U.S. patent number 3,789,461 [Application Number 05/125,524] was granted by the patent office on 1974-02-05 for apparatus for preparing spun yarn.
This patent grant is currently assigned to Asahi Kasei Kogyo Kabushiki Kaisha. Invention is credited to Fumio Nakajima, Hiroshi Nakano, Hideo Takai.
United States Patent |
3,789,461 |
Nakano , et al. |
February 5, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
APPARATUS FOR PREPARING SPUN YARN
Abstract
Apparatus for preparing spun yarn comprising back rolls for
feeding fiber from a supply thereof to front rolls spaced from the
back rolls and serving to draft fiber received therefrom. A stretch
breaking zone and a draft zone are arranged in succession in that
order between the back rolls and the front rolls. An endless bottom
apron extends between the back rolls and front rolls over the
stretch breaking zone and the draft zone, and the bottom apron
passes on respective support plates adjacent the back rolls and
front rolls. Output rolls are mounted in the stretch breaking zone
for drawing fiber from the back rolls and stretch breaking the
fiber, and input rolls are provided in the draft zone for receiving
fiber from the output rolls and for advancing the fiber to the
front rolls. Both the input and output rolls include top and bottom
rolls for advancing the fiber therebetween. The bottom apron
extends on and is driven by the bottom rolls of the input and
output roll means. A first top apron is mounted in the stretch
breaking zone, and a second top apron is mounted in the draft zone,
the first top apron passing on a further plate and on the upper
roll of the output rolls in the stretch breaking zone and driven by
the latter, the second top apron passing on a further plate and on
the upper roll of the input rolls in the draft zone and driven by
the latter. The first and second top aprons are opposed to the
bottom apron to control the feed of the fiber therethrough.
Inventors: |
Nakano; Hiroshi (Suita,
JA), Takai; Hideo (Fuji, JA), Nakajima;
Fumio (Yoshiwara, JA) |
Assignee: |
Asahi Kasei Kogyo Kabushiki
Kaisha (Osaka, JA)
|
Family
ID: |
26823661 |
Appl.
No.: |
05/125,524 |
Filed: |
March 18, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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618469 |
Feb 24, 1967 |
3596458 |
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Current U.S.
Class: |
19/.35;
19/244 |
Current CPC
Class: |
D01H
5/26 (20130101) |
Current International
Class: |
D01H
5/26 (20060101); D01H 5/00 (20060101); D01g
001/08 (); D01h 005/86 () |
Field of
Search: |
;19/.3-.6,244-260
;57/14BY,36 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Newton; Dorsey
Attorney, Agent or Firm: Waters, Roditi, Schwartz &
Nissen
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a division of co-pending application Ser. No.
618,469, filed Feb. 24, 1967 and now issued as U.S. Pat. No.
3,596,458.
Claims
What is claimed is:
1. Apparatus for preparing spun yarn of 100 percent elastic fiber
or blended spun yarn of elastic fiber and hard fiber, said
apparatus comprising: a back roll means for feeding fiber from a
supply thereof, a front roll means spaced from said back roll means
for drafting fiber received therefrom, a stretch breaking zone and
a draft zone arranged in succession in that order between the back
roll means and the front roll means, an endless bottom apron means
extending between the back roll means and front roll means over the
stretch breaking zone and the draft zone, respective plates
adjacent the back roll means and front roll means supporting the
bottom apron means at the opposite ends thereof, output roll means
in said stretch breaking zone for drawing fiber from said back roll
means and stretch breaking said fiber, input roll means in said
draft zone for receiving fiber from said output roll means and
advancing the fiber to said front roll means, said output roll
means including top and bottom rolls for advancing the fiber
therebetween, said input roll means including top and bottom rolls
for advancing the fiber therebetween, said bottom apron means
including an endless apron member which extends on and is driven by
the bottom rolls of said input and output roll means, a first top
apron means in said stretch breaking zone, a second top apron means
in said draft zone, each of the first and second top apron means
having a respective input and output, two further plates, one
adjacent the back roll means and the other adjacent the front roll
means, said first top apron means including a first endless top
apron member passing on said one further plate and the top roll of
said output roll means in said stretch breaking zone and driven by
the latter, said second top apron means including a second endless
top apron member passing on said other further plate and the top
roll of said input roll means in said draft zone and driven by the
latter, said first and second top apron means being opposed to said
bottom apron means to control the feed of the fiber therethrough,
and means to adjust the pressure applied by the top apron member in
the stretch-breaking zone to the bottom apron member.
