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Title:
APPARATUS AND METHOD FOR MAKING TEXTURED TISSUE PAPER
Document Type and Number:
WIPO Patent Application WO/2001/000925
Kind Code:
A1
Abstract:
An apparatus for making textured tissue paper includes a forming section for forming a wet paper web, a pressing device in which the wet paper web is pressed between a texturing fabric and a dewatering felt or fabric to texture and dewater the web, a non-through-air pre-dryer that thermally pre-dries the web without passing heated air or other gaseous fluid through the web, and a final dryer for final drying of the web. The pre-dryer in some embodiments comprises an impingement dryer that includes a rotatable roll for supporting the web and a hood system that partially surrounds the roll and includes nozzles for directing heated air against the web. The air deflected from the web is collected by the hood system and exhausted therefrom. The paper web in one embodiment is carried through the pre-dryer on the texturing fabric. In another embodiment, a separate pre-drying fabric transports the web through the pre-dryer. In yet another embodiment, the paper web is formed on the texturing fabric, which then carries the web through the pressing device. The final dryer can comprise a Yankee dryer or a through-air dryer.

Inventors:
KLERELID B E INGVAR
LINDEN ANDERS T
NILSSON LARS B
Application Number:
PCT/SE2000/000925
Publication Date:
January 04, 2001
Filing Date:
May 10, 2000
Export Citation:
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Assignee:
VALMET KARLSTAD AB (SE)
International Classes:
D21F5/04; D21F5/18; D21F9/00; D21F11/00; D21F11/14; (IPC1-7): D21F11/00; D21F11/14
Foreign References:
US4309246A1982-01-05
US5776307A1998-07-07
Attorney, Agent or Firm:
Hill Jr., Donald M. (NC, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:
1. An apparatus for texturing and drying a wet tissue paper web, comprising: a texturing fabric traveling in a continuous loop and adapted to support and transport the wet paper web; a pressing device operable to remove water from the paper web and to press the paper web against the texturing fabric to impart a texture to the paper web; a nonthroughair predryer through which the paper web is transported, the predryer being located downstream of the pressing device and being operable to predry the paper web in a manner such that substantial fluid penetration of the paper web is avoided; and a final dryer arranged after the predryer and operable to perform final drying of the paper web to achieve a desired dryness thereof.
2. The apparatus of claim 1, wherein the nonthroughair predryer comprises an impingement predryer having a blowing device operable to direct a stream of heated gaseous fluid against the textured paper web.
3. The apparatus of claim 2, wherein the blowing device includes an impingement nozzle system.
4. The apparatus of claim 2, wherein the predryer includes a support device having a support surface on which the texturing fabric and paper web are supported, the blowing device being disposed proximate the support device for directing heated gaseous fluid against the paper web.
5. The apparatus of claim 4, wherein the support device comprises a vacuum device arranged on an opposite side of the texturing fabric from the paper web, the vacuum device being operable to create sufficient vacuum to maintain the paper web in contact with the fabric while preventing substantial penetration of heated gaseous fluid from the blowing device through the paper web.
6. The apparatus of claim 5, wherein the vacuum device comprises a rotatable vacuum roll having a foraminous mantle about which the texturing fabric is looped with the texturing fabric disposed against the foraminous mantle and the paper web supported on an outer surface of the texturing fabric.
7. The apparatus of claim 2, wherein the final dryer comprises a Yankee dryer arranged after the predryer adjacent the texturing fabric loop, the Yankee dryer being partially enclosed by a hood system, and the texturing fabric loop having a transfer roll for transferring the paper web from the texturing fabric onto the Yankee dryer.
8. The apparatus of claim 7, wherein the predryer includes a hood system for collecting the heated gaseous fluid after the fluid has impinged on the paper web, and an exhaust duct connected to the hood system for exhausting the collected fluid therefrom, the exhaust duct being connected to the hood system of the Yankee dryer such that at least part of the fluid exhausted from the predryer is recycled in the hood system of the Yankee dryer.
9. The apparatus of claim 1, wherein the pressing device includes a heating element for causing thermal drying of the paper web in the nip.
10. The apparatus of claim 1, further comprising a forming section for forming a wet paper web, the forming section including a forming fabric traveling in a continuous loop, the forming section being operable to form a wet paper web on the forming fabric, the forming fabric loop and texturing fabric loop being consecutively arranged such that the wet paper web is transferred from the forming fabric onto the texturing fabric upstream of the pressing device.
11. The apparatus of claim 1, wherein the predryer includes an infrared dryer.
12. The apparatus of claim 1, wherein the final dryer comprises a throughair dryer, the throughair dryer including a rotatable dryer roll having a porous mantle and the texturing fabric being looped about the dryer roll for carrying the paper web through the throughair dryer, the throughair dryer being operable to pass heated air through the paper web and texturing fabric and through the porous mantle for thermally drying the paper web.
