POLYACRYLONITRILE-BASED FIBER BUNDLE FOR ARTIFICIAL HAIR, HEADDRESS PRODUCT CONTAINING SAME, AND METHOD FOR MANUFACTURING SAME

Description

TECHNICAL FIELD

One or more embodiments of the present invention relate to a polyacrylonitrile-based fiber bundle for artificial hair to be used in a hair ornament product such as a hairpiece, a hair ornament product including the same, and a production method therefor.

BACKGROUND

Conventionally, human hair and artificial hair have been used for hair ornament products such as hairpieces, but in recent years, the availability of human hair has become difficult, and demand for artificial hair has been increasing. For example, Patent Document 1 has proposed artificial hair using fibers of an acrylic polymer containing 35 to 75 mass % of acrylonitrile, 25 to 65 mass % of a halogen-containing vinyl monomer such as vinyl chloride, and 0 to 10 mass % of a vinyl monomer that can copolymerize with these monomers.

PATENT DOCUMENT

• • Patent Document 1: JP 2002-227018A

However, fibers of an acrylic polymer described in Patent Document 1 has high circular fullness of the fiber cross-section and poor bulkiness.

In recent years, decorative properties are often required in hair ornament products, and there is a need to improve the gloss and other properties that appeal to the consumers' sense of sight.

In the production of hair ornament products, fibers for artificial hair are crimped, and some fibers in the crimped fiber bundle are then displaced to make the hair tips look natural (the amount of hair becomes smaller and the hair becomes thinner toward the tips), rather than straight and aligned, which is called stretching. The fiber loss rate during the stretching process is required to be low.

One or more embodiments of the present invention provide a polyacrylonitrile-based fiber bundle for artificial hair, with high bulkiness, a radiant gloss whose light reflection becomes locally stronger or weaker depending on the viewing angle, and a reduced stretching loss rate, a hair ornament product containing the same, and a production method therefor.

SUMMARY

One or more embodiments of the present invention relate to a polyacrylonitrile-based fiber bundle for artificial hair, including polyacrylonitrile-based synthetic fibers A and polyacrylonitrile-based synthetic fibers B, wherein the polyacrylonitrile-based synthetic fibers A have fiber cross-sections with one or more shapes selected from the group consisting of a C-shape, a figure-6-shape, and a broad bean-shape with a hollow portion, the polyacrylonitrile-based synthetic fibers B have fiber cross-sections with one or more shapes selected from the group consisting of a drop-shape with a hollow portion and a drop-shape, the polyacrylonitrile-based synthetic fibers A have a flatness ratio of less than 1.5, and the polyacrylonitrile-based synthetic fibers B have a flatness ratio of 1.5 or more, the C-shape, the figure-6-shape, or the broad bean-shape with the hollow portion of the fiber cross-sections has an inscribed circle with a diameter of 15 to 50 μm, the drop-shape with the hollow portion of the fiber cross-sections has an inscribed circle with a diameter of more than 0 μm and less than 15 μm, fiber cross-sections of the polyacrylonitrile-based fiber bundle for artificial hair have a thickness of 13 to 40 μm, the polyacrylonitrile-based fiber bundle for artificial hair has a total content of the C-shaped fiber cross-sections, figure-6-shaped fiber cross-sections, and the broad bean-shaped fiber cross-sections with the hollow portions of 3 to 97%, and the polyacrylonitrile-based fiber bundle for artificial hair has a total content of the drop-shaped fiber cross-sections with the hollow portions and the drop-shaped fiber cross-sections of 3 to 97%.

One or more embodiments of the present invention relate to a hair ornament product containing the above-described polyacrylonitrile-based fiber bundle for artificial hair.

One or more embodiments of the present invention relate to a method for producing the above-described polyacrylonitrile-based fiber bundle for artificial hair, including: performing spinning by extruding a spinning solution containing an acrylonitrile-based polymer through a spinning nozzle having a C-shaped cross-section into a coagulation bath; and water-washing coagulated filaments obtained through the spinning, wherein a discharge amount of the spinning solution per spindle of the spinning nozzle is 0.10 kg/min or more, and the water-washing is performed at a temperature of 80° C. or lower.

With one or more embodiments of the present invention, it is possible to provide a polyacrylonitrile-based fiber bundle for artificial hair, with high bulkiness, a radiant gloss whose light reflection becomes locally stronger or weaker depending on the viewing angle (referred to simply as a “radiant gloss” hereinafter), and a reduced stretching loss rate, and a hair ornament product containing the same.

Also, with the production method of one or more embodiments of the present invention, it is possible to obtain, through wet spinning, polyacrylonitrile-based synthetic fibers for artificial hair, with high bulkiness, a radiant gloss, and a reduced stretching loss rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A1 having a C-shaped fiber cross-section.

FIG. 2 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A1 having a C-shaped fiber cross-section.

FIG. 3 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A2 having a figure-6-shaped fiber cross-section.

FIG. 4 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A2 having a figure-6-shaped fiber cross-section.

FIG. 5 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A3 having a broad bean-shaped fiber cross-section with a hollow portion.

FIG. 6 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber A3 having a broad bean-shaped fiber cross-section with a hollow portion.

FIG. 7 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber B1 having a drop-shaped fiber cross-section with a hollow portion.

FIG. 8 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber B1 having a drop-shaped fiber cross-section with a hollow portion.

FIG. 9 is a schematic cross-sectional view of a polyacrylonitrile-based synthetic fiber B2 having a drop-shaped fiber cross-section.

FIG. 10 is a schematic cross-sectional view of a spinning nozzle according to an example.

FIG. 11 is a schematic cross-sectional view of a spinning nozzle according to an example.

FIG. 12 is a schematic cross-sectional view of a spinning nozzle according to an example.

FIG. 13 is a photograph (400-fold magnification) showing cross-sections of a polyacrylonitrile-based fiber bundle according to Example 4.

DETAILED DESCRIPTION

The inventors of one or more embodiments of the present invention found that high bulkiness, a radiant gloss, and a low stretching loss rate are achieved by using, as artificial hair, a fiber bundle including polyacrylonitrile-based synthetic fibers A having fiber cross-sections with one or more shapes selected from the group consisting of a C-shape, a figure-6-shape, and a broad bean-shape with a hollow portion and polyacrylonitrile-based synthetic fibers B having fiber cross-sections with one or more shapes selected from the group consisting of a drop-shape with a hollow portion and a drop-shape, and setting the total content of the C-shaped and figure-6-shaped fiber cross-sections and the broad bean-shaped fiber cross-sections with the hollow portions and the total content of the drop-shaped fiber cross-sections with the hollow portions and the drop-shaped fiber cross-sections, in the fiber bundle, to be within predetermined ranges.

The inventors of one or more embodiments of the present invention also found that a fiber bundle in which the total content of the C-shaped and figure-6-shaped fiber cross-sections and the broad bean-shaped fiber cross-sections with the hollow portions and the total content of the drop-shaped fiber cross-sections with the hollow portions and the drop-shaped fiber cross-sections are within predetermined ranges is favorably obtained through wet spinning of a spinning solution containing an acrylonitrile-based polymer, by using a spinning nozzle having a C-shaped cross-section and setting the discharge amount of spinning solution and the water-washing temperature to be within predetermined ranges.

In this specification, the “fiber cross-section” means a transverse cross-section of fibers. In this specification, the “cross-sectional shape of a spinning nozzle” means the shape of a transverse cross-section of the spinning nozzle.

In this specification, when a numerical range is shown using “to,” the numerical range includes the values at both ends (i.e., the upper limit and the lower limit). For example, a numerical range “X to Y” is a range that includes X and Y, which are the values at the two ends of the range, and is the same range as “X or more and Y or less.” Any number in the range and any range falling within the range are specifically disclosed. Also, when a plurality of numerical ranges are described in this specification, numerical ranges obtained by using the upper limits and the lower limits of the different numerical ranges in combination as appropriate are included.

The polyacrylonitrile-based fiber bundle for artificial hair of one or more embodiments of the present invention (also referred to simply as a “fiber bundle for artificial hair” hereinafter) includes polyacrylonitrile-based synthetic fibers A having fiber cross-sections with one or more shapes selected from the group consisting of a C-shape, a figure-6-shape, and a broad bean-shape with a hollow portion and polyacrylonitrile-based synthetic fibers B having fiber cross-sections with one or more shapes selected from the group consisting of a drop-shape with a hollow portion and a drop-shape. That is to say, the polyacrylonitrile-based fiber bundle for artificial hair of one or more embodiments of the present invention has fiber cross-sections with one or more shapes selected from the group consisting of a C-shape, a figure-6-shape, and a broad bean-shape with a hollow portion (also referred to simply as a “hollow broad bean-shape” hereinafter) and fiber cross-sections with one or more shapes selected from the group consisting of a drop-shape with a hollow portion (also referred to simply as a “hollow drop-shape” hereinafter) and a drop-shape.

