Note: Descriptions are shown in the official language in which they were submitted.
CA 02425141 2003-04-22
PAPER HAVING IMPROVED PINHOLE CHARACTERISTICS AND
PAPERMAKING BELT FOR MAKING THE SAME
io FIELD OF THE INVENTION
The present invention is related to papermaking belts useful in paperrnaking
machines for making strong, soft. absorbent paper products and the paper
products
produces thereby. More particularly, this invention is concerned with
papermaking
belts comprised of a resinous framework and a reinforcing structure and the
multi
~5 density paper products produced thereby.
BACKGROUND OF THE INVENTION
Paper products are used for a variety of purposes. Paper towels, facial
tissues.
toilet tissues, and the like are in constant use in modern industrialized
societies. The
30 large demand for such pager products has created a demand for improved
versions
of the products. if the paper products such as paper towels, facial tissues,
toilet
tissues. and the like are to perform their intended tasks and to find wide
acceptance.
they must possess certain physical characteristics. Among the more important
of
these characteristics are suength, softness, and absorbency.
Strength is the ability of a paper web to retain its physical integrity during
use.
Softness is the pleasing tactile sensation consumers perceive when they use
the paper for its intended purposes.
35
Absorbency is the characteristic of the paper that allows the paper to take up
and retain fluids, particularly water and aqueous solutions and suspensions.
Important not only is the absolute quantity of fluid a given amount of paper
will
hold. but also the rate at which the paper will absorb the fluid.
Through air dried paper webs are made as described in U.S. Pat. 4,~ 1 x,345
issued to Johnson et al on Apr. 30, 1985: U.S. Pat. 4.528,239 issued to
Trokhan on
CA 02425141 2003-04-22
2
July 9, 1985; and U.S. Pat. 5,334,289 issued to Trokhan et al on Aug. 2, 1994 -
- all
three patents are assigned to The Procter and Gamble Company.
Paper produced by through air drying is disclosed in U.S. Pat. No. 4,529,480
and U.S. Pat. No. 4,637,859, both issued in the name of Trokhan. The paper of
these
patents is characterized by having two physically distinct regions: a
continuous
network region having a relatively high density and a region comprised of a
plurality
of domes dispersed throughout the whole of the network region. The domes are
of
relatively low density and relatively low intrinsic strength compared to the
network
region.
Generally, the papermaking process includes several steps. An aqueous
dispersion of the papermaking fibers is formed into an embryonic web on a
foraminous member, such as a Fourdrinier wire. This embryonic web is
associated
with a deflection member having a macroscopically monoplanar, continuous,
patterned non-random network surface which defines within the deflection
member a
1 S plurality of discrete, isolated deflection conduits. The papermaking
fibers in the
embryonic web are deflected into the deflection conduits and water is removed
through the deflection conduits to form an intermediate web. The intermediate
web is
dried and foreshortened by creping. The creping is a process of the removal of
the
dried intermediate web from the surface (usually, also drying surface, such as
the
surface of a Yankee dryer) with a doctor blade to form a finished paper web.
Deflection of the fibers into the deflection conduits can be induced by, for
example, the application of differential fluid pressure to the embryonic paper
web.
One preferred method of applying differential pressure is by exposing the
embryonic
web to a vacuum through the deflection conduits. As a result of a sudden
application
of the vacuum pressure, a deflection of the fibers into the deflection
conduits occurs,
which can lead to separation of the deflected fibers from each other and from
the
embryonic web. In addition, as a result of a sudden application of a vacuum
pressure,
a certain number of partially dewatered fibers separated from the embryonic
web
could completely pass through the papermaking belt. These phenomena causes
formation of pin-sized holes, or pinholes, in the domes of the finished paper
web, and
clogging the vacuum dewatering machinery.
The undesirable creation of pinholes in the domes of the paper web, or
pinholing, was mitigated by commonly assigned U.S. Patent No. 5,334,289,
issued
CA 02425141 2003-04-22
3
on Aug. 2, 1994 to Trokhan et al. This patent provided surface texture
irregularities
in the backside network. The backside irregularities mitigate the effect of a
sudden
application of a vacuum pressure. Still, search for improved products has
continued.
1t is an object of an aspect of the present invention to provide an improved
S papermaking belt which substantially reduces the pinholing in the finished
paper web
and the buildup of paper fibers on the vacuum dewatering machinery.
It is another object of an aspect of the present invention to develop a paper
in
which the number of pinholes in the dome region of the finished paper web is
substantially reduced.
SUMMARY OF THE INVENTION
A papermaking belt of the present invention is generally comprised of two
primary elements: a reinforcing structure and a framework. In its preferred
form, the
papermaking belt is an endless belt which has a paper-contacting side and a
backside
opposite the paper-contacting side.
The reinforcing structure has a paper-facing side and a machine-facing side
opposite the paper-facing side. The reinforcing structure has air permeability
not less
than 800 cfin and a Fiber Support Index not less than 75. In its preferred
form, the
reinforcing structure is a woven element. Preferably, the reinforcing
structure
comprises two parallel layers of interwoven yarns interconnected in a
contacting face-
to-face relationship by tie yarns. Alternatively, the reinforcing structure
can comprise
a non-woven element, such as felt.
The framework is joined to the reinforcing structure and extends outwardly
not more than about 6.5 mils from the paper-facing side of the reinforcing
structure,
one mil being equal to one-thousandths of an inch. A variety of suitable
resins can be
used as the framework.
