NO20170506A1 - Wet pressed paper and napkin products with elevated CD stretch and low tensile ratio made with a crepe process for a high solids content product - Google Patents

Description

Technical area

This application is aimed at a process where a track is compactly unwatered, crimped

a crepe cloth and dried, where the process is regulated to produce products with high CD stretch and low stretch quotients.

Background

Methods of making paper handkerchiefs, napkins, and the like are well known, including various characteristics such as Yankee drying, through drying, cloth creasing, dry creasing, wet creasing, and so on. Traditional wet-pressing processes have certain advantages over traditional air-drying processes, including: (1) sen-

expensive energy costs associated with the mechanical removal of water rather than evaporative drying with hot air; and (2) higher production rates that are more quickly achieved with processes that utilize wet pressing to form a web. On the other hand, air drying processes are generally introduced with new significant investments, especially for the production of soft, voluminous, high quality paper and napkin products.

Doll creasing has been used in connection with papermaking processes that include mechanical or compact dewatering of the paper stock as an opportunity to influence product properties. See US Patent Nos. 4,689,119 and 4,551,199 to Weldon;

4,849,054 and 4,834,838 to Klowak; and 6,287,426 to Edwards et al. The operation of cloth creasing processes has been hampered by difficulties in efficiently transferring a high or medium strength web to a dryer. See also US Patent No. 6,350,349 belonging to Hermans et al., which describes wet transfer of a web from a rotating transfer surface to a cloth. Several patents related to cloth creasing more generally are discussed in the following: US 4,834,838; US 4,482,429; US 4,445,638 in addition to US 4,440,597 additional

Rende Wells et al.

In connection with papermaking processes, cloth forming has also been used as an opportunity to provide structure and mass. In this regard, as seen in US Patent No. 6,610,173 to Lindsey et al. a method of embossing a paper tap during a wet pressing operation resulting in asymmetric protrusions corresponding to the deflection channels of a deflection member. US 6,610,173 teaches that a differential speed transmission during a pressing action serves to improve the shaping and embossing of a web with a deflection member. The paper webs produced are reported to have particular sets of physical and geometrical properties, such as a patterned compressed network and a repeating pattern of protrusions having asymmetric structures. Regarding wet forming of a web using structural fabrics, see also, the following US patents: 6,017,417 and 5,672,248 both belonging to Wendt et al; 5,508,818 and 5,510,002 belonging to Hermans et al. and 4,637,859 belonging to Trokhan. Regarding the use of cloths used to emboss structure into a nearly dry sheet, see US Patent No. 6,585,855 to Drew et al, in addition to US Patent Publication 2003/00064.

Thoroughly dried, crimped products are disclosed in the following patents: US Patent No. 3,994,771 to Morgan, Jr. et al; US Patent No. 4,102,737 to Morton; and US Patent No. 4,529,480 to Trokhan. The processes described in these patents include, very generally, forming a web on a porous support, thermally drying the web, applying the web to a Yankee dryer with a defined pinch point, in part by an embossing cloth, and crimping the product from the Yankee dryer. A relatively permeable path is typically required, which makes it difficult to use circuit mass composition at levels that are desired. Transfer to the Yankee typically takes place with a course firmness of from about 60% to about 70%; although in some processes the transfer occurs at much higher firmness, sometimes even approaching air-dry.

As mentioned above, thoroughly dried products tend to exhibit enhanced pulp and softness; however, thermal dewatering with hot air is prone to be

energy boosting. Wet-press operation in which the webs are mechanically dewatered is preferred from an energy perspective and can be more quickly added to pulp composition that includes recycled fibers that tend to form a web with less permeability than new fiber. Many improvements related to increasing the mass and absorbency of compact dewatering products that are typically partially dewatered with a papermaking felt.

Despite advances in the technique, previously known wet press processes have not produced the highly absorbent webs with preferred physical properties, particularly with elevated CD stretch at relatively low MD/CD stretch quotients, which have been sought for use in first-class paper and napkin products.

In accordance with the invention, the absorbency, mass and stretch of a wet pressed web can be greatly improved by wet cloth creasing of a web and rearrangement of the fibers of a crepe cloth, while maintaining the high speed, thermal efficiency and mass composition tolerance of recycled fiber from conventional wet pressing processes.

Summary of the Invention

The scope of the invention appears from the subsequent patent claims.

Accordingly, there is provided in a first aspect of the invention an absorbent sheet of cellulose fiber comprising a mixture of hardwood fiber and softwood fiber arranged in a network having: (i) a plurality of stacked fiber-enriched areas of relatively high specific area weight interconnected by means of (ii) a majority of lower local specific gravity connecting areas. The fiber direction of the connecting areas is aligned along the direction between stacked areas interconnected thereby. The relative basis weight, degree of stacking, hardwood-to-conifer ratio, fiber length distribution, fiber orientation, and geometry of network are monitored so that the sheet exhibits a percentage CD stretch of at least about 2.75 times the dry tensile value either to a sheet. In a preferred embodiment, the sheet exhibits a vacuum volume of at least about 5 g/g, a CD stretch of at least about 5 percent and an MD/CD stretch quotient of less than about 1.75.1 yet another preferred embodiment has the sheet an absorbency of at least about 5 g/g, a CD stretch of at least about 10 percent, and an MD/CD stretch quotient of less than about 2.5. A CD stretch of at least about 20 percent and a MD/CD stretch quotient of less than about 5 is believed to be achievable in accordance with the present invention.

As will be seen from the data which follows, a percentage CD stretch of at least about 3 or 3.5 times the dry stretch quotient is easily achieved in accordance with the present invention.

In general, a percentage CD stretch of at least about 4 and a dry stretch quotient of from about 0.4 to about 4 are typical for products according to the invention. Preferably, the products have a CD stretch of at least about 6.1 in some cases a CD stretch of at least about 10 is preferred.

The products according to the invention typically have a vacuum volume of at least about 5 or 6 g/g. Vacuum volumes of at least about 7 g/g, 9 g/g or 10 g/g are also typical.

The sheet according to the invention can mainly consist of (more than 50%) hardwood fiber or softwood fiber. The sheet typically comprises a mixture of these two fibers.

Further characteristics and advantages of the present invention will appear in the following detailed description.

Brief description of the drawings

The invention is described in detail below with reference to the Figures, in which:

Figure 1 is a photomicrograph (120X) in section along the machine direction of a fiber-enriched area of a cloth-stretched sheet; Figure 2 is a plot of MD/CD dry stretch quotient ratio versus jet/conduction velocity delta in feet per minute; Figure 3 is a photomicrograph (10X) of the fabric side of a fabric-wrapped web; Figure 4 is a schematic representation illustrating a paper machine that can be used to produce the products and carry out the process according to the present invention; Figures 5 and 6 are plots of CD stretch versus MD/CD stretch quotient for 13 pound (5.9 kg) sheets produced with various fabric and crepe ratios; Figures 7 through 9 are plots of CD stretch versus dry stretch quotient for various 10.9 kg (24 pound) sheets of the invention; and Figure 10 is a plot of thickness reduction versus calender load for various combinations of steel and rubber calender rolls.

Detailed description

Terminology used hereafter is given its ordinary meaning with example definitions set out immediately below.

The absorbency of the inventive products (SAT) is measured with a simple absorbency tester. The simple absorbency tester is a particularly useful device for measuring the water attraction and absorbency properties of a sample selection of paper, wipes or napkins. In this test, a sample of paper, tissue, or napkin 5.1 cm (2.0 inches) in diameter is measured between a flat top plastic cover and a grooved bottom sample plate. The paper, tissue, or napkin sample plate is held in place by a 0.32 cm (1/8 inch) wide circumferential edge area. The sample is not compressed by the holder. Deionized water at 23 °C (73 °F) is introduced to the sample in the center of the bottom sample plate through a 1 mm diameter channel. This water is at a hydrostatic peak of minus 5 mm. The flow is started by a pulse introduced at the start of the measurement by the instrument mechanism. The water is absorbed in this way by the paper, handkerchief or napkin sample from this central entry point radially outward by capillary action. When the amount of water absorption decreases below 0.005 gm of water per 5 seconds, the test ends. The amount of water removed from the container and absorbed by the sample is weighed and reported as grams of water per square meter of sample unless otherwise stated. In practice, an M/K Systems Inc. Gravimetric Absorbency Testing System is used. This is a commercial system available from M/K Systems Inc., 12 Garden Street, Danvers, Mass., 01923. The WAC or water absorption capacity also referred to as SAT is actually determined by the instrument itself. The WAC is defined as the point at which the weight-versus-time plot has a "zero" slope, that is, the sample has stopped absorbing. The termination criterion for a test is shown in the maximum change in water weight absorbed over a fixed period of time. This is basically an estimate of zero slope on the weight-versus-time graph. The program uses a change of 0.005 g over a 5 second time interval as the termination criterion; unless "Low Sat" is specified, in which case the cutoff criterion is 1 mg in 20 seconds.

Throughout this description and claims, when we refer to a starting web having an apparently random distribution of fiber orientation (or similar terminology), we are referring to the distribution of fiber orientation that results when known forming techniques are used to place a mass composition on the forming fabric. When examined microscopically, the fibers appear to be randomly oriented although, depending on the jet-to-wire speed, there can be a significant bias in relation to the machine direction orientation giving a machine direction tensile strength of the web that exceeds the transverse tensile strength.

