Note: Descriptions are shown in the official language in which they were submitted.
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FIBROUS STRUCTURE COMPRISING A FIBER FLEXIBILIZING AGENT SYSTEM
TECHNICAL FIELD
This invention relates to fibrous structures, especially fibrous structures
that are
incorporated into sanitary tissue products. More particularly, the present
invention relates to
fibrous structures comprising a fiber flexibilizing agent system and methods
for making such
fibrous structures.
BACKGROUND OF THE INVENTION
Conventional sanitary tissue products incorporate fibrous structures that
typically contain
fiber flexibilizing agents, such as softening agents. Fiber flexibilizing
agents reduce the opacity
of fibrous structures within which they are incorporated.
Accordingly, there is a need for fibrous structures that contain a fiber
flexibilizing agent
system wherein the net change in opacity of the fibrous structure resulting
from the fiber
flexibilizing agent system is greater than the net change in opacity of the
fibrous structure
resulting from individual components of the fiber flexibilizing agent system.
SUMMARY OF THE INVENTION
The present invention fulfills the need described above by providing a fibrous
structure
comprising a fiber flexibilizing agent system.
In one aspect of the present invention, a fibrous structure comprising a
fiber, preferably a
cellulosic fiber, and a fiber flexibilizing agent system comprising a fiber
flexibilizing agent
wherein the net change in opacity of the fibrous structure resulting from the
fiber flexibilizing
agent system is greater than the net change in opacity of the fibrous
structure resulting from
individual components of the fiber flexibilizing agent system, is provided.
In still another aspect of the present invention, a method for making a
fibrous structure
comprising the steps of:
a) providing a fibrous structure;
b) contacting the fibrous structure with a fiber flexibilizing agent system
comprising
a fiber flexibilizing agent such that the net change in opacity of the fibrous
structure
resulting from the fiber flexibilizing agent system is greater than the net
change in
opacity of the fibrous structure resulting from individual components of the
fiber
flexibilizing agent system, is provided.
In even another aspect of the present invention, a fibrous structure made by a
method in
accordance with the present invention, is provided.
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In yet another aspect of the present invention, a single-ply or mufti-ply
sanitary tissue
product comprising a fibrous structure in accordance with the present
invention is provided.
Accordingly, the present invention provides fibrous structures comprising a
fiber
flexibilizing agent system comprising a fiber flexibilizing agent; methods for
making such fibrous
structures; and sanitary tissue products comprising such fibrous structures.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic representation of a method in accordance with the
present invention.
Fig. 2 is a schematic representation of a transfer surface method embodiment
of the
present invention.
Fig. 3 is a schematic representation of a non-contact applicator method
embodiment of
the present invention.
Fig. 4 is a schematic representation of a nozzle suitable for use in a non-
contact applicator
method embodiment of the present invention.
Fig. 5 is a schematic representation of a spray discharge that can be obtained
from an
oscillatory nozzle of the present invention.
Fig. 6 is a schematic representation of a nozzle cleaning system that can be
used with a
nozzle of a non-contact applicator method embodiment of the present invention.
Fig. 7 is a schematic representation of an extrusion application embodiment of
the present
invention.
Fig. 8 is an exploded, schematic representation of a slot extrusion die
suitable for use in
an extrusion application method embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
"Fiber" as used herein means an elongate particulate having an apparent length
greatly
exceeding its apparent width, i.e. a length to diameter ratio of at least
about 10. More
specifically, as used herein, "fiber" refers to papermaking fibers. The
present invention
contemplates the use of a variety of papermaking fibers, such as, for example,
natural fibers or
synthetic fibers, or any other suitable fibers, and any combination thereof.
Papermaking fibers
useful in the present invention include cellulosic fibers commonly known as
wood pulp fibers.
Applicable wood pulps include chemical pulps, such as Kraft, sulfite, and
sulfate pulps, as well as
mechanical pulps including, for example, groundwood, thermomechanical pulp and
chemically
modified thermomechanical pulp. Chemical pulps, however, may be preferred
since they impart a
superior tactile sense of softness to tissue sheets made therefrom. Pulps
derived from both
deciduous trees (hereinafter, also referred to as "hardwood") and coniferous
trees (hereinafter,
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also referred to as "softwood") may be utilized. The hardwood and softwood
fibers can be
blended, or alternatively, can be deposited in layers to provide a stratified
web. U.S. Pat. No.
4,300,981 and U.S. Pat. No. 3,994,771 are incorporated herein by reference for
the purpose of
disclosing layering of hardwood and softwood fibers. Also applicable to the
present invention are
fibers derived from recycled paper, which may contain any or all of the above
categories as well
as other non-fibrous materials such as fillers and adhesives used to
facilitate the original
papermaking. In addition to the above, fibers and/or filaments made from
polymers, specifically
hydroxyl polymers may be used in the present invention. Nonlimiting examples
of suitable
hydroxyl polymers include polyvinyl alcohol, starch, starch derivatives,
chitosan, chitosan
derivatives, cellulose derivatives, gums, arabinans, galactans and mixtures
thereof.
"Sanitary tissue product" as used herein means a soft, low density (i.e. <
about 0.15
g/cm3) web useful as a wiping implement for post-urinary and post-bowel
movement cleaning
(toilet tissue), for otorhinolaryngolical discharges (facial tissue), and
mufti-functional absorbent
and cleaning uses (absorbent towels).
"Basis Weight" as used herein is the weight per unit area of a sample reported
in lbs/3000
ft2 or g/m2. Basis weight is measured by preparing one or more samples of a
certain area (m2) and
weighing the samples) of a fibrous structure according to the present
invention and/or a paper
product comprising such fibrous structure on a top loading balance with a
minimum resolution of
0.01 g. The balance is protected from air drafts and other disturbances using
a draft shield.
Weights are recorded when the readings on the balance become constant. The
average weight (g)
is calculated and the average area of the samples (m2). The basis weight
(g/m2) is calculated by
dividing the average weight (g) by the average area of the samples (m2).
"Weight average molecular weight" as used herein means the weight average
molecular
weight as determined using gel permeation chromatography according to the
protocol found in
Colloids and Surfaces A. Physico Chemical & Engineering Aspects, Vol. 162,
2000, pg. 107-
121.
"Ply" or "Plies" as used herein means an individual fibrous structure
optionally to be
disposed in a substantially contiguous, face-to-face relationship with other
plies, forming a
multiple ply fibrous structure. It is also contemplated that a single fibrous
structure can
effectively forni two "plies" or multiple "plies", for example, by being
folded on itself.
"Neat fibrous structure" and/or "fibrous structure in neat form" as used
herein means a
fibrous structure consisting only of fibers.
"Opacity of neat fibrous structure" as used herein means the resulting opacity
of the neat
fibrous structure as determined according to the Opacity Test described below.
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"Net change in opacity of the fibrous structure resulting from the fiber
flexibilizing agent
system" as used herein means the difference between the opacity of the fibrous
structure
comprising the fiber flexibilizing agent system and the opacity of the fibrous
structure in its neat
form.
"Net change in opacity of the fibrous structure resulting from individual
components of
the fiber flexibilizing agent system" as used herein means the sum of the
difference between the
opacity of the fibrous structures each comprising a single individual
component of the fiber
flexibilizing agent system and the opacity of the fibrous structure in its
neat form.
As discussed herein, the net change in opacity of the fibrous structure
resulting from the
fiber flexibilizing agent system is greater than the net change in opacity of
the fibrous structure
resulting from individual components of the fiber flexibilizing agent system.
