HK1034548A - Method for making soft tissue - Google Patents

Description

Method for making soft tissue

Background

Tissue products, such as bath tissue and facial tissue, have a number of characteristics that must be considered in order to help make them suitable and optimally suited for the intended purpose of the product when making the finished product with the desired attributes. Improving the softness of products has long been a major goal, and this is a particularly important factor for successful manufacture of quality products. Generally speaking, the main connotations of softness include stiffness and bulk (density), with lower stiffness and higher bulk (low density) generally improving perceived softness.

While increased softness is desirable for all types of tissue products, it has been a significant challenge to obtain improved softness in uncreped throughdried paper. Through-drying provides a relatively non-compressive method of removing moisture from fabrics by passing hot air through the fabric until it dries. More specifically, a wet laid fabric is transferred from the forming fabric to a rough, high permeability throughdrying fabric and held thereon until it is dry. Because there is little binding within the dried web and the web is less compressed, the final dried web is softer and looser than an uncreped sheet that is dried by conventional means. In this way, it is advantageous to eliminate the Yankee dryer and produce an uncreped throughdried product. However, uncreped throughdried paper is stiffer and rougher to the touch than a similar product that is creped. This is due in part to the inherent high stiffness and strength of the uncreped paper sheet and in part to the roughness of the throughdrying fabric belt with which the wet web conforms and is dried thereon.

Further, from the viewpoint of production, the throughdrying method is more energy-consuming than the wet-pressing method, and therefore, the cost is high. Furthermore, the throughdrying process requires high temperatures, which adversely affect the service life of the fabric tapes used in the manufacturing process.

Thus, what is lacking and needed in the art are methods of making tissue products having improved softness, and in particular, through-dried tissue products having improved softness, and more economical methods of making through-dried tissue products.

Summary of The Invention

It has been discovered that improved uncreped throughdrying fabrics can be produced by dewatering a fabric to a consistency of greater than about 30 percent, transferring the wet fabric from a forming fabric to one or more slow intermediate transfer fabric belts, and then further transferring the fabric to a throughdrying fabric belt to effect final drying of the fabric. It was particularly surprising to find that just before differential transfer, the consistency of the uncreped throughdried fabric increased resulting in: (1) higher tensile properties in the machine and cross directions, which helps to improve the runnability of the fabric; and (2) a reduced modulus when the tensile strength is adjusted to a normal value, which increases the flexibility. This finding allows the production of lower modulus tissue products at a given tensile strength compared to tissue products produced at lower consistencies using differential transport.

Accordingly, one aspect of the present invention is a method of making a soft tissue sheet comprising the steps of: depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric; dewatering the wet web to a consistency of from about 20% to about 30%; supplementally dewatering the wet web to a consistency of greater than about 30% using a non-compressive dewatering device; transferring the post-dewatered web to a transfer fabric belt traveling at a speed of about 10% to about 80% slower than the forming fabric belt; transferring the web to a throughdrying fabric; and throughdrying the fabric to a final dryness.

One particularly desirable apparatus for dewatering a web to a consistency of about 30 percent or greater comprises an air press located just upstream of the differential transfer. Although pressurized fluid jets in combination with a vacuum device have been discussed previously in the patent literature, such devices have not been widely used in tissue making. In principle, this seems to be because it has not been recognized in the past that dewatering a fabric to a consistency of greater than about 30% prior to differential conveyance would result in the improved product properties described above. Moreover, another reason hindering the adoption of such machines is believed to be due to difficulties in practical implementation, including web breaks, pressurized fluid leaks, seals and/or web wear, etc. The air press disclosed in the present invention overcomes these difficulties and provides a viable machine for dewatering wet fabrics to a desired consistency level previously thought impossible at speeds suitable for industrial use without the need for thermal dewatering.

During transport, the intermediate transport fabric or fabrics run at a lower speed than the forming fabric in order to stretch the paper. As the speed differential between the forming fabric belt and the slower conveying fabric belt increases (sometimes referred to as "negative draw" or "rush transfer"), the stretch imparted to the fabric while it is being conveyed also increases. The transfer fabric belt is relatively smooth and tight compared to the coarse weave of typical throughdrying fabric belts. From a practical point of view, it is desirable that the transfer fabric belt be as thin as possible while still being able to run. The knuckles provided on the surface of the transfer fabric belt may grip the fabric. Furthermore, if a "fixed gap" or "kiss" transfer is employed (wherein the fabric belts converge and diverge simultaneously, as will be described in more detail hereinafter), it may be advantageous to effect the transfer of one or more wet fabrics, with or without the presence of a transfer fabric belt. This transfer not only avoids significant compaction of the fabric in the wet-bonded formed state, but also smoothes the surface of the fabric and ultimately the dried paper sheet when used in conjunction with a differentially-conveyed and/or smooth-conveyed fabric belt.

The speed differential between the forming fabric belt and the transfer fabric belt, which is a low speed fabric belt, can be from about 10% to about 80% or more, preferably from about 10% to about 35%, and more preferably from about 15% to about 25%. The better speed differential depends on a number of factors, including the particular type of product being manufactured. As previously mentioned, the increase in stretch imparted to the fabric is proportional to the speed differential. For example, for an uncreped throughdried three ply wipe having a basis weight of about 20 grams per square meter per ply, a speed differential of from about 20% to about 25% between the forming fabric belt and a single transfer fabric belt will produce a stretch of from about 15% to about 20% in the finished product as each ply is manufactured.

The web may be stretched prior to drying by applying one differential transfer or two or more differential transfers to the wet web. Thus, one or more transfer fabric belts may be provided. The amount of stretch imparted to the fabric may be divided between one, two, three or more differential passes.

It is best to transport in a manner that allows the "sandwich" formed (consisting of forming fabric/transfer fabric) to exist for as short a time as possible. In particular, it is only present at the front edge of the vacuum skid or the transport skid suction nozzle to effect the transport. In effect, the forming fabric belt and the conveying fabric belt converge and diverge at the leading edge of the vacuum nozzle. The objective is to minimize the distance over which the fabric contacts both fabric strips simultaneously. It has been found that simultaneous convergence/divergence is critical to eliminate microfolding and thus improve the smoothness of the finished tissue or other product.

In fact, if a sufficient angle of convergence is maintained between the two fabric strips as they approach the front edge of the vacuum nozzle, and if a sufficient angle of divergence is maintained between the two fabric strips downstream of the vacuum nozzle, the two fabric strips converge and diverge synchronously only at the front edge of the vacuum nozzle. The minimum angle of convergence and divergence is about 0.5 degrees or greater, more specifically about 1 degree or greater, more specifically about 2 degrees or greater, and more specifically about 5 degrees or greater. The angles of convergence and divergence may be the same or different. A larger angle provides a larger margin of error during operation. A suitable range is from about 1 degree to about 10 degrees. The simultaneous convergence and divergence is achieved when the vacuum shoe is designed such that the rear edge of the vacuum nozzle is sufficiently recessed relative to the front edge of the vacuum nozzle to allow the web to diverge immediately as it passes the front edge of the vacuum nozzle. As will be described more clearly below in connection with the accompanying drawings.

The machine is adjusted to start with a fixed gap for further minimizing fabric compression during transfer, and the distance between the fabric belts should be equal to or greater than the thickness of the fabric so that the fabric is not significantly compressed when being transferred at the leading edge of the vacuum nozzle.

The smoothness can be increased by using an air press upstream of the differential transfer. This is preferably used in conjunction with a fixed gap carrying fabric belt section after drying. Calendered fabrics are not necessary to achieve the desired smoothness, but further processing of the paper, such as by calendering, embossing, or creping, can be beneficial to further improve the properties of the paper.

As used herein, a "transfer fabric" is a fabric that is positioned between the forming section and the drying section of the fabric manufacturing process. Suitable transfer fabrics should be those which provide a relatively high fiber support index and good vacuum tightness so as to maximize fabric/paper contact during transfer from the forming fabric. The fabric belt may have a relatively smooth surface profile to provide the fabric with a smooth finish, but still have sufficient texture to grip and maintain contact with the fabric during rush transfers. A thinner fabric strip may result in a higher degree of stretch in the fabric, which may be desirable for certain product applications.

The transfer fabric belt comprises a single-layer, multi-layer or composite permeable structure, with preferred fabric belts having at least some of the following characteristics: (1) on the side of the belt that is in contact with the wet web (top side), the number of strands per inch in the Machine Direction (MD) (mesh) is from 10 to 200 and the number of strands per inch in the Cross Direction (CD) (count) is from 10 to 200. The strands typically have a diameter of less than 0.050 inches, and (2) the distance between the highest point of the longitudinal wrist and the highest point of the lateral wrist at the top side is from about 0.001 to about 0.02 or 0.03 inches. Between these two peaks there are the knuckles formed by the MD or CD strands that give the profile a three-dimensional character, (3) on the top side, the length of the MD knuckle is equal to or greater than the length of the CD knuckle; (4) if the fabric strip is a multi-layer structure, the bottom layer preferably has a finer mesh than the top layer to control the depth of fabric penetration and maximize retained fibers; and (5) the fabric strip may exhibit some geometric pattern that is visually pleasing, with the patterns generally repeating every 2 to 50 warp yarns.

Particularly suitable transfer fabric belts include, for example, those manufactured by Asten forming fabric belts of Appleton, Wisconsin, identified as Fabric Nos. 934, 937, 939, and 959. Specific conveying belts that may be used also include those disclosed in U.S. patent No. 5,429,686 issued 7/4 of 1995 to Chiu et al, which is incorporated herein by reference. Suitable fabric tapes may include woven fabric tapes, non-woven fabric tapes or non-woven hybrid fabric tapes. The void fraction of the transfer fabric belt may be equal to or less than the fabric belt of the transfer fabric.

