MXPA99011254A - Method of making paper web using flexible sheet of material - Google Patents

Abstract

A process for making a paper sheet is disclosed. After a web is transferred from a forming wire (16) to a papermaking belt (20) preferably having deflection conduits, the web is overlaid with a flexible sheet (30) of material such that the web is disposed intermediate the sheet of material (30) and the papermaking belt (20). The sheet of material (30) has an air permeability less than the papermaking belt (20), and is preferably air-impermeable. An application of a fluid pressure differential (P) to the sheet of material causes deflection of at least a portion of the sheet of material towards the papermaking belt and, preferably, deflection of at least a portion of the web into the conduits of the papermaking belt and water removal from the web through the conduits of the papermaking belt.

Description

METHOD FOR DEVELOPING PAPER SIZE USING FLEXIBLE MATERIAL SHEET FIELD OF THE INVENTION The present invention relates to processes for manufacturing strong, soft and absorbent paper webs. More particularly, this invention relates to the papermaking process wherein a paper web is intermediate between a papermaking web and a flexible sheet of material.

BACKGROUND OF THE INVENTION Paper products are used for a variety of purposes. Paper towels, facial tissues, toilet paper and the like are in constant use in modern industrialized societies. A high demand for these paper products has created a demand for improved versions of the products. If paper products such as paper towels, facial tissues, toilet paper and the like are going to perform the tasks for which they are intended and will find wide acceptance, they must possess certain physical characteristics.

Among the most important of these characteristics are the resistance, softness and absorbency.

P948 Resistance is the ability of a paper web to retain its physical integrity during use. Softness is the pleasant sensation to the touch, which consumers perceive when they use the paper for the purposes for which they are intended. Absorbency is the characteristic of paper that allows paper to absorb and retain fluids, particularly water and aqueous solutions and suspensions. Not only is it important the absolute amount of fluid that a certain amount of paper will contain, but also the speed at which the paper will absorb the fluid. U.S. Patent 3,537,954 issued to Justus discloses a web formed between a top web and a bottom web. A repeat design is imparted to the weft in a clip where the weft is sandwiched between the fabric and a relatively soft and resilient papermaking felt. U.S. Patent 4,309,246 issued to Hulit et al. discloses supplying a non-compacted wet web to an open mesh print fabric formed of woven elements, and pressing the web between a papermaking felt and the printing web on a first press nip. The web is then carried by the printing fabric from the first nip press to a second nip press in a drying drum. The Patent of the P948 United States 4,144,124 issued to Turunen et al. exposes a paper machine that has a double-mesh former that has a pair of endless fabrics, which can be felts. One of the endless fabrics carries a paper web to a pressing section. The pressing section may include the endless fabric that carries the web of paper to the press section, an additional endless web, which may be a felt, and a mesh to mark the pattern in the web. PCT Publication 095/17548 which has a priority date of the United States of December 20, 1993 and published on June 29, 1995 in the name of Ampulski et al .; and PCT Publication WO96 / 00813 having a priority date of the United States of June 29, 1994 and published on January 11, 1996 in the name of Trokhan et al. They expose methods for papermaking that employ drainage of felt layers. While suitable methods for making paper webs are discovered in the field, paper scientists continue to look for even better methods to inexpensively build patterned paper structures with increased strength without sacrificing softness and absorbency. Air-dried paper webs are made, as described in U.S. Patent 4,514,345 issued to Johnson et al. on April 30, 1985; U.S. Patent 4,528,239 issued to Trokhan on July 9, 1985; and U.S. Patent 5,334, 289 granted to Trokhan et al on August 2, 1994, all three patents are assigned to the Procter and Gamble Company and are incorporated herein by reference. Paper produced by air-pass drying is disclosed in U.S. Patent No. 4,529,480 and U.S. Patent 4,637,859, both published in the name of Trokhan, the patents of which are incorporated herein by reference. The role of these patents is characterized by having two physically distinct regions: a continuous network region having a relatively high density and a region comprised of a plurality of domes scattered throughout the entire network region. The domes are of relatively low density and relatively low intrinsic resistance compared to the network region. In general, the processes for preparing air drying paper include several steps. An aqueous dispersion of the paper fibers is formed in an embryonic web on a foraminous member, such as a Fourdrinier mesh. This embryonic web is associated with a deflection member having a network surface with a non-random, macroscopically monoplanar, continuous pattern defining within the deflection member a plurality of discrete and isolated deflection conduits. The paper fibers in the embryonic web are deflected in the deflection ducts and the water is removed through the deflection ducts to form an intermediate web. The intermediate frame can, optionally, be dried and reduced by accretion. Accreting is a process for removing the dry intermediate web from the surface (usually also from the drying surface, such as the surface of a Yankee dryer) with a doctor blade to form a finished paper web. The deflection of the fibers in the deflection conduits can be induced, for example, by the application of differential fluid pressure to the embryonic paper web. A preferred method for applying differential pressure is exposing the embryonic web to a vacuum through the deflection conduits. As a result of a sudden application of the vacuum pressure, a deflection of the fibers towards the deflection conduits occurs, which can lead to the separation of the deflected fibers from each other and from the embryonic web. In addition, as a result of a sudden application of a vacuum pressure, a certain amount of partially drained fibers separated from the embryonic web could pass completely through the paper-forming web. This phenomenon causes the formation of small holes or pores in the domes of the finished paper web and obstructs the vacuum draining machinery. "The undesired creation of pores or small holes in the domes of the paper web was attenuated by commonly assigned United States Patent No. 5,334,289 issued August 2, 1994 to Trokhan et al., And incorporated here as a reference, this patent provides irregularities in the surface texture in the posterior network, subsequent irregularities attenuate the effect of a sudden application of vacuum pressure, and the search for improved products has continued.

