JPS6260502B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing water-swellable fibers, and more specifically, acrylonitrile fibers (hereinafter referred to as AN fibers) are treated with a specific alkali to hydrogel at least a portion of the outer layer of the fibers, and then Attaching certain water-miscible organic solvents,
The present invention relates to a method for producing water-swellable fibers which have a high degree of water swelling and high physical properties by drying, and also have a soft texture without sticking. In recent years, highly water-swellable polymers (hydrogel) have attracted attention for their special functions and are being applied to a wide range of fields of use. For example, the ability of such polymers to instantly absorb a large amount of water can be used to make diapers, sanitary products, etc., the ability to retain moisture can be used to make soil improvers, instant sandbags, etc., and the polymer can also be made by focusing on its affinity with human tissue. Attempts have been made to apply it to soft contact lenses, artificial organs, surgical suture materials, etc., and some of these applications have already entered the stage of practical use. Hydrogels that have such wide applicability are often preferably in the form of fibers depending on their uses, and several such fibrous hydrogels are known. However, in existing natural or synthetic fibers, even if they have a certain degree of water swelling ability, their degree of water swelling is extremely low, or they are water soluble, and in any case, their own weight is very low. It is far from the category of water-swellable fibers, which absorb and retain from twice to several hundred times as much water and are insoluble in water. Also,
Japanese Patent Publication No. 52-42916 describes a highly swellable fibrous structure obtained by introducing a specific crosslinked structure and a large amount of carboxyl groups in the form of salt into acrylic fibers. However, such fibrous structures have extremely large amounts of salt-type carboxyl groups introduced into them, and the entire inner and outer layers of the fibers are hydrogel-formed, so while they can provide a high degree of water-swelling performance, they are extremely brittle. In addition, the stagnation was remarkable and the concept was far from the concept of fibers. Furthermore, in JP-A No. 49-50217, at least a part of the AN-based polymer phase that is easily hydrolyzed by special spinning methods such as single-core sheath type, sea-island type, and two-component bonding type is The technical idea is to use composite fibers located in the 200°C as a starting material, crosslink the AN polymer phase, and then hydrolyze it to impart water swelling properties, while maintaining fiber strength with a polymer phase that is difficult to hydrolyze. Disclosed. However, this invention requires the use of expensive composite fibers produced by a special spinning method, and also requires crosslinking treatment prior to hydrolysis treatment, making it difficult to say that it is an industrially advantageous method. It was hot. Here, the present inventor has overcome the above-mentioned essential defects and achieved high water swelling while maintaining fiber properties without using any special fibers as a starting material and without requiring a separate crosslinking process. As a result of intensive study to obtain fibers with
By applying a specific alkali metal hydroxide aqueous solution to AN-based fibers to selectively hydrogelize only the outer layer of the fibers, water swelling performance can be advantageously imparted without impairing the physical properties of the fibers. After discovering the facts, he first proposed the invention in patent application No. 46058/1983.
However, especially in fibers in which the outer layer of the fiber has been selectively hydrogelated, that is, in which a large amount of salt-type carboxyl groups have been introduced into the outer layer of the fiber, the fibers tend to stick together during the subsequent drying process. It was desired to provide a means of making water-swellable fibers that could avoid this. Under these circumstances, the inventor
By treating the outer layer of the fiber with a specific alkali to hydrogel it, treating it with a specific water-miscible organic solvent, and drying it, it has a high water swelling degree and high physical properties, and is non-sticky. The present invention was achieved by discovering the fact that water-swellable fibers with a soft texture can be produced. That is, the object of the present invention is to provide a method for producing water-swellable fibers that have excellent water-swelling performance and fiber properties without using any special AN-based fibers as a starting material, and have a flexible texture without sticking. Our goal is to provide the following. Another object of the present invention is to provide a method for producing water-swellable fibers that facilitates purification operations such as removal of residual alkali, washing, dehydration, and drying. This will become clear from the description of the specification. The purpose of the present invention described above is to
A high concentration alkali metal hydroxide aqueous solution with a concentration of 6.0mol/1000g or more or a low concentration alkali metal hydroxide aqueous solution coexisting with electrolyte salts with a concentration of 0.5mol/1000g or more at a temperature of 100 to 250℃ for 30 minutes. 0.1 to 4.0 mmol/g of salt-type carboxyl group (-COOX, X is an alkali metal or
By introducing NH ₄ ), at least a part of the outer layer of the fiber is made of hydrogel and the rest is made of AN.
