FR2715049A1 - Tissue prod. e.g. bath tissue, premium household towel, facial tissue - Google Patents

Abstract

A soft tissue prod has at least one tissue ply. In one aspect the prod. has a Bulk of at least 9 cc/g; alternatively the plies are non-creped through dried tissue plies. In both aspects the prod has a MD max slope of no more than 10. Also claimed is a soft tissue prod with at least one non-creped through dried tissue and a MD stiffness factor of less than 150. Pref. this is a single ply bath tissue of 80 wt.% curled eucalyptus fibres. Also claimed are methods of making the tissue prods

Description

In the manufacture of paper fabric products, such as paper

  hygienic, attention must be paid to a wide variety of product characteristics so that the final product has the appropriate assortment of suitable properties taking into account the intended use of the product. Among these various properties, flexibility, in the sense given below, has always been a major objective for quality products. By flexibility, also called softness, is meant the feeling of sagging which a

  sheet of material when crumpled by hand (Sverige-

  Svensk Standard SS 15 20 05. Flexibility depends in particular on stiffness and bulk (specific gravity), lower stiffness and greater bulk (lower specific mass) improving

  generally perceived flexibility.

  Usually, tissue products have been made using a wet pressing process in which a significant amount of water is removed from the wet spread sheet by pressure or by wringing water from the sheet before final drying. In particular, while it is supported by an absorbent paper felt, the web is clamped between the felt and the surface of a rotary heated cylinder (drier-friction) using a pressure roller while the web is transferred to the dryer surface for final drying. The dried tablecloth is then separated from the Yankee dryer using a doctor blade (creping) which is used to partially untie the dried tablecloth by breaking many of the bonds which were previously formed during the wet pressing stages of the process. . Creping generally improves the flexibility of the web, however at the expense

  a significant loss of strength.

  More recently, transverse air drying has been

  become a predominant means of drying cloths.

  Cross-air drying provides a relatively non-compressive process of removing water from the web by passing hot air through the web until it is dry. More specifically, a wet spread sheet is transferred from the forming fabric to a coarse, very permeable transverse air drying fabric and retained on the transverse air drying fabric until it is dry. The resulting dried web is more flexible and thicker than a wet, uncrimped sheet dried because less paper bonds are formed and because the web is less dense. The dewatering of water from the wet sheet is eliminated although the subsequent transfer of the sheet to a drier for creping is always used for final drying and / or softening of the

resulting tissue.

  Although there is an incentive to eliminate the dryer-

  frictionner and to manufacture a non-crepe transverse air-dried fabric, attempts to manufacture sheets of transverse air-dried fabric without the use of a dryer (non-crepe) dryer have so far resulted in products which did not have the flexibility when compared to their crepe counterparts. This is partly due to the high stiffness and the inherent resistance of an uncrimped sheet because, without crimping, there is no mechanical rupture of the connections during the process. Because stiffness is a major component of flexibility, the use of non-creped cross-air-dried sheets has been limited to applications and markets where high strength is premium, such as for industrial rags and towels, rather than for applications where flexibility is required, such as toilet paper, quality household cleaning towels and tissues for the general public. It has now been discovered that fabrics having properties particularly suitable for use as toilet tissue can be made using certain pre-treated paper fibers according to an appropriate process. A method of fabric manufacturing by transverse air drying is preferred in which the web of fabric is not glued to a drier and therefore is not creped. The resulting fabrics according to the invention are characterized by a unique combination of strong bouffant and low stiffness when compared to the crepe toilet papers available and in particular to the products.

  non-creped transverse air dried.

  The stiffness of the products according to the invention can be represented objectively either by the maximum slope of the curve "load in the machine direction" / "elongation of the fabric" (hereinafter called "Maximum Slope SM", SM meaning "direction

  machine "), or by the Stiffness Factor SM (defined above

  after) which also takes into account the size of the fabric and the number of throws of the fabric. According to the invention, by overcoming the high inherent stiffness of the non-creped transverse air-dried sheets, it is possible to produce a fabric of acceptable flexibility having a large bulk and a low stiffness. In addition, the products according to the invention can have a high degree of extensibility of around 10% or more which offers durability in use. Such products of flexible, resistant and extensible fabrics having a strong bouffant have never been manufactured until now. Although this invention is particularly applicable to toilet paper, it is also useful for other paper products in which flexibility is a significant attribute, such as for tissues or

  paper towels for household use.

  Therefore, in one aspect, the invention relates to a flexible fabric comprising one or more non-creped transverse air-dried jets and having a Stiffness Factor SM of about 150 or less, and preferably also having a

Bouffant about 6 cm3 / g or more.

  The flexible fabric according to the invention can be manufactured by implementing a method for manufacturing a flexible fabric sheet comprising: (a) the formation of an aqueous suspension of paper fibers having a concentration of approximately 20% or more; (b) mechanical work of the aqueous suspension at a temperature of about 62 C (140 F) or more provided by an external heat source, such as steam, with an energy input of about 0.7457 kW-day (1 ch-day) per ton of dry fibers or more for waving the fibers; (c) diluting the aqueous suspension of wavy fibers to a concentration of about 0.5% or less and feeding the diluted suspension to a fabric fabrication crate; (d) depositing the dilute aqueous suspension on a forming fabric to form a wet web; (e) wringing out the wet sheet to a concentration of about 20 to about 30%; (f) transferring the spun web from the forming fabric to a transfer fabric (17) moving at a speed of about 10 to about 80% less than that of the forming fabric; (g) transferring the web to a transverse air drying fabric with the result that the web is rearranged macroscopically to conform to the surface of the transverse air drying fabric; and (h) transverse air drying of the web to a

final dry state.

  The bulk of the products according to the invention is calculated as being the quotient of the Caliber (as defined below),

  expressed in micron, divided by the basic weight, expressed g / m2.

