WO 96IOi.t2i PCT,'L'595~08'il
SOFT TISSUE PAPER FROM COARSE CELLULOSE F18ERS
TECHNICAL FIELD
This invention relates, in general, to tissue paper; and more
specifically to sanitary tissue paper made from low grade cellulose pulps
characterized as low grade because of their relatively high coarseness.
BACKGROUND OF THE INVENTION
As the world's supply of native fiber comes under increasing
economic and environmental scrutiny, pressure is mounting to utilize lower
grade cellulose fibers such as those produced from recycled paper and
those produced from higher yield mechanical or chemi-mechanical
processes: Unfortunately, such fibers, when added to sanitary tissues,
cause comparatively severe deterioration of the product characteristic
most sought after by consumers of sanitary tissues, namely the aesthetic
qualities and most specifically the softness.
The culpable fiber characteristic is mainly the coarseness. The
aforementioned lower grade cellulose fibers typically possess a high
coarseness. This contributes to the loss of the velvety feel which is
imparted by prime fibers selected because of their flaccidness. U.S.
Patent 4,300,981, Carstens, issued November 17, 1981, explains the
2~ textural and surface qualities which are imparted by these prime fibers.
Desirable surface qualities are absent when the lower grade fibers
are selected, if the lower grade fibers possess high coarseness. In the
case of the mechanical or chemi-mechanical liberated fiber, high
coarseness is due to the retention of the non-cellulosic components of the
original wood substance, such components including lignin and so-called
hemicelluloses. This makes each fiber weigh more without increasing its
length.
Recycled paper can also tend to have a high mechanical pulp
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content, but, even when all due care is exercised in selecting the
wastepaper grade to minimize this, a high coarseness still often occurs.
This is thought to be due to the impure mixture of fiber morphologies
which naturally occurs when paper from many sources is blended to make
a recycled pulp. For example, a certain wastepaper might be selected
because it is primarily North American hardwood in nature; however, one
will often find extensive contamination from coarser softwood fibers, even
to of the most deleterious species such as variations of Southern U.S. pine.
Over the history of papermaking, many inventors have directed
their energies toward overcoming the limitations of lower quality fibers to
make them acceptable for the uses described herein.
Of the many chemical additives which have been proposed for use in
softening tissues, no system has proven potent enough to make truly soft
tissue from furnishes described previously as being coarse, unless
excessive amounts or unnecessary additives resulting in comparatively
2 o expensive products which accordingly might be relegated to speciality
niches unavailable to the vast majority of the population.
Therefore, it is an object of an aspect of the present invention to
provide for a low density fibrous tissue structure which has a tactically
pleasing response.
It is an object of ari aspect of the invention to incorporate a critical
amount of fibers normally regarded as being coarse and inferior with
regard to the above object.
It is an object of an aspect of the present invention to provide the
tissue without excessive use of chemical treatments which add to the
expense of making and distributing the product.
3
These and other objects of aspects are obtained using the present invention
as will be taught in the following disclosure.
SUMMARY OF THE INVENTION
It has been found that an unexpected softness can be achieved via a
relationship between the coarseness of the fibers making up the tissue and
the coefficient of friction of the fiber furnish from which the tissue is
made.
This relationship makes it possible to provide for a soft tissue without the
need
to load unnecessary additives to mask the harshness of coarse fibers.
The present invention is a soft tissue paper comprised of chemically
softened cellulose fibers. The chemically softened cellulose fibers comprise a
sufficient amount of coarse fibers to raise the composite average coarseness
of the tissue paper to greater than about 11.0 mg/100m. The chemically
softened cellulose fibers have a depressed coefficient of friction (DCOF, in
percentage points) related to its composite average coarseness (C), in
mg1100m, by the equation:
DCOF> 4.27 * C - 44.23
The soft tissue paper has a specific tensile strength between about 9
and about 25 glin/g/m2 and a density between about 0.05 and about 0.20 glcc,
and the cellulose fibers comprise at least 10% of coarse cellulose fibers,
selected from the group consisting of recycled fibers, chemithermomechanical
fibers and mixtures thereof and the cellulose fibers comprise from about
0.05% to about 2.0% by weight of a chemical softener.
In its preferred embodiment the invention provides for a targeted
treatment, capable of essentially coating the fibers, in relation to their
specific
surface, with a substantive chemical softener, preferably in amounts ranging
from about 0.05% to about 2.0%, by weight. Preferred chemical softeners
include quaternary ammonium compounds having the formula:
<IMG>
WO 96104424 PCTIUS95108741
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In the structure named above each R1 is a C14-C22 hydrocarbyl
group, preferably tallow, R2 is a C1 - C6 alkyl or hydroxyalkyl group,
preferably C1-C3 alkyl, X' is a compatible anion, such as an halide (e.g.
chloride or bromide) or methyl sulfate. As discussed in Swern, Ed. in
Bailey's Industrial Oil and Fat Products, Third Edition, John Wiley and
Sons (New York 1964), tallow is a naturally occurring material having a
variable composition. Table 6.13 in the above-identified reference edited
by Swern indicates that typically 78% or more of the fatty acids of tallow
contain 16 or18 carbon atoms. Typically, half of the fatty acids present in
tallow are unsaturated, primarily in the form of oleic acid. Synthetic as well
as natural "tallows" fall within the scope of the present invention.
Preferably, each R1 is C16-C18 alkyl, most preferably each R1 is
straight-chain C18 alkyl. Preferably, each R2 is methyl and X' is chloride
or methyl sulfate.
Examples of quaternary ammonium compounds suitable for use in
the present invention include the well-known dialkyldimethylammonium
salts such as ditallowdimethylammonium chloride,
ditallowdimethylammonium methyl sulfate, di(hydrogenated) tallow
dimethyl ammonium chloride; with di(hydrogenated) tallow dimethyl
ammonium methyl sulfate being preferred. This particular material is
available commercially from Witco Chemical Company Inc. of Dublin, Ohio
under the tradename "Varisoft ~137".
Biodegradable mono and di-ester variations of the quaternary
ammonium compound can also be used, and are meant to fall within the
scope of the present invention.
All percentages, ratios, and proportions herein are by weight unless
othenivise specified.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flow diagram depicting one method of
producing preferred cellulose pulps wherein a length classifying
stage is performed first, followed by a centrifuging stage.
Figure 2 is a schematic flow diagram depicting an alternate method of
producing preferred cellulose pulps wherein a centrifuging stage
WO 96104424 PCTIUS95/08741
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is performed first, followed by a length classification stage.
