Polyamide multifilament and method for producing same

Abstract

The present invention addresses the problem of providing a polyamide multifilament having fine fineness, high strength, and good fluff quality. To solve said problem, the present invention provides a polyamide multifilament characterized by comprising a polyamide resin and having a total fineness of 30.0-150.0 dtex, a strength of 7.5-10.0 cN / dtex, and an elongation of 15.0-35.0%.

Description

[Technical Field]

[0001] The present invention relates to a polyamide multifilament. [Background technology]

[0002] Multifilaments made of polyamide 6 (also known as "polycaprolactam") and polyamide 66 (also known as "polyhexamethylene adipamide") have higher strength and elongation and superior fluff quality than general-purpose multifilaments made of polyester, polypropylene, etc., and are therefore used in a wide range of industrial applications, including airbags, strings for sports rackets, ropes, fishing nets, and bag belts.

[0003] Here, we will take airbags as an example. As an essential safety device that protects occupants in the event of a vehicle collision, the installation rate of airbags is rapidly increasing. In addition to the driver and front passenger protection that were introduced early on, airbags are now installed in a wide range of locations, including knee protection, chest protection built into the seat, and head protection installed in the ceiling above the window. With the increase in the number of installation locations, the demand for improved fuel economy every year, and the recent trend toward larger interior spaces in vehicles, various studies have been conducted to reduce the weight and size of the base fabrics used in airbags.

[0004] The total fineness of polyamide 66 yarn used for airbag fabrics was previously generally 940 dtex, but in recent years, 470 dtex has been mainly used, and even yarns with lower finenesses of 235 dtex or less are becoming more common.

[0005] Patent Documents 1 and 2 disclose techniques for obtaining fine, high-strength polyamide fibers with good fluff quality that can provide airbags with excellent compactness, with Patent Document 1 proposing a total fineness of 100 to 250 dtex and Patent Document 2 proposing a total fineness of 50 to 470 dtex. However, even in the examples section, only fibers with a fineness of up to 175 dtex are obtained, and no specific examples are given of raw yarns with a total fineness of 150 dtex or less, or even 100 dtex or less, that have high strength and are suitable for industrial use. The reason for this is that, as stated in Patent Document 1 (paragraph

[0021] ), it is difficult to consistently obtain high-strength fibers when the total fineness is small.

[0006] The reason for this is that when obtaining a multifilament with a small total fineness, the effects of retention in the molten state from melting polyamide chips until spinning and defects such as air bubbles remaining in the fiber during spinning become significant. In other words, a typical facility for producing fibers for high-strength industrial materials, such as yarn for airbags, is composed of a spinning section that discharges a high total fineness of about 235 to 2,000 dtex and a direct drawing machine that combines a multistage hot drawing machine to achieve high strength, but no consideration is given to the problems that arise when multifilament with a fineness of 100 dtex or less is produced using such equipment. More specifically, when fineness is reduced to 100 dtex or less using general equipment for producing fibers for industrial materials, as described in Patent Document 3 (paragraphs

[0005] to

[0008] ) and Patent Document 4 (paragraph

[0013] ), the polymer thickens due to long-term retention, thermal degradation, and gelation, generating minute foreign matter, which becomes mixed into the yarn, causing spinning problems and making it impossible to obtain polyamide fibers with high strength and good fluff quality.As such, it has been extremely difficult to produce polyamide fibers with high strength and good fluff quality despite being fine multifilaments.

[0007] On the other hand, in the field of high-strength polyamide multifilament for clothing, there has been a demand in recent years for higher strength and thinner, more compact fabrics of existing advanced processed products for clothing use, resulting in a demand for higher strength and an accompanying finer yarn.

