U.S. patent application number 09/921241 was filed with the patent office on 2002-03-07 for latex binder for nonwoven fibers and article made therewith.
Invention is credited to Diehl, David F., McBain, Carla Dittman.
Application Number | 20020028858 09/921241 |
Document ID | / |
Family ID | 23451728 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020028858 |
Kind Code |
A1 |
Diehl, David F. ; et
al. |
March 7, 2002 |
Latex binder for nonwoven fibers and article made therewith
Abstract
The invention relates to a latex that may be utilized as a
binder for nonwoven applications to form a permeable sublayer of
personal hygiene articles. The latex is prepared by a process
including the steps of (1) polymerizing a monomer mixture
comprising styrene, itaconic acid, surfactant and water soluble
free radical initiator to form a seed; (2) sequentially adding
equal increments of a monomer mixture of styrene, butadiene and
acrylic acid to the seed under emulsion polymerization conditions
to form a styrene-butadiene-acrylic acid copolymer; and then (3)
neutralizing the styrene-butadiene-acrylic acid copolymer to a pH
of about 4.5 to 7 to form the latex.
Inventors: |
Diehl, David F.; (Akron,
OH) ; McBain, Carla Dittman; (Wadsworth, OH) |
Correspondence
Address: |
Robert F. Rywalski
Omnova Solutions Inc.
175 Ghent Road
Fairlawn
OH
44333-3300
US
|
Family ID: |
23451728 |
Appl. No.: |
09/921241 |
Filed: |
August 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09921241 |
Aug 2, 2001 |
|
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09368555 |
Aug 5, 1999 |
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Current U.S.
Class: |
523/201 ;
524/460; 525/330.2 |
Current CPC
Class: |
D04H 1/64 20130101; C08L
55/02 20130101; C08L 51/003 20130101; D06M 15/227 20130101; C08F
8/00 20130101; D06M 15/693 20130101; C08F 257/02 20130101; C08L
2666/02 20130101; C08L 2666/02 20130101; D04H 1/587 20130101; C08L
55/02 20130101; D06M 15/263 20130101; C08L 51/003 20130101; Y10S
525/902 20130101; D21H 17/37 20130101; C08F 8/44 20130101; D06M
15/233 20130101; C08F 265/02 20130101 |
Class at
Publication: |
523/201 ;
524/460; 525/330.2 |
International
Class: |
C08L 009/04 |
Claims
What is claimed:
1. A latex which is particularly beneficial for utilization as a
binder for nonwoven applications made by the process which
comprises the steps of: (1) polymerizing a monomer mixture
comprising styrene, itaconic acid, surfactant and water soluble
free radical initiator to form a seed; (2) sequentially adding
equal increments of a monomer mixture of styrene, butadiene and
acrylic acid to the seed under emulsion polymerization conditions
to form a styrene-butadiene-acrylic acid copolymer; and then (3)
neutralizing the styrene-butadiene-acrylic acid copolymer to a pH
of about 4.5 to 7 to form the latex.
2. The latex of claim 1 wherein the monomer mixture includes about
34-70 wt % styrene.
3. The latex of claim 1 wherein the monomer mixture also includes
about 0.5-2.5 wt % itaconic acid, about 20-55 wt % butadiene and
about 6-10 wt % acrylic acid.
4. The latex of claim 3 wherein the monomer mixture includes 8 wt
%. acrylic acid.
5. The latex of claim 3 wherein the monomer mixture includes 2 wt %
itaconic acid.
6. The latex of claim 1 wherein the monomer mixture includes about
0.05-2.0 wt % surfactant.
7. The latex of claim 1 wherein the copolymer is neutralized by
addition of a base selected from potassium hydroxide, sodium
bicarbonate, and ammonium hydroxide, sodium hydroxide.
8. A method for making a composite useful as a personal hygiene
article which comprises: (1) treating a nonwoven fabric with a
latex binder to form a permeable sublayer, the latex prepared by a
process which comprises the steps of: (a) polymerizing a monomer
mixture comprising styrene, itaconic acid, surfactant and water
soluble free radical initiator to form a seed; (b) sequentially
adding equal increments of a monomer mixture of styrene, butadiene
and acrylic acid to the seed under emulsion polymerization
conditions to form a styrene-butadiene-acrylic acid copolymer; and
then (c) neutralizing the styrene-butadiene-acrylic acid copolymer
to a pH of about 4.5 to 7 to form the latex; (3) providing at least
one fluid permeable top sheet layer and at least one substantially
fluid impermeable backsheet layer; and (4) interposing the sublayer
material between the topsheet layer and backsheet layer.
9. The method of claim 8 wherein the permeable sublayer of the
personal hygiene article is a web comprised of randomly arranged
nonwoven fibers having an open structure and high loft.
