Note: Descriptions are shown in the official language in which they were submitted.
CA 022~0~89 1998-10-27
A TRANSFER SYSTEM AND PROCESS FOR MAKING A
STRETCHABLE FIBROUS WEB AND ARTICLE PRODUCED THEREOF
FIELD OF THE INVENTION
This invention generally relates to the field of paper
making, and more specifically, to a fibrous web produced by a
transfer system.
BACKGROUND
In a paper making machine, paper stock is fed onto
traveling endless belts or "fabrics" that are supported and
driven by rolls. These fabrics serve as the papermaking
surface of the machine. In many paper making machines, at
least two types of fabrics are used: one or more "forming"
fabrics that receive wet paper stock from a headbox or
headboxes, and a "dryer" fabric that receives the web from
the forming fabric and moves the web through one or more
drying stations, which may be through dryers, can dryers,
capillary dewatering dryers or the like. In some machines, a
separate transfer fabric may be used to carry the newly
formed paper web from the forming fabric to the dryer fabric.
Generally speaking, the term "first transfer" refers to
the transfer of the wet paper stock from a headbox to the
forming fabric, which will be referred to as the "first
carrier fabric". The term "second transfer" may be
understood as the transfer of the paper web that is formed on
the first carrier fabric to a transfer fabric or a dryer
CA 022~0~89 1998-10-27
fabric, which will be referred to as a "second carrier
fabric". These terms may be used in connection with twin wire
forming machines, Fourdrinier machines and the like.
At or near the second transfer, the first carrier fabric
and the second carrier fabric are guided to converge so that
the paper web is positioned between the two fabrics.
Generally speaking, centripetal acceleration, centrifugal
acceleration and/or air pressure (which is typically applied
as either a positive pressure or a negative pressure from a
"transfer head" that is adjacent to the fabrics) causes the
web to separate from the forming fabric and attach to the
dryer fabric.
While the second carrier fabric is often run at the same
speed as the first carrier fabric, it is known that the
second carrier fabric may be run at a speed that is less than
the speed of the first carrier fabric. This difference in
speed between the fabrics is typically expressed in terms of
a ratio of fabric velocities (i.e., velocity ratio) to
describe what is known in the industry as "negative draw."
As described in U.S. Patent No. 4,440,597, to Wells et al.,
the speed differential between the fabrics in the region of
the second transfer bunches the web and creates microfolds
that enhance the web's bulk and absorbency. This increases
the bulk and absorbency of the web, and also increases
stretch or extensibility in the machine direction (MD) of the
web. Too much negative draw, however, will create
- undesirable "macrofolding" in which part of the web buckles
and folds back on itself. FIG. l depicts a cross-sectional
representation (not to scale) of an exemplary macrofold in a
paper sheet. Generally speaking, macrofolds occur in such a
manner that adjacent machine direction spaced portions of the
web become stacked on each other in the Z-direction of the
web. The risk of macrofolding appears to impose a limitation
on the amount of negative draw (i.e., the velocity ratio)
that can be applied at the second transfer.
.
CA 022~0~89 1998-10-27
Generally speaking, it has been thought that the amount
of MD foreshortening and subsequent extensibility (i.e., MD
stretch) imparted to the web at the second transfer is very
closely proportional to or essentially the same as the
velocity ratio of the second carrier fabric to that of the
first carrier fabric. Thus, attempts to increase the MD
stretch or foreshortening of a web by increasing the velocity
ratio (i.e., negative draw) were thought to also increase the
likelihood of macrofolding.
Accordingly, a need exists for an improved process of
making a fibrous web with desirable machine direction
stretchability while avoiding macrofolding. For example, such
a need extends to a process of making a paper web with
desirable machine direction stretch while avoiding
macrofolding.
There is also a need for an improved second transfer
system for use in a paper making machine that allows greater
MD extensibility (i.e., MD stretch) to be achieved at the
same, or even lower, levels of negative draw than heretofore
thought possible. Meeting this need is important because it
is highly desirable to achieve greater MD extensibility
(i.e., MD stretch) at the same, or even lower, levels of
negative draw. It is also highly desirable to achieve even
the same amount of MD extensibility (i.e., MD stretch) at
lower levels of negative draw. Meeting this need would
provide the positive benefits of creating MD-oriented
extensibility or stretch in the web while avoiding or
lowering the risk of macrofolding. Meeting this need could
also allow more MD-oriented extensibility or stretch to be
built into the web without increasing the risk of
macrofolding.
Furthermore, webs produced by a conventional transfer
process using a convex transfer head surface, for example the
process described in U.S. Patent No. 4,440,597, and issued
April 3, 1984, may lack sufficient toughness, particularly
when wet. Generally, a towel incorporating a web produced by
CA 022~0~89 1998-10-27
a transfer process with improved toughness provides more
durability during scrubbing. In addition, a transfer process
produced web with improved toughness may resist deformation
and breaking during processing, thereby improving
manufacturing efficiencies. Generally moreover, improved
toughness permits manufacture of a towel with less strength,
but with comparable toughness of a conventional towel.
Generally, lowering the strength requirements permits the
manufacture of a towel with a softer feel.
Accordingly, a web that is manufactured by a transfer
process and has greater toughness will improve over
conventional webs.
DEFINITIONS
As used herein, the term "nonwoven web" refers to a web
that has a structure of individual fibers or filaments which
are interlaid forming a matrix, but not in an identifiable
repeating manner. Nonwoven webs have been, in the past,
formed by a variety of processes known to those skilled in
the art such as, for example, meltblowing, spunbonding, wet-
forming and various bonded carded web processes.
As used herein, the term "spunbonded web" refers to a web
of small diameter fibers and/or filaments which are formed by
extruding a molten thermoplastic material as filaments from a
plurality of fine, usually circular, capillaries in a
spinnerette with the diameter of the extruded filaments then
being rapidly reduced, for example, by non-eductive or
eductive fluid-drawing or other well known spunbonding
mechanisms. The production of spunbonded nonwoven webs is
illustrated in patents such as Appel, et al., U.S. Patent No.
4,340,563.
As used herein, the term "meltblown fibers" means fibers
formed by extruding a molten thermoplastic materlal through a
plurality of fine, usually circular, die capillaries as
molten threads or filaments into a high-velocity gas (e.g.
.
CA 022~0~89 1998-10-27
air) stream which attenuates the filaments of molten
thermoplastic material to reduce their diameters, which may
be to microfiber diameter. Thereafter, the meltblown fibers
are carried by the high-velocity gas stream and are deposited
on a collecting surface to form a web of randomly disbursed
meltblown fibers. The meltblown process is well-known and is
described in various patents and publications, including NRL
Report 4364, "Manufacture of Super-Fine Organic Fibers" by
V.A. Wendt, E.L. Boone, and C.D. Fluharty; NRL Report 5265,
"An Improved Device for the Formation of Super-Fine
Thermoplastic Fibers" by K.D. Lawrence, R.T. Lukas, and J.A.
