Note: Descriptions are shown in the official language in which they were submitted.
SOLUBLE MEDICAL FABRICS
Background of the Invention
S Field of the Invention
This invention relates to nonwoven fabrics and, in particular, to non-
woven fabrics for use in medical applications.
Medical fabrics in the form of such articles as bed sheets, gowns,
protective pads, and the like usually are disinfected by exposing them to caustic,
10 acidic, or other harsh conditions in a hospital or other commercial laundry.
Unfortunately, these reusable fabrics, even after such harsh treatment, still may
contain infectious wastes which could be transmitted to healthy individuals. Also,
j after a number of such disinfecting cycles, the worn-out fabric ultimately must
¦ be disposed of in, for example, a landfill.
Non-reusable articles made from medical fabrics are also known.
Unfor~unately, the disposal of large quantities of such articles in landfills has
become progressively more difficult and has raised a variety of environmental
concerns.
The present invention takes an entirely different approach to this problem
of conhminated medical fabrics. Namely, the medical fabrics of the invention
are designed to be processed in a conventional laundry, not for the purpose of
reuse but rather for disposal.
Specifically, the present medical fabrics have a composition such that they
dissolve when exposed to the high pH and high temperature conditions of a
commercial laundry. Once dissolved, the remains of the fabric pass into the
waste water treatment facility normally used to process the effluent from the
laundry without significant added burden to the environment. In this way, the
invention reduces ~he potential of ~ le coming into contact with infectious
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waste as well as solving the disposal problems associated with conventional
reusable and disposable medical fabrics.
In addition to having these improved disposal properties, the fabrics of the
invention also have the physical and fluid barrier properties required for a
commercial medical fabric. These properties are achieved by providing the fabricwith at least a two-layer structure, with one of the layers serving the primary
function of providing the overall physical properties for the laminate and the other
layer serving the primary function of providing a barrier to the passage of suchbodily fluids as urine and blood. Each layer has a composition which causes it
to dissolve when subjected to the temperature and pH conditions of a commercial
laundry. In this way, the fabrics of the invention satisfy the twin goals of
providing a material which (1) works successfully in a medical environment and
(2) can be disposed of readily without significant added burden to existing waste
disposal systems.
Description of the Prior Art
3~ Various materials which tend to decompose or degrade in the presence of
water or o~her liquids have been disclosed in the literature for the purpose of
producing a product which is "flushable", i.e., which can be disposed of in a
toilet. The patent documents described below illustrate this approach.
U.S. Patent No. 4,084,591 to Takebe et al. describes a material for use
in tarnpons which is (a) insoluble in menst~ual blood at body temperatures and (b)
soluble in water at room temperature. The material comprises a lower alkyl or
a lower hydroxyalkyl substituted cellulose ether.
U.S. Patent No. 2,518,486 to Mende discloses applicators for pharrnaceuti-
cal formulations which are made of a polyvinyl alcohol which softens and swells
~, upon contact with water.
European Patent Publication No. 176,316, discloses the preparation of a
nonwoven fabric from a water-soluble resin, in particular, from the starch
`~ polymer pullulan. The fabric is said to decompose in water or when buried in
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the ground. The fabric is disclosed as being useful as a component of such
moisture-absorptive sanitary goods as diapers, sanitary napkins, and toilet paper.
European Patent Publication No. 291,024 discloses a biodegradable tampon
applicator made of a moldable poly(3-hydroxybutyric acid) composition. Sample
5 applicators are described as being fully dissolved in a sludge/raw sewage mixture
after a period of 35 or more days.
Nonwoven materials employing a binder which is soluble under selected
conditions also have been disclosed. Examples of this approach follow.
U.S. Patent No. 3,480,016 to Costanza et al. discloses a scrim or paper
10 of biodegradable fibers such as cellulosic fibers bound together by a binder which
iS soluble in, for example, an alkaline medium. The patent lists carboxy ester
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lactones and copolymers of ethylenically unsaturated mono- and polycarboxylic
;, acids with ethylenically unsaturated esters or nitrites as suitable binders. The
patent states that the final product, e.g., a disposable diaper or sanitary napkin,
can include a moisture-imperneable film formed from the binder material.
Significantly, and in direct contrast to the present invention (see below), the
degrading agent, e.g., alkaline medium, disintegrates the binder but not the fibers
of which the scrim or paper is composed.
