ES3001015T3 - Multifilament polyamide and knitted lace manufactured using the same - Google Patents

Abstract

An embodiment of the present invention provides a high-strength polyamide multifilament capable of being formed into a knitted lace that has excellent durability, in which a pattern can be clearly seen, and that has excellent softness. An embodiment of the present invention relates to a polyamide multifilament characterized by having a single yarn fineness of 0.8 to 7 dtex, a strength of 7.5 to 8.5 cN/dtex, and a knot strength of 6.0 to 7.5 cN/dtex. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Multifilament polyamide and knitted lace manufactured using the same

Technical field

The present invention relates to a polyamide multifilament suitable for knitted lace. More particularly, the present invention relates to a polyamide multifilament which, when used as a lace ground yarn, is capable of providing a knitted lace having excellent durability, a beautiful pattern, and a good texture.

Background of the technique

Polyamide fibers and polyester fibers, which are synthetic fibers, are widely used in apparel and industrial applications due to their excellent mechanical and chemical properties. In particular, polyamide fibers excel in softness, high mechanical strength, colorability, heat resistance, hygroscopicity, and so on, and are therefore widely used in general apparel applications, including hosiery, underwear, and sportswear.

As consumers demand lace, they desire a lace with a beautiful pattern and a smooth texture. In order to make the lace pattern look beautiful, it is necessary to improve the fineness of the threads constituting the background structure. However, as the fineness improves, the mechanical strength of the threads decreases, so greater mechanical strength is desired. Furthermore, as the fineness of the threads constituting the background structure improves, the thread ratio of a pattern thread increases, and therefore, the stress applied to an intersecting portion of the background threads is greater. Consequently, increased durability of the intersecting portion is also desired. Furthermore, in order to soften the texture of the lace, it is strongly desired to improve the fineness of the individual threads constituting the background structure.

In order to increase the mechanical strength of polyamide fibers to be high, for example, Patent Document 1 proposes a nylon-6 fiber for fishing nets having a fineness of 250 dtex to 4400 dtex, which provides net fabric having excellent durability and weather resistance, high mechanical strength and high toughness, and a fishing net using the same.

Patent Document 2 discloses a polyamide fiber having a fineness of 300 dtex to 1,000 dtex, which has excellent shock absorption against shear stress and multidirectional impact, and excellent durability and fatigue resistance when the polyamide fiber is subjected to a knitting process and used for industrial materials, and a knitted material using the fiber.

List of references

Patent documents

Patent Document 1: JP-A-2008-31572

Patent Document 2: JP-A-2004-11082

Summary of the invention

Technical problem

However, since the fibers described in Patent Documents 1 and 2 have a high fineness, the transparency of lace cannot be obtained, and the fibers are not suitable for knitted lace. Furthermore, since the individual yarn has a high monofilament fineness, the texture of the knitted lace is unsatisfactory. An object of the present invention, which overcomes these problems, is to provide a high mechanical strength polyamide multifilament having excellent durability even with the improvement of the fineness and monofilament fineness. More particularly, an object of the present invention is to provide, by using a polyamide multifilament having high mechanical strength and high knot strength, a knitted lace that has excellent processability through high-order processing and product appearance quality, maintains the same level of mechanical strength as products in the related art, can achieve the improvement of the fineness and monofilament fineness, maintains the durability of the lace, has a beautiful pattern due to the transparency of the background lace yarn, and has an excellent texture.

Solution to the problem

In order to solve the above problem, the present invention relates to a polyamide multifilament having a monofilament fineness of 0.8 dtex to 7 dtex, a mechanical strength of 7.5 cN/dtex to 8.5 cN/dtex, and a knot strength of 6.0 cN/dtex to 7.5 cN/dtex, according to claim 1.

Preferably, the polyamide multifilament has a tensile strength at 15% elongation of 6.1 cN/dtex to 7.5 cN/dtex and preferably has a total fineness of 20 dtex to 44 dtex.

The present invention also relates to a knitted lace produced using the polyamide multifilament as a background lace yarn, and to a method for producing the polyamide multifilament which includes: ejecting a molten polyamide resin from a spinning machine to form filaments;

cool and solidify each of the filaments; and

stretch the obtained filaments,

wherein the method is performed using a polyamide multifilament production device that includes at least:

a spinning machine for ejecting a molten polyamide resin to form filaments;

a heating cylinder to gradually cool the filaments;

a cooling device for cooling and solidifying the filaments;

a fluid swirl generating nozzle device for imparting convergence to the threads by means of a swirling flow;

a take-up roller to collect and stretch the filaments; and

a stretching device for stretching the filaments, and

in which the following conditions (A) to (D) are satisfied:

(A) The heating cylinder is provided above the cooling device;

(B) The fluid swirl generating nozzle device is provided above the take-up roller;

(C) the stretching device is a multi-stage stretching device having two or more stages; and

(D) Low relaxation heat treatment is performed immediately after multi-stage stretching.

Preferably, the method for producing the polyamide multifilament includes performing the relaxation heat treatment between a drawing roller and a relaxation roller at a relaxation ratio of 0 to 1.5% and a heat setting temperature of 150°C to 200°C.

Advantageous effects of the invention

The polyamide multifilament of the present invention is a polyamide multifilament with high mechanical strength and high knot strength. Furthermore, by using the polyamide multifilament of the present invention, it is possible to obtain a knitted lace that has processability through high order processing and product appearance quality, maintains the durability of the lace, has a beautiful pattern due to the transparency of the background lace yarn, and has an excellent texture.

