Note: Descriptions are shown in the official language in which they were submitted.
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PAPER w'EB HAVING A RELATIVELY THINNER CONTINUOUS NETWORK
REGION & DISCRETE RELATIVELY THICKER REGIONS IN THE PLANE OF
THE CONTINUOUS NETWORK REGION
FIELD OF THE INVENTION
The present invention relates to a paper structure, and more particularly, to
a tissue
paper web having both bulk and smoothness, and to a method for making .such a
tissue
paper web.
BACKGROUND OF THE INVENTION
Paper structures, such as toilet tissue, paper towels, and facial tissue, are
widely
used throughout the home and industry. Many attempts have been made to make
such
tissue products more consumer preferred.
One approach to providing consumer preferred tissue products having bulk and
flexibility is illustrated in U.S. Patent 3,994,771 issued November 30, 1976
to Morgan et
al, which patent is incorporated herein by reference. Improved bulk and
flexibility may
also be provided through bilaterally staggered compressed and uncompressed
zones, as
shown in U.S. Patent 4,191,609 issued March 4, 1980 to Trokhan, which patent
is
incorporated herein by reference.
Another approach to making tissue products more consumer preferred is to dry
the
paper structure to impart greater bulk, tensile strength, and burst strength
to the tissue
products. Examples of paper structures made in this manner are illustrated in
U.S. Patent
4,637,859 issued January 20, 1987 to Trokhan, which patent is incorporated
herein by
reference. U.S. patent 4,637,859 shows discrete dome shaped protuberances
dispersed
throughout a continuous network, and is incorporated herein by reference. The
continuous network can provide strength, while the relatively thicker domes
can provide
softness and absorbency.
One disadvantage of the papermaking method disclosed in U.S. Patent 4,637,859
is
that drying such a web can be relatively energy intensive and expensive, and
typically
- involves the use of through air drying equipment. In addition, the
papermaking method
disclosed in U.S. 4,637,859 can be limited with respect to the speed at which
the web can
be finally dried on the Yankee dryer drum. This limitation is thought to be
due, at least in
part, to the pattern imparted to the web prior to transfer of the web to the
Yankee drum.
In particular, the discrete domes described in U.S. 4,637,859 may not be dried
as
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efficiently on the Yankee surface as is the continuous network described in
U.S.
4,637.859. Accordingly, for a given consistency level and basis weight, the
speed at
which the Yankee drum can be operated is limited.
The following publications show additional methods for making a paper web and
are incorporated herein by reference: WO 95/17548 published June 29, 1995 in
the name
of Ampulski et al. and having a December 20, 1993 US priority date; WO
96/00812
published January 11, 1996 in the name of Trokhan et al. and having a June 29,
1994
U.S. priority date; WO 96/00814 published January 11, 1996 in the name of Phan
and
having a June 29, 1994 priority date; U.S. Patent 5,556,509 issued September
17, 1996 to
Trokhan et al.; and U.S. Patent 5,549,790 issued August 27, 1996 to Phan.
U.S. Patents 4,326,000; 4,000,237; and 3,903,342 describe sheet materials
having
elastomeric bonding materials connecting surfaces of the sheet together in a
pattern.
Such a method has the disadvantage that application of the bonding materials
can be
relatively expensive and difficult to control at production speeds.
Additionally, the
elastomeric bonding material may reduce the absorbency of the web.
Conventional tissue paper made by pressing a web with one or more press felts
in
a press nip can be made at relatively high speeds. The conventionally pressed
paper,
once dried, can then be embossed to pattern the web, and to increase the macro-
caliper of
the web. For example, embossed patterns formed in tissue paper products after
the tissue
paper products have been dried are common.
However, embossing processes typically impart a particular aesthetic
appearance to
the paper structure at the expense of other properties of the structure. In
particular,
embossing a dried paper web disrupts bonds between fibers in the cellulosic
structure.
This disruption occurs because the bonds are formed and set upon drying of the
embryonic fibrous slurry. After drying the paper structure, moving fibers
normal to the
plane of the paper structure by embossing breaks fiber to fiber bonds.
Breaking bonds
results in reduced tensile strength of the dried paper web. In addition,
embossing is
typically done after creping of the dried paper web from the drying drum.
Embossing
after creping can disrupt the creping pattern imparted to the web. For
instance,
embossing can eliminate the creping pattern in some portions of the web by
compacting
or stretching the creping pattern. Such a result is undesirable because the
creping pattern
improves the softness and flexibility of the dried web.
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Scientists and engineers in the papermaking arts continue -to search for
improved
methods of making soft, strong, and absorbent tissue paper which can be dried
efficiently
at reduced expense.
Accordingly, one object of the present invention is to provide a paper web and
method for making a mufti-region paper web which allow relatively faster
drying with
relatively lower energy and expense.
Another object of the present invention is to provide a method for making a
multi-
region paper which can be formed on an existing paper machine (conventional or
through
air drying capability) without the need for substantial modification of the
papermaking
machine.
Another object of the present invention is to provide a paper web and method
for
making a paper web where the web has at least two different, nonembossed
regions
distinguishable by one or more of the following properties: thickness,
elevation, density,
and basis weight.
Another object is to provide a paper web and method of making the paper web
where the web has an enhanced bulk caliper, bulk density, and absorbent
capacity with a
relatively patterned face and relatively smooth opposite face, thereby
providing both the
properties of bulk and softness desired by consumers of paper products.
Another object of the present invention is to provide a paper web and method
of
making the paper web where the web is substantially free of binding materials,
such as
elastomeric binding materials, which adversly affect the absorbency.
SUMMARY OF THE INVENTION
The invention comprises a wetlaid paper web having first and second oppositely
facing surfaces. The paper comprises a relatively thinner region and a
relatively thicker
region, wherein the relatively thicker region is disposed in the plane of the
relatively
thinner region. The ratio of the thickness P of the relatively thicker region
to the
thickness K of the relatively thinner region can be at least about 1.5
In one embodiment, the paper web comprises a relatively thinner, continuous
network region which can have a relatively high density, and a plurality of
relatively
thicker discrete regions dispersed throughout the continuous network region.
The
discrete regions are disposed in the plane of the continuous network region,
and can have
a
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a density which is lower than that of the continuous network region: In one
embodiment,
each relatively thicker discrete region can encircle at least one discrete
densified region.
The paper web can have a basis weight of between about 7 and about 70 grams
per
square meter, a macro caliper of at least about 0.1 mm, and more preferably at
least about
0.2 mm, and a bulk density of less than or equal to about 0.12 gram per cubic
centimeter.
The paper web can also have an absorbent capacity of at least about 20
grams/gram.
The paper web can have a surface smoothness ratio greater than about 1.15,
more
preferably greater than about 1.20, even more preferably greater than about
1.25, still
more preferably greater than about 1.30, and most preferably greater than
about 1.40.
One surface of the web can have a surface smoothness value of less than about
900, and
more preferably less than about 850. The oppositely facing surface of the web
can have a
surface smoothness value of at least about 900, and more preferably at least
about 1000.
The procedures for measuring the thickness of a region, the macro caliper of a
web, the
basis weight of a web, the bulk density of a web, and the surface smoothness
ratio are
described below.
DESCRIPTION OF THE DRAWINGS
While the Specification concludes with claims particularly pointing out and
distinctly claiming the present invention, the invention will be better
understood from the
following description taken in conjunction with the associated drawings, in
which like
elements are designated by the same reference numeral, and:
Figure 1 is a plan view illustration of the first surface of a paper structure
according
to one embodiment of the present invention, the paper structure having a f
rst,
relatively thinner continuous network region and a plurality of relatively
thicker, discrete regions dispersed throughout the continuous network region.
Figure 2 is a cross-sectional illustration of the paper structure of Figure I
taken
along lines 2-2 in Figure 1 and showing the relatively thicker, discrete
regions
disposed in the plane of the continuous network region.
Figure 3 is a photomicrograph of a cross-section of a paper structure
of the type illustrated in Figures 1 and 2.
Figure 4 is a photograph of the first surface of a paper structure of the type
illustrated in Figures 1 and 2.
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S
Figure 5 is a photograph of the second surface of a paper structure of the
type
illustrated in Figures 1 and 2.
Figure 6 is a cross-sectional illustration of prior art paper of the type
shown in US
patent 4,637,859.
Figure 7A is a photomicrograph of a cross-section of a paper web of the type
shown in US patent 4,637,859.
Figure 7B is a plan view of one side of a paper web of the type shown in US
patent
4,637,859.
Figure 7C is a plan view of the other side of the paper web of Figure 7B
Figure 8A is a plan view illustration of an apparatus for use in making a
paper web
of the type illustrated in Figures 1 and 2, the apparatus comprising a
dewatering felt layer and a web patterning layer joined to the dewatering felt
layer and having a continuous network web contacting top surface.
Figure 8B is a cross-sectional illustration of the apparatus of Figure 8A
taken along
lines 8B in Figure 8A.
Figure 8C is a plan view illustration of an apparatus comprising a dewatering
felt layer and a web patterning layer, the web patterning layer comprising
discrete web contacting surfaces.
Figure 9A is an illustration of a papermachine for making a paper web with the
apparatus of Figures 8A and 8B.
Figure 9B is an illustration showing a paper web transferred to the apparatus
shown
in Figure 8B to form a paper web having a first surface conformed to the
apparatus and a second substantially smooth surface.
Figure 9C is an illustration of a paper web on the apparatus shown in Figure
8B
being carried between a vacuum pressure roll and a Yankee drying drum to
impart a pattern to the first surface of the paper web and to adhere the
second
surface of the paper web to the Yankee drum.
Figure 9D is an illustration of a cross-section of a two ply tissue comprising
two
webs of the type shown in Figure 2, with the relatively smoother second
surfaces of the webs facing outwardly.
Figure 10 is a cross-sectional illustration of a paper web made according to
an
alternative embodiment of the present invention and showing relatively
II
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6
thicker, discrete regions disposed in the plane of tire continous network
region, and wherein each discrete region encircles one or more discete
densified region.
