SPECIFICATION
CORE YARN SEWING THREAD
Technical Field
The present invention relates to a core yarn sewing thread excellent in sewabilities such as high-speed sewability and sewability in automatic sewing machine and in seam appearance. Background Art
The general constitution of a core yarn sewing thread consists of core fibers of a filament yarn and sheath fibers of a drafted staple fiber yarn, and can be made by feeding these core fibers and sheath fibers to a front roller of a spinning machine by paralleling in a sheath-core fashion and subjecting to a compound spinning to thereby once make a core yarn, and successively paralleling a plural of said core yarn and subjecting to upper-twisting in opposite direction to the twist direction of the conjugate spinning. Characteristics of this core yarn sewing thread are, compared to a spun yarn sewing thread of which constituting ratio of staple fiber is 100%, high in strength and also excellent in sewability, and accordingly, its production has quickly increased recently. However, since said core yarn sewing thread uses a filament yarn as the core fibers, there was a problem that its material cost was high compared to the spun yarn sewing thread made of 100% staple fibers. On the other hand, compared to a filament sewing thread made of 100% filament yarn, since hairiness of staple fibers used as sheath fibers of said core yarn sewing thread are

noticeable, the quality of seam line was not good in case where a thin filament woven fabric was sewn, and it was impossible to apply to high quality clothes. As a method for solving the fundamental problem of this core yarn sewing thread, for example, a "combined polyester sewing thread for sewing machine" (refer to the patent reference 1) of a compound yarn of an assembly-wound structure in which, a filament yarn which is already under-twisted and an ordinary spun yarn are paralleled and subjected to upper-twisting by an assembly-winder, is proposed. This sewing thread for sewing machine is a combined sewing thread for sewing machine rationally produced, but, since the filament yarn is not entirely covered by the spun yarn as general in the assembly-wound structure, its sewability is poor and a differences of dyeability and glossiness between the filament yarn and the spun yarn are noticeable, and accordingly, its appearance as a core yarn sewing thread is also poor. In addition, a "composite sewing thread for sewing machine" (refer to the patent reference 2) of a high modulus, a high strength and a high breaking elongation which is made by uniformly distributing filaments of a core yarn which are electrically opened by a static electricity in a cross section of a group of staple fibers to be sheath fibers, subjecting to a conjugate spinning to produce a core yarn, further, paralleling a plural of said core yarn and upper-twisting, is proposed. This composite sewing thread for sewing machine is excellent in view of sewability and uniform dyeing between sheath and core, but there are problems that its production cost is high due to passing the

opening process of filaments by static electricity or that, hairiness are likely to generate in its production process to bring about a poor quality, and the product is likely to have a high elongation to cause a puckering. Furthermore, other than those, a core yarn producing apparatus and its production method (refer to the patent reference 3), a two-layer structure yarn and a production method thereof (refer to the patent reference 4) are proposed.
In these apparatuses and methods, a hollow guide shaft in which a yarn pass is formed along a nozzle axis and a spinning part constituted with a rotational flow generating nozzle to function a rotational flow at the tip portion thereof are provided, and they are core yarn technologies in which filaments fed to the spinning part together with a drafted staple fiber bundle are bound by wrapping around, iowever, any of these prior arts, as an application of core /am spinning, makes no reference to an application to a sewing thread, and nothing is proposed as a production method of sewing thread which satisfies a high strength property with a small yarn fineness and is excellent in sewability and quality of seam line.
other than those, a composites sewing thread for sewing nachine constituted by a compound yarn in which staple fibers wrap around filaments (refer to patent reference 5) Ls proposed, but all of them have a problem of poor sewability iue to generating naps which may be caused by a hard friction inder a high sewing tension.
furthermore, a "covering sewing thread for sewing machine" by an air-jet spinning (refer to the patent reference 6) is

proposed, but because a coiling amount of the sheath fibers is extremely small compared to the total yarn amount, and because it is a method of binding/wrapping intermittently along the length direction of the yarn, the core portion is likely to be exposed, coiling is not uniform and the entire surface is not coiled, accordingly, there is a fatal defect that the core fibers are exposed between the sheath fibers. As mentioned above, with respect to a core yarn sewing thread excellent in sewability and yarn appearance, it is the present situation that satisfactory product has not been obtained.
Patent reference 1: JP-A-H02-33341
Patent reference 2: JP-B-S63-3977
Patent reference 3: JP-A-2002-69760
Patent reference 4: JP-A-2002-69774
Patent reference 5: JP Patent No. 2901806
Patent reference 6: JP-A-H02-160943 Problem to be Solved by the Invention
The present invention, in view of the above background arts, aims to provide a core yarn sewing thread that, in sewing by using an industrial lock stitch sewing machine, attains improvement in dyeing difference between core and sheath fibers, exposure of core fiber portion, seam puckering, seam appearance, etc. which have conventionally been regarded as drawbacks, and that excels in high-speed sewability, sewability in automatic sewing machine and high sewability of buttonhole, etc. Means for Solving the Problem
In order to solve the above-mentioned problem, the core yarn sewing thread of the present invention has the following

