Note: Descriptions are shown in the official language in which they were submitted.
133~381 ~
.
.. ~.,- .
PROCESS FOR PREPARING
SOFT TISSUE PAPER
~REATED ~ITH A POLYSILOXANE
ROBERT S. AMPULSKI
and
WOLFGANG U. SPENDEL
TECHNICAL FIELD
This invention relates, in general, to a process for preparing tissue
paper; and more specifically, to a process for preparing high bulk tissue
paper having a soft, silky, flannel-like tactile feel; and enhanced tactile
perceivable bulk, and physiological surface smoothness.
BACKGROUNQ OF_THE INVENTION
Soft tissue paper is generally preferred for disposable paper towels.
and facial and toilet tissues. However, known methods and means for
1~ enhancing softness of tissue paper generally adversely affect tensile
strength. Tissue paper product design is, therefore, senerally, an exercise
in balancing softness against tensile strength.
Both mechanical and chemical ~eans have been introduced in the pursuit
of making soft tissue paper: ti$sue paper which is perceived by users,
~o through their tactile sense, to be soft. Such tactile perceivable softnessmay bè charactèrized by, but not limited to, resilience, flexibility, and
smoothness; and subjective descrip~ors such as feeling like silk or flannel.
The present invention pertains to a process for improving the tactile
perceivable softness of tissue paper -- in particular high bulk~ creped
2j tissue paper -- through the incorporation of chemical; additives: in
particular, polysiloxane materials which impart a silky or~flannel-like feel
to the tissue paper without rendering it greasy or oily to the tactile sense
of users of products comprislng such t;ssue paper. Additionally, surfactant
1~3038~
material may be added to further enhance softness and/or surface smoothness
and/or to at least partially offset any reduction in wettability caused by
the polysiloxane; and binder material such as starch may be added to at
- least partially offset reductions in strength and or increasing in linting
propensity that results from the polysiloxane and, if used, the surfactant
additive.
Representative high bulk, creped tissue papers which are quite soft by
contemporary standards, and which are susceptible to softness enhancement
through the present invention are disclosed in the following U.S. Patents:
3,301,746 which issued January 31, 1967 to Lawrence H. Sanford and James B.
Sisson; 3,974,025 which issued August 10, 1976 to Peter G. Ayers; 3,994,771
which issued November 30, 1976 to George Morgan, Jr. and Thomas F. Rich;
4,191,609 which issued March 4, 1980 to Paul D. Trokhan; and 4,637,859 which
issued January 20, 1987 to Paul D. Trokhan. Each of these papers is
characterized by a pattern of dense areas: areas more dense than their
respective remainders, such dense areas resulting from being compacted
during papermaking as by the crossover knuckles of impr;nting carrier
fabrics. Other high bulk, soft tissue papers are disclosed in U.S. Patent
4.300,981 which issued November 17, 1981 to Jerry E. Carstens; and 4,440,597
which issued April 3, 1984 to Edward R. Wells and Thomas A. Hens1er.
Additionally, achieving high bulk tissue paper through the avoidance of
overall compaction prior to final drying is disclosed in U.S. Pa~ent
3,821,068 which issued June 28, 1974 to D. L. Shaw; and avoidance of
overall compaction in combination with the use of debonders and elastomeric
bonders in the papermaking furnish is disclosed in U.S. Patènt 3,812,000
which issued May 21, 1974 to J. L. Salvucci, Jr.
Chemical debonders such as those contemplated by Salvucci, referred to
above, and their operative theory are disclosed in such representative U.S.
Patents as 3,755,220 which issued August 28, 1973 to Friemark e~ al;
3~844,880 which issued October 29, 1974 to Meisel et al; and 4,158,594
which issued January 19, 1979 to Becker et al. Other chemical treatments
which have been proposed to improve tissue paper include, for example, that
disclosed in German Patent 3,420,940, Kenji Hara et al, to wit: to
impregnate toilet tissue paper with a combination of a vegetable, animal, or
~ ':
~ 3 3 ~
synthetic hydrocarbon oil, and a silicone oil such a~
dimethylsilicone oil to make it easier to clean and wipe
with.
Additionally, a well known mechanical method of
increasing tensile strength of paper made from
cellulosic pulp is by mechanically re~ining the pulp
prior to papermaking. In general, greater refining
results in greater tensile strength. However,
consistent with the foregoing discussion of tissue
tensile strength and softness, increased mechanical
refining of cellulosic pulp negatively impacts tissue
paper softness, all other aspects of the papermaking
furnish and process being unchanged. However, through
the use of the present invention, tensile strength can
be increased without negatively impacting softness; or,
alternatively, softness can be improved without
negatively impacting tensile strength. ~ -~
It is an object of an aspect of this invention to
provide a process for preparing tissue paper which has ~ `
an enhanced tactile sense of softness.
It is an ob~ect of an aspect of this invention to
provide a process for preparing tissue paper which has a
silky, flannel-like feel.
It is an object of an aspect of this invention to `
provide a process for preparing tissue paper which has
increased tactile softness at a particular level of
tensile strength relative to tissue paper which has been
softened by conventional techniques.
These and other objects are obtained using the
present invention, as will be seen from the following
disclosure.
SUMMARY OF THE INVENTION
The present invention encompasses a process for ;- -
making soft tissue paper. This process includes the ;~
35 steps of wet laying cellulosic fibers to form a web, ~-
applying to the web, at a fiber consistency of from
: .
133~)38~
about 10% to about 80% (total web weight basis), a
su~ficient amount of a polysiloxane such that between
about 0.004% and about 0.75% of said polysiloxane, dry
fiber weight basis, is retained by the tissue paper, and
5 then drying and :.
i . i.. :
' '
'...:
1~3~3~
creping the web. Preferably, the amount of polysiloxane retained by the
tissue paper is between .004% to about 0.3X, based on the dry fiber weight
of the tissue paper. The resulting tissue paper preferably has a basis
- weight of from about 10 to about 65 g/m2 and a ~iber density of less than
about 0.6 g/cc.
