JP2023132021A - thermoplastic long fiber - Google Patents

Abstract

To provide a thermoplastic filament having a dynamic friction coefficient stable in time, the thermoplastic filament capable of obtaining excellent high-order passage properties even after a storage in an extended period.SOLUTION: In a thermoplastic filament, a ratio of a pH buffer with an acid dissociation constant pKa within a range of 4.0 to 7.5 is 2.0 to 5.0 wt.% with regard to whole components of an oil solution, a filament-mirror face dynamic friction coefficient after aging is 0.45 or less, and a fluctuation range of the filament-mirror face dynamic friction coefficient is 0.15 or less. The thermoplastic filament is excellent in temporal stability.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to thermoplastic long fibers with good high-order passability.

Long fibers are used for clothing and industrial materials such as fishing nets, and monofilament in particular is used for screen gauze and industrial filters. The process to obtain such products is to manufacture yarn using a spinning machine and then undergo high-level processing such as weaving, knitting, dyeing, and sewing. However, it is possible to reduce manufacturing costs and create new products through joint development with overseas manufacturers. Therefore, processing is often carried out after raw yarn is transported overseas by sea. On the other hand, when yarn is transported by sea, there are concerns that the oil component attached to the yarn may deteriorate or volatilize because it is transported over the sea in a high-temperature, high-humidity environment, and in fact, in monofilament, the composition of the oil attached to the yarn changes before and after transportation. However, a problem has arisen in which friction increases and the warping tension becomes unstable. Several proposals have been made so far for the purpose of suppressing the deterioration of adhering oil components.

For example, Patent Document 1 describes that in polytrimethylene terephthalate-based polyester fibers, by adding an isocyanate-based antioxidant to the adhering oil agent, oxidative decomposition of smooth components is suppressed, and even after long-term storage from spinning to false twisting. It is proposed that good workability can be obtained.
Patent Document 2 proposes a fiber that generates less scum over time by volatilizing monomers and oligomers remaining on the yarn surface and in the yarn through heat treatment with a drawing heater.
Patent Document 3 describes that by setting the weight average molecular weight range of the fatty acid alkyl ester to a predetermined value or higher, volatilization and decomposition of the component during the heat treatment process and over time are suppressed, and the smoothness of the polyester monofilament is maintained. is suggesting.

Japanese Patent Application Publication No. 2003-342876 JP2020-143410A Japanese Patent Application Publication No. 2008-121125

An object of the present invention is to provide a thermoplastic long fiber that does not deteriorate in its attached oil component even after changes in the storage environment or after long-term storage and has good high-order passability.

One of the presumed mechanisms for the deterioration of the adhering oil component is an equilibrium reaction between the fatty acid alkyl ester, which is a smoothing agent, and water, in which the fatty acid alkyl ester is hydrolyzed to produce carboxylic acid and alcohol. Further, the protons (H ⁺ ) of the generated carboxylic acid act as a catalyst, accelerating the hydrolysis of the ester. As the proportion of fatty acid alkyl ester in all components of the oil agent decreases, the smoothing performance decreases and the dynamic friction of the long fibers increases, and the balance of the oil agent composition is disrupted, resulting in a decrease in the compatibility of the oil agent components and I think this becomes obvious and unevenness occurs in the friction in the longitudinal direction. Furthermore, when such long fibers are used in the knitting and weaving process, increases and fluctuations in running tension are exacerbated, leading to increased yarn breakage and quality defects such as unevenness in the opening of knitted fabrics and woven fabrics. To address these problems, prior art approaches to suppress acid generation have not been sufficient, and deterioration over time has not been completely suppressed.

Patent Document 1 does not contain an additive that captures protons of carboxylic acid generated by hydrolysis of a fatty acid alkyl ester, and therefore cannot completely suppress deterioration over time. Patent Document 2 proposes adding a pH buffer, but since the pH has decreased to 4 after one year and the acid dissociation constant pKa of carboxylic acid is also about 4, The capture was not working well and the effect of the pH buffer was insufficient. In Patent Document 3, the number of molecules contained in the oil agent is reduced by increasing the weight average molecular weight of the fatty acid alkyl ester, thereby suppressing the equilibrium reaction between the fatty acid alkyl ester and water from tilting toward hydrolysis. Hydrolysis could not be sufficiently suppressed because the protons of the carboxylic acid were not captured.

