Patent Application
20190017224
My invention relates to methods and apparatuses for manufacturing paper products such as paper towels and bathroom tissue. In particular, my invention relates to methods that use a molding roll to mold a paper web during the formation of the paper product.
Generally speaking, paper products are formed by depositing a furnish comprising an aqueous slurry of papermaking fibers onto a forming section to form a paper web, and then dewatering the web to form a paper product. Various methods and machinery are used to form the paper web and to dewater the web. In papermaking processes to make tissue and towel products, for example, there are many ways to remove water in the processes, each with substantial variability. As a result, the paper products likewise have a large variability in properties.
One such method of dewatering a paper web is known in the art as conventional wet pressing (CWP).
A CWP papermaking machine, such as papermaking machine 100, typically has low drying costs, and can quickly produce the parent roll 190 at speeds from about three thousand feet per minute to in excess of five thousand feet per minute. Papermaking using CWP is a mature process that provides a papermaking machine having high runability and uptime. As a result of the compaction used to dewater the web 102 at the press nip 130, the resulting paper product typically has a low bulk with a corresponding high fiber cost. While this can result in rolled paper products, such as paper towels or toilet paper, having a high sheet count per roll, the paper products generally have a low absorbency and can feel rough to the touch.
As consumers often desire paper products that feel soft and have a high absorbance, other papermaking machines and methods have been developed. Through-air-drying (TAD) is one method that results in paper products with high bulk.
The TAD fabric 216 carrying the paper web 102 next passes around through-air dryers 222, 224 where hot air is forced through the web to increase the consistency of the paper web 102, from about twenty-eight percent solids to about eighty percent solids. The web 102 is then transferred to the Yankee dryer section 140, where the web 102 is further dried. The sheet is then doctored off the Yankee drum 142 by doctor blade 152 and is taken up by a reel (not shown) to form a parent roll (not shown). As a result of the minimal compaction during the drying process, the resulting paper product has a high bulk with corresponding low fiber cost. Unfortunately, this process is costly to operate because a lot of water is removed by expensive thermal drying. In addition, the papermaking fibers in a paper product made by TAD typically are not strongly bound, resulting in a paper product that can be weak.
Other methods have been developed to increase the bulk and softness of the paper product as compared to CWP, while still retaining strength in the paper web and having low drying costs as compared to TAD. These methods generally involve compactively dewatering the wet web and then belt creping the web so as to redistribute the web fibers in order to achieve desired properties. This method is referred to herein as belt creping and is described in, for example, U.S. Pat. No. 7,399,378, U.S. Pat. No. 7,442,278, U.S. Pat. No. 7,494,563, U.S. Pat. No. 7,662,257, and U.S. Pat. No. 7,789,995 (the disclosures of which are incorporated by reference in their entirety).
The web 102 is then transferred onto a creping belt 322 in a belt creping nip 320 by the action of the creping nip 320. The creping nip 320 is defined between the backing roll 312 and the creping belt 322, with the creping belt 322 being pressed against the backing roll 312 by a creping roll 326. In the transfer at the creping nip 320, the cellulosic fibers of the web 102 are repositioned and oriented. The web 102 may tend to stick to the smoother surface of the backing roll 312 relative to the creping belt 322. Consequently, it may be desirable to apply release oils on the backing roll 312 to facilitate the transfer from the backing roll 312 to the creping belt 322. Also, the backing roll 312 may be a steam heated roll. After the web 102 is transferred onto the creping belt 322, a vacuum box 324 may be used to apply a vacuum to the web 102 in order to increase sheet caliper by pulling the web 102 into the creping belt 322 topography.
It generally is desirable to perform a rush transfer of the web 102 from the backing roll 312 to the creping belt 322 in order to facilitate transfer to creping belt 322 and to further improve sheet bulk and softness. During a rush transfer, the creping belt 322 is traveling at a slower speed than the web 102 on the backing roll 312. Among other things, rush transferring redistributes the paper web 102 on the creping belt 322 to impart structure to the paper web 102 to increase bulk and to enhance transfer to the creping belt 322.
After this creping operation, the web 102 is deposited on a Yankee drum 142 in the Yankee dryer section 140 in a low intensity press nip 328. As with the CWP papermaking machine 100 shown in
According to one aspect, my invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers, dewatering the nascent web from a consistency of about ten percent solids to about seventy percent solids, moving the dewatered web on a transfer surface, and applying a vacuum at a molding zone defined between the transfer surface and a molding roll. The molding roll includes (i) an interior, (ii) an exterior, and (iii) a permeable patterned surface on the exterior of the molding roll. The permeable patterned surface has a plurality of recesses and is permeable to air. The vacuum is applied in the interior of the molding roll to cause air to flow through the permeable patterned surface into the interior of the molding roll. The method also includes transferring the dewatered web from the transfer surface to the permeable patterned surface of the molding roll at the molding zone. The vacuum is applied during the transferring of the dewatered web from the transfer surface to the permeable patterned surface of the molding roll, and the papermaking fibers of the dewatered web are (i) redistributed on the permeable patterned surface and (ii) drawn into the plurality of recess of the permeable patterned surface, in order to form a molded paper web. The method further includes transferring the molded paper web to a drying section and drying the molded paper web in the drying section to form a fibrous sheet.