The polysiloxane is applied subsequent to formation of the wet web and
prior to drying to completion. Surprisingly, it has been found that
significant tissue softening benefits can be achieved by much lower levels
of polysiloxanes when the polysiloxane is applied to a wet web, as compared
to a dry web (e.g., during the converting operation). In fact, an important
feature of the process disclosed herein, is that the silicone level is low
enough to be economical. Also, tissue paper treated with low levels of
polysiloxane retain a high level of wettability, an important feature for a
tissue product.
Preferred polysiloxanes for use in the process of the present
invention include an amino-functional polydimethylpolysiloxane wherein less
than about 10 mole percent of the side chains on the polymer contain an
amino-functional group. Because molecular weights of polysiloxanes are
difficult to ascertain, the viscosity of a polysiloxane is used herein as an
objectively ascertainable indicia of molecular weight. Accordingly, for
example, about 2X substitution has been found to be very effective for
polysiloxanes having a viscosity of about one-hundred-twenty-five (125)
centistokes; and viscosities of about five-million (5,000,000) centistokes
or more are effective with or without substitution. In addition to such
substitution with amino-functional groups, effective substitution may be
made with carboxyl, hydroxyl, ether, polyether, 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.
: `
, " `-.
' ~
133~381
Exemplary commercially available polysiloxanes
include DOW 8075 and DOW 200 which are available from
Dow Corning; and SilwetTM 720 and UcarsilTM EPS which
are available from Union Carbide.
The process for preparing tissue paper treated with
a polysiloxane in accordance with the present invention
may further comprise the step of adding an effective
amount of a surfactant to enhance the tactile
perceivable surface smoothness of the tissue paper
and/or to at least partially offset any reduction of
wettability of the tissue paper which would otherwise
result from the incorporation of the polysiloxane. The
effective amount of surfactant is such that, preferably,
from about 0.01 to about 2 percent on a dry fiber weight
of the tissue paper; and, more preferably, from about
0.05 to about 1.0 percent is retained by tha tiss~e
paper. Also, preferably, the surfactant is noncationic; -
and is substantially nonmigratory in situ after the
tissue paper has been manufactured in order to
substantially obviate post-manufacturing changes in the
tissue paper's properties which might otherwise result
from the inclusion of surfactant. This may be achievad,
for instance, through the use of surfactants having melt
temperatures greater than the temperatures commonly
encountered during storage, shipping, merchandising, and
use of tissue paper product embodiments of the ~;
invention: for example, melt temperatures of about 50C
or higher.
Also, the process for preparing tissue paper in
accordance with the present invention may further
comprise the step of adding an effective amount of a
binder material such as starch to at least partially
offset any reduction of tensile strength and/or increase
in linting propensity which would otherwise result from
the incorporation of the polysiloxane and, if present,
surfactant material. The effective amount of binder
A` ~
-- 1~30381
5a
material is such that, preferably, from about 0.01 to
about 2 percent on a dry fiber weiyht basis of the
tissue paper, is retained by the tissue paper.
All percentages, ratios and proportions hsrein are
by weight, unless otherwise specified.
ThP present invention is described in more detail
below.
~ i` "'`! '
' '~ ''~`' .. .''`"
'''.,`''~"~'''','."`',,'`
'' ~ '''`''' ~" `' '
33~3~1
DE~AILED DESCRIPTION OF THE INYENTION
Briefly, the present invention provides tissue paper having a silky,
flannel-like feel, and enhanced tactile perceivable softness through the
addition of a polysiloxane additive to a wet tissue web. Such process may
S also include the addition of an effective amount of surfactant material
and/or a binder material such as starch to the wet web. ~enerally speaking,
surfactant may be included to enhance tactile perceivable, physiological
surface smoothness and/or to assure sufficient wettability for the intended
purposes of the tissue paper (e.g., as toilet tissue); and a binder material
such as starch may be included to at least partially offset `any reduction of
tissue paper tensile strength and/or exacerbation of linting propensity
which would otherwise be precipitated by the addition of the polysiloxane
and, if used, the surfactant. Surprisingly, it has been found that very low
levels of polysiloxane provide a significant tissue softening effect when
li applied to wet t;ssue webs in accordance with the present invention as
compared to application of polysiloxanes to dry tissue webs (e.g., in the
converting operations). To ensure high retention rates, the wet web is
formed and dewatered prior to application of the polysiloxane additive in
order to reduce the loss of the polysiloxane due to drainage of free water.
Importantly, it has been found that the levels of polysiloxane used to
soften the tissue paper are low enough that the tissue paper retains high
wettability.
The present invention is applicable to tissue paper in general,
including but not limited to conventionally felt-pressed tissue paper;
pattern densified tissue paper such as exemplified by Sanford-Sisson and its
progeny; and high bulk, uncompacted tissue paper such as exemplified by
Sal~ucci. The tissue paper may be of a homogenous or multilayered
construction; and tissue paper products made therefrom may be of a
single-ply or multi-ply construction. The tissue paper preferably has a
basis weight of between 10 g/m2 and about 65 g/m2, and density of about 0.60
g/cc or less. Preferably, basis weight will be below about 35 9/m2 or less;
and density will be about 0.30 g/c~ or less. Most preferably, density will
be between 0.04 g/cc and about 0.20 g/cc.
3~3~1
Conventionally pressed tissue paper and methods for making such paper
are known in the art. Such paper is typically made by depositing
papermaking furnish on a foraminous forming wire. This forming wire is
often referred to in the art as a Fourdrihier 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 dried at eleYated te~perature. The
particular techniques and typical equipment for making webs accordiny to the
process just described are well known to those skilled in the art. In a
typical process, a ~ow consistency pulp furnish is provided in 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 7X and about 25%
(total web weight basis) by vacuum dewatering and further drying by pressing
operations wherein the web is subjected to pressure developed by opposing
mechanical members, for example, cylindrical rolls. ~he dewatered web is
then further pressed and dried by a stream 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 may be employed, whereby additional
pressing is optionally incurred between the drums. The tissue paper
structures which are formed are referred to hereinafter as conventional,
pressed, tissue paper structures. Such sheets are considered to be
compacted since the web is subjected to substantial ~echanical compressional
forces while the fibers are moist and are then dried while in a compressed
state.
