JP7177986B2 - Shrinkable, moisture-absorbing acrylonitrile fiber, method for producing said fiber, and fiber structure containing said fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a shrinkable, moisture-absorbing acrylonitrile fiber, a method for producing the fiber, and a fiber structure containing the fiber.

Shrinkable acrylic fiber is a fiber that shrinks when heated. In bulky yarns and sliver knits, this shrinkage is used to create bulkiness, but it has poor hygroscopicity and is prone to static electricity. Alternatively, it was necessary to improve comfort such as being easily stuffy.

On the other hand, hygroscopic fibers have been actively developed in the field of textiles due to the recent heightened awareness of comfort. For example, crosslinked acrylate fibers obtained by chemically modifying acrylic fibers are known (Patent Document 1). The fiber contains a crosslinked structure and carboxyl groups and has excellent moisture absorption performance.

However, since the fibers have cross-links, it is difficult to impart shrinkability. In addition, the production of the fiber requires a step of introducing a crosslinked structure with hydrazine and a hydrolysis step for introducing a carboxyl group. It is necessary to have a process to Moreover, each of these steps requires a high temperature and a long time. For this reason, it is difficult to manufacture the fiber by continuous processing, and batch processing with low productivity has been performed. Therefore, conventional crosslinked acrylate fibers have low productivity and their manufacturing costs remain high.

As for the acrylic fiber having a carboxyl group, an acrylic fiber made of an acrylonitrile-based polymer containing a monomer having a carboxyl group such as acrylic acid as a copolymer component is known. However, when a large amount of acrylic acid is copolymerized, spinning becomes difficult, so it has been difficult to develop high hygroscopicity. In addition, since it does not have a crosslinked structure, it tends to be eluted under alkaline conditions such as alkaline soaping in dyeing, which is a problem when it is used for clothing.

JP-A-5-132858

As described above, conventionally, shrinkable acrylic fibers are known, but they have no hygroscopicity and have problems with comfort. In addition, although the crosslinked acrylate fiber is excellent in hygroscopicity, it is poor in shrinkability and requires many manufacturing steps, resulting in low productivity. Furthermore, it is difficult to improve the hygroscopicity of acrylic fibers containing acrylic acid as a copolymer component. The present invention was invented in view of the current state of the prior art, and its object is to provide shrinkable, hygroscopic acrylonitrile fibers that can be continuously produced in a simpler process than conventional ones. That's what it is.

As a result of intensive studies in order to achieve the above-mentioned object, the inventors of the present invention have found that a raw spinning solution in which an acrylonitrile-based polymer is dissolved is spun from a nozzle, then coagulated, washed with water, and drawn. We discovered that by hydrolyzing dry fibers and then drawing them, it is possible to obtain hygroscopic acrylonitrile-based fibers that have shrinkability while maintaining practical fiber properties without having a crosslinked structure. We have reached the perfection of the invention.

That is, the present invention is achieved by the following means.
(1) A hygroscopic acrylonitrile-based fiber composed of a polymer that does not substantially have a covalently crosslinked structure, and containing 0.2 to 2.0 mmol/g of carboxyl groups in the fiber. , a saturated moisture absorption rate at 20° C.×65% RH of 3 to 15.6 % by weight, a boiling water shrinkage rate of 5 to 50%, and a water swelling degree of 10 times or less. Moisture-absorbing acrylonitrile fiber.
(2) The shrinkable, moisture-absorbing acrylonitrile-based fiber according to (1), wherein the carboxyl groups are uniformly present throughout the fiber.
(3) The shrinkable hygroscopic acrylonitrile fiber according to (1), characterized in that the carboxyl groups are localized on the surface layer of the fiber.
(4) The shrinkable hygroscopic acrylonitrile fiber according to any one of (1) to (3), characterized in that the degree of neutralization of carboxyl groups is 25% or more.
(5) After spinning a spinning stock solution containing an acrylonitrile-based polymer from a nozzle, the undried fibers obtained through the steps of coagulation, washing with water, and drawing are hydrolyzed and then drawn. (2) A method for producing a shrinkable, hygroscopic acrylonitrile-based fiber.
(6) After spinning a spinning solution containing an acrylonitrile-based polymer from a nozzle, the undried fibers obtained through the steps of coagulation, washing, and drawing are heat-treated to densify the fibers or after densification. The method for producing shrinkable, hygroscopic acrylonitrile-based fibers according to (3), which comprises hydrolyzing the relaxation-treated fibers and then drawing them.
(7) The method for producing shrinkable, hygroscopic acrylonitrile-based fibers according to (5) or (6), wherein the undried fibers have a moisture content of 20 to 250% by weight.
(8) A fiber structure containing the shrinkable hygroscopic acrylonitrile fiber according to any one of (1) to (4).

The shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention does not substantially have a crosslinked structure due to covalent bonds, and therefore can exhibit practical shrinkability. In addition, since the shrinkable, hygroscopic acrylonitrile-based fiber of the present invention does not require a cross-linking introduction step in its production, the production process can be greatly reduced, and as a result, continuous continuous production using ordinary acrylic fiber production equipment is possible. It is possible and highly productive. Since the shrinkable, hygroscopic acrylonitrile fiber of the present invention has both shrinkability and hygroscopicity, it can be used for carpets, towels, knitwear, yarn, piles, blankets, sheets, cushioning materials, and the like.

The shrinkable, moisture-absorbing acrylonitrile fiber of the present invention is characterized in that it does not substantially have a crosslinked structure due to covalent bonds, unlike conventional crosslinked acrylate fibers. This eliminates the need for a step of introducing cross-linking, and as a result, it is possible to greatly reduce the number of manufacturing steps, and to perform production using simpler steps than conventional ones. Therefore, continuous production is possible without being limited to batch processing such as the production of conventional crosslinked acrylate fibers. Moreover, since it does not substantially have a crosslinked structure due to covalent bonds, it can exhibit practical contractility. In the present invention, the expression "substantially does not have a covalently crosslinked structure" means that <solubility in an aqueous sodium thiocyanate solution>, which will be described later, is 95% or more.

The shrinkable, moisture-absorbing acrylonitrile fiber of the present invention contains a carboxyl group, and the content thereof is 0.2 to 4.5 mmol/g, preferably 0, as determined by the method described later. .5 to 4.0 mmol/g, more preferably 0.5 to 3.5 mmol/g, still more preferably 0.8 to 2.0 mmol/g. When the shrinkable, moisture-absorbing acrylonitrile fiber of the present invention has a core-sheath structure, it is preferably 0.2 to 2 mmol/g, more preferably 0.5 to 1.0 mmol/g. If the amount of carboxyl groups is less than the lower limit of the above range, the hygroscopic performance described below may not be obtained. Beyond that, it violently swells or dissolves in water, making it difficult to handle.

The shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention has a saturated moisture absorption rate of 3% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, under an atmosphere of 20°C and 65% relative humidity. , and more preferably 15% by weight or more. When the saturated hygroscopicity is less than the above lower limit, it is difficult to impart significant hygroscopic performance even when applied to various fiber structures. The upper limit is preferably 35% by weight or less, more preferably 30% by weight or less, from the viewpoint of maintaining fiber physical properties.

The shrinkable, moisture-absorbing acrylonitrile fiber of the present invention preferably has a boiling water shrinkage of 5% to 50%, preferably 8% to 45%, more preferably 12% to 40%. If the boiling water shrinkage ratio is less than 5%, it is difficult to impart significant shrinkage performance even when applied to various fiber structures. Moreover, if the boiling water shrinkage exceeds 50%, it becomes difficult to maintain practical fiber physical properties.

