JPH11222714A - Cellulose acetate warn having specific cross section, its aggregate and production of the yarn - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain both of an acetate yarn of <=4 d/f single yarn fineness having smoothness on the surface as much as possible, an improved contact feeling between the skin and yarn, an excellent wet feeling and moist handle, by reducing a great number of complicated unevenness found in a conventional acetate yarn and its aggregate, and to provide a method for producing the yarn. SOLUTION: A cellulose acetate yarn 1 having >=45% acetylation degree is spun by a spinneret having plural spinning holes with a shape obtained by cutting off a part of a circle by one straight line and an angle θ made between the two ends of the straight line and the center of the circle satisfying of the equation 60 deg.<=θ<=120 deg. and <=2,000 μm<2> cross-section area. The cross-sectional shape of the prepared yarn 1 is an approximately C-shape of smooth circumference and both the ends 2 are approximately bonded to form a false hollow part 3. The area of the false hollow part 3 amounts to <=10% the whole cross-section area and the single yarn fineness is <=4 d/f. The unevenness produced in the acetate yarn is thus controlled and reduced, the formed recessed part is sealed in the interior of the yarn and the surface of the yarn is made into a smooth surface free from the unevenness to produce a handle having excellent wet feeling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellulose acetate fiber having a special cross section, an aggregate thereof, and a method for producing the fiber, and more particularly to a fabric having a unique wet texture due to its special and novel cross section. TECHNICAL FIELD The present invention relates to an acetate fiber capable of imparting the following, an aggregate thereof, and a method for producing the fiber.

[0002]

2. Description of the Related Art Cellulose acetate fibers have been mainly used as high-grade clothing materials which have excellent coloring properties because of their low refractive index and are dry, refreshing and have high fashionability. It is considered that the unique dry touch feeling of the acetate fiber is mainly derived from the fact that the fiber is produced by dry spinning. That is, generally, in dry spinning of acetate fibers, acetate flakes as a raw material polymer is dissolved in a highly volatile solvent such as acetone or methylene chloride to obtain a stock solution for spinning, and the stock solution is passed through a spinneret having a circular spinning hole. The solvent is discharged and the solvent in the spinning dope is evaporated and removed by the heated air to be solidified into a fibrous form.

[0003] In this dry spinning process, immediately after the spinning solution is discharged from the spinneret, the heat of the stock solution itself evaporates the solvent of the outer surface layer to form a so-called skin layer. The solvent inside the yarn evaporates due to the air. Because the volume shrinkage due to the evaporation of the solvent occurs randomly, many irregularities, usually about 4 to 12 irregularities, are formed on the fiber intricately in its cross-sectional shape,
The cross-sectional shape becomes extremely large. As a result, the fiber is considered to have a reduced contact area with human skin and the like, and a unique dry feeling and a refreshing feeling are produced.
The material is suitable for spring and summer women's clothing.

[0004] The cross-sectional shape of the fiber produced by such dry spinning is mainly determined by the shape of the spinning hole of the spinneret, the fluidity of the stock solution during solidification, and the drying speed. A spinning hole shape and a cross-sectional shape of a fiber obtained by the spinning hole have been proposed.

[0005] For example, in Japanese Patent Publication No. 37-7917,
A number of spinning hole shapes and cross-sectional shapes of fibers obtained from the spinneret are disclosed. For example, if the shape of the spinning hole is a regular triangle, a fiber having a substantially Y-shaped cross section is obtained, and if the shape of the spinning hole is a square, a fiber having a substantially X-shaped cross section is obtained. A fiber having a hollow substantially circular cross section is obtained from a 2/3 circular spinning hole, and a fiber having a hollow elliptical cross section is obtained from a crescent-shaped spinning hole. Further, in the case of a spinning hole in which three slit holes are arranged in a triangle, a fiber having a triangular cross section having a circular hollow can be obtained.

Japanese Patent Publication No. 37-12710 and Japanese Patent Publication No. 39-12012 disclose a spinning hole having a shape in which a part of a circle is cut off by one straight line. Further, when spinning the cellulose acetate fiber, by blowing hot air toward the linear portion of the spinning hole, the cross section of the obtained fiber becomes C-shaped.

The spinning hole disclosed in JP-A-60-134012 has a shape in which three vertices of a triangle are cut off by a circle centered on the center of gravity of the triangle, and the spinning hole is spun by such a spinning hole. Cellulose acetate fiber is approximately Y
It has a character-shaped cross section.

