Note: Descriptions are shown in the official language in which they were submitted.
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Title of Invention
METHOD FOR THE APPLICATION OF A VISCOUS COMPOSITION TO THE SURFACE OF A PAPER
WEB AND THEIR PRODUCTS
Background of the Invention
Consumers use paper wiping products, such as facial tissues and bath
tissues, for a wide variety of applications. Facial tissues are not only used
for nose
care but, in addition to other uses, can also be used as a general wiping
product.
Consequently, there are many different types of tissue products currently
commercially available.
In some applications, tissue products are treated with polysiloxane lotions in
order to increase the softness of the facial tissue. Adding silicone
compositions to
a facial tissue can impart improved softness to the tissue while maintaining
the
tissue's strength and while reducing the amount of lint produced by the tissue
during use.
In the papermaking industry, various manufacturing techniques have been
specifically designed to produce paper products which consumers find
appealing.
Manufacturers have employed various methods to apply chemical additives, such
as silicone compositions, to the surface of a tissue web. Currently, one
method of
applying chemicals to the surface of a tissue web is the Rotogravure printing
process. A Rotogravure printing process utilizes printing rollers to transfer
chemicals onto a substrate. Chemical emulsions that are applied to webs using
the Rotogravure printing process typically require the addition of water,
surfactants, and/or solvents in order for the emulsions to be printed onto the
substrate. Such additions are not only costly but also increase drying time
and
add process complexity.
Another method of applying chemical additives to the surface of a tissue
web is spray atomization. Spray atomization is the process of combining a
chemical with a pressurized gas to form small droplets that are directed onto
a
substrate, such as paper. One problem posed with atomization processes is that
manufacturers often find it difficult to control the amount of chemical that
is applied
to a paper ply. Thus, a frequent problem with spray atomization techniques is
that
a large amount of over-spray is generated, which undesirably builds upon
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machinery as well as the surfaces of equipment and products in the vicinity of
the
spray atomizer. Furthermore, over-spray wastes the chemical being applied, and
comprises a generally inefficient method of applying additives to a tissue
web.
Additionally, lack of control over the spray atomization technique also
affects the
uniformity of application to the tissue web.
In view of the above, a need exists in the industry for improving the method
for application of chemical additives to the surface of a paper web.
Further, besides the above-mentioned difficulties in applying chemical
additives to the surface of a paper web, some additives, such as softening
agents,
can also have a tendency to impart hydrophobicity to the treated paper' web.
Although hydrophobicity can be desirable in some applications, in other
applications, increased hydrophobicity can adversely affect the product. For
instance, increased hydrophobicity in a bath tissue can prevent the bath
tissue
from being wetted in a sufficient amount of time and prevent disintegration
and
dispersing when disposed in a commode or toilet. Hence, in some applications,
it
is difficult to find a proper balance between softness and absorbency, both of
which are desirable attributes for tissues, particularly bath tissues.
Thus, a need also exists for a process of applying hydrophobic
compositions to tissues for providing benefits to the tissue without
increasing the
hydrophibicity of the tissue beyond desirable limits.
Summary of the Invention
In general, the present invention is directed to an improved process for
applying compositions to paper webs, such as tissue webs, paper towels and
wipers. The present invention is also directed to improved paper products made
from the process.
According to one aspect of the present invention there is provided a
process for applying a chemical additive to a paper web comprising the steps
of:
(a) providing a paper web; and (b) extruding a viscous composition containing
a
chemical additive onto the paper web, wherein said composition is extruded
through a meltblown die to form attenuated fibers that are applied to the
paper
web, said composition comprising a hydrophobic composition.
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According to a further aspect of the present invention there is provided a
paper product comprising: (a) a paper web comprising cellulosic fibers wherein
the paper product further comprises: (i) a topical viscous hydrophobic
composition
on at least one side of said paper web, said viscous composition comprising a
chemical additive and being present on said paper web in the form of meltblown
attenuated fibers.
For example, in one embodiment, the present invention is directed to a
process for applying an additive to a paper web, such as a tissue web, that
includes the step of extruding a viscous composition onto the paper web. The
viscous composition has a viscosity sufficient for the composition to form
fibers as
the composition is extruded onto the web. In general, any suitable extrusion
device can be used to apply the composition to the web. In one embodiment, for
instance, the composition is extruded through a meltblown die and attenuated
prior
to being applied to the web.
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The composition can generally be any material that provides benefits to
paper webs. For instance, the composition can be a topical preparation that
improves the physical properties of the web, that provides the web with anti-
bacterial properties, that provides the web with medicinal properties, or that
provides any other type of wellness benefits to a user of the paper web. For
instance, the composition can contain an anti-acne agent, an anti-microbial
agent,
an anti-fungal agent, an antiseptic, an antioxidant, a cosmetic astringent, a
drug
astringent, an aiological agent, an emollient, an external analgesic, a
humectant, a
moisturizing agent, a skin conditioning agent, a skin exfoliating agent, a
sunscreen
agent, and mixtures thereof. In one embodiment, the composition is a softener.
The softener can be, for instance, a polysiloxane.
Of particular advantage, the process of the present invention is well-suited
to applying relatively high viscous compositions to paper webs. For instance,
the
composition can have a viscosity of at least 1000 cps, particularly 2000 cps
and
more particularly can have a viscosity of at least 3000 cps. Since the process
is
capable of handling high viscosity compositions, various chemical additives
can be
added directly to a paper web without having to dilute the additive with, for
instance, water or any other type of dilution agent to form a solution or
emulsion.
In one embodiment, the composition which is applied to the paper web can have
a
solids content of at least about 80%.
