Modacrylic fiber production method

Abstract

To provide a modacrylic fiber production method that enables recycling of modacrylic fiber products while dissolving the modacrylic fiber products in a spinning dope at a high concentration and performing wet spinning with the resulting spinning dope.SOLUTION: A modacrylic fiber is produced by a method comprising: contacting a modacrylic fiber product containing an oil-based agent with an alkaline aqueous solution to provide a deoiled fiber having the content of the oil-based agent reduced to a specified level or less; dissolving the deoiled fiber in a specific solvent to provide a spinning dope; and performing wet spinning with the spinning dope.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing modacrylic fibers.

Background Art

[0002] Modacrylic fibers, known as acrylic fibers, are used in various applications such as clothing, construction, and industrial materials because of their unique texture, excellent color development properties, and dyeing fastness. Regarding modacrylic fibers, which are petroleum products, there is a strong demand for their recycling in terms of the sustainability of human activities. As a method for recycling acrylic fibers, a method has been proposed in which crushed acrylic fibers are dissolved in a solvent, and then wet spinning is performed using the resulting solution of acrylic resin (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when dissolving a modacrylic fiber product containing an oil agent in a solvent, since the modacrylic fiber product is hardly soluble in the solvent, it is often impossible to prepare a dope (spinning stock solution) containing a modacrylic resin at a sufficiently high concentration.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing modacrylic fibers that recycles modacrylic fiber products by dissolving the modacrylic fiber products in a solvent at a high concentration to prepare a spinning stock solution and performing wet spinning using the resulting spinning stock solution.

Means for Solving the Problems

[0006] The inventors of the present invention have found that the above problems can be solved by a method for producing modacrylic fibers, which includes bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution to obtain defatted fibers with the oil agent content reduced to a specific amount or less, dissolving the defatted fibers in a specific solvent to obtain a spinning dope, and performing wet spinning using the spinning dope, and thus completed the present invention.

[0007] More specifically, the present invention provides the following (1) to (8). (1) Obtaining defatted fibers in which at least a part of the oil agent is removed by bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution; Dissolving the defatted fibers in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone to obtain a spinning dope; Performing wet spinning using the spinning dope, and in the defatted fibers, the following formula (a): Oil agent adhesion amount (%omf) in defatted fibers = mass of oil agent adhering to defatted fibers / mass of defatted fibers × 100 Formula (a) A method for producing modacrylic fibers, wherein the oil agent adhesion amount calculated by the formula is 0.15%omf or less. (2) The method for producing modacrylic fibers according to (1), wherein the alkaline aqueous solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, sodium hydrogen carbonate, and calcium hydroxide. (3) The method for producing modacrylic fibers according to (1) or (2), wherein the pH of the alkaline aqueous solution is 10.0 or more. (4) The method for producing modacrylic fibers according to any one of (1) to (3), wherein the temperature of the alkaline aqueous solution is 45°C or more and 98°C or less. (5) The method for producing modacrylic fibers according to any one of (1) to (4), including washing the defatted fibers obtained after contact with the alkaline aqueous solution. The method for producing modacrylic fibers according to any one of (1) to (5), including filtering the spinning dope before performing wet spinning. The method for producing modacrylic fibers according to any one of (1) to (6), wherein the concentration of the defatted fibers in the spinning dope is 5% by mass or more and 35% by mass or less. The method for producing modacrylic fibers according to any one of (1) to (7), wherein the electric conductivity of the spinning dope is 350 μS / cm or less.

Advantages of the Invention

[0008] According to the present invention, there is provided a method for producing modacrylic fibers for recycling modacrylic fiber products, which comprises dissolving a modacrylic fiber product in a solvent at a high concentration to prepare a spinning dope, and performing wet spinning using the obtained spinning dope.

Embodiments for Carrying Out the Invention

[0009] ≪Method for Producing Modacrylic Fibers≫ The method for producing modacrylic fibers comprises: bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution to obtain defatted fibers having at least a part of the oil agent removed; dissolving the defatted fibers in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone to obtain a spinning dope; performing wet spinning using the spinning dope. In the defatted fibers, the following formula (a): Oil agent adhesion amount (%omf) in defatted fibers = mass of oil agent adhering to defatted fibers / mass of defatted fibers × 100 Formula (a) The calculated oil agent adhesion amount is 0.15%omf or less. According to the above method for producing modacrylic fibers, the solubility of the modacrylic fiber product containing an oil agent in an organic solvent is increased, and insoluble components derived from the modacrylic fiber product are removed, so that wet spinning can be performed well.

[0010] In the specification of this application, the process of obtaining degreased fibers in which at least a part of the oil agent is removed by bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution is also referred to as the "degreasing step". The process of dissolving the degreased fibers in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone to obtain a spinning dope is also referred to as the "spinning dope preparation step". The process of performing wet spinning using the spinning dope is also referred to as the "spinning step".

[0011] Hereinafter, each step included in the above method for producing modacrylic fibers will be described.