A water-miscible organic solvent in which the moisture content of the obtained water-containing water-swellable fiber is higher in the gas phase than in the liquid phase when mixed with water. By drying after processing with
This can be achieved with industrial advantage. Here, the AN-based fiber according to the present invention is
A general term for fibers with a cross-sectional shape in which at least a part of the AN polymer is exposed on the fiber surface, including AN polymer single component spun fibers, two-component or three or more component AN polymer composite spun fibers. , composite spun fibers of AN-based polymers and other polymers such as polyvinyl chloride-based, polyamide-based, polyolefin-based, polystyrene-based, polyvinyl alcohol-based, cellulose-based, and the like. In addition, from the viewpoint of release between each component, water swelling performance, etc., it is preferable to employ fibers formed by single-component spinning or composite spinning of AN-based polymers as the starting acrylic fibers. In addition, the above AN-based polymer is 30% by weight or more, preferably
It is a general term for polymers containing 50% or more of AN combined, and is an AN homopolymer or AN and at least 1
It goes without saying that the name refers to copolymers of AN and other ethylenically unsaturated compounds, such as AN and starch,
It also includes a graft copolymer with polyvinyl alcohol or the like, or a mixed polymer of the AN homopolymer or AN copolymer with the other polymer.
Furthermore, if the AN content of the AN-based polymer is less than the recommended range of the present invention, sufficient water swelling performance cannot be imparted by hydrolysis treatment, which is not preferable. In addition, by using fibers having latent or actual crimps as the above-mentioned AN-based fibers as starting materials, it is possible to produce water-swellable fibers having crimps and having excellent waist, bulkiness, etc., which is preferable. . It takes
The crimp characteristics of AN-based fibers are not limited in any way as long as they have latent or actual crimp.
The number of crimps (Cn) per 25 mm of fiber length is 3 or more, preferably 5 or more, and the crimp degree (Ci) is 5% or more, preferably 7 in a state where crimps are visible.
% or more is desirable from the viewpoint of practical performance such as stiffness and bulk of the water-swellable fiber product finally obtained. The fibers produced in this way are not restricted in any way by the form of short fibers, long fibers, fiber tows, threads, knitted fabrics, nonwoven fabrics, etc., and the present invention can be applied to the fibers regardless of whether they are dry or hydrated. It can be used as a starting material, and even waste fibers discharged from the AN fiber manufacturing process, etc., or products in the middle of the fiber manufacturing process (e.g., coagulated yarn, drawn yarn, dried yarn, etc.) can be used to change the fiber form. It can be applied as long as it has. In order to obtain water-swellable fibers having high water-swellability and high physical properties using such AN-based fibers as a starting material, only the outer layer of the AN-based fibers is selectively hydrogelated so that at least a part of the outer layer of the fibers is It is necessary to make fibers made of hydrogel. As a one-step hydrolysis and crosslinking treatment method that selectively hydrogelizes only the outer layer of such AN fibers and can easily control the ratio of the outer layer, the present invention employs the means described below. . That is, a highly concentrated alkali metal hydroxide aqueous solution of 6.0 mol/1000 g or more is applied to the dry or hydrated AN fiber (hereinafter referred to as method A), or a 0.5 mol/1000 g or more solution is applied One of the methods (hereinafter referred to as method B) in which a low concentration alkali metal hydroxide aqueous solution in the presence of a high concentration electrolyte salt was applied was employed. In addition, when employing the above method A, if an alkaline aqueous solution with a concentration of less than 6.0 mol/1000 g solution is applied, the AN fiber becomes hydrophilic due to the hydrolysis reaction, but becomes water-soluble, which does not meet the purpose of the present invention. It is not possible to form an outer hydrogel layer. Also, from 6.25
8.85mol/1000g solution, further 6.25-8.50mol/1000
The present invention can be more effectively achieved by using an alkaline aqueous solution in the concentration range of g solution. Under conditions exceeding the upper limit of this preferred range, the activity of the alkali metal hydroxide decreases, requiring high-temperature treatment to increase the reaction rate, and making it difficult to remove residual alkali, which is not practical. do not have. In addition, when adopting method B, the amount of salt to coexist is 0.5 mol/1000 g.
