Patent Application
20240401271
The present disclosure relates generally to apparatuses and processes for removing water from wet fibrous webs, and more particularly, to apparatuses and processes for removing water from a capillary cylinder utilized in dewatering fibrous webs in a papermaking process.
In papermaking processes, a papermaking furnish may be formed into a wet fibrous web, and in turn, various devices may be used to remove water from the advancing fibrous web. For example, some manufacturing configurations may include drying devices such as vacuum boxes, hot air dyers, capillary dewatering apparatuses, and Yankee dryers, such as disclosed in U.S. Pat. Nos. 3,301,746; 4,556,450; and 5,598,643.
Dewatering apparatuses are used to remove water from fibrous structures of the type made in “wet-laid” papermaking processes. For metal porous covers currently used in these apparatuses, if the holes are made smaller to enable higher vacuum pressure and more dewatering, then the cover cannot be cleaned, and efficiency drops. Use of a vacuum is desired because it reduces the amount of water that must be evaporated downstream using hot air from burning natural gas. Further, the shape of the hole of metal porous cover is hypothesized to be a limiting factor to water removal efficiency. As such, there is a need for an improved dewatering apparatus that is easy to clean with improved efficiency, while using a vacuum.
In accordance with one aspect of the present disclosure, a capillary dewatering apparatus is provided, in which the dewatering apparatus may comprise a framework comprising a plurality of apertures, and a flexible member disposed around an exterior surface of the framework, wherein an inner surface of the flexible member is in contact with at least a portion of the exterior surface of the framework, and wherein the flexible member and the framework are not bonded.
In accordance with another aspect of the present disclosure, a dewatering apparatus is provided, in which the dewatering apparatus may comprise a rigid framework comprising a plurality of apertures, and a porous flexible member disposed such that an inner surface of the pourous flexible member is in contact with an exterior surface of the rigid framework, wherein a porosity of the porous flexible member is less than a porosity of the apertures in the rigid framework.
In accordance with another aspect of the present disclosure, a capillary dewatering process is provided, in which the process may comprise moving a wet web on a top side of a first belt, the first belt further comprising a bottom side; contacting the wet web with a top side of a flexible member, such that liquid flows from the wet web through a thickness of the flexible member; and contacting an exterior surface of a framework with a bottom side of the flexible member, such that the liquid flows from the flexible member to an interior portion of the framework. The flexible member may be porous. The framework may comprise a plurality of apertures. The flexible member may be configured to move independently of the framework.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following description which is taken in conjunction with the accompanying drawings in which like designations are used to designate substantially identical elements, and in which:
As used herein, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.
Fibrous structures such as paper towels, bath tissues, and facial tissues may be made in a “wet laying” process in which a slurry of fibers, usually wood pulp fibers, is deposited onto a forming wire and/or one or more papermaking belts such that an embryonic fibrous structure can be formed, after which drying and/or bonding the fibers together results in a fibrous structure. Further processing the fibrous structure can be carried out such that a finished fibrous structure can be formed. For example, in typical papermaking processes, the finished fibrous structure is the fibrous structure that is wound on the reel at the end of papermaking, and can subsequently be converted into a finished product (e.g., a sanitary tissue product) by ply-bonding and embossing, for example.
“Fibrous structure” as used herein means a structure that comprises a plurality of fibers. In one example, a fibrous structure according to the present disclosure means an orderly arrangement of fibers within a structure in order to perform a function. A bag of loose fibers is not a fibrous structure in accordance with the present disclosure. The terms “embryonic web,” and “embryonic fibrous web” are used to describe a wet web that forms a fibrous structure after drying, i.e., a dry web. Further, fibrous structures may be rolled, interleaved, perforated, and/or packaged to form final product(s), such as a sanitary tissue product.
A “ply” as used herein means an individual fibrous structure optionally to be disposed in a substantially contiguous, face-to-face relationship with other plies, forming a multiple ply fibrous structure. It is also contemplated that a single fibrous structure can effectively form two “plies” or multiple “plies,” for example, by being folded on itself. A ply may comprise multiple layers. Multiple plies may, for example be formed as follows: fibrous structure of the present disclosure may be combined with one or more additional fibrous structures, which is the same or different from the fibrous structures of the present disclosure to form a multi-ply sanitary tissue product; said additional fibrous structure may be combined with the fibrous structure of the present disclosure by any suitable means.
