BACKGROUND OF THE DISCLOSURE

Tissue products, such as facial tissues, paper towels, bath tissues, napkins, and other similar products, are designed to include several important properties. For example, the products should have good bulk, a soft feel, and should have good strength and durability. Unfortunately, however, when steps are taken to increase one property of the product, other characteristics of the product are often adversely affected.

To achieve the optimum product properties, tissue products are typically formed, at least in part, from pulps containing wood fibers and often a blend of hardwood and softwood fibers to achieve the desired properties. For example, one common practice in the manufacture of tissue products is to provide two furnishes (or sources) of wood pulp fiber. Sometimes, a two-furnish system is used in which the first furnish comprises a wood pulp fiber having a relatively short fiber length, such as a hardwood kraft pulp fiber, and the second furnish is made of wood pulp fiber having a relatively long fiber length, such as softwood kraft pulp fiber. The short fiber furnish may be used to provide the finished product with a softer handfeel, while the long fiber furnish may be used to provide the finished product with strength.

Typically, when attempting to optimize surface softness, as is often the case with tissue products, the papermaker will select the fiber furnish based in part on the coarseness of pulp fibers. Pulps having fibers with low coarseness are desirable because tissue paper made from fibers having a low coarseness can be made softer than similar tissue paper made from fibers having a high coarseness. To optimize surface softness even further, premium tissue products usually comprise layered structures where the low coarseness fibers are directed to the outer layer of the tissue sheet with the inner layer of the sheet comprising longer, coarser fibers.

Unfortunately, the need for softness is balanced by the need for strength. Tissue product strength can be measured by calculating the tensile strength of the tissue product. However, tensile strength of a tissue product is generally inversely related to softness, and thus, the paper maker is continuously challenged with the need to balance the need for softness with the need for strength. Additionally, while tensile strength is one measure of tissue strength, other properties such as tensile energy absorbed (TEA), tear strength, and wet burst strength are also important to strength or durability of the tissue in use. Thus, there remains a need for improvements in the manufacture of tissue products, which must be both soft and strong.

SUMMARY OF THE DISCLOSURE

The present inventors have created creped tissue products, particularly creped, through-air dried tissue products, and more particularly creped towel products comprising regenerated cellulose, having improved strength, softness, and bulk. In certain instances, the improved product properties are achieved by replacing conventional wood pulp fibers with regenerated cellulose fibers that surprisingly still provide adequate strength, softness, and bulk, particularly when the regenerated cellulose fibers are selectively disposed in one or more layers of a layered tissue towel product.

To produce the instant tissue products the inventors have successfully moderated the changes in strength, softness and bulk typically associated with substituting conventional wood pulp fibers with regenerated cellulose fibers by selectively disposing the regenerated cellulose fibers in one or more layers of a layered tissue towel product. Accordingly, in certain preferred embodiments, the invention provides tissue products in which regenerated cellulose fibers replace other fibers of the tissue product without negatively affecting the tissue product's strength, softness, or bulk. In a particularly preferred embodiment, the regenerated cellulose fibers are disposed in one of the two outer most layers of a layered tissue web, particularly the outer layer brought into contact with, and adhered to, the drying surface during manufacture.

In one embodiment the present invention provides a creped, through-air dried, tissue product comprising at least about 5 weight percent regenerated cellulose fibers, such as from about 5 to about 30 weight percent, more preferably from about 10 to about 20 weight percent regenerated cellulose fibers. The regenerated cellulose fibers preferably have a linear density less than 1.5 dtex, more preferably less than about 1 .0 dtex, still more preferably less than about 0.9 dtex, such as from about 0.3 to about 1 .5 dtex, and a fiber length of less than 6.0 mm.

In another embodiment the present invention provides a creped, through-air dried, tissue product comprising from about 5 to about 30 weight percent regenerated cellulose fibers, the tissue product having a basis weight from about 45 to about 65 grams per square meter (gsm), a geometric mean tensile strength of about 2,000 g/3” or greater, such as from about 2,000 to about 3,500 g/3” and a TS7 value less than about 20, such as from about 15 to about 20.

In yet another embodiment the present invention provides a tissue product consisting of a single, creped, through-air dried tissue ply comprising from about 5 to about 20 weight percent regenerated cellulose fibers, the tissue product having a geometric mean tensile strength from about 2,000 to about 3,500 g/3” and a TS7 value from about 15 to about 20.

In still other embodiments the present invention provides a creped, through-air dried tissue product comprising from about 5 to about 30 weight percent regenerated cellulose, the product having a wet:dry ratio of at least about 45 percent and a wet burst strength of at least about 300 grams force (gf), such as from about 300 to about 400 gf.

In yet other embodiments the present invention provides a creped, through-air dried tissue product comprising from about 5 to about 30 weight percent regenerated cellulose, the product having a geometric mean tensile strength of about 2,000 g/3” or greater, such as from about 2,000 to about 3,500 g/3” and a wet burst strength of at least about 300 grams force (gf), such as from about 300 to about 400 gf.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

FIG. 1 illustrates one device useful for forming a multi-layered web according to the present invention;

FIG. 2 is a schematic illustration of a process for making through-air dried paper sheets that may be used in accordance with this invention;

FIG. 3 is a schematic illustration of a process for making a printed/creped paper sheet that may be used in accordance with this invention;

FIG. 4 is a graph illustrating geometric mean slope (GM Slope) having units of grams versus geometric mean tensile (GMT) having units of grams per three inches for various samples including different amounts of regenerated cellulose fibers as described herein;

FIG. 5 is a graph illustrating TS7 Softness values versus GMT values for various samples including different amounts of regenerated cellulose fibers as described herein; and

FIG. 6 is a graph illustrating Stiffness Index versus geometric mean tensile energy absorption (GM TEA) having units of g*cm/cm ² for various samples including different amounts of regenerated cellulose fibers as described herein. DEFINITIONS

As used herein, the term "tissue product” generally refers to products made from one or more tissue plies, also referred to herein as webs, and includes various paper products, such as facial tissue, bath tissue, paper towels, napkins, wipers, medical pads, and the like.

The term "ply” refers to a discrete product element. Individual plies may be arranged in juxtaposition to each other. The term may refer to a plurality of web-like components in facing arrangement with one another such as in a multi-ply facial tissue, bath tissue, paper towel, wipe, or napkin.

As used herein, the term "layer” refers to a plurality of strata of fibers, chemical treatments, or the like, within a ply.

As used herein, the terms "layered tissue web,” "multi-layered tissue web,” "multi-layered web,” and "multi-layered paper sheet,” generally refer to sheets of paper prepared from two or more layers of aqueous papermaking furnish which are preferably comprised of different fiber types. The layers are preferably formed from the deposition of separate streams of dilute fiber slurries, upon one or more endless foraminous screens. If the individual layers are initially formed on separate foraminous screens, the layers are subsequently combined (while wet) to form a layered composite web.

As used herein, the term "fiber” means an elongate particulate having an apparent length greatly exceeding its apparent width. More specifically, and as used herein, fiber means such fibers suitable for a papermaking process and more particularly the tissue paper making process.

As used herein, the term "regenerated cellulose” refers to fibers that are derived from cellulose, and more preferably, wood cellulose, that are dissolved, purified, and extruded. Regenerated cellulose fibers are generally distinguishable from synthetic fibers, which are generally non-cellulosic, thermoplastic fibers.

As used herein, the term "thermoplastic” means a plastic which becomes pliable or moldable above a specific temperature and returns to a solid state upon cooling. Exemplary thermoplastic fibers can include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like), polyalkylenes (e.g., polyethylenes, polypropylenes and the like), polyacrylonitriles (PAN), and polyamides (nylons, for example, nylon-6, nylon 6,6, nylon-6, 12, and the like).

