JP7177982B2 - Hygroscopic acrylonitrile fiber, method for producing said fiber, and fiber structure containing said fiber - Google Patents

Description

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

Due to the recent heightened awareness of comfort, there is a demand for the development of materials having hygroscopic functions, and developments are also being actively carried out in the field of textiles. For example, crosslinked acrylate fibers obtained by chemically modifying acrylic fibers are known (Patent Document 1). The fiber contains a crosslinked structure and a carboxyl group, and has excellent hygroscopic performance and hygroscopic heat generation performance. However, crosslinked acrylate fibers have the following problems (i) and (ii).

(i) First, the crosslinked acrylate-based fiber exhibits a light pink to dark pink color due to the hydrazine crosslinked structure of the fiber, and thus has a drawback that the field of application is limited.

Regarding this problem, Patent Documents 2 and 3 disclose that the acid treatment A is performed after the cross-linking treatment with a hydrazine compound, and the acid treatment B is performed after the hydrolysis treatment with an alkali, respectively. can be mitigated.

However, even crosslinked acrylate fibers whose whiteness has been improved by the above-described method may become more reddish with the passage of time, heating, washing, and the like. Moreover, the above-described method requires many manufacturing steps, resulting in high manufacturing costs. For this reason, it is still difficult to develop applications.

The cause of the redness in conventional crosslinked acrylate fibers is the crosslinked structure formed by the reaction between the cyano group and hydrazine. However, since crosslinked acrylate fibers contain a large amount of highly hydrophilic carboxyl groups, it is considered difficult to maintain fiber properties due to swelling and dissolution in water without a crosslinked structure. For this reason, it is not easy to remove the crosslinked structure, which is the root cause of redness, and has hardly been studied so far.

Moreover, in fibers using copolymers such as acrylonitrile and methacrylic acid, it has been difficult to improve hygroscopicity while suppressing the degree of swelling in water.

In addition, (ii) the production of crosslinked acrylate fibers requires a step of introducing a crosslinked structure with hydrazine and a hydrolysis step for introducing carboxyl groups. A step is required to remove the residue of 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 the situation is that batch processing with low productivity has to be performed. In addition, since heat is generated by moisture absorption, the amount of heat generated becomes scarce when the amount of moisture absorbed is close to saturation.

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, it becomes difficult to spin, and it is 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.

As described above, the crosslinked acrylate fibers imparted with hygroscopicity have been produced in many steps and have low productivity, or it has been difficult to increase the hygroscopicity. In addition, such fibers are also used in clothing and the like that require heat retention due to their moisture-absorbing and heat-generating properties, but in some cases heat generation due to moisture absorption alone is insufficient.

JP-A-5-132858 JP 2010-216051 A JP 2009-114556 A

The present invention was invented in view of the current state of the prior art, and an object of the present invention is to provide a hygroscopic acrylonitrile that can be continuously produced in a simpler process than before and has high hygroscopicity and high heat build-up. To provide a system fiber.

As a result of intensive studies in order to achieve the above-mentioned object, the inventors of the present invention dissolved an acrylonitrile-based polymer, and after spinning a spinning dope containing a metal oxide from a nozzle, coagulated, washed with water, and stretched. By hydrolyzing the undried fibers obtained through each step, it is possible to obtain hygroscopic acrylonitrile fibers that maintain practical fiber physical properties without cross-linking and also have light-to-heat conversion performance. The inventors have found that the whiteness of fibers can be improved when titanium oxide is used as the metal oxide, and have arrived at the present invention.

