Note: Descriptions are shown in the official language in which they were submitted.
~ Fi~: 41780C~N4A
DUR~BLE' MLLT-BLOW~ S~lE~'r M~TF,RIAL
Field of the Invelltion
This invention relates to non-woven fabrics or
sheet materials and further relates ~o yarments made from
such fabrics.
Back round of the Invention
9 -
U.S. Patent No. 4,433,024 (Eian) advanced the
art of vapor-sorptive garments by providing a new
vapor-sorptive, fibrous sheet material or fabric that
achieves desired levels of toxic vapor sorption and yet
exposes the wearer of a garment made with the sheet
material to low heat and moisture stress. It has been
found, however, under testing that imposes mechanical
stress on the fabric, that yreater durability would be
desirable so as to maintain sorption for longer periods of
time in the face of such mechanical stress. The sheet
material is comprised of a fibrous web of melt-blown
organic polymeric fibers having vapor-sorptive particles
uniformly dispersed therein, and under mechanical stress
the particles can migrate away from their original
location thereby reducing vapor sorption in that region.
In particular, uniforms made from the fabric showed
dislocation of particles from high stress areas
corresponding to the elbows and knees of the uniforms
leaving the wearers susceptible to attack by toxic vapors
at those points in the uniforms.
Summary of the Invention
This invention provides a new melt-blown fibrous
sheet material having improved durability under mechanical
stress such that, for example, it will more durably hold
particulate material such as vapor-sorptive particles and
thereby achieve longer-lived vapor-sorptive garments.
Briefly summarizing, this new sheet material comprises:
()o~ ~
--2--
a) a coherent layer of melt-blown organic
polymeric fibers, and
b) a plurality of organic polymeric reinforcing
fibers extending transversely through the layer of
melt-blown fibers and being held in that position by
bonding to fibers on the opposing faces of the laver of
melt-blown fibers.
Reinforcing fibers incorporated into the web in
this manner have been found to greatly increase the
integrity and durability of the web. Solid particles,
such as vapor-sorptive particles, may be uniformly
dispersed in the layer of melt-blown fibers to provide a
vapor-sorptive fabric, and the reinforcing fibers have
been found to provide a more lasting holding of the
particles in their original location while still leaving
the particles free to sorb vapor. At the same time, the
web continues to impose only low heat and moisture stress.
The web is permeable in that it allows the passage of a
fluid through the web.
Detailed Description
The fibrous web of this invention can be
prepared by needling reinforcing fibers through a
preformed layer of melt-blown organic polymeric fibers and
thereafter bonding the reinforcing fibers, e.g., by
heating the web to temperatures at which the reinforcing
fibers soften and become thermally bonded, so that the
needled reinforcing fibers extending through the layer are
bonded to fibers on each side of the preformed layer.
In addition to the melt-blown fibers, the
preformed melt-blown fiber layer can also contain other
fibers or particles. Examples of suitable fibers are
staple fibers, e.g., synthetic fibers such as polyethylene
terephthalate or natural fibers such as cotton or wool.
Functional fibers such as heat-resistant fibers, e.g.,
polyimides, fiberglass or ceramics, can also be included,
and vapor-sorptive carbon fibers are especially useful
when incorporated into webs intended for vapor-sorptive
applications.
l~OO~i~
--3--
The layer of melt-b]own fibers is preferably
prepared by techniques as generally described in Wente,
Van A., "Superfine Thermoplastic Fibers," in Industrial
Engineering Chemistry, Vol. 48, pages 1342 et seq (1956),
and such layers with any other included fibers or
particles are preferably prepared as disclosed in U.S.
Patent Nos. 3,971,373 ~sraun)~ 4,433,024 (Eian), or
4,118,531 (Hauser). The melt-blown fibers are preferably
microfibers, averaging less than about 10 micrometers in
diameter, e.g., since such fibers offer more points of
contact with the particles per unit volume of fiber. Very
small fibers, averaging less than 5 or even 1 micrometer
in diameter may be used, especially with vapor-sorbtive
particles of very small size as discussed below.
Blown fibrous webs are characterized by an
extreme entanglement of the fibers, which provides
coherency and strength to a web and also adapts the web to
contain and retain particulate matter. The aspect ratio
(ratio of length to diameter) of blown fibers approaches
infinity, though the fibers have been reported to be
discontinuous. The fibers are long and entangled
sufficiently that it is generally impossible to remove one
complete fiber from the mass of fibers or to trace one
fiber from beginning to end.