As used herein, the term "fiber length” is defined and measured according to the Fiber Length Test as described in the Test Methods section. As used herein, the term "denier” refers to a unit of measure for the linear mass density of fibers. Fiber denier is to be measured according to ASTM D-1577, "Standard Test Methods for Linear Density of Textile Fibers.” Denier may be used herein interchangeably with Decitex (dtex). Generally, 1 Denier (den) = 1.111 Decitex (dtex).

As used herein the term "basis weight” generally refers to the conditioned weight per unit area of a tissue and is generally expressed as grams per square meter (gsm). Basis weight is measured as described in the Test Methods section below. While the basis weights of tissue products prepared according to the present invention may vary, in certain embodiments the products have a basis weight greater than about 30 gsm, such as greater than about 45 gsm, such as greater than about 50 gsm, such as from about 30 to about 100 gsm, such as from about 45 to about 70 gsm, such as from about 50 to about 65 gsm.

As used herein, the term "Caliper” refers to the thickness of a tissue product, web, sheet, or ply, typically having units of microns (pm) and is measured as described in the Test Methods section below.

As used herein, the term "Bulk” refers to the quotient of the caliper (pm) of a product or ply divided by the bone dry basis weight (gsm). The resulting bulk is expressed in cubic centimeters per gram (cc/g). Tissue products prepared according to the present invention may, in certain embodiments, have a bulk greater than about 8.0 cc/g, more preferably greater than about 9.0 cc/g and still more preferably greater than about 10.0 cc/g, such as from about 8.0 to about 12.0 cc/g.

As used herein, the term "Slope” refers to the slope of the line resulting from plotting tensile versus stretch and is an output of the MTS TestWorks™ in the course of determining the tensile strength as described in the Test Methods section herein. Slope is reported in the units of grams (g) per unit of sample width (inches) and is measured as the gradient of the least-squares line fitted to the load- corrected strain points falling between a specimen-generated force of 70 to 157 grams (0.687 to 1 .540 N) divided by the specimen width.

As used herein, the term "Geometric Mean Slope” (GM Slope) generally refers to geometric mean modulus of a product and is equal to the square root of the product of machine direction slope and cross-machine direction slope. While the GM Slope may vary amongst tissue products prepared according to the present disclosure, in certain embodiments, tissue products may have a GM Slope less than about 10.0 kg, more preferably less than about 9.0 kg and still more preferably less than about 8.0 kg, such as from about 6.0 to about 10.0 kg, such as from about 6.0 to about 8.0 kg. 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.

As used herein, the term "Stiffness Index” refers to the quotient of the geometric mean tensile slope, defined as the square root of the product of the MD and CD slopes (having units of kg), divided by the geometric mean tensile strength (having units of grams per three inches). x 1,000

While the Stiffness Index of tissue products prepared according to the present disclosure may vary, in certain instances the Stiffness Index ranges from about 2.0 to about 3.0.

As used herein, the term "TEA Index” refers the geometric mean tensile energy absorption (having units of g*cm/cm ² ) at a given geometric mean tensile strength (having units of grams per three inches) as defined by the equation:

While the TEA Index may vary, in certain instances tissue products prepared according to the present disclosure have a TEA Index greater than about 1 .35, such as greater than about 1 .40, such as greater than about 1 .45, such as from about 1 .35 to about 1 .50.

As used herein, the term "Wet/Dry Ratio" refers to the ratio of the wet cross-machine direction (CD) tensile strength to the dry CD tensile strength, expressed as a percentage. Wet and dry CD tensile are measured as set forth in the Test Methods section below. The Wet/Dry Ratio of inventive tissue products may vary depending on several factors such as, for example, the creping composition and the amount of wet strength additive, however, in certain instances the inventive tissue products may have a Wet/Dry Ratio greater than about 40 percent, such as greater than about 42 percent, such as greater than about 44percent, from about 40 to about 50 percent.

As used herein the term "permanent wet strength agent” generally refers to a chemical composition which allows a tissue product, when placed in an aqueous medium, to keep a majority of its initial tensile strength for a period of time greater than at least about 2 minutes. Permanent wet strength resins include, for example, diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), epichlorhydrin resin(s), and polyamide-epichlorohydrin (PAE).

As used herein, the term "TS7” generally refers to the softness of a tissue product surface measured using an EMTEC Tissue Softness Analyzer ("EMTEC TSA”) (EMTEC Electronic GmbH, Leipzig, Germany) interfaced with a computer running EMTEC TSA software (version 3.19 or equivalent). The units of the TS7 are dB V2 rms, however, TS7 values are often referred to herein without reference to units. Generally, the TS7 is the magnitude of the peak occurring at a frequency between 6 and 7 kHz which is produced by vibration of the tissue product during the test procedure. Generally, a peak in this frequency range having a lower amplitude, and hence a lower TS7 value, is indicative of a softer tissue product.

As used herein the term "substantially free” refers to the composition of one layer of a multilayered web which comprises less than about 1.00 percent, by weight of the given layer, regenerated cellulose. The foregoing amounts of fiber are generally considered negligible and do not affect the physical properties of the layer. Moreover, the presence of negligible amounts of regenerated cellulose in a given layer generally arise from regenerated cellulose applied to an adjacent layer and have not been purposefully disposed in a given layer.

DETAILED DESCRIPTION OF THE DISLOSURE

The present invention generally provides tissue products having improved strength, softness, and bulk. The improvement in strength, softness and bulk typically is generally achieved by substituting conventional wood pulp fibers with regenerated cellulose fibers and more particularly by selectively disposing the regenerated cellulose fibers in one or more layers of a layered tissue web used to form the tissue product. Accordingly, in certain preferred embodiments, the invention provides tissue products in which regenerated cellulose fibers replace other fibers of the tissue product without negatively affecting the tissue product's strength, softness, or bulk.

In certain embodiments the regenerated cellulose fibers are selectively disposed in a single layer of a multi-layered web. For example, the regenerated cellulose fibers may be selectively disposed in one of the two outer layers of a multi-layered tissue web. In a particularly preferred embodiment, the regenerated cellulose may be disposed in a first outer layer of tissue web, which layer is brought into contact with, and adhered to, a heated dryer surface during manufacture and subsequently removed by creping. By selectively disposing the regenerated cellulose fibers in the dryer contracting surface of a web, the surface properties of the web may be improved without negatively affecting the tensile properties. Further, the sheet bulk may be increased relative to similarly manufactured webs that are substantially free from regenerated cellulose and consist essentially of wood pulp fibers.

Without being bound by theory, it is believed that regenerated cellulose fibers have a reduced capacity for hydrogen bonding relative to natural cellulose fibers, and that regenerated cellulose fibers of sufficient length add strength to the sheet through physical forces such as friction and/or entanglement. By decreasing the degree of inter-fiber hydrogen bonding the stiffness of the web may be reduced, yet the inter-fiber mechanical engagement may maintain or improve tensile strength. In this manner the tissue maker may employ regenerated cellulose fibers to improve tensile without negatively affecting surface properties, such as softness. This is particularly true when the regenerated cellulose fibers are selectively disposed in a single layer of a multi-layered web and when they are used relatively sparingly, such as at add-on levels less than about 30 weight percent, based on the total weight of the web, and more preferably less than about 20 weight percent and still more preferably about 15 weight percent or less, such as from about 5 to about 30 weight percent, more preferably from about 5 to about 20 weight percent and still more preferably from about 5 to about 10 weight percent.

