U.S. patent application number 16/654494 was filed with the patent office on 2020-02-13 for treated fibers and fibrous structures comprising the same.
The applicant listed for this patent is Kimberly-Clark Worldwide, Inc.. Invention is credited to Jian Qin, Liyi Shi, Youquan Su.
Application Number | 20200048838 16/654494 |
Document ID | / |
Family ID | 62979479 |
Filed Date | 2020-02-13 |
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United States Patent
Application |
20200048838 |
Kind Code |
A1 |
Qin; Jian ; et al. |
February 13, 2020 |
TREATED FIBERS AND FIBROUS STRUCTURES COMPRISING THE SAME
Abstract
The present invention provides a treated fiber having reduced
hydrogen bonding capabilities, which may be useful in the
production of tissue products having improved bulk and softness.
The treated fiber comprises a water-insoluble inorganic compound
that is generated in situ by reacting at least one compound
selected from the group consisting of a silicate, a silyl, a
silane, and an alkaline metal and a precipitation agent in the
presence of the fiber at or above the critical fiber
consistency.
Inventors: |
Qin; Jian; (Appleton,
WI) ; Su; Youquan; (Shanghai, CN) ; Shi;
Liyi; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kimberly-Clark Worldwide, Inc. |
Neenah |
WI |
US |
|
|
Family ID: |
62979479 |
Appl. No.: |
16/654494 |
Filed: |
October 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16070640 |
Jul 17, 2018 |
10487452 |
|
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PCT/US18/13780 |
Jan 16, 2018 |
|
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16654494 |
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62450630 |
Jan 26, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21H 17/63 20130101;
D21H 17/68 20130101; D21H 17/67 20130101; D21H 17/59 20130101; D21H
27/40 20130101; D21H 11/20 20130101; D21H 21/22 20130101; D21H
27/002 20130101; D21C 9/005 20130101; D21H 27/34 20130101; D21H
17/70 20130101; D21H 27/005 20130101; D21H 27/30 20130101; D21C
9/18 20130101; D21C 9/004 20130101 |
International
Class: |
D21H 11/20 20060101
D21H011/20; D21C 9/18 20060101 D21C009/18; D21H 17/59 20060101
D21H017/59; D21H 27/00 20060101 D21H027/00; D21H 27/40 20060101
D21H027/40; D21H 17/63 20060101 D21H017/63; D21H 27/34 20060101
D21H027/34; D21C 9/00 20060101 D21C009/00 |
Claims
1. A tissue product comprising at least one multi-layered tissue
web having a first fibrous layer, a second fibrous layer, and a
third fibrous layer, the first and third fibrous layers comprising
untreated cellulosic fibers and the second fibrous layer comprising
treated fiber comprising at least about 5,000 ppm water-insoluble
inorganic selected from silicone, aluminum and zinc, wherein the
treated fiber comprises at least about 5 percent of the total
weight of the multi-layered web.
2. The tissue product of claim 1 wherein the multi-layered tissue
web comprises a creped tissue web and the tissue product has a
basis weight from about 10 to about 50 grams per square meter
(gsm).
3. The tissue product of claim 1 wherein the multi-layered tissue
web has a basis weight from about 10 to about 50 gsm, a sheet bulk
greater than about 10 cc/g and a tensile strength from about 500 to
about 1,500 g/3''.
4. The tissue product of claim 1 wherein the multi-layered tissue
web comprises from about 10 to about 20 weight percent treated
fiber, the tissue product having a basis weight from about 10 to
about 60 gsm, a sheet bulk greater than about 10 cc/g and a
Stiffness Index less than about 15.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional application of, and
claims priority to, U.S. patent application Ser. No. 16/070,640,
filed on Jul. 17, 2018, which is a national-phase entry, under 35
U.S.C. .sctn. 371, of PCT Patent Application No. PCT/US18/13780,
filed on Jan. 16, 2018, which claims benefit of U.S. Provisional
Application No. 62/450,630, filed Jan. 26, 2017, all of which are
incorporated herein by reference.
BACKGROUND
[0002] In the manufacture of paper products, such as facial tissue,
bath tissue, paper towels, dinner napkins, and the like, a wide
variety of product properties are imparted to the final product
through the use of chemical additives applied in the wet end of the
tissue making process. Two of the most important attributes
imparted to tissue through the use of wet end chemical additives
are strength and softness. Specifically for softness, a chemical
debonding agent is normally used. Such debonding agents are
typically quaternary ammonium compounds containing long chain alkyl
groups. The cationic quaternary ammonium entity allows for the
material to be retained on the cellulose via ionic bonding to
anionic groups on the cellulose fibers. The long chain alkyl groups
provide softness to the tissue sheet by disrupting fiber-to-fiber
hydrogen bonds in the sheet. The use of such debonding agents is
broadly taught in the art. Such disruption of fiber-to-fiber bonds
provides a two-fold purpose in increasing the softness of the
tissue. First, the reduction in hydrogen bonding produces a
reduction in tensile strength thereby reducing the stiffness of the
sheet. Secondly, the debonded fibers provide a surface nap to the
tissue web enhancing the "fuzziness" of the tissue sheet. This
sheet fuzziness may also be created through use of creping as well,
where sufficient interfiber bonds are broken at the outer tissue
surface to provide a plethora of free fiber ends on the tissue
surface. Both debonding and creping increase levels of lint and
slough in the product. Indeed, while softness increases, it is at
the expense of an increase in lint and slough in the tissue
relative to an untreated control. It can also be shown that in a
blended (non-layered) sheet the level of lint and slough is
inversely proportional to the tensile strength of the sheet. Lint
and slough can generally be defined as the tendency of the fibers
in the paper web to be rubbed from the web when handled.
[0003] It is also broadly known in the art to concurrently add a
chemical strength agent in the wet-end to counteract the negative
effects of the debonding agents. In a blended sheet, the addition
of such agents reduces lint and slough levels. However, such
reduction is done at the expense of surface feel and overall
softness and becomes primarily a function of sheet tensile
strength. In a layered sheet, strength chemicals are added
preferentially to the center layer. While this perhaps helps to
give a sheet with an improved surface feel at a given tensile
strength, such structures actually exhibit higher slough and lint
at a given tensile strength, with the level of debonder in the
outer layer being directly proportional to the increase in lint and
slough.
[0004] There are additional disadvantages with using separate
strength and softness chemical additives. Particularly relevant to
lint and slough generation is the manner in which the softness
additives distribute themselves upon the fibers. Bleached Kraft
fibers typically contain only about 2-3 milliequivalents of anionic
carboxyl groups per 100 grams of fiber. When the cationic debonder
is added to the fibers, even in a perfectly mixed system where the
debonder will distribute in a true normal distribution, some
portion of the fibers will be completely debonded. These fibers
have very little affinity for other fibers in the web and therefore
are easily lost from the surface when the web is subjected to an
abrading force. Thus, there remains a need in the art for fiber
treatments and treated fibers that positively affect the strength
and softness of the resulting fibrous structure, without the
limitations typically associated with the use of chemical additives
such as deboning agents.
SUMMARY
[0005] It has now been surprisingly discovered that the strength
and softness of a fibrous structure may be altered by at least
partially forming the structure from treated fiber comprising a
water-insoluble inorganic. The modified fibrous structure
properties are the result of the treated fibers decreased ability
to hydrogen bond with other fibers. The ability of a fiber to
hydrogen bond with other fibers is altered by treating the fiber
with a water-insoluble inorganic compound, where the
water-insoluble inorganic compound is formed in situ by reacting
silicate, a silyl, a silane, or an alkaline metal and a
precipitation agent in the presence of the fiber at or above its
critical fiber consistency. To sufficiently inhibit the hydrogen
bonding capability of the fiber and, in-turn, modify the physical
properties of a fibrous structure formed from the same, it is
important that the precipitation agent be added at or above the
critical fiber consistency.
