WO2025090428A1

WO2025090428A1 - Method of producing embossed tissue products

Info

Publication number: WO2025090428A1
Application number: PCT/US2024/052307
Authority: WO
Inventors: Massimo CAGNONE
Original assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Priority date: 2023-10-23
Filing date: 2024-10-22
Publication date: 2025-05-01
Anticipated expiration: 2026-04-23

Abstract

Multi-ply tissue products are formed using an embossing process. The embossing process includes prewetting a tissue ply, feeding the tissue ply into a heated nip and embossing the tissue ply, re-wetting the tissue ply with a bonding solution containing water, and joining the embossed tissue ply to a second tissue ply for forming a tissue product. The embossing pattern includes a pattern of male embossing elements that have a height and a spacing that produces products with high bulk.

Description

METHOD OF PRODUCING EMBOSSED TISSUE PRODUCTS

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related and has right of priority to U.S. Provisional Patent Application No. 63/592,231 filed on October 23, 2023, which is incorporated by reference in its entireties for all purposes.

BACKGROUND

Consumer tissue products such as facial tissue, bath tissue and paper wipers are generally used to absorb liquids and fluids. Such paper products are predominantly formed of cellulosic papermaking fibers by manufacturing techniques designed specifically to produce several important properties. For example, the products should have good bulk, a soft feel, and should be highly absorbent. Further, the products should also have a pleasant aesthetic appearance and should be resilient against delamination in the environment in which they are used.

In the past, many attempts have been made to enhance certain physical properties of such products. For instance, to enhance the aesthetic appearance, a decorative paper product has been created by embossing a pattern onto one or both sides of the paper web during manufacturing. This standard mechanical embossing resulted in the deformation or breaking of fibers in an attempt to physically press the pattern into the web. In some applications, the resulting embossed patterns were not well-defined and faded as the paper product aged. Also, embossing patterns into tissue webs typically reduce the strength of the web.

In some embodiments, those skilled in the art have used embossing to increase the thickness of the tissue product, particularly bath tissue. For instance, embossing patterns have been used in order to increase the thickness of multi-ply products in order to improve softness, tactile feel, and roll bulk. Conventional embossing technologies, however, including double embossed random lamination (DERL), double embosser synchronizer lamination (DESL), or point-to-point embossing have limits on the ability to generate volume at acceptable levels of basesheet degradation.

In view of the above, a need currently exists for an embossing process capable of not only creating decorative patterns into tissue products but also in a way that enhances bulk without severe degradation and strength.

SUMMARY

In general, the present disclosure is directed to a process for producing multi-layer embossed tissue products having enhanced bulk, a soft feel, and various other properties. The present disclosure is also directed to tissue products made from the process. In one embodiment, the present disclosure is directed to a method of producing an embossed multi-ply tissue product, which comprises prewetting a first tissue ply with a prewetting solution comprising water. The prewetting solution, for instance, can comprise greater than about 95% by weight water, such as greater than about 98% by weight water, and, in one embodiment, can comprise only water. The prewetting solution can be heated prior to application to the first tissue ply. For instance, the prewetting solution can be heated to a temperature of from about 60°C to about 95°C, such as from about 60°C to about 80°C. The prewetting solution can be sprayed onto a surface of the first tissue ply and can be applied to the tissue ply in an amount from about 1 % to about 10% by weight, such as in an amount from about 2% to about 6% by weight.

The prewetted tissue ply is then conveyed through a heated embossing nip. A first surface of the tissue ply contacts an embossing roll within the heated embossing nip. The embossing roll defines a pattern of male embossing elements. The male embossing elements comprise discrete shapes and have an embossing height of from about 0.6 mm to about 1.2 mm, such as from about 0.7 mm to about 1 mm, such as from about 0.65 mm to about 0.95 mm. The male embossing elements form line structures in which a spacing between adjacent embossing elements within the line structure is from about 1.1 mm to about 1 .7 mm, such as from about 1 .2 mm to about 1 .7 mm, such as from about 1 .5 mm to about 1 .7 mm. The heated embossing nip forms an embossing pattern in the first tissue ply while also causing water to evaporate from the first tissue ply. The embossing pattern comprises a pattern of protrusions that extend from a second surface of the first tissue ply.

In one embodiment, the pattern of male embossing elements comprises spaced apart rows of line structures. The pattern of male embossing elements can form dot embossments within the tissue ply. In one aspect, the line structures can be curvilinear. For instance, the line structures can have a wave-like pattern.

Optionally, the embossing roll can further include continuous line embossments. The continuous line embossments can have an embossing height of less than about 0.9 mm, and greater than about 0.4 mm, such as from about 0.5 mm to about 0.7 mm. The continuous line embossments can form a pattern of images that overlap the pattern of line structures formed by the male embossing elements.

As described above, the embossing nip is heated. For instance, the nip can be formed between the embossing roll and a backing roll. The embossing roll, the backing roll, or both can be heated for producing a heated nip. The nip can be heated to a temperature of from about 70°C to about 190°C. For instance, the tissue ply can be contacted with at least one roll at a temperature of greater than about 80°C, such as greater than about 100°C, such as greater than about 120°C, such as greater than about 140°C, and less than about 180°C, such as less than about 170°C. In one embodiment, the embossing roll is heated and the first tissue ply contacts the embossing roll for at least about 70°, such as at least about 90°, such as at least about 100°, such as at least about 120°.

After the first tissue ply has been embossed, an adhesive-free bonding solution is applied to the pattern of protrusions on the second surface of the first tissue ply. The bonding solution comprises water. Thereafter, the second surface of the first tissue ply is then contacted with a first surface of a second tissue ply for laminating the two tissue plies together. The bonding solution, for instance, can cause bonds to form between the two plies, such as hydrogen bonds.

The bonding solution, for instance, can comprise greater than about 95% by weight water, such as greater than about 98% by weight water, and, in one embodiment, comprises only water. The bonding solution can be applied by a roll applicator placed in contact with the second surface of the first tissue ply. The bonding solution can be heated prior to contact with the first tissue ply. For instance, the bonding solution can be heated to a temperature of from about 60°C to about 90°C.

In one aspect, the method of the present disclosure further includes the steps of, after applying the bonding solution, conveying the embossed and wetted first tissue ply into a second nip. A second tissue ply is also conveyed into the second nip. The first and second tissue plies are then joined together by the bonding solution. The second nip, for instance, may be formed by a marrying roll.

It was discovered that the process of the present disclosure creates a dramatically improved embossing efficiency. As used herein, the "embossing efficiency” is calculated by dividing the increase in caliper after embossing by the sum of the embossing pressure (in kg/cm) of the top and bottom nip. Tissue products made in accordance with the present disclosure can display an embossing efficiency of greater than about 25 microns per kg/cm, such as greater than about 28 microns per kg/cm, such as even greater than about 30 microns per kg/cm and less than about 100 microns per kg/cm. In the past, conventional embossing processes displayed embossing efficiencies of less than about 12 microns per kg/cm.

