Method for manufacturing modacrylic fibers

Abstract

This invention provides a method for producing modacrylic fibers that allows for the recycling of modacrylic fiber products by dissolving modacrylic fiber products in an organic solvent to prepare a low-viscosity spinning stock solution, and then stably performing wet spinning using the obtained spinning stock solution. [Solution] A method for producing modacrylic fibers, comprising: a washing step of contacting a modacrylic fiber product with water or steam at a temperature exceeding 100°C under pressurized conditions; a dissolution step of dissolving the modacrylic fiber product obtained in the washing step in an organic solvent to obtain a spinning stock; and a step of wet spinning the spinning stock.

Description

Technical Field

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

Background Art

[0002] Modacrylic fibers, known as acrylic fibers, have characteristics such as a unique texture, excellent color development, and good colorfastness, and are therefore used in various applications such as clothing, construction, and industrial materials. There is a strong demand for recycling modacrylic fibers 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 the 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 modacrylic fiber products in an organic solvent, depending on the type of fiber, the viscosity of the resulting spinning dope may not be sufficiently reduced. Therefore, when discharging the spinning dope from a nozzle for wet spinning, yarn breakage due to nozzle clogging often occurs, and it is often impossible to perform wet spinning stably.

[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 modacrylic fiber products in an organic solvent to prepare a low-viscosity spinning dope and stably performing wet spinning using the resulting spinning dope.

Means for Solving the Problems

[0006] The inventors of the present invention have discovered that the above problems can be solved by washing the modacrylic fiber product in a specific washing process before the process of dissolving the modacrylic fiber product in an organic solvent to prepare a spinning stock, and have completed the present invention.

[0007] Aspects of this disclosure relate to the following methods for producing modacrylic fibers.

[0008] [1] A washing process in which modacrylic fiber products are brought into contact with water or steam at a temperature exceeding 100°C under pressurized conditions, A dissolution step is performed in which the modacryl fiber product obtained in the washing step is dissolved in an organic solvent to obtain a spinning stock, A method for producing modacrylic fibers, comprising the step of wet spinning the aforementioned spinning stock. [2] A method for producing modacrylic fibers according to [1], comprising a pretreatment step of breaking up the modacrylic fiber product into smaller pieces before the washing step. [3] The method for producing modacrylic fibers according to [2], wherein the pretreatment step is a step of reducing the length of the modacrylic fiber product to 10 mm or less. [4] A method for producing modacrylic fibers according to any one of [1] to [3], wherein the viscosity of the spinning solution is 0.1 Pa·s or more and 20 Pa·s or less. [5] A method for producing modacrylic fibers according to any one of [1] to [4], wherein the pressure in the washing step is 0.35 MPa (absolute pressure) or less. [6] A method for producing modacrylic fibers according to any one of [1] to [5], wherein an epoxy group-containing compound is present in the dissolution step. [7] The method for producing modacrylic fiber according to [6], wherein the amount of epoxy group-containing compound used is 0.5 parts by mass or more and 1.2 parts by mass or less per 100 parts by mass of the modacrylic fiber product. [Effects of the Invention]

[0009] According to the present invention, a method for producing modacrylic fibers that allows for the recycling of modacrylic fiber products can be provided by dissolving modacrylic fiber products in an organic solvent to prepare a low-viscosity spinning stock solution, and then stably performing wet spinning using the obtained spinning stock solution. [Modes for carrying out the invention]

[0010] ≪Method for manufacturing modacrylic fibers≫ The method for producing modacrylic fibers in this embodiment is: A washing process in which modacrylic fiber products are brought into contact with water or steam at a temperature exceeding 100°C under pressurized conditions, A dissolution step is performed in which the modacryl fiber product obtained in the above washing step is dissolved in an organic solvent to obtain a spinning stock, The process includes a step of wet spinning the above-mentioned spinning stock solution. The above method for producing modacrylic fibers includes a washing step in which the modacrylic fiber product is washed. This allows for the preparation of a low-viscosity spinning stock by dissolving the modacrylic fiber product in an organic solvent, and enabling stable wet spinning using the obtained spinning stock.

[0011] In this specification, the process of wet spinning the spinning solution is also referred to as the "spinning process."

[0012] The following describes each step involved in the above-mentioned method for manufacturing modacrylic fibers.