  The resulting Bouffant is expressed in cm3 / g. For the products according to the invention, the bouffants can be about 6 cm3 / g or more, preferably 9 cm3 / g or more, usually about 9 to about 20 cm3 / g, and more specifically about 10 at around 15 cm3 / g. The products according to the invention draw their Bouffants indicated above from the base sheet, which is the sheet produced by the fabric making machine without post-treatment such as embossing. However, the base sheets according to the invention can be embossed to produce even superior bouffants or aesthetic effects, if desired, or they can remain unembossed. In addition, the base sheets according to the invention can be calendered to improve their smoothness or reduce their bulk if desired or if this is necessary to satisfy

  existing specifications for the product.

  The Maximum Slope SM of the products according to the invention can be about 10 or less, preferably about 5 or less, and usually about 3 to about 6. The determination of the Maximum Slope SM will be described below in relation to figure 6. The Maximum Slope SM is the maximum slope of the "load in the machine direction" / elongation curve. The Maximum Slope SM is expressed in kilograms per 7.62 cm (by 3 inches), but for convenience, the values of Maximum Slope SM are indicated

below without unit.

  The Stiffness Factor SM of the products according to the invention can be approximately 150 or less, preferably approximately 100 or less, and suitably approximately from 50 to approximately 100. The Stiffness Factor SM is calculated by multiplying the Slope Maximum SM by the square root of the caliber quotient divided by the number of jets. The Stiffness Factor SM is expressed in (kilograms per 7.62 cm) -microns0'5, i.e. in (kg per 3 inches) -microns05, but for simplicity, the values of Stiffness Factor SM are

shown below without unit.

  Caliber, as used here, is the thickness of a single sheet, but measured as the thickness of a stack of 10 sheets divided by 10, each sheet being placed in the stack with the same side on the above. The Caliber is expressed in microns. It is measured according to the TAPPI T402 "Standard Conditioning and Testing Atmosphere For Paper, Board, Pulp Handsheets and related Products" and T411 om-89 "Thickness (caliper) of Paper, Paperboard, and Combined Board" test methods with the Note 3 for stacked leaves. The micrometer used to carry out the T411 om-89 procedure is a Bouffant Micrometer (model TMI 49-72-00, Amityville, New York, USA) having an anvil diameter of 103.2 millimeters (4 1/16 inches) and anvil pressure of 3.39 kiloPascals (220 grams / inch2). Once the Caliber has been measured, the same 10 sheets of the stack are used to determine

  the average base weight of the leaves.

  The products according to the invention can be single-jet products or multiple-jet products, such as products with two jets, three jets, four jets or more. Single-jet products are advantageous because of their low manufacturing cost, while

  Multiple jets are preferred by many consumers.

  For multi-jet products, it is not necessary that all product jets are the same,

  provided that one of the jets is in accordance with the invention.

  The basic weight of the products according to the invention can range from approximately 5 to approximately 70 g / m2, preferably in approximately

  at around 40 g / m2 and better from around 20 to around 30 g / m2.

  For a single-jet toilet paper, a base weight of about 25 g / m2 is preferred. For two-ply paper, a base weight of about g / m2 is preferred. For three-ply paper, a base weight of about 15 g / m2 is preferred. The fabrics according to the invention can also be characterized by a relatively high degree of SM stretch. The amount of SM extensibility can be about 10% or more, suitably about 15 to about or 30%. The ST extensibility (ST meaning cross direction) can be about 3% or more, suitably about 7 to about 10%. The extensibility SM can be imparted to the sheet during the transfer of the sheet from the forming fabric to the transfer fabric, and / or by transfer from a transfer fabric to another transfer fabric, and / or by transfer from the tablecloth from a canvas

  transfer to the transverse air drying fabric.

  The ST extensibility is governed by the canvas model

transverse air drying.

  To be suitable as toilet paper, the product preferably has a tensile breaking strength SM of about 600 grams by 7.62 centimeters (by 3 inches) wide or more, and more preferably from about 700 to about 1500 grams. The tensile strength ST is preferably about 300 grams by 7.62 centimeters (by 3 inches) wide or more and more preferably about 400 about 600 grams. The tensile strength SM, the tensile strength SM, the tensile strength ST and the tensile strength ST are obtained according to the test method TAPPI 494 om-88 "Tensile Breaking Properties of Paper and Paperboard "using the following parameters: the speed of the square head is 254 mm / min (10 inches / min) (the total load is 4.540g (10 pounds), the jaw spacing (this is that is, the distance between the jaws (sometimes called gauge length) is 50.8 mm (2.0 inches) and the width of the specimen is 76.2 mm (3 inches). traction is a Sintech machine model CITS-2000 (Systems Integration Technology Inc., Stoughton, MA, USA; division of

  MTS Systems Corporation, Research Triangle Park, NC, USA).

  The paper fibers useful for the implementation of the invention comprise all cellulosic fibers which are known to be usable for the production of paper, in particular the fibers usable for making papers of relatively low density, such as tissues, toilet paper, paper napkins, paper napkins and the like. Suitable fibers include virgin fibers of softwood and hardwood as well as secondary or recycled cellulosic fibers, and their blends. As particularly suitable hardwood fibers, there may be mentioned eucalyptus and maple fibers. As used herein, the term "secondary fibers" means any cellulosic fiber which has been previously isolated from its original matrix by physical, chemical, or mechanical means and which, in addition, has been formed into a web of fibers, dried to a moisture content of about 10% by weight or less, then re-isolated from its web matrix by a means

  any physical, chemical or mechanical.

  A key component of tissue flexibility is sheet stiffness or resistance to folding. Previous methods reduce stiffness by creping, layering, patterned fastening on a drier or some combination of these methods. Neither the first nor the last of these processes is possible in the context of a transverse air drying process without creping. Therefore, layering can be expected to play a key role in reducing the stiffness of the sheet for a given overall tensile strength. Ideally, the desired overall strength could be provided by a very thin layer (for low stiffness) which has been treated to provide very high strength or modulus (perhaps by refining or chemical action). The remaining layer (s) would consist of fibers which have been treated to significantly reduce their strength (their modulus). The key to obtaining a low stiffness at the desired overall resistance therefore consists in the treatment or modification of the fibers so as to maximize the difference in resistance (of modulus) between the layers. An ideal modification for the weakest layer would be to simultaneously reduce the tensile strength and increase the bulk, as this would reduce the modulus to

maximum.