A nonlimiting example for clarity purposes is where the net change in opacity
of the
fibrous structure resulting from the fiber flexibilizing agent system is -
0.3% points and the net
change in opacity of the fibrous structure resulting from individual
components of the fiber
flexibilizing agent system is -0.5% points. Since the net change in opacity of
the fibrous
structure resulting from the fiber flexibilizing agent system is greater than
the net change in
opacity resulting from individual components of the fiber flexibilizing agent
system, this fibrous
structure would be within the scope of the present invention.
In another nonlimiting example, the net change in opacity of the fibrous
structure
resulting from the fiber flexibilizing agent system is +0.2% points and the
net change in opacity
of the fibrous structure resulting from individual components of the fiber
flexibilizing agent
system is -0.5% points. Since the net change in opacity of the fibrous
structure resulting from the
fiber flexibilizing agent system is greater than the net change in opacity
resulting from individual
components of the fiber flexibilizing agent system, this fibrous structure
would be within the
scope of the present invention.
In still another nonlimiting example, the net change in opacity of the fibrous
structure
resulting from the fiber flexibilizing agent system is +0.2% points and the
net change in opacity
of the fibrous structure resulting from individual components of the fiber
flexibilizing agent
system is +0.05% points. Since the net change in opacity of the fibrous
structure resulting from
the fiber flexibilizing agent system is greater than the net change in opacity
resulting from
individual components of the fiber flexibilizing agent system, this fibrous
structure would be
within the scope of the present invention.
Fibrous Structure
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The fibrous structure (web) of the present invention may be incorporated into
a single-ply
or mufti-ply sanitary tissue product.
The fibrous structure may be foreshortened, such as via creping, or non-
forshortened,
such as not creping.
The fibrous structures of the present invention are useful in paper,
especially sanitary
tissue paper products including, but not limited to: conventionally felt-
pressed tissue paper;
pattern densified tissue paper; and high-bulk, uncompacted tissue paper. The
tissue paper may be
of a homogenous or multilayered construction; and tissue paper products made
therefrom may be
of a single-ply or mufti-ply construction. The tissue paper preferably has a
basis weight of
between about 10 g/m2 and about 120 g/m2, and density of about 0.60 g/cc or
less. Preferably, the
basis weight will be below about 35 g/mz; and the density will be about 0.30
g/cc or less. Most
preferably, the density will be between about 0.04 g/cc and about 0.20 g/cc as
measured by the
Basis Weight Method described herein.
The fibrous structure may be made with a fibrous furnish that produces a
single layer
embryonic fibrous web or a fibrous furnish that produces a mufti-layer
embryonic fibrous web.
The fibrous structures of the present invention and/or paper products
comprising such
fibrous structures may have a total dry tensile of greater than about 59 g/cm
(150 g/in) and/or
from about 78 g/cm (200 g/in) to about 394 g/cm (1000 g/in) and/or from about
98 g/cm (250
g/in) to about 335 g/cm (850 g/in) as measured by the Total Dry Tensile Method
described herein.
The fibrous structures of the present invention and/or paper products
comprising such
fibrous structures may have a total wet tensile strength of greater than about
9 g/cm (25 g/in)
and/or from about 11 g/cm (30 g/in) to about 78 g/cm (200 g/in) and/or from
about 59 g/cm (150
g/in) to about 197 g/cm (500 g/in) as measured by the Total Wet Tensile
Strength Method
described herein. Wet strength can be provided by adding permanent wet
strength or temporary
wet strength resins as is well known in the art.
A nonlimiting suitable process for making a fibrous structure of the present
invention
comprises the steps of providing a furnish comprising plurality of cellulosic
fibers and a wet
strength agent; forming a fibrous structure from the furnish; heating the
fibrous structure to a
temperature of at least about 40°C and a moisture content of less than
about 5%; and contacting a
surface of the fibrous structure with a fiber flexibilizing agent system.
It is beneficial if the fiber flexibilizing agent of the present invention is
applied to an
overdried fibrous structure shortly after the fibrous structure is separated
from a drying means and
before it is wound onto a parent roll. Alternatively or additionally, the
composition can be
incorporated into the fibrous structure before or during its assembly or to
the dry fibrous structure
having a somewhat higher moisture content, for example, a web in moisture
equilibrium with its
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environment as the web is unwound from a parent roll as, for example, during
an off line
converting operation.
Fiber Flexibilizin$ AEent System
The fibrous structure of the present invention comprises a fiber and a fiber
flexibilizing
agent system.
The fiber flexibilizing agent system comprises a fiber flexibilizing agent and
optionally,
an opacity increasing agent.
When present in the fiber flexibilizing agent system, the fiber flexibilizing
agent and
opacity increasing agent are present in the fiber flexibilizing agent system
at a weight ratio of
from about 1:100 to about 10000:1 and/or from about 2:1 to about 100:1.
Fiber Flexibilizin~ Agent
The fibrous structure of the present invention comprises a fiber flexibilizing
agent system
comprising a fiber flexibilizing agent.
The fiber flexibilizing agent comprises a humectant and/or a plasticizer.
In one embodiment, the fiber flexibilizing agent has a vapor pressure of less
than about
2mm at 70°F.
Preferably, the fiber flexibilizing agent has a weight average molecular
weight of less
than about 1000 g/mol and/or from about 50 g/mol to about 1000 g/mol and/or
from about 100
g/mol to about 400 g/mol.
The term "humectant" as used herein means a material that raises the
equilibrium
moisture content in excess of that of the fibrous structure without a
humectant. The humectant
can be selected from the group consisting of hydroxyl-bearing organic
compounds such as
glycerol; pentaerythritol sugars such as starch hydrosolates an example of
which is high fructose
corn syrup; sugar alcohols such as sorbitol, maltitol, and mannitol;
deliquescent salts such as
calcium chloride and sodium lactate; triacetin; propylene glycol and mixtures
thereof.
The term "plasticizer" as used herein refers to a material capable of being
absorbed into
the fiber and imparting a greater flexibility thereto. Any compound bearing
hydrogen atoms
bonded to an oxygen or a nitrogen is classified as a plasticizer for purposes
of the present
invention, provided the total mass of such hydrogen atoms comprise at least
about 1 % by weight
of said plasticizer and said plasticizer has a vapor pressure less than about
2 mm Hg at 70°F.
Nonlimiting examples of suitable plasticizers include urea and low-water-
imbibing mono, di-,
and oligo- saccharides including dextrose and sucrose; allcyloxylated glycols;
ethylene carbonate;
propylene carbonate; and any combinations thereof.
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Also included as plasticizers are ethyloxylated and propyloxylated compounds
having a
vapor pressure less than about 2 mm Hg at 21°C (70°F).
Polyethylene glycol and polypropylene
glycol are nonlimiting examples of such plasticizers.
Other nonlimiting examples of plasticizers include anhydrides of sugar
alcohols such as
sorbitan; animal proteins such as gelatin; vegetable proteins such as soybean,
cottonseed, and
sunflower protein; alkyl glycols and alkoxylated glycol compounds including
polyethylene
glycol, polypropylene glycol and copolymers such as
polyoxyethylene/polyoxypropylene having
the following structure:
HO-(CHZ-CHZ-O)X(CHCH3-CH20)Y (CHZCHZ-O)Z OH
wherein x has a value ranging from about 2 to about 40, y has a value ranging
from about 10 to
about 50, and z has a value ranging from about 2 to about 40, and more
specifically x and z have
the same value. These copolymers are available as Pluronic~ from BASF Corp.,
Parsippany, NJ.