U.S. Patent No. 3,635,221 to Champaigne, Jr. describes a sanitary napkin
having a flushable wrapper composed of a nonwoven web of, for example, rayon
fibers held together by a binder, such as poly(vinyl alcohol) or methyl cellulose,
which is more soluble in cold water than in hot water. See also U.S. Patent
Nos. 4,258,849 and 4,372,447 to Miller which disclose the use of a poly(vinyl
- alcohol) binder in a flushable towelette, and U.S. Patent No. 4,343,403 to
;`~ 25 Daniels et al. which discloses a poly(vinyl acetate) latex impregnated towelette
which includes poly(vinyl alcohol) as a protective colloid. For a similar approach
' employing modified guar gum instead of a polyvinyl alcohol, see U.S. Patent No.
1 4,362,781 to Anderson.
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;. U.S. Patent No. 3,804,092 to Tunc describes a water-dispersible nonwoven
fabric employing an allcali cellulose ether sulfate resin as a binder. The fabric
is said to (a) retain a significant part of its dry tensile strength when in a fluid
containing about 0.8 percent or more of sodium chloride, e.g., a body fluid, andS ~b) disperse when in a fluid having a lower sodium chloride content, e.g., the water in a toilet bowl.
;-~ U.S. Patent No. 4,117,187 to Adams et al. discloses a premoistened
flushable wiper which includes a pH sensitive binder, specifically, an acid
insoluble-aLkali soluble acidic polymer. In the neutral or alkaline flush water of
10 a toilet, the binder loses its strength and the wiper disintegrates. See also U.S.
Patent No. 4,242,408 to Evani et al.
Multilayer materials which decompose under selected conditions also have
been disclosed. Some examples of this approach are described below.
U.S. Patent No. 3,777,759 to Oehmke et al. discloses a multilayer pad
15 for use as a diaper which includes (a) an inner layer which is a nonwoven webof short fibers held together with a water-insoluble, enzyme-degradable binder,
(b) one or more intermediate layers of nonwoven, moisture-absorbent fibers
containing no binder, and (c) an outer layer composed of the same material as the
inner layer and having a water-repellant coating on one of its surfaces. The pad20 is disposed of by placing it in, for example, a toilet, and adding an amount of
enzyme to the water which causes the nonwoven layers to disintegrate.
U.S. Patent No. 3,881,210 to Drach et al. describes a premoistened wiper
which includes a reinforcing layer of a water-dispersible thermoplastic materialsuch as a poly(vinyl alcohol) or a water-dispersible poly(vinyl acetate). The
l 25 thermoplastic material maintains the integrity of the wipe during storage, but
J disperses during flushing in a toilet bowl.
In addition to the foregoing, U.S. Patent 4,372,311 to Potts discloses
disposable articles, such as, diapers, catamenial devices, hospital bed liners, and
bandages, which are made from a water-soluble polymer and which are coated
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with a water-insoluble polymer which is photo- or biodegradable. Among the
water-soluble polymers disclosed in this patent is poly(vinyl alcohol). Among the
water-insoluble coating polymers are polycaprolactones. None of the above
references discloses or suggests a nonwoven, multilayer fabric which has suitable
S physical and fluid barrier properties for use as a medical fabric and which iscomposed of fibers which dissolve at the elevated temperatures and pH values
which exist in a hospital or commercial laundry.
Summary of the Invention
In view of the foregoing state of the art, it is an object of the present
invention to provide nonwoven fabrics for use in medical applications. More
particularly, it is an object of the invention to provide nonwoven fabrics whichsatisfy the physical and fluid barrier requirements of a medical fabric and which
15 can be disposed of more simply than conventional medical fabrics. It is a
specific object of the invention to provide medical fabrics which dissolve when
subjected to the temperature and pH conditions of a commercial laundry and
thus can be disposed of as part of the eMuent from such a laundry.
To achieve the foregoing and other objects, the invention in accordance
20 with certain of its aspects provides a nonwoven fabric comprising:
(a) a barrier layer which is substantially impermeable to water at room
temperature; and
(b) a support layer which provides physical strength for the fabric;
wherein the barrier and support layers are bonded to one another to form the
25 nonwoven fabric and each of the layers comprises fibers which dissolve in an
alkaline solution having a pH above about 12 and a temperature above about
70C in a period of time of less than about 10 minutes.