In fact, in one embodiment, a thickener can be added to the composition in
order to increase the viscosity. The thickener can be, for instance, a
polyethylene
oxide. It should be understood, however, that any suitable or conventional
thickener can also be used.
The amount of the composition that is applied to the paper web depends on
the particular application. For example, when applying a softener to a tissue
web,
the softener can be added in an amount from about 0.1 % to about 10% by weight
and particularly from about 0.1 % to about 5% by weight, based upon the weight
of
the web. As described above, in one embodiment, the composition is extruded
through a meltblown die onto the paper web. The meltblown die can have a
plurality of nozzles at a die tip. The nozzles can be arranged in one or more
rows
along the die tip. The fibers exiting the nozzles can have a diameter of from
generally about 5 microns to about 100 microns or greater.
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The process of the present invention provides great control over the amount
of composition applied to the web and the placement of the composition on the
web. It is believed that products made according to the process of the present
invention have various unique characteristics. For instance, in one
embodiment, a
product made according to the present invention includes a paper web
containing
cellulosic fibers. The viscous composition containing a chemical additive is
applied
to at least one side of the paper web. In accordance with the present
invention,
the composition is present on the paper web in the form of fibers, such as
continuous filaments.
In some applications, depending upon the composition that is applied to the
paper web, a paper web treated in accordance with the present invention will
have
improved strength characteristics, particularly an improved cross direction
wet:dry
ratio. For instance, when treating a paper web in accordance with the present
invention, the cross direction wet:dry ratio can increase by at least 25%,
particularly at least 40%, and more particularly by at least 50%. For example,
a
tissue web treated with a hydrophobic composition, such as a polysiloxane, can
have a wet:dry ratio of at least 0.45, particularly at least 0.48, and more
particularly
at least 0.52.
Various features and aspects of the present invention will be made apparent
from the following detailed description.
Brief Description of the Drawings
A full and enabling disclosure of this invention, is set forth in this
specification. The following Figures illustrate the invention:
Figure 1 is a schematic drawing showing application of a viscous
composition through a meltblown die tip onto a paper web in accordance with
the
present invention.
Figure 2 is a side view of one embodiment of a meltblown die that can be
used in accordance with the present invention;
Figure 3 is a bottom view of a portion of the meltblown die illustrated in
Figure 2 showing, in this embodiment, a row of nozzles through which
compositions are extruded; and
Figure 4 is a plan view of one embodiment of a paper web made in
accordance with the present invention.
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Repeated use of reference characters in the present specification and
drawings is intended to represent the same or analogous features of the
invention.
Detailed Description of the Invention
Reference now will be made to the embodiments of the invention, one or
more examples of which are set forth below. Each example is provided by way of
explanation of the invention, not as a limitation of the invention. In fact,
it will be
apparent to those skilled in the art that various modifications and variations
can be
made in the invention without departing from the scope or spirit of the
invention.
For instance, features illustrated or described as part of one embodiment can
be
used on another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention cover such modifications and variations as
come within the scope of the appended claims and their equivalents. It is to
be
understood by one of ordinary skill in the art that the present discussion is
a
description of exemplary embodiments only, and is not intended as limiting the
broader aspects of the present invention, which broader aspects are embodied
in
the exemplary constructions.
In general, the present invention is directed to applying viscous chemical
compositions through a meltblown die tip on to a paper web, such as a tissue
web.
It has been found by the present inventors that when compared with the
Rotogravure printing process and the spray atomizing process, the meltblown
process is more efficient.
For example, in comparison to the Rotogravure printing process, the
process of the present invention for applying compositions to paper webs can
be
simpler and less complex. The process of the present invention also provides
more flexibility with respect to operation parameters. For instance, it has
been
found that the process of the present invention provides better controls over
flow
rates and add on levels of the compositions being applied to the paper webs.
In
some applications, the process of the present invention may also allow the
compositions to be applied to the paper webs at higher speeds in comparison to
many Rotogravure printing processes.
In comparison to spray atomization processes, the process of the present
invention can provide greater control over application rates and can apply
compositions to paper webs more uniformly. The process of the present
invention
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also can better prevent against over application of the composition and can
provide better controls over placement of the composition onto the web.
Another advantage to the process of the present invention is that the
process is well suited to applying relatively high viscous chemical additives
to
paper webs. Thus, it has been discovered that additives can be applied to
paper
webs without first combining the additives with dilution agents, solvents,
surfactants, preservatives, antifoamers, and the like. As a result, the
process of
the present invention can be more economical and less complex than many
conventional application systems.
In one embodiment, a composition containing a chemical additive in
accordance with the present invention can be applied to a paper web in the
form of
fibers, such as, for instance, in the form or continuous fibers. Specifically,
it has
been discovered that under certain circumstances, compositions applied in
accordance with the present invention will fiberize when extruded through the
meltblown die tip. The ability to fiberize the compositions provides various
advantages. For example, when formed into fibers, the composition is easily
captured by the paper web. The fibers can also be placed on the web in
specific
locations. Further, when desired, the fibers will not penetrate through the
entire
thickness of the web, but instead, will remain on the surface of the web,
where the
chemical additives are intended to provide benefits to the consumer.
Another advantage of the present invention is that for some applications, a
lesser amount of the chemical additive can be applied to the web than what was
necessary in many rotogravure processes while still obtaining an equivalent or
better result. In particular, it is believed that since the chemical additive
can be
applied in a relatively viscous form without having to be formed into an
emulsion or
a solution and because the chemical additive can be applied as fibers
uniformly
over the surface of a web, it is believed that the same or better results can
be
obtained without having to apply as much of the chemical additive as was
utilized
in many prior art processes. For example, a softener can be applied to a web
in a
lesser amount while still obtaining the same softening effect in comparison to
Rotogravure processes and spray processes. Further, since less of the chemical
additive is needed, additional cost savings are realized.
