CN113039313A

CN113039313A - Polyamide multifilament yarn and core-spun elastic yarn

Info

Publication number: CN113039313A
Application number: CN201980075245.1A
Authority: CN
Inventors: 岸田泰辅; 吉冈大辅; 松见大介
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2018-11-21
Filing date: 2019-11-19
Publication date: 2021-06-25
Also published as: TW202028553A; TWI793386B; EP3885477A4; EP3885477A1; JP7363766B2; KR20210089669A; JPWO2020105637A1; WO2020105637A1

Abstract

The invention provides a high-strength polyamide multifilament yarn which can provide stockings having excellent durability, transparency and hand feeling. The object can be achieved by a polyamide multifilament having a total fineness of 6 to 20dtex, a tensile strength of 12cN/dtex or more, and a flatness of 1.5 to 5.0 expressed by the ratio (b/a) of the major diameter b to the minor diameter a of the cross section of a single fiber.

Description

Polyamide multifilament yarn and core-spun elastic yarn

Technical Field

The present invention relates to a polyamide multifilament yarn and a core elastic yarn suitable for silk stockings. More particularly, the present invention relates to a polyamide multifilament and a covered elastic yarn which can provide a silk stocking excellent in durability, high in transparency, and good in touch when used for a silk stocking.

Background

Polyamide fibers and polyester fibers, which are synthetic fibers, have excellent mechanical and chemical properties, and are therefore widely used for clothing and industrial applications. In particular, polyamide fibers have excellent properties in terms of their unique flexibility, high strength, color-developing properties during dyeing, heat resistance, moisture absorption, and the like. Therefore, polyamide fibers are widely used for general clothing applications such as silk stockings, underwear, and sportswear.

As consumer demands for silk stockings, silk stockings having high transparency and soft hand have been desired, and many techniques for improvement have been proposed. For example, patent document 1 proposes an elliptical or lenticular polyamide multifilament having a flatness of 1.5 to 5.0 and a fiber cross-sectional shape symmetrical to a major axis, and a stocking using the polyamide multifilament.

Further, patent document 2 proposes a high-strength polyamide multifilament having a total fineness of 4.0 to 6.0dtex and a product of strength and elongation of 9.1cN/dtex or more, and a stocking using the polyamide multifilament. In addition, as a production method for increasing the product of strength and elongation of the polyamide multifilament yarn, it has been proposed to use a cooling condition for promoting relaxation of polymer orientation and lowering the solidification point by maintaining the atmospheric temperature under the spinneret at a high temperature.

Prior art documents

Patent document 1: japanese laid-open patent publication No. 2009-203563

Patent document 2: international publication No. 2016/076184

Disclosure of Invention

Problems to be solved by the invention

However, in patent document 1, the durability of the silk stockings decreases as the fineness of the silk stockings decreases. Further, since the flat short shaft is made thinner than the circular cross-sectional diameter due to flattening, the yarn strength is reduced as compared with the circular cross-sectional diameter, and there is often a problem that the durability of the silk stockings is reduced.

Even if the conditions described in patent document 2, such as maintaining the atmospheric temperature under the spinneret at a high temperature to increase the product of strength and elongation and promoting relaxation of polymer orientation to lower the solidification point, are applied to patent document 1, the reduction in solidification point causes a reduction in flatness when a flat cross section is formed. In this case, the resulting silk stockings have unsatisfactory hand feeling and appearance.

Further, although the flat cross section can exhibit a texture and an aesthetic appearance, the flat short axis is smaller than the diameter of the circular cross section, so that the durability of the silk stockings is undeniably lowered, and further improvement of the durability is desired.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polyamide multifilament and a covered elastic yarn which are excellent in durability, transparency, soft touch, and appearance when used for silk stockings.

Means for solving the problems

To solve the above problems, the present invention is configured as follows.

(1) A polyamide multifilament having a total fineness of 6 to 20dtex, a hook strength of 12cN/dtex or more, and a flatness of 1.5 to 5.0 as represented by the ratio (b/a) of the major diameter b to the minor diameter a of the cross section of a single fiber.

(2) The multifilament polyamide yarn according to item (1) above, which has a tensile strength of 5.0cN/dtex or more at 15% elongation.

(3) A core-spun elastic yarn obtained by arranging the polyamide multifilament yarn according to the above (1) or (2) as a covered yarn.

ADVANTAGEOUS EFFECTS OF INVENTION

The polyamide multifilament of the present invention is a polyamide multifilament having high flatness and high hooking strength. When the polyamide multifilament yarn and the core elastic yarn of the present invention are used for a silk stocking, the silk stocking can be obtained which is excellent in durability, transparency, soft hand, and appearance.

Drawings

Fig. 1 is a schematic view showing one embodiment of a production apparatus that can be preferably used in the method for producing a polyamide multifilament of the present invention.

Fig. 2 is a schematic view showing an embodiment of a manufacturing apparatus used in a manufacturing method exemplified as a comparison of the manufacturing method of the polyamide multifilament of the present invention.

Fig. 3 is a schematic cross-sectional schematic view showing a spinning spinneret and a heating cylinder which can be preferably used in the method for producing a polyamide multifilament.

Fig. 4(a) and 4(b) show an embodiment of a rotary nozzle that can be preferably used in the method for producing a polyamide multifilament according to the present invention, fig. 4(a) is a schematic view of the entire rotary nozzle, and fig. 4(b) is a cross-sectional view a-a' of fig. 4 (a).

Fig. 5 is a view showing an embodiment of the discharge hole shape of a spinning spinneret preferably used in the method for producing a polyamide multifilament of the present invention.

FIG. 6 is a cross-sectional view of a fiber showing one embodiment of the multifilament polyamide yarn of the present invention.

Detailed Description

The present invention will be described in more detail below. In the present specification, "mass" and "weight" have the same meaning.