According to another aspect, my invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers, dewatering the nascent web from a consistency of about ten percent solids to about seventy percent solids, moving the dewatered web on a transfer surface and applying a vacuum at a first molding zone defined between the transfer surface and a first molding roll. The first molding roll includes (i) an interior, (ii) an exterior, and (iii) a permeable patterned surface on the exterior of the molding roll. The permeable patterned surface of the first molding roll has a plurality of recesses and is permeable to air. The vacuum is applied in the interior of the molding roll to cause air to flow through the permeable patterned surface into the interior of the first molding roll. The method also includes transferring the dewatered web from the transfer surface to the permeable patterned surface of the first molding roll at the first molding zone. The vacuum applied at the first molding zone is applied during the transfer of the dewatered web from the transfer surface to the permeable patterned surface of the first molding roll, and papermaking fibers on a first side of the dewatered web are (i) redistributed on the permeable patterned surface of the first molding roll and (ii) drawn into the plurality of recesses of the permeable patterned surface of the first molding roll, in order to form a paper web having a molded first side. The method further includes transferring the paper web from the first permeable patterned surface of the first molding roll at a second molding zone defined between the first molding roll and a second molding roll. The second molding roll includes (i) an exterior and (ii) a patterned surface on the exterior of the second molding roll. The patterned surface of the second molding roll has a plurality of recesses and is permeable to air. The paper web is transferred to the patterned surface of the second molding roll and the papermaking fibers on a second side of the paper web are redistributed (i) on the permeable patterned surface of the second molding roll and (ii) into the plurality of recesses of the patterned surface of the second molding roll, in order to form a molded paper web. In addition, the method includes transferring the molded paper web to a drying section and drying the molded paper web in the drying section to form a fibrous sheet.
These and other aspects of my invention will become apparent from the following disclosure.
My invention relates to papermaking processes and apparatuses that use a molding roll to produce a paper product. I will describe embodiments of my invention in detail below with reference to the accompanying figures. Throughout the specification and accompanying drawings, the same reference numerals will be used to refer to the same or similar components or features.
The term “paper product,” as used herein, encompasses any product incorporating papermaking fibers. This would include, for example, products marketed as paper towels, toilet paper, facial tissues, etc. Papermaking fibers include virgin pulps or recycle (secondary) cellulosic fibers, or fiber mixes comprising at least fifty-one percent cellulosic fibers. Such cellulosic fibers may include both wood and non-wood fibers. Wood fibers include, for example, those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers, and hardwood fibers, such as eucalyptus, maple, birch, aspen, or the like. Examples of fibers suitable for making the products of my invention include nonwood fibers, such as cotton fibers or cotton derivatives, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers. Additional papermaking fibers could include non-cellulosic substances such as calcium carbonite, titanium dioxide inorganic fillers, and the like, as well as typical manmade fibers like polyester, polypropylene, and the like, which may be added intentionally to the furnish or may be incorporated when using recycled paper in the furnish.
“Furnishes” and like terminology refers to aqueous compositions including papermaking fibers, and, optionally, wet strength resins, debonders, and the like, for making paper products. A variety of furnishes can be used in embodiments of my invention. In some embodiments, furnishes are used according to the specifications described in U.S. Pat. No. 8,080,130 (the disclosure of which is incorporated by reference in its entirety). As used herein, the initial fiber and liquid mixture (or furnish) that is dried to a finished product in a papermaking process will be referred to as a “web,” “paper web,” a “cellulosic sheet,” and/or a “fibrous sheet.” The finished product may also be referred to as a cellulosic sheet and or a fibrous sheet. In addition, other modifiers may variously be used to describe the web at a particular point in the papermaking machine or process. For example, the web may also be referred to as a “nascent web,” a “moist nascent web,” a “molded web,” and a “dried web.”
When describing my invention herein, the terms “machine direction” (MD) and “cross machine direction” (CD) will be used in accordance with their well understood meaning in the art. That is, the MD of a fabric or other structure refers to the direction that the structure moves on a papermaking machine in a papermaking process, while CD refers to a direction crossing the MD of the structure. Similarly, when referencing paper products, the MD of the paper product refers to the direction on the product that the product moved on the papermaking machine in the papermaking process, and the CD of the product refers to the direction crossing the MD of the product.
When describing my invention herein, specific examples of operating conditions for the paper machine and converting line will be used. For example, various speeds and pressures will be used when describing paper production on the paper machine. Those skilled in the art will recognize that my invention is not limited to the specific examples of operating conditions including speeds and pressures that are disclosed herein.
