Note: Descriptions are shown in the official language in which they were submitted.
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SOFT TISSUE PAPER HAVING A CHEMICAL SOFTENING
AGENT APPLIED ONTO A SURFACE THEREOF
FIELD OF THE INVENTION
This invention relates, in general, to tissue paper products. More
specifically, it relates
to tissue paper products containing chemical softening agent.
BACKGROUND OF THE INVENTION
Sanitary paper tissue products are widely used. Such items are commercially
offered in
formats tailored for a variety of uses such as facial tissues, toilet tissues
and absorbent towels.
All of these sanitary products share a common need, specifically to be soft to
the touch. Softness
is a complex tactile impression elicited by a product when it is stroked
against the skin. The
purpose of being soft is so that these products can be used to cleanse the
skin without being
irritating. Effectively cleansing the skin is a persistent personal hygiene
problem for many
people. Objectionable discharges of urine, menses, and fecal matter from the
perineal area or
otorhinolaryngogical mucus discharges do not always occur at a time convenient
for one to
perform a thorough cleansing, as with soap and copious amounts of water for
example. As a
substitute for thorough cleansing, a wide variety of tissue and toweling
products are offered to
aid in the task of removing from the skin and retaining the before mentioned
discharges for
disposal in a sanitary fashion. Not surprisingly, the use of these products
does not approach the
level of cleanliness that can be achieved by the more thorough cleansing
methods, and producers
of tissue and toweling products are constantly striving to make their products
compete more
favorably with thorough cleansing methods.
Accordingly, making soft tissue and toweling products which promote
comfortable
cleaning without performance impairing sacrifices has long been the goal of
the engineers and
scientists who are devoted to research into improving tissue paper. There have
been numerous
attempts to reduce the abrasive effect, i.e., improve the softness of tissue
products.
One area that has been exploited in this regard has been to select and modify
cellulose
fiber morphologies and engineer paper structures to take optimum advantages of
the various
available morphologies. Applicable art in this area include in U.S. Pat. Nos.
5,228,954;
5,405,499; 4,874,465; and 4,300,981.
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Another area which has received a considerable amount of attention is the
addition of
chemical softening agents (also referred to herein as "chemical softeners") to
tissue and toweling
products.
As used herein, the term "chemical softening agent" refers to any chemical
ingredient
which improves the tactile sensation perceived by the consumer who holds a
particular paper
product and rubs it across the skin. Although somewhat desirable for towel
products, softness is
a particularly important property for facial and toilet tissues. Such tactile
perceivable softness
can be characterized by, but is not limited to, friction, flexibility, and
smoothness, as well as
subjective descriptors, such as lubricious, velvet, silk or flannel, which
imparts a lubricious feel
to tissue. This includes, for exemplary purposes only, basic waxes such as
paraffin and beeswax
and oils such as mineral oil and silicone oil as well as petrolatum and more
complex lubricants
and emollients such as quaternary ammonium compounds with long alkyl chains,
functional
silicones, fatty acids, fatty alcohols and fatty esters.
Thus, it would be advantageous to provide for the addition of chemical
softeners to
already-dried paper webs either at the so-called dry end of the papermaking
machine or in a
separate converting operation subsequent to the papermaking step. Exemplary
art from this field
includes U.S. Pat. Nos. 5,215,626; 5,246,545; and 5,525,345. While each of
these references
represent advances over the previous so-called wet end methods particularly
with regard to
eliminating the degrading effects on the papermaking process, none are able to
completely
address the overall reduction of dust that accompanies such applications to
the dry paper web.
One of the most important physical properties related to softness is generally
considered
by those skilled in the art to be the strength of the web. 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. Achieving a high softening potential without degrading
strength has long
been an object of workers in the field of the present invention.
Accordingly, it is an object of the present invention to provide a soft tissue
paper that
emits less dust during use without performance impairing sacrifices such as in
the strength of the
paper.
SUMMARY OF THE INVENTION
The present invention provides for a tissue paper product having at least one
ply wherein
only one outer surface of the tissue paper product has a chemical softening
agent applied and
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substantially affixed thereto. The chemical softening agent provides the
tissue paper product
with a raw dispensing dust value. The dust value is at least about 13.6
percent less than the raw
dispensing dust value of a tissue paper product not having the chemical
softening agent applied
and substantially affixed thereto.
The present invention also provides for a through-air dried tissue paper
product having at
least one ply wherein only one outer surface of the tissue paper product has a
chemical softening
agent applied and substantially affixed thereto. The chemical softening agent
provides the tissue
paper product with a raw dispensing dust value of less than out 6485
particles.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "water soluble" refers to materials that are soluble
in water to at
least 3%, by weight, at 25 C.
As used herein, the terms "tissue paper web, paper web, web, paper sheet and
paper
product" are all used interchangeably to 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, forming an embryonic web, transferring the embryonic
web from the
forming surface to a transfer surface traveling at a lower speed than the
forming surface. The
web is then transferred to a fabric upon which it is through air dried to a
final dryness after
which it is wound upon a reel.
The terms "multi-layered tissue paper web, multi-layered paper web, multi-
layered web,
multi-layered paper sheet and multi-layered paper product" are all used
interchangeably in the
art to refer to sheets of paper prepared from two or more layers of aqueous
paper making furnish
which are preferably comprised of different fiber types, the fibers typically
being relatively long
softwood and relatively short hardwood fibers as used in tissue paper making.
