understood from the disclosure herein, connection between layers can be achieved using a variety of different techniques, some of which are described more fully below.

[0077] Figure 4AFIG4 is a cross-sectional view of a portion of a multilayer creping belt 400 according to an embodiment of the present invention. Belt 400 includes a polymeric top layer 402 and a fabric bottom layer 404. Polymeric top layer 402 provides a top surface 408 of belt 400, on which a web is creped during the creping operation of the papermaking process. Openings 406 are formed in polymeric top layer 402, as described above. Note that openings 406 extend from top surface 408 through the thickness of polymeric top layer 402 to the surface facing fabric bottom layer 404. Because woven fabric bottom layer 404 has a certain permeability, a vacuum can be applied to the woven fabric bottom layer 404 side of belt 400, thereby drawing airflow through openings 406 and woven fabric bottom layer 404. During the creping operation using belt 400, cellulosic fibers from the web are drawn into openings 406 in polymeric top layer 402, which results in the formation of dome structures in the web (as will be described more fully below). Vacuum can also be used to draw the web into openings 406.

[0078] Figure 4B Is looking down with Figure 4A A top view of the strip 400 showing a portion of the opening 406 is shown. Figure 4A and Figure 4B As will be apparent, while the woven fabric bottom layer 404 allows a vacuum to be drawn through the belt 400, the woven fabric bottom layer 404 also effectively closes the openings 406 in the top layer. That is, the woven fabric bottom layer 404 actually provides a plurality of openings having a relatively small cross-sectional area adjacent to the interface between the extruded polymer top layer 402 and the woven fabric bottom layer 404. Thus, the woven fabric bottom layer 404 can substantially prevent the cellulosic fibers from passing through the belt 400. As described above, the woven fabric bottom layer 404 also imparts strength, durability, and stability to the belt 400.

[0079] Figure 5A is a cross-sectional view of a portion of a multilayer creping belt 500 according to an embodiment of the present invention, comprising an extruded polymer top layer 502 and an extruded polymer bottom layer 504. Polymeric top layer 502 provides a top surface 508 on which a papermaking web is creped. In this embodiment, openings 506 in top layer 502 are aligned with three openings 510 in bottom layer. Figure 5B A top view of the belt portion 500 is shown (see Figure 5A) As will be apparent, the openings 510 in the polymer bottom layer 504 have a cross-section that is substantially smaller than the cross-section of the openings 506 in the polymer top layer 502. That is, the polymer bottom layer 504 includes a plurality of openings 510 having a smaller cross-sectional area adjacent to the interface between the polymer top layer 502 and the polymer bottom layer 504. This allows the extruded polymer bottom layer 504 to be used to substantially prevent fibers from being pulled through the tape structure in the same manner as the woven fabric bottom layer described above. It should be noted that, as indicated above, in alternative embodiments, a single opening in the extruded polymer bottom layer 504 can be aligned with the opening 506 in the extruded polymer top layer 502. In fact, any number of openings can be formed in the polymer bottom layer 504 for each opening in the polymer top layer 502.

[0080] The openings 406, 506, and 510 in the extruded polymer layer in the strips 400 and 500 are such that the walls of the openings 406, 506, and 510 extend normal to the surface of the strips 400 and 500. However, in other embodiments, the walls of the openings 406, 506, and 510 may be disposed at different angles relative to the surface of the strip. The angles of the openings 406, 506, and 510 may be selected and produced when the openings are formed by techniques such as laser drilling, cutting, or mechanical perforation.

[0081] The layers of a multilayer belt according to the present invention can be joined together by any means that provide sufficiently durable connections between the layers to allow the multilayer creping belt to be used in a papermaking process. In some embodiments, the layers are chemically joined together, such as with an adhesive. A specific example of an adhesive structure that can be used to join the layers is a double-coated adhesive tape. In other embodiments, the layers can be mechanically joined together, such as with hook-and-loop fasteners. In still other embodiments, the layers of the multilayer belt can be joined by techniques such as heat welding and laser fusing. Those skilled in the art will appreciate that a variety of lamination techniques can be used to join the layers described herein to form a multilayer belt.

[0082] Although Figure 4A 、 Figure 4B 、 Figure 5A and Figure 5B While the multi-layer tape embodiment depicted in the drawings includes two distinct layers, in other embodiments, additional layers may be provided between the top and bottom layers shown in the drawings. For example, an additional layer may be positioned between the top and bottom layers to provide another barrier that allows air to pass through the tape but prevents fibers from being pulled through the tape structure. In other embodiments, the means for attaching the top and bottom layers together may be configured as another layer. For example, an adhesive layer may be a third layer disposed between the top and bottom layers.

