Note: Descriptions are shown in the official language in which they were submitted.
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STITCH-BONDED THERMAL INSULATING FABRICS
sackground of the Invention
Field of the Invention
The present invention relates to stitch-bonded
thermal insulating fabrics, which are useful in apparel,
particularly for innerwear and sleepwear, blankets,
bedspreads, etc.
Background Information
Fabrics having a base layer stitched-bonded
with yarn are well-known in the art. Base layers of loose
material, such as matting, an array of loose filling
threads, or a layer of wadding, may be stitch-bonded,
i.e. bound or enmeshed with the loops of a multitude of
chain-stitched warp threads, to provide a fabric having
coherence, tensile strength, and durability as disclosed
in U.S. Patent No. 2,890,579 (Mauersberger). Nonwoven
fabric webs have been stitch-bonded to provide varied
patterned surfaces as disclosed in U.S. Patent Nos.
3,664,157 (Kochta et al.), 3,782,137 (Hughes), and
20 3,992,904 (Webb et al.). Stitch-bonding has also been
used to secure loop-pile threads to a base layer as
disclosed in U.S. Patent No. 3,597,941 (Jindra et al.).
British Patent Application No. 1,427,191 discloses a
stitch-bonded fabric having a base layer which contains
thermally bondable fibers to increase abrasion resistance
and pill resistance.
U.S. Patent No. 3,910,072 (Svoboda et al.)
discloses a stitchbonded fabric with thermoinsulating
properties which includes a base layer such as a
needled-reinforced fibrous fleece, a woven fabric or
knitted fabric, transversely arranged weft threads and
stitch-bonding warp threads.
Summary of the Invention
The present invention relates to a stable,
thermal insulating fabric which is a stitch-bonded,
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fibrous, nonwoven web of microfibers that average less than about
10 micrometers in diameter, said fabric having thermal resistance
per basis weight of at least about 0.00030 k.m2/watt/g/m2 and air
permeability of less than about 1 m3/sec~m2. The stitch-bonded
web preferabl~ has a tensile strength in the machine direction of
at least about 15 kg and tensile s~rength in the transverse
direction of at least about 10 kg.
In a preferred embodiment of the invention, the nonwoven
web further contains crimped bulking fibers that have a percent
crimp of at least 15 percent intermixed and intertangled with the
microfibers with the weight ratio of microfibers to crimped
bulking fibers in the range of from about 9:1 to l:g.
These stitch-bonded fabrics provide excellent thermal
lnsulatlng propertles at low basls weight and may be utllized in a
varlety of end products including bedspreads, blankets, outerwear,
linings, etc. and are particularly useful for innerwear, e.g.,
thermal underwear, and sleepwear.
Brief Descri~tion of the Drawinas
Figure 1 is a diagrammatic representation of the stitch
configuration used in stitch-bonding the fabrics of Examples 1 and
3;
Figure 2 i~ a dlagrammatic representatlon of the stltch
configuration used in ~tltch-bondlng the fabrlc of Example 2; and
Flgure 3 is a dlagrammatlc representation of the stltch
conflguratlon used ln stltch-bondlng the fabric of Example 4.
etailed DescrlPtlon of the Inventlon
Fibrous nonwoven webs, stitch-bonded according to the
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present invention typically have a basis weight in the range of 20
to 300 g/m2 and bulk density less than about 0.05 g~cm3.
Particularly preferred are webs produc2d according to the
teachings of United States Patent No. 4,118,531 (Hauser). These
webs include microfibers,
A
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generally averaging less than about 10 micrometers in
diameter, and bulking fibers, i.e., crimped, generally
larger-diameter fibers, which are randomly and thoroughly
intermixed and intertangled with the microfibers and
account for at least 10 weight percent of the fibers in
the web. The crimped bulking fibers function as
separators within the web, separating the microfibers to
produce a lofty resilient web. Such a web possesses
excellent thermal insulating properties.
The web may consist of a single layer, or may
be a multi-layer product in which the layers are
typically indistinguishable to at least casual
inspection. Preferred webs are soft and pliable, so that
the resulting fabric is soft and pliable.