“Sanitary tissue product” as used herein means a soft, low density (i.e., <about 0.25 g/cm3) fibrous structure useful as a wiping implement for post-urinary and post-bowel movement cleaning (toilet tissue), for otorhinolaryngological discharges (facial tissue), and multi-functional absorbent and cleaning uses (absorbent towels and napkins). The sanitary tissue product may be convolutedly wound upon itself about a core or without a core to form a roll of sanitary tissue product. Further, the fibrous structure making up the sanitary tissue product may be perforated to form interconnected sheets.
The term “compressible” as used herein means with respect to an inner ring of a process roller that the inner ring is compressible in a radial direction, i.e., the inner ring's thickness TIR is compressible. For example, an outer surface of the inner ring may deform radially inwardly a greater extent than an inner surface of the inner ring such that the outer surface deforms radially inward toward the inner surface.
The term “deformable” as used herein means with respect to an outer ring of a process roller that the outer ring is deformable inwardly, i.e., both the inner and outer surfaces of the outer ring may deform inwardly together, so as to conform to the shape of an adjacent mating roller.
“Machine Direction” or “MD” as used herein means the direction parallel to the flow of the fibrous structure through the papermaking machine and/or product manufacturing equipment.
“Cross Machine Direction” or “CD” as used herein means the direction perpendicular to the machine direction in the same plane of the fibrous structure.
The term “rigid” as used herein with respect to a framework means that a component holds its shape under the forces of its application in the papermaking process, i.e., it is not flexible like fabric.
The wet-laying process can be configured such that the finished fibrous structure has visually distinct features produced in the wet-laying process. Various forming wires and papermaking belts utilized can be configured to leave a physical, three-dimensional impression in the finished paper. Such three-dimensional impressions are known in the art, particularly in the art of “through air drying” (TAD) processes, with such impressions often being referred to a “knuckles” and “pillows.” Knuckles may be regions formed in the finished fibrous structure corresponding to the “knuckles” of a papermaking belt, i.e., the filaments or resinous structures that are raised at a higher elevation than other portions of the belt. Likewise, “pillows” may be regions formed in the finished fibrous structure at the relatively lower elevation regions between or around knuckles.
Thus, in the description below, the term “knuckles” or “knuckle region,” or the like can be used for either the raised portions of a papermaking belt or the corresponding portions formed in the paper made on the papermaking belt, and the meaning should be clear from the context of the description herein. Likewise “pillow” or “pillow region” or the like can be used for either the portion of the papermaking belt between, within, or around knuckles (also referred to in the art as “deflection conduits” or “pockets”), or the relatively lower elevation regions between, within, or around knuckles in the paper made on the papermaking belt, and the meaning should be clear from the context of the description herein. In general, knuckles or pillows can each be continuous, semi-continuous or discrete, as described herein.
Knuckles and pillows in paper towels and bath tissue can be visible to the retail consumer of such products. The knuckles and pillows can be imparted to a fibrous structure from a papermaking belt in various stages of production, i.e., at various consistencies and at various unit operations during the drying process, and the visual pattern generated by the pattern of knuckles and pillows can be designed for functional performance enhancement as well as to be visually appealing. Such patterns of knuckles and pillows can be made according to the methods and processes described in U.S. Pat. Nos. 4,514,345; 6,398,910; and 6,610,173, as well as U.S. Patent Publication No. 2016/0159007 A1; and U.S. Patent Publication No. 2013/0199741 A1 that describe belts that are representative of papermaking belts made with cured polymer on a woven reinforcing member. Fabric creped belts can also be utilized, such as disclosed in U.S. Pat. Nos. 7,494,563; 8,152,958; and 8,293,072. It is to be appreciated that some papermaking belts may comprise resin molding or resin deflection members, such as disclosed in U.S. Pat. No. 9,322,136, which is incorporated by reference herein. Additional descriptions of resins on papermaking belts are disclosed in U.S. Patent Publication Nos. 2017/0233951 A1; 2016/0090693 A1; 2016/0090692 A1; and 2016/0090698 A1, which are all incorporated by reference herein.