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It has also been discovered that in some applications treating paper webs in
accordance with the present invention can significantly increase the wet
strength of
the webs. For instance, when applying certain compositions such as hydrophobic
compositions, it has been discovered that the treated paper web will have an
improved cross direction wet:dry ratio. As used herein, the "wet:dry ratio" is
the
ratio of the wet tensile strength divided by the dry tensile strength. For
paper webs
treated in accordance with the present invention, the cross direction wet:dry
ratio
can increase by at least 25% particularly by at least 40%, and more
particularly by
at least 50%.
For instance, tissue webs treated in accordance with the present invention
with a hydrophobic composition, such as a polysiloxane, can have a cross
direction wet:dry ratio of at least 0.45, particularly at least 0.48, and more
particularly at least 0.50. By applying a hydrophobic composition to the
surface of
a tissue web in the form of continuous filaments, a network of non-wettable
tissue
is formed that can provide significant strength when the tissue is wet, but
still allow
for excellent absorbency due to a large amount of uncoated tissue between the
filaments.
In one aspect of the present invention, a composition containing a
hydrophobic chemical additive is applied to a tissue, such as a bath tissue.
The
chemical additive, can be, for instance, a softener. By applying the
hydrophobic
composition in a discontinuous manner, a tissue can be produced not only
having
a lotiony, soft feel, but also having good wettability, even with the addition
of the
hydrophobic composition. In this manner, viscous hydrophobic compositions can
be applied to bath tissues for improving the properties of the tissue without
adversely affecting the wettability of the tissue.
Possible ingredients or chemical additives that can be applied to paper
webs in accordance with the present invention include, without limitation,
anti-acne
actives, antimicrobial actives, antifungal actives, antiseptic actives,
antioxidants,
cosmetic astringents, drug astringents, aiological additives, deodorants,
emollients,
external analgesics, film formers, fragrances, humectants, natural
moisturizing
agents and other skin moisturizing ingredients known in the art, opacifiers,
skin
conditioning agents, skin exfoliating agents, skin protectants, solvents,
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sunscreens, and surfactants. The above chemical additives can be applied alone
or in combination with other additives in accordance with the present
invention.
In one embodiment of the present invention, the process is directed to
applying a softener to a tissue web. The softener can be, for instance, a
polysiloxane that makes a tissue product feel softer to the skin of a user.
Suitable
polysiloxanes that can be used in the present invention include amine,
aldehyde,
carboxylic acid, hydroxyl, alkoxyl, polyether, polyethylene oxide, and
polypropylene
oxide derivatized silicones, such as aminopolydialkylsiloxanes. When using an
aminopolydialkysiloxane, the two alkyl radicals can be methyl groups, ethyl
groups,
and/or a straight branched or cyclic carbon chain containing from about 3 to
about
8 carbon atoms. Some commercially available examples of polysiloxanes include
WETSOFT CTW, AF-21, AF-23 and EXP-2025G of Kelmar Industries, Y-14128, Y-
14344, Y-14461 and FTS-226 of the Witco Corporation, and Dow Corning 8620,
Dow corning 2-8182 and Dow Corning 2-8194 of the Dow Corning Corporation.
In the past, polysiloxanes were typically combined with water, preservatives,
antifoamers, and surfactants, such as nonionic ethoxylated alcohols, to form
stable
and microbial-free emulsions and applied to tissue webs. Since the process of
the
present invention can accommodate higher viscosities, however, the
polysiloxanes
can be added directly to a tissue web or to another paper product without
having to
be combined with water, a surfactant or any other dilution agent. For example,
a
neat composition, such as a neat polysiloxane can be applied to a web in
accordance with the present invention. Since the polysiloxane can be applied
to a
web without having to be combined with any other ingredients, the process of
the
present invention is more economical and less complex than many prior
processes. Further, as described above, it has also been discovered that
lesser
amounts of the chemical additive can be applied to the web while still
obtaining the
same or better results, which provides further cost savings.
In the past, polysiloxanes and other additives were also used sparingly in
some applications due to their hydrophobicity. For instance, problems have
been
experienced in applying polysiloxane softeners to bath tissues due to the
adverse
impact upon the wettability of the tissue. By applying the polysiloxanes as
fibers at
particular areas on the web, however, it has been discovered that hydrophobic
compositions can be applied to tissue webs for improving the properties of the
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webs while maintaining acceptable wettability properties. In particular, as
will be
described in more detail below, in one embodiment of the present invention, a
hydrophobic composition can be applied in a discrete or discontinuous manner
to a
paper web in order to maintain a proper balance between improving the
properties
of the web through the use of the composition and maintaining acceptable
absorbency and wettability characteristics.
Referring to Figure 1, one embodiment of a process in accordance with the
present invention is illustrated. As shown, a tissue web 21 moves from the
right to
the left and is comprised of a first side 45 that faces upwards and a second
side 46
that faces downward. The tissue web 21 receives a viscous composition stream
29 upon its first side 45.
In general, the composition stream 29 is applied to the web 21 after the web
has been formed. The composition can be applied to the web, for instance,
after
the web has been formed and prior to being wound. Alternatively, the
composition
can be applied in a post treatment process in a rewinder system. As
illustrated in
Figure 1, the web 21 can be calendared, using calendar rolls 25 and 26
subsequent to application of the composition. Alternatively, the web can be
calendared and thereafter the composition can be applied to the web. The
calendar rolls can provide a smooth surface for making the product feel softer
to a
consumer.
