U.S. patent number 3,766,002 [Application Number 05/094,602] was granted by the patent office on 1973-10-16 for nonwoven products.
This patent grant is currently assigned to National Starch and Chemical Corporation. Invention is credited to Donald S. Greif, Henry R. Hernandez, Fred D. Schultz.
United States Patent |
3,766,002 |
Greif , et al. |
October 16, 1973 |
NONWOVEN PRODUCTS
Abstract
This invention is directed to producing polymeric binding agents
in fibrous form for nonwoven fabrics and for nonwoven fabrics
incorporating such polymeric binding agents in fibrous form, the
fibrous form polymeric binding agents being obtained by introducing
an anionic latex in fine thread-like form into a precipitating
aqueous solution of a water-soluble cationic polymer, and thereby
forming a fibrous precipitate of the anionic latex in the cationic
solution. The nonwoven fabrics produced are characterized by their
unusually high strength.
Inventors: |
Greif; Donald S. (Bound Brook,
NJ), Schultz; Fred D. (Plainfield, NJ), Hernandez; Henry
R. (Somerville, NJ) |
Assignee: |
National Starch and Chemical
Corporation (New York, NY)
|
Family
ID: |
22246099 |
Appl.
No.: |
05/094,602 |
Filed: |
December 2, 1970 |
Current U.S.
Class: |
162/146;
156/307.3; 162/157.4; 162/164.6; 162/168.1; 162/168.7; 264/109;
264/183; 528/936; 156/62.2; 156/62.4; 156/308.2; 162/164.1;
162/164.7; 162/168.2; 162/168.3; 162/169; 264/143; 264/184 |
Current CPC
Class: |
D04H
1/54 (20130101); D04H 1/587 (20130101); D06M
15/233 (20130101); D06M 15/267 (20130101); D04H
1/64 (20130101); C08J 5/02 (20130101); D06M
15/31 (20130101); Y10S 528/936 (20130101) |
Current International
Class: |
D06M
15/31 (20060101); D06M 15/233 (20060101); D06M
15/267 (20060101); C08J 5/02 (20060101); D06M
15/21 (20060101); D01f 007/00 (); B32b
003/00 () |
Field of
Search: |
;260/821,94,9
;264/183,184,182,171,174,168,143,109 ;210/54
;162/26,157R,146,168,169 ;161/70,82,170,150 ;156/62.2,62.4,306 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Woo; Jay H.
Claims
We claim:
1. A nonwoven fabric formed from a self-supporting web comprised of
fibers bonded with a polymeric binding agent in fibrous form
prepared by introducing an anionic latex of a polymer, having a
glass transition temperature of from about -52.degree.C to
+25.degree.C, selected from the group consisting of polymers having
an anionic backbone and polymers having a neutral backbone in fine
thread-like form into a stirred precipitating aqueous solution
containing about 0.3 to about 5 percent, by weight, of a water
soluble cationic polymer and thereby forming a fibrous precipitate
of thread-like binder particles of the anionic latex in the
cationic polymer solution.
2. A process for preparing a polymeric binding agent in fibrous
form which consists in introducing an anionic latex of a polymer,
having a glass transition temperature of from about -52.degree.C to
+25.degree.C, selected from the group consisting of polymers having
an anionic backbone and polymers having a neutral backbone in fine
thread-like form into an agitated precipitating aqueous solution
containing about 0.3 to about 5 percent, by weight, of a water
soluble cationic polymer and thereby forming a fibrous precipitate
of thread-like binder particles of the anionic latex in the
cationic polymer solution.
3. The process of claim 1, in which the anionic latex is introduced
into the precipitating aqueous solution of the cationic polymer
through tubing having at least one orifice of a diameter of from
0.01 to 0.05 inches.
4. The process of claim 1, wherein the anionic latex is a homo- or
copolymer of monomers selected from the group consisting of: vinyl
acetate, vinyl chloride, vinyl esters of alpha-branched saturated
aliphatic monocarboxylic acids, vinylidene chloride, alkyl
acrylates and methacrylates, butadiene, acrylonitrile and
styrene.
5. The process of claim 1, wherein the polymer of the anionic latex
also contains a monomer selected from the group consisting of
N-methylol acrylamide, ethylenically unsaturated monocarboxylic
acids, and ethylenically unsaturated dicarboxylic acids.
