EP4006216A1

EP4006216A1 - Polyamide composite fiber and finished yarn

Info

Publication number: EP4006216A1
Application number: EP20847355.3A
Authority: EP
Inventors: Ru Huang; Sumio Yamaguchi
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2019-07-31
Filing date: 2020-07-27
Publication date: 2022-06-01
Also published as: EP4006216A4; CN114207200A; KR20220038683A; WO2021020354A1; JPWO2021020354A1; TW202113178A

Abstract

The present invention addresses the problem of providing a polyamide composite fiber obtained from a woven or knitted fabric having excellent stretchability or a finished yarn comprising the same. This polyamide composite fiber is an eccentric core-in-sheath type of polyamide composite fiber comprising two kinds of crystalline polyamide (A) and crystalline polyamide (B) differing in composition from each other, wherein the water absorptivity and thermal contraction stress of the polyamide composite fiber after being left to stand still for 72 hours in an environment in which the temperature is 30°C and the relative humidity is 90 RH% are 5.0% or less and 0.15 cN/dtex or more, respectively.

Description

TECHNICAL FIELD

The present invention relates to an eccentric sheath-core type composite fiber made of polyamide, and a finished yarn made of the eccentric sheath-core type composite fiber.

BACKGROUND ART

Polyamide fibers are softer and better in touch than polyester fibers, and have been conventionally widely used for clothing. A single-kind fiber yarn that is made of one kind of polymer such as nylon 6 and nylon 66, which are representatives of the polyamide fibers for clothing, has almost no stretchability in the fiber itself. Therefore, the single-kind fiber yarn is given stretchability by false twisting, and has been used for a stretchable woven or knitted fabric. However, it has been difficult to obtain a woven or knitted fabric having sufficiently satisfactory stretchability by subjecting such a single-kind fiber yarn to a process such as false twisting.
Therefore, Patent Literature 1 proposes a method of obtaining a stretchable woven or knitted fabric by using an elastic fiber, or a method of obtaining a stretchable woven or knitted fabric by using two kinds of polymers having different properties in combination and forming a composite fiber having a latent crimpability to cause crimping by a heat treatment such as a dyeing step. Further, as a polyamide composite fiber having the latent crimpability, Patent Literature 2 proposes a composite fiber obtained by arranging two kinds of polyamides having different viscosities in a side-by-side type or an eccentric sheath-core type configuration.
Patent Literature 3 proposes a highly heat-shrinkable polyamide composite fiber containing amorphous polyamide or a finished yarn made of the polyamide composite fiber, which shrinks due to a stress exceeding the binding force of the woven or knitted fabric even when a wet heat treatment or a dry heat treatment is performed in a state where high tension is applied in the warp direction, and can exhibit crimpability in the warp direction.

CITATION LIST

PATENT LITERATURE

Patent Literature 1: WO 2018/110523
Patent Literature 2: JP-A-2002-363827
Patent Literature 3: WO 2017/221713

SUMMARY OF INVENTION

TECHNICAL PROBLEM

However, when the composite fiber described in Patent Literature 1 is obtained from two kinds of polyamides having different properties, the stretchability may be lost when the composite fiber undergoes a processing step such as a refining step or a dyeing step due to swelling properties unique to the polyamide, and a sufficient stretch is not necessarily obtained in a product. The same applies to the polyamide composite fiber described in Patent Literature 2.
Furthermore, even if the composite fiber composed of polyamide described in Patent Literature 2 is excellent in crimpability in the state of a raw yarn or a finished yarn, wrinkles specific to the polyamide fiber are likely to be formed in a wet heat treatment step of refining or dyeing of a woven or knitted fabric, and wrinkles formed in the wet heat treatment step are difficult to be removed in a dry heat step of a heat-setting step. Therefore, in order to maintain the quality of the woven or knitted fabric, it is necessary to perform processing while applying tension to the woven or knitted fabric in the wet heat treatment step. As described above, the polyamide composite fiber described in Patent Literature 2 has a problem in that, by applying tension to the woven or knitted fabric in the wet heat treatment step, the crimping of the raw yarn or the finished yarn cannot be sufficiently exhibited, and as a result, the woven or knitted fabric has poor stretchability.
In addition, in the highly heat-shrinkable polyamide composite fiber described in Patent Literature 3, since the amorphous polyamide polymer promotes hygroscopic crystallization over time, the shrinkage properties also decrease over time, and the woven or knitted fabric may have low stretchability.
Therefore, an object of the present invention is to solve the above problems, and to provide a polyamide composite fiber from which a woven or knitted fabric having excellent stretchability can be obtained, and a finished yarn made of the polyamide composite fiber.