Brief description of the drawings

[Figure 1] Figure 1 shows an embodiment of a production device that can preferably be used to produce a polyamide multifilament according to an embodiment of the present invention.

[Figure 2] Figure 2 shows an embodiment of a production device illustrated as a comparison of the production of the polyamide multifilament according to the embodiment of the present invention.

[Figure 3] Figure 3 is a schematic cross-sectional model diagram showing a spinning machine and a heating cylinder that can be preferably used in the production of the polyamide multifilament according to the embodiment of the present invention.

[Figure 4] Figure 4 shows an embodiment of a swirl generating nozzle that can preferably be used to produce the polyamide multifilament according to the embodiment of the present invention.

Description of realizations

The present invention will be described in more detail below.

The polyamide multifilament according to one embodiment of the present invention includes a polyamide. Such a polyamide is a resin that includes a high-molecular-weight substance in which the so-called hydrocarbon group is attached to the main chain through an amide bond.

Such a polyamide is excellent in spinnability and mechanical properties, and is preferably one that primarily contains polycaproamide (nylon-6) or polyhexamethylene adipamide (nylon-66). One that primarily contains polycaproamide (nylon-6) is more preferred due to its resistance to gelation and satisfactory spinnability.

The above polycaproamide contains g-caprolactam as a constitutional unit, and 80 mol % or more thereof is constituted by g-caprolactam. The above polycaproamide preferably contains 90 mol % or more of g-caprolactam. The above polyhexamethylene adipamide contains hexamethylenediammonium adipate as a constitutional unit, and 80 mol % or more thereof is constituted by hexamethylenediammonium adipate. The above polyhexamethylene adipamide preferably contains 90 mol % or more of hexamethylenediammonium adipate.

Other components are not particularly limited, and examples thereof include units of aminocarboxylic acids, dicarboxylic acids, diamines, and the like, which are monomers for constituting polydodecanamide, polyhexamethylene adipamide, polyhexamethylene azelamide, polyhexamethylene bacamide, polyhexamethylene decanamide, poly-m-xylene adipamide, polyhexamethylene terephthalamide, polyhexamethylene isophthalamide, and the like.

In order to effectively achieve the effects of the present invention, it is preferable that the polyamide not contain any of the various additives, including tarnishing agents such as titanium oxide. However, the polyamide may contain various additives, for example, a heat resistance improver, provided that the inclusion thereof does not impair the effects of the present invention. The additives may be mixed as needed in a content in the range of 0.001% by weight to 0.1% by weight relative to the polymer.

The polyamide multifilament according to an embodiment of the present invention is characterized in that the monofilament fineness, mechanical strength and knot strength thereof are all within the specific ranges described above.

Typically, improving the fineness of the polyamide multifilament can result in knitted lace with increased transparency of the ground lace yarn and a beautiful pattern, but this reduces the product's mechanical strength and durability. Furthermore, as the yarn ratio of the pattern yarn increases, the stress applied to the ground yarn at the intersection increases. Therefore, to maintain durability, it is necessary to increase the mechanical strength and knot strength. Furthermore, to soften the texture of the lace, it is necessary to improve the fineness of the monofilament.

Therefore, the present inventors have diligently conducted research and have discovered that, in order to provide a knitted lace having excellent texture and durability, increased transparency of the background lace yarn, and a beautiful pattern, it is important to set the monofilament fineness, mechanical strength, and knot strength within the ranges specified above.

The polyamide multifilament according to the embodiment of the present invention has a monofilament fineness of 0.8 dtex to 7 dtex. Within such a range, a lace having a soft texture is obtained. In the case where the monofilament fineness is greater than 7 dtex, the texture of the lace becomes stiff. In the case where the monofilament fineness is less than 0.8 dtex, due to a high tension state, friction on a guide, etc., in a spinning step and a high-order processing step, the mechanical strength is reduced and fuzzing is likely to occur, and filament breakage increases in the high-order processing step and the mechanical strength and appearance quality of the product are reduced. The monofilament fineness is preferably 3.0 dtex to 6.6 dtex.

The polyamide multifilament according to the embodiment of the present invention has a mechanical strength of 7.5 cN/dtex to 8.5 cN/dtex. Within such a range, the durability of the lace is improved, and the fineness can be improved to achieve transparency. In the case where the mechanical strength is less than 7.5 cN/dtex, the durability of the lace is reduced. In the case where the mechanical strength is greater than 8.5 cN/dtex, due to the high tension state, friction on the guide, etc., in the spinning stage and the high-order processing stage, fuzzing is likely to occur, and filament breakage increases in the high-order processing stage and the appearance quality of the product is reduced. The mechanical strength is preferably 7.7 cN/dtex to 8.2 cN/dtex.

Since knitted lace has a special knit structure, the force is concentrated at the intersection point of the ground yarn and the pattern yarn. Therefore, increasing not only the mechanical strength along the fiber axis but also the knot strength is important for the durability of the lace. That is, in addition to improving the mechanical strength along the fiber axis, improving the mechanical strength of a portion of the stress concentration at the intersection point improves the durability of the lace.

Improving knot strength is particularly effective in achieving high fineness in polyamide multifilament yarns. If the fineness of the ground yarn is improved to achieve transparency in the lace ground yarn, the strand ratio of the pattern yarn increases, and as a result, the stress applied to the intersecting portion of the ground yarn increases. Therefore, if knot strength is improved, fineness can be improved.

