U.S. patent number 3,804,092 [Application Number 05/323,665] was granted by the patent office on 1974-04-16 for water dispersible nonwoven fabric.
This patent grant is currently assigned to Johnson & Johnson. Invention is credited to Deger Tunc.
United States Patent |
3,804,092 |
Tunc |
April 16, 1974 |
WATER DISPERSIBLE NONWOVEN FABRIC
Abstract
A water dispersible nonwoven fabric comprising one or more
layers of overlapping, intersecting fibers and from about four
percent to about thirty-five percent by weight of an alkali
cellulose ether sulfate resin binder, said nonwoven fabric having
good tensile strength and abrasion resistance in the presence of
body fluids such as urine, blood, and menstrual fluid. The nonwoven
fabrics may be incorporated in body fluid absorbent products such
as sanitary napkins, diapers, surgical dressings, and the like.
Inventors: |
Tunc; Deger (Edison, NJ) |
Assignee: |
Johnson & Johnson (New
Brunswick, NJ)
|
Family
ID: |
23260192 |
Appl.
No.: |
05/323,665 |
Filed: |
January 15, 1973 |
Current U.S.
Class: |
604/364; 428/913;
604/368; 604/373; 604/378; 428/359; 536/59; 604/370; 604/375;
442/148 |
Current CPC
Class: |
A61L
15/28 (20130101); A61L 15/62 (20130101); A61L
15/28 (20130101); C08L 1/26 (20130101); Y10S
428/913 (20130101); Y10T 428/2904 (20150115); Y10T
442/273 (20150401) |
Current International
Class: |
A61L
15/16 (20060101); A61L 15/62 (20060101); A61L
15/28 (20060101); A41b 013/02 (); A61f
013/16 () |
Field of
Search: |
;128/156,284,286,287,290,296 ;117/140,143A ;161/151,169
;260/224 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Claims
What is claimed is:
1. A water-dispersible nonwoven fabric comprising: a layer of
overlapping, intersecting fibers, said fibers having a length not
more than about two inches; and from about 4 to about 35 percent by
weight of the fabric of an alkali cellulose ether sulfate resin
binder distributed in said fabric, said resin binder having an
average of from about 0.1 to about 0.3 sulfate groups per
anhydroglucose unit.
2. A water-dispersible nonwoven fabric according to claim 1,
wherein said alkali cellulose ether sulfate resin has an average of
from about 0.15 to about 0.25 sulfate groups per anhydroglucose
unit.
3. A water-dispersible nonwoven fabric according to claim 1,
wherein the alkali cellulose ether sulfate resin is an alkali alkyl
cellulose sulfate, said alkyl group having from one to four carbon
atoms.
4. A water-dispersible nonwoven fabric according to claim 3,
wherein the alkali alkyl cellulose sulfate resin is sodium ethyl
cellulose sulfate.
5. A water-dispersible nonwoven fabric according to claim 3,
wherein the alkali alkyl cellulose sulfate resin is sodium methyl
cellulose sulfate.
6. A water-dispersible nonwoven fabric according to claim 1,
wherein the alkali cellulose ether sulfate resin is an alkali
hydroxyalkyl cellulose sulfate, said hydroxyalkyl group having from
one to four carbon atoms.
7. A water-dispersible nonwoven fabric according to claim 6 wherein
the alkali hydroxyalkyl cellulose sulfate resin is sodium
hydroxyethyl cellulose sulfate.
8. A water-dispersible nonwoven fabric according to claim 6,
wherein the alkali hydroxyalkyl cellulose sulfate resin is sodium
hydroxypropyl cellulose sulfate.
9. A water-dispersible nonwoven fabric according to claim 1,
wherein the alkali cellulose ether sulfate resin is an alkali
hydroxyalkyl alkyl sulfate, said hydroxyalkyl and said alkyl groups
each having from one to four carbon atoms.
10. A water-dispersible nonwoven fabric according to claim 9,
wherein the alkali hydroxyalkyl alkyl cellulose sulfate is sodium
hydroxypropyl methyl cellulose sulfate.
11. A water-dispersible nonwoven fabric according to claim 1
wherein, said fibers are viscose rayon fibers.
12. A water-dispersible nonwoven fabric according to claim 1
wherein the length of said fibers does not exceed about one and one
half inches.
13. A water-dispersible nonwoven fabric according to claim 1,
wherein said resin binder is distributed in said fabric in a
predetermined pattern.
14. A water-dispersible nonwoven fabric according to claim 1,
wherein said fibers are viscose rayon fibers having a length of
from about one half inch to about one and one half inches and said
resin binder is sodium ethyl cellulose sulfate.
15. A water-dispersible nonwoven fabric according to claim 1,
wherein there is from about 4 to about 20 percent of said resin
binder by weight of the fabric.
16. A water-dispersible nonwoven fabric comprising: a layer of
overlapping, intersecting textile fibers, said fibers being viscose
rayon fibers from about one half inch to about one and one half
inches in length; and from about 4 percent to about 20 percent of
sodium ethyl cellulose sulfate distributed in said fabric, said
sodium ethyl cellulose sulfate having an average of from about 0.15
to about 0.25 sulfate groups per anhydroglucose unit.
