Polyacrylonitrile fibers and headwear products containing them

Abstract

The present invention provides polyacrylonitrile fibers that exhibit good curl-setting properties when heated with hot water, and headwear products containing the same. [Solution] One or more embodiments of the present invention relate to a polyacrylonitrile fiber composed of an acrylonitrile copolymer, wherein the acrylonitrile copolymer contains 30% by mass or more of constituent unit A derived from acrylonitrile, and more than 0% by mass and less than 10% by mass of constituent unit B derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents, and the glass transition temperature is 90°C or lower.

Description

Technical Field

[0001] The present invention relates to polyacrylonitrile-based fibers that can be suitably used as a substitute for human hair, and a headdress product containing the same.

Background Art

[0002] In headdress products such as wigs, human hair has been conventionally used. In recent years, however, the demand for artificial hair as a substitute for human hair has been increasing. As artificial hair, for example, fibers using a copolymer obtained by copolymerizing acrylonitrile and other monomers such as vinyl chloride have been used. For example, Patent Document 1 describes artificial hair fibers mainly composed of an acrylic copolymer containing 35% by weight or more of acrylonitrile. Further, Patent Document 2 proposes synthetic fibers for artificial hair using an acrylonitrile-based polymer containing 30 to 80% by weight of acrylonitrile and 20 to 70% by weight of vinyl chloride and / or vinylidene chloride.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, in the case of artificial hair, curl setting property with hot water is required. However, fibers using a copolymer containing 30% by mass or more of acrylonitrile as described in Cited Documents 1 and 2 have a problem of poor curl setting property with hot water.

[0005] In order to solve the above problems, the present invention provides polyacrylonitrile-based fibers having good curl setting property with hot water, and a headdress product containing the same. [Means for solving the problem]

[0006] One or more embodiments of the present invention relate to a polyacrylonitrile fiber composed of an acrylonitrile copolymer, wherein the acrylonitrile copolymer contains 30% by mass or more of structural unit A derived from acrylonitrile, and more than 0% by mass and less than 10% by mass of structural unit B derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents, and the glass transition temperature is 90°C or lower.

[0007] One or more embodiments of the present invention relate to headwear products containing the polyacrylonitrile fiber. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide polyacrylonitrile fibers and headwear products that exhibit good curl-setting properties when heated with hot water. [Modes for carrying out the invention]

[0009] The inventors of the present invention have conducted extensive research to improve the hot water curl-set property (hereinafter also referred to as HWS property) of polyacrylonitrile fibers composed of an acrylonitrile copolymer containing 30% by mass or more of structural units derived from acrylonitrile. As a result, they found that by using an acrylonitrile copolymer obtained by copolymerizing a predetermined amount of an alkyl (meth)acrylate ester having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents, with acrylonitrile, and by lowering the glass transition temperature (hereinafter also referred to as Tg) of the polyacrylonitrile fibers to a predetermined temperature or lower, the HWS property of the polyacrylonitrile fibers is improved, and in particular, the HWS property is improved even when using hot water at 70°C or lower. In this specification, "(meth)acrylic acid" means one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0010] 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.

[0011] The polyacrylonitrile fibers of one or more embodiments of the present invention are composed of an acrylonitrile copolymer. 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.

[0012] The acrylonitrile copolymer contains 30% by mass or more of constituent unit A derived from acrylonitrile, preferably 30-80% by mass, more preferably 35-75% by mass, and even more preferably 40-70% by mass. When the content of constituent unit A in the acrylonitrile copolymer is within the above range, the heat resistance of the polyacrylonitrile fiber is improved.

[0013] The acrylonitrile copolymer contains more than 0% by mass and less than 10% by mass of constituent unit B derived from an alkyl (meth)acrylate having an alkyl group having 2 or more carbon atoms, which may have substituents. The inclusion of constituent unit B in the acrylonitrile copolymer improves the HWS properties of the polyacrylonitrile fibers. Furthermore, the inclusion of less than 10% by mass of constituent unit B in the acrylonitrile copolymer suppresses the fusion of fibers during the manufacturing process. In the following, unless otherwise specified, "alkyl (meth)acrylate" means an alkyl (meth)acrylate having an alkyl group having 2 or more carbon atoms, which may have substituents.

