Note: Descriptions are shown in the official language in which they were submitted.
WO92/01111 PCT/EP91/01255
2~37013
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, multi-
ply 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 efected 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
~0 surface which has better ply-bonding characteristics.
In prior apparatus, both sides of the outer
ply were dewatered positlvely, 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
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WO92/01111 2 0 ~ 6 013 PCT/EP91/01255
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, deficien-
cies and characteristics of the outer ply in a ply-
bonded 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 multi-
ply 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 we~. 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,
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WO92/01111 20~ 3 PCT/EPgl/0125
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 hàving improved ply-
bond characteristics.
Another object of this invention is 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
advantages 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 turn1ng roll.
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W O 92/01111 2 0 8 7 ~ 13 PC~r/EP91/01255 -
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.
Figure 3 is a side-elevation view, similar
to that shown in Figure l, but including a forming shoe
within the lower top ply forming wire upstream of where
the second, or upper, top ply forming wire comes into-
co-running engagement with the web over the first
forming wire.
10 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
10 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 ~ox 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
va~uum chamber seal 28.
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WO92/01111 2 ~ g ~ 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 save-
all 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, posslbly, the type of
forming wires- used~ the headbox sllce nozzle may -be
dlrected sllghtly toward one or the other of the formlng
wires.
Beneath the top ply former, which is the
designation for the apparatus ~ust descrlbed, 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 thls 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 40.
A source of sub-atmospheric a r pressure 42
is optionally linked to the foll box 16 to provlde
vacuum pressure to the lower slde of the web being
formed between the co-running forming wires lO, 20 over
the foil blades 18 in the foil box. Water is removed
from the lnner side of the looped second forming wire by
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WO92/01ll1 ~ Q 13 PCT/EP91/01255
a drain 44, and water is removed from within the looped
first forming wire by drain 46.
In the various configurations shown in
Figures 1-3, 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 lOa 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 20a,
is a first auto-slice 48a following the foil box, and a
second auto-slice 48a' intermediate the two vacuum boxes
17a, 17a'. ~oth auto-slices have a leading lip 33a, 33a' -
which is mounted in closely spaced ad~acency, or non-
pressure 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 lOa, 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
surface and into co-running engagement with the base ply
web W~ being carried on base ply forming wire 36a.
In the embodiment shown in Figure 3, a blade
forming shoe 50 has been mounted within the first
forming wire lOb upstream of the foil box 16b. The
second forming wire 20b is brought into engagement with
the we~ oveF the first forming wire lOb just prior to
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W092/01111 2d~ ~ ~13 PCT/EP91/01255
the beginning of their co-running travel over the foil
box 16b. The first forming wire is guided onto the
leading edge of foil box 16b by a guide roll 12b. The
headbox 34b discharges an aqueous slurry of stock onto
the first forming wire over the surface of guide roll
12b. As in the embodiment shown in Figure 2, the second
vacuum box 17b effects the transfer of the newly formed
top ply web WT onto the first forming wire which is
directed lnto ply-bonding contact with the base ply web
WB to form the multi-ply web W in a manner similar to
that described in con~unction with Figure 2.
While the cross-sectional profile of the
- first forming wire contour-over blade forming shoe 50,
or forming board, may be substantially planar, or
concave downward, the overall contour of the forming
zone extending from before the leading edge of the
forming shoe 50 to the trailing edge of vacuum box 17b'
is concave downwardly/convex upwardly as shown which is
similar to the configurations shown in Figures 1 and 2.
The vacuum pressure beneath forming wire lOb is zero or
low, regardless of how it is induced, so as to promote
better formation, and improved web propertles, such as
directional strength.
In the embodiments shown in Figure 2 and 3,
foil boxes 16a, 16b and vacuum boxes 17a, 17a' and 17b'
are connected to a source of sub-atmospheric air
pressure whlch are designated generally as 52a, 52a',
52b and 52b'. The profile contours of the wire-
contactlng surfaces of the foil boxes and vacuum boxes
is concave downwardly/convex upwardly. While the surface
of the foil boxes is defined by a series of spaced foils
whlch 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
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WO 92/Ot111 ~ ~ 8 7 ~ 1 3 PCT/EP9l/01255 --
drilled through their covers, which permit the
application 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, lOa, lOb, water is
urged from the stock slurry outwardly and downwardly
through the lower top ply web WT to within the looped
first forming wire. Due to the tension--of the second-
forming wire 10, lOa, lOb over the stock slurry over the
first forming wire water is expressed outwardly through
the top ply web W~ being formed between the first and
second forming wires and into the save-all 32, or auto-
slices 4~a, 48a', 48b, 48b'. The water is also urged
outwardly through the upper surface of the top ply web
by centrifugal force and the force of yravity in the
slightly down-turning portions of co-running forming
wlre travel in the generally horizontally disposed,
concave downwardly forming zone. The blades in the foil
box 16, 16a, 16b, operating with or without sub-
atmospheric vacuum pressure, urge the water gently towithin the foil boxes. Downstream, at a point where the
web is more dewatered, higher'sub-atmospheric vacuum
pressure is applied to vacuum boxes 17a', 17b' to
further dewater the top ply web through the lower
surface thereof.
In the embodiment shown in Figure 3, the
; headbox discharges the stock slurry onto the first
forming wire and additional dewatering through the lower
surface of the top ply web is effected by the blades 51
contacting the inner surface of the first forming wire
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` wo92/01111 2~ t ,~ PCT/EP91/01255
over the forming shoe 50. This is substantially similar
to the water removal operation at the beginning of a
conventional fourdrinier.
In all of the embodiments, the application
5 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
lO the top ply web over the first forming wire are removed
from the web, a relatively large proportion of the fines
lnitially near the upper surface of the top ply web
- ad~acent the second forming --wire---remain in the web
during the dewatering effected by the sub-atmospheric
l5 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
20 through the second forming wire. In other words, the
only forces urging water out of the upper surface of the
s top ply web are centrifugal f,orce, forming wire tension
and, in the slightly downwardly extending portion of
forming wire travel in the substantially horizontally
25 disposed 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
30 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
35 surface of one, or both, of the webs at their interface,
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WO92/01111 ~ PCT/EP91/01255 _
ply-bonding between the top ply web WT and the base ply
web WB is promoted by this invention. This allows ply-
bonding to be achieved at lower web moisture levels and
faster machine speeds, or some combination of both.
S 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 hi~her 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 without departing from
the spirit of the invention snd scope of the claims. For
example, the throat can extend from upstream of the
;, place where the top ply forming wires are gulded 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 con~unction
wlth 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, sh-et and paper include the term board.
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