Acrylonitrile copolymer, polyacrylonitrile fiber, method for producing the same, and fiber aggregate containing the same

Abstract

The present invention provides an acrylonitrile copolymer that exhibits high stretchability when fibrousized by wet spinning, as well as polyacrylonitrile fibers containing the same, a method for producing the same, and a fiber aggregate containing the same. [Solution] One or more embodiments of the present invention relate to an acrylonitrile copolymer containing 30% by mass or more of structural unit A derived from acrylonitrile, 40% by mass or more of structural unit B derived from vinyl halogenated monomer, and 0.5 to 8% by mass of structural unit C derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents.

Description

Technical Field

[0001] The present invention relates to an acrylonitrile copolymer with improved stretchability, a polyacrylonitrile fiber, a method for producing the same, and a fiber assembly containing the same.

Background Art

[0002] Polyacrylonitrile fibers using an acrylonitrile copolymer obtained by copolymerizing acrylonitrile and other vinyl halide monomers such as vinyl chloride are widely used in various applications such as pile materials, flame-retardant materials, and artificial hair because of their excellent touch and flame retardancy. Such an acrylonitrile copolymer obtained by copolymerizing acrylonitrile and a vinyl halide monomer has a lower decomposition start temperature than the softening temperature and is likely to decompose when melt-processed. Therefore, it is usually fiberized by a method of spinning a spinning solution containing an acrylonitrile copolymer and a solvent. For example, Patent Document 1 describes dissolving a polymer composed of 35 to 80% by weight of acrylonitrile and 15 to 65% by weight of vinyl chloride and further containing 0 to 0.5% by weight of a sulfonic acid-containing monomer in a solvent such as dimethylacetamide, dimethylformamide, or dimethyl sulfoxide, and performing wet spinning.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as described in Cited Document 1, the acrylonitrile copolymer has a problem of poor stretchability when fiberized by wet spinning.

[0005] To solve the aforementioned problems, the present invention provides an acrylonitrile copolymer having high stretchability when fibrousized by wet spinning, a polyacrylonitrile fiber containing the same, a method for producing the same, and a fiber aggregate containing the same. [Means for solving the problem]

[0006] One or more embodiments of the present invention relate to an acrylonitrile copolymer containing 30% by mass or more of structural unit A derived from acrylonitrile, 40% by mass or more of structural unit B derived from a vinyl halogenated monomer, and 0.5 to 8% by mass of structural unit C derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents.

[0007] One or more embodiments of the present invention relate to polyacrylonitrile fibers containing the acrylonitrile copolymer.

[0008] One or more embodiments of the present invention relate to a method for producing polyacrylonitrile fibers containing the acrylonitrile copolymer.

[0009] One or more embodiments of the present invention relate to a fiber assembly containing the polyacrylonitrile fiber. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an acrylonitrile copolymer having high stretchability when formed into fibers by wet spinning, a polyacrylonitrile fiber containing the same, a method for producing the same, and a fiber aggregate containing the same. [Modes for carrying out the invention]

[0011] The inventors of the present invention have conducted extensive research to improve the stretchability of an acrylonitrile copolymer obtained by wet spinning when the copolymer is formed into fibers from the acrylonitrile copolymer, which is obtained by copolymerizing acrylonitrile with other vinyl halogenated monomers such as vinyl chloride. As a result, they found that by copolymerizing the acrylonitrile copolymer with a predetermined amount of an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents, the stretchability when forming fibers by wet spinning is improved. In this specification, "(meth)acrylic acid" means one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0012] In this specification, when a numerical range is indicated by "~", the numerical range includes both endpoints (upper and lower limits). For example, the numerical range "X~Y" includes both endpoints, X and Y. Furthermore, when multiple numerical ranges are described in this specification, the range shall include numerical ranges formed by appropriately combining the upper and lower limits of different numerical ranges. Furthermore, when multiple upper and lower limits of a numerical range are described separately in this specification, the range shall include numerical ranges formed by appropriately combining the upper and lower limits.

[0013] The acrylonitrile copolymer contains 30% by mass or more of constituent unit A derived from acrylonitrile, preferably 30 to 59% by mass, and more preferably 35 to 55% by mass. When the content of constituent unit A in the acrylonitrile copolymer is within the above range, the heat resistance is improved.

[0014] The acrylonitrile copolymer further contains 40% by mass or more of constituent unit B derived from vinyl halogenated monomers, preferably 40-69% by mass, more preferably 45-63% by mass, and even more preferably 45-55% by mass. This results in good flame retardancy.

[0015] The vinyl halogen monomer is not particularly limited and includes, for example, vinyl chloride, vinyl bromide, and vinyl iodide, but vinyl chloride is preferred.

[0016] The acrylonitrile copolymer contains 0.5 to 8% by mass of constituent unit C derived from an alkyl (meth)acrylate ester having an alkyl group having 2 or more carbon atoms, which may have substituents. A content of 0.5% by mass or more of constituent unit C results in good drawability when the acrylonitrile copolymer is spun into fibers by wet spinning. Furthermore, the hot water curl-set properties (hereinafter also referred to as HWS properties) of the polyacrylonitrile fibers containing the acrylonitrile copolymer are improved. Additionally, a content of 8% by mass or less of constituent unit C makes it easier to suppress the fusion of fibers in the polyacrylonitrile fibers containing the acrylonitrile copolymer. In the following, unless otherwise specified, "(meth)acrylate alkyl ester" means an alkyl (meth)acrylate ester having an alkyl group having 2 or more carbon atoms, which may have substituents.