13. The apparatus of claim 1, further comprising a forming section for forming a wet paper web, the forming section being operable to form a wet paper web on the texturing fabric such that the wet paper web is formed, textured, and predried on the same texturing fabric.
14. The apparatus of claim 1, further comprising a predrying fabric traveling in a continuous loop arranged downstream of the pressing device and the texturing fabric loop, the paper web being transferred from the texturing fabric onto the pre drying fabric after the pressing device, the predrying fabric transporting the paper web through the predryer.
15. The apparatus of claim 14, wherein the final dryer comprises a Yankee dryer arranged after the predryer adjacent the predrying fabric loop, the Yankee dryer being adapted to support the paper web wrapped partially thereabout, and the predrying fabric loop having a transfer roll for transferring the paper web from the predrying fabric onto the Yankee dryer.
16. An apparatus for making a textured tissue paper, comprising: a forming section having a forming fabric traveling in a continuous loop and a headbox operable to form a wet paper web on the forming fabric; a texturing fabric traveling in a continuous loop adjacent to the forming fabric loop, the wet paper web being transferred from the forming fabric onto the texturing fabric; a pressing device operable to remove water from the paper web and to press the paper web against the texturing fabric to impart a texture to the paper web, the pressing device including first and second press members defining a nip therebetween, and a press felt passing through the nip and traveling in a continuous loop, the pressing device and texturing fabric loop being arranged such that the paper web passes through the nip while disposed between the press felt and the texturing fabric; an impingement predryer through which the paper web is transported, the predryer being located downstream of the pressing device and being operable to blow heated gaseous fluid against the paper web such that the fluid is substantially reflected therefrom; and a final dryer arranged after the predryer and operable to perform final drying of the paper web to achieve a desired dryness thereof.
17. The apparatus of claim 16, wherein the pressing device is operable to dewater the paper web to achieve a dryness of about 25 to about 40 percent.
18. The apparatus of claim 17, wherein the predryer is operable to dry the paper web to achieve a dryness of about 30 to about 60 percent.
19. A method of making a textured tissue paper, comprising: forming a wet paper web; pressing the wet paper web while supported on a texturing fabric so as to impart a texture to the paper web and dewater the paper web; predrying the paper web after the texturing and dewatering thereof, the predrying being carried out in a nonthroughair drying manner; and performing final drying of the paper web in a thermal drying device.
20. The method of claim 19, wherein the predrying is carried out while the paper web is on the texturing fabric.
21. The method of claim 19, wherein the final drying of the paper web comprises drying the paper web on a Yankee dryer.
22. The method of claim 19, wherein the predrying comprises impinging the paper web with a heated gaseous fluid.
23. The method of claim 22, wherein the final drying comprises drying the paper web on a Yankee dryer having a hood system, and further comprising collecting the heated gaseous fluid after the fluid has impinged on the paper web and recycling at least part of the collected fluid in the hood system of the Yankee dryer.
24. The method of claim 19, wherein the predrying includes infrared drying of the paper web.
25. The method of claim 19, wherein the final drying of the paper web comprises drying the paper web in a throughair dryer.
26. The method of claim 19, wherein the web is dewatered to a dryness of about 25 to about 40 percent and is predried to a dryness of about 30 to about 60 percent.
Description:
APPARATUS AND METHOD FOR MAKING TEXTURED TISSUE PAPER FIELD OF THE INVENTION The present invention relates to paper making and, more particularly, to apparatus and methods for making textured tissue paper.

BACKGROUND OF THE INVENTION Consumers generally prefer tissue products such as bath and facial tissue to be soft and absorbent. Softness and absorbency are affected by a number of factors, but two important factors contributing toward these characteristics are the degree of bulk or density of the paper, and the surface texture of the paper. Higher bulk generally contributes toward improved softness and absorbency, all other factors being equal.

The perceived softness of the tissue paper is also affected by the surface texture, with smoother surface textures generally being perceived as harsher to the touch, while knuckle-patterned surface textures or the like are generally perceived as having a softer feel.

The degree of bulk of a tissue web is inversely related to the degree of compaction of the web during its manufacture, and particularly to the degree of compaction of the web when it is relatively wet. Generally, the less the web is pressed while wet, the greater the bulk of the resulting tissue paper. Accordingly, if bulk were the only factor of importance in the manufacture of tissue, drying of the web would ideally be carried out entirely through non-compacting techniques.