Figure 11 is a photomicrograph of a cross-section of a paper structure
of the type illustrated in Figure 10.
Figure 12 a photograph of the first surface of a paper structure of the type
illustrated in Figure 10.
Figure 13 is a photograph of the second surface of a paper structure of the
type
illustrated in Figure 10.
Figure 14A is a plan view illustration of an apparatus for use in making a
paper web
of the type illustrated in Figure 10, the apparatus comprising a web
patterning layer joined to foraminous element formed of woven filaments.
Figure 14B is a cross-sectional illustration of the apparatus of Figure 14.
Figure 15A is an illustration of a papermachine for making a paper web with
the
apparatus of Figures 14A and 14B.
Figure 15B is an illustration showing a paper web transferred to the apparatus
shown in Figure 14B to form a paper web having a first surface conformed to
the apparatus and a second substantially smooth surface.
Figure 15C is an illustration of a paper web on the apparatus shown in Figure
14B
being carried between a pressure roll and a Yankee drying drum to impart a
pattern to the first surface of the paper web and to adhere the second surface
of the paper web to the Yankee drum.
Figure 16 is a cross-sectional illustration of a paper web made according to
one
embodiment of the present invention, wherein the web comprises multiple
fiber layers including a debonding layer.
DETAILED DESCRIPTION OF THE INVENTION
Figures 1-2 illustrate a paper web 20 made according to one embodiment of the
present invention, and Figures 3-5 are photographs of a paper structure of the
type
illustrated in Figures l and 2. For comparison purposes, Figures 6 and 7A-C
show a
paper web of the type described in U.S. Patent 4,637,859.
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The paper web made according to one embodiment of rthe present invention
comprises a relatively thinner region and a relatively thicker region, wherein
the
relatively thicker region is disposed in the plane of the relatively thinner
region. The
paper web is wetlaid, and can be substantially free of dry embossments.
Referring to
Figures 1-S, the paper web 20 has first and second oppositely facing surface
22 and 24,
respectively. The paper web 20 comprises a relatively thinner, continuous
network
region 30, having a thickness designated K. The portion of the surface 22
bordering the
region 30 is designated 32, and the portion of the surface 24 bordering region
30 is
designated 34.
The web 20 also includes a plurality of relatively thicker regions SO
dispersed
throughout the continuous network region 30. The relatively thicker regions SO
have a
thickness designated P, and extend from the surface 32 of the continuous
network region
30. The portion of the surface 22 bordering the regions SO is designated S2
and the
portion of the surface 24 bordering the regions SO is designated S4. The
thickness P is
greater than the thickness K. Preferably, the ratio of P/K is at least about
1.S. Refernng
to Figure 3, P can beat least about 0.3 mm, and preferably at least about 0.40
rnm. K can
be less than about 0.25 mm, and more preferably less than about 0.20 mm.
The continuous network region 30 and the discrete, relatively thicker regions
SO
can both be foreshortened, such as by creping. In Figures 1-2, the crepe
ridges of the
continuous network region are designated by numeral 3 S, and extend in a
generally cross-
machine direction. Similarly, the discrete, relatively thicker regions SO can
also be
foreshortened to have crepe ridges SS.
The continuous network region 30 can be a relatively high density,
macroscopically monoplanar continuous network region of the type disclosed in
U.S.
Patent 4,637,859. The relatively thicker regions SO can be relatively low
density, and
can be bilaterally staggered, as disclosed in U.S. patent 4,637,859. However,
the
relatively thicker regions SO are not domes of the type shown in U.S. Patent
4,637,859.
The relatively thicker regions SO are disposed in the plane of the continuous
network region 30. The elevation of the plane of the network region 30 is
schematically
illustrated by surface 23 (appears as a line in Figure 2). Surface 23 is
positioned midway
between the surfaces 32 and 34. While the plane of the network 30 is
illustrated as being
flat in Figure 2, it will be understood that the "plane of the network 30" can
comprise a
surface 23 having curvature.
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By the phrase "disposed in the plane of the continuous network region 30", it
is
meant that a relatively thicker region 50 includes a portion extending both
above and
below the surface 23. As shown in Figure 2, a portion of a thicker region 50
extends
along an imaginary line 25. The portion of the region 50 extending along the
imaginary
line 25 is disposed both above and below the surface 23, such that the
intersection of the
line 25 with the surface 52 is above the surface 23 and the intersection of
the line 25 with
the surface 54 is below the surface 23.
The procedure for measuring the thicknesses P and K, and the procedure for
determining the location of the surface 23 to determine if the region 50 is
disposed in the
plane of the region 30 are described below under "Measurement of Thickness and
Elevation."
In contrast to the paper web illustrated in Figures 1-2, the paper web 80
illustrated
in Figure 6, which is disclosed in US Patent 4,637,859, does not have
relatively thicker
regions disposed in the plane of a continuous network. U.S. Patent 4,637,859
discloses
domes 84 dispersed in a continuous network 83. In Figure 6, the domes 84 are
not
disposed in the plane of the network 83. Instead, as shown in Figure 6, the
lower surface
of the domes 84 is disposed above the surface 23 depicted in Figure 6. A
photomicrograph of a paper web of the type disclosed in U.S. 4,637,859 is
shown in
Figure 7A, and the oppositely facing surfaces of such a paper web are shown in
Figures
7B and 7C.
Accordingly, the paper web 20 shown in Figures 1 and 2 can have the strength
benefits of the continuous network region 30, the bulk density, macro-caliper,
absorbency
and softness benefits derived from the relatively thicker regions S0, yet have
a relatively
smooth surface 24 as compared to paper of the type illustrated in US
4,637,859.
In particular, the paper web 20 can have surface smoothness ratio greater than
about about 1.15, more preferably greater than about 1.20, even more
preferably greater
than about 1.25, still more preferably greater than about 1.30, and most
preferably greater
than about 1.40, where the surface smoothness ratio is the value of the
surface
smoothness of surface 22 divided by the value of the smoothness value of
surface 24.
In olie embodiment, the surface 24 of the web 20 can have a surface smoothness
value of less than about 900, and more preferably less than about 850. The
opposite
surface 22 can have a surface smoothness value of at least about 900, and more
preferably
at least about 1000.
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The method for measuring the value of the surface smoothness of a surface is
described below under "Surface Smoothness." The value of surface smoothness
for a
surface increases as the surface becomes more textured and less smooth.
Accordingly, a
relatively low value of surface smoothness indicates a relatively smooth
surface.
In contrast to paper webs 20 of the present invention, a sample of paper of
the
type disclosed in U.S. Patent 4,637,859 can exhibit a surface smoothness ratio
of about
1.07, and surface smoothness values of about 993 and 1065 on opposite
surfaces.
One advantage of a paper web 20 is the combination of the relatively smooth
surface 24 for providing softness, the relatively thicker regions 50 for
providing
relatively high bulk and absorbency, and the compacted relatively thinner,
relatively high
density network region 30 for strength. Additionally, the paper web 20 can be
formed
and dried relatively quickly and efficiently, as described below.
The paper web 20 having the relatively smooth surface 24 can be useful in
making a multiple ply tissue having smooth outwardly facing surfaces. For
instance, two
or more webs 20 can be combined to form a multiple ply tissue, such that the
two
outwardly facing surfaces of the multiple ply tissue comprise the surfaces 24
of the webs
20, and the surfaces 22 of the outer plies face inwardly. Such a multiple ply
tissue can
have the strength and bulk benefits associated with relatively thicker regions
dispersed
throughout a continuous network region, yet present a relatively smooth and
soft outward
surface to the consumer's touch.
An example of such a two ply tissue is illustrated in Figure 9D. The two webs
20
can be joined together in face to face relationship in any suitable manner,
including but
limited to adhesively, mechanically, and ultrasonically, and combinations of
those
methods.
The paper web 20 can have a basis weight of about 7 to about 70 grams per
square
meter. The paper web 20 can have a macro-caliper of at least about 0.1 mm, and
more
preferably at least about 0.2 millimeter and a bulk density of less than about
0.12 gram
per cubic centimeter (basis weight divided by macro-caliper). The procedures
for
measuring the basis weight, macro-caliper, and bulk density of a web are
described
below.
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The paper web 20 of the type shown in Figures 1-2 can also-have an absorbent
capacity of at least about 20 grams per gram. The method for measuring the
absorbent
capacity is described below. Accordingly, the paper web 20 exhibits the
absorbency
benefits of high bulk paper webs, in combination with the benefits of a
relatively smooth
surface usually associated with conventional felt pressed tissue paper.
Web Support Apparatus
Figures 8A and 8B illustrate a web support apparatus 200 for use in making a
paper web of the type illustrated in Figures 1 and 2. The web support
apparatus 200
comprises a dewatering felt layer 220 and a web patterning layer 250. The web
support
apparatus 200 can be in the fonm of a continuous belt for drying and imparting
a pattern
to a paper web on a paper machine. The web support apparatus 200 has a first
web facing
side 202 and a second oppositely facing side 204. The web support apparatus
200 is
viewed with the first web facing side 202 toward the viewer in Figure 8A. The
first web
facing side 202 comprises a first web contacting surface and a second web
contacting
surface.
In Figure 8A and 8B, the first web contacting surface is a first felt surface
230 of
the felt layer 220. The first felt surface 230 disposed at a first elevation
231. The first
felt surface 230 is a web contacting felt surface. The felt layer 220 also has
oppositely
facing second felt surface 232.
In Figure 8A and 8B the second web contacting surface is provided by the web
patterning layer 250. The web patterning layer 250, which is joined to the
felt layer 220,
has a web contacting top surface 260 at a second elevation 261. The difference
between
the first elevation 231 and the second elevation 261 is less than the
thickness of the paper
web when the paper web is transferred to the web support apparatus 200. The
surfaces
260 and 230 can be disposed at the same elevation, so that the elevations 231
and 261 are
the same. Alternatively, surface 260 can be slightly above surface 230, or
surface 230
can be slightly above surface 260.