An air press as disclosed herein is capable of dewatering a wet web to a high consistency, primarily due to the high pressure differential created across the web, and the resulting air flow through the web. In particular embodiments, for example, the air press may increase the consistency of the wet web by about 3% or more, particularly about 5% or more, such as from about 5% to about 20%, more particularly about 7% or more, such as from about 7% to about 20%. Thus, the consistency of the wet web exiting the press can be about 25% or greater, about 26% or greater, about 27% or greater, about 28% or greater, about 29% or greater, but desirably about 30% or greater, particularly about 31% or greater, more particularly about 32% or greater, such as from about 32% to about 42%, even more particularly about 33% or greater, more particularly about 34% or greater, such as from about 34% to about 42%, more particularly about 35% or greater,

the air press is able to reach these consistency levels while the machine is operating at industrial use speeds. As used herein, "high speed operation" or "industrial use speed" of a tissue machine refers to a machine speed in feet per minute that is at least the same as any one of the following values or ranges: 1000, parts by weight; 1500; 2000; 2500; 3000A; 3500, a table top; 4000; 4500; 5000; 5500; 6000; 6500; 7000; 8000; 9000; 10000, and a range having any of the above values as upper and lower limits. An optional steam jet or similar device may be used before the press to increase consistency after the press and/or to change the cross direction moisture profile of the web. Moreover, higher consistencies can be achieved when the machine speed is lower and the residence time in the air press is longer.

The pressure differential across the wet web created by the air press can be about 25 inches of mercury or greater, such as from about 25 to about 120 inches of mercury, particularly about 35 inches of mercury or greater, such as from about 35 to about 60 inches of mercury, more particularly from about 40 to about 50 inches of mercury. This can be accomplished in part by a gas plenum within the press that maintains a fluid pressure on the wet fabric side of greater than 0 to about 60 pounds per square inch gauge (psig), specifically greater than 0 to about 30psig, more specifically about 5psig or greater, such as about 5 to about 30psig, and still more specifically from about 5 to about 20 psig. The collection means of the aerostatic press desirably functions as a vacuum box operating at a vacuum of from 0 to about 29 inches of mercury, specifically from 0 to about 25 inches of mercury, more specifically greater than 0 to about 25 inches of mercury, and more specifically from about 10 to about 20 inches of mercury, for example about 15 inches of mercury. The pressure levels in the gas plenum and the collection means are preferably both monitored and controlled to predetermined levels.

The collection means desirably, but not necessarily, forms an integral seal with the gas plenum and draws a vacuum to function as a collection means for gases and liquids. The terms "integrally sealed" and "integrally sealed" as used herein mean: a relationship between the air plenum and the wet web, the air plenum being operatively associated with and in indirect contact with the web such that about 70% or more of the air supplied to the air plenum flows through the web when the air plenum is operated at a pressure differential across the web of about 30 inches of mercury or greater; a relationship between the air plenum and the collection device, the air plenum being in operable communication with and in indirect contact with the web and the collection device such that about 70% or more of the air supplied to the air plenum flows through the web and into the collection device when the air plenum and the collection device are operated at a pressure differential across the web of about 30 inches of mercury or greater.

It is apparent that the pressurized fluid used within the air press is sealed from the ambient air to create a substantial air flow through the fabric that results in a significant de-watering pressure of the air press. The flow of pressurized fluid through the aerostatic press is suitably from about 5 to about 500 standard cubic feet per minute (SCFM) per square inch of the open area, particularly about 10SCFM or more per square inch of the open area, for example from about 10 to about 200SCFM per square inch of the open area, more particularly about 40SCFM per square inch of the open area, for example from about 40 to about 120SCFM per square inch of the open area. Desirably, 70% or more, particularly 80% or more, and more particularly 90% or more of the pressurized fluid supplied to the air plenum is introduced into the vacuum box through the wet web. As used herein, the term "standard cubic feet per minute" refers to cubic feet per minute measured at 14.7 pounds per square inch absolute and 60 degrees Fahrenheit (F.).

The terms "air" and "pressurized fluid" are used interchangeably herein to refer to any gaseous substance used within a pneumatic press for dewatering fabrics. The gaseous substance suitably comprises air, steam or the like. Preferably, the pressurized fluid comprises air having an ambient temperature, or a heated gas that is a gas that is raised to a temperature of about 300 ° F or less, particularly about 150 ° F or less, by a method that is solely pressurized.

The air press is suitable for use in various types of machines for dewatering wet webs including paper, tissue, creped paper, cardboard strips, newsprint or the like. In particular, pneumatic presses may be incorporated into the tissue machine to mold the wet web onto the three-dimensional web to increase the bulk of the web. Pneumatic presses can be used in many locations on the machine, particularly where the fabric is sandwiched between two fabric belts, and where the fabric is transferred to a three-dimensional fabric belt. Because the pressure differential created by the air compressor is significantly greater than that which would be possible with conventional vacuum boxes, suction boxes, blow boxes, and the like. During the molding operation, a web of towels with a higher bulk can be produced by means of an air press. Many wet presses suitable for dewatering with an air press are disclosed in the following patent documents, namely: hermans et al, U.S. patent application filed on even date herewith but with an unclear application serial number entitled "method of making tissue on a modified conventional wet press"; hermans et al, U.S. patent application filed on even date herewith but with an unclear application number entitled "method for making low density tissue using low energy input"; druecke et al, U.S. patent application filed on even date herewith but with an unclear application number entitled "method of making a low density elastic web"; chen et al, filed on even date herewith but with no clear application serial number, entitled "low density elastic fabrics and methods of making such fabrics"; these documents are hereby incorporated by reference.

According to another aspect of the present invention, the method of making a creped throughdried tissue requires less total energy to be expended than conventional creping throughdrying methods. The method of the present invention uses an air press to non-compressively dewater the fabric, particularly to non-thermally dewater the fabric, prior to drying to a final dryness using a through-air dryer.

The present invention is also directed to a method of making a creped throughdrying fabric comprising the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric; (b) dewatering the wet web to a consistency of about 30 percent or greater using a non-compressive dewatering device adapted to cause a pressurized fluid to flow substantially through the web at a gauge pressure of about 5 pounds per square inch gauge or greater due to the integral seal with the wet web; (c) transferring the wet web to a throughdrying fabric; (d) throughdrying the non-press dewatered fabric; (e) transferring the throughdried fabric to a surface of a drying cylinder; and (f) removing the throughdried fabric from the dryer with a creping blade.

In another embodiment, a method of making a creped throughdrying fabric comprises the steps of: (a) depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric; (b) sandwiching the wet web between a pair of web belts; (c) passing the sandwiched wet web structure between an air plenum and a collection device, the air plenum and the collection device being operatively associated and adapted to create a pressure differential across the wet web of about 30 inches of mercury or greater and to create a flow of pressurized fluid through the wet web of about 10 standard cubic feet per minute per square inch or greater; (d) dewatering the wet web to a consistency of about 30% or greater with a pressurized fluid stream; (e) transferring the wet web to a throughdrying fabric; (f) throughdrying the non-press dewatered fabric; (g) transferring the throughdried fabric to a surface of a drying cylinder; and (h) removing the throughdried fabric from the dryer with a creping blade.

The forming process and apparatus may be conventional techniques well known in the paper industry. Such forming processes include modified fourdrinier wire forming machines, top surface forming machines (e.g. breast rolls), gap forming machines (e.g. twin fourdrinier wire forming machines, crescent moon forming machines) and the like. The forming wire or fabric belt may also be conventional, preferably a finer weave pattern with greater fiber support to produce a smoother sheet or fabric. The headbox used to deposit the fibers onto the forming fabric may be stratified or non-stratified.

The methods disclosed herein are applicable to any tissue web, including webs used to make facial tissues, bath tissues, paper towels, wipes, napkins, and the like. Such a web of towels may be a single ply product or a multi-ply product, e.g. two, four or more plies. Single layer products are advantageous due to lower manufacturing costs, while many consumers prefer multi-layer products. For a multi-layer product, the layers of the product need not be identical, so long as at least one layer is in accordance with the present invention. The fabric may be stratified or non-stratified (commingled), and the fibers making up the fabric may be any fibers suitable for papermaking.

Suitable basis weights for these tissue webs may be from about 5 to about 70 grams per square meter (gsm), preferably from about 10 to about 40gsm, and more preferably from about 20 to about 30 gsm. For a single ply bath tissue, a basis weight of about 25gsm is preferred. For a two ply towel, a basis weight of about 20 gsm/ply is preferred. For a three ply towel, a basis weight of about 15 gsm/ply is preferred. Generally, a larger basis weight fabric requires a lower gas flow to maintain the same operating pressure within the gas plenum. The width of the nozzles of the air press is preferably adjusted to adapt the system to various available air capacities, wider nozzles being used for heavier weight fabrics.

The drying process may be any non-compressive drying method that tends to maintain the bulk or thickness of the wet web, including without limitation, through-drying, infrared radiation, microwave drying, and the like. For commercial availability and practicality, through-drying is a well-known and preferred method for non-press dryer fabrics. Suitable through-drying fabric belts include, but are not limited to, Asten 920A and 937A, and Velostar P800 and 103A. The throughdrying fabric belts may also include those disclosed in U.S. patent 5,429,686 issued 7/4 of 1995 to Chiu et al. The fabric is preferably dried to a final dryness without creping, which tends to reduce the strength and bulk of the fabric,

although the mechanism is not fully understood, it is clear that the conveyor fabric and the throughdrying fabric can separately and independently affect the properties of the final paper sheet. For example, by varying the transfer fabric with the same throughdrying fabric, the sheet surface smoothness, as determined by the sensing plate, can be controlled over a wide range. Fabrics made by the method and machine of the present invention are not two-sided dissimilar unless calendered. However, the uncalendered fabrics may be laminated together with the smooth/matte side facing outward as desired, depending on the particular product specifications.

The numerous features and advantages of the present invention will be apparent from the following description. In the description, reference will be made to the accompanying drawings that show preferred embodiments of the invention. Such embodiments do not represent the full scope of the invention. Reference should therefore be made to the claims herein for interpreting the full scope of the invention.

Brief description of the drawings

Figure 1 schematically illustrates a process flow diagram representing a method and machine for making uncreped throughdried paper according to the present invention.

FIG. 2 representatively illustrates an enlarged top plan view of the air press in the process flow diagram of FIG. 1.

Fig. 3 is a side view of the exemplary gas press of fig. 2, with portions broken away and in section for illustrative purposes.

FIG. 4 is an enlarged representative cross-sectional view taken in the plane of line 4-4 of FIG. 3.

FIG. 5 is an enlarged typical cross-sectional view similar to FIG. 4, but taken generally in the plane of line 5-5 of FIG. 3.