The present invention is described in more detail below.
DETAILED DESCRIPTION OF THE INVENTION
Briefly, the present invention is a low extractives tissue paper which
has a heretofore unachieved level of softness when the coarseness of its
furnish is taken into account.
It has been found that it is possible to achieve these unexpected
softness levels by depressing the coefficient of friction of the surfaces of
individual fibers in relation to their surface area.
The term coefficient of friction, as used herein refers to the
coefficient of friction as determined from the force required to drag a
fritted
glass sled across the smooth surface of a paper specimen which has been
prepared by TAPPI standard method T-205. Details of the method used
for the measurement are provided hereinafter, however the coefficient of
friction could be determined by other methods which produce comparable
values.
The term depressed coefficient of friction, denoted by the acronym
DCOF throughout this specification, and expressed in units of percentage
points, refers to the percentage amount by which the coefficient of friction
is depressed via the addition of the chemical softener. In other words, to
measure the DCOF of a fiber furnish, a standard handsheet is prepared
using a sample of the fibers without chemical softener and a standard
handsheet is prepared using a sample of the fibers after addition of
chemical softener. The coefficient of friction is measured using each
handsheet, and the DCOF is computed using the following formula:
DCOF = COFg - COFA X 100
COFg
Where DCOF is the depressed coefficient of friction and COFg and
COFA are the coefficient of friction of the handsheet made from untreated
fibers and treated fibers respectively.
As used herein, the term chemical softener refers to a compound
capable of increasing the lubricity of papermaking fibers while being
WO 96104424 PCTIUS95108741
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essentially substantive to the fibers, i.e. will remain on the fibers even
when the fibers are dispersed in water. The present invention preferably
contains from about 0.05% to about 2.0% by weight, on a dry fiber basis,
of a chemical softener.
A most preferred form of chemical softener is 0.05% to 2.0% of a
quaternary ammonium compound having the formula:
R2 R1
N+ X-
R2 R1
In the structure named above each R1 is C14-C22 hydrocarbyl group,
preferably tallow, R2 is a C1 - C6 alkyl or hydroxyalkyl group, preferably
C1-C3 alkyl, X' is a compatible anion, such as an halide (e.g. chloride or
bromide) or methyl sulfate. As discussed in Swern, Ed. in Bailey's
Industrial Oil and Fat Products, Third Edition, John Wiley and Sons (New
York 1964), tallow is a naturally occurring material having a variable
composition. Table 6.13 in the above-identified reference edited by Swern
indicates that typically 78% or more of the fatty acids of tallow contain 16
or18 carbon atoms. Typically, half of the fatty acids present in tallow are
unsaturated, primarily in the form of oleic acid. Synthetic as well as natural
"tallows" fall within the scope of the present invention.
Preferably, each R1 is C16-C18 alkyl, most preferably each R1 is
straight-chain C18 alkyl. Preferably, each R2 is methyl and X- is chloride
or methyl sulfate.
Examples of quaternary ammonium compounds suitable for use in
the present invention include the well-known dialkyldimethylammonium
salts such as ditallowdimethylammonium chloride,
ditallowdimethylammonium methyl sulfate, di(hydrogenated) tallow
dimethyl ammonium chloride; with di(hydrogenated) tallow dimethyl
ammonium methyl sulfate being preferred. This particular material is
WO 96/O.ii24 PCTM: 595; OS"~ I
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available commercially from Witco Chemical Company Inc. of Dudiin. Ohio
under the tradename "Varisoft ~ 137".
Further examples of suitable quaternary ammonium compounds.
and preferred methods of adding such compounds to the cellulose fibers
are described in U.S. Patent 5,240.562, Phan et al., issued
August 31, 1993.
Biodegradable mono and di-ester variations of the quaternary
ammonium compound can also be used, and are meant to fall within the
scope of the present invention. These compounds have the formula:
R2 CH2 -CH2 -O-C-R1
N+ X-
R2 H2 -CH2 -O- -R~
and
R2 R1
' N+ X_
RZ H2 -CH2 -O-~~ -R~
O
In the structures named above each R~ is an aliphatic C13 - C19
hydrocarbyl group, such as tallow, RZ is a C1 - C$ alkyl or hydroxyalkyl
group or mixture thereof, X' is a compatible anion, such as an halide (e.g.,
chloride or bromide) or methyl sulfate. Preferably, each R~ is C16-C18
alkyl, most preferably each R1 is straight-chain C18 alkyl, and R2 is a
methyl.
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W O 96i O~t~24 PC.°T,2 S 95i08"i 1
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Other preferred chemical softeners suitable for use in the tissue
papers of the present invention include polysiloxane compounds,
preferably amino-functional polydimethylpolysiloxane compounds. In
addition to such substitution with amino-functional groups, effective
substitution may be made with carboxyl, hydroxyl, ether, poiyether,
aldehyde, ketone, amide, ester, and thiol groups. Of these effective
substituent groups, the family of groups comprising amino, carboxyl, and
hydroxyl groups are more preferred than the others; and amino-functional
groups are most preferred. Suitable types of such polysiloxanes are
described in U.S. Patent No. 5,059,282, Ampulksi et al., issued October
22, 1991.
Exemplary commercially available polysiioxanes include DOW 8075
and DOW 200 which are available from Dow Coming; and Silwet L720 and
Ucarsil EPS which are available from Union Carbide.
Still other preferred chemical softener additives suitable for the
present invention include nonionic surfactants selected from
alkylglycosides, including alkylglycoside esters such as Crodesta~' SL-40
which is available from Croda, Inc. (New York, NY); alkyiglycoside ethers
as described in U.S. Patent 4,011,389, issued to W. K Langdon, et al. on
March 8, 1977; alkyfpolyethoxylated esters such as PegosperseT'~' 200 ML
available from Glyco Chemicals, Inc. (Greenwich, CT);
alkyfpolyethoxylated ethers and esters such as Neodol~ 25-12 available
from Shell Chemical Co.; sorbitan esters such as Span 60 from ICI
America, Inc., ethoxyiated sorbitan esters, propoxylated sorbitan esters,
mixed ethoxylatedlpropoxylated sorbitan esters, and poiyethoxylated
sorbitan alcohols such as Tween 60 also from ICI America, Inc. It should
be understood, that the above listings of suitable chemical softeners are
intended to be merely exemplary in nature, and are not meant to limit the
scope of the invention.
