JPH04108128A - Latent bulky yarn and production thereof - Google Patents

Abstract

PURPOSE:To obtain a latent bulky yarn capable of carrying out dark dyeing by thermally drawing undrawn yarn or semi-drawn yarn of polyester based multifilament yarn at a definite drawing ratio and then blending and interlacing the above-mentioned drawn multifilament yarn with other specific multifilament yarn. CONSTITUTION:Undrawn or semi-drawn yarn of polyester based multifilament yarn having <=100X10<-3> n double refractive index is thermally drawn in <=natural draw ratio thereof to afford a drawn yarn (A) and the resultant yarn (A) is fed to same fluid nozzle together with other thermoplastic synthetic fiber (B) >=3% higher in shrinkage factor by boiling water than the yarn (A) and both yarns are blended and interlaced to provide the aimed latent bulky yarn.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a latent dyeing system in which the core portion is provided with yarn made of fibers having higher shrinkage than the sheath portion, and the sheath portion is provided with yarn mainly capable of deep dyeing. Regarding bulky yarn. More specifically, the core part is made of yarn made of fibers with higher shrinkage than the sheath part, the sheath part is mainly made of yarn that can be dyed deeply, and both are integrally formed by fluid treatment as a composite yarn. After the obtained yarn is made into a yarn state or a knitted fabric, heat treatment is performed in a relaxed state to shrink the yarns arranged mainly in the core part and to reveal the bulkiness of the yarns. The present invention relates to a novel latent bulky yarn that can be dyed and deep dyed, and a method for producing the same.

[Prior art] Conventionally, multifilament yarns are treated with turbulent fluid to generate loops and slack in individual filaments, and the bulky yarns that entangle the filaments with each other have been widely used in the clothing field as "Taslan" yarns. .

On the other hand, composite bulky processed yarns with a core-sheath structure are also known, which increase the bulkiness and improve the morphological stability of the yarns by subjecting multiple multifilament yarns to turbulent fluid treatment at different feed rates. ing.

JP-A No. 63-159540 discloses that in order to improve the intertwining and loop shape robustness of the above-mentioned composite bulky processed yarn, undrawn nylon 6 yarn is used as the core yarn, and the undrawn yarn is The stretched yarn is then supplied to a turbulent fluid region together with other yarns to give yarn length differences and at the same time to form intertwining and loops, thereby causing contraction due to elastic recovery of the strain caused by the stretching. A technique has been disclosed in which turbulence is generated during fluid processing and attempts to strengthen the entanglement by the contraction.

However, since the strain imparted by drawing is caused to contract by elastic recovery, it is necessary to apply an overfeed amount larger than the shrinkage amount when the yarn is treated with a turbulent fluid. The thread has a disadvantage of being difficult to handle because it is obviously bulky.

In addition, Japanese Patent Publication No. 61-11333 describes a filament bulky yarn that has loops and fluff on the surface and exhibits excellent bulkiness, as well as a uniform marbling tone after dyeing. A multifilament yarn consisting of at least two types having loops and entanglements, wherein at least one of the yarns has a birefringence of 25
A special bulky yarn characterized in that it is a highly oriented undrawn polyester yarn with a diameter of X10-'' to 130×10'!, and the filaments forming the multifilament yarn form a fluff of 30 co/M or more. and techniques related to its manufacturing method are presented.

However, although the special bulky yarn shown here exhibits an excellent marbling effect, since the bulky yarn is subjected to an abrasion treatment to generate fluff on the yarn surface, loops and fluffs are formed on the surface of the bulky yarn. Due to the protrusion, the friction coefficient of the yarn increases. Therefore, the running resistance of the yarn increases,
Even if control is strengthened, tension fluctuations tend to occur, which not only reduces product quality, but also causes thread breakage and reduces operability.

[Problems to be Solved by the Invention] The purpose of the present invention is to improve the above-mentioned deficiencies of the prior art, and although the obtained yarn exhibits a low bulk property, by heat treatment, It is an object of the present invention to provide a novel latent bulky yarn that has high latent bulkiness and also has excellent dyeability.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

That is, the first invention is a composite yarn formed by mixing at least two types of thermoplastic synthetic fiber multifilament yarns, and the individual filaments constituting the composite yarn have a mutually intertwined structure. , one of the composite yarns is polyester multifilament yarn A, whose birefringence Δn is within the range of 60 to 140×10 −3 , and the boiling water shrinkage rate of the composite yarn is is within the range of 5 to 30%, and when the composite yarn is treated with boiling water, the value of the ratio α of the initial tensile resistance before and after the hot water treatment is α≧0.2; After the boiling water treatment, the yarn has a form in which the yarn A of the polyester multifilament is mainly located in the sheath part, and the other yarn B is mainly located in the core part. It is based on bulky yarn.

