Polyamide monofilament

Abstract

This polyamide monofilament is characterized by including at most one knot having a fiber diameter that is at least 135% of the diameter of the fiber and at most one filament having a fiber diameter that is at most 80% of the diameter of the fiber, wherein the knot and filament are present at a position of 200,000 m in the longitudinal direction of the fiber.　Provided is a polyamide monofilament which is suitable for obtaining a filter having excellent filtration performance due to the excellent opening uniformity of a gauze fabric, and has excellent fiber diameter uniformity due to a small number of knots and filaments.

Description

[Technical Field]

[0001] The present invention relates to a polyamide monofilament. More specifically, it relates to a polyamide monofilament suitable for producing filters with excellent filtration performance, such as automobile filters, medical filters, and acoustic filters. In particular, the present invention provides a polyamide monofilament with few knots and fine threads and excellent fiber diameter uniformity, which is suitable for producing filters with excellent filtration performance and excellent mesh uniformity for gauze fabrics. [Background technology]

[0002] Polyamide fibers have excellent mechanical properties, chemical resistance, and heat resistance, and are therefore widely used in clothing, industrial materials, etc. In the industrial material application, they are particularly widely used in filters using monofilament woven fabrics (screen gauze fabrics), and their uses are diverse, including automotive filters, medical filters, and acoustic filters.

[0003] In the rapidly growing electronics field and the medical field, which require extremely high quality, there is an ever-increasing demand for uniform quality without clogging or opening. In particular, there is an increasing demand for nodule yarns, which are uneven in fineness in the longitudinal direction and localized abnormalities in fineness, and many technologies have been proposed to improve the quality of these monofilaments.

[0004] For example, Patent Document 1 cites that knots are caused by gelled polymers being mixed into the yarn, which prevents this part from being sufficiently stretched, and reports a technology in which a spinning pack is configured with a sintered filter made of short metal fibers to thoroughly disperse the gelled polymers.

[0005] Patent Document 2 reports a technology for obtaining a polyester monofilament having a core-sheath structure with a small number and size of nodes, including visible minute nodes, in order to reduce the fineness of a monofilament having high strength, high modulus, and a uniform fiber diameter in the longitudinal direction.

[0006] Patent Document 3 reports a melt spinning nozzle that enables extension of the cleaning cycle of the nozzle surface during high-speed spinning by using a melt spinneret in which a discharge hole 1 is formed by sequentially connecting an inlet hole 2, a metering hole 3 having a smaller cross-sectional area than the inlet hole 2, and a relaxation hole 4 having a larger cross-sectional area than the metering hole 3, and a melt spinning method using the same. By using this melt spinneret and melt spinning method, it is possible to further reduce the accumulation of dirt on the nozzle surface and reduce discharge fluctuations, and therefore it is expected that filaments with little yarn unevenness will be produced. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-231651 [Patent Document 2] International Publication No. 2019 / 044449 [Patent Document 3] Japanese Patent Application Publication No. 9-268417 Summary of the Invention [Problem to be solved by the invention]

[0008] However, while Patent Document 1 is effective as a technology for suppressing knot yarns, it makes no mention of fine yarns and is insufficient as a technology to resolve the issue of fine yarns. Previous methods for evaluating quality related to fineness abnormalities involved the capture rate of knots using a slub catcher or the evaluation of fineness unevenness in the longitudinal direction (averaged) using a Worcester tester, which could result in localized outflow of fine yarns, leading to serious complaints. Furthermore, this conventional technology had the problem of being prone to fineness unevenness in the longitudinal direction due to unstable discharge from the spinneret.

[0009] Furthermore, in Patent Document 2, a monofilament with few knots can be obtained from a polyester monofilament yarn with a core-sheath structure, but in the production of polyamide monofilament, polyamide itself is prone to thermal degradation and thermal decomposition, making it easy to produce thermally degraded polymers that cause knots, and it is more likely to produce sublimates of low molecular weight substances (monomers, oligomers, etc.) than polyester, so this conventional technology is insufficient to suppress knots and thin threads in polyamide monofilament. Specifically, there was a problem of knots and thin threads being easily produced due to contamination of the spinneret surface caused by sublimates of low molecular weight substances.