The framework has a first surface defining the paper-contacting side of the
papermaking belt, a second surface opposite the first surface, and deflection
conduits
extending between the first surface and the second surface. The first surface
comprises a paper-side network and paper-side openings where the deflection
conduits intercept the first surface. Essentially all paper-side openings are
dispersed
throughout, encompassed by, and isolated one from another by the paper-side
network. The second surface comprises a backside network encompassing backside
CA 02425141 2003-12-15
4
openings. The paper-side openings and the backside openings define the
deflection
conduits. A substantial portion of each paper-side opening is not less than
about 45
mils in each of its dimensions measured in the X-Y plane. In a preferred
embodiment,
the perimeter of each paper-side opening defines a closed figure; such as a
bow-tie
shaped figure, a diamond-shaped figure and the like, and the openings are
disposed in
the first surface in a non-random, repeating pattern.
A paper web having two regions and comprising: an essentially continuous,
essentially macroscopically monoplanar network region, and a dome region
comprising a plurality of discrete domes, essentially all of said domes being
dispersed
throughout, encompassed by, and isolated one from another by said network
region, at
least about 40% of an X-Y area of each of said domes being not less than about
45
mils in each of its dimensions measured in an X-Y plane at the level of said
network
region, the density of said network region being greater than the density of
said dome
region.
In one embodiment of the present invention, there is provided a papermaking
belt having a paper-contacting side and a backside opposite the paper-
contacting side,
the papermaking belt comprising:
a reinforcing structure having a paper-facing side and a machine-facing side
opposite the paper-facing side, the reinforcing structure having an air
permeability of
at least 800 cfin per square foot at a pressure differential of 100 Pa and a
Fiber
Support Index of at least 75; and
a framework joined to the reinforcing structure and extending outwardly at
most 6.5 mils from the paper-facing side of the reinforcing structure to form
an
essentially continuous network, the framework having a first surface defining
the
paper-contacting side of the papermaking belt, a second surface opposite the
first
surface, and deflection conduits extending between the first surface and the
second
surface, the first surface comprising a paper-side network and paper-side
openings
and the second surface comprising a backside network and backside openings, a
substantial portion of each of the paper-side openings being at least 45 mils
in each of
its dimensions measured in the X-Y plane at the level of the paper-side
network the
paper-side openings and the backside openings defining the deflection
conduits.
In another embodiment of the present invention, there is provided a
papermaking belt having a paper-contacting side and a backside opposite the
paper-
contacting side, the papermaking belt comprising:
CA 02425141 2003-04-22
4a
a reinforcing structure having a paper-facing side and a machine-facing side
opposite the paper-facing side, the reinforcing structure having air
permeability of at
least 800 cfin per square foot at a pressure differential of 100 Pa and a
Fiber Support
Index of at least 75; and
a framework joined to the reinforcing structure and extending outwardly at
most 6.5 mils from the paper-facing side of the reinforcing structure, the
framework
having a first surface defining the paper contacting side of the papermaking
belt, a
second surface opposite the first surface, and deflection conduits extending
between
the first and second surfaces, the first surface comprising a paper-side
network and
paper-side openings, a substantial portion of each of the paper-side openings
being at
least 45 mils in each of its dimensions measured in the X-Y plane at the level
of the
paper-side network, and the second surface comprising a backside network and
backside openings, the paper-side openings and the backside openings defining
the
deflection conduits;
the reinforcing structure comprising a first layer of a plurality of
interwoven
yarns having a top dead center longitude remaining within 1.5 yarn diameters
of the
paper-facing side, and a second layer of a plurality of interwoven yarns, the
first and
second layers being substantially parallel to each other and interconnected in
a
contacting face-to-face relationship by tie yarns.
In another embodiment of the present invention, there is provided a paper web
having two regions and comprising an essentially continuous, essentially
macroscopically monoplanar network region, and a dome region comprising
discrete
domes, the domes being dispersed throughout, encompassed by, and isolated one
from
another by the network region, a substantial portion of each of the domes
being at
least 45 mils in each of its dimensions measured in the X-Y plane at the level
of the
network region, the density of the network region being greater than the
density of the
dome region.
CA 02425141 2003-04-22
4b
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic side elevational view of one embodiment of a continuous
papermaking process which uses the papermaking 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
diamond-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.
FIG. 4 is a vertical cross-sectional view of a portion of the papermaking belt
shown in FIG. 2 as taken along line 4--4.
FIG. 5 is a simplified representation in vertical cross-section of a portion
of
the papermaking belt of FIGS. 2-4 showing the overburden.
CA 02425141 2003-04-22
S
FIG. Sa is an enlarged photograph of one embodiment of the reinforcing
structure of the papemzaking belt of the present invention. showing the top of
the
first layer of the interwoven yams interconnected in a contacting face-to-face
relationship with a second layer (not show~rt) of interwoven yarns by tie
yarns.
FIG. 6 is a simplified schematic representation of a vertical cross-section
showing fibers bridging the conduits of the papermaking belt.
o FIG. 7 is a simplified schematic representation of a cross-section similar
to
FIG. 6.
FIG. 8 is a simplified schematic representation of a cross-section showing
full
deflection of the fibers into the conduits of the papermaking belt.
l5
FIG. 9 is an enlarged photograph of one embodiment of the framework joined
to the reinforcing structure of the papermaking belt of the present invention,
showing the bow-tie openings of the deflection conduits.
20 FIG. 9a is a top plan schematic representation of one exemplary framework
having bow-tie openings of the deflection conduits, and the portion of the
paper web
produced using the belt having this exemplary framework.
