Polyamide multifilament and method for producing the same

Abstract

The problem to be solved by the present invention is to provide a polyamide multifilament with fine fineness, high strength and good fluff quality. In order to solve this problem, the purpose is a polyamide multifilament characterized by containing a polyamide resin and having a total fineness of 30 to 150 dtex, a strength of 7.5 to 10.0 cN / dtex, and an elongation of 15.0 to 35.0%.

Description

Technical Field

[0001] The present invention relates to polyamide multifilaments. Background Art

[0002] Compared with general-purpose multifilament yarns such as polyester and polypropylene, multifilament yarns of polyamide 6 (also known as "polycaprolactam") and polyamide 66 (also known as "polyhexamethylene adipamide") have higher strength and elongation and better fluff quality. Therefore, in terms of industrial applications, they are used in a wide range of applications such as airbags, sports racket strings, ropes, fishing nets, shoelaces, etc.

[0003] Here, as an example, airbags can be cited. As a safety device necessary to protect passengers during a vehicle collision, the installation rate of airbags has increased rapidly, and the installation sites of airbags have continued to expand. In addition to the driver protection and front passenger seat protection introduced at the beginning, there are also knee protection, chest protection hidden in the seat, and head protection installed in the ceiling above the window. With the increase in installation sites and the increasing demand for low fuel consumption, as well as the recent trend of expanding the space in the vehicle, various studies have been conducted on the base fabric used for airbags in order to make it lighter and smaller.

[0004] The total fineness of the polyamide 66 raw yarn used for the airbag base fabric was generally 940dtex in the past, but in recent years, 470dtex has been mainly used, and even low-fineness raw yarns below 235dtex have also been used.

[0005] Patent Documents 1 and 2 disclose a technique for obtaining a polyamide fiber with good fluff quality, fine fineness, and high strength, which can provide an airbag with excellent compactness. The total fineness is proposed to be 100 to 250 dtex in Patent Document 1, and 50 to 470 dtex in Patent Document 2. However, according to the examples, only fibers with a fineness of up to 175 dtex can be obtained at most, and there is no specific example of a raw yarn with a total fineness of less than 150 dtex or even less than 100 dtex and high strength that can be used as an industrial fiber. The reason for this is as described in Patent Document 1 (Paragraph

[0021] ), because if the total fineness becomes fine, it is difficult to stably obtain high-strength fibers.

[0006] The reason is that when obtaining multifilaments with a small total fineness, the influence of the retention of the molten state before the polyamide scraps are melted and spun, and the influence of defects such as bubbles remaining in the fiber during spinning become greater. That is, the general equipment for producing high-strength industrial material fibers such as raw yarns for airbags is composed of a spinning section that spits out a high total fineness of about 235 to 2000 dtex and a direct stretching machine that combines a multi-stage hot stretching machine for exhibiting high strength, but the problem that occurs when using such an apparatus to produce multifilaments with a fineness of less than 100 dtex is not considered. More specifically, when the fineness is reduced to 100 dtex or less by using a general equipment for producing industrial material fibers, as described in Patent Document 3 (paragraphs

[0005] to

[0008] ) and Patent Document 4 (paragraph

[0013] ), the long-term retention of the polymer causes viscosity increase, thermal degradation, and gelation, resulting in the generation of minute foreign matter, which is mixed into the yarn and thus causes yarn production problems, and it is impossible to obtain a polyamide fiber with high strength and good fluff quality. As a result, it is extremely difficult to produce a polyamide fiber with high strength and good fluff quality despite being a fine-fine multifilament.

[0007] On the other hand, in the field of high-strength polyamide multifilament for clothing, in recent years, due to the demand for further high-end processed products for clothing use to be made stronger, thinner, and smaller, higher strength of raw yarn and a corresponding finer fineness are required.

[0008] In response to the demand for high strength of polyamide fibers for clothing, Patent Document 5 proposes a method of further contacting the yarn that has been temporarily wound into a package after stretching, heat fixing or heat stretching to a hot plate heated to 170-205°C and heat stretching it to 1.15 times or more. However, this method is a two-step method divided into a spinning step and a stretching step. Not only does the step become complicated, but the winding speed is about 1000m / min and the production speed is slow, which has the risk of increasing costs. In addition, in Patent Document 6, the product obtained by the commercializable step can only obtain a polyamide multifilament with a strength of up to 7.3cN / dtex at most, which is insufficient in strength to improve the durability of fibers for industrial materials such as airbags or fabrics for clothing.

