Note: Descriptions are shown in the official language in which they were submitted.
CA 02613110 2008-10-01
PAPERMAKING MACHINE WITH PAPERMAKING BELT
CROSS REFERENCE TO RELATED APPLICATION
This application is a divisional of application No. 2,421,210 filed in Canada
on August
31, 2001.
FI@LD OP INVENTION
This invention relates to clothing for paperrnaldng machinery, and
particularly
clothing having differential intensive properties.
BACKGROUND OF THE INVENTION.
Conventional papermaldng requires the removal of significant amounts of water.
The final water removal is typically done by evaporative drying. A
conventional
papermaking machine has a dryer section with a plurality of drying cylinders.
The paper
web to be dried is guided in contacting relationship through the plurality of
cylinders.
The cylinders may be arranged in two or more staggered rows, so that the paper
web
assumes a serpentine path.
In the art, a single-wire draw may be used, particularly at the beginning of
the
multi-cylinder dryer. In a single-wire draw, the drying wire is arranged to
support the web
as it moves from one cylinder to a successive cylinder.
Also, twin-wire draws are known in the art. In a twin-wire draw, the paper web
has an open draw when it moves from one cylinder to a successive cylinder.
Also known
in the art is a Pistol-Grip draw. In a Pistol-Grip draw, the top wire of one
cylinder section
is wound below the bottom cylinder of the next cylinder section, and the web
is supported
by the top wire to the next top cylinder.
In some configurations, the paper web is held in contact with each drying
cylinder,
preferably over a sector larger than 180 degrees. This is to maximize contact
time with
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CA 02613110 2007-11-07
the drying cylinder and thereby increase the amount of drying which occurs on
each
cylinder. In such a configuration, when utilized with a twin-wire draw, the
web to be
dried is pressed into direction contact with the outer face of one row of
eylinders.
Correspondingly, the wire is pressed against the face of the other row of
cylinders. In a
twin-wire draw, the web usually has a substantially long open passage from one
cylinder
bank to another, The open passages have been susceptible to fluttering which
causes
wrinkles, or even breaks in the web. The fluttering becomes a more significant
drawback
as papermachine speeds increase to and above 150 meters per minute. Attempts
have
been made to overcome this drawback by reducing the length of the open draws
in the
web.
If desired, the web to be dried may be passed over a sector of a section roll
and
subjected to negative pressure while it is supported on the drying fabric. For
example,
cylinder groups may include a single-wire draw. In such a grouping, the drying
cylinders
may be placed in the upper row and reversing section rows placed in a lower
row or vice
versa.
In yet another amangement, a drying section may have a two-felt drying group.
The drying group may comprise an upper row of cylinders with an upper felt and
a lower
row of cylinders with a lower felt. Within one or both rows of cylinders,
adjacent
cylinders may form a sub-group having a deflection section roll. The web to be
dried
alternately passes through the upper and lower sub-groups. Also of
consideration is the
geometry of the drying cylinder arrangement. The drying cylinders may have pre-
determined diameters spaced apart at a selected pitch. For example, in a
single-wire
draw, the paper web to be dried is brought into direct contact with drying
cylinders.
Additionally, reversing cylinders faced outside the wire loop in gaps between
the drying
cylinders. The drying cylinders may include large and small diameter
cylinders. The
small diameter cylinders may be disposed so that their centers are at a
different level than
the centers of the large cylinders. The centers of the reversing cylinders may
be disposed
at yet a different level. This geometry may reduce the machine direction
length of the
dryer section of the paper machine.
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CA 02613110 2008-10-01
In yet another execution shown in the art, a dryer section includes dryer
groups
with a single-wire draw. Each group includes drying cylinders, reversing
cylinders, and a
drying wire for carrying the web under constant contact over the drying
cylinders and
reversing cylinders. This arrangement promotes entry of the web into direct
contact with
the drying cylinders and reversing cylinders. In a single-wire draw, drying
cylinders are
outside the wire loop with reversing cylinders inside the loop.
In yet another embodiment, a drying section may include individual drying
groups
served by two respective dryer wires or felts. The dryer wires or felts may
press the web
to be dried against the surface of the drying cylinder. At least one press
roll may be
disposed between and separating two groups of drying cylinders. The press roll
forms a
nip with a drying cylinder to dewater a web as it passes through the nip.
Attempts in the art have been made to minimize the amount of air entrained by
the
drying fabric as it approaches and contacts a drying cylinder. For example,
one benefit of
a twin-wire papermachine is that two-sided drying operation can occur. Also,
generally,
the dryer section is shorter. However, a single-wire papermachine has better
running
characteristics at high machine speeds. One attempt to resolve these competing
advantages is to utilize an air guiding surface located on the opposite side
of the dryer
wire, using blow box assemblies and air nozzles. However, this has proven to
be
expensive.
Examples of the foregoing papermaking machinery can be found in U.S. Pat. Nos.
4,888,883, iss. Dec. 26, 1989 to Kerttula; 5,046,266, iss. Sep. 10, 1991 to
Autio;
5,475,934 iss. Dec. 19, 1995 to Eskelinen et al.; 5,495,678, iss. Mar. 5, 1996
to Ilmarinen
et al.; 5,535,527, iss. Jul. 16, 1996 to Virta et al.; 5,537,755, iss. Jul.
