Note: Descriptions are shown in the official language in which they were submitted.
SOFT, STRONG, ABSORBENT TISSUE
PAPER AND PROCESS THEREFOR
Thomas Ward Osborn III
BACKGROUND OF THE II~VENTION
Field of the Invention
This invention re.lates to tissue paper webs.
More particularly, it relates to soft, strong,
absorbent tissue paper webs which can be used in
toweling and sanitary and facial tissue products.
Background Art
Paper webs or sheets, sometimes called tissue
or paper tissue webs or sheets, find extensive us~
in modern society. Such items as paper towels and
facial ~issues are staple items of commerce. It
has long been recognized that three important
physical attributes of these produets are their
softness; their absorbeney, particularly their
absorbency for aqueous systems; and their strengkh~
particularly their strength when wet. Research
and development efforts have been directed to the
improvement of each of these attributes without
deleteriously affecting the others as well as to
the improvement of two or three attributes simul-
taneously.
Softness is the tactile sensation perceived
by the consumer as he holds a particular product,
rubs it across his skin, or crumples it within his
hand. This tactile sensation is a combination of
several physical properties. One of the more
important physical properties related to softness
is generally considered by those skilled in the
art to be the stiffness of the sheet of paper ~rom
which the product is made.
'72~
Absorbency is the measure of the ability of a
product, and of the paper tissue webs from which
the product is made, to absorb quantities of
liquid, particularly aqueous solutions or dis-
persions. Overall absorbency as perceived by thehuman consumer is generally considered to be a
combination of the total quantity of liquid a
given mass of tissue paper will absorb at saturation
as well as the rate at which the mass absorbs the
liquid.
Strength is the ability of the product, and
its constituent webs, to maintain physical integrity
and to resist tearing, bursting, and shredding
under use conditions.
One exemplary result of the research directed
toward improved paper webs is~described in U.S.
Patent 3,301,746 issued to Sanford and Sisson on
January 31, 1967. Despite the high quality of
paper webs made by the process described in this
patent, and despite the commercial success of
products formed from these webs, research efforts
directed to finding improved products have con-
tinued.
For example, Becker et al. in U.S. Patent
4,158,594 issued January 19, 1979 describe a
method they contend will form a strong, soft,
fibrous sheet. More specifically, they teach that
the strength of a tissue paper web (which may have
been softened by the addition of chemical debonding
agents) can be enhanced by adhering, during
processing, one surface of the web to a creping
surface in a fine patterned arrangement by a
bonding material, such as an acrylic latex rubber
emulsion, a water soluble resin, or an elastomeric
bonding material, which has been adhered to one
119~7~ ~
su~face of the web and to the creping surface in
the fine patterned arrangement, and creping the
web from the creping surface to form a sheet
material.
The use of materials such as wet strength
resins to enhance the strength of a paper web is
widely known. For example, Westfelt described a
number of such materials and discussed their
chemistry in Cellulose Chemistry And Technology,
Volume 13, at pages 813-825 (1979~.
Then, too, Friedman in U.S. Patent 4,277,529
issued July 7, 1981, purports to disclose a
bonded, light weight tissue paper having improved
strength and excellent softness and absorbency.
The paper is produced by a process which comprises
applying a binder containing a cross-linkable
~ latex to the drie~ web.
DISCLOSURE OF THE INVENTION
Summary of the Invention
The present invention is a process for pro-
ducing tissue paper webs having improved softness,
strength, and absorbency and the web so produced.
Briefly, the process comprises the steps of
forming a papermaking furnish and making from that
furnish a patterned densified fibrous web having a
relatively high bulk field of relatively low fiber
density and a patterned array of spaced zones of
relatively high fiber density at least a sub-
stantial proportion of which are at least partially
impregnated with binder material. The papermaking
furnish comprises an aqueous slurry of papermaking
fibers and at least one water-soluble cationic
resin. The binder material comprises at least one
~ 7
latex polymer having anionic functional groups in
the polymer backbone. The web comprises paper-
makîng fibers, cationic resin, and binder.
Accordingly, it is an object of this in-
S vention to provide a process for making soft,strong, absorbent tissue paper webs.
