Note: Descriptions are shown in the official language in which they were submitted.
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WASHABLE WOOL STRETCH FABRICS WITH DIMENSIONAL STABILITY
The present invention relates to machine washable wool stretch fabrics having
good
dimensional stability. The fabrics also have improved heat-setting properties.
In one
aspect, the invention relates to stretch fabrics comprising wool fibers
together with elastic
fibers where the elastic fibers comprise crosslinked, heat-resistant elastic
fibers, and where
such fabric does not need heat setting, but the finishing fabric can deliver
very good
dimensional stability after many washes.
Fabrics made at least in part from wool fibers are well known in the art. It
is also
known that these fabrics may shrink or otherwise become distorted during wet
processing of
the fabric or as a result of consumer use and care. Wool is composed of an
outer layer of
overlapping scales surrounding an internal core composed of numerous long thin
spindle
shaped cells, largely composed of keratin. The outer layer is generally only
one scale in
thickness, except at the overlapping portion where one scale ends and another
commences.
The scales all generally point outwards along the fiber, towards the tip. It
is believed that
this structure leads to shrinkage during normal wet washing, as the profile of
the fibers
favors movement in the direction of the root end of the fiber. This behavior
can be
compared to a ratchet mechanism in that the relative movement is
unidirectional. The fibers
get more and more compacted until they are completely compacted and a wool
"felt" is
formed. Felting has been reported to increase in the presence of water,
particularly in
conjunction with mechanical agitation.
In order to combat the shrinkage, chemical treatments have been used to peel
off the
outer scales of the wool. Once the scales are removed, then the "felting"
phenomenon is
eliminated and shrinkage is minimized. The various chemical treatments
currently used are
generally done on the wool top, and include various chlorine treatments,
potassium
permanganate treatments in conjunction with hypochlorite (see GB 569,730),
sodium sulfate
treatments (sometimes referred to as the International Wool Secretariat
Process), oxidase or
peroxidase treatments (see US 5,980,579) and permonosulfuric acid treatments.
It has also
been suggested that pennonosulfuric acid treatments can be on a finished
garment made
from a wool fabric in order to control dimensional stability. These treatments
have
produced fabrics and garments which can be labeled "Machine Washable" or
"Total Easy
Care" which indicates that the garments are suitable for domestic machine-
washing using
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the approved Woolmark cycle (wool wash or 40 C gentle cycle) with a bleach and
enzyme-
free detergent.
Garments are said to be Machine Washable if they meet the following industry
standard:
Gannent/fabric dimensional stability:
dimensional stability following washing of less than 3 percent (washing can
be
done according to modified ISW Tm 31: 5 cycles of ISO 6330 5A wash, wet
measurement)
dimensional stability following steam pressing according to ISO 3005 of less
than f
3 percent
While machine washable wool garments exist, they do not currently contain
elastic
fiber to help provide stretch to the fabric. Stretchable garments have been
gaining in
popularity within the fashion industry. Spandex fiber has been used with wool
to make a
stretchable wool fabric but such fabric is not considered washable because
they do not
possess suitable dimensional stability. Further, the chemical treatments such
as the chlorine
and permonosulfuric acid treatments described above are believed to be too
harsh for
spandex, which would result in unacceptable levels of spandex fiber breakage,
therefore
limiting the process flexibility in that the chemical treatments should be
performed in the
absence of the spandex fiber.
Additionally, the dimensional instability manifests itself even before the
fabric is
exposed to water exposure as wool/spandex fabrics are reported to have very
poor
consistency in fabric width as indicated by varying widths between different
rolls of fabric
or variation of width within the same roll of fabric.
To overcome these issues, current fabric producers desiring to use a
wool/spandex
fabric will typically apply one or more additional heat setting processes at
high temperatures
in order to "fix" the fabric width and adjust the fabric width to within the
desired range.
Heat-setting is a common way of reducing or eliminating the dimensional
instability.
The heat-setting process typically involves passing the fabric through a
heating zone for a
time and at a temperature that resets the synthetic fiber's morphology memory
to the
dimensions of the fabric at the time when the heat-setting process was
applied. The time
and temperature needed for the heat treatment depend on factors such as the
fabric
construction, the weight of the fabric, other fibers present in the fabric,
the type of synthetic
fiber, and the previous heat history of the synthetic fiber. The issue of
dimensional
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instability is especially pronounced for stretch woven fabrics, particularly
knitted stretch
fabrics.