6. The process of claim 1, wherein the water-soluble cationic
polymer is selected from the group consisting of: acid salts of
aminoalkyl esters of carboxylic acid polymers, high molecular
weight polysulfur amidoamines, copolymers of .beta.-hydroxyalkyl
ethylenically unsaturated ester with vinyl tertiary amine,
polyamine polymers, polyalkylenimine polymers, amine modified
acrylamide polymers, quaternary amine-containing polymers, and
starches which have beem modified to contain cationic groups.
7. A process for preparing a polymeric binding agent in fibrous
thread-like binder particles form which consists in introducing in
fine thread-like form an anionic latex of an ethyl acrylate:butyl
acrylate:vinyl acetate: N-methylol acrylamide (60:30:10:3) polymer
having a glass transition temperature (Tg) of about -21.degree.C.
into an agitated precipitating solution comprising an aqueous
solution of a nitrate salt of poly(2-aminoethyl
acrylate:2-hydroxypropyl acrylate) (62.5:37.5), said salt being
present in a concentration of from about 0.3 to 4.5 percent, by
weight.
8. The process of claim 7 in which the anionic latex is introduced
into the precipitating solution through tubing having at least one
orifice of a diameter of from 0.01 to 0.05 inches.
9. A process for preparing a nonwoven sheet which comprises:
A. introducing an aqueous anionic latex of a polymer selected from
the group consisting of polymers having an anionic backbone and
polymers having a neutral backbone having a glass transition
temperature of from about +25.degree. to -52.degree.C through at
least one orifice having a diameter of from about 0.01 to 0.05
inches into an agitated, aqueous precipitating solution containing
about 0.3 to about 5%, by weight, of a water-soluble cationic
polymer;
B. admixing the resultant fibrous thread-like binder precipitated
particles with natural or synthetic fibers in a concentration such
that said binder constitutes from about 10 to 80 percent, by
weight, of the dry nonwoven sheet;
C. forming a nonwoven web from the resultant solids thereof,
and,
D. drying the resultant nonwoven web.
10. A process for preparing a nonwoven sheet which comprises:
A. introducing an aqueous anionic latex of a polymer selected from
the group consisting of polymers having an anionic backbone and
polymers having a neutral backbone and having a glass transition
temperature of from about +25.degree. to -52.degree.C through at
least one orifice having a diameter of from about 0.01 to 0.05
inches into an agitated, aqueous precipitating solution containing
about 0.3% to about 5%, by weight, of a water-soluble cationic
polymer thereby forming thread-like binder particles to which has
been added from about 20 - 90 percent, by weight, based on the
weight of the nonwoven, of natural or synthetic fibers;
B. forming a nonwoven web from the resultant solids thereof,
and,
C. drying the resultant nonwoven web.
Description
This invention relates to improved nonwoven products and fabrics
characterized by their unusually high strength and durability. In a
further aspect, the invention also relates to a process of
preparing a polymeric binding agent in fibrous form intended for
use in the production of the improved nonwoven products of this
invention.
The forming of bonded nonwoven fabrics by means of conventional dry
processing includes the impregnating, printing, spraying, coating
or otherwise depositing of an adhesive bonding agent (ordinarily a
polymeric material) onto a fibrous base web comprising relatively
lengthy fibers ranging from about one-half inch to two-and-one-half
inches, or more, composed of materials such as synthetic or natural
fibers. Also known are wet-laid processes wherein an aqueous slurry
or suspension of fibers together with a selected binding agent and
any desired optional ingredients are utilized in forming a web on a
wire screen, such as is ordinarily used in a paper making process.
It can be understood that such properties of nonwovens as softness,
durability, dry tensile strength and wet tensile strength (i.e. the
strength of the nonwoven after being substantially saturated with
water), are of primary importance and are highly dependent on the
selected binding agent and the process utilized in the formation of
the nonwoven. While a large number of variations in processes and
binding agents are available to the practitioner, none of these
heretofore known processes or binding agents results in an entirely
satisfactory nonwoven product which exhibits the optimum
combination of requisite properties. Thus, while certain processes
and binding agents of the prior art may lead to a product having
adequate dry strength, the product ordinarily will be lacking in
other desirable properties.