The polyacrylonitrile-based synthetic fibers A (also referred to simply as “fibers A” hereinafter) may include one or more selected from the group consisting of polyacrylonitrile-based synthetic fibers A1 having C-shaped fiber cross-sections (also referred to simply as “fibers A1” hereinafter), polyacrylonitrile-based synthetic fibers A2 having figure-6-shaped fiber cross-sections (also referred to simply as “fibers A2” hereinafter), and polyacrylonitrile-based synthetic fibers A3 having hollow broad bean-shaped fiber cross-sections (also referred to simply as “fibers A3” hereinafter). The polyacrylonitrile-based synthetic fibers B (also referred to simply as “fibers B” hereinafter) may include one or more selected from the group consisting of polyacrylonitrile-based synthetic fibers B1 having hollow drop-shaped fiber cross-sections (also referred to simply as “fibers B1” hereinafter) and polyacrylonitrile-based synthetic fibers B2 having drop-shaped fiber cross-sections (also referred to simply as “fibers B2” hereinafter).

In the C-shaped fiber cross-section of the fibers A1, the two ends may be apart from each other or may be in contact with each other. FIGS. 1 and 2 are schematic cross-sectional views each showing a fiber A1 having a C-shaped fiber cross-section according to an example. In the C-shaped fiber cross-section shown in FIG. 1, the two ends of the C-shape are apart from each other, and thus a hollow portion with an opening is formed. In the C-shaped fiber cross-section shown in FIG. 2, the two ends of the C-shape are in contact with each other, and thus a hollow portion with no opening is formed. When the two ends in the C-shaped fiber cross-section are in contact with each other as shown in FIG. 2, although the cross-sectional shape is similar to that of a hollow fiber that has a circular fiber cross-section and includes a circular hollow portion, a portion where the two ends of the C-shape are in contact can be confirmed through observation under a microscope.

In the figure-6-shaped fiber cross-section of the fibers A2, the two ends may be apart from each other or may be in contact with each other. FIGS. 3 and 4 are schematic cross-sectional views each showing a fiber A2 having a figure-6-shaped fiber cross-section according to an example. In one or more embodiments of the present invention, the figure-6-shape can also be considered as a modified C-shape, and specifically, it can also be considered as a shape in which one end of the C-shape is located on the inside (i.e., on a side close to the hollow portion) with respect to the other end. In the figure-6-shaped fiber cross-section shown in FIG. 3, the two ends are apart from each other, and thus a hollow portion with an opening is formed. In the figure-6-shaped fiber cross-section shown in FIG. 4, the two ends are in contact with each other, and thus a hollow portion with no opening is formed.

In the hollow broad bean-shaped (kidney-shaped) fiber cross-section of the fibers A3, the two ends may be apart from each other or may be in contact with each other. FIGS. 5 and 6 are schematic cross-sectional views each showing a fiber A3 having a hollow broad bean-shaped (kidney-shaped) fiber cross-section according to an example. In one or more embodiments of the present invention, the hollow broad bean-shape can also be considered as a modified C-shape, and specifically, it can also be considered as a shape in which the two ends of the C-shape are curved toward the hollow portion. In the hollow broad bean-shaped fiber cross-section shown in FIG. 5, the two ends are apart from each other, and thus a hollow portion with an opening is formed. In the hollow broad bean-shaped fiber cross-section shown in FIG. 6, the two ends are in contact with each other, and thus a hollow portion with no opening is formed.

In the hollow drop-shaped fiber cross-section of the fibers B1, the two ends may be apart from each other or may be in contact with each other. FIGS. 7 and 8 are schematic cross-sectional views each showing a fiber B1 having a hollow drop-shaped fiber cross-section according to an example. In the hollow drop-shaped fiber cross-section shown in FIG. 7, the two ends are apart from each other, and thus a hollow portion with an opening is formed. In the hollow drop-shaped fiber cross-section shown in FIG. 8, the two ends are in contact with each other, and thus a hollow portion with no opening is formed.

The diameter of the inscribed circle of the fiber cross-section of the fiber A is 15 to 50 μm. This provides the fiber bundle for artificial hair with favorable bulkiness. The diameter of the inscribed circle of the fiber cross-section of the fiber A is not particularly limited, but may be 18 μm or more, 20 μm or more, 22 μm or more, or 25 μm or more, for example, from the viewpoint of achieving favorable bulkiness and favorable touch and improving the curl setting properties. The diameter of the inscribed circle of the C-shaped fiber cross-section of the fiber A1 may be 25 to 50 μm. The diameter of the inscribed circle of the figure-6-shaped fiber cross-section of the fiber A2 may be 15 to 40 μm. The diameter of the inscribed circle of the hollow broad bean-shaped fiber cross-section of the fiber A3 may be 15 to 40 μm.

The diameter of the inscribed circle of the fiber cross-section of the fiber B1 is more than 0 μm and less than 15 μm. This reduces the stretching loss rate of the fiber bundle for artificial hair. The diameter of the inscribed circle of the fiber cross-section of the fiber B1 is not particularly limited, but may be 3 μm or more, 4 μm or more, or 5 μm or more, for example, from the viewpoint of further improving the bulkiness. The diameter of the inscribed circle of the fiber cross-section of the fiber B1 may be 14 μm or less, 13 μm or less, or 12 μm or less, for example, from the viewpoint of further reducing the stretching loss rate. More specifically, the diameter of the inscribed circle of the fiber cross-section of the fiber B1 may be 3 to 14 μm, 4 to 13 μm, or 5 to 12 μm.

In this specification, the “diameter of the inscribed circle of the fiber cross-section” means the diameter of an imaginary inscribed circle of the hollow portion of the fiber cross-section. For example, in FIGS. 1 to 8, the diameter of the inscribed circle is indicated as R1. Note that when there are a plurality of imaginary inscribed circles of the hollow portion of the fiber cross-section, the maximum diameter among all the diameters of the inscribed circles is taken as the diameter of the inscribed circle of the fiber cross-section. In this specification, the diameter of the inscribed circle of the fiber cross-section with each cross-sectional shape can be obtained by analyzing images for analysis of the cross-sectional size using image analysis software (e.g., “WinROOF”, Mitani Corporation), measuring the diameters of inscribed circles of 30 cross-sections in total for each cross-sectional shape or measuring the diameters of inscribed circles of all cross-sections in the photographs of the cross-sections for a cross-sectional shape with less than 30 cross-sections, and calculating the average value thereof. In this specification, the images for analysis of the cross-sectional size can be obtained by observing and photographing the fiber cross-sections of a polyacrylonitrile-based fiber bundle at 400-fold magnification using a laser microscope (e.g., “VK-X260” manufactured by KEYENCE CORPORATION) at a total of 10 points (range of observation and measurement: 675 μm in width×506 μm in length). In this specification, the diameter of the inscribed circle of the fiber cross-section with each cross-sectional shape can be specifically measured and calculated as described in “Examples.”

The diameter of the circumcircle of the fiber cross-section of the fiber A is not particularly limited, but may be 70 to 120 μm, for example, from the viewpoint of further improving the bulkiness and the touch. The diameter of the circumcircle of the C-shaped fiber cross-section of the fiber A1 may be 85 to 100 μm. The diameter of the circumcircle of the figure-6-shaped fiber cross-section of the fiber A2 may be 70 to 100 μm. The diameter of the circumcircle of the hollow broad bean-shaped fiber cross-section of the fiber A3 may be 90 to 117 μm.

The diameter of the circumcircle of the fiber cross-section of the fiber B is not particularly limited, but may be 90 to 130 μm, for example, from the viewpoint of further improving the bulkiness and the touch. The diameter of the circumcircle of the hollow drop-shaped fiber cross-section of the fiber B1 may be 93 to 130 μm. The diameter of the circumcircle of the drop-shaped fiber cross-section of the fiber B2 may be 105 to 130 μm.

In this specification, the “diameter of the circumcircle of the fiber cross-section” means the diameter of an imaginary circumcircle of the fiber cross-section. For example, in FIGS. 1 to 9, the diameter of the circumcircle is indicated as R2. Note that when there are a plurality of imaginary circumcircles of the fiber cross-section, the maximum diameter among all the diameters of the circumcircles is taken as the diameter of the circumcircle of the fiber cross-section. In this specification, the diameter of the circumcircle of the fiber cross-section with each cross-sectional shape can be calculated as with the diameter of an inscribed circle, by analyzing images for analysis of the cross-sectional size using image analysis software, and it can be specifically measured and calculated as described in “Examples.”

The thickness of the fiber cross-section of the fiber bundle for artificial hair is 13 to 40 μm. This provides the fiber bundle for artificial hair with favorable bulkiness and favorable touch. The thickness of the fiber cross-section of the fiber bundle for artificial hair may be 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm, for example, from the viewpoint of further improving the curl setting properties, particularly hot-water curl setting properties. In this specification, the “thickness of the fiber cross-section of the fiber bundle for artificial hair” means the average value of the thickness of 30 arbitrarily selected fiber cross-sections. In FIGS. 1 to 9, the thickness of the fiber cross-section is indicated as t. In each individual fiber cross-section of the fiber bundle for artificial hair, the thickness may be uniform over the entire fiber cross-section or may vary. When the fiber bundle for artificial hair includes a fiber cross-section with a varying thickness, both a maximum thickness t1 and a minimum thickness t2 may be 13 to 40 μm, 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm.

The thickness of the fiber cross-section of the fiber A may be 13 to 40 μm, 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm, from the viewpoint of the bulkiness, the touch, the curl setting properties, and the like. In each individual fiber cross-section of the fiber A, the thickness may be uniform over the entire fiber cross-section or may vary. When the fiber A includes a fiber cross-section with a varying thickness, both a maximum thickness and a minimum thickness of the fiber cross-section may be 13 to 40 μm, 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm.