For stretch fabrics, such as those incorporating spandex, typical heat-setting
conditions are from 180 C to 210 C for 15 to 90 seconds. These relatively
harsh conditions
may negatively affect the tenacity of companion fibers and lead to fabric
color alteration.
Furthermore, the heat-setting step is typically an additional step which adds
expense to the
fabric production process. The finished wool/spandex fabrics are reported to
have very poor
consistency in fabric width as indicated by varying widths between different
rolls of fabric
or variation of width within the same roll of fabric. The heat setting process
will cause the
finishing fabric stretch level to be inconsistent.
Accordingly it would be desirable to have a dimensionally stable wool fabric
containing
elastic fibers which did not require a special heat-setting step, such that
the heat-setting
could be accomplished simultaneously with other steps in the fabric production
process.
The present invention is accordingly directed to wool fabrics which
incorporate
stretch or elastic fibers, which fabrics retain their dimensional stability,
preferably without
the need for traditional heat setting steps. The present disclosure is also
directed to a
method of producing wool stretch fabrics having good dimensional stability
wherein the
method is characterized by a chemical treatment to remove wool scales and
further
characterized by the absence of any step in the production process which is
performed at a
temperature of 160 C or above. The stretch fabrics may also include other
fibers including
cellulosic, more preferably synthetic ones, including polyolefin such as
polyethylene and/or
polypropylene, polyester, polyamide, and segmented polyurethane fibers. The
finished
stretch fabrics preferably have a dimensional stability of less than 5
percent, more
preferably less then 3 percent, still more preferably within 2.0 percent and
most
preferably within 1.5 percent. Dimensional stability values indicated in this
invention refer
to the difference between the finished fabric length and widthwise dimensions
after vs.
before laundering plus tumble drying as defined by AATCC135-1987; preferably
by drying
method: A - tumble drying. Negative values indicate that the final washed
dimensions are
shorter than the initial ones which translates to shrinkage.
The present invention also relates to fabrics which can be characterized by
consistent
stretching at 9 percent-30 percent according to testing method IWS TM 179. The
present
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invention also can be characterized in that the finished fabric color is free
from discernable
yellowing.
The machine washable wool stretch fabrics of the present invention comprise at
least
wool fibers and elastic fibers. The wool fibers of the present invention can
be any type of
wool fiber used in the garment industry. Typically the wool used will be the
fiber from the
fleece of sheep or lambs but also includes fiber from the hair of Angora or
Cashmere goats,
camels, alpacas, llamas, vicunas and Angora rabbits, for example. The wool can
be present
in any amount, but 20-99 percent by weight is most preferred. Depending on the
desired
application it may be desirable to have at least 35 percent, 50 percent, 60
percent, or even 70
percent wool and similarly, the application may dictate having less than 98
percent, 97
percent, 96 percent, 95 percent, 80 percent, 75 percent or 70 percent wool.
Whatever the source, the wool fibers in their natural state can be
characterized by
having scales that tend to ratchet down and to interlock with each other
thereby binding the
fibers together in a process called felting. Accordingly, the wool fibers for
use in the
present invention are treated to remove at least a portion of the scales. This
treatment
process is generally known in the art, and any such processes may be used in
the present
invention. Typical processes include chlorine treatment and permonosulfuric
acid
treatment. Examples of potential chemical treatments for use in the present
invention
include those described in US 5,980,579, W02005/005710, EP 0 687 764, US
5,571,286,
US 5,755,827 and WO 9502085, which are each hereby incorporated by reference
in their
entirety.
The scale removing treatment can be done at any step in the process to make a
garment. For example, in many cases it will be most advantageous to remove the
scales as a
first step so that felting will not occur during any of the later production
processes, but in
other situations, it may be beneficial to wait until the final garment has
been prepared and
then treat the whole garment in order to remove at least a portion of the
scales from the
wool fibers. The treatment may also be done at intermediate steps, such as
after forming the
sliver, the top, the roving, the yam (including elastic yarns if combined with
elastic fiber), or
after making the fabric. Typically the treatment is done on the top or on the
finished
garinent.
The machine washable fabrics and garments of the present invention are stretch
or
elastic, which for the purposes of this invention, means that they contain an
elastic fiber.
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For purposes of the present invention an elastic fiber is one that will
recover at least about
50 percent, more preferably at least about 60 percent even more preferably 70
percent of its
stretched length after the first pull and after the fourth to 100 percent
strain (double the
length). One suitable way to do this test is based on the one found in the
International
Bureau for Standardization of Manmade Fibers, BISFA 1998, chapter 7, option A.