Fig. 6 is a side view of another sealing system used in the pneumatic press of fig. 2 and 3, with portions broken away and shown in cross-section for illustrative purposes.

Fig. 7 representatively illustrates an enlarged side view of the vacuum transfer skid illustrated in fig. 2.

FIG. 8 is an enlarged side view similar to FIG. 7 but showing the synchronous convergence and divergence of the web at the leading edge of a vacuum nozzle.

Fig. 9 is a view of a load/elongation curve for a tissue illustrating how the MD slope is determined.

Fig. 10 representatively shows an enlarged end view of another air press of the present invention with the air plenum seal of the air press in a raised position relative to the wet web and vacuum box.

Fig. 11 representatively illustrates a side view of the pneumatic press of fig. 10.

FIG. 12 representatively shows an enlarged cross-sectional view taken generally in the plane of line 12-12 of FIG. 10, but with the sealing device loaded against the web.

Fig. 13 representatively illustrates an enlarged cross-sectional view similar to fig. 12, but taken in the plane of line 13-13 of fig. 10.

Fig. 14 representatively shows a perspective view of several components of an air plenum seal device disposed against a fabric strip, with portions broken away and in section for purposes of illustration.

Fig. 15 is an enlarged sectional view typically illustrating another seal structure of the gas compressor of fig. 10.

Fig. 16 is an enlarged view typically illustrating a seal portion of the pneumatic press of fig. 10.

Figure 17 representatively illustrates a process flow diagram of the method of the present invention for making a creped throughdried paper sheet.

Detailed description of the invention

The invention will now be described in more detail with reference to the accompanying drawings. For purposes of uniformity and brevity, the same reference numbers will be used in different drawings to identify the same elements. In all of the illustrated embodiments, conventional papermaking machines and operations such as headbox, forming fabric, fabric transfer, drying and creping can be employed, all as would be readily understood by one skilled in the papermaking art. Nevertheless, various conventional components have been described in order to provide a background that may be utilized by various embodiments of the present invention.

Fig. 1 typically illustrates one embodiment of a method and machine for making tissue. For simplicity, various tension rollers are shown to limit the travel of several fabric belts, but are not numbered. An headbox 20 sprays or deposits an aqueous suspension of papermaking fibers 21 onto an endless forming fabric 22 which travels around a forming roll 23. The forming fabric belt 22 allows the newly formed wet web 24 to be partially dewatered to a consistency of about 10%.

After formation, the forming fabric belt 22 carries the wet web 24 to one or more vacuum or suction boxes 28, which vacuum or suction boxes 28 can be used to supplement the dewatering of the wet web 24 as the wet web 24 is supported on the forming fabric belt 22. In particular, a set of vacuum boxes 28 may be employed in order to dewater the fabric 24 to a consistency of about 20% to about 30%. The improved fourdrinier former is particularly useful for making heavier basis weight sheets suitable for use as wipes and towels, although other forming devices such as twin fourdrinier formers, crescent formers and the like can also be used. Alternatively, a hydro-needle former as disclosed in U.S. patent No. 5,137,600 issued 8/11 1992 to Barnes et al may be used to increase the bulk of the fabric.

Warm fabric 24 is then further dewatered by a suitable non-compressive supplemental dewatering process, such as a process selected from the group consisting of air press, infrared drying, microwave drying, sonic drying, through drying, superheated steam dewatering or saturated steam dewatering, supercritical fluid dewatering and displacement dewatering as described herein. In the illustrated embodiment, the non-compressive supplemental dewatering device includes an air press 30, which will be described in greater detail below. The air press 30 desirably increases the consistency of the wet web 24 to greater than about 30% so that, in certain embodiments, the consistency of the wet web 24 varies from about 31% to about 36% at a location away from the air press 30 and at a location prior to subsequent transfers. In particular embodiments, the air press 30 increases the consistency of the wet web 24 by about 5% or more, such as about 10%.

Preferably, a support fabric belt 32 is in contact with the wet web 24 in front of the air press 30. The wet web 24 is sandwiched between the support web 32 and the forming web 22 and is thus supported during the pressure drop created by the air press 30. Suitable fabric belts for the support fabric belt 32 include almost any fabric belt, including, for example, a forming fabric belt such as Albany International 94M.

The wet web 24 is then transferred from the forming fabric 22 to the transfer fabric 36, the transfer fabric 36 traveling at a slower speed than the forming fabric, in order to increase the fabric stretch. The transfer is preferably performed by means of a vacuum transfer skid 37 as described below with reference to fig. 7 and 8. The surface of the transfer fabric belt 36 is preferably relatively smooth to smooth the wet web 24. The degree of openness of the transfer fabric belt 36, as measured by pore volume, is relatively low and can be about the same as, or lower than, the degree of openness of the forming fabric belt 22. The step of rush transfer may be carried out by a number of methods known in the art, such as those disclosed in, for example, U.S. patent application Ser. No. 08/790980 entitled "method for improving rush transfer to produce a product having high bulk without macro-wrinkles", published by Lindsay et al, 1/29/1997; U.S. patent application Ser. No. 08/709427 entitled "method for making high bulk tissue webs using nonwoven substrates," filed on 1996, 9/6, Lindsay et al; united states patent No. 5667636 issued on 16/9/1997 to s.a.engel et al; and 5607551 issued 3/4 of 1997 to t.e.farrington, Jr et al; these documents are incorporated herein by reference.

The transfer fabric belt 36 passes around the rollers 38 and 39 before the wet web 24 is transferred to the throughdrying fabric belt 40, which throughdrying fabric belt 40 runs at substantially the same speed, and may run at a different speed if desired. The vacuum transfer skid 42, which is responsible for the transfer, may be designed the same as the vacuum transfer skid used for the previous transfer. As the fabric 24 is carried around the through-dryer 44, the fabric 24 is dried to a final dryness.

The dried fabric 50 is carried through one or more optional fixed gap fabric belt nips formed between carrier fabric belts 52 and 53 prior to being wound onto a reel 48 for conversion into a finished product. The bulk or thickness of the fabric 50 can be controlled by the fabric strip embossing nips formed between the rollers 54 and 55, 56 and 57, and 58 and 59. Suitable carrier webs for this purpose are Albany International 84M or 94M and Asten 959 or 937, all of which are relatively smooth webs having fine lines. The nip between each pair of rollers may be from about 0.001 inch to about 0.02 inch (0.025-0.51 mm). As shown, the carrier web section of the machine is designed with a series of fixed nips to control the caliper of the web, and can replace or supplement off-line calendering. Alternatively, a reel calender may be used to achieve the final caliper or to supplement off-line calendering.

Fig. 17 representatively illustrates a second embodiment of the machine and method for manufacturing tissue. The illustrated method of making a creped throughdried sheet comprises a papermaking headbox 20, which papermaking headbox 20 sprays or deposits an aqueous suspension of papermaking fibers between first and second forming fabric belts 150 and 152 of a twin fourdrinier forming machine to form a wet fabric 24. Preferably, as the fabric 24 is sandwiched between the forming fabric belts 150 and 152, the fabric is conveyed through an air press 30 which includes a gas plenum and a collection device such as a vacuum box, as will be described in detail below. The fabric 24 may also be carried around one or more vacuum or suction boxes (not shown) prior to the air press.

Wet fabric 24 is then transferred from second forming fabric belt 152 to transfer fabric belt 154. Vacuum draw roll 156 is used to transfer the wet web 24 from the transfer fabric belt 154 to a coarse throughdrying fabric belt 160. The throughdrying fabric belts are arranged to carry the fabric around two throughdryers 162 and 164. As shown, a separate transfer fabric belt 166 holds the fabric against the throughdrying fabric belt 160 to transfer the fabric between the two throughdryers. The web 24 is preferably dried on the second through-dryer 164 to a final dryness.

After the second throughdryer 164, a vacuum roll 168 is used to remove the fabric from the throughdrying fabric 160 such that the fabric is sandwiched between a press fabric belt 170 and a transfer fabric belt 172. The fabric is then pressed against the surface of a drying cylinder, such as a yankee dryer 174, using a press roll 176. The dried fabric 50 is preferably removed from the dryer by a creping blade for stretching and winding onto a roll. Of course, the number and arrangement of the through-dryers and fabric belts may be different from that shown in FIG. 17.

The operation of the through-dryer can be enhanced by noncompressively dewatering the web 24 to a higher consistency prior to the first through-dryer 162. In practice, the air press 30 preferably increases the consistency of the wet web 24 to greater than about 30 percent, such that in certain embodiments, the consistency of the wet web 24 varies from about 31 percent to about 36 percent at a location prior to exiting the air press 30 and the throughdryer. In particular embodiments, the air press 30 increases the consistency of the wet web 24 by about 5% or more, such as about 10%.

The top view of fig. 2 and the side view of fig. 3 show the gas press 30 in more detail, the latter being partly broken away for illustrative purposes. The gas press 30 generally includes an upper gas plenum 60 in combination with a lower collection device in the form of a vacuum or suction box 62. The terms "upper" and "lower" are used herein for ease of reference and understanding of the drawings and are not intended to limit the manner in which the components are oriented. The wet wipe fabric 24 sandwiched between the forming fabric 22 and the support fabric 32 (or between the forming fabrics 150 and 152) passes between the air plenum 60 and the vacuum box 62.

The illustrated gas plenum 60 is adapted to receive a supply of pressurized fluid via an air manifold 64, the manifold 64 being operatively connected to a source of pressurized fluid such as a compressor or blower (not shown). The gas plenum 60 is provided with a gas plenum cover 66, the cover 66 having a bottom surface 67 (fig. 3) that is disposed against the vacuum box 62 and against or in contact with the support fabric belt 32 during use. The cover 66 is provided with a slot 68 (fig. 5) extending transversely to the longitudinal direction and across substantially the entire width of the wet web 24, but preferably slightly less than the width of the web, to allow pressurized fluid to flow from the air plenum 60 through the web and wet web.

The vacuum box 62 is operatively connected to a vacuum source and is fixedly mounted to a support structure (not shown). The vacuum box 62 includes a lid 70, the lid 70 having a top surface 72, the forming fabric belt 22 running on the top surface 72. The vacuum chamber cover 70 is provided with a pair of slots 74 (fig. 3 and 5), the slots 74 corresponding to the positions of the slots 68 in the gas plenum cover 66. The pressurized fluid dewaters the wet web 24 as it is drawn from the air plenum 60 and into and through the vacuum box 62.

