Method for producing polyacrylonitrile fiber for artificial hair

Abstract

To provide a method for producing a polyacrylonitrile fiber for artificial hair that suppresses collapse of a fiber cross section and exhibits excellent bulkiness even when a load is applied to the fiber during a manufacturing process.SOLUTION: A method for producing a polyacrylonitrile fiber for artificial hair according to one or more embodiments of the present invention includes a spinning step of extruding a spinning dope containing an acrylonitrile-based polymer and an organic solvent into a coagulation bath using a spinning nozzle to obtain a coagulated yarn, and a wet drawing step of drawing the coagulated yarn in a drawing bath, wherein the spinning nozzle has a C-shaped cross section, one end of the C-shape is positioned closer to a hollow part than the other end, a load is applied to the coagulated yarn when the coagulated yarn is guided from the coagulation bath to the drawing bath by a guide roll, and the temperature of the drawing bath is 5°C or higher and lower than 30°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyacrylonitrile fibers for artificial hair, which can be suitably used for head accessories such as wigs. [Background technology]

[0002] In addition to human hair, artificial hair such as acrylic fibers is used in head accessories such as wigs. In recent years, efforts have been made to impart softness and bulkiness to the fibers used in such artificial hair. For example, Patent Document 1 describes that bulkiness and texture can be improved by forming the cross section of acrylic fibers into one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape with a hollow portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 047882 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, fibers having a fiber cross section of one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape with a hollow portion are produced using a spinning nozzle having a C-shaped cross section in which one end of the C-shape is located closer to the hollow portion than the other end.However, when producing fibers using such a spinning nozzle, if a load is applied to the fiber during the production process, the fiber cross section may be crushed.

[0005] In order to solve the above problems, the present invention provides a method for producing polyacrylonitrile fibers for artificial hair, which can suppress crushing of the fiber cross section even when a load is applied to the fibers during the production process, and can produce polyacrylonitrile fibers for artificial hair that are excellent in bulkiness. [Means for solving the problem]

[0006] One or more embodiments of the present invention relate to a method for producing polyacrylonitrile-based fibers for artificial hair, the method comprising: a spinning step in which a spinning solution containing an acrylonitrile-based polymer and an organic solvent is extruded into a coagulation bath using a spinning nozzle to obtain a coagulated thread; and a wet drawing step in which the coagulated thread is drawn in a drawing bath, wherein the spinning nozzle has a C-shaped cross section, and one end of the C-shape is positioned closer to the hollow portion than the other end, a load is applied to the coagulated thread when the coagulated thread is guided from the coagulation bath to the drawing bath by guide rolls, and the temperature of the drawing bath is 5°C or higher and lower than 30°C. [Effects of the Invention]

[0007] According to the present invention, polyacrylonitrile fibers for artificial hair that are suppressed from collapsing in the fiber cross section and have excellent bulkiness can be obtained. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic cross-sectional view of an example of a spinning nozzle. [Figure 2] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A1 having a C-shaped fiber cross section. [Figure 3] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A1 having a C-shaped fiber cross section. [Figure 4] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A2 having a figure-6 shaped fiber cross section. [Figure 5] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A2 having a figure-6 shaped fiber cross section. [Figure 6] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A3 having a broad bean-shaped fiber cross section with a hollow portion. [Figure 7] FIG. 1 is a schematic cross-sectional view of polyacrylonitrile fiber A3 having a broad bean-shaped fiber cross section with a hollow portion. [Figure 8]FIG. 1 is a schematic side view illustrating a step of guiding a coagulated yarn from a coagulation bath to a drawing bath by a guide roll. [Figure 9] FIG. 2 is a schematic cross-sectional view of an example of a spinning nozzle. [Figure 10] 1 is a cross-sectional photograph (200x magnification) of the polyacrylonitrile fiber of Example 1. [Figure 11] 1 is a cross-sectional photograph (200x) of the polyacrylonitrile fiber of Comparative Example 1. [Figure 12] 1 is a cross-sectional photograph (200x) of the polyacrylonitrile fiber of Comparative Example 2. [Figure 13] 1 is a cross-sectional photograph (200x) of the polyacrylonitrile fiber of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] The inventors of the present invention have conducted extensive studies to solve the above problems. As a result, they have found that when a spinning solution containing an acrylonitrile polymer and an organic solvent is extruded into a coagulation bath using a spinning nozzle (hereinafter simply referred to as a C-shaped spinning nozzle) having a C-shaped cross section, with one end of the C-shape positioned closer to the hollow than the other end, and the resulting coagulated fiber is guided from the coagulation bath to a drawing bath by a guide roll, crushing of the fiber cross section can be suppressed, even when a load is applied to the coagulated fiber, and polyacrylonitrile fibers for artificial hair (hereinafter simply referred to as polyacrylonitrile fibers) having excellent bulkiness can be obtained by adjusting the temperature of the drawing bath to a predetermined range different from that of conventional methods. In this specification, the cross-sectional shape of the spinning nozzle means the shape of the transverse cross section of the spinning nozzle.