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
zones are alternatively referred to as knuckle regions. The densified zones
may be discretely spaced within the high bulk field or may be
intèrconnected, either fully or partially, within the high bulk field.
Preferred processes for making pattern densified tissue webs are disclosed
in U.S. Patent No. 3,301,746, issued to Sanford and Sisson on January 31,
1967, U.S. Patent No. 3,974,025, issued to Peter G. Ayres on August 10,
. ..
~33~3~1
1976, and U.S. Patent No. 4,191,609, issued to Paul D.
Trokhan on March 4, 1980.
In general, pattern densified webs are preferably
prepared by depositing a papermaking furnish on a
foraminous forming wire such as a Fourdrinier wirP to
form a wet web and then juxtaposing the web against an
array of supports. The web is pressed against the array
of supports, thereby resulting in densified zones in the
web at the locations geographically corresponding 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.
Formation of the densified zones may be accomplished 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 array 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 supports wherein the high
bulk field is not compressed. The operations of
dewatering, optional predrying and ~ormation of the
densified ~ones may 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
55~ of the tissue paper surface comprises densified
knuckles having a relative density of at least 120% of
the density of the high bulk field. ;~
The array of supports is preferably an imprinting
carrier fabric having a patterned displacement of
knuckles which operate as the array of supports which
~k~
3 8 11
facilitate the formation of the densified zones upon ~ ;
application of pressure. The pattern of knuckles
constitutes the array of supports previously re~erred
to. Imprinting carrier fabrics are disclosed in U.S.
Patent No. 3,301,746, Sanford and Sisson, issued January
31, 1967, U.S. Patent No. 3,821,068, Salvucci, Jr. et
al., issued May 21, 1974, U.S. Patent No. 3,~74,025,
Ayers, issued August 10, 1976, U.S. Patent No. ;
3,573,164, Friedberg et al., issued March 30, 1971, U.S.
10 Patent No. 3,473,576, Amneus, issued October 21, 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 ~urnish may alternately bP ~-
initially deposited on a foraminous supporting ¢arrier
which also operates as an imprinting fabric. once
20 formed, the wet web is dewatered and, preferably, ~ -
thermally predried to a selected fiber consistency of
between about 40% and about 80%. 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 which 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 may be applied to
. . .~ . . ~ ~ . .
-: 133~381
9a
induce impression of densified zones during initial
dewatering, in a separate, subsequent process stage, or
a combination thereof.
Uncompacted, nonpattern-densified tissue paper
structures are described in U.S. Patent No. 3,812,000
issued to Joseph L. Salvucci, Jr. and Peter N. Yiannos
on May 21, 1974 and U.S. Patent No. 4,208,459, issued to
Henry E. Becker, Albert L. McConnell, and Richard
Schutte on June 17, 1980. In general, uncompacted,
nonpattern-densified tissue paper structures are
prepared by depositing a papermaking furnish on a
foraminous forming wire such as a Fourdrinier wire to
form a web, draining the web and removing additional
water without mechanical compression until the web has a
fiber consistency of at least 80%, and creping the web.
Water is removed from the web by vacuum dewatering the
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.
A
~ ~
~... .~ . .. ,.. ,.. -;. .
~3~38~
The papermaking fibers utilized for the present invention will normally
include fibers derived from wood pulp. Other cellulosic fibrous pulp
fibers, such as cotton linters, bagasse, etc., can be utilized and are
intended to be within the scope of this invention. Synthetic fibers, such
as rayon, polyethy1ene and polypropylene fibers, may also be utilized in
combination with natural cellulosic fibers. One exemplary polyethylene
fiber ~hich may be utilized is PulpexTM, available from Hercules, Inc. (~
mington, Delaware). `
Applicable wood pulps include chemical pulps, such as Kraft, sulfite,
and sulfate pulps, as well as mechanical pulps including, for example,
groundwood, thermomechanical pulp and chemically modified thermomechanical
pulp. Chemical pulps, however, are preferred since they impart a superior
tactile sense of softness to tissue sheets made therefrom. Pulps derived ~ -
from both deciduous trees (hereinafter, also referred to as "hardwood~) and
coniferous trees (hereinafter, also referred to as "softwoodn? may be
ùtilized.
In addition to papermaking fibers, the papermaking furnish
used to make tissue paper structures may have other components or
materials added thereto as may be or later become known in the art. The
types of additives desirable will be dependant upon the particular end use
of the tissue sheet contemplated. For example, in products such as toilet
paper, paper towels, facial tissues and other similar products, high wet
strength is a desirable attribute. Thus, it is often desirable to add to
the papermaking furnish chemical substances known in the art as ~et ` -strength" resins,
A general dissertation on the types of wet strength resins utilized in
tne paper art can be found in TAPPI monograph series No. 29, Wet Strength in
Paper and Paperboard, Technical Association of the Pulp and Paper Industry ~ ~N
(New York, 1965). The most useful wet strength resins have generally been
cationic in character. Polyamide-epichlorohydrin resins are cationic wet
strength resins which have been found to be of particular utility. Suitable
types of such resins are described in U.S. Patent Nos. 3,700,623, issued on
October 24, 1972 and 3,772,076, issued on November 13, 1973, both issued to
:
~33~38~
11
Keim and both being hereby incorporated by reference.
Once commercial source of a useful polyamide-
epichlorohydrin resins is Hercules, Inc. of Wilmington,
Delaware, which markets such resin under the mark
KymemeTM 557H.