constitution.
At first, the first invention is a core yarn sewing thread characterized in that a core yarn of substantially no-twist in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% or more and 60% or less with respect to the total yarn weight, is further twisted in a plural of them.
The second invention is a core yarn sewing thread characterized in that a core yarn in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% or more and 60% or less with respect to the total yarn weight, is subjected to under-twisting up to an under-twist number having a relation of the following Formula (1), and that a plural of them is further twisted.
10,000/Ds1/2 > Ts > 0 (t/m) Formula (1) Where, Ds: fineness of core yarn (dtex) The third invention is a core yarn sewing thread in which the fiber yarn to be the above-mentioned core fibers sewing thread is a filament yarn.
The fourth invention is a core yarn sewing thread in which the above-mentioned core yarn sewing thread is further subjected to upper-twisting of an upper-twist number having a relation of the following Formula (2).
12,000/Du1/2 > Tu > 4,000 Du1/2 (t/m) Formula (2)
Where, Du: fineness of the plural of the core yarn paralleled (dtex)

The fifth invention is a core yarn sewing thread of the above-mentioned from the first invention to the forth invention, wherein the upper-twist number (Tu) and the under-twist number (Ts) have a relation of the following Formula (3).
Formula (3) The sixth invention is a production method of a core yarn
sewing thread characterized in that a core yarn of
substantially no-twist in which, on entire surface of a fiber
yarn to be core fibers, a staple fiber yarn to be sheath fibers
is spirally coiled along the longitudinal direction in a
coiling amount of 20% or more and 60% or less with respect
to the total yarn weight, is subjected to under-twisting
having a relation of the following Formula (1), is further
twisted in a plural of them.
Formula (1) Where, Ds: fineness of core yarn (dtex) Effect of the Invention
According to the present invention, it is possible to decrease the dyeing difference between core and sheath fibers, to prevent the exposure of core fibers portion, and to solve the seam puckering after sewing, which have conventionally been regarded as drawbacks. In addition, it is possible to obtain a highly functional core yarn sewing thread excellent in sewabilities such as high-speed sewability and adaptability to an automatic sewing machine, and capable of reducing cost in sewing step. Furthermore, since, in said sewing thread, hairiness-like staple fiber ends are uniform and short and wrapped around the core fibers, there are effects such that a seamed surface after sewing

looks beautiful to bring about an excellent quality.
Brief Explanation of the Drawings
[Fig. 1] Fig.l is an appearance of one example of the core
yarn used in the core yarn sewing thread of the present
invention.
[Fig. 2] Fig.2 is an appearance of the core yarn sewing thread
of the present invention in which the core yarn of Fig. 1
is used.
Explanation of Numeral Codes
1: Filament yarn of the core portion
2: Staple fiber yarn of the sheath surrounding the core
hollow-wise and in parallel
3: A staple fiber yarn of sheath fibers uniformly and
closely coiled on the second outer layer
4: Hairiness
5: Slack
6: Loop Best Embodiment for Carrying Out the Invention In the present invention, as a result of intensive investigation on a high performance core yarn sewing thread which solves the above-mentioned problems, and further, of which yarn breakage during sewing is few, and which makes it easy to adjusting sewing conditions of a sewing machine, it was found that those problems can be solved together by making a sewing thread with a core yarn of substantially no-twist as it is, or by subjecting it to a low under-twist, and further, paralleling a plural of them and subjecting to upper-twisting.
Hereunder, the best embodiment of the core yarn sewing thread of the present invention is explained.

At first, the first invention is, as mentioned above, a core yarn sewing thread characterized in that a core yarn of substantially no-twist in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% or more and 60% or less with respect to the total yarn weight, is further twisted in a plural of them.
Here, as the core fibers, it is a matter of course that any of ordinary synthetic fibers can be used, but fiber yarns such as polyester-based or polyamide-based are preferable. Furthermore, so-called highly functional fibers such as an aromatic polyamide fiber and a polyethylene fiber, or a spandex-based fiber and a cellulose-based fiber are easily used, and it is not limited thereto.
In case where a filament yarn is used as core fibers, as a single filament fineness of said filament yarn, the range of 30 - 200 dtex is preferable, and as a number of single filament, the range of 12 to 200 filaments is preferable. For example, in case of a fineness of filament yarn of 33 dtex, 12 - 30 filaments, in case of 78 dtex, 24 - 72 filaments, and in case of 200 dtex, 50 to 200 filaments, are more preferable. This relates to the single filament fineness and the number of single filaments, and when the single filament fineness is large, the sewing thread becomes stiff and the seam stands out from a cloth. On the other hand, when it is small, hairiness may generate or strength may decrease in processes from twisting to final winding, and accordingly, it is necessary to suitably select a combination of the single filament fineness and the number