[0010] Specifically, in a C-shaped spinning nozzle, for example, when the number of nozzles is less than 1000, the coagulated fiber is hardly subjected to a load due to its own weight when being guided from the coagulation bath to the drawing bath by the guide rolls. On the other hand, in the case of a large spinning nozzle, for example, when the number of nozzle holes is 1000 or more, a load is applied to the coagulated fiber due to its own weight when being guided from the coagulation bath to the drawing bath by the guide rolls. When such a coagulated fiber is guided from the coagulation bath to the drawing bath by a guide roll, if a load is applied to the coagulated fiber, the cross section of the resulting polyacrylonitrile fiber will be crushed if the temperature of the drawing bath is kept at the conventional level. More specifically, fiber cross sections of one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape having a hollow portion (hereinafter also simply referred to as a "hollow broad bean shape") will be crushed into a teardrop shape or a hollow teardrop shape. However, in the present application, it has surprisingly been found that crushing of the fiber cross section can be suppressed by setting the temperature of the drawing bath lower than that of the conventional method.

[0011] In this specification, when a numerical range is indicated with "to", the numerical range includes both end values ​​(upper and lower limits). For example, a numerical range of "X to Y" includes both end values ​​X and Y, and is the same range as "X or more and Y or less". Any number within that range and any range included within that range are specifically disclosed. In addition, when multiple numerical ranges are described in this specification, they are intended to include numerical ranges that combine the upper and lower limits of different numerical ranges as appropriate.

[0012] In this specification, the singular expression includes the plural expression unless the context clearly indicates otherwise. Furthermore, in this specification, the plural expression includes the singular expression unless the context clearly indicates otherwise.

[0013] The method for producing the polyacrylonitrile fiber includes at least a spinning step (also referred to as a coagulation step) and a wet drawing step.

[0014] In the spinning step, a spinning solution containing an acrylonitrile polymer and an organic solvent is extruded into a coagulation bath using a spinning nozzle to obtain a coagulated thread.

[0015] The acrylonitrile-based polymer is not particularly limited as long as it contains 25% by mass or more of structural units derived from acrylonitrile, but for example, an acrylonitrile-based polymer containing 25 to 100% by mass of structural units derived from acrylonitrile and 0 to 75% by mass of structural units derived from other monomers can be used. The acrylonitrile-based polymer may contain 25 to 95% by mass of structural units derived from acrylonitrile and 5 to 75% by mass of structural units derived from other monomers, or 25 to 90% by mass of structural units derived from acrylonitrile and 10 to 75% by mass of structural units derived from other monomers, or may contain 30% to less than 85% by mass of structural units derived from acrylonitrile and more than 15% to 70% by mass of structural units derived from other monomers.

[0016] The other monomer is not particularly limited as long as it is copolymerizable 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, and sulfonic acid group-containing monomers. These may be used alone or in combination of two or more.

[0017] From the viewpoints of heat resistance, flame retardancy, and dyeability, the acrylonitrile-based polymer preferably contains 30 to 80 mass% of structural units derived from acrylonitrile, 20 to 70 mass% of structural units derived from a halogen-containing monomer, and 0 to 5 mass% of structural units derived from a sulfonic acid group-containing monomer. The acrylonitrile-based polymer may contain 35 to 75 mass% of structural units derived from acrylonitrile, 25 to 65 mass% of structural units derived from a halogen-containing monomer, and 0 to 5 mass% of structural units derived from a sulfonic acid group-containing monomer, or may contain 35 to 75 mass% of structural units derived from acrylonitrile, 24.5 to 64.5 mass% of structural units derived from a halogen-containing monomer, and 0.5 to 5 mass% of structural units derived from a sulfonic acid group-containing monomer.

[0018] 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. The halogen-containing monomers may be used alone or in combination of two or more. The halogen-containing monomer preferably includes one or more monomers selected from the group consisting of vinyl chloride and vinylidene chloride, and more preferably includes vinyl chloride from the viewpoint of tactile feel.

[0019] The sulfonic acid group-containing monomer is not particularly limited, and examples thereof include allylsulfonic acid, methallyl sulfonic acid, styrenesulfonic acid, isoprene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and metal salts thereof such as sodium salts and amine salts thereof. The sulfonic acid group-containing monomer may be used alone or in combination of two or more.

[0020] The organic solvent is not particularly limited, and any good solvent for acrylonitrile polymers can be used. Examples 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.

[0021] In the spinning solution, the concentration of the acrylonitrile polymer is not particularly limited, but from the viewpoint of easily controlling the collapse of the fiber cross section, it is preferably 20 to 50% by mass, more preferably 22 to 45% by mass, and even more preferably 25 to 40% by mass.

[0022] The spinning solution may contain a small amount of water, for example, 1.5 to 4.8 mass %, which can suppress the formation of voids.

[0023] The spinning solution preferably contains 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more of an epoxy group-containing compound per 100 parts by mass of the acrylonitrile-based polymer. The inclusion of an epoxy group-containing compound in the spinning solution is preferred because it can suppress odor, fiber discoloration due to heat, and fiber devitrification due to hot water. In particular, when dimethyl sulfoxide is used as the organic solvent, it can effectively suppress the generation of malodorous components due to decomposition of dimethyl sulfoxide when the artificial hair fiber is heated. Furthermore, from the viewpoints of spinnability, fiber quality, and cost, the spinning solution preferably contains 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less of an epoxy group-containing compound per 100 parts by mass of the acrylonitrile-based polymer. More specifically, the spinning solution may contain 0.1 to 5 parts by mass, 0.2 to 3 parts by mass, or 0.3 to 1 part by mass of an epoxy group-containing compound relative to 100 parts by mass of the acrylonitrile polymer.

[0024] Examples of the epoxy group-containing compound that can be used include glycidyl methacrylate-containing polymers, glycidyl acrylate-containing polymers, epoxidized vegetable oils, glycidyl ether-type epoxy resins, glycidyl amine-type epoxy resins, glycidyl ester-type epoxy resins, and cycloaliphatic epoxy resins. The epoxy group-containing compounds may be used alone or in combination of two or more.