The fluid pressure within the gas plenum 60 is preferably maintained at about 5 pounds per square inch (Psi) (0.35bar) or greater, and particularly in the range of about 5 to about 30Psi (0.35-2.07bar), such as about 15Psi (1.03 bar). The fluid pressure in the gas plenum 60 is preferably monitored and controlled to a predetermined level.

The bottom surface 67 of the gas plenum lid 66 is preferably slightly curved to facilitate fabric control. The surface 67 curves toward the vacuum box 62, i.e., about an axis on the vacuum box side of the fabric 24. The curvature of the bottom surface 67 allows the combined angle of the support fabric belt 32, wet fabric 24 and forming fabric belt 22 to vary, resulting in a net downward force that seals the vacuum box 62 from the entry of outside air and supports the wet fabric 24 during dewatering. The angle of curvature allows the pneumatic press 30 to be loaded and unloaded as needed at any time depending on the process conditions. The necessary angular variation depends on the pressure difference between the pressure side and the vacuum side, preferably above 5 degrees, in particular in the range of 5 to 30 degrees, typically about 7.5 degrees.

The top and bottom surfaces 72 and 67 preferably have different radii of curvature. In particular, the radius of curvature of the bottom surface 67 is preferably greater than the radius of curvature of the top surface 72 so as to form lines of contact between the gas plenum 60 and the vacuum box 62 at the front and rear edges 76 of the gas press 30. With proper attention to the position of the support web 32 and the forming web 22 and the loading and unloading mechanisms, the radii of curvature of these surfaces can be switched.

The front and rear edges 76 of the air press 30 may also be provided with end seals 78 (fig. 3), the seals 78 being held very close to or in contact with the support web 32 at any time. The end seals 78 minimize the escape of pressurized fluid longitudinally between the gas plenum 60 and the vacuum box 62. The end seals 78 may be made of a suitable low friction material such as an elastomeric plastic compound, a material that is preferably resistant to wear relative to the fabric strip, or the like. The end seals preferably have curved edges to prevent sanding of the fabric strip.

Referring additionally to fig. 4 and 5, the air press 30 is preferably provided with side seals 80 to prevent loss of pressurized fluid along the side edges 82 of the air press. The side seal 80 is made of a semi-rigid material that is adapted to deform or flex slightly when exposed to the pressurized fluid of the gas plenum 60. The illustrated side seal 80 defines a groove 84, the groove 84 being adapted to be mounted to the vacuum chamber cover 70 by a clamping bar 85 and fasteners 86 or other suitable means. In cross-section, each side seal 80 is L-shaped with one leg 88 extending upwardly from the vacuum chamber cover 70 into a side seal groove 89, the side seal groove 89 being located in the gas plenum cover 66. As shown in fig. 4 and 5, pressurized fluid from the gas plenum 60 causes the legs 88 to flex outwardly into sealing contact with the outer surface of the side seal groove 89 of the gas plenum cover 66. Alternatively, the position of the side seals 80 may be reversed such that they are fixedly mounted to the gas plenum cover 66 and in sealing contact with a contact surface defined by the vacuum chamber cover 70 (not shown). In either alternative design, it is preferred to force the side seals into engagement with the seal contacting surface using a pressurized fluid.

A position control mechanism 90 maintains the air plenum 60 adjacent the vacuum box 62 and in contact with the support fabric belt 32. The position control mechanism 90 includes a pair of rods 92, the rods 92 being connected by a cross member 93 and fixedly mounted to the gas plenum 60 with suitable fasteners 94 (fig. 3). The end of the lever 92 opposite the gas plenum 60 is rotatably mounted on a shaft 96. The position control mechanism 90 also includes a counterbalance drum 98 operatively connected to the fixed structure support 90 and one of the cross members 93. The equalization cylinder 98 may be extended or retracted, thereby causing the rod 92 to rotate about the axis 96, which moves the gas plenum 60 toward or away from the vacuum box 62.

In use, the control system extends balance cylinder 98 sufficiently to bring end seal 78 into contact with support fabric strip 32 and side seal 80 into side seal groove 89. The gas press 30 is activated such that pressurized fluid fills the gas plenum 60 and the semi-rigid side seal 80 is forced into sealing engagement with the gas plenum cover 66. The pressurized fluid also creates an upward force that moves the air plenum 60 away from the support fabric 32. The control system directs the balancing cylinder 98 to operate to adjust this upward force based on the fluid pressure within the gas plenum 60, which is continuously measured using the pressure monitoring system. Thus, the end seals 78 remain very close to or in contact with the support fabric strip 32 at any time. By proportionally reducing or increasing the force applied by the balancing cylinder 98, the control system may counteract irregular pressure drops or pressure spikes within the gas plenum 60. The airflow within the air compressor may also be monitored. As a result, the end seals 78 do not seize the fabric belts 32 and 22, which would otherwise cause excessive wear of the fabric belts.

Figure 6 typically illustrates an alternative sealing system for the gas compressor 30. The air plenum 100 is provided with a hinged arm 102 defining or supporting a sealing bar 104, the sealing bar 104 being adapted to rest on the support fabric belt 32 across the width of the wet web 24 to minimize the escape of pressurized fluid in the longitudinal direction. Although only one arm 102 is shown in fig. 6, it should be understood that a second arm may be provided and configured at the opposite end of the gas plenum 100 in a similar manner. The side of the gas plenum 100 may be fitted with a side seal 80 as shown in fig. 2-5, or may be fixedly mounted to the vacuum box 62 to minimize or eliminate side leakage of the pressurized fluid.

The articulating arm 102 is preferably made of a rigid material such as structural steel, graphite compound, or the like. The arm 102 has a first portion 106 and a second portion 108, the first portion 106 being at least partially disposed within the gas plenum 100 and the second portion being preferably located outside of the gas plenum. The arm 102 is pivotally mounted to the air plenum 100 by a hinge 110. A pressurized fluid impermeable hinge seal 112 is mounted to the inner surface of an arm 114 of the gas plenum 100 and to the first portion 106 to prevent the escape of pressurized fluid. The sealing bar 104 is preferably a separate component mounted on the first portion 106 and the sealing bar 104 is urged toward the support web 32 (not shown in FIG. 6) by contact with the pressurized fluid on the first portion 106. Suitable sealing rods 104 may be made of low electrical resistance, low coefficient of friction, and durable materials, such as ceramics, heat resistant polymers, and the like.

A balancing bladder 120 having an inflatable chamber 122 is mounted to the second portion 108 of the arm 102 by means of a bracket 124 or other suitable means. The chamber 122 is operatively connected to a source of pressurized fluid, such as air, to inflate the chamber. The arm 102 and the bladder 120 are arranged such that when the bladder (not shown) is inflated, the bladder presses against the outer surface of the wall 114 of the gas plenum 100, thereby causing the arm to pivot about the hinge 110. Alternatively, a mechanism with a compression cylinder (not shown) may be used as a means to rotate the arm 102 instead of a counterbalance bladder.

The control system is operated to proportionally inflate or deflate the bladder 120 based on the fluid pressure within the gas plenum 100. For example, as the pressure within the air plenum 100 increases, the control system is adapted to increase or inflate the pressure within the equalization chamber 120 so that the sealing bar 104 does not press excessively downward against the support fabric 32.

Fig. 7 and 8 more clearly show the design of the vacuum transfer shoe 37 used in the transfer fabric belt section of the manufacturing process. The vacuum transfer skid 37 defines a vacuum nozzle 130 (fig. 7) that is connected to a vacuum source and suitably has a length "L" of from about 0.5 to about 1 inch (12.7-25.4 mm). To produce uncreped throughdried bath tissue, a suitable vacuum nozzle length is about 1 inch (25.4 mm). The vacuum nozzle 130 has a front edge 132 and a rear edge 133 that form respective entry and exit lands 134 and 135 of the vacuum transfer sled 37. The rear edge 133 of the vacuum nozzle 130 is recessed relative to the front edge 132 due to the different orientation of the exit land 135 relative to the entry land 134. The angle "a" between the planes entering the junction area 134 and exiting the junction area 135 can be about 0.5 degrees or more, more specifically about 1 degree or more, and still more specifically about 5 degrees or more, to provide sufficient separation of the forming fabric belt 22 and the conveying fabric belt 36 as they converge and diverge.

Fig. 8 further illustrates the wet wipe fabric 24 traveling in the direction of the arrows toward the vacuum transfer shoe 37. While approaching the vacuum transfer shoe 37 is a transfer fabric belt 36 running at a slower speed. The angle of convergence between the two incoming fabric strips is indicated by "C". The divergence angle between the two fabric strips is denoted by "D". As shown, the two strips converge and diverge in unison at a point "P", which corresponds to the leading edge 132 of the vacuum nozzle 130. To effect transfer from forming fabric 22 to transfer fabric 36, it is necessary or desirable for the fabric to contact both fabrics throughout the length of vacuum nozzle 130. As is evident from FIG. 8, neither the forming fabric 22 nor the transfer fabric 36 need deflect too much to complete the transfer, which reduces fabric wear. Numerically, the change in direction of any one strip may be less than 5 degrees.

As noted above, the transfer fabric belt 36 travels at a slower speed than the forming fabric belt 22. If more than one conveying fabric belt is used, the speed difference between the fabric belts may be the same or different. Multiple transfer fabric belts can provide operational flexibility, as well as multiple fabric belt/speed combinations to affect the performance of the finished product.

The vacuum used for differential delivery may be from about 3 to about 15 inches of mercury, preferably about 5 inches of mercury. In addition to or instead of drawing the fabric onto the next fabric strip with a vacuum, a positive pressure on the opposite side of the fabric 24 may be used in addition to or instead of a vacuum shoe (negative pressure) to blow the fabric onto the next fabric strip. Also, one or more vacuum rolls may be used in place of one or more vacuum shoes.

