KR100481105B1 - Method and apparatus for making soft tissue - Google Patents

Abstract

The uncreped tissue sheet with improved softness was further dewatered using a non-compressed dewatering technique 30 prior to the differential speed transfer 37 to a consistency of greater than about 30%, followed by through-drying. 44). Air presses 30 that are particularly well suited to provide additional uncompressed dewatering include side 80 and / or end seals 78 to minimize the escape of pressurized fluid.

Description

METHOD AND APPARATUS FOR MAKING SOFT TISSUE}

Background of the Invention

Tissue products, such as bath and cleansing tissue, have a number of properties that must be considered in order to produce a final product having desirable properties that are appropriate and desirable for the purpose the product is directed to. Improving the softness of the product has been one of the main objectives for a long time, which has been a particularly important factor for the success of high quality products. In general, the main components of softness are stiffness and bulk (density), and generally low stiffness and large volume (low density) improve sensory softness.

Improved softness is the desire of all kinds of tissue products, but has been particularly challenging to achieve an improvement in the softness of uncreped through dry sheets. Throughdrying provides a relatively incompressible method of removing moisture from a web by passing hot air through the web until the web is dry. More specifically, the wet-laid web is transferred from the forming fabric to the coarse high permeability through-dry fabric and held in the through-dry fabric until it is dried. The final dried web is softer and bulkier than the uncreped sheet dried by the prior art because few bonds are formed and the web is less compact. As such, there is a benefit of removing the Yankee dryer to produce an uncreped through-drying product. However, uncreped through-dried sheets are typically significantly tighter and rougher than those creped. This is due in part to the inherent high stiffness and strength of the uncreped sheet, but on the one hand also due to the roughness of the through-drying fabric where the webs are mated and dried.

Accordingly, what is lacking and needed in the art is a method and apparatus for producing softened tissue products, in particular uncreped through-dried tissue products with improved softness.

Summary of the Invention

Now, prior to further delivery of the web to the through-drying fabric for final drying, the web is dewatered to a consistency of greater than about 30% prior to transferring the wet web from the molding fabric to one or more low speed intermediate transfer fabrics. It has been found that improved creep dry webs that are not creped can be made. In particular, increasing the consistency of uncreped through-drying webs before differential speed transfer surprisingly (1) tension in the machine and transverse directions, which contributes to an improvement in the runability of the web. It was found that the improvement of the properties and (2) the modulus was decreased when the tensile strength was adjusted to the normal value, i.e., the softness was increased. This finding enables the production of tissue products with lower modulus at a given tensile strength, even when compared to tissue products made by receiving differential speed transfer at low consistency.

One particularly preferred means by which the web can be dewatered to consistency above 30% includes an air press located upstream of the differential speed transfer. Pressurized fluid jets in combination with vacuum devices have been previously discussed in the patent literature, but such devices have not been widely used in the tissue manufacturing industry. Primarily, the cause appears to be due to the fact that prior to the differential speed transfer, dehydration of the web to greater than about 30% consistency resulted in an improvement in product properties as identified in the present invention. . In addition, it is believed that the impediment of the use of the device is due to difficulties in practical use, including disassembly of the tissue web, pressurized fluid leakage, sealing and / or fabric wear, and the like. The air press used in the present method overcomes the above difficulties and provides one practical device for achieving certain consistency before the differential speed transmitter.

Thus, one embodiment of the present invention is directed to a method of making a soft tissue sheet. The method includes depositing an aqueous suspension of papermaking fibers on a cyclic molded fabric to form a wet web, dewatering the wet web to a consistency of about 20 to about 30%, and consistency of the web by more than about 30%. Further dewatering the wet web using uncompressed dewatering means, transferring the additional dewatered web to a transfer fabric moving at a rate of about 10 to about 80% slower than the molding fabric, and passing the web to the through-drying fabric. Delivering and drying the web to final dryness.

The air press preferably provides a pressure differential of about 889 mm to about 1524 mm (35 to 65 in.) Hg across the wet web. It is an air plenum of an air press that maintains fluid pressure on one side of a wet web of about 351.55 to about 4218.6 g / cm 2 (5 to 60 psi), particularly about 351.55 to about 2109.3 g / cm 2 (5 to 30 psi). plenum). The pressurized fluid may be air at ambient temperature, heated air, steam, or the like. In total, the air press may be operable to increase the consistency of the wet web by at least about 3%, preferably at least about 5%. An optional steam shower may be employed before the air press to increase the consistency after the air press.

Another embodiment of the invention is directed to a wet web dewatering air press. In one embodiment, the air press comprises an air plenum with a plenum lid having a bottom face and a vacuum box with a vacuum box lid having a top face positioned closely to the bottom face of the plenum lid. The air press also includes means for supplying pressurized fluid to the air plenum and means for evacuating the vacuum box. The side seal member of the air press is adapted to contact the air plenum and the vacuum box to minimize the escape of pressurized fluid. The side sealing member is attached to one of the air plenum and the vacuum box and is located closely to the side sealing contact surface formed by the other of the air plenum and the vacuum box. The side sealing member is adapted to be bent in sealing contact with the side sealing contact surface upon exposure to pressurized fluid to improve the sealing efficiency.

Optionally, the air press may include a position control mechanism that functions to hold the air plenum closely to the vacuum box. In particular, the position control mechanism preferably comprises a rotatably mounted lever attached to the air plenum and a counterbalance cylinder attached to the lever. The position control mechanism is adapted to rotate the lever to react to pressure changes in the air plenum. In this way, the air plenum is in close contact or contact with the fabric passing between the air plenum and the vacuum box without clamping the fabric between the air plenum and the vacuum box.