When the concentration is low, below that of the solution, the AN fiber becomes hydrophilic through a hydrolysis reaction, but most of it becomes water-soluble, and the outer layer of the hydrogel is formed in one step in a low-concentration alkaline aqueous solution. It is not possible. In addition, by acting with an aqueous alkali solution having a salt concentration of 1.0 mol/1000 g solution or more or an alkali metal hydroxide concentration of 0.5 to 6.0 mol/1000 g solution, more preferably 1.0 to 5.0 mol/1000 g solution. , the present invention can be implemented more industrially advantageously. Here, examples of the alkali metal hydroxide used in the present invention include hydroxides of alkali metals such as Na, K, and Li, or mixtures thereof, and examples of the electrolyte salt include alkali-treated Any salt can be used as long as it is stable under the conditions, and the cation component constituting the salt is, for example, alkali metals such as Na, K, Li, etc.; alkali metals such as Be, Mg, Ca, Ba, etc. earth metal;
Other metals such as Cu, Zn, Al, Mn, Fe, Co, Ni; _NH4 , etc., and anionic components such as hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, chromic acid, dichromic acid,
Examples include one type or a mixture of two or more types of salts composed of acid groups such as chloric acid, hypochlorous acid, organic carboxylic acids, and organic sulfonic acids. In addition,
When using an electrolyte salt whose cationic component is an element with a valence of 2 or higher, the outer layer of the hydrogel produced tends to aggregate and coalesce, and the degree of swelling decreases. It is preferable to use Although it is preferable to use industrial water as the solvent for preparing the alkaline aqueous solution, as a solvent in place of water,
As long as it does not dissolve the AN fibers, a mixed solvent of water and an organic solvent such as methanol, ethanol, propanol, 2-methoxyethanol, 2-ethoxyethanol, dimethylformamide, dimethyl sulfoxide, etc. can be used, and if necessary, It is also possible to coexist other inorganic or organic substances. Here, specific methods for applying the alkali include a method of heating the AN fiber to be treated while immersed in the aqueous alkaline solution, or a method of heating after adhering the aqueous alkaline solution. However, from an industrial perspective, it is preferable to apply the alkaline aqueous solution and then heat it. In such a preferred embodiment, the amount of alkali deposited needs to be controlled within the range of 2 to 200%, preferably 5 to 100%, based on the dry weight of the fiber. If the amount of the aqueous alkaline solution deposited is less than 2%, it will not be possible to produce fibers with the desired degree of water swelling even if the specific aqueous alkaline solution recommended in the present invention is applied. If the amount of adhesion exceeds 200%, not only will the effect of improving water swelling performance reach a plateau, but it will also become difficult to remove excess alkali, which is not preferred in practice. Furthermore, there are no restrictions on the method of attaching a predetermined amount of the alkaline aqueous solution to the fibers as long as the amount of the attached amount can be controlled within the recommended range of the present invention. A predetermined amount of powder of alkali metal hydroxide alone or both alkali metal hydroxide and an electrolyte salt is attached to the fiber, or an alkaline aqueous solution is sprayed onto the fiber to be treated in a dry or hydrated state, as desired. Examples of methods include removing the liquid using a centrifugal dehydrator or the like, or immersing it in an aqueous solution and then squeezing and removing the liquid. In addition, in order to easily control the amount of the aqueous alkaline solution deposited and the concentration (amount of deposited) of the alkali metal hydroxide or electrolyte salt, a predetermined amount of the alkaline aqueous solution prepared in advance at a predetermined concentration is applied to the dry surface. process
An embodiment in which it is attached to AN-based fibers is industrially desirable. The fibers coated with a predetermined amount of the aqueous alkaline solution described above are then heated and subjected to a hydrolysis treatment. Although it is difficult to define the temperature conditions during such heating, generally, the higher the temperature, the higher the reaction rate and the more advantageous the treatment effect can be achieved, so it is preferably 80°C or higher. 100~250
It is desirable to adopt temperature conditions of °C. Also,
It is preferable to use a moist heat atmosphere such as saturated steam or superheated steam or heating means as the heating atmosphere in terms of ease of temperature control, thermal efficiency, and homogenization of hydrolysis and crosslinking reactions. It goes without saying that heating means such as a hot roller or a hot plate can be used as appropriate. In addition, the heat treatment time is as follows:
Type of AN fiber, amount of alkaline aqueous solution attached,
It is possible to change it variously depending on the temperature during heating or the desired degree of water swelling, etc., and it is difficult to define it unambiguously, but in particular, a heating temperature condition of 100 to 250°C is adopted, By adjusting the heat treatment time preferably within 30 minutes, more preferably within the range of 5 seconds to 20 minutes, water-swellable fibers in which only the outer layer of the fibers is selectively hydrogelated, which is the object of the present invention. can be produced industrially advantageously. By employing the specific hydrolysis conditions recommended for the present invention, although the alkaline hydrolysis treatment under known conditions actually produces only water-soluble polymers, the known In contrast to the results expected from the reaction conditions, homogeneous hydrogels are produced without crosslinking, and in high yields. The mechanism of action is, in particular, side reactions that accompany the hydrolysis reaction of nitrile groups in the outer fiber layer, forming intermolecular crosslinks or heterogeneous bonds such as intramolecular cyclic structures.