Unless otherwise specified, "flat weight", BWT, bwt also further refers to the weight of a 278.7 m<2>(3000 ft<2>) rice of the product. Firmness refers to the percent solids of a start-up course, for example calculated on a completely dry basis. "Air dry" means extensive residual moisture, usually up to about 10 percent moisture for pulp and up to about 6% for paper. A starting track has 50 percent water and 50 percent dried wood pulp that has a firmness of 50 percent.

The terminology "cellulose", "cellulose sheet" and the like is intended to include all products with added paper-making fibers that have cellulose as a main component. "Papermaking fibre" includes new wood pulp or recycled (secondary) cellulose fibers or fiber mixtures comprising cellulose fibres. Fibers suitable for making the webs of this invention include: non-wood fibers, such as cotton fiber or cotton derivatives, abaca, bastard jute (kenaf), sabai grass, flax, esparto grass, straw, jute hemp, bagasse, "milkweed floss fiber" and pineapple leaf fiber; and wood fibers such as those obtained from deciduous trees and conifers, including softwood fibers, such as northern and southern softwood kraft fiber; hardwood fiber, such as eucalyptus, maple, birch, aspen, or similar. Papermaking fibers may be released from their source material by any of a number of chemical pulping processes well known to one skilled in the art including sulfate, sulfite, polysulfide, soda pulp, etc. The pulp may be bleached if desired by chemical means including the use of chlorine, chlorine dioxide, oxygen and so on. The products of the present invention may comprise a mixture of conventional fibers (either extracted from virgin wood pulp or recycled sources) and high roughness wood pulp-rich tubular fiber, such as bleached chemical thermomechanical wood pulp (BCTMP). "Pulp compositions" and similar terminology refer to aqueous compositions comprising papermaking fibers, wet strength resins, release agents, and the like for making paper products.

As used herein, the term compact dewatering of the web or pulp composition refers to mechanical dewatering by wet printing on a dewatering felt, for example in some embodiments using mechanical pressure applied continuously across the web surface at a pinch point between a press roller and a press shoe where the web is in contact with a papermaking felt. The terminology "compact dewatering" is used to refer to processes where the initial dewatering of the web is largely transported out in thermal terms, which is the case, for example, in US Patent No. 4,529,480 to Trolchan and US Patent No. 5,607,551 to Farrington et al as noted above. Compact dewatering of a web thus referred to, for example, removing water from a starting web having a firmness of less than 30 percent or similar upon application of pressure and/or increasing the firmness of the web by about 15 percent or more upon application of pressure.

"Cloth side" and similar terminology refers to the side of the web that is in contact with the creasing and drying cloth. "Wiper side" or similar is the side of the pitch opposite the canvas side of the pitch.

Fpm refers to 30 cm per minute (feet per minute) while firmness refers to the weight percentage of fiber in the web.

MD means the machine direction and CD means across the machine direction.

Pinch point parameters include, without limitation, pinch point pressure, pinch point length, back roll hardness, fabric approach angle, fabric departure angle, uniformity and velocity delta between the surfaces in the pinch point.

Clamping point length means the length where the clamping point surfaces are in contact with each other.

"Direct-coupled" and similar terminology refers to a process step performed without removing the web from the paper machine in which the web is produced. A web is drawn or calendered direct-coupled when it is drawn or calendered without being cut before winding.

A moving transfer surface refers to the surface from the web that is creped into the crepe fabric. The moving transfer surface may be the surface of a rotating drum as described hereinafter or it may be the surface of a continuous smooth moving belt or other moving cloths having a surface structure and the like. The moving transfer surface needs to support the web and facilitate the high solids creep as will be understood from what is set forth below.

Thickness and/or mass mentioned here can be 1, 4 or 8 sheet thicknesses. The sheets are stacked and thickness measurements are taken about the central part of the stack. Preferably, the test samples are treated in an atmosphere of 23° ± 1.0°C (73.4° ± 1.8°F) at 50% relative humidity for at least about 2 hours and then read with a Thwing-Albert Model 89-11-JR or Progage Electronic Thickness Tester with 50.8-mm (2-in.) diameter anvil, 539 ± 10 gram dead weight load, and 0.587 cm/sec (0.231 in./sec) descent rate. For final product testing, each sheet from the product being tested must have the same number of layers as when the product is sold. For testing in general, eight sheets are selected and stacked together. For napkin testing, the napkins are unfolded before stacking. For base sheet testing free from the winder, each sheet tested must have the same number of layers as produced by the winder. For base sheet testing of the paper machine spool, single layers must be used. The sheets are stacked one after the other in the MD. In the case of specially ordered patterned or embossed products, one should try to avoid taking measurements in these areas if possible. Mass can also be expressed in units of volume/weight by dividing thickness by surface weight.

Dry tensile strength (MD and CD), elongation, ratio of these, modulus of rupture, stress and strain are measured with a standard Instron testing device or other suitable elongation tensile quotient tests which can be designed in various ways, typically using 7.62 or 2.54 cm ( 3 or 1 inch) wide strips of paper or tissue, treated at 50% relative humidity and 23°C (73.4), with the tensile quotient test performed at a crosshead speed of 5.08 cm/min (2 in/min).

Strain quotient is simply the ratio between the values determined using the previously mentioned methods. The tensile quotient refers to the MD/CD dry tensile quotient unless otherwise stated. Unless otherwise specified, a strain quotient property is a dry sheet property. The tensile quotient strength is sometimes referred to simply as the tensile quotient. Unless otherwise stated, tensile quotient strength, elongation, and so on are described herein.

"Dock creep ratio" is an expression of the speed differential between the creped cloth and the forming wire and is typically calculated as the ratio of the web speed immediately before creeping to the web speed immediately before subsequent creeping, because the forming wire and the transfer surface are typically, but not necessarily, driven at the same speed:

Doll creep ratio = transfer cylinder speed + doll creep speed Doll creep can also be expressed as a percentage calculated as:

Line creep (sometimes referred to as total creep), coil creep and so on are similarly calculated as presented below.

PLI or pli means kiloforce per linear cm (pound force per linear inch).

Dominant means more than about 50%, typically by weight; completely dry basis when referring to fibre.

Pusey and Jones (P+J) hardness (indentation) is sometimes referred to as P+J, which is measured according to ASTM D 531 and refers to the number of indentations (normal specimen and ratio).

Velocity delta means a difference in linear velocity.

The vacuum volume and/or vacuum volume ratio as referred to hereafter is determined by saturating a sheet with a non-polar POROFIL<®> liquid and measuring the amount of liquid absorbed. The volume of absorbed liquid corresponds to the vacuum volume within the sheet structure. The percentage weight gain (PWI) is expressed as grams of fluid absorbed per grams of fiber in the sheet structure times 100, as described below. More specifically, for each single-ply sheet sample to be tested, select 8 sheets and cut out a 2.54 cm x 2.54 cm (1 inch x 1 inch) square (2.54 cm in the machine direction and 2.54 cm in the transverse machine direction). For multi-layer product samples, each layer is measured as a separate unit. A number of samples should be separated into individual single layers and 8 sheets from each layer position used in testing. Weigh and list the dry weight of each test specimen to the nearest 0.0001 gram. Place the specimen in a dish containing POROFIL<®->fluid having a specific gravity of 1.875 grams per cubic centimeter, available from Coulter Electronics Ltd., Northwell Drive, Luton, Beds, England (Part No. 9902458.) After 10 seconds , grasp the specimen at the outermost edge (1-2 millimeters in) of a corner with tweezers and remove it from the liquid. Hold the specimen with that corner at the top and allow the excess liquid to drip for 30 seconds. Give a light tap (less than<V>2 second contact) to the lower corner of the specimen on #4 filter paper (Whatman Lt, Maidstone, England) to remove any excess of the last partial drop. Weigh the specimen at once, within 10 seconds, record the weight to the nearest 0.0001 gram. PWI for each sample, expressed as grams of POROFIL<®>per grams of fiber, calculated as follows:

in which

"Wi" is the dry weight of the specimen in grams; and

"W2" is the wet weight of the specimen in grams.

The PWI for all eight individual specimens is determined as described above and the average of the eight specimens is the PWI for the sample.

The vacuum volume ratio is calculated by dividing the PWI by 1.9 (liquid density) to express the ratio as a percentage, while the vacuum volume (gms/gm) is simply the weight gain ratio; that is, PWI divided by 100.

In accordance with the present invention, an absorbent paper tap is made by dispersing papermaking fiber in an aqueous pulp composition (slurry) and inserting the aqueous pulp composition onto the forming wire of a papermaking machine, typically by means of a jet emanating from an inlet box. Any suitable forming system can be used. For example, a comprehensive but non-exhaustive list includes, in addition to Fourdrinier formers, a crescent former, a C-wrapped twin wire former, an S-wrapped twin wire former or a suction twig catcher profile roll. The forming fabric can be any suitable porous element including single layer fabrics, double layer fabrics, triple layer fabrics, photopolymer fabrics and the like. Non-exhaustive background technology in the area of forming cloths is included in US patent no. 4,157,276; 4,605,585; 4,161,195; 3,545,705; 3,549,742; 3,858,623; 4,041,989; 4,071,050; 4,112,982; 4,149,571; 4,182,381; 4,184,519; 4,314,589; 4,359,069; 4,376,455; 4,379,735; 4,453,573; 4,564,052; 4,592,395; 4,611,639; 4,640,741; 4,709,732; 4,759,391; 4,759,976; 4,942,077; 4,967,085; 4,998,568; 5,016,678; 5,054,525; 5,066,532; 5,098,519; 5,103,874; 5,114,777; 5,167,261; 5,199,261; 5,199,467; 5,211,815; 5,219,004; 5,245,025; 5,277,761; 5,328,565; and 5,379,808 are all hereby incorporated in their entirety by reference. A forming fabric particularly useful with the present invention is Voith Fabrics Forming Fabric 2164 made by Voith Fabrics Corporation, Shreveport, LA.

