Core-sheath type composite fiber, and method for manufacturing the same

Abstract

The present invention provides a core-sheath type composite fiber and a method for producing the same, which does not use a core-sheath type composite spinneret, and uses 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 in the core and sheath portions. [Solution] A core-sheath type composite fiber is provided in which the sheath portion contains modacrylic resin A and the core portion contains acrylonitrile-based resin B, and each resin contains constituent units derived from acrylonitrile, constituent units derived from halogen-containing monomers, and constituent units derived from sulfonic acid group-containing vinyl monomers, and the absolute value of the difference in the content of acrylonitrile-derived constituent units between the core portion and the sheath portion |CtA1-CtB1| is 10.0 to 19.0% by mass.

Description

Technical Field

[0001] The present invention relates to a core-sheath type composite fiber using two kinds 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 vinyl monomer containing a sulfonic acid group, and a method for producing the same.

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. For example, in Patent Document 1, 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 60 to 95 parts by weight of the polymer (I) contains 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. A flame-retardant acrylic composite fiber in which 5 to 40 parts by weight of a polymer (II) is joined is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, in order to obtain a core-sheath type composite fiber, a core-sheath spinning die is used, and the spinning solution of Component A is introduced into the sheath portion and the spinning solution of Component B is introduced into the core portion, and wet spinning is performed. As described in Patent Document 1, in the production of a core-sheath type composite fiber, it was usually necessary to use a core-sheath type composite spinning die.

[0005] Unlike conventional methods, the present invention provides a core-sheath type composite fiber and a method for producing the same, which uses 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 in the core and sheath portions, without using a core-sheath type composite spinneret. [Means for solving the problem]

[0006] One or more embodiments of the present invention are core-sheath type composite fibers comprising a sheath and a core, wherein the sheath comprises modacryl resin A, and the core comprises acrylonitrile resin B, wherein modacryl resin A comprises 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 comprises constituent units derived from acrylonitrile This invention relates to a core-sheath type composite fiber containing 15-89.9% by mass of , 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, 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 10.0-19.0% by mass.

[0007] One or more embodiments of the present invention also relate to a method for producing a core-sheath composite fiber, comprising the steps of: dissolving a mixed resin, obtained by mixing modacryl resin A and acrylonitrile resin B, in a solvent to obtain a spinning solution; and extruding the spinning solution into a coagulation bath using a single-type nozzle. [Effects of the Invention]

[0008] The present invention provides a core-sheath type composite fiber that does not require the use of a core-sheath type composite spinneret, and uses a resin containing constituent units derived from acrylonitrile, halogen-containing monomers, and sulfonic acid group-containing vinyl monomers in the core and sheath portions. According to the manufacturing method of the present invention, a core-sheath type composite fiber can be obtained without using a core-sheath type composite spinneret, using 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 in the core and sheath portions. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional photograph (400x magnification) of the core-sheath type composite fiber (modacrylic fiber) of Example 6. [Figure 2] This is a cross-sectional photograph (400x magnification) of the modacrylic fiber in Comparative Example 5. [Modes for carrying out the invention]

[0010] The inventors of the present invention have conducted extensive research to obtain a core-sheath type composite fiber using 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, without using a core-sheath type composite spinning nozzle (also called a composite spinning nozzle). As a result, 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, and 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. We found that by using acrylonitrile-based resin B, setting the content of acrylonitrile-derived structural units in modacrylic resin A to 1% by mass CtA, and the content of acrylonitrile-derived structural units in acrylonitrile-based resin B to 1% by mass CtB, and setting |CtA1-CtB1| in the range of 10.0 to 19.0% by mass, a core-sheath type composite fiber can be obtained without using a core-sheath type composite spinneret, with the sheath containing modacrylic resin A and the core containing acrylonitrile-based resin B.

[0011] 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.

[0012] In the core-sheath type composite fiber of one or more embodiments of the present invention, the sheath portion contains modacrylic resin A, and the core portion contains acrylonitrile resin B. When the total mass of the resin components constituting the sheath portion is 100% by mass, the content of modacrylic resin A 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 sheath portion may consist of 100% by mass of modacrylic resin A. When the total mass of the resin components constituting the core portion is 100% by mass, the content of acrylonitrile resin B 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 core portion may consist of 100% by mass of acrylonitrile resin B.