In one embodiment, at least 0.1% and/or at least 2% and/or at least 5% and/or
at least 10% and/or
at least 15% to about 60% and/or to about 50% and/or to about 30% and/or to
about 20% by
weight of the fibrous structure of fiber flexibilizing agent is applied to the
fibrous structure more
specifically greater than about 5% and even more specifically greater than
about 10%. The
amount of fiber flexibilizing agent system should be less than about 60%, more
specifically less
than about 30% and even more specifically less than about 20%.
Opacity Increasing Agent
The fibrous structure may comprise an opacity increasing agent.
An opacity increasing agent ("opacifier") as used herein refers to any non-
fibrous
material added to the substrate to effect an increase in the opacity of the
subject fibrous structure.
The neat fibrous structures have a certain opacity as a result of its fibrous
constituents'
ability to scatter and/or absorb light coming into contact with the neat
fibrous structure.
Opacity increasing agents, when added to fibrous structures, increase the
opacity of the
fibrous structure by limiting light transmittance by either or both of two
mechanisms: 1) light is
reflected by scattering or 2) light is absorbed. Opacity increasing agents
include those materials
that increase the opacity of neat fibrous structures above the opacity of the
neat fibrous structure
as well as those materials that increase the opacity of an already reduced
opacity fibrous structure
even if the increased opacity resulting from the opacity increasing agent is
not greater than the
opacity of the neat fibrous structure.
1) Reflecting or scattering of light is accomplished when the light passes
from a medium
of one refractive index to another. A beam of light striking such an interface
obliquely will
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experience a combination of bending (refraction) and reflection. The extent of
reflection depends
on the striking angle and the difference in refractive index of the two
materials.
Scattering effect will be maximized when the number of interfaces between
refractive indicies is
maximized and when the level of the difference in refractive index is
maximized.
Opacity increasing agents which function by reflecting or scattering light are
small
particles and/or are particles having a high refractive index. While
generally, smaller is
preferred for increasing opacity, it is clear that excessively small particles
lose their ability to
opacify because they are smaller than the wavelength of the light that they
are intended to scatter.
Therefore, there is a practical optimum in particle size, which maximizes the
reflection or
scattering effect of a particulate. An ideal opacifier is finely divided
titanium dioxide, having an
average equivalent spherical diameter of about 0.2 micrometers. Since titanium
dioxide is costly
and has other negative side effects, other opacifiers are recommended. These
include, but are
not limited to, hydrated aluminum silicate (clay), calcium carbonate and
starch powder. Most
preferred for the present invention is starch powder. It is has a moderate
density, is not abrasive,
and is compatible with the most preferred fiber flexibilizing agent systems of
the present
invention. An acceptable grade of starch powder can be purchased from ACH Food
Companies
of Memphis, Tennessee under the trade name, Argo° Corn Starch.
2) Absorption of light is also effective in increasing opacity and chemicals
which absorb
light are included within the definition of opacifers as used herein.
Preferably, a light absorbing
opacifier will be used in combination with a reflective/scattering opacifier
in order to prevent the
substrate from appearing to have excessive color (selective absorption of the
visible spectrum) or
to appear excessively gray or black (broad absorption of the visible
spectrum). It is also possible
to counteract the absorption effect to some degree by including an optical
brightener, because it is
capable of increasing brightness without decreasing opacity.
Light absorbing properties are obtained by including a pigment having
significant
coloration. Suitable colored pigments can be purchased from Bayer AG
headquartered in
Leverkusen, Germany under the names HALOPONTTM, LEVANYL° and
PONOLITHTM. Light
absorbing properties can also be obtained by adding a dye. Suitable dyes can
be obtained from
Bayer AG under the tradenames LEVACELL°, LEVACELL° KS and
PONTAMINE°. Level of
inclusion of such pigments or dyes is goverened by the opacity level needed as
well as acceptable
levels of coloration imparted to the product. Inclusion rates as low as 0.001
% can impart a visible
color for example. If coloration is acceptable, rates in the range of 0.1% to
1% or higher can be
used. Often it is desirable to use a combination of colors in order to
generate a broad spectrum of
absorption so that the result appears gray rather than a pure color. Many
authorities believe that,
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at equivalent brightness, a blue tint is generally believed to appear more
"white" than an
equivalent brightness of yellow tint, so blue dyes or pigments might be
preferred depending on
the application. The depression in brightness which invariably accompanies the
use of light
absorbing molecules or particles can be partially or entirely counteracted by
the use of fluorescent
whitening agents (FWAs). Suitable FWAs can be purchased from Bayer under the
tradename
BLANKOPHOR~. Any of the before mentioned pigments, dyes, or FWAs can be added
to the
fibrous structure of the present invention by adding prior to forming the
structure, i.e. so-called
wet end addition in papermaking. They can also be added, for example, by
spraying, printing,
extrusion on the web during or after its formation. They also can be added to
the fiber
flexbilizing agent and applied concurrently. Wet end precipitation might
require fixatives and/or
retention aids as are well known to those skilled in the art.
Opacity is defined as the property of a paper to resist the transmission of
both diffuse and
nondiffuse light through it. It prevents show through of a user's fingers in
contact with the
backside of a fibrous structure. As used herein "opacified fibrous structure"
refers to a fibrous
structure made more opaque by addition of an opacifying agent, such as a
particulate.
Opacifying agents are used in the present invention for the optical
improvements they
afford. In general, optical properties affected by the inclusion of opacifying
agents are opacity,
brightness, and color. The degree to which each of these properties is altered
is very much
dependent upon the type of opacifying agent, the nature of the fiber furnish,
and the basis weight
of the final sheet. Almost all particulates will, upon inclusion into a
fibrous structure, result in
increased opacity. As basis weight is increased, maintenance of a constant
level of a particulate
will result in a smaller increase in measured opacity, relative to an
unmodified fibrous structure.
At very low basis weight, a particulate's opacifying performance is maximized;
at higher basis
weight, it's minimized.
The opacifying efficiency an opacity increasing agent possesses is related to
its ability to
scatter or absorb light at a wavelength of 572 nm. The scattering power of a
particulate is affected
by several fundamental factors, namely, its refractive index relative to the
surrounding medium,
and the particle size (and/or shape) and the number of light scattering
surfaces it makes available
upon inclusion in the dried web. The higher the refractive index the
particulate possesses, the
greater the light scattering at the air/opacity increasing agent or
fiber/opacity increasing agent
interface. In a fibrous structure according to the present invention, it is
one of these two interfaces
which offer the highest potential source for light scattering resulting in
increased opacity.
Opacity as used herein is defined by the following equation:
O = 100 - 100 X ( 1 - MO/100)~'~BW~
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wherein,
O = opacity in %,
MO = measured opacity in
BW = basis weight in gramslmeter2
Opacity, so defined, is normalized to the equivalent opacity of 1 g/m2 of
basis weight of
the fibrous structure. This makes comparisons of the opacifying power among
different fibrous
structures easier to accomplish by removing basis weight as a factor
contributing to opacity.
Measured opacity is calculated as the ratio of the apparent reflectance of one
sheet of
paper with a black backing to the apparent reflectance of the sheet with a
white backing. A sample
whose reflectance is not changed by changing its backing from white to black
will have an
opacity of 100 and a sample whose reflectance changes from a high value to
zero by changing the
backing from white to black will have an opacity of zero.