[0025] From the viewpoints of epoxy equivalent (mass of resin containing 1 equivalent of epoxy groups), suppression of fiber discoloration, solubility in dimethyl sulfoxide, and reduction of elution into the spinning bath, the epoxy group-containing compound is preferably a glycidyl methacrylate-containing polymer and / or a glycidyl acrylate-containing polymer, and more preferably polyglycidyl methacrylate (glycidyl methacrylate homopolymer).

[0026] The weight average molecular weight (Mw) of the epoxy group-containing compound is not particularly limited and may be determined appropriately, taking into consideration, for example, solubility in dimethyl sulfoxide and 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 weight average molecular weight is preferably 3,000 or more from the viewpoint of reducing elution into a spinning bath, and the weight average molecular weight is preferably 100,000 or less from the viewpoint of solubility in organic solvents such as dimethyl sulfoxide. More specifically, the weight average molecular weight (Mw) of the epoxy group-containing compound may be 3,000 to 100,000.

[0027] The spinning solution may contain other additives for improving fiber properties as needed, as long as the effects of the present invention are not impaired. Examples of such additives include gloss adjusters such as titanium dioxide, silicon dioxide, and cellulose acetate and other esters and ethers of cellulose derivatives; colorants such as organic pigments, inorganic pigments, and dyes; and stabilizers for improving light resistance and heat resistance.

[0028] The spinning nozzle has a C-shaped cross section, with one end of the C-shape being closer to the hollow portion than the other end (hereinafter, simply referred to as a C-shaped spinning nozzle). By using such a C-shaped spinning nozzle, it is possible to obtain acrylonitrile fibers having a fiber cross section of one or more shapes selected from the group consisting of a C-shape, a hexagonal shape, and a broad bean shape with a hollow portion, and the fibers have high bulkiness.

[0029] Figure 1 shows a schematic cross-sectional view of an example of a C-shaped spinning nozzle. In this C-shaped spinning nozzle, one end 1a of the C-shape is located inside (closer to the hollow portion) than the other end 1b. In the cross-section of the C-shaped spinning nozzle, the circumscribed circle diameter Cd, which is the diameter of the assumed circumscribed circle, may be 0.37 to 0.60 mm. The canal width Cw, which is the distance between the two ends of the C-shape, may be 0.06 to 0.24 mm or more. The slit width Aw, which is the thickness of the C-shape cross-section, may be 0.06 to 0.15 mm. The hole area of ​​the hollow portion is 0.0850 to 0.1256 mm. 2 Furthermore, the minor axis Cs1, which is the shortest distance between two lines parallel to the major axis (the diameter of the circumscribing circle, more specifically, the line connecting the two points of contact between the circumscribing circle and the C-shaped cross section) when the C-shaped figure is sandwiched between the two lines, may be 0.30 to 0.60 mm, and the offset width Cs2, which is the shortest distance between the outermost end of outer end 1b and the outermost end of inner end 1a of the C-shape, may be 0.01 to 0.15 mm.

[0030] The number of holes in the spinning nozzle is not particularly limited and may be, for example, 10 to 8,000, 100 to 8,000, or 1,000 to 8,000. From the viewpoint of increasing productivity, it is preferably 5,000 to 8,000. In one or more embodiments of the present invention, a load is applied to the coagulated fiber when the coagulated fiber is guided from the coagulation bath to the drawing bath by a guide roll. However, for example, when the number of holes in the spinning nozzle is 1,000 or more, a load is applied to the coagulated fiber due to its own weight when the coagulated fiber is guided from the coagulation bath to the drawing bath by a guide roll. Normally, when the coagulated fiber is guided from the coagulation bath to the drawing bath by a guide roll, no load is applied to the coagulated fiber by the guide roll. However, when the number of holes in the spinning nozzle is less than 1,000, for example, and no load is applied to the coagulated fiber due to its own weight when the coagulated fiber is guided from the coagulation bath to the drawing bath by a guide roll, a load may be applied to the coagulated fiber via a guide roll 13 as shown in FIG. 8. The load applied to the coagulated yarn may be 1.3 g or more, 3.3 g or more, 6 g or more, or 10 g or more per fiber (more specifically, filament) of the coagulated yarn. For example, in the case of a spinning nozzle with 1,000 or more holes, it is estimated that a load of 10 g or more is applied per fiber of the coagulated yarn.

[0031] The coagulation bath can be an aqueous solution of the above-mentioned organic solvent, and the concentration of the organic solvent in the aqueous solution may be 20 to 70 mass%, 25 to 65 mass%, or 30 to 60 mass%. If the organic solvent concentration in the coagulation bath is too low, the coagulation will proceed too quickly, resulting in a coarse coagulation structure and tending to form voids inside the fiber. From the viewpoint of easily suppressing cross-sectional collapse of acrylonitrile-based fibers, the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath is preferably 33 mass% or more, and may be 33 to 50 mass%.

[0032] The temperature of the coagulation bath is not particularly limited, and may be, for example, 5 to 40°C, 10 to 35°C, 15 to 30°C, or 18 to 25°C.

[0033] The spinning speed is not particularly limited, but is preferably 2 to 17 m / min from the viewpoint of industrial productivity, for example. The nozzle draft is not particularly limited, but is preferably 0.8 to 2.0 from the viewpoint of production process stability, for example.

