U.S. patent application number 12/966494 was filed with the patent office on 2011-06-16 for water-dispersible and multicomponent fibers from sulfopolyesters.
This patent application is currently assigned to EASTMAN CHEMICAL COMPANY. Invention is credited to Scott Ellery George, William Alston Haile, Wesley Raymond Hale, Waylon Lewellyn Jenkins.
Application Number | 20110140297 12/966494 |
Document ID | / |
Family ID | 33517571 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110140297 |
Kind Code |
A1 |
Haile; William Alston ; et
al. |
June 16, 2011 |
WATER-DISPERSIBLE AND MULTICOMPONENT FIBERS FROM
SULFOPOLYESTERS
Abstract
Disclosed are water-dispersible fibers derived from
sulfopolyesters having a Tg of at least 25.degree. C. The fibers
may contain a single sulfopolyester or a blend of a sulfopolyester
with a water-dispersible or water-nondispersible polymer. Also
disclosed are multicomponent fibers comprising a water dispersible
sulfopolyester having a Tg of at least 57.degree. C. and a water
non-dispersible polymer. The multicomponent fibers may be used to
produce microdenier fibers. Fibrous articles may be produced from
the water-dispersible fibers, multicomponent fibers, and
microdenier fibers. The fibrous articles include water-dispersible
and microdenier nonwoven webs, fabrics, and multilayered articles
such as wipes, gauze, tissue, diapers, panty liners, sanitary
napkins, bandages, and surgical dressings. Also disclosed is a
process for water-dispersible fibers, nonwoven fabrics, and
microdenier webs. The fibers and fibrous articles have further
applications in flushable personal care and cleaning products,
disposable protective outerwear, and laminating binders.
Inventors: |
Haile; William Alston;
(Kingsport, TN) ; George; Scott Ellery;
(Kingsport, TN) ; Hale; Wesley Raymond;
(Kingsport, TN) ; Jenkins; Waylon Lewellyn;
(Kingsport, TN) |
Assignee: |
EASTMAN CHEMICAL COMPANY
Kingsport
TN
|
Family ID: |
33517571 |
Appl. No.: |
12/966494 |
Filed: |
December 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11204868 |
Aug 16, 2005 |
7902094 |
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12966494 |
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10850548 |
May 20, 2004 |
6989193 |
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11204868 |
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10465698 |
Jun 19, 2003 |
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10850548 |
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Current U.S.
Class: |
264/115 ;
264/172.15 |
Current CPC
Class: |
Y10T 442/638 20150401;
Y10T 428/249938 20150401; Y10T 442/641 20150401; D01F 6/84
20130101; Y10T 428/29 20150115; D04H 1/4391 20130101; A61P 17/00
20180101; Y10T 428/25 20150115; Y10T 428/2931 20150115; Y10T
428/2913 20150115; Y10T 428/2927 20150115; Y10T 442/3154 20150401;
Y10T 442/3146 20150401; D04H 1/4374 20130101; Y10T 442/637
20150401; Y10T 428/249921 20150401; Y10T 428/2969 20150115; Y10T
442/3163 20150401; Y10T 442/64 20150401; D01F 8/14 20130101; Y10T
442/681 20150401; D04H 1/435 20130101; A61K 8/85 20130101; A61Q
19/00 20130101; D04H 1/4382 20130101; Y10T 428/2929 20150115; Y10T
442/68 20150401; Y10T 428/2915 20150115 |
Class at
Publication: |
264/115 ;
264/172.15 |
International
Class: |
D04H 3/16 20060101
D04H003/16; D01D 5/34 20060101 D01D005/34 |
Claims
1. A process for producing at least one multicomponent fiber having
a sheath core cross section, said process comprising spinning at
least one water dispersible sulfopolyester having a glass
transition temperature (Tg) of at least 57.degree. C. and at least
one water-nondispersable polymer immiscible with said
sulfopolyester into said multicomponent fiber, wherein said
sulfopolyester comprises: (i) residues of one or more dicarboxylic
acids; (ii) about 4 to about 40 mole %, based on the total
repeating units, of residues of at least one sulfomonomer having 2
functional groups and one or more sulfonate groups attached to an
aromatic or cycloaliphatic ring wherein said functional groups are
hydroxyl, carboxyl, or a combination thereof; (iii) one or more
diol residues wherein at least 25 mole %, based on the total diol
residues, is a poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer in the
range of 2 to about 500; and (iv) 0 to about 25 mole %, based on
the total repeating units, of residues of a branching monomer
having 3 or more functional groups wherein said functional groups
are hydroxyl, carboxyl, or a combination thereof; wherein said
multicomponent fiber has sheath component comprising said water
dispersible sulfopolyester and a core component comprising at least
one water-nondispersible polymer immiscible with said
sulfopolyester.
2. The process according to claim 1 wherein said sulfopolyester
comprises (i) about 50 to about 96 mole % of one or more residues
of isophthalic acid or terephthalic acid, based on the total acid
residues; (ii) about 4 to about 30 mole %, based on the total acid
residues, of a residue of sod iosulfoisophthalic acid; (iii) one or
more diol residues wherein at least 25 mole %, based on the total
diol residues, is a poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer in the
range of 2 to about 500; and (iv) 0 to about 20 mole %, based on
the total repeating units, of residues of a branching monomer
having 3 or more functional groups wherein said functional groups
are hydroxyl, carboxyl, or a combination thereof.
3. The process according to claim 1 further comprising quenching
said multicomponent fiber thereby solidifying said multicomponent
fiber.
4. The process according to claim 1 further comprising applying at
least one finish to said multicomponent fiber.
5. The process according to claim 4 wherein said finish further
comprises at least one additive.
6. The process according to claim 5 wherein said additive is at
least one selected from the group consisting of emulsifiers,
antistatics, antimicrobials, antifoams, lubricants,
thermostabilizers, and UV stabilizers.
7. The process of claim 3 further comprising drawing said
multicomponent fiber.
8. The process according to claim 7 further comprising texturizing
said multicomponent fiber.
9. A process for dispersing at least one fibrous article in water,
said process comprising: A. spinning at least one water dispersible
sulfopolyester having a glass transition temperature (Tg) of at
least 57.degree. C. and at least one water-nondispersable polymer
immiscible with said sulfopolyester into at least one
multicomponent fiber, wherein said multicomponent fiber has a
sheath component comprising said water dispersible sulfopolyester
and a core component comprising at least one water-nondispersible
polymer immiscible with said sulfopolyester said sulfopolyester
comprising: (i) residues of one or more dicarboxylic acids; (ii)
about 4 to about 40 mole %, based on the total repeating units, of
residues of at least one sulfomonomer having 2 functional groups
and one or more sulfonate groups attached to an aromatic or
cycloaliphatic ring wherein said functional groups are hydroxyl,
carboxyl, or a combination thereof; (iii) one or more diol residues
wherein at least 25 mole %, based on the total diol residues, is a
poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer in the
range of 2 to about 500; and (iv) 0 to about 25 mole %, based on
the total repeating units, of residues of a branching monomer
having 3 or more functional groups wherein said functional groups
are hydroxyl, carboxyl, or a combination thereof; B. overlapping
and collecting said multicomponent fiber of Step A to form at least
one fibrous article; and C. contacting said fibrous article with
water to remove said sulfopolyester thereby substantially removing
said sulfopolyester and dispersing said water-nondispersible
polymer.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation application claiming
priority to application Ser. No. 11/204,868 filed on Aug. 16, 2005
now allowed, which is a divisional of application Ser. No.
10/850,548, filed May 20, 2004, now issued as U.S. Pat. No.
6,989,193, which is a continuation-in-part of application Ser. No.
10/465,698, filed Jun. 19, 2003, abandoned; all of which are hereby
incorporated by reference to the extent they do contradict the
statements herein.
FIELD OF THE INVENTION
[0002] The present invention pertains to water-dispersible fibers
and fibrous articles comprising a sulfopolyester. The invention
further pertains to multicomponent fibers comprising a
sulfopolyester and the microdenier fibers and fibrous articles
prepared therefrom. The invention also pertains to processes for
water-dispersible, multicomponent, and microdenier fibers and to
nonwoven fabrics prepared therefrom. The fibers and fibrous
articles have applications in flushable personal care products and
medical products.
BACKGROUND OF THE INVENTION
[0003] Fibers, melt blown webs and other melt spun fibrous articles
have been made from thermoplastic polymers, such as
poly(propylene), polyamides, and polyesters. One common application
of these fibers and fibrous articles are nonwoven fabrics and, in
particular, in personal care products such as wipes, feminine
hygiene products, baby diapers, adult incontinence briefs,
hospital/surgical and other medical disposables, protective fabrics
and layers, geotextiles, industrial wipes, and filter media.
Unfortunately, the personal care products made from conventional
thermoplastic polymers are difficult to dispose of and are usually
placed in landfills. One promising alternative method of disposal
is to make these products or their components "flushable", i.e.,
compatible with public sewerage systems. The use of
water-dispersible or water-soluble materials also improves
recyclability and reclamation of personal care products. The
various thermoplastic polymers now used in personal care products
are not inherently water-dispersible or soluble and, hence, do not
produce articles that readily disintegrate and can be disposed of
in a sewerage system or recycled easily.
[0004] The desirability of flushable personal care products has
resulted in a need for fibers, nonwovens, and other fibrous
articles with various degrees of water-responsivity. Various
approaches to addressing these needs have been described, for
example, in U.S. Pat. Nos. 6,548,592; 6,552,162; 5,281,306;
5,292,581; 5,935,880; and 5,509,913; U.S. patent application Ser.
Nos. 09/775,312; and 09/752,017; and PCT International Publication
No. WO 01/66666 A2. These approaches, however, suffer from a number
of disadvantages and do not provide a fibrous article, such as a
fiber or nonwoven fabric, that possesses a satisfactory balance of
performance properties, such as tensile strength, absorptivity,
flexibility, and fabric integrity under both wet or dry
conditions.
[0005] For example, typical nonwoven technology is based on the
multidirectional deposition of fibers that are treated with a resin
binding adhesive to form a web having strong integrity and other
desirable properties. The resulting assemblies, however, generally
have poor water-responsivity and are not suitable for flushable
applications. The presence of binder also may result in undesirable
properties in the final product, such as reduced sheet wettability,
increased stiffness, stickiness, and higher production costs. It is
also difficult to produce a binder that will exhibit adequate wet
strength during use and yet disperse quickly upon disposal. Thus,
nonwoven assemblies using these binders may either disintegrate
slowly under ambient conditions or have less than adequate wet
strength properties in the presence of body fluids. To address this
problem, pH and ion-sensitive water-dispersible binders, such as
lattices containing acrylic or methacrylic acid with or without
added salts, are known and described, for example, in U.S. Pat. No.
6,548,592 B1. Ion concentrations and pH levels in public sewerage
and residential septic systems, however, can vary widely among
geographical locations and may not be sufficient for the binder to
become soluble and disperse. In this case, the fibrous articles
will not disintegrate after disposal and can clog drains or sewer
laterals.
[0006] Multicomponent fibers containing a water-dispersible
component and a thermoplastic water non-dispersible component have
been described, for example, in U.S. Pat. Nos. 5,916,678;
5,405,698; 4,966,808; 5,525,282; 5,366,804; 5,486,418. For example,
these multicomponent fibers may be a bicomponent fiber having a
shaped or engineered transverse cross section such as, for example,
an islands-in-the-sea, sheath core, side-by-side, or segmented pie
configuration. The multicomponent fiber can be subjected to water
or a dilute alkaline solution where the water-dispersible component
is dissolved away to leave the water non-dispersible component
behind as separate, independent fibers of extremely small fineness.
Polymers which have good water dispersibility, however, often
impart tackiness to the resulting multicomponent fibers, which
causes the fiber to stick together, block, or fuse during winding
or storage after several days, especially under hot, humid
conditions. To prevent fusing, often a fatty acid or oil-based
finish is applied to the surface of the fiber. In addition, large
proportions of pigments or fillers are sometimes added to water
dispersible polymers to prevent fusing of the fibers as described,
for example, in U.S. Pat. No. 6,171,685. Such oil finishes,
pigments, and fillers require additional processing steps and can
impart undesirable properties to the final fiber. Many
water-dispersible polymers also require alkaline solutions for
their removal which can cause degradation of the other polymer
components of the fiber such as, for example, reduction of inherent
viscosity, tenacity, and melt strength. Further, some
water-dispersible polymers can not withstand exposure to water
during hydroentanglement and, thus, are not suitable for the
manufacture of nonwoven webs and fabrics.
[0007] Alternatively, the water-dispersible component may serve as
a bonding agent for the thermoplastic fibers in nonwoven webs. Upon
exposure to water, the fiber to fiber bonds come apart such that
the nonwoven web loses its integrity and breaks down into
individual fibers. The thermoplastic fiber components of these
nonwoven webs, however, are not water-dispersible and remain
present in the aqueous medium and, thus, must eventually be removed
from municipal wastewater treatment plants. Hydroentanglement may
be used to produce disintegratable nonwoven fabrics without or with
very low levels (<5 wt %) of added binder to hold the fibers
together. Although these fabrics may disintegrate upon disposal,
they often utilize fibers that are not water soluble or
water-dispersible and may result in entanglement and plugging
within sewer systems. Any added water-dispersible binders also must
be minimally affected by hydroentangling and not form gelatinous
buildup or cross-link, and thereby contribute to fabric handling or
sewer related problems.
[0008] A few water-soluble or water-dispersible polymers are
available, but are generally not applicable to melt blown fiber
forming operations or melt spinning in general. Polymers, such as
polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid are
not melt processable as a result of thermal decomposition that
occurs at temperatures below the point where a suitable melt
viscosity is attained. High molecular weight polyethylene oxide may
have suitable thermal stability, but would provide a high viscosity
solution at the polymer interface resulting in a slow rate of
disintegration. Water-dispersible sulfopolyesters have been
described, for example, in U.S. Pat. Nos. 6,171,685; 5,543,488;
5,853,701; 4,304,901; 6,211,309; 5,570,605; 6,428,900; and
3,779,993. Typical sulfopolyesters, however, are low molecular
weight thermoplastics that are brittle and lack the flexibility to
withstand a winding operation to yield a roll of material that does
not fracture or crumble. Sulfopolyesters also can exhibit blocking
or fusing during processing into film or fibers, which may require
the use of oil finishes or large amounts of pigments or fillers to
avoid. Low molecular weight polyethylene oxide (more commonly known
as polyethylene glycol) is a weak/brittle polymer that also does
not have the required physical properties for fiber applications.
Forming fibers from known water-soluble polymers via solution
techniques is an alternative, but the added complexity of removing
solvent, especially water, increases manufacturing costs.