In another embodiment, the air press comprises an air plenum with a plenum cover having a bottom surface and means for supplying pressurized fluid to the air plenum. The air press also includes a vacuum box with a vacuum box cover having a top surface closely located at the bottom surface of the plenum cover, and means for vacuuming the vacuum box. An arm pivotally mounted to the air plenum includes first and second portions, the first portion of the arm being at least partially disposed inside the air plenum. The sealing bar is formed from or is mounted to the first portion of the arm. The air press also includes means for pivoting the arm according to the fluid pressure in the air plenum.

In this embodiment, the sealing bar portion of the pivotable arm serves as an end seal to prevent the escape of pressurized fluid from between the air plenum and the vacuum box. The sealing bar may coincide with the fabric irregularity or misalignment of the support structure. End seals, also referred to as transverse or CD seals, improve the containment of pressurized fluid, resulting in efficient operation of the air press. Loading the end seals is controlled to keep the sealing bar in contact with the underlying moving fabric without causing excessive wear of the fabric.

Improved results can be obtained without sacrificing efficiency. The method and apparatus of the present invention can function at commercially competitive web speeds. For example, the molding fabric may be controlled to move at a speed of at least about 609.6 m / min (2000 ft · min (fpm)), more preferably at least about 1219.2 m / min (4000 fpm).

The intermediate transfer fabric or fabrics are moving at a slower rate than the molding fabric during transfer to impart stretch in the sheet. As the speed difference between the molding fabric and the slow transfer fabric increases (also called "negative draw" or "rush transfer"), the stretch imparted to the web during transfer increases. The transfer fabric may be relatively smooth and dense compared to the coarse weave of a typical through dry fabric. The delivery fabric is preferably fine so that it can be operated from a practical point of view. Gripping of the web is accomplished by the presence of knuckles on the transfer fabric surface. It may also be advantageous if one or more wet web transfers are made by using "fixed gaps" or "kisses" where the fabrics converge and diverge simultaneously, with or without the presence of a transfer fabric, which will be described below. It will be described in detail. Such a transfer is observed to avoid significant compression of the web while in wet bond formation, as well as to smooth the surface of the web and the final dry sheet when used in combination with a differential speed transfer and / or a smooth transfer fabric.

The speed difference between the molding fabric and the transfer fabric can be about 10 to about 80% or more, preferably about 10 to 35%, most preferably about 15 to 25%, where the transfer fabric is a slow fabric. The optimum speed differential will depend on a wide range of factors, including the type of product to be manufactured. As mentioned above, the increase in stretch imparted to the web is proportional to the speed difference. For an uncreped through dry triple wiper having a basis weight of about 20 g / m 2 / per square meter per ply, for example between about 20 to about 25% between a molding fabric and a single delivery fabric The difference in speed in the manufacture of each ply of produces a stretch in the final product of about 15 to about 20%.

The stretch can be imparted to the web using a single differential speed transfer or two or more differential speed transfers of the wet web prior to drying. Thus, the stretch imparted to the web may be split between one, two, three or more differential speed transfers.

The delivery is preferably carried out so that the final "sandwich" (composed of molded fabric / web / delivery fabric) is present for as short a duration as possible. In particular, they are only present at the shear edges of the vacuum shoe or the transfer shoe slot used to carry out the delivery. In practice, the forming fabric and the transfer fabric converge and diverge at the shear edges of the vacuum slots. This intention is to minimize the distance that the web contacts both fabrics simultaneously. It has been found that simultaneous convergence / diffusion is the key to removing macrofolds to improve the softness of the final tissue or other product.

In fact, simultaneous convergence and divergence of the two fabrics is achieved when sufficient convergence angle is maintained between the two fabrics as they approach the front edge of the vacuum slot, and sufficient divergence angle is maintained between the two fabrics downstream of the vacuum slot. Will only occur at the front edge of the vacuum slot. The minimum angle of convergence and divergence is at least about 0.5 ms, specifically about 1 ms or more, specifically about 2 ms or more, and more specifically about 5 ms or more. Convergence and divergence angles may be the same or different. Increasing the angle increases the error margin during operation. About 1 ms to about 10 ms is an appropriate range. Simultaneous convergence and divergence occurs when the trailing edge of the vacuum slot, which is sufficiently concave with respect to the leading edge, is designed in the vacuum shoe so that the fabric can diverge immediately as it passes over the leading edge of the vacuum slot. In conjunction with the drawings it will be described clearly.

When initially installing a fabric with a fixed gap in a machine to further minimize the compression of the web during delivery, the distance between the fabrics may be such that the thickness of the web or It must be at least a caliper.

The use of an air press upstream of the differential speed transmission increases the smoothness. It is best used in combination with the fixed gap carrier fabric portion before drying. Although calendering of the web is not essential to achieve a certain level of smoothness, further processing of the sheet, such as calendering, embossing or creping, may be advantageous to further improve sheet properties.

As used herein, a "transfer fabric" is a fabric that is located between the forming and drying sections in a web manufacturing process. Suitable transfer fabrics include papermaking fabrics that provide a high fiber support index and provide good vacuum sealing to maximize contact of the fabric / sheet during transfer from the molding fabric. The fabric may have a relatively smooth surface contour to give the web smoothness, but it must have sufficient tissue to grip the web and maintain contact during rush delivery. Fine fabrics can produce high stretch in the web, which is good in some product areas.

The transfer fabric is a monolayer, multilayer, or composite layer permeable structure. Good fabrics have the following characteristics: (1) the number of machine direction (MD) strands / 2.54 cm (mesh) in terms of the delivery fabric in contact with the wet web (top); And 200 and the number of transverse machine direction (CD) strands in 1 in. (Count) of 10 to 200 cm. Strand diameter is typically less than 1.27 mm (0.05 in.); (2) On the upper side, the distance between the highest point of the MD knuckle and the highest point of the CD knuckle is about 0.025 (0.001 in.) To 0.051 mm (0.02 in.) Or 0.076 mm (0.03 in.). Between the two heights there may be a knuckle formed by either an MD or a CD that provides three-dimensional properties to the topography; (3) On the upper side, the length of the MD knuckle is more than the length of the CD knuckle; (4) If the fabric is of a multi-layer configuration, the bottom layer is preferably a finer mesh than the top layer to maximize fiber retention to control the web penetration depth; And (5) the fabric may be made to exhibit any geometrical pattern that gives visual enjoyment, which is typically repeated every 2 to 50 warp yarns; Have at least some of them.