SOLUTION TO PROBLEM

The polyamide composite fiber of the present invention is an eccentric sheath-core type polyamide composite fiber containing two kinds of crystalline polyamides having different compositions, crystalline polyamide (A) and crystalline polyamide (B), in which a water absorption rate after the polyamide composite fiber is allowed to stand for 72 hours under a condition of a temperature being 30°C and a relative humidity being 90 RH% is 5.0% or less, and a thermal shrinkage stress is 0.15 cN/dtex or more.
According to a preferred aspect of the polyamide composite fiber of the present invention, the polyamide composite fiber has a rigid amorphous fraction of 40% to 60% and a stretch elongation ratio of 30% or more.
According to a preferred aspect of the polyamide composite fiber of the present invention, the crystalline polyamide (A) is nylon 6 or a copolymer thereof.
According to a preferred aspect of the polyamide composite fiber of the present invention, the crystalline polyamide (B) is nylon 610 or a copolymer thereof.
According to a preferred aspect of the polyamide composite fiber of the present invention, the crystalline polyamide (A) is a core component, and the crystalline polyamide (B) is a sheath component.
In the present invention, a finished yarn made of the polyamide composite fiber is obtained.
According to a preferred aspect of the finished yarn of the present invention, the stretch elongation ratio thereof is 100% or more.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can provide a polyamide composite fiber and a finished yarn from which a woven or knitted fabric having excellent stretchability can be obtained. The present invention can further provide a polyamide composite fiber and a finished yarn which shrinks due to a stress exceeding the binding force of the woven or knitted fabric even when a wet heat treatment or a dry heat treatment is performed in a state where high tension is applied in the warp direction, and can sufficiently exhibit crimpability in the warp direction, and from which a woven or knitted fabric having excellent stretchability can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a model cross-sectional view illustrating a cross section of an eccentric sheath-core type polyamide composite fiber of the present invention.
FIGs. 2(A) to 2(C) are model cross-sectional views respectively illustrating cross-sections of other eccentric sheath-core type polyamide composite fibers of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a polyamide composite fiber of the present invention and a finished yarn containing the polyamide composite fiber will be described.
In the present description, "mass" has the same meaning as "weight".
The polyamide composite fiber of the present invention is an eccentric sheath-core type polyamide composite fiber containing two kinds of crystalline polyamides having different polymer compositions, crystalline polyamide (A) and crystalline polyamide (B), in which a water absorption rate after the polyamide composite fiber is allowed to stand for 72 hours under a condition of a temperature being 30°C and a relative humidity being 90 RH% is 5.0% or less, and a thermal shrinkage stress is 0.15 cN/dtex or more.
The polyamide composite fiber of the present invention is an eccentric sheath-core type composite fiber and is constituted by two kinds of crystalline polyamides having different polymer compositions, crystalline polyamide (A) and crystalline polyamide (B). The eccentric sheath-core type polyamide composite fiber refers to a composite fiber in which two or more kinds of polyamides form an eccentric sheath-core structure.
The polyamide composite fiber of the present invention is required to have a composite cross section formed by bonding two kinds of crystalline polyamides, and two kinds of crystalline polyamides having different polymer compositions are present in a bonded state without being substantially separated. In the present invention, the polyamide composite fiber is preferably an eccentric sheath-core type composite fiber in which the crystalline polyamide (A) is used as a core component, the crystalline polyamide (B) is used as a sheath component, and the crystalline polyamide (A) is covered with the crystalline polyamide (B).
The term "eccentric" as used in the present invention means that the position of the center of gravity of the core component is different from the center of the cross section of the composite fiber in the cross section of the polyamide composite fiber.
FIG. 1 is a model cross-sectional view illustrating a cross section of an eccentric sheath-core type polyamide composite fiber (hereinafter, also referred to as "polyamide eccentric sheath-core type composite fiber") of the present invention. In FIG. 1, a polyamide eccentric sheath-core type composite fiber 10A is constituted by a core component (crystalline polyamide (A)) 1 and a sheath component (crystalline polyamide (B)) 2, and the position of the center of gravity of the crystalline polyamide (A) as the core component is different from the center of the cross section of the composite fiber.
FIGs. 2(A) to 2(C) are model cross-sectional views respectively illustrating cross-sections of other polyamide eccentric sheath-core type composite fibers of the present invention. FIGs. 2(A), 2(B), and 2(C) respectively illustrate modes of polyamide eccentric sheath-core type composite fibers 10B to 10C that are different in shape arrangement states of the core component (crystalline polyamide (A)) 1 and the sheath component (crystalline polyamide (B)) 2 of the eccentric sheath-core type composite fiber, and similarly to FIG. 1, the position of the center of gravity of the crystalline polyamide (A) as the core component is different from the center of the cross section of the composite fiber.
A composite ratio between the crystalline polyamide (A) and the crystalline polyamide (B) (crystalline polyamide (A):crystalline polyamide(B)) is preferably within a range of 6:4 to 4:6 (mass ratio). When the mass ratio is set to 6:4 to 4:6 in this manner, the water absorption rate of the polyamide composite fiber of the present invention can be controlled to 5.0% or less, and the obtained woven or knitted fabric is provided with excellent stretchability.
The polyamide composite fiber of the present invention is constituted by two kinds of crystalline polyamides having different polymer compositions. The crystalline polyamide is a polyamide that forms crystals and has a melting point, and is a polymer in which so-called hydrocarbon groups are linked to a main chain via amide bonds. Specific examples of the crystalline polyamide include polycapramide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polytetramethylene adipamide, and a condensation polymerization type polyamide of 1,4-cyclohexanebis and a linear aliphatic dicarboxylic acid, and copolymers thereof or mixtures thereof. However, from the viewpoint of easy reproduction of a uniform system and stable exhibition of functions, it is preferable to use a homopolyamide.
The crystalline polyamide (A) is a kind of polyamide different from the crystalline polyamide (B), and examples thereof include nylon 6, nylon 66, nylon 4, nylon 610, nylon 11, nylon 12, and copolymers containing these as main components. The crystalline polyamide (A) may contain components besides lactams, aminocarboxylic acids, diamines, and dicarboxylic acids in a repeating structure thereof as long as the effects of the present invention are not inhibited. However, an elastomer containing a polyol or the like in a repeating structure is excluded from the viewpoint of the silk-reeling property and the strength.
From the viewpoint of the yarn production property, the strength, and the peeling resistance, the crystalline polyamide (A) is preferably a polymer in which a content of a single kind of lactam, an aminocarboxylic acid, or a combination of a diamine and a dicarboxylic acid in the repeating structure is 90% or more, more preferably 95% or more. The components are particularly preferably nylon 6 or a copolymer thereof from the viewpoint of thermal stability.
The crystalline polyamide (B) is obtained by, for example, a combination of diamine units and dicarboxylic acid units containing sebacic acid units as a main component. Among these, nylon 610, which has stable polymerizability, less yellowing of crimped finished yarns and good dyeability, and a copolymer thereof are most preferably used. Here, the sebacic acid can be produced, for example, by refining seeds of castor oil, and is regarded as a plant-derived raw material.
Examples of the dicarboxylic acid constituting the dicarboxylic acid units other than the sebacic acid units include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, phthalic acid, isophthalic acid, and terephthalic acid, and these dicarboxylic acids can be blended within a range that does not impair the effects of the present invention.
These dicarboxylic acids are also preferably plant-derived dicarboxylic acids. The copolymerization amount of the dicarboxylic acid units other than the sebacic acid units is preferably 0 to 40 mol%, more preferably 0 to 20 mol%, and still more preferably 0 to 10 mol%, based on all the dicarboxylic acid units.
The diamines that constitute the diamine units are diamines having two or more carbon atoms, preferably diamines having 4 to 12 carbon atoms, and specific examples thereof include putrescine, 1,5-pentanediamine, hexamethylenediamine, trimethylenediamine, nonanediamine, methylpentanediamine, phenylenediamine, and ethambutol. These diamines are also preferably plant-derived diamines.