[0008] In response to this demand for higher strength polyamide fibers for clothing, Patent Document 5 proposes a method in which the yarn, after being stretched, heat-set, or hot-stretched, and then wound onto a package, is further contacted with a hot plate heated to 170-205°C and hot-stretched to 1.15 times or more. However, this method involves two separate steps, the spinning step and the stretching step, which not only complicates the process but also raises concerns about the slow production speed (approximately 1000 m / min) and high costs. Furthermore, Patent Document 6 only produces polyamide multifilaments with a strength of up to 7.3 cN / dtex, a level that is insufficient for improving the durability of industrial fibers such as airbags and clothing fabrics. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2017-222939 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-20566 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-254945 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-133566 [Patent Document 5] Japanese Patent Application Publication No. 11-247022 [Patent Document 6] Japanese Patent Application Laid-Open No. 2002-88577 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to solve the above problems and to provide a polyamide multifilament that is fine, has high strength, is excellent in toughness, and has good fluff quality, and as described above, is to provide a polyamide multifilament that can reduce the weight of industrial materials such as airbags and improve the durability of clothing fabrics. Furthermore, according to the present invention, a polyamide multifilament that is good in terms of production efficiency can be obtained. [Means for solving the problem]

[0011] The present invention has been made through extensive research to solve the above problems, and mainly comprises the following features. (1) A polyamide multifilament made of polyamide, having a total fineness of 50 to 120 dtex, a strength of 8.0 to 9.7 cN / dtex, an elongation of 17.0 to 30.0%, and a coefficient of variation of elongation at a load of 3 cN / dtex of 1.00% or less. (2) The polyamide multifilament according to (1) above, having a fluff count of 0 to 3 fluffs per 10,000 meters. (3) The polyamide multifilament according to (1) or (2) above, wherein the number of bubbles contained in the polyamide filaments constituting the polyamide multifilament is 50 bubbles / cm or less. (5) The above (1) The method for producing the polyamide multifilament according to claim 1, further comprising the steps of preparing polyamide chips and spinning the polyamide chips using a direct spinning-drawing method, wherein |ηa-ηb|<0.3 is satisfied when the relative viscosity of the polyamide chips in sulfuric acid is ηa and the relative viscosity of the spun polyamide multifilament is ηb. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a polyamide multifilament that is fine but has high strength, excellent toughness, and good fluff quality, and it is possible to reduce the weight of industrial materials and improve the durability of clothing fabrics. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a process for producing a polyamide multifilament of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below with reference to examples, but the present invention is not limited to the specific examples described below.

[0015] Examples of raw materials used for the polyamide multifilament of the present invention include nylon 6, nylon 66, nylon 12, nylon 46, nylon 56, nylon 610, copolymer polyamides of nylon 6 and nylon 66, and copolymer polyamides obtained by copolymerizing nylon 6 with polyalkylene glycol, dicarboxylic acid, diamine, etc. These are known as polymers in which repeating units are linked by amide bonds. While there are no particular limitations on the polyamide, polyamide 66, which has excellent impact resistance and heat resistance, is preferred. The polyamide multifilament of the present invention may contain components other than polyamide as needed. Examples of such components include end-capping agents such as monocarboxylic acids, matting agents such as titanium oxide, polymerization catalysts and heat-resistant agents such as phosphorus compounds, antioxidants and heat stabilizers such as copper compounds and alkali metal or alkaline earth metal halides. The polyamide content of the polyamide multifilament is preferably 95% by weight or more, and more preferably 97% by weight or more. If the polyamide content is less than 95% by weight, heat resistance may be reduced.

[0016] The polyamide multifilament of the present invention has a total fineness of 30 to 150 dtex. A more preferred range is 50 to 120 dtex. If the total fineness is less than 30 dtex, it is difficult to ensure a sufficient total strength as a multifilament, and single yarn breakage is likely to occur when drawing is performed at a high ratio to obtain high strength, and the possibility of fluffing increases. If the total fineness exceeds 150 dtex, it will not lead to weight reduction of industrial materials or improvement in the durability of clothing fabrics.

[0017] The strength of the polyamide multifilament of the present invention is 7.5 to 10.0 cN / dtex, more preferably 8.0 to 9.7 cN / dtex. When the strength is in this range, the polyamide fiber is suitable for industrial materials such as airbags and for durable clothing fabrics. A strength of less than 7.5 cN / dtex is insufficient to improve the durability of fibers for industrial materials such as airbags and for clothing fabrics. When polyamide fibers have a strength exceeding 10.0 cN / dtex, mechanical drawing at a high ratio is required, which makes single yarn breakage more likely and deteriorates the fluff quality. Such polyamide multifilaments are unsuitable for industrial materials such as airbags, which require high quality.

