Mixed resin, fibers containing the same, and methods for manufacturing the same.

Abstract

The present invention provides a mixed resin that, when used in wet spinning, yields fibers in which the generation of macrovoids is suppressed, fibers containing the same, and methods for producing the same. [Solution] The mixed resin consists of modacryl resin A containing 35-69.9% by mass of acrylonitrile-derived constituent units, 30-64.9% by mass of halogen-containing monomer constituent units, and 0.1-1.5% by mass of sulfonic acid group-containing vinyl monomer constituent units, and acrylonitrile-based resin B containing 15-89.9% by mass of acrylonitrile-derived constituent units, 7.1-82% by mass of halogen-containing monomer constituent units, and 3-20% by mass of sulfonic acid group-containing vinyl monomer constituent units. When the content of acrylonitrile constituent units in resin A is denoted as CtA1% by mass and the content of acrylonitrile constituent units in resin B is denoted as CtB1% by mass, |CtA1-CtB1| is 0-19.0% by mass, and the content of sulfonic acid group-containing vinyl monomer constituent units is 1.2-5.0% by mass.

Description

Technical Field

[0001] The present invention relates to a mixed resin using two types of resins containing a structural unit derived from acrylonitrile, a structural unit derived from a halogen-containing monomer, and a structural unit derived from a sulfonic acid group-containing vinyl monomer, fibers containing the same, and methods for producing them.

Background Art

[0002] Fibers composed of a copolymer obtained by copolymerizing acrylonitrile and a halogen-containing monomer such as vinyl halide and vinylidene halide are used in various products such as artificial hair, flame-retardant materials, and pile fabrics. Such a copolymer of acrylonitrile and a halogen-containing monomer has a decomposition start temperature lower than the softening temperature and is likely to decompose when melt-processed. Therefore, it is usually fibrillated by a wet spinning method. For example, Patent Document 1 describes that Component A is a polymer (I) composed of 40% by weight or more of acrylonitrile and 20 to 60% by weight of a halogen-containing monomer, and Component B is a polymer composition in which 5 to 40 parts by weight of a polymer (II) composed of 30 to 75% by weight of acrylonitrile, 25 to 70% by weight of a vinyl monomer, and optionally 0 to 10% by weight of a sulfonic acid-containing monomer is mixed with 60 to 95 parts by weight of the polymer (I). The polymer composition is dissolved in dimethylformamide and wet-spun to obtain a flame-retardant acrylic composite fiber in which Component A and Component B are joined. Further, Patent Document 2 describes that a polymer composed of 35 to 80% by weight of acrylonitrile and 15 to 65% by weight of vinyl chloride or vinylidene chloride units and further containing 0 to 0.5% by weight of a sulfonic acid-containing monomer is dissolved in a solvent such as dimethylacetamide, dimethylformamide, or dimethyl sulfoxide and wet-spun.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

[0004] However, when copolymers of acrylonitrile and halogen-containing monomers such as vinyl halides and vinylidene halides are dissolved in good solvents such as dimethylacetamide, dimethylformamide, and dimethyl sulfoxide and wet-spun, a problem arose in that voids (also called air pockets) were generated inside the fibers, reducing the density of the fibers.

[0005] To solve the aforementioned conventional problems, the present invention provides a mixed resin containing a structural unit derived from acrylonitrile, a structural unit derived from a halogen-containing monomer, and a structural unit derived from a sulfonic acid group-containing vinyl monomer, which can be used in wet spinning to obtain fibers in which the generation of macrovoids is suppressed, as well as fibers containing the same and methods for producing them. [Means for solving the problem]

[0006] One or more embodiments of the present invention are a mixed resin comprising modacryl resin A and acrylonitrile resin B, wherein modacryl resin A contains 35 to 69.9% by mass of constituent units derived from acrylonitrile, 30 to 64.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 1.5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, and acrylonitrile resin B contains 15 to 89.9% by mass of constituent units derived from acrylonitrile and 7.1% by mass of constituent units derived from halogen-containing monomers. The present invention relates to a mixed resin containing 82% by mass of a compound and 3 to 20% by mass of constituent units derived from a sulfonic acid group-containing vinyl monomer, wherein, when the content of constituent units derived from acrylonitrile in modacryl resin A is CtA1% by mass and the content of constituent units derived from acrylonitrile in acrylonitrile-based resin B is CtB1% by mass, |CtA1-CtB1| is 0 to 19.0% by mass, and the content of constituent units derived from sulfonic acid group-containing vinyl monomer in the mixed resin is 1.2 to 5.0% by mass.

[0007] One or more embodiments of the present invention are methods for producing the mixed resin, comprising: step A, polymerizing monomer composition A to obtain modacryl resin A; step B, polymerizing monomer composition B to obtain acrylonitrile-based resin B; and step B, mixing modacryl resin A and acrylonitrile-based resin B, wherein monomer composition A contains 35 to 69.9% by mass of acrylonitrile, 30 to 64.9% by mass of halogen-containing monomer, and 0.1 to 1.5% by mass of sulfonic acid group-containing vinyl monomer, and monomer composition B contains 15 to 89.9% by mass of acrylonitrile. The present invention relates to a method for producing a mixed resin, comprising 7.1 to 82% by mass of halogen-containing monomers and 3 to 20% by mass of sulfonic acid group-containing vinyl monomers, wherein the acrylonitrile content in monomer composition A is 2% by mass of CtA, and the acrylonitrile content in monomer composition B is 2% by mass of CtB, so |CtA2-CtB2| is 0 to 19.0% by mass, and step A is carried out in the presence of water, a water-soluble polymerization initiator, and an emulsifier, and step B is carried out in the presence of water and a water-soluble polymerization initiator, with substantially no emulsifier present.

[0008] One or more embodiments of the present invention relate to acrylonitrile fibers containing a mixed resin.