If necessary, a pigment, a heat stabilizer, an antioxidant, a weathering agent, a flame retardant, a plasticizer, a release agent, a lubricant, a foaming agent, an antistatic agent, a moldability improver, a reinforcing agent, and the like may be added to and blended with the crystalline polyamide (A) and the crystalline polyamide (B).
The polyamide composite fiber of the present invention is required to have a water absorption rate of 5.0% or less after being allowed to stand for 72 hours under a condition of a temperature being 30°C and a relative humidity being 90 RH% (a temperature of 30°C × a relative humidity of 90 RH%). The water absorption rate herein is a value measured in accordance with JIS L 1013. When the water absorption rate of the polyamide composite fiber treated for 72 hours at a temperature of 30°C × a relative humidity of 90 RH% is 5.0% or less, the swelling of the polyamide fiber under a wet heat condition of a refining step and a dyeing step is reduced, and the elongation of the woven or knitted fabric during these steps is reduced. Accordingly, it is possible to perform steps such as a refining step and a dyeing step without applying extra tension to the woven or knitted fabric. As a result, a woven or knitted fabric having excellent stretchability is obtained.
In contrast, as the water absorption rate increases, the polyamide fiber tends to swell with water. When the water absorption rate is more than 5.0%, wrinkles and textures are likely to occur in the refining or relaxing treatment step and the dyeing step, and the polyamide fibers are generally subjected to a stretching treatment, causing the stretchability to be reduced.
The water absorption rate is preferably 4% or less. The lower limit of the water absorption rate cannot be specified, and is practically about 1.0%.
The water absorption rate can be controlled depending on the polymer selection of the crystalline polyamide (A) and the crystalline polyamide (B) and the core/sheath composite ratio.
The polyamide composite fiber of the present invention is required to have a thermal shrinkage stress of 0.15 cN/dtex or more. Here, using a thermal shrinkage stress measuring machine (for example, model "KE-2", manufactured by Kanebo Engineering Ltd.), the thermal shrinkage stress is measured by connecting fiber yarns to be measured to form a loop having a circumferential length of 16 cm, applying an initial load of 1/30 g of fineness (dtex) of yarns to the loop, performing measurement with a temperature rising rate of 100°C/min from a temperature of 40°C to a temperature of 210°C, and a peak value of the obtained thermal stress curve is regarded as the maximum thermal stress (cN/dtex).
In the case where the thermal shrinkage stress is 0.15 cN/dtex or more, a woven or knitted fabric shrinks due to a stress exceeding the binding force of the woven fabric even when a wet heat treatment or a dry heat treatment is performed in a state in which high tension is applied in the warp direction. Therefore, it is possible to obtain a woven or knitted fabric that can sufficiently exhibit crimpability in the warp direction and has good stretchability. In the case where the thermal shrinkage stress is less than 0.15 cN/dtex, sufficient crimping is not exhibited in the wet heat treatment step in which high tension is applied. Therefore, a woven or knitted fabric having poor stretchability is obtained.
The thermal shrinkage stress is preferably 0.20 cN/dtex or more, more preferably 0.25 cN/dtex or more. When the thermal shrinkage stress is too high, the holes of a woven fabric at crossing points are likely to be clogged, and the stretchability is inhibited. Therefore, the upper limit of the thermal shrinkage stress is preferably 0.50 cN/dtex. The thermal shrinkage stress can be controlled by using a high-viscosity polymer, controlling rigid amorphous fractions of fibers under the thermal stretching conditions of a low spinning temperature, and a low spinning speed and a high stretching ratio, or the like.
A rigid amorphous fraction of the polyamide composite fibers of the present invention is preferably 40% to 60%. The rigid amorphous phase refers to an amorphous phase whose amount is determined according to a method described in the items of Examples, and is an intermediate state between a crystalline state and a mobile amorphous state (a completely amorphous state in related arts). The molecular motion in the rigid amorphous fractions is frozen even at the glass transition temperature (Tg) or higher, and the rigid amorphous fractions are in a fluid state at a temperature higher than Tg (for example, see "DSC (3)-Glass transition behavior of polymers-", Journal of the Textile Society (Fibers and Industry), TODOKI Minoru, Vol. 65, No. 10 (2009)).
The rigid amorphous fraction is represented by "100% - crystallinity - mobile amorphous fraction". In the present invention, the polyamide composite fiber includes a crystalline portion, a rigid amorphous portion, and a mobile amorphous portion. The thermal shrinkage stress depends on the binding force of a rigid amorphous chain at the time of forming a fiber structure and the shrinkage of a mobile amorphous chain that is exhibited when the heat treatment is performed. The thermal shrinkage stress can be exhibited by setting the rigid amorphous fraction within the above range.
The rigid amorphous fraction can be controlled by spinning. The rigid amorphous fraction can be controlled by the use of high-viscosity polymers and the design of production methods, similarly to the thermal shrinkage stress.
When the rigid amorphous fraction is 40% or more, the binding force of the rigid amorphous chain can be exhibited, and the desired thermal shrinkage stress can be obtained without impairing the shrinkability of the mobile amorphous chain. When the rigid amorphous fraction is 60% or less, the binding force of the rigid amorphous chain can be exhibited, the shrinkage force of the mobile amorphous chain can be retained, and the desired thermal shrinkage stress can be obtained. The rigid amorphous fraction is preferably 45% to 55%.
The polyamide composite fiber of the present invention preferably has a stretch elongation ratio of 30% or more. The stretch elongation ratio is an index of crimpability of a raw yarn, and a higher value indicates a higher crimping-exhibiting ability.
As for the polyamide composite fiber of the present invention, a difference in shrinkage is exhibited depending on a difference in orientation between the crystalline polyamide (A) and the crystalline polyamide (B) when the fibers are formed, and crimping is exhibited. However, polyamide fibers are likely to be wrinkled in the refining or dyeing step of a woven or knitted fabric in general, and in order to maintain the quality of the woven or knitted fabric, the processing is performed in a state in which high tension is applied in the warp direction. Therefore, the difference in shrinkage may decrease due to the influence of external force (high tension). The raw yarn has a constant thermal shrinkage stress to maintain the difference in shrinkage, so that crimpability of the raw yarn can be maintained. When the stretch elongation ratio is 30% or more, a woven or knitted fabric having more excellent stretchability can be obtained. The stretch elongation ratio is more preferably 100% to 200%. Since the stretch elongation ratio is exhibited by the difference in shrinkage between both components of the crystalline polyamide (A) and the crystalline polyamide (B), the larger the difference in shrinkage, the higher the stretch elongation ratio.
The polyamide composite fiber of the present invention preferably has a total fineness of a yarn of 20 to 120 dtex. In particular, when used for sportswear, down jackets, outerwear, and innerwear, the total fineness is more preferably 30 to 90 dtex. The single fiber fineness of polyamide composite fiber cannot be specified, and is generally within a range of 1.0 to 5.0 dtex.
Next, a method for producing the polyamide composite fiber of the present invention by melt spinning will be described.
In the crystalline polyamides used in the present invention, the relative viscosity of the crystalline polyamide (A) is preferably 3.1 to 3.8. The relative viscosity of the crystalline polyamide (B) is preferably 2.6 to 2.8. The relative viscosity ratio (A/B) of the crystalline polyamide (A) to the crystalline polyamide (B) is more preferably 1.2 to 1.4.
When a crystalline polyamide having a relative viscosity within such a range is selected, a difference in shrinkage is exhibited after the heat treatment, and a three-dimensional spiral structure is formed to exhibit the crimping. In addition, the polyamide makes a transition from the amorphous state to the crystalline state by receiving the melting heat during the yarn producing step. At this time, since the crystalline polyamide (A) having a high relative viscosity has a high molecular binding force, the rate of transition from the amorphous state to the crystalline state is lower than that of the crystalline polyamide (B) having a low relative viscosity. When the polyamide is cooled during the transition from the amorphous state to the crystalline state after ejection from the spinneret, rigid amorphous phase as the intermediate state is likely to be generated, the rigid amorphous fraction of the composite fibers increases, and both the thermal shrinkage stress and the stretch elongation ratio are improved.