It is a further object of this invention to
provide soft, strong, absorbent tissue paper
sheets.
It is a still further object of this invention
to provide soft, strong, absorbent paper towel
products.
These and other objects will become readily
apparent from a reading of the following detailed
description of the invention.
Detailed Description of the Invention
Inhile this specification concludes with
claims particularly pointing out and distinctly
claiming the subject matter regarded as the
invention, it is believed that the invention can
be better understood from a reading of the fol-
lowing detailed description and of the appended
examples.
As used herein, the terms "tissue paper web",
"paper web", "web", and "paper sheet" all refer to
sheets of paper made by a process comprising the
steps of forming an aqueous papermaking furnish;
depositing this furnish on a foraminous surface,
such as a Fourdrinier wire; and removing the water
from the furnish, as by gravity or vacuum-assisted
drainage, with or without pressing, and by evapora-
tion. As discussed fully hereinafter, the furnish
comprises an aqueous slurry of papermaking fibers
and at least one water-soluble cationic resin.
Further, the resulting web preferably has a
relatively high bulk field of relatively low
fiber density and a patterned array of spaced
zones of relatively high fiber density at least a
S subs~antial proportion of which have been at
least partially impregnated with binder material.
The binder material is a latex as described more
fully hereinafter. The resulting web exhibits
softness, absorbency, and strength greater than
that produced by use of the cationic resin alone
or by the latex binder material alone. The
strength of the resulting web is ~lso greater
than that that would be expected from a knowledge
of the strength impro~ements provided by the
resin alone and the binder material alone.
As used herein, "papermaking furnish" is an
aqueous slurry of paper~aking ibers and chemicals
as desc~ibed hereinafter.
The firs~ step in the process of this in-
vention is the forming of an aqueous papermaking
furnish. This furnish comprises papermaking
fibers, (hereinafter sometimes reerred to as
wood pulp) and at least one water-soluble cationic
resin as hereinafter described.
It is anticipated that wood pulp in all its
varieties will normally comprise the papermaking
fibers used in this invention. However, other
cellulosic fibrous pulps, such as cotton liners,
bagasse, rayon, etc., can be used and none are
disclaimed. Wood pulps useful herein include
both sulphite and sulfate pulps as well as mechanical
and thermomechanical pulps all well known to
B those skilled in the art. Pulps derived from
both deciduous and coniferous trees can be used.
Preferably, the papermaking fibers used in this
invention comprise Kraft pulp derived from northern
softwoods.
The water-soluble cationic resins used in
this invention can be of several types. In general,
resins which have previously found utility in
papermaking as wet strength resins are useful
herein. It is to be understood that the cationic
resins are water-soluble at the time they are added
to the papermaking furnish. It is quite possible,
and even to be expected, that subsequent events
such as cross-linking will render the resins in-
soluble in water. Further, the cationic resins
can be soluble only under specific conditions, such
as in a limited pH range, and still be water-soluble
as that term is used herein. --
Of particular utility are the various poly-
amide-epichlorohydrin resins. These materials are
low molecular weight polymers provided with reactivP
functional groups such as amino, epoxy, and
azetidinium groupsO The patent literature is
reple~te with descriptions of processes for making
such materials. U.S. Patent 3,700,623 issued to
Keim on October 24, 1972 and U.S. Patent 3,772,076
issued to Keim on ~ovember 13, 1973 are examples
of such paten~s.
Polyamide-epichlorohydrin resins sold under
the trademarks"KYmene 557H" and "xymene 2064" by
, Hercules Incorporated of Wilmington, Delaware, are
particularly useful in this invention. These
resins are generally described in the aforementioned
patents to Keim.
31'~ 7
-- 7 --
Base~activated polyamide-epichlorohydrin
resins useful in the present invention are sold
under the~santo Res" trademark, such as "santo Res
31, by Monsanto Company, St. Louis, Missouri. These
types of materials are generally described in U.S.
Patents 3,855,15~ issued to Petrovich on December
17, 1974; 3,899,388 issued to Petrovich on August
12, 1975; 4,129,528 issued to Petrovich on December
12, 1978; 4,147,586 issued to Petrovich on April
3, 1979; and 4,222,921 issued to Van Een~m on
September 16, 1980.
