Note: Descriptions are shown in the official language in which they were submitted.
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ACRYLIC FIBERS FOR LOW PILL FABRICS
BACKGROUND OF THE INVENTION
This invention relates to acrylic fibers from
which low pill fabrics can be made. By ~acrylic fibers~
S is meant manufactured fibers in which the fiber-forming
substance is any long chain synthetic polymer composed
of at least 85% by weight of acrylonitrile units
[-CH2~H(CN)-]. The term "fibers" includes fibers of
extreme or indefinite length (filaments) and fibers of
short length (staple).
In commercial practice, acrylic fibers, after being
manufactured in filament form (e.g. tow) by either wet-
spinning or dry-spinning processes, are either converted
to a strand of loosely assembled staple (sliver) by
stretch breaking of the tow or to individual staple by
cutting of the tow. The staple, with or without
blending with other staple, and the sliver, with or
without combining with other sliver, is processed in a
conventional manner into spun yarn. The spun yarns are
then used in a conventional manner to make knitted or
woven fabrics. A major problem associated with these
fabrics is that of pilling. Pillinq i5 the formation of
small pills on the surface of the fabrics. The pill8,
i.e., bunches or balls of tangled ~ibers, are held to
the surface of a fabric by one or more ~ibers. The
pills are normally produced when the fabric is rubbed
(abraded) at wear areas, e.g., the elbow and collar
areas of a shirt or the pocket area of a pair of
trousers. Pilling is especially a problem with sweaters
due to their bulky knit construction. Pills greatly
distract from the appearance of garmenta. Although
considerable effort has been expended in the past to
solve the pilling problem, a satisfactory solution has
not heretofore been found.
SUMMARY OF THE I~VENTION
The present invention provides acrylic fibers
having a denier fiber (dpf) in the range of 0.5 to 6.0
and being characterized in having an elongation-to-break
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of no greater than 35% and a knot tenacity no greater
than 1.7 grams per denier. Elongation-to-break and knot
tenacities given herein are determined according to ASTM
tests designations D 2101-82 and D 3217-79,
respectively. The fibers are further characterized in
that the elongation and knot tenacity are selected such
that when a test fabric is made from yarn consisting of
the fibers in 2-inch (5.08-cm) staple form and tested
for pilling according to Test A, hereinafter defined,
the test fabric on a scale of 1 to 5 has a Pilling Value
of at least 3.5 and preferably at least 4.0 and most
preferably at least 4.5. (A Pilling Value of 5
represents no pilling and a Pilling Value of 1
represents very severe pilling.) Typically, woven or
knitted fabrics made from conventional acrylic staple
have a Pilling Value in the range of 1 to 2.
Fabrics made from spun yarn consisting of acrylic
staple of the present invention are unique in that pills
which form on the surface of such fabrics break off and
become separated from the fabric, thereby reducing the
pilling characteristics of the fabric. The loss of this
small amount of fiber from the fabric is insignificant
and, as compared to the unsightly appearance otherwise
caused by the pill5, is highly beneficial.
PREFERRED EMBODIMENTS OF THE
INVENTION
According to the preferred embodiment, the
acrylic fibers of the invention are prepared by the
modified wet-spinning process disclosed in Example 1
given hereinafter. This process differs from the
conventional wet-spinning process in that (1) the wet-
stretch orientation taken is in the range of 1.5 to 4.5
with a range of 2.5 to 4.5 being preferred, whereas
conventionally the range is from 4.75 to 6.5, (2) the
concentration of dimethlyacetamide (DMAc) in the aqueous
spin bath is in the range of 35 to 45% by weight with a
range of 37 to 43% by weight being preferred, whereas in
the conventional process the range is from 45 to 62% by
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weight and (3) the autoclave relaxation (annealing
pressure) used is in the range of 10 to 20 psig (0.70 to
1.40 Kg/cm2) with a pressure of 13 to 18 psig (0.91 to
1.27 Kg/cm2) being preferred, whereas in the conventional
process the range is from 30 to 37 psig (2.11 to 2.60
Kg/cm2). In using the modified wet-spinning process to
prepare acrylic tow of the invention, the wet-stretch,
DMAc spin bath concentration and annealing pressure are
correlated within the modified ranges just given to
provide tow such that when a test fabric is made from
yarn consisting of 2-inch (5.08-cm) staple cut from the
tow and tested for pilling according to Test A, the test
fabric has a Pilling Value of at least 3.5.
According to one embodiment of the invention the
fibers are modacrylic fibers instead of acrylic fibers.
Modacrylic fibers differ from acrylic fibers in that
they are composed of less than 85% but at least 35% by
weight of acrylonitrile units.