The polyamide composite fiber of the present invention has a composite cross section formed by bonding two kinds of crystalline polyamides, and has an eccentric sheath-core type structure in which the crystalline polyamide (A) as a core component is covered with the crystalline polyamide (B) as a sheath component. In the case of the conventional side-by-side type structure in which the crystalline polyamide (A) is not covered with the crystalline polyamide (B) as the sheath component, the crystalline polyamides having a difference in relative viscosity described above are melted to form a composite cross section in the spinning pack, and at the time of ejection from the spinneret, the polymer flow resistances are different and a difference in the flow rate is generated. Accordingly, bending of yarns is likely to occur, and the operability deteriorates. Therefore, in the production of the crystalline polyamide (A) and the crystalline polyamide (B) having a difference in melt viscosity, it is possible to stably produce the composite fibers with ordinary equipment by adopting the eccentric sheath-core type structure in the present invention.
Next, a method for producing the polyamide composite fiber of the present invention by the melt spinning and the composite spinning will be described.
First, a method for producing the polyamide composite fiber of the present invention by high-speed direct spinning of the melt spinning will be described below as an example.
The crystalline polyamide (A) and the crystalline polyamide (B) are separately melted, weighed and transported using a gear pump to form a composite flow so that a sheath-core structure is formed by a normal method as it is, and using a spinneret for eccentric sheath-core type composite fibers, polyamide composite fiber yarns are ejected from the spinneret so as to have a cross section illustrated in FIG. 1. The ejected polyamide composite fiber yarns are cooled to reach a temperature of 30°C by being blown with cooling air by means of a yarn cooling device such as chimney. Subsequently, the cooled yarns are coated with oil by an oil supply device, converged, drawn by a drawing roller at 1500 to 4000 m/min, passed through the drawing roller and a stretching roller, and stretched at 1.5 to 3.0 times in accordance with a ratio of the circumferential speed of the drawing roller to the circumferential speed of the stretching roller at that time. The yarns are heat-set by a stretching roller and are wound into a package at a winding rate of 3000 m/min or more.
In addition, a method for producing the polyamide composite fiber of the present invention by the high-speed direct spinning of the melt spinning will be described below as an example.
The crystalline polyamide (A) and the crystalline polyamide (B) are separately melted, weighed and transported using a gear pump to form a composite flow so that a sheath-core structure is formed by a normal method as it is, and using a spinneret for eccentric sheath-core type composite fibers, polyamide composite fiber yarns are ejected from the spinneret so as to have a cross section illustrated in FIG. 1. The ejected polyamide composite fiber yarns are cooled to reach a temperature of 30°C by being blown with cooling air by means of a yarn cooling device such as chimney. Subsequently, the cooled yarns are coated with oil by an oil supply device, converged, drawn by a drawing roller at 3000 to 4500 m/min, passed through the drawing roller and a stretching roller, and stretched slightly at 1.0 to 1.2 times in accordance with a ratio of the circumferential speed of the drawing roller to the circumferential speed of the stretching roller at that time. Further, the yarns are wound into a package at a winding rate of 3000 m/min or more.
In particular, the spinning temperature is appropriately designed based on the melting point of the crystalline polyamide (A) having a high relative viscosity. When the spinning temperature rises, the crystalline portion tends to increase, and the rigid amorphous fraction tends to decrease. When the spinning temperature decreases, the mobile amorphous fraction tends to increase, and the rigid amorphous fraction tends to decrease slightly. Therefore, the spinning temperature is preferably 35°C to 70°C higher than the melting point of the crystalline polyamide (A), and more preferably 45°C to 60°C higher than the melting point of the crystalline polyamide (A). By setting the spinning temperature appropriately, the rigid amorphous fraction in the polyamide composite fiber of the present invention can be controlled, and a desired thermal shrinkage stress and a desired stretch elongation ratio can be obtained.
In addition, by appropriately designing the draft stretching (drawing rate), the rigid amorphous fraction of the polyamide composite fiber of the present invention is increased, and the thermal shrinkage stress and the stretch elongation ratio are improved. The drawing rate is preferably 1500 to 4000 m/min.
In the case of obtaining stretched yarns, by performing thermal stretching using the drawing roller as a heating roller, the rigid amorphous fraction in the polyamide composite fiber of the present invention is increased, and the thermal shrinkage stress is improved. The stretching ratio is preferably 1.5 to 3.0 times, more preferably 2.0 to 3.0 times. The thermal stretching temperature is preferably 30°C to 90°C, more preferably 40°C to 60°C.
In addition, by performing heat-setting using the stretching roller as a heating roller, the thermal shrinkage stress of the polyamide composite fiber of the present invention can be appropriately designed. The heat-setting temperature is preferably 130°C to 180°C.
In addition, the entanglement may also be performed by using a known entanglement apparatus in the steps up to the winding. If necessary, the number of entanglements may also be increased by applying entanglements multiple times. Furthermore, an oil agent may also be additionally applied immediately before the winding.
In the finished yarn made of the polyamide composite fiber of the present invention, the eccentric sheath-core type polyamide composite fiber of the present invention is used as at least a part of the yarns. The production method in the yarn processing is not limited, and examples thereof include a mixed fiber spinning method and a false twisting method. As the mixed fiber spinning method, air-mixed spinning, twisting or composite false twisting may be applied, and the air-mixed spinning is preferably used since the control of the air-mixed spinning is easy and the production cost is low. As the false twisting method, it is preferable to perform false twisting by using a pin type, a friction type, a belt type or the like according to the fineness and the number of twists.
The finished yarn made of the polyamide composite fiber of the present invention preferably has a stretch elongation ratio of 100% or more. When the stretch elongation ratio is set to 100% or more, sufficient exhibition of crimping and crimping of the false-twisted yarn are combined, and a woven or knitted fabric having excellent stretchability is obtained. The crimpability increases as the stretch elongation ratio is increased, but processing wrinkles are likely to occur, and production is carried out in a state in which high tension is applied in the warp direction to prevent the wrinkles, resulting in inhibition of the stretchability of the woven or knitted fabric. Therefore, the stretch elongation ratio is more preferably 120% to 200%.
The finished yarn made of the polyamide composite fiber of the present invention preferably has a stretch elongation ratio of 100% or more as described above. The stretchable woven or knitted fabric is formed by using the polyamide composite fiber or the finished yarn of the present invention in at least a part thereof. According to the present invention, it is possible to provide a woven or knitted fabric that can sufficiently exhibit the crimping even when a high tension is applied in the warp direction in the wet heat treatment step, and have excellent stretchability.
The stretchable woven or knitted fabric made of the polyamide composite fiber or the finished yarn of the present invention can be woven and knitted according to a known method. The weave of the woven or knitted fabric is not limited.
In the case of the woven fabric, the weave thereof may be any of a plain weave, a twill weave, a sateen weave, a modified weave thereof, and a mixed weave thereof depending on the intended application. To make a woven fabric with a firm and bulging texture, the plain weave with many restraint points, or the ripstop weave obtained by combing plain weave, flat cords, and further mat weave is preferred.
In the case of a knitted fabric, the weave thereof may be any of plain weave of a circular knitted fabric, interlock weave, half weave of a warp knitted fabric, satin weave, jacquard weave, modified weave thereof, and mixed weave thereof depending on the intended application, and the half weave of a single tricot knitted fabric or the like is preferred from the viewpoint that the knitted fabric is thin, stable, and excellent in the stretch ratio.
The application of the woven or knitted fabric made of the polyamide composite fiber or the finished yarn of the present invention is not limited, and the application for clothing is preferred, and applications for sport clothing represented by down jackets, windbreakers, golf wear, and rainwear, casual wear, and women's and men's clothing are more preferred. In particular, the polyamide composite fiber or the finished yarn can be suitably used for sportswear and down jackets.