As shown in the figures, a composition containing a chemical additive is
extruded to form a composition stream 29 that is directed onto the web 21. In
general, any suitable extrusion device can be used in accordance with the
present
invention. In one embodiment, for instance, the extruder includes a meltbiown
die
27. A meltbiown die is an extruder that includes a plurality of fine, usually
circular,
square or rectangular die capillaries or nozzles that can be used to form
fibers. In
one embodiment, a meltblown die can include converging high velocity gas (e.g.
air) streams which can be used to attenuate the fibers exiting the nozzles.
One
example of a meitblown die is disclosed, for instance, in U.S. Patent No.
3,849,241
to Butin, et al.
As shown in Figure 1, meitblown die 27 extrudes the viscous composition
stream 29 from die tip 28. As illustrated, the melt down die can be placed in
association with air curtain 30a-b. The air curtain 30a-b may completely
surround
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the extruded composition stream 29, while in other applications the air
curtain 30a-
b may only partially surround the composition stream 29. When present, the air
curtain can facilitate application of the composition to the paper web, can
assist in
forming fibers from the composition being extruded and/or can attenuate any
fibers
that are being formed. Depending upon the particular application, the air
curtain
can be at ambient temperature or can be heated.
An exhaust fan 31 is located generally below the tissue web 21. The
exhaust fan 31 is provided to improve air flow and to employ a pneumatic force
to
pull the composition stream 29 down on to the first side 45 of the tissue web
21.
The exhaust fan 31 serves to remove from the immediate vicinity airborne
particles
or other debris through an exhaust duct 32. The exhaust fan 31 operates by
pulling air using the rotating propeller 33 shown in dotted phantom in Figure
1.
In Figure 2, a more detailed view of the meltblown die 27 is shown in which
air intake 34a-b brings air into the meltblown die 27. Air travels into air
duct 35
and air duct 36, respectively, from air intake 34a and 34b. The air proceeds
along
air pathway 37 and air pathway 38, respectively, to a point near the center of
die
tip 28 at which the air is combined with viscous composition 40 containing the
desired chemical additives that emerges from a reservoir 39 to die tip 28.
Then,
the composition travels downward as viscous composition stream 29, shielded by
air curtain 30a-b.
Figure 3 shows a bottom view of the meltblown die 27 as it would appear
looking upwards from the tissue web 21 (as shown in Figure 1) along the path
of
the composition stream 29 to the point at which it emerges from die tip 28. In
one
embodiment, the meltblown die 27 is comprised of orifices 42 (several of which
are
shown in Figure 3), and such orifices 42 may be provided in a single row as
shown
in Figure 3. In other embodiments, there could be only a few scattered
orifices 42;
or perhaps, instead, a number of rows or even a series of channels could be
used
to release the composition stream 29 from meltblown die 27. In some cases, a
combination of channels and orifices 42 could be used. In other cases (not
shown), multiple rows of openings could be provided, and there is no limit to
the
different geometrical arrangement and patterns that could be provided to the
meltblown die 27 for extruding a composition stream 29 within the scope of the
invention.
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In one specific embodiment of the invention, a pressurized tank (not shown)
transfers a gas, such as air, to the meltblown die 27 for forcing the
composition
through the die tip. Composition 40 is forced through the meltblown die 27 and
extruded through, for instance, holes or nozzles spaced along the length of
the die
tip. In general, the size of the nozzles and the amount of the nozzles located
on
the meltblown die tip can vary depending upon the particular application.
For example, the nozzles can have a diameter from about 10 mils to about
50 mils, and particularly from about 14 mils to about 25 mils. The nozzles can
be
spaced along the die tip in an amount from about 3 nozzles per inch to about
50
nozzles per inch, and particularly from about 5 nozzles per inch to about 30
nozzles per inch. For example, in one embodiment, a die tip can be used that
has
approximately 17 nozzles per inch, and wherein each nozzle has a diameter of
about 14 mils.
Two streams of pressurized air converge on either side of the composition
stream 29 after it exits the meltblown die 27. The resulting air pattern
disrupts the
laminar flow of the composition stream 29 and attenuates the fibers being
formed
as they are directed onto the surface of the web. Different sized orifices or
nozzles
will produce fibers having a different diameter.
In general, the fibers that can be formed according to the present invention
include discontinuous fibers and continuous fibers. The fibers can have
various
diameters depending upon the particular application. For instance, the
diameter of
the fibers can vary from about 5 microns to about 100 microns. In one
embodiment, continuous fibers are formed having a diameter of about 25
microns.
The flow rate of the composition 40 may be, for instance, from about 2
grams/inch to about 9 grams/inch in one embodiment. The flow rate will depend,
however, on the composition and chemical additive being applied to the paper
web, on the speed of the moving paper web, and on various other factors. In
general, the total add on rate of the composition (including add on to both
sides of
the web if both sides are treated) can be up to about 10% based upon the
weight
of the paper web. When applying a softener to the paper web, for instance, the
add on rate can be from about 0.1 % to about 5% by weight, and particularly
from
about 0.5% to about 3% by weight of the paper web.
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The viscosity of the composition can also vary depending upon the
particular circumstances. When it is desired to produce fibers through the
meltblown die, the viscosity of the composition should be relatively high. For
instance, the viscosity of the composition can be at least 1000 cps,
particularly
greater than about 2000 cps, and more particularly greater than about 3000
cps.
For example, the viscosity of the composition can be from about 1000 to about
50,000 cps and particularly from about 2000 to about 10,000 cps.
As stated above, the purpose for air pressure or air curtain 30a-b on either
side of the composition stream 29 (in selected embodiments of the invention)
is to
assist in the formation of fibers, to attenuate the fibers, and to direct the
fibers onto
the tissue web. Various air pressures may be used.