The nascent web 102 is then transferred along a felt run 118 to a dewatering section 410. In some applications, however, a dewatering section separate from the forming section 110 is not required, as will be discussed, for example, in the second embodiment below. The dewatering section 410 increases the solids content of the nascent web 102 to form a moist nascent web 102. The preferable consistency of the moist nascent web 102 may vary depending upon the desired application. In this embodiment, the nascent web 102 is dewatered to form a moist nascent web 102 having a consistency preferably between about twenty percent solids and about seventy percent solids, more preferably between about thirty percent solids to about sixty percent solids, and even more preferably between about forty percent solids to about fifty-five percent solids. The nascent web 102 is dewatered concurrently with being transferred from the papermaking felt 116 to a backing roll 312. The dewatering section 410 shown uses a shoe press roll 314 to dewater the nascent web 102 against the backing roll 312, as described above with reference to
After being dewatered, the moist nascent web 102 is transferred from the surface of the backing roll 312 to a molding roll 420 in a molding zone. In this embodiment, the molding zone is a molding nip 430 formed between the backing roll 312 and the molding roll 420. In the molding nip 430, the papermaking fibers are redistributed by a patterned surface 422 of the molding roll 420 resulting in a paper web 102 that has variable and patterned fiber orientations and variable and patterned basis weights. In particular, the patterned surface 422 preferably includes a plurality of recesses (or “pockets”) and, in some cases, projections that produce corresponding protrusions and recesses in the molded web 102. The molding roll 420 is rotating in a molding roll direction, which is counterclockwise in
The use of the molding roll 420 imparts substantial benefits to the papermaking process. Wet molding the web 102 with the molding roll 420 improves desirable sheet properties such as bulk and absorbency over paper products produced by CWP shown in
In the first embodiment, the moist nascent web 102 may be transferred from the backing roll 312 to the molding roll 420 by a rush transfer. During a rush transfer, the molding roll 420 is traveling at a slower speed than the web 102 and the backing roll 312. In this regard, the web 102 is creped by the speed differential and the degree of creping is often referred to as the creping ratio. The creping ratio in this embodiment may be calculated according to Equation (1) as:
Creping Ratio (%)=(S1/S2−1)×100% Equation (1)
where S1 is the speed of the backing roll 312 and S2 is the speed of the molding roll 420.
Preferably, the web 102 is creped at a ratio of about five percent to about sixty percent. But, high degrees of crepe can be employed, approaching or even exceeding one hundred percent. The creping ratio is often proportional to the degree of bulk in the sheet, but inversely proportional to the throughput of the paper machine and thus yield of the papermaking machine 400. In this embodiment, the velocity of the paper web 102 on the backing roll 312 may preferably be from about one thousand feet per minute to about six thousand five hundred feet per minute. More preferably velocity of the paper web 102 on the backing roll 312 is as fast as the process allows, which is typically limited by the drying section 440. For higher bulk product where a slower paper machine speeds can be accommodated, a higher creping ratio is used.
The molding nip 430 may also be loaded in order to effect sheet transfer and to control sheet properties. When rush transfer or other methods, such as vacuum transfer discussed in the third embodiment below, are used, it is possible to have little or no compression at the molding nip 430. When molding nip 430 is loaded, the backing roll 312 preferably applies a load to the molding roll 420 from about twenty pounds per linear inch (“PLI”) to about three hundred PLI, more preferably from about forty PLI to about one hundred fifty PLI. But, for high strength, lower bulk sheets, those skilled in the art will appreciate that, in a commercial machine, the maximum pressure may be as high as possible, limited only by the particular machinery employed. Thus, pressures in excess of one hundred fifty PLI, five hundred PLI, or more may be used, if practical, and, when a rush transfer is used, provided the difference in speed between the backing roll 312 and the molding roll 420 can be maintained and sheet property requirements are met.
After being molded, the molded web 102 is transferred to a drying section 440 where the web 102 is further dried to a consistency of about ninety-five percent solids. The drying section 440 may principally comprise a Yankee dryer section 140. As discussed above, the Yankee dryer section 140 includes, for example, a steam filled drum 142 (“Yankee drum”) that is used to dry the web 102. In addition, hot air from wet end hood 144 and dry end hood 146 is directed against the web 102 to further dry the web 102 as it is conveyed on the Yankee drum 142. The web 102 is transferred from the molding roll 420 to the Yankee drum 142 at a transfer nip 450. Although the papermaking machine 400 of this embodiment is shown with a direct transfer from the molding roll 420 to the drying section 440, other intervening processes may be placed between the molding roll 420 and drying section 440 without deviating from the scope of my invention.
In this embodiment, transfer nip 450 is also a pressure nip. Here, a load is generated between the Yankee drum 142 and the molding roll 420 preferably having a line loading of from about fifty PLI to about three hundred fifty PLI. The web 102 will then transfer from the surface of the molding roll 420 to the surface of the Yankee drum. At consistencies from about twenty-five percent to about seventy percent, it is sometimes difficult to adhere the web 102 to the surface of the Yankee drum 142 firmly enough so as to thoroughly remove the web 102 from the molding roll 420. In order to increase the adhesion between the web 102 and the surface of the Yankee drum 142 as well as improve crepe at doctor blade 152, an adhesive may be applied to the surface of the Yankee drum 142. The adhesive can allow for high velocity operation of the system and high jet velocity impingement air drying, and also allow for subsequent peeling of the web 102 from the Yankee drum 142. An example of such an adhesive is a poly(vinyl alcohol)/polyamide adhesive composition, with an example application rate of this adhesive being at a rate of less than about forty milligrams per meter squared of sheet. Those skilled in the art, however, will recognize the wide variety of alternative adhesives, and further, quantities of adhesives, that may be used to facilitate the transfer of the web 102 to the Yankee drum 142.