FIG. 10 is a vertical sectional view of a portion of the paper web shown in
25 FIG. 9a as taken along line 10--10.
FIG. 11 is an enlarged schematic representation of one exemplary paper-side
opening, having a bow-tie shaped cor. figuration, of the deflection conduit of
the
papermaking belt of the present invention.
FIG. 1 I a is an enlarged schematic representation of one exemplary paper-side
opening. having a diamond-shaped configuration, of the deflection conduit of
the
papetmaking belt of the present invention.
FIGs. 11 and l la are schematic only. illustrating the method of establishing
whether a substantial part of the opening of the deflection conduit is not
less than
CA 02425141 2003-04-22
6
about 45 mils in each of its X-Y dimensions. FIGs. 11 and I la should not be
used to
scale the areas of the openings 42 which meet the 45 mil criterion.
FIG. 12 is a representation of two digitized images of pinholes of the paper
web samples, as seen on a computer screen.
S
DETAILED DESCRIPTION OF THE INVENTION
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 Papermaking Belt
In the representative papermaking machine schematically illustrated in FIG. l,
the 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 1 l
and a
backside 12 opposite the paper-contacting side 11. The papermaking belt 10
carnes a
1 S paper web (or "fiber web") in various stages of its formation (an
embryonic web 27
and an intermediate web 29). 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. No. 3,994,771, 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 2l.The loop around which the
papermaking
belt 10 travels includes a means for applying a fluid pressure differential to
the
embryonic web 27, such as vacuum pickup shoe 24a and multislot vacuum bo~c 24.
In
FIG. 1, the papermaking belt 10 also travels around a predryer such as blow-
through
dryer 26, and passes between a nip formed by the impression nip roll 20 and a
Yankee
dryer drum 28.
Although the preferred embodiment of the papermaking belt of the present
invention is in 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, it
generally has
certain physical characteristics set fourth below. The papermaking belt 10 of
the
present invention may be made according to commonly assigned U.S. Pat. No.
5,334,289, issued in the name of Trokhan et al.
CA 02425141 2003-04-22
7
.As shown in FIGS. ?-4. the papermaking belt 10 of the present invention is
generally comprised of two primary elements: a framework 32, and a reinforcing
structure 33. The framework 32 has a first surface 34, a second surface 3~
opposite
the first surface 34. and deflection conduits 36 extending between the first
surface
3-1 and the second surface 35. The first surface 34 of the framework 32
contacts the
embryonic web fibers to be dewatered. and defines the paper-contacting side 1
1 of
the papertnaking belt 10. The deflection conduits 36 e~ctending between the
first
surface 34 and the second surface 35 channel water from the embryonic web 27
to which rest on the first surface 34 to the second surface 35 and provide
areas into
which the fibers of the embryonic web 27 can be deflected and rearranged. As
used
herein, the term "dome" indicates the area of the paper web formed by the
fibers
deflected into the individual deflection conduit 36. The first surface 34 of
the
framework 32 comprises a paper-side network 34a and paper-side openings 42
t 5 formed therein. That is to say, the paper-side network 34a comprises a
surface of
the solid portion of the framework 32. or a portion of the first surface 34.
which
surrounds and defines the paper-side openings 42 in the first surface 34.
The second surface 35 of the framework 32 comprises a backside network 35a
'o and backside openings 43. The backside network 35a surrounds and defines
the
backside openings 43 in the second surface 35. The paper-side openings 42 and
the
backside openings 43 define the deflection conduits 36. The paper-side opening
42
preferably are uniform shape and are distributed in a non-random. repeating
pattern.
The pattern comprising a bilaterally staggered array is preferred. The
backside
25 openings 43 are also preferably uniform shape and are distributed in anon-
random.
repeating pattern. Accordingly, the deflection conduits 36 are preferably
arranged
in a non-random, repeating pattern comprising bilaterally staggered array. In
FIG.
2. the openings 42 are shown as having a diamond-shaped configuration, but it
will
be apparent to one skilled in the art that the paper-side network 34a and the
backside
3o network 35a can be provided with a variety of patterns having various
shapes, sizes.
and orientations. The practical shapes of the paper-side openings 42 and the
backside openings 43 include, but are not limited to, circles, ovals, polygons
of six
and fewer sides, bow-tie shaped figures, weave-like patterns.
35 The profile of the cross-section of the walls 44 of the deflection conduits
36
can be relatively straight, curved, partially straight and partially curved,
or irregular
when viewed in cross section. It should be noted that the drawings
schematically
CA 02425141 2003-04-22
8
show the walls 44 of the conduits 36 as straight lines for ease of
illustration only. The
profile of the cross-section of the walls 44 of the deflection conduits 36 is
disclosed in
greater detail in U.S. Pat. No. 5,334,289.
A variety of suitable resins can be used as the framework 32. U.S. Pat. No.
4,529,480 describing the suitable resins for the framework 32.
As shown in FIGS. 2-S, and 9, the framework 32 is joined to the reinforcing
structure 33. The reinforcing structure 33 has a paper-facing side 51 and a
machine-
facing side 52, opposite the paper-facing side 51. The framework 32 extends
outwardly from the paper-facing side 51 of the reinforcing structure 33. The
reinforcing structure 33 strengthens the resin framework 32 and has 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
embryonic web
27, and to permit water removed from the embryonic web 27 to pass through the
papermaking belt 10.
1 S As used herein, the term "overburden" means the portion of the resin
framework 32 extending from the paper-facing side 51 of the reinforcing
structure 33.
