JP2019143284A - Shrinkable moisture absorption acrylonitrile-based fiber, manufacturing method of the fiber and fiber structure containing the fiber - Google Patents

Abstract

To provide a shrinkable moisture absorption acrylonitrile-based fiber capable of being produced with simple processes, for overcoming situation that shrinkable acrylic fiber is known conventionally, but it has no moisture absorption property and a problem in comfortableness, a crosslinked acrylate-based fiber has no shrinkability and low productivity even though it is excellent in moisture absorption property, and further enhancing moisture absorption property of an acrylic fiber containing acrylic acid as a copolymer component is difficult.SOLUTION: There is provided a shrinkable moisture absorption acrylonitrile-based fiber constituted by a polymer having practically no crosslinking structure by a covalent bond, containing 0.2 to 4.5 mmol/g of carboxyl group in the fiber, having saturation moisture absorption rate at 20°C×65% RH of 3 wt.% or more, boiling water shrinkage rate of 5 to 50%, and water swelling degree of 10 times or less.SELECTED DRAWING: None

Description

The present invention relates to a shrinkable hygroscopic acrylonitrile fiber, a method for producing the fiber, and a fiber structure containing the fiber.

Shrinkable acrylic fiber is a fiber that develops shrinkage when heated, and bulky yarns and sliver knits use its shrinkage to develop bulkiness, but it has poor hygroscopicity and is prone to static electricity. Or it was necessary to improve in terms of comfort, such as being easily stuffy.

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

However, since the fiber has crosslinks, it is difficult to impart shrinkage. In addition, in the production of the fiber, a step of introducing a crosslinked structure with hydrazine and a hydrolysis step for introducing a carboxyl group are necessary, and after each step, residues of the chemical used in the reaction are removed. The process to do is necessary. In addition, each of these processes requires a high temperature and a long time. For this reason, it is difficult to produce the fibers by continuous processing, and batch processing with low productivity has been performed. Therefore, the conventional crosslinked acrylate fiber has low productivity and its production cost remains high.

Further, in terms of acrylic fibers having a carboxyl group, acrylic fibers made of an acrylonitrile-based polymer having a monomer having a carboxyl group such as acrylic acid as a copolymerization component are known. However, if acrylic acid is copolymerized in a large amount, spinning becomes difficult, and it has been difficult to achieve high hygroscopicity. In addition, since it does not have a cross-linked structure, it has been a problem when it is used for apparel applications such as elution under alkaline conditions such as alkaline soaping in dyeing.

JP-A-5-132858

As described above, conventionally, shrinkable acrylic fibers are known, but they are not hygroscopic and have a problem in comfort. Moreover, although the crosslinked acrylate fiber is excellent in hygroscopicity, it has poor shrinkage, has many production steps, and has low productivity. Furthermore, it has been difficult to increase the hygroscopicity of acrylic fibers containing acrylic acid as a copolymer component. The present invention has been made in view of the current state of the prior art, and the object thereof is to provide a hygroscopic acrylonitrile fiber having shrinkage, which can be continuously produced by a simpler process than before. There is.

As a result of diligent investigations to achieve the above-mentioned object, the present inventor obtained a spinning stock solution in which an acrylonitrile-based polymer was dissolved from a nozzle, and was obtained through the steps of coagulation, water washing and stretching. By hydrolyzing the dried fiber and further performing a stretching treatment, it was found that a moisture-absorbing acrylonitrile-based fiber having shrinkage while retaining practical fiber properties can be obtained without having a crosslinked structure. The invention has been completed.

