Patent Application
20200240082
Our invention relates to methods and apparatuses for manufacturing paper products such as paper towels and bathroom tissue. In particular, our invention relates to methods that use a patterned cylinder to mold a paper web during 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 may result in paper products having these characteristics.
The 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 of 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 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. Nos. 7,399,378, 7,442,278, 7,494,563, 7,662,257, and 7,789,995 (the disclosures of which are incorporated by reference herein in their entirety).
The web 102 is then transferred onto a creping belt or fabric 322 in a 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 or fabric 322, with the creping belt or fabric 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 or fabric 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 or fabric 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 topography of the creping belt or fabric 322.
It generally is desirable to perform a rush transfer of the web 102 from the backing roll 312 to the creping belt or fabric 322 in order to facilitate transfer of the web 102 to creping belt or fabric 322 and to further improve sheet bulk and softness. During a rush transfer, the creping belt or fabric 322 is traveling at a slower speed than is the web 102 on the backing roll 312. Among other things, rush transferring redistributes the paper web 102 on the creping belt or fabric 322 to impart structure to the paper web 102 in order to increase bulk and to enhance transfer to the creping belt or fabric 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, our invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers and moving the nascent web on a transfer surface. The method also includes bringing a permeable patterned surface of a patterned cylinder into contact with the nascent web having a consistency from about twenty percent solids to about seventy percent solids. The patterned cylinder includes an interior and an exterior. The permeable patterned surface (i) is formed on the exterior of patterned cylinder, (ii) has at least one of a plurality of recesses and a plurality of protuberances, and (iii) is permeable to air. The method further includes conveying the nascent web between the transfer surface and the permeable patterned surface over an arc length of the permeable patterned surface. The arc length forms at least a portion of a molding zone. The method still further includes applying a vacuum over at least a portion of the arc length. The vacuum is applied in the interior of the patterned cylinder to cause air to flow through the permeable patterned surface into the interior of the patterned cylinder. The method also includes transferring the nascent web from the transfer surface to the permeable patterned surface of the patterned cylinder in the molding zone. The vacuum is applied during the transferring of the nascent web from the transfer surface to the permeable patterned surface of the patterned cylinder, such that papermaking fibers of the nascent web are (i) redistributed on the permeable patterned surface and (ii) drawn into the plurality of recesses of the permeable patterned surface in the molding zone to form a molded paper web. The method further includes transferring the molded paper web to a pick-up surface, and drying the molded paper web in a drying section to form a fibrous sheet.
According to another aspect, our invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers and moving the nascent web on a transfer surface. The method also includes bringing a patterned surface of a patterned cylinder into contact with the nascent web having a consistency from about twenty percent solids to about seventy percent solids. The patterned surface (i) is formed on the exterior of patterned cylinder and (ii) has at least one of a plurality of recesses and a plurality of protuberances. The method further includes conveying the nascent web between the transfer surface and the patterned surface over an arc length of the patterned surface, the arc length forming at least a portion of a molding zone. The method still further includes transferring the nascent web from the transfer surface to the patterned surface of the patterned cylinder in the molding zone, such that papermaking fibers of the nascent web are (i) redistributed on the patterned surface and (ii) shaped by at least one of the plurality of recesses and the plurality of protuberances of the patterned surface in the molding zone to form a molded paper web. The method further includes transferring the molded paper web to a pick-up surface, and drying the molded paper web in a drying section to form a fibrous sheet.
According to a further aspect, our invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers. The method also includes dewatering the nascent web by moving the nascent web on an outer surface of a steam filled drum to form a dewatered web having a consistency from about thirty percent solids to about sixty percent solids. The method further includes applying a vacuum at a molding zone. The molding zone is a nip defined between the outer surface of the steam filled drum and a permeable patterned surface of a patterned cylinder. The patterned cylinder includes an interior and an exterior. The permeable patterned surface (i) is formed on the exterior of patterned cylinder, (ii) has at least one of a plurality of recesses and a plurality of protuberances, and (iii) is permeable to air. The method still further includes transferring the dewatered web from the outer surface of the steam filled drum to the permeable patterned surface of the patterned cylinder in the molding zone. The vacuum is applied during the transferring of the nascent web from the transfer surface to the permeable patterned surface of the patterned cylinder, such that papermaking fibers of the nascent web are (i) redistributed on the permeable patterned surface and (ii) shaped by at least one of the plurality of recesses and the plurality of protuberances of the permeable patterned surface in the molding zone to form a molded paper web. In addition, the method includes transferring the molded paper web to a pick-up surface, and drying the molded paper web in a drying section to form a fibrous sheet.