[0083] Openings in the creping belt

[0084] We have discovered that a specific alignment of openings formed in the top surface / top layer of a creping belt produces a paper product with outstanding properties while simultaneously providing better transfer of the web onto the creping belt during the papermaking process. Specifically, we have discovered that lines of openings arranged along lines offset from the MD and CD directions provide both excellent paper product and sheet transfer. Specific examples of paper products and processes for making paper products are discussed below.

[0085] exist Figure 6 An example of a creping belt 1000 having offset lines of openings 1002 in its top surface is shown in FIG. (specifically, only some of the openings 1002 are indicated by reference lines in the figure). In belt 1000, openings 1002 are arranged along lines that are offset by an angle α from lines in the MD. One such line of openings 1002 is at Figure 6 The openings 1002 are also arranged along lines that are offset by an angle β from the lines along the CD direction, with one such line being at Figure 6 Indicated as L2.

[0086] In a particular embodiment of the present invention, the opening lines are set at an angle of about 12 degrees to about 21 degrees relative to the line in the MD direction. In this regard, it should be noted that the lines of offset openings can be rotated in a counterclockwise direction relative to the MD lines, such as in Figure 6 In the case of the belt shown, or the lines of offset openings may be rotated in a clockwise direction, as in Figure 7 The band shown (which will be discussed more fully below).

[0087] The openings may have different cross-sectional shapes, including non-circular shapes. However, when the openings do have a circular cross-section on the top surface of the strip, in embodiments of the present invention, the openings may have a diameter of about 0.5 mm to about 5.0 mm, and thus, the openings may have a diameter of about 0.785 mm. 2 to about 7.85mm 2 In more specific embodiments, the opening may have a diameter of about 0.75 mm to about 2.5 mm, and thus the opening may have a cross-sectional area of about 1.75 mm. 2 to about 2.0mm 2 The cross-sectional area of the tape is 100 mm / s. In combination with the size of the opening, the percentage of open area on the top surface created by the opening can be in the range of about 10% to about 90%. In other words, the percentage of the top surface of the tape that forms the contact area (i.e., the area excluding the opening) is in the range of about 10% to about 90%. Figure 7 Specific parameters for an embodiment of a belt having offset lines of circular openings are shown in FIG. Figure 7 All of the tapes shown have a multi-layer structure as described above, with openings formed in the top layer of the tape.

[0088] Without wishing to be bound by theory, we believe that superior paper products can be produced using creping belts with open offset lines due to the configuration of the contact area the belt provides in the creping nip of a papermaking machine. As discussed above, in the creping nip, the papermaking web is transferred onto the top of the belt. Generally, web transfer to the creping belt is a difficult operation because the web is unstable at this point in the papermaking process due to its high moisture content. We believe that, with open offset lines, the creping belt provides a contact area that is more conducive to web transfer than belts with other opening arrangements. Specifically, the open offset lines provide a balanced contact area with both MD-like and CD-like components. That is, the offset of the open lines provides a more CD-like contact area in the creping nip compared to an alignment with open lines extending along the lines in the MD. This CD-like nature of the creping belt's contact area enables the belt to better retain the web as it moves through the creping nip in the MD. At the same time, the contact area of the belts remains sufficiently MD-like to avoid undesirable effects that can result from excessive CD-like contact area, such as reduced softness in the paper product. Furthermore, the contact area created by alignment with the offset lines of openings can also provide beneficial reorientation of the cellulose fibers of the web, as demonstrated in paper products produced in the trials discussed below.

[0089] To examine the effects of the offset alignment of openings in a creping belt according to an embodiment of the present invention, a finite element analysis (FEA) model of web transfer onto a creping belt was created using Abacus software manufactured by Dassault Systèmes SE of Vélizy-Villacoublay, France. As will be appreciated by those skilled in the art, such FEA models utilize the components of a dynamic system by associating the geometry defining each component with an appropriate material model and specifying component interactions. The software automatically selects appropriate load increments and convergence tolerances and continuously adjusts them during the analysis to ensure an accurate solution. In this case, the creping belt geometry, creping nip parameters, and web consistency were considered to create a model of web transfer.

