Modacrylic resin, modacrylic fibers containing the same, and methods for producing the same.

Abstract

This invention provides modacrylic fibers with high flame retardancy and strength, and a method for producing the same. [Solution] A modacryl resin comprising modacryl resin A and modacryl resin B, wherein modacryl resin A contains 35% to less than 55% by mass of acrylonitrile-derived constituent units, 40 to 64.5% by mass of halogen-containing monomer-derived constituent units, and 0.5 to 5% by mass of sulfonic acid group-containing vinyl monomer-derived constituent units; modacryl resin B contains 55 to 84.9% by mass of acrylonitrile-derived constituent units, 15 to 44.9% by mass of halogen-containing monomer-derived constituent units, and 0.1 to 5% by mass of sulfonic acid group-containing vinyl monomer-derived constituent units; the ratio MwB / MwA of the mass average molecular weight MwA of modacryl resin A to the mass average molecular weight MwB of modacryl resin B is 1.5 to 3.5; the content of modacryl resin A is 50 to 90% by mass; and the content of modacryl resin B is 10 to 50% by mass.

Description

Technical Field

[0001] The present invention relates to a modacrylic resin that can be suitably used for flame-retardant materials, a modacrylic fiber containing the same, and methods for producing them.

Background Art

[0002] Modacrylic fibers using a copolymer obtained by copolymerizing acrylonitrile and a halogen-containing monomer such as vinyl chloride are used as flame-retardant materials because they have flame retardancy. For example, Patent Document 1 describes a flame-retardant nonwoven fabric using a flame-retardant fiber obtained by melt spinning a copolymer composed of 51.0% by weight of acrylonitrile, 48.0% by weight of vinylidene chloride, and 1.0% by weight of sodium p-styrenesulfonate. Patent Document 2 describes a flame-retardant fabric using a fiber composed of a copolymer consisting of 49.5% by weight of acrylonitrile, 49.5% by weight of vinyl chloride, and 1.0% by weight of sodium styrenesulfonate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, modacrylic fibers as described in Patent Documents 1 and 2 have slightly lower strength than other synthetic fibers, and improvement in strength is required.

[0005] In order to solve the above conventional problems, the present invention provides a modacrylic resin that can improve strength while maintaining high flame retardancy of modacrylic fibers when used in wet spinning, a modacrylic fiber containing the same, and methods for producing them. [Means for solving the problem]

[0006] One or more embodiments of the present invention relate to a modacryl resin comprising modacryl resin A and modacryl resin B, wherein modacryl resin A contains 35% by mass or more and less than 55% by mass of constituent units derived from acrylonitrile, 40 to 64.5% by mass of constituent units derived from halogen-containing monomers, and 0.5 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers; modacryl resin B contains 55 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 44.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers; the ratio MwB / MwA of the mass average molecular weight MwA of modacryl resin A to the mass average molecular weight MwB of modacryl resin B is 1.5 to 3.5; the content of modacryl resin A is 50 to 90% by mass; and the content of modacryl resin B is 10 to 50% by mass.

[0007] One or more embodiments of the present invention relate to a method for producing modacryl resin, comprising: step A, polymerizing monomer composition A to obtain modacryl resin A; step B, polymerizing monomer composition B to obtain modacryl resin B; and step B, mixing modacryl resin A and modacryl resin B, wherein monomer composition A contains 35% by mass or more and less than 55% by mass of acrylonitrile, 40 to 64.5% by mass of halogen-containing monomer, and 0.5 to 5% by mass of sulfonic acid group-containing vinyl monomer; monomer composition B contains 55 to 84.9% by mass of acrylonitrile, 15 to 44.9% by mass of halogen-containing monomer, and 0.1 to 5% by mass of sulfonic acid group-containing vinyl monomer; 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, under conditions where an emulsifier is substantially absent.

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

[0009] One or more embodiments of the present invention relate to a method for producing modacrylic fibers, comprising the steps of wet spinning the modacrylic resin and stretching the undrawn yarn obtained by wet spinning. [Effects of the Invention]

[0010] According to one or more embodiments of the present invention, it is possible to provide a modacrylic resin that yields modacrylic fibers with improved strength while maintaining high flame retardancy, and modacrylic fibers that have high flame retardancy and improved strength. [Modes for carrying out the invention]