[0013] Modacrylic 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, the core-sheath type composite fiber can have heat resistance, flame retardancy, and dyeability.

[0014] 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.

[0015] If the content of acrylonitrile-derived structural units in modacryl resin A is CtA1 by mass, and the content of acrylonitrile-derived structural units in acrylonitrile-based resin B is CtB1 by mass, then |CtA1-CtB1| is 10.0 to 19.0% by mass. Since the absolute difference between the content of acrylonitrile-derived structural units in modacryl resin A and the content of acrylonitrile-derived structural units in acrylonitrile-based resin B is 10.0 to 19.0% by mass, a core-sheath composite fiber can be obtained without using a core-sheath type composite spinneret. From the viewpoint of easily exhibiting a core-sheath structure, |CtA1-CtB1| is preferably 11 to 19.0% by mass, and more preferably 12 to 19.0% by mass.

[0016] It is preferable that CtB1 is higher than CtA1. That is, it is preferable that the content of acrylonitrile-derived structural units in acrylonitrile resin B is higher than the content of acrylonitrile-derived structural units in modacrylic resin A. This makes it easier for the resulting fibers to achieve both heat resistance and flame retardancy. It also makes it easier to polymerize acrylonitrile resin B.

[0017] Acrylonitrile-based resin B preferably contains 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, and more preferably 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. In this case, acrylonitrile-based resin B is also referred to as modacrylic resin B.

[0018] 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.

[0019] 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.

[0020] In the modacrylic resin A, the structural unit derived from the sulfonic acid group-containing vinyl monomer is not particularly limited. For example, it 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. 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.

[0021] In the acrylonitrile-based resin B, the structural unit derived from the sulfonic acid group-containing vinyl monomer is not particularly limited. For example, it 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. The salt may be an alkali metal salt such as a sodium salt. In the acrylonitrile-based resin B having a high 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 a modacrylic resin having a halogen-containing monomer and a sulfonic acid group-containing vinyl monomer as copolymerization components and a high polymerization ratio of acrylonitrile can be easily obtained.

[0022] The mass average molecular weight MwA of the modacrylic resin A is not particularly limited. For example, from the viewpoints of increasing the resin concentration of 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.

[0023] The mass average molecular weight MwB of the acrylonitrile-based resin B is not particularly limited. For example, from the viewpoints of increasing the resin concentration of the spinning solution to realize 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 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 0.60, or 0.10 to 0.50. In this specification, the specific viscosity can be measured as described in the examples.

[0025] The specific viscosity of the acrylonitrile-based resin B is not particularly limited. For example, when dimethylformamide is used as the solvent, the specific viscosity at 30 °C may be 0.05 to 0.60, or 0.10 to 0.50.

[0026] In the core-sheath type composite fiber, the composite ratio of the sheath part and the core part is not particularly limited. From the viewpoint of the expression property of the core-sheath structure, in terms of mass ratio, the sheath part / core part is preferably 50 / 50 to 90 / 10, more preferably 50 / 50 to 85 / 15, and even more preferably 50 / 50 to 80 / 20. More specifically, the mass ratio of the modacrylic resin A constituting the sheath part to the acrylonitrile-based resin B constituting the core part, modacrylic resin A / acrylonitrile-based resin B is preferably 50 / 50 to 90 / 10, more preferably 50 / 50 to 85 / 15, and even more preferably 50 / 50 to 80 / 20.

[0027] The core-sheath type composite fiber can be produced by a wet spinning method using the modacrylic resin A and the acrylonitrile-based resin B. More specifically, the method for producing the core-sheath type composite fiber includes Step 1 of dissolving a mixed resin obtained by mixing the modacrylic resin A and the acrylonitrile-based resin B in a solvent to obtain a spinning solution, and Step 2 of extruding the spinning solution into a coagulation bath using a single type of nozzle.

[0028] Step 1 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 obtain acrylonitrile resin B by polymerizing monomer composition B, (3) Step C of mixing modacryl resin A and acrylonitrile resin B, (4) Step D: Dissolving the obtained mixed resin in a solvent.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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. Furthermore, the resulting modacryl resin A is more likely to form a sheath.