The invention is particularly useful to support
any kind of solid particle that may be dispersed in an air
stream ("solid" particle, as used herein, refers to
particles in which at least an exterior shell is solid, as
distinguished from liquid or gaseous). A wide variety of
particles have utility in a three-dimensional arrangement
in which they can interact with (for example, chemically
or physically react with, or physically contact and modify
or be modified by) a medium to which the particles are
exposed. More than one kind of particle is used in some
sheet products of the invention, either in mixture or in
--4--
different layers. Air-purifying devices such as
respirators in which the particles are intended for
filtering or purifying purposes constitute a utility for
sheet products of the invention. Typical particles for
use in filtering or purifying devices include activated
carbon, alumina, sodium bicarbonate, and silver particles
which remove a component from a fluid by adsorption,
chemical reaction or amalgamation; or such particulate
catalytic agents as hopcalite, which catalyze the
conversion of a hazardous gas to a harmless form, and thus
remove the hazardous component. In other embodiments of
the invention, the particles deliver rather than remove an
ingredient with respect to the medium to which the
particles are exposed.
The present invention is especially useful with
sorptive particles, particularly vapor-sorptive particles.
~s used herein, sorptive particles are particles having
sufficient surface area to sorb, at least temporarily,
fluids which may be passed through the web. In certain
embodiments, the particles sorb and bind the fluid; while
in other embodiments, the particles sorb the fluid only
temporarily, e.g., long enough to effect a chemical change
in the fluid. Vapor-sorptive particles perform such a
function where the fluid is a vapor. Examples of suitable
vapor-sorptive particles include alumina, hopcalite and
porous polymeric sorbents. The preferred vapor-sorptive
particles are activated carbon particles. A chemical
reagent, e.g., potassium car~onate, or a catalytic agent,
including enzymatic agents, may be included with the
vapor-sorptive particles to chemically change or degrade
sorbed vapors.
In preferred products of the invention, solid
particles comprise at least about 20 volume percent of the
solid content of the fibrous web, more preferably at least
about S0 volume percent, and they are present at a density
of at least about 50 g/m2 Of the area of the fibrous web.
As also taught in the previously mentioned
U.S.Pat. 4,433,024, the layer of melt-blown fibers is
desirably compacted to a thickness less than 2 millimeters
and more desirably less than 1 millimeter to reduce heat
stress on a person wearing a garment of the sheet
material. In the completed sheet material, the insulation
value contributed by the fibrous web of this invention is
generally less than 0.4 clo, and preferably less than 0.2
clo as measured by the guarded-plate test of ASTM-1518;
preferably the insulation value of the complete sheet
material including porous supporting fabrics attached to a
fibrous web of this invention is also less than those
values.
The reinforcing fibers are bonded after they are
needled through the layer of melt-blown fibers, meaning
that at least a portion of the exterior of the fibers will
soften upon the application of heat, pressure, ultrasonic
energy, solvent or the like and thereby wet and bond to
fibers that it contacts. Such bonding should occur under
conditions such as elevated temperature that do not result
in softening the melt-blown fibers and destruction of the
fibrous nature of the layer of melt-blown fibers. The
reinforcing fiber should also comprise a non-bonding
portion continuous through its length. This non-bonding
portion retains its dimensional integrity during bonding
and thus contributes a measure of structural rigidity to
the web.
~ icomponent fibers are preferred as the
reinforcing fiber, and preferably have a component that
bonds at a temperature lower than the melt-blown fibers.
Suitable bicomponent fibers include those disclosed in
U.S. Patent Nos. 4,483,976, 4,551,378, and 4,552,603. For
example, bicomponent fibers of polyethylene (lower
melting) and polypropylene (higher melting~ have been very
effective with webs of the invention in which the melt-
blown fibers are polypropylene. The denier of the
1~0()~
--6--
reinforcing fibers may vary and is preferably less than
about 3. Particularly preferred reinforcing fibers have a
heat-fusible elliptical sheath and a heat-infusible core
extendiny along the length of the fibers. Side-by-side
and concentric sheath/core varieties are also useful.
~ he reinforciny fibers can be carded, garneted,
or air-laid into a web, e.g., on a liner that supports the
web for handling, then assembled against the layer of
melt-blown fibers, and then needled or needle-tacked into
the layer of melt-blown fibers. Such a preformed web of
reinforcing fibers is generally lightweight, sufficient
only to provide a handleable web, in order to minimize the
heat stress and stiffness of the completed fibrous web.
Despite the low amount of reinforcing fibers, the
resultiny fibrous web is greatly strenythened into a sheet
material that has greatly increased utility, e.g. in a
particle-loaded vapor-sorptive yarment. For example,
tensile strengths of at least 250 gm/cm width have been
obtained. Also, good coherent strength has been obtained,
as indicated by peel strengths from a fabric to which the
web has been adhered of 500 gm/5 cm width or more. In
preferred embodiments, the reinforcing webs are of
insufficient density to lower the air permeability of the
complete fibrous web to levels below 1 ft3/min/ft as
measured by Test Method 5450 in Federal Test Method
Standard l91A, but for some uses such permeability is not
needed. The precise density of the reinforcing web can
vary, but preferred reinforcing webs range from about 10
g/m2 to about 50 g/m2. For best results, reinforcing
fibers are included on both sides of the layer of
melt-blown fibers.