Further, the second aspect of the invention is that when two or more types of thermoplastic synthetic fiber multifilament yarns are introduced into the same fluid nozzle and a plurality of filament yarns are intertwined to form a composite yarn, one of the filament yarns has a birefringence of △ n is 100×10'3
After hot drawing the following undrawn or semi-drawn polyester multifilament yarns at a natural draw ratio of 80% or less, use other thermoplastic synthetic fiber multis with a boiling water shrinkage rate of 3% or more higher than that of the yarns. This method is based on a method for producing a latent bulky yarn, which is characterized by introducing a filament yarn and a filament yarn into the same fluid nozzle to mix and entangle them.

The present invention will be explained in more detail with reference to the drawings.

FIGS. 1(a) and 1(b) are schematic diagrams schematically illustrating the appearance of the latent bulky yarn according to the present invention.

The latent bulky yarn 1 shown in FIG. 1(a) is obtained by applying turbulent fluid treatment (usually referred to as taslan treatment) as an entangling means, and both yarns A and B are arranged with a difference in yarn length. , the filaments constituting yarn A are located mainly on the outside, forming a sheath, and have a long yarn length, - the universal yarn B has a short yarn length, and the filaments constituting yarn B is located relatively centrally and forms a core. The yarn as a whole is bulkier than that shown in FIG. 1(b), and the individual filaments constituting the latent bulky yarn are randomly mixed and intertwined.

Although this latent bulky yarn 1 has a yarn length difference between yarn A and the other yarn B due to the yarn structure, the yarn length difference does not need to be so large and can be as much as 20%. Any amount is sufficient, and about 10% is preferable.

When this yarn length difference increases, loops and slacks occur frequently on the surface of the yarn, which increases the coefficient of friction when the yarn runs, which not only reduces the quality of the product as described above, but also
Care must be taken as this will also impede operability.

The latent bulky yarn 1' shown in FIG.
The polyester multifilament yarn A (hereinafter simply referred to as yarn A, individual filaments are indicated by thin lines) and the other yarn B (individual filaments are indicated by thick lines). ) are arranged in a state in which they are aligned with each other, and the individual filaments constituting the latent bulky yarn 1' are composed of a convergent part 2 which is converged by intertwining and a non-convergent part 3 which is not condensed. Both are placed intermittently. In this embodiment, the yarn lengths of the yarns A and B described above are substantially the same, and a difference of about 5% is allowed. The number and strength of entanglements vary depending on the conditions in which the yarn is used, but when used as weft yarns for weft knitting or fabrics, the number is small and the strength is relatively weak, but there are few problems.
When used in warp knitting and warp threads of textiles, it is necessary to increase the number and strength.

Figures 2(a) and (b) are similar to Figures 1(a) and (b).
FIG. 2 is a schematic view schematically showing the appearance of a manifested bulky yarn obtained by heat-treating the latent bulky yarn shown in FIG.

As shown in FIG. 2(a), the latent bulky yarn obtained by the turbulent fluid treatment is heat-treated to develop bulkiness, and the actual bulky yarn has entangled parts 2 as shown in FIG. 2(b). and unconfounded part 3
Although they are similar in that the filaments constituting yarn B are located in the center without showing an alternating arrangement with
The filaments that make up Yarn A arranged on the outside of the composite yarn are mixed and intertwined with the individual filaments that make up Yarn B while forming individual loops and slacks at random. This shows the complex aspects of the process. Of course, due to the heat treatment, the difference in yarn length between yarns A and B increases due to the large heat shrinkage rate of yarn B, so naturally the bulk increases.

As shown in FIG. 2(b), the actual bulky yarn 1', which is obtained by heat-treating the latent bulky yarn obtained by fluid entangling treatment to develop bulkiness, has entangled portions 2 and non-entangled portions 3 arranged alternately. Among the individual multifilaments constituting the apparent bulky yarn in the unentangled portion 3,
Each multifilament made of yarn B shrinks due to heat shrinkage, and its length becomes short, so that it has a nearly straight shape. However, the shrinkage of the individual multifilaments constituting yarn A due to heat treatment is smaller than that of the individual multifilaments constituting yarn B. Therefore, yarn A
The individual multifilaments constituting the yarn B are relatively longer than the individual multifilaments constituting the yarn B. Therefore, in order to match the yarn lengths of both yarns, the individual multifilaments constituting the yarn A are curved individually or collectively in a direction perpendicular to the yarn axis.

