EP1294982B1 - Procede de fabrication de papier tissu - Google Patents

Procede de fabrication de papier tissu Download PDF

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Publication number
EP1294982B1
EP1294982B1 EP01946608A EP01946608A EP1294982B1 EP 1294982 B1 EP1294982 B1 EP 1294982B1 EP 01946608 A EP01946608 A EP 01946608A EP 01946608 A EP01946608 A EP 01946608A EP 1294982 B1 EP1294982 B1 EP 1294982B1
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EP
European Patent Office
Prior art keywords
wet web
fabric
web
drying cylinder
wet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP01946608A
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German (de)
English (en)
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EP1294982A2 (fr
Inventor
Michael Alan Hermans
Frank Stephen Hada
Steven Jack Hickey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kimberly Clark Worldwide Inc
Kimberly Clark Corp
Original Assignee
Kimberly Clark Worldwide Inc
Kimberly Clark Corp
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Filing date
Publication date
Priority claimed from US09/607,711 external-priority patent/US6497789B1/en
Priority claimed from US09/607,712 external-priority patent/US6454904B1/en
Application filed by Kimberly Clark Worldwide Inc, Kimberly Clark Corp filed Critical Kimberly Clark Worldwide Inc
Publication of EP1294982A2 publication Critical patent/EP1294982A2/fr
Application granted granted Critical
Publication of EP1294982B1 publication Critical patent/EP1294982B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
    • D21F11/14—Making cellulose wadding, filter or blotting paper
    • D21F11/145—Making cellulose wadding, filter or blotting paper including a through-drying process
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • D21F1/48—Suction apparatus
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • D21F1/48—Suction apparatus
    • D21F1/52—Suction boxes without rolls
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
    • D21F11/14—Making cellulose wadding, filter or blotting paper

Definitions

  • the present invention relates generally to methods for making paper products. More particularly, the invention concerns methods for making cellulosic webs having high bulk and absorbency on a modified conventional wet-pressed machine.
  • the newly-formed wet web is typically transferred onto a papermaking felt and thereafter pressed against the surface of a steam-heated Yankee dryer while it is still supported by the felt.
  • a steam-heated Yankee dryer As the web is transferred to the surface of the Yankee dryer, water is expressed from the web and is absorbed by the felt.
  • the dewatered web typically having a consistency of about 40 percent, is then dried while on the hot surface of the Yankee dryer. The web is then creped to soften it and provide stretch to the resulting tissue sheet.
  • a disadvantage of wet pressing is that the pressing step densities the web, thereby decreasing the bulk and absorbency of the tissue sheet. The subsequent creping step only partially restores these desirable sheet properties.
  • the newly-formed web is first dewatered using vacuum and then transferred to a relatively porous fabric and non-compressively dried by passing hot air through the web.
  • the resulting web can then be transferred to a Yankee dryer for creping. Because the web is substantially dry when transferred to the Yankee dryer, the density of the web is not significantly increased by the transfer. Also, the density of a throughdried sheet is relatively low by nature because the web is dried while supported on the throughdrying fabric.
  • the disadvantages of the throughdrying method are the relatively high operational energy costs and the capital costs associated with the throughdryers.
  • jets of air for dewatering the web are not per se effective in terms of water removal or energy efficiency. Blowing air on the sheet for drying is well known in the art and used in the hoods of Yankee dryers for convective drying. In a Yankee dryer hood, however, the vast majority of the air from the jets does not penetrate the web. Thus, if not heated to high temperatures, most of the air would be wasted and not effectively used to remove water. In Yankee dryer hoods, the air is heated to as high as 900 degrees Fahrenheit (482°C) and high residence times are allowed in order to effectuate drying.
  • wet-pressed tissue can be made having bulk and absorbency properties equivalent to those of comparable throughdried products, while maintaining reasonable machine productivity.
  • the present invention provides a method for making a cellulosic web as claimed in claims 1 and 38. More particularly, wet-pressed cellulosic webs can be made by vacuum dewatering a wet web up to approximately 30 percent consistency, then using an integrally sealed air press to noncompressively dewater the sheet to 30 to 40 percent consistency.
  • the wet web is desirably then transferred to a "molding" fabric substituted for the conventional wet-pressing felt in order to impart more contour or three-dimensionality to the wet web.
  • the wet web is preferably thereafter pressed against the Yankee dryer while supported by the molding fabric and dried.
  • the resulting product has exceptional wet bulk and absorbency exceeding that of conventional wet-pressed towels and tissue and equal to that of presently available throughdried products.
  • noncompressive dewatering and “noncompressive drying” refer to dewatering or drying methods, respectively, for removing water from cellulosic webs that do not involve compressive nips or other steps causing significant densification or compression of a portion of the web during the drying or dewatering process.
  • wet-molded tissue sheets are those which are conformed to the surface contour of a molding fabric while at a consistency of about 30 to about 40 percent and then dried by thermal conductive drying means, such as a heated drying cylinder, as opposed to other drying means such as a throughdryer, before optional additional drying means.
  • the "molding fabrics" suitable for purposes of this invention include, without limitation, those papermaking fabrics which exhibit significant open area or three-dimensional surface contour sufficient to impart greater z-directional deflection of the web. Such fabrics include single-layer, multi-layer, or composite permeable structures. Preferred fabrics have at least some of the following characteristics: (1) On the side of the molding fabric that is in contact with the wet web (the top side), the number of machine direction (MD) strands per inch (mesh) is from 10 to 200 (3.94 to 78.74 per centimeter) and the number of cross-machine direction (CD) strands per inch (count) is also from 10 to 200 (3.94 to 78.74 per centimeter).
  • MD machine direction
  • CD cross-machine direction
  • the strand diameter is typically smaller than 0.050 inch (1.27 mm); (2) On the top side, the distance between the highest point of the MD knuckle and the highest point of the CD knuckle is from about 0.001 to about 0.02 or 0.03 inch (0.025 mm to about 0.508 mm or 0.762 mm).
  • the fabric In between these two levels, there can be knuckles formed either by MD or CD strands that give the topography a 3-dimensional hill/valley appearance which is imparted to the sheet during the wet molding step; (3) On the top side, the length of the MD knuckles is equal to or longer than the length of the CD knuckles; (4) If the fabric is made in a multi-layer construction, it is preferred that the bottom layer is of a finer mesh than the top layer so as to control the depth of web penetration and to maximize fiber retention; and, (5) The fabric may be made to show certain geometric patterns that are pleasing to the eye, which typically repeat between every 2 to 50 warp yarns.
  • the invention resides in a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; b) dewatering the wet web to a consistency of about 10 percent to about 30 percent; c) transferring the wet web to an endless second fabric; d) sandwiching the wet web between the second fabric and a support fabric and dewatering the wet web to a consistency of greater than 30 percent using a noncompressive dewatering device that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the web due to an integral seal formed with the wet web; (e) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially dry the wet web; and, (f) drying the dewatered wet web to a final dryness.
  • a noncompressive dewatering device that is adapted to cause a press
  • the invention resides in a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web wherein the wet web; (b) transferring the wet web to an endless second fabric; (c) sandwiching the wet web between the second fabric and a support fabric and dewatering the wet web to a consistency of up to about 30 percent; (d), supplementally dewatering the wet web to a consistency of about 30 to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the web due to an integral seal formed between an air plenum and a collection device; (e) configuring the second fabric to provide an unsupported sheet wrap angle of the dewatered wet web about a pressure roll of less than 90 degrees; (f) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially
  • the invention resides in a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; (b) dewatering the wet web to a consistency of up to about 10 percent; (c) transferring the wet web to an endless second fabric; (d) sandwiching the wet web between the second fabric and a support fabric; e) passing the wet web sandwiched between the second fabric and the support fabric between an air plenum and a collection device with the second fabric disposed between the wet web and the collection device, the air plenum and collection device being operatively associated and adapted to create a pressure differential across the wet web of about 30 inches of mercury (101.6 kPa) or greater and a stream of pressurized fluid through the wet web of about 10 standard cubic feet per minute per square inch (43.9 ⁇ 10 3 cm 3 /min/cm 2 ) or greater f) dewatering the wet web using the stream
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; (b) dewatering the wet web to a consistency to about 10 to about 30 percent; (c) transferring the wet web to an endless second fabric; (d) sandwiching the wet web between the second fabric and a support fabric and dewatering the wet web to a consistency of greater than about 30 percent using a non-compressive dewatering device that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed with the wet web; (e) transferring the wet web back to the second fabric; (f) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially dry the wet web; and, (g) drying the wet web to a final dryness.
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; (b) transferring the wet web to an endless second fabric; (c) sandwiching the wet web between the second fabric and a support -fabric and dewatering the wet web to a consistency to about 30 percent ; (d) further dewatering the wet web to a consistency of greater than about 30 percent to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed between an air plenum and a collection device; (e) transferring the wet web back to the second fabric such that the sheet wrap of the wet web on the pressure roll is less than 90 °; (f) pressing the dewatered wet web against the surface of a heated drying cylinder to at
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; (b) dewatering the wet web to a consistency of about 10 percent to about 30 percent; (c) transferring the wet web to another fabric; (d) sandwiching the wet web between the second fabric and a support fabric, one of which utilizes the space and components formerly used in the bottom felt run of a tow press wet press machine; (e) dewatering the wet web to a consistency of greater than about 30 percent to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the web due to an integral seal formed between an air plenum and a collection device; (f) transferring the wet Web back to the second fabric; (g) pressing the dewatered and wet web against the surface of
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web to make a wet web; (b) transferring the wet web to an endless second fabric; (c) sandwiching the wet web between the second fabric and a support fabric and dewatering the wet web to a consistency of about 10 percent to about 30 percent; (d) further dewatering the wet web to a consistency of greater than about 30 percent to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the web due to an integral seal formed between an air plenum and a collection device; (e) transferring the wet web back to the second fabric to give the web a bulk of about 8 cubic centimeter per gram or greater; (f) pressing the dewatered web against the surface of a heated drying cylinder
  • the present invention provides a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless first fabric to form a wet web; (b) transferring the wet web to an endless second fabric; (c) sandwiching the web between the second fabric and a support fabric; (d) passing the second and support fabrics with the wet web sandwiched therewithin between an air plenum and a collection device with the second fabric disposed between the wet web and the collection device, the air plenum and the collection device being operatively associated and adapted to create a pressure differential across the wet web of about 30 inches of mercury or greater (101.6 kPa) and a stream of pressurized fluid through the wet web of about 10 standard cubic feet per minute per square inch (43.9 ⁇ 10 3 cm 3 /min/cm 2 ) or greater; (e) dewatering the wet web using the stream of pressurized fluid to a consistency of about 30 percent or greater; (e) pressing the
  • another embodiment of the present invention resides in a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web wherein the wet web is sandwiched between the first and second fabrics; (b) dewatering the wet web to a consistency of about 30 percent or greater using a noncompressive dewatering device that is adapted to cause a pressurized fluid at about 5 pounds per square inch gauge (34.5 kPa gauge) or greater to flow substantially through the web due to an integral seal formed with the wet web; (c) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially dry the dewatered wet web; and, (d) drying the dewatered wet web to a final dryness.
  • a noncompressive dewatering device that is adapted to cause a pressurized fluid at about 5 pounds per square inch gauge (34.5 kPa gauge) or greater to flow
  • the invention resides in a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web wherein the wet web is sandwiched between the first and second fabrics; (b) dewatering the wet web to a consistency of about 10 to about 30 percent; (c) supplementally dewatering the wet web to a consistency of about 30 to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed between an air plenum and a collection device to give the dewatered wet web a bulk of about 8 cubic centimeter, per gram or greater; (d) pressing the dewatered wet web against the surface of a heated drying cylinder with a fabric to preserve the bulk of about 8 cubic centimeter per gram or greater, and, (e) drying
  • the present invention provides a method for making a cellulosic web, comprising: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web wherein the wet web is sandwiched between the first and second fabrics; (b) passing the wet web sandwiched between the first and second fabrics between an air plenum and a collection device with the second fabric disposed between the wet web and the collection device, the air plenum and collection device being operatively associated and adapted to create a pressure differential across the wet web of about 30 inches of mercury (101.6 kPa) or greater and a stream of pressurized fluid through the wet web of about 10 standard cubic feet per minute per square inch (43.9 ⁇ 10 3 cm 3 /min/cm 2 ) or greater, c) dewatering the wet web using the stream of pressurized fluid to a consistency of about 30 percent or greater, (d) pressing the dewatered wet web against the surface of a heated drying cylinder with
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web; (b) dewatering the wet web to a consistency to about 10 percent or greater using a combination of centrifugal force and fabric tension around the forming roll; (c) using a non-compressive dewatering device that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed with the wet web; (d) transferring the wet web back to or retaining on the second fabric; (e) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially dry the wet web; and, (f) drying the wet web to a final dryness.