Polyacrylamide resins have also been *ound to be of
utility as wet strength rasins. These resins are
described in U.S. Patent Nos. 3,556,932, is~ued on
January 19, 1971 to Coscia, et al. and 3,556,933, issued
10 on January 19, 1971 to Williams et al. One commercial
source of polyacrylamide resins is American Cyanamid Co.
of Stanford, Connecticut, which markets one such resin
under the mark ParezTM 631 NC.
Still other water-soluble cationic resins ~inding
utility in this invention are urea formaldehyde and
melamine formaldehyde resins. The more common
functional groups of these polyfunctional resins are
nitrogen containing groups such as amino groups and
methylol groups attached to nitrogen. Polyethylenimine ~-
20 type resins may also find utility in the present ;
invention. It is to be understood that the addition of
chemical compounds such as the wet strength resins
discussed above to the pulp furnish is optional and is
not necessary for the practice of the present
development.
~ypes of polysiloxane materials which are suitable -
for use in the present invention include polymeric,
oligomeric, copolymeric, and other multiple-monomeric `-
siloxane materials. As used harein, the term
polysiloxane shall include all of such polymeric,
oligomeric, copolymeric and other multiple-monomeric `
siloxane materials. Additionally, the polysiloxane can
be either a straight chain, a branched chain or have a
cyclic structure. ~ ;
f,~
~- ~L3~38
lla
Preferred polysiloxane materials include those
having monomeric siloxane units of the following
structure:
(1) ~ si - o-
''`~' : '.'`:
.. . ... . ..
:~ . . .: . .
: .
133~8~
l2
wherein, Rl and R2 for each siloxane monomeric unit can independently be any
alkyl, aryl, alkenyl, alkaryl, aralkyl, cycloalkyl, halogenated hydrocarbon,
or other radical. Any of such radicals can be substituted or
unsubstituted. R1 and R~ radicals of any particular monomeric unit may
S differ from the corresponding functionalities of the next adjoining
monomeric uni~. Additionally, the radicals can be either a straight chain,
a branched chain, or have a cyclic structure. The ra~icals Rl and R2 can,
additionally and independently, be other silicone ~unctionalities such as,
but not limited to siloxanes, polysiloxanes, and polysilanes. The radicals
Rl and R2 can also contain any of a variety of organic functionalities
including, for example, alcohol, carboxylic acid, and amine functionalities.
The degree of substitution and the type of substituent have ~-
been found to affect the relative degree of soft, silky feeling
and hydrophilicity imparted to the tissue paper structure. In
general, the degree of soft, silky feeling imparted by the
polysiloxane increases as the hydrophilicity of the substituted
polysiloxane decreases. Aminofuno~ional - polysiloxanes are ~ -
especially preferred in the present invention. ~-~
Preferred polysiloxanes include straight chain organopoly~
siloxane materials of the following general formula~
,
R1 R7 ~ Rg R4
(2) R2 -Si-0 -Si-0 -Si-0 -Si - Rs ~ ~;
'~ I i I ' .' ~'
R3 R8 a RIo b R6
,:
wherein each Rl - Rg radical can independently be any Cl - Clo
unsubstituted alkyl or aryl radical, and Rlo is any substituted Cl
- CIo alkyl or aryl radical. Preferably each Rl - Rg radical is
independently any CI - C4 unsubstituted alkyl group. Those
skilled in the art will recognize that technically there is no
difference whether, for example, Rg or Rlo is the substituted radical.
Preferably the mole ratio of b to (a + b) is between 0 and about 2~o~ more
133~381
13
preferably between 0 and about 10%, and most preferably between about 1% and
about 5%.
In one particularly preferred em~odiment, R1 - Rg are methyl
groups and Rlo is a substituted or unsubstituted alkyl, aryl, or
alkenyl group. Such material shall be generally described herein
as polyd;methylsiloxane which has a particular functionality as
may be appropriate in that particular case. Exemplary polydi-
methylsiloxanes include, for example, polydimethylsiloxane,
polydimethylsiloxane having an alkyl hydrocarbon R1o radical and
polydimethylsiloxane having one or more amino, ca~boxyl, hydroxyl,
ether, polyether, aldehyde, ketone, amide, ester, thiol and~or
other Rlo functionalities including alkyl and alkenyl analogues of
such functionalities. For example, an amino functional alkyl
group as R1o could be an amino-functional or an aminoalkyl-
functional polydimethylsiloxane. ~he exemplary listing of these
polydimethylsiloxanes is not meant to thereby exclude others not
specifically listed.
Viscosity of polysiloxanes useful for this invention may vary
as widely as the viscosity of polysiloxanes in general vary, so ~ 9
long as the polysiloxane is flowable or can be made to be flowable
for application to the tissue paper. This includes, but is not
limited to, viscosity as low as about 25 centistokes to about
20,000,000 centistokes or even higher. High viscosity poly~
siloxanes which themselves are resistant to flowing can be
effectively deposited upon the tissue paper webs by such ~ethods
as, for example, emulsifying the polysiloxane in surfactant or
providing the polysiloxane in solution with the aid of a solvent,
such as hexane, listed for exemplary purposes only. Particular
methods for applying polysiloxanes to tissue paper webs are
discussed in more detail below.
Parenthetically, while not wishing to be bound by a theory of
operation, it is believed that the tactile-benefit efficacy of the
polysiloxane is directly related to its average molecular ~eight;
.
~33~38~
1~
and that viscosity is directly related to molecular weight. Accordingly,
due to the relative difficulty of directly determining molecular weights of
polysiloxanes as compared to determining their viscosities, viscosity is
used herein as the apparent operative parameter with respect to impareing
enhanced tactile response to tissue paper: i.e., softness, silkiness, and
flannel-like.