EXAMPLES

Next, the polyamide composite fiber and the finished yarn of the present invention will be specifically described by Examples.

A. Melting Point:
Thermal analysis was performed using Q1000 manufactured by TA Instruments, and data processing was executed by Universal Analysis 2000. In the thermal analysis, a chip sample in a mass of about 5 g (heat amount data being standardized by mass after measurement) was measured in a nitrogen flow (50 mL/min) at a temperature rising rate of about 10°C/min within a temperature range of -50°C to 300°C. Melting point was measured based on the melting peak.
B. Relative Viscosity:
A polyamide chip sample in an amount of 0.25 g was dissolved in 25 mL of sulfuric acid having a concentration of 98 mass% to reach a concentration of 1 g/100 ml. Using an Ostwald viscometer, the obtained solution was measured in terms of a flow time (T1) at a temperature of 25°C. Subsequently, the sulfuric acid alone having a concentration of 98 mass% was measured in terms of a flow time (T2). The ratio of T1 to T2, i.e., T1/T2, was defined as the sulfuric acid relative viscosity.
C. Total Fineness:
The measurement was performed according to JIS L1013. The fiber sample was wound 200 times at a tension of 1/30 (g) using a test machine having a frame circumference of 1.125 m to prepare skeins. The skeins were transferred to a desiccator and dried at a temperature of 105°C for 60 minutes, followed by being cooled for 30 minutes under an environment with a temperature of 20°C and a relative humidity of 55% RH, and a mass value of the skeins was measured. The mass of the fiber yarns per 10,000 m was calculated based on the above mass value, and the total fineness of the fiber yarns was calculated with the official moisture content as 4.5%. The measurement was performed five times, and the average value was defined as the total fineness.
D. Thermal Shrinkage Stress:
Using a KE-2 type thermal shrinkage stress measuring machine manufactured by Kanebo Engineering Ltd., a fiber sample was connected to form a loop having a circumferential length of 16 cm, followed by applying an initial load of 1/30 g of the total fineness of yarns to the loop, a load at the time of changing the temperature from 40°C to 210°C with a temperature rising rate of 100°C/min was measured, and a peak value of the obtained thermal stress curve was defined as the thermal shrinkage stress.
E. Stretch elongation ratio:
The fiber sample was taken out in a skein form, immersed in boiling water at a temperature of 90°C for 20 minutes, air-dried, and the length A was determined after subjected to a load of 2 mg/d for 30 seconds, and then the length B was determined after subjected to a load of 100 mg/d for 30 seconds. The stretch elongation ratio was calculated from the following formula. $Stretch elongation ratio (%) = [(B - A) / B] \times 100$
F. Rigid Amorphous Fraction:
The rigid amorphous fraction was measured using Q1000 manufactured by TA Instruments as a measuring instrument. The following values were used: a difference (ΔHm - ΔHc) between the amount of heat of melting (ΔHm) and the amount of heat of cold crystallization (ΔHc) obtained from differential scanning calorimetry (hereinafter abbreviated as DSC), a difference in specific heat (ΔCp) obtained from temperature modulation DSC measurement, and a theoretical value of polyamides of 100% crystalline state (complete crystalline state) and a theoretical value of polyamides of 100% amorphous state (complete amorphous state). Here, ΔHm0 is the amount of heat of melting of polyamides (complete crystalline state). In addition, ΔCp0 is a difference in specific heat of polyamides (completely amorphous state) before and after reaching the glass transition temperature (Tg).