It has been found that the compounds such as the above mentioned
quaternary ammonium compounds in such low amounts (i.e., from 0.05°~
2.0%) carry a concomitant high economic value. in fact, in these low
amounts, for the subject paper, it is not necessary to counteract any
hydrophobicity through the use of polyhydroxy compounds or other wetting
agents which would result in further savings.
As used herein, the term composite average coarseness, refers to
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the coarseness determined on the fibrous finished product of tissue,
without regard as to whether the product is composed of several furnishes
of different coarseness values. The method of determining coarseness of
cellulose fibers is described in detail hereinafter.
The composite average coarseness can also be determined for a
product comprised of a blend of different types of cellulose fibers from the
coarseness of the individual fibers from which the product is comprised.
The exact weight proportions of the different types of fibers needs to be
known in order to perform this calculation. To do this, the following
formula is used to determine the resultant composite average coarseness
C when two fiber types, type 1 and type 2, possessing coarseness C1 and
C2, respectively are blended in weight fractions f1 and f2, respectively:
C= C1'f1 +f1If2~
1 + {f21f1 ) ' (C11C2)
The tissue papers of the present invention are comprised of
cellulose fibers having a composite average coarseness greater than
about 11.0mglm, more preferably, greater than about 12 mglt OOm.
A preferred method for producing cellulose pulps having a desired
combination of fiber length and fiber coarseness is described in U.S.
Patent Application Serial No. 081082,683, ~nson,
The term cellulose fibers, as used herein, refers to naturally-
occurring fibrous material derived from wood or other biological material.
Wood-derived materials are of particular interest. Cellulose wood fibers
from.a uariety of sources may be employed to produce products according
to the present invention. These include chemical pulps, which are purified
to remove substantially all of the lignin originating from the wood ,
substance. These chemical pulps include those made by either the
alkaline Kraft (sulfate) or the acid, sulfite processes. Applicable wood
fibers can also be derived from mechanical pulps,'a term which as used
herein, refers to chemi-thermomechanical as well as groundwood,
thermomechanicai, and semi-chemical pulps, all of which retain a
substantial portion of lignin originating from the wood substance.
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WO 96/04424 PCT/US95108741
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Both hardwood pulps and softwood pulps as well as blends of the two
may be employed. The terms hardwood and softwood pulp as used herein
refer to fibrous pulp derived from the woody substance of deciduous trees
(angiosperms) and coniferous trees (gymnosperms), respectively. Also
applicable to this invention are fibers derived from recycled paper, which
may contain any or all of the above categories as well as minor amounts of
other fibers, fillers, and adhesives used to facilitate the original
papermaking.
Fibers derived from recycled paper made with chemical pulp fibers
and comprising a blend of hardwood and softwood fibers may also be
employed to produce products according to the present invention. The
term "recycled paper", as used herein, generally refers to paper which has
been collected with the intent of liberating its fibers and reusing them.
These can be pre-consumer, such as might be generated in a paper mill or
print shop, or post-consumer, such as that originating from home or office
collection. Recycled papers are sorted into different grades by dealers to
facilitate their reuse. One grade of recycled paper of particular value in
the present invention is ledger paper. Ledger paper is usually comprised
of chemical pulps and typically has a hardwood to softwood ratio of from
about 1:1 to about 2:1. Examples of ledger papers include bond, book,
photocopy paper, and the like.
Preferably, the cellulose fibers used to make the tissue paper of the
present invention comprise at least 10%, and more preferably from about
20% to about 60% by weight, of coarse cellulose fibers selected from the
group consisting of recycled fibers, chemi-thermomechanical fibers and
mixtures thereof.
Softness, as used herein, refers to the tactile quality of a tissue
paper, as judged relatively by expert panel and reported in average panel
judging units.
Softness is known to be affected by structural artifacts of
papermaking other than the fiber morphology as disclosed herein. For
example, it is well known to those skilled in the art that softness of
sanitary
tissue is a function of its weighfiand tensile strength.
This is true of articles made according to the present invention as
- well. Inventors express the combination of these parameters as a ratio
WO 96104424 PCTIUS95/08741
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wherein the tensile strength, in glin is divided by basis weight, in glm2.
This ratio is referred to herein as the specific tensile strength. The
specific
tensile useful for the present invention ranges from about 9 glin/glm2 to
about 25 g/in/glm2, and, more preferably, from about 11 glin/g/m2 to 17
glinlg/m2.
Softness is further affected by the bulk resultant from the type of
forming and drying performed in papermaking. For example, U.S. Patent
3,301,746 issued to Sanford and Sisson in 1967 was pivotal in defining
means of preparing exceptionally soft paper useful for sanitary tissues and
the like. This art recognized the importance of density in providing
softness.
The term density, as used herein, is calculated from the thickness
and the weight per unit area, wherein the thickness is determined using
any suitably calibrated caliper capable of subjecting the specimen to a
uniform compressive load of 95 g/in2. The density ranges useful for the
present invention range from about .05 glcc to about 0.2 glcc, preferably
from about .08 g/cc to about 0.15 glcc.
As used herein, the term centrifugal screen refers to a pressure
screen such as the Model 100 Centrisorter, a tradename of the Bird
Machinery Corporation of South Walpole, MA, equipped with a screen
basket with hole size capable of separating the fibers in an inlet stream
into two fractions having a measurable length difference.
The term fiber length, as used herein, refers to the weighted
average fiber length as determined on the Kajaani FS-200, described in
detail hereinafter. Preferably, the tissue papers of the present invention
have a composite average fiber length between about 1 mm and about 1.5
mm.-
The term hydraulic cyclone, as used herein, refers to a device such
as a 3°' Centricleaner, a tradename of the Sprout-Bauer Company of
Springfield, OH.
A. Tissue Papers
The present invention is a soft tissue paper comprised of chemically
softened cellulose fibers. The chemically softened cellulose fibers
WO 96!04424 PCT/US95108741
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comprise a sufficient amount of coarse fibers to raise the composite
average coarseness of the tissue paper to greater than about 11.0
mg1100m. The chemically softened cellulose fibers have a depressed
coefficient of friction (DCOF, in percentage points) related to the
composite average coarseness (C), in mg1100m, by the equation:
DCOF > 4.27 * C - 44.23, more preferably,
DCOF>4.75*C -44.23
The tissue paper has a specific tensile strength between about 9
and about 25 g/in/glm2 and a density between about 0.05 and about 0.20
glcc.