[0013] <Washing process> In the washing process, modacrylic fiber products are exposed to water or steam at over 100°C under pressurized conditions. By including the above washing step, a low-viscosity spinning solution can be produced, resulting in modacrylic fibers with excellent spinning stability. Hereinafter, modacrylic fibers obtained by the method of the present invention may be referred to as "recycled modacrylic fibers."

[0014] (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 or individuals who produce modacrylic fibers.

[0015] The modacrylic fiber products may be colored fibers or uncolored fibers. When the modacrylic fiber products are colored, typically, the modacrylic fiber products contain pigments. The pigments may be 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. According to the above method, even if the modacrylic fiber products contain pigments such as carbon black, it is possible to recycle the modacrylic fiber products and perform wet spinning well to produce modacrylic fibers.

[0016] In addition to the above-mentioned pigments, the modacrylic fiber products may contain various additives. Examples of the various additives contained in the modacrylic fiber products include, for example, gloss modifiers such as titanium dioxide, silicon dioxide, esters and ethers of cellulose derivatives; stabilizers for improving light resistance and heat resistance; dyes; anti-odor stabilizers such as polyglycidyl methacrylate.

[0017] Also, the modacrylic fiber products often contain an oil agent. The oil agent is not particularly limited as long as it is an oil agent conventionally added to modacrylic fiber products. The oil agent may be a compound usually used for the purpose of antistatic, preventing adhesion of modacrylic fibers and improving the texture during the production of the modacrylic fibers constituting the modacrylic fiber products. Typically, the oil agent adheres to the fiber surface in the modacrylic fiber products.

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

[0019] Modacrylic fiber products are mainly composed of modacrylic resin. Hereinafter, the modacrylic resin will be described.

[0020] (Modacrylic resin) For example, a modacrylic copolymer in which the mass ratio 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. In addition, the structural unit derived from other monomers other than acrylonitrile essentially includes the structural unit derived from the hydrophilic functional group-containing monomer.

[0021] As such a modacrylic copolymer, a modacrylic copolymer in which the mass ratio 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.

[0022] More specifically, a modacrylic copolymer in which the mass ratio 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 mass ratio 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 mass ratio of the structural unit derived from the hydrophilic functional group-containing monomer is 0.5% by mass or more and 5% by mass or less can be particularly preferably used. In the above modacryl copolymer, if the content of structural units derived from acrylonitrile is 35% by mass or more and 79.5% by mass or less, the resulting modacryl fibers have good heat resistance. In the modacryl copolymer, if the content of structural units derived from vinyl chloride and / or vinylidene chloride is 20% by mass or more and 64.5% by mass or less, the resulting modacryl fibers have good flame retardancy. In the modacryl copolymer, if the content of hydrophilic functional group-containing monomers is 0.5% by mass or more and 5% by mass or less, the resulting modacryl fibers have good hydrophilicity.

[0023] With respect to the modacryl resin, it is more preferable that the ratio of the mass of constituent units derived from acrylonitrile to the mass of the modacryl copolymer is 35% by mass or more and 74.5% by mass or less, the ratio of the mass of constituent units derived from vinyl chloride and / or vinylidene chloride is 25% by mass or more and 64.5% by mass or less, and the ratio of constituent units derived from hydrophilic functional group-containing monomers is 0.5% by mass or more and 5% by mass or less. It is preferable that the modacryl copolymer contains constituent units derived from vinyl chloride in order to obtain modacryl fibers with excellent tactile properties.

[0024] The ratio of constituent units derived from hydrophilic functional group-containing monomers to the mass of modacryl resin is preferably 0.5% by mass or more and 3% by mass or less, and more preferably 0.5% by mass or more and 2.5% by mass or less.

[0025] The monomer containing hydrophilic functional groups is a monomer copolymerizable with acrylonitrile and is not particularly limited as long as it has hydrophilic functional groups. The hydrophilic functional group is not particularly limited as long as it is a functional group capable of forming hydrogen bonds. Specifically, examples include hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphate groups, sulfonylamide groups, and sulfonylimide groups. These groups may also form salts. As described above, among the hydrophilic functional group-containing monomers, sulfonic acid group-containing monomers are preferred in terms of preventing void formation.