The web 102 is removed from the Yankee drum 142 with the help of a doctor blade 152. After being removed from the Yankee dryer section 140, is taken up by a reel (not shown) to form a parent roll 190. Those skilled in the art will also recognize that other operations may be performed on the papermaking machine 400, especially, downstream of the Yankee drum 142 and before the reel (not shown). These operations may include, for example, calendering and drawing.
With use, the patterned surface 422 of the molding roll 420 may require cleaning. Papermaking fibers and other substances may be retained on the patterned surface 422 and, in particular, the pockets. At any one time during operation, only a portion of the patterned surface 422 is contacting and molding the paper web 102. In the arrangement of rolls shown in
An example papermaking machine 500 of the second embodiment using a TAD drying section 540 is shown in
Creping Ratio (%)=(S3/S4−1)×100% Equation (2)
where S3 is the speed of the transfer fabric 512 and S4 is the speed of the molding roll 520. Likewise, the molding roll 520 has a permeable patterned surface 522, which is similar to the patterned surface 422 of the molding roll 420, preferably having a plurality of recesses (or “pockets”) and, in some cases, projections that produce corresponding protrusions and recesses in the molded web 102.
Alternatively, the nascent web 102 may be minimally dewatered with a separate vacuum dewatering zone 212 in which suction boxes 214 remove moisture from the web 102 to achieve desirable consistencies of about ten percent solids and about thirty-five percent solids before the sheet reaches molding nip 530. Hot air may also be used in dewatering zone 212 to improve dewatering.
After molding, the web 102 is then transferred from the molding roll 520 to a drying section 540 at a transfer nip 550. As in the papermaking machine 200 discussed above with reference to
Creping Ratio (%)=(S4/S5−1)×100% Equation (3)
where S4 is the speed of the molding roll 520 and S5 is the speed of the TAD fabric 216. When rush transfer is used in both the molding nip 530 and the transfer nip 550, the total creping ratio (calculated by adding the creping ratios in each nip) is preferably between about five percent to about sixty percent. But as with molding nip 430 (see
The TAD fabric 216 carrying the paper web 102 next passes around through-air dryers 222, 224 where hot air is forced through the web to increase the consistency of the paper web 102, to about eighty percent solids. The web 102 is then transferred to the Yankee dryer section 140, where the web 102 is further dried and, after being removed from the Yankee dryer section 140 by doctor blade 152, is taken up by a reel (not shown) to form a parent roll (not shown).
Wet molding the moist nascent web 102 on the molding roll 520 at consistencies between about ten percent solids to about thirty-five percent solids produces a premium product with the associated costs of TAD discussed above, but still retains the other advantages of using a molding roll 520 including increased bulk and reduced fiber cost.
Additionally, this configuration gives a means to control so-called sidedness of the sheet. Sidedness can occur when one side of the paper web 102 has (or is perceived to have) different properties on one side of the paper web 102 and not the other. With a paper web 102 made using a CWP paper machine (see
I have found that the molded structure imparted to the paper web 102 may not continue through the full thickness of the paper web 102. Transfer of the wet web 102 in molding nip 530 thus predominately molds a first side 104 of the paper web 102, and transfer in the transfer nip 550 predominately molds a second side 106 of the paper web 102. Individually controlling the nip parameters at both the molding nip 530 and the transfer nip 550 can counteract sidedness. For example, the patterned surface 522 of the molding roll 520 may be designed with pockets and projections that impart recesses and protrusions that are deeper and higher, respectively, on the first side 104 of the paper web 102 (prior to the paper web 102 being applied to the Yankee drum 142) than are imparted by the TAD fabric 216 to the second side 106 of the paper web 102. Then, when the first side 104 of the paper web 102 is applied to the Yankee drum 142, the Yankee drum 142 will smooth the first side 104 of the paper web 102 by reducing the height of the protrusions such that, when the paper web 102 is peeled from the Yankee drum 142 by the doctor blade 152, both the first and second sides 104, 106 of the paper web 102 have substantially the same properties. For example, a user may perceive that both sides have the same roughness and softness, or commonly measured paper properties are within normal control tolerances for the paper product. Counteracting sidedness is not limited to adjusting the patterned structure of the molding roll 520 and the TAD fabric 216. Sidedness can also be counteracted by controlling other nip parameters including the creping ratio and/or the loading of each nip 530, 550.
In other wet molding processes, such as fabric creping (shown in
The use of a vacuum transfer allows the molding nip 620 to utilize reduced or no nip loading. Vacuum transfer may thus be a less-compactive or even a non-compactive process. Compaction may be reduced or avoided between the projections of patterned surface 612 and the papermaking fibers located in the corresponding recesses formed in the web 102. As a result, the paper web 102 may have a higher bulk than one made from a compactive process, such as fabric creping (shown in
Another advantage of using vacuum at the point of transfer is flexibility in the use of release agents on the backing roll 312 or transfer fabric 512. In particular, release agents can be reduced or even eliminated. As discussed above, the paper web 102 tends to stick to the smoother of two surfaces during a transfer. Thus, release agents are preferably used in fabric creping to assist in the transfer of the paper web 102 from the backing roll 312 to the creping belt 322 (see
As discussed in the second embodiment, it is preferable for some applications to wet crepe the moist nascent web 102 when it is very wet (e.g., at consistencies from about ten percent solids to about thirty-five percent solids). Webs having these low solid contents may be difficult to transfer. I have found that these very wet webs may be effectively transferred using vacuum at the point of transfer. And, thus, still another advantage of molding roll 610 is the ability to wet crepe very wet moist nascent webs 102 using vacuum box 614.