[ multifilament polyamide ]

The polyamide constituting the polyamide multifilament according to the embodiment of the present invention is a resin composed of a high molecular weight material in which so-called hydrocarbon groups are linked to each other in the main chain via amide bonds. The polyamide is excellent in yarn formability and mechanical properties. Examples of the polyamide include polycaprolactam (nylon 6) and polyhexamethylene adipamide (nylon 66), and polycaprolactam (nylon 6) is preferable because it is less likely to gel and has good yarn formability.

Here, the polyamide may contain 80 mol% or more of a component mainly constituting a unit of the polyamide. The polyamide preferably contains 90 mol% or more of a component constituting a unit. In polycaprolactam, epsilon-caprolactam, which mainly constitutes polycaprolactam, is a component to be a unit. In addition, hexamethyleneadipamide, which mainly constitutes polyhexamethyleneadipamide, is a component constituting a unit.

The other components contained in the polyamide are not particularly limited, and examples thereof include aminocarboxylic acids, dicarboxylic acids, diamines, and the like, which are monomers constituting polyhexamethylene dodecanamide, polyhexamethylene adipamide, polyhexamethylene azelamide, polyhexamethylene sebacamide, polyhexamethylene dodecanamide, polymetaxylylene adipamide, polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, and the like.

In order to effectively exhibit the effects of the present invention, it is preferable that the polyamide does not contain various additives such as a matting agent typified by titanium oxide, but additives such as a heat-resistant agent may be contained as needed within a range not to impair the effects of the present invention. The content thereof is preferably 0.001 to 0.1% by weight based on the polymer (polyamide).

The polyamide multifilament according to the embodiment of the present invention has a total fineness of 6 to 20dtex, a hooking strength of 12cN/dtex or more, and a ratio of a long diameter b to a short diameter a (b/a, hereinafter referred to as "flatness") of a cross section of a single fiber of 1.5 to 5.0. By reducing the total fineness of the polyamide multifilament yarn and increasing the flatness, a silk stocking having high transparency and soft hand can be obtained. On the other hand, polyamide multifilaments having a reduced total fineness and an improved flatness have a reduced yarn strength as compared with circular cross sections because the flat minor axis is smaller than the diameter of the circular cross section, and thus have reduced durability when used in silk stockings. Here, since the silk stockings have a large stress applied to the intersection of the hook point of the needle loop and the sinker loop in terms of the texture structure, the durability of the silk stockings can be evaluated by the hook strength. As a result of intensive studies, it has been found that the total fineness, the hooking strength and the flatness are set within the above ranges in order to provide silk stockings having excellent transparency, excellent texture and excellent durability.

The polyamide multifilament yarn according to the embodiment of the present invention has a total fineness of 6 to 20 dtex. By setting the total fineness within this range, a silk stocking having high transparency and soft hand can be obtained. When the total fineness is 20dtex or less, the transparency and the texture of the silk stockings are improved. When the total fineness is 6dtex or more, the durability of the silk stockings is improved. The total fineness is more preferably 6 to 11 dtex.

The polyamide multifilament yarn according to the embodiment of the present invention has a hook strength of 12cN/dtex or more. By setting the hook strength within this range, the durability of the silk stockings can be improved, and flattening for improving transparency and hand feeling can be achieved. By setting the hook strength to 12cN/dtex or more, the durability, transparency and beauty of the silk stockings are improved. The higher the hooking strength, the better, but in the present invention, the upper limit thereof is about 17 cN/dtex. The hooking strength is preferably 13cN/dtex or more. The hooking strength was measured based on "8.7 hooking strength" of JIS L1013 (2010).

The breakage of the silk stockings often occurs when the stockings are worn by being strongly pulled from the toes to the thighs. In this case, in the case of the silk stocking knitted fabric, the higher the fineness and the flatness of the polyamide multifilament yarn, the less the yarn (filament) can withstand the stress applied to the hook point of the needle loop and the sinker loop, and the more easily the yarn is broken. Therefore, it has been found that not only the strength in the fiber axis direction (tensile strength) but also the hook strength is improved, and it is also important to improve the durability of the silk stockings. That is, in addition to the strength (tensile strength) in the fiber axis direction of the conventional polyamide filament, the durability of the silk stocking is improved by increasing the strength (hook strength) of the stress concentration portion at the hook point between the needle loop and the sinker loop.

The polyamide multifilament yarn according to an embodiment of the present invention has a flat fiber cross section having a flatness of 1.5 to 5.0, which is represented by the ratio (b/a) of the major axis b to the minor axis a. By setting the flatness within this range, the bending flexibility of the fiber is improved, and a silk stocking having excellent hand feeling can be obtained. Further, since the covering property of the covering yarn is made uniform by the high bending flexibility, a silk stocking excellent in transparency and appearance can be obtained. When the flatness is 1.5 or more, the feeling, transparency, and appearance of the silk stockings are improved. When the flatness is 5.0 or less, the fabric is excellent in hand, transparency and appearance, and the durability of the silk stockings can be made sufficient without excessively low oriented crystallization of the polymer (polyamide). The flatness is preferably 2.5 to 4.0. Fig. 6 shows one embodiment of a fiber cross section of a polyamide multifilament according to an embodiment of the present invention.

The cross-sectional shape of the polyamide multifilament yarn according to the embodiment of the present invention is not particularly limited as long as it has a flat shape, and the surface morphology is not particularly limited. For example, the polyamide multifilament yarn according to the embodiment of the present invention may have a lens-shaped cross section, a bean-shaped cross section, or a profile cross section having 3 to 8 convex portions and the same number of concave portions.

The polyamide multifilament yarn according to the embodiment of the present invention preferably has a tensile strength at 15% elongation (hereinafter referred to as "15% strength") of 5.0cN/dtex or more, which is one index of the physical properties of the yarn. The 15% strength was measured based on "8.5 tensile strength and elongation" of JIS L1013 (2010). A tensile strength-elongation curve was plotted, and a value obtained by dividing a tensile strength (cN) at 15% elongation by a fineness was taken as a 15% strength. The 15% strength is a value simply indicating the fiber modulus, and if the 15% strength is high, it indicates that the gradient of the tensile strength-elongation curve is high and the fiber modulus is high, while if the 15% strength is low, it indicates that the gradient of the tensile strength-elongation curve is low and the fiber modulus is low.