[0009] Prior art literature

[0010] [Patent Document]

[0011] Patent Document 1: Japanese Patent Application Publication No. 2017-222939

[0012] Patent Document 2: Japanese Patent Application Publication No. 2003-20566

[0013] Patent Document 3: Japanese Patent Application Publication No. 2007-254945

[0014] Patent Document 4: Japanese Patent Application Publication No. 2008-133566

[0015] Patent Document 5: Japanese Patent Application Laid-Open No. 11-247022

[0016] Patent Document 6: Japanese Patent Application Publication No. 2002-88577 Summary of the invention

[0017] Problems to be solved by the invention

[0018] The object of the present invention is to solve the above problems and to provide a polyamide multifilament having a fine fineness, high strength, excellent toughness and good fluff quality, and to provide a polyamide multifilament capable of achieving lightweighting of industrial materials such as the above-mentioned airbags and improving the durability of clothing fabrics. In addition, according to the present invention, a polyamide multifilament having good production efficiency can be obtained.

[0019] [Methods to solve the problem]

[0020] The present invention has been intensively studied to solve the above-mentioned problems, and mainly includes the following solutions.

[0021] (1) A polyamide multifilament comprising polyamide, having a total fineness of 30 to 150 dtex, a strength of 7.5 to 10.0 cN / dtex, and an elongation of 15.0 to 35.0%.

[0022] (2) A polyamide multifilament comprising 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 the elongation at a load of 3 cN / dtex of 1.00% or less.

[0023] (3) The polyamide multifilament according to (1) or (2) above, wherein the number of fuzz is 0 to 3 per 10,000 meters.

[0024] (4) The polyamide multifilament according to any one of (1) to (3) above, wherein the number of bubbles contained in the polyamide filaments constituting the polyamide multifilament is 50 / cm or less.

[0025] (5) A method for producing a polyamide multifilament, which is the method for producing a polyamide multifilament as described in (1) or (2) above, comprising the steps of preparing polyamide scraps and spinning the polyamide multifilaments using a direct spinning and stretching method, wherein, when the sulfuric acid relative viscosity of the polyamide scraps is ηa and the sulfuric acid relative viscosity of the polyamide multifilaments obtained by spinning is ηb, |ηa-ηb|<0.3.

[0026] Effects of the Invention

[0027] According to the present invention, a polyamide multifilament having high strength and excellent toughness and good pile quality despite a fine fineness can be provided, thereby achieving weight reduction of industrial materials and improvement of the durability of clothing fabrics. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram for explaining an example of the process of producing the polyamide multifilament of the present invention. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the specific examples described below.

[0030] As the raw materials used for the polyamide multifilament of the present invention, for example, nylon 6, nylon 66, nylon 12, nylon 46, nylon 56, nylon 610, or copolymerized polyamide of nylon 6 and nylon 66, copolymerized polyamide formed by copolymerizing nylon 6 with polyalkylene glycol, dicarboxylic acid, diamine, etc., are listed, which are known as polymers in which a repeating unit is connected via an amide bond. As long as it is a polyamide, there is no particular restriction, but it is preferred to use polyamide 66 with excellent impact resistance and heat resistance. The polyamide multifilament of the present invention may also contain components other than polyamide as needed, and as such components, for example, terminal blocking agents such as monocarboxylic acids, matting agents such as titanium oxide, polymerization catalysts such as phosphorus compounds or heat-resistant agents, antioxidants or heat-resistant stabilizers such as copper compounds and halides of alkali metals or alkaline earth metals can be listed. The content of polyamide contained in the polyamide multifilament is preferably 95% by weight or more, and more preferably 97% by weight or more. When the content of polyamide is less than 95% by weight, the heat resistance will be reduced.

[0031] The total fineness of the polyamide multifilament of the present invention is 30 to 150 dtex, preferably in the range of 50 to 120 dtex. When the total fineness is less than 30 dtex, it is difficult to ensure a sufficient value of total strength as a multifilament. In addition, when the multifilament is stretched at a high ratio to obtain high strength, single filament breakage is likely to occur, and the possibility of fuzz generation increases. When the total fineness exceeds 150 dtex, it is impossible to achieve lightweighting of industrial materials or improvement of the durability of clothing fabrics.