2. Apparatus as claimed in claim 1 comprising means for feeding
roving from a second supply directly to the input rolls means in
said draft zone.
3. Apparatus as claimed in claim 1 comprising a second input roll
means for feeding a second fiber to said input roll means in said
draft zone, said second input roll means and said input roll means
in said draft zone having different surface speeds to form a second
draft zone which is distinct from the first draft zone.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spun yarn of an elastic fiber
having excellent elastic elongation of more than 100 percent and a
quick recovery from stretching to an elongation which is less than
its breaking elongation, and a blended spun yarn of said elastic
fiber with any of the known hard fibers. The invention also relates
to an apparatus for producing same.
2. Prior Art
Spandex is the first synthetic elastomeric fiber industrially
utilized and is now used in the forms of bare yarn, covered yarn or
core-spun yarn. However, the spandex fibers actually employed in
these fields are all as filament yarns, and no spun spandex yarn
has been developed up to now. Furthermore, most of the spandex
filament yarns used in these fields are of fine-denier such as, for
example, 140 d, 70 d and 40 d, and these fine-denier yarns are
extremely expensive thereby preventing expansion of the market
therefor.
SUMMARY OF THE INVENTION
The invention is directed to a spun yarn consisting of 100 percent
of an elastic staple fiber which has a breaking elongation of more
than 100 percent, an elastic recovery from high stretching of more
than 90 percent and a Young's modulus of less than 0.5 g/d.
The invention is also directed to apparatus comprising a back roll,
an intermediate roll and a stretch-breaking zone between said rolls
wherein the improvement comprises top and bottom approns in the
stretch-breaking zone, said aprons being driven at the same speed
as the intermediate roll.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a direct spinning machine which
is conventional.
FIG. 2 graphically shows the correlation between the distance (ho)
from the back roll to the intermediate roll and the draft ratio of
the spandex spun yarn prepared by using the apparatus as shown in
FIG. 1.
FIG. 3 shows a part of a direct spinning machine equipped with a
pair of endless approns and employed in the present invention.
FIG. 4 is a cross sectional view of the direct spinning machine
particularly useful in the practice of the present invention.
FIG. 5 is a staple diagram representing the correlation between
fiber length and content in the spun yarn of elastic fiber prepared
by using the apparatus shown in FIG. 4.
FIG. 6 is a graph showing the correlation between the effective
coefficient of fiber strength in yarn strength and the fiber number
in cross section of yarn prepared by using an elastic fiber (a) or
a hard fiber (b).
DETAILED DESCRIPTION
A principal object of the present invention is to provide a cheap
fine-denier spandex spun yarn. The market price of the coarser yarn
of, for example, 3000 d or 5000 d is less than about one third the
price of the above-mentioned finer yarn, and the price difference
between the two was more than 5 dollars per pound as of August,
1966. Therefore, if it were possible to manufacture a finer yarn
from this inexpensive coarser yarn with a reasonable spinning cost
of, for example, less than one dollar per pound, it is beyond
question that the market for spandex would be greatly expanded.
A second object of the present invention is to provide a single
covered spandex yarn or core-spun yarn having greatly reduced
kinking properties. A highly twisted spandex yarn tends to produce
kinking due to the high elasticity thereof. Therefore, in the
covered yarn technology, spandex is always supplied in the form of
double covered yarn and no single covered yarn has yet been used.