[0018] The elongation of the polyamide multifilament of the present invention is 15.0% to 35.0%, and more preferably 17.0% to 30.0%. Although a higher elongation is preferable, in order to obtain a predetermined strength with polyamide, the elongation is practically 35.0% or less. By setting the elongation within this range, the toughness and breaking work load of the polyamide multifilament can be increased, and excellent durability can be maintained.

[0019] Although it depends on the total fineness and single fiber fineness, the strength and elongation product is 38cN / dtex (% 1 / 2 ) or more, and more preferably 40 cN / dtex·(% 1 / 2) or more. A high strength-strain product suppresses the occurrence of fluffing and thread breakage, resulting in a polyamide multifilament of extremely high quality despite its high strength. Note that strength (cN / dtex) and elongation (%) refer to values ​​measured under the constant rate elongation conditions specified in the standard test of JIS L1013 (1999) 8.5.1, and the strength-strain product is a value calculated by [strength x √(elongation)]. There is no particular upper limit, but a value of 50.0 cN / dtex·(% 1 / 2 ) or less is practical.

[0020] The polyamide multifilament of the present invention preferably has a yarn unevenness (U%) of 1.2% or less. More preferably, it is 1.0% or less, and particularly preferably, it is 0.8% or less. By setting U% to 1.2% or less, dye unevenness and streaks do not occur when dyeing the fabric for clothing, resulting in a good appearance and excellent product quality. There is no particular lower limit, but a value of 0.3% or more is practical.

[0021] Furthermore, the polyamide multifilament of the present invention preferably has a coefficient of variation in elongation at a load of 3 cN / dtex of 1.00% or less. It is more preferably 0.80%, and particularly preferably 0.50% or less. Having a coefficient of variation of 1.00% or less ensures uniform elongation when a constant load is applied to industrial fabrics such as airbags, which is advantageous in terms of suppressing misalignment. Furthermore, since this coefficient of variation is due to variations in crystal structure, it also leads to suppression of dye unevenness in the case of clothing fabrics. A simple way to suppress the coefficient of variation in elongation at a load of 3 cN / dtex of 1.00% or less is to control the difference between the relative viscosity in sulfuric acid of the polyamide chips used and the relative viscosity in sulfuric acid of the resulting polyamide multifilament. If this viscosity difference is large, local thickening or hydrolysis due to thermal crosslinking or the like may occur during the process from the raw material chips to yarn. In the case of thickening, areas where the crystalline orientation increases locally in the longitudinal direction of the fiber are generated, while in the case of hydrolysis, areas where the crystalline orientation decreases locally in the longitudinal direction of the fiber are generated, which is likely to cause variations in elongation. The coefficient of variation of elongation at a load of 3 cN / dtex can be determined by the method explained in the Examples section.

[0022] The polyamide multifilament of the present invention preferably has a fluff count of 0 to 3 fluffs / 10,000 m or less, particularly 0 to 2 fluffs / 10,000 m, and even more preferably 0 to 1 fluff / 10,000 m. A low fluff count enables the filament to be used in applications requiring excellent fluff quality, such as airbags. The fluff count is determined by measuring the total number of fluffs over a filament length of 100,000 m or more while rewinding at a speed of 150 m / min, and converting the value into the number of fluffs per 10,000 m.

[0023] The polyamide multifilament of the present invention preferably has a bubble count of 50 bubbles / cm or less, i.e., 0 to 50 bubbles / cm, particularly 0 to 30 bubbles / cm, and even more preferably 0.2 to 20 bubbles / cm. If the number of bubbles contained in the polyamide filament exceeds 50 bubbles / cm, the strength of the bubble-containing single fiber decreases. This means that the bubbles in the single fiber inhibit drawing. In addition, excessive absorption of moisture from the air by the molten polymer can cause hydrolysis, a decrease in the viscosity of the polyamide, and insufficient crystal orientation, resulting in decreased strength. Furthermore, the fluff quality also deteriorates. On the other hand, if the bubble count is 0.2 or more, the molten polymer can absorb moisture from the air, resulting in a raw yarn with excellent fluff quality. One method for reducing bubbles is to set the extruder pressure during extrusion of the polyamide to 20.0 to 80.0 kPa.