23, 1996 to
Kotitschke; 5,539,999, iss. Jul. 30, 1996 to Kuhasalo; 5,560,123, iss. Oct. 1,
1996 to
Eskelinen; 5,572,801, iss. Nov. 12, 1996 to Ahokas et al.; 5,666,741, iss.
Sep. 16, 1997 to
Bubik et al.; and 6,105,277, iss. Aug. 22, 2000 to Lindberg et al.
As can be seen from the foregoing examples, the papermachine clothing must
serve a variety of competing purposes. It must support the web without
separation. It
must allow adequate permeability for transport of water to be removed from the
web. It
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CA 02613110 2008-10-01
must provide contact of the web against the drying cylinders, while also
contacting the
reversing cylinders. Attempts have been made in the art to provide suitable
drying
= fabrics. For example, belt-like material having selected permeabilities are
known. The
selected permeabilities are provided by varying the spacing of the machine
direction
yams, the diameter of the machine direction yarns, or adding chemical
treatment in the
spaces between the machine direction yams.
In yet another attempt in the art, the clothing has a controlled void volume.
The
void volume is controlled by providing a multi-layer fabric, a synthetic,
polymeric
thermoplastic resin foam may fill the void spaces to control the void volume.
In yet another embodiment, to reverse the adverse effects of over-pressure on
the
sheet at the outer face of a dryer fabric, void spaces at the fabric-cylinder
interface receive
boundary air compressed between the papermachine clothing and the cylinder.
The void
space forming surface may include spaced parallel ribs defining grooves
therebetween.
The grooves reduce the rate and extent to which boundary air moves into the
reducing
space between the fabric and cylinder is compressed. This has a corresponding
effect on
reducing the amount of air forced through the fabric.
In yet another attempt in the art, the dryer fabric includes a plurality of
spiral coils
extending in the machine direction. Adjacent coils are intermeshed and held
together by a
hinge yarn. This arrangement is said to reduce occurrences of slack edges.
Slack edges in
the dryer fabric do not fully press the paper sheet against the cylinder,
causing different
drying rates to occur in the machine direction. This results in a non-uniform
moisture
profile across the sheet.
Examples of the foregoing attempts in the `art may be found in U.S. Pat. Nos.
3,867,766, iss. Feb. 25, 1975 to Wagner; 4,224,372, iss. Sep. 23, 1980 to
Romanski;
4,364,421, iss. Dec. 21, 1982 to Martin; 4,813,156, iss. Mar. 21, 1989 to
Ashworth et al.;
and 4,857,391, iss. Aug. 15, 1989 to Westhead.
However, the foregoing attempts in the art have not proven entirely
successful.
For example, woven drying clothing is limited to the patterns which are
provided by a
repeatable and stable weave. Unlimited patterns are not feasible. Only limited
geometries of grooves may be provided to handle the entrained air. The present
invention
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CA 02613110 2007-11-07
overcomes these disadvantages and provides greater flexibility and options in
determining
the geometry of the papermachinery clothing.
Additionally, papermachine clothing is known to experience wear during the
papermaking process. Such wear shortens the life of the papermachine clothing,
increasing the manufacturing costs. Wear of papermachine clothing is
attributed to the
temperature extremes which occur in papermaking, the two-way bending which
occurs as
the clothing passes over drying rolls and reversing rolls, as well as the
friction against the
rolls and drag across vacuum boxes.
Various attempts have been made in the art to mitigate the wear of
papermachine
clothing which is inherent in the papermaldng process. For example, clothing
having
stacked warps has become common. In a stacked warp airangement, oftentimes a
first
layer of lower, or machine-contacting, warp threads is provided. Also, a
second layer of
upper, or paper-contacting, warps is provided. The two layers of warps are
interwoven by
weft yarns. The lower layer of warps may be of larger diameter to provide
stability and
wear-resistance. The upper layer of warps may be of finer diameter to provide
a fiiner
surface which provides more consistent and uniform support for the paper web.
An
example of stacked warps is found in U.S. Pat. No. 5,114,777, issued to
Gaisser.
Yet another attempt in the art is to provide warp and/or weft yarns of
noncircular
cross-section. Particularly, the yarns of the papermachine clothing may be
rectangular,
having a greater dimension in the width direction than in the height or Z-
direction. This
geometry provides more area in contact with the papeamalting machinery, thus
reducing
the contact stresses at any particular point in the yarn. Additionally,
noncircular, or
rectangular, shaped yams provide the benefit that more area is presented to
the paper side
of the papermachine clothing as well. By presenting more area tD the
papermachine side
of the clothing, more contact against the drying cylinders occurs. By
providing more
contact of the paper against the drying cylinder, more rapid and uniform
drying of the
paper web is possible.
Accordingly, the art has shown considerable need for a fabric which presents
high
contact area to the paper to be dried thereupon. Further, there is a need for
a papermaking
fabric having such high contact area without sacrificing permeability.
Finally, there is a
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CA 02613110 2008-10-01
need for such a fabric which provides relatively uniform pressure against all
regions of the
paper to be dried thereupon.
One of skill will recognize that the problems of wear of the papermachine
clothing
is not limited to production of conventional or hard grades of paper. Such
wear also
occurs when producing tissue and corrugated grades of paper as well.
