U.S. patent number 3,563,241 [Application Number 04/775,767] was granted by the patent office on 1971-02-16 for water-dispersible nonwoven fabric.
This patent grant is currently assigned to E. I. DuPont de Nemours and Company. Invention is credited to Franklin James Evans, Charles Shambelan.
United States Patent |
3,563,241 |
Evans , et al. |
February 16, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
WATER-DISPERSIBLE NONWOVEN FABRIC
Abstract
A soft, water-dispersible, nonwoven fabric of fibers secured in
place by random fiber entanglement with at least 10 percent of the
fibers chemically modified to have a surface that becomes slippery
when wet with water to promote water-dispersibility. Processes for
producing the above entangled fabrics which include both fiber
modification to the water-sensitive form prior to fiber
entanglement and subsequent to fiber entanglement are also
disclosed.
Inventors: |
Evans; Franklin James
(Wilmington, DE), Shambelan; Charles (Chattanooga, TN) |
Assignee: |
E. I. DuPont de Nemours and
Company (Wilmington, DE)
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Family
ID: |
25105434 |
Appl.
No.: |
04/775,767 |
Filed: |
November 14, 1968 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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693757 |
Oct 6, 1967 |
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660411 |
Aug 15, 1967 |
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594024 |
Nov 14, 1966 |
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486502 |
Sep 10, 1965 |
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Current U.S.
Class: |
604/364; 264/518;
428/219; 428/409; 604/368; 604/376; 604/394; 160/169; 264/546;
428/340; 604/370; 604/378 |
Current CPC
Class: |
C08B
3/00 (20130101); A61L 15/28 (20130101); D21H
25/005 (20130101); D04H 1/495 (20130101); A61L
15/28 (20130101); C08L 1/26 (20130101); D21H
17/66 (20130101); Y10T 428/27 (20150115); D21H
13/08 (20130101); Y10T 428/31 (20150115); D21H
11/20 (20130101) |
Current International
Class: |
A61L
15/16 (20060101); A61L 15/28 (20060101); C08B
3/00 (20060101); D21H 25/00 (20060101); D21H
13/00 (20060101); D21H 11/20 (20060101); D21H
17/66 (20060101); D21H 11/00 (20060101); D21H
13/08 (20060101); D21H 17/00 (20060101); A61f
013/16 () |
Field of
Search: |
;161/153,169
;128/284,290,296 ;264/88,120,154 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of our abandoned applications
identified as follows: Ser. No. 693,757, filed Oct. 6, 1967 (which
is a continuation-in-part of our application Ser. No. 660,411,
filed Aug. 15, 1967 and now abandoned); Ser. No. 594,024, filed
Nov. 14, 1966; and Ser. No. 486,502, filed Sept. 10, 1965.
Reference is also made herein to a related patent of one of the
inventors, Belgium Pat. No. 673,199, Jun. 2, 1966 and to Guerin,
U.S. Pat. No. 3,214,819, dated Nov. 2, 1965. All are assigned to
the assignee of the present application.
Claims
We claim:
1. A soft, water-dispersible, nonwoven fabric of fibers secured in
place by random fiber entanglement providing a unitary nonwoven
fabric having a weight of about 0.3 to about 5.0 oz./yd..sup.2 with
an elongation in at least one direction of at least 9 percent; said
fabric comprising at least 10 percent water-sensitive fibers having
a water-sensitive surface and less than about 3 inches in length;
the balance of said fibers comprising nonwater-sensitive fibers of
less than about 0.5 inch length; said water-sensitive fibers having
a wet coefficient of sliding friction f.sub.2 of less than about
1.3 as measured on an entangled nonwoven fabric consisting
essentially of the water-sensitive fibers; and said
water-dispersible fabric having a dry coherence value (C.sub.h,
dry) of greater than about 0.2 and a wet coherence value (C.sub.h,
wet) of less than about 0.6 with the C.sub.h (wet) being less than
the C.sub.h (dry).
2. A fabric as defined in claim 1 wherein the C.sub.h (wet) is less
than about 0.5 and the f.sub.w is less than about 1.1.
3. A fabric as defined in claim 1 wherein the C.sub.h (wet) is less
than about 0.3, the average wet tensile strength of the fabric is
within the range of about 0.0 to 0.1 lbs. per inch and the f.sub.w
is less than about 1.0.
4. A fabric as defined in claim 1 wherein at least 40 percent of
the fibers are water-sensitive.
5. A fabric as defined in claim 1 wherein the water-sensitive
fibers have a single layer absorbency of at least 1 when measured
on a nonwoven fabric consisting essentially of the water-sensitive
fibers.
6. A fabric as defined in claim 1 wherein the fabric comprises at
least 40 percent water-sensitive fibers having ionizable groups and
said fabric is further characterized as having a NaCl tensile
strength of at least 0.05 lb./in. in 1 percent NaCl aqueous
solution with the NaCl tensile strength being at least 1.5 times
the tensile strength of the fabric in distilled water, a bending
length of less than about 3.0 cm., and an internal bond strength of
greater than about 0.08 foot pounds.
7. A fabric as defined in claim 1 which comprises essentially
water-sensitive fibers.
8. A nonwoven fabric as defined in claim 1 which comprises ordered
fiber groups arranged in regular parallel rows extending in two
principal fabric directions and interconnected in a network by
fibers randomly entangled with each other to define an ordered
geometric pattern of apertures, and including fiber groups forming
ridgelike protrusions on at least one face of the fabric.
9. A nonwoven fabric as defined in claim 1 wherein said fibers are
entangled in a repeating pattern characterized by groups of
entangled fibers forming a regular pattern of ridgelike protrusions
separated by grooves lying along parallel straight lines, the
ridge-forming groups being interconnected by arrays of generally
parallel fibers bridging under the ridge-separating grooves and
entangled in adjacent groups.
10. A nonwoven fabric as defined in claim 1 wherein said fibers are
entangled in a repeating pattern of fiber bands of substantially
greater width than thickness which extend continuously along
substantially straight parallel axes spaced regularly in one fabric
direction, the bands being interconnected by generally parallel
fibers which extend laterally between adjacent bands and are held
in place by fiber entanglement in the bands.
11. A nonwoven fabric as defined in claim 1 wherein said fabric is
essentially a nonpatterned structure.
12. A nonwoven fabric as defined in claim 1 wherein the fabric
comprises 30 percent to 90 percent of said water-sensitive fibers
and 70 percent to 10 percent of said nonwater-sensitive fibers and
said nonwater-sensitive fibers are more heavily concentrated in a
surface layer than in the center of the fabric, the fabric having a
surface layer containing at least 80 percent of the
nonwater-sensitive fibers and a center containing at least 70
percent of the water-sensitive fibers.
13. A sanitary napkin comprising an absorbent core with a covering
of the fabric of claim 1.
14. A diaper comprising an absorbent core sandwiched between two
layers of the fabric of claim 1.
15. A fabric as defined in claim 1 wherein the water-sensitive
fibers comprise modified cellulosic fibers.
16. A fabric as defined in claim 15 wherein the water-sensitive
fibers have ionizable groups and said fabric is further
characterized as having a NaCl tensile strength of at least 0.05
lb./in. in 1 percent NaCl aqueous solution with the NaCl tensile
strength being at least 1.5 times the tensile strength of the
fabric in distilled water, a bending length of less than about 3.0
cm., and an internal bond strength of greater than about 0.08 foot
pounds.
17. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of cyanoethyl cellulose
having a degree of substitution within the range of about 0.15 to
0.80.
18. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of hydroxyethyl
cellulose having a degree of substitution within the range of about
0.1 to 0.9.
19. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of carboxymethyl
cellulose having a degree of substitution within the range of about
0.1 to 0.4.
20. A nonwoven fabric as defined in claim 19 wherein at least a
portion of the carboxymethyl cellulose is converted to a sodium
salt form.
21. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of carboxyethyl
cellulose having a degree of substitution within the range of about
0.1 to 0.4.
22. A nonwoven fabric as defined in claim 21 wherein at least a
portion of the carboxyethyl cellulose is converted to a sodium salt
form.
23. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of cellulose phosphate
having a degree of substitution within the range of about 0.10 to
0.4.
24. A fabric as defined in claim 23 wherein at least a portion of
the cellulose phosphate is converted to a sodium salt form.
25. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of cellulose
hemisuccinate having a degree of substitution within the range of
about 0.2 to 0.40.
26. A nonwoven fabric defined in claim 25 wherein at least a
portion of the cellulose hemisuccinate is converted to a sodium
salt form.
27. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of cellulose sulfate
having a degree of substitution within the range of about 0.1 to
0.4.
28. A nonwoven fabric as defined in claim 27 wherein at least a
portion of the cellulose sulfate is converted to a sodium salt
form.
29. A fabric as defined in claim 15 wherein at least the surface of
the water-sensitive fibers are of cellulose phosphate-cellulose
acetate.
30. A fabric as defined in claim 29 wherein at least a portion of
the cellulose phosphate is converted to a sodium salt.
31. The fabric as defined in claim 15 wherein said water-sensitive
fibers are chemically modified cellulosic fibers having a degree of
substitution within the range of about 0.1 to about 1.5 as
represented by the formula ##SPC18##
wherein R is primarily a hydrocarbon group free from aliphatic
unsaturation which may contain noninterfering hydrophobic
substituents, either oxygen linkages and ester oxygen linkages in
the chain; B is a hydrophilic substituent; Y is selected from the
group consisting of hydrogen, an acid group having ionizable
hydrogen attached to oxygen, and monovalent cation salts of the
acid; said formula meeting the following criteria: when Y is
hydrogen and t is zero, R has less than 5 carbon atoms; when Y is
hydrogen and t is one, R has less than 8 carbon atoms; when Y is
said acid group and t is zero, R has less than 10 carbon atoms;
when Y is said salt of the acid and t is zero, R has less than 19
carbon atoms; q, r, and s are zero or one but when r is one, q and
s are one; t is zero or any integer up to the number of replaceable
hydrogens in R, and u is 1 or 2.
32. A nonwoven fabric as defined in claim 1 wherein said
water-sensitive fibers comprise modified polyvinyl alcohol
fibers.
33. A fabric as defined in claim 32 wherein said water-sensitive
fibers have phosphate groups converted to a salt form.
34. A fabric as defined in claim 1 wherein said water-sensitive
fibers comprise modified acrylic fibers.
35. A fabric as defined in claim 34 wherein said acrylic fibers are
hydrolyzed and converted to a salt form.
36. A fabric as defined in claim 1 wherein said water-sensitive
fibers comprise modified nylon fibers.
37. A fabric as defined in claim 36 wherein the nylon fibers have
grafted acrylic acid groups converted to a salt form.
38. A nonwoven fabric as defined in claim 15 wherein at least the
surface of said water-sensitive fibers are of cellulose
hemiphthalate
Description
BACKGROUND OF THE INVENTION
The invention relates to soft, nonwoven fabric structures of fibers
secured in place by random fiber entanglement to provide a pleasing
appearance, drape and hand comparable to woven textile fabrics. The
present invention is more particularly concerned with highly
absorbent textilelike structures for single-use purposes, which
have adequate strength and durability in use and are suitable for
disposal in sewage systems after use.
Woven or knitted cotton fabrics have been used for diapers and
other purposes where absorbency is desired. These have a relatively
low capacity for absorbing fluids. Because of their cost, they are
generally reused after an inconvenient and possible unhygienic
laundering. The inconvenience of disposal after use is also a
problem.
The present invention provides inexpensive, soft, highly absorbent,
textilelike structures which are readily disposable in sewage
systems. They are well adapted for sanitary fabric use, such as
diapers, bandages and panties, where unusually high absorbency for
body fluids and ease of disposal after a single use are especially
desirable in a structure having a textilelike pattern of pleasing
appearance and soft tactile hand. They have adequate strength and
surface stability for such uses.
SUMMARY OF THE INVENTION
The fabric of this invention is defined as (I.) A soft,
water-dispersible, nonwoven fabric of fibers secured in place by
random fiber entanglement
A. comprising:
1. at least 10 percent fibers having a water-sensitive surface, the
water-sensitive fibers having a wet coefficient of sliding friction
(f.sub.w) of not greater than 1.3 and a length of less than 3
inches, the f.sub.w being measured on a nonwoven fabric consisting
essentially of the water-sensitive fibers;
2. the balance of the fibers comprising non-water-sensitive fibers
of less than about 0.5 inch length;
B. the fabric being characterized by:
1. a dry coherence value (C.sub.h, dry) of greater than about
0.2,
2. a wet coherence value (C.sub.h, wet) of less than about 0.6,
with the C.sub.h (wet) being less than the C.sub.h (dry).
A more readily water-dispersible fabric of this invention (II) are
the fabrics of I characterized by a C.sub.h (wet) of less than 0.5
and the use of fibers having a water-sensitive surface which have a
f.sub.w of no greater than 1.1.
The most highly water-dispersible fabrics of this invention (III)
are the fabrics of I characterized by a C.sub.h (wet) of no greater
than 0.3, an average wet strip-tensile strength of about 0.0 to 0.1
pounds/inch and the use of fibers having a water-sensitive surface
which have a f.sub.w of less than about 1.0.
The preferred fabrics of this invention have a weight of about 0.3
to about 5 oz./yd..sup.2 and contain at least 40 percent (and, more
preferably, at least 50 percent) of fibers having a water-sensitive
surface having ionizable groups (acidic groups as a free acid or
partially or completely in the form of a salt of an alkali metal or
ammonium ion). The preferred fabrics are characterized as
follows:
a. tensile strength in 1 percent NaCl solution of at least 0.05
lb./in.;
b. a ratio of tensile strength in 1 percent NaCl to tensile
strength in distilled water of at least 1.5;
c. a bending length of less than about 3.0 cm.; and
d. an internal bond strength of greater than about 0.08 ft.
lbs.
The cellulosic species of the water-sensitive fibers exemplified
are embraced by the following description: The water-sensitive
cellulosic fibers are chemically modified cellulosic fibers having
a degree of substitution within the range of about 0.1 to about 1.5
and are represented by the formula
wherein R is primarily a hydrocarbon group free from aliphatic
unsaturation which may contain noninterfering hydrophobic
substituents, either oxygen linkages and ester oxygen linkages in
the chain; B is a hydrophilic substituent; Y is selected from the
group consisting of hydrogen, an acid group having ionizable
hydrogen attached to oxygen, and monovalent cation salts of the
acid; said formula meeting the following criteria: when Y is
hydrogen and t is zero, R has less than 5 carbon atoms; when Y is
hydrogen and t is one, R has less than eight carbon atoms; when Y
is said acid group and t is zero, R has less than 10 carbon atoms;
when Y is said salt of the acid and t is zero, R has less than 19
carbon atoms; q, r, and s are zero or one but when r is one, q and
s are one; t is zero or any integer up to the number of replaceable
hydrogens in R, and u is one or two.