Specific suitable transfer fabrics include, for example, the numbers 934, 937, 939, and 959 manufactured by Asten Forming Fabrics, Inc., Appleton, Wisconsin. Specific transfer fabrics that may be used also include the fabrics disclosed in US Pat. No. 5,429,686, issued to Chiu et al. On July 4, 1995, which is described herein for reference. The void volume of the transfer fabric can be below the fabric through which the web is delivered.

The forming process and tackle can be prior art as is well known in the paper industry. Such molding processes include Fordrinier, roof formers (such as suction breast rolls), gap formers (twin wire formers, crimps). Lesson formers, etc.). Wire or fabric forming processes may also be prior art, and fine tissue with large fiber supports is good for the production of smooth sheets or webs. The head box used to deposit the fibers on the molding fabric may or may not be laminated.

The methods disclosed herein may be applied to certain tissue webs, including webs for making facial tissues, bath tissues, paper towels, meal napkins, and the like. The tissue web may be a one-ply product or a multi-ply product such as two, three, four or more. Single layer products are advantageous because of their low manufacturing cost, but multiple layer products are preferred by many consumers. For multiple ply products, not all plies of the product need to be identical if at least one ply is in accordance with the present invention. The web may or may not be laminated (mixed), and the fibers that make up the web may be any fiber suitable for papermaking.

A suitable basis weight of the tissue web may be about 5 to about 70 gsm (g / m 2), preferably about 10 to about 40 gsm, more preferably about 20 to about 30 gsm. For a single layer of bath tissue a basis weight of about 25 gsm is good. For double layered tissue, a basis weight of about 20 gsm / ply is good. A base weight of about 15 gsm / ply is good for triple tissues. In general, heavier basis weight webs will require lower air flow to maintain the same operating pressure in the air plenum. The slot width of the air press is preferably adjusted to match the available air capacity with the system, and wide slots are used for webs with heavy basis weights.

The drying process can be any uncompressed drying method including, without limitation, through drying, infrared-red irradiation, microwave drying, etc., which tend to preserve the volume or thickness of the wet web. Because of commercial utility and practicality, through-drying is a well known and preferred means for non-compressive drying of webs. Suitable through-dry fabrics include, without limitation, Asten 920A and 937A and Velostar P800 and 103A. Through-dry fabrics are disclosed in U.S. Patent No. 5,429,686, filed July 4, 1995 to Chiu et al. The web is preferably dried to final dryness without creping because creping tends to lower web strength and volume.

Although not fully understood mechanically, it is evident that the transfer fabric and through-dry fabric can contribute separately and independently of the final sheet properties. For example, sheet surface smoothing as determined by a sensory panel can be handled over a wide range by replacing the delivery fabric with the same through-dry fabric. Webs produced by the present methods and apparatus tend to have just two sides unless they are calendared. However, uncalendered webs may overlap the smooth / rough sides together as required by the specific product type.

Many features and advantages of the invention will be apparent from the following description. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. Such embodiments do not represent all the scope of the present invention. Accordingly, reference should be made to the claims herein to interpret all the scope of the invention.

<Brief Description of Drawings>

1 is a schematic process flow diagram illustrating a method and apparatus according to the present invention for producing an uncreped through-drying sheet.

FIG. 2 is an enlarged plan view showing an air press from the process flow diagram of FIG.

FIG. 3 is a side view showing the air press shown in FIG. 2 in a partially cut cross-sectional state for illustration.

4 is an enlarged cross-sectional view taken generally from the plane of lines 4-4 of FIG.

FIG. 5 is an enlarged cross-sectional view showing a view similar to FIG. 4 except that it is generally taken from the plane of lines 5-5 of FIG.

6 is a side view showing an alternative sealing system for the air press shown in FIGS. 2 and 3 in a partially cut cross-sectional state for illustration.

FIG. 7 is an enlarged side view showing the vacuum transfer shoe shown in FIG.

FIG. 8 is an enlarged side view showing a view similar to FIG. 7 except that it shows simultaneous convergence and divergence of the fabric at the front edge of the vacuum slot.

FIG. 9 is a generalized graph of load / elongation curves for tissue showing a method of determining MD slope. FIG.

<Detailed Description of the Invention>

The present invention will now be described in detail with reference to the drawings. Similar elements will be given the same reference numerals for different consistency and simplicity. In all the embodiments shown, conventional papermaking devices and operations can be used for head boxes, molded fabrics, web delivery, drying and creping, and those skilled in the paper industry will readily understand all of the above. Nevertheless, various prior art components are shown to provide a peripheral context in which various embodiments of the present invention may be used.

1 illustrates one embodiment of a method and apparatus for making tissue. For simplicity, various tension rolls that are schematically used to form multiple fabric runs are shown without reference numerals. The paper head box 20 sprays or deposits an aqueous suspension of paper fiber 21 on the circulating molding fabric 22 which moves around the forming roll 23. The forming fabric 22 may partially dewater the formed wet web 24 to a consistency of about 10%.