Young; and U.S. Patent No. 3,849,241, issued November 19,
1974, to Buntin, et al.
As used herein, the term "microfibers" means small
diameter fibers having an average diameter not greater than
about 100 microns, for example, having a diameter of from
about 0.5 microns to about 50 microns, more specifically
microfibers may also have an average diameter of from about 1
micron to about 20 microns. Microfibers having an average
diameter of about 3 microns or less are commonly referred to
as ultra-fine microfibers. A description of an exemplary
process of making ultra-fine microfibers may be found in, for
example, U.S. Patent No. 5,213,881, entitled "A Nonwoven Web
With Improved Barrier Properties".
As used herein, the term "fibrous cellulosic material"
refers to a nonwoven web including cellulosic fibers (e.g.,
- pulp) that has a structure of individual fibers which are
interlaid, but not in an identifiable repeating manner. Such
webs have been, in the past, formed by a variety of nonwoven
manufacturing processes known to those skilled in the art
such as, for example, air-forming, wet-forming and/or paper-
making processes. Exemplary fibrous cellulosic materials
include papers, tissues and the like. Such materials can be
treated to impart desired properties utilizing processes such
as, for example, calendering, creping, hydraulic needling,
hydraulic entangling and the like. Generally speaking, the
CA 022~0~89 1998-10-27
fibrous cellulosic material may be prepared from cellulose
fibers from synthetic sources or sources such as woody and
non-woody plants. Woody plants include, for example,
deciduous and coniferous trees. Non-woody plants include,
for example, cotton, flax, esparto grass, milkweed, straw,
jute, hemp, and bagasse. The cellulose fibers may be
modified by various treatments such as, for example, thermal,
chemical and/or mechanical treatments. It is contemplated
that reconstituted and/or synthetic cellulose fibers may be
used and/or blended with other cellulose fibers of the
fibrous cellulosic material. Fibrous cellulosic materials
may also be composite materials containing cellulosic fibers
and one or more non-cellulosic fibers and/or filaments. A
description of a fibrous cellulosic composite material may be
found in, for example, U.S. Patent No. 5,284,703.
As used herein, the term "pulp" refers to cellulosic
fibrous material from sources such as woody and non-woody
plants. Woody plants include, for example, deciduous and
coniferous trees. Non-woody plants include, for example,
cotton, flax, esparto grass, milkweed, straw, jute, hemp, and
bagasse. Pulp may be modified by various treatments such as,
for example, thermal, chemical and/or mechanical treatments.
As used herein, the term "machine direction" (hereinafter
may be referred to as "MD") is the direction of a material
parallel to its forward direction during processing.
As used herein, the term "cross direction" (hereinafter
may be referred to as "CD") is the direction of a material
perpendicular to its machine direction.
As used herein, the term "machine direction tensile"
(hereinafter may be referred to as "MDT") is the force per
machine direction unit width required to rupture a sample and
may be reported as kilogram-force per meter.
As used herein, the term "cross direction tensile"
(hereinafter may be referred to as "CDT") is the force per
cross direction unit width required to rupture a sample and
may be reported as kilogram-force per meter.
CA 022~0~89 1998-10-27
As used herein, the term "basis weight" (hereinafter may
be referred to as "BW") is the weight per unit area of a
sample and may be reported as kilogram-force per meter
squared.
As used herein, the term "geometric mean breaking length"
(hereinafter may be referred to as "GMBL") is the measurement
of the strength of a material, generally a fabric or nonwoven
web, and may be reported in length measurements, such as
meters. The greater the geometric mean breaking length
generally relates to a stronger material. The geometric mean
breaking length is calculated by the formula:
GMBL = (MDT*CDT) 0-5 /BW
As used herein, the term "peak energy" is the measurement
the toughness of a material, generally a fabric or nonwoven
web, and may be reported in static energy measurements, such
as kilogram times meter times centimeter, which may be
hereinafter be abbreviated as "cm-kgm". The peak energy is
the area under the tensile load versus strain curve from the
origin to the breaking point of the material.
As used herein, the term "wet mullen burst" is a test
used to measure the overall toughness of a water saturated
material, such as fabric or nonwoven web. The higher
material rupture pressure, typically reported in pascals,
generally relates to a tougher water saturated material.
- As used herein, the term "dry mullen burst" is a test
used to measure the overall toughness of a material, such as
fabric or nonwoven web, treated approximately 12 hours at 23
degrees centigrade at 50 percent humidity prior to testing.
The higher material rupture pressure, typically reported in
pascals, generally relates to a tougher material.
As used herein, the term "gauge length" is the length of
a sample, typically reported in centimeters, measured between
the points of attachment while under uniform tension.
.
CA 022~0~89 1998-10-27
As used herein, the term "slack" is the lack of tension
in a sample and reported in length measurements, such as
millimeters.
As used herein, the term "percent stretch" is a test used
to measure the toughness of a material, such as fabric or
nonwoven web. The percent stretch is the increase in length
expressed as a percentage of the corrected gauge length,
which is gauge length plus slack. The higher percent stretch
generally relates to a tougher material.
As used herein, the term "elmendorf tear" is a test used
to measure the toughness of a material, such as fabric or
nonwoven web. The test measures the force, typically
reported in centinewtons, required to start or propagate a
rip in a material. The higher required force generally
relates to a tougher material.
As used herein, the term "tensile modulus" is the slope
of the tensile load versus strain curve measured from the
origin until the sample reaches its inelastic point. This
measurement may be reported in units of force per area, such
as gram-force per centimeter squared. The higher curve slope
generally relates to a tougher sample.
As used herein, the term "calender" refers to a process
for fabrics or nonwoven webs that reduces the caliper and
imparts surface effects, such as increased gloss and
smoothness. Generally, the process includes passing the
fabric through two or more heavy rollers, sometimes heated,
- and under heavy pressure.
As used herein, the term "noncalender" refers to a fabric
or nonwoven web that has not undergone a calender process.
As used herein, the terms "permeable" and "permeability"
refer to the ability of a fluid, such as, for example, a gas
to pass through a particular porous material. Permeability
may be expressed in units of volume per unit time per unit
area, for example, (cubic feet per minute) per square foot of
material (e.g., (ft3/minute/ft2). Permeability was
determined utilizing a Frazier Air Permeability Tester
CA 02250~89 1998-10-27
available from the Frazier Precision Instrument Company and
measured in accordance with Federal Test Method 5450,
Standard No. l9lA, except that the sample size was 8" X 8"
instead of 7" X 7". Although permeability is generally
expressed as the ability of air or other gas to pass through
a permeable sheet, sufficient levels of gas permeability may
correspond to levels of liquid permeability to enable the
practice of the present invention. For example, a sufficient
level of gas permeability may allow an adequate level of
liquid to pass through a permeable sheet with or without
assistance of a driving force such as, for example, an
applied vacuum or applied gas pressure.