[0024] FIG. 1 is a schematic diagram of a direct spinning and drawing apparatus preferably used in the present invention.

[0025] The method for producing the polyamide multifilament of the present invention will be described below using FIG. 1 as an example.

[0026] First, raw polyamide chips that are the raw material for the polyamide multifilament of the present invention are prepared. The polyamide can be polymerized by a known polymerization method.

[0027] The relative viscosity in sulfuric acid (hereinafter sometimes simply referred to as "viscosity") of the polyamide raw material chips used in the polyamide multifilament of the present invention is preferably 2.8 to 3.9, more preferably 3.3 to 3.9. If the viscosity of the chips is 4.0 or higher, when the total fineness is within the range specified in the present invention, the polymer will remain in the polymer for a long period of time, resulting in thickening, thermal degradation, and gelation, which will generate minute foreign matter and deteriorate the fluff quality. If the viscosity of the chips is less than 2.8, it will be difficult to obtain a polyamide multifilament having the strength specified in the present invention. The relative viscosity in sulfuric acid is the value measured at 25°C using an Ostwald viscometer using a solution in which 1 g of chips is dissolved in 100 ml of 98% sulfuric acid and 98% sulfuric acid without the chips dissolved therein. The measurement details are as explained in the Examples section.

[0028] When producing the polyamide multifilament of the present invention, a direct spinning and drawing method is used. Here, the sulfuric acid relative viscosity of the polyamide chips used as raw materials is ηa, and the sulfuric acid relative viscosity of the spun polyamide multifilament is ηb. Preferably, |ηa - ηb| is less than 0.2. For example, polyamide multifilaments produced with |ηa - ηb| < 0.3 have extremely good fluff quality, high strength and elongation, and little variation in elongation at 3% elongation. While the details are unclear, satisfying |ηa - ηb| < 0.3 is thought to be because thickening and thermal degradation due to long-term retention of the polymer are suppressed, or hydrolysis of the polyamide is suppressed. Furthermore, if acceptable from a productivity standpoint, screening can also be performed in an inspection process after the polyamide multifilament is produced.

[0029] Next, an example of a production method that satisfies |ηa - ηb| < 0.3 will be described. Polyamide chips having the above-described relative viscosity in sulfuric acid are prepared and dried, then fed to an extruder-type spinning machine, and then transferred to a spinneret by a metering pump for melt spinning. To prevent polymer thickening, thermal degradation, and gelation, the pressure in the extruder supply section is preferably 20.0 to 80.0 kPa rather than vacuum (0.0 kPa). It is more preferably 40.0 to 60.0 kPa. If the pressure in the extruder supply section is less than 20.0 kPa, the polymer thickening, thermal degradation, and gelation can cause poor fluff quality and may prevent the production of high-strength yarn. If the pressure in the extruder supply section is 80.0 kPa or higher, the number of bubbles contained in the polyamide filaments increases, and furthermore, the hydrolysis reaction of the polymer becomes dominant, preventing the production of high-strength yarn.

[0030] Referring to FIG. 1, polyamide extruded from a spinneret 1 is preferably passed through a heating cylinder 2 that surrounds an area of ​​5 to 300 cm from directly below the spinneret. The temperature inside the heating cylinder is preferably −30 to +30°C relative to the melting point of the polymer polyamide, and more preferably −15 to +15°C. By passing the spun yarn through a high-temperature atmosphere surrounded by the heating cylinder rather than immediately cooling it, the orientation of the melt-spun polyamide molecules is relaxed, and the uniformity of the molecular orientation between the single fibers can be increased, enabling the polyamide multifilament to have high strength. On the other hand, if the spun yarn is immediately cooled without passing through a high-temperature atmosphere, the orientation of the undrawn yarn increases and the variation in the degree of orientation between the single fibers increases. If such an undrawn yarn is hot-drawn, it may not be possible to obtain a high-strength polyamide multifilament.