As described later, the polyamide multifilament yarn according to the embodiment of the present invention can realize a high fiber modulus without fuzz by performing multi-stage, high-ratio drawing. When the 15% strength is within the above range, the balloon (balloon) in the coating step can be stabilized without being loosened, and the coating property can be made uniform. That is, by obtaining a covering yarn having excellent uniform covering properties, a silk stocking having excellent transparency and excellent aesthetic properties of a knitted fabric can be obtained. More preferably, the 15% strength is 5.5 to 6.5 cN/dtex.

The polyamide multifilament yarn according to the embodiment of the present invention preferably has a tensile strength of 6.5cN/dtex or more. When the tensile strength is 6.5cN/dtex or more, the orientation crystallization of the polymer (polyamide) is good, and the hook strength is improved. More preferably, the tensile strength is 6.8 to 7.3 cN/dtex.

[ Process for producing Polyamide multifilament ]

Next, an example of a method for producing a polyamide multifilament yarn according to an embodiment of the present invention will be specifically described. Fig. 1 is a schematic view showing one embodiment of a production apparatus preferably used in the method for producing a polyamide multifilament according to the embodiment of the present invention.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, first, a polyamide polymer is melted, metered and conveyed by a gear pump, and finally extruded from discharge holes provided in the spinning spinneret 1 to form respective filaments. As shown in fig. 1, the filaments discharged from the spinning spinneret 1 are cooled and solidified to room temperature by a gas supply device 2 for blowing steam to suppress the contamination of the spinning spinneret with time, a heating tube 3 provided so as to surround the entire circumference to gradually cool the filaments, and a cooling device 4. Then, an oil agent is applied to each filament by an oil supply device 5, and each filament is bundled to form a multifilament, and bundling properties are imparted by a fluid rotating nozzle device 6. Then, the multifilament yarn is subjected to secondary drawing in an extraction (drawing) roller 7, a 1 st drawing roller 8 and a2 nd drawing roller 9, and is relaxed in a relaxation roller 10. The loosened multifilament yarn is twisted by a twist-imparting device 11 and wound by a winding device 12.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, the relative viscosity of sulfuric acid of the polyamide is preferably 2.5 to 4.0. When the relative viscosity of sulfuric acid of the polyamide is within this range, a polyamide multifilament yarn having high hook strength, 15% strength and tensile strength can be obtained.

The melting temperature when the polyamide is melted is preferably higher than the melting point (Tm) of the polyamide by 20 ℃ (Tm +20 ℃) and lower than (Tm +95 ℃).

In order to achieve a desired flatness and high strength in the production of the polyamide multifilament yarn according to the embodiment of the present invention, it is necessary to set the discharge linear velocity to an appropriate value by appropriately adjusting the discharge holes of the spinning spinneret 1. Fig. 5 shows an embodiment of the hole shape of the discharge hole. By designing the single-hole discharge area of the spinning spinneret 1 to be small, the discharge linear velocity of the polymer can be increased. Therefore, stress can be reduced between the spinneret surface and the extraction roller, orientation of the polymer can be suppressed, the mechanical draw ratio can be increased, and high strength can be easily achieved. The discharge linear velocity is a value obtained by dividing the discharge amount by the discharge hole area, and is preferably 25 to 50 m/min, more preferably 30 to 40 m/min.

Conventionally, in a spinning spinneret, in order to achieve a desired flatness, it is necessary to increase the discharge hole length N in the radial direction of the discharge hole (conventional technique). In this case, the single-hole discharge area of the spinning spinneret 1 increases, and as a result, the discharge linear velocity of the polymer decreases, and the desired strength cannot be obtained. In contrast, the discharge hole width H in the short diameter direction is minimized without increasing the discharge hole length N in the long diameter direction, and the flatness can be dramatically improved. According to this method, the single-hole discharge area of the spinning spinneret 1 can be reduced while improving the flatness, and a range of a desired discharge linear velocity can be adopted. As a result, the yarn can be made to have high strength. The discharge hole width H is preferably 0.060 to 0.080mm, and more preferably 0.065 to 0.075 mm.

The cooling conditions for each filament are generally set to conditions for increasing the solidification point (quenching conditions) in order to achieve high flatness. In order to achieve high strength, as described in patent document 2, conditions (slow cooling conditions) are generally set to promote relaxation of polymer orientation and to lower the solidification point, such as maintaining the atmospheric temperature under the spinneret at a high temperature. That is, conventionally, in order to achieve both high flatness and high strength as in the case of the polyamide multifilament of the present invention, there has been a contradiction in terms of method. Therefore, in the present invention, in order to analyze a dense temperature profile and achieve a desired flatness and high strength, it has been found that a slow cooling zone for maintaining an atmospheric temperature at a high temperature is provided under a spinneret to sufficiently promote relaxation of the orientation of the polymer, and then the polymer is rapidly solidified in the cooling zone.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, as shown in fig. 3, a heating cylinder 3 is provided above a cooling device 4 so as to surround the entire circumference of each filament. The orientation relaxation of the polyamide discharged from the spinning spinneret 1 can be improved by providing the heating tube 3 above the cooling device 4 and setting the temperature of the atmosphere in the heating tube 3 to be preferably in the range of 280 to 310 ℃. By promoting the orientation relaxation in the slow cooling region from the spinneret surface to the lower surface of the heating cylinder, it is possible to achieve a desired high strength such as a hook strength. When the heating cylinder 3 is not provided, the slow cooling region disappears, and the orientation from the spinneret surface to the cooling is not slow enough, so that it is difficult to achieve a desired high strength such as a hook strength.