The vacuum level in the molding nip 620 is suitably large enough to draw the paper web 102 from the backing roll 312 or transfer fabric 512. Preferably, the vacuum is from about zero inches of mercury to about twenty-five inches of mercury, and more preferably from about ten inches of mercury to about twenty-five inches of mercury.
Likewise, the MD length of the vacuum zone of the molding roll 610 is large enough to draw the paper web 102 from the backing roll 312 or transfer fabric 512 and into the molding surface 612. Such MD lengths may be as small as about two inches or less. The preferable lengths may depend on the rotational speed of the molding roll 610. The web 102 is preferably subject to vacuum for a sufficient amount of time to draw the papermaking fibers into the pockets. As a result, the MD length of the vacuum zone is preferably increased as the rotational speed of the molding roll 610 is increased. The upper limit of MD length of the vacuum box 614 is driven by the desire to reduce energy consumption and maximize the area within the molding roll 610 for other components such as a cleaning section 640. Preferably, the MD length of the vacuum zone is from about a quarter of an inch to about five inches, more preferably from about a quarter of an inch to about two inches.
Those skilled in the art will recognize that the vacuum zone is not limited to a single vacuum zone, but a multi-zone vacuum box 614 may be used. For example, it may be preferable to use a two stage vacuum box 614 in which the first stage exerts a high level vacuum to draw the paper web 102 from the backing roll 312 or transfer fabric 512 and the second stage exerts a lower level vacuum to mold the paper web 102 by drawing it against the permeable patterned surface 612 and the pockets therein. In such a two stage vacuum box, the MD length and vacuum level of the first stage is preferably just large enough to effect transfer of the paper web 102. The MD length of the first stage is preferably from about a quarter of an inch to about five inches, more preferably from about a half of an inch to about two inches. Likewise, the vacuum is preferably from about zero inches of mercury to about twenty-five inches of mercury, and more preferably from about ten inches of mercury to about twenty inches of mercury. The MD length of the second stage is preferably larger than the first. Because vacuum is applied to the paper web 102 over a longer distance, the vacuum can be reduced resulting in a paper web 102 having higher bulk. The MD length of the second stage is preferably from about a quarter of an inch to about five inches, more preferably from about a half of an inch to about two inches. Likewise, the vacuum is preferably from about ten inches of mercury to about twenty-five inches of mercury, and more preferably from about fifteen inches of mercury to about twenty-five inches of mercury.
By drawing a vacuum in molding nip 620, the moist nascent web 102 may be advantageously dewatered. The vacuum draws out water from the moist nascent web 102, as the web 102 travels on the permeable patterned surface 612 through the vacuum zone (vacuum box 614). Those skilled in the art will recognize that the degree of dewatering is a function of several considerations including the dwell time of the moist nascent web 102 in the vacuum zone, the strength of the vacuum, the crepe nip load, the temperature of the web, and the initial consistency of the moist nascent web 102.
Those skilled in the art will recognize, however, that the molding nip 620 is not limited to this design. Instead, for example, features of the molding nip 430 of the first embodiment or molding nip 530 of the second embodiment may be incorporated with the molding roll 610 of the third embodiment. For example, it may be desirable to even further increase the bulk of the paper web 102 by combining the molding roll 610 having the vacuum box 614 with a rush transfer, which further crepes the web 102, and the vacuum molds it at the same time.
The molding roll 610 of the third embodiment may also have a blow box 616 at transfer nip 630 where the web 102 is transferred from the permeable patterned surface 612 of the molding roll 610 to the surface of the Yankee drum 142 or TAD fabric 216. Although blow box 616 provides several benefits in transfer nip 630, the web may be transferred to the drying section 440, 540 without it, as discussed above with reference to transfer nip 450 (see
Positive air pressure may be exerted from the blow box 616 through the permeable patterned surface 612 of the molding roll 610. The positive air pressure facilitates the transfer of the molded web 102 at transfer nip 630 by pushing the web away from the permeable patterned surface 612 of the molding roll 610 and towards the surface of the Yankee drum 142 (or TAD fabric 216). The pressure in the blow box 616 is set at a level consistent with good transfer of the sheet to the drying section 440, 540 and is dependent on box size, and roll construction. There should be enough pressure drop across the sheet to cause it to release from the patterned surface 612. The MD length of the blow box 616 is preferably from about a quarter of an inch to about five inches, more preferably from about a half of an inch to about two inches.
By using a blow box 616, the contact pressure between the molding roll 610 and the Yankee drum 142 or TAD fabric 216 may be reduced or even eliminated, thus resulting in less compaction of the web 102 at contact points, thus higher bulk. In addition, the air pressure from the blow box 616 urges the fibers at the permeable patterned surface 612 to transfer with the rest of the web 102 to the Yankee drum 142 or TAD fabric 216, thus reducing fiber picking. Fiber picking may cause small holes (pin holes) in the web 102.