[0034] Next, in a wet drawing step, the coagulated yarn is drawn in a drawing bath to obtain a first drawn yarn. The temperature of the drawing bath is 5°C or higher and lower than 30°C. When the temperature of the drawing bath is 5°C or higher, drawing at a desired draw ratio is possible. When the temperature of the drawing bath is lower than 30°C, crushing of the fiber cross section of the coagulated yarn formed by extruding and coagulating the spinning solution from the C-shaped spinning nozzle, more specifically, of the fiber cross section having one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape with a hollow portion, can be suppressed.

[0035] The stretching bath can be an aqueous solution of the organic solvent described above or water. The concentration of the organic solvent in the aqueous solution of the organic solvent for the stretching bath is preferably lower than the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath. More specifically, the concentration of the organic solvent in the aqueous solution of the organic solvent for the stretching bath is preferably 25% by mass or less, from the viewpoint of easily suppressing cross-section collapse of the acrylonitrile-based fiber.

[0036] The wet stretching may be a single-stage stretching performed in one stage, or a multi-stage stretching performed in two or more stages. In the case of multi-stage stretching, the temperature of the stretching bath during any wet stretching is 5° C. or higher and lower than 30° C. The stretching ratio is not particularly limited, but may be, for example, 1.5 to 8 times or 1.8 to 6 times from the viewpoint of increasing the strength and productivity of the fiber.

[0037] When an aqueous solution of an organic solvent is used as the drawing bath, it is preferable to carry out a water-washing step after the wet drawing step. In the water-washing step, the primarily drawn yarn is washed with water to remove the organic solvent from the primarily drawn yarn, i.e., to remove the solvent. The water-washing step can be carried out with warm water at 30 to 80°C, 40 to 80°C, 50 to 80°C, or 60 to 78°C.

[0038] The method for producing the polyacrylonitrile fiber usually includes a drying step performed after a drawing step or a water-washing step. It may also include a step of applying an oil agent (fiber treatment agent) before the drying step. It may also include a dry drawing (secondary drawing) step and a heat-relaxing step performed after the drying step.

[0039] In the oil application step, a fiber treatment agent containing a fatty acid ester-based oil and a polyoxyethylene-based surfactant can be used in a state of being dissolved or dispersed in water (also referred to as an oil solution). Specifically, it is preferable to apply the fiber treatment agent by introducing an oil solution containing the fiber treatment agent at a predetermined concentration into an oil bath and immersing the first-drawn yarn (polyacrylonitrile-based fiber) in the oil solution. The temperature of the oil bath is not particularly limited, but may be, for example, 40°C or higher, and may be 40 to 80°C. The immersion time is not particularly limited, but may be, for example, 1 to 10 seconds, or 1 to 5 seconds.

[0040] The oil solution may contain other additives for improving fiber properties, as needed, within the range that does not impair the effects of the present invention. Examples of such other additives include fiber-sizing agents such as urethane polymers and cationic ester polymers.

[0041] Next, in the drying step, the polyacrylonitrile fiber after the fiber treatment agent is applied can be dried. The drying temperature is not particularly limited, but may be, for example, 110 to 190°C. The dried polyacrylonitrile fiber may then be further dry-stretched (secondary stretched) if necessary. The stretching temperature for the secondary stretching is not particularly limited, but may be, for example, 110 to 190°C or lower. The stretch ratio for the secondary stretching is not particularly limited, but is, for example, preferably 1 to 4 times, more preferably 1 to 3 times, and even more preferably 1 to 2 times. The total stretch ratio including the primary stretching before drying is preferably 2 to 10 times, more preferably 2 to 8 times, even more preferably 2 to 6 times, and particularly preferably 2 to 4 times.

[0042] The polyacrylonitrile fibers obtained by drying or further stretching after drying are preferably further relaxed in a heat-relaxing treatment step. The relaxation rate is not particularly limited, but is preferably, for example, 5% or more, and more preferably 10 to 30%. The heat-relaxing treatment can be carried out at a high temperature, for example, 140 to 200°C.

[0043] The polyacrylonitrile fiber obtained by the above-mentioned production method preferably has a fiber cross section of one or more shapes selected from the group consisting of C-shaped, 6-shaped, and hollow bean-shaped. Specifically, the polyacrylonitrile fiber may contain one or more fibers selected from the group consisting of polyacrylonitrile fiber A1 (hereinafter also simply referred to as "fiber A1") having a C-shaped fiber cross section, polyacrylonitrile fiber A2 (hereinafter also simply referred to as "fiber A2") having a 6-shaped fiber cross section, and polyacrylonitrile fiber A3 (hereinafter also simply referred to as "fiber A3") having a hollow bean-shaped fiber cross section. This improves the bulkiness of the polyacrylonitrile fiber. In this specification, fiber cross section means the cross section of the fiber.

[0044] From the viewpoint of a low cross-sectional collapse rate, the polyacrylonitrile fiber preferably contains 91% by mass or more, more preferably 92% by mass or more, even more preferably 93% by mass or more, even more preferably 94% by mass or more, and even more preferably 95% by mass or more of one or more fibers selected from the group consisting of fiber A1, fiber A2, and fiber A3. In the polyacrylonitrile fiber, the content of fiber cross sections of each cross-sectional shape can be measured and calculated as described in the Examples.