The thickness of the fiber cross-section of the fiber B may be 13 to 40 μm, 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm, from the viewpoint of the bulkiness, the touch, the curl setting properties, and the like. In each individual fiber cross-section of the fiber B, the thickness may be uniform over the entire fiber cross-section or may vary. When the fiber B includes a fiber cross-section with a varying thickness, both a maximum thickness and a minimum thickness may be 13 to 40 μm, 15 to 40 μm, 16 to 38 μm, 16 to 36 μm, or 17 to 34 μm.

In this specification, the “thickness of the fiber cross-section of the fiber bundle for artificial hair” can be obtained as with the diameter of an inscribed circle, by analyzing images for analysis of the cross-sectional size using image analysis software, measuring the thicknesses (e.g., the maximum thicknesses and the minimum thicknesses) of 30 cross-sections in total, and calculating the average value thereof, and it can be specifically measured as described in “Examples.”

In this specification, the thickness of the fiber cross-section with each cross-sectional shape can be obtained by measuring the thicknesses (e.g., the maximum thicknesses and the minimum thicknesses) of 30 cross-sections in total for each cross-sectional shape or measuring the thicknesses (e.g., the maximum thicknesses and the minimum thicknesses) of all cross-sections in the photographs of the cross-sections for a cross-sectional shape with less than 30 cross-sections, and calculating the average value thereof.

The flatness ratio of the fiber cross-section of the fiber A is less than 1.5, and the flatness ratio of the fiber cross-section of the fiber B is 1.5 or more. This provides the fiber bundle for artificial hair with a radiant gloss.

The flatness ratio of the hollow drop-shaped fiber cross-section of the fiber B1 may be 1.5 to 3.0, and the flatness ratio of the drop-shaped fiber cross-section of the fiber B2 may be 2.5 to 3.0. This makes it easy to suppress white blurring while imparting a radiant gloss to the fiber bundle for artificial hair.

The flatness ratio of the C-shaped fiber cross-section of the fiber A1 may be 1.0 to 1.2, the flatness ratio of the figure-6-shaped fiber cross-section of the fiber A2 may be 1.1 or more and less than 1.5, and the flatness ratio of the hollow broad bean-shaped fiber cross-section of the fiber A3 may be 1.2 to 1.4. This provides the fiber bundle for artificial hair with favorable touch.

From the viewpoint of facilitating the suppression of white blurring, the overall average flatness ratio of the fiber cross-sections (average flatness ratio of all cross-sections) of the fiber bundle for artificial hair may be 2.2 or less, 2.0 or less, or 1.8 or less. From the viewpoint of facilitating the provision of a radiant gloss, the average flatness ratio of all cross-sections of the fiber bundle for artificial hair may be 1.1 or more. More specifically, the average flatness ratio of all cross-sections of the fiber bundle for artificial hair may be 1.1 to 2.2, 1.1 to 2.0, or 1.1 to 1.8.

In this specification, the “flatness ratio of a fiber cross-section” is calculated by major axis/minor axis of the fiber cross-section. The major axis is the same as the diameter of the circumcircle, and the minor axis means the shortest distance between two straight lines that are parallel to the major axis (more specifically, the major axis that connects two contact points of the circumcircle and the figure of the fiber cross-section) when the figure of the fiber cross-section is sandwiched by the two straight lines. For example, in FIGS. 1 to 9, the major axis (the diameter of the circumcircle) is indicated as R2, and the minor axis is indicated as R3. Note that in the drop-shaped fiber cross-section, the maximum thickness t1 may match the minor axis R3.

In this specification, the flatness ratio of the fiber cross-section with each cross-sectional shape can be obtained as with the diameter of an inscribed circle, by analyzing images for analysis of the cross-sectional size using image analysis software, measuring the major axes and the minor axes of 30 cross-sections in total for each cross-sectional shape, calculating flatness ratio=major axis/minor axis for each cross-section, and calculating the average value thereof, or calculating the average value of the flatness ratios of all cross-sections in the photographs of the cross-sections for a cross-sectional shape with less than 30 cross-sections.

In this specification, the average flatness ratio of all cross-sections of the fiber bundle for artificial hair can be obtained by calculating the average value of the flatness ratios of all cross-sectional shapes.

In this specification, the flatness ratio of a fiber cross-section with each cross-sectional shape and the average flatness ratio of all cross-sections can be specifically measured as described in “Examples.”

In the fiber bundle for artificial hair, the angle between the ends in the C-shaped fiber cross-section may be 0 to 5°, 0 to 3°, or 0° or more and less than 1°. When the angle between the ends in the C-shaped fiber cross-section is within the above-mentioned range, single fibers do not interlock with each other, and thus a fiber breakage during brushing in the processing of hair ornament products is suppressed. In this specification, the “angle between the ends” means an angle between line segments that connect the center of the imaginary inscribed circle and the two ends in the C-shaped fiber cross-section. For example, in FIG. 1, the angle between the ends is indicated as 0. When the two ends in the C-shaped fiber cross-section are in contact with each other as shown in FIG. 2, the “angle between the ends” is 0°.

In this specification, the angle between the ends in the C-shaped fiber cross-section can be obtained as with the diameter of an inscribed circle, by analyzing images for analysis of the cross-sectional size using image analysis software, measuring the angle between line segments that connect the center of the imaginary inscribed circle and the two ends in 30 C-shaped fiber cross-sections in total or all C-shaped fiber cross-sections in the photographs of the cross-sections if the number of C-shaped fiber cross-sections is less than 30, and calculating the average value thereof.

In the fiber bundle for artificial hair, the total content of the C-shaped, figure-6-shaped, and hollow broad bean-shaped fiber cross-sections is 3 to 97%, and the total content of the hollow drop-shaped and drop-shaped fiber cross-sections is 3 to 97%. This provides the fiber bundle for artificial hair, with high bulkiness, a radiant gloss, and a reduced stretching loss rate. In this specification, the content of each fiber cross-section in the fiber bundle for artificial hair can be measured as described in “Examples.”

The total content of the hollow drop-shaped and drop-shaped fiber cross-sections in the fiber bundle for artificial hair may be 60% or less or 55% or less from the viewpoint of facilitating the suppression of white blurring while imparting a radiant gloss, 50% or less, 45% or less, 40% or less, or 35% or less, from the viewpoint of further improving the bulkiness, and may be 30% or less from the viewpoint of facilitating the suppression of stretching loss. The total content of the hollow drop-shaped and drop-shaped fiber cross-sections in the fiber bundle for artificial hair may be 3% or more, 4% or more, or 6% or more, from the viewpoint of imparting a radiant gloss while suppressing stretching loss. More specifically, the total content of the hollow drop-shaped and drop-shaped fiber cross-sections in the fiber bundle for artificial hair may be 3 to 60%, 3 to 55%, 3 to 50%, 4 to 45%, 4 to 40%, 6 to 35%, or 6 to 30%.

Specifically, in the fiber bundle for artificial hair, it is preferable that the total content of the C-shaped, figure-6-shaped, and hollow broad bean-shaped fiber cross-sections is 40 to 97% and that the total content of the hollow drop-shaped and drop-shaped fiber cross-sections is 3 to 60%, it is more preferable that the total content of the C-shaped, figure-6-shaped, and hollow broad bean-shaped fiber cross-sections is 50 to 96% and that the total content of the hollow drop-shaped and drop-shaped fiber cross-sections is 4 to 50%, it is even more preferable that the total content of the C-shaped, figure-6-shaped, and hollow broad bean-shaped fiber cross-sections is 60 to 95% and that the total content of the hollow drop-shaped and drop-shaped fiber cross-sections is 5 to 40%, and it is particularly preferable that the total content of the C-shaped, figure-6-shaped, and hollow broad bean-shaped fiber cross-sections is 70 to 94% and that the total content of the hollow drop-shaped and drop-shaped fiber cross-sections is 6 to 30%.

The fiber bundle for artificial hair may include the fibers B1 having hollow drop-shaped fiber cross-sections from the viewpoint of imparting a radiant gloss. The fiber bundle for artificial hair may include one or more selected from the group consisting of the fibers A1 having C-shaped fiber cross-sections and the fibers A2 having figure-6-shaped fiber cross-sections, and may include the fibers A1 having C-shaped fiber cross-sections and the fibers A2 having figure-6-shaped fiber cross-sections, from the viewpoint of bulkiness. The fiber bundle for artificial hair may include one or more selected from the group consisting of the fibers A1 having C-shaped fiber cross-sections and the fibers A2 having figure-6-shaped fiber cross-sections, and the fibers B1 having hollow drop-shaped fiber cross-sections, may include the fibers A1 having C-shaped fiber cross-sections, the fibers A2 having figure-6-shaped fiber cross-sections, and the fibers B1 having hollow drop-shaped fiber cross-sections.

In one or more embodiments of the present invention, an acrylonitrile-based polymer contained in each of the fibers A and the fibers B is not particularly limited as long as it contains a constituent unit derived from acrylonitrile in an amount of 25 mass % or more, and examples thereof include an acrylonitrile-based polymer containing a constituent unit derived from acrylonitrile in an amount of 25 to 100 mass % and a constituent unit derived from another monomer in an amount of 0 to 75 mass %. The acrylonitrile-based polymer may contain a constituent unit derived from acrylonitrile in an amount of 95 mass % or less and a constituent unit derived from another monomer in an amount of 5 mass % or more, a constituent unit derived from acrylonitrile in an amount of 90 mass % or less and a constituent unit derived from another monomer in an amount of 10 mass % or more, or a constituent unit derived from acrylonitrile in an amount of 30 mass % or more and less than 85 mass % and a constituent unit derived from another monomer in an amount of more than 15 mass % and 70 mass % or less.