[0032] The strength of the polyamide multifilament of the present invention is 7.5 to 10.0 cN / dtex, preferably 8.0 to 9.7 cN / dtex. If the strength is within this range, it becomes a polyamide fiber suitable for industrial materials such as airbags or fabrics for clothing with excellent durability. When the strength is less than 7.5 cN / dtex, it is insufficient to improve the durability of fibers for industrial materials such as airbags or fabrics for clothing. When the strength is set to be greater than 10.0 cN / dtex, it becomes necessary to perform high-ratio mechanical stretching, single filament breakage is likely to occur, and the quality of the fluff deteriorates. This polyamide multifilament is not suitable for fibers for industrial materials such as airbags that require quality.

[0033] In addition, the elongation of the polyamide multifilament of the present invention is 15.0% to 35.0%, preferably 17.0% to 30.0%. The higher the elongation, the more preferred it is. In order to obtain a specified strength with polyamide, the elongation is actually 35.0% or less. By setting it in this range, the toughness and work of rupture of the polyamide multifilament can be increased, and excellent durability can be maintained.

[0034] Although it depends on the total fineness and single fiber fineness, the strength-elongation product is preferably 38 cN / dtex·(% 1 / 2 ) or more, more preferably 40 cN / dtex·(% 1 / 2 ) or more. Due to the high strength-elongation product, the generation of fuzz and wire breakage can be suppressed, and a polyamide multifilament with extremely high strength and high quality can be obtained. In addition, the strength (cN / dtex) and elongation (%) refer to the values ​​measured under the constant speed elongation conditions shown in the standard time test of JIS L1013 (1999) 8.5.1, and the strength-elongation product is the value calculated by [strength × √ (elongation)]. There is no particular upper limit, but it is practically 50.0 cN / dtex·(% 1 / 2 )the following.

[0035] The polyamide multifilament of the present invention preferably has a yarn unevenness (U%) of 1.2% or less, more preferably 1.0% or less, and particularly preferably 0.8% or less. By setting U% to 1.2% or less, uneven dyeing and streaks do not occur when dyeing a cloth for clothing, resulting in a good appearance and excellent product quality. The lower limit is not particularly limited, but is practically 0.3% or more.

[0036] In addition, the coefficient of variation of the elongation of the polyamide multifilament of the present invention at a load of 3 cN / dtex is preferably 1.00% or less, more preferably 0.80%, and particularly preferably 0.50% or less. Since the coefficient of variation is 1.00% or less, when a certain load is applied to a fabric for industrial use such as an airbag, the elongation of the multifilament is uniform, which is advantageous in suppressing mesh misalignment. In addition, since the coefficient of variation is caused by the deviation of the crystal structure, it is involved in suppressing uneven dyeing in the case of a fabric for clothing. As a means for suppressing the coefficient of variation of the elongation at a load of 3 cN / dtex to be less than 1.00%, it is relatively simple to control the difference between the relative viscosity of sulfuric acid of the polyamide scraps used and the relative viscosity of sulfuric acid of the obtained polyamide multifilament. When the difference in viscosity is large, local thickening or hydrolysis due to thermal crosslinking or the like occurs before the raw scraps become yarns. When the fiber is thickened, the crystal orientation increases locally in the fiber length direction. On the other hand, when the fiber is hydrolyzed, the crystal orientation decreases locally in the fiber length direction, which easily causes deviation in elongation. In addition, the coefficient of variation of elongation at a load of 3 cN / dtex can be obtained by the method described in the example.

[0037] The polyamide multifilament of the present invention preferably has a fuzz count of 0 to 3 per 10,000 meters, particularly preferably 0 to 2 per 10,000 meters, and more preferably 0 to 1 per 10,000 meters. Since the fuzz count is small, it can be developed toward applications requiring excellent fuzz quality, such as airbags. The fuzz count refers to the total number of fuzz measured on a filament length of more than 100,000 meters while unwinding at a speed of 150 m / min, and converted into the number of fuzz counts per 10,000 meters.

