SYSTEMS AND METHODS FOR CLEANING COMPOSITE LAMINATED IMPRINTING FABRICS

Abstract

A system and method of cleaning an imprinting fabric used to make bath tissue, paper towel, or facial tissue, in which the imprinting fabric is washed with water from high pressure impact showers and flooding showers, and water remaining on the imprinting fabric after the step of washing is removed with a vacuum roll on a sheet side of the imprinting fabric. The system and method does not involve removing water from the fabric with a uhle box on the sheet side of the imprinting fabric.

Claims

1. A method of cleaning an imprinting fabric used in a papermaking process to make bath tissue, paper towel, or facial tissue, comprising: washing the imprinting fabric with water from high pressure impact showers and flooding showers; and removing water remaining on the imprinting fabric after the step of washing with a vacuum roll on a sheet side of the imprinting fabric, the sheet side of the imprinting fabric being configured to be in direct contact with a paper web during the papermaking process.

2. The method of claim 1, wherein the vacuum roll comprises a metal wire mesh, rubber, or polyurethane material shell with an internal stationary vacuum box.

3. The method of claim 3, further comprising removing water remaining on the imprinting fabric with a uhle box on a woven side of the imprinting fabric that is opposite to the sheet side.

4. The method of claim 1, wherein the method does not comprise removing water from the fabric with a uhle box on the sheet side of the imprinting fabric.

5. The method of claim 1, wherein a vacuum box resides completely inside a contact zone between the vacuum roll and imprinting fabric and extends between 1 to 90 degrees along a circumference of the vacuum roll.

6. The method of claim 1, wherein vacuum pulled through the vacuum roll is between −5 to −100 kilopascals.

7. The method of claim 1, wherein total air flow through a section of roughly one meter of a vacuum box is between 100-1000 cubic meters per minute.

8. A structured fabric cleaning station comprising: at least one impact shower; at least one flooding shower; at least one uhle box disposed at a fabric side of an imprinting fabric; and at least one vacuum roll disposed at a nonwoven side of the imprinting fabric, wherein the cleaning station does not comprise a uhle box at the nonwoven side of the imprinting fabric.

9. The structured fabric cleaning station of claim 8, wherein the vacuum roll comprises a metal wire mesh, rubber, or polyurethane material shell with an internal stationary vacuum box.

10. The structured fabric cleaning station of claim 8, wherein a vacuum box resides completely inside a contact zone between the vacuum roll and imprinting fabric and extends between 1 to 90 degrees along a circumference of the vacuum roll.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Exemplary embodiments of the present disclosure will be described with references to the accompanying figures, wherein:

[0049] FIG. 1 is a block diagram of an imprinting section of a TAD machine in accordance with an exemplary embodiment of the present invention; and

[0050] FIG. 2 is a perspective view of a vacuum roll according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0051] Bath tissue, paper towel, and facial tissue paper can be made using technologies that use imprinting fabrics to improve the quality of the paper product, for example by improving sheet caliper and softness. Maintaining the cleanliness of the imprinting fabric is important to maintain productivity of the paper machine and quality of the finished product. In order to maintain the cleanliness of the imprinting fabric, flooding and impact showers are utilized along with both sheet and non-sheet side (roll side) stationary uhle boxes. However, use of a stationary uhle box on the sheet side of a laminated composite imprinting fabric can cause delamination and failure of the overlaid imprinting fabric. Overlaid imprinted fabrics can be produced by many methods, but they all involve adding polymer elements on the surface of a belt or fabric to create patterns in the paper. The overlaid fabric can be produced by laminating two sheets of materials or printing polymer on top of a woven or nonwoven carrier fabric. In addition to lamintation, screen printing or nozzle printing can also be used.

[0052] In accordance with exemplary embodiments of systems and methods of the present invention, a vacuum roll rather than a uhle box is used on the sheet side of the fabric after the cleaning showers. This configuration removes the excess water and any remaining fibers from the fabric without any damage to the fabric itself. Conventional cleaning stations do not use a vacuum roll on a sheet side of a structured fabric.