of single filaments.
Furthermore, a larger number of the single filament is preferable since it brings about a softer bending or torsional property and improves seam puckering, but it may cause difficulty of obtaining a deep color in dyeing. As a matter of course, it is possible to use as a sewing thread out of said fineness range, but it is important to design a yarn according to its purposes or uses since various problems may arise in appearance and durability of seam or in color adjustment with a cloth.
As the sheath fibers, a staple fiber yarn is used, but similar to the core fibers, all synthetic fibers can usually be used, and among them, a polyester-based fiber or a polyamide-based fiber are suitable. In addition, not only the synthetic fibers, but also natural fibers such as cotton, silk or cellulose-based or acrylic fiber can easily be used. Here, the "staple fiber yarn" mentioned in the present invention is, like cotton or wool, a fiber of a length of about several cm to 10 + several cm, and denotes raw materials such as for a spun yarn, a futon or batting, and as concrete forms, staple fibers, discontinuous fibers or those simply called as staple are mentioned.
As staple fibers, it is preferable that a single fiber fineness is in the range of 0.1 - 3 dtex, and the range of 0.5 - 1.5 dtex is more preferable since it brings about high sewability by a good spinnability of core yarn, a surface smoothness of core yarn sewing thread or a flexibility of core yarn sewing thread. Furthermore, as to their fiber length, either of about 51 mm or less in short fiber spinning or 51 mm or more in long fiber spinning may be acceptable,

but it can be said that, in view of appearance after sewing by the core yarn sewing thread, the former spinning system, and in view of high strength property, the latter spinning system is preferable.
As a number of mono-filament to sheath fibers which wrap the core fibers,40 fibers or more is necessary. There is no upper limit, but if it is 500 fibers or more, it is not preferable since the core yarn may become rigid or irregular. And, if it is less than 40 fibers , it is not preferable since coiling property becomes insufficient. It is proper that a fiber ratio of the core fibers to the sheath fibers is in the range of 1 to 0.5 - 1 to 4.0, and it is the most preferable combination that the fineness of said sheath fibers is larger than that of the core fibers by about 50 - 200%.
It is necessary that a weight of staple fiber yarn to be the sheath fibers is 20% or more and 60% or less with respect to the total yarn weight which includes the core fibers. If it is wrapped less than 20%, since said core fibers may be exposed or since strength decreases, an insufficient coiling or slip of fibers may occur to bring about an insufficient core yarn formation. On the other hand, if it is coiled at a weight exceeding 60%, although there is no exposure of the core fibers, a decrease of strength may become large. Accordingly, it is preferable that the sheath fibers coil around in the range of 30% - 50%.
As determination method of the weight of the above-mentioned sheath fiber weight, core fibers and sheath fibers are separated from a core yarn sewing thread of 1 inch length by using a magnifying glass, furthermore, coiling staple

fibers only are taken out, and weighed (g) . It is the value calculated as a weight ratio of the weight with respect to the total yarn weight.
As a coiling condition of the sheath fibers to the core fibers, it is preferable that the single fibers of the sheath spirally coil closely and on entire surface along longitudinal direction of the core fibers. It is because, in this way, an exposure of the core fiber is not found and said sheath fibers closely coils in one direction and uniformly on entire surface, to strengthen convergence and to form a preferable core yarn as a sewing thread. Such a core yarn which is spirally coiled closely in one direction on entire surface, has characteristic that, although it is coiled by sheath fibers, has substantially no-twist as a whole, and has almost no torque. Here, "substantially no-twist" mentioned in the present invention means that the core fibers has no-twist, and concretely, means that the number of twist of the core fibers is about 5 t/m or less.
As a spirally coiling direction of the sheath fibers, in view of it's use is a sewing thread, it is preferable to be S-direction as that of the under-twist direction of ordinary sewing thread. On the contrary, if it is Z-direction, it is not preferable since a torque of twist increases to cause a poor processability, and, in addition, since it is a yarn structure in which the wrapping direction is once to be untwisted, a decrease of strength or an irregular yarn may occur. That is, it is preferable that the core yarn sewing thread of the present invention is a core yarn sewing thread having a structure in which a core yarn subjected to under-twisting of the same direction as the coiling