Based on the following formulae (1) and (2), the crystallinity (Xc) and the mobile amorphous fraction (Xma) were determined. The rigid amorphous fraction (Xra) was calculated by the following formula (3). Note that the rigid amorphous fraction was calculated based on an average value obtained by measuring these two times. (1) $Xc (%) = (Δ Hm - Δ Hc) / Δ Hm 0 \times 100$
(2) $Xma (%) = Δ Cp / Δ Cp 0 \times 100$
(3) $Xra (%) = 100 - (Xc + Xma)$
The measurement conditions of DSC and temperature modulation DSC are shown below.

(DSC Measurement)

Measurement device: Q1000 manufactured by TA Instruments
Data processing: Universal Analysis 2000 manufactured by TA Instruments
Atmosphere: Nitrogen flow (50 mL/min)
Sample amount: about 10 mg
Sample container: Standard aluminum container
Calibration of temperature and heat amount: high-purity indium (Tm = 156.61°C, ΔHm = 28.71 J/g)
Temperature range: about -50°C to 300°C
Temperature rising rate: 10°C/min First temperature rise process (first run)

(Temperature Modulation DSC Measurement)

Measurement device: Q1000 manufactured by TA Instruments
Data processing: Universeal Analysis 2000 manufactured by TA Instruments
Atmosphere: Nitrogen flow (50 mL/min)
Sample amount: about 5 mg
Sample container: Standard aluminum container
Calibration of temperature and heat amount: high-purity indium (Tm = 156.61°C, ΔHm = 28.71 J/g)
Temperature range: about -50°C to 210°C
Temperature rising rate: 2°C/min

G. Strength and Elongation:
The fiber sample was measured using "TENSILON" (registered trademark) UCT-100 manufactured by Orientec Co., Ltd. under a constant speed elongation condition specified in JIS L1013 (chemical fiber filament yarn testing method, 2010). The elongation was determined from the elongation at a point at which the maximum strength in the tensile strength-elongation curve is shown. As the strength, a value obtained by dividing the maximum strength by the fineness was defined as the strength. The measurement was performed 10 times, and the average values were defined as the strength and the elongation.
H. Water Absorption Rate Under Environment with Temperature of 30°C and Relative Humidity of 90 RH%:
In accordance with JIS-L-1013 (2010 edition), a fiber sample in an absolutely dry state was measured in terms of the mass after standing at a temperature of 30°C and a relative humidity of 90 RH% for 72 hours, thereby measuring the moisture content thereof.
I. Woven Fabric Evaluation:

(a) Production of Wefts
Polycaprolactam (N6) (relative viscosity: 2.70, melting point: 222°C) was melted and ejected at a temperature of 275°C using a spinneret having 12 spinneret ejection holes. After the polycaprolactam was melted and ejected, the obtained yarns were cooled, coated with oil, and entangled, and then, drawn with a drawing roller at 2570 m/min and subsequently stretched by 1.7 times, followed by being heat-fixed at a temperature of 155°C and wound at a winding rate of 4000 m/min, and nylon 6 yarns of 70 dtex/12 filaments were obtained.
(b) Production of Woven Fabric
Eccentric sheath-core type polyamide composite yarns obtained in Examples 4 to 11 and Comparative Examples 1 to 3 were used as warps (warp density: 90 yarns/2.54 cm), and the nylon 6 yarns obtained in the above (a) were used as wefts (weft density: 90 yarns/2.54 cm) to weave a plain woven fabric (warp/composite fibers) (basis weight: 40 g/cm²). Eccentric sheath-core type polyamide composite false-twist finished yarns obtained in Examples 1 to 3 were used as warps (warp density: 90 yarns/2.54 cm), and the nylon 6 yarns obtained in the above (a) were used as wefts (weft density: 90 yarns/2.54 cm) to weave a plain woven fabric (warp/finished yarn) (basis weight: 40 g/cm²).

The obtained woven fabric was refined at a temperature of 80°C for 20 minutes, then stained at a temperature of 100°C for 30 minutes using a dye of Kayanol Yellow N5G 1%owf whose pH is adjusted to 4 with acetic acid, followed by being subjected to a Fix treatment at a temperature of 80°C for 20 minutes, and finally heat-treated at a temperature of 170°C for 30 seconds to improve the texture.

(C) Stretch Rate (stretchability) in Warp Direction of Woven Fabric

Using a tensile tester, each of the woven fabric samples having a width of 50 mm × 300 mm obtained in Examples 1 to 10 and Comparative Examples 1 to 4 was stretched to 14.7 N at a tensile rate of 200 mm/min in the warp direction of the woven fabric at a grip interval of 200 mm and the stretch rate was measured. The stretch rate was evaluated in the following three grades "A", "B", and "C". A woven fabric with a stretch rate of 15% or more was determined to have stretchability.

