JPH05171507A - Conjugate fiber comprising inner and outer layers - Google Patents

Abstract

PURPOSE:To provide the conjugate fiber comprising inner and outer layers, having excellent characteristics consisting of excellent dry touch, tension, stiffness and color-developing property and most suitable as a refreshing feeling raw material for clothes. CONSTITUTION:The conjugate fiber comprising an inner layer and an outer layer and having a follow part is characterized in that >=0.1wt.% of fine particles having an average primary particle diameter of >=200mum are contained in the inner layer and/or the outer layer, that the dissolution rate of the outer layer component in a solvent is >=3 times that of the inner layer component, that the external shape of the inner layer in the cross section of the fiber has a polyangular cross section ranging from a triangular cross section to a hexagonal cross section and having extremely sharp tops and highly straight linear sides between the adjacent tops.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow inner / outer layer composite fiber. More specifically, by eluting the outer layer portion with a solvent treatment, the cross section of the fiber is composed of highly linear side portions and sharp apex portions, and the outer layer portion is formed. The present invention relates to a fiber suitable for a woven or knitted fabric for high-quality clothing, which has fine dents on the surface of the fiber after elution, and has excellent dryness, tension / elasticity, lightness, and color developability.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to use a modified cross-section fiber or a hollow fiber for imparting a high-grade feeling such as a glossy feeling, a dry touch and a lightweight feeling to a woven or knitted fabric for polyester clothing. These woven and knitted fabrics using modified cross-section fibers and hollow cross-section fibers have distinctive luster, texture, and lightness compared to round cross-sections, and are preferably used for clothing. Further, some fibers have been proposed that combine the excellent texture characteristics of the modified cross-section fibers with the lightweight characteristics of the hollow cross-section fibers. For example, Japanese Patent Publication No. 44-1892
No. 3 and Japanese Patent Publication No. 58-4092 propose a polygonal cross-section fiber having a hollow portion.
Japanese Patent No. 9650 proposes a field-shaped hollow cross-section fiber. However, since all of these modified cross-section fibers are produced by single-component spinning, the vertex of the fiber cross-section is rounded due to the effect of surface tension during the cooling process after discharging from the spinneret, and a cross-sectional shape with a sharp portion is obtained. Absent. Therefore, those characteristics are not satisfied in the field of clothing requiring a feeling of dryness.

In addition, recently, in view of various requirements, some modified cross-section fibers having sharp apexes, which are obtained by applying the composite spinning technique, have been proposed. For example, Japanese Patent Application Laid-Open No. 53-24529 proposes a method of obtaining a modified cross-section fiber having a sharp edge in the cross-section of the fiber by laminating nylon and polyethylene terephthalate, spinning them, and peeling off the joint during stretching. There is. However, in such a proposal, it is not possible to form a hollow portion, so that it does not have a light weight feeling, and the peeled portion remains as it is, resulting in a special texture.

Therefore, the inventors of the present invention disclosed in Japanese Patent Laid-Open No. 3-12480
No. 7, we proposed a polygonal hollow cross-section fiber that is excellent in dryness, tension, and elasticity. However, the fiber has an increased amount of specular reflection light due to highly linear sides and hollow interface, and thus is compared with ordinary fibers. However, there is a drawback that the color developability is inferior, and it has been difficult to develop into application fields where color developability is required.

[0005]

An object of the present invention is an inner / outer layer composite fiber having a hollow portion which could not be achieved by the above-mentioned conventional techniques or a combination thereof, and the outer layer portion is eluted to cross the fibers after elution. The linearity of the side of the surface is high,
Also, because the radius of curvature of the apex is small, it is excellent in dryness, tension, waist, and lightweight, and by forming fine recesses on the fiber surface, it is for high-quality clothing that improved the color development that was a drawback of hollow fibers. The present invention provides a fiber suitable for a woven or knitted fabric.

[0006]

That is, the object of the present invention is to provide an inner layer component and / or an outer layer component having an average primary particle diameter of 200 m in an inner / outer layer composite fiber having a hollow portion.
It contains 0.1% by weight or more of fine particles of μ or less, the dissolution rate of the outer layer component in the solvent is 3 times or more that of the inner layer component, and the outer shape of the inner layer portion in the cross-section of the fiber is a polygon of a triangle or more and a hexagon or less. It is achieved by the inner / outer layer composite fiber.

