Note: Descriptions are shown in the official language in which they were submitted.
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1
s HIGH CALIPER PAPER AND PAPERMAKING
BELT FOR PRODUCING THE SAME
to
FIELD OF THE INVENTION
The present invention is related to papermaking belts useful in papermaking
machines for making low density, soft, absorbent paper products and the paper
products
produced thereby. More particularly, this invention is concerned with
papermakin~ belts
comprising a patterned framework and a reinforcing structure and the high
caliper/low
density paper products produced thereby.
BACKGROUND OF THE INVENTION
2o Cellulosic fibrous webs such as paper are well known in the art. Such
fibrous
webs are in common use today for paper towels. toilet tissue, facial tissue,
napkins and
the like. The large demand for such paper products has created a demand for
improved
versions of the products and the methods of their manufacture.
In order to meet the needs of the consumer, cellulosic fibrcus webs must
exhibit
?a several characteristics. They must have sufficient tensile strength to
prevent the structures
from tearing or shredding durinE; ordinary use or when relatively small
tensile forces are
applied. The cellulosic fibrous webs must be absorbent, so that liquids may be
quickly
absorbed and fully retained by the fibrous structure.
Tensile strength is the ability of the cellulosic fibrous web to retain its
physical
3o integrity during use. Tensile strE:ngth is a function of the basis weight
of the cellulosic
fibrous web.
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Absorbency is the property of the cellulosic fibrous web which allows it to
attract
and retain contacted fluids. Absorbency is influenced by the density of the
cellulosic
fibrous web. If the web is too dense, the interstices between fibers may be
too small and
the rate of absorption may not be great enough for the intended use. If the
interstices are
too large, capillary attraction of contacted fluids is minimized preventing
fluids from
being retained by the cellulosic fibrous web due to surface tension
limitations.
Also, the web should exhibit softness, so that it is tactilely pleasant and
not harsh
during use. Softness is the ability of the cellulosic fibrous web to impart a
particularly
desirable tactile sensation to the user's skin. Softness is universally
proportional to the
to ability of the cellulosic fibrous web to resist deformation in a direction
normal to the
plane of the cellulosic fibrous web.
Caliper is the apparent thickness of a cellulosic fibrous web measured under a
certain mechanical pressure and is a function of basis weight and web
structure. Strength,
absorbency, and softness are influenced by the caliper of the cellulosic
fibrous web.
t > Processes for the manufacturing of paper products generally involve the
preparation of an aqueous slung of cellulosic fibers and subsequent removal of
water
from the slurry while contemporaneously rearranging the fibers to form an
embryonic
web. Various types of machinery can be employed to assist in the dewatering
process. A
typical manufacturing process employs a Fourdrinier wire papermaking machine
where
'o the paper slurry is fed onto a surface of a traveling endless belt where
the initial
dewatering and rearranging of fibers is carried out.
After the initial forming, the paper web is carried through a drying process
on
another fabric referred to as the drying fabric which is in the form of an
endless belt. The
drying process can involve mechanical compaction of the paper web, vacuum
dewatering,
through air drying, and other types of processes. During the drying process,
the
embryonic web takes on a specific pattern or shape caused by the arrangement
and
deflection of cellulosic fibers.
U.S. Patent No. 4,529,480 issued to Trokhan on July 16, 1985 introduced a
paperrnaking belt comprising a foraminous woven member which was surrounded by
3o hardened photosensitive resin framework. The resin framework was provided
with a
plurality of discrete, isolated channels known as deflection conduits. The
papermaking
CA 02344538 2004-10-15
belt used in the process was termed a deflection member because the
papermaking fibers
deflected into conduits and became rearranged therein upon the application of
a fluid
pressure differential. The utilization of the belt in the papertnaking process
provided the
possibility of creating paper having certain desired characteristics of
strength, absorption,
and softness.
The paper produced using the process disclosed in U.S. Patent No. 4,529,480 is
described in U.S. Patent No. 4,637,859 issued to Trokhan ,
The paper is characterized by having two physically distinct regions
distributed
across its surfaces. One region is a continuous network region which has a
relatively high
density and high intrinsic strength. The other region is one which is
comprised of a
plurality of domes which are completely encircled by the network region. The
domes in
the latter region have relatively low densities and relatively low intrinsic
strength
compared to the network region.
The domes are produced as fibers fill the deflection conduits of the
papetmtaking
t~ belt during the papermaking process. The deflection conduits prevent the
fibers
depositinL therein from being compacted as the paper web is compressed during
the
drying process. As a result, the domes are thicker having a lower density and
intrinsic
strength compared to the compacted regions of the web. Consequently, the
caliper of the
paper web is limited by the intrinsic strength of the domes.
2o Once the drying phase of the papermaking process is finished, the
arrangement
and deflection of fibers is complete. However, depending on the type of the
finished
product, paper may go through additional processes such as calendering,
softener
application, and convening. These processes tend to compact the dome regions
of the
paper and reduce the thickness. Thus, producing high caliper finished paper
products
25 having two physically distinct regions requires forming cellulosic fibrous
structures in the
domes having a resistance to mechanical pressure.