The shrinkable, hygroscopic acrylonitrile-based fiber of the present invention preferably has a degree of swelling with water of 10 times or less, preferably 8 times or less, and more preferably 5 times or less, as determined by the method described below. As described above, the shrinkable, moisture-absorbing acrylonitrile fiber of the present invention does not substantially have a crosslinked structure due to covalent bonds. falls off or dissolves in some cases, making handling difficult. The lower limit is not particularly limited, but from the viewpoint that the shrinkable moisture-absorbing acrylonitrile-based fiber of the present invention has a saturated moisture absorption rate of 3% by weight or more in an atmosphere of 20° C. and a relative humidity of 65%, it is at least 0.03 times. , is considered to be 0.3 times or more in the normal case.

Moreover, in the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention, it is more desirable that the carboxyl groups are uniformly present throughout the fiber. Here, "uniformly present throughout the fiber" means that the coefficient of variation CV of the magnesium element content in the fiber cross section measured by the measuring method described later is 50% or less. If the carboxyl group is localized, the part becomes embrittled due to moisture absorption and water absorption. The presence of carboxyl groups over the entire fiber suppresses embrittlement even when it absorbs moisture and water, making it easier to obtain fiber physical properties that can withstand practical use without having a crosslinked structure. From this point of view, the CV value is preferably 30% or less, more preferably 20% or less, and still more preferably 15% or less.

However, depending on the required physical properties and applications, the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention can employ a core-sheath structure in which carboxyl groups are substantially uniformly present only on the fiber surface. In this case, the core-sheath structure is composed of a surface layer portion made of a carboxyl group-containing polymer and a center portion made of an acrylonitrile polymer. In this way, by having a core-sheath structure consisting of a central portion and a surface layer surrounding it, while obtaining practical fiber physical properties such as hard elasticity in the central portion, moisture absorption rate is high in the surface layer with a high carboxyl group concentration. can be significantly increased.

The surface layer occupies preferably 20 to 80%, more preferably 30 to 70%, of the cross section of the core-sheath structure fiber. If the area occupied by the surface layer is small, functions such as hygroscopicity may not be exhibited sufficiently. .

As for the state of the carboxyl group, it is preferable that the counter ion is a cation other than H when higher hygroscopic performance is desired. More specifically, the proportion of cations other than H as counter ions, that is, the degree of neutralization is preferably 25% or more, more preferably 35% or more, and even more preferably 50% or more.

Examples of cations include alkali metals such as Li, Na and K; alkaline earth metals such as Be, Ca and Ba; metals such as Cu, Zn, Al, Mn, Ag, Fe, Co and _Ni ; Examples include cations such as amines, and multiple types of cations may be mixed. Among them, Li, Na, K, Mg, Ca, Zn and the like are suitable.

Moreover, in the above case, excellent deodorant performance against acidic gases such as acetic acid and isovaleric acid and aldehydes such as formaldehyde can be exhibited. In addition, Mg and Ca ions provide high flame retardancy, and Ag and Cu ions provide high antibacterial performance.

On the other hand, if H is increased as a counter ion of the carboxyl group, the deodorant performance, antiviral performance, and antiallergen performance against amine gases such as ammonia, triethylamine, and pyridine can be enhanced.

As the method for producing the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention described above, a spinning stock solution in which an acrylonitrile-based polymer is dissolved is spun from a nozzle, and the undried state obtained through the steps of coagulation, washing, and drawing. can be obtained by hydrolyzing and drawing the fibers. This manufacturing method will be described in detail below.

First, the raw material acrylonitrile-based polymer preferably contains 40% by weight or more, more preferably 50% by weight or more, and still more preferably 85% by weight or more of acrylonitrile as a polymerization composition. Therefore, as the acrylonitrile-based polymer, in addition to acrylonitrile homopolymers, copolymers of acrylonitrile and other monomers can also be employed. Other monomers in the copolymer include, but are not limited to, vinyl halides and vinylidene halides; (meth)acrylic acid esters; sulfonic acid group-containing monomers such as methallylsulfonic acid and p-styrenesulfonic acid; salts, acrylamide, styrene, vinyl acetate and the like. Note that the notation of (meta) indicates both those with and without the word meta.