10. The method of claim 9 wherein the web is formed by carding.
11. The method of claim 9 wherein the fibers are selected from
natural textile fibers, artificial organic textile fibers, vinyl
resin fibers and mixtures thereof.
12. The method of claim 9 wherein the fibers are selected from
polyolefins, polyesters, acrylics, and polyamides.
13. The method of claim 12 wherein the polyolefin fibers include
polypropylene, polyethylene, polybutene and their copolymers.
14. The method of claim 12 wherein the polyester fibers include any
long synthetic polymer composed of at least 85% by weight of an
ester of a dihydric alcohol and terephthalic acid.
15. The method of claim 12 wherein the acrylic fibers include any
fiber forming substance containing a long chain synthetic polymer
composed of at least 85% by weight acrylonitrile units
--CH.sub.2CH(CN)--.
16. The method of claim 9 wherein the fibers are graphite
fibers.
17. The method of claim 9 wherein the fibers are of a length of
about 0.25 to 2 inches and about 1.2-15 denier.
18. The method of claim 8 wherein the latex binder is applied on
the fiber mat is about 15-40 wt %.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a latex binder for treating
nonwoven fibers and a method of manufacture of a personal hygiene
article including the latex binder. More particularly, the present
invention relates to a latex binder for treating nonwoven fibers to
make a nonwoven fabric that is particularly suitable for use as a
permeable sublayer of a personal hygiene article.
BACKGROUND OF THE INVENTION
[0002] A nonwoven fabric is a web or continuous sheet of fibers
laid down mechanically. The fibers may be deposited in a random
manner or oriented in one direction. Most widely used fibers
include cellulosics, polyamides, polyesters, polypropylene and
polyethylene. The spun fibers, which may be drawn, are laid down
directly onto a belt by carding, airlaying or wet-laying. The sheet
is then bonded together with a latex binder and subsequently
treated in an oven or a calendar to complete the bonding
process.
[0003] Commonly used lattices for nonwoven fabrics are those
prepared from polymers of butadiene-styrene,
butadiene-acrylonitrile, vinyl acetate, acrylic monomers such as
methyl acrylate, ethyl acrylate, methyl methacrylate and the like.
It will be appreciated that to be useful as a nonwoven fabric in
many applications, such as a permeable sublayer of a personal
hygiene article, the latex binder should possess several desired
physical properties. The desired physical properties include
adequate tensile strength, a high modulus or stiffness under
certain conditions, and good textile qualities such as tenacity,
handle and the like.
[0004] It is an object of the present invention to provide a
nonwoven fabric having a high modulus. It is another object of the
present invention to provide a nonwoven fabric having desired
physical properties. Yet another object of the present invention is
to provide a nonwoven fabric of chemically bonded fibers that is
simple and economical to manufacture.
SUMMARY OF THE INVENTION
[0005] Briefly, the present invention relates to a latex that is
particularly suitable for utilization as a binder for nonwoven
applications. The latex is prepared by a process including the
steps of:
[0006] (1) polymerizing a monomer mixture comprising styrene,
itaconic acid, surfactant and water soluble free radical initiator
to form a seed;
[0007] (2) sequentially adding equal increments of a monomer
mixture of styrene, butadiene and acrylic acid to the seed under
emulsion polymerization conditions to form a
styrene-butadiene-acrylic acid copolymer; and then
[0008] (3) neutralizing the styrene-butadiene-acrylic acid
copolymer to a pH of about 4.5 to 7 to form the latex.
[0009] The latex is particularly suitable to treat nonwoven fibers
to form a permeable sublayer of a personal hygiene article. The
permeable sublayer is typically interposed between a topsheet layer
and a backsheet layer typically used to form the personal hygiene
article.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] The present invention relates to a latex suitable for
utilization as a binder to chemically bond fibers and form a
nonwoven fabric. The nonwoven fabric is particularly suitable for
use as a permeable sublayer of a personal hygiene article of a type
well known in the art. Examples of personal hygiene articles
include diapers, feminine hygiene articles and the like.
[0011] The permeable sublayer of the personal hygiene article is a
web or mat comprised of randomly arranged nonwoven fibers having an
open structure and high loft. The web may be formed by carding when
the fibers are of such a character, by virtue of their length and
flexibility, as to be capable of carding. During carding the
crimped fibers are placed on a moving support and then treated with
a latex binder as described herein.
[0012] The fibers may include natural textile fibers such as jute,
sisal, ramie, hemp, and cotton as well as many artificial organic
textile fibers or filaments including rayon, those of cellulose
esters such as cellulose acetate, vinyl resin fibers such as those
of polyvinyl chloride, copolymers of vinyl chloride with vinyl
acetate, vinylidene chloride or acrylonitrile, copolymers of
acrylonitrile with vinyl chloride, vinyl acetate,
methacrylonitrile, vinyl pyridine, polymers and copolymers of
olefins such as ethylene and propylene, also condensation polymers
such as polyamides or nylon types, polyesters such as ethylene
glycol terephthalate polymers and the like.