As the cellulosic fibrous web is formed, the fibers are predominantly oriented
in
the X-Y plane of the web providing negligible Z-direction structural rigidity.
Once the
fibers oriented in the X-Y plane are compacted by mechanical pressure, the
fibers are
3o pressed together increasing the density of the paper web while decreasing
the thickness.
Orienting fibers in the Z direction of the web, enhances the web's Z-direction
structural
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4
rigidity and its corresponding resistance to mechanical pressure. Accordingly,
maximizing fiber orientation in the Z-direction maximizes caliper.
Deflection conduits provide a means for producing a Z-direction fiber
orientation
by enabling the fibers to deflect along the periphery of the deflection
conduits. The total
fiber deflection is dependent on the size and shape of the deflection conduits
relative to
the fiber length.
Large conduits allow smaller fibers to accumulate in the bottom of the conduit
which in turn limits the deflection of subsequent fibers depositing therein.
Conversely,
small conduits allow large fibers to bridge across the conduit opening with
minimal fiber
1o deflection.
The shape of the conduits also influences fiber deflection. For instance,
deflection
conduits defined by a periphery forming sharp corners or small radii increase
the potential
for fiber bridging which minimizes fiber deflection. See US Patent No.
5,679,2?? issued
to Rasch et al. October ? 1, 1997 for examples of various conduit shapes that
can effect
t < fiber bridging.
Accordingly, the present invention provides a papermaking belt comprising a
continuous network region and a plurality of discrete deflection conduits
which are sized
and shaped to optimize fiber deflection and corresponding Z-direction fiber
orientation.
The invention further provides a paper web comprising an essentially
continuous,
3u essentially macroscopically monoplanar network region and a plurality of
discrete domes
dispersed therethroughout. The domes are sized and shaped to yield optimum
caliper.
SUMMARY' OF THE INVENTION
The present invention is directed to a papermaking belt having a patterned
framework capable of producing a low density/high caliper paper web and the
paper web
produced thereby. The papermaking belt comprises a reinforcing structure
having a
patterned framework disposed thereon. The patterned framework includes a
continuous
network region and a plurality of discrete deflection conduits, wherein the
deflection
conduits are isolated from one another by the continuous network region.
3o The deflection conduits are generally elliptical in shape and sized
relative to a
mean web fiber length, L , such that the mean width, W , of the conduits is L
< W <3 L .
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The deflection conduits have ar,~ aspect ratio ranging from at least about 1.0
to about 2.0
and a minimum radius of curvature wherein the ratio of minimum radius of
curvature to
mean width ranges from at least about 0.29 to about 0.50.
The deflection conduits may be arranged in a hexagonal pattern in order to
a maximize the concentration of c;anduits per unit area while at the same time
minimizing
the area of the continuous network region. The continuous network region
provides a
knuckle area having a width ranging from at least about 0.007 inches to about
0.020
inches.
The paper produced on such papermaking belt comprises an essentially
to macroscopically monoplanar network region and a plurality of discrete domes
dispersed
throughout and isolated from ore another by the continuous network region. The
domes
take on the shape and arrangement of the generally elliptical deflection
conduits
previously described.
BRIEF DESCRIPTION OF THE DRAWING
These and other features, aspects and advantages of the present invention will
become better understood with regard to the following description, appended
claims, and
accompanying drawings where:
'U FIG. 1 is a schematic side elevational view of one embodiment of a
papermaking
machine which uses the papennaking belt of the present invention.
FIG. 2 is a top plan view of a portion of the papermaking belt of the present
invention, showing the framework joined to the reinforcing structure and
having
25 elliptically-shaped paper-side openings of the deflection conduits.
FIG. 3 is a vertical cross-sectional view of a portion of the papermaking belt
shown in FIG. 2 as taken along line 3--3.
3o FIG. 4 is a vertical cross-sectional view of a portion of the papermaking
belt
shown in FIG. 3 depicting fibers bridging the deflection conduit.
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6
FIG. 5 is a vertical cross-sectional view of a portion of the papermaking belt
shown in FIG. 3 depicting fibers collecting in the bottom of the deflection
conduit.
FIG. 6 is a vertical cross-sectional view of a portion of the papermaking belt
shown in FIG. 3 depicting a fiber cantilevered over the deflection conduit
opening to
illustrate fiber defection.
FIG. 7 is a vertical cross-sectional view of a portion of the papermaking belt
to shown in FIG. 3 depicting a fiber bridging the deflection conduit opening
to illustrate
fiber defection.
FIG. 8a & 8b are a top plan views of conduit shapes having tight radii or
sharp
corners making them prone to fiber bridging.
t~
FIG. 9 is a schematic representation of an elliptically shaped conduit having
a
rectilinear periphery.
FIG. 10 is a schematic representation of an elliptically shaped conduit having
a
?o cuwilinear periphery.
FIG. 1 1 is a top plan schematic representation of deflection conduits
arranged in a
hexagonal pattern with major axes oriented parallel to the machine direction
of the belt.
_'s FIG. 12 is a top plan schematic representation of deflection conduits
arranged in a
hexagonal pattern with major axes oriented diagonal to the machine direction
of the belt.