[0009] One or more embodiments of the present invention relate to a method for producing acrylonitrile fibers, comprising the step of dissolving the mixed resin in an organic solvent and wet spinning, wherein the organic solvent comprises one or more selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide. [Effects of the Invention]

[0010] According to one or more embodiments of the present invention, a mixed resin can be provided which contains a resin containing constituent units derived from acrylonitrile, constituent units derived from halogen-containing monomers, and constituent units derived from sulfonic acid group-containing vinyl monomers, and which can be used in wet spinning to obtain fibers in which the generation of macrovoids is suppressed, and an acrylonitrile-based fiber containing the mixed resin in which the generation of macrovoids is suppressed can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional photograph (200x magnification) of the modacrylic fiber from Example 1. [Figure 2] This is a cross-sectional photograph (200x magnification) of the modacrylic fiber in Comparative Example 1. [Figure 3] This is a cross-sectional photograph (200x magnification) of the modacrylic fiber in Comparative Example 3. [Modes for carrying out the invention]

[0012] The inventors of the present invention conducted extensive research to solve the above-mentioned problems. As a result, they found that by using a mixed resin (hereinafter also referred to as mixed resin X) consisting of modacryl resin A, which contains constituent units derived from acrylonitrile, halogen-containing monomers, and sulfonic acid group-containing vinyl monomers, with a low content of constituent units derived from sulfonic acid group-containing vinyl monomers, and acrylonitrile-based resin B, which contains constituent units derived from acrylonitrile, halogen-containing monomers, and sulfonic acid group-containing vinyl monomers, with a content of constituent units derived from sulfonic acid group-containing vinyl monomers being at least twice that of modacryl resin A, and by setting the difference between the content of constituent units derived from acrylonitrile in modacryl resin A and the content of constituent units derived from acrylonitrile in acrylonitrile-based resin B to a predetermined range, and by setting the content of constituent units derived from sulfonic acid group-containing vinyl monomers in the mixed resin to a predetermined range, it is possible to obtain fibers with suppressed void (macrovoid) generation when the mixed resin is used in wet spinning.

[0013] 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.

[0014] (Mixed resin X and method for producing the same) In the mixed resin X, modacryl resin A contains 35-69.9% by mass of constituent units derived from acrylonitrile, 30-64.9% by mass of constituent units derived from halogen-containing monomers, and 0.1-1.5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Acrylonitrile-based resin B contains 15-89.9% by mass of constituent units derived from acrylonitrile, 7.1-82% by mass of constituent units derived from halogen-containing monomers, and 3-20% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. As a result, fibers containing the mixed resin X can have heat resistance, flame retardancy, and dyeability.

[0015] Modacrylic resin A preferably contains 40 to 64.8% by mass of constituent units derived from acrylonitrile, 35 to 59.8% by mass of constituent units derived from halogen-containing monomers, and 0.2 to 1.2% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, and more preferably contains 45 to 59.7% by mass of constituent units derived from acrylonitrile, 40 to 54.7% by mass of constituent units derived from halogen-containing monomers, and 0.3 to 1.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0016] When the content of acrylonitrile-derived structural units in modacrylic resin A is denoted as CtA1 by mass, and the content of acrylonitrile-derived structural units in acrylonitrile-based resin B is denoted as CtB1 by mass, |CtA1-CtB1| is 0 to 19.0% by mass. The absolute difference between the content of acrylonitrile-derived structural units in modacrylic resin A and the content of acrylonitrile-derived structural units in acrylonitrile-based resin B being 0 to 19.0% by mass allows for the production of fibers with suppressed macrovoid formation when the mixed resin X is used in wet spinning. From the viewpoint of compatibility, |CtA1-CtB1| is preferably 0.5 to 16% by mass, and more preferably 1 to 10% by mass.

[0017] It is preferable that the CtB1 is higher than the CtA1. That is, it is preferable that the content of the structural unit derived from acrylonitrile in the acrylonitrile-based resin B is higher than the content of the structural unit derived from acrylonitrile in the modacrylic resin A. Thereby, the obtained fiber is likely to have both heat resistance and flame retardancy. Also, the acrylonitrile-based resin B is likely to be polymerized.

[0018] The acrylonitrile-based resin B preferably contains 40 to 72% by mass of the structural unit derived from acrylonitrile, 25 to 57% by mass of the structural unit derived from the halogen-containing monomer, and 3 to 15% by mass of the structural unit derived from the sulfonic acid group-containing vinyl monomer, and more preferably contains 45 to 72% by mass of the structural unit derived from acrylonitrile, 25 to 52% by mass of the structural unit derived from the halogen-containing monomer, and 3 to 10% by mass of the structural unit derived from the sulfonic acid group-containing vinyl monomer. In this case, the acrylonitrile-based resin B is also referred to as a modacrylic resin B.

[0019] The halogen-containing monomer may be a vinyl halide or a vinylidene halide. The vinyl halide is not particularly limited, and examples thereof include vinyl chloride, vinyl bromide, and vinyl iodide. The vinylidene halide is not particularly limited, and examples thereof include vinylidene chloride, vinylidene bromide, and vinylidene iodide. These halogen-containing monomers may be used alone or in combination of two or more. The halogen-containing monomer preferably contains one or more selected from the group consisting of vinyl chloride and vinylidene chloride, and more preferably contains vinyl chloride.

[0020] The sulfonic acid group-containing vinyl monomer is not particularly limited, and for example, allyl sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and salts thereof can be used. Examples of the salt include alkali metal salts such as sodium salt and potassium salt, and ammonium salt. These sulfonic acid group vinyl monomers may be used alone or in combination of two or more. The sulfonic acid group-containing vinyl monomer preferably contains at least one selected from the group consisting of styrene sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, and metal salts thereof.

[0021] In the modacrylic resin A, the structural unit derived from the sulfonic acid group-containing vinyl monomer is not particularly limited, but for example, it is preferably a structural unit derived from at least one selected from the group consisting of styrene sulfonic acid and an alkali metal salt of styrene sulfonic acid, and more preferably a structural unit derived from an alkali metal salt of styrene sulfonic acid. In the modacrylic resin A having a low content of the structural unit derived from the sulfonic acid group-containing vinyl monomer, by using such a structural unit derived from the sulfonic acid group-containing vinyl monomer, the cost can be reduced, and the stability of emulsion polymerization using a halogen-containing monomer and a sulfonic acid group-containing vinyl monomer as copolymerization components can be enhanced.

[0022] In acrylonitrile resin B, the constituent units derived from sulfonic acid group-containing vinyl monomers are not particularly limited, but are preferably derived from one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and their metal salts, and more preferably from one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, and their metal salts. The salt may be an alkali metal salt such as a sodium salt. In acrylonitrile resin B with a high content of constituent units derived from sulfonic acid group-containing vinyl monomers, using such constituent units derived from sulfonic acid group-containing vinyl monomers can reduce costs and make it easier to obtain a modacryl resin in which halogen-containing monomers and sulfonic acid group-containing vinyl monomers are copolymer components and the polymerization ratio of acrylonitrile is high.