By needling, it is meant any operation that will
cause the reinforcing fibers to pass through the layer and
extend between the opposing faces of the layer. While
water-jet needling can be used, mechanical needling is
preferred. Such a needling apparatus typically includes a
horizontal surface on which a web is laid or moves and a
needle board which carries an array of downwardly
lX~OO~i~
--7--
depending needles. The needle board reciprocates the
needles into, and out of, the web and reorients some of
the fibers of the web, especially the reinforcing fibers,
into planes transverse, or substantially so, to the planar
surfaces of the web. The needles chosen can push ibers
through the web from one direction, or e.g., by use of
barbs on the needles, can both push fibers through the
layer from the top and pull fibers from the bottom.
Preferred embodirnents of this invention are
double-needled, i.e., a web of reinforcing fibers is
needled from each of the opposing surfaces of the
particle-loaded layer of melt-blown fibers. The density
of the needling can vary, but we have obtained quite
satisfactory results with densities less than 50 punches
per square inch, e.g., 10-20 punches per square inch.
After needling, an assembly of bicomponent
thermobondable reinforcing fibers and layer of melt-blown
fibers can be moved through an oven and heated to a
temperature higher than the fusion temperature of a
fusible component of the bicomponent reinforcing fibers,
whereupon the reinforcing fibers become bonded together or
to other adjacent fibers. At least some portion of the
reinforcing fibers extend completely through the layer of
melt-blown fibers, and become bonded to fibers, e.g.,
other reinforcing fibers or melt-blown fibers, on each
side of the layer. The bicomponent fibers generally tend
to crimp, e.g., curl, during this thermobonding operation
as a result of different shrinkage characteristics of the
components of the bicomponent fiber. At least in part
because of this crimping action, the whole assembly is
drawn together in a more compacted durable sheet product.
The crimping of the fibers may also serve to obstruct or
close openings created by the needle-tacking operation,
thereby retaining the vapor-sorptive properties of the
web.
Some of the reinforcing fibers are not drawn
fully through the layer of melt-blown fibers but may be
bonded to the melt-blown fibers through softening of the
00~ ,
bonding portion of the reinforcing Eiber. However, as
noted above, the temperatures used generally do not soften
the melt-blown fibers, and the fibrous structure of the
melt-blown fibers is retained intact except for the
compact;ng of the structure that occurs through the action
of the reinforcing fibers.
The finished fibrous web, i.e., the composite
layer oE melt-blown fibers and needled bonded reinforcing
fibers, may serve as a stand-alone sheet material or
fabric. The faces of the reinforced web are generally
substantially planar; i.e., the needled reinforcing fibers
do not appreciably extend from the surface of the web in a
direction normal to the plane of the surface. In the
stand-alone form, the reinforced web is also preferably
free ot any adhesive apart from the bonding portion of the
reinforcing fibers because such adhesive could coat the
solid particles and thereby reduce or eliminate their
sorptive capability. However, at least for use in
vapor-sorptive garments, it is preferred to attach a
support fabric to the described composite fibrous web,
generally on both sides of the web, to complete sheet
material of the invention. The fabric is preferably
adhered to the web with an adhesive applied in a
discontinuous manner, e.g., by use of spray adhesives
which apply scattered droplets, or by printing in a
pattern, to preserve permeability. The adhesive should
not penetrate throughout, or fill the layer of melt-blown
fibers, so as to preserve the properties of that layer.
The fabrics can also be sewn to the fibrous web or
attached by ultrasonic welding.
A variety of support fabrics may be used. For
use in garments, the support fabric on at least one face
of the web should have a yrab strength (as measured by
Test Method Number 5100 in the Federal Test Method
35 Standard Number l91A) of at least 100 kilograms per
centimeter thickness, and preferably at least 500
kilograms per centimeter of thickness. The sheet material
_9_
is typically used to form all or substantially all of a
garment, i.e., wearing apparel that is used to cover a
substantial part of the human body, including coats,
jackets, trousers, hoods, casualty bags in which an
injured or wounded person is placed, and the like. The
sheet material is also useful in tents, filters and the
like, especially those where the improved strength Erom
reinforcernent is advantageous.