Foaming of the aqueous mass composition on a forming wire or cloth can be used as an opportunity to control the permeability or vacuum volume of the sheet on the cloth creasing. Foam forming techniques are described in US Patent No. 4,543,156 and Canadian Patent No. 2,053,505, the disclosures of which are hereby incorporated herein by reference. The foamed fiber pulp composition is made from an aqueous slurry of fiber mixed with a foamed liquid solution prior to its introduction into the inlet box. The wood pulp supplied to the system has a firmness in the range from about 0.5 to about 7 weight percent fiber, preferably in the range from about 2.5 to about 4.5 weight percent. The wood pulp is added to a foamed liquid comprising water, air and surfactant comprising 50 to 80 percent air by volume forming a foamed fiber pulp composition with a firmness in the range of from about 0.1 to about 3 percent fiber by weight in simple mixing from natural turbulence and mixing inherent in the process elements. The supply of the wood pulp as a low strength slurry results in an excess of foamed liquid recovered from the forming wire. The foamed surplus liquid is drained from the system and used elsewhere or treated for the recovery of surfactant from there.

The pulp composition may include chemical additives to change the physical properties of the paper produced. These chemicals are well known to those skilled in the art and can be used in any known combination. Such additives can be surface modifiers, plasticizers, debinding agents, strengthening agents, dispersions, opacifiers, optical brighteners, dyes, pigments, grading factors, barrier chemicals, staying aids, insolubilizers, organic or inorganic cross-linkers, or combinations thereof; said chemicals optionally comprising polyols, starch, PPG esters, PEG esters, phospholipids, surfactants, polyamines, HMCP or the like.

The wood pulp can be mixed with strength setting agents such as wet strength agents, dry strength agents and debonders/plasticizers and so on. Suitable wet strength agents are known to those skilled in the art. An extensive but non-exhaustive list of useful strength aids includes urea-formaldehyde resins, melamine-formaldehyde resins, glyoxylated polyacrylamide resins, polyamide-epichlorohydrin resins and the like. Thermosetting polyacrylamides are produced by reacting acrylamide with diallylethane ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which ultimately reacts with glyoxal to produce a cationic cross-linking wet strength resin, glyoxylated polyacrylamide. These materials are generally described in US Patent No. 3,556,932 to Coscia et al. and 3,556,933 belonging to Williams et al, both of which are hereby incorporated herein in their entirety. Resins of this type are commercially available under the trademark PAREZ 63 INC of Bayer Corporation. Various molar ratios of acrylamide V-DADMAC/glyoxal can be used to produce crosslinking resins useful as wet strength agents. Also, other dialdehydes can be substitutes for glyoxal to produce thermosetting wet strength properties. Of particular use are polyamide-epichlorohydrin wet strength resins, an example of which is commercially available under the trademarks Kymene 557LX and Kymene 557H of Hercules Incorporated of Wilmington, Delaware and Amres® of Georgia-Pacific Resins, Inc. These resins and processes for making resins are described in US Patent No. 3,700,623 and US Patent No. 3,772,076 which are hereby incorporated herein by reference in their entirety. A comprehensive description of polymeric pihalohydrin resins is provided in Chapter 2: Alkaline- Curine Polvmeric Amine- Epichlorohydrin of Espy in Wet Strand Resins and Their Application (L. Chan, Editor, 1994), herein incorporated by reference in its entirety. A reasonably comprehensive list of wet strength resins is described by Westfelt in Cellulose Chemistry and Technology Volume 13, p. 813, 1979, which is hereby incorporated herein by reference.

Suitable temporary wet strength agents can also be included. An extensive but non-exhaustive list of useful temporary wet strength agents includes aliphatic and aromatic aldehydes including glyoxal, malonic dialdehyde, succinic dialdehyde, glutaraldehyde and dialdehyde starch, in addition to substituted or reacted starches, disaccharides, polysaccharide, chitosan, or other reacted polymeric reaction products of monomers or polymers having aldehyde groups and optionally, nitrogen groups. Representative nitrogen containing polymers, which can suitably be reacted with aldehyde containing monomers or polymers, include vinylamides, acrylamides and related nitrogen containing polymers. These polymers transfer a positive charge to the aldehyde comprising the reaction product. In addition, other commercially available temporary wet strength agents, such as PAREZ 745 manufactured by Bayer, can be used in conjunction with those described, for example, in US Patent No. 4,605,702.

The temporary wet strength resins can be any of various water-soluble organic polymers comprising aldehydic units and cationic units used to increase the dry and wet tensile quotient strength of a paper product. Such resins are described in US Patent No. 4,675,394; 5,240,562; 5,138,002; 5,085,736; 4,981,557; 5,008,344; 4,603,176; 4,983,748; 4,866,151; 4,804,769 and 5,217,576. Modified starch sold under the trade names CO-BOND<®>1000 and CO-BOND<®>1000 Plus from National Starch and Chemical Company of Bridgewater, N.J. can be used. Prior to use, cationic aldehydic water soluble polymers can be prepared by preheating an aqueous wood pulp with approximately 5% solids retention at a temperature of approximately 115°C (240°F) and a pH of about 2.7 for approximately 3.5 minutes. Finally, the wood pulp may be cooled and dewatered by adding water to produce a mixture of approximately 1.0% solids at less than about 54°C (130°F).

Other temporary wet strength agents, also available from National Starch and Chemical Company are sold under the trade names CO-BOND<®>1600 and CO-BOND<®>2300. These starches are supplied as aqueous colloidal solutions and do not require preheating before use.

Temporary wet strength agents such as glyoxylated polyacrylamide can be used. Temporary wet strength agents such as glyoxylated polyacrylamide resins are produced by reacting acrylamide with diallyldimethylammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which ultimately reacts with glyoxal to produce a cationic cross-linking temporary or semi-permanent wet strength resin, glyoxylated polyacrylamide. These materials are generally described in US Patent No. 3,556,932 to Coscia et al. and US Patent No. 3,556,933 to Williams et al, both hereby incorporated herein by reference. Resins of this type are commercially available under the trade name PAREZ 63 INC from Bayer Industries. Various molar ratios of acrylamide/DADMAC/glyoxal can be used to produce crosslinking resins useful as wet strength agents. Also, other dialdehydes can be substitutes for glyoxal to produce wet strength characteristics.

Suitable dry strengthening agents include starch, guar gum, polyacrylamides, carboxymethyl cellulose and the like. Of particular use is carboxymethylcellulose, an example of which is sold under the trade name Hercules CMC from Hercules Incorporated of Wilmington, Delaware. According to one embodiment, the wood pulp may comprise from about 0 to about 6.8 kg (15 pounds)/ton of dry strength agent. According to another embodiment, the wood pulp may comprise from about 0.45 to about 2.27 kg (about 1 to about 5 pounds)/ton of dry strength agent.

Suitable staplers are also known to those skilled in the art. Debonders or softeners can also be incorporated into the wood mass or sprayed onto the track after its formation. The present invention can also be used with emollients including but not limited to the class of amidoamine salts derived from partially acid neutralized amines. Such material is presented in US patent no. 4,720,383. Evans, Chemistry and Industry, 5 July 1969, pp. 893-903; Egan, J. Am. Oil Chemisfs Soc . Vol. 55 (1978), pp. 118-121; and Trivedi et al, J. Am. Oil Chemisfs Soc, June 1981, pp. 754-756, hereby incorporated by reference in their entirety, states that plasticizers are often commercially available only as complex mixtures rather than simple compositions. While the following discussion will focus on the predominant types, it should be understood that commercially available mixtures will usually be used in practice.

Quasoft 202-JR is a suitable plasticizer, which can be recovered by alkylation of a condensed product of oleic acid and diethylenetriamine. Synthesis conditions use a deficit of alkylating agent (eg, diethyl sulfate) and only an alkylating step, followed by pH adjustment to protonate the non-ethylated species, resulting in a mixture consisting of cationic ethylated and cationic non-ethylated species . A minor proportion (eg, about 10%) of the resulting amidoamine cyclizes to imidazoline compounds. As only the imidazoline parts of these substances are quaternary ammonium mixtures, the compositions as a whole are pH-sensitive. Therefore, in the practice of the present invention with this class of chemicals, the pH of the inlet box should be approximately 6 to 8, preferably 6 to 7 and most preferably 6.5 to 7.

Quaternary ammonium compounds, such as dialkyldimethyl quaternary ammonium salts are also suitable, especially when the alkyl groups comprise from about 10 to 24 carbon atoms. These mixtures have the advantage of being relatively insensitive to pH.