This can be explained by the fact that it progresses specifically under the above-mentioned specific conditions, but the details have not yet been elucidated. In addition, the amount of salt type carboxyl group (-COOX) introduced into the water-swellable fiber thus prepared is
0.1~4.0mmol/g, more preferably 0.5~
It is desirable to adjust it within the range of 3.5 mmol/g. If the amount of the salt-type carboxyl group is outside the lower limit of the recommended range of the present invention, the water swelling performance will be insufficient, and if it exceeds the upper limit of the range, the physical properties of the fiber will deteriorate and the fiber will become brittle with poor flexibility. This is not desirable. Next, it is necessary to treat the hydrated water-swellable fiber thus produced with a water-miscible organic solvent whose moisture content when mixed with water is higher in the gas phase than in the liquid phase. Here, water-miscible organic solvents whose moisture content is higher in the gas phase than in the liquid phase when mixed with water are:
Refers to a water-miscible organic solvent that has the physical property that water preferentially evaporates in a water-mixed system, and includes, for example, the following solvents. A low-boiling water-miscible organic solvent that has a boiling point similar to or lower than that of water and that can form an azeotrope (lowest azeotrope) giving a minimum boiling point with water, or the organic solvent has a minimum boiling point composition. Aqueous mixed solvents containing water in proportions less than A high-boiling water-miscible organic solvent having a boiling point higher than water and capable of forming a minimum azeotrope with water, or an aqueous mixed solvent in which the organic solvent contains water in a proportion below the minimum boiling point composition. A high-boiling water-miscible organic solvent that has a boiling point higher than water and cannot form an azeotrope with water, or an aqueous mixed solvent in which the organic solvent contains water in any proportion. By using the solvents shown in the above item, it is possible to produce water-swellable fibers that effectively prevent sticking and have a soft texture, and also make the subsequent drying process industrially advantageous. This is desirable because it can be implemented. Water-miscible organic solvents that fall into this category include ethyl alcohol,
Examples include i-propyl alcohol, n-propyl alcohol, sec-butyl alcohol, t-butyl alcohol, allyl alcohol, acetonitrile, acrylonitrile, and ethyl acetate. In addition, as the solvent belonging to the above item, n-
Butyl alcohol, i-butyl alcohol, n-
amyl alcohol, i-amyl alcohol, t-
Examples include amyl alcohol, cyclohexanol, n-hexyl alcohol, and i-amyl ether. Note that two or more types of organic solvents selected from the above items may be used in combination as long as water can be evaporated preferentially. In addition, such solvent treatment may be carried out using aqueous (undried) water that has been subjected to alkaline hydrolysis and then used as is, or that has been subjected to appropriate operations such as washing with water, acid treatment, conversion to a desired salt-type carboxyl group, and dehydration. It is necessary to apply it to swellable fibers. Furthermore, even if the dried water-swellable fibers are treated with a solvent, it is not possible to eliminate the agglutination that occurs during drying, and only fibers with a rough texture can be obtained, so drying before solvent treatment is not recommended. Must be avoided. In addition, when using a solvent that does not satisfy the characteristics according to the present invention, the water-miscible organic solvent will preferentially evaporate in the subsequent drying process, and the water content in the aqueous mixed solvent that adheres to the fibers will gradually increase. However, sticking between the fibers cannot be avoided, and the object of the present invention cannot be achieved. Thus, even without using any special fiber as a starting material, it is possible to obtain a fiber in which at least a portion of the outer fiber layer is made of hydrogel and has an inner layer made of AN polymer and/or other polymers,
Surprisingly, the fibers have a water swelling degree of 2 to 300 c.c./g, preferably 3 to 200 c.c./g, and
In terms of fiber properties such as wet and dry strength, wet and dry elongation, and knot strength, it exhibits performance that is almost comparable to ordinary AN-based fibers for clothing. By performing the above solvent treatment according to the present invention,
It was thought that it was essentially impossible to avoid agglutination because the outer layer of the fibers was selectively hydrogelated, but it effectively suppresses agglutination of water-swellable fibers and has a flexible texture. It is a particular advantage of the present invention that fibers can be provided. Furthermore, since the fiber has an inner layer made of an AN-based polymer or the like, it also has the unique property of not undergoing dimensional change in the length direction even in a swollen state. In this way, it is not necessary to use fibers made of polymers with special compositions containing crosslinking monomers etc. as copolymerization components or composite fibers produced by special spinning methods. AN