[0012] <Degreasing Step> In the degreasing step, degreased fibers in which at least a part of the oil agent is removed are obtained by bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution. The method of bringing the modacrylic fiber product containing an oil agent into contact with the alkaline aqueous solution is not particularly limited as long as degreased fibers with an oil agent adhesion amount of 0.15% omf or less in the degreased fibers can be obtained. Examples of the method of bringing the modacrylic fiber product containing an oil agent into contact with the alkaline aqueous solution include, for example, a method of immersing the modacrylic fiber product containing an oil agent in the alkaline aqueous solution, and a method of pouring the alkaline aqueous solution over the modacrylic fiber product containing an oil agent. Examples of the method of pouring the alkaline aqueous solution over the modacrylic fiber product containing an oil agent include a method of spraying the alkaline aqueous solution onto the modacrylic fiber product containing an oil agent with a spray, and a method of spraying it with a shower. As the method of bringing the modacrylic fiber product containing an oil agent into contact with the alkaline aqueous solution, a method of immersing the modacrylic fiber product containing an oil agent in the alkaline aqueous solution is preferable.

[0013] When the modacrylic fiber product containing an oil agent is brought into contact with the alkaline aqueous solution by immersion, the modacrylic fiber product containing an oil agent may be stirred or shaken in the alkaline aqueous solution.

[0014] When a modacrylic fiber product containing an oil agent and an alkaline aqueous solution are brought into contact by immersion, the immersion time is not particularly limited as long as a degreased fiber having an oil agent adhesion amount of 0.15% omf or less can be obtained. As the immersion time, for example, 30 minutes or more is preferable, 2 hours or more is more preferable, 4 hours or more is further preferable, and 6 hours or more is most preferable. The upper limit of the immersion time is not particularly limited, but it may be, for example, 2 days or less, 1 day or less, or 12 hours or less.

[0015] By bringing a modacrylic fiber product containing an oil agent and an alkaline aqueous solution into contact, at least a part of the oil agent contained in the modacrylic fiber product is removed from the modacrylic fiber product. When at least a part of the oil agent is removed from the modacrylic fiber product so that the content of the oil agent in the degreased fiber is the above-mentioned specific amount, a degreased fiber that dissolves in an organic solvent at a high concentration can be obtained.

[0016] Hereinafter, a method for obtaining a degreased fiber will be described.

[0017] (Oil agent) The oil agent is not particularly limited as long as it is an oil agent that has been conventionally added to modacrylic fiber products. Also, the oil agent may be a compound that is usually used for the purpose of antistatic, preventing adhesion of modacrylic fibers, and improving the texture during the production of the modacrylic fibers that make up the modacrylic fiber product. Typically, the oil agent adheres to the fiber surface in a modacrylic fiber product. The oil agent adhering to the fiber surface is considered to particularly inhibit the dissolution of the modacrylic fiber product in an organic solvent. Therefore, by reducing the content of the oil agent in the degreased fiber to the above-mentioned specific amount, the degreased fiber can be dissolved in the solvent at a high concentration.

[0018] Examples of the oil agent include anionic surfactants such as phosphate esters and sulfate esters; cationic surfactants such as quaternary ammonium salts and imidazolium salts; nonionic surfactants such as ethylene oxide and / or propylene oxide adducts of oils and fats, partial esters of polyhydric alcohols, etc.; animal and vegetable oils and fats; mineral oils; fatty acid esters; silicone-based surfactants such as amino-modified silicone, etc.

[0019] (Modacrylic fiber products) The modacrylic fiber products are not particularly limited. The modacrylic fiber products include not only modacrylic fibers manufactured for sales purposes, but also modacrylic fibers manufactured for test and research purposes, and modacrylic fibers manufactured for the purpose of being used by companies and individuals that produce modacrylic fibers.

[0020] The modacrylic fiber products may be either colored fibers or uncolored fibers. When the modacrylic fiber products are colored, typically, the modacrylic fiber products contain pigments. The pigments may be either organic pigments or inorganic pigments. The modacrylic fiber products may contain two or more kinds of pigments, and may contain dyes together with the pigments. Carbon black is preferably used because it is easily available, etc. According to the above method, even if the modacrylic fiber products contain pigments such as carbon black, the modacrylic fibers can be produced by performing wet spinning well while recycling the modacrylic fiber products.

[0021] In addition to the above-mentioned oil agent and pigments, the modacrylic fiber products may contain various additives. Examples of the various additives contained in the modacrylic fiber products include brightening agents such as titanium dioxide, silicon dioxide, and esters and ethers of cellulose derivatives; stabilizers for improving light resistance and heat resistance, etc.; dyes; anti-odor stabilizers such as polyglycidyl methacrylate, etc.

[0022] The modacrylic fiber products mainly consist of modacrylic resins. Hereinafter, the modacrylic resins will be described.