FIG. 13 is a vertical cross-sectional view of a portion of the papermaking
belt
shown in FIG. 3 depicting fibers deflecting into the deflection conduit and
illustrating the
3o relation between the conduit width, the conduit Z-direction height , and
the web stretch.
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7
Figure 14 is a vertical cross-sectional view of a portion of the papermaking
belt
shown in FIG. 3 depicting fibers deflecting into the deflection conduit and
illustrating the
relation between the web deflection angle and the angle forming the
knuckle/conduit
opening interface.
Figure 15 is a top plan schematic representation of a paper web having domes
arranged in a hexagonal pattern.
Figure 16 is a vertical cross-sectional view of a portion of the paper web
shown in
to FIG. 15 as taken along line 16--~16.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
As used herein, the following terms have the following meanings:
f s Machine direction, designated MD, is the direction parallel to the flow of
the paper web
through the papermaking equipment.
Cross machine direction, designated CD, is the direction perpendicular to the
machine
direction in the X-Y plane.
Center of area is a point within the deflection conduit that would coincide
with the center
20 of mass of a thin uniform distribution of matter bounded by the periphery
of the deflection
conduit.
Major axis is the longest axis crossing the center of area of the conduit and
joining two
points along the perimeter of the: conduit.
Minor axis is the shortest axis or width crossing the center of area of the
conduit and
25 joining two points along the perimeter of the conduit.
Aspect Ratio is the ratio of the rnajor axis length to the minor axis length.
The mean width of the conduit is the average length of straight lines drawn
through the
center of area of the conduit and. joining two points on the perimeter
thereof.
Radius of curvature is the instantaneous radius of curvature at a point on a
curve.
3o Curvilinear pertains to curved lines.
Rectilinear pertains to straight lines.
CA 02344538 2004-10-15
8
Z-direction height is the ponion of the resin framework extending from the
paper facing
side of the reinforcing structure.
Mean fiber length is the length weighted average fiber length.
The specification contains a detailed description of (1) the papermaking belt
of the
present invention and (2) the finished paper product of the present invention.
( 1 ) The PapetmakinQ Belt
In the representative papermaking machine schematically illustrated in FIG. 1,
the
1o papermaking belt of the present invention takes the form of an endless
belt, papermaking
belt 10. The papermaking belt 10 has a paper-contacting side 11 and a backside
12
opposite the paper-contacting side 11. The papermaking belt 10 carries a pager
web (or
"rber web") in various stages of its formation (an embryonic web 27 and an
intermediate
~~eb 391. Processes of forming embryonic webs are described in many
references, such
as U.S. Pat. No. 3.301,746, issued to Sanford and Sisson on Jan. 31, 1974, and
U.S. Pat.
l\'o. 3.994.?71, issued to Morgan and Rich on Nov. 30, 1976.
The papermaking belt 10 travels in the direction indicated by directional
arrow
B around the return rolls 19a and 19b, impression nip roll 20, return rolls
19c, 19d, 19e,
19f, and emulsion distributing roll 21. The loop around which the papermaking
belt 10
'ti travels includes a means for applying a fluid pressure differential to the
embryonic web
~'7, such as vacuum pickup shoe (PUS) 24a and mufti-slot vacuum box 24. In
FIG. l, the
papetmaking belt 10 also travels around a predryer such as blow-through dryer
26, and
passes between a nip funned by the impression nip roll 20 and a Yankee drying
drum 28.
Ahhough the preferred embodiment of the papermaking belt of the present
?: invention is i~ the form of an endless belt 10, it can be incorporated into
numerous other
forms which include, for instance, stationary plates for use in making
handsheets or
rotating drums for use with other types of continuous process. Regardless of
the physical
form which the papermaking belt 10 takes for the execution of the claimed
invention, it
generally has cenain physical characteristics set forth below. The papermaking
belt 10 of
3o the present invention may be made according to commonly assigned U.S. Pat.
No.
CA 02344538 2004-10-15
9
5,334,289, issued in the name of Trokhan et al.
As shown in Figure 2, the belt 10 according to the present invention comprises
two primary components: a framework 30 and a reinforcing structure 32. The
framework
30 preferably comprises a cured polymeric photosensitive resin. The framework
30 and
belt 10 have a first surface 1 I which defines the paper contacting side I 1
of the belt 10
and an opposed second surface 12 oriented towards the papermaking machine on
which
the belt 10 is used.
As used herein, X, Y and Z directions are orientations relating to the
papermaking
t o belt 10 of the present invention (or paper web 27 disposed on the belt) in
a Canesian
coordinate system. The papermaking belt 10 according to the present invernion
is
macroscopically monoplanar. The plane of the papermaking belt 10 defines its X-
Y
directions. Perpendicular to the X-Y directions and the plane of the
papet~rrtaking belt 10
is the Z-direction of the belt 10. Likewise, the web 27 according to the
present invention
can be thought of as macroscopically monoplanar and lying in an X-Y plane.
Perpendicular to the X-Y directions and the plane of the web 27 is the Z-
direction of the
web ?7.
Preferably the framework 30 defines a predetermined pattern and provides a
knuckle area 36 which imprints a like pattern onto the web 37 of the present
invention. A
?o panicularly preferred pattern for the framev~~ork 30 is an essentially
continuous network.