[0009] Accordingly, there is a need for a water-dispersible fiber
and fibrous articles prepared therefrom that exhibit adequate
tensile strength, absorptivity, flexibility, and fabric integrity
in the presence of moisture, especially upon exposure to human
bodily fluids. In addition, a fibrous article is needed that does
not require a binder and completely disperses or dissolves in
residential or municipal sewerage systems. Potential uses include,
but are not limited to, melt blown webs, spunbond fabrics,
hydroentangled fabrics, dry-laid non-wovens, bicomponent fiber
components, adhesive promoting layers, binders for cellulosics,
flushable nonwovens and films, dissolvable binder fibers,
protective layers, and carriers for active ingredients to be
released or dissolved in water. There is also a need for
multicomponent fiber having a water-dispersible component that does
not exhibit excessive blocking or fusing of filaments during
spinning operations, is easily removed by hot water at neutral or
slightly acidic pH, and is suitable for hydroentangling processes
to manufacture nonwoven fabrics. Other extrudable and melt spun
fibrous materials are also possible.
SUMMARY OF THE INVENTION
[0010] We have unexpectedly discovered that flexible,
water-dispersible fibers may be prepared from sulfopolyesters. Thus
the present invention provides a water-dispersible fiber
comprising: [0011] (A) a sulfopolyester having a glass transition
temperature (Tg) of at least 25.degree. C., the sulfopolyester
comprising: [0012] (i) residues of one or more dicarboxylic acids;
[0013] (ii) about 4 to about 40 mole %, based on the total
repeating units, of residues of at least one sulfomonomer having 2
functional groups and one or more sulfonate groups attached to an
aromatic or cycloaliphatic ring wherein the functional groups are
hydroxyl, carboxyl, or a combination thereof; [0014] (iii) one or
more diol residues wherein at least 25 mole %, based on the total
diol residues, is a poly(ethylene glycol) having a structure
[0014] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0015] (iv) 0 to about 25 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; [0016] (B)
optionally, a water-dispersible polymer blended with the
sulfopolyester; and [0017] (C) optionally, a water-nondispersible
polymer blended with the sulfopolyester with the proviso that the
blend is an immiscible blend; wherein the fiber contains less than
10 weight percent of a pigment or filler, based on the total weight
of the fiber. The fibers of the present invention may be
unicomponent fibers that rapidly disperse or dissolve in water and
may be produced by melt-blowing or melt-spinning. The fibers may be
prepared from a single sulfopolyester or a blend of the
sulfopolyester with a water-dispersible or water-nondispersible
polymer. Thus, the fiber of the present invention, optionally, may
include a water-dispersible polymer blended with the
sulfopolyester. In addition, the fiber may optionally include a
water-nondispersible polymer blended with the sulfopolyester,
provided that the blend is an immiscible blend. Our invention also
includes fibrous articles comprising our water-dispersible fibers.
Thus, the fibers of our invention may be used to prepare various
fibrous articles, such as yarns, melt-blown webs, spunbonded webs,
and nonwoven fabrics that are, in turn, water-dispersible or
flushable. Staple fibers of our invention can also be blended with
natural or synthetic fibers in paper, nonwoven webs, and textile
yarns.
[0018] Another aspect of the present invention is a
water-dispersible fiber comprising: [0019] A) a sulfopolyester
having a glass transition temperature (Tg) of at least 25.degree.
C., the sulfopolyester comprising: [0020] (i) about 50 to about 96
mole % of one or more residues of isophthalic acid or terephthalic
acid, based on the total acid residues; [0021] (ii) about 4 to
about 30 mole %, based on the total acid residues, of a residue of
sodiosulfoisophthalic acid; [0022] (iii) one or more diol residues
wherein at least 25 mole %, based on the total diol residues, is a
poly(ethylene glycol) having a structure
[0022] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; [0023] (iv) 0 to about 20 mole %,
based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; [0024] (B)
optionally, a first water-dispersible polymer blended with the
sulfopolyester; and [0025] (C) optionally, a water-nondispersible
polymer blended with the sulfopolyester to form a blend with the
proviso that the blend is an immiscible blend; wherein the fiber
contains less than 10 weight percent of a pigment or filler, based
on the total weight of the fiber. The water-dispersible, fibrous
articles of the present invention include personal care articles
such as, for example, wipes, gauze, tissue, diapers, training
pants, sanitary napkins, bandages, wound care, and surgical
dressings. In addition to being water-dispersible, the fibrous
articles of our invention are flushable, that is, compatible with
and suitable for disposal in residential and municipal sewerage
systems.
[0026] The present invention also provides a multicomponent fiber
comprising a water-dispersible sulfopolyester and one or more water
non-dispersible polymers. The fiber has an engineered geometry such
that the water non-dispersible polymers are present as segments
substantially isolated from each other by the intervening
sulfopolyester, which acts as a binder or encapsulating matrix for
the water non-dispersible segments. Thus, another aspect of our
invention is a multicomponent fiber having a shaped cross section,
comprising: [0027] A) a water dispersible sulfopolyester having a
glass transition temperature (Tg) of at least 57.degree. C., the
sulfpolyester comprising: [0028] (i) residues of one or more
dicarboxylic acids; [0029] (ii) about 4 to about 40 mole %, based
on the total repeating units, of residues of at least one
sulfomonomer having 2 functional groups and one or more sulfonate
groups attached to an aromatic or cycloaliphatic ring wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof;
[0030] (iii) one or more diol residues wherein at least 25 mole %,
based on the total diol residues, is a poly(ethylene glycol) having
a structure
[0030] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0031] (iv) 0 to about 25 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; and [0032]
B) a plurality of segments comprising one or more
water-nondispersable polymers immiscible with the sulfopolyester,
wherein the segments are substantially isolated from each other by
the sulfopolyester intervening between the segments; [0033] wherein
the fiber contains less than 10 weight percent of a pigment or
filler, based on the total weight of the fiber. The sulfopolyester
has a glass transition temperature of at least 57.degree. C. which
greatly reduces blocking and fusion of the fiber during winding and
long term storage. The sulfopolyester may be removed by contacting
the multicomponent fiber with water to leave behind the water
non-dispersible segments as microdenier fibers. Our invention,
therefore, also provides a process for microdenier fibers
comprising: [0034] A. spinning a water dispersible sulfopolyester
having a glass transition temperature (Tg) of at least 57.degree.
C. and one or more water-nondispersable polymers immiscible with
the sulfopolyester into multicomponent fibers, the sulfpolyester
comprising: [0035] (i) about 50 to about 96 mole % of one or more
residues of isophthalic acid or terephthalic acid, based on the
total acid residues; [0036] (ii) about 4 to about 30 mole %, based
on the total acid residues, of a residue of sodiosulfoisophthalic
acid; [0037] (iii) one or more diol residues wherein at least 25
mole %, based on the total diol residues, is a poly(ethylene
glycol) having a structure
[0037] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0038] (iv) 0 to about 20 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; [0039]
wherein the fibers have a plurality of segments comprising the
water-nondispersable polymers wherein the segments are
substantially isolated from each other by the sulfopolyester
intervening between the segments and the fibers contain less than
10 weight percent of a pigment or filler, based on the total weight
of the fibers; and [0040] B. contacting the multicomponent fibers
with water to remove the sulfopolyester thereby forming microdenier
fibers.
[0041] The water non-dispersible polymers may be
biodistintegratable as determined by DIN Standard 54900 and/or
biodegradable as determined by ASTM Standard Method, D6340-98. The
multicomponent fiber also may be used to prepare a fibrous article
such as a yarn, fabric, melt-blown web, spun-bonded web, or
non-woven fabric and which may comprise one or more layers of
fibers. The fibrous article having multicomponent fibers, in turn,
may be contacted with water to produce fibrous articles containing
microdenier fibers. Thus, another aspect of the invention is a
process for a microdenier fiber web, comprising: [0042] A. spinning
a water dispersible sulfopolyester having a glass transition
temperature (Tg) of at least 57.degree. C. and one or more
water-nondispersable polymers immiscible with the sulfopolyester
into multicomponent fibers, the sulfpolyester comprising: [0043]
(i) about 50 to about 96 mole % of one or more residues of
isophthalic acid or terephthalic acid, based on the total acid
residues; [0044] (ii) about 4 to about 30 mole %, based on the
total acid residues, of a residue of sodiosulfoisophthalic acid;
[0045] (iii) one or more diol residues wherein at least 25 mole %,
based on the total diol residues, is a poly(ethylene glycol) having
a structure
[0045] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0046] (iv) 0 to about 20 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof. [0047]
wherein the multicomponent fibers have a plurality of segments
comprising the water-nondispersable polymers and the segments are
substantially isolated from each other by the sulfopolyester
intervening between the segments and the fibers contain less than
10 weight percent of a pigment or filler, based on the total weight
of said fibers; [0048] B. overlapping and collecting the
multicomponent fibers of Step A to form a nonwoven web; and [0049]
C. contacting the nonwoven web with water to remove the
sulfopolyester thereby forming a microdenier fiber web.
[0050] Our invention also provides a process for a process for
water-dispersible, nonwoven fabric comprising: [0051] I. heating a
water-dispersible polymer composition to a temperature above its
flow point, wherein the polymer composition comprises [0052] (A) a
sulfopolyester having a glass transition temperature (Tg) of at
least 25.degree. C., the sulfopolyester comprising: [0053] (i)
residues of one or more dicarboxylic acids; [0054] (ii) about 4 to
about 40 mole %, based on the total repeating units, of residues of
at least one sulfomonomer having 2 functional groups and one or
more metal sulfonate groups attached to an aromatic or
cycloaliphatic ring wherein the functional groups are hydroxyl,
carboxyl, or a combination thereof; [0055] (iii) one or more diol
residues wherein at least 20 mole %, based on the total diol
residues, is a poly(ethylene glycol) having a structure
[0055] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; [0056] (iv) 0 to about 25 mole %,
based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; [0057] (B)
optionally, a water-dispersible polymer blended with the
sulfopolyester; and [0058] (C) optionally, a water-nondispersible
polymer blended with the sulfopolyester to form a blend with the
proviso that the blend is an immiscible blend; wherein the polymer
composition contains less than 10 weight percent of a pigment or
filler, based on the total weight of the polymer composition;
[0059] II. melt spinning filaments; and [0060] III. overlapping and
collecting the filaments of Step II to form a nonwoven web.
[0061] Our invention thus offers a novel and inexpensive process
for a water-dispersible nonwoven fabric by melt-spinning a
water-dispersible sulfopolyester and forming a nonwoven web. The
nonwoven fabric may be in the form of a flat fabric or a
3-dimensional shape and may be incorporated into a variety of
fibrous articles such as the personal care articles noted
hereinabove or used for the manufacture of water-dispersible and/or
flushable protective outerware such as, for example, surgical gowns
and protective clothing for chemical and biohazard cleanup and
laboratory work.
DETAILED DESCRIPTION
[0062] The present invention provides water-dispersible fibers and
fibrous articles that show tensile strength, absorptivity,
flexibility, and fabric integrity in the presence of moisture,
especially upon exposure to human bodily fluids. The fibers and
fibrous articles of our invention do not require the presence of
oil, wax, or fatty acid finishes or the use of large amounts
(typically 10 wt % or greater) of pigments or fillers to prevent
blocking or fusing of the fibers during processing. In addition,
the fibrous articles prepared from our novel fibers do not require
a binder and readily disperse or dissolve in home or public
sewerage systems. In a general embodiment, our invention provides a
water-dispersible fiber comprising a sulfopolyester having a glass
transition temperature (Tg) of at least 25.degree. C., wherein the
sulfpolyester comprises: (i) residues of one or more dicarboxylic
acids; (ii) about 4 to about 40 mole %, based on the total
repeating units, of residues of at least one sulfomonomer having 2
functional groups and one or more sulfonate groups attached to an
aromatic or cycloaliphatic ring wherein the functional groups are
hydroxyl, carboxyl, or a combination thereof; (iii) one or more
diol residues wherein at least 25 mole %, based on the total diol
residues, is a poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500; and (iv) 0
to about 25 mole %, based on the total repeating units, of residues
of a branching monomer having 3 or more functional groups wherein
the functional groups are hydroxyl, carboxyl, or a combination
thereof. Our fiber may optionally include a water-dispersible
polymer blended with the sulfopolyester and, optionally, a
water-nondispersible polymer blended with the sulfopolyester with
the proviso that the blend is an immiscible blend. Our fiber
contains less than 10 weight percent of a pigment or filler, based
on the total weight of the fiber. The present invention also
includes fibrous articles comprising these fibers and may include
personal care products such as wipes, gauze, tissue, diapers, adult
incontinence briefs, training pants, sanitary napkins, bandages,
and surgical dressings. The fibrous articles may have one or more
absorbent layers of fibers.
[0063] The fibers of our invention may be unicomponent fibers,
bicomponent or multicomponent fibers. For example, the fibers of
the present invention may be prepared by melt spinning a single
sulfopolyester or sulfopolyester blend and include staple,
monofilament, and multifilament fibers with a shaped cross-section.
In addition, our invention provides multicomponent fibers, such as
described, for example, in U.S. Pat. No. 5,916,678, which may be
prepared by extruding the sulfopolyester and one or more water
non-dispersible polymers, which are immiscible with the
sulfopolyester, separately through a spinneret having a shaped or
engineered transverse geometry such as, for example, an
"islands-in-the-sea", sheath-core, side-by-side, or segmented pie
configuration. The sulfopolyester may be later removed by
dissolving the interfacial layers or pie segments and leaving the
smaller filaments or microdenier fibers of the water
non-dispersible polymer(s). For example, the sulfopolyester and
water non-dispersible polymers may be fed to a polymer distribution
system where the polymers are introduced into a segmented spinneret
plate. The polymers follow separate paths to the fiber spinneret
and are combined at the spinneret hole which comprises either two
concentric circular holes thus providing a sheath-core type fiber,
or a circular spinneret hole divided along a diameter into multiple
parts to provide a fiber having a side-by-side type. Alternatively,
the immiscible water dispersible sulfopolyester and water
non-dispersible polymers may be introduced separately into a
spinneret having a plurality of radial channels to produce a
multicomponent fiber having a segmented pie cross section.
Typically, the sulfopolyester will form the "sheath" component of a
sheath core configuration. In fiber cross sections having a
plurality of segments, the water non-dispersible segments,
typically, are substantially isolated from each other by the
sulfopolyester. Alternatively, multicomponent fibers may be formed
by melting the sulfopolyester and water non-dispersible polymers in
separate extruders and directing the polymer flows into one
spinneret with a plurality of distribution flow paths in form of
small thin tubes or segments to provide a fiber having an
islands-in-the-sea shaped cross section. An example of such a
spinneret is described in U.S. Pat. No. 5,366,804. In the present
invention, typically, the sulfopolyester will form the "sea"
component and the water non-dispersible polymer will for the
"islands" component.
[0064] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the present
invention. At the very least, each numerical parameter should at
least be construed in light of the number of reported significant
digits and by applying ordinary rounding techniques. Further, the
ranges stated in this disclosure and the claims are intended to
include the entire range specifically and not just the endpoint(s).