[0010] Furthermore, in Patent Document 3, the upper limit of the diameter of the relaxation holes is low at 0.75 mm, and the dirt accumulation density per unit circumference is large, which has the problem of making knots more likely to occur.

[0011] Therefore, the present invention provides a polyamide monofilament for use in high-quality filters, which has uniform fineness unevenness and suppresses knots. The presence of knots leads to thread breakage and scum formation during warping and weaving. Furthermore, when monofilament containing knots is woven, the knots have a large diameter relative to the fiber diameter, resulting in clogging in the woven fabric adjacent to the knots, significantly reducing the quality of the fabric. Furthermore, with the trend toward higher filter quality, the presence of fine threads thinner than normal fiber diameters has become apparent. The presence of fine threads widens the opening of the woven fabric, allowing foreign matter to pass through and leading to poor filtration, so suppressing the presence of fine threads is extremely important. The present invention provides a polyamide monofilament with excellent fiber diameter uniformity and few knots or fine threads, which is suitable for producing a gauze fabric with excellent mesh uniformity and a filter with good filtration performance. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention employs the following configuration. (1) A polyamide monofilament characterized in that, in a length of 200,000 m, there is one or less knot with a fiber diameter of 135% or more of the fiber diameter, and one or less fine thread with a fiber diameter of 80% or less of the fiber diameter. (2) The polyamide monofilament according to (1), characterized in that the CV% of the fiber diameter when measured over 200,000 m in the longitudinal direction of the fiber is 1% or less. (3) A polyamide monofilament according to (1) or (2), characterized in that there are 10 or less knots with a fiber diameter of 120% or more but less than 135% of the fiber diameter and 10 or less fine threads with a fiber diameter of more than 80% but not more than 90% of the fiber diameter, present in 200,000 m in the longitudinal direction of the fiber. (4) The polyamide monofilament according to any one of (1) to (3), characterized in that the minimum value of the strength-strain product when measured 50 times consecutively is 90% or more and 100% or less of the average value. (5) The polyamide monofilament according to any one of (1) to (4), characterized in that the fineness is 6 to 50 dtex. [Effects of the Invention]

[0013] According to the present invention, a polyamide monofilament having excellent uniformity of fiber diameter with few knots and fine threads can be provided, which is suitable for obtaining a filter having excellent mesh uniformity of a gauze fabric and good filtration performance. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a vertical cross-sectional view showing an example of an outlet hole in a melt spinneret used in the production of the polyamide monofilament of the present invention. [Figure 2] 1 is a process schematic diagram showing an example of a method for producing a polyamide monofilament of the present invention. [Figure 3] FIG. 1 is a longitudinal cross-sectional view showing an example of a spinning pack used in melt spinning the polyamide monofilament of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The implementation of the present invention will now be described in detail.

[0016] In this invention, knots refer to localized, lump-like fiber diameter abnormalities present in the longitudinal direction of the fiber, and refer to fiber diameters that are 120% or more thicker than the standard fiber diameter. Fine threads refer to fiber diameters that are 90% or less thinner than the standard fiber diameter. Knots and fine threads are measured using an optical outer diameter detector (PSD-200 manufactured by Sensoptic) at a running speed of 800 m / min, a thread length interval of 0.07 mm, and a thread length of 200,000 m. The optical outer diameter detector records the fiber diameter, standard deviation of the fiber diameter, the number and size of knots, and the number and size of fine threads as numerical values.