[0011] The inventors of the present invention conducted extensive research to solve the above-mentioned problems. As a result, they found that by using a modacryl resin (hereinafter also referred to as modacryl resin X), which is a mixed resin consisting of modacryl resin A, which has a low content of structural units derived from acrylonitrile, and modacryl resin B, which has a high content of structural units derived from acrylonitrile, and by setting the ratio of the mass average molecular weight MwA of modacryl resin A to the mass average molecular weight MwB of modacryl resin B, MwB / MwA, and the blending ratio of modacryl resin A to modacryl resin B within a predetermined range, modacryl fibers containing modacryl resin X exhibit high flame retardancy and improved strength. Modacrylic resin X can preferably be obtained by mixing modacrylic resin A obtained by emulsion polymerization and modacrylic resin B obtained by emulsion polymerization without emulsifiers (also called precipitation polymerization). Modacrylic resin is usually produced by radical emulsion polymerization. Generally, to increase fiber strength, it is thought that the molecular weight of the resin constituting the fiber should be increased. In the case of modacrylic resin, since halogen-containing monomers such as vinyl chloride have a high chain transfer coefficient, it is difficult to increase the molecular weight by increasing the content of halogen-containing monomers. Although there remains the possibility of increasing the molecular weight by increasing the proportion of acrylonitrile, increasing acrylonitrile impairs the stability of emulsion polymerization, making it difficult to achieve both polymerization stability and molecular weight increase. Therefore, in this application, by using modacrylic resin X, which is obtained by mixing modacrylic resin A, which has a low content of constituent units derived from acrylonitrile obtained by emulsion polymerization, with modacrylic resin B, which has a high content of constituent units derived from acrylonitrile obtained by emulsion polymerization (precipitation polymerization) without emulsifiers, we were able to obtain modacrylic fibers that have high flame retardancy and improved strength.

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

[0013] (Modacrylic resin X and method for producing the same) Modacrylic resin A contains 35% to less than 55% by mass of constituent units derived from acrylonitrile, 40 to 64.5% by mass of constituent units derived from halogen-containing monomers, and 0.5 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Modacrylic resin B contains 55 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 44.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. This results in good flame retardancy and strength of modacrylic fibers containing modacrylic resin X.

[0014] Modacrylic resin A preferably contains 38-54% by mass of constituent units derived from acrylonitrile, 42-61.5% by mass of constituent units derived from halogen-containing monomers, and 0.5-5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers, and more preferably contains 40-50% by mass of constituent units derived from acrylonitrile, 45-59.5% by mass of constituent units derived from halogen-containing monomers, and 0.5-5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0015] Modacrylic resin B preferably contains 60 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 39.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers; more preferably contains 65 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 34.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers; and even more preferably contains 70 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 29.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0016] From the viewpoint of further enhancing flame retardancy and strength, it is more preferable that modacryl resin X consists of modacryl resin A, which has a low content of structural units derived from acrylonitrile and a high content of structural units derived from halogen-containing monomers, and modacryl resin B, which has a high content of structural units derived from acrylonitrile and a low content of structural units derived from halogen-containing monomers. In other words, in modacryl resin X, it is preferable that the content of structural units derived from acrylonitrile in modacryl resin A is lower than the content of structural units derived from acrylonitrile in modacryl resin B, and that the content of structural units derived from halogen-containing monomers in modacryl resin A is higher than the content of structural units derived from halogen-containing monomers in modacryl resin B.

[0017] The halogen-containing monomer may be a vinyl halide or a vinylidene halide. The vinyl halide is not particularly limited and examples include vinyl chloride, vinyl bromide, and vinyl iodide. The vinylidene halide is not particularly limited and examples include vinylidene chloride, vinylidene bromide, and vinylidene iodide. These halogen-containing monomers may be used individually or in combination of two or more. Preferably, the halogen-containing monomer includes one or more selected from the group consisting of vinyl chloride and vinylidene chloride.

[0018] The sulfonic acid group-containing vinyl monomer is not particularly limited, but 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 salts include alkali metal salts such as sodium salts and potassium salts, and ammonium salts. These sulfonic acid group vinyl monomers may be used individually or in combination of two or more. Preferably, the sulfonic acid group-containing vinyl monomer contains one or more 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.

[0019] In the modacrylic resin A, the structural unit derived from the sulfonic acid group-containing vinyl monomer is not particularly limited, but is preferably a structural unit derived from one or more selected from the group consisting of styrenesulfonic acid and alkali metal salts of styrenesulfonic acid, and more preferably a structural unit derived from an alkali metal salt of styrenesulfonic acid. Thereby, the stability of emulsion polymerization using a halogen-containing monomer and a sulfonic acid group-containing vinyl monomer as copolymerization components can be enhanced.

[0020] In the modacrylic resin B, the structural unit derived from the sulfonic acid group-containing vinyl monomer is not particularly limited, but is preferably a structural unit derived from 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 a structural unit derived from one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, and metal salts thereof. Thereby, it becomes easier to obtain a modacrylic resin in which a halogen-containing monomer and a sulfonic acid group-containing vinyl monomer are used as copolymerization components and the polymerization ratio of acrylonitrile is high. The salt may be an alkali metal salt such as a sodium salt.

