JP2011157647A - Wiping cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiping cloth having extremely excellent wiping property and dust collecting property. <P>SOLUTION: The wiping cloth comprises a microfiber satisfying requirements that (a) the microfiber is a polyester microfiber having a main repeating unit composed of a trimethylene terephthalate, has an average single fiber diameter of 50-2,000 nm, CV% of average single fiber diameter of 0-25% and a strength of 1.5-6.0 cN/dtex, (b) the microfiber is obtained by eluting the island component of a sea-island type conjugate fiber comprising a polytrimethylene terephthalate as an island component and a hot water-soluble polyester as a sea component and (c) the hot water-soluble polyester is a polyester in which ≥5 mol% of 5-sodium sulfoisophthalate is copolymerized based on the total acid components of the polyester and ≥5% of a polyethylene glycol compound is copolymerized based on the total weight of the polyester. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wiping cloth having softness and softness that has flexibility and strength, little dust generation, and excellent wipeability.

  Conventionally, wiping cloths have been used for cleaning cloths, glasses and lens wipes. And many of them have used natural fibers such as cotton fibers as fiber materials with good water absorption, and ultrafine fibers that are expected to increase the adsorption power by increasing the fiber surface area in the fabric. Today, wiping cloth is widely deployed in industrial fields such as IC and semiconductor manufacturing factories and clean rooms. The wiping cloth for industrial use is required not to generate dust as well as the wiping ability of conventional oil, water, etc., and the dust trapping power.

  However, as described in Patent Document 1, for example, a wiping cloth in which natural fibers are located in a large amount on the surface of the fabric has a problem that fluff falls on the surface of the object to be wiped and generates dust. Further, as described in Patent Document 2, for example, in a high-density entangled knitted fabric mainly composed of a superfine yarn of 0.2 dtex or less and a yarn of 0.5 to 10 dtex, the superfine yarn is There was a problem of dust generation due to coming out on the surface of the wiping cloth.

  On the other hand, polyamides such as nylon 6 and nylon 66 and polyesters such as polyethylene terephthalate are generally used as the ultrafine fiber material. However, the ultrafine fiber made of polyamide has poor weather resistance due to the inherent properties of this material, and has other disadvantages such as yellowing and low acid resistance, while the ultrafine fiber made of polyethylene terephthalate has excellent weather resistance. However, there is a problem that there is no flexibility like nylon 6 and the dust collecting power is insufficient when a wiping cloth is used.

  In order to solve such a problem, an ultrafine multifilament made of polytrimethylene terephthalate (Patent Document 3 (Patent No. 3199669)) can be used, but this method is a method by direct spinning and the fineness obtained. However, there is a limit to productivity and processability.

  On the other hand, as a method for producing polytrimethylene terephthalate ultrafine fibers, for example, Patent Document 4 (Japanese Patent Laid-Open No. 2006-265786) discloses polytrimethylene terephthalate ultrafine yarns obtained by eluting sea components from sea-island fibers. Yes. However, in this case as well, the fineness was as large as 0.01 to 0.5 dtex, and the wiping property and dust collection property were insufficient in terms of flexibility and denseness for use as a wiping cloth.

  Patent Document 5 (WO 2005/095686) proposes a sea-island composite fiber having a number of islands of 100 islands or more per filament of sea-island fiber as a method for obtaining a polyester ultrafine fiber. It is true that polytrimethylene terephthalate can be obtained with this method. There was a problem that it was difficult to crystallize in alignment with polyethylene terephthalate, and the strength was low and it was easily broken.

Therefore, in the case of sea-island fibers with polytrimethylene terephthalate as an island component for wiping cloth, the sea component must be compatible with both the solubility removal property, the strength of the obtained ultrafine fiber, and the yarn-making property. There was a need to select what was done.
As described above, in the conventional method, there are still problems in securing processability and fiber strength when the polytrimethylene terephthalate is further miniaturized, and a solution to this point is desired.

Japanese Patent Laid-Open No. 61-228821 JP 63-2111364 A Japanese Patent No. 3199669 JP 2006-265786 A WO2005 / 095686

  The object of the present invention is to wipe off and collect dust, including high-strength and uniform polytrimethylene terephthalate ultrafine fibers, which are formed from sea-island type composite fibers that are excellent in yarn formation and island component formation during elution. It is to provide an extremely excellent wiping cloth.