SU~IARY OF THE INVENTION
Accordingly, it is an object of this invention to provide
an improved process of making a fibrous web with desirable
machine direction stretch while avoiding macrofolding.
It is also an object of this invention to provide a
second transfer system for use in a paper making machine that
allows greater machine direction stretch to be achieved at
the same, or even lower, levels of negative draw than
heretofore thought possible.
It is also an object of this invention to provide a
fibrous cellulosic web having a relatively low density
structure, good absorbency, good strength and relatively high
levels of MD extensibility or stretch than heretofore thought
possible without macrofolding.
These and other objects are addressed by the process of
the present invention for making a machine direction
extensible fibrous web utilizing an improved second transfer
system having a lengthened transfer zone. The process
includes the steps of: l) forming a fibrous web from an
liquid suspension of fibrous material, the fibrous web having
a consistency ranging from about 12% to about 38% (after the
headbox); 2) transporting the fibrous web on a first carrier
CA 022~0~89 1998-10-27
fabric at a first velocity to a lengthened transfer zone that
begins at a transfer shoe and terminates at a portion of a
transfer head and has a machine direction oriented length
ranging from about 0.75 inches to about 10 inches; 3)
guiding the first carrier fabric and fibrous web over the
transfer shoe so they converge at a first angle with a second
carrier fabric moving along a linear path through the
lengthened transfer zone at a second velocity which is less
than the first velocity, wherein the first angle is
sufficient to generate centrifugal force to aid transfer of
the fibrous web to a second carrier fabric and wherein the
first and second carrier fabrics begin diverging immediately
after the transfer shoe at a second angle such that the
distance between the first and second carrier fabrics through
the lengthened transfer zone is approximately equal to the
thickness of the fibrous web; 4) applying a sufficient level
of gaseous pressure differential at the transfer head to
complete the separation of the fibrous web from the first
carrier fabric and attachment to the second carrier fabric;
and 5) drying the fibrous web.
The fibrous web (e.g., paper sheets) produced by the
process of the present invention has greater machine
direction extensibility than fibrous webs (e.g., paper
sheets) processed with the same carrier fabrics in
differential speed transfer processes without the improved
second transfer system having a lengthened transfer zone.
According to the invention, the fibrous web may have a
consistency ranging from about 18% to about 30%. For
example, the fibrous web may have a consistency ranging from
about 20% to about 28~.
The lengthened transfer zone begins at a transfer shoe
and terminates at a portion of a transfer head. Desirably,
the lengthened transfer zone terminates at a leading or top
edge of a vacuum slot in the transfer head. When measured
between the transfer shoe land and the leading or top edge of
a vacu~m slot in the transfer head, the machine direction
CA 022~0~89 1998-10-27
oriented length of the lengthened transfer zone may range
from about 0.75 to about 10 inches. For example, the machlne
direction oriented length of the lengthened transfer zone may
range from about 2 to about 5 inches. As another example, the
machine direction oriented length of the lengthened transfer
zone may range from about 3 to about 4 inches. As yet another
example, the machine direction oriented length of the
lengthened transfer zone may be about 3.5 inches. Of course,
it is contemplated that the lengthened transfer zone having
similar dimensions may terminate at other portions of the
transfer head such as, for example, the trailing edge of the
vacuum slot, the trailing edge of the transfer head or the
like.
The first angle at the transfer shoe may range from about
2 degrees to about 20 degrees. For example, the first angle
at the transfer shoe may range from about 8 degrees to about
12 degrees.
According to an aspect of the invention, the first and
second carrier fabrics diverge immediately after the transfer
shoe at a second angle ranging from about 0.01 degree to
about 1 degree such that the distance between the first and
second carrier fabrics through the lengthened transfer zone
is approximately equal to the thickness of the fibrous web.
For example, the second angle may range from about 0.075
degree to about 0.5 degree. As another example, the second
angle may be about 0.1 degree. Generally speaking, the
- distance between the first and second carrier fabrics through
the lengthened transfer zone may range from about 0.0075 inch
to about 0.0125 inch for a paper sheet having a basis weight
of about 32 grams per square meter (~1 ounce per square
yard).
In an embodiment of the process of the present invention,
the fibrous web may be a paper sheet including, but not
limited to, paper towel, paper tissue, crepe wadding, paper
napkin, or the like.
.
11
CA 022~0~89 1998-10-27
The process of the present invention may utilize any
conventional drying technique. Desirably, the drying
technique is a non-compressive drying technique. Exemplary
drying techniques include, but are not limited to, Yankee
dryers, heated cans, through-air dryers, infra-red dryers,
heated ovens, microwave dryers and the like. The process of
the present invention may also include any conventional post-
treatment steps including, but not limited to, creping,
double re-recreping, mechanical softening, embossing,
printing or the like.
The present invention also encompasses a machine
direction extensible fibrous web formed by the process
described above.
An aspect of the present invention relates to an improved
transfer configuration for a paper making machine that is
designed to produce in a fibrous web, at any given amount of
negative draw, a greater amount of machine direction-oriented
extensibility or stretch than was heretofore thought
possible. This improved transfer configuration includes
first carrier fabric having a first surface on which a
fibrous web is transported to the transfer configuration; a
second carrier fabric having a second surface on which the
fibrous web is transported away from the transfer
configuration; and a lengthened transfer zone structure for
constraining the first and second carrier fabrics to move
through a substantially linear, lengthened transfer zone, the
lengthened transfer zone defined as the area in which the
first and second surfaces are separated by a distance that is
approximately equal to the thickness of the fibrous web, and
wherein the lengthened transfer zone structure further
constrains the first and second carrier fabrics as to cause
the transfer zone to have a machine direction oriented length
that is within the range of about 1.5 inches to about ten
inches, the lengthened transfer means having the ability to
increase the amount of machine direction stretch or
CA 022~0~89 1998-10-27
extensibility that is built into the fibrous web at any given
level of negative draw.
Generally speaking, the distance between the first and
second carrier fabrics within the transfer zone should be
sufficient so that both the first carrier fabric and the
second carrier fabric are in contact with the fibrous web.
An aspect of the improved transfer configuration of the
present invention is that the first and second carrier
fabrics are constrained so as to form a substantially linear,
lengthened transfer zone. The second carrier fabric should
pass through the lengthened transfer zone along a linear
path. The first carrier fabric should also pass through the
lengthened transfer zone along a linear path. The fabrics
may diverge at a slight angle which may range from about 0.05
to about 0.125 degrees.