[0021] The ratio MwB / MwA of the mass average molecular weight MwA of the modacrylic resin A and the mass average molecular weight MwB of the modacrylic resin B is 1.5 to 3.5. Thereby, while enhancing the spinnability and drawability when wet-spinning the modacrylic resin X with a mixed resin of the modacrylic resin A and the modacrylic resin B, a modacrylic fiber having high flame retardancy and strength can be obtained. MwB / MwA is more preferably 1.7 to 3.4, still more preferably 1.9 to 3.3, and still more preferably 2.1 to 3.2.

[0022] The mass average molecular weight MwA of the modacrylic resin A is not particularly limited as long as MwB / MwA satisfies the above-mentioned range. For example, from the viewpoints of increasing the resin concentration of the spinning solution to achieve a dense fiber structure and the stability of emulsion polymerization, the mass average molecular weight is preferably 10,000 to 300,000, more preferably 20,000 to 200,000, and even more preferably 30,000 to 150,000.

[0023] The mass average molecular weight MwB of the modacrylic resin B is not particularly limited as long as MwB / MwA satisfies the above-mentioned range. For example, from the viewpoints of increasing the resin concentration of the spinning solution to achieve a dense fiber structure and being able to achieve both fiber strength, the mass average molecular weight is preferably 100,000 to 500,000, more preferably 120,000 to 400,000, and even more preferably 150,000 to 300,000.

[0024] The specific viscosity of the modacrylic resin A is not particularly limited. For example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.05 to 0.35, or 0.10 to 0.30. In this specification, the specific viscosity can be measured as described in the examples.

[0025] The specific viscosity of the modacrylic resin B is not particularly limited. For example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.35 to 0.60, or 0.35 to 0.50.

[0026] Modacrylic resin X contains 50 to 90% by mass of modacrylic resin A and 10 to 50% by mass of modacrylic resin B. This makes it possible to obtain modacrylic fibers with improved strength while maintaining high flame retardancy using modacrylic resin X. From the viewpoint of further improving flame retardancy and strength, modacrylic resin X preferably contains 55 to 85% by mass of modacrylic resin A and 15 to 45% by mass of modacrylic resin B, more preferably contains 60 to 80% by mass of modacrylic resin A and 20 to 40% by mass of modacrylic resin B, and even more preferably contains 65 to 75% by mass of modacrylic resin A and 25 to 35% by mass of modacrylic resin B.

[0027] Modacrylic resin X may contain modacrylic resin A and modacrylic resin B in the above-mentioned proportions, and its monomer composition is not particularly limited. However, from the viewpoint of easily obtaining modacrylic fibers with improved flame retardancy and strength, it is preferable to contain 40-65% by mass of constituent units derived from acrylonitrile, 30-59% by mass of constituent units derived from halogen-containing monomers, and 1.0-5.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. It is more preferable to contain 45-60% by mass of constituent units derived from acrylonitrile, 35-54% by mass of constituent units derived from halogen-containing monomers, and 1.0-5.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. It is even more preferable to contain 45-60% by mass of constituent units derived from acrylonitrile, 37-54% by mass of constituent units derived from halogen-containing monomers, and 1.0-3.0% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0028] The mass-average molecular weight NwX of the modacryl resin X is not particularly limited, but from the viewpoint of increasing the resin concentration in the spinning solution, achieving a dense fiber structure, and easily achieving both fiber strength and mass-average molecular weight, it is preferably 80,000 to 500,000, more preferably 100,000 to 400,000, and even more preferably 150,000 to 300,000.

[0029] The specific viscosity of modacryl resin X is not particularly limited, but for example, when dimethylformamide is used as the solvent, the specific viscosity at 30°C may be 0.20 to 0.60 or 0.22 to 0.50.

[0030] The method for producing modacrylic 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 modacrylic resin B, and (3) The process includes step C of mixing modacrylic resin A and modacrylic resin B.

[0031] 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.

[0032] The monomer composition A preferably contains 35% to less than 55% by mass of acrylonitrile, 40 to 64.5% by mass of halogen-containing monomers, and 0.5 to 5% by mass of sulfonic acid group-containing vinyl monomers. This makes it possible to obtain modacryl resin A containing 35% to less than 55% by mass of constituent units derived from acrylonitrile, 40 to 64.5% by mass of constituent units derived from halogen-containing monomers, and 0.5 to 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.

[0033] Monomer composition A preferably contains 38-54% by mass of acrylonitrile, 42-61.5% by mass of halogen-containing monomers, and 0.5-5% by mass of sulfonic acid group-containing vinyl monomers, and more preferably contains 40-50% by mass of acrylonitrile, 45-59.5% by mass of halogen-containing monomers, and 0.5-5% by mass of sulfonic acid group-containing vinyl monomers.