The present disclosure relates to methods for making fibrous webs, and in particular, to methods and apparatuses for removing water from a wet fibrous web during the manufacture of a fibrous structure. During the process of making a fibrous structure, various methods and apparatuses may be utilized to remove water from a wet porous web, such as a capillary dewatering apparatus. In some configurations, a capillary dewatering apparatus may include a capillary cylinder having an outer perimeter surface comprising a capillary porous media. A molding member, such as a papermaking belt comprising an air permeable fabric, may advance the wet fibrous web onto the rotating capillary cylinder. As such, the fibrous web is positioned between the capillary porous media and the air-permeable fabric. The capillary porous media comprises a first surface and a second surface positioned radially inward of the first surface, and water flows from the fibrous web through pores in the first surface and radially inward toward the second surface.
It is to be appreciated that various process and equipment configurations may be used to make fibrous structures. For example,
After the aqueous dispersion of fibers is deposited onto the foraminous member 104, the embryonic fibrous web 106 is formed, typically by the removal of a portion of the aqueous dispersing medium by techniques, such as for example, vacuum boxes, forming boards, hydrofoils, and other various equipment known to those of skill in the art. The embryonic fibrous web 106 may travel with the foraminous member 104 about return roll 110 and may be brought into contact with a molding member 114. The molding member 114 may comprise an air permeable fabric 118. The embryonic fibrous web 106 is transferred from the foraminous member 104 onto molding member 114. The transfer may be completed by any means known to those of skill in the art including, but not limited to, vacuum transfer, rush transfer, couch transfer, or combinations thereof. Various approaches to transfer may include those described in U.S. Pat. Nos. 4,440,597; 5,830,321; 6,733,634; 7,399,378; and 8,328,985. During the transfer onto the molding member 114, the embryonic fibrous web 106 may be deflected into deflection conduits or molded into the topology of the molding member 114. In addition, while in contact with the molding member 114, the embryonic fibrous web 106 can be further dewatered to form an intermediate fibrous web 116. The molding member 114 can be in the form of an endless belt 120, also referred to herein as a papermaking belt. In this simplified representation of
It is to be appreciated that the molding member 114 may be configured in various ways, such as an endless belt as just discussed or some other configuration, such as a stationary plate that may be used in making handsheets or a rotating drum that may be used with other types of continuous processes. As previously mentioned, the molding member 114 may comprise an air permeable fabric 118, and as such, the molding member 114 may be foraminous. As such, the forming member 114 may include continuous passages connecting a first surface 128 with a second surface 130. The first surface 128 (or “upper surface” or “working surface” or “outer surface”) may be configured as the surface with which the embryonic fibrous web 106 is associated. And the second surface 130 (or “lower surface” or “inner surface”) may be configured as the surface with which the molding member return rolls 122 are associated. Thus, the molding member 114 may be constructed in such a manner that when water is caused to be removed from the embryonic fibrous web 106 and/or intermediate fibrous web 116 in the direction of the molding member 114, such as by the application of differential fluid pressure such with a vacuum box 132, the water may be discharged from the apparatus 100 without having to again contact the embryonic fibrous web 106 in either a liquid state or vapor state.
As previously mentioned, various methods and apparatuses may be used to dry the intermediate fibrous web 116. Examples of such suitable drying process include subjecting the intermediate fibrous web 116 to conventional and/or flow-through dryers and/or Yankee dryers. In one example of a drying process, the intermediate fibrous web 116 in association with the molding member 114 passes around the molding member return rolls 122 and travels in the direction indicated by directional arrows 126. The intermediate fibrous web 116 may advance to a predryer section or system 134. The predryer system may 134 may include a conventional flow-through dryer (hot air dryer) and/or a capillary dewatering apparatus 136, such as shown in
With continued reference to
As previously mentioned, the predryer system 134 may include a capillary dewatering apparatus 136. As shown in
The inner radial volume of the capillary cylinder 152 may also be segmented into various zones, having different air pressures and wherein various different operations may be carried out. For example, as shown in
The dewatering apparatus 136 may comprise a framework 151, 152 (e.g., a capillary cylinder) comprising a plurality of apertures or pores, and a flexible member 119 (also referred to herein as a porous flexible member) disposed around an exterior surface 156 (or “perimeter surface”) of the framework 151, 152, in which an inner surface (not labeled in
In accordance with aspects of the present disclosure, a length of the flexible member 119 may exceed an outer perimeter of a contact surface of the framework 151, 152, in which the contact surface is defined by the exterior surface 156. In aspects, the length of the flexible member 119 may be at least two times larger than the outer perimeter of the contact surface of the framework 151, 152. In aspects, the length of the flexible member 119 may be at least five times larger than the outer perimeter of the contact surface of the framework 151, 152. In aspects, the length of the flexible member 119 is at least ten times larger than the outer perimeter of the contact surface of the framework 151, 152.