After molding, the molding fabric 22 carries the wet web 24 to one or more vacuum or suction boxes 28, which are employed to provide additional dewatering of the wet web 24 while being supported by the molding fabric 22. It may be. In particular, a plurality of vacuum boxes 28 may be used to dewater web 24 to a consistency of about 20-30%. While other forming devices such as twin wire formers, crescent formers, etc. may be used instead, the already described Ford Liner is particularly useful for making useful base-heavy sheets such as wipers and towels. Hydroneedling, such as, for example, disclosed in US Pat. No. 5,137,600 to Barnes et al., Issued August 11, 1992, may optionally be employed to increase the volume of the web.

The wet web 24 may then be improved, for example, by suitable additional uncompressed dewatering means selected from the group consisting of air presses, infrared drying, microwave drying, sonic drying, through drying and displacement dewatering. Dehydration is provided. In the embodiment shown, the additional uncompressed dewatering means comprises an air press 30, which will be described in more detail below. The air press 30 preferably raises the consistency of the wet web 24 to about 30%, specifically about 31%, specifically about 32%, more specifically about 33%. In certain embodiments, the wet web 24 exits the air press 30 and has a consistency of about 31 to about 36% before subsequent delivery. In certain embodiments, the air press 30 increases the consistency of the wet web 24 by at least about 3%, preferably at least about 5%.

Preferably the support fabric 32 is in contact with the wet web 24 in front of the air press 30. The wet web 24 is interposed between the support fabric 32 and the forming fabric 22 to be supported during the pressure drop generated by the air press 30. Suitable fabrics for use as support fabric 32 include almost any fabric, including molded fabrics such as Albany International 94M.

Wet web 24 is then transferred from molding fabric 22 to transfer fabric 36 moving at a slower speed than molding fabric to impart increased stretch in the web. It is preferred that the transfer is performed by the cooperation of the vacuum transfer shoe 37 as described below with respect to FIGS. 7 and 8. The surface of the transfer fabric 36 is relatively smooth to provide smoothness to the wet web 24. As measured by the void volume, the openness of the transfer fabric 36 may be relatively low and about the same or even lower than the molding fabric 22.

The transfer fabric 36 passes through the rolls 38, 39 before the wet web 24 is delivered to the through-dry fabric 40 moving at about the same speed, or, if desired, at another speed. Delivery is carried out by the vacuum transfer shoe 42, which may be of the same design used for conventional delivery. The web 24 is dried to the final dryness as the web is transported through the through dryer 44.

Before being wound on the reel 48 for subsequent deformation into the shape of the final product, the dried web 50 is formed with one or more optional fixed gap fabric nips formed between the carrier fabrics 52, 53. Can be conveyed through. The volume or caliper of the web 50 can be controlled by fabric embossing nips formed between the rolls 54 and 55, 56 and 57, 58 and 59. Suitable carrier fabrics for this purpose include Albany International 84M or 94M and Asten 959 or 937, all of which are relatively smooth fabrics with fine patterns. The nip gap between the various roll pairs may be between about 0.025 and about 0.51 mm (0.001 and 0.02 in.). As shown, the carrier fabric portion of the machine is designed to be operated by a series of fixed gap nips that serve to control the calipers of the web and can replace or supplement off-line calendaring. As an alternative, a reel calendar can be employed to achieve a final caliper or to supplement off-line calendaring.

The air press 30 is shown in detail by the top view of FIG. 2 and the side view of FIG. 3, and FIG. 3 has a cut out portion for explanation. The air press 30 generally includes an upper air plenum 60 in combination with a lower vacuum or suction box 62. The terms "top" and "bottom" are used herein to facilitate the citation and understanding of the drawings, and are not intended to limit the manner in which the parts are oriented. The intervening portion of the wet tissue web 24 between the forming fabric 22 and the support fabric 32 passes between the air plenum 60 and the vacuum box 62.

The illustrated air plenum 60 is adapted to receive pressurized fluid through an air manifold 64 connected to a pressurized fluid source (not shown), such as a compressor or blower. The air plenum 60 is fitted with a plenum lid 66 having a bottom face 67 in close contact with the vacuum box 62 and in contact with or in contact with the support fabric 32 during use (see FIG. 3). The plenum sheath 66 has a slot 68 extending generally perpendicular to the machine direction across the full width of the wet web 24 to allow pressurized fluid to pass from the air plenum 60 through the fabric and the wet web. 5) is formed.

The vacuum box 62 is operatively connected to a vacuum source and mounted to be fixed to a support structure (not shown). The vacuum box 62 includes a lid 70 having a top surface 72 on which the forming fabric 22 is moved. The vacuum box cover 70 is formed with a pair of slots 74 (see FIGS. 3 and 5) corresponding to the position of the slot 68 of the plenum cover 66. The pressurized fluid dewaters the wet web 24 as the pressurized fluid is withdrawn from the air plenum 60 into the vacuum box 62 and through the vacuum box 62.

The fluid pressure in the air plenum 60 is preferably maintained in the range of about 0.35 bar (5 psi) or more, specifically about 0.35 to about 2.07 bar (5 to 30 psi), such as about 1.03 bar (15 psi). . The fluid pressure in the air plenum 60 is preferably monitored and controlled to a predetermined level.

The bottom face 67 of the plenum lid 66 is preferably smoothly curved to facilitate web control. Surface 67 is curved towards vacuum box 62 and about an axis disposed on the vacuum box side of web 24. The curvature of the bottom surface 67 is a support fabric 32, wet web that seals the vacuum box 62 against entry of external air during the dehydration process and causes net downward force to support the wet web 24. The angle change of the combination of the 24 and the molding fabric 22 is made possible. The angle of curvature allows loading and unloading of the air press 30 as often as needed depending on the process conditions. The required angular change depends on the pressure difference between the pressure and the vacuum side, preferably in excess of 5 kPa, specifically within 5 to 30 kPa, typically like 7.5 kPa.