A (good): 20% or more
B (acceptable): 15% or more and less than 20%
C (not acceptable): less than 15%

[Example 1]

Nylon 6 (N6) with a relative viscosity of 3.3 and a melting point of 222°C was used as the crystalline polyamide (A), and nylon 610 (N610) with a relative viscosity of 2.7 and a melting point of 225°C was used as the crystalline polyamide (B). The crystalline polyamide (A) was used as a core component and the crystalline polyamide (B) was used as a sheath component. Each of the crystalline polyamide (A) and the crystalline polyamide (B) was melted, and was ejected in a melted manner (spinning temperature: 270°C) at a composite ratio (mass ratio) of the crystalline polyamide (A) to the polyamide (B) of 5:5 (crystalline polyamide (A): crystalline polyamide (B) = 5:5) using a spinneret for eccentric sheath-core type composite fibers (12 holes, round holes). The yarns ejected from the spinneret were cooled and solidified by a yarn cooling device, coated with a hydrous oil agent by an oil supply device, entangled by a fluid entangling nozzle device, followed by being drawn at 3700 m/min with a drawing roller (room temperature: 25°C) and being stretched by 1.1 times with a stretching roller (room temperature: 25°C), and then wound into a package at a winding rate of 4000 m/min. Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 49%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.16 cN/dtex, and a rigid amorphous fraction of 41%, were obtained.
Using the obtained polyamide composite fiber yarns, disc false twisting was performed under conditions of a heater temperature of 190°C, a stretch ratio of 1.25 times and the number of twists (D/Y) of 1.95 to obtain false-twist finished yarns having a stretch elongation ratio of 130%. The obtained false-twist finished yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 1.

[Example 2]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 53%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.21 cN/dtex, and a rigid amorphous fraction of 46%, were obtained in the same method as in Example 1 except that nylon 6 (N6) with a relative viscosity of 3.6 and a melting point of 222°C was used as the crystalline polyamide (A).
The obtained polyamide composite fiber yarns were subjected to disc false twisting in the same method as in Example 1 to obtain false-twist finished yarns having a stretch elongation ratio of 150%. The obtained false-twist finished yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 1.

[Example 3]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 67%, a water absorption rate of 3.6%, a thermal shrinkage stress of 0.25 cN/dtex, and a rigid amorphous fraction of 53%, were obtained in the same method as in Example 1 except that a copolymerized product of nylon 6 and nylon 66 (N6/N66) with a relative viscosity of 3.6 and a melting point of 200°C was used as the crystalline polyamide (A).

The obtained polyamide composite fiber yarns were subjected to disc false twisting in the same method as in Example 1 to obtain false-twist finished yarns having a stretch elongation ratio of 200%. The obtained false-twist finished yarns were used as warps to form a woven fabric. The obtained woven fabric had more excellent stretchability than those of Examples 1 and 2. The results are shown in Table 1.

Table 1

			Example 1	Example 2	Example 3
Crystalline polyamide (A) component (core)			N6	N6	N6/N66
Crystalline polyamide (B) component (sheath)			N610	N610	N610
Relative viscosity of crystalline polyamide (A) component (core)			3.3	3.6	3.6
Relative viscosity of crystalline polyamide (B) component (sheath)			2.7	2.7	2.7
Raw yarn property	Total fineness	dtex	62	62	62
	Strength	cN/dtex	3.5	3.4	3.5
	Elongation	%	66	65	66
	Stretch elongation ratio	%	49	53	67
	Water absorption rate	%	3.8	3.8	3.6
	Thermal shrinkage stress	cN/dtex	0.16	0.21	0.25
	Rigid amorphous fraction	%	41	46	53
False twisted yarn	Stretch elongation ratio	%	130	150	200
Woven fabric performance		Stretchability	B	B	A

[Example 4]

A copolymerized product of nylon 6 and nylon 66 (N6/N66) with a relative viscosity of 3.6 and a melting point of 200°C was used as the crystalline polyamide (A), and nylon 610 (N610) with a relative viscosity of 2.7 and a melting point of 225°C was used as the crystalline polyamide (B). The crystalline polyamide (A) was used as a core component and the crystalline polyamide (B) was used as a sheath component. Each of the crystalline polyamide (A) and the crystalline polyamide (B) was melted, and was ejected in a melted manner (spinning temperature: 270°C) at a composite ratio (mass ratio) of the crystalline polyamide (A) to the polyamide (B) of 5:5 (crystalline polyamide (A):crystalline polyamide (B) = 5:5) using a spinneret for eccentric sheath-core type composite fibers (12 holes, round holes). The yarns ejected from the spinneret were cooled and solidified by a yarn cooling device, coated with a non-hydrous oil agent by an oil supply device, entangled by a fluid entangling nozzle device, followed by being drawn at 1700 m/min with a slightly-heating drawing roller (temperature: 50°C) and being stretched by 2.4 times with a heating stretching roller (heat-setting temperature: 150°C), and then wound into a package at a winding rate of 4000 m/min. Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 117%, a water absorption rate of 3.6%, a thermal shrinkage stress of 0.29 cN/dtex, and a rigid amorphous fraction of 55%, were obtained. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric had more excellent stretchability than that of Example 5. The results are shown in Table 2.

[Example 5]