OBJECTIVES AND ADVANTAGES OF THE INVENTION Accordingly, it is an object of the present invention to provide a process for the production of paper, which substantially reduces the formation of 'pores in the finished paper web and the accumulation of paper fibers in the vacuum draining machinery. It is another object of the present invention to provide a process for making paper that - it allows to produce a sheet of paper that has a more uniform base weight distribution and a more uniform density distribution, in relation to the papers produced by the drying processes P948 air of the prior art. It is further object of the present invention to provide a novel method for draining and molding a paper web. It is still another object of the present invention to provide a method for improving the removal of water from a web, during the pressing of the web.

SUMMARY OF THE INVENTION A process for making a paper sheet of the present invention comprises the steps of: (a) providing an aqueous dispersion of paper fibers; (b) forming a web of papermaking fibers from the aqueous dispersion into a forming mesh; (c) transferring the web from the forming mesh to a papermaking web having one side in contact with the web and a reverse opposite to the side in contact with the web, the web for paper making has a permeability to the web. air tape; (d) providing a flexible sheet of material having a first side and a second side opposite the first side, the sheet of material has a sheet air permeability less than the air permeability of the tape; (e) superimposing the web with the web of material so that the web is arranged intermediate between the first side of the web of material and the side "in contact with the web of the web for paper processing; differential pressure of fluid to the sheet of material so that a pressure associated with the second side of the sheet of material is greater than the pressure associated with the first side of the sheet of material, thereby deflecting at least a portion of the sheet of material towards the papermaking web, (g) removing the sheet of material from the weft, and (h) drying the weft to form the sheet of paper.The papermaking web is preferably comprised of a frame and a reinforcing structure attached to the frame The frame has a surface facing the weft, a surface facing the machine, and a variety of "deflection conduits extending intermediate to the frame. between the surface facing the weft and the surface facing the machine. The surface facing the weft defines the side in contact with the weft of the papermaking web, and the surface facing the machine defines the back side of the web for papermaking. The reinforcing structure is placed between the surface facing the weft and the surface of the frame facing the machine. The reinforcing structure has a first side and a second side opposite and parallel to the first side. The first side corresponds to the surface facing the weft and is parallel thereto, and the second side corresponds to the surface of the frame facing the machine and is parallel thereto. A distance between the surface of the frame, facing the frame and the first side of the reinforcing structure is an overload. The surface facing the weft comprises a web of weft side formed therein and defining weft side openings of the webs for making paper. The machine-facing surface comprises a side-to-machine network formed therein and defining side-to-machine openings of the papermaking web ducts. Preferably, the reinforcement structure has air permeability of more than 1000 cfm per square foot at a differential pressure of 100 Paséales. Preferably, the flexible sheet of material has a low air permeability of less than 5 scfm at a differential pressure of 0.5 inches of water, and more preferably, the flexible sheet of material is impermeable to air. When the fluid pressure differential is applied to the sheet of material, the deflection of at least a portion of the sheet of material causes deflection of at least a portion of the papermaking fibers in the mesh to the interior of the raceways. Deflection of the band to make paper and the removal of water from the weft through the ducts. Portions of the sheet of material, optionally, may or may not be deflected inside the deflection conduits of the papermaking web. If the sheet of material is deflected into the deflection conduits, preferably, a maximum deflection of the sheet of material is greater than 25% of the overload of the papermaking web, in a Z direction. Optionally, the process of the present invention may include an additional stage of predrying the frame before or subsequent to step (g), and / or an additional step of printing the network side of the frame in the frame by interposing the frame between the strip for making paper and a rigid surface, such as a Yankee drying drum. The process may also include an optional stage of shortening the plot, as occurs by the acrespado.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side elevational view of a continuous process mode for papermaking of the present invention. Figure 2 is a fragmentary schematic representation of a vertical cross-section showing the web covered with a flexible sheet of material, and the weft fibers that are deflected into a web duct for paper making. Figure 3 is a schematic fragmentary representation of a vertical cross section similar to that shown in Figure 2 and also showing the flexible sheet of material deflected into the paper strip web duct. Figure 4 is a schematic fragmentary representation of a vertical cross section similar to those shown in Figures 2 and 3, and showing the formation of "mushroom" domes DETAILED DESCRIPTION OF THE INVENTION A machine for representative paper making, suitable for the process of the present P948 invention, is illustrated schematically in Figure 1. An aqueous dispersion of papermaking fibers, or pulp, is prepared in an equipment not shown and is deposited in a head box 15 which can be of any conventional design. From the head box 15, the aqueous dispersion of papermaking fibers is delivered to a forming mesh 16, which is usually a foraminous member, also known as a Fourdrinier mesh. In Figure 1, the forming mesh 16 is shown schematically being supported by a front roller 19a and a plurality of return rolls, of which only two (19b and 19c) are illustrated. The forming mesh 16 is pushed in the direction indicated by a directional arrow A by a driving means well known to a person skilled in the art and therefore not shown. The purpose of the head box 15, of the forming mesh 16, of the return rollers 19a, 19b, 19c and of the various devices and auxiliary units (not shown) associated with the head box 15 and with the forming mesh 16 , is to form an "embryonic" web of paper fibers. For clarity, as used herein, reference is made to the frame 10, regardless of the stages of its processing, with the same number "10", for example, "embryonic" frame 10, "intermediate" frame 10, frame P948"presecada" 10, etc. The finished product, a paper web, is referred to by the number "50" (Figure 1). The embryonic web 10 is formed by the removal of a portion of an aqueous dispersion medium, using techniques well known in the art. Processes for forming embryonic frames are described in many references, such as, for example, U.S. Patent No. 3,301,764 issued to Sanford and Sisson on January 31, 1974, and U.S. Pat.