The heating tube length L varies depending on the fineness of the multifilament yarn, but is preferably 30 to 90 mm. By setting the heating cylinder length L to 30mm or more, a distance sufficient to promote relaxation of polymer orientation is obtained, and high strength is easily achieved. Further, by setting the heating cylinder length L to 90mm or less, a desired flatness can be easily achieved. The heating cylinder length L is more preferably 40-70 mm.

In addition, the heating cylinder 3 is preferably multilayered. In the region of fine fineness such as the polyamide multifilament yarn according to the embodiment of the present invention, if the temperature distribution in the heating cylinder 3 is constant, the state of thermal convection is likely to be disturbed, which affects the solidified state of each filament and causes deterioration of yarn unevenness (U%). Therefore, by making the heating cylinder 3 have a plurality of layers, the temperature setting is gradually lowered from the upper layer to the lower layer, and the heat convection from the upper layer to the lower layer is intentionally formed. Further, by providing the downflow flow in the same direction as the accompanied flow of the yarn, disturbance of the heat convection in the heating tube 3 can be suppressed, yarn waving is small, and a multifilament with small yarn unevenness (U%) can be obtained. The multilayer heating cylinder is preferably composed of 2 or more layers, and the length of a single layer of the multilayer heating cylinder is preferably in the range of 10 to 25 mm.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, any of a cooling device that blows out cooling rectification wind from a fixed direction, a ring-shaped cooling device that blows out cooling rectification wind from the outer peripheral side to the center side, a ring-shaped cooling device that blows out cooling rectification wind from the center side to the outer peripheral side, and the like can be used as the cooling device 4.

To achieve the desired flatness, the cure point of the polymer (polyamide) needs to be increased. This is because the elastic force acting on the polymer (polyamide) acts in the direction of minimizing the surface area, and therefore, faces outward, thereby shortening the working time thereof. That is, the polymer (polyamide) coming out of the lower surface of the heating cylinder 3 and entering the cooling zone needs to have the solidification point as close as possible to the upper end of the cooling zone. In order to obtain a desired flatness, it is preferable that a vertical distance LS (hereinafter referred to as a cooling start distance LS) from the lower surface of the spinning spinneret 1 to the upper end of the cooling air blowing section of the cooling device 4 shown in fig. 1 is in a range of 130mm or less. From the viewpoint of the knoop heat exchange type, it is preferable to increase the cooling air speed as an effective means for bringing the solidification point close to the upper end, and the range thereof also depends on the range of the single fiber fineness, but it is preferable that the average value is in the range of 30.0 to 40.0 m/min in the section from the upper end face to the lower end face of the cooling zone. When the cooling wind speed is 30.0 m/min or more, the heat exchange speed of the polymer (polyamide) becomes high, and the solidification point approaches the upper end face of the cooling region, so that the desired flatness can be easily achieved. On the other hand, the cooling wind speed is preferably 40 m/min or less from the viewpoint of operability.

Like the cooling wind speed, the cooling wind temperature in the cooling area is also an important factor in the heat exchange. The cooling air temperature is preferably 20 ℃ or lower. When the cooling air temperature is 20 ℃ or lower, the heat exchange rate of the polymer (polyamide) becomes high, and the solidification point approaches the upper end face of the cooling zone, so that the desired flatness can be easily achieved.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, the position of the oiling device 5, that is, the vertical distance Lg (hereinafter, referred to as the oiling position Lg) from the lower surface of the spinning spinneret 1 to the oiling nozzle position of the oiling device 5 in fig. 1, depends on the fineness of the single yarn and the cooling efficiency of the filament from the cooling device 4, but is preferably 800 to 1500 mm. The oil supply position Lg is more preferably 1000-1300 mm. When the oiling position Lg is 800mm or more, the filament temperature is lowered to an appropriate level at the time of finish application, and when 1500mm or less, yarn waving due to a down draft is also small, and a multifilament with low yarn unevenness (U%) can be obtained. When the oiling position Lg is 1500mm or less, the distance from the solidification point to the oiling position becomes shorter, and the spinning tension decreases with the decrease in flow. This suppresses the spinning orientation and improves the stretchability, and is therefore preferable from the viewpoint of high strength, such as improvement in hook strength. When the oiling position Lg is 800mm or more, the yarn from the spinneret to the oiling guide is appropriately bent and is less susceptible to the influence of friction of the guide, and the reduction of high strength such as improvement of hooking strength is reduced.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, it is preferable to provide the fluid rotating nozzle device 6 in front of the drawing roll 7. The fluid rotating type nozzle (rotating nozzle) has a shape shown by reference numeral 6a in fig. 4(a) and 4(b), and imparts a yarn convergence property by a swirling flow W from one direction in the tube. The length LA of the rotary nozzle varies depending on the fineness of the multifilament, but is preferably 5 to 50mm from the viewpoint of imparting the bundling property.

The discharge pressure of the swirling flow W is preferably 0.05 to 0.20 MPa. By setting the discharge pressure in this range, it is possible to impart appropriate bundling properties to the filaments, and the reduction in stretchability during stretching under high tension is small, and scattering of the monofilaments during stretching is less likely to occur. Therefore, even if the fineness is reduced, the polyamide multifilament having less fuzz can be obtained.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, the drawing is preferably a multi-stage drawing of 2 stages or more. In the case of 1-stage drawing, when high-magnification drawing is performed to obtain a high-fiber-modulus and high-strength raw yarn, the drawing tension is increased, and the drawing point is located on the draw-off roll, so that the drawing property is deteriorated, the strength is reduced, and fuzzing is likely to occur. By performing the multi-stage drawing of 2 stages or more, the load applied to the yarn during drawing is dispersed, and the drawing point is stabilized between the rolls. Therefore, the drawing property is stable, and the fiber has high strength in the hook strength, 15% strength and tensile strength, and a fiber having a high fiber modulus and a fluffy polyamide multifilament are easily obtained.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, the total draw ratio is preferably in the range of 3.5 to 5.0 times, in order to achieve a hook strength of 12cN/dtex or more. The total stretching ratio is more preferably 3.8 to 4.7 times. The stretch ratio in the first stage is preferably 2.5 to 3.5 times, and more preferably 2.7 to 3.3 times. In addition, in the stretching, it is preferable to heat the extraction roll 7 to 40 to 60 ℃, the 1 st stretching roll 8 to 130 to 170 ℃, and the 2 nd stretching roll 9 to 150 to 200 ℃. The speed of the extraction roller 7 is preferably 500 to 1300 m/min, more preferably 700 to 1100 m/min.