The present disclosure is also directed to tissue products made according to the process described above. The multi-ply tissue product can display a sheet bulk of greater than about 10 cm³/g, such as greater than about 11 cm³/g, such as even greater than about 12 cm³/g. The tissue product can display a caliper of at least 2100 microns per 12 plies, such as at least about 2,300 per 12 plies, such as at least about 2450 microns per 12 plies, and less than about 8000 microns per 12 plies. The multi-ply product can have an overall basis weight of from about 30 gsm to about 80 gsm, such as from about 35 gsm to about 65 gsm. Each ply contained within the product can independently have a basis weight of from about 12 gsm to about 28 gsm. The tissue product of the present disclosure can be spirally wound into rolls with periodic lines of perforation for producing bath tissues and paper towels. Alternatively, the tissue product can be cut into individual sheets and marketed as interfolded stacks.

Other features and aspects of the present disclosure are discussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

Figure 1 is a plan view of one embodiment of a tissue product made in accordance with the present disclosure;

Figure 2 is a plan view of one embodiment of an image made from continuous line elements that can be embossed into the tissue product of the present disclosure;

Figure 3 is a cross-sectional view of a portion of an embossing roller showing a pattern of male embossing elements;

Figure 4 is a cross-sectional view of one embodiment of an embossing process in accordance with the present disclosure;

Figure 5 is a perspective view of one embodiment of a spirally wound roll of tissue product made in accordance with the present disclosure; and

Figure 6 is a side view of an interfolded stack of individual sheets of a tissue product made in accordance with the present disclosure.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DEFINITIONS

As used herein the term “machine direction” or “MD” generally refers to the direction in which a tissue web or product is produced. The term “cross-machine direction” or “CD” refers to the direction perpendicular to the machine direction.

As used herein the term “Fibrous Structure” refers to a structure comprising a plurality of elongated particulate having a length to diameter ratio greater than about 10 such as, for example, papermaking fibers and more particularly pulp fibers, including both wood and non-wood pulp fibers, and synthetic staple fibers. A non-limiting example of a fibrous structure is a tissue web comprising pulp fibers.

As used herein the term “Tissue Web” or “Tissue Ply” refers to a fibrous structure provided in sheet form and being suitable for forming a tissue product.

As used herein the term “Tissue Product” refers to products made from tissue webs and includes, bath tissues, facial tissues, paper towels, industrial wipers, foodservice wipers, napkins, medical pads, and other similar products. Tissue products may comprise one, two, three or more plies. As used herein the term “Pattern” generally refers to the arrangement of one or more design elements. Within a given pattern the design elements may be the same or may be different, further the design elements may be the same relative size or may be different sizes. For example, in one embodiment, a single design element may be repeated in a pattern, but the size of the design element may be different from one design element to the next within the pattern.

As used herein, the term “Embossing Pattern or Design” generally refers to a decorative shape disposed across at least one dimension of a fibrous structure surface, the pattern may comprise a line element, discrete elements or other shapes. The embossing pattern comprises a portion of the fibrous structure lying out of plane with the surface plane of the fibrous structure. In general, the embossing pattern results from embossing the fibrous structure resulting in protrusions having a z- directional elevation on one side of the fibrous structure and raised areas on the opposite side of the fibrous structure.

As used herein the term “Line Structure” refers to an element, such as an embossing element, in the shape of a line, which may be continuous or discontinuous, such as discrete or interrupted. The line element may be of any suitable shape such as straight, bent, kinked, curled, curvilinear, serpentine, sinusoidal, and mixtures thereof that may form a regular or irregular, periodic or nonperiodic lattice work of structures wherein the line element exhibits a length along its path of at least 10 mm. In one example, the line element may comprise a plurality of discrete elements, such as dots and/or dashes for example, that are oriented together to form a line element.

As used herein the term “Continuous Embossment” or “Continuous Line Embossments” refers to an element, such as an embossing element, disposed on a fibrous structure that extends without interruption throughout one dimension of the fibrous structure.

As used herein the term “Discrete Elements or Shapes” refers to an element, such as an embossing element, disposed on a fibrous structure that does not extend continuously in any dimension of the fibrous structure.

As used herein the term “Basis Weight” (BW) generally refers to the bone dry weight per unit area of a tissue and is generally expressed as grams per square meter (gsm). Basis weight is measured using TAPPI test method T-220. While basis weight may be varied, tissue products prepared according to the present invention generally have a basis weight greater than about 10 gsm, such as from about 10 to about 80 gsm and more preferably from about 30 to about 60 gsm.

As used herein, the term “caliper” is the representative thickness of a single sheet (caliper of tissue products comprising two or more plies is the thickness of a single sheet of tissue product comprising all plies) measured in accordance with TAPPI test method T402 using a ProGage 500 Thickness Tester (Thwing-Albert Instrument Company, West Berlin, N.J.). The micrometer has an anvil diameter of 2.22 inches (56.4 mm) and an anvil pressure of 132 grams per square inch (per 6.45 square centimeters) (2.0 kPa).

As used herein the term “Sheet Bulk” refers to the quotient of the caliper (generally having units of pm) divided by the bone dry basis weight (generally having units of gsm). The resulting sheet bulk is expressed in cubic centimeters per gram (cc/g). While sheet bulk may vary depending on any one of a number of factors, tissue products prepared according to the present invention may have a sheet bulk greater than about 10.0 cc/g.

As used herein, the term “ply attachment strength” refers to the peak force, typically having units of grams (g), necessary to separate two plies of a tissue product. Ply attachment strength is measured as described in the Test Method section.

As used herein, the term “geometric mean tensile” (GMT) refers to the square root of the product of the machine direction tensile strength and the cross-machine direction tensile strength of the web. The GMT of tissue products prepared according to the present invention may vary, however, in certain instances the GMT may be about 800 g/3" or greater, such as about 900 g/3” or greater, such as about 1 ,000 g/3" or greater, such as about 1 ,100 g/3” or greater, such as about 1,200 g/3” or greater, such as about 1 ,300 g/3” or greater, such as about 1 ,400 g/3” or greater, such as about 1 ,600 g/3" or greater such as from about 800 to about 1 ,700 g/3”.

As used herein the term “dot embossment” or “dot emboss element” means an embossment or an embossing element that exhibits an aspect ratio of about 1 :1 .25 or less, such as an aspect ratio from about 1 .0 to about 1.25. Non-limiting examples of dot embossments are embossments having a circular, oval, square, or triangular cross-sectional shape.