[0014] From the viewpoint of further improving the HWS properties of the polyacrylonitrile fibers, the acrylonitrile copolymer preferably contains 0.5% by mass or more of constituent unit B, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more of constituent unit B, even more preferably 2% by mass or more, and even more preferably 2.5% by mass or more. This makes it easier to improve HWS properties, especially without using plasticizers such as dimethyl sulfone, which will be described later. From the viewpoint of more effectively suppressing the fusion of polyacrylonitrile fibers, the acrylonitrile copolymer preferably contains 9% by mass or less of constituent unit B, more preferably 8.5% by mass or less, even more preferably 8% by mass or less, even more preferably 7.5% by mass or less, and even more preferably 7% by mass or less.

[0015] 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 reducing the Tg of the acrylonitrile copolymer and ease of handling, 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.

[0016] 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 and more effectively reducing the Tg of the acrylonitrile copolymer, 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.

[0017] 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 HWS of polyacrylonitrile fibers, the alkyl (meth)acrylate 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.

[0018] The acrylonitrile copolymer preferably further contains 10% by mass or more of constituent unit C derived from vinyl halogenated monomers. This improves the flame retardancy of the polyacrylonitrile fibers. In the acrylonitrile copolymer, the content of constituent unit C is more preferably 10 to 60% by mass, even more preferably 15 to 55% by mass, even more preferably 20 to 55% by mass, and even more preferably 30 to 55% by mass.

[0019] The vinyl halogen monomer is not particularly limited and includes, for example, vinyl chloride, vinyl bromide, and vinyl iodide, but vinyl chloride is preferred.

[0020] The acrylonitrile copolymer may contain constituent units derived from other monomer components in addition to constituent units A, B, and C. Examples of other monomer components include sulfonic acid group-containing vinyl monomers. The sulfonic acid group-containing vinyl monomer is not particularly limited, but examples include allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and metal salts and amine salts of these, such as their sodium salts. The sulfonic acid group-containing vinyl monomer may be used individually or in combination of two or more types.

[0021] In the acrylonitrile copolymer, the content of constituent units D derived from sulfonic acid group-containing vinyl monomers is not particularly limited, but from the viewpoint of reducing the Tg of the acrylonitrile copolymer and the polyacrylonitrile fibers, it is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. From the viewpoint of increasing the hydrophilicity of the polyacrylonitrile fibers, the content of constituent units derived from sulfonic acid group-containing vinyl monomers may be 0.5% by mass or more.

[0022] More specifically, the acrylonitrile copolymer may contain, for example, 30 to 80% by mass of the structural unit A derived from acrylonitrile, more than 0% and less than 10% by mass of the structural unit B derived from (meth)acrylic acid alkyl ester, 10 to 60% by mass of the structural unit C derived from vinyl halide monomer, and 0 to 5% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer. It may contain 35 to 75% by mass of the structural unit A derived from acrylonitrile, 0.5 to 9% by mass of the structural unit B derived from (meth)acrylic acid alkyl ester, 15 to 55% by mass of the structural unit C derived from vinyl halide monomer, and 0.5 to 5% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer. It may contain 35 to 75% by mass of the structural unit A derived from acrylonitrile, 1 to 9% by mass of the structural unit B derived from (meth)acrylic acid alkyl ester, 15 to 55% by mass of the structural unit C derived from vinyl halide monomer, and 0.5 to 5% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer. It may contain 35 to 75% by mass of the structural unit A derived from acrylonitrile, 1.5 to 8.5% by mass of the structural unit B derived from (meth)acrylic acid alkyl ester, 15 to 55% by mass of the structural unit C derived from vinyl halide monomer, and 0.5 to 5% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer. It may contain 40 to 70% by mass of the structural unit A derived from acrylonitrile, 2 to 8% by mass of the structural unit B derived from (meth)acrylic acid alkyl ester, 20 to 55% by mass of the structural unit C derived from vinyl halide monomer, and 0.5 to 3% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer. It may contain 40 to 70% by mass of the structural unit A derived from acrylonitrile, 2.5 to 7.5% by mass of the structural unit B derived from the (meth)acrylic acid alkyl ester, 25 to 55% by mass of the structural unit C derived from vinyl halide monomer, and 0.5 to 3% by mass of the structural unit D derived from sulfonic acid group-containing vinyl monomer.