[0013] The fibers may be of one composition or mixtures of fibers
in a given web. The preferred fibers include polyolefins,
especially polyesters, poly(ethylene terephthalate), and acrylics,
polyamides, polypropylene. The polyolefin fibers include
polypropylene, polyethylene, polybutene and their copolymers. The
polyester fibers include any long chain synthetic polymer composed
of at least 85% by weight of an ester of a dihydric alcohol and
terephthalic acid such as polyethylene terephthalate, and, in
addition liquid crystal polyesters, thermotropic polyesters and the
like. The acrylic fibers include any fiber forming substance
containing a long chain synthetic polymer composed of at least 85%
by weight acrylonitrile units --CH.sub.2CH(CN)--. It will be
appreciated that other types of fibers may also be employed in
accordance with the teachings of the present invention. For
example, high modulus fibers more commonly known as graphite fibers
made from rayon, polyacrylonitrile or petroleum pitch may also be
used.
[0014] The fibers may be of most any suitable size and randomly
arranged to most any suitable thickness depending upon the desired
end use of the nonwoven fabric. The fibers are typically of a
length of about 0.25 to 2 inches and typically about 1.2-15 denier.
The fibers may be laid in an overlapping, intersecting random
arrangement to a thickness of about 0.25 inches or less to form a
mat of fibers. The fibers may be arranged by most any convenient
known manner such as by wet laying, air-laying or carding.
[0015] The fabric of the present invention is made by forming a mat
of randomly arranged fibers. After the fibers are randomly arranged
as desired, a latex binder is applied to the fibers. The latex
binder is applied in an effective amount which will result in the
fabric having sufficient strength and cohesiveness for the intended
end use application. As well known in the art, the latex binder may
be applied to the layer of randomly arranged fibers in a spaced,
intermittent pattern of binder sites, or uniformly applied
throughout the layer of fibers. It will be further appreciated that
the exact amount of the latex binder employed depends, in part,
upon factors such as the type of fiber, weight of fibrous layer,
nature of latex binder and the like. For example, end uses which
require a stronger fabric may utilize more binder. A typical
content of latex binder applied on a fiber mat is about 15-40 wt %.
It is preferred that the minimum amount of latex binder be applied
to obtain the desired required physical properties of the nonwoven
fabric such as tensile, hand and the like as well known in the
art.
[0016] The latex is then cured using methods well known in the art
such as by application of heat or radiation. The term "cured"
refers to the latex being cross-linked to increase the tensile
strength properties. The curing of the treated fibers is affected
at a temperature above the glass transition temperature of the
binder.
[0017] To obtain a sufficient thickness for the end use intended a
plurality of webs may also be superimposed upon one another to
achieve a sufficient thickness. The webs may be superimposed by
alternating layers of carded webs disposed with their fiber
orientation directions disposed at angles such as 60 degrees or 90
degrees with respect to intervening layers.
[0018] The latex binder utilized in accordance with the present
invention may be prepared by well-known conventional emulsion
polymerization techniques using one or more ethylenically
unsaturated monomers and a polymeric surfactant as herein disclosed
and additional conventional additives such as free-radical
initiators, optional chain transfer agents, chelating agents and
the like can be utilized as set forth in U.S. Pat. No. 5,166,259 to
Schmeing and White.
[0019] In accordance with a preferred embodiment of the present
invention, the latex is prepared by polymerizing a monomer mixture
comprising styrene, itaconic acid, surfactant and a water soluble
free radical initiator to form a seed. A monomer mixture is then
added incrementally to the seed under emulsion polymerization
conditions. The monomer mixture includes styrene, butadiene, and
acrylic acid. The monomer mixture is preferably added incrementally
to the seed to form a styrene-butadiene-acrylic acid copolymer. In
the preferred embodiment, the monomer mixture includes about 34-70
wt % styrene of the total composition. The monomer mixture also
includes about 0.5-2.5 wt % itaconic acid, preferably 2 wt %
itaconic acid of the total composition, about 20-55 wt % butadiene
and acrylic acid in an amount of about 6-10 wt %, preferably 8 wt
%.
[0020] A surfactant is added to the monomer mixture in an amount of
about 0.05-2.0 wt %. The surfactant may be most any suitable
emulsifier, soap, or the like well known in the art and suitable at
the pH of the latex in accordance with the present invention.