The top and bottom surfaces 72, 67 preferably have different radii of curvature. In particular, the radius of curvature of the bottom face 67 is such that the top face 72 forms a contact line between the air plenum 60 and the vacuum box 62 at the front and rear edges 76 of the air press 30. It is preferable that the radius of curvature is larger than. Depending on the location of the support fabric 32 and the forming fabric 22 interposition and proper attention to the loading and unloading mechanism, the radius of curvature of the surface may be reversed.

The front and rear edges of the air press 30 may also be provided with end seals 78 (see FIG. 3) which are always in close contact with or in contact with the support fabric 32. The end seal 78 minimizes the escape of pressurized fluid between the air plenum 60 and the vacuum box 62 in the machine direction. Suitable end seals 78 may be made of elastic plastic composite or the like.

4 and 5, the air press 30 is preferably provided with a side sealing member 80 to prevent loss of pressurized fluid along the side edges 82 of the air press. The side seal member 80 includes a semi-rigid material that is adapted to be slightly deformed or bent when exposed to the pressurized fluid of the air plenum 60. The illustrated side seal member 80 is formed with a slot 84 for attaching to the vacuum box cover 70 using clamping bars 85 and fasteners 86 or other suitable means. In sectional view, each side sealing member 80 forms an L-shape with the leg 88 protruding upward from the vacuum box lid 70 into the side sealing slot 89 formed in the plenum lid 66. Pressurized fluid from the air plenum 60 causes the leg 88 to bend outwardly in sealing contact with the outward surface of the side sealing slot 89 of the plenum cover 66 as shown in FIGS. 4 and 5. do. Alternatively, the position of the side seal member 80 may be reversed to be securely attached to the contact surface formed by the vacuum box cover 70 (not shown) and fixedly attached to the plenum cover 66. In this predetermined alternative design, the side sealing member is preferably pressed to engage the sealing contact surface by the pressurized fluid.

Position control mechanism 90 maintains air plenum 60 in close contact with vacuum box 62 and in contact with support fabric 32. The position control mechanism 90 comprises a pair of levers 92 connected by a transverse piece 93 and attached to be fixed to the air plenum 60 by suitable fasteners 94 (see FIG. 3). ). An end of the lever 92 opposite the air plenum 60 is rotatably mounted to the shaft 96. The position control mechanism 90 also includes a balance cylinder 98 for operatively connecting the fixed structural support 99 and one of the cross sections 93. The equilibrium cylinder 98 extends or retracts to rotate the lever 92 relative to the shaft 96, which moves the air plenum 60 closer to or further from the vacuum box 62.

In use, the equilibrium cylinder 98 extends sufficiently such that the end seal 78 contacts the support fabric 32 by the control system such that the side seal member 80 is positioned in the side seal slot 89. The air press 30 is operated such that pressurized fluid is filled in the air plenum 60 and the semi-rigid side sealing member 80 is pressurized to seal the plenum cover 66. Pressurized fluid also generates an upward force that tends to move the air plenum 60 away from the support fabric 32. The control system induces the operation of the balance cylinder 98 to offset the upward force by continuously measuring the fluid pressure in the air plenum 60 by a pressure monitoring system. Thus, the end seal 78 always remains in close proximity or contact with the support fabric 32. The control system reacts to any pressure drop or peak in the air plenum 60 according to the proportional increase and decrease of the force applied by the balance cylinder 98. Eventually, the end seal 78 would not clamp the fabrics 32 and 22, otherwise it would have caused excessive wear of the fabric.

6 shows an alternative sealing system for the air press 30. The air plenum 100 is pivotable in which a sealing bar 104 is formed or transported to be burned onto the support fabric 32 across the width of the wet web 24 to minimize escape of pressurized fluid in the machine direction. Arm 102 is provided. Although only one arm 102 is shown in FIG. 6, it is to be understood that the second arm may be employed and configured in a similar manner at the opposite end of the air plenum 100. The sides of the air plenum 100 are coupled to the side seal member 80 as described in connection with FIGS. 2-5, or secured to the vacuum box 62 to minimize or eliminate side leakage of pressurized fluid. It may be mounted.

The pivotable arm 102 preferably includes a rigid material, such as structural steel, graphite composite, and the like. Arm 102 has a first portion 106 at least partially disposed inside of air plenum 100 and a second portion 108 preferably disposed outside of air plenum. Arm 102 is pivotally mounted to air plenum 100 by hinge 110. Both the inner surface of the wall 114 of the air plenum 100 and the first portion 106 are attached a hinge seal 112 that is impermeable to the pressurized fluid to prevent escape of the pressurized fluid. The sealing bar 104 is preferably a separate element that is mounted to the first portion 106 and moved toward the support fabric 32 (not shown in FIG. 6) by contact of the pressurized fluid to the first portion. Suitable sealing bars 104 may be made of low resistance, low friction coefficient, durable materials such as ceramics, heat resistant polymers, and the like.

The second portion 108 of the arm 102 is mounted with a balance bladder 120 having an inflatable chamber 122 by bracket 124 or other suitable means. Chamber 122 is operatively connected to a source of pressurized fluid, such as air, to expand the chamber. Arm 102 and bladder 120 are such that the bladder when inflated (not shown) is pressed against the outer surface of wall 114 of air plenum 100 pivoting the arm against hinge 110. Is located. Alternatively, a mechanism using a pressurized cylinder (not shown) may be used instead of the balance bladder as a means to pivot the arm 102.

The control system is operable to inflate or deflate the bladder 120 proportionally with the pressure of the fluid in the air plenum 100. For example, as the pressure in the air plenum 100 is increased, the control system may adjust the pressure or balance bladder in the balance bladder 120 such that the sealing bar 104 is not excessively clamped down against the support fabric 32. It is intended to increase the expansion of 120.