The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a cross-sectional view of a composite fiber for explaining the cross-sectional shape of the fiber of the present invention. 1 is an outer layer part, 2 is an inner layer part, 3 is a hollow part, 4 is a vertex part, and 5 is a side part. It is a fiber.

It is essential that the conjugate fiber of the present invention has a hollow portion in the cross section of the fiber. This is because a hollow portion increases the excluded volume by that amount, so that a material having a lighter feeling than a woven or knitted material obtained by a conventional polyester fiber can be obtained. The hollowness is expressed by the cross-sectional area of the hollow portion with respect to the sum of the cross-sectional area of the inner layer component and the cross-sectional area of the hollow portion in the cross section of the fiber. The higher the hollowness, the higher the feeling of lightness. On the other hand, if the hollow ratio is too high, the shape-retaining property of the fiber cross section is remarkably deteriorated, and the hollow part is easily crushed in the steps after weaving and the cross section is easily deformed, which makes it difficult to achieve the object of the present invention. From the above, the hollow rate is preferably in the range of 10 to 40%, more preferably in the range of 20 to 35%.

The composite fiber of the present invention has an inner-outer layer composite structure, and the composite fiber elutes the outer layer component by solvent treatment after weaving. At that time, by keeping the outer shape of the inner layer portion in the cross section of the fiber as it is, it is possible to give the cloth a silky feeling, tension and waist. Therefore, the dissolution rate of the outer layer component in the solvent needs to be 3 times or more that of the inner layer component, preferably 5 times or more, more preferably 10 times or more that of the inner layer component. Specific polymers used for the inner layer component include, but are not limited to, polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6 and nylon 66, polyesters such as polyethylene terephthalate and polybutylene terephthalate. Polyester having polyethylene terephthalate as a main component is preferable. On the other hand, examples of the outer layer component include water-soluble partially saponified polyvinyl alcohol, modified polyester obtained by copolymerizing 5-sodium sulfoisophthalic acid component which is hydrolyzed by alkali, or styrene-based polymer such as polystyrene soluble in organic solvent. it can. The combination of the inner layer component and the outer layer component is preferably compatible in order to improve the spinnability, and in that respect, polyester is used as the inner layer component and 5-
Most preferably, a modified polyester obtained by copolymerizing a sodium sulfoisophthalic acid component is combined.

Further, it is essential that the inner layer component and / or the outer layer component contain 0.1% by weight or more of fine particles having an average primary particle diameter of 200 mμ or less.

By incorporating these fine particles into a polymer and eluting the components of the outer layer, fine recesses are formed on the fiber surface, and the coloring and sharpness, which have hitherto been the drawbacks of hollow fibers, are greatly improved. Furthermore, the fine recesses on the fiber surface also have the effect of suppressing glitter due to specularly reflected light at the sides of the fiber cross section. The reason why the color development is improved by providing fine recesses on the fiber surface is that the light incident on the recesses efficiently penetrates into the fiber due to the presence of many fine recesses and is absorbed by dye molecules. This is because, at the same time, the amount of specular reflection light is reduced and glitter is suppressed. It is preferable that the fine recesses are long in the fiber axis direction, have a maximum width of 0.05 to 1.5 μm, and have a length / maximum width ratio of 1.5 or more. The term "fine particles" here can be widely applied to inorganic fine particles typified by silica and organic fine particles typified by polystyrene. As the inorganic fine particles, dry method silica, wet method silica, aluminum oxide-containing dry method silica, aluminum oxide, calcium carbonate,
Calcium phosphate, barium sulfate, zirconium oxide,
Talc, kaolinite, zeolite, etc. are preferably applicable, and among them, from the aspect of color development improving effect, aggregation during polymerization, yarn breakage during spinning / drawing, etc., a silanol group on the particle surface has an alkyl group. More preferred is dry process silica which is hydrophobized by blocking with a compound. As the organic fine particles, divinylbenzene / ethylvinylbenzene copolymer, styrene-methylmethacrylate / divinylbenzene copolymer, etc. are preferably applicable, and highly crosslinked divinylbenzene / ethylvinylbenzene copolymer is used in terms of heat resistance. Coalescence is more preferred. In the present invention, silica refers to fine particles containing 80% or more of silicon oxide.