The present invention also encompasses a process of
making a machine direction extensible or stretchable fibrous
web in which the process includes the steps of (a)
transporting a fibrous web on a first surface of a first
carrier fabric to a transfer configuration; (b) moving a
second carrier fabric that has a second surface to the
transfer configuration, the second carrier fabric being moved
at a speed that is less than the speed of the first carrier
fabric to create an amount of negative draw; (c)
constraining, at the transfer configuration, the first and
second carrier fabrics to move through a lengthened transfer
- zone that is defined as the area in which the first and
second surfaces are separated by a distance that is
approximately equal to the thickness of the fibrous web, the
transfer zone having a machine direction oriented length that
is within the range of about 1.5 inches to about ten inches;
and (d) transporting the foreshortened web away from the
transfer configuration on the second surface of the second
carrier fabric.
According to an aspect of the process described above,
the distance between the first and second carrier fabrics
13
CA 022~0~89 1998-10-27
within the transfer zone should be sufficient so that both
the first carrier fabric and the second carrier fabric are ln
contact with the fibrous web.
A machine direction stretchable web made according to the
transfer system or process discussed above is also considered
to be an important aspect of the invention.
The present invention further encompasses a machine
direction extensible noncalendered fibrous web produced by a
transfer system of at least eight percent negative draw
including a matrix of fibrous web material having a wet
mullen burst pressure at least about lO percent greater than
a convex transfer system produced web. Moreover, the matrix
of fibrous web material has a wet mullen burst of at least
about 74500 pascals. In addition, the matrix of fibrous web
material has a GMBL ranging from about 2047 to about 2704.
Furthermore, the fibers of the fibrous web matrix may be
generated from the group consisting of a bonded carded web,
spunbonded web, meltblown fiber web, and multi-ply fibrous
web. Moreover, the matrix of fibrous web material may have
an elmendorf tear greater than about 66.5 centinewton. Also,
the matrix of fibrous web material may have a tensile modulus
of at least about 1544 gram per- centimeter squared.
Additionally, the matrix of fibrous web material may have
greater strength at lower negative draw percent. Furthermore,
the matrix of fibrous web material may have a greater machine
direction toughness at about the same GMBL as a convex
- transfer produced web.
The present invention still further encompasses a
noncalendered paper sheet produced by a transfer system of at
least eight percent negative draw including a matrix of
fibrous web material having a wet mullen burst pressure at
least about lO percent greater than a convex transfer system
produced sheet. In addition, the sheet may have a wet mullen
burst of at least about 74500 pascals. Moreover, the sheet
may have a GMBL ranging from about 2047 to about 2704.
Furthermore, the matrix of fibrous web material may be made
14
CA 022~0~89 1998-10-27
of a mixture of fibers and at least one other fiber selected
from the group consisting of wood pulp and staple fibers.
Moreover, the matrix of fibrous web material may be made of a
mixture of fibers and at least one particulate selected from
the group consisting of activated carbon, clays, fillers,
adsorbents, zeolites, superabsorbents, silica, and
hydrocolloid. Additionally, the matrix of fibrous web
material may be selected from the group consisting of a
bonded carded web, spunbonded web, meltblown fiber web, and
multi-ply fibrous web. Also, the matrix of fibrous web
material may have an elmendorf tear greater than about 66.5
centinewton. Furthermore, the matrix of fibrous web material
may have a tensile modulus of at least about 1544 gram per
centimeter squared. Moreover, the matrix of fibrous web
material may have greater strength at lower negative draw
percent. Also, the matrix of fibrous web material may have
greater machine direction toughness at about the same GMBL as
a convex transfer produced web.
These and various other advantages and features of
novelty which characterize the invention are pointed out with
particularity in the claims annexed hereto and forming a part
hereof. However, for a better understanding of the invention,
its advantages, and the objects obtained by its use,
reference should be made to the drawings which form a further
part hereof, and to the accompanying descriptive matter, in
which there is illustrated and described a preferred
- embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a cross-sectional representation (not to scale)
of an exemplary macrofold in a paper sheet.
FIG. 2 is a schematic view of an exemplary improved
transfer configuration.
CA 022~0~89 1998-10-27
FIG. 3 is a schematic view showing in more detail certain
features of an exemplary improved transfer configuration
shown in FIG. 2.
FIG. 4 is a schematic view of an exemplary "point
contact" transfer configuration.
FIG. 5 is a graphical depiction of machine direction
stretch versus negative draw for samples that were produced
with an exemplary improved transfer configuration versus
samples that were produced with an exemplary "convex" or
"point contact" transfer configuration.
FIG. 6 is a graphical depiction of wet mullen bursting
pressure reported by pascal versus geometric mean breaking
length reported by meter for samples that were produced with
an exemplary improved transfer configuration versus samples
that were produced with an exemplary "convex" or "point
contact" transfer configuration.
FIG. 7 is a graphical depiction of dry mullen bursting
pressure reported by pascal versus geometric mean breaking
length reported by meter for samples that were produced with
an exemplary improved transfer configuration versus samples
that were produced with an exemplary "convex" or "point
contact" transfer configuration.
FIG. 8 is a graphical depiction of tear reported by
centinewton versus geometric mean breaking length reported by
meter for samples that were produced with an exemplary
improved transfer configuration versus samples that were
produced with an exemplary "convex" or "point contact"
transfer configuration.
FIG. 9 is a graphical depiction of tensile load reported
by gram per centimeter versus strain reported by centimeter
for samples that were produced with an exemplary improved
transfer configuration versus samples that were produced with
an exemplary "convex" or "point contact" transfer
configuration.
FIG. lO is a graphical depiction of peak energy reported
by cenrimeter times kilogram times meter divided by seconds
16
CA 022~0~89 1998-10-27
~ .
squared versus geometric mean breaking length reported by
meter for samples that were produced with an exemplary
improved transfer configuration versus samples that were
produced with an exemplary "convex" or "point contact"
transfer configuration.
FIG. ll is a graphical depiction of machine direction
stretch reported by percent versus geometric mean breaking
length reported by meter for samples that were produced with
an exemplary improved transfer configuration versus samples
that were produced with an exemplary "convex" or "point
contact" transfer configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S)
Referring now to the drawings, wherein like reference
numerals designate corresponding structure throughout the
views, and referring in particular to FIGS. 2 and 3, there is
shown (not to scale) an exemplary improved transfer
configuration lO for a paper making machine. Such an improved
transfer configuration and its associated process of making
fibrous webs are designed to produce in a fibrous web, at any
given amount of negative draw, a greater amount of machine
direction oriented extensibility or stretch than was
heretofore thought possible. That is, at a specified velocity
ratio between the first and second carrier fabrics, the
transfer configuration and its associated process of making
fibrous webs produce fibrous webs having greater machine
direction extensibility than fibrous webs processed with the
same carrier fabrics in differential speed transfer
configurations without a lengthened transfer zone. Thus, webs
having greater levels of machine direction extensibility may
be achieved without macrofolding. Alternatively and/or
additionally, webs having currently obtainable levels of
machine direction extensibility may be achieved at a reduced
CA 022~0~89 1998-10-27
risk of macrofolding thus allowing more reliable operation of
such processes.