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, containing 0.2 to 4.5 mmol / g carboxyl group in the fiber, A shrinkable hygroscopic acrylonitrile system characterized by having a saturated moisture absorption at 20 ° C. × 65% RH of 3% by weight or more, a boiling water shrinkage of 5 to 50%, and a water swelling degree of 10 times or less. fiber.
(2) The shrinkable moisture-absorbing acrylonitrile fiber according to (1), wherein the carboxyl group is uniformly present throughout the fiber.
(3) The shrinkable moisture-absorbing acrylonitrile system according to (1), which has a core-sheath structure composed of a surface layer part made of a polymer containing a carboxyl group and a central part made of an acrylonitrile polymer. fiber.
(4) The shrinkable hygroscopic acrylonitrile fiber according to any one of (1) to (3), wherein the neutralization degree of the carboxyl group is 25% or more.
(5) A spinning stock solution containing an acrylonitrile-based polymer is spun from a nozzle, and is then stretched after hydrolyzing undried fibers obtained through the respective steps of coagulation, washing with water and stretching (2) The manufacturing method of the shrinkable hygroscopic acrylonitrile fiber as described in 1 above.
(6) After spinning a spinning stock solution containing an acrylonitrile-based polymer from a nozzle, the undried fibers obtained through the respective steps of coagulation, washing with water and stretching are heat-treated, or after densification The method for producing a shrinkable hygroscopic acrylonitrile fiber according to (3), comprising hydrolyzing the relaxed fiber.
(7) The method for producing shrinkable hygroscopic acrylonitrile fiber according to (5) or (6), wherein the moisture content of the undried fiber is 20 to 250% by weight.
(8) A fiber structure containing the shrinkable hygroscopic acrylonitrile fiber according to any one of (1) to (4).

Since the shrinkable hygroscopic acrylonitrile fiber of the present invention has substantially no covalently crosslinked structure, it can exhibit practical shrinkage. In addition, since the shrinkable hygroscopic acrylonitrile fiber of the present invention does not require a cross-linking introduction process in production, the production process can be greatly reduced. As a result, continuous continuous production using a normal acrylic fiber production facility is possible. It is possible and productive. Since the shrinkable hygroscopic acrylonitrile fiber of the present invention has both shrinkability and hygroscopicity, it can be used for carpets, towels, knits, wool yarns, piles, blankets, sheets, cushion materials and the like.

Unlike the conventional crosslinked acrylate fiber, the shrinkable hygroscopic acrylonitrile fiber of the present invention is characterized by substantially not having a covalently crosslinked structure. This eliminates the need for a cross-linking introduction step, and as a result, the number of manufacturing steps can be greatly reduced, and production can be performed with a simpler process than in the past. Accordingly, continuous production is possible without being limited to batch processing such as production of conventional crosslinked acrylate fibers. In addition, since it does not substantially have a cross-linked structure due to a covalent bond, practical shrinkage can be expressed. In the present invention, “substantially has no cross-linked structure due to a covalent bond” means that a <solubility in an aqueous sodium thiocyanate solution> described later is 95% or more.

The shrinkable hygroscopic acrylonitrile fiber of the present invention contains a carboxyl group, and the content thereof is 0.2 to 4.5 mmol / g in a value determined by the method described later, preferably 0. 0.5 to 4.0 mmol / g, more preferably 0.5 to 3.5 mmol / g, and still more preferably 0.8 to 2.0 mmol / g. Moreover, when the shrinkable hygroscopic 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. When the amount of carboxyl groups is less than the lower limit of the above range, the moisture absorption performance described later may not be obtained. When the amount exceeds the upper limit, the hydrophilicity of the fiber becomes too high, and the degree of water swelling described later is increased. Beyond that, it swells and dissolves violently in water, making it difficult to handle.

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

The shrinkable hygroscopic acrylonitrile fiber of the present invention has a boiling water shrinkage of 5% to 50%, preferably 8% to 45%, more preferably 12% to 40%. When the boiling water shrinkage rate is less than 5%, it is difficult to provide significant shrinkage performance even when applied to various fiber structures. Further, when the boiling water shrinkage rate exceeds 50%, it is difficult to maintain practical fiber properties.

It is desirable that the shrinkable hygroscopic acrylonitrile fiber of the present invention has a water swelling degree of 10 times or less, preferably 8 times or less, more preferably 5 times or less, which is obtained by the method described later. The shrinkable hygroscopic acrylonitrile fiber of the present invention may not substantially have a covalently crosslinked structure as described above, and when the water swelling degree exceeds 10 times, the fiber becomes brittle. Drops off or dissolves in some cases, making handling difficult. The lower limit is not particularly limited, but at least 0.03 times or more from the viewpoint that the shrinkable hygroscopic acrylonitrile fiber of the present invention has a saturated moisture absorption rate of 3% by weight or more at 20 ° C. and a relative humidity of 65%. In normal cases, it seems to be 0.3 times or more.