  As a result of studies conducted by the present inventors to solve such problems, the sea-island type composite fiber containing polytrimethylene terephthalate as an island component is used to form a specific copolymer polyester polymer as a sea component, thereby forming an island component. The ultra-fine fibers can be made uniform and have high physical properties, thereby achieving the object.

That is, according to the present invention,
A wiping cloth containing ultrafine fibers, characterized by satisfying the following requirements:
a) Polyester ultrafine fiber whose main repeating unit is trimethylene terephthalate, the average single fiber diameter is 50 to 2000 nm, the CV% of the average single fiber diameter is 0 to 25%, and the strength is 1.5 to 6. 0 cN / dtex.
b) It is an ultrafine fiber obtained by elution treatment of a sea component of a sea-island type composite fiber having polytrimethylene terephthalate as an island component and hot water-soluble polyester as a sea component.
c) The sea component is a copolymerized polyester of a polyethylene glycol compound and 5-sodium sulfoisophthalic acid, the polyethylene glycol compound is 5 to 12% by weight based on the total weight of the polyester, and 5-sodium sulfoisophthalic acid is the total acid of the polyester. It is a polyester copolymerized with 5 to 8 mol% with respect to the component.
Is provided.

  The wiping cloth of the present invention includes trimethylene terephthalate having an average single yarn fiber diameter of 50 to 2000 nm, which is extremely fine and uniform, and high strength. Therefore, the wiping cloth is excellent in flexibility and wiping property.

Hereinafter, the wiping cloth of the present invention will be described in detail.
The wiping cloth of the present invention contains ultrafine fibers at least in part, and the ultrafine fibers are mainly composed of polytrimethylene terephthalate. Polytrimethylene terephthalate is a polyester obtained using terephthalic acid as the main acid component and 1,3-propanediol as the main glycol component. As used herein, “main” refers to containing 80 mol% or more, and includes a copolymer component capable of forming another ester bond at a ratio of 20 mol% or less within a range not impairing the effects of the present invention. It may be a thing. The copolymerizable compound includes dicarboxylic acids such as isophthalic acid, cyclohexanedicarboxylic acid, adipic acid, dimer acid, sebacic acid and 2,6-naphthalenedicarboxylic acid, and glycol components such as ethylene glycol and diethylene glycol. , Butanediol, neopentyl glycol, cyclohexane dimethanol, polyethylene glycol, polypropylene glycol and the like, but are not limited thereto.

Further, various additives such as matting agents, heat stabilizers, flame retardants, antistatic agents, lubricants, color pigments, antifoaming agents, and the like may be copolymerized or mixed as necessary.
The polytrimethylene terephthalate used in the present invention can be polymerized by a known method.

  The polytrimethylene terephthalate ultrafine fiber constituting the wiping cloth of the present invention preferably has an intrinsic viscosity of 0.8 to 2.0. When the intrinsic viscosity is less than 0.8, mechanical properties such as strength are deteriorated and wear resistance is inferior. When the intrinsic viscosity is more than 2.0, ultrafine fibers cannot be stably produced. A more preferable intrinsic viscosity is 0.9 to 1.5.

  Further, the average diameter of the polytrimethylene terephthalate ultrafine fiber needs to be 50 to 2000 nm. If it is less than 50 nm, the strength of the total fiber is lowered, and it is difficult to use as an industrial material. If it exceeds 2000 nm, sufficient flexibility and performance as an ultrathin thread are lowered, resulting in poor wiping as a wiping cloth. . A preferred range is 300-1500 nm.

  Furthermore, CV% of the average single fiber diameter of the polytrimethylene terephthalate ultrafine fiber is 0 to 25%. When CV% exceeds 25%, the diameter variation is large and the wiping performance is significantly reduced, more preferably 0 to 20%, still more preferably 0 to 15%. Since the ultrafine fiber of the present invention has a small CV% and a small variation in diameter, the distribution of the surface area of the fiber is also small, and excellent wiping performance can be imparted. In addition, when the sea-island composite fiber is stretched, the fine fibers are not broken and the dusting property of the wiping cloth is improved.