No. 3,994,771 issued to Morgan and Rich on November 30, 1976, both patents are incorporated herein by reference. After the embryonic web 10 is formed in the forming mesh 16, the web is transformed from the forming web 16 to a paper web 20 having an air permeability Ab of web. Conventional equipment, such as vacuum shoe 26a (Figure 1), can be used to achieve handover. A person skilled in the art will understand that the vacuum pick-up shoe 26a, shown schematically in Figure 1, is the preferred means for transferring the weft 10 of the forming mesh 16 to the paper-making web 20. Other equipment, as for example the intermediate band or the like (not shown) can be used for the purpose of P948 transferring the web 10 from the forming web 16 to the papermaking web 20. U.S. Patent 4,440,597 commonly assigned, issued April 3, 1984 to Wells is incorporated herein by reference. The preferred embodiment of the papermaking web 20 used in the process of the present invention is an endless band., fluid-permeable, macroscopically monoplanar, supported by a plurality of rollers, four of which, 29a, 29b, 29c, 29d, are schematically illustrated in Figure 1. The papermaking web 20 travels in the direction indicated by a directional arrow "B", as illustrated in Figure 1. However, the papermaking web 20 of the present invention can be incorporated in numerous other forms including, for example, stationary plates for use in sheetmaking of test, or rotating drums for use with other types of continuous process. Regardless of the physical form of the papermaking band 20, it generally has certain characteristics. As shown in Figures 1-3, the papermaking web, or simply the "tape" 20 has a side 21 in contact with the web and a back side 22 opposite the side 21 in contact with the web. As it should be clear from the definition, the side P948 21 in contact with the web makes contact and supports with it, the web 10 in the web 20. The back side 22 is in contact with the machinery used in the papermaking process, as for example with a shoe 26a of vacuum collection and a vacuum box 26b of multiple slots. The papermaking web 20 is permeable to air and permeable to the fluid in at least one direction, particularly the direction of the side 21 in contact with the web towards the back side 22. As used herein, the term " "fluid permeable" refers to the condition wherein a fluid carrier (including air) of a fibrous pulp can be transmitted through the web 20 without significant obstruction. However, it is not necessary, nor is it desired, that the entire surface area of the band 20 be permeable to the fluid. It is only necessary that the liquid carrier of the fibrous pulp be easily removed from the pulp leaving on the side 21 in contact with the web of the web 20, an embryonic web 10 of the paper fibers. Figures 2, 3 and 4 show cross-sectional fragments of the preferred band 20. As used herein, the general plane of the band 20 forms a plane X-Y, and a direction Z is a direction perpendicular to the plane X-Y. The band 20 shown in Figures 2 and 3 P948 comprises a frame 23 and a reinforcing structure 25 attached to the frame 23. The frame 23 has a surface 23a oriented towards the frame, a surface 23b facing the machine, and a plurality of deflection conduits 24 extending intermediate to the frame. surface 23a facing the weft and surface 23b oriented towards the machine. In a preferred embodiment, the frame 23 comprises a continuous pattern, and the plurality of deflection conduits 24 comprises a plurality of discrete orifices, or perforations, extending from the surface 23a facing the weft, towards the surface 23b facing the machine. This modality is exposed mainly in the patents of the United States assigned in common form and incorporated herein by reference, No. 4,528,239 granted on July 9, 1985 to Trokhan, 4,529,480 granted on July 16, 1985 to Trokhan; 4,637,859 issued on January 20, 1987 to Trokhan; 5,098,522 issued March 24, 1992 to Trokhan et al .; 5,275,700 granted on January 4, 1994 to Trokhan; 5,334,289 issued on August 2, 1994 to Trokhan; and 5,364,504 issued November 15, 1985 to Smurkoski et al. In another embodiment, the frame 23 comprises a pattern arrangement of protuberances extending from the surface 23a facing the frame, to the P948 surface 23b facing the machine, and the plurality of ducts 24 comprises an essentially continuous pattern surrounding the protuberances. In addition, the individual protrusions may also have holes or perforations, disposed therein and extending from the surface 23a facing the weft to the surface 23b facing the machine, of the frame 23. This embodiment of the strip for processing Paper is mainly disclosed in the commonly assigned United States Patent, which is incorporated herein by reference, No. 4,245,025 issued September 14, 1993 to Trokhan et al. and U.S. Patent 5,527,428 issued June 18, 1996 to Trokhan et al. The present invention can also be used with woven ribbons that do not have a frame, such as, for example, the band disclosed in the European Patent Application having the Publication Number: 0 677 612 A2, filed on 12.04.95; and the band in accordance with commonly assigned United States Patent 4,239,065, issued December 16, 1980 to Trokhan and incorporated herein by reference. As shown in Figures 2, 3 and 4, the surface 23a facing the web defines the side 21 in contact with the web of the web 20 for papermaking, and the surface 23b oriented towards the machine defines the side P948 back 22 of band 20 for papermaking. Therefore, it could also be said that the deflection ducts 24 extend intermediate between the side 21 in contact with the web of the web 20 and the back side 22 of the web 20. Preferably, the ducts 24 are arranged in a pre-selected pattern in the frame 23. More preferably, the pattern of the arrangement of the ducts 24 is repetitive and non-random. The deflection conduits, or simply "conduits" 24 channel the water of the fibers remaining on the surface 23a oriented towards the frame, of the frame 23 (or the side 21 in contact with the web of the band 20) towards the surface 23b oriented towards the machine, of the frame 23 (or the rear side 22 of the band 20) and provide areas where the fibers of the frame 10 can be deflected and rearranged to form domes 11 in the frame 10. As used herein, the term "dome" indicates an element of the weft 10 formed by the fibers deflected towards the individual deflection conduit 24. Of course, if the papermaking web 20 having an essentially continuous pattern of the plurality of conduits 24 is to be used, the domes 11 will also comprise an essentially continuous pattern. Domes 11 correspond in a general way, in geometry, and during the process for making paper in position, towards P948 Deflection Conduits 24. By forming towards the deflection conduits 24 during the papermaking process, the regions of the weft 10 comprising the domes 11 are deflected in the Z direction, thereby extending, essentially perpendicular to the plane of the frame 10 and thereby increasing a thickness, or gauge, of the frame 10. As defined herein, the direction Z is orothogonal to the general plane of the frame 10 and the band 20, as illustrated in FIG. Figures 2 and 3. The domes 24 protrude outwardly from the essentially continuous network of the weft 10. The surface 23a facing the weft of the frame 23 comprises a network of weft side formed therein and defining openings 24a of side of the weft of the ducts 24 of the strip 20 for papermaking. The machine-facing surface 23b of the frame 23 comprises a machine-side network formed therein and defining openings 24b on the machine side of the ducts 24 of the paper-making web 20. The paper having domes can be made by air-pass drying processes in accordance with commonly assigned United States Patents, No. 4,528,239; 4,529,480; 5,245,025; 5,364,504 and 5,275,700, cited above and incorporated herein by reference.