[0090] Figure 8 and Figure 9 The output of this model is shown for the transfer of a web onto two different belts. Figure 8 The case of a creping belt having offset lines of openings as described herein is shown. For comparison, Figure 9The case of a belt with openings arranged along lines extending in the MD and CD is shown. In these figures, the MD is in the vertical direction and the CD is in the horizontal direction. Therefore, the web is modeled as moving downward in the figures, with the upper portion of the figures representing the web before transfer to the creping belt, the lower portion of the figures representing the web after transfer to the creping belt, and the middle portion of the figures representing the area where the web first contacts the belt. In the figures, coloring indicates the web's speed at each point, with lighter colors (e.g., orange) indicating higher speeds and darker colors (green and blue) indicating lower speeds. A reference line TL has been added to the figures to indicate a sharp change in speed, indicating where the web first contacts the belt.

[0091] from Figure 8 and Figure 9 It is evident from the model shown that there is a significant difference in sheet transfer onto a belt with offset lines of openings compared to sheet transfer onto a belt with openings aligned in the MD and CD. Figure 8 ), the web first contacts the creping belt with line TL extending substantially in the CD across the plurality of openings in the MD and then extending substantially in the MD. On the other hand, the web first contacts the creping belt with line TL ( Figure 9 ) extends sinusoidally across the opening. Figure 8 and Figure 9 Another difference visible in the belt models shown is how the web is decelerated within the opening. Figure 8 The opening in the belt with the offset opening shown is very unevenly decelerated because the web moving into the opening slows down significantly in this area shortly after the web first contacts the belt. Figure 9 In the illustrated aligned openings of the belt with aligned openings, the web deceleration upon entering the openings is very uniform. We believe the sweeping transfer lines shown by the model for the belt with offset lines of openings are superior. Furthermore, better transfer leads to improvements in many aspects of the papermaking process, including the consistency of the product produced during the process.

[0092] Figure 6 、 Figure 7 and Figure 10 The openings in the exemplary band shown are arranged in a repeating pattern having six openings positioned around one opening. Figure 10In the embodiment of the present invention, a central opening of a hexagonal pattern is represented as X, with six openings AF surrounding the central opening X. Those skilled in the art will recognize that other opening patterns that differ from the depicted hexagonal pattern but still result in the openings being arranged along lines that are offset from the lines in the MD and CD directions are possible. Furthermore, such other patterns will have at least some of the same aspects of the tape and resulting paper properties described herein. Therefore, the present invention should not be construed as limited to the patterns of openings described herein.

[0093] One aspect of a creping belt resulting from offset lines of openings according to an embodiment of the present invention can be seen in Figure 10 For each line along MD, the length of the line across an opening is different from the length of the line across the adjacent openings on either side of the opening. For example, line MD spans Figure 10 The length of line MD across this diameter is different from the length of line MD across adjacent openings 2 and 3. The offset configuration in CD also provides a similar relationship between adjacent openings. For example, line CD extends across the diameter of opening 1 in CD, and the length of line CD along this diameter is different from the length of line CD across adjacent openings 4 and 5.

[0094] Another aspect of the offset openings in the creping belt according to embodiments of the present invention relates to the rotational symmetry of the opening pattern. As will be understood by those skilled in the art, rotational symmetry refers to the degree to which an object can be rotated and still appear the same. Figure 10 As shown, each hexagonal pattern of openings has 60° of rotational symmetry, even if there are offsets in the openings. For example, if a hexagonal pattern with a central opening marked as X is rotated 60° so that opening A moves to the position of opening B in the figure, the pattern will appear identical to before the rotation. Also note that the hexagonal pattern has a symmetry level of six, as there are six rotational positions to which the pattern can be moved and still appear identical.

[0095] Yet another aspect of offset openings in creping belts according to embodiments of the present invention relates to the lack of mirror images about the pattern. For example, when considering a creping belt having an opening 1 in the center of the pattern Figure 10 When looking at the hexagonal pattern in the figure, it can be seen that the pattern is not mirrored about either the MD or CD lines. This also applies to all other patterns shown in the figures and is a result of the offset of the openings in the MD and CD directions. It should also be noted that offset openings provide a combination of properties; for example, rotational symmetry can exist in the opening pattern, but mirroring of the opening pattern about either the MD or CD lines is not possible.

[0096] As discussed above, the area of the belt's top surface that the web first contacts during the transfer operation can be significant in this operation. One aspect of the invention related to this contact area can be seen by evaluating how the amount of contact area varies along the MD lines in the belt. The MD line contact profile sum is the sum of the total contact area taken along the MD lines in the belt. By determining the MD line contact profile sum (for different arrangements of openings in different belts), the MD line contact profile sum can be used to quantify belt differences resulting from the opening arrangement.