Further, WO 96/35010 discloses an attempt to change the cross-sectional shape of cellulose acetate fiber by adding 5 to 40 parts by weight of a polymer substance capable of plasticizing cellulose acetate to a spinning dope. Have been. For example, when a spinning dope containing such a polymer substance is spun from a circular spinning hole, a fiber having a cocoon-shaped cross section in which the central portion of an ellipse is narrowed is obtained. When a square spinning hole is used, a fiber having a cross-shaped cross section is obtained, and when a triangular spinning hole is used, a fiber having a Y-shaped cross section is obtained.
When a fan-shaped spinning hole of 0 ° to 250 ° is used, a fiber having a substantially C-shaped cross section in which the ends are almost joined to form a pseudo hollow portion is obtained.

[0009]

With the diversification of consumer needs in recent years, acetate fibers have been required to have not only a dry feeling but also various textures and touches. In particular, acetate fibers are required to have a wet feeling and a supple drape that are completely opposite to the dry feeling of acetate fibers.

In order to provide a wet feeling, it is effective to make the fiber cross section smooth with little unevenness. In order to improve the drape property, the single fiber fineness is 4d.
It is effective to use ultrafine fibers of not more than / f. However, among the fibers disclosed in the above-mentioned publications, fibers having a cross section with large irregularities are all excellent in dry feeling, and cannot meet such demands.

[0011] Further, in the fiber having a substantially C-shaped cross section having a single pseudo-hollow portion which is close to a circle with little unevenness disclosed in International Publication WO96 / 35010, the dry feeling is reduced, As described above, the spinning hole for spinning a fiber having a V-shaped cross section has a sector shape of 230 ° to 250 °, and has a convoluted shape in which a portion protruding at an angle toward the center of the circle has a complicated shape. Not only is it difficult to form a fine spinning hole of 50 μm or less, but also the spinning dope is liable to be clogged at the projecting portion, and the spinneret must be frequently cleaned, so that stable spinning is impossible. Become. For this reason, there is a problem that an ultrafine fiber having a single fiber fineness of 4 d / f or less cannot be substantially obtained, and the drape property is impaired because the fineness is large.

Accordingly, the present invention reduces the cross-sectional shape of the conventional acetate fiber having many irregularities and the dry feel based on the same, and has a delicate drape property having a wet texture rich in wet feeling, which is completely opposite to that. It is an object of the present invention to provide an acetate fiber having the same and an aggregate thereof, and a method for producing the fiber. Specifically, it reduces the many intricate irregularities seen in conventional acetate fibers, has a smooth surface, and has a moist texture rich in wet feeling with improved contact feeling between skin and fibers. It is an object to provide an ultrafine acetate fiber having a single fiber fineness of 4 d / f or less, an aggregate thereof, and a method for producing the fiber.

[0013]

According to the present invention, there is provided a cellulose acetate fiber having a degree of acetylation of 45% or more, the cross-sectional shape of which is substantially C-shaped with a smooth peripheral surface. , The two ends of which are roughly joined to form a pseudo-hollow portion, and the area of the pseudo-hollow portion occupies 10% or less of the total cross-sectional area,
A special section cellulose acetate fiber having a single fiber fineness of 4 d / f or less is a main component.

That is, because of the characteristics of dry spinning of acetate fibers as described above, volume shrinkage due to evaporation of the solvent is inevitable, and the present inventors control and reduce irregularities generated in acetate fibers, By confining the formed concave portion inside the fiber, irregularities on the fiber surface are reduced, and a moist texture rich in wet feeling is realized.

The acetate fiber of the present invention has a cross-sectional shape of approximately C in order to exhibit a wet and moist texture.
Character-shaped, that is, a shape with a single concave portion recessed from the circumference toward the center of the circle, and the peripheral surface is extremely smooth,
Further, the pseudo hollow portion is formed by substantially joining both end portions, and the area of the pseudo hollow portion greatly affects a desired manner of expressing a moist texture rich in wet feeling.
In other words, when the area of the pseudo hollow portion is large with respect to the total cross-sectional area of the fiber, the weight becomes impaired due to the same fineness, and the feeling of weight is impaired. It will give you a rich and firm texture. Therefore, the cross-sectional area of the pseudo hollow portion is set to 10% or less of the total cross-sectional area, and more preferably 5% or less.