[0017] The polyamide monofilament of the present invention has, in the longitudinal direction of 200,000 m of the fiber, one or less knots with a fiber diameter of 135% or more of the fiber diameter and one or less fine threads with a fiber diameter of 80% or less of the fiber diameter. By controlling the knots and fine threads within these ranges, the monofilament has good uniformity, the gauze fabric has excellent mesh opening uniformity, and a filter with good filtration performance can be obtained. If the number of knots with a fiber diameter of 135% or more of the fiber diameter exceeds one, the resulting gauze fabric will have openings and clogging in the areas adjacent to the knots, resulting in reduced mesh opening uniformity. Furthermore, during advanced processing, the fabric will get caught on the reed, increasing thread breakage and scum. If the number of fine threads with a fiber diameter of 80% or less of the fiber diameter exceeds one, openings will occur in the gauze fabric and reduced mesh opening uniformity. If openings occur in the gauze fabric, foreign matter will pass through when the fabric is made into a filter, resulting in reduced filtration performance.

[0018] The polyamide monofilament of the present invention preferably has, in the longitudinal direction of 200,000 m of the fiber, 10 or fewer knots with a fiber diameter of 120% to 135% of the fiber diameter and 10 or fewer fine threads with a fiber diameter of more than 80% to 90% of the fiber diameter. By limiting the number of knots with a fiber diameter of 120% to 135% of the fiber diameter to 10 or fewer, defects that could lead to clogging of the gauze fabric can be suppressed, the mesh opening uniformity of the gauze fabric can be improved, and the filtration performance of the filter can be enhanced. Furthermore, by limiting the number of fine threads with a fiber diameter of more than 80% to 90% of the fiber diameter to 10 or fewer, defects that could lead to opening of the gauze fabric can be suppressed, the mesh opening uniformity of the gauze fabric can be improved, and the filtration performance of the filter can be enhanced. More preferably, in the longitudinal direction of 200,000 m of the fiber, there are 5 or fewer knots with a fiber diameter of 120% to 135% of the fiber diameter and 5 or fewer fine threads with a fiber diameter of more than 80% to 90% of the fiber diameter.

[0019] The polyamide monofilament of the present invention preferably has a fiber diameter CV% of 1.0% or less when measured over 200,000 m in the longitudinal direction. The fiber diameter CV% can be calculated as a percentage by dividing the fiber diameter standard deviation by the average fiber diameter, and indicates the degree of uniformity in the longitudinal direction of the fiber. A lower value indicates better uniformity in the fiber diameter. By setting the CV% to 1.0% or less, a monofilament with excellent uniformity in the fiber diameter and no uniformity in the longitudinal direction of the fiber can be obtained. Furthermore, a filter with excellent filtration performance and excellent mesh uniformity of the gauze fabric can be obtained. An even more preferable fiber diameter CV% is 0.8% or less.

[0020] The polyamide monofilament of the present invention preferably has a minimum strength-strain product of 90% to 100% of the average value when measured 50 times in succession. If knots or fine threads exist, they tend to break and weaken the yarn, which locally reduces the durability of the gauze fabric. By ensuring that the minimum strength-strain product is 90% or more, the durability of the gauze fabric and the filter are improved.

[0021] The polyamide monofilament of the present invention, when used in high-mesh filters, preferably has a fineness of 6 to 50 dtex. It is more preferably 8 to 47 dtex. In particular, when used in high-definition high-mesh filters, it is preferably 6 to 13 dtex. Furthermore, as will be described later, in the production of the polyamide monofilament of the present invention, by setting the fineness to 50 dtex or less, it is possible to suppress cooling unevenness even in air-cooling equipment, thereby obtaining polyamide monofilaments that are free of knots and fine fibers and have excellent filtration performance. Furthermore, by setting the fineness to 6 dtex or more, it is possible to suppress discharge fluctuations, and to obtain polyamide monofilaments that are free of knots and fine fibers and have excellent filtration performance.

[0022] The polyamide monofilament of the present invention preferably has a strength of 4.0 cN / dtex or more and an elongation of 30 to 60%. By setting the values in these ranges, the durability of the gauze fabric can be ensured.

