U.S. patent number 3,732,139 [Application Number 05/195,373] was granted by the patent office on 1973-05-08 for absorbent fibrous nonwoven fabric and method of forming the same.
This patent grant is currently assigned to Johnson & Johnson. Invention is credited to Michael R. Fechillas.
United States Patent |
3,732,139 |
Fechillas |
May 8, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
ABSORBENT FIBROUS NONWOVEN FABRIC AND METHOD OF FORMING THE
SAME
Abstract
Synthetic resin binder compositions for bonding nonwoven
fabrics, methods of using the same, and the resulting bonded
nonwoven fabrics, wherein the synthetic resin binder compositions
comprise from about 10 percent to about 50 percent by weight of a
polymodal molecular weight distribution synthetic acrylic ester
resin in which (1) one mode or peak is present in the molecular
weight range of from about 300 to about 2,000 and another mode or
peak is present in the molecular weight range of from about 4,000
to about 600,000 and (2) from about 10 percent to about 40 percent
by weight has a molecular weight in the range of from about 300 to
about 2,000 and from about 90 percent to about 60 percent by weight
has a molecular weight in the range of from about 4,000 to about
600,000 said polymodal molecular weight distribution synthetic
acrylic ester resin having a swell index in tetrahydrofuran of from
about 50 to about 200, from about 50 percent to about 90 percent by
weight of insolubles in tetrahydrofuran, and a second order glass
transition temperature of from about -40.degree. C to about
+5.degree. C.
Inventors: |
Fechillas; Michael R. (New
Brunswick, NJ) |
Assignee: |
Johnson & Johnson (New
Brunswick, NJ)
|
Family
ID: |
27498060 |
Appl.
No.: |
05/195,373 |
Filed: |
November 3, 1971 |
Current U.S.
Class: |
442/327; 156/291;
526/304; 604/372; 428/522; 604/366; 604/371; 604/375 |
Current CPC
Class: |
B32B
5/26 (20130101); D04H 1/66 (20130101); D04H
1/587 (20130101); D04H 1/641 (20130101); B32B
5/022 (20130101); D06M 15/267 (20130101); D06M
15/29 (20130101); D04H 1/64 (20130101); B32B
2305/02 (20130101); Y10T 428/31935 (20150401); Y10T
442/60 (20150401) |
Current International
Class: |
D04H
1/64 (20060101); D06M 15/29 (20060101); D06M
15/267 (20060101); D06M 15/21 (20060101); B32b
005/00 () |
Field of
Search: |
;161/99,106,146,148,157,170,227,251,254,256 ;117/138.8 ;156/333,291
;260/81.6E,81.6R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Powell; William A.
Assistant Examiner: Bell; James J.
Claims
What is claimed is:
1. A method of bonding a fibrous web of overlapping, intersecting
fibers into a bonded nonwoven fabric which comprises: applying to a
fibrous web of overlapping, intersecting fibers a synthetic acrylic
ester resin binder composition comprising from about 10 percent to
about 50 percent by weight of a polymodal synthetic acrylic ester
resin in which from about 10 percent to about 40 percent by weight
has a molecular weight in the range of from about 330 to about
2,000 and in which from about 90 percent to about 60 percent by
weight has a molecular weight in the range of from about 4,000 to
about 600,000 said polymodal synthetic acrylic ester resin having a
swell index in tetrahydrofuran of from about 50 to about 200 and
containing from about 50 percent to about 90 percent by weight of
insolubles in tetrahydrofuran.
2. A method of bonding a fibrous web of overlapping, intersecting
fibers into a bonded nonwoven fabric as defined in claim 1 wherein
said polymodal synthetic acrylic ester resin has a second order
glass transition temperature of from about -40.degree. C to about
+5.degree. C.
3. A method of bonding a fibrous web of overlapping, intersecting
fibers into a bonded nonwoven fabric which comprises: applying to a
fibrous web of overlapping, intersecting fibers a synthetic acrylic
ester resin binder composition comprising from about 10 percent to
about 50 percent by weight of a polymodal synthetic acrylic ester
resin in which one mode is present in the molecular weight range of
from about 300 to about 2,000 and another mode is present in the
molecular weight range of from about 4,000 to about 600,000, said
polymodal synthetic acrylic ester resin having a swell index in
tetrahydrofuran of from about 50 to about 200 and containing from
about 50 percent to about 90 percent by weight of insolubles in
tetrahydrofuran.