The above-mentioned cellulose acetate has an average of 2 of the three hydroxyl groups present in the repeating unit of cellulose.
Acetate ester is obtained by acetylating up to 3 hydroxyl groups, and particularly preferably acetylated at an average of 2.1 to 3.0 (acetylation degree: 45 to 62%).

Further, the wet feeling and the moist texture, which are the objects of the present application, are greatly related to the flexibility and drape of the yarn. That is, any of the yarns having no stiffness and having a small bending resistance and a high flexibility and a high drapability have a large contact feeling with human skin, and are effective in imparting a wet feeling and a moist feeling. Therefore, appropriately selecting the fineness and specific gravity of the yarn, together with the specialization of the cross-sectional shape of the fiber as described above, can achieve the purpose of imparting a wet feeling. From this viewpoint, it is effective to reduce the thickness of the yarn to improve the wet feeling, and the acetate fiber has a single fiber fineness of 4 d / f.
Or less, and the single fiber fineness is 3 d / f
In the following, the wet feeling can be further improved.

It is also very effective to increase the specific gravity of the yarn in order to improve the drapability. In order to increase the specific gravity, a high specific gravity inorganic substance or the like can be contained and held in the cellulose acetate fiber. . The acetate fiber preferably contains 5 to 30% by weight of a particulate inorganic substance having a specific gravity of 3.5 or more and a refractive index of 1.3 to 1.9, and the particulate inorganic substance is preferably barium sulfate.
Such a fiber is obtained by spinning the fine particle inorganic substance using a spinning dope having a weight ratio of 5:95 to 30:70 with respect to acetate. The acetate fiber containing the inorganic substance substantially has a specific gravity of 1.35 to 1.64, and can further improve the wet feeling. Further, by adopting an inorganic substance having a refractive index of 1.3 to 1.9 and a refractive index close to the refractive index of the acetate fiber,
There is no loss of the glossiness and color developing properties that are characteristic of cellulose acetate.

Further, the present invention has another main structure of a cellulose acetate fiber aggregate comprising the above-mentioned cellulose acetate fiber having a special cross section of 60% or more of the total number of fibers. That is, the fiber aggregate in which the number of single fibers of cellulose acetate having the above-described special cross-sectional shape is 60% or more of the total number of fibers exhibits a sufficient wet feeling to the knitted fabric when the knitted fabric is used. However, if the proportion is less than 60%, the desired wet feeling cannot be sufficiently imparted, and the single fiber is preferably 70% or more of the total number of fibers.

Here, a general method for producing an acetate fiber will be described. The acetate fiber is prepared by dissolving acetate flakes in a solvent such as acetone or methylene chloride to prepare a spinning solution, and using this solution as a spinneret having a circular spinning hole. And obtained by dry spinning. In this dry spinning, the solvent evaporates at the same time as the spinning solution is discharged from the spinneret, and the fibers harden. At this time, the outer side hardens first, forming the skin layer, and then the inner layer. As the solvent escapes, the outer skin layer partially enters the inside, and irregularities are formed on the fiber surface. When spinning is performed under normal conditions using a spinneret having the above-described circular spinning hole, the frequency of appearance of these irregularities increases, and about 4 to 12 convex portions are formed.

As described above, in dry spinning, the volume shrinkage due to the evaporation of the internal solvent and the formation speed and degree of formation of the skin layer greatly affect the cross-sectional shape. Therefore, in order to obtain the acetate fiber of the present invention having a cross-sectional shape as described above,
By making a difference in the formation speed and degree of formation of some skin layers from the other part in the cross section, by intentionally providing a part of the surface that is relatively low in strength and easily deformable when subjected to stress In addition, it is necessary to concentrate the strain generated at the time of volume shrinkage in that portion and maintain the other portion in a relatively smooth state.

Therefore, the present invention has a shape in which a part of a circle is cut off by one straight line, the angle θ between both ends of the straight line and the center of the circle is 60 ° ≦ θ ≦ 120 °, and the sectional area is 2000 μm.
Using a spinneret having a spinning hole of ² or less, and a degree of acetylation of 4
Still another main structure is a method for producing cellulose acetate fibers having a special cross section, wherein dry spinning of cellulose acetate fibers of 5% or more is performed.