Another advantage of the blow box 616 is that it assists in maintaining and cleaning the patterned surface 612. The positive air pressure through the roll can help to prevent the accumulation of fibers and other particulate matter on the roll.
As with the molding rolls 420, 520 of the first and second embodiments, a cleaning section 640 may be constructed opposite to the free surface of the molding roll 610 (e.g., cleaning section 460 as shown in
In this embodiment, the vacuum box 720 is a dual zone vacuum box, having a first vacuum zone 722 and a second vacuum zone 724. The first vacuum zone 722 is positioned opposite to the backing roll 312 or roll 532 and is used to transfer the moist nascent web 102 from the backing roll 312 or transfer fabric 512 to the molding roll 610. The first vacuum zone 722 is preferably shorter and uses a greater vacuum than the second vacuum zone 724. The first vacuum zone 722 is preferably less than about two inches and preferably draws a vacuum between about two inches of mercury and about twenty-five inches of mercury.
In this embodiment, the nascent web 102 is heated on the molding roll 610 using a steam shower 730. Any suitable steam shower 730 may be used with my invention including, for example, a Lazy Steam injector manufactured by Wells Enterprises of Seattle Washington. The steam shower 730 is positioned proximate to the molding nip 710 and opposite to the second vacuum zone 724 of the vacuum box 720. The steam shower 730 generates steam (for example saturated or superheated steam). The steam shower 730 directs the steam toward the moist nascent web 102 on the patterned surface 612 of the molding roll 610 and the second vacuum zone 724 of the vacuum box 720 uses a vacuum to draw the steam though the web 102, thus, heating the web 102 and the papermaking fibers therein. The second vacuum zone 724 is preferably from about two inches to about twenty-eight inches and preferably draws a vacuum between about five inches of mercury and about twenty-five inches of mercury. Although, the steam shower 730 may be suitably used without a vacuum zone. The temperature of the steam is preferably from about two hundred twelve degrees Fahrenheit to about two hundred twenty degrees Fahrenheit. Any suitable heated fluid may be emitted by the steam shower, including, for example, heated air or other gas.
Heating the moist nascent web 102 in the molding nip 710 is not limited to a heated fluid emitted from a steam shower 730. Instead, other techniques to heat the moist nascent web 102 may be used including, for example, heated air, a heated backing roll 312, or heating the molding roll 420, 520, 610 itself. The molding roll 420, 520, 610, and in particular the molding roll 420, 520 of the first and second embodiments, may be heated like the backing roll 312 by using any suitable means including, for example, steam or induction heating. By using air, for example, the moist nascent web 102 may be heated and dried while being molded on the molding rolls 420, 520 of the first and second embodiments.
As with the previous embodiments, this embodiment includes a cleaning section 940. Because of the additional space afforded by the molding fabric 910, the cleaning section 940 may be located on the fabric run between the molding roll 920 and the support roll 930. Any suitable cleaning device may be used. Similar to the third embodiment, a shower 942 enclosed in a receptacle 945 may be positioned on an interior of the fabric run to direct water and/or a cleaning solution outward through the molding fabric 910. A vacuum box 944 may be located opposite to the shower 942 to collect the water and/or cleaning solution. Similar to the first and second embodiments, a needle jet may also be used in an enclosure 948 to direct water and/or a cleaning solution at an angle from a nozzle 946. Enclosure 948 maybe under vacuum to collect the solution emitted by the spray nozzle 946.
As discussed above in the second embodiment, I have found that the molded structure imparted to the paper web 102 by each molding roll 1010, 1020 may not continue through the full thickness of the paper web 102. The sheet properties of each side of the paper web 102 may thus be individually controlled by the corresponding molding roll 1010, 1020. For example, the patterned surfaces 1012, 1022 of each molding roll 1010, 1020 may have a different construction and/or pattern to impart a different structure to each side of the paper web 102. Although there are advantages to constructing each molding roll 1010, 1020 differently, the construction is not so limited, and the molding rolls 1010, 1020, particularly, the patterned surfaces 1012, 1022, may be constructed the same.
Sidedness can be counteracted by individually controlling the structure of each side of the molded paper web 102 with the two different molding rolls 1010, 1020 of this embodiment. For example, the patterned surface 1012 of the first molding roll 1010 may have deeper pockets and higher projections than the patterned surface 1022 of the second molding roll 1020. In this way, the first side 104 of the paper web 102 will have recesses and protrusions that are deeper and higher than the second side 106 of the paper web 102 prior to the paper web 102 being applied to the Yankee drum 142. Then, when the first side 104 of the paper web 102 is applied to the Yankee drum 142, the Yankee drum 142 will smooth the first side 104 of the paper web 102 by reducing the height of the protrusions such that, when the paper web 102 is peeled from the Yankee drum 142 by the doctor blade 152, both the first and second sides 104, 106 of the paper web 102 have substantially the same properties. For example, a user may perceive that both sides have the same roughness and softness, or commonly measured paper properties are within normal control tolerances for the paper product.