In FIG. 5 the overburden is designated as OB. More particularly, the
overburden is
defined by the distance between the first surface 34 (and, for this purpose,
the paper-
side network 34a) of the framework 32 and the paper-facing side 51 of the
reinforcing
structure 33.
It has been believed that the increase of thickness and absorbency of the
paper
can be achieved by increasing a caliper of the embryonic web 27. One way of
increasing the caliper is to increase the overburden OB. In theory, the
greater the
overburden OB, the more fibers can be deflected and accumulated in the
deflection
conduits 36. The greater overburden enables the conduits 36 to serve
adequately their
purpose of providing a space into which the fibers of the embryonic web 27 can
be
deflected so that these fibers can be rearranged without the constraint of the
strands of
the reinforcing structure 33. The preferred range of the overburden used in
the prior
art is disclosed in U.S. Pat. No. 5,334,289 as being between about 4 mils and
about 30
mils (0.102 mm and 0.762 mm).
However, there are at least two practical problems associated with a
relatively
high overburden. First, excessive deflection and accumulation of fibers into
the
CA 02425141 2003-04-22
9
deflection conduits can decrease the air permeability of the belt. As a
result, the
deflected fibers can be ripped apart from each other by an application of a
vacuum
pressure destroying existing bonds between the fibers. thus creating pinholes
in the
paper substrate. Moreover, some of the deflected fibers can be "blown away"
through the papermaking belt 10 by an application of a vacuum pressure. even
further exaggerating the effect of pinholing. Second, pinholing causes the hoc
drying air to predominantly go through the formed pinholes. since the pinholes
are
the natural paths of less resistance for the drying air. Thus, pinholing
interferes with
the effective drying of the intermediate web 29, decreasing the drying speed
and/or
i o increasing the cost of drying. Consequently, the speed of the whole
papermaking
process needs to be decreased or the cost of pre-drying needs to be increased.
While not intending to be limited by theory, it is believed that much of the
caliper generation can be achieved at the creping operation. As shown in FIG.
1, in
~ 5 the drying operation, the web 29 is adhered to a Yankee surface 28 and
then
removed from the Yankee surface 28 with a doctor blade 30. It has been found
that
the effective caliper generation occurs at the preferred Yankee speed of not
Iess than
about 1000 feet per minute (fpm). More preferably, the Yankee speed is not
less
than about 300 fpm.
The findings that the desired caliper generation can be achieved at this
creping
speed tends to unexpectantly eliminate need to increase the overburden OB. In
the
present invention, the preferred range of the overburden is between about 1
mil and
about 6.~ mils (0.0254 rnm and 0.1651 mm)> which is considerably less than
would
be expected from the prior art findings. The more preferred range of the
overburden
is between about 2.5 and about 5.5 mils. The most preferable overburden range
is
between about 4 and about 5 mils.
It has also been found the low overburden can be particularly advantageous if
3o used in combination with large domes and high fiber support. As used
herein, the
term "large dome" refers to a dome, a substantial portion of which is not less
than
about 45 mils in each of its dimensions measured in the X-Y plane at the level
of
paper-side network 34a. As used herein. X, Y and Z directions are orientations
relating to the papermaking belt 10 of the present invention (or paper web
disposed
on the belt) in a Cartesian coordinate system. In the Cartesian coordinate
system
described herein, the paper-contacting side 11 and the backside 12 of the
paperrnaking belt 10 lie in the plane formed by the X and Y axes. The X axis
is the
CA 02425141 2003-04-22
cross-machine direction, the Y axis is the machine direction, and the Z axis
is
perpendicular to the plane defined by the X and Y axes. As used herein. the
tetTn
"substantial portion" means not less than about 40% of the X-Y area of the
individual dome and -- accordingly -- not less than about 40% of the area of
the
individual paper-side opening 42 of the deflection conduit 36. measured in the
X-Y
plane at the level of the network region 83 and the paper-side network 34a.
Because the X-Y geometry of the domes reflects the geometry of the paper-
side openings 42 of the conduits 36, it will be apparent to one skilled in the
art that
in order to produce a paper with large domes, the substantial portion of the
paper-
side opening 42 of the conduit 36 should also be not less than about 45 mils
in each
of its dimensions measured in the X-Y plane at the level of the paper-side
network
34a. In FIGS. 8 and 10, the symbol "A" indicates one of the dimensions of the
opening 42 as measwed in the X-Y plane at the level of the paper-side network
34a.
~5
FIGS. I I and l la illustrate what is meant by a requirement that a
substantial
portion of the paper-side opening 42 is not less than about 45 mils in each of
its
dimensions measured in the X-Y plane at the level of paper-side network 34a.
In
FIG. 1 I , an exemplary paper-side opening 42 in the form of a bow-tie shaped
figwe
?0 is shown. The symbols "S I " through "S I 8" represent individual areas of
the paper-
side opening 42. The individual areas S 1 through S I 8 are formed by
corresponding
border lines B I through B I 8 and the perimeter of the opening 42. The length
of
each border line B 1, B2. .... B 18 is equal to 4~ mils. As FIG. 11 shows, at
least
some of the dimensions of the individual areas S 1 through S 18 are less than
45 mils.
~5 The number of the border lines and the location of each border line are
found such
as to maximize the resulting areas formed by the multiplicity of the border
lines and
the perimeter of the opening 42. The symbol "S" represents the portion of the
opening 42 formed by subtracting from the whole area of the opening 42 the
resulting areas formed by the border Lines and the perimeter of the paper-side
30 opening 42. In FIG. 11, the perimeter of the area S is designated by a
dotted line.