For the same reason, in preparing core-spun yarn, a steaming
treatment has generally been used to prevent such kinking despite a
lowering of the excellent elasticity resulting therefrom. To the
contrary, the present spandex spun yarn, which is used to cover
yarn or core-spun yarn, is twisted, in the spinning process, in a
direction opposite that of the twists thereafter given in the
core-spinning or covering process, so that this counter twist
reduces, or makes negligible the kinking properties of core-spun
yarn or single covered yarn under some conditions of twist
multiplication.
A third object of the present invention is to provide a blended
spun yarn of an elastic fiber and a hard fiber (natural or man-made
fiber) with an optional blending ratio. Hitherto, the content of
the elastic fiber in a blended spun yarn as far as has been
reported to date is limited to the order of less than 30 percent as
described in U.S. Pat. No. 3,007,227. Therefore, this novel blended
spun yarn having no limitation in the blending ratio of elastic
fiber affords a new kind of product and contributes towards rapid
development of new markets for spandex fibers.
The aforesaid and other objects will become apparent to those
skilled in the art from a consideration of the following
specification, drawing and claims. The principle of the method is
to employ a direct spinning system; i.e., a multifilament yarn or a
tow of elastic fiber becomes spun yarn through the consecutive
steps of breaking, drawing and twisting in one process.
In a conventional spinning system requiring a carding process such
as the cotton spinning system, worsted spinning system, and
modifications thereof, woolen spinning system etc., or in the
conventional spinning system or the tow to top converter system
requiring the drawing of thick slivers, it is impossible to make a
pure spun yarn of umlimited fiber or blended spun yarn of elastic
fiber with an ulimited blending ratio for the following reasons. In
the first place, since very pliant elastic fibers are apt to adhere
to the top end of the metallic wire, the carding action is poor. In
the second place, in a drawing or roving process comprising drawing
a sliver constructed of several thousands or several ten thousands
of fibers, it is difficult to pick up a single fiber out of the
sliver and to separately draw away each fiber, because frictional
resistance between the pliant fibers is large and it tends to cause
stretching of fibers having an extremely small Young's modulus.
Therefore, in these spinning systems, an elastic fiber can be
carded or drawn only in the case where it is blended with a larger
proportion of a hard fiber having a considerably high Young's
modulus in order to make the elastic fiber move together with the
said hard fiber. In other words, the spinning of the elastic fiber
is limited only to the case where the proportion of the elastic
fiber is considerably low. In this connection, U.S. Pat. No.
3,007,227 discloses that in processing the fiber blends on
conventional textile machinery, it has been found more practical to
employ between 10 percent and 25 percent of the elastic fiber in
the blend, although special equipment may be selected to more
readily accommodate broader ranges of the elastic fibers. If the
proportion of the elastic fiber in the blend is raised,
sufficiently beyond 30 percent, fiber processing operations into
yarn become more difficult to control and the resulting yarn and
fabric quality suffers: for example, when 50 percent elastic fiber
is used.
A direct spinning system employed for the manufacture of the
present spun yarn of elastic fiber is described below in
conjunction with the drawings.
In FIG. 1, multifilament yarn 2 released from bobbin 1 is fed, via
a pair of rolls 6,6' to a breaking zone A, and is stretch-broken
between said back rolls and a pair of intermediate rolls 7,7' the
surface speed of rolls 7,7' being 10 to 20 times faster than the
speed of rolls 6,6'. Thereby, a mass of broken and transformed
fibers 3 is then sent to the subsequent draft zone B, in which it
is drafted to a desired count yarn between intermediate roll 7,7'
and front rolls 9,9' having a surface speed several times faster
than that of rolls 7,7'. The fleece 4 comes out of the front rolls
9,9' and is passed through a pig tail 10, twisted to a desired
twisting condition by means of revolving spindle 12, and wound, via
ring and traveller 11, on a cop as spun yarn 5. If the elastic
fiber a is to be blended with a hard fiber, roving 14 of hard fiber
is released from another bobbin 13, passed over a guide roll 15,
and fed to the intermediate rolls 7,7' and blended therein with the
elastic fibers 3. In another method, after passing over the guide
roll 15, said roving 14 of hard fiber is fed to cradle 8 and
blended with the elastic fiber therein. Some of the conventional
direct spinning machines may possess a gear with edges in the
breaking zone A, or a floating control roll and a single apron as a
substitute for cradle 8 in the draft zone B. However, the principal
action of these modified machines on the fiber is the same as that
of the machine shown in FIG. 1. When the total denier of elastic
fibers in the draft zone is too coarse and therefore a considerably
high draft ratio is required to draw them to a desired yarn count,
the already described difficulty of sliver drawing also occurs
here. Therefore, it is desirable to adjust the draft ratio in the
breaking zone so that the draft ratio in the subsequent draft zone
is less than 10, preferably less than 5.