The temperature of the composition as it is applied to a paper web in
accordance with the present invention can vary depending upon the particular
application. For instance, in some applications, the composition can be
applied at
ambient temperatures. In other applications, however, the composition can be
heated prior to or during extrusion. The composition can be heated, for
instance,
in order to adjust the viscosity of the composition. The composition can be
heated
by a pre-heater prior to entering the meltblown die or, alternatively, can be
heated
within the meltblown die itself using, for instance, an electrical resistance
heater.
In one embodiment, the composition containing the chemical additive can
be a solid at ambient temperatures (from about 20 C to about 23 C). In this
embodiment, the composition can be heated an amount sufficient to create a
flowable liquid that can be extruded through the meltblown die. For example,
the
composition can be heated an amount sufficient to allow the composition to be
extruded through the meltblown die and form fibers. Once formed, the fibers
are
then applied to a web in accordance with the present invention. The
composition
can resolidify upon cooling.
Examples of additives that may need to be heated prior to being deposited
on a paper web include compositions containing behenyl alcohol. Other
compositions that may need to be heated include compositions that contain a
wax,
that contain any type of polymer that is a solid at ambient temperatures,
and/or
that contain a silicone. One particular embodiment of a composition that may
need
to be heated in accordance with the present invention is the following:
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INGREDIENT WEIGHT PERCENT
Mineral Oil 25
Acetylated Lanolin Alcohol
(ACETULAN available from
Amerchol) 10
Tridecyl Neopentoate 10
Cerasin Wax 25
DOW Corning 200 20 cSt 30
The above composition is well suited for use as a lotion when applied to a
cellulosic web.
The above compositions can be heated to a temperature, for instance, from
about 75 C to about 150 C.
In Figure 1, the composition containing the chemical additive is applied to
the top surface of a paper web. It should be understood, however, that the
composition can be applied to both sides of the paper web or, alternatively,
can be
applied between a pair of adjacent layers. As described above, the composition
containing the additives of the present invention is generally applied after
the web
is formed. The composition can be applied while the web is dry or while the
web is
wet.
The process of the present invention can be used to apply compositions
and chemical additives to numerous and various different types of products.
For
most applications, however, the present invention is directed to applying
chemical
additives to paper products, particularly wiping products. Such products
include
facial tissues and bath tissues that have a basis weight of less than about 60
gsm,
particularly from about 20 gsm to about 60 gsm, and more particularly from
about
25 gsm to about 45 gsm. The tissue web can be made exclusively of pulp fibers
or, alternatively, can contain pulp fibers mixed with other fibers.
In one embodiment, a hydrophobic composition is applied to a tissue web in
accordance with the present invention while preserving the wettability and
absorbency characteristics of the web. For example, many chemical additives
that can be applied to tissue products are hydrophobic and thus when applied
to a
bath tissue across the surface of the tissue can adversely interfere with the
ability
of the tissue to become wet and disperse when being disposed of after use. For
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instance, various polysiloxane softening agents when applied to a tissue can
render a tissue unacceptable for use as a bath tissue due to the hydrophobic
nature of the polysiloxane, although improving the softness and feel of the
tissue.
In accordance with one embodiment of the present invention, however,
hydrophobic compositions such as polysiloxanes can be applied to tissue webs
and other paper products without adversely interfering with the wettability of
the
web. In this embodiment of the present invention, the hydrophobic composition
is
applied to the web in a discontinuous manner. For instance, in accordance with
the present invention, the hydrophobic composition can be applied evenly
across
the surface of the web yet be applied to contain various voids in the coverage
for
permitting the web to become wet when contacted with water. For example, in
one
embodiment, the hydrophobic composition is applied to the web as fibers that
overlap across the surface of the web but yet leave areas on the web that
remain
untreated. In other applications, however, it should be understood that the
viscous
composition can be extruded onto the web so as to cover the entire surface
area.
Referring to Figure 4, one embodiment of a paper web 21 treated in
accordance with the present invention is shown. In this figure, the paper web
is
illustrated in a dark color to show the presence of fibers or filaments 50
appearing
on the surface of the web. As shown, the filaments 50 intersect at various
points
and are randomly dispersed over the surface of the web. It is believed that
the
filaments 50 form a network on the surface of the web that increases the
strength,
particularly the wet strength of the web.
In the embodiment shown in Figure 4, the filaments 50 only cover a portion
of the surface area of the web 21. In this regard, the composition used to
form the
filaments can be applied to the web so as to cover from about 20% to about 80%
of the surface of the web, and particularly from about 30% to about 60% of the
surface area of the web. By leaving untreated areas on the web, the web
remains
easily wettable. In this manner, extremely hydrophobic materials can be
applied to
the web for improving the properties of the web while still permitting the web
to
become wet in an acceptable amount of time when contacted with water.
In one embodiment of the present invention, a hydrophobic softener can be
applied to a bath tissue and still permit the bath tissue to disperse in water
when
disposed of. The softener, for instance, can be an aminopolydialkylsiloxane.
In
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the past, when it has been attempted to apply softeners to bath tissue,
typically a
hydrophilically modified polysiloxane was used. The hydrophobic polysiloxanes,
such as aminopolydialkylsiloxanes, however, not only have better softening
properties, but are less expensive. Further, as described above, the process
of
the present invention allows lesser amounts of the additive to be applied to
the
tissue product while still obtaining the same or better results than many
conventional processes.
One test that measures the wettability of a web is referred to as the "Wet
Out Time" test. The Wet Out Time of paper webs treated in accordance with the
present invention can be about 10 seconds or less, and more specifically about
8
seconds or less. For instance, paper webs treated in accordance with the
present
invention can have a Wet Out Time of about 6 seconds or less, still more
specifically about 5 seconds or less, still more specifically from about 4 to
about 6
seconds.