[0026] Examples of sulfonic acid group-containing monomers that can be used include allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and their sodium salts and other metal salts and amine salts. The sulfonic acid group-containing monomer may be used individually or in combination of two or more types.

[0027] (Washing pressure) In the cleaning process, the pressurized condition means 0.1 MPa or higher. The pressure in the cleaning process (cleaning pressure) is preferably 0.35 MPa or lower, and more preferably 0.3 MPa or lower. In this specification, cleaning pressure [MPa] means absolute pressure.

[0028] (Cleaning medium, cleaning temperature) In the washing process, the washing medium is water or steam, and water is preferred from the viewpoint of producing a low-viscosity spinning solution. The washing temperature is above 100°C, preferably 105°C or higher, and more preferably 120°C or higher.

[0029] (Washing time) In the washing process, the washing time is not particularly limited, but is preferably 10 minutes or more, and more preferably 30 minutes or more.

[0030] (Contact method) The method of bringing modacrylic fiber products into contact with water exceeding 100°C (hereinafter also referred to as "hot water") is not particularly limited, and one example is immersing the modacrylic fiber products in the hot water (immersion washing). The method of exposing modacrylic fiber products to steam exceeding 100°C is not particularly limited; for example, a method of exposing modacrylic fiber products to the above-mentioned steam (steam cleaning) is one example. Note that "steam exceeding 100°C" means water vapor exceeding 100°C.

[0031] The equipment used in the cleaning process is not particularly limited as long as it is capable of generating the aforementioned high-temperature, high-pressure hot water or steam. As a commercially available product, it is preferable to use, for example, an autoclave (high-pressure steam sterilizer).

[0032] <Dissolution process> In the dissolution process, the modacrylic fiber product obtained in the washing process is dissolved in an organic solvent to obtain a spinning solution.

[0033] (organic solvent) As the organic solvent, any organic solvent conventionally used to dissolve modacryl resin can be used without particular limitation. Preferred organic solvents include at least one selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetone. Among these organic solvents, dimethyl sulfoxide is more preferred from the viewpoint of safety.

[0034] The amount of organic solvent used is preferably 100 parts by mass or more and 400 parts by mass or less, and more preferably 150 parts by mass or more and 300 parts by mass or less, per 100 parts by mass of the modacryl fiber product.

[0035] (Other ingredients) In the dissolution process, components other than the organic solvent described above (hereinafter also referred to as "other components") may be present, as long as they do not impair the effects of the present invention. Examples of other components include water, epoxy group-containing compounds, and oils.

[0036] (water) The amount of water used is preferably 0.5 parts by mass or more and 100 parts by mass or less per 100 parts by mass of modacrylic fiber product, more preferably 1 part by mass or more and 60 parts by mass or less, and even more preferably 2 parts by mass or more and 40 parts by mass or less.

[0037] (Epoxy group-containing compound) Epoxy group-containing compounds are used to prevent the degradation of modacryl resin contained in modacryl fiber products due to dehydrochlorination. Examples of epoxy group-containing compounds include polyglycidyl methacrylate (PGMA), glycerol polyglycidyl ether, and ethylene glycol diglycidyl ether. Among these, polyglycidyl methacrylate (PGMA) is preferred.

[0038] The amount of epoxy group-containing compound used is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.1 parts by mass or more and 5 parts by mass or less, even more preferably 0.2 parts by mass or more and 1.2 parts by mass or less, and still more preferably 0.5 parts by mass or more and 1.2 parts by mass or less, per 100 parts by mass of modacryl fiber product.

[0039] (melting temperature) In the dissolution process, the dissolution temperature is not particularly limited, but is preferably 45°C to 70°C, and more preferably 50°C to 70°C.

[0040] (dissolution time) In the dissolution process, the dissolution time is not particularly limited, but is preferably 60 minutes or more and 300 minutes or less, and more preferably 120 minutes or more and 240 minutes or less.

[0041] In the dissolution process, the rotation speed during dissolution is not particularly limited, but is preferably 100 rpm to 300 rpm, and preferably 150 rpm to 250 rpm.

[0042] (Spinning solution) The spinning solution obtained in the manner described above will be explained below.

[0043] The concentration of modacryl fiber product in the spinning solution is not particularly limited, as long as the desired effect is not impaired. From the viewpoint of good spinning in the spinning process described later, the concentration of modacryl fiber product (solid content concentration) relative to the mass of the spinning solution 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, and even more preferably 20% by mass or more and 35% by mass or less.