4. A method of bonding a fibrous web of overlapping, intersecting
fibers into a bonded nonwoven fabric as defined in claim 3 wherein
said polymodal synthetic acrylic ester resin has a second order
glass transition temperature of from about -40.degree. C to about
+5.degree. C.
5. A bonded, porous, absorbent fibrous nonwoven fabric having
excellent strength, softness, drape and excellent fold and tack
properties comprising: a fibrous web of overlapping, intersecting
fibers; and a synthetic resin binder bonding said overlapping,
intersecting fibers into a bonded nonwoven fabric, said synthetic
resin binder comprising a polymodal synthetic acrylic ester resin
in which from about 10 percent to about 40 percent by weight has a
molecular weight in the range of from about 300 to about 2,000 and
in which from about 90 percent to about 60 percent by weight has a
molecular weight in the range of from about 4,000 to about 600,000,
said polymodal synthetic acrylic ester resin having a swell index
in tetrahydrofuran of from about 50 to 200, and containing from
about 50 percent to about 90 percent by weight of insolubles in
tetrahydrofuran.
6. A bonded, porous, absorbent fibrous nonwoven fabric as defined
in claim 5, wherein said polymodal synthetic acrylic ester resin
has a second order glass transition temperature of from about
-40.degree. C to about +5.degree. C.
7. A bonded, porous, absorbent fibrous nonwoven fabric having
excellent strength, softness, drape and excellent fold and tack
properties comprising: a fibrous web of overlapping, intersecting
fibers; and a synthetic resin binder bonding said overlapping,
intersecting fibers into a bonded nonwoven fabric, said synthetic
resin binder comprising a polymodal synthetic acrylic ester resin
in which one mode is present in the molecular weight range of from
about 300 to about 2,000 and another mode is present in the
molecular weight range of from about 4,000 to about 600,000, said
polymodal synthetic acrylic ester resin having a swell index in
tetrahydrofuran of from about 50 to about 200 and containing from
about 50 percent to about 90 percent by weight of insolubles in
tetrahydrofuran.
8. A bonded, porous, absorbent fibrous nonwoven fabric as defined
in claim 5, wherein said polymodal synthetic acrylic ester resin
has a second order glass transition temperature of from about
-40.degree. C to about +5.degree. C.
Description
BACKGROUND OF THE INVENTION
The present invention relates to porous, absorbent, fibrous sheet
materials and to their methods for manufacture. More particularly,
the present invention is concerned with the so-called bonded,
"nonwoven" textile fabrics, i.e., fabrics produced from textile
fibers without the use of conventional spinning, weaving, knitting,
or felting operations.
THE NONWOVEN FABRICS
Although not limited thereto, the invention is of primary
importance in connection with nonwoven fabrics derived from
"oriented" or carded fibrous webs composed of textile-length
fibers, the major proportion of which are oriented predominantly in
one direction. Typical of such fabrics are the so-called "MASSLINN"
nonwoven fabrics, some of which are described in greater
particularity in U.S. Pat. Nos. 2,705,687 and 2,705,688, issued
Apr. 5, 1955 to D. R. Petterson et al., and I. S. Ness et al.,
respectively.
Another aspect of the present invention is its application to
nonwoven fabrics wherein the textile-length fibers were originally
predominantly oriented in one direction but have been reorganized
and rearranged in predetermined designs and patterns of fabric
openings and fiber bundles. Typical of such latter fabrics are the
so-called "KEYBAK" bundled nonwoven fabrics some of which are
described in greater particularity in U.S. Pat. Nos. 2,862,251 and
3,033,721, issued Dec. 2, 1958 and May 8, 1962, respectively, to F.
Kalwaites.
Still another aspect of the present invention is its application to
nonwoven fabrics wherein the textile-length fibers are disposed at
random by air-laying techniques and are not predominantly oriented
in one direction. Typical nonwoven fabrics made by such procedures
are termed "isotropic" nonwoven fabrics and are described in
greater particularity, for example, in U.S. Pat. Nos. 2,675,363 and
2,676,364, issued Apr. 27, 1964 to C. H. Plummer et al.