Other water-soluble cationic resins useful
herein are the polyacrylamide resins such as those
sold under the"Parez"trademark, such as"ParPz
631NC, by American Cyanamid Company of Stanford,
Conn. These materials are generally described in
~ U.S. Patents 3,556,932 issued to Coscia et al on
January 19, 1971; and 3,5569933 issued to Williams
et al on January 19, 1971.
Still other water-soluble cationic resins
finding utility in this invention are the urea
formaldehyde and melamine formaldehyde resins.
These polyfunctional, reactive polymers have
molecular weights on the order of a few thousand.
The more common functional groups include nitrogen
containing groups such as amino groups and methylol
groups attached to nitrogen.
Although less preferred, polyethylenimine
type resins find utility in the present invention.
3~ More complete descriptions of the afore-
mentioned water-soluble cationic resins, including
their manufacture, can be found in TAPPI monograph
P~j
.~L'3 ~7'~7
- 8
series No. 29, Wet Strength In ~e~ and ~perboard,
Technical Association of the Pulp and Paper
Industry (New York; 1965)
It is anticipated that this invention will
find its primary utility in the field of toweling,
facial tissue, and similar products requiring wet
strength properties. The water-soluble cationic
resin has accordingly been described as a wet
strength resin. The present invention also finds
utility in products such as sanitary tissues where
wet strength is not required, but where dry strength
is a positive attribute. When use in this type
of product is contemplated, the water-soluble
cationic resin can be any of the various dry
strength resins commonly used in papermaking. For
example, products sold under the 'lAccostrengthll
trademark by American Cyanamid Company can be used
herein. "Accostrength 98" ,T for example, is described
, as being a normally water-insoluble polysalt
coacervate rendered water-soluble by the inclusion
of an ionization suppressor and is useful herein.
~U.S. Patent 3,660,338 issued to Economou on May2, 1972,
describes such materials mor ~ully.) These dry
strength resins can be used on ~he same basis as
the wet strength resins.
The papermaking furnish can be readily formed
or prepared by mixing techniques and equipment
well known to those skilled in the papermaking
art.
In its broadest aspect, the next stage in the
process of this invention is the formation of an
embryonic web from the papermaking furnish. This
embryonic web is then at least partially impregnated
with binder material (preferably in discrete, spaced
. ~, .
4'7
.
_ 9 _
apart zones) and then dried to form the web of
this invention.
It has been surprisin~ly discovered that the
following described unique, preferred papermaking
process is particularly useful for making a tissue
paper web of such strength as to be use~ul in a
wide variety of soft, strong, absorbent products.
The tissue paper web in which the present in-
vention preferably finds utility is a pattern
densified fibrous web having a relatively high
bulk field of relatively low fiber density and a
patterned array of spaced zones of relatively high
fiber density. At least a substantial proportion
of the relatively high density spaced zones are at
least partially impregnated with binder material.
The high bulk field is preferably substantially
uncompacted and devoid of binder material.
- Accordingly, the second step in the preferred
embodiment of the process of this invention com-
prises the forming from the papermaking furnish a
patterned densified embryonic web ha~ing a multi-
plicity of discrete zones of relatively high
density disposed in a predeiermined pattern array.
The third step of the preferred comprises
supporting the embryonic web on an array of spaced
supports so that each of a predetermined sub-array
of the high density zones is juxtaposed one of a
corresponding sub-array of the supports.
The array of spaced supports can be the knuckles
of an endless imprinting carrier fabric and the
sub-array of such supports can be only t~e top-sur-
face-plane knuckles of the fabric in fabrics having
both top-surface-plane knuckles and sub-top-surface
7~
- 10 -
knuckles. In fabrics having no sub-top-surface
knuckles, the sub-array of supports would, in
fact, be the array of supports.
The ourth step of the preferred process is
at least partially impregnating at least a substantial
proportion of the supported predetermined sub-
array of high density zones with a binder material
by biasing the predetermined sub-array of supports
toward a contacting type impregnating means with
the sub-array of the high density zones disposed
between ~he sub-array of the supports a~d ~he
impregnating means. ~or maximum strengt~, all of
the high density zones should be impregnated with
binder material. Only a portion of the high
density zones need be partially impregnated in
webs wherein such partial impregnation provides
sufficient strength for their intended use.