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web; (b) dewatering the wet web to a consistency to about 10 percent or greater using a combination of centrifugal force and fabric tension around a forming roll; (c) further dewatering the wet web to a consistency of 10 to about 30 percent; (d) supplementally dewatering the wet web to a consistency of about 30 to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed between an air plenum and a collection device; (e) transferring the wet web back to or retaining on the second fabric; (f) pressing the dewatered wet web against the surface of a heated drying cylinder to at least partially dry the we
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web; (b) dewatering the wet web to a consistency of about 10 to about 30 percent; (c) supplementally dewatering the web to a consistency of about 30 to about 40 percent using an air press that is adapted to cause a pressurized fluid at about 5 pounds per square inch (34.5 kPa) gauge or greater to flow substantially through the wet web due to an integral seal formed between an air plenum and a collection device; (d) transferring the wet web back to or retaining on the second fabric to give the wet web a bulk of about 8 cubic centimeter per gram or greater; (e) pressing the dewatered wet web against the surface of a heated drying cylinder with a fabric to preserve the bulk of about 8 cubic centimeter per gram or greater; and, (f) drying the
  • the invention resides in a method for making a cellulosic web, comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers between an endless first fabric and an endless second fabric to form a wet web wherein at least one of the endless fabrics is a three-dimensional molding fabric; (b) passing the first and second fabrics with the wet web sandwiched therewithin between an air plenum and a collection device with the three dimensional molding fabric disposed between the wet web and the collection device, the air plenum and the collection device being operatively associated and adapted to create a pressure differential across the wet web of about 30 inches of mercury (101.6 kPa) or greater and a stream of pressurized fluid through the wet web of about 10 standard cubic feet per minute per square inch (43.9 ⁇ 10 3 cm 3 /min/cm 2 ) or greater; (d) dewatering the wet web using the stream of pressurized fluid to a consistency of about 30 percent or greater, (e) pressing the dewater
  • first fabric is used herein to refer to any fabric used in tissue making as described herein or known in the art, including, but not limited to, forming, molding, and other support fabrics used in making tissue.
  • first fabric is preferably a forming fabric.
  • second fabric is used herein to refer to any fabric used in tissue making as described herein or known in the art, including, but not limited to, forming, molding, and other support fabrics used in making tissue.
  • the second fabric is preferably a molding fabric as described herein. Where the second fabric is a molding fabric, the resulting web is a molded web.
  • support fabric is used herein to refer to any fabric used in tissue making as described herein or known ,in the art, including, but not limited to, forming, molding, or any other fabric used in making tissue.
  • integral seal and "integrally sealed” are used herein to refer to: the relationship between the air plenum and the wet web where the air plenum is operatively associated and in indirect contact with the web such that about 85 percent or greater of the air fed to the air plenum flows through the web when the air plenum is operated at a pressure differential across the web of about 30 inches of mercury (101.6 kPa) or greater, and the relationship between the air plenum and the collection device where the air plenum is operatively associated and in indirect contact with the web and the collection device such that about 85 percent or greater of the air fed to the air plenum flows through the web into the collection device when the air plenum and collection device are operated at a pressure differential across the web of about 30 inches of mercury (101.6 kPa) or greater.
  • the air press is able to dewater the wet web to very high consistencies due In large part to the high pressure differential established across the web and the resulting air flow through the web.
  • the air press can increase the consistency of the wet web by about 3 percent or greater, particularly about 5 percent or greater, such as from about 5 to about 20 percent, more particularly about 7 percent or greater, and more particularly still about 7 percent or greater; such as from about 7 to 20 percent.
  • the consistency of the wet web upon exiting the air press is about 30 percent or greater, particularly about 31 percent or greater, more particularly about 32 percent or greater, such as from about 32 to about 42 percent, more particularly about 33 percent or greater, even more particularly about 34 percent or greater, such as from about 34 to about 42 percent, and still more particularly about 35 percent or greater.
  • the term "textured" or "three-dimensional” as applied to the surface of a fabric, felt, or uncalendered paper web indicates that the surface is not substantially smooth and coplanar. Additionally, the present machine configuration is amenable to incorporating a rush transfer step, which again results in a significant increase in bulk and absorbency relative to the existing wet pressing processes.
  • Optional steam showers or the like may be employed before the air press to increase the post air press consistency and/or to modify the cross-machine direction moisture profile of the web. Furthermore, higher consistencies may be achieved when machine speeds are relatively low and the dwell time in the air press is relatively high.
  • the pressure differential across the wet web provided by the air press is about 30 inches of mercury (101.6 kPa) or greater, such as up to about 120 inches of mercury (406.4 kPa), particularly about 35 inches of mercury (118.5 kPa) or greater, such as from about 35 to about 60 inches of mercury (118.5 kPa to 203.2 kPa), and more particularly from about 40 to about 50 inches of mercury (135.5 kPa to 169.3 kPa).
  • an air plenum of the air press maintaining a fluid pressure on one side of the wet web of greater than 0 to about 60 pounds per square inch gauge (psig), i.e 101 kPa to 515 kPa, particularly greater than 0 to about 30 psig (101 kPa to 308 kPa), more particularly about 5 psig (13.6 kPa) or greater, such as about 5 to about 30 psig (136 kPa to 308 kPa), and more particularly still from about 5 to about 20 psig (136 kPa to 239 kPa).
  • psig pounds per square inch gauge
  • the collection device of the air press desirably functions as a vacuum box operating at 0 to about 29 inches of mercury (0 to 98 kPa) vacuum, particularly 0 to about 25 inches of mercury (0 to 85 kPa) vacuum, particularly greater than 0 to about 25 inches of mercury (0 to 85 kPa) vacuum, and more particularly from about 10 to about 20 inches of mercury (34 to 68 kPa) vacuum, such as about 15 inches of mercury (51 kPa) vacuum.
  • the collection device of the air press may operate at 30 inches of mercury (102 kPa) vacuum or greater.
  • the collection device desirably but not necessarily forms an integral seal with the air plenum and draws a vacuum to facilitate its function as a collection device for air and liquid. Both pressure levels within both the air plenum and the collection device are desirably monitored and controlled to predetermined levels.
  • the pressurized fluid used in the air press is sealed from ambient air to create a substantial air flow through the web, which results in the tremendous dewatering capability of the air press.
  • the flow of pressurized fluid through the air press is suitably from about 10 to about 500 standard cubic feet per minute (SCFM) per square inch of open area (43.9 ⁇ 10 3 to 2194.6 ⁇ 10 3 cm 3 /min/cm 2 ), particularly about 10 SCFM per square inch of open area (43.9 ⁇ 10 3 cm 3 /min/cm 2 ) or greater such as from about 10 to about 200 SCFM per square inch of open area (43.9 ⁇ 10 3 to 877.8 ⁇ 10 3 cm 3 /min/cm 2 ), and more particularly about 40 SCFM per square inch of open area (175.6 ⁇ 10 3 cm 3 /min/cm 2 ) or greater, such as from about 40 to about 120 SCFM per square inch of open area (175.6 ⁇ 10 3 to 526.7 ⁇ 10 3 cm 3 /min/cm 2 ).
  • SCFM standard cubic feet
  • air and pressurized fluid are used interchangeably herein to refer to any gaseous substance used in the air press to dewater the wet web.
  • the gaseous substance suitably comprises air, steam or the like.
  • the pressurized fluid comprises air at ambient temperature, or air heated only by the process of pressurization to a temperature of about 300 °F (149°C) or less, more particularly about 150 °F (66°C) or less.
  • the wet web is desirably attached to the Yankee dryer or other heated drying cylinder surface in a manner that preserves a substantial portion of the texture imparted by previous treatments, especially the texture imparted by molding on three-dimensional fabrics.
  • the conventional manner used to produce wet-pressed creped paper is inadequate for this purpose, for in that method, a pressure roll is used to dewater the wet web and to uniformly press the wet web into a dense, flat state.
  • the conventional substantially smooth press felt is replaced with a textured material such as a foraminous fabric and desirably a throughdrying fabric.
  • the conventional substantially smooth press felt of the conventional crescent-former tissue machine is replaced with a textured material such as a foraminous fabric and desirably a throughdrying fabric.
  • Tissue webs made according to the present method desirably have a bulk after being molded onto the three-dimensional fabric of about 8 cubic centimeters per gram (6c/g) or greater, particularly about 10 cc/g or greater, and more particularly about 12 cc/g or greater, and that bulk is maintained after being pressed onto the heated drying cylinder using the textured foraminous fabric.
  • the zone of maximum load applied to the web should be about 400 psi (2758 kPa) or less, particularly about 350 psi (2413 kPa) or less, more particularly about 150 psi (1034 kPa) or less, such as between about 2 and about 50 psi (13.8 kPa to 344.7 kPa), and most particularly about 30 psi (206.8 kPa) or less, when averaged across any one-inch square region encompassing the point of maximum pressure.
  • the pressing pressures measured in pounds per lineal inch (pli) at the point of maximum pressure are desirably about 400 pli (181 kg per lineal 2.5 cm) or less, and particularly about 350 pli (159 kg per lineal 2.5 cm) or less.
  • Low-pressure application of a three-dimensional web structure onto a heated drying cylinder helps to maintain substantially uniform density in the dried web. Substantially uniform density is promoted by effectively dewatering the web with noncompressive means prior to the Yankee dryer attachment, and by selecting a foraminous fabric to contact the web against the dryer that is relatively free of high, inflexible protrusions that could apply high local pressure to the web.
  • the fabric is desirably treated with an effective amount of a fabric release agent to promote detachment of the web from the fabric once the web contacts the dryer surface.
  • the absorbency of a tissue sheet may be characterized by its Absorbent Capacity and its Absorbent Rate.
  • Absorbent Capacity is the maximum amount of distilled water which a sheet can absorb, expressed as grams of water per gram of sample sheet. More specifically, the Absorbent Capacity of a sample sheet can be measured by cutting a 4 inch by 4 inch (101.6 by 101.6 mm) sample of the dry sheet and weighing it to the nearest 0.01 gram. The sample is dropped onto the surface of a room temperature distilled water bath and left in the bath for 3 minutes. The sample is then removed using tongs or tweezers and suspended vertically using a 3-prong clamp to drain excess water. Each sample is allowed to drain for 3 minutes.
  • the sample is then placed in a weighing dish by holding the weighing dish under the sample and releasing the clamp.
  • the wet sample is weighed to the nearest 0.01 gram.
  • the Absorbent Capacity is the wet weight of the sample minus the dry weight (the amount of water absorbed), divided by the dry weight of the sample. At least five representative samples of each product should be tested and the results averaged.
  • the "Absorbent Rate” is the time it takes for a product to become thoroughly wetted out in distilled water. It is determined by dropping a pad comprised of twenty sheets, each measuring 2.5 inches by 2.5 inches (63.5 by 63.5 mm), onto the surface of a distilled water bath having a temperature of 30 °C. The elapsed time, in seconds, from the moment the sample hits the water until it is completely wetted (as determined visually) is the Absorbent Rate.
  • tissue or tissue products
  • cellulosic web is used to broadly refer to webs comprising or consisting of cellulosic fibers regardless of the finished product structure.
  • Fiber types may be used for the present invention including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like.
  • All known papermaking fibers may be used, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulosic fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers) or synthetic fibers (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulping processes), thermomechanically pulped, chemithermomechanically pulped, and the like.
  • mechanically pulped e.g., groundwood
  • the mixtures of any subset of the above mentioned or related fiber classes may be used.
  • the fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties, such as disclosed in U.S. Patents 5,348,620 issued September 20, 1994 and 5,501,768 issued March 26, 1996 , both to M. A. Hermans et al.
  • Chemical additives may be also be used and may be added to the original fibers, to the fibrous slurry or added on the web during or after production.
  • Such additives include opacifiers, pigments, wet strength agents, dry strength agents, softeners, emollients, humectants, viricides, bactericides, buffers, waxes, fluoropolymers, odor control materials and deodorants, zeolites, dyes, fluorescent dyes or whiteners, perfumes, debonders, vegetable and mineral oils, humectants, sizing agents, superabsorbents, surfactants, moisturizers, UV blockers, antibiotic agents, lotions, fungicides, preservatives, aloe-vera extract, vitamin E, or the like.
  • the application of chemical additives need not be uniform, but may vary in location and from side to side in the tissue. Hydrophobic material deposited on a portion of the surface of the web may be used to enhance properties of the web.
  • the headbox may be stratified to permit production of a multilayered structure from a single headbox jet in the formation of a web.
  • the web is produced with a stratified or layered headbox to preferentially deposit shorter fibers on one side of the web for improved softness, with relatively longer fibers on the other side of the web or in an interior layer of a web having three or more layers.
  • the web is desirably formed on an endless loop of foraminous forming fabric which permits drainage of the liquid and partial dewatering of the web.
  • the process of the present invention may be carried out on an apparatus as shown in Figure 1 modified from a typical wet pressed tissue paper machine.
  • An embryonic wet web 10 formed as a slurry of papermaking fibers is deposited from a headbox 12 onto an endless loop of a first fabric 14.
  • a twin-wire former is also possible and do not change the functionality of this modification.
  • the consistency and flow rate of the slurry determines the dry web basis weight, which desirably is between about 5 and about 80 grams per square meter (gsm), and more desirably between about 8 and about 40 gsm.
  • the embryonic wet web 10 is partially dewatered by natural drainage commonly associated with the first fabric 14 and the forming roll 62 while the wet web 10 is carried on the first fabric 14. Additional dewatering may be accomplished by any dewatering means or devices such as a vacuum box 46. Once the partial dewatering step is completed, the wet web 10 is transferred to or retained on the second fabric 24 with or without the use of a vacuum shoe 50.
  • At least one of the fabrics 14 and 24 may be a forming fabric, preferably the first fabric 14.
  • at least one of the fabrics 14 and 24 may be a molding fabric, preferably the second fabric 24.
  • an air press 16 is used to noncompressively dewater the wet web 10.
  • the illustrated air press 16 comprises an assembly of a pressurized air plenum 18 disposed above the wet web 10, a water and fluid collection device 20, shown in the form of a vacuum box, disposed beneath a support fabric 22 in operable relation with the pressurized air plenum 18, and the second fabric 24 .
  • the fluid collection device 20 may be disposed next to the second fabric 24 in operable relation with the pressurized air plenum 18 and the support fabric 22 ). While passing through the air press 16 , the wet web 10 is sandwiched between the second fabric 24 and the support fabric 22 in order to facilitate sealing against the wet web 10 without damaging the wet web 10.