[0038] The number of bubbles contained in the polyamide filaments constituting the polyamide multifilament of the present invention is preferably 50 / cm or less, that is, 0 to 50 / cm, particularly preferably 0 to 30 / cm, and more preferably 0.2 to 20 / cm. When the number of bubbles contained in the polyamide filaments is greater than 50 / cm, the strength of the single fiber containing the bubbles decreases. This means that the bubbles in the single fiber hinder stretching. In addition, the polymer in the melt will excessively absorb moisture in the air, so as to cause hydrolysis, reduce the viscosity of the polyamide, and cause insufficient crystal orientation, resulting in reduced strength. In addition, the quality of the fluff also deteriorates. On the other hand, when it is more than 0.2, the raw yarn with good fluff quality can be obtained by the molten polymer absorbing moisture in the air. As a method of reducing bubbles, for example, setting the pressure of the extruder when extruding polyamide to 20.0 to 80.0 kPa can be cited.

[0039] Figure 1 This is a schematic diagram of a direct spinning and stretching device preferably used in the present invention.

[0040] Below, with Figure 1The method for producing the polyamide multifilament of the present invention will be described by taking it as an example.

[0041] First, raw material scraps of polyamide as a raw material of the polyamide multifilament of the present invention are prepared. A well-known polymerization method can be used for the polymerization method of polyamide.

[0042] The sulfuric acid relative viscosity (hereinafter also simply referred to as "viscosity") of the polyamide raw material scraps used in the polyamide multifilament of the present invention is preferably 2.8 to 3.9, and more preferably 3.3 to 3.9. If the viscosity of the scraps is 4.0 or more, when the total fineness is within the specified range of the present invention, microscopic foreign matter is generated due to thickening, thermal degradation, and gelation caused by the long-term retention of the polymer, and the fluff quality deteriorates. When the viscosity of the scraps is less than 2.8, it is difficult to obtain a polyamide multifilament having the strength specified in the present invention. In addition, the sulfuric acid relative viscosity refers to the value measured at 25°C using an Ostwald viscometer using a solution of 1 g of the scraps dissolved in 100 ml of 98% sulfuric acid and 98% sulfuric acid in which the scraps are not dissolved. The details of the measurement are described in the items of the embodiments.

[0043] When the polyamide multifilament of the present invention is produced, a direct spinning and stretching method is used, and when the sulfuric acid relative viscosity of the polyamide scrap used as a raw material is ηa and the sulfuric acid relative viscosity of the polyamide multifilament obtained by spinning is ηb, |ηa-ηb|<0.3 is preferred. |ηa-ηb| is more preferably less than 0.2. For example, a polyamide multifilament produced with |ηa-ηb|<0.3 can obtain a polyamide multifilament having extremely good fluff quality, high strength and elongation, and less deviation in elongation at 3% elongation. Although the details are not clear, it is believed that by satisfying |ηa-ηb|<0.3, thickening or thermal degradation caused by long-term retention of the polymer can be suppressed, or hydrolysis of the polyamide can be suppressed. In addition, if it is permitted in terms of productivity, screening can also be performed in the inspection step after the production of the polyamide multifilament.

[0044] Next, an example of a manufacturing method satisfying |ηa-ηb|<0.3 is described. A polyamide scrap having the aforementioned relative viscosity of sulfuric acid is prepared, dried, and then supplied to an extruder-type spinning machine, and distributed to a spinning spinneret by a metering pump for melt spinning. At this time, in order to suppress the thickening, thermal degradation, and gelation of the polymer, the pressure of the extruder supply part is preferably not a vacuum (pressure 0.0 kPa), but 20.0 to 80.0 kPa, and more preferably 40.0 to 60.0 kPa. When the pressure of the extruder supply part is less than 20.0 kPa, the quality of the fluff deteriorates due to the thickening, thermal degradation, and gelation of the polymer, and sometimes a high-strength yarn cannot be obtained. When the pressure of the extruder supply part is 80.0 kPa or more, the number of bubbles contained in the polyamide filament increases, and even a high-strength yarn cannot be obtained because the hydrolysis reaction of the polymer proceeds preferentially.

[0045] Reference Figure 1 For explanation, the polyamide discharged from the spinning spinneret 1 is preferably passed through a heating cylinder 2 that surrounds a range of 5 to 300 cm from directly below the spinning spinneret. The temperature in 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 not cooling the spun yarn immediately but slowly cooling it in a high-temperature environment surrounded by the above-mentioned heating cylinder, the orientation of the polyamide molecules after melt spinning can be relaxed, and the uniformity of molecular orientation between single fibers can be improved, so that the strength of the polyamide multifilament can be increased. On the other hand, if it is not passed through a high-temperature environment but cooled immediately, the orientation of the undrawn yarn becomes higher, and the orientation deviation between single fibers becomes larger. When the undrawn yarn is heat-drawn, it is possible that a high-strength polyamide multifilament cannot be obtained.