The other monomer is not particularly limited as long as it can copolymerize with acrylonitrile, and examples thereof include unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and salts thereof, acrylic acid esters such as methyl acrylate, methacrylic acid esters such as methyl methacrylate, esters of unsaturated carboxylic acids such as glycidyl methacrylate, vinyl esters such as vinyl acetate and vinyl butyrate, halogen-containing monomers, sulfonic acid group-containing monomers, and the like. These monomers may be used alone or in a combination of two or more.

The acrylonitrile-based polymer may contain a constituent unit derived from acrylonitrile in an amount of 30 to 80 mass %, a constituent unit derived from a halogen-containing monomer in an amount of 20 to 70 mass %, and a constituent unit derived from a sulfonic acid group-containing monomer in an amount of 0 to 5 mass %, from the viewpoint of thermal resistance, flame retardance, and dyeability. The acrylonitrile-based polymer may contain a constituent unit derived from acrylonitrile in an amount of 35 to 75 mass %, a constituent unit derived from a halogen-containing monomer in an amount of 25 to 65 mass %, and a constituent unit derived from a sulfonic acid group-containing monomer in an amount of 0 to 5 mass %, or a constituent unit derived from acrylonitrile in an amount of 35 to 75 mass %, a constituent unit derived from a halogen-containing monomer in an amount of 24.5 to 64.5 mass %, and a constituent unit derived from a sulfonic acid group-containing monomer in an amount of 0.5 to 5 mass %.

Examples of the halogen-containing monomer include halogen-containing vinyl monomers such as vinyl chloride and vinyl bromide, and halogen-containing vinylidene monomers such as vinylidene chloride and vinylidene bromide. These halogen-containing monomers may be used alone or in a combination of two or more. The halogen-containing monomer may contain one or more selected from the group consisting of vinyl chloride and vinylidene chloride, or vinyl chloride from the viewpoint of touch.

The sulfonic acid group-containing monomer is not particularly limited, and examples thereof include allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, isoprenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, and metallic salts (e.g., sodium salts) thereof and amine salts thereof. These sulfonic acid group-containing monomers may be used alone or in a combination of two or more.

In one or more embodiments of the present invention, a fiber treatment agent may be adhered to the fiber bundle for artificial hair from the viewpoint of further improving the touch, and it is preferable that the fiber treatment agent contains a fatty acid ester oil and polyoxyethylene surfactant. In general, better touch can be achieved by using the fatty acid ester oil and the polyoxyethylene surfactant, which are used to improve the texture of a polyacrylonitrile-based synthetic fiber, together, compared with the case of using only one of the fatty acid ester oil and the polyoxyethylene surfactant.

In one or more embodiments of the present invention, the adhesion amount of the fiber treatment agent with respect to 100 parts by mass of the fiber bundle for artificial hair may be 0.1 to 1.0 part by mass, 0.1 to 0.6 parts by mass, or 0.15 to 0.35 parts by mass, from the viewpoint of further improving the touch. In this specification, the adhesion amount of the fiber treatment agent in the fiber bundle for artificial hair is measured and calculated as described in “Examples.”

In one or more embodiments of the present invention, the fiber bundle for artificial hair may contain other additives to improve the fiber characteristics if necessary as long as the effects of one or more embodiments of the present invention are not inhibited. Examples of the additives include the following functional agents: gloss control agents such as titanium dioxide, silicon dioxide, and esters and ethers of cellulose derivatives including cellulose acetate; coloring agents such as organic pigments, inorganic pigments, and dyes; stabilizers for improving light resistance and heat resistance; fiber sizing agents such as a urethane polymer and a cationic ester polymer for improving the processability of the fibers during braiding or twisting; inorganic or organic deodorants for capturing isovaleric acid that is an odor component generated from the scalp; and aromatic agents for giving an aroma such as a citrus aroma to the artificial hair fibers.

The method for producing the fiber bundle for artificial hair is not particularly limited, but it can be produced through wet spinning using a spinning solution containing the above-described acrylonitrile-based polymer from the viewpoint of productivity. The spinning solution can be obtained by, for example, dissolving the acrylonitrile-based polymer in an organic solvent. The organic solvent is not particularly limited, and a good solvent for the acrylonitrile-based polymer can be used as appropriate. Examples of the good solvent include dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and acetone. Acetone may be used from the viewpoint of versatility. Dimethyl sulfoxide may be used from the viewpoint of high safety. The spinning solution may contain, for example, an acrylonitrile-based polymer in an amount of 20 to 30 mass %, 22 to 30 mass %, or 25 to 30 mass %. The spinning solution may contain a small amount of water, for example, such as water in an amount of 1.5 to 4.8 mass %. This can reduce the formation of voids.

The spinning solution may contain an epoxy group-containing compound in an amount of 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more, with respect to 100 parts by mass of the acrylonitrile-based polymer. It is preferable that spinning solution contains the epoxy group-containing compound because foul odor, coloring of the fibers caused by heat, devitrification of the fibers caused by hot water, and the like can be suppressed. In particular, when dimethyl sulfoxide is used as the organic solvent, the epoxy group-containing compound can effectively reduce the generation of malodorous components caused by the decomposition of the dimethyl sulfoxide while the fiber bundle for artificial hair is being heated. Also, the spinning solution may contain the epoxy group-containing compound in an amount of 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, with respect to 100 parts by mass of the acrylonitrile-based polymer, from the viewpoint of spinnability, fiber quality, and cost. More specifically, the spinning solution may contain the epoxy group-containing compound in an amount of 0.1 to 5 parts by mass, 0.2 to 3 parts by mass, or 0.3 to 1 part by mass, with respect to 100 parts by mass of the acrylonitrile-based polymer.

Examples of the epoxy group-containing compound include a glycidyl methacrylate-containing polymer, a glycidyl acrylate-containing polymer, an epoxidized vegetable oil, a glycidyl ether epoxy resin, a glycidyl amine epoxy resin, a glycidyl ester epoxy resin, and a cyclic aliphatic epoxy resin. These epoxy group-containing compounds may be used alone or in a combination of two or more.

The epoxy group-containing compound may be a glycidyl methacrylate-containing polymer and/or a glycidyl acrylate-containing polymer, or polyglycidyl methacrylate (homopolymer of glycidyl methacrylate), from the viewpoint of epoxy equivalent (i.e., the mass of the resin containing 1 equivalent of epoxy group), suppressing the coloring of the fibers, the solubility in dimethyl sulfoxide, and reducing the elution into a spinning bath.

The mass average molecular weight (Mw) of the epoxy group-containing compound is not particularly limited, and may be determined as appropriate in view of, for example, the solubility in dimethyl sulfoxide and the elution into a spinning bath. When the epoxy group-containing compound is a glycidyl methacrylate-containing polymer and/or a glycidyl acrylate-containing polymer, the mass average molecular weight may be, for example, 3,000 or more from the viewpoint of reducing the elution into the spinning bath and may be 100,000 or less from the viewpoint of the solubility in an organic solvent such as dimethyl sulfoxide. More specifically, the mass average molecular weight (Mw) of the epoxy group-containing compound may be 3,000 to 100,000.

The spinning solution may contain other additives to improve the fiber characteristics if necessary as long as the effects of one or more embodiments of the present invention are not inhibited. Examples of the other additives include gloss control agents such as titanium dioxide, silicon dioxide, and esters and ethers of cellulose derivatives including cellulose acetate; coloring agents such as organic pigments, inorganic pigments, and dyes; and stabilizers for improving light resistance and heat resistance. The other additives may be added in an amount of 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, with respect to 100 parts by mass of the acrylonitrile-based polymer.

The production method through wet spinning includes at least a spinning process (also referred to as a “coagulation process”) and a water-washing process. The production method may include a wet drawing (primary drawing) process that is to be performed before, simultaneously with, or after the water-washing process. Typically, the production method includes a drying process that is to be performed after the water-washing process. The production method may include an oil (fiber treatment agent) application process that is to be performed before the drying process. The production method may include a dry drawing (secondary drawing) process and a thermal relaxation process that are to be performed after the drying process.

First, in the spinning process, the spinning solution is extruded through a spinning nozzle into a coagulation bath (also referred to as a “coagulation solution”) to form coagulated filaments (also referred to as “undrawn yarns”).

The spinning nozzle is not particularly limited, and, for example, an ordinary nozzle with a C-shaped cross-section, specifically a nozzle with a C-shaped cross-section with two ends being apart from each other can be used as appropriate. An end of the C-shape may include a linear portion, or may have an arc shape. Also, the two ends of the C-shape may be symmetrically or asymmetrically located relative to the central axis of the hollow portion. In the nozzle with a C-shaped cross-section, for example, a circumcircle diameter Cd is not particularly limited, but may be 0.37 to 0.60 mm, a canal width Cw is not particularly limited, but may be 0.06 to 0.24 mm, a slit width Aw is not particularly limited, but may be 0.06 to 0.15 mm, and a pore area is not particularly limited, but may be 0.0850 to 0.1256 mm². In the nozzle with a C-shaped cross-section, a flatness ratio is not particularly limited, but may be 1.0 to 1.2, for example. In this specification, the flatness ratio of the nozzle can be calculated by circumcircle diameter Cd/minor axis Cs in a nozzle cross-section.