[0017] From the viewpoint of further improving the stretchability and HWS properties of the polyacrylonitrile fiber containing the acrylonitrile copolymer, the acrylonitrile copolymer preferably contains 1% by mass or more of constituent unit C, more preferably 1.5% by mass or more, more preferably 2% by mass or more, and even more preferably 2.5% by mass or more. Furthermore, from the viewpoint of more effectively suppressing the fusion of fibers in the polyacrylonitrile fiber containing the acrylonitrile copolymer, the acrylonitrile copolymer preferably contains 7.5% by mass or less of constituent unit C, and even more preferably 7% by mass or less.

[0018] The number of carbon atoms in the alkyl group is not particularly limited as long as it is 2 or more, but from the viewpoint of further improving the stretchability of the acrylonitrile copolymer, the number of carbon atoms in the alkyl group is preferably 2 to 30, more preferably 2 to 18, even more preferably 3 to 10, even more preferably 3 to 8, and even more preferably 3 to 6. Examples of alkyl groups with 2 or more carbon atoms include, but are not limited to, ethyl, propyl, butyl, pentyl, and hexyl groups.

[0019] Examples of the substituents include, but are not limited to, amino groups, amide groups, carboxyl groups, hydroxyl groups, and alkoxy groups. From the viewpoint of polymerization stability with acrylonitrile, the substituent is preferably one or more selected from the group consisting of hydroxyl groups, amino groups, and alkoxy groups, and more preferably a hydroxyl group. Examples of the hydroxyalkyl group having 2 or more carbon atoms include, but are not limited to, 2-hydroxyethyl group, 3-hydroxypropyl group, 2-hydroxypropyl group, 4-hydroxybutyl group, 2-hydroxybutyl group, 5-hydroxypentyl group, 2-hydroxypentyl group, 6-hydroxyhexyl group, and 2-hydroxyhexyl group. Examples of the alkoxyalkyl group having 2 or more carbon atoms include, but are not limited to, methoxyethyl group, methoxypropyl group, methoxybutyl group, ethoxyethyl group, and ethoxybutyl group.

[0020] Examples of the alkyl (meth)acrylate esters include, but are not limited to, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-hexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. From the viewpoint of more effectively improving the stretchability of the acrylonitrile copolymer, the alkyl (meth)acrylate ester is preferably at least one selected from the group consisting of ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-hexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; more preferably at least one selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; and even more preferably at least one selected from the group consisting of butyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate.

[0021] In addition to the structural unit A, structural unit B, and structural unit C, the acrylonitrile copolymer may contain a structural unit derived from another monomer component. Examples of the other monomer component include vinyl monomers containing a sulfonic acid group. The vinyl monomer containing a sulfonic acid group is not particularly limited. For example, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and metal salts and amine salts such as sodium salts thereof can be used. The vinyl monomer containing a sulfonic acid group may be used alone or in combination of two or more.

[0022] In the acrylonitrile copolymer, the content of the structural unit D derived from the vinyl monomer containing a sulfonic acid group is not particularly limited. For example, from the viewpoints of hydrophilicity and spinnability, it is preferably 0.5 to 5% by mass, and may be 0.5 to 4% by mass or 0.5 to 3% by mass.

[0023] More specifically, the acrylonitrile copolymer may contain, for example, 30 to 59% by mass of the structural unit A derived from acrylonitrile, 40 to 69% by mass of the structural unit B derived from a vinyl halide monomer, 0.5 to 8% by mass of the structural unit C derived from an alkyl (meth)acrylate, and 0.5 to 5% by mass of the structural unit D derived from a vinyl monomer containing a sulfonic acid group. It may also contain 35 to 55% by mass of the structural unit A derived from acrylonitrile, 4\alpha to 60% by mass of the structural unit B derived from a vinyl halide monomer, 1 to 8% by mass of the structural unit C derived from an alkyl (meth)acrylate, and 0.5 to 5% by mass of the structural unit D derived from a vinyl monomer containing a sulfonic acid group.

[0024] The acrylonitrile copolymer can be obtained by known polymerization methods such as bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. Among these, from an industrial perspective, suspension polymerization, emulsion polymerization, or solution polymerization is preferred, and emulsion polymerization is more preferred. In the case of emulsion polymerization, acrylonitrile, a vinyl halide monomer, an alkyl (meth)acrylate, and other monomers such as a vinyl monomer containing a sulfonic acid group as needed are polymerized in the presence of a water-soluble polymerization initiator and an emulsifier to obtain an acrylonitrile copolymer.

[0025] In emulsion polymerization, when the total mass of the monomers is 100 parts by mass, acrylonitrile may be 30 to 59 parts by mass, the vinyl halide monomer may be 40 to 69 parts by mass, the alkyl (meth)acrylate may be 0.5 to 8 parts by mass, and the vinyl monomer containing a sulfonic acid group may be 0.5 to 5 parts by mass. Acrylonitrile may also be 35 to 55 parts by mass, the vinyl halide monomer may be 40 to 60 parts by mass, the alkyl (meth)acrylate may be 1 to 8 parts by mass, and the vinyl monomer containing a sulfonic acid group may be 0.5 to 5 parts by mass.

[0026] As the water-soluble polymerization initiator, a water-soluble polymerization initiator generally used for polymerization can be appropriately used and is not particularly limited. For example, water-soluble inorganic peroxides and water-soluble azo compounds can be mentioned. From the perspective of easy availability, water-soluble inorganic peroxides are preferred. Examples of the water-soluble inorganic peroxides include persulfates and hydrogen peroxide. From the perspective of ease of polymerization, it is preferably a persulfate. Examples of the persulfate include ammonium persulfate (also referred to as ammonium peroxydisulfate), sodium persulfate, and potassium persulfate. The amount of the water-soluble polymerization initiator is not particularly limited. For example, from the perspective of controlling the reaction heat, it may be 0.1 to 1 part by mass, or 0.15 to 0.75 part by mass, based on 100 parts by mass of the total mass of the monomers.