17. An absorbent product for contacting body fluids comprising: an
absorbent core and a fluid-pervious, water-dispersible nonwoven
fabric covering at least a portion of said absorbent core; said
nonwoven fabric comprising a layer of overlapping, intersecting
fibers, said fibers having a length not more than about two inches;
and, distributed in said fabric, from about 4 to about 35 percent
by weight of the fabric of an alkali cellulose ether sulfate resin
binder, said resin binder having an average of from about 0.1 to
about 0.3 sulfate groups per anhydroglucose unit.
18. An absorbent product according to claim 17 wherein said
absorbent core includes a fluid-pervious element.
19. An absorbent product according to claim 18, wherein the
fluid-pervious element is tissue.
20. An absorbent product according to claim 18, wherein the
fluid-pervious element is gauze.
21. An absorbent product according to claim 18, wherein the
fluid-pervious element is a plastic netting.
22. An absorbent product according to claim 17, wherein said
absorbent core includes a fluid-impervious element.
23. An absorbent product according to claim 22, wherein the
fluid-impervious element comprises polyethylene.
24. An absorbent product according to claim 17, wherein the
absorbent core includes a fluid-pervious element and a
fluid-impervious element.
25. An absorbent product according to claim 24, wherein the fluid
pervious element is tissue and the fluid-impervious material
comprises polyethylene.
Description
This invention relates to new nonwoven fabrics which are readily
dispersible in water and are flushable. More particularly, this
invention relates to nonwoven fabrics which, in addition to having
the above-mentioned desirable characteristics, exhibit satisfactory
tensile strength when they are contacted with body fluids.
Nonwoven fabrics are widely used as components of such disposable
goods as sanitary napkins, diapers, bandages, and the like. Such
fabrics, if they are to function effectively, must maintain their
structural integrity, as well as exhibit satisfactory tensile
strength, when they are wet or damp with the various body fluids,
for example, blood, menstrual fluid and urine, with which they come
into contact during use. It has been recognized that if such
nonwoven fabrics, while retaining their strength in body fluids,
were to lose substantially all their tensile strength when exposed
to water and become readily dispersible therein, disposal problems
would be substantially eliminated since the fabrics could be easily
and conveniently flushed away in a water closet.
Unfortunately, in an attempt to provide nonwoven fabrics having
certain in-use characteristics, prior methods have rendered the
fabric nondispersible in water. For example, nonwovens have been
bonded with body fluid-insoluble resins which impart in-use
strength. Generally, however, such resins have also been water
insoluble as well and have impeded flushing of the fabric.
Therefore, less desirable methods of disposal such as incineration
or dumping must be employed.
SUMMARY OF INVENTION
I have now discovered a bonded nonwoven fabric which, in addition
to having good strength when dry, and satisfactory strength and
abrasion resistance in the presence of most body fluids, such as
urine, blood, menstrual fluid and the like, is easily dispersible
in water and hence is flushable in home water closets and capable
of disposal in standard sewer systems or septic systems. In this
connection when an article, for example, a barrier means, an
absorbent core, a nonwoven fabric or the like is referred to herein
as being flushable, it is meant that that article may be deposited
in, and flushed through, a water closet without any undue clogging
of the water closet or its auxiliary piping. When such an article
is referred to herein as being water dispersible, it is meant that
that article, when placed in water, loses its integrity and is
flushable.
The improved nonwoven fabric of this invention comprises one or
more layers of overlapping, intersecting fibers and from about four
percent to about 35 percent by weight of the fabric of binder. The
binder comprises an alkali cellulose ether sulfate resin, such as,
for example, an alkali alkyl cellulose sulfate, an alkali
hydroxyalkyl cellulose sulfate or an alkali hydroxyalkyl alkyl
cellulose sulfate wherein each of the alkyl and hydroxyalkyl groups
contains not more than four carbon atoms.
Examples of the alkali cellulose ether sulfates which may be used
as binders for the nonwoven fabrics herein described are such
alkali alkyl cellulose sulfates as sodium methylcellulose sulfate,
potassium ethyl cellulose sulfate, sodium propyl cellulose sulfate
and potassium butyl cellulose sulfate; such alkali hydroxyalkyl
cellulose sulfates as sodium hydroxyethyl cellulose sulfate, sodium
hydroxypropyl cellulose sulfate and sodium hydroxybutyl cellulose
sulfate; and such alkali hydroxyalkyl alkyl cellulose sulfates as
sodium hydroxypropyl methyl cellulose sulfate, potassium
hydroxyethyl ethyl cellulose sulfate and sodium hydroxyethyl propyl
cellulose sulfate.