Biodegradable plasticizers can be utilized. Representative biodegradable cationic plasticizers/detachers are described in US Patent Nos. 5,312,522; 5,415,737; 5,262,007; 5,264,082; and 5,223,096, all incorporated herein in their entirety by reference. The mixtures are biodegradable diesters of quaternary ammonia mixtures, quatemized amine esters, and biodegradable vegetable oil-based esters which are functional with quaternary ammonium chloride and diesterdierucyldimethylammonium chloride and are representatives of biodegradable plasticizers.

In some embodiments, a particularly preferred release composition comprises a quaternary amine component in addition to a nonionic surfactant.

The starter web is typically unwashed on a papermaking felt. Any suitable felt can be used. For example, felt can have double-ply base weave, triple-ply base weave, or laminated base weave. Preferred felts are those that have a laminated base weave design. A wet-press felt that may be particularly useful with the present invention is Vektor 3 made by Voith Fabric. Background art in the press felt area includes US Patent No. 5,657,797; 5,368,696; 4,973,512; 5,023,132; 5,225,269; 5,182,164; 5,372,876; and 5,618,612. A differential printing felt presented in US patent no. 4,533,437 belonging to Curran et al. can also be used.

All kinds of suitable crepe belts or cloths can be used. Suitable crepe fabrics include single-layer, multi-layer, or composite preferably open mesh structures. Cloths may have at least one of the following characteristics: (1) on the side of the crepe cloth in contact with the wet web (the "top" side), the number of machine direction (MD) strands per inch (mesh) is from 10 to 200, and the number of transverse machine direction (CD) strands per inch (count) is also from 10 to 200; (2) Strand diameter is typically less than 0.050 inch; (3) at the top, the distance between the highest point of the MD guide spindle and the highest point of the CD guide spindle is from about 0.001 to about 0.02 or 0.03 inches; (4) Between these two levels there may be a guide spindle formed either by MD or CD strands which give the topography of a three-dimensional hill/valley appearance which is communicated to the sheet during the wet forming step; (5) The cloth can be oriented in any way to achieve the desired effect during processing and for properties in the product; the long bias control spindle can be on the top side to increase MD grooves in the product, or the long die guide spindle can be on the top side if more CD grooves are desired to influence creasing characteristics as the web is transferred from the transfer cylinder to the creasing cloth ; and (6) the fabric can be made to display certain geometric patterns that please the eye, which are typically repeated between every two to 50 warp yarns. Suitable commercially available coarse cloths include a number of cloths made by Voith Fabrics.

Accordingly, the creped fabric may be one of the classes described in US Patent No. 5,607,551 to Farrington et al, Cols. 7-8 thereof, in addition to the fabrics described in US Patent No. 4,239,065 to Trokhan and US Patent No. 3,974,025 to Ayers. Such cloths can have about 20 to about 60 stitches per inch and is formed from monofilament polymer fiber having diameters typically ranging from about 0.008 to about 0.025 inch. Both warp and weft monofilament can, but do not necessarily have to be of the same diameter.

In some cases, the filaments are so woven and complementary serpentine configured at least in the Z direction (thickness of the fabric) to provide a first array or array of co-planar top-surface plane crossings of both sets of filaments; and a predetermined second grouping or series of subordinate-peak-surface intersections. The rows are spun so that portions of top-surface-plane intersections define a series of braid-basket-like voids in the top surface of the fabric where the voids are distributed in a zigzag relationship in both the machine direction (MD) and across the machine direction (CD ), and such that each cavity includes at least one sub-peak-surface intersection point. The cavities are discretely circumferentially closed in the plane by a pile-like lineament that includes portions of a plurality of top-surface plane junctions. The loop of cloth may comprise heat-set monofilaments of thermoplastic material; the top surfaces of the co-planar top-surface plane crossings may be mono-planar flat surfaces. Specific embodiments of the invention include satin weaving in addition to hybrid weaving of three or larger sheds, and mesh counts of from about 10 X 10 to about 120 X 120 filaments per inch (4X4 to about 47 X 47 per centimeter). Although the preferred range of mesh counts is from about 18 by 16 to about 55 by 48 filaments per inch (9X8 to about 22 X 19 per centimeter).

Instead of a printed cloth, a drying cloth can be used as a crepe cloth if desired. Suitable cloths are described in US Patent Nos. 5,449,026 (woven style) and 5,690,149 (stacked MD tape yarn style) to Lee as well as US Patent No. 4,490,925 to Smith (spiral style).

A crepe adhesive applied to the Yankee cylinder is preferably able to cooperate with the web at intermediate humidity to facilitate transfer from the crepe cloth to the Yankee and solidly secure the web to the Yankee cylinder while drying to a fastness of 95% or more on the cylinder, preferably with a high volume drying hood. Critical to stabilizing system operation at high production rates, the adhesive is a water absorbent, re-wettable, demonstrably non-crosslinking adhesive. Examples of preferred adhesives are those comprising poly(vinyl alcohol) of the general class described in US Patent No. 4,528,316 to Soerens et al. Other suitable adhesives are disclosed in pending United States Provisional Patent Application Serial No. 60/372,255, filed April 12, 2002, entitled "Improved Creping Adhesive Modifier and Process for Producing Paper Products" (Attorney Docket No. 2394). Appropriate adhesives are optionally provided with modifiers and so on. It is preferred to use crosslinks sparingly or not at all in the adhesive in many cases; so that the resin is substantially uncrosslinked in use.

The present invention is understood with reference to the Figures, particularly Figures 1 and 2. Figure 1 shows a cross-section (120X) along the MD of a cloth-stretched sheet 10 illustrating a fiber-enriched, stacked area 12. It is seen that the web has microfolds horizontally to the machine direction, i.e., the furrows or presses are extended in CD (into the photograph). It will be understood that fibers of the fiber-enriched area 12 are oriented unilaterally in CD, particularly on the right side of area 12, where the web is in contact with a guide spindle of the creped fabric. The speed delta of the jet/forming wire (spreading speed-wire speed) has an important influence on the stretch quotient as seen in Figure 2; an influence markedly different from that seen in conventional wet-pressed products.

Figure 2 is a plot of MD/CD tensile quotient (strength at break) versus the difference between inlet box spread rate and the formed wire speed (fpm). The upper U-shaped curve is typical of a conventional wet-pressed absorbent sheet. The lower, wider curve is typical of cloth-wrapped products of the invention. It is quickly understood from Figure 2 that MD/CD stretch quotient of less than 1.5 or so has been achieved in accordance with the invention over a large range of spreading velocity deltas, a range that is more than twice what a CWP curve shows. Consequently, control of the inlet box spreading forming wire speed can be used to achieve desired sheet properties.

It is also seen from Figure 2 that MD/CD ratio below square (ie below 1) is difficult; if not impossible to achieve with conventional processing. Moreover, square or sub-sheets are formed by means of the invention without much fiber addition or "flocks" which is not the case with CWP products with low MD/CD tensile quotients. This difference is partly due to the relatively low speed deltas required to achieve a low stretch quotient in CWP products and may be due to the fact that the fiber is redistributed on the crepe fabric when the web is creped from the transfer surface in accordance with the invention.

In many products, cross-machine properties are more important than MD properties, especially in commercial napkin manufacturing where CD wet strength is critical. A main source of product failure is "marker displacement" or the tearing off of just a piece of napkin rather than the actual sheet. In accordance with the invention, the CD relative stretch quotient can be selectively increased by controlling the inlet box to shape warp speed delta and fabric creep. Figure 3 is a photomicrograph (lOX) of the fabric side of a fabric-reinforced web. It is again seen in Figure 2 that sheet 10 has a plurality of very pronounced high basis weight, fiber-enriched areas 12 which have fibers oriented unilaterally in the transverse machine direction (CD) connected with relatively low basis weight connecting areas 14, which has fiber orientation one-sided in a direction between stacked or fiber-enriched areas.

Orientation bias is also seen in Figure 1, particularly where the CD-sided fiber of stacked fiber-enriched regions 12 has been cut during fabrication of the specimens at the midpoint of region 12. To the left of region 12, in the connecting region, it is seen that fiber is one-sided more along the machine direction between fiber-enriched areas. These characteristics are also quickly observed in Figure 3 at lower magnification, where fiber bias in areas 14 is extended between stacked areas.

Figure 4 is a schematic diagram of a paper machine 15 having a conventional twin wire forming section 17, a filer 19, a shoe press section 16, a crepe cloth 18 and a Yankee dryer 20 suitable for practicing the present invention. Forming section 12 comprises a pair of forming cloths 22, 24 supported by a plurality of rollers 26, 28, 30, 32, 34, 36 and a forming roller 38. An inlet box 40 delivers papermaking pulp composition in the form of a jet to a pinch point 42 between forming roll 38, roll 26 and the cloths. Control of the jet velocity relative to the forming webs is an important aspect of controlling the stretch quotient as understood by those skilled in the art. The mass composition forms a start-up web 44 which is dewatered on the cloths with the assistance of vacuum, for example, by means of vacuum box 46.