According to yet another aspect, our invention relates to a method of making a fibrous sheet. The method includes forming a nascent web from an aqueous solution of papermaking fibers. The method also includes dewatering the nascent web by moving the nascent web on an outer surface of a steam filled drum to form a dewatered web having a consistency from about thirty percent solids to about sixty percent solids. The method further includes transferring the dewatered web from the outer surface of the steam filled drum to a patterned surface of a patterned cylinder in a molding zone. The molding zone is a nip defined between the outer surface of the steam filled drum and the patterned surface of the patterned cylinder. The patterned surface (i) is formed on the exterior of patterned cylinder and (ii) has at least one of a plurality of recesses and a plurality of protuberances. Whereby papermaking fibers of the nascent web are (i) redistributed on the patterned surface and (ii) shaped by at least one of the plurality of recesses and the plurality of protuberances of the patterned surface in the molding zone to form a molded paper web. In addition, the method includes transferring the molded paper web to a pick-up surface, and drying the molded paper web in a drying section to form a fibrous sheet.
These and other aspects of our invention will become apparent from the following disclosure.
Our invention relates to papermaking processes and apparatuses that use a patterned cylinder to produce a paper product. We will describe embodiments of our 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 recycled (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 our 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 our 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 herein 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,” a “dewatered web,” and a “dried web.”
When describing our 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 our 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 our invention is not limited to the specific examples of operating conditions including speeds and pressures that are disclosed herein.
As the nascent web 102 leaves the forming section 110, it is transferred along a felt run 118 and subsequently transferred to a patterned surface 422 of a patterned cylinder 420. The nascent web 102 is cylinder creped and molded on the patterned cylinder 420 to form a molded web 102, as will be discussed further below. The nascent web 102 may be cylinder creped and molded when it is wet and the fibers are mobile, such as at consistencies from about twenty percent solids to about seventy percent solids. In some embodiments, the nascent web 102 may be cylinder creped and molded without significant dewatering occurring after the forming section 110 and before the patterned cylinder 420, in which case, the nascent web 102 is preferably cylinder creped and molded at a consistency from about twenty percent solids to about thirty-five percent solids. The preferable consistency of the nascent web 102 may, however, vary depending upon the desired application.
In some embodiments, however, a dewatering section 410, separate from the forming section 110, may be used to dewater the nascent web 102 upstream of the patterned cylinder 420. 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 thirty percent solids to about sixty percent solids, and more preferably between about forty percent solids to about fifty-five percent solids.
In this embodiment, the nascent web 102 is dewatered as it is moved on the papermaking felt 116. The dewatering section 410 shown in
Regardless of whether or not the nascent web 102 is dewatered in the dewatering section 410, the nascent web 102 is moved by a transfer surface to a molding zone 430. In this embodiment, the transfer surface is the papermaking felt 116. The patterned surface 422 of the patterned cylinder 420 is brought into contact with the nascent web 102 in the molding zone 430, as the nascent web 102 is moved on the papermaking felt 116. The patterned surface 422 may include a plurality of recesses (or cells) 424 that are formed on a shell 426 of the patterned cylinder 420.
Although the cells 424 and protuberances 425 may have any suitable depth or height, respectively, they are preferably from about ten-thousandths of an inch (mils) to about fifty mils. The cells 424 and protuberances 425 need not be uniform in either pattern or depth and height. For example, the patterned surface 422 may impart both a background pattern and a signature pattern to the web 102.
As shown in
To further assist in molding the nascent web 102, a vacuum may also be applied in the molding zone 430. As can be seen in
As shown in
A vacuum is established in the vacuum box 432 and is used to draw a fluid, such as air, through the channels 428 of the shell 426, creating a vacuum in the molding zone 430. The vacuum in the molding zone 430, in turn, draws the paper web 102 onto the permeable patterned surface 422 of the patterned cylinder 420 and, in particular, into the plurality of cells 424. The vacuum thus molds the paper web 102 and reorients the papermaking fibers in the paper web 102 to have variable and patterned fiber orientations.