[0006] Hence in one aspect, the present invention provides a method
for treating a fiber, such as wood pulp fiber, with a
water-insoluble inorganic compound, the method comprising the steps
of dispersing fiber in water to form a fiber slurry, adding at
least a first reagent selected from the group consisting of a
silicate, a silyl, a silane, and an alkaline metal to the fiber
slurry, thereby forming a modified fiber slurry, partially
dewatering the modified fiber slurry to a consistency of at least
about 15 percent and adding a precipitation agent to the partially
dewatered modified fiber slurry to form and water-insoluble
inorganic in situ which results in a treated fiber comprising the
water-insoluble inorganic.
[0007] In another embodiment, the method comprises creating a fiber
slurry comprising water and fibers, such as wood pulp fibers,
having a consistency of about 15 percent or greater and more
preferably greater than about 20 percent and still more preferably
greater than about 30 percent, such as from about 15 to about 85
percent and more preferably from about 20 to about 50 percent. A
water-soluble compound is applied to the fiber slurry, thereby
forming a modified fiber slurry. A precipitation agent is then
added to the modified fiber slurry and reacted with the
water-soluble compound to form a water-insoluble inorganic compound
that is deposited on the fiber to form a treated fiber. The process
may further include dewatering of the treated fiber, thereby
forming a crumb-form formation of the treated fiber which may
subsequently be dispersed in water to form a treated fiber slurry
useful in the manufacture of tissue webs and products.
[0008] In yet another embodiment, the present invention provides a
method of manufacturing a treated fiber comprising the steps of
providing a fiber slurry having a consistency equal to, or greater
than, about 15 percent; adding a first reagent selected from the
group consisting of a silicate, a silyl, a silane, and an alkaline
metal to the fiber slurry, and adding a precipitation agent to the
fiber slurry to form a treated fiber comprising a water-insoluble
inorganic.
[0009] Preferably the methods of the present invention yield a
treated fiber, such as a treated wood pulp fiber, that comprises
from about 5,000 to about 20,000 ppm water-insoluble inorganic. For
example, in certain embodiments, the invention provides a treated
fiber comprising from about 5,000 to about 20,000 ppm silicon
dioxide. In other embodiments the treated fiber may comprises from
about 5 to about 20 mg of water-insoluble inorganic per kilogram of
fiber, such as from about 8 to about 20 mg/kg and more preferably
from about 10 to about 20 mg/kg. When dispersed in water, the
slurry of treated fiber may be used in a process to produce a
fibrous structure where the presence of the water-insoluble
inorganic compound inhibits inter-fiber bonding and modifies the at
least one physical property of the resulting fibrous structure.
[0010] In another aspect, the present invention provides a method
for applying water-insoluble inorganic compounds to the pulp fiber
during the pulp processing stage. During the pulp processing stage,
upstream of a paper machine, one can obtain treated pulp fibers
according to the present invention. Furthermore, the treated pulp
fiber can be transported to several different paper machines that
may be located at various sites, and the quality of the finished
product from each paper machine will be more consistent. Also, by
treating the pulp fiber before the pulp fiber is made available for
use on multiple paper machines or multiple runs on a paper machine,
the need to install equipment at each paper machine for the
water-insoluble inorganic addition can be eliminated. Thus, another
aspect of the present invention is a uniform supply of treated pulp
fiber, replacing the need for costly and variable chemical
treatments at one or more paper machines.
[0011] In yet another aspect, the present invention provides a
treated pulp fiber and slurries comprising the same, where the
amount of water-insoluble inorganic retained by the treated fibers
is about 2.0 kilograms per metric ton or greater. In particularly
desirable embodiments, the amount of retained water-insoluble
inorganic is at least about 2.0 kg/metric ton, such as from about
2.0 to about 20 kg/metric ton and more preferably from about 5.0 to
about 20 kg/metric ton. Once the treated fibers are redispersed at
the paper machine, the amount of unretained water-insoluble
inorganic in the process water phase is from about 0 and about 10
percent, more particularly from about 0 and about 5.0 percent, and
still more particularly from about 0 and about 2.5 percent, of the
amount of water-insoluble inorganic retained by the pulp
fibers.
[0012] In still other aspects, the present invention provides a
method for making fibrous structures comprising treated fibers
where the fibrous structures differ in at least one physical
parameter, such as sheet bulk, relative to a comparable fibrous
structure substantially free of treated fiber. The method
comprising mixing modified pulp fibers with water to form a treated
fiber slurry. The treated fiber slurry is formed into a wet fibrous
web. When formed into a slurry the treated fibers have retained
from between about 40 to about 100 percent, such as from about 50
to about 80 percent, of the water-insoluble inorganic. The wet
fibrous web is then dried and converted into a finished product
having enhanced qualities due to the treated fibers.
[0013] Thus, in certain embodiments the present invention provides
a method of increasing the bulk of a tissue web comprising the
steps of dispersing fiber in an aqueous solvent to form a fiber
slurry, adding a first reagent selected from the group consisting
of a silicate, a silyl, a silane, and an alkaline metal to the
fiber slurry, partially dewatering the fiber slurry to a
consistency equal to, or greater than, about 15 percent to form a
partially dewatered fiber slurry, adding a precipitation agent to
the partially dewatered fiber slurry to form a treated fiber
comprising a water-insoluble inorganic, and forming a tissue web
from the treated fiber, wherein the tissue web has a sheet bulk
greater than about 5.0 cc/g and a basis weight less than about 60
gsm.
[0014] In yet other embodiments the present invention provides a
tissue product comprising at least one multi-layered tissue web
having a first fibrous layer, a second fibrous layer, and a third
fibrous layer, the first and third fibrous layers comprising
untreated cellulosic fibers and the second fibrous layer comprising
treated fiber comprising at least about 5,000 ppm water-insoluble
inorganic selected from silicone, aluminum and zinc, wherein the
treated fiber comprises at least about 5 percent of the total
weight of the multi-layered web.
DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a SEM micrograph of an untreated hardwood kraft
fiber; and
[0016] FIGS. 2A and 2B are SEM micrographs of treated hardwood
kraft fiber.
DEFINITIONS
[0017] As used herein the term "fiber" refers to 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 and more particularly wood pulp
fibers.
[0018] As used herein the term "slurry" refers to a mixture
comprising fibers and water.
[0019] As used herein the term "critical fiber consistency"
generally refers to the consistency of a fiber slurry at which a
substantial portion of the water is held by intra-fiber voids and
pores, but not by inter-fiber gaps and interphase.
[0020] As used herein the term "water-soluble" refers to the
ability of an inorganic compound or complex of the present
invention to remain in solution. Generally the water-soluble
compounds of the present invention form an aqueous solution and do
not form a precipitate when mixed with water. Further, the
solutions should be essentially colorless and clear. In this
regard, the aqueous solutions of water-soluble compounds of the
present invention appear clear.
[0021] As used herein the term "water-insoluble" generally refers
to inorganic compounds and complexes of the present invention that
form a precipitate and do not remain in an aqueous solution at
25.degree. C. Further, water-insoluble compounds and complexes may
be separated from the aqueous phase by most physical or mechanical
separation techniques, such as centrifugation, sedimentation, or
filtration.
[0022] As used herein the term "fibrous structure" generally refers
to a structure, such as a sheet, that comprises a plurality of
fibers. In one example, a fibrous structure according to the
present invention means an orderly arrangement of fibers within a
structure in order to perform a function. Nonlimiting examples of
fibrous structures of the present invention include paper, fabrics
(including woven, knitted, and non-woven), and absorbent pads (for
example for diapers or feminine hygiene products).
[0023] Nonlimiting examples of processes for making fibrous
structures include known wet-laid papermaking processes and
air-laid papermaking processes. Such processes typically include
steps of preparing a fiber composition in the form of a suspension
in a medium, either wet, more specifically aqueous medium, or dry,
more specifically gaseous, i.e. with air as medium. The aqueous
medium used for wet-laid processes is oftentimes referred to as a
fiber slurry. The fiber slurry is then used to deposit a plurality
of fibers onto a forming wire or belt such that an embryonic
fibrous structure is formed, after which drying and/or bonding the
fibers together results in a fibrous structure. Further processing
the fibrous structure may be carried out such that a finished
fibrous structure is formed. For example, in typical papermaking
processes, the finished fibrous structure is the fibrous structure
that is wound on the reel at the end of papermaking, and may
subsequently be converted into a finished product, e.g. a tissue
product.