Re~erences disclosing polysiloxanes include U. S. Patent
2,826,551, issued March 11, 1958 to Geen; U. S. Patent 3,~64,500,
issued June 22, 1976 to Drakoff; U.S. Patent 4,364,837, issued
December 21, 1982 to Pader; and British Patent 849,433, published
September 28, 1960 to ~oolston. Also, Silicon Compounds, pp.
181-217, distributed by Petrarch Systems, Inc., 1984, contains an
extensive listing and description of polysiloxanes in general.
The polysiloxane is applied subsequent to for~ation of the wet ~eb and
prior to drying to completion. It has been found that addition of the
polysiloxane to the wet end of the paper machine (i.e., the paper furnish)
is impractical due to low retention levels of the polysiloxane. Therefore.
in a typical process, the web is formed and then dewatered prior to
application of the polysiloxane in order to reduce the loss of polysiloxane
due to drainage of free water. The polysiloxane is preferably applied to
the wet web at a fiber consistency level of between 1~% and about 80X (ba'sed
on the weight of the wet web), ~ore preferably at a fiber consistency level
between about 15X and about 35%, in the manufacture~ of 'conventionally
pressed tissue paper; and to a wet ~eb having a fiber consistency of between
2~ about 20% and about 35% in the manufacture of tissue paper in papermaking
machines wherein the newly formed web is transferred from a fine mesh
Fourdrinier to a relatively coarse imprinting/carrier fabric. This is
because it is preferable to make such transfers at sufficiently low fiber
consistencies that the fibers have substantial mobility during the transfer:
and it is preferred' to apply the polysiloxane after their mobility has
substantially dissipated as ~ater re~oval progresses through the papermaking
machine. Also, addition of the polysiloxane at higher fiber consistencies
assures greater retention in and on the paper: i.e., less polysilo~ane is
lost in the water being drained from the web to increase its fibe
1~3~38:~
consistency. Surprisingly, retention rates in excess of about 90X are
expected at the preferred fiber consistencies ~i~hout the utilization of
chemical retention aids.
.
The polysiloxane is preferably applied ~o the wet web ;n an aqueous
solution, emulsion, or suspension. The polysiloxane can also be applied in
a solution containing a suitable, nonaqueous solvent, in which the
polysiloxane dissolves or with which th'2 polysiloxane is miscible: for
example, hexane. The polysiloxane may be supplied in neat form or, ~;
preferably, emulsified with a suitable surfactant emulsifier. Emulsified
polysiloxane is preferable for ease of application since a neat polysiloxane
aqueous solution must be agitated to inhibit separation into ~ater and
polysiloxane phases. `;
.
The polysiloxane should be applied uniformly to the wet tissue paper
web so that substantially the entire sheet benefits ~rom the tactile effect
of the polysiloxane. Applying the polysiloxane to the wet tissue paper web
in continuous and patterned distribut~ons are both within the scope of the
invention and meet the above criteria. ;~
Methods of uniformly applying the polysiloxane to the web inc1ude
spraying and gravure printing. Spraying has been found to be economical,
and susceptible to accurate control over quantity and d1stribution of the
polysiloxane, so is most preferred. Preferably, an aqueous ~ixture
containing an emulsified polysiloxane is sprayed onto the wet tissue web as
it courses through the papermaking machine: for example, and not by ~ay of
limitation, referring to a papermaking machine of the general configuration
disclosed in Sanford-Sisson (referenced hereinbefore), either before the
predryer, or after the predryer, depending on the desired fiber consistency
level. A less preferred method includes deposition of the polysiloxane onto
a forming wire or fabric which is then contacted by the tissue web.
Equipment suitable fdr spraying polysiloxane containing ljquids onto wet
30 webs include external mix, air atomi7ing nozzles, such as the 2 ,nm nozzle i`~
available from V.I.B. Systems, Inc., Tucker, Georgia. Equipment suitable
for printing polysiloxane contain;ng liquids onto wet webs includes
rot~gravure printers.
~3~38~
~6
It has been found, surprisingly, that lo~ levels of polysiloxane
applied to ~et tissue paper ~ebs can provide a softened, silky,
flannel-like, nongreasy tactile sense of feel to the tissue paper without
the aid of additional materials such as oils or lotions. Importantly,
these benefits can be obtained for many of the embodiments of the present
invention in combination with high wettability within the ranges desirable
for toilet paper application. Preferably, tissue paper treated with
polysiloxane in accordance with the present invention comprises about 0.~5X
or less polysiloxane. It is an unexpected benefit of this invention that
tissue paper treated with about 0.~5% or less polysiloxane can have imparted
thereto substantial softness and silkiness benefits by such a low level of
polysiloxane. In general, tissue paper having less than about 0.3X
polysiloxane, preferably less than about 0.2%, can provide substantial
increases in softness and silkiness an~ flannel-like quality yet remain
sufficiently wettable for use as toilet paper ~ithout requiring the addition
of surfactant to offset any negative i~pact on ~ettability which results
from the polysiloxane.
'.
The minimum level of pslysiloxane to be retained by the
tissue paper is at least an effective level for imparting a
tactile difference in softness or silkiness or flannel-like
quality to the paper. The minimum effective level ~ay vary depending upon
the particular type of sheet, the method of application, the particular type
of polysiloxane, and whether the polysiloxane is supplemented by starch.
surfactant, or other additives or treatments. ~ithout limiting the range of
applicable polysiloxane retention by the tissue paper, preferably at least
about 0.004%, more preferably at least about O.OlX, and most preferably at
least about 0.02~ polysiloxane is retained by the tissue paper.
Preferably, a sufficient amount of polysiloxane to impart a
tactile sense of softness is disposed in both surfaces of the
tissue paper: i.e., disposed on the outwardly facing surfaces of
the surface-level fibers. ~hen polysiloxane is applied to one
surface of the tissue paper, some of it will, generally, at least
partially penetrate to the tissue paper interior. In a preferred
~33~3~ `
1~
embodiment, sufficient polysiloxane to effec~ a tactile response penetrates
through the entire thickness of the tissue paper such ehat both surfaces
have imparted thereto the benefits of polysiloxane. One method found to be
useful for facilitating polysiloxane penetration to the opposing surface
when the polysiloxane is applied to one surface of a wet tissue paper web is
to vacuum dewater the tissue paper from the other surface of the wet tissue
paper at the point of application of the polysiloxane.