Although spun yarn of elastic fiber can be prepared by using the
conventional direct spinning machine illustrated in FIG. 1, it is
difficult or impossible to obtain as good quality yarn, as will be
obtained if the special pretreatment described hereinafter is
applied to the elastic fiber. It is most preferable to employ the
direct spinning machine equipped with the special apron apparatus
of the present invention as shown in FIG. 4.
The first reason why it is difficult to obtain a good quality yarn
with the machine shown in FIG. 1 is as follows: As compared with a
hard fiber having smaller breaking elongation and poor recovery
from stretching, the elastic fiber used for the preparation of the
present spun yarn possesses at least 100 percent breaking
elongation and quick recovery from stretching to an elongation
which is less than its breaking elongation. In order to obtain spun
yarn having such excellent elasticity using the elastic fiber and
to prevent yarn breaking strength from being reduced by slipping
between fibers in the yarn, it is necessary to employ a fiber of at
least 0.5 inch minimum length, more than 1 inch average length and
3 inches as the preferable average length. When the average length
of the fiber exceeds 4 inches and the total denier of the fiber is
coarse, the drawing operation in the draft zone is quite difficult
to carry out. Since the breaking elongation of spandex fiber, for
example, is in general in the range of 400 - 800 percent, the
broken length of the fiber will be about 20 inches (3 inches
.times. (5 - 9)) considering the fiber length under no load as
being 3 inches. In this connection, the distance (gauge length)
between the back rolls 6,6' and the intermediate rolls 7,7' will be
determined by using the following equation:
L/ho = Dlog.sub.e D-1/D-(1 +.epsilon.)
wherein D is draft ratio; ho is the distance between back roll and
intermediate roll; .epsilon. is the breaking elongation of elastic
fiber and L is the stretched fiber length which has been forwarded
by the intermediate roll until it is broken. Taking the conditions
of .epsilon. = 6 and L = 20 inches, the correlation between ho and
D is shown in FIG. 2. (Correctly speaking, L plus one half ho
should be 20 inches, but for the sake of simple calculation L is
taken as 20 inches) According to FIG. 2, even a large draft ratio
of 20 gives only a narrow roll distance of about 2.6 inches in the
case of a 3 inch fiber length. If the average free length of the
fiber is less than 2 inches, this roll distance will be much
smaller than that of the above case. Therefore, in the direct
spinning system shown in FIG. 1, approximately one thousand ends of
fibers must be distributed in a relatibely small breaking zone. As
already described, the elastic fiber possesses a large frictional
resistance acting between fibers, so that the end of a fiber tends
to be forwarded with the movement of the end of another fiber
thereby causing a number of ends to be simultaneously caught by the
intermediate roll, and stretched and broken in the breaking zone.
That is, an evenly spun yarn can not be obtained in this method.
Indeed, the above may be avoided by further widening the roll
distance to give a considerably larger distribution of fiber ends,
but it may also result in the necessity of employing a longer fiber
length, (e.g., providing ho = 4 and D = 20, free fiber length
should then be 4 inches as shown in FIG. 2), which in turn causes a
different problem in the draft zone as previously stated.
Therefore, one solution concerning the present invention for
obtaining a better quality yarn with the direct spinning machine as
shown in FIG. 1 is to subject the elastic fiber to a heat-setting
treatment prior to feeding it into said machinery. That is, the
elastic fiber is heat set while in a stretched state to reduce its
breaking elongation and increase its Young's modulus. For example,
if the elastic fiber is previously modified to have 200 percent of
breaking elongation, a fiber having a 3 inch free length should be
broken at a stretched fiber length of 9 inches (3 inches .times.