That is, the present invention is achieved by the following means.
(1) A hygroscopic acrylonitrile fiber composed of a polymer substantially free of covalently crosslinked structures, wherein the fiber contains 0.2 to 4.5 mmol/g of carboxyl groups and 0.1 mmol/g of carboxyl groups. It contains a metal oxide having a photothermal conversion property of 15% by weight, a saturated moisture absorption rate at 20° C.×65% RH of 5% by weight or more, and a water swelling degree of 10 times or less. hygroscopic acrylonitrile fiber.
(2) The hygroscopic acrylonitrile-based fiber according to (1), wherein the carboxyl groups are uniformly present throughout the fiber.
(3) The hygroscopic acrylonitrile fiber according to (1), characterized in that the carboxyl groups are localized on the surface layer of the fiber .
(4) The 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) The hygroscopic acrylonitrile fiber according to any one of (1) to (4), wherein the metal oxide is titanium oxide.
(6) After spinning a spinning stock solution containing an acrylonitrile polymer and a metal oxide from a nozzle, hydrolyzing the undried fibers obtained through the steps of coagulation, washing, and drawing (2 ) method for producing a hygroscopic acrylonitrile-based fiber.
(7) A fiber obtained by spinning a spinning solution containing an acrylonitrile-based polymer and a metal oxide from a nozzle and then subjecting the undried fiber to the steps of coagulation, washing, and drawing, and then heat-treating the undried fiber to densify it or The method for producing a hygroscopic acrylonitrile-based fiber according to (3), which comprises hydrolyzing the fiber that has been subjected to relaxation treatment after densification.
(8) The method for producing a hygroscopic acrylonitrile fiber according to (6) or (7), wherein the undried fiber has a moisture content of 20 to 250%.
(9) A fiber structure containing the hygroscopic acrylonitrile fiber according to any one of (1) to (5).

The hygroscopic acrylonitrile-based fiber of the present invention does not substantially have a crosslinked structure due to covalent bonds, and does not require a crosslink introduction step in production, so that the production process can be greatly reduced. Continuous production using acrylic fiber manufacturing equipment is possible, and productivity is high. Moreover, since the hygroscopic acrylonitrile-based fiber of the present invention contains a metal oxide, it can have not only heat generation due to moisture absorption but also heat generation due to photothermal conversion.

Unlike conventional hygroscopic acrylonitrile fibers, the hygroscopic acrylonitrile fibers of the present invention have substantially no crosslinked structure due to covalent bonds. 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. In addition, continuous production is possible without being limited to batch processing such as the production of conventional crosslinked acrylate fibers. 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.

In addition, the hygroscopic acrylonitrile fiber of the present invention contains a carboxyl group, and the content thereof is 0.2 to 4.5 mmol/g, preferably 0.2 to 4.5 mmol/g, as determined by the method described later. 0.5 to 4.0 mmol/g, more preferably 1.0 to 3.5 mmol/g. When the 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. 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 hygroscopic acrylonitrile fiber of the present invention has a saturated moisture absorption rate of 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more, at 20° C. and a relative humidity of 65%. It is desirable to have If 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 hygroscopic acrylonitrile fiber of the present invention preferably has a water swelling degree of 10 times or less, preferably 8 times or less, more preferably 5 times or less, as determined by the method described later. The hygroscopic acrylonitrile-based fiber of the present invention does not have a cross-linked structure by covalent bonds as described above, and if the degree of swelling with water exceeds 10 times, the fiber becomes brittle and partly falls off. or, in some cases, dissolve, making handling difficult. The lower limit is not particularly limited, but from the viewpoint that the hygroscopic acrylonitrile fiber of the present invention has a saturated moisture absorption rate of 5% by weight or more in an atmosphere of 20° C. and a relative humidity of 65%, it is usually 0.05 times or more. Seem.

Also, the hygroscopic acrylonitrile fiber of the present invention contains 0.1 to 15% by weight, preferably 0.2 to 10% by weight, of metal oxide relative to the weight of the polymer constituting the fiber. . If the amount of metal oxide contained in the fiber is less than 0.1% by weight, sufficient light-to-heat conversion may not be obtained, and if it exceeds 15% by weight, the physical properties of the fiber may deteriorate, resulting in spinning processing, It may become impractical.

The above-mentioned metal oxide is not particularly limited as long as it has photothermal conversion properties. One selected from these may be used alone, or two or more may be used in combination. In addition, oxides of Si, Ti, Zn, Al, and Zr are preferable because they can express not only the light-to-heat conversion property but also the effect of improving the whiteness of the fiber. High whiteness is also possible. Among them, titanium oxide is particularly preferable in view of safety and price in addition to the effect of improving whiteness.