And, still another aspect of the present invention is its
application to nonwoven fabrics which comprise textile-length
fibers and which are made basically by conventional or modified
aqueous papermaking techniques such as are described in greater
particularity in pending patent application Ser. No. 4,405, filed
Jan. 20, 1970, and now abandoned, by P. R. Glor and A. H. Drelich.
Such fabrics are also basically "isotropic" and generally have like
properties in all directions.
The conventional base starting material for the majority of these
nonwoven fabrics is usually a fibrous web comprising any of the
common textile-length fibers, or mixtures thereof, the fibers
varying in average length from approximately one-half inch to about
21/2 inches. Exemplary of such fibers are the natural fibers such
as cotton and the synthetic or man-made cellulosic fibers, notably
rayon or regenerated cellulose.
Other textile-length fibers of a synthetic or man-made origin may
be used in various proportions to replace either partially or
perhaps even entirely the previously-named fibers. Such other
fibers include: polyamide fibers such as nylon 6, nylon 66, nylon
610, etc.; polyester fibers such as "Dacron," "Fortrel" and
"Kodel"; acrylic fibers such as "Acrilan, " "Orlon" and "Creslan";
modacrylic fibers such as "Verel" and "Dynel"; polyolefinic fibers
derived from polyethylene and polypropylene; cellulose ester fibers
such as "Arnel" and "Acele"; polyvinyl alcohol fibers; etc.
These textile-length fibers may be replaced either partially or
entirely by fibers having an average length of less than about
one-half inch and down to about one-quarter inch. These fibers, or
mixtures thereof, are customarily processed through any suitable
textile machinery (e.g., a conventional cotton card, a
"Rando-Webber," a papermaking machine, or other fibrous web
producing apparatus) to form a web or sheet of loosely associated
fibers weighing from about 100 grains to about 2,000 grains per
square yard or even higher.
If desired, even shorter fibers, such as wood pulp fibers or cotton
linters, may be used in varying proportions, even up to 100 percent
where such shorter length fibers can be handled and processed by
the available apparatus. Such shorter fibers have lengths less than
one-fourth inch, down to one-eighth inch or less, for fluid
processes.
THE BONDING METHODS
The resulting fibrous web or sheet, regardless of its method of
production, is then normally subjected to at least one of several
types of bonding operations to anchor the individual fibers
together to form a self-sustaining web. One method is to impregnate
the fibrous web over its entire surface areas with various
well-known bonding agents, such as natural or synthetic resins.
Such over-all impregnation produces a nonwoven fabric of good
longitudinal and cross-strength, acceptable durability and
washability, and satisfactory abrasion resistance. However, the
nonwoven fabric sometimes does not completely possess the softness,
drape and hand of a woven or knitted textile fabric. Consequently,
although such over-all impregnated nonwoven fabrics are
satisfactory for many uses, they are still unsatisfactory in some
instances as general purpose textile fabrics.
Another well-known bonding method is to print the fibrous webs with
intermittent or continuous straight or wavy lines, or discrete
areas of binder extending generally transversely or diagonally
across the web and additionally, if desired, along the fibrous web.
The resulting nonwoven fabric, as exemplified by a product
disclosed in the Goldman U.S. Pat. No. 2,039,312 and sold under the
Trademark, "MASSLINN" is more satisfactory as a textile fabric than
over-all impregnated webs in that the softness, drape and hand of
the resulting nonwoven fabric more nearly approach those of a woven
or knitted textile fabric.
As stated previously, the properties of longitudinal and cross
strength, durability, washability, abrasion resistance, softness,
drape and hand are important and critical in nonwoven fabrics.
HOwever, there is still another property which is also important
and critical, particularly in those uses wherein the nonwoven
fabric is to be folded and/or tucked and wherein the fold and/or
tuck is to be maintained without any appreciable resilient
"spring-back" or undesirable opening-up of the folded and/or tucked
nonwoven fabric.
