Note: Descriptions are shown in the official language in which they were submitted.
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WO 94/19523 ' PCT/US94/01481
TITLE
Abrasion-resistant Resin-impregnated Nonwoven Fabric
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for making a resin-impregnated
nonwoven fabric. More particularly, the invention concerns such a process
wherein
a starting nonwoven fibrous layer is significantly contracted in area causing
groups
of its fibers to buckle out of plane, the buckled groups of fibers are
immobilized in
their buckled position, and the fabric is dimensionally stabilized. Novel
products
of the process have unexpectedly high abrasion resistance in comparison to
known
contracted nonwovens in which the buckled fibers are not immobilized and the
fabric is not stabilized.
Description of the Prior Art
Processes are known wherein a nonwoven fibrous layer is buckled, shirred,
gathered or puckered so that the final area of the fibrous layer is much
contracted in
comparison to the original area of the layer. For example, such processes are
disclosed by Bassett United States Patent 3,468,748, Wideman U.S. 4,606,964,
and
Zafiroglu U.S. 4,773,238. The contraction can cause groups of fibers of the
nonwoven fibrous layer to buckle out of plane and to form generally "U-shaped"
loops projecting from the plane of the layer. Further treatments of such
contracted
layers also are known. For example, Hansen U.S. 3,575,782, discloses making a
shirred elastic fabric by sealing partially extended, spaced apart, aligned
elastic
yarns between thin porous nonwoven fibrous webs and then allowing the yarns to
contract, the sealing agent being a soft flexible polymeric binder (e.g.,
rubber
latex). Although useful in some applications, the impregnated shirred fabrics
of
Hansen often are excessively stretchable and insufficiently resistant to
abrasion for
satisfactory use in other applications, such as athletic shoe parts, luggage
surface
layers, work clothes pockets, wear surfaces of automotive timing belts, marine
abrasion pads and the like.
An aim of this invention is to enhance the utility of resin-impregnated
nonwoven fabrics by providing such fabrics with high abrasion resistance and
low
stretchability.
The present invention provides a process comprising the steps of:
contracting a nonwoven fibrous layer in area to an area that is no greater
than one-
half its original non-contracted area of the layer and causing groups of
fibers of the
nonwoven fibrous layer to buckle out of the plane of the layer and form
inverted U-
shaped loops projecting in a direction generally perpendicular to the plane of
the
CA 02155968 2001-O1-15
layer, immobilizing the buckled groups of fibers, and stabilizing the
dimensions of the contracted fibrous layer. Preferably, the fibrous layer area
is contracted to less than one-third the original area. In one embodiment of
the process, a contractible element or array of contractible elements is
intermittently attached to the nonwoven fibrous layer, the intermittently
attached element or array of elements is contracted to cause an
accompanying contraction of the nonwoven fibrous layer and the buckling of
the groups of fibers. Preferably, the buckled groups of fibers are immobilized
by impregnating the fibrous layer with a resin and then curing and/or drying
the resin. Preferably, the dimensions of the contracted layer are stabilized
simultaneously with the immobilization of the buckled groups of fibers during
the resin-impregnation-and-curing step. Typically, the dry resin preferably
amounts to in the range of 10 to 90% of the total weight of the impregnated
layer, preferably 25 to 75%. The layer of impregnated and immobilized
projecting loops form an abrasion-resistant surface. Alternatively, the
dimensions of the contracted fibrous layer can be stabilized by attaching a
substantially non-stretchable element or array of non-stretchable elements to
the back surface (i.e., the surface opposite to the abrasion-resistant
surface)
of the contracted, buckled, fibrous layer.
The present invention also provides a novel, resin-impregnated
nonwoven fabric which comprises a fibrous layer from which groups of fibers
axe buckled out of plane. The buckled groups of fibers have an average
spacing in the range of 0.5 to 3 mm, preferably 1 to 2 mm. The fabric is
stretchable (as defmed hereinafter) in any linear direction by no more than
50%, preferably by no more than 25% and most preferably by no more than
5%. Contracted, resin-impregnated fabrics weigh in the range of 150 to 1200
glm2, of which 10 to 90 weight percent is composed of fibers, and the groups
of buckled fibers have an average loopiness (i.e., height-to-base ratio
measured as described hereinafter) of at least 0.5, most preferably in the
range of 0.7 to 1.5.
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CA 02155968 2001-O1-15
Further aspects of the invention are as follows:
A process for preparing an abrasion-resistant resin-impregnated
nonwoven fabric comprising the steps of:
impregnating the fibers of a nonwoven layer with resin;
contracting the area of the nonwoven fibrous layer to an area that is no
greater than one-half the original non-contracted area of the layer and
causing groups of fibers of the nonwoven fibrous layer to buckle out of the
plane of the layer and form inverted U-shaped loops projecting in a direction
generally perpendicular to the plane of the layer;
curling and/or drying the resin so that the buckled groups of fibers are
immobilized and so that the buckled groups of fibers are prevented from
moving from side to side or collapsing into the layer when the surface of the
layers is abraded; and
stabilizing the dimensions of the contracted fibrous layer such that the
stretchability of the layer in any linear direction is no more than 50%.