In accordance with aspects of the present disclosure, the flexible member 119 comprise a variety of materials. In aspects, the flexible member 119 may be an apertured film, for example as shown in
With reference to
While a vacuum 132 is useful in removing water from the fibrous web 117, if the vacuum pressure P1 is too high, it may cause punctures to form in the fibrous web 117, which is not desired. The pressure at which punctures are likely to form in the fibrous web is known as “breakthrough pressure.” Improved capillary dewatering enables a lower vacuum pressure P1 to be applied, as more water is removed from the fibrous web 117 by the capillary dewatering process, thus avoiding use of a pressure near breakthrough pressure. Smaller effective pore diameters in the flexible member 119 increase the efficiency of water removal in capillary dewatering. However, conventional metal framework structures are difficult to clean if the pore diameters are too small, as these smaller pores are easily clogged and thus the water removal efficiency declines with the smaller pore.
In aspects, the flexible member 119 may comprise between two and eight layers 228, 230, for example as shown in exemplary
Cleaning may be performed by a cleaning means 174 such as a shower. Cleaning means 174 may be located within the framework 151, 152 (such as depicted in exemplary
In general, a porosity of the flexible member 119 may be less than a porosity of the apertures in the rigid framework 151, 152. In accordance with aspects of the present disclosure, the flexible member 119 may have an effective pore diameter of 1-20 μm (microns). In aspects, the flexible member 119 may have an effective pore diameter of 1-5 μm. As used herein, the term “porosity” refers to the fractional volume that is not occupied by solid material. The porosity of a material or object (or a portion/region thereof) may be calculated as follows:
where φ=porosity, Vv=void volume, and VT=total volume.
The effective pore size may be determined using capillary flow porometry. Typically, pores are thought of in terms such as voids, holes or conduits in a porous material. Usually, the pores in natural and manufactured porous materials are not perfectly cylindrical, nor all uniform. Therefore, the effective pore diameter, as disclosed herein, may not equate exactly to measurements of void dimensions obtained by other methods such as microscopy. However, the effective pore diameter provides an accepted means to characterize relative differences in void structure between materials.
The equipment operates by changing the test chamber air pressure in user-specified increments, either by decreasing pressure (increasing pore size) to absorb liquid, or increasing pressure (decreasing pore size) to drain liquid. The liquid volume absorbed at each pressure increment is the cumulative volume for the group of all pores between the preceding pressure setting and the current setting.
In addition to the test materials, a blank condition (no sample between plexiglass plate and Millipore Filter) is run to account for any surface and/or edge effects within the chamber. Any pore volume measured for this blank run is subtracted from the applicable pore grouping of the test sample. This data treatment can be accomplished manually or with the available TRI/Autoporosimeter Data Treatment Software, Release 2000.1.
Referring now to
In accordance with aspects of the present disclosure, the flexible member and the framework are not bonded to each other. In aspects, the framework may be stationary, and the flexible member may be configured to rotate around the framework. In aspects, the wet web and the framework may form a nip through which the flexible member runs. In aspects, the flexible member and/or the framework may rotate at a similar rate as the wet web, in which the framework is or is capable of being stationary.
In accordance with aspects of the present disclosure, the capillary dewatering process 300 may further comprise applying a vacuum to the wet web, in which the vacuum is disposed within the framework. In aspects, the wet web may have a breakthrough pressure, and the vacuum may be applied at a pressure below the breakthrough pressure of the wet web.