3). In this case, from the abovesaid equation, ho will be 4.1
inches when D is 20. This condition means a good distribution of
fiber ends. Furthermore, a longer free fiber length such as 4
inches can be successfully employed, because the fiber has a high
Young's modulus, so that little trouble is found in the drawing
step in the draft zone. In this case, ho is 5.4 inches, so that it
gives a quite favorable distribution of fiber ends. Spun yarn thus
prepared from the pre-treated fiber possesses a high Young's
modulus and low breaking elongation. However, this spun yarn may
conveniently be converted to the state in which it has the original
properties as possessed by the unmodified elastic fiber, by
subjecting the yarn to a relaxation treatment under free loading
conditions (for example, in skein or in the form of woven fabric or
knitted fabric) in boiling water or a steam box. This recovery may
be somewhat influenced by the stretching ratio and heating
temperature employed in the pre-treatment, but almost complete
recovery can be obtained. Some of the test results in the case of
spandex fiber is shown in the following Table 1. ##SPC1##
The second reason why a good quality spun yarn is hard to obtain by
the direct spinning machine as shown in FIG. 1 is hereinunder
described.
The elastic fiber employed in the present invention possesses a
quick recovering property from various degrees of stretching, so
that the fiber ends which are broken in the stretch-breaking zone
spring back to form hock ends. These hock ends not only obstruct
the even drawing of the fiber, but also often get entangled with an
adjacent fiber to obtain its movement as a single fiber, and cause
many fibers to be stretched and broken simultaneously. In this
case, as shown in FIG. 3, it is preferable to employ a pair of
endless aprons 16,16' placed between the back rolls 6,6' and the
intermediate rolls 7,7' and driven at a speed which is faster than
the surface speed of the back rolls 6,6' and slower than the
surface speed of the intermediate rolls 7,7', to prevent the spring
back of broken fiber ends and, to reform the hock ends of the fiber
if such occurs.
In order to obtain the best quality spun yarn of elastic fiber, it
is recommended to employ the direct spinning machine as shown in
FIG. 4. In this figure, the area between back rolls 29,29' and
intermediate rolls 31,31' is the stretch-breaking zone A, and the
area between the intermediate rolls 31,31' and front rolls 38,38'
is the draft zone B. Multi-filament yarn 22 of elastic fiber is
released from bobbin 21, passed through back rolls 29,29', and
introduced via tensors 30,30' into the clearance between top apron
33 and bottom apron 35, these aprons being driven by intermediate
rolls 31,31' and rotating with a surface speed several times faster
than that of back rolls 29,29'. The elastic fiber having a large
breaking elongation is thus stretched by means of faster moving
aprons 33 and 35. The clearance between the top tensor 30 and the
bottom tensor 30' and the resilient action of adjustable spring 46
for the press rolls 34 are adjusted so as to permit slippage of the
stretched fiber before breaking. The stretched elastic fiber is
further advanced while slipping to the intermediate rolls 31,31',
where it is nipped by rolls 31,31', stretched in a desired draft
ratio and broken. After passing through the rolls 31,31', the
stretch-broken elastic fiber immediately shrinks by its own
elasticity to a pre-determined free fiber length, and the thus
obtained fiber 24 is, while being carried on the bottom apron 35,
sent to cradle rolls 36,36' and drafted to a desired count fleece
25 in the draft zone provided between the cradle rolls 36,36' and
front rolls 38,38'. This fleece 25 is then passed through pig tail
39, twisted by rotation of the spindle, and wound, via ring and
traveller 40, on cop 41 as a spun yarn 26. As is clear from the
above, the elastic fiber in the stretch-breaking zone is stretched
fully by a pair of faster moving apron means and fed to the
intermediate rolls 31,31' as it is. Therefore, the fiber length
being forwarded by the intermediate rolls before the fiber is
brought to its breaking elongation, is considerably small and
almost the same as that of hard fiber. Consequently, it is possible
to select and fix the distance between the back rolls and
intermediate rolls over a considerable size. Furthermore, by
controlling the pressure of springs 46 on press rolls 34 and the
clearance between the top and the bottom tensors 30,30' it is
possible to change the extent of stretch and the position of
slippage of the fiber placed between the aprons 33,35. Therefore,
the breaking point can be concentrated in a desired position or
distributed throughout the apron, and the fiber length can be
controlled in any desired size. These are exemplified in FIG. 5.