However, foregoing attempts to reduce wear of the papermachine clothing have
not been entirely successful. For example, stacked warp papermachine fabrics
are more
expensive than single layer fabrics. Also, such fabrics are prone to
sleaziness.
Rectangular-shaped warps are not amenable to all types of weaves,
particularly, high open
area weaves which may be desirable for certain types of papermaldng, such as
through air
drying, useful for making tissue paper. Rectangular cross section filaments
for a dryer
fabric are illustrated in Statutory Invention Registration H1073, published
Jul. 7, 1992 in
the name of Hsu .
The art has also shown considerable need for a way to reduce the wear of
papermachine clothing, without constraining the type of weave or type of yarns
used for
the papermachine clothing. Moreover, there is considerable need in the art for
a way to
reduce wear that is applicable to any type of clothing, including fornung
wires, or weave.
Further, it would be desirable that such a way to reduce the wear of
papermachine
clothing reduce the sleaziness of the clothing without affecting its paper-
contacting
surface.
SUIVIlVIARY OF THE INVENTION
The present invention discloses a single wire draw paper machine for making
paper in combination with a papermaking belt. The papermaking belt carries a
nascent paper web. The papermaking machine comprises at least two belts. Each
belt
has mutually opposed faces: a paper-contacting face and a machine-contacting
face.
Each belt comprises a reinforcing element of woven filaments with a patterned
framework. The framework has a pattern independent of the reinforcing element.
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CA 02613110 2008-10-01
The pattern of the framework defines at least one of a first face and a second
face.
The two belts each have a mutually different pattern in the framework.
The present invention further discloses a twin wire draw paper machine for
making paper in combination with a papermaking belt. The papermaking belt
carries
a nascent paper web. The papenmaking machine comprises at least two belts.
Each
belt has mutually opposed faces: a paper-contacting face and a machine-
contacting
face. Each belt comprises a reinforcing element of woven filaments with a
patterned
framework. The framework has a pattern independent of the reinforcing element.
The pattern of the framework defines at least one of a first face and a second
face.
The two belts each have a mutually different pattern in the framework.
The present invention further discloses a paper machine for making hard
6a
CA 02613110 2008-10-01
grades of paper. The papermaking machine comprises at least two belts. Each
belt
comprises a reinforcing element of woven filaments with a patterned framework.
The
framework has a pattern independent of the reinforcing element. The pattern of
the
framework defines at least one of a first face and a second face. The two
belts each
have a mutually different pattem in the framework.
BRIEF DESCRIPTION OF TBE DRAWINGS
Fig. 1 is a fragmentary vertical elevational view of a dryer section in a
single-wire
papermachine.
Fig. 2 is a fragmentary vertical elevational view of a dryer section in a twin-
wire
papermachine.
Fig. 3A is a fragmentary top plan view of papermachine clothing according to
the
present invention.
Fig. 3B is a fragmentary vertical sectional view of papermachine clothing
according to Fig. 3A.
Figure 4 is a fragmentary schematic side elevational view of a mask and liquid
resin
used to make a belt according to the present invention and showing the
incident radiation
upon the mask being blocked by an opaque region in the mask.
DETAII.ED DESCRIPTION OF TI3E INVENTION
Referring to Fig. 1, a dryer section 10 in a single-wire draw papermaking
machine
20 is illustrated. The dryer groups 21 comprise drying cylinders 32 heated by
known
means, such as steam. The web is pressed against the heated cylinder faces by
means of a
dryer fabric 30. In a single-wire draw machine, the web runs from one drying
cylinder to
another cylinder. Successive cylinders 22 are typically disposed in two rows
placed at
different elevations. The same dryer fabric 30 spans the gap between the rows
of
cylinders 22, although it is to be recognized that more than one dryer fabric
30 may be
used and spaced in the machine direction from other fabrics.
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CA 02613110 2007-11-07
Referring in more detail to Fig. 1, the dryer groups 21 comprise two
substantially
horizontal rows of steam-heated dryer cylinders 32. Dryer fabric 30 guides a
paper web
W on an outer face of the cylinders 22 through respective dryer groups 21. The
dryer
fabric 30 presses the web against the outer faces of the heated cylinders 22
so that
evaporative drying occurs.
Underneath the rows of drying cylinders 32 are nonheated reversing cylinders
34
or guide rolls. The reversing cylinders 34 may have suction sectors or
equivalent
arrangements so that the web remains on the outer face of the drying wire at
high speeds.
Referring to Fig. 2, a multi-cylinder drying section of a papermalcing machine
20
is illustrated. The multi-cylinder dryer section 10 has a plurality of upper
drying cylinders
36 and lower drying cylinders 38. The paper web W to be dried is passed in
succession
between upper and lower cylinders 36,38. The paper web W is in direct contact
with each
drying cylinder. Preferably, the paper web W contacts each drying cylinder
over a sector
of at least, and preferably greater than 180 degrees. The dryer section 10
comprises an
upper dryer fabric 40 and a lower dryer fabric 42, each being arranged to
press the paper
web W against its respective drying cylinders 32. The upper and lower dryer
fabrics
40,42 may be guided by guide rolls. Also, a dryer fabric 30 transfer device
comprising a
section box and auxiliary rolls may be utilized. Of course, it is to be
realized that various
section boxes may be added or omitted as desired. Further, any number of upper
and
lower drying cylinders 36,38 in the plurality may be utilized as desired.