Fig. 10-13 illustrate another embodiment of an air press 200 for dewatering a wet web 24. The gas press 200 generally includes an upper gas plenum 202 in combination with a lower collection device in the form of a vacuum box 204. The wet web 24, sandwiched between the upper 206 and lower 208 support belts, travels in the machine direction 205 between the air plenum and the vacuum box. The air plenum and the vacuum box are operatively associated such that pressurized fluid supplied to the air plenum flows through the wet web and is eliminated or exhausted through the vacuum box.

Each continuous web 206 and 208 runs around a series of rollers (not shown) to guide, drive and tension the web in a manner well known in the art. The tension of the webbing belt can be adjusted to a predetermined value, suitably from about 10 to about 60 pounds per linear inch (pli), particularly from about 30 to about 50pli, and more particularly from about 35 to about 45 pli. The fabric strips used to transport the wet web 24 through the air press 200 include almost any fluid permeable fabric strip, such as Albany international 94M, Appleton Mills 2164B, or the like.

Figure 10 shows an end view of the air press 200 across the width of the wet web 24 and figure 11 shows a side view of the air press in the machine direction 205. In both figures, several components of the air plenum 202 are shown in raised or retracted positions relative to the wet web 24 and the vacuum box 204. In the retracted position, it is not possible to effectively seal the pressurized fluid. In the present invention, the "retracted position" of the air press means that the components of the air plenum 202 do not impinge on the wet web and the support web.

The gas plenum 202 and vacuum box 204 are shown mounted within a suitable frame structure 210. The illustrated frame structure includes upper and lower support plates 211 separated by a number of vertically oriented support rods 212. The gas plenum 202 defines a chamber 214 (fig. 13), the chamber 214 being adapted to receive pressurized fluid supplied via one or more suitable air tubes 215 operatively connected to a source of pressurized fluid (not shown). Accordingly, the vacuum box 204 defines a plurality of vacuum chambers (described below in connection with fig. 13) that are preferably operatively connected to low and high vacuum sources (not shown) via appropriate fluid conduits 217 and 218, respectively (fig. 11, 12 and 13). The water drained from the wet web 24 is then separated from the air stream. The figures illustrate, without limitation, various fasteners for mounting components of the gas compressor.

Fig. 12 and 13 show enlarged cross-sectional views of the air compressor 200. In these figures, the air press is in an operating position wherein the components of air plenum 202 are lowered into non-contacting relation with wet web 24 and support web belts 206 and 208. The degree of non-contact has been found to result in proper sealing of the pressurized fluid with minimal contact force and therefore reduced webbing wear, as will be described in detail below.

The air plenum 202 includes a stationary member 220 that is fixedly attached to the frame structure 210 and a sealing device 260 that is movably attached relative to the frame structure and the wet web. Alternatively, the entire gas plenum may be movably mounted relative to the frame structure.

Referring particularly to fig. 13, the stationary part 220 of the gas plenum includes a pair of upper bearing means 222 that are spaced apart from each other and disposed below the upper bearing plate 211. The upper bearing means defines outer surfaces 224, the outer surfaces 224 facing directly towards each other and being defined in part between the gas plenum chambers 214. The upper bearing means also defines a bottom surface 226 directed towards the vacuum box 204. In the illustrated embodiment, each bottom surface 226 defines an elongated recess 228 within which an upper pneumatic loading tube 230 is fixedly mounted. The upper pneumatic loading tube 230 is suitably located in the transverse middle and preferably extends across the full width of the wet web.

The stationary component 220 of the gas plenum 202 further comprises a pair of lower support means 240, the lower support means 240 being spaced apart from each other and vertically spaced apart from the upper support means 222. The lower bearing apparatus defines a top surface 242 and an outer surface 244. The top surface 242 is directed toward the bottom surface 226 of the upper bearing assembly 222 and, as shown, also defines an elongated recess 246 within which a lower pneumatic loading tube 248 is securely mounted. The lower pneumatic loading tube 248 is suitably centered in the cross direction and suitably extends across about 50% to 100% of the width of the wet web. In the illustrated embodiment, a transverse support plate 250 is fixedly mounted to the outer surface 244 of the lower support apparatus and is used to stabilize the sealing apparatus 260 for vertical movement.

Referring additionally to fig. 14, the sealing device 260 includes a pair of transverse seals referred to as CD seals 262 (fig. 12-14) spaced apart from one another, a plurality of carriers 263 (fig. 14) connected to the CD seals, and a pair of longitudinal seals referred to as MD seals 264 (fig. 12 and 14). The CD seal is vertically movable relative to the stationary member 220. Optionally but preferably, the bracket 263 is fixedly mounted to the CD seal to provide structural support so as to move vertically with the CD seal. In the machine direction 205, MD seals 264 are disposed between the upper support devices 222 and between the CD seals 262. As described in detail below, portions of the MD seal may move vertically relative to the stationary member 220. In the cross direction, the MD seal is disposed near the edges of the wet web 24. In one particular embodiment, the MD seal is movable in the cross direction in order to accommodate the range of possible wet web widths.

The illustrated CD seal 262 includes a main upstanding wall portion 266, a transverse flange 268 projecting outwardly from a top 270 of the wall portion, and a sealing disc 272 (fig. 13) mounted on an opposite bottom 274 of the wall portion. In this way, the outwardly projecting flanges 268 form opposed upper and lower control surfaces 276 and 278 that are substantially perpendicular to the direction of movement of the seal. The wall portion 266 and the flange 268 may comprise separate components as shown or a single component.

As described above, the components of the sealing device 260 are vertically movable between a retracted position, shown in fig. 10 and 11, and an operating position, shown in fig. 12 and 13. In particular, wall portion 266 of CD seal 262 is disposed within and slidable relative to position control plate 250. The amount of vertical movement is determined by the ability of lateral flange 268 to move between bottom surface 226 of upper support apparatus 222 and top surface 242 of lower support apparatus 240.

The vertical position of the transverse flange 268 and the CD seal 262 are controlled by actuating the pneumatic loading tubes 230 and 248. The loading tube is operatively connected to the pneumatic source and to a control system (not shown) of the pneumatic press. Activation of upper load tube 230 may generate a downward force on upper control surface 276 of CD seal 262, causing flange 268 to move downward until it contacts top surface 242 of lower support device 240, or to stop moving under an upward force generated by the tension in lower load tube 248 or the fabric strip. Retraction of the CD seal 262 may be accomplished by activating the lower loading tube 248 or deactivating the upper loading tube. In this case, the lower loading tube presses upward on the lower control surface 278, causing the flange 268 to move upward against the bottom surface of the support 222. Of course, the upper and lower loading tubes may be operated at different pressures to move the CD seal. Another means for controlling the vertical movement of the CD seal may include other types of connections such as pneumatic cylinders, hydraulic cylinders, bolts, jacks, mechanical connectors, or other suitable means. Suitable loading tubes are available from Seal Master corporation of Kent, Ohio.

As shown in fig. 13, a pair of bridge span plates 279 span the gap between upper bearing 222 and CD seal 262 to prevent the pressurized fluid from escaping. Thus, the bridge deck defines a portion of the plenum 214. The bridge span plate may be fixedly mounted on the outer surface 224 of the upper bearing means and may slide relative to the inner surface of the CD seal or vice versa. The bridge span plate may be made of a fluid permeable semi-rigid low friction material such as LEXAN, a metal plate or the like.

The function of the sealing plate 272 is combined with other features of the air press to minimize pressurized fluid from escaping longitudinally between the air plenum 202 and the wet web 24. Further, the sealing sheet is preferably formed in such a manner as to reduce the amount of wear of the fabric belt. In a particular embodiment, the sealing plate is made of an elastomeric plastic compound, ceramic, coated metal substrate or the like.

Referring particularly to fig. 12 and 14, the MD seals 264 are spaced apart and adapted to prevent the loss of pressurized fluid along the sides of the air press. Fig. 12 and 14 each show one of the MD seals 264, with the MD seal 264 being disposed in the cross direction adjacent to the edge of the wet web 24. As shown, each MD seal includes a cross support 280, an end deckle band 282 operably coupled to cross support 280, and a drive 284 for moving the end deckle band relative to the cross support. The cross-support members 280 are generally disposed adjacent the side edges of the wet web 24 and generally between the CD seal members. As shown, each cross support defines a downwardly directed channel 281 (FIG. 14) in which an end stop paper frame strip is mounted. In addition, each cross support defines an annular bore 283 within which the driver 284 is mounted.

The end deckle band 282 is movable relative to the cross support 280 due to the cylinder drive 284. A coupling 285 (fig. 12) couples the end stop frame strap to the output shaft of the cylinder drive. The couplers may include one or more inverted T-shaped rods so that the end paper frame strip may slide within the channel 281, for example for replacement.

As shown in FIG. 14, the cross supports 280 and end deckle bands 282 define slots to receive a fluid impermeable sealing band 286, such as an O-ring material or the like. The sealing band helps seal the gas plenum 214 of the gas press against leakage. The sealing tape slot is preferably widened at the interface between cross supports 280 and end paper frame tape 282 to accommodate relative movement between these components.

A bridge span plate 287 (fig. 12) is disposed between the MD seal 264 and the upper support plate 211 and is fixedly mounted thereto. The lateral portion of the air chamber 214 (fig. 13) is defined by the bridge plate. A sealing means, such as a fluid impermeable gasket material, is preferably disposed between the bridge plate and the MD seal to allow relative movement thereof and to prevent loss of pressurized fluid.

Regardless of the vertical position of CD seal 262, drive 284 suitably provides for the controlled loading and unloading of end deckle band 282 against upper support fabric 206. The load can be precisely controlled to meet the necessary sealing force. The end deckle band may be retracted when it is not necessary to eliminate the entire end deckle and fabric band wear. Suitable actuators may be provided by Bimba, Inc. or springs (not shown) may be used, thereby holding the end deckle against the fabric strip, although the ability to control the position of the end deckle may be sacrificed.

Referring to fig. 12, each end deckle band 282 has a top surface or edge 290 disposed adjacent to link 285, an opposite bottom surface or edge 292 disposed in use in contact with webbing 206, and a side surface or edge 294 proximate to CD seal 262. The bottom surface 292 is suitably shaped to match the curvature of the vacuum box 204. The bottom surface 292 is preferably shaped to conform to the curvature of the webbing at the location where the CD seal 262 hits the webbing without the webbing hitting. Thus, the central portion 296 of the bottom surface is laterally surrounded longitudinally by spaced apart ends 298. The shape of central portion 296 generally conforms to the shape of the vacuum box, while the shape of end portions 298 generally conforms to the deflection of the fabric strip caused by CD seal 262. To prevent the protruding end 298 from wearing, the end deckle band is preferably retracted before the CD seal 262 is retracted. The end deckle bands are preferably made of a gas impermeable material which minimizes abrasion of the fabric bands. Specific materials suitable for the end deckle include polyethylene, nylon or the like.