A recently proposed wet-laid process for forming nonwovens
describes the preparation and use of polymeric binding agents in
fibrous form, which form of the binding agent will tend to have
beneficial effects upon many properties of the final product. The
fibrous binding agent itself is proposed to be obtained by a
process of mixing a latex of a carboxyl-group containing polymer
together with an aqueous solution of a cationic polymeric material
at a pH of 6 to 9. After a period of time, no more than 60 minutes,
the pH of the mixture is adjusted to 2 to 4, whereupon the very
fine polymeric particles which are originally formed are allegedly
converted into fibrous particles. In repeated attempts at carrying
out this proposed process, particular difficulty was encountered in
obtaining a fibrous precipitate, i.e. a precipitate composed of
particles having a slender, thread-like structure. Each attempt at
forming the fibrous precipitate according to the proposed process
resulted in a precipitate of agglomerated particles. Close
examination of the resultant precipitate with the aid of a
microscope confirmed the formation of pear-shaped agglomerates
measuring approximately 50-100 microns, rather than the desired
slender, thread-like structures.
Accordingly, the primary object of this invention is to provide a
new and improved polymeric binder in fibrous form for use in
nonwoven products. Another object of this invention is to provide a
new and improved nonwoven product characterized by its improved
durability and dry and wet strength as compared to typical
nonwovens formed by means of conventional, known processes.
By the term "nonwoven products" herein we mean bonded nonwoven
sheet material comprising a bonded self-supporting fibrous base
web; a representative example of a nonwoven product being a
nonwoven fabric.
By the term "fibrous" herein with reference to the polymeric
binding agent we mean thread-like particles having a length which
is at least several times larger than the diameter of the
precipitated polymer.
In accordance with this invention, it has been found that superior
polymeric binding agents in fibrous form may be prepared by a
controlled, instantaneous precipitation wherein an anionic latex is
brought into intimate contact with an aqueous solution of a
cationic polymer under critical, specified conditions. The
precipitated binder particles are instantaneously obtained in
distinctly fibrous form and are particularly intended for use in
the production of nonwoven products by means of a wet-laid process.
The resultant nonwovens utilizing the fibrous binder display a
number of substantially improved desired properties and
particularly exhibit unusual strength and durability as compared to
comparable nonwovens formed by conventional processes.
With respect to the preparation of the fibrous binding agent, it is
first necessary to prepare an aqueous solution of water-soluble
cationic polymer which is to be used in precipitating the anionic
latex. Among the classes of water-soluble polymers useful herein as
included:
a. acid salts of aminoalkyl esters of carboxylic acid polymers as
described in U.S. Pat. No. 3,372,149 issued Mar. 5, 1968, including
homopolymers and copolymers of these carboxylic acids with methyl
vinyl ether, vinyl acetate, acrylamide, methacrylamide, lower alkyl
esters of acrylic and methacrylic acid, etc.
b. high molecular weight polysulfur amidoamines as described in
U.S. Pat. No. 3,464,969 issued Sept. 2, 1969. These compounds are
the reaction product of a low molecular weight polyamide with a
sulfur containing reagent such as a sulfur halide or sulfur acid
and thereafter, if desired, chain extended by reaction with an
epihalohydrin.
c. copolymers of .beta.-hydroxyalkyl ethylenically unsaturated
ester with vinyl tertiary amine as described in U.S. Pat. No.
3,227,672 issued Jan. 4, 1966.
Representative other water-soluble cationic polymers suitable for
use in precipitating the anionic latex may be selected from such
classes of polymers as polyamine polymers, polyalkylenimine
polymers, amine modified acrylamide polymers, quaternary
amine-containing polymers, and the like. Starches which have been
modified to contain cationic groups may also be utilized in
preparing the precipitating solution.
The concentration of the cationic polymer in the precipitating
solution will ordinarily be from about 0.3 to 4.5 percent and
preferably from about 0.4 to 1.5 percent, by weight. Precipitating
solutions containing less than about 0.3 percent of the cationic
polymer will tend to precipitate the anionic latex in minute
granular form. Solutions of the cationic polymer which contain more
than about 5 percent of the cationic polymer will tend to
precipitate the anionic latex in an agglomerate form.
By the term "anionic latex" as used herein we mean an aqueous latex
or emulsion of a polymer having an anionic or neutral polymeric
backbone. In preparing the latex or emulsion of an anionic polymer
one may employ either an anionic surfactant or a non-ionic
surfactant or a combination of an anionic and non-ionic surfactant.