The present invention overcomes the above-mentioned problems and provides thermoplastic long fibers that do not deteriorate in the attached oil component even after changes in the storage environment or after long-term storage and have good high-order passability.

The purpose of the present invention can be achieved by using the following thermoplastic long fibers.
The coefficient of dynamic friction between the thread and the mirror after aging is 0.45 or less, which is coated with an oil containing 2.0 to 5.0% by weight of a pH buffering agent with an acid dissociation constant pKa of 4.0 to 7.5. , thermoplastic long fibers whose fluctuation range in the coefficient of dynamic friction between yarn and mirror surface is 0.15 or less.
Here, aging refers to a treatment in which the sample is left in a constant temperature machine at a temperature of 70° C. and a humidity of 95 Rh% for 7 days.

By limiting the oil component, the adhered oil component does not deteriorate even after storage environment changes or long-term storage, has good high-order passability, and suppresses uneven opening of knitted and woven fabrics. Thermoplastic long fibers can be provided.

FIG. 1 is a diagram for calculating other peak intensities, with the maximum peak intensity being 1.00 when the adhered oil agent is measured by GPC.

Examples of the thermoplastic long fibers used in the present invention include polyester fibers, polyamide fibers, and polyolefin fibers.

Polyester fibers include polyethylene terephthalate as a fiber material polymer, copolyester containing a part of a repeating unit other than ethylene terephthalate, and a polyester polymer blend in which a part of a polymer other than polyethylene terephthalate is mixed with polyethylene terephthalate. Can be mentioned. In addition, polyamide fibers include those using polyamide as a fiber material polymer, copolyamide that partially contains something other than polyamide as a repeating unit, and polyamide polymer blend that partially mixes a polymer other than polyamide with polyamide. .

Among these, polyester fibers are particularly preferred. This is because polyester fibers are relatively inexpensive and have excellent properties such as mechanical properties, so they are used in many fields such as clothing and materials.

In the oil agent attached to the thermoplastic long fibers of the present invention, in order to suppress the generation of acids (protons), a pH buffering agent having an acid dissociation constant pKa of 4.0 to 7.5 is added to the oil agent component in an amount of 2.0 to 5. Contains .0% by weight. Since the acid dissociation constant pKa of the carboxylic acid generated by the decomposition of the fatty acid alkyl ester used as a smoothing agent is generally 4 to 5, the decomposition of the fatty acid alkyl ester is accelerated when the pH of the adhering oil agent is less than 5.0. be done. The acid dissociation constant pKa of the pH buffer is in the range of 4.0 to 7.5 in order to maintain the pH of the attached oil at 5.0 or higher and to suppress the decomposition of the fatty acid alkyl ester.

When the acid dissociation constant pKa of the pH buffer is less than 4.0, the pH of the adhering oil decreases to less than 5.0, promoting the decomposition of the fatty acid alkyl ester. Further, when the acid dissociation constant pKa of the pH buffer exceeds 7.5, the ester bond of the fatty acid alkyl ester of the smoothing agent causes alkaline hydrolysis. Preferably, the acid dissociation constant pKa of the pH buffer is 4.5 to 7.0, and the pH of the adhering oil agent is maintained at 5.8 or higher to further suppress the decomposition of the fatty acid alkyl ester.

The pH buffering agent used in the thermoplastic long fibers of the present invention is not particularly limited, but carboxylates, phosphates, etc. can be used. In order to prevent oxidative decomposition and hydrolysis of the pH buffer, the functional group is preferably an alkyl group. Further, it is preferable that the average molecular weight of the pH buffering agent is 300 or more because volatilization can be suppressed and a pH suppressing effect can be stably obtained. For example, aliphatic monocarboxylate, aliphatic dicarboxylate, polyoxyethylene alkyl ether carboxylate, monoalkyl phosphate salt, dialkyl phosphate salt, polyoxyalkyl phosphate salt, polyoxyalkylene phosphate salt , polyoxyethylene alkyl ether phosphate. A plurality of pH buffers with different acid dissociation constants pKa may be used, and two or more buffers with different acid dissociation constants pKa may be used in consideration of the acid dissociation constant pKa of the generated acid and the pH range to be maintained. preferable.