A process for preparing an abrasion-resistant impregnated nonwoven
fabric comprising the steps of:
contracting the area of a nonwoven fibrous layer to an area that is no
greater than one-half the original non-contracted area of the layer and
causing groups of fibers of the nonwoven fibrous layer to buckle out of the
plane of the layer and form inverted U-shaped loops projecting in a direction
generally perpendicular to the plane of the layer;
impregnating the buckled groups of fibers with a resin, cutting and/or
drying the resin so that the buckled groups of fibers are immobilised and so
that the buckled groups of fibers are prevented from moving from side to side
or collapsing into the layer when the surface of the layer is abraded; and
stabilizing the dimensions of the contracted fibrous layer such that the
stretchability of the layer in any linear direction is no more than 50%.
A resin-impregnated nonwoven fabric comprising a fibrous layer from
which groups of fibers are buckled out of plane. The buckled groups of fibers
2a
CA 02155968 2001-O1-15
having an average spacing in the range of 0.5 to 3mm and an average loop
height to-base rate of at least 0.5 and being immobilized so that the buckled
groups of fibers are prevented from moving from side to side or collapsing
into the layer when the surface of the layers is abraded and the fabric being
stretchable in any linear direction by no more than 50% and its weight being
in the range of 150 to 1200g/m3 of which weight 10 to 90 weight percent
consists of resin.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood by referring to the attached
drawings wherein Figures 1-4 present graphs of abrasion resistance as
functions of total gather of the contracted, resin-impregnated fabrics of
Examples 1-4, respectively, and Figures 5 and 6 represent magnified
schematic cross-sections of groups of buckled fibers formed into projecting U-
shaped loops 10, with height H and base B, indicated thereon. Figure 5, in
which contractible elements 20 are stitching yams, is representative of
Examples 1, 2, 4 and 5, and Figure 6, in which the contractible element 30 is
a thin elastic sheet, is representative of Example 3.
2b
' PCT/US94/01481
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~ETAI ED DESCRIPTION OF PREFEFtRFD EMBODIMENTS
The invention is further illustrated by the following description of preferred
embodiments. These are included for the purposes of illustration and are not
intended to limit the scope of the invention, which is defined by the appended
claims.
As noted above, in the first step in the process of the present invention, a
nonwoven fibrous layer is contracted to an area that is no greater than one-
half its
original planar area.
The starting nonwoven fibrous layer that is to be contracted and buckled in
accordance with the invention typically is a thin, supple, substantially
nonbonded
web of staple fibers, continuous filaments, plexifilamentary strands or the
like. The
term "fibers" is used collectively herein to include each of these fibrous
materials.
The fibers may be natural fibers or may be formed from synthetic organic
polymers. Fibers of less than about 5 dtex and of at least S-mm length are
preferred. Preferred starting layers are capable of buckling, as shown in the
examples below, over relatively short intervals (e.g., 1-mm). A suitable
starting
layer typically weighs in the range of 15 to 100 grams per square meter,
preferably
less than 60 g/m2. Suitable materials for the starting nonwoven layers include
carded webs, air-laid webs, wet-laid webs, spunlaced fabrics, spunbonded
sheets,
and the like. Generally, thick lofty webs, felted webs, adhesively or
thermally
bonded webs, or the like are not suited for use as the starting fibrous layer;
such
materials usually are di~cult to buckle over short intervals.
The contraction and buckling of the fibrous layer can be accomplished in
any of several known ways. In one method, a contractible element or an array
of
contractible elements is intermittently attached to the fibrous layer. Then,
the
element or array of elements is caused to contract so that the area of the
fibrous
layer is decreased significantly and groups of fibers buckle out of the plane
of the
layer. Before the contractible elements are attached, additional gathering or
contraction can be imparted to the fibrous starting layer, by over-feeding the
layer
to the apparatus being employed to attach the contractible elements.
Many types of contractible elements are suitable for use in the invention.
For example, the nonwoven fibrous layer can be stitch-bonded with elastic
yarns
under tension. Textured stretch yarns, covered or bare spandex yarns, and the
like
are suitable yarns for the stitching. After the stitching, the tension can be
released
from the stitching thread to cause the desired contraction and buckling of the
fibrous layer. Instead of stitching, warps or cross warps of extended elastic
elements can be intermittently attached to the fibrous layer by hydraulic
entanglement, adhesive or thermal point bonding, or the like. Thereafter,
tension
on the extended elements is released to cause layer contraction and buckling.
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WO 94/19523 PCT/US94/01481 -
~1~~9~~
Other types of contractible elements, which shrink on being treated with
heat, moisture, chemicals or the like can be attached intermittently to the
fibrous
layer without initial tension or extension in the elements. After attachment,
the
contraction of the contractible elements can be activated by appropriate
treatment.