If the preferred essentially continuous net~~ork pattern is selected for the
framework 30,
discrete deflection conduits 34 will extend between the first surface 11 and
the second
surface 12 of the belt 10. The essentially cominuous network surrounds and
defines the
deflection conduits 34.
25 The framework 30 prints a pattern corresponding to that of the framework 30
onto
the web 27 carried thereon. Imprinting occurs anytime the belt 10 and web 27
pass
between two rigid surfaces having a clearance sufficient to cause imprinting.
This
generally occurs in a nip between two rolls and most commonly occurs when the
belt 10
transfers the paper to a Yankee drying drum 28. imprinting is caused by
compression of
30 the framework 30 against the paper 27 at the pressure roll 20.
CA 02344538 2004-10-15
l0
The first surface 11 of the belt 10 contacts the web 27 carried thereon.
During
papermaking, the first surface of the belt 10 may imprint a pattern onto the
web 27
corresponding to the pattern of the framework 30.
The second surface 12 of the belt 10 is the machine contacting surface of the
belt
s 10. The second surface may be made with a backside network having
passageways
therein which are distinct from the deflection conduits 34. The passageways
provide
irregularities in the texture of the backside of the second surface of the
belt 10. The
passageways allow for air leakage in the X-Y plane of the bell 10, which
leakage does not
necessarily flow in the Z-direction through the deflection conduits 34 of the
belt 10. Belts
to 10 incorporating such backside texturing may be made according to any of
commonly
assigned U.S. Patents: 5,098,522 issued March 24, 1992 to Smurkoski et al.;
5,364,504
issued November 15, 1994 to Smurkoski et al.; and 5,260,171 issued November 9,
1993
to Smurkoski et al.
The second primary component of the belt 10 according to the present invention
is
t; the reinforcing structure 3?. The reinforcing structure 32, like the
framework 30, has a
first or paper facing surface l3 and a second or machine facing surface 12
opposite the
paper facing surface. The reinforcing structure 32 is primarily disposed
between the
opposed surfaces of the belt 10 and may have a surface coincident the backside
of the belt
10. The reinforcing structure 32 provides support for the framework 30. The
reinforcing
.o component is tyically woven. as is well known in the art. The portions of
the reinforcing
structure 3? registered with the deflection conduits 34 prevent fibers used in
papennaking
from passing completely through the deflection conduits 34 and thereby reduces
the
occurrences of pinholes. if one does not wish to use a woven fabric for the
reinforcing
structure 32, a nonwoven element, screen, net, or a plate having a plurality
of holes
2s therethrough may provide adequate strength and support for the framework 30
of the
present inventron.
As shown in Fies. 3, the framework 30 is joined to the reinforcing structure
32.
The framework 30 extends outwardly from the paper-facing side 13 of the
reinforcing
structure 32. The reinforcing structure 3? strengthens the resin framework 30
and has
3o suitable projected open area to allow the vacuum dewatering machinery
employed in the
papermaking process to perform adequately its function of removing water from
the
CA 02344538 2004-10-15
11
embryonic web 27, and to permit water removed from the embryonic web 27 to
pass
through the papermaking belt 10.
The belt 10 according to the present invention may be made according to any of
commonly assigned U.S. Patents: 4,514,345, issued April 30, 1985 to Johnson et
al.;
4,528,239, issued 3uly 9, 1985 to Trokhan; 5,098,522, issued March 24, 1992;
5.260,171.
issued Nov. 9, 1993 to Smurkoski et al.; 5,275,700, issued Jan. 4, 1994 to
Trokhan;
5,328,565, issued July 12, 1994 to Rasch et al.; 5,334,289, issued Aug. 2,
1994 to
Trokhan et al.; 5,431,786, issued July 1 I; 1995 to Rasch et al.; 5,496,624,
issued March 5,
1996 to Stelljes, Jr. et al.; 5,500,277, issued March 19, 1996 to Trokhan et
al.; 5,514,523,
to issued May 7, 1996 to Trokhan et al.; 5,554,467, issued Sept. 10, 1996, to
Trokhan et al.;
5,566,724, issued Oct. 22, 1996 to Trokhan et al.; 5.624,790, issued April 29,
1997 to
Trokhan et al.; 5,628,876 issued May 13, 1997 to Ayers et al.; 5,679,?2 issued
Oct..2l,
1997 to Rasch et al.; and 5,714,041 issued Feb. 3, 1998 to Ayers et al..
1: The ability to produce a paper web having a panicular thickness is a
function of
the caliper of the web. Caliper is the apparent thickness of a cellulosic
fibrous web
measured under a cenain mechanical pressure. Caliper is a function of web
basis v~~eieht
and web structure. Basis -eight is the weight in pounds of 3000 square feet of
paper.
Web structure penains to orientation and density of fibers making up the web
27.
?o Fibers making up the web ?7 are typically oriented in the X-Y plane and
provide
minimal structural support in the Z-direction. Thus, as the web 27 is
compressed by the
patterned framework 30, the web 27 is compacted creating a patterned, high
density
region that is reduced in thickness. Conversely, portions of the web 27
covering the
deflection conduits 34 are not compacted and as a result, thicker. low density
regions are
25 produced.