The layers are
preferably formed from the deposition of separate streams of dilute fiber
slurries upon one or
more endless foraminous surfaces. If the individual layers are initially
formed on separate
foraminous surfaces, the layers can be subsequently combined when wet to form
a multi-layered
tissue paper web.
As used herein, the term "single-ply tissue product" means that it is
comprised of one ply
of uncreped tissue; the ply can be substantially homogeneous in nature or it
can be a multi-
layered tissue paper web. As used herein, the term "multi-ply tissue product"
means that it is
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comprised of more than one ply of uncreped tissue. The plies of a multi-ply
tissue product can
be substantially homogeneous in nature or they can be multi-layered tissue
paper webs.
As used herein, the term "substantively affixed chemical softening agent" is
defined as a
chemical agent which imparts lubricity or emolliency to tissue paper products
and also possesses
permanence with regard to maintaining the fidelity of its deposits without
substantial migration
when exposed to the environmental conditions to which products of this type
are ordinarily
exposed during their typical life cycle. Waxes and oils for example are
capable of imparting
lubricity or emolliency to tissue paper, but they suffer from a tendency to
migrate because they
have little affinity for the cellulose pulps which comprise the tissue papers
of the present
invention. While not wishing to be bound by theory, the substantively affixed
chemical softeners
of the present invention are believed to interact with the cellulose by
covalent, ionic, or
hydrogen bonding any of which are sufficiently potent to stem migration under
normal
environmental conditions.
Preferably, the substantively affixed chemical softening agents comprise
quaternary
ammonium compounds. Preferred quaternary compounds have the formula:
(R1)4-m - N+ - [RZ]m X
wherein:
mislto3;
R1 is a C1 -C6 alkyl group, hydroxyalkyl group, hydrocarbyl or substituted
hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof;
R2 is a C14-C22 alkyl group, hydroxyalkyl group, hydrocarbyl or substituted
hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof;
and
X- is any softener-compatible anion are suitable for use in the present
invention.
Preferably, each Rl is methyl and X- is chloride or methyl sulfate.
Preferably, each R2 is
C16-C18 alkyl or alkenyl, most preferably each R2 is straight-chain C18 alkyl
or alkenyl.
Optionally, the R2 substituent can be derived from vegetable oil sources.
Such structures include the well-known dialkyldimethylammonium salts (e.g.
ditallowdimethylammonium chloride, ditallowdimethylammonium methyl sulfate,
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di(hydrogenated tallow)dimethyl ammonium chloride, etc.), in which Rl are
methyl groups, R2
are tallow groups of varying levels of saturation, and X- is chloride 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 or 18 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.
It is also known that
depending upon the product characteristic requirements the saturation level of
the ditallow can
be tailored from non hydrogenated (soft) to touch, partially or completely
hydrogenated (hard).
All of above-described levels of saturations are expressly meant to be
included within the scope
of the present invention.
Particularly preferred variants of these softening agents are what are
considered to be
mono or diester variations of these quaternary ammonium compounds having the
formula:
(R1)4-m - N+ - [(CH2)n - Y - R31m X
wherein:
Y is --O--(O)C--, or --C(O)--O--, or --NH--C(O)--, or --C(O)--NH--;
mislto3;
nisOto4;
each R1 is a C1 -C6 alkyl group, hydroxyalkyl group, hydrocarbyl or
substituted
hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof;
each R3 is a C13 -C.21 alkyl group, hydroxyalkyl group, hydrocarbyl or
substituted
hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; and
X- is any softener-compatible anion.
Preferably, Y=--O--(O)C--, or --C(O)--O--; m=2; and n=2. Each Rl substituent
is
preferably a C1 -C3, alkyl group, with methyl being most preferred.
Preferably, each R3 is C13-
C17 alkyl and/or alkenyl, more preferably R3 is straight chain C15-C17 alkyl
and/or alkenyl, C15-
C17 alkyl, most preferably each R3 is straight-chain C17 alkyl. Optionally,
the R3 substituent can
be derived from vegetable oil sources.
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As mentioned above, X- can be any softener-compatible anion, for example,
acetate,
chloride, bromide, methylsulfate, formate, sulfate, nitrate and the like.
Preferably X- is chloride
or methyl sulfate.
Specific examples of ester-functional quaternary ammonium compounds having the
structures detailed above and suitable for use in the present invention may
include the diester
dialkyl dimethyl ammonium salts such as diester ditallow dimethyl ammonium
chloride,
monoester ditallow dimethyl ammonium chloride, diester ditallow dimethyl
ammonium methyl
sulfate, diester di(hydrogenated)tallow dimethyl ammonium methyl sulfate,
diester
di(hydrogenated)tallow dimethyl ammonium chloride, and mixtures thereof.
Diester ditallow
dimethyl ammonium chloride and diester di(hydrogenated)tallow dimethyl
ammonium chloride
are particularly preferred. These particular materials are available
commercially from Witco
Chemical Company Inc. of Dublin, Ohio under the tradename "ADOGEN SDMC".
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.
It is also known that depending upon the product characteristic requirements,
the saturation level
of the ditallow can be tailored from non hydrogenated (soft) to touch,
partially or completely
hydrogenated (hard). All of above-described levels of saturations are
expressly meant to be
included within the scope of the present invention.