[0027] The water-soluble polymerization initiator, such as the persulfate (oxidizing agent), may be used in combination with a reducing agent from the viewpoint of improving polymerization efficiency. Examples of the reducing agent include sodium bisulfite, ammonium bisulfite, and sodium thiosulfate. The mass ratio of the oxidizing agent, such as the persulfate, to the reducing agent is not particularly limited; for example, 1 to 4 parts by mass of the reducing agent may be used for every 1 part by mass of the oxidizing agent, such as the persulfate. Furthermore, the oxidizing agent, such as the persulfate, and the reducing agent may be used in combination with polymerization accelerators such as sulfuric acid, iron sulfate, and copper sulfate from the viewpoint of improving polymerization efficiency. 0.5 to 2 parts by mass of the polymerization accelerator may be used for every 1 part by mass of the oxidizing agent, such as the persulfate.

[0028] The emulsifier may be any surfactant containing hydrophilic and lipophilic groups, and is not particularly limited, but for example, anionic surfactants can be used. Examples of anionic surfactants include fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, alkyl sulfosuccinates, alkenyl succinates, rosinates, polyoxyethylene lauryl sulfates, α-olefin sulfonates, and alkyl ether phosphate ester salts. Examples of salts include potassium salts, sodium salts, and ammonium salts. The number of carbon atoms in the alkyl or alkenyl group is not particularly limited, and may be, for example, 8 to 22 or 10 to 18. The amount of the emulsifier is not particularly limited, but for example, from the viewpoint of polymerization stability and cleanability in post-treatment, it may be 0.1 to 3 parts by mass or 0.3 to 2 parts by mass per 100 parts by mass of the total mass of monomers.

[0029] The monomers, water-soluble polymerization initiators (oxidizing agents, etc.), emulsifiers, and water mentioned above, along with reducing agents and polymerization accelerators as needed, can be supplied to a polymerization reactor, and emulsion polymerization can be carried out by raising the temperature of the polymerization reactor. The monomers, water-soluble polymerization initiators (oxidizing agents, etc.), reducing agents, polymerization accelerators, and emulsifiers can be supplied to the polymerization reactor in any way, such as a single supply, a continuous uniform supply, or a continuous non-uniform supply. The polymerization temperature is not particularly limited, but for example, from the viewpoint of heat removal during the polymerization reaction and resin quality, it may be 40 to 70°C or 45 to 65°C. The emulsion of the acrylonitrile copolymer obtained by polymerization (also called latex) can be subjected to salting out, dehydration, washing with water, and drying in the same way as in general emulsion polymerization to obtain the acrylonitrile copolymer.

[0030] The polyacrylonitrile fibers of one or more embodiments of the present invention include the acrylonitrile copolymer described above. When the total mass of the resin components constituting the polyacrylonitrile fibers is 100% by mass, the content of the acrylonitrile copolymer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may consist of 100% by mass of the acrylonitrile copolymer.

[0031] The single fiber fineness of the polyacrylonitrile fiber may be appropriately selected depending on the application, and is not particularly limited; for example, it may be 1 to 100 dtex. When used in artificial hair, it is more preferably 20 to 90 dtex, even more preferably 25 to 75 dtex, and particularly preferably 30 to 60 dtex. When used as a pile material or flame retardant material, it may be 1 to 50 dtex, 1.5 to 30 dtex, or 1.7 to 15 dtex.

[0032] The polyacrylonitrile fiber may contain a plasticizer, but from a cost viewpoint, the plasticizer content is preferably 3% by mass or less. Since the polyacrylonitrile fiber is composed of the acrylonitrile copolymer described above, the HWS properties are improved even if the plasticizer content is low or if no plasticizer is present. The plasticizer content of the polyacrylonitrile fiber may be 2.5% by mass or less, 2.0% by mass or less, 1.5% by mass or less, or 1.0% by mass or less. In this specification, the plasticizer content in the polyacrylonitrile fiber can be measured as described below.

[0033] (Plasticizer content) Approximately 2 g (mass W10) of polyacrylonitrile fiber is cut into 12-15 cm pieces and placed in a glass sample bottle filled with pure water, ensuring the pure water does not overflow. The pieces are then left to stand in 95°C hot water for 2 hours to extract the plasticizer from the polyacrylonitrile fiber. Subsequently, the plasticizer extract is analyzed by gas chromatography to obtain the mass (W11) of plasticizer in the polyacrylonitrile fiber. The plasticizer content in the polyacrylonitrile fiber is calculated using the following formula 1. [Formula 1] Plasticizer content (mass%) = 100 × (W11 / W10)

[0034] The plasticizer is not particularly limited, and any plasticizer that can be used in acrylonitrile copolymers can be used as appropriate. Examples of plasticizers include sulfone compounds such as dimethyl sulfone, diethyl sulfone, dipropyl sulfone, and dibutyl sulfone; sulfoxide compounds such as dipropyl sulfoxide, diisopropyl sulfoxide, methylphenyl sulfoxide, dibutyl sulfoxide, and benzyl sulfoxide; lactides such as lactide lactate; lactams such as pyrrolidone, N-vinylpyrrolidone, and ε-caprolactam; and lactones such as γ-butyrolactone and ε-caprolactone. Furthermore, the plasticizer may be used alone or in combination of two or more types.

[0035] From the viewpoint of improving the tactile feel of the polyacrylonitrile fiber after curl setting with hot water, the plasticizer preferably has a melting point of 60°C or higher, and more preferably 90°C or higher. The plasticizer preferably consists of one or more selected from the group consisting of dimethyl sulfone, lactide lactate, and ε-caprolactam, and more preferably one or more selected from the group consisting of dimethyl sulfone and lactide lactate.