  The strength of the polytrimethylene terephthalate ultrafine fiber needs to be 1.5 to 6.0 cN / dtex as the tensile strength when the ultrafine fiber is measured as a fiber bundle. When the tensile strength is 1.5 cN / dtex, it causes dust generation during wiping, making it difficult to put it to practical use. Moreover, the fiber exceeding 6.0 cN / dtex is not preferable in consideration of the balance with the elongation in the production process. A more preferable range is 1.8 to 5.5 cN / dt. The elongation at break is preferably 10 to 80%, and the shrinkage in boiling water is preferably 5 to 20%.

  As a method for producing the polytrimethylene terephthalate ultrafine fiber, it is necessary to remove the sea component from the conventionally known sea-island composite fiber having a multi-island structure. In this case, the sea component polymer can be appropriately selected as long as it is a combination having higher solubility than the island component polymer, but the dissolution rate ratio (sea / island) is preferably 200 or more. When this dissolution rate ratio is less than 200, part of the island component of the fiber cross-section surface layer is dissolved while the sea component of the fiber cross-section center is dissolved, so the sea component is completely dissolved and removed. For this purpose, the island component is reduced by a percentage, and the strength of the island component is deteriorated and the strength is deteriorated due to solvent erosion.

  When sea component removal by alkali elution is performed, the sea component polymer is, for example, an alkaline aqueous solution easily soluble polymer, and is compatible with both easy alkali solubility and sea-island cross-sectional formability. It is necessary to copolymerize sulfoisophthalic acid in an amount of 5 mol% or more, preferably 5 to 8 mol%, based on the total polyester acid component. Further, it is necessary that the polyethylene glycol having a number average molecular weight of 4000 to 12000 is copolymerized by 5% by weight or more, preferably 5 to 12% by weight, based on the total weight of the polyester. The intrinsic viscosity of the sea component is preferably 0.4 to 0.6. Here, 5-sodium isophthalic acid contributes to improving the hydrophilicity and melt viscosity of the resulting copolymer, and polyethylene glycol (PEG) improves the hydrophilicity of the resulting copolymer.

  The definition of these copolymerization amounts is important for obtaining the polytrimethylene terephthalate ultrafine fiber constituting the wiping cloth of the present invention, and 5-sodium isophthalic acid is 5 to 8 with respect to all the acid components constituting the polyester. It is necessary to be mol%, preferably 6 to 8 mol%. If it exceeds 10 mol%, the spinning property is remarkably deteriorated and stable production becomes difficult, and a product having a predetermined strength cannot be obtained. If it is less than 5 mol%, the difference in dissolution rate from polytrimethylene terephthalate is not sufficient. Elimination of sea components is impossible.

  On the other hand, polyethylene glycol is required to be 5 to 12% by weight, preferably 6 to 10% by weight, based on the total sea component polyester weight. When the copolymerization amount of polyethylene glycol exceeds 12% by weight, polyethylene glycol originally has a melt viscosity lowering action and a plasticizing action, so that the fiber cross-section formability becomes difficult, and if it is less than 5% by weight, the stability of the spinning process In particular, the stretchability is lowered, it is difficult to ensure strength, and it is difficult to dissolve only the sea components. Therefore, it is preferable to copolymerize both components within the above range.

  The sea-island type composite fiber composed of the sea component polymer and the island component polymer preferably has a sea component melt viscosity higher than that of the island component polymer during melt spinning. In such a relationship, even if the composite mass ratio of the sea components is as low as less than 40%, the islands are joined together, or the sea island type sea island where most of the island components are joined together. A cross-sectional shape different from the mold is not formed. A preferable melt viscosity ratio (sea / island) is 1.1 to 2.0, and more preferably 1.3 to 1.5. If this ratio is less than 1.1 times, the island components can be easily joined to each other at the time of process stable melt spinning, whereas if it exceeds 2.0 times, the viscosity difference is too large and spinning is performed. The stability of the process tends to decrease.

  Next, the greater the number of island components, the higher the productivity when producing ultrafine fibers by dissolving and removing sea components, and the resulting ultrafine fibers are also significantly thinner, with the softness and smoothness unique to ultrafine fibers. In addition, since glossiness and the like can be expressed, it is important that the number of island components is 100 or more, and preferably 500 or more. Here, when the number of island components is less than 100, high multifilament yarns composed of ultrafine fibers cannot be obtained even if sea components are dissolved and removed, and the object of the present invention cannot be achieved. If the number of island components is too large, not only the manufacturing cost of the spinneret increases, but also the processing accuracy of the spinneret itself tends to decrease. Therefore, the number of island components is preferably 1000 or less.