  • the air press 16 provides substantial rates of water removal, enabling the web to achieve dryness levels well over 30 percent prior to attachment to the drying cylinder 30, such as a Yankee dryer, desirably without the requirement for substantial compressive dewatering.
  • the drying cylinder 30 such as a Yankee dryer
  • Several embodiments of the air press 16 are described in greater detail hereinafter.
  • Other suitable embodiments are disclosed in U.S. Patent Application Serial No. 08/647,508 filed May 14,1996 by M.A. Hermans et al. titled "Method and Apparatus for Making Soft Tissue,"
  • the wet web 10 travels further sandwiched between the second fabric 24 and the support fabric 22 until the wet web 10 is transferred back to the second fabric 24, preferably a textured fabric, with or without the assistance of a vacuum transfer shoe 26 at a transfer station.
  • the second fabric 24 may comprise a three-dimensional throughdrying fabric such as those disclosed in U.S. Patent 5,429,686.issued July 4, 1995 to K. F. Chiu et al. , or may comprise other woven, textured webs or nonwoven fabrics.
  • the second fabric 24 may be treated with a fabric release agent such as a mixture of silicones or hydrocarbons to facilitate subsequent release of the wet web 10 from the second fabric 24.
  • the fabric release agent can be sprayed on the second fabric 24 prior to the pick-up of the web.
  • the wet web 10 may be further molded against the second fabric 24 through application of vacuum pressure or light pressing (not shown), though the molding that occurs at least due to vacuum forces at the transfer shoe 26 during pick-up may be adequate to mold the wet web 10.
  • the wet web 10 on the second fabric 24 is then pressed against a heated drying cylinder 30 by means of a pressure roll 32.
  • the heated drying cylinder 30 is equipped with a vapor hood or Yankee dryer hood 34.
  • the hood 34 typically employs jets of heated air at temperatures about 300 °F (149°C) or greater, particularly about 400 °F (204°C) or greater, more particularly about 500 °F (260°C) or greater, and most particularly about 700 °F (371°C) or greater, which are directed toward the wet web 10 from nozzles or other flow devices such that the air jets have maximum or locally averaged velocities in the hood 34 of one of the following levels: about 10 meters per second (m/s) or greater, about 50 m/s or greater, about 100 m/s or greater, or about 250 m/s or greater.
  • the wet web 10 when affixed to the heated drying cylinder 30 suitably has a fiber consistency of about 30 percent or greater, particularly about 35 percent or greater, such as between about 35 and about 50 percent, and more particularly about 38 percent or greater.
  • the dryness of the wet web 10 upon being removed from the heated drying cylinder 30 is increased to about 60 percent or greater, particularly about 70 percent or greater, more particularly about 80 percent or greater, more particularly still about 90 percent or greater, and most particularly between about 90 and about 98 percent.
  • the wet web 10 can be partially dried on the heated drying cylinder 30 and wet creped at a consistency of about 40 to about 80 percent and thereafter dried (after-dried) to a consistency of about 95 percent or greater.
  • Non-traditional hoods and impingement systems can be used as an alternative to or in addition to the Yankee dryer hood 34 to enhance drying of the wet web 10.
  • Additional heated drying cylinders 30 or other drying means, particularly noncompressive drying may be used after the first heated drying cylinder 30.
  • Suitable means for after-drying include one or more heated drying cylinders 30, such as Yankee dryers and can dryers, throughdryers, or any other commercially effective drying means.
  • the wet web 10 which may be molded if the second fabric 24 is a molding fabric, can be completely dried on the heated drying cylinder 30 and dry creped. The amount of drying on the heated drying cylinder 30 will depend on such factors as the speed of the wet web 10, the size of the heated drying cylinder 30, the amount of moisture in the wet web 10, and the like. '
  • the resulting dried web 36 is drawn or conveyed from the heated drying cylinder 30, for example by a creping blade 28, after which it is reeled onto a roll 38.
  • An interfacial control mixture 40 is illustrated being applied to the surface of the rotating heated drying cylinder 30 In spray form from a spray boom 42 prior to the wet web 10 contacting the surface of the heated drying cylinder 30.
  • the interfacial control mixture 40 could be applied directly to either the wet web 10 or the surface of the heated drying cylinder 30 by gravure printing or could be incorporated into the aqueous fibrous slurry in the wet end of the paper machine.
  • the wet web 10 may be further treated with chemicals, such as by printing or direct spray of solutions onto the drying web 10, including the addition of agents to promote release from the surface of the heated drying cylinder 30.
  • the interfacial control mixture 40 may comprise a conventional creping adhesive and/or dryer release agent for wet-pressed and creped operation.
  • the wet web 10 may also be removed from the surface of the heated drying cylinder 30 without creping using an interfacial control mixture 40 of the type disclosed in U.S. Patent Application Serial No. unknown filed on the same day as the present application by F. G. Druecke et al. titled "Method Of Producing Low Density Resilient Webs," .
  • FIG. 2 An alternative embodiment is shown in Figure 2, that is similar to Figure 1, except that a roll 55 of the run of the support fabric 22 is so oriented to change the direction of the second fabric 24, the support fabric 22, and the wet web 10 such that the wet web 10 is less likely to be released from the suction pressure roll 32 before the wet web 10 is transferred to the Yankee dryer or other heated drying cylinder 30.
  • the roll 55 reduces the unsupported sheet wrap angle ⁇ thereby minimizes the opportunity of the wet web 10 to separate from the second fabric 24 before the wet web 10 is transferred to the heated drying cylinder 30.
  • the embryonic wet web 10 formed as a slurry of papermaking fibers is deposited from a headbox 12 onto an endless loop of a first fabric 14. At least one of the fabrics 14 and 24 may be a forming fabric, preferably the first fabric 14. In addition, at least one of the fabrics 14 and 24 may be a molding fabric, preferably the second fabric 24.
  • the embryonic wet web 10 is partially dewatered by the natural drainage commonly associated with the first fabric 14 and the forming roll 52 while the wet web 10 is carried on the first fabric 14.
  • the wet web 10 may be further dewatered by an optional vacuum box 46 or other suitable dewatering devices while on the first fabric 14.
  • the wet web 10 is transferred to the second fabric 24 with or without the use of a vacuum shoe 50.
  • the wet web 10 is sandwiched between the second fabric 24 and a support fabric 22 and optionally is further dewatered by a vacuum box 47 or other suitable dewatering devices while between the second fabric 24 and the support fabric 22.
  • An air press 16 is used to noncompressively dewater the wet web 10 as the wet web 10 is sandwiched between the second fabric 24 and the support fabric 22.
  • the illustrated air press 16 comprises an assembly of a pressurized air plenum 18 disposed in operable relation with a vacuum box 20. While passing through the air press 16, the wet web 10 is sandwiched between the second fabric 24 and the support fabric 22 with the support fabric 22 disposed between the wet web 10 and the vacuum box 20. (In alternative embodiments, the second fabric 24 may be disposed between the web wet 10 and the vacuum box 20).
  • the wet web 10 is then transferred with or without the assistance of the vacuum shoe 26 back to the second fabric 24.
  • the wet web 10 on the second fabric 24 is then pressed against a drying cylinder 30 by means of a pressure roll 32, preferably in a manner to minimized the unsupported sheet wrap angle ⁇ on the pressure roll 32.
  • the unsupported sheet wrap angle ⁇ may range from 0 to about 90 degrees, from 0 to about 45 degrees, and from 0 to about 10 degrees. Additionally, lower unsupported sheet wrap angle ⁇ reduces the size of the vacuum zone required thereby reducing energy requirements for the vacuum generated in the pressure roll.
  • the unsupported sheet wrap angle ⁇ is defined as the portion of the circumference of the pressure roll 32 (expressed in degrees) wrapped by the wet web 10 from the first contact point of the wet web 10 on the pressure roll 32 to the last contact point of the wet web 10 on the pressure roll 32 as the wet web 10 is transferred to the drying cylinder 30.
  • the heated drying cylinder 30 is equipped with a vapor hood or Yankee dryer hood 34.
  • the resulting dried web 36 is drawn or conveyed from the drying cylinder 30. and removed without creping, after which it is reeled onto a roll 38.
  • the angle at which the dried web 36 is pulled from the surface of the heated drying cylinder 30 is suitably from about 0 to about 100 degrees and measured tangent to the surface of the heated drying cylinder 30 at the point of separation, although this may vary at different operating speeds.
  • An interfacial control mixture 40 may be applied to the surface of the rotating heated drying cylinder 30 in spray form from a spray boom 42.
  • the interfacial control mixture 40 may comprise a mixture of polyvinyl alcohol, sorbitol, and Hercules M1336 polyglycol applied in an aqueous solution having less than 5 percent solids by weight, at a dose of between 50 and 75 milligrams per square meter.
  • the amount of adhesive compounds and release agents must be balanced to adhere the wet web 10 so that is does not go up into the hood 34 yet to permit the dried web 36 to be pulled off the drying cylinder 30 without creping.
  • the air press 200 for dewatering the wet web 10 is shown in Figures 3 - 6.
  • the air press 200 generally comprises an upper air plenum 202 in combination with a lower collection device 204 in the form of a vacuum box.
  • the wet web 10 travels in a machine direction 205 between the air plenum 202 and vacuum box 204 while sandwiched between an upper support fabric 206 and a lower support fabric 208.
  • the air plenum 202 and vacuum box 204 are operatively associated with one another so that pressurized fluid supplied to the air plenum 202 travels through the wet web 10 and is removed or evacuated through the vacuum box 204.
  • Each continuous fabrics 206 and 208 travels over a series of rolls (not shown) to guide, drive and tension the fabrics 206 and 208 in a manner known in the art.
  • the fabric tension is set to a predetermined amount, suitably from about 10 to about 60 pounds per lineal inch (pli), i.e. 14 to 27 kg per lineal 2.5 cm, particularly from about 30 to about 50. pli (14 to 23 kg per lineal 2.5 cm), and more particularly from about 35 to about 45 pli (16 to 20 kg per lineal 2.5 cm).
  • the fabrics 206 and 208 that may be useful for transporting the wet web 10 through the air press 200 include almost any fluid permeable fabric, for example Albany International 94M, Appleton Mills 2164B, or the like.
  • FIG 3 An end view of the air press 200 spanning the width of the wet web 10 is shown in Figure 3, and a side view of the air press 200 in the machine direction 205 is shown in Figure 4.
  • Figure 4 An end view of the air press 200 spanning the width of the wet web 10 is shown in Figure 3, and a side view of the air press 200 in the machine direction 205 is shown in Figure 4.
  • FIGs 3 and 4 several components of the air plenum 202 are illustrated in a raised or retracted position relative to the wet web 10 and the vacuum box 204. In the retracted position, effective sealing of pressurized fluid is not possible.
  • a "retracted position" of the air press 200 means that the components of the air plenum 202 do not impinge upon the wet web 10 and support fabrics 206 and 208.
  • the illustrated air plenum 202 and the vacuum box 204 are mounted within a suitable frame structure 210.
  • the illustrated frame structure 210 comprises upper and lower support plates 211 separated by a plurality of vertically oriented support bars 212.
  • the air plenum 202 defines a plenum chamber 214 ( Figure 6) that is adapted to receive a supply of pressurized fluid through one or more suitable air conduits 215 operatively connected to a pressurized fluid source (not shown).
  • the vacuum box 204 defines a plurality of vacuum chambers (described hereinafter in relation to Figure 6) that are desirably operatively connected to low and high vacuum sources (not shown) by suitable fluid conduits 217 and 218, respectively ( Figures 4, 5, and 6). The water removed from the wet web 10 is thereafter separated from the air streams.
  • Various fasteners for mounting the components of the air press 200 are shown in the Figures 4, 5, and 6 but are not labeled.
  • FIGS 5 and 6 Enlarged section views of the air press 200 are shown in Figures 5 and 6.
  • the air press 200 is shown in an operating position wherein components of the air plenum 202 are lowered into an impingement relationship with the wet web 10 and support fabrics 206 and 208.
  • the degree of impingement that has been found to result in proper sealing of the pressurized fluid with minimal contact force and therefore reduced fabric wear is described in greater detail hereinafter.
  • the air plenum 202 comprises both stationary components 220 that are fixedly mounted to the frame structure 210 and a sealing assembly 260 that is movably mounted relative to the frame structure 210 and the wet web 10. Alternatively, the entire air plenum 202 could be moveably mounted relative to a frame structure 210.
  • the stationary components 220 of the air plenum 202 include a pair of upper support assemblies 222 that are spaced apart from one another and positioned beneath the upper support plate 211.
  • the upper support assemblies 222 define facing surfaces 224 that are directed toward one another and that partially define therebetween the plenum chamber 214.
  • the upper support assemblies 222 also define bottom surfaces 226 that are directed toward the vacuum box 204.
  • each bottom surface 226 defines an elongated recess 228 in which an upper pneumatic loading tube 230 is fixedly mounted.
  • the upper pneumatic loading tubes 230 are suitably centered the cross-machine direction and desirably extend over the full width of the wet web 10.
  • the stationary components 220 of the air plenum 202 also include a pair of lower support assemblies 240 that are spaced apart from one another and vertically spaced from the upper support assemblies 222.
  • the lower support assemblies 240 define top surfaces 242 and facing surfaces 244.
  • the top surfaces 242 are directed toward the bottom surfaces 226 of the upper support assemblies 222 and, as illustrated, define elongated recesses 246 in which lower pneumatic loading tubes 248 are fixedly mounted.
  • the lower pneumatic loading tubes 248 are suitably centered in the cross-machine direction and suitably extend over about 50 to 100 percent of the width of the wet web.