The difference in elevation is greater than or equal to 0.0 mils and less than
about
8.0 mils. In one embodiment, the difference in elevation is less than about
6.0 mils (0.15
mm}, more preferably less than about 4.0 mils (0.10 mm), and most preferably
less than
about 2.0 mil (0.05 mm), in order to maintain a relatively smooth surface 24,
as
described below.
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The dewatering felt layer 220 is water permeable and is capable of receiving
and
containing water pressed from a wet web of papenmaking fibers. The web
patterning
layer 250 is water impervious, and does not receive or contain water pressed
from a web
of papermaking fibers. The web patterning layer 250 can have a continuous web
contacting top surface 260, as shown in Figure 8A. Alternatively, the web
patterning
layer can be discontinuous or semicontinuous. A discontinuous top surface 260
is
illustrated in Figure 8C.
The web patterning layer 250 preferably comprises a photosensitive resin which
can
be deposited on the first surface 230 as a liquid and subsequently cured by
radiation so
that a portion of the web patterning layer 250 penetrates, and is thereby
securely bonded
to, the first felt surface 230. The web patterning layer 250 preferably does
not extend
through the entire thickness of the felt layer 220, but instead extends
through less than
about half the thickness of the felt layer 220 to maintain the flexibility and
compressibility of the web support apparatus 200, and particularly the
flexibility and
compressibility of the felt layer 220.
A suitable dewatering felt layer 220 comprises a nonwoven batt 240 of natural
or
synthetic fibers joined, such as by needling, to a support structure formed of
woven
filaments 244. Suitable materials from which the nonwoven batt can be formed
include
but are not limited to natural fibers such as wool and synthetic fibers such
as polyester
and nylon. The fibers from which the batt 240 is formed can have a denier of
between
about 3 and about 20 grams per 9000 meters of filament length.
The felt layer 220 can have a layered construction, and can comprise a mixture
of
fiber types and sizes. The felt layer 220 is formed to promote transport of
water received
from the web away from the first felt surface 230 and toward the second felt
surface 232.
The felt layer 220 can have finer, relatively densely packed fibers disposed
adjacent the
first felt surface 230. The felt layer 220 preferably has a relatively high
density and
relatively small pore size adjacent the first felt surface 230 as compared to
the density and
pore size of the felt layer 220 adjacent the second felt surface 232, such
that water
entering the first surface 230 is carried away from the first surface 230.
The dewatering felt layer 220 can have a thickness greater than about 2 mm. In
one
embodiment the dewatering felt layer 220 can have a thickness of between about
2 mm
and about 5 mm.
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PCT Publications WO 96/00812 published January 11;- 1996, WO 96/25555
published August 22, 1996, WO 96/25547 published August 22, 1996, all in the
name
of Trokhan et al.; U.S. patent application 08/701,600 "Method for Applying a
Resin to a
Substrate for Use in Papermaking" filed August 22, 1996;
U.S. Patent Application 08/640,452 "High Absorbence/Low Reflectance Felts with
a
Pattern Layer" filed April 30, 1996; and U.S. Patent Application 08/672,293
"Method of
Making Wet Pressed Tissue Paper with Felts Having Selected Permeabilities"
filed June
28, 1996 are incorporated herein by reference for the purpose of disclosing
applying a
photosensitive resin to a dewatering felt and for the purpose of disclosing
suitable
dewatering felts.
The dewatering felt layer 220 can have an air permeability of less than about
200
standard cubic feet per minute (scfm), where the air permeability in scfm is a
measure
of the number of cubic feet of air per minute that pass through a one square
foot area
of a felt layer, at a pressure differential across the dewatering felt
thickness of about
O.S inch of water. In one embodiment, the dewatering felt layer 220 can have
an air
l permeability of between about 5 and about 200 scfm, and more preferably less
than
about 100 scfm.
The dewatering felt layer 220 can have a basis weight of between about 800 and
about 2000 grams per square meter, an average density (basis weight divided by
thickness) of between about 0.3 S gram per cubic centimeter and about 0.45
gram per
cubic centimeter. The air permeability of the web support apparatus 200 is
less than or
equal to the permeability of the felt layer 220.
One suitable felt layer 220 is an Amflex 2 Press Felt manufactured by the
Appleton
Mills Company of Appleton, Wisconsin. The felt layer 220 can have a thickness
of about
3 millimeter, a basis weight of about 1400 gm/square meter, an air
permeability of about
30 scfm, and have a double layer support structure having a 3 ply muldfilament
top and
bottom warp and a 4 ply cabled monofilament cross-machine direction weave. The
batt
240 can comprise polyester fibers having a denier of about 3 at the first
surface 230, and a
denier of between about 10-1 S in the batt substrate underlying the first
surface 230.
The web support apparatus 200 shown in Figure 8A has a web patterning layer
250
having a continuous network web contacting top surface 260 having a plurality
of
discrete openings 270 therein. Suitable shapes for the openings 270 include,
but are not
limited to circles, ovals elongated in the machine direction (MD in Figure
8A), polygons,
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irregular shapes, or mixtures of these. The projected surface -area of the
continuous
network top surface 260 can be between about 5 and about 75 percent of the
projected
. area of the web support apparatus 200 as viewed in Figure 8A, and is
preferably between
about 25 percent and about 50 percent of the projected area of the apparatus
200.
In the embodiment shown in Figure 8a, the continuous network top surface 260
can
have less than about 700 discrete openings 270 per square inch of the
projected area of
the apparatus 200, and preferably between about 10 and about 400 discrete
openings 270
therein per square inch of projected area of the apparatus as viewed in Figure
8A. The
discrete openings 270 can be bilaterally staggered in the machine direction
(MD) and
cross-machine direction (CD) as described in U.S. Patent 4,637,859 issued
January 20,
1987. In one embodiment, the openings 270 can be over-lapping and bilaterally
staggered, with the openings sized and spaced such that in both the machine
and cross-
machine directions the edges of the openings 270 extend past one another, and
such that
any line drawn parallel to either the machine or cross-machine direction will
pass through
at least some openings 270.
Papermaking Method Description
A paper structure 20 according to the present invention can be made with the
papermaking apparatus shown in Figures 9A, 9B, and 9C. Referring to Figure 9A,
the
method of making the paper structure 20 of the present invention is initiated
by providing
an aqueous dispersion of papermaking fibers in the form of a slurry, and
depositing the
slurry of papermaking fibers from a headbox 500 onto a foraminous, liquid
pervious
forming member, such as a forming belt 542, followed by forming an embryonic
web of
papermaking fibers 543 supported by the forming belt 542. For simplicity the
forming
belt 542 is shown as a single, continuous Fourdrinier wire. It will be
understood that
any of the various twin wire formers known in the art can be used.
It is anticipated that wood pulp in ail its varieties will normally comprise
the paper
making fibers used in this invention. However, other cellulose fibrous pulps,
such as
cotton liners, bagasse, rayon, etc., can be used and none are disclaimed. Wood
pulps
useful herein include chemical pulps such as Kraft, sulfite and sulfate pulps
as well as
mechanical pulps including for example, ground wood, thermomechanical pulps
and
Chemi-ThermoMechanical Pulp (CTMP). Pulps derived from both deciduous and
coniferous trees can be used.
Both hardwood pulps and softwood pulps as well as blends of the two may be
employed. The terms hardwood pulps as used herein refers to fibrous pulp
derived from
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14
the woody substance of deciduous trees (angiosperms): wherein softwood pulps
are
fibrous pulps derived from the woody substance of coniferous trees
(gymnosperms).
Hardwood pulps such as eucalyptus having an average fiber length of about 1.00
millimeter are particularly suitable for tissue webs described hereinafter
where softness is
important, whereas northern softwood Kraft pulps having an average fiber
length of about
2.5 millimeter are preferred where strength is required. Also applicable to
the present
invention are fibers derived from recycled paper, which may contain any or ail
of the
above categories as well as other non-fibrous materials such as fillers and
adhesives used
to facilitate the original paper making.
The paper filrnish can comprise a variety of additives, including but not
limited to
fiber binder materials, such as wet strength binder materials, dry strength
binder
materials, and chemical softening compositions. Suitable wet strength binders
include,
but are not limited to, materials such as polyamide-epichlorohydrin resins
sold under the
trade name of KYMENE~ 557H by Hercules Inc., Wilmington, Delaware. Suitable
temporary wet strength binders include but are not limited to modified starch
binders
such as NATIONAL STARCH~ 78-0080 marketed by National Starch Chemical
Corporation, New York, New York. Suitable dry strength binders include
materials such
as carboxymethyl cellulose and cationic polymers such as ACCO~ 711. The ACCO~
family of dry strength materials are available from American Cyanamid Company
of
Wayne, New Jersey.
Preferably, the paper furnish deposited on the forming wire comprises a
debonding agent to inhibit formation of some fiber to fiber bonds as the web
is dried.
The debonding agent, in combination with the energy provided to the web by the
dry
creping process, results in a portion of the web being debulked. In one
embodiment, the
debonding agent can be applied to fibers forming an intermediate fiber layer
positioned
between two or more layers. The intermediate layer acts as a debonding layer
between
outer layers of fibers. The creping energy can therefore debulk a portion of
the web along
the debonding layer. Debulking of the web can result in voids 3 I 0 ( Figure
16).
As a result, the web can be formed to have a relatively smooth surface for
efficient
drying on the Yankee. Yet, because of the rebulking at the creping blade, the
dried web
can also have differential density regions, including a continuous network
relatively high
density region, and discrete relatively low density regions which are created
by the
creping process.
Suitable debonding agents include chemical softening compositions such as
those
disclosed in U.S. Patent 5,279,767 issued January 18, 1994 to Phan et al.
Suitable
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biodegradable chemical softening compositions are disclosed in- U.S. Patent
5,312,522
issued May 17, 1994 to Phan et al. U.S. Patents 5,279,767 and 5,312,522 are
incorporated herein by reference. Such chemical softening compositions can be
used as
debonding agents for inhibiting fiber to fiber bonding in one or more layers
of the fibers
making up the web.