The present invention is useful with tissue paper in general,
including but not limited to conventionally felt-pressed tissue paper; high
bulk pattern densified tissue paper; and high bulk, uncompacted tissue
paper. The tissue paper can be of a homogenous or multi-layered
construction; and tissue paper products made therefrom can be of a
single-ply or multi-piy construction. The tissue paper preferably has a
basis weight of between about 10 glm2 and about 65 glm2, and density of
about 0.6 glcc or less. More preferably, the basis weight will be about 40
glm2 or less and the density will be about 0.3 g/cc or less. More
preferably, the density will be between about 0.05 glcc and about 0.2 glcc,
and most preferably, from about 0.08g1cc to about 0.15g/cc. See Column
13, lines 61-67, of U.S. Patent 5,059,282 (Ampulski et al), issued October
22, 1991, which describes how the density of tissue paper is measured.
(Unless otherwise specified, all amounts and weights relative to the paper
are on a dry basis.)
fn one preferred embodiment of the present invention, the tissue
papers are of a single ply, multi-layered construction. Preferably, the
single ply comprises three superposed layers, an inner layer and two outer
layers, with the inner layer being located between the two outer layers.
The inner layer preferably comprises cellulose fibers with a length-
weighted average length of at least about 1 mm, and each of the two outer
layers preferably comprises fibers with a length-weighted average length
less than about 1 mm. In this preferred embodiment the inner layer
comprises from about 15% to about 35% of the total sheet weight. The
WO 96/04424 PCTlIJS95/08741
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coarse cellulose fibers are selected from a group consisting of recycled
fibers, chemi-thermomechanical fibers and mixtures thereof. The coarse
fibers are preferably located in the outer layers where they comprise at
least about 10% and more preferably from about 20 to about 60% of the
total sheet weight and at least about 12% and, more preferably from about
25 to about 75% by weight, of the outer layers.
Conventionally pressed tissue paper and methods for making such
paper are well known in the art. Such paper is typically made by
depositing a papermaking furnish on a foraminous forming wire, often
referred to in the art as a Fourdrinier wire. Once the furnish is deposited
on the forming wire, it is referred to as a web. The web is dewatered by
pressing the web and drying at elevated temperature. The particular
techniques and typical equipment for making webs according to the
process just described are well known to those skilled in the art. In a
typical process, a low consistency pulp furnish is provided from a
pressurized headbox. The headbox has an opening for delivering a thin
deposit of pulp furnish onto the Fourdrinier wire to form a wet web. The
web is then typically dewatered to a fiber consistency of between about 7%
and about 25% (total web weight basis) by vacuum dewatering and further
dried by pressing operations wherein the web is subjected to pressure
developed by opposing mechanical members, for example, cylindrical rolls.
The dewatered web is then further pressed and dried by a steam drum
apparatus known in the art as a Yankee dryer. Pressure can be developed
at the Yankee dryer by mechanical means such as an opposing cylindrical
drum pressing against the web. Multiple Yankee dryer drums can be
employed, whereby additional pressing is optionally incurred between the
drums. The tissue paper structures that are formed are referred to
hereafter as conventional, pressed, tissue paper structures. Such sheets
are considered to be compacted since the entire web is subjected to
substantial mechanical compressional forces while the fibers are moist and
are then dried while in a compressed state.
Preferably, the tissue papers of the present invention are pattern
densified. Pattern densified tissue paper is characterized by having a
relatively high bulk field of relatively low fiber density and an array of
densified zones of relatively high fiber density. The high bulk field is
alternatively characterized as a field of pillow regions. The densified
WO 96IO~i.i2~ PCTIL'S95i08"s t
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zones are alternatively referred to as knuckle regions. The densified
zones are dispersed within the high bulk zone. The densified zones can
be discretely spaced within the high bulk field or can be interconnected,
either fully or partially, within the high bulk field. The patterns can be
formed in a nonornamental configuration or can be formed so as to provide
an ornamental designs) in the tissue paper. Preferred processes for
making pattern densified tissue webs are disclosed in U.S. Patent No.
3,301,746 (Sanford et al), issued January 31, 1967; U.S. Patent No.
3,974,025 (Avers), issued August 10, 1976; and U.S. Patent No. 4,191,609
(Trokhan) issued March 4, 1980; and U.S. Patent 4,637,859 (Trokhan)
issued January 20, 1987.
In general, pattern densified webs are preferably prepared by
depositing a papermaking furnish on a foraminous forming wire such as a
Fourdrinier wire to form a wet web and then juxtaposing the web against
an an-ay of supports. The web is pressed against the array of supports,
thereby resulting in dens~ed zones in the web at the locations
geographically con-esponding to the points of contact between the array of
supports and the wet web. The remainder of the web not compressed
during this operation is referred to as the high bulk field. This high bulk
field can be further dedensified by application of fluid pressure, such as
with a vacuum type device or a blow-through dryer, or by mechanically
pressing the web against the an-ay of supports. The web is dewatered,
and optionally predried, in such a manner so as to substantially avoid
compression of the high bulk field. This is preferably accomplished by
fluid pressure, such as with a vacuum type device or blow-through dryer,
or alternately by mechanically pressing the web against an array of
supparts wherein the high bulk field is not compressed. The operations of
dewetering, optional predrying and formation of the densified zones can be
integrated or partially integrated to reduce the total number of processing
steps performed. Subsequent to formation of the densified zones,
dewatering, and optional predrying, the web' is dried to completion,
preferably still avoiding mechanical pressing. Preferably, from about
8°~ to
about 5S°~ of the tissue paper surface comprises densified knuckles
having a relative density of at least 125°.6 of the density of the high
bulk
field.
The array of supports is preferably an imprinting carrier fabric
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PCT,~:595i087.~ 1
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having a patterned displacement of knuckles that operate as the array of
supports that facilitate the formation of the densified zones upon
application of pressure. The pattern of knuckles constitutes the array of
supports previously referred to. Suitable imprinting carrier fabrics are
disclosed in U.S. Patent No. 3,301,746 (Sanford et al), issued
January 31, 1967; U.S. Patent No. 3,821,068 (Salvucci et al), issued
May 21, 1974; U.S. Patent No. 3,974,025 (Avers), issued August 10, 1976:
U.S. Patent No. 3,573,164 (Friedberg et al.), issued March 30, 1971: U.S.
Patent No. 3,473,576 (Amneus), issued October21, 1969; U.S. Patent No.