The low density regions, referred to as domes, give the web 27 an apparent
thickness. Since the fibers making up a typical dome are predominently
oriented in the X-
Y plane of the web 27, the fibers provide negligible Z-direction support.
Consequently,
the domes are highly susceptible to being deformed and reduced in thickness
during
3o subsequent papermaking operations. Thus, the caliper of the web 27 is
generally limited
by the domes' ability to v~~ithstand mechanical pressure.
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However, deflection conduits 34 provide a means for deflecting fibers in the Z-
direction along the periphery 38. Fiber deflection produces a fiber
orientation which
includes a Z-direction component. Such fiber orientation not only creates an
apparent
web thickness but also provides certain amount of structural rigidity in the Z-
direction
which assists the web 27 in sustaining its thickness throughout the
papermaking process.
Accordingly, for the present invention, deflection conduits 34 are sized and
shaped to
maximize fiber deflection along the peripheries 38.
Water removal from the embryonic web 27 begins as the fibers ~0 are deflected
into the deflection conduits 34. The water removal results in a decrease in
fiber mobility
to which tends to fix the fibers in place after they have been deflected and
rearranged.
Deflection of the fibers into the deflection conduits 34 can be induced by,
the application
of differential fluid pressure to the embryonic web 27. One preferred method
of applying
differential pressure is by exposing the embryonic web 27 to a vacuum through
deflection
conduits 34. In FIG. 1 the preferred method is illustrated by the use of pick-
up shoe 24.
t ~ Without being limited by theory, it is believed that the rearrangement of
the fibers
in the embryonic web 27 relative to the deflection conduits 34 can generally
take one of
two models, dependent on a number of factors including fiber length. As
schematically
shown in FIG. 4, the ends of longer fibers SO can be restrained on the top of
the knuckles
36 allowing the middle parts of fibers 50 to be bent into the conduit 34
without being
_'o fully deflected. Thus, "bridging" of the deflection conduit 34 occurs.
Alternatively, as
shown in FIG. 5, fibers SO (predominantly, the shorter ones) can actually be
fully
deposited into the conduit 34 with little, if any, deflection creating a pile
of fibers SO
therein and minimizing the deflection of subsequent fibers depositing in and
around the
conduit 34.
25 Fiber deflection is function of the web's resistance to bending. The higher
the
web bending stiffness the greater the resistance to deflection. The bending
stiffness of a
web is dominated by two factors: ( 1 ) the bending stiffness of individual
fibers; and (2)
fiber-to-fiber bonding strength. However, the web at the pick-up shoe 24a is
wet and the
fiber-to-fiber bonds are not well established due to the presence of large
amounts of water
3o in the web. Thus, the dominant factor is the individual fiber stiffness.
The stiffer the
fiber the smaller the deflection.
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13
Although fiber deflection is dependent on the inherent stiffness of the fibers
50,
the magnitude of the deflection i.s largely determined by whether or not the
fibers 50 are
long enough to span the width of a conduit 34. Figures 6 and 7 show two
possible
scenarios of fiber deflection. In Figure 6, the fiber SO is fixed at point A
and cantilevered
over the opening of the conduit :34. When this fiber 50 is subjected to a
uniform Ioad,
such as a vacuum, the result is a: high bending moment at point A and a
deflection at
point B defined by
fH = F L3/8EI ( 1;1
where,
fa - deflection at point B;
F - Force ~~niformly distributed over the length of the fiber;
L - Length of a fiber from the points) of support;
E - Modulus of Elasticity;
5 I - momen.t of inertia
In Figure 7, the fiber segment SO is longer than conduit width, resulting in
two
fixed points A and B. If the fiber segment 50 experiences the same vacuum, the
supporting forces at A and B create offsetting bending moments resulting in a
fiber
?'o deflection at point C defined by
f~ = F L3/384EI (2)
where fc is the fiber deflection at point C
Assuming that the parameters F, L, E, and I are the same for fibers shown in
Figures 6 and 7, it is evident that the fiber deflection fB is 48 times larger
than the fiber
deflection f~.
fa = 48 f~ (3)
..o Accordingly, fiber deflection can be enhanced by sizing the deflection
conduits 34
to minimize the occurrences of fiber bridging. However, the size of the
conduit is also
CA 02344538 2001-03-16
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14
limited by the number of small fibers in the furnish capable of accumulating
in the
conduits 34 and consequently, inhibiting the larger fibers from deflecting
therein.
Furnish normally includes both hardwood and softwood. An example of
hardwood fiber is Eucalyptus (EUC) while an example of softwood fiber is
Northern
Softwood Kraft (NSK). An example of a furnish comprises 30% by weight softwood
and
70% by weight hardwood. Since the average fiber length of softwood is about
three times
the average fiber length of hardwood, sizing the deflection conduits relative
to the average
softwood fiber length results in conduits that are highly susceptible to the
accumulation of
shorter hardwood fibers, thereby limiting the deflection of the longer fibers.
Thus, it is
to preferred that the conduit width, W, be sized relative to the mean fiber
length of the
furnish, L , where
W >_ L (4).
t ~ For the present invention, the mean fiber length is the length weighted
average
fiber length determined by
~n L.