[0031] The undrawn yarn 5 that has passed through the high-temperature atmosphere is then cooled and solidified by blowing air at 10 to 80°C, preferably 10 to 50°C, onto it in a cross-flow cooler 3. If the cooling air temperature exceeds 80°C, the vibration of the single fibers during spinning increases, causing collisions between the single fibers and deteriorating spinnability.

[0032] The cooled yarn thus obtained is then oiled by a known oiling device 4, taken up by a take-up roll 6, stretched, and then wound up. Any known oil can be used as the oil, but in order to prevent the single yarn from winding on the take-up roll 6, the amount of oil applied is preferably 0.3 to 1.5% by weight, and more preferably 0.5 to 1.0% by weight.

[0033] The spinning speed, defined as the rotation speed of the take-up roll 6, is preferably 500 to 1200 m / min, and more preferably 600 to 800 m / min. If the spinning speed is 500 m / min or higher, the final production speed will be sufficient, allowing polyamide multifilament to be produced efficiently and inexpensively. A spinning speed of 1200 m / min or lower is preferable because it can suppress the occurrence of yarn breakage and fluff. The drawing speed, defined as the maximum speed of the drawing roll, is preferably 2800 m / min or higher, and more preferably 3000 m / min or higher.

[0034] The spun yarn obtained by the above-mentioned methods can be drawn, heat-treated for relaxation, and wound up using known methods. To give a specific example of two-stage drawing, the spun yarn taken up by the take-up roller 6 (1FR) is wound around the yarn feed roller 7 (2FR), the first drawing roller 8 (1DR), the second drawing roller 9 (2DR), and the relaxation roller 10 (RR) in this order, where it is subjected to heat treatment and drawing, and then wound up on the winder 11.

[0035] Pre-stretching is performed between 1FR and 2FR, first-stage stretching is performed between 2FR and 1DR, and second-stage stretching is performed between 1DR and 2DR. The temperature of 2FR is set to 30 to 50°C, the temperature of 1DR is set to 100 to 225°C, and pre-stretching and first-stage stretching are preferably hot stretched at around the glass transition temperature. The remaining stretching and heat setting temperatures are preferably usually in the range of 180 to 240°C, more preferably 200 to 220°C.

[0036] Regarding the total draw ratio (hereinafter also referred to simply as "draw ratio"), i.e., the ratio when drawing between the take-up roller 6 and the second drawing roller 9, a high draw ratio is preferably used to obtain a high-strength polyamide multifilament, and within the fineness range described in the present invention, drawing at 3.8 to 5.0 times is sufficient. The winding speed is preferably 2000 to 5000 m / min, more preferably 2500 to 4500 m / min. Furthermore, it is preferable to wind the multifilament into a cheese strip using a winding device under conditions of a winding tension of 20 to 250 gf.

[0037] By using the method described above, thickening, thermal degradation, gelation, and hydrolysis of the polyamide polymer are suppressed, the effect of bubbles on the mechanical properties is small, and even if the total fineness is as small as 150 dtex or less, a polyamide multifilament having high strength and high elongation, i.e., high toughness, and of good quality can be obtained. [Example]

[0038] The present invention will be described in detail below with reference to examples. However, the present invention should not be construed as being limited to the embodiments specifically shown in the examples. The definitions and measurement methods of each property in the present invention are as follows.

[0039] (1) Sulfuric acid relative viscosity (ηr): Using polymer chips or raw yarn as a sample, 0.25 g of the sample was dissolved in 25 ml of 98% sulfuric acid, and the viscosity was measured at 25°C using an Ostwald viscometer. The viscosity was calculated using the following formula. The measured value was calculated as the average value of five samples.

[0040] ηr = number of seconds for sample solution to flow down / number of seconds for sulfuric acid only to flow down.

[0041] (2) Total fineness: Measured according to JIS L1090 ​​(1999).

[0042] (3) Number of single fibers: Calculated according to the method of JIS L1013 (1999) 8.4.

[0043] (4) Single fiber fineness: Calculated by dividing the total fineness by the number of single fibers.