Still another way of accomplishing the contraction and buckling of the fibrous
layer involves intermittently attaching the fibrous layer to a stretchable
substrate
that necks-in in a direction perpendicular to the direction in which the
substrate is
pulled. For example, certain substrates, when stretched by 15% in one
direction,
can automatically experience substantially irreversible contraction (i.e.,
neck in) in
a direction perpendicular to the stretch by an amount that is two or three
times the
percentage stretch. Thus, appropriate intermittent attachment of a fibrous
layer to
the stretchable substrate before the stretching and necking-in operation, and
then
applying the stretching forces to the combined layer and substrate, can
significantly
decrease the area of the fibrous layer and cause buckling of groups of fibers
as
required by the process of the invention.
When performing the contracting step in accordance with the process of the
invention, the area of the fibrous web is decreased to an area that typically
is no
greater than one-half, preferably no greater than one-third, of the original
area of
the non-contracted layer.
Several of the above-described methods of attaching contractible elements
to the fibrous layer and then contracting the elements and the layer are
illustrated in
the Examples below.
To achieve high resistance to abrasion in the resin-impregnated fabrics of
the present invention, the buckled groups of fibers of the contracted fibrous
layer
generally extend in a direction perpendicular to the plane of the nonwoven
fibrous
web and are immobilized in that position. The buckled groups of fibers are
packed
closely together as a result of the contraction of the layer. Dried and/or
cured resin
prevents the buckled groups of fibers from moving from side to side or
collapsing
into the layer when the surface of the layer is abraded or rubbed.
Various types of resins are suitable for immobilizing the fiber bundles.
Particularly useful are various resins of polyurethane, epoxy, rubber and the
like.
The resin may be applied in any of several conventional ways. For example, the
fibrous layer may be resin-impregnated by dipping, spraying, calendering,
applying
with a doctor knife, or other such techniques. The resin may be applied from a
solution, slurry or by melting a layer of the resin and forcing it into the
contracted
fibrous layer. The resin can be introduced as adhesive particles or as binder
fibers
that are activated by heat. In most instances, the resin or binder can be
introduced
into the fibrous layer before, during or after contraction. However, care must
be
taken, when introducing the resin or binder into the layer before contraction,
not to
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WO 94/19523 PCT/iJS94/01481
immobilize the fibers before the contraction or gathering of the layer is
effected.
Accordingly, it is preferred to apply the resin, after the fibrous layer has
been
subjected to the desired contraction step and then to allow the resin to dry,
harden
andlor cure.
Figure 5 and 6 schematically represent (in magnification) typical
immobilized loops formed by the buckled groups of fibers of the contracted or
gathered fibrous layer, with height H and base B dimensions designated on the
figures. Typically, the loops of buckled groups of fibers have an average
spacing
in the range of 0.5 to 3 mm, preferably 1 to 2 mm. Various practical methods
are
available to determine the H and B dimensions of the loops, as described below
in
the paragraphs on test methods.
The resin-impregnated contracted fibrous layer of the invention typically
has a stretchability in any linear direction of no more than 50%, preferably
no more
than 25% and most preferably by no more than 5%. As used herein, a fabric is
deemed to be "substantially non-stretchable" if the fabric has a
stretchability of less
than 5%. Stretchability is an inverse measure of the dimensional stability of
the
fabric.
Stretchability of the fabric can be controlled in several ways. Most
conveniently, the stretchability is limited to very low values by the use of a
hard
resin that stabilizes the dimensions of the fabric while it simultaneously
immobilizes the buckled fiber loops. The degree of fabric dimensional
stability
obtained by this method is also indicative of the degree of buckled fiber loop
immobilization. Very low levels of fabric stretchability (i.e., high
dimensional
stability) achieved by resin impregnation are always accompanied the high
levels
of buckled fiber loop immobilization. Fabric stability can also be achieved by
the
attachment of strong, substantially non-stretchable strips, films, sheets,
webs,
cross-warps and the like to the back surface of the abrasion-resistant layer.
The
attachment may be by any convenient means, such as gluing, thermal bonding and
the like.
Fabrics contracted in accordance with the invention are suitable for molding
into shaped articles, such as tires, timing belts, gloves, shoes, luggage,
edge and
corner protectors, and the like. Conventional means for shaping the fabric are
employed. For example, the resin-impregnated contracted fabric can be placed
in a
mold before the resin is still has hardened, and then allowed to set while in
the
mold .
The following methods and procedures are used to measure various
characteristics of the resin-impregnated fabrics of the invention.
The height H and the base B of the U-shaped loops of buckled groups of
fibers are determined from magnified (e.g., 15-20X) photomicrographs of cross-
WO 94/19523 PCT/US94/01481
sections of the loops taken through the loops in a plane perpendicular to the
plane
of the fibrous layer. The data are then used to calculate an "HB ratio". A low
magnification microscope with strong top and/or back lighting on the sample
permit direct measurement of the H and B. Usually the average loop height H is
equal to the thickness of the contracted fibrous layer. As used herein, "loop
spacing" is synonymous with the loop base B, (i.e., the distance between the
legs of
the inverted "U" that formed the loop of buckled fibers). Alternatively, the
average
loop height H is sometimes easier to measure directly with a "touch"
micrometer
having a 1 /4-inch (0.64-cm) diameter flat cylindrical probe which applies a
10-
gram load to the contacted surface. A digital micrometer, model APB-1D,
manufactured by Mitutoyo of Japan is suitable for measuring these thicknesses
or
heights.