Impregnating means such as a full field
gravure applicator can be used to impregnate the
high density zones of the webs biased against it
whereas less-than-full-field gravure applicators
can be used to only partially im~regnate all or
some of the high density zones o the web, or
wholly impregnate only some of the high density
zones. The impregnation accomplished in this
fourth step must be accomplished before the
embryonic web is substantially dried. As used
herein, the embryonic web is not substantially
dried if it contains at least about 25% moisture.
(Unless otherwise specified, all percentages in
this specification are weight percentages.)
The la~ices used herein are aqueous emulsions
of synthe~ic rubbers or plastics obtained by poly-
~ '7~';'
meriza~ion, They can be, but need not be, curableas by cross-linking. The polymer struc~ure must
contain anionic functional groups which provide an
anionic character to the latex. Examples of suitable
functional groups include carboxyl, sulfonate,
phosphonate and hydroxyl groups. Carboxyl groups
are preferred~ These functional groups are
sometimes said to be present in the polymer
"backbone". Further, the polymer structure can
contain more ~han one ~ype of anionic functional group.
Recent developments in latex chemistry have
resulted in the creatio~ of latices which are
considered to be`cationic, but which contain
normally anionic functional g~oups such as carboxyl
groups within the polymer structure; such latices
are suitable for use in the present invention.
Latices containing functional ~roups as
described above can be produced by methods well known
to those skilled in the art. For example, acrylic,
methacrylic, fumaric or itaconic acid can be
reacted with styrene and butadiene ~n con~enticnal
processes to form styrene-butadiene rubber ha~ing
carboxyl groups in the polymer strueture. Those
same acids can be reacted with ac~ylic monomer~
to make acrylic latices having carboxyl functional
groups in the polymer structure. ThesP ~inyl
acids can also be reacted with Pthylene ~in~l
acetate to make functiollal-group containing Latices.
Specific examples of latices useful in the
present invention include"Rhoplex TR-520"and "Rhoplex
TR-90~", acrylic emulsion polymers made by Rohm and Haas
Company of Philadelphia, Pennsylvania. The
former is based on ethyl acrylate and the latter
on ethyl acrylate and butyl acrylate; Both contain
carboxyl groups in the polymer structure. Mixtures
of these two latices can also be used.
*Trademark
**Trademark
'7
- 12 -
Other sui~able latices are the carboxylated
styrene/butadiene copolymer supplied under the
designation XD~30295. 00 and the carboxylated
ctyrene-butadiene-butyl acrylate terpolymer
supplied under the designation XD 30221.02 by The
Dow Chemical Company of Midland, Michigan.
Mixtures of latices can be used in the
present invention.
The latex emulsion preferably has a viscosity
of less th2n 100 centipoise, most preferably less
than 30 centipoise.
The fifth step of the pref~rred process com-
prises drying the embryonic web to fo~m a paper
web. Techniques and equipment ~ell known to
those skilled in the art can be used in this
step. -
Further, the process can comprise an optionalstep of subjecting the impregnated zones to addi-
tional mechanical pressure or compaction after
they are impregnated to increase binder pene-
tration and interfiber bonding thereL~.
Still urther, the p~ocess can include an
optional and preferred drying step immediately
preceding the impregnating s~ep wherein the
~5 embryonic web is dried in the absence of substantial
mechanical compression to an average moisture
content of from about 25 to about 80% by weight
of the embryonic we~. Preferably, this drying
step is sufficiently asymmetrical to dry the
unsupported portions of the embryonic ~eb substan-
tially more than the high density portions.
Preferably, the web is creped, calendered
and reeled after being dried to ~urther increase
its stretch, bulk and softness, and to control
its caliper.
~L~9~727
- 13 -
~ le amount of binde~ impregnated into the
embryonic web is preferably from about 2Z to
abou~ 30% by weight of the papermaking fiber
although it is not intended to limit the present
invention to this range o binder level.