For example, a range stated to be 0 to 10 is intended to disclose
all whole numbers between 0 and 10 such as, for example 1, 2, 3, 4,
etc., all fractional numbers between 0 and 10, for example 1.5,
2.3, 4.57, 6.1113, etc., and the endpoints 0 and 10. Also, a range
associated with chemical substituent groups such as, for example,
"C1 to C5 hydrocarbons", is intended to specifically include and
disclose C1 and C5 hydrocarbons as well as C2, C3, and C4
hydrocarbons.
[0065] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
[0066] The unicomponent fibers and fibrous articles of the present
invention are water-dispersible and, typically, completely disperse
at room temperature. Higher water temperatures can be used to
accelerate their dispersibility or rate of removal from the
nonwoven or multicomponent fiber. The term "water-dispersible", as
used herein with respect to unicomponent fibers and fibrous
articles prepared from unicomponent fibers, is intended to be
synonymous with the terms "water-dissipatable",
"water-disintegratable", "water-dissolvable", "water-dispellable",
"water soluble", water-removable", "hydrosoluble", and
"hydrodispersible" and is intended to mean that the fiber or
fibrous article is therein or therethrough dispersed or dissolved
by the action of water. The terms "dispersed", "dispersible",
"dissipate", or "dissipatable" mean that, using a sufficient amount
of deionized water (e.g., 100:1 water:fiber by weight) to form a
loose suspension or slurry of the fibers or fibrous article, at a
temperature of about 60.degree. C., and within a time period of up
to 5 days, the fiber or fibrous article dissolves, disintegrates,
or separates into a plurality of incoherent pieces or particles
distributed more or less throughout the medium such that no
recognizable filaments are recoverable from the medium upon removal
of the water, for example, by filtration or evaporation. Thus,
"water-dispersible", as used herein, is not intended to include the
simple disintegration of an assembly of entangled or bound, but
otherwise water insoluble or nondispersible, fibers wherein the
fiber assembly simply breaks apart in water to produce a slurry of
fibers in water which could be recovered by removal of the water.
In the context of this invention, all of these terms refer to the
activity of water or a mixture of water and a water-miscible
cosolvent on the sulfopolyesters described herein. Examples of such
water-miscible cosolvents includes alcohols, ketones, glycol
ethers, esters and the like. It is intended for this terminology to
include conditions where the sulfopolyester is dissolved to form a
true solution as well as those where the sulfopolyester is
dispersed within the aqueous medium. Often, due to the statistical
nature of sulfopolyester compositions, it is possible to have a
soluble fraction and a dispersed fraction when a single
sulfopolyester sample is placed in an aqueous medium.
[0067] Similarly, the term "water-dispersible", as used herein in
reference to the sulfopolyester as one component of a
multicomponent fiber or fibrous article, also is intended to be
synonymous with the terms "water-dissipatable",
"water-disintegratable", "water-dissolvable", "water-dispellable",
"water soluble", "water-removable", "hydrosoluble", and
"hydrodispersible" and is intended to mean that the sulfopolyester
component is sufficiently removed from the multicomponent fiber and
is dispersed or dissolved by the action of water to enable the
release and separation of the water non-dispersible fibers
contained therein. The terms "dispersed", "dispersible",
"dissipate", or "dissipatable" mean that, using a sufficient amount
of deionized water (e.g., 100:1 water:fiber by weight) to form a
loose suspension or slurry of the fibers or fibrous article, at a
temperature of about 60.degree. C., and within a time period of up
to 5 days, sulfopolyester component dissolves, disintegrates, or
separates from the multicomponent fiber, leaving behind a plurality
of microdenier fibers from the water non-dispersible segments.
[0068] The water-dispersible fiber of the present invention is
prepared from polyesters or, more specifically sulfopolyesters,
comprising dicarboxylic acid monomer residues, sulfomonomer
residues, diol monomer residues, and repeating units. The
sulfomonomer may be a dicarboxylic acid, a diol, or
hydroxycarboxylic acid. Thus, the term "monomer residue", as used
herein, means a residue of a dicarboxylic acid, a diol, or a
hydroxycarboxylic acid. A "repeating unit", as used herein, means
an organic structure having 2 monomer residues bonded through a
carbonyloxy group. The sulfopolyesters of the present invention
contain substantially equal molar proportions of acid residues (100
mole %) and diol residues (100 mole %) which react in substantially
equal proportions such that the total moles of repeating units is
equal to 100 mole %. The mole percentages provided in the present
disclosure, therefore, may be based on the total moles of acid
residues, the total moles of diol residues, or the total moles of
repeating units. For example, a sulfopolyester containing 30 mole %
of a sulfomonomer, which may be a dicarboxylic acid, a diol, or
hydroxycarboxylic acid, based on the total repeating units, means
that the sulfopolyester contains 30 mole % sulfomonomer out of a
total of 100 mole % repeating units. Thus, there are 30 moles of
sulfomonomer residues among every 100 moles of repeating units.
Similarly, a sulfopolyester containing 30 mole % of a dicarboxylic
acid sulfomonomer, based on the total acid residues, means the
sulfopolyester contains 30 mole % sulfomonomer out of a total of
100 mole % acid residues. Thus, in this latter case, there are 30
moles of sulfomonomer residues among every 100 moles of acid
residues.
[0069] The sulfopolyesters described herein have an inherent
viscosity, abbreviated hereinafter as "Ih.V.", of at least about
0.1 dL/g, preferably about 0.2 to 0.3 dL/g, and most preferably
greater than about 0.3 dL/g, measured in a 60/40 parts by weight
solution of phenol/tetrachloroethane solvent at 25.degree. C. and
at a concentration of about 0.5 g of sulfopolyester in 100 mL of
solvent. The term "polyester", as used herein, encompasses both
"homopolyesters" and "copolyesters" and means a synthetic polymer
prepared by the polycondensation of difunctional carboxylic acids
with difunctional hydroxyl compound. As used herein, the term
"sulfopolyester" means any polyester comprising a sulfomonomer.
Typically the difunctional carboxylic acid is a dicarboxylic acid
and the difunctional hydroxyl compound is a dihydric alcohol such
as, for example glycols and diols. Alternatively, the difunctional
carboxylic acid may be a hydroxy carboxylic acid such as, for
example, p-hydroxybenzoic acid, and the difunctional hydroxyl
compound may be a aromatic nucleus bearing 2 hydroxy substituents
such as, for example, hydroquinone. The term "residue", as used
herein, means any organic structure incorporated into the polymer
through a polycondensation reaction involving the corresponding
monomer. Thus, the dicarboxylic acid residue may be derived from a
dicarboxylic acid monomer or its associated acid halides, esters,
salts, anhydrides, or mixtures thereof. As used herein, therefore,
the term dicarboxylic acid is intended to include dicarboxylic
acids and any derivative of a dicarboxylic acid, including its
associated acid halides, esters, half-esters, salts, half-salts,
anhydrides, mixed anhydrides, or mixtures thereof, useful in a
polycondensation process with a diol to make a high molecular
weight polyester.
[0070] The sulfopolyester of the present invention includes one or
more dicarboxylic acid residues. Depending on the type and
concentration of the sulfomonomer, the dicarboxylic acid residue
may comprise from about 60 to about 100 mole % of the acid
residues. Other examples of concentration ranges of dicarboxylic
acid residues are from about 60 mole % to about 95 mole %, and
about 70 mole % to about 95 mole %. Examples of dicarboxylic acids
that may be used include aliphatic dicarboxylic acids, alicyclic
dicarboxylic acids, aromatic dicarboxylic acids, or mixtures of two
or more of these acids. Thus, suitable dicarboxylic acids include,
but are not limited to succinic; glutaric; adipic; azelaic;
sebacic; fumaric; maleic; itaconic; 1,3-cyclo-hexanedicarboxylic;
1,4-cyclohexanedicarboxylic; diglycolic;
2,5-norbornane-dicarboxylic; phthalic; terephthalic;
1,4-naphthalenedicarboxylic; 2,5-naphthalenedicarboxylic; diphenic;
4,4'-oxydibenzoic; 4,4'-sulfonyldibenzoic; and isophthalic. The
preferred dicarboxylic acid residues are isophthalic, terephthalic,
and 1,4-cyclohexanedicarboxylic acids, or if diesters are used,
dimethyl terephthalate, dimethyl isophthalate, and
dimethyl-1,4-cyclohexane-dicarboxylate with the residues of
isophthalic and terephthalic acid being especially preferred.
Although the dicarboxylic acid methyl ester is the most preferred
embodiment, it is also acceptable to include higher order alkyl
esters, such as ethyl, propyl, isopropyl, butyl, and so forth. In
addition, aromatic esters, particularly phenyl, also may be
employed.
[0071] The sulfopolyester includes about 4 to about 40 mole %,
based on the total repeating units, of residues of at least one
sulfomonomer having 2 functional groups and one or more sulfonate
groups attached to an aromatic or cycloaliphatic ring wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof.
Additional examples of concentration ranges for the sulfomonomer
residues are about 4 to about 35 mole %, about 8 to about 30 mole
%, and about 8 to about 25 mole %, based on the total repeating
units. The sulfomonomer may be a dicarboxylic acid or ester thereof
containing a sulfonate group, a diol containing a sulfonate group,
or a hydroxy acid containing a sulfonate group. The term
"sulfonate" refers to a salt of a sulfonic acid having the
structure "--SO.sub.3M" wherein M is the cation of the sulfonate
salt. The cation of the sulfonate salt may be a metal ion such as
Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.++, Ca.sup.++, Ni.sup.++,
Fe.sup.++, and the like. Alternatively, the cation of the sulfonate
salt may be non-metallic such as a nitrogenous base as described,
for example, in U.S. Pat. No. 4,304,901. Nitrogen-based cations are
derived from nitrogen-containing bases, which may be aliphatic,
cycloaliphatic, or aromatic compounds. Examples of such nitrogen
containing bases include ammonia, dimethylethanolamine,
diethanolamine, triethanolamine, pyridine, morpholine, and
piperidine. Because monomers containing the nitrogen-based
sulfonate salts typically are not thermally stable at conditions
required to make the polymers in the melt, the method of this
invention for preparing sulfopolyesters containing nitrogen-based
sulfonate salt groups is to disperse, dissipate, or dissolve the
polymer containing the required amount of sulfonate group in the
form of its alkali metal salt in water and then exchange the alkali
metal cation for a nitrogen-based cation.
[0072] When a monovalent alkali metal ion is used as the cation of
the sulfonate salt, the resulting sulfopolyester is completely
dispersible in water with the rate of dispersion dependent on the
content of sulfomonomer in the polymer, temperature of the water,
surface area/thickness of the sulfopolyester, and so forth. When a
divalent metal ion is used, the resulting sulfopolyesters are not
readily dispersed by cold water but are more easily dispersed by
hot water. Utilization of more than one counterion within a single
polymer composition is possible and may offer a means to tailor or
fine-tune the water-responsivity of the resulting article of
manufacture. Examples sulfomonomers residues include monomer
residues where the sulfonate salt group is attached to an aromatic
acid nucleus, such as, for example, benzene; naphthalene; diphenyl;
oxydiphenyl; sulfonyldiphenyl; and methylenediphenyl or
cycloaliphatic rings, such as, for example, cyclohexyl;
cyclopentyl; cyclobutyl; cycloheptyl; and cyclooctyl. Other
examples of sulfomonomer residues which may be used in the present
invention are the metal sulfonate salt of sulfophthalic acid,
sulfoterephthalic acid, sulfoisophthalic acid, or combinations
thereof. Other examples of sulfomonomers which may be used are
5-sodiosulfoisophthalic acid and esters thereof. If the
sulfomonomer residue is from 5-sodiosulfoisophthalic acid, typical
sulfomonomer concentration ranges are about 4 to about 35 mole %,
about 8 to about 30 mole %, and about 8 to 25 mole %, based on the
total moles of acid residues.
[0073] The sulfomonomers used in the preparation of the
sulfopolyesters are known compounds and may be prepared using
methods well known in the art. For example, sulfomonomers in which
the sulfonate group is attached to an aromatic ring may be prepared
by sulfonating the aromatic compound with oleum to obtain the
corresponding sulfonic acid and followed by reaction with a metal
oxide or base, for example, sodium acetate, to prepare the
sulfonate salt. Procedures for preparation of various sulfomonomers
are described, for example, in U.S. Pat. Nos. 3,779,993; 3,018,272;
and 3,528,947.
[0074] It is also possible to prepare the polyester using, for
example, a sodium sulfonate salt, and ion-exchange methods to
replace the sodium with a different ion, such as zinc, when the
polymer is in the dispersed form. This type of ion exchange
procedure is generally superior to preparing the polymer with
divalent salts insofar as the sodium salts are usually more soluble
in the polymer reactant melt-phase.
[0075] The sulfopolyester includes one or more diol residues which
may include aliphatic, cycloaliphatic, and aralkyl glycols. The
cycloaliphatic diols, for example, 1,3- and
1,4-cyclohexanedimethanol, may be present as their pure cis or
trans isomers or as a mixture of cis and trans isomers. As used
herein, the term "diol" is synonymous with the term "glycol" and
means any dihydric alcohol. Examples diols include ethylene glycol;
diethylene glycol; triethylene glycol; polyethylene glycols;
1,3-propanediol; 2,4-dimethyl-2-ethyl-hexane-1,3-diol;
2,2-dimethyl-1,3-propanediol; 2-ethyl-2-butyl-1,3-propanediol;
2-ethyl-2-isobutyl-1,3-propanediol; 1,3-butanediol; 1,4-butanediol;
1,5-pentanediol; 1,6-hexanediol; 2,2,4-trimethyl-1,6-hexanediol;
thiodiethanol; 1,2-cyclohexanedimethanol;
1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol;
2,2,4,4-tetramethyl-1,3-cyclobutanediol; p-xylylenediol, or
combinations of one or more of these glycols.
[0076] The diol residues may include from about 25 mole % to about
100 mole %, based on the total diol residues, of residue of a
poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500.
Non-limiting examples of lower molecular weight polyethylene
glycols, e.g., wherein n is from 2 to 6, are diethylene glycol,
triethylene glycol, and tetraethylene glycol. Of these lower
molecular weight glycols, diethylene and triethylene glycol are
most preferred. Higher molecular weight polyethylene glycols
(abbreviated herein as "PEG"), wherein n is from 7 to about 500,
include the commercially available products known under the
designation CARBOWAX.RTM., a product of Dow Chemical Company
(formerly Union Carbide). Typically, PEG's are used in combination
with other diols such as, for example, diethylene glycol or
ethylene glycol. Based on the values of n, which range from greater
than 6 to 500, the molecular weight may range from greater than 300
to about 22,000 g/mol. The molecular weight and the mole % are
inversely proportional to each other; specifically, as the
molecular weight is increased, the mole % will be decreased in
order to achieve a designated degree of hydrophilicity. For
example, it is illustrative of this concept to consider that a PEG
having a molecular weight of 1000 may constitute up to 10 mole % of
the total diol, while a PEG having a molecular weight of 10,000
would typically be incorporated at a level of less than 1 mole % of
the total diol.