L = -. (5)
~nrL~
where
L, = Average lengths of fibers in class i.
'u n, = Number of fibers measured in class i.
The length weighted average fiber length for the present invention is about
0.043 inches.
As shown in Figures 9 and 10, the conduits 34 may take on a variety of
different
shapes having either variable or constant widths. Conduit shapes having
variable widths
?5 are defined in terms of the major axis 40, the minor axis 42, and the mean
width 46. As
defined, the major axis 40 is the longest axis or width crossing the center of
area of the
conduit, the minor axis 42 is the shortest width crossing the center of area
of the conduit,
and the mean width 46 is the average width crossing center of area of the
conduit.
The mean width 46 is determined by first measuring the length of a line drawn
3o through the center of area in the CD joining two points on the perimeter of
the conduit.
The lengths of similar lines oriented at 09 angular increments with respect to
the CD
CA 02344538 2001-03-16
WO 00/19014 PCT/US99/21877
(such as 1 S degrees or less ranging from 0° to 165° where
0° represents the CD) are
measured and averaged to determine the mean width.
Since fiber bridging is most likely to occur along the minor axis 42, it is
preferred
to size the minimum width of the conduit 34 relative to the mean fiber length,
L , such
5 that
W ;~ ? L (6)
Therefore, for the present invention, the preferred min conduit width is at
least about
0.043 inches.
Since the accumulation of~smaller fibers can occur along both the major and
minor
to axes 40, 42 of the conduit, it is difficult to define an upper limit for
either or both axes 40,
42 resulting in minimal fiber accumulation and maximum fiber deflection.
However, for
the present invention, it has been found that sizing the conduits 34 such that
the mean
width 46 ranges between the mean fiber length L and three times the mean fiber
length,
3 L, results in maximum caliper generation.
L<W <3L
Accordingly, for the present invc:mion, it is preferred to size the conduits
such that the
mean conduit width ranges from about 0.043 inches to about 0.129 inches.
The web 27 is approximately a two-dimensional fiber network. An ideal fiber
network comprises a random distribution of fibers where the fiber orientation
does not
:!0 favor a particular direction. For such an ideal network, the mean fiber
length, L, is same
in all directions.
However fiber networks .are typically arranged in the web having a fiber
orientation that is biased in a particular direction. For such biased
networks, the mean
fiber length will vary relative to angular orientation in the X-Y plane of the
web 27.
~;5 Theoretically, such mean fiber length is designated, LB , where
l~
L a = n ~;m Le; (7)
and
B - the angular orientation in the X-Y plane relative to CD
Ld~ = Component Lengths of fibers at angular orientation, B, in X-Y plane.
CA 02344538 2001-03-16
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16
Le = Mean fiber length at angular orientation, 8, in X-Y plane.
n = Number of fibers measured at angular orientation, B, in X-Y plane.
For the present invention, the fibers 50 making up the two dimensional fiber
network are predominantly oriented in the machine direction MD. Consequently,
the
mean fiber length in the machine direction is greater than the mean fiber
length in the
cross machine direction CD.
LAID ~ LCD
From equation 4, it follows that
w'A1D ~ WCD l9)
Thus, as show in Figure 11, it is preferred to orient the conduits 34 such
that the major
axes 40 run parallel to the machine direction of the belt. However, since the
fiber
orientation typically favors the MD, one skilled in the art would appreciate
that the major
axis 40 may also be oriented at a diagonal, where, as illustrated in Figure
12, diagonal is
1 ~ defined as an angle 54 oriented 22.5° ~ 22.5° relative to
MD.
The shape of the conduit is defined in terms of an aspect ratio, R,, , which
is
defined as the ratio of the major axis 40 to the minor axis 42. For maximum
deflection of
fibers, it follows from equation (8) & (9) that the aspect ratio, R.a, be
defined as
R _ LAIn -_ wvD (10)
A_
L cD wcD
However, it is not practical to measure the mean fiber length in a particular
direction of
the web in the X-Y plane for a web condition just prior to the fibers being
deflected into
the deflection conduits 34. Therefore, the inherent physical properties of the
web which
are a function of fiber length need to be considered in order to determine a
preferred
2s aspect ratio, R,a, for a conduit shape providing maximum fiber deflection.
The physical properties of a paper web 27 are largely influenced by the
orientation
of fibers in the X-Y plane of the web 27. For instance, a web 27 having a
fiber orientation
which favors MD, has a higher tensile strength in MD than in CD, a higher
stretch in CD
than in MD, and a higher bending stiffness in MD than in CD.
CA 02344538 2001-03-16
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17
In addition to fiber orientation, the web tensile strength is proportional to
the
corresponding lengths of fibers oriented in a particular direction in the X-Y
plane.
Therefore, the web tensile strenlnh in the MD and CD is proportional to the
mean fiber
lengths in the MD and CD.