  • lateral support plates 250 are fixedly attached to the facing surfaces 244 of the lower support assemblies 240 and function to stabilize vertical movement of the sealing assembly 260.
  • the sealing assembly 260 comprises a pair of cross-machine direction sealing members referred to as CD sealing members 262 ( Figures 5 - 7) that are spaced apart from one another, a plurality of braces 263 ( Figure 7) that connect the CD sealing members 262, and a pair of machine direction sealing members referred to as MD sealing members 264 ( Figures 5 and 7).
  • the CD sealing members 262 are vertically moveable relative to the stationary components 220.
  • the optional but desirable braces 263 are fixedly attached to the CD sealing members 262 to provide structural support, and thus move vertically along with the CD sealing members 262.
  • the MD sealing members 264 are disposed between the upper support assemblies 222 and between the CD sealing members 262.
  • portions of the MD sealing members 264 are vertically moveable relative to the stationary components 220. In the cross-machine direction, the MD sealing members 264 are positioned near the edges of the wet web 10. In one particular embodiment, the MD sealing members 264 are moveable in the cross-machine direction in order to accommodate a range of possible wet web widths.
  • the illustrated CD sealing members 262 include a main upright wall section 266, a transverse flange 268 projecting outwardly from a top portion 270 of the wall section, and a sealing blade 272 mounted on an opposite bottom portion 274 of the wall section 266 ( Figure 6).
  • the outwardly-projecting flange 268 thus forms opposite, upper and lower control surfaces 276 and 278 that are substantially perpendicular to the direction of movement of the sealing assembly 260.
  • the wall section 266 and flange 268 may comprise separate components or a single component as illustrated.
  • the components of the sealing assembly 260 are vertically moveable between the retracted position shown in Figures 3 and 4 and the operating position shown in Figures 5 and 6.
  • the wall sections 266 of the CD sealing members 262 are positioned inward of the position control plates 250 and are slideable relative thereto. The amount of vertical movement is determined by the ability of the transverse flanges 268 to move between the bottom surfaces 226 of the upper support assemblies 222 and the top surfaces 242 of the lower support assemblies 240.
  • the vertical position of the transverse flanges 268 and thus the CD sealing members 262 is controlled by activation of the pneumatic loading tubes 230 and 248.
  • the loading tubes 230 and 248 are operatively connected to a pneumatic source and to a control system (not shown) for the air press.
  • Activation of the upper loading tubes 230 creates a downward force on the upper control surfaces 276 of the CD sealing members 262 resulting in a downward movement of the flanges 268 until they contact the top surfaces 242 of the lower support assemblies 240 or are stopped by an upward force caused by the lower loading tubes 248 or the fabric tension.
  • Retraction of the CD sealing members 262 is achieved by activation of the lower loading tubes 248 and deactivation of the upper loading tubes 230.
  • the lower loading tubes 248 press upwardly on the lower control surfaces 278 and cause the flanges 268 to move toward the bottom surfaces of the upper support assemblies 222.
  • the upper and lower loading tubes 230 and 248 can be operated at differential pressures to establish movement of the CD sealing members 262.
  • Alternative means for controlling vertical movement of the CD sealing members 262 can comprise other forms and connections of pneumatic cylinders, hydraulic cylinders, screws, jacks, mechanical linkages, or other suitable means.
  • Suitable loading tubes 230 and 248 are available from Seal Master Corporation of Kent, Ohio.
  • a pair of bridge plates 279 span the gap between the upper support assemblies 222 and the CD sealing members 262 to prevent the escape of pressurized fluid.
  • the bridge plates 279 thus define part of the air plenum chamber 214.
  • the bridge plates 279 may be fixedly attached to the facing surfaces 224 of the upper support assemblies 222 and slideable relative to the inner surfaces of the CD sealing members 262, or vice versa.
  • the bridge plates 279 may be formed of a fluid impermeable, semi-rigid, low-friction material such as LEXAN, sheet metal or the like.
  • the sealing blades 272 function together with other features of the air press 200 to minimize the escape of pressurized fluid between the air plenum 202 and the wet web 10 in the machine direction. Additionally, the sealing blades 272 are desirably shaped and formed in a manner that reduces the amount of fabric wear. In particular embodiments, the sealing blades 272 are formed of resilient plastic compounds, ceramic, coated metal substrates, or the like.
  • each MD sealing member 264 is spaced apart from one another and adapted to prevent the loss of pressurized fluid along the side edges of the air press 200.
  • Figures 5 and 7 each show one of the MD sealing members 264, which are positioned in the cross-machine direction near the edge of the wet web 10.
  • each MD sealing member 264 comprises a transverse support member 280, an end deckle strip 282 operatively connected to the transverse support member 280, and actuators 284 for moving the end deckle strip 282 relative to the transverse support member 280.
  • the transverse support members 280 are normally positioned near the side edges of the wet web 10 and are generally located between the CD sealing members 262.
  • each transverse support member 280 defines a downwardly directed channel 281 ( Figure 7) in which the end deckle strip 282 is mounted.
  • each transverse support member 280 defines circular apertures 283 in which the actuators 284 are mounted.
  • the end deckle strips 282 are vertically moveable relative to the transverse support members 280 due to the cylindrical actuators 284.
  • the coupling members 285 ( Figure 5) link the end deckle strips 282 to the output shaft of the cylindrical actuators 284.
  • the coupling members 285 may comprise an inverted T-shaped bar or bars so that the end deckle strips 282 may slide within the channel 281, such as for replacement.
  • both the transverse support members 280 and the end deckle strips 282 define slots to house a fluid impermeable sealing strip 286, such as O-ring material or the like.
  • the sealing strip 286 helps seal the air chamber 214 of the air press 200 from leaks.
  • the slots in which the sealing strip 286 resides is desirably widened at the interface between the transverse support members 280 and the end deckle strips 282 to accommodate relative movement between those components.
  • a bridge plate 287 ( Figure 5) is positioned between the MD sealing members 264 and the upper support plate 211 and fixedly mounted to the upper support plate 211.
  • the lateral portions of the air plenum chamber 214 ( Figure 6) are defined by the bridge plate 287.
  • Sealing means such as a fluid impervious gasketing material is desirably positioned between the bridge plate 287 and the MD sealing members 264 to permit relative movement therebetween and to prevent the loss of pressurized fluid.
  • the actuators 284 suitably provide controlled loading and unloading of the end deckle strips 282 against the upper support fabric 206, independent of the vertical position of the CD sealing members 262.
  • the load can be controlled exactly to match the necessary sealing force.
  • the end deckle strips 282 can be retracted when not needed to eliminate all end deckle and fabric wear.
  • Suitable actuators are available from Bimba Corporation.
  • springs (not shown) may be used to hold the end deckle strips 282 against the upper support fabric 206 although the ability to control the position of the end deckle strips 282 may be sacrificed.
  • each end deckle strip 282 has a top surface or edge 290 disposed adjacent to the coupling members 285, an opposite bottom surface or edge 292 that resides during use in contact with the upper support fabric 206, and the lateral surfaces or edges 294 that are in close proximity to the CD sealing members 262.
  • the shape of the bottom surface 292 is suitably adapted to match the curvature of the vacuum box 204. Where the CD sealing members 262 impinge upon the fabrics 206 and 208, the bottom surface 292 is desirably shaped to follow the curvature of the fabric impingement.
  • the bottom surface 292 has a central portion 296 that is laterally surrounded in the machine direction by spaced apart end portions 298.
  • the shape of the central portion 296 generally tracks the shape of the vacuum box 204 while the shape of the end portions 298 generally tracks the deflection of the fabrics 206 and 208 caused by the CD sealing members 262.
  • the end deckle strips 282 are desirably retracted before the CD sealing members 262 are retracted.
  • the end deckle strips 282 are desirably formed of a gas impermeable material that minimizes fabric wear. Particular materials that may be suitable for the end deckle strips 282 include polyethylene, nylon, or the like.
  • the MD sealing members 264 are desirably moveable in the cross-machine direction and are thus desirably slideably positioned against the CD sealing members 262.
  • movement of the MD sealing members 264 in the cross-machine direction is controlled by a threaded shaft or bolt 305 that is held in place by brackets 306 ( Figure 7).
  • the threaded shaft 305 passes through a threaded aperture in the transverse support member 280 and rotation of the shaft causes the MD sealing member to move along the shaft.
  • Alternative means for moving the MD sealing members 264 in the cross-machine direction such as pneumatic devices or the like may also be used.
  • the MD sealing members 264 are fixedly attached to the CD sealing members 262 so that the entire sealing assembly 260 is raised and lowered together (not shown).
  • the transverse support members 280 are fixedly attached to the CD sealing members 262 and the end deckle strips 282 are adapted to move independently of the CD sealing members 262 (not shown).
  • the vacuum box 204 comprises a vacuum box cover 300 having a top surface 302 over which the lower support fabric 208 travels.
  • the vacuum box cover 300 and the sealing assembly 260 are desirably gently curved to facilitate web control.
  • the illustrated vacuum box cover 300 is formed, from the leading edge to the trailing edge in the machine direction 205, with a first exterior sealing shoe 311, a first sealing vacuum zone 312, a first interior sealing shoe 313, a series of four high vacuum zones 314, 316, 318, and 320 surrounding three interior shoes 315, 317, and 319, a second interior sealing shoe 321, a second sealing vacuum zone 322, and a second exterior sealing shoe 323 ( Figure 6).
  • Each of these sealing shoes 315, 317, and 319 and vacuum zones 314, 316, 318, and 320 desirably extend in the cross-machine direction across the full width of the web.
  • the shoes 315, 317, and 319 each include a top surface desirably formed of a ceramic material to ride against the lower support fabric 208 without causing significant fabric wear.
  • Suitable vacuum box covers and shoes may be formed of plastics, NYLON, coated steels or the like, and are available from JWI Corporation or IBS Corporation.
  • the four high vacuum zones 314, 316, 318, and 320 are passageways in the cover 300 that are operatively connected to one or more vacuum sources (not shown) that draw a relatively high vacuum level.
  • the high vacuum zones 314, 316, 318, and 320 may be operated at a vacuum of 0 to 25 inches of mercury (0 to 84.7 kPa) vacuum, and more particularly about 10 to about 25 inches of mercury (33.9 kPa to 84.7 kPa) vacuum.
  • the cover 300 could define, a plurality of holes or other shaped openings (not shown) that are connected to a vacuum source to establish a flow of pressurized fluid through the web.
  • the high vacuum zones 314, 316, 318, and 320 comprise slots each measuring 0.375 inch (0.95 cm) in the machine direction and extending across the full width of the wet web.
  • the dwell time that any given point on the web is exposed to the flow of pressurized fluid which in the illustrated embodiment is the time over slots 314, 316, 318 and 320, is suitably about 10 milliseconds or less, particularly about 7.5 milliseconds or less, more particularly 5 milliseconds or less, such as about 3 milliseconds or less or even about 1 millisecond or less.
  • the number and width of the high pressure vacuum slots 314, 316, 318 , and 320 and the machine speed determine the dwell time.
  • the selected dwell time will depend on the type of fibers contained in the wet web and the desired amount of dewatering.
  • the first and second sealing vacuum zones 312 and 322 may be employed to minimize the loss of pressurized fluid from the air press 200.
  • the sealing vacuum zones 312 and 322 are passageways in the cover 300 that may be operatively connected to one or more vacuum sources (not shown) that desirably draw a relatively lower vacuum level as compared to the four high vacuum zones 314, 316, 318, and 320.
  • the amount of vacuum that is desirable for the sealing vacuum zones is 0 to about 100 inches water column (0 to 24.9 kPa), vacuum.
  • the air press 200 is desirably constructed so that the CD sealing members 262 are disposed within the sealing vacuum zones 312 and 322. More specifically, the sealing blade 272 of the CD sealing member 262 that is on the leading side of the air press 200 is disposed between, and more particularly centered between, the first exterior sealing shoe 311 and the first interior sealing shoe 313, in the machine direction. The trailing sealing blade 272 of the CD sealing member 262 is similarly disposed between, and more particularly centered between, the second interior sealing shoe 321 and the second exterior sealing shoe 323, in the machine direction.
  • the sealing assembly 260 can be lowered so that the CD sealing members 262 deflect the normal course of travel of the wet web 10 and fabrics 206 and 208 toward the vacuum box 204, which is shown in slightly exaggerated scale in Figure 6 for purposes of illustration.
  • the sealing vacuum zones 312 and 322 function to minimize the loss of pressurized fluid from the air press 200 across the width of the wet web 10.
  • the vacuum in the sealing vacuum zones 312 and 322 draws pressurized fluid from the air plenum 202 and draws ambient air from outside the air press 200. Consequently, an air flow is established from outside the air press 200 into the sealing vacuum zones 312 and 322 rather than a pressurized fluid leak in the opposite direction. Due to the relative difference in vacuum between the high vacuum zones 314, 316, 318, and 320 and the sealing vacuum zones 312 and 322, though, the vast majority of the pressurized fluid from the air plenum 202 is drawn into the high vacuum zones 314, 316, 318, and 320 rather than the sealing vacuum zones 312 and 322.
  • the deformable sealing deckles 330 desirably extend across the full width of the wet web 10 to seal the leading end, the trailing end, or both the leading and the trailing end of the air press 200.
  • the sealing vacuum zone 312 and 322 may be disconnected from the vacuum source when the deformable sealing deckle 330 extends across the full web width.
  • a vacuum device or blow box may be employed downstream of the air press 200 to cause the web 10 to remain with one of the fabrics 206 or 208 as the fabrics 206 and 208 are separated.
  • the deformable sealing deckles 330 desirably either comprise a material that preferentially wears relative to the fabric 208, meaning that when the fabric 208 and the material are in use the material will wear away without causing significant wear to the fabric 208, or comprise a material that is resilient and that deflects with impingement of the fabric 208.