Next, using such an acrylonitrile-based polymer, fibrilization is performed by wet-spinning, and the following explanation is given for the case where an inorganic salt such as sodium rhodanate is used as a solvent. First, the above acrylonitrile-based polymer is dissolved in a solvent to prepare a spinning dope. After the spinning dope is spun from the nozzle, the undried fiber (hereinafter also referred to as gel-like acrylonitrile-based fiber) after being subjected to each step of coagulation, washing, and drawing is adjusted to a moisture content of 20 to 250% by weight, preferably 25 to 130% by weight, more preferably 30 to 100% by weight.

Here, when undried gelatinous acrylonitrile fibers are used as raw fibers to be hydrolyzed, carboxyl groups can be uniformly present throughout the fibers as described above. On the other hand, when hydrolysis treatment is applied to fibers that are densified by further heat-treating gel-like acrylonitrile fibers in an undried state or fibers that are further relaxed after densification are used as raw materials, the carboxyl groups are It can be a core-sheath structure localized in the surface layer.

When gel-like acrylonitrile-based fibers are used as raw fibers and the moisture content of the fibers is less than 20% by weight, the chemical agent does not penetrate into the inside of the fibers in the hydrolysis treatment described below, and carboxyl groups are generated throughout the fibers. may not be possible. If it exceeds 250% by weight, the fiber contains a large amount of water and the strength of the fiber becomes too low, which is not preferable because the spinnability is lowered. When more emphasis is placed on high fiber strength, it is desirable to make it within the range of 25 to 130% by weight. There are many methods for controlling the moisture content of gelled acrylonitrile fibers within the above range. 5 to 20 times, preferably about 7 to 15 times.

When the gel-like acrylonitrile-based fiber is further heat-treated, for example, by alternately performing dry heat treatment at 110°C and wet heat treatment at 60°C, voids inside the fiber disappear and densified fibers are formed. can get. Further, by performing an autoclave treatment at 120° C. for 10 minutes thereafter, a fiber having a somewhat relaxed fiber structure can be obtained. When these fibers are used as raw materials and subjected to a hydrolysis treatment, which will be described later, the reaction progresses from the surface layer of the fibers, facilitating the formation of a structure such as a core-sheath structure. As the reaction progresses, the degree of swelling with water tends to increase, and the resulting fiber may become difficult to handle.

Gel-like acrylonitrile-based fibers, or fibers that have undergone further heat treatment, are then subjected to a hydrolysis treatment. As a means for such hydrolysis treatment, there is a means of heat treatment in a state of impregnation or immersion in a basic aqueous solution of alkali metal hydroxide, alkali metal carbonate, ammonia or the like, or an aqueous solution of nitric acid, sulfuric acid, hydrochloric acid or the like. mentioned. 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. Impregnated with a treatment agent of up to 20% by weight, preferably 1.0 to 15% by weight, after squeezing, in a moist and hot atmosphere at a temperature of 100 to 140°C, preferably 110 to 135°C, for 10 to 60 minutes. It is preferable industrially and fiber properties to set within the range. The moist and hot atmosphere means an atmosphere filled with saturated steam or superheated steam. The treatment hydrolyzes the nitrile groups in the gel-like acrylonitrile-based fibers or the fibers that have been further subjected to the heat treatment to generate carboxyl groups.

The fibers subjected to the hydrolysis treatment as described above contain cations such as alkali metals and ammonium depending on the type of alkali metal hydroxide, alkali metal carbonate, ammonia, etc. used in the hydrolysis treatment. A salt-type carboxyl group to be used as a counterion is generated, but subsequently, if necessary, a treatment for converting the counterion of the carboxyl group may be performed. By performing an ion exchange treatment with an aqueous solution of a metal salt such as nitrate, sulfate or hydrochloride, a salt-type carboxyl group having a desired metal ion as a counter ion can be obtained. Furthermore, by adjusting the pH of the aqueous solution and the concentration and type of the metal salt, it is possible to mix different types of counterions and adjust their proportions.