[0045] In the C-shaped fiber cross section of fiber A1, the two ends may be separated from each other or may be in contact with each other. Figures 2 and 3 are each a schematic cross-sectional view of an example fiber A1 having a C-shaped fiber cross section. In the C-shaped fiber cross section shown in Figure 2, the two ends of the C shape are separated from each other, forming a hollow portion with an opening. In the C-shaped fiber cross section shown in Figure 3, the two ends of the C shape are in contact with each other, forming a hollow portion without an opening. When the two ends of the C-shaped fiber cross section are in contact with each other as in Figure 3, the cross-sectional shape is similar to that of a hollow fiber with a circular fiber cross section and a circular hollow portion, but when observed under a microscope, the point where the two ends of the C shape are in contact can be confirmed.

[0046] In the 6-shaped fiber cross section of fiber A2, the two ends may be separated from each other or may be in contact with each other. FIGS. 4 and 5 are each a schematic cross-sectional view of an example of fiber A2 having a 6-shaped fiber cross section. In one or more embodiments of the present invention, the 6-shaped fiber cross section can also be considered a modified C-shape, specifically, a C-shape in which one end is located more inward (closer to the hollow portion) than the other end. In the 6-shaped fiber cross section shown in FIG. 4, the two ends are separated from each other, forming a hollow portion with an opening. In the 6-shaped fiber cross section shown in FIG. 5, the two ends are in contact with each other, forming a hollow portion without an opening.

[0047] In the hollow bean-shaped (kidney-shaped) fiber cross section of fiber A3, the two ends may be separated from each other or may be in contact with each other. FIGS. 6 and 7 are each a schematic cross-sectional view of fiber A3 having an example hollow bean-shaped (kidney-shaped) fiber cross section. In one or more embodiments of the present invention, the hollow bean shape can be considered a modified C-shape, specifically, a C-shape in which both ends are bent toward the hollow portion. In the hollow bean-shaped fiber cross section shown in FIG. 6, the two ends are separated from each other, forming a hollow portion with an opening. In the hollow bean-shaped fiber cross section shown in FIG. 7, the two ends are in contact with each other, forming a hollow portion without an opening.

[0048] The polyacrylonitrile fibers are not particularly limited, but may have, for example, an overall average flatness ratio of the fiber cross section (total cross section average flatness ratio) of 1.1 to 2.2, 1.1 to 2.0, or 1.1 to 1.8. In this specification, the "flatness ratio of the fiber cross section" is calculated by dividing the major axis by the minor axis of the fiber cross section, where the major axis refers to the circumscribed circle diameter, which is the diameter of the assumed circumscribed circle of the fiber cross section, and the minor axis refers to the shortest distance between two lines parallel to the major axis (more specifically, the lines connecting the two tangent points of the assumed circumscribed circle and the fiber cross section) when the fiber cross section is sandwiched between the two lines. For example, in Figures 2 to 7, the major axis is indicated by R1 and the minor axis is indicated by R2. When there are multiple assumed circumscribed circles for the fiber cross section, the largest diameter of all the circumscribed circles is taken as the circumscribed circle diameter of the fiber cross section.

[0049] From the viewpoint of suitable use as artificial hair, the single fiber fineness of the polyacrylonitrile fiber is preferably 20 to 95 dtex, more preferably 25 to 85 dtex, even more preferably 30 to 75 dtex, and particularly preferably 35 to 65 dtex. In this specification, the single fiber fineness of the polyacrylonitrile fiber can be measured as described in the examples.

[0050] The polyacrylonitrile fiber may be used alone as artificial hair, or may be used in combination with other artificial hair fibers. Furthermore, the polyacrylonitrile fiber may be used to form a head accessory. The head accessory may contain other artificial hair fibers in addition to the polyacrylonitrile fiber. Examples of other artificial hair fibers include, but are not limited to, polyvinyl chloride fibers, nylon fibers, polyester fibers, and regenerated collagen fibers.

[0051] The head accessories include weaving, wigs, braids, toupees, hair extensions, and hair accessories. [Example]

[0052] The following examples will illustrate one or more embodiments of the present invention, but the present invention is not limited to the following examples.

[0053] The measurement and evaluation methods used in the examples and comparative examples are as follows.

[0054] (single fiber fineness) Measurement was carried out using an auto-blow type fineness measuring instrument "DENICON DC-21" (manufactured by Search Co., Ltd.), and the average value of the measurements of 30 fibers was calculated to be the single fiber fineness.

[0055] (Amount of fiber treatment agent attached) Approximately 2 g of sample (fiber) (sample mass W0) was cut into 12-15 cm pieces and packed into a stainless steel tube (oil extraction tube) with a 1 mm hole at the bottom. Next, 35 mL of a 1:1 (by mass) mixture of ethanol and cyclohexane was prepared as the fiber treatment agent extraction solution, and approximately 20 mL of this mixture was placed into the oil extraction tube. The lid of the oil extraction tube was adjusted to allow the extraction solution to drip at a rate of approximately 1 drop per 1-1.5 seconds, and the fiber treatment agent extraction was initiated. A tray (empty tray mass W1) heated to 120 °C was used as a receiver for the dripping solution, and the dripping solution was set to fall onto it. Once the dripping was complete, the lid was removed, and the fiber inside the oil extraction tube was pressed with a stainless steel rod to squeeze out the extract. This procedure was repeated using the remaining extraction solution (approximately 15 mL). After the extraction was completed, the tray was placed in a 90°C oven and removed after 5 minutes. The total mass (W2) of the tray, in which the extract had dried and only the fiber treatment agent remained, was measured, and the amount of fiber treatment agent attached per 100 parts by mass of fiber was calculated using the following formula 1. [Formula 1] Amount of fiber treatment agent attached (parts by mass) = (W2 - W1) / (W0 + W1 - W2) x 100