Ply attachment strength is measured using a SP-2100 Slip/Peel Tester (IMASS, Inc. Strongsville, OH) having a servo/screw drive capable of producing speeds ranging from 0.2 to 300 in/min (0.5 to 762 cm/min) and a 25 Ibf (10 kgf) force. The test equipment platen travel rate is set at 28.0 inches per minute. The SP-2100 Slip/Peel Tester measures the Kinetic peak force it takes to separate two bonded tissue plies from one another. Bath tissue samples are generally prepared by separating individual sheets along the perforations, taking care not to damage, tear or compress the sample. Generally, the ply attachment strength of the individual bath tissue sheets is evaluated without cutting of individual samples to size. If, however, the sample exceeds 4 inches by 4 inches, the sample is cut to a size of 4 inches by 4 inches +/-0.25 inches prior to testing. For each sample, the plies are separated by hand for a distance of approximately 15 mm from the perforated edge to create two free sample ends that may be clamped into the test apparatus. The test sample is secured to the test apparatus using the provided clamp clips. The sample is preloaded by adjusting the manual positioning knob until the display reads 2 ± 0.5 grams. The test is then commenced by activating the test apparatus. Generally, plies of the laminate are manually separated for a distance of about 2 inches along the length of the specimen. When the carriage stops and the average Kinetic Peak (i.e., peak load) needed to completely separate the plies from one another is recorded to the 0.1 gram. Samples having more than two plies are tested by placing one outer ply in the specimen clip and the other plies in the hold down device.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure.

In general, the present disclosure is directed to an embossing process that increases the caliper of the individual tissue plies in a manner that dramatically and unexpectedly enhances bulk of the final product. Various different embossing techniques are combined together in a manner that optimizes bulk and softness while minimizing the degradation of strength. As will be described in greater detail below, the process of the present disclosure produces an embossing efficiency that is greater than conventional embossing processes

Multi-ply tissue products are produced in accordance with the present disclosure using a process that both embosses at least one of the plies while laminating the plies together. In one embodiment, one of the tissue plies is prewetted and then fed into a heated embossing nip. The embossing nip can be formed between an embossing roll and a backing roll. In accordance with the present disclosure, the embossing roll includes a pattern of raised male embossing elements that comprise discrete shapes and can be arranged on the embossing roll to form line structures. The height of the male embossing elements and the spacing between the male embossing elements is carefully controlled in a manner that results in enhanced bulk with minimal strength degradation.

The embossing roll forms an embossing pattern within one of the tissue plies resulting in a pattern of protrusions on a surface of the tissue ply. The protrusions are then wetted with an aqueous composition that is adhesive-free. After the aqueous composition or bonding solution is applied to the tissue ply, the tissue ply is laminated to a second tissue ply for producing a multi-ply product. The wetted areas on the first tissue ply form bonds, such as hydrogen bonds, with the second tissue ply.

Conventional embossing processes in the past were generally not capable of increasing bulk to optimum levels without displaying a strength loss in the cross-direction of greater than about 40%, such as even greater than about 50%. The embossing pattern of the present disclosure in combination with the process steps overcomes the drawbacks of conventional embossing processes and is capable of producing multi-ply tissue products having a bulk greater than about 8 cm³/g, such as greater than about 10 cm³/g, such as greater than about 11 cm³/g, such as even greater than about 12 cm³/g while minimizing strength degradation. Tissue products made according to the present disclosure, for instance, can display a bulk of up to about 20 cm³/g.

Overall, the process of the present disclosure can dramatically and unexpectedly improve embossing efficiency. For instance, the process of the present disclosure can display an embossing efficiency of greater than about 15 microns per kg/cm, such as greater than about 20 microns per kg/cm, such as greater than about 23 microns per kg/cm, such as greater than about 25 microns per kg/cm, such as greater than about 28 microns per kg/cm, such as greater than about 30 microns per kg/cm, and less than about 100 microns per kg/cm.

In general, any suitable tissue ply can be embossed in accordance with the present disclosure. The tissue ply, for instance, can comprise any suitable nonwoven material that can be made through a wetlaid process, air-laying, or through a foam forming process. The tissue ply generally contains cellulose fibers, particularly cellulose pulp fibers. For instance, the tissue ply can contain greater than about 40% by weight, such as greater than about 50% by weight, such as greater than about 60% by weight, such as greater than about 70% by weight cellulose pulp fibers. The multiply products in accordance with the present disclosure can be used to produce numerous products including bath tissue, facial tissue, table napkins, paper towels, and the like. The tissue product can contain at least two tissue plies, such as three tissue plies or four tissue plies.

The multi-ply embossed tissue products of the present invention generally have a total product basis weight of at least about 20 gsm, such as at least about 30 gsm, such as at least about 35 gsm, such as at least about 40 gsm, such as at least about 45 gsm and less than about 75 gsm. In certain instances, the product basis weight may range from about 20 gsm to about 70 gsm, such as from about 30 gsm to about 65 gsm, such as about 40 gsm to about 60 gsm. In one aspect, the multi-ply embossed tissue products may comprise two, three or four tissue plies where the basis weight of each individual tissue plie is less than about 25 gsm, such as from about 10 gsm to about 25 gsm, such as from about 10 gsm to about 20 gsm.

The multi-ply embossed tissue products of the present invention generally have a geometric mean tensile (GMT) of about 800 g/3” or greater, such as about 900 g/3” or greater, such as about 1 ,000 g/3" or greater, such as about 1,100 g/3” or greater, such as about 1 ,200 g/3” or greater, such as about 1 ,300 g/3” or greater, such as about 1 ,400 g/3” or greater, such as about 1 ,600 g/3” or greater and less than about 4000 g/3”. In certain instances, the GMT may range from about 800 g/3” to about 1 ,700 g/3”, such as from about 900 g/3” to about 1 ,600 g/3”, such as from about 1 ,000 g/3” to about 1 ,500 g/3”. In certain instances, the multi-ply embossed tissue products may comprise two, three, or four tissue plies where the GMT of each individual tissue plie is less than about 600 g/3”, such as from about 200 g/3” to about 425 g/3”, such as from about 350 g/3” to about 550 g/3”. Generally, the multi-ply products of the present invention are embossed and comprise two or more tissue plies bonded together along a plurality of bonded areas. In certain instances, the bonded areas may correspond to the embossments disposed on the one or more tissue plies. The bonded areas are generally substantially free from adhesives, and more preferably free from adhesives. The embossed area, relative to the total area of the ply surface, and in-turn the bonded area, may range from about 2% to about 80%, such as from about 2% to about 30%, such as form about 2% to about 20%.