Stretchability is determined by: (a) cutting a sample measuring 2-inches
(5.1-cm) wide by 4-inches (10.2-cm) long sample from the layer; (b) marking a
standard length, Lo, parallel to the long dimension of the sample; (c)
suspending a
10-pound (454-gram) weight from sample for 2 minutes; (d) with the weight
still
suspended from the sample, re-measuring the "standard length", the re-measured
length being designated L f and (e) determining the stretchability as %S by
the
formula, %S = 100 (L f -Lo)/Lo.
To determine the abrasion resistance of samples a Wyzenbeek "Precision
Wear Test Meter", manufactured by J. K. Technologies Inc. of Kankakee,
Illinois,
is employed with an 80-grit emery cloth wrapped around the oscillating drum of
the tester. The drum is oscillated back and forth across the face of the
sample at 90
cycles per minute under a load of six pounds (2.7 Kg). The test is conducted
in
accordance with the general procedures of ASTM D 4157-82. The thickness of the
sample is measured with the aforementioned micrometer before and after a given
number of abrasion cycles to determine the wear in mm of thickness lost per
1,000
cycles.
The unit weight of a fabric or fibrous layer is measured according to ASTM
Method D 3776-79. The density of the resin-impregnated fabric is determined
from its unit weight and its thickness, measured as described above.
Over-feed ratio, contraction ratio and total gather are parameters reported
herein which measures of how much an initial fibrous layer contracts or
gathers as
a result of the operations to which the layer is subjected. The over-feed
ratio is
defined as the ratio of the initial area of the starting fibrous layer to the
area of the
layer immediately up-stream of a first processing step (e.g., a stitchbonding
step).
Over-feed causes gathering or compression of the layer in the direction in
which it
is being fed to the operation. The contraction ratio is a measure of the
amount of
further contraction the layer undergoes as a result of the specific operation
to which
6
CA 02155968 2001-O1-15
it is subjected (e.g., stitchbonding, release of tension from yarns to which
the
fibrous layer was intermittently attached). The contraction ratio is defined
as
the area of the fibrous layer as it enters the specific operation divided by
the
area of the fibrous layer as it leaves the specific operation. The total
gather is
defined as the product of the over-feed and contraction ratios. The fraction
of
original area is the reciprocal of the total gather and is equivalent to the
ratio
of the final area of the fibrous layer to the initial area of the starting
fibrous
layer.
EXAMPLES
The following Examples illustrate the invention and compare samples
made in accordance with the invention to samples that are outside the scope
of the invention. The examples also illustrate how the abrasion resistance of
resin-impregnated samples is affected by changes in over-all gather, loop
height-to-base ratio, fiber immobilization and fabric stabilization. In the
Examples, all percentages, unless stated otherwise, are based on the total
weight of the resin-impregnated contracted fibrous layer. A summary table of
data accompanies each example and records the unit weight, composition,
thickness, fiber concentration in the impregnated fibrous layer, loop spacing,
loop height-to-base ratio, various gather parameters, stretchability and the
abrasion resistance or each sample. Samples of the invention are designated
with Arabic numerals; comparison samples, with upper case letters. The
reported results are believed to be fully representative of the invention, but
do
not constitute all the tests involving the indicated fibrous layers and
resins.
Example 1
This example illustrates the manufacture of resin-impregnated
contracted fibrous samples of the invention, in which the contraction of the
fibrous starting layer is accomplished by several different techniques,
including: over-feeding (Samples 1, 2 and B); stitchbonding with elastomeric
yam under tension and then heat setting to achieve different amounts of
contraction (Samples 1,2, A and B); stretching a neckable web to which the
fibrous layer had been attached (Sample 3); and intermittently attaching
7
CA 02155968 2001-O1-15
tensioned elastic yams to a fibrous layer and releasing the tension (Sample
4). The contracted-and- resin-impregnated samples of the invention are
compared to similarly prepared samples outside the invention.
For each of the samples prepared by the procedures of this example,
the starting fibrous layer was made of Kelvar~ mid staple fibers of 7/8-inch
(2.2-cm) length and 1.5 denier (1.7 dtex). Kevlar~ a fiber is a product
manufactured and sold by E. I. du Pont de Nemours and Company of
Wilmington, Delaware.
The starting fibrous layer of Samples I and 2 of the invention and
comparison Samples A and B consists of one or two layers of lightweight
Type Z-11 Sontara~ spunlaced fabric of Kevlar~ aramid staple fiber (made
and sold by E. I. du Pont de Nemours and Company). The starting fibrous
layer was stitchbonded with 280-den (311-dtex) yarn of 70-den (78-dtex)
Lycra spandex covered with textured polyester yam. A Liba warp-knitting
machine was employed with one bar fully threaded at 12 gauge (4.8 needles
per cm) and forming 14 courses per inch (5.5 per cm). A 1-0,2-3 repeating
stitch pattern was employed. (Conventional warp knitting nomenclature is
used herein to describe the stitch pattern.) Each sample was then heat set at
380°F (193°C) for 2 minutes on a tenter frame with different
amounts of
longitudinal and transverse stretch.