The fabrics prepared in accordance with this invention have good
dry tensile strength depending upon, among other things, the amount
of binder applied to the fabric and the manner in which it is
applied. They are abrasion resistant and retain a significant part
of their dry tensile strength in solutions containing about 0.8
percent or more by weight of sodium chloride, and yet are readily
dispersible in water. Because of this latter property, the nonwoven
fabrics of this invention are uniquely suited for use in products
to be contacted with such body fluids as blood, menstrual fluid,
urine and the like. These fluids, in general, exhibit properties
which, with respect to the binder, are analogous to aqueous salt
solutions having a salt content which varies from about 0.8 to
about 1.5 percent by weight of sodium chloride. On the other hand
tap water normally supplied to water closets and the like generally
has an extremely low concentration of salt, for example, less than
250 parts per million of chloride ion. It has been discovered that
the nonwoven fabrics made as described herein maintain their
integrity for a substantial period of time in solutions having a
salt concentration exhibiting the properties of body fluids whereas
they display a far lower resistance to dispersion in tap water.
This unique property is a function of the degree of sulfate
substitution (hereinafter, "D.S.") which expresses the average
number of sulfate groups per anhydroglucose unit of the cellulosic
ether. The nonwoven fabric bonded by the aforementioned cellulosic
resins will exhibit increasing dispersibility in water and
decreasing strength in salt solutions as the D.S. of the cellulosic
resin is increased. It has been discovered that a non-woven fabric
bonded by resins having a D.S. varying from about 0.10 to about
0.30 is useful in products designed to be contacted by various body
fluids. In another aspect of this invention, the nonwoven fabrics
are incorporated into such body fluid absorbent products as
sanitary napkins, diapers, surgical dressings and the like. These
products generally include an absorbent core, comprising one or
more layers of an absorbent fibrous material. The core may also
comprise one or more layers of a fluid-pervious element, such as
tissue, gauze, plastic netting, etc. These are generally useful as
wrapping materials to hold the components of the core together.
Additionally, the core may comprise a fluid-impervious element or
barrier means to preclude the passage of fluid through the core and
on to its outer surfaces. In accordance with this aspect of the
instant invention, a body fluid absorbent product is provided
having a nonwoven fabric in contact with an absorbent core, the
nonwoven fabric comprising a layer of overlapping intersecting
fibers from about 4 to about 35 percent by weight of fabric of an
alkali cellulose ether sulfate resin binder having an average of
from about 0.10 to about 0.30 sulfate groups per anhydroglucose
unit.
The invention will be more clearly understood by reference to the
attached drawings taken together with the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a bonded nonwoven fabric in accordance
with the present invention;
FIG. 2 is a perspective view of a sanitary napkin embodying this
invention with parts broken away to show the interior construction
thereof;
FIG. 3 is a cross-sectional view taken approximately along lines
3--3 of FIG. 2;
FIG. 4 is a perspective view of a disposable diaper embodying this
invention with parts broken away to show the interior construction
thereof; and
FIG. 5 is a cross-sectional view taken approximately along lines
5--5 of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2, there is shown a water dispersible
nonwoven fabric 10. The fabric comprises a layer of overlapping,
intersecting fibers 11 having substantially uniformly distributed
therein an alkali cellulose ether sulfate binder 12 as hereinafter
described.
The alkali cellulose ether sulfates used as the binder for the
nonwoven fabrics of this invention may be produced by first forming
the ether derivatives of cellulose and then sulfating with a
suitable sulfating agent. The ether derivatives are generally
prepared by reacting a purified form of cellulose with either an
alkyl halide, and alkylene oxide or both to form either the alkyl
ether, the hydroxyalkyl ether or the hydroxyalkylalkyl ether,
respectively. Unsulfated cellulose ethers are presently available
as, for example, the methylcellulose and hydroxypropyl
methylcellulose ethers sold under the trandemark METHOCEL and the
ethylcellulose ethers sold under the trademark ETHOCEL, all
available from the Dow Chemical Company, Inc. of Midland, Michigan.
Hydroxyethyl cellulose ethers are available from Hercules,
Incorporated, and Union Carbide Corporation under the trademarks
NATROSOL and CELLOSIZE, respectively.
Table A below illustrates properties of typical ethers suitable for
sulfating and use in accordance with this invention:
TABLE A
Ethyl cellulose 4-5,000 cps.sup.1 2.21-2.58.sup.3 Methyl cellulose
8-10,000 cps.sup.2 1.64-1.92.sup.3 Hydroxypropyl Methyl cellulose
50-60,000 cps.sup.2 19-33% by weight methyl 4-12% by weight
propylene glycol ehter
The ethers may be sulfated in accordance with a process described
in U. S. Patent application Ser. No. 232,371, filed Mar. 7, 1972
whereby an alkali sulfating agent is prepared by reacting acetic
anhydride with sulfuric acid and an alkali sulfate, all in an
acetic acid solution, to form alkali acetyl sulfate. The alkali
acetyl sulfate is then reacted with the cellulose ether to yield
the alkali cellulose ether sulfate resin.