Examples of suitable emulsifiers and surfactants include alkyl
sulfates, alkyl sulfosuccinates, alkyl aryl sulfonates,
alpha-olefin sulfonates, fatty or rosin acid salts, only or octyl
phenol reaction products of ethylene oxide and the like. Other
surfactants that may be used include those identified in Surface
Active Agents, Schwartz and Berry, Vol. 1, Interscience Publishers,
Inc., New York, 1958; Surface Activity, Moilet, Collie and Black,
D. Van Nostrand Company, Inc., New York, 1961; Organic Chemistry,
Feiser and Feiser, D.C. Heath and Company, Boston, 1944; and The
Merck Index, Seventh Edition, Merck & Co., Inc., Rahway, N.J.,
1960, all of which are hereby incorporated by reference.
[0021] The copolymer is then neutralized to a pH of about 4.5 to
7.0 to form the latex. The pH of the latex is neutralized by
addition of a base. Examples of a suitable base include potassium
hydroxide, sodium bicarbonate, ammonium hydroxide, sodium hydroxide
and the like. The amount of base added to the latex is adjusted to
obtain the desired pH range as is well known in the art.
[0022] Polymerization is typically carried out from about 150
degrees Fahrenheit to 170 degrees Fahrenheit. Polymerization is
generally conducted for about 4 to 24 hours, however polymerization
conditions may vary as desired to provide different conversion
levels of monomer to copolymer. The monomer mixture is allowed to
react until substantially constant solids at which time at least
99% of the monomers have been converted.
[0023] The invention will be further clarified by a consideration
of the following example, which is intended to be purely exemplary
of the invention.
EXAMPLE
[0024] Initially, a charge of deionized water, styrene and itaconic
acid, and water soluble free radical initiator were added to a
reactor having a volume of about 20 gallons and having a capacity
to hold about 140 lb. of latex. The reactor was then evacuated with
a vacuum (about 20 inches of mercury), purged with nitrogen and
heated to a desired temperature. Ammonium persulfate was then added
to the reactor as about a 10% solution in deionized water.
[0025] A charge comprising styrene, butadiene and acrylic acid was
then charged to the reactor sequentially.
[0026] The first increment was added to the reactor approximately 5
minutes after the ammonium persulfate was added. Additional
increments were then added to the reactor at staged intervals of
about 15 or 20 minutes. The increments may be added over most any
suitable number of staged intervals depending upon the amount of
latex binder to be polymerized. For example, the increments may be
added from 6 stages up to 12 or more stages. After the last
increment was added to the reactor the reaction was monitored until
the solid level of the latex in the reactor indicated an acceptable
conversion level.
[0027] The resulting latex binder was then applied to polyester
fibers. After applying the latex binder to the nonwoven fibers the
latex binder was oven dried at 212 degrees Fahrenheit to bond the
fibers and then cured at 300 degrees Fahrenheit for 1 minute to
form a dimensionally stable nonwoven fabric.
[0028] Representative physical properties of the styrene-butadiene
latex binder are shown in Table 1. As shown in Table 1, the fibers
had a higher hand value and higher dry tensile properties as
compared to polyester fibers treated with GenFlo 3060. GenFlo 3060
is a styrene butadiene rubber latex commercially available from
GenCorp Inc.
1 TABLE 1 GenFlo 3060 Latex Latex content (%) 39.5 39.9 Yellow
Index -7.6 -7.7 Hand Value 44.3 68.8 Cross Direction, dry Tensile
(grams) 323 503 Elongation (%) 27 17 TEA 199 206 Cross Direction,
wet Tensile (grams) 162 141 Elongation (%) 39 4 TEA 79 10
[0029] All of the reported performance properties were determined
after conditioning the fibers for about 24 hours at TAPPI
(Technical Association of the Pulp and Paper Industry) Standard
Conditions of approximately 72 degrees Fahrenheit and about 50%
relative humidity. The tensile values, both dry and wet, were
determined in accordance with ASTM D 1117-80 entitled "Standard
Methods of Testing Nonwoven Fabrics" published in the 1980 Annual
Book of ASTM Standards. Following the ASTM standard test method,
dry tensile measurements were determined by using 1 inch wide and 4
inch long strips of fabric pulled at a rate of 5 inches per minute
at an initial jaw separation of about 3 inches on an Instron. The
wet tensile measurements were determined in substantially the same
manner as the dry tensile measurements except the fabric strip was
soaked in water solution for about 30 seconds prior to testing on
the Instron. The Hand Values are a quantitative measure of the
fabric as well known in the textile industry. The Hand Values
reported are an average value of the readings determined on a
Thwing Albert Handle-O-Meter by using a 5 inch square piece of the
fabric. The fabric was tested on the Handle-O-Meter in both the
Machine and Cross machine directions.
[0030] The patents and documents referred to herein are hereby
incorporated by reference.
[0031] Having described presently preferred embodiments of the
present invention, it is to be understood that it may be otherwise
embodied within the scope of the appended claims.
* * * * *