Referring to FIG. 1 , one embodiment of a tissue product made in accordance with the present disclosure is shown. The surface of a top or a first tissue ply 12 is illustrated. In accordance with the present disclosure, an embossing pattern 14 has been formed into the surface of the first tissue ply 12. The embossing pattern 14 comprises rows of embossed line structures 16. The line structures 16 are discontinuous meaning that the line structures 16 are made from discrete embossments or dot embossments. In this embodiment, the line structures are curvilinear and have a wave-like shape. The line structures extend in the cross-direction and are spaced from one another such that they do not intersect.

The embossing pattern 14 can be formed into the tissue ply 12, in one embodiment, by prewetting the tissue ply and then contacting the tissue ply with a heated embossing roll containing a corresponding pattern of male embossing elements. For example, referring to FIG. 3, a cross- sectional view of a portion of a surface of the embossing roll is illustrated showing a row of the male embossing elements 18. In accordance with the present disclosure, the male embossing elements 18 have a carefully controlled height in conjunction with a controlled spacing. The height, H, of the embossing elements 18, for instance, is from about 0.6 mm to about 1 .2 mm. The height H of the male embossing elements 18, for instance, can be greater than about 0.7 mm, such as greater than about 0.8 mm, such as greater than about 0.85 mm, and less than about 1 mm, such as less than about 0.95 mm.

Each male embossing element 18 includes a top surface 20. The largest dimension of the top surface 20 (length, width, or diameter) is generally greater than about 0.2 mm, such as greater than about 0.3 mm, such as greater than about 0.4 mm, and less than about 0.9 mm, such as less than about 0.8 mm, such as less than about 0.7 mm, such as less than about 0.6 mm.

As shown in FIG. 3, the male embossing elements 18 are also spaced apart a distance S. The distance S is measured from the center of one male embossing element 18 to the center of an adjacent male embossing element 18. The spacing applies not only to the spacing within each line structure, but also the spacing between rows although for many patterns, the spacing between the rows is greater than the spacing S within each line structure. In accordance with the present disclosure, within each line structure, the spacing S is from about 1 .1 mm to about 1 .7 mm. The spacing S within each line structure, for instance, is greater than about 1.2 mm, such as greater than about 1 .3 mm, such as greater than about 1 .35 mm, such as greater than about 1 .4 mm, such as greater than about 1.45 mm, and less than about 1.6 mm, such as less than about 1.55 mm. The spacing of the male embossing elements 18 between adjacent line structures is at least greater than 1.1 mm, and is generally greater than about 1 .5 mm, such as greater than about 2 mm, such as greater than about 3 mm, such as greater than about 4 mm, such as greater than about 5 mm, such as greater than about 6 mm, such as greater than about 7 mm, such as greater than about 10 mm, such as greater than about 15 mm, such as greater than about 20 mm, such as greater than about 25 mm, such as greater than about 30 mm, and generally less than about 10,000 mm, such as less than about 1 ,000 mm.

As shown in FIG. 3, the male embossing elements 18 include at least one side wall 22. The side wall 22 angles from the embossing roll to the top 20 of each embossing element 18. The angle of the side wall 22 can be from about 10° to about 60°. For instance, the angle can be less than about 55°, such as less than about 50°, and greater than about 15°, such as greater than about 20°, such as greater than about 25°, such as greater than about 30°. In one embodiment, the side wall forms an angle of from about 40° to about 50°. Alternatively, the angle of the side wall can be from about 10° to about 30°, such as from about 20° to about 30°

The embossing roll can include a pattern of male embossing elements 18 to form the embossing pattern shown in FIG. 1 . Alternatively, the embossing pattern on the embossing roll can further include continuous line embossments. The line embossments can overlap with the pattern of the male embossing elements 18. For instance, the line embossments can be arranged on the embossing roll, in one embodiment, where the line structures are interrupted. The line embossments can be used to form decorative patterns within the tissue product 10 as shown in FIG. 2. For instance, as shown in FIG. 2, the continuous line embossments can be used to produce an image, such as a puppy 26. As shown, the continuous line embossments can extend in the machine direction, in the cross-direction, and/or at different angles. The line embossments on the embossing roll generally have an embossing height that is less than the height of the male embossing elements. In one aspect, the continuous line embossments can have an embossing height of less than about 0.9 mm, such as less than about 0.8 mm, such as less than about 0.7 mm, and greater than about 0.4 mm, such as greater than about 0.5 mm.

Referring now to FIG. 4, one embodiment of a process that may be used to produce the tissue product 10 is illustrated. In the embodiment illustrated in FIG. 4, a first tissue ply 12 is embossed and laminated to a second tissue ply 24. As will be explained in greater detail below, in one aspect, the first tissue ply 12 can be laminated to the second tissue ply 24 without using an adhesive. Thus, the final tissue product 10 can be free of adhesives used in the past, such as a starch, a methylcellulose, or a polymer adhesive containing polypropylene, polyisobutylene, a polyurethane, a polyacrylate, a polyvinyl acetate, an ethylene vinyl acetate, or a polyvinyl alcohol. Without having to use an adhesive, the softness of the tissue product 10 can be enhanced.

As shown in FIG. 4, the first tissue ply 12 is conveyed past a series of idler rollers 122 towards a nip 124 that is located between an embossing roll 126 and a backing roll 128. Prior to entering the nip 124, in one aspect, the first tissue ply 12 can be prewetted with a prewetting solution at a prewetting station 123. The prewetting solution applied to the first tissue ply 12 can comprise water in an amount greater than about 90% by weight, such as in an amount greater than about 94% by weight, such as in an amount greater than about 96% by weight, such as in an amount greater than about 98% by weight, and, in one embodiment, comprises only water.

The prewetting solution may be applied to a surface of the basesheet by any suitable means. Any contact or contactless application means suitable for applying a prewetting solution to a tissue basesheet, such as spraying, dipping, padding, printing, slot extruding, rotogravure printing, flexographic printing, offset printing, screen printing, and mixtures thereof can be used to apply the prewetting solution to the surface of the tissue basesheet prior to embossing.

In certain aspects non-contact printing methods such as ink jet printing, digital printing, spraying, and topical application using a WEKO fluid application system (commercially available from Weitmann & Konrad GmbH & Co., Leinfelden-Echterdingen, Germany) may be used to apply the prewetting solution to the web prior to embossing. In certain preferred embodiments the prewetting solution is applied without direct contact between the ply and the applicator, such as by a liquid applicator comprising a nozzle system to spray the prewetting solution onto the outer surface of the tissue ply as it is conveyed past the applicator.

In one example, the prewetting solution is applied to the surface of the tissue ply during the converting process by spraying at least one surface of the tissue ply with an prewetting solution and then simultaneously drying and embossing the wetted tissue ply by conveying it through a heated embossing nip. The embossed tissue web may then be plied to a second tissue web, which may or not be embossed, without the addition of an adhesive.