It is to be noted that in this embodiment of
the invention, the soft, strong, absorbent tissue
paper web of papermaking fibers comprises a
multiplicity of relati~ely high density zones
impregna~ed with a binder material interposed
between and among a plurality of usually vaulted
or arcuate shaped relatively low density spa~
portions which are substantially unco~pacted and
devoid of binder material. Water-soluble cationic
resin is, in general, distributed throughout the
web and is present in both the.high denslty and
low density zones.
The process for making the pa~tern densified
fibrous web described above is described in more
detail in European Patent Application 81200093.5
filed on behalf o the inventors P. G. Ayers and
J. M. Raley on January 26, 1981 and published~
August 19, 1981,
Optionally, the papermaking furnish can
comprise materials such as chemical debonders
which enhance the softness of the resulting
~issue paper web by reducing the interfibes
bonding therein. Of particular use herein is the
debonder combination comprising at leas~ one
quaternary ammonium compound and at least one
nonionic surfactant. The preferred quaternary
ammonium compounds are selected rom the group
consisting of quaternary ammonium com~ounds
having the structure
., .
~3~
14 -
CH3 +
CH3 - N - CH3 X , and
_ R
quaternary ammonium compounds having the structur~,
lo ~ fH3 +
~ H(OCH2CH2~m - I - (CH2CH~O~n X .
R
In the two structures noted above R is an aliphatic
hydrocarbon radical selected from the group con-
sisting of alkyl having from ~about 12 to about 18
carbon atoms, alkylene having from about 12 to
about 18 carbon atoms, coconut and tallow; m and n
are both integers each having a value of at least
1; the sum of m and n is from about 2 to about 15;
and X is a halogen.
As used in this context, '~coconut" refers to
the alkyl and alkylene moieties derived from coconut
oil and from the synthetic mixtures designed to re-
semble natural coconut oil. As used in this context,
"tallow" refers to the alkyl and alkylene moieties
derived from tallow and from the synthetic mixtures
designed to resemble natural tallow.
Preferably, the alkyl and alkylene radicals
have from about 15 to about 18 carbon atoms.
Alkylenes are ~enerally preferred to alkyls. Coconut
is more preferred than the alkyl and alkylene
radicals just described.
In the case of the methylpolyoxyethylene
quaternary ammonium compounds, the sum of m and n
is preferably about 2.
Any of the halide salts can be used. Typically,
and preferably, the chloride is used.
Specific examples of quaternary ammonium salts
useful in this invention include trimethyloctadecyl-
ammonium chloride, trimethylcocoammonium chloride,
trimethyltallowammonium chloride, trimethylolelyl-
ammoniu~ chloride, methylbis(2-hydroxyethyl)coco-
ammonium chloride, methylbis(2-hydroxyethyl)oleyl-
ammonium chloride, methylbis(2-hydroxyethyl)octadecyl-
ammonium chloride, methylbis(2-hydroxyethyl)tallow-
amTnonium chloride, methylpolyoxyethylene(l5)coco-
ammonium chloride, and methylpolyoxyethylene(l5)olyl-
ammonium chloride.
The most preferred quaternary ammonium com-
pound is methylbis(2-hydroxyethyl)cocoammonium
chloride.
The quaternary ammonium salt is added to the
papermaking furnish at a level of from about 0.5
to about 5.0 grams per kilogram of bone dry
papermaking fiber. Preferably 7 it is added at
from about 1.0 to about 2.5 grams per kilogram.
Nonionic surfactants useful in the present
invention include the ether and ester adducts of
ethylene oxide and fatty chemicals. That is to
say, the nonionic surfactants useful herein can be
described as the ethylene oxide adducts of, re-
spectively, fatty alcohols and fatty acids. The
fatty moiety of the nonionic surfactant should
comprise from about 12 to about 18 carbon atoms.
The ethylene oxide moiety of the nonionic sur
factant should comprise from about 2 to about 12
moles ethylene oxide, preferably from about 2 to
about 9 moles. Preferably, the fatty moiety is
unsaturated. Specific examples of nonionic sur-
factants useful in the present invention include
polyoxyethylene(2)oleyl ether and polyoxvethylene-
~t~
- 16 -
(9)oleyl ester. The former is known in CFTA
nomenclature as Oleth-2, the latter as PEG-9
oleate.