Thus, the present invention may provide improvements in
levels of machine direction extensibility or machine
direction stretch of from about 2.5% to about 50% or more at
the same level of negative draw. For example, the improvement
in machine direction extensibility or machine direction
stretch may range from about 5% to about 30% or more. As
another example, the improvement in machine direction
extensibility or machine direction stretch may range from
about 5% to about 20% or more. As yet another example, the
improvement in machine direction extensibility or machine
direction stretch may range from about 5% to about 15% or
more. Moreover, the present invention may provide a greater
total amount of machine direction extensibility or stretch
than could be achieved in fibrous webs processed with the
same carrier fabrics in differential speed transfer
configurations without a lengthened transfer zone.
For purposes of the present invention, the term "machine
direction" as used with respect to a fibrous web refers to
the direction parallel to the direction of formation of a
fibrous web. Generally speaking, the machine direction
stretch or extensibility may be determined with conventional
tensile testing equipment utilizing conventional testing
techniques. For example, the machine direction stretch may be
determined on equipment such as, for example, a Thwing-Albert
Intellect STD2 tensile tester utilizing a one-inch wide strip
of material cut so the length of the material is aligned in
the machine direction. Typically, the material is conditioned
at 50% relative humidity before it is mounted on the tester.
The jaws of the tester are set so there is a two-inch gap and
so they move apart at a rate of two inches per minute.
As mentioned previously, the term "negative draw" refers
to a ratio of velocities of first and second carrier fabrics
cooperating in the second transfer of a fibrous web. The
18
CA 022~0~89 1998-10-27
negative draw may be stated as a percentage and can be
calculated by the equation:
Negative Draw(%) = (Vl - V2)/ Vl x 100
where Vl is the speed of the first carrier fabric and V2 is
the speed of the second carrier fabric.
According to an embodiment of the present invention, the
improved transfer configuration includes a first carrier
fabric 12 having a first surface 14 on which a fibrous web 16
is transported to a lengthened transfer zone 18 at a first
velocity. The transfer configuration also includes a second
carrier fabric 20 having a second surface 22 which the
fibrous web 16 is transported away from the lengthened
transfer zone 18 at a second velocity that is less than the
first velocity.
Generally speaking, the first carrier fabric 12 may be a
paper making forming fabric or other fabric used in wet
formation processes. The second carrier fabric 20 may be a
through-air dryer fabric, intermediate transfer fabric or
other fabric useful in stages of a wet formation process
following the initial forming step.
The lengthened transfer zone 18 begins at a transfer shoe
24 and terminates at a leading portion or top edge 26 of a
vacuum slot 30 in a transfer head 28. The lengthened transfer
zone begins at a transfer shoe and terminates at a portion of
- a transfer head. As noted above, it is contemplated that the
lengthened transfer zone may terminate at other portions of
the transfer head such as, for example, the trailing edge of
the vacuum slot, the trailing edge of the transfer head or
the like. For example, a lengthened transfer zone 18' is
shown in FIGS. 2 and 3 as beginning at a transfer shoe and
terminating at the trailing edge "T" of the transfer head 28.
The transfer shoe 24 may be a rotatable cylinder or
roller (not shown) or may be a stationary chock, wedge or
guide. ~s is evident from FIG. 3, the transfer configuration
19
CA 022~0~89 1998-10-27
,
includes means for guiding the first carrier fabric 12 and
the fibrous web 16 over the transfer shoe 24 so they converge
with the second surface 22 of the second carrier fabric 20.
The transfer shoe should have a shape or configuration
that causes the moving fabric 12 and fibrous web 16 to
generate at least some centrifugal force to aid transfer of
the fibrous web as the first carrier fabric 12 and fibrous
web 16 converge with the second carrier fabric 20. The
transfer shoe 24 may be curved, bent, angled or exhibit some
other topographical change that helps generate centrifugal
force in the moving carrier fabric 12 and fibrous web 16 to
aid transfer. In some embodiments, the transfer shoe may be a
roller or stationary cylinder.
The first carrier fabric 12 and the second carrier fabric
20 converge at an angle ~. That is, angle ~ is the angle
between the first carrier fabric 12 and the second carrier
fabric 20 just ahead of the transfer shoe. Generally
speaking, the size of the first angle ~ may vary depending on
factors including, but not limited to, the velocity of the
first carrier fabric, the consistency of the fibrous web, the
composition of the fibrous web, the structure of the first
carrier fabric. For example, the first angle ~ may range from
about 2 degrees to about 20 degrees. As another example, the
first angle ~ may range from about 8 degrees to about 12
degrees.
- Immediately after the transfer shoe 24, the first carrier
fabric and the second carrier fabric begin diverging at a
second angle ~ such that the distance between the first and
second carrier fabrics is about equal to the thickness of the
fibrous web throughout the lengthened transfer zone. In
general, the fabrics may diverge at a second angle ~ which
may range from about 0.01 degree to about 1 degree.
According to the invention, the first and second carrier
fabrics 12, 20, are desirably set up statically (i.e., prior
CA 022~0~89 1998-10-27
to running the process) so they almost touch or even
partially touch each other at the transfer shoe. From that
point, the fabrics travel in a substantially linear, but
slightly diverging, path so that during operation they each
remain in contact with the fibrous web to the terminal point
of the lengthened transfer zone. With this set-up, the
separation or thickness between the first and second carrier
fabrics may vary slightly from a minimum distance at the
transfer shoe to a maximum at the termination of the
lengthened transfer zone. At the terminal point, the
separation or distance between the first and second carrier
fabrics 12, 20 should be approximately equal to the thickness
of the fibrous web.
The means for guiding the first carrier fabric 12 and the
fibrous web 14 over the transfer shoe 24 so they converge and
then immediately begin diverging at a slight angle includes
the transfer shoe as well as any conventional conveyor or
fabric guidance means commonly used with paper making or web
handling equipment.
As may best be seen in FIG. 3, a fibrous web 16 is
transported to a lengthened transfer zone 18 on the first
surface 14 of the first carrier fabric 12, where it is
transferred to the second surface 22 of the second carrier
fabric 20. As also shown in FIG. 3, the lengthened transfer
zone 18 is constructed and arranged to constrain the first
and second carrier fabrics 12, 20 to move through the
lengthened transfer zone along a substantially linear path
such that the first and second surfaces 14, 22 are separated
by a distance that is approximately equal to the thickness of
the fibrous web at least when leaving the lengthened transfer
zone. In this way, the first and second surfaces 14, 22 of
the carrier fabrics are in contact with fibrous web
substantially throughout the lengthened transfer zone. For
example, the distance between the first and second carrier
fabrics (at least when leaving the lengthened transfer zone)
may range from about 0.0075 inch to about 0.0125 inch for a
21
CA 022~0~89 1998-10-27
paper sheet having a basis weight of about 32 gram.