The prewetting solution can be applied by a single device or multiple devices may be configured to apply the prewetting solution to the tissue ply. The one or more application devices may apply the same prewetting solution or may be configured to apply different prewetting solutions. In those instances where the process employs a single device it may be configured to apply two or more different prewetting solutions by providing the device with two or more chambers capable of separately delivering the different solutions.

The prewetting applicator can be configured and arranged to apply a prewetting solution to the one or more tissue plies immediately prior to the one or more plies being conveyed to an embossing unit or may be configured to apply the prewetting solution while the ply is engaged by one of the embossing rolls. Regardless, it is generally preferred that the wetted ply does not have sufficient time to dry before embossments are imparted to the web by the heated embossing roll.

In certain instances, the applicator unit may be configured to apply the prewetting solution to only a portion of the tissue ply surface. For example, in certain instances the applicator may be configured such that only the embossed portion of the ply is treated In other instances, the applicator unit may be configured such that the prewetting solution covers at least about 90% of the surface area of the tissue ply, such as at least about 92%, such as at least about 95%, such as about 100%. Further, the prewetting solution may be applied in a pattern or may be applied randomly.

The applicator unit may be configured to provide a controlled amount of aqueous composition to the tissue ply such that the basis weight of the tissue ply is increased in the range from about 1% to about 10%, such as from about 2% to about 8%. For instance, the prewetting solution can be applied to the first tissue ply 12 in an amount greater than about 3% by weight and in an amount less than about 7% by weight, such as in an amount less than about 6% by weight, such as in an amount less than about 5% by weight. Preferably the wetted tissue ply is dried as it is brought into contact with the heated embossing roll. In this manner, the embossed tissue ply may have a basis weight substantially similar to the unembossed tissue ply prior to application of the prewetting solution.

In certain instances, it may be desirable to heat the aqueous composition prior to wetting of the tissue ply. In this manner the temperature of the prewetting solution being applied to the tissue ply may be about 50°C or greater, such as about 55°C or greater, such as about 60°C or greater, such as about 65°C or greater, such as about 70°C or greater. The temperature of the prewetting solution may range from about 50°C to about 80°C, such as from about 60°C to about 75°C, such as from about 65°C to about 70°C.

After being prewetted, the first tissue ply 12 is fed into the first nip 124 which can be a heated nip. As described above, the nip 124 is formed between an embossing roll 126 and a backing roll 128. The embossing roll 126 includes a pattern of male embossing elements 18 as shown in FIG. 3 that embosses a pattern into the first tissue ply 12. During embossing, the tissue ply 12 is heated to a temperature sufficient to evaporate the prewetting solution or water and dried.

The nip 124 can be heated using any suitable heating means. For instance, the embossing roll 126 can be heated, the backing roll 128 can be heated, or both rolls can be heated. In one aspect, the embossing roll 126 is heated. The nip 124 or the surface of the embossing roll 126, for instance, can be heated to a temperature of greater than about 70°C, such as greater than about 80°C, such as greater than about 90°C, such as greater than about 100°C, such as greater than about 110°C, such as greater than about 120°C, such as greater than about 130°C, such as greater than about 140°C, and less than about 220°C, such as less than about 200°C, such as less than about 190°C, such as less than about 180°C, such as less than about 170°C. In one aspect, the embossing roll 126 can be combined with a heating device that can be housed within the roll for heating by conduction.

Alternatively, the embossing roll 126 can be heated by radiation and/or convection. As described above, the nip 124 formed between the embossing roll 126 and the backing roll 128 is heated for heating the tissue ply 12 as the tissue ply is embossed.

In certain aspects the wetted tissue ply remains in contact with the heated embossing roll for a sufficiently long time to allow the drying of the ply itself, but without reducing the processing speed of the tissue product. The duration of contact can be influenced by the temperature of the embossing roll, the size of the roll and the degree to which the wetted tissue ply wraps the roll. Generally, it is preferred to optimize the conditions not only to improve embossing clarity and ply attachment, but also to maintain sufficient processing speed and to maintain the efficiency of the drying process of the wet paper ply just embossed. In general, the first tissue ply 12 can be wrapped around the embossing roll greater than about 90°, such as greater than about 100°, such as greater than about 120°, such as greater than about 130°, and less than about 350°, such as less than about 330°, such as less than about 320° in order to apply sufficient heat to the tissue ply.

The embossing roll 126 is generally a hard and non-deformable roll, such as a steel roll. The backing roll 128 can be a substantially smooth roll that, in one embodiment, can include a covering made of natural or synthetic rubber. The natural or synthetic rubber, for instance, can be polybutadiene or copolymers of ethylene and propylene or the like. In one aspect, the backing roll 128 has a hardness of greater than about 40 Shore A, such as from about 40 Shore A to about 100 Shore A including all increments of 1 Shore A therebetween. For example, in one aspect, the hardness of the backing roll 128 can be from about 50 Shore A to about 70 Shore A.

After the first tissue ply is embossed, it is laminated to a second tissue ply to form a multi-ply tissue product. The lamination process is carried out without the use of an adhesive. Instead, a bonding solution comprising an aqueous composition, preferably free from any adhesives, is applied just prior to the lamination step such that the ply does not prematurely dry prior to being joined with the second ply. In this manner it may be preferable that the aqueous composition be applied to the first ply immediately prior to, or while, the first ply is brought into contacted with the heated embossing roll and then joined to the second ply in a second nip formed between the heated embossing roll and a marrying roll. Accordingly, in certain embodiments, a joining station may be configured such that the upper steel embossing roll abuts an aqueous composition delivery assembly and a marrying roll to further laminate and join the first embossed ply to the second ply to form a multi-ply embossed tissue product according to the present disclosure. In particular, the upper steel embossing roll may abut an aqueous composition delivery applicator which distributes an aqueous composition onto the embossed ply, particularly the protruding embossments of the embossed ply. After application of the aqueous composition, the embossed and wetted ply (or partially dried ply) may be joined to the second ply by a marrying roll, which may be arranged such that it abuts the upper steel embossing roll. In this manner, the upper steel embossing roll and marrying roll may form a nip therebetween through which the plies pass and are joined together to form a multi-ply tissue product.

For instance, as shown in FIG. 4, the first tissue ply 12 enters the heated nip 124 and is embossed by the embossing roll 126 by the pattern of male embossing elements 18. Not only is the tissue ply 12 heated in the nip 124 but is also subjected to pressure against the embossing roll 126 for forming an embossing pattern into the tissue ply 12.