[0077] Certain dimer, trimer, and tetramer diols may be formed in
situ due to side reactions that may be controlled by varying the
process conditions. For example, varying amounts of diethylene,
triethylene, and tetraethylene glycols may be formed from ethylene
glycol from an acid-catalyzed dehydration reaction which occurs
readily when the polycondensation reaction is carried out under
acidic conditions. The presence of buffer solutions, well-known to
those skilled in the art, may be added to the reaction mixture to
retard these side reactions. Additional compositional latitude is
possible, however, if the buffer is omitted and the dimerization,
trimerization, and tetramerization reactions are allowed to
proceed.
[0078] The sulfopolyester of the present invention may include from
0 to about 25 mole %, based on the total repeating units, of
residues of a branching monomer having 3 or more functional groups
wherein the functional groups are hydroxyl, carboxyl, or a
combination thereof. Non-limiting examples of branching monomers
are 1,1,1-trimethylol propane, 1,1,1-trimethylolethane, glycerin,
pentaerythritol, erythritol, threitol, dipentaerythritol, sorbitol,
trimellitic anhydride, pyromellitic dianhydride, dimethylol
propionic acid, or combinations thereof. Further examples of
branching monomer concentration ranges are from 0 to about 20 mole
% and from 0 to about 10 mole %. The presence of a branching
monomer may result in a number of possible benefits to the
sulfopolyester of the present invention, including but not limited
to, the ability to tailor rheological, solubility, and tensile
properties. For example, at a constant molecular weight, a branched
sulfopolyester, compared to a linear analog, will also have a
greater concentration of end groups that may facilitate
post-polymerization crosslinking reactions. At high concentrations
of branching agent, however, the sulfopolyester may be prone to
gelation.
[0079] The sulfopolyester used for the fiber of the present
invention has a glass transition temperature, abbreviated herein as
"Tg", of at least 25.degree. C. as measured on the dry polymer
using standard techniques, such as differential scanning
calorimetry ("DSC"), well known to persons skilled in the art. The
Tg measurements of the sulfopolyesters of the present invention are
conducted using a "dry polymer", that is, a polymer sample in which
adventitious or absorbed water is driven off by heating to polymer
to a temperature of about 200.degree. C. and allowing the sample to
return to room temperature. Typically, the sulfopolyester is dried
in the DSC apparatus by conducting a first thermal scan in which
the sample is heated to a temperature above the water vaporization
temperature, holding the sample at that temperature until the
vaporization of the water absorbed in the polymer is complete (as
indicated by an a large, broad endotherm), cooling the sample to
room temperature, and then conducting a second thermal scan to
obtain the Tg measurement. Further examples of glass transition
temperatures exhibited by the sulfopolyester are at least
30.degree. C., at least 35.degree. C., at least 40.degree. C., at
least 50.degree. C., at least 60.degree. C., at least 65.degree.
C., at least 80.degree. C., and at least 90.degree. C. Although
other Tg's are possible, typical glass transition temperatures of
the dry sulfopolyesters our invention are about 30.degree. C.,
about 48.degree. C., about 55.degree. C., about 65.degree. C.,
about 70.degree. C., about 75.degree. C., about 85.degree. C., and
about 90.degree. C.
[0080] Our novel fibers may consist essentially of or, consist of,
the sulfopolyesters described hereinabove. In another embodiment,
however, the sulfopolyesters of this invention may be a single
polyester or may be blended with one or more supplemental polymers
to modify the properties of the resulting fiber. The supplemental
polymer may or may not be water-dispersible depending on the
application and may be miscible or immiscible with the
sulfopolyester. If the supplemental polymer is
water-nondispersible, it is preferred that the blend with the
sulfopolyester is immiscible. The term "miscible", as used herein,
is intended to mean that the blend has a single, homogeneous
amorphous phase as indicated by a single composition-dependent Tg.
For example, a first polymer that is miscible with second polymer
may be used to "plasticize" the second polymer as illustrated, for
example, in U.S. Pat. No. 6,211,309. By contrast, the term
"immiscible", as used herein, denotes a blend that shows at least
2, randomly mixed, phases and exhibits more than one Tg. Some
polymers may be immiscible and yet compatible with the
sulfopolyester. A further general description of miscible and
immiscible polymer blends and the various analytical techniques for
their characterization may be found in Polymer Blends Volumes 1 and
2, Edited by D. R. Paul and C. B. Bucknall, 2000, John Wiley &
Sons, Inc.
[0081] Non-limiting examples of water-dispersible polymers that may
be blended with the sulfopolyester are polymethacrylic acid,
polyvinyl pyrrolidone, polyethylene-acrylic acid copolymers,
polyvinyl methyl ether, polyvinyl alcohol, polyethylene oxide,
hydroxy propyl cellulose, hydroxypropyl methyl cellulose, methyl
cellulose, ethyl hydroxyethyl cellulose, isopropyl cellulose,
methyl ether starch, polyacrylamides, poly(N-vinyl caprolactam),
polyethyl oxazoline, poly(2-isopropyl-2-oxazoline), polyvinyl
methyl oxazolidone, water-dispersible sulfopolyesters, polyvinyl
methyl oxazolidimone, poly(2,4-dimethyl-6-triazinylethylene), and
ethylene oxide-propylene oxide copolymers. Examples of polymers
which are water-nondispersible that may be blended with the
sulfopolyester include, but are not limited to, polyolefins, such
as homo- and copolymers of polyethylene and polypropylene;
poly(ethylene terephthalate); poly(butylene terephthalate); and
polyamides, such as nylon-6; polylactides; caprolactone; Eastar
Bio.RTM. (poly(tetramethylene adipate-co-terephthalate), a product
of Eastman Chemical Company); polycarbonate; polyurethane; and
polyvinyl chloride.
[0082] According to our invention, blends of more than one
sulfopolyester may be used to tailor the end-use properties of the
resulting fiber or fibrous article, for example, a nonwoven fabric
or web. The blends of one or more sulfopolyesters will have Tg's of
at least 25.degree. C. for the water-dispersible, unicomponent
fibers and at least 57.degree. C. for the multicomponent fibers.
Thus, blending may also be exploited to alter the processing
characteristics of a sulfopolyester to facilitate the fabrication
of a nonwoven. In another example, an immiscible blend of
polypropylene and sulfopolyester may provide a conventional
nonwoven web that will break apart and completely disperse in water
as true solubility is not needed. In this latter example, the
desired performance is related to maintaining the physical
properties of the polypropylene while the sulfopolyester is only a
spectator during the actual use of the product or, alternatively,
the sulfopolyester is fugitive and is removed before the final form
of the product is utilized.
[0083] The sulfopolyester and supplemental polymer may be blended
in batch, semicontinuous, or continuous processes. Small scale
batches may be readily prepared in any high-intensity mixing
devices well-known to those skilled in the art, such as Banbury
mixers, prior to melt-spinning fibers. The components may also be
blended in solution in an appropriate solvent. The melt blending
method includes blending the sulfopolyester and supplemental
polymer at a temperature sufficient to melt the polymers. The blend
may be cooled and pelletized for further use or the melt blend can
be melt spun directly from this molten blend into fiber form. The
term "melt" as used herein includes, but is not limited to, merely
softening the polyester. For melt mixing methods generally known in
the polymers art, see Mixing and Compounding of Polymers (I.
Manas-Zloczower & Z. Tadmor editors, Carl Hanser Verlag
Publisher, 1994, New York, N.Y.).
[0084] Our invention also provides a water-dispersible fiber
comprising a sulfopolyester having a glass transition temperature
(Tg) of at least 25.degree. C., wherein the sulfpolyester
comprises: (i) about 50 to about 96 mole % of one or more residues
of isophthalic acid or terephthalic acid, based on the total acid
residues; (ii) about 4 to about 30 mole %, based on the total acid
residues, of a residue of sodiosulfoisophthalic acid; (iii) one or
more diol residues wherein at least 25 mole %, based on the total
diol residues, is a poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500; (iv) 0 to
about 20 mole %, based on the total repeating units, of residues of
a branching monomer having 3 or more functional groups wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof.
As described hereinabove, the fiber may optionally include a first
water-dispersible polymer blended with the sulfopolyester; and,
optionally, a water-nondispersible polymer blended with the
sulfopolyester such that the blend is an immiscible blend. Our
fiber contains less than 10 weight percent of a pigment or filler,
based on the total weight of the fiber. The first water-dispersible
polymer is as described hereinabove. The sulfopolyester should have
a glass transition temperature (Tg) of at least 25.degree. C., but
may have, for example, a Tg of about 35.degree. C., about
48.degree. C., about 55.degree. C., about 65.degree. C., about
70.degree. C., about 75.degree. C., about 85.degree. C., and about
90.degree. C. The sulfopolyester may contain other concentrations
of isophthalic acid residues, for example, about 60 to about 95
mole %, and about 75 to about 95 mole %. Further examples of
isophthalic acid residue concentrations ranges are about 70 to
about 85 mole %, about 85 to about 95 mole % and about 90 to about
95 mole %. The sulfopolyester also may comprise about 25 to about
95 mole % of the residues of diethylene glycol. Further examples of
diethylene glycol residue concentration ranges include about 50 to
about 95 mole %, about 70 to about 95 mole %, and about 75 to about
95 mole %. The sulfopolyester also may include the residues of
ethylene glycol and/or 1,4-cyclohexanedimethanol, abbreviated
herein as "CHDM". Typical concentration ranges of CHDM residues are
about 10 to about 75 mole %, about 25 to about 65 mole %, and about
40 to about 60 mole %. Typical concentration ranges of ethylene
glycol residues are about 10 to about 75 mole %, about 25 to about
65 mole %, and about 40 to about 60 mole %. In another embodiment,
the sulfopolyester comprises is about 75 to about 96 mole % of the
residues of isophthalic acid and about 25 to about 95 mole % of the
residues of diethylene glycol.
[0085] The sulfopolyesters of the instant invention are readily
prepared from the appropriate dicarboxylic acids, esters,
anhydrides, or salts, sulfomonomer, and the appropriate diol or
diol mixtures using typical poly-condensation reaction conditions.
They may be made by continuous, semi-continuous, and batch modes of
operation and may utilize a variety of reactor types. Examples of
suitable reactor types include, but are not limited to, stirred
tank, continuous stirred tank, slurry, tubular, wiped-film, falling
film, or extrusion reactors. The term "continuous" as used herein
means a process wherein reactants are introduced and products
withdrawn simultaneously in an uninterrupted manner. By
"continuous" it is meant that the process is substantially or
completely continuous in operation and is to be contrasted with a
"batch" process. "Continuous" is not meant in any way to prohibit
normal interruptions in the continuity of the process due to, for
example, start-up, reactor maintenance, or scheduled shut down
periods. The term "batch" process as used herein means a process
wherein all the reactants are added to the reactor and then
processed according to a predetermined course of reaction during
which no material is fed or removed into the reactor. The term
"semicontinuous" means a process where some of the reactants are
charged at the beginning of the process and the remaining reactants
are fed continuously as the reaction progresses. Alternatively, a
semicontinuous process may also include a process similar to a
batch process in which all the reactants are added at the beginning
of the process except that one or more of the products are removed
continuously as the reaction progresses. The process is operated
advantageously as a continuous process for economic reasons and to
produce superior coloration of the polymer as the sulfopolyester
may deteriorate in appearance if allowed to reside in a reactor at
an elevated temperature for too long a duration.
[0086] The sulfopolyesters of the present invention are prepared by
procedures known to persons skilled in the art. The sulfomonomer is
most often added directly to the reaction mixture from which the
polymer is made, although other processes are known and may also be
employed, for example, as described in U.S. Pat. Nos. 3,018,272,
3,075,952, and 3,033,822. The reaction of the sulfomonomer, diol
component and the dicarboxylic acid component may be carried out
using conventional polyester polymerization conditions. For
example, when preparing the sulfopolyesters by means of an ester
interchange reaction, i.e., from the ester form of the dicarboxylic
acid components, the reaction process may comprise two steps. In
the first step, the diol component and the dicarboxylic acid
component, such as, for example, dimethyl isophthalate, are reacted
at elevated temperatures, typically, about 150.degree. C. to about
250.degree. C. for about 0.5 to about 8 hours at pressures ranging
from about 0.0 kPa gauge to about 414 kPa gauge (60 pounds per
square inch, "psig"). Preferably, the temperature for the ester
interchange reaction ranges from about 180.degree. C. to about
230.degree. C. for about 1 to about 4 hours while the preferred
pressure ranges from about 103 kPa gauge (15 psig) to about 276 kPa
gauge (40 psig). Thereafter, the reaction product is heated under
higher temperatures and under reduced pressure to form
sulfopolyester with the elimination of diol, which is readily
volatilized under these conditions and removed from the system.
This second step, or polycondensation step, is continued under
higher vacuum and a temperature which generally ranges from about
230.degree. C. to about 350.degree. C., preferably about
250.degree. C. to about 310.degree. C. and most preferably about
260.degree. C. to about 290.degree. C. for about 0.1 to about 6
hours, or preferably, for about 0.2 to about 2 hours, until a
polymer having the desired degree of polymerization, as determined
by inherent viscosity, is obtained. The polycondensation step may
be conducted under reduced pressure which ranges from about 53 kPa
(400 torr) to about 0.013 kPa (0.1 torr). Stirring or appropriate
conditions are used in both stages to ensure adequate heat transfer
and surface renewal of the reaction mixture. The reactions of both
stages are facilitated by appropriate catalysts such as, for
example, alkoxy titanium compounds, alkali metal hydroxides and
alcoholates, salts of organic carboxylic acids, alkyl tin
compounds, metal oxides, and the like. A three-stage manufacturing
procedure, similar to that described in U.S. Pat. No. 5,290,631,
may also be used, particularly when a mixed monomer feed of acids
and esters is employed.
[0087] To ensure that the reaction of the diol component and
dicarboxylic acid component by an ester interchange reaction
mechanism is driven to completion, it is preferred to employ about
1.05 to about 2.5 moles of diol component to one mole dicarboxylic
acid component. Persons of skill in the art will understand,
however, that the ratio of diol component to dicarboxylic acid
component is generally determined by the design of the reactor in
which the reaction process occurs.
[0088] In the preparation of sulfopolyester by direct
esterification, i.e., from the acid form of the dicarboxylic acid
component, sulfopolyesters are produced by reacting the
dicarboxylic acid or a mixture of dicarboxylic acids with the diol
component or a mixture of diol components. The reaction is
conducted at a pressure of from about 7 kPa gauge (1 psig) to about
1379 kPa gauge (200 psig), preferably less than 689 kPa (100 psig)
to produce a low molecular weight, linear or branched
sulfopolyester product having an average degree of polymerization
of from about 1.4 to about 10. The temperatures employed during the
direct esterification reaction typically range from about
180.degree. C. to about 280.degree. C., more preferably ranging
from about 220.degree. C. to about 270.degree. C. This low
molecular weight polymer may then be polymerized by a
polycondensation reaction.