[0033] 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).

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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 10.0 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 10.0 to 19.0% by mass. Preferably, |CtA2-CtB2| is 11 to 19.0% by mass. This makes it easier for |CtA1-CtB1| to be 11-19.0 mass%. It is more preferable for |CtA2-CtB2| to be 12-19.0 mass%. This makes it easier for |CtA1-CtB1| to be 12-19.0 mass%.

[0039] 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.

[0040] 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. The salt may also be an alkali metal salt such as a sodium salt. This reduces costs and makes it easier to obtain a modacryl resin in which halogen-containing monomers and sulfonic acid group-containing vinyl monomers are copolymerized and the polymerization ratio of acrylonitrile is high. In addition, the obtained acrylonitrile-based resin B is more likely to form the core.

[0041] 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.

[0042] 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.

[0043] 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).

[0044] In step C, a mixed resin X can be obtained by mixing (dry blending) modacryl resin A and acrylonitrile resin B (preferably modacryl 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.

[0045] By mixing modacryl resin A obtained by emulsion polymerization and modacryl resin B obtained by emulsion polymerization without an emulsifier, costs can be reduced and polymerization stability can be improved. Specifically, by obtaining modacryl resin A with a low content of constituent units derived from acrylonitrile and constituent units derived from sulfonic acid group-containing vinyl monomers through emulsion polymerization, the amount of styrene sulfonic acid and / or its metal salt used as sulfonic acid group-containing vinyl monomers can be reduced, thereby reducing costs and improving polymerization stability when copolymerizing with halogen-containing monomers. Furthermore, by obtaining modacryl resin B with a high content of constituent units derived from acrylonitrile and constituent units derived from sulfonic acid group-containing vinyl monomers through emulsion polymerization without an emulsifier, 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 can be used as sulfonic acid group-containing vinyl monomers, and polymerization stability when copolymerizing with halogen-containing monomers can be improved. 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.

[0046] The mixed resin X is not particularly limited, but for example, when the mass of the mixed resin X is 100% by mass, it is preferable to contain 50-90% by mass of modacryl resin A and 10-50% by mass of acrylonitrile resin B, preferably 50-85% by mass of modacryl resin A and 15-50% by mass of acrylonitrile resin B, and more preferably 50-80% by mass of modacryl resin A and 20-50% by mass of acrylonitrile resin B. This makes it easier to obtain core-sheath type composite fibers with the above-mentioned composite ratio.

[0047] In the mixed resin X, the composition of each monomer is not particularly limited, but for example, from the viewpoint of easily suppressing the generation of voids, 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.

[0048] In step D, the mixed resin X is dissolved in a solvent to obtain a spinning solution. Examples of the solvent include organic solvents such as dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and acetone, as well as inorganic solvents such as rhodane aqueous solution and nitric acid aqueous solution. Organic solvents are preferred, and one or more selected from the group consisting of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide are preferred, with dimethyl sulfoxide being more preferred. In the spinning solution, the concentration (solid content concentration) of the mixed resin X is not particularly limited, but may be, for example, 22 to 28% by mass.

[0049] The spinning solution is not particularly limited, but may contain, for example, water. The amount of water added is preferably 0.5 to 15 parts by mass, more preferably 2.0 to 14 parts by mass, even more preferably 3.5 to 13 parts by mass, and even more preferably 5 to 12 parts by mass, per 100 parts by mass of the mixed resin X, from the viewpoint of further enhancing the effect of suppressing void formation in the fibers and the expression of the core-sheath structure.