Using waste fibers discharged from the production process of fibers, etc., or products in the middle of the production process, etc. as starting materials, the outer layer of the fibers is produced by a process of only hydrolysis treatment with an alkaline aqueous solution without prior crosslinking treatment. It is also a major feature of the present invention that water-swellable fibers with controlled water swelling degree and physical properties can be produced by selectively hydrogelating fibers, and by adjusting the hydrolysis treatment conditions. In addition, the water-swellable fibers produced in this way are non-adhesive and have homogeneous and excellent physical properties such as strength, elongation, elasticity, and flexibility, and can be handled in exactly the same way as existing clothing fibers. This is also a characteristic advantage of the present invention. Furthermore, the solvent treatment according to the present invention can serve as a purification operation such as washing the water-swellable fibers and removing residual alkali, and since the organic solvent also has a dehydration effect because it shrinks the water-swellable fibers, subsequent Another effect of the present invention is that the drying process becomes easier. The water-swellable fiber of the present invention, which has both such high water-swellability and excellent physical properties, can be used alone or by blending or making with existing natural, semi-synthetic or synthetic fibers, etc., as desired. New fiber materials or textile products with hygroscopicity, water absorption, and water retention properties, such as diapers, sanitary products, paper, etc., or dehydration materials from organic solvents that are immiscible with water, sealing materials, cation exchange fibers, etc. Furthermore, like existing hydrogel powders, it can be applied to instant sandbags, artificial soil, drainage, heat insulation, cold insulation materials, etc. In order to further facilitate understanding of the present invention, Examples are described below, but the gist of the present invention is not limited in any way by the description of these Examples. It should be noted that all percentages and parts described in the Examples are based on weight unless otherwise specified. In addition, the degree of water swelling, the amount of salt-type carboxyl group (-COOX), bulkiness, and waist tension described in the following examples were measured or calculated by the following method. (1) Degree of water swelling (cc/g) Approximately 0.1 g of sample fiber was immersed in pure water, kept at 25°C for 24 hours, then wrapped in nylon cloth (200 mesh) and placed in a centrifugal dehydrator (30G x 30 minutes). G is gravitational acceleration) to remove water between the fibers. Measure the weight of the sample prepared in this way (W ₁
g). Next, the sample is dried in a vacuum dryer at 80°C until it reaches a constant weight, and the weight is measured (W ₂
g). From the above measurement results, it was calculated using the following formula. Therefore, the actual water swelling degree is a numerical value indicating how many times the weight of the fiber can absorb and retain water. Degree of water swelling = W ₁ - W ₂ /W ₂ (2) - COOX group amount (mmol/g) Approximately 1 g of a sufficiently dried sample was purified (Xg),
After adding 200 ml of water to this, a 1N aqueous hydrochloric acid solution was added while heating to 50°C to adjust the pH to 2, and then a titration curve was determined using a 0.1N aqueous sodium hydroxide solution according to a conventional method. From the titration curve, the amount of caustic soda aqueous solution consumed by carboxyl groups (Yc.c.)
I asked for From the above measurement results, it was calculated using the following formula. -COOX group amount = 0.1Y/X If polyvalent cations are included, it is necessary to determine the amount of these cations by a conventional method and correct the above formula. (3) Bulky property (m ³ /g) and waist tension property (g/cm) After opening approximately 10g of sample fiber, 10×10 (cm)
Measure the weight of the test pieces created by stacking them in a rectangular shape (W ₃ g). Next, the test piece was compressed and unloaded three times using a constant speed compression tester at a speed of 100 mm/min to a compression load of 5 g/cm ² , and from the third compression curve, the initial load was 0.5 g/cm ² The thickness (hocm) of the test piece at the time was determined, and the bulkiness was calculated using the following formula. Bulkyness = 10 x 10 x ho/W _3. The compression work (waist tension property) was determined from the compression curve obtained by compressing the above-mentioned compression-unloading test piece three times and then compressing it to a load of 50 g/cm ² . ) was calculated as the integral value of the thickness of the test piece and the compressive load. Example 1 AN-based fiber consisting of 90% AN and 10% methyl acrylate (single fiber fineness: 3 ^d , fiber length: 51
mm, intrinsic viscosity in dimethylformamide (DMF) solution at 30°C; 1.3) 5 parts to 30% (7.5 mol/1000
g solution) The fibers were immersed in 95 parts of aqueous caustic soda solution, boiled for 6 minutes while stirring, and then the residual alkali in the fibers was washed away, and then immersed in i-propyl alcohol to shrink the water-swellable fibers. Remove the water adhering to the fibers until the moisture content is below 10%.