It will be understood that substituents Rl, R2 and R3 may optionally be
substituted with
various groups such as alkoxyl, hydroxyl, or can be branched. As mentioned
above, preferably
each Rl is methyl or hydroxyethyl. Preferably, each R2 is C12-C18 alkyl and/or
alkenyl, most
preferably each R2 is straight-chain C16-C18 alkyl and/or alkenyl, most
preferably each R2 is
straight-chain C18 alkyl or alkenyl. Preferably R3 is C13-C17 alkyl and/or
alkenyl, most
preferably R3 is straight chain C15-C17 alkyl and/or alkenyl. Preferably, X-
is chloride or methyl
sulfate. Furthermore the ester-functional quaternary ammonium compounds can
optionally
contain up to about 10% of the mono(long chain alkyl) derivatives, e.g., (R2)2
-N+--((CH2)2 OH)
((CH2)2 OC(O)R3) X- as minor ingredients. These minor ingredients can act as
emulsifiers and
can be useful in the present invention.
Other types of suitable quaternary ammonium compounds for use in the present
invention are described in U.S. Pat. Nos. 5,543,067; 5,538,595; 5,510,000;
5,415,737, and
European Patent Application No. 0 688 901 A2.
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Di-quat variations of the ester-functional quaternary ammonium compounds can
also be
used, and are meant to fall within the scope of the present invention. These
compounds have the
formula:
0 (Rl)2 (Rl)2 0
II I I II
R1 - C - O - (CH2)2 - N+ - (CH2)n N+ - (CH2)2 - O - C - R3 2 X-
In the structure named above each Rl is a C1-C6 alkyl or hydroxyalkyl group,
R3 is C11-
C21 hydrocarbyl group, n is 2 to 4 and X- is a suitable anion, such as a
halide (e.g., chloride or
bromide) or methyl sulfate. Preferably, each R3 is C13-C17 alkyl and/or
alkenyl, most preferably
each R3 is straight-chain C15-C17 alkyl and/or alkenyl, and Rl is a methyl.
While not wishing to be bound by theory, it is believed that the ester
moiety(ies) of the
quaternary compounds provides a measure of biodegradability. It is believed,
the ester-
functional quaternary ammonium compounds used herein biodegrade more rapidly
than do
conventional dialkyl dimethyl ammonium chemical softeners.
The use of quaternary ammonium ingredients before is most effectively
accomplished if
the quaternary ammonium ingredient is accompanied by an appropriate
plasticizer. The
plasticizer can be added during the quaternizing step in the manufacture of
the quaternary
ammonium ingredient or it can be added subsequent to the quaternization but
prior to the
application as a chemical softening agent. The plasticizer is characterized by
being substantially
inert during the chemical synthesis, but acts as a viscosity reducer to aid in
the synthesis and
subsequent handling, i.e. application of the quaternary ammonium compound to
the tissue paper
product. Preferred pasticizers are comprised of a combination of a non-
volatile polyhydroxy
compound and a fatty acid. Preferred polyhydroxy compounds include glycerol
and
polyethylene glycols having a molecular weight of from about 200 to about
2000, with
polyethylene glycol having a molecular weight of from about 200 to about 600
being
particularly preferred. Preferred fatty acids comprise C6-C23 linear or
branched and saturated or
unsaturated analogs with isostearic acid being the most preferred.
While not wishing to be bound by theory, it is believed that a synergism
results from the
relationship of the polyhydroxy compound and the fatty acid in the mixture.
While the
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polyhydroxy compound performs the essential function of viscosity reduction,
it can be quite
mobile after being laid down thus detracting from one of the objects of the
present invention, i.e.
that the deposited softener be substantively affixed. The inventors have now
found that the
addition of a small amount of the fatty acid is able to stem the mobility of
the polyhydroxy
compound and further reduce the viscosity of the mixture so as to increase the
processability of
compositions of a given quaternary ammonium compound fraction.
Alternative embodiments of preferred substantively affixed chemical softening
agents
comprise well-known organo-reactive polydimethyl siloxane ingredients,
including the most
preferred - amino functional polydimethyl siloxane.
A most preferred form of the substantively affixed softening agent is to
combine the
organo-reactive silicone with a suitable quaternary ammonium compound. In this
embodiment
the organo-reactive silicone is preferred to be an amino polydimethyl siloxane
and is used at an
amount ranging from 0 up to about 50% of the composition by weight, with a
preferred usage
being in the range of about 5% to about 15% by weight based on the weight of
the polysiloxane
relative to the total substantively affixed softening agent.
The soft tissue paper of the present invention preferably has a basis weight
ranging from
between about 5 g/m2 and about 120 g/m2, more preferably between about 10 g/m2
and about 55
g/m2, and even more preferably between about 10 g/m2 and about 30 g/m2. The
soft tissue paper
of the present invention preferably has a density ranging from between about
0.01 g/m3 and
about 0.19 g/cm3, more preferably between about 0.03 g/m3 and about 0.6 g/cm3,
and even more
preferably between about 0.1 g/cm3 and 0.2 g/cm3.
The soft tissue paper of the present invention further comprises papermaking
fibers of
both hardwood and softwood types wherein at least about 50% of the papermaking
fibers are
hardwood and at least about 10% are softwood. The hardwood and softwood fibers
are most
preferably isolated by relegating each to separate layers wherein the tissue
comprises an inner
layer and at least one outer layer.
The tissue paper product of the present invention is preferably creped, i.e.,
produced on a
papermaking machine culminating with a Yankee dryer to which a partially dried
papermaking
web is adhered and upon which it is dried and from which it is removed by the
action of a
flexible creping blade.
Creping is a means of mechanically compacting paper in the machine direction.