The average primary particle diameter of the fine particles in the present invention is required to be 200 mμ or less, preferably 100 mμ or less, more preferably 50 mμ or less.
If the average primary particle size exceeds 200 mμ, the effect of improving the color developability is deteriorated, which is not preferable.

The fine particles may be contained in both the inner layer component and the outer layer component, or in either component, but it is preferable that they are contained only in the inner layer component from the viewpoints of stability of spinning / drawing and fiber strength. The content of fine particles in the polymer is 0.1
It is necessary that the content is at least wt%. When the content of the fine particles is less than 0.1% by weight, the effect of improving the color developability is hardly recognized. It is preferably 0.2% by weight or more. The content is preferably 7% by weight or less, more preferably 2.5% by weight or less, from the viewpoint of stability of spinning / drawing, fiber strength, and anti-fibrillarity.

In order to exert the effect of the present invention, it is necessary that the cross-sectional shape of the inner layer portion is a polygonal cross section of not less than triangular and not more than hexagonal. When it comes to a polygonal section of heptagon or more,
Since the apex of the cross section is not sharp,
When the material is woven and the components of the outer layer are eluted, the texture of the present invention, such as dry feeling and dry feeling, cannot be satisfied. In addition, a pentagon or less is more preferable in order to further exhibit the above-mentioned characteristics. FIG. 2 is a cross-sectional view showing an example of the cross-sectional shape of the conjugate fiber of the present invention. 2A shows a triangular inner layer portion, FIG. 2B shows a square inner layer portion, and FIG.
Shows an example in which the inner layer portion has a pentagonal shape, and FIG. 2D shows an example in which the inner layer portion has a hexagonal shape.

Further, in order to fully exhibit the dry feeling and the dry feeling, it is preferable that the apex portion of the inner layer portion is sharp and the linearity of the side portion is high. Then, the radius of curvature of the apex portion and the variation rate of the side portion in the cross section of the inner layer portion will be described in detail with reference to the drawings. First, the curvature radius r of the apex portion 4 in the cross section of the inner layer portion of the fiber of the present invention is ^preferably 2d ^0.5 μm (d: single fiber fineness (denier) of the inner layer portion) or less. For example, if the single fiber fineness of the composite fiber is 2 denier and the composite ratio of the inner layer portion is 50% by weight, the single fiber fineness of the inner layer portion is 1 denier, and the radius of curvature r of the apex portion 3 is preferably 2.0 μm or less. When the single fiber fineness of the composite fiber is 6 denier and the composite ratio of the inner layer portion is 50% by weight, the single fiber fineness d of the inner layer portion is d.
Is 3 denier, and the radius of curvature r of the vertex 3 is about 3.5.
μm or less is preferable. This is because with a cross-sectional shape having a smooth vertex with a radius of curvature r of more than 2d ^0.5 μm, it is not possible to sufficiently exhibit the feeling of dryness, tension, waist, etc. when weaving and eluting the outer layer components. More preferably, the radius of curvature r at the apex is d ^0.5 μm or less.

Next, in the present invention, the variation rate of the side portion between the adjacent apexes is important. In FIG. 1, a reference line L is drawn on each side between adjacent apexes 4. The reference line L is L
The area formed by adding the concave portion and the convex portion of the side portion is drawn so as to be the minimum. At this time, the reference line L on each side
The point farthest away from is denoted by T, and the distance between T and L is denoted by t.
On the other hand, in the reference line L corresponding to the side portion where T is present, when the length between the intersections with the adjacent reference lines is s, the variation rate of the side portion in the cross section of the fiber is determined by the following formula.

Variability (%) = (t / s) × 100 In the cross section of the inner layer portion of the conjugate fiber of the present invention, it is preferable that the variation rate of the side portion between adjacent apexes is 10% or less. The variation rate is closely related to the glossy feeling and the surface touch, and in a cross-sectional shape having a side portion where the variation rate exceeds 10%, a smooth and unique surface touch does not appear.
The variation rate is more preferably 8% or less.

Further, it is preferable that the side portion has a convex portion within the range of the variation rate described above. Due to the presence of this convex portion, the reflected light is dispersed in a random direction, so that the amount of specularly reflected light at the side portion is reduced, and a coloring effect without anisotropy can be obtained. It is preferable that the convex portion has an arc shape with a height of 3 μm or less and a radius of curvature of 15 μm or less in consideration of the above-mentioned variation rate.