[0050] In the wet spinning step 2, the spinning solution is extruded into a coagulation bath using a single-type nozzle and coagulated to obtain undrawn yarn (coagulated yarn). Wet spinning can be carried out in the same manner as wet spinning of general modacrylic fibers, except that a spinning solution is used in which the mixed resin X is dissolved in a solvent. Next, the obtained undrawn yarn (coagulated yarn) is washed with water and then dried to obtain core-sheath type composite fibers, specifically core-sheath type acrylonitrile composite fibers. Washing may be carried out using water at 20°C or higher. Drying may be carried out at room temperature (25±5°C). By using mixed resin X, core-sheath type acrylonitrile composite fibers can be obtained without using a core-sheath type composite spinning nozzle. When mixed resin X consists of modacrylic resin A and modacrylic resin B, the obtained core-sheath type acrylonitrile composite fibers are also called core-sheath type modacrylic composite fibers.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Undrawn or drawn yarn may be used as is in filament form as a core-sheath type composite fiber (specifically, a core-sheath type acrylonitrile composite fiber, preferably a core-sheath type modacrylic composite fiber), or it may be cut to a predetermined length as needed and used in a stapled state as a core-sheath type acrylonitrile composite fiber (preferably a core-sheath type modacrylic composite fiber). The drawn yarn may be crimped before cutting as needed.

[0055] The core-sheath type composite fiber may be either a short fiber or a long fiber (filament), and can be appropriately selected depending on the purpose and method of use. The fiber length of the core-sheath type composite fiber can be appropriately selected depending on the purpose and method of use. For example, in the case of a short-cut fiber, the fiber length may be 0.1 to 5 mm, and in the case of a short fiber, the fiber length may be 15 to 176 mm, 20 to 160 mm, 25 to 138 mm, or 30 to 128 mm.

[0056] The core-sheath type composite fiber may be used in various flame-retardant materials such as flame-retardant nonwoven fabrics and flame-retardant woven fabrics. In addition, the acrylonitrile fiber (preferably modacrylic fiber) 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]

[0057] 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.

[0058] 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 was measured according to JIS L 1013. (5) Core-sheath structure Cross-sections of modacryl fibers were cut by freeze-fracturing, and the cross-sections were observed using a scanning electron microscope (Hitachi High-Technologies Corporation, field emission scanning electron microscope: S-4800) to confirm the presence or absence of core and sheath formation. In addition, a micro-Raman spectrometer (RENISHAW, "inVia") was used. TM Raman spectra of the core and sheath were obtained using a Qontor(registered trademark) confocal Raman microscope, and their respective constituent components were analyzed.

[0059] (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.

[0060] (Manufacturing example 2) In the polymerization reactor, 52.7 parts by mass of vinyl chloride, 4 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, 0.35 parts by mass of sulfuric acid (64% by mass), and 0.87 parts by mass 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 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 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, 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 II. The obtained modacryl resin II 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.

[0061] (Manufacturing Example 3) In the 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 (hereinafter also referred to as AMPSNa), 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. 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, 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 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 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.

[0062] (Manufacturing example 4) In the 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, 264 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, 1.0 part by mass of sodium styrenesulfonate dissolved in 19 parts by mass of deionized water was supplied from immediately after the start of polymerization until 5.5 hours, and 0.34 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 IV. The obtained modacryl resin IV consisted of 62.3% by mass of constituent units derived from acrylonitrile, 28.5% by mass of constituent units derived from vinyl chloride, 7.9% by mass of constituent units derived from sodium 2-acrylamido-2-methyl-1-propanesulfonate, and 1.3% by mass of constituent units derived from sodium styrenesulfonate. Its mass-average molecular weight was approximately 65,000 and its specific viscosity was 0.174.

[0063] (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. 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, 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.

[0064] (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 dehydrated and dried in a hot air dryer at 60°C for 24 hours to obtain modacryl 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.

[0065] (Manufacturing example 7) 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, 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 VII. The obtained modacryl resin VII 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.

[0066] (Manufacturing example 8) 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 VIII. The obtained modacryl resin VIII 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.

[0067] (Example 1) 75 parts by mass of modacrylic resin I and 25 parts by mass of modacrylic resin III were mixed with a hand mixer to obtain a mixed resin 1 consisting of 75% by mass of modacrylic resin I and 25% by mass of modacrylic resin III. Next, 10.5 parts by mass of water were added to 100 parts by mass of mixed resin 1, and the resin was dissolved in dimethyl sulfoxide to a concentration of 27% by mass to obtain a spinning solution. The obtained spinning solution was extruded into a 25% by mass aqueous solution of dimethyl sulfoxide (coagulation bath) using a single nozzle with an H-shaped (dumbbell-shaped) pore shape, a pore diameter (equivalent diameter) of 0.3 mm, and 12 holes, and allowed to solidify. Then it was washed with water at 25°C and dried at room temperature (25±5°C) to obtain modacrylic fibers.

