AU657691B2 - Multy-ply web former and method - Google Patents

Description

.I i~ scn~ OPI DATE 04/02/92 AOJP DATE 12/03/92 APPLN. ID 82139 91 PCT NUMBER PCT/EP91/01255 INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 92/01111 D21F 11/04, 9/00 Al (43) International Publication Date: 23 January 1992 (23.01.92) (21) International Application Number: (22) International Filing Date: PCT/EP91/01255 4 July 1991 (04.07.91) (74) Agent: WAXWEILER, Jean; Office Dennemeyer S.a.r.l., rue des Bruyeres, P.O. Box 1502, L-1015 Luxembourg (LU).

(81) Designated States: AU, BR, CA, FI, JP, KR, NO, PL, SU 4

US.

Priority data: 90113178.9 10 July 1990 (10.07.90) (34) Countries for which the regional or international application wasfiled:

EP

AT et al.

(71) Applicant (for all designated States except US): BEtefT CORPORATION [US/US]; P.O. Be 350, 1 St. La-, rence Avenue, Beloit, WI 53511 (US), (72) Inventors; and Inventors/Applicants (for US only): BLACKLEDGE, James [GB/GB]; 75 Worden Lan, Leyland, Lancashire 2BD SALVAI, Nazzareno [IT/IT]; Via Frassati, 14, San Pietro Val Lemina, 1-10060 Torino TURN- ER, James, Arthur [GB/GB]; 2 Norwood Avenue, Beech Hill, Wigan WN6 7P4 (GB).

Title: UL -TY-PLY WEB FORMER AD METHO (54) Title: MULTY-PLY WEB FORMER AND METHOD Published With international search report.

With amended claims and statement.

F.m r s (57) Abstract A multi-ply paper web is formed by bringing a top ply liner into ply-bonding engagement with a base ply web (WB) traveling on a base ply forming wire The top ply liner (WT) is formed between two co-running forming wires (10, 20) in a convex upwardly/concave downwardly curved, substantially horizontal forming zone. Dewatering in the forming zone is effected by applying sub-atmospheric air pressurc solely beneath the lower surface of the top ply liner (WT) being formed.

Water is removed from the upper surface of the top ply liner (WT) solely by wire tension, gravity and centrifugal force created by passing the co-running forming wires (10, 20) over the convex upwardly curved path of travel. This permits a greater concentration of pulp stock fines to remain in the upper surface of the top ply liner (WT) to effect greater ply-bonding affinity with the base ply (Wn) when the two plies WR) are brou ht oether and bonded.

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r I WO 92/01111 PCT/EP91/01255 Multy-ply web former and method This invention relates to multi-ply paper formation. More specifically, this invention relates to two-wire, multi-ply paper formation. Still more particularly, this invention relates to two-wire, multiply web formation wherein the outer ply to be ply-bonded to the base ply of the multi-ply web, has its surface dewatered essentially by wire tension and centrifugal force.

In prior forming arrangements for forming a multi-ply paper web product, a relatively coarse base ply is first produced and a second, outer ply is produced to be brought into ply-bonding contact with the previously formed base ply. The outer ply, which is intended to form the outer surface of the printed container, such as a box, is formed of a finer grade of pulp stock so as to provide a smoother, higher quality surface. In order to form the outer ply at commercially desirable speeds, dewatering was effected through both of its surfaces before the outer ply was brought into ply-bonding contact with the base ply of the paper web sheet. This produces an acceptable paper product, mainly due to the quality of the pulp stock used to produce the outer ply, but the requirements of producing a better product with cheaper pulp, and the need to produce a better product at higher speeds regardless of pulp quality, or a combination of both, have necessitated the conception of an improved multi-ply web former having an outer surface which exhibits the desired printability, and feel and visual smoothness while having an inner surface which has better ply-bonding characteristics.