In certain preferred embodiments of the invention, the fibers are composed
of a material selected from the group consisting of ethylene-acrylic acid (EAA)
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copolymers, methacrylic acid polymers, blends of EAA copolymers and
` methacrylic acid polymers, and poly(vinyl alcohol) (PVOH) polymers, in
~, particular, PVOH polymers which have been treated so that they do not dissolve
in water or become sticky at room temperature, e.g., 20C.
SIn other preferred embodiments, the fibers making up the barrier layer
have a mean diameter which is smaller than the mean diameter of the fibers
making up the support layer. In particular, the mean diameter of the fibers of
the barrier layer preferably are in the range from about 1 micrometer to about 20
' micrometers while those making up the support layer preferably have a mean
10diameter in the range from about 10 micrometers to about 30 micrometers.
In further preferred embodiments, the nonwoven fabric includes two
support layers, one on each side of the barrier layer. For this construction, the
support layers are preferably produced using a melt or solution spinning process,
i.e., they are of the "spunbonded" type, while the barrier layer is produced using
15a melt or solution blowing process, i.e., they are of the "meltblown" type, so that
the overall fabric has a spunbonded-meltblown-spunbonded (SMS) structure.
Further preferred properties of the barrier and support layers are discussed
below in connection with the description of the preferred embodiments of the
3 invention
20In accordance with other aspects of the invention, a method for the
disposal of nonwoven fabrics of the foregoing type is provided wherein the fabric
is subjected to a pH above about 12 and a temperature above about 70C for a
period of time sufficient to dissolve the fibers making up the fabric. For the
preferred fabrics of the invention, that period is less than about 5 minutes.
J 25The accompanying drawings, which are incorporated in and constitute part
of the specification, illustrate the preferred embodiments of the invention, and.~ together with the description, serve to explain the principles of the invention. It
is to be understood, of course, that both the drawings and the description are
explanatory only and are not restrictive of the invention.
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Brief Description of the Drawings
Figure 1 is a schematic (not-to-scale) diagram of a soluble medical fabric
constructed in accordance with the present invention.
S Figure 2 is a schematic diagram of an apparatus which can be used to
produce the medical fabrics of the present invention.
Description of the Preferred Embodiments
As discussed above, the present invention relates to nonwoven fabrics for
.~ medical use which comprise a barrier layer and at least one and preferably two
support layers. Such a fabric is schematically shown in Figure 1 where the
.
. fabric is identified by the reference numeral 10, the barrier layer by the reference
numeral 13, and the support layers by the reference numerals 11 and 15.
The barrier layer provides the fabric's fluid control properties. In
particular, this layer should be able to withstand a hydrohead of at least about 10
centimeters of water, where the hydrohead is measured using method 5514 of
Federal Test Method Standard No. l91A (7/20178). Depending upon the specific
materials, fiber diameters, and method of preparation, the barrier layer will insome cases be able to withstand a hydrohead as high as about 50 centimeters of
water and in other cases as high as about 500 centimeters of water.
~i The perrneability of the barrier layer should be less than 100 cubic feet per
minute per square foot at 0.5 inches of water (cfm/ft2 ~ 0.5" water) (less than
about 500 liters per second per square meter at about 1.3 centimeters of water
(lps/m~ ~ 1.3 cm water), where the penneability (specifically, the Frazier
permeability) is measured using method 5450 of Federal Test Method Standard
No. l91A (7/20l78). Preferably, the permeability is in the range of from about
5 to about 50 cfm/sq.ft. ~ 0.5" water (from about 25 to about 250 lps/m2 ~ 1.3
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cm water) and in some cases may be as low as lo6 cfm/sq.ft. ~) 0.5" water
(about 5 lps/m2 ~ 1.3 cm water).
These hydrohead and permeabilit~ properties are achieved by using fibers
having a relatively small mean diameter to form the barrier layer so that the
S fabric's pores have a relatively small diameter and follow highly tortuous paths.
Preferably, the mean diameter of the fibers is in the range of from about 0.1
micrometer to about 20 micrometers and more preferably in the range from about
2 micrometers to about 5 mierometers. Also, it is desirable for the mean length
of the fibers making up the balTier layer to be relatively short and, in particular,
10 shorter than the mean length of the fibers making up the support layer. When
fibers of these types are used, the basis weight of the barrier layer will typically
be in the range of from about 15 to about 30 grams per square meter where basis
weight is determined using method 5041 of Federal Test Method Standard No.
191A (7l20l78).