Referring to Figs. 3A and 3B, the dryer fabric 30 according to the present
invention may generally be considered a papermaking belt 25. The papermaldng
belt 25
may be used for, or in combination with, a cylinder drying section of a
papermaking
machine 20. Specifically, the papermaking belt 25 may be usable in, or in
combination
with, a single-wire draw or a twin-wire draw papermalcing machine 20. The belt
25
according to the present invention is macroscopically monoplanar. The plane of
the belt
25 defines the XY directions. Perpendicular to the XY directions and plane of
the belt 25
is the Z-direction of the belt 25.
Likewise, the paper web W made on the belt 25 according to the present
invention
may be thought of as macroscopically planar and lying in an XY plane.
Perpendicular to
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CA 02613110 2007-11-07
the XY directions and plane of the paper web W is the Z-direction of the paper
web W.
The paper web W may be considered to be a printing lraft, newsprint,
linerboard or
writing grade of paper web W. CollectiveIy, these grades of paper are referred
to
hereinbelow as "hard" grades of paper. Such paper will typically have a basis
weight of
20 to 450, and more typically 30 to 300, grams per square meter.
The belt 25 comprises two primary components: a framework 112 and a
reinforcing
element 114. The framework 112 may comprise a molded or extraded thermoplastic
or
pseudo-thermoplastic material and preferably comprises a cured polymeric
photosensitive
resin. The reinforcing element 114 may comprise a woven fabric as is known in
the art.
The framework 112 and belt 25 have a first surface which defines the paper web
W
contacting side of the belt 25 and an opposed second surface oriented towards
the
papermaking machine 20 on which the belt 25 is used. The framework 112 may
optionally
have synclines 118 therein, as further described below.
The framework 112 is disposed on and defines the flrst surface of the belt 25.
Preferably the framework 112 defines a predetermined pattern, which imprints a
like pattern
onto the paper web W of the invention. Deflection conduits 116 extend between
the first
surface and the second surface. The framework 112 borders and defines the
defleetion
conduits 116. One preferred, and typical geometry comprises a framework 112
which
defines an essentially continuous network (hereinafter a continuous framework
112) and
discrete isolated (hereinafter discontinuous) deflection conduits 116.
The framework 112 may present a relatively high surface area to the paper web
W
thereon. The relatively high surface area provides two benefits: First, in a
single-wire
papermaking machine 20, the high surface area provides more contact with the
paper web
W against the drying cylinders 32. This increases conduction of heat from the
face of the
cylinders 22 to the paper web W and provides increased drying efficiency.
Additionally, the
high contact area provides for more uniform application of pressure of the
paper web W
against the drying cylinder, thereby providing a more consistent and uniform
appearance
throughout the sheet.
Preferably, the framework 112 provides a surface area of at least 30%, more
preferably at least 50%, and still more preferably at least 70%, and even more
preferably at
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CA 02613110 2007-11-07
least 90% of the surface area of the belt 25. One of skill will recognize that
as the surface
area increases, the amount of contact and uniformity of the imprint against
the drying
cylinders 32 will likewise increase. However, the present invention provides
the advantage
that, for a given permeability, any desired imprint fabric and distribution of
surface area
against the paper web W to be dried is attainable.
In contrast to the belts 25 limited by the weaves and technology of the prior
art, the
belt 25 according to the present invention decouples the fabric permeability
and its imprint
area. Typically, in the prior art, to make a papermaking belt 25 more
permeable, one had to
use a coarser weave. In a coarser weave, the filaments may be spaced apart on
a relatively
greater pitch. The diameter of the filaments may change. The present invention
allows the
permeability to be controlled by the framework 112, independent of the
diameter, pitch and
type of weave selected for the reinforcing element 114. This provides one of
ordinary skill
with greater latitude in selecting and making papermaking belts 25 for use in
making hard
grades of paper web W. Another potential benefit of the present invention is
that as the
amount of framework 112 increases, the sleaziness of the belt 25 can be
reduced in an
inversely proportional relationship.
In a twin-wire draw papermaking machine 20, the increased contact area with
the face
of the drying cylinder provides the benefits noted above relative to single-
wire draw
papermaking machines 20. Additionally, in a twin-wire draw, as the backside of
the belt 25
contacts the outer face of the opposite row of drying cylinders 32, further
benefits can be
realized. For example, the permeability of the belt 25 may be optimized to
reduce the
entrainment of air between the belt 25 the drying cylinder. Reducing the
entrainment of air
between the backside of the belt 25 and the drying cylinder likewise reduces
the tendency of
the paper web W to lift off of the belt 25.
Additionally, in the twin-wire draw or the single-wire draw machine, the
provision of
the framework 112 against the backside of the belt. 25 presents an increased
surface area
over which friction and wear against the rotating elements of the papermachine
may be
spread. This provides more uniform stress distribution and increased belt 25
life.
Referring to Fig. 4, the belt 25 may be made as follows. A photosensitive, and
preferably photo-curable, resin is provided. The resin is cast onto the
reinforcing element
CA 02613110 2007-11-07
114 of the papermaking belt 25. The resin is cast in liquid form and metered
to the
desired thickness. Preferably some of the resin extends above the top surface
of the
framework 112, although it is not necessary as described below. Alternatively,
a
thermally curable resin may be utilized.