The particle size of the metal oxide is not particularly limited, but the average primary particle size is preferably in the range of 1 to 1000 nm, more preferably in the range of 50 to 600 nm. If the average primary particle size is less than the lower limit, problems such as a large amount of dust flying around or clogging of spinning nozzles due to agglomeration may occur during fiber production. On the other hand, if the average primary particle size exceeds the upper limit, the physical properties of the fiber may be impaired.

Moreover, in the hygroscopic acrylonitrile-based fiber of the present invention, it is 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, the hygroscopic 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, 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 carboxyl group-containing polymer and a center portion made of an acrylonitrile-based 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, when 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 hygroscopic acrylonitrile-based fiber of the present invention described above, an acrylonitrile-based polymer is dissolved and a spinning stock solution containing a metal oxide is spun from a nozzle, followed by the steps of coagulation, washing, and drawing. A method of obtaining by hydrolyzing the undried fibers obtained through the process can be exemplified. 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. In addition, the notation of (meta) represents both those with and without the word meta.

Next, using such an acrylonitrile-based polymer and the metal oxide as described above, fiberization is performed by wet spinning, and the case where an inorganic salt such as sodium rhodanate is used as a solvent will be explained as follows. become. First, the above acrylonitrile-based polymer is dissolved in a solvent, and then a metal oxide is added 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, if the moisture content of the gel-like acrylonitrile-based fibers is less than 20% by weight, the chemical agent does not penetrate into the inside of the fibers in the hydrolysis treatment described later, and the carboxyl groups are removed throughout the fibers. may not be able to spawn over time. 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. 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.

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 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 hygroscopic acrylonitrile-based fiber according to the present invention is obtained as described above, and each of the above-described treatments can be continuously performed by using existing continuous acrylic fiber production equipment. 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 hygroscopic acrylonitrile-based fiber of the present invention, functional materials other than metal oxides may be added to the spinning dope. Examples of such functional materials include carbon black, pigments, antibacterial agents, deodorants, hygroscopic agents, antistatic agents, and resin beads.

Here, in the hygroscopic acrylonitrile-based fiber of the present invention obtained by the above-described production method, the undried gel-like acrylonitrile-based fiber is hydrolyzed, so the chemical is not hydrolyzed sequentially from the fiber surface. It is thought that it permeates deep inside the fiber and 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.

From the above, it is speculated that the structure of the hygroscopic acrylonitrile-based 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. be done. 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 having a crosslinked structure by covalent bonding. In addition, since the surface layer of the fiber is not locally hydrolyzed, but the entire fiber is uniformly hydrolyzed, it is suppressed that the metal oxide present on the surface layer is dropped due to hydrolysis. , the added metal oxide can be used without waste.

Furthermore, the light-to-heat conversion performance of the fiber of the present invention is remarkably higher than that of conventionally known fibers containing metal oxides. There have been no such reports so far, and the cause is not clear. It is presumed that the light-to-heat conversion effect is dramatically improved because the metal oxide existing in the innermost part is also effectively used because it becomes easier to reach.

The hygroscopic acrylonitrile-based fiber of the present invention is, as described above, a fiber obtained by further heat-treating an undried gel-like acrylonitrile-based fiber to make it densified, or a fiber that is further subjected to a relaxation treatment after densification as a raw material fiber. By adopting as, even when taking a core-sheath structure, the carboxyl groups are uniformly present in the surface layer, and the core has a hard and elastic structure, so even without obtaining a crosslinked structure by covalent bonds, Similarly, it is thought that there is little decrease in fiber physical properties.