The paper web 102 is also transferred from the papermaking fabric 116 to the permeable patterned surface 422 of the patterned cylinder 420 in the molding zone 430. A first transfer nip 434 is formed between a support roll 436, supporting the papermaking fabric 116, and the patterned cylinder 420. As the papermaking fabric 116 and the permeable patterned surface 422 exit the first transfer nip 434, they diverge, and the paper web 102 remains on the permeable patterned surface 422 of the patterned cylinder 420. As discussed above when a vacuum is applied, the vacuum box 432 preferably extends and draws a vacuum beyond the first transfer nip 434 to assist in holding the paper web 102 on the permeable patterned surface 422, instead of following the papermaking felt 116. The first transfer nip 434 may also be loaded at a higher pressure than the loads imparted by the papermaking fabric 116 upstream of the first transfer nip 434 to assist in transferring the web 102.
The vacuum drawn by the vacuum box 432 is preferably set to achieve a desired depth of fiber penetration into the cells 424 of the permeable patterned surface 422 and to achieve consistent transfer of the paper web 102 from the papermaking felt 116 to the permeable patterned surface 422. Preferably, the vacuum is from about five inches of mercury to about twenty-five inches of mercury.
To further assist molding and transfer, the nascent web 102 may be transferred from the papermaking fabric 116 to the patterned cylinder 420 by a rush transfer. During a rush transfer, the patterned cylinder 420 is traveling at a slower speed than the papermaking fabric 116 and thus the paper web 102. 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 (expressed in terms of percent) 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 papermaking fabric 116 and S2 is the speed of the patterned cylinder 420. The creping ratio is often proportional to the degree of bulk in the sheet, but inversely proportional to the throughput of the papermaking machine 400 and thus yield of the papermaking machine 400. In this embodiment, the velocity of the paper web 102 on the papermaking felt 116 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 papermaking felt 116 is as fast as the process allows, which is typically limited by the drying section 450. For higher bulk product where a slower papermaking machine speeds can be accommodated, a higher creping ratio is used.
After being molded in the molding zone 430, the molded paper web 102 is conveyed to a second transfer nip 440, where the molded paper web 102 is transferred from the permeable patterned surface 422 of the patterned cylinder 420 to a pick-up surface. In this embodiment the pick-up surface is a pick-up fabric 442, although other suitable pick-up surfaces may be used including a belt or a roll for example. The second transfer nip 440 may be formed between the patterned cylinder 420 and a support roll 444, supporting the pick-up fabric 442.
The patterned cylinder 420 may also have a blow box 446 at the second transfer nip 440 where the web 102 is transferred from the permeable patterned surface 422 to the pick-up fabric 442. Any suitable construction for the blow box 446 may be used, including the blow box shown and described for use in the molding roll of commonly assigned published International Application No. WO 2017/139123, No. WO 2017/139124, and No. WO 2017/139125 (the disclosures of which are incorporated by reference in their entirety). Positive air pressure may be exerted from the blow box 446 through the channels 428 and permeable patterned surface 422 of patterned cylinder 420. The positive air pressure facilitates the transfer of the molded web 102 at second transfer nip 440 by pushing the web 102 away from the permeable patterned surface 422 and towards the pick-up fabric 442. The pressure in the blow box 446 is set at a level sufficient to achieve consistent transfer of the molded web 102 to the pick-up fabric 442 and low enough to avoid inducing defects into the web 102 because the of air from the blow box 446. There should be enough pressure drop across the web 102 to cause it to release from the permeable patterned surface 422. The blow box 446 may preferably extend and blow air beyond the second transfer nip 440 to assist in retaining the molded web 102 on the pick-up fabric 442, instead of following the permeable patterned surface 422 of the patterned cylinder 420.
In the embodiment shown in
A speed differential between the patterned cylinder 420 and the pick-up fabric 442 may also be used to assist in transferring the molded web 102 from the patterned cylinder 420 to the pick-up fabric 442. When a speed differential is used, the creping ratio (expressed in terms of percent) is calculated using Equation (2), which is similar to Equation (1), as follows:
Creping Ratio (%)=(S2/S3−1)×100% Equation (2)
where S2 is the speed of the patterned cylinder 420 and S3 is the speed of the pick-up fabric 422. Preferably, the web 102 is creped at a ratio of about twenty percent to about two hundred percent, and more preferably from about sixty percent to about one hundred fifteen percent. When rush transfer is used in both the molding zone 430 and the second transfer nip 440, the total creping ratio can be calculated by adding the creping ratios in each nip and controlled to achieve the preferred creping ratios discussed above.