According to the present invention, S should comprise a substantial portion of
the
opening 42.
In FIG. 11 a, an exemplary paper-side opening 42 in the form of a diamond-
35 shaped figure is shown. Analogously to the example shown in FIG. 1 I, the
symbols
"S? l ." "S2?," "S23," "S24" represent individual areas, or portions of the
paper-side
opening 42, formed by the border lines B21, B22, B23, B24, each of them being
CA 02425141 2003-04-22
equal to .~~ mils. and the perimeter of the opening =l2. The symbol "S*"
represents
the portion of the opening -12 formed by subtracting the resulting areas of
the
opening 42 formed by the border lines B?1-B24 and the line defining the
perimeter
of the paper-side opening -t2 from the whole area of the opening 42. According
to
the present invention. S* should comprise a substantial portion of the opening
42.
It should be pointed out that the resulting area or the sum of the resulting
areas formed by the border lines and the perimeter of the opening 42 may be
equal
or smaller than the arithmetic sum of the individual areas formed by the
border lines
1o and the perimeter of the opening 42. FIG. 11 illustrates the situation when
the sum
of the resulting areas formed by the border lines B 1 through B 18 and the
perimeter
are smaller than the sum of the individual areas S 1 through S 18. FIG. 11 a
illustrates
the situation when the resulting areas formed by the border lines B21 through
B24
and the perimeter of the opening 42 are equal to the sum of the individual
areas S21
ts S24.
It should be noted that the examples shown in FIGs, 11 and 11 a are presented
for the purposes of illustration only, and not for the purposes of limitation.
The
paper-side openings 42 can comprise a variety of shapes including, but not
limited
?o to, ovals, polygons, weave-like patterns and the like, and the same method
of
establishing whether the substantial part of the opening 42 is not less than
45 mils in
any of its dimensions measured in X-Y plane would apply. FIGs. 11 and 11 a are
schematic only, illustrating the method of establishing whether the
substantial part
of the opening 42 is not less than about 45 mils in each of its dimensions
measured
25 in the X-Y plane. FIGs. 11 and 1 l a should not be used to scale the real
dimensions
of the openings 42, the lengths and locations of the border lines, and the
areas
formed by the border lines and the perimeters) of the openings 42.
The domes are formed when the deflection of the fibers into the deflection
3o conduits 36 occurs. When the fibers are deflected into the deflection
conduits 36,
water removal from the embryonic web 27 and through the deflection conduits 36
begins. This water removal results in a decrease in fiber mobility in the
embryonic
web 27. This decrease in fiber mobility tends to fix the fibers in place after
they
have been deflected and rearranged. Deflection of the fibers into the
deflection
35 conduits 36 can be induced by, for example, 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
CA 02425141 2003-04-22
1'
conduits 36. In FIG. 1 the preferred method is illustrated by the use of
vacuum box
?4. Optionaiy. positive pressure in the form of air pressure can be used.
~L'ithout being limited by theory, it is believed that the rearrangement of
the
fibers in the embryonic web ?7 can generally take one of two models dependent
on
a number of factors including fiber length. The free ends of longer fibers can
be
merely bent into the conduits 36 while their opposite ends are restrained in
the
region of network surfaces. As schematically shown in FIG. 6, these free ends
of
the longer fibers can bond together in the area of the deflection conduit 36
without
t0 reaching the reinforcing structure 33. Or, as schematically shown in FIG.
7. the
middle parts of longer fibers can be bent into the conduit 36 without being
fully
deflected. Thus, "bridging" of the deflection conduit 36 occurs. Alternatively-
,
fibers (predominantly. the shorter ones) can actually be fully deflected into
the
conduit 36 and contact the reinforcing structure 33. as shown in FIG. 8.
t5
As noted above, in the present invention, the substantial portion of the paper-
side opening 42 of the deflection conduit 36 is not less than about 45 mils in
each of
its dimensions measured in the X-Y plane. This size allows substantially all
fibers
that have been deflected to be fully deflected into the deflection conduits
36, as
2~ schematically shown in F1G. 8. While applicants decline to be bound by any
particular theory. it appears that, providing the low overburden and high
fiber
support are present. full deflection of the fibers into the conduits 36
provides more
caliper, improves thickness impression and enhances strength of the finished
paper
product. compared to paper having domes formed by other methods than full
~5 deflection of the fibers into the conduits 36.
The reinforcing structure 33 is one of the primary elements of the
papermaking belt of the present invention. The reinforcing swcture 33
strengthens
the resin framework 32 and has a suitable projected open area in order to
allow the
3o vacuttm dewatering machinery employed in the papermaking process to
adequately
perform its function of removing water from partially-formed webs of paper,
and to
permit water removed from the paper web to pass through the papermaking belt
10.
Therefore, the reinforcing structure 33 should be highly permeable to fluids
such as
air and water. By "highly permeable" it is meant that the reinforcing
structure 33
35 should have an air permeability not less than about 800 cubic feet per
minute (cfm)
per square foot of its surface at a pressure differential of 100 Pascals. The
reinforcing structure 33 of the present invention has the preferred air
permeability
CA 02425141 2003-04-22
13
between about 900 and about 1100 cfm per square foot of its surface at a
pressure
differential of 100 Pascals. More preferably, the air permeability of the
reinforcing
structure 33 of the present invention is between about 950 and about 1050 cfin
per
square foot at a pressure differential of 100 Pascals.The most preferable air
permeability of the reinforcing structure 33 of the present invention is about
1000 cfm
per square foot at a pressure differential of 100 Pascals.