As used herein, "Wet Out time" is related to absorbency and is the time it
takes for a given sample to completely wet out when placed in water. More
specifically, the Wet Out Time is determined by cutting 20 sheets of the
tissue
sample into 2.5 inch squares. The number of sheets used in the test is
independent of the number of plies per sheet of product. The 20 square sheets
are stacked together and stapled at each corner to form a pad. The pad is held
close to the surface of a constant temperature distilled water bath (23 +/-2
C),
which is the appropriate size and depth to ensure the saturated specimen does
not
contact the bottom of the container and the top surface of the water at the
same
time, and dropped flat onto the water surface, staple points down. The time
taken
for the pad to become completely saturated, measured in seconds, is the Wet
Out
Time for the sample and represents the absorbent rate of the tissue. Increases
in
the Wet Out Time represent a decrease in the absorbent rate.
Any suitable tissue can be treated in accordance with the present
invention. Further, a tissue product of the present invention can generally be
formed by any of a variety of papermaking processes known in the art. In fact,
any
process capable of forming a paper web can be utilized in the present
invention.
For example, a papermaking process of the present invention can utilize
adhesive
creping, wet creping, double creping, embossing, wet-pressing, air pressing,
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through-air drying, creped through-air drying, uncreped through-drying, as
well as
other steps in forming the paper web.
Besides tissue products, however, the process of the present invention can
also be applied to paper towels and industrial wipers. Such products can have
a
basis weight of up to about 200 gsm
and particularly up to about 150 gsm. Such products can be made from pulp
fibers
alone or in combination with other fibers, such as synthetic fibers.
In one embodiment, various additives can be added to the composition in
order to adjust the viscosity of the composition. For instance, in one
embodiment,
a thickener can be applied to the composition in order to increase its
viscosity. In
general, any suitable thickener can be used in accordance with the present
invention. For example, in one embodiment, polyethylene oxide can be combined
with the composition to increase the viscosity. For example, polyethylene
oxide
can be combined with a polysiloxane softener to adjust the viscosity of the
composition to ensure that the composition will produce fibers when extruded
through the meltblown die.
EXAMPLE 1
In order to further illustrate the present invention, a conventional
polysiloxane formulation was applied to a through-dried tissue web using a
rotogravure coater. For purposes of comparison, a neat
aminopolydimethylsiloxane was applied to the same bath tissue according to the
present invention. In particular, the neat polydimethylsiloxane was fiberized
using
a uniform fiber depositor marketed by ITW Dynatec and applied in a
discontinuous
fashion to the tissue web.
More specifically, a single-ply, three-layered uncreped throughdried bath
tissue was made using eucalyptus fibers for the outer layers and softwood
fibers
for the inner layer. Prior to pulping, a quaternary ammonium softening agent
(C-
6027 from Goldschmidt Corp.) was added at a dosage of 4.1 kg/Mton of active
chemical per metric ton of fiber to the eucalyptus furnish. After allowing 20
minutes of mixing time, the slurry was dewatered using a belt press to
approximately 32% consistency. The filtrate from the dewatering process was
either sewered or used as pulper make-up water for subsequent fiber batches
but
not sent forward in the stock preparation or tissuemaking process. The
thickened
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pulp containing the debonder was subsequently re-dispersed in water and used
as
the outer layer furnishes in the tissuemaking process.
The softwood fibers were pulped for 30 minutes at 4 percent consistency
and diluted to 3.2 percent consistency after pulping, while the debonded
eucalyptus fibers were diluted to 2 percent consistency. The overall layered
sheet
weight was split 30%/40%/30% among the eucalyptus/refined softwood/eucalyptus
layers. The center layer was refined to levels required to achieve target
strength
values, while the outer layers provided the surface softness and bulk. Parez
631 NC was added to the center layer at 2-4 kilograms per tonne of pulp based
on
the center layer.
A three layer headbox was used to form the web with the refined northern
softwood kraft stock in the two center layers of the headbox to produce a
single
center layer for the three-layered product described. Turbulence-generating
inserts recessed about 3 inches (75 millimeters) from the slice and layer
dividers
extending about 1 inch (25.4 millimeters) beyond the slice were employed. The
net slice opening was about 0.9 inch (23 millimeters) and water flows in all
four
headbox layers were comparable. The consistency of the stock fed to the
headbox was about 0.09 weight percent.
The resulting three-layered sheet was formed on a twin-wire, suction form
roll, former with forming fabrics being Lindsay 2164 and Asten 867a fabrics,
respectively. The speed of the forming fabrics was 11.9 meters per second. The
newly-formed web was then dewatered to a consistency of about 20-27 percent
using vacuum suction from below the forming fabric before being transferred to
the
transfer fabric, which was traveling at 9.1 meters per second (30% rush
transfer).
The transfer fabric was an Appleton Wire T807-1. A vacuum shoe pulling about 6-
15 inches (150-380 millimeters) of mercury vacuum was used to transfer the web
to the transfer fabric.
The web was then transferred to a throughdrying fabric (Lindsay wire
T1205-1). The throughdrying fabric was traveling at a speed of about 9.1
meters
per second. The web was carried over a Honeycomb throughdryer operating at a
temperature of about 350 F, (175 C.) and dried to final dryness of about 94-98
percent consistency. The resulting uncreped tissue sheet was then wound into a
parent roll.
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The parent roll was then unwound and the web was calendered twice. At
the first station the web was calendered between a steel roll and a rubber
covered
roll having a 4 P&J hardness. The calendar loading was about 90 pounds per
lineal inch (pli). At the second calendaring station, the web was calendered
between a steel roll and a rubber covered roll having a 40 P&J hardness. The
calender loading was about 140 pli. The thickness of the rubber covers was
about
0.725 inch (1.84 centimeters).