As the spinning nozzle, a nozzle that, for example, has a cross-section with a C-shape whose two ends are apart from each other and in which each of the ends of the C-shape includes a linear portion and a protrusion bulging outward may be used. Also, it is more preferable that the linear portions of the two ends are parallel to each other. That is to say, a nozzle (also referred to as a “type-I spinning nozzle” hereinafter) that has a cross-section with a C-shape whose two ends are apart from each other and in which each of the ends of the C-shape includes a linear portion and a protrusion bulging outward and the linear portions of the two ends are parallel to each other may be used. FIG. 10 is a schematic cross-sectional view of a type-I spinning nozzle according to an example. In the cross-section of the type-I spinning nozzle, one of the two ends of the C-shape includes a linear portion 1a and a protrusion 2a, and the other includes a linear portion 1b and a protrusion 2b, the linear portions 1a and 1b being parallel to each other. In the type-I spinning nozzle, the circumcircle diameter Cd may be 0.37 to 0.60 mm, the canal width Cw may be 0.06 to 0.24 mm, the slit width Aw may be 0.06 to 0.15 mm, and the pore area may be 0.0850 to 0.1256 mm². The flatness ratio of the type-I spinning nozzle is not particularly limited, but may be 1.0 to 1.2, for example.

As the spinning nozzle, a nozzle that, for example, has a cross-section with a C-shape in which one end of the C-shape is located on the inside with respect to the other end (also referred to as a “type-II spinning nozzle” hereinafter) may be used. FIG. 11 is a schematic cross-sectional view of a type-II spinning nozzle according to an example. In the type-II spinning nozzle, one end 3a of the C-shape is located on the inside (i.e., on a side close to the hollow portion) with respect to the other end 3b. In the cross-section of the type-II spinning nozzle, the circumcircle diameter Cd may be 0.37 to 0.60 mm, the canal width Cw may be 0.06 to 0.24 mm, the slit width Aw may be 0.06 to 0.15 mm, and the pore area may be 0.0850 to 0.1256 mm². The flatness ratio of the type-II spinning nozzle is not particularly limited, but may be 1.0 to 1.2, for example.

A fiber bundle for artificial hair with the above-described cross-sectional shape and the above-described cross-sectional content can be favorably obtained by setting the discharge amount of the spinning solution per spindle of the spinning nozzle to 0.10 kg/min or more. From the viewpoint of facilitating the lowering of the total content of the hollow drop-shaped and drop-shaped fiber cross-sections in the fiber bundle for artificial hair into a favorable range, the discharge amount of the spinning solution per spindle of the spinning nozzle may be 0.3 to 15 kg/min, 0.4 to 12 kg/min, or 3 to 11 kg/min.

An aqueous solution containing an organic solvent such as dimethyl sulfoxide at a concentration of 20 to 70 mass %, 25 to 65 mass %, or 30 to 60 mass % can be used for the coagulation bath. If the concentration of the organic solvent in the coagulation bath is too low, the coagulation is accelerated, and thus it is likely that a coagulation structure will be coarse and voids will be formed inside the fiber.

The temperature of the coagulation bath is not particularly limited, but may be 5 to 40° C., for example. From the viewpoint of facilitating the lowering of the total content of the hollow drop-shaped and drop-shaped fiber cross-sections in the fiber bundle for artificial hair into a favorable range, the temperature of the coagulation bath may be 10 to 35° C., 15 to 30° C., or 18 to 25° C.

The spinning rate is not particularly limited, but may be 2 to 17 m/min, for example, from the viewpoint of industrial productivity. The nozzle draft is not particularly limited, but may be 0.8 to 2.0, for example, from the viewpoint of the stability of the production process.

Next, in the water-washing process, the coagulated filaments are washed with water to remove an organic solvent such as dimethyl sulfoxide, that is, to perform desolvation. A fiber bundle for artificial hair with the above-described cross-sectional shape and the above-described cross-sectional content can be favorably obtained by setting the water-washing temperature to 80° C. or lower. Specifically, the water-washing process may be performed using warm water at 30 to 80° C., 40 to 80° C., 50 to 80° C., or 60 to 78° C.

From the viewpoint of productivity, drawn yarns can be obtained by performing the wet drawing (primary drawing) simultaneously with the water-washing process. The draw ratio is not particularly limited, but may be 2 to 8 times, for example, from the viewpoint of improving the fiber strength and the productivity.

In the oil application process, an aqueous solution or aqueous dispersion (also referred to as an “oil solution”) of the fiber treatment agent containing a fatty acid ester oil and a polyoxyethylene surfactant can be used. Specifically, it is preferable that the fiber treatment agent at a predetermined concentration is introduced into an oil bath, and drawn yarns (a polyacrylonitrile-based fiber bundle) are immersed in the oil bath so that the fiber treatment agent is applied. The temperature of the oil bath is not particularly limited, but may be any temperature of 40° C. or higher, and may be 40 to 80° C., for example. The immersion time is not particularly limited, but may be 1 to 10 seconds or 1 to 5 seconds, for example.

The oil solution may contain other additives to improve the fiber characteristics if necessary as long as the effects of one or more embodiments of the present invention are not inhibited. Examples of the other additives include fiber sizing agents such as a urethane polymer and a cationic ester polymer.

Next, in the drying process, the polyacrylonitrile-based fiber bundle to which the fiber treatment agent has been applied can be dried. The drying temperature is not particularly limited, but may be 110 to 190° C., for example. Then, the dried polyacrylonitrile-based fiber bundle may be further subjected to dry drawing (secondary drawing) as necessary. The drawing temperature of the secondary drawing is not particularly limited, but may be 110 to 190° C., for example. The draw ratio in the secondary drawing is not particularly limited, but may be 1 to 4 times, 1 to 3 times, or 1 to 2 times, for example. The total draw ratio that includes the primary drawing before the drying process may be 2 to 10 times, 2 to 8 times, 2 to 6 times, or 2 to 4 times.

Furthermore, the polyacrylonitrile-based fiber bundle that has been dried or that has been dried and then drawn may be relaxed in the thermal relaxation process. The relaxation rate is not particularly limited, but may be 5% or more, or 10 to 30%, for example. The thermal relaxation treatment can be performed at a high temperature such as 140 to 200° C., for example.

The single fiber fineness of the polyacrylonitrile-based fiber bundle may be 20 to 95 dtex, 25 to 85 dtex, 30 to 75 dtex, or 35 to 65 dtex, from the viewpoint of making the acrylic fibers suitable for artificial hair. In this specification, the single fiber fineness of the polyacrylonitrile-based fiber bundle can be measured as described in “Examples.”

The fiber bundle for artificial hair alone may be used as artificial hair, or a combination of the fiber bundle for artificial hair and other fibers for artificial hair may be used as artificial hair. In addition, hair ornament products can be produced using the fiber bundle for artificial hair. The hair ornament products may include other fibers for artificial hair in addition to the above-mentioned fiber bundle for artificial hair. The other fibers for artificial hair are not particularly limited, and examples thereof include polyvinyl chloride fibers, nylon fibers, polyester fibers, and regenerated collagen fibers.

Examples of the hair ornament products include weaving hair, a wig, a braid, a toupee, a hair extension, and a hair accessory.

Examples

Hereinafter, one or more embodiments of the present invention will be described by way of examples, but one or more embodiments of the present invention are not limited to the following examples.

The measuring methods and the evaluation methods used in the examples and comparative examples are as follows.

Single Fiber Fineness of Fiber Bundle

The single fiber fineness of a fiber bundle was determined by measuring 30 fibers using an autovibro type fineness measuring apparatus “DENICON DC-21” (manufactured by Search), and calculating an average of the measured values.

Adhesion Amount of Fiber Treatment Agent

A sample (fiber bundle) of about 2 g (sample mass W0) was cut into 12 to 15 cm and packed in a stainless-steel tube (oil extraction tube) having a hole of about 1 mm at the lower end. Next, 35 mL of a mixed solution containing ethanol and cyclohexane at a mass ratio of 1:1 was prepared as an extractant for the fiber treatment agent, and about 20 mL of the extractant was poured into the oil extraction tube. The lid of the oil extraction tube was adjusted so that the drop rate of the extractant was about 1 drop per 1 to 1.5 seconds. Then, the extraction of the fiber treatment agent was started. In this case, a tray (empty tray mass W1) heated to 120° C. by a heater was used as a saucer for liquid drops and placed in such a way that the dropping liquid fell there. When the dropping was finished, the lid was once removed, and the fibers present in the oil extraction tube were pushed with a stainless-steel rod to squeeze the extractant. This operation was repeated by using the remaining extractant (about 15 mL). Upon the completion of the extraction, the tray was placed in an oven at 90° C. and taken out of the oven after 5 minutes. Consequently, the extractant dried out and only the fiber treatment agent remained on the tray. The total mass (W2) of this tray was measured, and the amount of the fiber treatment agent adhered to 100 parts by mass of the fiber bundle was calculated by Formula 1 below.