This property of being tucked and folded in position is desirable
in many nonwoven fabric products, not only during the
manufacturing, processing, handling and packaging of the product
but also in its subsequent use. One prime example of such a product
requiring good tuck and fold properties is a sanitary napkin
wherein the tabs of the nonwoven fabric cover extending from each
end are tucked together and folded inwardly during manufacturing
and packaging and must be subsequently unfolded outwardly but
remain in tucked position to facilitate fastening of the tabs to a
sanitary belt during use.
THE INVENTIVE CONCEPT
It has been discovered that the above-described properties, and
particularly the fabric strength and the tuck and fold
characteristics, are functions of the molecular weight distribution
of the resin binder used. For example, polymers having high average
molecular weight distribution tend to be strong, although they also
tend to have poor tuck and fold characteristics. Also polymers
having low average molecular weight distribution tend to have good
tuck and fold characteristics, although they tend to be lacking in
strength.
It has further been discovered that the above-described properties,
and particularly the fabric strength and the tuck and fold
characteristics can be obtained by using a synthetic resin binder
composition comprising from about 10 percent to about 50 percent by
weight of a polymodal molecular weight distribution synthetic
acrylic ester resin in which (1) one mode is present in the
molecular weight range of from about 300 to about 2,000 and another
mode is present in the molecular weight range of from about 4,000
to about 600,000 and (2) from about 10 percent to about 40 percent
by weight has a molecular weight in the range of from about 300 to
about 2,000 and from about 90 percent to about 60 percent by weight
has a molecular weight in the range of from about 4,000 to about
600,000, said polymodal molecular weight distribution synthetic
acrylic ester resin having a swell index in tetrahydrofuran of from
about 50 to about 200, from about 50 percent to about 90 percent by
weight of insolubles in tetrahydrofuran, and a second order glass
transition temperature of from about -40.degree. C to about
+5.degree. C.
THE "POLYMODAL" CONCEPT
It is believed that the term "polymodal" should be defined more
specifically in order to avoid any confusion as to its meaning and
scope. In statistical analysis, the particular item in a series of
statistical data which occurs oftenest is called the mode. If one
were to draw a graph showing the molecular weight distribution of a
typical conventional polymer of resin, the result would normally be
the well-known bell-shaped curve of normal distribution. The
highest point, or mode, of this bell-shaped curve indicates the
particular molecular weight which occurs oftenest in the resin.
Usually, only one highest point or mode occurs and hence such a
bell-shaped normal distribution curve is called monomodal. As will
be described in detail hereinafter, such a monomodal curve is noted
in FIG. 1 of the drawings.
By special techniques well known in the polymerization art, it is
possible for a curve of the molecular weight distribution of a
polymer or resin to rise to a peak at a particular molecular weight
and then recede and then rise again to a second peak at a
subsequent different molecular weight. It is also possible for the
graph to recede and rise still again to show a third peak, and so
on. Such resins having two, three, or more modes or peaks are
described herein as bimodal, trimodal, etc. or generically as
"polymodal," meaning that the curve representing their molecular
weight distribution will show two, three, or more modes or
peaks.
Such polymodal characteristics can be built into polymers or resins
and specifically into synthetic acrylic acid ester resins in
several ways. For example, one way is to add a limited amount of a
chain transfer agent, such as lauryl mercaptan, at a specific point
in time during the polymerization reaction. Lower molecular weight
distributional modes are obtained by such techniques. Or, one can
selectively graft additional polymer blocks on existing polymer
chains by a post polymerization reaction by adding a limited amount
of another polymer and a free radical initiator such as an organic
peroxide. Such graft polymerization will lead to higher molecular
weight distributional modes.
THE RESINS USED
Specific examples of such synthetic acrylic ester resins which lend
themselves to such techniques include the polymerized alkyl esters
of acrylic acid such as ethyl acrylate, ethyl-hexyl acrylate,
methyl acrylate, propyl acrylate, butyl acrylate, etc. Other
acrylates, such as hydroxyethyl acrylate, dimethyl amino ethyl
acrylate, etc. are also of use. These synthetic acrylic ester
resins may be used as homopolymers derived from one monomer, or may
be used as copolymers or terpolymers of two or three monomers in
various combinations, such as a copolymer of ethyl acrylate and
butyl acrylate, or as a terpolymer of ethyl acrylate, butyl
acrylate, and ethyl hexyl acrylate. Various mixtures in various
proportions of these synthetic acrylic ester resins are also of use
within the scope of the present inventive concept.
