Polylactic acid monofilament, method for melt-spinning same, and fiber product

Abstract

The present invention addresses the problem of providing a polylactic acid monofilament that is excellent in both high-order processability and product quality and capable of reducing breakage of a textured yarn in warping and weaving steps and the like and suppressing misalignment after weaving as much as possible. The polylactic acid monofilament has a fineness of 50.0 dtex or less and an elongation variation (CV%) of 7.0% or less in the longitudinal direction of the yarn (measured 30 times per 50 cm yarn length).

Description

Polylactic acid monofilament, melt spinning method thereof, and textile products

[0001] The present invention relates to a polylactic acid monofilament. More specifically, the present invention relates to an excellent polylactic acid monofilament that exhibits reduced yarn breakage during processing steps such as warping and weaving, prevents misalignment in products, and combines high-order passability with high product quality.

[0002] With environmental issues such as preventing global warming, conserving fossil fuel resources, and reducing waste now receiving significant attention, biodegradable polymers made from biomass, particularly polylactic acid, are attracting attention. Polylactic acid is a polymer made from lactic acid obtained by fermenting starch extracted from plants, and among biodegradable polymers made from biomass, it offers the best balance of transparency, mechanical properties, heat resistance, and cost.

[0003] Common methods for producing polylactic acid monofilaments include a two-step method (Patent Document 1) in which the unstretched yarn is first wound up and then stretched, a one-step method (Patent Document 2) in which the unstretched yarn is stretched and wound up in a single step, and a one-step or two-step method in which a polylactic acid multifilament is first wound up and split into monofilaments using a splitting machine (Patent Document 3).

[0004] Patent Document 1 proposes a polylactic acid monofilament with specified strength, elongation, and boiling water shrinkage. Improvements to the drawing process have made it possible to suppress the boiling water shrinkage to 10% or less, preventing weave misalignment and weave fraying. Patent Document 2 proposes a drum-shaped package made of polylactic acid monofilament with specified package hardness, realizing a package configuration that prevents loop dropout during high-speed unwinding. Patent Document 3 proposes a polylactic acid multifilament for separation containing spherical inorganic particles of a specific particle size and with a specified single yarn fineness. The inclusion of spherical inorganic particles of a specific particle size enables excellent separation properties.

[0005] JP 2022-115855 A International Publication No. 2019 / 208352 JP 2009-256857 A

[0006] However, from the viewpoint of obtaining a polylactic acid monofilament that is excellent in both high-order passability and product quality, with little processed yarn breakage during warping and weaving processes and capable of minimizing weave misalignment after weaving, the polylactic acid monofilament of Patent Document 1 may indeed be said to have little weave misalignment, but it does not incorporate any ingenuity into the oiling process, which is particularly important in the production process of polylactic acid monofilaments, and as a result, there are problems such as large variations in strength and elongation along the length of the polylactic acid monofilament and in the dynamic friction coefficient due to the inability to apply oil uniformly, and the dynamic friction coefficient itself becoming high depending on the oil agent applied, which can lead to processed yarn breakage during the warping and weaving processes.

[0007] The polylactic acid monofilament of Patent Document 2 has excellent package formability, but again, no ingenuity is incorporated into the oiling process. Example 1 describes a method of oiling the monofilament with an oiling roller, using an oiling agent diluted with mineral oil, but this is insufficient from the viewpoint of uniform oiling, and it is difficult to obtain a polylactic acid monofilament that is excellent in both high passability and product quality.

[0008] The polylactic acid multifilament for splitting in Patent Document 3 is the same as that in Patent Document 2. Example 1 describes a method of oiling with an oil agent diluted with mineral oil, but simply oiling the oil agent components described in Example 1 is still insufficient from the viewpoint of uniform oiling, and it is difficult to obtain a polylactic acid monofilament that is excellent in both high-order passability and product quality.

[0009] The present invention aims to provide a polylactic acid monofilament that is excellent in both high-order passability and product quality, with little breakage during processing during warping and weaving processes, etc., and with minimal weave misalignment after weaving, which has been difficult to achieve with conventional techniques.