Formula 1

Adhesion ⁢ amount ⁢ of ⁢ fiber ⁢ treatment ⁢ agent ⁢ ( parts ⁢ by ⁢ mass ) = [ ( W ⁢ 2 - W ⁢ 1 ) / ( W ⁢ 0 + W ⁢ 1 - W ⁢ 2 ) ] × 1 ⁢ 0 ⁢ 0

Method for Observing Fiber Cross-Section

Preparation of Sample

The polyacrylonitrile-based fiber bundle was cut into 15 cm long, and an appropriate amount of thereof was packed in a heat-shrinkable tube (model number “FEP-040” manufactured by Junkosha Inc., inner diameter before shrinkage: φ4.5 mm, inner diameter after shrinkage: φ3.3 mm, length: 1 m). Then, the tube was allowed to stand in an oven at 105° C. for 5 minutes. Then, the tube was taken out of the oven and left to cool. After the heat-shrinkable tube was cooled, the tube that had shrunk in a state of being filled with the polyacrylonitrile-based fiber bundle was cut to a length of about 3 mm with a razor blade. Thus, samples for observation of the fiber cross-section were prepared.

Observation and Photography

The samples for observation of the fiber cross-section were observed at 400-fold magnification and photographed using a laser microscope (VK-X260, manufactured by KEYENCE CORPORATION) to obtain images for analysis of the cross-sectional size (range of observation and measurement: 675 μm in width×506 μm in length) at a total of 10 points and images for analysis of the cross-sectional content (range of observation and measurement: 3375 μm in width×1102 μm in length) at a total of 9 points.

Method for Analyzing Photograph of Cross-Section

Image analysis software (WinROOF, Mitani Corporation) was used to import the photographs (images) of the cross-sections, and the following parameters were defined and measured.

Diameter of Inscribed Circle

For each cross-sectional shape, the diameters of inscribed circles of 30 cross-sections in total were measured, and the average value thereof was taken as the diameter of an inscribed circle for the cross-sectional shape. For example, in FIGS. 1 to 8, the diameter of the inscribed circle is indicated as R1. For a cross-sectional shape with less than 30 cross-sections, the diameters of inscribed circles of all cross-sections in the photographs of the cross-sections were measured, and the average value thereof was taken as the diameter of an inscribed circle.

Diameter of Circumcircle

For each cross-sectional shape, the diameters of circumcircles of 30 cross-sections in total were measured, and the average value thereof was taken as the diameter of a circumcircle for the cross-sectional shape. For example, in FIGS. 1 to 9, the diameter of the circumcircle is indicated as R2. For a cross-sectional shape with less than 30 cross-sections, the diameters of circumcircles of all cross-sections in the photographs of the cross-sections were measured, and the average value thereof was taken as the diameter of a circumcircle.

Thickness

The maximum thicknesses (maximum wall thicknesses) of 30 cross-sections in total were measured, and the average value thereof was taken as the maximum thickness t1 of the fiber cross-sections of the fiber bundle.

The minimum thicknesses (minimum wall thicknesses) of 30 cross-sections in total were measured, and the average value thereof was taken as the minimum thickness t2 of the fiber cross-sections of the fiber bundle.

For example, in FIGS. 1 to 9, the thickness is indicated as t.

Flatness Ratio

For each cross-sectional shape, the major axes and the minor axes of 30 cross-sections in total were measured, flatness ratio=major axis/minor axis was calculated, and the average value thereof was taken as the flatness ratio for the cross-sectional shape. For example, in FIGS. 1 to 9, the major axis (the diameter of the circumcircle) is indicated as R2, and the minor axis is indicated as R3. For a cross-sectional shape with less than 30 cross-sections, the major axes and the minor axes of all cross-sections were measured, flatness ratio=major axis/minor axis was calculated, and the average value thereof was taken as the flatness ratio for the cross-sectional shape.

The average value of the flatness ratios of all cross-sectional shapes was taken as the average flatness ratio of all cross-sections.

Angle Between Ends

In the C-shaped fiber cross-section, an angle between line segments that connected the center of an inscribed circle and the two ends of the C-shape was measured, and the average value of those from 30 cross-sections in total was taken as the angle between the ends. For example, in FIG. 1, the angle between the ends is indicated as 0. If the number of C-shaped fiber cross-sections is less than 30, an angle between line segments that connected the center of an inscribed circle and the two ends of the C-shape was measured in all C-shaped fiber cross-sections in the photographs of the cross-sections, and the average value thereof was taken as the angle between the ends.

Content of Fiber Cross-Section with Each Cross-Sectional Shape

In nine photographs of the cross-sections, the total number of fiber cross-sections and the number of fiber cross-sections with each cross-sectional shape were measured, and the content of the fiber cross-sections with each cross-sectional shape was calculated by the following formulas.

Content ⁢ ( % ) ⁢ of ⁢ C - shaped ⁢ f ⁢ iber ⁢ cross - sections = [ number ⁢ of ⁢ C - shaped ⁢ fiber ⁢ cross - sections / total ⁢ number ⁢ of ⁢ fiber ⁢ cross - sections ] × 100 Content ⁢ ( % ) ⁢ of ⁢ figure - 6 - shaped ⁢ fiber ⁢ cross - sections = [ number ⁢ of ⁢ figure - 6 - shaped ⁢ fiber ⁢ cross - sections / total ⁢ number ⁢ of ⁢ fiber ⁢ cross - sections ] × 100 Content ⁢ ( % ) ⁢ of ⁢ hollow ⁢ board ⁢ bean - shaped ⁢ fiber ⁢ cross - sections = [ number ⁢ of ⁢ hollow ⁢ board ⁢ bean - shaped ⁢ fiber ⁢ cross - sections / total ⁢ number ⁢ of ⁢ fiber ⁢ cross - sections ] × 100 Content ⁢ ( % ) ⁢ of ⁢ hollow ⁢ drop - shaped ⁢ fiber ⁢ cross - sections = [ number ⁢ of ⁢ hollow ⁢ drop - shaped ⁢ fiber ⁢ cross - sections / total ⁢ number ⁢ of ⁢ fiber ⁢ cross - sections ] × 100 Content ⁢ ( % ) ⁢ of ⁢ drop - shaped ⁢ fiber ⁢ cross - sections = [ number ⁢ of ⁢ drop - shaped ⁢ fiber ⁢ cross - sections / total ⁢ number ⁢ of ⁢ fiber ⁢ cross - sections ] × 100

Method for Evaluating Bulkiness

Sample Preparation Method

About 270 g of the polyacrylonitrile-based fiber bundle was processed at a take-up speed of 1.5 to 2 m/min, a gear temperature of 90 to 100° C., and a gear pitch of 2.5 mm to have a crimp angle of 141°+3° (the average of 5 fibers, each of which had been measured at one point). Thus, a crimped tow was obtained.

Volume Evaluation Method

A professional beauty evaluator made two BRDs (braids) using the crimped tow of 45.7 cm×4 g (length×weight) for each braid. The width and thickness of one BRD were measured at 10 points each by a vernier caliper. Based on the average value of the widths and the average value of the thicknesses of the two BRDs, the width and the thickness were calculated. Next, the product of the width and the thickness (width× thickness) was calculated as a volume evaluation value. The ratio of the volume evaluation value to a volume evaluation value at a comparative level (Reference Example 1) was calculated and taken as a volume increase rate. If the volume increase rate was 10% or more, the sample was acceptable (favorable). If the volume increase rate was less than 10%, the sample was unacceptable.

Method for Evaluating Gloss

A 30 cm×30 g (length×weight) fiber bundle was taken as a sample, and the sample was placed on a semi-cylindrical stand of 10 cm in diameter and was subjected to sensory evaluation by one professional beauty evaluator. At this time, the sample was observed from the vertical and horizontal directions, and the gloss of the sample was scored in the range of 1 to 5 points in increments of 0.25 points, with the gloss of Comparative Level 1 (fibers with gloss equivalent to that of human hair in Reference Example 1) being scored as 1 point and the gloss of Comparative Level 2 (polyvinyl chloride fibers, “ADVANTAGE-MT” manufactured by Kaneka Corporation) being scored as 4 points. A gloss evaluation score of 2 or more indicates that the sample has a radiant gloss. A gloss evaluation score of more than 4 indicates that the radiant gloss may be too strong and white blurring may appear in the sample, and thus a range of 2 to 4 is the preferred range.

• • 1: Gloss equivalent to that of fibers of Comparative Level 1
  • 2: Slightly stronger radiant gloss than that of fibers of Comparative Level 1
  • 3: Slightly weaker radiant gloss than that of fibers of Comparative Level 2
  • 4: Radiant gloss equivalent to that of fibers of Comparative Level 2
  • 5: Stronger radiant gloss than that of fibers of Comparative Level 2

Method for Measuring Stretching Loss Rate

Sample Preparation Method

About 270 g of the polyacrylonitrile-based fiber bundle was processed at a take-up speed of 1.5 to 2 m/min, a gear temperature of 90 to 100° C., and a gear pitch of 2.5 mm to have a crimp angle of 141°±3° (the average of 5 fibers, each of which had been measured at one point). Thus, a polyacrylonitrile-based fiber bundle that had been crimped (referred to as a “crimped tow” hereinafter) was obtained. Three crimped tows of 65 cm and 25.0 g each were prepared.