[0044] The spinning solution may contain modacrylic resin not derived from modacrylic fiber products. Modacrylic resin not derived from modacrylic fiber products is usually virgin material. For example, the concentration of modacrylic resin in the spinning solution can be adjusted by dissolving a virgin modacrylic resin material in a spinning solution containing a modacrylic fiber product in a dissolved state. If the spinning solution contains modacrylic resin derived from modacrylic fiber products and modacrylic resin not derived from modacrylic fiber products, the ratio of the mass of modacrylic resin derived from modacrylic fiber products to the total mass of 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.

[0045] The spinning solution may contain water. The water content of the spinning solution is not particularly limited, as long as the desired effect is not impaired. From the viewpoint of the solubility of modacryl fiber products in the spinning solution, the water content of the spinning solution 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.

[0046] The spinning solution may contain a pigment. Various well-known pigments can be used as the pigment, as needed. The pigment may be an organic pigment or an inorganic pigment. Furthermore, the spinning solution may contain two or more pigments, and may also contain dyes along with the pigments.

[0047] The pigment added to the spinning solution may be a solid powder pigment, or a pigment dispersion containing pigment dispersed in a dispersion medium may be used. In terms of the dispersibility of the pigment in the spinning solution and modacrylic fibers, it is preferable to prepare the spinning solution using a pigment dispersion.

[0048] As a pigment, carbon black is preferred because it can color modacrylic fibers to a desired shade of black and is readily available.

[0049] To color the modacrylic fibers to the desired degree while suppressing yarn breakage during the spinning process, the pigment content in the spinning solution is preferably 0.01 parts by mass or more and 2.00 parts by mass or less, and more preferably 0.02 parts by mass or more and 0.60 parts by mass or less, per 100 parts by mass of the spinning solution.

[0050] The spinning solution may, if necessary, contain other additives to improve fiber properties, provided that the desired effect is not inhibited. Examples of such additives include gloss modifiers such as titanium dioxide, silicon dioxide, and esters and ethers of cellulose derivatives, including cellulose acetate; and stabilizers to improve light resistance and heat resistance.

[0051] The viscosity of the spinning solution is measured using a viscoelasticity measuring instrument. The viscosity of the spinning solution is the dynamic viscosity measured at a rotor angular velocity of 1.0 Hz for a sample dissolved at a dissolution temperature of 60°C for 3 hours. From the viewpoint of enabling stable wet spinning without yarn breakage during wet spinning, the dynamic viscosity of the spinning solution is preferably 0.1 Pa·s to 20 Pa·s, more preferably 0.1 Pa·s to 15 Pa·s, and even more preferably 0.1 Pa·s to 10 Pa·s.

[0052] <Spinning Process> In the spinning process, wet spinning is performed using a spinning solution. As for wet spinning methods, The process involves extruding the spinning solution from a nozzle into a coagulation bath and allowing it to coagulate, A preferred method includes stretching the fibers produced by coagulating the spinning solution in a stretching bath.

[0053] Hereafter, the process of extruding the spinning stock solution from a nozzle into a coagulation bath and allowing it to coagulate will also be referred to as the "coagulation process." The process of stretching the fibers produced by coagulating the spinning stock solution in a stretching bath will also be referred to as the "stretching process."

[0054] (solidification process) In the coagulation process, the spinning solution is extruded in fibrous form from a nozzle into the coagulation bath, and the extruded fibrous spinning solution is then coagulated. The spinning solution is discharged into the coagulation bath from a nozzle of a size and shape corresponding to the fiber diameter and cross-sectional shape of the modacrylic fiber.

[0055] In the coagulation process, the spinning solution is first extruded through the spinning nozzle into the coagulation bath. The coagulated solution, extruded in fibrous form, coagulates and becomes fibers in the coagulation bath. As the coagulation bath, it is preferable to use a mixture of water and an organic solvent, from the viewpoint of being able to easily control the coagulation state. For example, an aqueous solution of an organic solvent is preferred as the liquid to be poured into the coagulation bath. 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.