[0023] (Modacrylic resin) For example, a modacrylic copolymer in which the ratio of the mass of the structural unit derived from acrylonitrile to the mass of the modacrylic resin is 35% by mass or more and less than 85% by mass, and the ratio of the structural unit derived from other monomers other than acrylonitrile is more than 15% by mass and 65% by mass or less can be preferably used as the modacrylic resin. As such a modacrylic copolymer, a modacrylic copolymer in which the ratio of the mass of the structural unit derived from acrylonitrile to the mass of the modacrylic resin is 35% by mass or more and 80% by mass or less, and the ratio of the structural unit derived from other monomers other than acrylonitrile is 20% by mass or more and 65% by mass or less is more preferable.

[0024] More specifically, a modacrylic copolymer in which the ratio of the mass of the structural unit derived from acrylonitrile to the mass of the modacrylic resin is 35% by mass or more and 79.5% by mass or less, the ratio of the mass of the structural unit derived from vinyl chloride and / or vinylidene chloride is 20% by mass or more and 64.5% by mass or less, and the ratio of the mass of the structural unit derived from a sulfonic acid group-containing vinyl monomer is 0.5% by mass or more and 5% by mass or less can be particularly preferably used. In the above modacrylic copolymer, when the content of the structural unit derived from acrylonitrile is 35% by mass or more and 79.5% by mass or less, the heat resistance of the obtained modacrylic fiber is good. In the modacrylic copolymer, when the content of the structural unit derived from vinyl chloride and / or vinylidene chloride is 20% by mass or more and 64.5% by mass or less, the flame retardancy of the obtained modacrylic fiber is good. By including 0.5% by mass or more and 5% by mass or less of the sulfonic acid group-containing vinyl monomer in the modacrylic copolymer, the hydrophilicity of the obtained modacrylic fiber is good.

[0025] Regarding the modacrylic resin, the ratio of the mass of the structural unit derived from acrylonitrile to the mass of the modacrylic copolymer is 35% by mass or more and 74.5% by mass or less, the ratio of the mass of the structural unit derived from vinyl chloride and / or vinylidene chloride is 25% by mass or more and 64.5% by mass or less, and it is more preferable that the ratio of the structural unit derived from the sulfonic acid group-containing vinyl monomer is 0.5% by mass or more and 5% by mass or less. In terms of obtaining modacrylic fibers with excellent touch, it is preferable that the modacrylic copolymer contains a structural unit derived from vinyl chloride.

[0026] Examples of the above sulfonic acid group-containing vinyl monomer include allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and metal salts and amine salts such as sodium salts thereof. The sulfonic acid group-containing vinyl monomer may be used alone or in combination of two or more.

[0027] (Alkaline aqueous solution) The type of the alkaline aqueous solution is not particularly limited as long as the aqueous solution exhibits alkalinity. Examples of the alkaline compound that gives the alkaline aqueous solution include hydroxides of alkali metals, carbonates of alkali metals, bicarbonates of alkali metals, hydroxides of alkaline earth metals, carbonates of alkaline earth metals, bicarbonates of alkaline earth metals, ammonium salts, amine compounds, and the like. Specific examples of the alkaline compound include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate; bicarbonates of alkali metals such as sodium bicarbonate and potassium bicarbonate. From the viewpoints of the ease of obtaining the alkaline compound or the alkaline aqueous solution and the ease of preparing the alkaline aqueous solution, it is preferable that the alkaline aqueous solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, sodium bicarbonate, and calcium hydroxide.

[0028] The pH of the alkaline aqueous solution is preferably 9.0 or higher, more preferably 10.0 or higher. When the pH of the alkaline aqueous solution is 9.0 or higher, the degreasing effect of removing the sizing agent from the modacrylic fiber product containing the sizing agent is high. In the specification and claims of the present application, the pH of the alkaline aqueous solution is the value at 25°C. Further, the pH of the alkaline aqueous solution is preferably 14.0 or lower, more preferably 13.0 or lower. From the viewpoint of efficiently removing the sizing agent from the modacrylic fiber product containing the sizing agent, the pH of the alkaline aqueous solution is preferably 9.0 or higher and 14.0 or lower, more preferably 10.0 or higher and 14.0 or lower, and even more preferably 10.0 or higher and 13.0 or lower. When it is difficult to remove the sizing agent by using an alkaline aqueous solution having a low pH value, the sizing agent can be removed to a desired degree by extending the contact time between the modacrylic fiber product and the alkaline aqueous solution.

[0029] The temperature of the alkaline aqueous solution is not particularly limited. As the temperature of the alkaline aqueous solution, for example, 0°C or higher and 98°C or lower is preferable. From the viewpoint of enhancing the degreasing effect of removing the sizing agent from the modacrylic fiber product containing the sizing agent, the temperature of the alkaline aqueous solution is more preferably 45°C or higher and 98°C or lower, and even more preferably 55°C or higher and 98°C or lower. When it is difficult to remove the sizing agent by using a low-temperature alkaline aqueous solution, the sizing agent can be removed to a desired degree by extending the contact time between the modacrylic fiber product and the alkaline aqueous solution.