The direction within the cross section perpendicular to the yarn axis is random. The individual multifilaments that make up yarn B are short, so they are located in the core, and the individual multifilaments that make up yarn A are located in the sheath. .

Although it does not show a clear core-sheath structure as shown in FIG. 2(a), it does show a somewhat misshapen and ambiguous core-sheath structure.

In the present invention, even such an ambiguous form represents a core-sheath structure.

The core yarn and sheath yarn constituting the latent bulky yarn according to the present invention are composed of the same or different types of thermoplastic synthetic fiber multifilament yarns, and are characterized in that they have different internal structures. The thread B, which serves as the core thread, maintains the strength of the fabric using this thread and contributes to the stiffness, tension, and tailoring quality of the fabric. Furthermore, it contributes to operability in yarn processing and knitting and weaving processes. In addition, the sheath yarn has the texture of the resulting fabric,
It contributes to properties such as touch, gloss, and color that affect texture and appearance. Therefore, the core yarn is made of a relatively thick single fiber fineness, low elongation, and high strength, and the sheath thread A is a polyester yarn with a relatively thin single fiber fineness and high elongation. Multifilament is used.

On the other hand, yarn A used as a sheath yarn has a fine single fiber fineness, and the higher the elongation, the softer the texture, and the more amorphous the internal structure, so it can be dyed in a deep color, making it possible to dye it in a deep color. Incompletely drawn polyester multifilament yarn is used, which can add variation and depth to the fabric. Therefore, by appropriately selecting the physical properties of the core thread and the sheath thread, a fabric having physical properties suitable for each use can be obtained.

The core yarn B used in the present invention is a thermoplastic synthetic fiber multifilament yarn, and its type is not particularly limited, but polyolefin, polyamide, and polyester types are suitable. In particular, in fields where deep colors are desired, not only homopolymers but also copolymers are preferred, and polyester and polyamide-based materials are suitable.

The ratio of yarn A in the composite yarn is preferably in the range of 30 to 70%. If it is less than 30%, it may not be possible to obtain good texture, touch, and dyeability of the fabric, and if it is more than 70%, the proportion of yarn B may decrease and the strength of the fabric may decrease.

The latent bulky yarn according to the present invention is produced by shrinking the core yarn through heat treatment as described above and creating a substantial yarn length difference between the filaments forming the core yarn and sheath yarn forming the composite yarn. It is made with an obvious bulky thread. Therefore, the water-making shrinkage rate representing the magnitude of heat shrinkage of the yarn B, which becomes the core yarn, is large, and the yarn A, which is the incompletely drawn yarn that becomes the sheath yarn, is large.
The shrinkage rate of water in water production is small, and the difference between the two needs to be at least 5%. If this difference is less than 5%, a yarn with satisfactory apparent bulk cannot be obtained. Although an actual bulky yarn can be obtained by reversing the water production shrinkage rate of yarn B, which becomes the core yarn, and the water production shrinkage rate of yarn A, which becomes the sheath yarn, this does not achieve the object of the present invention. It won't happen.

Further, the shape stability described below of the apparent bulky yarn obtained by heat treatment influences the shape stability of the fabric using this yarn.

In addition, the thread A that becomes the sheath thread used in the present invention is determined by taking into account the texture and dyeing characteristics of the fabric to be manufactured, but it has a finer single fiber fineness than the thread B that becomes the core thread, A polyester multifilament yarn is used that has a relatively large elongation at break of at least 40%, a difference in elongation from the core yarn of at least 20%, and a large amount of amorphous portions. Of course, homopolymers are often used, but copolymers are suitable for dyeing deep colors.

As mentioned above, the morphological stability of the actual bulky yarn is determined by the amount of resistance to elongation of the yarn.

Usually, the initial tensile resistance is determined by strength, elongation curve (S-S
This is indicated by the magnitude of the inclination angle of the curve (curve), but it is quite difficult to determine this inclination.

In the present invention, the strength at 10% elongation is determined from the strength elongation curve before and after hot water treatment, and when the strength before treatment is set to 1 and the strength after treatment is set to 2, α'' k 2 / k
The value of 1 was defined as the ratio of the initial tensile resistance before and after hot water treatment, and the closer the value of α was to 1, the better the shape stability. If the value of α is less than 0.2, the stability of the actual bulky yarn will deteriorate, which is not preferable.