However, high speed, energy efficiency, and machine size are also important considerations in the manufacture of all types of paper including tissue. All of these are significantly affected by the performance and size of the drying section of the machine, since the bulk of the energy used in paper making is expended in the drying section, and the drying section tends to take up a significant percentage of the total space occupied by a paper making machine. High machine speeds require that water be removed from the paper as quickly as possible. Press-type dewatering devices tend to be relatively small and are capable of removing water quickly when the web is relatively wet, but are generally not capable of achieving a dry solids content much above about 40 to about 45 percent. Vacuum boxes and other non-evaporative convective-type dewatering devices are relatively small and can remove water quickly

when the web is relatively wet, but become less effective as the dry solids content increases.

In terms of energy efficiency, press-type dewatering devices and non- evaporative dewatering devices such as vacuum boxes and air jets consume relatively small amounts of energy compared to evaporative or thermal drying devices such as through-air dryers, and also are typically smaller than thermal dryers, particularly through-air dryers. However, some amount of thermal drying is typically required for final drying of the web prior to winding the web onto a roll. Thus, in many paper making processes, an attempt to compromise between drying rate and energy efficiency is frequently made by using press-type dewatering devices and other non- evaporative dewatering devices for initial dewatering of the web, followed by thermal drying to remove the remaining water from the web.

In tissue making, however, the quest for high bulk and softness has generally led designers to avoid press-type dewatering in favor of non-compacting drying devices, despite the beneficial effects that press-type dewatering has on machine size and efficiency. For example, commonly owned U. S. Patent No. 5,230,776 describes a tissue making apparatus for making soft, high-bulk tissue, in which the wet paper web coming from the forming section of the machine is dewatered by suction boxes to a maximum dry solids content of about 25 percent, and then a combination of suction boxes and a steam blowing tube are used for suctioning and blowing air and steam through the web to further dewater the web. An optional infrared heater is located after the suction boxes, and final drying and creping of the web are performed in a Yankee dryer.

Although the tissue paper produced in accordance with the'776 patent is of high quality and has good softness and high bulk, the machine speeds achievable with the process tend to be low because the drying rate is low. Accordingly, it would be desirable to provide a tissue making apparatus and method capable of making high- quality tissue paper of good softness and high bulk while operating at higher machine speeds than those achievable with the apparatus and methods of the'776 patent.

As noted above, pressing is a relatively energy-efficient process for non- thermal or mechanical dewatering of the relatively wet web, and can reduce the moisture load imposed on the later evaporative drying devices, but pressing has a

deleterious effect on bulk. Nevertheless, pressing has been proposed and used for drying tissue webs, particularly in the production of textured tissue webs where dewatering and imprinting of the web can be carried out simultaneously in the same press nip. For instance, U. S. Patent Nos. 5,776,307 and 4,309,246 each describes tissue making apparatus and methods in which a tissue paper web is carried through a press nip between an imprinting fabric and a dewatering felt for imprinting and dewatering the web. In the'307 patent, evaporative drying is performed after the pressing step by means of a through-air dryer, and final drying and creping are performed in a Yankee dryer. The through-air dryer requires a large amount of space and consumes a large amount of energy. The large energy consumption of the through-air dryer is in part a result of the relatively high resistance to air flow through the paper web when the paper web has a relatively low dryness, as would typically be the case for a web leaving a press-type dewatering device.

In the'246 patent, vacuum boxes acting in conjunction with air or steam jets suction and blow air and/or steam through the web and imprinting fabric to remove water from the web prior to or after the pressing and imprinting step, and final drying and creping are performed after the pressing and imprinting step in a Yankee dryer.

The web entering the Yankee dryer is said to have a dryness of about 20 to 38 percent, and hence a large thermal load is imposed on the Yankee dryer in order to finally dry the paper web to the desired dryness of 92 to 98 percent. Additionally, one of the problems inherent in machines that form textured tissue and dry the tissue on a heated cylinder, such as the machine described in the'246 patent, is that the knuckled pattern of the tissue surface results in reduced web surface area in contact with the cylinder, thereby reducing the heat transfer between the web and the heated cylinder.

Accordingly, drying capacity of the Yankee dryer may be reduced, and thus, all other factors being equal, a larger-capacity Yankee dryer may be required in order to achieve the requisite dryness leaving the Yankee dryer.