A mask 120 having opaque and transparent areas is placed over the resin.
Curing
radiation R of the proper wavelength is applied through the transparent areas
of the mask
120. Portions of the resin immediately below and adjacent the transparent
areas of the
mask 120 are cured. Regions of the curable resin disposed beneath the opaque
areas are
not cured and are later washed or vacuumed away. The distribution of
transparent and
opaque areas in the mask 120 determines the pattern of the resulting framework
112 in the
belt 25.
The XY position of the framework 112 is deternnined by the transparent regions
of
the mask 120. The Z-direction height of the framework 112 is determined by the
depth of
the resin prior to curing.
Instead of a curable resin as described above, epoxy moldable clay or putty
may be
applied and externally introduced to form the framework 112. Alternatively,
bicomponent
dual-melting point filaments may be used for the papermaking belt 25. To make
a
papermaking belt 25 of the present invention, first the belt 25 is woven from
the
bicomponent filaments. The belt 25 is then disposed on a flat, rigid,
horizontal surface with
the backside downwardly oriented. Heat is locally applied but limited to the
regions desired
to be melted and form the framework 112. The localized heat melts the sheets
of the
filaments at XY positions coincident the desired portions of the framework
112. The
melted sheet material flows downward toward the horizontal support surface.
The
horizontal support surface acts as a heat sink, allowing the sheet material to
refreeze and
form a portion of the framework 112. Additionally, the framework 112 may be
printed or
extruded onto the reinforcing element 114. Suitable methods for accomplishing
the
addition of a framework 112 to a reinforcing element 114 are found in commonly
assigned
Patent Application No. WO 00/09803, published Feb. 24, 2000 and WO 00/09308,
also
published Feb. 24, 2000.
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CA 02613110 2008-10-01
Referring back to Figs. 3A and 3B, suitable belts 25 having a continuous
framework
112 and discontinuous deflection conduits 116 are illustrated in commonly
assigned U.S.
pat. nos. 4,514,345, issued April 30, 1985 to Johnson et al.; 4,528,239,
issued July 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 11, 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, 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.; 5,679,222
issued Oct. 21, 1997 to Rasch et al.; 5,714,041 issued Feb. 3, 1998 to Ayers
et al.;
5,948,210, issued Sept. 7, 1999 to Huston; 5,954,097, issued Sept. 21, 1999 to
Boutilier;
5,972,813, issued Oct. 26, 1999 to Polat et al.; 6,010,598, issued Jan. 4,
2000 to Boutilier et
al.; and, 6,110,324, iss. Aug. 29, 2000 to Trokhan et al.
The second surface of the belt 25 is the machine contacting surface of the
belt 25.
The second surface may have a backside network with passageways therein which
are
distinct from the deflection conduits 116. The passageways provide
irregularities in the
texture of the backside of the second surface of the belt 25. The passageways
allow for air
leakage in the X-Y plane of the belt 25, which leakage does not necessarily
flow in the
Z-direction through the deflection conduits 116 of the belt 25.
The second primary component of the belt 25 according to the present invention
is the
reinforcing element 114. The reinforcing element 114, like the framework 112,
has a paper
web W facing side and a machine facing side opposite the paper web W facing
side. The
reinforcing element 114 is primarily disposed between the opposed surfaces of
the belt 25
and may have a surface coincident the backside of the belt 25. The reinforcing
element 114
provides support for the framework 112. The reinforcing element 114 is
typically woven, as
is well known in the art. The reinforcement is usually woven with warp and
weft filaments,
and may comprise a single layer or be of a multi-layer construction.
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If desired, the belt 25 may be executed as a press felt, as is commonly used
in
conventional drying, and is well known in the art. A suitable press felt for
use according
to the present invention may be made according,to the teachings of commonly
assigned
U.S. Patent Nos. 5,549,790, issued Aug. 27, 1996 to Phan; 5,556,509, issued
Sept. 17,
1996 to Trokhan et al.; 5,580,423, issued Dec. 3, 1996 to Ampulski et al.;
5,609,725,
issued Mar. 11, 1997 to Phan; 5,629,052 issued May 13, 1997 to Trokhan et al.;
5,637,194, issued June 10, 1997 to Ampulski et al.; 5,674,663, issued Oct. 7,
1997 to
McFarland et al.; 5,693,187 issued Dec. 2, 1997 to Ampulski et al.; 5,709,775
issued Jan.
20, 1998 to Trokhan et al.; 5,776,307 issued Jul. 7, 1998 to Ampulski et al.;
5,795,440
issued Aug. 18, 1998 to Ampulski et al.; 5,814,190 issued Sept. 29, 1998 to
Phan;
5,817,377 issued October 6, 1998 to Trokhan et al.; 5,846,379 issued Dec. 8,
1998 to
Ampulski et al.; 5,855,739 issued Jan. 5, 1999 to Ampulski et al.; 5,861,082
issued Jan.
19, 1999 to Ampulski et al.; 5,871,887 issued Feb. 16, 1999 to Trokhan et al.;
5,897,745
issued Apri127, 1999 to Ampulski, et al.; 5,904,811 issued May 18, 1999 to
Ampulski et
al.; and 6,051,105, issued April 18, 2000 to Ampulski.
In an alternative embodiment, the belt 25 may be
executed as a press felt according to the teachings of U.S. Pat. No. 5,569,358
issued Oct.
