Easily beaten acrylonitrile fiber, pulp-like acrylonitrile fiber, structure containing said fiber, and method for producing said fiber

Abstract

To provide an acrylonitrile-based fiber having a property on excellent beating speed, and a pulp-like acrylonitrile-based fiber that has a low drainage degree and is obtained by beating the fiber, under a situation in which a pulp-like fiber is applied in various fields such as papermaking, packaging materials, paints, building materials, industrial materials, beauty care, and health care, pulp formation of the acrylonitrile-based fiber has also been studied, and in the study, a beating rate of the acrylonitrile-based fiber used as a raw material is slow and therefore a product with a low drainage level is hardly obtained, and satisfactory on a particle trapping property and a binder property is not always obtained.SOLUTION: There is provided an easy-to-beat acrylonitrile-based fiber, in which the fiber composed of a polymer that has a carboxyl group amount of 0.2 to 4.0 mmol / g and that has substantially no cross-linking structure due to a covalent bond, and a hydrophilic component is contained inside the fiber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an easily beaten acrylonitrile fiber, a pulp-like acrylonitrile fiber, a structure containing the fiber, and a method for producing the fiber. [Background technology]

[0002] Pulp-like fibers are characterized by their hyperbranched structure and high specific surface area, and are excellent in adhesive properties, ability to capture functional particles such as activated carbon, and as a binder. As a result, they are used in a wide range of fields, including papermaking, packaging materials, paints, building materials, industrial materials, beauty, and health.

[0003] On the other hand, since it is difficult to turn acrylic fibers into pulp even after a beating process, studies are being conducted to make it possible to turn acrylic fibers into pulp. For example, Patent Document 1 reports that beating properties can be imparted to acrylic fibers by kneading a hydrophilic resin into the fibers, and that fibrillated acrylic fibers can be obtained by beating the fibers thus obtained.

[0004] Patent Document 2 reports that beatenability is imparted to undried fibers during the manufacturing process of acrylic fibers by subjecting them to a hydrolysis treatment, and that carboxyl group-containing beaten acrylonitrile-based fibers are obtained by beating the fibers thus obtained. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-154958 A [Patent Document 2] Patent No. 6656608 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the fibrillated acrylic fiber of Patent Document 1 and the carboxyl group-containing beaten acrylonitrile fiber of Patent Document 2 have beating properties, the beating speed is slow, making it difficult to obtain a product with low freeness, and the particle capture property and binding property are not necessarily satisfactory.

[0007] The present invention has been devised in view of the current state of the prior art, and an object of the present invention is to provide an acrylonitrile fiber excellent in beating speed and a pulp-like acrylonitrile fiber having low freeness obtained by beating the fiber. [Means for solving the problem]

[0008] As a result of intensive research by the present inventors to achieve the above-mentioned object, it was found that the beating speed of the obtained fiber can be dramatically improved by adding a hydrophilic component to the spinning dope, which is obtained by spinning a spinning dope containing an acrylonitrile polymer dissolved therein from a nozzle, and then hydrolyzing the undried fiber obtained through each process of coagulation, washing with water and drawing, that is, in the fiber having a structure in which, macroscopically, parts having carboxyl groups are present throughout the fiber structure, while, more microscopically, more carboxyl groups are present on the surface than in the interior of each fibril constituting the fiber, the beating speed of the obtained fiber can be dramatically improved by adding a hydrophilic component to the spinning dope, and thus the present invention was arrived at.

[0009] That is, the present invention is achieved by the following means. (1) The polymer has a carboxyl group content of 0.2 to 4.0 mmol / g and is substantially free of a cross-linked structure due to a covalent bond; It is a polymer containing 30 to 90% by weight of the monomer represented by the following formula 1 as a structural unit. Easy-to-beat acrylonitrile fiber containing hydrophilic components inside the fiber and having a freeness of 600 ml or less. . [ka] ( 2 2. A structure containing the pulp-like acrylonitrile fiber described in (1). ( 3 ) ( 2A sanitary product, a filter, a carbon sheet for a fuel cell diffusion membrane, a friction material, a functional paper product, a moisture-permeable paper, or a battery component, comprising the structure according to any one of the preceding claims. ( 4 ) A hydrophilic component is added to the spinning solution in which an acrylonitrile polymer is dissolved. 0.5 to 10.0% by weight based on the weight of the acrylonitrile polymer The method for producing pulp-like acrylonitrile fibers includes adding the acrylonitrile-based compound, spinning the acrylonitrile-based compound from a nozzle, coagulating, washing and drawing the resulting undried fibers, hydrolyzing the resulting fibers and then beating the resulting fibers. Effect of the Invention