[0089] The water dispersible and multicomponent fibers and fibrous
articles of this invention also may contain other conventional
additives and ingredients which do not deleteriously affect their
end use. For example, additives such as fillers, surface friction
modifiers, light and heat stabilizers, extrusion aids, antistatic
agents, colorants, dyes, pigments, fluorescent brighteners,
antimicrobials, anticounterfeiting markers, hydrophobic and
hydrophilic enhancers, viscosity modifiers, slip agents,
tougheners, adhesion promoters, and the like may be used. The
fibers and fibrous articles of our invention do not require the
presence of additives such as, for example, pigments, fillers,
oils, waxes, or fatty acid finishes, to prevent blocking or fusing
of the fibers during processing. The terms "blocking or fusing", as
used herein, is understood to mean that the fibers or fibrous
articles stick together or fuse into a mass such that the fiber
cannot be processed or used for its intended purpose. Blocking and
fusing can occur during processing of the fiber or fibrous article
or during storage over a period of days or weeks and is exacerbated
under hot, humid conditions. In one embodiment of the invention,
the fibers and fibrous articles will contain less than 10 wt % of
such anti-blocking additives, based on the total weight of the
fiber or fibrous article. For example, the fibers and fibrous
articles may contain less than 10 wt % of a pigment or filler. In
other examples, the fibers and fibrous articles may contain less
than 9 wt %, less than 5 wt %, less than 3 wt %, less than 1 wt %,
and 0 wt % of a pigment or filler, based on the total weight of the
fiber. Colorants, sometimes referred to as toners, may be added to
impart a desired neutral hue and/or brightness to the
sulfopolyester. When colored fibers are desired, pigments or
colorants may be included in the sulfopolyester reaction mixture
during the reaction of the diol monomer and the dicarboxylic acid
monomer or they may be melt blended with the preformed
sulfopolyester. A preferred method of including colorants is to use
a colorant having thermally stable organic colored compounds having
reactive groups such that the colorant is copolymerized and
incorporated into the sulfopolyester to improve its hue. For
example, colorants such as dyes possessing reactive hydroxyl and/or
carboxyl groups, including, but not limited to, blue and red
substituted anthraquinones, may be copolymerized into the polymer
chain. When dyes are employed as colorants, they may be added to
the copolyester reaction process after an ester interchange or
direct esterification reaction.
[0090] For the purposes of this invention, the term "fiber" refers
to a polymeric body of high aspect ratio capable of being formed
into two or three dimensional articles such as woven or nonwoven
fabrics. In the context of the present invention, the term "fiber"
is synonymous with "fibers" and intended to mean one or more
fibers. The fibers of our invention may be unicomponent fibers,
bicomponent, or multicomponent fibers. The term "unicomponent
fiber", as used herein, is intended to mean a fiber prepared by
melt spinning a single sulfopolyester, blends of one or more
sulfopolyesters, or blends of one or more sulfopolyesters with one
or more additional polymers and includes staple, monofilament, and
multifilament fibers. "Unicomponent" is intended to be synonymous
with the term "monocomponent" and includes "biconstituent" or
"multiconstituent" fibers, and refers to fibers which have been
formed from at least two polymers extruded from the same extruder
as a blend. Unicomponent or biconstituent fibers do not have the
various polymer components arranged in relatively constantly
positioned distinct zones across the cross-sectional area of the
fiber and the various polymers are usually not continuous along the
entire length of the fiber, instead usually forming fibrils or
protofibrils which start and end at random. Thus, the term
"unicomponent" is not intended to exclude fibers formed from a
polymer or blends of one or more polymers to which small amounts of
additives may be added for coloration, anti-static properties,
lubrication, hydrophilicity, etc. By contrast, the term
"multicomponent fiber", as used herein, intended to mean a fiber
prepared by melting the two or more fiber forming polymers in
separate extruders and by directing the resulting multiple polymer
flows into one spinneret with a plurality of distribution flow
paths but spun together to form one fiber. Multicomponent fibers
are also sometimes referred to as conjugate or bicomponent fibers.
The polymers are arranged in substantially constantly positioned
distinct zones across the cross-section of the conjugate fibers and
extend continuously along the length of the conjugate fibers. The
configuration of such a multicomponent fiber may be, for example, a
sheath/core arrangement wherein one polymer is surrounded by
another or may be a side by side arrangement, a pie arrangement or
an "islands-in-the-sea" arrangement. For example, a multicomponent
fiber may be prepared by extruding the sulfopolyester and one or
more water non-dispersible polymers separately through a spinneret
having a shaped or engineered transverse geometry such as, for
example, an "islands-in-the-sea" or segmented pie configuration.
Unicomponent fibers, typically, are staple, monofilament or
multifilament fibers that have a shaped or round cross-section.
Most fiber forms are heatset. The fiber may include the various
antioxidants, pigments, and additives as described herein.
[0091] Monofilament fibers generally range in size from about 15 to
about 8000 denier per filament (abbreviated herein as "d/f"). Our
novel fibers typically will have d/f values in the range of about
40 to about 5000. Monofilaments may be in the form of unicomponent
or multicomponent fibers. The multifilament fibers of our invention
will preferably range in size from about 1.5 micrometers for melt
blown webs, about 0.5 to about 50 d/f for staple fibers, and up to
about 5000 d/f for monofilament fibers. Multifilament fibers may
also be used as crimped or uncrimped yarns and tows. Fibers used in
melt blown web and melt spun fabrics may be produced in microdenier
sizes. The term "microdenier", as used herein, is intended to mean
a d/f value of 1 d/f or less. For example, the microdenier fibers
of the instant invention typically have d/f values of 1 or less,
0.5 or less, or 0.1 or less. Nanofibers can also be produced by
electrostatic spinning.
[0092] As noted hereinabove, the sulfopolyesters also are
advantageous for the preparation of bicomponent and multicomponent
fibers having a shaped cross section. We have discovered that
sulfopolyesters or blends of sulfopolyesters having a glass
transition temperature (Tg) of at least 57.degree. C. are
particularly useful for multicomponent fibers to prevent blocking
and fusing of the fiber during spinning and take up. Thus, our
invention provides a multicomponent fiber having shaped cross
section, comprising: [0093] A) a water dispersible sulfopolyester
having a glass transition temperature (Tg) of at least 57.degree.
C., the sulfpolyester comprising: [0094] (i) residues of one or
more dicarboxylic acids; [0095] (ii) about 4 to about 40 mole %,
based on the total repeating units, of residues of at least one
sulfomonomer having 2 functional groups and one or more sulfonate
groups attached to an aromatic or cycloaliphatic ring wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof;
[0096] (iii) one or more diol residues wherein at least 25 mole %,
based on the total diol residues, is a poly(ethylene glycol) having
a structure
[0096] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0097] (iv) 0 to about 25 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; and [0098]
B) a plurality of segments comprising one or more
water-nondispersable polymers immiscible with the sulfopolyester,
wherein the segments are substantially isolated from each other by
the sulfopolyester intervening between the segments; wherein the
fiber has an islands-in-the-sea or segmented pie cross section and
contains less than 10 weight percent of a pigment or filler, based
on the total weight of the fiber. The dicarboxylic acids, diols,
sulfopolyester, sulfomonomers, and branching monomers residues are
as described previously for other embodiments of the invention. For
multicomponent fibers, it is advantageous that the sulfopolyester
have a Tg of at least 57.degree. C. Further examples of glass
transition temperatures that may be exhibited by the sulfopolyester
or sulfopolyester blend of our multicomponent fiber are at least
60.degree. C., at least 65.degree. C., at least 70.degree. C., at
least 75.degree. C., at least 80.degree. C., at least 85.degree.
C., and at least 90.degree. C. Further, to obtain a sulfopolyester
with a Tg of at least 57.degree. C., blends of one or more
sulfopolyesters may be used in varying proportions to obtain a
sulfopolyester blend having the desired Tg. The Tg of a
sulfopolyester blend may be calculated by using a weighted average
of the Tg's of the sulfopolyester components. For example,
sulfopolyester having a Tg of 48.degree. C. may be blended in a
25:75 wt:wt ratio with another sulfopolyester having Tg of
65.degree. C. to give a sulfopolyester blend having a Tg of
approximately 61.degree. C.
[0099] The multicomponent fiber comprises a plurality of segments
one or more water-nondispersable polymers immiscible with the
sulfopolyester in which the segments are substantially isolated
from each other by the sulfopolyester intervening between the
segments. The term "substantially isolated", as used herein, is
intended to mean that the segments are set apart from each other to
permit the segments to form individual fibers upon removal of the
sulfopolyester. For example, the segments may be touching each
others as in, for example, a segmented pie configuration but can be
split apart by impact or when the sulfopolyester is removed.
[0100] The ratio by weight of the sulfopolyester to water
non-dispersible polymer component in the multicomponent fiber of
the invention is generally in the range of about 60:40 to about
2:98 or, in another example, in the range of about 50:50 to about
5:95. Typically, the sulfopolyester comprises 50% by weight or less
of the total weight of the multicomponent fiber.
[0101] The segments of multicomponent fiber may comprise one of
more water non-dispersible polymers. Examples of
water-nondispersible polymers which may be used in segments of the
multicomponent fiber include, but are not limited to, polyolefins,
polyesters, polyamides, polylactides, polycaprolactone,
polycarbonate, polyurethane, and polyvinyl chloride. For example,
the water non-dispersible polymer may be polyester such as
poly(ethylene)terephthalate, poly(butylene) terephthalate,
poly(cyclohexylene)cyclohexanedicarboxylate,
poly(cyclohexylene)terephthalate, poly(trimethylene)terephthalate,
and the like. In another example, the water-nondispersible polymer
biodistintegratable as determined by DIN Standard 54900 and/or
biodegradable as determined by ASTM Standard Method, D6340-98.
Examples of biodegradable polyesters and polyester blends are
disclosed in U.S. Pat. Nos. 5,599,858; 5,580,911; 5,446,079; and
5,559,171. The term "biodegradable", as used herein in reference to
the water non-dispersible polymers of the present invention, is
understood to mean that the polymers are degraded under
environmental influences such as, for example, in a composting
environment, in an appropriate and demonstrable time span as
defined, for example, by ASTM Standard Method, D6340-98, entitled
"Standard Test Methods for Determining Aerobic Biodegradation of
Radiolabeled Plastic Materials in an Aqueous or Compost
Environment". The water non-dispersible polymers of the present
invention also may be "biodisintegratable", meaning that the
polymers are easily fragmented in a composting environment as
defined, for example, by DIN Standard 54900. For example, the
biodegradable polymer is initially reduced in molecular weight in
the environment by the action of heat, water, air, microbes and
other factors. This reduction in molecular weight results in a loss
of physical properties (tenacity) and often in fiber breakage. Once
the molecular weight of the polymer is sufficiently low, the
monomers and oligomers are then assimilated by the microbes. In an
aerobic environment, these monomers or oligomers are ultimately
oxidized to CO.sub.2, H.sub.2O, and new cell biomass. In an
anaerobic environment, the monomers or oligomers are ultimately
converted to CO.sub.2, H.sub.2, acetate, methane, and cell
biomass.
[0102] For example, water-nondispersible polymer may be an
aliphatic-aromatic polyester, abbreviated herein as "AAPE". The
term "aliphatic-aromatic polyester", as used herein, means a
polyester comprising a mixture of residues from aliphatic or
cycloaliphatic dicarboxylic acids or diols and aromatic
dicarboxylic acids or diols. The term "non-aromatic", as used
herein with respect to the dicarboxylic acid and diol monomers of
the present invention, means that carboxyl or hydroxyl groups of
the monomer are not connected through an aromatic nucleus. For
example, adipic acid contains no aromatic nucleus in its backbone,
i.e., the chain of carbon atoms connecting the carboxylic acid
groups, thus is "non-aromatic". By contrast, the term "aromatic"
means the dicarboxylic acid or diol contains an aromatic nucleus in
the backbone such as, for example, terephthalic acid or
2,6-naphthalene dicarboxylic acid. "Non-aromatic", therefore, is
intended to include both aliphatic and cycloaliphatic structures
such as, for example, diols and dicarboxylic acids, which contain
as a backbone a straight or branched chain or cyclic arrangement of
the constituent carbon atoms which may be saturated or paraffinic
in nature, unsaturated, i.e., containing non-aromatic carbon-carbon
double bonds, or acetylenic, i.e., containing carbon-carbon triple
bonds. Thus, in the context of the description and the claims of
the present invention, non-aromatic is intended to include linear
and branched, chain structures (referred to herein as "aliphatic")
and cyclic structures (referred to herein as "alicyclic" or
"cycloaliphatic"). The term "non-aromatic", however, is not
intended to exclude any aromatic substituents which may be attached
to the backbone of an aliphatic or cycloaliphatic diol or
dicarboxylic acid. In the present invention, the difunctional
carboxylic acid typically is a aliphatic dicarboxylic acid such as,
for example, adipic acid, or an aromatic dicarboxylic acid such as,
for example, terephthalic acid. The difunctional hydroxyl compound
may be cycloaliphatic diol such as, for example,
1,4-cyclohexanedimethanol, a linear or branched aliphatic diol such
as, for example, 1,4-butanediol, or an aromatic diol such as, for
example, hydroquinone.
[0103] The AAPE may be a linear or branched random copolyester
and/or chain extended copolyester comprising diol residues which
comprise the residues of one or more substituted or unsubstituted,
linear or branched, diols selected from aliphatic diols containing
2 to about 8 carbon atoms, polyalkylene ether glycols containing 2
to 8 carbon atoms, and cycloaliphatic diols containing about 4 to
about 12 carbon atoms. The substituted diols, typically, will
comprise 1 to about 4 substituents independently selected from
halo, C.sub.6-C.sub.10 aryl, and C.sub.1-C.sub.4 alkoxy. Examples
of diols which may be used include, but are not limited to,
ethylene glycol, diethylene glycol, propylene glycol,
1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, polyethylene
glycol, diethylene glycol, 2,2,4-trimethyl-1,6-hexanediol,
thiodiethanol, 1,3-cyclohexanedimethanol,
1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,
triethylene glycol, and tetraethylene glycol with the preferred
diols comprising one or more diols selected from 1,4-butanediol;
1,3-propanediol; ethylene glycol; 1,6-hexanediol; diethylene
glycol; or 1,4-cyclohexanedimethanol. The AAPE also comprises
diacid residues which contain about 35 to about 99 mole %, based on
the total moles of diacid residues, of the residues of one or more
substituted or unsubstituted, linear or branched, non-aromatic
dicarboxylic acids selected from aliphatic dicarboxylic acids
containing 2 to about 12 carbon atoms and cycloaliphatic acids
containing about 5 to about 10 carbon atoms. The substituted
non-aromatic dicarboxylic acids will typically contain 1 to about 4
substituents selected from halo, C.sub.6-C.sub.10 aryl, and
C.sub.1-C.sub.4 alkoxy. Non-limiting examples of non-aromatic
diacids include malonic, succinic, glutaric, adipic, pimelic,
azelaic, sebacic, fumaric, 2,2-dimethyl glutaric, suberic,
1,3-cyclopentanedicarboxylic, 1,4-cyclohexanedicarboxylic,
1,3-cyclohexanedicarboxylic, diglycolic, itaconic, maleic, and
2,5-norbornanedicarboxylic. In addition to the non-aromatic
dicarboxylic acids, the AAPE comprises about 1 to about 65 mole %,
based on the total moles of diacid residues, of the residues of one
or more substituted or unsubstituted aromatic dicarboxylic acids
containing 6 to about 10 carbon atoms. In the case where
substituted aromatic dicarboxylic acids are used, they will
typically contain 1 to about 4 substituents selected from halo,
C.sub.6-C.sub.10 aryl, and C.sub.1-C.sub.4 alkoxy. Non-limiting
examples of aromatic dicarboxylic acids which may be used in the
AAPE of our invention are terephthalic acid, isophthalic acid,
salts of 5-sulfoisophthalic acid, and 2,6-naphthalenedicarboxylic
acid. More preferably, the non-aromatic dicarboxylic acid will
comprise adipic acid, the aromatic dicarboxylic acid will comprise
terephthalic acid, and the diol will comprise 1,4-butanediol.
