Patent Application
20180073195
The present invention relates to systems and methods for making an absorbent structure utilizing a water laid asset with a structured fabric
Across the globe there is great demand for disposable products including towel, sanitary tissue, and facial tissue. Important quality attributes of disposable sanitary tissue and facial tissue include softness and strength, while those of disposable towel include absorbency and strength. The various methods used to produce these products vary in their ability to generate these quality attributes.
Use of a structured fabric can deliver superior levels of bulk that improve absorbency and bulk softness of absorbent structures in disposable products. The higher the bulk and absorbency desired, the higher coarseness structured fabric that needs be utilized. A coarse fabric uses thick monofilament polymeric fibers to create deep valleys in the fabric for cellulosic or synthetic fibers (which compromise the absorbent structure) to penetrate and generate bulk. In structured fabrics made using topically applied and cured resin, an increased resin thickness is needed in order to obtain higher bulk. The downside of using these highly coarse or thick structured fabrics is that the surface smoothness will be negatively impacted. Further, when using TAD, UCTAD, ETAD, or the ATMOS (Twin Wire Configuration) methods (employing a structured fabric) to produce an absorbent structure, the fibers of the absorbent structure penetrate into the structured fabric through the application of vacuum pressure or as an effect of the speed differential between the absorbent structure and the structured fabric. These methods limit the maximum penetration depth and correspondingly, bulk that can be achieved. In an ATMOS process that utilizes a crescent former, the absorbent structure is formed directly between a wire and structured fabric, however, the structured fabric is placed in the inner position (with the structured fabric located between the absorbent structure and the forming roll) rather than the outer position (with the structured fabric located between the absorbent structure and the saveall pan). This means that the drainage of the absorbent structure occurs through the outer wire rather than the structured fabric. The centrifugal force around the forming roll forces water and fiber towards the outer wire limiting the fiber penetration into the structured fabric. Use of vacuum at the wet shaping box helps pull fibers deeper into the fabric, but the total penetration is much less than the void volume available in the fabric. A limitation of the NTT process is that the absorbent structure has to be pressed into the structured fabric which creates compaction that limits absorbency and softness potential.
There is a need in the art for a paper making machine whereby a web is pressed deeply into a structuring fabric in an efficient manner.
An object of the present invention is to provide a superior method for producing absorbent structures by directly forming and draining a nascent web through a structured fabric. Advantageously, in accordance with exemplary embodiments of the present invention, no fabric crepe, vacuum, or pressing is required to force the web that forms the absorbent structure into the structured fabric. Further, the nascent web is nearly 99.5% water during initial drainage through the structured fabric. This highly viscous nascent web can, therefore, penetrate deeply into the structured fabric using the centrifugal force from the forming roll to allow for high levels of total bulk generation with low coarseness structured fabrics. This preserves the smooth surface of the nascent web while still allowing for high levels of bulk, softness and absorbency.
A method of forming a fibrous web according to an exemplary embodiment of the present invention comprises: providing a fiber slurry; depositing the fiber slurry between an inner forming wire and an outer forming wire, wherein the outer forming wire comprises a structured fabric and the inner forming wire contacts a segment of a forming roll; and rotating the forming roll so that the fiber slurry moves into contact with the structured fabric.
In an exemplary embodiment, the step of depositing is performed by a single layer headbox, a double layer headbox or a triple layer headbox.
In an exemplary embodiment, fiber within the fiber slurry comprise natural fibers, synthetic fibers or a combination of natural and synthetic fibers.
In an exemplary embodiment, the fiber slurry comprises up to 99.95% water.
In an exemplary embodiment, the method further comprises the step of draining the fiber slurry through the structured fabric.
In an exemplary embodiment, the method further comprises: separating the inner forming wire from the outer forming wire; and applying negative pressure from a vacuum box located on an underside of the outer forming wire to adhere a web formed from the fiber slurry to the outer forming wire.
In an exemplary embodiment, the method further comprises the step of dewatering the web by passing the web across one or more vacuum boxes.
In an exemplary embodiment, the method further comprises the step of drying the web, the drying step performed using a belt press having a hot air impingement hood, through air drying cylinders with associated air recirculation systems, or pressure rolls and steam heated cylinders with or without hot air impingement hoods.