In the production of the polyamide multifilament yarn according to the embodiment of the present invention, it is preferable that the relaxation rates [ (2 nd drawing roll speed-relaxation roll speed)/(relaxation roll speed) × 100] of the 2 nd drawing roll 9 and the relaxation roll 10 are 0 to 1.5%. By setting the relaxation ratio within this range, the heat setting is performed in a state of low relaxation ratio and less relaxation than in the case of producing a general polyamide multifilament. Therefore, the linearity of the molecular chain is improved, the amorphous portion inside the fiber has a uniform and appropriately supported structure, and high strength such as hook strength is easily achieved. If the relaxation rate is more than 1.5%, heat setting is performed in a state where the relaxation is large, and therefore the linearity of the molecular chain is lowered, and it is difficult to achieve high strength such as improvement of hook strength.

For example, by using the conditions in the direct spinning and drawing method shown in FIG. 1, a polyamide multifilament having a total fineness of 6 to 20dtex, a high hooking strength of 12cN/dtex or more, and a high flatness of 1.5 to 5.0 can be obtained.

[ covering elastic yarn ]

The polyamide multifilament yarn according to the embodiment of the present invention can be used as a covering yarn of a core spun yarn.

The elastic core yarn according to the embodiment of the present invention (hereinafter also simply referred to as "core yarn") is an elastic core yarn in which the above polyamide multifilament is disposed as a covered yarn. The core yarn includes a single core yarn in which one layer of a covering yarn is wound around an elastic yarn as a core yarn, and a double core yarn in which two layers of covering yarns are wound around the elastic yarn.

As the elastic yarn, polyurethane elastic fiber, polyamide elastic fiber, polyester elastic fiber, natural rubber fiber, synthetic rubber fiber, butadiene fiber, or the like can be used, and it may be selected as appropriate depending on the elastic property, heat-setting property, durability, and the like. Among these, polyurethane elastic fibers and polyamide elastic fibers are preferable from the viewpoint of the above properties.

The thickness of the elastic yarn varies depending on the kind of the silk stockings and the setting of the tightening pressure, but is usually about 8 to 40dtex in order to achieve both durability, transparency and flexibility. Among them, the preferred thickness of the stretch yarn is 14 to 25 dtex. By setting the thickness of the stretch yarn within this range, the stretch, durability, flexibility, and transparency as silk stockings can be easily realized.

The number of coating twists may be designed in consideration of fineness and shrinkage of the coated yarn, hand feeling of the product, transparency, and durability. If the number of coating twists is increased, the apparent thickness tends to be small, and the transparency tends to be improved, but if the number is too high, the elastic yarn is too tightly stretched, the durability is lowered, and the productivity of the coating process tends to be lowered. Further, if the number of coating twists is too low, the coating property is lowered, and the durability, transparency and flexibility are liable to be lowered. Therefore, for example, in the case of using 6dtex covering yarn for single core yarn, the number of covering twists is preferably designed to the standard of 2000 to 2600T/m. In the production of the double-core yarn, the number of upper twists may be set to 0.7 to 0.95 times the number of twists below the number of upper twists. As the twisting direction, the lower twist and the upper twist may be set in either the same direction or the opposite direction, but in order to suppress the torque, it is preferable to coat in the opposite direction. The draft magnification may be designed to match the target wearing pressure, and for example, the draft magnification is preferably set to 2.5 to 3.5 times.

When the core elastic yarn according to the embodiment of the present invention is manufactured, a covering process by a conventional method may be performed. For example, the processing described in encyclopedia of fibers (Nippon Boehringer Co., Ltd., 14 years, 3 months, 25 days, p439) can be performed. That is, in one example, the elastic yarn is drawn at a constant speed, the covered yarn wound around the H-bobbin is wound around the elastic yarn in advance with a constant number of covered turns in a state where a constant tensile force is applied between the two rollers, and the obtained core elastic yarn is wound around the bobbin.

The polyamide multifilament yarn according to the embodiment of the present invention and the core elastic yarn according to the embodiment of the present invention can be used for a silk stocking in which they are partially used. Among them, silk stockings are preferably used for legs because they exhibit a glossy feeling excellent in transparency, a bare foot feeling, and a shadow effect. Here, the silk stockings include silk stockings typified by panty stockings, and socks, and the leg portion refers to a range from a suspender portion to a toe portion in the case of a panty stocking, for example.

In addition, as the knitting machine of the silk stockings, a general stocking knitting machine can be used, and there is no particular limitation. For example, knitting can be performed by a general method in which a 2-port or 4-port yarn-feeding knitting machine feeds a core yarn to perform knitting. In the case of the single covered yarn, a method of alternately weaving the S-direction covered single covered yarn and the Z-direction covered single covered yarn is preferable. Other methods include interlacing of single-covered yarn with raw silk, interlacing of double-covered yarn with raw silk, and knitting of double-covered yarn with double-covered yarn. Further, the number of needles used in the knitting machine is generally 360 to 474, and the smaller the number of needles, the higher the transparency but the durability tends to be poor. The more the number of needles is, the higher the durability is, but the transparency tends to be lowered. Therefore, the number of needles can be selected according to the fineness of the covering yarn or elastic yarn to be used and the target durability, transparency, and flexibility. As an example, the coated yarn is preferably 6 to 20dtex, and the number of needles is preferably 400 to 440.

The dyeing after knitting, the subsequent post-processing, and the final setting conditions may be performed by a known method. As the dye, an acid dye or a reactive dye may be used. Further, the color and the like are not limited.