At the same time, the reinforcing structure 33 of the present invention has
also
an important function of supporting the fibers fully deflected into the
conduits 36, not
allowing them to be blown through the belt 10. Therefore, the high fiber
support
provided by the reinforcing structure 33 of the present invention is of
primary
importance. By "high fiber support" it is meant that the reinforcing structure
33 of the
present invention has a Fiber Support Index of not less than about 75. As used
herein,
the Fiber Support Index or FSI is defined in Robert L. Beran, "The Evaluation
and
Selection of Forming Fabrics," Tappi /April 1979. Vol. 62. No. 4, which is
attached as
an Appendix 1 herein. Preferably, the reinforcing structure of the present
invention
has FSI not less than 85. More preferably, the FSI is greater than 90.
The reinforcing structure 33 can take any number of different forms. It can
comprise a woven element, a non-woven element, a screen, a net, a scrim, or a
band
or plate having plurality of holes. Preferably, the reinforcing structure 33
comprises a
woven element, and more particularly, a foraminous woven element, such as
disclosed in U.S. Pat. No. 5,334,289. More preferably, the reinforcing
structure
comprises a first layer of interwoven yarns and a second layer of interwoven
yarns
being substantially parallel to each other and interconnected in a contacting
face-to-
face relationship by a tie yarns. The first layer and the second layer can
individually
comprise a plurality of machine-direction yarns interwoven with a plurality of
cross-
machine direction yarns. This type of the reinforcing structure 33 is
illustrated in FIG.
Sa. U.S. Patent No. 5,496,624 in the names of Stelljes, Jr. et al. shows a
suitable
reinforcing structure 33. According to U.S. Patent No. 5,496,624, the web
facing first
layer is woven so that the top dead center longitude of each yarn of the first
layer that
is in the top plane of the paper-facing side 51 does not extend more than 1.5
yarn
diameters, and preferably not more than 1.0 yarn diameters away from the top
CA 02425141 2003-04-22
14
plane of the paper-facing side 51, and remains within 1.0 or 1.5 yarn
diameters of the
paper-facing side 51 at all positions, unless such yarn is a tie yarn
interconnecting the
first and the second layers.
While a woven element is preferable for the reinforcing structure 33 of the
present invention, a papermaking belt 10 according to the present invention
can be
made using a felt as a reinforcing structure, as set forth in the patent
applications: U.S.
Patent No. 5,629,052 in the name of Trokhan et al. and entitled: "Method Of
Applying A Curable Resin To A Substrate For Use In Papermaking;" U.S. Patent
No.
5,556,509 in the name of Trokhan et al. entitled: "Paper Structures Having At
Least
Three Regions Disposed At Different Elevations, and Apparatus And Process For
Making The Same;" U.S. Patent No. 5,837,103 in the name of Trokhan et al. and
entitled: "Web Patterning Apparatus Comprising A Felt Layer And A
Photosensitive
Resin Layer." All of these patent applications are assigned to The Procter &
Gamble
Company.
The Paper
Papermaking fibers useful in the present invention include those cellulosic
fibers commonly known as wood pulp fibers. Fibers derived from soft woods
(gymnosperms or coniferous trees) and hard woods (angiosperms or deciduous
trees)
are contemplated for use in this invention. Preferably, the weight ratio: soft
wood
fbers/hard wood fibers is about 25/75. The particular species of trees from
which the
fibers are derived are immaterial. In addition to the various wood pulp
fibers, other
cellulosic fibers, such as cotton linters, rayon, and bagasse, can be used in
this
invention. Synthetic fibers, such as polyester and polyolefin fibers can also
be used.
As shown in FIGS. 9 and 10, the improved finished paper web 80 of the
present invention is characterized as having two distinct regions: a network
region 83
and a dome region 84. The network region 83 corresponds to and is formed on
the
paper-side network 34a of the first surface 34 of the papermaking belt 10. The
network region 83 is an essentially continuous, macroscopically monoplanar
region
having a non-random, repeating pattern. It is described as "continuous"
because it
comprises the system of essentially uninterrupted lines forming at least one
essentially
unbroken net-like pattern of essentially uniform physical characteristics. The
pattern
is said to be "essentially" continuous because it is recognized that the
interruptions in
the pattern may be tolerable, but not preferred. The network region
CA 02425141 2003-04-22
83 is described as "macroscopically monoplanar" because the top surface of the
network region (i.e.. the surface lying on the same side of the paper web as
the
protrusions of the domes) is essentially planar when the paper web 80 as a
whole is
placed in a planar configuration. It is "essentially" monoplanar because minor
deviations from absolute planarity are tolerable, but not preferred.
The dome region 84 comprises a plurality of domes dispersed throughout the
whole of the network region 83. Essentially each individual dome is
encompassed
by. and isolated one from another, by the network region 83. The domes are
t o distributed in a non-random repeating pattern. Preferably this repeating
pattern
comprises a bilaterally staggered array. A substantial portion of each dome is
greater than about 45 mils in each of its dimension measured in the X-Y plane
at the
level of the network region 83. In the plane of the paper web 80 (or in X-Y
plane),
the shape of the domes is defined by the network region 83. That is to say,
the
t s shape of the domes in the X-Y plane is defined by the configuration of the
paper-
side openings 42 of the deflection conduits 36.