When the elastic fiber is stretch-broken in such a way, the spring
back of the fiber end can be effectively controlled by the top and
bottom aprons, so that no problems are caused in this regard as
compared with the case using the machinery as shown in FIG. 1.
Thus, a better quality yarn can be spun in accordance with this
invention.
When it is required to prepare a blended spun yarn of elastic fiber
and hard fiber, the same apparatus as shown in FIG. 4 is
conveniently employed with a slight modification thereon. That is,
another roving 43 consisting of hard fiber alone is released from
another bobbin 42, passed over guide roll 44 and blended with
elastic fiber 24 at the cradle rolls 36,36'. For convenience in
varying the blend ratio or yarn count, it is possible to place
rolls 45,45' in a position between the guide roll 44 and the cradle
roll 36 so that the hard fiber roving 43 is drafted by the surface
speed difference between the rolls 45,45' and the cradle rolls
36,36'. However, since it is difficult to place some apparatus for
controlling floating short fibers in the roving in the position
between the cradle rolls 36,36' and the rolls 45,45', the draft
ratio in this area must not exceed 5, the preferable draft ratio
being 1 to 3.
In this type of blending system, mixing of each fiber is in general
not so good. However, the spun yarn has elasticity and these
characteristic properties are brought by the elastic fiber
employed. Therefore, the elastic fiber is apt to be concentrated in
the center of the yarn and the hard fiber will be distributed at
the periphery, and thus complete mixing of the fibers is
unnecessary in this case.
When it is required to give high elasticity to the blended spun
yarn, this may be accomplished by adjusting the clearance between
the top and the bottom tensors 37,37' of the cradle in the draft
zone B, such that the elastic fiber can be nipped (however,
slippable on the brink of breaking) and the hard fiber can be
slipped therebetween. Thus, by adjusting the clearance between the
tensors, any elastic spun yarn having from 0 to more than 100
percent of elasticity may be prepared at will.
As will be clearly understood, the present spun yarn of elastic
fiber can be easily prepared by using the methods and the apparatus
described hereinabove.
The present spun yarn of elastic fiber is a distinctive product and
differs from any of the known spun yarns of hard fibers. The
following are the reasons therefor.
Firstly, spun yarn containing 30 percent to 100 percent by weight
of an elastic fiber having more than 100 percent elastic
elongation, extremely small Young's modulus and excellent quick
recovery from various degrees of stretching to an elongation less
than its breaking elongation, has never been prepared, though
filament yarn of elastic fiber has been heretofore known. As
mentioned above, the present spun yarn of elastic fiber is hardly
prepared or can not be prepared at all by merely using a
conventional spinning system, and in order to obtain a better
quality spun yarn it is necessary to modify the elastic fiber
beforehand by giving a special heat-set treatment thereto or to
employ a modified direct spinning system equipped with a certain
device. That is, in case of a hard fiber, its spun yarn is obtained
as a matter of course by using any conventional spinning system or
conventional direct spinning system, so far as its filament yarn
exists. However, in the case of an elastic fiber, it is not the
same as that in the case of hard fiber to obtain its spun yarn,
even if its filament yarn exists.