P948 U.S. Patent No. 5,628,876 commonly assigned, issued May 13, 1997 in the name of Ayer et al. , exhibits a semi-continuous pattern of the frame 23 that can also be used in the band 20 for the purposes of the present invention. The above patent is incorporated herein by reference. The reinforcing structure 25 of the preferred band 20 is attached to the frame 23 and is positioned between the surface 23a facing the frame and the surface 23b facing the machine, of the frame 23. The reinforcing structure 25 has a first side 25a and a second side 25b. The first side 25a of the reinforcing structure 25 corresponds to and is substantially parallel to the surface 23a oriented towards the frame, of the frame 23. The second side 25b corresponds to and is substantially parallel to the surface 23a oriented towards the machine, of the frame 23. As used herein and as shown in Figures 2 and 3, the portion of the frame 23 extending from the first side 25a of the reinforcing structure 25 is an "OB overload". More particularly, the OB overload is defined by the distance between the first side 25a of the reinforcing structure 25 and the surface facing the weft 23a, of the beater 23. Different modes of the papermaking web 20 may require the OB overload to be in the interval P948 between 1 thousand and approximately 250 mils. The reinforcement structure 25 can take any number of different forms. It may comprise a woven element, a nonwoven element, a mesh, a band or plate with a plurality of holes. Preferably, the reinforcing structure 25 of the band 10 comprises a woven element, and more particularly, a foraminous woven element. The reinforcing structure 25 may comprise a single layer structure. This type of reinforcing structure 25 is illustrated schematically in Figures 2 and 3. The reinforcing structure 25 may comprise a multiple layer structure. In the latter case, each layer may comprise a plurality of threads in the machine direction interwoven with a plurality of threads in the cross machine direction. U.S. Patent No. 5,496,624, issued March 5, 1996 to Stelljes et al. It is incorporated herein by reference to show an example of a reinforcement structure. Reinforcement structure 25 reinforces the frame 23. The reinforcing structure 25 has a suitable projected open area to allow draining of the machine used in the papermaking process of the present invention to adequately perform its function of removing water from the weft 10 and from P948 allowing the water removed from the web 10 to pass through the web 20. Therefore, the reinforcing structure 25 must be highly permeable to fluids, such as air and water. As used herein, by "highly permeable", it is understood that the reinforcing structure 25 has an air permeability of not less than about 200 cubic feet per minute (cfm) per square foot of its surface at a differential. pressure of 100 Paséales. Air permeability is measured using a Valmet permeability measuring device, Model Wigo Taifun Type 1000, available from Valmet Corp. of Pansio, Finland. A person skilled in the art will readily understand that the air permeability of the reinforcing structure 25 influences the resulting air permeability of the strip 20. The process of the present invention allows one to use the reinforcing structure 25 that the air permeability of more than 1000 cfm per square foot at a pressure difference of approximately 100 Paséales. Various embodiments of the preferred band 20 comprising the frame 23 and the reinforcing structure 25 are set forth in United States Patent No. 4,528,239 issued to Trokhan on July 9, 1985; U.S. Patent No. 4,637,859 issued to Trokhan on January 20, 1987; the Patent of the States P948 United No. 5,098,522 issued to Smurkoski et al. On March 24, 1992; U.S. Patent No. 5,245,025 issued to Trokhan et al on September 14, 1993; U.S. Patent No. 5,275,700 issued to Trokhan on January 4, 1994; U.S. Patent No. 5,334,289 issued to Trokhan et al. On August 2, 1994; U.S. Patent No. 5,364,504 issued to Smurkoski on November 15, 1994; and U.S. Patent No. 5,527,428 issued June 18, 1996 to Trokhan et al .; All patents are assigned in common form and are incorporated herein by reference. While in the present invention a woven element is preferred for the reinforcing structure 25 of the papermaking web 20, a papermaking web 20 can be made using a filter as a reinforcing structure, as set forth in U.S. Patent 5,556,509 issued September 17, 1996 to Trokhan et al. and patent applications: Series No. 08 / 391,372 filed on 2/15/95 in the name of Trokhan et al. and entitled: "Method of Applying to Curable Resin to a Substrate for Use in Papermaking"; Series No. 08 / 461,832 filed on 05/06/95 in the name of Trokhan et al. and entitled: "Web Patterning Apparatus Comprising a Felt Layer and a Photosensitive Resin Layer". This patent P948 and applications are assigned to Procter & Gamble Company and are incorporated here as a reference. According to the present invention, after the web 10 is transformed from the forming mesh 10 to the web 20 for paper making, the web 10 is coated with a flexible sheet of material 30, as shown in Figures 1 - 3. Preferably, the flexible sheet of material, or simply the "sheet" 30 is elastically resilient or elastically deformable. By the term "elastically deformable" is meant that the sheet 30 is capable of stretching under the pressure and proportionally thereto, - until approaching the geometry of the deflection ducts 24 and recovering their shape after the application of pressure interruptions. A preferred sheet 30 is the EXXTRAFLEX® film type "EXX 7 A-1" (having a thickness of approximately 1.5 mils) available from Exxon Chemical America's Film Division's plant, Lake Zurich, IL., Exxon Corporation (New Jersey Corporation), Flemington, NJ 08822. U.S. Pat. No. 5,518,801 issued May 21, 1996 to Chappell et al. and which is incorporated herein by reference, discloses a weft material exhibiting a rubbery behavior along at least one axis when subjected to an applied and subsequently released elongation. Alternatively, the sheet 30 is a P948 deformable non-resilient sheet, maintained loosely in a relationship close to the band 20, so that when the pressure is applied to the sheet 30, the sheet 30 is able to approximate the geometry of the deflection ducts 24 of the band 20. A person skilled in the art will understand that the elastically deformable sheet 30, held loosely in a "close relationship with the web 20 can also be used and still be preferred where feasible." Figure 1 shows the web 30 as a web endless supported by rollers 39a, 39b, 39c and traveling in a direction indicated by a directional arrow "C." While the sheet 30 is preferred in the form of an endless band, the sheet 30 may be incorporated into numerous other forms, such as plates for example, A person skilled in the art will also appreciate that when the endless sheet 30 is used in the process of the present invention, in order to maintain friction Sufficient between the sheet 30 and the rollers 39a, 39b, 39c it may be necessary to have the sheet 30 comprising practically non-resilient endless loops, or wheelbarrows (not shown), which have satisfactory tension characteristics. As best shown in Figures 2 and 3, when the web 10 is covered (or "covered") by the sheet of material 30, the web 10 is placed intermediate P948 between the sheet of material 30 and the band 20 for papermaking As shown in Figures 2 and 3, the sheet 30 has two sides, a first side 31 associated with the frame 10, and a second side 32 opposite the first side 31. Therefore, when the weft 10 is covered with the sheet 30, the weft 10 is placed between the first side 31 of the sheet 30 and the side 21 in contact with the weft (or the surface 23a facing the plot, of the frame 23) of the band 20 for the production of paper. In accordance with the present invention, the sheet 30 has an air permeability AS lower than the air permeability Ab of the belt, of the band 20 for papermaking. Preferably, the sheet 30 of the present invention is impermeable to air. By the term "impermeable to air" it is meant that, for all practical purposes, air can not pass through the sheet 30 without destroying the physical integrity of the sheet 30. After the screen 10 has been coated with the sheet 30, a fluid pressure differential of a suitable fluid is applied to the sheet 30. Of course, a person skilled in the art will readily understand that because the sheet 30 is at this point in close association with the ready frame 10 in band 20 for paper making, the pressure differential P948 of fluid is also applied to the weft 10 and to the web 20. As shown in Figure 1, a method for applying the fluid pressure differential is: arranging the weft 10 in association with the sheet 30 and the web 20 of such that the sheet 30 is exposed to the vacuum pressure through the ducts 24 by means of the vacuum application from the rear side 22 of the strip 20. In Figure 1, the directional arrows indicated by a "P" symbol. "show schematically the direction of application of the vacuum pressure effected by the vacuum box 26b of multiple slots. Preferably, a vacuum pressure of between about 15 and 25 inches (38.1 and 63.5 cm) of Mercury is applied to the vacuum box 26b of multiple slots. In the preferred embodiment of the present invention, the difference in fluid pressure will normally be a positive pressure (i.e., greater than atmospheric pressure) in the form of air pressure or current. The preferred fluid is air. Alternatively, or additionally, a negative pressure may be applied to the sheet 30 in the direction of the arrows "P" shown in Figure 1. The means for applying the preferred positive pressure are conventional and are in the sphere of knowledge of a person experienced in the art and, therefore, not shown in Figure 1.