[0034] 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 enhances the stability of emulsion polymerization in which acrylonitrile and halogen-containing monomers and sulfonic acid group-containing vinyl monomers are copolymer components.

[0035] 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 0.10 to 1.00 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).

[0036] 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.

[0037] 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 emulsifier is not particularly limited, but for example, from the viewpoint of polymerization stability and cleanability in post-treatment, it may be 0.10 to 3.00 parts by mass or 0.30 to 2.00 parts by mass per 100 parts by mass of the total mass of monomers (monomer composition A).

[0038] 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.

[0039] Step B is not particularly limited, but from the viewpoint of easily obtaining a modacryl resin with a high content of constituent units derived from acrylonitrile, it is desirable to carry out the monomer composition B by emulsifier-free emulsion polymerization in the presence of water and a water-soluble polymerization initiator, under conditions where emulsifiers are substantially absent. 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.

[0040] The monomer composition B preferably contains 55 to 84.9% by mass of acrylonitrile, 15 to 44.9% by mass of halogen-containing monomers, and 0.1 to 5% by mass of sulfonic acid group-containing vinyl monomers. This makes it possible to obtain modacryl resin B containing 55 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 44.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers.

[0041] Monomer composition B preferably contains 60-84.9% by mass of acrylonitrile, 15-39.9% by mass of halogen-containing monomers, and 0.1-5% by mass of sulfonic acid group-containing vinyl monomers; more preferably contains 65-84.9% by mass of acrylonitrile, 15-34.9% by mass of halogen-containing monomers, and 0.1-5% by mass of sulfonic acid group-containing vinyl monomers; and even more preferably contains 70-84.9% by mass of acrylonitrile, 15-29.9% by mass of halogen-containing monomers, and 0.1-5% by mass of sulfonic acid group-containing vinyl monomers.

[0042] 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 their metal salts, and more preferably one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, and their metal salts. This makes it easier to obtain a modacryl resin in which halogen-containing monomers and sulfonic acid group-containing vinyl monomers are copolymerized components and the polymerization ratio of acrylonitrile is high. The salt may also be an alkali metal salt such as a sodium salt.

[0043] 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.

[0044] In step B, the amount of the water-soluble polymerization initiator is not particularly limited, but for example, it may be 0.10 to 1.00 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.

[0045] 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. Modacrylic resin B (powder) can be obtained by dehydrating the slurry of modacrylic resin B obtained by polymerization with salt and drying, in the same manner as in general precipitation polymerization.

[0046] In step C, modacrylic resin X can be obtained by mixing modacrylic resin A and modacrylic resin B in a known manner (dry blending). 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.

[0047] The fact that modacryl resin X is a mixture of modacryl resin A and modacryl resin B is not particularly limited, but can be confirmed, for example, based on the difference in the solubility of modacryl resin A and modacryl resin B in a given solvent. Specifically, it can be confirmed when modacryl resin X is dissolved in acetone at a concentration of 10% by mass, and modacryl resin A dissolves while modacryl resin B does not.

[0048] (Modacrylic fiber and method for producing the same) In one or more embodiments of the present invention, the modacrylic fiber contains modacrylic resin X. The modacrylic fiber contains modacrylic resin X, which is a mixture of modacrylic resin A and modacrylic resin B, and has excellent flame retardancy as well as good fiber strength. When the total mass of the resin components constituting the modacrylic fiber is 100% by mass, the content of modacrylic resin X 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 modacrylic resin X.

[0049] The single fiber fineness of the modacrylic fiber is not particularly limited and can be set appropriately depending on the purpose and application. For example, it may be 1 to 100 dtex, 1.3 to 80 dtex, 1.5 to 30 dtex, or 1.7 to 15 dtex.

[0050] The modacrylic fibers may be short fibers or long fibers (filaments), and can be appropriately selected depending on the purpose and method of use. The fiber length of the modacrylic fibers 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.

[0051] From the viewpoint of having excellent practical strength, the modacrylic fiber preferably has a strength (tensile strength) of 3 cN / dtex or more, more preferably 3.15 cN / dtex or more, and even more preferably 3.30 cN / dtex or more. In this specification, the strength (tensile strength) of modacrylic fiber can be measured according to JIS L 1015 in the case of short fibers (staples), and according to JIS L 1013 in the case of long fibers (filaments).

[0052] The elongation of the modacrylic fiber is not particularly limited, but may be 10-40% or 15-35% from a practical standpoint. In this specification, the elongation (stretch rate) of modacrylic fiber can be measured according to JIS L 1015 for short fibers (staples) and according to JIS L 1013 for long fibers (filaments).