If the proportion of the pH buffering agent per adhering oil component is less than 2.0% by weight, a sufficient pH reduction suppressing effect cannot be obtained. Further, even if the proportion of the pH buffer exceeds 5.0% by weight, no further effect of suppressing the pH decrease is obtained, and the coefficient of dynamic friction increases. The preferred proportion of pH buffer is 2.4-4.6% by weight.

In the oil agent that adheres to the thermoplastic long fibers of the present invention, by appropriately adding a pH buffer, fatty acid alkyl esters are prevented from decomposing into carboxylic acids, so changes in the oil agent composition due to aging are small. Become. For example, using THF (tetrahydrofuran), components extracted from the thermoplastic long fibers of the present application can be measured by GPC to confirm changes in the oil composition due to aging. When the molecular weight distribution curve of the GPC results is plotted as shown in Figure 1, with intensity on the vertical axis and molecular weight on the horizontal axis, each molecular weight appears as a peak, and the intensity at the top of the peak is determined by the form of the compound and the content in the oil. It appears depending on. By setting the maximum peak intensity as 1.00 and calculating the other peak intensities, it is possible to read the change in the oil component ratio, and for the peak intensity of the same molecular weight before and after aging, (peak intensity before aging) - It is known that the peak intensity after aging satisfies -0.05 to +0.05. If it exceeds ±0.05, the oil component has volatilized or decomposed, and dynamic friction increases, resulting in frequent abnormal stoppage of the knitting loom and yarn breakage due to excessive tension. More preferably, it is within ±0.03.

The thermoplastic long fibers of the present invention have a yarn-mirror dynamic friction coefficient of 0.45 or less after aging, and a fluctuation range of the yarn-mirror dynamic friction coefficient of 0.15 or less, so that they can be used for knitting and weaving even after long-term storage. It reduces friction between the long fibers and the process guide during the process, eliminates abnormal stoppage of the knitting loom or yarn breakage due to excessive tension, and suppresses the occurrence of quality defects due to uneven opening of knitted fabrics and woven fabrics. When the coefficient of dynamic friction exceeds 0.45, abnormal stoppage of the knitting loom and thread breakage due to excessive tension occur frequently. The preferred range of the thread-mirror dynamic friction coefficient after aging is 0.40 or less. Further, if the fluctuation range of the dynamic friction coefficient between the thread and the mirror surface exceeds 0.15, quality defects such as irregularities in the opening of the knitted fabric or woven fabric due to excessive tension may occur. The preferred range of variation in the dynamic friction coefficient between the thread and the mirror surface is 0.13 or less.
Here, aging refers to a treatment in which the sample is left in a constant temperature machine at a temperature of 70° C. and a humidity of 95 Rh% for 7 days.

The pH of the oil adhering to the thermoplastic long fibers of the present invention is preferably 5.5 to 7.4, and the pH of the oil adhering after aging is preferably 5.2 to 7.1. If the pH of the adhering oil is 5.5 or higher, even if a small amount of acid is generated during aging, the pH can be maintained at 5.2 or higher, reducing the risk of corroding metal process guides such as reeds with acid. , is preferable because the guide replacement cycle can be extended. If the pH of the attached oil is 7.4 or less and the pH after aging is 7.1 or less, the oil components will be prevented from precipitating, the oil will be applied in a homogeneous state, and the precipitation of the components will be suppressed even after adhesion. This is preferable because there is less scum in the weaving process and the range of variation in the dynamic friction coefficient between the thread and the mirror surface can be further reduced. More preferably, the pH of the deposited oil is 5.8 to 7.1, and the pH of the deposited oil after aging is 5.5 to 6.8.

The thermoplastic long fibers of the present invention preferably have a reduction rate of 10% or less in the amount of oil deposited before and after aging, so that dynamic friction can be kept low even after long-term storage. It is more preferable that the weight loss rate is 5% or less because dynamic friction can be kept low.

In the oil component attached to the thermoplastic long fibers of the present invention, a fatty acid alkyl ester can be used as a smoothing agent. Further, a weight average molecular weight of 450 or more is preferable because it is difficult to decompose during the manufacturing process or over time, and a weight average molecular weight of 650 or less is preferable because it does not have a large effect on dynamic friction. Additionally, additives such as modified silicone may be added within a range that does not worsen dynamic friction.

The fineness of the thermoplastic long fibers of the present invention is not particularly limited, but the finer the fineness, the lower the breaking strength, and the easier it is for yarn breakage to occur due to increased dynamic friction. noticeable.