In accordance with this invention, it has been discovered that by
modifying the D.S. of the cellulosic resin binder, the salt
resistance and water dispersibility of the bonded nonwoven fabric
can be modified to provide fabrics which will function effectively
when contacted by various body fluids and which may be flushed away
in a water closet. Specifically, by lowering the degree of
sulfation of the cellulosic resins, the fabrics of this invention
become more resistant to salt solutions in that they retain their
integrity after being subjected to these solutions for long periods
of time and in that they exhibit higher tensile strengths when
subjected to a given salt concentration for a given period of time.
In general, if the D.S. of the cellulosic resin is maintained at
below about 0.3, an adequately salt resistant nonwoven fabric
results. Preferably, the D. S. should be maintained at below about
0.25. While the resistance of the nonwoven fabrics to salt
solutions having a salt concentration exhibiting the properties of
body fluids increases greatly with decreasing D.S., the ability of
the fabrics to disperse readily in water is maintained until
extremely low D.S. values are reached. Adequate water
dispersibility is achieved when the D.S. of the cellulosic resin is
maintained at a value of at least about 0.10. Preferably, the D. S.
should be not less than about 0.15.
The aforementioned alkali cellulose ether sulfate resins are used
to bond a base layer of fibers to provide the nonwoven fabric of
this invention. Suitable base layers comprise most of the
well-known fibers, the choice depending upon, for example, fiber
cost and the intended end use of the finished fabric. For instance,
the base layer may include natural fibers such as cotton, linen,
jute, hemp, cotton linters, wool, wood pulp, etc. Similarly,
regenerated cellulosic fibers such as viscose rayon and
cuprammonium rayon, modified cellulosic fibers, such as cellulose
acetate, or synthetic fibers such as those derived from polyvinyl
alcohol, polyesters, polyamides, polyacrylics, etc., alone or in
combination with one another, may likewise be used. Natural fibers
may be blended with regenerated, modified, and/or synthetic fibers
if so desired.
The length of the fiber is important in producing the fabrics of
the present invention. The minimum length of the fibers depends on
the method selected for forming the base layer. For example, where
the base layer is formed by carding, the length of the fiber should
usually be a minimum of 1/2 inch in order to insure uniformity.
Where the base layer is formed by air deposition or water
deposition techniques, the minimum fiber length may be about 0.05
inch. It has been found that when a substantial quantity of fibers
having a length greater than about 2 inches is placed in the
fabric, though the fibers will disperse and separate in water,
their length tends to form "ropes" of fibers which are undesirable
when flushing in home water closets. It is preferred that the fiber
length be 11/2 inches or less so that the fibers will not "rope"
when they are flushed through a toilet.
The base layers suitable for conversion into the fabric of the
present invention may be formed by carding, garnetting, air
deposition, water deposition, or any of the other various
techniques known in the art, The fibers in the layer may be
oriented predominantly in one direction as in a card web or a card
web laminate or they may be randomly oriented as in a layer formed
by air deposition techniques. For sanitary napkin coverings,
disposable diaper facings and similar uses where the fabric is to
be flushable, the web is fairly thin and should weigh between 150
to 400 grains per square yard. Where the fabric must possess a
substantial amount of strength, uniform fiber distribution is
important so as to avoid weak spots in the final nonwoven fabric.
Uniform base layers may be produced by carding in which case it is
advantageous to use fibers which have good carding characteristics
and can be blended into a uniform carded web with facility. Fibers
of viscose rayon and cotton are both satisfactory in this
respect.
The amount of alkali cellulose ether sulfate binder distributed in
the base layer should be from about 4 to 35 percent by weight of
the final nonwoven fabric. If less than about 4 percent of the
cellulosic binder is employed, the fabric does not have sufficient
strength and abrasion resistance to be of any utility. If more than
about 35 percent of the cellulosic binder is employed, the fabric
may lose desirable properties such as absorbency and softness.
It is preferred that the amount of alkali cellulose ether sulfate
binder be between about 4 to 20 percent by weight of the final
nonwoven fabric in order to ensure optimum water
dispersibility.
The binder may be distributed in the base layer by printing,
spraying, impregnating or by any other technique wherein the amount
of binder may be metered and the binder can be distributed
uniformly within the base layer. The binder may be distributed
throughout the entire base layer or it may be distributed therein
in a multiplicity of small closely spaced areas. The binder may be
distributed in lines running across, or at an angle to, the width
of the web or in separate small shaped areas having circular,
angular, square, or triangular configurations. It is preferred that
when the binder is applied to the fibrous layer there be left
unbonded areas in the layer. These unbonded areas of fibers readily
absorb water which attacks the binder areas and makes the fabric
dispersible in shorter periods of time.
For ease of application to the base fibrous layer, the cellulosic
resin binder may be dissolved in water, methanol, ethanol, or in
suitable mixtures thereof, to provide solutions containing up to
about 30 percent by weight of binder solids. Plasticizers, such as
glycerol, polyethylene glycol, and castor oil, may be added to the
solution of the cellulosic resin, the amount of such plasticizers
varying according to the softness required in the final fabric.
Perfumes, coloring agents, antifoams, bactericides, surface active
agents, thickening agents and similar additives may be incorporated
into the solution of the cellulosic resin binder if so desired.