A further drawback associated with some machines, particularly those employing a Yankee dryer for final drying of a paper web, is that insufficient pre- drying of the web is performed before the web is transferred from the texturing fabric to pass through subsequent drying devices. As a result, the textured pattern of the web can be degraded in subsequent drying operations because the relatively high

moisture content of the web allows rearrangement of the fibrous structure of the web.

In particular, the passage of the web through the nip between a transfer roll and the heated cylinder of a Yankee dryer can cause compaction of the web and degradation of its surface texture pattern, and the degradation in texture tends to be worsened by higher moisture content of the web entering the nip.

SUMMARY OF THE INVENTION Accordingly, it would be desirable to provide a papermaking machine capable of achieving a higher dryness of the paper web entering the final drying device, so that a reduced thermal load and increased capacity of the final drying device can be achieved. Furthermore, it would be desirable to provide a machine capable of forming a textured paper web and drying the paper web to a relatively high dryness while still supported on a texturing fabric. It would also be desirable to provide a machine that avoids or reduces the degree of compaction of the textured paper web during pre-drying and drying operations.

The above needs are met and other advantages are achieved by apparatus and methods in accordance with the present invention for making textured tissue paper of high bulk and softness, in which drying of a tissue paper web coming from the forming section is accomplished by a unique combination of pressing the paper web against a texturing fabric in a pressing device to dewater and texture the paper web, followed by pre-drying the textured paper web in a non-through-air pre-dryer operable to pre-dry the paper web without causing substantial penetration of heated gaseous fluid through the paper web. Accordingly, a fan power requirement of the pre-dryer can be reduced relative to a through-air pre-drying process, since air or other heated gaseous fluid is not passed through the web.

Various types of non-through-air pre-dryer devices can be used in connection with the present invention, including rotary and non-rotary impingement pre-dryers, infrared pre-dryers, and other devices capable of thermally drying the paper web without causing substantial penetration of heated gaseous fluid through the web. In accordance with one preferred embodiment of the invention, the pre-dryer comprises an impingement pre-dryer operable to impinge a surface of the paper web with a heated gaseous fluid while not penetrating through the web. The impingement pre-

dryer advantageously includes a support device having a support surface on which the paper web is supported, and a blowing device disposed proximate the support device and operable to direct a stream of heated gaseous fluid against the paper web on the support device.

In accordance with one preferred embodiment of the invention, the impingement pre-dryer is a rotary type device having a rotatable vacuum roll with a foraminous mantle about which the texturing fabric is looped, the texturing fabric transporting the paper web through the pre-dryer with the texturing fabric disposed against the foraminous mantle and the paper web supported on an outer surface of the texturing fabric. The vacuum roll advantageously exerts a vacuum having a magnitude less than a break-through vacuum above which the heated gaseous fluid is suctioned through the paper web into the interior of the vacuum roll, such that the heated gaseous fluid impinges on the paper web without penetrating all the way through it. The vacuum exerted by the vacuum roll is only for the purpose of ensuring a safe web run so that the web remains on the roll without dropping off at any point. Thus, if in a particular application no vacuum is needed to ensure a safe web run, then a solid roll can be used instead of a vacuum roll.

The blowing device advantageously comprises a nozzle system that directs heated air or other gaseous fluid against the paper web. The impinging fluid is reflected by the paper web. Preferably, the impingement pre-dryer includes an enclosure or hood system that partially surrounds the support device and collects the fluid after it has impinged on the paper web. The impingement dryer preferably is an integrated hood-type impingement dryer having burners and blowers built into the hoods.

As an alternative to a rotary impingement pre-dryer, the pre-dryer can comprise a non-rotary impingement drying device as described in commonly owned U. S. Patent No. 5,845,415, the entire disclosure of which is incorporated herein by reference. Such impingement drying device includes an enclosure containing one or more blow boxes disposed on one side of a fabric and an impingement dryer disposed on an opposite side of the fabric adjacent the paper web. The blow box or boxes support the paper web and fabric as they travel generally linearly through of the device.

A final dryer follows the pre-dryer for final drying of the paper web.

Preferably, the final dryer comprises a Yankee dryer having a rotatable heated cylinder adapted to support the paper web wrapped partially thereabout. The texturing fabric loop has a transfer roll for transferring the paper web from the texturing fabric onto the heated cylinder. The transfer roll is operable to exert a relatively light pressure against the heated cylinder sufficient to transfer the paper web onto the heated cylinder while substantially preventing degradation in the texturing of the paper web. By pre-drying the paper web to a higher dryness, the pre-dryer compensates for reduced heat transfer between the web and cylinder that may be caused by the reduction in contact surface area between the cylinder and the textured surface of the web, such that the drying capacity of the Yankee dryer can be increased. Additionally, degradation in the texturing of the web caused by pressure exerted in the nip tends to be minimal because a light pressing is used and the web has a higher dryness than would otherwise be the case if no pre-drying in accordance with the invention were performed.