Although the number of filaments of the thermoplastic long fibers of the present invention is not particularly limited, in the case of monofilaments, the running tension increases due to an increase in dynamic friction, causing fraying and fuzzing, and yarn breakage at that point, so the effects of the present invention are more pronounced. .

A preferred method for producing the thermoplastic long fibers of the present invention will be explained.
The process for producing the thermoplastic long fibers of the present application may employ any known production method, and a method for producing polyester monofilament will be described as an example.

Polyethylene terephthalate (PET) melted by an extruder is supplied to a spinneret using a metering pump so as to have a desired fineness, and a yarn is discharged. The melt spinning temperature is preferably 280 to 310° C. from the viewpoint of sufficiently melting PET and suppressing thermal decomposition due to excessive heat application.

When forming a core/sheath composite, the core/sheath is separately melted and weighed using two extruders, and both components are combined using a known core/sheath composite die and then discharged.

For the purpose of suppressing the orientation of the yarn and making the orientation uniform, a heating cylinder may be used at a portion where the discharged yarn is cooled. When a heating cylinder is used, the atmospheric temperature inside the heating cylinder is preferably 200 to 330°C. If the atmospheric temperature inside the heating cylinder is 200° C. or higher, the effect of the heating cylinder can be sufficiently obtained. If the atmospheric temperature in the heating cylinder is 330° C. or lower, fiber diameter unevenness in the yarn longitudinal direction is suppressed.

It is preferable to use chimney air cooling as the cooling method. For cooling with chimney air, for example, a method of blowing from one direction substantially perpendicular to the running direction of the yarn, or a method of blowing from one direction substantially perpendicular to the running direction of the yarn and from the entire circumference can be used. It is preferable to apply a spinning oil to the cooled yarn before it is taken up by a roller. The lubricated yarn is preferably taken up by a take-up roller having a surface speed of 300 to 3000 m/min. Thereafter, either a two-step method in which the yarn is wound as an undrawn yarn and then stretched, or a direct spinning/drawing method in which the yarn is fed directly to the stretching step may be used. From the viewpoint of production efficiency and orientation uniformity of the obtained monofilament, the direct spinning and drawing method is preferable.

The composition of the oil agent used in the manufacturing process of the present invention is not particularly limited, but it contains 30% by weight or more of a fatty acid alkyl ester smoothing agent from the viewpoint of improving smoothness and suppressing fuzzing and yarn breakage during knitting and weaving. It is preferable to use an oil agent. Further, it is preferable to add 6 to 8% by weight of modified silicone to the oil agent, as this further improves smoothness. The oil agent may be mixed with water to form an emulsion and applied to the yarn using an oil supply guide or an oiling roller. The amount of oil to be supplied at this time is preferably 0.1 to 2.0% by weight based on the drawn yarn because smoothness is good and yarn falling and collapse during package formation are suppressed.

Next, the thermoplastic long fibers of the present invention will be explained in detail with reference to Examples. Evaluation of Examples and Comparative Examples was performed by the following method.

(1) Fineness A 500 m skein of polyester monofilament was taken, and the fineness was determined by multiplying the mass (g) of the skein by 20.

(2) Dynamic friction characteristics between thread and mirror surface It is expressed as the friction coefficient μ when measured under the following conditions using a friction tester (manufactured by Eiko Sangyo) and a 0.3S mirror finish chrome pin with a pin diameter of 35 mmφ. did.
Tension on the entry side of running yarn: T1 = 10g
Tension at exit side of running yarn: T2 = measured value Contact angle: 90°
Yarn running speed: 2.5 m/min μ=(2/π)×ln(T2/T1).

(3) pH of attached oil agent
Precisely weigh 10 g of the sample, heat it under reflux for 3 hours using a Soxhlet extractor using methanol as a solvent, and extract the oil. After extraction, methanol is removed, dried, adjusted to a 0.1% aqueous solution, and washed with a pH meter. (manufactured by Horiba, Ltd.) to measure pH.

(4) Measurement of oil adhesion amount Precisely weigh 10 g of sample, heat under reflux for 3 hours using methanol as a solvent using a Soxhlet extractor to extract oil, remove methanol after extraction, dry, and remove before and after extraction. The amount of oil adhesion was calculated from the difference in weight of the containers.