[0030] (Degreased fiber) The degreased fiber is a fiber obtained by removing at least a part of the sizing agent from the modacrylic fiber product containing the sizing agent. The sizing agent adhesion amount in the degreased fiber is 0.15% omf or less. The sizing agent adhesion amount in the degreased fiber is represented by the following formula (a): Sizing agent adhesion amount in degreased fiber (% omf) = mass of sizing agent adhering to degreased fiber / mass of degreased fiber × 100 Formula (a) It can be calculated by. The specific measurement method of the sizing agent adhesion amount in the degreased fiber will be described in detail in the examples.

[0031] Hereinafter, a method for obtaining defatted fibers from which at least a part of the oil agent has been removed will be described. By bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution, defatted fibers from which at least a part of the oil agent has been removed can be obtained. Specifically, after bringing the modacrylic fiber product containing the oil agent into contact with the alkaline aqueous solution, the defatted fibers can be obtained by separating the alkaline aqueous solution from the defatted fibers. The method for separating the alkaline aqueous solution from the defatted fibers is not particularly limited. Examples of the method for separating the alkaline aqueous solution from the defatted fibers include filtration and the like.

[0032] From the viewpoint of removing the alkaline component from the defatted fibers, it is preferable to wash the defatted fibers after contact with the alkaline aqueous solution. As a specific procedure, after bringing the modacrylic fiber product containing the oil agent into contact with the alkaline aqueous solution, the alkaline aqueous solution is separated from the defatted fibers, and the obtained defatted fibers are washed. The method for washing the defatted fibers obtained after contact with the alkaline aqueous solution is not particularly limited. Examples of the method for washing the defatted fibers obtained after contact with the alkaline aqueous solution include immersing the defatted fibers in water, flowing water over the defatted fibers, or spraying water on the defatted fibers with a shower.

[0033] In order to adjust the water content of the spinning dope within the preferred range described below, part or all of the water adhering to the degreased fiber may be removed. The water is derived from an alkaline aqueous solution or washing water for removing the alkaline component. Typically, the water adheres to the surface of the degreased fiber or penetrates into minute gaps or pores present in the degreased fiber. The method for removing the water adhering to the degreased fiber is not particularly limited as long as the desired effect is not impaired. Examples of the method for removing the water adhering to the degreased fiber include hot air drying and vacuum drying. The drying temperature for hot air drying is not particularly limited. As the drying temperature for hot air drying, for example, 110°C or higher and 190°C or lower is preferred, and 110°C or higher and 170°C or lower is more preferred. The drying time is not particularly limited. As the drying time, for example, 2 hours or longer is preferred, and 4 hours or longer is more preferred.

[0034] By using the degreased fiber from which at least part of the sizing agent has been removed obtained by the above method, the degreased fiber can be dissolved in an organic solvent at a high concentration, and in the spinning process described below, spinning can be performed favorably. The degreased fiber is then subjected to a spinning dope preparation process.

[0035] <Spinning Dope Preparation Process> In the spinning dope preparation process, the degreased fiber is dissolved in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone to obtain a spinning dope. By using the above solvent, the degreased fiber can be dissolved favorably, and in the spinning process described below, spinning can be performed favorably. From the viewpoint of safety, it is preferred to dissolve the degreased fiber in dimethyl sulfoxide to obtain a spinning dope.

[0036] The electrical conductivity of the spinning dope is not particularly limited as long as the desired effect is not impaired. From the viewpoint of performing wet spinning favorably, the electric conductivity of the spinning dope is preferably, for example, 350 μS / cm or less, more preferably 300 μS / cm or less. The lower limit of the electric conductivity is not particularly limited. The lower limit of the electric conductivity may be, for example, 50 μS / cm or more, or 100 μS / cm or more. The electric conductivity of the spinning dope is measured using a portable conductivity meter (Hanchen DDB-303A). Specifically, the terminals of the portable conductivity meter are inserted into the spinning dope, and a value of the electric conductivity corrected to the electric conductivity measured at 25°C by the temperature correction function of the portable conductivity meter is obtained. This corrected value of the electric conductivity is taken as the value of the electric conductivity of the spinning dope.

[0037] The concentration of the degreased fibers in the spinning dope is not particularly limited as long as the desired effect is not impaired. From the viewpoint of performing spinning favorably in the spinning process described later, the concentration of the degreased fibers in the spinning dope is preferably 5% by mass or more and 35% by mass or less, more preferably 10% by mass or more and 35% by mass or less, still more preferably 20% by mass or more and 35% by mass or less, based on the mass of the spinning dope.

[0038] The spinning dope may contain a modacrylic resin not derived from a modacrylic fiber product. The modacrylic resin not derived from a modacrylic fiber product is usually a virgin material. For example, the concentration of the modacrylic resin in the spinning dope can be adjusted by dissolving a virgin material of the modacrylic resin in the spinning dope containing the degreased fibers in a dissolved state. When the spinning dope contains a modacrylic resin derived from the degreased fibers and a modacrylic resin not derived from the degreased fibers, the preferred concentration of the modacrylic resin in the spinning dope is the same as the preferred concentration of the degreased fibers in the spinning dope described above. When the spinning dope contains a modacrylic resin derived from the degreased fibers and a modacrylic resin not derived from the degreased fibers, the ratio of the mass of the modacrylic resin derived from the degreased fibers to the total mass of the modacrylic resin may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 50% by mass or more, 80% by mass or more, or 90% by mass or more.