Moreover, in the shrinkable hygroscopic acrylonitrile fiber of the present invention, it is more desirable that the carboxyl group exists uniformly throughout the fiber. Here, being 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 measurement method described later is 50% or less. When the carboxyl group is localized, the portion is easily embrittled by moisture absorption and water absorption. The presence of the carboxyl group throughout the fiber suppresses embrittlement even if it absorbs moisture or absorbs water, and makes it easy to obtain fiber properties that can withstand practical use without having a crosslinked structure. From this point, the CV value is preferably 30% or less, more preferably 20% or less, and still more preferably 15% or less.

However, the shrinkable hygroscopic acrylonitrile fiber of the present invention can adopt a core-sheath structure in which carboxyl groups are present substantially uniformly only on the fiber surface depending on the required physical properties and applications. In this case, the core-sheath structure is composed of a surface layer portion made of a polymer containing a carboxyl group and a central portion made of an acrylonitrile-based polymer. By having a core-sheath structure consisting of the central part and the surface layer surrounding the central part in this way, the moisture absorption rate is obtained at the surface layer part with a high carboxyl group concentration while obtaining practical fiber properties that are hard and elastic at the central part. Can be significantly increased.

The area occupied by the surface layer portion in the cross section of the fiber having the core-sheath structure is preferably 20 to 80%, and more preferably 30 to 70%. If the area occupied by the surface layer is small, there is a possibility that functions such as hygroscopicity cannot be sufficiently exhibited. If the area occupied by the surface layer is large, the central part may become thin and practical fiber physical properties may not be obtained. .

As the state of the carboxyl group, the counter ion is preferably a cation other than H when higher moisture absorption performance is desired. More specifically, it is desirable that the ratio in which the counter ion is a cation other than H, that is, the degree of neutralization is preferably 25% or more, more preferably 35% or more, and still 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, NH ₄ , Examples include cations such as amines, and a plurality of types of cations may be mixed. Of these, Li, Na, K, Mg, Ca, Zn and the like are preferable.

Further, in the above case, excellent deodorizing performance against acid gases such as acetic acid and isovaleric acid, and aldehydes such as formaldehyde can be exhibited. Moreover, if it is Mg or Ca ion, a flame retardance performance is high, and if it is Ag or Cu ion, a high effect can be acquired regarding antibacterial performance.

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

As a method for producing the shrinkable hygroscopic acrylonitrile fiber of the present invention described above, a spinning stock solution in which an acrylonitrile polymer is dissolved is spun from a nozzle, and is obtained in an undried state obtained through steps of coagulation, water washing and stretching. The method of obtaining the fiber of this by hydrolyzing and extending | stretching can be mentioned. Below, this manufacturing method is explained in full detail.

First, the acrylonitrile-based polymer as a raw material contains acrylonitrile as a polymerization composition, preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 85% by weight or more. Therefore, as the acrylonitrile-based polymer, a copolymer of acrylonitrile and another monomer can be employed in addition to the acrylonitrile homopolymer. Other monomers in the copolymer are not particularly limited, but vinyl halides and vinylidene halides; (meth) acrylic acid esters; sulfonic acid group-containing monomers such as methallyl sulfonic acid and p-styrene sulfonic acid, and the like Salt, acrylamide, styrene, vinyl acetate and the like can be mentioned. The notation (meta) represents both those with and without the meta word.

Next, using such an acrylonitrile-based polymer, fiber formation is performed by wet spinning, and the case where an inorganic salt such as sodium rhodanate is used as a solvent will be described as follows. First, the above acrylonitrile-based polymer is dissolved in a solvent to prepare a spinning dope. The spinning solution is spun from a nozzle and then subjected to coagulation, water washing, and stretching processes, and the moisture content of the undried fiber after stretching (hereinafter also referred to as gel-like acrylonitrile fiber) is 20 to 250% by weight, preferably 25 to 130% by weight, more preferably 30 to 100% by weight.