[0056] (Method for observing fiber cross section) <Sample preparation> An appropriate amount of polyacrylonitrile fiber cut to a length of 15 cm was stuffed into a heat-shrinkable tube (manufactured by Junkosha, model number "FEP-040", inner diameter before shrinkage φ4.5 mm, inner diameter after shrinkage φ3.3 mm, length 1 m) and left in an oven at 105°C for 5 minutes. After that, it was removed and allowed to cool, and then the heat-shrinkable tube that had been stuffed with polyacrylonitrile fiber and shrunk was cut to a length of approximately 3 mm using a razor to prepare a sample for fiber cross-section observation. <Observation and photography> The sample for fiber cross-section observation was observed using a laser microscope (KEYENCE VK-X260), and images for cross-section size analysis (observation measurement range: 675 μm horizontal x 506 μm vertical) were taken at 200x magnification in two locations, and images for cross-section content interpretation (observation measurement range: 3375 μm horizontal x 1102 μm vertical) were taken in two locations.

[0057] (Method of analyzing cross-sectional photographs) The cross-sectional photographs (images) were imported into image analysis software (WinROOF, Mitani Corporation), and measurements were performed after defining the following parameters. <Aspect ratio> The major and minor axes of 30 randomly selected cross sections were measured, and the flattening ratio (major axis / minor axis) was calculated. The average value of these was used as the flattening ratio. For example, in Figures 2 to 7, the major axis (circumscribed circle diameter) is indicated by R1, and the minor axis is indicated by R2. <Content of fiber cross sections of each cross section shape> For the two cross-sectional photographs taken, the number of all fiber cross sections and the number of fiber cross sections with each of the C-shaped, 6-shaped, and hollow broad bean-shaped cross sections were counted, and the content of fiber cross sections with each cross-sectional shape and the cross-sectional collapse rate were calculated based on the following formula. C-shaped fiber cross section content (%) = [Number of C-shaped fiber cross sections ÷ Number of all fiber cross sections] × 100 Content of 6-shaped fiber cross sections (%) = [Number of 6-shaped fiber cross sections ÷ Number of all fiber cross sections] × 100 Content of hollow bean-shaped fiber cross sections (%) = [Number of hollow bean-shaped fiber cross sections ÷ Number of all fiber cross sections] × 100 Cross-sectional collapse rate (%) = 100 - (content of C-shaped fiber cross sections + content of 6-shaped fiber cross sections + content of hollow bean-shaped fiber cross sections)

[0058] (Method for evaluating bulkiness) <Sample preparation method> Approximately 270 g of polyacrylonitrile fiber bundle was processed under conditions of 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 so that the crimp angle was 141°±3° (average value of five fibers measured at one location on each fiber), to obtain crimped tow. <Volume determination method> Using crimped tow measuring 45.7 cm x 4 g (length x weight) per strand, a professional beauty evaluator created braids (BRDs) (two strands). The width and thickness of each BRD were measured at 10 points with a vernier caliper, and the width and thickness values ​​were calculated from the average values ​​of the two strands. Next, the width x thickness value was calculated as a volume judgment value, and the ratio to the volume judgment value of the comparison standard (Reference Example 1) was calculated to obtain the volume increase rate. A volume increase rate of 10% or more was considered pass (good), and a rate of less than 10% was considered fail.

[0059] (Experimental example) (Experiment No. 1) An acrylonitrile-based polymer consisting of 49% by mass of acrylonitrile, 50% by mass of vinyl chloride, and 1% by mass of sodium styrenesulfonate was dissolved in acetone to prepare an acrylonitrile-based polymer solution with a resin concentration of 27.0% by mass. Next, carbon black and liquid red and blue cationic dyes (manufactured by Hodogaya Chemical Co., Ltd.) were added as colorants 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 per 100 parts by mass of the acrylonitrile-based polymer, respectively. Furthermore, 1.0 part by mass of polyglycidyl methacrylate (weight average molecular weight 12,000) was added per 100 parts by mass of the acrylonitrile-based polymer to prepare a spinning solution. This spinning solution was extruded into a coagulation bath of 35% by mass acetone aqueous solution at 21°C using a spinning nozzle 1 (number of holes: 100) having the shape shown in Figure 1 and the size shown in Table 1, and wet-spun at a spinning speed of 10 m / min and a nozzle draft of 1.17. After that, as shown in Figure 8, coagulated yarn 2 was guided from coagulation bath 10 to drawing bath 20 by guide rolls 11 to 13, and drawn 1.9 times. No load was applied to the coagulated yarn when coagulated yarn 2 was guided from coagulation bath 10 to drawing bath 20 by guide rolls 11 to 13. The drawing bath temperature was 50°C, and the aqueous solution contained 20% by mass acetone. Next, after washing with water at 80°C, the first drawn yarn was immersed for 1 to 2 seconds in an oil bath (40°C) containing an oil solution containing a fiber treatment agent (total concentration of fatty acid ester-based oil and polyoxyethylene-based surfactant: 1.8% by mass) to impregnate the yarn with the oil. After drying at 130°C, the yarn was stretched 2.5 times and subjected to a 10% relaxation treatment at 150°C to obtain a polyacrylonitrile fiber with a single fiber fineness of approximately 51 dtex (amount of fiber treatment agent attached: 0.3 parts by mass).

