Stretchable insulating fabric

An elastically stretchable fabric having enhanced thermal insulation properties comprising at least one elastically stretchable carrier web having substantially uniform stretch properties and a thin coherent coated layer of melt-blown microfibers carried on at least one surface of the carrier web, said melt-blown microfibers being selected from the group consisting of polypropylene, polyethylene, polyurethane, polyethylene terephthalate or mixtures thereof.

FIELD OF THE INVENTION 
The present invention relates to stretchable fabrics having enhanced 
thermal insulation properties, and which are particularly useful in thin, 
close-fitting outdoor apparel such as skiwear, gloves and work clothing. 
BACKGROUND ART 
Nonwoven thermally insulating elastically stretchable fabrics are taught in 
U.S. Pat. No. 4,551,378. Although these fabrics offer good insulating 
properties and comfort in wearing, the present invention makes possible 
even better insulating properties. Fabric as taught in U.S. Pat. No. 
4,551,378 can be a component of fabric of the invention. 
A different stretchable nonwoven thermal insulating fabric, which in one 
embodiment comprises a nonwoven web formed from thin fibrous layers 
laminated together, with the fibers comprising a polyester type copolymer 
containing butylene terephthalate, is taught in U.S. Pat. No. 4,438,172. 
Another nonwoven thermal insulating fabric having stretch properties is 
commercially available under the trademark "Viwarm" from a Japanese 
manufacturer. The material is a spray-bonded, lightly needle-tacked 
nonwoven web of a blend of one- and three-denier single-component 
polyester fibers, the three-denier fiber having sufficient crimp to 
provide stretch properties. The product has a high "power stretch" (i.e., 
it requires a large force to stretch the fabric), and it does not have the 
combination of thermal insulating properties and low density offered in 
the present invention. 
A different item of background prior art, relevant because it teaches 
blends of fibers useful in some embodiments of the present invention, is 
U.S. Pat. No. 4,118,531. This patent teaches blends of melt-blown 
microfibers and crimped staple textile fibers, which form lofty, 
high-insulating-value fabric or sheet material. 
SUMMARY OF THE INVENTION 
The present invention provides a new elastically stretchable fabric having 
a surprisingly high insulating value in view of its relative thinness, and 
which can be repeatedly stretched without losing its thermal insulative 
properties or its dimensional integrity. Briefly summarized, the new 
stretchable fabric, sometimes referred to herein as a "stretch fabric," 
comprises at least one elastically stretchable fibrous carrier web having 
substantially uniform stretch properties and carrying a thin coherent 
layer of microfibers coated on at least one surface of the carrier web. A 
coated layer of melt-blown microfibers is preferred and when deposited on 
the carrier web as a thin layer, preferably having a weight less than 
about 30 g/m.sup.2, greatly enhances the thermal insulating character of 
the fabric and functions as a substantially integral part of the fabric, 
e.g., stretches and retracts with the carrier web as the latter stretches 
and retracts and remains in adherent contact with the carrier web. It is 
preferred that the thermal insulating property of the fabric is at least 
20% greater than the thermal insulating property of the carrier web, and 
more preferably at least 50% greater. 
DETAILED DESCRIPTION 
Carrier webs used in the present invention may comprise any elastically 
stretchable fibrous material, but preferably comprise a nonwoven web of 
bicomponent fibers bonded together by fusion of fibers at points of 
contact and thermally crimped in situ as is described in U.S. Pat. No. 
4,551,378, which is incorporated herein by reference. The carrier webs 
should have substantially uniform low power stretch properties such as 
provided by the webs described in that patent. The carrier web (and 
finished fabric of the invention) preferably substantially recovers its 
original dimensions and insulation properties after repeated (i.e., 10 or 
more) extensions of 40% above its original dimension. 
It is usually desirable that the bulk density of the carrier web be kept 
relatively low so as to provide good thermal insulating properties while 
keeping the web weight low. Weights of about 30 to 150 g/m.sup.2 and 
densities ranging from about 0.005 to 0.020 g/cm.sup.3 are preferable in 
the carrier web for most apparel applications. Also, carrier webs included 
in webs of the present invention are preferably permeable so as to 
facilitate the transfer of moisture through the total construction. 