After being molded, the molded web 102 is transferred by the pick-up fabric 442 to a drying section 450 where the web 102 is further dried to a consistency of about ninety-five percent solids. The drying section 450 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 the web 102 is conveyed on the Yankee drum 142.
The web 102 is deposited on the surface of the Yankee drum 142 at a nip 452. A creping adhesive may be applied to the surface of the Yankee drum 142 to help the web 102 adhere to the Yankee drum 142. As the Yankee drum 142 rotates, the web 102 may be removed from the Yankee drum 142 by a doctor blade 152 where it is then wound on a reel (not shown) to form a parent roll. The reel may be operated slower than the Yankee drum 142 at steady-state in order to impart a further crepe to the web 102.
With use, the permeable patterned surface 422 of the patterned cylinder 420 may require cleaning. Papermaking fibers and other substances may be retained on the patterned surface 422 and, in particular, the cells 424 and channels 428. 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
The web 102 is then transferred by the transfer fabric 512 to the molding zone 430, where web 102 is molded and transferred from the transfer fabric to the permeable patterned surface 422 of the patterned cylinder 420, as discussed above with reference to
The fabric 216 carrying the paper web 102 next passes around through-air dryers 222, 224 where hot air is forced through the web 102 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).
Alternatively, the nascent web 102 may be minimally dewatered with a separate dewatering zone 212. In this embodiment, the dewatering zone 212 is a vacuum dewatering zone in which suction boxes 214 remove moisture from the web 102 to achieve desirable consistencies of about twenty percent solids and about thirty-five percent solids before the sheet reaches molding zone 430. Hot air may also be used in dewatering zone 212 to improve dewatering.
The moist nascent web 102 is transferred from the Yankee drum 142 to the patterned cylinder 420 in the molding nip 610. To further assist molding and transfer, the moist nascent web 102 may be transferred from the Yankee drum 142 to the patterned cylinder 420 by a rush transfer. When a speed differential is used, the creping ratio (expressed in terms of percent) is calculated using Equation (3), which is similar to Equations (1) and (2), as follows:
Creping Ratio (%)=(S4/S5−1)×100% Equation (3)
where S4 is the speed of the Yankee drum 142 and S5 is the speed of the patterned cylinder 420. Preferably, the moist nascent web 102 is creped at a ratio of about twenty percent to about two hundred percent, and more preferably from about sixty percent to about one hundred fifteen percent.
As with the previous embodiments, the patterned surface 422 of the patterned cylinder 420 may be permeable to allow a vacuum to be drawn by a vacuum box 432 in the molding nip 610 to assist both in transfer and molding of the web 102. When the permeable patterned surface 422 is used, other features such as the blow box 446 and cleaning section 460 may also be used.
After being molded, the molded web 102 is transferred from the patterned cylinder 420 to a drying section 620 to form a dried web 102. In this embodiment, a non-compactive drying process, such as the TAD drying section 530 shown and described above in the second embodiment with reference to
Multiple patterned cylinders 420 may be used in the embodiments discussed above to mold and impart a pattern to the nascent (moist nascent) web 102. For example, a first, background pattern may be imparted by a first patterned cylinder 420 and then a second, signature pattern may be superimposed over the background pattern by a second patterned cylinder 420. When two patterned cylinders 420 are used with the embodiments described above, both patterned cylinders 420 may be located upstream of the drying section (450, 530, 620, respectively) and process the web 102 without intermediate drying between the two patterned cylinders 420, resulting in both patterns being imparted to the web 102 at similar consistencies.
Another variation using two patterned cylinders 420 may be a combination of the first embodiment and the third embodiment. The first patterned cylinder 420 may be located and operated as described in the first embodiment 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.
This invention can be used to produce desirable paper products, such as paper towels and bath tissue. Thus, this invention is applicable to the paper products industry.
This application is a continuation of copending U.S. patent application Ser. No. 16/023,451, filed Jun. 29, 2018, which claims the benefit of priority of U.S. Provisional Patent Application No. 62/542,378, filed Aug. 8, 2017, which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62542378 | Aug 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16023451 | Jun 2018 | US |
| Child | 16851181 | US |