[0039] When dissolving the degreased fiber in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone, heating may be performed as necessary. The heating temperature is not particularly limited as long as thermal degradation of the degreased fiber and the solvent does not occur.

[0040] The spinning dope may contain water. The water content of the spinning dope is not particularly limited as long as the desired effect is not impaired. From the viewpoint of the solubility of the degreased fiber in the spinning dope, the water content of the spinning dope is preferably 0.5% by mass or more and 12.0% by mass or less, more preferably 1.0% by mass or more and 9.0% by mass or less, and even more preferably 1.5% by mass or more and 7.0% by mass or less.

[0041] The spinning dope may contain a pigment. As the pigment, various well-known pigments can be used as necessary. The pigment may be an organic pigment or an inorganic pigment. Also, the spinning dope may contain two or more pigments, and may contain a dye together with the pigment.

[0042] As the pigment added to the spinning dope, a solid powdery pigment may be used, or a pigment dispersion liquid containing a pigment dispersed in a dispersion medium may be used. From the viewpoint of the dispersibility of the pigment in the spinning dope and the modacrylic fiber, it is preferable to prepare the spinning dope using the pigment dispersion liquid.

[0043] As the pigment, carbon black is preferable because it can color the modacrylic fiber into a desired hue of black and is easily available.

[0044] From the viewpoint of suppressing the occurrence of thread breakage in the spinning process while coloring the modacrylic fiber to the desired degree, the content of the pigment in the spinning dope is preferably 0.01 part by mass or more and 2.00 parts by mass or less, more preferably 0.02 part by mass or more and 0.60 part by mass or less, based on 100 parts by mass of the spinning dope.

[0045] The spinning dope may contain, if necessary, other additives for improving fiber properties, as long as the desired effects are not inhibited. Such additives include, for example, titanium dioxide, silicon dioxide, and lustering agents such as esters and ethers of cellulose derivatives including cellulose acetate; stabilizers for improving light resistance and heat resistance, etc.

[0046] The spinning dope is then subjected to a spinning process.

[0047] <Spinning process> In the spinning process, wet spinning is performed using the spinning dope. As the wet spinning method, extruding the spinning dope from a nozzle into a coagulation bath for coagulation, and stretching the fibers formed by coagulating the spinning dope in a stretching bath, is preferably included.

[0048] Hereinafter, extruding the spinning dope from a nozzle into a coagulation bath for coagulation is also referred to as the "coagulation step". Stretching the fibers formed by coagulating the spinning dope in a stretching bath is also referred to as the "stretching step".

[0049] (Coagulation step) In the coagulation step, the spinning dope is extruded from a nozzle into the coagulation bath in a fibrous form, and the fibrously extruded spinning dope is coagulated. The spinning dope is discharged into the coagulation bath from a nozzle having a size and shape corresponding to the fiber diameter and cross-sectional shape of the modacrylic fiber.

[0050] In the coagulation step, first, the spinning dope is extruded through a spinning nozzle into the coagulation bath. The coagulated liquid extruded in a fibrous form coagulates in the coagulation bath to form fibers. From the viewpoint of easy control of the coagulation state, it is preferable to use a mixed liquid of water and an organic solvent as the coagulation bath. For example, as the liquid introduced into the coagulation bath, an aqueous solution of an organic solvent is preferable. The concentration of the organic solvent in the aqueous solution of the organic solvent is preferably 20% by mass or more and 75% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and even more preferably 40% by mass or more and 70% by mass or less.

[0051] The organic solvent contained in the liquid extruded into the coagulation bath is not particularly limited as long as it is a good solvent for the modacrylic resin. From the viewpoint of the productivity of modacrylic fibers, one or more selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfone, ε-caprolactam, ethylene carbonate, and sulfolane are preferable. From the viewpoint of safety, dimethyl sulfoxide is more preferable. From the viewpoints of the quality of modacrylic fibers and the simplicity of process control, it is preferable that the organic solvent in the spinning dope and the organic solvent in the liquid extruded into the coagulation bath are the same organic solvent.

[0052] The temperature of the spinning dope extruded into the coagulation bath is preferably 35°C or lower. The temperature of the liquid extruded into the coagulation bath is preferably 10°C or higher and 30°C or lower, more preferably 10°C or higher and 25°C or lower.

[0053] (Drawing process) The fibers produced by coagulating the spinning dope in the coagulation bath are then drawn in the drawing bath. The method of transferring the fibers to be drawn from the coagulation bath to the drawing bath is not particularly limited. Typically, the fibers to be drawn are passed over a roll in the coagulation bath and one or more fiber transfer rolls outside the coagulation bath, and by rotating the rolls, the fibers to be drawn are transferred into the drawing bath.