In prior apparatus, both sides of the outer ply were dewatered positively, that is, they were dewatered by the application of sub-atmospheric air pressure directly to both surfaces to enhance the removal of water through both of the web surfaces. When SUBSTITUTE

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lv WO 92/01111 PCT/EP91/01255 2 both surfaces are positively dewatered, fines and fillers in the pulp stock are urged outwardly in both directions to the respective surfaces of the web and removed during the dewatering process. Thus, while the web is rapidly dewatered, which was the desired effect, the fines and fillers which contribute so much to the ply bonding characteristics of the outer side of the web produced, were removed in large quantities which deleteriously effected web quality as well.

The aforementioned shortcomings, deficiencies and characteristics of the outer ply in a plybonded multi-ply paper web, and the resultant multi-ply paper product, have been obviated by this invention.

In this invention, the outer ply of a multiply web, which is sometimes referred to as a "white top liner", is produced by dewatering through one side of the web using only centrifugal force and the force of the tension of the forming wire over the web. The outer ply is formed in the general direction opposite to the direction of the traveling base ply to which it is ply bonded. The generally upwardly facing surface of the top ply is dewatered by the tension of the upper, outer forming wire being concave downwardly held over the web which has been formed by the aqueous pulp stock slurry projected between the outer and inner forming wires. In addition, one, or more, water collection devices, such as water skimming slots, which may or may not be assisted by a vacuum, assist in removing water expressed inwardly of the outer forming wire. The fines and fillers in the pulp stock slurry are thus exposed to sub-atmospheric (vacuum) pressure only within the lower forming wire in a generally concave downward direction for a relatively long distance. This affects the rate of water removal as well as permits the retention of a greater proportion of fines and fillers in the web, W092/01111 PCr/EP91/01255 3 particularly the top surface of the web, due to the fact that migration of the fines and fillers through the lower surface of the web is hindered by the web fibers.

The downwardly directed, relatively gentle dewatering through the lower surface of the outer web ply is effected by subjecting the ply to a sub-atmospheric pressure over a relatively long dewatering zone, which can take the form of a vacuum or suction box, or a plurality of spaced foil blades, or a combination of both.

Accordingly, it is an object of this invention to provide a method and apparatus for producing a multi-ply paper sheet having improved plybond characteristics.

Another object of this invention ia to provide a method and apparatus for producing the outer ply of a multi-ply paper sheet wherein the surface to be ply-bonded is dewatered solely by centrifugal force, wire tension and gravity.

A feature and advantage of this invention is the provision of a white top liner in a multi-ply paper sheet, which sheet can be produced at improved speeds while exhibiting improved ply-bonding characteristics and a commercially desirable outer surface.

These and other objects, features and Vadvantages of the invention will become readily apparent to those skilled in the art upon reading the following description of the preferred embodiments in conjunction with the attached drawings.

Figure 1 is a side-elevational view of the former showing a foil box within the first wire for substantially the length of the forming zone between the throat and the turning roll.

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I Il 1- Figure 2 is a side-elevational view of the former showing a foil box followed by two suction boxes within the first, or lower, top ply forming wire.

As shown in Figure 1, a first, lower looped top ply forming wire 10 is shown looped about guide rolls 12, 12', 12'' and turning roll 14. Disposed within the first forming wire is a foil box 16 which has an outer contour defined by a plurality of foils 18 arranged to distend the first forming wire in a concave downwardly, or convex upwardly, shaped curve which defines a forming zone extending substantially between guide roll 12 and turning roll 14.

Disposed above the first, lower forming wire is a looped second, upper forming wire 20 which is directed to travel in its looped path by guide rolls 22, 22', 22'' and 22''' Guide rolls 12, 22 direct their respective forming wires 10, 20 into a throat 24 which converges near the leading edge of foil box 16. In the embodiment shown in Figure 1, the throat 24 extends to just after the beginning of foil box 16.