The latent bulky yarn according to the present invention can of course be used without twisting, but it can also be used with heating (twisted, intermediate twisted, strongly twisted) like a normal woven yarn.

Especially in strong twisting, twist coefficient (twist coefficient = number of twists (T/m)
However, D is the fineness of latent bulky yarn) is 30.00! Values greater than 0 can also be used. In the case of highly twisted yarns, in order to facilitate handling of the yarns, it is preferable to heat-treat the yarns in a packaged state to an extent that does not impair the heat shrinkage characteristics of the yarns to prevent twisting.

When the latent bulky yarn according to the present invention is heated and used, the appearance and texture of the fabric obtained differs depending on the degree of twist. especially,
It is thought that in the case of fabrics using highly twisted yarns, as the yarns contract, a rotating force acts on the yarns themselves, increasing the bulk of the fabric.

FIG. 3 illustrates an apparatus for producing a latent bulky yarn according to the present invention.

As shown in FIG. 3, an undrawn or semi-drawn polyester multifilament yarn 10, which is the yarn A, is supplied from the first feed roller 11, and the yarn is connected to the first feed roller 11. The yarn is hot-stretched between stretching rollers 12 to a predetermined stretching ratio, resulting in an incompletely drawn yarn. The drawn incompletely drawn yarn is then supplied from the drawing roller 12 to the fluid treatment nozzle 15 as a sheath yarn. The yarn B, which is the drawn yarn 2 that becomes the core yarn, is supplied from the feed roller 13 of the second option and is supplied to the fluid treatment nozzle 15 via the yarn guide 14. The two yarns entering the fluid treatment nozzle 15 are formed into a composite latent bulky yarn through an intertwined structure, and are then taken up by a take-up roller 16 and wound into a package 18 by a winding device 17.

As shown in FIG. 3, a polyester multifilament undrawn yarn or semi-drawn yarn is used as the yarn A that becomes the sheath yarn, and is stretched at a predetermined stretching ratio by the first feed roller 11 and the stretching roller 12. However, this drawing ratio is 80% of the natural drawing ratio of the undrawn yarn or semi-drawn yarn used.
% or less, and is maintained in the state of incompletely drawn yarn, which is not completely drawn. During stretching, hot plate 1
8, the flood shrinkage rate of yarn A, which becomes the sheath yarn, is the same as that of yarn B, which becomes the core yarn after hot drawing.
It is sufficient to appropriately set the flood shrinkage rate to be at least 3% smaller than the flood shrinkage rate.

Further, the hot stretching method is not particularly limited as long as it can be hot stretched, such as a hot roller or a hot pin, in addition to the hot plate.

In this incompletely drawn state, the yarn has a high elongation, a lower hot water shrinkage rate than yarn B, is flexible, has a low degree of orientation, and exhibits unique characteristics such as high dyeability. These properties can be ascertained by measuring the birefringence Δn, and Δn is preferably 60 to 140×10 −3 .

When Δn is 60×10 −3 or less, the fabric has a soft feel and can be dyed in a deep color, but there are problems with properties such as fastness of dyeing and frosting. Also, Δn is 140X10
If it is -3 or more, the texture becomes rough and hard, and the deep color effect decreases, which is not preferable.

For the latent bulky yarn according to the present invention, the state of the latent bulky yarn,
Alternatively, the latent bulky yarn is heat treated in the form of a fabric to impart bulkiness. In order to develop bulkiness through heat treatment, the core yarn must be shrunk more than the sheath yarn through the heat treatment to generate a yarn length difference between the core yarn and the sheath yarn. For this purpose, it is necessary to appropriately select the difference in heat shrinkage rate between the core thread and the sheath thread. Therefore, it is necessary to select a material whose boiling water shrinkage rate of the core yarn is at least 5% greater than that of the sheath yarn. If it is less than 5%, a yarn with a satisfactory apparent bulk cannot be obtained. If a core yarn having a high shrinkage rate in boiling water is used, an actual bulky yarn with a high degree of bulk can be obtained, but the form stability of the actual bulky yarn will decrease (it will become easier to stretch). Therefore, the boiling water shrinkage rate of the core yarn should be at most 30%, preferably 20% or less.

The fluid treatment nozzle 15 shown in FIG. 3 can be used appropriately depending on the purpose of use of the latent bulky yarn. In other words, if you want to increase the bulkiness, you can use a turbulent fluid treatment (taslan) nozzle, and if you want to slightly suppress the bulkiness, you can use a fluid interlace nozzle.