Dieste~s, such as PEG-4 dilaurate (two moles
S of lauric acid adducted with 4 moles of ethylene
- oxide~, are also useful in the present invention.
The nonionic surfactant is present in the
papermaking furnish at a level of from about 0.5
to about 5.0 grams per kilogram bone dry paper-
making fiber, preferably from about 1.0 to about
2.5 grams per kilogram.
Preferably, either the quaternary ammonium
compound or the nonionic surfactant contains an
unsaturated (alkylene) moiety. More preferably,
both contain such an unsaturated (alkylene) moiety.
Other chemicals commonly-used in papermaking
can be added to the papermaking furnish so long as
~ they do not significantly and adversely affect the
end result of the present invention.
The process of this invention (and, of necessity,
the resulting web) has hereinbefore been described
in detail in terms of a process which makes a
pattern densified fibrous web having a relatively
high bulk field of relative low fiber density and
a patterned array of spaced zones of relatively
high fiber density at least a substantial pro-
portion of which are at least partially impreg-
nated with binder material. This is the system
which is highly preferred and in which the present
invention finds greatest utility. It is to be
recognized, however, that certain other paper-
making process are known to produce webs having
binder material impregnated therein, usually in
.
- 17 -
some discrete pattern, but wherein the locus of
the impregnated zones does not substantially
correspond with at least a portion of the locus
of zones of relatively high fiber density. The
present invention finds utility in such other
processes and the webs thereby produced, but such
use is no~ preferred.
The tissue paper webs of this invention can
be used in any application wh~re soft, absorbent
tissue paper webs are required. One partieularly
advantageous use of the tissue paper webs of this
invention is in paper towel products. For example,
two tissue paper webs of this invention can be
embossed and adhesively secured together in face-
to-face relation (as taught by U.S. Patent
3,414,459 which issued to Wells on DecembPr 3,
1968) ~o fonn 2-ply paper towels~
As noted hereinbefore, the webs of this
invention (and ~he products made from these webs)
20 exhibit greater tensile strength than either webs
made with water-soluble cationic resin in the
papermaking furnish but without latex bi~des
material impregnation or webs made with latex
binder material impregnation but withou~ water-
soluble cationic resin~ in the papermaking furnish.In fact, the'webs of this invention exhibit
greater tensile strength than would be expected
from a consideration of the two other webs de-
scribed in the immediately preceding sentence.
In addition, the webs of this invention ~and the
products formed from them) are soft, absorbent,
and exhibit a surprising degree of strength in
alkaline, chlorine-containing environments.
In order to better describe the present
invention, and not by way of limitation, the
t~7
following examples are presented.
EXAMPLE I
A 5% aqueous slurry of unbeaten northern
5 sof~wood Kraft wood pulp fibers was formed in a
conventional repulper. Mèthylbis-(2-hydroxyethyl)
cocoammonium chloride (as sold under the trademark
~'Ethoquad C-12" by Armak Company of Chicago,
Illinois) was added to the pulp slurry at the rate
10 of 2 grams of ~uaternar~ ammonium compound per
kilogram of bone dry ~iber. Oleth-2 (as sold
under the trademark "Brij 93" by I.C.I. Americas
Inc. of Wilmington, Delaware), dissolved in
isopropyl alcohol, was added to the fiber slurry
lS at a rate of 2 grams of nonionic surfactant per
~ilogram of bone dry fiber. T~e papermaking
furnish was completed by the addition of "Kymene
557H" to the aqueous slurry through an inline
mixer at a rate of 10 grams of resin per kilogram
20 of bone dry fiber.