The starter web is advanced to a papermaking felt 48 which is supported by a plurality of rollers 50, 52, 54, 55 and the felt is in contact with a shoe press roller 56. The web is of low tenacity as it is transferred to the felt. Transfer can be assisted by vacuum; for example, roller 50 may be a vacuum roller if desired, or a collection or vacuum shoe as known in the art. As the web reaches the shoe press roll it has a firmness of 10-25 percent, preferably 20 to 25 percent or similar as it enters pinch point 58 between shoe press roll 56 and transfer roll 60. Transfer roll 60 may be a heated roll if desired. Instead of a shoe press roller, roller 56 may be a conventional suction pressure roller. If a shoe press is used, it is desirable and preferred that roller 54 is a vacuum roller which is effective in removing the water form felt before the felt enters the pinch point of the shoe press, since water from the pulp composition will be pressed into the felt in the pinch point of the shoe press. However, the use of a vacuum roll or STR of 54 is typically desirable to ensure that the web remains in contact with the felt during the change of direction as those skilled in the art will appreciate from the diagram.

Web 44 is wet pressed onto the felt at pinch point 58 with the assistance of press shoes 62. The web is therefore compactly dewatered at 58, typically by increasing firmness at 15 or more points at this stage of the process. The configuration shown at 58 is commonly referred to as a shoe press; in connection with the present invention, cylinder 60 is operative as a transfer cylinder which is operated to advance web 44 at high speed, typically 1000 fpm-6000 fpm to the crepe fabric.

Cylinder 60 has a smooth surface 64 which can be supplied with adhesive and/or release agents if necessary. Web 44 engages transfer surface 64 of cylinder 60 which rotates at a high angular velocity as the web continues to advance in the machine direction indicated by arrows 66. On the cylinder, web 44 has an apparently generally random distribution of fibers.

Direction 66 is referred to as the machine direction (MD) of the web in addition to that of paper machine 10; however, across the machine direction (CD) the direction in the plane of the web is normal to MD.

Web 44 enters pinch point 58 typically with a firmness of 10-25 percent or similar and is dewatered and dried to a firmness of from about 25 to about 70 by the time it is transferred to crepe fabric 18 as shown in the diagram.

Fabric 18 is supported by a plurality of rollers 68, 70, 72 and a press pinch roller or solid pressure roller 74 so that a fabric strap pinch point 76 is formed with transfer cylinder 60 as shown in the diagram.

The creped fabric defines a crepe pinch point over the distance where creped fabric 18 is adapted to be in contact with roll 60; significant pressure is added to the path towards the transfer cylinder. For this purpose, backing (or creping) rollers 70 can be provided with a soft deformable surface which increases the length of the creping pinch point, and increases the fabric creping angle between the fabric and the sheet and the contact point, or a shoe press roller can be used as the roller 70 to increase effective contact with the web in high-power cloth tape clamping point 76 where the web 44 is transferred to cloth 18 and advanced in the machine direction. By using different equipment on the crepe clamping point, it is possible to adjust the mannequin creasing angle or the removal angle from the crepe clamping point. Accordingly, it is possible to influence the nature and amount of fiber redistribution, delamination/de-bonding that may occur at dolly strap pinch point 76 by adjusting these pinch point parameters. In some embodiments it may be desirable to rearrange the inter-fiber characteristics in the z-direction while in other cases it may be desirable to affect properties only in the plane of the web. Crimp point parameters affect the distribution of fibers in the web in different directions, including inducing changes in the z-direction in addition to MD and CD. However, the transfer from the transfer cylinder to the crepe fabric is highly efficient in that the fabric moves slower than the web and a significant change in speed occurs. Typically, the web is crimped anywhere from 10-60 percent and even higher during transfer from the transfer cylinder to the fabric.

Crimp pinch point 76 is typically extended over a fabric crimp pinch point distance of anywhere from about 1/8" to about 2", typically 1/2" to 2". For a crepe cloth with 32 CD strands per inch, web 44 will accordingly hit anywhere from about 4 to 64 weft filaments at the pinch point.

The pinch point pressure in pinch point 76, that is, the load between support roller 70 and transfer roller 60 is suitably 20-100, preferably 40-70 pounds per linear inch (PLI).

After fabric creasing, the web continues its progress along MD 66 where it is wet-pressed onto Yankee cylinder 80 at transfer pinch point 82. Transfer at pinch point 82 occurs at a web strength of typically from about 25 to about 70 percent. At these strengths, it is difficult to attach the web to surface 84 of cylinder 80 firmly enough to thoroughly remove the web from the cloth. Typically, a poly(vinyl alcohol)/polyamide adhesive composition as noted above at 86 is applied as needed.

If desired, a vacuum box can be added at 67 to increase thickness. Typically, a vacuum of from about 5 to about 30 inches of mercury is used.

The web is dried on the Yankee cylinder 80 which is a heated cylinder and with high jet velocity droplet impact air in the Yankee hood 88. While the cylinder rotates, the web 44 is crimped from the cylinder by the creasing doctor 89 and wound up on the take-up roll 90. Creping of the paper from a Yankee dryer can be done by use a corrugated crepe sheet, such as disclosed in United States Patent No. 5,690,788, the disclosure of which is incorporated by reference. The use of a corrugated crepe sheet has been shown to bring several advantages when used in the production of napkin products. In general, napkin products are creped using a corrugated sheet that has a high thickness, increased CD stretch, and a higher void volume than equivalent napkin products produced using conventional crepe sheets. All of these changes brought about by the use of corrugated sheets tend to correlate with improved softness perception of the napkin products.

A calendering station 85 with rollers 85(a), 85(b) is optionally provided to calender the sheet if desired.

When a wet-creped process is used, a drop-impact air dryer, a through-air dryer, or a plurality of drum dryers may be used in place of a Yankee. Drip air dryers are set forth in the following patents and applications, Statement incorporated herein by reference:

US Patent No. 5,865,955 by Ilvespaaet et al.

US Patent No. 5,968,590 by Ahonen et al.

US Patent No. 6,001,421 to Ahonen et al.

US Patent No. 6,119,362 by Sundqvist et al.

United States Patent Application No. 09/733,172, entitled Wet Crepe, Impinge-ment-Air Dry Process for Making Absorbent Sheet, now US Patent No. 6,432,267.

A through-drying unit known in the art is described in US Patent No. 3,432,936 to Cole et al, as well as US Patent No. 5,851,353 which describes a tumble dryer system.

Representative Examples

Using an apparatus of the general class of Figure 4, absorbent sheets were prepared with different weights, crepe ratios, and so on. This fabric exhibits high CD stretch at low dry stretch quotient as seen particularly in Figures 5 to 9. As understood from the foregoing discussion and the following examples, the relative basis weight of the fiber enriched areas and connecting areas, degree of stacking, fiber orientation and geometry of the web controlled by an appropriate selection of fabric and webs, in addition to control of web creasing ratio, pinch point parameters and jet-to-wire velocity delta.

Data for representative products appears in Table 1 for base sheets and Table 2 for reverse sheets.

In connection with the following Tables and Examples, the following abbreviations are occasionally used:

BRT - Bath towel

CD, MD - Without further specification, refers to tensile strength

CD%, MD% - Stretch on breaks in the direction indicated

CMC - Carboxy methyl cellulose

CWP - Conventional Wet Press

FC - Doll Crepe or Doll Crepe Ratio

GM, GMT - Geometric Mean, typical strain quotient Mod - Modulus

Ratio - Dry tensile quotient, MD/CD

SPR - Solid pressure roll, roll 74 seen in Figure 4

STR - Suction return roller, roller 54 as seen in Figure 4

T - Tons

TAD - Air dried

'819 - Referred to embossed pattern of USP 6,827,819

Paper products

Paper products (non-permanent wet strength grades where softness is the key parameter) made with the high solids cloth creasing process described herein can use many of the

same process parameters used to make napkin products (permanent wet strength grades where absorbency is important, strength in use is critical, and softness is less important than in paper grades.) In both categories, 1-ply and 2-ply products can be made .

Fibre: Soft paper products are optimally produced using large amounts of hardwood fibre. These fibers are not as coarse as the longer and stronger softwood fibers. Further, these

finer, shorter fibers show much higher counts per grams of fiber. On the negative10 side, these hardwood pulps usually contain more fine particles that are a result of the wood structures that the pulp has created. Removal of these small particles can increase the number of fibers present in the final paper sheet. Also, removal of these small particles reduces adhesive anchoring potential during the drying process, making it easier to

do not attach the sheet either with chemicals or with sheet crimping on the dry end of the pa-ice pir machine. The key advantage gained from high fiber counts per gram of wood pulp is opaque sheet or lack of transparency. Since a large part of a sheet of paper's execution

judged visually even before the sheet is touched, this optical property is an important contributor to the perception of quality. Softwood fibers are usually needed to provide a mesh-like structure on which hardwood fibers can be arranged to optimize softness and optical properties. But even in the case of softwood, fiber roughness and fiber per gram important properties. Long, thin and flexible softwood fibers such as northern softwood present many more fibers per grams than long, coarse, thick and stiff southern conifers. The net result of fiber selection is that with this technology, like all others, northern softwood and

low particles, low roughness hardwoods such as eucalyptus make softer sheets at a given stroke-25 quotient than northern hardwoods do and more like southern hardwoods.