29, 1996 to Cameron.
If desired, in a variant embodiment, the belt 25 according to the present
invention may
further comprise synclines 118 in the essentially continuous network
comprising the
framework 112. The synclines 118 intercept the paper web W facing side of the
framework
112 and extend in the Z-direction into the framework 112. The "synclines" 118
are surfaces
of the framework 112 having a Z-direction vector component extending from the
first
surface of the belt 25 towards the second surface of the belt 25. The
synclines.118 do not
extend completely through the framework 112, as do the deflection conduits
116. Thus, the
difference between a syncline 118 and a deflection conduit 116 may be thought
of as the
deflection conduit 116 represents a through hole in the framework 112, whereas
a syncline
118 represents a blind hole, fissure, chasm, or notch in the framework 112.
The synclines
118 in the framework 112 of the present invention allow for lateral leakage on
the top side,
i.e. the first surface, of the framework 112 between the felt 10 and the paper
web W.
13
CA 02613110 2008-10-01
The imprinting surface may comprise one or a plurality of alternating
synclines 118
and lands 34 respectively. As used hbrein, a "land" 34 refers to the surface
of the
framework 112 which is coincident the paper web W contacting side of the belt
25 and
disposed between the synclines 118.
The belt 25 imprints the paper web W against the drying cylinders 32 of a
single-
wire or twin-wire drying section of a papermaking machine 20. More
particularly, the
portions of the framework 112 which contact the paper web W imprint and
increase the
density of such paper web W. Conversely, deflection conduits 116 do not
imprint the
paper web W.
However, the paper web W may be de-densified as it passes over any of the
aforementioned vacuum boxes or transfer devices. Such de-densification occurs
due to
deflection of the paper web W into the deflection conduits 116. It would be
apparent to
one of ordinary skill that as the paper web W passes over more and more drying
cylinders
32, the fibers have less mobility, and thus will encounter less deflection
into the deflection
conduits 116. Accordingly, the amount of de-densification which occurs is
prophetically
sensitive to the placement of the vacuum boxes among and between the various
drying
cylinders 32.
Furthermore, an intermediate density region of the paper web W may occur. For
example, the syncline 118 neither densifles nor de-densifies the paper web W.
Since the
synclines 118 do not imprint the paper web W against the drying cylinder, no
densification occurs. Since a vacuum cannot be drawn through the syncline 118,
de-
densification cannot occur. Accordingly, the regions of the paper web W
registered with
the syncline 118 will have a density intermediate that of regions registered
with the lands
134 of the framework 112 and the deflection conduits 116.
Instead of being essentially continuous and forming discrete isolated
deflection
conduits 116, a semicontinuous framework 112 may be made and employed
according to
the teachings of commonly assigned U.S. Pat. Nos. 5,628,876, iss. May 13, 1997
to Ayers
et al. and 5,714,041, iss. Feb. 13, 1998 to Ayers et al.
A semicontinuous framework 112 extends in one direction
throughout the belt 25. A semicontinuous framework 112 may be straight,
sinusoidal, or
14
CA 02613110 2008-10-01
otherwise undulating. I.ikewise, the framework 112 may be provided in a
pattern which
is discrete, i.e., discontinuous.
Referring again to Fig. 4, as disclosed in the aforementioned patentq,
the synclineous belt 25 according to the present invention may be made
by curing a photosensitive resin through a mask 120 as described above. The
mask 120 has
first regions 42 which are transparent to actinic radiation R (indicated by
the arrows) and
second regions 44 which are opaque to the actinic radiation R. The regions 42
in the mask
120 which are transparent to the actinic radiation R will form like regions in
the
photosensitive resin which cure and become the framework 112 of the belt 25
according to
the present invention. Conversely, the regions 44 of the mask 120 which are
opaque to the
actinic radiation R will cause the resin in the positions corresponding
thereto to remain
uncured. This uncured resin is removed during the beltmaking process and does
not form
part of the belt 25 according to the present invention.
In order to form the synclines 118 in the belt 25 according to the present
invention, the
mask 120 may have opaque lines 46 corresponding to the desired synclines 118.
The
opaque lines 46 are sufficiently narrow in width that radiation R incident
thereupon at any
angle nearly perpendicular to the belt 25 is blocked from penetrating the belt
25 to any
depth 30. That portion of resin centered under and immediately below the
opaque line 46
will not receive radiation R at any depth 30. However, as the angle of
incidence of the
20, radiation R decreases (becomes less perpendicular and more parallel to the
surface), the
depth 30 of the syncline 118 correspondingly decreases.
It will be apparent to one of ordinary skill that as the desired depth 30 of
the synclines
118 increases, the width of the opaque line 46 should likewise increase. Of
course, the
opaque lines 46 may be applied in any desired pattern corresponding to the
pattern desired
for the synclines 118. For the embodiments described herein, having a syncline
118 with a
maximum depth 30 of 0.2 to 75 mils., an appropriate opaque line 46 width is
from 0.001
inches to 0.040 inches, depending upon the perpendicularity of the radiation R
incident
upon the belt 25 and the amount of curing energy imparted to the resin.