[0044] (5) Tenacity, strength, and elongation: Measurements were made under the constant-speed elongation conditions specified in JIS L1013 (1999) 8.5.1 Standard Time Test. Multifilament samples were tested using Orientec's "TENSILON" UCT-100, with a grip distance of 25 cm and a pulling speed of 30 cm / min. Tenacity was determined from the maximum strength on the SS curve, elongation from the elongation at the point where the maximum strength was shown on the SS curve, and strength was calculated by dividing the strength by the total fineness. Samples were taken every 1 m along the length of the multifilament sample, and measurements were taken at five points. The average value was calculated from the measured data.

[0045] (6) Yarn unevenness (U%): Measured using a USTER TESTER IV manufactured by Zellweger USTER at a sample length of 500 m, a measuring yarn speed of 25 m / min, and 1 / 2 inert.

[0046] (7) Coefficient of variation of elongation at a load of 3 cN / dtex: An SS curve was obtained under the same conditions as in the tenacity-elongation measurement in (5) above, and the elongation at a load of 3 cN / dtex was determined. The multifilament sample was sampled at 1 m intervals in the longitudinal direction of the fiber, and measurements were performed at 10 points. The average value and standard deviation were calculated from the measurement data, and the coefficient of variation was calculated using the following formula: Coefficient of variation = [standard deviation] / [mean value] × 100 (%).

[0047] (8) Number of fluffs: The obtained fiber package was rewound at a speed of 150 m / min, and a laser fluff detector "Flytec V" manufactured by Heberlein was placed 2 m away from the yarn during rewinding, and the total number of fluffs detected was evaluated. The evaluation was carried out on multifilaments of 100,000 m or more, and the number was converted to the number per 10,000 m and displayed.

[0048] (9) Number of bubbles: The number of bubbles observed was evaluated using a Keyence VHX-5000 microscope with a 1000x magnification lens. If bubbles are present in the fiber, stretching will be inhibited from the bubbles. Therefore, bubbles were observed with a 1000x magnification optical lens, and then stretching inhibition was confirmed with a polarized lens to confirm the presence of bubbles. Fibers of the same length were cut out from all of the polyamide filaments constituting the polyamide multifilament. However, sampling was performed so that the total length of the cut fibers was 100 cm. The cut samples were observed, and the total number of bubbles was converted to the number per cm and displayed. The cut sample does not need to be exactly 100 cm, as long as the total length of the measurement was 100 cm.

[0049] Example 1 Nylon 66 chips obtained by liquid-phase polymerization were mixed with a 5 wt% aqueous solution of copper acetate as an antioxidant, resulting in the adsorption of 68 ppm of copper relative to the polymer weight. Next, a 50 wt% aqueous solution of potassium iodide and a 20 wt% aqueous solution of potassium bromide were added to the polymer chips at 0.1 wt parts of potassium per 100 wt parts of the polymer chips, and solid-state polymerization was carried out using a batch-type solid-state polymerization apparatus to produce nylon 66 pellets with a relative viscosity in sulfuric acid of 3.75. The resulting nylon 66 pellets were fed into a 110 mm diameter extruder and melted at a melt temperature of 300°C and a pressure of 50.0 kPa in the extruder feed zone. The molten polymer was discharged using a metering pump, and the output rate was adjusted to obtain multifilaments with a total fineness of 80 dtex. The polymer was then filtered through a metal nonwoven filter with a 40 μm mesh size within the spin pack, and then spun through a spinneret with 24 circular holes using an apparatus configured as shown in Figure 1. A 20 cm long heating cylinder was installed 3 cm below the nozzle surface and heated so that the atmospheric temperature inside the cylinder reached 250°C. Here, the atmospheric temperature inside the cylinder refers to the air temperature at the center of the heating cylinder, 1 cm away from the inner wall. A cross-flow chimney that blows air from one direction was installed directly below the heating cylinder, and cold air at 18°C ​​was blown onto the yarn at a speed of 35 m / min to cool and solidify it, after which an oil agent was applied to the yarn.