A case where a turbulent fluid treatment nozzle is used as the fluid treatment nozzle 15 will be described.

It is effective to set the supply speed of the core yarn supplied to the turbulent fluid treatment nozzle to be slower than the supply rate of the sheath yarn, and in that case, the core yarn and the sheath yarn are fluid-treated in the turbulent fluid nozzle. There is a difference in yarn length between the two. Therefore, although the individual filaments of both are mixed and intertwined together after undergoing fluid treatment to form a composite yarn, the filaments that constitute the short yarn as a whole are mainly concentrated in the core. The filaments that gather together to form long threads bend randomly to form loops and slacks, and bulge out in the direction perpendicular to the thread axis, causing the filaments and threads that make up short threads to bend. They maintain the same length in the longitudinal direction. Therefore, the greater the difference in yarn length between the two, the greater the swelling. However, when the yarn length difference is increased, the bulge due to loops and slack increases, which not only increases the apparent thickness (diameter) of the composite yarn, but also increases the coefficient of friction of the composite yarn, causing guides, needles, etc.
Since the frictional resistance between the reed feathers and other objects in contact increases, not only the ability of the composite yarn to pass through higher-order processing deteriorates, but also the quality of the product.

When producing a potentially bulky yarn using the apparatus shown in FIG. By keeping the yarn length difference between the core yarn and sheath yarn in the potentially bulky yarn processed and formed by the nozzle to about 10%, the generation of bulkiness is suppressed as much as possible and intertwining and mixing are promoted. .

When this latent bulky yarn is used as the warp of a fabric, a tension roller 16' is provided between the take-up roller 16 and the take-up device 17, and the tension roller 16' is 0.1 to 0.4 g/d (d is the denier of the composite yarn). It is more effective in terms of weaving properties to tighten the fabric by applying a tension of 100 mL, or to apply a light heat treatment such as a hot plate between the take-up roller 16 and the tension roller 16' to suppress loops.

The main function of the latent bulky yarn according to the present invention is to satisfactorily mix and entangle the individual filaments forming the composite yarn using the turbulent fluid treatment nozzle, and to suppress the bulkiness as much as possible. The imparting of properties is carried out in the state of the latent bulky yarn or after the latent bulky yarn is made into a fabric by heat treatment.

Next, a case will be described in which a fluid entangling nozzle is used as a fluid treatment nozzle.

In FIG. 3, the speeds of the drawn yarn that becomes the core yarn and the incompletely drawn yarn that becomes the sheath yarn that are supplied to the fluid entangling nozzle by the feed roller 13 and the drawing roller 12 are substantially equal, and the speed difference is at most It is within 5% at most. If the yarn lengths of the two yarns are significantly different, it is difficult to obtain a satisfactory result even when the fluid entangling nozzle 15 performs the entangling process.

The number and strength of entanglement are determined by appropriately selecting the shape of the fluid entanglement nozzle 15, the dimensions of each part, the pressure of the compressed air supplied to the nozzle, the tension of the yarn being supplied, the yarn speed, etc. These values are determined by the properties of the fabric to which the latent bulky yarn is provided and the high-order processing conditions under which the fabric is manufactured. Generally 2
The number is preferably about 0 to 100 pieces/m. If the number is 100 pieces/m or more, the distance between the intertwined parts becomes too small, and even if the latent bulky yarn is later heat-treated, a satisfactory actual bulky yarn cannot be obtained. Moreover, when the number is less than 20 pieces/m, the cohesiveness of the latent bulky yarns decreases, and the operability in higher-order processing decreases.

FIG. 4 is a schematic diagram showing another example of the apparatus for manufacturing the latent bulky yarn according to the present invention, which is of a different embodiment from the apparatus shown in FIG. 3.

In FIG. 3, yarn B, which will become the core yarn, is fed to the fluid treatment nozzle 15 from the feed roller 13, while in FIG. The difference is that the thread A, which becomes the sheath thread from No. 12, is simultaneously fed in a drawn state. In other words, this is a system in which the feed roller 13 is omitted. The other parts are not much different from those shown in FIG. Therefore, the symbols for other parts are the same as in FIG. 3.

In FIG. 4, since the feeding speeds of the yarn B serving as the core yarn and the yarn A serving as the sheath yarn are the same, it is particularly suitable to use a fluid entangling nozzle as the fluid treatment nozzle 15. Of course, turbulent fluid treatment nozzles can also be used. In terms of equipment, there is no foot roller 13, which is advantageous in terms of cost.