A portion of the web was then fed into the rubber-rubber nip of a
rotogravure- coater to apply the polydimethylsiloxane emulsion to both sides
of the
web. The aqueous emulsion contained 25% polydimethylsiloxane; 8.3%
surfactant; 0.75% antifoamer and 0.5% preservative.
The gravure rolls were electronically engraved, chrome over copper rolls
supplied by Specialty Systems, Inc., Louisville, Kentucky. The rolls had a
line
screen of 200 cells per lineal inch and a volume of 6.0 Billion Cubic Microns
(BCM)
per square inch of roll surface. Typical cell dimensions for this roll were
140
microns in width and 33 microns in depth using a 130 degree engraving stylus.
The rubber backing offset applicator rolls were a 75 shore A durometer cast
polyurethane supplied by American Roller company, Union Grove, Wisconsin. The
process was set up to a condition having 0.375 inch interference between the
gravure rolls and the rubber backing rolls and 0.003 inch clearance between
the
facing rubber backing rolls. The simultaneous offset/offset gravure printer
was run
at a speed of 2000 feet per minute using gravure roll speed adjustment
(differential) to meter the polysiloxane emulsion to obtain the desired
addition rate.
The gravure roll speed differential used for this example was 1000 feet per
minute.
The process yielded an add-on level of 2.5 weight percent total add-on based
on
the weight of the tissue (1.25% each side).
Another portion or section of the formed tissue web was then fed through a
uniform fiber depositor (a type of meltblown die) as described above. The
uniform
fiber depositor had 17 nozzles per inch and operated at an air pressure of 20
psi.
The die applied a fiberized neat polysiloxane composition onto the web. The
polysiloxane used in this example was obtained from Kelmar Industries. The
polysiloxane was added to the web to yield an add-on level of 2.5 weight
percent
total add-on based on the weight of the tissue (1.25% each side).
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After the two webs were formed, each web was tested for Wet Out Time
and for geometric mean tensile strength (GMT). Geometric mean tensile strength
is the square root of the product of the machine direction tensile strength
and the
cross-machine direction tensile strength of the web. Machine-direction and
cross-
machine direction tensile strengths were measure using an Instron tensile
tester
using a 3-inch jaw width, a jaw span of 4 inches and a process speed of 10
inches
per minute. Prior to testing, the samples were maintained under TAPPI
conditions
(73 F, 50% relative humidity) for 4 hours. Tensile strength was reported in
units of
grams per inch.
The Wet Out Time was measured as described above. The following
results were obtained:
WOT GMT
(Seconds) (Grams)
Sample I using gravure roll process 5.2 732
Sample 2 using uniform fiber depositor 4.6 765
Besides the above test, the samples were also subjectively tested for
softness and stiffness. It was determined from the test that although the
softness
of both. samples were comparable, Sample Number 2 was less stiff.
EXAMPLE 2
The following example was performed in order to illustrate the improvement
in strength properties that are obtained through the process of the present
invention.
In this example, two ply tissue webs were prepared, and treated with an
amino functional hydrophobic silicone softening agent under simulated
commercial
conditions. In particular, the treated tissue webs were treated while the webs
were
moving at a speed of 3000 feet per minute.
Each ply of the two ply tissue webs were made from a layered fiber furnish.
Specifically, each ply contained a first layer of eucalyptus fibers and a
second layer
of softwood fibers. The eucalyptus fibers comprised 65% by weight of the ply,
while the softwood fibers comprised 35% by weight of the ply. The two plies
were
attached together such that the eucalyptus fibers formed the outside surfaces
of
the tissue web.
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As described above, an amino functional hydrophobic silicone softening
agent was applied to the treated tissue webs. An equivalent tissue web was
also
left untreated for comparison. The silicone softening agent was product number
Y-
14128 obtained from the Witco Corporation. The silicone composition was
applied
to each side of the treated tissue webs using a meltblown die. The silicone
composition was applied to yield a total add-on level from about 0.75% to
about
1.25% by weight based on the weight of the tissue.
The meltblown die included 17 orifices per inch and was operated at an air
pressure of 20 psi and 30 psi in different sample runs. It was observed during
operation of the meltblown die that by increasing the air pressure of the
meltblown
die, thinner fibers were produced having more cross directional orientation.
After the tissue webs had been treated, the samples were examined and
compared for various physical characteristics. Basis weights were determined
for
the various tissue webs on both a bone dry basis and a conditioned basis
wherein
the tissue web had been conditioned under TAPPI conditions (50% RH, 22.7 C).
Caliper and bulk of the tissue webs were also determined. Caliper and bulk of
the
web were determined by use of an EMVECO 200A Tissue Caliper Tester at a load
of about 2.00 kPa over an area of about 2500 mm2.
Tensile strengths were measured using an Instron tensile tester using a 3-
inch jaw width, a jaw span of 4 inches and a cross head speed of 10 inches per
minute after maintaining the sample under TAPPI conditions (50% RH, 22.7 C)
for
4 hours before testing. Wet strength was measured in the same manner as dry
strength except that the tissue sample was folded without creasing about the
midline of the sample, held at the ends, and dipped in deionized water for
about
0.5 seconds at a depth of about 0.5 centimeters to wet the central portion of
the
sample. The wetted region was touched for about 1 second against an absorbent
towel to remove excess drops of fluid, and the sample was unfolded and set
into
the tensile tester jaws and immediately tested. The cross direction wet:dry
ratio
was determined and is reported in the table below. As stated above, the
wet:dry
ratio is the ratio of the wet tensile strength divided by the dry tensile
strength. The
wet:dry ratio was determined using the wet and dry cross direction tensile
strengths.