[0097] The sum of the MD line contact profiles can be determined using a model representation with openings. Figure 11 An example of such a model representation of the arrangement of openings in a creping belt is shown. Figure 11 , the contact profile sum is calculated along the line marked CPS. As will be appreciated by those skilled in the art, Figure 11 The model representation shown can be created using a graphics program by specifying the dimensions of the openings and the relationship of the openings to each other (e.g., the distance between the centers of the openings and the angle formed between the centers of the openings). An example of such a graphics program is Adobe Illustrator, manufactured by Adobe Systems of San Jose, California. Figure 11 The model shown indicates that the MD line contact profile sum can be easily calculated, for example, by having a graphics program calculate the contact area along the MD line based on the white pixels of the line CPS in the model moving in the CD direction across the model.

[0098] Figure 12 Shown Figure 11 The band shown represents the sum of the MD line contact profiles. Figure 12 In the Graph, the X-axis is the position of the MD lines along the CD direction, and the Y-axis "Intensity" is the sum of the contact areas (white pixels) of the MD lines. Therefore, a peak in intensity represents the MD line with the largest total contact area, while a valley represents the MD line with the lowest total contact area.

[0099] It is worth noting that in Figure 11 In the case of the opening pattern of the creping belt shown, the MD line contact profile sum has peaks at substantially repeated distances along the CD of the belt, as shown in FIG. Figure 12 The most significant repetitive peak is Figure 12 5 in the MD lines. We have noted that such regularly repeating peaks in the sum of the MD line contact profiles are generally present in tapes with offset openings, as described herein. However, the distance along the CD at which the most significant peaks repeat varies significantly with the angle of offset from the MD lines. In this regard, Table 1 below provides the following graphs for tapes with: Figure 11The ribbons of the configuration shown, but with different offset angles relative to the lines in the MD, show the distance in the CD over which the most significant peak of the sum of the MD line contact profiles repeats.

[0100] Table 1

[0101]

[0102]

[0103] It is noteworthy that when the offset angle is small, the distance in the CD direction between the significant repetitive peaks for the belts shown in Table 1 starts out relatively large, for example, about 1.4 mm for belts with an offset angle of 0-9 degrees. However, at an offset angle of 13 degrees, the distance between the most significant repetitive peaks drops sharply to about 0.4 mm and remains relatively low (less than about 0.55 mm) for all belts with an offset angle of 13-21 degrees. Then, starting at an offset angle of 24 degrees, the distance between the significant repetitive peaks increases again. We believe that the short distance between the most significant repetitive peaks in the MD contact profile sum for belts with an offset angle in the range of 13-21 degrees indicates a characteristic of the belt that facilitates web transfer to the belt, as described above.

[0104] process

[0105] Another aspect of the present invention relates to a process for manufacturing paper products, wherein such a process utilizes a belt as described herein to perform a creping operation. In such a process, any papermaking machine of the general type described above can be used. Of course, those skilled in the art will recognize various variations and alternative configurations of papermaking machines that can be used to perform the inventive process described herein. Furthermore, those skilled in the art will recognize that well-known variables and parameters that are part of any papermaking process can be readily determined and used in conjunction with the inventive process. For example, the specific type of furnish used to form a web in the papermaking process can be selected based on the desired characteristics of the product.

[0106] In some TAD processes according to embodiments of the present invention, the web has a consistency (i.e., solids content) of between about 15% and about 25% when the web is transferred to the creping belt. In other non-TAD processes according to embodiments of the present invention, belt creping occurs under pressure in the creping nip while the web has a consistency of between about 30% and about 60%. In such processes, the paper machine may have, for example, Figure 1The configuration shown and described above. Details of this type of process can be found in the aforementioned U.S. Patent No. 8,394,239 B2. In this process, web consistency, the velocity delta occurring at the belt creping nip, the pressure employed at the creping nip, and the belt and nip geometry are used to rearrange the fibers while the web remains sufficiently flexible to undergo structural changes. Without being bound by theory, it is believed that the slower surface speed of the creping belt causes the web to be essentially molded into the openings in the creping belt, with the fibers realigned in proportion to the creping ratio. Some fibers move to a CD orientation, while others fold into MD ribbons. Due to this creping action, sheets of high thickness can be formed. As described herein, multilayer belts having openings arranged in offset lines are well suited for these processes.

[0107] Another aspect of processes according to embodiments of the present invention is the application of a vacuum to the creping belt. As described above, a vacuum can be applied while the web is being deposited on the creping belt during the papermaking process. The vacuum serves to draw the web into the openings in the creping belt. Notably, in processes involving multi-layer belt structures, both with and without the use of a vacuum, the web is drawn into the plurality of openings in the top 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 embodiments of the present invention, the applied vacuum is between about 5 in.Hg and about 30 in.Hg. As described in detail above, the bottom layer of the multi-layer belt acts as a screen to prevent fibers from being pulled through the belt structure. This bottom layer screen function is particularly important when a vacuum is applied, as it prevents fibers from being pulled through the vacuum box structure that generates the vacuum.