4,239,065 (Trokhan), issued December 16, 1980; and U.S. Patent No.
4,528,239 (Trokhan), issued July 9, 1985.
Preferably, the furnish is first formed into a wet web on a foraminous
forming carrier, such as a Fourdrinier wire. The web is dewatered and
transferred to an imprinting fabric. The furnish can alternately be initially
deposited on a foraminous supporting carrier that also operates as an
imprinting fabric. Once formed, the wet web is dewatered and, preferably,
thermally predried to a selected fiber consistency of between about 40%
and about 80°r6. Dewatering is preferably performed with suction boxes
or
other vacuum devices or with blow-through dryers. The knuckle imprint of
the imprinting fabric is impressed in the web as discussed above, prior to
drying the web to completion. One method for accomplishing this is
through application of mechanical pressure. This can be done, for
example, by pressing a nip roll that supports the imprinting fabric against
the face of a drying drum, such as a Yankee dryer, wherein the web is
disposed between the nip roll and drying drum. Also, preferably, the web
is molded against the imprinting fabric prior to completion of drying by
application of fluid pressure with a vacuum device such as a suction box,
or with a blow-through dryer. Fluid pressure can be applied to induce
impression of densified Zones during initial dewatering, in a separate,
subsequent process stage, or a combination thereof.
Uncompacted, nonpattem-densified tissue paper structures are
described in U.S. Patent No. 3,812,000 (Salvucci et al), issued
May 21, 1974 and U.S. Patent No. 4,208,459 (Bedcer et al), issued
June 17, 1980. In general, uncompacted, nonpattern-densified tissue paper
structures are prepared
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WO 96/04424 j f ~ II ~ 7 ~ PCT/US95I08741
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by depositing a papermaking furnish on a foraminous forming wire such as
a Fourdrinier wire to form a wet web, draining the web and removing
additional water without mechanical compression until the web has a fiber
consistency of at least about 80%, and creping the web. Water is removed
from the web by vacuum dewatering and thermal drying. The resulting
structure is a soft but weak, high bulk sheet of relatively uncompacted
fibers. Bonding material is preferably applied to portions of the web prior
to creping.
Compacted non-pattern-densified tissue structures are commonly
known in the art as conventional tissue structures. In general, compacted,
non-pattern-densified tissue paper structures are prepared by depositing a
papermaking furnish on a foraminous wire such as a Fourdrinier wire to
form a wet web, draining the web and removing additional water with the
aid of a uniform mechanical compaction (pressing) until the web has a
consistency of 25-50%, transferring the web to a thermal dryer such as a
Yankee and creping the web. Overall, water is removed from the web by
vacuum, mechanical pressing and thermal means. The resulting structure
is strong and generally of singular density, but very low in bulk,
absorbency and softness.
B. Coarseness & Fiber Len4th Determination
The term "average fiber length, as used herein,. refers to the length
weighted average fiber length as determined with a suitable fiber length
analysis instrument such as a Kajaani Model FS-200 fiber analyzer
available from Kajaani Electronics of Norcross, Georgia. The analyzer is
operated according to the manufacturer's recommendations with the report
range set at 0 mm to 7.2 mm and the profile set to exclude fibers less than
0.2 mm in length from the calculation of fiber length and coarseness.
Particles of this size are excluded from the calculation because it is
believed that they consist largely of non-fiber fragments which are not
functional for the uses toward which the present invention are directed.
The term "coarseness", abbreviated "C" in the algebraic formulae
contained herein, refers to the fiber mass per unit of unweighted fiber
length reported in units of milligrams per ten meters of unweighted fiber
~ length (mg1100m) as measured using a suitable fiber coarseness
WO 96/04424 PCT/US95108741
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measuring device such as the above mentioned Kajaani FS-200 analyzer.
The coarseness C of the pulp is an average of three coarseness
measurements of three fiber specimens taken from the pulp. The
operation of the analyzer for measuring coarseness is similar to the
operation for measuring fiber length. Care must be taken in sample
preparation to assure an accurate sample weight is entered into the
instrument.
An acceptable method is to dry two aluminum weighing dishes for
each fiber specimen in a drying oven for thirty minutes at 110° C. The
dishes are then placed in a desiccator having a suitable desiccant such as
anhydrous calcium sulfate for at least fifteen minutes to cool. The dishes
should be handled with tweezers to avoid contaminating them with oil or
moisture. The two dishes are taken out of the desiccator and immediately
weighed together to the nearest 0.0001 gram.
Approximately one gram of a fiber specimen is placed in one of the
dishes, and the two dishes (one empty) are placed uncovered in the drying
oven for a period of at least sixty minutes at 110° C to obtain a bone
dry
fiber specimen. The dish with the fiber specimen is then covered with the
empty dish prior to removing the dishes from the oven. The dishes and
specimen are then removed from the oven and placed in a desiccator for at
least 15 minutes to cool. The covered specimen is removed and
immediately weighed with the dishes to within 0.0001 gram. The
previously obtained weight of the dishes can be subtracted from this
weight to obtain the weight of the bone dry fiber specimen. This weight of
fiber is referred to as the initial sample weight.
An empty 30 liter container is prepared by cleaning it and weighing it
on a scale capable of at least 25 kilograms capacity with 0.01 gram
accuracy. A standard TAPPI disintegrator, such as the British disintegrator
referred to in TAPPI method T205, is prepared by cleaning its container to
remove all fibers. The initial sample weight of fibers is emptied into the
disintegrator container, ensuring that all fibers are transferred to the
disintegrator.
The fiber sample is diluted in the disintegrator with about 2 liters of
water and the disintegrator is run for ten minutes. The contents of the
disintegrator are washed into the 30 liter container, ensuring that all fibers
are washed into the container. The sample in the 30 liter container is then
PCT/US95108741
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diluted with water to obtain a water-fiber slurry weighing 20 kilograms,
within 0.01 gram.
The sample beaker for the Kajaani FS-200 is cleaned and weighed to
within 0.01 gram. The slurry in the 30 liter container is stirred with
vertical
and horizontal strokes, taking care to not set up a circular motion which
would tend to centrifuge the fibers in the slurry. A 100.0 gram measure
accurate to within 0.1 gram is transferred from the 30 liter container to the
Kajaani beaker. The fiber weight in the Kajaani beaker, in milligrams, is
obtained by multiplying five (5) times the initial sample weight (as recorded
in grams).