Since the frictional characteristics of the water-sensitive fibers
when wet promote water dispersibility by fiber-to-fiber slippage as
is manifest from the low wet coherency value (C.sub.h, wet) of the
fabric, a wide variety of fibers are useful in the practice of this
invention as only the surface characteristics of the fibers must be
established. This is apparent from Examples 15 and 16 which
illustrate useful products of this invention wherein the
water-sensitive fibers are only modified on or near the surface of
the fibers (heterogeneously), thereby forming a water-sensitive
skin on the fibers.
Included among the noncellulosic fibers exemplified that can be
modified to a water-sensitive form useful in the practice of this
invention are polyvinyl alcohol fibers, acrylic fibers, nylon
fibers, and casein fibers.
The process for preparing soft, water-dispersible, unitary nonwoven
structures of this invention from initial layers of fibrous
material, at least 10 percent of said fibrous material being fibers
having a water-sensitive surface of less than about 3 inches length
and up to 90 percent of said fibrous material comprising
non-water-sensitive fibers of less than about 0.5 inch in length,
comprises supporting the initial fibrous material on an apertured
member; impinging fine, essentially columnar streams of a
deswelling liquid for said water-sensitive fibers on the fibrous
material at an energy flux of at least 23,000 ft.
poundals/in..sup.2 sec.; and traversing the supported fibrous
material with said streams at a Y value of 3 .times. 10.sup.6 to 25
.times. 10.sup.6 ft./min. to entangle the fibers into a structure
having a weight within the range of about 0.3 to about 5
oz./yd..sup.2 with a dry coherence value ( C.sub.h, dry) of greater
than about 0.2; said Y value being the weight of liquid used in
lbs./min.; and said water-sensitive fibers having a wet coefficient
of sliding friction of less than about 1.0 as measured on an
entangled nonwoven fabric consisting essentially of the modified
fibers.
Another useful process for preparing the product of this invention
is defined in detail on page 28. In this process the fabric is
first made of unmodified fibers and then the fibers of the
entangled fabric are modified to a water-sensitive form.
The coherence value (C.sub.h) is a measure or indication of the
proportion of fibers that break (rather than disentangle or slip
apart) when a long and short strip of a fabric is broken. The
products of this invention have a wet coherence value (C.sub.h,
wet) in water that is less than the dry coherence value (C.sub.h,
dry) indicating that more fibers are disentangling in the wet state
than in the dry state. This behavior is in contrast to a product
made of unmodified rayon or cotton alone. The wet coherence of
entangled rayon or cotton nonwovens such as are used in Examples
X--XVIII are greater than the dry coherence. This is presumably due
to the greater friction between wet rayon or cotton fibers.
The broad invention (I) includes nonwoven fabrics of entangled
fibers that will disentangle into smaller pieces in water under
relatively mild agitation (such as used in the breakup time test of
Example XXI) within about 100 seconds or under the turbulent
conditions of the flow through institution-size sewer mains. The
less dispersible products of this class may be soaked in a water
tank with some agitation to promote breakup and then disposed into
a large sewer main such as would be present in a hospital. The use
of high-powered machinery such as paper beaters or grinders is not
required to break up such fabrics.
The invention in its narrower scope (III) includes nonwoven fabrics
of entangled fibers that are so highly water-dispersible that they
can be disposed of in the usual household toilet by dipping a few
times and then flushing. A C.sub.h (wet) of no greater than 0.3
characterizes such behavior in soft water. When composed of
homogeneously modified water-sensitive fibers, such fabrics
preferably have single layer (S.L.) absorbencies (defined later) of
at least about 2.0. The preferred products of this class have a
C.sub.h (wet) value of less than about 0.15 and are flushable in
the form of diaper-size portions (such as 13 in. .times. 17 in.) in
a household toilet without the need of predipping before flushing.
Such preferred products contain at least 40 percent of
water-sensitive fibers and have a salt-free fabric weight of about
0.3 to 5 oz./yd..sup.2.
The invention in its intermediate scope (II) includes nonwoven
fabrics of entangled fibers that have a water-dispersibility
greater than class I as measured by a breakup time (B.U.T.) of 40
seconds or less.
The products are termed "fabrics" since they have the appearance,
handle, and elongation-at-the-break (at least 90 percent in at
least one direction) of textile fabrics. The preferred products
have an average elongation in both directions of at least 20
percent. Preferred products have a drape as measured by a bending
length of less than 3.0 cm. in both directions. The fabrics are not
papers and do not resemble papers at all in their essential
properties.
Products having a C.sub.h (dry) of at least 0.2 generally have
average dry tensile strengths of about 1 lb./in. or greater with
abrasion resistance which is adequate for many uses. The broad
class of products includes products that may be satisfactory as
absorbent pads, for example, while lacking the strength to be used
for such products as diapers. In general, the dry integrity will
increase with higher C.sub.h (dry) values.
Another class of preferred products is characterized by a
sufficient resistance to disentangling when wet with body fluids
such as urine or menstrual fluid that the fabric can survive the
stresses accompanying body movements and removal of the used fabric
without disintegration. Such products have an average tensile
strength in synthetic urine of at least 0.04 lb./in. and more
preferably at least about 0.2 lb./in. Such products when comprised
of homogeneously modified fibers are also characterized by an S.L.
absorption of less than about 13.
It is to be understood that although a fabric may contain strips of
non-water-sensitive fibers, the portion of the fabric having
water-sensitive fibers is to be considered for determining if the
fabric falls within the scope of applicant's invention and
claims.
Although the products of the invention as shown in the examples
utilize water-sensitive fibers that are uniform along their length,
it will be understood that the products can be surface-treated,
e.g., cross-linked, to change the wet hand, without substantially
changing the dispersibility of the product.
WATER-SENSITIVE FIBERS
Fibers which are slippery in water as determined by a wet
coefficient of sliding friction of no greater than about 1.3
(preferably no greater than about 1.0) as measured on an entangled
nonwoven fabric consisting essentially of the fibers are generally
suitable. The fibers must also be insoluble in synthetic urine.
The fibers may be homogeneous, i.e., have a substantially uniform
chemical composition throughout their cross section, or may be
heterogeneous, thereby having an adherent coating or skin of a
water-sensitive composition. The composition of the skin or the
entire fiber (if homogeneous) should be such that a homogeneous
fiber of that composition will have a S.L. absorbency of at least 1
and preferably at least 2.
The water-sensitive polymers which form the fibers and the
water-sensitive fibers themselves are well known. An easy and
well-known route to such products is by the modification of
cellulose. Suitable chemical reactions involving derivatives of the
hydroxyl group are discussed in "Cellulose" Vol. II by Ott and
Spurlin, pages 673 to 1026 (Interscience Publishers, Inc., N.Y.,
1954) and water-soluble derivatives given. Also useful is
oxycellulose. Further products are cited in "A Survey of Soluble
Chemically Modified Cotton Fiber" by R. Reinhardt et al. in Textile
Research Journal 27, 59--65 (1957). The chemical modification of
cellulose and other polymers is discussed at length in "Chemical
Reactions of Polymers" by E. M. Fettes (Interscience Publishers,
N.Y., 1964).
The reactions used to convert cellulose to a water-sensitive
derivative such as esterification and etherification can be applied
to noncellulosic polymers that have reactive hydroxyl groups along
the chain. Such polymers are readily obtained by hydrolysing
polymers such as polyvinyl acetate (to give polyvinyl alcohol) or
copolymers of vinyl acetate with monomers such as ethylene, vinyl
chloride and methyl methacrylate.
Another route to water-sensitive fibers is to hydrolyse polymers
having pendant side groups of esters, amides and nitriles to
carboxyl groups or amides. Polymers and copolymers from
acrylonitrile, alkyl acrylates, alkyl methacrylates, acrylamides
and vinyl phosphonate are suitable for this purpose. The same type
of polymer can also be made by copolymerizing acidic monomers such
as acrylic acid, methacrylic acid, maleic anhydride, styrene
sulfonic acid, and vinyl sulfonic acid, and the like with another
monomer such as acrylonitrile, styrene, vinyl chloride or
vinylidine chloride. The combinations of monomers and the
appropriate polymerization techniques are well known.
Another route is to start with known water-soluble fibers such as
polyvinyl alcohol, polyacrylic acid, polymethacrylic acid,
polyacrylamide, N-alkyl derivatives of polyacrylamide such as
N-isopropyl- and N,N-dimethyl-, polymethacrylamide,
polyethyleneoxide, polyvinyl methyl ether, amylose, sodium
alginate, polystyrene sulfonic acid, polyvinyl sulfonic acid,
polyallyl fibriclike acid, polyvinyl tetrazole, polyvinyl benzoic
acid, polyvinyl pyrolidone, polyvinyl amine, polyvinyl pyridine,
poly cis dimethoxy ethylene and polymethylol acrylamide and
cross-link them by ionic bonds (such as calcium ion on an acid
polymer), or covalent bonds with difunctional reactants (diamines,
glycols, etc.) or by the application of high energy ionizing
radiation (e.g. by a 2 MEV Vandegraff electron accelerator). The
water solubility of these fibers can also be reduced by increasing
the molecular orientation e.g. by further drawing.
Another route to water-sensitive fibers is the irradiation bonding
of acidic compounds to fibers as taught in U.S. Pat. No. 2,999,056
to Tanner.
The following condensation polymers are known to be water
soluble:
poly(methylene thio dibutyramide)
poly(methylene thio divaleramide),
polymers from ethylene diamine, pentamethylene diamine,
2,2'-(ethylene dioxy) bis [ethylamine] or ethylene glycol with the
diacid methyl imino diacetic acid;
polymers from 3,3'-Diamino-N-methyl dipropyl amine and such diacids
as adipic, sebacic, dodecanedioic or isophthalic;
polymers from 2,2'-(ethylene dioxy) bis [ethylamine] and diacids
such as adipic, 6-hydroxy undecanedioic, 1,4-piperazine diacetic
acid, or oxy diacetic acid;
polymers from ethylene diamine or tetramethylene diamine with oxy
diacetic acid;
polymers from amino acids as alpha amino proprionic, beta amino
proprionic or N-methyl alpha amino proprionic acid.
The above polymers can be cross-linked to reduce the
water-solubility and still retain adequate water-sensitivity or the
polymers can be made as copolymers with condensation monomers such
as hexamethylene diamine and adipic acid to give a water-sensitive
polymer directly.
One means of selecting cellulose esters and ethers is by the
expression Cellulose-O-A where the compound A-OH is soluble in
water at about 20.degree. C. to the extent of at least 3 percent
(by weight).
A can be an organic or inorganic molecule or a combination of
organic and inorganic as shown below: ##SPC1##
Preferably the group A above and substituent Y of the formula on
page 4 contain or consist entirely of an ionic group such as an
acidic group as a free acid or partially or completely in the form
of a salt of an alkali metal or ammonium ion. Such groups include
-COOH, -PO(OH).sub.2, -OP(OH).sub.2, -OSO.sub.2 OH, -SO.sub.2 OH,
-OB(OH).sub.2 attached to a carbon atom or groups as -PO(OH).sub.2,
P(OH.sub.2), and -SO.sub.2 OH 2OH which may compose all of group A
and are connected to the cellulose through oxygen.
Suitable acid groups for the cellulose ethers and esters include
those groups having oxygen connected directly to carbon, sulfur or
phosphorus (with molecular weights less than about 100). These
acidic groups have an ionization constant for the first hydrogen of
at least 1 .times. 10.sup.-5.
Suitable hydrophilic substituents, i.e., B of the formula on page
4, for the cellulose ether or ester derivatives include sulfamyl,
sulfonamide, phosphoramide, phosphonamide, hydroxyl, carbamyl,
amino, lower alkyl substituted amino, lower alkyl substituted amino
(low molecular weight groups less than about 80). These groups are
those which increase the water solubility of a given hydrocarbon
when replacing a hydrogen.
The hydrophobic or noninterfering substituents referred to on page
4 are those groups that have little effect on the water-sensitivity
of a cellulose compound such as halogen, nitrile, and nitro, but
which may be present to a limited extent due to the synthesis
used.
Suitable cellulose ethers include lower alkyl ethers such as
methyl-, ethyl-, propyl-. Substituted ethers such as cyano ethyl-,
cyano methyl-, hydroxy ethyl-, acry- amido-, amino ethyl-, dimethyl
amino ethyl-, ethyl amino ethyl, dinitro methyl-, poly(ethylene
oxide)-. Preferred cellulose ethers containing acid groups include
carboxy methyl-, carboxy ethyl-, sulfoxy ethyl-, sulfoxy butyl,
sulfato ethyl-, phospho propyl-, phosphate ethyl, malonic-, carboxy
benzyl, sulfoxy benzyl.
Suitable cellulose esters include the lower alkyl esters such a
formate, acetate, proprionate, and substituted esters such as
hydroxy acetate, hydroxy butyrate, .alpha. -hydroxy dimethyl
proprionate, ethyl carbonate, to mention a few.
Preferred cellulose esters containing an acid group include
cellulose phosphate, cellulose sulfate, cellulose sulfite,
cellulose phosphite, cellulose borate, cellulose hemi oxalate,
cellulose hemi malonate, cellulose hemi succinate, cellulose hemi
glutarate, cellulose hemi phthalate, cellulose hemi maleate and
cellulose hemi adipate.
The above basic esters and ether-forming groups may have a wide
variety of other substituents as desired. Such compounds are well
known in the art and the water solubility of the theoretical A-OH
can be found in handbooks and the chemical literature.
It will be understood that the water-sensitivity of these fibers is
dependent upon the nature of the cellulose itself, the manner in
which the fibers are formed, the degree of substitution (D.S.) of
the cellulose, the distribution of the groups throughout the fiber
and the degree of neutralization of any ionic groups.
In general the highest water-sensitivity for a given D.S. for a
given compound is observed with fibers made by extruding a solution
of the desired derivative. Thus extruded fibers of cyanoethyl
cellulose of D.S. 0.15 to 0.80, hydroxyethyl cellulose of D.S. 0.1
to 0.9, sodium carboxymethyl cellulose of D.S. 0.1 to 0.3 and
sodium carboxyethyl cellulose of D.S. 0.1 to 0.3 are suitable for
making the most highly water-dispersible products.
Suitable fibers for the most highly water-dispersible products made
by chemical modification of cellulose fibers include sodium
carboxymethyl cellulose of D.S. 0.2 to 0.4, sodium cellulose
sulfate of D.S. 0.2 to 0.4 sodium cellulose phosphate of D.S. 0.2
to 0.4 and sodium cellulose hemisuccinate of D.S. 0.2 to 0.4. In
general a higher D.S. is required for this type of fiber to obtain
a given degree of water-sensitivity than with the extruded fibers.