[0023] The manufacturing method for obtaining the polyamide monofilament of the present invention is described below.

[0024] The polyamide referred to in the present invention is a high molecular weight polymer in which hydrocarbon groups are linked to the main chain via amide bonds, and is preferably a polyamide composed primarily of polycaproamide or polyhexamethylene adipamide because of its excellent dyeability, washing fastness, and mechanical properties. "Predominantly" here refers to a polyamide containing primarily ε-caprolactam units constituting polycaproamide, and primarily polyhexamethylenediaminediammonium adipamide units, with these units preferably comprising 80 mol% or more, more preferably 90 mol% or more. Other components are not particularly limited, but include, for example, aminocarboxylic acid and dicarboxylic acid units, which are monomers constituting polydodecanoamide, polyhexamethylene azelamide, polyhexamethylene sebacamide, polyhexamethylene dodecanoamide, polymethaxylene adipamide, polyhexamethylene terephthalamide, and polyhexamethylene isophthalamide.

[0025] The degree of polymerization of the polyamide may be appropriately selected from the range commonly used for producing industrial fibers, but is preferably in the range of 2.0 to 3.3, more preferably 2.4 to 3.3, in terms of relative viscosity in 98% sulfuric acid. By setting the degree of polymerization in this range, it becomes possible to obtain polyamide monofilaments having the strength required for gauze fabrics with good spinning properties.

[0026] In the production of the polyamide monofilament of the present invention, the moisture content of the polyamide resin chips to be spun is preferably adjusted to 0.11 to 0.15% by drying or other methods. By adjusting the moisture content within this range, it is possible to suppress knots and thin fibers in the polyamide monofilament. The moisture content here is a value measured by placing a polyamide resin chip sample in a trace moisture meter, evaporating the moisture at 230°C for 30 minutes, and reading the moisture value.

[0027] The melt spinning temperature of the polyamide resin chips is preferably a temperature above the melting point of the polyamide resin, i.e., the melting point plus 20 to 40° C. By setting the temperature within this range, it is possible to suppress knots and thin threads in the polyamide monofilament.

[0028] In the method for producing the polyamide monofilament of the present invention, the basic production process may be a known technique, for example, a method in which the spinning and drawing steps are carried out continuously (direct spinning and drawing method), or a method in which an undrawn yarn is once wound up and then drawn (two-step method).

[0029] An example of a method for producing a polyamide monofilament of the present invention will be described with reference to the process schematic diagram in Figure 2. First, polyamide resin chips melted in an extruder are fed to a melt spinning pack 10, and a spun yarn is discharged from a spinneret 11 with round orifices, each having two discharge holes arranged circumferentially. Next, the yarn is cooled by a uniflow chimney 12 blowing air from one direction, and the yarn is divided into individual yarns. Spinning oil is applied to the yarns by an oil supply guide 13, and the yarns are taken up by a first godet roller 14, stretched between a second godet roller 15 and a third godet roller 16, heat-treated by a third and fourth godet roller (16, 17), and wound up by a winding device 18.

[0030] The melt spinning pack used in the production of the polyamide monofilament of the present invention is a melt spinning pack that is arranged with at least a spinneret, a pressure plate, a metal wire filter, and a sand filter layer or a straightening plate, and the melt spinning pack described in Patent Document 1 is used, in which a sintered filter made of short metal fibers having an approximately polygonal cross section is provided between the metal wire filter and the sand filter layer or the straightening plate.