The
result is an increase in basis weight (mass per unit area) as well as dramatic
changes in many
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physical properties, particularly when measured in the machine direction.
Creping is generally
accomplished with a flexible blade, a so-called doctor blade, against a Yankee
dryer in an on
machine operation.
A Yankee dryer is a large diameter, generally 8-20 foot drum which is designed
to be
pressurized with steam to provide a hot surface for completing the drying of
papermaking webs
at the end of the papermaking process. The paper web which is first formed on
a foraminous
forming carrier, such as a Fourdrinier wire, where it is freed of the copious
water needed to
disperse the fibrous slurry is generally transferred to a felt or fabric in a
so-called press section
where de-watering is continued either by mechanically compacting the paper or
by some other
de-watering method such as through-drying with hot air, before finally being
transferred in the
semi-dry condition to the surface of the Yankee for the drying to be
completed.
While the characteristics of the creped paper webs, particularly when the
creping process
is preceded by methods of pattern densification, are preferred for practicing
the present
invention, uncreped tissue paper is also a satisfactory substitute and the
practice of the present
invention using uncreped tissue paper is specifically incorporated within the
scope of the present
invention. Uncreped tissue paper, a term as used herein, refers to tissue
paper which is non-
compressively dried, most preferably by throughdrying. Resultant throughdried
webs are pattern
densified such that zones of relatively high density are dispersed within a
high bulk field,
including pattern densified tissue wherein zones of relatively high density
are continuous and the
high bulk field is discrete.
To produce uncreped tissue paper webs, an embryonic web is transferred from
the
foraminous forming carrier upon which it is laid, to a slower moving, high
fiber support transfer
fabric carrier. The web is then transferred to a drying fabric upon which it
is dried to a final
dryness. Such webs can offer some advantages in surface smoothness compared to
creped paper
webs.
Tissue paper webs are generally comprised essentially of papermaking fibers.
Small
amounts of chemical functional agents such as wet strength or dry strength
binders, retention
aids, surfactants, size, chemical softeners, crepe facilitating compositions
are frequently included
but these are typically only used in minor amounts. The papermaking fibers
most frequently
used in tissue papers are virgin chemical wood pulps. Additionally, filler
materials may also be
incorporated into the tissue papers of the present invention.
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Embodiments of the present invention wherein the substantively affixed
softening agent
comprises a quaternary ammonium compound further comprise from about 1% to
about 50% of
a polyhydroxy compound and from about 0.1% to about 10% of a fatty acid, each
as a
percentage of the weight of the quaternary ammonium compound.
Polyhydroxy compounds useful in this embodiment of the present invention
include
polyethylene glycol, polypropylene glycol and mixtures thereof.
Fatty acids useful in this embodiment of the present invention comprises C6-
C23 linear,
branched, saturated, or unsaturated analogs. The most preferred form of such a
fatty acid is
isostearic acid.
One particularly preferred chemical softening agent contains from about 0.1%
to about
70% of a polysiloxane compound.
Polysiloxanes which are applicable to chemical softening compositions of the
present
invention include polymeric, oligomeric, copolymeric, and other multiple
monomeric siloxane
materials. As used herein, the term polysiloxane shall include all of such
polymeric, oligomeric,
copolymeric, and other multiple-monomeric materials. Additionally, the
polysiloxane can be
straight chained, branched chain, or have a cyclic structure.
Preferred polysiloxane materials include those having monomeric siloxane units
of the
following structure:
R 1
I
Si O
I
RZ
wherein, Rl and Rl 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. Rl and R2 radicals of any
particular monomeric unit
may differ from the corresponding functionalities of the next adjoining
monomeric unit.
Additionally, the radicals can be either a straight chain, a branched chain,
or have a cyclic
structure. The radicals Rl and R2 can, additionally and independently be other
silicone
functionalities such as, but not limited to siloxanes, polysiloxanes, and
polysilanes. The radicals
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Rl and R2 can also contain any of a variety of organic functionalities
including, for example,
alcohol, carboxylic acid, and amine functionalities.
Reactive, organo-functional silicones, especially amino-functional silicones
are preferred
for the present invention.
Preferred polysiloxanes include straight chain organopolysiloxane materials of
the
following general formula:
.... RI R7 R9 R4
1 1 . F.1 .1
R Z- Si O Si - O Si - 0 Si R 5
I I I I
R 3 R g L R 10 R 6
a b
wherein each Rl -R9 radical can independently be any C1-Clo unsubstituted
alkyl or aryl radical,
and Rlo of any substituted C1-Clo alkyl or aryl radical. Preferably each R1 -
R9 radical is
independently any C1- C4 unsubstituted alkyl group those skilled in the art
will recognize that
technically there is no difference whether, for example, R9 or Rlo is the
substituted radical.
Preferably the mole ratio of b to (a+b) is between 0 and about 20%, more
preferably between 0
and about 10%, and most preferably between about 1 Io and about 5 Io.
In one particularly preferred embodiment, R1 -R9 are methyl groups and Rlo is
a
substituted or unsubstituted alkyl, aryl, or alkenyl group. Such material
shall be generally
described herein as polydimethylsiloxane which has a particular functionality
as may be
appropriate in that particular case. Exemplary polydimethylsiloxane include,
for example,
polydimethylsiloxane having an alkyl hydrocarbon Rlo radical and
polydimethylsiloxane having
one or more amino, carboxyl, hydroxyl, ether, polyether, aldehyde, ketone,
amide, ester, thiol,
and/or other functionalities including alkyl and alkenyl analogs of such
functionalities. For
example, an amino functional alkyl group as Rlo could be an amino functional
or an aminoalkyl-
functional polydimethylsiloxane. The 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 long as the polysiloxane can be rendered
into a form which
can be applied to the tissue paper product herein. 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
polysiloxanes which themselves are resistant to flowing can be effectively
deposited by
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emulsifying with a surfactant or dissolution into a vehicle, such as hexane,
listed for exemplary
purposes only.