[0053] The method for producing the modacrylic fibers is not particularly limited, but a wet spinning method is preferred, for example. Wet spinning can be carried out in the same way as for general wet spinning of modacrylic fibers, except that a spinning solution is used in which modacrylic resin X is dissolved in a solvent. Specifically, the method for producing the modacrylic fibers preferably includes a wet spinning step (coagulation step) and a drawing step.

[0054] First, in the solidification process, an undrawn yarn (solidified yarn) can be obtained by extruding a spinning solution, in which modacryl resin X is dissolved in a solvent, through a nozzle into a solidification bath and allowing it to solidify. The nozzle can be used as appropriate according to the desired fiber cross-section. The fiber cross-section is not particularly limited and can be circular, elliptical, H-shaped, or other irregular shapes. Examples of the solvent include organic solvents such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and acetone, as well as inorganic solvents such as rhodane salt aqueous solution and nitric acid aqueous solution. As the solidification bath, for example, an aqueous solution of an organic solvent with a concentration of 20 to 70% by mass can be used.

[0055] Next, in the stretching process, the unstretched yarn is stretched to obtain stretched yarn. The stretching process can be either wet stretching or dry stretching, or both, but for simplicity, dry stretching alone is also acceptable. In wet drawing, the drawing bath can be water or an aqueous solution of an organic solvent with a lower concentration than that of the coagulation bath. Desolvent removal may be performed in a water washing step after the coagulation step and before wet drawing, but if water is used as the drawing bath, drawing and washing may be performed simultaneously. The temperature of the drawing bath is not particularly limited, but for example, it may be 30 to 110°C. After wet drawing, the drawn yarn can be dried in a drying step. Washing may be performed using warm water at 30°C or higher. In the case of dry stretching, the solvent can be removed in a water washing step after the solidification step, followed by drying in a drying step, and then dry stretching can be performed. The stretching temperature for dry stretching is not particularly limited, but for example, it may be 110 to 190°C.

[0056] In the stretching process, the stretch ratio (length of the fiber after stretching / length of the fiber before stretching) is not particularly limited and may be, for example, greater than 1x and less than or equal to 8x, 1.1 to 6x, or 1.5 to 5x.

[0057] The drawn yarn is preferably relaxed in a heat relaxation process as needed. The relaxation rate is not particularly limited, but is preferably 5 to 30%. The heat relaxation process can be carried out at a high temperature, for example, in a dry heat atmosphere or a superheated steam atmosphere at 130 to 200°C.

[0058] The drawn yarn may be used as is as modacrylic fiber (filament), or it may be cut to a predetermined length as needed and used as modacrylic fiber (staple). The drawn yarn may also be crimped before cutting as needed.

[0059] Because the modacrylic fibers exhibit excellent flame retardancy and good fiber strength, they can be suitably used alone in various flame-retardant materials such as flame-retardant nonwoven fabrics and flame-retardant woven fabrics. Furthermore, the 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]

[0060] 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.

[0061] First, we will explain the various measurement and evaluation methods. (1) Composition analysis of modacrylic resin The nitrogen content (mass%) in modacryl 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 the modacryl 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 was calculated. (2) Mass-average molecular weight of modacrylic resin The values ​​were measured and calculated using GPC (Gel Permeation Chromatography) with a Tosoh HLC-8320GPC. Polystyrene was used as the standard polymer, and dimethylformamide was used as the mobile phase (eluent). (3) Specific viscosity (ηsp) of modacrylic resin 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, strength and elongation The single fiber fineness, strength (tensile strength), and elongation (stretch rate) of modacrylic fibers were measured according to JIS L 1015. Modacrylic fibers cut to a length of 25 mm were used as samples. (5) Critical oxygen index The limiting oxygen index (LOI) of modacryl fibers was measured in accordance with the flammability test method according to JIS-L 1091 Method E. Specifically, a 60mm long twisted sample was prepared using 0.25g of fiber, and the measurement was performed according to the flammability test method according to JIS-L 1091 Method E, except for the use of this sample.