The polyamide multifilament according to the embodiment of the present invention has a knot strength of 6.0 cN/dtex to 7.5 cN/dtex. Within such a range, the durability of the lace is improved, and the fineness can be improved to achieve transparency. In the case where the knot strength is less than 6.0 cN/dtex, the filament cannot withstand the stress applied to the intersection point of the ground yarn and the pattern yarn and breaks, and the durability of the lace is reduced. The higher the knot strength, the more preferable. However, an upper limit thereof in the present invention is 7.5 cN/dtex. The knot strength is preferably 6.3 cN/dtex to 7.5 cN/dtex.

The polyamide multifilament according to the embodiment of the present invention preferably has a tensile strength at 15% elongation (hereinafter, it may be referred to as “15% strength”), which is an index of raw yarn properties, of 6.1 cN/dtex to 7.5 cN/dtex. The 15% strength is determined by performing a measurement in accordance with JIS L1013(2010), Tensile Strength and Elongation, by drawing a tensile strength-elongation curve, dividing the tensile strength (cN) at 15% elongation by the total fineness, and taking the resulting value as the 15% strength. The 15% strength is a value that roughly represents the modulus of the fiber, and a high 15% strength indicates that the slope of the tensile strength-elongation curve is large and the fiber modulus is high. On the other hand, a low mechanical strength of 15% indicates that the slope of the tensile strength-elongation curve is small and the fiber modulus is low.

As will be described later, the polyamide multifilament according to the embodiment of the present invention is subjected to a high-ratio, multi-stage drawing. A high fiber modulus is achieved by high-ratio drawing, and in particular, the occurrence of fuzz formation is prevented while a high fiber modulus is achieved by multi-stage drawing.

Since the polyamide multifilament according to the embodiment of the present invention has a 15% strength of 6.1 cN/dtex to 7.5 cN/dtex, the appearance quality of the product is improved. In the case where the 15% strength is 6.1 cN/dtex or more, changes in fiber structure and crystal orientation in a dyeing step are small, fiber shrinkage is prevented, and fiber stiffness is easily maintained. That is, dimensional change and shrinkage unevenness during heat setting in a lace production step are reduced, the surface of the textile material becomes smooth and beautiful, and the appearance quality of the product is improved. In the case where the 15% strength is 7.5 cN/dtex or less, filament breakage and the occurrence of fuzz formation are prevented in the high-order processing step, and the appearance quality of the product is improved. The mechanical strength at 15% is preferably 6.4 cN/dtex to 6.9 cN/dtex.

The polyamide multifilament according to the embodiment of the present invention preferably has a strength-elongation product of 9.5 cN/dtex or more. If the strength-elongation product is 9.5 cN/dtex or more, the durability of the lace is good, the filament breakage in the high-order processing step is small, and the processability through high-order processing is good. The polyamide multifilament according to the embodiment of the present invention more preferably has a strength-elongation product of 10.0 cN/dtex or more. The higher the strength-elongation product, the more preferable it is. However, an upper limit thereof in the present invention is about 11.5 cN/dtex.

The polyamide multifilament according to the embodiment of the present invention preferably has a total fineness of 20 dtex to 44 dtex. Within such a range, a knitted lace having a beautiful pattern, an excellent texture, and good durability is obtained. When the total fineness is 44 dtex or less, a knitted lace having increased transparency of the background lace yarn, a beautiful pattern, and a soft texture is obtained. In the case where the total fineness is 20 dtex or more, the mechanical strength and knot strength are sufficient, and the durability of the lace is good. The total fineness is more preferably 22 dtex to 33 dtex.

The polyamide multifilament according to the embodiment of the present invention preferably has a fineness variation value, % U, which is an index of thickness unevenness in the longitudinal direction of the fiber, of 1.2% or less. Within such a range, after the knitted lace is dyed, there are no spots or streaks due to the unevenness of the multifilament, and the appearance quality of the product is good. The fineness variation value, % U, is more preferably 1.0% or less. The smaller the % U is, the more preferable. However, a lower limit thereof in the present invention is about 0.4%.

The cross-sectional shape of the polyamide multifilament according to the embodiment of the present invention is not particularly limited. For example, the multifilament may have a circular cross-section, a flat cross-section, a lens-shaped cross-section, a trifoliate cross-section, a multilobular cross-section, an irregular cross-section having three to eight protrusions and the same number of recesses, a hollow cross-section, or any other common irregular cross-section.

The present invention also provides a method for producing the above polyamide multifilament. The method for producing the polyamide multifilament according to the present invention includes the steps of ejecting a molten polyamide resin from a spinning machine to form filaments, cooling and solidifying each of the filaments, and drawing the obtained filaments.

This method is performed using a polyamide multifilament production device including at least (1) a spinning die for ejecting a molten polyamide resin to form filaments, (2) a heating cylinder for gradually cooling the filaments, (3) a cooling device for cooling and solidifying the filaments, (4) a fluid swirl generating nozzle device for imparting convergence to the yarns by a swirling flow, (5) a take-up roller for collecting and drawing the filaments, and (6) a drawing device for drawing the filaments.

In this method, the following conditions (A) to (D) are satisfied:

(A) The heating cylinder is provided above the cooling device;

(B) The fluid swirl generating nozzle device is provided above the take-up roller;

(C) the stretching device is a multi-stage stretching device having two or more stages; and

(D) Low relaxation heat treatment is performed immediately after multi-stage stretching.

Hereinafter, an example of the method for producing the polyamide multifilament according to the embodiment of the present invention will be described in detail. Figure 1 shows an embodiment of a production device that can preferably be used to produce the polyamide multifilament according to the embodiment of the present invention.