In accordance with an alternative embodiment of the invention, the final dryer comprises a through-air dryer that includes a rotatable dryer roll having a porous mantle. The texturing fabric is looped about the dryer roll for carrying the paper web through the through-air dryer. The through-air dryer passes heated air through the paper web and texturing fabric and through the porous mantle for thermally drying the paper web. The pre-dryer facilitates a reduction in the energy usage in the through-air dryer, relative to a machine not employing pre-drying, by increasing the dryness of the web entering the through-air dryer such that the resistance to air passing through the web and the moisture load on the through-air dryer are reduced. Furthermore, drying the web while supported on the texturing fabric tends to preserve the texturing of the web.

The texturing fabric and pressing device can be arranged in various ways with respect to the forming section of the machine and the pre-dryer. In one preferred embodiment of the invention, the forming section forms a wet paper web on a forming fabric, and the paper web is transferred from the forming fabric onto the texturing fabric upstream of the pressing device. The texturing fabric carries the paper web through the pressing device and through the impingement pre-dryer. In

accordance with an alternative embodiment of the invention, the forming section forms the paper web on the texturing fabric, which then carries the web through the pressing device and pre-dryer.

In yet another embodiment of the invention, the paper web is formed on a forming fabric and transferred onto a texturing fabric, and the texturing fabric carries the web through the pressing device. The web is then transferred from the texturing fabric onto a pre-drying fabric, which transports the web through the pre-dryer. The pre-drying fabric can transfer the web onto a heated cylinder by means of a transfer roll, or the pre-drying fabric can transport the web through a through-air dryer for final drying of the web. An advantage of using a separate pre-drying fabric is that the texturing fabric and pre-drying fabric can each be optimized in terms of mechanical strength and thermal resistance.

The pressing device can be any of a number of types, including a roll press or an extended nip shoe press. If additional drying capacity is desired, the pressing device can include a heating element for causing thermal drying of the paper web in the nip. The pressing device advantageously provides an outgoing web dryness of about 25 to about 40 percent.

The tissue making apparatus and methods of the invention are capable of making high-bulk tissue paper of similar quality to paper produced on tissue machines that employ through-air dryers for drying the paper web. Use of a single texturing fabric to transport the web through the pressing device and pre-dryer and up to or through the final dryer helps preserve the textured surface of the paper. The pre-dryer facilitates improved production capacity for a given final dryer by increasing the dryness of the web entering the final dryer, and also compensates for the reduced heat transfer in a Yankee dryer that may be caused by the reduction in contact area of the textured web surface.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages of the invention will become more apparent from the following description of certain preferred embodiments thereof, when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic side elevation of a paper making apparatus in accordance with a first preferred embodiment of the invention; FIG. 2 is a schematic side elevation of a paper making apparatus in accordance with a second preferred embodiment of the invention; FIG. 3 is a schematic side elevation of a paper making apparatus in accordance with a third preferred embodiment of the invention; FIG. 4 is a schematic side elevation of a paper making apparatus in accordance with a fourth preferred embodiment of the invention; FIG. 5 is a schematic side elevation of a paper making apparatus in accordance with a fifth preferred embodiment of the invention; FIG. 6 is a schematic side elevation of a paper making apparatus in accordance with a sixth preferred embodiment of the invention; FIG. 7 is a schematic side elevation of a paper making apparatus in accordance with a seventh preferred embodiment of the invention; and FIG. 8 is a schematic side elevation of a paper making apparatus in accordance with an eighth preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Like numbers refer to like elements throughout.

With respect to FIG. 1, a paper making apparatus in accordance with a first preferred embodiment of the invention is broadly designated with the reference numeral 10. The apparatus 10 includes a forming section 12 for forming a wet paper web, a press section 14 for partially dewatering and texturing the web, a pre-drying section 16 for pre-drying the web, and a final drying section 18 for final drying of the web.