The second forming wire 20 is guided to remain over the first forming wire for a short circumferential distance over the surface of turning roll 14. Turning roll 14 is a suction roll having a vacuum chamber 26 extending between circumferentially spaced seals 28, 30. The first and second forming wires are shown engaged for a short distance past the upstream vacuum chamber seal 28.

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Ai WO92/01111 PCT/EP91/01255 Positioned within the looped second forming wire 20 is a save-all 32, which can take the form of a so-called autoslice. In either configuration, the saveall or auto-slice represents a blade, lip or slot 33 which is positioned in closely spaced adjacency, or even non-pressure contact, with the inner side of looped forming wire 20. More than one such lip or slot 33 may be used.

A headbox 34 is positioned to direct an aqueous slurry of stock fibers into the throat 24.

Depending on operating parameters, such as machine speed, stock consistency and, possibly, the type of forming wires used, the headbox slice nozzle may be directed slightly toward one or the other of the forming wires.

Beneath the top ply former, which is the designation for the apparatus just described, is a base ply forming wire 36 on which a base ply web WB has been formed upstream of the top ply former by other means. A pivoted guide roll 38 wraps the base ply forming wire 36 around a portion of the periphery of the turning roll 14 beginning at a point over the trailing seal 30. The top ply web WT is thus brought into co-running engagement with the base ply web WB, and ply-bonding occurs between the webs during this period of contact. Transfer of the composite, multi-ply paper sheet so formed to the base ply wire 36 is assured by the application of vacuum pressure in transfer box SA source of sub-atmospheric a.r pressure 42 is optionally linked to the foil box 16 to provide vacuum pressure to the lower side of the web being formed between the co-running forming wires 10, 20 over the foil blades 18 in the foil box. Water is removed from the inner side of the looped second forming wire by i; in•nn •r li• n 6 a drain 44, and water is removed from within the looped first forming wire by drain 46.

In the various configurations shown in Figures 1-2, corresponding elements in each figure will be correspondingly numbered with a letter postscript to distinguish between corresponding elements in the various figures. Similarly, like 'elements within a particular figure will be distinguished by a different number of prime superscripts after each element number.

As shown in Figure 2, the dewatering elements within the first forming wire 10a comprise a foil box 16a, and two vacuum boxes 17a, 17a'. The last forming box 17a', in the downstream direction, effects the transfer of the newly formed top ply web WT onto the first forming wire.

Within the looped second forming wire is a first auto-slice 48a following the foil box, and a second auto-slice 48a' intermediate the two vacuum boxes 17a, 17a'. Both auto-slices have a leading lip 33a, 33a' which is mounted in closely spaced adjacency, or nonpressure contact, with the inner side of looped forming wire 20a. A headbox 34a discharges an aqueous stock fiber stream into the throat 24a formed between the forming wires 10a, 20a converging over guide rolls 12a, 22a.

Turning roll 14a, which in this configuration is a plane surfaced roll with no vacuum chamber, brings the first forming wire around its a surface and into co-running engagement with the base ply web WB being carried on base ply forming wire 36a.

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SUBSTITUTE SHEET \l 7 In the embodiment shown in Figure 2, foil box 16a and vacuum boxes 17 and 17a' are connected to a source of sub-atmospheric air pressure which are designated generally as 52a and 52a'. The profile contours of the wire-contacting surfaces of the foil box and vacuum boxes is concave downwardly/convex upwardly.

While the surface of the foil box is defined by a series of spaced foils which are parallel and spaced in the machine direction and which extend in the cross-machine direction, the contours of the vacuum boxes are usually comprised of an arcuate surface which is perforated, such as with holes SUES3TITUTZ

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-I Udrilled through their covers, which permit the aplication of vacuum pressure to the underside of the first looped forming wire.