While not wishing to be bound by theory, it is believed that the tactile
benefit efficacy is
related to average molecular weight and that viscosity is also related to
average molecular
weight. Accordingly, due to the difficulty of measuring molecular weight
directly, viscosity is
used herein as the apparent operative parameter with respect to imparting
softness to tissue
paper.
References disclosing polysiloxanes include U.S. Pat. Nos. 2,826,551;
3,964,500;
4,364,837; 5,059,282; 5,529,665; 5,552,020; and British Patent 849,433.
It is anticipated that wood pulp in all its varieties will normally comprise
the tissue
papers with utility in this invention. However, other cellulose fibrous pulps,
such as cotton
linters, bagasse, rayon, etc., can be used and none are disclaimed. Wood pulps
useful herein
include chemical pulps such as, sulfite and sulfate (sometimes called Kraft)
pulps as well as
mechanical pulps including for example, ground wood, ThermoMechanical Pulp
(TMP) and
Chemi-ThermoMechanical Pulp (CTMP). Pulps derived from both deciduous and
coniferous
trees can be used.
Hardwood pulps and softwood pulps, as well as combinations of the two, may be
employed as papermaking fibers for the tissue paper of the present invention.
The term
"hardwood pulps" as used herein refers to fibrous pulp derived from the woody
substance of
deciduous trees (angiosperms), whereas "softwood pulps" are fibrous pulps
derived from the
woody substance of coniferous trees (gymnosperms). Blends of hardwood Kraft
pulps,
especially eucalyptus, and northern softwood Kraft (NSK) pulps are
particularly suitable for
making the tissue webs of the present invention. A preferred embodiment of the
present
invention comprises the use of layered tissue webs wherein, most preferably,
hardwood pulps
such as eucalyptus are used for outer layer(s) and wherein northern softwood
Kraft pulps are
used for the inner layer(s). Also applicable to the present invention are
fibers derived from
recycled paper, which may contain any or all of the above categories of
fibers.
In one preferred embodiment of the present invention, which utilizes multiple
papermaking furnishes, the furnish containing the papermaking fibers which
will be contacted
by the particulate filler is predominantly of the hardwood type, preferably of
content of at least
about 80% hardwood.
Optional Chemical Additives
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Other materials can be added to the aqueous papermaking furnish or the
embryonic web
to impart other characteristics to the product or improve the papermaking
process so long as they
are compatible with the chemistry of the substantively affixed softening agent
and do not
significantly and adversely affect the softness, strength, or low dusting
character of the present
invention. The following materials are expressly included, but their inclusion
is not offered to be
all-inclusive. Other materials can be included as well so long as they do not
interfere or
counteract the advantages of the present invention.
It is common to add a cationic charge biasing species to the papermaking
process to
control the zeta potential of the aqueous papermaking furnish as it is
delivered to the
papermaking process. These materials are used because most of the solids in
nature have
negative surface charges, including the surfaces of cellulosic fibers and
fines and most inorganic
fillers. One traditionally used cationic charge biasing species is alum. More
recently in the art,
charge biasing is done by use of relatively low molecular weight cationic
synthetic polymers
preferably having a molecular weight of no more than about 500,000 and more
preferably no
more than about 200,000, or even about 100,000. The charge densities of such
low molecular
weight cationic synthetic polymers are relatively high. These charge densities
range from about
4 to about 8 equivalents of cationic nitrogen per kilogram of polymer. One
example material is
Cypro 514®, a product of Cytec, Inc. of Stamford, Conn. The use of such
materials is
expressly allowed within the practice of the present invention.
The use of high surface area, high anionic charge microparticles for the
purposes of
improving formation, drainage, strength, and retention is taught in the art.
Common materials
for this purpose are silica colloid, or bentonite clay. The incorporation of
such materials is
expressly included within the scope of the present invention.
If permanent wet strength is desired, the group of chemicals: including
polyamide-
epichlorohydrin, polyacrylamides, styrene-butadiene latices; insolubilized
polyvinyl alcohol;
urea-formaldehyde; polyethyleneimine; chitosan polymers and mixtures thereof
can be added to
the papermaking furnish or to the embryonic web. 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. Pat. Nos. 3,700,623 and 3,772,076. One commercial
source of useful
polyamide-epichlorohydrin resins is Hercules, Inc. of Wilmington, Del., which
markets such
resin under the mark Kymene 557H®).
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Many paper products must have limited strength when wet because of the need to
dispose of them through toilets into septic or sewer systems. If wet strength
is imparted to these
products, it is preferred to be fugitive wet strength characterized by a decay
of part or all of its
potency upon standing in presence of water. If fugitive wet strength is
desired, the binder
materials can be chosen from the group consisting of dialdehyde starch or
other resins with
aldehyde functionality such as Co-Bond 1000® offered by National Starch
and Chemical
Company, Parez 750® offered by Cytec of Stamford, Conn. and the resin
described in U.S.
Pat. No. 4,981,557 issued on Jan. 1, 1991, to Bjorkquist and incorporated
herein by reference.