Here, when an undried gel acrylonitrile fiber is used as the raw fiber to be subjected to the hydrolysis treatment, the carboxyl groups can be uniformly present throughout the fiber as described above. On the other hand, when hydrolyzed fiber that has been densified by further heat-treating gel-like acrylonitrile fiber in an undried state, or fiber that has been further densified after densification, the carboxyl group is a fiber. It can be set as the core-sheath structure localized in the surface layer part.

When gel-like acrylonitrile fiber is used as the raw fiber, when the moisture content of the fiber is less than 20% by weight, the chemical does not penetrate into the fiber in the hydrolysis treatment described later, and carboxyl groups are generated throughout the fiber. May not be possible. If it exceeds 250% by weight, the fiber contains a large amount of moisture, and the fiber strength becomes too low. When the fiber strength is more important, it is desirable that the fiber strength is within the range of 25 to 130% by weight. There are many methods for controlling the moisture content of the gel-like acrylonitrile fiber within the above range. For example, the coagulation bath temperature is −3 ° C. to 15 ° C., preferably −3 ° C. to 10 ° C., and the draw ratio is About 5 to 20, preferably about 7 to 15 times is desirable.

Further, when the gel-like acrylonitrile fiber is further heat-treated, for example, by alternately performing a dry heat treatment at 110 ° C. and a wet heat treatment at 60 ° C., the void inside the fiber disappears and the dense fiber is obtained. can get. Further, by performing an autoclave treatment at 120 ° C. for 10 minutes thereafter, fibers with a somewhat relaxed fiber structure can be obtained. When these fibers are used as raw materials and a hydrolysis treatment described later is performed, the reaction proceeds from the fiber surface layer portion, and a structure such as a core-sheath structure is easily obtained. As the reaction proceeds, the degree of water swelling tends to increase, and handling of the resulting fiber may be difficult.

The gel-like acrylonitrile fiber or the fiber that has been further heat-treated is then subjected to a hydrolysis treatment. As a means for such hydrolysis treatment, there is a means for heat treatment in a state of impregnation or immersion in a basic aqueous solution such as alkali metal hydroxide, alkali metal carbonate or ammonia, or an aqueous solution such as nitric acid, sulfuric acid or hydrochloric acid. Can be mentioned. Specific treatment conditions may be set as appropriate in consideration of the above-described range of carboxyl group amount and the like, and various conditions such as the concentration of the treatment agent, reaction temperature, and reaction time may be set as appropriate. After impregnating and squeezing up to 20% by weight, preferably 1.0 to 15% by weight of a treatment agent, under conditions of treatment at a temperature of 100 to 140 ° C., preferably 110 to 135 ° C. for 10 to 60 minutes in a moist heat atmosphere. It is preferable in terms of industrial and fiber properties to set within the range. The wet heat atmosphere refers to an atmosphere filled with saturated steam or superheated steam. By this treatment, the nitrile group in the gel-like acrylonitrile fiber or the fiber subjected to further heat treatment is hydrolyzed to generate a carboxyl group.

In the fiber subjected to the hydrolysis treatment as described above, a cation such as alkali metal or ammonium corresponding to the type of alkali metal hydroxide, alkali metal carbonate, ammonia or the like used in the hydrolysis treatment is contained. Although the salt-type carboxyl group used as a counter ion has been generated, a treatment for converting the counter ion of the carboxyl group may be performed as necessary. When ion exchange treatment is performed with an aqueous metal salt solution 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 counter ions and to adjust the ratio thereof.

The fiber subjected to the hydrolysis treatment as described above and the fiber further subjected to the ion exchange treatment are subsequently subjected to a stretching treatment, and the shrinkage is imparted by this treatment. The draw ratio is usually set to 1.1 to 2.0 times. If the draw ratio is lower than 1.1 times, the shrinkage may be lowered. Conversely, if the draw ratio is higher than 2.0 times, the fiber properties may be deteriorated. Moreover, although this extending | stretching process is performed under a heating, it is preferable that the temperature is lower than the temperature of the above-mentioned hydrolysis process. The heating means may be wet heat such as steam or dry heat such as a dry heat roller.