Other binding agents such as polyvinyl alcohol or aqueous
dispersions of, for example, polyvinyl chloride, polyvinyl acetate,
polyacrylates, polymethacrylates, copolymers of acrylates and
methacrylates, copolymers of vinyl acetate with acrylates and/or
methacrylates and copolymers of acrylates and/or methacrylates with
vinyl chloride may be added to the cellulosic binder solution in
order to obtain fabrics having various desired properties.
Referring now to FIGS. 2 and 3 of the drawing, illustrated therein
is an embodiment of the water dispersible non-woven fabric of this
invention as used with a sanitary napkin 20.
Napkin 20 comprises an absorbent core which is contacted by a
fluid-pervious cover 26 comprising the bonded nonwoven fabric of
this invention. The absorbent core comprises a pad 22 of absorbent
fibrous material such as comminuted wood pulp fibers, cotton
linters, rayon fibers, cotton staple, bleached sulfite linters,
other cellulosic or modified cellulosic fibers and the like. The
absorbent core further comprises a fluid-impervious element or
barrier means 24 which, for example, may be a thin polyethylene
sheet or any other suitable material. As best seen in FIG. 3,
barrier means 24 overlies the sides and the bottom surface of
absorbent pad 22 (the bottom surface being that portion worn away
from the body). Fluid-pervious cover 26 surrounds absorbent pad 22
and barrier means 24 with the lateral edges thereof overlapped and
secured on the bottom surface of napkin 20. Cover 26 is extended
beyond the ends of the absorbent core to form the usual attachment
tabs 28. While FIGS. 2 and 3 illustrate a tabbed napkin, it will be
understood by one skilled in the art that the advantages accruing
to the use of the nonwoven fabrics of this invention are equally
applicable to a tabless product, e.g., one where tabs are not used
as attachment means and other attachment means such as, for
example, adhesive means, are used. It will also be understood that
the absorbent core may comprise, in addition to the absorbent pad
and barrier means, a fluid-pervious element such as gauze, tissue,
plastic netting and the like if increased strength and/or
dimensional stability are desired. It will be further understood
that the fluid pervious cover of this invention need not completely
surround the absorbent pad as illustrated in FIGS. 2 and 3. For
example one could provide a fluid pervious cover, the edges of
which are adhered to the edges of the barrier means; in such a
case, the barrier means and fluid pervious cover would cooperate to
form an enclosure for the pad of absorbent fibrous material.
The nonwoven fabric of this invention is uniquely suited to serve
as a fluid-pervious covering in a sanitary napkin, such as shown in
FIGS. 2 and 3, because is is resistant to abrasion and exhibits
satisfactory tensile strength when it has been dampened or wetted
with menstrual fluid, which has a salt content of about 0.8 to
about 1.5 percent by weight. The fabics of this invention are
resistant to solutions containing more than about 0.8 percent salt,
and notwithstanding such salt resistance, the fabrics are
completely dispersible when introduced into water or into salt
solutions whose salt content is less than about 0.8 percent by
weight. It will be apparent that, by employing a water-dispersible
material for the barrier means and a water-dispersible absorbent
pad, the sanitary napkin of FIGS. 2 and 3 may be conveniently and
completely disposed of by flushing through a water closet.
Alternatively, the illustrated napkin may be provided with a
non-water dispersible barrier means and a water-dispersible
absorbent pad. In that case, fluid-pervious covering 26 is first
removed and the barrier means is separated from the pad; the pad
and covering can then be dropped into a water closet for disposal.
In either case, the unique nonwoven fabric of this invention will
be completely dispersed in a water closet under the swirling action
of the water supplied thereto and will not impair the normal
operation of the water closet and associated plumbing. Referring to
FIGS. 4 and 5 of the drawing, there is illustrated therein another
embodiment of the water dispersible nonwoven fabric of this
invention as used with a disposable diaper 30.
Diaper 30 comprises an absorbent core and a fluid-pervious facing
36 comprising the nonwoven fabric of this invention. The absorbent
core comprises an absorbent layer 32 of fibrous material such as
comminuted wood pulp fibers, cotton linters, rayon fibers, cotton
staple, bleached sulfite linters, other cellulosic or modified
cellulosic fibers, and the like. The absorbent core further
comprises a body fluid-impervious element or barrier means 34 which
overlies the bottom surface of absorbent layer 32. Barrier means 34
may comprise for example, a thin sheet of polyethylene or other
suitable material. Where barrier means 34 is not water dispersible,
it is convenient that it be easily removed from the remainder of
the diaper so as to minimize disposal problems. Fluid-pervious
facing 36 overlies the top surface of absorbent layer 32. In the
embodiment illustrated in FIGS. 4 and 5, it will be observed that
barrier means 34 and fluid-pervious facing 36 are substantially
coextensive and are joined together at their peripheries 38 by
methods well known in the art such bonding, adhesive bonding
stitching, and heat sealing techniques.