  • the deformable sealing deckles 330 are desirably gas impermeable, and desirably comprise a material with high void volume, such as a closed cell foam or the like.
  • the deformable sealing deckles 330 comprise a closed cell foam measuring 0.25 inch (0.64 cm) in thickness.
  • the deformable sealing deckles 330 themselves become worn to match the path of the fabrics 206 and 208.
  • the deformable sealing deckles 330 are desirably accompanied by backing plate 332 for structural support, for example an aluminum bar.
  • sealing deckles 330 In embodiments where full width sealing deckles 330 are not used, sealing means of some sort are required laterally of the web. Deformable sealing deckles 330 as described above, or other suitable means known in the art, may be used to block the flow of pressurized fluid through the fabrics 206 and 208 laterally outward of wet web 10.
  • the degree of impingement of the CD sealing members 262 into the upper support fabric 206 uniformly across the width of the wet web 10 has been found to be a significant factor in creating an effective seal across the web.
  • the requisite degree of impingement has been found to be a function of the maximum tension of the upper and lower support fabrics 206 and 208, the pressure differential across the web and in this case between the air plenum chamber 214 and the sealing vacuum zones 312 and 322, and the gap between the CD sealing members 262 and the vacuum box cover 300.
  • h min T W ⁇ cosh Wd T - 1 ;
  • Figure 9 shows the trailing CD sealing member 262 deflecting the upper support fabric 206 by an amount represented by arrow "h".
  • the maximum tension of the upper and lower support fabrics 206 and 208 is represented by arrow "T”.
  • the fabric tension can be measured by a model tensometer available from Huyck Corporation or other suitable methods.
  • the gap "d'' of significance for the determining impingement is the gap on the higher pressure differential side of the sealing blade 272, that is, toward the plenum chamber 214, because the pressure differential on that side has the most effect on the position of the fabrics 206 and 208 and the web 10.
  • the gap between the sealing blade 272 and the second exterior shoe 323 is approximately the same or less than gap "d”.
  • Adjusting the vertical placement of the CD sealing members 262 to the minimum degree of impingement as defined above is a determinative factor in the effectiveness of the CD seal.
  • the loading force applied to the sealing assembly 260 plays a lesser role in determining the effectiveness of the seal, and need only be set to the amount needed to maintain the requisite degree of impingement.
  • the amount of fabric wear will impact the commercial usefulness of the air press 200.
  • the degree of impingement is desirably equal to or only slightly greater than the minimum degree of impingement as defined above.
  • the force applied to the fabric is desirably kept constant over the cross machine direction. This can be accomplished with either controlled and uniform loading of the CD sealing members 262 or controlled position of the CD sealing members 262 and uniform geometry of the impingement of the CD sealing members 262.
  • a control system causes the sealing assembly 260 of the air plenum 202 to be lowered into an operating position.
  • the CD sealing members 262 are lowered so that the sealing blades 272 impinge upon the upper support fabric 206 to the degree described above. More particularly, the pressures in the upper and lower loading tubes 230 and 248 are adjusted to cause downward movement of the CD sealing members 262 until movement is halted by the transverse flanges 268 contacting the lower support assemblies 240 or until balanced by fabric tension.
  • the end deckle strips 282 of the MD sealing members 264 are lowered into contact with or close proximity to the upper support fabric 206. Consequently, the air plenum 202 and the vacuum box 204 are both sealed against the wet web 10 to prevent the escape of pressurized fluid.
  • the air press 200 is then activated so that pressurized fluid fills the air plenum 202 and an air flow is established through the web 10.
  • high and low vacuums are applied to the high vacuum zones 314, 316, 318, and 320 and the sealing vacuum zones 312 and 322 to facilitate air flow, sealing and water removal.
  • pressurized fluid flows from the air plenum 202 to the high vacuum zones 314, 316, 318, and 320 and the deformable sealing deckles 330 seal the air press 200 in the cross machine direction.
  • the resulting pressure differential across the wet web 10 and resulting air flow through the web 10 provide for efficient dewatering of the web 10.
  • the air press 200 uses the CD sealing members 262 that impinge upon the fabrics 206 and 208 and the wet web 10. The degree of impingement is determined to maximize the effectiveness of the CD seal.
  • the air press 200 utilizes the sealing vacuum zones 312 and 322 to create an ambient air flow into the air press 200 across the width of the wet web 10 .
  • deformable sealing deckles 330 are disposed in the sealing vacuum zones 312 and 322 opposite the CD sealing members 262.
  • the CD sealing members 262 are desirably disposed at least partly in passageways of the vacuum box cover 300 in order to minimize the need for precise alignment of mating surfaces between the air plenum 202 and the vacuum box 204. Further, the sealing assembly 260 can be loaded against a stationary component such as the lower support assemblies 240 that are connected to the frame structure 210.
  • Suitable lubrication systems may include chemical lubricants such as emulsified oils, debonders or other like chemicals, or water.
  • Typical lubricant application methods include a spray of diluted lubricant applied in a uniform manner in the cross machine direction, an hydraulically or air atomized solution, a felt wipe of a more concentrated solution, or other methods well known in spraying system applications.
  • cross-machine direction flow uniformity may be improved with mechanisms such as tapered ductwork on the pressure and vacuum sides, shaped using computational fluid dynamic modeling. Because web basis weight and moisture content may not be uniform in the cross-machine direction, is may be desirably to employ additional means to obtain uniform air flow in the cross-machine direction, such as independently-controlled zones with dampers on the pressure or vacuum sides to vary the air flow based on sheet properties, a baffle plate to take a significant pressure drop in the flow before the wet web, or other direct means.
  • Alternative methods to control CD dewatering uniformity may also include external devices, such as zoned controlled steam showers, for example a Devronizer steam shower available from Honeywell-Measurex Systems Inc. of Dublin, Ohio or the like.
  • FIG. 10 The process of other embodiments of the present invention may be carried out on an apparatus as shown in Figure 10 modified from a typical crescent-former tissue paper machine.
  • An embryonic wet web 410 formed as a slurry of papermaking fibers is deposited from a headbox 412 between an endless loop of a first fabric 414 and an endless loop of a second fabric 424.
  • the second fabric 424 generally replaces the felt of a standard crescent-former tissue machine.
  • the consistency and flow rate of the slurry determines the dry web basis weight, which desirably is between about 5 and about 80 grams per square meter (gsm), and more desirably between about 8 and about 40 gsm.
  • At least one of the fabrics 414 and 424 may be a forming fabric, preferably the first fabric 414.
  • at least one of the fabrics 414 and 424 may be a molding fabric, preferably the second fabric 424.
  • the embryonic wet web 410 is partially dewatered by the pressure due to the tension on the first fabric 414 and the centrifugal force created as the wet web 410 passes around the forming roll 452 while the wet web 410 is carried between the first fabric 414 and the second fabric 424. Once the partial dewatering step is completed, the wet web 410 is transferred to or retained on the second fabric 424 with or without the use of a vacuum shoe 450.
  • an air press 416 is used to noncompressively dewater the wet web 410.
  • the illustrated air press 416 comprises an assembly of a pressurized air plenum 418 disposed above the wet web 410, a fluid collection device 420, shown in the form of a vacuum box, disposed beneath a support fabric 422 in operable relation with the pressurized air plenum 418 and the second fabric 424.
  • the fluid collection device 420 may be disposed next to the second fabric 424 in operable relation with the pressurized air plenum 418 and the support fabric 422). While passing through the air press 416, the wet web 410 is sandwiched between the second fabric 424 and the support fabric 422 in order to facilitate sealing against the wet web 410 without damaging the wet web 410.
  • the air press 416 provides substantial rates of water removal, enabling the web to achieve dryness levels well over 30 percent prior to attachment to the drying cylinder 430, such as a Yankee dryer, desirably without the requirement for substantial compressive dewatering.
  • the drying cylinder 430 such as a Yankee dryer
  • Several embodiments of the air press 416 are described in greater detail hereinafter.
  • Other suitable embodiments are disclosed In U.S. Patent Application Serial No. 08/647,508 filed May 14, 1996 by M.A. Hermans et al. titled "Method and Apparatus for Making Soft Tissue.”
  • the wet web 410 travels further with the second fabric 424 and the support fabric 422 until the wet web 410 is transferred back to the second fabric 424, preferably a textured fabric, with or without the assistance of a vacuum transfer shoe 426 at a transfer station.
  • the second fabric 424 may comprise a three-dimensional throughdrying fabric such as those disclosed in U.S. Patent 5,429,686 issued July 4, 1995 to K F. Chiu et al. , or may comprise other woven, textured webs or nonwoven fabrics.
  • the second fabric 424 may be treated with a fabric release agent such as a mixture of silicones or hydrocarbons to facilitate subsequent release of the wet web 410 from the second fabric 424.
  • the fabric release agent can be sprayed on the second fabric 424 prior to the pick-up of the web.
  • the wet web 410 may be further molded against the second fabric 424 through application of vacuum pressure or light pressing (not shown), though the molding that occurs at least due to vacuum forces at the transfer shoe 426 during pick-up may be adequate to mold the wet web 410.
  • the wet web 410 on the second fabric 424 is then pressed against a drying cylinder 430 by means of a pressure roll 432.
  • the drying cylinder 430 is equipped with a vapor hood or Yankee dryer hood 434.
  • the hood 434 typically employs jets of heated air at temperatures about 300 °F (149°C) or greater, particularly about 400 °F (204°C) or greater, more particularly about 500 °F (260°C) or greater, and most particularly about 700 °F (371°C) or greater, which are directed toward the tissue web 410 from nozzles or other flow devices such that the air jets have maximum or locally averaged velocities in the hood 434 of one of the following levels: about 10 meters per second (m/s) or greater, about 50 m/s or greater, about 100 m/s or greater, or about 250 mls or greater.
  • the wet web 410 when affixed to the heated drying cylinder 430 suitably has a fiber consistency of about 30 percent or greater, particularly about 35 percent or greater, such as between about 35 and about 50 percent, and more particularly about 38 percent or greater.
  • the dryness of the wet web 410 upon being removed from the heated drying cylinder 430 is increased to about 60 percent or greater, particularly about 70 percent or greater, more particularly about 80 percent or greater, more particularly still about 90 percent or greater, and most particularly between about 90 and about 98 percent.
  • the wet web 410 can be partially dried on the heated drying cylinder 430 and wet creped at a consistency of about 40 to about 80 percent and thereafter dried (after-dried) to a consistency of about 95 percent or greater.
  • Non-traditional hoods and impingement systems can be used as an alternative to or in addition to the Yankee dryer hood 434 to enhance drying of the wet web 410.
  • Additional heated drying cylinders 430 or other drying means, particularly noncompressive drying, may be used after the first heated drying cylinder 430.
  • Suitable means for after-drying include one or more heated drying cylinders 430, such as Yankee dryers and can dryers, throughdryers, or any other commercially effective drying means.
  • the wet web 410 which may be molded if the second fabric 424 is a molding fabric, can be completely dried on the heated drying cylinder 430 and dry creped. The amount of drying on the heated drying cylinder 430 will depend on such factors as the speed of the wet web 410, the size of the heated drying cylinder 430, the amount of moisture in the wet web 410, and the like.
  • the resulting dried web 436 is drawn or conveyed from the heated drying cylinder 430, for example by a creping blade 428, after which it is reeled onto a roll 438.
  • An interfacial control mixture 440 is illustrated being applied to the surface of the rotating heated drying cylinder 430 in spray form from a spray boom 442 prior to the wet web 410 contacting the surface of the heated drying cylinder 430.
  • the interfacial control mixture 440 could be applied directly to either the wet web 410 or the surface of the heated drying cylinder 430 by gravure printing or could be incorporated into the aqueous fibrous slurry in the wet end of the paper machine.
  • the wet web 410 may be further treated with chemicals, such as by printing or direct spray of solutions onto the drying web 410, including the addition of agents to promote release from the surface of the heated drying cylinder 430.
  • the interfacial control mixture 440 may comprise a conventional creping adhesive and/or dryer release agent for wet-pressed and creped operation.
  • the dried web 436 may also be removed from the surface of the heated drying cylinder 430 without creping using an interfacial control mixture 440 of the type disclosed in U.S. Patent Application Serial No. unknown filed on the same day as the present application by F. G. Druecke et al. titled "Method Of Producing Low Density Resilient Webs,".
  • FIG. 11 An alternative embodiment is shown in Figure 11, where an embryonic wet web 510 formed as a slurry of papermaking fibers is deposited from a headbox 512 between an endless loop of a first fabric 514 and an endless loop of a second fabric 524.
  • the second fabric 524 generally replaces the felt of the standard crescent-former tissue machine.
  • At least one of the fabrics 514 and 524 may be a forming fabric, preferably the first fabric 514.
  • at least one of the fabrics 514 and 524 may be a molding fabric, preferably the second fabric 524.
  • the embryonic wet web 510 is partially dewatered by the pressure due to tension on the first fabric 514 and the centrifugal force created as the wet web 510 passes around the forming roll 552 while the wet web 510 is carried between the first fabric 514 and the second fabric 524.
  • the wet web 510 is optionally further dewatered by a vacuum box 546 or other suitable devices while between the first fabric 514 and the second fabric 524 and is transferred to or retained on the second fabric 524 with or without the use of a vacuum shoe 550.
  • An air press 516 is used to noncompressively dewater the wet web 510 as it is sandwiched between the second fabric 524 and a support fabric 522.