Under
such a test, the fiber is placed between grips set 4 inches apart, the grips
are then pulled
apart at a rate of about 20 inches per minute to a distance of eight inches
and then allowed to
immediately recover. It is preferred that the elastic textile articles of the
present invention
have a high percent elastic recovery (that is, a low percent permanent set)
after application
of a biasing force. Ideally, elastic materials are characterized by a
combination of three
important properties, that is, (i) a low stress or load at strain; (ii) a low
percent stress or load
relaxation, and (iii) a low percent permanent set. In other words, there
should be (i) a low
stress or load requirement to stretch the material, (ii) zero or low relaxing
of the stress or
unloading once the material is stretched, and (iii) complete or high recovery
to original
dimensions after the stretching, biasing or straining is discontinued.
Elastic fibers include certain fibers made from polyolefins such as
polyethylene or
polypropylene, and segmented polyurethane. The elastic fiber for use in the
present
invention is preferably durable enough to survive the scale removing treatment
so that such
treatment may be done in the presence of the elastic fiber. It is therefore
preferred that the
elastic fiber be a cross linked polyolefin fiber, more preferably a cross
linked polyethylene
fiber, of which cross linked homogeneously branched ethylene polymers are
particularly
preferred. This material is described in US 6,437,014, (which is hereby
incorporated by
reference in its entirety) and is generically known as lastol. Such fibers are
available from
The Dow Chemical Company under the trade name DOW XLA fibers. It is preferred
that
the elastic fibers comprise from 2 to 20 percent by weight of the article.
Depending on the
desired application, it may be preferred that the article comprise at least 3,
4, 5, 6, 7, 8, 9, or
even 10 percent elastic fiber, and similarly, the desired application may
dictate having less
than 20, 15, 10, 9, 8, 7,6 or 5 percent elastic fiber. It may be desirable for
knitted articles to
contain relatively more of the elastic fiber than woven articles.
It is also possible, although not necessarily preferred, that more than one
type of
elastic fiber may be used in the articles of the present invention. It is
preferred that the
elastic fibers not include fiber made from segmented polyurethane, however, as
this material
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is likely to degrade under the relatively harsh chemical treatments used for
de-scaling and
further promotes dimensional instability in the absence of heat setting at
temperatures
greater than 160 C.
The elastic fibers for use in the present invention can be of any thickness,
although
20-140 denier is most preferred, particularly when the fiber is the preferred
cross linked
homogeneously branched ethylene polymers. Forty denier and 70 denier lastol
fiber are
especially preferred due to commercial availability. In addition to a
monofilament fiber, the
elastic fiber may also be a conjugate fiber, for example, a sheath/core
bicomponent fiber.
The elastic.fiber may be used bare, or it may first be incorporated into a
multifilament, for
example, covered yam, or into staple fibers, for example, corespun yam, as is
generally
known in the art.= In a preferred embodiment the elastic fiber is siro spun
with the wool to
form an elastic wool yam.
The textile articles of the present invention may further comprise additional
non-
elastic natural or synthetic fibers. Non-elastic synthetic fibers include
those made from
materials such as polyester, nylon, polyethylene, polypropylene, and blends
thereof. Natural
fibers include fibers made from cellulosic materials such as cotton, flax,
ramie, rayon,
viscose and hemp. Natural fibers from other materials can also be used in the
textile articles
of the present invention, including fibers such as silk or mohair.
The washable wool stretch fabrics of the present invention can be made by any
conventional means. Thus, the articles of the present invention include
fabrics which have
been woven (where the elastic fiber or yam can be in the warp direction, the
weft direction
or both) or knitted, including warp knitting, (for example, Milanese, Raschel
and Tricot
knitting) weft knitting (for example, circular knitting and flat knitting) and
garment knitting
technologies such as seamless articles. The type of knitting construction is
also not intended
to be a limiting factor of the present invention. Known construction types
include plain
single jersey, single jerseys containing tuck and miss stitches (such as
Lapique, Cross-mis
lxl, Lacoste & Plain pique), double jerseys (such as Plain Rib and Plain
Interlock), double
jerseys containing tuck and miss stitches (such as Milano Rib, Cardigan,
Single Pique &
Punto di Roma).