The polyamide multifilament according to the embodiment of the present invention can be produced in the following manner. A polyamide resin is melted, and the polyamide polymer is weighed and transported by a gear pump and finally extruded through ejection holes formed in a spinneret 1, thereby forming filaments. The filaments ejected from the spinneret 1 are passed through the following parts shown in Fig. 1: a gas feeder 2, which ejects steam in order to prevent the spinneret from becoming dirty over time; a heating cylinder 3 arranged for gradual cooling so as to completely surround the ejected filaments; and a cooling device 4. The filaments are cooled to room temperature and solidified in the cooling device 4. Thereafter, a sizing agent is applied to the filaments with a sizing device 5, and the filaments are collected to form a multifilament, which is entangled with a fluid swirl generating nozzle device 6, subjected to a two-stage drawing on a take-up roll 7, a first drawing roll 8, and a second drawing roll 9, and then relaxed on a relaxation roll 10. The relaxed yarns are entangled by an entanglement imparting device 11 and wound by a winding device 12.

In the production of the polyamide multifilament according to the embodiment of the present invention, it is preferable that the polyamide resin has a relative viscosity of sulfuric acid of 2.5 to 4.0. Within such a range, a polyamide multifilament having high mechanical strength, knot strength, and a strength-elongation product can be obtained.

The melting temperature is preferably 20 °C to 95 °C higher than the melting point (Tf) of the polyamide.

In the production of the polyamide multifilament according to the embodiment of the present invention, the heating cylinder 3 is provided above the cooling device 4 so as to completely surround the filaments. By providing the heating cylinder 3 above the cooling device 4 and regulating the temperature of the atmosphere within the heating cylinder so as to be within the range of 100° C. to 300° C., the polyamide polymer ejected from the spinneret 1 can be caused to undergo orientation relaxation without thermal deterioration. As a result of the orientation relaxation due to the gradual cooling from the spinneret surface to the cooling, a multifilament having a high mechanical strength, a high strength at 15%, and a high strength-elongation product can be obtained. In the case where the heating cylinder is omitted, the orientation relaxation due to gradual cooling from the spinning surface to the quench is insufficient and it tends to be difficult to obtain fibers with satisfactory overall strength, 15% strength and strength-elongation product.

In the production of the polyamide multifilament according to the embodiment of the present invention, the heating cylinder preferably has a multi-layer configuration. In the case where the temperature distribution in the heating cylinder is constant in a high fineness or high fineness region of monofilament for garments, such as the polyamide multifilament according to the embodiment of the present invention, thermal convection is prone to become disordered to affect the solidification of the filaments and this is a deterioration factor of the % U. Therefore, a heating cylinder having a multi-layer configuration is provided and temperatures are set to decrease in stages from the upper layers to the lower layers. Therefore, thermal convection from the upper layers to the lower layers is intentionally generated to produce a downward air flow in the same direction as the flow accompanying the filaments. As a result, disordered thermal convection in the heating cylinder is prevented and filament oscillation is reduced, thereby obtaining a multifilament having a small % U.

The length L of the multi-layer heating cylinder, although depending on the fineness of the filaments, is preferably 40 mm to 100 mm. It is preferable for the multi-layer heating cylinder to have two or more layers, and the single-layer length L1 of the multi-layer heating cylinder is preferably within the range of 10 mm to 25 mm.

The atmospheric temperature in the multi-layer heating cylinder is within the range of 100 °C to 300 °C, and it is preferable to form a slight temperature gradient between the layers. For example, in the case where the length L of the multi-layer heating cylinder is 75 mm and the monolayer length L1 is 25 mm, the heating cylinder has a three-layer configuration, the upper layer has an atmospheric temperature of 250 °C to 300 °C, the middle layer has an atmospheric temperature of 200 °C to 250 °C, and the lower layer has an atmospheric temperature of 100 °C to 200 °C.

Due to this configuration, a temperature profile of atmosphere from the spinneret to the cooling can be controlled in stages over the range of 100 °C to 300 °C, thereby obtaining a polyamide multifilament having high mechanical strength, satisfactory 15% strength, high strength-elongation product, and good % U.

In the production of the polyamide multifilament according to the embodiment of the present invention, use may be made of any one of the methods in which the cooling device 4 is a cooling device configured to blow out cooling/rectifying air from a certain direction, or an annular cooling device configured to blow out cooling/rectifying air from the peripheral side toward the center, or an annular cooling device configured to blow out cooling/rectifying air from the center side toward the periphery, or the like.

The vertical distance LS (hereinafter referred to as the “cooling start distance LS”) from the bottom surface of the spinneret to the upper end of the cooling air blowing portion of the cooling device 4 is preferably within the range of 159 mm to 219 mm from the viewpoints of preventing filament wobble and reducing %U, and is more preferably 169 mm to 189 mm. With respect to the speed of the cooling air blown out from the cooling air blowing surface, it is preferable that the speed thereof be within the range of 20.0 m/min to 40.0 m/min as an average for the area from the upper end to the lower end of the cooling air blowing portion, from the viewpoints of the mechanical strength, the strength-elongation product, and %U.

In the production of the polyamide multifilament according to the embodiment of the present invention, the position of the sizing device 5, that is, the vertical distance Lg (hereinafter referred to as “sizing position Lg”) from the bottom surface of the spinning machine to the sizing nozzle position of the sizing device 5 in Fig. 1 , is preferably 800 mm to 1,500 mm, and more preferably 1,000 mm to 1,300 mm, although the distance Lg depends on the fineness of the monofilament and the cooling efficiency of the filaments by the cooling device.