Chemicals: Paper sheets have typically used various chemicals to help meet consumer demand for performance and softness. Generally, it is preferred to add a dry strength chemical to the long fiber portion of the wood pulp mixture, rather than

to use a refining rolling mill to develop draw quotient. Refining develops small particles and tends to create more tapes with high bond strength because refining makes the fibers more flexible, increasing the potential for fiber-fiber contacts during drying. On the other hand, dry strength additives increase the strengths of the available tape without increasing the number of tapes. Such a sheet ends up being according to the case

nature more flexible even before the doll cradling step of the doll cradling process. Addition of a

A non-adhesive chemical to the hardwood portion is desirable so that these hardwood fibers have a lower tendency of adhesive anchoring to each other, but retain the ability to be adhesively anchored to the network of softwood fibers which is mainly responsible for the working tensile strength of the paper. In some cases, a preliminary wet-strength agent may also be added along with softwood and hardwood fibers to improve perceived wet-strength performance without sacrificing flushability or septic tank safety.

Doll creasing: This process step is mainly responsible for the unique and desirable property of a sheet of paper. Increasing fabric creasing increases thickness and decreases stretch quotient. Furthermore, fabric creasing changes the stretch quotient measured in the base sheets allowing sheets with equal MD/CD stretch quotient or sheets with lower MD than CD stretch quotient. However, it is desirable for paper sheets to show the same stretch quotient in the two directions as most products that have been used in a manner independent of sheet direction. For example, "penetration" in a toilet paper is affected by this stretch ratio either together with the fact that the cloth creasing develops higher CD stretch, especially at lower MD/CD ratios than conventional technology. With other technologies, materials of equal tensile quotients are difficult to run through high-speed processing equipment due to the propensity for tears initiated at one edge to propagate to the other side of the sheet causing a break. In contrast to conventional products, cloth-reinforced sheets of equal stretch quotient made using the inventive process will retain the tendency to tear along the MD direction, thereby producing a tendency to self-heal in the event that an edge tear occurs and begins to propagate into the sheet . This unexpected and unique property, together with the resistance of the stretch placed in the sheet at this stage to being pulled out, allows efficient high speed operation at stretch ratios of one or less. Furthermore, these same properties lead to clean tears on perforations in the final products. Levels of cloth tape for paper products range from about 30 percent up to about 60 percent. While more is possible, this range allows for a variety of quality levels without changing the productivity of the paper machine.

Tablecloths: The design of the tablecloths is a prominent aspect of the process. But the parameters of the cloth are beyond the size and depth of the dimples woven into it. Their shape and location are also very important. Diameters of strands that make up the woven cloth are also important. For example, the size of the guide spindle that stands on the leading edge of the recess into the sheet to be crimped determines the parameters of fabric crimping ratio and basis weight of which holes appear in the sheet. The challenge, especially for paper grades, is to make these indentations as deep as possible with the finest possible rod diameter, thereby allowing larger fabric doily creasing ratios that lead to higher sheet thickness at a given ratio. Obviously, canvas design must change based on the weight of the sheet being produced. For example, a very high quality, premium, 2 ply bathroom paper exhibits high strength, thickness and softness, and can be made on a 44M designer cloth. 44G can also be used to make a heavier (up to 2x) weight single layer sheet with very good results. Another feature of the canvas design is to emboss a pattern into the sheet. Some canvas designs can impress a very noticeable pattern, while others produce a pattern that seems to disappear into the background. Many times consumers will want to see an embossed pattern on the sheet while converting and in these examples a smaller sheet pattern may be more desirable. Some grades can be made without embossing so that more distinct pattern embossing at the cloth creasing step will help to emboss a "premium" look to the sheet. Consumers will see low-quality, plain sheets and lower-priced products.

Creping: Since in a typical fabric creping process of the invention the sheet is transferred to a Yankee dryer for final drying, the sheet can (and usually is) creped by this dryer to further enhance softness. Paper products benefit greatly from this creping step which adds thickness and softness to the sheet. A particularly smooth surface is created on the Yankee side of the sheet. Furthermore, since the ratio of bobbin crease and fabric crease can vary independently of the production rate (coil speed), there is a significant area for changing the properties of the final sheet. Increasing the bobbin crepe/cloth crepe ratio decreases the two-sidedness of the paper, since less cloth crepe will be placed in for a level of MD stretch. There are less prominent "eyebrow" structures in the paper that can affect the two-sidedness. Further,

increasing the ratio also increases opacity and the perception of thickness at the same measured thickness. It is often desirable to maintain a reasonable ratio (say 25 to 50 per cent spool crepe/cloth crepe) to streamline consumer perceptions of these "intangible" properties associated with the visual appearance of the sheet.

Calendering: By all means, more calendering is better as long as a reasonable level of thickness is maintained in the sheet for subsequent conversion. Too little thickness requires too much

embossing which then degrades the overall quality. Therefore, a strategy for producing quality toilet paper is to use the coarse cloth without making holes in the sheet, reduce the cloth crepe level so that more of the MD stretch comes from the coil crepe portion and still obtain sufficient thickness before calendering so that at least about 20-40% of this thickness can be removed during the calendering step. These calibration levels tend to reduce the two-sidedness of sheets. Alternatively, a quality sheet can be made with a finer fabric with a lower bobbin crepe/fabric crepe ratio. Since the finer fabric produces more smaller domes, more fabric creasing can be used to achieve the desired thickness without undue increase in duplex. In most cases, reduced bilaterality is achieved. In this scenario, the bobbin crease/cloth crease ratio can be as low as around 5-10%. Calendering can then be maximized to achieve the desired softness. This procedure is desirable when relative

strong fibers are used while fabric creasing dramatically reduces tensile strengths and when the design of the fabric produces less than average duplexity in the sheet.

Napkin products

Napkin products behave in a way similar to paper sheets to different process parameters. However, in many cases napkin products utilize the same parameters but in an opposite direction with some in the same direction. For example, both product forms want thickness as thickness relates directly to softness in napkin products and absorbency in paper products. In the following parameters, only the differences from napkin situations will be presented.

Fiber: Paper requires functional strength in use, which usually means when wet. To reach this required stretch quotient, long softwood fibers are used in proportions roughly opposite to those of napkin products. Ratios of 70 to 90 percent softwood fiber are common. Refining can be used, but tends to close up the sheet so much that the subsequent cloth creasing cannot "open" the structure. This results in slower absorption rates and lowers capacity. Unlike napkin products, small particles can be used in paper sheets if not too much hardwood is used, as this in turn tends to close the sheet, and also reduce its stretch quotient capacity.

Chemicals: Surprisingly, staplers can also be used in paper! But their use must be done judiciously. Likewise, refining the fibers must be regulated to lower levels to keep the sheet open and quickly absorbent. Therefore, chemical strengthening agents are added routinely. Of course, wet strength chemicals must be added to prevent shredding in use. However, to achieve high wet tensile quotient levels, the ratio of wet to dry tensile quotient must be maximized. If stretch quotient levels become too high, the paper sheet will be too "paper-like" and will be judged as low quality by consumers. Therefore, wet strength agents and CMC are added to increase the CD wet/dry ratio from the typical 25% up to the desired 30-35% range. So to produce a softer sheet and therefore a sheet perceived by consumers as more premium sheet, de-staplers can be added which preferentially reduce the CD dry tensile quotient above the wet value. De-stitchers and softeners can also be sprayed onto the sheet after it has dried to further improve the feel.

Doll making; Increasing the fabric strength directly increases the absorbency. Therefore, it is desirable to maximize the fabric creasing. However, FC also reduces the stretch quotient so there is balance that must be maintained. Paper sheets may not sometimes exhibit high levels of MD stretch due to the type of holder used. In these cases, FC must also be limited. Therefore, paper requires a rougher cloth design on average than napkins do. Furthermore, as these wet sheets will typically exhibit significant wet strength, they may be more difficult to shape to the same firmness as a napkin sheet.

Cloths: Coarse cloths are desirable for paper in general. Two-ply paper sheets are typically made on a 44G or 36G canvas or coarser with good results, although good results can be achieved with finer canvases, especially if the crepe ratio of the canvas is increased. Single-ply sheets often require a smoother, coarser cloth along with other technology to make and accept the sheet. The longer fibers in the sheets and the high strength allow the use of these cloths, and higher FC ratios before holes occur in the sheets.

Creping: Very little creasing is done on paper sheets. Creping increases thickness but does so in a way similar to CWP sheets. This thickness disappears when wet, and the sheet expands. Thickness from cloth creasing acts like a dry sponge when wet. The sheet expands in the Z direction and shrinks in the MD & CD directions. This behavior adds mass to the perceived absorbency of the papers and makes them appear similar to TAD papers. In many cases, the use of serrated blades of Taurus technology in connection with the cloth creasing process will improve the absorbency, thickness and softness of the paper sheet. CD stiffness is reduced while CD stretch increases. The high thickness produced on the sheet allows more calendering and hence smoother sheets. In some cases it is desirable to pull the sheet off the Yankee drying surface without creasing. This may be the case for laundry room hand paper where softness is less important than getting more sheets on a roll. See US Patent No. 6,187,137 to Druecke et at.

Calendering: Paper sheets benefit from calendering for two key reasons. First, calendering softens the sheets and improves the tactile feel. Second, it "crashes" the domes produced by the sheets adding more Z-direction depth to the feel of the sheet and often improving absorbent properties at a given thickness.