One suitable softener for providing debonding of fibers in one or more layers
of
fibers forming the web 20 is a papermaking additive comprising DiEster
Di(Touch
Hardened) Tallow Dimethyl Ammonium Chloride. A suitable softener is ADOGEN~
brand papermaking additive available from Witco Company of Greenwich, CT.
The embryonic web 543 is preferably prepared from an aqueous dispersion of
papermaking fibers, though dispersions in liquids other than water can be
used. The
fibers are dispersed in the Garner liquid to have a consistency of from about
0.1 to about
0.3 percent. The percent consistency of a dispersion, slurry, web, or other
system is
defined as 100 times the quotient obtained when the weight of dry fiber in the
system
under consideration is divided by the total weight of the system. Fiber weight
is always
expressed on the basis of bone dry fibers.
The embryonic web 543 can be formed in a continuous papermaking process, as
shown in Figure 9A, or alternatively, a batch process, such as a handsheet
making process
can be used. After the dispersion of papermaking fibers is deposited onto the
forming
belt 542, the embryonic web 543 is formed by removal of a portion of the
aqueous
dispersing medium by techniques well known to those skilled in the art. The
embryonic
web is generally monoplanar, and is formed to have substantially smooth,
macroscopically monoplanar first and second faces using any suitable forming
belt 542.
Vacuum boxes, forming boards, hydrofoils, and the like are useful in effecting
water removal from the dispersion. The embryonic web 543 travels with the
forming belt
542 about a return roll 502 and is brought into the proximity of the web
support apparatus
200.
The next step in making the paper structure 20 comprises transferring the
embryonic web 543 from the forming belt 542 to the apparatus 200 and
supporting the
transferred web (designated by numeral 545 in Figure 9B) on the first side 202
of the
apparatus 200. The embryonic web preferably has a consistency of between about
5 and
about 20 percent at the point of transfer to the apparatus 200.
The web is transferred to the apparatus 200 such that the first face 547 of
the
transferred web 545 is supported on and conformed to the surface 202 of the
apparatus
n
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16
200, with parts of the web 545 supported on the surface 260--and parts of the
web
supported on the felt surface 230. The second face 549 of the web is
maintained in a
substantially smooth, macroscopically monoplanar configuration. Referrring to
Figure
9B, the elevation difference between the surface 260 and the surface 230 of
the web
support apparatus 200 is sufficiently small that the second face of the
embryonic web
remains substantially smooth and macroscopically monoplanar when the web is
transferred to the apparatus 200. In particular, the difference in elevation
between the
surface 260 and the surface 230 should be smaller than the thickness of the
embryonic
web at the point of transfer.
The steps of transferring the embryonic web 543 to the apparatus 200 can be
provided, at least in part, by applying a differential fluid pressure to the
embryonic web
543. For instance, the embryonic web 543 can be vacuum transferred from the
forming
belt 542 to the apparatus 200 by a vacuum source 600 depicted in Figure 9A,
such as a
vacuum shoe or a vacuum roll. One or more additional vacuum sources 620 can
aiso be
provided downstream of the embryonic web transfer point to provide further
dewatering.
The web 545 is carried on the apparatus 200 in the machine direction (MD in
Figure 9A} to a nip 800 provided between a vacuum pressure roll 900 and a hard
surface
875 of a heated Yankee dryer drum 880. Referring to Figure 9C, a steam hood
2800 is
positioned just upstream of the nip 800. The steam hood 2800 directs steam
onto the
surface 549 of the web 545 as the surface 547 of the web 545 is carried over a
vacuum
providing portion 920 of the vacuum pressure roll 900.
The steam hood 2800 is mounted opposite a section of the vacuum providing
portion 920. The vacuum providing portion 920 draws the steam into the web 545
and
the felt layer 220. The steam provided by steam hood 2800 heats the water in
the paper
web 545 and the felt layer 220, thereby reducing the viscosity of the water in
the web and
the felt layer 220. Accordingly, the water in the web and the felt layer 220
can be more
readily removed by the vacuum provided by roll 900.
The steam hood 2800 can provide about 0.3 pound of saturated steam per pound
of dry fiber at a pressure of less than about 15 psi. The vacuum providing
portion 920
provides a vacuum of between about 1 and about 15 inches of Mercury, and
preferably
between about 3 and about 12 inches of Mercury at the surface 204. A suitable
vacuum pressure roll 900 is a suction pressure roll manufactured by Winchester
Roll
Products. A suitable steam hood 2800 is a model DSA manufactured by Measurex-
Devron Company of North Vancouver, British Columbia, Canada.
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17
The vacuum providing portion 920 is in communication with a source of vacuum
(not shown). The vacuum providing portion 920 is stationary relative to the
rotating
surface 910 of the roll 900. The surface 910 can be a drilled or grooved
surface through
which vacuum is applied to the surface 204. The surface 910 rotates in the
direction
shown in Figure 9C. The vacuum providing portion 920 provides a vacuum at the
surface 204 of the web support apparatus 200 as the web and apparatus 200 are
carned
through the steam hood 2800 and through the nip 800. While a single vacuum
providing portion 920 is shown, in other embodiments it may be desirable to
provide
separate vacuum providing portions, each providing a different vacuum at the
surface 204
as the apparatus 200 travel around the roll 900.
The Yankee dryer typically comprises a steam heated steel or iron drum.
Referring
to Figure 9C, the web 545 is carried into the nip 800 supported on the
apparatus 200,
such that the substantially smooth second face 549 of the web can be
transferred to the
surface 875. Upstream of the nip, prior_to the point where the web is
transferred to the
surface 875, a nozzle 890 applies an adhesive to the surface 875.
The adhesive can be a polyvinyl alchohol based adhesive. Alternatively, the
adhesive can be CREPTROL~ brand adhesive manufactured by Hercules Company of
Wilmington Delaware. Other adhesives can also be used. Generally, for
embodiments
where the web is transferred to the Yankee drum 880 at a consistency greater
than about
45 percent, a polyvinyl alchohol based creping adhesive can be used. At
consistencies
lower than about 40 percent, an adhesive such as the CREPTROL~ adhesive can be
used.
The adhesive can be applied to the web directly, or indirectly {such as by
application to the Yankee surface 875), in a number of ways. For instance, the
adhesive
can be sprayed in micro-droplet form onto the web, or onto the Yankee surface
875.
Alternatively, the adhesive could also be applied to the surface 875 by a
transfer roller or
brush. In yet another embodiment, the creping adhesive could be added to the
paper
furnish at the wet end of the papermachine, such as by adding the adhesive to
the paper
furnish in the headbox 500. From about 2 pounds to about 4 pounds of adhesive
can be
applied per ton of paper fibers dried on the Yankee drum 880.
As the web is carried on the apparatus 200 through the nip 800, the vacuum
providing portion 920 of the roll 900 provides a vacuum at the surface 204 of
the web
. support apparatus 200. Also, as the web is carried on the apparatus 200
through the nip
800, between the vaccuum pressure roll 900 and the dryer surface 800, the web
patterning layer 250 of the web support apparatus 200 imparts the pattern
corresponding
to the surface 260 to the first face 547 of the web 545. Because .the second
face 549 is a
i
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18
substantially smooth, macroscopically monoplanar face, substantially all of
the of the
second surface 549 is positioned against, and adhered to, the dryer surface
875 as the web
is carried through the nip 800. As the web is carried through the nip, the
second face 549
is supported against the smooth surface 875 to be maintained in a
substantially smooth,
macroscopically monoplanar configuration. Accordingly, a predetermined pattern
can be
imparted to the first face 547 of the web 545, while the second face 549
remains
substantially smooth. The web 545 preferably has a consistency of between
about 20
percent and about 60 percent when the web 545 is transferred to the surface
875 and the
pattern of surface 260 is imparted to the web.
As the web is carried through the nip 800, it is believed that the heated
surface
875 can boil the water in the web 545. It is believed that the vacuum provided
by the
vacuum pressure roll 900 draws the boiling water from the web through the
portions of
the felt layer 220 which are not covered by the web imprinting layer 250.
Without being limited by theory, it is believed that, as a result of having
substantially all of the second face 549 positioned against the Yankee surface
875, drying
of the web 545 on the Yankee is more efficient than would be possible with a
web which
has only selective portions of the second face against the Yankee. In
particular, it is
believed that by positioning substanially all of the second face 549 against
the Yankee
surface 875, the above described patterned paper having both bulk and
smoothness and
having a basis weight of at least about 8 lbs per 3000 square feet, and
preferably at least
about 10 lbs per 3000 square feet, can be dried on the Yankee drum 880 from a
consistency of less than about 50 percent, and more preferably less than about
30 percent,
to a consistency of at least about 90 percent, and more preferably at least
about 95
percent, while removing water at a water removal rate of at least about I 1
tons of water
per hour at a web speed of at least about 4500 feet/minute, and more
preferably at least
about 5000 feetlminute.
In particular, it is believed that the present invention permits a web 545
having a
basis weight of at least about 8 pounds per 3000 square feet, and more
preferably at least
about 10 pounds per 3000 square feet, to be dried from a relatively low
consistency to a
relatively high consistency on the Yankee drum at a Yankee drum speed of at
least about
4500 feet per minute. In particular, it is believed that the present invention
permits a
web 545 having the above basis weight characteristics to be dried from a
consistency of
less than about 30 percent and more preferably less than about 25 percent
(when the web
is transferred to the drum 880), to a consistency of at least about 90
percent, and more
preferably at least about 95 percent (when the web is removed from the drum by
creping)
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19
at a web speed of at least about 4500 feet per minute, more preferably at
least about 5000
feet per minute, and most preferably at least about 6000 feet per minute on
the Yankee
drum.