[0010] The easily beaten acrylonitrile fiber of the present invention has an excellent beating speed, and can easily obtain a pulp-like acrylonitrile fiber with low freeness. In addition, since such a pulp-like acrylonitrile fiber has excellent binding properties and particle capture properties, it can be suitably used as a binder for supporting functional particles in filters, etc. Furthermore, since the pulp-like acrylonitrile fiber of the present invention can also exhibit functions such as ion exchange, moisture absorption, deodorization, antiviral, and antiallergenic properties derived from the carboxyl group, it is also useful as a functional material for imparting these functions to paper and filters. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a SEM photograph of the pulp-like acrylonitrile fiber of Example 3. [Diagram 2] FIG. 1 is a view showing an SEM photograph of the pulp-like acrylonitrile fibers of Comparative Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The easily beaten acrylonitrile fiber of the present invention contains a carboxyl group, and the content thereof is 0.2 to 4.0 mmol / g, preferably 0.4 to 3.0 mmol / g, and more preferably 0.6 to 2.0 mmol / g, in the method described below. If the amount of carboxyl groups is less than 0.2 mmol / g, the binder property, particle capture property, etc. of the pulp-like acrylonitrile fiber obtained after beating may not be sufficient, and if it exceeds 4.0 mmol / g, the hydrophilicity of the fiber becomes too high, and it swells or dissolves in water violently, which adversely affects the fiber properties. In addition, in order to obtain good beating properties in the easily beaten acrylonitrile fiber, it is desirable to contain a carboxyl group in the range shown above.

[0013] In addition, in the easily beaten acrylonitrile-based fiber of the present invention, since the presence of a crosslinked structure due to a covalent bond causes each polymer constituting the fiber to be linked and reduces the beatability, one that does not substantially have a crosslinked structure due to a covalent bond is adopted. As a result, the pulp-like acrylonitrile-based fiber of the present invention also has substantially no crosslinked structure due to a covalent bond. Here, "substantially no crosslinked structure due to a covalent bond" means that there is no crosslinked structure intentionally formed using a crosslinking agent or the like, and does not mean that there is no even a trace amount of crosslinked structure that may be unintentionally by-produced in the hydrolysis treatment described later.

[0014] In the present invention, it is preferable that the internal structure of the easily beaten acrylonitrile fiber has a structure in which the portion having a carboxyl group is present throughout the entire fiber structure made of an acrylonitrile polymer, but is not uniformly mixed at the molecular level. A specific example of such a structure is one in which small fibers (so-called fibrils) constituting the acrylonitrile fiber have a core-sheath structure in which the surface layer has a carboxyl group and the center does not have a carboxyl group, that is, a structure consisting of an aggregate of small fibers having a core-sheath structure with a carboxyl group in the sheath portion. Here, "existing throughout the fiber" means that the coefficient of variation CV of the magnesium element content in the fiber cross section measured by the measurement method described below is 50% or less. The coefficient of variation CV is preferably 40% or less, more preferably 30% or less.

[0015] If the carboxyl groups are unevenly distributed in the fiber structure or uniformly distributed at the molecular level, sufficient beating properties may not be obtained. In a structure in which the parts having carboxyl groups are distributed throughout the fiber and are not uniformly mixed at the molecular level, the parts having carboxyl groups swell in water and become easily torn, which facilitates fibrillation by beating.

[0016] Furthermore, the surface of each beaten fibril becomes rich in carboxyl groups, which increases hydrophilicity and water diffusibility, and also makes it easier to exhibit particle capture, adhesiveness, ion exchange, etc. On the other hand, the inside of each fibril is composed of an acrylonitrile polymer, which makes it difficult to shrink and contributes to dimensional stability.

[0017] In order to further improve the beating property of the easily beaten acrylonitrile fiber, it is preferable that the counter ion of the carboxyl group is a cation other than hydrogen ion. More specifically, it is desirable that the proportion of the counter ion that is a cation other than hydrogen ion, i.e., the degree of neutralization, is preferably 25% or more, more preferably 35% or more, and even more preferably 50% or more.

[0018] Examples of the cations include alkali metals such as Li, Na, and K, alkaline earth metals such as Mg, Ca, and Ba, metals such as Cu, Zn, Al, Mn, Ag, Fe, Co, and Ni, and cations such as NH4 and amines. A mixture of multiple types of cations is also acceptable. Among them, Li, Na, K, Mg, Ca, and Zn are preferred.

[0019] The easily beaten acrylonitrile fiber of the present invention has a hydrophilic component inside the fiber. The hydrophilic component is in a phase-separated state with the acrylonitrile polymer inside the fiber, and voids are easily formed, which contributes to improving the beating property. The content of the hydrophilic component is preferably 0.5 to 10.0% by weight, more preferably 1.0 to 5.0% by weight, based on the weight of the acrylonitrile polymer used as a raw material. If the content of the hydrophilic component is less than 0.5% by weight, the above-mentioned effect of improving the beating property may not be obtained, and if it exceeds 10.0% by weight, problems such as frequent yarn breakage during the spinning process during fiber production, which deteriorates operability, may occur.