[0036] The polyacrylonitrile fiber may contain an oily agent from the viewpoint of suppressing static electricity generation, etc. The oily agent may be a nonionic surfactant such as a sorbitan fatty acid ester or polyoxyethylene triglyceride. Examples of the sorbitan fatty acid ester include sorbitan fatty acid esters of saturated fatty acids having 10 to 24 carbon atoms, and more specifically, sorbitan monostearate, sorbitan monolaurate, and sorbitan monopalmitate. Examples of the polyoxyethylene triglyceride include polyoxyethylene castor oil. In the polyacrylonitrile fiber, the content of the oily agent may be 0.1 to 0.9% by mass. In this specification, the content of the oily agent in the polyacrylonitrile fiber (also referred to as the amount of oily agent attached) can be measured as described below.

[0037] (Oil content) Cut approximately 2g (mass W0) of polyacrylonitrile fiber into 12-15cm lengths and pack them into a stainless steel tube (oil extraction tube) with a hole of approximately 1mm at the bottom. Next, prepare 35mL of a mixture of ethanol and cyclohexane (weight ratio) as the oil extract, and add approximately 20mL to the oil extraction tube. Adjust the lid of the oil extraction tube so that the extraction rate is approximately 1 drop / 1-1.5 seconds, and begin oil extraction. At this time, use a tray (empty tray weight W1) heated to 120°C by a heater as a receiving tray for the dripping liquid, and set it so that the dripping liquid falls into it. Once the dripping is complete, remove the lid and use a stainless steel rod to push the fibers inside the oil extraction tube to squeeze out the extract. Repeat this operation using the remaining extract (approximately 15mL). After extraction is complete, place the tray in a 90°C oven, remove it after 5 minutes, measure the total tray weight (W2) of the tray after the extract has dried and only the oil remains, and calculate the oil content (mass %) using the following formula 2. [Formula 2] Oil content (by weight %) = 100 × [(W2 - W1) / W0]

[0038] The polyacrylonitrile fiber may, if necessary, contain additives to improve its fiber properties, as long as they do not hinder the effects of the present invention. Examples of such additives include gloss modifiers such as titanium dioxide, silicon dioxide, and esters and ethers of cellulose derivatives such as cellulose acetate; colorants such as organic pigments, inorganic pigments, and dyes; stabilizers to improve light resistance and heat resistance; fiber consolidators such as urethane polymers and cationic ester polymers to improve processability during braiding and twisting; inorganic or organic deodorants to capture isovaleric acid, an odor component generated from the scalp; and fragrances to impart a citrus or other scent to the artificial hair fiber. The amount of the additive may be 20 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less per 100 parts by mass of the acrylonitrile copolymer.

[0039] The polyacrylonitrile fiber can be produced by a wet spinning method. The method for producing the polyacrylonitrile fiber may include the steps of: extruding a spinning solution containing the acrylonitrile copolymer into a coagulation solution (also called a coagulation bath) to produce a coagulated yarn; wet-drawing the coagulated yarn to obtain a wet-drawn yarn; and dry-drawing the wet-drawn yarn to obtain a polyacrylonitrile fiber.

[0040] First, in a wet spinning process (also called a coagulation process), a spinning solution containing an acrylonitrile copolymer and an organic solvent can be extruded into a coagulation bath using a spinning nozzle to form yarn (also referred to as coagulated yarn).

[0041] The organic solvent is not particularly limited, and any organic solvent used in wet spinning of acrylonitrile copolymers can be used as appropriate, such as acetone, dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), and dimethylformamide (DMF). The concentration (solid content concentration) of the acrylonitrile copolymer in the spinning solution is not particularly limited, but may be, for example, 22 to 28% by mass. The spinning solution may also contain a small amount of water, for example, 1.5 to 4.8% by mass of water. This helps to suppress the formation of voids.

[0042] The spinning solution is not particularly limited, but for example, it may contain 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more of an epoxy group-containing compound per 100 parts by mass of acrylonitrile copolymer. Including an epoxy group-containing compound in the spinning solution is preferable because it can suppress odor, discoloration of fibers due to heat, and devitrification of fibers due to hot water. In particular, when dimethyl sulfoxide is used as the organic solvent, it is possible to effectively suppress the generation of malodorous components due to the decomposition of dimethyl sulfoxide when polyacrylonitrile fibers are heated. Furthermore, from the viewpoint of spinnability, fiber quality, and cost, the spinning solution may contain 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less of an epoxy group-containing compound per 100 parts by mass of acrylonitrile copolymer.

[0043] Examples of epoxy group-containing compounds 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 cyclic aliphatic-type epoxy resins. The epoxy group-containing compound may be used alone or in combination of two or more types.

[0044] The epoxy group-containing compound is preferably a glycidyl methacrylate-containing polymer and / or a glycidyl acrylate-containing polymer, and more preferably a polyglycidyl methacrylate, from the viewpoint of epoxy equivalent (mass of resin containing one equivalent of epoxy groups), suppression of fiber discoloration, solubility in organic solvents such as dimethyl sulfoxide, and reduction of elution into the spinning bath.

[0045] The mass-average molecular weight (Mw) of the epoxy group-containing compound is not particularly limited and may be determined appropriately, for example, considering its solubility in organic solvents such as dimethyl sulfoxide and its elution into the spinning bath. When the epoxy group-containing compound is a glycidyl methacrylate-containing polymer and / or a glycidyl acrylate-containing polymer, for example, from the viewpoint of reducing elution into the spinning bath, it is preferable that the mass-average molecular weight is 3,000 or more, and from the viewpoint of solubility in organic solvents such as dimethyl sulfoxide, it is preferable that the mass-average molecular weight is 100,000 or less.

[0046] The spinning solution may, if necessary, contain other additives to improve fiber properties, as long as they do not impede the effects of the present invention. Examples of such additives include gloss modifiers such as titanium dioxide, silicon dioxide, cellulose derivatives such as esters and ethers; colorants such as organic pigments, inorganic pigments, and dyes; and stabilizers to improve light resistance and heat resistance.