The design of the vacuum transfer shoe 37 used in the transfer fabric portion during the process (FIG. 1) is shown more clearly in FIGS. 7 and 8. The vacuum transfer shoe 37 is formed with a vacuum slot 130 (see FIG. 7), which is connected to a vacuum source and has a length of about 12.7 to about 25.4 mm (0.5 to 1 in.) Appropriate "L". A suitable vacuum slot is about 25.4 mm (1 in.) For making tissues for uncreped through dry baths. The vacuum slot 130 has a front edge 132 and a rear edge 133 and is formed corresponding to the entry and exit land regions 134 and 135 of the vacuum transfer shoe 37. The trailing edge 133 of the vacuum slot 130 is retracted with respect to the leading edge 132, which is caused by the other direction of the exit land area 135 relative to the entry land area 134. The angle "A" between the entry land area 134 and the plane of the exit land area 135 is about 0.5 mm, in order to provide sufficient separation of the forming fabric 22 and the transfer fabric 36 as they converge and diverge. It may be 1 ms, more specifically about 5 ms or more.

8 further shows the wet tissue web 24 moving in the direction shown by the arrow pointing towards the vacuum transfer shoe 37. Also, a slow moving transfer fabric 36 is approaching the vacuum transfer shoe 37. The angle of convergence between the two entering fabrics is indicated by "C". The divergence angle between the two fabrics is indicated by "D". As shown, the two fabrics converge and diverge simultaneously at point "P", which corresponds to the front edge 132 of the vacuum slot 130. It is not necessary or desirable for the web to be in contact with all of the fabric over the entire length of the vacuum slot 130 to effect transfer from the forming fabric 22 to the transfer fabric 36. As is apparent from FIG. 8, neither the forming fabric 22 nor the transfer fabric 36 need to be deflected in excess of a small amount to effect delivery, which can reduce fabric wear. Numerically, the direction change of the two fabrics can be less than 5 ms.

As mentioned above, the transfer fabric 36 is moving at a slower speed than the molding fabric 22. If more than one transfer fabric is used, the speed difference between the fabrics may be the same or different. Multiple delivery fabrics can provide a wide range of fabric / speed combinations as well as operational flexibility to affect the properties of the end product.

The vacuum level used for the differential speed transfer may be between about 76.2 and about 381 mm (3 to 15 in.) Hg, preferably about 127 mm (5 in.) Hg. The vacuum shoe (negative pressure) may be added or replaced by using positive pressure from the opposite side of the web 24 to blow the web onto the next fabric in addition to or instead of to suck it onto the next fabric by vacuum. Also, a vacuum roll or vacuum rolls may be used to replace the vacuum shoe.

Yes

The following examples are provided to aid in a more detailed understanding of the present invention. Specific amounts, ratios, compositions, and variables are illustrative only and are not intended to specifically limit the scope of the present invention.

As a reference to examples, MD Tensile Strength, MD Stretch and CD Tensile Strength can be determined using the following parameters: TAPPI Test Method 494 OM-88 Breaking Properties of Paper and Paperboard ", ie crosshead speed is 254 mm / min (10.0 in./min); full-scale load is 4540 g (10 lb.); jaw span (also called jaw span, distance between jaws, gauge length) is 50.8 mm (2.0 in.) and sample width is 76.2 mm (3 in.) Tensile test machine is a North Carolina Research Triangle Park ( Model CITS-2000, Syntech, manufactured by Systems Integration Technology Inc. of Stoughton, Massachusetts, a division of MTS Systems Corporation, Research Triangle Park. to be.

The stiffness of the examples sheet can be objectively expressed by either the maximum slope of the machine direction (MD) load / elongation curve for the tissue (hereinafter referred to as MD slope) or the machine direction stiffness (defined below), In addition, the caliper of the tissue and the number of plies should be considered. Hereinafter, a method of determining the MD tilt in relation to FIG. 9 will be described. MD slope is the maximum slope of the machine direction load / elongation curve for the tissue. The unit of MD slope is kg / 7.62 cm (3 in.). MD stiffness is calculated by multiplying the MD slope by the square root divided by the caliper index. The unit of MD stiffness is kg / 7.62 cm (3 in.)-Microns ^0.5 .

9 is a generalized load / elongation curve for a tissue sheet showing a method of determining MD slope. As shown, two points P1 and P2 lying along the load / elongation curve (the distance between them are exaggerated for explanation) are selected. Tensile testers are programmed to calculate linear regression to the points sampled at P1 through P2 (Systems Integration Technologies Inc., Stauton, Mass., MTS Systems Corporation, Triangle Park, North Carolina Research). (General Applications Program) version 2.5). This calculation is made repeatedly over the curve by adjusting points P1 and P2 in a regular manner along the curve (described below). The highest value among the calculated values is the maximum slope, and when performed in the machine direction of the sample, it is called MD slope.

Tensile testing machine programs should be set up so that 500 points, such as P1 and P2, span the span of 63.5 mm (2 and 1/2 in.) Spans. This provides a sufficient number of spots to necessarily exceed certain practical stretch amounts for the specimen. With a crosshead speed of 254 mm (10 in.) / Min, it translates into points every 0.030 seconds. The program includes setting the tenth point as an initial point (such as P1), counting 30 points to the fortyth point (such as P2), and performing a linear regression on the 30 points. The slope between is calculated. Next, the program counts 10 points up to the twentieth point (this is P1) and counts 30 points until the procedure (50th point (which is P2)) and calculates the slope, Repeat the step of saving). This process continues for the total amount of elongation of the sheet. Next, the maximum slope is selected as the highest value from the above arrangement. The unit of maximum inclination is the sample width in kg / 76.2 mm (3 in.) (Of course, the amount of deformation is dimensionless since the length of the elongation divided by the length of the jaw span. )

Examples 1-4

To illustrate the present invention, a number of uncreped through-dry tissues are generally manufactured using the method as shown in FIG. In particular, Examples 1-4 comprise three layers of layers comprising disperged, debonded eucalyptus fibers with the outer layer dispensed and refined northern softwood kraft fibers with the center layer refined. Bath tissue. Senebral eucalyptus fibers were pulped for 15 minutes to 10% consistency and dehydrated to 30% consistency. The pulp was then transferred to a Maule shaft disperger. The disperser was operated at 70 ?? (160 ??) with a power input of 1.8 ㎾-days / ton (2.2 HPD / T). Following the dispersing process, a softening agent (Witco C6027) was added to the pulp in an amount of 7.5 kg / metric ton dry fiber (0.75 wt%).