Examples

The present invention will be described in more detail below with reference to examples.

Hereinafter, the evaluation method is described for each evaluation item.

A. Tensile strength, elongation product of strength, 15% strength

The fiber sample was measured based on "8.5 tensile strength and elongation" of JIS L1013(2010) to draw a tensile strength-elongation curve. As test conditions, the type of the test machine was a constant-speed elongation type, the grip interval was 50cm, and the tensile speed was 50 cm/min. When the tensile strength at break is lower than the maximum strength, the maximum tensile strength and the elongation at break are measured.

The elongation, tensile strength, product of tensile strengths and 15% strength were determined by the following formulas.

Elongation is elongation at break (%)

Tensile Strength (tensile Strength at Break (cN)/Total denier (dtex)

Tensile elongation product { tensile strength (cN/dtex) } × { elongation (%) +100}/100 }

Tensile Strength (cN)/Total denier (dtex) at 15% elongation

B. Hook strength

A hook was formed in the center of the nip of the sample based on "8.7 hook strength" of JIS L1013(2010), and the measurement was performed under the same conditions as the above-described strength and elongation. The hooking strength is determined by the following equation.

Hooking Strength tensile Strength at Break (cN)/Total denier (dtex)

C. Total fineness, single fineness

The fiber sample (multifilament) was placed on a 1.125 m/circumference measuring tape, rotated 500 turns to prepare a loop strand, dried by a hot air dryer (105. + -. 2 ℃ C. times.60 minutes), weighed by balance, and multiplied by the standard moisture content to calculate the total fineness. Further, the standard water content was 4.5%. The calculated total fineness was divided by the number of filaments to obtain a value as the fineness of a single filament.

D. Relative viscosity of sulfuric acid (. eta.r)

A0.25 g polyamide chip sample was dissolved in 1g of 100ml of 98 mass% sulfuric acid, and the flow-down time at 25 ℃ was measured using an Ostwald viscometer (T1). Subsequently, the downflow time of sulfuric acid having a concentration of only 98 mass% was measured (T2). The ratio of T1 to T2, namely T1/T2, was taken as the relative viscosity of sulfuric acid.

E. Yarn unevenness (U%)

Using a USTER (registered trademark) TESTER IV manufactured by Uster Technologies, Inc., a specimen length: 500m, measurement linear velocity V: 100 m/min, twist (rotational speed): s twist, 30000/min, 1/2Inert, fiber samples were measured.

F. Flatness and cross-sectional shape

A thin section was cut along the cross-sectional direction at an arbitrary position of the fiber used for the covering wire, all filaments of the fiber cross-section were photographed by a transmission microscope, printed out at 1000-fold magnification from a printer (SCT-P66, manufactured by mitsubishi electric corporation), scanned in (black and white photograph, 400dpi) by a scanner (GT-5500 WINS, manufactured by seiko epriston corporation), and the ratio L/S of the diameter L of the circumscribed circle OL to the diameter S of the inscribed circle IC was calculated by using image processing software (WinROOF, manufactured by sangu corporation) in a state of being enlarged to 1500-fold on a display, and the flatness was found as b/a from the number average of values obtained from all filaments. Further, whether the fiber has a flat fiber cross section (elliptical cross-sectional shape) or not was visually confirmed from the photographed photograph.

G. Evaluation of Silk stockings

(a) Durability

The breaking strength at any 3 points was measured based on the mullen method (method a) breaking strength test method described in JIS L1096(2010), and the average value thereof was evaluated by the following criteria for grade 4. A. B is qualified in durability.

A：1.6kg/cm²The above

B：1.4kg/cm²Above and less than 1.6kg/cm²

C：1.2kg/cm²Above and less than 1.4kg/cm²

D: less than 1.2kg/cm²

(b) Flexibility

The silk stocking products were evaluated for flexibility by examiners (5 persons) who had a large experience in hand evaluation. A lace knitted fabric produced by the same method as in example 1 using 11dtex, 8-filament and nylon 6 multifilament with a circular cross section was used as a reference and subjected to relative evaluation. As a result, the evaluation score of each examiner was obtained, and the average value of 5 examiners (rounded up to the decimal point) was: 5 is A, 4 is B, 3 is C, and 1-2 is D. A. B is qualified flexibility.

And 5, dividing: is very excellent

And 4, dividing: is slightly superior to

And 3, dividing: general purpose

And 2, dividing: a little bit worse

1 minute: difference (D)

(c) Transparency of

As the evaluation sample, a sample which was refined, undyed and subjected to a finishing process thereafter was used, and the evaluation was performed using a white gray cloth. A. B is that the transparency is qualified.

A: is very excellent

B: is slightly superior to

C: general purpose

D: a little bit worse

(d) Aesthetic property of knitting

As the evaluation sample, a sample which was refined, undyed and subjected to a finishing process thereafter was used, and the evaluation was performed using a white gray cloth. A. And B, the weaving aesthetic property is qualified.

A: is very excellent

B: is slightly superior to

C: general purpose

D: a little bit worse

[ example 1 ]

(production of Polyamide multifilament)