[0050] The undrawn yarn treated with the oiling agent was wound around the first roller rotating at a surface speed of 800 m / min and then drawn at a total draw ratio of 4.3x. The drawn yarn was continuously stretched by 5% between the take-up roller and the second roller without being wound up, then subsequently drawn in a first stage at a rotational speed ratio of 2.80x, followed by a second stage at a rotational speed ratio of 1.46x, and then wound up at a speed of 3400 m / min. The roller surfaces of the first and second rollers were mirror-finished, while the first, second, and third rollers were matte-finished. The roller temperatures were as follows: first roller unheated, second roller 40°C, first roller 150°C, second roller 225°C, and third roller 150°C. Nylon 66 multifilament was obtained by this melt spinning and drawing. Entanglement was performed in the entanglement device by spraying high-pressure air perpendicular to the running yarn. Guides for regulating the running yarn were provided before and after the interlacing device, and the pressure of the jetted air was kept constant at 0.2 MPa.

[0051] (Examples 2 to 4, Reference Example 5) The same procedure as in Example 1 was carried out except that the total fineness and total draw ratio of the polyamide multifilaments were changed as shown in Table 1.

[0052] (Examples 6 to 8) The same procedure as in Example 1 was carried out except that the number of single fibers of the polyamide multifilament was changed as shown in Table 1.

[0053] (Reference Example 9, Example 10) The same procedure as in Example 1 was carried out except that the overall stretching ratio was changed as shown in Table 1.

[0054] (Reference examples 11 and 12) The same procedure as in Example 1 was carried out except that the pressure in the extruder supply section and the total draw ratio were changed as shown in Table 1.

[0055] The physical properties of the polyamide multifilaments obtained in Examples 1 to 4, 6 to 8, and 10, and Reference Examples 5, 9, 11, and 12 were evaluated, and the results are shown in Table 1.

[0056] [Table 1]

[0057] As is clear from Table 1, the polyamide multifilament of the present invention has a fineness and high strength, and yet has good fluff quality.

[0058] In Examples 1 to 4 and Reference Example 5, polyamide multifilaments of the present invention were produced with various total finenesses. Compared with Reference Examples 11 and 12 and Comparative Examples 1 to 5 described below, thickening was suppressed by melting the polymer in an atmosphere with a pressure of 50.0 kPa in the extruder supply section, and the desired polyamide multifilaments were obtained. Furthermore, the smaller the total fineness and the finer the single fiber fineness, the more advantageous the cooling, and the higher the strength-elongation product of the polyamide multifilament. On the other hand, when the single fiber fineness was reduced too much, as in Example 8, uniform cooling in the chimney airflow was poor, resulting in an impact on the yarn unevenness (U%). Reference Examples 11 and 12 are examples in which spinning was performed with the pressure in the extruder supply section set to 25.0 kPa and 75.0 kPa, respectively. A tendency for thickening or hydrolysis to occur from the tip to the multifilament was observed, which impacted the coefficient of variation of elongation at a load of 3 cN / dtex.

[0059] (Reference example 1) The same procedure as in Example 1 was carried out except that the total fineness of the polyamide multifilaments was set to 175 dtex and they were melted in an atmosphere with a pressure of 0.0 kPa in the extruder supply section.

[0060] (Comparative Examples 1 and 2) The same procedure as in Reference Example 1 was carried out except that the total fineness of the polyamide multifilaments was changed to 110 dtex and the total draw ratio was changed as shown in Table 2.

[0061] (Comparative Examples 3 to 4) The same procedure as in Reference Example 1 was carried out except that the total fineness of the polyamide multifilaments was changed to 80 dtex and the total draw ratio was changed as shown in Table 2.

[0062] (Comparative Example 5) The same procedure as in Comparative Example 4 was carried out except that the pressure in the extruder supply section and the total draw ratio were changed as shown in Table 2.

[0063] (Reference example 2) The physical properties of a typical polyamide multifilament for clothing produced according to the description in Example 1 of International Publication WO2016 / 076184 are shown in Reference Example 2.

[0064] [Table 2]

[0065] The physical properties of the polyamide multifilaments obtained in Comparative Examples 1 to 5 and Reference Examples 1 and 2 were evaluated, and the results are shown in Table 2.