[0062] (Example 1) <Preparation of Modacrylic Resin A> In the polymerization reactor, 52.7 parts by mass of vinyl chloride (hereinafter also referred to as VCM), 4 parts by mass of acrylonitrile (hereinafter also referred to as AN), 166 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, 41.3 parts by mass of acrylonitrile was supplied from immediately after the start of polymerization until the 5th hour, and 2.0 parts by mass of sodium styrenesulfonate (hereinafter also referred to as SSS) dissolved in 27 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, the 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 A1. The obtained modacryl resin A1 consisted of 46.0% by weight of constituent units derived from acrylonitrile, 52.0% by mass of constituent units derived from vinyl chloride, and 2.0% by mass of constituent units derived from sodium styrenesulfonate. Its mass-average molecular weight was approximately 95,000, and its specific viscosity was 0.193. <Preparation of Modacrylic Resin B> In the polymerization reactor, 17 parts by mass of vinyl chloride, 16 parts by mass of acrylonitrile, 166 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, 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, 3.0 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as AMPSNa) dissolved in 27 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 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, 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 B1. The obtained modacryl resin B1 consisted of 80.4% by mass of constituent units derived from acrylonitrile, 16.9% by mass of constituent units derived from vinyl chloride, and 2.7% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was 223,729, and its specific viscosity was 0.428. <Fabrication of Modacrylic Resin X> 67 parts by mass of modacrylic resin A1 and 33 parts by mass of modacrylic resin B1 were mixed with a hand mixer to obtain modacrylic resin X1 (mixed resin) consisting of 67% by mass of modacrylic resin A1 and 33% by mass of modacrylic resin B1. <Production of Modacrylic Fibers> Modacrylic resin X1 was dissolved in dimethyl sulfoxide to a resin concentration of 22% by mass to prepare a spinning solution. The resulting spinning solution was extruded into a 50% by mass aqueous solution of dimethyl sulfoxide using a circular nozzle with a nozzle diameter of 0.07 mm and 2000 holes, and allowed to solidify. Then it was washed with hot water at 85°C and dried at 140°C. After drying, it was stretched 2.5 times at 140°C, and then subjected to a further heat relaxation treatment at 170°C for 5 minutes (relaxation rate of 12%) to produce modacrylic fibers.

[0063] (Example 2) <Fabrication of Modacrylic Resin X> Modacrylic resin X1 was prepared in the same manner as in Example 1. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that the stretching ratio was set to 3.0 times.

[0064] (Example 3) <Fabrication of Modacrylic Resin X> Modacrylic resin X1 was prepared in the same manner as in Example 1. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that the stretching ratio was increased to 3.5 times.

[0065] (Example 4) <Fabrication of Modacrylic Resin X> Modacrylic resin X1 was prepared in the same manner as in Example 1. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that the stretching ratio was set to 4.0 times.

[0066] (Example 5) <Fabrication of Modacrylic Resin X> Modacrylic resin X1 was prepared in the same manner as in Example 1. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that the stretching ratio was increased to 4.5 times.

[0067] (Example 6) <Preparation of Modacrylic Resin A> Modacrylic resin A1 was obtained in the same manner as in Example 1. <Preparation of Modacrylic Resin B> In the polymerization reactor, 27 parts by mass of vinyl chloride, 14 parts by mass of acrylonitrile, 166 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, 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, 3.0 parts by mass of sodium methallyl sulfonate (hereinafter also referred to as SMS), dissolved in 56 parts by mass of acrylonitrile and 27 parts by mass of deionized water, was supplied from immediately after the start of polymerization until 2.5 hours later. 0.27 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, 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 B2. The obtained modacryl resin B2 consisted of 78.1% by mass of constituent units derived from acrylonitrile, 20.3% by mass of constituent units derived from vinyl chloride, and 1.6% by mass of constituent units derived from sodium methallyl sulfonate. Its mass-average molecular weight was approximately 288,000, and its specific viscosity was 0.588. <Fabrication of Modacrylic Resin X> 67 parts by mass of modacrylic resin A1 and 33 parts by mass of modacrylic resin B2 were mixed with a hand mixer to obtain modacrylic resin X2 (mixed resin) consisting of 67% by mass of modacrylic resin A1 and 33% by mass of modacrylic resin B2. I made it. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 3, except that modacrylic resin X2 was used.

[0068] (Example 7) <Preparation of Modacrylic Resin A> Modacrylic resin A1 was obtained in the same manner as in Example 1. <Preparation of Modacrylic Resin B> In the polymerization reactor, 17 parts by mass of vinyl chloride, 16 parts by mass of acrylonitrile, 306 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, 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, 3.0 parts by mass of sodium 2-acrylonitrile dissolved in 64 parts by mass of acrylonitrile and 27 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 hours later, 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 polymerization was completed, 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 B3. The obtained modacryl resin B3 consisted of 80.6% by mass of constituent units derived from acrylonitrile, 17.6% by mass of constituent units derived from vinyl chloride, and 1.8% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was 291,748, and its specific viscosity was 0.481. <Fabrication of Modacrylic Resin X> 67 parts by mass of modacrylic resin A1 and 33 parts by mass of modacrylic resin B3 were mixed with a hand mixer to obtain modacrylic resin X3 (mixed resin) consisting of 67% by mass of modacrylic resin A1 and 33% by mass of modacrylic resin B3. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 3, except that modacrylic resin X3 was used.

[0069] (Comparative Examples 1-5) Modacrylic fibers were prepared in the same manner as in Examples 1 to 5, except that modacrylic resin A1 was used instead of modacrylic resin X1.