[0068] (Example 2) Modacryl fibers were prepared in the same manner as in Example 1, except that a 40% by mass aqueous solution of dimethyl sulfoxide was used as the coagulation bath.

[0069] (Example 3) Modacryl fibers were prepared in the same manner as in Example 1, except that a 47% by mass aqueous solution of dimethyl sulfoxide was used as the coagulation bath.

[0070] (Example 4) 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 5) 85 parts by mass of modacrylic resin I and 15 parts by mass of modacrylic resin III were mixed with a hand mixer to obtain a mixed resin 2 consisting of 85% by mass of modacrylic resin I and 15% by mass of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 3, except that mixed resin 2 was used instead of mixed resin 1.

[0072] (Example 6) 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 3 consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 3, except that mixed resin 3 was used instead of mixed resin 1.

[0073] (Example 7) 65 parts by mass of modacrylic resin I and 35 parts by mass of modacrylic resin III were mixed with a hand mixer to obtain a mixed resin 4 consisting of 80% by mass of modacrylic resin I and 20% by mass of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 3, except that mixed resin 4 was used instead of mixed resin 1.

[0074] (Example 8) Mixed resin 3 was dissolved in dimethyl sulfoxide to a resin concentration of 27% by mass to prepare a spinning solution. Modacrylic fibers were prepared in the same manner as in Example 6, except that the obtained spinning solution was used.

[0075] (Example 9) Modacrylic fibers were prepared in the same manner as in Example 6, except that 5.5 parts by mass of water were added to 100 parts by mass of mixed resin 3, and the resin was dissolved in dimethyl sulfoxide to a concentration of 27% by mass to form a spinning solution.

[0076] (Example 10) Mixed resin 5 was obtained in the same manner as in Example 6, except that modacrylic resin IV was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 6, except that mixed resin 5 was used instead of mixed resin 3.

[0077] (Example 11) Mixed resin 6 was obtained in the same manner as in Example 3, except that modacrylic resin IV was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 3, except that mixed resin 6 was used instead of mixed resin 1.

[0078] (Example 12) Mixed resin 7 was obtained in the same manner as in Example 6, except that modacrylic resin II was used instead of modacrylic resin I. Modacrylic fibers were prepared in the same manner as in Example 6, except that mixed resin 7 was used instead of mixed resin 3.

[0079] (Example 13) Mixed resin 8 was obtained in the same manner as in Example 12, except that modacrylic resin IV was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 6, except that mixed resin 8 was used instead of mixed resin 3.

[0080] (Comparative Example 1) Modacrylic fibers were prepared in the same manner as in Example 6, except that 10.5 parts by mass of water were added to 100 parts by mass of modacrylic resin I, and the resin was dissolved in dimethyl sulfoxide to a concentration of 27% by mass to form a spinning solution.

[0081] (Comparative Example 2) Modacrylic fibers were prepared in the same manner as in Example 6, except that 10.5 parts by mass of water were added to 100 parts by mass of modacrylic resin II, and the resin was dissolved in dimethyl sulfoxide to a concentration of 27% by mass to form a spinning solution.

[0082] (Comparative Example 3) Mixed resin 9 was obtained in the same manner as in Example 6, except that modacrylic resin V was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 6, except that mixed resin 9 was used instead of mixed resin 3.

[0083] (Comparative Example 4) Mixed resin 10 was obtained in the same manner as in Example 7, except that modacrylic resin VI was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 7, except that mixed resin 10 was used instead of mixed resin 4.

[0084] (Comparative Example 5) 70 parts by mass of modacrylic resin I and 30 parts by mass of modacrylic resin VII were mixed with a hand mixer to obtain a mixed resin 11 consisting of 70% by mass of modacrylic resin I and 30% by mass of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 3, except that mixed resin 11 was used instead of mixed resin 1.

[0085] (Comparative Example 6) Mixed resin 12 was obtained in the same manner as in Example 6, except that modacrylic resin VIII was used instead of modacrylic resin III. Modacrylic fibers were prepared in the same manner as in Example 6, except that mixed resin 12 was used instead of mixed resin 3.