Summary of data for Serviett

Several paper machine process tools and embossing patterns are used to produce 1-ply retail and commercial bath tissue. Process variables include: fabric crepe percentage, bobbin crepe percentage, softening additive level, softening type, softening location, fiber type, HW/SW ratio, calendering load, rubber and steel calendering, crepe fabric style, MD/CD ratio and Yankee coating chemistry. Embossing patterns include: '819, M3, Double Hearts, Butterflies and Swirls, Butterflies and Swirls with Micro, and Mosaic Iris. The best commercial 1 ply bathroom napkin (BRT) prototype comprises 40% Nordlig HW and 60% recycled fiber, at 20 lb basis weight and 450 GMT, a 17.5 sensory softness was achieved. The best retail 1-layer BRT prototype comprises 80% Southern HW and 20% Southern SW, at 20.5 lb basis weight and 450 GMT, a 16.9 sensory softness was achieved.

The objects included determining: the process need to manufacture 1-ply retail napkin with a sensory softness of 17.0 using southern hardwood (HW) and softwood (SW); the process requirements that produce 1-ply commercial tissue with a sensory softness of 17.0 using HW and recycled fiber, and the effects of fiber and other process variables on sensory softness and physical properties.

The commercial 1-ply BRT sensory softness score of 17.0 was achieved at 20 lb basis weight. Consumer testing will determine the impact of reduced basis weight on consumer acceptance of the product.

Using Southern HW and SW to make 1-ply retail tissue at 21.4 lb/3,000 sq.ft., the highest sensory softness achieved at 450 GMT was 16.9.

Using Southern HW and SW to make 1 ply retail napkin at 20.5 lb/3000 sq. ft. ft., the highest sensory softness achieved at 450 GMT was 16.9.

Using 40% HW and 60% recycled fiber (FRF) to make 1-ply commercial napkin at 20.2 lb/3000 sq. ft., the highest sensory softness achieved at 450 GMT was 17.5. For all work reported here, the average sensory softness was 16.9. Using 100% FRF to make 1-ply commercial napkin PS at 22.1 lb/3000 sq. ft., the highest sensory softness achieved at 450 GMT was 16.4.

Using Aracruz HW and Maraton SW to make 1 ply retail napkin at 19.8 lb/3000 sq. ft. ft., the highest sensory softness achieved at 450 GMT was 18.3. For all work reported here, the average sensory softness was 18.0.

Steel/steel calendering results in a higher thickness reduction on the equivalent load and higher sensory softness than rubber/steel calendering.

Increasing calender load appears to increase sensory softness, but calendering higher than 65 PLI decreases softness using virgin HW and recycled fiber. For HW and SW, 80 PLI may be the upper limit.

At constant line creep percentage, an increase in fabric creep percentage results in an increase in CD stretch and a decrease in CD modulus of rupture. However, final product sensory softness was not affected at constant GMT.

At a constant line crease percentage, varying the amount of fabric crease percentage versus spool crease percentage did not affect the sensory softness.

The types of crepe fabrics used in this study affected base sheet thickness but did not significantly affect sensory softness. Coarse mesh fabrics developed higher base sheet thicknesses and permitted higher calendering levels.

1-layer BRT with a 1.0 MD/CD stretch quotient (MD stretch quotient equal to CD stretch quotient) was similar in sensory softness to 1-layer BRT with a traditional MD/CD ratio of 1.8 (high MD stretch quotient). In this case, softness was dependent on GMT, not CD strength or CD modulus.

Mass composition effect

The fiber mixtures in Tables 3 and 4 were run at the same process conditions and 1-layer BRT was produced. Sensory softness was measured and adjusted to 450 GMT using the strength - softness values from data in the Appendix with the formula: (Sensory softness) + ((450 - GMT)<*>(-0.0035)). Eucalyptus and Maraton SW pulp composition led to significantly higher softness than the others. The Southern HW and SW pulp composition is currently used for detail 2-ply napkin. It is the mass composition that was currently used in the development of 1-layer BRT prototypes at PM#2. Replacing the Southern SW with Marathon SW slightly improved softness (first table). Dated, 16.9, the best sensitivity was achieved at 450 GMT (second table). The average for all work includes only Southern fibre, which is 16.4. Achieving the 17.0 sensitivity target at 450 GMT represents a significant technical challenge. The dollop process of the invention produces a very low modulus sheet that is acceptable for detail or commercial BRT. However, because the sheet is attached to the Yankee with a cloth, there is less contact area on the dryer. During the Yankee creping process, less softening of the sheet surface occurs compared to conventional addition to the Yankee with a felt. This results in a flannel-like feel compared to the silky feel of conventional crepe. The air side of the sheet, as in conventional wet-press creping, is less smooth than the dry side. In a 1-layer product, the air side contributes to total softness, as it cannot be hidden to the inside as in a 2-layer product. This combination leads to a lower sensitivity rating. The current approach to improving softness is to build thickness with a relatively coarse crepe fabric, adding a softening agent and calendering with "high" loads to smooth the sheet and reduce duplex. Napkin (commercial) pulp composition, for 1-ply BRT, is 40% Nordlig HW and 60% recycled fiber. In the table below, FRF is Fox river recycled wet-board. FRF is a high clarity recycled fiber. With only a few data points, 17.5 sensory softness is the best so far. The average, so far, is 16.9. Here, the 17.0 softness target will be less of a challenge. All data in the tables below are for a mixed base sheet. HW and SW will usually be made in separate wooden masses and run from different chests. Fiber is usually mixed on the fan pumps to create a homogeneous mixture of fiber.

Rubber/ steel Calendering

To reduce double-sidedness of 1-layer BRT, a rubber roll and a conventional steel calender roll are compared with a conventional steel/steel calender ring. The rubber roller is placed against the drying side of the sheet. Tables 5-7 below show the effect of calender load on base sheet thickness using rubber rolls of different hardness. Both rubber rolls gave similar levels of thickness reduction for equivalent calender loads. The steel/steel rolls gave a significantly higher thickness reduction at the same load as seen in the diagram below. The 56 P + J roll, which is harder than the (nominal) 80 P + J roll, should have had more thickness loss at a corresponding load. The (nominal) 80 P + J roll has been used previously and its current measured P + J value was 70. Its cover thickness was 5/8 inch combined compared to 1 inch for the 56 P + J roll. The calculated pinch point width for a 70 P + J roll with a 5/8-inch cover thickness is slightly less than for the 56 P + J roll with a 1-inch cover. This explains the high thickness reduction seen with the "80 P + J" roll. While the calendering load is increased, the two-sidedness was significantly reduced for all types of calender rolls. However, the sheets calendered with rubber/steel rollers did not feel as soft as the steel/steel calendered base sheets. Figure 9 shows that for a given GMT, sensory softness is about 0.4 softness units higher for steel/steel calendered sheet.

Several base sheets were calendered on different loads using the steel/steel rolls. The Ka-landing station is located before the spool of the paper machine. These base sheets were then embossed during conversion into 1-layer BRT. The diagram below shows that there is little effect due to calendering load on sensory softness for sheets that contained premium fibre, i.e. eucalyptus HW and Marathon SW. For the sheets comprising Nordlig HW and Fox River Secondary Fiber, softness improved at 65 PLI calender load, but decreased as calender load increased to 80 PLI. The South sheet increased slightly in softness as the calender load increased. Variable process conditions and different embossing patterns make it difficult to quantify the calendering effect on softness. However, it appears that a calender improves softness, but over-calendering degrades softness.

Comparison of spray softeners

Hercules Dl 152, TQ456 and TQ236 were compared when spray plasticizers were added to the air side of the sheet. The table below shows the results. When adjusted for GMT, there was no difference in softness between softeners. Hercules M-5118 was also tried as a spray softener. This material is a polypropylene glycol ether, as is known in the field. However, when sprayed on the air side of the sheet at 2 lb/T, while the sheet was on the 4-foot dryer (transfer cylinder, Figure 3), the sheet would not adhere to the crepe fabric. When the sprayer was placed on the drying side of the sheet, either on the felt before the suction reverses the roll

(STR) or on the crepe fabric before the solid pressure roll (SPR), the sheet would not stick to the 4-foot dryer or the Yankee dryer, respectively. The other plasticizers did not cause coalescence problems and did not adversely affect Yankee coatings at 2 lb/T. However, at 4 lb/T and higher, all led to unstable Yankee coatings. Results appear in Table 8.

Comparison of wet-end- mvkgj ears

The wet-end addition of plasticizers to the thick stock (typically HW) at levels up to 16 lb/T was possible without creating Yankee coating instability. The table below shows a comparison of Hercules TQ236, TQ456, Dl 152 and Clearwater CS359. All were made under similar process conditions. Steel/steel calender rolls were loaded with 50 PLI. The '819 embossed pattern was used for conversion. At similar addition rates and GMT, all plasticizers performed similarly. In the case where refining increased to compensate for the increase in softeners, which act as a debonder, no softness improvement was seen. In this case, only the Southern SW was refined and mykgj ears were only added to the Southern HW. This was a test of the "few but strong ties" theory. By refining only SW for strength, a greater amount of softening agents can then be added to HW to theoretically improve softness. Refining only SW (20% of the sheet) did not lead to a softer sheet. Although unconfirmed by the Sensory Panel, Dl 152 was chosen as the softener of choice based mainly on subjective evaluation of softness. Results are summarized in Table 9.