The support layer or layers provide the fabric's physical properties,
including, in particular, the fabric's physical strength. With regard to strength,
the support layer should have a breaking length of at least about 0.1 kilometer
and preferably of at least about 1 kilometer, where breaking length is measured
using Method 5102 of Federal Test Method Standard No. l91A (7l20l78).
20 Depending upon the specific materials, fiber diameters, and method of prepara-
tion, the support layer in some cases will have a breaking length as high as about
S l~lometers and in other cases as high as about 10 kilometers.
The support layer also should have a grab tensile strength of at least about
1 pound (about 0.45 kg) and preferably of at least about 3 pounds (about 1.3 kg),
25 where grab tensile strength is measured using method 5100 of Federal Test
Method Standard No. l91A (7/20/78). In some cases, the grab tensile strength
of the support layer may be as high as 20 pounds (about 9.1 kg) and in others,
as high as 50 pounds (about 22 kg).
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To achieve adequate strength properties, the support layer in general will
comprise fibers having a larger mean diameter than the mean diameter of the
fibers making up the barrier layer. Preferably, the mean diameter of the supportlayer fibers is in the range of from about 10 micrometers to about 30 micro-
5 meters. When fibers of these sizes are used, the basis weight of the support layertypically will be in the range of from about 10 to about 30 grams per squaret~', meter.
' In addition to providing the fabric's overall strength properties, the support
layer also serves to provide abrasion resistance and the basic esthetics of the
10 fabric including its appearance and hand or feel. In some cases, it may be
desirable to add a binder to the support layer to improve its abrasion resistance,
as is well known to those having ordinary skill in the art.
The barrier and support layers can be made of the same or different
`j materials. In either case, the material must be such that it will dissolve when
15 subjected to the allcaline, high temperature conditions of a commercial laundry.
In particular, the barrier and support layers should dissolve in an alkaline solution
having a pH above about 12 and a temperature above about 70C in a period of
time of less than about 10 minutes and preferably less than about 5 minutes. As
used herein, materials which "dissolve" under these conditions include materials20 which go into solution under such conditions as well as materials which disperse
into small pieces (e.g., a colloidal state), such that the fiber structure of the fabric
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is no longer visible.
Whereas the fabric must dissolve when commercially laundered, it should
not dissolve under conditions of normal use. Preferably, the fibers of the support
~'.,;J, 25 layer should be able to withstand an elevated pH (e.g., a pH greater than about
12) under room temperature conditions (e.g., 20C) and an elevated temperature
(e.g., a temperature above about 70C) at neutral pH without substantially
dissolving so that only the combined elevated temperature and elevated pH
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conditions of a commercial laundry will dissolve the fabric. The barrier layer
also should have these properties.
,' A variety of polymeric materials known in the art can be used for the
support and barrier layers. In general terrns, the polymers will contain pendantcarboxylic acid, acid ester, or hydroxyl groups so that they are susceptible to
dissolution at elevated temperatures and pH's. Preferred materials include
ethylene/acrylic acid (EAA) copolymers; blends of EAA copolymers and
(meth)acrylate/(meth)acrylic acid copolymers, such as those described in U.S.
Patent No. 4,870,148 assigned to RB Kunststoffpatent-Verwertugs AG and
~,; 10 Belland AG, both of Switzerland, issued September 26, 1989 and which is
incorporated herein by reference (such copolymers are commercially available
from Belland AG); and poly(vinyl alcohol) (PVOH) polymers, in particular,
PVOH polymers which have been treated so that they do not dissolve in water
or become sticky at room temperature. The treatment of the PVOH polymer
can be performed (1) via covalent cross-linking utilizing a chemical reaction
associated with the polymer's hydroxyl groups such as acehlization, reaction with
~, dialdehyde, amination, etherification, esterification, or urethane forrnation, (2) via
inorganic complex formation, or (3) via crystallization through heat treatment.
In Example 1 presented below, a hydrolyzed PVOH polymer having a
molecular weight of 78,000 and a degree of hydrolysis of 99.7% was used.