On the other hand, without using undried gel-like acrylonitrile-based fibers as described above, fibers densified by further heat treatment, and fibers further relaxed after densification, undried fibers are not used. , 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 hygroscopic acrylonitrile-based fiber of the present invention described above 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 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 polyacrylonitrile-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, clothing, filters, curtains and carpets, bedding, cushions, insoles, etc.), and how the hygroscopic acrylonitrile fiber of the present invention contributes to the expression of such functions. is determined as appropriate in consideration 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 16 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 measuring the weight of the sample after dehydration (W6 [g]), the sample is dried at 115°C for 3 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 5 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

<Titanium oxide content and titanium oxide retention rate>
The titanium oxide content (C1 [%]) contained in the fiber was measured from the peak intensity of the sample measured with a fluorescent X-ray analyzer. Regarding the titanium oxide retention rate, the titanium oxide content (C2 [%]) of the dried gel-like acrylonitrile fiber before hydrolysis treatment in the manufacturing process of the sample was measured with the same device as described above, and the following formula was obtained. I asked for it.
Titanium oxide retention rate (%) = C1/C2 x 100

<Photothermal conversion>
5 g of a cotton-like sample was placed in a cylindrical cylinder with an inner diameter of 2 cm and hot-pressed at 80° C. for 10 minutes to prepare a measurement sample with a diameter of 2 cm and a thickness of 5 mm. After the measurement sample was allowed to stand still in a room at 25° C. to stabilize the temperature, it was illuminated with an incandescent lamp (SUN CLIP DX-II (AC 100 V, 600 W), manufactured by Hakuba Photo Industry) for 5 minutes from 1 m vertically above. The temperature (°C) of the sample immediately after irradiation was measured by thermography.

<Whiteness>
With a Hitachi U-3000 type spectrophotometer, the reflectance (X%, Y%, Z%) of the sample at 595 nm, 553 nm, and 453 nm is measured with aluminum oxide (Al ₂ O ₃ ) as a reference, and the following formula is used. Measured whiteness. The smaller the value, the greater the whiteness.
Whiteness = 0.817 x ((XZ)/Y) x 100) - 3.71

<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>
After dissolving 10 parts of an acrylonitrile-based polymer consisting of 90% acrylonitrile and 10% methyl acrylate in 90 parts of a 44% sodium thiocyanate aqueous solution, 0.25 parts by weight of titanium oxide was added to prepare a spinning stock solution at -2.5. C., coagulated, washed with water and stretched 12 times to obtain a gelatinous acrylonitrile fiber with a moisture content of 35%. The fibers are immersed in a 2.5% sodium hydroxide aqueous solution and squeezed, then hydrolyzed at 123° C. for 25 minutes in a moist and hot atmosphere, washed with water and dried to obtain the hygroscopic acrylonitrile of Example 1. system fibers were obtained.

<Examples 2 to 4>
In the formulation of Example 1, Example 2 was performed in the same manner except that the concentration of the aqueous sodium hydroxide solution was changed to 7.5% in Example 2, 10% in Example 3, and 20% in Example 4. ∼4 hygroscopic acrylonitrile-based fibers were obtained.

<Example 5>
The hygroscopic acrylonitrile fiber of Example 3 was immersed in an aqueous nitric acid solution, adjusted to pH 5.0, and heated at 60° C. for 30 minutes. Then, it was washed with water and dried to obtain a hygroscopic acrylonitrile fiber of Example 5.

<Example 6>
The hygroscopic acrylonitrile fiber of Example 4 was immersed in an aqueous nitric acid solution, adjusted to pH 5.0, and heated at 60° C. for 30 minutes. Then, it was washed with water and dried to obtain a hygroscopic acrylonitrile fiber of Example 6.

<Example 7>
A hygroscopic acrylonitrile fiber of Example 7 was obtained in the same manner as in Example 1, except that the amount of titanium oxide added was changed to 0.05 parts by weight.

<Example 8>
The hygroscopic acrylonitrile fiber of Example 8 was prepared in the same manner as in the formulation of Example 1, except that the amount of titanium oxide added was changed to 0.05 parts by weight and the concentration of the aqueous sodium hydroxide solution was changed to 20%. got

<Example 9>
A hygroscopic acrylonitrile fiber of Example 9 was obtained in the same manner as in Example 1, except that the amount of titanium oxide added was changed to 0.5 parts by weight.