Measured opacity is determined using a modified Hunter Color Meter. The
modified
Hunter Color Meter consists of a Hunter LabScan XE Sensor with DP9000
processor, model #
LSXE/DP9000 with universal software, model # LSXE/LTNI having the following
options: sensor
port-down stand with sample clamp assembly, part number HL#D02-1009-350,
automated
variable sample illumination (to obtain 25 mm (1 inch) viewing area), and
automated UV control,
with a ColorQUEST DP-9000 Spectrocolorimeter, Labscan Spectro Color Meter, or
Hunter Color
Difference Meter D25D2M or D25D2A all available from Hunter Associates
Laboratories, Inc. of
Reston, VA.
A Hunter Color Associates spring-loaded sample (HL#D02-1009-350) raising
stage,
rather than the lab jack supplied with the instrument, is used. In addition,
standard plates of
colors white and black are required. The plates will need to be cleaned
between readings using a
clean, soft, absorbent laboratory wipe.
Because the effects of humidity and temperature are negligible on opacity, the
samples do
not need to be conditioned. However, they should be kept free from corrosive
vapors, dirt and
excess lint. Also, creasing, wrinkling and tearing of the samples should be
avoided. Before
testing, set the instrument color scale to "XYZ", the Observer setting to
"10°", and the Illuminant
setting to D65. For pre-test instrument standardization, follow the procedures
in the
manufacturer's instrument manual. Place the selected opacity sample on the
white uncalibrated
plate. Raise the sample and plate into place under the sample port and
determine the "Y" value.
Lower the sample and plate. Without rotating the sample itself, remove the
white plate and
replace with the black tile. Again, raise the sample and tile and determine
the "Y" value. For
opacity, some colorimeter models have the capability to perform this operation
automatically,
check the manufacturer's operator's manual.
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Measured Opacity = Y reading of black plate x 100
Y reading of white tile
Report Measured Opacity to three significant figures and use the before-
mentioned
mathematical relationship using basis weight to determine the % Opacity.
Nonlimiting examples of opacity increasing agents may include pigments,
particulates,
fillers, dyes and fluorescent whitening agents (FWAs).
Nonlimiting examples of particulate and/or pigment-based opacity increasing
agents
suitable for use in the present invention include clay, calcium carbonate,
titanium dioxide, talc,
aluminum silicate, calcium silicate, alumina trihydrate, activated carbon,
pearl starch, calcium
sulfate, glass microspheres, diatomaceous earth, and mixtures thereof.
The fiber flexibilizing agent system can beneficially be applied to a hot
tissue web. As
used herein, the term "hot tissue web" refers to a tissue web that has an
elevated temperature
relative to room temperature. Specifically, the elevated temperature of the
web is at least about
43°C., more specifically at least about 54°C, and even more
specifically at least about 65°C. The
hot web has a low equilibrium moisture content that facilitates adding the
composition at the
highest levels requiring minimal re-drying of the web and in some instances no
re-drying at all.
Applicants have found that the levels of up to about 30% of some fiber
flexibilizing agent systems
can be added to the hot tissue web at the dry end of the papernlaking machine
without the
necessity for re-drying of the web.
The moisture content of a tissue web is related to the temperature of the web
and the
relative humidity of the surrounding environment. As used herein, the term
"overdried tissue web"
refers to a tissue web that is dried to a moisture content less than its
equilibrium moisture content
at standard test conditions of 23°C and 50% relative humidity. The
equilibrium moisture content
of a tissue web placed in the standard testing conditions is approximately 7%.
A tissue web of the
present invention can be overdried by raising the drying temperature of drying
means known in
the art, such as, for example, a Yankee dryer or through-air drying. An
overdried tissue web can
have a moisture content of less than about 7%, more specifically less than
about 6%, and even
more specifically less than about 3%.
Other, optional, materials can be added to the aqueous papermaking furnish,
the .
embryonic web, or to the finished web to impart other desirable
characteristics to the product or
improve the papermaking process so long as they are compatible with the
chemistry of the fiber
flexibilizing agent system and do not significantly and adversely affect the
softness or strength
character of the present invention. The following materials are expressly
included, but their
inclusion is not offered to be all-inclusive.
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Retention aids can be useful for retaining fine particulate materials which
are applied via
the wet end of papermaking. A number of materials are marketed as so-called
"retention aids", a
term as used herein, referring to additives used to increase the retention of
the fine furnish solids
in the web during the papermaking process. Without adequate retention of the
fine solids, they are
either lost to the process effluent or accumulate to excessively high
concentrations in the
recirculating white water loop and cause production difficulties including
deposit build-up and
impaired drainage. Chapter 17 entitled "Retention Chemistry" of "Pulp and
Paper, Chemistry and
Chemical Technology", 3rd ed. Vol. 3, by J. E. Unbehend and K. W. Britt, A
Wiley Interscience
Publication, incorporated herein by reference, provides the essential
understanding of the types
and mechanisms by which polymeric retention aids function. A flocculant
agglomerates
suspended particles generally by a bridging mechanism. While certain
multivalent cations are
considered common flocculants, they are generally being replaced in practice
by superior acting
polymers which carry many charge sites along the polymer chain.
It is common to add a cationic charge biasing species to the papermaking
process to
control the zeta potential of the aqueous papermaking furnish as it is
delivered to the papermaking
process. These materials are used because most of the solids in nature have
negative surface
charges, including the surfaces of cellulosic fibers and fines and most
inorganic fillers. Charge
biasing can be done by the use of relatively low molecular weight cationic
synthetic polymers,
specifically those having a molecular weight of no higher than about 500,000
and more
specifically no higher than about 200,000, or even no higher than about
100,000. The charge
densities of such low molecular weight cationic synthetic polymers are
relatively high. These
charge densities range from about 4 to about 8 equivalents of cationic
nitrogen per kilogram of
polymer. An exemplary material is Alcofix 159~, a product of Ciba Geigy, Inc.
headquarted in
Basel, Switzerland. The use of such materials is expressly included in the
scope of the present
invention.
The use of high surface area, high anionic charge micro-particles for the
purposes of
improving fornlation, drainage, strength, and retention is taught in the art.
The disclosure of U.S.
Patent 5,221,435 is incorporated herein by reference. Common materials for
this purpose include,
without limitation, silica colloid, or bentonite clay.
If some measure of permanent wet strength is desired, the group of chemicals:
including
polyamide-epichlorohydrin, polyacrylamides, styrene-butadiene lattices;
insolubilized polyvinyl
alcohol; urea-formaldehyde; polyethyleneimine; chitosan polymers and mixtures
thereof can be
added to the papermaking furnish or to the embryonic web. Such resins include,
without
limitation, cationic wet strength resins, such as polyamide-epichlorohydrin
resins. Suitable types
of such resins are described in U.S. Patents Nos. 3,700,623 and 3,772,076, the
disclosure of both
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13
being hereby incorporated by reference. One commercial source of useful
polyamide-
epichlorohydrin resins is Hercules, Inc. of Wilmington, Delaware, which
markets such resin under
the mark Kymene 557H~.
Some fibrous structures benefit from so-called temporary wet strength. This is
especially
useful if such products are to be disposed in the sewer and septic systems.
One method of
delivering temporary wet strength is to provide for the formation of acid-
catalyzed hemiacetal
formation through the introduction of ketone or, more specifically aldehyde
functional groups on
the papermaking fibers or in a binder additive for the papermaking fibers. One
binder material
that have been found particularly useful for imparting this form of fugitive
wet strength is Parez
750 offered by Cytec of Stamford, CT.