[0056] The organic solvent contained in the liquid poured into the coagulation bath is not particularly limited, as long as it is a good solvent for modacryl resin. From the viewpoint of modacryl fiber productivity, 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 preferred. From the viewpoint of safety, dimethyl sulfoxide is more preferred. From the viewpoint of modacryl fiber quality and ease of process control, it is preferable that the organic solvent in the spinning solution and the organic solvent in the liquid poured into the coagulation bath are the same organic solvent.

[0057] The temperature of the spinning solution extruded into the coagulation bath is preferably 35°C or lower. The temperature of the liquid poured into the coagulation bath is preferably between 10°C and 30°C, and more preferably between 10°C and 25°C.

[0058] (Stretching process) The fibers produced by coagulating the spinning solution in a coagulation bath are then stretched in a stretching bath. The method of transferring the fibers from the coagulation bath to the stretching bath is not particularly limited. Typically, the fibers to be stretched are placed on a roll in the coagulation bath and on one or more fiber transfer rolls outside the coagulation bath, and the fibers to be stretched are transferred into the stretching bath by rotating the rolls.

[0059] The fibers being transported into the stretching bath are stretched by rotation between a first stretching roll located upstream of the fibers being stretched and a second stretching roll located downstream of the fibers being stretched, while the fibers are submerged in the liquid contained within the stretching bath. Here, the stretching ratio is adjusted by controlling the tension applied to the fibers being stretched by the first and second stretching rolls, and the rotational speed of the first and second stretching rolls. The stretching ratio is preferably between 100% and 800%, and more preferably between 120% and 300%. The stretched modacrylic fibers are then stretched over rolls such as clover rolls located outside the stretching bath and recovered from the stretching bath as needed.

[0060] The bath liquid used in the stretching bath is not particularly limited as long as it allows for good stretching. For example, water or an aqueous solution containing an organic solvent can be used. The bath liquid used in the stretching bath is preferably an aqueous solution of an organic solvent containing 10% to 90% by mass of water relative to the mass of the bath liquid. The temperature of the bath in the stretching bath is preferably in the range of 30°C to 110°C, and more preferably in the range of 40°C to 95°C.

[0061] It is preferable that the stretching in the stretching bath be carried out in multiple stages. Furthermore, it is preferable that the average stretching speed is different in at least two of the multiple stretching stages. Performing the stretching in the stretching bath in multiple stages makes it easier to control the stretching conditions at each stage of the stretching process, such as the initial, middle, and late stages. Here, "stretching is performed in multiple steps" means that the stretching and the release of the tension for stretching are repeated two or more times. Multiple stretching processes may be carried out in the same stretching bath, or they may be carried out using multiple different stretching baths. It is preferable to use multiple different stretching baths because the temperature of the stretching bath and the composition of the liquid placed in the stretching bath can be changed for each stretching bath.

[0062] (Water washing process) Stretched modacryl fibers are typically washed in a water washing process. In the water washing process, the stretched modacryl fibers are washed in a stretching bath to remove organic solvents from the fibers. In the water washing process, it is preferable to use warm water at 25°C or higher, or an aqueous solution of an organic solvent with a lower concentration than that of the coagulation bath, as the washing solution. Water washing can be carried out by immersing the stretched modacryl fibers in a bath filled with these washing solutions, or by spraying water onto the moving modacryl fibers. The means of spraying water in the water washing process are not particularly limited, but from the viewpoint of ease of spraying, it is preferable to spray water using a nozzle. The direction in which the water is sprayed 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 multiple 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 desolvation effect to remove organic solvents, the water temperature is preferably 40°C or higher, and more preferably 50°C or higher.

[0063] While not particularly limited, in the water washing process, from the viewpoint of enhancing the effect of removing organic solvents, the ratio of 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.

[0064] (Dehydration process) When the stretched modacrylic fibers are washed with water, the washed modacrylic fibers are dewatered in the dewatering process. In the dewatering process, the washed modacrylic fibers are dewatered by passing them between nip rolls while being sandwiched between them.

[0065] A "nip roll" is generally any type of roll used in the production of fibers by the wet spinning method, and is not particularly limited. Examples of nip rolls include rubber nip rolls and metal nip rolls. A rubber nip roll (also referred to as a rubber roll) is preferably used as the upper nip roll, and a metal nip roll (also referred to as a metal roll) is preferably used as the lower nip roll.