[0023] The glass transition temperature (Tg) of the acrylonitrile copolymer is not particularly limited. For example, from the viewpoint of easily reducing the Tg of the polyacrylonitrile fiber to 90°C or lower without using a plasticizer, it is preferably 97°C or lower, more preferably 96°C or lower, and even more preferably 95°C or lower. Also, the lower limit of the Tg of the acrylonitrile copolymer is not particularly limited. For example, from the viewpoint of heat resistance, it may be 80°C or higher. In this specification, the glass transition temperature (Tg) of the acrylonitrile copolymer can be determined using a known method such as a differential scanning calorimeter (DSC), and specifically, it can be measured as described in the examples.

[0024] The acrylonitrile copolymer can be obtained, for example, 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, an alkyl (meth)acrylate, and, if necessary, other monomers such as a vinyl halide monomer and a vinyl monomer containing a sulfonic acid group 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 monomers is 100 parts by mass, acrylonitrile may be 30 to 80 parts by mass, alkyl (meth)acrylate may be more than 0 to 10 parts by mass, vinyl halogenated monomer may be 10 to 60 parts by mass, and sulfonic acid group-containing vinyl monomer may be 0 to 5 parts by mass; acrylonitrile may be 35 to 75 parts by mass, alkyl (meth)acrylate may be 0.5 to 9 parts by mass, vinyl halogenated monomer may be 15 to 55 parts by mass, and sulfonic acid group-containing vinyl monomer may be 0.5 to 5 parts by mass; acrylonitrile may be 35 to 75 parts by mass, alkyl (meth)acrylate may be 1 to 9 parts by mass, vinyl halogenated monomer may be 15 to 55 parts by mass, and sulfonic acid group-containing vinyl monomer may be The amount may be 0.5 to 5 parts by mass; 35 to 75 parts by mass of acrylonitrile, 1.5 to 8.5 parts by mass of alkyl (meth)acrylate, 15 to 55 parts by mass of vinyl halogenated monomer, and 0.5 to 5 parts by mass of sulfonic acid group-containing vinyl monomer; 40 to 70 parts by mass of acrylonitrile, 2 to 8 parts by mass of alkyl (meth)acrylate, 20 to 55 parts by mass of vinyl halogenated monomer, and 0.5 to 3 parts by mass of sulfonic acid group-containing vinyl monomer; 40 to 70 parts by mass of acrylonitrile, 2.5 to 7.5 parts by mass of alkyl (meth)acrylate, 25 to 55 parts by mass of vinyl halogenated monomer, and 0.5 to 3 parts by mass of sulfonic acid group-containing vinyl monomer.

[0026] The water-soluble polymerization initiator can be any water-soluble polymerization initiator commonly used in polymerization, and is not particularly limited. For example, water-soluble inorganic peroxides and water-soluble azo compounds can be used, but water-soluble inorganic peroxides are preferred from the viewpoint of availability. Examples of water-soluble inorganic peroxides include persulfates and hydrogen peroxide, and persulfates are preferred from the viewpoint of ease of polymerization. Examples of persulfates include ammonium persulfate (also called ammonium peroxydisulfate), sodium persulfate, and potassium persulfate. The amount of the water-soluble polymerization initiator is not particularly limited, but for example, from the viewpoint of controlling the heat of reaction, it may be 0.1 to 1 part by mass, or 0.15 to 0.75 parts by mass, per 100 parts by mass of the total mass of 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 fiber has a glass transition temperature (Tg) of 90°C or lower. This results in good HWS properties, particularly when using hot water at 70°C or lower. The Tg of the polyacrylonitrile fiber is preferably 89.5°C or lower, and more preferably 89.0°C or lower. The lower limit of the Tg of the polyacrylonitrile fiber is not particularly limited, but from the viewpoint of tactile feel and spinnability, it is preferably 80°C or higher. By using the acrylonitrile copolymer described above, the Tg of the polyacrylonitrile fiber can be adjusted to 90°C or lower even when the plasticizer content is low (for example, 3% by mass or less) or when no plasticizer is used.

[0031] The single fiber fineness of the polyacrylonitrile fiber is not particularly limited, but from the viewpoint of suitability for use in artificial hair, for example, it is more preferably 20 to 90 dtex, even more preferably 25 to 75 dtex, and particularly preferably 30 to 60 dtex.

[0032] The tensile stress of the polyacrylonitrile fiber is not particularly limited, but from the viewpoint of further improving the HWS properties, especially when using hot water below 70°C, it is preferable that the tensile stress at 20% strain at 70°C be 0.062 N / tex or less, and more preferably 0.060 N / tex or less. The lower limit of the tensile stress of the polyacrylonitrile fiber at 20% strain at 70°C is not particularly limited, but from the viewpoint of product strength, for example, it is preferable that it be 0.030 N / tex or more.