  Modification methods for producing flexible fibers for relatively weak layers include mechanical modification, chemical modification and combinations of mechanical modifications and chemical modifications. The mechanical modifications are implemented by methods which permanently deform the fibers by mechanical action. These methods introduce undulations, beaks, and micro-compressions into the fiber which reduce the fiber-fiber bond, reduce the tensile strength of the sheet, and increase the bulk, extensibility, porosity and flexibility of the sheet. Examples of suitable mechanical modification methods include flash drying, dry stripping and high concentration wet waving. While any mechanical process and device that gives the fibers a ripple can increase the flexibility of the sheet, those that produce more ripples or stiffer ripples or a more lasting ripple when the product is exposed to water will increase the flexibility of the leaf to a greater degree and are therefore preferred. In addition, flexibility-enhancing chemicals can be added to the mechanically modified fibers either before or after the mechanical modification to produce an additional increase in flexibility compared to that obtained in isolation by mechanical treatment or by the addition of chemicals to the wet end of the production chain. A preferred means of modification of the fibers for the implementation of the invention is to pass the fibers through a tree disperser, which is a high concentration wet ripple which works the fibers (makes them undergo high shear forces and a high degree of interfiber friction) at a high temperature. The fibers which have been passed through a tree disperser (a process which is sometimes referred to hereinafter by "dispersal") are called "dispersed fibers". These fibers have certain properties which make them particularly advantageous for the manufacture of non-creped transverse air-dried fabrics because of their

  ability to give bulk and flexibility.

  The concentration of an aqueous suspension of fibers which is subjected to dispersion must be high enough to give significant fiber-fiber contact or to allow work which will modify the surface properties of the treated fibers. Specifically, the concentration can be at least about 20, preferably about 20 to about 60, and more preferably about 30 to about 50% by dry weight. The concentration is mainly governed by the type of machine used to process the fibers. For some tree dispersers, for example, there is a risk of clogging the machine

  at concentrations greater than about 40% by dry weight.

  For other types of dispersers, such as the Bivis machine (commercially available from Clextral, Firminy Cedex, France), concentrations greater than 50 can be used without it clogging up. This device can generally be described as a disperser with a pressurized twin-screw shaft, each shaft having several screw arms oriented in the direction of the flow of the material followed by several arms oriented in the opposite direction to create back pressure. . The screw arms are notched to allow material to pass through the notches from one set of arms to another. It is desirable to use a concentration which is as high as possible for the particular machine used for the purposes

  increase the fiber-fiber contact as much as possible.

  The temperature of the fiber suspension during dispersal can be about 60 C (about 140 F) or more, preferably about 67 C (about 150 F) or more, and better still about 99 C (about 210 F ) at most and better still about 104 C (about 220 F) or more. The upper limit of the temperature is dictated by whether or not the apparatus is under pressure, since the aqueous fiber suspensions in the apparatus operating at atmospheric pressure cannot be heated beyond the boiling point. some water. It is interesting to note that it is believed that the degree and the permanence of the waviness are strongly affected by the amount of lignin in the fibers subjected to the dispersing process, the greatest effects being able to be obtained with the fibers having the content of highest lignin. Therefore, high-yielding pulps with a high lignin content are particularly advantageous in that fibers which have hitherto been considered flexible can be transformed into fibers having the desired flexibility. . Such high-yielding pulps, listed in descending order of lignin content, are the mechanical shredder pulp, the thermomechanical pulp (tmp), the chemomechanical pulp (cmp), the bleached chemothermomechanical pulp (bctmp). These pulps have a lignin content of around 15% or more while chemical pulps (kraft and sulfite) are low pulp

  yield having a lignin content of about 5% or less.

  The amount of energy applied to the fiber suspension during dispersal also affects the properties of the fibers. In general, the increase in

  energy supply increases the waviness of the fibers.

  However, it has also been found that the waviness of the fibers reaches a maximum when the energy supplied is approximately 1.6 kilowatt-days per ton (2 ch-days per ton) of dry fibers in suspension. A preferred range of energy supply is from about 0.8 to 2.5 kilowatt-days per tonne (from about 1 to about 3 ch-day per tonne) and better still from about 1.6 kilowatt-days per tonne ton (approximately 2 ch-day per ton) or more. During the working of the fibers during dispersing, it is necessary for the fibers to undergo substantial friction or shearing of fiber-fiber as well as friction or shearing contact with the surfaces of the mechanical devices used to treat the fibers. It is desirable that there is some compression, i.e. the fibers are pressed together, to increase or increase the effect of friction or shearing on the fibers. The measurement of the appropriate amount of shear and compression to be used is a function of the end result, which is to obtain a high bulk and a low stiffness in the resulting fabric. A number of tree dispersers or equivalent mechanical devices known in the paper industry can be used to achieve the expected results to varying degrees. Suitable shaft dispersers include, but are not limited to, non-pressurized shaft dispersers and pressurized shaft dispersers such as the Bivis machines described above. Tree dispersers can be characterized by their relatively high ratio between volume and interior surface and they basically rely on fiber-to-fiber contact to cause modification of the fibers. They differ in this from disc refiners or disc dispersers which are mainly based on the metal surface-fiber contact rather than on a fiber-fiber contact. Although dispersing is a preferred method of modulus reduction for fibers of flexible layers, the intention is not to be limited to the use of fibers treated in this manner. Mechanical or chemical devices can be used to reduce the strength and modulus of these fibers and used with a strong layer to directionally reduce the

stiffness of the leaf.