(5) Measurement of GPC The molecular weight distribution of the THF-soluble components of the sample measured by GPC was measured as follows.
Gel permeation chromatography (GPC) measuring device: GPC-8220GPC (manufactured by Tosoh Corporation)
Column: TSK-GEL SUPER HZ2000, TSK-GEL SUPER HZ2500, TSK-GEL SUPER HZ3000
Temperature: 40℃
Solvent: THF
Flow rate: 0.35 ml/min Sample: THF sample solution adjusted to 0.15% by mass Sample pretreatment: 10 g of the sample was accurately weighed, and heated to reflux for 3 hours using a Soxhlet extractor using methanol as a solvent. The oil was extracted, and after extraction, methanol was removed, dried, dissolved in tetrahydrofuran THF (containing stabilizer, manufactured by Wako Pure Chemical Industries, Ltd.) at 0.15% by weight, and filtered through a 0.45 μm filter, and the filtrate was used as a sample. there was.

The measurement was performed by injecting 10 μL of the THF sample solution. In measuring the molecular weight of the sample, the molecular weight distribution of the sample was calculated from the relationship between the logarithm value and the count number of a calibration curve prepared using several types of monodisperse polystyrene standard samples. An RI (refractive index) detector was used as a detector.

The THF-soluble GPC measurement results were plotted as a molecular weight distribution curve with intensity on the vertical axis and molecular weight on the horizontal axis, and the intensity of the entire molecular weight distribution curve was corrected by setting the maximum peak intensity to 1.00.

(6) Evaluation by GPC Measure the GPC of the adhered oil agent before aging, set the maximum peak intensity as 1.00, and calculate other peak intensities. Next, the GPC of the adhered oil agent after aging is measured, and in the same manner as before aging, the other peak intensities are calculated, with the maximum peak intensity being set as 1.00. For peaks with the same molecular weight, if the following formula is satisfied, the test is passed.
-0.05≦(Peak intensity before aging) -(Peak intensity after aging)≦0.05
Note that aging is performed by leaving the sample still in a constant temperature machine at a temperature of 70° C. and a humidity of 95 Rh% for 7 days.

(7) Evaluation of running tension In order to reproduce the warping process, a package containing wound long fibers was placed on a creel, passed through a tensor at a distance of 30 cm from the end of the package, and then passed through a tension meter at a speed of 200 m/min. I picked it up with a speed roller. At that time, a weight was placed on the tensioner, the tension at the exit side of the tensioner was set to 4 g, and the tester was run for 30 minutes, and the maximum value and fluctuation range of the running tension were measured.

(Example 1) PET monofilament PET polymerized and pelletized by a conventional method was melted using an extruder. Thereafter, the molten polymer was introduced into the spin pack by passing through piping provided in a spin block kept at 295° C. and a metering pump that metered the polymer flow rate to a desired polymer flow rate. A filter and a known spinneret are installed in the spin pack in turn. Yarn was spun from this spinneret. A heating cylinder with an internal atmosphere temperature of 273° C. was provided, and the yarn spun from the spinneret was passed through it. Thereafter, air at 25° C. was blown onto the yarn at a wind speed of 15 m/min from one direction perpendicular to the yarn using a cooler, and the yarn was cooled and solidified. A spinning oil was applied to the cooled and solidified yarn using an oiling roll so that the amount of spinning oil was 0.3% based on the drawn yarn.

The components of the oil include 3.0% aliphatic dicarboxylate salt (pKa=5.5) as a pH buffer, 1.0% alkyl phosphate salt (pKa=6.8), and a known fatty acid ester smoothing agent. 60% modified silicone, 7% modified silicone, and other known metal abrasives, antistatic agents, and surfactants are emulsified at a concentration of 8% in distilled water.

After oiling, the yarn was taken as it was to a non-heated first godet roll at a speed of 735 m/min. The first hot roll was heated to a temperature of 90°C at a speed of 742 m/min without being wound up, the second hot roll was heated to a temperature of 90°C at a speed of 2385 m/min, 130° C. at a speed of 3373 m/min. The film was drawn around a third hot roll heated to a temperature of 0.degree. C., and subjected to stretching and heat setting. Furthermore, after winding it around two unheated godet rolls at a speed of 3375 m/min, it was wound into a package by controlling the spindle rotation speed so that the winding tension was 0.425 g/dtex. A monofilament was obtained. The properties of this polyester monofilament are shown in Table 1. Even after aging, it was possible to keep the coefficient of dynamic friction low, suppress a decrease in pH, and suppress changes in GPC (molecular weight distribution) and running tension.