P948 The application of the fluid pressure differential causes deflection of at least a portion of the sheet 30 towards the band 20. Because the sheet 30 is associated with the weft 10, the deflection of at least a portion of the weft 10 to the band 20 causes deflection of at least a portion of the weft 10 towards the band 20. Figures 2 and 3 show in greater detail, the effect of the application of the fluid pressure differential to the sheet 30 disposed in the band 20 for the production of preferred paper, comprising the reinforcing structure 25 and the resin frame 23 having the deflection conduits 24. In Figures 2 and 3, a pressure P2 associated with the second side 32 of the sheet 30 is greater than the pressure Pl associated with the first side 31 of the sheet 30. (In Figures 2 and 3, both the pressure Pl the pressure P2 are indicated schematically by the directional arrows). As indicated in the foregoing, the sheet 30 is preferably impermeable to air. Therefore, in the preferred embodiment of the present invention, the sheet 30 can be seen as a "barrier" dividing an area around it into two zones: a zone of the relatively high pressure P2 associated with the second side 32 of the sheet 30, and a zone of the relatively low pressure Pl associated with the first side 30. The resulting pressure P948 P = P2-Pl comprises the difference in fluid pressure. The fluid pressure differential causes the entire sheet 30 to generally press the web 10 in the web 20. In other words, the web 10 is "sandwiched" between the web 20 for paper processing and the web 20. sheet 30, with the sheet 30 printing the web 10 in the web 20 under the application of the fluid pressure differential P. In addition, at least a portion of the sheet 30 (mainly the regions corresponding to the conduits 24 of the band 20 in the Z direction) is deflected from the general plane of the sheet 30 towards the band 20 in the Z direction, as shown Figures 2, 3 and 4. Of course, the sheet 30 must have sufficient flexibility to be able to be partially deflected in the "Z direction under the application of the fluid pressure differential." Without being limited by theory, the applicant it believes that under the application of the fluid pressure differential, the sheet 30 prints the web 10 in the web 20, expels water from the web 10 through the conduits 24, causes the formation of the domes 11 in the web 10 and densifies the weft 10. Figures 2, 3 and 4 show that some portion of the fibers in the weft 10, and therefore the weft 10 itself, has been displaced towards the conduit 24 below P948 of the surface 23a oriented towards the frame, of the frame 23 (or the side 21 of the band 20, in contact with the weft) to form the dome 11. In air drying processes of the prior art, where the fibers are deflected towards the deflection conduits as a direct result of the movement of air caused by the action of the fluid pressure differential, the arrangement of the individual fibers in the weft and their significant displacement towards the conduits, can occur. the deflection, the fibers are comparatively free to be rearranged and migrate from the weft surface adjacent the web to the deflection conduits under the direct action of the through air, thereby creating a relative scarcity of the weft on the surface network and a relative superfluidity of the web within the deflection ducts.Therefore, the papers produced by air drying processes of the technique before They may have regions of a relatively low basis weight (ie, the weight of the fibers in the projected areas on the plane of the paper web of the network regions) and regions of relatively high weight (i.e. the fibers in the projected areas on the plane of the paper web of the dome regions). In addition, the density (weight per unit volume) of the network region of the prior art P948 produced by the drying by air passage can be high with respect to the density of the domes. In the process of the present invention, when the fibers of the weft 10 are deflected towards the ducts, the weft 10 is in direct contact with the sheet 30. The fibers in the weft 10 are not attached (or are subject to a degree much less extensive in the case of a non-preferred air-permeable sheet 30) to the direct action of the air passage. In contrast to air drying processes, the deflection of the fibers towards the ducts 24 occurs mainly under the deflection of the sheet 30. The deflection regions of the sheet 30, and not the air itself, prints the portions of the weft 10 corresponding to the conduits 24 in the conduits 24. Therefore, it is believed that, while some arrangements of the fibers in the weft 10 may occur even during the deflection, the migration of the fibers from the regions of The web of the weft side of the surface 23a oriented towards the web, towards the deflection conduits 24 is significantly diminished, if not completely eliminated, in comparison with the migration of the fibers from the network regions in the web of the web. drying by air passage. As a result, the paper sheet 50 produced by the process of the present invention has a more uniform low weight distribution P948 throughout the general plane of the weft 10 and a more uniform density distribution, with respect to the papers produced by processes assisted by differential high airflow pressure, of the prior art. Of course, it should be understood that if the non-preferred air permeable sheet 30 is used, some movement of the air through the air permeable sheet 30 may take place. In this case, a more significant migration of the fibers of the network regions of the surface 23a oriented towards the web can occur towards the conduits 24. Then, the paper web 50 will have a less uniform basis weight distribution in the whole plane general of the weft 10 and a less uniform density distribution, as compared to the paper web 10 produced by the process using the preferred air impermeable sheet 30. However, because the sheet 30 prints the weft 10 in the band 20, it is believed that even if some rearrangement of the fibers takes place in the event that the air permeable sheet 30 is used, it is still significantly inhibited. by the pressing force of the sheet 30 on the weft 10. Either at the moment when the fibers in the weft 10 are deflected towards the ducts 24 to form the domes 11, or after this deflection occurs, the water is removed of the plot 10. As discussed in P948 greater detail here in the above, in the processes assisted by high differential pressure of air flow of the prior art, the deflection of the fibers in the conduits, the removal of water from the weft, and the rearrangement of the fibers occur under the direct action of the air passing through the weft under the application of the fluid pressure differential. This sometimes leads to a number of undesirable consequences, for example, the separation of individual fibers, from the web 10, some of which can pass completely through the web 20 for papermaking (a phenomenon known as " porosity ") and consequently, clog the vacuum draining machinery. In contrast to the processes assisted by high pressure air flow difference of the prior art, the deflection of the fibers in the conduits 24 and the removal of water from the weft 10 occur, in accordance with the present invention, under the deflection of the flexible sheet 30, thus effectively eliminating the cause of the porosity of the weft 10 and the clogging of the vacuum draining machinery. Figure 2 shows a "deflection E", and Figure 3 shows a "maximum deflection E-max" of the sheet 30. As discussed above, while the sheet 30 completes pressing the frame 10 in the band 20 under the action of the fluid pressure differential, P948 mainly the regions of the sheet 30 which are associated with (or which correspond in a direction Z a) the deflection conduits 24 are "deflected" (or move in the Z direction) to a greater extent. As used herein, these regions are defined as "deflected" regions or portions of the sheet 30. The domes 11 of the frame 10 correspond, in general, in geometry and in position to the deflected regions of the sheet 30. The rest of the sheet 30 (a non-deflected portion) is an "undeflected" portion or region of the sheet 30. Essentially, each individual deflected region of the sheet 30 is encompassed by, and isolated from, the substantially flat portion. and without deflection of the sheet 30. Of course, when the above-described band 20 having the frame 23 comprised of the pattern array of protuberances and the plurality of conduits 34 comprised of essentially continuous pattern, the deflected regions of the sheet 30 is used. they comprise an essentially continuous pattern extending in the Z direction. As defined above, the Z direction (indicated in Figures 2 and 3 by a symbol "Z") is perpendicular to the general plane of the frame 10 and the band 20 and, therefore, to the general plane of the sheet 30, as illustrated in Figures 2 and 3. The term "deflection" ("maximum deflection") of the sheet 30 indicates a distance "E" in Figure 2.