The insulating quality of microfibers is
generally independent of the material from which they are
formed, and microfibers may be formed from nearly any
fiber-forming material. Representative polymers for
forming melt-blown microfibers include polypropylene,
polyethylene, polyethylene terephthalate, polyamides, and
other polymers as known in the art. Useful polymers for
forming microfibers from solution include polyvinyl
chloride, acrylics, and acrylic copolymers, polystyrene,
and polysulfone. Inorganic materials also form useful
microfibers.
The finer the microfibers in the web the better
the thermal resistance. Blown microfibers (prepared by
extruding a liquid fiber-forming material through an
orifice into a high-velocity gaseous stream) can conven-
iently be prepared in diameters smaller than ten
micrometers. To form useful webs, the aspect ratio (ratio
of length to diameter) of the microfibers should approach
infinity, though blown microfibers are usually thought to
be discontinuous.
The optional crimped bulking fibers, i.e.,
having a continuous wavy, curly, or jagged character
along their length, are available in several different
forms for use as the bulking fibers in the web.
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Three-dimensionally crimped fibers generally encourage
greater loftiness in the web. However, good webs can be
produced from fibers having any of the known types of
crimp.
The number of crimps per unit of length can
vary rather widely in the bulking fibers. In general, the
greater the number of crimps per centimeter, the greater
the loft of the web. However, larger-diameter fibers will
produce an equally lofty web with fewer crimps per unit
of length than a smaller-diameter fiber.
Crimped bulking fibers also vary in the
amplitude or depth of their crimp. Although amplitude of
crimp is difficult to uniformly characterize in numerical
values because of the random nature of many fibers, an
indication of amplitude is given by percent crimp. The
latter quantity is defined as the difference between the
uncrimped length of the fiber (measured after fully
straightening a sample fiber) and the crimped length
(measured by suspending the sample fiber with a weight
attached to one end equal to 2 miligrams per decitex of
the fiber, which straightens the large-radius bends of
the fiber) divided by the crimped length and multiplied
by 100. Bulking fibers used in the present invention
generally exhibit an average percent crimp of at least
about 15 percent, and preferably at least about 25
percent.
The crimped bulking fibers should, as a
minimum, have an average length sufficient to include at
least one complete crlmp and preferably at least three or
four crimps. The bulking Eibers should average between
about 2 and 15 centimeters in length. Preferably the
bulking fibers are less than about 7-10 centimeters in
length.
Synthetic crimped bulking fibers are preferred
and may be made from many different materials but
naturally occurring fibers may also be used. Polyester
crimped staple fibers are readily available and provide
useful properties. Other useful fibers include acrylics,
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polyolefins, polyamides, rayons, acetates, etc. Webs of
the invention may include more than one variety of
bulking fiber, as well as more than one variety of
microfiber.
S The finer the staple fibers, the greater the
insulating efficiency of a composite web, but the web
will generally be more easily compressed when the staple
fibers are of a low denier. Most often, the bulking
fibers will have sizes of at least 3 decitex and
preferably at least 6 decitex, which correspond approxi-
mately to diameters of about 15 and 25 micrometers,
respectively.
The amount of crimped bulking fibers included
or blended with microfibers will depend upon the
particular use to be made of the fabric of the invention.
Generally at least 10 weight-percent of the blend will be
bulking fibers to provide the desired low weight for a
given amount of thermal resistance, and preferably at
least 25 weight-percent of the blend will be bulking
fibers. On the other hand, to achieve good insulating
value, especially in the desired low thickness, micro-
fibers will account for at least 25, and preferably at
least 50 weight-percent of the blend. Stated another way,
the weight ratio of microfibers to bulking fibers in webs
useful in the invention will generally be between 9:1 and
1:3, and preferably between 3:1 and 1:1.