[0031] The main cause of knots in polyamide monofilaments is thought to be the generation of thermally modified gelled polymers due to viscosity variations in the molten polyamide polymer, which results in the polymer not being completely melted and the resulting yarn being discharged from the spinneret hole with the gelled material mixed in, resulting in insufficient drawing of this portion. To improve knots, it is necessary to disperse this gelled material. To disperse the gelled material, it is necessary to increase the filtration accuracy of the metal wire filter, sand filter layer, or straightening plate that constitutes the melt spinning pack. Furthermore, by using metal short fibers with a roughly polygonal shape, entanglement of the metal short fibers occurs, further improving filterability and dispersibility. A roughly polygonal shape with an acute cross-sectional shape is preferred. Collisions of the thermally modified gelled polymer with the acute corners of the cross section allow for fine dispersion, and the more acute cross-sectional shape allows for even finer fragmentation of the thermally modified gelled polymer.

[0032] The spinneret used in the production of the polyamide monofilament of the present invention is a melt spinning nozzle formed by sequentially connecting a polymer inlet hole, a metering hole having a smaller cross-sectional area than the inlet hole, and a relaxation hole having a larger cross-sectional area than the metering hole.

[0033] In the melt spinning of polyamide, low molecular weight polymers (monomers, oligomers, etc.) discharged from the spinneret sublimate and accumulate as dirt around the polymer discharge holes over time. Generally, a release agent such as silicone is applied to the polymer discharge side surface of the melt spinneret to improve the releasability of the polymer. However, as mentioned above, the accumulation of dirt around the polymer discharge holes and the deterioration of the polymer's releasability cause the polymer discharge state from the spinneret to become unstable, resulting in unevenness in the length of the yarn, the formation of knots and thin yarns, and even yarn breakage. As a countermeasure, Patent Document 3 (JP 9-268417 A) clearly states the provision of a melt spinneret for high-speed spinning at a take-up speed of 2000 m / min or more, in which the ratio (D2 / D1) of the metering hole diameter (D1) to the relaxation hole diameter (D2) is 1.75 to 2.5, and the relaxation hole diameter (D2) is 0.40 to 0.75 mm, thereby suppressing fineness unevenness through discharge stabilization and reducing yarn breakage, thereby enabling extension of the cleaning cycle of the spinneret surface. Furthermore, although it is said to be effective for single filament finenesses up to 8 denier (9 dtex), even when applied to the production of polyamide monofilament with a single filament fineness of 6 dtex or more taken up at a speed of 1000 m / min or less, the polymer discharge state becomes unstable over time, resulting in yarn unevenness such as knots and thin yarns.

[0034] Figure 1 shows an example of a discharge hole provided in a spinneret used in the present invention. In Figure 1, discharge hole 1 is formed so that inlet hole 2, metering hole 3, and relaxation hole 4 are continuous in this order along the flow direction of the molten polymer. In the configuration of discharge hole 1, metering hole 3 is narrowed to have a smaller cross-sectional area than inlet hole 2, and measures the molten polymer that flows in from inlet hole 2. Relaxation hole 4, which is adjacent to metering hole 3, has a larger cross-sectional area than metering hole 3, thereby reducing the accumulation density of dirt per unit circumference around the polymer discharge hole and enabling the effect of reducing ballast by relaxing the pressure of the molten polymer.

[0035] In the spinneret used in the production of the present invention, the relaxation hole diameter (D2) is made larger than the metering hole diameter (D1) as described above, which tends to reduce the back pressure of the discharge hole. To address this, it is necessary to reduce the metering hole diameter (D1) accordingly. On the other hand, if the metering hole diameter (D1) is small, it becomes difficult to uniformly fill the entire discharge hole with the molten polymer, resulting in unstable discharge. The metering hole diameter (D1) is preferably designed so that the ratio (L1 / D1) of the metering hole length (L1) is 2.0 to 3.5. By setting the ratio within this range, it is possible to ensure back pressure and metering ability while stabilizing the discharge of the molten polymer, resulting in polyamide monofilaments with few knots and thin fibers and excellent fiber diameter uniformity. A ratio of 2.5 to 3.0 is even more preferable.