If enhanced absorbency is needed, surfactants may be used to treat the tissue
paper webs
of the present invention. The level of surfactant, if used, is preferably from
about 0.01% to about
2.0% by weight, based on the dry fiber weight of the tissue paper. The
surfactants preferably
have alkyl chains with eight or more carbon atoms. Exemplary anionic
surfactants are linear
alkyl sulfonates, and alkylbenzene sulfonates. Exemplary nonionic surfactants
are
alkylglycosides including alkylglycoside esters such as Crodesta SL-40®
which is available
from Croda, Inc. (New York, N.Y.); alkylglycoside ethers as described in U.S.
Pat. No.
4,011,389, issued to W. K. Langdon, et al. on Mar. 8, 1977; and
alkylpolyethoxylated esters
such as Pegosperse 200 ML available from Glyco Chemicals, Inc. (Greenwich,
Conn.) and
IGEPAL RC-520® available from Rhone Poulenc Corporation (Cranbury, N.J.).
The present invention is further applicable to the production of multi-layered
tissue paper
webs. Multilayered tissue structures and methods of forming multilayered
tissue structures are
described in U.S. Pat. Nos. 3,994,771; 4,300,981; 4,166,001; and European
Patent Publication
No. 0 613 979 Al. The layers preferably comprise different fiber types, the
fibers typically being
relatively long softwood and relatively short hardwood fibers as used in multi-
layered tissue
paper making. Multi-layered tissue paper webs resultant from the present
invention comprise at
least two superposed layers, an inner layer and at least one outer layer
contiguous with the inner
layer. Preferably, the multi-layered tissue papers comprise three superposed
layers, an inner or
center layer, and two outer layers, with the inner layer located between the
two outer layers. The
two outer layers preferably comprise a primary filamentary constituent of
relatively short paper
making fibers having an average fiber length between about 0.5 and about 1.5
mm, preferably
less than about 1.0 mm. These short paper making fibers typically comprise
hardwood fibers,
preferably hardwood Kraft fibers, and most preferably derived from eucalyptus.
The inner layer
preferably comprises a primary filamentary constituent of relatively long
paper making fiber
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having an average fiber length of least about 2.0 mm. These long paper making
fibers are
typically softwood fibers, preferably, northern softwood Kraft fibers.
Preferably, the majority of
the particulate filler of the present invention is contained in at least one
of the outer layers of the
multi-layered tissue paper web of the present invention. More preferably, the
majority of the
particulate filler of the present invention is contained in both of the outer
layers.
The tissue paper products made from single-layered or multi-layered uncreped
tissue
paper webs can be single-ply tissue products or multi-ply tissue products.
The term "dust" is used herein to refer to the tendency of a tissue paper web
to release
fibers or particulate fillers as measured in a controlled abrasion test,
described infra. Dust can
be related to strength since the tendency to release fibers or particles is
directly related to the
degree to which such fibers or particles are anchored into the structure. As
the overall level of
anchoring is increased, the strength will be increased. However, it is
possible to have a level of
strength which is regarded as acceptable but have an unacceptable level of
dust. This is because
dust can be localized. For example, the surface of a tissue paper web can be
prone to dust, while
the degree of bonding beneath the surface can be sufficient to raise the
overall level of strength
to quite acceptable levels. In another case, the strength can be derived from
a skeleton of
relatively long papermaking fibers, while fiber fines or the particulate
filler can be insufficiently
bound within the structure. The tissue paper webs of the present invention are
relatively low in
lint. Levels of lint below about 12 are preferable, and below about 10 are
more preferable.
The multi-layered tissue paper webs of to the present invention can be used in
any
application where soft, absorbent multi-layered tissue paper webs are
required. Particularly
advantageous uses of the multi-layered tissue paper web of this invention are
in toilet tissue and
facial tissue products. Both single-ply and multi-ply tissue paper products
can be produced from
the webs of the present invention.
Application of a Chemical Softening Agents to Paper Webs
In accordance with the present invention, chemical softening agents may be
applied to a
paper web by any application method known in the industry such as, for
example, spraying,
printing, extrusion, brushing, by means of permeable or impermeable rolls
and/or pads. In a first
embodiment, the claimed softening agent may be applied to a paper web with a
slot die.
Specifically, the chemical softening agent may be extruded onto the surface of
a paper web via a
heated slot die. The slot die may be any suitable slot die or other means for
applying chemical
softening agent to the paper web. The slot die or other glue application means
may be supplied
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by any suitable apparatus. For example, the slot die may be supplied by a
heated hopper or drum
and a variable speed gear pump through a heated hose. The chemical softening
agent is
preferably extruded onto the surface of the paper web at a temperature that
permits the chemical
softening agent to bond to the paper web. Depending on the particular
embodiment, the
chemical softening agent can be at least partially transferred to rolls in a
metering stack (if used)
and then to the paper web.
Additionally, the chemical softening agent may be applied to a paper web by an
apparatus comprising a fluid transfer component. The fluid transfer component
preferably
comprises a first surface and a second surface. The fluid transfer component
further preferably
comprises pores connecting the first surface and the second surface. The pores
are disposed
upon the fluid transfer component in a non-random pre-selected pattern. A
fluid supply is
operably connected to the fluid transfer component such that a fluid (such as
the chemical
softening agent) may contact the first surface of the fluid transfer
component. The apparatus
further comprises a fluid motivating component. The fluid motivating component
provides an
impetus for the fluid to move from the first surface to the second surface via
the pores. The
apparatus further comprises a fluid receiving component comprising a paper
web. The paper
web comprises a fluid receiving (or outer) surface. The fluid receiving
surface may contact
droplets of fluid formed upon the second surface. Fluid may pass through pores
from the first
surface to the second surface and may transfer to the fluid receiving surface.