[0024] As used herein, the term "tissue product" refers to products
made from tissue webs and includes, bath tissues, facial tissues,
paper towels, industrial wipers, foodservice wipers, napkins,
medical pads, and other similar products. Tissue products may
comprise one, two, three or more plies.
[0025] As used herein, the terms "tissue web" and "tissue sheet"
refer to a fibrous sheet material suitable for forming a tissue
product.
[0026] As used herein, the term "layer" refers to a plurality of
strata of fibers, chemical treatments, or the like, within a
ply.
[0027] As used herein, the terms "layered tissue web,"
"multi-layered tissue web," "multi-layered web," and "multi-layered
paper sheet," generally refer to sheets of paper prepared from two
or more layers of aqueous papermaking furnish which are preferably
comprised of different fiber types. The layers are preferably
formed from the deposition of separate streams of dilute fiber
slurries, upon one or more endless foraminous screens. If the
individual layers are initially formed on separate foraminous
screens, the layers are subsequently combined (while wet) to form a
layered composite web.
[0028] As used herein the term "ply" refers to a discrete product
element. Individual plies may be arranged in juxtaposition to each
other. The term may refer to a plurality of web-like components
such as in a multi-ply facial tissue, bath tissue, paper towel,
wipe, or napkin.
[0029] As used herein, the term "basis weight" generally refers to
the bone dry weight per unit area of a tissue and is generally
expressed as grams per square meter (gsm). Basis weight is measured
using TAPPI test method T-220.
[0030] As used herein, the term "geometric mean tensile" (GMT)
refers to the square root of the product of the machine direction
tensile and the cross-machine direction tensile of the web, which
are determined as described in the Test Methods section.
[0031] As used herein, the term "caliper" is the representative
thickness of a single sheet (caliper of tissue products comprising
two or more plies is the thickness of a single sheet of tissue
product comprising all plies) measured in accordance with TAPPI
test method T402 using an EMVECO 200-A Microgage automated
micrometer (EMVECO, Inc., Newberg, Oreg.). The micrometer has an
anvil diameter of 2.22 inches (56.4 mm) and an anvil pressure of
132 grams per square inch (per 6.45 square centimeters) (2.0
kPa).
[0032] As used herein, the term "sheet bulk" refers to the quotient
of the caliper (.mu.m) divided by the bone dry basis weight (gsm).
The resulting sheet bulk is expressed in cubic centimeters per gram
(cc/g).
[0033] As used herein, the term "slope" refers to slope of the line
resulting from plotting tensile versus stretch and is an output of
the MTS TestWorks.TM. in the course of determining the tensile
strength as described in the Test Methods section herein. Slope is
reported in the units of grams (g) per unit of sample width
(inches) and is measured as the gradient of the least-squares line
fitted to the load-corrected strain points falling between a
specimen-generated force of 70 to 157 grams (0.687 to 1.540 N)
divided by the specimen width. Slopes are generally reported herein
as having units of grams per 3 inch sample width or g/3''.
[0034] As used herein, the term "geometric mean slope" (GM Slope)
generally refers to the square root of the product of machine
direction slope and cross-machine direction slope. GM Slope
generally is expressed in units of kg/3'' or g/3''.
[0035] As used herein, the term "Stiffness Index" refers to the
quotient of the geometric mean slope (having units of g/3'')
divided by the geometric mean tensile strength (having units of
g/3'').
[0036] As used herein the term "substantially free" refers to a
layer of a tissue that has not been formed with the addition of
treated fiber. Nonetheless, a layer that is substantially free of
treated fiber may include de minimus amounts of treated fiber that
arise from the inclusion of treated fibers in adjacent layers and
do not substantially affect the softness or other physical
characteristics of the tissue web.
DETAILED DESCRIPTION
[0037] The present invention provides a treated fiber having
reduced hydrogen bonding capabilities. The treated fiber formed in
accordance with the present invention may be useful in the
production of tissue products having improved bulk and softness.
More importantly, the treated fiber is adaptable to current tissue
making processes and may be incorporated into a tissue product to
improve bulk and softness without an unsatisfactory reduction in
tensile. The fiber formed in accordance with the invention is
fiber, such as a wood pulp fiber, comprising a water-insoluble
inorganic compound that inhibits the ability of the fiber to
hydrogen bond with other fibers. The water-insoluble inorganic
compound is generated in situ by reacting at least one compound
selected from the group consisting of a silicate, a silyl, a
silane, and an alkaline metal and a precipitation agent in the
presence of the fiber at or above the critical fiber consistency.
Upon generation, the water-insoluble inorganic compound is
deposited on the fiber where it may inhibit the fiber's ability to
hydrogen bond with other fibers.
[0038] Accordingly, in certain embodiments the present invention
provides a treated fiber having reduced hydrogen bonding
capabilities. The treated fiber formed in accordance with the
present invention may be useful in the production of fibrous
structures, and more particularly tissue products, having improved
bulk and softness. More importantly, the treated fiber is adaptable
to a wide range of fibrous structure manufacturing processes,
including both air-laid and wet-laid processes, and as such may be
useful in the production of a broad range of structures having
improved properties, such as improved bulk and softness without an
unsatisfactory reduction in tensile.
[0039] The effect of treated fibers of the present invention on the
physical properties of fibrous structures comprising the same, will
vary depending on a range of factors including, for example, the
method used to manufacture the fibrous structure, the degree of
fiber modification, the amount of treated fiber incorporated in the
fibrous structure and the manner in which the treated fiber is
incorporated in the fibrous structure. Thus, in one embodiment, it
may be desirable to affect the degree of modification so as to
moderate the hydrogen bonding between fibers. Preferably the degree
to which the water-insoluble inorganic compound inhibits hydrogen
bonding between fibers is sufficient to enhance bulk and softness
of a resulting fibrous structure, but not so significant as to
negatively affect its tensile strength. For example, preferably the
treated fiber increases sheet bulk by at least about 25 percent,
more preferably at least about 40 percent and still more preferably
at least about 50 percent, such as from about 25 to about 100
percent, while only decreasing the tissue product's tensile index
by less than about 25 percent, and more preferably by less than
about 20 percent and still more preferably by less than about 10
percent.
[0040] Fibers suitable for modification include natural or
cellulosic fibers, such as wood fibers including, for example,
hardwood and softwood fibers, and non-wood fibers including, for
example, cotton fibers. In one particularly preferred embodiment,
wood fibers and more particularly wood pulp fibers are used as a
starting material for preparing the treated fibers of the present
invention. Wood pulp fibers may be formed by a variety of pulping
processes, such as kraft pulp, sulfite pulp, thermomechanical pulp,
and the like. Further, the wood fibers may be any high-average
fiber length wood pulp, low-average fiber length wood pulp, or
mixtures of the same. One example of suitable high-average length
wood pulp fibers include softwood fibers such as, but not limited
to, northern softwood, southern softwood, redwood, red cedar,
hemlock, pine (e.g., southern pines), spruce (e.g., black spruce),
combinations thereof, and the like. One example of suitable
low-average length wood pulp fibers includes hardwood fibers, such
as, but not limited to, eucalyptus, maple, birch, aspen, and the
like. In certain instances, eucalyptus fibers may be particularly
desired to increase the softness of the web. Eucalyptus fibers can
also enhance the brightness, increase the opacity, and change the
pore structure of the tissue product to increase its wicking
ability. Moreover, if desired, secondary fibers obtained from
recycled materials may be used, such as fiber pulp from sources
such as, for example, newsprint, reclaimed paperboard, and office
waste.
[0041] The chemical composition of the treated fiber of the
invention depends, in part, on the extent of processing of the
fiber from which the treated fiber is derived. In general, the
treated fiber of the invention is derived from a wood fiber that
has been subjected to a pulping process (i.e., a wood pulp fiber).