In an exemplary embodiment, the method further comprises the step of creping the web from a steam heated cylinder.
In an exemplary embodiment, the method further comprises the steps of calendering and reeling the web.
In an exemplary embodiment, the structured fabric comprises woven monofilaments, the woven monofilaments comprising synthetic polymers.
In an exemplary embodiment, the synthetic polymers comprise polyethylene, polypropylene or nylon.
In an exemplary embodiment, the structured fabric further comprises an overlaid resin.
In an exemplary embodiment, the structured fabric is formed by laying down successive layers of material under computer control.
In an exemplary embodiment, the process of laying down successive layers of material comprises: Fused Deposition Modeling (FDM), PolyJet Technolgy, Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Selective Laser Sintering (SLS), Stereolithography (SLA), or Laminated Object Manufacturing (LOM)
A wet section of a paper forming machine according to an exemplary embodiment of the present invention comprises: a headbox; a forming roll disposed adjacent to the headbox; an inner forming wire in contact with the forming roll, the inner forming wire configured to run around the forming roll; and an outer forming wire comprising a structured fabric, wherein the headbox is configured to deliver a fiber slurry to an area between the inner forming wire and the outer forming wire.
The features and advantages of exemplary embodiments of the present invention will be more fully understood with reference to the following, detailed description when taken in conjunction with the accompanying figures, wherein:
Headbox 201 deposits the slurry into a forming surface comprising a outer structured fabric and an inner forming wire. As shown, in embodiments of the invention, the forming surface is a nip formed by an inner forming wire 205 which runs around forming roll 202, and an outer forming wire 203. In embodiments of the invention, outer forming wire 203 is a woven or polymer overlaid structured fabric (“outer forming wire” and “structured fabric” may be used interchangeably herein below). The slurry is drained through the structured fabric to form a web.
In embodiments of the invention, the slurry contains up to 99.95% water, fibers (either natural, synthetic or a combination of both), chemical polymers, and additives.
In embodiments of the invention, because the outer forming wire 203 is a structured fabric, the centrifugal force created by the rotating forming roll 202 forcefully presses the highly viscous nascent web into the structured fabric of the outer forming wire 203. As a result, the web penetrates deeply into the structured fabric allowing for high levels of total bulk generation with low coarseness structured fabrics.
In embodiments of the invention, the structured fabric is a woven structure that is formed of monofilaments (e.g. yarns, threads) composed of synthetic polymers (preferably polyethylene, polypropylene, or nylon). In embodiments of the invention, the structured fabric is provided with a hardened, cured overlaid resin.
It will be understood that the structured fabric may be manufactured using any of various processes for forming a three-dimensional object, but most preferably through an additive processes in which successive layers of material are laid down under computer control. These processes are generally classified as 3-D printing technologies. For example, these processes include but are not limited to any of the following: Fused Deposition Modeling (FDM), PolyJet Technolgy, Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Selective Laser Sintering (SLS), Stereolithography (SLA), or Laminated Object Manufacturing (LOM).
In embodiments of the invention, after passing through the forming surface, the inner forming wire 205 separates from the web, and the web is then carried on the structured fabric 203. In embodiments of the invention, a vacuum box 204 is used to assist in web adherence to structured fabric 203. The web is preferably conveyed across one or more dewatering boxes 206 to facilitate dewatering and imprinting the structure of the structured fabric into the web.
After passing the one or more dewatering boxes 206, the web is conveyed on the structured fabric 203 to a belt press. In embodiments of the invention, the belt press is comprised of a permeable belt 207 which contacts the inner (non-web supporting) side of the structured fabric 203 and a permeable dewatering fabric 212, which contacts the web. Preferably, a hot air impingement hood 209 is provided within the belt press that contains a steam shower 208, and a vacuum roll 210. In embodiments of the invention, vacuum roll 210 has through and blind drilled holes in its cover (rubber or polyurethane in different embodiments of the invention). The web is heated by the steam and hot air of the hot air impingement hood 209 to lower the viscosity of the water within the web which is being pressed by the belt press to move the water into the dewatering fabric 212 and into the vacuum roll 210. The vacuum roll 210 holds a significant portion of the water within the through and blind drilled holes in the roll cover until vacuum is broken at the exit of the vacuum box, upon which time the water is deposited into a save-all pan 211. The air flow through the web, provided by the hot air hood 209 and vacuum of the vacuum roll 210, also facilitates water removal as moisture is trapped in the air stream. At this stage, the web properties are influenced by factors such as the structured fabric design and low intensity pressing. The bulk softness of the web is preserved due to the low intensity nip of the belt press which will not compress the web portions within the valleys of the structured fabric 203. The smoothness of the web is influenced by the unique surface topography imprinted by the structured fabric 203 which is dependent on the parameters of weave pattern, mesh, count, weft and warp monofilament diameter, caliper and percentage of the fabric that is knuckle verses valley.