The conjugate fiber of the present invention is an inner-outer layer conjugate fiber having a hollow portion, and the ratio of the cross-sectional area of the inner layer portion to the total cross-sectional area of fibers excluding the hollow portion is 0.40 or more and 0.75 or less. Is preferred. The ratio of the cross-sectional area of the inner layer is 0.4
If it is less than 0, the fabric structure becomes loose after the outer layer portion is dissolved after forming the fabric, and the so-called texture shift in which the texture moves is likely to occur. On the other hand, when the ratio of the cross-sectional area of the inner layer portion exceeds 0.75, it becomes difficult to make the outer shape of the entire fiber into a shape close to a circle while maintaining the linearity of the outer shape of the inner layer portion. In the case of the quadrilateral shape, it has a structure close to the closest packing in the cloth, so that it has a drawback that the feeling of dryness is reduced and the feeling of lightness is also reduced. More preferable cross-sectional area ratio is 0.45 or more, 0.6
It is 5 or less.

The hollow inner / outer layer composite fiber of the present invention can be produced, for example, by the following method. That is, the above-mentioned two kinds of polymers are separately melted and weighed, and a composite mouthpiece device shown in FIG.
Discharge from a mouth hole composed of ~ 6 slits.
FIG. 3 is a vertical cross-sectional view of a main part of a composite spinneret device preferably used in the present invention. FIG. 4 is a bottom view of the die showing an example of the shape of the die hole used in the present invention. 3 and 4,
6 is an upper introduction plate, 7 is a lower introduction plate, 8 is a base, and 9 is a slit. The polymer A as the inner layer component is introduced from the upper introduction plate 5, and the polymer B as the outer layer component is introduced from the lower introduction plate 7, and becomes a composite flow of the inner and outer layers by the die 8 and is discharged from the die hole formed by the slit 9.

By discharging a composite flow from such a die hole, the flow velocity of the polymer of the outer layer component having a low melt viscosity is high, so that the polymer flows ejected from each slit immediately after the ejection are in the center of the die hole. The two ends of the polymer flow bend toward each other and collide and fuse with each other to be bonded to each other to form a composite fiber having a hollow cross section in which the cross-sectional shape of the inner layer portion is polygonal.

The composite fiber obtained by the above-described method has the spinneret holes shown in FIGS. 4A, 4B, 4C, and 4D, respectively. , (B),
As shown in (c) and (d), the cross-sectional shape of the inner layer portion is polygonal and the conjugate fiber has a hollow portion. In the case of the mouthpiece hole of FIG. 4 (b) described above, four slits having the same arc shape and the same size are arranged point-symmetrically, and similarly, in the case of the mouthpiece hole of FIG. 4 (a), three are formed. 4 are arranged in point symmetry in the case of the die hole of FIG. 4 (c), and 6 slits in the case of the die hole of FIG. 4 (d).

The composite fiber thus obtained is subjected to a solvent treatment in an appropriate step thereafter to elute the outer layer portion and leave the inner layer portion to obtain a polygonal hollow fiber. At this time, when a modified polyester obtained by copolymerizing a third component such as an aromatic or aliphatic dicarboxylic acid or diol is used as the outer layer component, an alkali hot aqueous solution such as sodium hydroxide hot aqueous solution is preferably used. May be any solvent as long as it can preferentially elute and remove the outer layer component with respect to the inner layer component. Of course, water can be used as a solvent if polymers having different dissolution rates in water are selected. Although any process may be used for this treatment, it is preferable that the process is performed after weaving and knitting in consideration of production stability.

[0024]

The present invention will be described in more detail with reference to the following examples. Each characteristic value in the examples was obtained by the following method. A. Average primary particle size Particle powder was photographed with an electron microscope at a magnification of 100,000 times, and the longest diameter of each primary particle was measured from the obtained image.
The value obtained as an average of 000 was displayed.