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Various other results obtained from the above tensile testing method are
also reported in the table below. Machine direction (MD) and cross direction
(CD)
tensile strengths for the tissue webs are reported in units of grams of
loading to
breakage per 3-inches sample width. The ratio of MD tensile strength to CD
tensile strength for the dry tissue webs is also reported. Percent stretch of
the dry
tissue web at peak load was determined, as was total energy absorbed (TEA)
which has units of centimeters-grams of force per square centimeter. Geometric
mean tensile (GMT) strength is defined as the square root of the product of
the CD
tensile strength and the MD tensile strength. The modulus of the tissue web is
defined as the slope of the tensile strength curve measured over a specific
load
range during the tensile test, for example between about 70 grams and 150
grams
of loading. The slope was determined in both the cross direction and the
machine
direction for the dry tissue webs. The geometric mean modulus (GMM) is
reported
as the square root of the product of the CD modulus and the MD modulus.
The Hercules Size Test is a measure of absorbency, with lower numbers
indicating a more absorbent product. The test measures the time required for
the
reflectance of a tissue web to decrease to a predetermined value as a dye
solution
penetrates through the tissue web. Results are reported in seconds, with
values
less than about 5 indicating a reasonably absorbent product.
Void volume of the resultant sheet was determined according to the
following void-volume test. First, the sheet was saturated with a non-polar
liquid
and the volume of liquid absorbed was measured. The volume of liquid absorbed
is equivalent to the void volume within the sheet structure. The void volume
is
expressed as grams of liquid absorbed per gram of fiber in the sheet.
The test includes the following steps. For each sample to be tested, sheets
are selected and a 1 inch x 1 inch square (1 inch in the machine direction and
1
inch in the cross machine direction) is cut out. The dry weight of each test
specimen is weighed and recorded to the nearest 0.0001 gram.
The specimen is placed in a dish containing POROFILTM pore wetting liquid
of sufficient depth and quantity to allow the specimen to float freely
following
absorption of the liquid. (POROFILTM liquid, having a specific gravity of
1.875
grams per cubic centimeter, available from Coulter Electronics Ltd., Northwell
Drive, Luton, Beds., England; Part No. 9902458.) After 10 seconds, the
specimen
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is held at the very edge (1-2 millimeters in) of one corner with tweezers and
removed from the liquid. The specimen is held with that corner uppermost and
excess liquid is allowed to drip for 30 seconds. The lower corner of the
specimen
is lightly dabbed (less than 1/2 second contact) with #4 filter paper (Whatman
Ltd.,
Maidstone, England) in order to remove any excess of the last partial drop.
The
specimen is immediately weighed, within 10 seconds. The weight is recorded to
the nearest 0.0001 gram. The void volume for each specimen, expressed as
grams of POROFIL per gram of fiber, is calculated as follows:
Void volume = [(W2 - W1)/W1] , wherein
WI = dry weight of the specimen, in grams, and
W2 = wet weight of the specimen, in grams.
Fuzziness, Grittiness, Silkiness, and Stiffness values were obtained through
a Sensory Profile Panel testing method. A group of 12 trained panelists were
given a series of tissue prototypes, one sample at a time. For each sample,
the
panelists rate the tissue for fuzziness (high values are preferred),
grittiness (low
values are preferred), silkiness (high values are preferred), and stiffness
(low
values are preferred) on a scale of 1 (low) to 16 (high) in a sequential,
monadic
fashion. Results are reported as an average of panel rankings.
The results are described below in Table 1.
Table I
Untreated Y-14128 at 20 psi Y-14128 at 30 psi
Basis Weight
(g/m2) 27.63 28.52 28.46
conditioned
Basis Weight
(g/m2) (bone dry) 25.77 26.74 26.61
Caliper m 166 178 172
Bulk cm / 6.01 6.24 6.04
MD Tensile - Dry 1012 897 866
(g/3in)
CD Tensile - Dry 410 366 364
/3in
GMT- Dry (g/3in) 644 573 561
MD/CD ratio - Dry 2.47 2.45 2.38
CD Tensile - Wet
/3in 143 176 189
Wet:Dry Ratio 0.35 0.48 0.52
MD Stretch - Dry 12.9 13.6 14.6
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%
CD Stretch - Dry 5.9 5.2 4.9
MD TEA - Dry
-cm/cm2 10.44 9.85 10.3
CD TEA - Dry
(g-CMcm2) 2.73 2.37 2.18
MD Slope - Dry 9.86 8.18 7.63
(kg)
CD Slope - Dry 8.97 9.41 10.24
(kg)
GMM - Dry (kg) 9.40 8.77 8.84
Hercules Size Test
(sec.) 0.6 1.7 2.4
Void Volume
fluid/g fiber) 7.83 7.88 7.75
Fuzziness 6.61 6.77 6.72
Grittiness 1.44 1.40 1.32
Stiffness 3.99 3.26 3.34
Silkiness 9.73 9.75 9.85
As shown above, the cross direction wet:dry ratio significantly improved
after the tissue web had been treated in accordance with the present
invention.
This improvement is due not only to the increase in the wet strengths of the
treated
tissue webs, but also due to the slight decrease in dry strengths upon
treatment of
the webs. Generally, lower dry strength products are softer products. Improved
softness is illustrated by the fact that the treated webs are perceived as
silkier,
fuzzier, less gritty and less stiff than are the untreated webs. The treated
webs
also maintain good absorbency with very little change in void volume.
It is understood by one of ordinary skill in the art that the present
discussion
is a description of exemplary embodiments only, and is not intended as
limiting the
broader aspects of the present invention, which broader aspects are embodied
in
the exemplary constructions. The invention is shown by example in the appended
claims.
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