Pulp fibers are produced by pulping processes that seek to separate
cellulose from lignin and hemicellulose leaving the cellulose in
fiber form. The amount of lignin and hemicellulose remaining in a
pulp fiber after pulping will depend on the nature and extent of
the pulping process. Thus, in certain embodiments the invention
provides a treated wood pulp fiber comprising lignin, cellulose,
hemicellulose and a water-insoluble inorganic compound.
[0042] Generally the water-insoluble inorganic compound may
comprise a metal selected from the silicon, aluminum and zinc, or
combinations thereof. The water-insoluble inorganic compound is
generally formed in situ and deposited on the fiber thereby
inhibiting fiber-fiber bonding. Preferably a high degree of
water-insoluble inorganic is retained on the fiber when the fiber
is dispersed in water. For example, at least about 40 percent of
the water-insoluble inorganic, and more preferably at least about
45 percent and still more preferably at least about 50 percent,
such as from about 40 to about 100 percent, is retained when the
fiber is dispersed in water. Accordingly, in certain embodiments,
the amount of water-insoluble inorganic retained by the fiber may
be at least about 1,000 ppm and more preferably 5,000 ppm and still
more preferably at least about 9,000 ppm, such as from about 5,000
to about 50,000 ppm. The amount of retained water-insoluble
inorganic may be assessed by well-known analytical techniques such
as, for example, inductively coupled plasma spectroscopy (ICP) and
more particularly ICP optical emission spectroscopy (ICP-OES).
[0043] Generally the water-insoluble inorganic portion of the
treated fiber of the present invention results from reacting at
least one compound selected from the group consisting of a
silicate, a silyl, a silane, and an alkaline metal and a
precipitating agent in the presence of the fiber at or above the
critical fiber consistency. Treatment of fibers in this manner
generally results in a fiber comprising a water-insoluble inorganic
and having reduced ability to participate in hydrogen bonding with
other fibers. For example, as shown in FIGS. 2A and 2B, the treated
fiber comprises a water-insoluble inorganic deposited on the fiber
surface while the untreated (FIG. 1) fiber is substantially free
from any particles on its surface. The extent of deposition on the
fiber surface and the size of the inorganic deposits may vary
depending on the fiber, the resulting water-insoluble inorganic
compound or complex, as well as the reaction conditions, however,
in certain embodiments the deposits may have an average particle
diameter less than about 200 nanometers, and more preferably less
than about 150 nanometers and still more preferably less than about
100 nanometers.
[0044] In certain embodiments, the inorganic compound or complex
may be deposited on the fiber surface in a relatively uniform
manner and act as a barrier to prevent hydrogen bonds from being
formed between the fibers. At the same time, due to its rigid
nature, the inorganic compound or complex may increase the fiber's
modulus. In certain embodiments treated fibers have relatively
uniform distribution of silicon whereas the untreated fibers are
substantially free from silicon. The distribution of a given
inorganic compound on the fiber surface may be measured using a
scanning electron microscope having single beams with different
angles in the far field.
[0045] As noted previously, formation of a treated fiber generally
results by reacting at least one compound, generally referred to
hereinafter as the first reagent, selected from the group
consisting of a silicate, a silyl, a silane, and an alkaline metal
and a precipitating agent in the presence of the fiber at or above
the critical fiber consistency. In one particularly preferred
embodiment the first reagent is a water-soluble compound having a
water solubility of greater than about 100 mg/mL and more
preferably greater than about 200 mg/mL and still more preferably
greater than about 500 mg/mL, when measured at 25.degree. C. The
water solubility of the first reagent provides the advantage of
simplifying the modification process, reducing costs and improving
reaction yields of treated fibers.
[0046] The water-soluble compound may be organic or inorganic.
Suitable water-soluble compounds include silicates and alkaline
metals including alkaline earth metals. In certain preferred
embodiments the water-soluble compound is a silicate selected from
the group consisting of sodium silicate, potassium silicate,
lithium silicate and quaternary ammonium silicates. In one
particularly preferred embodiment the water-soluble compound
comprises a silicate and more preferably alkaline metal silicates
such as sodium silicate, potassium silicate or lithium silicate,
and combinations thereof. For example, sodium silicates useful in
the present invention may have a SiO:Na.sub.2O ratio between about
2:1 to about 4:1 and more preferably from about 2:1 to about
2.85:1.
[0047] In other embodiments the first reagent is a silane compound,
such as tetraethoxysilane (TEOS), or a silyl, such as
trimethylsilyl isocyanate. In a particularly preferred embodiment
the first reagent is a silane and more particularly an
alkoxysilane. Particularly useful alkoxysilane include a class of
materials commonly referred to as "sol-gel," as described in a
recent review article by Ciriminna et al. (Chem. Rev. (2013), 113
(8), pp 6592-6620. The alkoxysilane provides reactive silyl groups
that can be hydrolyzed in the presence of small amounts of water to
form compounds having silanol (SiOH) groups that may be further
reacted to form --Si--O--Si-- linkages, thereby forming a
crosslinked matrix. The alkoxysilane has a formula of Si(OR)4,
wherein R is an alkyl group. The alkoxy portion (i.e., --OR) of the
alkoxysilane contains from 1 to about 12 carbon atoms, from 1 to
about 8 carbon atoms, or from 1 to about 4 carbon atoms. The alkoxy
group can be straight or branched. In embodiments, the hydrolyzable
alkoxysilane includes tetramethoxysilane, tetraethoxysilane (TEOS),
tetrapropoxysilane, tetraisopropoxy silane, or combinations
thereof.
[0048] Further, in certain embodiments, where the first reagent is
a silane compound, the silane compound may be dissolved in an
organic solvent. Suitable organic solvents may include, for
example, alcohols, cellosolves such as methyl cellosolve, ethyl
cellosolve, butyl cellosolve and cellosolve acetate, ketones such
as acetone and methyl ethyl ketone, and ethers such as dioxane and
tetrahydrofuran. Preferred are alcohols such as, for example,
methanol, ethanol, isopropanol and butanol.
[0049] Suitable precipitation agents may vary depending upon the
first reagent. For example, where the first reagent is an alkaline
earth metal silicate, such as sodium silicate, the precipitation
agent may be an acid, an acid forming compound, ammonium salts, or
sodium aluminate. In those embodiments where the water-soluble
compound is an alkaline earth silicate, particularly preferred
precipitation agents are acids and more preferably inorganic acid,
such as hydrochloric acid and sulfuric acid.
[0050] In other embodiments, where the first reagent is a silane
compound, such as tetraethoxysilane (TEOS), the precipitation agent
may be water, or may be a basic substance. Suitable basic
substances include, for example, ammonia, dimethylamine and
diethylamine. In a particularly preferred embodiment the first
reagent is tetraethoxysilane (TEOS) and the precipitation agent is
ammonia.
[0051] A variety of suitable processes may be used to generate
fibers comprising water-insoluble inorganic, which is generally
referred to herein as "treated fibers." Possible modification
processes include any synthetic method(s) which may be used to
associate the water-insoluble inorganic compound with the fibers.
More generally, the treatment of fibers according to the present
invention may use any process or combination of processes which
promote or cause the generation of a treated fiber. For example, in
certain embodiments the fiber is first reacted with a first reagent
to form a modified fiber, the modified fiber may be partially
dewatered to at least about the critical fiber consistency followed
by reaction with a precipitation agent to form a water-insoluble
inorganic compound and ultimately a treated fiber.
[0052] While a treated fiber may be created by sequentially
treating the fiber with a first reagent and then a precipitating
agent, the invention is not so limited. In other embodiments the
fiber is first reacted with a precipitation agent and then with a
first reagent to form a water-insoluble inorganic compound and
ultimately a treated fiber. In still other embodiments, the first
reagent and a precipitation agent may be added simultaneously to
the fiber to generate a treated fiber. Regardless of the order of
addition of the first reagent and the precipitation agent, it is
important that the consistency of the fiber is at or above the
critical fiber concentration when the precipitation agent is added
to the fiber. In this manner the water-insoluble inorganic compound
that is formed in situ upon mixing of the first reagent and the
precipitation agent is deposited on the fiber and retained thereby,
effectively inhibiting its ability to participate in hydrogen
bonding.