[0020] In addition, the hydrophilic component is not particularly limited, but examples of the organic material include an organic polymer compound having a hydrophilic side chain such as a polyalkylene oxide chain, a polyether amide chain, or a polyether ester chain, or a hydrophilic functional group such as a carboxyl group. In addition, examples of the inorganic material include metal oxide particles such as titanium oxide or tin oxide, and carbonaceous fine particles such as carbon black or graphite having a hydrophilic group such as a hydroxyl group or a carboxyl group.

[0021] Particularly useful examples of such hydrophilic components include acrylonitrile-based hydrophilic resins obtained by the above-mentioned method of copolymerizing a vinyl monomer having a hydrophilic side chain with acrylonitrile (hereinafter referred to as method [1]) and a method of copolymerizing a vinyl monomer having a reactive functional group with acrylonitrile and then grafting a reactive compound containing a hydrophilic functional group (hereinafter referred to as method [2]).

[0022] The acrylonitrile hydrophilic resin preferably contains 10 to 70% by weight, more preferably 15 to 50% by weight, and even more preferably 15 to 30% by weight of acrylonitrile. If the content of acrylonitrile is in the range of 10 to 70% by weight, it can have a certain degree of affinity with the above-mentioned acrylonitrile polymer. That is, microvoids are formed at the boundary between the acrylonitrile polymer and the acrylonitrile hydrophilic resin, and a structure in which the respective microvoids are connected can be obtained. If it is below the lower limit of the range, the affinity of the hydrophilic resin with the acrylonitrile polymer is too low, resulting in a state of high incompatibility. For this reason, the hydrophilic resin once dispersed is united, the region of the hydrophilic resin in the fiber becomes large, and frequent yarn breakage occurs in the spinning process, which may deteriorate the operability. In addition, if it exceeds the upper limit of the range, it is considered that the compatibility with the acrylonitrile polymer becomes too high and sufficient beating property cannot be obtained.

[0023] In the above-mentioned method [1], it is preferable to use the monomer represented by the above-mentioned Chemical formula 2 as the vinyl monomer having a hydrophilic side chain, from the viewpoint of further increasing the affinity between the obtained hydrophilic resin and the acrylonitrile-based polymer. The combined content of the monomer is preferably 30 to 90% by weight, more preferably 50 to 85% by weight, and even more preferably 70 to 85% by weight, based on the weight of the obtained copolymer. The lower alkyl group in Chemical formula 2 generally refers to a group having 5 or less carbon atoms, and more practically 3 or less carbon atoms. In addition, when copolymerizing with acrylonitrile, other vinyl compounds may be copolymerized in addition to the above-mentioned vinyl monomer.

[0024] Suitable examples of vinyl monomers having hydrophilic side chains include reaction products of 2-methacryloyloxyethyl isocyanate and polyethylene glycol monomethyl ether, and suitable examples of monomers represented by Chemical Formula 2 include methoxypolyethylene glycol (30 mol) methacrylate, methoxypolyethylene glycol (30 mol) acrylate, and polyethylene glycol-2,4,6-tris-1-phenylethylphenyl ether methacrylate (number average molecular weight: about 1600).

[0025] In addition, suitable examples of the vinyl monomer having a reactive functional group used in the above-mentioned method [2] include 2-hydroxyethyl methacrylate, acrylic acid, methacrylic acid, N-hydroxymethylacrylamide, N,N-dimethylaminoethyl methacrylate, glycidyl methacrylate, 2-methacryloyloxyethyl isocyanate, etc., and suitable examples of the reactive compound having a hydrophilic group include polyethylene glycol monomethyl ether, polyethylene glycol monomethacrylate, etc.

[0026] The acrylonitrile hydrophilic resin of the present invention preferably has a water swelling degree as low as possible. The upper limit is preferably 300 g / g or less, more preferably 150 g / g or less. If it exceeds 300 g / g, problems such as thread breakage are likely to occur during the spinning process. Various methods can be used to adjust the water swelling degree, and examples of such methods include copolymerizing a crosslinkable monomer or changing the size of l or m of the monomer shown in Chemical Formula 2.