The fluid transfer component may comprise a hollow cylindrical shell. The
cylindrical
shell may be sufficiently structural to function without additional internal
bracing. The
cylindrical shell may comprise a thin outer shell and structural internal
bracing to support the
cylindrical shell. The cylindrical shell may comprise a single layer of
material or may comprise
a laminate. The laminate may comprise layers of a similar material or may
comprise layers
dissimilar in material and structure. In one embodiment the cylindrical shell
comprises a
stainless steel shell having a wall thickness of about 0.125 inches (3 mm). In
another
embodiment (not shown) the fluid transfer component may comprise a flat plate.
In another
embodiment the fluid transfer component may comprise a regular or irregular
polygonal prism.
The fluid application width of the apparatus may be adjusted by providing a
single fluid
transfer component of appropriate width. Multiple individual fluid application
components may
be combined in a series to achieve the desired width. In a non-limiting
example, a plurality of
stainless steel cylinders each having a shell thickness of about 0.125 inches
(3 mm) and a width
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of about 6 inches (about 15 cm) may be coupled end to end with an appropriate
seal - such as an
o-ring seal between each pair of cylinders. In this example, the number of
shells combined may
be increased until the desired application width is achieved.
The fluid transfer component preferably further comprises pores connecting the
first
surface 110 and the second surface. Connecting the surfaces refers to the
pores each providing a
pathway for the transport of a fluid from the first surface 110 to the second
surface. In one
embodiment, the pores may be formed by the use of electron beam drilling as is
known in the
art. Electron beam drilling comprises a process whereby high energy electrons
impinge upon a
surface resulting in the formation of holes through the material. In another
embodiment, the
pores may be formed using a laser. In another embodiment, the pores may be
formed by using a
drill bit. In yet another embodiment, the pores may be formed using electrical
discharge
machining as if known in the art.
In one embodiment, an array of pores may be disposed to provide a uniform
distribution
of fluid droplets to maximize the ratio of fluid surface area to applied fluid
volume. In one
embodiment, this may be used to apply a chemical softening agent in a pattern
of dots to
maximize the potential for adhesion between two surfaces for any volume of
applied chemical
softening agent.
The pattern of pores upon the second surface may comprise an array of pores
having a
substantially similar diameter or may comprise a pattern of pores having
distinctly different pore
diameters. In an alternative embodiment, the array of pores may comprise a
first set of pores
having a first diameter and arranged in a first pattern. The array further
comprises a second set
of pores having a second diameter and arranged in a second pattern. The first
and second
patterns may be arranged to interact each with the other.
Alternatively, the chemical softening agent may be sprayed directly onto the
surface of a
paper web using equipment suitable for such a purpose and as well known to
those of skill in the
art.
Analytical and Testing Procedures
A. Density
The density of multi-layered tissue paper, as that term is used herein, is the
average
density calculated as the basis weight of that paper divided by the caliper,
with the appropriate
unit conversions incorporated therein. Caliper of the multi-layered tissue
paper, as used herein,
is the thickness of the paper when subjected to a compressive load of 95 g/in2
(15.5 g/cm2).
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B. Dispensing Dust Test Method
Dust is measured using a particle counter commercially available (Sympatec
QICPIC,
Sympatec GmbH, Am Pulverhaus 1, 38678 Clausthal-Zellerfeld, Germany). The
instrument is
used according to the manufacturer's recommendation and a frame rate of 400
frames/sec is
selected. The particle size range is set to 20 to 10,000 micrometers.
Sympatec's standard chute
for guiding particles into the instrument was modified by removing the flights
within the chute
and by attaching a funnel to the top of the chute. The funnel is constructed
of stainless steel and
has 4 trapezoidal sides, 14 inches across the wide part (top), tapering to 2
inches wide at the
bottom, i.e. point of attachment with the chute. The trapezoid sides are 12
inches long. A
vacuum is attached to the exit of the instrument to create an airflow through
the instrument, and
consequently the chute and the funnel. The vacuum is sufficient to create an
airspeed entering
the funnel of 470 feet/min. The airspeed is measured using an Extech
Instruments
ThermoAnemometer Mode1407113 and Anemometer metal probe, SN Q138487. The probe
was
mounted in a plastic tube in a square of foam (necessitated by the square
shape of the funnel).
The probe assembly was placed in the funnel so that the foam sealed against
the funnel walls
and the anemometer was centered above the shaft opening. The linear flow was
calculated for
the bottom of the funnel where the drop shaft begins (the 2"x2" opening).
To perform the dust test, sanitary tissue product is dispensed, i.e. pulled
apart at the
perforations, manually at the top of the funnel to release dust. The force to
rupture the product
at the perforations is a function of the dispensing tensile and the operator
merely applies enough
force directly in tension across the perforations to dispense the product in a
manner typical of
tissue dispensing. Care should be taken not to tear the product across any
perforations, rather it
should be dispensed by pulling directly in tension across the perforations.
The dust fibers and/or
particles so liberated are directed into a modified Sympatec chute and the
chute delivers them to
the measurement zone of the instrument by gravity and vacuum.