The D.S. ranges for the above sodium salts are for completely
neutralized derivatives. Partially neutralized or partially
cross-linked (e.g., by polyvalent cations) derivatives of higher
D.S. can also provide the desired water-sensitivity.
The bulk of the water-sensitive fibers present will preferably be
textile fibers of about 0.5 to 15 denier (preferably less than 5
denier) with a length from about 0.25 to 2 inches. Smaller fibers
made by chemical modification of paper making fibers, cotton
linters and the like, may be present in amounts as large as 90
percent.
NON-WATER-SENSITIVE FIBERS
These fibers are the usual textile fibers of commerce (e.g. rayon,
cotton, nylon, acrylic or polyester) and are characterized by a SL
absorption (in fabric form) of less than about 0.9. The fibers
should be no longer than about 0.5 inch. Fibers of 1 to 5 denier
are most satisfactory but smaller fibers such as paper-making
fibers and cotton linters can be used. Preferably the fibers are
biodegradable since the products are to be dispersed in sewage
systems. Cellulosic fibers such as cotton or viscose rayon are
especially useful.
DESCRIPTION OF THE DRAWINGS
In the accompanying illustrations of the invention,
FIG. 1 is a photomicrograph at 10X magnification of a
representative portion of the fabric prepared as disclosed in
Example I, showing the top or upstream face of the fabric by direct
illumination,
FIG. 2 is a photomicrograph at 10X magnification corresponding to
FIG. 1, but showing the bottom face of the fabric which is next to
the screen support during production,
FIG. 3 is a photomicrograph at 10X magnification of a
representative portion of the fabric prepared as disclosed in
Example VIII, showing the top face of the fabric by direct
illumination, and
FIG. 4 is a photomicrograph at 10X magnification corresponding to
FIG. 3, but showing the bottom face of the fabric.
The dispersibility of the products are a function of the length,
and the degree of water-sensitivity of the fibers, the composition
and the extent of entanglement. Thus, at about 100, 40 and 10
percent water-sensitive fibers content the length of the
water-sensitive fibers should not exceed 3 in., about 1.5 in. and
0.75 in. respectively when using a moderate degree of entanglement
and fibers with a moderate degree of water-sensitivity.
FIGS. 5 and 6 illustrate a sanitary napkin comprising an absorbent
core covered with the flushable fabric of the invention as the
outer wrapper 48 which has end extensions forming attachment tabs
in the usual manner. Within the cover there is the absorbent core
formed of a composite of absorbent creped tissue 50 known as a
cellulose wadding and loosely felted fibrated wood pulp 49 commonly
known as fluff. The thickness and composition of each of these
absorbent layers may vary considerably and may be interchanged in
position or have one or the other type omitted depending on how
much total absorbent capacity and softness is desired in the core.
All components of the core must be water dispersible. Between the
core and the bottom and sides of the napkin wrapper is creped
tissue 51 which has been treated with a hydrophobic material to act
as a menstrual fluid barrier.
FIGS. 7 and 8 illustrate a diaper comprising an absorbent core
covered with a wrapper 48 consisting of the flushable fabric of the
invention. The core consists preferably of wood fluff 49 but can be
any fiber blend or composite which is water dispersible.
FIGS. 1 to 4 illustrate products of this invention of fibers
secured in place by random fiber entanglement in a repeating
pattern of ordered fiber groups arranged in parallel rows
interconnected by fibers extending between adjacent rows to form a
unitary structure. A wide variety of such patterns can be prepared
by using different patterning supports, as disclosed in the
applications referenced previously. The product of FIGS. 1 and 2 is
prepared on a plain weave, 24 .times. 24 mesh/inch woven wire
screen. The resulting product has ordered fiber groups arranged in
regular parallel rows extending in two principal fabric directions
and interconnected in a network by fibers randomly entangled with
each other to defined an ordered geometric pattern of apertures.
Fiber groups which form ridgelike protrusions on the face of the
fabric are seen in FIG. 2. In this embodiment the ordered fiber
groups follow paths located between adjacent parallel wires of the
screen.
The product of FIGS. 3 and 4 is prepared on a grid of 40 mil
diameter parallel rods spaced 12 to the inch. The repeating pattern
of the product is characterized by groups of entangled fibers
forming a regular pattern of ridgelike protrusions separated by
grooves lying along parallel straight lines, the ridge-forming
groups being interconnected by arrays of generally parallel fibers
bridging under the ridge-separating grooves and entangled in
adjacent groups. As disclosed in our previously referenced
application, a somewhat similar product is prepared on oblong
screens having five to 12 heavy wires per inch in one direction and
about 3 to 5 times as many finer wires per inch in the other screen
direction. The product has a repeating pattern of fiber bands of
substantially greater width than thickness which extend
continuously along substantially straight parallel axes spaced
regularly in one fabric direction, the bands being interconnected
by generally parallel fibers which extend laterally between
adjacent bands and are held in place by fiber entanglement in the
bands. The band-interconnecting fibers may be grouped in bundles
spaced regularly along the edges of the bands and defining rows of
apertures therebetween. Useful products can also be made which have
no repeating pattern of ordered fiber groups or apertures and can
resemble felts, for example. Such products can be made by using
fine mesh screens such as 80 or more mesh per inch as a support for
the fibers while entangling.
Process Considerations When Using Water-Sensitive Fibers As
Starting Material
Products of the present invention can be produced by treating webs
containing water-sensitive fibers with essentially columnar (i.e.
having a total divergence of not greater than 5.degree.) streams of
a liquid exerting an energy flux of at least 23,000 foot-poundals
per square inch-second (9100 Joules/cm..sup.2 min.) at the web.
This energy flux of a stream (EF) can be calculated by means of the
formula:
EF = 77 PG/A ft.-poundals/in..sup.2 sec.
(= 98 PG/A Joules/cm..sup.2 minute)
where P is the pressure at which the liquid is jetted in pounds per
square inch gage (p.s.i.) [kilograms per square centimeter
(kg/cm..sup.2 ]; G is the average volume flow for one jet stream in
cubic feet (liters) per minute and A is the cross-sectional area of
the streams in square inches (centimeters), at a location just
prior to impact with the fibrous webs. This area can be determined
from photographs of the stream with the webs removed, or by means
of micrometer probes. Suitable streams can be obtained by
propelling a suitable liquid at high pressures through
small-diameter orifices under conditions such that the emerging
streams remain essentially columnar at least until they strike the
fibrous material. The intensity of the streams is sufficient to
entangle the fibers firmly in place. The treatment is stopped short
of the maximum obtainable entanglement to provide a product having
a dry coherence value (C.sub.h, dry) high enough for in-use
integrity and a low wet coherence value (C.sub.h, wet) so that the
fibers will readily disperse in a sewage system. The low wet
C.sub.h results to a large extent from the combination of the low Y
value and the slipperiness of the water-sensitive fibers when wet.
This involves a critical control of the extent of treatment, taking
into account the rate of application of energy by the streams, the
rate at which the fibrous layer is traversed and the weight of the
layer. For control purposes, it has been found sufficient to use a
value, hereinafter designated the Y value, which is equal to the
weight of liquid used in lbs./min., times the liquid velocity in
ft./min., divided by the weight of the fibrous material treated in
lbs./min. When the fibrous material is treated a plurality of
times, the Y value is the sum of the values calculated for each
individual treatment. The total treatment conditions should be
adjusted to provide a Y value of 3 .times. 10.sup.6 to 24 .times.
10.sup.6 ft./min. whenever low-swelling fibers are present in the
fabric. The weight of liquid used and the weight of fibrous
material treated are measured for a convenient time interval. The
liquid velocity is then calculated from the lb. liquid/min. by
dividing by the density of the liquid in lbs./ft..sup.3 and by the
total orifice area in ft..sup.2.
A deswelling liquid is used in the streams to avoid swelling the
water-sensitive fibers during treatment which would result in
damage. A variety of aqueous salt solutions have been found
suitable including sodium sulfate (17--20 percent), ammonium
sulfate (20--30 percent), and sodium citrate (30 percent).
Nonaqueous liquids can also be used.
Preparation of Cyanoethyl Cellulose Fibers
Regenerated cyanoethyl cellulose fibers having about 0.4 to 0.8
degree of substitution are especially preferred as the
water-sensitive fibers. A suitable method for preparing them from
wood pulp cellulose is as follows:
Conventional wood pulp sheets are steeped in 18 percent caustic
soda solution at 27.5.degree. C. for 45 minutes. The sheets of
alkali cellulose are pressed to a 3/1 press weight ratio, shredded
and stored at 0.degree. C. They are allowed to warm to room
temperature a predetermined time before the next treatment.
22 pounds of alkali cellulose that has been held at 0.degree. C.
(typically 15.8 percent NaOH, 31.2 percent cellulose with a D.P. of
300--400) is added to a 12-gallon baratte with water at 40.degree.
C. circulating through the barrate jacket. The baratte is rotated
at 5 r.p.m. A mixture of 2.35 pounds (1066 grams) of carbon
disulfide and 2.75 pounds (1250 grams) of acrylonitrile is added to
the alkali cellulose over a period of 20 minutes. When the
temperature of the alkali cellulose reaches 19.degree. C., the
40.degree. jacket water is replaced with 20.degree. C. water. When
the temperature of the reaction mixture drops 1.degree. C. from its
highest value, the reaction is considered complete. The xanthate
crumb is transferred to an agitated dissolving tank containing
111.4 pounds (51.8 kilo) of a 3.72 percent solution of NaOH in soft
water and mixed for 60 minutes. The resulting viscose solution of
cyanoethyl cellulose is transferred to plastic-lined boxes and
stored at 0.degree. C. for 16 to 24 hours before using.
The above viscose solution is then filtered through a filter press,
deaerated, heated to about 20.degree. C. and pumped through candle
filters to a spinneret having 2200 orifices of 0.003-inch (0.076
mm.) diameter, and is extruded into a 48-inch (1.22 m.) long
coagulating bath (typically 9 percent H.sub.2SO.sub.4, 9 percent
ZnSo.sub.4 and 17 percent Na.sub.2SO.sub.4 at 60--65.degree. C.).
The filament bundle is forwarded over a feed roll and a skew idler
roll where regeneration of the yarn is completed. The regenerated
yarn is forwarded to another feed roll idler-roll set where it is
sprayed with a solution (35.degree. C.) containing 17 percent
Na.sub.2SO.sub.4 and 3 percent Na.sub.2HPO.sub.4 to neutralize the
acid in the yarn and keep it in a deswollen condition. The neutral
yarn is passed through squeeze rolls to remove excess solution and
then wound up on packages at 60 yards (Ca 55 m.) per minute.
A sample of the dry yarn contains 30.5 percent of salts and 19
percent soluble (at 10.degree. C.) material. The yarn has the
typical following properties calculated on a water-insoluble-fiber
weight: ##SPC2##
Preparation of Initial Layer of Fibrous Material
The initial layer may be a web or batt of fibers assembled by known
methods such as carding, random laydown, air deposition or by
papermaking processes. The fibers may be disposed in random
relationship with one another or in any degree of alignment. A
plurality of layers of the same or different composition or
orientation can be used. When prepared by assembling dry fibers,
the water-sensitive fibers can be up to about 3 inches in length in
the final assembly. Preferably the initial layer is formed on a
papermaking machine, such as a Fourdrinier machine, from a slurry
of water-sensitive fibers of 1 to 15 denier and 0.25 to 2.0-inch
staple length. Conventional textile fibers of 1 to 5 denier and
0.125 to 0.5-inch staple length can also be included in the slurry.
Slurries of staple fibers over 0.25 in. in length may be
conveniently processed on a drum-type paper machine such as the
"Rotoformer" manufactured by the Sandy Hill Corp., 29 Allen Street,
Hudson Falls, N.Y. Conventional short wood pulp fibers may be
substituted for part or all of the textile fibers in the
slurry.
Preparation of the initial layer on a papermaking machine starts
directly with formation of the slurry, since beating usually is not
required. The fibers are added to water and well agitated to give a
uniform slurry in the stock chest of the machine. A consistency of
0.1 to 0.40 percent fibers is suitable unless the fibers contain
less than 30 percent of water-sensitive fibers. Slurries containing
a high proportion of nonwater-sensitive fibers, e.g., 90 percent of
conventional textile fibers, are prepared at consistencies of about
0.03 to 0.09 percent fiber. The slurry is fed to the headbox of the
papermaking machine and is diluted with about an equal volume of
water en route to the headbox. A double headbox supplied with
different compositions of stock slurry can be used to prepare a
laminated initial layer. From the headbox the slurry is deposited
on the wire of the papermaking machine to form a fiber layer. The
machine wire may be several feet wide and of conventional type,
e.g., 7.5-mil diameter wire in a 70 .times. 52 mesh/inch
construction. The fibers drain as they are conveyed on the machine
wire, the drainage being assisted by the usual suction boxes. The
partially drained layer of fibers is sprayed with a 17 to 20
percent aqueous sodium sulfate solution, or other deswelling
liquid, to cause deswelling of the highly water-absorbent fibers in
the layer. For example, the layer may be sprayed with banks of
nozzles at 2, 3 and 4.75 feet from the breast roll of the machine,
using about 1.3 gallons per minute of the deswelling liquid. The
deswollen layer passes from a vacuum couch roll to a pressing
section where water and excess salt are removed. The layer may be
dried on rolls heated to 120.degree. C. and stored for subsequent
treatment. Alternatively, the damp layer can be passed directly to
the fluid treatment with high energy flux streams to form the
products of this invention.
Apparatus suitable for use in the continuous treatment of fibrous
layers to entangle the fibers into the structures of the present
invention is described in the examples.
The pattern produced by the hydraulic entangling is dependent upon
the design of the apertured patterning member. The term "apertured
member" includes any screen, perforated or grooved plate or the
like on which the fiber assembly is supported during the hydraulic
entangling and which by reason of its apertures and/or surface
contours influences the movement of fibers into a pattern in
response to the fluid streams. The apertured member may have a
planar or nonplanar surface or a combination of the two types.
Plain weave screens of from 3 to 80 mesh (wires per inch or per
2.54 cm.) having wire diameters of from 0.005 to 0.040 inch (0.127
to 1.02 mm.), and having from about 10 percent to 98 percent open
area are suitable apertured members and in general afford the type
of pattern shown in FIG. 3.
Twill weave screens and Dutch twill of the above general
construction may also be used.
An assembly of a grid of parallel rods contiguous with a second
grid and so oriented that the rods of each grid are not parallel to
the rods of the other grid can be used as an apertured member.
Structures of the type shown in FIGS. 3 and 4 can be made using
such supports.