The MD seal 264 is preferably movable in the cross direction so that it is preferably slidably disposed against the CD seal 262. In the illustrated embodiment, movement of the MD seal 264 in the cross direction is controlled by a threaded shaft or screw 305, the threaded shaft or screw 305 being held in place by a bracket 306 (fig. 14). Threaded shaft 305 passes through a threaded hole in cross support 280 and rotation of the shaft moves MD seal 264 along the shaft. Another means for moving the MD seal in the cross direction may also be used, such as a pneumatic device or the like. In an alternative embodiment, the MD seal is fixedly mounted to the CD seal so that the entire seal is raised and lowered together (not shown). In another alternative embodiment, cross supports 280 are fixedly mounted to the CD seal and the end deckle bands are adapted to move independently of the CD seal (not shown).

The vacuum box 204 includes a lid 300, the lid 300 having a top surface 302 over which the lower support fabric belt 208 travels. As described in another embodiment above, the vacuum chamber cover 300 and the sealing device 260 are preferably slightly curved to facilitate fabric handling. The illustrated vacuum chamber lid is provided with a first outer sealing slide 311, a first sealed vacuum zone 312, a first inner sealing slide 313, a series of four high vacuum zones 314, 316, 318 and 320 surrounding three inner slides 315, 317 and 319, a second inner sealing slide 321, a second sealed vacuum zone 322, and a second outer sealing slide 323 (fig. 13) along the longitudinal direction 205 from the front edge to the rear edge. Each of these tracks and zones preferably extends across the full width of the fabric in the cross direction. Each slide rail includes a top surface, preferably made of a ceramic material, to seat against the lower support fabric belt 208 without causing significant fabric belt wear. Suitable vacuum chamber covers and slides may be made of plastic, nylon, coated steel or the like and are available from JWI or IBS.

The four high vacuum regions 314, 316, 318 and 320 are channels within the lid 300 that are operably connected to one or more vacuum sources (not shown) to draw a higher vacuum level. For example, the high vacuum zone may operate at a vacuum of 0 to 25 inches of mercury, particularly about 10 to about 25 inches of mercury. As another illustrative example, the cover 300 may define a plurality of holes or other shaped openings (not shown) that are connected to a vacuum source to create a pressurized fluid flow through the fabric. In one embodiment, the high vacuum zone includes nozzles, each measuring 0.375 inch in the machine direction, that extend across the full width of the wet web. The dwell time of exposure to the pressurized fluid stream at any given point on the web, in the illustrated embodiment the time span nozzles 314, 316, 318, and 320, is suitably about 10 milliseconds or less, specifically about 7.5 milliseconds or less, more specifically 5 milliseconds or less, such as about 3 milliseconds or less, and even about 1 millisecond or less. The number and width of the high pressure vacuum nozzles and the speed of the machine determine the dwell time. The residence time selected depends on the type of fibers contained in the wet fabric and the desired amount of dewatering.

First and second sealed vacuum zones 312 and 322 may be employed to minimize loss of pressurized fluid from the pneumatic press. The sealed vacuum zones are channels within the lid 300 that are operably connected to one or more vacuum sources (not shown) that are desirably drawn to a lower vacuum level than the four high vacuum zones. In particular, the desired vacuum level for the sealed vacuum region is from 0 to about 100 inches of water vacuum.

The air press 200 preferably constitutes a CD seal 262 disposed within the sealed vacuum zones 312 and 322. In particular, the sealing plate 272 of the CD seal 262 on the front side of the gas press is arranged in the longitudinal direction between the first outer sealing slide 311 and the first inner sealing slide 313, in particular in the middle between them. The rear sealing plate 272 of the CD seal is similarly arranged in the longitudinal direction between the second inner sealing slide 321 and the second outer sealing slide 323, in particular in the middle between them. As a result, the sealing device 260 can be lowered so that the CD seals are offset from the normal running trajectory of the wet web 24 and the web belts 206 and 208 toward the vacuum box, which is shown on a slightly enlarged scale in FIG. 13 for illustrative purposes.

The sealed vacuum zones 312 and 322 function to minimize the loss of pressurized fluid from the air press 200 across the width of the wet web 24. The vacuum within sealed vacuum zones 312 and 322 draws pressurized fluid from gas plenum 202 and ambient gas from outside the gas press. As a result, a gas flow is introduced into the sealed vacuum region from outside the gas press, rather than the pressurized fluid leaking in the opposite direction. Due to the relative difference in vacuum between the high vacuum region and the sealed vacuum region, most of the pressurized fluid from the gas plenum flows into the high vacuum region rather than the sealed vacuum region.

In another embodiment, partially shown in fig. 15, neither or both of sealed vacuum zones 312 and 322 are evacuated. Instead, a deformable sealing frame 330 is disposed within the sealing zones 312 and 322 (only 322 shown) to prevent leakage of pressurized fluid in the longitudinal direction. In this case, the air press is sealed longitudinally by a sealing flap 272 that strikes the fabric belts 206 and 208 and the wet web 24, and the fabric belts and wet web are disposed in close proximity to or in contact with the deformable sealing deckle 330. The CD seal 262 impinges the web and wet web and is disposed on the other side of the web and wet web by a deformable sealing deckle 330, where the profile is found to form a particularly effective air plenum seal.

The deformable sealing frame 330 preferably extends across the full width of the wet web to seal the front or back or both ends of the air press 200. The sealed vacuum zone may be disconnected from the vacuum source as the deformable sealed deckle is stretched across the full width of the fabric. A full width flexible seal frame is used at the rear of the press and a vacuum or blow box is used downstream of the press to hold the fabric 24 to one of the fabric strips as they separate.

The deformable sealing frame 330 preferably comprises two materials, one material being a material that wears preferentially relative to the fabric strip 208, meaning that when the fabric strip and material are in use, the material wears without significant wear of the fabric strip occurring while the fabric strip is being used, and the other material is resilient and deflects while hitting the fabric strip. In either case, the deformable sealing deckle is preferably gas impermeable and preferably comprises a material having a high porosity, such as a closed cell membrane or the like. In one particular embodiment, the deformable sealing deckle includes a closed-cell membrane measuring 0.25 inches in thickness. Optimally, the deformable sealing frame itself wears to match the path of the fabric strip. The deformable sealing frame is preferably attached with backing plates 332 for structural support, such as aluminum rods.

In embodiments where a full width deckle is not used, some sort of sealing means is required in the cross direction of the fabric. The above-described deformable sealing deckle or other suitable means known in the art may be used to block the flow of pressurized fluid from the wet web laterally outward through the web.

The degree of impingement of the CD seal in the upper support web 206 uniformly across the width of the wet web was found to be an important factor for forming an effective seal across the web. It has also been found that the degree of impingement necessary is a function of the maximum tension of the upper and lower support fabric belts 206 and 208, the pressure differential across the fabrics and between the plenum 214 and the sealed vacuum zones 312 and 322, and the gap between the CD seal 262 and the vacuum chamber lid 300.

Referring additionally to the schematic illustration of the rear seal portion of the air press shown in fig. 16, the minimum desired amount of impact, h (min), of the CD seal 262 in the upper support web 206 is found to be represented by the following equation:

h(min)=(T/W)[cosh(Wd/T)-1]；

wherein T is the measured fabric strip tension in pounds per inch;

w is the pressure differential across the fabric measured in psi; and

d is the gap in the longitudinal direction measured in inches

Figure 16 shows the rear CD seal 262 offsetting the upper support web 206 by the amount indicated by arrow "h". The maximum tension of the upper and lower support fabric belts 206 and 208 is indicated by arrow "T". The web tension is measured by a standard tension meter supplied by Huyck corporation or other suitable method. The gap between the sealing plate 272 of the CD seal and the second inner seal slide 321, measured in the longitudinal direction, is indicated by arrow "d". The gap "d" used to determine the degree of impingement is the gap on the higher pressure differential side of the sealing plate 272, i.e., toward the plenum, since the pressure differential on that side has the greatest effect on the fabric strip and the fabric position. Preferably, the gap between the sealing plate and the second outer slide 323 is almost the same as or even smaller than the gap "d".

Adjusting the vertical position of CD seal 262 to the minimum degree of impingement described above is a determining factor in the effectiveness of the CD seal. The loading force exerted on the sealing device 260 plays a minor role in determining the effectiveness of the seal and only needs to be adjusted to the amount needed to maintain the necessary degree of impact. Of course, the amount of fabric belt wear will adversely affect the commercial application of the air press 200. In order to achieve an effective seal while the fabric strip is substantially not worn, the degree of impact is preferably equal to or slightly greater than the minimum degree of impact. To minimize the non-uniformity of the belt wear across the width of the belt, the force applied to the belt is preferably kept constant in the cross direction. This can be achieved by either controlled and uniform loading of the CD seal or controlled location of the CD seal and uniform geometry of the impact of the CD seal.

In use, the control system lowers the sealing device 260 of the gas plenum 202 to an operating position. First, the CD seal 262 is lowered so that the sealing plate 272 strikes the support fabric 206 to the extent described above. In particular, the pressures within the upper and lower load tubes 230 and 248 are adjusted to move the CD seal 262 downward until movement is stopped by the transverse flange 268 contacting the lower support device 240 or until tension is balanced by the webbing. Second, the end deckle band 282 of MD seal 264 is lowered into contact with or into close proximity to the upper support fabric band. As a result, both the air plenum 202 and the vacuum box 204 are sealed against the wet web to prevent the pressurized fluid from escaping.

The air press is then activated so that the pressurized fluid fills the air plenum 202 and creates an air flow through the fabric. In the embodiment shown in fig. 13, high vacuum and low vacuum are applied to high vacuum zones 314, 316, 318 and 320 and sealed vacuum zones 312 and 322 to facilitate gas flow, sealing and water removal. In the embodiment of fig. 15, pressurized fluid flows from the gas plenum to the high vacuum zones 314, 316, 318, and 320, and the deformable sealing deckle 330 seals the gas press laterally. The pressure differential across the wet web and the air flow generated through the web effectively dewaters the web.