[0047] The spinning nozzle can be used as appropriate to match the desired fiber cross-section. The fiber cross-section of the polyacrylonitrile fiber is not particularly limited and may be circular, elliptical, or irregularly shaped.

[0048] In the wet spinning process described above, the spinning speed is not particularly limited, but from the viewpoint of industrial productivity, for example, it is preferably 2 to 17 m / min.

[0049] The solidification bath can be an aqueous solution of the organic solvent described above. In the solidification bath (aqueous solution of organic solvent), the concentration of the organic solvent may be 30 to 60% by mass, or 35 to 55% by mass. The temperature of the solidification bath may be, for example, 5 to 40°C.

[0050] Next, the coagulated yarn may be wet-drawn to form a wet-drawn yarn. Wet drawing can be carried out in a coagulation bath and / or a drawing bath.

[0051] The stretch ratio in the coagulation bath is not particularly limited, but from the viewpoint of preventing fiber breakage in the coagulation bath, for example, it is preferably 1 to 2 times, and more preferably 1.25 to 1.5 times. In this specification, the stretch ratio (times) is indicated by the ratio of the lengths of the yarn (fibers) before and after stretching.

[0052] The stretching bath may be an aqueous solution of the organic solvent described above. In the stretching bath, the concentration of the organic solvent may be 20-70% by mass, 30-60% by mass, or 45-55% by mass. The temperature of the stretching bath may be 30-90°C. The stretching ratio in the stretching bath is not particularly limited and may be, for example, greater than 1x and less than or equal to 8x, or 1.5-6x.

[0053] A washing and drying process may be performed after the wet stretching process (stretching in a solidification bath and / or stretching in a stretching bath). Alternatively, an oil application process may be performed before the drying process. Furthermore, a dry stretching process and a heat relaxation treatment process may be performed after the drying process.

[0054] In the washing process, the organic solvent can be removed by washing the wet-drawn yarn with water at 30°C or higher, more specifically, with water at 30-90°C.

[0055] In the oil application process, an oil composition is used, which is obtained by dissolving or dispersing an oil in water. The oil composition may further contain a plasticizer. This allows for the application of an oil, or an oil and a plasticizer, to the wet-drawn yarn. The oils and plasticizers described above can be used as appropriate. Specifically, it is preferable to apply the oil by introducing the oil composition into an oil tank and immersing the wet-drawn yarn. The temperature of the oil tank (oil composition) is not particularly limited, but may be, for example, 40 to 80°C. The immersion time is not particularly limited, but may be, for example, 1 to 10 seconds.

[0056] In the drying process, the wet-drawn yarn is dried. The drying temperature is not particularly limited, but may be, for example, 110 to 190°C. The dried wet-drawn yarn is preferably dry-drawn. The drying temperature is not particularly limited, but may be, for example, 110 to 190°C. The draw ratio in the dry-drawn process is not particularly limited, but may be, for example, greater than 1x and less than or equal to 5x, 1 to 4x, or 1 to 3x. The total draw ratio, including the wet-drawn yarn before drying, is preferably 2 to 10x, more preferably 2 to 8x, and even more preferably 2 to 6x.

[0057] In this application, the use of the above-mentioned acrylonitrile copolymer makes it easier to improve the stretchability when manufacturing polyacrylonitrile fibers. From the viewpoint of excellent stretchability, polyacrylonitrile fibers preferably have a total stretch ratio of 12 or more at 130°C, more preferably 13 or more, and even more preferably 14 or more. In this specification, the total stretch ratio at 130°C is obtained by multiplying the maximum stretch ratio in dry stretching at 130°C (hereinafter also referred to as D2MAX130) by the wet stretch ratio in the manufacturing process. Here, the wet stretch ratio means the stretch ratio in stretching in the coagulation bath and / or the stretch ratio in stretching in the stretching bath.

[0058] After dry stretching, the resulting polyacrylonitrile fibers are preferably further relaxed in a heat relaxation process. The relaxation rate is not particularly limited, but is preferably 5% or more, and more preferably 10-30%. The heat relaxation treatment can be carried out at a high temperature, for example, in a dry heat atmosphere or a superheated steam atmosphere at 140-200°C.

[0059] The present invention comprises one or more fiber aggregates containing the polyacrylonitrile fibers described above. The fiber aggregate may consist of 100% by mass of the polyacrylonitrile fibers, or may contain other fibers as needed.

[0060] The fiber aggregate may also be a headwear product. Since polyacrylonitrile fibers have good HWS properties, it is possible to provide a headwear product with good HWS properties. In addition to the polyacrylonitrile fibers, the headwear product may also contain human hair or other artificial hair fibers. Other artificial hair fibers are not particularly limited, but examples include polyvinyl chloride fibers, nylon fibers, polyester fibers, and regenerated collagen fibers.

[0061] Examples of the aforementioned headwear products include hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories, and doll hair.

[0062] The fiber aggregate may be a flame-retardant fiber aggregate. Examples of composite forms of the flame-retardant fiber aggregate include blended cotton, blended spun cotton, blended fiber, plied yarn, plywood, composite yarn such as core-sheath, interwoven fabrics, interknitted fabrics, and laminated fabrics. Specifically, the flame-retardant fiber aggregate may be cotton used for stuffing, spun yarn, nonwoven fabric, woven or knitted fabrics, and braided fabrics.

[0063] The polyacrylonitrile fibers and flame-retardant fiber aggregates can be used in various textile products (applications). Examples of such textile products include the following. In addition to the polyacrylonitrile fibers described above, the textile products may also include other fibers, such as natural fibers, regenerated fibers, and synthetic fibers other than polyacrylonitrile fibers.