[0070] (Comparative Example 6) <Preparation of Modacrylic Resin B> In the polymerization reactor, 17 parts by mass of vinyl chloride, 16 parts by mass of acrylonitrile, 166 parts by mass of deionized water, 0.02 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, 3.0 parts by mass of sodium 2-acrylamido-2-methyl-1-propanesulfonate dissolved in 27 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 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 B4. The obtained modacryl resin B4 consisted of 79.0% by mass of constituent units derived from acrylonitrile, 18.4% by mass of constituent units derived from vinyl chloride, and 2.6% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate. Its mass-average molecular weight was 130,446 and its specific viscosity was 0.258. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that modacrylic resin B4 was used instead of modacrylic resin X1.

[0071] (Comparative Example 7) <Preparation of Modacrylic Resin A> Modacrylic resin A1 was obtained in the same manner as in Example 1. <Preparation of Modacrylic Resin B> In the polymerization reactor, 17 parts by mass of vinyl chloride, 16 parts by mass of acrylonitrile, 166 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, 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, 3.0 parts by mass of sodium methallyl sulfonate dissolved in 64 parts by mass of acrylonitrile and 27 parts by mass of deionized water was supplied from immediately after the start of polymerization until 2.5 hours later, and 0.27 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 B5. The obtained modacryl resin B5 consisted of 82.0% by mass of constituent units derived from acrylonitrile, 15.5% by mass of constituent units derived from vinyl chloride, and 2.5% by mass of constituent units derived from sodium methallyl sulfonate. Its mass-average molecular weight was 364,822, and its specific viscosity was 0.747. <Production of Modacrylic Fibers> In an attempt to produce modacrylic fibers in the same manner as in Example 1, except that modacrylic resin B5 was used instead of modacrylic resin B1, when the stretching ratio was increased to more than 2 times, the fibers broke, and modacrylic fibers could not be obtained.

[0072] (Comparative Example 8) <Preparation of mixed resins> 78 parts by mass of modacrylic resin A1 and 22 parts by mass of modacrylic resin B5 were mixed with a hand mixer to obtain a mixed resin consisting of 78% by mass of modacrylic resin A1 and 22% by mass of modacrylic resin B5. <Production of Modacrylic Fibers> Modacrylic fibers were prepared in the same manner as in Example 1, except that the mixed resin obtained above was used instead of modacrylic resin X1.

[0073] (Comparative Example 9) <Production of Modacrylic Fibers> When attempting to produce modacrylic fibers in the same manner as in Comparative Example 8, except that the stretching ratio was tripled, it was not possible to stretch the fibers.

[0074] (Reference example 1) In the polymerization reactor, 43 parts by mass of vinyl chloride, 4 parts by mass of acrylonitrile, 175 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 of sodium lauryl sulfate 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, 2.0 parts by mass of sodium styrenesulfonate dissolved in 51 parts by mass of acrylonitrile and 18 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. The latex solidified during polymerization, and the polymerization could not be completed.

[0075] In the examples and comparative examples, the composition of the modacryl resin (content of constituent units derived from each monomer), mass-average molecular weight (Mw), and specific viscosity (ηsp) were measured as described above. The results are shown in Tables 1 and 2 below. In addition, the single fiber fineness, elongation, strength, and LOI value of the modacryl fibers were measured in the examples and comparative examples as described above, and the results are shown in Tables 1 and 2 below. 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, SMS represents a constituent unit derived from sodium methallylsulfonate, and SM represents a constituent unit derived from a sulfonic acid group-containing vinyl monomer.

[0076] [Table 1]

[0077] [Table 2]

[0078] As can be seen from the results in Table 1 above, in Examples 1 to 7, modacrylic fibers with high flame retardancy and strength were obtained. On the other hand, as can be seen from the results in Table 2 above, in Comparative Examples 1 to 5, where only modacrylic resin A was used, the strength of the modacrylic fibers was low. Also, in Comparative Example 6, where only modacrylic resin B was used, the flame retardancy of the modacrylic fibers was low. In Comparative Examples 7 to 9, where the ratio MwB / MwA of the mass average molecular weight MwA of modacrylic resin A to the mass average molecular weight MwB of modacrylic resin B was greater than 3.5, spinning or drawing was not possible, or the strength of the resulting modacrylic fibers was low.