[0010] To achieve the above object, the present invention has the following configurations: (1) A polylactic acid monofilament having a fineness of 50.0 dtex or less and a coefficient of variation in elongation (CV%) of 7.0% or less in the longitudinal direction of the yarn (measured 30 times every 50 cm of the yarn length). (2) The polylactic acid monofilament according to (1) above, having an oil adhesion rate of 0.30% by mass or more and 1.30% by mass or less. (3) The polylactic acid monofilament according to (1) or (2) above, having a dynamic friction coefficient of 0.250 or more and 0.350 or less with a matte finish having a surface roughness of 10S. (4) The polylactic acid monofilament according to any one of (1) to (3) above, having a coefficient of variation in dynamic friction coefficient (CV%) of 7.0% or less in the longitudinal direction of the yarn (measured at 600 points over a yarn length of 27.5 m). (5) A melt-spinning method for polylactic acid monofilament according to (1) above, in which a polylactic acid polymer is melt-spun, the spun yarn is oiled, and then the oil is drawn with a take-up roller and a drawing roller and wound up, in which the viscosity of the oil diluted with mineral oil is adjusted to 3.9 mPa·sec or more and 4.7 mPa·sec or less using a matte oiling roller having a surface roughness of 20S or more and 40S or less before oiling. (6) A melt-spinning method for polylactic acid monofilament according to (5) above, in which the temperature of the yarn just before contacting the oiling roller is 40°C or less and the temperature variation of the yarn is 3.0°C or less. (7) A textile product comprising the polylactic acid monofilament according to any of (1) to (4) above.

[0011] The present invention can provide an excellent polylactic acid monofilament that is less susceptible to yarn breakage during processing steps such as warping and weaving, can prevent misalignment of the product, and has both high passability and high product quality.

[0012] The polylactic acid in the present invention is a polymer in which lactic acid is polymerized through ester bonds, and the repeating unit is [—C(CH ３ )HC(=O)O-]. In the monomer units constituting polylactic acid, [-C(CH ３ )HC(=O)O-] units are 75 mol % or more, preferably 95 mol % or more.

[0013] The other components are not particularly limited as long as they do not inhibit the effects of the present invention, but it is preferable not to contain inorganic particles such as titanium oxide and silica, as these may cause a decrease in strength and elongation or increase variation in elongation when made into a monofilament.

[0014] Lactic acid has two optical isomers, D-lactic acid and L-lactic acid, and its polymers include poly(D-lactic acid) consisting only of the D isomer, poly(L-lactic acid) consisting only of the L isomer, and polylactic acid consisting of both. As the optical purity of the D-lactic acid or L-lactic acid in polylactic acid decreases, the crystallinity decreases, resulting in a large drop in the melting point. Therefore, to improve heat resistance, the optical purity is preferably 90 mol% or higher.

[0015] The polylactic acid monofilament of the present invention has a fineness of 50.0 dtex or less. By setting the fineness to 50.0 dtex or less, the flexibility of the polylactic acid monofilament, such as its ease of bending, can be maintained, thereby suppressing yarn breakage during advanced processing steps such as weaving. There is no particular need to set a lower limit for the fineness, but from the viewpoint of stably obtaining polylactic acid monofilament and from the viewpoint of practical durability of the product, the fineness is preferably 10.0 dtex or more.

[0016] From the viewpoint of practical durability of the product, the strength of the polylactic acid monofilament of the present invention is preferably 2.5 cN / dtex or more. A more preferred strength is 3.0 cN / dtex or more. Naturally, a higher strength is preferable, but it is difficult with current technology to produce polylactic acid monofilaments with a strength of more than 6.0 cN / dtex with good productivity.

[0017] The elongation of the polylactic acid monofilament of the present invention is preferably 20% to 60%. A more preferred elongation is 30% to 50%. When the elongation is 20% or more, the flexibility of the polylactic acid monofilament, such as its ease of bending, can be maintained, making it easier to prevent thread breakage during advanced processing steps such as weaving. When the elongation is 60% or less, the dimensional stability of the product after weaving can be easily maintained.

[0018] The polylactic acid monofilament of the present invention has a longitudinal elongation variation (CV%) of 7.0% or less. A preferred CV% is 6.0% or less. Generally, the dimensional stability of a product can be maintained by optimizing the boiling water shrinkage rate and elongation, as described in Patent Document 1. However, to prevent misalignment of the product, attention must be paid to minute variations in the longitudinal elongation of the polylactic acid monofilament. Variations in elongation in the longitudinal direction, in particular, affect the misalignment of the product. Furthermore, the tension during processing steps such as warping and weaving also fluctuates, which also affects yarn breakage during the processing steps. The longitudinal elongation variation (CV%) in the present invention is calculated by measuring the elongation 30 times consecutively every 50 cm of the yarn length in the longitudinal direction, using the following formula: Elongation variation (CV%) = (standard deviation at 30 elongations) / (average value at 30 elongations) × 100 (%) If the elongation variation (CV%) exceeds 7.0%, dimensional changes will occur in the fine parts of the polylactic acid monofilament, resulting in increased weave misalignment in the woven product. In addition, the processing tension in the warping and weaving processes will fluctuate significantly, resulting in frequent yarn breakage in the warping and weaving processes, making stable advanced processing difficult.