[0108] paper products

[0109] The following experiments demonstrate the high quality paper products that can be made in accordance with embodiments of the present invention.

[0110] Use with Figure 7 The configuration of belt 6 shown is used to make towel grade substrate. Figure 1 The test was conducted on a paper machine similar to the one shown, using a non-TAD process in which the sheet was transferred to the belt at a higher consistent speed (as described above). The parameters for this test are shown in Table 2.

[0111] Table 2

[0112]

[0113]

[0114] In addition, a towel base sheet made of a belt having the configuration of belt 6 was also converted according to the specifications shown in Table 3.

[0115] Table 3

[0116] Number of layers 2 Roller diameter (inches) 5.70-6.05 Sheet counting 120-160 Sheet length (inches) 5.9-7.0 Sheet width (inches) 11.0

[0117] exist Figure 13 and Figure 14 The results of the experiment are shown in FIG, where the characteristics of the substrate are Figure 13 and the characteristics of the converted products are shown in Figure 14 As will be appreciated by those skilled in the art, the product exhibits excellent properties.

[0118] use Figure 7 As described above, using a non-TAD process, in conjunction with Figure 1 The tests were carried out on a paper machine similar to the one shown in FIG. Three different furnishes were used in the tests: an integrated furnish of 65% Hw and 35% SW, a premium furnish of 65% eucalyptus (Euc) and 35% NSWK, and a furnish with 100% Euc. The parameters of the tests are shown in Table 4.

[0119] Table 4

[0120]

[0121]

[0122] Some of the tissue basesheets produced in this trial were converted according to the specifications shown in Table 5.

[0123] Table 5

[0124] Number of layers 2 Roller diameter (inches) 4.45 Sheet counting 176 Sheet length (inches) 4.00 Sheet width (inches) 4.00 Roller compression 18％ Core diameter (inches) 1 5 / 8

[0125] The following shows the results of the experiment, in which the characteristics of the substrate are Figures 15 to 17 and the characteristics of the converted products are shown in Figure 18 As will be appreciated by those skilled in the art, the product exhibits excellent properties.

[0126] Figure 19A is a photomicrograph of a tissue grade substrate produced in the experiment with Tape 4 above, and Figure 19B It is used Figure 7Photomicrographs of towel-grade basesheet produced using belt 5 are shown. In these photomicrographs, the circular, lighter areas are domes formed in the offset lines of openings in the creping belt, and the darker areas between the domes are connecting areas formed on the contact (top) surface of the creping belt. As is apparent from the photomicrographs, the domes have the same arrangement as the openings in the creping belt. That is, the domes form along lines that are offset from lines along the MD (vertical in the diagram) and from lines along the CD (horizontal in the diagram). Because the domes are offset in the MD and CD in the same manner as the openings in the creping belt, the domes have the same properties as the openings in the creping belt described above. For example, for each line along the MD, the length across the dome is different from the length across the adjacent domes on either side of the dome. As another example, a hexagonal dome pattern with 60° rotational symmetry exists, and the diameter of the central dome along each hexagonal pattern is not mirrored about the MD and CD lines.

[0127] While the openings in the creping belt are typically circular, such circular openings can still form the web to produce domes with elliptical shapes in the paper product. Such elliptical domes can occur when the openings in the creping belt have a diameter of about 1.5 mm or greater. Another unique aspect of paper products according to embodiments of the present invention relates to the elliptical nature of the domes present in some products. We have discovered that the major axis of the elliptical domes in some of the present invention products is oriented at a different angle relative to the CD than in other paper products having elliptical domes. We believe this difference stems from the presence of lines of offset openings in the creping belt, as described herein.

[0128] This difference in the orientation angle of the dome's major axis can be determined using image analysis software, such as Wolfram Mathematica from Wolfram Research, Champaign, Illinois. An example of the steps for calculating the orientation angle of the dome's major axis will now be described. First, a grayscale micrograph of the paper product is converted to a black and white representation of the micrograph. Figure 20A and Figure 20B An example of such a micrograph and its converted black and white representation is shown in . For the conversion, the cutoff value is set so that the parts of the grayscale image darker than the cutoff level are made black, and the parts of the grayscale image lighter than the cutoff level are made white. As shown in Figure 20B As can be seen in the converted image shown, the domes appear white and the connecting areas between the domes appear black.