In this embodiment, the paper web 102 is transferred from the backing roll 312 or second forming fabric 206 in a first molding zone, which is a first molding nip 1030 in this embodiment. The same considerations that apply to the features of the molding nips 430, 530 (see
After the first side 104 of the paper web 102 is molded by the first molding roll 1010, the paper web 102 is then transferred from the first molding roll 1010 to the second molding roll 1020 in a second molding zone, which is a second molding nip 1040 in this embodiment. The paper web 102 may be transferred in both molding nips 1030, 1040 by, for example, rush transfer. Similar to Equations (1) and (2), the creping ratio in this embodiment for each nip 1030, 1040 may be calculated according to Equations (4) and (5) as:
Creping Ratio One (%)=(S1/S6−1)×100% Equation (4)
Creping Ratio Two (%)=(S6/S7−1)×100% Equation (5)
where S1 is the speed of the backing roll 312 or second forming fabric 206, S6 is the speed of the first molding roll 1010 and S7 is the speed of the second molding roll 1020. Preferably, the web 102 is creped in each of the two molding nips 1030, 1040 at a ratio of about five percent to about sixty percent. But, high degrees of crepe can be employed, approaching or even exceeding one hundred percent. A unique opportunity exists with two molding nips that can be used to further modify sheet properties. Since each crepe ratio primarily affects the side of the sheet being molded the two crepe ratios can be varied relative to each other to control or vary sheet sidedness. Control systems can be used to monitor sheet properties and use these property measurements to control individual crepe ratios as well as differences between the two crepe ratios.
The paper web 102 is transferred from the second molding roll 1020 to the drying section 440, 540 in transfer nip 1050. As shown in
After the first side 104 of the paper web 102 is molded on the first molding roll 1110, the paper web is transferred from the first molding roll 1110 to the second molding roll 1120 in a second molding zone, which is a second molding nip 1140 in this embodiment, using any combination of a vacuum transfer using vacuum box 1124 of the second molding roll 1120, pressure differential using blow box 1116 of the first molding roll 1110, rush transfer (see Equation (5)). The second side 106 of the paper web 102 is then molded on the permeable patterned surface 1122 of the second molding roll 1120. The types of transfers used individually or in combination can be varied to control sheet properties and sheet sidedness. The considerations and parameters that apply to the blow box 616 and vacuum box 614 in the third embodiment also apply to the blow box 1116 of the first molding roll 1110 and the vacuum box 1124 of the second molding roll 1120.
The paper web 102 is transferred from the second molding roll 1120 to the drying section 440, 540 in transfer nip 1150. As shown in
Various properties of the resultant fibrous sheet (also referred to herein as paper properties or web properties) can be measured by techniques known in the art. Some properties may be measured in real time, while the paper web 102 is being processed. For example, moisture content and basis weight of the paper web 102 may be measured by a web property scanner positioned after the Yankee drum 142 and before the parent roll 190. Any suitable web property scanner known in the art may be used, such as an MXProLine scanner manufactured by Honeywell of Morristown, N.J., that is used to measure the moisture content with beta radiation and basis weight with gamma radiation. Other properties, for example, tensile strength (both wet and dry), caliper, and roughness, are more suitably measured offline. Such offline measurements can be conducted by taking a sample of the paper web 102 as it is produced on the paper machine and measuring the property in parallel with production or by taking a sample from the parent roll 190 and measuring the property after the parent roll 190 has been removed from the paper machine.
As discussed above in the first through the eighth embodiments, various process parameters can be adjusted to have an impact on the resulting fibrous sheet. These process parameters include, for example: the consistency of the moist nascent web 102 at the molding nips 430, 530, 620, 710, 1030, 1040, 1130, 1140 or molding zone 820; creping ratios; the load at the molding nips 430, 530, 620, 710, 1030, 1040, 1130, 1140; the vacuum drawn by vacuum boxes 614, 720, 1114, 1124; and the air pressure generated by blow boxes 616, 1116, 1126. Typically, a measured value for each paper property of the resultant fibrous sheet lies within a desired range for that paper property. The desired range will vary depending upon the end product of the paper web 102. If a measured value for a paper property falls outside the desired range, an operator can adjust the various process parameters of this invention so that, in a subsequent measurement of the paper property, the measured value is within the desired range.
The vacuum drawn by vacuum boxes 614, 720, 1114, 1124 and the air pressure generated by blow boxes 616, 1116, 1126 are process parameters that can be readily and easily adjusted while the paper machine is in operation. As a result, the papermaking processes of my invention, in particular those described in embodiments three through six and eight, may be advantageously used to make consistent fibrous sheet products by real time or near real time adjustment to the papermaking process.