In operation, with particular reference to Figures 1 and 2, the headbox discharges an aqueous stock slurry into the throat between the co-running forming wires. Since the only application of sub-atmospheric air pressure to the fibrous stock slurry between the forming wires is provided by the foil box or vacuum boxes beneath the first forming wire 10, 10a, water is urged from the stock slurry outwardly and downwardly through the lower top ply web WT to within the looped first forminc wire. Due to the tension of the second forming wire 10, 10a, over the stock slurry over the first forming wire water is expressed outwardly through the top ply web WT being formed between the first and second forming wires and into the save-all 32, or autoslices 48a, 48a'. The water is also urged outwardly through the upper surface of the top ply web by centrifugal force and the force of gravity in the slightly down-turning portions of co-running forming wire travel in the generally horizontally disposed, concave downwardly forming zone. The blades in the foil box 16, 16a, operating with or without subatmospheric vacuum pressure, urge the water gently to within the foil boxes. Downstream, at a point where the web is more dewatered, higher sub-atmospheric vacuum pressure is applied to vacuum boxes 17a' to s, j further dewater the top ply web through the lower surface thereof.

k uBS-nuTE S H E 9 In all of the embodiments, the application of sub-atmospheric air pressure solely to the lower side of the top ply web through the first forming wire urges the fines and any fillers in the stock slurry to migrate downwardly toward the lower surface of the top ply web.

Thus, while some of the fines near the lower surface of the top ply web over the first forming wire are removed from the web, a relatively large proportion of the fines initially near the upper surface of the top ply web adjacent the second forming wire remain in the web during the dewatering effected by the sub-atmospheric air pressure. Not only do these fines remain in the web, but a relatively larger total proportion of the fines initially in the stock remain in the web due to the absence of any application of sub-atmospheric air pressure to the stock slurry between the forming wires through the second forming wire. In other words, the only forces urging water out of the upper surface of the top ply web are centrifugal force, forming wire tensior and, in the slightly downwardly extending portion j forming wire travel in the substantially horizontai.1.y disrosed forming section, gravity. Water expressed through the top (second) forming wire, therefore, need only be collected by the save-all'or auto-slices; it is not urged through the top wire by these elements.

Thus, a relatively higher proportion of fines remain in the upper surface of the top ply web being formed, and it is this surface which is brought into ply-bonding contact with the upper surface of the base ply web WB over the turning roll. Since ply-bonding is enhanced by a higher proportion of fines in the surface of one, or both, of the webs at their interface, m h J iP

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ply-bonding between the top ply web WT and the base ply web WB is promoted by this invention. This allows plybonding to be achieved at lower web moisture levels and faster machine speeds, or some combination of both.

In this invention, both upward (through the second forming wire) and downward (through the first forming wire) dewatering is effected, but the dewatering is controlled as described. More fines remain at or near the top surface of the top ply web for better ply bonding, and more fines and fibers remains in the whole top ply Web due to the application of sub-atmospheric pressure on only the lower side through the first forming wire. In other words, the bottom of the top ply web is also of a higher quality. This promotes good top ply smoothness and printing properties in the composite multi-ply web W.

Naturally, variations in the method and apparatus described can be made. For example, the throat can extend from upstream of the place where the top ply forming wires are guided to travel in substantially the same direction to where the wires converge. Also, while the foil boxes, and forming shoe, have been described as operated in conjunction with sub-atmospheric air pressure, it is contemplated that, under certain circumstances, they need not be so operated. Finally; it is to be understood that the terms web, sheet and paper include the term board.