As shown, in order to form a two-ply tissue product, a second tissue ply 24 is conveyed around an idler roll 142 and then pressed into a nip 144 located between a substantially smooth roll 146 which may be made of rubber and a marrying roll 148, which may be a steel roll. The second tissue ply 24 is adapted to form the bottom ply in the resulting multi-ply tissue product 10. As it is conveyed, the second tissue ply passes through a second nip 150 created between the embossing roll 126 and the marrying roll 148 where it is brought into contact with the first tissue ply 12, which now bears the embossing design as a result of being embossed by the embossing roll 126. The first and second plies 12 and 24 are joined together as they pass through the nip 150 to form a multi-ply tissue product 10.

As shown in FIG. 4, after the first tissue ply passes through the first nip 124 between the embossing roll 126 and the backing roll 128, a bonding unit 152 can apply a bonding solution to the distil ends of protrusions on the opposite surface of the first tissue ply 12 that is in contact with the embossing roll 126. For instance, as the tissue ply 12 is embossed on a first surface, protrusions form on the second surface according to the embossing pattern. In one aspect, the bonding unit 152 is positioned and configured only to apply a bonding solution to the top of the protrusions on the first tissue ply 12.

In one embodiment, the bonding unit 152 can include a distribution roll and a dosing roll. The bonding solution, which can comprise water is stored in a tank, is collected onto the distribution roll, and subsequently transferred to the dosing roll. The dosing roll contacts the protrusions on the first tissue ply 12 for applying the bonding solution to the tissue ply in a controlled manner. The bonding solution applied to the first tissue ply can contain water in an amount greater than about 50% by weight, such as in an amount greater than about 70% by weight, such as in an amount greater than about 80% by weight, such as in an amount greater than about 90% by weight, such as in an amount greater than about 95% by weight, such as in an amount greater than about 97% by weight, such as in an amount greater than about 99% by weight. In one embodiment, the bonding solution only comprises water. When the first tissue ply 12 is brought into contact with the second tissue ply 24, the bonding solution can cause hydrogen bonds to form due to the presence of the cellulose pulp fibers in each tissue ply.

It should be understood that the bonding unit 152 represents merely one way of applying the bonding solution to the first tissue ply 12. Various other techniques and methods can be used to apply the bonding solution to the first tissue ply 12. For instance, the bonding solution can be applied to the tissue ply using a gravure roll, through a digital printer, using a knife blade, or spraying the bonding solution onto the tissue ply 12.

In one aspect, the bonding solution is heated prior to being applied to the tissue ply 12. For instance, the bonding solution can be heated to a temperature of from about 60°C to about 90°C, including all increments of 1 °C therebetween. For instance, the bonding solution can be heated to a temperature of greater than about 65°C, such as greater than about 70°C, such as greater than about 75°C, and less than about 85°C.

The bonding solution is generally applied to the first tissue ply 12 in an amount less than about 6% by weight, such as in an amount less than about 5% by weight, such as in an amount less than about 4% by weight, such as in an amount less than about 3% by weight, such as in an amount less than about 2% by weight, such as in an amount less than about 1% by weight. The bonding solution is applied to the first tissue ply 12 in an amount greater than about 0.1% by weight, such as in an amount greater than about 0.5% by weight, such as in an amount greater than about 1% by weight, such as in an amount greater than about 1 .5% by weight, such as in an amount greater than about 2% by weight.

As shown in FIG. 4, the embossed first tissue ply 12 with the applied bonding solution advances into the second nip 150 between the embossing roll 126 and the marrying roll 148. At this point, the non-embossed second ply 24 is attached to the embossed first ply 12 and both plies are then conveyed around the marrying roll 148 to form the two-ply tissue product 10 which is subsequently spirally wound into a roll (not shown).

Through the above process, a tissue product 10 can be formed as shown in FIG. 1. The tissue product 10 can comprise a two-ply tissue product in which the first ply 12 is the embossed ply that forms the top of the product. The second ply 24, on the other hand, can be a non-embossed ply that remains relatively planar and forms the bottom surface of the product. In other embodiments, the tissue product 10 can include a third ply and/or a fourth ply.

Generally, the multi-ply products of the present disclosure are embossed and comprise two or more tissue plies bonded together along a plurality of bonded areas. In certain instances, the bonded areas may correspond to the embossments disposed on the one or more tissue plies. The bonded areas are generally substantially free from adhesives, and more preferably free from adhesives. The embossed area, relative to the total area of the ply surface, and in-turn the bonded area, may range from about 2% to about 50%, such as from about 2% to about 30%, such as form about 2% to about 20%.

The presence of bonded areas between plies of the multi-ply products provides the products with a certain degree of ply attachment, which may be measured according to the ply attachment strength test method described herein. Surprisingly, the multi-ply tissue products of the present disclosure achieve a relatively high degree of ply attachment without use of adhesive. For example, the multi-ply tissue products may have a ply attachment strength of at least about 5 gf, such as at least about 6 gf, such as at least about 7 gf, such as from about 5 gf to about 15 gf, such as from about 5 gf to about 12 gf.

In general, any suitable tissue web can be embossed in accordance with the present disclosure and incorporated into the tissue product 10. Bath tissue, facial tissue, paper towels, industrial wipers, and the like can be formed in accordance with the present disclosure. The tissue product 10 can be packaged as individual sheets contained in a dispenser or can be offered to consumers in the form of a spirally wound roll. Tissue products and the tissue plies incorporated into the product can generally have a bulk density of greater than about 3 cc/g, such as greater than about 5 cc/g, such as greater than about 6 cc/g, such as greater than about 7 cc/g, such as greater than about 8 cc/g, such as greater than about 9 cc/g, such as greater than about 10 cc/g, such as greater than about 11 cc/g, such as greater than about 12 cc/g, and generally less than about 20 cc/g.

Fibers suitable for making tissue webs comprise any natural or synthetic cellulosic fibers including, but not limited to nonwoody fibers, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and woody or pulp fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as eucalyptus, maple, birch, and aspen. Pulp fibers can be prepared in high-yield or low-yield forms and can be pulped in any known method, including kraft, sulfite, high-yield pulping methods and other known pulping methods. Fibers prepared from organosolv pulping methods can also be used, including the fibers and methods disclosed in U.S. Pat. No. 4,793,898, issued Dec. 27, 1988 to Laamanen et al.; U.S. Pat. No. 4,594,130, issued Jun. 10, 1986 to Chang et al.; and U.S. Pat. No. 3,585,104. Useful fibers can also be produced by anthraquinone pulping, exemplified by U.S. Pat. No. 5,595,628 issued Jan. 21 , 1997, to Gordon et al.

A portion of the fibers, such as up to 50% or less by dry weight, or from about 5% to about 30% by dry weight, can be synthetic fibers such as rayon, polyolefin fibers, polyester fibers, bicomponent sheath-core fibers, multi-component binder fibers, and the like. An exemplary polyethylene fiber is Pulpex®, available from Hercules, Inc. (Wilmington, Del.). Any known bleaching method can be used. Synthetic cellulose fiber types include rayon in all its varieties and other fibers derived from viscose or chemically-modified cellulose.