While FIG. 4 illustrates a disposable diaper having a particular
construction, it will be recognized by those skilled in the art
that the advantages accruing to the use of the nonwoven fabrics of
this invention are equally applicable to disposable diapers having
other, widely varying constructions. The absorbent core is not
limited to the structure illustrated, but may include a
fluid-pervious element, such as gauze, tissue, plastic netting and
the like, if it is desired to increase strength and/or structural
integrity.
The nonwoven fabric of this invention is uniquely suited to serve
as the fluid-pervious facing of a disposable diaper as shown in
FIG. 4 because it is resistant to abrasion and exhibits acceptable
tensile strength when dampened or wetted with urine. Urine, as in
the case of menstrual fluid, has a salt content of about 0.8 to
about 1.5 percent by weight. As already indicated, the nonwoven
fabrics herein are resistant to solutions containing about 0.8
percent or more by weight of sodium chloride. It will be apparent
that by employing a water-dispersible material for the barrier
means and a water-dispersible, absorbent layer, the diaper of FIG.
4 can be safely and conveniently disposed of by flushing through a
water closet. When the diaper of FIG. 4 has been provided with a
barrier sheet that is not water dispersible, but has a
water-dispersible, absorbent layer, then the layer and the facing
may be safely flushed after they have been separated from the
barrier means.
Those skilled in the art will readily understand that the
water-dispersible nonwoven fabric of this invention may be
advantageously employed in the preparation of a wide variety of
absorbent products designed to be contacted with body fluids. Many
such absorbent products need only comprise a core of absorbent
material in combination with said nonwoven fabric. For example, an
absorbent surgical dressing could be made comprising a relatively
thin, rectangular layer of absorbent material with the nonwoven
fabric overlying one or more sides thereof. Similarly, as in the
case of a tampon, the nonwoven fabric could overlie a cylindrical
core of absorbent material. Alternatively, the core of absorbent
material could be in the form of a sphere, a cube, a disc, or other
desirable geometrical configuration.
In order to better illustrate the invention, the following examples
are given:
EXAMPLE I
Sodium ethyl cellulose sulfate is prepared as follows:
A sulfating agent, sodium acetyl sulfate, is prepared by combining
the following ingredients:
Parts by Weight Sodium Sulfate 8.1 Acetic Anhydrid (98% pure) 42.8
Glacial Acetic Acid 13.8 Sulfuric Acid (95% pure) 5.3
The sodium sulfate is first added to a mixture of the acetic
anhydride and acetic acid at room temperature, the sulfuric acid
then being added at a rate such that the temperature of the mixture
does not exceed 54.4.degree.C. The resulting solution is
neutralized by adding small increments of sodium sulfate and is
then cooled to 4.4.degree.C. and filtered.
ETHOCEL Std., a trademark of the Dow Chemical Company for
ethylcellulose ether, is dissolved in acetic acid in a proportion
of 45.4 parts by weight of resin in 115 parts of acetic acid.
ETHOCEL Std. has a degree of ethyl substitution of 2.46 to 2.58 and
a 90 percent by weight solution of the resin dissolved in a mixture
of toluene and ethyl alcohol in the proportions of 80 to 20 parts
by weight, respectively, and measured at 25.degree.C., has a
viscosity of 40 to 50 cps. The resin is dissolved in the acetic
acid by mixing in a jacketed sigma blade mixer, for about 30
minutes at a jacket temperature of 38.degree.C. The jacket
temperature is then dropped to 15.degree.C. and held at that
temperature until the reaction mixture has cooled at
21.degree.C.
The sulfating solution is then added incrementally over a period of
20 minutes, taking care not to exceed a reaction temperature of
32.degree.C. The resulting reacted mixture is then added to an
aqueous, ten percent by weight, sodium hydroxide solution in a
ratio of one part by weight of reacted mixture to ten parts by
weight of the sodium hydroxide solution. This mixture is stirred
vigorously and the pH is maintained at approximately ten by the
addition of requisite quantities of additional ten percent sodium
hydroxide solution.
The resulting precipitated resin is separated from its mother
liquor by filtering in a Buchner funnel. The precipitate is then
dried at a temperature of 50.degree.C. in a forced-air oven and
ground in a Wiley mill, to a particle size of from one to two
millimeters in diameter. The ground particles are washed by
combining them with ten times their weight of boiling water and
stirring vigorously while adjusting the pH to a value of 5.5 with
the addition of ten percent by weight of hydrochloric acid
solution. The precipitate resulting from this washing step is
filtered, dried and ground in the manner described above. The
washing step and the filtering, drying, and grinding are repeated
once again.
The resulting resin has a degree of sulfate substitution of
0.43.
EXAMPLE II
With appropriate changes in the amount of sulfating agent employed,
the procedure of Example I was followed to prepare a series of
sodium ethyl cellulose sulfate resins having degrees of sulfate
substitution equal to, respectively, 0.33, 0.28, and 0.24. Binder
solutions wre then prepared by dissolving these resins in water to
give a solution containing 21/2 percent by weight resin solids. A
fibrous web of 1 9/16 inch, 1.5 denier, dull viscose rayon weighing
about 11/2 ounces per square yard was formed by an air deposition
technique using a Randowebber (commercially available from Curlator
Corporation). Nonwoven fabrics were then prepared by saturating
swatches of the fibrous web with the above described binder
solutions and drying at 150.degree.F for 90 minutes. The nonwoven
fabrics so prepared comprised about 23 percent by weight of binder
solids.