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Claims (6)

1. A method for forming a multi-ply paper web, including the steps of forming a base ply web (WB) on a looped traveling foraminous base forming wire (36), bringing first and second looped forming wires (10,20;10a,20a) into co-running engagement over the first looped forming wire (10;10a) which is inwardly curved relative to its interior, along a path of travel thereof, projecting an aqueous top ply stock stream onto one or the other, or both, of the first and second looped forming wires (10,20;10a,20a) closely upstream of a throat (24) formed by the converging first and second forming wires, expressing water upwardly through the second forming wire (20;20a) over its co-running path of travel with the first forming wire (10;10a) solely by wire tension and centrifugal force to thereby form an upper web surface of the top ply web (WT), and bringing the upper web surface of the top ply web (WT) into co-running engagement with the base ply. web (WB) to effect ply-bonding therewith to form a multi-ply web, wherein the improvement comprises the. step of: dewatering the top ply stock stream through the first forming wire (10;'10a) by applying sub- i~j atmospheric air pressure to the stock stream solely beneath its co-running path of travel with the second forming wire (20;20a) to thereby form a lower web surface of the top ply web (WT). 1 SUBSTITUTE SHEET 12

6. Apparatis for forming a multi-ply paper web, including a looped base ply forming wire (WB) for carrying and dewatering a base ply web (WB), first and second looped top ply forming wires (10,20;10a,20a) arranged to converge in a throat (24) and travel in co-running engagement over a path of travel which is curved toward the interior of the first looped forming wire (10;10a), headbox means (34;34a) for depositing an aqueous top ply stock slurry on the first forming wire (10;10a) closely upstream of the throat or in the throat (24) to initiate formation of a top ply web (WT) having lower and upper surfaces, means (32;48a,48a') for receiving water expressed upwardly and inwardly through the second looped forming wire (20;20a) solely by centrifugal force and forming wire tension between the co-running first and second forming wire, (10,20;10a,20a), guide means for guiding the second forming wire (20;20a) away from the first forming wire (10;10a), turning means (14;14a) for directing the first forming wire (10;10a) and web into co-running engagement with the base ply web (WB) to effect ply- bonding between the upper surface of the top ply web (WT) and the base ply (WB), wherein the improvement comprises: sub-atmospheric air pressure dewatering apparatus (16;16a,17a,17a') within the first top ply 30 forming wire (10;10a) upstream of the turning means (14;14a) for creating sub-atmospheric air pressure to the top ply stock stream in the direction inwardly of the looped first forming wire (10;10a) and forming a top ply web (WT) having its lower surface on the first forming wire (10;10a). SSUBSTITUTE SHEET i I 4 '.355 13, dewatering the top ply stock stream downwardly therethrough and forming a top ply web having its lower surface oiNthe first forming wire; means for receiving water expressed upwardly and inwardly through the second looped forming wire solely by centrifugal -force and forming wire tension, the upper surface of the top ply web facing the second wire; guide means for guiding the second forming wire away from the first forming wire; turning means for directing the first forming wire and web into co-running engagement th the base ply web to effect ply bonding between the uper surface of the top ply and the base ply web.

7. Apparatus for forming a multi-ply paper web as set forth in claim 6, wherein: the headbox deposits the top ply stock onto the first top ply forming wire closely upstream of where the first and second forming wires converge; dewatering means are disposed beneath the first forming wire upstream where the first and second forming wires converge.

8. Apparatus for forming a multi-ply paper' web as set forth in claim 6, wherein: the turning means comprises a sucti6n roll.

9. Apparatus for forming a .multi-ply paper web as set forth in claim 6, wherein: the means for receiving water comprises an auto-slice.

10. Apparatus for forming a multi-ply paper web as set forth'in claim 6, wherein: the sub-atmospheric dewatering apparatus comprises a first vacuum forming shoe and at least one ,vacuum box downstream of the forming shoe. .1 i' i 13A 8. Apparatus for forming a multi-ply paper web as set forth in claim 6, wherein: the turning means (14;14a) comprises a suction roll. 9. Apparatus for forming a multi-ply paper web as set forth in claim 6, wherein: the means (32;48a,48a') for receiving water comprises an auto-slice (33;48a). Apparatus for forming a multi-ply paper web as set forth in claim 6, wherein: the sub-atmospheric dewatering apparatus comprises a first vacuum forming shoe (16a) and at least one vacuum box (17a) downstream of the forming shoe (16a). x^' SU135TITUTE SHMET