[0064] (Textile products) (1) Clothing and daily necessities Clothing (including jackets, underwear, sweaters, vests, trousers, etc.), gloves, socks, scarves, hats, bedding, pillows, cushions, stuffed animals, etc. (2)Special clothing Work clothes, cold-weather clothing, etc., worn by workers handling fire, such as protective suits and firefighting suits. (3) Interior materials Upholstery, curtains, wallpaper, carpets, etc. (4) Industrial materials Filters, flame-resistant padding, lining materials, etc. [Examples]

[0065] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0066] (Composition of acrylonitrile copolymer) The nitrogen content in the acrylonitrile copolymer was measured using an elemental analyzer (Yanaco CHN Coder). This nitrogen content was considered to be derived from acrylonitrile, and the content of constituent units derived from acrylonitrile in the acrylonitrile copolymer was calculated. Using a nuclear magnetic resonance spectrometer (Jeol, "ECA-500NMR"), 1 ¹H NMR measurements were performed to calculate the mass percentage content of constituent units derived from alkyl (meth)acrylates and sulfonic acid group-containing vinyl monomers in the acrylonitrile copolymer. Based on the content (mass%) of constituent units derived from acrylonitrile, alkyl (meth)acrylate, and sulfonic acid group-containing vinyl monomers, the content (mass%) of constituent units derived from vinyl halogenated monomers in the acrylonitrile copolymer was calculated.

[0067] (Fiber fusion) During the manufacturing process of polyacrylonitrile fibers, the degree of fiber fusion after the drying process was evaluated using the following three-level criteria. A: The fibers are not fused together. B: The fibers are fused together, but can be easily torn apart by hand. C: The fibers are strongly fused together, making it difficult to tear by hand.

[0068] (Stretchability) In the process of preparing polyacrylonitrile fibers, 50 mg of the fiber after the drying process was taken, fixed to a jig in the shape of a 6 cm circumference ring, and stretched in a dryer at 130°C. The stretch ratio (times) at which fiber breakage occurred was measured and taken as the maximum stretch ratio (times) for dry stretching at 130°C. The total stretch ratio was calculated by multiplying the stretch ratio (times) of wet stretching (stretching in a coagulation bath and / or stretching in a stretching bath) by the maximum stretch ratio (times) for dry stretching at 130°C.

[0069] (Single fiber fineness of polyacrylonitrile-based fibers) Using an autobibro type fiber fineness analyzer (DENICON DC-21A, manufactured by Search), the single fiber fineness of 100 fibers was measured individually, and the average value was calculated.

[0070] (Strength and elongation of polyacrylonitrile fibers) The strength (tensile strength) and elongation (stretch rate) of polyacrylonitrile fibers were measured according to JIS L 1015. Polyacrylonitrile fibers cut to a length of approximately 25 mm were used as samples.

[0071] (HWS nature) Polyacrylonitrile fibers (multifilaments) were cut to a length of approximately 27 cm, and the resulting fiber bundles were wrapped around a 15 mm diameter metal pipe and secured at both ends with rubber bands to prevent movement. The fiber bundles wrapped around the metal pipe were immersed in 70°C hot water for 15 seconds, and then dried in a 40°C dryer for 2 hours. After drying, the fiber bundles were removed from the metal pipe, suspended with the rubber band attached to one end facing upwards, and the length of the fiber bundle (cm) from directly below the rubber band to the tip of the fiber bundle was measured. A shorter fiber bundle indicates higher HWS (High Wave Strengthening) properties.

[0072] (Example 1) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out using a 14L pressure-resistant polymerization reactor. The polymerization conditions were as follows: 1650g of acrylonitrile, 1850g of vinyl chloride, 36g of sodium styrene sulfonate, and 110g of 2-hydroxyethyl methacrylate (hereinafter also simply referred to as "HEMA") were mixed with 5600g of deionized water, 32g of sodium lauryl alcohol sulfate (emulsifier), 0.095g of ferrous sulfate, 19g of sodium bisulfite, and 13g of sulfuric acid, with 10.7g of ammonium peroxydisulfate as a polymerization initiator. The reaction was carried out at a temperature of 49°C for 5.67 hours. In this emulsion polymerization, 1510g of acrylonitrile and the entire amount of sodium styrene sulfonate were continuously added to the polymerization system as polymerization progressed in order to adjust the resulting polymer composition. In addition, 9.9g of ammonium peroxydisulfate was continuously added to the polymerization system as polymerization progressed in order to adjust the reaction rate. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was heated to 90°C, and salting out was performed by adding 260 g of sodium chloride (1000 g of 26 wt% aqueous solution) to obtain a polymer suspension. The obtained polymer suspension was filtered, washed with hot water, dehydrated, and dried to obtain an acrylonitrile-based copolymer consisting of 47.5 wt% of constituent units derived from acrylonitrile, 47.7 wt% of constituent units derived from vinyl chloride, 1.1 wt% of constituent units derived from sodium styrene sulfonate, and 3.7 wt% of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 90.7 wt%. <Preparation of polyacrylonitrile-based fibers> The obtained acrylonitrile copolymer was dissolved in dimethyl sulfoxide to prepare a resin solution with an acrylonitrile copolymer concentration of 28.0% by mass and a water concentration of 2.9% by mass. Next, red dye (CI Basic Red 46) and blue dye (CI Basic Blue 41) were added to the resin solution as colorants, in amounts of 8.49 parts by mass and 28.4 parts by mass, respectively, per 100 parts by mass of the acrylonitrile copolymer. Furthermore, polyglycidyl methacrylate (weight-average molecular weight 12,000) was added in an amount of 0.8 parts by mass per 100 parts by weight of the acrylonitrile copolymer to prepare a spinning solution. The spinning solution was extruded into a coagulation bath of a 47% by mass DMSO aqueous solution at 20°C using a spinning nozzle (pore diameter 0.3 mm, number of pores 100) and stretched to 1.41 times its original size. After wet spinning at a spinning speed of 3 m / min, it was stretched to 2.1 times its original size in a stretching bath of a 50% by mass DMSO aqueous solution at 85°C, and then washed with hot water at 90°C. Subsequently, the yarn was immersed for 1 to 3 seconds in an oil bath (60°C) containing an oil composition consisting of 0.8% by mass sorbitan monostearate, 1.2% by mass polyoxyethylene castor oil, and 98% by mass distilled water to impregnate the yarn with the oil, and then dried at 140°C. After drying, it was stretched to 3 times its original size at 140°C and subjected to a 27% relaxation treatment at 150°C to obtain polyacrylonitrile fibers (multifilaments) with a single fiber fineness of approximately 46 dtex.