[0027] Furthermore, the acrylonitrile-based hydrophilic resin may be soluble in water and a solvent for the acrylonitrile-based polymer, but is preferably insoluble in water and a solvent for the acrylonitrile-based polymer and has the property of being stably dispersed in the solvent. Being insoluble in water and a solvent for the acrylonitrile-based polymer prevents the acrylonitrile-based hydrophilic resin from dissolving out of the fiber during the spinning process, and therefore effectively improves the beating property of the finally obtained acrylonitrile-based fiber. Furthermore, the property of being stably dispersed prevents troubles such as nozzle clogging and thread breakage during the spinning process, and therefore contributes to stable spinning.

[0028] As a method for synthesizing the above-mentioned acrylonitrile hydrophilic resin, a well-known polymerization means can be adopted, similar to the acrylonitrile polymer, and in some cases, as described above, a graft reaction can be used to introduce a hydrophilic component.

[0029] The easily beaten acrylonitrile fiber of the present invention described above has a structure consisting of an aggregate of small fibers having a core-sheath structure with a carboxyl group in the sheath portion, and has a structure in which the acrylonitrile polymer and the hydrophilic component are in a phase-separated state. In the easily beaten acrylonitrile fiber of the present invention having such a structure, the part having a carboxyl group swells with water and becomes easily torn, and the phase-separated part formed by the hydrophilic component also becomes easily beaten, so that the characteristic that fibrillation progresses dramatically with a smaller shear force than before can be expressed. In other words, the effects of the two structures are superimposed, making it possible to fibrillate more finely, and the beating speed is excellent, and low freeness can be easily realized. Such a characteristic cannot be achieved by either of the two structures alone, and is the result of the synergistic effects of these structures.

[0030] The pulp-like acrylonitrile fiber of the present invention is obtained by beating the above-mentioned easily beatable acrylonitrile fiber. The freeness of the pulp-like acrylonitrile fiber is preferably 600 ml or less, more preferably 400 ml or less, and even more preferably 200 ml or less. If the freeness exceeds 600 ml, the binder property, particle capture property, etc. may not be significantly exhibited. In addition, since the easily beatable acrylonitrile fiber of the present invention has an excellent beating speed, it can be beaten in a shorter time than conventionally, and further, it is possible to easily obtain a pulp-like acrylonitrile fiber having a low freeness of 200 ml or less, which was difficult to achieve conventionally.

[0031] In addition, the pulp-like acrylonitrile fiber of the present invention has functions such as binder properties, particle capture properties, and reinforcing material functions, as well as ion exchange properties, moisture absorption properties, deodorizing properties, and antiviral properties derived from carboxyl groups, and can be used alone or in combination with other materials as a useful structure for many applications. In the structure, it is desirable to set the content of the pulp-like acrylonitrile fiber of the present invention to preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 20% by weight or more, from the viewpoint of obtaining the effects of the pulp-like acrylonitrile fiber of the present invention.

[0032] The external appearance of such a structure may be a paper-like material, a sheet-like material, a laminate, a spherical or cylindrical molded body, etc. The form in which the pulp-like acrylonitrile fiber of the present invention is contained within the structure may be one in which it is substantially uniformly distributed by mixing with materials such as other fibers or resin compositions, one in which it is concentrated in any one of the layers (which may be single or multiple) in the case of a structure having multiple layers, or one in which it is distributed in a specific ratio in each layer, etc.

[0033] Applications of the structure of the present invention include diffusion layers and absorption layers in hygiene products such as diapers, urine absorption pads, and sanitary napkins; activated carbon support sheets, filters such as water purification filters, deodorizing filters, and filtration filters; carbon sheets for fuel cell diffusion membranes, friction materials such as clutch facings and brake pads; functional paper products such as deodorizing wallpaper, moisture absorbing wallpaper, moisture permeable paper, and latent heat exchange sheets; and functional paper products such as battery components such as separators and electrode reinforcing materials.

[0034] In each of the above applications, the properties of the pulp-like acrylonitrile fiber of the present invention can be effectively utilized. For example, in the diffusion layer application of sanitary products, the hydrophilicity of the fibrils can improve the diffusibility of urine, etc., and in the absorption layer application of sanitary products or activated carbon support sheet application, the particle capture property can be utilized to fix water-absorbent resin or activated carbon particles.

[0035] The above-mentioned method for producing the easily beaten acrylonitrile-based fiber of the present invention includes a method in which a hydrophilic component is added to a spinning dope in which an acrylonitrile-based polymer is dissolved, and the resulting undried fiber is spun from a nozzle and subjected to each step of coagulation, washing with water, and drawing, and then hydrolyzed. The fiber is beaten to produce the pulp-like acrylonitrile-based fiber of the present invention. The production method is described in detail below.