As the polyamide, a nylon 6 sheet having a sulfuric acid relative viscosity (. eta.r) of 3.3 and a melting point of 225 ℃ was dried by a conventional method so that the water content was 0.03 mass% or less. The obtained nylon 6 sheet was melted at a spinning temperature (melting temperature) of 298 ℃ and discharged from the spinning spinneret 1 (discharge amount 18.9 g/min). The number of holes of the spinning spinneret 1 was 36, 6 filaments/spinneret, and as shown in fig. 5, a spinneret having discharge holes with circular holes at both ends of a slit (when the discharge hole width was H, the discharge hole length was N, and the diameter of the circular hole was D, N/H was 4.9, D/H was 1.4, and the discharge hole width H was 0.07mm) was used. The spinning machine performs spinning using the spinning machine of the form shown in fig. 1. The heating cylinder 3 used was a heating cylinder having a heating cylinder length L of 50mm, and the atmosphere temperature in the heating cylinder 3 was set to 290 ℃. The filaments discharged from the spinning spinneret 1 were passed through a cooling device 4 having a cooling start distance LS of 102mm, a cooling air temperature of 18 ℃ and a cooling air speed of 38 m/min, and the filaments (filaments) were cooled and solidified to room temperature. Then, the oiling position Lg from the spinneret surface was set to 1300mm, an oiling agent was applied by an oiling device 5, and the filaments were bundled to form a multifilament, and bundling was applied by a fluid rotating nozzle device 6 having a rotating nozzle length LA of 25 mm. As shown in fig. 4, in the fluid rotating nozzle device 6, high-pressure air (swirling flow W) is injected from the direction of the arrow toward the moving filaments (multifilament 20) to impart the bundling property. The pressure of the injected air (swirling flow W) was 0.1MPa (flow rate: 15L/min). Then, the stretching of the 1 st stage is performed so that the stretching magnification between the draw-out roll 7 and the 1 st stretching roll 8 is 2.9 times, and the stretching of the 2 nd stage is performed so that the stretching magnification between the 1 st stretching roll 8 and the 2 nd stretching roll 9 is 1.5 times. Then, 2.0% relaxation heat treatment was performed between the 2 nd drawing roll 9 and the relaxation roll 10, and after the yarn (multifilament) was entangled by the entanglement-imparting device 11, the yarn was wound at 3000 m/min by the winding device 12. At this time, the total draw ratio represented by the ratio of the draw-out speed (speed of draw-out roll 7) to the draw-out speed (speed of 2 nd draw-out roll 9) was adjusted to 4.3 times. The surface temperature of each roll was set to 40 ℃ for the draw roll, 155 ℃ for the 1 st draw roll, 185 ℃ for the 2 nd draw roll, and room temperature for the relax roll. The interlacing treatment is performed by jetting high-pressure air to the moving yarn (multifilament) from a right-angle direction in the interlacing device 11. The pressure of the injected air was 0.2 MPa. Thus, a nylon 6 multifilament having an elliptical cross-sectional shape and a total fineness of 9dtex and 6 filaments was obtained. The obtained nylon 6 multifilament yarn was evaluated, and the results are shown in table 1.

(production of Silk stockings)

The obtained multifilament was used as a covering yarn for covering elastic yarn, and 18 denier polyurethane elastic yarn (manufactured by Nisshinbo Co., Ltd., Mobilon (registered trademark) K-L22T) was used as a core yarn, and the yarn was drawn by 3.5 times and covered with a covering twist number of 2400 t/m.

Using the above-mentioned core-spun elastic yarn, a super4 knitting machine (the number of stitches is 400) manufactured by yokoku co, the S-direction single core-spun yarn and the Z-direction single core-spun yarn were alternately supplied to a yarn feeding port of the knitting machine, and a leg knitted fabric was knitted with only the core-spun yarn. Then, the resulting mixture was refined at 60 ℃ for 30 minutes using soaping agent (ニューサンレックス (registered trademark) E; 2g/L (manufactured by Niwaki chemical Co., Ltd.), dyed at a bath ratio of 1:50 and 100 ℃ for 60 minutes to a beige color of pantyhose (Telon Red A2R; 0.14% owf, Telon yellow A2R; 0.16% owf, Telon blue A2R; 0.12% owf (manufactured by DyStar), leveling agent (SeraGalN-FS; 0.5% owf (manufactured by DyStar)), pH slipping agent (ammonium sulfate; 4.0% owf), dyed at a bath ratio of 1:50 and 100 ℃ for 60 minutes to a beige color of pantyhose, and finally treated at 30 ℃ for 90 minutes with sodium carbonate (final treatment) using fixing agent (ハイフィックス (registered trademark) SW-A; 5% owf (manufactured by Yoghurt chemical Co., Ltd.)), (NWH 201; 1% owf (センカ) to a finish at 30 seconds), making into panty hose product. The leg portions of the resulting pantyhose products were evaluated and the results are shown in table 1.

The obtained pantyhose are excellent in all of durability, flexibility, transparency, and knitting beauty.

[ example 2 ]

Nylon 6 multifilament having a total fineness of 6dtex and 4 filaments was obtained in the same manner as in example 1, except that the number of holes and the discharge amount of the spinning spinneret were changed, to obtain stockings. The evaluation results are shown in Table 1.

[ example 3 ]

A nylon 6 multifilament having a total fineness of 20dtex and 14 filaments was obtained in the same manner as in example 1, except that the number of holes and the discharge amount of the spinning spinneret were changed, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 4 ]

The stretching in the 1 st stage is performed so that the stretching magnification between the draw roll 7 and the 1 st stretching roll 8 is 2.9 times, and the stretching in the 2 nd stage is performed so that the stretching magnification between the 1 st stretching roll 8 and the 2 nd stretching roll 9 is 1.2 times. Further, the total draw ratio represented by the ratio of the draw-out speed (speed of the draw-out roller 7) to the draw-out speed (speed of the 2 nd draw-out roller 9) was adjusted to 3.5 times. Otherwise, a nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 5 ]

The stretching in the 1 st stage is performed so that the stretching magnification between the draw roll 7 and the 1 st stretching roll 8 is 3.4 times, and the stretching in the 2 nd stage is performed so that the stretching magnification between the 1 st stretching roll 8 and the 2 nd stretching roll 9 is 1.4 times. Further, the total draw ratio represented by the ratio of the draw-out speed (speed of the draw-out roller 7) to the draw-out speed (speed of the 2 nd draw-out roller 9) was adjusted to 5.0 times. Otherwise, a nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 6 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained by the same method as in example 1 except that the discharge hole of the spinning spinneret was changed to 3.9 in terms of N/H when the discharge hole width was H and the discharge hole length was N, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 7 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained by the same method as in example 1 except that the discharge hole of the spinning spinneret was changed to 8.8 in terms of N/H when the discharge hole width was H and the discharge hole length was N, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 8 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the discharge hole width H of the spinning spinneret was changed to 0.08mm, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 9 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the discharge hole width H of the spinning spinneret was changed to 0.06mm, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 10 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the cooling air flow rate was changed to 30 m/min, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ example 11 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the heating cylinder length L was changed to 75mm, to obtain a silk stocking. The evaluation results are shown in Table 1.