[0036] In the spinneret used in the production of the present invention, the ratio (D2 / D1) of the metering hole diameter (D1) to the relaxation hole diameter (D2) is preferably 2.6 to 4.0. By setting the ratio within this range, the cross-sectional area of the molten polymer is greatly expanded by the relaxation holes, which have a larger diameter than the metering holes. This relieves the pressure of the molten polymer constricted by the metering holes, suppresses threading by dirt around the discharge holes, and reduces discharge fluctuations. Furthermore, the shear rate and stress of the molten polymer are reduced, suppressing the generation of frictional heat and reducing dirt. Furthermore, since the relaxation hole diameter is large, the circumferential length is larger relative to the polymer discharge rate, and therefore the accumulation density of dirt per unit circumferential length can be reduced. Therefore, the discharge of the molten polymer is stable, and polyamide monofilaments with good fiber diameter uniformity can be obtained. A ratio of 3.0 to 3.7 is even more preferable.

[0037] In the spinneret used in the production of the present invention, the relaxation hole diameter (D2) is 0.8 to 1.4 mm. Setting the relaxation hole diameter (D2) in this range stabilizes the discharge of the molten polymer and suppresses polymer bending and twitching due to fouling around the discharge holes. Improved discharge stability suppresses the generation of knots and thin threads due to poor discharge, resulting in a polyamide monofilament with excellent filtration performance. If the relaxation hole diameter (D2) is less than 0.8 mm, the accumulation density of fouling per unit circumference increases, making polymer bending and twitching more likely to occur due to fouling around the discharge holes. Furthermore, the effect of relaxing the pressure of the molten polymer decreases, increasing the shear rate of the molten polymer, causing fouling around the discharge holes due to frictional heat, and reducing discharge stability. If the relaxation hole diameter (D2) is 1.4 mm or more, it becomes difficult to uniformly fill the entire discharge hole (particularly within the relaxation hole), making the discharge state more susceptible to fluctuations, resulting in the generation of knots and thin threads, as well as frequent spun yarn breakage. A more preferable range is 1.0 to 1.2 mm.

[0038] Furthermore, since increasing the size of the relaxation holes 4 reduces the rate at which the polymer is discharged from the polymer discharge holes (shear rate), it is preferable to optimize the spinning speed. When the spinning speed is increased, the greater the difference between the shear rate and the spinning speed, the more irregular the crystal orientation becomes, making it more likely that knots and thin threads will form. Therefore, in the method for producing polyamide monofilament of the present invention, the spinning speed is 300 to 1,000 m / min, preferably 300 to 600 m / min in the two-step process and 300 to 800 m / min in the one-step process. By setting the spinning speed within these ranges, polyamide monofilament with fewer knots and thin threads and excellent fiber diameter uniformity can be obtained. [Example]

[0039] The present invention will now be described in more detail with reference to the following examples, in which physical properties were measured by the methods described below.

[0040] A. Number of nodes and threads (1) Place one package on the creel. (2) The yarn is unwound at a speed of 800 m / min and passed through an optical inspection device (PSD-200 manufactured by Sensoptic). (3) The fiber diameter is measured at intervals of 0.07 m along the length of the fiber. The measurement is carried out for 250 minutes. (4) A node having a fiber diameter of 135% or more of the fiber diameter. Each measurement value that increased by 35% or more (135% or more fiber diameter) relative to the standard fiber diameter was counted as one node. (5) A knot having a fiber diameter of 120% or more but less than 135% of the fiber diameter. Each measurement value that increased by 20% or more but less than 35% (fiber diameter that increased by 120% or more but less than 135%) relative to the standard fiber diameter was counted as one node. (6) Fine threads with a fiber diameter of 80% or less of the fiber diameter Each measurement that was 20% or more smaller than the standard fiber diameter (less than 80% fiber diameter) was considered a fine fiber. (7) Fine yarns with a fiber diameter of more than 80% but not more than 90% of the fiber diameter Each measured value that was 10% or more but less than 20% smaller than the standard fiber diameter (more than 80% but not more than 90% of the standard fiber diameter) was considered to be one fine fiber.