Accordingly, in particularly preferred embodiments one of the outer surfaces of the tissue web comprises regenerated cellulose fibers and more particularly regenerated cellulose fibers having a linear density of about 1 .0 dtex or less and a fiber length of about 3.0 mm. The outer surface layer comprising regenerated cellulose may be substantially free from short wood pulp fibers, such as eucalyptus hardwood kraft pulp fibers (EHWK), and may still have desirable surface properties, such as a TS7 value of about 20.0 or less. It should be understood that, when referring to a layer that is substantially free from a particular fiber type, such as short wood pulp fibers, negligible amounts of the fibers may be present therein, however, such small amounts often arise from the fibers applied to an adjacent layer, and do not typically substantially affect the web surface properties, or other physical characteristics of the web.

Preferably a layered or stratified web is formed that contains regenerated cellulose fibers in at least one of the outer layers. Generally, the regenerated cellulose have a fiber length of 5.0 mm or less, more preferably 4.0 mm or less and still more preferably 3.0 mm or less, such as from 2.5 to 5.0 mm, such as from 2.5 to 4.0 mm, such as from 2.5 to 3.0 mm. The regenerated cellulose fibers may have a linear density ranging from about 0.3 dtex to about 6 dtex, from about 0.5 dtex to about 5 dtex, or from about 0.9 dtex to about 2.0 dtex, specifically reciting all values within these ranges and any ranges created thereby. In a particularly preferred embodiment, the regenerated cellulose has a fiber length of 3.0 mm and linear density of about 1.0 dtex or less. Suitable regenerated cellulose fibers are commercially available from Kelheim Fibres GmbH (Kelheim, Germany).

The regenerated cellulose fibers are generally arranged in the web such that they make up at least one layer of the stratified web and more preferably an outer layer of the web such that the fibers form an outer surface of the resulting tissue product. For example, in one particular embodiment of the present invention, the web comprises first and second outer layers forming the first and second surfaces of the web, and a middle layer disposed therebetween. Each outer layer can comprise from about 15 to about 40 percent by weight of the web and particularly from about 20 to about 35 percent by weight of the web. The middle layer, however, can comprise from about 40 to about 60 percent by weight of the web, and particularly about 50 percent by weight of the web.

In one embodiment, one of the product's outer layers consists essentially of regenerated cellulose fibers and the layer comprises from about 20 to about 40 percent by weight of the product. For example, the product may comprise first and second outer layers and at least one of the outer layers consists essentially of regenerated cellulose fibers, such as a regenerated cellulose fiber having a fiber length of about 3.0 mm and a density of about 1.0 dtex or less. In other embodiments, regenerated cellulose fibers are selectively disposed in only one of the two outer layers of the multi-layered web where the layer containing the regenerated cellulose fibers comprises from about 20 to about 40 percent by weight of the web.

In certain embodiments one or more layers of the multi-layered web may contain wood pulp fibers, such as softwood kraft pulp fibers, or a mixture of softwood kraft pulp fibers and high yield softwood pulp fibers. For example, a first outer layer and a middle layer of a three layered web may consist essentially of Northern softwood kraft pulp fibers (NSWK) or a mixture of Southern softwood kraft pulp fibers (SSWK) and NSWK. In other instances, one or more layers may comprise bleached chemi- thermomechanical pulp (BCTMP) softwood fibers. For example, the web may comprise BCTMP softwood fibers in the middle layer in an amount from about 40 to about 60 percent by weight of the middle layer, and particularly in an amount of about 50 percent by weight of the middle layer.

In certain embodiments tissue products of the present invention may be formed from a multilayered tissue web having first and second outer layers and a middle layer disposed there between where the first outer layer comprises softwood fibers and regenerated cellulose fibers and is the layer contacted by the dryer surface and creped during manufacture. The middle layer may comprise a mixture of NSWK and SSWK and the second outer layer may consist essentially of NSWK.

Regardless of the precise layering structure it is generally preferred that the regenerated cellulose is selectively disposed in at least one layer and the total amount of regenerated cellulose fibers is about 25 percent or less, or in some embodiments 20 percent or less, or in some embodiments 15 percent or less of the total weight of the wet-laid tissue product. In a particularly preferred embodiment regenerated cellulose fibers are utilized in the tissue web as a replacement for high fiber length wood fibers such as softwood fibers, and more specifically, NSWK fibers. In one particular embodiment the regenerated cellulose fibers are substituted for at least 2.0 percent, more preferably at least 2.5 percent, even more preferably at least 4.0 percent, and yet even more preferably at least 5.0 percent of the NSWK fibers. In certain embodiments the middle layer of a three layered web may be formed without a substantial amount of inner fiber-to-fiber bond strength. In this regard, the fiber furnish used to form the middle layer 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 into the headbox. Suitable debonding agents that may be used in the present invention include cationic debonding agents, particularly quaternary ammonium compounds, mixtures of quaternary ammonium compounds with polyhydroxy compounds, and modified polysiloxanes.

Suitable cationic debonding agents include, for example, 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. Patent No. 5,529,665, the contents of which are incorporated herein in a manner consistent with the present disclosure.

In one embodiment, the debonding agent used in the process of the present invention is an organic quaternary ammonium chloride and particularly a silicone based amine salt of a quaternary ammonium chloride. Useful debonders are commercially available under the tradename ProSoft (commercially available from Solenis, Wilmington, DE). The debonding agent can be added to the fiber slurry in an amount of from about 1 .0 kg per metric tonne to about 15 kg per metric tonne of fibers present within the slurry.

Particularly useful quaternary ammonium debonders include imidazoline quaternary ammonium debonders, such as oleyl-imidazoline quaternaries, dialkyl dimethyl quaternary debonders, ester quaternary debonders, diamidoamine quaternary debonders, and the like. The imidazoline-based debonding agent can be added in an amount of between 1 .0 to about 10 kg per metric tonne.

In another embodiment, a layer or other portion of the web, including the entire web, can be provided with wet or dry strength agents. As used herein, "wet strength agents" are materials used to immobilize the bonds between fibers in the wet state. Any material that when added to a tissue web or sheet at an effective level results in providing the sheet with a wet geometric tensile strength :dry geometric tensile strength ratio in excess of 0.1 will, for purposes of this invention, be termed a wet strength agent. Typically, these materials are termed either as permanent wet strength agents or as "temporary" wet strength agents. For the purposes of differentiating permanent from temporary wet strength, permanent will be defined as those resins which, when incorporated into paper or tissue products, will provide a product that retains more than 50 percent of its original wet tensile strength after exposure to water for a period of at least five minutes. Temporary wet strength agents are those which show less than 50 percent of their original wet strength after being saturated with water for five minutes. Both classes of material find application in the present invention. The amount of wet strength agent or dry strength added to the pulp fibers can be at least about 0.1 dry weight percent, more specifically about 0.2 dry weight percent or greater, and still more specifically from about 0.1 to about 3 dry weight percent, based on the dry weight of the fibers.

Particularly preferred wet strength agents include resin binder materials selected from the group consisting of polyamide-epichlorohydrin resins, polyacrylamide resins, and mixtures thereof. Of particular utility are the various polyamide-epichlorohydrin resins. These materials are low molecular weight polymers provided with reactive functional groups such as amino, epoxy, and azetidinium groups. Particularly useful polyamide-epichlorohydrin resins include those marketed under the tradename KYMENE (Solenis, Wilmington, DE).

Useful dry strength additives include carboxymethyl cellulose resins, starch based resins, and mixtures thereof. Examples of preferred dry strength additives include carboxymethyl cellulose, and cationic polymers available under the tradename ACCO (commercially available from American Cyanamid Company, Wayne, NJ) such as ACCO 711 and ACCO 514.

Suitable temporary wet strength resins include, but are not limited to, those resins described in U.S. Patent Nos. 3,556,932 and 3,556,933. Other temporary wet strength agents that should find application in this invention include modified starches.