The fibers subjected to the hydrolysis treatment as described above and the fibers further subjected to the ion exchange treatment are subsequently subjected to a drawing treatment, and shrinkability is imparted by this treatment. The draw ratio is usually set to 1.1 to 2.0 times. If the draw ratio is less than 1.1 times, the shrinkage may be low, and if it is more than 2.0 times, the physical properties of the fiber may deteriorate. Moreover, the stretching treatment is performed under heating, and the temperature is preferably lower than the temperature of the hydrolysis treatment described above. The heating means may be wet heat such as steam, or dry heat such as a dry heat roller.

The shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention is obtained in the manner described above, and each of the above-described treatments can be carried out continuously by using a normal continuous production facility for acrylic fibers. In addition, if necessary, additional treatments such as washing with water, drying, and cutting into specific fiber lengths may be performed. Although the case where an inorganic salt such as sodium rhodanate is used as a solvent has been described above, the above conditions are the same when an organic solvent is used. However, since the types of solvents are 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.

Further, in the production of the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention, a functional material may be added to the spinning dope. Examples of such functional materials include titanium oxide, carbon black, pigments, antibacterial agents, deodorants, hygroscopic agents, antistatic agents, and resin beads.

Here, in the shrinkable hygroscopic acrylonitrile fiber of the present invention obtained by the above-described production method, the undried gel-like acrylonitrile fiber is hydrolyzed, so that hydrolysis is not performed sequentially from the fiber surface, but the drug permeates deep inside the fiber and uniformly hydrolyzes the entire fiber. When viewed microscopically, acrylonitrile-based fibers generally have a mixture of crystalline portions in which the acrylonitrile-based polymer is oriented and amorphous portions in which the structure is disordered. Thus, it is believed that the crystalline portion is hydrolyzed from the outside while the amorphous portion is hydrolyzed entirely. As a result, after hydrolysis, microscopically, part of the crystalline portion remains as a portion with a high nitrile group concentration without being hydrolyzed, and the amorphous portion becomes a portion with a high carboxyl group concentration. it is conceivable that.

As described above, the structure of the shrinkable hygroscopic acrylonitrile fiber of the present invention obtained by the above-described production method is a structure in which a portion with a high carboxyl group concentration and a portion with a high nitrile group concentration are uniformly present throughout the fiber. guessed. And, because of such a structure, it is thought that deterioration of fiber physical properties during moisture absorption and water absorption is suppressed even without substantially having a crosslinked structure by covalent bond.

In addition, the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention is made from a fiber obtained by further heat-treating an undried gel-like acrylonitrile-based fiber, as described above, or a fiber that has been subjected to further relaxation treatment after densification. By adopting it as a fiber, even if it has a core-sheath structure, the carboxyl groups are uniformly present in the surface layer, and the core has a hard and elastic structure, so there is no need to obtain a cross-linked structure by covalent bonds. , Similarly, it is thought that there is little decrease in fiber physical properties.

In addition, since the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention has the structure described above, it retains the characteristics of ordinary acrylonitrile-based fibers and does not have a crosslinked structure due to covalent bonds. Stretching is possible even after hydrolysis, and it is thought that shrinkability can be imparted by this.

In addition, without using undried fibers such as gel-like acrylonitrile fibers in an undried state as described above, fibers densified by further heat treatment, and fibers further relaxed after densification, , When the acrylonitrile-based fiber after drying is subjected to hydrolysis treatment, the degree of densification due to drying has progressed, so the chemical hardly penetrates deep inside the fiber, and the surface layer of the fiber A more localized hydrolysis will occur at . The fiber obtained in this manner is not practical because the surface layer of the fiber is eluted into water.