  Fabric softeners, sometimes called debonders, can be used to increase the flexibility of the fabric product, and such fabric softeners can be incorporated into the fibers before, during or after dispersing. Such agents can also be sprayed or applied to the web after formation while it is wet, or added to the wet end of the fabric making machine before formation. Suitable agents include, but are not limited to, fatty acids, waxes, quaternary ammonium salts, dihydrogenated dimethyl tallow ammonium chloride, quaternary ammonium methyl sulfate, polyethylene carboxylate, cocamide diethanolamine , cocobetaine, sodium laurylsarcosinate, partially ethoxylated quaternary ammonium salts, distearyl dimethyl ammonium chloride, polysiloxanes and the like. As chemical softening agents available commercially and suitable for carrying out the invention, mention may be made, without being limiting, of Berocell 596 and 584 (quaternary ammonium compounds) manufactured by Eka Nobel Inc., Adogen 442 (dihydrogenated dimethyl-tallow-ammonium chloride) manufactured by Sherex Chemical Company, Quasoft 203 (quaternary ammonium salt) manufactured by Quaker Chemical Company and Arquad 2HT-75 (di (hydrogenated tallow) chloride dimethylammonium) manufactured by Akzo Chemical Company. The suitable amount of softening agents varies greatly with the compounds chosen and the results expected. Such amounts can range, without being limiting, from about 0.05 to about 1% by weight relative to the weight of fibers, more particularly from about 0.25 to about 0.75% by weight, and more particularly still be around 0.5%

in weight.

  Referring now to the fabric manufacturing process according to the invention, the forming process and the apparatus can be conventional as is well known in the paper industry. Such training methods include the use of flat table machines, suction head roll formers and gap formers (such as double fabric formers, crescent formers), etc. A double cloth former is preferred for faster speed operations. The forming fabrics can also be conventional, the finest weavings which offer a greater support to the fibers being preferred to produce a smoother sheet and the coarser weaves giving a greater bulk. The arrival boxes used for depositing the fibers on the forming fabric may or may not be multi-layer, although the multi-layer arrival boxes are advantageous in that they allow fine tuning of the properties of the fabric. in

  modifying the composition of the various layers.

  More specifically, for a single jet product, it is preferable to produce a three-layer fabric having fibers dispersed both on the "air side" of the fabric and on the "canvas side" of the fabric (the "air side" refers on the side of the fabric which is not in contact with the fabric during drying, while the "fabric side" refers to the opposite side of the fabric which is in contact with the air drying fabric during drying) . The center of the fabric is preferably made of ordinary softwood fibers or secondary fibers, which have not been dispersed, to give sufficient strength to the fabric. However, it is within the scope of the invention to include dispersed fibers in all layers. For a product with two jets, it is preferable to have fibers dispersed on the canvas side of the fabric sheet and to join the two sheets together so that the layers of dispersed fibers become the faces of the product facing outwards. However, the dispersed fibers (virgin fibers and secondary fibers) can be present in any layer or in all the layers depending on the properties expected for the sheet. In all cases, the presence of the dispersed fibers can increase bulk and reduce stiffness. The amount of fiber dispersed in any layer can range from 1 to 100% by weight, and more specifically about 20% or more, about 50% or more, or about 80% or more. It is preferred that the dispersed fibers be treated with a debonder as described here to further increase the bulk and reduce the stiffness. In the manufacture of fabrics according to the invention, it is preferable to include a transfer fabric to improve the smoothness of the sheet and / or give it sufficient extensibility. As used herein, the term "transfer fabric" refers to a fabric which is disposed between the forming section and the drying section of the web manufacturing process. The fabric may have a relatively smooth surface to give the web a smooth character, but it must have a texture sufficient to retain the web and maintain contact during rapid transfer. It is preferred that the transfer of the web from the forming fabric to the transfer fabric is carried out by a "fixed space" transfer or a "light touch" transfer in which the web is not substantially compressed between the two canvases to maintain the size or bulk of the

  fabric and / or reduce wear on the canvas as much as possible.

  Transfer fabrics include permeable single-layer, multi-layer or composite structures. Preferred fabrics have at least one of the following characteristics: (1) on the face of the transfer fabric which is in contact with the wet web (the upper side), the number of strands in the direction of the machine (SM) per centimeter is 4 to 80 (10 to 20 strands per inch) (warp count) and the number of crosswise strands (ST) per centimeter is also 4 to 80 (weft count). The strand diameter is usually less than 1.3 mm (0.050 inch); and (2) on the upper face, the distance between the highest point of a SM joint and the highest point of a ST joint ranges from approximately 0.025 to approximately 0.5 or 0.75 mm (d '' about 0.001 to about 0.02 or 0.03 inch). Between these two levels, there can be joints formed either by the strands SM or by the strands ST to give a characteristic of three-dimensional topography. Suitable specific transfer fabrics include, by way of example, those made by Asten Forming Fabrics, Inc., Appleton, Wisconsin, USA and designated by the numbers 934, 937, 939 and 959 and Albany 94M manufactured by Albany International,

  Appleton Wire Division, Appleton, Wisconsin, USA.

  To give extensibility to the fabric, a speed difference is provided between the fabrics at one or more transfer points of the wet sheet. The speed difference between the forming fabric and the transfer fabric can range from about 5 to 75% or more, preferably from about to about 35%, and more preferably from about 15 to about 25%, based on of the slowest transfer fabric speed. The optimal speed difference depends on a variety of factors, including the particular type of product to be manufactured. As indicated above, the increase in extensibility conferred on the sheet is proportional to the speed difference. For a single jet non-creped transverse air-dried toilet paper having a basis weight of about 25 g / m2, for example, a speed difference of about 20 to about 25% between the forming fabric and a single transfer fabric produces extensibility

  in the final product ranging from about 15 to about 25%.