Other additives can also be used to augment this wet strength mechanism. This
technique
for delivering temporary wet strength is well known in the art. Exemplary art,
incorporated
herein by reference for the purpose of showing methods of delivering the
fugitive wet strength to
the web, includes the following US Patent No. 5,690,790; 5,656,746; 5,723,022;
4,981,557;
5,008,344; 5,085,736; 5,760,212; 4,605,702; 6,228,126; 4,079,043; 4,035,229;
4,079,044; and
6,127,593.
While the hemiacetal formation mechanism is one suitable technique for
generating
temporary wet strength, there are other methods, such as providing the sheet
with a binder
mechanism which is more active in the dry or slightly wet condition than in
the condition of high
dilution as would be experienced in the toilet bowl or in the subsequent sewer
and septic system.
Such methods have been primarily directed at web products which are to be
delivered in a slightly
moist or wet condition, then will be disposed under situation of high
dilution. The following
references are incorporated herein by reference for the purpose of showing
exemplary systems to
accomplish this, and those skilled in the art will readily recognize that they
can be applied to the
webs of the present invention which will be supplied generally at lower
moisture content than
those described therewithin: US Patent Nos. 4,537,807; 4,419,403; 4,309,469;
and 4,362,781.
If enhanced absorbency is needed, surfactants may be used to treat the tissue
paper webs
of the present invention. The level of surfactant content, if used, can be
from about 0.01 % to
about 2.0% by weight, based on the dry fiber weight of the tissue web. The
surfactants can
beneficially have alkyl chains with eight or more carbon atoms. Exemplary
anionic surfactants
include linear alkyl sulfonates and alkylbenzene sulfonates. Exemplary
nonionic surfactants
include alkylglycosides including alkylglycoside esters such as Crodesta SL-
40~ which is
available from Croda, Inc. (New York, NY); alkylglycoside ethers as described
in U.S. Patent
4,011,389, issued to Langdon, et al. on March 8, 1977; and
alkylpolyethoxylated esters such as
Pegosperse 200 ML available from Glyco Chemicals, Inc. (Greenwich, CT) and
IGEPAL RC-
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14
520~ available from Rhone Poulenc Corporation (Cranbury, NJ). Alternatively,
cationic softener
active ingredients with a high degree of unsaturated (mono and/or poly) and/or
branched chain
alkyl groups can greatly enhance absorbency.
The present invention also expressly includes variations in which chemical
softening
compositions and/or agents can be added as a part of the papermaking process
as part of the
furnish preparation or subsequent to web formation. Such chemical softening
compositions may
also comprise a fiber flexibilizing agent. Chemical softening compositions
and/or agents may be
included by wet end addition. Suitable chemical softening compositions and/or
agents comprise
quaternary ammonium compounds including, but not limited to, the well-known
dialkyldimethylammonium salts (e.g., ditallowdimethylammonium chloride,
ditallowdimethylammonium methyl sulfate, di(hydrogenated tallow)dimethyl
ammonium
chloride, etc.). Particularly suitable variants of these softening
compositions include mono or
diester variations of the before mentioned dialkyldimethylammonium salts and
ester quaternaries
made from the reaction of fatty acid and either methyl diethanol amine and/or
triethanol amine,
followed by quaternization with methyl chloride or dimethyl sulfate. Another
class of
papermaking-added chemical softening compositions comprises the well-known
organo-reactive
polydimethyl siloxane ingredients, including amino functional polydimethyl
siloxane. These may
be wet end-added or surface-applied. Other applicable art in the field of
surface-applied chemical
softeners incorporated herein by reference includes US Patent Nos. 6,179,961;
5,814,188;
6,162,329, and the application W00022231A1 in the names of Vinson et. al.
Filler materials may
also be incorporated into the tissue of the present invention. U.S. Patent
5,611,890, incorporated
herein by reference, discloses filled tissue paper products that are
acceptable as substrates for the
presentinvention.
The above description of optional fiber flexibilizing agents is intended to be
merely
exemplary in nature, and is not meant to limit the scope of the invention.
According to the present invention, the fiber flexibilizing agent system can
be applied to a
paper web while it is in a dry condition. The term "dry condition" refers to
the state, and "dry
paper web" refers to the web itself; both defined herein as having a low
moisture content of less
than about 20%, and more specifically less than about 10%, and even more
specifically less than
about 3%. Therefore "dry tissue web" as used herein includes both webs which
are dried to a
moisture content less than the equilibrium moisture content thereof (so-called
"overdried webs")
and webs which have a low level of moisture remaining, specifically up as much
as about 20%
moisture.
In one embodiment, the fiber flexibilizing agent system of the current
invention may be
applied after the tissue web has been dried and creped, and, more
specifically, while the web is
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still at an elevated temperature, Fig 4, reference numeral 50. The softening
composition can be
applied to the dried and creped web before the web is wound onto the parent
roll. Thus, the
softening composition can be applied to a hot, overdried web after the web has
been creped and
after the web has passed through the calender rolls (not shown) which control
the caliper. The
composition can be applied to either side or both sides of the tissue.
The fiber flexibilizing agent system can be beneficially applied to the web in
a uniform
fashion so that substantially the entire web surface benefits from the effect
of the composition.
Following application to the hot web, a minimal portion of the volatile
components of the
composition evaporates. Since the composition comprises maximum content of non-
volatile
agents, any water present in the composition becomes part of the new
equilibrium moisture
content of the tissue treated with the composition.
One method of macroscopically uniformly applying the softening composition to
the web
is spraying. Spraying has been found to be economical, and can be accurately
controlled with
respect to quantity and distribution of the composition. The dispersed
composition can be applied
onto the dried, creped tissue web before the web is wound into the parent
roll. Those skilled in
the art will recognize that spraying should be controlled to achieve a maximum
possible
distribution, i.e. small droplet size, limited by transfer efficiency. One
acceptable spraying system
uses ITW Dynatec UFD nozzles, offered by Illinois Tool Works of Glenview, IL.
One suitable
nozzle model has five fluid orifices, each 0.46mm X 0.51mm in size. The center
of the 5 fluid
orifices is oriented directly vertical to the path of the tissue paper web,
while the outer orifices are
angled at 15 degrees relative to vertical, and the two intermediate nozzles
are angled at 7.5
degrees relative to vertical. Each fluid orifice has an associated air orifice
situated on either side
of it, for a total of 10 air orifices, each of O.Slmm X O.Slmm size. The fluid
orifice extends 0.5
cm beyond the lower surface of the nozzle. Nozzles are spaced about 5 cm apart
and about 5 cm
above the tissue paper web while it is being treated. Air pressure sufficient
to create a uniformly
atomized spray is used.
The following Example illustrates preparation of tissue paper according to the
present
invention. This example demonstrates the production of layered tissue paper
webs comprising the
fiber flexibilizing agent system according to the present invention. The
composition is applied to
one side of the web and the webs are combined into a two-ply bath tissue
product. A pilot-scale
Fourdrinier papermaking machine is used for the production of the tissue.
An aqueous slurry of NSK of about 3% consistency is made up using a
conventional
repulper and is passed through a stock pipe toward the headbox of the
Fourdrinier.
In order to impart temporary wet strength to the finished product, a 1 %
dispersion of
Parez 750~ is prepared and is added to the NSK stock pipe at a rate sufficient
to deliver 0.3%
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16
Parez 750~ based on the dry weight of the NSK fibers. The absorption of the
temporary wet
strength resin is enhanced by passing the treated slurry through an in-line
mixer.