[0086] In Production Examples 1 to 8, the composition (content of constituent units derived from each monomer), mass-average molecular weight (Mw), and specific viscosity (ηsp) of the modacrylic resin were measured as described above. The composition (content of constituent units derived from each monomer) of the mixed resin was measured as described above, and the results are shown in Tables 1 to 3 below. In addition, the single fiber fineness of the modacrylic fibers was measured as described above in the Examples and Comparative Examples. In addition, the presence or absence of a core-sheath structure in the modacrylic fibers was confirmed as described above in the Examples and Comparative Examples, and the constituent components of the core and sheath were analyzed as described above, and the results are shown in Tables 1 to 3 below. Figures 1 and 2 show cross-sectional photographs (400x magnification) of the fibers of Example 6 and Comparative Example 5, respectively. In Tables 1-3 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. In Tables 1-3 below, the amount of water added is per 100 parts by mass of the mixed resin.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] As can be seen from Tables 1 and 2, and Figure 1, the modacryl fibers of Examples 1 to 13 were core-sheath type composite fibers having a core-sheath structure. In the modacryl fibers of Examples 1 to 13, the sheath portion was composed of modacryl resin A, which had a low content of constituent units derived from sulfonic acid group-containing vinyl monomers, and the core portion was composed of modacryl resin B, which had a high content of constituent units derived from sulfonic acid group-containing vinyl monomers. In the modacryl fibers of Examples 1 to 13, the difference (CtB1-CtA1) between the content of constituent units derived from acrylonitrile in modacryl resin A constituting the sheath portion (CtA1 by mass) and the content of constituent units derived from acrylonitrile in modacryl resin B constituting the core portion (CtB1-CtA1) was in the range of 10.0 to 19.0 by mass. In Examples 1 to 13, by using a mixed resin consisting of modacrylic resin A and modacrylic resin B, it was possible to obtain core-sheath type composite fibers using a single-type spinning nozzle without using a core-sheath type composite spinning nozzle.

[0091] On the other hand, in the case of modacryl fibers in Comparative Examples 1 and 2, which used only modacryl resin A, it was not possible to obtain core-sheath type composite fibers with a single-type spinning nozzle. Furthermore, as can be seen from Table 3 and Figure 2, although two types of modacryl resin were used, in Comparative Examples 3 to 6, where the absolute difference in the acrylonitrile content of the two types of modacryl resin was less than 10% by mass or more than 20% by mass, it was not possible to obtain core-sheath type composite fibers with a single-type spinning nozzle.

[0092] The present invention is not particularly limited, but preferably includes, for example, the following embodiments. [1] A core-sheath type composite fiber consisting of a sheath and a core, The sheath portion contains modacrylic resin A, and the core portion contains 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. A core-sheath type composite fiber in which, when the content of acrylonitrile-derived constituent units in modacryl resin A is defined as CtA 1% by mass, and the content of acrylonitrile-derived constituent units in acrylonitrile-based resin B is defined as CtB 1% by mass, |CtA 1 - CtB 1| is 10.0 to 19.0% by mass. [2] The core-sheath composite fiber according to [1], wherein the CtB1 is higher than the CtA1. [3] The core-sheath type composite fiber according to [1] or [2], wherein when the total mass of Modacri resin A and acrylonitrile resin B is 100% by mass, Modacri resin A is 50 to 90% by mass and acrylonitrile resin B is 10 to 50% by mass. [4] The halogen-containing monomer comprises one or more selected from the group consisting of vinyl chloride and vinylidene chloride, as described in any of [1] to [3]. [5] The core-sheath type composite fiber according to any one of [1] to [4], 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. [6] A core-sheath type composite fiber according to any one of [1] to [5], wherein the Modacri resin A comprises one or more sulfonic acid group-containing vinyl monomers selected from the group consisting of styrene sulfonic acid and its metal salts. [7] In the acrylonitrile resin B, the sulfonic acid group-containing vinyl monomer is one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof, the core-sheath type composite fiber according to any one of [1] to [6]. A method for producing a core-sheath type composite fiber according to any one of [8] [1] to [7], A step of dissolving a mixed resin, which is a mixture of modacryl resin A and acrylonitrile resin B, in a solvent to obtain a spinning solution, and A method for producing a core-sheath type composite fiber, comprising the step of extruding the spinning solution into a coagulation bath using a single-type nozzle. [9] The method for producing a core-sheath type composite fiber according to [8], wherein the solvent is one or more selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

[10] The coagulation solution is an aqueous solution of one or more solvents selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide, the method for producing a core-sheath type composite fiber according to [8] or [9].