X. Construction of the Permeable Molding Roll
I will now describe the construction of the permeable molding roll 610, 920, 1110, 1120 used with the papermaking machines of the third through sixth and eighth embodiments. For simplicity, the reference numerals used to describe the molding roll 610 (
The vacuum box 614 and the blow box 616 are located in the void 1320 and are supported by shaft 1230 and a rotary connection 1352 to driven endplate 1212 through support structure 1354. Support structure 1354 allows both vacuum and pressurized air to be conveyed to vacuum box 614 and blow box 616, respectively, through the shaft 1230. Both the vacuum box 614 and the blow box 616 are stationary, and the permeable shell 1310 rotates around the stationary boxes 614, 616. Although
A seal is formed between each end 1420, 1430 of the vacuum box 614 and an inside surface of the permeable shell 1310. In this embodiment, a tube 1422 is positioned in a cavity formed in the first top end 1420 of the vacuum box 614. Pressure is applied to inflate the tube 1422 and to press a sealing block 1424 against the inside surface of the permeable shell 1310. Likewise, two tubes 1432 are positioned inside cavities formed in the second top end 1430 and used to press a sealing block 1434 against the inside surface of the permeable shell 1310. In addition, an internal roll shower 1440 may be positioned upstream of the vacuum box to apply a lubricating material, such as water, to the bottom surface of the permeable shell 1310, thereby reducing frictional forces and wear between the sealing blocks 1424, 1434 and the permeable shell 1310. Similarly, each end in the CD direction of the vacuum box 614 and blow box 616 are sealed. As may be seen in
The structural layer 1510 provides the permeable shell 1310 support. In this embodiment, the structural layer 1510 is made from stainless steel, but any suitable structural material may be used. The thickness of the shell is designed to withstand the forces exerted during paper production, including, for example, the forces exerted when the molding nip 620 in the third embodiment is a pressure nip. The thickness of the structural layer 1510 is designed to withstand the loads on the roll to avoid fatigue and other failure. For example, the thickness will depend on the length of the roll, the diameter of the roll, the materials used, the density of channels 1512, and the loads applied. Finite element analysis can be used to determine practical roll design parameters and roll crown, if needed. The structural layer 1510 has a plurality of channels 1512. The plurality of channels 1512 connects the outer layer of the permeable shell 1310 with the inside of the molding roll 610. When a vacuum is drawn or a pressure is exerted from either of the vacuum box 614 or blow box 616, respectively, the air is pulled or pushed through the plurality of channels 1512.
The molding layer 1520 is patterned to redistribute and to orient the fibers of the web 102 as discussed above. In the third embodiment, for example, the molding layer 1520 is the permeable patterned surface 612 of the molding roll 610. As discussed above, my invention is particularly suited for producing absorbent paper products, such as tissue and towel products. Thus, to enhance the benefits in bulk and absorbency, the molding layer 1520 is preferably patterned on a fine scale suitable to orient fibers of the web 102. The density of each of the pockets and projections of the molding layer 1520 is preferably greater than about fifty per square inch and more preferably greater than about two hundred per square inch.
The molding layer 1520 is not limited, however, to woven structures. For example, the molding layer 1520 may be a layer of plastic or metal that has been patterned by knurling, laser drilling, etching, machining, embossing, and the like. The layer of plastic or metal may be suitably patterned either before or after it is applied to the structural layer 1510 of molding roll 610.
Referring back to
The plurality of channels 1512 preferably have a construction consistent with the structural needs of the permeable shell 1310 and the ability to uniformly apply vacuum or pressure to the molding surface to effect sheet transfer and molding. In the embodiments shown in
It may be difficult, however, to achieve a sufficient density of the plurality of channels 1512 to apply uniform air pressure to the molding layer 1520 and still have the structural layer provide sufficient structural support with the embodiment shown in
When the air distribution layer 1530 is used, the density of the plurality of channels 1512 may be spread out and the diameters increased. In the embodiment shown in
As shown in
The pyramid-shaped projections 1710 are separated by grooves 1730. The grooves 1730 of the knurled outer surface 1518 are similar to the grooves 1514 described above with reference to
I will now describe the construction of the non-permeable molding roll 420, 520, 1010, 1020 used with the papermaking machines of the first, second, and seventh embodiments. For simplicity, the reference numerals used to describe the molding roll 420 of the first embodiment above will be used to describe corresponding features below.
The non-permeable molding roll 420 has a first end 1810 and a second end 1820. Either one or both of the first or second ends 1810, 1820 may be driven by any suitable means known in the art. In this embodiment, both ends have shafts 1814, 1824 that are, respectively, connected to endplates 1812, 1822. The end plates 1812, 1822 support each end of a shell (not shown) on which the patterned surface 422 is formed. The roll may be made from any suitable structural material known in the art including, for example, steel. The shell forms the structural support for the patterned surface 422 and may be constructed as a stainless steel cylinder, similar to the permeable shell 1310 discussed above but without the channels 1512. The molding roll 420, however, is not limited to this construction. Any suitable roll construction known in the art may be used to construct the non-permeable molding roll 420.
The patterned surface 422 may be formed similarly to the molding layer 1520 discussed above. For example, the patterned surface 422 may be formed by a woven fabric (such as the fabric discussed above with reference to
Although this invention has been described in certain specific exemplary embodiments, many additional modifications and variations would be apparent to those skilled in the art in light of this disclosure. It is, therefore, to be understood that this invention may be practiced otherwise than as specifically described. Thus, the exemplary embodiments of the invention should be considered in all respects to be illustrative and not restrictive and the scope of the invention to be determined by any claims supportable by this application and the equivalents thereof, rather than by the foregoing description.
The invention can be used to produce desirable paper products, such as paper towels and bath tissue. Thus, the invention is applicable to the paper products industry.
This application is based on U.S. Provisional Application No. 62/292,377, filed Feb. 8, 2016, which is incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/015710 | 1/31/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62292377 | Feb 2016 | US |