[0104] Other possible compositions for the AAPE's of our invention
are those prepared from the following diols and dicarboxylic acids
(or polyester-forming equivalents thereof such as diesters) in the
following mole percentages, based on 100 mole percent of a diacid
component and 100 mole percent of a diol component: [0105] (1)
glutaric acid (about 30 to about 75%); terephthalic acid (about 25
to about 70%); 1,4-butanediol (about 90 to 100%); and modifying
diol (0 about 10%); [0106] (2) succinic acid (about 30 to about
95%); terephthalic acid (about 5 to about 70%); 1,4-butanediol
(about 90 to 100%); and modifying diol (0 to about 10%); and [0107]
(3) adipic acid (about 30 to about 75%); terephthalic acid (about
25 to about 70%); 1,4-butanediol (about 90 to 100%); and modifying
diol (0 to about 10%).
[0108] The modifying diol preferably is selected from
1,4-cyclohexanedimethanol, triethylene glycol, polyethylene glycol
and neopentyl glycol. The most preferred AAPE's are linear,
branched or chain extended copolyesters comprising about 50 to
about 60 mole percent adipic acid residues, about 40 to about 50
mole percent terephthalic acid residues, and at least 95 mole
percent 1,4-butanediol residues. Even more preferably, the adipic
acid residues comprise about 55 to about 60 mole percent, the
terephthalic acid residues comprise about 40 to about 45 mole
percent, and the diol residues comprise about 95 mole percent
1,4-butanediol residues. Such compositions are commercially
available under the trademark EASTAR BIO.RTM. copolyester from
Eastman Chemical Company, Kingsport, Tenn., and under the trademark
ECOFLEX.RTM. from BASF Corporation.
[0109] Additional, specific examples of preferred AAPE's include a
poly(tetramethylene glutarate-co-terephthalate) containing (a) 50
mole percent glutaric acid residues, 50 mole percent terephthalic
acid residues, and 100 mole percent 1,4-butanediol residues, (b) 60
mole percent glutaric acid residues, 40 mole percent terephthalic
acid residues, and 100 mole percent 1,4-butanediol residues or (c)
40 mole percent glutaric acid residues, 60 mole percent
terephthalic acid residues, and 100 mole percent 1,4-butanediol
residues; a poly(tetramethylene succinate-co-terephthalate)
containing (a) 85 mole percent succinic acid residues, 15 mole
percent terephthalic acid residues, and 100 mole percent
1,4-butanediol residues or (b) 70 mole percent succinic acid
residues, 30 mole percent terephthalic acid residues, and 100 mole
percent 1,4-butanediol residues; a poly(ethylene
succinate-co-terephthalate) containing 70 mole percent succinic
acid residues, 30 mole percent terephthalic acid residues, and 100
mole percent ethylene glycol residues; and a poly(tetramethylene
adipate-co-terephthalate) containing (a) 85 mole percent adipic
acid residues, 15 mole percent terephthalic acid residues, and 100
mole percent 1,4-butanediol residues; or (b) 55 mole percent adipic
acid residues, 45 mole percent terephthalic acid residues, and 100
mole percent 1,4-butanediol residues.
[0110] The AAPE preferably comprises from about 10 to about 1,000
repeating units and preferably, from about 15 to about 600
repeating units. The AAPE may have an inherent viscosity of about
0.4 to about 2.0 dL/g, or more preferably about 0.7 to about 1.6
dL/g, as measured at a temperature of 25.degree. C. using a
concentration of 0.5 gram copolyester in 100 ml of a 60/40 by
weight solution of phenol/tetrachloroethane.
[0111] The AAPE, optionally, may contain the residues of a
branching agent. The mole percentage ranges for the branching agent
are from about 0 to about 2 mole %, preferably about 0.1 to about 1
mole %, and most preferably about 0.1 to about 0.5 mole % based on
the total moles of diacid or diol residues (depending on whether
the branching agent contains carboxyl or hydroxyl groups). The
branching agent preferably has a weight average molecular weight of
about 50 to about 5000, more preferably about 92 to about 3000, and
a functionality of about 3 to about 6. The branching agent, for
example, may be the esterified residue of a polyol having 3 to 6
hydroxyl groups, a polycarboxylic acid having 3 or 4 carboxyl
groups (or ester-forming equivalent groups) or a hydroxy acid
having a total of 3 to 6 hydroxyl and carboxyl groups. In addition,
the AAPE may be branched by the addition of a peroxide during
reactive extrusion.
[0112] Each segment of the water non-dispersible polymer may be
different from others in fineness and may be arranged in any shaped
or engineered cross-sectional geometry known to persons skilled in
the art. For example, the sulfopolyester and a water-nondispersible
polymer may be used to prepare a bicomponent fiber having an
engineered geometry such as, for example, a side-by-side,
"islands-in-the-sea", segmented pie, other splitables, sheath/core,
or other configurations known to persons skilled in the art. Other
multicomponent configurations are also possible. Subsequent removal
of a side, the "sea", or a portion of the "pie" can result in very
fine fibers. The process of preparing bicomponent fibers also is
well known to persons skilled in the art. In a bicomponent fiber,
the sulfopolyester fibers of this invention may be present in
amounts of about 10 to about 90 weight % and will generally be used
in the sheath portion of sheath/core fibers. The other component
may be from a wide range of other polymeric materials such as, for
example, poly(ethylene)terephthalate, poly(butylene)terephthalate,
poly(trimethylene)terephthalate, polylactides and the like as well
as polyolefins, cellulose esters, and polyamides. Typically, when a
water-insoluble or water-nondispersible polymer is used, the
resulting bicomponent or multicomponent fiber is not completely
water-dispersible. Side by side combinations with significant
differences in thermal shrinkage can be utilized for the
development of a spiral crimp. If crimping is desired, a saw tooth
or stuffer box crimp is generally suitable for many applications.
If the second polymer component is in the core of a sheath/core
configuration, such a core optionally may be stabilized.
[0113] The sulfopolyesters are particularly useful for fibers
having an "islands-in-the-sea" or "segmented pie" cross section as
they only requires neutral or slightly acidic (i.e., "soft" water)
to disperse, as compared to the caustic-containing solutions that
are sometimes required to remove other water dispersible polymers
from multicomponent fibers. Thus another aspect of our invention is
a multicomponent fiber, comprising: [0114] A) a water dispersible
sulfopolyester having a glass transition temperature (Tg) of at
least 57.degree. C., the sulfopolyester comprising: [0115] (i)
about 50 to about 96 mole % of one or more residues of isophthalic
acid or terephthalic acid, based on the total acid residues; [0116]
(ii) about 4 to about 30 mole %, based on the total acid residues,
of a residue of sodiosulfoisophthalic acid; [0117] (iii) one or
more diol residues wherein at least 25 mole %, based on the total
diol residues, is a poly(ethylene glycol) having a structure
[0117] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; [0118] (iv) 0 to about 20 mole %,
based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; and [0119]
(B) a plurality of segments comprising one or more
water-nondispersible polymers immiscible with the sulfopolyester,
wherein the segments are substantially isolated from each other by
the sulfopolyester intervening between the segments; [0120] wherein
the fiber has an islands-in-the-sea or segmented pie cross section
and contains less than 10 weight percent of a pigment or filler,
based on the total weight of the fiber. The dicarboxylic acids,
diols, sulfopolyester, sulfomonomers, branching monomers residues,
and water non-dispersible polymers are as described previously. For
multicomponent fibers, it is advantageous that sulfopolyester have
a Tg of at least 57.degree. C. The sulfopolyester may be a single
sulfopolyester or a blend of one or more sulfopolyester polymers.
Further examples of glass transition temperatures that may be
exhibited by the sulfopolyester or sulfopolyester blends are at
least 65.degree. C., at least 70.degree. C., at least 75.degree.
C., at least 85.degree. C., and at least 90.degree. C. For example,
the sulfopolyester may comprise about 75 to about 96 mole % of one
or more residues of isophthalic acid or terephthalic acid and about
25 to about 95 mole % of a residue of diethylene glycol. As
described hereinabove, examples of the water-nondispersible
polymers are polyolefins, polyesters, polyamides, polylactides,
polycaprolactone, polycarbonate, polyurethane, and polyvinyl
chloride. In addition, the water-nondispersible polymer may be
biodegradable or biodisintegratable. For example, the
water-nondispersible polymer may be an aliphatic-aromatic polyester
as described previously.
[0121] Our novel multicomponent fiber may be prepared by any number
of methods known to persons skilled in the art. The present
invention thus provides a process for a multicomponent fiber having
a shaped cross section comprising: spinning a water dispersible
sulfopolyester having a glass transition temperature (Tg) of at
least 57.degree. C. and one or more water-nondispersable polymers
immiscible with the sulfopolyester into a fiber, the sulfopolyester
comprising: [0122] (i) residues of one or more dicarboxylic acids;
[0123] (ii) about 4 to about 40 mole %, based on the total
repeating units, of residues of at least one sulfomonomer having 2
functional groups and one or more sulfonate groups attached to an
aromatic or cycloaliphatic ring wherein the functional groups are
hydroxyl, carboxyl, or a combination thereof; [0124] (iii) one or
more diol residues wherein at least 25 mole %, based on the total
diol residues, is a poly(ethylene glycol) having a structure
[0124] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0125] (iv) 0 to about 25 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; wherein
the fiber has a plurality of segments comprising the
water-nondispersable polymers and the segments are substantially
isolated from each other by the sulfopolyester intervening between
the segments and the fiber contains less than 10 weight percent of
a pigment or filler, based on the total weight of the fiber. For
example, the multicomponent fiber may be prepared by melting the
sulfopolyester and one or more water non-dispersible polymers in
separate extruders and directing the individual polymer flows into
one spinneret or extrusion die with a plurality of distribution
flow paths such that the water non-dispersible polymer component
form small segments or thin strands which are substantially
isolated from each other by the intervening sulfopolyester. The
cross section of such a fiber may be, for example, a segmented pie
arrangement or an islands-in-the-sea arrangement. In another
example, the sulfopolyester and one or more water non-dispersible
polymers are separately fed to the spinneret orifices and then
extruded in sheath-core form in which the water non-dispersible
polymer forms a "core" that is substantially enclosed by the
sulfopolyester "sheath" polymer. In the case of such concentric
fibers, the orifice supplying the "core" polymer is in the center
of the spinning orifice outlet and flow conditions of core polymer
fluid are strictly controlled to maintain the concentricity of both
components when spinning. Modifications in spinneret orifices
enable different shapes of core and/or sheath to be obtained within
the fiber cross-section. In yet another example, a multicomponent
fiber having a side-by-side cross section or configuration may be
produced by coextruding the water dispersible sulfopolyester and
water non-dispersible polymer through orifices separately and
converging the separate polymer streams at substantially the same
speed to merge side-by-side as a combined stream below the face of
the spinneret; or (2) by feeding the two polymer streams separately
through orifices, which converge at the surface of the spinneret,
at substantially the same speed to merge side-by-side as a combined
stream at the surface of the spinneret. In both cases, the velocity
of each polymer stream, at the point of merge, is determined by its
metering pump speed, the number of orifices, and the size of the
orifice.
[0126] The dicarboxylic acids, diols, sulfopolyester,
sulfomonomers, branching monomers residues, and water
non-dispersible polymers are as described previously. The
sulfopolyester has a glass transition temperature of at least
60.degree. C. Further examples of glass transition temperatures
that may be exhibited by the sulfopolyester or sulfopolyester blend
are at least 65.degree. C., at least 70.degree. C., at least
75.degree. C., at least 85.degree. C., and at least 90.degree. C.
In one example, the sulfopolyester may comprise about 50 to about
96 mole % of one or more residues of isophthalic acid or
terephthalic acid, based on the total acid residues; and about 4 to
about 30 mole %, based on the total acid residues, of a residue of
sodiosulfoisophthalic acid; and 0 to about 20 mole %, based on the
total repeating units, of residues of a branching monomer having 3
or more functional groups wherein the functional groups are
hydroxyl, carboxyl, or a combination thereof. In another example,
the sulfopolyester may comprise about 75 to about 96 mole % of one
or more residues of isophthalic acid or terephthalic acid and about
25 to about 95 mole % of a residue of diethylene glycol. As
described hereinabove, examples of the water-nondispersible
polymers are polyolefins, polyesters, polyamides, polylactides,
polycaprolactone, polycarbonate, polyurethane, and polyvinyl
chloride. In addition, the water-nondispersible polymer may be
biodegradable or biodisintegratable. For example, the
water-nondispersible polymer may be an aliphatic-aromatic polyester
as described previously. Examples of shaped cross sections include,
but are not limited to, islands-in-the-sea, side-by-side,
sheath-core, or segmented pie configurations.
[0127] Typically, upon exiting the spinneret, the fibers are
quenched with a cross flow of air whereupon the fibers solidify.
Various finishes and sizes may be applied to the fiber at this
stage. The cooled fibers, typically, are subsequently drawn and
wound up on a take up spool. Other additives may be incorporated in
the finish in effective amounts like emulsifiers, antistatics,
antimicrobials, antifoams, lubricants, thermostabilizers, UV
stabilizers, and the like.
[0128] Optionally, the drawn fibers may be textured and wound-up to
form a bulky continuous filament. This one-step technique is known
in the art as spin-draw-texturing. Other embodiments include flat
filament (non-textured) yarns, or cut staple fiber, either crimped
or uncrimped.