[0073] (Example 2) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that the amount of 2-hydroxyethyl methacrylate added was 219 g. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 47.0% by weight of constituent units derived from acrylonitrile, 45.9% by weight of constituent units derived from vinyl chloride, 1.0% by weight of constituent units derived from sodium styrenesulfonate, and 6.1% by weight of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 97.6% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0074] (Example 3) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that 98 g of 2-hydroxyethyl acrylate (hereinafter simply referred to as "HEA") was added instead of 2-hydroxyethyl methacrylate. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 47.0% by weight of constituent units derived from acrylonitrile, 49.3% by weight of constituent units derived from vinyl chloride, 1.1% by weight of constituent units derived from sodium styrenesulfonate, and 2.6% by weight of constituent units derived from 2-hydroxyethyl acrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 97.9% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0075] (Example 4) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that 120 g of n-butyl methacrylate (hereinafter also simply referred to as "BMA") was added instead of 2-hydroxyethyl methacrylate. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 46.0% by weight of constituent units derived from acrylonitrile, 49.2% by mass of constituent units derived from vinyl chloride, 1.0% by mass of constituent units derived from sodium styrenesulfonate, and 3.8% by mass of constituent units derived from butyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 93.8% by mass. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0076] (Example 5) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that the amount of 2-hydroxyethyl methacrylate added was 37 g. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 47.8% by weight of constituent units derived from acrylonitrile, 50.0% by weight of constituent units derived from vinyl chloride, 1.1% by weight of constituent units derived from sodium styrenesulfonate, and 1.1% by weight of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 90.5% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, and using an oil composition consisting of 0.8% by mass of sorbitan monostearate (oil), 1.2% by mass of polyoxyethylene castor oil (oil), 1.0% by mass of dimethyl sulfone (plasticizer), and 97% by mass of distilled water, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0077] (Example 6) <Preparation of acrylonitrile copolymers> An acrylonitrile copolymer was obtained in the same manner as in Example 1, consisting of 47.5% by weight of constituent units derived from acrylonitrile, 47.7% by weight of constituent units derived from vinyl chloride, 1.1% by weight of constituent units derived from sodium styrene sulfonate, and 3.7% by weight of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 90.7% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 5.

[0078] (Example 7) <Preparation of acrylonitrile copolymers> In the same manner as in Example 2, an acrylonitrile copolymer was obtained consisting of 47.0% by weight of constituent units derived from acrylonitrile, 45.9% by weight of constituent units derived from vinyl chloride, 1.0% by weight of constituent units derived from sodium styrene sulfonate, and 6.1% by weight of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 97.6% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 5.

[0079] (Example 8) <Preparation of acrylonitrile copolymers> In the same manner as in Example 3, an acrylonitrile copolymer was obtained consisting of 47.0% by weight of constituent units derived from acrylonitrile, 49.3% by weight of constituent units derived from vinyl chloride, 1.1% by weight of constituent units derived from sodium styrene sulfonate, and 2.6% by weight of constituent units derived from 2-hydroxyethyl acrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 97.9% by weight. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 5.

[0080] (Example 9) <Preparation of acrylonitrile copolymers> In the same manner as in Example 4, an acrylonitrile copolymer was obtained consisting of 46.0% by weight of constituent units derived from acrylonitrile, 49.2% by mass of constituent units derived from vinyl chloride, 1.0% by mass of constituent units derived from sodium styrene sulfonate, and 3.8% by mass of constituent units derived from n-butyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 93.8% by mass. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 5.

[0081] (Comparative Example 1) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that 2-hydroxyethyl methacrylate was not added and the amount of sodium styrene sulfonate added was 73 g. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 46.5% by weight of constituent units derived from acrylonitrile, 51.4% by mass of constituent units derived from vinyl chloride, and 2.1% by mass of constituent units derived from sodium styrene sulfonate. The polymerization conversion rate based on the amount of vinyl chloride added was 94.6% by mass. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0082] (Comparative Example 2) <Preparation of acrylonitrile copolymers> An acrylonitrile copolymer was obtained in the same manner as in Comparative Example 1, consisting of 46.5% by weight of constituent units derived from acrylonitrile, 51.4% by mass of constituent units derived from vinyl chloride, and 2.1% by mass of constituent units derived from sodium styrene sulfonate. The polymerization conversion rate based on the amount of vinyl chloride added was 94.6% by mass. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 5.

[0083] (Comparative Example 3) <Preparation of acrylonitrile copolymers> Emulsion polymerization was carried out in the same manner as in Example 1, except that the amount of acrylonitrile added was 150 g, the amount of sodium styrene sulfonate added was 75 g, and the amount of 2-hydroxyethyl methacrylate added was 400 g. Polymerization proceeded smoothly, and a polymer emulsion was obtained. The obtained polymer emulsion was subjected to salting out, filtration, hot water washing, dehydration, and drying to obtain an acrylonitrile-based copolymer consisting of 43.0% by weight of constituent units derived from acrylonitrile, 45.0% by mass of constituent units derived from vinyl chloride, 2.0% by mass of constituent units derived from sodium styrene sulfonate, and 10.0% by mass of constituent units derived from 2-hydroxyethyl methacrylate. The polymerization conversion rate based on the amount of vinyl chloride added was 90.5% by mass. <Preparation of polyacrylonitrile-based fibers> Except for using the acrylonitrile copolymer obtained above, the process for producing polyacrylonitrile fibers (multifilaments) was carried out in the same manner as in Example 1, but significant fusion between fibers was observed during the drying process.