Chemically treated natural cellulosic fibers can be used such as mercerized pulps, chemically stiffened or crosslinked fibers, or sulfonated fibers. For good mechanical properties in using papermaking fibers, it can be desirable that the fibers be relatively undamaged and largely unrefined or only lightly refined. While recycled fibers can be used, virgin fibers are generally useful for their mechanical properties and lack of contaminants. Mercerized fibers, regenerated cellulosic fibers, cellulose produced by microbes, rayon, and other cellulosic material or cellulosic derivatives can be used. Suitable papermaking fibers can also include recycled fibers, virgin fibers, or mixes thereof. In certain embodiments capable of high bulk and good compressive properties, the fibers can have a Canadian Standard Freeness of at least 200, more specifically at least 300, more specifically still at least 400, and most specifically at least 500.

Other papermaking fibers that can be used in the present disclosure include paper broke or recycled fibers and high yield fibers. High yield pulp fibers are those papermaking fibers produced by pulping processes providing a yield of about 65% or greater, more specifically about 75% or greater, and still more specifically about 75% to about 95%. Yield is the resulting amount of processed fibers expressed as a percentage of the initial wood mass. Such pulping processes include bleached chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP), pressure/pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulfite pulps, and high yield Kraft pulps, all of which leave the resulting fibers with high levels of lignin. High yield fibers are well known for their stiffness in both dry and wet states relative to typical chemically pulped fibers.

In general, any process capable of forming a paper web can also be utilized in the present disclosure. For example, a papermaking process of the present disclosure can utilize creping, wet creping, double creping, embossing, wet pressing, air pressing, through-air drying, creped through-air drying, uncreped through-air drying, hydroentangling, air laying, as well as other steps known in the art. The tissue web may be formed from a fiber furnish containing pulp fibers in an amount of at least about 50% by weight, such as at least about 60% by weight, such as at least about 70% by weight, such as at least about 80% by weight, such as at least about 90% by weight, such as 100% by weight.

The tissue web can also be formed without a substantial amount of inner fiber-to-fiber bond strength. In this regard, the fiber furnish used to form the base web can be treated with a chemical debonding agent. The debonding agent can be added to the fiber slurry during the pulping process or can be added directly to the headbox. Suitable debonding agents that may be used in the present disclosure include cationic debonding agents such as fatty dialkyl quaternary amine salts, mono fatty alkyl tertiary amine salts, primary amine salts, imidazoline quaternary salts, silicone quaternary salt and unsaturated fatty alkyl amine salts. Other suitable debonding agents are disclosed in U.S. Pat. No. 5,529,665 to Kaun which is incorporated herein by reference. In particular, Kaun discloses the use of cationic silicone compositions as debonding agents.

In one embodiment, the debonding agent used in the process of the present disclosure is an organic quaternary ammonium chloride and, particularly, a silicone-based amine salt of a quaternary ammonium chloride. For example, the debonding agent can be PROSOFT® TQ1003, marketed by the Hercules Corporation. The debonding agent can be added to the fiber slurry in an amount of from about 1 kg per metric tonne to about 10 kg per metric tonne of fibers present within the slurry.

In an alternative embodiment, the debonding agent can be an imidazoline-based agent. The imidazoline-based debonding agent can be obtained, for instance, from the Witco Corporation. The imidazoline-based debonding agent can be added in an amount of between 2.0 to about 15 kg per metric tonne.

In one embodiment, the debonding agent can be added to the fiber furnish according to a process as disclosed in PCT Application having an International Publication No. WO 99/34057 filed on Dec. 17, 1998 or in PCT Published Application having an International Publication No. WO 00/66835 filed on Apr. 28, 2000, which are both incorporated herein by reference. In the above publications, a process is disclosed in which a chemical additive, such as a debonding agent, is adsorbed onto cellulosic papermaking fibers at high levels. The process includes the steps of treating a fiber slurry with an excess of the chemical additive, allowing sufficient residence time for adsorption to occur, filtering the slurry to remove unadsorbed chemical additives, and redispersing the filtered pulp with fresh water prior to forming a nonwoven web.

Optional chemical additives may also be added to the aqueous papermaking furnish or to the formed embryonic web to impart additional benefits to the product and process and are not antagonistic to the intended benefits of the invention. The following materials are included as examples of additional chemicals that may be applied to the web along with the additive composition of the present invention. The chemicals are included as examples and are not intended to limit the scope of the invention. Such chemicals may be added at any point in the papermaking process, including being added simultaneously with the additive composition in the pulp making process, wherein said additive or additives are blended directly with the additive composition.

Additional types of chemicals that may be added to the paper web include, but is not limited to, absorbency aids usually in the form of cationic, anionic, or non-ionic surfactants, humectants and plasticizers such as low molecular weight polyethylene glycols and polyhydroxy compounds such as glycerin and propylene glycol. Materials that supply skin health benefits such as mineral oil, aloe extract, vitamin e, silicone, lotions in general and the like may also be incorporated into the finished products.

In general, the products of the present invention can be used in conjunction with any known materials and chemicals that are not antagonistic to its intended use. Examples of such materials include but are not limited to odor control agents, such as odor absorbents, activated carbon fibers and particles, baby powder, baking soda, chelating agents, zeolites, perfumes or other odor-masking agents, cyclodextrin compounds, oxidizers, and the like. Superabsorbent particles, synthetic fibers, or films may also be employed. Additional options include cationic dyes, optical brighteners, humectants, emollients, and the like.

Tissue webs that may be treated in accordance with the present disclosure may include a single homogenous layer of fibers or may include a stratified or layered construction. For instance, the tissue web ply may include two or three layers of fibers.

The basis weight of tissue webs made in accordance with the present disclosure can vary depending upon the final product. For example, the process may be used to produce bath tissues, facial tissues, paper towels, industrial wipers, and the like. In general, the basis weight of the tissue products may vary from about 10 gsm to about 110 gsm, such as from about 20 gsm to about 90 gsm. For bath tissue and facial tissues, for instance, the basis weight may range from about 10 gsm to about 40 gsm. For paper towels, on the other hand, the basis weight may range from about 25 gsm to about 80 gsm.

In multiple ply products, the basis weight of each tissue web present in the product can also vary. In general, the total basis weight of a multiple ply product will generally be the same as indicated above, such as from about 20 gsm to about 110 gsm. Thus, the basis weight of each ply can be from about 10 gsm to about 60 gsm, such as from about 20 gsm to about 40 gsm.