Stretching

The mass (W10) of one crimped tow was measured. In the crimped tow, the fibers were displaced by pinching a few fibers at a time with the tips of the fingers to form a tapered shape with less hair at both ends of the tow. Fibers that were displaced too far were pulled out and returned to the tow. After displacing, combing was performed twice, 10 times on one side and 10 times on the other side, using a comb, and the mass (W11) of fibers lost due to stretching was measured. The stretching loss rate was calculated by the following formula. The average value of the stretching loss rates of three crimped tows in total was used. If the stretching loss rate was 8% or less, the sample was acceptable. If the stretching loss rate was more than 8%, the sample was unacceptable.

Stretching ⁢ loss ⁢ rate ⁢ ( % ) = [ W ⁢ 11 / W ⁢ 10 ] × 100

Example 1

An acrylonitrile-based polymer containing 49 mass % of acrylonitrile, 50 mass % of vinyl chloride, and 1 mass % of sodium styrenesulfonate was dissolved in acetone to produce an acrylonitrile-based polymer solution having a resin concentration of 28.0 mass %. Next, carbon black, a liquid red and blue cationic dyes (manufactured by Hodogaya Chemical Co., Ltd.) were added as coloring agents to the acrylonitrile-based polymer solution in amounts of 0.6 parts by mass, 0.25 parts by mass, and 0.4 parts by mass, with respect to 100 parts by mass of the acrylonitrile-based polymer, respectively. Moreover, polyglycidyl methacrylate (mass average molecular weight: 12,000) was added to this solution in an amount of 1.0 part by mass with respect to 100 parts by mass of the acrylonitrile-based polymer to produce a spinning solution. A spinning nozzle a having a shape shown in FIG. 10 and a size shown in Table 1 was used to extrude the spinning solution into a coagulation bath containing a 35 mass % aqueous solution of acetone at 25° C. at a discharge amount per spindle of the spinning nozzle of 0.40 kg/min so that wet spinning was performed at a spinning rate of 6 m/min and a nozzle draft of 1.17. Then, the solvent of the obtained coagulated filaments was removed by hot water at 80° C. and the coagulated filaments were drawn to 1.9 times their original length. Next, the obtained water-washed primary drawn yarns were immersed in an oil bath (60° C.) containing a fiber treatment agent (containing a fatty acid ester oil and a polyoxyethylene surfactant with a total concentration of 1.8 mass %) for 3 to 5 seconds. Thus, the filaments were impregnated with the oil. Thereafter, the filaments were dried at 130° C. and further drawn to 2.7 times their original length. The resulting yarns were subjected to a 9% relaxation treatment at 140 to 145° C. Thus, a polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained.

Example 2

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 1, except that the spinning solution was extruded at a discharge amount per spindle of the spinning nozzle of 3.59 kg/min and that the solvent was removed by hot water at 76° C.

Example 3

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 1, except that a spinning nozzle b having a shape shown in FIG. 11 and a size shown in Table 1 was used to extrude the spinning solution into a coagulation bath containing a 30 mass % aqueous solution of acetone at 25° C.

Example 4

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 2, except that the spinning nozzle b was used to extrude the spinning solution into a coagulation bath containing a 30 mass % aqueous solution of acetone at 25° C.

Example 5

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 4, except that the spinning nozzle b was used to extrude the spinning solution into a coagulation bath containing a 30 mass % aqueous solution of acetone at 18° C. at a discharge amount per spindle of the spinning nozzle of 8.10 kg/min and that the wet spinning was performed at a spinning rate of 14 m/min and a nozzle draft of 1.22.

Example 6

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 5, except that a coagulation bath containing a 30 mass % aqueous solution of acetone at 21° C. was used.

Example 7

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 5, except that a coagulation bath containing a 30 mass % aqueous solution of acetone at 25° C. was used.

Example 8

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 5, except that a coagulation bath containing a 30 mass % aqueous solution of acetone at 28° C. was used.

Example 9

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 2, except that the solvent was removed by hot water at 60° C.

Example 10

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 2, except that the solvent was removed by hot water at 70° C.

Comparative Example 1

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 1, except that the spinning solution was extruded at a discharge amount per spindle of the spinning nozzle of 0.04 kg/min.

Comparative Example 2

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 3, except that the spinning solution was extruded at a discharge amount per spindle of the spinning nozzle of 0.04 kg/min.

Comparative Example 3

A polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.25 parts by mass) having a single fiber fineness of about 51 dtex was obtained in the same manner as in Example 1, except that a coagulation bath containing a 30 mass % aqueous solution of acetone at 25° C. was used and that the solvent was removed by hot water at 85° C.

Reference Example 1

An acrylonitrile-based polymer containing 46 mass % of acrylonitrile, 52 mass % of vinyl chloride, and 2 mass % of sodium styrenesulfonate was dissolved in dimethyl sulfoxide to produce a resin solution having a resin concentration of 28.0 mass % and a moisture concentration of 3.5 mass %. Next, carbon black, a red dye (C.I Basic Red 46), and a blue dye (C.I Basic Blue 41) were added as coloring agents to the resin solution in amounts of 2.1 parts by mass, 0.04 parts by mass, and 0.07 parts by mass, with respect to 100 parts by mass of the acrylonitrile-based polymer, respectively. Moreover, polyglycidyl methacrylate (mass average molecular weight: 12,000) was added to this solution in an amount of 1.0 part by mass with respect to 100 parts by mass of the acrylonitrile-based polymer to produce a spinning solution. A spinning nozzle c having a shape shown in FIG. 12 and a size shown in Table 2 was used to extrude the spinning solution into a coagulation bath containing a 52 mass % aqueous solution of DMSO at 20° C. so that wet spinning was performed at a spinning rate of 2 m/min and a nozzle draft of 1.15. Then, the coagulated filaments were drawn to 2.4 times their original length in a drawing bath containing a 30 mass % aqueous solution of DMSO at 90° C. Subsequently, the filaments were washed with hot water at 80° C. Next, the water-washed primary drawn yarns were immersed in an oil bath (60° C.) containing a fiber treatment agent (containing a fatty acid ester oil and a polyoxyethylene surfactant with a total concentration of 6 mass %) for 3 to 5 seconds. Thus, the filaments were impregnated with the fiber treatment agent. Thereafter, the filaments were dried at 140° C. and further drawn to 2 times their original length. The resulting yarns were subjected to a 20% relaxation treatment at 160° C. Thus, a polyacrylonitrile-based fiber bundle (the adhesion amount of the fiber treatment agent: 0.45 parts by mass) having a single fiber fineness of about 46 dtex was obtained.

	TABLE 1
	Pore	Slit	Canal	Diameter of	Flat-
	area	width	width	circumcircle	ness
	(mm2)	Aw (mm)	Cw (mm)	Cd (mm)	ratio

Spinning nozzle a	0.10094	0.08	0.06	0.55	1.1
Spinning nozzle b	0.1023	0.09	0.077	0.49	1.0

	TABLE 2
	L1	L2	L3	L4	Pore area
	(mm)	(mm)	(mm)	(mm)	(mm2)

Spinning nozzle c	0.279	0.07	0.088	0.175	0.08538

The cross-sections of the polyacrylonitrile-based fiber bundles of the examples and the comparative examples were observed using a microscope as described above. The image analysis was performed as described above using the photographs of the cross-sections to measure and calculate the content of each cross-sectional shape, the diameter of a circumcircle, the diameter of an inscribed circle, and the flatness ratio of each cross-sectional shape, the angle between the ends in the C-shaped fiber cross-section, and the maximum thickness and the minimum thickness of the fiber cross-sections of each of the polyacrylonitrile-based fiber bundles. The average flatness ratio of all cross-sections of each of the polyacrylonitrile-based fiber bundles was calculated. FIG. 13 shows a photograph of the cross-sections of the polyacrylonitrile-based fiber bundle of Example 4. The bulkiness, the gloss, and the stretching loss rate of the polyacrylonitrile-based fiber bundles of the examples and the comparative examples were evaluated and calculated as described above. Tables 3 and 4 below show the results.

	TABLE 3
	Cross-sectional content (%)

							Total
							of C-
			Total				shape,
			of				figure-
			hollow				6-shape,
			drop-				and	Diameter of inscribed circle of
			shape			Hollow	hollow	each fiber cross-section (μm)

	Hollow		and			broad	broad	Hollow
	drop-	Drop-	drop-	C-	Figure-	bean-	bean-	drop-	C-
	shape	shape	shape	shape	6-shape	shape	shape	shape	shape
Ex. 1	52	0	52	30	18	0	48	7	44
Ex. 2	80	1	81	13	6	0	19	7	44
Ex. 3	5	0	5	5	88	2	95	8	43
Ex. 4	19	1	20	3	75	2	80	8	43
Ex. 5	8	1	9	6	80	5	91	8	40
Ex. 6	14	3	17	4	77	2	83	8	40
Ex. 7	18	3	21	3	74	2	79	8	40
Ex. 8	29	2	31	3	64	2	69	8	41
Ex. 9	21	0	21	69	10	0	79	7	44
Ex. 10	30	0	30	55	15	0	70	7	44
Com.	0	0	0	99	1	0	100	—	45
Ex. 1
Com.	0	0	0	8	42	50	100	—	43
Ex. 2
Com.	100	0	100	0	0	0	0	7	—
Ex. 3

Diameter of inscribed circle of

each fiber cross-section (μm)