[0079] The present invention is not particularly limited, but preferably includes, for example, the following embodiments. [1] A modacrylic resin comprising modacrylic resin A and modacrylic resin B, Modacryl resin A contains 35% to less than 55% by mass of constituent units derived from acrylonitrile, 40 to 64.5% by mass of constituent units derived from halogen-containing monomers, and 0.5 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Modacryl resin B contains 55-84.9% by mass of constituent units derived from acrylonitrile, 15-44.9% by mass of constituent units derived from halogen-containing monomers, and 0.1-5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. The ratio MwB / MwA of the mass-average molecular weight MwA of modacryl resin A and the mass-average molecular weight MwB of modacryl resin B is 1.5 to 3.5. A modacryl resin having a content of 50-90% by mass of modacryl resin A and a content of 10-50% by mass of modacryl resin B. [2] The modacrylic resin according to [1], wherein the halogen-containing monomer comprises one or more selected from the group consisting of vinyl chloride and vinylidene chloride. [3] The modacryl resin according to [1] or [2], 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, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof. [4] Modacrylic resin B, wherein the mass-average molecular weight MwB is 150,000 to 300,000, as described in any of [1] to [3]. A method for producing modacrylic resin as described in any of [5] [1] to [4], Step A: Polymerizing monomer composition A to obtain modacrylic resin A, Step B involves polymerizing monomer composition B to obtain modacrylic resin B, and The process includes a step of mixing modacrylic resin A and modacrylic resin B. Monomer composition A contains 35% by mass or more and less than 55% by mass of acrylonitrile, 40 to 64.5% by mass of halogen-containing monomers, and 0.5 to 5% by mass of sulfonic acid group-containing vinyl monomers. Monomer composition B contains 55-84.9% by mass of acrylonitrile, 15-44.9% by mass of halogen-containing monomers, and 0.1-5% by mass of sulfonic acid group-containing vinyl monomers. Step A is carried out in the presence of water, a water-soluble polymerization initiator, and an emulsifier. Step B is a method for producing modacrylic resin, carried out in the presence of water and a water-soluble polymerization initiator, and under conditions where an emulsifier is substantially absent. [6] The method for producing modacryl resin according to [5], wherein the monomer composition 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. Modacrylic fiber containing the modacrylic resin described in any of [7] [1] to [4]. [8] Modacrylic fiber as described in [7], having a strength of 3 cN / dtex or more. [9] Modacrylic fiber as described in [7] or [8], having a critical oxygen index of 26 or higher.

[10] A method for producing modacrylic fibers, A process of wet spinning a modacrylic resin as described in any of [1] to [4], and A method for producing modacrylic fibers, comprising the step of drawing an undrawn yarn obtained by wet spinning.

Claims

1. A modacrylic resin comprising modacrylic resin A and modacrylic resin B, Modacryl resin A contains 35% by mass or more and less than 55% by mass of constituent units derived from acrylonitrile, 40 to 64.5% by mass of constituent units derived from halogen-containing monomers, and 0.5 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. Modacryl resin B contains 55 to 84.9% by mass of constituent units derived from acrylonitrile, 15 to 44.9% by mass of constituent units derived from halogen-containing monomers, and 0.1 to 5% by mass of constituent units derived from sulfonic acid group-containing vinyl monomers. The ratio MwB / MwA of the mass-average molecular weight MwA of modacryl resin A and the mass-average molecular weight MwB of modacryl resin B is 1.5 to 3.

5. A modacryl resin having a content of 50 to 90% by mass of modacryl resin A and a content of 10 to 50% by mass of modacryl resin B.

2. The modacrylic 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.

3. The modacryl 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.

4. The modacryl resin according to claim 1, wherein the mass-average molecular weight MwB of modacryl resin B is 150,000 to 300,000.

5. A method for producing modacrylic resin according to any one of claims 1 to 4, Step A: Polymerizing monomer composition A to obtain modacrylic resin A, Step B involves polymerizing monomer composition B to obtain modacrylic resin B, and The process includes a step of mixing modacrylic resin A and modacrylic resin B. Monomer composition A contains 35% by mass or more and less than 55% by mass of acrylonitrile, 40 to 64.5% by mass of halogen-containing monomers, and 0.5 to 5% by mass of sulfonic acid group-containing vinyl monomers. Monomer composition B contains 55 to 84.9% by mass of acrylonitrile, 15 to 44.9% by mass of halogen-containing monomers, and 0.1 to 5% by mass of sulfonic acid group-containing vinyl monomers. Step A is carried out in the presence of water, a water-soluble polymerization initiator, and an emulsifier. Step B is a method for producing modacrylic resin, carried out in the presence of water and a water-soluble polymerization initiator, and under conditions where an emulsifier is substantially absent.

6. The method for producing modacryl resin according to claim 5, wherein the monomer composition 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.

7. Modacrylic fiber comprising the modacrylic resin described in any one of claims 1 to 4.

8. The modacrylic fiber according to claim 7, having a strength of 3 cN / dtex or more.

9. The modacryl fiber according to claim 7, wherein the critical oxygen index is 26 or higher.

10. A method for producing modacrylic fibers, A step of wet spinning a modacrylic resin according to any one of claims 1 to 4, and A method for producing modacrylic fibers, comprising the step of drawing an undrawn yarn obtained by wet spinning.

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