The paper web W of the present invention may have three primary regions if
made
using a fabric having the aforementioned system of lands 134, deflection
conduits 116 and
CA 02613110 2007-11-07
synclines 118. A first region 122 which may be imprinted and comprises a high
density
region, a second region 124 which comprises dcflected region, and a third
region 126 which
corresponds to the synclines 118 and the framework 112 during paperDnaking. It
is believed
that all three regions have generally equivalent basis weights. However, the
highest density
region will be the imprinted region, corresponding to the position of the
lands 134 of the
framework 112 of the belt 25. The lowest region will be those corresponding in
position to
the deflection conduits 116. The regions of the paper web W corresponding to
the synclines
118 and the papermaking belt 25 will have an intermediate density. This is
illustrated in
Table I for various patterns of belts 25.
TABLE I
High Density Resion Med. Densitv Remion Low Density Region
Discontinuous Discontinuous Discontinuous
Discontinuous Discontinuous Semicontinuous
Discontinuous Discontinuous Continuous
Discontinuous Senaicontinuous Discontinuous
Discontinuous Semicontinuous Semicontinuous
Discontinuous Continuous Discontinuous
Sennicontinuous Discontinuous Discontinuous
Semicontinuous Discontinuous Semicontinuous
Semicontinuous Semicontinuous Discontinuous
Semicontinuous Semicontinuous Semicontinuous
Continuous Discontinuous Discontinuous
Likewise, the three regions of the paper web W according to the present
invention
may be thought of as being disposed at three different elevations. As used
herein, the
elevation of a region refers to its distance from a reference plane. For
convenience, the
16
CA 02613110 2008-10-01
reference plane is horizontal and the elevational distance from the reference
plane is
vertical. The elevation of a particular region of the paper web W according to
the present
invention may be measured using any non-contacting measurement device suitable
for such
purpose as is well known in the art. A particularly suitable measuring device
is a non-
contacting Laser Displacement Sensor having a beam size of 0.3 X 1.2
millimeters at a
range of 50 millimeters. Suitable non-contacting Laser Displacement Sensors
are sold by
the Idec Company as models MX1A/B. Alternatively, a contacting stylis gauge,
as is
known in the art, may be utilized to measure the different elevations. Such a
stylis gauge is
described in commonly assigned U.S. Patent 4,300,981 issued to Carstens.
The paper web W according to the present invention is placed on the reference
plane
with the imprinted region 22 in contact with the reference plane. The domes
and synclines
118 extend vertically away from the reference plane. In this arrangement, the
vertices 35 of
the synclines 118 will be disposed intermediate the domes 24 and the imprinted
region 22.
Optionally, the paper web W according to the present invention may be
foreshortened. The optional foreshortening may be accomplished by creping or
by wet
microcontraction. Creping and wet microcontraction are disclosed in commonly
assigned
U.S. Patents 4,440,597, issued to Wells et al. and 4,191,756, issued to
Sawdai.
Foreshortening the paper
web W may make it more desirable to use anisotropically arranged synclines
118, as
discussed above. Of course, the paper web W made according to the present
invention is
typically not foreshortened at all.
It will be recognized that several variations in the paper web W according to
the
present invention are feasible. For example, the resulting paper web W may be
embossed as
is well known in the art. One or more plies of the paper web W may be joined
together to
make a laminate, corrugated product, etc. Furthennore, the paper web W made
according to
the present invention may be air laid or otherwise made with less water than
occurs in
conventional wet laid systems commonly known in the art.
While the foregoing cellulosic structures, particularly hard grades of paper
web W,
have been described in terms of density and basis weight, it is to be
recognized that the three
17
CA 02613110 2007-11-07
region structures may be described in terms of other properties as well. For
example,
intensive properties such as opacity, absorbency and caliper may be executed
in the same
manner as described above with respect to density and basis weight.
Furthermore, the
invention may be applied to other sheet goods, such as nonwoven materials,
tissue grades of
paper web W, dryer-added fabric softeners, topsheets/backsheets for disposable
absorbent
articles such as diapers and sanitary napkins, etc.
Furthermore, variations in the papermaking belt 25 are feasible. For example,
the
synclines 118 could be made by having translucent or other such lines 46 in
the mask 120
which have a transparencylopaqueness intermediate that of the first regions 42
and the
second regions 44 of the mask 120. For example, instead of opaque lines 46 in
the mask
120, the synclines 118 may be formed by regions which have an intermediate
gray level and
allow ,limited penetration of the incident radiation R.
Other variations are also feasible. For example, a particular papermaldng belt
25
may have two or more pluralities of synclines 118. A first plurality of
synclines 118 may
have a first depth 30 andlor width. A second plurality of synclines 118 may
have a second
depth 30 and/or width, etc. The pitch, amplitude and even the existence of the
undulations
may vary within a given papermaking belt 25.
In yet another variation, to reduce the air entrainment, noted above, the
backside of
the papermaking belt 25 may be provide with grooves. Preferably, the grooves
are generally
parallel the machine direction, although other orientations may be used as
desired. For such
an embodiment to occur, one of skill may cast the framework 112 onto the
backside of the
belt 25. The grooves, or any other desired patterns, are cast into this
framework 112. 'GVhile
the framework 112 extends outwardly from the backside of the belt 25, it may
also extend
to a position coincident, or below, the paper web W contacting surface of the
papermaking
belt 25.
If desired, the belt 25 may be cast once on each face, providing mutually
different
frameworlc 112 surfaces on the paper web W-contacting side and backside of the
belt 25.