The fiber spun from the spinning hole has a cross-sectional shape immediately after spinning that substantially matches the shape of the spinning hole.
That is, the fiber surface has a flat surface spun from the linear portion of the spinning hole and an arc surface spun from the arc portion of the spinning hole. In the fiber having such a fiber surface, when the fiber surface is dried immediately after spinning, the drying speed of the flat surface is slower than the drying speed of the arc surface, and the flat surface delays the formation of the skin layer than the arc surface. . for that reason,
After that, during volume shrinkage due to evaporation of the solvent inside the fiber, the stress of the volume shrinkage is concentrated on a flat surface with a small degree of dryness, and the flat surface is depressed toward the inside of the yarn and a single concave is formed. A concave portion is formed, and furthermore, when the concave concave portion enters into the interior due to volume shrinkage, both ends thereof are substantially joined to form a pseudo hollow portion.

Therefore, when the dimension of the straight line portion of the spinning hole is long, that is, when the angle θ between both ends of the straight line and the center of the circle is larger than 120 °, the sectional area of the pseudo hollow portion becomes large. It is not preferable because the wet feeling is small and the feeling of bulkiness is large and firm. On the other hand, when the dimension of this straight line portion is too short, that is,
When the angle θ between both ends of the straight line and the center of the circle is smaller than 60 °, the difference in drying speed between the flat surface and the arc surface of the fiber immediately after spinning is small, and the formation of the skin layer on both surfaces is reduced. Because of relatively uniformity, concentration of stress due to volume shrinkage in the linear portion as described above is eliminated,
As a result, the cross section has a plurality of irregularities substantially the same as the fiber spun by the circular spinning hole.

The shape of the spinning hole is extremely simple in a special hole shape for spinning a fiber having a special cross-sectional shape, and is easily formed. Therefore, the spinning hole has a hole diameter of 50 μm or less and an area of 2000 μm.
It is possible to produce a spinneret having a fine spinning hole of μm ² or less. As a result, it is possible to spin acetate fibers having a fineness of 4 d / f or less, and a fiber having the fineness and structure as described above can be obtained, whereby the wet feeling can be improved. .

Furthermore, when dry spinning of the acetate fiber is usually performed, the temperature of the spinning solution discharged from the spinneret is set at about 65 ° C. or more and 75 ° C. or less. However, in the present invention, by setting the temperature of the spinning solution to a range lower than the above-mentioned normal temperature, it becomes easy to obtain an acetate fiber having the above-mentioned special cross-sectional shape. That is, the temperature of the spinning dope discharged from the spinneret is 45 to 65 ° C., preferably 50 to 6 ° C.
It is preferable to set the temperature to 0 ° C. When the spinning dope temperature is 4
If the temperature is lower than 5 ° C., the solvent in the spinning dope does not dry sufficiently,
During the spinning process, a plurality of single fibers may adhere to each other or cause a yarn breakage. On the other hand, if the temperature is higher than 65 ° C., the solvent becomes extremely easy to evaporate, and even if the shape of the spinning hole is a special shape as described above, the difference in the formation rate of the skin layer between the flat surface and the arc surface of the fiber becomes small. In addition, the number of irregularities in the fiber cross section per single fiber increases.

The spinning dope discharged from the spinneret contains 5 to 30% by weight of a fine particle inorganic substance having a refractive index of 1.3 to 1.9 and a specific gravity of 3.5 or more. Desirable for a reason.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings and representative examples. FIG. 1 is a cross-sectional view schematically showing a special cross section cellulose acetate fiber which is a typical embodiment of the present invention, and FIG. 2 is a cross-sectional view of a spinning hole of a spinneret used in the method for producing the special cross section cellulose acetate fiber of the present invention. It is a top view.

The cross-sectional shape of the cellulose acetate fiber 1 having a special cross section shown in FIG. 1 is substantially C-shaped with a smooth peripheral surface, and both ends 2 and 2 are roughly joined to form a pseudo hollow portion 3. The area of the pseudo hollow portion 3 occupies 10% or less of the total sectional area. Further, the cellulose acetate fiber having the special cross section 1
Has a single fiber fineness of 4 d / f or less.

The fiber 1 has less irregularities on the fiber surface, so that the contact area between the fiber surface and human skin is large, and since the single fiber fineness is small, the fiber 1 is a flexible fiber rich in drapability and has a wet feeling. A moist texture is obtained.

A typical shape of a spinning hole formed in a spinneret used in the manufacturing method of the present invention for manufacturing such a fiber will be described with reference to FIG. The spinning hole 10 has a shape in which a part of a circle having a diameter R is cut off by one straight line 11. The angle θ between both ends 11a, 11a of the straight line 11 and the center O of the circle is set between 60 ° ≦ θ ≦ 120 °.