In the case where the distance Lg is 800 mm or more, the temperature of the filaments decreases to a temperature suitable for sizing. In the case where the distance Lg is 1,500 mm or less, the filament oscillation due to the downward airflow is small, and a multifilament having a small % U can be obtained. Furthermore, a case where the distance Lg is 1,500 mm or less is preferred from the standpoints of mechanical strength, the strength-elongation product, and 15% mechanical strength, since the distance from the solidification point to the sizing position is short, resulting in a decreased accompanying flow and reduced spinning tension, and thus, yarn orientation is reduced and drawability is excellent. In the case where the distance Lg is 800 mm or more, the bending of the filaments in the area from the spinneret to the sizing guide is appropriate and the filaments are less likely to be affected by friction on the guide, thus preventing the decrease of the strength-elongation product and the strength to 15%.

In the production of the polyamide multifilament according to the embodiment of the present invention, the fluid vortex generating nozzle device 6 is provided on the take-up roller 7. Patent Document 1 has proposed performing stretching while performing an entanglement treatment during stretching. This is effective in the coarse region of monofilament for industrial use, but in a high-fineness or high-fineness region of monofilament for clothing, such as the polyamide multifilament according to the embodiment of the present invention, when the entanglement treatment is performed during stretching, entanglement of the individual yarn is likely to occur. Furthermore, since an entanglement point is formed, the stretchability of the yarn at the entanglement point is reduced during stretching under a high tension, and the stress is concentrated on the other part where entanglement is not applied. As a result, the mechanical strength is reduced and fuzzing is likely to occur. Therefore, by applying a fluid-vortex generating nozzle before drawing and imparting appropriate convergence to the yarn without entanglement points, uniform drawing is achieved and a polyamide multifilament having high mechanical strength and no lint can be obtained.

The fluid swirl generating nozzle has a shape as shown in Figure 4, and a swirling flow from one direction in the cylinder imparts convergence to the filament. The length LA of the swirl generating nozzle depends on the fineness of the filament, and is preferably 5 mm to 50 mm from the standpoint of imparting convergence.

The vortex flow injection pressure is preferably 0.05 MPa to 0.20 MPa. If the injection pressure is within this range, the filaments can be properly converged, the drawability is not reduced during drawing under high tension, and individual yarn separation does not occur during drawing. Therefore, a high-strength polyamide multifilament without lint formation can be obtained, while improving the fineness and the fineness of the monofilament.

In the production of the polyamide multifilament according to the embodiment of the present invention, the stretching is multi-stage stretching having two or more stages. In the case of one-stage stretching, when high-ratio stretching is applied to obtain a raw yarn having a high fiber modulus and a high mechanical strength, the stretching tension is high and the stretching point is located at the take-up roller. As a result, the drawability deteriorates, the mechanical strength is reduced, and fuzzing is likely to occur. With the multi-stage stretching having two or more stages, the load applied to the yarn during stretching is dispersed, the stretching point is stable between the rollers, the drawability is stable, and a polyamide multifilament having high mechanical strength, a high fiber modulus, an appropriate 15% mechanical strength, and no fuzzing can be obtained.

The total stretching ratio is preferably 3.5 to 5.0 times, and more preferably 3.8 to 4.7 times, so as to obtain the strong elongation range specified in the present invention. The stretching ratio in the first stage is preferably 2.5 to 3.5 times, and more preferably 2.7 to 3.3 times. During stretching, the take-up roller 7 is heated to 40°C to 60°C, the first stretching roller 8 is heated to 130°C to 170°C, and the second stretching roller 9 is heated to 150°C to 200°C (heat-setting temperature). The speed of the take-up roller 7 is preferably 500 m/min to 1,300 m/min, and more preferably 700 m/min to 1,100 m/min.

In the production of the polyamide multifilament according to the embodiment of the present invention, the relaxation ratio [(drawing roller speed - relaxation roller speed)/(relaxation roller speed) * 100] between the drawing roller 9 and the relaxation roller 10 is preferably 0 to 1.5%. Within such a range, the relaxation ratio is lower than that of producing a typical polyamide multifilament, and the heat setting is in a less relaxed state (low relaxation heat treatment), and thus the linearity of the molecular chain is improved, and an amorphous portion in the fiber is stretched uniformly and moderately. Therefore, a polyamide multifilament having high mechanical strength, high knot strength, and a high strength-elongation product can be obtained. In the case where the relaxation ratio is greater than 1.5%, the heat setting is in a state of high relaxation, so that the linearity of the molecular chain is reduced, and the mechanical strength and the strength of the knots are reduced.

For example, in the case where the conditions in the direct spinning drawing method as shown in Figure 1 are adopted, a polyamide multifilament having a high monofilament fineness of 0.8 dtex to 7 dtex, a high mechanical strength of 7.5 cN/dtex to 8.5 cN/dtex, and a high knot strength of 6.0 cN/dtex to 7.5 cN/dtex can be obtained.

The polyamide multifilament according to the embodiment of the present invention is fed as a ground yarn, which is a raw yarn, to a lace knitting machine to knit a lace textile material by a conventional method. The lace textile material may be any of the conventional knitted knitted materials, such as embroidery lace, Raschel lace, or Leaver lace.

Regarding the conditions for dyeing after knitting, after further processing and final fixing, these stages can be carried out using conventional methods. The dyes are not limited to the use of dyes, including acid dyes and reactive dyes, and the dyeing process is not limited in terms of color, etc.

Examples

Hereinafter, the present invention will be described in more detail with reference to examples.