  Furthermore, the sea-island composite fiber of the present invention preferably has a sea-island composite mass ratio (sea: island) in the range of 40:60 to 5:95, particularly in the range of 30:70 to 10:90. It is preferable that it exists in. If it exists in the said range, the thickness of the sea component between island components can be made thin, the dissolution removal of a sea component will become easy, and the conversion to an ultrafine fiber of an island component will become easy. Here, when the proportion of the sea component exceeds 40%, the thickness of the sea component becomes too thick. On the other hand, when the proportion is less than 5%, the amount of the sea component becomes too small and the mutual connection occurs between the islands. It becomes easy.

  The sea component and the island component are melted separately, combined into a sea-island shape in the base, and discharged. Then, after solidifying with cooling air or the like, the undrawn fiber is taken up at a speed of preferably 400 to 6000 m / min, more preferably 1000 to 3000 m / min. A lower spinning speed is preferable because higher fiber strength is obtained, but productivity is insufficient at 400 m / min or less, and spinning stability is poor at 6000 m / min or more.

  The unstretched fiber of the obtained sea-island type composite fiber is stretched by either a winding method or a winding method after passing through a stretching step without winding. The drawing temperature is 60 to 90 ° C, preferably 70 ° C to 80 ° C, preheated on a preheating roller and drawn at a draw ratio of 1.1 to 6.0 times, preferably 1.2 to 5.0 times. It is preferable to carry out heat setting at 120 to 180 ° C, preferably 130 to 160 ° C. If it is a slit type heater, 180-220 degreeC is used preferably. In the case where the preheating temperature is insufficient, the intended high-strength drawing cannot be achieved. If the set temperature is too low, the shrinkage rate of the obtained drawn fiber is too high, which is not preferable. On the other hand, if the set temperature is too high, the physical properties of the obtained drawn fiber are remarkably lowered, which is not preferable.

  In the present invention, in order to produce a sea-island type composite fiber having a particularly fine island component diameter with high efficiency, the fiber structure is generally prior to neck stretching (orientation crystallization stretching) with so-called orientation crystallization. It is also possible to adopt a fluid drawing process in which only the fiber diameter is refined without being changed. Specifically, the drawn composite fiber is immersed in a hot water bath in the range of 60 to 100 ° C., preferably in the range of 60 to 80 ° C. and uniformly heated, while the draw ratio is 10 to 30 times and the supply speed is 1 to 10 m. / Min, the winding speed is 300 m / min or less, and it is particularly preferable to carry out the pre-flow stretching in the range of 10 to 300 m / min.

  The fiber form of the polytrimethylene terephthalate ultrafine fiber constituting the wiping cloth of the present invention is not particularly limited, and normal air processing or false twist crimping may be applied. Further, it may be included in the wiping cloth of the present invention as a composite yarn with other polyester multifilament yarn by air mixed fiber, synthetic twisted yarn or composite false twist.

  In the polyester multifilament yarn used for the combined yarn, the number of filaments is not particularly limited, but is preferably in the range of 10 to 300 (preferably 30 to 150). The fiber form of the polyester multifilament yarn is not particularly limited, but is preferably a long fiber (multifilament yarn). The cross-sectional shape of the single fiber is not particularly limited, and may be a known cross-sectional shape such as a circle, a triangle, a flat shape, or a hollow shape. In addition, normal air processing and false twist crimping may be applied.

  The polymer that forms the polyester multifilament yarn is not particularly limited as long as it is a polyester polymer, and may be the same type as the ultrafine fiber. Preferred examples of the other polymer include polyethylene terephthalate, polybutylene terephthalate, stereocomplex polylactic acid, polylactic acid, polyester obtained by copolymerizing the third component, and the like. Such polyester may be material recycled or chemically recycled polyester. Furthermore, the polyester obtained using the catalyst containing the specific phosphorus compound and titanium compound which are described in Unexamined-Japanese-Patent No. 2004-270097 and 2004-21268 may be sufficient. The polymer may contain one or more cationic dyes, dyeing agents, and heat stabilizers as necessary within the range not impairing the object of the present invention.

  The wiping cloth of the present invention may be in either woven or knitted form. The production method may be a conventional method. For example, in the case of a woven fabric, after weaving a woven fabric having a predetermined cover factor and thickness using at least a part of the sea-island composite fiber, the sea component of the sea-island composite fiber is used. The wiping cloth containing ultrafine fibers having a single fiber diameter of 10 to 2000 nm can be produced by dissolving and removing with an alkaline aqueous solution using a known alkali weight reduction device.