The nonwoven fabrics identified as A, B, C, respectively, were
tested for tensile strength after immersion in water, and after
immersion in aqueous solutions containing, respectively, 0.9
percent and 1.6 percent sodium chloride.
The following procedure was used for the determination of tensile
strengths in tap water and in aqueous salt solutions. The fabric to
be tested was equilibrated for 24 hours at 72.degree.F. and 65
percent relative humidity. Fabric grain weight was determined in
the usual way. Three inch by one inch strips were cut from the
fabric, immersed in the desired test solution, removed, drained for
15 seconds, and gently blotted between paper toweling. The test
strips were then tested on an Instron tester using a jaw spacing of
2 inches and a pull speed of 2 inches per minute. Raw test data was
converted to tensile strength units of pounds per gram of fabric
(hereinafter, "Lbs./Gm.").
The results of the tensile strength tests, which are set forth in
Table II, show generally that the tensile strength of a given
nonwoven fabric increases as the salt content of the solution in
which the fabric is immersed is increased. It is also noted that as
the degree of sulfate substitution in the cellulosic binder
decreases, tensile strength after immersion in water remains at the
same general level while tensile strength after immersion in each
of the salt solutions increases. ##SPC1##
EXAMPLE III
A fibrous web was prepared from 11/8 inch, 1.5 denier, extra dull
viscose rayon by a standard carding operation. The web weighed
about 280 grains per square yard. Two sodium ethyl cellulose
sulfate resins were prepared by the method of Example I, except
that different amounts of the sulfating agent were employed in
order to vary the degree of sulfate substitution. The resins had
degrees of sulfate substitution equal to 0.19 and 0.23. The resin
having a degree of sulfate substitution equal to 0.19 was dissolved
in 2:1 (weight) methanol/water mixture to give a binder solution,
designated X, containing 11 percent solids. The resin having a
degree of sulfate substitution equal to 0.23 was dissolved in
methanol to give a binder solution, designated Y, containing 7
percent solids. Nonwoven fabric D was then made by using an
engraved roll to print bond a sample of the above mentioned fibrous
web with binder solution X and then drying the printed web over
steam heated cans held at about 270.degree.F. Nonwoven fabric E was
prepared in the same way using binder solution Y.
The pattern engraved on the print roll comprised 6 horizontal wavy
lines per inch, each engraving being 0.024 inch wide and 0.010 inch
in depth. The non-woven fabrics so prepared comprised about 82
percent by weight of viscose rayon and about 18 percent by weight
of resin binder.
The fabrics were tested, after equilibration for 24 hours at
72.degree.F and 65 percent relative humidity, for tensile strength,
pinning strength, and flexural resistance.
Tensile strength was determined by pulling 7 inch long by 3 inch
wide samples on a Scott IP-IV incline plane tester having a jaw
spacing of 3 inches. Results of the tensile strength tests were
reported in pounds per three inch width of fabric.
Pinning strength was determined on a modified Scott IP-IV incline
plane tester wherein each of the usual jaws carried a safety pin
for grasping the sample to be tested. Fabric strips measuring 7
inches by 3 inches were used for this test. The space between the
safety pins was 3 inches. Results of pinning strength tests were
reported in pounds.
Flexural resistance tests, which measure the softness of the
nonwoven fabric, were run on a modified Thwing-Albert
Handle-O-Meter. Test results are reported in arbitrary units--the
higher the number, the softer the fabric.
For purposes of comparison, a water dispersible nonwoven fabric
made according to the Example set forth in Column 5 of U.S. Pat.
No. 3,554,788 was used as a control. Test results for the
experimental fabrics and the control are given in Table III. The
results show that fabrics D and E, prepared with sodium ethyl
cellulose sulfate having degrees of sulfate substitution of 0.19
and 0.23, respectively, are suitable for use as fluid pervious
facings in sanitary napkins having tabs. ##SPC2##
EXAMPLE IV
Sanitary napkins were prepared using the construction of a
commercially-available flushable napkin sold by Personal Products
Company, Milltown, New Jersey, a corporation of the state of New
Jersey, as MODESS (trademark of Johnson & Johnson) flushable
feminine napkins. The construction of the MODESS flushable napkin
is generally similar to that illustrated in FIGS. 2 and 3. The
nonwoven fabrics of Example III, including the control fabric
described therein, were used in place of the nonwoven fabric
normally provided as the covering material. Fifteen napkins were
prepared for each of the fabrics to be tested. The sanitary napkins
so made were then tested for flushability by flushing them through
a testing system designed for such purposes. The testing system
comprises an American Standard toilet fitted with 3 inch (I.D.)
copper piping, approximately 11-12 feet long. This pipe is
connected to the toilet by way of an elbow and a suitable length of
vertically placed piping. At the opposite end of the pipe, and at
right angles thereto, there is placed an exit pipe about 20 inches
long. There is a tubular wire mesh screen, about 18 inches long,
concentrically placed within the exit pipe, the screen carrying
several rows of barbs to simulate any internal rough surfaces in a
sewage system. The test is conducted by dropping the sanitary
napkin into the toilet bowl, waiting 15 seconds, and then flushing.