Although wet strength agents as described above find particular advantage for use in connection with this invention, other types of bonding agents can also be used to provide the necessary wet resiliency. They can be applied at the wet end of the basesheet manufacturing process or applied by spraying or printing after the basesheet is formed or after it is dried.

Tissue webs, also referred to herein as basesheets, useful in forming tissue products according to the present invention may be manufactured using a variety of wet-laid papermaking processes known in the art. For example, a papermaking process of the present disclosure can utilize adhesive creping, wet creping, double creping, embossing, wet-pressing, air pressing, through-air drying, creped through- air drying, uncreped through-air drying, as well as other steps in forming the tissue web. Examples of papermaking processes and techniques useful in forming tissue webs according to the present invention include, for example, those disclosed in U.S. Patent Nos. 5,048,589, 5,399,412, 5,129,988 and 5,494,554, all of which are incorporated herein in a manner consistent with the present disclosure. In one embodiment the tissue web is wet-laid, through-air dried and creped.

The multi-layered webs of the presented invention are generally formed from multiple layers of fiber furnish using manufacturing techniques well-known in the art, such as stratified headbox. Layered webs produced by any means known in the art, however, are within the scope of the present invention, including those disclosed in U.S. Patent No. 5,494,554, which is incorporated herein by reference in a manner consistent with the present disclosure.

Referring to FIG. 1 , one embodiment of a device for forming a multi-layered stratified pulp furnish is illustrated. As shown, a three-layered headbox 10 generally includes an upper headbox wall 12 and a lower headbox wall 14. Headbox 10 further includes a first divider 16 and a second divider 18, which separate three fiber stock layers.

Each of the fiber layers comprises a dilute aqueous suspension of papermaking fibers. In one embodiment, for instance, middle layer 20 contains softwood kraft fibers either alone or in combination with other fibers such as high yield fibers. At least one of the outer layers 22 and 24, on the other hand, contain short, low coarseness cellulosic fibers, such as hardwood kraft pulp fibers and more preferably Eucalyptus kraft pulp fibers.

An endless traveling forming fabric 26, suitably supported and driven by rolls 28 and 30, receives the layered papermaking stock issuing from headbox 10. Once retained on fabric 26, the layered fiber suspension passes water through the fabric as shown by the arrows 32. Water removal is achieved by combinations of gravity, centrifugal force and vacuum suction depending on the forming configuration.

Forming multi-layered tissue webs is also described and disclosed in U.S. Patent No. 5,129,988, the contents of which are incorporated herein in a manner consistent with the present disclosure.

The basis weight of tissue webs used in the process of the present invention can vary depending upon the final product. For example, the process of the present invention can be used to produce facial tissues, bath tissues, paper towels, industrial wipers, and the like. For these products, the basis weight of the tissue web can vary from about 30 to about 100 gsm, and particularly from about 35 to about 80 gsm. In one particular embodiment, it has been discovered that the present invention is particularly well suited for the production of wiping products having a basis weight of from about 50 to about 65 gsm.

As stated above, the manner in which the tissue web is formed can also vary depending upon the particular application. In general, the tissue web can be formed by any of a variety of papermaking processes known in the art. For example, the tissue web may comprise a through-air dried web such as an uncreped through-air dried web. Other through-air dried webs that may be used in the present invention include pattern-densified or imprinted webs. In another alternative embodiment, the tissue web may be made according to an air forming process.

For example, referring to FIG. 2, shown is a method for making through-air dried paper sheets that may be used in accordance with this invention. (For simplicity, the various tensioning rolls schematically used to define the several fabric runs are shown but not numbered. It will be appreciated that variations from the apparatus and method illustrated in FIG. 2 can be made without departing from the scope of the invention). Shown is a twin wire former having a papermaking headbox 34, such as a layered headbox, which injects or deposits a stream 36 of an aqueous suspension of papermaking fibers onto the forming fabric 38 positioned on a forming roll 39. The forming fabric serves to support and carry the newly-formed wet web downstream in the process as the web is partially dewatered to a consistency of about 10 dry weight percent. Additional dewatering of the wet web can be carried out, such as by vacuum suction, while the wet web is supported by the forming fabric.

The wet web is then transferred from the forming fabric 38 to a transfer fabric 40. In one embodiment, the transfer fabric can be traveling at a slower speed than the forming fabric in order to impart increased stretch into the web. This is commonly referred to as a "rush” transfer. Preferably the transfer fabric can have a void volume that is equal to or less than that of the forming fabric. The relative speed difference between the two fabrics can be from 0 to 60 percent, more specifically from about 15 to 45 percent. Transfer is preferably carried out with the assistance of a vacuum shoe 42 such that the forming fabric and the transfer fabric simultaneously converge and diverge at the leading edge of the vacuum slot.

The web is then transferred from the transfer fabric 40 to the throughdrying fabric 44 with the aid of a vacuum transfer roll 46 or a vacuum transfer shoe, optionally again using a fixed gap transfer as previously described. The throughdrying fabric can be traveling at about the same speed or a different speed relative to the transfer fabric. If desired, the throughdrying fabric can be run at a slower speed to further enhance stretch. Transfer can be carried out with vacuum assistance to ensure deformation of the sheet to conform to the throughdrying fabric, thus yielding desired bulk and texture. Suitable throughdrying fabrics are described in U.S. Patent Nos. 5,429,686 and 5,672,248, which are incorporated by reference.

In one embodiment, the throughdrying fabric contains high and long impression knuckles. For example, the throughdrying fabric can have from about 5 to about 300 impression knuckles per square inch which are raised at least about 0.005 inches above the plane of the fabric. During drying, the web can be macroscopically arranged to conform to the surface of the throughdrying fabric and form a textured, three-dimensional surface.

The side of the web contacting the throughdrying fabric is typically referred to as the "fabric side” of the tissue web. The fabric side of the tissue web, as described above, may have a shape that conforms to the surface of the throughdrying fabric after the fabric is dried in the throughdryer. The opposite side of the tissue web, on the other hand, is typically referred to as the "air side”. The air side of the web may be smoother than the fabric side during normal throughdrying processes.

The level of vacuum used for the web transfers can be from about 3 to about 15 inches of mercury (75 to about 380 millimeters of mercury), preferably about 5 inches (125 millimeters) of mercury. The vacuum shoe (negative pressure) can be supplemented or replaced by the use of positive pressure from the opposite side of the web to blow the web onto the next fabric in addition to or as a replacement for sucking it onto the next fabric with vacuum. Also, a vacuum roll or rolls can be used to replace the vacuum shoe(s).

While supported by the throughdrying fabric, the web is dried to a consistency of about 94 percent or greater by the throughdryer 48 and thereafter transferred to a carrier fabric 50. The dried basesheet 52 is transported to the reel 54 using carrier fabric 50 and an optional carrier fabric 56. An optional pressurized turning roll 58 can be used to facilitate transfer of the web from carrier fabric 50 to fabric 56. Suitable carrier fabrics for this purpose are Albany International 84M or 94M and Asten 959 or 937, all of which are relatively smooth fabrics having a fine pattern. Although not shown, reel calendering or subsequent off-line calendering or embossing may be used.

In one embodiment, the reel 54 shown in FIG. 2 can run at a speed slower than the fabric 56 in a rush transfer process for building bulk into the tissue web 52. For instance, the relative speed difference between the reel and the fabric can be from about 5 to about 25 percent and, particularly from about 12 to about 14 percent. Rush transfer at the reel can occur either alone or in conjunction with a rush transfer process upstream, such as between the forming fabric and the transfer fabric.