  Extensibility can be imparted to the web using a single transfer at different speeds or two or more transfers at different speeds from the wet web before drying. Therefore, there may be one or more transfer fabrics. The amount of extensibility imparted to the sheet can therefore be distributed between one, two, three transfers at different speeds or more. The tablecloth is transferred to the last cloth (the transverse air drying cloth), for the final drying, preferably with the assistance of the vacuum to guarantee a macroscopic rearrangement of the tablecloth in order to give it bouffant and appearance wanted. The use of separate transverse air drying and transfer fabrics provides a significant improvement over the prior art in that it allows the two fabrics to be designed specifically to independently meet key product requirements. . For example, transfer fabrics are generally optimized to allow an efficient transformation of the very rapid transfer level into high SM extensibility and to improve the smoothness of the sheet while transverse air drying fabrics are designed to provide bulk and ST extensibility. It is therefore useful to have rather fine and relatively flat transfer fabrics and transverse air drying fabrics which are coarser and three-dimensional in the optimal configuration. The result is that a relatively smooth sheet leaves the transfer section and is then rearranged macroscopically (with the assistance of the vacuum) to give the high bulk and high ST stretch of the air drying fabric. No visible trace (at least macroscopically) of the transfer fabric remains in the finished product. The topology of the sheet is completely changed from that which it had on the transfer fabric to that it has after the transverse air drying fabric and the fibers are rearranged macroscopically, with a significant fiber-fiber movement. The drying process can be any non-compressive drying process which tends to preserve the bulk or the thickness of the wet sheet including, without being limiting, drying by transverse air, infrared radiation, drying by micro- wave, etc. Because of its commercial availability and its convenience, drying by transverse air is well known and it constitutes a preferred means of non-compressive drying of the sheet for the implementation of the invention. Suitable transverse air drying fabrics include, but are not limited to, the products Asten 920A and 937A and Velostar P800 and 103A. The sheet is preferably dried until the final dry state on the transverse air drying fabric, without being compressed against the surface of a drier-frictionneur, and without subsequent creping. This gives a product of relatively uniform density compared to products manufactured by a process in which the sheet is pressed against a drier-friction while it is still wet and supported by the drying cloth by transverse air or by another cloth, or by comparison with products spread in the air and linked by points. If the appearance and bulk of the final product are governed by the model of transverse air drying fabric, the extensibility SM of the web is basically governed by the transfer fabrics, which gives the process according to the invention a more great flexibility. In the drawings: - Figure 1 is a diagram illustrating a method of manufacturing non-creped air-dried sheets according to the present invention; - Figure 2 is a diagram illustrating a method of treating fibers according to the present invention which uses a shaft disperser to work the fibers; Figure 3 is an exploded perspective view of the tree disperser of Figure 2; - Figure 4 is a flow diagram of a variant of the method according to the invention using a pair of dispersers with Bivis shaft in series; - Figure 5 is a generalized plot of a load / stretch curve of the fabric, illustrating the determination of the Maximum Slope SM; - Figure 6 is a graph of the Bouffant according to the Stiffness according to Panel (stiffness as determined by a panel of people trained in sensory evaluation) for the toilet papers manufactured according to the present invention and for creped toilet papers available in the trade illustrating the high level of bulk and the low stiffness of the products according to the invention; FIG. 7 is a graph of Stiffness according to Panel as a function of the Maximum Slope SM for the toilet papers manufactured according to the present invention and for commercially available toilet papers illustrating the correlation between the Stiffness according to Panel and the Maximum Slope SM; - Figure 8 is a graph of the Bouffant as a function of the Maximum Slope SM for the toilet papers manufactured according to the present invention and for commercially available toilet papers, further illustrating the strong Bouffant and the low stiffness of the products according to the invention ; FIG. 9 is a graph similar to that of FIG. 8, but indicating the stiffness according to Panel as a function of the stiffness factor SM, illustrating the correlation between the stiffness according to Panel and the stiffness factor SM; - Figure 10 is a graph similar to that of Figure 9, but concerning the Bouffant as a function of the Stiffness Factor SM, further illustrating the strong Bouffant and the

  low stiffness of the products according to the invention.

  The invention will now be described in detail by

reference to the drawings.

  FIG. 1 illustrates a means for implementing the method according to the invention. (For the sake of simplicity, the different tension rollers, schematically used to define the different paths of the fabrics, are shown but are not numbered. It will be understood that variants can be made to the apparatus and to the process illustrated in the figure 1 without departing from the scope of the invention). We see a double fabric former having a multi-layer paper input box 10 which injects or deposits a stream 11 of an aqueous suspension of paper fibers on the formation fabric 13 which serves as support and carries the newly formed wet web. downstream of the process while the web is partially wrung to a concentration of around 10% by dry weight. An additional spin can be performed from the web, for example using a vacuum, while the wet web is supported by the forming fabric. Reference 12

indicates a backing.

  The wet web 15 is then transferred from the forming fabric to a transfer fabric 17 moving more slowly than the forming fabric in order to impart increased extensibility to the web. The transfer is preferably carried out with the assistance of a suction shoe 18 and a fixed gap or space between the forming fabric and the transfer fabric or a transfer by

  touching to avoid compression of the wet sheet.

  The web is then transferred from the transfer fabric to the transverse air drying fabric 19 with the aid of a suction transfer roller 20 or a suction transfer shoe, optionally again using a fixed space transfer as previously stated. The transverse air drying fabric can move at approximately the same speed as the transfer fabric or at a different speed. If desired, the transverse air drying fabric can move more slowly to further increase the extensibility. The transfer is preferably carried out with the assistance of the vacuum to ensure the deformation of the sheet so that it conforms to the drying cloth by transverse air, obtaining

  thus the bouffant and the desired appearance.

  The vacuum level used for tablecloth transfers can range from around 75 to around 380 mm Hg (from around 3 to

  about 15 inches Hg), preferably 125 mm Hg (5 inches Hg).

  The suction shoe (negative pressure) can be supplemented or replaced by the use of a positive pressure exerted from the opposite side of the tablecloth to blow the tablecloth over and into the nearby fabric in addition to, or in replacement of the aspiration of said sheet towards and into the neighboring fabric under the effect of the vacuum. Again, one or more suction rollers can be used to replace the or

the suction shoe (s).

  While it is supported by the transverse air drying fabric, the web undergoes its final drying to a concentration of approximately 94% or more under the effect of the transverse air dryer 21, after which it is transferred to a transport fabric 22. The dried base sheet 23 is transported to the spool 24 using the support fabric 22 and an optional support fabric 25. An optional pressurized rotary roller 26 can be used to facilitate the transfer of the web from support fabric 22 to fabric 25. As suitable support fabrics suitable for this purpose, Albany International 84M or 94M and Asten 959 can be used. or 937, which are all relatively smooth canvases with a fine outline. Although not shown, inline calendering or separate subsequent calendering can be used to increase smoothness

  and the flexibility of the base sheet.