[0019] The polylactic acid monofilament of the present invention preferably has an oil adhesion rate of 0.30% by mass to 1.30% by mass. A more preferred oil adhesion rate is 0.40% by mass to 1.20% by mass. When the oil adhesion rate is 0.30% by mass or more, the dynamic friction coefficient with the matte finish becomes an appropriate value, and the oil agent necessary for advanced processing in warping, weaving, and other processes is sufficiently adhered, enabling more stable advanced processing. When the oil adhesion rate is 1.30% by mass or less, no excess oil agent is adhered, thereby suppressing the generation of scum due to accumulation of oil agent residue during warping, weaving, and other processes.

[0020] The polylactic acid monofilament of the present invention preferably has a dynamic friction coefficient of 0.250 to 0.350 with a textured surface having a surface roughness of 10S. A more preferred dynamic friction coefficient is 0.270 to 0.330. If the dynamic friction coefficient with the textured surface is 0.250 or higher, appropriate dynamic friction with the textured surface can be maintained, which enables stable winding with a high-speed take-up winder and facilitates package formation. If the dynamic friction coefficient is 0.350 or lower, the friction with the textured surface is not extremely high, which makes advanced processing such as warping and weaving more stable.

[0021] The polylactic acid monofilament of the present invention preferably has a kinetic friction coefficient variation (CV%) of 7.0% or less in the yarn longitudinal direction against a matte finish having a surface roughness of 10S. A more preferable kinetic friction coefficient variation (CV%) is 6.0% or less. The kinetic friction coefficient variation (CV%) in the yarn longitudinal direction in the present invention is defined as the kinetic friction coefficient of a yarn traveling at a yarn speed of 55 m / min for a measurement time of 30 seconds (yarn length 27.5 m) measured by a CV% of 50 x 10 －３ The dynamic friction coefficient variation (CV%) is calculated from 600 data points sampled at second intervals using the following formula: Dynamic friction coefficient variation (CV%) = (standard deviation of dynamic friction coefficients at 600 points) / (average value of dynamic friction coefficients at 600 points) x 100 (%). When the dynamic friction coefficient variation (CV%) is 7.0% or less, the processing tension during warping and weaving processes is less likely to fluctuate, enabling more stable advanced processing. Furthermore, misalignment of the product after weaving can be further suppressed. The surface roughness of the matte finish used in measuring the dynamic friction coefficient refers to the maximum height Ry as specified in JIS B 0601 (1994).

[0022] The boiling water shrinkage of the polylactic acid monofilament of the present invention is preferably 20% or less. If the boiling water shrinkage is 20% or less, the dimensional stability of the product after weaving is easily maintained. A lower boiling water shrinkage is preferable, but it is difficult with current technology to produce polylactic acid monofilament with a boiling water shrinkage of less than 5% with good productivity.

[0023] The textile product containing the polylactic acid monofilament of the present invention is a sheet-like product containing the polylactic acid monofilament, and may also be a composite material using the sheet-like product, such as a sheet or composite material suitable as a filter cloth, filter, strainer, or screen material for food.

[0024] There are no particular limitations on the method for processing the polylactic acid monofilament of the present invention into a textile product. However, the polylactic acid monofilament of the present invention can suppress thread breakage during processing steps such as warping and weaving, can prevent misalignment of the weave of the textile product, and can achieve both high-order processability and product quality. Therefore, it is preferable to process the polylactic acid monofilament of the present invention into a woven fabric, and a plain weave fabric is preferred.

[0025] The polylactic acid monofilament contained in the textile product is preferably 40% by mass or more, and may be 100% by mass.