[0023] The mass-average molecular weight MwA of modacryl resin A is not particularly limited, but from the viewpoint of increasing the resin concentration in the spinning solution, realizing a dense fiber structure, and polymerization stability, the mass-average molecular weight is preferably 10,000 to 500,000, more preferably 20,000 to 400,000, and even more preferably 30,000 to 200,000.

[0024] The mass-average molecular weight MwB of acrylonitrile resin B is not particularly limited, but from the viewpoint of increasing the resin concentration in the spinning solution, realizing a dense fiber structure, and polymerization stability, the mass-average molecular weight is preferably 10,000 to 500,000, more preferably 20,000 to 400,000, and even more preferably 30,000 to 200,000.

[0025] The specific viscosity of modacryl resin A is not particularly limited, but for example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.05 to 0.60 or 0.10 to 0.50. In this specification, the specific viscosity can be measured as described in the examples.

[0026] The specific viscosity of acrylonitrile resin B is not particularly limited, but for example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.05 to 0.60 or 0.10 to 0.50.

[0027] In the mixed resin X, the content of constituent units derived from sulfonic acid group-containing vinyl monomer is 1.2 to 5.0% by mass. This makes it easier to obtain fibers with suppressed macrovoid formation when the mixed resin X is used in wet spinning. In the mixed resin X, the content of constituent units derived from sulfonic acid group-containing vinyl monomer is preferably 1.5 to 4.5% by mass, more preferably 1.5 to 4.0% by mass, even more preferably 1.5 to 3.5% by mass, and even more preferably 1.5 to 3.0% by mass.

[0028] In the mixed resin X, the content of constituent units derived from sulfonic acid group-containing vinyl monomers should satisfy the above-mentioned range, and the content of constituent units derived from acrylonitrile and halogen-containing monomers is not particularly limited, but for example, it is preferable to contain 35 to 65% by mass of constituent units derived from acrylonitrile, 30 to 63.8% by mass of constituent units derived from halogen-containing monomers, and 1.2 to 5.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, more preferably 35 to 60% by mass of constituent units derived from acrylonitrile, 36 to 63.5% by mass of constituent units derived from halogen-containing monomers, and 1.5 to 4.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, and even more preferably 40 to 55% by mass of constituent units derived from acrylonitrile, 42 to 58.5% by mass of constituent units derived from halogen-containing monomers, and 1.5 to 3.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0029] In the mixed resin X, the content of constituent units derived from sulfonic acid group-containing vinyl monomers should satisfy the above-mentioned range, and the content of modacryl resin A and acrylonitrile resin B is not particularly limited, but for example, it is preferable to contain 50 to 90% by mass of modacryl resin A and 10 to 50% by mass of acrylonitrile resin B, more preferably 50 to 85% by mass of modacryl resin A and 15 to 50% by mass of acrylonitrile resin B, and even more preferably 50 to 80% by mass of modacryl resin A and 20 to 50% by mass of acrylonitrile resin B.

[0030] The mass-average molecular weight MwX of the mixed resin X is not particularly limited, but from the viewpoint of increasing the resin concentration of the spinning solution and easily realizing a dense fiber structure, the mass-average molecular weight is preferably 10,000 to 500,000, more preferably 20,000 to 400,000, and even more preferably 50,000 to 300,000.

[0031] The specific viscosity of the mixed resin X is not particularly limited, but for example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.05 to 0.60 or 0.10 to 0.50.

[0032] The mixed resin X is preferably a mixture of modacryl resin A obtained by emulsion polymerization and modacryl resin B obtained by emulsion polymerization without emulsifiers (also called precipitation polymerization). By emulsion polymerization, modacryl resin A is obtained with a low content of constituent units derived from acrylonitrile and constituent units derived from sulfonic acid group-containing vinyl monomers, thereby reducing the amount of styrene sulfonic acid and / or its metal salt used as sulfonic acid group-containing vinyl monomers, thereby reducing costs and improving polymerization stability when copolymerizing with halogen-containing monomers. By emulsion polymerization without emulsifiers, modacryl resin B is obtained with a high content of constituent units derived from acrylonitrile and constituent units derived from sulfonic acid group-containing vinyl monomers, thereby allowing the use of one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, and their metal salts as sulfonic acid group-containing vinyl monomers, while also improving polymerization stability when copolymerizing with halogen-containing monomers.

[0033] The method for producing the mixed resin X is not particularly limited, but it is desirable to include, for example, the following steps. (1) Step A to obtain modacryl resin A by polymerizing monomer composition A, (2) Step B to polymerize monomer composition B to obtain acrylonitrile resin B, and (3) Step C, which involves mixing modacryl resin A and acrylonitrile resin B.

[0034] Step A can be carried out by polymerization in an aqueous medium due to the ease of polymerization control and the ease of separation and washing of polymer particles after polymerization, and emulsion polymerization is preferable. In the case of emulsion polymerization, modacrylic resin A can be obtained by polymerizing monomer composition A in the presence of water, a water-soluble polymerization initiator, and an emulsifier.

[0035] The monomer composition A preferably contains 35 to 69.9% by mass of acrylonitrile, 30 to 64.9% by mass of halogen-containing monomers, and 0.1 to 1.5% by mass of sulfonic acid group-containing vinyl monomers. This makes it possible to obtain modacryl resin A containing 35 to 69.9% by mass of constituent units derived from acrylonitrile, 30 to 64.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 1.5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. The halogen-containing monomers and sulfonic acid group-containing vinyl monomers can be those described above as appropriate.

[0036] Monomer composition A preferably contains 40 to 64.8% by mass of acrylonitrile, 35 to 59.8% by mass of halogen-containing monomers, and 0.2 to 1.2% by mass of sulfonic acid group-containing vinyl monomers, and more preferably contains 45 to 59.7% by mass of acrylonitrile, 40 to 54.7% by mass of halogen-containing monomers, and 0.3 to 1.0% by mass of sulfonic acid group-containing vinyl monomers.

[0037] In monomer composition A, the sulfonic acid group-containing vinyl monomer is not particularly limited, but is preferably one or more selected from the group consisting of styrene sulfonic acid and alkali metal salts of styrene sulfonic acid, and more preferably an alkali metal salt of styrene sulfonic acid. This reduces costs and improves the stability of emulsion polymerization using acrylonitrile, halogen-containing monomer, and sulfonic acid group-containing vinyl monomer as copolymer components.