  In order to remove the sea component, it is preferable to treat with an aqueous solution of an alkali metal compound such as sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, among which sodium hydroxide and potassium hydroxide are particularly preferably used. The concentration, treatment temperature, and treatment time of the aqueous alkali solution vary depending on the type of alkali compound used, but the concentration is 10 to 300 g / L, the temperature is 40 ° C. to 180 ° C., and the treatment time is in the range of 2 minutes to 20 hours. Is preferred.

The fabric may be subjected to a dyeing process before and / or after the dissolution with the alkaline aqueous solution, or before and / or after the heat setting. Moreover, you may give a calendar process (heat-pressing process) and an embossing. Furthermore, conventional brushing processing, water repellent processing, and various functions that provide functions such as ultraviolet ray shielding or antistatic agents, antibacterial agents, deodorants, insect repellents, phosphorescent agents, retroreflective agents, negative ion generators, etc. Processing may be additionally applied.
The wiping cloth thus obtained not only has high wiping properties, but also generates less material dust.

The invention is further illustrated by the following examples.
In the following examples and comparative examples, the following measurements and evaluations were performed.

(1) Average single yarn fiber diameter The fiber diameter was determined by TEM observation 30000 times the fine fiber after sea component dissolution and removal. Here, the fiber diameter of the single yarn that was not glued was measured. In the fiber diameter data of 100 randomly selected fine fibers, the average single yarn fiber diameter r was calculated.

(2) Average single fiber diameter variation CV%
When determining the average single yarn fiber diameter of (1), the standard deviation σ was calculated, and the fiber diameter variation coefficient CV% defined below was calculated.
CV% = standard deviation σ / average single yarn fiber diameter r × 100 (%)

(3) Tubular knitting was made from high-strength sea-island composite fibers, and sea components were eluted with an alkaline solution to make ultrafine fiber bundles. This ultrafine fiber bundle was measured for strength at break and elongation under conditions of a sample length of 20 cm and a speed of 20 cm / min with a tensile tester in an atmosphere of 20 ° C. and 65% RH. The number of measurements was 10, and the average value of strength was calculated using the fineness determined from the average single yarn fiber diameter, and the strength (cN / dtex) was obtained.

(4) Process stability Spinnability, stretchability, and weight loss were evaluated as follows.
Spinnability: Spinning was performed for 48 hours, ◯ when the yarn was broken or troubled 0 to 1 times, Δ when the yarn was broken several times, and × when the winding was impossible in several hours.
Stretchability: When the composite fiber obtained by spinning is stretched and heat-set, ○ when there is almost no fluff or breakage, △ when breakage is observed several times, and the process is unstable and impossible Was marked with x.
Weight loss: Treated in an alkaline solution and observed the cross section of the fiber with SEM, ○ that can remove only the sea component is ○, and that that could not find the weight loss condition that can remove only the sea component is × did.

(5) Wipeability coloring liquid (Suminol Fast Blue 4GL: 0.2%, water: 20.0%, ethylene glycol (degree of polymerization 300): 79.8%) on an acrylic plate having a size of 30 cm × 20 cm After uniformly applying on the screen printing stage, an 8 cm × 6 cm sample with a load of 200 g was slid at 2000 mm / min on the acrylic plate, and the ratio of the colored liquid remaining on the acrylic plate was determined. Measurements were taken after taking photographs, and the results were shown as follows.
○: Residual liquid on acrylic plate is less than 20% of coating amount ×: Residual liquid on acrylic plate is 20% or more of coating amount

(6) In the dust-generating wiping test, the acrylic plate was wiped off in the same manner without applying a colored liquid on the acrylic plate, and the acrylic plate after wiping was observed, and judged by the presence or absence of fiber waste.
○: Fiber scraps do not adhere to the acrylic plate ×: Fiber scraps even slightly adhere to the acrylic plate