An aqueous slurry of eucalyptus fibers of about 3% by weight is made up using
a
conventional repulper. In order to impart a temporary wet strength to the
finished product and to
reduce the dustiness or tinting of the surface of the tissue paper, a 1%
dispersion of Parez 750~ is
prepared and is added to the eucalyptus stock pipe at a rate sufficient to
deliver 0.375%.Parez
750~ based on the dry weight of the eucalyptus fibers. The absorption of the
temporary wet
strength resin is enhanced by passing the treated slurry through an in-line
mixer.
The NSK fibers are diluted with white water at the inlet of a fan pump to a
consistency of
about 0.15% based on the total weight of the NSK fiber slurry. The eucalyptus
fibers, likewise,
are diluted with white water at the inlet of a fan pump to a consistency of
about 0.15% based on
the total weight of the eucalyptus fiber slurry. The eucalyptus slurry and the
NSK slurry are both
directed to a layered headbox capable of maintaining the slurries as separate
streams until they are
deposited onto a forming fabric on the Fourdrinier.
The paper machine has a layered headbox having a top chamber, a center
chamber, and a
bottom chamber. The eucalyptus fiber slurry is pumped through the top and
bottom headbox
chambers and, simultaneously, the NSK fiber slurry is pumped through the
center headbox
chamber and delivered in superposed relation onto the Fourdrinier wire to form
thereon a three-
layer embryonic web, of which about 70% is made up of the eucalyptus fibers
and 30% is made
up of the NSK fibers. 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 87 machine-direction and 76 cross-machine-direction monofilaments per
inch,
respectively.
The embryonic wet web is transferred from the Fourdrinier wire, at a fiber
consistency of
about 15% at the point of transfer, to a patterned drying fabric. The drying
fabric is designed to
yield a pattern densified tissue with discontinuous low-density deflected
areas arranged within a
continuous network of high density (knuckle) areas. This drying fabric is
formed by casting an
impervious resin surface onto a fiber mesh supporting fabric. The supporting
fabric is a 45 x 52
filaments per inch, dual layer mesh. The thickness of the resin cast is about
10 mil above the
supporting fabric. The knuckle area is about 40% and the open cells remain at
a frequency of
about 90 per square inch.
Further de-watering is accomplished by vacuum assisted drainage until the web
has a fiber
consistency of about 30%.
While remaining in contact with the patterned forming fabric, the patterned
web is pre-
dried by air blow-through pre-dryers to a fiber consistency of about 65% by
weight. The semi-dry
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17
web is then transferred to the Yankee dryer and adhered to the surface of the
Yankee dryer with a
sprayed creping adhesive comprising a 0.125% aqueous solution of polyvinyl
alcohol. The
creping adhesive is delivered to the Yankee surface at a rate of 0.1% adhesive
solids based on the
dry weight of the web. The fiber consistency is increased to about 98% before
the web is dry
creped from the Yankee 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
a temperature of about 350°F (177°C) and a speed of about 800
fpm (feet per minute) (about 244
meters per minute). The paper is wound in a roll using a surface driven reel
drum having a
surface speed of about 656 feet per minute.
In a free span between the doctor blade and the reel in a position at which
the web is
essentially horizontal, an applicator comprising spaced apart ITW Dynatec UFD
nozzles, made by
Illinois Tool Works of Glenview, IL, are positioned at a point terminating
about S cm above the
web. Each of the nozzles has five fluid orifices, 0.46mm X O.Slmm in size. The
center of the
five fluid orifices is oriented directly vertical to the path of the tissue
paper web, while the outer
orifices are angled at 15 degrees relative to vertical, and the two
intermediate nozzles are angled
at 7.5 degrees relative to vertical. Each fluid orifice has an associated air
orifice situated on either
side of it, for a total of ten air orifices, each 0.51mm X 0.5lmrn in size.
The fluid orifice extends
0.5 cm beyond the lower surface of the nozzle. Nozzles are spaced about 5 cm
apart and about 5
cm above the tissue web while it is being treated. Fluid is directed at the
web in order to deliver
about 15% by weight of the fiber flexibilizing agent system. About 15 psi of
air pressure is
sufficient to create a uniformly atomized spray.
The fiber flexibilizing agent system comprises material listed in the
following TABLE:
Trade Name Chemical % By WT Supplier
Name
Water Water 24.5%
Carbowax Polyethylene52.7% Dow Chemical
200
Glycol 200 Midland, MI
Argo~ Corn Starch,22.8% ACH Food Companies,
Unmodified Memphis, TN
The paper is subsequently converted into a single-ply toilet tissue having a
basis weight of
about 34 g/m2. It has about 15.8 g/cm of wet tensile strength. It has about
15% of the fiber
flexibilizing agent system and is a soft, low liming toilet tissue product.
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1~
Aunlication Methods
The present invention provides methods for treating a fibrous structure in
need of
treatment. The method comprises contacting the fibrous structure with a fiber
flexibilizing agent
system comprising a fiber flexibilizing agent.
Fig. 1 schematically represents a fibrous structure making method. 10 that is
suitable for
applying a fiber flexibilizing agent system comprising a fiber flexibilizing
agent (not shown) by
an application method in accordance with the present invention 12 to a fibrous
structure 14. The
fibrous structure 14 can be formed by any suitable fibrous structure forming
process known in the
art, including but not limited to conventional papermaking processes and/or
through-air dried
papermaking processes. The fibrous structure 14 is carried via a carrier
fabric 16 to a cylindrical
dryer 18, such as a Yankee dryer, at which point the fibrous structure 14 can
be transferred to the
cylindrical dryer 18. A pressure roll 20 may be used to aid the transfer to
the cylindrical dryer 18
while the transfer fabric 16 travels past a turning roll 22. In one
embodiment, the surface 24 of
the cylindrical dryer 18 may have an adhesive 26 applied to it via an adhesive
source, such as a
spray applicator 28. The cylindrical dryer 18 may be heated, such as steam-
heated, to facilitate
drying of the fibrous structure 14 as the fibrous structure 14 is in direct
andlor indirect contact
with the surface 24 of the cylindrical dryer 18. Heated air may also be
applied to the fibrous
structure 14 via a heated air source, such as a drying hood 30. The fibrous
structure 14 may then
be transferred from the cylindrical dryer 18. A creping operation utilizing a
creping blade 32 may
be used to remove the fibrous structure 14 from the cylindrical dryer 18. Once
the fibrous
structure 14 has been removed from the cylindrical dryer 18, the fibrous
structure 14 is then
treated with a fiber flexibilizing agent (not shown) via the application
method 12. One or both
sides of the fibrous structure 14 may be treated with the fiber flexibilizing
agent. Once the fibrous
structure 14 has been treated with the fiber flexibilizing agent via the
application method 12, the
treated fibrous structure 14' can then be wound onto a parent roll 34 by any
suitable method
known to those of ordinary skill in the art, such as via a reel 36.
Preferably, the fiber flexibilizing agent system is applied to a dry fibrous
structure. The
term "dry fibrous structure" as used herein includes both fibrous structures
which are dried to a
moisture content of less than the equilibrium moisture content thereof
(overdried-see below) and
fibrous structures which are at a moisture content in equilibrium with
atmospheric moisture. A
semi-dry fibrous structure includes a fibrous structure with a moisture
content exceeding its
equilibrium moisture content.
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19
As used herein, the term "hot fibrous structure" refers to a fibrous
structure, which is at an
elevated temperature relative to room temperature. Preferably the elevated
temperature of the
fibrous structure is at least about 43°C, and more preferably at least
about 65°C.