Regardless of the specific acrylate or mixture of acrylates which
are used, it is essential that they be polymodal insofar as their
molecular weight distribution is concerned.
THE DRAWINGS
This aspect of the invention concept will be described and
illustrated by reference to the attached drawings wherein:
FIG. 1 is a molecular weight distribution curve of a typical prior
art synthetic resin showing a substantially symmetrical bell curve
of normal distribution with an average molecular weight of about
120,000. This is a monomodal curve;
FIG. 2 is a molecular weight distribution curve of a polymodal
synthetic acrylic ester resin, showing one mode or peak at a
molecular weight of about 710, another mode or peak at a molecular
weight of about 62,000 and a third mode or peak at a molecular
weight of about 8 million; and
FIG. 3 is a molecular weight distribution curve of another
polymodal synthetic acrylic ester resin, showing one mode or peak
at a molecular weight of about 620 and another mode or peak at a
molecular weight of about 30,000.
With reference to the molecular weight distribution curves shown in
the drawings, they are obtained by analysis on a Gel Permeation
Chromatographic Analysis Machine equipped with 4 linear 7 .times.
10.sup.6, 3 .times. 10.sup.6, 10.sup.5, and 10.sup.3 A.degree.
"Styragel" columns. The solvent is tetrahydrofuran which is
maintained at a flow rate of 1 ml per minute at 25.degree. C. The
sample concentration is one-half percent. The sample load of 20
milligrams (1 weight/volume percent) is placed on the head of the
column blank. The injection timing is 120 seconds. The sensitivity
is 2X.
PRIOR ART BINDERS
Use of a synthetic resin such as illustrated in FIG. 1 having an
average molecular weight of about 120,000 and possessing only one
mode or peak will not yield a satisfactory resin binder.
If, by means of suitable and sufficient amounts of inhibitors
during the polymerization reaction, the average molecular weight
were to be shifted to the left in FIG. 1 to a lower single mode or
peak value between 300 and 4,000, for example, and the
substantially symmetrical curve of molecular weight distribution
maintained, the result again would be an unsatisfactory resin
binder. In such a case, the resulting resin binder would almost
certainly not have sufficient strength and would almost surely be
too tacky and too sticky.
And if, by means of suitable and sufficient amounts of inhibitors
during the polymerization reaction, the average molecular weight
were to be shifted to the right to FIG. 1 to a higher single mode
or peak value between 400,000 and 8 million for example, and the
substantially symmetrical curve of molecular weight distribution
maintained, the result again would be an unsatisfactory resin
binder. In such a case, the resulting resin binder may have
sufficient strength but it would not have sufficient fold and tack
properties.
THE INVENTION BINDERS
It is only when the proper amounts of suitable inhibitors or chain
transfer agents are employed, or when suitable graft polymerization
techniques are used, at the correct time during a polymerization
reaction as to bring about a resin having a polymodal molecular
weight distribution as described herein that satisfactory synthetic
resin binders are obtained.
It has been established that optimum values are obtained only when
from about 10 percent by weight to about 40 percent by weight of
the synthetic resins is in the lower molecular weight range of from
about 300 to about 2,000 and from about 90 percent by weight to
about 60 percent by weight of the synthetic resins is in the higher
molecular weight range of from about 4,000 to about 600,000 or
more.
It has also been established that, even though the molecular weight
distribution falls within the desired polymodal weight ranges, it
is also essential that the synthetic resin be cross-linked to
within certain desired limits. Failure to cross-link the synthetic
resin sufficiently will lead to an undesirably overly tacky and
sticky synthetic resin. On the other hand, cross-linking to too
great an extent will lead to a synthetic resin which is undesirably
insufficiently tacky.
The extent of cross-linking can be established by determining (1)
the swell index and (2) the percent insolubles of the synthetic
resin.