[0066] The aforementioned washing and dewatering processes may be performed alternately multiple times, once each. After performing the aforementioned washing process two or more times, pressing with a nip roll may be performed one or more times.

[0067] (drying process) Modacrylic fibers stretched in the stretching bath, and modacrylic fibers dehydrated as described above, are then dried in a drying process. In the drying process, 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 from the modacrylic fibers. Examples of drying methods include hot air drying and drying by contact with heated rolls. The drying temperature is not particularly limited, but for example, 110°C to 190°C is preferred, and 110°C to 170°C is more preferred.

[0068] The fineness of the modacrylic fibers obtained in the manner described above is appropriately determined according to the intended use of the modacrylic fibers.

[0069] Before drying the modacrylic fibers, an oiling agent may be applied to them. The oiling agent is as described above.

[0070] The dried modacrylic fibers obtained by the above method may be further stretched as needed. The stretching method is not particularly limited and can be dry or wet.

[0071] The dried modacrylic fibers obtained by the above method are preferably further relaxed in a heat relaxation treatment step. The relaxation rate is not particularly limited, but is preferably 5% or more, and more preferably 10% or more. 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 to 200°C, preferably 140°C to 190°C. Alternatively, it can be carried out in a pressurized steam or heated pressurized steam atmosphere at 120°C to 180°C, with a pressure of 0.05 MPa to 0.4 MPa, preferably 0.1 MPa to 0.4 MPa.

[0072] <Other processes> The method for producing modacrylic fibers may include steps other than the washing, dissolving, and spinning steps described above (hereinafter also referred to as "other steps"), as long as they do not impair the effects of the present invention. Examples of other steps include a pretreatment step that breaks down the modacrylic fiber product into smaller pieces before the washing step, and an oil removal step.

[0073] <Pre-treatment process> In the pretreatment process, the modacrylic fiber product is broken down into smaller pieces before the washing process.

[0074] In the aforementioned washing process, it is preferable to use the modacrylic fiber product that was used as a raw material.

[0075] In the pretreatment step, it is preferable to reduce the modacrylic fiber product to a length of 10 mm or less.

[0076] The method for breaking down modacrylic fiber products into smaller pieces is not particularly limited, and known pulverizers can be used. [Examples]

[0077] The present invention will be described in more detail by the following examples. However, the present invention is not limited to the following examples.

[0078] [Examples 1-4 and Comparative Examples 1-3] (Materials used) In the examples and comparative examples, AFRELLE (manufactured by Kaneka Corporation) was used as the modacrylic fiber product. The modacrylic resin constituting the modacrylic fiber product (AFRELLE) contains 46% by mass of constituent units derived from acrylonitrile, 52% by mass of constituent units derived from vinyl chloride, and 2% by mass of constituent units derived from sodium styrenesulfonate.

[0079] In the examples and comparative examples, the following components were used in the dissolution process. Organic solvent: Dimethyl sulfoxide Water: pure water Epoxy group-containing compound: Polyglycidyl methacrylate (PGMA) (manufactured by Sigma-Aldrich)

[0080] [Example 1] (Pre-treatment process) Using a pulverizer, the modacrylic fiber product was crushed to a length of 10 mm or less, and then sorted through a Φ10 mm mesh to obtain the crushed modacrylic fiber product.

[0081] (Washing process) 100g of the above-mentioned crushed modacrylic fiber product was placed in an autoclave (Sugiyama Gen HV-50II), followed by 1000g of pure water, and the modacrylic fiber product was immersed until it was submerged in the pure water. Next, it was immersed and washed at 105°C for 15 minutes under a pressurized condition of 0.225 MPa (absolute pressure), and then centrifugal dewatering was performed at 2500G for 5 minutes using an Alumis high-speed dewatering machine APD-6.0.

[0082] (melting process) 100 g of the washed modacryl fiber product was placed in a 1 L dissolution container. Next, 234.8 g of dimethyl sulfoxide and 10.0 g of pure water were added to the dissolution container. Then, 0.8 mass% (0.8 g) of polyglycidyl methacrylate was added to the modacryl fiber product. The internal temperature of the dissolution container was maintained at 60°C, and the mixture was stirred at 200 rpm for 180 minutes to dissolve the modacryl fiber product. The solid content concentration of the resulting spinning solution was 23 mass%. For the spinning stock solution being dissolved in the dissolving solution, after dissolving the spinning stock solution for 3 hours, the dynamic viscosity (Pa·s) was measured at 60°C with a rotor angular velocity of 1.0 Hz using a viscoelasticity analyzer (HAAKE MARS rheometer MARS40).