In comparison, it is believed that the Yankee dryer speed for drying paper
having
a continuous network and discrete domes as disclosed in U.S. Patent 4,637,859
and a
basis weight of at least about 10 pounds per 3000 square feet cannot be as
high as 3500
ft/min if the paper is to be dried from a consistency from about 30 percent to
about 90
percent on the Yankee drum. Typically, paper of the type shown in U.S. Patent
4,637,859 is predried upstream of the Yankee drum to have a consistency upon
transfer to
the Yankee drum of about 60 percent to about 70 percent. Without being limited
by
theory, it is believed that if paper of the type shown in US Patent 4,637,859
is dried
without the use of a predrier, then the Yankee dryer speed is limited to less
than about
3000 feet/min.
The final step in forming the paper structure 20 comprises creping the web 545
from the surface 875 with a doctor blade 1000, as shown in Figure 9A. Without
being
limited by theory, it is believed that the energy imparted by the doctor blade
1000 to the
web 545 bulks, or de-densifies, at least some portions of the web, especially
those
portions of the web which are not imprinted by the web patterning surface 260.
Accordingly, the step of creping the web from the surface 875 with the doctor
blade 1000
provides a web having a first, compacted, relatively thinner region
corresponding to the
pattern imparted to the first face of the web, and a second relatively thicker
region. In
general, the doctor blade has a bevel angle of about 25 degrees and is
positioned with
respect to the Yankee dryer to provide an impact angle of about 81 degrees.
The paper structure 20 shown in Figure 2 exhibits forshortening due to creping
in
both the continuous region 30 and the discrete regions 50. The creping
frequency in the
region 30 is different than the creping region in the regions 50. Generally,
the creping
frequency in the regions SO is lower than the creping frequency in the
continuous network
30.
In an alternative embodiment, the web imprinting apparatus 200 can comprise a
resin patterning layer 250 which defines a plurality of discrete web
contacting top
surfaces 260 joined to the dewatering felt layer 220, as shown in the plan
view of Figure
8C. In Figure 8C, the web contacting felt surface 230 is in the form of a
continuous
network surrounding the discrete surfaces 260. Such an apparatus can be used
to form a
paper web according to the present invention, wherein the paper structure
comprises a
n
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plurality of relatively thinner, discrete regions dispersed throughout a
relatively thicker
continuous network region.
In another alternative embodiment of the present invention, the web support
apparatus 200 can comprise a resin layer disposed on a foraminous background
element
comprising a fabric of woven filaments. Referring to Figures 14A-15C, the
apparatus
200 can comprise a resin layer 250 disposed on a woven fabric 1220. The resin
layer 250
has a continuous network web contacting surface 260 defining discrete openings
270, as
shown in Figure 14A. The woven fabric 1220 comprises machine direction
filaments
1242 and cross machine direction filaments 1241.
In Figure 14A and 14B, the first web contacting surface at a first elevation
1231 is
provided by discrete knuckle surfaces 1230 located at cross-over points of the
filaments
1241 and 1242. The top surfaces of the filaments 1241 and 1242 can be sanded
or
otherwise ground to provide relatively flat, generally oval shaped knuckle
surfaces 1230
(detail of oval shapes not shown in Figure 14A). The second web contacting
surface is
provided by the web patterning layer 250. The web patterning layer 250, which
is
joined to the woven fabric 1220, has a web contacting top surface 260 at a
second
elevation 261.
The difference between the first elevation 1231 and the second elevation 261
is less
than about thickness of the paper web when the paper web is transferred to the
web
support apparatus 200. The continuous surface 260 and the discrete surfaces
1230 can be
disposed at the same elevation, so that the elevations 1231 and 261 are the
same.
Alternatively, surface 260 can be slightly above the surfaces 1230, or
surfaces 1230 can
be slightly above surface 260.
The difference in elevation is greater than or equal to 0.0 mils and less than
about
5.0 mils. In one embodiment, the difference in elevation is less than about
4.0 mils {0.10
mm), more preferably less than about 2.0 mils (0.05 mm), and most preferably
less than
about 1.0 mil (0.025 mm), in order to maintain a relatively smooth surface 24,
as
described below.
The web support apparatus 200 shown in Figures 14A and 14B can be used to
form the paper web shown in Figures 10-13. Referring to Figure 10, the paper
web 20
comprises a continuous network, relatively thinner region 30 corresponding to
the surface
.260 and a plurality of discrete, relatively thicker regions 50 dispersed
throughout the
continuous network region 30. The regions 50 correspond to the openings 270 in
the
surface 260. Each of the relatively thicker regions 50 encircles at least one
densified
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21
region 70. The densified regions 70 correspond to the surfaces 1230 of the
woven fabric
1220.
Referring to Figure 11, P can be at least about 0.35 mm, and preferably at
least
about 0.44 mm. K can be less than about 0.20 mm, and more preferably less than
about
0.10 mm.
Figures 15A-15C illustrate formation of the web 20 shown in Figure 10 using
the
web support apparatus 200. As described above with respect to Figures 9A-9C,
an
embryonic web 543 having first and second smooth surfaces is formed on a
forming wire
542 and transferred to the web support apparatus 200. The web 543 is vacuum
transferred to the apparatus 200, to provide a web 545 supported on the
apparatus 200.
As shown in Figure 15B, the first surface 547 is conformed to the surface 260
and the
surfaces 1230, and the second surface 549 is maintained as a substantially
smooth,
macroscopically monoplanar surface.
In contrast to Figures 9A-9C, the web 545 and web support apparatus 200 are
next
carned through a through air drying apparatus 650, wherein heated air is
directed through
the web 545 while the web 545 is supported on the apparatus 200. The heated
air is
directed to enter the surface 549 and to pass through the web 545 and then
through the
apparatus 200.
The through air drying apparatus 650 can be used to dry the web 545 to a
consistency of from about 30 percent to about 70 percent. U.S. Patent
3,303,576 to
Sisson and U.S, patent 5,247,930 issued to Ensign et al. are incorporated
herein by
reference for the purpose of showing suitable through air dryers for use in
the practice of
the present invention.
The partially dried web 545 and the apparatus 200 are directed to pass through
a
nip 800 formed between a pressure roll 900 and a Yankee drum 880. The
continuous
network surface 260 and the discrete surfaces 1230 are impressed into the
surface 547 of
the web 545 as the web is carried through the nip 800. An adhesive supplied by
nozzle
890 is used to adhere substantially all of the substantially smooth surface
549 to the
surface 875 of the heated Yankee drum 880.
Figure 16 is a cross-sectional illustration of a paper web 20 showing a paper
web
according to an embodiment of the invention, wherein the paper web has three
fiber
layers designated 301,302, and 303. A paper web having a layered structure can
be
made using the papermaking equipment and methods illustrated in Figures 8A,B
and
9A-C, or alternatively, those illustrated in Figures 14A,B and 15A-C.
Il
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22
While a single forming wire 542 is shown in Figure 9A, it--will be understood
that
other forming wire configurations can be used in combination with one or more
headboxes, each headbox having a a capability of providing one or more layers
of fiber
furnish, in order to provide a multiple layer web. U.S. Patent 3,994,771
issued to Morgan
et al. and U.S. Patent 4,300,981 issued to Carstens et al. and commonly
assigned U.S.
Patent Application "Layered Tissue Having Improved Functional Properties"
filed
October 24, 1996 in the names of Phan and Trokhan disclose layering and are
incorporated by reference herein. Various types of forming wire
configurations,
including twin wire former can be used. Additionally, various types of headbox
designs
can be employed to provide a web having one or more fiber layers
Referring to Figure 16, one or more headboxes can be used to deliver three
layers of furnish corresponding to layers 301, 302, and 303 onto the forming
wire 542,
such that the embryonic web comprises the layers 301, 302, and 303. The first
layer 301
can comprise relatively long papermaking fibers disposed adjacent the first
surface 22 of
the web. The relatively long papermaking fibers in the first layer 301 can
comprise
softwood fibers such as Northern Softwood fibers having an average fiber
length of
about 3 millimeters or more. The second layer 302 can comprise relatively
short
papermaking fibers disposed adjacent the second surface 24 of the web. The
relatively
short papermaking fibers in the second layer 302 can comprise hardwood fibers
such as
Eucalyptus fibers having an average fiber length of about 1.5 millimeters or
less.
The third layer 303 is disposed intermediate the first and second layers 301
and
302. The third layer can be a debonding layer characterized in having a void
spaces 310
having substantially no fibers therein. Such void spaces are shown in the
photomicrograph of Figures 3 and 11.
In particular, the void spaces can be located in the relatively thicker
regions 50.
The third layer can comprise a debonding agent, such as ADOGEN~ brand
additive, to
reduce fiber to fiber bonds in the third layer 303, thereby facilitating
opening of the fiber
structure in layer 303 to provide the void spaces 310. The third layer 303 can
comprise
softwood fibers, hardwood f hers, or a combination of hardwood and softwood
fibers.
In yet another embodiment, the layers 301 and 302 can each comprise relatively
short hardwood fibers, and the third layer 303 can comprise relatively long
softwood
fibers. For instance, the layers 301 and 302 can each be predominately formed
of
Eucalyptus fibers, and the third layer 303 can be predominately formed of
relatively long
Northern Softwood fibers.
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23
Alternatively, other methods can be employed to facilitate debulking of the
web
or debonding of fibers intermediate outer layers of the web. U.S. Patent
4,225,382 to
Kearney et al, is incorporated herein by reference for the purpose of
disclosing multiple
layer webs comprised of well bonded layers separated by an interior layer.
EXAMPLES
All percentages are weight percentages based on dry fiber weight unless
otherwise
indicated.
Example 1:
This examples provides a 3 layer tissue web made with the papermaking
apparatus shown in Figures 14A,B and 15A-C.