A. Mechanical strength, elongation, strength-elongation product, and 15% strength

A fiber sample was examined according to JIS L1013 (2010), Tensile Strength and Elongation, to draw a tensile strength-elongation curve. The test conditions included a constant-speed extension-type tester, a mandrel-to-mandrel distance of 50 cm, and a stretching rate of 50 cm/min. If the tensile strength at break was lower than the ultimate tensile strength, the ultimate tensile strength and corresponding elongation were measured. The mechanical strength and the strength-elongation product were determined using the following equations.

Elongation = elongation at break (%)

Mechanical strength = [tensile strength at break (cN)]/[total fineness (dtex)]

Product of mechanical strength-elongation = {mechanical strength (cN/dtex)}*{elongation (%) 100}/100 Mechanical strength at 15% = [tensile strength at 15% elongation (cN)]/[total fineness (dtex)] B. Knot strength

According to JIS L1013 (2010), Knot Strength, a knot portion was formed in the center of the sample piece, and the measurement was performed under the same conditions as the previous mechanical strength and elongation measurements. Knot strength was determined using the following equation.

Knot strength = [tensile strength at break (cN)]/[total fineness (dtex)]

C. Total fineness and monofilament fineness

A fiber sample was placed on a sizing reel with a circumference of 1.125 m, and the sizing reel was rotated 500 times to produce a looped hank. The hank was dried in a hot-air drying oven (105±2 °C for 60 min) and weighed using a balance. The measured weight was multiplied by the conventional moisture regain, and the fineness was calculated from the resulting value. The conventional moisture regain was assumed to be 4.5%.

D. Relative viscosity of sulfuric acid (qr)

A polyamide chip sample was dissolved in an amount of 0.25 g in sulfuric acid having a concentration of 98% by mass, such that the sample amount was 1 g per 100 ml of sulfuric acid. Using an Ostwald viscometer, the solution was examined for a flow time (T1) at 25 °C. Subsequently, sulfuric acid alone having a concentration of 98% by mass was examined for a flow time (T2). The ratio of T1 to T2, i.e., T1/T2, was taken as the relative viscosity of sulfuric acid.

E. % of U

Using a USTER TESTER IV device, manufactured by Zellweger Uster AG, a fiber sample was examined under the following conditions: sample length, 500 m; test yarn speed V, 100 m/min; twister (rotation speed), type S at 30,000/min; and semi-inert.

F. Number of lint

The obtained fiber sample was rewound at a speed of 500 m/min, a laser lint detector was installed at a position 2 mm from the yarn being rewound, and the total number of detected defects was converted into the number per 100,000 m and displayed.

G. Assessment of fit

(a) Softness

A lace product was evaluated for relative softness by inspectors (five people) with extensive experience in texture evaluation, using a nylon-6 multifilament having a fineness of 40 dtex and including 4 filaments and taking a knitted lace produced by the same method as in Example 1 as a reference.

The grades evaluated by the inspectors were averaged, and the average was rounded to the nearest whole number. Grades 5, 4, 3, and 1-2 on average were indicated by S, A, B, and C, respectively.

5: very excellent

4: slightly excellent

3: reasonable

2: slightly deficient

1: deficient

S and A were considered acceptable in terms of softness.

(b) Durability

Bursting strength was evaluated as follows. Three arbitrarily selected portions were examined for bursting strength using the bursting strength test method according to JIS L1096 (2010), Mullen type method (Method A), and an average value of the measured values was evaluated in the following four grades.

S: 150 kPa or more

A: 120 kPa or more but less than 150 kPa

B: 110 kPa or more but less than 120 kPa

C: less than 110 kPa

S and A were considered acceptable in terms of durability.

(c) Product appearance quality (lint)

Number of pilling in a lace textile material: The number of pilling portions (a state in which the fibers on the surface of the knitted textile material formed fluff and the fluffs were further intertwined with each other to form small spherical nodules) per roll of the lace textile material was shown according to the following criteria.

S: 0 or more and less than 2

A: 2 or more and less than 5

B: 5 or more and less than 10

C: 10 or more

S and A were considered acceptable in terms of appearance quality.

(d) Capacity to pass through procedure

Suitability for knitting: The number of yarn breaks that occurred during knitting per roll of the lace textile material (80 m) was shown according to the following criteria.

S: 0 or more and less than 5 thread breaks

A: 5 or more and less than 10 thread breaks

B: 10 or more and less than 20 thread breaks

C: 20 or more and less than 30 thread breaks

S and A were considered acceptable in terms of procedural passability.

(e) Appearance quality (pattern appearance)

A product was evaluated for relative pattern appearance by inspectors (five people). The grades evaluated by the inspectors were averaged, and the average was rounded to the nearest whole number. Grades 5, 4, 3, and 1-2 on average were indicated by S, A, B, and C, respectively.

5: very excellent

4: slightly excellent

3: reasonable

2: slightly deficient

1: deficient

S and A were considered acceptable in terms of appearance quality.

[Example 1]

(Production of polyamide multifilament)

Nylon-6 (N6) chips having a relative viscosity of sulfuric acid (qr) of 3.3 and a melting point of 225 °C were dried as polyamide in a conventional method to result in a moisture content of 0.03 mass % or less. The nylon-6 chips thus obtained were melted at a spinning temperature (melting temperature) of 298 °C and ejected from a spinneret (ejecting amount: 38.6 g/min). The spinneret used had 20 holes, which were round and had a diameter of 0.25, and was to produce 4 yarns per spinneret.