Without adequate permeability, moisture will accumulate in the garment and 
adversely impact its ability to keep the wearer warm. Carrier webs should 
have a permeability (such as a Frazier permeability) of at least about 
0.25 m.sup.3 /sec/m.sup.2 (50 ft.sup.3 /min/ft.sup.2) with a flow 
resistance of 124 Pa (1/2 inch water gauge pressure). 
The microfiber-based coated layers of the present invention are typically 
comprised of fibers having an average diameter of less than about 10 
micrometers. They can be prepared by a variety of techniques including 
solution-blowing or melt-blowing processes, but preferably are prepared by 
a melt-blowing process. A number of polymeric materials may be used for 
the preparation of the microfibers, including but not limited to 
polyethylene, polypropylene, polyethylene terephthalate (PET), and 
polyurethanes. Combinations of such polymers can be used as bicomponent 
fibers, e.g., as polyethylene/polypropylene or polypropylene/polyethylene 
terephthalate bicomponent fibers taught in microfiber form in U.S. Pat. 
No. 4,547,420, or also in some cases as blends. Coating weights are chosen 
to provide sufficient thermal insulation for the contemplated use of the 
finished fabric, but generally are at least about 5 g/m.sup.2 and 
preferably at least 10 g/m.sup.2. The most preferred range, especially for 
melt-blown microfibers, is about 10-20. 
Crimped staple textile fibers may be included in the microfiber-based 
coated layers in the fabrics of the present invention to achieve increased 
loft, but microfibers generally comprise at least 50 or 60 weight-percent 
of the coating. 
The microfibers used in the invention are typically prepared by means of a 
melt-blowing process, for example, as taught by Wente, Van A., "Superfine 
Thermoplastic Fibers," in Industrial Engineering Chemistry, Vol. 48, pages 
1342 et seq, (1956), or in Report No. 4364 of the Naval Research 
Laboratories, published May 25, 1954, entitled "Manufacture of Superfine 
Organic Fibers" by Wente, Van A.; Boone, C. D. and Fluharty, E. L. The 
microfibers are typically collected directly onto the carrier web, as by 
interposing the webs in an air stream of the fibers. The carrier web can 
be held in either a relaxed or an extended configuration. Microfibers or 
mixtures of microfibers and staple textile fibers are able to penetrate 
into the web to a greater degree when the carrier web is in a stretched 
configuration and become more mechanically entwined, but good entwining is 
also achieved in the relaxed state. Melt-blown microfibers have good 
conformance and become well-entwined with the carrier web so as to remain 
adhered to the web with just mechanical entwining. 
The present invention is further described by the following non-limiting 
examples.

EXAMPLES 1-6 
A series of fabrics of the invention were prepared using as the carrier web 
a 34-g/m.sup.2 -basis weight elastically stretchable nonwoven web as 
described in U.S. Pat. No. 4,551,378 made from staple highly eccentric 
sheath-core type bicomponent fibers having a polypropylene core and 
polyethylene sheath (Chisso ES fibers available from Chisso Corporation, 
Osaka, Japan). Polypropylene melt-blown microfiber coated layers were 
applied to the carrier web by feeding the carrier web under slight tension 
around a portion of the rotating collector drum of a melt-blowing 
apparatus similar to that described in U.S Pat. No. 4,118,531, which is 
incorporated herein by reference. A range of coating weights and 
collector/die distances were utilized in preparing a variety of samples, 
as described in Table I. 
TABLE I 
______________________________________ 
Finished Finished 
Coating Collector 
Web Web 
Weight Distance Thickness Density 
Example 
(g/m.sup.2) 
(cm) (cm) (g/m.sup.3) 
______________________________________ 
1 Control -- .22 .015 
2 8 6 .261 .013 
3 8 14 .244 .014 
4 16 10 .28 .012 
5 24 6 .332 .010 
6 24 14 .285 .012 
______________________________________ 
Insulating % Thickness % Clo 
Value Increase Increase 
Example 
(Clo) (Clo/cm) From Coating 
From Coating 
______________________________________ 
1 .34 1.545 Control -- 
2 .451 1.73 18.6 32.6 
3 .477 1.96 10.9 40.3 
4 .53 1.89 28.0 56.0 
5 .604 1.82 50.9 77.6 
6 .582 2.04 29.5 71.2 
______________________________________ 
The power stretch (force required to stretch) of all the above samples fell 
within the range of 400 to 800 g for a 40% elongation of the sample. 