Secondary, since elastic fibers possess an extremely small Young's
modulus, the fibers in the twisted spun yarn stick to one another
to cause a considerable frictional resistance between the fibers,
and therefore when such a spun yarn is stretched, there hardly
occurs any slipping between the fibers. To the contrary, in the
case of a hard fiber, in order to maintain a satisfactory yarn
tensile breaking strength, the spun yarn must be comprised of more
than 50 ends of fibers. If the fiber number in the cross section of
the yarn is less than 50 ends, the said yarn strength abruptly
decreases due to slippage between the fibers. Therefore, even
considering fiber length, fiber denier, and twist multiplier, 30
ends are the minimum limit for practical use. Furthermore, even if
the spun yarn of a hard fiber possesses a satisfactory tensile
strength under the best of conditions, it can not be free from
slipping at the time of breaking the fiber. Therefore, it is
impossible to bring the effective coefficient of fiber strength in
yarn strength (i.e., yarn tensile strength single fiber strength x
fiber number in cross section of yarn) to 100 percent, the mean
value being 50 to 60 percent and the maximum value being 70.
Contrary to the above, in a spun yarn of an elastic fiber, no
decrease in the yarn strength is detected for the abovesaid reasons
even in a product having as few as 15 fiber ends in the cross
section of spun yarn, and the effective coefficient of fiber
strength in yarn strength is almost 100 percent. In this regard,
the correlation between the effective coefficient and the fiber
number in the cross section of yarn is shown in FIG. 6, wherein (a)
represents the curve for an elastic fiber and (b) the curve for a
hard fiber. From these curves, it will be seen that the minimum
fiber number in cross section of the present spun yarn to maintain
the yarn strength is quite different from the corresponding value
of the conventional hard spun yarn, and that the maximum effective
coefficients are quite different from each other.
Thirdly, when fibers are stretch-broken in a direct spinning
system, there is a great difference between an elastic fiber and a
hard fiber in their respective stretch-breaking phenomenon. That
is, in the case of a hard fiber, though the maximum fiber length
may be controlled by using a particular breaker, it is impossible
to prevent the occurrence of short fibers, the minimum fiber length
thereof being about several mm, for the following reasons. Namely,
the breaking of the fiber occurs throughout the breaking zone, and
since the breaking elongation (.epsilon., in the aforesaid
equation) of hard fiber is less than 0.4, and in general is 0.2 -
0.3, the L value becomes almost zero. On the contrary, in the case
of elastic fibers, the breaking elongation of the fiber is in
general 400 - 800 percent and therefore .epsilon. is in a range
between 4 and 8 and L can be a considerably larger value. Thus, in
the present spun yarn of elastic fiber, the minimum fiber length is
quite long as compared with the case of hard fiber and the short
fiber content is extremely small as a result.
The following examples will serve to illustrate the spun yarn of
elastic fiber, the preparation thereof and the useful effects
obtained by this invention.
EXAMPLE 1
Employing a multi-filament yarn (5000 d/500 fil.) of spandex
elastic fiber having 300 percent breaking elongation, 0.2 g/d
Young's modulus (stress in 100 percent extention), and 98 percent
recovery from 100 percent extention, pure spandex spun yarn of 400
d having 40 ends of fiber in cross section was obtained by using
the direct spinning machine as shown in FIG. 4, under the following
conditions.
Stretch-breaking zone draft ratio 10 distance between back roll and
intermediate roll 9 inch Draft zone draft ratio 1.2 twist 26
T/inch
Employing the same conditions as state above, except that the draft
ratio in the draft zone is increased to 3.4, another pure spandex
spun yarn of 150 d having 15 ends of fiber, and 31 T/inch was
prepared. The mechanical properties of these two spun yarns are
shown in Table 2. ##SPC2##
As clearly seen from the above Table 2, the breaking elongation of
spun yarn after spinning decreased and the Young's modulus slightly
increased compared with that of multifilament yarn, because the
elastic fiber is subjected to the stretch-breaking treatment.
However, as a result of the after boiling treatment, such as
dyeing, the inner structural strain of the fiber was removed and
the said breaking elongation and Young's modulus were restored to
the normal conditions. However, the Young's modulus of the thus
after-treated yarn was slightly lowered compared to that of the
original material filament yarn. It might be due to the twists in
the finished spun yarn. Even in the spun yarn constructed with 15
ends of fibers, the breaking strength (g/d) was almost identical
with that of material filament yarn. Thus, the effective
coefficient of fiber length in yarn strength was 100 percent.