A 3% by weight aqueous slurry of NSK is made up in a conventional re-
pulper. A 2% by weight aqueous solution of the temporary wet strength resin
- (i.e., National starch 78-0080 marketed by National Starch and Chemical
corporation of New-York, NY) is added to the NSK stock pipe at a rate of 0.2%
by weight of the dry fibers (Ratio of weight of wet strength resin to dry
fiber
weight is 0.002). The NSK slurry is diluted to about 0.2% consistency at the
fan
pump. Second, a 3% by weight aqueous slung of Eucalyptus fibers is made up in
a conventional re-pulper. A 2% by weight aqueous solution of the debonder
(i.e.,
ADOGEN~ 442 ) is added to the Eucalyptus stock pipe at a rate of 0.1 % by
weight of the dry fibers. The Eucalyptus slurry is diluted to about 0.2%
consistency at the fan pump.
Three individually treated furnish streams (stream 1 = 100% NSK; stream 2
= 100% Eucalyptus; stream 3 = 100% Eucalyptus) are kept separate through the
headbox and deposited onto a Fourdrinier wire to form a three layer embryonic
web containing two outer Eucalyptus layers and a middle NSK layer. Dewatering
occurs through the Fourdrinier wire and is assisted by a deflector and vacuum
boxes. The Fourdrinier wire is of a 5-shed, satin weave configuration having
110
machine-direction and 95 cross-machine-direction monofilaments per inch,
respectively.
The embryonic wet web is vacuum transferred from the Fourdrinier wire , at
a fiber consistency of about 8% at the point of transfer, to the web support
n
CA 02271874 1999-OS-11
WO 98/21406 PCT/US97/20814 --
24
apparatus 200 having a foraminous background element comprising a woven
fabric 1220 and a web patterning layer 250 made of photosensitive resin. A
pressure differential of about 16 inches of mercury is used to transfer the
web to
the web support apparatus 200. The foraminous background element is of a 5-
shed, satin weave configuration having 68 machine-direction and 51 cross-
machine-direction monofilaments per inch, the machine direction filaments
having a diameter of about 0.22 mm and the cross-machine direction filaments
having a diameter of about 0.29 mm. Such a foraminous background element is
manufactured by Appleton Wire Company, Appleton, Wisconsin.
The web patterning layer 250 has continuous network web contacting
surface 260 with a projected area which is between about 30 and about 40
percent
of the projected area of the apparatus 200. The difference between elevation
1231
of the web contacting surface of the foraminous background element and the
elevation 261 of the continuous network web contacting surface 260 is about
.001
inch (.0254mm).
The web is transferred to the apparatus 200 to provide a web 545 supported
on the apparatus 200 and having a substantially smooth second surface 549, as
shown in Figure 15B. Further de-watering is accomplished by vacuum assisted
drainage and by through air drying, as represented by devices 600, 620, and
650,
until the web has a fiber consistency of about 65%.
Transfer to the Yankee dryer at the nip 800 is effected with a pressure roll
900. The surface 250 and the surfaces 1230 are imprinted on the first surface
547
of the web 545 to provide a patterned surface 547. Substantially all of the
second
surface 549 is adhered to the surface 875 of the a Yankee dryer drum 880 using
a
polyvinyl alcohol based creping adhesive. The nip pressure in nip 800 is at
least
about 400 pli.
The web consistency is increased to between about 90% and 100% before
dry creping the web from the surface 875 with a doctor blade 1000. The doctor
blade has a bevel angle of about 25 degrees and is positioned with respect to
the
Yankee dryer to provide an impact angle of about 81 degrees; the Yankee dryer
is
operated at about 800 fpm {feet per minute) (about 244 meters per minute). The
dry web is formed into roll at a speed of 650 fpm (200 meters per minutes).
The web made according to the above procedure is converted into a three-
layer, one-ply toilet tissue paper. The one-ply toilet tissue paper has a
basis
weight of about 17.5 pounds per 3000 square feet, contains about 0.02% by
CA 02271874 1999-OS-11
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weight of the temporary wet strength resin, and about 0.01 % by weight of the
debonder.
Importantly, the resulting one-ply tissue paper is soft , absorbent and
suitable for use as toilet tissue. The one ply tissue web has the following
characteristics:
Basis Weight: 17.5 lb/3000 sq ft. (28.5 gm/sq. meter)
Macro-Caliper: 13.6 mils (0.0136 inches)
Bulk Density: 0.08 gram/cubic centimeter
Surface Smoothness
of surface 22: 890
Surface Smoothness
of surface 24: 1070
Smoothness Ratio: 1.20
Example 2:
This example provides a 2 layer tissue web made with the papermaking
apparatus shown in Figures 14A,B and 1 SA-C.
A 3% by weight aqueous slurry of NSK is made up in a conventional re-
pulper. A 2% solution of a temporary wet strength resin (e.g. PAREZ~ 750
marketed by American Cyanamid Company of Stanford, Ct:) is added to the NSK
stock pipe at a rate of 0.2% by weight of the dry fibers. The NSK slurry is
diluted
to about 0.2% consistency at the fan pump. Second, a 3% by weight aqueous
slurry of Eucalyptus fibers is made up in a conventional re-pulper. A 2%
solution
of the debonder (i.e., ADOGEN~ 442 marketed by Witco Corporation of Dublin,
OH) is added to the Eucalyptus stock pipe at a rate of 0.1 % by weight of the
dry
fibers. The Eucalyptus slurry is diluted to about 0.2% consistency at the fan
PAP.
The two furnish streams (stream 1 = 100% NSK / stream 2 = 100%
Eucalyptus) are mixed in the headbox and deposited onto a Fourdrinier wire 542
to form an embryonic web containing NSK and Eucalyptus fibers. Dewatering
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26
occurs through the Fourdrinier wire and is assisted by a deflector and vacuum
boxes. The Fourdrinier wire is of a 5-shed, satin weave configuration having
110
machine-direction and 95 cross-machine-direction monofilaments per inch,
respectively.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of about 8% at the point of transfer, to a web support apparatus
200
comprising a woven fabric 1220 and a web patterning layer 250 having a
continuous network surface 260.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of about 8% at the point of transfer, to the apparatus 200, to
provide a
web 545 having a substantially smooth, macroscopically monoplanar surface 549
and a surface 547 which conforms to the surfaces 1230 and the surface 260. A
pressure differential of about 16 inches of mercury is used to transfer the
web to
the 200. The woven fabric 1220 is of a 3-shed, satin weave configuration
having
79 machine-direction and 67 cross-machine-direction monofilaments per inch,
the
machine direction filaments having a diameter of about 0.18 mm and the cross-
machine direction filaments having a diameter of about 0.21 mm. Such a
foraminous background element is manufactured by Appleton Wire Company,
Appleton, Wisconsin.
The web patterning layer 250 has web contacting top surface 260 having a
projected area which is between about 30 and about 40 percent of the projected
area of the apparatus 200. The difference between the elevation 1231 of the
web
contacting surface 1230 and the elevation 261 of the surface 260 is about 1
mil
(0.001 inch, 0.0254 mm).
Further de-watering of the web 545 is accomplished by vacuum assisted
drainage and by though air drying, as represented by devices 600, 620, and
650,
until the web has a fiber consistency of about 65%. Transfer to the Yankee
dryer
is effected at the nip 800 formed between a pressure roll 900 and the Yankee
dryer drum 880.
The surface 250 and the surfaces 1230 are imprinted on the first surface
547 of the web 545 to provide a patterned surface 547. Substantially all of
the
second surface 549 is adhered to the surface 875 of the a Yankee dryer drum
880
using a polyvinyl alcohol based creping adhesive. The nip pressure in nip 800
is
at least about 400 pli.
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27
The web consistency is increased to between about 90%-end 100% before
dry creping the web with a doctor blade 1000. The doctor blade has a bevel
angle
of about 25 degrees and is positioned with respect to the Yankee dryer to
provide
an impact angle of about 81 degrees; the Yankee dryer is operated at about 800
fpm (feet per minute) (about 244 meters per minute). The dry web is formed
into
roll at a speed of 650 fpm (200 meters per minutes).
The web is converted to provide a two-ply bath tissue paper. Each ply has a
basis weight of about 12.8 pounds per 3000 square feet and contains about
0.02%
of the temporary wet strength resin and about 0.01 % of the debonding agent.
The resulting two-ply tissue paper is soft , absorbent and suitable for use as
bath
tissue. Each ply has the following properties:
Basis Weight: 12.81b/3000 sq ft (20.8 gm/sq.
meter).
Macro-Caliper: 11.4 mils
Bulk Density: 0.07 gram/cubic centimeter
Surface Smoothness
of surface 22: 850
Surface Smoothness
of surface 24: 1006
Smoothness Ratio:1.18
Example 3:
This example provides a 2 ply tissue paper, each ply having 3 layers, and each
ply
made with papermaking apparatus of the type shown in Figures 8A,B
and 9A-C.
A 3% by weight aqueous slurry of Northern Softwood Kraft (NSK) fibers
is made using a conventional re-pulper. A 2% solution of the temporary wet
strength resin (i.e., National Starch 78-0080 marketed by National Starch and
Chemical corporation of New-York, New York) is added to the NSK stock pipe at
n
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28
a rate of 0.2% by weight of the dry fibers. The NSK slurry ~s-diluted to about
0.2% consistency at the fan pump. Second, a 3% by weight aqueous slurry of
Eucalyptus fibers is made up using a conventional re-pulper. A 2% solution of
the debonder (i.e., ADOGEN~ 442 marketed by Witco Corporation of Dublin,
OH) is added to one of the Eucalyptus stock pipe at a rate of 0.1 % by weight
of
the dry fibers. The Eucalyptus slurry is diluted to about 0.2% consistency at
the
fan pump.
Three individually treated furnish streams (stream 1 = 100% NSK; stream 2
= 100% Eucalyptus coated with debonder; stream 3 = 100% Eucalyptus) are kept
separate through the headbox and deposited onto a Fourdrinier wire to form a
three layer embryonic web containing an outer Eucalyptus layer, a debonded
Eucalyptus layer and an NSK layer. Dewatering occurs through the Fourdrinier
wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is
of a
5-shed, satin weave configuration having 110 machine-direction and 95 cross-
machine-direction monofilaments per inch, respectively.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of about 8% at the point of transfer, to a web support apparatus
200
having a dewatering felt layer 220 and a photosensitive resin web patterning
layer
250.