Process Using non-water-sensitive Fibers As The Starting
Material
Products of this invention can be made by preparing an assembly of
non-water-sensitive fibers, entangling the fibers to give a
nonwoven fabric and then chemically modifying some or all of the
fibers in the fabric to a water-sensitive form. Suitable reactions
on cellulose include: chloroacetic acid and alkali to produce
carboxmethyl cellulose; alkali and ethylene oxide to produce
hydroxyethyl cellulose, alkali and acrylamide or acrylonitrile to
produce cyanoethyl cellulose, phosphoric acid and urea to produce
cellulose acid phosphate; succinamic acid to produce cellulose hemi
succinate; urea and sulfuric acid (or sulfamic acid) to produce
cellulose sulfate; and the like. Such reactions work well with
rayon; with cotton it may be necessary to degrade the cotton,
mercerize it or use stronger reaction conditions.
In addition to the preparation of a cellulose derivative in the
nonwoven form it will be obvious to one skilled in the art that
many other reactions are suitable for preparing water-sensitive
fibers from noncellulosic fibers such as the hydrolysis of
polyvinyl acetate fibers to polyvinyl alcohol, the hydrolysis of
cross-linked polyvinyl alcohol fibers, hydrolysis of acrylic
fibers, the use of the above-mentioned reactions for rayon on
noncellulosic fibers having hydroxyl groups such as copolymers
containing vinyl alcohol units, and the like.
It will be understood that the nonwoven fabrics to be treated can
contain fibers that will not be chemically modified by the reaction
used.
The assembly of non-water-sensitive fibers is conveniently made
into a nonwoven using hydraulic entangling as previously discussed.
The critical limits of entangling (Y values) for the assemblies
containing water-sensitive fibers do not apply in the case of
assemblies of 100 percent inert fibers and a greater entangling
treatment can be applied.
The chemically-modified nonwoven fabric may be treated with
deswelling salt solutions and dried in the manner already
described.
Products can also be made by entangling a web of fibers in the acid
form with water and then converting the entangled fibers to a more
water-sensitive salt form.
Water-dispersible nonwoven fabrics of this invention can be made by
(1) assembling a layer comprising cellulosic fibers of less than
about 5 inches in length, (2) treating the fibrous layer with
essentially columnar streams of a liquid to entangle the fibers
into a coherent nonwoven fabric, and (3) chemically modifying the
nonwoven fabric with water-sensitive groups to reduce its wet
coefficient of sliding friction, the conditions of the process
being selected so that the natural logarithm of the breakup time in
seconds (A) (Test defined in Example XXI) in the following equation
is less than 4.6.
where R is the yield resistance time (YRT - defined in Example
XXVI) of the cellulosic nonwoven fabric before chemical
modification, L is the weight average length of the fibers in
inches, and f.sub.w is the wet coefficient of sliding friction of
the chemically modified nonwoven.
A higher degree of water dispersibility can be achieved by using
conditions to give a value of less than 3.7 for A. More preferably,
the value of A should be less than 3.4 to yield products of higher
water-dispersibility which can be flushed in household toilets.
R is a measure of the entanglement of the cellulosic nonwoven
fabric. The value of R for a given fiber layer increases as the
duration of the liquid entangling treatment is increased (i.e., by
slower speeds or by repeated treatments) for a given set of
conditions. The value of R increases as the pressure on the liquid
streams is increased for a given orifice. The value of R increases
as the diameter of the liquid orifice is increased at a given
pressure. R is dependent upon the average fiber length (L). In
general, R increases with L when all other conditions remain
constant.
Preferably R should have a value of at least 10 to provide
integrity and should preferably be less than about 400. The fiber
length (L) should preferably be less than 2 inches.
The coefficient of sliding friction(f.sub.w) is a measure of the
chemical modification of the nonwoven. In general for a given
cellulosic nonwoven, the f.sub.w decreases as the extent of the
modification with the water-sensitive groups increases up to a
certain level. This modification is controlled by the usual
variables of a chemical reaction--concentration, time, and
temperature.
The products of this invention are capable of many modifications.
They can be tinted, printed with designs, and made in a wide
variety of patterns.
In addition to the use of simple nonwoven fabrics of this invention
for sanitary purposes various combinations are possible. The
nonwoven fabric may be used as a cover for a very high absorbency
pad for special applications.
Characterization Procedures
Papers made by deposition of fibers on a moving screen such as a
Fourdrinier machine usually show different properties in the
continuous direction (i.e., direction of travel on the paper
machine) termed "machine direction" (MD) and in the direction
transverse to travel termed "cross direction" (CD). These terms are
also applied in a like manner to nonwoven fabrics made by passing a
long web of fibers under a hydraulic entangling assembly in one
direction (MD). Products made from hand paper sheets usually have
very similar properties in any two directions at right angles and
the direction is not designated.
Tensile Strength and Elongation
Tensile strengths and elongations are measured on an Instron
testing machine using a 2-inch length between the jaws and
elongating at 50 percent per minute. Results for Examples 1 to 9
are determined on 0.5 inch wide strips while the remainder are
determined on 1.0 inch wide strips. In some cases the breaking
force determined in the coherence value test is used to calculate
the tensile strength; such values are marked with "c." All tensiles
are normalized to pounds/inch of width. All three methods give
approximately the same results.
Samples are soaked for 5 minutes in distilled water at room
temperature and then clamped in the tester and broken in air to
determine wet tensile strength. These values are referred to as the
wet strip-tensile strength. The same method is used to determine
tensile strength after soaking in synthetic urine or other
liquids.
Coherence Value (C.sub.h)
The coherence value (C.sub.h) is a measure of the degree to which
the fibers within the fabric break as opposed to slipping apart
whenever a long strip of the fabric is pulled apart.
The test, in essence, comprises measuring the tensile strength of a
long strip of the fabric and dividing this value by the tensile
strength of the strip as determined at substantially zero length
(Instron clamping jaws together). It is readily apparent that
during the zero length strip-tensile measurement fiber slippage
cannot occur and hence the maximum tensile strength for the strip
is obtained. Therefore the maximum (C.sub.h) is 1 with lower
C.sub.h values indicating fiber slippage. A C.sub.h (wet) of no
greater than about 0.6 is necessary to achieve the desired
dispersibility of the products of this invention while a C.sub.h
(dry) of at least 0.2 is required to yield adequate in-use
strength.
Samples of salt-free fabrics are cut into 1.6 inch (4.1 cm.) wide
strips. The strips are then cut to about 2-inch and 1-inch (5 and
2.5 cm.) adjacent samples. The longer sample is broken using
1.5-inch (3.8 cm.) gauge (distance between the rubber-coated jaws
of the Instron Tester). The shorter sample is broken using zero
gauge. The coherence value (C.sub.h) is the breaking strength of
the longer sample divided by the breaking strength of the shorter
sample. The average results from at least 3 pairs of such breaks in
each direction of the fabric is reported as C.sub.h in the
examples.
For C.sub.h,wet values, a bath of distilled water is raised a round
the sample which is clamped in the Instron machine and the sample
soaked for at least 1 minute before breaking it in the bath. All
samples are elongated at a rate of 0.5 inch (12.6 mm) per
minute.
Salt-free fabrics for use in coherence value determinations are
prepared by extracting with a solution made from 60 volumes of
methanol and 40 volumes of water. About 100 g. of the fabric,
divided into 4 portions is placed in 1500 ml. of solution, then
gently worked to insure saturation, soaked 15 minutes, and then
gently squeezed and pressed between blotters. This is repeated
using fresh solution until the solution is clear (normally 3
washes). Three additional treatments are then given followed by a
final treatment in 100 percent methanol. The blotted samples are
opened and dried in air. Twisting or pulling of the fabric during
the treatments are avoided. The final fabrics are soft and
conformable.
Single Layer Absorbency
The single layer (designated SL) absorbency method has been divised
to measure fiber absorbency in the fabric state and to minimize
interstitial water. A 3 in. .times. 3 in. (7.6 .times. 7.6 cm)
sample in a 100 mesh screen basket is immersed for 1 minute in 150
ml. of a 0.1 percent aqueous NaCl solution and the basket then
dipped in and out of the solution 5 times and drained for 15
seconds. The procedure is repeated in a fresh salt solution and the
sample soaked for 5 minutes before draining the basket for 30
seconds. The wet sample is dropped from the basket onto a dry
blotter and immediately dropped from the first blotter to a second
dry blotter and covered with another dry blotter. The 2 blotters (5
.times. 5 in.) and the enclosed sample are covered with a 5 in.
.times. 5 in. cluminum plate and a weight added on top to give a
total weight for the weight and plate of 3 kg. The sample is
pressed at the 3 kg. pressure for 5 minutes and weighted
immediately. The sample is dried for 2 hours in a hot air oven at
125.degree. C., cooled in a dessicator and weighed immediately. The
SL absorption is obtained by dividing (pressed wet weight minus dry
weight) by the dry (final) weight to yield grams of solution/grams
of dry fabric.
If the SL absorbency is less than 1.0 g./g., the determination
should be repeated using blotters that have been slightly dampened
(about 0.2 g/g of dry blotter) with a fine spray of the salt
solution. Such a procedure avoids a false reading caused by some of
the solution from the fibers (as well as interstitial) being
absorbed by the dry blotters.
Conversely, if the blotters appear to be fully soaked the procedure
should be repeated with the addition of a paper towel on the
outside face of each blotter as all of the interstitial solution is
not removed otherwise.
Water-Sensitive Fiber Frictional Characteristics
The coefficient of sliding friction, (f) (or kinetic friction) is
the ratio of the force (F) needed to pull one surface over another
to the force (N) normal to the surfaces in contact.
A piece of fabric of about 2 in. .times. 6 Inc. (5.1 .times. 15.3
cm.) is placed on the horizontal bottom of a metal tank with the
longer length in the direction of sliding and one end held in place
with a heavy metal block. A second portion of fabric of 1 in.
.times. 3 in. (2.5 .times. 7.6 cm.) is wrapped around a sled so
that the bottom, front and back faces of the sled have 1 thickness
of cloth and the top face has 1 to 2 thicknesses. A 5 gram brass
weight is placed on top of the fabric. The sled consists of a 1
.times. 1 .times. 0.063 in. (25 .times. 25 .times. 1.6 mm.) piece
of poly(methyl methacrylate) plastic with an outer layer of crocus
cloth (abrasive face out) held to the plastic with double-faced
adhesive tape. The sled has a filament attached to each side near
the forward edge forming a yoke. A 0.1 percent aqueous solution of
NaCl is slowly added to the tank to a depth of about 8 mm., the
sled, fabric and weight placed on top of the lower fabric, the yoke
attached to a filament leading under a pulley in the tank and
upward to the crosshead of an Instron Tester and the tester started
so as to pull to sled at a rate of 2 in. (5.0 cm.) per minute. The
sliding is continued for about 90 seconds. The charted force from
30 seconds to the end is averaged and reported as F after suitable
correction for the force necessary to overcome the friction of the
pulley. Force N is the sum of the sled weight (1.9 g.), the fabric
(normally about 0.15 g.) and the 5.0 g. weight, minus the buoyancy
of the solution. The solution completely covers the sled and about
50 percent of the weight. (Total effective force, N, 5.8 gms).
The above conditions should be followed since f varies with N. The
results of this test are reported as the wet coefficient of sliding
friction (f.sub.w).
The test is made on an entangled nonwoven fabric consisting of 100
percent of the water-sensitive fibers and having a C.sub.h (dry) of
at least 0.2. Fabric pattern or structure variation has been found
to have little effect on the sliding friction with essentially
planar fabrics.
Products of this invention have been made of fibers which have
f.sub.w values (as measured on an entangled nonwoven fabric
containing 100 percent of the fibers) of from 0.3 to 1.3.
The F.sub.w values of rayon increase as the amount of entanglement
of the nonwoven fabric is increased and increase as the average
fiber length is decreased at a constant entanglement condition.
Thus, at a near minimum entanglement condition f.sub.w varies from
1.30 for 1.38 inch average fiber length to 1.44 for a 0.38 inch
average fiber length. At a near maximum entangling condition, the
f.sub.w ranges from 1.77 to 1.90 for the same blends respectively.
When rayon nonwoven fabrics are modified to a water-sensitive fiber
form, the f.sub.w is no more than about 80 percent of the starting
rayon f.sub.w values for the lesser dispersible products and can be
as low as 40 percent or lower of the starting values for the highly
dispersible products.
Bending Length
BEnding length is 0.5 the length of a strip of sample that bends
under its own weight to a 45.degree. angle. It is determined on 1
.times. 6 inch sample of a Drape-Flex Stiffness Tester (made by
Fabric Development Tests, Brooklyn 32, N.Y.). The procedure
utilized for the bending length determination is as described in
American Standards of Testing Materials (ASTM) test number D
1388-55T. Unless otherwise stated the CD value is given as it is
usually lower than the MD value.
Fabric Weight
Fabric weights are expressed in ounces/square yards, hereafter
designated as oz./yd..sup.2, and are based on the weight of the
fibers present minus water-soluble impurities.
Liquid Absorption
The liquid absorbency of a sample is determined by soaking a small
sample in an excess of the liquid at 25.degree. C. unless otherwise
designated (1 g. in 3000 g. of liquid). The sample is removed from
the liquid and spread out to cover a 5 .times. 5 cm. area on
bleached sulfite blotter paper. The sample is placed between layers
of blotter paper and loaded with a 3 kilogram weight to give a
pressure of 120 g./cm..sup.2. Pressure is applied for 5 minutes
after which the sample is removed and weighed, giving the wet
weight. Then the sample is dried to constant weight using a Noble
and Woods sheet dryer at 100.degree. C. Absorbency equals the water
absorbed (wet weight minus dry weight) divided by the dry weight.
In the case of absorbency determinations in body fluids, the dry
weight must be corrected for solids dissolved in the liquid
absorbed.
In examples 1--8, absorbencies of urine are measured in a salt
solution of essentially the same composition as human urine [16 g.
NaCl, 35 g. urea, 2 g. MgSO.sub.4, and 3 g.
Ca(H.sub.2PO.sub.4).sub.2H.sub.s(per liter of solution in distilled
water.] In examples 9--18, the "synthetic urine" comprises a salt
solution containing 10 g. NaCl, 24 g. urea, 0.6 MgSO.sub.4, and 0.7
g. calcium acetate monohydrate per liter of solution in distilled
water. All water absorbencies are measured in distilled water
unless otherwise stated. Except for examples 1--8, "synthetic
urine" is of the composition as used in examples 9--18.
Dispersibility
The dispersibility is determined in a 250 ml. filter flask having
an added side arm at the bottom of the conical wall and containing
a magnetically rotated bar. The bar is 3.8 cm. long by 8 mm. in
diameter, weights 11.73 grams and is rotated at 500 revolutions per
minute. A 3 .times. 3-inch sample is folded in half and inserted
under the surface of the water (at the top side arm). Tap water at
about 25.degree. C. is added through the bottom tube at a rate of
0.70 liters/minute for period of 2 minutes. The effluent liquid
from the upper side arm is filtered and the residue dried to
constant weight at 100.degree. C. to give the weight of fibers
dispersed. The contents of the filter flask are filtered after the
test and dried to yield the weight of undispersed fibers. The
percent dispersibility is equal to 100 times the weight of fibers
dispersed divided by the total weight of fibers recovered.