  • the illustrated air press 516 comprises an assembly of a pressurized air plenum 518 disposed in operable relation with a vacuum box 520. While passing through the air press 516, the wet web 510 is sandwiched between the second fabric 524 and the support fabric 522 with the support fabric 522 disposed between the wet web 510 and the vacuum box 520. (In alternative embodiments, the second fabric 524 may be disposed between the wet web 510 and the vacuum box 520).
  • the wet web 510 is then transferred with or without the assistance of the vacuum shoe 526 to the second fabric 524.
  • a roll 555 of the run of the support fabric 522 is so oriented to change the direction of the second fabric 524, the support fabric 522, and the wet web 510 such that the wet web 510 is less likely to be released from the suction pressure roll 532 before the wet web 510 is transferred to the Yankee dryer or other heated drying cylinder 530.
  • the roll 555 reduces the unsupported sheet wrap angle ⁇ thereby minimizes the opportunity of the wet web 510 to separate from the second fabric 524 before the wet web 510 is transferred to the heated drying cylinder 530.
  • the wet web 510 on the second fabric 524 is then pressed against a heated drying cylinder 530 by means of a pressure roll 532.
  • the wet web 510 on the second fabric 524 is then pressed against a drying cylinder 530 by means of a pressure roll 532, preferably in a manner to minimized the unsupported sheet wrap angle ⁇ on the pressure roll 532.
  • the unsupported sheet wrap angle ⁇ may range from 0 to about 90 degrees, from 0 to about 45 degrees, and from 0 to about 10 degrees. Additionally, lower unsupported sheet wrap angle ⁇ reduces the size of the vacuum zone required thereby reducing energy requirements for the vacuum generated in the pressure roll.
  • the unsupported sheet wrap angle ⁇ is defined as the portion of the circumference of the pressure roll 532 (expressed in degrees) wrapped by the wet web 510 from the first contact point of the wet web 510 on the pressure roll 532 to the last contact point of the wet web 510 on the pressure roll 532 as the wet web 510 is transferred to the drying cylinder 530.
  • the heated drying cylinder 530 is equipped with a vapor hood or Yankee dryer hood 534.
  • the resulting dried web 536 is drawn or conveyed from the heated drying cylinder 530 and removed without creping, after which it is reeled onto a roll 538.
  • the angle at which the dried web 536 is pulled from the surface of the heated drying cylinder 530 is suitably about 80 to about 100 degrees, measured tangent to the surface of the heated drying cylinder 530 at the point of separation, although this may vary at different operating speeds.
  • An interfacial control mixture 540 may be applied to the surface of the rotating heated drying cylinder 530 in spray form from a spray boom 542.
  • the interfacial control mixture 540 may comprise a mixture of polyvinyl alcohol, sorbitol, and Hercules M1336 polyglycol applied in an aqueous solution having less than 5 percent solids by weight, at a dose of between 50 and 75 milligrams per square meter.
  • the amount of adhesive compounds and release agents must be balanced to adhere the wet web 510 so that is does not go up into the hood 534 yet to permit the dried web 536 to be pulled off the heated drying cylinder 530 without creping.
  • FIG. 12 Another alternative embodiment is shown in Figure 12. This embodiment is similar to that of Figure 11 except that the first fabric 614 is extended to act as the support fabric 522 shown in Figure 11. This provides a potential reduction in capital cost and operating cost with the reduction in the number of fabrics required to modify this process.
  • an embryonic wet web 610 formed as a slurry of papermaking fibers is deposited from a headbox 612 between an endless loop of a first fabric 614 and an endless loop of a second fabric 624.
  • the second fabric 624 generally replaces the felt of the standard crescent-former tissue machine.
  • At least one of the fabrics 614 and 624 may be a forming fabric, preferably the first fabric 614.
  • at least one of the fabrics 614 and 624 may be a molding fabric, preferably the second fabric 624.
  • the embryonic wet web 610 is partially dewatered by the pressure due to the tension on first fabric 614 and the centrifugal force created as the wet web 610 passes around the forming roll 652 and further dewatered by an optional vacuum box 646 or other suitable devices while between the first fabric 614 and the second fabric 624.
  • An air press 616 is used to non-compressively dewater the wet web 610 as it is sandwiched between the first fabric 614 and a second fabric 624.
  • the illustrated air press 616 comprises an assembly of a pressurized air plenum 618 disposed in operable relation with a vacuum box 620.
  • the wet web 610 While passing through the air press 616, the wet web 610 is sandwiched between the second fabric 624 and the support fabric 622 with the support fabric 622 disposed between the wet web 610 and the vacuum box 620. (In alternative embodiments, the second fabric 624 may be disposed between the wet web 610 and the vacuum box 620).
  • the wet web 610 is then transferred with or without the assistance of the vacuum shoe 626 to the second fabric 624.
  • the wet web 610 on the second fabric 624 is then pressed against a drying cylinder 630 by means of a pressure roll 632.
  • the heated drying cylinder 630 is equipped with a vapor hood or Yankee dryer hood 634.
  • the resulting dried web 636 is drawn or conveyed from the heated drying cylinder 630 and removed without creping, after which it is reeled onto a roll 638.
  • the angle at which the dried web 636 is pulled from the surface of the heated drying cylinder 630 is suitably about 80 to about 100 degrees, measured tangent to the surface of the heated drying cylinder 630 at the point of separation, although this may vary at different operating speeds.
  • An interfacial control mixture 640 may be applied to the surface of the rotating heated drying cylinder 630 in spray form from a spray boom 642.
  • the interfacial control mixture 640 may comprise a mixture of polyvinyl alcohol, sorbitol, and Hercules M1336 polyglycol applied in an aqueous solution having less than 5 percent solids by weight, at a dose of between 50 and 75 milligrams per square meter.
  • the amount of adhesive compounds and release agents must be balanced to adhere the wet web 610 so that is does not go up into the hood 634 yet to permit the dried web 636 to be pulled off the heated drying cylinder 630 without creping.
  • the air press 200 for dewatering the wet web 410, 510, or 610 was discussed above in Figures 3-6.
  • a sealing assembly that may be used with the equipment shown in Figs. 10,11 and 12 is shown as the sealing assembly 260 as discussed above in Figures 7, 8 , and 9 .
  • a 12-inch (30 cm) wide tissue was produced on an experimental tissue machine, having a fabric width of 22 inches (56 cm), from a fibrous slurry comprised of an unrefined 50:50 fiber blend of bleached kraft northern softwood fibers and bleached kraft eucalyptus fibers.
  • the tissue was formed using a stratified, three-layer headbox with the slurry being deposited from each stratum to form a blended sheet haying a nominal basis weight of 19 gsm.
  • the headbox injected the slurry between two Lindsay Wire 2164B forming fabrics, in a twin wire forming section, with a suction roll former.
  • 1000 ml/minute of Parez 631 NC at 6 percent solids was added to the stock prior to the forming process.
  • the embryonic wet web While disposed between the two forming fabrics and traveling at 1000 feet per minute (fpm), i.e 305 m/min the embryonic wet web was transported over four vacuum boxes operating with respective vacuum pressures of approximately 11, 14, 13 and 19 inches of mercury (37.3 kPa, 47.4 kPa, 44.8 kPa, 64.3 kPa) vacuum.
  • the embryonic wet web still contained between the two forming fabrics, passed through an air press including an air plenum and a collection box that were operatively associated and integrally sealed with one another.
  • the air plenum was pressurized with air at approximately 150 degrees Fahrenheit (66°C) to 15 pounds per square inch (103.4 kPa) gauge, and the collection box was operated at approximately 11 inches of mercury (37.3 kPa) vacuum.
  • the wet web was exposed to the resulting pressure differential of approximately 41.5 inches of mercury (140.5 kPa) and air flow of 68 SCFM per square inch (299 ⁇ 10 3 cm 3 /min/cm 2 ) for a dwell time of 7.5 milliseconds over four slots, each 3/8" (0.95 cm) in length.
  • the consistency of the wet web was approximately 30 percent just prior to the air press and 39 percent upon exiting the air press.
  • the dewatered wet web was then transferred using a vacuum pickup shoe operating at approximately 10 inches of mercury (33.9 kPa) vacuum onto a three-dimensional fabric, a Lindsay Wire T-216-3 TAD fabric.
  • a silicon emulsion in water was sprayed onto the sheet side of the T-216-3 fabric just prior to transfer from the forming fabric to facilitate the eventual transfer to the Yankee dryer.
  • the silicone was applied at a flow rate of 400 ml/minute at 1.0% solids.
  • the TAD fabric was thereafter pressed against the surface of a Yankee dryer with a conventional pressure roll operating at a maximum pressing pressure of 350 pli (159 kg per lineal 2.5 cm). The fabric was wrapped over about 39 inches (99 cm) of the Yankee dryer surface by a transfer roll which was unloaded and slightly removed from the Yankee dryer.
  • the wet web was adhered to the Yankee dryer using an adhesive mixture, of polyvinyl alcohol AIRVOL 523 made by Air Products and Chemical Inc. and sorbitol in water applied by four #6501 spray nozzles by Spraying Systems Company operating at approximately 40 psig (377 kPa) with a flow rate of about 0.4 gallons per minute (gpm), i.e 1762 cm 3 /min.
  • the spray had a solids concentration of about 0.5 weight percent.
  • the dried web was creped from the Yankee dryer at a final dryness of approximately 92% consistency and wound on a core. The product was then converted into 2-ply bathroom tissue using standard techniques. Results obtained for Example 1 are shown below in Table 1 .
  • a 12-inch (30 cm) wide tissue was produced on an experimental tissue machine, having a fabric width of 22 inches (56 cm), from a fibrous slurry comprised of an unrefined 50:50 fiber blend of bleached kraft northern softwood fibers and bleached kraft eucalyptus fibers.
  • the tissue was formed using a stratified, three-layer headbox with the slurry being deposited from each stratum to form a blended sheet having a nominal basis weight of 19 gsm.
  • the headbox injected the slurry between two Lindsay Wire 2164B forming fabrics, in a twin wire forming section, with a suction roll former.
  • 1000 ml/minute of Parez 631 NC at 6 percent solids was added to the stock prior to the forming process.
  • the embryonic wet web While disposed between the two forming fabrics and traveling at 1000 feet per minute (fpm), i.e. 305 m/min, the embryonic wet web was transported over four vacuum boxes operating with respective vacuum pressures of approximately 11, 14, 13 and 19 inches of mercury (37.3 kPa, 47.4 kPa, 44.0 kPa, 64,3 kPa) vacuum.
  • the embryonic wet web still contained between the two forming fabrics, passed through an air press including an air plenum and a collection box that were operatively associated and integrally sealed with one another.
  • the air plenum was pressurized with air at approximately 150 degrees Fahrenheit (66°C) to 15 pounds per square inch (103.4 kPa) gauge, and the collection box was operated at 11 inches of mercury (37.3 kPa) vacuum.
  • the wet web was exposed to the resulting pressure differential of approximately 41.5 inches of mercury (140.5 kPa) and air flow of 68 SCFM per square inch (299 ⁇ 10 3 cm 3 /min/cm 2 ) for a dwell time of 7.5 milliseconds over four slots, each with 3/8" (0.95 cm) length.
  • the consistency of the wet web was approximately 30 percent just prior to the air press and 39 percent upon exiting the air press.
  • the dewatered wet web was then rush transferred using a vacuum pickup shoe operating at approximately 10 inches of mercury (33.9 kPa) onto a three-dimensional fabric, a Lindsay Wire T-216-3 TAD fabric, traveling 20% percent slower than the forming fabrics.
  • a silicone emulsion in water was sprayed onto the sheet side of the T-216-3 fabric just prior to transfer from the forming fabric to facilitate the eventual transfer to the Yankee dryer.
  • the TAD fabric was thereafter pressed against the surface of a Yankee dryer with a conventional pressure roll operating at a maximum pressing pressure of 350 pli (159 kg per lineal 2.5 cm). The fabric was wrapped over about 39 inches (99 cm) of the Yankee dryer surface by a transfer roll which was unloaded and slightly removed from the Yankee dryer.
  • the wet web was adhered to the Yankee in a controlled manner using an interfacial control mixture comprised, on a percent active solids basis, of approximately 26 percent polyvinyl alcohol, 46 percent sorbitol, and 28 percent of Hercules M1336 polyglycol applied at a dose of between 50 and 75 mg/m 2 .
  • the compounds were prepared in an aqueous solution having less than 5 percent solids by weight.
  • the wet web was dried on the Yankee dryer to approximately 90% consistency and then "peeled" from the Yankee dryer by applying sufficient winding tension to remove the dried web just prior to the creping blade. The dried web was then wound on a core without additional pressing. The product was then converted into 2-ply bathroom tissue using standard techniques. Results obtained for Example 2 are shown above in Table 1.
  • a wet web was formed from a 50:40:10 blend of bleached kraft northern softwood, bleached kraft eucalyptus and softwood BCTMP fibers using a Fourdrinier former operating at approximately 3500 fpm (1067 m/min).
  • the resulting wet web at a basis weight of approximately 20 gsm was transferred from the forming fabric to a standard wet-press felt (using a couch roll).
  • the wet web was carried to a 15 foot (4.6 m) Yankee dryer and transferred to the Yankee dryer using standard techniques.
  • the wet web was dried on the Yankee dryer using standard techniques and removed from the dryer at approximately 95% consistency using a creping blade.
  • the web was transferred over an open draw to a second Yankee dryer (this dryer operating without the normal hood) and adhered to the Yankee dryer using a Latex adhesive.
  • the dried web was then creped again and wound on a core.
  • the product was then converted into 2-ply bathroom tissue using standard techniques.
  • the process used in this example is known as the single re-creped process U.K patent documents GB 2179949 B , GB 2152961 A , and GB 2179953 B . Results obtained for Example 3 are shown above in Table 1.