direction is paralleled in a plural of them and subjected to upper-twisting in Z-direction which is opposite to the under-twist direction.
As the angle of the sheath fibers coiled along the longitudinal direction of the yarn uniformly on entire
surface, the range of 20° - 70° is preferable. Here, the angle means the angle between the longitudinal direction of the
yarn and the wrapping sheath fibers. If it is less than 20°, yarn convergence decreases to cause a slip of fibers and
spinnability decreases greatly. And if it exceeds 70° in average, it is not preferable, although coiling ability increases, yarn fineness unevenness arises to decrease spinnability. In view of spinnability and yarn formation,
a more preferable wrapping angle is in the range of 30 - 60°. At measuring the coiling angle, from a photograph of yarn structure taken from said core yarn by a scanning electron micrograph at a magnitude of 40, angles of 10 coiled sheath fibers are measured, and their average is calculated. Here, in case where the core yarn is subjected to under-twisting, the measurement is carried out after reducing the under-twist number to the original, 0. By taking the above constitution, in the core yarn sewing thread of the present invention, by the core yarn used being a structure in which the sheath staple fibers spirally coil the fiber yarn to be core fibers in a fixed direction and in a uniform interval on entire surface, an appearance of the core yarn sewing thread becomes smooth, and as a result, good effects are given to sewing abilities such as back sewability or sewability in automatic sewing machine, and excellence of seam appearance. In actual data of commercialized core yarn

sewing threads, since, when a strength at break of sewing thread is high, yarn breakage during sewing becomes few and tension control of machine becomes easy, it is preferable that the strength at break is at least 5 cN/dtex or more, and further, 7 cN/dtex or more is preferable.
As a boiling water shrinkage of the core yarn sewing thread, in order to prevent a puckering after sewing, it is preferable to be 5% or less, more preferably, 3% or less.
! Regarding the first invention, since the core yarn has substantially no-twist as mentioned above and is tightly coiled on entire surface along its longitudinal direction, it is characterized in that under-twisting may not be necessary. However, in a structure of an ordinary sewing thread, under-twisting to increase convergence, to prevent a twist crack or to increase strength is necessary. Furthermore, regarding the second invention, since the core yarn has substantially no-twist as mentioned above and is tightly coiled on entire surface along its longitudinal direction, it is characterized in that under-twisting to increase convergence, to prevent a twist crack or to increase strength in a structure of an ordinary sewing thread may be few. The core yarn is a structure strongly coiled by single fibers to be sheath fibers, and therefore, compared to a core yarn made by ordinary ring spinning, its handling associated with the torque caused by twisting becomes easy. Accordingly, it is possible to omit steam treatment for twist set.
As a preferable range of the under-twist number (Ts) imparted to said core yarn sewing thread is,
10,000/Ds1/2 > Ts > 0 (t/m) Formula (1)

and it is suitable for sewability that the under-twist number is as small as possible. Here, Ds is a yarn fineness of the core yarn. When the under-twist number exceeds the relation of 10, 000/Ds1/2, a big decrease of sewability is brought about and, especially in back sewability or sewability in automatic sewing machine, it is not preferable since yarn breakage occurs frequently or high-speed sewability is spoiled. For example, in a combination of 230 dtex corresponding to core fibers of 78 dtex and sheath fibers of 151 dtex, when the under-twisting exceeds 800 t/m, sewability decreases considerably, but when the under-twisting is 600 t/m or less, sewability is likely to increase. Regarding a preferable sewability, it is more suitable that the under-twist number is as lower as possible, and 0, i.e., a state of almost no under-twist, is most excellent but, as mentioned above, when upper-twist processability or thread uniformity after upper-twisting is considered, it is practically preferable to impart under-twisting of about 50 - 100 t/m since stability of processability is increased.
The third invention is further characterized in that a fiber yarn to be the core fibers of the core yarn is a filament yarn. In this case, thread surface becomes more smooth and uniform, and yarn strength becomes higher, to thereby make sewing thread performance into that of a high quality. However, as mentioned above, when a filament yarn is used, the cost of sewing thread becomes high. Under such circumstances, according to purpose of sewing, it is preferable to select a sewing thread of 100% staple fiber or a core yarn sewing thread in which filaments are mixed.

As preferable characteristics of the filaments, not only to be high in strength, but also its elongation should be as low as possible, concretely, it is preferable to be 10% or less, more preferably, 5% or less. Furthermore, it is preferable that a boiling water shrinkage and a dry heat shrinkage are also low, i.e., it is preferable that both are 5% or less. By being in this range, a puckering after sewing can be prevented very effectively.
Regarding the fourth invention, it is a core yarn sewing thread in which the above-mentioned core yarn sewing thread is further subjected to upper-twisting to an upper-twist number having a relation of the following Formula (2).
12,000/Du1/2 > Tu > 4,000 Du1/2 (t/m) Formula (2) The above range is preferable. Here, Du is a fineness of a plurality of the core yarns paralleled. It is not preferable that the upper-twist number exceeds 12, 000/Du1/2, since strength decreases greatly to lower sewability, and that it is less than 4,000/Du1/2, since yarn convergence is spoiled and strength decreases greatly to lower sewability. It is preferable that an upper-twist number is lower than that imparted to an ordinary sewing thread, for example, in case of a core yarn 230 dtex which corresponds to core fibers of 78 dtex and sheath fibers of 151 dtex, it is preferable to impart upper-twisting of 500 t/m to 250 t/m in Z-direction. Regarding the fifth invention, in the present invention, since an under-twist number is 0 or as small as possible, it is of a relation quite opposite to the twist design thought of the conventional core yarn sewing thread. That is, in the range of ordinarily produced ring spinning core yarn sewing thread, it is in a relation of under-twist number,