B. Intrinsic viscosity [η] Orthochlorophenol (hereinafter OCP) 10 ml
On the other hand, 0.10 g of a sample was dissolved and measured at a temperature of 25 ° C. using an Ostwald viscometer. C. Melt viscosity The melt viscosity is a value measured by a melt indexer type MX-101-B manufactured by Takara Kogyo Co., Ltd. at the same temperature as the spinning temperature and a shear rate of 30 (1 / SEC). D. Hollow ratio A fiber with a thickness of 5 μm dyed in the outer layer is taken as a section, and the cross-sectional area of the inner layer and the cross-sectional area of the hollow are measured by observing the photograph to determine the sum of the cross-sectional area of the inner layer and the cross-sectional area of the hollow. It was expressed as a percentage of the cross-sectional area of the hollow portion. Hollow ratio (%) = hollow area cross-sectional area / (inner layer + hollow area cross-sectional area) x 100

E. L value (brightness) 7 dyes Dianix Black BG-FS200
% Owf, and 0.5 g of Sun Salt 1200 per liter of dye as an auxiliary agent and 0.5% of Fixer PH500.
5 g was added and mixed, and dyeing was carried out at a dyeing temperature of 130 ° C. for 60 minutes with a bath ratio of cloth: dye = 1: 50. Furthermore, as reduction cleaning, 2 liters of hydrosulfite per liter of water is used.
g, sandit 0.5g, caustic soda 0.5g
It was treated with the added and mixed washing liquid at 80 ° C. for 20 minutes. After drying the obtained cloth, SM-3 manufactured by Suga Test Instruments Co., Ltd.
Was used to measure the L value (brightness).

F. Feeling characteristics (dry feeling, tension, waist) For each item, a sensory test was conducted by pairing the sample with a reference sample and evaluated in four levels. Then, they were comprehensively evaluated and expressed as "extremely good", "good", "inferior", and "extremely inferior". As a reference sample, a Y-section polyester filament yarn having the same fineness and the same number of filaments as the sample original yarn, which is usually used as a standard product, is woven and processed in the same manner as the sample, and this is “inferior”. And

Example 1 Dry process silica having an intrinsic viscosity [η] of 0.75 as an inner layer component and having a silanol group on the particle surface blocked by a compound having an alkyl group to make it hydrophobic and having an average primary particle diameter of 15 mμ. Polyethylene terephthalate blended with 0.45% by weight of as an outer layer component has an intrinsic viscosity [η] of 0.3.
8. Add 5-sodium sulfoisophthalic acid component to 4.5.
Using a modified polyester copolymerized by mol% and using a composite spinneret device shown in FIG. 3 at a spinning temperature of 295 ° C. using a normal composite spinning machine, the composite ratio of the inner layer portion from the spinneret hole shown in FIG. It was discharged at 50% by weight and wound up at a speed of 1500 m / min. The melt viscosities of the individual polymers of the inner layer component and the outer layer component were 4400 poise and 1700 poise, respectively.
The ratio of the dissolution rate of the outer layer component to the inner layer component in a 2 wt% sodium hydroxide hot aqueous solution at 98 ° C was about 35 times. This unstretched yarn was woven with a normal hot roll-hot plate stretching machine at a draw ratio of 2.5 to obtain a multifilament composite fiber, which was woven as a warp and a weft, and the temperature was 98 ° C.
Relax scouring at 180 ℃, intermediate setting at 180 ℃, and then treating with 2wt% sodium hydroxide at 98 ℃ hot aqueous solution to elute the outer layer components into 50 denier 24 filaments.
A habutae was obtained by finishing setting at 0 ° C. As a result of sensory evaluation of each of the obtained samples, it was a feel that could not be achieved by the conventional woven fabrics using polyester filaments of irregular cross section, and all the feel properties were extremely excellent. The results are shown in Table 1.

Example 2 Example 2 was carried out under the same conditions as in Example 1 except that polyethylene terephthalate containing 2.30% by weight of calcium carbonate having an average primary particle diameter of 180 mμ was used as the inner layer component. The obtained results are shown in Table 1. The sample of Example 2 was slightly inferior to Example 1 in color developability, but was excellent in texture such as dry feeling, tension and waist.

Example 3 Example 3 was carried out under the same conditions as in Example 1 except that the content of dry process silica in the inner layer component was 0.15% by weight. The obtained results are shown in Table 1. The color of the sample of Example 3 was slightly inferior to that of Example 1.