Desirably, the dlstance between the first and second carrier
fabrics may be ten one-thousandths of an inch (O.Ol") for a
paper sheet having a basis weight of about 32 gram. Of
course, heavier basis weight fibrous webs may require greater
distance between the carrier fabrics and lower basis weight
fibrous webs may require less distance between the carrier
fabrics. The distance between the fibrous webs may be
influenced by factors including, but not limited to, the
topography of the carrier fabrics, the consistency of the
fibrous web, and the composition of the fibrous web.
The present invention may be used with a variety of wet-
formed fibrous webs having a variety of basis weights.
Desirably, the fibrous webs are composed of pulp (e.g., paper
stock) but it is contemplated that blends of pulp and other
fibrous and/or particulate materials may be used. For
example, the fibrous webs may include natural and synthetic
fibers of various lengths, including but not limited to
staple lengths. Particulate materials may be incorporated in
the fibrous web and may include, but are not limited to,
activated carbon, silica, hydrocolloid, clays, fillers,
adsorbents, zeolites, superabsorbents and the like. The
transfer configuration and process of the present invention
may be used to make machine direction stretchable fibrous
webs having a wide range of basis weights. For example, the
basis weight of the fibrous web may range from about 8 gram
to about 70 gram. As another example, the basis weight of
the fibrous web may range from about 17 gram to about 50
gram. As yet another example, the basis weight of the
fibrous web may range from about 32 gram to about 42 gram.
Referring to FIG. 3, the lengthened transfer zone 18
extends for a distance Ltz in the machine direction of the
paper making machine. The transfer zone length Ltz is
substantially greater than the comparable transfer length of
conventional systems. Generally speaking, conventional
systems seek to provide a "point contact" transfer zone.
22
CA 022~0~89 1998-10-27
That is, conventional systems appear to be designed so the
transfer zone is very small.
It is also evident from FIG. 3, that the first and second
carrier fabrics are constrained so as to form a substantially
linear, lengthened transfer zone. That is, second carrier
fabric should pass through the lengthened transfer zone along
a linear path. The first carrier fabric should also pass
through the lengthened transfer zone along a linear path. In
general, divergence of the first and second carrier fabrics
after the transfer shoè at a slight angle which may range
from about 0.01 to about 1 degree is encompassed by the
expression "substantially linear". Minor variations in the
path of the carrier fabrics caused by applied air pressure or
vacuum to assist web transfer are also encompassed by the
expression "substantially linear". Of course, the term
"substantially linear" refers to such a configuration that is
linear in at least one dimension or direction (e.g., the
machine direction) and may also encompass a configuration
that is linear in two dimensions or directions direction
(e.g., the machine direction and the perpendicular or cross-
machine direction).
This elongated, substantially linear transfer zone is
thought to produce an increase in the amount of extensibility
or stretch that is possible in the machine direction at any
given level of negative draw. In fact, the amount of machine
direction extensibility or stretch can be increased to a
percentage amount that actually exceeds the ratio of negative
draw. Desirably, Ltz of the lengthened transfer zone 18 is
within the range of about 0.75 inches to about 10 inches.
For example, Ltz may be within the range of about 2 inches to
about 5 inches. In an embodiment of the invention, Ltz may
be about 3.5 inches.
Although the inventors should not be held to a particular
theory of operation, it is believed that the increased length
of the transfer zone 18 and its substantially linear
configuration creates a rearrangement of the fibers in the
23
CA 022~0~89 1998-10-27
web prior to drying that increases its extensibility. The
rearrangement of fibers prior to drying provides a fibrous
web having increased bulk and extensibility without the
levels of strength loss associated with conventional creping
treatments. As the fibers are being rearranged, the first and
second carrier fabrics are diverging or separating creating
more room and providing little, if any, pressing force on the
fibrous web while, at the same time, remaining in contact
with the fibrous web.
The increased length of the transfer zone 18 is also
thought to allow a more stable transfer of the wet fibrous
web. The longer transfer zone may help distribute or diffuse
various forces within the traveling fibrous web as it
decelerates. This may allow less disruption of the fibers as
they are reoriented in the longer transfer zone creating a
sheet with high machine direction stretch and greater
strength at a target level of stretch. In contrast, short
transfer zones (e.g., "point contact" transfer systems)
appear to concentrate various forces in the traveling fibrous
web in a small area which may contribute to a greater
likelihood of macrofolding and lower machine direction
extensibility.
Creping requires pressing a wet fibrous web against a
creping cylinder and drying the web to a point where it
adheres to the creping cylinder. These steps add density to
the web. The dried web is impacted on the crepe blade to
foreshorten the web. This interaction with the crepe blade
weakens some fiber-to-fiber bonds in the web. The resulting
microfolded sheet has machine direct stretch and improved
bulk but reduced strength.
In contrast, the present invention produces a sheet with
good bulk in combination with strength and machine direction
stretch because the sheet was never densified by pressing
against a crepe cylinder or weakened by impact with a crepe
blade. In contrast to conventional creping processes,
desirable levels of strength are retained because the sheet
24
CA 022~0~89 1998-10-27
consistency in the present invention is such that most of the
fiber-to-fiber bonding (e.g., "paper bonding") has yet to
occur when the fibers are rearranged. Fibrous webs made
according to the present invention have a desirable
combination of strength and machine direction stretch and may
be characterized through tensile testing as Total Energy
Absorbed (i.e., the total area under a plot of stress versus
strain values).
The transfer configuration 10 includes a suction slot or
opening in the transfer head 28 that is positioned downstream
from the transfer shoe 24 to facilitate separation of the
fibrous web 16 from the first surface 14 of the first carrier
fabric 12. Desirably, the transfer head 28 includes an
internal suction passage 30, and top and bottom lips 32, 34
respectively. The suction slot or opening is used to apply a
gaseous pressure differential to complete the transfer of the
fibrous web 16 from the first carrier fabric 12 to the second
carrier fabric 20. The pressure differential may be in the
form of an applied gas stream or a vacuum or both. The
particular level of gaseous pressure differential may vary
depending on factors including, but not limited to, the basis
weight of the fibrous web, the consistency of the fibrous
web, the type of fibers in the web, the types of carrier
fabrics and treatments that may have been applied to the web
prior to the transfer zone. For a given fibrous web and
carrier fabrics, and in view of the disclosure provided
herein, the level of gaseous pressure differential needed to
achieve satisfactory transfer may be readily determined by
one of skill in the art.