In one embodiment, the tissue web 52 is a textured web which has been dried in a three- dimensional state such that the hydrogen bonds joining fibers were substantially formed while the web was not in a flat, planar state. For instance, the web can be formed while the web is on a highly textured throughdrying fabric or other three-dimensional substrate. Processes for producing uncreped throughdried fabrics are, for instance, disclosed in U.S. Patent Nos. 5,672,248, 5,656,132 and 6,096,169.

Once the tissue web is formed, a bonding material is applied to at least one side of the web and the treated side of the web is then creped. FIG. 3 is a schematic representation of a print/crepe process in which a flexible polymeric binder material is applied to one outer surface of the throughdried basesheet as produced in accordance with FIG. 2 Although gravure printing of the binder is illustrated, other means of applying the flexible polymeric binder material can also be used, such as foam application, spray application, flexographic printing, or digital printing methods, such as ink jet printing, and the like. Shown is tissue web 52 passing through a flexible polymeric binder material application station 65. Station 65 includes a transfer roll 67 in contact with a rotogravure roll 68, which is in communication with a reservoir

69 containing a suitable binder 70. The flexible polymeric binder material 70 is applied to one side of the web 52 in a pre-selected pattern . Preferably the side of the web 52 that is treated with the binder material

70 is formed from a layer of long cellulosic fibers and more preferably long, low coarseness cellulosic libers such as Northern softwood kraft fibers.

After the flexible polymeric binder material 70 is applied, the sheet 52 is adhered to a creping roil 75 by a press roll 76. The sheet 52 is carried on the surface of the creping roll 75 for a distance and then removed therefrom by the action of a creping blade 78 The creping blade 78 performs a controlled pattern creping operation on the side of the sheet 52 to which the flexible polymeric binder material 70 was applied.

Once creped, the sheet 52 is pulled through an optional drying station 80. The drying station can include any form of a heating unit, such as an oven energized by infrared heat, microwave energy, hot air, or the like. Alternatively, the drying station may comprise other drying methods such as photocuring, UV-curing, corona discharge treatment, electron beam curing, curing with reactive gas, curing with heated air such as through-air heating or impingement jet heating, infrared heating, contact heating, inductive heating, microwave or Rl ^:: heating, and the like. The drying station may be necessary in some applications to dry the sheet and/or cure the flexible polymeric binder material. Depending upon the flexible polymeric binder material selected, however, drying station 80 may not be needed. Once passed through the drying station 80, the sheet 52 can be wound into a roll of material or product 85.

The bonding materials applied to each side of the tissue web are selected for not only assisting in creping the web but also for adding dry strength, wet strength, stretchability, and tear resistance to the tissue web. Depending on the desired result, the bonding material may be applied only to one side of the web or to both sides of the web. In either case, only one side of the web is creped. The bonding material may be applied to one side of the tissue web in an amount from about 1 to about 25 percent by weight, such as from about 2 to about 10 percent by weight, based upon the total weight of the web.

In general, any suitable bonding material may be applied to the tissue web in accordance with the present invention. The bonding material may be, for instance, an ethylene vinyl acetate copolymer. Particular bonding materials that may be used in the present invention include latex compositions, such as carboxylated vinyl acetate-ethylene terpolymers, acrylates, vinyl acetates, vinyl chlorides and methacrylates. Some water-soluble bonding materials may also be used including polyacrylamides, polyvinyl alcohols, and cellulose derivatives such as carboxymethyl cellulose. Other bonding materials include styrene-butadiene copolymers, polyvinyl acetate polymers, vinyl-acetate ethylene copolymers, vinyl-acetate acrylic copolymers, ethylene-vinyl chloride copolymers, ethylene-vinyl chloride-vinyl acetate terpolymers, acrylic polyvinyl chloride polymers, nitrile polymers, and the like. Other examples of suitable latex polymers may be described in U.S. Patent No. 3,844,880.

In one embodiment, the bonding materials used in the process of the present invention comprise a crosslinkable ethylene vinyl acetate copolymer. In particular, the ethylene vinyl acetate copolymer can be cross-linked with N-methyl acrylamide groups using an acid catalyst. Suitable acid catalysts include ammonium chloride, citric acid, and maleic acid. Suitable crosslinkable ethylene vinyl acetate copolymer are commercially available from Wacker Chemie AG (Adrian, Ml) under the trade name AIRFLEX.

The bonding materials are applied to the base web as described above in a preselected pattern. In one embodiment, for instance, the bonding materials can be applied to the web in a reticular pattern, such that the pattern is interconnected forming a net-like design or grid on the surface.

In an alternative embodiment, however, the bonding materials are applied to the web in a pattern that represents a succession of discrete shapes. Applying the bonding material in discrete shapes, such as dots, provides sufficient strength to the web without covering a substantial portion of the surface area of the web.

According to the present invention, the bonding materials are applied to only one side of the web so as to cover from about 15 to about 75 percent of the surface area of the web. More particularly, in most applications, the bonding material will cover from about 20 to about 60 percent of the surface area of the web. At the foregoing web coverage, the amount of bonding material may range from about 1 to about 25 percent by weight, such as from about 2 to about 10 percent by weight, based upon the total weight of the web.

At the above amounts, the bonding materials can penetrate the tissue web from about 10 to about 70 percent of the total thickness of the web. In many applications, the bonding material may penetrate from about 10 to about 15 percent of the thickness of the web.

The process that is used to apply the bonding materials to the tissue web in accordance with the present invention can vary. For example, various printing methods can be used to print the bonding materials onto the base sheet depending upon the particular application. Such printing methods can include direct gravure printing, offset gravure or flexographic printing.

In the embodiment shown in FIG. 3 only one side of the web is treated with a bonding material leaving an untreated side. Leaving one side of the tissue web untreated may provide various benefits and advantages under some circumstances. For instance, the untreated side may increase the ability of the tissue web to absorb liquids faster. Further, the untreated side may have a greater texture than if the side were treated with a bonding material. Generally, it is preferred that the surface of web that is treated with a bonding material comprises regenerated cellulose and is brought into contact with the surface of a dryer after the bonding material is applied.

According to the process of the current invention, numerous and different tissue products can be formed. The tissue products can be, for instance, facial tissues, bath tissues, paper towels, napkins, industrial wipers, and the like. In certain embodiments the tissue products may be a single-ply tissue product. In an alternative embodiment, tissue webs made according to the present invention may be incorporated into multiple ply products. For instance, in one embodiment, a tissue web made according to the present invention can be attached to one or more other tissue webs for forming a wiping product having desired characteristics. The other webs laminated to the tissue web of the present invention can be, for instance, a wet-creped web, a calendered web, an embossed web, a through-air dried web, a creped through-air dried web, an uncreped through-air dried web, and the like.

The basis weight of tissue products produced according to the present invention are generally greater than about 30 gsm, such as greater than about 45 gsm, such as greater than about 50 gsm, such as from about 30 to about 100 gsm, such as from about 45 to about 70 gsm, such as from about 50 to about 65 gsm. In one particular embodiment, the present invention provides a single-ply paper towel product having a basis weight of from about 35 to about 80 gsm, more preferably from about 50 to about 65 gsm.

At the foregoing basis weights, the tissue products of the present invention may have a relatively high bulk. Tissue products made in accordance with the present invention, for instance, may have a bulk greater than 10.0 cc/g. For example, in one embodiment, the bulk of tissue products made according to the present invention may be about 11.0 cc/g or greater, such as about 12.0 cc/g or greater, such as about 13.0 cc/g or greater, such as from about 10.0 to 14.0 cc/g, such as from about 12.0 to about 14.0 cc/g. In one particularly preferred embodiment the present invention provides a single-ply, through-air dried, creped, tissue product comprising from about 5 to about 15 weight percent regenerated cellulose fiber, the product having a basis weight from about 50 to about 65 gsm and a sheet bulk from about 12.0 to about 14.0 cc/g.