  • a wet web was formed from a 65:35 blend of bleached kraft northern softwood and bleached kraft eucalyptus fibers.
  • the wet web was formed using a twin wire former in a layered configuration with the eucalyptus on the outside (air side) of the wet web.
  • the wet web was dewatered to a consistency of approximately 27 percent using conventional vacuum dewatering technology and then throughdried using standard technology to a consistency of approximately 90 percent.
  • the wet web was then transferred to a Yankee dryer, adhered using PVA as the adhesive, and dried to a consistency of 97 percent.
  • the dried web was then wound on a core.
  • the product was then converted into 2-ply bathroom tissue using standard techniques. Results obtained for Example 4 are shown above in Table 1.
  • Table 1 clearly shows the improvement in sheet/roll properties that can be achieved using this invention.
  • the product of this invention yielded bath tissue that exhibited higher sheet caliper, 1667 microns versus 1288, than that of the control ( Example 3 ) despite the additional re-creping step employed specifically to increase the bulk of the control. Without this re-creping step, the difference would be even larger, as the re-creping step typically adds about 30% more caliper. From the standpoint of roll properties, this additional caliper allowed the removal of 27 sheets (from 280 count to 253 count) while maintaining the same roll diameter.
  • the rolls produced using this invention were firmer at the same roll diameter (104 versus 134 with lower numbers indicating greater firmness) despite the reduction in sheet count.
  • the invention allowed a reduction in roll weight from 158 grams to 133 grams (16%) while producing superior roll properties.
  • Example 2 The improvement in roll properties is even more striking when the uncreped example ( Example 2 ) is considered.
  • the sheet count was reduced to 180 sheets (again versus 280 for the control) while maintaining roll diameter and firmness.
  • the roll weight was reduced by 40%.
  • the product of this invention was compared to creped throughdried, the product described in Example 4. It is clear the products have roughly equal properties in terms of roll bulk etc. In fact, the throughdried example showed a relatively low firmness, indicating the product of this invention is even better than that of the throughdried process.
  • a wet web was formed from a fiber blend of 50:30:20 southern bleached kraft pine, bleached kraft northern softwood, and bleached kraft eucalyptus on an experimental tissue machine running approximately 50 fpm (15 m/min).
  • the resulting wet web at an approximate basis weight of 41 grams per meter square, was carried on the forming fabric and then transferred to a T-216-3 molding fabric.
  • the embryonic wet web was passed through an air press including an air plenum and a collection box that were operatively associated and (integrally) sealed with one another.
  • the wet web was dewatered from the post forming consistency of approximately 10% to 32-35% consistency.
  • a fiber blend of 65:35 bleached kraft southern softwood and softwood BCTMP was formed into a wet web at a machine speed of 250 fpm (76 m/min) using a Fourdrinier style former.
  • the resulting wet web at an approximate basis weight of 50 grams per square meter, was transferred to a standard wet-pressing felt and conveyed to a Yankee dryer.
  • the wet web was transferred to the Yankee dryer at a pressure roll nip using standard wet-pressing techniques.
  • the wet web was adhered to the dryer using polyvinyl alcohol and creped at approximately 55 percent consistency.
  • the dried web was then conveyed over an open draw to a series of can dryers where it was dried to approximately 95 percent consistency and wound on a core.
  • Example 6 The product was then converted into 1-ply towels using standard techniques. Results obtained for Example 6 are shown below in Table 2 . Table 2 Table 2 clearly shows the product advantages inherent to this invention. The paper towels produced using this invention have superiority to the heavy wet-creped control in terms of caliper and absorbency despite a 19% reduction in basis weight.
  • a wet web was formed using a fiber blend of 50:50 bleached kraft northern softwood and bleached kraft eucalyptus using the forming equipment and configuration described in Example 1. in this case, the machine speed was 2500 fpm (762 m/min).
  • the resulting wet web at an approximate basis weight of 20 pounds/2880 ft2 (9 kg/268m 2 ), was passed through four vacuum boxes at 19.8, 19.8, 22.6, and 23.6 inches of mercury (67.1, 67.1, 76.5 and 79.9 kPa), respectively.
  • the resulting wet web was then sent through the additional integrally-sealed dewatering system also described in Example 1.
  • the air press was set to maintain a pressure of 15 psig (204.7 kPa) in the plenum and pre and post air press samples were taken for consistency measurement. Results obtained for Example 7 are shown below in Table 3 .
  • Example 7 The experiment of Example 7 was repeated except this time the air press was reconfigured to eliminate the integral seal between the air press plenum and the associated collection box. Specifically, the sealing load and hence the impingement of the cross-machine sealing blades was reduced until a leak between the plenum and the collection box became apparent. At this point, the air press plenum/collection box arrangement was set to a nominal 0.1 inch (0.3 cm) gap, though it was not possible to actually see the spacing between the plenum and the box as it was occupied by the fabrics and the wet web. The air flow to the plenum increased to the maximum obtainable from the compressor and a post dewatering consistency sample taken. Results obtained for Example 8 are shown below in Table 3 .
  • any reduction in the integral seal results in a significant loss in the dewatering capability of the air press. Specifically, approximately 25% less water was removed (0.61 pounds/pound versus 0.81) when the integral seal was lost, even though the plenum and collection box were still in apparent contact with the fabrics. The associated 2% loss in post dewatering consistency would translate to approximately a 10% reduction in machine speed on a machine that was speed limited due to drying limitations. Such a limitation would be expected on a wet-pressed machine that was converted to the configuration of this invention.
  • a wet web was formed, with a fiber blend of 50:50 bleached kraft northern softwood and bleached kraft eucalyptus, into a 20 gsm sheet at 2000 fpm (610 m/min) as described in Example 1.
  • the wet web was then vacuum dewatered using 4 vacuum boxes at vacuum levels of approximately 18, 18, 17 and 21, inches of mercury (61.0, 61.0, 57.6 and 71.1 kPa) respectively.
  • a vacuum box consistency sample was taken. The results are shown in Table 4 .
  • Example 9 The experiment of Example 9 was repeated but with a steam "blow box" (Devronizer) added to increase the dewatering.
  • the steam box was not integrally sealed to the vacuum box, and it thus thought to be similar to an apparatus disclosed in U.S. Patent 5,230,776 .
  • Steam flow to the Devronizer was approximately 136 kg (300 pounds) per hour. Again a consistency sample was taken to determine the increase attributable to the addition of the steam blow box. The results are shown in Table 4.
  • Example 8 The experiment of Example 8 was repeated but with the integrally sealed air press of Example 1 added to the process.
  • the air press was operated at 15 psig (204.7 kPa) plenum pressure and a vacuum level of 17 inches of mercury (57.6 kPa). Again, a consistency sample was taken to determine the increase attributable to the addition of the integrally sealed air press. The results are shown in Table 4.
  • Table 4 ID Consistency % Example 9 24.2
  • Example 10 24.8

Claims (72)

  1. Procédé de fabrication d'un voile cellulosique (36), comprenant :
    a) le dépôt d'une suspension aqueuse de fibres papetières sur une première toile sans fin (14) pour former un voile humide (10) ;
    b) le transfert du voile humide (10) vers une seconde toile sans fin (24);
    c) la prise en sandwich du voile humide (10) entre la seconde toile (24) et une toile support (22) ;
    d) le passage du voile humide (10), pris en sandwich entre la seconde toile (24) et la toile support (22), entre une chambre sous pression d'air (18) et un dispositif de collecte (20), tandis que la seconde toile (24) est disposée entre le voile humide (10) et le dispositif de collecte (20), la chambre sous pression d'air (18) et le dispositif de collecte (20) étant associés opérationnellement et adaptés à créer une différence de pression, d'un côté à l'autre du voile humide (10), de 101,6 kPa (30 pouces de mercure) ou plus et un courant de fluide pressurisé au travers du voile humide (10) de 43,9 x 103 cm3 par minute et par cm2 (10 pieds cube standard par minute et par pouce 2) ou plus ;
    e) l'essorage du voile humide (10) en utilisant le courant de fluide pressurisé jusqu'à une concentration en fibres de 30 pour cent ou plus ;
    f) le pressage du voile humide essoré (10), avec la seconde toile (24), contre la surface d'un cylindre de séchage chauffé (30) ; et
    g) le séchage du voile humide essoré (10) jusqu'à une siccité finale.
  2. Procédé selon la revendication 1, dans lequel la suspension aqueuse de fibres papetières est déposée sur la première toile (14), le voile humide (10) est essoré jusqu'à une concentration en fibres allant jusqu'à 10 pour cent, après quoi le voile humide est transféré vers la seconde toile (24).
  3. Procédé selon la revendication 1 ou 2, dans lequel la différence de pression d'un côté à l'autre du voile humide (10) est comprise entre 118,5 et 203,2 kPa (entre 35 et 60 pouces de mercure).
  4. Procédé selon la revendication 1, 2 ou 3, dans lequel le fluide pressurisé est pressurisé entre 135,8 et 308,2 kPa (entre 5 et 30 livres par pouce2, pression relative).
  5. Procédé selon l'une quelconque des revendications précédentes, dans lequel le dispositif de collecte (20) comprend une caisse à vide qui tire un vide allant de plus de 0 à 84,7 kPa (plus de 0 à 25 pouces de mercure).
  6. Procédé selon la revendication 1, dans lequel le temps de séjour dans la presse à air (16) est de 10 millisecondes ou moins.
  7. Procédé selon la revendication 6, dans lequel le temps de séjour dans la presse à air (16) est de 7,5 millisecondes ou moins.
  8. Procédé selon la revendication 1, dans lequel le voile humide (10) se déplace à une vitesse de 305 mètres par minute (1000 pieds par minute) ou plus et dans lequel la concentration en fibres du voile humide augmente de 5 pour cent ou plus, de l'entrée à la sortie de la presse à air (16).
  9. Procédé selon la revendication 1, dans lequel le voile humide (10) se déplace à une vitesse de 610 mètres par minute (2000 pieds par minute) ou plus et dans lequel la concentration en fibres du voile humide augmente de 5 pour cent ou plus, de l'entrée à la sortie de la presse à air (16).
  10. Procédé selon la revendication 1, dans lequel 85 pour cent, ou plus, du fluide pressurisé fourni à la chambre sous pression d'air (18) s'écoule au travers du voile humide (10).
  11. Procédé selon la revendication 10, dans lequel 90 pour cent, ou plus, du fluide pressurisé fourni à la chambre sous pression d'air (18) s'écoule au travers du voile humide (10).
  12. Procédé selon l'une quelconque des revendications précédentes, dans lequel la température du fluide pressurisé est de 300 degrés Celsius ou moins.
  13. Procédé selon la revendication 12, dans lequel la température du fluide pressurisé est de 150 degrés Celsius ou moins.
  14. Procédé selon l'une quelconque des revendications précédentes, dans lequel le cylindre de séchage chauffé (30) inclut une hotte de séchoir (34) et dans lequel la seconde toile (24) qui est pressée contre le cylindre de séchage se sépare de la hotte de séchoir avant que le voile humide (10) pénètre dans la hotte de séchoir.
  15. Procédé selon l'une quelconque des revendications précédentes, dans lequel la seconde toile (24), qui est pressée contre le cylindre de séchage (30), enveloppe le cylindre de séchage sur une distance inférieure à la distance totale sur laquelle le voile (10) est en contact avec le cylindre de séchage.
  16. Procédé selon l'une quelconque des revendications précédentes, dans lequel le voile humide essoré (10) est transféré vers le cylindre de séchage chauffé (30) en utilisant une paire de rouleaux de transfert (32, 55) qui forment un enveloppement étendu d'une envergure prédéterminée.
  17. Procédé selon la revendication 16, dans lequel l'un au moins des rouleaux de transfert (55) n'est pas sollicité contre le cylindre de séchage chauffé (30).
  18. Procédé selon la revendication 16, dans lequel l'un au moins des rouleaux de transfert (32) est sollicité contre le cylindre de séchage chauffé (30).
  19. Procédé selon l'une quelconque des revendications précédentes, dans lequel le voile humide essoré (10) est pressé contre le cylindre de séchage (30) selon une pression de 159 kg par 2,5 cm linéaires (350 livres par pouce linéaire) ou moins.
  20. Procédé selon l'une quelconque des revendications précédentes, dans lequel un agent anti-adhérent est ajouté à la seconde toile (24), qui est pressée contre le cylindre de séchage chauffé (30), pour faciliter le transfert du voile humide essoré (10).
  21. Procédé selon l'une quelconque des revendications précédentes, dans lequel le courant de fluide pressurisé transfère le voile humide essoré (10) vers la seconde toile (24).
  22. Procédé selon l'une quelconque des revendications précédentes, dans lequel le voile séché (36) est enlevé du cylindre de séchage chauffé (30), sans crêpage.
  23. Procédé selon l'une quelconque des revendications 1 à 21, dans lequel le voile humide essoré (10) est séché jusqu'à une concentration en fibres de 95 pour cent ou plus, puis crêpé.
  24. Procédé selon l'une quelconque des revendications 1 à 21, dans lequel le voile humide essoré (10) est partiellement séché jusqu'à une concentration en fibres allant de 40 à 80 pour cent sur la surface du cylindre de séchage chauffé (30), crêpé à l'état humide, puis soumis à un séchage final jusqu'à une concentration en fibres de 95 pour cent ou plus.
  25. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'appareil est une version modifiée de machine de fabrication de papier mousseline, pressé à l'état humide.
  26. Procédé selon l'une quelconque des revendications précédentes, dans lequel la seconde toile (24) remplace un feutre d'une machine classique de fabrication de papier mousseline, pressé à l'état humide.