[0026] The method for producing the polylactic acid monofilament of the present invention uses melt spinning, and the general steps of melt spinning can be any commonly used method. For example, polylactic acid polymer is melted, metered and transported using a gear pump, and extruded from a spinneret to form a monofilament. The monofilament is cooled to room temperature by blowing cooling air using a cooling device such as a chimney, oiled using an oiling device, and then passed through a take-up roller and a stretching roller, during which it is stretched according to the ratio of the peripheral speeds of the take-up roller and the stretching roller. After stretching, it is wound up using a winding device (a one-step method). Alternatively, a two-step method may be used in which the monofilament oiled using an oiling device is first wound up as an unstretched yarn and then stretched. Furthermore, a splitting method such as that described in Patent Document 3 may also be used.

[0027] In the melt spinning of the polylactic acid monofilament of the present invention, the weight-average molecular weight (Mw) of the polylactic acid polymer used is preferably 100,000 to 300,000. A weight-average molecular weight (Mw) of 100,000 or more makes it easier to maintain the strength of the polylactic acid monofilament. A weight-average molecular weight (Mw) of 300,000 or less prevents the melt viscosity of the molten polymer from becoming too high, enabling stable production. Furthermore, the moisture content of the raw material polylactic acid polymer pellets is preferably 300 ppm or less in order to suppress hydrolysis of polylactic acid.

[0028] In the melt spinning of the polylactic acid monofilament of the present invention, oiling is performed using an oiling roller. If oiling is performed using a guide, monofilaments such as polylactic acid, which are prone to high friction, will experience excessive abrasion on the oiling guide, resulting in a decrease in the strength and elongation of the polylactic acid monofilament, variations in elongation, and in the worst case, making stable winding difficult. Oiling using an oiling roller makes it possible to oil the polylactic acid monofilament while reducing abrasion.

[0029] The surface of the oiling roller is given a matte finish with a surface roughness of 20S to 40S. By setting the surface roughness within this range, it becomes possible to oil the polylactic acid monofilament while reducing abrasion to the polylactic acid monofilament. If the surface roughness is less than 20S, abrasion to the polylactic acid monofilament increases when oiled with the oiling roller, resulting in a decrease in the strength and elongation of the polylactic acid monofilament and variations in elongation. If the surface roughness exceeds 40S, the surface of the oiling roller becomes too rough, which in turn increases damage to the polylactic acid monofilament when oiled with the oiling roller, resulting in a decrease in the strength and elongation of the polylactic acid monofilament and variations in elongation. If the surface roughness is matte finished with a surface roughness of 20S to 40S, the surface roughness of the oiling roller becomes appropriate, reducing abrasion and damage to the polylactic acid monofilament when oiled with the oiling roller and stabilizing the strength and elongation of the polylactic acid monofilament. A matte finish with a surface roughness of 23S to 37S is preferred.

[0030] Furthermore, it is preferable to apply a plating treatment such as hard chrome plating to the oiling roller to improve the durability of the surface condition, as long as it does not affect the surface roughness. The surface roughness of the matte-finished roller refers to the maximum height Ry as specified in JIS B 0601 (1994).

[0031] The oiling roller may be made of metal, plastic, or the like, but from the viewpoint of durability, it is preferable to use a metal material with a matte surface finish. Metal materials include carbon steel, cast iron, stainless steel, aluminum alloy, and the like, with carbon steel and stainless steel being preferred.

[0032] In the melt spinning of the polylactic acid monofilament of the present invention, an oil diluted with mineral oil is used. When an oil diluted with water, so-called emulsion oil, is applied to the polylactic acid monofilament, the friction of the polylactic acid monofilament becomes too great, resulting in a decrease in the strength and elongation of the polylactic acid monofilament and variations in elongation. Furthermore, advanced processing such as warping and weaving becomes unstable. Due to the components of the oil, the oil does not spread well on the oiling roller, making uniform oiling difficult and resulting in variations in elongation and dynamic friction coefficient. Using an oil diluted with mineral oil enables uniform oiling while maintaining appropriate friction on the polylactic acid monofilament.

[0033] The viscosity of the oil diluted with mineral oil is 3.9 mPa·s to 4.7 mPa·s. By keeping the viscosity of the oil in this range, the oil spreads firmly on the oiling roller, enabling uniform oiling. If the viscosity of the oil is less than 3.9 mPa·s, the viscosity of the oil is too low to be lifted firmly by the oiling roller, and the oil does not spread. As a result, the oil is not distributed uniformly, resulting in variations in elongation and dynamic friction coefficient. If the viscosity of the oil exceeds 4.7 mPa·s, the viscosity of the oil is too high, and the oil does not spread firmly on the oiling roller. As a result, the oil is not distributed uniformly, resulting in variations in elongation and dynamic friction coefficient. The preferred viscosity of the oil is 4.0 mPa·s to 4.6 mPa·s.