In addition to treating tissue paper with polysiloxane as
described above, it has been Found desirable to also treat such
tissue paper with surfactant material. This is in addition to any
surfactant material that may be present as an emulsifying agent
- for the polysiloxane.
Tissue paper having in excess of about 0.3% polysiloxane is
preferably treated with surfactant ~hen contemplated for uses
wherein high wettability is desired. Most pref~rably, a non~
cationic surfactant is applied to the wet tissue paper web, in
order to obtain an additional softness benefit, on a constant tensile basis,
as previously discussed. The amount of surfactant required to increase
hydrophilicity to a desired level will depend upon the type and level of
~o polysiloxane and the type of surfactant. However, as a general guideline,
between about 0.01~ and about 2X surfactant retained by the tissue paper,
preferably between about 0.05% and about 1.~%, is believed to be sufficient
to provide sufficiently high wettability for most applicati~ns, including
toilet paper, for polysiloxane levels of about 0.75X or less.
Surfactants which are preferred for use in the present
invention are noncationic; and, more preferably, are nonionic.
However, cationic surfactants may be used. Noncationic surfactants
include anionic, nonionic, amphoteric, and zwitterionic
surfactants. Preferably, as stated hereinbefore, the surfactant is
substantially nonmigratory in situ after the tissue paper has been
133038~
18
manufactured in order to substantially obviate post-manufacturing
changes in the tissue paper's properties which might other~ise
result fro~ the inclusion of surfactant. This may be achieved,
for instance, through the use of surfactant~ ~having melt
temperatures greater than the temperatures commonly encountered
during storage, shipping, merchandising, and use of tissue paper `~
product embodiments of the invention: for example, ~elt
temperatures of about SO~C or hi~her. Also, the surfactant is
preferably water-soluble when applied to the wet ~eb. `~
The level of noncationic surfactant applied to wet tissue
paper webs to provide the aforementioned softness/tensile benefit
ranges from the minimum effective level needed for imparting such
benefit, on a constant tenslle basis for the ~nd product, to about
two (2) percent: preferably bet~een about 0.01% and about lX
noncationic surfactant retained by the web; morg preferably,
between about 0.05X and about 1.0X; and, most preferably, between about
0.05% and about 0.3%.
The surfactants preferably have alkyl chains with eight or
more carbon atoms. Exemplary anionic surfactants are linear alkyl
'0 sulfonates, and alkylben~ene sulfonates. E~emplary nonionic
surfactants are alkylglycosides including alkylglycoside esters such as
CrodestaTM SL-40 which is available from Croda, Inc. ~New York, NY); alkyl-
glycoside ethers as described in U. S. Patent 4,011,389, issued to ~. K.
Langdon, et al. on March 8, 1977; and alkylpolyethoxylated esters such as
2~ PegosperseTM 200 ML available from Glyco Chemicals, Inc~ (Greenwich, CT).
Alkylpolyglycosides are particularly preferred for use in the present
invention. The above listings of exempiary surfactants are intended to be
merely exemplary in nature, and are not meant to limit the scope of the
invention.
The surfactant, in addition to any emulsifying surfactant
that may be present on the polysilo~ane, may be applied by the
same methods and apparatuses used to apply pol~siloxanes. These methods
lnclude spraying and gravure printing. Preferably, an aqueous mixture
~ 3 3 ~
lq
containing the surfactant is sprayed on to the w~t tissue web as it courses
through the paper making machine~ Other ~ethods include application to a
forming wire or fabric prior to contact with the ~eb. Any surfactant other
than polysiloxane emulsifying surfactant material, is hereinafter referred
to as ~surfactant," and any surfactant present as the emulsifying component
of emulsified polysiloxane is hereinafter referred to as ~emulsifying
agent~.
The surfactant, may be applied to the tissue paper simultane-
ously ~ith, after, or before the polysiloxane. In a typical
process, the surfactant is applied subsequent to for~ation of the
wet web and prior to final drying. Preferably, surfactants are applied to
the wet tissue webs at fiber consistency levels of between about 10% and
about 80%; and, more preferably, between about 15% and about 35%.
Surprisingly, retention rates of noncationic surfactant applied to wet ~ebs
are high even though the surfaetant is applie~ under conditions wherein it
is not ionically substantive to the fibers. Retention rates in excess of
about 90% are expected at the preferred fiber consistencies without the
utilization of chemical retention aids.
As stated hereinbefore, it is also desirable to treat
polysiloxane containing tissue paper with a relatively low level
of a binder for lint control and/or to increase tensile strength. As used
herein the term ~binder~ refers to the various wet and dry strength
additives known in the art. The binder may be applied to the tissue paper
simultaneously with, after or before the polysiloxane and the surfactant. if
2; used. Preferably, binders are added to the wet tissue webs at fiber
consisten~y le~els of between about 10% and about 80%, and, ~ore preferably,
between about 15~ and about 35%.
Starch has been found to be the preferred binder for use in the
present invention. Preferably, the tissue paper is treated with an aqueous
solution of starch and, as mentioned above, the sheet is ~oist at the time
of application. In addition to reducing linting of the finished tissue
paper product, law levels of starch also imparts a modest improvement in the
tensile strength of tissue paper without imparting boardiness (i.e.
stiffness) which would result from additions of high levels of starch.
~33~38~
2G
Also, this provides tissue paper having improved strength/softness
relationship compared to tissue paper which has been strengthened by
traditional methods of increasing tensile s~rength: for example, shee~s
having increased tensile strength due to increased refining of the pulp; or
through the addition of other dry s~rength additives. ~his resul~ is
especially surprising since starch has traditionally been used to build
strength at the expense of so~tness in applications wherein softness is not
an important characteristic: for example, paperboard. Additionally,
parenthetically, starch has been used as a filler for printing and writing
paper to improve surface printability.