P948 (distance "E-max" in Figure 3) to which the part of the sheet 30 is associated with the duct 26 that is displaced or pulled, in the Z direction under the action of the fluid pressure differential. In other words, "deflection" is measured by the distance Z direction between a point F displaced furthest in the Z direction on the first side 31 of the deflected portion of the sheet 30 and the remainder of the first side 31 of the portion generally not deflected and otherwise generally flat, of the sheet 30. As illustrated in Figures 2 and 3, the deflected portions of the sheet 30 can (Figure 3) or can not (Figure 2) deflect towards the conduits 24. By "deflection" to the ducts 24"it is understood that the point F further displaced in the Z direction of the first side 31 of the deflected part of the sheet 30 is located" below "the level of the surface 23a facing the frame, of the frame 23 (or the side 21 in contact with the frame) of the band 20, as shown in Figure 3. In contrast, Figure 2 shows that the point F moved further away in the Z direction on the first side 31 of the deflected part of the sheet 30 is located "above" the level of the surface 23a oriented towards the frame, of the frame 23 (or the side 21 in contact with the frame) of the band 20. The deflection P94E maximum E-max indicates the deflection necessary for the sheet 30 to deflate towards the conduits 24 in the Z direction. A person skilled in the art will appreciate that the flexibility, thickness and air permeability of the sheet 30, a specific design of the band 20, which includes the relative size and geometry of the ducts 24, but is not limited thereto. , and the amount of differential pressure applied to the sheet 30, are interrelated characteristics of the process of the present invention. While Figures 2 and 3 show the modalities of the strip 20 for paper making where the openings 24a of the side of the weft are larger than the corresponding openings 24b of the back side in at least one direction of the XY plane. Figure 4 shows the mode of the band 20 for papermaking where the side openings 24a are smaller than the corresponding rear side openings 24b, in at least one direction of the X-Y plane. This design of the papermaking web having a substantially continuous frame 23 and a plurality of deflection conduits 24 allows to create domes 11"of mushroom" in the paper web. As used herein, dome 11"of mushroom" is a dome 11 whose portion in a cross section is larger than a portion.