This material was obtained from Polyscience, Inc., Warrington, PA, Cahlog
No. 15129. In Example 2, an AIRVOL 125 PVOH polymer obtained from Air
~ Products and Chemical, Inc., Allentown, PA, was used. This material is
,. described by the manufacturer as being of medium molecular weight and super
hydrolyzed.
i In Example 3, a barrier layer was prepared by meltblowing an EAA
copolymer sold by Dow Chemical, Midland, MI, under the trademark
PRIMACOR 5991. This material has a melt index of 2600 and a 20% acid
content. The material was found to disperse completely in 40 seconds using a
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90C, pH 13 solution. Support layers can also be made from this material using
a melt spinning process. The PRIMACOR 5991 can be replaced with PRIMA-
- COR 5990 which has a melt index of 1300, with similar results.
A blend of an EAA copolymer with a Belland AG polymer discussed
S above also has worked successfully in the practice of the invention, as described
in Example 4. Specifically, a support layer of this material was produced by
melt spinning a blended composition containing 70 percent by weight of a Bellandmethacrylic acid/ethyl acrylate copolymer (GBC 2620 WB), 28 percent by weight
of an EAA copolymer (PRIMACOR 5990), and 2 percent by weight of a fatty
acid slip agent (SLIP-QUICKn', Synthetic Products Co.). The resulting
spunbonded material was found to undergo an immediate fragmentation upon
immersion in a 90C, pH 13 aqueous solution and gradual dissolution thereafter
which was completed in a period of time of less than three minutes.
The barrier and support layers preferably are each produced by a melt
¦ 15 blowing process, a melt spinning process, a solution blowing process, or a
solution spinning process. When the fabric comprises a banier layer sandwiched
between two support layers, the barrier layer is preferably produced by a melt
blowing process or a solution blowing process and the support layers are
produced by a melt spinning process or a solution spinning process.
Traditional melt blowing processes are illustrated by, for example, U.S.
Patent Nos. 3,016,599 to Perry, Jr.; 3,704,198 to Prentice; 3,755,527 to Keller
et al.; 3,849,241 to Butin et al.; 3,978,185 to Butin et al.; 4,100,324 to
Anderson et al.; 4,295,809 to Mikami et al.; 4,375,446 to Fujii et al.; 4,663,220
to Wisneski et al; and 4,820,577 to Morman et al. See, also, V. A. Wente,
"Superfine7hermoplasticFibers",IndustrialandEngineeringChemistry,Vol.48,
No. 8, pp. 1342-1346 (1956); V. A. Wente et al., "Manufacture of Superfine
Organic Fibers", Navy Research Laboratory, Washington, D.C., NRL Report
4364 (111437), dated May 25, 1954, United States Department of Commerce,
Office of Technical Services; and Robert R. Butin and Dwight T. Lohkamp,
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"Melt Blowing - A One-Step Web Process for New Nonwoven Products", Journal
of the Technical Association of the Pulp and Paper Industry, Yol. 56, No.4, pp.
74-77 (1973)-
In overview, the melt blowing process involves forming relatively small
~, 5 diameter fibers from a thermoplastic resin and then randomly depositing those
fibers on, for example, a moving screen to form a nonwoven web. More
particularly, the process comprises heating the resin to a molten state and thenextruding the molten resin as threads from a die having a plurality of linearly
arranged small diameter capillaries. The molten threads or filaments exit the die
a' 10 into a high velocity stream of a heated gas which usually is air. The heated gas
serves to attenuate, or draw, the threads of rnolten resin to for n fibers having
diameters which are less than the diameter of the capillaries of the die. The
!i fibers thus obtained are usually deposited in a random fashion on a moving
porous collecting device, such as a screen or wire, thereby resulting in the
forrnation of the desired nonwoven web.
Traditional melt spinning references include, among others, U.S. Patent
Nos. 3,341,394 to Kinney; 3,655,862 to Dorschner et al.; 3,692,618 to
Dorschner et al.; 3,705,068 to Dobo et al.; 3,802,817 to Matsuki et al.;
3,853,651 to Porte; 4,064,605 to Aldyama et al.; 4,091,140 to Harrnon;
4,100,319 to Schwartz; 4,340,563 to Appel et al.; 4,405,297 to Appel et al.;
4,434,204 to Hartman et al.; 4,627,811 to Greiser et al.; and 4,644,045 to
Fowells.
Like melt blowing, melt spinning begins with a extruded polymer and ends
up with a nonwoven fabric formed on a moving collection device, e.g., a moving
screen. Unlike melt blowing, after being extruded, the filaments are spun and
drawn before being deposited on the screen. As a result, the fibers making up
a melt spun fabric (also known as a spunbonded fabric) are in general longer
(more continuous) than those making up a meltblown fabric.