[0034] The main component of the oil is mineral oil used for dilution, and preferably contains surfactants, antistatic agents, extreme pressure agents, and other ingredients, excluding ingredients active against polylactic acid. The viscosity of oil diluted with mineral oil can be adjusted by blending one mineral oil or two or more mineral oils with different viscosities to achieve the desired viscosity. For example, 30-second, 40-second, 80-second, and 100-second mineral oils can be blended. The number of seconds referred to here is Redwood seconds. Furthermore, adjusting the viscosity of emulsion oils that are diluted with water is difficult in the first place.

[0035] Furthermore, the temperature of the yarn immediately before contacting the oiling roller is preferably 40° C. or less, and more preferably 37° C. or less. By keeping the yarn temperature at 40° C. or less, the fiber structure of the polymer discharged from the spinneret is determined, and oiling by the oiling roller can be performed in this state. This prevents uneven thickness in the yarn longitudinal direction and poor advanced processability in the warp and weaving process, allowing for the production of a monofilament with excellent quality.

[0036] Furthermore, it is preferable that the temperature variation of the yarn immediately before contacting the oiling roller is 3° C. or less. By keeping the temperature variation of the yarn to 3° C. or less, it is possible to suppress variation in fiber properties among the yarns, improve the advanced processability in the warp and weaving process, and suppress uneven shrinkage, thereby improving the quality of the monofilament.

[0037] In order to keep the yarn temperature at 40° C. or less and its variation at 3° C. or less, it is preferable to strengthen the cooling of the polymer after it is discharged from the spinneret and ensure flow straightening. Therefore, it is preferable to adopt a horizontally blowing air cooler with high cooling efficiency as the cooling method, and to install a filter on the side opposite the blowing port for the purpose of cutting off the accompanying air current.

[0038] The accompanying airflow cut-off filter referred to here is preferably a filter with gaps to prevent the cooling air sent from the transverse air-blowing type air cooler from stagnating in the yarn running section, and is installed so as to cover the side opposite the outlet so as to prevent the atmosphere of the cooling process from being taken in as an accompanying airflow. The size of the filter may be determined arbitrarily based on the cooling efficiency and the state of variation in yarn temperature, but it is preferable that the filter cover the downstream part of the cooling process down to the floor surface. The presence of an accompanying airflow can improve cooling efficiency, but its irregularity can cause variation in cooling efficiency for each yarn. Therefore, by installing an accompanying airflow cut-off filter, it is possible to suppress the accompanying airflow in the transverse air-blowing type air cooler and reduce variation in yarn temperature.

[0039] The air temperature of the transverse blowing air cooler can be set arbitrarily as long as the cooling is sufficient, but in order to keep the yarn temperature at 40°C or less and at a uniform temperature, the air temperature is preferably 20°C or less.

[0040] Furthermore, the tension of the running yarn between the oiling roller and the next roller immediately after passing through the oiling roller is preferably 0.1 g / dtex to 2.0 g / dtex. This tension varies depending on the rotation speed and surface friction of the oiling roller and the rotation speed of the next roller, but can be controlled by installing a guide directly below the oiling roller and adjusting the angle between the oiling roller and the yarn. By keeping the tension of the running yarn within this range, the stiffness of the running yarn on the oiling roller can be controlled within an appropriate range, and variations in oiling can be suppressed and made uniform, thereby suppressing poor advanced processability in the warp and weaving process and producing a monofilament of excellent quality.

[0041] In order to suppress the above-mentioned variation in yarn temperature, it is preferable to keep the variation in the spinneret surface temperature to 3°C or less. The spinneret surface temperature here refers to the temperature measured at the spinneret surface using a thermocouple. The temperature is measured at a position within 10 mm from the polymer discharge port.

[0042] Generally, as part of the temperature control of melting equipment, the temperature of the nozzle is controlled along with that of the metering pump and piping. However, while the metering pump and piping are contained within equipment that uniformly controls the temperature, the nozzle discharges the polymer and is therefore in contact with the cooling section, i.e., the atmosphere below room temperature, making it prone to temperature variations depending on this condition.