Referring back to Figs. 1 and 2, the papermaking machine 20, one of ordinary
sk3ll
will recognize the benefits of the claimed invention are even greater than
described above.
Referring back to Fig. 1, it is to be recognized that a single-wire draw
papermachine may
18
CA 02613110 2007-11-07
employ a plurality of wires. Each fabric is spaced apart in the machine
direction from a
preceding fabric. The present invention allows the capability to utilize
different frameworks
112 at different fabric positions. For example, in a single-wire draw
papernnaldng machine
20, belts 25 of successively decreasing paper web W-contacting surface area
may be
provided in the machine direction. This anangement provides the benefit that a
more
uniform contact surface is presented to the paper web W while it is in its
embryonic state
and the fibers are more susceptible to imprinting and hence non-uniform
characteristics. A
higher permeability papermaking belt 25 may be provided later in the
papermaking process
providing the advantages of less air entrainment and increased flow area for
water to be
expressed through the belt 25.
Referring back to Fig. 2, in a twin-wire draw papermaldng machine 20,
different
papermaldng belts 25 may be simultaneously employed in opposed nins of the
machine.
For example, one may desire to imprint a different pattern on different sides
of the paper
web W. One papermalang belt 25 may be utilized with the upper row of drying
cylinders 32
and a different papermalting belt 25 utilized with the lower row of drying
cylinders 32. This
arrangement provides increased flexibility and versatility not previously
attainable with the
prior art. For example, unmatched patterns in the framework 112 minimize
imprinting of
the paper web W. Imprinting may be further minimized using a belt 25 having a
random
pattern framework 112. Such a variation may be combined with those noted above
so that a
twin-wire draw papermaking machine 20 having different belts 25 for different
banks of
drying cylinders 32 and different belts 25 in the machine direction may be
utilized for even
more versatility.
If desired, the papermaking belt 25 having the framework 112 according to the
present invention may be used as a forming wire. This atrangement provides the
benefit
that the framework 112 may be used to produce a watermark when hard grades of
paper web
W are being provided. The resin, or other material forming the framework 112,
serves the
dual functions of preventing flow of the furnish through that portion of the
papermaldng
belt 25 coincident the framework 112, as well as providing an imprinting
surface for
producing the watermark while the paper web W is still in an embryonic state.
19
CA 02613110 2008-10-01
As noted above, the framework 112 may extend outwardly from the surface of the
reinforcing element 114. In such a geometry, the framework 112 will imprint
the paper web
W as described above. Alternatively, the framework 112 may have one or more
proximal
ends juxtaposed with the backside of the papermaking belt 25. The framework
112 may
extend upwardly towards the paper-contacting side of the papermaking belt 25
terminating
in distal ends disposed between the backside and topside of the papermaking
belt 25.
Alternatively, the proximal end of the framework 112 may be disposed
intermediate the
topside and backside of the papermaking belt 25 as well. Such embodiments are
illustrated
and described in the commonly assigned, aforementioned and incorporated U.S.
Pat. No.
6,110,324.
Conversely, a fabric earlier in the papermaking process may be provided with a
greater open area in the deflection conduits 116. This allows for a higher
rate of water
removal. Fabrics which occur.later, in the papermaking process may have a
greater area of
the framework 112 associated with the top of the papermaking belt 25. This
allows for
more contact of the paper web W to occur against the drying cylinders 32,
thereby
increasing contact and thermal conduction. It will be recognized that any
number of
arrangements are feasible with the present invention, wherein a plurality of
different drying
fabrics are employed.
Of course, the papermaking belts 25 according to the present invention may be
intermixed with papermaking belts 25 according to the prior art as well.
If desired, the papermaking belt 25 may have batting added thereto, as is
commonly
known for felt drying. If batting is selected to be added to the papermaking
belt 25, the
framework 112 may be applied to the topside of the batting of the papermaking
belt 25. A
removable curable material may be backfilled to the desired elevation starting
from the
backside of the belt 25 to prevent curing of the resin forming the framework
112 below the
desired elevation. Backfilling is disclosed in commonly assigned U.S. Pat.
Nos. 5,629,052,
iss. May 13, 1997 to Trokhan et al. and 5,674,663, iss. Oct. 7, 1997 to
McFarland et al.
Of course, in addition to imprinting the paper web W, and providing multi-
density
paper web W, the framework 112 increases the wear resistance of the
papermaking fabric.
CA 02613110 2007-11-07
Thus, the benefits cited above of increased life for the papermaking belt 25
occur due to the
framework 112 providing resistance to abrasion and friction. As the amount of
surface area
of the framework 112 disposed on the backside of the papermaking belt 25
increases, the
resistance to friction and wear increases in an inversely proportional
relationship.
If desired, the framework 112 may be applied below the bottom surface of the
optional batting. This arrangement provides the benefit of the improved wear
resistance
noted above. To achieve such an arrangement with the framework 112 extending
outwardty
from the backside of the papermaking belt 25, the belt 25 is inverted from the
casting
position described above and the optional backfill applied through the top
surface of the belt
25. Of course, it will be apparent to one of ordinary skill that a first
pattern may be applied
to the backside of the belt 25 for improved wear resistance and a second
pattern may be
applied to the topside of the belt 25 for imprinting onto the paper web W.
21