[Example 1]
Polytrimethylene terephthalate having an intrinsic viscosity of 0.96 (35 ° C. in orthochlorophenol) as an island component, and 6 mol% of 5-sodium sulfoisophthalic acid as a sea component and 8% by weight of polyethylene glycol having a number average molecular weight of 4000 were copolymerized. Using polyethylene terephthalate having an intrinsic viscosity of 0.54, melted separately, and merged in a composite die, and a sea-island type composite unstretched fiber having a weight ratio of sea: island = 30: 70, number of islands = 836 is set at a spinning temperature of 270 It was melt-spun at a temperature of 1500 ° C. and a spinning speed of 1500 m / min and wound up. Spinning was carried out for 48 hours, but no breakage was observed. The obtained undrawn yarn was roller-drawn at a drawing temperature of 80 ° C. and a draw ratio of 3.5 times, and then heat-set with a non-contact heater at 220 ° C. to obtain a sea-island type composite drawn yarn. In the drawing process, no fluff or yarn breakage occurred, and all undrawn yarns could be drawn without problems.
The obtained sea-island type composite drawn yarn was 56 dtex / 10 fil, and a tubular knitting was prepared. When the weight was reduced in an alkaline solution at 90 ° C. and 3.5 g / l, only the sea component was eluted. The average fiber diameter was 710 nm, CV% was 12%, the strength was 2.2 cN / dtex, and the elongation was 61%.
Next, the multi-filament (33 dtex / 12fil, single yarn fineness 2.8 dtex, boiling water shrinkage 35.0%, manufactured by Teijin Fibers Ltd.) made of the sea-island type composite drawn yarn and ordinary polyethylene terephthalate was mixed with interlace processing. A yarn was obtained. The blended yarn is twisted at 300 times / m (S direction), and all the warp yarns and weft yarns are arranged at a weaving density of 215 warps / 2.54 cm and weft densities of 105 / 2.54 cm. A weaving machine having a satin structure of 5 sheets was obtained by this weaving method.
The fabric was subjected to a wet heat treatment at 60 ° C., and then a 28% reduction (alkaline reduction) was performed at 60 ° C. with a 3.5% NaOH aqueous solution in order to remove sea components of the sea-island type composite drawn yarn. Thereafter, conventional wet heat processing and dry heat processing were performed to obtain a wiping cloth.
Table 1 shows the physical properties of the obtained wiping cloth.

[Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3]
A sea-island composite fiber was obtained in the same manner as in Example 1 using a sea polymer having the composition shown in Table 1 as the sea component. Table 1 shows the physical properties of the ultrafine yarn obtained by elution from the obtained sea-island type composite fiber and the performance of the wiping cloth obtained in the same manner as in Example 1.
As shown in Table 1, in Examples 1 and 2, there are no problems in spinnability, stretchability, and weight loss, and it is possible to obtain excellent strength and uniformity as an ultrafine fiber, and excellent performance as a wiping cloth. I had it.
Comparative Example 1 in which the copolymerization amount of 5-sodium sulfoisophthalic acid was increased and the copolymerization amount of polyethylene glycol was decreased as the composition of the sea polymer was poor in spinnability and stretchability, and the strength as an ultrafine fiber was low. Dust generation was seen. In Comparative Examples 2 and 3 in which the copolymerization amounts of 5-sodium sulfoisophthalic acid and polyethylene glycol were reduced, the weight loss was poor and ultrafine fibers could not be obtained.

  The wiping cloth of the present invention is extremely excellent in wiping and dust collection. Therefore, it is useful for applications such as mobile phones, glasses, lenses, liquid crystal materials, large-scale integrated circuits, electronic information materials, electronic devices, pharmaceuticals, medical instruments, pearls, jewelry, furniture, and automobile parts.

Claims (1)

A wiping cloth containing ultrafine fibers characterized by satisfying the following requirements.
a) The ultrafine fiber is a polyester ultrafine fiber whose main repeating unit is trimethylene terephthalate, the average single fiber diameter is 50 to 2000 nm, the CV% of the average single fiber diameter is 0 to 25%, and the strength is 1. 5 to 6.0 cN / dtex.
b) It is an ultrafine fiber obtained by elution treatment of a sea component of a sea-island type composite fiber having polytrimethylene terephthalate as an island component and hot water-soluble polyester as a sea component.
c) The sea component is a copolymerized polyester of a polyethylene glycol compound and 5-sodium sulfoisophthalic acid, the polyethylene glycol compound is 5 to 12% by weight based on the total weight of the polyester, and 5-sodium sulfoisophthalic acid is the total acid of the polyester. It is a polyester copolymerized with 5 to 8 mol% with respect to the component.