[0038] 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, 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 1.0 parts by mass, or 0.15 to 0.75 parts by mass, per 100 parts by mass of the total mass of monomers (monomer composition A).

[0039] The water-soluble polymerization initiator, such as the persulfate (oxidizing agent), is preferably 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. A polymerization accelerator of 0.5 to 2 parts by mass may be used for every 1 part by mass of the oxidizing agent, such as the persulfate.

[0040] 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 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 3.0 parts by mass or 0.3 to 2.0 parts by mass per 100 parts by mass of the total mass of monomers (monomer composition A).

[0041] The monomer, water-soluble polymerization initiator (oxidizing agent, etc.), emulsifier, and water mentioned above, along with a reducing agent and polymerization accelerator 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 monomer, water-soluble polymerization initiator (oxidizing agent, etc.), reducing agent, polymerization accelerator, and emulsifier can be supplied to the polymerization reactor in any way, such as a single supply, continuous uniform supply, or 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. Modacrylic resin A (powder) can be obtained by salting out, dehydrating, washing with water, and drying the latex of modacrylic resin A obtained by polymerization, in the same way as in general emulsion polymerization.

[0042] Step B is not particularly limited, but it is preferable to carry out emulsion polymerization of monomer composition B in the presence of water and a water-soluble polymerization initiator, under conditions where emulsifiers are substantially absent. In particular, it is easier to obtain acrylonitrile-based resin B, preferably modacryl resin B, which has a high content of constituent units derived from acrylonitrile, i.e., CtB1 is higher than CtA1. In this specification, "substantially absent emulsifiers" means that emulsifiers are not intentionally supplied to the polymerization reactor, and if emulsifiers are present as impurities, etc., then "substantially absent emulsifiers" is appropriate.

[0043] Monomer composition B contains 15 to 89.9% by mass of constituent units derived from acrylonitrile, 7.1 to 82% by mass of constituent units derived from halogen-containing monomers, and 3 to 20% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. When the acrylonitrile content in monomer composition A is CtA2% by mass and the acrylonitrile content in monomer composition B is CtB2% by mass, |CtA2-CtB2| is 0 to 19.0% by mass. This makes it possible to obtain acrylonitrile-based resin B containing 15 to 89.9% by mass of constituent units derived from acrylonitrile, 7.1 to 82% by mass of constituent units derived from halogen-containing monomers, and 3 to 20% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, with |CtA1-CtB1| being 0 to 19.0% by mass. It is preferable that |CtA2-CtB2| is 0 to 16% by mass. This makes it easier for |CtA1-CtB1| to be between 0 and 16 mass%. It is more preferable for |CtA2-CtB2| to be between 0 and 10 mass%. This makes it easier for |CtA1-CtB1| to be between 0 and 10 mass%.

[0044] The monomer composition B preferably contains 40-72% by mass of acrylonitrile, 25-57% by mass of halogen-containing monomers, and 3-15% by mass of sulfonic acid group-containing vinyl monomers. This makes it possible to obtain an acrylonitrile-based resin B (modacrylic resin B) containing 40-72% by mass of constituent units derived from acrylonitrile, 25-57% by mass of constituent units derived from halogen-containing monomers, and 3-15% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. The monomer composition B more preferably contains 45-72% by mass of acrylonitrile, 25-52% by mass of halogen-containing monomers, and 3-10% by mass of sulfonic acid group-containing vinyl monomers. This makes it possible to obtain an acrylonitrile-based resin B (modacrylic resin B) that contains 45-72% by mass of constituent units derived from acrylonitrile, 25-52% by mass of constituent units derived from halogen-containing monomers, and 3-10% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0045] In monomer composition B, the sulfonic acid group-containing vinyl monomer is not particularly limited, but is preferably one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof, and more preferably one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, and metal salts thereof. The salt may also be an alkali metal salt such as a sodium salt. This reduces costs and makes it easier to obtain an acrylonitrile-based resin B (modacrylic resin B) in which halogen-containing monomers and sulfonic acid group-containing vinyl monomers are copolymerized components and the polymerization ratio of acrylonitrile is high.

[0046] In step B, the water-soluble initiator described in step A can be used as appropriate. Furthermore, when using an oxidizing agent such as a persulfate as a water-soluble polymerization initiator, it is preferable to use it in combination with a reducing agent or polymerization accelerator from the viewpoint of improving polymerization efficiency, and the reducing agent and polymerization accelerator described in step A can be used as appropriate.

[0047] In step B, the amount of the water-soluble polymerization initiator is not particularly limited, but for example, it may be 0.1 to 1.0 parts by mass per 100 parts by mass of the total mass of monomers (monomer composition B). This makes it easier to obtain a modacrylic resin in an aqueous medium under conditions where a halogen-containing monomer and a sulfonic acid group-containing vinyl monomer are copolymerized components and the polymerization ratio of acrylonitrile is high. In step B, the amount of the reducing agent is not particularly limited, but for example, it may be 1 to 4 parts by mass per 1 part by mass of an oxidizing agent such as a persulfate. In step B, the amount of the polymerization accelerator is not particularly limited, but for example, it may be 0.5 to 2 parts by mass per 1 part by mass of an oxidizing agent such as a persulfate.

[0048] The monomers, water-soluble polymerization initiators (such as oxidizing agents), and water mentioned above, along with a reducing agent and a polymerization accelerator as needed, can be supplied to the polymerization reactor, and the temperature of the polymerization reactor can be increased to perform emulsion polymerization without emulsifiers. The monomers, water-soluble polymerization initiators, reducing agents, and polymerization accelerators 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 slurry of acrylonitrile resin B (preferably modacrylic resin B) obtained by polymerization can be dehydrated with salt and dried in the same way as in general precipitation polymerization to obtain powder of acrylonitrile resin B (preferably modacrylic resin B).

[0049] In step C, a mixed resin X can be obtained by mixing (dry blending) modacrylic resin A and acrylonitrile resin B (preferably modacrylic resin B) in a known manner. A powder (solid) mixer can be used for the mixing, and the mixer is not particularly limited, but examples include a hand mixer, tumbler mixer, V-type mixer, ribbon mixer, Hemmiel mixer, and super mixer.

[0050] The mixed resin X is not particularly limited to being a mixture of modacryl resin A and acrylonitrile resin B (preferably modacryl resin B), but can be confirmed, for example, by the difference in solubility of modacryl resin A and acrylonitrile resin B in a given solvent, or by nuclear magnetic resonance (NMR) analysis.