Tu > upper-twist number, Ts, but in the core yarn sewing thread of the present invention, since the tight and uniform spiral coiling on entire surface exhibits the same effect as under-twisting, it is characterized to be in a relation of
Formula (3)
which is quite opposite to the conventional twist design thought. Here, the under-twist number is in the range of from the same as the upper-twist number or more and less than 150%, but more preferably, 110 - 130%. However, if it is 150% or more, it is rather not preferable since it may cause a strong torque of twist or a decrease of strength. Thus obtained core yarn sewing thread is high in yarn convergence compared to conventional ones, since the uniform and tight coiling of the sheath fibers is strong. Furthermore, since the number of hairiness is extremely small compared to the conventional ring spinning core yarn sewing thread, an excellent effect that it is possible to finalize a yarn appearance or a seam beautifully by the core yarn sewing thread.
The above explained constitution of the core yarn sewing thread of the present invention is explained in detail with reference to the drawings. Fig. 1 is an illustration of appearance of an example of core yarn used in a sewing thread of the present invention.
Fig. 1 shows a structure before subjecting to the under-twisting, and 1 denotes filament yarn of core fibers, 2 denotes sheath fiber portion of staple fibers surrounding the core fibers in hollow-like fashion and 3 denotes a portion spirally coiling in S-direction on entire surface almost

uniformly and tightly.
Fig. 2 is an example of the core yarn sewing thread of the present invention in which two of core yarns subjected to under-twisting are paralleled and subjected to upper-twisting to make a double-twisted yarn, and 4, 5 and 6 denote states of a hairiness, a slack and a loop,' respectively.
Next, the production method of the core yarn sewing thread of the present invention is explained. As an example, in the following, a production method where core fibers of the core yarn are filaments is explained.
At first, by using staple fibers after the drawing step in spinning process, i.e., a staple fiber bundle, said staple fiber bundle placed at a center of feed portion of a spinning machine and staple fiber bundles placed on both sides or under said staple fiber bundle are further bundled as a staple fiber bundle and drafted, and the drafted fiber bundle and filaments are paralleled, and supplied to a spinning device in which a rotational air flow is applied to subject it to a spinning by air by entangling the staple fibers to the core fibers comprising the filaments, and produce a core yarn with substantially no-twist in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% or more and 60% or less with respect to the total yarn weight. Since the speed of this spinning speed is a speed of 10 - 30 times of that of the conventional ring type spinning, and further since it is possible to omit a roving step, it is possible to reduce production cost greatly. As apparatuses for such a spinning by air, for

example, Murata Vortex Spinner Machine (MVS) (product of Murata Machinery, Ltd.) is mentioned.
Next, the core yarn sewing thread of the present invention can be produced by paralleling a plural of said core yarn obtained and directly subjecting to upper-twisting in Z-direction which is the opposite direction to the wrapping direction by the rotational air flow, or once subjecting said core yarn obtained to under-twisting in the same direction as the coiling direction by the rotational air flow and subjecting to upper-twisting in the opposite direction to the under-twisting. Here, when performing the under-twisting or the upper-twisting after paralleling a plural of the core yarn, it is possible to use a publicly known apparatus and method, but regarding the under-twisting, as mentioned above, it is preferable that the core yarn is subjected to under-twisting of the under-twist number having a relation of the following Formula (1),
Formula (1)
Where, Ds: fineness of the core yarn (dtex) and, regarding the upper-twisting, it is preferable to subject to upper-twisting of the upper-twist number having the relation of the following Formula (2).
12,000/Du1/2 > Tu > 4,000 Du1/2 (t/m) Formula (2) Where, Du: fineness of a plurality of the core yarns paralleled (dtex)
After subjecting to the upper-twisting, the paralleled yarn is subjected to a heat set to remove residual shrinkage or residual torque after the upper-twisting. After the set, a product of core yarn sewing thread of the present invention is obtained by making it into a softly wound cheese,