This fiber weight, which is accurate to 0.01 mg, is entered into the
Kajaani FS-200 profile. A minimum fiber length of 0.2 mm is entered into
the Kajaani profile so that 0.2 mm is the minimum fiber length considered
in the coarseness calculation. A preliminary coarseness is then calculated
by the Kajaani FS-200.
The coarseness is obtained by multiplying this preliminary
coarseness value by a factor corresponding to the weight weighted
cumulative distribution of fibers with length greater than 0.2 mm. The FS-
200 instructions provide a method for obtaining this weight weighted
distribution. However, the values are reported as a percentage and are
accumulated beginning at "0" fiber length. To obtain the factor described
above, the "weight-weighted cumulative distribution of fibers with length
less than 0.2 mm" (which is provided as an output of the instrument) is
obtained from the instrument display. This display value is subtracted from
100, and the result is divided by 100 to obtain the factor corresponding to
the weight weighted cumulative distribution of fibers with length greater
than 0.2 mm. The resulting coarseness is therefore a measure of the
coarseness of those fibers in a fiber sample having a fiber length greater
than 0.2 mm. The coarseness measurement is repeated, starting with
oven drying two weighing dishes and a fiber specimen, to obtain three
values of coarseness. The value of coarseness C used herein is obtained
by averaging the three coarseness values and converting the units to
express the value in mg1100m.
WO 96J04~i2.i PCTIL'S95i08~.i 1
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C. Coefficient of Friction
The coefficient of friction is obtained using a KES-4BF surface
analyzer with a modified friction probe as described in "Methods for the
Measurement of the Mechanical Properties of Tissue Paper", Ampulski, et.
al., 1991 International Paper Physics Conference, published by TAPPI
press ,
The substrate used for the friction evaluation, as disclosed herein,
is a laboratory prepared handsheet, prepared according to TAPPI standard
T-205 incorporated herein by reference . The friction is measured on the
smooth side of the handsheet (the side which is dried against a metal plate
according to the method).
The substrate is advanced at 1 mmlsec constant rate for the
measurement and the friction probe is modified from the standard
instrument probe to a two centimeter diameter 40-60 micron glass frit.
When using a 12.5 g normal force on the probe and the heretofore
specified translation rate for the substrate, the coefficient of friction can
be
calculated by dividing the frictional force by the normal force. The
frictional force is the lateral force on the probe during the scanning, an
output of the instrument.
The average of coefficient of friction obtained by a single scan in
the forward direction and a single scan in the reverse direction is reported
as the coefficient of friction far the specimen.
Therefore, to measure the depressed coefficient of friction of a fiber
furnish, a standard handsheet is prepared using a sample of the fibers
without chemical softener and a standard handsheet is prepared using a
sample of the fibers after addition of the chemical softener. The coeffccient
of friction is measured using each handsheet, and the DCOF is computed
using the following formula:
OCOF = 'COFR - COFA X 100
COF~ ''
Where OCOF is the depressed coefficient of friction and COFg and
COFA are the coefficient of friction of the handsheet made from untreated
_. . :-~~.,w.
WO 96/04424 PCTIUS95108741
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fibers and those from fibers treated with chemical softener, respectively.
D. Coarse Cellulose Fibers
While many suitable sources of coarse cellulose fibers can be
applied to make tissue paper according to the present invention, two
embodiments are preferred for its practice.
One preferred embodiment employs a chemi-thermomechanical
pulp derived from hardwood fibers, such as Aspen CTMP.
A second preferred embodiment employs recycled fibers. If
recycled fibers are employed in the present invention, it is preferred that
they be pre-conditioned according to the following process steps to most
favorably dispose them to the product use.
These include the two basic arrangements of two stage fractionating
processes comprising a length classifying stage and a centrifuging stage.
Figure 1 is a flow diagram depicting one arrangement which can be
used to produce cellulose pulps preferred for use in the tissue papers of
the present invention. In this arrangement, the length classifying stage is
performed first, followed by the centrifuging stage.
In Figure 1, an aqueous slurry 21 comprising wood pulp fibers is
directed to form the input stream to a length classifying stage 32. A
satisfactory length classifier is a centrifugal pressure screen such as a Bird
"Centrisorter" manufactured by the Bird Escher Wyss Corporation of South
Walpole, Massachusetts. The slurry 21 is processed in the length
classifying stage 32 to provide an accepts stream 33 of the classifying
stage 32 and a rejects stream 34 of the classifying stage 32. The rejects
stream-34 comprises fibers having an average fiber length exceeding that
of the fibers in the accepts stream 33. The length classifying stage 32 is
configured and operated as described below to provide the accepts stream
33 having an average fiber length which is at least 20%, and preferably at
least 30% less than the average fiber length of the rejects stream
comprising slurry 34. The fibers in rejects stream 34 are directed to
alternative end uses where the characteristics sought as objectives of the
present invention are less valued. In this regard they may be blended with
other rejects streams, maintained separate or discarded.
WO 96104424 ;~ i ~~ L~_ ~ 7 ~ PCT/US95108741
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Without being limited by theory, the fiber weight of the accepts
stream 33 of the length classifying stage 32 should be between about 30 to
70 percent of the fiber weight of the input stream to the length classifying
stage 32, so that there is about a thirty to seventy percent mass split of the
fibers entering the length classifying stage 32 between the accepts stream
33 and the rejects stream 34. Such a mass split is desirable to ensure that
length classifying stage 32 functions to fractionate the input stream by fiber
length, rather than just functioning to remove debris such as knots and
shives from the input stream.
At least a portion of the accepts stream 33 of the length classification
stage 32 is directed as shown in Figure 1 to provide an input stream 41 to
a second fractionation stage comprising a centrifuging stage 42. A
satisfactory centrifuging stage 42 comprises one or more hydraulic
cyclones; such as 3 inch "Centricleaner" hydraulic cyclones manufactured
by the CE Bauer Company of Springfield, Ohio.
For best operation of the centrifuging stage 42, it may be necessary
to adjust the consistency of the input stream 41 to the centrifuging stage
42 prior to processing the input stream 41 in the centrifuging stage 42. For
instance, if it is desirable to remove water from input stream 41 to increase
the consistency of input stream 41, a suitable sieve 36 can be positioned
intermediate the length classifying stage 32 and the centrifuging stage 42,
as illustrated in Figure 1. A suitable sieve 36 comprises a CE Bauer
"Micrasieve" equipped with a 100 micron screen.