The starting fibrous layer of Sample 3 was a 0.85-ozlyd2 (29-g/m2) air-
laid web of the Kevlar~ aramid fibers. The web was attached to a highly
entangled layer of 0.7-ozlyd2 (24-gJm2) Style 8417 Sontar~ spunlaced fabric
of polyester fibers. The attachment was made by conventional hydraulic
entanglement techniques. The polyester spunlaced fabric with the air-laid
aramid-fiber web atop it were supported on a 24-mesh, 21 %-open-area
screen while being passed at 10 yards per minute (9.1 m/min) under
columnar streams of water which emerged from a row of 0.007-inch (0.18-
mm) diameter orifices. The row of orifices were located about 1 inch (2.5 cm)
above the screen and extended transverse of length of the moving assembly.
The orifices were spaced in the row at 10 per inch (3.9/cm) and were supplied
8
CA 02155968 2001-O1-15
with water at a pressure of 500 psig (3450 kPa). The hydraulic jet treatment
caused lanes of attachment between the yams and the web to be formed,
which were spaced at a frequency of 10 per inch (3.9/cm). The thusly
assembled web and spunlaced fabric was stretched in the longitudinal
direction by 15%. The longitudinal stretch was accompanied by a contraction
in the transverse direction (i.e., necking-in) that resulted in a decrease in
area
to 40% of the original not-stretched and not necked-in area. The contraction
caused groups of fibers to form inverted U-shaped loops which projected from
the plane of the assembly. The loops in the contracted fabric were spaced
along the transverse direction with a frequency of 28 loops per inch (11/cm).
Sample 4 was prepared by placing a layer of aramid fiber web over a
tensioned 12-gauge warp (i.e., 12/inch or 4.7/cm) of 140-den (154-dtex)
Lycra~ spandex which was wrapped with 70-den (78-dtex) polyester yarn and
then subjecting the warp and web to a hydraulic entanglement treatment.
Each yarn in the tensioned warp had about a 30% residual stretch (i.e., could
have been stretched an additional 30%) with the polyester yarn wrapping
extended to about 8 turns per inch (3.1/cm). The hydraulic treatment
consisted of passing the assembled web and warp, while supported on a 24-
mesh, 21 %-open-area screen, at 10 yds/min (9.1 m/min) under columnar jets
of water emerging from a row of 0.005-inch (0.13-mm) diameter orifices
located about 1 inch (2.5 cm) above the assembly. The row of orifices were
positioned transverse to the array of yams and numbered 40 per inch
(15.7/cm). The assembly was subjected to the hydraulic jets in three passes
under the orifices. The pressure of the water supplied to the orifices was
200,
1000 and 1800 psig (1380, 6890 and 12,400 kPa) during the first, second and
third passes, respectively. After the hydraulic jet treatment, tension was
released from the yams of the warp. The tension release caused contraction
to about 1/3 of the original area of the starting aramid fiber web and
gathering
of groups of aramid fibers into inverted U-shaped loops.
Control sample C consisted of three superimposed flat layers of Type
Z- 11 Sontara~ made of Kevlar~ aramid staple fibers.
9
CA 02155968 2001-O1-15
Each of the above-described samples were impregnated with a
polyurethane resin. The resin was applied from a solution of "ZAR" clear
polyurethane finish (manufactured and sold by United Gilsonite Laboratories
of Scranton, Pennsylvania) by dipping the sample into the finish, allowing the
excess to drip from the sample, and then drying the sample in air for 48 hours
at 25°C and 40% relative humidity. Each of the samples were then
subjected
to abrasion testing. Table I summarizes the test results along with various
characteristics of the dried, resin-impregnated samples. The results of the
abrasion tests are presented graphically in Figure 1.
The Table and Figure clearly demonstrate the unexpectedly large
advantages in abrasion resistance possessed by Samples 1-4, which were
made in accordance with the invention, over the comparison Samples A, B
and C, which were outside the invention. Note that when samples had a total
gather of less than 2.0 and/or a loop H/B ratio of less than 0.5, the abrasion
resistance of the resin-impregnated fabric was very much lower than the
abrasion resistance of the fabrics of the invention. Samples 1-4 of the
invention were about 240 to 475% more resistant to abrasion than
comparison samples that had not been contracted. Note also that the
abrasion resistance appears to be largely unaffected by the concentration of
fiber in the impregnated layer, within the range of fiber concentrations
tested.