[0043] Therefore, in order to make the die surface temperature uniform, it is important to control the atmospheric temperature directly below the die, and it is preferable to install a heater for the purpose of keeping the die surface warm. The heater here is preferably installed between the die surface and the cooling section, and is preferably tower-shaped to cool the die uniformly.

[0044] The thickness and set temperature of the heater can be set as desired in consideration of variations in the nozzle surface temperature, but in consideration of the cooling efficiency up to the oiling roller, it is preferable that the thickness be 10 to 30 mm and the set temperature be below the "melting temperature of polylactic acid polymer."

[0045] Furthermore, when spinning multiple yarns using one spinneret, it is important to control the temperature distribution on the spinneret surface within the same spinneret to suppress the temperature difference on the spinneret surface at the polymer discharge port for each yarn. By installing a heater similar to that described above, the temperature variation on the spinneret surface can be kept to 3°C or less.

[0046] In the melt spinning method of the present invention for producing polylactic acid monofilaments, heated drawing is preferred. In the case of a one-step method, a heated take-up roller is often used, and the heating temperature is preferably 80°C to 120°C. When the temperature of the take-up roller is 80°C or higher, the polylactic acid monofilament can be drawn uniformly without unevenness in the crystal structure, and the quality of the polylactic acid monofilament is stabilized without devitrification or a decrease in strength and elongation. When the temperature of the take-up roller is 120°C or lower, yarn breakage due to a decrease in spinning tension is reduced, enabling stable production.

[0047] The draw ratio may be adjusted as appropriate to achieve the desired elongation range, but a draw ratio of 2 to 4 is preferred from the viewpoint of stable spinning. Regarding heat setting after drawing, in the case of a one-step method, a heated drawing roller is preferably used, and the heat setting temperature is preferably 100°C to 130°C. When the heat setting temperature of the drawing roller is 100°C or higher, the oriented crystallinity of the polylactic acid monofilament can be increased, thereby reducing the boiling water shrinkage of the polylactic acid monofilament. When the heat setting temperature of the drawing roller is 130°C or lower, yarn breakage due to a decrease in winding tension is reduced, enabling stable production.

[0048] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The measurement methods for the property values ​​in the examples are as follows.

[0049] (1) Correct fineness: Measured in accordance with JIS L1013 (2010) 8.3.1 (Method A). The official moisture regain was set to 0%.

[0050] (2) Strength, elongation, and longitudinal elongation variation (CV%) were measured in accordance with JIS L1013 (2010) 8.5, tensile strength and elongation percentage. Thirty consecutive measurements were performed with a grip distance of 50 cm and a pulling speed of 50 cm / min, and the average value was calculated. Regarding elongation variation (CV%), the standard deviation of the elongation from the 30 consecutive measurements was also calculated, and the coefficient of variation (CV%) was calculated using the following formula: Elongation variation (CV%) = (standard deviation of 30 elongations) / (average value of 30 elongations) × 100 (%).

[0051] (3) Boiling Water Shrinkage: Measured in accordance with JIS L1013 (2010) 8.18.1. A sample was wound 20 times into a skein using a measuring machine with a frame circumference of 1.125 m, and the skein length was measured after leaving it for 24 hours. The skein length was then measured after immersion in boiling water (99±1°C) for 30 minutes and air-dried. The boiling water shrinkage (%) was calculated from the skein lengths before and after immersion in boiling water.

[0052] (4) Oil Adhesion Rate: (a) Approximately 10 g of yarn sample weight (S) was weighed, immersed in 70 ml of n-hexane, and stirred (20°C x 5 minutes) to extract the oil. (b) The same sample was again immersed in 70 ml of n-hexane and stirred (20°C x 5 minutes) to extract the oil. (c) The n-hexane extracted in (a) and (b) above was transferred to a flask whose weight (W0) had been measured after drying, and the n-hexane was evaporated at 100°C. (d) The flask was further dried in a vacuum dryer (40°C x 60 minutes, 10 torr or less). (e) After cooling in a desiccator containing a desiccant, the weight (W1) of the flask was measured. (f) The oil adhesion rate was calculated using the following formula: Oil Adhesion Rate (mass%) = (W1 - W0) / S x 100.