[0046] The unstretched yarn 5 after passing through the high temperature environment is then cooled and solidified by blowing air at 10 to 80°C, preferably 10 to 50°C, by a cross-flow cooling device 3. When the cooling air temperature is higher than 80°C, the shaking of the single fibers during spinning increases, so that the single fibers collide with each other, which causes the deterioration of the spinning properties.

[0047] Then, the obtained cooled sliver can be provided with oil by a known oil supply device 4, and then taken up by a take-up roller 6, and then drawn up. A known oil can be used as the oil, and in order to suppress the attachment of the monofilaments to the take-up roller 6, the amount of the oil is preferably 0.3 to 1.5% by weight, more preferably 0.5 to 1.0% by weight.

[0048] In addition, the spinning speed defined by the rotation speed of the traction roller 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 more, the final production speed is sufficient, the production efficiency is good, and the polyamide multifilament can be produced at a low price. If it is 1200 m / min or less, it is more preferred because the generation of broken wires or fluff can be suppressed. In addition, the stretching speed represented by the maximum speed of the stretching roller is preferably 2800 m / min or more, and more preferably 3000 m / min or more.

[0049] The spun yarn obtained by the above-mentioned methods can be stretched or relaxed, heat-treated, and wound up using well-known methods. Specifically, a two-stage stretching is exemplified here, where the spun yarn drawn by the drawing roller 6 (1FR) is wound around the yarn supply roller 7 (2FR), the first stretching roller 8 (1DR), the second stretching roller 9 (2DR), and the relaxation roller 10 (RR) in this order, and heat-treated and stretched, and then wound up on the winder 11.

[0050] The pre-drawing stretching is performed between 1FR and 2FR, the first stage stretching is performed between 2FR and 1DR, and the second stage stretching is performed between 1DR and 2DR. The temperature of 2FR is set at 30-50°C, and the temperature of 1DR is set at 100-225°C. The pre-drawing stretching and the first stage stretching are preferably performed by heat stretching at around the glass transition temperature. The other stretching and heat setting temperatures are usually preferably performed at a temperature in the range of 180-240°C, and more preferably 200-220°C.

[0051] Regarding the comprehensive stretching ratio (hereinafter also simply referred to as "stretching ratio"), that is, the ratio when stretching between the traction roller 6 and the second stretching roller 9, in order to obtain a high-strength polyamide multifilament, it is preferred to adopt a high stretching ratio. If it is within the fineness range described in the present invention, it is sufficient to stretch at 3.8 to 5.0 times. In addition, the winding speed is usually preferably 2000 to 5000 m / min, more preferably 2500 to 4500 m / min. In addition, it is preferred to wind the yarn into a flat bobbin shape with a winding device under the condition of a winding tension of 20 to 250 gf.

[0052] If the method described above is used, the viscosity increase or thermal degradation, gelation, and hydrolysis of the polyamide polymer can be suppressed. In addition, the influence of bubbles on the mechanical properties is also small. Even if the total fineness is a fine fineness of less than 150 dtex, a polyamide multifilament with high strength and high elongation, that is, high toughness and good quality, can be obtained.

[0053] Example

[0054] The present invention is described in detail below by way of examples. However, the present invention is not to be construed as being limited to the specific embodiments shown in the examples. The definitions and determination methods of various characteristics in the present invention are as follows.

[0055] (1) Sulfuric acid relative viscosity (ηr): 0.25 g of polymer scraps or raw yarn was dissolved in 25 ml of 98% sulfuric acid and measured at 25°C using an Ostwald viscometer. The relative viscosity was calculated using the following formula. The measured value was calculated as the average value of 5 samples.

[0056] ηr = number of seconds for sample solution to flow down / number of seconds for sulfuric acid alone to flow down.

[0057] (2) Total fineness: measured in accordance with JIS L1090 ​​(1999).

[0058] (3) Single fiber number: calculated according to the method of JIS L1013 (1999) 8.4.

[0059] (4) Single fiber fineness: Calculated by dividing the total fineness by the number of single fibers.