[0129] To facilitate analysis, the orientation of the product in the micrograph used to create the black and white converted representation should be recorded and maintained the same when comparing different products. For example, in the micrograph shown in FIG20 , the product's MD is aligned vertically and its CD is aligned horizontally, and therefore, the MD and CD are also aligned vertically and horizontally, respectively, in the black and white converted representation shown in FIG20 . Given a black and white representation with known alignment, image analysis software can be used to calculate the orientation of the major axis, as well as other elliptical properties of the dome, such as the elongation of the dome, the length of the major axis of the dome, the length of the minor axis of the dome, etc.

[0130] Using this type of image analysis, the oval characteristics of domes in products according to embodiments of the present invention were compared to the oval characteristics of domes in other paper products. The results are shown in Table 6 below. Products 1-3 were made using a creping belt having offset lines of openings. Specifically, Products 1 and 2 were made with Figure 7 The belt 4 is manufactured in the configuration shown, and the product 3 is made of a belt having Figure 7 Belts of the configuration of belt 6 shown were made. For comparison, products 4-8 were made using creping belts that did not have offset openings, i.e., the openings in the belts had openings aligned in the MD. All products 1-9 were made using the same papermaking machine and the same general method, with parameters such as reel creping and / or conversion factors being varied.

[0131] Table 6

[0132]

[0133] In the results shown in Table 6, the orientation angles are measured relative to a line along the CD, with positive angles meaning counterclockwise from the CD line and negative angles meaning clockwise from the CD line. Also note that the "count" in Table 6 refers to the number of domes examined when determining orientation, elongation, and major and minor axis measurements. Also note that the elongation in Table 6 is calculated as 1-(major axis length / minor axis length) and therefore indicates the degree of elliptical dome formation.

[0134] As can be seen from the results shown in Table 6, products manufactured with belts having offset lines of openings had different orientations in the major axes of their domes compared to the orientations of the major axes of products manufactured with belts without offset openings. Specifically, the major axes of the domes of products 1-3 had a median orientation of approximately 4 to 5 degrees in the clockwise direction. On the other hand, the major axes of the domes of products 4-8 had a median orientation of their major axes significantly more in the opposite (counterclockwise) direction, with orientations ranging from approximately 2° in the clockwise direction to approximately 2.5° in the counterclockwise direction. The differences in orientation are all the more noteworthy given the otherwise similar elliptical nature of the domes, where the median values for the lengths of the major and minor axes were relatively similar for all products. Without being bound by theory, we believe that these differences in orientation are a result of the area of the belt contacting the web as the web is transferred onto the belt. As discussed above, in the creping nip, the papermaking web is transferred onto the top side of the creping belt, and in this process, the web's cellulose fibers are repositioned and oriented. Thus, the contact area of the belt has a significant impact on the transfer operation and subsequent fiber orientation in the web. And, as also discussed above, the contact area of the belt with open offset lines is significantly different than the contact area of the belt without open offset lines. We believe that these different contact areas of the creping belt produce the observed differences in the major axis orientation of the domes.

[0135] Paper products in embodiments of the present invention have a relative density that is indicative of the process used to manufacture the product using a creping belt. To understand this aspect of the present invention, a technique can be used to provide a representation of the local fiber density in paper products such as those of the present invention, with a resolution approaching the underlying resolution of three-dimensional X-ray microcomputed tomography (XR-μCT) representations obtained from synchrotron or laboratory instruments. An example of such a laboratory instrument is the MicroXCT-200 from XRadia, Inc. of Pleasanton, CA. Specifically, using the technique described below, the fiber density perpendicular (normal) to the center surface of the paper product can be determined. Note that density can vary in the out-of-plane direction due to embossing, creping, drying characteristics, etc.

[0136] Using fiber density determination techniques, an XR-μCT dataset is received after it undergoes a Radon transform or a John transform to convert the radially projected X-ray image into a three-dimensional dataset consisting of a stack of two-dimensional grayscale images. For example, paper product data received from a synchrotron accelerator at the European Synchrotron Radiation Facility in Grenoble, France, consists of 2000 slices, each with a size of 2000 × approximately 800 pixels, with eight-bit grayscale values. The grayscale value represents the attenuation of mass, which for materials of relatively uniform molecular mass is very close to the three-dimensional distribution of mass or shape. Paper products are mainly composed of cellulose fibers, so a constant X-ray attenuation coefficient is assumed, and therefore a direct relationship between grayscale and mass is valid.