The moisture content of a fibrous structure is related to the temperature of
the fibrous
structure and the relative humidity of the environment in which the fibrous
structure is placed. As
used herein, the term "overdried fibrous structure" refers to a fibrous
structure that is dried to a
moisture content less than its equilibrium moisture content at standard test
conditions of 23°C and
50% relative humidity. The equilibrium moisture content of a fibrous structure
placed in standard
testing conditions of 23°C and 50% relative humidity is approximately
7%. A fibrous structure of
the present invention can be overdried by raising it to an elevated
temperature through use of
drying means known to the art such as a Yankee dryer or through air drying.
Preferably, an
overdried fibrous structure will have a moisture content of less than 7%, more
preferably from
about 0 to about 6%, and most preferably, a moisture content of from about 0
to about 3%, by
weight.
Fibrous structure exposed to the normal environment typically has an
equilibrium
moisture content in the range of 5 to 8%. When a fibrous structure is dried
and creped the
moisture content in the fibrous structure is generally less than 3%. After
manufacturing, the
fibrous structure absorbs water from the atmosphere. In a preferred process of
the present
invention, advantage is taken of the low moisture content in the fibrous
structure as it leaves the
doctor blade as it is removed from the Yankee dryer (or the low moisture
content of similar
fibrous structures as such fibrous structures are removed from alternate
drying means if the
process does not involve a Yankee dryer).
In one embodiment, the fiber flexibilizing agent system of the present
invention is applied
to an overdried fibrous structure shortly after it is separated from a drying
means and before it is
wound onto a parent roll.
Alternatively, the fiber flexibilizing agent system of the present invention
may be applied
to a semi-dry fibrous structure, for example while the fibrous structure is on
the Fourdrinier cloth,
on a drying felt or fabric, or while the fibrous structure is in contact with
the Yankee dryer or
other alternative drying, means.
Finally, the fiber flexibilizing agent system can also be applied to a dry
fibrous structure
in moisture equilibrium with its environment as the fibrous structure is
unwound from a parent
roll as for example during an off line converting operation.
In another embodiment, the fiber flexibilizing agent system of the present
invention may
be applied after the fibrous structure has been dried and creped, and, more
preferably, while the
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fibrous structure is still at an elevated temperature. Preferably, the fiber
flexibilizing agent system
is applied to the dried and creped fibrous structure before the fibrous
structure is wound onto the
parent roll.
The fiber flexibilizing agent via the fiber flexibilizing agent system can be
added to either
side of the fibrous structure singularly, or to both sides; preferably, the
fiber flexibilizing agent is
applied to only one side of the fibrous structure; the side of the fibrous
structure with raised
regions, which will later be orientated toward the exterior surface of the
sanitary tissue paper
product.
The fibrous structure of the present invention may be moving at a speed of
greater than
about 100 m/min and/or greater than about 300 m/min and/or greater than about
500 m/min when
the fiber flexibilizing agent system is applied thereto.
Alternatively, effective amounts of fiber flexibilizing agent via the fiber
flexibilizing
agent systems of the present invention may also be applied to a fibrous
structure that has cooled
after initial drying and has come into moisture equilibrium with its
environment. The method of
applying the fiber flexibilizing agent systems of the present invention is
substantially the same as
that described above for application of such compositions to a hot and/or
overdried fibrous
structure.
1) Transfer Surface Application (i.e., by means of Calender Rolls and/or
turning rolls and/or
~readin~ rolls and/or Yankee dryers)
As represented in Fig. 2, the application method 12 of Fig. 1 may comprise
applying the
fiber flexibilizing agent system comprising a fiber flexibilizing agent to a
surface of a fibrous
structure 14 using a transfer surface 38, such as a calender roll and/or a
cylindrical dryer, turning
rolls, or spreading rolls (not shown). "Spreader roll(s)" as used herein
include rollers designed to
apply cross direction stresses in order to smooth moving/traveling fibrous
structures for example
to remove wrinkles. Nonlimiting examples include bowed rollers commercially
available from
Stowe Woodward - Mount Hope Company of Westborough, MA. "Turning roll(s)" as
used
herein refers to any predominantly straight roller engaging the
moving/traveling fibrous structure.
Turning rolls include idlers which may be externally driven or they may be
driven by the
moving/traveling fibrous structure. Externally driven turning rolls are
preferred since it is easier
to maintain the relative speed difference of the roller surface compared to
the fibrous structure as
prescribed herein.
A fiber flexibilizing agent system comprising a fiber flexibilizing agent 40
is applied to
the transfer surface 38 by any suitable means known in the art. When the a
surface of a fibrous
structure 14 contacts the transfer surface 38, the fiber flexibilizing agent
system 40, especially the
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21
fiber flexibilizing agent, is transferred from the transfer surface 38 to the
surface of the fibrous
structure 14 thus producing a treated fibrous structure 14'. Another potential
transfer surface,
such as another calender roll, such as 38' may be needed depending upon the
manner the fibrous
structure 14 contacts the transfer roll 38. The additional transfer surface
38' may, but does not
have contain the fiber flexibilizing agent system 40. The transfer surface 38
may comprise a
doctor blade 42 such that excess fiber flexibilizing agent system 40 is
removed from the transfer
surface 38. Calender roll transfer surface 38 is moving at a different speed
than the fibrous
structure 14. For example, the calender roll may be moving, such as rotating,
at a speed
differential compared to the speed of the fibrous structure of at least about
0.3% and/or at least
about 0.5% and/or at least about 0.7% and/or at least about 1%.
The transfer surface is normally maintained at a temperature near that of the
fibrous
structure which is contacting it. Therefore, it is typically at temperature of
from about 15°C
(60°F) to about 82°C (1~0°F).
Preferably, the fiber flexibilizing agent system is applied to the transfer
surface in a
macroscopically uniform fashion for subsequent transfer to the fibrous
structure so that
substantially the entire surface of the fibrous structure benefits from the
effect of the fiber
flexibilizing agent system. Following application to the transfer surface, at
least a portion of the
volatile components of any vehicle preferably evaporates leaving preferably a
thin film containing
any remaining unevaporated portion of the volatile components of the vehicle,
the fiber
flexibilizing agent, and other nonvolatile components of the fiber
flexibilizing agent system. By
"thin film" it is meant any thin coating, haze or mist on the transfer
surface. This thin film can be
microscopically continuous or be comprised of discrete elements. If the thin
film is comprised of
discrete elements, the elements can be of uniform size or varying in size;
further they may be
arranged in a regular pattern or in an irregular pattern, but macroscopically
the thin film is
uniform. Preferably the thin film is composed of discrete elements.
Methods of macroscopically uniformly applying the fiber flexibilizing agent
system to the
transfer surface include spraying and printing. Spraying has been found to be
economical, and
can be accurately controlled with respect to quantity and distribution of the
fiber flexibilizing
agent system, so it is more preferred. Preferably, the dispersed fiber
flexibilizing agent system is
applied from the transfer surface onto the dried, creped fibrous structure
after the Yankee dryer
and before the parent roll. A particularly convenient means of accomplishing
this application is to
apply the fiber flexibilizing agent system to one or both of a pair of heated
calender rolls which,
in addition to serving as hot transfer surfaces for the present fiber
flexibilizing agent system, also
serve to reduce and control the thickness of the dried fibrous structure to
the desired caliper of the
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22
finished product. Such convenient means are described in greater detail in
U.S. Pat. No.
6,162,329.
In one embodiment, the transfer surface may be cleaned by any suitable
cleaning method
known in the art.