[0053] While the order of addition is generally non-limiting, in
certain preferred embodiments it may be beneficial to separate the
addition of the first reagent and the precipitation agent to obtain
the treated fiber of the present invention. For example, in certain
embodiments, the addition of the first reagent and the
precipitation agent are separated from one another by at least
about 5 minutes, such as from about 5 to about 10 minutes and more
preferably from about 5 to about 20 minutes. Between the addition
of the first reagent and the addition of the precipitation agent it
may be preferable to mix the fiber slurry.
[0054] Generally fiber treatment may be carried out at a variety of
fiber consistencies at or above the critical fiber consistency. For
example, in one embodiment treatment is carried out at a fiber
consistency greater than about 15 percent, more preferably greater
than about 20 percent, such as from about 15 to about 85 percent
and more preferably from about 20 to about 60 percent and still
more preferably from about 30 to about 50 percent. In those
embodiments where the first reagent is added to the fiber slurry
prior to addition of the precipitation agent it is particularly
preferred that modification be carried out at a fiber consistency
greater than about 15 percent, such as from about 15 to about 40
percent, so as to limit hydrolysis of the reagent or the resulted
water-insoluble precipitate remaining in water phase in the
inter-fiber space.
[0055] The amount of the first reagent will vary depending on the
type of fiber, the desired degree of treatment and the desired
physical properties of the fibrous structure formed with treated
fibers. However, by reacting the first reagent and the
precipitating agent in the presence of fiber at or above the
critical fiber consistency, the amount of first reagent required to
provide a treated fiber having inhibited hydrogen bonding is
greatly as reduced. Thus, the amount of the first reagent may
generally be less than about 100 percent and more preferably less
than about 60 percent and still more preferably less than about 50
percent, based on the dry weight of the fiber. Accordingly, in
certain embodiments the mass ratio of dried fiber to the first
reagent is from about 1:0.05 to about 1:1, more preferably from
about 1:0.05 to about 1:0.5 and still more preferably from about
1:0.1 to about 1:0.3. As such, the weight percentage of the first
reagent, based upon dried fiber, is generally about 100 percent or
less, such as from about 5 to about 100 percent and more preferably
from about 5 to about 50 percent and more preferably from about 10
to about 30 percent.
[0056] In certain preferred embodiments, the first reagent compound
is a metal silicate which is added at a dosage from about 100 to
1,000 pounds per metric ton (based on SiO.sub.2 and the dry weight
of the fiber) more preferably from about 100 to 600 lbs/ton, and
still more preferably from about 100 to 400 lbs/ton.
[0057] Preferably reaction of the first reagent and the
precipitation agent in the presence of the fiber results in the
treated fiber slurry having a neutral pH, such as a pH from about
6.8 to about 7.2. Further, the reaction conditions, such as time,
temperature and pH may be modified to obtain the desired degree of
treatment. Accordingly, in certain embodiments, the treatment
according to the invention can be carried at a temperature from
about 0 about 100.degree. C., such as from about 20 to about
70.degree. C. In certain embodiments the treatment time at
20.degree. C. may range from about 5 minutes to 5 hours, such as
from about 5 minutes to 3 hours, and in a particularly preferred
embodiment from about 5 minutes to 1 hour.
[0058] Generally after formation of the water-insoluble inorganic
compound as a result of reacting the first reagent and the
precipitation agent, the water-insoluble inorganic compound is
deposited on the fiber and retained thereon. Water-insoluble
inorganic that is not retained on the fiber may be removed from the
fiber slurry by washing. After washing, the amount of
water-insoluble inorganic retained by the fiber may be assessed by
well-known analytical techniques such as, for example, inductively
coupled plasma spectroscopy (ICP) and more particularly ICP optical
emission spectroscopy (ICP-OES). Accordingly, in one embodiment the
treated fiber comprises at least about 1,000 ppm and more
preferably 5,000 ppm and still more preferably at least about 9,000
ppm, such as from about 5,000 to about 50,000 ppm, metal selected
from the group consisting of silicon, aluminum and zinc, or
combinations thereof.
[0059] In certain embodiments the treated fiber may be subjected to
further treatment by dispersing the treated fiber in water,
partially dewatering the fiber to at least the critical fiber
consistency and then reacting the fiber with a second reagent and a
precipitating agent. For example, in one embodiment, a treated
fiber prepared by reacting fiber with a silicate or an alkaline
metal and having a fiber consistency of at least about 15 percent
may be provided and then reacted with a second reagent, such as a
silane, and a precipitating agent. In a particularly preferred
embodiment a treated fiber having a fiber consistency of at least
about 15 percent may be provided and then mixed with a silane
compound, such as tetraethoxysilane (TEOS), and then a
precipitation agent, which may be water or a basic substance, such
as ammonia or sodium hydroxide.
[0060] After formation, and optionally washing, the treated fibers
may be dried. The consistency of the dried treated fibers may range
from about 65 to about 100 percent. In other embodiments, the
consistency of the dried treated fiber may range from about 80 to
about 100 percent or from about 85 to about 95 percent.
[0061] The dried treated fiber may be redispersed in an aqueous
solvent, such as water, to form a fiber slurry useful in the
manufacture of fibrous structures. Preferably the treated fiber
retains at least about 40 percent of the water-insoluble inorganic,
and more preferably at least about 45 percent and still more
preferably at least about 50 percent, such as from about 40 to
about 100 percent, when the treated fibers are redispersed in
water.
[0062] When redispersed in water, the treated fibers of the present
invention may be used to form a fibrous structure and more
specifically a wet-laid web, such as a tissue web. When forming
tissue webs from the treated fibers of the present invention, it is
generally preferred that no additional inorganic fillers such as
titanium dioxide, clay calcium carbonate, calcium sulphate, and the
like, are added, either in the wet end of tissue formation or as a
post-treatment to the formed tissue. The use of such fillers in
tissue products typically increases the abrasiveness and stiffness
of the tissue products while decreasing their softness.
Furthermore, the foregoing inorganic fillers may leave a residue
further disadvantaging the use of such fillers.
[0063] Rather than add an inorganic filler to the furnish or to the
tissue web after formation or by post-treatment, it is generally
preferred that inorganic matter be introduced to the tissue web by
use of a treated fiber according to the present invention. The
introduction of inorganic compounds to the tissue web in this
manner overcomes the limitations of using traditional fillers as
the treated fibers generally do not stiffen the sheet and are not
abrasive. In fact, in certain instances the treated fibers may
actually reduce the stiffness of the web and improve other
important physical properties, such as sheet bulk. Moreover, the
use of treated fibers may simplify the tissue manufacturing process
as no retention aids are necessary to retain the inorganic material
in the tissue web as it is already associated with the fiber and is
retained at high levels.
[0064] When forming tissue webs from treated fiber, the tissue web
may comprise from about 0.1 to about 100 percent, more preferably
from about 1.0 to about 70 percent and still more preferably from
about 5.0 to about 50 percent and still more preferably from about
10 to about 30 percent, based upon the weight of the web, treated
fibers. The amount of treated fiber incorporated into the web may
vary depending on a number of different factors including, for
example, the method of web manufacturing, the desired properties of
the resulting web and the intended end use of the web.
[0065] While the amount of treated fiber used in the formation of
fibrous structures according to the present invention may vary, it
is generally preferred that treated fiber be incorporated in an
amount sufficient to improve at least one physical property of the
structure. For example, when forming tissue webs and products it
may be desirable to add a sufficient amount of treated fiber to
improve the sheet bulk while decreasing the stiffness of the web or
product.
[0066] In particularly preferred embodiments the effect on one or
more structure properties may be controlled by selectively
depositing the treated fibers in one or more layers of the
structure. For example, the inventors have discovered that the
increase in bulk and decrease in stiffness is most acute when the
treated fibers are selectively incorporated into a single layer of
a multi-layered web, and particularly the middle layer of a three
layered web. Webs produced in this manner not only display a
surprising increase in bulk, but also produce webs having reduced
stiffness without a significant deterioration in strength.