[0051] (Acrylonitrile fibers and methods for producing the same) In one or more embodiments of the present invention, the acrylonitrile fiber contains a mixed resin X. The acrylonitrile fiber contains a mixed resin X which is a mixture of modacrylic resin A and acrylonitrile resin B (preferably modacrylic resin B), thereby suppressing voids. When the acrylonitrile fiber contains a mixed resin X which is a mixture of modacrylic resin A and modacrylic resin B, it is also called a modacrylic fiber. When the total mass of the resin components constituting the acrylonitrile fiber is 100% by mass, the content of the mixed resin X is preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and the resin components constituting the acrylonitrile fiber may consist of 100% by mass of the mixed resin X.

[0052] The method for producing the acrylonitrile fiber (preferably modacrylic fiber) is not particularly limited, but for example, a wet spinning method is preferred. Wet spinning can be performed by dissolving a mixed resin X in an organic solvent containing one or more selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), and dimethylformamide (DMF), and then extruding the spinning solution through a nozzle into a coagulation bath to coagulate it. Wet spinning can be performed in the same manner as wet spinning of general modacrylic fiber, except that the aforementioned spinning solution is used. Next, the obtained undrawn yarn (coagulated yarn) can be washed with water and then dried to obtain the acrylonitrile fiber (preferably modacrylic fiber). Washing may be performed using water at 20°C or higher. Drying may be performed at room temperature (25±5°C). By using the mixed resin X, acrylonitrile fiber (preferably modacrylic fiber) with suppressed voids can be obtained.

[0053] The nozzle can be used as appropriate to match the desired fiber cross-section. The fiber cross-section is not particularly limited and can be circular, elliptical, H-shaped (also called dumbbell-shaped), or other irregular shapes. As the coagulation bath, an aqueous solution of the organic solvent described above can be used, and the concentration of the organic solvent is not particularly limited, but may be, for example, 20-70% by mass, 25-65% by mass, or 30-60% by mass.

[0054] The single fiber fineness of the undrawn yarn (filament) is not particularly limited and can be set appropriately depending on the purpose and application, for example, it may be 0.5 to 500 dtex or 1 to 300 dtex. In this specification, the single fiber fineness of the undrawn yarn (filament) can be measured in accordance with JIS L 1013.

[0055] The acrylonitrile fiber (undrawn yarn) preferably has 10 or fewer voids per fiber cross-section, more preferably 5 or fewer, even more preferably 3 or fewer, and still more preferably 1.0 or fewer. In this specification, the number of voids per fiber cross-section of the acrylonitrile fiber (undrawn yarn) can be measured and calculated as described in the examples.

[0056] In the aforementioned acrylonitrile fiber (undrawn yarn), it is preferable that the mixed resin X forms a single phase. When |CtA1-CtB1| is 0 to 10% by mass, the compatibility between modacrylic resin A and acrylonitrile resin B (preferably modacrylic resin B) is good, and the mixed resin X, consisting of modacrylic resin A and acrylonitrile resin B (preferably modacrylic resin B), is more likely to exist as a single phase in the fiber.

[0057] The undrawn yarn may be wet-drawn before washing or before drying after washing, if necessary. Alternatively, it may be dry-drawn after drying, if necessary. In the drawing process, the draw ratio (length of the fiber after drawing / length of the fiber before drawing) is not particularly limited and may be, for example, greater than 1 and less than or equal to 8 times, 1.1 to 6 times, or 1.5 to 5 times. The drawn yarn may be relaxed in a heat relaxation process, if necessary.

[0058] Undrawn or drawn yarns may be used as filaments in their original state as acrylonitrile fibers (preferably modacrylic fibers), or they may be cut to a predetermined length as needed and used as stapled acrylonitrile fibers (preferably modacrylic fibers). The drawn yarns may be crimped before cutting as needed.

[0059] The acrylonitrile fiber (preferably modacrylic fiber) may be either short fiber or long fiber (filament), and can be appropriately selected depending on the purpose and method of use. The fiber length of the acrylonitrile fiber (preferably modacrylic fiber) can be appropriately selected depending on the purpose and method of use. For example, in the case of short-cut fibers, the fiber length may be 0.1 to 5 mm, and in the case of short fibers, the fiber length may be 15 to 176 mm, 20 to 160 mm, 25 to 138 mm, or 30 to 128 mm.

[0060] The acrylonitrile fibers (preferably modacrylic fibers) may be used in various flame-retardant materials such as flame-retardant nonwoven fabrics and flame-retardant woven fabrics. Furthermore, the acrylonitrile fibers (preferably modacrylic fibers) may be used in combination with other fibers in various flame-retardant materials such as flame-retardant nonwoven fabrics and flame-retardant woven fabrics. [Examples]

[0061] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0062] First, we will explain the various measurement and evaluation methods. (1) Composition analysis of the resin The nitrogen content (mass%) in modacryl resin (or mixed resin) was determined using an elemental analyzer (JM-11, manufactured by J-Science Lab Co., Ltd.), and then converted to the content (mass%) of constituent units derived from acrylonitrile. Using a nuclear magnetic resonance spectrometer (Jeol, "ECA-500NMR"), 1 1H NMR measurements were performed to calculate the content (mass%) of constituent units derived from sulfonic acid group-containing vinyl monomers in modacryl resin (or mixed resin). Based on the content (mass%) of constituent units derived from acrylonitrile and the content (mass%) of constituent units derived from sulfonic acid group-containing vinyl monomers, the content (mass%) of constituent units derived from halogen-containing monomers in modacryl resin (or mixed resin) was calculated. (2) Mass-average molecular weight of the resin The mass-average molecular weight of modacryl resin was measured and calculated using the GPC method with gel permeation chromatography (HLC-8320GPC, manufactured by Tosoh Corporation). Polystyrene was used as the standard polymer, and dimethylformamide was used as the mobile phase (eluent). (3) Specific viscosity of the resin (ηsp) 1.0 g of modacryl resin was dissolved in 500 mL of dimethylformamide, and the specific viscosity was measured at 30°C using an Ostwald viscometer. (4) Single fiber fineness The single fiber fineness of modacrylic fibers (undrawn yarn) was measured according to JIS L 1013. (5) Void number Cross-sections of modacrylic fibers (undrawn yarns) were cut out, and cross-sectional images were taken using a microscope (Keyence Corporation, product name "VK-X120"). The number of voids present in 12 arbitrarily selected fiber cross-sections from the obtained images was measured, and the arithmetic mean was calculated to determine the number of voids per fiber cross-section.