T MD,CD (Tensile Strength) x L MD.CD (I I)
Accordingly, from equation 8, it follows that
TMD ~ TCD (I~)
Furthermore, by substituting T"m for L°m in equation 10, the aspect
ratio, R~, ,
TcD Lco
defining the conduit shape is expressed as
R _ Tim __ W.,m ( 13 )
,-
Tco I';'co
The tensile strengths of the web 27 in MD and CD were measured using a
ns Thwing-Albert Intelect II Standard Tensile Tester manufactured by Thwing-
Albert
instrument Co. of Philadelphia, PA. Consequently, the preferred conduit shape
providing
optimum fiber deflection and corresponding caliper generation has an aspect
ratio ranging
from 1 to about 2. A more preferred shape has an aspect ratio ranging from
about 1.3 to
1.7. A most preferred shape has an aspect ratio ranging from 1.4 to 1.6.
ao The shape of the deflection conduit 34 is not only significant for
minimizing fiber
bridging across the width of the conduit but also for minimizing fiber
bridging along the
perimeter 38 of the conduit walls.. Conduit walls forming tight radii or sharp
corners
provide additional locations for fiber bridging. Examples of unfavorable
conduit shapes
for this purpose are shown in Figures Sa & 8b.
~5 As shown in Figures 9 and 10, a preferred conduit shape for the present
invention
is one that is generally elliptical which includes, but is not limited to,
circles, ovals, and
polygons of six or more sides. Figure 9 illustrates an elliptically shaped
conduit having a
rectilinear periphery comprising individual wall segments 44. For such conduit
shape,
CA 02344538 2001-03-16
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18
fiber bridging along the periphery is minimized by providing an included angle
39
between adjacent wall segments which is at least about 120 degrees.
Figure 10 illustrates an elliptically shaped conduit having a curvilinear
periphery
concave toward the center of the conduit. The curvilinear periphery includes a
minimum
radius of curvature 48. Similarly, fiber bridging along the periphery is
minimized by
limiting the shape such that the ratio of the minimum radius of curvature 48
to the mean
conduit width is at least 0.29 and no more than 0.50.
0.29 < r'°W'°~ <_ 0.50 (14)
to
As illustrated in Figure 13, ideally, the web 27 on top of the knuckle 36
experiences zero stretch, while above the conduits 34 the web 27 deflects
fully therein
expenenc~ng an average stretch, s ,
where
20B
E~ W (15)
and
- Average stretch
OB = is the Z-direction height
VV - is the conduit width.
Critical stretch determines when the web 27 will break. If the stretch is
greater
than the critical stretch in the web 27, the network will be broken causing
pinholes in the
web. The critical stretch in the web ?7 depends on the network properties such
as fiber
length and fiber orientation. The fiber-to-fiber bonding does not play a role
in critical
stretch because the web at the pick up shoe is wet and the fiber-to-fiber
bonds are not well
established.
The total distance the web 27 deflects into the conduits 34 is dependent on
the Z-
direction height 60. Since the critical stretch of the web is directly
proportional to OB 60
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19
it follows that OB is limited by the critical stretch of the web 27.
Accordingly, from
equation 15 a reasonable range for OB 60 is expressed as
OB < E~.r~rm W ~ 16~
2
The critical stretch E~.",;~ar is a complicated function of fiber length,
fiber
orientation and basis weight. Qualitatively, the critical stretch increases
when fiber length
and/or basis weight increases. For the present invention, the preferred Z-
direction height
60 for maximum web deflection ranges from at least about 0.005 inches to about
0.039
inches.
The total deflection a web will undergo in the deflection conduits is also
largely
determined by the angle formins; the knuckle/conduit interface of the
patterned
framework. The web deflection angle 62 is defined as the angle of the web at
the
knuckle/conduit interface with respect to the Z-direction. An illustration of
the web
deflection is shown in Figure 14. Fibers 50 accumulating at the
knuckle/conduit interface
are oriented with a Z-direction component which enables them to provide the
support
structure capable of withstanding external compressive forces. Fibers oriented
parallel to
the Z-direction at the knuckle/conduit interface provide maximum support.
However,
since a web 27 is not infinitely flexible it is not capable of completely
following the
contour of the conduit 34. In addition, due to manufacturing limitations, the
walls of the
deflection conduits are sloped forming a resin angle 64 at the knuckle/conduit
interface.
The resin angle 64 further limits the web deflection since the deflection
angle 62 cannot
be less than the resin angle 64. hor the presem invention, the resin angle is
preferably
sloped between S degrees and 10 degrees. The web deflection angle typically
ranges from
:zs about 20 degrees to about 50 del;rees.
Since the extemai force applied to paper during the various processes are
reacted
by the supporting force from the fibers in the knuckle/pocket interface, the
greater the
number of fibers in this region the higher the supporting force and
corresponding caliper.
The number of fibers 50 in the transition interface can be optimized by
maximizing the
3o total perimeter 38 of the interface. This is equivalent to maximizing the
number of
CA 02344538 2001-03-16
WO 00/19014 PCT/US99/21877
deflection conduits 34 per unit area or to minimizing the percentage of
knuckle area 36.
Theoretically, conduits 34 can be packed to an extreme. However, as shown in
Figures 1 1
and 12 the knuckles 36 separating conduits 34 are required to have a minimum
width 52
in order to enable the resin to securely attach to the secondary 32. For the
present
invention, the preferred minimum knuckle width 52 ranges from at least about
0.007
inches to about 0.020 inches.