Prior to molding, the soft wood fibers were pulped for 30 minutes at 3.2% consistency, and the dispersed unbound eucalyptus fiber was diluted to 2.5% consistency. Overall laminated sheet weight was 35% / 30% / 35% for Examples 1, 2 and 4 and 33% for Example 3 between the dispersed eucalyptus / purified soft wood / dispersed eucalyptus layers. / 34% / 33%. The central layer was refined to the level necessary to achieve the target strength value, while the outer layer was provided with softness and volume. For the added dry and temporary wet strength, a reinforcement identified by Parez 631 NC was added to the core layer.

In the above examples a four-layer Beloit Concept III head box was employed. Refined northern softwood kraft stock was used in the two core layers of the head box to produce a single core layer for the described three layer product. Turbulence generating inserts recessed about 75 mm (3 in.) From the slice and a layer divider was employed extending about 150 mm (6 in.) Beyond the slice. The net slice opening was about 23 mm (0.9 in.) And the water flow of all four head boxes was comparable. The consistency of the stock transferred to the head box was about 0.09% by weight.

The final three-layer sheet was formed on a twin-wire suction roll, and the molding machine with the molding fabric was an Appleton Mills 2164-B fabric. The speed of the molding fabric ranged between 11.8 and 12.3 m / s. The newly formed web was then dewatered from the bottom of the forming fabric to 25 to 26% using a vacuum suction device without an air press and delivered to a transfer fabric that was moved to 9.1 m / s (29 to 35% rush delivery). It was dehydrated up to 32-33% consistency by air press before. The transfer fabric was Appleton Mills 2164-B. A vacuum shoe was used to draw about 150 to 380 mm (6 to 15 in.) Hg vacuum to deliver the web to the transfer fabric.

The web was then delivered to a through dry fabric moving at a speed of about 9.1 m / s. Appleton Mills T124-4 and T124-7 through dry fabrics were used. The web was transported through a Honeycomb through dryer operating at a temperature of about 175 ° (350 °) and dried to a final dryness of consistency of about 94-98%.

The procedure of manufacturing the example sheet is as follows. That is, four rolls of the sheet of Example 1 were produced. The consistency data reported in Table 1 was based on two measurements taken one at the beginning and at the end of the four rolls. Other data shown in Table 1 represent averages based on four measurements, one per roll. Next, the air press was turned on. The data immediately before and after the operation of the air press are shown in Table 3 (individual data points). The data indicate that the air press significantly increased the tensile strength value. Next, the process was modified to reduce the tensile strength value to a level comparable to the Example 1 sheet. After this process adjustment period, four rolls of Example 2 sheet (invention) were produced. Later, four rolls of Example 3 sheet (invention) were made using another through-drying fabric with the air press in operation. The air press was shut off and the process was adjusted to restore the tensile strength values comparable to the Example 3 sheet. Next, four rolls of Example 4 sheet were made. The consistency data for each example in Table 2 is the average based on two measurements, one at the beginning and the end of each of the four rolls of each set. The other data in Table 2 is based on the average of four measurements, one per roll. In Table 2, the example 4 data is provided in the left column and the example 3 data is provided in the right column so that the left column shows data without air presses and the right column shows data with air presses.

Tables 1-3 provide a more detailed description of the process conditions as well as the final tissue properties for Examples 1-4. As used in Tables 1 to 3 below, the column headings have the following meanings. That is, "Consistency @ Rush Transfer" is the web consistency at the point of transfer from the forming fabric to the transfer fabric and is expressed in percent solids, and "MD tensile" is Machine direction tensile strength and expressed in g / 7.62 cm (3 in.) Of sample width, “CD tensile” is transverse machine direction tensile strength and in g / sample width of 7.62 cm (3 in.) "MD stretch" is the machine direction stretch and is expressed as% elongation at sample breakdown, and "MD slope" is as defined above and is 7.62 cm of g / sample width. Expressed as 3 in., The "Caliper" has an anvil diameter of 103.2 mm (4 1/16 in.) And anvil pressure of 3.39 kPa (220 g / in. ² ). 1 sheet caliper measured by Bulk Micrometer (TMI Model 49-72-00, Armityville, NY) Expressed in μm, “MD stiffness” is the machine direction stiffness factor as defined above and expressed in kg / 7.62 cm (3 in.)-Microns ^0.5 and “Basic Weight” is the final The basis weight, expressed in g / m 2, "TAD Fabric" means through-drying fabric, "Refiner" is the power input to purify the center layer, expressed in ㎾, and "Rush ( Rush) "is the speed difference between the molded fabric and the slower transfer fabric divided by the speed of the transfer fabric, expressed in%," HW / SW "is the hard wood (HW) and soft wood (SW) in three-ply tissue It is the weight deficit of and is expressed in% of the total fiber weight, "Parez" is the addition rate of the Parez 631 NC and is expressed in metric tons of kg / central fiber.

As shown by the previous example, the air press produces a significantly higher consistency upstream of the differential speed transfer that smooths the sheet as evidenced by the low modulus value. Preferably, the modulus (MD stiffness) of the tissue product is at least 20% smaller than comparable tissue products made without further dehydration up to a consistency greater than about 30%. In addition, the machine direction tensile strength of the tissue product is at least 20% greater and the cross direction tensile strength of the tissue product is at least 20% greater than comparable tissue products made without further dehydration up to about 30% consistency. In addition, the machine direction stretch of the tissue product is at least 17% greater than comparable tissue products made without further dehydration up to a consistency greater than about 30%.