In general, suitable starch for practicing the present
invention is characterized by water solubility, and
hydrophilicity. Exemplary starch materials include corn starch
and potato starch, albeit it is not intended to thereby limit the
scope of suitable starch materials; and waxy corn starch that is
known industrially as amioca starch is particularly preferred~
A~ioca starch differs from common corn starch in ~hat it is
entirely amylopectin, whereas co~mon corn starch contains both
amplopectin and amylose. Various unique characteristics of amioca
starch are further described in "Amioca - The Starch From ~axy Corn~, H. H.
Schopmeyer, Food Industries, December 1945, pp. 106-108 (Vol. pp.
1476-14~8).
The starch can be in granular or dispersed for~ albeit
granular form is preferred. The starch is preferably sufficiently
cooked to induce swelling of the granules. More preferably, the
starch granules are swollen, as by cooking, to a point just pnior
to dispersion of the starch granule. Such highly swollen starch granules
shall be referred to as being Rfully cooked.q The conditions for dispersion
in general can vary depending upon the size of the starch granules, the
degree of crystallinity of the granules, and the amount of amylose present.
Fully cooked amioca starch, for example, ~an be prepared by heating an
aqueous slurry of about 4X consistency of starch granules at about 190~F
(about 88-C) for between about 30 and about 40 minutes. `
` ' ' ~
~33~381
.
21
Other exemplary starch materials which may be used include
modified cationic starches such as those madified to have nitrogen
containing groups such as amino groups and methylol group
attached to nitrogen, available from National 5tarch and Ohemical
Company, (Bridgewater, Ne~ Jersey). 5uch modified starch
materials have heretofore been used primarily as a pulp furnish
additive to increase wet and/or dry strength. However ~hen
applied in accordance with this invention by application to a wet tissue
paper web they may have reduced effect on wet strength relative to ~et-end
addition of the same modified starch materials. Considering that such
modified starch materials are more expensive than un~odified starches, the
latter have generally been preferred.
~.
The starch should be applied to the tissue paper while the
paper is in a ~oist condition. The starch based material is ~dded
to the wet tissue paper web, preferably when the ~eb has a ~iber consistency
of about ~OX or less. Non-cationic starch ~aterials are sufficiently
retained in the web to provide an obser~able effect on softness at a
particular strength level relative to increased refining; and~ are
preferably applied to wet tissue webs having fiber consistencies bet~een
about lOX and about 80%, more preferably, between about 15% and 35%.
Starch is preferably applied to tissue paper webs in an
aqueous solution. Methods of application include, the same pre-
viously described with reference to application of polysiloxane:
preferably by spraying; and, less preferably, by printing. The
starch may be applied to the tissue paper web simul~aneously with, prior to, `
or subsequent to the addition of polysiloxane and/or surfactant.
At least an effective amount of a binder, preferably starch, to
provide lint control and concomitant strength increase upon drying relative
to a non-binder treatèd but otherwise identical sheet is preferably applied
to the sheet. Preferably, between about 0.01Z and about 2.0X of a binder is
retained in the dried sheet, calculated on a dry fiber weight basis; and,
more preferably, between about O.lX and about 1.0% of a binder material,
preferably starch-based, is retained.
, ~:
.~
:: '
~ 3 3 ~
22
Analysis of ~he amoun~s o~ ~reatment chemicals herein re-
tained on tissue paper webs can be performed by any method
accepted in the applicable art. For example, the level of poly-
siloxane retained by the t~ssue paper can be determined by solvent
extraction of the polysilo~ane ~ith an organic solvent followed by atomic
absorption spectroscopy to determine the level of silicon in the extract;
the level of nonionic surfactants, such as a1kylglycosides, can be
determined by ex~raction in an organic so1ven~ ~ollowed by gas
chromatography to determine the level of surfactant in the extract; ~he
level of anionie surfactants, such as linear alkyl sulfonates, can be
determined by water extraction followed by colorimetry analysis of the
extract; the level of starch can be determined by amylase digestion of the ;-
starch to glucase followed by colori~etry analysis to determine glucose
level. These methods are exemplary, and are not meant to exclude other
methods which ~ay be useful for determining leYels of particular components
retained by the tissue paper. ` ~ ;
Hydrophilicity of tissue paper refers, in general, to the
propensity of the tissue paper to be wetted with water.
Hydrophilicity of tissue paper may be somewhat quantified by
determining the period of time required for dry tissue paper to
become completely wetted with water. This period of time is
referred to as ~wetting time.~ In order to provide a consistent
and repeatable test for wetting time, the follo~ing procedure may be used
for wetting time determinations: first, a dry (greater ~han 90% fiber
consistency level) sample unit sheet, approximately 4-3/8 inch x 4-3/4 inch ~;
(about 11.1 cm x 12 cm) of tissue pàper structure is provided; second, the
sheet is folded into four (4) juxtaposed quarters, and then crump1ed into a
ball approximately 0.75 inches (about 1.9 cm) to about 1 inch (about 2.5 cm)
in diameter; third, the balled sheet is placed on the sur~ace of a body of ~ "
distilled water at 72-F (abou~ 22CC), and a timer is simultaneously started;
fourth, the timer is stopped and read when wetting of the balled sheet is
completed. Complete wetting is observed vlsually. `~
The preferred hydrophilicity of tissue paper depends upon its
intended end use. It is desirable for tissue paper used in a
. .:
~33~
23
variety of applications, e.g., toilet paper~ to completely wet in
a relatively short period of time to prevent clogging once the
toilet is flushed. Preferably, wetting time is 2 minutes or less.
More preferably, wetting time is 30 seconds or less. Most preferably,
wetting time is 10 seconds or less.