Experiments were carried out comparing the machine
direction stretch of a fibrous web produced with an exemplary
transfer configuration 10 of the present invention as
described above with a fibrous web prepared in the same
manner except that a conventional "point contact" transfer
system. The experiments utilized the same first and second
carrier fabrics for each set of comparisons. The same pulp
CA 022~0~89 1998-10-27
stock was used to form a fibrous web at a basis weight of
approximately 32 gram. The flrst carrier fabric for each
example was an Asten 856 forming fabric available from Asten
Wire of Appleton, Wisconsin. The second carrier fabrics were
Appleton 44GST (used with the long warp knuckle side up) and
Appleton 44MST (used with the long shute knuckle side up)
available from Appleton Wire Division of Appleton, Wisconsin.
In operation, the fibrous web 16 at a consistency of
about 22-28% was transported on the first surface 14 of the
first carrier fabric 12 to a transfer configuration 10.
Simultaneously, the second carrier fabric 20 is moved past
the transfer configuration 10 at a speed that is less than
the speed of the first carrier fabric 12. The difference in
speed is expressed as a velocity ratio referred to as
negative draw.
In the examples utilizing an exemplary lengthened
transfer configuration 10 of the present invention, the first
and second carrier fabrics 12, 20 were then constrained to
move through the lengthened transfer zone 18 in a
substantially linear path and separated by a distance
approximately equal to the thickness of the fibrous web 16 so
that both the first and second carrier fabrics were in
contact with the fibrous web 16 through the lengthened
transfer zone 18. In these examples, the basis weight of the
fibrous web 16 was approximately 32 gram and the distance
between the first and second carrier fabrics was
approximately ten one-thousandths of an inch (0.01").
In examples utilizing the conventional "point contact"
transfer configuration, the fibrous web was transferred by
having both the first and second carrier fabrics "wrap" a
partially curved transfer head. FIG. 4 is an illustration of
such an exemplary conventional "point contact" transfer
system. A first carrier fabric 12 having a first surface 14
on which is transported a fibrous web 16 converges with a
second carrier fabric 20 having a second surface 22. The two
26
CA 022~0~89 1998-10-27
fabrics converge at an angle a of about 3 degrees before
contacting a partially curved transfer head 40 having a top
lip 42 and a bottom lip 44 separated by a vacuum slot 46.
The top lip 42 is curved, having an eight-inch radius. The
bottom lip 44 is flat and is aligned at an angle so that the
surface of the transfer shoe 40 from the front 48 of the
vacuum slot 46 to the trailing end 50 of the bottom lip 44
falls away from the "point contact." More particularly, the
bottom lip 44 is aligned at an angle of about 2.5 degrees
from a line tangent to the front 48 of the vacuum slot 46.
The second carrier fabric 20 wraps the top lip 42 for a
short distance (about 0.25 inch) before reaching the vacuum
slot 46. The first carrier fabric 12 and the fibrous web 16
converge with the second carrier fabric 20 at the transfer
head 40 just before the front 48 of the vacuum slot 46. The
fibrous web 16 sandwiched between the first and second
carrier fabrics 12, 20 pass over the vacuum slot 46 and
immediately begin to diverge. At this point, the fibrous web
16 is transferred to second surface 22 of the second carrier
fabric 20 and the first and second carrier fabrics 12, 20
diverge at an angle ~ of about 0.2 degrees (not to scale).
In each set of examples, the webs immediately passed to a
through air dryer after exiting the transfer configuration.
The machine direction extensibility or machine direction
stretch was measured utilizing a Thwing-Albert Intellect STD2
tensile test equipment with conventional software set for a
one inch wide strip of material (oriented with the length in
the machine direction), a two-inch gap between the test jaws
and a cross-head speed of 2 inches per minute.
FIG. 5 is a graphical representation of the results of
the experiments conducted to measure the performance of the
transfer system of the present invention as described above
with the "point contact" transfer system depicted in FIG. 4.
FIG. 5 shows a plot of machine direction stretch (in percent)
versus negative draw for the Appleton 44GST and Appleton
27
CA 022~0~89 1998-10-27
44MST fabrics used in the new transfer system and the "point
contact" transfer system described above. In each case, the
new transfer yielded greater machine direction stretch at a
given rate or amount of negative draw.
Additional experiments carried out compared samples from
sheets prepared by the transfer process of the present
invention (hereinafter referred to as "straight transfer")
versus samples from sheets prepared by the conventional
"convex" or "point contact" transfer configuration
(hereinafter referred to as "convex transfer"). Pulp stock
including about 44 percent mobile wet lap pine, about 44
percent OWENSBORO recycled fiber, and about 12 percent mobile
wet lap hard wood formed the fibrous web run through both
transfer systems. During the straight transfer runs, the
mobile pulp was refined at 0.5 horsepower-days/ton.
Afterwards, the entire furnish was refined with a machine
tickler refiner at 0.2 to 0.6 horsepower-days/ton, which was
then run with added kymene at 11.5 pounds/ton and 4 pounds
per ton of carboxy methyl cellulose dry strength resin. The
first carrier fabric 12 utilized with each transfer system
was Asten 866B forming fabric available from Asten Wire of
Appleton, Wisconsin. The second carrier fabric 20 used for
each system was Albany 44GST from Appleton Wire Division of
Appleton, Wisconsin. The two transfer systems were run with
similar furnish and machine parameters.
In operation, the first carrier fabric 12 moves at a
speed greater than the second carrier fabric 20. The speeds
of the carriers may be varied, thereby varying the speed
ratio of the two carriers. This ratio may be expressed as a
percent negative draw as previously described.
Fibrous web sheets were created on both the transfer
configurations at varying negative draw percent. Several
experiments were run on the samples from these sheets. Each
data point depicted on the FIGS. 6-11 represents the mean of
seven samples cut from a section extending in the cross
28
CA 022~0~89 l998-l0-27
direction of a sheet. All samples tested had a thickness of
about 0.045 centimeters.
FIGS. 6 and 7 represent data taken by running the
respective wet mullen burst and dry mullen burst tests.
These test measure the toughness of a material by inflating
the material with a diaphragm until it ruptures. These tests
may be undertaken utilizing conventional testing equipment
and techniques. These tests were conducted utilizing a
Mullen Burst Strength Tester, such as those manufactured by
B.F. Perkins & Son Inc., whose address is GPO 366, Chicopee,
MA 01021 or Testing Machines Inc., whose address is 400
Bayview Avenue, Amityville, NY 11701. The test procedure
included clamping about a sample having a length and width of
about 12.7 centimeter above a rubber diaphragm, inflating the
diaphragm by pressure generated by forcing liquid into a
chamber at about 95 milliliters per minute, and recording the
pressure at which the sample ruptures. The rupture pressure
was reported in pascals.
The wet mullen burst procedure further included
saturating the sample with purified water and blotting the
excess prior to clamping into the apparatus. FIG. 6 is a
graphical representation of the data presented in Table 1.