[0053] A vacuum roll in accordance with an exemplary embodiment of the present invention may include an external shell with holes and/grooves formed completely through the shell. The external shell may be made of materials, such as, for example, metal, rubber, polyurethane, metal wire mesh and combinations thereof, to name a few. A stationary vacuum box may be disposed within the shell. The shell has a contact zone in which the shell is in contact with the impring fabric. The vacuum box resides completely inside the contact zone and extends between 1 to 90 degrees along the circumference of the vacuum roll, more preferably 2 to 45 degress or 2-30 degress, and most preferablly 2-20 degress. Seals may be disposed at the border of the contact zone. A vacuum system is used to remove water, entrained air, cellulosic fibers, chemistry and other material in the fabric through the vacuum box of the vacuum roll. The vacuum system may include components, such as, for example, a centrifugal pump or blower, piping and a separator, to name a few. The vacuum pulled through the vacuum roll is between −5 to −100 kilopascals (kpa), more preferably −10 to −90 kpa, and most preferably −30 to −70 kpa. The total air flow through a section of roughly one meter of the vacuum box is between 100-1000 cubic meters per min, more preferably 200-800 cubic meters per minute or 250-600 cubic meters per minute, most preferably 250-500 cubic meters per minute. Vacuum rolls are available through The Voith Group (Heidenheim, Germany), Andtriz AG (Graz, Austria), and Valmet (Espoo, Finland).

[0054] FIG. 1 shows an imprinting section of a TAD machine accordance to an exemplary embodiment of the present invention. The imprinting fabric 11 receives the paper web from a forming fabric 14 at a second transfer vacuum box 2. The web travels on the imprinting fabric 11 across a moulding box 3 and through two TAD drums 4 with air impingement hoods 5 before being transferred to the Yankee dryer 12 at the pressure roll 6. The imprinting fabric 11 then travels across a guide roll 7 into a cleaning station that uses a flooded nip shower 8 and a sheet and non sheet side impact shower 9. Excess water is removed using a non sheet side uhle box 10 and a sheet side vacuum roll 13. The non sheet side uhle box can have a single or double slot with each slot between 5 to 20 mm, more preferably 10 to 15 mm and pulls a vacuum of −20 to −60 kpa of vacuum, more preferably −30 to −50 kpa. The preferred pressure of the impact showers 9 is between 10 to 50 bar, more preferably 20 to 40 bar. The preferred flow through each meter of the flooding shower 8 is 60 to 160 gallons per minute, more preferably 80 to 150 gallons per minute.

[0055] FIG. 2 shows a vacuum roll, generally designated by reference number 100, according to an exemplary embodiment of the present invention. As previously described, the vacuum roll 100 includes a perforated outer shell 110 and a vacuum box 120 disposed within the outer shell 110. The vacuum box 120 resides completely inside the contact zone of the outer shell 110 and extends between 1 to 90 degrees along the circumference of the vacuum roll 100, more preferably 2 to 45 degress or 2-30 degress, and most preferablly 2-20 degress. Seals 130 may be disposed at the border of the contact zone.

EXAMPLES

Example 1

[0056] A laminated composite imprinting fabric, P10SM TPU 30×9, was provided having a web contacting layer with the following characteristics and geometries: extruded netting with MD strands of 0.26 mm width×CD strands of 0.46 mm width, with a mesh of 30 MD strands per inch and a count of 9 CD strands per inch, % contact area of 26% with solely MD strands in plane in static measurement and then with 48% contact area under load as the structure compressed and the CD ribs moved into the same plane as the MD strands, due to use of the thermoplastic polyurethane (“TPU”) elastomeric material. The TPU material is a softer material and measured in the range of 65 to 75 Shore A Hardness while the woven supporting layer comprised of harder polyethylene terephthalate (“PET”) measured 95 to 105 Shore A Hardness using a portable Shore A Durometer test device calibrated per ASTM D 2240, the Mitutoyo Hardmatic HH-300 series, ASTD. The distance between MD elements in the web contacting layer was 0.60 mm, and the distance between the CD elements was 2.25 mm. The overall pocket depth was equal to the thickness of the TPU netting, which was equal to 0.50 mm. The pocket depth from the top surface of the netting to the CD mid-rib element was 0.25 mm. The TPU netting was a natural color, the permeability of the TPU laminated belt was 410 cubic feet per minute (“CFM”) and the laminated belt had a caliper of 0.99 mm. The peel force required to remove the web contacting layer from the woven supporting layer was 1400 grams per foot and the shear number was 225. The embedment distance was 0.14 mm. The supporting layer had a 0.27×0.22 mm cross-section rectangular MD yarn at 56 yarns/inch, and a 0.35 mm CD yarn at 41 yarns/inch. The weave pattern of the base layer was a 5-shed, 1 MD yarn over 4 CD yarns, then under 1 CD yarn, then repeated. The material of the base fabric yarns was 100% PET, and the yarns were transparent. The fabric was sanded at 25% contact area, with an air permeability of 675 CFM. The weft yarns received 0.40% carbon black content by weight in the CD, and the warp yarns received 0.14% carbon black content by weight in the MD. The base fabric and a Mylar protective cover fabric were not placed under any tension during the production process. Mylar, also known as BoPET (Biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, and chemical and dimensional stability. Other films can be used if they are non-stick and they are able to maintain dimensional stability. Suitable other non-stick films include polytetrafluorethylene (TEFLON), silicone treated films and the like. By non-stick is meant having a surface energy between about 10 mj/m.sup.2 to about 200 mj/m.sup.2. The TPU netting was placed under 0.50 PLI of tension during production. The welding laser was set to 40% power level (161 watts), at a welding head speed of 50 mm/sec and an optical line width of 34 mm with a 1 mm overlap between laser passes (line energy was set to 3200 J/m).