Typically adding treated fibers to the center layer would decrease
bonding and significantly decrease strength. To lessen this effect,
one skilled in the art would typically blend or add treated fibers
to the outer layers. Here however, the most beneficial use of
treated fibers is in the middle layer of a multi-layered web.
[0067] Although based upon their inability to participate in
hydrogen bonding the treated fibers would not appear to be a
suitable replacement for wood fibers, and particularly softwood
fibers that customarily constitute a large percentage of the center
layer of a multi-layered tissue web, it has now been discovered
that by selectively incorporating treated fibers into a
multi-layered web, even in amounts up to 100 percent by weight of
the center layer, these negative effects may be minimized. Even
more surprising is that modified hardwood pulp fibers may be used
in the middle-layer of a multi-layered web without a deleterious
effect.
[0068] Accordingly, in one embodiment the present disclosure
provides a multi-layered tissue web comprising treated fibers
selectively disposed in one or more layers, wherein the tissue
layer comprising treated fibers is adjacent to a layer comprising
untreated fiber and which is substantially free from untreated
fiber. In a particularly preferred embodiment the web comprises
three layers where treated fibers are disposed in the middle layer
and the first and third layers are substantially free from treated
fibers. However, it should be understood that the tissue product
can include any number of plies or layers and can be made from
various types of pulp and treated fibers. The tissue webs may be
incorporated into tissue products that may be either single or
multi-ply, where one or more of the plies may be formed by a
multi-layered tissue web having cotton selectively incorporated in
one of its layers.
[0069] Regardless of the exact construction of the tissue product,
at least one layer of a multi-layered tissue web incorporated into
the tissue product comprises treated fibers, while at least one
layer comprises unmodified papermaking fibers. Suitable papermaking
fibers may comprise wood pulp fibers formed by a variety of pulping
processes, such as kraft pulp, sulfite pulp, thermomechanical pulp,
etc. Further, the wood fibers may have any high-average fiber
length wood pulp, low-average fiber length wood pulp, or mixtures
of the same. One example of suitable high-average length wood pulp
fibers include softwood fibers such as, but not limited to,
northern softwood, southern softwood, redwood, red cedar, hemlock,
pine (e.g., southern pines), spruce (e.g., black spruce),
combinations thereof, and the like. One example of suitable
low-average length wood fibers include hardwood fibers, such as,
but not limited to, eucalyptus, maple, birch, aspen, and the like,
which can also be used. In certain instances, eucalyptus fibers may
be particularly desired to increase the softness of the web.
Eucalyptus fibers can also enhance the brightness, increase the
opacity, and change the pore structure of the web to increase its
wicking ability. Moreover, if desired, secondary fibers obtained
from recycled materials may be used, such as fiber pulp from
sources such as, for example, newsprint, reclaimed paperboard, and
office waste.
[0070] The layer comprising treated fiber may be formed entirely
from treated fiber or may consist essentially of a blend of treated
and untreated fibers. In one embodiment, treated fibers have a
silicon content of at least about 1,000 ppm, and more preferably at
least about 5,000 ppm, such as from about 5,000 to about 50,000
ppm, are incorporated into a single layer of a multi-layered web
where the treated layer comprises greater than about 2.0 percent,
by weight of the layer, treated fiber, such as from about 2.0 to
about 40 percent and more preferably from about 5.0 to about 30
percent. In a particularly preferred embodiment the treated fibers
are incorporated in the web in a manner to increase the web's sheet
bulk and reduce the sheet's stiffness.
[0071] Webs that include the treated fibers can be prepared in any
one of a variety of methods known in the web-forming art. In a
particularly preferred embodiment treated fibers are incorporated
into tissue webs formed by through-air drying and can be either
creped or uncreped. For example, a papermaking process of the
present disclosure can utilize adhesive creping, wet creping,
double creping, embossing, wet-pressing, air pressing, through-air
drying, creped through-air drying, uncreped through-air drying, as
well as other steps in forming the paper web. Some examples of such
techniques are disclosed in U.S. Pat. Nos. 5,048,589, 5,399,412,
5,129,988 and 5,494,554 all of which are incorporated herein in a
manner consistent with the present disclosure. When forming
multi-ply tissue products, the separate plies can be made from the
same process or from different processes as desired.
[0072] In one embodiment the web is formed by a process commonly
referred to as conventional wet-pressed using couch forming,
wherein two wet web layers are independently formed and thereafter
combined into a unitary web. To form the first web layer, untreated
fibers are prepared in a manner well known in the papermaking arts
and delivered to the first stock chest, in which the fiber is kept
in an aqueous suspension. A stock pump supplies the required amount
of suspension to the suction side of the fan pump. Additional
dilution water also is mixed with the fiber suspension.
[0073] To form the second web layer, treated and untreated fibers
may be mixed together and delivered to the second stock chest, in
which the fiber is kept in an aqueous suspension. A stock pump
supplies the required amount of suspension to the suction side of
the fan pump. Additional dilution water is also mixed with the
fiber suspension. The entire mixture is then pressurized and
delivered to a headbox. The aqueous suspension leaves the headbox
and is deposited onto an endless papermaking fabric over the
suction box. The suction box is under vacuum which draws water out
of the suspension, thus forming the second wet web. In this
example, the stock issuing from the headbox is referred to as the
"dryer side" layer as that layer will be in eventual contact with
the dryer surface. In some embodiments, it may be desired for a
layer containing the synthetic and pulp fiber blend to be formed as
the "dryer side" layer.
[0074] After initial formation of the first and second wet web
layers, the two web layers are brought together in contacting
relationship (couched) while at a consistency of from about 10 to
about 30 percent. Whatever consistency is selected, it is typically
desired that the consistencies of the two wet webs be substantially
the same. Couching is achieved by bringing the first wet web layer
into contact with the second wet web layer at roll.
[0075] After the consolidated web has been transferred to the felt
at the vacuum box, dewatering, drying and creping of the
consolidated web is achieved in the conventional manner. More
specifically, the couched web is further dewatered and transferred
to a dryer (e.g., Yankee dryer) using a pressure roll, which serves
to express water from the web, which is absorbed by the felt, and
causes the web to adhere to the surface of the dryer.
[0076] The wet web is applied to the surface of the dryer by a
press roll with an application force of, in one embodiment, about
200 pounds per square inch (psi). Following the pressing or
dewatering step, the consistency of the web is typically at or
above about 30 percent. Sufficient Yankee dryer steam power and
hood drying capability are applied to this web to reach a final
consistency of about 95 percent or greater, and particularly 97
percent or greater. The sheet or web temperature immediately
preceding the creping blade, as measured, for example, by an
infrared temperature sensor, is typically about 250.degree. F. or
higher. Besides using a Yankee dryer, it should also be understood
that other drying methods, such as microwave or infrared heating
methods, may be used in the present invention, either alone or in
conjunction with a Yankee dryer.
[0077] At the Yankee dryer, the creping chemicals are continuously
applied on top of the existing adhesive in the form of an aqueous
solution. The solution is applied by any convenient means, such as
using a spray boom that evenly sprays the surface of the dryer with
the creping adhesive solution. The point of application on the
surface of the dryer is immediately following the creping doctor
blade, permitting sufficient time for the spreading and drying of
the film of fresh adhesive.
[0078] The dried web is removed from the Yankee dryer by the
creping blade and the creped tissue web may be subjected to further
converting to produce a tissue product, which may be single or
multi-plied. For instance, in one aspect, a single ply wet pressed
web made according to the present disclosure can be attached to one
or more other fibrous webs for forming a tissue product having
desired characteristics, such as improved bulk, good tensile
strength and relatively low stiffness. The other webs laminated to
the single-ply webs of the present disclosure can be, for instance,
a wet-creped web, a calendered web, an embossed web, a through-air
dried web, a creped through-air dried web, an uncreped through-air
dried web, an airlaid web, and the like. In other embodiments two
or more single-ply webs of the present disclosure are plied
together to form a multi-ply tissue product.