The centrifuging stage 42 processes input stream 41 to provide an
accepts stream 43 of the centrifuging stage 42 and a rejects stream 44 of
the centrifuging stage 42. The accepts stream 43 exits the overflow side of
the hydraulic cyclone and the rejects stream 44 exits the underflow side
(the "tip") of the hydraulic cyclone.
When the process depicted in Figure 1 is operated according to the
3o present invention, the normalized coarseness of the fibers in accepts
stream 43 is at least 3 percent, and preferably at least 10 percent less than
that of the fibers in the rejects stream 44 of .the centrifuging stage 42. The
process depicted in Figure 1 can be operated to provide an accepts
stream 43 comprising the cellulose pulps preferred for the present
invention.
WO 96104424 ~ ~ ~ ~_ r, ~ ~ PCTlUS95108741
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The accepts stream 43 comprising the cellulose pulps of the present
invention includes at least 10 percent softwood fibers, has an incremental
surface area less than 0.085 square millimeters, and has a coarseness
related to average fiber length by the algebraic expression recited above.
The average fiber length of the accepts stream 43 is preferably about 0.70
mm to about 1.1 mm, and more preferably about 0.75 mm to about 0.95
mm to provide this coarseness to fiber length relationship.
The fiber weight of the accepts stream 43 of the centrifuging stage 42
should be between about 30 to 70 percent of the fiber weight of the input
stream 41 to the centrifuging stage 42, so that there is about a thirty to
seventy percent mass split of the fibers entering the centrifuging stage 42
between the accepts stream 43 and the rejects stream 44, respectfully.
Such a mass split is desirable to ensure that the centrifuging stage 42
provides an accept stream 43 having a reduced normalized coarseness
relative to rejects stream 44, rather than just functioning to remove debris
such as knots and shives from the input stream 41.
Figure 2 is a flow diagram depicting another arrangement which can
be used to produce cellulose pulps preferred for use in the tissue papers
of the present invention. In this arrangement, the centrifuging stage is
performed first, followed by the length classifying stage.
In Figure 2, an aqueous slurry 21 comprising wood pulp fibers is first
directed to form the input stream to the centrifuging stage 52. The
centrifuging stage 52 comprises at least one hydraulic cyclone. The
centrifuging stage 52 processes the input stream to provide an accepts
stream 53 of the centrifuging stage 52 and a rejects stream 54 of the
centrifuging stage 52. The accepts stream 53 exits the overflow side of the
hydraulic cyclone, and the rejects stream exits the under flow side (the tip)
of the hydraulic cyclone. When operated according to the present
invention, the normalized coarseness of the fibers in accepts stream 53 is
at least 3 percent, and preferably at least 10 percent less than that of the
fibers in the rejects stream 54 of the centrifuging stage 52, and the
average fiber length of the fibers in the accepts stream 53 is preferably
about equal to or greater than that of the slurry 21.
At least a portion of the accepts stream 53 of the centrifuging stage
52 is directed to provide an input stream 61 to a length classifying stage
62. The length classifying stage 62 can comprise a screen, such as the
WO 96104424 ~ ~ ~ ~ ~ ~ PCT/US95108741
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centrifugal screen described above. It may be desirable to adjust the
consistency of the input stream 61 prior to processing the input stream 61
in the length classifying stage 62. For instance, if it is desirable to remove
water from input stream 61 to increase its consistency, a suitable sieve 60
can be positioned intermediate the centrifuging stage 52 and the length
classifying stage 62 as illustrated in Figure 2. A suitable sieve 60
comprises a CE Bauer "Micrasieve" equipped with a 100 micron screen.
The length classifying stage 62 processes input stream 61 to provide
an accepts stream 63 of the length classifying stage and a rejects stream
64 of the length classifying stage. The rejects stream 64 comprises fibers
having an average fiber length exceeding that of the fibers in the accepts
stream 63. The average fiber length is at least 20 percent less, and
preferably at least 30 percent less than the average fiber length of the
rejects stream 64 to the length classification stage.
The process depicted in Figure 2 can be operated to provide an
accepts stream 63 comprising the cellulose pulps preferred for the present
invention. The accepts stream 63 comprising the cellulose pulps of the
present invention includes at least 10 percent softwood fibers, has an
incremental surface area less than 0.085 square millimeters, and has a
coarseness related to average fiber length by the algebraic expression
recited above. The average fiber length of the accepts stream 63 is
preferably about 0.7 mm to about 1.1 mm, and more preferably about 0.75
mm to about 0.95 mm to provide the aforementioned coarseness to fiber
length relationship.
The operating parameters of the length classification and centrifuging
stages can be adjusted for the specific characteristics of the fibers
contained in slurry 21 in order to achieve the necessary change in the
average fiber length and normalized coarseness respectively required by
the present invention. For the embodiment wherein the length
classification stage comprises a centrifugal screen, such operating
parameters include the consistency of the input and output slurry; the size,
shape, and density of perforations in the screen media; the speed at which
the screen pulsator rotates; and the flow rates of the inlet and each of the
outlet streams.
It may also be desirable to use dilution water to aid in the removal of
the longer fiber rejects stream from the screen in the sieve 60 if it tends to
WO 96104424 ,,, k ~ PCT/US95/08741
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be excessively thickened by the action of the screen. For the embodiment
wherein the centrifuging stage comprises a hydraulic cyclone; examples of
operating parameters include the consistency of the input stream, the
diameter of the cone, the cone angle, the size of the underflow opening,
and the pressure drop from the inlet slurry to each leg of the outlet.
E. Fiber Treatment with Chemical Softener
The present invention requires that the cellulose fibers possess a
depressed coefficient of friction achieved via the addition of a chemical
softener.
The preferred method of adding the chemical softener to the cellulose
fibers is to add the softener to an aqueous slurry of papermaking fibers, or
furnish, in the wet end of the papermaking machine at some suitable point
ahead of the fourdrinier wire or sheet forming stage. However, since the
chemical softeners within the scope of this invention are expressly
substantive to the fibers, applications of the chemical softeners prior to the
papermaking process, for example by adding to aqueous pulp mixtures
formed during production of the pulp are also anticipated. In addition,
chemical softener application subsequent to the formation of the tissue
web, including points prior to, during, or after drying can also be designed
to meet the requirements of the present invention and are expressly
included within its scope.
The following examples illustrate the practice of this invention, but are not
intended to be limiting thereof.
EXAMPLE 1
This example illustrates the preparation of a single-ply bath tissue
product utilizing a recycled fiber source normally regarded as being inferior
for making this type of product.