The forming section 12 can be of various types, including single-wire and

twin-wire types. Preferably, the forming section 12 comprises a C-former or crescent former having a forming roll 20 and an inner forming fabric 22 and an outer forming fabric 24 that are wrapped partially about the forming roll 20. The inner forming fabric 22 forms a continuous loop about a plurality of guide rolls 26 (only one shown) and is driven by a suitable drive roll (roll 20 and/or roll 26, for example), and the forming roll 20 is disposed inside the loop of the inner forming fabric. The outer forming fabric 24 forms a continuous loop about a plurality of guide rolls 28 and a breast roll 30, and the forming roll 20 is outside the loop of the outer forming fabric 24. A headbox 32 is operable to deposit a slurry of paper-forming stock between the inner and outer forming fabrics 22 and 24 so as to form a wet paper web therebetween. In the embodiment shown in FIG. 1, the outer forming fabric 24 diverges from the paper web and inner forming fabric 22 at a point generally where the paper web leaves the forming roll 20, and the inner forming fabric 22 carries the paper web downstream to a transfer point where the paper web is transferred from the inner forming fabric 22 onto a texturing fabric 34.

The texturing fabric 34 forms a continuous loop, guided by a plurality of guide rolls 36 (one shown) and also by various components of the pre-dryer section 16 as further described below. The texturing fabric 34 transports the paper web through the press section 14 and pre-drying section 16 and up to the final drying section 18. The texturing fabric 34 can be of various constructions and surface configurations. The loop of the texturing fabric 34 is adjacent to the loop of the forming fabric 22, the two fabrics becoming tangent at a transfer point 38 where the forming fabric is turned by a guide roll 26 so as to diverge from the direction of travel of the texturing fabric 34.

Accordingly, the paper web is transferred from the inner forming fabric 22 onto the texturing fabric 34 at the transfer point. Various types of devices can be used to facilitate transfer of the web onto the texturing fabric 34, including transfer suction boxes, air or steam jets, and other devices known in the art.

The press section 14 includes a pressing device 40 having a pair of press elements 42 and 44 that form a nip 46 between them. The illustrated pressing device 40 is a shoe press (press element 42 being a counter roll and press element 44 being a press shoe), but other types of pressing devices capable of exerting controlled pressure on the paper web can be used instead. For instance, a roll press can

alternatively be used in place of the shoe press. The texturing fabric 34 carrying the paper web is arranged to pass through the nip 46. A dewatering felt 48 is also arranged to pass through the nip 46 such that the paper web is disposed between the texturing fabric 34 and the dewatering felt 48. The dewatering felt 48 forms a continuous loop about a plurality of rolls 50. The pressing device 40 is operable to press the paper web between the texturing fabric 34 and the dewatering felt 48 so that water is squeezed from the paper web into the felt 48. The pressing device 40 may optionally include a heating element 45 operable for causing thermal drying of the paper web. Advantageously, the pressing device 40 dewaters the web to a dryness of about 25 to about 40 percent, and more typically about 30 to 35 percent. At the same time, the paper web is forced to conform to the textured surface of the texturing fabric 34. Thus, the paper web is simultaneously dewatered and textured in the pressing device 40. Where the pressing device 40 is a roll press, a typical linear nip load is about 70 to about 150 kN/m; where the pressing device 40 is a shoe press, a typical linear nip load is about 500 to about 1200 kN/m.

After leaving the pressing device 40, the texturing fabric 34 transports the paper web through the pre-drying section 16 such that the paper web is pre-dried while supported on the texturing fabric, thus helping to preserve the texturing of the paper web. Various types of pre-drying devices can be used, including impingement pre-dryers, infrared pre-dryers, microwave pre-dryers, or combinations thereof. In the embodiment depicted in FIG. 1, the pre-drying section 16 comprises an impingement pre-dryer 52. The pre-dryer 52 includes a non-heated vacuum roll 54 having a cylindrical foraminous mantle 56 through which suction is applied by a suitable vacuum system (not shown) to retain the paper web wrapped partially about the vacuum roll. The vacuum roll 54 is partially enclosed by a housing or hood system formed as a pair of hood halves 58 that engage opposite sides of the vacuum roll.

Each hood half 58 encloses a burner 60 operable to heat air, and a blower 62 that forces the heated air through a blowing device or nozzle system 64 so as to impinge on the surface of the paper web wrapped about the vacuum roll 54. Although air is a preferred medium, other gaseous fluids, such as steam, can also be used. The vacuum roll 54 operates at a vacuum that is below the"break-through"vacuum above which the impingement air would be suctioned through the web and texturing fabric 34 into

the vacuum roll 54. Accordingly, the air impinging on the paper web does not penetrate through the web and texturing fabric 34 and pass into the interior of the vacuum roll 54, but rather is deflected by the web so as to remain within the respective hood 58. After the air impinges on the paper web, it is collected by each of the hood halves 58 and exhausted from each hood half 58 by an exhaust blower (not shown) and through an exhaust duct 66 and is at least partially recycled in the final drying section 18, as further described below. The paper web leaving the pre-dryer 52 advantageously has a dryness of about 30 to about 60 percent.