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Solution blowing and spinning processes are similar to melt blowing and
spinning processes, respectively. They differ in that the solution processes
extrude a polymer solution rather than a molten polymer. Solvent is removed
from the extruded threadlines and the threadlines are attenuated to the desired
diameter through the use of high velocity gas or a vapor stream. Solution
blowing differs from solution spinning in that the drawing in the former case iscarried out with a higher velocity gas stream while the threadline viscosity is
much lower. Drawing in a solution blowing process normally occurs over a short
distance near the orifices of the extrusion die and the blown fibers tend to be
finite in length but substantially continuous.
s The solution blowing and spinning processes allow nonwoven fabrics to be
readily prepared from water-soluble polymers. Such polymers often are not melt
processable in that they cannot be heated to the temperatures required to yield
, suitable viscosities for melt processing. The solution processes also facilitate the
use of polymer blends or mixtures of polymers with other chemicals, assuming
all the polymers and/or chemicals are soluble in the same solvent. Also, in the
case of water-soluble polymers, thermal bonding of the nonwoven fabric can be
¦ performed readily in the presence of moisture.
Specific techniques for the preparation of nonwoven fabrics from solutions
of PVOH polymers are disclosed in copending and commonly assigned U.S.
patent application Serial No. 07/810,470, filed December 19, 1991 and entitled
"Method of Preparing a Nonwoven Web of Poly(Vinyl Alcohol) Fibers", the
relevant portions of which are incorporated herein by reference.
The barner and support layers of the fabrics of the invention can be
bonded to one another by a variety of techniques known in the art for preparing
laminates of nonwoven materials. For example, the layers can be bonded
together using a heated press and/or a suitable water-soluble adhesive.
Alternatively, the layers can be thermally pattern bonded, typically by means ofnip rolls, at least one of which is heated and has a pattern embossed on its
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surface. Various treatments can be applied to the barrier and support layers
either before or after assembly into the fabric laminate. For example, hydro-
phobic surface properties and/or alcohol repellency can be imparted to the fabric
by treatment with fluorocarbons or other materials known to those having
S ordinary skill in the art. Other treatments now known or subsequently developed
in the art can be used in the practice of the invention.
Without intending to limit it in any manner, the present invention will be
more fully described by the following examples.
Example 1
PVOH fibers were formed by means of a bench-scale apparatus, a
schematic representation of which is shown in Figure 2. Referring to this figure,
apparatus 500 consisted of cylindrical steel reservoir 502 having a capacity of
15 about 60 cm3. The reservoir was enclosed by an electrically heated steel jacket.
The temperature of the reservoir was thermostatically controlled by means of a
feedback thermocouple (not shown) mounted in the body of the reservoir.
Moveable piston 504 was located in upper end 506 of reservoir 502.
Extrusion die assembly 503 was mounted to the lower end of reservoir 502 by
20 means of electrically heated, therrnostatically controlled connecting pipe 512.
Extrusion die assembly 503 consisted of manifold 514 and die tip 516. Manifold
514 was connected to a primary gaseous source (not shown) by means of conduit
518. Me tip 516 had a single extrusion orifice (not shown), surrounded by a
circular 0.075-inch (l.9-mm) gap (not shown) recessed from the orifice tip by
25 approximately 0.070 inches. The extrusion orifice had a diameter of 0.016 inch
(0.41 mm) and a length of 0.060 inch (1.5 mm). A second thermocouple (not
shown) was mounted near die tip 516.
Extrusion of the poly(vinyl alcohol) solution was accomplished by the
downward motion, shown by arrow 520, of piston 504 in reservoir 502, piston
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504 being driven by a constant-speed electric motor (not shown~ The extrusion
rate typically was in the range of from about 0.03 to about 0.5 grams per minute.
The extruded threadline (not shown) was surrounded and attenuated by a
cylindrical, humidified primary air stream exiting said circular gap. Attenuating
S air pressures typically were of the order of 0-8 psig. The wet threadlines then
were dried by a secondary air stream which exited essentially normal to the
threadline from manifold 522 connected by conduit 524 to a secondary gaseous
source (not shown). Distance 526 of the secondary source manifold opening
from the descending threadline was about 5 cm. Distance 528 of the axis of the
10 secondary gaseous source from the die tip also was about 5 cm.