Conventional toilet tissues have a dispersibility of 7 percent.
Flushability
The flushability of a sample is determined by dropping a 10 .times.
26-inch sample that has been folded to 10 .times. 13 in. into the
bowl of a household toilet (Model F2122 made by the American
Radiator and Standard Sanitary Corporation of New York, N.Y.) and
flushing. The discharge from the toilet is passed through a length
of horizontal flass pipe 2.33 ft. (71 cm.) long and of 10.8 cm.
inside diameter containing an artificial obstruction. The
obstruction is constructed of standard flattened expanded metal
with 0.5 in. (1.27 cm.) wide perforations, formed into a cylinder
of 1 ft. (30.5 cm.) long and about 10.8 cm. in diameter and
provided with 41 inside projections randomly distributed and made
by making parallel pairs of cuts about 0.25 to 0.75 in. (0.63 to
1.9 cm.) long and about 0.3 in. (0.75 cm.) apart, and beding the
cut sections to stand perpendicular to the walls of the cylinder.
One flushing gives a flow of about 20 liters of water in 7 to 8
seconds. The toilet is flushed 3 times for each sample. The
percentage of the sample that passes the hooks in the glass pipe is
estimated and recorded after each flush. A sample is termed
"flushable" if at least 60 percent passes by the hooks after 2
flushes. At least 85 percent of a sample of the preferred products
passes by the hooks after 2 flushes.
It has been observed that samples of examples 1--9 termed
"Flushable" by the above test have a dispersibility of at least
about 20 percent (i.e., in 2 minutes), or require less than 20
minutes to completely disperse in the small-scale dispersion test.
Preferred products have a dispersibility of at least 40
percent.
For products of the type prepared in Examples I--V, the following
relationship between breakup time (B.U.T.) and percent
dispersibility is observed:
Wickability
The wickability of a sample is determined by fastening the ends of
a 2 .times.5.5-inch strip to a perforated metal plate with rubber
bands, resting the end of the plate under about 0.5 inches of
"synthetic urine" at about 25.degree. C. at an angle of 25.degree.
to the level of the water and noting the time in minutes for the
liquid to wick the sample for a distance of 5 inches from the top
of the liquid. Preferred products have a wickability in "synthetic
urine" of less than 5 minutes. All product in the examples
containing low-swelling fibers and made from a water dispersion
have wickabilities of less than 30 minutes.
Loose Fiber Test
The loose fiber test is a measurement of the fabric integrity and
is conducted by rolling a wet sample of the nonwoven fabric (9.8
.times. 12 cm.) located on a glass plate once with a dry rubber
roller having a surface area equal to the sample. The fibers
adhering to the roller are collected, washed with acetone, dried
and weighed. Before testing, the sample is thoroughly wet with an
excess of distilled water, covered with 2 paper towels and blotted
by rolling lightly once with the above roller.
Nonwoven structures with no entanglement of the fibers lose about
0.12 gram by this test (or 14 percent of the original 0.86-gram
sample). The preferred products of this invention show zero loss by
this test. Useful structures may show a loss as high as 8 percent.
Fabrics having a loss of less than about 10 percent are deemed to
be unitary.
The invention will be better understood from the following specific
illustrations of products and processes for making them. The
examples are not intended to be limitative.
Examples
In the examples all solutions are aqueous unless otherwise stated.
All screens are designed by mesh [(per inch or per 2.54 cm.)] and
are understood to be the same in both directions, i.e. square mesh
unless otherwise stated. The amount of liquid on a fabric is
designated by pick up which is the grams of liquid on the fabric
per gram of original dry fabric.
EXAMPLE I
Cyanoethyl cellulose fibers of 0.4 degree of cyanoethyl
substitution, 2 denier per fiber, and 0.5-inch staple length are
prepared as previously described. A mixture of 80 parts of these
fibers (based on the dry weight of the water-insoluble fiber) and
20 parts of viscose rayon 0.25-inch staple of 1.5 dpf is added to
water at 30.degree. C. in a stock chest and well agitated to give a
uniform slurry containing 0.24 percent fibers. This slurry is
diluted to a consistency of 0.12 percent and fed to a headbox on a
Fourdrinier machine as described previously. The machine wire is 31
inches wide made of 7.5-mil diameter wire in a 70 .times. 52
mesh/inch construction. The partially-drained fiber layer
containing swollen cyanoethyl cellulose is sprayed with a 20
percent water soltuion of Na.sub.2SO.sub.4 at 40.degree. C. at 2,
3, and 4.75 feet from the breast roll. The nozzles supply about 1.3
gallons/minute. The salt soltuion deswells the fibers. The wet
paper is passed from the couching roll to a pressing section where
it is pressed and is then dried on rolls heated to 120.degree. C.
The dry layer (A) has a fabric weight (water-insoluble fiber) of
1.54 oz./yd..sup.2.
A second layer (B) with a fabric weight of 0.80 oz./yd.sup.2 is
made from a mixture containing 10 percent of the above cyanoethyl
cellulose staple and 90 percent of the aryon staple by the above
procedure with omission of the salt solution spray. The stock chest
consistency of 0.06 percent is reduced to 0.02 percent just prior
to entering the headbox.
An assembly of layer (A) covered with layer (B) is continuously fed
to a belt of a 24 .times. 24 mesh/inch screen woven of 20-mil
diameter wire moving at 6 feet per minute.
The assembly (on the screen) is hydraulically entangled by streams
of a 20 percent water solution of Na.sub.2SO.sub.4 at 50.degree. C.
from a single row of 5-mil diameter orifices spaced about 25 mils
(0.63 mm.) center-to-center in a 12-mil (.30 mm.) thick plate
mounted on a manifold. The orifices are spaced about 1 inch from
the fibers and a pressure of 300 p.s.i. is maintained on the salt
solution in the manifold. Both ends of the horizontal manifold are
oscillated by eccentrics on a 0.5-inch diameter eccentricity at a
rate of 9 to 10 revolutions/second. At the pressure used, the
27-inch long row of orifices delivers 165 pounds of salt solution
per minute through the 1080 orifices onto the 27-inch wide layer of
fibers. The total weight of the double layer of fibers passing
under the fluid streams in 1 minute is 0.220 pounds. The Y value is
thus 11 .times. 10.sup.6 feet/minute.
If the salt solution is replaced with water alone, the papers are
washed away and/or driven partially through the screen.
The unitary nonwoven fabric produced is pressed between blotting
papers at 1450 p.s.i. Portions of the pressed products (about
50--60 percent solids) of about 10 .times. 26 inch are dried and
softened by tumbling in a home laundry dryer at about 45.degree. C.
with 4 baseballs of 9.7 cm. in diameter.
Drying without softening yields a web that is stiff, boardlike, has
poor drape and no aesthetic appeal.
The dry, softened product is a unitary nonwoven fabric with the 2
layers intimately connected. It has the appearance and hand of a
soft woven fabric. FIG. 1 is a photograph at 10X magnification of
the face of the fabric that faced the liquid streams and FIG. 2
shows the fabric face which was next to the screen.
The softened, nonwoven fabric has a fabric weight (as is) of 2.6
oz./yd..sup.2, contains 12.5 percent of Na.sub.2SO.sub.4, 41.1
percent cyanoethyl cellulose and 46.4 percent of rayon and has a
density of 0.138 g./cm..sup.3. Properties corrected to a salt-free
basis of the product are given below. ##SPC3##
For use as a diaper the nonwoven fabric is folded to give a double
thickness with the rayon-rich faces on the outside. The diaper is
pinned about the baby in the usual manner. The diaper will absorb
the total urine output of an average 6-months old baby for a period
of 4 hours (i.e., 75 grams of urine). Even under this extreme
condition the diaper retains its integrity, does not tear at the
pins, leaves no loose fibers on the skin and is nonirritating The
soiled diaper is dropped into a toilet and flushed away. This
product is completely biodegradable so that no problems with sewage
disposal are caused.
The nonwoven fabric may be used as a water-flushable sanitary
garment.
EXAMPLE II
This example shows the effects of variables in the hydraulic
entangling step.
Two single layers of fibers are made from cyanoethyl cellulose
fibers and viscose rayon staple of Example I by the method of
Example I. One layer contains 70 percent of the cyanoethyl
cellulose fibers and has a nominal fabric weight of 1.18
oz./yd..sup.2. The other layer contains 10 percent of the
cyanoethyl cellulose fibers and has a nominal fabric weight of
0.77.
A series of nonwoven fabrics are made by hydraulically entangling a
top layer of the aryon-rich fibers to a layer of the cyanoethyl
cellulose-rich fibers under various conditions. Each of the
products has an average composition of 46.5 percent cyanoethyl
cellulose fibers.
Items (a) to (h) are prepared with an orifice assembly having 540
orifices of 5-mil diameter evenly spaced in a single 27-inch row.
Items (i) to (k) are prepared with an orifice assembly having 1080
of the orifices of 5-mil diameter in a single 27-inch row. The same
patterning screen and general conditions of Example I are used for
both series, but pressures from 200 to 500 p.s.i. are used to give
different total flow rates (W) and the rate of traverse (V.sub.s)
is varied. The entangling conditions and properties of the products
are given in Table I. Tensile properties have been corrected by the
average value of 17.2 percent Na.sub.2SO.sub.4 content to a
salt-free fiber basis. The products have S.L. absorbencies within
the range of about 3.1 to 3.4. ##SPC4##
Items (a) to (f), (i), and (j) are products of the invention with
dry strip-tensile strengths sufficient for use demands (such as
pinning), wet strip-tensile strengths low enough to give ready
flushability but high enough in body fluids to be useful, a water
and urine absorbency of 7 grams/gram at 25.degree. C., bending
lengths of 1.1 to 1.8 cm. and a soft handle. These products have
densities of from 0.113 to 0.159 g./cm..sup.3 based on thicknesses
measured with an Ames gauge.
Items (g), (h), and (k) show the effects of excessive hydraulic
entangling on wet tensile properties and flushability. The effect
of the liquid flow rate used at the same or similar duration of
treatment is shown for items (d) vs. (g), and (c) vs. (h).
Items (a)--(f) and (i) are the most highly water-dispersible
fabrics and correspond to fabric definition III in the summary of
this invention. Item (j) falls within the intermediate dispersible
definition II and items (h) and (k) are not water-dispersible. Item
(g) falls within the water-dispersible fabrics of class I.
EXAMPLE III
The fibers of Example I are used to make a composite sheet having
two layers of fibers as described below, using a double-layer
headbox and the method of Example I.
Portions of the layer are dried with softening to give item (a).
##SPC5##
Portions of the sheet are treated with fluid streams of 20 percent
aqueous Na.sub.2SO.sub.4 at various pressures and speeds by the
method of Example I but with an orifice assembly having 280
orifices of 5-mil diameter evenly spaced in a single row 14 inches
long. The aperture patterning member is a 20 .times. 20 mesh screen
of 0.025-inch diameter wire. The rayon-rich face of the sheet faces
the fluid streams. Pressures range from 50 to 500 p.s.i. The rate
of traverse (V.sub.s) is 6 feet per minute for item (c) and 2 feet
per minute for item (d). The total flow rate (W) of the fluid
streams and the calculated Y values are given in Table II.
Properties of the products have an absorbency of 9.2 grams of water
per gram of material at 25.degree. C. and S.L. absorbencies of
about 4.1. ##SPC6##
Both untreated products (items a and b) have dry strengths
sufficient for use, but their usefulness is drastically limited by
the low elongations at break. Urine wet strengths are too low for
them to be useful as a diaper or sanitary garment. Both products
have the appearance and hand of a paper. They lose 14 percent of
their dry weight in the loose-fiber test.
Item (c) represents a preferred product of this invention. It has
the appearance, handle and elongation of a fabric. It does not lose
fibers in the loose-fiber test.
Item (d) has the appearance and handle of a fabric but the fibers
have been so firmly entangled that it is not dispersible.
The importance of using essentially columnar, high impact streams
of liquid is shown by comparison experiments with spray nozzles. A
63-mil diameter solid cone spray nozzle ("Sprayco No. 2112," made
by Spray Engineering Co. of Burlington, Mass.) delivers 1.25
gallons per minute of water at 50 p.s.i. pressure. It was found
that the spray entrains large amounts of air, thereby generating a
high degree of air turbulence at the surface of the layer of fibers
which leads to nonuniformities in the treated product. In order to
protect the fibers from this turbulence, a fine screen was
interposed on the surface of the sheet exposed to the streams.
On a hand sheet mold (serving as a suction box) is placed in
sequence an apertured patterning plate, a sheet of the above
two-layer composite with the rayon-rich face up, and a 400-mesh
screen on the top. The assembly is sprayed with a 20 percent water
solution of Na.sub.2SO.sub.4 at 50.degree. C. from the 63-mil
diameter solid cone spray nozzle located 4 inches above the top
screen. The aperture plate has 63-mil diameter holes arranged on
94-mil staggered centers giving 132 holes/inch.sup.2 and 41 percent
open area. The spray is moved in one direction at a rate of about 4
feet per minute, which sprays about half the width of the sheet.
The spraying is repeated until the entire sheet has received 8
exposures to the spray in one direction and 8 at 90.degree. to
that. Samples are prepared at 50, 75 and 100 p.s.i. and dried. In
each case there is no entangling of fibers in the two layers. The
rayon fibers on the top face of the product have been washed into
clumps in each case. The underlying layer of fibers appears
embossed at the 2 lower pressures and patterned at the higher. The
rayon fibers on the top face are readily removed by the loose fiber
test. All samples have dry elongations of less than 7 percent.
Other properties are not measured since the products are so
nonuniform.
Similar results are obtained when the composite sheet is treated
with the rayon-rich layer of fibers on the bottom in contact with
the patterning plate.
The inability of the above spraying procedure to entangle the
fibers is even more strikingly demonstrated when the above
double-layer composite sheet is replaced with 2 separately-prepared
layers of fibers as in Example I. At pressures of 50, 100 and 150
p.s.i. the products are readily separated by hand into the two
original layers.
Y values of less than 0.01 .times. 10.sup.6 are calculated for the
above spray treatments, when the liquid velocity is calculated from
the liquid flow rate (W) and the area of the spray as it strikes
the paper.
EXAMPLE IV
Preparation of Hydroxyethyl Cellulose (HEC) Fibers
This example illustrates the use of highly water-absorbent fibers
of different types of cellulose ethers in preparing the
products.
Conventional wood pulp sheets are steeped in 18 percent caustic
soda solution at 27.5.degree. C. for 45 minutes. The sheets of
alkali cellulose are pressed to a 3/1 press weight ratio, shredded,
and stored at 0.degree. C.