Nylon 6 (N6) with a relative viscosity of 3.3 and a melting point of 222°C was used as the crystalline polyamide (A), and nylon 610 (N610) with a relative viscosity of 2.7 and a melting point of 225°C was used as the crystalline polyamide (B). The crystalline polyamide (A) was used as a core component and the crystalline polyamide (B) was used as a sheath component. Each of the crystalline polyamide (A) and the crystalline polyamide (B) was melted, and was ejected in a melted manner (spinning temperature: 270°C) at a composite ratio of the crystalline polyamide (A) to the polyamide (B) of 5:5 (crystalline polyamide (A):crystalline polyamide (B) = 5:5) using a spinneret for eccentric sheath-core type composite fibers (12 holes, round holes). The yarns ejected from the spinneret were cooled and solidified by a yarn cooling device, coated with a non-hydrous oil agent by an oil supply device, entangled by a fluid entangling nozzle device, followed by being drawn at 1700 m/min with a slightly-heating drawing roller (temperature: 50°C) and being stretched by 2.4 times with a heating stretching roller (heat-setting temperature: 150°C), and then wound into a package at a winding rate of 4000 m/min. Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 83%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.20 cN/dtex, and a rigid amorphous fraction of 46%, were obtained. The obtained composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Example 6]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 81%, a water absorption rate of 3.3%, a thermal shrinkage stress of 0.18 cN/dtex, and a rigid amorphous fraction of 45%, were obtained in the same method as in Example 5 except that the composite ratio of the crystalline polyamide (A) to the crystalline polyamide (B) was changed to 4:6 (crystalline polyamide (A): crystalline polyamide (B) = 4:6). The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Example 7]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 87%, a water absorption rate of 4.3%, a thermal shrinkage stress of 0.23 cN/dtex, and a rigid amorphous fraction of 47%, were obtained in the same method as in Example 5 except that the composite ratio of the crystalline polyamide (A) to the crystalline polyamide (B) was changed to 6:4 (crystalline polyamide (A):crystalline polyamide (B) = 6:4). The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Example 8]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 103%, a water absorption rate of 4.1%, a thermal shrinkage stress of 0.20 cN/dtex, and a rigid amorphous fraction of 46%, were obtained in the same method as in Example 5 except that nylon 6 (N6) with a relative viscosity of 3.6 and a melting point of 222°C was used as the crystalline polyamide (A), and a copolymerized product of nylon 610 and nylon 510 (N610/N510) with a relative viscosity of 2.7 and a melting point of 225°C was used as the crystalline polyamide (B). The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric had more excellent stretchability than that of Example 5. The results are shown in Table 2.

[Example 9]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 82%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.18 cN/dtex, and a rigid amorphous fraction of 43%, were obtained in the same method as in Example 5 except that the yarns were drawn at 2050 m/min with a slightly-heating drawing roller (50°C) and stretched by 2.0 times with a heating stretching roller (heat-setting temperature: 150°C). The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Example 10]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 82%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.18 cN/dtex, and a rigid amorphous fraction of 43%, were obtained in the same method as in Example 5 except that the spinning temperature was changed to 280°C. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Example 11]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 95%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.22 cN/dtex, and a rigid amorphous fraction of 49%, were obtained in the same method as in Example 5 except that the spinning temperature was changed to 260°C. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was excellent in the stretchability. The results are shown in Table 2.

[Comparative Example 1]

Polyamide composite yarns of 62 dtex/12 filaments were obtained in the same method as in Example 5 except that nylon 6 (N6) with a relative viscosity of 2.7 and a melting point of 222°C was used as the crystalline polyamide (A). The composite yarns of Comparative Example 1, which had almost no difference in relative viscosity, had a small difference in shrinkage after the heat treatment and had crimping with a low stretch elongation ratio of 13%, a thermal shrinkage stress of 0.13 cN/dtex, and a low rigid amorphous fraction of 39%. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric, and the obtained woven fabric was inferior in stretchability. The results are shown in Table 2.

[Comparative Example 2]

Polyamide composite yarns of 62 dtex/12 filaments were obtained in the same method as in Example 5 except that the composite ratio of the polyamide (A) to the polyamide (B) was changed to 7:3 (polyamide (A):polyamide (B) = 7:3). The polyamide composite yarns of Comparative Example 2 in which the ratio of the polyamide (A) having a high water absorption rate was increased had a high water absorption rate of 5.8%. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric in the same manner as in Example 5. However, since wrinkles remained, processing was performed to increase the tension in the warp direction to an extent that no wrinkles remained. As a result, a woven fabric having poor stretchability was obtained. The results are shown in Table 2.

[Comparative Example 3]

Polyamide composite fiber yarns of 62 dtex/12 filaments were obtained in the same method as in Example 5 except that nylon 6 (N6) with a relative viscosity of 3.3 and a melting point of 222°C was used as the crystalline polyamide (A), and nylon 6 (N6) with a relative viscosity of 2.7 and a melting point of 225°C was used as the crystalline polyamide (B). The polyamide composite fiber yarns of Comparative Example 3 produced by using polyamides having high water absorption rate had a high water absorption rate of 6.2%. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric in the same manner as in Example 5. However, since wrinkles remained, processing was performed to increase the tension in the warp direction to an extent that no wrinkles remained. As a result, a woven fabric having poor stretchability was obtained. The results are shown in Table 2.

[Comparative Example 4]

Polyamide composite fiber yarns of 62 dtex/12 filaments, which had a stretch elongation ratio of 53%, a water absorption rate of 3.8%, a thermal shrinkage stress of 0.13 cN/dtex, and a rigid amorphous fraction of 36%, were obtained in the same method as in Example 5 except that the spinning temperature was changed to 300°C. The obtained polyamide composite fiber yarns were used as warps to form a woven fabric. The obtained woven fabric was inferior in stretchability. The results are shown in Table 2.
Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the present invention. The present application is based on Japanese Patent Application No. 2019-141540 filed on July 31, 2019 , the entire contents of which are incorporated herein by reference.

REFERENCE SIGNS LIST

1: Core component (crystalline polyamide (A))
2: Sheath component (crystalline polyamide (B))
10A to 10D: Polyamide eccentric sheath-core type composite fiber

Claims

A polyamide composite fiber which is an eccentric sheath-core type polyamide composite fiber comprising two kinds of crystalline polyamides having different compositions, crystalline polyamide (A) and crystalline polyamide (B),
wherein a water absorption rate after the polyamide composite fiber is allowed to stand for 72 hours under a condition of a temperature being 30°C and a relative humidity being 90 RH% is 5.0% or less, and a thermal shrinkage stress is 0.15 cN/dtex or more.
The polyamide composite fiber according to claim 1, having a rigid amorphous fraction of 40% to 60% and a stretch elongation ratio of 30% or more.
The polyamide composite fiber according to claim 1 or 2, wherein the crystalline polyamide (A) is nylon 6 or a copolymer thereof.
The polyamide composite fiber according to any one of claims 1 to 3, wherein the crystalline polyamide (B) is nylon 610 or a copolymer thereof.
The polyamide composite fiber according to any one claims 1 to 4, wherein the crystalline polyamide (A) is a core component, and the crystalline polyamide (B) is a sheath component.
Afinished yarn made of the polyamide composite fiber according to any one of claims 1 to 5.
The finished yarn according to claim 6, having a stretch elongation ratio of 100% or more.