In the present case, the swell index is determined by casting a
film of the synthetic resin and immersing the cast film in a
"solvent" or swelling agent for the noncross-linked synthetic resin
and observing the absorption of the solvent by the film and the
extent of the swelling. In the present case, the solvent or
swelling agent which is used is tetrahydrofuran. When the
cross-linked synthetic resin is immersed in the solvent, which, in
the absence of cross-linkages, would actually be a solvent for the
resin, the synthetic resin film swells to many times its original
volume by absorbing the solvent in which it is immersed. The
swelling is greater the fewer cross-linkages and the better the
solvent. The swell index is determined by determining the weight of
the film before immersion and after immersion. The increase in
weight is, of course, the weight of the solvent absorbed by the
film. The swell index is the ratio of the weight of the film after
immersion to the weight before immersion.
In the present case, a swell index of from about 50 to about 200
has been found to be acceptable. A preferred range of the swell
index extends from about 60 to about 180.
With regard to the determination of the percent insolubles in the
synthetic resin, it is to be noted that such determination will not
only indicate the extent of the cross-linking but also will
correlate to the molecular weight of the synthetic resin. This is
explained by the fact that the greater the cross-linking, the
higher the molecular weight will become because of the linking
together of more and more chains or "mers" of the synthetic
resin.
The solvent used for the extraction of the insolubles in the
synthetic resin is tetrahydrofuran and it has been established that
a range of from about 50 percent to about 90 percent by weight of
insolubles is acceptable. A preferred range for the percent
insolubles extends from about 80 percent to about 90 percent.
Naturally, more highly cross-linked and higher molecular weight
synthetic resins will yield higher percent insolubles. And, lower
cross-linked and lower molecular weight synthetic resins will yield
lower percent insolubles.
Too high a percent insolubles will indicate an undesirably
insufficiently tacky or sticky synthetic resin. Too low a percent
insolubles will indicate an undesirably overly tacky and sticky
synthetic resin.
Another factor to be considered in the determination of acceptable
synthetic acrylic acid ester resins is the second order glass
transition temperature (symbol T.sub.2) which is used to
distinguish a thermodynamic transition at which there occurs a
relatively sharp change in the derivative of an extensive property
of the synthetic resin, such as volume or heat content, from a
first-order phase transition such as crystallization at which there
is a sharp change in the extensive property itself.
Within the scope of the present inventive concept, it has been
established that a second order glass transition temperature range
of from about -40.degree. C to about +5.degree. C is most desirable
and advantageous in order to obtain the necessary balance of
properties with particular emphasis on the fold and tack
property.
PREFERRED EMBODIMENTS
The invention will be further described by reference to the
following examples wherein there are disclosed preferred
embodiments of the present invention. However, it is to be
appreciated that such Examples are illustrative but not limitative
of the broader aspects of the inventive concept.
EXAMPLE I
A fibrous card web weighing about 214 grains per square yard and
comprising 100 percent extra dull bleached rayon fibers, 3 denier
and 1-9/16 inches in length, is intermittently bonded by the
rotogravure process using an engraved binder printing roll having
four horizontal wavy lines per inch, as measured in the machine or
long direction. The width of each line as measured peripherally on
the engraved binder printing roll is 0.019 inch.
The binder resin in an N-methylol acrylamide cross-linked copolymer
of ethyl acrylate and butyl acrylate and the polymodal molecular
weight distribution curve is shown in FIG. 2 of the drawings. The
swell index of the resin in tetrahydrofuran is 177.2. The percent
by weight of insolubles of the resin in tetrahydrofuran is 88.6
percent. The second order glass transition temperature is
-15.degree. C.
The aqueous binder composition comprises 9 pounds of a 50 percent
solids aqueous dispersion of the binder resin, (real weight of
resin 4.5 pounds), 1.4 pounds of a conventional thickening agent,
0.05 pounds of a conventional antifoam agent, and small amounts of
conventional pigments, anti-oxidants, etc. The binder is applied to
the wet web and drying takes place on heated drying cans at a
temperature of about 270.degree. F. The finished dry weight of the
bonded nonwoven fabric is about 260 grains per square yard.
The properties of the bonded nonwoven fabric are:
Dry Cross Tensile 6.9 pounds Wet Cross Tensile 3.2 pounds Dry Long
Tensile 45.5 pounds Wet Long Tensile 19.8 pounds Pinning Strength
3.07 pounds Handle-o-Meter Softness 84.4 Tab Retention 22.1
grams
The bonded nonwoven fabric is excellent for use as a cover or
wrapper for a sanitary napkin.