2) Non-Contact (i.e., SprayLpplication
As represented in Fig. 3, the application method 12 of Fig. 1 may comprise
applying a
fiber flexibilizing agent system comprising a fiber flexibilizing agent using
a non-contact
applicator, such as nozzles 44, to apply the fiber flexibilizing agent system
onto the surface of the
fibrous structure 14 to produce a treated fibrous structure 14'. In addition
to a spray application,
as illustrated in Fig. 3, the fiber flexibilizing agent system comprising a
fiber flexibilizing agent
may also be non-contact applied via a drip and/or curtain (not shown). In Fig.
3, an array of
nozzles 44, preferably oscillatory nozzles, are mounted to a fiber
flexibilizing agent distribution
manifold 46. The fiber flexibilizing agent 48 is applied via at least one
nozzle 44 to the surface of
the fibrous structure 14 in the form of a spray, preferably an oscillatory
spray.
A nozzle cleaning system 50 can be employed to keep the nozzles 44 free from
debris,
dust and/or residual fiber flexibilizing agent. Further, a post turning roll
52 may optionally be
employed on the treated surface of fibrous structure 14' to direct particles,
preferably fiber
flexibilizing agent particles, that may not be in contact with the surface of
the fibrous structure
14', into contact with the surface of the fibrous structure 14'. If optional
post turning roll 52 is
employed, it is preferably driven at a surface speed differential compared to
fibrous structure 14'.
Preferably, this surface speed differential greater than 0.1%, more preferably
greater than 0.3, and
most preferably greater than 0.5%.
Fig. 4 schematically represents one embodiment of an oscillatory nozzle 44'
having a
liquid exit orifice 54 and an air exit orifice 56. Oscillatory nozzle is a
termed used herein to refer
to a nozzle which promotes an oscillatory motion in the extrudate upon exit
from the nozzle.
Without being bound by theory, oscillatory flow motion is believed to be the
result of alternating
forces induced when the fluid flow is flanked on each side by atomizing air
jets which are
directed generally parallel to the fluid stream. Angle of air stream directed
from each of the
flanleing air exit orifices 56 relative to liquid exit orifice 54 should
therefore be limited to no more
than about 20°, preferably less than about 10°. Deeper angles
tend to prematurely obliterate the
fluid jet resulting in creation of an aerosol fraction, which tends to migrate
away from the
application zone and promote the creation of kgnarr. A nonlimiting example of
a suitable nozzle
comprising a non-contact applicator is commercially available from Illinois
Tool Works Dynatec
as part no. 107921.
CA 02506801 2005-05-19
WO 2004/048693 PCT/US2003/037096
23
Fig. 5 schematically illustrates one embodiment of a spray produced by an
oscillatory
nozzle 44'. The fiber flexibilizing agent 48 exits the liquid exit orifice 54
where it is stressed by
an air stream that is exiting from the air exit orifice 56. As the fiber
flexibilizing agent 48 moves
away from the liquid exit orifice 54 it begins to oscillate, represented ~by
zone A. As the
amplitude of the oscillation increases, the fiber flexibilizing agent 48
elongates, as represented by
zone B. As the fiber flexibilizing agent 48 elongates in zone B, the fiber
flexibilizing agent
breaks into sections of elongated fiber flexibilizing agent 48'. The elongated
fiber flexibilizing
agent 48' then begins to contract back to a droplet 48", preferably a
spherical-shaped droplet.
An embodiment of a nozzle cleaning system 50 for use with nozzles 44 is
represented in
Fig. 6. The nozzle cleaning system 50 comprises a traversing cleaning nozzle
58 that when in
operation, directs air 60 towards the liquid exit orifice 54 and the air exit
orifice 56 of a nozzle 44,
preferably each nozzle 44, thus removing any accumulated debris from the exit
orifices 54 and 56.
In one embodiment, nozzles 44 are positioned adjacent to the fibrous structure
14' at a
separation distance of less than about 10 cm and/or less than about 5 cm
and/or less than about 3
cm and/or less than about 1 cm and/or less than about 0.51 cm.
A nonlimiting example of a suitable non-contact applicator is commercially
available
from Illinois Tool Works.
31 Extrusion Application
As represented in Fig. 7, the application method 12 of Fig. 1 may comprise
applying the
fiber flexibilizing agent 48 using an extrusion system, such as a slot
extrusion die 62. The fiber
flexibilizing agent 48 is extruded out of the slot extrusion die 62 onto the
surface of the fibrous
structure 14 to produce a treated fibrous structure 14'.
Fig. 8 shows, in an exploded view, an embodiment of a slot extrusion die 62
suitable for
use in accordance with the present invention. The fiber flexibilizing agent 48
flows into a fiber
flexibilizing agent distribution chamber 64 of a slot extrusion distribution
section 66 towards a
shim 68. The fiber flexibilizing agent 48 is spread via capillary force at
flared ends 70 (discharge
surface) of a distribution channel 72 of the shim 68 wherein it then exits the
slot extrusion die 62.
Slot extrusion lip 74 ensures that the fiber flexibilizing agent 48 exits the
slot extrusion die 62 via
the flared ends 70 of the distribution channel 72 of the shim 68.
In one embodiment, the discharge surface of the applicator is in contact with
the fibrous
structure for a distance greater than about 10 cm and/or greater than about 15
cm and/or greater
than about 20 cm.
In another embodiment, the discharge surface may be cleaned by any suitable
cleaning
method known in the art.
CA 02506801 2005-05-19
WO 2004/048693 PCT/US2003/037096
24
Total Dry Tensile Strength Method:
"Total Dry Tensile Strength" or "TDT" of a fibrous structure of the present
invention
and/or a paper product comprising such fibrous structure is measured as
follows. One (1) inch by
five (5) inch (2.5 cm X 12.7 cm) strips of fibrous structure and/or paper
product comprising such
fibrous structure are provided. The strip is placed on an electronic tensile
tester Model 1122
commercially available from Instron Corp., Canton, Massachusetts in a
conditioned room at a
temperature of 73°F ~ 4°F (about 28°C ~ 2.2°C) and
a relative humidity of 50% ~ 10%. The
crosshead speed of the tensile tester is 2.0 inches per minute (about 5.1
cm/minute) and the gauge
length is 4.0 inches (about 10.2 cm). The TDT is the arithmetic total of MD
and CD tensile
strengths of the strips.
"Machine Direction" or "MD" as used herein means the direction parallel to the
flow of
the fibrous structure through the papermaking machine and/or product
manufacturing equipment.
"Cross Machine Direction" or "CD" as used herein means the direction
perpendicular to
the machine direction in the same plane of the fibrous structure and/or paper
product comprising
the fibrous structure.
Total Wet Tensile Strength Method:
An electronic tensile tester (Thwing-Albert EJA Materials Tester, Thwing-
Albert
Instrument Co., 10960 Dutton Rd., Philadelphia, Pa., 19154) is used and
operated at a crosshead
speed of 4.0 inch (about 10.16 cm) per minute and a gauge length of 1.0 inch
(about 2.54 cm),
using a strip of a fibrous structure of 1 inch wide and a length greater than
3 inches long. The two
ends of the strip are placed in the upper jaws of the machine, and the center
of the strip is placed
around a stainless steel peg (0.5 cm in diameter). After verifying that the
strip is bent evenly
around the steel peg, the strip is soaked in distilled water at about
20°C for a soak time of 5
seconds before initiating cross-head movement. The initial result of the test
is an array of data in
the form load (grams force) versus crosshead displacement (centimeters from
starting point).
The sample is tested in both MD and CD orientations. The wet tensile strength
of a
fibrous structure is calculated as follows:
Total Wet Tensile Strength = Peak LoadMD (gf) / 2 (inchW;dcn) + Peak Load~D
(gf) / 2 (inchW;ath)