In preparing the latex or emulsion of a neutral polymer one may
employ an anionic surfactant or a combination of an anionic and
non-ionic surfactant. Typical anionic surfactants which are useful
in preparing these polymers include sodium alkyl sulfates, sodium
alkyl aryl sulfonates, sodium naphthalene sulfonates, etc.
Since the relative softness or hardness of the polymeric binder
will affect its adhesive or binding properties as well as the
properties of the nonwoven which is formed therewith, it is
important that the polymers of the anionic latices used herein fall
within a specified range in this respect. The polymers of the
anionic latices used in the process of this invention should
display a glass transition temperature (Tg) of from about
+25.degree. to -52.degree.C. Tg is a measure of a polymer's
softness or hardness, wherein higher temperatures indicate a
relatively harder polymer and lower temperatures indicate a softer
polymer. Moreover, the polymers of the anionic latices used herein
should have a molecular weight as characterized by an intrinsic
viscosity in acetone at 30.degree.C. of at least 0.25.
Illustrative of the polymers useful in the preparation of the
anionic latex herein are homo- and copolymers of such monomers as
vinyl acetate, vinyl chloride, vinyl esters of alpha-branched
saturated aliphatic monocarboxylic acids, vinylidene chloride,
alkyl acrylates and methacrylates, butadiene, acrylonitrile, and
styrene, etc., provided the polymers have a Tg within the range
specified hereinabove. If desired, a crosslinking or functional
monomer, i.e. a monomer having a functional group such as
N-methylol, carboxyl or sulfoxyl group, may also be copolymerized
with the above mentioned monomers. Examples of such functional
monomers are N-methylol acrylamide, ethylenically unsaturated mono-
and dicarboxylic acids such as acrylic and methacrylic acids,
maleic acid, etc. The concentration of these functional
crosslinking monomers is preferably less than about 8 percent,
based on the weight of the total polymer. In addition to the
surfactant employed in preparing the latex, the latices may also
contain such optional additives as plasticizers, defoamers,
dispersing agents, antioxidants, and any other conventional
additives commonly used in commercial anionic latex
formulations.
The anionic latex which is utilized in forming the fibrous
precipitate is employed in a solids concentration of about 5 to 45
percent, by weight. Latices having a solids concentration exceeding
about 50 percent solids, by weight, are functional and may be
employed by the results achieved therewith are less desirable.
Experiments using concentrations of anionic latex between 10 and 40
percent solids, by weight, have shown that the use of the higher
solids concentrations yields a fibrous precipitate in which the
fibers have a relatively larger diameter.
The process for preparing the polymeric binding agent in fibrous
form according to the present invention consists in introducing the
anionic latex in fine thread-like form into the precipitating
aqueous solution of a water-soluble cationic polymer, which is
stirred at moderate speeds, and thereby forming a fibrous
precipitate of the anionic latex in the cationic solution. To
accomplish this the anionic latex may conveniently be introduced by
means of tubing having a very small orifice or preferably an
assembly of orifices through which the latex is discharged into the
cationic polymer solution. It is preferred that the diameter of the
orifices through which the latex is discharged fall within a range
of from about 0.01 to 0.05 inches. While orifices which fall
outside of the preferred range can also be used, their undesirable
effect upon the form of the polymeric precipitate discourages their
use. The orifice or orifice assembly of the tubing equipment can
either be submerged below the surface of the cationic polymer
solution or, if desired, raised to a point just above the surface
of the cationic polymer solution so that the anionic latex, in
effect, is sprayed onto the precipitating solution. From a
practical viewpoint, the latter variation is preferred since the
submerged procedure may lead to clogging of the openings when the
precipitating is interrupted.
The forming of the fibrous precipitate can be carried out at
temperatures ranging from about 40.degree. to 180.degree.F with the
preferred temperatures being from about 40.degree. to 120.degree.F.
Most conveniently, the reaction is carried out at room temperature.
Generally, the use of temperatures above about 120.degree.F. in
combination with the softer polymers is not desirable because of
the poor form of the resultant precipitate.
The reactants which are employed to form the fibrous precipitate,
i.e. the anionic latex and the precipitating solution, are
generally employed at their existing pH values, and the reaction
therewith is carried out at the existing pH providing the pH of the
reaction media does not exceed about pH 7.5.