The dewatering felt 220 is a Amflex 2 Press Felt manufactured by Appleton
Mills of Appleton, Wisconsin. The felt 220 comprises a batt of polyester
fibers.
The batt has a surface denier of 3, a substrate denier of 10-15. The felt
layer 220
has a basis weight of 1436 gm/square meter, a caliper of about 3 millimeter,
and
an air permeability of about 30 to about 40 scfm.
The web patterning layer 250 comprises a continuous network web
contacting surface 260 having an projected area of about 30 to about 40
percent of
the projected area of the web support apparatus 200. The difference between
the
elevation 261 of the surface 260 and the elevation 231 of the felt surface 230
is
about 0.005 inch (0.127 millimeter).
The embryonic web is transferred to the apparatus 200 to provide a web 545
supported on the apparatus 200 and having a macroscopically monoplanar,
substantially smooth surface 549. Transfer is provided at the vacuum transfer
point with a pressure differential of about 20 inches of Mercury.
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29
Further de-watering is accomplished by vacuum assisted drainage, such as
by apparatus 620, until the web has a fiber consistency of about 25%. The web
545 is then carried adjacent the steam hood 2880 and into the nip 800 formed
between a vacuum pressure roll 900 and the Yankee dryer drum 880.
The surface 260 is imprinted into the surface 547 of the web 545 at the nip
800 by pressing the web 545 and the web support apparatus 200 between the
vacuum presure roll 900 and the Yankee dryer drum 880 at a nip pressure of
about
400 pli. A creping adhesive is used to adhere the web to the Yankee dryer. The
fiber consistency is increased to at least about 90% before dry creping the
web
with a doctor blade. The doctor blade has a bevel angle of about 25 degrees
and is
positioned with respect to the Yankee dryer to provide an impact angle of
about
81 degrees; the Yankee dryer is operated at about 800 fpm (feet per minute)
(about 244 meters per minute). The dry web is formed into roll at a speed of
650
fpm .
The web is converted into a two-ply bath facial tissue paper, each ply
comprising three fiber layers. The two-ply toilet tissue paper contains about
1.0% of the temporary wet strength resin and about 0.1 % of the debonder.
Each ply has the following properties:
Basis Weight: 9.8 lb per 3000 sq. ft (15.9 gm/square
meter)
Macro-Caliper: 6 mils
Bulk Density: 0.10 grams/ cubic centimeter
Surface Smoothness
of surface 22: 740
Surface Smoothness
of surface 24: 960
Smoothness Ratio: 1.30
Example 4:
This example provides a tissue web made with the papermaking
apparatus of the type shown in Figures 8A,B and 9A-C.
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A 3% by weight aqueous slurry of Northern Softwood Kr-aft is made up in
a conventional re-pulper. A 2% solution of the temporary wet strength resin
PAREZ~ 750) is added to the NSK stock pipe at a rate of 0.2% by weight of the
dry fibers. The NSK slurry is diluted to about 0.2% consistency at the fan
pump.
Second, a 3% by weight aqueous slurry of Eucalyptus fibers is made up using a
conventional re-pulper. A 2% solution of the debonder (ADOGEN~ 442) is
added to the Eucalyptus stock pipe at a rate of 0.1 % by weight of the dry
fibers.
The Eucalyptus slurry is diluted to about 0.2% consistency at the fan pump.
The two individually treated fiunish streams (stream 1 = 100% NSK; stream
2 = 100% Eucalyptus) are mixed through the headbox and deposited onto a
Fourdrinier wire to form a single-layer web of NSK fibers and coated
Eucalyptus
fibers, the Eucalyptus fibers being coated with debonder. Dewatering occurs
through the Fourdrinier wire and is assisted by a deflector and vacuum boxes.
The
Fourdrinier wire is of a 5-shed, satin weave configuration having 110 machine-
direction and 95 cross-machine-direction monofilaments per inch, respectively.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of about 8% at the point of transfer, to a web support apparatus
200
having a dewatering felt layer 220 and a photosensitive resin web patterning
layer
250.
The dewatering felt 220 is a Amflex 2 Press Felt manufactured by Appleton
Mills of Appleton, Wisconsin. The web patterning layer 250 comprises a
continuous web contacting surface 260. The web patterning layer 250 has a
projected area equal to about 35 percent of the projected area of the web
support
apparatus 200. The difference in elevation between the top web contacting
surface 260 and the first felt surface 230 is about 0.005 inch (0.127
millimeter).
The embryonic web is transferred to the web support apparatus 200 and
deflected in a first deflection step to form a generally monoplanar web 545.
Transfer is provided at the vacuum transfer point with a pressure differential
of
about 20 inches of mercury. Further de-watering is accomplished by vacuum
assisted drainage until the web has a fiber consistency of about 25%. The web
545 is carried by the web support apparatus 200 adjacent to the steam hood
2800
and into the nip 800 formed between the vacuum pressure roll 900 and the
Yankee drum 880. The web 545 -is then compacted against the compaction surface
875 of the Yankee dryer drum 880 at a compression pressure of at least about
400
pli. A polyvinyl alcohol based creping adhesive is used to adhere the
compacted
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31
web to the Yankee dryer. The fiber consistency is increased to at least about
90%
before dry creping the web from the surface of the dryer drum 880 with a
doctor
blade. The doctor blade has a bevel angle of about 25 degrees and is
positioned
with respect to the Yankee dryer to provide an impact angle of about 81
degrees;
the Yankee dryer is operated at about 800 fpm (feet per minute) (about 244
meters
per minute). The dry web is formed into roll at a speed of 650 fpm (200 meters
per minutes).
The web is converted to provide a single-Layer, two-ply bath tissue paper.
Each ply of the two-ply bath tissue paper has a basis weight about 12.6 pounds
per 3000 square feet, and contains about 0.2% by weight of the temporary wet
strength resin and about 0.1 % by weight of the debonder.
The resulting two-ply
tissue paper is soft,
absorbent, and is
suitable for use as
a
bath tissue.
The tissue web has
the following properties:
Basis Weight: 12.6 lb/3000 sq ft (20.5 gm/sq
meter)
Macro-Caliper: 8.8 mils
Bulk Density: 0.092 gram/cubic centimeter
Surface Smoothness
of surface 22: 890
Surface Smoothness
of surface 24: 1050
Smoothness Ratio: 1.18
PROPHETIC EXAMPLE:
The following prophetic example illustrates a method of making 2 ply
tissue paper using a commercial size papermaking equipment of the type shown
in
Figures 8A,B and 9A-C.
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32
A 3% by weight aqueous slurry of Northern Softwood Kraft is made up in
a conventional re-pulper. A 2% solution of the temporary wet strength resin
(i.e.,
PAREZ~ 750 marketed by American Cyanamid corporation of Stanford, CT) is
added to the NSK stock pipe at a rate of 0.2% by weight of the dry fibers. The
NSK slurry is diluted to about 0.2% consistency at the fan pump. Second, a 3%
by weight aqueous slurry of Eucalyptus fibers is made up using a conventional
re-
pulper. A 2% solution of the debonder (i.e., Adogen~ 442 marketed by Witco
Corporation of Dublin, OH) is added to the Eucalyptus stock pipe at a rate of
0.1 % by weight of the dry fibers. The Eucalyptus slurry is diluted to about
0.2%
consistency at the fan pump.
The two individually treated furnish streams (stream 1 = 100% NSK; stream
2 = 100% Eucalyptus) are mixed through the headbox and deposited onto a
Fourdrinier wire to form a single-layer web of NSK fibers and Eucalyptus
fibers,
the Eucalyptus fibers being coated with debonder. Dewatering occurs through
the Fourdrinier wire and is assisted by a deflector and vacuum boxes. The
Fourdrinier wire is of a 5-shed, satin weave configuration having 110 machine-
direction and 95 cross-machine-direction monofilaments per inch, respectively.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of about 10% at the point of transfer, to a web support apparatus
200
having a dewatering felt layer 220 and a photosensitive resin web patterning
layer
250.
The dewatering felt 220 is a Amflex 2 Press Felt manufactured by Appleton
Mills of Appleton, Wisconsin. The web patterning layer 250 comprises
continuous web patterning layer 250 having about 69 bilaterally staggered,
oval
shaped openings 270 per square inch of the web contacting surface 220. The web
patterning layer 250 has a projected area equal to about 35 percent of the
projected area of the web support apparatus 200. The difference in elevation
between the top web contacting surface 260 and the first felt surface 230 is
about
0.005 inch (0.127 millimeter).
The embryonic web is transferred to the web support apparatus 200 to form
a generally monoplanar web 545. Transfer is provided at the vacuum transfer
point with a pressure differential of about 20 inches of mercury. Further de-
watering is accomplished by vacuum assisted drainage until the web has a fiber
consistency of about 30%. The web 545 is carried by the web support apparatus
200 to the nip 800. The vacuum pressure roll 900 has a compression surface 910
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33
having a hardness of about 60 P&J. The web 545 is then compacted against the
compaction surface 875 of the Yankee dryer drum 880 by pressing the web 545
and the web support apparatus 200 between the compression surface 910 and the
Yankee dryer drum 880 surface at a compression pressure of at least about 400
pli. A polyvinyl alcohol based creping adhesive is used to adhere the
compacted
web to the Yankee dryer. The fiber consistency is increased to at least about
90%
before dry creping the web from the surface of the dryer drum 880 with a
doctor
blade. The doctor blade has a bevel angle of about 20 degrees and is
positioned
with respect to the Yankee dryer to provide an impact angle of about 76
degrees;
the Yankee dryer is operated at about 4500 fpm (feet per minute) (about 1372
meters per minute). The dry web is formed into roll at a speed of 3690 fpm (
1125
meters per minute).