Next, a cellulose acetate fiber dry-spun using a spinneret having the above-described spinning hole 10 will be described with reference to examples. Note that the present invention is not limited to the following embodiments.

Various evaluations in the following Examples and Comparative Examples were measured as follows. (Hollow ratio) Cross-sectional photographs as shown in FIGS. 3 and 4 were taken, and the ratio of the pseudo-hollow portion to the entire cross-sectional area of the fiber was determined from the photographs and expressed as%. (Hand) A knitted fabric was formed with a flat knitting structure using the obtained cellulose acetate fiber (multifilament), and after refining and dyeing, a sensory evaluation was performed by touch. At this time,
Comparative Example 1 was used as a standard, and those having a wet feeling were judged to be slightly good, and those having a wet feeling were judged to be good.

Comparative Example 1 Cellulose acetate flakes having an average acetylation degree of 61.2% were dissolved in a methylene chloride / methanol mixed solvent (91/9) to prepare a spinning dope. This spinning dope was adjusted to 72 ° C., and spinning was performed at 730 m / min with a spinneret having a circular spinning hole having a hole diameter of 38 μm, to obtain a cellulose acetate multifilament having 75 denier / 20 filaments.

Examples 1-3, Comparative Examples 2-4 Cellulose acetate flakes having an average acetylation degree of 61.2% were dissolved in a methylene chloride / methanol mixed solvent (91/9) to prepare a spinning dope. . This spinning dope was adjusted to 60 ° C. and spun at a spinning speed of 500 m / min using a spinneret shown in Table 1 to obtain a cellulose acetate multifilament of 75 denier / 30 filaments. Table 1 shows the evaluation results of the cross-sectional shape, hollow ratio, and hand of each filament.

[0036]

[Table 1] As in Comparative Example 2, when the angle θ between both ends of the straight line of the spinning hole and the center of the circle is large and the dimension of the straight line is long, the pseudo hollow portion is formed in a state where both ends of the concave portion are separated from each other without being joined to each other. Is not formed, a concave portion having a large area is formed, and a wet feeling cannot be obtained. Further, even if the pseudo hollow portion is formed as in Comparative Example 3, if the angle θ is large and the dimension of the straight line is long, the area of the pseudo hollow portion becomes large, resulting in a hard texture. On the other hand, even when the angle θ is too small as in Comparative Example 4, a large number of irregularities are formed on the surface of the fiber, and the contact area with human skin is small, resulting in a hard feeling with a dry feeling. .

[Comparative Example 5, Examples 4 to 8] Average acetylation degree 6
A 1.2% cellulose acetate flake was dissolved in a methylene chloride / methanol mixed solvent (91/9) to prepare a spinning stock solution. This spinning stock solution was adjusted to 57 ° C. and spun using a spinneret shown in Table 2 to obtain a predetermined acetate multifilament. Table 2 shows the results. FIG. 3 is a cross-sectional photograph of Example 5, and FIG. 4 is a cross-sectional photograph of Comparative Example 5.

[0038]

[Table 2] As for the cellulose acetate multifilament of Example 5, the single fiber has a substantially C-shaped cross section as a whole as shown in FIG. 3, and its peripheral surface is smooth and both ends are roughly joined to form a pseudo hollow portion. Has formed. The area of the pseudo hollow portion is 8% of the total sectional area. Furthermore, this multifilament is 7
5d / 20f, that is, the single fiber fineness is about 3.8 d /
f.

On the other hand, in Comparative Example 5, the spinning hole diameter R
Is large, and the area of the spinning hole is within the range of the present invention (2000 μm).
m ² or less) are using larger spinneret than. Therefore, as shown in FIG. 4, the obtained cellulose acetate multifilament single fiber has a substantially C-shaped cross section as a whole and both ends are almost joined to form a pseudo hollow portion. Is not smooth but irregularities are formed,
Further, the hollow ratio of the pseudo hollow portion is as large as 16%.
Therefore, the contact area with human skin is small, so that a wet feeling cannot be obtained, and drape property is also small.