As described above, the shrinkable hygroscopic acrylonitrile fiber of the present invention can be obtained. However, each of the above-mentioned treatments can be carried out continuously by diverting a normal acrylic fiber continuous production facility. Moreover, you may add processes, such as washing with water, drying, and cut | disconnecting to specific fiber length as needed. As described above, the case where an inorganic salt such as sodium rhodanate is used as a solvent has been described, but the above conditions are the same even when an organic solvent is used. However, since the types of solvents are different, the coagulation bath temperature is controlled by selecting a temperature suitable for the solvent and controlling the moisture content of the gel-like acrylonitrile fiber within the above range.

In the production of the shrinkable hygroscopic acrylonitrile 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 gel-like acrylonitrile fiber in an undried state is hydrolyzed, so that the chemical is not sequentially hydrolyzed from the fiber surface. Is considered to penetrate into the inner part of the fiber and hydrolyze uniformly throughout the fiber. Further, when viewed microscopically, generally, an acrylonitrile-based fiber is mixed with a crystalline portion where an acrylonitrile-based polymer is oriented and an amorphous portion where the structure is disordered. For this reason, the crystal part is hydrolyzed from the outside, but the amorphous part is considered to be hydrolyzed as a whole. As a result, after the hydrolysis, microscopically, a part of the crystalline part remains as a part with a high nitrile group concentration without being hydrolyzed, and an amorphous part becomes a part with a high carboxyl group concentration. it is conceivable that.

From the above, the structure of the shrinkable hygroscopic acrylonitrile fiber of the present invention obtained by the above-described production method has a structure in which a portion having a high carboxyl group concentration and a portion having a high nitrile group concentration are present uniformly throughout the fiber. Guessed. And since it is such a structure, even if it does not have a crosslinked structure by a covalent bond substantially, it is thought that the fall of the fiber physical property at the time of moisture absorption and water absorption is suppressed.

In addition, as described above, the shrinkable hygroscopic acrylonitrile fiber of the present invention is a fiber obtained by further densifying the gel-like acrylonitrile fiber in an undried state as described above, or a fiber further relaxed after densification. By adopting as a fiber, even when taking a core-sheath structure, the carboxyl group is uniformly present in the surface layer part, and the central part is a hard and elastic structure, so it is possible to obtain a crosslinked structure by covalent bond Similarly, it is considered that there is little decrease in fiber properties.

In the shrinkable hygroscopic acrylonitrile fiber of the present invention, since it has the structure as described above, the characteristics of ordinary acrylonitrile fiber remain, and further, since it does not have a cross-linked structure due to covalent bond, etc. It is considered that the film can be stretched even after hydrolysis, and that shrinkage can be imparted.

Without using undried fibers such as gel acrylonitrile fibers in the undried state as described above, fibers densified by further heat treatment of the fibers, and fibers further relaxed after densification When the acrylonitrile fiber after drying is hydrolyzed, the degree of densification has further progressed due to drying, so that the drug hardly penetrates into the inner part of the fiber, and the fiber surface layer part. In this case, more local hydrolysis is performed. The fibers obtained in this manner are eluted from the fiber surface layer portion into water, etc., and cannot be practically used.

The shrinkable hygroscopic acrylonitrile fiber of the present invention described above can be used as a fiber structure useful in many applications, either alone or in combination with other materials. 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 further preferably 20% by weight or more. It is desirable from the viewpoint of obtaining the effect of the shrinkable hygroscopic acrylonitrile fiber. Moreover, there is no restriction | limiting in particular as a kind of other raw material, The natural fiber, organic fiber, semi-synthetic fiber, synthetic fiber currently used are used, Furthermore, inorganic fiber, glass fiber, etc. can be employ | adopted depending on a use. Specific examples include cotton, hemp, silk, wool, nylon, rayon, polyester, acrylic fiber, and the like.

Appearance forms of the fiber structure include yarns, non-woven fabrics, paper-like materials, sheet-like materials, laminates, and cotton-like materials (including spherical and massive materials). As the form of inclusion of the fiber of the present invention in the structure, in the case of a structure having a plurality of layers distributed substantially uniformly by mixing with other materials, any layer (single or even A plurality of them may be present in a concentrated manner, and others may be distributed at a specific ratio in each layer.