(Example 2) Polyamide monofilament N66 polymerized and pelletized by a conventional method was melted using an extruder. Thereafter, the molten polymer was introduced into the spin pack by passing through piping provided in a spin block kept at 289° C. and a metering pump that metered the polymer flow rate to a desired polymer flow rate. A filter and a known spinneret are installed in the spin pack in turn. Yarn was spun from this spinneret. Thereafter, air at 25° C. was blown onto the yarn at a wind speed of 15 m/min from one direction perpendicular to the yarn using a cooler, and the yarn was cooled and solidified. A spinning oil was applied to the cooled and solidified yarn using an oiling roll so that the amount of spinning oil was 0.3% based on the drawn yarn.

The components of the oil include 2.0% aliphatic dicarboxylate salt (pKa=5.5) as a pH buffer, 0.5% alkyl phosphate salt (pKa=6.8), and a known fatty acid ester smoothing agent. It is the same as Example 1 except that it was set to 62%.

After oiling, the yarn is taken up as it is with an unheated godet roll at a speed of 774 m/min, and without being wound up, it is passed through a hot roll heated to a temperature of 190°C at a speed of 3200 m/min, where it is stretched and heat set. went. Furthermore, the spindle rotation speed was controlled at a speed of 3000 m/min and the product was wound into a package to obtain a nylon monofilament of 8.0 dtex. It had a good dynamic friction coefficient and was able to suppress changes in running tension.

(Example 3) PET multifilament PET polymerized and pelletized by a conventional method was melted using an extruder. Thereafter, the molten polymer was introduced into the spin pack by passing through piping provided in a spin block kept at 280° C. and a metering pump that metered the polymer flow rate to a desired polymer flow rate. A filter and a known spinneret are installed in the spin pack in turn. Yarn was spun from this spinneret. Thereafter, air at 25° C. was blown onto the yarn at a wind speed of 25 m/min from one direction perpendicular to the yarn using a cooler, and the yarn was cooled and solidified. A spinning oil was applied to the cooled and solidified yarn using an oiling roll so that the amount of spinning oil was 1.0% based on the drawn yarn.

The components of the oil were 3.0% aliphatic dicarboxylate (pKa=5.5) and 1.0% aliphatic polyoxyalkylene phosphate salt (pKa=6.3) as pH buffers. The rest is the same as in Example 1.

After oiling, the yarn is passed through a first hot roll heated to 80°C at a speed of 1500 m/min and a second hot roll heated to 160°C at a speed of 4200 m/min, then stretched and heated. I did a set. Furthermore, after winding it around two non-heated godet rolls at a speed of 4221 m/min, it was wound into a package by controlling the spindle rotation speed so that the winding tension was 0.212 g/dtex. A filament of polyester long fibers was obtained. It had a good dynamic friction coefficient and was able to suppress changes in running tension.

(Comparative Example 1) PET Monofilament A monofilament was obtained in the same manner as in Example 1 except that 1.0% of aliphatic dicarboxylate (pKa=5.5) was used as the pH buffer. After aging, the coefficient of kinetic friction increased and the pH decreased to 4.8. Furthermore, in the molecular weight distribution measured by GPC, the difference in peak intensity for the same molecular weight before and after aging was 0.05 or more, and the running tension increased and fluctuations became large.

Claims (3)

The thread-mirror dynamic friction coefficient after aging is 0.45 or less, to which an oil agent containing 2.0 to 5.0% by weight of a pH buffering agent with an acid dissociation constant pKa of 4.0 to 7.5 is attached. , thermoplastic long fibers whose fluctuation range in the coefficient of dynamic friction between yarn and mirror surface is 0.15 or less.
Here, aging refers to a treatment in which the sample is left in a constant temperature machine at a temperature of 70° C. and a humidity of 95 Rh% for 7 days. The thermoplastic long fiber according to claim 1, wherein the pH of the oil adhering to the fiber is 5.5 to 7.4, and the pH of the oil adhering after aging is 5.2 to 7.1. The thermoplastic long fiber according to claim 1 or 2, wherein the rate of reduction in the amount of oil deposited before and after aging is 10% or less.

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