[0066] In Reference Example 1, a polyamide multifilament having a total fineness of 175 dtex was produced, and although some polymer thickening occurred due to the polymer being melted under vacuum (in an atmosphere with an extruder supply section pressure of 0.0 kPa), it is clear that with this total fineness, a polyamide multifilament having the strength required for an industrial fiber was obtained. However, because the total fineness was large, it was not sufficient to achieve the object of the present invention, which is to reduce the weight of industrial materials such as airbags and improve the durability of clothing fabrics with high production efficiency.

[0067] In Comparative Example 1, a polyamide multifilament having a total fineness of 110 dtex was produced by the same method as in Reference Example 1, but spinning was not possible in this case. In Comparative Example 2, the same polyamide multifilament as in Comparative Example 1 was spun at a draw ratio of 3.6 times, and spinning was possible. However, the obtained polyamide multifilament had thickened and thermally deteriorated due to long-term polymer retention, had lost strength, and had a large amount of fluff.

[0068] In Comparative Example 3, a polyamide multifilament having a total fineness of 80 dtex was produced under the same spinning conditions as in Comparative Example 2, but spinning was not possible in this case. In Comparative Example 4, spinning was performed by reducing the draw ratio to 3.2 times in Comparative Example 3, and spinning was possible. However, the obtained polyamide multifilament thickened and deteriorated due to the long polymer residence time, lost strength, and produced a large amount of fluff. It can be seen that, compared to Comparative Examples 1 and 2, in Comparative Examples 3 and 4, the polymer residence time was increased due to the finer fineness, and the viscosity of the polymer became even more pronounced, causing the polymer to lose its stretchability, making spinning at a high draw ratio impossible.

[0069] In Comparative Example 5, the polymer was melted in an atmosphere with a pressure of 101.3 kPa in the extruder supply section, but in this case, the hydrolysis reaction of the polymer became significant, and the viscosity of the multifilament was significantly lower than the tip viscosity. Furthermore, the amount of bubbles in the yarn increased, causing frequent fuzzing, and the strength specified in the present invention could not be achieved.

[0070] Reference Example 2 is an example of polyamide multifilament produced in a general facility for producing clothing fibers, based on the description in WO2016 / 076184. In this case, the polymer residence time is shorter than when general facility for producing fibers for industrial materials is used, and it can be seen that there is almost no polymer thickening. On the other hand, because the number of drawing stages was one and the drawing ratio was low, the strength was insufficient, and there was a tendency for crystal structure variation to occur in the fiber longitudinal direction, which significantly affected the coefficient of variation of elongation at a load of 3 cN / dtex. [Industrial Applicability]

[0071] The polyamide multifilament of the present invention has a fineness, high strength and good fluff quality, and is therefore suitable for reducing the weight of industrial materials such as airbags and for improving the durability of clothing fabrics. [Explanation of symbols]

[0072] 1: Spinneret 2: Heating cylinder 3: Cross-flow cooling device 4: Refueling device 5: Thread 6: Take-up roller (1FR) 7: Yarn feeding roller (2FR) 8: First drawing roller (1DR) 9: Second drawing roller (2DR) 10: Relaxation roller (RR) 11: Winder

Claims

1. A polyamide multifilament made of polyamide, having a total fineness of 50 to 120 dtex, a strength of 8.0 to 9.7 cN / dtex, an elongation of 17.0 to 30.0%, and a coefficient of variation of elongation at a load of 3 cN / dtex of 1.00% or less.

2. The polyamide multifilament according to claim 1, wherein the number of fluffs is 0 to 3 fluffs per 10,000 m.

3. The polyamide multifilament according to claim 1 or 2, wherein the number of bubbles contained in the polyamide filaments constituting the polyamide multifilament is 0.2 to 20 bubbles / cm or less.

4. 2. A method for producing a polyamide multifilament according to claim 1, comprising the steps of preparing polyamide chips, supplying the polyamide chips to an extruder-type spinning machine having an extruder supply section with a pressure of 20.0 to 80.0 kPa, and spinning the polyamide chips using a direct spinning drawing method, wherein |ηa-ηb|<0.3 is satisfied, where ηa is the relative viscosity of sulfuric acid for the polyamide chips and ηb is the relative viscosity of sulfuric acid for the spun polyamide multifilament.

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