The appearance form and content of the fiber structure exemplified above, other materials constituting the fiber structure, and other members combined with the fiber structure are determined depending on the type of the final product (for example, Contribution of the shrinkable moisture-absorbing acrylonitrile fiber of the present invention to the functions, characteristics, and shapes required for carpets, towels, knits, yarns, piles, blankets, sheets, cushion materials, etc. It is decided as appropriate in consideration of the manner of

Examples are shown below for facilitating the understanding of the present invention. However, these are merely examples, and the gist of the present invention is not limited thereto. In the examples, parts and percentages are shown on a weight basis unless otherwise specified. Each characteristic was measured by the following method.

<Solubility in aqueous sodium thiocyanate>
About 1 g of the dried sample is precisely weighed (W1 [g]), 100 ml of 58% aqueous sodium thiocyanate solution is added, soaked at 80 ° C. for 1 hour, filtered, washed with water, and dried. The dried sample is precisely weighed (W2 [g]), and the solubility is calculated by the following equation.
Solubility [%] = (1-W2 / W1) × 100
When the solubility is 95% or more, it is determined that the crosslinked structure due to the covalent bond is substantially absent.

<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 bath pH becomes 4 or more, it is dried at 105 ° C. for 5 hours in a hot air dryer. About 0.2 g of the dried sample is precisely weighed (W3 [g]), and 100 ml of water, 15 mol of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride are added and stirred. Next, the sample is scraped using a wire mesh and washed with water. Add 2 to 3 drops of phenolphthalein solution to the obtained filtrate (including washing water), 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 carboxyl group amount [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 thermo-hygrostat adjusted to 20 ° C. × 65% RH for 24 hours. The weight of the sample thus absorbed is measured. (W5 [g]). From the above measurement results, calculation is performed according to the following equation.
Saturated moisture absorption [%] = (W5−W4) / W4 × 100

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

<Degree of neutralization>
About 0.2 g of a sample dried for 3 hours at 105 ° C. with a hot air dryer (W8 [g]) was weighed, and 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride were added thereto. In addition, stir. Next, the sample is scraped using a wire mesh and washed with water. Add 2-3 drops of phenolphthalein solution to the obtained filtrate (including washing solution) and titrate with 0.1 mol / l hydrochloric acid according to a conventional method to determine the amount of consumed hydrochloric acid (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 obtained 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
Degree of neutralization [%] = [(total carboxyl group amount−H type carboxyl group amount) / total carboxyl group amount] × 100

<Boiling water shrinkage>
The sample fiber is conditioned for 24 hours in an atmosphere of 20 ° C. × 65% RH, and the fiber length (L1) is measured. Next, the sample fiber is contracted in boiling water for 30 minutes, the fiber length (L2) after contraction is measured, and the boiling water contraction rate is calculated according to the following equation.
Boiling water shrinkage (%) = (L1-L2) / L1 × 100

<Distribution state of carboxyl group in fiber structure>
A fiber sample is subjected to an ion exchange treatment by immersing it in an aqueous solution in which magnesium nitrate corresponding to twice the amount of carboxyl groups contained in the fiber is dissolved, and washed with water and dried to obtain carboxyl groups. The counter ion of is magnesium. A magnesium salt type fiber sample is selected from 10 points at roughly equal intervals from the outer edge to the center of the fiber cross section using an energy dispersive X-ray spectrometer (EDS), and the magnesium element content at each measurement point is measured. To do. A coefficient of variation CV [%] is calculated from the obtained numerical value of each measurement point according to the following equation.
Coefficient of variation CV [%] = (standard deviation / average value) × 100

<Ratio of the area which the surface layer part accounts in the cross section of the fiber of a core sheath structure>
The sample fiber was immersed in a dyeing bath containing 2.5% cationic dye (Nicilon Black G 200) and 2% acetic acid with respect to the fiber weight so as to have a bath ratio of 1:80 and boiled for 30 minutes. After washing, dewatering and drying. The obtained dyed fiber is sliced thinly perpendicular to the fiber axis, and the fiber cross section 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 becomes green because the dye is not sufficiently fixed. In the fiber cross section, the fiber diameter (D1) and the diameter (D2) of the center dyed black with the part starting to change from green to black as the boundary are measured, and the surface layer area ratio is calculated by the following formula To do. In addition, let the average value of the surface layer part area ratio of 10 samples be the surface layer part area ratio of a sample fiber.
Surface portion area ratio (%) = [{(( D1) / 2) 2 π - ((D2) / 2) 2 π} / ((D1) / 2) 2 π] × 100