Many of the structural and operational features of the air press help to allow only a small escape of pressurized fluid with little wear of the fabric belt. The degree of impact is determined in order to optimize the effect of the CD seal. In one embodiment, the air press utilizes sealed vacuum zones 312 and 322 to create ambient air that flows into the air press across the width of the wet web. In another embodiment, the deformable seal 330 is disposed in the sealed vacuum zones 312 and 322 opposite the CD seal. In either case, to minimize the need for precise alignment of mating surfaces between the gas plenum 202 and the vacuum box 204, the CD seal 262 is preferably disposed at least partially within the channel of the vacuum box cover 300. Furthermore, the sealing device 260 may be loaded against a stationary component, such as the lower bearing device 240 connected to the frame structure 210. As a result, the loading force of the gas compressor is independent of the pressurized fluid pressure within the gas plenum. The fabric belt wear is minimized due to the use of the fabric belt low wear material and the lubrication system. Suitable lubricating systems may include chemical lubricants such as emulsified oil, a separating agent or other similar chemicals, or water. Typical lubricant application methods include spraying dilute lubricant, atomized solutions of water or gas, more concentrated felt wiping solutions in a uniform manner in the cross direction, or other methods known in the art for spray system applications.

The ability to operate at higher inflation pressures is seen to depend on the ability to prevent leakage. The presence of leaks can be detected by excessive air flow, increased operating noise, moisture dispersion, and in extreme cases, regular or irregular excursions within the wet fabric including holes and threads, etc., as compared to previous or anticipated operations. Leaks are repaired by calibrating or adjusting the seal components of the gas compressor.

In an air press, uniform air flow in the cross direction is desirable to provide uniform dewatering of the fabric. Flow uniformity in the cross direction can be improved with mechanisms on the pressure and vacuum sides, such as tapered tubing, whose shape can be designed using computational fluid dynamics modeling. Since the basis weight and moisture content of the fabric cannot be made uniform in the cross direction, it is preferable to use additional means in order to obtain uniform air flow in the cross direction. For example, independently controlled areas with air flow regulators on the pressure or vacuum side to vary the air flow depending on the paper properties, a baffle to achieve a significant pressure drop in the air flow before wetting the fabric, or other directing means. Another method of controlling CD dewatering uniformity may also include external devices such as a regional control steam jet such as the Devrizer steam jet available from Honeywell-Measurex Systems of Dublin.

Examples of the present invention

The following examples are included to facilitate a more detailed understanding of the invention. The particular amounts, ratios, components, and parameters are exemplary and not intended to specifically limit the scope of the present invention.

Referring to the examples, the MD tensile, MD elongation, and CD tensile were obtained according to TAPPI test method 4940M-88 "tensile break Properties of paper and paperboard" using the following parameters: crosshead speed was 10.0in/min (254 mm/min); the full amplitude load is 10 lb (4540 g); the jaw span (distance between jaws, sometimes referred to as the grip length) is 2.0 inches (50.8 mm); and the sample width was 3 inches (76.2 mm). The tensile testing machine is System Integration Technology, Inc. of Stoughton, Massachusetts; sintech, model CITS-2000, available from division of MTS systems corporation, located at the triangular Research Park (Research Triangle Park) of North Carolina.

The stiffness of the paper of this example can be expressed in terms of the maximum slope of the Machine Direction (MD) load elongation curve of the towel (hereinafter MD slope), or in terms of machine direction stiffness (as defined herein), which further takes into account the thickness of the towel and the number of plies of the product. How to determine the MD slope will be described below in conjunction with fig. 9. The MD slope is the maximum slope of the machine direction load elongation curve for a tissue. The MD slope is in units of kilograms per 3 inches (7.62 cm). MD stiffness is calculated as the square root of the thickness divided by the number of layers multiplied by the MD slope. The unit of MD stiffness is (kg/3 inches) micron^0.5。

FIG. 9 is a load elongation curve for a generic towel illustrating how the MD slope is determined. As shown, two points P1 and P2 are selected along the load elongation curve, the distance between which is exaggerated for illustrative purposes. The tensile tester was programmed (GAP 2.5 edition, Systems Integration Technology, Stoughton, Massachusetts; a division of MTS Systems, Inc. of Research Triangle Park, N.C.) so that it could calculate the dotted linear regression of these samples taken from P1 to P2. This curve is repeatedly calculated by regular adjustment points P1 and P2 along the curve (described below). The highest of these calculations is the maximum slope, which if calculated by sampling in the machine direction of the sample, is referred to as the MD slope.

The tensile tester program should be programmed to take 500 points such as P1 and P2 on a 2.5 inch (63.5m) stretch span. This provides a sufficient number of points to substantially exceed any actual elongation of the sample. A crosshead speed of 10 inches/minute (254mm/min) was used to move to a point every 0.030 seconds. The program calculates the slope between these points by counting 30 points from the 10 th point as the initial point (e.g., P1) to the fortieth point (e.g., P2), and calculating a linear regression over these 30 points. It stores the slope calculated by the regression in a matrix. The procedure then runs out 10 points to the twentieth point (which becomes P1) and repeats the procedure again (counting out 30 points that will go to the fiftieth point (which becomes P2), the slope is calculated and stored in the matrix as well). The process is continued throughout the entire elongated portion of the paper. The maximum slope is then selected from the matrix as the highest value. The maximum slope is in units of Kg/3 inch sample width. (of course, strain is dimensionless since strain is the length of the elongated portion divided by the length of the jaw span.

Examples 1 to 4. To illustrate the present invention, several uncreped throughdried tissue sheets were produced in a manner substantially as shown in figure 1. More specifically, examples 1-4 are three-ply single piece bath towels in which the outer ply comprises debonded and debonded eucalyptus fibers and the middle ply comprises refined northern softwood kraft fibers. Cenebra eucalyptus fibers were slurried at 10% consistency for 15 minutes and dewatered to 30% consistency. The pulp was then transferred to a Maule shaft disperger. The disperger was operated at a power input of 2.2HPD/T (1.8 kW/l/metric ton) and a temperature of 160 Fahrenheit (70 deg.C.). After dispergation, a softener (Witco C6027) was added to the pulp in an amount of 7.5 kg/metric ton dry fiber (0.75 weight percent).

Prior to forming, softwood fibers were pulped at a consistency of 3.2% for 30 minutes while debonded and unbound eucalyptus fibers were diluted to a consistency of 2.5%. For examples 1, 2 and 4, the total stratified sheet weight was 35%/30%/35% between the debonded eucalyptus layer/the refined cork layer/the debonded eucalyptus layer, and 33%/34%/33% for example 3. The middle layer is refined to the extent required for the target strength value, while the outer layer is soft and loose. To increase dry and temporary wet strength, an enhancer designated Parez 631 NC was added to the middle layer.

These examples employ a four-level Beloit Concept iii high headbox. Refined northern softwood kraft stock is used in both middle layers of the headbox to make a single middle layer of the three-layer product. A turbulence generating insert recessed about 3 inches (75mm) from the limiter plate and an interlayer baffle extending about 6 inches (150mm) from the limiter plate were used. The mesh limiting plate holes are about 0.9 inches (23mm) and the flow in all four layers of the headbox is similar. The consistency of the stock supplied to the headbox was about 0.09 weight percent.

The three sheets were formed on a twin fourdrinier suction roll forming machine whose forming fabric was an Appleton Mills2164-B fabric. The speed of the forming fabric belt ranges between 11.8 and 12.3 meters/second. The newly formed web was then dewatered to a consistency of 25-26% using vacuum suction from below the forming fabric, instead of an air press, and to a consistency of 32-33% using an air press before being transferred to the transfer fabric, which was running at 9.1 m/s (29-35% rush). The transfer fabric belt was an Appleton Mills 2164-B. The fabric was transferred to the transfer fabric belt using a vacuum skid pulled at a vacuum of about 6-15 inches (150-.

The fabric was then transferred to a throughdrying fabric belt running at a speed of about 9.1 meters/second. Appleton Mills type T124-4 and T124-7 throughdrying fabric strips were used. The fabric was loaded onto a honeycomb throughdryer operating at about 350 degrees Fahrenheit (175 degrees Celsius) and dried to a final dryness of about 94-98 percent consistency.

The order of making the sheet of this example is as follows: four rolls of the paper of example 1 were made. The consistency data in table 1 are based on two measurements, one at the beginning of the four rolls and one at the end of the four rolls. The other data shown in table 1 is based on an average of four measurements, one for each volume. The air compressor was then started. The data before and after the gas compressor was started are shown in table 3 (single data points). The data shows that the air press caused a significant increase in the stretch value. The process was then changed to reduce the stretch value to a similar degree to the paper of example 1. After this process adjustment stage, four rolls of the paper of example 2 (inventive) were manufactured. Four rolls of the paper of example 3 (invention) were then made with different throughdrying fabric belts and with the air press activated. The air press was turned off and the process adjusted to regain similar tensile strength values as the paper of example 3. Four rolls of the paper of example 4 were then made. The consistency data for each example in table 2 is based on an average of two measurements, once at the beginning of a group per four rolls and once at the end of a group per four rolls. The other data in table 2 is based on the average of four measurements of each example sheet, once per roll. In table 2, the data of example 4 is shown in the left column, the data of example 3 is shown in the right column so as to be consistent with tables 1 and 3, tables 1 and 3 show the data without the air compressor in the left column, and the data with the air compressor in the right column.