[0033] The strength of the polyacrylonitrile fiber is not particularly limited, but may be 0.50 to 2.00 cN / dtex, 0.75 to 2.00 cN / dtex, or 1.00 to 2.00 cN / dtex, for example, from the viewpoint of product strength. The elongation (stretch rate) of the polyacrylonitrile fiber is not particularly limited, but may be 30 to 100%, 30 to 90%*, or 40 to 80%, for example, from the viewpoint of product strength. In this specification, the strength and elongation of the polyacrylonitrile fiber can be measured as described in the examples.

[0034] 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% by mass or less, 1.5% by mass or less, or 1% by mass or less. In this specification, the plasticizer content in the polyacrylonitrile fiber can be measured as follows.

[0035] (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)

[0036] 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.

[0037] 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.

[0038] 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.

[0039] (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 (weight %) = 100 × [(W2 - W1) / W0]

[0040] 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.

[0041] The polyacrylonitrile fiber may be produced by any spinning method, such as a dry spinning method or a wet spinning method. If the method for producing the polyacrylonitrile fiber is a wet spinning method, the method 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.

[0042] 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Headwear products can be constructed using the polyacrylonitrile fibers described above. The headwear products may also contain human hair or other artificial hair fibers in addition to the polyacrylonitrile fibers, as long as they do not impair the effects of the present invention. Other artificial hair fibers are not particularly limited, but examples include polyvinyl chloride fibers, nylon fibers, polyester fibers, and regenerated collagen fibers.

[0062] Examples of the aforementioned headwear products include hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories, and doll hair. [Examples]

[0063] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0064] (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)acrylate 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.

[0065] (Glass transition temperature of acrylonitrile copolymers) A differential scanning calorimetry (DSC) SSC-5200 manufactured by Seiko Instruments was used. A sample of acrylonitrile copolymer (2.0 mg) was first heated to 200°C at a rate of 25°C / min, held for 10 minutes, and then pre-adjusted by lowering the temperature to 50°C at a rate of 25°C / min. Measurements were then taken while the temperature was raised to 200°C at a rate of 10°C / min. The differential values ​​were determined from the obtained DSC curve (SSDC), and the glass transition temperature of the acrylonitrile copolymer was determined from its maximum point.

[0066] (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.

[0067] (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.

[0068] (Glass transition temperature of polyacrylonitrile fibers) Using a 0.046 mg sample of a single polyacrylonitrile fiber cut to 10 mm, the loss elasticity (E″) and storage elasticity (E′) of the polyacrylonitrile fiber were measured in accordance with JIS K 7244 under the conditions of a frequency of 0.05 Hz, a load of 26 mN ± 17 mN, and a heating rate of 5 °C / min. The dynamic viscoelasticity (tanδ) was calculated using the following formula, and the temperature at which the dynamic viscoelasticity (tanδ) reached its maximum value was defined as the peak temperature of tanδ (glass transition, Tg). Dynamic viscoelasticity (tanδ) = Loss elasticity (E″) / Storage elasticity (E′)

[0069] (Tensile stress of polyacrylonitrile fibers) A single polyacrylonitrile fiber, cut to a length of 10 mm, was used as a sample. The tensile stress at 20% strain was measured using a dynamic viscoelasticity analyzer (TA Instruments, DMA Q800) under the conditions of a temperature of 70°C, a preload load of 0.001 N, and a load ramp of 0.03 N / min.

[0070] (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.

[0071] (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 approximately 25 mm in length were used as samples.

[0072] (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.

[0073] (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.

[0074] (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.

[0075] (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.

[0076] (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.

[0077] (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.

[0078] (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.

[0079] (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.

[0080] (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.

[0081] (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.

[0082] (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.

[0083] (Comparative 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 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 mass of constituent units derived from vinyl chloride, 1.1% by mass of constituent units derived from sodium styrenesulfonate, and 1.1% 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, a polyacrylonitrile fiber (multifilament) with a single fiber fineness of approximately 46 dtex was obtained in the same manner as in Example 1.

[0084] (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.