Examples
A web of melt-blown polypropylene microfibers
loaded with particles of activated carbon was prepared by
the process described in U.S. Patent No. 4,433,024. The
microfibers and carbon particles ranged respectively
between about 0.5 ~nd lO micrometers an-1 between about 40
and 3UO micrometers in diameter. The carbon had static
carbon tetrachloride capacity of at least 60% and is
available from Calgon under the designation RFMC. The
fibers in the web weighed about 18 grams per square meter,
and the complete, particle-loaded web weighed about 145
grams per square meter.
An air-laid randomized reinforcing web of
polyethylene/polypropylene eccentric sheath/core fibers
(available as ChissoTM ES fibers from Chisso Corporation,
Osaka, Japan) having a denier of 1.5 and a length of 38 mm
was formed by air-laying with a Rando-Webber TM unit
available from Curlator Corporation, Rochester, N.Y. The
weight of the air-laid web was about 12 g/m2. The
air-laid web was collected on a paper liner, which was
discarded when the reinforcing web was laid down on the
melt-blown fiber web.
To reinforce the melt-blown microfiber web, the
reinforcing web was laid out onto the microfiber web and
run through a needletacker available from James Hunter
Machine Company. The needletacker had multiple rows of
barbed tacking needles having a round shank and a
triangular point (available from Singer Company under the
l~O(~
--10--
designation 418 812 050 0). Each needle was spaced
approximately 0.6 cm apart, the needles stroked at a
frequency of 1~5 strokes per minute and the web moved past
the ncedles at a rate of 64 yards per hour, which means
tlle needle punch density was about 13 strokes per square
inch. As the combined webs were run through the
needletacker, the needles moved vertically in a direction
normal to the face of the webs and pierced first the
air-laid web and then the microfiber web. This action
drove reinforcing fibers through the microfiber web to
extend from the opposite face of the microfiber web. The
needle-tacked web was then turned over and a second
reinforcing web was needle-tacked as described above to
the opposite face of the microfiber web. The
lS double-tacked web was then passed hori~ontally through a
convection oven having a vertical air stream which acted
to lift or float the web while in the oven. The oven was
maintained at about 150C and the dwell time was about 1
minute.
The resulting web was then tested for strength
and carbon tetrachloride capacity. The dynamic carbon
tetrachloride capacity was measured according to military
standard MIL-C-43858 (GL), which was greater than the 1.8
g/cm called for in the standard. The tensile strength of
the web was tested as follows. A sample was cut into
strips of about 2.5 cm by about 30 cm and placed in an
Instron TM tensile tester with a jaw gap of about 25 cm
and a crosshead speed of about 30 cm/min. The web
exhibited an average tensile strength in the cross web
direction of about 470 g/cm and in the down web direction
of about 500 g/cm. Comparable webs which have not been
reinforced have a tensile strength in the down web
direction of about 220 g/cm width or less.
A second mechanical test was also conducted to
evaluate the coherent strength of the web and was
accomplished by laminating a sample web to a support
fabric and measuring the force required to peel the web
--ll--
away from the support fabric. rhe adhesive used to
laminate the sample had a strength sufficient to ensure a
coherent failure of the reinforced web under the
conditions of the test. This test was performed on a web
sample having a dimension of about 5 cm by about 15 cm.
The web and suppor~ fabric along the 5 cm side were
manually separated along the 15 cm length sufficient to
place one of the separated web and fabric into the upper
jaw of an InstronTM tensile tester and the other into the
lower jaw. The jaw gap was set at about 2.5 cm and the
crosshead speed at 30 cm/min. The web exhibited an average
peel strength of about 900 g/5 cm width in the cross web
direction and about 1000 g/5 cm width in the down web
direction.
Other samples of the càrbon-loaded microfiber
web were laminated between support fabrics as follows.
Two fabrics were spray-coated on one side with droplets of
adhesive (3M Brand Spray Adhesive 77) in an amount of
about 8 grams per square meter on each fabric. One of the
fabrics, adapted to serve as the outer fabric in a
garment, was a water repellent 50/50 nylon-cotton twill
having a weight of 160 grams per square meter (available
from Gilbraltar Industries and meeting the requirements of
military specification MIL-C-43892). The other fabric,
adapted to serve as the inner fabric or liner, was a nylon
tricot knit fabric having a nominal weight of 64 grams per
square meter (available from Engineered Fabrics
Incorporated, Style 532; this fabric meets military
specification MIL-C-43858 (GL)). After the sprayed
adhesive had dried, the carbon-loaded microfiber web was
assembled between the adhesive-coated sides of the two
fabrics, and the assembly was passed through a nip roll
heated to about 200-220F. The adhesive softened and
penetrated into the large-surface edges of the melt-blown
web, and upon cooling of the assembly, a laminate was
formed. The laminate continued to exhibit a dynamic carbon
tetrachloride capacity of 1.8 g/cm2.