subjecting to a cheese dyeing process and finally winding.
Examples
Hereunder, the present invention is explained in detail with
reference to Examples.
Here, measuring methods are as follows.
(1) Fiber fineness, yarn count, strength, elongation and
boiling water shrinkage
They were measured according to JIS L1090-2003.
(2) Number of hairiness
By F-Index Tester of Shikibo Ltd., number of hairiness per 1 m was measured.
(3) U%
Measured by Evenness Tester 80 of Keisokki Kogyo Co., Ltd.
(4) Sewability
Using T/C broad cloth, the number of needle rotations of a sewing machine was changed, and sewabilities for forward and reverse stitching, and sewability in automatic sewing machine were tested.
(5) Evaluation method of sewing
A. High-speed sewability: The maximum number of
rotation (needles/min) of a sewing machine capable of sewing
2 m with 10 piled sheets of T/C broad cloth in the range of
1,000 - 5,000 (needles/min) was tested.
B. Back sewability: Number of yarn breakage (average
number/n=10) in sewing 1 m with 4 piled sheets of T/C broad
cloth at 1,500 (needles/min) was measured and evaluated by
the following standard.
x: sewing is impossible A: 2 - 5

o: 1 - 2 oo: 0
C. Adaptability to automatic sewing machine: A tension
capable of sewing 2 m with 4 piled sheets of T/C broad cloth
at 1,500 (needles/min) was measured and evaluated by the
following standard.
*: sewing is impossible
A: sewable (tension range is uncertain)
o: 100 - 200g
oo: 50 - 300g
D. Strength of seam line: According to JIS L-1093, tear
strength per 1 inch seam width (N) was measured.
E. Quality of seam line: Evaluated by visual
inspection.
A: Hairiness can be found
o: Almost not noticeable
oo: No hairiness (6) Coiling properties of sheath fiber
A: Surrounding fiber amount: A core yarn sewing thread of 1 inch length was separated into core fibers and sheath fibers to weigh the surrounding staple fibers (g), and a weight ratio of the surrounding fiber amount to the total yarn weight was calculated.
B: Coiling amount: A core yarn sewing thread of 1 inch length was separated into core fibers and sheath fibers, and only the short fibers were taken out from the coiled fibers and weighed (weight: g). The weight ratio of the coiling amount to the total yarn weight was calculated. Examples 1 and 2 At first, by Murata Vortex Spinner Machine (MVS) (product

of Murata Machinery, Ltd.), and by using a polyester yarn of multi-filament to be core fibers of 56 dtex-24 filaments having a strength of 6.1 cN/dtex and a sliver to be sheath fibers of polyester raw staple fiber of a fiber fineness of 1.3 dtex and a length of 38 mm, a S-directionally wrapped core yarn was produced at a spinning speed of 300 m/min, a nozzle pressure of 0.6 MPa, an outer diameter of spindle of 1.2 mm, an over feed ratio of 1-2%, a main draft of 40 times, a total draft of 140 times and a nozzle gauge of 21 mm. Subsequently, in order to convert said core yarn into a double twist sewing thread, said core yarn was adjusted to under-twisting of 0 t/m (Example 1), and 400 t/m (Example 2), and upper-twisting, both in Z-direction, of 780 t/m to obtain a double twist sewing thread. Here, the weights of polyester raw staple fiber to be the sheath to the total yarn weight were 31%, in the core yarn of primary twist 0 t/m of Example 1, and 32%, in the core yarn of primary twist 400 t/m of Example 2. Next, the double twist core yarn was wound on a cheese,
subjected to a steam set at 110°C for 20 minutes for a twist setting, successively wound on a soft cheese, subjected to
a scouring at 60°C for 10 minutes, and after a relaxation
treatment, subjected to a cheese dyeing at 130°C for 40 minutes to finish into black, and produced a core yarn sewing
thread.
Characteristics and a result of evaluation of sewability of
the obtained core yarn sewing thread were shown in Table 1
mentioned below.
Comparative example 1
On the other hand, as a comparative example, results of

evaluation in which "EPIC" of COATS of U.S. (ArtN529 Tktl50 Tex21 WHT) was used are shown in Table 1 mentioned below. "EPIC" is a commercial core yarn of a double twist sewing thread produced by a ring spinning machine using the polyester raw filament and the polyester raw staple fiber. Here, regarding the yarn wt%, a surrounding fiber amount is 0% and the coiling amount is 61%. Examples 3 and 4
By using the same spinning machine and the raw yarn/staple fiber as Example 1, a core yarn was prepared in the same way as Example 1.
This core yarn was subjected to under-twisting of 800 t/m (Example 3) and 1,100 t/m (Example 4) , and further subjected to upper-twisting of 780 t/m in Z-direction to thereby obtain a double twisted core yarn. Here, the weight of polyester raw staple fiber to be the sheath fibers to the total yarn weight were 32%, as to the core yarn of under-twisting of 800 t/m of Example 3, and 35%, as to the core yarn of under-twisting of 1,100 t/m of Example 4. Subsequently, a core yarn sewing thread was prepared in the same way as Example 1, and characteristics and a result of evaluation of sewability were shown in the following Table 1.
[Table 1]
From Table 1, it was found that when the under-twist number decreases from 1,100 t/m to 0 t/m, high-speed sewability, back sewability and quality of seam line are apt to be excellent. In particular, when the under-twist number is
400 t/m or less in which the upper-twist number, Tu > the under-twist number, Ts, they are very excellent compared to