[ comparative example 1 ]

As shown in fig. 2, the 2 nd stretching roller 9 and the relaxation roller 10 are not provided, and the draw-out roller 7 and the 1 st stretching roller 8 have a draw ratio of 2.7 times between the draw-out roller 7 and the 1 st stretching roller 8. The spinning spinneret 1 used was a spinneret having a discharge hole width H of 0.10mm, and the filaments discharged from the spinning spinneret 1 were passed through a cooling device 4 having an air speed of 25 m/min. Otherwise, a nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 to obtain a silk stocking. The evaluation results are shown in Table 2.

In the multifilament of comparative example 1 produced under the conditions of patent document 1, only the conditions for improving the tensile product as in patent document 2 are applied, and the flatness is reduced. In addition, the hooking strength is low. Therefore, the silk stockings are inferior in flexibility, transparency, knitting beauty and durability.

[ comparative example 2 ]

A nylon 6 multifilament having a total fineness of 5dtex and 3 filaments was obtained in the same manner as in example 1, except that the number of holes and the discharge amount of the spinning spinneret were changed, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 2 has a small fineness, and therefore not only the yarn strength but also the hooking strength is reduced. Therefore, the obtained silk stockings have poor durability.

[ comparative example 3 ]

Nylon 6 multifilament having a total fineness of 22dtex and 17 filaments was obtained in the same manner as in example 1, except that the number of holes and the discharge amount of the spinning spinneret were changed, to obtain stockings. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 3 had a large fineness, and therefore the resulting stockings had poor flexibility and transparency.

[ comparative example 4 ]

The stretching in the 1 st stage is performed so that the stretching magnification between the draw roll 7 and the 1 st stretching roll 8 is 2.7 times, and the stretching in the 2 nd stage is performed so that the stretching magnification between the 1 st stretching roll 8 and the 2 nd stretching roll 9 is 1.2 times. The adjustment was made so that the total draw ratio represented by the ratio of the draw-out speed (speed of draw-out bar 7) to the drawing speed (speed of 2 nd drawing roll 9) was 3.2 times. Otherwise, a nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 4 had low total draw ratio, so that the hook strength was low, and the durability of the obtained silk stockings was poor.

[ comparative example 5 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained by the same method as in example 1 except that the discharge hole of the spinning spinneret was changed to 3.5 in terms of N/H when the discharge hole width was H and the discharge hole length was N, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 5 had low flatness, and therefore the resulting stockings had poor flexibility, transparency, and knitting appearance.

[ comparative example 6 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained by the same method as in example 1 except that the discharge hole of the spinning spinneret was changed to N/H of 10.7 when the discharge hole width was H and the discharge hole length was N, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 6 had low hooking strength because of high flatness, and the resulting stockings had poor durability.

[ comparative example 7 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the discharge hole width H of the spinning spinneret was changed to 0.09mm, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 7 had a large discharge hole width H, and therefore the discharge linear velocity was lowered, and the hooking strength was lowered. Therefore, the obtained silk stockings have poor durability.

[ comparative example 8 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the heating cylinder length L was changed to 25mm, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 8 had a short heating cylinder length L, an ambient temperature of 250 ℃, and insufficient relaxation of the orientation of the polyamide polymer in the slow cooling region from the spinneret surface to the lower surface of the heating cylinder, and therefore, the flatness was also increased, and the hooking strength was lowered. Therefore, the obtained silk stockings have poor durability.

[ comparative example 9 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the heating cylinder length L was changed to 100mm, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 9 had a long heating cylinder length L, and the cooling start distance LS became long, resulting in a low flatness. Therefore, the obtained silk stockings are inferior in flexibility, transparency and knitting beauty.

[ comparative example 10 ]

A nylon 6 multifilament having a total fineness of 9dtex and 6 filaments was obtained in the same manner as in example 1 except that the cooling air flow rate was changed to 25 m/min, to obtain a silk stocking. The evaluation results are shown in Table 2.

The multifilament obtained in comparative example 10 had a low cooling air speed, and the solidified point was not the upper end surface of the cooling region, resulting in a low flatness. Therefore, the obtained silk stockings are inferior in flexibility, transparency and knitting beauty.

The present invention has been described in detail with reference to the specific embodiments, but it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. The present application is based on the Japanese patent application (Japanese application No. 2018 and 218431) filed on 21/11/2018, the contents of which are incorporated herein by reference.

Description of the reference numerals

1 spinning nozzle

2 gas supply device

3 heating cylinder

4 Cooling device

5 oil supply device

6 fluid rotary nozzle device

6a rotating nozzle

7 draw-out stick

8 st stretching roller

9 nd 2 stretching roller

10 slack roll

11 interlacing device

12 coiling device

20 multifilament yarn

a short diameter

b major axis

Diameter of the D round hole

H discharge hole width

Length of L heating cylinder

LS Cooling Start distance

Lg fuel supply position

Length of LA rotary nozzle

Length of N discharge hole

W swirl flow

Claims

1. A polyamide multifilament having a total fineness of 6 to 20dtex, a hook strength of 12cN/dtex or more, and a flatness of 1.5 to 5.0, which is represented by the ratio b/a of the major diameter b to the minor diameter a of the cross section of a single fiber.

2. The polyamide multifilament according to claim 1, which has a tensile strength of 5.0cN/dtex or more at 15% elongation.

3. A core-spun elastic yarn comprising the polyamide multifilament yarn according to claim 1 or 2 as a covering yarn.