Generally, the tissue products of the present invention have a geometric mean tensile (GMT) strength of about 2,000 g/3” or greater, more preferably about 2,200 g/3” or greater, and still more preferably about 2,400 g/3” or greater, such as from about 2,000 to about 4,000 g/3”, such as from about 2,000 to about 3,000 g/3”. In one particularly preferred embodiment the present invention provides a single-ply, through-air dried, creped, tissue product comprising from about 5.0 to about 10.0 weight percent regenerated cellulose fiber, the product having a GMT from about 2,000 to about 3,000 g/3”. Despite having relatively high degrees of tensile strength, the tissue products of the present invention are relatively soft. For example, the tissue products may have a GMT of about 2,000 g/3” or greater, such as from about 2,000 to about 3,000 g/3”, and a TS7 value less than about 20.0, such as from about 15.0 to about 20.0. In other instances, the tissue products may have a TS7 value of about 20.0 or less, more preferably about 18.0 or less, and still more preferably about 16.0 or less, such as from about 15.0 to about 20.0.

The tissue products of the present invention may have a geometric mean slope (GM Slope) less than about 10.0 kg, more preferably less than about 9.0 kg and still more preferably less than about 8.0 kg, such as from about 6.0 to about 10.0 kg, such as from about 6.0 to about 8.0 kg. In one particularly preferred embodiment the present invention provides a single-ply, through-air dried, creped, tissue product comprising from about 5.0 to about 10 weight percent regenerated cellulose fiber, the product having a GMT from about 2,000 to about 3,000 g/3” and a GM Slope from about 6.0 to about 8.0 kg.

In certain instances, the inventive products have a reduced GM Slope at a given geometric mean tensile strength compared to similar tissue products prepared using conventional wood pulp fibers. Accordingly, in certain embodiments, the products of the present invention may comprise regenerated cellulose fibers, such as from about 5 weight percent to about 20 weight percent regenerated cellulose fibers, and a have a GM Slope (having units of grams) less than or equal to:

GM Slope (g) < 2.2152(GMT) + 893.36

Where GMT is the geometric mean tensile strength having units of grams per three inches and generally ranges from about 2,000 to about 4,000 g/3”, such as from about 2,200 to about 3,600 g/3”.

At the foregoing tensile and modulus, the tissue products of the present invention generally have a low degree of stiffness. For example, in certain embodiments, the tissue products may have a Stiffness Index of about 3.0 or less, more preferably about 2.75 or less, still more preferably about 2.5 or less, such as from about 2.0 to about 3.0. In one particularly preferred embodiment the present invention provides a single-ply, through-air dried, creped, tissue product comprising from about 5.0 to about 10.0 weight percent regenerated cellulose fiber, the product having a GMT from about 2,000 to about 3,000 g/3” and a Stiffness Index from about 2.0 to about 3.0.

In still other instances the tissue products of the present invention may have a geometric mean stretch (GM Stretch) of about 20 percent or more, more preferably about 22 percent or more, and still more preferably about 24 percent or more, such as from about 20 to about 25 percent.

In yet other instances the inventive tissue products may demonstrate improved wet tensile properties as a result of the substation of wood pulp fibers with regenerated cellulose fibers. For example, the inventive tissue products may have a Wet/Dry Ratio greater than about 40 percent, such as greater than about 42 percent, such as greater than about 44 percent, from about 40 to about 50 percent. In other instances, the products may have a CD Wet Tensile from about 750 g/3” or more, such as about 775 g/3” or more, such as about 800 g/3” or more, such as about 825 g/3” or more, such as from about 750 to about 900 g/3”. At the foregoing the levels of wet tensile strength, the inventive tissue products may have a wet burst strength of about 300 gf or more, such as about 320 gf or more, such as about 340 gf or more, such as about 360 gf or more, such as from about 300 to about 400 gf.

TEST METHODS

Tissue Softness Analyzer

Softness and surface smoothness were measured using an EMTEC Tissue Softness Analyzer (“TSA”) (Emtec Electronic GmbH, Leipzig, Germany). The TSA comprises a rotor with vertical blades which rotate on the tissue sample applying a defined contact pressure. The blades are pressed against the sample with a load of 100 mN and the rotational speed of the blades is two revolutions per second. Contact between the vertical blades and the tissue sample creates vibrations, which are sensed by a vibration sensor. The sensor transmits a signal to a PC for processing and display. The signal is displayed as a frequency spectrum. The frequency spectrum is analyzed by the associated TSA software to determine the amplitude of the frequency peak occurring in the range between 200 to 1000 Hz. This peak is generally referred to as the TS750 value (having units of dB V2 rms) and represents the surface smoothness of the tissue sample. A high amplitude peak correlates to a rougher surface, while a low amplitude peak correlates to a smoother surface. A further peak in the frequency range between 6 and 7 kHZ represents the softness of the sample. The peak in the frequency range between 6 and 7 kHZ is herein referred to as the TS7 value (having units of dB V2 rms). The lower the amplitude of the peak occurring between 6 and 7 kHZ, the softer the sample.

Tissue product samples were prepared by cutting a circular sample having a diameter of 112.8 mm. All samples were allowed to equilibrate at TAPPI conditions for at least 24 hours prior to completing the TSA testing. After conditioning each sample was tested as is, i.e., multi-ply products were tested without separating the sample into individual plies. The sample is secured, and the measurements are started via the PC. The PC records, processes, and stores all of the data according to standard TSA protocol. The reported TS750 and TS7 values are the average of five replicates, each one with a new sample. Basis Weight

Prior to testing, ail samples are conditioned under TAPP! conditions (23 ± 1 °C and 50 ± 2 percent relative humidity) for a minimum of 4 hours. Basis weight of sample is measured by selecting twelve (12) products (also referred to as sheets) of the sample and making two (2) stacks of six (6) sheets. In the event the sample consists of perforated sheets of bath or towel tissue, the perforations must be aligned on the same side when stacking the usable units. A precision cutter is used to cut each stack into exactly 10.16 * 10.16 cm (4.0 * 4.0 inch) squares. The two stacks of cut squares are combined to make a basis weight pad of twelve (12) squares thick. The basis weight pad is then weighed on a top loading balance with a minimum resolution of 0.01 grams. The top loading balance must be protected from air drafts and other disturbances using a draft shield. Weights are recorded when the readings on the top leading balance become constant. The mass of the sample (grams) per unit area (square meters) is calculated and reported as the basis weight, having units of grams per square meter (gsm).

Caliper

Caliper is measured in accordance with TAPPI test methods Test Method T 580 pm-12 "Thickness (caliper) of towel, tissue, napkin and facial products.” The micrometer used for carrying out caliper measurements is an Emveco 200-A Tissue Caliper Tester (Emveco, Inc., Newberg, OR). The micrometer has a load of 2 kilopascals, a pressure foot area of 2,500 square millimeters, a pressure foot diameter of 56.42 millimeters, a dwell time of 3 seconds and a lowering rate of 0.8 millimeters per second.