In embodiments of the invention, after exiting the belt press, the web then travels through a second press comprised of a hard roll and soft roll. Press roll 213 located on the inside surface of the dewatering fabric 212 contains a vacuum box to facilitate water removal as the web passes through the nip of the hard and soft rolls. Thereafter, the web is transported by the structured fabric 203 to a wire turning roll 214 (having an optional vacuum box) to a nip between a blind and through drilled polyurethane or rubber covered press roll 215 and steam heated pressure cylinder 216. In embodiments of the invention press roll 215 is a solid polyurethane or rubber roll without vacuum. The web solids are up to 50% solids as the web is transferred to the steam heated cylinder 216. Heated cylinder 216 is preferably coated with chemicals that improve web adhesion to the dryer, improve heat transfer through the web, and assist in web removal at the creping doctor 220. The chemicals are constantly being applied using a sprayboom 218, while excess chemical is removed using a cleaning doctor blade 219. The web is dried by the steam heated cylinder 216 along with an installed hot air impingement hood 217 to a solids content of around 97.5%. The web is removed from the steam heated cylinder 216 using a ceramic doctor blade 220 with a pocket angle of 90 degrees at the creping doctor. At this stage, the web properties are influenced by the creping action occurring at the creping doctor. A larger creping pocket angle will increase the frequency and fineness of the crepe bars imparted to the web's first exterior surface, which improves surface smoothness. In one preferred embodiment of the invention, a ceramic doctor blade is used which allows for a fine crepe bar pattern to be imparted to the web for a long duration of time as compared to a steel or bimetal blade. The creping action imparted at the blade also improves web flexibility, which is improved as the web adherence to the dryer is increased. The creping force is influenced by the chemistry applied to the steam heated cylinder, the percentage of web contact with the cylinder surface which is a result of the knuckle pattern of the structured fabric, and the percent web solids upon creping.
Subsequent to the creping step, the web optionally travels through a set of calenders 221 running, for example, 15% slower than the steam heated cylinder. The action of calendering improves sheet smoothness but results in lower bulk softness by reducing overall web thickness. The amount of calendering can be influenced by the attributes needed in the finished product. For example, a low sheet count, 2-ply, rolled sanitary tissue product will need less calendering than the same roll of 2-ply sanitary product at a higher sheet count and the same roll diameter and firmness. Thus, the thickness of the web may need to be reduced using calendering to allow for more sheets to fit on a roll of sanitary tissue given limitations to roll diameter and firmness. After calendering, the web is reeled using a reel drum 222 into a parent roll 223.
The parent roll 223 can be converted into 1 or 2-ply rolled sanitary or towel products or 1, 2, or 3 ply folded facial tissue products.
In other embodiments of the invention, rather than adhering the web to a steam heated cylinder, the web can be removed from the structured fabric to directly proceed to the calendering section. Any variety of methods can be used to remove the web from the structured fabric. For example, rather than vacuum being supplied to the pressure roll, positive air pressure is used to transfer the sheet from the structured fabric onto a vacuum roll. The vacuum roll contains a vacuum zone and a zone with positive air pressure used to release the sheet from the roll and allow it to proceed through the calenders. A tube threader system may be used to thread the sheet from this vacuum roll through the calenders and reel drum after a web break. A similar system is used to thread after a break from the creping doctor when a steam heated cylinder is utilized.
Having described this invention with regard to specific embodiments, it is to be understood that the description is not meant as a limitation since further modifications and variations may be apparent or may suggest themselves to those skilled in the art. It is intended that the present application cover all such modifications and variations.
| Number | Date | Country | |
|---|---|---|---|
| 62393468 | Sep 2016 | US |