[0036] First, the acrylonitrile polymer, which is the raw material of the easily beaten acrylonitrile fiber, contains acrylonitrile in a polymerization composition of preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 85% by weight or more. Therefore, as the acrylonitrile polymer, in addition to acrylonitrile homopolymer, a copolymer of acrylonitrile and other monomers can be used. The other monomers in the copolymer are not particularly limited, but include vinyl halide and vinylidene halide; carboxyl group-containing monomers such as acrylic acid and methacrylic acid and their salts and ester derivatives; sulfonic acid group-containing monomers such as methallylsulfonic acid and p-styrenesulfonic acid and their salts, acrylamide, styrene, vinyl acetate, etc.

[0037] Next, the acrylonitrile polymer and hydrophilic component are used to form fibers by wet spinning. The following will explain the case where an inorganic salt such as sodium rhodanate is used as the solvent. First, the above-mentioned acrylonitrile polymer is dissolved in a solvent to prepare a spinning solution. After adding a hydrophilic component to the spinning solution and spinning it from a nozzle, the water content of the undried fiber (hereinafter also referred to as gel-like acrylonitrile fiber) is adjusted to 20 to 250% by weight, preferably 25 to 130% by weight, and more preferably 30 to 100% by weight.

[0038] Here, voids exist in the gelled acrylonitrile fiber, but when the moisture content of the fiber is less than 20% by weight, the voids are small, so that the chemicals do not penetrate into the fiber in the hydrolysis treatment described below, and carboxyl groups may not be generated throughout the fiber. When the moisture content exceeds 250% by weight, the fiber contains a lot of moisture inside, and the fiber strength becomes too low, which is not preferable because of the decrease in spinnability. When the high fiber strength is more important, it is preferable to set the moisture content within the range of 25 to 130% by weight. There are many methods for controlling the moisture content of the gelled acrylonitrile fiber within the above range, but for example, the coagulation bath temperature is -3°C to 15°C, preferably -3°C to 10°C, and the stretch ratio is 5 to 20, preferably 7 to 15 times.

[0039] The gel-like acrylonitrile fiber is then subjected to a hydrolysis treatment, by which the nitrile groups in the gel-like acrylonitrile fiber are hydrolyzed to produce carboxyl groups.

[0040] Examples of such hydrolysis treatment methods include a method of impregnating or immersing the fiber in a basic aqueous solution such as an alkali metal hydroxide, an alkali metal carbonate, or ammonia, or an aqueous solution such as nitric acid, sulfuric acid, or hydrochloric acid, and then subjecting the fiber to heat treatment. As specific treatment conditions, various conditions such as the concentration of the treatment agent, reaction temperature, and reaction time may be appropriately set in consideration of the range of the amount of carboxyl groups described above. In general, it is preferable to set the conditions within the range of 0.5 to 20% by weight, preferably 1.0 to 15% by weight, impregnated with the treatment agent, squeezed, and then treated in a moist heat atmosphere at a temperature of 105 to 140°C, preferably 110 to 135°C, for 10 to 60 minutes, from the viewpoints of industry and fiber physical properties. In addition, if the temperature is less than 105°C, the fiber may become strongly colored. The moist heat atmosphere refers to an atmosphere filled with saturated steam or superheated steam.

[0041] In the fibers subjected to the hydrolysis treatment as described above, salt-type carboxyl groups are generated with cations such as alkali metals and ammonium as counter ions according to the types of alkali metal hydroxides, alkali metal carbonates, ammonia, etc. used in the hydrolysis treatment, and subsequently, a treatment for changing the counter ions of the carboxyl groups may be carried out as necessary. By carrying out an ion exchange treatment with an aqueous solution of a metal salt such as a nitrate, sulfate, or hydrochloride, it is possible to obtain salt-type carboxyl groups with a desired metal ion as the counter ion. Furthermore, by adjusting the pH of the aqueous solution or the concentration and type of the metal salt, it is possible to mix different types of counter ions and adjust their ratio.

[0042] The fiber having carboxyl groups introduced thereinto is obtained as described above, i.e., the easily beaten acrylonitrile fiber of the present invention. The pulp-like acrylonitrile fiber of the present invention is obtained by beating the fiber. The method of beating is not particularly limited, and a beating machine such as a beater or a refiner can be used.

[0043] The acrylonitrile fiber according to the present invention is obtained in the above manner, and the production of the easily beaten acrylonitrile fiber can be carried out continuously by utilizing existing continuous production facilities for acrylic fiber. In the above-mentioned method, an inorganic salt such as sodium rhodanate is used as a solvent, but the above conditions are the same even when an organic solvent is used. However, since the type of solvent is different, the temperature of the coagulation bath is selected to be suitable for the solvent, and the moisture content of the gelled acrylonitrile fiber is controlled within the above range.