The above-described shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention can be used alone or in combination with other materials as a useful fiber structure in many applications. In the fiber structure, the content of the shrinkable hygroscopic acrylonitrile fiber of the present invention is preferably 5% by weight or more, more preferably 10% by weight or more, and still more preferably 20% by weight or more. It is desirable from the viewpoint of obtaining the effect of the shrinkable, moisture-absorbing acrylonitrile-based fiber. Further, the types of other materials are not particularly limited, and commonly used natural fibers, organic fibers, semi-synthetic fibers, and synthetic fibers can be used, and inorganic fibers, glass fibers, etc. can also be used depending on the application. Specific examples include cotton, linen, silk, wool, nylon, rayon, polyester, and acrylic fibers.

Appearance forms of the fiber structure include threads, non-woven fabrics, paper-like materials, sheet-like materials, laminates, cotton-like bodies (including spherical and lumpy ones), and the like. The fiber of the present invention may be contained in the structure by mixing it with other materials and distributing it substantially uniformly. There are those that exist concentrated in a plurality of layers, and those that are distributed in each layer at a specific ratio.

The type of final product (for example, Carpet, towel, knit, yarn, pile, blanket, sheet, cushion material, etc.), and the contribution of the shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention to expressing such functions. It is determined as appropriate in consideration of the method of

EXAMPLES 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 by these. In the examples, parts and percentages are expressed by weight unless otherwise specified. Moreover, the measurement of each characteristic was implemented by the following method.

<Solubility in sodium thiocyanate aqueous solution>
About 1 g of the dried sample is precisely weighed (W1 [g]), 100 ml of 58% sodium thiocyanate aqueous solution is added, and the sample is immersed at 80° C. for 1 hour, filtered, washed with water, and dried. The sample after drying is accurately weighed (W2 [g]) and the solubility is calculated by the following formula.
Solubility [%] = (1-W2/W1) x 100
When the solubility is 95% or more, it is determined that the material does not substantially have a crosslinked structure due to covalent bonds.

<Measurement of carboxyl group content>
About 1 g of a sample is weighed, immersed in 50 ml of 1 mol/l hydrochloric acid for 30 minutes, washed with water, and immersed in pure water at a bath ratio of 1:500 for 15 minutes. After washing with water until the pH of the bath reaches 4 or more, it is dried at 105° C. for 5 hours with a hot air dryer. Approximately 0.2 g of the dried sample (W3 [g]) is weighed, 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. The sample is then filtered using a wire mesh and washed with water. Add 2 to 3 drops of phenolphthalein solution to the obtained filtrate (including the washing solution) and titrate with 0.1 mol/l hydrochloric acid according to a conventional method to determine the amount of hydrochloric acid consumed (V1 [ml]), The total amount of carboxyl groups is calculated by the following formula.
Total amount of carboxyl groups [mmol / g] = (0.1 × 15-0.1 × V1) / W3

<Measurement of saturated moisture absorption>
The sample is dried with a hot air dryer at 105° C. for 3 hours, and the weight is measured (W4 [g]). Next, the sample is placed in a constant temperature and humidity chamber adjusted to the conditions of 20° C. and 65% RH for 24 hours. The weight of the moisture-absorbed sample is measured. (W5 [g]). From the above measurement results, it is calculated by the following formula.
Saturated moisture absorption [%] = (W5-W4) / W4 x 100

<Water swelling degree>
After the sample is immersed in pure water, it is dehydrated for 5 minutes at 1200 rpm with a desktop centrifugal dehydrator. After the weight of the sample after dehydration is measured (W6 [g]), the sample is dried at 105°C for 5 hours, the weight is measured (W7 [g]), and the water swelling degree is calculated by the following equation.
Water swelling degree [times] = W6/W7-1

<Neutralization degree>
About 0.2 g of the sample dried at 105° C. for 3 hours in a hot air dryer was precisely weighed (W8 [g]), and 100 ml of water, 15 ml of 0.1 mol/l sodium hydroxide, and 0.4 g of sodium chloride were added thereto. Add and stir. The sample is then filtered using a wire mesh and washed with water. Add 2 to 3 drops of phenolphthalein solution to the obtained filtrate (including washings) and titrate with 0.1 mol/l hydrochloric acid according to a conventional method to determine the amount of hydrochloric acid consumed (V2 [ml]). The amount of H-type carboxyl groups contained in the sample is calculated by the following formula, and the degree of neutralization is determined from the result and the total amount of carboxyl groups described above.
H-type carboxyl group amount [mmol / g] = (0.1 × 15-0.1 × V2) / W8
Neutralization degree [%] = [(total carboxyl group amount - H-type carboxyl group amount) / total carboxyl group amount] × 100