those of Examples 3 and 4. On the other hand, the core yarn sewing thread of Comparative example 1 was low in the strength of seam line, and poor in the quality of seam line. Furthermore, although the sewing threads of Examples 3 and 4, in which the under-twist number was increased, were low in high-speed sewability and back sewability, they were excellent in strength of seam line and quality of seam line, and it is preferable to use them by sewing at a decreased sewing speed. Example 5
Next, by Murata Vortex Spinner Machine (MVS) (product of Murata Machinery, Ltd.), and by using a sliver, of polyester raw staple fibers to be core fibers and sheath fibers, of which raw fiber strength is 5.7 cN/dtex, fineness is 1.45 dtex and length is 38 mm, an S-directionally wrapped single yarn for sewing thread of 100% staple fiber of a yarn count 30 was produced at a spinning speed of 350 m/min, a nozzle pressure of 0.5 MPa, an outer diameter of spindle of 1.3 mm, a total draft of 225 times and a condenser width of 3 mm. This single yarn, since it is constituted with staple fibers disposed in the core portion, and also with a sheath of surrounding staple fibers and wrapping staple fibers on entire surface, forms a core yarn structure of which core portion is consisted of the staple fibers. In order to make this core yarn into a double twist sewing thread, the core yarn was subjected to upper-twisting in Z-direction of 150 t/m to obtain a double twist sewing thread. In this core yarn, the weight of the sheath fiber to the weight of the yarn was 41%. Subsequently, the double twist core yarn was wound on a cheese,

subjected to a steam set at 110°C for 20 minutes two times as a twist setting, successively wound on a soft cheese,
subjected to a scouring at 60°C for 10 minutes, and after a relaxation treatment, subjected to a cheese dyeing at 133°C for 40 minutes to finish into black, and produced a core yarn sewing thread.
Characteristics and a result of evaluation of sewability of the obtained core yarn sewing thread were shown in following Table 2. [Table 2]
As shown in the above Table 2, the sewing thread of Example 5, compared to the core yarn sewing thread of Comparative example 2 obtained by a ring spinning machine, was very few in number of hairiness, beautiful in seam appearance, low in yarn thickness unevenness, U%, to bring about a smooth thread surface. Comparative example 2
This time, by using the same staple fiber as Example 5, a single yarn of S-direction of a yarn count about 30 was produced at a spindle rotation of 12,000 rpm, a draft of 40 times and a spinning speed of 20 m/min. In order to make the single yarn into a double twist sewing thread, the single yarn was subjected to upper-twisting of ordinary 780 t/m in Z-direction to obtain a double twist core yarn. The double twist spun yarn was wound on a cheese, subjected to a steam
set at 110°C for 20 minutes twice as a twist setting, successively wound on a soft cheese, subjected to a scouring
at 60°C for 10 minutes, and after a relaxation treatment, subjected to a cheese dyeing at 130°C for 40 minutes to finish into black, and produced an ordinary spun yarn sewing thread

by ring spinning.
Characteristics and a result of evaluation of sewability of the obtained core yarn sewing thread were shown in the above-mentioned Table 2.
As shown in Table 2, since the number of hairiness of the sewing thread of Comparative example 2 was large, hairiness were noticeable on surface of the seam, extremely noticeable in a sewing of filament cloth, and thus became a defect. Comparative examples 3, 4, 5 and 6
By Murata Jet Spinner Machine (MJS) (product of Murata Machinery, Ltd.), and by using a polyester yarn of multi-filament to be core fibers of 56 dtex-24 filaments having a strength of 6.1 cN/dtex and a sliver to be sheath fibers of polyester raw staple fiber of a fineness of 1.3 dtex and a length of 38 mm, an S-directionally bound and wrapped core yarn was produced at a spinning speed of 200 m/min, a nozzle pressure for an air twisting in Z-direction of 0.5 MPa and a air pressure for an air untwisting in S-direction of 0.5 MPa, an over-feed ratio of 0.0 % and a total draft of 40 times.
Compared to Examples 1, 2, 3 and 4, insufficient coverings such as a yarn unevenness based on a structural difference between bound portions and unbound portions, or a fact that the core filaments could be observed in inner layer side of the unbound portions, are noticeable.
Subsequently, in order to make said core yarn into a double twist sewing thread, said core yarn was subjected to under-twisting of 0 t/m in S-direction (Comparative example 3) , and 400 t/m (Comparative example 4) , 800 t/m (Comparative example 5) and 1,100 t/m (Comparative example 6) and to