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WO 94/19523 ~ PCT/US94101481 -
TABLE I
Sample Identification A ~ ~ 1_ 2_ ~ 4_
Product unit weight, g/m2
Fibrous Layer 110 78 119 212 220 70 180
Total 1000 600 540 1010 710 260 410
Weight percent
Fibrous Layer 11 13 22 21 31 27 44
Contractible elements 2 6 0 5 12 33 4
Resin 87 81 78 74 57 40 52
Fiber concentration, g/cm3 0.08 0.08 0.14 0.13 0.17 0.11 0.11
Total thickness, mm 1.2 0.9 0.8 1.5 1.2 0.6 1.5
Loop base, B, mm 2.8 2.3 Na+ 1.9 1.4 1.0 1.3
Loop H/B ratio 0.43 0.37 Na 0.80 0.86 0.60 1.20
Gather
Over-feed ratio 1.0 1.36 1.0 1.30 1.31 Na Na
Contraction ratio 1.0 1.4 1.0 2.0 4.2 2.5 3.1
Total gather 1.0 1.9 1.0 2.6 5.5 2.5 3.1
Fraction of original area 1.0 0.53 1.0 0.38 0.18 0.40 0.32
Stretchability, % 0 0 0 0 0 0 0
Abrasion resistance
Test duration, 103 cycles 2.5 3.0 6.0 7.0 12.0 8.0 9.0
Wear, mm/103 cycles 0.12 0.08 0.12 0.05 0.025 0.032 0.030
normalized wear* 100 69 100 42 21 27 25
Notes: * % normalized wear is normalized to Sample C.
+ "Na" means not applicable.
Ea;amnle 22
This example illustrates the fabrication of resin-impregnated, contracted
nonwoven fabrics of the invention, Samples 5 and 6, in which the starting
fibrous
layer is a sheet of flash-spun plexifilamentary film-fibril polyethylene
strands and
compares their abrasion resistance with similarly prepared comparison Samples
D
and E which were not subjected to the desired amount of gather. Whereas
Samples
5 and 6 were subjected to a total gather of 2.7 and 5.7 respectively,
comparison
Samples D and E, which are outside the invention, were subjected respectively
to
no contraction at all (Sample D) or to a total gather of only 1.76 (Sample E).
As a
result of the appropriate contraction, the Samples of the invention were about
20 to
CA 02155968 2001-O1-15
100 times as resistant to abrasion as were the comparison samples. Table II,
below, summarizes detailed characteristics of the samples. Figure 2
graphically displays the advantages in abrasion resistance having resin-
impregnated fabrics of the invention prepared with total gathers of at least
2Ø
Further details on the fabrication of the samples are given in the following
paragraphs.
The starting fibrous layer of each of the samples of this example was a
lightweight, non-bonded sheet Of flash-spun plexifilamentary fllm-fibril
polyethylene strands which had been treated with hydraulic jets in accordance
with the general procedures of Simpson et al, U. S. Patent 5,023,130. The
hydraulic jet treatment consisted of supporting the non-bonded sheet on a 24-
mesh, 21 %-open-area screen, and passing the sheet one time at 10 yds/min
(9.1 rn/mm) under columnar jets of water emerging from a row of 0.005-inch
(0.13-mm) diameter orifices, spaced at 40 orifices per inch (15.7/cm) in the
row, the row of orifices being positioned about 1 inch (2.5 cm) above the
screen and transverse to the direction of movement of the sheet. Water was
supplied to the orifices at a pressure of 500 psig (3450 kPa). Such starting
fibrous layers are available commercially as Typro~ from E. I. du Pont de
Nemours and Company. One or two layers of 1.3 oz/yd2 (44 g/m2) commercial
Typro~ was used for the samples of this example.
The hydraulic-jet-treated fibrous layers of Typro~ sheet of Samples 5,
6 and comparison E were contracted by stitchbonding with a "Liba" machine
with the stitching yams under tension and then releasing the tension from the
yams. Comparison sample D, was not stitched or contracted. For Samples 5
and 6 of the invention, the stitching yarn was a 140-den (154-dtex) Lycra~
spandex wrapped with 70-den (78-dtex) polyester yarn and one fully threaded
12-gauge bar formed 1-0,1-2 stitches, 14 courses per inch (5.5/cm). For
comparison Sample E, the stitching thread was a 70-den (78-dtex) textured
nylon yarn and one fully threaded 12-gauge bar formed 1-0, 1-2 stitches, 9
courses per inch (3.5/cm). All samples were impregnated with a polyurethane
resin by the same manner as in Example 1, except that the polyurethane resin
employed in this Example, when dry is much softer than the polyurethane
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CA 02155968 2001-O1-15
resin of Example 1. The dry resin of Example 2, had a Shore A durometer
hardness of about 53.
Further details of the samples and their performance are given in the
following table.