The texturing fabric 34 carrying the paper web is guided to pass around the vacuum roll 54 by turning rolls 68. The turning rolls 68 can be steam-heated drying cylinders, if desired, to achieve additional drying capacity in the pre-dryer section 16.

Alternatively, the turning rolls 68 can be non-heated rolls. Advantageously, the rolls 68 are plated with polished chrome so as to minimize sticking of paper fibers to the rolls.

Following pre-drying in the impingement pre-dryer 52, the paper web is transported by the texturing fabric 34 to the final drying section 18, which in the embodiment of FIG. 1 comprises a Yankee dryer system 70. The Yankee dryer system 70 includes a rotatable Yankee dryer 72. The texturing fabric loop includes a transfer roll 74 that forms a nip with the Yankee dryer 72, and the texturing fabric 34 and paper web pass through the nip. The transfer roll 74 presses against the Yankee dryer 72 with just enough pressure to cause the paper web to be transferred from the texturing fabric 34 onto the Yankee dryer, while not substantially damaging the texturing of the paper web. Advantageously, the linear nip load is about 30 to about 90 kN/m. The Yankee dryer system 70 also includes a pair of hood halves 76 that surround a portion of the circumference of the Yankee dryer 72 and are supplied with heated air by a hot air system. The hood halves 76 can be moved apart for access to the Yankee dryer 72 and interior of the housing. The hot air system includes a burner 78 and a blower 80 for each hood half 76. Advantageously, a portion of the air supplied to each hood half 76 comes from the exhaust duct 66 leading from the impingement pre-dryer 52 so as to"pre-heat"the intake air into the hot air system of the Yankee dryer system, which operates at a higher temperature than the pre-dryer.

The paper web is dried on the Yankee dryer 72 and is creped by a doctor blade 82 to

form a creped paper web W. The paper web is then subjected to final finishing operations such as calendering, if desired, and is wound onto a roll in a reel-up (not shown).

Because the paper web is textured, the surface area of the web in contact with the Yankee dryer 72 is reduced relative to a non-textured web. As a result, the heat transfer in the Yankee dryer system 70 may be reduced relative to an identical Yankee dryer drying a non-textured web. However, in accordance with the present invention, the pre-dryer 52 dries the paper web to a dryness entering the Yankee dryer system 70 that exceeds the level of dryness achieved in conventional tissue machines at the ingoing side of the Yankee dryer. In this way, the pre-dryer 52 compensates for the reduced heat transfer in the Yankee dryer system 70.

The invention is also applicable to tissue making machines that use through- air drying for the final drying of the paper. FIG. 2 depicts a paper making apparatus of this type. The apparatus 100 includes a forming section 12, press section 14, and pre-drying section 16 substantially identical to those of the apparatus 10 in FIG. 1.

After the pre-dryer 52, however, the texturing fabric 34 transports the paper web through a through-air dryer (TAD) 102 for final drying of the paper web. The through-air dryer 102 includes a rotatable roll 104 having a porous mantle 106 about which the texturing fabric 34 and paper web are partially wrapped. The paper web is disposed on the outer surface of the texturing fabric 34 on the roll 104, so that the texturing fabric 34 is against the porous mantle 106. The roll 104 is partially enclosed by a hood 108 to which heated air is supplied by a supply duct system (not shown).

The interior of the roll 104 is subjected to a vacuum by a vacuum system (not shown) such that the heated air supplied into the hood 108 is suctioned through the paper web and the texturing fabric 34 and through the porous mantle 106 into the interior of the roll 104, and is then exhausted from the interior of the roll and at least partially recycled. Thus, the heated air flowing through the paper web dries the web. It will be understood that the hood 108 can be formed as a pair of hood halves that are movable away from each other and from the roll 104, if desired, for access to the interior of the hood halves and roll for maintenance purposes.