[0054] The fibers transferred into the drawing bath are passed over a first drawing roll provided on the upstream side in the moving direction of the fibers to be drawn and a second drawing roll provided on the downstream side in the moving direction of the fibers to be drawn in the liquid extruded into the drawing bath, and are drawn by rotation. Here, the draw ratio is adjusted by adjusting the tension applied to the fibers drawn by the first drawing roll and the second drawing roll and the rotational speeds of the first drawing roll and the second drawing roll. The draw ratio is preferably more than 100% and 800% or less, more preferably 120% or more and 300% or less. The drawn modacrylic fibers are passed over a roll such as a clover roll provided outside the drawing bath and are appropriately recovered from the drawing bath.

[0055] The bath solution immersed in the stretching bath is not particularly limited as long as good stretching can be performed. For example, water or an aqueous solution containing an organic solvent can be used. As the bath solution in the stretching bath, an aqueous solution of an organic solvent containing 10% by mass or more and 90% by mass or less of water based on the mass of the bath solution is preferable. The temperature in the stretching bath is preferably in the range of 30°C or higher and 110°C or lower, and more preferably in the range of 40°C or higher and 95°C or lower.

[0056] The stretching in the stretching bath is preferably carried out in multiple steps. Further, it is preferable that the average values of the stretching speeds are different at least in two of the multiple stretches. When the stretching in the stretching bath is carried out in multiple steps, it is easy to control the stretching conditions for each period such as the initial stage, the middle stage, and the later stage in the stretching process. Here, the stretching being carried out in multiple steps means that stretching and the release of the tension for stretching are repeated any number of times of two or more. The multiple stretches may be carried out in the same stretching bath or may be carried out using a plurality of different stretching baths. It is preferable to use a plurality of different stretching baths in that the temperature of the stretching bath and the composition of the liquid immersed in the stretching bath can be changed for each stretching bath.

[0057] (Water washing step) The drawn modacrylic fibers are usually washed in a water washing process. In the water washing process, the drawn modacrylic fibers in the drawing bath are washed with water to remove the organic solvent from the modacrylic fibers. In the water washing process, it is preferable to use an aqueous solution of an organic solvent with a lower concentration of the organic solvent than warm water or a coagulation bath at 25°C or higher as the washing liquid. The water washing can be carried out by immersing the drawn modacrylic fibers in a bath filled with these washing liquids or spraying water onto the moving modacrylic fibers. The means for spraying water in the water washing process is not particularly limited, but from the viewpoint of easy spraying, it is preferable to spray water with a nozzle. The direction of spraying water is not particularly limited, and it may be sprayed from the side or from below. From the viewpoint of uniformly spraying water, it is preferable to use a shower nozzle having a plurality of holes. The temperature of the water used for spraying water is not particularly limited. For example, water in the temperature range of 20 to 95°C can be used. From the viewpoint of enhancing the desolventizing effect of removing the organic solvent, the temperature of the water is preferably 40°C or higher, and more preferably 50°C or higher.

[0058] Although not particularly limited, in the water washing process, from the viewpoint of enhancing the effect of removing the organic solvent, the ratio of the total fineness to the width of the modacrylic fiber bundle is preferably 300,000 dtex / cm or less, more preferably 200,000 dtex / cm or less, and even more preferably 100,000 dtex / cm or less.

[0059] (Dehydration process) When the drawn modacrylic fibers are washed with water, the washed modacrylic fibers are dehydrated in a dehydration process. In the dehydration process, the washed modacrylic fibers are passed between nip rolls while being sandwiched between the nip rolls for dehydration.

[0060] The "nip roll" is usually not particularly limited as long as it is used when manufacturing fibers by the wet spinning method. As the nip roll, for example, a rubber nip roll, a metal nip roll, etc. can be used. As the upper nip roll, a rubber nip roll (also referred to as a rubber roll) is preferably used, and as the lower nip roll, a metal nip roll (also referred to as a metal roll) is preferably used.

[0061] The above-described water washing step and dehydration step may be alternately repeated a plurality of times one by one. After performing the above-described water washing two or more times, pressing by nip rolls may be performed one or more times.

[0062] (Drying step) The modacrylic fibers stretched in the stretching bath and the modacrylic fibers dehydrated as described above are then dried in the drying step. In the drying step, it is preferable that the moisture contained in the modacrylic fibers is almost completely removed. The drying method is not particularly limited as long as it can remove the moisture of the modacrylic fibers. Examples of the drying method include hot air drying and drying by contacting with a heating roll. The drying temperature is not particularly limited, but for example, 110°C or higher and 190°C or lower is preferable, and 110°C or higher and 170°C or lower is more preferable.

[0063] The fineness of the modacrylic fibers obtained as described above is appropriately determined according to the use of the modacrylic fibers.