One pound of the alkali cellulose is held at 26.degree. C. for 27
hours, is added to a 5-liter baratte and the air is evacuated.
Fifty-three grams of ethylene oxide are added over a 90-minute
period as it is revolved on its side in a 25.degree. C. water bath.
The baratte is flushed with nitrogen and the hydroxyethyl cellulose
produced is removed and dissolved in dilute aqueous NaOH at
0.degree. to 10.degree. C. to give a solution containing 6 percent
of the cellulose ether and 7 percent caustic. The solution is
frozen at - 30.degree. C., heated to room temperature and filtered.
The filtered solution is extruded through a spinneret containing
504 orifices of 3-mil diameter into a coagulating bath (12 percent
H.sub.2SO.sub.4 and 18 percent Na.sub.2SO.sub.4) and the yarn is
neutralized. The dry yarn has a dpf of 2.6, a dry tenacity of 0.98
g.p.d., a dry elongation of 9.8 percent (all reduced to a salt-free
basis), an absorbency for water and for urine at 25.degree. C. of
12 and 11 g./g., respectively, and a degree of hydroxyethyl
substitution of 0.61.
Preparation of Sodium Carboxyethyl Cellulose (CbEC) Fibers
Cyanoethyl cellulose fibers are prepared as for Example I except
that the modified viscose solution is aged for 3 days at 25.degree.
C., and is then spun and neutralized as previously described. The
fibers are washed with 70.degree. C. distilled water, deswollen
with acetone and dried at 100.degree. C. The fiber has a degree of
substitution of carboxyethyl groups of 0.13 and a degree of
substitution of cyanoethyl groups of 0.04. It has an absorbency for
distilled water and for urine at 25.degree. C. of 34 and 8 g./g.,
respectively.
Preparation of Cyanoethyl Cellulose Fibers by Another Route
A solution of cyanoethyl cellulose (CNEC) is prepared according to
British Patent No. 633,807 by adding the acrylonitrile to
conventional viscose. The solution is spun to fibers and
neutralized as described previously. The fibers have the following
typical properties calculated on a water-insoluble fiber weight:
##SPC7##
Each of the above cellulose ether fibers is cut to 0.5-inch staple
length and handsheets are prepared from aqueous slurries of the
fibers in an 8 .times. 8-inch sheet mold. The handsheet and the
sheet mold screen are removed from the sheet mold box, the fibers
are deswelled by wetting with 18 percent aqueous sodium sulfate for
about 1 minute, and the sheet is then dried. The following sheets
are prepared in this manner, the weights and percentages being
based on the water-insoluble fiber content:
Sheet a, 2.0 oz./yd..sup.2, 39 percent HEC fibers and 61 percent of
0.25-inch viscose rayon fibers;
Sheet b, 1.43 oz./yd..sup.2, 100 percent HEC fibers;
Sheet c, 1.43 oz./yd..sup.2, 100 percent CbEC fibers; and
Sheet d, 1.43 oz./yd..sup.2, 100 percent CNEC fibers.
Sheet (a) is hydraulically entangled with essentially columnar
streams of 20 percent aqueous sodium sulfate solution as in Example
I. Sheet (b) is plied with a layer B of Example I, containing 10
percent cyanoethyl cellulose fibers and 90 percent rayon fibers,
and the assembly is hydraulically entangled, as above, to form a
composite (b-B). Composites (c-B) and (d-B) are similarly prepared.
The treatments were varied in the range of Y values from 6.6
.times. 10.sup.6 to 20 .times. 10.sup.6 to give different
structural properties.
The products are dried and softened as in Example I. All have
dry-strip-tensile strengths of at least 1.8 lbs./inch and dry
elongations of at least 38 percent. Other properties are given in
Table III. ##SPC8##
EXAMPLE V
Cyanoethyl cellulose (CNEC) fibers of 0.5 inch length containing
43.9 percent of Na.sub.2SO.sub.4 and analyzing 3.5 percent N
(salt-free basis) and 0.5 percent COOH (salt-free basis) with a
D.S. (cyanoethyl) of 0.465 and an absorbency in distilled water of
19 grams/gram and 0.25 inch length rayon staple are used as
fibers.
Handsheets of different compositions and a fabric weight
(salt-free) of 1.5 oz./yd..sup.2 are made from aqueous slurries of
the above fibers. The sheets are deswollen in 20 percent
Na.sub.2SO.sub.4 solution, pressed between couch rolls and dried
between nylon fabric and blotting paper on a sheet dryer at
100.degree. C.
All sheets are hydraulically entangled by passing the sheet resting
on a 24 .times. 24 mesh screen at 3 feet a minute under oscillating
streams of 20 percent aqueous Na.sub.2SO.sub.4. Water is used as
the entangling fluid for the 100 percent rayon sheets. The streams
are produced by a plate containing a single row (14" long) of 0.007
inch diameter venturi shape, orifices spaced 20/inch which is
mounted on a manifold. The orifice plate is located about 1 inch
above the handsheet.
The entangled sheets are blotted and then dried and softened by
tumbling in a home laundry dryer at 60.degree. C. with three
baseballs of 9.7 cm. in diameter for 25 minutes.
The physical properties obtained at various Y values (by altering
the pressure of the entangling fluid) are given in Table IV. All
samples have dry elongations of from 20 to 56 percent.
Items a, b, and c represent unsuccessful attempts to make useful
flushable products of 100 percent rayon. Water pressures of 100,
150, and 200 p.s.i. are used. The combination of a dry tensile
strength of at least 0.3 lb./in. and a wet tensile strength of less
than 0.1 lb./in. is not obtained. At higher Y values needed to
increase the dry strength the product is not dispersible due to the
higher wet strength obtained.
Items d, f, h, j, k, l, m and n represent products of this
invention.
Items e, g, and i have been excessively entangled to give wet
tensiles of 0.1 lb./in. or higher and dispersibilities of 15 and
less so that they are not dispersible.
It is seen that the hydraulic entangling conditions are extremely
critical, particularly at the lowest cyanoethyl cellulose levels.
The results in the table and results at other (unreported) Y values
can be expressed by the following equation:
Thus the maximum Y values for 10 and 100 percent of cellulose
ethers is about 15 and 25 respectively. This relationship applies
only to the preferred blends of cyanoethyl cellulose with rayon. In
the absence of low-swelling fibers, much higher Y values may be
used as shown in the following Example VI. ##SPC9##
EXAMPLE VI
Cyanoethyl cellulose fibers of about 2 denier per filament and 0.5
inch length, with a D.S. (cyanoethyl) of 0.45 are used alone,
without any rayon staple. Handsheets of 1.5 oz./yd..sup.2 are made
by the method of Example V and dried at 65.degree. C.
The sheets are hydraulically entangled as in Example V, except the
screen is moved at 5 feet per minute. One pass is made at a
hydraulic pressure of 100 p.s.i., followed by 5 passes at 500
p.s.i. The aggregate Y value of the treatments is calculated to be
103.5 .times. 10.sup.6 ft. per min. The dried product has the
strength and appearance of a woven fabric.
Although the dry strength of this fabric is high, the absence of
any low-swelling fibers permits complete dissimination in turbulent
water. The dispersibility of the fabric is 55.8 percent and the dry
elongation is 27 percent.
EXAMPLE VII
Cyanoethyl cellulose fiber similar to that of Example I is dried
and cut to 1.5 inch length. It is made into a batt by an air
deposition process, using a Rando-Webber machine (made by Curlator
Corporation of East Rochester, N.Y.). The batt has a fabric weight
of 1.57 oz./yd..sup.2 including salts and soluble organic matter,
or a fabric weight of 1.0 oz./yd..sup.2 on water-insoluble fiber
basis.
Two layers of the above batt are plied together, completely wetted
with a 20 percent solution of Na.sub.2SO.sub.4 and then
hydraulically entangled using the apparatus and conditions of
Example I. The sample is dried and softened. The soft, fabriclike
product has the following properties: ##SPC10##
EXAMPLE VIII
Initial fibrous layers are made, using the method and fibers
similar to those of Example I. Layer (A) contains 70 percent
cyanoethyl cellulose fibers and 30 percent rayon, and has a fabric
weight (water-insoluble) of 1.29 oz./yd.sup.2. Layer (B) contains
10 percent of the cyanoethyl cellulose fibers and 90 percent of
rayon, and has a fabric weight (water-insoluble) of 0.79
oz./yd..sup.2. Layer (A) is supported on an apertured patterning
plate and covered with layer (B). The assembly is passed at 3
feet/minute under essentially columnar streams of concentrated
aqueous sodium sulfate solution from 560 orifices of 5-mil diameter
evenly spaced in a single 14-inch row. A flow rate of 56.5
pounds/minute is used, which gives a Y value of 11 .times. 10.sup.6
ft./min.
The apertured patterning plate is a commercial plastic netting
consisting of a grid of 40-mil diameter polyethylene rods. The
lower face of the grid contains parallel rods spaced 12 per inch.
The upper face of the grid contains a similar array of rods
arranged 45.degree. to the axis of the lower rods. The rods are
fused together where they contact each other. The open area of the
plate is 27.1 percent of the total area.
The soft, fabriclike product is illustrated in FIGS. 3 and 4. It
has the following properties: ##SPC11##
Useful products having similar properties with S.L. absorbencies of
about 3.6--4 are also made from the above initial fibrous layers in
similar manner at Y values between 8.6 .times. 10.sup.6 and 17
.times. 10.sup.6, using the following apertured patterning
supports:
1. A grid of 0.038-inch diameter rods spaced 12 inch and having an
open area of 54.4 percent.
2. A grid of 0.020-inch diameter rods spaced 25 per inch and having
an open area of 50.0 percent.
3. Twill screen of 0.023-inch diameter wire, 24 .times. 24 mesh in
a 2 .times. 2 twill weave having 20 percent open area.
4. Twill screen of 0.017-inch diameter wire, 30 .times. 30 mesh in
a 2 .times. 2 twill weave having 23.9 percent open area.
EXAMPLE IX
Handsheets with a fabric weight of 0.5 oz./yd..sup.2 (17
g./m..sup.2) are made from an aqueous dispersion containing 10
parts of cotton stale fibers of 0.25 inch length (0.63 cm.) and 1
part of cyanoethyl cellulose fibers of 0.5 inch length (1.27 cm.)
(having a D.S. of 0.47) as a binder.
The above handsheet is placed on top of a batt of 100 percent rayon
staple fibers (1.56" length and 1.5 d.p.f.) fabric weight of 1
oz./yd..sup.2 ( 33.9 g./m..sup.2) and the layered structure,
supported on a screen (20 .times. 20 mesh) is hydraulically
entangled using a 20 percent aqueous solution of Na.sub.2SO.sub.4
at 60.degree. C. as the jetting fluid with two treatments at 400
p.s.i. The salt is washed out with water and the fabric dried.
The doubled-layered integral fabric is saturated with an aqueous
solution containing 20 percent sodium chloroacetate and 3 percent
sodium hydroxide, and pressed to a wet press ratio of 2.8. The wet
fabrics are placed on a hot metal plate covered with a fabric
coated with polyfluoroethylene at 125.degree. C. for 5 minutes. The
baked fabrics are acidified by immersing in an aqueous bath
containing 5 percent H.sub.2SO.sub.4, then neutralized in a bath
containing 3 percent disodium phosphate and 17 percent sodium
sulfate adjusted to a pH of 8.5. The fabric is dried at about
80.degree. C.
The fabric has a dispersibility of 40 percent so that it is
disposable in home sewage systems. When the fabric is soaked in
synthetic urine and blotted, the cotton-covered fabric side is
distinctly less swollen and feels dryer than the modified rayon
side. The cotton has been scarcely affected by the treatment.
EXAMPLE X
A nonwoven fabric of 1.2 oz./yd..sup.2 (41 g./m..sup.2) weight is
made by passing a random web of 0.75 in. (19 mm.) rayon fiber on a
24 mesh screen at 5 yards (4.6 m.) per minute under 3 rows of water
streams coming from orifices having an upper cylindrical section of
0.005 inch (0.13 mm.) diameter with a lower frustoconical section
as an exit and spaced 40 per inch (per 2.54 cm.) at pressures of
400, 500, and 600 p.s.i. (23, 35, and 42 kg./cm..sup.2)
respectively. The orifices are about 12 mm. above the web. The
rayon fabric has a C.sub.h, dry and C.sub.h, wet of 0.35 and 0.71
respectively.
The nonwoven rayon fabric is passed through a tank containing a
solution of 50 percent urea and 18 percent H.sub.3PO.sub.4 at room
temperature. The fabric is squeezed by a pair of rubber-covered
rolls to a pickup of about 2.0 g./g. The wet fabric is continuously
passed through a commercial fabric over (Benz) where it is exposed
to opposed jets of air at 164.degree. C. for a period of about 91
seconds and then wound up at about 6.3 feet (1.9 meters) per
minute.
The baked fabric (cellulose acid phosphate) is then carried on a
screen underneath sprays of tap water for washing and excess water
is removed by squeeze rolls. The wet fabric is then carried under
sprays of a solution containing 17 percent Na.sub.2SO.sub.4, 3
percent Na.sub.2HPO.sub.4 and 1 percent sodium hexametaphosphate
adjusted to a pH of 6.0 and excess solution is removed by squeeze
rolls.
The wet, modified fabric (sodium cellulose phosphate) is then
passed through an oven where it is exposed to air at 34--40.degree.
C. issuing from pairs of opposed slots transverse to the direction
of fabric so that the fabric flutters between the 2 opposed jets of
air. The dry fabric is then softened by passing between a pair of
meshing grooved rolls with the grooves running in the direction of
travel of the fabric followed by 3 pairs of meshing groove rolls
having grooves transverse to the direction of travel of the fabric.
All of the rolls are set at 3.6 lb./inch of width (0.645 kg./cm.)
pressure. The softening treatment is repeated.
Diaper size portions of the product are flushable. The properties
are given in Table V. This is a preferred specie having an average
tensile in synthetic urine of at least 0.2 lb./in.
EXAMPLE XI
This example illustrates the use of cellulose sodium hemi succinate
in this invention.
The nonwoven rayon fabric of Example X is passed through a tank
containing a solution at 60.degree. C. of 30 percent succinamic
acid and 0.60 percent sulfamic acid, and squeezed by rolls to a
pickup of about 2.0--2.1. The wet fabric is continuously passed
through a circulating air oven (205.degree. C.) at a speed to give
a residence time of about 95 seconds.
The fabric of cellulose hemi succinate is washed by passing through
a tank of soft water, squeezed and then neutralized and bleached by
passing through a tank containing a solution at room temperature of
3 percent Na.sub.2HPO.sub.4, 17 percent Na.sub.2SO.sub.4 and about
0.5 percent KHSO.sub.5 adjusted to a pH of about 8.5--9.0. The
fabric of cellulose sodium hemi succinate is squeezed and dried in
circulating air at room temperature.