[0060] (Experiment Nos. 2-8) As shown in Figure 8, when coagulated yarn 2 was guided from coagulation bath 10 to drawing bath 20 by guide rolls 11 to 13, a load shown in Table 2 below per fiber was applied to the coagulated yarn via guide roll 12. The same procedure as in Experiment 1 was carried out to obtain polyacrylonitrile fibers (amount of fiber treatment agent attached: 0.3 parts by mass) with a single fiber fineness of approximately 51 dtex.

[0061] The cross-sectional collapse rates of the polyacrylonitrile fibers obtained in Experiments 1 to 8 were evaluated as described above, and the results are shown in Table 2 below.

[0062] [Table 1]

[0063] [Table 2]

[0064] As can be seen from the data in Table 2 above, the cross-sectional crushing rate increases as the load applied per fiber of the coagulated yarn increases, but when the load applied per fiber of the coagulated yarn exceeds 10 g, the increase in the cross-sectional crushing rate almost levels off. By setting the load applied per fiber of the coagulated yarn to 10 g, it is possible to simulate the load caused by the weight of the coagulated yarn during mass production with a nozzle having 1,000 or more holes.

[0065] Example 1 An acrylonitrile-based polymer consisting of 49% by mass of acrylonitrile, 50% by mass of vinyl chloride, and 1% by mass of sodium styrenesulfonate was dissolved in acetone to prepare an acrylonitrile-based polymer solution with a resin concentration of 27.0% by mass. Next, carbon black and liquid red and blue cationic dyes (manufactured by Hodogaya Chemical Co., Ltd.) were added as colorants 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 per 100 parts by mass of the acrylonitrile-based polymer, respectively. Furthermore, 1.0 part by mass of polyglycidyl methacrylate (weight average molecular weight 12,000) was added per 100 parts by mass of the acrylonitrile-based polymer to prepare a spinning solution. This spinning solution was extruded into a coagulation bath of 35% by mass acetone aqueous solution at 21°C using a spinning nozzle 1 (number of holes: 100) having the shape shown in Figure 1 and the size shown in Table 1, and wet-spun at a spinning speed of 10 m / min and a nozzle draft of 1.17. After that, as shown in Figure 8, coagulated yarn 2 was guided from coagulation bath 10 to drawing bath 20 using guide rolls 11 to 13, and stretched 1.9 times. When coagulated yarn 2 was guided from coagulation bath 10 to drawing bath 20 using guide rolls 11 to 13, a load of 10 g was applied to each fiber of the coagulated yarn via guide roll 12. The temperature of the drawing bath was 25°C, and the aqueous solution contained 20% by mass acetone. Next, after washing with water at 80°C, the first drawn yarn was immersed for 1 to 2 seconds in an oil bath (40°C) containing an oil solution containing a fiber treatment agent (total concentration of fatty acid ester-based oil and polyoxyethylene-based surfactant: 1.8% by mass) to impregnate the yarn with the fiber treatment agent.The yarn was then dried at 130°C, stretched 2.5 times, and subjected to a 10% relaxation treatment at 150°C to obtain a polyacrylonitrile fiber with a single fiber fineness of approximately 51 dtex (amount of fiber treatment agent attached: 0.3 parts by mass).

[0066] (Comparative Example 1) Polyacrylonitrile fibers (amount of fiber treatment agent attached: 0.3 parts by mass) having a single fiber fineness of about 51 dtex were obtained in the same manner as in Example 1, except that the temperature of the drawing bath was set to 70°C.

[0067] (Comparative Example 2) Polyacrylonitrile fibers (amount of fiber treatment agent attached: 0.3 parts by mass) having a single fiber fineness of about 51 dtex were obtained in the same manner as in Example 1, except that the temperature of the drawing bath was set to 60°C.

[0068] (Comparative Example 3) Polyacrylonitrile fibers (amount of fiber treatment agent attached: 0.3 parts by mass) having a single fiber fineness of about 51 dtex were obtained in the same manner as in Example 1, except that the temperature of the drawing bath was set to 50°C.

[0069] (Reference example 1) An acrylonitrile-based polymer consisting of 46% by mass of acrylonitrile, 52% by mass of vinyl chloride, and 2% by mass of sodium styrenesulfonate was dissolved in dimethyl sulfoxide to prepare an acrylonitrile-based polymer solution with a resin concentration of 28.0% by mass and a water concentration of 3.5% by mass. Next, carbon black, a red dye (CI Basic Red 46), and a blue dye (CI Basic Blue 41) were added as colorants to the acrylonitrile-based polymer solution in amounts of 2.1 parts by mass, 0.04 parts by mass, and 0.07 parts by mass per 100 parts by mass of the acrylonitrile-based polymer, respectively. Furthermore, 1.0 part by mass of polyglycidyl methacrylate (weight average molecular weight 12,000) was added per 100 parts by mass of the acrylonitrile-based polymer to prepare a spinning solution. This spinning solution was extruded into a coagulation bath of 52% by mass DMSO aqueous solution at 20°C using a spinning nozzle having the shape shown in Figure 9 and the dimensions shown in Table 3. The spinning solution was wet-spun at a spinning speed of 2 m / min and a nozzle draft of 1.15, and then stretched 2.4 times in a stretching bath of 30% by mass DMSO aqueous solution at 90°C. The stretched yarn was then washed with warm water at 80°C. The washed, primarily stretched yarn was then immersed for 3 to 5 seconds in an oil bath (60°C) containing a fiber treatment agent (a total concentration of fatty acid ester-based oil and polyoxyethylene-based surfactant: 6% by mass) to impregnate the yarn with the fiber treatment agent. The yarn was then dried at 140°C, stretched 2 times, and subjected to a 20% relaxation treatment at 160°C to obtain a polyacrylonitrile fiber with a single fiber fineness of approximately 46 dtex (fiber treatment agent deposition amount: 0.45 parts by mass).