[0060] (5) Strength, strength, and elongation: The test was performed under the constant speed elongation conditions shown in the standard test of JIS L1013 (1999) 8.5.1. For multifilament samples, a universal testing machine (TENSILON) UCT-100 manufactured by ORIENTEC was used, and the test was performed at a gripping interval of 25 cm and a pulling speed of 30 cm / min. The strength was determined from the maximum strength in the SS curve, the elongation was determined from the elongation at the point indicating the maximum strength in the SS curve, and the strength was determined by dividing the strength by the total fineness. For the multifilament sample, samples were taken every 1 m in the longitudinal direction, and the measurement was performed at 5 points. The average value was calculated from the measurement data.

[0061] (6) Yarn unevenness (U%): The yarn unevenness was measured using USTER TESTER IV manufactured by Zellweger Uster Co., Ltd. under the conditions of sample length: 500 m, yarn measurement speed: 25 m / min, and 1 / 2 Inert.

[0062] (7) Coefficient of variation of elongation under 3 cN / dtex load: Under the same conditions as the strength-elongation measurement in (5) above, an SS curve was obtained to obtain the elongation under a load of 3 cN / dtex. In addition, during the measurement, samples were taken at intervals of 1 m in the fiber length direction of the multifilament sample to be measured, and the measurement was performed at 10 points. The average value and standard deviation were calculated from the measurement data and the coefficient of variation was obtained by the following formula.

[0063] Coefficient of variation = [standard deviation] / [mean value]×100 (%).

[0064] (8) Number of fluffs: The obtained fiber package was unwound at a speed of 150 m / min, and a laser fluff detector "Flytec V" manufactured by HEBERLEIN was set 2 m away from the unwound yarn to evaluate the total number of fluffs detected. The evaluation was performed for multifilaments of 100,000 m or more and expressed as the number per 10,000 m.

[0065] (9) Number of bubbles: The number of bubbles observed was evaluated by using a microscope "VHX-5000" manufactured by KEYENCE Corporation and a lens with a magnification of 1000 times. When bubbles are present in the fiber, a portion that hinders stretching occurs with the bubble as the starting point. Therefore, after observing the bubble with an optical lens with a magnification of 1000 times, the stretching hindering portion is confirmed by a polarizing lens to confirm the bubble. Fibers of the same length are cut out from all polyamide filaments constituting the polyamide multifilament. However, the sampling is performed in such a way that the total length of the cut fibers becomes 100 cm. The cut samples are observed and the total number of bubbles is converted into the number per 1 cm and expressed. In addition, the cut samples do not have to be strictly 100 cm as long as the total length of the measured length is ensured to be 100 cm.

[0066] (Example 1)

[0067] A 5 wt% aqueous solution of copper acetate as an antioxidant was added to the nylon 66 scraps obtained by liquid phase polymerization and mixed, and 68 ppm of copper was added relative to the weight of the polymer to allow it to be adsorbed. Next, a 50 wt% aqueous solution of potassium iodide and a 20 wt% aqueous solution of potassium bromide were added and adsorbed in an amount of 0.1 parts by weight relative to 100 parts by weight of the polymer scraps, and solid phase polymerization was performed using a batch solid phase polymerization apparatus to obtain nylon 66 pellets having a relative viscosity of sulfuric acid of 3.75. The obtained nylon 66 pellets were supplied to an extruder having a diameter of 110 mm, and melted at a melting temperature of 300°C and a pressure of 50.0 kPa in the supply part of the extruder. The molten polymer was distributed to the spinning assembly by adjusting the discharge amount by a metering pump in such a manner that a multifilament with a total fineness of 80 dtex could be obtained. The molten polymer was then filtered through a metal nonwoven filter with a roughness of 40 μm in the spinning assembly, and then passed through a spinneret with a circular hole and 24 holes, and used. Figure 1 The spinning is performed by using the device of the structure shown. A heating cylinder with a length of 20 cm is set 3 cm below the spinneret surface, and heated to an ambient temperature of 250°C inside the cylinder. The ambient temperature inside the cylinder here refers to the air temperature of the portion 1 cm away from the inner wall in the middle of the length of the heating cylinder. A cross-flow type smoke shower that blows air from one direction is installed directly below the heating cylinder, and cold air of 18°C ​​is blown onto the yarn at a speed of 35 m / min to cool and solidify the yarn, and then an oil agent is applied to the yarn.