Diapers made of the product are tested on babies and found to have
excellent integrity in use and the used diapers are completely
flushable. Properties of the product are given in Table V.
EXAMPLE XII
This example illustrates the use of fibers of sodium cellulose
sulfate in the invention.
A nonwoven fabric of 1.3 oz./yd..sup.2 (44 g./m..sup.2) weight is
made from a random web of 0.75 inch (19 mm. crimped, rayon fibers
using the apparatus and speed of Example X at pressures of 300,
500, 800 and 800 p.s.i. (21, 35, 56 and 56 kg./cm..sup.2
respectively) for the 4 rows of orifices.
The rayon fabric is placed in solution at 50.degree. containing 300
g. urea, 100 g. 99 percent H.sub.2SO.sub.4 and 75 g. of water for 2
minutes. It is then pressed to a pickup of 3.2 and the wet fabric
heated in an oven at about 169.degree. C. for 3 minutes. The heated
fabric is neutralized in a solution containing 17 percent
Na.sub.2SO.sub.4 and 3 percent Na.sub.2HPO.sub.4 adjusted to a pH
of 8.5, squeezed to a pickup of 1 g./g. and dried. The product is
flushable. Properties are given in Table V.
EXAMPLE XIII
This example shows the use of sodium carboxymethyl cellulose fibers
in this invention.
A nonwoven fabric of 0.8 oz./yd..sup.2 (27 g./m..sup.2) weight is
made from 1.56 inch (39 mm.) rayon fibers of 1.5 d.p.f. using the
procedure and equipment of Example X except that 2 additional rows
of orifices at 200 and 300 p.s.i. (14 and 21 kg./cm..sup.2)
pressure are used. The fabric has a C.sub.h, dry and a C.sub.h, wet
of 0.74 and 0.96 respectively.
The fabric is chemically modified by passing it continuously
through a bath containing 2.1 percent NaOH and 15.8 percent sodium
chloracetate squeezing it to a pickup of 1.1 g./g. heating in an
oven with air at 140.degree. C. for 18 seconds, acidifying to the
carboxymethyl cellulose with a bath of 5 percent H.sub.2SO.sub.4,
washing in water and forming the sodium salt in a bath of 2 percent
Na.sub.2HPO.sub.4 and 8.5 percent Na.sub.2SO.sub.4 adjusted to a pH
of 8.5. The fabric (A) is dried at 40.degree. C. in a tumble dryer
with baseballs of 9.7 cm. diameter.
Sanitary napkins are made wrapping a 19" .times. 7" (64 .times.
17.8 cm.) portion of the fabric around a core, overlapping the
fabric on the bottom of the napkin and gluing the overlap with
small spots of a water soluble adhesive. The core consists of wood
fluff wrapped with crepe tissue paper which contains a coating of a
poly (fluoro alkyl methacrylate) on the sides and bottom of the
paper to serve as a fluid barrier. The napkins are used and then
flushed. The vast majority (223 out of 230) of the napkins flush
with 1 rush of water. The other 7 require a second flush to clear
the bowl.
A second fabric (B) of 1.25 oz./yd..sup.2 (42 g./m..sup.2) having a
C.sub.h, dry and C.sub.h, wet of 0.66 and 0.78 respectively is made
as above except at a speed of 7 yards (6.4 m.) per minute under
jets at 300, 500, 600, 700 and 900 p.s.i. (21, 35, 42, 49 and 63
kg./cm..sup.2). The fabric is chemically modified as above except
that the reagent solution contains 2.22 percent NaOH and 18.4
percent sodium chloracetate and the final salt-forming solution
contains 1 percent Na.sub.2HPO.sub.4 and 4.25 percent
Na.sub.2SO.sub.4 adjusted to a pH of 8.5.
Diapers are assembled with a layer of the above fabric, a wood
fluff, a crepe tissue wadding, wood fluff and the above fabric in
order. A medium size diaper uses 11 .times. 14" (28 .times. 35 cm.)
fabric and 5 .times. 12" (12.7 .times. 30 cm.) cores of wood fluff
and crepe tissue. The 2 fabric layers are glued together around the
edges of the core with about 3 mm. spots of a water-soluble
adhesive spaced about 5 cm. apart.
The diapers are used on babies in wear tests and are found to have
good integrity in use and all are successfully flushed in home
toilets after use.
Properties of the fabrics are given in Table V.
EXAMPLE XIV
This example shows the preparation of a nonpatterned product of the
invention.
A nonwoven fabric of 2.3 oz./yd..sup.2 (88 g./m..sup.2) is made
from the rayon fiber of Example X using the general method and a
single row of orifices of that example with a 150 mesh per inch
(per 2.54 cm.) screen (37 percent open area) used as the support to
carry the web at 4 yards (3.7 m.) per minute under the oscillating
row of orifices for one pass at each of the pressures of 200, 500,
1000, and 1200 p.s.i. (14, 35, 70 and 84 kg./cm..sup.2)
respectively. The nonforaminous fabric is smooth and resembles a
felt with faint grooves.
A portion of the dry fabric is immersed in a solution of 50 percent
urea and 18 percent H.sub.3PO.sub.4 for 2 minutes, drained and
blotted to a pickup of about 1.6--1.7. The wet fabric is is heated
in an air oven at 160.degree. C. for 4 minutes. The fabric is then
washed in an aqueous solution of 5 percent H.sub.2SO.sub.4 and 17
percent Na.sub.2SO.sub.4, drained, blotted, and converted to the
sodium salt of cellulose phosphate in an aqueous solution of 4
percent Na.sub.2HPO.sub.4 and 17 percent Na.sub.2SO.sub.4 adjusted
to a pH of 8.4. The fabric is drained, blotted, and air dried.
A medium size diaper is made similar to that in Example XIII. The
diaper breaks into 2 portions after dipping it 10 times in a toilet
bowl and 85 percent of the diaper passes the hoods after 3 flushes.
Properties of the product are given in Table V.
EXAMPLE XV
This example shows the use of a heterogeneous water-sensitive fiber
in the invention.
A nonwoven fabric of 0.8 oz./yd..sup.2 (27 g./m..sup.2) weight is
made from a random web of 0.5" (12.6 mm.) rayon using the apparatus
and method of Example X but with 4 rows of orifices at 300, 400,
500 and 500 p.s.i. (21, 28, 35 and 35 kg./cm..sup.2).
The dry fabric is placed in a solution of 70 volumes of water and
30 volumes of N-dimethyl formamide for 1 minute and then squeezed
to a pickup of 1 g./g. The wet fabric is then placed in a 0.25N
solution of SO.sub.3 in N-dimethyl formamide at room temperature
for 1 minute and squeezed to a pickup of 1 g./g. The fabric is then
treated in a 5 percent aqueous solution of H.sub.2SO.sub.4 for 1
minute, squeezed and then treated in an aqueous solution containing
17 percent Na.sub.2SO.sub.4 and 3 percent Na.sub.2HPO.sub.4
adjusted to a pH of 8.5 for 1 minute, squeezed and air dried to
yield a fiber of cellulose (rayon) with an outer skin of the sodium
salt of cellulose sulfate.
A 17 .times. 13 inch (44 .times. 33 cm.) portion of the fabric is
soaked in synthetic urine, dipped 2 times in water and flushes 100
percent. Although the fabric is quite slippery when wet it has a
S.L. absorbency of an inert fiber fabric which shows that the
modification of the individual filaments are confined to or near
the surface or skin. The fabric has the properties as given in
Table V. The average D.S. of the rayon core and the modified skin
is 0.008.
EXAMPLE XVI
This example shows the use of a heterogeneous, water-sensitive
fiber.
A nonwoven fabric of 1.0 oz./yd..sup.2 (34 g./m..sup.2) weight is
made from a random web of 0.75 inch (19 mm.) rayon using the
apparatus and procedure of Example X with pressures of 200, 500,
700, and 800 p.s.i. (14, 35, 49, 56 kg./cm..sup.2) respectively for
the 4 rows of orifices. The product has a C.sub.h, dry and a
C.sub.h, wet of 0.74 and 0.78 respectively.
The fabric is passed through a tank containing a solution of 50
percent urea and 18 percent H.sub.3PO.sub.4 and squeezed to a
pickup of 2.03 g./g. The wet fabric is then passed through a tenter
frame oven where it is heated by moving air at 163.degree. C. for a
period of 3 minutes. The next day the fabric is washed with water,
treated with a solution containing 3 percent Na.sub.2SO.sub.4 and
12 percent Na.sub.2HPO.sub.4 adjusted to a pH of 8.5 to form the
sodium salt of cellulose phosphate, dried with 67.degree. C. air
and softened as in Example X.
Diapers made similarly to those of Example XIII and used on babies
show satisfactory integrity and are 100 percent flushable after 1
dip.
The fabric has the properties given in Table V.
EXAMPLE XVII
The example shows the conversion of a cotton fabric to sodium
carboxy methyl cellulose.
A nonwoven fabric of about 0.8 oz./yd..sup.2 (27 g./m..sup.2)
weight is made from a random web of carded middling cotton of 1.03"
(26 mm.) length using a single row of orifices of Example X on 24
.times. 24 mesh screen and 1 pass at 5 yards (4.6 m.) per minute at
each of the pressures of Example XVI with the orifices
oscillating.
The cotton fabric is dewaxed by boiling in a detergent solution for
30 minutes and rinsing. A portion of the fabric is soaked in a
solution of 27.3 percent sodium chloracetate and 9.1 percent NaOH
for 2 minutes, drained and blotted to a pickup of about 3.0. The
wet fabric is heated in an air oven at 125.degree. C. for 5
minutes, acidified in a solution of 5 percent H.sub.2SO.sub.4 and
17 percent Na.sub.2SO.sub.4, neutralized in a solution of 4 percent
Na.sub.4HPO.sub.4 and 17 percent Na.sub.2SO.sub.4 (at pH of 8.4),
blotted and air dried.
A medium size diaper, soaked in synthetic urine breaks up after 1
dip in water and is 95 percent flushable on 1 flush.
The fabric has the properties given in Table V.
EXAMPLE XVIII
This example shows the conversion of a cotton fabric to a sodium
cellulose sulfate.
A nonwoven of about 1 oz./yd..sup.2 (34 g./m..sup.2) and having a
C.sub.h, dry/wet of 0.41/0.63 is made using the cotton fiber,
apparatus and procedure of Example XVII except at twice the
speed.
The cotton fabric is dewaxed by boiling in a solution of detergent
and Na.sub.3PO.sub.4 for 30 minutes and rinsing. A portion of the
dewaxed fabric is secured (against shrinkage) by its edges to a
metal screen and mercerized in 25 percent NaOH at 18.degree. C. for
3 minutes. The fabric is washed in water to a neutral pH and air
dried.
The mercerized fabric is immersed for 2 minutes in a solution
containing 40 percent urea and 20 percent sulfamic acid, removed,
squeezed gently to obtain a pickup of 5.9, placed on an inert
plastic screen and heated in a circulating air oven at 150.degree.
C. for 5 minutes. The heated fabric is neutralized to the sodium
salt in a solution containing 3 percent Na.sub.2HPO.sub.4 and 17
percent Na.sub.2SO.sub.4 (pH 8.5), drained, blotted and air
dried.
Although the dispersibility is only 17 percent, the sample is
essentially completely dispersed in 45 seconds of the test
indicating flushability of a diaper size portion. Properties of the
product are given in Table V.
EXAMPLE XIX
The example illustrates the greater internal bond strength of the
fabrics of this invention over the prior art structures.
The internal bond test, originally designed to measure the internal
bond strength of papers, is useful as a measure of the vertical
entangling component through the thickness of the fabric.
In essence, the test consists of measuring the force necessary to
rupture the test specimen when the plane surfaces are mounted
between and held by two pieces of adhesive tape.
As expected, a laminar type structure is readily parted (low
internal bond) whereas a structure held together by a vertical
component requires higher forces since the vertical component
requires higher forces since the vertical fibers must be
broken.
The Internal Bond Strength of a nonwoven is determined on an
Internal Bond Tester (model B - made by Sisalkraft-Scott Co. of
Providence, R.I.) by measuring the force required to shear a sample
in its major plane with a weighted pendulum. The sample is fastened
to a lower fixed steel plate and to an upper aluminum right angle
striking bar (which contacts the pendulum) by means of double-faced
sensitive tape (Scotch Brand type 400 made by 3M Co. of St. Paul,
Minn.). ##SPC12## The faces of the steel plate, striking bar,
nonwoven and tape are 1 inch .times. 1 inch (2.54 .times. 2.54 cm.)
The tester includes a jig for mounting five samples at a time at a
standard pressure. Five samples are tested in both machine and
cross direction and the average value reported. The nonwoven should
be in a salt-free state as obtained by extraction for the Coherence
Value (C.sub.h) determination. Pressures of 200 p.s.i. (14
kg./cm..sup.2) are used, although lower pressures may be required
with very thin and porous samples to prevent forcing the upper tape
into contact with the lower tape. Meaningful results are not
obtained with coarsely apertured products [i.e. 12 or less
apertures or mesh per inch (per 2.54 cm.) with a fabric weight of
less than about 1 oz./yd..sup.2 (34 g./m..sup.2)] due to the
adhesion of tape to tape through the thickness of the fabric.
Fabrics from a number of the previous examples are tested as well
as papers and a resin-bonded commercially available nonwoven.
The preferred products of this invention have internal bond
strengths of at least 0.80 foot-pounds (ft.-lb.) [1.1
kilogram-centimeter (kg.-cm.) ] while the more preferred products
having the most dry integrity have internal bond strengths of at
least 0.15 ft.-lbs. (2.1 kg./cm.). ##SPC13##
typical rayon nonwovens
used for example X--XVIII 0.25 to >0.5 3.4 to >6.9
commercial, resin-bonded,
rayon nonwovens (Handiwipe 0.05--0.07 0.7--1.0
- Binder in one-sixteenth inch bands
on one-fourth inch centers across
width for strength - made
by Colgate-Palmolive.
papers, used as starting 0.01 to 0.05 0.14--0.7
material for examples 1and 2.
EXAMPLE XX
This example is a further illustration of the wide variety of
substituents with which the cellulosic fibers may be modified to
the water-sensitive form to obtain the product of the present
invention. A rayon nonwoven fabric is made water-dispersible by
modifying the fibers to sodium cellulose hemiphthalate.
The starting fabric is 100 percent rayon of three-fourths inch
fibers having a basis weight of 1.4 oz./yd..sup.2. The fibers are
hydraulically entangled. The fabric (10 in. .times. 10 in.) is
immersed in a 23 percent aqueous phthalamic acid solution
containing 0.46 percent MgCl.sub.2.6H.sub.2 O for 2 minutes. It is
then removed and couched between polyethylene sheets to a pickup
ratio of 4.53/1. The fabric and acid are reacted on a sheet dryer
at 150.degree. C. for 7 minutes. The modified fabric is then
neutralized in a bath of 3 percent Na.sub.2HPO.sub.4/ 17 percent
Na.sub.2SO.sub.4 (pH 8.5--9). The neutralized fabric is removed,
blotted, and then dried in a tumble dryer for 25 minutes. The
process is repeated using a fresh reaction solution (pickup ratio
3.39/1).