TABLE 1
GMBL Negative Draw Burst Pressure of Burst Pressure of
meters Percent Straight Transfer Convex Transfer
pascals pascals
2066 12 66200
2026 15 60000
1979 15 66200
2704 8.3 74500
2487 12 75200
2273 15 76500
2047 20 73800
CA 022~0~89 l998-l0-27
As depicted in FIG. 6, the sheets formed by the straight
transfer process exhibit a higher burst pressure at all
negative draw percents as compared to the sheets formed by
the convex transfer. Accordingly, the sheets formed by the
straight transfer have a greater overall toughness when wet
than the sheets formed by the convex transfer process.
Conversely, the dry mullen burst samples were not
saturated with water, but were conditioned for approximately
12 hours at 23 degrees Centigrade at 50~ relative humidity
prior to testing. FIG. 7 is a graphical representation of
the data presented in Table 2.
TABLE 2
GMBL Negative Draw Burst Pressure of Burst Pressure of
meters Percent Straight Transfer Convex Transfer
pascals pascals
2066 12 71700
2026 15 80700
1979 15 77200
2704 8.3 75200
2487 12 77200
2273 15 81400
2047 20 77900
As depicted in FIG. 7, the sheets formed by the straight
transfer process exhibit approximately the same burst
pressure at all negative draw percents as compared to the
- sheets formed by the convex transfer. Consequently, the
increased bursting pressure for the wet sheets is unexpected.
FIG. 8 represents data taken by running the elmendorf
tear test. This test measures the toughness of a material by
measuring the work required to propagate a tear when part of
the sample is held in a clamp and an adjacent part is moved
by the force of a pendulum freely falling in an arc. This
test may be undertaken utilizing conventional testing
equipment and techniques. This test was conducted utilizing
a TEXTEST FX 3700 manufactured by Schmid Corporation of
CA 022~0~89 1998-10-27
.
Spartanburg, South Carolina 29304. The test procedure
included clamping eight plies of fibrous web sample, cutting
a notch through the plies in the machine direction leaving
about 6.3 centimeters uncut, and swinging a pendulum through
the plies, thereby completely tearing them. Each ply was
about 10.16 centimeters long, about 6.35 centimeters wide,
and about 0.045 centimeters thick. The pendulum weight was
adjusted to its mid potential energy range. The tear energy
was recorded in centinewtons. FIG. 8 is a graphical
representation of the data presented in Table 3.
TABLE 3
GMBL Negative Tear Energy Tear Energy
meters Draw Straight Transfer Convex Transfer
Percent centinewton centinewton
2066 12 59.6
2026 15 62.2
1979 15 60.6
2704 8.3 83.7
2487 12 66.5
2273 15 82.1
2047 20 68.3
As depicted in FIG. 8, the sheets formed by the straight
transfer process exhibit a higher tear energy at all negative
draws as compared to the sheets formed by the convex
transfer. Accordingly, the sheets formed by the straight
transfer have a greater overall toughness with regard to tear
resistance than the sheets formed by the convex transfer
process.
FIGS. 9, 10, and 11 represent data acquired by running
the tensile strength and stretch test. This test measures
the machine direction toughness of a material by pulling at a
constant extension rate until the material breaks. This test
may be undertaken utilizing conventional testing equipment
and techniques. This test was conducted utilizing a SINTECH
31
CA 022~0~89 l998-l0-27
.
2 tensile tester manufactured by Sintech Corporation, whose
address is 1001 Sheldon Drive, Cary, North Carolina 27513.
The test procedure included securing a sample at either end
in the cross direction with about 10.16 centimeter clamps and
stretching at a rate of about 25.40 centimeter per minute
until the sample breaks. Each sample had a machine direction
length of about 15.24 centimeters and a cross direction width
of about 7.62 centimeters. This testing procedure obtained
data regarding tensile load versus strain.
FIG. 9 is a graphical representation of the data
presented in Table 4.
TABLE 4
Strain Negative Tensile Load Tensile Load
Centimeter Draw Straight Transfer Convex Transfer
Percent gram per centimeter gram per centimeter
0. 0000 15 O. O O . O
0.0508 15 78.4 62.7
0.1016 15 156.9 125.6
0.1524 15 235.3 188.4
0.2032 15 313.7 238.0
0.2540 15 365.0 275.5
0.3048 15 400.0 301.8
0.3556 15 433.0 325.0
0.4064 15 459.2 350.0
0.4572 15 485.0 367.4
1.0160 15 754.4 593.0
1.3462 15 918.4
1.5748 15 833.1
As depicted in FIG. 9, the sheets formed by the straight
transfer process exhibit a greater initial slope at fifteen
percent negative draw as compared to the sheets formed by the
convex transfer. This slope may be referred to as a tensile
modulus and is measured in the elastic range of the samples.
The straight transfer sample has a tensile modulus of 1544
gram per square centimeter versus 1236 gram per square
centimeter for the convex transfer. Accordingly, the sheets
.
32
CA 022~0~89 1998-10-27
formed by the straight transfer have a greater machine
direction toughness with regard to tensile modulus at fifteen
percent negative draw than the sheets formed by the convex
transfer process.
FIG. lO is a graphical representation of the data
presented in Table 5.
TABLE 5
GMBL Negative Draw Peak Energy Peak Energy
meters Percent Straight Transfer Convex Transfer
(centimeters~kg~m) (centimeters~kg~m)
2066 12 4.436
2026 15 5.484
1979 15 5.380
2704 8.3 5.070
2487 12 5.227
2273 15 5.968
2047 20 6.455
As depicted in FIG. lO, the sheets formed by the straight
transfer process exhibit greater machine direction toughness
and lower strength at higher negative draws. This
characteristic of the straight transfer sheets permits
creating a sheet with less strength, but greater toughness.
A sheet with less strength tends to provide a material with a
softer feel.
FIG. ll is a graphical representation of the data
presented in Table 6.
- TABLE 6
GMBL Negative Machine Direction Stretch Machine Direction Stretch
meters Draw Straight Transfer Convex Transfer
Percent Percent Stretch Percent Stretch
2066 12 12.1
2026 15 15.5
1979 15 15.3
2704 8.3 9.1
2487 12 11.1
2273 15 13.9
2047 ~20 17.9
33
CA 022~0~89 1998-10-27
As depicted in FIG. ll, the sheets formed by the straight
transfer process exhibit higher machine direction stretch at
about the same GMBL as compared to sheets formed by the
convex transfer process. This indicates a tougher sheet
allowing lower strength to obtain the same functional
utility.
It is to be understood, however, that even though
numerous characteristics and advantages of the present
invention have been set forth in the foregoing description,
together with details of the structure and function of the
invention, the disclosure is illustrative only, and changes
may be made in detail, especially in matters of shape, size
and arrangement of parts within the principles of the
invention to the full extent indicated by the broad general
meaning of the terms in which the appended claims are
expressed.