[0137] XR-μCT datasets generated by Radon or John transforms show void spaces as finite grayscale values, and masses at higher grayscale values in the range of 0 to 255. Slice images also show visible artifacts that arise from movement of the paper sample during exposure, or from inaccurate movement of the rotation or z-positioning stage. These artifacts appear as lines projected from the mass at various orientations. If the paper sample is rotated within the X-ray beam on an axis perpendicular to the principal plane of the paper sample, it may also contain "ringing" artifacts and a central "needle" of higher grayscale that must be dealt with, as this indicates a mass that is not present in the paper sample. This can be particularly the case for XR-μCT datasets received from synchrotrons.

[0138] The segmentation process refers to the separation of the different phases of the material contained in the paper product sample. This only distinguishes solid cellulose fibers and air (void space). In order to obtain a representative tomographic imaging data set, the following segmentation process can be adopted using an open software called ImageJ, which is an image processing program in the public domain developed at the National Institutes of Health (United States National Institute of Health). First, the image is homogenized by using a diffusion technique with edge detection and conditional means filtering, and binarization is used as the main method for segmentation. Next, the image stack is subjected to particle identification and removal, where particles are defined as any component that is discontinuous for the scan subject. Finally, grayscale is re-established based on the original scan data on the fully segmented one-bit image. All slices are processed in the same way so that a data set is generated that clearly distinguishes fiber mass and void space.

[0139] The relative density of a paper product sample can be calculated from a segmented XR-μCT dataset by first generating surfaces approximating the upper and lower boundaries of the sample and then calculating the central surface between the two. The surface normal vector determined at each location within the central surface is then used to determine the mass per unit volume within the cylinder, which is 1×1 pixel multiplied by the distance (in pixels) between the upper and lower surfaces along the surface normal vector. All calculations can be performed using the MathWorks, Inc. of Natick, Massachusetts. The specific procedures include surface determination, surface normals and 3D thickness, 3D density and 3D density representation, as will now be described.

[0140] For surface determination, slices in an XR-μCT dataset are XZ projections, where the XY plane is the principal plane of the specimen and is the same plane formed by the MD or CD. Therefore, the Z axis is perpendicular to the XY plane, and each slice represents a unit step in the Y direction. Therefore, each slice will produce a curve connecting the maximum (upper) and minimum (lower) positions of the fibers indicated in the slice.

[0141] Those areas along the Z axis where no mass is found (i.e., those areas where there are through-holes in the material) may present problems in creating a continuous center surface. To overcome this, the hole can be filled by dilating it by two pixels around the perimeter (increasing the hole size), and an average value can be determined for the surrounding positions with a finite Z value for maximum, minimum, or center, depending on the surface being adjusted. The hole can then be filled with the average Z position value so that no discontinuities occur and surface smoothing will not be adversely affected by void spaces.

[0142] A robust three-dimensional smoothing spline function can then be applied to each surface. The algorithm for executing this function is described by D. Garcia, Computational Statistics and Data Analysis, 54: 1167-1178 (2010), the disclosure of which is incorporated by reference in its entirety. The smoothing parameters can be varied to produce a series of files that provide a range of surface smoothness that render individual fiber details to a greater or lesser degree.

[0143] Available The function "surfnorm" calculates a three-dimensional surface normal at each vertex within a smooth central surface. The algorithm is based on a cubic fit of the x, y, and z matrices. Diagonal vectors are calculated and intersected to form the normal. Line segments parallel to the surface normal, passing through each vertex and terminating at the upper and lower smooth surfaces, can be used to determine the thickness of the paper product sample perpendicular to the central surface.

[0144] The three-dimensional relative fiber density is determined along a path perpendicular to the central surface as follows: assuming a rectangular prism, where two dimensions are one pixel and the third dimension is the length of a line segment extending from the two outer smooth surfaces through the vertex. The mass contained within this volume is determined as voxels with finite mass, as indicated by the grayscale value from the tomographic data set. Therefore, if all voxels along the line segment have a grayscale value of 255, the maximum relative density at the vertex is equal to one. The maximum value for the cell wall of cellulose fibers is taken to be 1.50 g / cm 3 .

[0145] A convenient representation of three-dimensional fiber density can be made by mapping the fiber density in four dimensions using a smooth central surface to show the extent of out-of-plane deformation of the sample, and indicating the three-dimensional density as a spectral plot with a value at each position within the map. These maps can be shown as relative density with a maximum value of 1, or normalized to a maximum value of 1.50 g / cm as indicated. 3 The density of cellulose.