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

<Example 1>
A spinning stock solution prepared by dissolving 10 parts of an acrylonitrile-based polymer composed of 90% acrylonitrile and 10% methyl acrylate in 90 parts of a 48% aqueous sodium thiocyanate solution was spun into a -2.5 ° C. coagulation bath, coagulated, washed with water, The gel-like acrylonitrile fiber having a water content of 35% was obtained by stretching 12 times. After immersing the fiber in a 2.0% aqueous sodium hydroxide solution and squeezing so that the liquid absorption with respect to the fiber weight is 100%, a hydrolysis treatment is performed in a humid heat atmosphere at 123 ° C. for 25 minutes, After being washed with water and dried, the shrinkable hygroscopic acrylonitrile fiber of the present invention was obtained by stretching 1.5 times with steam at 105 ° C. in a wet heat state. The evaluation results of the obtained fiber are shown in Table 1.

<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 conducted with the concentration and draw ratio of the sodium hydroxide aqueous solution shown in Table 1. The evaluation results of the obtained fiber are shown in Table 1.

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

<Example 11>
In Example 4, instead of the gel-like acrylonitrile fiber, the fiber was obtained by alternately performing dry heat treatment at 110 ° C. for 2.5 minutes and wet heat treatment at 60 ° C. for 2.5 minutes twice. The shrinkable hygroscopic acrylonitrile fiber of the present invention was obtained in the same manner except that the densified fiber was used. The evaluation results of the obtained fiber are shown in Table 1.

<Example 12>
In Example 11, in place of the densified fiber, the contraction property of the present invention was similarly obtained except that the fiber was further relaxed by performing an autoclave treatment at 120 ° C. for 10 minutes. A hygroscopic acrylonitrile fiber was obtained. The evaluation results of the obtained fiber are shown in Table 1.

<Comparative Example 1>
A hygroscopic acrylonitrile fiber having no shrinkability was obtained in the same manner as in Example 3 except that the stretching treatment after hydrolysis was omitted. The evaluation results of the obtained fiber are shown in Table 1.

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 the saturated hygroscopic rate at 20 ° C. × 65% RH is 3 It has the characteristics that it is not less than wt%, the boiling water shrinkage is 5% to 50%, and the water swelling degree is 10 times or less.

Claims (8)

A hygroscopic acrylonitrile-based fiber composed of a polymer having substantially no covalently crosslinked structure, containing 0.2 to 4.5 mmol / g carboxyl group in the fiber, A shrinkable hygroscopic acrylonitrile-based fiber having a saturated moisture absorption rate of 3% by weight or more at 65% RH, a boiling water shrinkage of 5 to 50%, and a water swelling degree of 10 times or less. 2. The shrinkable hygroscopic acrylonitrile fiber according to claim 1, wherein carboxyl groups are uniformly present throughout the fiber. The shrinkable hygroscopic acrylonitrile fiber according to claim 1, which has a core-sheath structure composed of a surface layer portion made of a polymer containing a carboxyl group and a central portion made of an acrylonitrile polymer. The shrinkable hygroscopic acrylonitrile fiber according to any one of claims 1 to 3, wherein the neutralization degree of the carboxyl group is 25% or more. 3. The spinning solution containing an acrylonitrile polymer is spun from a nozzle, and then dried after hydrolyzing undried fibers obtained through the respective steps of coagulation, washing with water and stretching. A method for producing shrinkable hygroscopic acrylonitrile fiber. Spinning stock solution containing acrylonitrile-based polymer is spun from the nozzle, then the dried fiber obtained through the coagulation, water washing and stretching steps is heat-treated to be densified fibers or densified and further relaxed. The method for producing shrinkable hygroscopic acrylonitrile fiber according to claim 3, comprising hydrolyzing the fiber. The method for producing shrinkable hygroscopic acrylonitrile fiber according to claim 5 or 6, wherein the moisture content of the undried fiber is 20 to 250% by weight. The fiber structure containing the shrinkable hygroscopic acrylonitrile-type fiber in any one of Claims 1-4.