  FIG. 2 is a diagram generally illustrating the steps of the method for treating secondary paper fibers for dispersal. (For virgin fibers, the fibers can be boiled with water to the desired concentration and introduced directly into the disperser). A papermaking composition 40 to be treated is supplied to a triturator 41 for high concentration (Model SR6C-W, Bird Escher Wyss, Mansfield, MA, USA) with the addition of dilution water 42 to reach a concentration of about 15%. Before being pumped out of the pulper, the pulp suspension is diluted to a concentration of around 6%. The crushed fibers are sent to a scalping screen 43 (FT-E, Bird Escher Wyss) with an additional quantity of dilution water to remove the large contaminants. The input concentration to the scalping screen is approximately 4%. Items rejected from the scalping screen are directed to waste disposal 44. Items accepted by the scalping screen are sent to a high density scrubber 45 [7 inch cyclone, Bird Escher Wyss) to remove heavy contaminants that have escaped the scalping screen. The elements rejected from the high density purifier are sent to waste disposal 32. The elements accepted by the high density purifier are sent to a fine screen 46A (Centrisorter model 200, Bird Escher Wyss) to remove even more contaminants. small. Dilution water 42 is added to the feed stream of the fine screen to achieve a feed concentration of about 2%. The elements rejected by the fine screen are directed to a second fine screen 46B (Axiguard, model 1, Bird Escher Wyss) to remove additional contaminants. The elements accepted are recycled into the feed stream of the fine screen 46A and the rejected elements are directed towards the elimination of waste 44. The elements accepted by the fine screen, with the addition of dilution water to reach a concentration approximately 1% are then passed through a series of four flotation cells 47, 48, 49, 50 (Aerator Model CF1, Bird Escher Wyss) to remove ink particles and sticky elements. The rejected elements from each of the flotation cells are directed to the elimination of waste 44. The accepted elements from the last flotation cell are sent to a washer 51 (thickener with double pressure space model 100, Black Clawson Co. , Middletown, OH, USA) to remove very small ink particles and increase the concentration to approximately 10%. Items rejected by the washer are directed to waste disposal 44. Accepted items from the washer are sent to a carpet press 52 [Arus-Andritz CFP model 50.8 cm (20 inch), Andritz-Ruthner Inc., Arlington, Tx, USA] to reduce the water content to about%. The rejects from the carpet press are directed to waste disposal 44. The resulting partially dehydrated fibrous material is then sent to a tree disperser 53 (GR 11 Ing. S. Maule & CSpA, Torino, Italy), described in detail in Figure 4 for working the fibers to improve their properties according to the present invention. Steam 54 is added to the disperser feed stream to raise the temperature of the feed material. The resulting treated fibers 55 can be used directly as paper raw materials or further processed if desired.

longed for.

  Figure 3 is an exploded perspective view of a preferred apparatus for treating fibers according to the

  present invention as illustrated in Figure 2.

  The particular device is a GR II type tree disperser, manufactured by Ing. S. Maule & C. S.p.A., Torino, Italy. We see an upper cylindrical cover 61 and a lower cylindrical cover 62 which, when closed, enclose a rotary shaft 63 having a series of arms 64. The upper cover contains two rows of knurled fingers 65 and three inspection openings 66 At one end of the upper cover is an inlet port 67. At the inlet end of the rotary shaft is located a drive motor 68 adapted to rotate the shaft. At the outlet end of the rotary shaft is a bearing 69 which supports the rotary shaft. The inlet end of the rotary shaft contains a screw feed section which is arranged below the inlet and is used to force the feed material through the disperser. The outlet 71 of the disperser comprises an articulated flap 72 having a lever 73 which, when the disperser is closed, is engaged with hydraulic air bags 74 mounted on the upper cover. Air bags offer adjustable resistance to rotation of the hinged flap and therefore a means of adjusting the

  back pressure inside the disperser.

  The increase in back pressure increases the degree to which the fibers are worked. During operation the knurled fingers cooperate with the arms of the rotary shaft to work with them the feed material. FIG. 4 is a flow diagram of a variant method according to the invention using a pair of double-shaft dispersers (Bivis machine). As illustrated, the paper pulp, at a concentration of 50%, is sent to a screw feeder. The screw feed doses the raw material to the first of the two Bivis machines mounted in series. Each Bivis machine has three compression / expansion zones. Steam is injected into the first Bivis machine to raise the temperature of the fibers to around 100 C (212 F). The worked dough is transferred to the second Bivis machine operating under the same conditions as the first. The worked dough from the second machine can be soaked by dropping it in a cold water bath after which it is dehydrated

  to a suitable concentration.

  Figures 5-10 will be discussed below in

relationship to the examples.

Examples

  Examples 1-20. To illustrate the invention, a number of non-crepe transverse air dried fabrics were produced using the process substantially as illustrated in Figure 1. More specifically, Examples 1 to 19 were all single jet toilet tissue with three layers in which the outer layers consist of dispersed loose eucalyptus fibers and the central layer consists of refined northern softwood kraft fibers. Example 20 was a two-ply toilet paper with each ply formed as described in the previous examples. Cenebra eucalyptus fibers were triturated for 15 minutes at a concentration of 10% and the pulp was dehydrated to a concentration of 30%. The dough was then sent to a Maule tree disperser as shown in Figure 3. The disperser operated at 70 C (160 F) with a contribution

  energy of 1.8 kilowatt-days per ton (2.2 hp / day / t).

  After dispersing, a softening agent (Berocell 584) was added to the dough in an amount of 4.53 kg (10 pounds) of Berocell per ton of dry fiber (0.5% by weight). Before formation, the softwood fibers were triturated for 30 minutes at a concentration of 2.5%, while the loose and dispersed eucalyptus fibers were diluted to a concentration of 2%. The overall weight of the laminated sheet was distributed in 37.5% / 25% / 37.5% among the layers of "dispersed eucalyptus" / "refined resinous" / "dispersed eucalyptus". The core layer has been refined to levels required to achieve the desired strength values, while the outer layers provide the

flexibility and bouffant.