[0068] The unstretched sliver with oil applied is wound around 1FR rotating at a surface speed of 800m / min and pulled, and then stretched at a comprehensive stretch ratio of 4.3 times. The pulled sliver is not temporarily wound up, but continuously applied with a 5% draw between the pulling roller and 2FR, and then the first stage of stretching is performed at a rotation speed ratio of 2.80 times, and then the second stage of stretching is performed at a rotation speed ratio of 1.46 times, and it is wound up at a speed of 3400m / min. The roller surfaces of 1FR and 2FR are mirror-finished, and 1DR, 2DR, and RR are roughened. In addition, the temperature of each roller is: 1FR is set to non-heating, 2FR is set to 40°C, 1DR is set to 150°C, 2DR is set to 225°C, and RR is set to 150°C. Nylon 66 multifilament is obtained by melt spinning and stretching. The intertwining treatment is performed by spraying high-pressure air from a right angle to the traveling sliver in the intertwining imparting device. Guides for controlling the running yarns were provided before and after the intertwining imparting device, and the pressure of the injected air was set at a fixed value of 0.2 MPa.

[0069] (Examples 2 to 5)

[0070] The same procedure as in Example 1 was carried out except that the total fineness of the polyamide multifilament and the comprehensive stretch ratio were changed to those shown in Table 1.

[0071] (Examples 6 to 8)

[0072] 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.

[0073] (Examples 9-10)

[0074] The same procedure as in Example 1 was carried out except that the total stretching ratio was changed to that shown in Table 1.

[0075] (Examples 11-12)

[0076] The same procedure as in Example 1 was carried out except that the pressure of the extruder supply section and the comprehensive stretch ratio were changed to those shown in Table 1.

[0077] Table 1 shows the results of evaluating the physical properties of the polyamide multifilaments obtained in Examples 1 to 12.

[0078]

[0079] As shown in Table 1, the polyamide multifilament of the present invention has good fluff quality despite its fineness and high strength.

[0080] In Examples 1 to 5, the polyamide multifilaments of the present invention were produced with various total finenesses. Compared with Examples 11 and 12 and Comparative Examples 1 to 5 described below, by melting the polymer under an environment of a pressure of 50.0 kPa in the extruder supply section, the viscosity increase can be suppressed, and the target polyamide multifilaments can be obtained. In addition, the smaller the total fineness is and the finer the single fiber fineness is, the more favorable the cooling is, and there is a tendency for the strength-elongation product of the polyamide multifilament to increase. On the other hand, as in Example 8, when the single fiber fineness is excessively fined, the uniform cooling by chimney wind becomes insufficient, and the influence on the unevenness of the yarn (U%) is shown. Examples 11 to 12 are examples of yarn production with the pressure of the extruder supply section being 25.0 kPa and 75.0 kPa, respectively. The tendency of viscosity increase or hydrolysis occurring from the scrap to the multifilament can be seen, and the influence on the coefficient of variation of the elongation at a load of 3 cN / dtex can be confirmed.

[0081] (Reference Example 1)

[0082] The same procedure as in Example 1 was carried out except that the total fineness of the polyamide multifilament was set to 175 dtex and the polyamide multifilament was melted under an environment with a pressure of 0.0 kPa in the supply part of the extruder.

[0083] (Comparative Examples 1-2)

[0084] The same procedure as in Reference Example 1 was performed except that the total fineness of the polyamide multifilament was set to 110 dtex and the comprehensive stretching ratio was changed to that shown in Table 2.

[0085] (Comparative Examples 3 to 4)

[0086] The same procedure as in Reference Example 1 was performed except that the total fineness of the polyamide multifilament was 80 dtex and the comprehensive stretching ratio was changed as shown in Table 2.

[0087] (Comparative Example 5)

[0088] The same procedure as in Comparative Example 4 was performed except that the pressure of the extruder supply section and the comprehensive stretch ratio were changed as shown in Table 2.

[0089] (Reference Example 2)

[0090] As Reference Example 2, the physical properties of a general polyamide multifilament for clothing produced according to the description of Example 1 of International Publication WO2016 / 076184 are shown.

[0091]

[0092] Table 2 shows the results of evaluating the physical properties of the polyamide multifilaments obtained in Comparative Examples 1 to 5 and Reference Examples 1 and 2.

[0093] In Reference Example 1, a polyamide multifilament with a total fineness of 175 dtex was produced. Since the polymer was melted under vacuum (under an extruder supply pressure of 0.0 kPa), the polymer viscosity increased to some extent. However, it was found that a polyamide multifilament with a strength at a level required for industrial fibers could be obtained at this total fineness. However, since the total fineness was large, it was not sufficient to achieve the purpose of the present invention, which was to achieve good production efficiency, lightweight industrial materials such as airbags, and improved durability of clothing fabrics.