Tensile

Tensile testing is conducted on a tensile testing machine maintaining a constant rate of elongation and the width of each specimen tested is 3 inches. Testing is conducted under TAPPI conditions. Prior to testing samples are conditioned under TAPPI conditions (23 ± 1°C and 50 ± 2 percent relative humidity) for at least 4 hours and then cutting a 3 ± 0.05 inches (76.2 ± 1 .3 mm) wide strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (Thwing-Albert Instrument Company, Philadelphia, PA, Model No. JDC 3-10, Serial No. 37333) or equivalent. The instrument used for measuring tensile strengths was an MTS Systems Sintech 11S, Serial No. 6233. The data acquisition software was MTS TestWorks® for Windows Ver. 3.10 (MTS Systems Corp., Research Triangle Park, NC). The load cell was selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, such that the majority of peak load values fall between 10 to 90 percent of the load cell's full-scale value. The gauge length between jaws was 4 ± 0.04 inches (101.6 ± 1 mm) for facial tissue and towels and 2 ± 0.02 inches (50.8 ± 0.5 mm) for bath tissue. The crosshead speed was 10 ± 0.4 inches/min (254 ±1 mm/min), and the break sensitivity was set at 65 percent. The sample was placed in the jaws of the instrument, centered both vertically and horizontally. The test was then started and ended when the specimen broke. The peak load was recorded as either the "MD tensile strength" or the "CD tensile strength" of the specimen depending on direction of the sample being tested. Ten representative specimens were tested for each product or sheet and the arithmetic average of all individual specimen tests was recorded as the appropriate MD or CD tensile strength having units of grams per three inches (g/3”). Tensile energy absorbed (TEA) and slope are also calculated by the tensile tester. TEA is reported in units of g’cm/cm ² and slope is recorded in units of kilograms (kg). Both TEA and Slope are directionally dependent and thus MD and CD directions are measured independently.

Wet tensile strength measurements are measured in the same manner as described above, but the previously conditioned sample strip is saturated with distilled water immediately prior to loading the specimen into the tensile test equipment. Preferably, prior to performing a wet tensile test, the sample is aged to ensure the wet strength resin has cured. Artificial aging may be used for samples that were to be tested immediately after or within days of manufacture. For artificially aging sample strips are heated for 4 minutes at 105 ± 2°C. For natural aging, the samples are held at 22 ± 2°C and 50 percent relative humidity for a period of 12 days prior to testing.

Following aging the samples are wetted individually and tested. Sample wetting is performed by first laying a single test strip onto a piece of blotter paper (Fiber Mark, Reliance Basis 120). A pad is then used to wet the sample strip prior to testing. The pad is a green, Scotch-Brite brand (3M) general purpose commercial scrubbing pad. To prepare the pad for testing, a full-size pad is cut approximately 2.5 inches long by 4 inches wide. A piece of masking tape is wrapped around one of the 4-inch long edges. The taped side then becomes the "top” edge of the wetting pad. To wet a tensile strip, the tester holds the top edge of the pad and dips the bottom edge in approximately 0.25 inches of distilled water located in a wetting pan. After the end of the pad has been saturated with water, the pad is then taken from the wetting pan and the excess water is removed from the pad by lightly tapping the wet edge three times across a wire mesh screen. The wet edge of the pad is then gently placed across the sample, parallel to the width of the sample, in the approximate center of the sample strip. The pad is held in place for approximately one second and then removed and placed back into the wetting pan. The wet sample is then immediately inserted into the tensile grips, so the wetted area is approximately centered between the upper and lower grips. The test strip should be centered both horizontally and vertically between the grips. (It should be noted that if any of the wetted portion comes into contact with the grip faces, the specimen must be discarded, and the jaws dried off before resuming testing.) The tensile test is then performed, and the peak load recorded as the wet tensile strength of this specimen. As with the dry tensile test, MD and CD directions are measured independently and ten representative specimens were tested for each product or sheet and the arithmetic average of all individual specimen tests was recorded as the appropriate MD or CD tensile strength.

All products were tested in their product forms without separating into individual plies.

Fiber Length

Tissue samples are prepared and stained as set forth in TAPPI T 401 , which provides for the identification of the types of fibers present in a sample and their quantitative estimation. If the tissue sample includes more than one cellulosic fiber type, the different fiber types will accept the stain in a different fashion to allow identification of the particular fiber type(s) to be analyzed. The stained sample is then analyzed using an image analysis system to determine fiber length.

The image analysis system includes a computer having a frame grabber board, a stereoscope, a video camera, and image analysis software. A VH5900 monitor microscope and a video camera having a VH50 lens with a contact type illumination head, available from the Keyence Company of Fair Lawn, NJ, can be used. The stereoscope and video camera acquire the image to be recorded. The frame grabber board converts the analog signal of this image to a digital format readable by the computer.

The image saved to the computer file is measured using suitable software such as the Optimas Image Analysis software, version 3.0, available from the BioScan Company of Edmonds, WA.

The slide is placed on the stereoscope stage. The stereoscope is adjusted to a 15* magnification level. The stereoscope light source intensity is set to the maximum value, and the stereoscope aperture is set to the minimum aperture size in order to obtain the maximum image contrast. The Optimas software is run with the multiple mode set and ARAREA (area) and ARLENGTH (length) measurements selected.

Under "Sampling Options," the following default values are used: sampling units are selected, set number equals 64 intervals, and minimum boundary length is 10 samples. The following options are not selected: Remove Areas Touching Region of Interest (ROI), Remove Areas Inside Other Areas, and Smooth Boundaries. The software contrast and brightness settings are set to 0 and 170, respectively. The software threshold settings are set to 125 and 255.

The image analysis software is calibrated in millimeters with a metric ruler placed in the field of view. The calibration is performed to obtain a screen width of 6.12 millimeters.

The region of interest is selected so that no fibers intersect the boundary of the region of interest. The operator positions the slide and acquires the image data (area and length) in one field. The slide is then repositioned, and image data are acquired in a second field. Data collection is continued until data from the entire slide is acquired. The use of grid lines on the slide, while not essential, is highly useful to prevent the microscopist from missing an area or reading an area more than once. Fibers crossing the grid lines are not included in the data collection.

While it is desirable to have a slide composed solely of individual fibers which do not cross, inevitably some images comprised of crossed fibers will be created. Crossed fiber images are deleted with the paint option available in the Optimas software if none of the crossed fibers are unobstructed. Unobstructed fibers in crossed fiber images are retained by painting over those fibers in the crossed fiber image which are at least partially obstructed by other fibers.

The image analysis software provides the projected fiber surface area and the fiber length for each fiber image recorded with the image analysis system.

Burst Strength (Wet or Dry)

Burst Strength is measured using an EJA Burst Tester (series #50360, commercially available from Thwing-Albert Instrument Company, Philadelphia, PA). The test procedure is according to TAPPI T570 pm-00 except the test speed. The test specimen is clamped between two concentric rings whose inner diameter defines the circular area under test. A penetration assembly, the top of which is a smooth, spherical steel ball, is arranged perpendicular to and centered under the rings holding the test specimen. The penetration assembly is raised at 6 inches per minute such that the steel ball contacts and eventually penetrates the test specimen to the point of specimen rupture. The maximum force applied by the penetration assembly at the instant of specimen rupture is reported as the burst strength in grams force (gf) of the specimen.

The penetration assembly consists of a spherical penetration member which is a stainless steel ball with a diameter of 0.625 ± 0.002 inches (15.88 ± 0.05 mm) finished spherical to 0.00004 inches (0.001 mm). The spherical penetration member is permanently affixed to the end of a 0.375 ± 0.010 inch (9.525 ± 0.254 mm) solid steel rod. A 2000 gram load cell is used and 50 percent of the load range i.e., 0-1000 g is selected. The distance of travel of the probe is such that the upper most surface of the spherical ball reaches a distance of 1 .375 inches (34.9 mm) above the plane of the sample clamped in the test. A means to secure the test specimen for testing consisting of upper and lower concentric rings of approximately 0.25 inches (6.4 mm) thick aluminum between which the sample is firmly held by pneumatic clamps operated under a filtered air source at 60 psi. The clamping rings are 3.50 ± 0.01 inches (88.9 ± 0.3 mm) in internal diameter and approximately 6.5 inches (165 mm) in outside diameter. The clamping surfaces of the clamping rings are coated with a commercial grade of neoprene approximately 0.0625 inches (1 .6 mm) thick having a Shore hardness of 70-85 (A scale). The neoprene needs not cover the entire surface of the clamping ring but is coincident with the inner diameter, thus having an inner diameter of 3.50 ± 0.01 inches (88.9 ± 0.3 mm) and is 0.5 inches (12.7 mm) wide, thus having an external diameter of 4.5 ± 0.01 inches (114 ± 0.3 mm). For each test a total of 3 sheets of product are combined.