Wool fabrics and particularly knitted wool fabrics, are known to suffer from a
lack
of dimensional stability over home laundering, for example, excessive
stretching or
shrinkage. Traditional methods for producing knitted fabrics therefore include
a heat setting
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step, particularly when the fabric includes fibers incorporating synthetic
polymers. The
heat-setting step is done after knitting and can be done either prior or post
dyeing. The heat
setting process generally involves applying a biasing force to hold the fabric
at its desired
dimensions (typically with the use of tenter frames) and subjecting it to high
temperatures,
particularly temperatures higher than any temperature that the fiber or
article is likely to
experience in subsequent processing (for example, dyeing) or use (for example,
washing,
drying and/or ironing). Although not intending to be bound by theory, it is
believed that the
heat-setting process generally works as follows: The heat-setting temperatures
are such that
at least some of the crystallites in the fiber will melt. The fabric is then
removed from the
heat, and the molten portions are allowed to recrystallize, and then the
biasing force can be
removed. The recrystallization causes the fabric to have a "memory" of the
dimensions at
~which the fabric was maintained during the heat-setting process, even after
the biasing force
is removed.
It has been discovered that by selecting certain synthetic elastic fibers for
use in the
knitted. fabrics, the heat setting step can be omitted, while still=producing
a fabric having
acceptable dimensional stability. One aspect of the present invention is
therefore directed to
a method for making a machine washable wool knitted fabric characterized in
that the entire
process occurs at a temperature less than about 160 C. Depending on the
content of other
fibers which make up the fabric, even lower temperatures can be used without
sacrificing
dimensional stability. Thus, the entire process may occur at a temperature of
less than
150 C, 140 C, 125 C, 100 C or even 80 C.
In certain embodiments of this invention, the process can further be
characterized by
an absence of tentering. Thus, yams or fibers containing at least some elastic
material can
be knitted into fabric and the fabric can directly be subjected to the desired
finishing
treatments without the need for placing the fabric into a tenter frame and
exposing it to the
high temperatures normally associated with heat-setting.
It is preferred that the finishing treatments include at least one step in
which the
temperature is higher than 80 C. In this way, the fabric will be "fixed" in a
similar manner
to the typical heat setting process, but at a lower temperature and without
the need for
special apparatus to ensure a biasing force. Typical finishing steps are
conducted at
temperatures of 80 C or greater, which is sufficient for this purpose, and yet
such fabrics
will not normally be exposed to temperatures this high during normal use and
care.
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The present invention is also directed to machine washable wool textile
articles
having stretch and dimensional stability. For purposes of the present
invention, "textile
articles" includes finished fabric as well as products made from the fabric
including bed
sheets and other linens, and garments. It is preferred that the articles of
the present
invention, particularly the plain single jersey knit fabrics of the present
invention, recover
promptly to dimensions which are less than 20 percent over its original
dimension.after
being stretched up to (1) 100 percent widthwise and/or (2) 45 percent
lengthwise (all at
extension rate of 500 mm/min for a specimen 50 mm wide and gauge length 100
mm).
More preferably, the article will return to within 15 percent of the original
dimensions, and
more preferably to within 10 percent. It should be understood that the amount
of stretch and
recovery will be a function of the weight of the fabric and the fabric
construction. It is also
contemplated that the articles of the present invention will have stretch in
more that one
direction, and indeed for many applications this will be preferred. It is not
necessary that the
articles have the same amount of stretch in each direction to be within the
scope of this
invention.
The textile articles of the present invention are dimensionally stable. For
purposes
of this invention "dimensionally stable" means that the stretch fabrics change
less than 5
percent in either direction (growth or shrinking), more preferably less than 3
percent in
either direction, and even more preferably less than 2 percent in either
direction and most
preferably within 1.5 percent. Shrinkage is generally perceived as being the
typical form
of dimensional instability and the fabrics of the present invention will have
a dimensional
stability higher (that is, less negative) than -5 percent in the width and/or
the lengthwise
direction. preferably higher than -4 percent, more preferably higher than -3
percent and most
preferably higher than -2 percent (with 0 percent representing no shrinkage or
growth).
Dimensional stability values are calculated by the difference between the
finished fabric's
length and widthwise dimensions after vs. before laundering. To determine
dimensional
stability, the length and width of the finished article are measured, then the
article is
subjected to, laundering (such as the method described in AATCC135-1987 drying
method:
A - tumble drying. After laundering the length and width are measured again,
and the
percentage is calculated according to the formula: dimensional stability =(new
dimension -
original dimension)/original dimension. As will be readily understood by one
in the art, the
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negative values indicate that the final washed dimensions are shorter than the
initial ones
which translates to shrinkage.