EXAMPLE 2
Pure spandex spun yarn (400 d, 26 T/inch S twist) prepared by the
method of Example 1, was employed as a core yarn and an acrylic
fiber roving (fiber denier 2 d, fiber length 2 inches) was used as
a sheath fiber. Stretching the core yarn with a draft ratio of 2,
corespinning was carried out. The thus obtained core-spun yarn
possessed 40 percent of elastic fiber content, 22 Nm (metric count)
of yarn count (i.e., corresponding to 410 d), and 12.2 T/inch of Z
twist. Since the twist direction of pure spandex spun yarn was S
while the twist direction of core-spinning was Z, the twisting
torques of the yarn disappeared. The kink number of the thus
prepared core-spun yarn was 26 and this product was found to be
useful for the following knitting or weaving process. For the sake
of comparison, similar core-spinning was carried out with non-twist
filament yarn (210 d) of elastic fiber and acrylic fiber roving,
and consequently the kink number of core-spun yarn obtained was 52.
This core-spun yarn had to be steam set to decrease the kink number
to 20 for the subsequent process.
EXAMPLE 3
Employing the direct spinning machine shown in FIG. 4, a
multi-filament yarn (5000 d/500 fil.) of spandex elastic fiber
having 300 percent breaking elongation, 0.2 g/d (stress in 100
percent extention) Young's modulus, and 98 percent recovery from
100 percent extention, was stretch-broken in the stretch-breaking
zone under the conditions of 7.45 draft ratio and 9 inches distance
between the back roll and intermediate roll. Another roving
consisting of 2 d fiber denier, 2 inches fiber length acrylic
fibers having 0.1 g/m sliver weight, was continuously fed to the
cradle roll in the draft zone, and blended with the elastic fiber
coming from the stretch-breaking zone. Then the blended yarn was
drawn with a draft ratio of 2.24 to give a desired yarn count of
1/13 Km (metric count), twisted (23 twist/inch) by revolution of
the spindle and wound up on a cop. The breaking strength and the
breaking elongation of this product were 683 g and 107 percent,
respectively. After subjecting the product to free relaxation in
boiling water, these values changed to 558 g and 277 percent. The
spun yarn obtained by this Example comprised 43 percent spandex
fiber and the remainder was hard fiber. Excellent elasticity and
good recovery from stretching were found for the spun yarn (after
spinning) within the limit of 50 percent extention and on the
relaxed spun yarn (after relaxation in boiling water) within the
limit of 150 percent extention, respectively.
The term "elastic fiber" used herein refers to the synthetic fibers
having elasticity due to construction with soft segment and hard
segment such as spandex fiber having a urethane group as a bonding
group or the fibers having urea group or acid amide group as a
bonding group, and includes fibers formed by extruding or cutting
natural rubber or synthetic rubber. Therefore, this elastic fiber
has the following characteristic mechanical properties.
breaking elongation more than 100% (generally 400-800%) elastic
recovery from high stretching more than 90% (generally more than
95%) Young's modulus less than 0.5 g/d (generally 0.03-0.1 g/d)
wherein the elastic recovery from high stretching is indicated by
the percentage of recovered stretch to the net stretched length of
the fiber just after being stretched to 1/2 of the breaking
elongation thereof, kept for one minute, and then released from
stretching and the Young's modulus represents the stress when the
fiber is 100 percent extended.
The term "hard fiber" used herein refers to fibers having less than
50 percent breaking elongation, and including natural fibers such
as cotton, wool, linen, jute and silk, regenerated cellulosic
fibers such as viscose, cuprammonium, and acetate, and synthetic
fibers consisting of homopolymers such as polyamides,
polyacrylonitrile, polyesters, polyvinylchloride, and
polyvinylalcohol, or consisting of copolymers thereof.
The present invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention as described hereinabove and
as defined in the appended claims.
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