After each napkin is flushed, the screen is removed and the residue
thereon is visually rated by comparison with a set of standard
photographs. A flushability rating of excellent (1), good (2), fair
(3), or poor (4) is then assigned to the napkin under test.
Table IV shows the average flushability rating of 15 runs for each
of the test fabrics and the control. The napkins covered with the
experimental fabrics were found to have better flushing
characteristics than the napkin covered with the control fabric.
All napkins were considered to be satisfactory for safe flushing
through an average plumbing system.
TABLE IV
Resin-Degree of Flushability Rating Fabric Substitution (Average of
15 runs) D 0.19 1.9 (Good) E 0.23 3.0 (Fair) Control (None) 3.5
(Fair-Poor) (U.S. Pat. No. 3,554,788)
EXAMPLE V
Fabrics D and E of Example III were tested for wet strength in the
presence of water and aqueous salt solutions of varying
concentrations. A sample of the fabric to be tested was placed
across the mouth of a standard 400 ml. beaker and held in place
with a rubber band. An area of the fabric approximately 2 inches in
diameter was wetted with the desired test solution and a 54 gram
steel ball was placed on the wetted area. The time in seconds
required for the steel ball to break through the test fabric was
recorded. The test was repeated six times for each fabric and the
results for each fabric were averaged. In some instances testing
was discontinued when a fabric under test did not fail within a
certain period of time. Test results which are summarized in Table
V show that Fabric D (D.S. = 0.19) and Fabric E (D.S. = 0.23) have
very low strength when wet with water. For a given degree of
sulfate substitution, fabric wet strength increases as the sodium
chloride concentration in the test solution is increased. At any
given concentration of salt in the test solution, fabric wet
strength decreases as the degree of sulfate substitution
increases.
Swatches of fabrics D and E, when placed in water and even slightly
agitated, were observed to lose their integrity. ##SPC3##
EXAMPLE VI
Fabric D of Example III was tested for abrasion resistance in the
presence of menstrual fluid with the aid of a panel of 10 women. A
quantity of MODESS flushable sanitary napkins, of the general type
marketed by Personal Products Company of Milltown, New Jersey,
under the designation MODESS flushable feminine napkins, was
prepared using Fabric D of Example III in place of the cover
provided on the commercial napkin. Each member of the test panel
was provided with four such napkins for use during
menstruation.
The average time of use was 4.75 hours; the average weight of fluid
deposited on a napkin was 7.58 grams, which is considered heavy
menstrual flow. Of the forty returned products, 92.5 percent showed
slight to no abrasion while the remaining 7.5 percent showed
moderate to heavy abrasion. It was concluded from this test that
Fabric D had very good resistance to wet abrasion in the presence
of menstrual fluid.
EXAMPLE VII
The procedure of Example VI was repeated except that Fabric E of
Example III was used as the covering material for the napkins to be
tested. Results of the panel test showed that Fabric E had good to
excellent abrasion resistance in the presence of menstrual
fluid.
EXAMPLE VIII
A disposable diaper is made as follows: An absorbent fibrous layer,
measuring about 11 inches by about 15 inches, is prepared from
comminuted wood pulp. The absorbent layer, which weighs about 20-25
grams, is then placed on a piece of 1 mil polyethylene film
measuring about 12 inches by about 16 inches. This polyethylene
film serves as a backing layer. A piece of nonwoven fabric D
(Example III), also measuring about 12 inches by 16 inches, is
placed over the absorbent layer in substantially coextensive
relationship with the polyethylene film. This nonwoven fabric
serves as the facing of the disposable diaper. Nonwoven fabric D
and the polyethylene film are joined along their peripheries with
any suitable adhesive means, for example, an aqueous based
polyvinyl acetate adhesive, so that the absorbent layer is confined
therebetween. Nonwoven fabric D has acceptable strength and good
abrasion resistance in the presence of urine. After use, nonwoven
fabric D and the absorbent layer are separated from the
polyethylene film. The nonwoven fabric and the absorbent layer are
then easily and safely disposed of by flushing in a toilet. It will
be undersood that the above example is given for purposes of
illustration only. Those skilled in the art will recognize that the
polyethylene film could be replaced by other types of film or by
any suitable woven or nonwoven fabric. The absorbent layer may
comprise any of the other absorbent materials, for example,
cellulose wadding, well known in the art. Additionally, it will be
recognized that if the diaper comprises, in addition to the
nonwoven fabric of this invention, a flushable absorbent layer and
a flushable backing material, then the entire diaper may be
disposed of by flushing in a toilet.
* * * * *