In accordance with aspects of the present disclosure, the capillary dewatering process 300 may further comprise cleaning the flexible member at a location separate from the framework. A variety of cleaning techniques and means may be used to clean the flexible member, including using a flooded nip or cleaning boxes, as well as using cleaning water that is distinct from the water removed from the web.
In accordance with aspects of the present disclosure, the capillary dewatering process 300 may further comprise subjecting the wet web to thermal drying, in which after contacting the exterior of the framework with a bottom side of the flexible member but before thermal drying, the wet web has a consistency of greater than 30%. In aspects, the wet web has a consistency of between 30%-55%. In aspects, the wet web has a consistency of between 30%-50%. Consistency may be calculated according to the following formula:
Consistency is typically expressed in terms of a percentage. The wet weight is equal to the dry fiber weight plus the weight of the water (i.e., the water content) that is not removed by the dewatering process. The dry weight may be measured after conditioning in a conditioned room at a temperature of 23.0° C.±1.0° C. and a relative humidity of 50%±2% for a minimum of 2 hours prior to weighing dry weight using a Mettler Toledo balance model PB3001 or a similar instrument. The wet weight is determined by weighing the wet web following the dewatering process in a sealed and tared container on a Mettler Toledo balance model PB3001, and then the consistency may be determined by comparing the wet weight to the dry weight per the formula above. Alternatively, both wet and dry weight can be measured using an Ohaus® MB45 moisture balance (or an equivalent instrument) set to a drying temperature of 130° C., with moisture determined after the weight changes less than 1 mg in 60 seconds (i.e., A60 hold time). After testing is complete, the fibrous paper sample dry weight is re-checked by drying the paper sample for three drying cycles on an 11.5 inch Adirondack Machine Corp. drum dryer, wherein each drying cycle is done at 230° F. and 0.9 R.P.M., with a residence time of 54 seconds per cycle. Following the three drying cycles, the dried fibrous paper is weighed on a Mettler Toledo balance model PB3001.
In accordance with aspects of the present disclosure, the capillary dewatering process 300 may further comprise pre-wetting the flexible member. The process 300 may comprise pre-wetting both the capillary layer and the reservoir layer of the flexible member.
Testing is performed to determine the efficiency of dewatering of a prior art 6-layer metal plate framework (“Sample A”), as compared with an exemplary flexible member in accordance with present disclosure comprising an effective pore diameter of 1 μm (as determined using capillary flow porometry) (“Sample B”). Each Sample is 15 inches long. Sample A and Sample B are pre-wetted to saturation. Dry fibrous paper (also 15 inches long) is placed in a conditioned room at a temperature of 23.0° C.±1.0° C. and a relative humidity of 50%±2% for a minimum of 2 hours, then the dry weights of the un-wetted fibrous paper are taken. The un-wetted fibrous paper is then placed on top of the saturated sample. Next, the fibrous paper is wetted with a quantity of water to achieve 23% consistency and then rested for 2 minutes, which is sufficient time for the water to spread throughout the fibrous paper.
To test each sample, the saturated wet sample with the 23% consistency fibrous paper on top is pulled across a vacuum table for four minutes, with the vacuum table having vacuum slots with a slot width of 0.0625 inches, such that the average residence time in the vacuum slot is 1 second, which is enough residence time for water transport. The vacuum of the vacuum table is applied through the vacuum slot at a vacuum pressure of 6 Hg (which is less than the air breakthrough pressure of the capillary layer fabric) to dewater the wetted paper,. After dewatering, the vacuum is turned off and the dewatered paper is weighed in a sealed tared container to determine the wet weight, and thus the percent consistency per formula above. Next, each sample member is cleaned by backflushing water in a flat pan containing 2 liters of deionized water (from reverse osmosis water purification). Another fibrous paper is then wetted, and the dewatering process and backflush cleaning is repeated three more times, using the same sample member. The percent consistency for each repeat of the experiment is show below in TABLE 1.
As can be seen in Table 1, the dewatering efficiency of the prior art member (Sample A) decreased with each repeat of the dewatering experiment. By contrast, the dewatering efficiency of the exemplary flexible member (Sample B) increased with each repeat of the dewatering experiment. The absolute loss in dewatering performance between the first and fourth dewatering experiment is shown in TABLE 2.
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”
Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