[0064] Before drying the modacrylic fibers, an oil agent may be attached to the modacrylic fibers. The oil agent is as described above.

[0065] The dried modacrylic fibers obtained by the above method may be further stretched as necessary. The stretching method is not particularly limited, and examples include dry and wet methods.

[0066] The dried modacrylic fiber obtained by the above method is preferably further relaxed in a heat relaxation treatment step. The relaxation rate is not particularly limited, but for example, 5% or more is preferable, and 10% or more is more preferable. The heat relaxation treatment can be carried out in a dry heat atmosphere or superheated steam atmosphere at a high temperature, for example, 130°C or higher and 200°C or lower, preferably 140°C or higher and 190°C or lower. Alternatively, it can be carried out in a pressurized steam or heated pressurized steam atmosphere at 120°C or higher and 180°C or lower, 0.05 MPa or higher and 0.4 MPa or lower, preferably 0.1 MPa or higher and 0.4 MPa or lower.

Examples

[0067] The present invention will be described more specifically by the following examples. Note that the present invention is not limited to the following examples.

[0068] 〔Example 1〕 (Degreasing step) 200 parts by mass of a modacrylic fiber product (AFRELLE (manufactured by Kaneka)) was immersed in an alkaline aqueous solution at 70°C (pH 11.3 (value at 25°C)) consisting of 80 parts by mass of sodium carbonate and 1400 parts by mass of pure water for 240 minutes. Then, the degreased fiber was filtered off from the alkaline aqueous solution in which the degreased fiber was immersed to obtain a degreased fiber. More than 2000 parts by mass of pure water was poured over the degreased fiber with the alkaline aqueous solution attached for 3 minutes to wash the degreased fiber and remove the aqueous sodium carbonate solution adhering to the surface of the degreased fiber, and then it was dried at 140°C for 4 hours. When the obtained degreased fiber was dissolved in dimethyl sulfoxide at 60°C, the degreased fiber dissolved in dimethyl sulfoxide whether the concentration of the degreased fiber was 25.0% by mass or 27.5% by mass.

[0069] (Spinning dope preparation step) 200 parts by mass of defatted fiber after drying, 588 parts by mass of dimethyl sulfoxide, and 12 parts by mass of pure water were put into a dissolution tank. The internal temperature of the dissolution tank was maintained at 60 °C for 30 minutes to dissolve the defatted fiber in dimethyl sulfoxide containing a small amount of water. Then, the solution in the dissolution tank was stirred at 170 rpm for 30 minutes. Next, the solution in the dissolution tank was stirred at 330 rpm for 30 minutes. After stirring, the solution in the dissolution tank was filtered through a mesh filter with an opening size of 2 mm to obtain a spinning dope. The concentration of the defatted fiber in the obtained spinning dope was 25% by mass. Also, as a result of measuring the electrical conductivity of the obtained spinning dope by the method described later, the electrical conductivity of the spinning dope was 185 μS / cm.

[0070] (Spinning process) The spinning dope at 35 °C was supplied to a nozzle having 10 discharge holes with an opening area of 0.085 mm 2 and discharged into a coagulation bath in which an aqueous solution of 47% by mass of dimethyl sulfoxide at a temperature of 25 °C was filled with a nozzle discharge speed of 10 m / min, and spinning was performed at a draft ratio of 1.25. After washing with water in an 80 °C water bath, the fiber was immersed in an oil agent (a mixture of 65% by mass of castor oil ether and 35% by mass of sorbitan stearate). Then, it was dried, and then the fiber was stretched at 125 °C with a draw ratio of 230%, and relaxation treatment was performed at 155 °C to obtain a modacrylic fiber.

[0071] [Example 2] In the defatting step, modacrylic fiber was obtained in the same manner as in Example 1 except that sodium carbonate was changed to sodium hydroxide. The pH value of the alkaline aqueous solution was pH 13.8 (value at 25 °C). As a result of measuring the electrical conductivity of the obtained spinning dope by the method described later, the electrical conductivity of the spinning dope was 306 μS / cm.

[0072] [Example 3] Modacrylic fiber was obtained in the same manner as in Example 2 except that the immersion time was changed from 240 minutes to 30 minutes.

[0073] [Comparative Example 1] (Spinning dope preparation process) Without performing the defatting process, 200 parts by mass of a modacrylic fiber product, 588 parts by mass of dimethyl sulfoxide, and 12 parts by mass of pure water were placed in a dissolution tank. The internal temperature of the dissolution tank was maintained at 60 °C for 30 minutes to dissolve the modacrylic fiber product in dimethyl sulfoxide containing a small amount of water. Then, the solution in the dissolution tank was stirred at 170 rpm for 30 minutes. Next, the solution in the dissolution tank was stirred at 330 rpm for 30 minutes. After stirring, needle-like undissolved residues were observed in the solution in the dissolution tank. Therefore, the spinning dope could not be prepared.