A well defined fibrous precipitate is formed instantaneously on
contact of the latex with the precipitating solution. No waiting
period or pH adjustments are required. Chiefly for practical
purposes relating to agitation and the like, the precipitated
solids which are accumulated in the precipitating solution should
preferably not exceed about 18%, by weight.
When the addition of the latex to the precipitating solution is
completed, the solids are ordinarily separated from the supernatant
liquid, washed with water, and subsequently suspended in clean
water in anticipation of their use as a binding agent in forming
the nonwoven product. If desired, the thus precipitated binding
agent may be employed directly in forming the nonwoven, without
washing.
The actual forming of the nonwoven may be carried out by admixing
the selected fiber together with the prepared fibrous binding agent
in water. Illustrative of the fibers which can be used herein
either alone or in combination with one another are fibers from
such natural materials as wool and cotton hemp, and synthetic
cellulose fibers such as regenerated cellulose and rayon. Other
fibers include fibers from nylon, polyesters i.e. "Dacron",
acrylics i.e. "Orlon", polyolefins, polyurethanes, asbestos, and
glass, as well as ceramic and metallic fibers. In general, the
fibrous polymeric binding agent on a dry solids basis should be
from about 10 to 80 percent or more, by weight, of the dry finished
nonwoven product. The upper limit on binder concentration is not
particularly critical and is at the direction of the practitioner
with respect to the desired properties of the finished product.
The suspended material is then formed into a nonwoven sheet by
feeding or depositing the mixture onto a wire screen, such as is
employed in a conventional papermaking process, and removing the
excess water. The resultant wet, self-supporting web is then dried
by any means such as air oven, drying can, or the like. Ordinarily,
drying is effected at temperatures of from about 210.degree. to
280.degree.F for periods of 2 to 8 minutes. If the latex used in
forming the fibrous binding agent is a heat-activated, so-called
"self-reactive" type, i.e. crosslinks upon exposure to heat, or if
a crosslinking agent which is heat-activated, such as is well known
in the art, is optionally added to the latex, an additional step of
curing at temperatures of from about 280.degree. to 380.degree.F
for a period of 3 to 5 minutes may be required. It can be easily
understood that the drying and curing periods may be combined into
one step if desired, and other time-temperature relationships can
be employed, keeping in mind that the upper temperature limits are
governed by the nature of the fibers and the fibrous binding
agent.
The softness and flexibility of ths nonwovens described herein can
be enhanced by the addition of small amounts of external
plasticizers, and such plasticizers as, for example, dibutyl
phthalate and tricresyl phosphate, may be added, if desired, to the
latex before it is added to the precipitating solution or added to
the fiber suspension at any time before it is fed onto the wire
screen. Other optional ingredients as, for example, dyes, pigments,
preservaties, etc. may likewise be added to the fiber suspension
before the suspension is fed onto the wire screen, if desired.
The nonwoven products formed with the fibrous binders of this
invention are particularly characterized by their outstanding
strength and durability. In testing these products, test
pro-cedures established by the Technical Association of the Pulp
and Paper Industry (TAPPI) were followed. The Finch edge tear test
was determined by means of TAPPI test T470 M-54, wherein higher
readings indicate a proportionately stronger fabric. The percent
elongation was determined by means of TAPPI test T457 M-46. The dry
tensile strength was determined by means of TAPPI test T404 ts-66,
and the Mullen burst strength was determined by means of TAPPI test
T403 ts-63 .
The following examples will further illustrate the embodiment of
our invention. The concentration of the monomer components of the
copolymers is given in parts by weight.
EXAMPLE I
This example illustrates the novel process of this invention in the
formation of a representative nonwoven as well as the improved
properties thereof.
A cationic precipitating solution was prepared by dissolving 10
grams of the nitrate salt of poly(2-aminoethyl acrylate:
2-hydroxypropyl acrylate) (62.5:37.5) in 1 liter of water with
stirring which was continued at a moderate rate (about 120 rpm)
throughout the precipitating step. A tubing device comprising
copper tubing (1/4 inch diameter) shaped in the form of a circle
about 3 inches in diameter and having 26 small openings (0.025 inch
diameter) was fixed so as to position the openings to be about 1
inch from the surface of the precipitating solution. An aqueous
anionic latex of an ethyl acrylate:butyl acrylate:vinyl acetate:
N-methylol acrylamide (60:30:10:3) polymer having a Tg of about
-21.degree.C. (700 millimeters, 20 percent solids, by weight) was
forced through the tubing device and out of the multiple openings
by means of air pressure. The addition of the entire quantity of
the latex required about 12 minutes and resulted in a fibrous
precipitate, which after washing and drying, weighed 142 grams. The
precipitated polymer fibers measured, on the average, about 6
microns in diameter ad up to 500 microns in length. The pH of the
supernatant liquid at the conclusion of the latex addition was
found to be 2.8. In preparation for its use as a binding agent in
the nonwoven, the precipitate was suspended in water in a
concentration of about 5 percent, by weight.