<Boiling water shrinkage>
The sample fiber is allowed to stand in an atmosphere of 20° C. and 65% RH for 24 hours to condition the humidity, and the fiber length (L1) is measured. Next, the sample fiber is shrunk in boiling water for 30 minutes, the fiber length (L2) after shrinkage is measured, and the boiling water shrinkage ratio is calculated according to the following formula.
Boiling water shrinkage (%) = (L1-L2) / L1 x 100

<Distribution of carboxyl groups in fiber structure>
The fiber sample is subjected to ion exchange treatment by immersing it in an aqueous solution containing twice the amount of carboxyl groups contained in the fiber, in which magnesium nitrate is dissolved at 50°C for 1 hour, followed by washing with water and drying to remove carboxyl groups. Let the counterion be magnesium. A magnesium salt-type fiber sample is measured by an energy dispersive X-ray spectrometer (EDS) at 10 measurement points at approximately equal intervals from the outer edge to the center of the fiber cross section, and the content of magnesium element at each measurement point is measured. do. A coefficient of variation CV [%] is calculated from the obtained numerical value of each measurement point by the following equation.
Variation coefficient CV [%] = (standard deviation / average value) × 100

<Proportion of the area occupied by the surface layer in the cross section of the fiber with the core-sheath structure>
The sample fiber is immersed in a dyeing bath containing 2.5% cationic dye (Nichilon Black G 200) and 2% acetic acid based on the fiber weight so that the bath ratio is 1:80, and boiled for 30 minutes. After that, it is washed with water, dehydrated and dried. The obtained dyed fiber is thinly sliced perpendicular to the fiber axis, and the cross section of the fiber is observed with an optical microscope. At this time, the central portion made of the acrylonitrile-based polymer is dyed black, and the surface layer portion having many carboxyl groups is green because the dye is not sufficiently fixed. Measure the fiber diameter (D1) in the fiber cross section and the diameter (D2) of the central part dyed black bordering on the part where the color starts to change from green to black, and calculate the surface layer area ratio by the following formula. do. The average value of the surface layer area ratios of 10 samples is taken as the surface layer area ratio of the sample fiber.
Surface layer area ratio (%) = [{((D1)/2) ² π-((D2)/2) ² π}/((D1)/2) ² π] × 100

<Measurement of moisture content of undried fibers after drawing>
After the stretched undried fiber is immersed in pure water, it is dehydrated for 2 minutes with a centrifugal dehydrator (TYPE H-770A manufactured by Kokusan Centrifugal Co., Ltd.) at a centrifugal acceleration of 1100 G (G indicates gravitational acceleration). . After the weight after dehydration is measured (W9 [g]), the undried fibers are dried at 120°C for 15 minutes, the weight is measured (W10 [g]), and the weight is calculated by the following formula.
Moisture content (%) of undried fiber after stretching = (W9-W10)/W9 x 100

<Example 1>
A spinning dope prepared by dissolving 10 parts of an acrylonitrile-based polymer consisting of 90% acrylonitrile and 10% methyl acrylate in 90 parts of a 48% sodium thiocyanate aqueous solution is spun in a coagulation bath at -2.5°C, coagulated, washed with water, A gel-like acrylonitrile-based fiber having a moisture content of 35% was obtained by stretching 12 times. The fiber is immersed in a 2.0% sodium hydroxide aqueous solution, squeezed so that the liquid absorption amount to the fiber weight is 100%, and then hydrolyzed in a moist and hot atmosphere at 123 ° C. for 25 minutes, After washing with water and drying, it was stretched 1.5 times with steam at 105° C. in a moist heat state to obtain a shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention. Table 1 shows the evaluation results of the obtained fibers.