[0044] In addition, in the above-mentioned manufacturing method, since the gel-like acrylonitrile fiber having a void structure is hydrolyzed, it is considered that the hydrolysis does not proceed sequentially from the fiber surface, but the chemical penetrates into the inner part of the fiber through the voids, and hydrolysis occurs throughout the entire fiber. Furthermore, from a microscopic perspective, since acrylonitrile fibers generally exist as a collection of fine fibrils, it is expected that the chemical penetrates between the fibrils, hydrolysis proceeds from the fibril surface, and the original acrylonitrile polymer remains inside the fibrils without being hydrolyzed. That is, a structure is formed in which the parts having carboxyl groups exist throughout the fiber, and are not uniformly mixed at the molecular level, and fibrillation is facilitated with the parts having carboxyl groups as boundaries. It is also assumed that after beating, the particle capture ability is improved by the carboxyl groups on the surface of each fibril, and the acrylonitrile polymer remaining inside exhibits low heat shrinkage.

[0045] In the above-mentioned manufacturing method, when the gel-like acrylonitrile fiber, i.e., the undried fiber after drawing is not used, and the dried acrylonitrile fiber is subjected to hydrolysis treatment, the chemical does not penetrate deep inside the fiber, and hydrolysis is carried out successively from the surface of the fiber, leading to a structure in which the surface layer of the fiber has many carboxyl groups and the deep inside of the fiber has few carboxyl groups. In such a structure, the beating property is significantly deteriorated. EXAMPLES

[0046] Examples are shown below to facilitate understanding of the present invention, but these are merely illustrative and the gist of the present invention is not limited thereto. In the examples, parts and percentages are by weight unless otherwise specified. In addition, each property was measured by the following method.

[0047] <Carboxyl group distribution within the fiber structure> The sample before beating is immersed in an aqueous solution of magnesium nitrate equivalent to twice the amount of carboxyl groups contained in the sample at 50°C for 1 hour to carry out ion exchange treatment, and then washed with water and dried to convert the counter ion of the carboxyl groups to magnesium. The magnesium salt type sample is measured for the magnesium element content at 10 measurement points selected at approximately equal intervals from the outer edge to the center of the fiber cross section using an energy dispersive X-ray spectrometer (EDS). The coefficient of variation CV [%] is calculated from the values ​​obtained at each measurement point using the following formula. Coefficient of variation CV [%] = (standard deviation / average value) x 100

[0048] <Amount of carboxyl groups> Approximately 1 g of the sample before beating is weighed out, soaked in 50 ml of 1 mol / l hydrochloric acid for 30 minutes, washed with water, and soaked in pure water with a bath ratio of 1:500 for 15 minutes. After washing with water until the bath pH is 4 or higher, it is dried in a hot air dryer at 105°C for 5 hours. Approximately 0.2 g of the dried sample is precisely weighed out (W1 [g]), and 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride are added and stirred. Next, the sample is filtered using a wire mesh and washed with water. Two to three drops of phenolphthalein solution are added to the obtained filtrate (including the washing liquid), and titration is performed using 0.1 mol / l hydrochloric acid according to the usual method to determine the amount of hydrochloric acid consumed (V1 [ml]), and the total amount of carboxyl groups is calculated using the following formula. Total amount of carboxyl groups [mmol / g] = (0.1 × 15 - 0.1 × V1) / W1

[0049] <Neutralization level> The sample before beating is dried at 105°C for 5 hours in a hot air dryer, and approximately 0.2 g is weighed out (W2 [g]). 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride are added and stirred. The sample is then filtered through a wire mesh and washed with water. 2 to 3 drops of phenolphthalein solution are added to the obtained filtrate (including the washings), and titration is performed with 0.1 mol / l hydrochloric acid according to the usual method to determine the amount of hydrochloric acid consumed (V2 [ml]). The amount of H-type carboxyl groups contained in the sample is calculated using the following formula, and the degree of neutralization is calculated from this result and the total amount of carboxyl groups mentioned above. H-type carboxyl group amount [mmol / g] = (0.1 × 15 - 0.1 × V2) / W2 Degree of neutralization [%] = [(total amount of carboxyl groups - amount of H-type carboxyl groups) / total amount of carboxyl groups] x 100

[0050] <Freeness (CSF)> JIS P 8121-2:2012 Pulp - Freeness test method - Part 2: Measure according to the Canadian standard freeness method. However, when the freeness is 20 or less, the freeness value is used as a reference value without correcting the amount of filtered water.

[0051] <Paper strength (binding properties)> A water slurry was prepared with a weight ratio of 30 / 70 pulp-like acrylonitrile fiber / acrylic short fiber (fineness 0.4 dtex, fiber length 3.0 mm) and spun into a square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd. with a basis weight of 50 g / m. 2 The paper was made so that the adhesive strength was improved, and then dried using a heat calendar to prepare paper for evaluation. The resulting paper was cut into pieces measuring 2cm (W) x 10cm (L), and the breaking strength was measured at a pulling speed of 2cm / min using a tensile tester (A&D RTA500 (U-1573)). The higher the breaking strength, the better the adhesiveness.