[0074] [Comparative Example 2] Defatted fibers were obtained in the same manner as in Example 1, except that 200 parts by mass of a modacrylic fiber product was immersed in 1480 parts by mass of pure water. Attempting to prepare a spinning dope in the same manner as in Example 1 using the obtained defatted fibers, needle-like undissolved residues were observed and the spinning dope could not be prepared.

[0075] 〔Comparative Example 3〕 (Defatting process) Defatted fibers were obtained in the same manner as in Example 1, except that 200 parts by mass of a modacrylic fiber product was immersed in 1480 parts by mass of an aqueous anionic surfactant solution containing 1 part by mass of sodium alkyl ether sulfate. Attempting to prepare a spinning dope in the same manner as in Example 1 using the obtained defatted fibers, needle-like undissolved residues were observed and the spinning dope could not be prepared.

[0076] 〔Comparative Example 4〕 (Defatting process) 200 parts by mass of a modacrylic fiber product (AFRELLE (manufactured by Kaneka)) was immersed in 1480 parts by mass of dilute hydrochloric acid at 50 °C. The dilute hydrochloric acid was prepared by mixing pure water and a 37.0% hydrochloric acid aqueous solution at a mass ratio (pure water: hydrochloric acid aqueous solution) of 10:2. During the immersion, the dilute hydrochloric acid was colored. This is because the pigment contained in the modacrylic fiber product was dispersed in the dilute hydrochloric acid. From this, it is considered that the modacrylic resin was chemically damaged and decomposed by immersing the modacrylic fiber product in hydrochloric acid. Therefore, in Comparative Example 4, defatted fibers were not obtained and the spinning dope was not prepared.

[0077] <ph> The pH of the alkaline aqueous solution was measured at 25 °C using a pH meter (manufactured by Horiba, Ltd.). The results are shown in Table 1.

[0078] <Oil agent adhesion amount in degreased fiber> The oil agent adhesion amount in the degreased fiber is calculated by the following formula (a): Oil agent adhesion amount in degreased fiber (%omf) = mass of oil agent adhering to degreased fiber / mass of degreased fiber × 100 Formula (a) It was calculated according to. Specifically, the oil agent adhesion amount was measured according to the following method. First, a mixed solvent of cyclohexane and ethanol with a mass ratio of 1:1 and the degreased fiber were thoroughly mixed in a test tube. Then, the mixed solvent in the test tube containing the oil agent extracted from the degreased fiber was dropped onto a tray. After evaporating the mixed solvent on the tray, the mass of the residue on the tray was measured. The mass of the degreased fiber added to the test tube was used as the "mass of the degreased fiber" in formula (a), and the mass of the residue was used as the "mass of the oil agent adhering to the degreased fiber" in formula (a), and the oil agent adhesion amount in the degreased fiber was calculated according to formula (a). The results are shown in Table 1. Note that the oil agent adhesion amount in the modacrylic fiber product of Comparative Example 1 was measured according to the above method except that the degreased fiber was changed to a modacrylic fiber product. In Table 1, for the oil agent adhesion amount in the modacrylic fiber product of Comparative Example 1, it is described as the oil agent adhesion amount in the degreased fiber for convenience.

[0079] <Electrical conductivity of spinning dope> The electrical conductivities of the spinning dopes of Example 1 and Example 2 were measured using a portable conductivity meter (Hanchen DDB-303A). The terminals of the portable conductivity meter were inserted into 50 mL of the spinning dope, and a value corrected to the electrical conductivity measured at 25 °C by the temperature correction function of the portable conductivity meter was obtained.

[0080]

Table 1

Claims

1. By bringing a modacrylic fiber product containing an oil agent into contact with an alkaline aqueous solution, obtaining degreased fibers from which at least a part of the oil agent has been removed; Dissolving the degreased fibers in at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone to obtain a spinning dope; Performing wet spinning using the spinning dope, and In the degreased fibers, the following formula (a): Oil agent adhesion amount (%) omf in degreased fibers = mass of oil agent adhering to degreased fibers / mass of degreased fibers × 100 Formula (a) A method for producing modacrylic fibers, wherein the oil agent adhesion amount calculated by the above formula is 0.15% omf or less.

2. The method for producing modacrylic fibers according to claim 1, wherein the alkaline aqueous solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, sodium hydrogen carbonate, and calcium hydroxide.

3. The method for producing modacrylic fibers according to claim 1, wherein the pH of the alkaline aqueous solution is 10.0 or more.

4. The method for producing modacrylic fibers according to claim 1, wherein the temperature of the alkaline aqueous solution is 45°C or more and 98°C or less.

5. The method for producing modacrylic fibers according to claim 1, including washing the degreased fibers obtained after contact with the alkaline aqueous solution.

6. The method for producing modacrylic fibers according to claim 1, including filtering the spinning dope before performing the wet spinning.

7. The method for producing modacrylic fibers according to claim 1, wherein the concentration of the degreased fibers in the spinning dope is 5% by mass or more and 35% by mass or less.

8. The method for producing a modacrylic fiber according to claim 1, wherein the electric conductivity of the spinning dope is 350 μS / cm or less.

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