[0146] Figure 21A and Figure 21B Shows the use of Figure 7 The XR-μCT relative density determination histogram of the paper product manufactured with 4 is shown. Specifically, Figure 21A shows the density determination of the dome of the paper product, and Figure 21B The density determination of the connected areas of the paper product is shown. For comparison, Figure 21C and Figure 21D A histogram showing XR-μCT relative density determinations for paper products made using woven structured fabrics is shown. As discussed above, structured fabrics are a well-known alternative to creping belts in the papermaking process. As is also well known in the art, paper products made with structured fabrics include domed areas formed in the pockets between the woven yarns of the structured fabric during the papermaking process, and the presence of connected areas formed during the papermaking process on the knuckles that comprise the forming surface of the structured fabric. Figure 21C shows the density determination of domes formed in the pocket areas of the fabric, and Figure 21D The density determination of the connected areas of the paper product formed on the knuckles of the fabric is shown. 21A to 21D In all of , the x-axis shows the relative density value, and the y-axis shows the number of pixels at each relative density value (in a logarithmic scale).

[0147] use 21A to 21D The analysis shown determines the average value of the relative density of domes formed in the openings of the creping belt ( Figure 21A ) is about 14.9, and the average value of the relative density of domes formed in the recesses of the fabric ( Figure 21C) is about 16.8. In addition, the average value of the relative density of the connection area formed on the contact surface of the creping belt ( Figure 21B ) is about 24.0, whereas the average value of the relative density of the connection areas formed on the nodes in the structured fabric ( Figure 21D ) is about 18.5. Thus, the average relative density of domes formed by the belt is about 12% less than the density of domes formed by the structured fabric, whereas the average relative density of the connected areas of the product formed by the belt is about 30% higher than the average relative density of the connected areas formed on the structured fabric. We have found that these relationships also hold true for paper products made with other creping belts compared to paper products made with other structured fabrics. That is, the relative density of domes in products made with the creping belt is lower than the relative density of domes in products made with the structured fabric, and the relative density in the connected areas in products made with the creping belt is higher than the relative density in the connected areas in products made with the structured fabric. Thus, the average relative density of the different areas (dome and connected areas) of the paper product indicates whether the product was made with a creping belt or a structured fabric.

[0148] 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 in light of this disclosure. Therefore, it should be understood that the present invention may be practiced in a manner other than that specifically described. Therefore, the exemplary embodiments of the present invention should be considered in all respects to be illustrative and not restrictive, and the scope of the present invention is determined by any claims that may be supported by this application and its equivalents, rather than by the foregoing description.

[0149] Industrial Applicability

[0150] The apparatus, process, and products described herein can be used to produce commercial paper products, such as toilet paper and paper towels. Thus, the apparatus, process, and products have many applications related to the paper products industry.

Claims

1. A belt for creping a web in a papermaking process, the belt comprising: a first layer formed of a polymeric material, the first layer providing a first surface of the belt upon which the web is deposited, and the first layer having a plurality of openings extending therethrough, wherein the openings are arranged along lines that are offset from lines in both a machine direction (MD) and a cross-machine direction (CD) of the belt such that (i) for each line in the machine direction, a length across the line of openings is different from a length across the lines of adjacent openings on either side of the opening, and (ii) for each line in the cross-machine direction, a length across the line of openings is different from a length across the lines of adjacent openings on either side of the opening; and A second layer is attached to the first layer, the second layer providing a second surface of the tape.

2. The belt according to claim 1, wherein The openings are arranged in (i) a repeating pattern of openings arranged around a central opening, (ii) such that the openings are not mirrored about a line extending along a diameter of the central opening in the machine direction (MD), and (iii) such that the openings are not mirrored about a line extending along a diameter of the central opening in the cross-machine direction (CD).

3. The tape of claim 2, wherein the repeating pattern comprises six openings arranged around a central opening.

4. The belt of claim 1, wherein the openings are arranged in a pattern having an angle of rotational symmetry of 60 degrees and a degree of rotational symmetry of 6.

5. The belt according to claim 1, wherein The openings are arranged in a pattern such that the repetitive peak in the sum of the machine direction line contact profile occurs below 0.55 mm in the cross machine direction.

6. The belt according to claim 5, wherein The repetitive peak of the sum of the machine direction line contact profile occurs between 0.4 mm and 0.55 mm along the cross machine direction.

7. The belt according to any one of claims 1 to 5, wherein The opening has a diameter of 0.5 mm to 5.0 mm.

8. The belt according to any one of claims 1 to 5, wherein The opening has a diameter of 0.75 mm to 2.5 mm.

9. The belt according to any one of claims 1 to 5, wherein The belts have a contact area of 10% to 90%.

10. The belt according to any one of claims 1 to 5, wherein The openings are arranged in lines rotated 13 to 21 degrees relative to a line in the machine direction.

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