upper-twisting, all in Z-direction, of 780 t/m to obtain double twist sewing threads.
Next, the double twist core yarns were wound on cheeses,
subjected to a steam set at 110°C for 20 minutes as a twist setting, successively wound on soft cheeses, subjected to
a scouring at 60°C for 10 minutes, and after a relaxation treatment, subjected to a cheese dyeing at 130°C for 40 minutes to finish into black, but they were core yarn sewing threads of which yarn unevenness or insufficient covering were noticeable.
Characteristics and results of evaluation of sewability of the obtained core yarn sewing threads were shown in Table 3 mentioned below. Comparative example 7
In the same way as Comparative example 3, by Murata Jet Spinner Machine (MJS) (product of Murata Machinery, Ltd.), and by using a polyester yarn of multi-filament to be core fibers of 56 dtex-24 filaments having a strength of 6.1 cN/dtex and a sliver to be sheath fibers of polyester raw staple fiber of a fineness of 1.3 dtex and a length of 38 mm, it was controlled to decrease the coiling amount of sheath to 20% or less at a spinning speed of 200 m/min, by changing a nozzle pressure for an air twisting in Z-direction, a nozzle pressure of an air untwisting in S-direction and an over-feed ratio, but a core yarn suitable for a sewing thread could not be obtained since the coiling amount was too small. Comparative example 8
In the same way as Comparative example 3, by Murata Jet Spinner Machine (MJS) (product of Murata Machinery, Ltd.), and by using a polyester yarn of multi-filament to be core

fibers of 56 dtex-24 filaments having a strength of 6.1 cN/dtex and a sliver to be sheath fibers of polyester raw staple fiber of a fineness of 1.3 dtex and a length of 38 mm, a bound and wrapped core yarn was produced at a spinning speed of 200 m/min, a nozzle pressure for an air twisting in Z-direction of 0,5 MPa and a air pressure for an air untwisting in S-direction of 0.5 MPa, an over-feed ratio of 0.0 % and a total draft of 45 times.
Subsequently, in order to make said core yarn into a double twist sewing thread, said core yarn was subjected to under-twisting of 800 t/m, and to upper-twisting, both in Z-direction, of 900 t/m to obtain a double twist core yarn. Next, the double twist core yarn was wound on a cheese,
subjected to a steam set at 110°C for 20 minutes for a twist setting, successively wound on a soft cheese, subjected to
a scouring at 60°C for 10 minutes, and after a relaxation treatment, subjected to a cheese dyeing at 130°C for 40 minutes to finish into black, to thereby produce a core yarn sewing thread.
Characteristics and results of evaluation of sewability of the obtained core yarn sewing threads were shown in Table 3 mentioned below.
However, the obtained core yarn sewing thread was a core yarn sewing thread of which yarn unevenness and insufficiency of covering were noticeable, like those of Comparative examples 3, 4, 5 and 6,. [Table 3] rial applicability
The core yarn sewing thread of the present invention is applicable not only as a sewing thread for general clothes

which can be provided to an industrial lock stitch sewing machine in which a high-speed sewability, a sewability in automatic sewing machine, a back sewability and a good seam appearance are required, but also, for example, it is applicable to clothes for ladies or to pants for gentlemen in which characteristics of surface smoothness as a filament-staple conjugated yarn, an extremely few generation of pills, excellence in tenseness and touch are made advantage of.

CLAIMS
[1] A core yarn sewing thread characterized in that a plurality of core yarns of substantially no-twist in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% - 60% with respect to the total yarn weight, is further twisted.
[2] A core yarn sewing thread characterized in that a plurality of core yarns in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% - 60% with respect to the total yarn weight, is subjected to under-twisting of an under-twist number (Ts) having a relation of the following Formula (1) .
10,000/Ds1/2 > Ts > 0 (t/m) Formula (1) Where, Ds: fineness of the core yarn (dtex) [3] A core yarn sewing thread according to Claim 1 or 2, wherein
the fiber yarn to be core fibers is a filament yarn. [4] A core yarn sewing thread according to any one of Claims 1 to 3, wherein the core yarn sewing thread is further subjected to under-twisting of an upper-twist number (Tu) having a relation of the following Formula (2).
12,000/Du1/2 > Tu > 4,000 Du1/2 (t/m) Formula (2)
Where, Du: fineness of a plurality of the core yarns
paralleled (dtex)
[5] A core yarn sewing thread according to any one of Claims 1
to 4, wherein the upper-twist number (Tu) and the under-twist
number (Ts) have a relation of the following Formula (3).
Tu > Ts (t/m) Formula (3)

[6] A production method of a core yarn sewing thread characterized in that a core yarn of substantially no-twist in which, on entire surface of a fiber yarn to be core fibers, a staple fiber yarn to be sheath fibers is spirally coiled along the longitudinal direction in a coiling amount of 20% - 60% with respect to the total yarn weight, is subjected to under-twisting of an under-twist number (Ts) having a relation of the following Formula (1), and a plurality of said core yarns is further twisted,
10,000/Ds1/2 > Ts > 0 (t/m) Formula (1) Where, Ds: fineness of the core yarn (dtex)