<Examples 2 to 9>
A shrinkable hygroscopic acrylonitrile fiber of the present invention was obtained in the same manner as in Example 1, except that the experiment was performed with the concentration of the aqueous sodium hydroxide solution and the draw ratio shown in Table 1. Table 1 shows the evaluation results of the obtained fibers.

<Example 10>
After the hydrolysis treatment, the shrinkable hygroscopic acrylonitrile fiber of the present invention was obtained in the same manner as in Example 7, except that treatment with a 6% nitric acid aqueous solution was added at room temperature for 30 minutes. Table 1 shows the evaluation results of the obtained fibers.

<Example 11>
In Example 4, instead of the gel-like acrylonitrile-based fiber, the fiber was alternately subjected to dry heat treatment at 110 ° C. for 2.5 minutes and wet heat treatment at 60 ° C. for 2.5 minutes. A shrinkable, moisture-absorbing acrylonitrile-based fiber of the present invention was obtained in the same manner, except that the densified fiber was used. Table 1 shows the evaluation results of the obtained fibers.

<Example 12>
In Example 11, instead of the densified fiber, the contractile property of the present invention was tested in the same manner, except that the fiber was further relaxed by autoclaving at 120 ° C. for 10 minutes. A hygroscopic acrylonitrile fiber was obtained. Table 1 shows the evaluation results of the obtained fibers.

<Comparative Example 1>
Moisture-absorbing acrylonitrile-based fibers having no shrinkage were obtained in the same manner as in Example 3, except that the stretching treatment after hydrolysis was omitted. Table 1 shows the evaluation results of the obtained fibers.

As shown in Table 1, the shrinkable hygroscopic acrylonitrile fibers of Examples 1 to 12 contain 0.2 to 4.5 mmol/g of carboxyl groups and have a saturated moisture absorption of 3 at 20°C x 65% RH. % by weight or more, a boiling water shrinkage rate of 5% to 50%, and a water swelling degree of 10 times or less.

Claims (8)

A hygroscopic acrylonitrile-based fiber composed of a polymer that does not substantially have a crosslinked structure by covalent bonds, the fiber contains 0.2 to 2.0 mmol/g of carboxyl groups, and is heated at 20°C. A shrinkable hygroscopic acrylonitrile characterized by having a saturated moisture absorption rate of 3 to 15.6 % by weight at ×65% RH, a boiling water shrinkage rate of 5 to 50%, and a water swelling degree of 10 times or less. system fiber. 2. The shrinkable hygroscopic acrylonitrile fiber according to claim 1, wherein the carboxyl groups are uniformly present throughout the fiber. 2. The shrinkable, hygroscopic acrylonitrile fiber according to claim 1, wherein the carboxyl groups are localized on the surface layer of the fiber. The shrinkable, moisture-absorbing acrylonitrile fiber according to any one of claims 1 to 3, wherein the degree of neutralization of carboxyl groups is 25% or more. After spinning a spinning stock solution containing an acrylonitrile-based polymer from a nozzle, the undried fibers obtained through the steps of coagulation, water washing and drawing are hydrolyzed and then drawn. 3. The method for producing the shrinkable, hygroscopic acrylonitrile-based fiber according to . After spinning a spinning stock solution containing an acrylonitrile-based polymer from a nozzle, the undried fiber obtained through each step of coagulation, washing with water, and drawing is heat-treated to densify the fiber or further relaxed after densification. 4. A method for producing a shrinkable, hygroscopic acrylonitrile-based fiber according to claim 3, comprising stretching the fiber after hydrolyzing it. 7. The method for producing shrinkable hygroscopic acrylonitrile fibers according to claim 5 or 6, wherein the undried fibers have a moisture content of 20 to 250% by weight. A fiber structure containing the shrinkable, hygroscopic acrylonitrile-based fiber according to any one of claims 1 to 4.