[0085] In the examples and comparative examples, the composition and glass transition temperature of the acrylonitrile copolymer were measured as described above. During the preparation of the examples and comparative examples, the fusion of polyacrylonitrile fibers after drying was evaluated as described above. The oil and plasticizer content, as well as the single fiber fineness, strength, elongation, tensile stress, 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 Tables 1 and 2 below. In Table 1 below, "―" means not measured, and "D2MAX130" means the maximum draw ratio in dry drawing at 130°C.

[0086] [Table 1]

[0087] As can be seen from Table 1, the polyacrylonitrile fibers of the examples, which are composed of an acrylonitrile copolymer containing more than 0% by mass and less than 10% by mass of constituent unit B derived from an alkyl (meth)acrylate ester having a linear or branched alkyl group having 2 or more carbon atoms which may have substituents, and which have a Tg of 90°C or lower, exhibited good HWS properties. Furthermore, the polyacrylonitrile fibers of the examples also exhibited good stretchability.

[0088] On the other hand, the polyacrylonitrile fiber of Comparative Example 1, which was composed of an acrylonitrile copolymer that did not contain constituent unit B derived from an alkyl (meth)acrylate ester having a linear or branched alkyl group having 2 or more carbon atoms that may have substituents, exhibited poor HWS properties and poor stretchability. Furthermore, the polyacrylonitrile fiber of Comparative Example 2, which was composed of an acrylonitrile copolymer containing constituent unit B derived from an alkyl (meth)acrylate ester having a linear or branched alkyl group having 2 or more carbon atoms that may have substituents, but had a Tg exceeding 90°C, exhibited poor HWS properties. In addition, in Comparative Example 3, which used an acrylonitrile copolymer containing 10% by mass or more of constituent unit B derived from an alkyl (meth)acrylate ester having a linear or branched alkyl group having 2 or more carbon atoms that may have substituents, strong fusion between fibers occurred during the drying process, making dry stretching impossible.

[0089] The present invention is not particularly limited, but preferably includes, for example, the following embodiments. [1] A polyacrylonitrile fiber composed of an acrylonitrile copolymer, The acrylonitrile copolymer contains 30% by mass or more of structural unit A derived from acrylonitrile, and more than 0% by mass and less than 10% by mass of structural unit B derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents. Polyacrylonitrile fibers with a glass transition temperature of 90°C or lower. [2] The polyacrylonitrile fiber according to [1], wherein the substituent is a hydroxyl group. [3] The acrylonitrile copolymer is a polyacrylonitrile fiber according to [1] or [2], comprising 1.5 to 8% by mass of the constituent unit B. [4] The (meth)acrylate alkyl 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, according to any one of [1] to [3]. [5] The acrylonitrile copolymer further comprises 10% by mass or more of constituent unit C derived from a vinyl halogenated monomer, as described in any one of [1] to [4]. [6] A polyacrylonitrile fiber according to any one of [1] 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 polyacrylonitrile fiber according to any one of [1] to [7], wherein the tensile stress at 20% strain at 70°C is 0.062 N / tex or less. [9] Headwear products containing polyacrylonitrile fibers as described in any of [1] to [8].

[10] The headwear product according to [9], wherein the headwear product includes at least one selected from the group consisting of hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories, and doll hair.

Claims

1. A polyacrylonitrile fiber composed of an acrylonitrile copolymer, The acrylonitrile copolymer contains 30% by mass or more of structural unit A derived from acrylonitrile, and more than 0% by mass and less than 10% by mass of structural unit B derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 2 or more carbon atoms, which may have substituents. Polyacrylonitrile fibers with a glass transition temperature of 90°C or lower.

2. The polyacrylonitrile fiber according to claim 1, wherein the substituent is a hydroxyl group.

3. The polyacrylonitrile fiber according to claim 1, wherein the acrylonitrile copolymer contains 1.5 to 8% by mass of the constituent unit B.

4. The polyacrylonitrile fiber 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.

5. The polyacrylonitrile fiber according to claim 1, wherein the acrylonitrile copolymer further contains 10% by mass or more of constituent unit C derived from a vinyl halogenated monomer.

6. The polyacrylonitrile fiber according to claim 1, wherein the plasticizer content is 3% by mass or less per 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. The polyacrylonitrile fiber according to claim 1, wherein the tensile stress at 20% strain at 70°C is 0.062 N / tex or less.

9. A headwear product comprising a polyacrylonitrile fiber according to any one of claims 1 to 8.

10. The headwear product according to claim 9, wherein the headwear product includes at least one selected from the group consisting of hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories, and doll hair.

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