[11] Modacryl resin A is obtained by polymerizing monomer composition A in the presence of water, a water-soluble polymerization initiator, and an emulsifier, wherein monomer composition A comprises 35 to 69.9% by mass of acrylonitrile, 30 to 69.9% by mass of halogen-containing monomer, and 0.1 to 1.5% by mass of sulfonic acid group-containing vinyl monomer. A method for producing a core-sheath type composite fiber according to any one of [8] to

[10] .

[12] Acrylonitrile resin B is obtained by polymerizing monomer composition B in the presence of water and a water-soluble polymerization initiator, and under conditions where an emulsifier is substantially absent, wherein 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, and 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 10.0 to 19.0% by mass, the method for producing a core-sheath type composite fiber according to

[11] .

Claims

1. A core-sheath type composite fiber including a sheath and a core, The sheath portion contains modacryl resin A, and the core portion contains 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. A core-sheath type composite fiber in which, when the content of constituent units derived from acrylonitrile in modacryl resin A is 1% by mass (CtA) and the content of constituent units derived from acrylonitrile in acrylonitrile-based resin B is 1% by mass (CtB), |CtA1 - CtB1| is 10.0 to 19.0% by mass.

2. The core-sheath type composite fiber according to claim 1, wherein CtB1 is higher than CtA1.

3. The core-sheath type composite fiber according to claim 1, wherein when the total mass of Modacri resin A and acrylonitrile resin B is 100% by mass, Modacri resin A is 50 to 90% by mass and acrylonitrile resin B is 10 to 50% by mass.

4. The core-sheath type composite fiber according to claim 1, wherein the halogen-containing monomer comprises one or more selected from the group consisting of vinyl chloride and vinylidene chloride.

5. The core-sheath type composite fiber 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.

6. The core-sheath type composite fiber according to claim 1, wherein the Modacri 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.

7. The core-sheath type composite fiber according to claim 1, wherein in the acrylonitrile resin B, the sulfonic acid group-containing vinyl monomer is one or more selected from the group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, and metal salts thereof.

8. A method for producing a core-sheath type composite fiber according to any one of claims 1 to 7, A step of dissolving a mixed resin, which is a mixture of modacryl resin A and acrylonitrile resin B, in a solvent to obtain a spinning solution, and A method for producing a core-sheath type composite fiber, comprising the step of extruding the spinning solution into a coagulation bath using a single-type nozzle.

9. The method for producing a core-sheath type composite fiber according to claim 8, wherein the solvent is one or more selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

10. The method for producing a core-sheath type composite fiber according to claim 8, wherein the coagulation solution is an aqueous solution of one or more solvents selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and dimethylformamide.

11. The modacryl resin A is obtained by polymerizing monomer composition A in the presence of water, a water-soluble polymerization initiator, and an emulsifier, wherein monomer composition A contains 35 to 69.9% by mass of acrylonitrile, 30 to 69.9% by mass of halogen-containing monomer, and 0.1 to 1.5% by mass of sulfonic acid group-containing vinyl monomer, according to the method for producing a core-sheath type composite fiber as described in claim 8.

12. The acrylonitrile resin B is obtained by polymerizing monomer composition B in the presence of water and a water-soluble polymerization initiator, and under conditions where an emulsifier is substantially absent, wherein monomer composition B contains 15 to 89.9% by mass of acrylonitrile, 7.1 to 82% by mass of halogen-containing monomer, and 3 to 20% by mass of sulfonic acid group-containing vinyl monomer, and 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 10.0 to 19.0% by mass, the method for producing a core-sheath type composite fiber according to claim 11.

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