The sheets are stacked on top of one another in a manner such that the machine direction of the sheets is aligned. Where samples comprise multiple plies, the plies are not separated for testing. In each instance the test sample comprises 3 sheets of product. For example, if the product is a 2-ply tissue product, 3 sheets of product, totaling 6 plies are tested. If the product is a single ply tissue product, then 3 sheets of product totaling 3 plies are tested.

Samples are conditioned under TAPPI conditions for a minimum of four hours and cut into 127 x 127 ± 5 mm squares. For wet burst measurement, after conditioning the samples were wetted for testing with 0.5 mL of deionized water dispensed with an automated pipette. The wet sample is tested immediately after insulting.

The peak load (gf) and energy to peak (g-cm) are recorded and the process repeated for all remaining specimens. A minimum of five specimens are tested per sample and the peak load average of five tests is reported.

EXAMPLES

A pilot tissue machine was used to produce a layered, uncreped through-air dried ("UCTAD”) towel basesheet in accordance with this invention generally as described in FIG. 2. After manufacture on the tissue machine, the UCTAD basesheet was printed on one side with a latex-based binder generally as described in FIG. 3. The binder-treated sheet was adhered to the surface of a Yankee dryer to re-dry the sheet. The dried sheet was creped and wound onto a roll without any additional thermal curing. The resulting sheet was converted into rolls of single-ply paper towels in a conventional manner.

The basesheet was made from a stratified fiber furnish containing a center layer of fibers (40 percent by weight of the basesheet) positioned between two outer layers of fibers (each outer layer comprising 30 percent by weight of the basesheet). The first outer layer contacted the through-air drying fabric during manufacture (fabric layer) and the second outer layer (air layer) was treated with binder and contacted the Yankee dryer. The furnish composition of each layer is summarized in Table 1 , below. The weight percentages in Table 1 reflect the weight percentage within a given fibrous layer. In all instances the furnish forming the first outer layer was subjected to refining to control the strength of the resulting basesheet. A debonding agent (ProSoft® TQ1003, Solenis, Wilmington, DE) was added to the furnish forming the middle. Each of the layers were also treated with a wet strength additive (Kymene 920A, Solenis, Wilmington, DE) and carboxymethyl cellulose (CMC). The control codes contained a Northern softwood kraft pulp (NSWK) and Southern softwood kraft pulp (SSWK), as set forth in Table 1 . The inventive codes were prepared by replacing a portion of the NSWK forming the air layer with regenerated cellulose fibers (DANUFIL® Short Cut Viscosefibre, Kelheim Fibres GmbH). The regenerated cellulose fibers (RCF) had a fiber length of 3.0 mm and a linear density of about 0.9 dtex.

TABLE 1

The fiber furnish was diluted to approximately 0.2 percent consistency and delivered to a layered headbox. The basesheet was then rush transferred to a transfer fabric (Fred, described in U.S. Patent No. 7,611 ,607 and commercially available from Voith Fabrics, Appleton, Wl) traveling 15 percent slower than the forming fabric using a vacuum roll to assist the transfer. At a second vacuum-assisted transfer, the basesheet was transferred and wet-molded onto the throughdrying fabric (T1205-2, described in U.S. Patent No. 8,500,955 and commercially available from Voith Fabrics, Appleton, Wl). The sheet was dried with a through-air dryer resulting in a basesheet having an air-dry basis weight of about 45 grams per square meter (gsm).

The resulting sheet was fed to a gravure printing line, traveling at about 1 ,500 feet per minute where a latex binder was printed onto the second outer layer (air layer) of the sheet. Samples were produced using two different print nip widths - 5 and 12 mm. The printed side of the sheet was then pressed against and doctored off a rotating drum, which had a surface temperature of approximately 132°C. Finally, the sheet was wound onto a roll without any additional thermal curing.

The latex binder material in this example was a carboxylated vinyl acetate-ethylene terpolymer, Vinnapas EP1133 (Wacker Chemie AG, Allentown, PA). The add-on amount of the binder applied to the sheet was approximately 7 weight percent. Certain relevant processing conditions of each of the codes are summarized in Table 2. The physical properties of the samples are summarized in Tables 3 and 4 and further illustrated in FIGS. 4-6. TABLE 2

TABLE 3

TABLE 4

While the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto and the following embodiments: Embodiment 1 : A wet-laid tissue product comprising regenerated cellulose fibers providing 25 percent or less of the total weight of the wet-laid tissue product, the regenerated cellulose fibers comprising a linear density of less than about 1 .0 dtex and a fiber length of less than about 6.0 mm.

Embodiment 2: The wet-laid tissue product of embodiment 1 , wherein the regenerated cellulose has a linear density of about 0.9 dtex.

Embodiment 3: The wet-laid tissue product of embodiment 1 or 2, wherein the regenerated cellulose fibers include an average diameter of less than 10.0 pm.

Embodiment 4: The wet-laid tissue product of any one of the preceding embodiments, wherein the regenerated cellulose fibers provide between 0.1 to 10.0 percent of the total weight of the wet-laid tissue product.

Embodiment 5: The wet-laid tissue product of embodiment 4, wherein the regenerated cellulose fibers provide between 0.1 to 5.0 percent of the total weight of the wet-laid tissue product.

Embodiment 6: The wet-laid tissue product of any one of the preceding embodiments, further comprising Northern softwood kraft fibers, wherein the Northern softwood kraft fibers provide between 40 to 80 percent of the total weight of the wet-laid tissue product.

Embodiment 7: The wet-laid tissue product of any one of the preceding embodiments, further comprising Southern softwood kraft fibers.

Embodiment 8: The wet-laid tissue product of any one of the preceding embodiments, wherein the wet-laid tissue product includes only a single ply.

Embodiment 9: The wet-laid tissue product of any one of embodiments 1 through 7, wherein the wet-laid tissue product includes multiple plies, and wherein the regenerated cellulose fibers are disposed within at least one outer ply of the multiple plies.

Embodiment 10: The wet-laid tissue product of any one of the preceding embodiments, wherein the wet-laid tissue product is through-air dried.

Embodiment 11 : The wet-laid tissue product of any one of the preceding embodiments, the product having a geometric mean slope, having units of grams, less than or equal to 2.2152(GMT)+893.36, where GMT is the geometric mean tensile strength having units of grams per three inches (g/3”) and wherein the GMT is from about 2,000 to about 4,000 g/3”.

Embodiment 12: The wet-laid tissue product of any one of the preceding embodiments, having a GMT from about 2,200 to about 3,600 g/3”. Embodiment 13: The wet-laid tissue product of any one of the preceding embodiments, having a basis weight from about 50 to about 65 gsm and a sheet bulk from about 12.0 to about 14.0 cc/g.

Embodiment 14: The wet-laid tissue product of any one of the preceding embodiments, having a Stiffness Index of about 3.0 or less. Embodiment 15: The wet-laid tissue product of any one of the preceding embodiments, having a Wet/Dry Ratio from about 40 to about 50 percent and a Wet Tensile of about 750 g/3” or more.