The dried modified fabric is white, has good aesthetics, and is
suitable for flushable diapers and sanitary napkins as the
dispersibility is 50 percent with 100 percent dispersibility
occuring after 15 sec. The SLWA is 19.7 g./g. and D.S. is 0.36.
EXAMPLE XXI
This example shows the use of fibers of a phosphate of polyvinyl
alcohol in water-dispersible nonwovens. A nonwoven fabric of about
1.09 oz./yd..sup.2 weight is made from commercial, water-insoluble,
crosslinked polyvinyl alcohol fibers of 1.5 dpf and 1.5 inch length
that is carded and then cut to 0.75 inch length. The fibers are
made into a random web by air laying and hydraulically entangled on
a 24-mesh screen at 3 yards a minute under a single row of water
streams of Example X at pressures of 100, 200 and 300 p.s.i. for
each of the 3 treatments. The fabric has a S.L. absorbency of 0.17
and a f.sub.wet of 1.47.
The polyvinyl alcohol nonwoven fabric is treated with a 50 percent
aqueous solution of urea to leave a pickup of 2 g./g. and then
baked at 160.degree. C. for 6 minutes. This fabric is then soaked
in an aqueous solution containing 45 percent urea and 16.2 percent
H.sub.3PO.sub.4, the pickup adjusted to 3 g./g., and the fabric
baked at 160.degree. C. for 5 minutes. The product is wrapped in
cheesecloth for subsequent handling to protect the fabric. The
product is washed in a 5 percent aqueous solution of sulfuric acid
containing 15 percent of Na.sub.2SO.sub.4 and then converted to the
salt form in a bath (a) adjusted to a pH of 8.4 containing 17
percent Na.sub.2SO.sub.4 and 4 percent Na.sub.2HPO.sub.4. The
product (after salt removal) contains 2.7 percent P.
Properties of the salt-free product are given in Table VI.
The product is water dispersible as judged from its breakup time
(B.U.T.) of about 100 seconds. The starting fabric of polyvinyl
alcohol fibers has a B.U.T. of greater than 120 seconds.
The B.U.T. is determined by dropping a 3 in. .times. 3-inch piece
of fabric (folded in half twice) into 800 ml. of distilled water
(room temperature) contained in a 1-liter beaker. The water is
stirred by an egg-shaped (dimensions major axis 2.5 in. with a
minor axis of about seven-eighths inch No.
4620--Teflon.RTM.-covered, egg-shaped of the Cole and Parmer Co. of
Chicago, Ill.) magnetic stirring rod that is driven by a 9-inch
diameter stirring base ("Jumbo Magnetic Stirrer," Model 14-511-75VI
by Fisher Scientific Co. of King of Prussia, Pa.) to give a stirrer
speed of 390 revolutions per minute which gives a vortex in the
water of about 11/8 inches. B.U.T. is the time from submergence
until the fabric separates into 2 or more distinct pieces. Mere
fraying of loose fibers from the edges is not considered as a
separation.
EXAMPLE XXII
This example shows the preparation of a water-dispersible fabric by
the hydrolysis of a nonwoven fabric of acrylic fibers.
A nonwoven fabric of about 1.1 oz./yd..sup.2 weight is made from
1.5 dpf, 0.75 in. long fibers of a copolymer of
acrylonitrile/sodium styrene sulfonate (96/4 percent) by entangling
a random web on a 24-mesh screen at 3 yards/minute under a single
row of water streams of Example X at pressures of 100, 200, 200,
and 600 p.s.i. for each of the treatments. The acrylic fabric has a
S.L. absorbency of 0.03 and a B.U.T. greater than 120 seconds.
The entangled nonwoven fabric is hydrolyzed by refluxing
(109.5.degree. C.) in an aqueous solution of 10 percent HCl, 10
percent NaCl for 24.75 hours. To minimize mechanical damage, a
double layer of the nonwoven is wrapped in an acrylic woven fabric,
placed between 2 Teflon.RTM. screens that are held apart and
attached to a rotating shaft in the hydrolysis bath. After
refluxing, the fabric is cooled, converted to the salt form in the
bath (a) of Example XXI and air dried. The samples are extracted
with 60 percent aqueous solutions of acetone with a final acetone
wash to remove the salt before testing.
Properties of the product are given in Table VI. The fabric has a
B.U.T. of 30 seconds.
EXAMPLE XXIII
This example shows the preparation of a water-dispersible fabric
from nylon-acrylic acid grafted fibers.
The starting fiber is a 2 dpf 6-6 nylon fiber that has been grafted
with acrylic acid using the process of U.S. Pat. No. 2,999,056 to
Tanner. The graft is in the form of the calcium salt that has been
partially changed to the sodium salt. The staple is carded and cut
to five-eighth inch, made into a random web and entangled with the
apparatus, method and speed of Example XXI using one treatment at
100 p.s.i. and 3 treatments at 200 p.s.i. A similar fabric
converted completely to the sodium salt form has a S.L. absorbency
of 0.3 and a B.U.T greater than 120 seconds.
The entangled nonwoven fabric is soaked in a 25 percent aqueous
solution of acrylic acid for 30 minutes, padded to a pickup of 0.8
g./g. and exposed under a resonant transformer at 2 MeV and 1
milliamp for a 4 megarad dosage for further grafting. The washed
and dried sample has a weight gain of about 16 percent. The fabric
is wrapped in cheesecloth, boiled 0.5 hour in a solution of 3
percent NaOH/10 percent Na.sub.2SO.sub.4, excess liquid removed and
reneutralized to pH 8.7 in a bath containing 1.5 percent
Na.sub.2SO.sub.4 6 percent Na.sub.2HPO.sub.4 and 3 percent sodium
hexametaphosphate and dried.
Properties of the product are given in Table VI. The product has a
B.U.T. of about 33 seconds.
EXAMPLE XXIV
This example shows the preparation of a water-dispersible fabric
from casein fibers.
The starting fibers are commercial casein fibers of about 5.3 dpf.
The 4 in. staple is carded and the card silver cut to 0.75 in.
length. A random web of the cut fiber is entangled using the
method, speed, and apparatus of Example XXI with one treatment at
each of the following pressures: 100, 200, 200, 700 and 1000 p.s.i.
The fabric has a S.L. absorbency of 0.3 and a B.U.T. greater than
120 seconds.
The entangled nonwoven fabric is immersed in a 50 percent aqueous
solution of urea for 2 minutes, drained, the pickup adjusted to 1
g./g. and baked for 5 minutes at 160.degree. C. The dry product is
wrapped in cheesecloth and neutralized in a bath (a) of Example
XXI. Properties of the dried product are given in Table VI. The
product has a B.U.T. of 12 seconds.
A water-dispersible fabric (B.U.T. of 20 seconds) is also made by
neutralizing the original nonwoven (without urea treatment) with
bath (a) of Example XXI.
EXAMPLE XXV
This example shows the preparation of a water-dispersible fabric
from cellulose acetate fibers.
The starting fibers are commercial cellulose acetate (D.S. 2.4)
fibers of 1.5 dpf, 0.75 in. length. A random web of the fibers is
entangled using the method, apparatus, and speed of Example XXI for
one treatment at each of the following pressures: 100, 200, 200 and
500 p.s.i.
The cellulose acetate nonwoven is treated in an aqueous solution at
45.degree. C. containing 0.3 percent sodium hydroxide and 1 percent
sodium acetate, washed free of base and dried to give a product
with D.S. acetate of about 1.6.
The hydrolyzed fabric is soaked with an aqueous solution containing
45 percent urea and 16.2 percent H.sub.3PO.sub.4, the pickup
adjusted to 1.2 and then baked 5 minutes at 160.degree. C. The
baked fabric is washed in a solution containing 5 percent
H.sub.2SO.sub.4 and 15 percent Na.sub.2SO.sub.4, then converted to
the salt form using the solution (a) of Example XXI, extracted free
of salt with aqueous methanol and dried.
The properties of the final sodium phosphate cellulose-cellulose
acetate are given in Table VI. It has a B.U.T. of about 23 seconds.
The initial and hydrolyzed nonwoven have S.L. absorbencies of 0.22
and 0.35 respectively and B.U.T. of greater than 120 seconds.
##SPC14##
EXAMPLE XXVI
This example illustrates the relationship between fiber length,
coefficient of wet friction of the fabrics, and the degree of fiber
entanglement with the degree of water-dispersibility of the
product.
Random webs of 1 oz./yd..sup.2 weight made from 1.5 dpf. rayon
staple of different lengths are entangled at 6 ypm. using the
apparatus and method of Example X with four different
treatments.
The different fiber lengths used are identified as follows:
a. 1.36 in. average (75 percent 1 9/16 in., 25 percent 0.25
in.)
b. 0.75 in. (100 percent 0.75 in.)
c. 0.38 in. average (75 percent 0.25 in., 25 percent 0.75 in.)
The entanglement conditions used are identified as follows:
##SPC15##
Portions of the above rayon nonwoven are sewed into long lengths
and converted into sodium cellulose phosphate by a continuous
process. The fabric is run through an aqueous bath at 80.degree. F.
containing 50 percent urea and 16 percent H.sub.3PO.sub.4; squeezed
to the desired pickup by rolls; baked for about 15 seconds by
passing through an oven at 375.degree. F.; washed with sprays of a
0.5 percent aqueous solution of sulfuric acid; converted to the
salt form with sprays of an aqueous solution adjusted to a pH of
6.0 containing 1 percent N.sub.2SO.sub.4, 2 percent
Na.sub.2HPO.sub.4, and 3 percent sodium hexametaphosphate; and then
dried. One roll of fabric is run with 15 p.s.i. pressure on the
squeeze rolls while 27 p.s.i. is used on a second run (modification
levels A and C respectively).
Properties of the rayon fabrics and the modified fabrics are given
in Table VII.
Items 9 and 11 (identical except for modification levels) have S.L.
absorbencies of 1.63 and 2.20 respectively and analyze 3.51 and
4.08 percent P respectively.
The rayon fabrics used to make items 12, 13, and 14 (all A
modification) when modified at the C level have a f.sub.w of 0.79,
0.90 and 0.93 respectively with a b.u.t. of 10, 11 and 15 seconds
respectively.
A portion of item 3 is soaked in 0.5 percent H.sub.3PO.sub.4 to
convert the fibers to the free acid form, rinsed in distilled water
and air dried. The salt-free product has a B.U.T. of 45 seconds,
dry and wet coherence values of 0.53 and 0.35 respectively, and a
coefficient of wet friction of 0.73.
Water-dispersible fabrics are made by using a blend of 50 percent
polyester fiber of 1.5 dpf and 0.25 inch length and 50 percent 1.5
dpf 0.75 inch length rayon in the above procedure which yields a
final product composed of polyester fibers and sodium cellulose
phosphate fibers.
One such product has a B.U.T. of 75 seconds and dry and wet
coherence values of 0.53 and 0.37 respectively. Other products
receiving a higher degree of modification have B.U.T. as low as 8
seconds.
Qualitatively it will be observed that with a given fiber blend and
a given modification level, the B.U.T. increases as the
entanglement level of the rayon fabric (as judged by the process
conditions or Y.R.T.) increases-- compare items 14 and 5; 13, 11
and 3; 12 and 1. It is also noted that with a given rayon fabric
the B.U.T. decreases as the chemical modification (as judged by
modification level and f.sub.w ) increases compare items 1 and 2; 3
and 4; 5 and 6; 9 and 11.
The yield resistance time (YRT) values given for the rayon fabrics
are a measure of the degree of entanglement of the fibers. The YRT
is determined as follows:
Yield Resistance Time Test
The test consists of measuring the time required for a plunger
rubbing on a fabric supported at its edges to produce a given
deflection or yield in the fabric. The test is run on Appearance
Retention Tester (Fabric Development Test, Brooklyn, N.Y.). The
tester consists of a sliding shaft and head which is free to move
up and down in a fixed arm of the frame. The shaft and head weigh
1982 grams but are counterbalanced with a weight of 1400 grams so
that the net weight is 582 grams. The chromium-plated,
smooth-surfaced head is 2.5 inches in diameter with a curved
downward face having a radius of curvature of 3 inches. The
vertical position of the head is recorded on a strip chart recorder
by means of a transducer attached to the shaft and equipped with a
power supply. The other main element of the tester is a hollow
cylinder with an inside diameter of 6.687 inches eccentrically
positioned beneath the center of the head. The cylinder is revolved
at a speed of 90 revolutions per minute in such a manner that the
center of the head describes about a 1.5 in. circle on the fabric
which is clamped taut to the cylinder.
A square piece (about 9 in. .times. 9 in.) of the fabric is dipped
in water. Excess water is removed by passing the fabric between
wringer rolls which have been adjusted to provide a pickup of 2.5
grams of water per gram of dry fabric when four layers of a regular
woven Curity cotton diaper is passed between the rolls. The wet
fabric is securely clamped over the hollow cylinder. The head is
lowered onto the fabric, the chart position noted, and the tester
is started. The time in seconds required for the head to make a
vertical deflection in the fabric of 12.5 mm. is recorded as the
Yield Resistance Time (YRT). ##SPC16## EXAMPLE XXVII
This example shows the use of layers of paper fibers and rayon
fibers to make a dispersible product.
A random web (0.6 oz./yd..sup.2) of 0.75 in. long rayon fibers (1.5
dpf.) is placed on a 24 .times. 24 mesh screen, covered with two
layers of Kraft paper (0.5 oz./yd..sup.2 for each layer), and the
assembly passed at 10 ypm. under a single row of water streams of
Example X at a pressure of 900 p.s.i. Three such entangling
treatments are given.
The entangled nonwoven fabric is treated with an aqueous solution
of 37.8 percent urea and 15.5 percent H.sub.3PO.sub.4 to a pickup
of 1.7 solution/g. of fabric, placed between aluminum plates and
heated in an oven at 198--204.degree. C. for 10--15 seconds. The
baked fabric is washed in dilute sulfuric acid, converted to the
sodium cellulose phosphate form, and dried. The product which is
isotropic has the following properties: ##SPC17##
Similar properties are obtained using 38 and 45 percent of wood
pulp in the starting layer to be entangled on 150 mesh screens and
150 mesh screens followed by a treatment on 24 mesh screens.
The paper fibers and rayon fibers can be intimately mixed before
entanglement if desired.
Use of the above phosphorylation reaction on the Kraft paper alone
produces a cellulose phosphate with a D.S. of about 0.3.
* * * * *