Thickness of fiber

Hollow

cross-section (μm)

			broad	Maximum	Mininum		Volume	Stretching
		Figure-	bean-	thickness	thickness		increase	loss rate
		6-shape	shape	t1	t2	Gloss	rate (%)	(%)
	Ex. 1	29	—	20	13	3.75	28	5.1
	Ex. 2	30	—	20	13	4.75	15	6.7
	Ex. 3	27	24	22	14	2.25	33	3.7
	Ex. 4	27	24	22	14	3	30	4.4
	Ex. 5	26	22	26	15	2.5	33	2.0
	Ex. 6	27	23	25	14	3	31	3.1
	Ex. 7	28	23	25	14	3	29	4.2
	Ex. 8	27	24	25	14	3.5	28	5.1
	Ex. 9	29	—	20	13	3	29	4.0
	Ex. 10	29	—	20	13	3.25	28	4.4
	Com.	30	—	20	13	1	38	3.2
	Ex. 1
	Com.	28	22	22	14	1	37	2.4
	Ex. 2
	Com.	—	—	20	13	5	10	9.2
	Ex. 3

	TABLE 4
	Diameter of circumcircle of	Flatness ratio of each
	each fiber cross-section (μm)	fiber cross-section

Hollow

Hollow

Average

Angle between

Hollow

broad

Hollow

broad

flamess ratio

ends in C-shaped

drop-

Drop-

C-

Figure-

bean-

drop-

Drop-

C-

Figure-

bean-

of all cross-

fiber cross-

shape

shape

shape

6-shape

shape

shape

shape

shape

6-shape

shape

sections

section (°)

Ex. 1	120	—	96	93	—	2.2	—	1	1.1	1.2	1.6	0.9
Ex. 2	121	123	97	93	—	2.3	2.8	1.1	1.2	—	2	0.8
Ex. 3	121	—	90	87	100	2.1	—	1	1.2	1.2	1.2	0.9
Ex. 4	122	125	90	86	97	2.1	2.8	1	1.2	1.2	1.3	0.2
Ex. 5	121	124	89	86	95	2.1	2.8	1	1.2	1.2	1.2	0
Ex. 6	122	124	87	86	96	2.2	2.8	1	1.2	1.2	1.3	0
Ex. 7	121	124	87	85	98	2.1	2.8	1	1.1	1.1	1.3	0.4
Ex. 8	123	124	87	87	105	2.1	2.8	1	1.1	1.2	1.4	0.3
Ex. 9	120	—	96	94	—	2.2	—	1	1.2	1.2	1.3	0.8
Ex. 10	121	—	97	94	—	2.2	—	1	1.2	1.2	1.4	0.9
Com.	—	—	96	94	—	—	—	1.1	1.1	—	1.1	0.5
Ex. 1
Com.	—	—	98	93	100	—	—	1	1.1	1.2	1.1	0
Ex. 2
Com.	120	—	—	—	—	2.3	—	—	—	—	2.3	—
Ex. 3

As is clear from Tables 3 and 4, the polyacrylonitrile-based fiber bundles of the examples had favorable bulkiness and radiant gloss, and their stretching loss rates were low.

The polyacrylonitrile-based fiber bundle of Example 2 in which the total content of the hollow drop-shaped and drop-shaped fiber cross-sections was more than 60% had a gloss evaluation score of more than 4, whereas the polyacrylonitrile-based fiber bundles of Examples 1 and 3 to 10 in which the total content of the drop-shaped and hollow drop-shaped fiber cross-sections was 3 to 60% had a gloss evaluation score of 2 to 4 and had a better radiant gloss. The polyacrylonitrile-based fiber bundles of Examples 1 and 3 to 10 had better bulkiness than that of Example 2. The polyacrylonitrile-based fiber bundles of Examples 3 to 7, 9, and 10 in which the total content of the hollow drop-shaped and drop-shaped fiber cross-sections was 3 to 30% had lower stretching loss rates than those of Examples 1, 2, and 8 in which the total content of the hollow drop-shaped and drop-shaped fiber cross-sections was more than 30%.

On the other hand, the polyacrylonitrile-based fiber bundles of Comparative Examples 1 and 2 not including polyacrylonitrile-based synthetic fibers having hollow drop-shaped and drop-shaped fiber cross-sections did not have a radiant gloss. The polyacrylonitrile-based fiber bundle of Comparative Example 3 in which the hollow drop-shaped cross-sectional content was 100% had a high stretching loss rate.

One or more embodiments of the present invention are not particularly limited, but may include the following embodiments, for example.

• • [1] A polyacrylonitrile-based fiber bundle for artificial hair, including polyacrylonitrile-based synthetic fibers A and polyacrylonitrile-based synthetic fibers B,
  • wherein the polyacrylonitrile-based synthetic fibers A have fiber cross-sections with one or more shapes selected from the group consisting of a C-shape, a figure-6-shape, and a broad bean-shape with a hollow portion,
  • the polyacrylonitrile-based synthetic fibers B have fiber cross-sections with one or more shapes selected from the group consisting of a drop-shape with a hollow portion and a drop-shape,
  • the polyacrylonitrile-based synthetic fibers A have a flatness ratio of less than 1.5, and the polyacrylonitrile-based synthetic fibers B have a flatness ratio of 1.5 or more,
  • the C-shape, the figure-6-shape, or the broad bean-shape with the hollow portion of the fiber cross-sections has an inscribed circle with a diameter of 15 to 50 μm,
  • the drop-shape with the hollow portion of the fiber cross-sections has an inscribed circle with a diameter of more than 0 μm and less than 15 μm,
  • fiber cross-sections of the polyacrylonitrile-based fiber bundle for artificial hair have a thickness of 13 to 40 μm, and
  • the polyacrylonitrile-based fiber bundle for artificial hair has a total content of the C-shaped fiber cross-sections, figure-6-shaped fiber cross-sections, and the broad bean-shaped fiber cross-sections with the hollow portions of 3 to 97%, and a total content of the drop-shaped fiber cross-sections with the hollow portions and the drop-shaped fiber cross-sections of 3 to 97%.
  • [2] The polyacrylonitrile-based fiber bundle for artificial hair according to [1], including one or more selected from the group consisting of polyacrylonitrile-based synthetic fibers A1 having C-shaped fiber cross-sections and polyacrylonitrile-based synthetic fibers A2 having figure-6-shaped fiber cross-sections.
  • [3] The polyacrylonitrile-based fiber bundle for artificial hair according to [1] or [2], including polyacrylonitrile-based synthetic fibers B1 having drop-shaped fiber cross-sections with hollow portions.
  • [4] The polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [3], wherein the polyacrylonitrile-based fiber bundle for artificial hair has the total content of the drop-shaped fiber cross-sections with the hollow portions and the drop-shaped fiber cross-sections of 3 to 60%.
  • [5] The polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [4], wherein the C-shaped fiber cross-sections have a flatness ratio of 1.0 to 1.2, the figure-6-shaped fiber cross-sections have a flatness ratio of 1.1 or more and less than 1.5, and the broad bean-shape with the hollow portion has a flatness ratio of 1.2 to 1.4.
  • [6] The polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [5], wherein the drop-shaped fiber cross-sections with the hollow portions have a flatness ratio of 1.5 to 3.0, and the drop-shaped fiber cross-sections have a flatness ratio of 2.5 to 3.0.
  • [7] The polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [6], wherein a single fiber fineness is 35 to 65 dtex.
  • [8] The polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [7], wherein each of the polyacrylonitrile-based synthetic fibers A and the polyacrylonitrile-based synthetic fibers B contains an acrylonitrile-based polymer, and the acrylonitrile-based polymer contains a constituent unit derived from acrylonitrile in an amount of 30 to 80 mass %, a constituent unit derived from a halogen-containing monomer in an amount of 20 to 70 mass %, and a constituent unit derived from a sulfonic acid group-containing monomer in an amount of 0 to 5 mass %.
  • [9] A hair ornament product including the polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [8].
  • [10] The hair ornament product according to [9], wherein the hair ornament product is at least one selected from the group consisting of weaving hair, a wig, a braid, a toupee, a hair extension, and a hair accessory.
  • [11] A method for producing the polyacrylonitrile-based fiber bundle for artificial hair according to any one of [1] to [8], including:
  • performing spinning by extruding a spinning solution containing an acrylonitrile-based polymer through a spinning nozzle into a coagulation bath; and
  • water-washing coagulated filaments obtained through the spinning,
  • wherein the spinning nozzle has a C-shaped cross-section with two ends being apart from each other,
  • a discharge amount of the spinning solution per spindle of the spinning nozzle is 0.10 kg/min or more, and
  • the water-washing is performed at a temperature of 80° C. or lower.
  • [12] The method for producing the polyacrylonitrile-based fiber bundle for artificial hair according to [11], wherein the discharge amount of the spinning solution per spindle of the spinning nozzle is 0.10 to 15 kg/min.
  • [13] The method for producing the polyacrylonitrile-based fiber bundle for artificial hair according to or [12], wherein in the spinning nozzle, each of the two ends of the C-shape has a linear portion and a protrusion bulging outward and the linear portions of the two ends are parallel to each other, or one end of the C-shape is located on a side close to a hollow portion with respect to the other end.

DESCRIPTION OF REFERENCE NUMERALS

• • 1a, 1b Linear portion at end of spinning nozzle
  • 2a, 2b Protrusion at end of spinning nozzle
  • 3a, 3b End of spinning nozzle

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the invention should be limited only by the attached claims.