EXAMPLE 7 
A fabric of the invention similar to that of Example 4 was prepared, except 
that 6-denier polyethylene terephthalate staple fibers, 3.8 cm in length, 
were incorporated (using apparatus as taught in U.S. Pat. No. 4,118,531) 
into the coated layer in an amount of 8 g/m.sup.2 in addition to the 16 
g/m.sup.2 of microfibers. The finished material had a thickness of 0.44 cm 
and a clo value of 0.826 which corresponded to a thickness increase of 
100%, a clo increase of 142.9% and a clo/cm of 1.88. 
EXAMPLES 8-11 
A series of fabrics of the invention were prepared using a carrier web as 
used in Example 1 except that the latter had a basis weight of about 40 
g/m.sup.2. Nylon melt-blown microfiber coatings were applied to the 
carrier web using conditions, and obtaining results, as described in Table 
II. 
TABLE II 
______________________________________ 
Finished 
Finished 
Coating Collector Web Web 
Weight Distance Thickness 
Density 
Example (g/m.sup.2) 
(cm) (cm) (g/m.sup.3) 
______________________________________ 
8 15 8 0.21 0.0267 
9 20 16 0.22 0.0282 
10 29 24 0.23 0.0291 
11 Control -- 0.22 0.0191 
______________________________________ 
Perme- % Thick- 
ability ness % Clo 
Insulating (ft.sup.3 / Increase 
Increase 
Value min/ m.sup.3 / 
From From 
Example 
(Clo) (Clo/cm) ft.sup.2) 
s/m.sup.2 
Coating 
Coating 
______________________________________ 
8 0.354 1.68 190 .965 (4.5)* 
15.3 
9 0.369 1.67 145 .737 0.0 20.2 
10 0.428 1.86 80 .40 4.5 39.4 
11 0.307 1.39 -- -- Control 
-- 
______________________________________ 
*thickness decreased 
EXAMPLES 12-15 
A series of fabrics of the invention were prepared using a carrier web as 
described in Example 1 except that it had a basis weight of about 43 
g/m.sup.2. Polyethylene terephthalate (PET) melt-blown microfibers were 
coated onto the carrier web under conditions, and with results, as 
described in Table III. 
TABLE III 
______________________________________ 
Finished 
Finished 
Coating Collector Web Web 
Weight Distance Thickness 
Density 
Example (g/m.sup.2) 
(cm) (cm) (g/m.sup.3) 
______________________________________ 
12 14 8 0.25 0.0228 
13 17 16 0.25 0.0244 
14 25 24 0.28 0.0250 
15 Control -- 0.22 0.0191 
______________________________________ 
Perme- % Thick- 
ability ness % Clo 
Insulating (ft.sup.3 / Increase 
Increase 
Value min/ m.sup.3 / 
From From 
Example 
(Clo) (Clo/cm) ft.sup.2) 
s/m.sup.2 
Coating 
Coating 
______________________________________ 
12 0.430 1.72 218 1.11 13.6 40.1 
13 0.408 1.64 226 1.15 13.6 32.9 
14 0.474 1.53 170 .86 27.3 54.4 
15 0.307 1.39 -- -- Control 
-- 
______________________________________ 
EXAMPLES 16-18 
A series of fabrics of the invention were prepared using a carrier web as 
described in Examples 1-6 except that it had a basis weight of about 84.4 
g/m.sup.2. 
TABLE IV 
______________________________________ 
Finished 
Finished 
Coating Collector Web Web 
Weight Distance Thickness 
Density 
Example (g/m.sup.2) 
(cm) (cm) (g/m.sup.3) 
______________________________________ 
16 14 16 0.457 0.0215 
17 8.2 16 0.473 0.0196 
18 Control -- 0.420 0.0201 
______________________________________ 
Perme- % Thick- 
ability ness % Clo 
Insulating (ft.sup.3 / Increase 
Increase 
Value min/ m.sup.3 / 
From From 
Example 
(Clo) (Clo/cm) ft.sup.2) 
s/m.sup.2 
Coating 
Coating 
______________________________________ 
16 0.780 1.71 218 1.11 8.8 21.1 
17 0.774 1.64 229 1.63 12.6 15.5 
18 0.644 1.53 52 .26 Control 
-- 
______________________________________