  These examples used a Beloit Concept III four-layer arrival box. The refined northern softwood kraft raw material was used in the two central layers of the inward box to produce a single central layer for the three-layer product described. The turbulence inserts were set back about 75 mm (3 inches) from the ruler and the bulkheads between layers projected about 150 mm (about 6 inches) beyond the ruler. Flexible lip extensions extending about 150 mm (about 6 inches) beyond the rule have also been used as the sign US-5,129,988 issued July 14, 1992 in the name of Farrington Jr and titled "Extended Flexible Headbox Slice With Parallel Flexible Lip Extensions and Extended Internal Dividers ". The net opening of the ruler was approximately 23 mm (approximately 0.9 inches) and the water flows in the four layers of the incoming box were comparable. The concentration of the raw material brought to the cash register

  arrival was about 0.09% by weight.

  The resulting three-layer sheet was formed on a suction drum with double fabric, a former with forming fabrics (12 and 13 in Figure 1) which were respectively Asten 866 and Asten 856A fabrics having respectively a volume of voids of approximately 64.5% and 61%. The speed of the formation cloth was 12.1 meters per second. The newly formed web was removed from its water to a concentration of about 20-27% using a vacuum box located below the forming fabric before being transferred to the transfer fabric which was moving a speed of 9.7 meters per second (25% of fast transfer). The transfer fabric used included an Asten 934 fabric and an Albany 94M fabric. A vacuum shoe drew a vacuum of approximately 150-380 mm Hg (6-15 inches Hg) to transfer the web to the canvas.

transfer.

  The web was then transferred to a transverse air drying fabric moving at a speed of about 9.7 meters per second. Velostar 800 and Asten 934 transverse air drying fabrics were used. The tablecloth was conveyed on a Honeycomb transverse air dryer at a temperature of about 175 C (about 350 F) and dried to a concentration about 94-98%

(final dryness).

  Table 1 gives a more detailed description of the

  process conditions as well as the properties of the resulting fabrics of Examples 1 to 20 illustrating the invention. As used in Table 1 below, the column headings have the following meanings: "SAT fabric" means transverse air drying fabric (the designation "C" or "T" applied to the drying fabric by transverse air refers to the face of the fabric which is presented to the web: "C" means that the face has predominantly warp joints and "T" means that the face has predominantly weft joints; # 1 Trans Vacuum "means that vacuum is used to transfer the web from the forming fabric to the transfer fabric, expressed in mm Hg; # 2 Trans Vacuum means that vacuum is used to transfer the web from the transfer fabric up to the transverse air drying fabric, expressed in mm Hg; "Conc. @ # 1 trans" means concentration of the sheet at the transfer point from the forming fabric to the transfer fabric, expressed as a percentage of solids; "Conc. @ # 2 trans "means concentration of the web at the point of transfer from the transfer fabric to the transverse air drying fabric, expressed as a percentage of solids; "Res. Tract. SM" means the tensile strength in the machine direction, expressed in g per 7.62 cm (per 3 inch) of sample width; "Ext. Break SM" means extensibility in the machine direction, expressed as a percentage of elongation at the time of sample rupture; "Max Slope SM" as defined above is expressed in kg per 7.62 cm (per 3 inch) of sample width; "Res. Tract. ST" is the tensile strength in the cross direction, expressed in g by

  7.62 cm (by 3 inches) of sample width; "Ext. Rupt.

  ST "is the extensibility in the cross direction, expressed as a percentage of elongation, at the time of the rupture of the sample;" MGR "is the geometric mean of the tensile strength expressed in grams per 7.62 cm (by 3 inches) of sample width; "Base weight" is the finished base weight, expressed in g / m2; "Size" is the size of ten sheets divided by ten, as previously described and expressed in micron ; "Bouffant" is the Bouffant as defined above and expressed in cm3; "Raid. Panel "is the stiffness of the sheet as determined by a panel trained in sensory evaluation estimating the relative acuity of the folds when a sheet is taken in the hand, expressed by a number on a scale going from 1 to 14, the highest numbers expressing the greatest stiffness (commercial toilet paper ranges from about 3 to about 8), and "Fact. raid. SM "is the stiffness factor in the machine direction as defined above, expressed in (kg

  per 76.2 mm) -microns0'5 or in (kg per 3 inches) -microns0'5.

TABLE 1

  # 1 # 2 Conc. Conc. Res. Ext. Slope Ex. Canvas Trans Trans @ # 1 @ # 2 tract. rupt. max transfer TAD Vacuum Trans trans vacuum SM SM SM i i ilmm m ii ii 1 ALBANY 94M C VELOSTAR 380 200 20-22 22) 24 775 19.2 5.087

  2 ASTEN 934 C ASTEN 934 380 100 20.22 27,729 721 19.3 4.636

  3 ASTEN 934 C ASTEN 934 150 100 20 222 22 724 712 18.9 4.815

  4 ALBANY 94M T VELOSTAR 150 200 20 722 27, 29 799 19.2 5.149

  ALBANY 94M T VELOSTAR 380 100 20 722 27.29 834 22.0 5.223

  6 ALBANY 94M T ASTEN 934 380 100 20.22 27, 29 897 20.2 5.621

  7 ALBANY 94M T VELOSTAR 150 100 20 722 22, 24 815 19.1 5.543

  8 ALBANY 94M C VELOSTAR 150 100 25.27 27, 29 843 21.7 5.698

  9 ALBANY 94M C VELOSTAR 380 100 20i22 27, 29 867 20.0 5> 696

  ASTEN 934 C ASTEN 934 380 200 20.22 22.24 721 20.6 4.709

  11 ALBANY 94M T VELOSTAR 380 200 25.27 27.29 819 20.2 5.441

  12 ASTEN 934 C ASTEN 934 150 200 20.22 27.29 709 20.2 4.913

  13 ALBANY 94M C VELOSTAR 380 200 25) 27 27.29 531 20.1 3.496

  14 ASTEN 934 C ASTEN 934 380 200 2527 27, 29 472 19.5 3.244

  ALBANY 94M T VELOSTAR 380 200 25) 27 27.29 631 21.4 4.036

  16 ASTEN 937 T ASTEN 934 380 200 25.27 2,729 535 20) 9 3.933

  17 VELOSTAR 800 C ASTEN 934 380 200 25D27 27> 29 427 16.3 3.901

  18 ASTEN 934 T ASTEN 934 380 200 25.27 27.29 530 21.3 4.206

  19 ALBANY 94M T VELOSTAR 380 200 25.27 27.29 600 20.8 4.754

  ALBANY 94M T VELOSTAR 380 200 25'27 2729 708 18.7 5.970

5970 (TABLE 1 (Continued)

Res. Ext. Fact.