The dried threadline was collected on foraminous screen 530 under which
a vacuum box (not shown) was located. Foraminous screen 530 was 35-40 cm
from the opening of manifold 522 from which the secondary gaseous source
exited. Region 532 generally represents the combination of primary gaseous
source, secondary gaseous source, and threadline flows.
The poly(vinyl alcohol) solution was prepared by mixing 20 parts of the
Polyscience's polymer discussed above, 80 parts of water, and 2 parts of a
polyethylene glycol, PEG 400 (Union Carbide Corporation, South Charleston,
West Virginia) for about five hours at 90-110C in a glass reaction kettle. Theresulting solution was deaerated before use.
Extrusion of the poly(vinyl alcohol) solution was carried out at about
70C. The choice of solution temperature was found to be a function of PVOH
concentration and solution viscosity with temperatures ranging from, for example,
room temperature up to about 95C as the PVOH concentration was varied
between 10-15% and 20-30%. The primary gaseous source typically was heated
compressed air humidified by the addition of atomized water droplets through theuse of an "Oil Fog" lubricator or steam, although the latter most often was used.
The relative humidity of the primary gaseous source was greater than 90 percent.The temperature of the primary gaseous source was approximately 55C. The
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secondary gaseous source was compressed air heated to a temperature of
260-370C. The exit velocities of the primary and secondary gaseous sources
were about 800 feet per second (about 244 meters per second) and 500 feet per
second (about 152 meters per second)t respectively.
S The fiber siæ was controlled by adjusting the humidified air flow to make
macrofiber and microfiber solution blown webs. At an extrusion rate of 0.3
grams/minute, macrofibers were obtained at a pressure of 0-5 psig and
rnicrofibers were obtained at 5-10 psig.
The macrofiber webs were used as support layers, while the microfiber
web was used as a barrier layer. The layers were placed in a heated Carver
Laboratory Press (Model 2518, Fred S. Carver, Inc., Menomonee Falls,
Wisconsin) at a tempsrature of approximately 82C. The top plate of the press
had a sinusoidal embossing pattern and the bottom plate was smooth.
When placed in a 90C, pH 13 aqueous solution, the nonwoven, three
layer, PVOH fabric produced in this way broke up into small pieces in about 7
seconds and was completely dissolved in 30 seconds.
A two layer fabric formed in the same way and consisting of one micro-
fiber web and one macrofiber web was immersed in a large beaker containing
a hot alkaline solution agitated with a magnetic stirrer (pH = 13, T = 70C)
Only a small residue could be seen in the beaker after 30-40 seconds, and none
was visible after 60 seconds.
Example 2
.
Nonwoven webs were made from the AIRVOL polymer described
previously using an apparatus having a six-inch (15.2-cm) wide die having 180
orifices (30 orifices per inch or about 11.8 orifices per cm). Each orifice had a
diameter of 0.46 mm. The die was constructed essentially as described in U.S.
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Patent Nos. 3,755,527, 3,795,571, and 3,849,241, each of which is incorporated
herein by reference.
The primary gaseous source was divided into two streams, the exits of
which were located parallel with and closely adjacent to the row of extrusion
5 orifices. Each primary gaseous stream exit was about 0.38 mm in width. The
ducts leading to the two primary gaseous stream exits were at an angle of 30
from the vertical, i.e., the plane in which the centers of the extrusion orifices
were located. Thus, the vertical angles of incidence for the two primary gaseousstreams were 30 and -30, respectively; the absolute value of the vertical angle
10 of incidence for each of the two primary gaseous streams was 30. The
horizontal angle of incidence for each primary gaseous stream was 90.
The secondary gaseous source also was divided into two secondary gaseous
streams. The first secondary gaseous stream was introduced on the back side of
the threadline curtain. The vertical angle of incidence for the first secondary
15 gaseous stream was -30; the horizontal angle of incidence was 90. The exit
of the first secondary gaseous stream was located about 5 cm below the die tip
and about 2.5 cm from the threadline curtain.
The second secondary gaseous stream was introduced on the front side of
the threadline curtain. The vertical angle of incidence for the second secondary20 gaseous stream was about 0 and the horizontal angle of incidence was 90.
Thus, the second secondary gaseous stream exited the secondary gaseous s~eam
conduit approximately parallel with the threadline curtain. The exit of the second
secondary gaseous stream was located about 5 cm below the die tip and about 10
cm from the threadline curtain. The moving foraminous surface (a rotating wire
25 drum) was located roughly 22-76 cm below the secondary gaseous source exits
which were approximately equal distances below the die tip. A vacuum of 2-6
inches (0.005-0.015 atm) water was maintained under the wire.