Furthermore, the number of conduits per unit area can be maximized by packing
conduits 34 into more efficient arrangements. A preferred arrangement of
conduits 34 is
one forming a hexagonal pattern as shown in Figures 11 and 12.
The Paper
The paper 80 of the present invention has two primary regions. The first
region
comprises an imprinted region 82 which is imprinted against the framework 30
of the belt
t ~ 1 U. The imprinted region 82 preferably comprises an essentially
continuous network.
The continuous network 82 of the first region of the paper 80 is made on the
essentially
continuous framework 30 of the belt 10 and will generally correspond thereto
in geometry
and be disposed very closely thereto in position during papermaking.
The second region of the paper 80 comprises a plurality of domes 84 dispersed
~o throughout the imprinted network region 82. The domes 84 generally
correspond in
geometry, and during papermaking, in position to the deflection conduits 34 in
the belt 10.
By conforming to the deflection conduits 34 during the papermaking process,
the fibers in
the domes 84 are deflected in the Z-direction between the paper facing surface
of the
framework 30 and the paper facing surface of the reinforcing structure 32. As
a result, the
'S domes 84 protrude outwardly from the essentially continuous network region
82 of the
paper 80. The domes 84 are preferably discrete, isolated one from another by
the
continuous network region 82.
Without being bound by theory, it is believed the domes 84 and essentially
continuous network regions 82 of the paper 80 may have generally equivalent
basis
weights. By deflecting the domes 84 into the deflection conduits 34, the
density of the
domes 84 is decreased relative to the density of the essentially continuous
network region
CA 02344538 2004-10-15
21
82. Moreover, the essentially continuous network region 82 (or other pattern
as may be
selected) may later be imprinted as. for example, against a Yankee dr~~ing
drum. Such
imprinting increases the density of the essentially continuous network region
82 relative
to that of the domes 84. The resulting paper 80 may be later embossed as is
well known
in the art.
The paper 80 according to the present invention may be made according to any
of
commonly assigned U.S. Patents: 4,529,480, issued July 16, 1985 to Trokhan;
4,637,859,
issued Jan. 20, 1987 to Trokhan; 5,364,504, issued Nov. 15, 1994 to Smurkoski
et al.; and
5,529,664, issued June 25, 1996 to Trol:han et al. and 5,679,222 issued Oct.
21, 1997 to
Rasch et al..
The shapes. of the domes 84 in the X-Y plane include, but are not limited to,
circles, ovals, and polygons of six or more sides. Pmfcrably. ihc domes S.~
arc ~zcnciallv
elliptical in shay romprisin~~ either cuwilincar or rectilinear peripheries
8h. The
cun~ilinear periphery 86 comprises a minimum radius of cun~ature such that the
ratio of
t ~ the minimum radius of cun~ature to mean width of the dome ranges from at
least about
0.29 to about 0.50. The rectilinear periphery 86 may comprise of a number of
wail
segments "here the included angle between adjacent wall segments is at least
about 120
deerees.
Providing a paper 80 having high caliper requires maximizing the number Z-
2o direction fibers per unit area in the web. The majority of the Z-direction
fibers are
oriented along the periphery 86 of the domes 84 where fiber deflection occurs.
Thus, Z-
direction fiber orientation and corresponding caliper of the paper web is
largely dependent
on the number of domes per unit area.
As shown in Figure 15, the number of domes 84 per unit area is maximized by
2s minimizing the distance between adjacent domes which is accomplished by
arranging the
domes into efficient patterns. For the present invention, the preferred
minimum distance
88 between domes 84 is at least about 0.007 inches and no more than 0.020
inches. The
preferred arrangement of the domes 84 is one forming a hexagonal pattern.
The number of domes 84 per unit area of the paper 80 is largely dependent on
the
3o size and shape of the deflection conduits previously described. For the
present invention,
the preferred mean width of the domes 84 is at least about 0.043 inches and
less than
CA 02344538 2001-03-16
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22
about 0.129 inches. The preferred generally elliptical shape for the domes is
one having
an aspect ratio ranging from 1 to about 2. A more preferred generally
elliptical shape has
an aspect ratio ranging from about 1.3 to 1.7. A most preferred generally
elliptical shape
has an aspect ratio ranging from 1.4 to 1.6.
The caliper of the paper web is typically measured under a pressure of 95
grams
per square inch using a round presser foot having a diameter of 2 inches,
after a dwell
time of 3 seconds. The caliper can be measured using a Thwing-Albert Thickness
Tester
Model 89-100, manufactured by the Thwing-Albert Instrument Company of
Philadelphia,
Pennsylvania. The caliper is measured under TAPPI temperature and humidity
I o conditions.
For the present invention, the caliper was measured on a paper web comprising
two plies. The caliper of the two ply. paper web is preferably between 20 mils
and 40
mils. More preferably the caliper of the two ply paper web is between 38 mils
and 46
mils. Most preferably the caliper of the two ply paper web is between 25 mils
and 30
mils.
Vv'hiie particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention.
It is imended to cover in the appended claims all such changes and
modifications that are
'u within the scope of the invention.