[0052] <Activated carbon capture amount> Add 1 g of pulp-like acrylonitrile fiber (solid content equivalent) to 1 L of pure water and stir. Add 6 g of powdered activated carbon (Taihei Chemical Industry Co., Ltd. Brocol B activated carbon / average particle size 90 μm) and stir for 30 minutes. Then, pass the mixture through a sieve with 173 μm mesh (area 200 cm). 2 ) and the weight (A [g]) of the filtered material on the sieve after drying at 105°C for 5 hours was measured, and the amount of activated carbon captured per 1 g of sample was calculated using the following formula. Activated carbon capture amount (g / g)=(A-1) / 1

[0053] <Moisture content of gel-like acrylonitrile fiber> The gelled acrylonitrile fiber is immersed in pure water and then dehydrated for 2 minutes in a centrifugal dehydrator (TYPE H-770A manufactured by Kokusan Centrifugal Machinery Co., Ltd.) at a centrifugal acceleration of 1100G (G indicates the acceleration of gravity). After the dehydration, the weight is measured (referred to as W3 [g]), and the undried fiber is dried at 120°C for 15 minutes, and the weight is measured (referred to as W4 [g]) and calculated according to the following formula. Moisture content of gelled acrylonitrile fiber (%) = (W3-W4) / W3 x 100

[0054] <Example 1> 27.5 parts by weight of acrylonitrile and 72.5 parts by weight of methoxypolyethylene glycol (30 mol) methacrylate were suspension polymerized to prepare an acrylonitrile hydrophilic resin. Next, 10 parts of an acrylonitrile polymer consisting of 90% acrylonitrile and 10% methyl acrylate were dissolved in 90 parts of a 44% aqueous sodium thiocyanate solution, and 0.3 parts of the above-mentioned acrylonitrile hydrophilic resin were added to prepare a spinning solution. This spinning solution was spun into a coagulation bath at -2.5°C, coagulated, washed with water, and stretched 12 times to obtain a gel-like acrylonitrile fiber with a moisture content of 35%. The fiber was immersed in a 1.5% aqueous sodium hydroxide solution, squeezed, and then subjected to hydrolysis treatment at 123°C for 25 minutes in a moist heat atmosphere, washed with water, and dried at 105°C for 1 hour to obtain an easily beaten acrylonitrile fiber of the present invention. The fibers were cut to 3 mm and made into a 3% concentration aqueous slurry, and then beaten using a refiner (KRK type manufactured by Kumagai Riki Kogyo Co., Ltd.) for the number of passes shown in Table 1 to obtain pulp-like acrylonitrile fibers of Example 1. The freeness of the easily beaten acrylonitrile fibers cut to 3 mm was 760 ml.

[0055] <Examples 2 to 5> The pulp-like acrylonitrile fibers of the present invention in Examples 2 to 5 were obtained in the same manner as in Example 1, except that the concentration of the sodium hydroxide aqueous solution was changed to 4.0% and the beating treatment was performed with the number of passes shown in Table 1. Also, an SEM photograph of the pulp-like acrylonitrile fibers of Example 3 is shown in FIG.

[0056] <Examples 6 to 8> The easily beaten acrylonitrile fibers of the present invention were obtained in the same manner as in Example 1, except that the concentration of the aqueous sodium hydroxide solution was changed to 7.5% in Example 6, 10.0% in Example 7, and 20.0% in Example 8. The fibers were beaten for the number of passes shown in Table 1 to obtain pulp-like acrylonitrile fibers of Examples 6 to 8.

[0057] <Example 9> An easily beaten acrylonitrile fiber was obtained in the same manner as in Example 4, except that a step of adjusting the pH to 3.5 with nitric acid in pure water and holding at 60° C. for 30 minutes was inserted between the hydrolysis treatment step and the water washing step. In addition, a pulp-like acrylonitrile fiber of Example 9 of the present invention was obtained by beating the fiber with the number of passes shown in Table 1.