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WO 94/19523 - PCT/US94/01481 -
TABLE II
Sample Identification p
Product unit weight,
g/m2
Fibrous Layer 44 82 260 272
Total 132 214 1075 1105
Weight percent
Fibrous Layer 33 38 24 25
Contractible elements 0 10 7 10
Resin 67 52 69 65
Fiber concentration, 0.24 0.36 0.20 0.25
glcm3
Total thickness, mm 0.18 0.23 1.32 1.07
Loop base, B, mm Na 2.64 1.47 1.37
Loop H/B ratio Na 0.09 0.89 0.78
Gather
Over-feed ratio Na 1.0 1.0 1.37
Contraction ratio 1.0 1.76 2.74 4.17
Total gather 1.0 1.76 2.74 5.7
Fraction of original 1.0 0.57 0.36 0.17
area
Stretchability, % 0 0 0 0
Abrasion resistance
Test duration, 103 cycles0.12 0.14 20 20
Wear, mm/103 cycles 0.60 0.45 0.0240.006
normalized wear* 100 75 4 1
Notes: * % normalized ized SampleC.
wear is normal to
+ "Na" means not applicable.
m 1
This example illustrates the effect of total gather on abrasion resistance
with
a commercial nonwoven material which is sold by Kimberly-Clark Corporation of
Neenah, Wisconsin, and is referred to as "KC stretchbonded composite (B-16,
SBL-13)". This material has inverted U-shaped loops on each of its two
surfaces,
as shown schematically in Figure 6. In this example, Sample 7 of the invention
is
shown to be 3 to 5 times as abrasion resistant as any of four comparison
Samples F,
G, H or I. Sample 7 has a total gather of 2.8 and a loop H/B ratio of 0.63, as
compared to the comparison samples which have gathers in the range of 1 to 1.8
and loop ratios in the range of 0.11 to 0.32.
The KC stretchbonded composite which is starting fibrous layer for each of
the samples of this example, has a very thin elastic layer that is located mid-
plane
between two spunbonded sheets of polypropylene fibers. The sheets apparently
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CA 02155968 2001-O1-15
were thermally spot-bonded to the elastic layer while the elastic layer was
under tension. Thereafter, the layer apparently was allowed to relax and
gather by what appears to have been a factor of 2.8 in the longitudinal
direction. To test the effects of total gather on the abrasion resistance of
this
material, polyurethane resin of Example I was applied in the same manner as
in Example I to samples of KC stretchbonded composite that were fully
relaxed or stretched by different amounts to form Sample 7 (fully relaxed,
total
gather = 2.8) and comparison Samples F, G, H and I (with total gathers of
1.0, 1.1, 1.4 and 1.8, respectively). Further details of samples and their
abrasion-test performance are given in Table III. Abrasion performance is
plotted in Figure 3, as a function of total gather.
TABLE III
Sample Identification F G H I 7
Unit weight, g/m2
Fibrous two layers 22 24 30 39 60
Contractible layer 33 37 45 59 89
Total 614 678 885 925 1230
Weight Percent
Fibrous two layers 3.6 3.5 3.4 4.2 4.9
Contractible layer 5.4 5.6 5.1 6.4 7.2
Resin 91.1 91.9 91.5 89.2 87.9
Fiber concentration, 0.08 0.08 0.08 0.09 0.11
g/m2
Total thickness, mm 0.28 0.29 0.38 0.45 0.57
Loop base, B, mm 2.5 2.3 1.8 1.4 0.9
Loop H/B ratio 0.11 0.12 0.21 0.32 0.63
Gather
Total Gather 1.0 1.1 1.4 1.8 2.8
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Fraction of original1.0 0.91 0.71 0.56 0.36
area
Stretchability, 0 0 0 0 0
%
Abrasion resistance
Test duration, 1.1 1.1 0.5 0.7 1.1
103
cycles
Wear, mm/103 cycles0.46 0.32 0.30 0.31 0.09
normalized wear* 100 70 65 67 20
Note: % normalized malizedto ple
wear is nor Sam F.
Example 4
A series of resin-impregnated, stitchbonded contracted samples was
made by the procedures as were used in Example I for Samples 1, 2, A, B
and C, and with the same materials except that natural rubber RSS #1,
manufacturing code 220-B40 was substituted for the polyurethane resin used
in Example 1 to impregnate the fibrous layer of Kevlar~ fibers. The same
kinds of improvement in
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CA 02155968 2001-O1-15
abrasion resistance with increasing total gather as were shown in Example 1
are also demonstrated in this example. Sample details and abrasion test
results are summarized in Table IV. Figure 4 displays the abrasion results
graphically.