[0079] The basis weight of tissue webs made in accordance with the
present disclosure can vary depending upon the final product. For
example, the process may be used to produce bath tissues, facial
tissues, paper towels, and the like. In general, the basis weight
of the tissue web may vary from about 5 to about 50 gsm, such as
from about 10 to about 40 gsm. Tissue webs may be converted into
single and multi-ply bath or facial tissue products having basis
weight from about 10 to about 80 gsm and more preferably from about
20 to about 50 gsm.
[0080] Multi-ply tissue products produced according to the present
invention may have a GMT greater than about 500 g/3'', such as from
about 500 to about 900 g/3'' and more preferably from about 600 to
about 750 g/3''. At these strengths, the tissue products generally
have GM Slopes less than about 10 kg/3'', such as from about 5 to
about 9 kg/3'', and in particularly preferred embodiments from
about 6 to about 8 kg/3''. The relatively slow GM Slope and modest
GMT yield products having relatively low Stiffness Index, such as
less than about 15, for example from about 8 to about 15 and in
particularly preferred embodiments from about 10 to about 12.
Further, the multi-ply products generally have improved sheet bulk
compared to tissue products substantially free from agave fibers,
such as sheet bulks at least about 10 percent greater and ranging
from about 7.0 to about 10.0 cc/g.
[0081] In addition to having sufficient strength to withstand use
and relatively low stiffness, the tissue webs and products of the
present disclosure also have good bulk characteristics, regardless
of the method of manufacture. For instance, conventional creped wet
pressed tissue products prepared using treated fibers may have a
sheet bulk greater than about 8 cc/g, such as from about 8 to about
15 cc/g and more preferably from about 10 to 12 cc/g. In other
embodiments through-air dried tissue and more preferably uncreped
through-air dried tissue comprising treated fibers have a sheet
bulk greater than about 10 cc/g, such as from about 10 to about 25
cc/g and more preferably from about 16 to about 22 cc/g.
[0082] The increase in bulk is particularly acute when the treated
fiber is disposed in the center layer of a three layer structure.
Surprisingly, the increase in bulk is accompanied by minimal
degradation in strength and a decrease in the Stiffness Index. A
comparison of various tissue webs illustrating this effect are
shown in the table below. Accordingly, in certain preferred
embodiments the present disclosure provides a tissue web having
enhanced bulk and softness without a significant decrease in
tensile, where the web has three layers--a first, a second and a
third layer, wherein treated fibers are selectively disposed in the
second layer and comprise from about 5 to about 50 percent, and
more preferably from about 10 to about 30 percent of the weight of
the web. In a particularly preferred embodiment the present
disclosure provides a two-ply tissue product where each tissue ply
comprises three layers with treated fibers selectively disposed in
the middle layer, the tissue product having a GMT from about 600 to
about 800 g/3'', a sheet bulk greater than about 8 cc/g, such as
from about 8 to about 12 cc/g and a Stiffness Index less than about
15, such as from about 8 to about 12.
[0083] In other embodiments the present disclosure provides a
two-ply tissue product comprising an upper multi-layered tissue web
and a lower multi-layered tissue web that are plied together using
well-known techniques. The multi-layered webs comprise at least a
first and a second layer, wherein treated fibers are selectively
incorporated in only one of the layers, such that when the webs are
plied together the layers containing the treated fibers are brought
into contact with the user's skin in-use. For example, the two-ply
tissue product may comprise a first and second tissue web, wherein
the tissue webs each comprise a first and second layer. The first
layer of each tissue web comprises wood fibers and treated fibers
and, while the second layer of each tissue web is substantially
free of treated fibers. When the tissue webs are plied together to
form the tissue product the second layers of each web are arranged
in a facing relationship such that the treated fibers are brought
into contact with the user's skin in-use.
[0084] In other embodiments, tissue products produced according to
the present disclosure have GMT greater than about 500 g/3'', such
as from about 500 to about 900 g/3'' and more preferably from about
600 to about 750 g/3''. At these strengths, the tissue products
generally have GM Slopes less than about 10 kg/3'', such as from
about 5 to about 9 kg/3'', and in particularly preferred
embodiments from about 6 to about 8 kg/3''. The relatively slow GM
Slope and modest GMT yield products having relatively low Stiffness
Index, such as less than about 15, for example from about 8 to
about 15 and in particularly preferred embodiments from about 10 to
about 12.
Test Methods
Sheet Bulk
[0085] Sheet Bulk is calculated as the quotient of the dry sheet
caliper expressed in microns, divided by the bone dry basis weight,
expressed in grams per square meter (gsm). The resulting Sheet Bulk
is expressed in cubic centimeters per gram. More specifically, the
Sheet Bulk is the representative caliper of a single tissue sheet
measured in accordance with TAPPI test methods T402 "Standard
Conditioning and Testing Atmosphere For Paper, Board, Pulp
Handsheets and Related Products" and T411 om-89 "Thickness
(caliper) of Paper, Paperboard, and Combined Board." The micrometer
used for carrying out T411 om-89 is an Emveco 200-A Tissue Caliper
Tester (Emveco, Inc., Newberg, Oreg.). The micrometer has a load of
2 kilo-Pascals, a pressure foot area of 2500 square millimeters, a
pressure foot diameter of 56.42 millimeters, a dwell time of 3
seconds and a lowering rate of 0.8 millimeters per second.
Tensile
[0086] Tensile testing was done in accordance with TAPPI test
method T-576 "Tensile properties of towel and tissue products
(using constant rate of elongation)" wherein the testing is
conducted on a tensile testing machine maintaining a constant rate
of elongation and the width of each specimen tested is 3 inches.
More specifically, samples for dry tensile strength testing were
prepared by cutting a 3.+-.0.05 inch (76.2.+-.1.3 mm) wide strip in
either the machine direction (MD) or cross-machine direction (CD)
orientation using a JDC Precision Sample Cutter (Thwing-Albert
Instrument Company, Philadelphia, Pa., Model No. JDC 3-10, Serial
No. 37333) or equivalent. The instrument used for measuring tensile
strengths was an MTS Systems Sintech 11S, Serial No. 6233. The data
acquisition software was an MTS TestWorks.RTM. for Windows Ver.
3.10 (MTS Systems Corp., Research Triangle Park, N.C.). The load
cell was selected from either a 50 Newton or 100 Newton maximum,
depending on the strength of the sample being tested, such that the
majority of peak load values fall between 10 to 90 percent of the
load cell's full scale value. The gauge length between jaws was
4.+-.0.04 inches (101.6.+-.1 mm). The crosshead speed was 10.+-.0.4
inches/min (254.+-.1 mm/min), and the break sensitivity was set at
65 percent. The sample was placed in the jaws of the instrument,
centered both vertically and horizontally. The test was then
started and ended when the specimen broke. The peak load was
recorded as either the "MD tensile strength" or the "CD tensile
strength" of the specimen depending on direction of the sample
being tested. Ten representative specimens were tested for each
product or sheet and the arithmetic average of all individual
specimen tests was recorded as the appropriate MD or CD tensile
strength the product or sheet in units of grams of force per 3
inches of sample. The geometric mean tensile (GMT) strength was
calculated and is expressed as grams-force per 3 inches of sample
width. Tensile energy absorbed (TEA) and slope are also calculated
by the tensile tester. TEA is reported in units of gm*cm/cm.sup.2.
Slope is recorded in units of kg. Both TEA and Slope are
directional dependent and thus MD and CD directions are measured
independently. Geometric mean TEA and geometric mean slope are
defined as the square root of the product of the representative MD
and CD values for the given property.
EXAMPLES
[0087] Treated fibers were prepared from eucalyptus hardwood kraft
(EWHK) pulp fibers by first dispersing 10 g of EHWK fibers in 1,000
g of water and mechanically blending using a mixer to form a
uniform slurry. To the EHWK fiber slurry, a first reagent (specific
compound and amount set forth in Table 1, below) was added and
mixed for 5 minutes to form a treated fiber slurry. After mixing,
the treated fiber slurry was placed into an oven at 90.degree. C.
and dried for several hours until the treated fiber slurry reached
a fiber consistency of about 15 percent. The partially dried
modified fiber was then mixed with a precipitation agent (specific
compound and amount set forth in Table 1, below) under constant
agitation for about 30 minutes to yield a treated EHWK fiber. The
treated EHWK fiber was then washed with water to remove the
byproduct of the reactants and then placed in a 110.degree. C. oven
for 2 hours to yield a dried treated EHWK fiber.