P948 adjacent to the weft surface 10 associated with the surface 23a facing the weft, of the frame 23. It is believed that the weft 10 having mushroom domes is softer in relation to the wefts produced under air-pass drying conditions. traditional, due to the ability to easily collapse fungus domes 11, compared with traditional domes 11. It is also believed that fungus dome 11 of the type shown in Figure 4, in combination with similar fungal domes corresponding to one against the other, they can be used successfully as means of restraint. In the latter case, mushroom domes 11 should be treated, preferably, (thermally, with a binding agent or some other form) to become stiffer. Synthetic fibers or filaments can be used for the purpose of forming a fastening means. United States patents commonly assigned, No. 5,058,247 issued October 22, 1991 to Thomas et al .; 5,116,563 issued May 26, 1992 to Thomas et al .; 5,230,851 granted on July 27, 1993 to Thomas et al .; 5,540,673 issued July 30, 1996 to Thomas et al .; 5,565,255 issued on October 15, 1996 to Young et al., are incorporated herein by reference. A person skilled in the art will readily understand that the properties of the sheet 30, as P948 thickness and flexibility have a great influence on the amount of flow pressure difference necessary to achieve a required deflection of the sheet 30 for a certain papermaking band 20. For a given sheet 30, the geometry of the web for papermaking and the screen gauge, the difference in fluid pressure must be sufficient to achieve the maximum desired E-max deflection of the sheet 30. In the case of where the non-preferred air-permeable sheet 30 is used, the relative air permeability of the sheet 30 and the band 20, or the Ab / As ratio, is one of the defining characteristics of the day deflection degree of the sheet 30 towards the band 20. When air permeable sheet 30 is used, the preferred Ab / As ratio is greater than about 2.0. The most preferred ratio Ab / As is greater than about 10.0. The most preferred Ab / As ratio is greater than about 20.0. Referring now to Figure 1, at some point in the process, the sheet 30 is removed from over the weft 10. Preferably, the sheet 30 is not removed before the deflection process of the fibers towards the conduits 24 and the water withdrawal from plot 10 is practically finished. The deflection process of the fibers towards the ducts 24 and the withdrawal of the water from the P948 frame 10 is considered practically finished when a consistency of at least 25% of frame 10 is achieved. Optionally, the process of the present invention may include a step of pre-screening the web 10. Any convenient means conventionally known in the papermaking art can be used to pre-screen the web 10. For example, flow-through driers, non-thermal capillary drainage devices, and Yankee dryers, together and in combination, can be used satisfactorily to dry the weft 10. Figure 1 'shows the optional pre-dryer 27. As noted above, the sheet 30 is removed, preferably before start predrying step, especially if a team flow passage for the pre-drying step is used. The amount of water removed in predryer 27 is controlled so that the frame 10 exiting predryer 27 has a _del consistency of from about 30% to about 98%. The pre-dried web 10, which is still associated with the web 20, passes around the return roller 29c and travels in the direction indicated by the directional arrow "B" towards the print roller 29b. An optional step for printing the web of the weft side of the surface 23a facing the weft, in the weft 10, can be carried out by interposing the P948 frame 10 between the web 20 (with which the web 10 is still associated) and a rigid surface 40a of the Yankee dryer 40. As illustrated in Figure 1, the web 10 in association with the web 20 passes through the nip formed between the printing roller 29b and the Yankee drying drum 40. The next step of the process of the present invention is to dry the weft 10. If the optional step of printing the weft 10 is carried out, the weft 10 is separated from the web 20. for papermaking after the web of the weft side of the surface 23a facing the weft has been printed on the weft 10. While the weft 10 is separated from the web 20, weft 10 adheres to the surface 40a of the Yankee dryer drum 40 where the weft 10 is dried to a consistency of at least about 90%. After the drying step, the optional step of shortening the drying web 10 can be used in the process of the present invention. The shortening is a shortening in length of a dry paper web that occurs when energy is applied to the dry web in such a way that the length of the web is reduced and the fibers in the web are rearranged with an accompanying break in the web. some fiber-fiber joints. The reduction can be effected in any of the well known ways. He P948 most common, and preferred, method of reduction is the acrespado. In the accreting operation, the dry weft 10 adheres to a surface and is then removed from that surface with a doctor blade 45. As shown in Figure 1, the surface to which the weft 10 normally adheres also works "as a drying surface Typically, this surface is the surface 40a of a Yankee dryer drum 40, as shown in Figure 1. The adhesion of the optionally printed web 10 to the Yankee dryer drum surface 40 is facilitated by of the use of a tackifying adhesive Typical tackifying adhesives may include any suitable glue, such as, for example, those based on polyvinyl alcohol Specific examples of suitable adhesives are described in US Patent No. 3,926,716 issued to Bates. on December 16, 1975, incorporated herein by reference. the adhesive is applied either to web 10 immediately before its passage through the nip described above, or more preferably to the surface of Yankee dryer drum 40 prior to the point at which the weft against the surface of Yankee dryer drum 40 by the platen roller 29b is pressed. The particular means of P948 glue application and the technique to apply the glue used in the practice of the present invention are conventional, and therefore, are not shown in Figure 1. Any technique for applying the accrete adhesives, known to those skilled in the art, such as spraying, can be used. Generally, only the non-deflected portions of the weft 10 that have been associated with web of the weft side of the surface 23a facing the weft, of the web 10 for papermaking, are adhered directly to the surface of the web. Yankee dryer drum 40. The paper web 10 produced by the process of the present invention can optionally be calendered and re-rolled either with or without differential speed winding or cut and stored all by conventional means which are not illustrated in Figure 1. The paper web 10 is then ready to be used. To increase the feeling of softness to the touch of the paper web 50 produced by means of the process of the present invention, chemical softeners may be added to the web 10, as one skilled in the art will readily recognize. Suitable chemical softeners may be added, in accordance with the teachings of commonly assigned United States Patents, No. 5,217,576, issued on June 8, 1993 to P948 Phan and No. 5,262,007 issued on November 16, 1993 to Phan et al., The disclosures of these patents are incorporated herein by reference. Additionally, silicone may be applied to the paper, in accordance with the present invention, as shown by commonly assigned United States Patents, No. 5,215,626 issued June 1, 1993 to Ampulski et al. , and No. 5,389,204 granted on February 14, 1995 to Ampulski; The disclosures of these patents are incorporated herein by reference.