Spinning was carried out using a spinning machine having the configuration shown in Figure 1. The heating cylinder used was a two-layer heating cylinder having a heating cylinder length L of 50 mm and monolayer lengths L1 and L2 of 25 mm each. The temperatures were set so that the atmosphere temperature in the upper layer of the heating cylinder was 300 °C and the atmosphere temperature in the lower layer of the heating cylinder was 150 °C. The filaments ejected from the spinneret were gradually cooled to atmosphere temperatures of 150 °C to 300 °C in the two-layer heating cylinder and passed through the cooling device 4 having a cooling start distance LS of 169 mm and supplying cold air at 18 °C at a speed of 35 m/min. Thus, the filaments were cooled to room temperature and solidified.

After that, the filaments were collected while being sized at a sizing position Lg of 1,300 mm, in terms of distance from the spinning surface, thereby forming a multifilament. The fluid swirl generating nozzle device 6 having a swirl generating nozzle length LA of 25 mm was used to impart convergence. Convergence was imparted by injecting high-pressure air into the moving yarn in the fluid swirl generating nozzle device 6 in the direction of the arrow. The injected air pressure was 0.1 MPa (flow rate: 15 L/min). Thereafter, the multifilament was subjected to a first step-drawing such that the draw ratio between the take-up roller 7 and the first draw roller 8 was 2.9 times, and then subjected to a second draw ratio such that the draw ratio between the first draw roller 8 and the second draw roller 9 was 1.5 times. Subsequently, 1.0% relaxation was applied between the second draw roller 9 and the relaxation roller 10, the yarn was entangled by the entanglement-imparting device 11, and then wound by the winding device 12. At this time, the total draw ratio represented by the ratio of the take-up speed to the draw speed was set to 4.35 times. The surface temperature of each roller was set so that the take-up roller was 40°C, the first draw roller was 150°C, the second draw roller was 185°C, and the relaxation roller was at room temperature. The entanglement treatment was performed by injecting high-pressure air from the direction perpendicular to the moving yarn into the entanglement imparting device. The pressure of the injected air was 0.2 MPa. Thus, a nylon-6 multifilament with a fineness of 33 dtex and comprising 5 filaments was obtained.

The obtained nylon-6 multifilament was evaluated, and the results are shown in Table 1.

(Knitted lace production)

The multifilament was then warped and set as a back yarn for a 28-G Raschel lace ground yarn to have a chain length of 21.0 cm and also as a face yarn for the ground yarn to have a chain length of 100.0 cm, and then knitted together with pattern yarns of 235 dtex to 330 dtex. The resulting textile material was subjected to scouring, dyeing, and finishing fixation, thereby obtaining a knitted lace for use in underwear. The obtained lace product was evaluated, and the results thereof are shown in Table 1.

[Example 2]

A nylon-6 multifilament having a fineness of 33 dtex and comprising 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the mechanical strength and knot strength were changed by setting the relaxation ratio between the second drawing roller 9 and the relaxation roller 10 to 0%. The evaluation results are shown in Table 1.

[Example 3]

A nylon-6 multifilament having a fineness of 33 dtex and comprising 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the mechanical strength and knot strength were changed by setting the relaxation ratio between the second drawing roller 9 and the relaxation roller 10 to 1.5%. The evaluation results are shown in Table 1.

[Example 4]

A nylon-66 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that nylon-66 (N66) chips having a relative viscosity of sulfuric acid (^r) of 3.2 and a melting point of 265 °C were used as the polyamide. The evaluation results are shown in Table 1.

[Comparative example 1]

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the relaxation ratio between the second drawing roller 9 and the relaxation roller 10 was 2.0% and the knot strength was 5.9 cN/dtex. The evaluation results are shown in Table 1.

Since the relaxation rate was 2.0%, heat-setting was performed in a state of high relaxation, reducing the linearity of the molecular chain and reducing knot strength. Therefore, the durability of the knitted lace was poor.

[Table 1]

[Example 5]

A nylon-6 multifilament having a fineness of 22 dtex and including 7 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the spinning machine used had an ejection rate of 38.6 g/min and 42 holes, and 6 yarns were produced per spinning machine. The evaluation results are shown in Table 2. The durability of the knitted lace was good, the durability was maintained while the fineness was improved, and the texture was soft. In addition, as the fineness was improved, the transparency of the background lace yarn was increased, and the pattern had a more beautiful appearance than in Example 1.

[Example 6]

A nylon-6 multifilament having a fineness of 22 dtex and including 20 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinning machine used had an ejection rate of 25.8 g/min, 80 holes, and a diameter of 0.18, and was to produce 4 yarns per spinning machine. The evaluation results are shown in Table 2. The durability of the knitted lace was good, the durability was maintained even when the fineness was improved, and the texture was very soft. In addition, as the fineness was improved, the transparency of the background lace yarn was increased, and the pattern had a more beautiful appearance than in Example 1.

[Example 7]

A nylon-6 multifilament having a fineness of 42 dtex and including 6 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinning machine used had an ejection rate of 49.2 g/min, 24 holes, and a diameter of 0.30, and was to produce 4 yarns per spinneret. The evaluation results are shown in Table 2. The knitted lace had good durability and a good texture. In addition, since the % U was very good, it was a knitted lace without uneven dyeing compared with Example 1.

[Comparative example 2]

A nylon-6 multifilament having a fineness of 33 dtex and comprising 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the fluid swirl generating nozzle device 6 was not installed. The evaluation results are shown in Table 2.

Since the monofilament fineness was high in a high-fineness region or high-fineness monofilament for garments, when the entanglement treatment was performed during stretching, individual yarn entanglement occurred, the yarn's stretchability at the entanglement point decreased, mechanical strength decreased, and lint formation frequently occurred. Therefore, the knitted lace was deficient in process passability, durability, and product appearance quality (lint formation).