[0063] (Manufacturing Example 1) In the polymerization reactor, 50.7 parts by mass of vinyl chloride (hereinafter also referred to as VCM), 4 parts by mass of acrylonitrile (hereinafter also referred to as AN), 186 parts by mass of deionized water, 0.02 parts by mass of ammonium persulfate, 0.53 parts by mass of sodium bisulfite, 0.003 parts by mass of iron sulfate, 0.35 parts by mass of sulfuric acid (64% by mass), and 0.87 parts by mass of sodium lauryl sulfate were charged. Then, the temperature in the polymerization reactor was raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 5.5 hours. During polymerization, 44.8 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until the 5th hour, and 0.5 parts by mass of sodium styrenesulfonate (hereinafter also referred to as SSS) dissolved in 7 parts by mass of deionized water and 0.27 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water were continuously supplied at a constant rate from the start to the end of polymerization. After the polymerization was completed, unreacted monomers in the polymerization reactor were recovered, and the latex was discharged. The obtained modacryl resin latex was subjected to salting-out, dehydration, washing with water, and drying to obtain modacryl resin I. The obtained modacryl resin I consisted of 49.5% by weight of constituent units derived from acrylonitrile, 50.0% by mass of constituent units derived from vinyl chloride, and 0.5% by mass of constituent units derived from sodium styrenesulfonate. Its mass-average molecular weight was approximately 87,000, and its specific viscosity was 0.170.

[0064] (Manufacturing example 2) In the polymerization reactor, 30 parts by mass of vinyl chloride, 10 parts by mass of acrylonitrile, 10 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as AMPSNa), 383 parts by mass of deionized water, 0.04 parts by mass of ammonium persulfate, 1.06 parts by mass of sodium bisulfite, 0.005 parts by mass of iron sulfate, and 0.35 parts by mass of sulfuric acid (64% by mass) were charged. Then, the temperature in the polymerization reactor was raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 6 hours. During polymerization, 50 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until 5.5 hours, and 0.54 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water was continuously supplied at a constant rate from the start to the end of polymerization. After the polymerization was completed, the unreacted monomers in the polymerization reactor were recovered, and the slurry was discharged. The obtained slurry was dehydrated and dried in a hot air dryer at 60°C for 24 hours to obtain modacryl resin II. The obtained modacryl resin II consisted of 56.6% by mass of constituent units derived from acrylonitrile, 38.0% by mass of constituent units derived from vinyl chloride, and 5.4% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was approximately 59,000, and its specific viscosity was 0.126.

[0065] (Manufacturing Example 3) In the polymerization reactor, 20 parts by mass of vinyl chloride, 12 parts by mass of acrylonitrile, 5 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate, 263 parts by mass of deionized water, 0.03 parts by mass of ammonium persulfate, 0.66 parts by mass of sodium bisulfite, 0.013 parts by mass of iron sulfate, and 0.35 parts by mass of sulfuric acid (64% by mass) were charged. Then, the temperature in the polymerization reactor was raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 6 hours. During polymerization, 58 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until 5.5 hours, 5.0 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate dissolved in 20 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 hours, and 0.54 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water was supplied continuously at a constant rate from the start to the end of polymerization. After the polymerization was completed, the unreacted monomers in the polymerization reactor were recovered, and the slurry was discharged. The obtained slurry was dehydrated and dried in a hot air dryer at 60°C for 24 hours to obtain Modacryl Resin III. The obtained Modacryl Resin III consisted of 59.1% by mass of constituent units derived from acrylonitrile, 33.4% by mass of constituent units derived from vinyl chloride, and 7.5% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was approximately 70,000, and its specific viscosity was 0.167.

[0066] (Manufacturing example 4) In a polymerization reactor, 20 parts by mass of vinyl chloride, 12 parts by mass of acrylonitrile, 10 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate, 283 parts by mass of deionized water, 0.03 parts by mass of ammonium persulfate, 0.66 parts by mass of sodium bisulfite, 0.026 parts by mass of iron sulfate, and 0.35 parts by mass of sulfuric acid (64% by mass) were charged. The temperature in the polymerization reactor was then raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 6 hours. During polymerization, 58 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until 5.5 hours later, and 0.34 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water was continuously supplied at a constant rate from the start to the end of polymerization. After polymerization was completed, unreacted monomers in the polymerization reactor were recovered, and the slurry was discharged. The obtained slurry was dehydrated and dried in a hot air dryer at 60°C for 24 hours to obtain modacryl resin IV. The obtained modacryl resin IV consisted of 64.5% by mass of constituent units derived from acrylonitrile, 27.7% by mass of constituent units derived from vinyl chloride, and 7.8% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was approximately 65,000, and its specific viscosity was 0.163.

[0067] (Manufacturing example 5) In the polymerization reactor, 10 parts by mass of vinyl chloride, 16 parts by mass of acrylonitrile, 263 parts by mass of deionized water, 0.03 parts by mass of ammonium persulfate, 0.53 parts by mass of sodium bisulfite, 0.026 parts by mass of iron sulfate, and 0.35 parts by mass of sulfuric acid (64% by mass) were charged. Then, the temperature in the polymerization reactor was raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 6 hours. During polymerization, 64 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until 5.5 hours, 10.0 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate dissolved in 30 parts by mass of deionized water was supplied from immediately after the start of polymerization until 5.5 hours, and 0.27 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water was supplied continuously at a constant rate from the start to the end of polymerization. After the polymerization was completed, the unreacted monomers in the polymerization reactor were recovered, and the slurry was discharged. The obtained slurry was dehydrated and dried in a hot air dryer at 60°C for 24 hours to obtain modacryl resin V. The obtained modacryl resin V consisted of 81.4% by mass of constituent units derived from acrylonitrile, 10.3% by mass of constituent units derived from vinyl chloride, and 8.3% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was approximately 120,000 and its specific viscosity was 0.269.