Further, according to Examples 4 to 8, the diameter R of the spinning hole was obtained.
It can be seen that when the particle size becomes smaller, the hollow ratio of the obtained single fiber also becomes smaller, and accordingly, the fiber becomes rich in wet feeling and the texture is improved. Since the spinneret used in the present invention has a relatively simple shape as described above, the spinneret has a hole diameter R of 3 as in Examples 7 and 8.
It is possible to produce a spinneret having a spinning hole with a small diameter of 0 μm or less, and 75 d / 50 f as in Example 8.
It is possible to produce cellulose acetate fibers having a small fineness such as (1.5 d / f).

Examples 9 to 11 Average degree of acetylation 61.2%
Of cellulose acetate flakes in methylene chloride /
It was dissolved in a mixed solvent of methanol (91/9), and further, barium sulfate was added to the solution at a ratio of 18% by weight to the acetate (barium sulfate: acetate was 15.3: 84.7) to prepare a spinning dope. . The spinning dope was adjusted to 57 ° C., and the spinning speed shown in Table 3 was adjusted to 500 m / s.
The spinning was carried out in minutes to obtain a predetermined acetate multifilament. Table 3 shows the results.

[0042]

[Table 3] Even when barium sulfate is added to the spinning dope, no inconvenience occurs during spinning. In addition, when Examples 9 to 11 and Examples 4 to 6 are compared, Examples showing that Barium sulfate is added 9 to 11 have a slightly smaller hollow ratio. Furthermore, in Examples 9 to 11, since the fiber contains barium sulfate, the specific gravity is increased, the drape property is improved, the wet feeling is increased, the texture is improved, and the normal color development is not impaired.

Examples 12 to 14 Average degree of acetylation 55.5
% Cellulose acetate flakes was dissolved in an acetone / water mixed solvent (95/5) to prepare a spinning dope.
The spinning solution was adjusted to 57 ° C. and spun at a spinning speed of 500 m / min with a spinneret as shown in Table 4 to obtain a predetermined acetate multifilament. Table 4 shows the results.

[0044]

[Table 4] Even if the solvent is changed, there is no particular difference in the cross-sectional shape and texture of the obtained fiber, and a fiber having a moist texture rich in wet feeling can be obtained.

[0045]

As described above, a cellulose acetate fiber having a special cross-sectional shape having an entirely round shape and an extremely smooth surface, which has never existed before, as in the present invention,
It is possible to provide a cloth having a moist texture rich in wet feeling that has never been seen before, and its significance is extremely large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a cross-section of a special cross-section cellulose acetate fiber according to a representative embodiment of the present invention.

FIG. 2 is a plan view showing a shape of a spinning hole of a spinneret used in the production method of the present invention.

FIG. 3 is a micrograph (× 400) of a cross section of the acetate multifilament of Example 5.

FIG. 4 is a micrograph (400 × magnification) of a cross section of an acetate multifilament of Comparative Example 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Special section cellulose acetate fiber 2 Both ends 3 Pseudo hollow part 10 Spinning hole 11 Straight line 11a Both ends of a straight line

Claims (7)

[Claims] 1. A cellulose acetate fiber having an acetylation degree of 45% or more, the cross-sectional shape of which is substantially C-shaped with a smooth peripheral surface, and both ends of which are roughly joined to form a pseudo-hollow portion. The area of the pseudo hollow portion occupies less than 10% of the total cross-sectional area,
A special-section cellulose acetate fiber having a single fiber fineness of 4 d / f or less. 2. The refractive index is 1.3 to 1.9 and the specific gravity is 3.5.
The cellulose acetate fiber having a special cross-section according to claim 1, which contains 5 to 30% by weight of the above-mentioned inorganic particles. 3. The special section cellulose acetate fiber according to claim 2, wherein the inorganic fine particle is barium sulfate. 4. A cellulose acetate fiber aggregate having a special cross section, comprising the cellulose acetate fiber having a special cross section according to claim 1 in an amount of 60% or more of the total number of fibers. 5. A shape in which a part of a circle is cut off by one straight line, and an angle θ between both ends of the straight line and the center of the circle is 60 °.
A process for producing cellulose acetate fiber having a special cross-section, wherein a cellulose acetate fiber having an acetylation degree of 45% or more is dry-spun using a spinneret having a spinning hole with ≤θ≤120 ° and an area of 2000 µm ² or less. 6. The method according to claim 5, wherein the temperature of the spinning solution discharged from the spinneret is 45 to 65 ° C. 7. The spinning dope discharged from the spinneret contains 5 to 30% by weight of a fine particle inorganic substance having a refractive index of 1.3 to 1.9 and a specific gravity of 3.5 or more. The manufacturing method as described.