[0053] (5) Dynamic friction coefficient, variation in dynamic friction coefficient in the yarn longitudinal direction (CV%) (a) The measurement device used was a yarn running friction coefficient measuring device (model: ME-P01-T) manufactured by Eiko Sangyo Co., Ltd., and the friction body was a φ15.9 mm hard chrome-plated matte body (surface roughness 10S). (b) The yarn path was adjusted so that the contact angle with the friction body was 180 degrees. (c) The polylactic acid monofilament was run at a yarn speed of 55 m / min, and the tension (T1) at the friction body entrance was adjusted with a tensor so that it was 0.1 N. (d) The measurement time was 30 seconds (measurement length 27.5 m), and the tension (T1) at the friction body entrance and the tension (T2) at the friction body exit were detected. Note that each tension was detected using a 50 x 10 －３ Measurements were performed every 10 seconds, and data was detected for each of 600 points. (e) The dynamic friction coefficient was calculated using the following formula. The simple moving average of the most recent five measurements was used for the dynamic friction coefficient. Dynamic friction coefficient = [ln(T2 / T1)] / π (f) The coefficient of variation (CV%) of the dynamic friction coefficient in the longitudinal direction of the yarn was calculated using the average value and standard deviation of the 600 points of data, as shown in the following formula: Dynamic friction coefficient variation (CV%) = (standard deviation of 600 dynamic friction coefficients) / (average value of 600 dynamic friction coefficients) x 100 (%).

[0054] (6) Viscosity of Oil Solution Diluted with Mineral Oil (a) A Brookfield viscometer (model: BLII) manufactured by Toki Sangyo Co., Ltd. was used. (b) Measurement was performed at a specified temperature of 30°C and a rotor rotation speed of 60 rpm. When the pointer stabilized, the reading on the pointer was read and converted into viscosity. The measurement was performed three times, and the average value was calculated.

[0055] (7) Yarn temperature with oiling roller The temperature was measured 3 cm before the position where the yarn contacted the oiling roller using a TH-BM type non-contact thermometer for measuring running yarn temperature manufactured by Tokyo Seiko Co., Ltd., and this was recorded as the yarn temperature (°C) with the oiling roller. In addition, the temperatures of 10 yarns were measured using the same measurement method, and the difference between the maximum and minimum values ​​was recorded as the yarn temperature variation (°C).

[0056] (8) Warping Eight hundred polylactic acid monofilament packages were set on a warping machine, and warping was performed at 900,000 m per package at a speed of 200 m / min. The total number of yarn breakages was counted. A total number of yarn breakages of 10 or less was considered to be acceptable.

[0057] (9) Weavability The polylactic acid monofilament warp beam obtained in (8) above was set on a sulzer-type loom, and a plain weave fabric was woven at a weave density of 350 threads / 2.45 cm in both the warp and weft directions and a loom rotation speed of 250 rpm. Weaving was continued until weaving yarn breakage occurred or the weaving length reached 100 m, and the number of times that a base fabric with a weaving length of 100 m was obtained out of five weaving tests was counted. A base fabric obtained three or more times was considered to have passed the test.

[0058] (10) Fabric Quality The fabric obtained in (9) above was observed for the presence or absence of misalignment in 1 square meter. Fabrics with misalignment in 3 or more places were rated C, fabrics with misalignment in 1 to 2 places were rated B, and fabrics with no misalignment were rated A.

[0059] (Examples 1, 4-14, Comparative Examples 3-6) Polylactic acid polymer pellets containing no inorganic particles and having a weight-average molecular weight of 140,000 were melted at 230°C and fed to a spinning pack and extruded through a spinneret. A 220°C heater was attached directly below the spinneret surface to maintain the spinneret surface temperature. The extruded yarn was cooled using a blow-off cooling device equipped with an accompanying airflow cut filter, and an oil solution diluted with mineral oil was applied using a hard chrome-plated matte oiling roller (material: carbon steel SS400). The yarn passed through a guide below the oiling roller, stretched 3.14 times between a take-up roller heated to 104°C and a stretching roller heated to 115°C, and wound on a high-speed take-up winder at a speed of 3,500 m / min. The surface roughness of the matte oiling roller, the oil adhesion rate, the yarn temperature with the oiling roller, and the yarn temperature variation are shown in Tables 1 and 2. The viscosity of the oil was adjusted to the viscosities shown in Tables 1 and 2 by blending other ingredients such as surfactants with mineral oil 30 seconds and mineral oil 100 seconds as bases. The fineness, strength, elongation, elongation variation in the longitudinal direction (CV%), boiling water shrinkage, oil adhesion rate, dynamic friction coefficient, and dynamic friction coefficient variation in the longitudinal direction (CV%) of the obtained polylactic acid monofilaments are shown in Tables 1 and 2. The obtained polylactic acid monofilaments were warped and woven, and the quality of the obtained base fabric was evaluated. The results are shown in Tables 1 and 2.