[0068] (Manufacturing example 6) In the polymerization reactor, 20 parts by mass of vinyl chloride, 12 parts by mass of acrylonitrile, 5 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate, 263 parts by mass of deionized water, 0.03 parts by mass of ammonium persulfate, 0.66 parts by mass of sodium bisulfite, 0.026 parts by mass of iron sulfate, and 0.35 parts by mass of sulfuric acid (64% by mass) were charged. Then, the temperature in the polymerization reactor was raised to 50°C to start polymerization, and polymerization was carried out at 50°C for 6 hours. During polymerization, 58 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until 5.5 hours, 5.0 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate dissolved in 20 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 hours, and 0.54 parts by mass of ammonium persulfate dissolved in 17 parts by mass of deionized water was supplied continuously at a constant rate from the start to the end of polymerization. After the polymerization was completed, the unreacted monomers in the polymerization reactor were recovered, and the slurry was discharged. The obtained slurry was dewatered and dried in a hot air dryer at 60°C for 24 hours to obtain modacrylic resin VI. The obtained modacryl resin VI consisted of 72.5% by mass of constituent units derived from acrylonitrile, 22.5% by mass of constituent units derived from vinyl chloride, and 5.0% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was approximately 112,000, and its specific viscosity was 0.227.

[0069] (Example 1) <Preparation of mixed resins> 70 parts by mass of modacrylic resin I and 30 parts by mass of modacrylic resin II were mixed with a hand mixer to obtain a mixed resin I consisting of 70% by mass of modacrylic resin I and 30% by mass of modacrylic resin II. <Production of modacrylic fibers> Mixed resin I was dissolved in dimethyl sulfoxide to a resin concentration of 27% by mass to obtain a spinning solution. The obtained spinning solution was extruded into a 47% by mass aqueous solution of dimethyl sulfoxide (coagulation bath) using a nozzle with an H-shaped (dumbbell-shaped) pore shape, a pore diameter (equivalent diameter) of 0.3 mm, and 12 holes, and allowed to coagulate. Then it was washed with water at 25°C and dried at room temperature (25±5°C) to obtain modacrylic fibers.

[0070] (Example 2) <Preparation of mixed resins> Mixed resin I was prepared in the same manner as in Example 1. <Production of modacrylic fibers> Modacryl fibers were prepared in the same manner as in Example 1, except that a 55% by mass aqueous solution of dimethyl sulfoxide was used as the coagulation bath.

[0071] (Example 3) <Preparation of mixed resins> 80 parts by mass of modacrylic resin I and 20 parts by mass of modacrylic resin II were mixed with a hand mixer to obtain a mixed resin II consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin II. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin II was used.

[0072] (Example 4) <Preparation of mixed resins> Mixed resin II was prepared in the same manner as in Example 3. <Production of modacrylic fibers> Modacryl fibers were prepared in the same manner as in Example 3, except that a 55% by mass aqueous solution of dimethyl sulfoxide was used as the coagulation bath.

[0073] (Example 5) <Preparation of mixed resins> 50 parts by mass of modacrylic resin I and 50 parts by mass of modacrylic resin II were mixed with a hand mixer to obtain a mixed resin III consisting of 50% by mass of modacrylic resin I and 50% by mass of modacrylic resin II. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin III was used.

[0074] (Example 6) <Preparation of mixed resins> 80 parts by mass of modacrylic resin I and 20 parts by mass of modacrylic resin III were mixed with a hand mixer to obtain a mixed resin IV consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin III. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin IV was used.

[0075] (Example 7) <Preparation of mixed resins> 80 parts by mass of modacrylic resin I and 20 parts by mass of modacrylic resin IV were mixed with a hand mixer to obtain a mixed resin V consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin IV. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin V was used.

[0076] (Comparative Example 1) Modacrylic fibers were prepared in the same manner as in Example 1, except that modacrylic resin A1 was used instead of mixed resin I.

[0077] (Comparative Example 2) Modacryl fibers were prepared in the same manner as in Comparative Example 1, except that a 70% by mass aqueous solution of dimethyl sulfoxide was used as the coagulation bath.

[0078] (Comparative Example 3) <Preparation of mixed resins> 80 parts by mass of modacrylic resin I and 20 parts by mass of modacrylic resin V were mixed in a hand mixer to obtain a mixed resin VI consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin V. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin VI was used.

[0079] (Comparative Example 4) <Preparation of mixed resins> 65 parts by mass of modacrylic resin I and 35 parts by mass of modacrylic resin VI were mixed with a hand mixer to obtain a mixed resin VII consisting of 65% by mass of modacrylic resin I and 35% by mass of modacrylic resin V. <Production of modacrylic fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that mixed resin VII was used.

[0080] In Production Examples 1 to 6, the composition of the modacrylic resin (content of constituent units derived from each monomer), mass-average molecular weight (Mw), and specific viscosity (ηsp) were measured as described above. The composition of the mixed resin (content of constituent units derived from each monomer) was measured as described above. In addition, the single fiber fineness and void number of the modacrylic fibers were measured as described above in the Examples and Comparative Examples. These results are shown in Tables 1 and 2 below. Figures 1 to 3 show cross-sectional photographs (200x magnification) of the modacrylic fibers of Example 1, Comparative Example 1, and Comparative Example 3, respectively. In Tables 1 and 2 below, AN represents a constituent unit derived from acrylonitrile, VCM represents a constituent unit derived from vinyl chloride, SSS represents a constituent unit derived from sodium styrenesulfonate, AMPSNa represents a constituent unit derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate, and SM represents a constituent unit derived from sulfonic acid group-containing vinyl monomer.

[0081] [Table 1]

[0082] [Table 2]

[0083] As can be seen from Table 1 and Figure 1 above, in Examples 1 to 7, modacrylic fibers with almost no voids and good appearance were obtained. On the other hand, as can be seen from Table 2 and Figure 2, in the case of modacryl fibers of Comparative Examples 1 and 2, which used only modacryl resin A, a large number of voids were generated, resulting in a poor appearance. Also, as can be seen from Table 2 and Figure 3, in the case of modacryl fibers of Comparative Examples 3 and 4, which used two types of modacryl resin, but where the difference in the content of constituent units derived from acrylonitrile between the two types of modacryl resins exceeded 20% by mass, many voids were present in the fiber cross-section, resulting in a poor appearance.