[0083] (Spinning process) Spinning solution at 60℃, opening area 0.085mm 2 The material was supplied to a nozzle having 10 discharge holes, and the nozzle discharge speed was set to 8 m / min. The material was discharged into a coagulation bath filled with a 47% by mass aqueous solution of dimethyl sulfoxide at a temperature of 25°C, and spinning was performed at a draft ratio of 1.25 and a spinning speed of 10 m / min. After washing in an 80°C water washing bath, the obtained fibers were immersed in an oil (a mixture of 65% by mass castor oil ether and 35% by mass sorbitan stearate, to which pure water was added so that the mixture was 2.09% by mass). The immersed fibers were then dried, and subsequently stretched at 125°C with a draw ratio of 230%, followed by a relaxation treatment at 155°C to obtain modacrylic fibers.

[0084] [Example 2] In the washing process, a base was placed in an autoclave (Sugiyama Gen HV-50II), 100g of crushed modacrylic fiber product was placed on the base, and 2000g of pure water was poured in up to the bottom of the modacrylic fiber so that the modacrylic fiber was not submerged in water. Next, steam washing was performed at 105°C for 15 minutes under a pressurized condition of 0.225 MPa, followed by centrifugal dewatering at 2500G for 5 minutes using an Alumis high-speed dewatering machine APD-6.0. 100g of washed modacryl fiber product was placed in a 1L dissolution container. Next, 234.8g of dimethyl sulfoxide and 10.0g of pure water were added to the dissolution container. Then, 0.8% by mass (0.8g) of polyglycidyl methacrylate was added to the modacryl fiber product. The internal temperature of the dissolution container was maintained at 60°C, and the mixture was stirred at 200 rpm for 180 minutes to dissolve the modacryl fiber product. The solid content concentration of the obtained spinning solution was 23% by mass. The dynamic viscosity (Pa·s) of the above spinning solution was measured under the same conditions as in Example 1.

[0085] [Example 3] In the washing process, 100g of crushed modacrylic fiber product was placed in an autoclave (Sugiyama Gen HV-50II), followed by 4000g of pure water, and the modacrylic fiber product was immersed until it was submerged in the pure water. Next, under a pressurized condition of 0.30MPa, the product was washed by immersion at 120°C for 15 minutes, after which it was dewatered by centrifugal force at 2500G for 5 minutes using an Alumis high-speed dewatering machine APD-6.0. 100g of washed modacryl fiber product was placed in a 1L dissolution container. Next, 234.8g of dimethyl sulfoxide and 10.0g of pure water were added to the dissolution container. Then, 0.8% by mass (0.8g) of polyglycidyl methacrylate was added to the modacryl fiber product. The internal temperature of the dissolution container was maintained at 60°C, and the mixture was stirred at 200 rpm for 180 minutes to dissolve the modacryl fiber product. The solid content concentration of the obtained spinning solution was 23% by mass. The dynamic viscosity (Pa·s) of the above spinning solution was measured under the same conditions as in Example 1.

[0086] [Example 4] In the washing process, a base was placed in an autoclave (Sugiyama Gen HV-50II), 100g of crushed modacrylic fiber product was placed on the base, and 2000g of pure water was poured in up to the bottom of the modacrylic fiber so that the modacrylic fiber was not submerged in water. Next, steam washing was performed at 120°C for 15 minutes under a pressurized condition of 0.30 MPa, followed by centrifugal dewatering at 2500G for 5 minutes using an Alumis high-speed dewatering machine APD-6.0. 100g of washed modacryl fiber product was placed in a 1L dissolution container. Next, 234.8g of dimethyl sulfoxide and 10.0g of pure water were added to the dissolution container. Then, 0.8% by mass (0.8g) of polyglycidyl methacrylate was added to the modacryl fiber product. The internal temperature of the dissolution container was maintained at 60°C, and the mixture was stirred at 200 rpm for 180 minutes to dissolve the modacryl fiber product. The solid content concentration of the obtained spinning solution was 23% by mass. The dynamic viscosity (Pa·s) of the above spinning solution was measured under the same conditions as in Example 1.