[0084] In the examples and comparative examples, the composition of the acrylonitrile copolymer was measured as described above. During the preparation of the examples and comparative examples, the fusion of the polyacrylonitrile fibers after drying was evaluated as described above. The oil and plasticizer content, as well as the single fiber fineness, strength, elongation, HWS properties, and drawability of the polyacrylonitrile fibers obtained in the examples and comparative examples were measured and evaluated as described above. These results are shown in Table 1 below. In Table 1 below, "―" means not measured, and "D2MAX130" means the maximum draw ratio in dry drawing at 130°C.

[0085] [Table 1]

[0086] As can be seen from Table 1, the acrylonitrile copolymers of the examples, which contained 0.5 to 8% by mass of constituent unit B derived from alkyl (meth)acrylate esters having linear or branched alkyl groups having 2 or more carbon atoms that may have substituents, exhibited good drawability in wet spinning. Furthermore, the polyacrylonitrile fibers of the examples exhibited good HWS (Heat Welding Score).

[0087] On the other hand, the acrylonitrile copolymers of Comparative Examples 1 and 2, which did not contain constituent unit C derived from alkyl (meth)acrylate esters having linear or branched alkyl groups having 2 or more carbon atoms that may have substituents, exhibited poor drawability in wet spinning. Furthermore, when the acrylonitrile copolymer of Comparative Example 3, which contained more than 8% by mass of constituent unit C derived from alkyl (meth)acrylate esters having linear or branched alkyl groups having 2 or more carbon atoms that may have substituents, was used, strong fusion of fibers occurred during the drying process, making dry stretching impossible.

[0088] The present invention is not particularly limited, but preferably includes, for example, the following embodiments. [1] An acrylonitrile copolymer containing 30% by mass or more of structural unit A derived from acrylonitrile, 40% by mass or more of structural unit B derived from vinyl halogenated monomer, and 0.5 to 8% by mass of structural unit C derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents. [2] The acrylonitrile copolymer according to [1], wherein the substituent is a hydroxyl group. [3] The acrylonitrile copolymer according to [1] or [2], wherein the alkyl (meth)acrylate ester is at least one selected from the group consisting of ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. [4] The acrylonitrile copolymer further comprises 0.5 to 5% by mass of constituent unit D derived from a sulfonic acid group-containing vinyl monomer, as described in any of [1] to [3]. [5] Polyacrylonitrile fibers containing an acrylonitrile copolymer as described in any of [1] to [4]. [6] The polyacrylonitrile fiber according to [5], wherein the plasticizer content is 3% by mass or less per 100% by mass of the polyacrylonitrile fiber. [7] The polyacrylonitrile fiber according to [6], wherein the plasticizer is one or more selected from the group consisting of dimethyl sulfone, lactide lactate, and ε-caprolactam. [8] A method for producing polyacrylonitrile fibers containing an acrylonitrile copolymer as described in any of [1] to [4], A step of producing coagulated yarn by extruding the spinning solution containing the acrylonitrile copolymer into a coagulation solution, A step of wet-drawing the coagulated yarn to obtain a wet-drawn yarn, and The process includes drying the wet-drawn yarn to obtain polyacrylonitrile fibers, A method for producing polyacrylonitrile fibers, wherein the total draw ratio of the polyacrylonitrile fibers at 130°C is 12 times or more. [9] A fiber aggregate containing polyacrylonitrile fibers as described in any of [5] to [7].

[10] The fiber aggregate is a headwear product, as described in [9].

Claims

1. An acrylonitrile copolymer comprising 30% by mass or more of structural unit A derived from acrylonitrile, 40% by mass or more of structural unit B derived from vinyl halogenated monomer, and 0.5 to 8% by mass of structural unit C derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents.

2. The acrylonitrile copolymer according to claim 1, wherein the substituent is a hydroxyl group.

3. The acrylonitrile copolymer according to claim 1, wherein the alkyl (meth)acrylate ester is at least one selected from the group consisting of ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate.

4. The acrylonitrile copolymer according to claim 1, further comprising 0.5 to 5% by mass of constituent unit D derived from a sulfonic acid group-containing vinyl monomer.

5. A polyacrylonitrile fiber comprising an acrylonitrile copolymer according to any one of claims 1 to 4.

6. The polyacrylonitrile fiber according to claim 5, wherein the plasticizer content is 3% by mass or less with respect to 100% by mass of the polyacrylonitrile fiber.

7. The polyacrylonitrile fiber according to claim 6, wherein the plasticizer is one or more selected from the group consisting of dimethyl sulfone, lactide lactate, and ε-caprolactam.

8. A method for producing polyacrylonitrile fibers containing an acrylonitrile copolymer according to any one of claims 1 to 4, A step of producing coagulated yarn by extruding the spinning solution containing the acrylonitrile copolymer into a coagulation solution, A step of wet-drawing the coagulated yarn to obtain a wet-drawn yarn, and The process includes drying the wet-drawn yarn to obtain polyacrylonitrile fibers, A method for producing polyacrylonitrile fibers, wherein the total draw ratio of the polyacrylonitrile fibers at 130°C is 12 times or more.

9. A fiber aggregate comprising the polyacrylonitrile fiber described in claim 5.

10. The fiber assembly according to claim 9, wherein the fiber assembly is a head ornament product.

Images