[0094] 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 the yarn could not be produced. In Comparative Example 2, the same polyamide multifilament as in Comparative Example 1 was produced at a draw ratio of 3.6 times, and the yarn could be produced. However, the obtained polyamide multifilament increased in viscosity, thermally deteriorated, lost in strength, and generated a lot of fuzz due to the long-term retention of the polymer.

[0095] In Comparative Example 3, a polyamide multifilament with a total fineness of 80 dtex was produced under the same spinning conditions as in Comparative Example 2, but spinning was not possible at this time. In Comparative Example 4, spinning was performed by reducing the draw ratio in Comparative Example 3 to 3.2 times, and spinning was possible. However, the obtained polyamide multifilament increased in viscosity, deteriorated, lost strength, and generated a lot of fuzz due to the long-term retention of the polymer. Compared with Comparative Examples 1 and 2, it can be seen that Comparative Examples 3 and 4 increased in viscosity due to the increase in the retention time of the polymer due to the fineness, and the polymer lost its stretchability more significantly, making it impossible to perform spinning at a high draw ratio.

[0096] In Comparative Example 5, the same method as in Example 1 was used except that the polymer was melted under an extruder supply pressure of 101.3 kPa. However, the hydrolysis reaction of the polymer became significant at this time, resulting in a viscosity of the multifilament yarn that was significantly lower than that of the shredded material. Furthermore, the amount of bubbles in the yarn increased, resulting in a large amount of fuzz, and the strength specified in the present invention could not be achieved.

[0097] Reference Example 2 is an example of manufacturing polyamide multifilament in a general equipment for manufacturing fibers for clothing according to the description of WO2016 / 076184. At this time, compared with the case of using a general equipment for manufacturing fibers for industrial materials, it can be seen that there is almost no polymer viscosity increase due to the short residence time of the polymer. On the other hand, since the number of stretching stages is 1 and the stretching ratio is low, the strength is insufficient, and there is a tendency for the crystal structure to deviate easily in the fiber length direction, which greatly shows the influence on the coefficient of variation of the elongation at a load of 3 cN / dtex.

[0098] Possibility of industrial application

[0099] The polyamide multifilament of the present invention has a fine fineness, high strength and good fluff quality, and is therefore suitable for achieving weight reduction of industrial materials such as airbags and improvement of durability of fabrics for clothing.

[0100] Description of the accompanying drawings

[0101] 1: Spinning spinneret

[0102] 2: Heating tube

[0103] 3: Cross flow cooling device

[0104] 4: Oil supply device

[0105] 5: Yarn Strip

[0106] 6: Traction roller (1FR)

[0107] 7: Yarn supply roller (2FR)

[0108] 8: 1st stretching roller (1DR)

[0109] 9: 2nd stretching roller (2DR)

[0110] 10: Relaxation roller (RR)

[0111] 11: Winding machine

Claims

1. A polyamide multifilament comprising 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%, a coefficient of variation of the elongation at a load of 3 cN / dtex of less than 1.00%, a number of fuzz of 0 to 3 pieces / 10,000 meters, and a number of bubbles contained in the polyamide filaments constituting the polyamide multifilament of 0.2 to 20 pieces / cm.

2. A method for producing a polyamide multifilament, which is the method for producing a polyamide multifilament according to claim 1, comprising: Steps for preparing polyamide scrap, and The step of supplying the polyamide scraps to an extruder type spinning machine having a pressure of 20.0 to 80.0 kPa in the extruder supply part, and producing the fibers by a direct spinning and stretching method, When the sulfuric acid relative viscosity of the polyamide scrap is ηa and the sulfuric acid relative viscosity of the polyamide multifilament obtained by spinning is ηb, |ηa-ηb|<0.

3.

3. A method for producing a polyamide multifilament, which is the method for producing a polyamide multifilament according to claim 1, comprising: Steps for preparing polyamide scrap, and The step of supplying the polyamide scraps to an extruder type spinning machine having a pressure of 40.0 to 60.0 kPa in the extruder supply part, and producing the fibers by a direct spinning and stretching method, When the sulfuric acid relative viscosity of the polyamide scrap is ηa and the sulfuric acid relative viscosity of the polyamide multifilament obtained by spinning is ηb, |ηa-ηb|<0.3.

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