After replacing with propyl alcohol, water-swellable fibers (2018) which were white to slightly yellow in color were produced by drying. The fibers obtained in this way did not dissolve in water, and when squeezed in a water-swollen state, it was found that the AN polymer core remained at 1.8 mmol/g.
It was confirmed that it contains a --COONa group of , and has a water swelling degree of 103 c.c./g. In addition, the fibers (2000) had almost no adhesion and had a soft texture. The results of measuring the physical properties of the fibers (2) are listed in Table 1 together with the physical property values of the AN fibers to be treated.

[Table] As is clear from the above results, it is understood that the water-swellable fibers () according to the present invention have a flexible texture without sticking, and are excellent in both strength and elongation and water-swellability. Ru. On the other hand, as a comparative example, hydrolysis treatment was carried out according to the above recipe except that 10% and 20% caustic soda aqueous solutions were used. In all cases, the treated AN fibers dissolved in the aqueous solution and became viscous. Only a solution was formed, and water-swellable fibers could not be formed. In addition, when the hydrolysis treatment was performed according to the above recipe except that the boiling time was extended to 40 minutes, 7.1 mmol/
Although it contains a -COONa group of 257 c.c./g and has an extremely high degree of water swelling of 257 c.c./g, it is extremely brittle.
In addition, when the fiber was squeezed in a water-swollen state,
Substantially no AN polymer core remained. Further, when water-swellable fibers were produced according to the above recipe except that the solvent treatment was omitted, the fibers showed significant adhesion and had a rough and hard texture. Example 2 After opening the AN-based fiber described in Example 1, a 2.5 mol/1000 g solution of caustic soda aqueous solution in which 4.0 mol/1000 g solution of sodium nitrate coexisted was uniformly spread on the fiber to give 30% adhesion. Ta. Next, this fiber is placed in an autoclave,
After heating in saturated steam at 115° C. for 5 minutes, the fibers were treated with a solvent according to the recipe described in Example 1 and dried to produce water-swellable fibers ( ). The fibers produced in this way have a soft texture with almost no adhesion, and
Contains 1.3 mmol/g of -COONa group, 76 c.c./g
It was confirmed that the material had a degree of water swelling of In addition, when treated in the same manner as above except that t-butyl alcohol was used instead of i-propyl alcohol, water-swellable fibers () with a soft texture and almost no adhesion were obtained. It was done. Example 3 Two-component bonded AN-based composite fiber (manufactured by Nippon Exlan Kogyo Co., Ltd., single fiber fineness: 6 ^d , fiber length: 38
Example 2
Water-swellable fibers ( ) were prepared by heating, solvent treatment, and drying according to the described recipe. This fiber () contained 1.5 mmol/g of COONa groups, had an AN polymer core remaining, and had a soft texture with almost no adhesion. In addition,
The results of measuring various performances of this fiber (2) are listed in Table 2 together with the performance values of the AN composite fiber to be treated.

[Table] Numerical values,
As is clear from the above results, the water-swellable fiber according to the present invention has almost all the adhesion, flexibility, crimp properties, strength and elongation, bulkiness, and waist tension properties of the treated AN-based composite fiber. It is understood that it maintains a comparable level and has excellent water swelling performance.

Claims (1)

[Scope of Claims] 1. High concentration alkali metal hydroxide aqueous solution of 6.0 mol/1000 g solution or more or low concentration alkali metal hydroxide aqueous solution in which electrolyte salts of 0.5 mol/1000 g solution or more coexist in acrylonitrile fiber. The solution is allowed to act at a temperature of 100-250℃ for no more than 30 minutes to reduce the concentration of 0.1
~4.0 mmol/g salt-type carboxyl group (-
By introducing _COOX , A method for producing water-swellable fibers, which comprises treating the water-containing water-swellable fibers with a water-miscible organic solvent having a higher moisture content in the gas phase than in the liquid phase when mixed with water, and then drying the fibers. . 2. The manufacturing method according to claim 1, wherein the water-swellable fiber is a fiber having a degree of water swelling of 2 c.c./g or more.