The QICPIC measures the number of particles passing through the measurement
zone
using dynamic image analysis. Five perforations are separated per measurement
and the Raw
Dispensing Dust value is simply the total number of particles counted.
The raw data needs to be normalized for width of the product at the
perforations. The
Raw Dispensing Dust value is multiplied by the width of the product at the
perforations in
inches and divided by 4.27. This result is the Dispensing Dust value. Products
more than
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about 6" wide should be precut in width with scissors to 4.27 inches wide
prior to testing to
prevent being too wide to dispense properly in tension.
The Normalized Dispensing Dust value is determined by any one of the following
relationships:
1) Dispensing Dust value divided by Dispensing Tensile and multiplied by 150
yields the
Tensile Normalized Dispensing Dust value; 2) Dispensing Dust Value divided by
Lint test result
and multiplied by 7 yields the Lint Normalized Dispensing Dust value; and 3)
Dispensing Dust
value divided by the product Density and multiplied by 0.08 yields the Density
Normalized
Dispensing Dust value.
The calculated dust valves as related to the application rate to the paper web
(in lb/ton)
and application method (spray, extrusion, or printing) compared to a non-
treated paper web area
provided in Table 1 below.
Table 1. Calculated Dust Valves (in # particles) Compared to Application Rate
of Chemical
Softening Agent to Substrate and Application Method and Dust Reduction
Application Rate of Chemical Softening Spray Extrusion Print None
Agent to Substrate (particles) (particles) (particles) (particles)
101b/ton 6435 5080 6485 7510
13.6% ------
Percent Dust Reduction 14.3% 32.4%
201b/ton 5815 5325 ------ 7510
------ ------
Percent Dust Reduction 22.6% 29.1%
C. Measurement of Panel Softness of Tissue Papers
Ideally, prior to softness testing, the paper samples to be tested should be
conditioned
according to Tappi Method #T4020M-88. Here, samples are preconditioned for 24
hours at a
relative humidity level of 10 to 35% and within a temperature range of 22 to
40 C. After this
preconditioning step, samples should be conditioned for 24 hours at a relative
humidity of 48 to
52% and within a temperature range of 22 . to 24 C.
Ideally, the softness panel testing should take place within the confines of a
constant
temperature and humidity room. If this is not feasible, all samples, including
the controls, should
experience identical environmental exposure conditions.
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Softness testing is performed as a paired comparison in a form similar to that
described
in "Manual on Sensory Testing Methods", ASTM Special Technical Publication
434, published
by the American Society For Testing and Materials 1968 and is incorporated
herein by
reference. Softness is evaluated by subjective testing using what is referred
to as a Paired
Difference Test. The method employs a standard external to the test material
itself. For tactile
perceived softness two samples are presented such that the subject cannot see
the samples, and
the subject is required to choose one of them on the basis of tactile
softness. The result of the
test is reported in what is referred to as Panel Score Unit (PSU). With
respect to softness testing
to obtain the softness data reported herein in PSU, a number of softness panel
tests are
performed. In each test ten practiced softness judges are asked to rate the
relative softness of
three sets of paired samples. The pairs of samples are judged one pair at a
time by each judge:
one sample of each pair being designated X and the other Y. Briefly, each X
sample is graded
against its paired Y sample as follows:
1. a grade of plus one is given if X is judged to may be a little softer than
Y, and a grade
of minus one is given if Y is judged to may be a little softer than X;
2. a grade of plus two is given if X is judged to surely be a little softer
than Y, and a
grade of minus two is given if Y is judged to surely be a little softer than
X;
3. a grade of plus three is given to X if it is judged to be a lot softer than
Y, and a grade
of minus three is given if Y is judged to be a lot softer than X; and, lastly:
4. a grade of plus four is given to X if it is judged to be a whole lot softer
than Y, and a
grade of minus 4 is given if Y is judged to be a whole lot softer than X.
The grades are averaged and the resultant value is in units of PSU. The
resulting data are
considered the results of one panel test. If more than one sample pair is
evaluated then all sample
pairs are rank ordered according to their grades by paired statistical
analysis. Then, the rank is
shifted up or down in value as required to give a zero PSU value to which ever
sample is chosen
to be the zero-base standard. The other samples then have plus or minus values
as determined by
their relative grades with respect to the zero base standard. The number of
panel tests performed
and averaged is such that about 0.2 PSU represents a significant difference in
subjectively
perceived softness.
Calculations
All results are in units of grams/inch. For purposes of this specification,
the tensile
strength should be converted into a"specific total tensile strength" defined
as the sum of the
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tensile strength measured in the machine and cross machine directions, divided
by the basis
weight, and corrected in units to a value in meters.
The dimensions and values disclosed herein are not to be understood as being
strictly
limited to the exact dimension and values recited. Instead, unless otherwise
specified, each such
dimension and/or value is intended to mean both the recited dimension and/or
value and a
functionally equivalent range surrounding that dimension nand/or value. For
example, a
dimension disclosed as "40 mm" is intended to mean "about 40 mm".
All documents cited in the Detailed Description of the Invention are, in
relevant part,
incorporated herein by reference; the citation of any document is not to be
construed as an
admission that it is prior art with respect to the present invention. To the
extent that any
meaning or definition of a term in this document conflicts with any meaning or
definition of the
same term in a document incorporated by reference, the meaning or definition
assigned to that
term in this document shall govern.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made without departing from the spirit and scope of the
invention. It is
therefore intended to cover in the appended claims all such changes and
modifications that are
within the scope of this invention.