All different types of products can be made in accordance with the present disclosure. For instance, in one embodiment, the tissue product 10 of the present disclosure can be used to produce a spirally wound roll 200 as shown in FIG. 5. The spirally wound roll 200, for instance, can comprise a bath tissue. As shown, the tissue product 10 includes an embossing pattern 14. The spirally wound roll of the tissue product 10 can be periodically perforated for allowing a user to tear off individual sheets.

In an alternative embodiment, the tissue product 10 can be formed into a spirally wound roll that comprises a paper towel or industrial wiper.

In still another embodiment, the tissue product 10 of the present disclosure can be cut into individual sheets and formed into a stack 300 as shown in FIG. 6. The stack of individual sheets 300 can be interfolded if desired. In one embodiment, the stack of individual sheets 300 can comprise a facial tissue product.

The present disclosure may be better understood with reference to the following example.

Example

A tissue product was made in accordance with the present disclosure using the process generally illustrated in FIG. 4. The tissue product produced was a two-ply product. Each tissue ply had a basis weight of 18 gsm and an initial caliper of 1354 microns per 12 plies.

One of the tissue plies was prewetted with water. Water was applied to the tissue ply in an amount of about 4% by weight. The embossing roll included a pattern of male embossing elements having a height of 0.9 mm in a pattern similar to that shown in FIG. 1 . The spacing between the male embossing elements within each line structure was 1.55 mm. The tissue ply was fed through a heated nip, embossed, and re-wetted with a bonding solution comprising water. The embossed tissue ply was then fed into a second nip and joined to a second tissue ply.

Each tissue ply was made from cellulose pulp fibers, particularly softwood kraft fibers.

The tissue ply was embossed using a top nip at 14 kg/cm and a bottom nip at 25 kg/cm.

The finished product had a dramatically improved thickness. In particular, the finished product displayed a caliper of 2,590 microns per 12 plies.

The embossing efficiency was calculated as follows:

(2590 microns-1354 microns) \ (14 kg/cm + 25 kg/cm) = 31 .4 microns per kg/cm

As shown above, the embossing efficiency of the process was greater than 30 microns per kg/cm. This is a dramatic improvement from conventional processes. For instance, conventional DERL embossing processes typically have an embossing efficiency using the same tissue plies of less than about 12 microns per kg/cm.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention so further described in such appended claims.

Claims

What Is Claimed:

1 . A method of producing an embossed multi-ply tissue product comprising: prewetting a first tissue ply with a prewetting solution comprising water, the first tissue ply having a first surface and a second and opposite surface; conveying the prewetted first tissue ply through a heated embossing nip, the first surface of the first tissue ply contacting an embossing roll while in the nip, the embossing roll defining a pattern of male embossing elements, the male embossing elements comprising discrete shapes and having an embossing height of from about 0.6 mm to about 1.2 mm, the embossing elements forming line structures in which a spacing between adjacent embossing elements within the line structures is from about 1.1 mm to about 1 .7 mm, and wherein the heated embossing nip forms an embossing pattern in the first tissue ply while also causing water to evaporate from the first tissue ply, the embossing pattern comprising a pattern of protrusions extending from the second surface of the first tissue ply; applying an adhesive-free bonding solution to the pattern of protrusions on the second surface of the first tissue ply, the bonding solution comprising water; and thereafter contacting the second surface of the first tissue ply with a first surface of a second tissue ply, the bonding solution causing bonds to form between the two plies.

2. A method as defined in claim 1 , wherein the prewetting solution is sprayed onto the first tissue ply, the prewetting solution comprising greater than about 95% by weight water.

3. A method as defined in any of the preceding claims, wherein the prewetting solution is applied to the first tissue ply in an amount of from about 2% to about 6% by weight.

4. A method as defined in any of the preceding claims, wherein the prewetting solution is heated to a temperature of from about 60°C to about 95°C prior to being applied to the first tissue ply.

5. A method as defined in any of the preceding claims, wherein the pattern of male embossing elements comprises spaced apart rows of line structures, the male embossing elements forming dot embossments.

6. A method as defined in any of the preceding claims, wherein the line structures are curvilinear.

7. A method as defined in any of the preceding claims, wherein the line structures have a wave-like pattern.

8. A method as defined in any of the preceding claims, wherein the embossing roll further comprises continuous line embossments, the line embossments having an embossing height of less than about 0.9 mm and greater than about 0.4 mm.

9. A method as defined in claim 8, wherein the line embossments form a pattern of images overlapping the pattern of male embossing elements.

10. A method as defined in any of the preceding claims, wherein the heated embossing nip is located between the embossing roll and a backing roll, and wherein the embossing roll, the backing roll, or both are heated to a temperature of from about 70°C to about 190°C.

11. A method as defined in any of the preceding claims, wherein the bonding solution is applied by a roll applicator placed in contact with the second surface of the first tissue ply.

12. A method as defined in any of the preceding claims, wherein the bonding solution comprises greater than about 95% by weight water.

13. A method as defined in any of the preceding claims, wherein the bonding solution is heated to a temperature of from about 60°C to about 90°C prior to being applied to the first tissue ply.

14. A method as defined in any of the preceding claims, wherein the method further comprises the following steps: conveying the embossed first tissue ply after applying the bonding solution into a second nip; conveying the second tissue ply into the second nip; and joining the first and second tissue plies together.

15. A method as defined in any of the preceding claims, wherein the bonding solution causes hydrogen bonding to occur between the first tissue ply and the second tissue ply.

16. A method as defined in any of the preceding claims, wherein the method produces an embossing efficiency of greater than about 25 microns per kg/cm, such as greater than about 28 microns per kg/cm, such as greater than about 30 microns per kg/cm.

17. A multi-ply tissue product produced according to the process as defined in any of the preceding claims.

18. A multi-ply tissue product as defined in claim 17, wherein the tissue product has a sheet bulk of greater than about 10 cm³/g, such as greater than about 11 cm³/g, such as greater than about 12 cm³/g.

19. A multi-ply tissue product as defined in claim 17 or 18, wherein the tissue product has a caliper of at least about 2,100 microns per 12 plies, such as at least about 2,300 per 12 plies, such as at least about 2450 microns per 12 plies.

20. A multi-ply tissue product as defined in any of claims 17-19, wherein the first tissue ply and the second tissue ply each independently have a basis weight of from about 12 gsm to about 28 gsm, and wherein the multi-ply tissue product has a total basis weight of from about 30 gsm to about 80 gsm, such as from about 35 gsm to about 65 gsm.

21 . A multi-ply tissue product as defined in any of claims 17-20, wherein the tissue product is in the form of a spirally wound roll.

22. A multi-ply tissue product as defined in any of claims 17-20, wherein the tissue product comprises a stack of individual sheets folded together.