FIG. 3 depicts a variation on the apparatus 100 of FIG. 2. The apparatus 100' depicted in FIG. 3 includes a press section 14 having a pressing device 40'arranged

relative to the forming section 12 such that the wet paper web is transferred from the inner forming fabric 22 onto a lower surface of a dewatering felt 48 and then carried through the nip of the pressing device. The paper web is transferred onto the upper surface of the texturing fabric 34 in the nip, and the texturing fabric 34 then carries the web through the pre-drying section 16. The apparatus 100'includes an"inverted" impingement pre-dryer 52'in which the hood halves 58 are disposed generally above the turning rolls 68 rather than below them. Accordingly, the paper web is carried from the pressing device 40'to the pre-dryer 52'and from the pre-dryer 52'to the through-air dryer 102'on an upper surface of the texturing fabric 34. The through-air dryer 102'is also of the"inverted"type having the hood 108 located above the roll 104 rather than below the roll. The embodiment shown in FIG. 3 is thus advantageous relative to the embodiments of FIGS. 1 and 2 insofar as inverted web runs are avoided. If desired, the pre-drying section 16 can include an infrared dryer 110.

It should be noted that although the description thus far has assumed the through-air dryers are of the in-flow type in which air flows from the hood inwardly through the paper web and into the interior of the roll from which it is then exhausted, the invention is equally applicable to out-flow type through-air dryers in which the drying air flows from the interior of the roll outwardly through the paper web into the hood from which it is then exhausted. It will also be appreciated that although FIGS.

2 and 3 show embodiments having a single TAD, in some circumstances it may be advantageous to use more than one TAD.

In accordance with another preferred embodiment of the invention, the paper can be formed on the same texturing fabric that transports the paper through the press and pre-drying sections. Thus, FIG. 4 shows an apparatus 200 in which the inner forming fabric of the previously described embodiments has been eliminated and the texturing fabric 34 has been routed around the forming roll 20 to take the place of the inner forming fabric. The paper web is formed on the texturing fabric 34, which then transports the paper web through the press section 14, pre-drying section 16, and final drying section 18 as in the embodiment of FIG. 1.

A further alternative embodiment of the invention is depicted in FIG. 5. The apparatus 300 of FIG. 5 is similar to the apparatus 10 of FIG. 1, but employs a

separate pre-drying fabric 302 for transporting the paper web through the pre-drying section 16 and up to the final drying section 18. The texturing fabric 34 carries the paper web only through the press section 14, and the paper web is then transferred onto the pre-drying fabric 302 with the aid of a suction roll 304 or the like. The advantage of using the separate pre-drying fabric 302 is that the texturing fabric 34 and pre-drying fabric 302 can each be optimized for mechanical strength and thermal resistance as required to perform their separate functions.

Other variations on the inventive concept are possible. For instance, the forming section 12 shown in the embodiment of FIG. 3 has a crescent former in which a headbox 32 is arranged in a lower position relative to the forming roll 20 such that the web is carried on an upper surface of the inner forming fabric 22 to a transfer point at which the web is transferred onto a lower surface of the dewatering felt 48.

Alternatively, however, it is possible to arrange the crescent former as shown in FIG.

6, such that the headbox 32 is in an upper position relative to the forming roll 20 and the web is carried on a lower surface of the inner forming fabric 22 to a transfer point where the web is transferred onto the upper surface of the texturing fabric 34. The inner forming fabric 22 can be arranged to pass through the nip of the pressing device 40', in which case the transfer point is defined at the nip. The inner forming fabric 22 takes the place of the dewatering felt 48 used in the embodiment of FIG. 3.

However, the transfer point can alternatively be arranged upstream of the pressing device 40'by use of a separate dewatering felt 48 as shown in FIG. 7. The inner forming fabric 22 carries the web on its lower surface up to the texturing fabric 34, where the web is transferred onto the upper surface of the texturing fabric 34. The texturing fabric 34 then carries the web through the pressing device 40'where the web is pressed between the texturing fabric 34 and the dewatering felt 48. In other respects, the embodiment shown in FIG. 7 is similar to that of FIG. 3.

Finally, FIG. 8 shows yet another embodiment of the invention, in which the pre-drying section 16 comprises a pair of non-rotary impingement-type dryers 152 of the type substantially described in U. S. Patent No. 5,845,415, incorporated herein by reference. Of course, it will be understood that a single dryer 152 could be used, or more than two such dryers 152 could be used. The non-rotary impingement-type dryer 152 includes a flat impingement dryer 154 arranged adjacent one side of the

paper web for blowing air onto the web. The fabric 34 carrying the paper web is supported by a plurality of blow boxes 156 and supporting rolls 158 arranged on an opposite side of the fabric and web from the impingement dryer 154 so as to define a generally planar supporting surface for the fabric and web. A blow box 160 is arranged after the impingement dryer 152 for stabilizing the web run leading into the final dryer 18. The pre-dryer 16 may further include an optional infrared dryer such as the infrared dryer 110 shown in FIG. 3 for further pre-drying of the paper web prior to the web entering the final drying section 18.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.