[0041] B. CV% of fiber diameter (1) Place one package on the creel. (2) The yarn is unwound at a speed of 800 m / min and passed through an optical inspection device (PSD-200 manufactured by Sensoptic). (3) The fiber diameter is measured at intervals of 0.07 m along the length of the fiber. The measurement is carried out for 250 minutes. (4) The standard deviation of the fiber diameter and the average fiber diameter were read, and the CV% of the fiber diameter was calculated using the following formula. CV% of fiber diameter = (standard deviation of fiber diameter) / (average fiber diameter) × 100.

[0042] C. Strength, elongation, and elongation product The fiber samples were measured 50 times using Orientec Co., Ltd.'s "Tensilon" (registered trademark) in accordance with JIS L1013 (2010) under constant-speed elongation conditions, a grip distance of 50 cm, and a pulling speed of 50 cm / min. Tenacity was determined from the point showing maximum strength in the tensile strength-elongation curve, and elongation was determined from the elongation showing maximum strength. The strength was calculated as the value obtained by dividing the maximum strength by the total fineness. The strength-elongation product was calculated using the following formula, and the minimum and average values of the individual values from the 50 measurements were calculated. Strength elongation product = strength [cN / dtex] × (1+ elongation [%] / 100).

[0043] D. Opening rate Polyamide monofilaments were warped using a warper to a density of 20 threads / mm, and then woven using a rapier loom to a density of 20 threads / mm (so that the opening was square). This test fabric was observed using a scanning electron microscope (Nikon ESEM-2700) at 1000x magnification, and the interfiber distance at each of 20 random openings (measured at the widest point within each opening) was measured to the order of 0.1 μm. The opening variation rate was calculated using the following formula. Opening variation rate (%) = (standard deviation of interfiber distance) / (average interfiber distance) × 100 The aperture variation rate was considered acceptable if it was 3% or less, which is an indicator of a high-precision filter.

[0044] [Example 1] The melt spinning pack shown in Figure 3 was used, and was composed of a spinneret 30, a pressure plate 27, a metal wire filter 26, a sintered filter 25, and a sand filter material 24. The spinneret 30 had four discharge holes, each with a metering hole diameter φ(D1) of 0.30 mm, a metering hole length (L1) of 0.75 mm, a relaxation hole diameter φ(D2) of 1.0 mm, and a metering hole length (L2) of 1.0 mm. The sintered filter 25 was a sintered filter (thickness 2 mm, filtration accuracy 40 μm) made of stainless steel short fibers with a roughly polygonal cross section, a length of 1.0 to 3.0 mm, an equivalent diameter of 30 to 60 μm, and an aspect ratio variation of 10 to 100.

[0045] Nylon 66 chips with a relative viscosity of 2.8 in 98% sulfuric acid were dried and adjusted to a moisture content of 0.13%, then melted at a melt temperature of 290°C. The polymer output per melt spinning pack was adjusted to 6.5 g / min, and the chips were fed to the melt spinning pack. The resulting spun yarn was extruded from a spinneret with two circular nozzles arranged in a circular arrangement. Next, water vapor was introduced into the spinneret at 130°C through a heated gas flow path (not shown) heated by a heating means provided on the downstream side of the spinneret. The heated water vapor was then introduced into the spinneret at a temperature of 130°C and a spinneret area of 1 cm. 2 After feeding the yarn at a rate of 150 mg / min per yarn, the yarn was cooled using a uniflow chimney with air blown from one direction, and the yarn was divided into individual yarns and treated with a spinning oil solution using an oil supply guide to a deposition amount of 0.5%. The yarn was then wound up at a spinning speed of 500 m / min. The undrawn yarn was drawn 4.3 times in a drawing machine to obtain nylon 66 monofilament.