[0070] [Table 3]

[0071] The aspect ratio, cross-sectional collapse rate, and bulkiness of the polyacrylonitrile fibers of the Examples and Comparative Examples were evaluated as described above. The results are shown in Table 4. Figures 10 to 13 show cross-sectional photographs of the polyacrylonitrile fibers of Example 1 and Comparative Examples 1 to 3, respectively.

[0072] [Table 4]

[0073] As can be seen from Table 4 and FIG. 10, the polyacrylonitrile-based fibers of the Examples had a low cross-sectional crush rate, specifically a low content of hollow teardrop-shaped and teardrop-shaped fiber cross sections formed by crushing C-shaped, 6-shaped, and hollow broad bean-shaped cross sections, and had good bulkiness.

[0074] On the other hand, as can be seen from Table 4 and FIGS. 11 to 13, the polyacrylonitrile fibers of Comparative Examples 1 to 3 had cross-sectional crush rates exceeding 9%.

[0075] The present invention is not particularly limited, but may include, for example, the following embodiments.

[0076] [1] A method for producing polyacrylonitrile fibers for artificial hair, comprising: A spinning step in which a spinning solution containing an acrylonitrile polymer and an organic solvent is extruded into a coagulation bath using a spinning nozzle to obtain a coagulated thread; and a wet drawing step of drawing the coagulated yarn in a drawing bath, The spinning nozzle has a C-shaped cross section, and one end of the C-shape is located closer to the hollow portion than the other end, a load is applied to the coagulated yarn when the coagulated yarn is guided from the coagulation bath to the drawing bath by a guide roll, A method for producing polyacrylonitrile fibers for artificial hair, wherein the temperature of the drawing bath is 5°C or higher and lower than 30°C. [2] The method for producing polyacrylonitrile fibers for artificial hair according to [1], wherein a load of 10 g or more per fiber is applied to the coagulated yarn when the coagulated yarn is guided from the coagulation bath to the drawing bath by a guide roll. [3] The method for producing polyacrylonitrile fibers for artificial hair according to [1] or [2], wherein an aqueous solution of the organic solvent is used as the coagulation bath, and the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath is 33% by mass or more. [4] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [3], wherein the stretching bath is an aqueous solution of the organic solvent or water, and the concentration of the organic solvent in the aqueous solution of the organic solvent for the stretching bath is lower than the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath. [5] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [4], wherein the concentration of the organic solvent in the aqueous solution of the organic solvent for the drawing bath is 25 mass % or less. [6] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [5], wherein the concentration of the acrylonitrile polymer in the spinning solution is 20 to 50% by mass. [7] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [6], wherein the organic solvent contains at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylacetamide, N,N-dimethylformamide, and acetone. [8] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [7], wherein the polyacrylonitrile fibers for artificial hair have a fiber cross section of one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape with a hollow portion. [9] The method for producing polyacrylonitrile fibers for artificial hair according to any one of [1] to [8], wherein the polyacrylonitrile fibers for artificial hair have a single fiber fineness of 35 to 65 dtex. [Explanation of symbols]

[0077] 1. Spinning nozzle 1a, 1b End of spinning nozzle 2 Coagulated thread 10 Coagulation bath 11, 12, 13 Guide rolls 20 Stretching bath

Claims

1. A method for producing polyacrylonitrile fibers for artificial hair, comprising: A spinning step in which a spinning solution containing an acrylonitrile polymer and an organic solvent is extruded into a coagulation bath using a spinning nozzle to obtain a coagulated thread; and a wet drawing step of drawing the coagulated yarn in a drawing bath, The spinning nozzle has a C-shaped cross section, and one end of the C-shape is located closer to the hollow portion than the other end, a load is applied to the coagulated yarn when the coagulated yarn is guided from the coagulation bath to the drawing bath by a guide roll, A method for producing polyacrylonitrile fibers for artificial hair, wherein the temperature of the drawing bath is 5°C or higher and lower than 30°C.

2. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein a load of 10 g or more per fiber is applied to the coagulated yarn when the coagulated yarn is guided from the coagulation bath to the drawing bath by a guide roll.

3. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein an aqueous solution of the organic solvent is used as the coagulation bath, and the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath is 33% by mass or more.

4. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the stretching bath is an aqueous solution of the organic solvent or water, and the concentration of the organic solvent in the aqueous solution of the organic solvent for the stretching bath is lower than the concentration of the organic solvent in the aqueous solution of the organic solvent for the coagulation bath.

5. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the concentration of the organic solvent in the aqueous solution of the organic solvent for the drawing bath is 25% by mass or less.

6. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the concentration of the acrylonitrile polymer in the spinning solution is 20 to 50% by mass.

7. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylacetamide, N,N-dimethylformamide, and acetone.

8. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the polyacrylonitrile fibers for artificial hair have a fiber cross section of one or more shapes selected from the group consisting of a C-shape, a 6-shape, and a broad bean shape having a hollow portion.

9. 2. The method for producing polyacrylonitrile fibers for artificial hair according to claim 1, wherein the single fiber fineness of the polyacrylonitrile fibers for artificial hair is 35 to 65 dtex.

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