[0129] The sulfopolyester may be later removed by dissolving the
interfacial layers or pie segments and leaving the smaller
filaments or microdenier fibers of the water non-dispersible
polymer(s). Our invention thus provides a process for microdenier
fibers comprising: [0130] A. spinning a water dispersible
sulfopolyester having a glass transition temperature (Tg) of at
least 57.degree. C. and one or more water-nondispersable polymers
immiscible with the sulfopolyester into multicomponent fibers, the
sulfopolyester comprising: [0131] (i) about 50 to about 96 mole %
of one or more residues of isophthalic acid or terephthalic acid,
based on the total acid residues; [0132] (ii) about 4 to about 30
mole %, based on the total acid residues, of a residue of
sodiosulfoisophthalic acid; [0133] (iii) one or more diol residues
wherein at least 25 mole %, based on the total diol residues, is a
poly(ethylene glycol) having a structure
[0133] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0134] (iv) 0 to about 20 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof; [0135]
wherein the fibers have a plurality of segments comprising the
water-nondispersable polymers wherein the segments are
substantially isolated from each other by the sulfopolyester
intervening between the segments and the fibers contain less than
10 weight percent of a pigment or filler, based on the total weight
of the fibers; and [0136] B. contacting the multicomponent fibers
with water to remove the sulfopolyester thereby forming microdenier
fibers. Typically, the multicomponent fiber is contacted with water
at a temperature of about 25.degree. C. to about 100.degree. C.,
preferably about 50.degree. C. to about 80.degree. C. for a time
period of from about 10 to about 600 seconds whereby the
sulfopolyester is dissipated or dissolved. After removal of the
sulfopolyester, the remaining microfibers typically will have an
average fineness of 1 d/f or less, typically, 0.5 d/f or less, or
more typically, 0.1 d/f or less. Typical applications of these
remaining microfibers include artificial leathers, suedes, wipes,
and filter media. The ionic nature of sulfopolyesters also results
in advantageously poor "solubility" in saline media, such as body
fluids. Such properties are desirable in personal care products and
cleaning wipes that are flushable or otherwise disposed in sanitary
sewage systems. Selected sulfopolyesters have also been utilized as
dispersing agents in dye baths and soil redeposition preventative
agents during laundry cycles.
[0137] The instant invention also includes a fibrous article
comprising the water-dispersible fiber, the multicomponent fiber,
or the microdenier fibers described hereinabove. The term "fibrous
article" is understood to mean any article having or resembling
fibers. Non-limiting examples of fibrous articles include
multifilament fibers, yarns, cords, tapes, fabrics, melt blown
webs, spunbonded webs, thermobonded webs, hydroentangled webs,
nonwoven webs and fabrics, and combinations thereof; items having
one or more layers of fibers, such as, for example, multilayer
nonwovens, laminates, and composites from such fibers, gauzes,
bandages, diapers, training pants, tampons, surgical gowns and
masks, feminine napkins; and the like. Further, the fibrous
articles may include replacement inserts for various personal
hygiene and cleaning products. The fibrous article of the present
invention may be bonded, laminated, attached to, or used in
conjunction with other materials which may or may not be
water-dispersible. The fibrous article, for example, a nonwoven
fabric layer, may be bonded to a flexible plastic film or backing
of a water-nondispersible material, such as polyethylene. Such an
assembly, for example, could be used as one component of a
disposable diaper. In addition, the fibrous article may result from
overblowing fibers onto another substrate to form highly assorted
combinations of engineered melt blown, spunbond, film, or membrane
structures.
[0138] The fibrous articles of the instant invention include
nonwoven fabrics and webs. A nonwoven fabric is defined as a fabric
made directly from fibrous webs without weaving or knitting
operations. For example, the multicomponent fiber of the present
invention may be formed into a fabric by any known fabric forming
process like knitting, weaving, needle punching, and
hydroentangling. The resulting fabric or web may be converted into
a microdenier fiber web by exerting sufficient force to cause the
multicomponent fibers to split or by contacting the web with water
to remove the sulfopolyester leaving the remaining microdenier
fibers behind. Our invention thus provides a process for a
microdenier fiber web, comprising: [0139] A. spinning a water
dispersible sulfopolyester having a glass transition temperature
(Tg) of at least 57.degree. C. and one or more water-nondispersable
polymers immiscible with the sulfopolyester into multicomponent
fibers, the sulfpolyester comprising: [0140] (i) about 50 to about
96 mole % of one or more residues of isophthalic acid or
terephthalic acid, based on the total acid residues; [0141] (ii)
about 4 to about 30 mole %, based on the total acid residues, of a
residue of sodiosulfoisophthalic acid; [0142] (iii) one or more
diol residues wherein at least 25 mole %, based on the total diol
residues, is a poly(ethylene glycol) having a structure
[0142] H--(OCH.sub.2--CH.sub.2).sub.n--OH wherein n is an integer
in the range of 2 to about 500; and [0143] (iv) 0 to about 20 mole
%, based on the total repeating units, of residues of a branching
monomer having 3 or more functional groups wherein the functional
groups are hydroxyl, carboxyl, or a combination thereof. [0144]
wherein the multicomponent fibers have a plurality of segments
comprising the water-nondispersable polymers wherein the segments
are substantially isolated from each other by the sulfopolyester
intervening between the segments; and the fiber contains less than
10 weight percent of a pigment or filler, based on the total weight
of the fiber; [0145] B. overlapping and collecting the
multicomponent fibers of Step A to form a nonwoven web; and [0146]
C. contacting the nonwoven web with water to remove the
sulfopolyester thereby forming a microdenier fiber web.
[0147] The nonwoven assembly is held together by 1) mechanical
fiber cohesion and interlocking in a web or mat; 2) various
techniques of fusing of fibers, including the use of binder fibers,
utilizing the thermoplastic properties of certain polymers and
polymer blends; 3) use of a binding resin such as starch, casein, a
cellulose derivative, or a synthetic resin, such as an acrylic
latex or urethane; 4) powder adhesive binders; or 5) combinations
thereof. The fibers are often deposited in a random manner,
although orientation in one direction is possible, followed by
bonding using one of the methods described above.
[0148] The fibrous articles of our invention further also may
comprise one or more layers of water-dispersible fibers,
multicomponent fibers, or microdenier fibers. The fiber layers may
be one or more nonwoven fabric layers, a layer of loosely bound
overlapping fibers, or a combination thereof. In addition, the
fibrous articles may include personal and health care products such
as, but not limited to, child care products, such as infant
diapers; child training pants; adult care products, such as adult
diapers and adult incontinence pads; feminine care products, such
as feminine napkins, panty liners, and tampons; wipes;
fiber-containing cleaning products; medical and surgical care
products, such as medical wipes, tissues, gauzes, examination bed
coverings, surgical masks, gowns, bandages, and wound dressings;
fabrics; elastomeric yarns, wipes, tapes, other protective
barriers, and packaging material. The fibrous articles may be used
to absorb liquids or may be pre-moistened with various liquid
compositions and used to deliver these compositions to a surface.
Non-limiting examples of liquid compositions include detergents;
wetting agents; cleaning agents; skin care products, such as
cosmetics, ointments, medications, emollients, and fragrances. The
fibrous articles also may include various powders and particulates
to improve absorbency or as delivery vehicles. Examples of powders
and particulates include, but are not limited to, talc, starches,
various water absorbent, water-dispersible, or water swellable
polymers, such as super absorbent polymers, sulfopolyesters, and
poly(vinylalcohols), silica, pigments, and microcapsules. Additives
may also be present, but are not required, as needed for specific
applications. Examples of additives include, but are not limited
to, oxidative stabilizers, UV absorbers, colorants, pigments,
opacifiers (delustrants), optical brighteners, fillers, nucleating
agents, plasticizers, viscosity modifiers, surface modifiers,
antimicrobials, disinfectants, cold flow inhibitors, branching
agents, and catalysts.
[0149] In addition to being water-dispersible, the fibrous articles
described above may be flushable. The term "flushable" as used
herein means capable of being flushed in a conventional toilet, and
being introduced into a municipal sewage or residential septic
system, without causing an obstruction or blockage in the toilet or
sewage system.
[0150] The fibrous article may further comprise a water-dispersible
film comprising a second water-dispersible polymer. The second
water-dispersible polymer may be the same as or different from the
previously described water-dispersible polymers used in the fibers
and fibrous articles of the present invention. In one embodiment,
for example, the second water-dispersible polymer may be an
additional sulfopolyester which, in turn, comprises: (i) about 50
to about 96 mole % of one or more residues of isophthalic acid or
terephthalic acid, based on the total acid residues; (ii) about 4
to about 30 mole %, based on the total acid residues, of a residue
of sodiosulfoisophthalic acid; (iii) one or more diol residues
wherein at least 15 mole %, based on the total diol residues, is a
poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500; (iv) 0 to
about 20 mole %, based on the total repeating units, of residues of
a branching monomer having 3 or more functional groups wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof.
The additional sulfopolyester may be blended with one or more
supplemental polymers, as described hereinabove, to modify the
properties of the resulting fibrous article. The supplemental
polymer may or may not be water-dispersible depending on the
application. The supplemental polymer may be miscible or immiscible
with the additional sulfopolyester.
[0151] The additional sulfopolyester may contain other
concentrations of isophthalic acid residues, for example, about 60
to about 95 mole %, and about 75 to about 95 mole %. Further
examples of isophthalic acid residue concentrations ranges are
about 70 to about 85 mole %, about 85 to about 95 mole % and about
90 to about 95 mole %. The additional sulfopolyester also may
comprise about 25 to about 95 mole % of the residues of diethylene
glycol. Further examples of diethylene glycol residue concentration
ranges include about 50 to about 95 mole %, about 70 to about 95
mole %, and about 75 to about 95 mole %. The additional
sulfopolyester also may include the residues of ethylene glycol
and/or 1,4-cyclohexanedimethanol. Typical concentration ranges of
CHDM residues are about 10 to about 75 mole %, about 25 to about 65
mole %, and about 40 to about 60 mole %. Typical concentration
ranges of ethylene glycol residues are about 10 to about 75 mole %,
about 25 to about 65 mole %, and about 40 to about 60 mole %. In
another embodiment, the additional sulfopolyester comprises is
about 75 to about 96 mole % of the residues of isophthalic acid and
about 25 to about 95 mole % of the residues of diethylene
glycol.
[0152] According to the invention, the sulfopolyester film
component of the fibrous article may be produced as a monolayer or
multilayer film. The monolayer film may be produced by conventional
casting techniques. The multilayered films may be produced by
conventional lamination methods or the like. The film may be of any
convenient thickness, but total thickness will normally be between
about 2 and about 50 mil.
[0153] The film-containing fibrous articles may include one or more
layers of water-dispersible fibers as described above. The fiber
layers may be one or more nonwoven fabric layers, a layer of
loosely bound overlapping fibers, or a combination thereof. In
addition, the film-containing fibrous articles may include personal
and health care products as described hereinabove.
[0154] As described previously, the fibrous articles also may
include various powders and particulates to improve absorbency or
as delivery vehicles. Thus, in one embodiment, our fibrous article
comprises a powder comprising a third water-dispersible polymer
that may be the same as or different from the water-dispersible
polymer components described previously herein. Other examples of
powders and particulates include, but are not limited to, talc,
starches, various water absorbent, water-dispersible, or water
swellable polymers, such as poly(acrylonitiles), sulfopolyesters,
and poly(vinyl alcohols), silica, pigments, and microcapsules.
[0155] Our novel fiber and fibrous articles have many possible uses
in addition to the applications described above. One novel
application involves the melt blowing a film or nonwoven fabric
onto flat, curved, or shaped surfaces to provide a protective
layer. One such layer might provide surface protection to durable
equipment during shipping. At the destination, before putting the
equipment into service, the outer layers of sulfopolyester could be
washed off. A further embodiment of this general application
concept could involve articles of personal protection to provide
temporary barrier layers for some reusable or limited use garments
or coverings. For the military, activated carbon and chemical
absorbers could be sprayed onto the attenuating filament pattern
just prior to the collector to allow the melt blown matrix to
anchor these entities on the exposed surface. The chemical
absorbers can even be changed in the forward operations area as the
threat evolves by melt blowing on another layer.
[0156] A major advantage inherent to sulfopolyesters is the facile
ability to remove or recover the polymer from aqueous dispersions
via flocculation or precipitation by adding ionic moieties (i.e.,
salts). Other methods, such as pH adjustment, adding nonsolvents,
freezing, and so forth may also be employed. Therefore, fibrous
articles, such as outer wear protective garments, after successful
protective barrier use and even if the polymer is rendered as
hazardous waste, can potentially be handled safely at much lower
volumes for disposal using accepted protocols, such as
incineration.
[0157] Undissolved or dried sulfopolyesters are known to form
strong adhesive bonds to a wide array of substrates, including, but
not limited to fluff pulp, cotton, acrylics, rayon, lyocell, PLA
(polylactides), cellulose acetate, cellulose acetate propionate,
poly(ethylene)terephthalate, poly(butylene)terephthalate,
poly(trimethylene)terephthalate, poly(cyclohexylene)terephthalate,
copolyesters, polyamides (nylons), stainless steel, aluminum,
treated polyolefins, PAN (polyacrylonitriles), and polycarbonates.
Thus, our nonwoven fabrics may be used as laminating adhesives or
binders that may be bonded by known techniques, such as thermal,
radio frequency (RF), microwave, and ultrasonic methods. Adaptation
of sulfopolyesters to enable RF activation is disclosed in a number
of recent patents. Thus, our novel nonwoven fabrics may have dual
or even multifunctionality in addition to adhesive properties. For
example, a disposable baby diaper could be obtained where a
nonwoven of the present invention serves as both an
water-responsive adhesive as well as a fluid managing component of
the final assembly.
[0158] Our invention also provides a process for water-dispersible
fibers comprising (I) heating a water-dispersible polymer
composition to a temperature above its flow point, wherein the
polymer composition comprises (i) residues of one or more
dicarboxylic acids; (ii) about 4 to about 40 mole %, based on the
total repeating units, of residues of at least one sulfomonomer
having 2 functional groups and one or more metal sulfonate groups
attached to an aromatic or cycloaliphatic ring wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof;
and (iii) one or more diol residues wherein at least 20 mole %,
based on the total diol residues, is a poly(ethylene glycol) having
a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500; (iv) 0 to
about 25 mole %, based on the total repeating units, of residues of
a branching monomer having 3 or more functional groups wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof;
wherein the polymer composition contains less than 10 weight
percent of a pigment or filler, based on the total weight of the
polymer composition; and (II) melt spinning filaments. As described
hereinabove, a water-dispersible polymer, optionally, may be
blended with the sulfopolyester. In addition, a
water-nondispersible polymer, optionally, may be blended with the
sulfopolyester to form a blend such that blend is an immiscible
blend. The term "flow point", as used herein, means the temperature
at which the viscosity of the polymer composition permits extrusion
or other forms of processing through a spinneret or extrusion die.
The dicarboxylic acid residue may comprise from about 60 to about
100 mole % of the acid residues depending on the type and
concentration of the sulfomonomer. Other examples of concentration
ranges of dicarboxylic acid residues are from about 60 mole % to
about 95 mole % and about 70 mole % to about 95 mole %. The
preferred dicarboxylic acid residues are isophthalic, terephthalic,
and 1,4-cyclohexanedicarboxylic acids or if diesters are used,
dimethyl terephthalate, dimethyl isophthalate, and
dimethyl-1,4-cyclohexanedicarboxylate with the residues of
isophthalic and terephthalic acid being especially preferred.