TABLE
IV
Sample identification J K L 8 9
Product unit weight,
g/m2
Fibrous Layer 122 108 78 210 224
Total 549 797 831 956 1003
Weight percent
Fibrous Layer 22 14 9 22 22
Contractible elements 0 3 4 4 8
Resin 78 83 87 74 70
Fiber concentration, 0.20 0.11 0.07 0.15 0.18
g/cm3
Total Thickness, mm 0.6 1.0 1.1 1.4 1.5
Loop base, B, mm Na 2.8 2.4 1.87 1.42
Loop H/B ratio Na 0.36 0.45 0.76 1.07
Gather
Over-feed ratio Na 1.0 1.36 1.13 1.31
Contraction ratio 1.0 1.0 1.4 2.3 4.2
Total gather 1.0 1.0 1.9 2.6 5.5
Fraction of original 1.0 1.0 0.52 0.38 0.18
area
Stretchability, % 0 0 0 0 0
Abrasion resistance
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Test duration, 4 12 15 15 15
103
cycles
Wear, mm/103 cycles0.03 0.03 0.01 0.00 0.00
3 4 5 7 3
normalized wear 100 100 45 21 10
*
Notes: * % normalized wear is normalized to Sample J
"Na" means not applicable
Example 5
This example illustrates the deleterious effects of excessive
stretchability on the abrasion resistance of resin-impregnated contracted
fabrics. Three pairs of samples, (10 and 11 ), (12 and M) and (N and 0), were
prepared by the procedures of Example I, Sample 2. The starting fibrous layer
of Kevlar~ aramid fiber of each sample was stitchbonded with about 25%
over-feed to provide samples with differing amounts of total gather. The
stitch
bonded layers were then resin-impregnated with the same polyurethane resin
as in Example 1, with the resin amounting to a much lower percent of the total
weight of the resin-impregnated sample; namely, about 6 to 33 percent
versus about 57 to 87% in Example 1. The lesser amounts of resin were
applied to the fibrous layer by dipping the layer a
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WO 94119523 PCT/US94/01481
"ZAR" polyurethane resin solution that had been diluted with an organic
solvent.
Details of sample construction and results of abrasion testing are summarized
in
Table V, below. When the resin in the sample amounted to less than about 20%
of
the total sample weight, the sample was excessively stretchable. To assure
that at
least one sample in each pair was dimensionally stable and substantially non-
stretchable, inelastic strips were adhesively attached to the back of Samples
10, 12
and 13, but not to the other member of the pair (i.e., samples 11, M and O).
TABLE V
Sample Identification ~.Q 11 ~ ~ 1~
Unit weight, g/m2
Fibrous Layer 166 166 227 227 197 197
Total 509 509 400 400 302 302
Weight percent
Fibrous Layer 47.0 47.0 56.8 56.8 65.2 65.2
Contractible elements 20.3 20.3 24.6 24.6 28.1 28.1
Resin 32.7 32.7 18.6 18.6 6.7 6.7
Fiber concentration, g/cm3 0.10 0.10 0.13 0.13 0.1 S 0.1 S
Total thickness, mm 1.7 1.7 1.8 1.8 1.3 1.3
Loop base, B, mm 1.1 1.1 1.2 1.2 1.5 1.5
Loop H/B ratio 1.55 1.55 1.45 1.45 1.52 1.52
Gather
Over-feed ratio 1.25 1.25 1.24 1.24 1.23 1.23
Contraction ratio 4.7 4.7 4.5 4.5 3.9 3.9
Total gather 5.9 5.9 5.6 5.6 4.8 4.8
Fraction of original area 0.17 0.17 0.18 0.18 0.21 0.21
Stretchability, % 0 10 0 70 0 100
Abrasion resistance
Test duration, 103 cycles 20 20 5 2.1 4 0.8
Wear, mm/103 cycles 0.048 0.051 0.071 0.61 0.114 1.30
Relative wear within pair 1.0 1.06 1.0 8.6 1.0 11.4
Relative wear rating* 1.0 1.06 1.47 12.7 2.3 27.1
Notes: Relative wear within pair is relative to the more abrasion-resistant
sample and relative wear rating of individual samples is relative to Sample
10.
The results summarized in Table V show that even with high total gather
and high loop H/B ratios within the invention, unless the loops are
immobilized by
sufficient resin and unless the fabric is dimensionally stable, contracted
resin-
impregnated fabric has inadequate abrasion resistance. Note that
stretchability of
10% in Sample 11 was not deleterious to abrasion resistance. Note also that
dimensional stabilization of Samples 12 and N resulted in considerably greater
CA 02155968 2001-O1-15
abrasion resistance than the corresponding samples (M and 0 respectively)
that was not so stabilized. Note however, that the lack of immobilization of
the
loops in Samples N and 0, because of the very low resin content of the
samples, also resulted in much poorer abrasion resistance.
Although the invention was illustrated primarily with fibrous layers of
Kevlar~ aramid staple fibers and of flash-spun continuous plexifilamentary
strands of polyethylene film fibrils, which layers were impregnated with
polyurethane or rubber resins, other natural or synthetic fibrous materials
(e.g., nylon, polyester, rayon, cotton and the like) and other resins (e.g.,
epoxy, polystyrene, etc.) can be used in accordance with the present
invention to the produce abrasion-resistant, resin-impregnated fabrics. The
resins can be applied from aqueous solutions as well as solutions of the resin
in organic solvents. Also, the resin-impregnated fabrics of the invention are
useful, not only as flat sheet-like articles, but as shaped or molded articles
as
well as. When used in molded products, some of the contraction imposed on
the flat fabric is removed by the molding operation. In such cases, the
residual amount of contraction in the molded article is very important in
determining the abrasion-resistant characteristics of the resin-impregnated
article. Resin-impregnated fabric of the invention can be used as a single
layer or in multiple superimposed layers or in combination with other gathered
fabrics, flat fabrics or sheets and in flat or in shaped form. The fabric can
be
permanently attached to or molded over articles, such as elbow pads for
jackets, back-packs, luggage, shoes, or portions thereof, and the like.
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