Tables 1-3 describe the process conditions and final tissue properties of examples 1-4 in more detail. In tables 1-3 below, the column headings are as follows: "consistency and rush transfer" means the consistency of the fabric as it is transferred from the forming fabric to the transfer fabric, expressed as percent solids; "MD tensile" is machine direction tensile, expressed in grams per 3 inch (7.62cm) sample width; "CD tensile" means the tensile strength in the cross direction, such thatGrams/3 inch (7.62cm) sample width; "MD tensile" is the elongation in the machine direction, and represents the percent elongation at break of a specimen; "MD slope" is as defined above, expressed in kilograms per 3 inches (7.62cm) of sample width; "caliper" refers to the thickness of 1 sheet of paper, in microns, as measured by a bulk density micrometer (model TMI 49-72-00, Amityville, N.Y.) having an anvil diameter of 4 and 1/16 inches (103.2mm) and an anvil pressure of 220 grams per square inch (3.39 kPa); "MD stiffness" is the stiffness coefficient in the machine direction, as defined above, in kilograms per 3 inches per micrometer^0．5Represents; "basis weight" means the basis weight after forming, expressed in grams per square meter; "TAD fabric belt" means a through-air-drying fabric belt; "refiner" refers to the power input, expressed in kilowatts, to refine the middle layer; "rush" means the difference in speed between the forming fabric belt and the slower conveying fabric belt divided by the speed of the conveying fabric belt, expressed as a percentage; "HW/SW" refers to the subdivision of the weight of Hardwood (HW) and Softwood (SW) fibers in a three ply, single tissue, expressed as a percentage of the total fiber weight; and "Parez" means Parez 631 NC is the rate of addition; expressed in kilograms per metric ton of middle layer fiber.

Table 1 example 1 consistency and rush transfer (%) 25.2-26.132.5-33.4 MD tensile (grams/3 ") 933944 CD tensile (grams/3") 676662 MD elongation (%) 24.524.7 MD slope (kg/3 ") 4.9943.776 caliper (microns) 671607 MD stiffness (kg/3"). micro-electrons (air-pressure-free press) (with air-pressure press and process adjustment)^0.512993 basis weight (gsm) 34.635.2 TAD fabric belt T-124-4T-124-4 Refiner (kW) 3226 rapid (%) 32 29HW/SW(％) 70/30 70/30Parez(kg/mt) 4.0 3.2

Table 2 example 4 example 5 (without air press) (with air press and process adjustment) consistency and rush transfer (%) 24.632.4 MD tensile (grams/3 ") 961907 CD tensile (grams/3") 714685 MD elongation (%) 23.524.4 MD slope (kg/3 ") 5.6683.942 thickness (microns) 716704 MD stiffness (kg/3"). microns^0.5152105 basis weight (gsm) 35.035.1 TAD fabric tape T-124-7T-124-7 Refiner (kW) 4034.5 rapid (%) 3531 HW/SW (%) 66/3470/30 Parez (kg/mt) 2.52.5

TABLE 3 (airless) (air press) consistency and rush transfer (%) 25.232.5 MD tensile (grams/3 ') 9151099 CD tensile (grams/3') 661799 CD wet tensile 127150 MD tensile (%) 24.428.5 MD slope (kg/3 ') 4.9964.028 thickness (micrometers) 665630 MD stiffness (kg/3') microns^0.5129101 basis weight (gsm)34.334.6 TAD fabric belt T-124-4T-124-4 Refiner (kW) 3232 rapid (%) 3232 HW/SW (%) 70/3070/30 Parez (kg/mt) 4.04.0

As shown in the previous example, the air press produces a significantly higher consistency upstream of the differential conveyance, which results in smoother sheets, as evidenced by lower modulus values. Preferably, the tissue product has a modulus (MD stiffness) that is at least 20% less than the modulus of a similar tissue product made without supplemental dewatering to a consistency of greater than about 30%. Further, the tensile strength of the tissue product in the machine direction is at least 20% greater and the tensile strength of the tissue product in the cross direction is also at least 20% greater than the tensile strength of a similar tissue product made without supplemental dewatering to a consistency of greater than about 30%. Additionally, the tissue product has a machine direction stretch of at least 17% greater than the machine direction stretch of a similar tissue product made without supplemental dewatering to a consistency of greater than about 30%.

The foregoing detailed description is for illustrative purposes only, and various modifications and changes may be made without departing from the spirit and scope of the invention. For example, optional features described as part of one embodiment may be employed to yield another embodiment. Also, two named components may represent portions of the same structure. In addition, various methods and machines disclosed in U.S. patent application 5667636, published 1997, 9, 16, in s.a. engle, which is incorporated herein by reference, can also be used. The invention should not be limited by the specific embodiments described, but only by the claims.

Claims (34)

1. A method of making a soft tissue comprising the steps of:

depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric;

dewatering the wet web to a consistency of about 20% to about 30%;

supplementally dewatering the wet web to a consistency of greater than about 30% using a non-compressive dewatering device;

transferring the post-dewatered web to a transfer fabric which travels at a speed of about 10% to about 80% slower than the forming fabric;

transferring the web to a throughdrying fabric; and

the fabric is throughdried to a final dryness.

2. The method of claim 1, wherein the non-compressive dewatering device is selected from the group consisting of pneumatic, infrared, microwave, sonic, through and displacement dewatering devices.

3. The method of claim 1, wherein the non-compressive dewatering device comprises an air press.

4. The method of claim 3, wherein the air press increases the consistency of the wet web by at least about 3%.

5. The method of claim 3, wherein the gas compressor includes a gas plenum, and the fluid pressure within the gas plenum is maintained within the range of about 5 to about 30 psi.

6. The method of claim 3, 4 or 5, wherein the air press provides a pressure differential across the wet web of from about 35 to about 60 inches of mercury.

7. The method of claim 3, 4 or 5, wherein the air press dewaters the wet web to a consistency of greater than about 31 percent.

8. The method of claim 7, wherein the air press dewaters the wet web to a consistency of greater than about 32 percent.

9. The method of claim 3, 4 or 5, wherein the air press dewaters the wet web to a consistency of from about 31% to about 36%.

10. The method of claim 1, wherein the wet web is dewatered to a consistency of from about 20% to about 30% using a plurality of vacuum boxes.

11. The method of claim 3 wherein the wet web is sandwiched between the forming fabric and the support fabric as the wet web is conveyed through the air press.

12. The method of claim 1, 3 or 4, wherein the forming fabric is traveling at a speed of at least about 2000 feet per minute.

13. A tissue product made by the method of claim 1.

14. The tissue product of claim 13 having a modulus of at least about 20% less than the modulus of a comparative tissue product made by the method of claim 1 without supplemental dewatering to a consistency of greater than about 30%.

15. The tissue product of claim 13 having a md tensile of at least about 20% as compared to the md tensile of a comparative tissue product made by the method of claim 1 without supplemental dewatering to a consistency greater than about 30%.

16. The tissue product of claim 13 having a cd tensile of at least about 20% as compared to a cd tensile of a comparative tissue product made by the method of claim 1 without supplemental dewatering to a consistency greater than about 30%.

17. The tissue product of claim 13 having a machine direction stretch of at least about 17% as compared to the machine direction stretch of a comparative tissue product made by the method of claim 1 without supplemental dewatering to a consistency of greater than about 30%.

18. A method of making a creped throughdrying fabric comprising the steps of:

(a) depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric;

(b) dewatering the wet web to a consistency of about 30 percent or greater using a non-compressive dewatering device adapted to cause a pressurized fluid to flow substantially through the web at a gauge pressure of about 5 pounds per square inch gauge or greater due to the integral seal with the wet web;

(c) transferring the wet web to a throughdrying fabric;

(d) throughdrying the non-press dewatered fabric;

(e) transferring the throughdried fabric to a surface of a drying cylinder; and

(f) the throughdried fabric is removed from the dryer with a creping blade.

19. A method of making a creped throughdrying fabric comprising the steps of:

(a) depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric;

(b) dewatering the wet web to a consistency of about 10% to about 30%;

(c) supplementally dewatering the wet web to a consistency of from about 30% to about 40% using an air press adapted to cause a pressurized fluid to flow substantially through the web at a gauge pressure of about 5psig or greater due to the integral seal between the air plenum and the collection device;

(d) transferring the wet web to a throughdrying fabric;

(e) throughdrying the non-press dewatered fabric;

(f) transferring the throughdried fabric to a surface of a drying cylinder; and

(g) the throughdried fabric is removed from the dryer with a creping blade.

20. A method of making a creped throughdrying fabric comprising the steps of:

(a) depositing an aqueous suspension of papermaking fibers onto an endless forming fabric to form a wet fabric;

(b) sandwiching the wet web between a pair of web belts;

(c) passing the sandwiched wet web between an air plenum and a collection device, the air plenum and collection device being operatively coupled and adapted to create a pressure differential across the wet web of about 30 inches of mercury or greater and to create a flow of pressurized fluid through the wet web of 10 standard cubic feet per minute per square inch or greater;

(d) dewatering the wet web to a consistency of about 30% or greater with a pressurized fluid stream;

(e) transferring the wet web to a throughdrying fabric;

(f) throughdrying the non-press dewatered fabric;

(g) transferring the throughdried fabric to a surface of a drying cylinder; and

(h) the throughdried fabric is removed from the dryer with a creping blade.

21. The method of claim 18, wherein the non-compressive dewatering device increases the consistency of the web by about 5% to about 20%.

22. The method of claim 19, wherein the web is additionally dewatered to a consistency of about 32 percent or greater.

23. The method of claim 22, wherein the web is additionally dewatered to a consistency of about 34 percent or greater.

24. The method of claim 18, 19 or 20, wherein the pressure differential across the fabric is about 35 to about 60 inches of mercury.

25. The method of claim 18, 19 or 20 wherein the pressurized fluid is pressurized to about 5 to about 30 psi.

26. The method of claim 18, 19 or 20, wherein the collection means comprises a vacuum box drawing a vacuum of greater than 0 to about 25 inches of mercury.

27. The method of claim 19 or 20, wherein the residence time in the air press is about 10 or less.

28. The method of claim 27, wherein the residence time in the air press is about 7.5 or less.

29. The method of claim 19, wherein the fabric is dewatered to a consistency of about 10% to about 30% using one or more vacuum boxes prior to the air press.

30. The method of claim 19 or 20, wherein about 85% or more of the pressurized fluid supplied to the air plenum flows through the wet web.

31. The method of claim 30, wherein about 90% or more of the pressurized fluid supplied to the air plenum flows through the wet web.

32. The method of claim 18, 19 or 20, wherein the temperature of the pressurized fluid is about 300 degrees celsius or less.

33. The method of claim 32, wherein the temperature of the pressurized fluid is about 150 degrees celsius or less.

34. A tissue made by the method of claim 18, 19 or 20.