The bonded nonwoven fabric cover wraps very easily around the
absorbent core of the sanitary napkin and the extending ends are
easily tucked into the desired configuration. The tucked ends are
then folded inwardly and remain in folded condition saitsfactorily
during processing, handling and packaging. Subsequently, when the
folded ends are unfolded for use, the tucks therein do not open up
and securing of the ends to a sanitary belt is rendered very
simple.
EXAMPLE II
A fibrous card web weighing about 210 grains per square yard and
comprising 100 percent extra dull bleached rayon fibers, 3 denier
and 1-9/16 inches in length, is intermittently bonded by the
rotogravure process using an engraved roll having four horizontal
wavy lines per inch, as measured in the machine or long direction.
The width of each line as measured peripherally on the engraved
roll is 0.019 inch.
The binder resin is an N-methylol acrylamide cross-linked copolymer
of ethyl acrylate, butyl acrylate, and ethyl-hexyl acrylate and the
polymodal molecular weight distribution curve is shown in FIG. 3 of
the drawings. The swell index of the resin in tetrahydrofuran is
60.77. The percent by weight of insolubles of the resin in
tetrahydrofuran is 54.3 percent. The second order glass transition
temperature is -18.degree. C.
The aqueous binder composition comprises 10 pounds of a 46.5
percent solids aqueous dispersion of the binder resin, (real weight
of resin is 4.65 pounds) 1.4 pounds of a conventional thickening
agent, 0.05 pounds of a conventional antifoam agent, and small
amounts of conventional pigments, antioxidants, etc. The binder is
applied to the wet web and drying takes place on heated drying cans
at a temperature of about 270.degree. F. The finished dry weight of
the bonded nonwoven fabric is about 260 grams per square yard.
The properties of the bonded nonwoven fabric are:
Dry Cross Tensile 3.4 pounds Wet Cross Tensile 2.2 pounds Dry Long
Tensile 37.3 pounds Wet Long Tensile 20.2 pounds Pinning Strength
2.87 pounds Handle-o-Meter Softness 90 Tab Retention 25 grams
The bonded nonwoven fabric is excellent for use as a cover or
wrapper for a sanitary napkin.
The bonded nonwoven fabric cover wraps very easily around the
absorbent core of the sanitary napkin and the extending ends are
easily tucked into the desired configuration. The tucked ends are
then folded inwardly and remain in folded condition satisfactorily
during processing, handling and packaging. Subsequently, when the
folded ends are unfolded for use, the tucks therein do not open up
and securing of the ends to a sanitary belt is rendered very
simple.
In these examples, reference has been made to Tab Retention values
measured in grams. These values are relative, rather than absolute,
and represent the result of considerable empirical testing data
derived as follows:
Porous, absorbent, fibrous nonwoven fabrics having a weight of from
about 240 grains per square yard to about 280 grains per square
yard is bonded with a resin in the manner described in the
preceding examples. The fabric is then folded and tucked in very
much the same way that the tabs on the ends of sanitary napkins are
folded and tucked during commercial manufacture. See U.S. Pat. Nos.
2,918,065, 3,076,459, and 3,076,460 for typical folding and tucking
procedures. The folded and tucked ends are then passed through cold
(room temperature) pressure-applying rolls which press the ends
together with approximately the same pressure as is applied during
the conventional commercial handling and processing of the product.
An Instron Tensile Testing Machine is then used in conventional
manner to determine the force in grams required to separate or
unfold the ends. This is very similar to a standard Peel Adhesion
Test. Test values less than about 4 grams show low adhesivity and
are undesirable inasmuch as the ends would undesirably unfold and
open up subsequently during commercial handling and processing.
Packaging problems would also be introduced. Values in excess of
about 30 grams show adhesivity which is too great and are also
undesirable as the ends are too tightly adhered and the surfaces
therefore are sticky and tacky which could lead to an undesirable
"blocking" or adhering to adjacent products. Values between 20 and
25 are deemed most desirable and are preferred.
Having now described the invention in specific detail and
exemplified the manner in which it may be carried into practice, it
will be readily apparent to those skilled in the art that
innumerable variations, applications, modifications, and extensions
of the basic principles involved may be made without departing from
its spirit and scope.
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