The web is converted to provide a two-ply bath tissue paper. Each ply of
the two-ply bath tissue paper can have a basis weight about 12.5 pounds per
3000
square feet, and contains about 0.2% by weight of the temporary wet strength
resin and about 0.1 % by weight of the debonder. The resulting two-ply tissue
paper is soft, absorbent, and is suitable for use as a bath tissue.
ANALYTICAL PROCEDURES
Measurement of Thickness and Elevation of Paper Features:
The location of the plane 23 of the region 30, the thickness of the region 30
and the thickness of the region 50 are determined using photomicrographs of
microtomed cross-sections of the paper web. An example of such a
photomircrograph is shown in Figure 3, where the location of plane 23 is
indicated, along with the thickness P of region 50 and the thickness K of
region
30.
Ten samples, each measuring about 2.54 by 5.1 centimeters ( 1 inch by 2
inch) are choosen randomly from a sheet or roll of tissue paper. If ten
samples
cannot be obtained from a single sheet, then additional sheets made under the
same conditions (preferably the same parent roll) can be used.
Microtomes for each sample are made by stapling each sample onto a rigid
cardboard holder. The cardboard holder is placed in a silicon mold. The paper
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34
sample is immersed in a resin such as Merigraph photopolymer~manufactured by
Hercules, Inc.
The sample is cured to harden the resin mixture. The sample is removed
from the silicon mold. Prior to immersion in photopolymer the sample is marked
with a reference point to accurately determine where microtome slices are
made.
Preferably, the same reference point is utilized in both the plan view (e.g.
Figure
4) and various sectional views (e.g. Figure 3) of the sample of the web 20.
The sample is placed in a model 860 microtome sold by the American
Optical Company of Buffalo, New York and leveled. The edge of the sample is
removed from the sample, in slices, by the microtome until a smooth surface
appears.
A sufficient number of slices are removed from the sample, so that the
various regions of the paper web (e.g. 30 and 50) may be accurately
reconstructed.
For the embodiment described herein, slices having a thickness of about 60
microns per slice are taken from the smooth surface. Multiple slices may be
required so that the thicknesses P and K may be ascertained.
A sample slice is mounted on a microscope slide using oil and a cover slip.
The slide and the sample are mounted in a light transmission microscope and
observed at about 40X magnification. Photomicrographs are taken along the
slice, and the individual photomicrographs are arranged in series to
reconstruct
the profile of the slice. The thicknesses and elevations may be ascertained
from
the reconstructed profile, as illustrated in Figure 3, which is a
photomicrograph of
a cross-section of a paper structure of the type illustrated in Figures 1 and
2.
The thicknesses are established using Hewlett Packard ScanJet IIC color
flatbed scanner to scan the photomicrograph and store the photomicrograph in a
picture file format on a personal computer. The Hewlett Packard Scanning
software is DeskScan II version 1.6 . The scanner settings type is black and
white
photo. The path is LaserWriter NT, NTX. The brightness and contrast setting is
125. The scaling is 100%. The file is scanned and saved in a picture file
format on
a Macintosh IICi computer. The picture file is opened with a suitable photo-
imaging software package or CAD program, such as PowerDraw version 6.0,
available from Engineered Software of North Carolina.
Referring to Figure 3, the thicknesses of the region 30 and 50 are indicated
by circles having their diameters labeled K and P, respectively. First, the
largest
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circle that can be inscribed in the region 50 being investigated is drawn
using the
PowerDraw software. The diameter of this circle is labeled P. The thickness P
of
the region 50 is the diameter of this circle multiplied by the appropriate
scale
factors (The scale factor is the magnification of the photomicrograph
multiplied
by the magnification of the
scanned image).
Next, the smallest circles that can be inscribed in the portions of the region
30 on either side of the region 50 are drawn. The diameters of these circles
are
labeled K. The thickness K of the region 30 adjacent the region 50 is the
average
of the two diameters multiplied by the above mentioned scale factor.
The plane of the region 30 adjacent the region 50 is located by drawing a
line connecting the centers of the two circles having the diameter K, as shown
in
Figure 3. -
For each of the ten samples, each occurance of a relatively thicker region 50
disposed between relatively thinner portions of a region 30 are investigated.
For
each case where a relatively thinner region 30 is identified on each side of a
relatively thicker region 50, the line representing plane 23 is drawn. If this
line
intersects the region 50 in at least 25 percent of the occurances, then the
paper
from which the samples where taken is said to have relatively thicker regions
disposed in the plane of the relatively thicker region, according to the
present
invention. For instance, if the ten samples yield 50 occurances of a a
relatively
thinner region 30 on either side of a relatively thicker region 50, then the
relatively thicker regions 50 are said to be disposed in the plane of the
relatively
thinner region 30 if and only if the line drawn representing plane 23
intersects the
the thicker region 50 in at least I 3 of the 50 occurances.
Surface Smoothness:
The surface smoothness of a side of a paper web is measured based upon
the method for measuring physiological surface smoothness (PSS) set forth in
the
1991 International Paper Physics Conference, TAPPI Book 1, article entitled
"Methods for the Measurement of the Mechanical Properties of Tissue Paper" by
Ampulski et al. found at page 19, which article is incorporated herein by
reference. The PSS measurement as used herein is the point by point sum of
amplitude values as described in the above article. The measurement procedures
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36
set forth in the article are also generally described in U.S. Patents
4,959,125
issued to Spendel and 5,059,282 issued to Ampulski et al, which patents are
incorporated herein by reference.
For purposes of testing the paper samples of the present invention, the
method for measuring PSS in the above article is used to measure surface
smoothness, with the following procedural modifications:
Instead of importing digitized data pairs (amplitude and time) into SAS
software for 10 samples, as described in the above article, the Surface
Smoothness measurement is made by acquiring, digitizing, and statistically
processing data for the 10 samples using LABVIEW brand software available
from National Instruments of Austin, Texas. Each amplitude spectrum is
generated using the "Amplitude and Phase Spectrum.vi" module in the
LABVIEW software package, with "Amp Spectrum Mag Vnms" selected as the
output spectrum. An output spectrum is obtained for each of the 10 samples.
Each output spectrum is then smoothed using the following weight factors
in LABVIEW: 0.000246, 0.000485, 0.00756, 0.062997. These weight factors are
selected to imitate the smoothing provided by the factors 0.0039, 0.0077,
.120, 1.0
specified in the above article for the SAS program.
After smoothing, each spectrum is filtered using the frequency filters
specified in the above article. The value of PSS, in microns, is then
calculated as
described in the above mentioned article, for each individually filtered
spectrum.
The Surface Smoothness of the side of a paper web is the average of the 10 PSS
values measured from the 10 samples taken from the same side of the paper web.
Similarly, the Surface Smoothness of the opposite side of the paper web can be
measured. The smoothness ratio is obtained by dividing the higher value of
Surface Smoothness, corresponding to the more textured side of the paper web,
by
the lower value of Surface Smoothness, corresponding to the smoother side of
the
paper web.
Basis Weight:
Basis weight is measured according to the following procedure.
The paper to be measured is conditioned at 71-75 degrees Fahrenheit at 48
to 52 percent relative humidity for a minimum of 2 hours. The conditioned
paper
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37
is cut to provide twelve samples measuring 3.5 inch by 3.5 inch: The samples
are
cut, six samples at a time, with a suitable pressure plate cutter, such as a
Thwing-
Albert Alfa Hydraulic Pressure Sample Cutter, Model 240-10. The two six
sample stacks are then combined into a 12 ply stack and conditioned for at
least
15 additional minutes at 71 to 75 F and 48 to 52 percent humidity.
The 12 ply stack is then weighed on a calibrated analytical balance. The
balance is maintained in the same room in which the samples were conditioned.
A suitable balance is made by Sartorius Instrument Company, Model A200S.
This weight is the weight in grams of a 12 ply stack of the paper, each ply
having
an area of 12.25 square inches.
The basis weight of the paper web (the weight per unit area of a single
ply) is calculated in units ,of pounds per 3,000 square feet, using the
following
equation:
Weig-ht of 12 ply stack~~Qramsl x 3000 x 144 sc~inch per sq ft
(453.6 gm/lb) x (12 plies) x (12.25 sq. in. per ply)
or simply: Basis Weight (lb/3,000 ft2) _
Weight of 12 ply stack (gm) x 6.48
Macro-Caliper or Dry Caliper:
The Macro-Caliper or dry caliper is measwed using the procedure for
measuring dry caliper disclosed in U.S. Patent 4,469,735, issued Sept. 4, 1984
to
Trokhan, which patent is incorporated herein by reference.
Bulk Density:
Bulk Density is the basis weight of the web divided by the web's macro-
caliper.
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Absorbent Capacity:
The absorbent capacity of a web is measured using the Horizontal
Absorbative Capacity Test disclosed in above referenced U.S. Patent 4,469,735.
Measurement of Web support apparatus Elevations:
The elevation difference between the elevation 231 of the first felt surface
and the
elevation 261 of the web contacting surface 260 is measured using the
following
procedure. The web support apparatus is supported on a flat horizontal surface
with the
web patterning layer facing upward. A stylus having a circular contact surface
of about
1.3 square millimeters and a vertical length of about 3 millimeters is mounted
on a
Federal Products dimensioning gauge (model 432B-81 amplifier modified for use
with an
EMD-4320 W 1 breakaway probe) manufactured by the Federal Products Company of
Providence, Rhode Island. The instrument is calibrated by determining the
voltage
difference between two precision shims of known thickness which provide a
known
elevation difference: The instrument is zeroed at an elevation slightly lower
than the first
felt surface 230 to insure unrestricted travel of the stylus. The stylus is
placed over the
elevation of interest and lowered to make the measurement. The stylus exerts a
pressure
of about 0.24 grams/square millimeter at the point of measurement. At least
three
measurements are made at each elevation. The measurements at each elevation
are
averaged. The difference between the average values is the calculated to
provide the
elevation difference.
The same procedure is used to measure the difference between elevations 1231
and 261 illustrated in Figure 14B.