[0087] [Comparative Example 1] Recycled modacrylic fibers were obtained in the same manner as in Example 1, except that the washing process was omitted. The solid content concentration of the obtained spinning solution was 23% by mass. The dynamic viscosity (Pa·s) of the above spinning solution was measured under the same conditions as in Example 1.

[0088] [Comparative Example 2] Under atmospheric pressure, 100g of pulverized modacrylic fiber product was placed in a container, followed by 1000g of pure water, and the product was immersed until it was completely submerged. Next, it was washed with agitation at 80°C for 60 minutes. After that, it was filtered and rinsed with more than 2000g of pure water, and then centrifugal dewatering was performed at 2500G for 5 minutes using an Alumis ADP-6.0 centrifugal dewatering machine. 100g of washed modacryl fiber product was placed in a 1L dissolution container. Next, 234.8g of dimethyl sulfoxide and 10.0g of pure water were added to the dissolution container. Then, 0.8% by mass (0.8g) of polyglycidyl methacrylate was added to the modacryl fiber product. The internal temperature of the dissolution container was maintained at 60°C, and the mixture was stirred at 200 rpm for 180 minutes to dissolve the modacryl fiber product. The dynamic viscosity (Pa·s) of the obtained spinning solution was measured under the same conditions as in Example 1.

[0089] [Comparative Example 3] Recycled modacrylic fibers were obtained in the same manner as in Comparative Example 2, except that they were stirred and washed at 95°C for 60 minutes. The dynamic viscosity (Pa·s) of the obtained spinning solution was measured under the same conditions as in Example 1.

[0090] <Rating> [Spinning stability] The spinning stability in each spinning process of Examples 1-4 and Comparative Examples 1-3 was evaluated according to the following evaluation criteria. The results are shown in Table 1. ◎: Stable spinning was achieved. ○: Spinning was successful, but slight variations in fineness occurred. ×: The yarn broke when the spinning speed was increased.

[0091] Table 1 shows the evaluation results for washing temperature, washing time, washing medium, washing pressure (absolute pressure) in the washing process, viscosity after dissolving the spinning stock solution for 3 hours in the dissolution process (hereinafter also referred to as "dissolution viscosity"), and spinning stability in the spinning process for Examples 1 to 4 and Comparative Examples 1 to 3.

[0092] [Table 1]

[0093] The results in Table 1 show that in the methods of Examples 1 to 4, which include a washing step in which modacrylic fiber products are brought into contact with water or steam at over 100°C under pressurized conditions, the dissolution viscosity becomes very low, at 20 Pa·s or less, and thus recycled modacrylic fibers with excellent spinning stability can be obtained. On the other hand, in Comparative Example 1, which does not include a washing step, and in Comparative Examples 2 and 3, which do not meet the above conditions for the washing step, the dissolution viscosity becomes very high, and thus recycled modacrylic fibers with excellent spinning stability cannot be obtained.

Claims

1. A washing process in which modacrylic fiber products are brought into contact with water or steam at a temperature exceeding 100°C under pressurized conditions, A dissolution step is performed in which the modacryl fiber product obtained in the washing step is dissolved in an organic solvent to obtain a spinning stock, A method for producing modacrylic fibers, comprising the step of wet spinning the aforementioned spinning stock.

2. A method for producing modacrylic fibers according to claim 1, comprising a pretreatment step of breaking up the modacrylic fiber product into smaller pieces prior to the washing step.

3. The method for producing modacrylic fibers according to claim 2, wherein the pretreatment step is a step of reducing the length of the modacrylic fiber product to 10 mm or less.

4. The method for producing modacrylic fibers according to claim 1 or 2, wherein the viscosity of the spinning stock is 0.1 Pa·s or more and 20 Pa·s or less.

5. The method for producing modacrylic fibers according to claim 1 or 2, wherein the pressure in the washing step is 0.35 MPa (absolute pressure) or less.

6. A method for producing modacrylic fibers according to claim 1 or 2, wherein an epoxy group-containing compound is present in the dissolution step.

7. The method for producing modacrylic fibers according to claim 6, wherein the amount of epoxy group-containing compound used is 0.5 parts by mass or more and 1.2 parts by mass or less per 100 parts by mass of the modacrylic fiber product.

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