Preferably, the acrylic and modacrylic fibers of
the invention are composed of a fiber-forming copolymer
formed by reacting acrylonitrile with one or more vinyl
monomers copolymerizable therewith. Such monomers are
well-known in the art and include by way of example
vinyl acetate, vinylidene chloride, methylacrylate,
methylmethacrylate, vinyl bromide, styrene, sodium
styrene sulfonate, 2-methyl-2-acrylamidosulfonic acid,
and sodium sulphophenyl methallyl ether.
TEST A
Pilling Performance Values for acrylic fibers
having a dpf in the range of 0.5 to 6.0 are determined
as follows:
The fibers in filament for (e.g. tow), are cut to
2-inch ~5.08-cm) staple and then processed into sliver
and spun into 16 cotton count spun yarn having 11 turns
per inch (4.33 turns per cm) in the Z-direction on a
conventional short staple ring spinning frame. Two of
these yarns are plied with 5 turns per inch (1.97 turns
per cm) of twist in the S-direction. The resulting
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16/2-ply cotton count yarn is knitted into a 7 cut
jersey fabric and tested for pilling according to ASTM
Test designation D 3512 - 82. A rating (Pilling Value)
of 5 is the best rating (no pilling) while a rating
(Pilling Value) of 1 is the worst rating (very severe
pilling). When the appearance of the test fabric is
between two ratings (e.g. between 2 and 3) a half value
is assigned (e.g. 2.5).
The following examples are given to further
illustrate the invention. In the examples, percentages
are by weight unless otherwise specified.
EXAMPLE 1
This example illustrates a wet-spinning process
for producihg the acrylic fibers of the present
invention.
A copolymer comprising 92.5% acrylonitrile and
7.5% vinylacetate was dissolved in DMAc in an amount
sufficient to provide a 25% polymer solution. This
polymer solution, at a temperature of 105 degrees C.,
was extruded through 12 spinnerets, each having 60,000
circular orifices of a diameter of 3.0 mils (0.076 mm)
at the rate of 245g grams of polymer solution per
spinneret per minute. Each spinneret was immersed in an
aqueous DMAc spin bath having a DMAc concentration of
40~ and a temperature of 41 degrees C. Water was added
during spinning to maintain this concentration and
temperature. ~he rate of fiber production was 975
pounds (442 Kg) per hour~ Each resulting filament
bundle (tow) was withdrawn from the spin bath by means
of rolls at a linear speed of 36 ft. (10.97 m.) per
minute, washed with water to remove DMAc and wet-
stretched 3.5 times in a series of mass transfer units
at 70 to 97 degrees C. as described in U.S. patent
4,059,668. An aqueous finish comprising an emulsifier,
a wetting agent and a lubricant and antistatic agent for
the tow was applied to each tow and the tows were dried
and collapsed by being passed under tension, first, over
rolls heated internally to a surface temperature of
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about 160 degrees C. by means of steam and, then, over
rolls cooled to a surface temperature of about 55
degrees C. by means chilled water. The peripheral speed
of both the heated and cooled rolls was 127 ft. (38.71
meters) per minute. The tow was then crimped by being
passing through a conventional stuffer box crimper using
pressurized steam. From the crimper, the tow was
piddled into a can and annealed by placing the can in an
autoclave and subjecting the tow to 20 steam treatment
cycles where each cycle consisted of pressurizing the
autoclave with steam to a pressure of 15 psig (1.05
Kg/cm2) then venting the autoclave to reduce the pressure
to atmospheric pressure. After annealing, the final dpf
of each tow was 3Ø The 3.0 dpf tows were cut to 2.0-
inch (5.08-cm) staple. A knit test fabric was made from
16/2-ply cotton count yarn consisting of the staple and
tested according to Test A. The fabric had a Pilling
Value of 4Ø
COMPARATIVE EXAMPLE
In this example, a test fabric was made and
tQsted as described in Example 1, except in this
instance the DMAc spin bath concentration was 51%, the
wet-stretch orientation was 6.02 times, and the
annealing pressure was 33.8 psig (3.38 Kg/cmZ). In this
instance, the test fabric had a Pilling Performance
Value of 1.5.
EXAMPLE 2
This example illustrates the blending of acrylic
staple of the invention with commercially available
acrylic staple having a higher than normal boiling water
shrinkage (BWS) value, i.e., a value of 18 to 20% BWS
instead of the normal 0 to 3%.
Three (3) dpf staple tow was made as described in
the Comparative Example, except that an annealing
pressure of 44 psig (3.09 Kg/cm2) was used. The tow was
hot-stretched under conditions to provide a final dpf of
2.5 and a BWS value of 18 to 20% and then cut to 2-inch
(5.08 cm) staple. This staple was then blended with
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staple made as described in Example 1 in an amount
sufficient to provide a blend consisting of 60% by
weight of the staple of Example 1 and 40% by weight of
the high shrinkage staple. A knit test fabric was made
from 16/2-ply cotton count yarn consisting of the staple
blend and tested according to Test A. This fabric also
had a Pilling Value of 4.5.