Thereafter, 20 millileters of the suspension containing the fibrous
precipitate (1 gram, dry weight) was added to a suspension of 2
grams of rayon fibers (1.5 denier, 0.375 inch length) in 1600
milliliters of water with moderate agitation. The resultant
well-mixed suspension was poured into the head box of a standard
Noble & Wood laboratory sheet making apparatus to form an 8 by
8 inch fibrous web. Excess water was removed by vacuum and the
nonwoven was dried by means of a drying can at 210.degree.F. for a
period of 8 minutes. The finished nonwoven sheet measured about
0.011 inches in thickness and possessed a desirably flexible, soft
hand.
The superior strength characteristics of this nonwoven are
indicated in Table I, following, wherein testing results obtained
with the above-identified TAPPI tests are summarized. A comparable
nonwoven which had been prepared with no binder as well as a
comparable nonwoven which had been prepared with an identical
polymeric binder which, however, was precipitated according to
prior art techniques and did not possess a fibrous form were tested
in similar manner for comparison purposes.
TABLE I
Nonwoven Fabric Formed With: No Non-Fibrous Fibrous Test Procedure
Binder Binder Binder Finch Edge Tear (lb./square inch) 0.03 0.08
8.7 Percent Elongation 0.6 0.7 10.2 Dry Tensile Strength
(lbs./square inch) 0.02 0.03 4.6 Mullen Burst Strength (lb.square
inch) 2.6 2.9 34.7
Thus, it is seen that in all of the above tests, the nonwoven
fabric of this invention surpasses, by far, the values obtained
with the nonwoven fabric prepared with no binder as well as the
nonwoven fabric prepared with the identical binder in non-fibrous
form.
In a repetition of the above procedure, the cationic precipitating
solution was employed in a concentration of 0.5 percent, by weight.
About 350 milliliters of the identical anionic latex which,
however, had a solids concentration of 40 percent, by weight, was
forced through the tubing device. A nonwoven was prepared as
described above, employing 1 gram of the resultant fibrous
precipitate and 2 grams of the rayon fibers, which exhibited a
soft, flexible hand as well as strength characteristics comparable
to the nonwoven of this invention described above.
EXAMPLE II
This example illustrates the process of this invention utilizing a
polymeric fibrous binding agent prepared from another anionic
latex.
The procedure of Example I was repeated except that the latex used
therein was replaced with an aqueous anionic latex of an ethyl
acrylate:vinylidene chloride:N-methyol acrylamide (60:40:0.4)
polymer having a T.sub.3 of -13.degree.C., and the temperature of
the latex and precipitating solution was about 80.degree.C.
The resultant nonwoven fabric was soft and flexible, and exhibited
strength properties comparable to those of the non-woven fabric of
this invention described in Example I.
EXAMPLE III
This example illustrates the process of this invention utilizing a
polymer fibrous binding agent in the formation of a nonwoven
comprising glass fibers.
The procedure of Example I was repeated except that the rayon
fibers employed to form the nonwoven therein were replaced by an
equal amount of glass fibers having a diameter of about 3.8 microns
and a length of about 1 inch. Another nonwoven was prepared for
comparison purposes employing the identical glass fibers with no
binding agent. In each of the testing procedures identified in
Example I, the nonwoven formed with the fibrous binding agent of
this invention was found to exhibit substantially higher strength
characteristics as compared to the nonwoven formed without such
binder.
EXAMPLE IV
This example illustrates a variation in the process of forming the
nonwoven fabric of this invention. In this variation the fibrous
binding agent is formed in situ directly in a suspension of fibers
which are being utilized for the formation of the nonwoven fabric.
This variation thereby eliminates the need for preparing the
binding agent separately and can be useful in certain applications
of the process.