[0057] The composite belt was used on a TAD machine using a specific furnish recipe and paper machine running conditions, as follows:

[0058] Two webs of through air dried tissue were laminated to produce a roll of 2-ply sanitary (bath) tissue. Each tissue web was multilayered with the fiber and chemistry of each layer selected and prepared individually to maximize product quality attributes of softness and strength. The first exterior layer, which was the layer that contacted the Yankee dryer, was prepared using 100% eucalyptus with 1.375 kg/ton of the amphoteric starch, Redibond 2038 (Corn Products, 10 Finderne Avenue, Bridgewater, N.J. 08807). The interior layer was composed of 50% northern bleached softwood kraft fibers, 50% eucalyptus fibers, and 1.5 kg/ton of T526, a softener/debonder (EKA Chemicals Inc., 1775 West Oak Commons Court, Marietta, Ga., 30062) and 2.0 kg/ton of Hercobond 1194 glyoxylated polyacrylamide (Ashland, 500 Hercules Road, Wilmington Del., 19808). The second exterior layer was composed of 50% northern bleached softwood kraft fibers, 50% eucalyptus fibers and 4.125 kg/ton of Redibond 2038 and 2.0 kg/ton of Hercobond 1194.

[0059] All the softwood fibers were refined at 30 kwh/ton to impart the necessary tensile strength.

[0060] The fiber and chemicals mixtures were diluted to solids of 0.5% consistency and fed to separate fan pumps, which delivered the slurry to a triple layered headbox. The headbox pH was controlled to 7.0 by addition of a caustic to the thick stock that was fed to the fan pumps. The headbox deposited the slurry to a nip formed by a forming roll, an outer forming wire, and inner forming wire. When the fabrics separated, the web followed the inner forming wire and dried to approximately 25% solids using a series of vacuum boxes and a steam box.

[0061] The web was then transferred to the laminated composite fabric with the aid of a vacuum box to facilitate fiber penetration into the fabric to enhance bulk softness and web imprinting. The web was dried with the aid of two TAD hot air impingement drums to approximately 82% solids before being transferred to the Yankee dryer.

[0062] The web was held in intimate contact with the Yankee drum surface running at 1100 m/min using an adhesive coating chemistry. The Yankee dryer was provided with steam at 4.5 bar with a installed hot air impingement hood over the Yankee dryer. In accordance with an exemplary embodiment of the present invention, the web was creped from the yankee dryer at 15% crepe (speed differential between the Yankee dryer and reel drum) at approximately 96.0% solids. The web was was reeled into two equally sized parent rolls and transported to the converting process.

[0063] After the sheet transferred to the Yankee dryer, the laminated composite imprinting fabric proceeded to the cleaning station comprising a flooding shower, a sheet side and roll side impact fan shower, a sheet side vacuum roll, and a roll side uhle box. The fan showers were operating at 30 bar, the flooded nip shower was using 530 liters mer minute per meter length of the shower, the roll side (non-sheet side) uhle box with two 12.5 mm slots was operating at 34 kpa, and the vacuum roll with roughly a 7.5 degree vacuum box and a perforated brass shell at 67% open area was operating at a vacuum of −45 kpa with an air flow of approximately 325 cubic meters per minute.

[0064] The imprinting fabric was cleaned in the cleaning station with no productivity issues related to fabric cleanliness and no delamination of the imprinting fabric.

[0065] Now that embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon can become readily apparent to those skilled in the art. Accordingly, the exemplary embodiments of the present invention, as set forth above, are intended to be illustrative, not limiting. The spirit and scope of the present invention is to be construed broadly.