  Ex. Tract. rupt. MGR Pds Caliber Bouf- Raid. raid.

ST ST base fant Panel SM

1,557 8.5 657 29.2 287 9.8 4.1 86

2,529 5.4 618 28.7 323 11.2 4.0 83

3,563 5.0 633 28.8 323 11.2 4.1 86

4,534 8.2 654 28.9 305 10.5 4.6 90

629 6.9 725 30.2 305 10o, 1 4.7 91

6,632 3.9 753 29.3 287 9.8 4.5 95

7,571 6.9 682 28.9 297 10.3 4.5 96

8,623 6.4,724 28.7 292 10.2 4.7 97

9,638 7.2,744 29.7 297 10.0 4.6 98

511 5.3 607 28.3 361 12.7 3.5 89

11,577 7.9 687 29.1 312 10.7 4.2 96

12,503 5.2,598 28.9 348 12.0 4.0 92

13,428 8.3,477 20.7 249 12.0 3.5 55

14,324 6.0 391 19.6 315 16.0 3.4 58

356 11.2 474 19.8 269 13.5 3.4 66

16,383 5.8 453 20.1 325 16.1 3.8 71

  17,306 14.8 362 19.6 330 16.8 3.4 71

18,299 9.4 398 19.9 335 16.8 3.2 77

19,415 4.5 499 20.0 287 14.3 3.8 81

494 8.6 591 38.0 388 10.1 3.2 83

  Referring now to Figures 5-10 different aspects of the present invention will be described

in more detail.

  FIG. 5 is a generalized load / elongation curve for a sheet of fabric illustrating the determination of the Maximum Slope SM. As can be seen, two points P1 and P2 are selected situated on the load / extension curve, the distance between the two points being exaggerated for purposes of illustration. The traction measurement device is programmed (GAP [General Application Program], version 2.5, Systems Integration Technology Inc., Stoughton, MA, USA; division of MTS Systems Corporation, Research Triangle Park, NC, USA) so that 'it calculates a linear regression for the points which are sampled from Pi and P2. This calculation is done repeatedly on the curve by adjusting the points Pl and P2 so

  regular along the curve (as described below

  after). The highest value of these calculations is the Maximum Slope and, when the measurement is made in the direction

  machine of the specimen, it is called Maximum Slope SM.

  The program of the traction measuring device must be set so that 500 points, such as Pi and P2, are taken over an elongation distance of 63.5 mm (2.5 inches) this gives a sufficient number of points for essentially exceeding any practical elongation of the specimen. With a square head speed of 254 mm / min (10 inches per min), there is a point translation every 0.030 second. The program calculates the slopes among these points by setting the tenth point as the initial point (for example Pl), counting 30 points to the 40th point (for example P2) and performing a linear regression on these thirty points. It stores the slope for this regression in a row. The program then counts ten points up to the th point (which becomes Pi) and repeats the procedure [counting 30 points which leads to the 50th point (which becomes P2), calculating the slope and re-storing in the row]. This process continues for the entire lengthening of the sheet. the Maximum Slope is then chosen as the highest value in this row. The Maximum Slope is expressed in kg per 76.2 mm (3 inches) in width. (The traction naturally has no dimension since the length of the extension is divided by the length of the jaw gap. This calculation is taken into account by the program of the

test machine).

  FIG. 6 is a graph of the Bouffant as a function of the Stiffness according to Panel for the toilet papers manufactured according to the present invention (examples 1-20 are indicated by the points a-t, respectively) and for a certain number of creped toilet papers commercially available, indicated either by "1" representing a single-jet product, "2" representing a two-jet product and "3" representing a three-jet product. This graph shows the unique combination of high bulk and low stiffness possessed by the

product according to the invention.

  Figure 7 is a graph showing the Stiffness according to Panel as a function of the Maximum Slope SM for the same products illustrating the correlation between the Maximum Slope SM and the stiffness as measured by a trained sensory panel. This graph shows that the Maximum Slope SM is

  an objective measure of stiffness assessed by the panel.

  Figure 8 is a graph of Bouffant versus Max Slope SM for the same products, illustrating the combination of strong Bouffant and low stiffness (as measured by Max Slope SM) offered by the products

according to the invention.

  FIG. 9 is a graph similar to that of FIG. 7 but, here again, the stiffness according to Panel is plotted as a function of the stiffness factor SM instead of the maximum slope SM, illustrating that the stiffness factor SM is

  also a valid measure of stiffness.

  Figure 10 is a graph similar to that of Figure 8 with the Bouffant plotted as a function of the Stiffness Factor SM illustrating the combination of strong Bouffant and low stiffness (as measured by the Stiffness Factor

  SM) offered by the products according to the invention.

  As is apparent from the above description, the

  flexible fabrics dried by transverse air can be manufactured without the use of a friction drier. The effects resulting from the usual functions of the Yankee-Fryer are obtained by effecting respectively a rapid transfer of the sheet at the wet end of the installation of

  manufacturing and by drying by transverse air.

Claims (10)

  1. Flexible paper fabric product comprising one or more non-crepe cross-air-dried fabric jets   and having a Stiffness Factor SM of about 150 or less.   2. Product according to claim 1, having a Bouffant about 6 cm3 / g or more.   3. Product according to claim 1, having a   machine direction extensibility of about 10% or more.   4. Product according to claim 1, having a   machine direction extensibility from about 15 to about 25.   5. Product according to claim 1, having a dried spray by non-creped transverse air.   6. Product according to claim 1, having two jets   non-creped transverse air dried.   7. Product according to claim 1, having three jets   non-creped transverse air dried.   8. Product according to claim 1, having four jets   non-creped transverse air dried.   9. Product according to claim 1, in which said jets comprise two or more layers, at least one of the layers being an outward facing layer.   and consisting of about 20% or more of wavy fibers.   10. Product according to claim 1, in which said jets comprise two or more layers, at least one of the layers being an outward facing layer.   and consisting of about 80% or more of wavy fibers.