This papermaking furnish was then used to
make an embryonic web on a pilot scale papermaking
machine. Afte~ dilution with water to form a
slurry containing approximately~0.12% fiber, the
2~ papermaking furnish was deposited on a Fourdrinier
wire of a 4-shed satin weave having about 31 x 24
machine direction (MD) by cross machine direction
(CD) filament mesh count per centimeter to form
the embryonic web. Water was progressi~ely
30 removed as the embryonic web was being carried
through the machine first on the hereinbefore
described Fourdrinier wire and after the embryonic
web was transferred to an imprinting fabric which
B had a 5-shed satin weave of 14 x 13, MD by CD,
Z ~
- 19 -
filam~n~ mesh count per centimeter such as de-
scribed in U.S. Paten~ 4,191,609 issued to Paul
D. Trokhan on March 4, 1980. Dewatering was accomplished by
vacuum assisted drainage until the embryonic web
had a fiber consistency of abou~ 32~. ~s a
result of the transfer from the Fourdrinier wire
to the imprinting fabric and the vacuum assisted
dewatering, the embryonic web became patterned
' densified when the resulting discrete spaced high
density zones we~e juxtaposed the top-surace-
plane knuckles of the imprinting ~abric. Vacuum
induced differential fluid pressure caused the
unsupported por~ions of the embryonic web to be
displaced into the interfilamentary ~oids of the
imprinting fabric for~ing rela~ ly low density
spans between the knuckles. The now patterned
-densified em~ryonic web was predried by air blow-
through to an ave~age fiber consistency of about
1 65%.
The embryonic web, while still d sposed on
the imprintin~ fabric, was carried forward thxvugh
a full field pattern pressu~e biased ~ravure
impregnating de~ice in such a manner that the
relatively high density zones were pressed against
the gravure cylinder and thereby impregnated with
binder material comprising water based emulsi~
polymer containing ~nionic functional groups i~
the polymer structure. The relatlvely low density
; span zones were not so impregnated.
In this Example 9 the binder material was
hereinbefore described TR 5~G latex. In addition
to the latex, the binder material contained about
- 20 -
*
1O/D Pluronic L-92"ethylene oxide~based nonionic
surfactant as made by BASF Wyandotte Corp. of
Parsippany, Mew Jersey, abou~ 0.5~/0 ammonium nitrate,
trace levels of commercial defoamers"Foammaster
160-L ~s made by the Diamond Shamrock Corp. of
Cleveland, Ohio/and"Colloid 694"as made by Colloids
Inc. of Newark, New Jersey, and ammonium hydroxide
to adjust the pH to 5.0~+ 0.5. Binder material
was impregnated into the web at a level of approxi-
mately 5% by weight of fiber.
Following impregnation, the web was adheredto *t*he*surface of a Yankee dryer with"Gelvatol 20-
90, a polyvinyl alcohol/acetate creping adhesive
manufactured by Monsant~ Company. The web was
1~ creped from the surfaoe of the Yankee dryer in a
conventional manner by a doct~r blade and was
formed into rolls by reeling at 80% of the Yankee
` speed.
Two plys of the web were formed into paper
20~ towel products by laminating them together using
polyvinyl alcohol`as the adhesive and the technique
described in the ~.S~ -Patent, 3,414,459. The lamin-
ate was stored at about 22~C for about six da~s.
Two types of control towels were made by the
foregoing process except that in the first case the
papermaking furnish did not contain the water-soluble
cationic resin and in ~he second case the embryonic
webs were not impregnated with binder material.
The paper towel of this invention formed from webs
of this invention as made by the process of this
invention, when compared to the control paper
towels, was found to exhibit wet tensile strength
significantly greater than that of either control
towel.
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EXAMPLE II
. .
The process of Example I ~as repeated except
that the papermaking furnish did not contain
either the methylbis-~2-hydroxyethyl) cocoammonium
chloride or the Oleth-2. Control towels were
prepared in a manner analogous to that used to
prepare control towels in Example I. Towels
prepared from the webs of this invention made
according to this Example II exhibited significant
strength improvement relative to the control
towels. This strength improvement was similar to
the strength improvement demonstrated in Example
I.
EXAMPLE III .
The process of Example I is repeated except that
the water-soluble cationic resin is"Parez 631 N~l-
and the hinder material is Dow latex XD-30295.
The binder material contains, in addition to the
latex, 1.0% diammonium phosphate and sufficient
ammonium hydroxide to adjust the pH of the ~mul-
sion to 8.5. The resulting web, is soft, strong,
absorbent, and useful in making towels.
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