The shapes of the domes in the X-Y plane include, but are not limited to,
circles. ovals, polygons of six and fewer sides, bow-tie shaped figures, weave-
like
Zo patterns. Preferably, domes are in the form of a closed fgured, such as a
bow-tie
shaped figure, diamond-shaped figure and the like. FIG. 9a schematically shows
the
exemplary X-Y geometry of a part of the paper web 80 (and, nattually, of the
_ openings 42 of the deflection conduits 36) having the domes in the form of a
bow-
tie shaped figure.
Only a portion of the paper web (and the first stuface 34a) showing a
repeating pattern is shown in FIG. 9a. In FIG. 9a, the symbol "MD" indicates
machine direction, i.e., the direction which is parallel to the flow of the
web through
the equipment. The symbol "CD" indicates cross machine direction, i.e., the
3o direction perpendicular to the machine direction in the X-Y plane.
Preferably, there
are not more than about 80 bow-tie shaped domes per square inch of the paper
web,
oriented in a bilaterally staggered array pattern as shown in FIG. 9a. It will
be
apparent to one skilled in the art that when the domes comprise other than bow-
tie
shaped figure, the ntirnber of the domes can be different from that indicated
above.
It will also be apparent to one skilled in the art that the particular design
of the
presented in FIG. 9a bow-tie dome is one exemplary design. Other designs of
bow-
tie figures can be utilized in the present invention, as well as other,
different from
CA 02425141 2003-04-22
16
the bow'-tie shapes of the dome. The practical shapes of the domes include.
but not
limited to, circles. ovals, polygons of six and fewer sides, bow-tie shaped
fiUures.
weave-like patterns and the like.
The network region 83 of the paper 80 of the present invention has a high
density ~weieht per unit volume) relative to the density of the dome region
84. The
difference in the densities primarily occurs as a result of deflection of
fibers into the
deflection conduits 36. At the time the embryonic web 27 is associated with
the
framework 3?, the embryonic web 27 has an essentially uniform basis weight.
During deflection. fibers are free to rearrange and migrate from adjacent the
surface
to of the paper-side network 34a into the deflection conduits 36 thereby
creating a
relative paucity of fibers over the surface of the paper-side network 34a and
a
relative supert7uity of fibers fully deflected into the deflection conduits
36. Some
deflected fibers are "pulled apart" and separated from each other by the
application
of the vacuum pressure destroying bonds existing between these fibers. At the
same
t 5 time. the application of the vacuum pressure tends to compress the network
region
83 i i.e.. that portion of the embryonic web 27 which corresponds with the
paper-side
network 34a1 over the surface of the paper-side network 34a, while the dome
region
84 (i.e., the portion of the embryonic web 27 within the deflection conduits
36) is
not compressed over the surface of the paper-side network 34a. This
compression
20 of the network region 83 tends to further exaggerate the difference in
densities
between the two regions. In addition, pressing the network area 83 against the
Yankee dryer drum 28 even further increases the density of the network 83.
As was shown above, the combination of large domes, low overburden and
25 high fiber support of the belt's reinforcing structure reduces the number
of pinholes
in the paper of the present invention. In a paper web having the caliper
between
about 1 I mils and 17 mils and the dome area of about 65%, the number of
pinholes
in the dome area, meastued by the analytical procedure described below is not
greater than 700 pinholes per 100 square inches of the paper web. Preferably,
the
3o number of pinholes is not greater than 5000 pinholes per 100 square inches
of the
paper web.
The caliper of the paper web is measured under a pressure of 9~ gramS per
square inch using a round presser foot having a diameter of 2 inches. The
dwell
35 time is 3 seconds. The caliper can be measured using a Thwing-Albert
Thickness
Tester :vlodel 89-100, manufactured by the Thwing-Albert Instrument Company of
Philadelphia. Pennsylvania. The caliper is measured under TAPPI temperature
and
CA 02425141 2003-04-22
humidity conditions. The caliper of the finished paper web is preferably
between 9
mils and 30 mils. More preferably, the caliper is between 11 mils and 30 mils.
The
most preferable caliper of the finished paper web is between 12 mils and 1 ~
mils.
CA 02425141 2003-04-22
Analytical Procedures
Pinholing
For an analytical method of identifying. counting and characterizing pinholes
in a specimen of a paper web, a Macintosh computer with a math-coprocessor. at
least 4 MB of RAM. and a monitor capable of 2~6 shades of gray may be used in
conjunction with the optical scanner HP ScanJet IIp full page scanner with
DeskScan software Version 1.5.2. or later. Macintosh Quadra 800 with MB of 8
RAM, and Iomega External Removable Cartridge Drive are preferred. An Apple
High Resolution color monitor. Model M 1212 (or a model allowing a higher
resolution) can be used. Suitable software is Microsoft Excel, Version 4.0 or
later.
and Image Version 1.45, available from the National Institute of Health, in
Washington. D.C.. and QuicKeys ?v 2.1.
~ 5 A parent roll of the finished paper web 80 is divided along its
longitudinal
axis into five approximately equal parts. Usually, two parent rolls produced
by the
same equipment and at the same time are used for testing. At least one paper
web
sample, randomly taken from each of the five parts of each parent roll is
tested.
Thus. ten paper web samples are usually tested.
A web sample is placed on the glass of an optical scanner under a black
background board. The image through the scanner is digitized and viewed in two
dimensions on a computer monitor. The settings are as follows: Brightness is
106;
Contrast is 178; Scaling is 200. Print Path is set at 100 dots per inch. The
scanning
size is about 10 square inches. The sample is scanned into the computer as an
image file composed of pixels. The term "pixel" indicates the smallest
discrete
digitized picture element generated by a computer. The pixel of about 0.0001
square inches is used.