[0046] The obtained nylon 66 monofilament was evaluated for the number of knots, unevenness in fineness, strength-strain product, and filter opening ratio. The results are shown in Table 1.

[0047] [Examples 2 to 6, Comparative Examples 1 and 2] Nylon 66 monofilament was obtained by spinning and drawing in the same manner as in Example 1, except that the metering hole diameter (D1) 7, metering hole length (L1) 6, relaxation hole diameter (D2) 9, and relaxation hole length (L2) 8 shown in Figure 1 were changed as shown in Table 1. The results are shown in Table 1.

[0048] [Table 1]

[0049] [Example 7] Nylon 66 monofilaments were obtained by spinning and drawing in the same manner as in Example 1, except that the spinning speed was changed as shown in Table 2. The results are shown in Table 2.

[0050] [Example 8] A spinneret with two discharge holes was used, the discharge rate was adjusted so that the polymer discharge rate per melt spinning pack was 15 g / min, and spinning and drawing were carried out in the same manner as in Example 1, except that the metering hole diameter (D1) 7, the metering hole length (L1) 6, the relaxation hole diameter (D2) 9, and the relaxation hole length (L2) 8 shown in Figure 1 were changed as shown in Table 2, to obtain a nylon 66 monofilament. The results are shown in Table 2.

[0051] [Example 9] Nylon 66 monofilament was obtained in the same manner as in Example 1, except that the spinning apparatus shown in Figure 2 was used, and the yarn was taken up at a spinning speed of 760 m / min with the first godet roller 14, stretched 4.1 times between the second godet roller 15 and the third godet roller 16, heat-treated at 170°C with the third and fourth godet rollers (16, 17), and wound at 3000 m / min with the winding device 18. The results are shown in Table 2.

[0052] Comparative Example 3 Nylon 66 monofilament was obtained by spinning and drawing in the same manner as in Example 1, except that the discharge hole was composed only of inlet hole 2 and metering hole 3, and the metering hole diameter (D1) and metering hole length (L1) were changed as shown in Table 2. The results are shown in Table 2.

[0053] [Table 2] [Explanation of symbols]

[0054] 1: Discharge hole 2:Inflow hole 3:Measuring hole 4: Relaxation hole 5:Inflow hole diameter 6:Measuring hole length (L1) 7:Measuring hole diameter (D1) 8: Relaxation hole length (L2) 9: Relaxation pore diameter (D2) 10: Melt spinning pack 11: Melt spinneret 12: Chimney 13: Refueling Guide 14: First Godelor 15: The Second Godelora 16: The Third Godelora 17: The 4th Godelor 18: Winding device 19: Polymer introduction section 20: Upper pack block 21: Intermediate pack block 22: Lower pack block 23:Protruding step 24: Sand filter material 25: Sintered filter 26: Metal wire filter 27: Pressure plate 28: Polymer passage hole 29: Packing 30: Spinneret 31:Discharge hole

Claims

1. A polyamide monofilament characterized in that, over 200,000 m in the longitudinal direction of the fiber, there is one or less knots with a fiber diameter of 135% or more of the fiber diameter, and one or less fine threads with a fiber diameter of 80% or less of the fiber diameter.

2. 2. The polyamide monofilament according to claim 1, wherein the CV% of the fiber diameter when measured in the longitudinal direction of the fiber for 200,000 m is 1% or less.

3. A polyamide monofilament according to claim 1 or claim 2, characterized in that there are 10 or less nodes with a fiber diameter of 120% or more but less than 135% of the fiber diameter and 10 or less fine threads with a fiber diameter of more than 80% but less than 90% of the fiber diameter present in a length of 200,000 m of the fiber.

4. 4. The polyamide monofilament according to claim 1, wherein the minimum value of the strength-strain product when measured 50 times consecutively is 90% or more and 100% or less of the average value.

5. 5. The polyamide monofilament according to claim 1, wherein the fineness is 6 to 50 dtex.

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