[0060]

[0061]

[0062] (Example 2) Polylactic acid monofilaments were obtained by melt spinning in the same manner as in Example 1 under the conditions shown in Table 1, except that the draw ratio was set to 2.5 times. The fineness, strength, elongation, elongation variation in the longitudinal direction (CV%), boiling water shrinkage, oil adhesion rate, dynamic friction coefficient, and dynamic friction coefficient variation in the longitudinal direction (CV%) of the obtained polylactic acid monofilaments are shown in Table 1. The obtained polylactic acid monofilaments were warped and woven, and the quality of the obtained base fabric was evaluated. The results are shown in Table 1.

[0063] (Example 3) Polylactic acid monofilaments were obtained by melt spinning in the same manner as in Example 1 under the conditions shown in Table 1, except that the draw ratio was set to 3.7 times. The fineness, strength, elongation, elongation variation in the longitudinal direction (CV%), boiling water shrinkage, oil adhesion rate, dynamic friction coefficient, and dynamic friction coefficient variation in the longitudinal direction (CV%) of the obtained polylactic acid monofilaments are shown in Table 1. The obtained polylactic acid monofilaments were warped and woven, and the quality of the obtained base fabric was evaluated. The results are shown in Table 1.

[0064] Comparative Example 1 Polylactic acid monofilaments were obtained by melt spinning in the same manner as in Example 1, except that oil was supplied using a ceramic guide. The fineness, strength, elongation, elongation variation in the longitudinal direction (CV%), boiling water shrinkage, oil adhesion rate, dynamic friction coefficient, and dynamic friction coefficient variation in the longitudinal direction (CV%) of the obtained polylactic acid monofilaments are shown in Table 2. The obtained polylactic acid monofilaments were warped and woven, and the quality of the obtained base fabric was evaluated. The results are shown in Table 2.

[0065] (Comparative Example 2) Polylactic acid monofilaments were obtained by melt spinning in the same manner as in Example 1 under the conditions shown in Table 2, except that an oil solution diluted with water was applied. The fineness, strength, elongation, elongation variation in the longitudinal direction (CV%), boiling water shrinkage, oil adhesion rate, dynamic friction coefficient, and dynamic friction coefficient variation in the longitudinal direction (CV%) of the obtained polylactic acid monofilaments are shown in Table 2. The obtained polylactic acid monofilaments were warped and woven, and the quality of the obtained base fabric was evaluated. The results are shown in Table 2.

[0066] As is clear from the results in Tables 1 and 2, the polylactic acid monofilament of the present invention exhibits extremely significant effects, such as less yarn breakage during warping and weaving processes and maximally reducing misalignment after weaving, compared to conventional polylactic acid monofilaments.

Claims

1. Polylactic acid monofilament having a fineness of 50.0 dtex or less and a variation in elongation (CV%) in the longitudinal direction of the yarn (measured 30 times every 50 cm of yarn length) of 7.0% or less.

2. The polylactic acid monofilament according to claim 1, having an oil adhesion rate of 0.30% by mass or more and 1.30% by mass or less.

3. The polylactic acid monofilament according to claim 1, which has a dynamic friction coefficient of 0.250 or more and 0.350 or less with respect to a matte finish having a surface roughness of 10S.

4. A polylactic acid monofilament according to claim 1, having a dynamic friction coefficient variation (CV%) of 7.0% or less in the longitudinal direction of the yarn (measured at 600 points over a yarn length of 27.5 m).

5. A melt spinning method for polylactic acid monofilament according to claim 1, in which a polylactic acid polymer is melt spun, the spun yarn is oiled, and then stretched with a take-up roller and a stretching roller and wound up, in which a matte oiling roller having a surface roughness of 20S or more and 40S or less is used to adjust the viscosity of the oil diluted with mineral oil to 3.9 mPa·s or more and 4.7 mPa·s or less before oiling.

6. A method for melt spinning polylactic acid monofilaments according to claim 1, wherein the temperature of the yarn just before contacting the oiling roller is 40°C or less and the variation in the yarn temperature is 3.0°C or less.

7. A textile product comprising the polylactic acid monofilament according to claim 1 or 2.

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