Hydrophilicity characters of ~issue paper embodiments of the
present invention may, of course, be determined immediately after
manufacture. However, substantial increases in hydrophobicity may
occur during the first two weeks after the tissue paper is made:
i.e., after the paper has aged two (2) weeks following its
manufacture. Thus, the above stated wetting times are preferably
measured at the end of such two week period. Accordingly, wetting times
measured at the end of a two week aging period at room temperature are
referred to as "two week wetting times.
The density of tissue paper, as that term is used herein, is
the average dens;ty calculated as the basis weight of that paper
divided by the caliper, with the appropria~e unit conversions
incorporated therein. Caliper of the tissue paper, as used
herein, is the thickness of the paper when subjected to a compressive load
of 95 g/ln2 (15.5 g/cm2).
EXAMPLE I
The purpose of this example is to illustrate one method that can be
used to make soft tissue paper sheets treated with a polysiloxane in
accordance with the present invention.
A pilot scale Fourdrinier papermaking machine is used in the practice
of the present invention. The paper machine has a layered headbox having a
top chamber, a center chamber, and a bottom chamber. ~here applicable as
indicated in the following examples, the procedure described below also k
applies to such later examples. Briefly, a first fibrous slurry comprised
primarily of short papermak;ng fibers is pumped through the top and bottom
~33~3~
24
headbox chambers and, simultaneously, a second fibrous slurry comprised
primarily of long papermaking fibers is pumped through the center headbox
chamber and delivered in superposed relation onto the Fourdrinier wire to
- form thereon a three-layer embryonic web. The first~ slurry has a fiber
consistency of about O.llX and its fibrous content is Eucalyptus Hardwood
Kraft. The second slurry has a fiber consistency of about 0.15% and its
fibrous content is Northern Softwood Kraft. Dewatering occurs through the
Fourdrinier wire and is assisted by a deflector and vacuum boxes. The
Fourdrinier wire is of a 5-shed, satin weave configuration having 87
machine-direction and 76 cross-machine-direction monofilaments per inch,
respectively. The embryonic wet web is transferred from the Foudrinier
wire, at a fiber consistency of about 22% at the point of transfer, to a
carrier fabric having a 5-shed satin weave, 35 machine-direction and 33
cross-machine-direction monofilaments per inch, respectively. The
non-fabric side of the web is sprayed with an aqueous solution containing an -
emulsified polysiloxane composition, further described below, by a 2
spray nozzle located directly opposite a vacuum de~atering box. The wet web
has a fiber consistency of about 22% (total web weight basis) when sprayed
by the aqueous solution. The sprayed web is carried on the carrier fabric
past the vacuum dewatering box, through blow-through predryers after which -
the web is transferred onto a Yankee dryer. The other process and machine
conditions are listed below. The fiber consistency is about 27% after the
vacuum dewatering box and, by the action of the predryers, about 65% prior
to transfer onto the Yankee dryer; creping adhesive comprising a 0.25% ~ ë.`
aqueous solution of poly~inyl alcohol is spray applied by applioators; the
fiber consistency is increased to an estimated 9 ~ before dry creping the
web with a doctor blade. The doctor blade has a bevel angle of about 24
degrees and is positioned with respect to the Yankee dryer to provide an
impact angle of about 83 degrees; the Yankee dryer is operated at about
350-F (177-C); the Yankee dryer is operated at about 800 fpm (feet per
minute) (about 244 meters per minute). The dry creped web is then passed ~ibetween two calender rolls. The two calender rolls are biased together at
roll weight and operated at surface speeds of 660 fpm (about 201 meters per
minute).
. ~ .
The aqueous solution sprayed through the spray nozzle onto the wet web
contains 0.71% by weight of Dow Corning Q2-7224 (a 35% nonionic emulsion of
. .
~ :~33~3~
2~
an amino-functional polydimethylpolysiloxane marketed by Dow Corning Corp.).
The volumetric flow rate of the aqueous solution through the noz71e is about
3 gal./hr.-cross -direction ft (about 37 liters/hr-meter). The retention
rate of the polysiloxane applied to the web, in general, is about 90%.
The resulting tissue paper has a basis weight of 30g/m2, a density of
.lOg/cc, and contains .025% by weight, of the amino^functional
polydimethylpolysiloxane compound.
Importantly, the resulting tissue paper has a silky, flannel-like feel,
and enhanced tactile softness.
EXAMPLE II
.:
The purpose of this example is to illustrate one method that can be
used to make soft tissue paper sheets wherein the tissue paper is treated
with polysiloxane, surfactant and starch.
: .:
A 3-layer papen sheet is produced in accordance with the hereinbefore
described process of Example I. The tissue web is, in addition to being
treated with a polysiloxane compound as described aboYe, also treated with
CrodestaTM SL-40 (an alkyl glycoside polyester nonionic surfactant marketed
by Croda Inc.) and with a fully cooked amioca starch prepared as described
in the specification. The surfactant and starch are applied simultaneously
with the emulsified polysiloxane composition as part of the aqueous solution
sprayed through th~ papermachine spray nozzle. Concentration of the
CrodestaTM SL-40 nonionic surfactant in the aqueous solution is adjusted so
that the level of surfactant retained is about 0.15X, based upon the weight
of the dry fibers. Similarly, concentration of the starch in the aqueous
solution is adjusted so that the level of amioca starch retained is about
0.2%, based upon the weight of the dry fibers. ~i~-
.
The resulting tissue paper has a basis weight of 30y/m2, a density of
.lOg/cc, and contains .025% by weight of the Dow Q2-7224
polydimethypolysiloxane, 0.15% by weight of CrodestaTMSL-40 nonionic
,.
"-- 13~038~
26
surfactant and 0.2% by weight of the cooked amioca
starch. Importantly, the resulting tissue paper has a
silky flannel-like feel, enhancsd tactile softness and
has higher wettability and lower propensity for lint
than tissue paper treated only with the polysiloxane
composition.
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