Comparative Example 1 The same conditions as in Example 2 were carried out except that calcium carbonate having an average primary particle diameter of 230 mμ was used as fine particles. The results of the obtained samples are shown in Table 1. Although the obtained sample has an excellent texture such as a dry feeling and a lightweight feeling,
The L value (brightness) was as high as 16.2 and the color development was poor.

Comparative Example 2 The procedure of Example 1 was repeated, except that the content of the dry process silica as an inner layer component was changed to 0.05% by weight. The obtained results are shown in Table 1 as Comparative Example 2. The sample of Comparative Example 2 showed almost no recesses on the fiber surface, and was inferior in color developability.

Example 4 The same procedure as in Example 1 was carried out except that the polymer composition of the outer layer component was changed and the copolymerization amount of the 5-sodium sulfoisophthalic acid component was 1.7 mol%. 2% by weight of polymer
The ratio of dissolution rates in a hot aqueous solution of sodium hydroxide at 98 ° C was about 4 times. The obtained results are shown in Table 1. Example 4
The sample of No. 1 was slightly inferior to Example 1 in texture properties such as dry feel, tension and waist, but was excellent in color developability and sharpness. Comparative Example 3 The polymer composition of the outer layer component was changed to 5 The same conditions as in Example 1 were used except that the copolymerization amount of the sodium sulfoisophthalic acid component was 1.0 mol%. 2% by weight of polymer
The ratio of dissolution rates in a hot aqueous solution of sodium hydroxide at 98 ° C was about twice. The obtained results are shown in Table 1. Comparative Example 3
The sample of No. 2 has a rounded shape and a substantially circular cross-sectional shape because the outer layer part was completely dissolved by the treatment with 2% by weight sodium hydroxide at 98 ° C after the weaving, and the apex of the inner layer part was also reduced. The feeling of dryness, tension and waist were inferior. Example 5 It was carried out under the same conditions as in Example 1 except that the die to be discharged was the die hole shown in FIG. The results obtained are shown in Table 1.
It was shown to. The sample had the cross-sectional shape shown in FIG. 2 (a), and had a smoother surface touch than that of the sample of Example 1, and was excellent in tension, waist, and lightweight feeling.

Example 6 The same procedure as in Example 1 was carried out except that the die to be discharged was the die hole shown in FIG. 4 (d). The results obtained are shown in Table 1.
I wrote it in. The sample had the cross-sectional shape shown in FIG. 2 (d), and was favorable in terms of tension, waist, lightweight feeling, and a soft feeling as well as a soft feeling, which was preferable.

Comparative Example 4 The same conditions as in Example 1 were used except that a die having die holes having seven slits arranged on the circumference was used. The obtained results are shown in Table 1. The sample of Comparative Example 4 was a hollow fiber having a heptagonal cross-section in the outer shape of the inner layer, but it had almost no dry surface touch and was poor in refreshing feeling and had no characteristics.

[0036]

[Table 1]

[0037]

EFFECTS OF THE INVENTION The composite fiber of the present invention is one in which the outer layer component is subjected to elution treatment, and the woven or knitted fabric using such a fiber has excellent characteristics such as dryness, tension / elasticity, lightness and color development. Therefore, it is most suitable as a refreshing feeling material for clothing, which could not be obtained with the conventional modified cross-section fibers.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a fiber for explaining the cross-sectional shape of the fiber of the present invention.

FIG. 2 is a cross-sectional view of a fiber showing an example of the cross-sectional shape of the fiber of the present invention.

FIG. 3 is a longitudinal sectional view of a main part of a composite mouthpiece device preferably used in the present invention.

FIG. 4 is a bottom view of a die showing an example of a die hole shape used in the present invention.

[Explanation of symbols]

 1: Outer layer part 2: Inner layer part 3: Hollow part 4: Apex part 5: Side part 6: Upper introduction plate 7: Lower introduction plate 8: Base 9: Slit

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Claims (1)

[Claims] 1. An inner / outer layer composite fiber having a hollow portion, wherein the inner layer component and / or the outer layer component contains 0.1% by weight or more of fine particles having an average primary particle diameter of 200 mμ or less, and the outer layer component with respect to a solvent. The inner / outer layer composite fiber is characterized in that the dissolution rate is 3 times or more that of the inner layer component, and the outer shape of the inner layer portion in the cross section of the fiber is a polygonal shape from a triangle to a hexagon.