The cellulose fiber types used in the preparation are:
Northern Softwood Kraft (NSK) pulp, eucalyptus hardwood Kraft
pulp and a market recycled pulp, obtained from Ponderosa Fibers'
Oshkosh, WI mill.
WO 96104424 f ~ ~ C~ ~ ~ ~ PCT/U595/08741
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The virgin Kraft pulps are used as delivered, while the Ponderosa
pulp is pre-treated by forming an aqueous slurry and subjecting it to a
sequential treatment in a centrifugal screen from which a short fiber
fraction is acquired which is then passed through a hydraulic cyclone, from
which the accepts or overflow fraction is captured.
The screening accepts are about 25% of the feed material and have
a fiber length about 50% lower than the starting pulp. A single-pass
through the cyclones is taken at about 75 psi pressure drop from inlet to
accepts and 0.1 % solids in the feed. The accepts accordingly comprise
about 50% of the fiber which is fed to them. This step is known from
previous work to result in a fiber with exceptionally low coarseness as a
function of its fiber length.
While highly useful in reducing the negative effects of the recycled
fiber, the above fractionating treatment is known to be only effective at
permitting use of the recycled fiber as a partial component of soft tissue
products.
To allow even higher inclusion of the recycled fiber, the resultant
tissue product is formed so that it conforms to the practice of the present
invention.
The papermaking is done on a pilot scale Fourdrinier papermaking
machine. This papermaking machine is operated with enough whitewater
purge to assure that essentially no non-substantive additives will remain in
the papermaking web after draining on the forming wire.
First a 1 % solution of a quaternary salt (dihydrogenated tallow
dimethyl ammonium methyl sulfate), obtained from Witco Chemical
Company of Dublin, OH is prepared. To aid in the preparation of this
solution, an equivalent amount of polyethylene glycol of 400 molecular
weight is optionally included. The quaternary salt, with the PEG optionally
added, are first heated to about 150°F, then added to water at about
the
same temperature while the water is being agitated.
The papermaking headbox is equipped with separator leaves so
that long NSK fibers and the shorter eucalyptus or recycled fibers can be
laid down in separate layers to deposit each fiber type in its optimum
location. This type of forming is common and will be recognized as such
by those skilled in the art.
WO 96104424 PCTIUS95108741
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Two comparative paper structures are formed.
The first is formed by directing 20% of the sheet weight as NSK into
the center layer of a three-layered composite wherein the outer layers are
comprised exclusively of the eucalyptus pulp.
The second is formed by directing 20% of the sheet weight as NSK
into the center layer of a three-layered composite wherein the outer layer
next to the forming wire is comprised exclusively of the pre-treated
recycled pulp, and the other outer layer is comprised of a blend of the pre
treated recycled pulp with eucalyptus in a proportion of 3:5 by weight. The
overall content of the recycled pulp is therefore 55%.
Otherwise, the forming is completed similarly on the two furnishes.
When forming the structure comprised of the recycled pulp, the quaternary
salt is added to the stocks during approach flow when their consistencies
are about 3%. The quaternary salt is proportioned so that the ratio added
to the wire-side furnish is twice that of the felt side furnish. No quaternary
salt is added to the NSK. The amount of quaternary salt added is
sufficient to retain 0.105% in the finished product. The only other change
necessary in the process when using the recycled fiber, is a slight refining
of the NSK to compensate for some strength losses.
Since the composite coarseness of this product is known to be in
excess of 11.0 and the level of treatment with the quaternary salt is
sufficient to result in a depression of coefficient of friction (DCOF) of more
than 4%, the product made in accordance with this example meets the
requirements laid out by this invention.
Confirmation is gained when the product containing the recycled
fibers is judged softer by a panel of expert softness judges.
EXAMPLE 2
This example illustrates the preparation of a single-ply bath tissue
product utilizing a chemi-thermomechanical fiber source normally regarded
as being inferior for making this type of product.
The cellulose fiber types used in the preparation are:
Northern Softwood Kraft (NSK) pulp, eucalyptus hardwood Kraft
pulp and a market hardwood CTMP pulp, designated as 86 brightness1350
freeness by the manufacturer which is the Quesnel River Pulp and Paper
-27-
Company.
The pulps are all used as delivered and the resultant tissue product
is formed so that it conforms to the practice of the present invention.
The papermaking is done on a pilot scale Fourdrinier papermaking
machine. This papermaking machine is operated with enough water purge
so that essentially no non-substantive additives will remain in the
papermaking web after draining on the forming wire.
First a 1 % solution of a quaternary salt (diester dihydrogenated
tallow dimethyl ammonium chloride), obtained from Witco Chemical
Company of Dublin, OH is prepared. To aid in the preparation of this
solution, an equivalent amount of polyethylene glycol of 400 molecular
weight is optionally included. The quaternary salt, with the PEG optionally
added, are first heated to about 185°F, then added to water at about
the
same temperature while the water is being agitated.
The papermaking headbox is equipped with separator leaves so
that long NSK fibers and the shorter eucalyptus or recycled fibers can be
laid down in separate layers to dep~sit each fiber type in its optimum
location. This type of forming is common and will be recognized as such
by those skilled in the art.
Two comparative paper structures are formed.
The first is formed by directing 20°~ of the sheet weight as NSK
into
the center layer of a three-layered composite wherein the outer layers are
comprised exclusively of the eucalyptus pulp.
The second is formed by directing 20% of the sheet weight as NSK
into the center layer of a three-layered composite wherein the outer layers
are supplied by a furnish comprising a blend of eucalyptus and CTMP in
proportions of 7:4. The overall content of the CTMP pulp is therefore
28°~.
Othervvise, the forming is completed similarly on the two furnishes.
When forming the structure comprised of the CTMP pulp, the quaternary
salt is added to the stocks during approach flow when their consistencies
are about 3%. The quaternary salt is proportionect~so that the ratio added
to the wire-side furnish is half that of the felt side furnish. No quaternary
salt is added to the NSK The amount of quaternary salt added is
sufficient to retain 0.325°r6 in the finished product.
WO 96104424 PCTIUS95108741
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Since the composite coarseness of this product is known to be in
excess of 11.0 and the level of treatment with the quaternary salt is
sufficient to result in a depression of coefficient of friction (DCOF) of more
than 10%, the product made in accordance with this example meets the
requirements laid out by this invention.
Confirmation is gained when the product containing the CTMP fibers
is judged softer by a panel of expert softness judges.