3o FIG. 12 illustrates the digitized image of the paper web sample having
pinholes, as it could be seen on the computer screen. The image file is
processed by
an image analysis application that identifies and measures each pinhole in the
image
according to the specific criteria. For the samples described therein. the
threshold of
gray level of 2~4 has been found to work well in the detection of pinholes.
The
macro selectively measures all of the "suspected" pinholes that have gray
value of
254. Then. the data file which lists the size of each pinhole it has found is
created.
Microsoft Excel is then used to tabulate the data regarding the size. number
and
CA 02425141 2003-04-22
19
distribution of all found pinholes. Appendix '? represents the resulting
Pinhole
Analysis. As can be seen from the Appendix '. the pinhole analysis allows to
evaluate not only the number of pinholes, but also -- the numerical
distribution of
the pinholes according to their size, an average single pinhole size, and
other
relevant data.
FIG. 12 shows the digitized images of the paper web samples produced using
two different belts. The Image A is the image of the sample produced using the
papermaking belt having a high overburden (OB is about 7.~ mils). The Image B
is
I o the image of the sample produced using the papermaking belt having a low
overburden according to the present invention (OH is about 4.9 mils). Other
characteristics of the two belts, such as dome size and Fiber Support Indet,
are
about equal. Visual comparison of the two samples shown in FIG. 12,
illustrates
that the paper web produced using the belt with a low overburden according to
the
t5 present invention has significantly less number of pinholes (Image B)
compared to
the paper web produced using the papermaking belt having a higher overburden
(Image A).
This visual evaluation can be confirmed by the analytical data compiled in
3o Appendix 2. In Appendix 2, the Diagram A represents the data relating to
the
samples produced using the belt having a high overburden of about 7.~ mils.
The
Diagram B represents the data relating to the samples produced using the belt
having a low overburden of about 4.9 mils. As Appendix 2 shows, the number of
pinholes in the samples produced using the belt having a high overburden is
11325
25 pinholes per 100 square inches (Diagram A). The number of pinholes in the
samples produced using the belt having the low overburden according to the
present
invention is 1592 pinholes per 100 square inches (Diagram B).
As can also be seen from the Appendix 2, the low overbwden belt of the
3o present invention improves pinholing not only in terms of the amount of the
pinholes, but also -- in terms of the size of the pinholes. For example, as
presented
in the Diagram A. in the samples produced using the high overburden belt, the
average number of pinholes having an area of about one pixel is X852, and the
average number of pinholes having an area of about 20 pixels and larger is 51.
In
35 the samples produced using the low overburden belt of the present
invention. the
corresponding numbers are 1084 and 1, as presented in the Diagram B.
CA 02425141 2003-04-22
Bv way of illustration. and not by way of limitation, the following e~camples
are presented.
TABLE I:
Pinhole
NumberArea
of (Square
Belt PinholesMils
per
Tvpe Fiber Air Network per 100
of 100
ReinforcingSupportOverburdenperm Area lincalenderedsquaresquarc
StructureIndex (mil) (cfm)(%) Caliper inchesinches)
(mil)
PVT-53394 7.5 487 40 23.5 9,646 654,484
PVT-53394 2.9 477 40 I9.0 2,671 121.631
pVT-54394 3.1 453 35 17.9 2.045 86,377
PVT-5.~;94 4.9 494 35 20.5 3.?84 100,101
The belts having the same Fiber Support Index and relatively similar air
permeability were tested in plant manufacturing conditions. As can be seen
from
the Table I. the pinhole counts related to the belts having a low overburden
of 2.9
io mils, 3.1 mils, and 4.9 mils (second, third. and fourth lines of the Table
I) are
significantly less than the pinhole count related to the belt having a high
overburden
of 7.~ mils (first line of the Table I).
At the same time, comparison of the belts having relatively close overburdens
(second and third lines of the Table I) but different ratio of the network
area/dome
area shows that the pinhole count related to the belt with the smaller network
area
(35%), and therefore -- larger dome area (65%), is lower than the pinhole
count
related to the belt having larger network area (40%) and therefore -- smaller
dome
area (60%).
CA 02425141 2003-04-22
,I
TABLE II:
Pinhole
NumberArea
of (Square
Belt PinholesMiis
per
Type Fiber Air Network per 100
of 100
Reinforcin_SupportOverburdenperm Area Uncalenderedsquaresquare
StructureIndex (mil) (cfm) (%) Caliper inchesinches)
(mil)
HMT-50269 1 1.4 488 40 ?0.8 I O, 584,128
t
34
HMT-50269 7.8 479 40 18.4 5.395 260,584
HMT-50269 3.9 532 40 15.6 1.101 42.908
PVT-54394 11.3 485 40 18.7 1,767 69.693
PVT-54394 9, I 415 40 17.9 3,51:1l4?.039
PVT-54394 4.0 463 40 13.5 139 4,490
Table II represents the results of testing several belts at the pilot plant
under
simulated conditions. As could be seen from the Table II, the best results in
pinholing count ( I ,1 O 1 and 139 ) were achieved using the belts having low
overburden of 3.9 mils and 4.0 mils (third and Birth lines of the Table II).
As
between these two belts having low overburdens, the best results in pinholing
were
received using the belt with the higher Fiber Support Index of 94 (sixth line
of the
to Table II).