[0084] The present invention is not particularly limited, but preferably includes, for example, the following embodiments. [1] A mixed resin comprising modacryl resin A and acrylonitrile resin B, Modacryl resin A contains 35-69.9% by mass of constituent units derived from acrylonitrile, 30-64.9% by mass of constituent units derived from halogen-containing monomers, and 0.1-1.5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Acrylonitrile resin B contains 15 to 89.9% by mass of constituent units derived from acrylonitrile, 7.1 to 82% by mass of constituent units derived from halogen-containing monomers, and 3 to 20% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. If the content of acrylonitrile-derived constituent units in modacryl resin A is denoted as CtA1 by mass, and the content of acrylonitrile-derived constituent units in acrylonitrile-based resin B is denoted as CtB1 by mass, then |CtA1-CtB1| is between 0 and 19.0% by mass. A mixed resin in which the content of constituent units derived from sulfonic acid group-containing vinyl monomers is 1.2 to 5.0% by mass. [2] The mixed resin according to [1], wherein |CtA1-CtB1| is 0 to 10% by mass. [3] The mixed resin according to [1] or [2], wherein the CtB1 is higher than the CtA1. [4] A mixed resin according to any one of [1] to [3], wherein the content of modacryl resin A is 50 to 90% by mass and the content of acrylonitrile resin B is 10 to 50% by mass. [5] The mixed resin according to any one of [1] to [4], wherein the halogen-containing monomer comprises one or more selected from the group consisting of vinyl chloride and vinylidene chloride. [6] The mixed resin according to any one of [1] to [5], wherein the sulfonic acid group-containing vinyl monomer comprises one or more selected from the group consisting of styrene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, and metal salts thereof. [7] Modacryl resin A, wherein the sulfonic acid group-containing vinyl monomer comprises one or more selected from the group consisting of styrene sulfonic acid and its metal salts, as a mixed resin according to any one of [1] to [6]. [8] The mixed resin according to any one of [1] to [7], wherein the acrylonitrile resin B comprises one or more sulfonic acid group-containing vinyl monomers selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof. A method for producing a mixed resin as described in any of [9] [1] to [8], Step A: Polymerizing monomer composition A to obtain modacrylic resin A, Step B involves polymerizing monomer composition B to obtain acrylonitrile resin B, and The process includes a step of mixing modacryl resin A and acrylonitrile resin B. Monomer composition A contains 35-69.9% by mass of acrylonitrile, 30-64.9% by mass of halogen-containing monomers, and 0.1-1.5% by mass of sulfonic acid group-containing vinyl monomers. Monomer composition B contains 15-89.9% by mass of acrylonitrile, 7.1-82% by mass of halogen-containing monomers, and 3-20% by mass of sulfonic acid group-containing vinyl monomers. If the acrylonitrile content in monomer composition A is CtA 2% by mass, and the acrylonitrile content in monomer composition B is CtB 2% by mass, then |CtA 2 - CtB 2| is 0 to 19.0% by mass. Step A is carried out in the presence of water, a water-soluble polymerization initiator, and an emulsifier, and Step B is a method for producing a mixed resin, carried out in the presence of water and a water-soluble polymerization initiator, but under conditions where an emulsifier is substantially absent. Acrylonitrile fibers containing the mixed resin described in any of [1] to [8].

[11] The acrylonitrile fiber according to

[10] , wherein the mixed resin forms a single phase.

[12] A method for producing acrylonitrile fibers, The process includes dissolving the mixed resin described in any of [1] to [8] in an organic solvent and wet spinning it, A method for producing acrylonitrile fibers, wherein the organic solvent comprises one or more selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

Claims

1. A mixed resin comprising modacryl resin A and acrylonitrile resin B, Modacryl resin A contains 35 to 69.9% by mass of constituent units derived from acrylonitrile, 30 to 64.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 1.5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Acrylonitrile resin B contains 15 to 89.9% by mass of constituent units derived from acrylonitrile, 7.1 to 82% by mass of constituent units derived from halogen-containing monomers, and 3 to 20% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. If the content of constituent units derived from acrylonitrile in modacryl resin A is denoted as CtA 1% by mass, and the content of constituent units derived from acrylonitrile in acrylonitrile-based resin B is denoted as CtB 1% by mass, then |CtA 1 - CtB 1| is between 0 and 19.0% by mass. The mixed resin wherein the content of constituent units derived from sulfonic acid group-containing vinyl monomers in the mixed resin is 1.2 to 5.0% by mass.

2. The mixed resin according to claim 1, wherein the |CtA1-CtB1| is 0 to 10% by mass.

3. The mixed resin according to claim 1, wherein CtB1 is higher than CtA1.

4. The mixed resin according to claim 1, wherein the content of modacryl resin A is 50 to 90% by mass, and the content of acrylonitrile resin B is 10 to 50% by mass.

5. The mixed resin according to claim 1, wherein the halogen-containing monomer comprises one or more selected from the group consisting of vinyl chloride and vinylidene chloride.

6. The mixed resin according to claim 1, wherein the sulfonic acid group-containing vinyl monomer comprises one or more selected from the group consisting of styrene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, and metal salts thereof.

7. The mixed resin according to claim 1, wherein the modacryl resin A contains one or more sulfonic acid group-containing vinyl monomers selected from the group consisting of styrene sulfonic acid and its metal salts.

8. The mixed resin according to claim 1, wherein the acrylonitrile resin B comprises one or more sulfonic acid group-containing vinyl monomers selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof.

9. A method for producing a mixed resin according to any one of claims 1 to 8, Step A: Polymerizing monomer composition A to obtain modacrylic resin A, Step B involves polymerizing monomer composition B to obtain acrylonitrile resin B, and The process includes a step of mixing modacryl resin A and acrylonitrile resin B. Monomer composition A contains 35 to 69.9% by mass of acrylonitrile, 30 to 64.9% by mass of halogen-containing monomer, and 0.1 to 1.5% by mass of sulfonic acid group-containing vinyl monomer. Monomer composition B contains 15 to 89.9% by mass of acrylonitrile, 7.1 to 82% by mass of halogen-containing monomers, and 3 to 20% by mass of sulfonic acid group-containing vinyl monomers. When the acrylonitrile content in monomer composition A is CtA 2% by mass, and the acrylonitrile content in monomer composition B is CtB 2% by mass, |CtA 2 - CtB 2| is 0 to 19.0% by mass. Step A is carried out in the presence of water, a water-soluble polymerization initiator, and an emulsifier, and Step B is a method for producing a mixed resin, carried out in the presence of water and a water-soluble polymerization initiator, and under conditions where an emulsifier is substantially absent.

10. Acrylonitrile fiber comprising the mixed resin described in any one of claims 1 to 8.

11. The acrylonitrile fiber according to claim 10, wherein the mixed resin forms a single phase.

12. A method for producing acrylonitrile fibers, The process includes dissolving the mixed resin according to any one of claims 1 to 8 in an organic solvent and wet spinning it, A method for producing acrylonitrile fibers, wherein the organic solvent comprises one or more selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

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