Fibrous webs for stitch-bonding according to
the invention can be supplied in any desired thickness
depending again on the particular use to be made of the
stitch-bonded fabric, but a convenient thickness is
between about 4 and 20 millimeters. The loft or density
of the web prior to stitch-bonding can also be varied for
particular uses, though generally the webs will have a
loft of at least about 30 cubic centimeters/gram, and
preferably of at least about 50 cubic centimeters/gram.
Fibrous webs used in the invention may include
minor amounts of other ingredients in addition -to the
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microfibers and crimped bulking fibers. For example,
fiber finishes may be sprayed onto a web to improve the
hand and feel of the web. Additives, such as dyes and
fillers, may also be added to webs of the invention by
introducing them to the fiber-forming liquid of the
microfibers or crimped bulking fibers.
Stitch-bonding of the microfiber or composite
web can be carried out on known stitch-bonding equipment.
Particularly preferred are the stitch-bonding machines
which are equipped with at least two guide bars such as
Malimo "Maliwatt" machines or the "Arachne" machines. The
two guide bar machines are particularly preferred for
their lapping and patterning capabilities, lapping
stitches providing increased fabric strength in the
transverse direction. Machines having a gauge of 3.5 to
28 needles/25 mm are preferred for most end use
applications of the fabric of the invention, with 7
needles/25 mm particularly preferred where the fabric of
the invention is for use in thermal underwear or
sleepwear.
The stitch-bonding stabilizes the fabric
sufficiently to permit the fabric to be used without the
need for a supporting fabric layer as is required with
the unstitch-bonded web. Whereas, prior to
stitch-bonding, a fibrous web, especially of blown
microfibers, will tear or separate to form voids of poor
or no insulating quality under tensile forces such as
experienced during garment manufacture or use, the fabric
formed by stitch-bonding has increased tensile strength
and generally can be repeatedly stretched small amounts
without rupture or deformatlon.
As may be seen from the drawings, the
stitch-bonding comprises a repeating pattern of
spaced-apart stitching lines extending over the whole
area of the web. As shown in Figure 1-3, the stitching
lines preferably overlap over at least portions of their
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length. The stitch-bonding tends to subdivide or separate
the fibrous web into islands or stripes which are
reinforced by the stitching yarns. When tensile force is
applied to the web, the force tends to be applied to the
stitch-bonding yarns and the localized islands or stripes
of fibrous web experience little or no stress.
Preferred stitch-bonding patterns are those
which crosslap at least two stitches and which provide a
diamond pattern on one face of the fabric. These types of
patterns reduce the number of holes caused by the
stitching, provide stretch and shape retention, and
improve loft. The fabric weight is also affected by the
pattern selection as some patterns tend to draw-in, or
reduce the width, of the web more than others, with
patterns having longer diagonal lapping generally drawing
the fabric in more than patterns with less diagonal
lapping.
Stitch length may vary depending on the end use
application of the fabric and the pattern effects
desired. Generally, a stitch length of about 1.0 to 2.5
mm is preferred, with a stitch length of about 1.5 mm
particularly preferred for fabric to be used in thermal
underwear and sleepwear.
Yarns used for stitch-bonding can be any of the
well-known, commercially available spun or continuous
filament yarns. Because of their higher strength at
comparable denier, continuous filament yarns are
generally preferred. Generally, yarn sizes preferred are
in the range of about 60 to 300 denier, prc~erably about
100 to 150 denier. Finer denier yarns reducc weight and
cost of the fabric but are weaker.
The stitch-bonded fabric of the invention
preferably has a thermal resistance of at least about
0.035 k-m /watt, more preferably at least about 0.045
k m2/watt to provide desirable thermal insulating
properties. When calculated on the basis weight of the
fabric, the thermal resistance is preferably at least
about 0.00030 k m/watt/g/m2, more preferably at least
about 0.00035 k m2/watt/g/m2.
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The stitch-bonded fabric preferably has low air
permeability to reduce the infiltration of cold air and
the effusion of warm air. Air permeability preferably is
less than about 1 m3/sec/m2 at 124 Pa, more preferably
less than about 0.75 m3/sec/m2 at 124 Pa.