The above detailed description has been given for the purpose of explanation. As such, many variations and modifications may be made without departing from the spirit and scope of the invention. For example, alternative or optional features described as part of one embodiment may be used to invent other embodiments. Also, two named parts may represent the same structural part. In addition, PCT Patent Application Publication No. WO 95/00706, filed Jan. 5, 1995, and filed Oct. 27, 1994, by Engel et al., Entitled "Smooth crepe-free, through-drying sheet. Various process and device arrangements, such as those disclosed in US Patent Application No. 08 / 330,166, "Method For Making Smooth Uncreped Throughdried Sheets," may be employed, the disclosures of which are incorporated herein by reference. It is described. Accordingly, the invention should be limited only by the claims, not the specific embodiments described.

Claims (27)

Depositing an aqueous suspension of papermaking fibers on the cyclic molded fabric to mold the wet web, Dewatering the wet web to a consistency of 20-30%, Further dewatering the wet web using uncompressed dewatering means to a consistency greater than 30%, Delivering the additional dewatered web to a transfer fabric moving at a rate of 10 to 80% slower than a molding fabric; Delivering the web to a through-drying fabric; And drying the web to a final dryness. The method of claim 1, wherein the uncompressed dewatering means is selected from the group consisting of air press, infrared drying, microwave drying, sonic drying, through drying and displacement dehydration. 2. The method of claim 1 wherein the uncompressed dewatering means comprises an air press. 4. The method of claim 3 wherein the air press increases the consistency of the wet web by at least 3%. 4. The method of claim 3 wherein the air press comprises an air plenum and the fluid pressure in the air plenum is maintained within the range of 351.55 to 2109.3 g / cm 3 (5 to 30 psi). . 6. The method of claim 3, 4 or 5, wherein the air press provides a pressure difference between 889 mm and 1524 mm (35 to 60 in.) Hg across the wet web. . 6. The method of claim 3, 4 or 5, wherein the air press dewaters the wet web to greater than 31% consistency. 8. The method of claim 7, wherein the air press dewaters the wet web to greater than 32% consistency. 6. The method of claim 3, 4 or 5, wherein the air press dewaters the wet web to a consistency of 31 to 36%. 2. The method of claim 1 wherein the step of dewatering the wet web to a consistency of 20-30% is accomplished using a plurality of vacuum boxes. 4. The method of claim 3 wherein the wet web is sandwiched between a forming fabric and a support fabric when conveyed through an air press. 5. The method of claim 1, 3 or 4, wherein the forming fabric is moved at a speed of at least 609.6 m (2000 ft.) / Min. A tissue product prepared according to the method of claim 1. The tissue product of claim 13, wherein the modulus of the tissue product is at least 20% less than a comparable tissue product prepared according to the method of claim 1, except that the modulus of the tissue product is not further dehydrated to greater than 30% consistency. . The method of claim 13, wherein the machine direction tensile strength of the tissue product is at least 20% greater than a comparable tissue product prepared according to the method of claim 1, except that no further dehydration is performed until the consistency exceeds 30%. Tissue products. The method of claim 13, wherein the transverse tensile strength of the tissue product is at least 20% greater than a comparable tissue product prepared according to the method of claim 1, except that no further dehydration is performed until the consistency exceeds 30%. Tissue products. The method of claim 13, wherein the machine direction stretch of the tissue product is at least 17% greater than the comparable tissue product prepared according to the method of claim 1, except that no further dehydration is made until the consistency exceeds 30%. Tissue products. An air plenum with a plenum cover having a bottom surface, Means for supplying pressurized fluid to the air plenum; A vacuum box having a vacuum box cover having an upper surface closely located at a bottom surface of the plenum cover, Means for evacuating the vacuum box, Attached to one of the air plenum and the vacuum box, positioned closely to the side seal contact surface formed by the other of the air plenum and vacuum box, and bent to seal contact with the side seal contact surface upon exposure of the pressurized fluid. And a side sealing member adapted to contact the air plenum and the vacuum box to minimize escape of pressurized fluid. 19. The wet web dewatering air press as set forth in claim 18, wherein the side sealing member is attached to a vacuum box cover, and the plenum cover is formed with a side sealing slot and a side sealing contact surface. 19. The wet web dewatering air press of claim 18 further comprising an end seal attached to the plenum cover. 21. The wet web dewatering air press according to claim 18 or 20, further comprising a position control mechanism adapted to hold the air plenum closely to the vacuum box. 23. The wet web dewatering air press as set forth in claim 21 wherein said position control mechanism includes a lever attached to said air plenum and rotatably mounted, and a balancing cylinder adapted to rotate said lever. 22. The wet web dewatering air press of claim 21 further comprising a control system adapted to induce the operation of the balance cylinder in accordance with the measurement of the fluid pressure in the air plenum. 21. The wet web dewatering air press of claim 18, 19 or 20, wherein the top and bottom surfaces are curved towards the vacuum box. 25. The wet web dewatering air press of claim 24 wherein the top and bottom surfaces have different radii of curvature. An air plenum with a plenum cover having a bottom surface, Means for supplying pressurized fluid to the air plenum; A vacuum box having a vacuum box cover having an upper surface closely located at a bottom surface of the plenum cover, Means for evacuating the vacuum box, An arm at least partially disposed within said air plenum and having a first portion and a second portion having a sealing bar, said arm pivotally mounted to said air plenum; And means for pivoting the arm according to the fluid pressure in the air plenum. 27. The wet web dewatering air press of claim 26 further comprising a hinge seal impermeable to pressurized fluid and attached to both the air plenum and the first portion.