[0159] The sulfomonomer may be a dicarboxylic acid or ester thereof
containing a sulfonate group, a diol containing a sulfonate group,
or a hydroxy acid containing a sulfonate group. Additional examples
of concentration ranges for the sulfomonomer residues are about 4
to about 25 mole %, about 4 to about 20 mole %, about 4 to about 15
mole %, and about 4 to about 10 mole %, based on the total
repeating units. The cation of the sulfonate salt may be a metal
ion such as Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.++, Ca.sup.++,
Ni.sup.++, Fe.sup.++, and the like. Alternatively, the cation of
the sulfonate salt may be non-metallic such as a nitrogenous base
as described previously. Examples of sulfomonomer residues which
may be used in the process of the present invention are the metal
sulfonate salt of sulfophthalic acid, sulfoterephthalic acid,
sulfoisophthalic acid, or combinations thereof. Another example of
sulfomonomer which may be used is 5-sodiosulfoisophthalic acid or
esters thereof. If the sulfomonomer residue is from
5-sodiosulfoisophthalic acid, typical sulfomonomer concentration
ranges are about 4 to about 35 mole %, about 8 to about 30 mole %,
and about 10 to 25 mole %, based on the total acid residues.
[0160] The sulfopolyester of our includes one or more diol residues
which may include aliphatic, cycloaliphatic, and aralkyl glycols.
The cycloaliphatic diols, for example, 1,3- and
1,4-cyclohexanedimethanol, may be present as their pure cis or
trans isomers or as a mixture of cis and trans isomers.
Non-limiting examples of lower molecular weight polyethylene
glycols, e.g., wherein n is from 2 to 6, are diethylene glycol,
triethylene glycol, and tetraethylene glycol. Of these lower
molecular weight glycols, diethylene and triethylene glycol are
most preferred. The sulfopolyester may optionally include a
branching monomer. Examples of branching monomers are as described
hereinabove. Further examples of branching monomer concentration
ranges are from 0 to about 20 mole % and from 0 to about 10 mole %.
The sulfpolyester of our novel process has a Tg of at least
25.degree. C. Further examples of glass transition temperatures
exhibited by the sulfopolyester are at least 30.degree. C., at
least 35.degree. C., at least 40.degree. C., at least 50.degree.
C., at least 60.degree. C., at least 65.degree. C., at least
80.degree. C., and at least 90.degree. C. Although other Tg's are
possible, typical glass transition temperatures of the dry
sulfopolyesters our invention are about 30.degree. C., about
48.degree. C., about 55.degree. C., about 65.degree. C., about
70.degree. C., about 75.degree. C., about 85.degree. C., and about
90.degree. C.
[0161] The water-dispersible fibers are prepared by a melt blowing
process. The polymer is melted in an extruder and forced through a
die. The extrudate exiting the die is rapidly attenuated to
ultrafine diameters by hot, high velocity air. The orientation,
rate of cooling, glass transition temperature (T.sub.g), and rate
of crystallization of the fiber are important because they affect
the viscosity and processing properties of the polymer during
attenuation. The filament is collected on a renewable surface, such
as a moving belt, cylindrical drum, rotating mandrel, and so forth.
Predrying of pellets (if needed), extruder zone temperature, melt
temperature, screw design, throughput rate, air temperature, air
flow (velocity), die air gap and set back, nose tip hole size, die
temperature, die-to-collector (DCP) distance, quenching
environment, collector speed, and post treatments are all factors
that influence product characteristics such as filament diameters,
basis weight, web thickness, pore size, softness, and shrinkage.
The high velocity air also may be used to move the filaments in a
somewhat random fashion that results in extensive interlacing. If a
moving belt is passed under the die, a nonwoven fabric can be
produced by a combination of over-lapping laydown, mechanical
cohesiveness, and thermal bonding of the filaments. Overblowing
onto another substrate, such as a spunbond or backing layer, is
also possible. If the filaments are taken up on an rotating
mandrel, a cylindrical product is formed. A water-dispersible fiber
lay-down can also be prepared by the spunbond process.
[0162] The instant invention, therefore, further provides a process
for water-dispersible, nonwoven fabric comprising (A) heating a
water-dispersible polymer composition to a temperature above its
flow point, wherein the polymer composition comprises: (i) residues
of one or more dicarboxylic acids; (ii) about 4 to about 40 mole %,
based on the total repeating units, of residues of at least one
sulfomonomer having 2 functional groups and one or more metal
sulfonate groups attached to an aromatic or cycloaliphatic ring
wherein the functional groups are hydroxyl, carboxyl, or a
combination thereof; (iii) one or more diol residues wherein at
least 20 mole %, based on the total diol residues, is a
poly(ethylene glycol) having a structure
H--(OCH.sub.2--CH.sub.2).sub.n--OH
wherein n is an integer in the range of 2 to about 500; (iv) 0 to
about 25 mole %, based on the total repeating units, of residues of
a branching monomer having 3 or more functional groups wherein the
functional groups are hydroxyl, carboxyl, or a combination thereof;
wherein the sulfopolyester has a glass transition temperature (Tg)
of at least 25.degree. C.; wherein the polymer composition contains
less than 10 weight percent of a pigment or filler, based on the
total weight of the polymer composition; (B) melt-spinning
filaments; and (C) overlapping and collecting the filaments of Step
B to form a nonwoven fabric. As described hereinabove, a
water-dispersible polymer, optionally, may be blended with the
sulfopolyester. In addition, a water-nondispersible polymer,
optionally, may be blended with the sulfopolyester to form a blend
such that blend is an immiscible blend. The dicarboxylic acid,
sulfomonomer, and branching monomer residues are as described
previously. The sulfpolyester has a Tg of at least 25.degree. C.
Further examples of glass transition temperatures exhibited by the
sulfopolyester are at least 30.degree. C., at least 35.degree. C.,
at least 40.degree. C., at least 50.degree. C., at least 60.degree.
C., at least 65.degree. C., at least 80.degree. C., and at least
90.degree. C. Although other Tg's are possible, typical glass
transition temperatures of the dry sulfopolyesters our invention
are about 30.degree. C., about 48.degree. C., about 55.degree. C.,
about 65.degree. C., about 70.degree. C., about 75.degree. C.,
about 85.degree. C., and about 90.degree. C. The invention is
further illustrated by the following examples.
EXAMPLES
[0163] All pellet samples were predried under vacuum at room
temperature for at least 12 hours. The dispersion times shown in
Table 3 are for either complete dispersion or dissolution of the
nonwoven fabric samples. The abbreviation "CE", used in Tables 2
and 3 mean "comparative example".
Example 1
[0164] A sulfopolyester containing 76 mole %, isophthalic acid, 24
mole % of sodiosulfoisophthalic acid, 76 mole % diethylene glycol,
and 24 mole % 1,4-cyclohexanedimethanol with an Ih.V. of 0.29 and a
Tg of 48.degree. C. was meltblown through a nominal 6-inch die (30
holes/inch in the nosepiece) onto a cylindrical collector using the
conditions shown in Table 1. Interleafing paper was not required. A
soft, handleable, flexible web was obtained that did not block
during the roll winding operation. Physical properties are provided
in Table 2. A small piece (1''.times.3'') of the nonwoven fabric
was easily dispersed in both room temperature (RT) and 50.degree.
C. water with slight agitation as shown by data in Table 3.
TABLE-US-00001 TABLE 1 Melt Blowing Conditions Operating Condition
Typical Value Die Configuration Die tip hole diameter 0.0185 inches
Number of holes 120 Air gap 0.060 inches Set back 0.060 inches
Extruder Barrel Temperatures (.degree. F.) Zone 1 350 Zone 2 510
Zone 3 510 Die Temperatures (.degree. F.) Zone 4 510 Zone 5 510
Zone 6 510 Zone 7 510 Zone 8 510 Air Temperatures (.degree. F.)
Furnace exit 1 350 Furnace exit 2 700 Furnace exit 3 700 Die
530-546 Extrusion Conditions Air pressure 3.0 psi Melt pressure
after pump 99-113 psi Take Up Conditions Throughput 0.3 g/hole/min
0.5 g/hole/min Basis weight 36 g/m.sup.2 Collector speed 20 ft/min
Collector distance 12 inches
TABLE-US-00002 TABLE 2 Physical Properties of Nonwovens Filament
Diameter Exam- (.mu.m) IhV Tg/Tm (.degree. C.) ple Minimum Maximum
Average (before/after) (sulfopoly./PP) 1 5 18 8.7 0.29/0.26 39/not
applicable 2 3 11 7.7 0.40/0.34 36/not applicable CE 1 2 20 8 Not
36/163 measured CE 2 4 10 7 Not 36/164 measured CE 3 4 11 6 Not
35/161 measured
TABLE-US-00003 TABLE 3 Dispersbility of Nonwovens Water Initial
Significant Complete Temperature Disintegration Disintegration
Dispersion Example (.degree. C.) (minutes) (minutes) (minutes) 1 23
<0.25 1 2 50 <0.17 0.5 1 2 23 8 14 19 50 <0.5 5 8 80
<0.5 2 5 CE 1 23 0.5 >15 No dispersion of PP 50 0.5 >15 No
dispersion of PP CE 2 23 0.5 >15 No dispersion of PP 50 0.5
>15 No dispersion of PP CE 3 23 <0.5 6 No dispersion of PP 50
<0.5 4 No dispersion of PP
Example 2
[0165] A sulfopolyester containing 89 mole %, isophthalic acid, 11
mole % of sodiosulfoisophthalic acid, 72 mole % diethylene glycol,
and 28 mole % ethylene glycol with an Ih.V. of 0.4 and a Tg of
35.degree. C. was meltblown through a 6-inch die using conditions
similar to those in Table 1. A soft, handleable, flexible web was
obtained that did not block during a roll winding operation.
Physical properties are provided in Table 2. A small piece
(1''.times.2'') of the nonwoven fabric was easily and completely
dispersed at 50.degree. C. and 80.degree. C.; at RT (23.degree.
C.), the fabric required a longer period of time for complete
dispersion as shown by the data in Table 3.
[0166] It was found that the compositions in Examples 1 and 2 can
be overblown onto other nonwoven substrates. It is also possible to
condense and wrap shaped or contoured forms that are used instead
of conventional web collectors. Thus, it is possible to obtain
circular "roving" or plug forms of the webs.
Comparative Examples 1-3
[0167] Pellets of a sulfopolyester containing 89 mole %,
isophthalic acid, 11 mole % of sodiosulfoisophthalic acid, 72 mole
% diethylene glycol, and 28 mole % ethylene glycol with an Ih.V. of
0.4 and a Tg of 35.degree. C. were combined with polypropylene
(BaseII PF 008) pellets in bicomponent ratios (by wt %) of:
[0168] 75 PP:25 sulfopolyester (Example 3)
[0169] 50 PP:50 sulfopolyester (Example 4)
[0170] 25 PP:75 sulfopolyester (Example 5)
[0171] The PP had a MFR (melt flow rate) of 800. A melt blowing
operation was performed on a line equipped with a 24-inch wide die
to yield handleable, soft, flexible, but nonblocking webs with the
physical properties provided in Table 2. Small pieces
(1''.times.4'') of nonwoven fabric readily disintegrated as
reported in Table 3. None of the fibers, however, were completely
water-dispersible because of the insoluble polypropylene
component.
Example 3
[0172] A circular piece (4'' diameter) of the nonwoven produced in
Example 2 was used as an adhesive layer between two sheets of
cotton fabric. A Hannifin melt press was used to fuse the two
sheets of cotton together by applying a pressure 35 psig at
200.degree. C. for 30 seconds. The resultant assembly exhibited
exceptionally strong bond strength. The cotton substrate shredded
before adhesive or bond failure. Similar results have also been
obtained with other cellulosics and with PET polyester substrates.
Strong bonds were also produced by ultrasonic bonding
techniques.
Comparative Example 4
[0173] A PP (Exxon 3356G) with a 1200 MFR was melt blown using a
24'' die to yield a flexible nonwoven fabric that did not block and
was easily unwound from a roll. Small pieces (1''.times.4'') did
not show any response (i.e., no disintegration or loss in basis
weight) to water when immersed in water at RT or 50.degree. C. for
15 minutes.
Example 4
[0174] Unicomponent fibers of a sulfopolyester containing 82 mole %
isophthalic acid, 18 mole % of sodiosulfoisophthalic acid, 54 mole
% diethylene glycol, and 46 mole % 1,4-cyclohexanedimethanol with a
Tg of 55.degree. C. were melt spun at melt temperatures of
245.degree. C. (473.degree. F.) on a lab staple spinning line.
As-spun denier was approximately 8 d/f. Some blocking was
encountered on the take-up tubes, but the 10-filament strand
readily dissolved within 10-19 seconds in unagitated, demineralized
water at 82.degree. C. and a pH between 5 and 6.
Example 5
[0175] Unicomponent fibers obtained from a blend (75:25) of a
sulfopolyester containing 82 mole % isophthalic acid, 18 mole % of
sodiosulfoisophthalic acid, 54 mole % diethylene glycol, and 46
mole % 1,4-cyclohexanedimethanol (Tg of 55.degree. C.) and a
sulfopolyester containing 91 mole % isophthalic acid, 9 mole % of
sodiosulfoisophthalic acid, 25 mole % diethylene glycol, and 75
mole % 1,4-cyclohexanedimethanol (Tg of 65.degree. C.),
respectively, were melt spun on a lab staple spinning line. The
blend has a Tg of 57.degree. C. as calculated by taking a weighted
average of the Tg's of the component sulfopolyesters. The
10-filament strands did not show any blocking on the take-up tubes,
but readily dissolved within 20-43 seconds in unagitated,
demineralized water at 82.degree. C. and a pH between 5 and 6.
Example 6
[0176] The blend described in Example 5 was co-spun with PET to
yield bicomponent islands-in-the-sea fibers. A configuration was
obtained where the sulfopolyester "sea" is 20 wt % of the fiber
containing 80 wt % of PET "islands". The spun yarn elongation was
190% immediately after spinning. Blocking was not encountered as
the yarn was satisfactorily unwound from the bobbins and processed
a week after spinning. In a subsequent operation, the "sea" was
dissolved by passing the yarn through an 88.degree. C. soft water
bath leaving only fine PET filaments.
Example 7
[0177] This prophetic example illustrates the possible application
of the multicomponent and microdenier fibers of the present
invention to the preparation of specialty papers. The blend
described in Example 5 is co-spun with PET to yield bicomponent
islands-in-the-sea fibers. The fiber contains approximately 35 wt %
sulfopolyester "sea" component and approximately 65 wt % of PET
"islands". The uncrimped fiber is cut to 1/8 inch lengths. In
simulated papermaking, these short-cut bicomponent fibers are added
to the refining operation. The sulfopolyester "sea" is removed in
the agitated, aqueous slurry thereby releasing the microdenier PET
fibers into the mix. At comparable weights, the microdenier PET
fibers ("islands") are more effective to increase paper tensile
strength than the addition of coarse PET fibers.
* * * * *