Emboss pattern Effect

Different embossing patterns were used to determine if a particular pattern interacted with the fabric-stretched base sheet to produce high softness. Previous studies have shown that most embossed patterns do not improve base sheet softness apart from strength gradation. In most cases, process conditions were similar but not constant for the comparisons that follow. However, they were similar enough to determine whether a significant softness improvement had occurred. The tables below show that no significant improvement in softness can be attributed to any of the patterns tested. "Double Hearts," "819" (US Patent No. 6,827,819) and "Butterflies and Swirls" patterns appear to provide similar sensual softness. See Tables 10-13 below. Directional "Mosaic Iris" pattern gave higher sensory softness values than "Butterflies and Swirls with Micro" pattern. Based on this limited data, the "Butterflies and Swirls with Micro" pattern is not recommended for fabric-wrapped base sheets. "M3" and "Mosaic Iris" embossed patterns gave similar softness values, and should be considered equal, to those in Table 10 for constant mass composition and GMT.

Puppet Krepp Versus Coil Krepp

Base sheets were produced with constant line crepe, but with a large variety of cloth crepe

percent. Line creep or total creep is calculated by dividing transfer cylinder speed (also appx forming speed) by coil speed. 1 is then subtracted from this value. The resulting value is multiplied by 100 and expressed as a percentage. For warping, transfer cylinder speed is divided by Yankee speed, because this is also warping speed, then 1 is subtracted and multiplied by 100. For spool warping, Yankee speed is divided by spool speed and 1 is subtracted to then multiplied by 100. Usually the transfer cylinder speed and spool speed are held constant and the Yankee speed is varied to create different cloth/spool

cancer relationship. Base sheet data shows that the highest MD stretch occurred at the highest coil crease. The lowest geometric mean (GM) modulus of rupture and the highest CD elongation occurred at the highest fabric creep. None of the sheets showed any signs of driving problems. Besides Yankee speed, other process variables were held constant with the exception of Yankee coating addition, which increased for Example 56.1 terms of physical properties, the sheets were remarkably similar for the extreme range of fabric/coil crepe ratios used. Results are summarized in Table 14. For these samples, the transfer cylinder was a 4-foot diameter dryer.

All sheets were turned into finished 1-ply BRT rolls that either use no embossing pattern or a pattern as described in United States Patent No. 6,827,819. Physical data as seen in Tables 15 and 16 below was very similar to base sheet data from above. The sheets with all fabric crepe and no coil crepe (Ex. 57) had significantly higher CD elongation and lower CD modulus of rupture. GM module was indicatively lower. However, sensory softness data indicates no softness benefit for either sheet.

Crepe effect

Different crepe fabric designs were used to fabricate base sheets to convert into 1-ply BRT. Table 17 below shows base sheet data under similar process conditions. In crepe fabric type series, MD and CD filament counts are shown as 42X31, for example. MD count appears first. MD or CD refers to the longest guide spindle on the side of the fabric towards the sheet. M, G and B refer to weave styles. The highest uncalendered thickness was achieved with 56X25 mesh cloths. This is allowed for higher levels of calendering while achieving target roll diameter and firmness in converted products. Higher levels of calendering should reduce the two build-up and may improve softness.

When converted using '819 pattern, 56X25G sheet, on 80 PLI calendering, it had higher directional sensitivity.

MD/ CD Stretch quotient effect

Dukkrepp process has had the ability to easily control MD/CD stretch quotient over a much larger range than conventional wet presses and TAD processes. Ratios from 4.0 to 0.4 have been produced without pushing the process to its limits. Traditionally, napkin products have required MD stretch quotient to be higher than CD stretch quotient to maximize formation. For maximum softness, the CD stretch quotient was kept as low as possible. This increases the risk of failure in use by consumers. If CD stretch quotient is increased and MD stretch quotient is decreased, GMT remains constant. Therefore, at equivalent total strength there may be less chance of failure. The table below shows 1-layer terminated BRT data for two separate samples in which the MD/CD tensile quotients varied. A comparison of examples 90, 89, 107 and 108 is presented in Table 18 below. Reducing the MD/CD ratio increased both CD and GM modulus. However, sensory smoothness was not significantly affected when GMT was accounted for. CD Stretch increased by about 100 grams/3 inches. This should greatly reduce the risk of failure in use. The natural elongation of base sheets can prevent breakage due to low strength. For high speed commercial operation, perf blade type may need to change to accommodate low strength and high stretch.

Southern HW Level

The effect of Southern HW level on sensory softness has been shown in Table 19 below. No softness improvement at 75% HW was observed. In both cases, softness was well below the target of 17.0. 80 P + J rubber/steel calendering rolls were used.

Doll strap Against Syringe Soft ears

Process variables were manipulated to determine which, if anything, would result in an end product with a sensory softness of 17.0 using Southern HW and SW. One such comparison was between base sheets without sprayed plasticizers that use high fabric creep to control strength, and low fabric creep that uses spray softener to control strength. Table 20 shows that softness was similar when adjusted for GMT. In both cases, softness was well below the target of 17.0. 80 P + J rubber/steel calendering rolls were used.

Forming Box Vacuum

The forming box was placed on the crepe fabric, between the crepe roll and the solid pressure roll. Sheet solids were usually between 38 and 44% at this time. The effect of vacuum on sheet thickness can be seen in the table. An increase of almost 8 mils of "8-sheet thickness" was observed with 21 inches of mercury vacuum on the forming box. This is around a 14% increase. Both rolls were calendered at 50 PLI with steel/steel rolls. The amount of thickness development is dependent on the coarseness of the cloth fabric and the amount of applied vacuum. Other sheet properties were not significantly affected. Drying was affected by the use of the forming box. Without a significant change in the Yankee hood temperature, sheet moisture after the Yankee increased from 2.66 to 3.65%.

Vacuum pulls the sheet deeper into the crepe fabric, therefore there is less contact with the Yankee and more drying is required to maintain sheet moisture. See Table 21.1 in this case the Yankee hood temperatures were not adjusted.

Effect of sheet moisture in fabric creep, on base sheet properties

By manipulating process variables, the sheet moisture entering the cloth creasing portion of the process can be varied. On the paper machine used, pulp composition with a 120 mm shoe press and 22 lb sheet, solids can vary from about 34 to 46%. For the low solids ratio, STR vacuum was reduced, shoe press load was reduced and 4-foot dryer steam was reduced. To dry this sheet to about 2% moisture on the coil, Yankee steam and hood temperature had to be increased. The low dryness base sheet was about 270 grams/3 in. lower in GMT than the high solids sheet. See the table below. This was mainly due to the lower compression that takes place on the lower shoe press loading. The dolly strapping step rearranged the fiber to a high degree, but apparently was not capable of complete rearrangement of all the compression of pressing. Other physical characteristics, including SAT capacity, were not significantly different when the difference in strength was taken into account. This experiment should be repeated at constant pressure using only vacuum and steam to change the dryness of the sheet. However, based on this experiment, the effect of sheet dryness on base sheet properties in the range studied here is not expected to be significant. The drying impact is significant and it pays to expand the area of dryness samples. Results are summarized in Table 22 below.

Claims (14)

1. Cellulosic fiber absorbent sheet comprising a mixture of hardwood fiber and softwood fiber arranged in a network having: (i) a plurality of stacked fiber-enriched regions of relatively high specific area density, wherein the stacked fiber-enriched regions have a one-sided fiber orientation in the cross-machine direction (CD ) of the sheet, and is interconnected by means of (ii) a plurality of lower specific area weight interconnecting areas whose fiber orientation is one-sided along the machine direction (MD) between stacked fiber-enriched areas interconnected thereby, wherein the sheet exhibits a percentage cross-machine direction (CD) stretch that is at least about 2.75 times the dry stretch quotient of the sheet. 2. The cellulose absorbent sheet of claim 1, which exhibits a vacuum volume of at least about 5 g/g, a CD stretch of at least about 5 percent, and a machine direction to cross-machine direction (MD/CD) stretch quotient of less than about 1.75. 3. The cellulose absorbent sheet of claim 1, which exhibits a vacuum volume of at least about 5 g/g, a CD stretch of at least about 10 percent, and a machine direction to cross-machine direction (MD/CD) stretch quotient of less than one around 2.5. 4. The cellulose absorbent sheet of claim 1, which exhibits a vacuum volume of at least about 5 g/g, a CD stretch of at least about 20 percent, and a machine direction to cross machine direction (MD/CD) stretch quotient of less than one around 5. 5. Absorbent cellulose sheet according to claim 1, which shows a percent CD stretch which is at least about 3 times the dry stretch quotient of the sheet. 6. Absorbent cellulosic sheet according to claim 1, which exhibits a percent CD stretch which is at least about 3.5 times the dry stretch quotient of the sheet. 7. Absorbent cellulose sheet according to claim 1, wherein the sheet exhibits a percent CD stretch of at least about 4 and a dry stretch quotient of from about 0.4 to about 4. 8. Absorbent cellulose sheet according to claim 7, wherein the sheet shows a percent CD stretch of at least about 6. 9. Absorbent cellulose sheet according to claim 7, wherein the sheet shows a percent CD stretch of at least about 10. 10. Absorbent sheet according to claim 1, with a vacuum volume of at least 7 g/g. 11. Absorbent sheet according to claim 1, with a vacuum volume of at least 9 g/g. 12. Absorbent sheet according to claim 1, with a vacuum volume of at least 10 g/g. 13. Absorbent sheet according to claim 1, which consists mainly of hardwood fiber. 14. Absorbent sheet according to claim 1, which consists mainly of softwood fiber.