[0058] <Comparative Examples 1 to 4> 27.5 parts by weight of acrylonitrile and 72.5 parts by weight of methoxypolyethylene glycol (30 mol) methacrylate were suspension polymerized to prepare an acrylonitrile-based hydrophilic resin. Next, 10 parts of an acrylonitrile-based polymer consisting of 90% acrylonitrile and 10% methyl acrylate were dissolved in 90 parts of a 44% aqueous sodium thiocyanate solution, and 0.3 parts of the above-mentioned acrylonitrile-based hydrophilic resin were added to prepare a spinning dope. This spinning dope was spun into a coagulation bath at -2.5°C, coagulated, washed with water, and stretched 12 times to obtain a gel-like acrylonitrile-based fiber with a moisture content of 35%. The fiber was subjected to a wet heat treatment at 123°C for 25 minutes in a wet heat atmosphere, washed with water, and then dried at 105°C for 1 hour to obtain an acrylonitrile-based fiber containing a hydrophilic resin and not containing a carboxyl group. The fibers were cut into 3 mm pieces and made into a 3% concentration aqueous slurry, which was then beaten using a refiner (KRK type manufactured by Kumagai Riki Kogyo Co., Ltd.) with the number of passes shown in Table 1 to obtain pulp-like acrylonitrile fibers of Comparative Examples 1 to 4. Also, a SEM photograph of the pulp-like acrylonitrile-based fiber of Comparative Example 4 is shown in FIG.

[0059] <Comparative Examples 5 to 7> 10 parts of an acrylonitrile-based polymer consisting of 90% acrylonitrile and 10% methyl acrylate was dissolved in 90 parts of a 44% aqueous sodium thiocyanate solution to prepare a spinning dope. This spinning dope was spun into a coagulation bath at -2.5°C, coagulated, washed with water, and stretched 12 times to obtain a gel-like acrylonitrile-based fiber with a moisture content of 35%. The fiber was immersed in a 4.0% aqueous sodium hydroxide solution, squeezed, and then hydrolyzed in a moist heat atmosphere at 123°C for 25 minutes, washed with water, and dried at 105°C for 1 hour to obtain an acrylonitrile-based fiber that does not contain a hydrophilic resin and contains a carboxyl group. The fiber was cut into 3 mm pieces and made into a 3% aqueous slurry, and then beaten using a refiner (KRK type manufactured by Kumagai Riki Kogyo Co., Ltd.) with the number of passes listed in Table 1 to obtain pulp-like acrylonitrile-based fibers of Comparative Examples 5 to 7.

[0060] The evaluation results of the fibers obtained in the above-mentioned Examples and Comparative Examples are shown in Table 1. In the table, "-" indicates that no measurement was performed.

[0061] [Table 1]

[0062] As shown in Table 1, in Examples 1 to 8, the beating speed is fast as can be seen from the freeness corresponding to the number of passes through the refiner, and the obtained pulp-like acrylonitrile-based fiber is also excellent in paper strength (breaking strength) and activated carbon capture ability. Note that in Example 9, in which the neutralization degree of Example 4 was reduced, the freeness was lowered, indicating that the higher the neutralization degree, the faster the beating.

[0063] In addition, it can be seen that Comparative Examples 1 to 4, which were not hydrolyzed, have a slower beating speed as can be seen from the freeness corresponding to the number of passes through the refiner, and furthermore, the paper strength (breaking strength) and activated carbon capture ability are also low compared to Examples 2 to 5. Similarly, it can be seen that Comparative Examples 5 to 7, which were hydrolyzed but did not contain a hydrophilic resin, have a slower beating speed as can be seen from the freeness corresponding to the number of passes through the refiner, compared to Examples 2 to 5.

[0064] Also, from Fig. 1, it is seen that the pulp-like acrylonitrile fiber of Example 3 has a smooth fibril surface, and hence has excellent beating properties. On the other hand, the pulp-like acrylonitrile fiber of Comparative Example 4 shown in Fig. 2 has an irregular fibril surface, and therefore has poor beating properties, and it is seen that it is somehow beaten by repeatedly applying a shear force.

Claims

1. The pulp-like acrylonitrile fiber is obtained by beating an easily beaten acrylonitrile fiber, which contains a hydrophilic component in the fiber interior and is a polymer having a carboxyl group amount of 0.2 to 4.0 mmol / g and substantially no crosslinked structure due to a covalent bond, and which contains 30 to 90% by weight of a monomer represented by the following Chemical Formula 1 as a constituent unit, and has a freeness of 600 ml or less. 【Chemistry 1】

2. A structure comprising the pulp-like acrylonitrile fiber according to claim 1.

3. A sanitary product, a filter, a carbon sheet for a fuel cell diffusion membrane, a friction material, a functional paper product, a moisture permeable paper, or a battery component, comprising the structure according to claim 2.

4. A method for producing a pulp-like acrylonitrile-based fiber, comprising adding a hydrophilic component to a spinning solution in which an acrylonitrile-based polymer is dissolved, in an amount of 0.5 to 10.0% by weight based on the weight of the acrylonitrile-based polymer, spinning the resulting solution from a nozzle, and then carrying out steps of coagulation, water washing and stretching to obtain undried fiber, which is then subjected to hydrolysis and then beating.

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