P948

Claims (10)

1. CLAIMS. 1. A process for making a sheet of paper, the process comprises the steps of: (a) providing an aqueous dispersion of paper fibers; (b) forming a web of the paper fibers from the aqueous dispersion in a forming mesh; (c) transferring the web from the forming mesh to a web for making paper having one side in contact with the web and a back side opposite to the side in contact with the web, the web for paper making has a permeability of Ab airband, preferably greater than about 200 cubic feet per minute per square foot of its surface at a pressure differential of 100 Passes; (d) provide a flexible sheet of material having a first side and a second side opposite the first side, the sheet of material has a sheet permeability to air A less than air band permeability Ab, (e) cover the weft with the sheet of material, which preferably comprises an elastically deformable sheet, so that the weft is arranged intermediate between the first side of the sheet of material and the side in contact with the weft of the band for the P948 paper processing; (f) applying a fluid pressure differential to the sheet of material so that a pressure P2 associated with the second side of the sheet of material is greater than a pressure Pl associated with the first side of the sheet of material, thereby causing the deflection of at least a portion of the sheet of material towards the papermaking web and the removal of water from the web through the papermaking web; (g) removing the sheet of material from the weft; and (h) drying the web to form the sheet of paper.
2. 2. The process according to claim 1, wherein the papermaking web comprises: a frame having a surface facing the weft defining the side in contact with the weft of the papermaking web, a surface machine-oriented defining the back side of the papermaking web, and a plurality of deflection conduits extending intermediate between the surface facing the weft and the surface facing the machine, the surface facing the weft has a network of side of the frame formed therein and defining openings of side of the frame of the P948 ducts and the machine-facing surface have a machine-side network formed therein that defines machine-side openings in the ducts, and a reinforcing structure attached to the frame and placed between the surface facing the machine. raster and the machine-oriented surface of the frame, the reinforcing structure has a first side corresponding to the surface of the frame facing the frame, and a second side corresponding to the surface of the frame facing the machine, the structure of The reinforcement preferably has an air permeability of more than about 1000 cubic feet per minute per square foot of its surface at a pressure differential of 100 Pases, the surface of the frame facing the weft and the first side of the structure of the frame. reinforcement define an overload between them.
3. The process according to claims 1 and 2, wherein the deflection of at least the portion of the sheet of material causes a deflection of at least a portion of the paper fibers in the weft towards the deflection conduits and the removal of water of the plot through the conduits.
4. 4. The process according to claims 1, 2 and 3, wherein the sheet of material has the permeability to P948 sheet air As less than about 25 standard cubic feet per minute at a pressure differential of 100 Pascals, and preferably, the sheet material is air impermeable.
5. 5. The process according to claims 1, 2, 3 and 4, wherein portions of the sheet of material are deflected towards the deflection conduits of the papermaking web to form a maximum deflection, the maximum deflection is preferably greater than about 25% of the overload of the band for the production of paper.
6. The process according to claims 1, 2, 3, 4 and 5, comprising an additional step of pre-screening the web in association with the web for papermaking to a consistency of from about 30% to about 95%, Preferably, an additional stage of preseping the frame is carried out before step (g).
7. The process according to claims 1, 2, 3, 4, 5 and 6, comprising a further step of printing on the web the side network of the weft facing the weft, interposing the web between the web for papermaking and a rigid surface before step (h), the rigid surface preferably comprises a Yankee drying drum.
8. 8. The process according to claims 1, 2, 3, 4, 5, 6 and 7 further comprising a step of shortening the frame, the shortening step comprises the accretion.
9. 9. The process according to claims 1, 2, 3, 4, 5, 6 and 7, wherein the fluid pressure differential comprises a positive pressure. 10. "The process according to claims 1, 2, 3, 4, 5, 6, 7 and 8, wherein the fluid pressure differential comprises a negative pressure. P948