[Comparative example 3]

A nylon-6 multifilament having a fineness of 150 dtex and including 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the fluid vortex generating nozzle device 6 was not installed and the spinning machine used had an ejection amount of 43.9 g/min, 5 holes, and a diameter of 0.50, and was to produce 1 yarn per spinning machine. The evaluation results are shown in Table 2.

Because the fineness and fineness of the monofilament were high, the knitted lace lace lacked softness. Furthermore, because the fineness of the ground yarn was high, the ground lace lace lace lacked transparency, and the pattern did not look attractive.

[Comparative example 4]

A nylon-6 multifilament having a fineness of 22 dtex and comprising 32 filaments and a knitted lace was obtained in the same manner as in Example 1, except that the spinning machine used had an ejection rate of 19.3 g/min, 96 holes, and a diameter of 0.16, and was capable of producing 3 yarns per spinning machine. The evaluation results are shown in Table 2.

Since the monofilament fineness was smaller than in Examples 5 and 6, the texture was improved, but the polyamide fiber cooled rapidly in the cooling portion, reducing its stretchability, reducing its mechanical strength and knot strength, deteriorating its % U, and increasing its lint formation. Therefore, the knitted lace was deficient in process passability, durability, and product appearance quality (lint formation, unevenness).

[Comparative example 5]

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that, as shown in Figure 2, neither the second drawing roller 9 nor the relaxation roller 10 were installed, only one step of stretching was performed on the take-up roller 7 and the first drawing roller 8 so that the stretching ratio between the take-up roller 7 and the first drawing roller 8 was 4.35 times, and relaxation at a relaxation ratio of 1.0% was performed between the first drawing roller 8 and the winding device 12. The evaluation results are shown in Table 2.

Since high-strength stretching was performed in the single-stage stretch, stretchability deteriorated, mechanical strength was reduced, and lint formation occurred. Therefore, the knitted lace was deficient in process passability, product appearance quality (lint formation), and durability.

[Comparative example 6]

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace was obtained in the same manner as in Example 1, except that, as shown in Figure 2, neither the second drawing roller 9 nor the relaxation roller 10 were installed, only one step of stretching was performed on the take-up roller 7 and the first drawing roller 8 so that the stretching ratio between the take-up roller 7 and the first drawing roller 8 was 4.35 times, and relaxation at a relaxation ratio of 5.0% was performed between the first drawing roller 8 and the winding device 12. The evaluation results are shown in Table 2.

Because high-stretching was performed in the single-stage stretching process, stretchability deteriorated, mechanical strength was reduced, and lint formation occurred. Furthermore, because the relaxation ratio was 5.0%, heat setting was performed in a state of high relaxation, reducing molecular chain linearity and reducing knot strength. Therefore, the knitted lace was deficient in process passability, appearance quality, and durability.

[Table 2]

Although the present invention has been described in detail using specific embodiments, it is apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2018 10324 filed on January 25, 2018, the entire contents of which are incorporated herein by reference.

List of reference signs

1: spinning machine

2: Gas feeder

3: Heating cylinder

4: Cooling device

5: Sizing device

6: Swirl generating nozzle device in fluid

7: Pickup roller

8: First stretching roller

9: Second stretching roller

10: Relaxation roller

11: entanglement imparting device

12: Winding device

L: length of multi-layer heating cylinder

L1: monolayer length of multilayer heating cylinder

LS: cooling start distance

Lg: sizing position

LA: swirl generating nozzle length

Claims (6)

1. A polyamide multifilament having a monofilament fineness of 0.8 dtex to 7 dtex, a mechanical strength of 7.5 cN/dtex to 8.5 cN/dtex, and a knot strength of 6.0 cN/dtex to 7.5 cN/dtex, wherein the mechanical strength and the knot strength are measured by the methods of the description. 2. Polyamide multifilament according to claim 1, having a tensile strength at 15% elongation of 6.1 cN/dtex to 7.5 cN/dtex, wherein the tensile strength at 15% elongation is measured by the method of the description. 3. Polyamide multifilament according to claim 1 or 2, having a total fineness of 20 dtex to 44 dtex. 4. Knitted lace produced using the polyamide multifilament according to any one of claims 1 to 3 as a background lace yarn. 5. Method for producing the polyamide multifilament according to any one of claims 1 to 3, the method comprising: expelling a molten polyamide resin from a spinneret (1) to form filaments; cool and solidify each of the filaments; and stretch the obtained filaments, wherein the method is performed using a polyamide multifilament production device that includes at least: a spinning machine (1) for ejecting a molten polyamide resin to form filaments; a heating cylinder (3) to gradually cool the filaments; a cooling device (4) for cooling and solidifying the filaments; a fluid swirl generating nozzle device (6) for imparting convergence to the threads by means of a swirling flow; a take-up roller (7) for collecting and stretching the filaments; and a stretching device for stretching the filaments, and in which the following conditions (A) to (D) are satisfied: (A) the heating cylinder (3) is provided above the cooling device (4); (B) the fluid swirl generating nozzle device (6) is provided above the pick-up roller (7); (C) the stretching device is a multi-stage stretching device having two or more stages; and (D) Low relaxation heat treatment is performed immediately after multi-stage stretching. 6. Method for producing the polyamide multifilament according to claim 5, wherein the relaxation heat treatment is carried out between a stretching roller (8, 9) and a relaxation roller (10) at a relaxation ratio of 0 to 1.5% and a heat setting temperature of 150°C to 200°C.