TABLE-US-00001 TABLE 1 Sample Code First Reagent (g) Precipitation
Agent (g) HC-01 20% Sodium Silicate (100 g) 10% Solution HCl (100
g)
[0088] The treated fiber prepared as described above was subjected
to further treatment by dispersing 10 g of HC-01 treated fiber in
water to form a slurry having a consistency of about 15 percent.
Approximately 0.1 g of 0.5% sodium hexametaphosphate was mixed into
the HC-01 fiber slurry and then tetraethyl orthosilicate (TEOS) was
added together with ethanol (5 g) as described in Table 2, below.
After mixing for about 5 minutes, ammonia was added to trigger
hydrolysis of TEOS. Mixing continued for another 60 minutes while
the mixture was heated to 90.degree. C. The twice treated EHWK
fiber was then washed with water to remove the byproduct of the
reactants and then placed in a 110.degree. C. oven for 2 hours to
yield a dried treated EHWK fiber.
TABLE-US-00002 TABLE 2 Sample Code Second Reagent (g) Precipitation
Agent (g) HC-02 Tetraethyl Orthosilicate 10% Solution NH.sub.3 (2
g) (TEOS) (20 g) HC-04 Tetraethyl Orthosilicate 10% Solution
NH.sub.3 (2 g) (TEOS) (10 g)
[0089] The HC-01 was also subject to further modification by
dispersing 10 g of HC-01 treated fiber in water to form a slurry
having a consistency of about 15 percent. Approximately 0.1 g of
0.5% sodium hexametaphosphate was mixed into HC-01 fiber slurry and
then hydroxyl silicone oil (Mw of about 3,000) was added to the
fiber slurry along with ethanol (5 g) as indicated in Table 3,
below. After mixing for about 5 minutes, a solution of NaOH was
added. Mixing continued for another 60 minutes while the mixture
was heated to 90.degree. C. The twice treated EHWK fiber was then
washed with water to remove the byproduct of the reactants and
placed in a 110.degree. C. oven for 2 hours to yield a dried
treated EHWK fiber.
TABLE-US-00003 TABLE 3 Sample Code Second Reagent (g) Precipitation
Agent (g) HC-06 Hydroxy silicone oil (10 g) 50% Solution NaOH (50
g)
[0090] Treated pulps prepared as described above were used to form
handsheets. Handsheets were prepared using a lab handsheet former
(Retention & Drainage Analyzer, GE-RDA-T6, commercially
available from GIST Co., Ltd., Daejeon, Korea). The pulp (untreated
or treated) was mixed with distilled water to form slurries at a
ratio of 25 g pulp (on dry basis) to 2 L of water. The pulp/water
mixture was subjected to disintegration using an L&W
disintegrator Type 965583 for 5 minutes at a speed of 2975.+-.25
RPM. After disintegration the mixture was further diluted by adding
4 L of water. Handsheets were formed using the wet laying handsheet
former followed by pressing using opposed sheets of blotter paper
on each side of the handsheet at a pressure of 98 psi for one
minute and then a two minute contact on a hot surface to dry the
handsheet. The dried handsheet was then cut into a 7.5.times.7.5
inch sample prior to physical testing. The physical properties of
the handsheets are reported in Table 4, below.
TABLE-US-00004 TABLE 4 Fiber Type Caliper (mm) Density (g/cc) Basis
Weight (gsm) Untreated EHWK 0.16 0.352 54.5 HC-01 0.41 0.157 63.4
HC-02 0.59 0.109 63.6 HC-04 0.45 0.106 47.6 HC-06 0.38 0.149
56.6
[0091] The silicon content of various fiber (treated and untreated)
was assessed by weighing approximately 0.5 g of each fiber sample
into a digestion vessel. Five milliliters of concentrated nitric
acid and 1 mL of concentrated hydrofluoric acid were added then
digested in a CEM microwave extractor. The silicon was determined
by Inductively Coupled Plasma Optical Emissions Spectroscopy,
ICP-OES using FIB-W003 "Guidelines for Metal Analysis by Inductive
Coupled Plasma (ICP) Spectroscopy" with a CCV standard, which was
within 11 percent. The results are reported in Table 5, below.
TABLE-US-00005 TABLE 5 Sample ID Silicon (ppm) Unmodified EHWK 721
HC-01 9,347 HC-02 20,868 HC-04 17,246 HC-06 9,464
[0092] While treated fibers and methods of preparing the same, as
well as tissue webs and products comprising treated fibers, have
been described in detail with respect to the specific embodiments
thereof, it will be appreciated that those skilled in the art, upon
attaining an understanding of the foregoing, may readily conceive
of alterations to, variations of, and equivalents to these
embodiments. Accordingly, the scope of the present invention should
be assessed as that of the appended claims and any equivalents
thereto and the foregoing embodiments:
[0093] In a first embodiment the present invention provides a
method of manufacturing a treated fiber comprising the steps of
providing a fiber slurry having a consistency equal to, or greater
than, about 15 percent; adding a first reagent selected from the
group consisting of a silicate, a silyl, a silane, and an alkaline
metal to the fiber slurry, and adding a precipitation agent to the
fiber slurry to form a treated fiber comprising a water-insoluble
inorganic.
[0094] In a second embodiment the present invention provides the
method of the first embodiment wherein the first reagent is a
water-soluble compound having a water solubility of greater than
about 100 mg/mL at 25.degree. C.
[0095] In a third embodiment the present invention provides the
method of the first or second embodiments wherein the first reagent
is a silicate or an alkaline metal.
[0096] In a fourth embodiment the present invention provides the
method of the first or second embodiments wherein the first reagent
is a silicate selected from the group consisting of sodium
silicate, potassium silicate, lithium silicate and quaternary
ammonium silicates.
[0097] In a fifth embodiment the present invention provides the
method of the first or second embodiments wherein the first reagent
is a sodium silicate having a SiO:Na.sub.2O ratio from about 2:1 to
about 4:1.
[0098] In a sixth embodiment the present invention provides the
method of the first or second embodiments wherein the first reagent
is a silane selected from the group consisting of a
tetramethoxysilane, tetraethoxysilane (TEOS), tetrapropoxysilane,
tetraisopropoxy silane, or combinations thereof.
[0099] In a seventh embodiment the present invention provides the
method of any one of the first through sixth embodiments wherein
the treated fiber comprises at least about 5,000 ppm
water-insoluble inorganic selected from silicone, aluminum and zinc
and combinations thereof.
[0100] In an eighth embodiment the present invention provides the
method of any one of the first through seventh embodiments wherein
at least about 75 percent of the water-insoluble inorganic is
retained when the fiber is dispersed in water at 20.degree. C.
[0101] In a ninth embodiment the present invention provides a
treated fiber prepared by any one of the methods of the first
through eighth embodiments.
[0102] In a tenth embodiment the present invention provides treated
fiber comprising a fiber and a water-insoluble inorganic selected
from the group consisting of silicon, aluminum and zinc, or
combinations thereof, disposed thereon, where the amount of
water-insoluble inorganic retained by the treated fibers is about
2.0 kilograms per metric ton of fiber or greater when the fiber is
dispersed in water at 20.degree. C.
[0103] In an eleventh embodiment the present invention provides the
treated fiber of the tenth embodiment wherein the fiber is a
hardwood fiber selected from the group consisting of eucalyptus,
maple, birch, aspen, and combinations thereof.
[0104] In a twelfth embodiment the present invention provides the
treated fiber of the tenth or eleventh embodiments wherein the
treated fiber comprises at least about 1,000 ppm water-insoluble
inorganic.
[0105] In a thirteenth embodiment the present invention provides
the treated fiber of any one of the tenth through twelfth
embodiments wherein the treated fiber comprises from about 5,000 to
about 50,000 ppm water-insoluble inorganic.
* * * * *