To provide adequate fabric strength for the
fabric to be used independently, i.e., without additional
protective exterior fabric layers, the fabric generally
should have a tensile strength of at least about 15 kg,
preferably 20 kg, ~n the stitch-bonding machine direction
and at least about 10 kg, preferably 20 kg, in the
transverse direction.
To further increase the strength of the fabric
and/or to provide decorative pattern effects, laid in
weft yarns may also be included in the fabric.
The invention will be further illustrated by
the following examples. In these examples, the fabric
properties are evaluated by the following test methods:
Thickness: A 10.2 cm x 15.2 cm die cut sample
is subjected to a compressive force of 413.6 Pa for 30
seconds, allowed to recover for 30 seconds with the force
removed, subjected to a compressive force of 87.1 Pa for
30 seconds, allowed to recover for 30 seconds with the
force removed, and then measured for thickness after
being subjected to a compressive force of 14.5 Pa for 30
seconds and while under such force.
Tensile Strength: A test sample 10 cm wide and
7.5 cm long (in the test direction) is ex-tended to break
at a rate of 50 cm/min.
Thermal Resistance: A sample is tested on a
guarded hot plate as described in ASTM Test Method
D1518-64 with the test sample subjected to a force of
14.5 Pa during testing.
Air Permeability: A sample is tested on a
Frazier Air Permeability Tester according to ASTM Test
Method D-737.
9 ~253~2~;
Example
A composite fibrous web was prepared according
to the process described in U.S. Patent No. 4,118,531,
using polypropylene blown microfibers 1 to 5 micrometers
in diameter and 6 denier, 3.75 cm long, 2.8 to 4.4
crimp/cm polyester staple fibers. The web contained 65
weight percent blown microfibers and 35 weight percent
staple fibers. The web weight was 44 g/m2. This web was
then stitch-bonded on a "Maliwatt" stitch-bonding machine
with 150 denier/24 filament polyester yarn using the
stitch configuration shown in Figure 1 and the machine
parameters set forth in Table 1. The fabric was then
evaluated for basis weight, thickness, strength, thermal
resistance, and air permeability. The results are shown
in Table 2.
Examples 2-4
In each of these examples, a web was prepared
as in Example 1. The webs were stitch-bonded on a
"Maliwatt" stitch-bonding machine with 150 denier/24
filament polyester yarn using the stitch configurations
shown in Figures 2, 1, and 3 respectively and the machine
parameters set forth in Table 1. The fabrics were
evaluated as in Example 1. The results are shown in Table
2.
Table 1
Example
_2_ 3 4
No. of bars 2 2 2 2
Stitch length (mm) 1.5 2.0 2.0 2.0
30 Yarn ends/2.5 cm
Bar 1 7 7 7 7
Bar 2 7 7 7 7
Offset space 1 0
Needle gauge M* M M M
35 *M denotes medium
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Comparative Examples 1-3
In Comparative Example 1, a web was made as in
Example 1. The web was not stitch-bonded. The web was
tested in the same manner as the fabric of Example 1. In
Comparative Example 2, a commercially available fleecy
jersey knit polypropylene fabric used in thermal
insulating innerwear was tested in the same manner as the
fabric of Example 1. In Comparative Example 3, a
conventional cotton/wool blend fabric used in thermal
insulating innerwear was tested in the same manner as the
fabric of Example 1. The results are shown in Table 2.
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The stitch-bonded fabrics of Examples 1-4 were
subjected to ten launderings. The fabrics were then
evaluated for basis weight, thickness and thermal
resistance. The results are shown in Table 3. The web of
Comparative Example 1 disintegrated after one laundering.
Table 3
Example
1 2 3 4
Basis weight(g/m ) 114 129 127 102
Thickness (cm) 0.36 0.37 0.36 0.35
Thermal resistance
(k'm2/watt) 0.080 0.089 0.072 0.074
(k'm2/watt/cm) 0.22 0.24 0.20 0.21
Various modifications and alterations of this
invention will be apparent to those skilled in the art
without departing from the scope and spirit of the
invention and this invention should not be restricted to
that set forth herein for illustrative purposes.