[Example] Examples 1 and 2 and Comparative Examples 1 to 5 used the device shown in FIG.
The overfeed rate of yarn B, which will become the core yarn, is 8%, the air pressure is 5 kg/cnf, the fluid treatment nozzle is a turbulent fluid treatment nozzle, and the drawing conditions of yarn A, which will be the sheath yarn, are shown in Table 1.2. Latent bulky yarn was manufactured under the following conditions.

Example 3.4 and Comparative Example 6 used the apparatus shown in FIG.
kg, /c11! The fluid treatment nozzle was a fluid entanglement treatment nozzle, and the latent bulky yarn was produced under the conditions for drawing the yarn A, which will become the sheath yarn, as shown in Table 1.2.

The characteristics and combinations of yarns A and B used in each example and comparative example are shown in Table 3.

The 10-level latent bulk yarns obtained in the above 4 Examples and 6 Comparative Examples were twisted with an Italian twisting machine at a twist coefficient of 12,000 (twist coefficient = number of twists (T/m) x 7D), and then PET drawn with a warp of 50D. The weft of the thread is woven into a plain weave. The obtained gray fabric was subjected to the usual relaxing process, intermediate setting, alkaline reduction, and 135℃.
Liquid jet dyeing and finishing set After that process, the dyeing finishing process was carried out. The physical properties, touch/feel, dark color effect, and overall evaluation of the obtained fabric were determined. The results are shown in Table 1.2.

[Effects of the Invention] As described above, the latent bulky yarn according to the present invention has the following excellent effects.

1) Since it is a latent bulky yarn, handling of the yarn is extremely easy. Therefore, operability is extremely high.

2) By heat-treating the yarn or knitted fabric, a product with excellent bulkiness can be obtained, and the resulting product has excellent morphological stability.

3) The surface has a soft, firm and excellent texture, and highly dyeable multifilaments are arranged, so it can exhibit high color effects. This effect is particularly great for dark colors.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are schematic diagrams schematically illustrating the appearance of the latent bulky yarn according to the present invention. Figures 2(a) and (b) are similar to Figures 1(a) and (b).
FIG. 2 is a schematic view schematically showing the appearance of a bulky yarn obtained by heat-treating the latent bulky yarn shown in FIG. FIG. 3 illustrates an apparatus for producing a latent bulky yarn according to the present invention. FIG. 4 is a schematic diagram showing another example of the apparatus for manufacturing the latent bulky yarn according to the present invention, which is of a different embodiment from the apparatus shown in FIG. 3. Patent applicant Toshi Textile Co., Ltd. Patent applicant
Toshi Co., Ltd. Representative Patent Attorney Mikio Kagawa (d) (b) Figure 1 (convex), Figure '42

Claims (4)

[Claims] (1) A composite yarn formed by blending at least two types of thermoplastic synthetic fiber multifilament yarns, the individual filaments constituting the composite yarn having a mutually intertwined structure, and the composite yarn One of them is polyester multifilament yarn A, whose birefringence Δn is within the range of 60 to 140×10^-^3, and the boiling water shrinkage rate of the composite yarn is 5. ~30%, and when the composite yarn is treated with boiling water, the value of the ratio α of the initial tensile resistance before and after the hot water treatment is α≧0.2; The yarn after water treatment is a latent bulky yarn characterized in that the yarn A of the polyester multifilament mentioned above is mainly located in the sheath part, and the other yarn B is mainly located in the core part. . (2) When two or more types of thermoplastic synthetic fiber multifilament yarns are introduced into the same fluid nozzle and a plurality of filament yarns are entangled to form a composite yarn, one of the filament yarns has a birefringence Δn of 100. ×10^-^3 or less polyester multifilament yarn, undrawn or semi-drawn yarn, after hot drawing at 80% or less of its natural drawing ratio,
Production of a latent bulky yarn characterized by introducing another thermoplastic synthetic fiber multifilament yarn having a boiling water shrinkage rate of 3% or more higher than that of the yarn into the same fluid nozzle to mix and entangle both yarns. Method. (3) The method for producing a latent bulky yarn according to claim (2), wherein a turbulent fluid treatment nozzle is used as the fluid nozzle. (4) The method for producing a latent bulky yarn according to claim (3), wherein a fluid entanglement treatment nozzle is used as the fluid nozzle.