  27. Procédé selon l'une quelconque des revendications précédentes, dans lequel la chambre sous pression d'air (18) est située au sein du circuit de la seconde toile sans fin (24).
  28. Procédé selon l'une quelconque des revendications précédentes, dans lequel un sabot à vide (50) transfère le voile humide essoré (10) vers la seconde toile (24) avant le transfert du voile humide essoré sur le cylindre de séchage chauffé (30).
  29. Procédé selon l'une quelconque des revendications précédentes, dans lequel la première toile (14) est une toile de formation.
  30. Procédé selon l'une quelconque des revendications précédentes, dans lequel la seconde toile (24) est une toile de moulage.
  31. Procédé selon l'une quelconque des revendications 1 à 26, dans lequel la chambre sous pression d'air (18) est située dans la section de presse d'une version modifiée de machine de fabrication de papier mousseline pressé à l'état humide.
  32. Procédé selon la revendication 1, comprenant en outre la configuration de la seconde toile (24) pour réaliser un arc (α) d'enveloppement par le voile humide essoré (10), autour d'un rouleau presseur (32), inférieur à 90 degrés.
  33. Procédé selon la revendication 1, dans lequel l'arc (α) d'enveloppement par le voile humide essoré (10), autour du rouleau presseur (32), est inférieur à 45 degrés.
  34. Procédé selon la revendication 1, dans lequel l'arc (α) d'enveloppement par le voile humide essoré (10), autour du rouleau presseur (32), est inférieur à 10 degrés.
  35. Procédé selon l'une quelconque des revendications précédentes, comprenant, en outre, le positionnement, dans le sens travers, d'éléments d'étanchéité pour dévier la course de déplacement du voile humide (10) et des première (14) et seconde (24) toiles, en direction du dispositif de collecte (20).
  36. Procédé selon la revendication 35, dans lequel la quantité minimale d'impact des éléments d'étanchéité, dans le sens travers, dans les toiles supports (22) est définie par l'équation : h min = T W ⁢ cosh Wd T - 1 ;
    Figure imgb0006
    où : "T" est la tension des première (14) et seconde (24) toiles mesurée en livres par pouce ; "W" est une différence de pression d'un côté à l'autre du voile (10) mesurée en livres par pouce carré ; et "d" est un interstice entre une lame d'étanchéité et le dispositif de collecte (20) dans le sens machine, mesuré en pouce.
  37. Procédé selon la revendication 1, dans lequel la suspension aqueuse de fibres papetières est déposée entre la première toile sans fin (14) et la seconde toile sans fin (24).
  38. Procédé de fabrication d'un voile cellulosique, comprenant:
    a) le dépôt d'une suspension aqueuse de fibres papetières entre une première toile sans fin (14) et une seconde toile sans fin (24) pour former un voile humide (10), le voile humide (10) étant pris en sandwich entre les première (14) et seconde (24) toiles;
    b) le passage du voile humide (10), pris en sandwich entre les première (14) et seconde (24) toiles, entre une chambre sous pression d'air (18) et un dispositif de collecte (20), tandis que la seconde toile (24) est disposée entre le voile humide (10) et le dispositif de collecte (20), la chambre sous pression d'air (18) et le dispositif de collecte (20) étant associés opérationnellement et adaptés à créer une différence de pression, d'un côté à l'autre du voile humide (10), de 101,6 kPa (30 pouces de mercure) ou plus et un courant de fluide pressurisé au travers du voile humide (10) de 43,9 x 103 cm3 par minute et par cm2 (10 pieds cube standard par minute et par pouce2) ou plus ;
    c) l'essorage du voile humide (10) en utilisant le courant de fluide pressurisé jusqu'à une concentration en fibres de 30 pour cent ou plus ;
    d) le pressage du voile humide essoré (10), avec la seconde toile (24), contre la surface d'un cylindre de séchage chauffé (30) ; et
    e) le séchage du voile humide essoré (10) jusqu'à une siccité finale.
  39. Procédé selon la revendication 38, dans lequel la différence de pression d'un côté à l'autre du voile humide (10) est comprise entre 118,5 et 203,2 kPa (entre 35 et 60 pouces de mercure).
  40. Procédé selon la revendication 38 ou 39, dans lequel le fluide pressurisé est pressurisé entre 135,8 et 308,2 kPa (entre 5 et 30 livres par pouce2, pression relative).
  41. Procédé selon l'une quelconque des revendications 38, 39 ou 40, dans lequel le dispositif de collecte (20) comprend une caisse à vide qui tire un vide allant de plus de 0 à 84,7 kPa (plus de 0 à 25 pouces de mercure).
  42. Procédé selon la revendication 38, dans lequel le temps de séjour dans la presse à air (16) est de 10 millisecondes ou moins.
  43. Procédé selon la revendication 42, dans lequel le temps de séjour dans la presse à air (16) est de 7,5 millisecondes ou moins.
  44. Procédé selon la revendication 38, dans lequel le voile humide (10) se déplace à une vitesse de 305 mètres par minute (1000 pieds par minute) ou plus et dans lequel la concentration en fibres du voile humide augmente de 5 pour cent ou plus, de l'entrée à la sortie de la presse à air (16).
  45. Procédé selon la revendication 38, dans lequel le voile humide (10) se déplace à une vitesse de 610 mètres par minute (2000 pieds par minute) ou plus et dans lequel la concentration en fibres du voile humide augmente de 5 pour cent ou plus, de l'entrée à la sortie de la presse à air (16).
  46. Procédé selon la revendication 38, dans lequel 85 pour cent, ou plus, du fluide pressurisé fourni à la chambre sous pression d'air (18) s'écoule au travers du voile humide (10).
  47. Procédé selon la revendication 46, dans lequel 90 pour cent, ou plus, du fluide pressurisé fourni à la chambre sous pression d'air (18) s'écoule au travers du voile humide (10).
  48. Procédé selon l'une quelconque des revendications 38 à 47, dans lequel la température du fluide pressurisé est de 300 degrés Celsius ou moins.
  49. Procédé selon la revendication 48, dans lequel la température du fluide pressurisé est de 150 degrés Celsius ou moins.
  50. Procédé selon l'une quelconque des revendications 38 à 49, dans lequel le cylindre de séchage chauffé (30) inclut une hotte de séchoir (34) et dans lequel la seconde toile (24) qui est pressée contre le cylindre de séchage se sépare de la hotte de séchoir avant que le voile humide essoré (10) pénètre dans la hotte de séchoir.
  51. Procédé selon la revendication 38, dans lequel la seconde toile (24), qui est pressée contre le cylindre de séchage (30), enveloppe le cylindre de séchage sur une distance inférieure à la distance totale sur laquelle le voile (10) est en contact avec le cylindre de séchage.
  52. Procédé selon l'une quelconque des revendications 38 à 51, dans lequel le voile humide essoré (10) est transféré vers le cylindre de séchage chauffé (30) en utilisant une paire de rouleaux de transfert (32, 55) qui forment un enveloppement étendu d'une envergure prédéterminée.
  53. Procédé selon la revendication 52, dans lequel l'un au moins des rouleaux de transfert (55) n'est pas sollicité contre le cylindre de séchage chauffé (30).
  54. Procédé selon la revendication 52, dans lequel l'un au moins des rouleaux de transfert (32) est sollicité contre le cylindre de séchage chauffé (30).
  55. Procédé selon l'une quelconque des revendications 38 à 54, dans lequel le voile humide essoré (10) est pressé contre le cylindre de séchage (30) selon une pression de 159 kg par 2,5 cm linéaires (350 livres par pouce linéaire) ou moins.
  56. Procédé selon l'une quelconque des revendications 38 à 55, dans lequel un agent anti-adhérent est ajouté à la seconde toile (24), qui est pressée contre le cylindre de séchage chauffé (30), pour faciliter le transfert du voile humide essoré (10)..
  57. Procédé selon l'une quelconque des revendications 38 à 56, dans lequel le courant de fluide pressurisé transfère le voile humide essoré (10) vers la seconde toile (24).
  58. Procédé selon l'une quelconque des revendications 38 à 57, dans lequel le voile humide essoré (36) est enlevé du cylindre de séchage chauffé (30), sans crêpage.
  59. Procédé selon l'une quelconque des revendications 38 à 57, dans lequel le voile humide essoré (10) est séché jusqu'à une concentration en fibres de 95 pour cent ou plus, puis crêpé.
  60. Procédé selon l'une quelconque des revendications 38 à 58, dans lequel le voile humide essoré (10) est partiellement séché jusqu'à une concentration en fibres allant de 40 à 80 pour cent sur la surface du cylindre de séchage chauffé (30), crêpé à l'état humide, puis soumis à un séchage final jusqu'à une concentration en fibres de 95 pour cent ou plus.
  61. Procédé selon l'une quelconque des revendications 38 à 60, dans lequel l'appareil est une version modifiée de machine de fabrication de papier mousseline, à formeur en croissant
  62. Procédé selon l'une quelconque des revendications 38 à 61, dans lequel la seconde toile (24) remplace un feutre d'une machine de fabrication de papier mousseline, à formeur en croissant.
  63. Procédé selon l'une quelconque des revendications 38 à 60, dans lequel la chambre sous pression d'air (18) est située au sein du circuit de la seconde toile sans fin (24).
  64. Procédé selon l'une quelconque des revendications 38 à 62, dans lequel la chambre sous pression d'air (18) est située au sein du circuit de la première toile sans fin (14).
  65. Procédé selon l'une quelconque des revendications 38 à 64, dans lequel un sabot à vide (50) transfère la voile humide essoré (10) vers la seconde toile (24) avant le transfert du voile humide essoré (10) sur le cylindre de séchage chauffé (30).
  66. Procédé selon l'une quelconque des revendications 38 à 65, dans lequel la première toile (14) est une toile formation.
  67. Procédé selon l'une quelconque des revendications 38 à 66, dans lequel la seconde toile (24) est une toile de moulage.
  68. Procédé selon l'une quelconque des revendications 38 à 67, comprenant, en outre, le positionnement, dans le sens travers, d'éléments d'étanchéité pour dévier la course de déplacement du voile humide (10) et des première (14) et seconde (24) toiles, en direction du dispositif de collecte (20) .
  69. Procédé selon la revendication 68, dans lequel la quantité minimale d'impact des éléments d'étanchéité, dans le sens travers, dans les toiles supports (22) est définie par l'équation : h min = T W ⁢ cosh Wd T - 1 ;
    Figure imgb0007
    où : "T" est la tension des première (14) et seconde (24) toiles mesurée en livres par pouce ; "W" est une différence de pression d'un côté à l'autre du voile mesurée en livres par pouce carré ; et "d" est un interstice entre une lame d'étanchéité et le dispositif de collecte (20) dans le sens machine, mesuré en pouce.
  70. Procédé selon l'une quelconque des revendications 38 à 69, comprenant en outre la configuration de la seconde toile (24) pour réaliser un arc (α) d'enveloppement par le voile humide essoré (10), autour d'un rouleau presseur (32), inférieur à 90 degrés.
  71. Procédé selon la revendication 70, dans lequel l'arc (α) d'enveloppement par le voile humide essoré (10), autour du rouleau presseur (32), est inférieur à 45 degrés.
  72. Procédé selon la revendication 70, dans lequel l'arc (α) d'enveloppement par le voile humide essoré (10), autour du rouleau presseur (32), est inférieur à 10 degrés.
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US607711 1990-11-01
US607712 1996-02-27
US09/607,711 US6497789B1 (en) 2000-06-30 2000-06-30 Method for making tissue sheets on a modified conventional wet-pressed machine
US09/607,712 US6454904B1 (en) 2000-06-30 2000-06-30 Method for making tissue sheets on a modified conventional crescent-former tissue machine
PCT/US2001/019807 WO2002002869A2 (fr) 2000-06-30 2001-06-21 Procede de fabrication de feuilles de tissu sur une presse humide conventionnelle modifiee

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US5230776A (en) * 1988-10-25 1993-07-27 Valmet Paper Machinery, Inc. Paper machine for manufacturing a soft crepe paper web
US6149767A (en) * 1997-10-31 2000-11-21 Kimberly-Clark Worldwide, Inc. Method for making soft tissue
US6083346A (en) * 1996-05-14 2000-07-04 Kimberly-Clark Worldwide, Inc. Method of dewatering wet web using an integrally sealed air press
US6187137B1 (en) * 1997-10-31 2001-02-13 Kimberly-Clark Worldwide, Inc. Method of producing low density resilient webs

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6953065B2 (en) 2002-10-24 2005-10-11 Albany International Corp. Paired warp triple layer forming fabrics with optimum sheet building characteristics
US7048012B2 (en) 2002-10-24 2006-05-23 Albany International Corp. Paired warp triple layer forming fabrics with optimum sheet building characteristics
DE102009021264A1 (de) 2009-05-14 2010-12-09 Fleissner Gmbh Verfahren und Vorrichtung zur Herstellung eines Faserpulpe-Vliesstoffes

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BR0112114A (pt) 2003-09-30
EP1294982A2 (fr) 2003-03-26
DE60130761D1 (de) 2007-11-15
DE60130761T2 (de) 2008-07-17
CA2415937A1 (fr) 2002-01-10
CA2415937C (fr) 2009-05-19
AU2001268634B2 (en) 2005-04-28
ATE374862T1 (de) 2007-10-15
CO5650179A2 (es) 2006-06-30
CN1440480A (zh) 2003-09-03
KR20030034111A (ko) 2003-05-01
WO2002002869A3 (fr) 2002-05-16
AU6863401A (en) 2002-01-14
BR0112114B1 (pt) 2013-04-02
WO2002002869A2 (fr) 2002-01-10
KR100822568B1 (ko) 2008-04-16
MXPA02012362A (es) 2005-04-19

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