To 1,000 milliliters of a 1 percent, by weight, of an aqueous
solution of the nitrate salt of poly(2-aminoethyl acrylate:
2-hydroxypropyl acrylate) (62.5:37.5) was added 10 grams of rayon
fibers as described in Example I. About 250 milliliters of an
aqueous anionic latex of an ethyl acrylate:butyl acrylate:vinyl
actate:N-methylol acrylamide (60:30:10:3) polymer having a Tg of
about -21.degree.C. and 20 percent solids, by weight, was forced
through a tubing device as described in Example I into the
precipitating solution and thereby forming the fibrous precipitate.
When the precipitation was completed, the solids of the resultant
suspension were washed with water, and thereafter were formed into
a nonwoven essentially as described in Example I. The finished
nonwoven sheet after drying possessed a soft, flexible hand similar
to the nonwoven of this invention described in Example I.
EXAMPLE V
This example illustrates the preparation of additional fibrous
binding agents of this invention utilizing other anionic latices
and precipitation solutions.
About 400 milliliters of an aqueous, anionic latex of a vinylidene
chloride:methyl acrylate:N-methylol acrylamide (90:10:3) terpolymer
having a Tg of about -25.degree.C. (20 percent solids, by weight)
was forced through a tubing device into a cationic precipitating
solution prepared by dissolving 15 grams of polyethyleneimine in 1
liter of water. The precipitating solution was stirred at a
moderate rate throughout the entire precipitating step. Close
examination of the resultant precipitate after washing and drying
revealed discrete, fibrous, thread-like particles.
In a repetition of the above procedure, the aqueous latex employed
therein was replaced, in identical proportion, with an aqueous,
anionic latex of a styrene:butyl acrylate:acrylic acid (45:55:2)
terpolymer having a Tg of -9.degree.C. In still another repetition
of the above procedure, an aqueous, anionic latex of a copolymer
(85:15) of vinyl acetate and a mixture of vinyl esters of isomers
of an alpha-branched saturated aliphatic monocarboxylic acid having
10 carbon atoms in the carboxylic acid moiety was employed. The
latter monomer is sold by Shell Chemical Company, New York, N. Y.
under the product name "VV-10 Vinyl Monomer." The polymer exhibits
a Tg of + 25.degree.C. The resultant precipitates exhibited a
distinctly fibrous form in each instance.
EXAMPLE VI
This example illustrates the preparation of additional fibrous
binding agents of this invention.
About 400 milliliters of an aqueous, anionic latex of a
styrene:butadiene (30:70) copolymer having a Tg of about
-52.degree.C. (20 percent solids, by weight) was precipitated in
the usual manner according to the procedure of this invention with
a precipitating solution was prepared by dispersing 10 grams of a
high amylose corn starch which had previously been etherified by
treatment with 12.5 percent, by weight, of beta diethyl aminoethyl
chloride according to U.S. Pat. No. 2,813,093 in 1 liter of water.
The precipitating solution was stirred at a moderate rate
throughout the entire precipitating step. The resultant precipitate
exhibited a distinct, fibrous form.
While the described process represents a preferred manner of
preparing and obtaining the precipitated fibrous binding agent and
of forming the nonwoven, it can be appreciated that inherent
variations in the process can easily be utilized and are intended
to be within the scope of the present invention. For example,
instead of introducing the latex to a solution of the cationic
polymer, it is also possible (with less desirable results, however)
to introduce the cationic polymer into the latex. Likewise, another
variation makes use of a Y-shaped mixing tube, wherein the tube is
a means for simultaneously and intimately contacting the
precipitating solution and the separately fed anionic latex which
is emitted through tiny orifices. In still another variation of the
described process, the drying of the wet nonwoven may be combined
with sufficient pressure so as to soften the binder particles to a
point where they will essentially envelope a large portion of the
fibers of the nonwoven.
It is to be noted that while the preparation of the fibrous binding
agent in accordance with the process of this invention has been
described with respect to a batch process, it is also possible to
utilize a continuous process for this purpose.
Summarizing, it is thus seen that this invention provides a novel
process of preparing a polymeric binding agent in fibrous form as
well as an improved nonwoven product displaying superior
strength.
It will be understood that variations can be made in proportions,
materials and procedures without departing from the scope of this
invention which is defined by the following claims.
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