~slThe poly(vinyl alcohol) solution was prepared by heating 25 parts of
¦polymer and 75 parts of water in a two-liter Buchi autoclave at 95-100C with
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stirring at 200-1,000 rpm. Optionally, PEG 400 was included in an amount
ranging from about 10 percent to about S0 percent, based on the amount of
poly(vinyl alcohol) employed.
The solution was pumped by means of a Zenith metering pump to the die
S through a transfer line heated at about 82C. The solution was extruded at about
82C. The primary gaseous source was pure steam at a temperature of
approximately 99-105C and a pressure of 20-50 inches water (0.05-0.12 atm).
The secondary gaseous source was compressed air heated to a temperature of
260-316C; the flow rate was 90-130 cfm (42.5-61.4 liters per second). The
10 exit velocities of the primary and secondary gaseous sources were about 800 feet
per second (about 244 meters per second) and 500 feet per second (about 152
meters per second), respectively. The die tip temperature was maintained at
82C and the extrusion rate was 0.19-0.28 g per minute per orifice.
Macrofibers having fiber diameters in the 10-30 micrometer range and
15 microfibers having diameters in the 1-20 micrometer range were prepared usingthese procedures. Layers of these fibers were laminated and bonded together.
The resulting nonwoven fabric was found to readily disperse when immersed in
a hot, alkaline solution having a pH above 12 and a temperature above 70C.
Example 3
The EAA copolymer described previously (PRIMACOR 5991) was
meltblown using the apparatus described in Example 1. The polymer was
extruded at a temperature in the range of 93 to 130C, attenuated by 142C
25 hot primary air at a pressure in the range of 10-20 psig, and collected onto a
~oraminous web former under a vacuum. The fiber si~e was in the range of 1-4
micrometers. The barrier layer so formed was bonded to a macrofiber PVOH
web produced in accordance with the procedures of Example 1 using the Carver
press operated at a temperature of approximately 82C. The resulting laminate
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was found to rapidly dissolve in a hot alkaline solution having a pH above 12 and
a temperature above 70C.
Example 4
S
A spunbonded web was fonned from a blend of an EAA copolymer with
a Belland AG polymer. Specifically, the material was produced by melt spinning
a blended composition containing 70 percent by weight of a Belland methacrylic
acid/ethyl acrylate copolymer (GBC 2620 WB), 28 percent by weight of an EAA
10 copolymer (PRIMACOR 5990), and 2 percent by weight of a fatty acid slip agent(SLIP-QUIC~, Synthetic Products Co.). The blend was prepared by mixing the
foregoing components by means of a drum-shaking apparatus, extruding the
resulting mixture through a twin-screw compounding extruder equipped with a
multiorifice die, and passing the extruded strands through a quenching trough and
a pelletizer. The pellets were dried in a spin dryer to remove excess water fromthe quenching step before being packaged.
The web was formed in accordance with U.S. Patent No. 4~340,563 which
is incorporated herein by reference. The extrusion apparatus consisted of a
single-screw extruder for melting and conveying the polymer blend, a metering
~' 20 pump, and an extrusion die. The extruded threadlines were attenuated by air
streams. The attenuated fibers were collected and conveyed on a moving forming
wire, compacted in an unheated nip, and bonded to form a web in a thermal
-1 bonding unit consisting of a positively driven, heated embossing roll and a
smooth nip roll.
Ihe blend was extruded under conditions selected to maintain the melt
temperature as close to 170C as possible. The feed zone of the extruder was
maintained at 93C or below to prevent bridging of threadlines or filaments in
the throat of the extruder. The attenuating air was cooled to 10C. Heat was
supplied to the bonding rolls to maintain a surface temperature of 93C
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The spunbonded web so formed was found to rapidly fragment into fibers
and small fiber clumps in a hot alkaline solution having a pH above 12 and a
temperature of 90C, with gradual dissolution of the fragments thereafter which
was completed in a period of time of less than three minutes. At 70C, the
S material disintegrated into fragments in a little over three minutes, with gradual,
almost complete dissolution after 25 minutes.
Having thus described the invention, numerous changes and modifications
thereof will be readily apparent to those having ordinary skill in the art without
departing from the spirit or scope of the invention.
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