It should be understood that depending on the fibers present in the fabric,
some heat
setting may be beneficial, even if no such heat setting is required as a
result of using the
preferred elastic fibers of the present invention. For example, if polyester
is present,
temperatures around 160 C may advantageously be used to provide dimensional
stability to
the polyester content only. Even fabrics containing cotton are often exposed
to temperatures
as high as 140 C in order to dry after wet finishing treatments. Thus, it may
be desirable to
have a finishing step as high as 140 C for the cotton-containing fabrics of
the present
invention.
After forming the greige fabric any finishing processes known in the art may
be
used. This includes processes such as scouring, mercerizing, dyeing and
drying. It is
preferred that at least one of the finishing processes be conducted at a
temperature which is
greater than any to which the end consumer will likely expose the garment, for
example,
80 C or greater.
EXAMPLES
Example 1: Polyester blend with wool and DOW XLATM fiber 40D
Wool fiber is cheinically treated with a chlorine treatment on the wool top to
remove
wool scales. This treated wool fiber is then blended with polyester fiber to
produce a yam
which is about 65 percent by weight polyester and 35 percent by weight wool.
The blended
fiber is then dyed. The dyed fiber is then combined with 40 denier DOW XLATM
fiber
(available from the Dow Chemical Company) at a draft of 4.3 via siro spinning
to produce
an elastic yam. The elastic yarn is used in the weft direction to make a
fabric with a warp
yam (the warp yam is dyed polyester/wool fiber prepared as above, without siro
spinning
with DOW XLATM fiber) count (Nm) 52 two ply and a weft yarn count (Nm) 52 two
ply
having 24 ends/cm and 22.5 picks/cm. The resulting fabric contains about 33
percent by
weight wool, 63 percent polyester and 4 percent Dow XLA fiber. The resulting
fabric has a
weight (as determined by ASTM D3776-1996 (2002)) of 240.7 gm/m2 (240.7 GSM).
The
fabric is finished according to standard processes, and measured. The finished
fabric
exhibits a stretching level of 16 percent as determined according to IWS TM
179. The
fabric is subjected to IWS test method 31:5 cycles of ISO 6330 5A Wash, wet
measurement.
The fabric is then re-measured.
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The fabric exhibits weft washing shrinkage (testing method IWS TM 31) of less
than
1.9 after 5 washes. As the industry standard for "machine washable" garments
is. less than 3
percent, this fabric easily meets the industry standard.
.5 Examples 2- 5 wool (Super 100 Superwash wool blend with DOW XLATM fiber 40D
Super 100 Superwash wool fiber is chemically treated fiber which has been
treated
with a chlorine treatment on wool top to remove wool scales. The treated wool
is then
combined with 40 denier DOW XLATM fiber at a draft of 4.3 via siro spinning to
produce
the elastic yarn. The yam is used in the weft direction (the warp was 100
percent wool) to
make fabrics with a warp yarn count (Nm) 80 two ply and a weft yam count (Nm)
76 two
ply. The resulting fabric is about 96 percent wool and about 4 percent DOW
XLATM elastic
fiber, which may vary depending on the particular weave construction.
A series of different weave constructions as set forth in Table 1 is prepared
and the
fabrics are dyed and finished according to standard processes. Each had a
width of
approximately 150 cm. The dimensional stability of these fabrics is tested
after 5 cycles of
washing according method ISO 6330 5A wash, wet measurement, as in Example 1
(that is,
IWS TM3 1). The fabrics are also tested for dimensional stability following
steam pressing
according to testing method ISO 3005. The stretch and unrecoverable extension
in the weft
direction was determined according to IWS TM 179. These examples are
summarized in
Table I, and as can be seen from the table, all of the examples meet the
industry standard for
"machine washable".
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Table 1
Example weave Weight Dimensional Dimensional Stretch% Unrecoverable
No. (g/ma) stability stability extension%
after after steam
washing pressing
warp/weft warp/weft
2 2/1 290 2.2/-0.9 0.3/0.6 16.5 2.8
Gabardine
3 2/1 Serge 265 2.0/-.02 0.2/0:9 16.5. 2.6
4 2/2 300 1.5/-0.2 0.3/1.1 19.3 3.8
Herringbone
2/1 265 1.7/0.1 0.3/2.5 17.3 2
Herringbone
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