<Example 10>
The hygroscopic acrylonitrile fiber of Example 10 was prepared in the same manner as in the formulation of Example 1, except that the amount of titanium oxide added was changed to 0.5 parts by weight and the concentration of the aqueous sodium hydroxide solution was changed to 20%. got

<Example 11>
A hygroscopic acrylonitrile fiber of Example 11 was obtained in the same manner as in Example 1, except that the amount of titanium oxide added was changed to 1 part by weight.

<Example 12>
A hygroscopic acrylonitrile fiber of Example 12 was obtained in the same manner as in the formulation of Example 1, except that the amount of titanium oxide added was changed to 1 part by weight and the concentration of the aqueous sodium hydroxide solution was changed to 20%. rice field.

<Example 13>
In Example 2, 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 hygroscopic acrylonitrile fiber of Example 8 having a core-sheath structure was obtained in the same manner, except that the densified fiber was used.

<Example 14>
It has a core-sheath structure in the same manner as in Example 13, except that instead of the densified fibers, relaxed fibers that were further relaxed by autoclaving at 120 ° C. for 10 minutes were used. A hygroscopic acrylonitrile fiber of Example 9 was obtained.

<Comparative example 1>
A hygroscopic acrylonitrile fiber containing no metal oxide of Comparative Example 1 was obtained in the same manner as in the formulation of Example 4, except that titanium oxide was not added.

<Comparative Example 2>
A hygroscopic acrylonitrile fiber containing no metal oxide of Comparative Example 2 was obtained in the same manner as in Example 6, except that titanium oxide was not added.

<Comparative Example 3>
After dissolving 10 parts of an acrylonitrile-based polymer consisting of 90% acrylonitrile and 10% methyl acrylate in 90 parts of a 44% sodium thiocyanate aqueous solution, 0.25 parts by weight of titanium oxide was added to prepare a spinning stock solution at -2.5. C., coagulated, washed with water, stretched 12 times, and dried in an atmosphere of dry bulb/wet bulb=120.degree. C./60.degree. The raw fiber was treated in a 35% hydrazine aqueous solution at 100°C for 3 hours, then in a 2.5% sodium hydroxide aqueous solution at 90°C for 2 hours, then dehydrated, washed with water and dried to remove the crosslinked structure and carboxyl groups. A fiber having a

<Comparative Example 4>
A fiber having a crosslinked structure and a carboxyl group of Comparative Example 4 was obtained in the same manner as in Comparative Example 3, except that the sodium hydroxide aqueous solution concentration was changed to 5%.

<Comparative Example 5>
A spinning dope prepared by dissolving 10 parts of an acrylonitrile-based polymer consisting of 88% acrylonitrile and 12% methacrylic acid in 90 parts of a 44% sodium thiocyanate aqueous solution is spun, coagulated, washed with water, stretched, and dried. An acrylic fiber having carboxyl groups was obtained.

<Comparative Example 6>
The acrylic fiber of Comparative Example 2 was heat-treated in a 1 g/l soda ash aqueous solution at 90° C. for 30 minutes, then washed with water and dried to obtain an acrylic fiber having neutralized carboxyl groups.

<Comparative Example 7>
An acrylic fiber having neutralized carboxyl groups was obtained in the same manner as in the formulation of Comparative Example 6, except that the treatment temperature with the 1 g/l soda ash aqueous solution was changed to 100°C.

<Comparative Example 8>
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 44% 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 fibers were heat-treated at 123° C. for 25 minutes in a moist and hot atmosphere, washed with water and dried to obtain acrylic fibers of Example 8.

<Comparative Example 9>
An acrylic fiber of Comparative Example 9 was obtained in the same manner as in the formulation of Comparative Example 8, except that 0.25 parts by weight of titanium oxide was added to the spinning dope.

Table 1 shows the evaluation results of the fibers obtained in the above Examples and Comparative Examples.

As shown in Table 1, the hygroscopic acrylonitrile fibers of Examples 1 to 14 had a saturated hygroscopicity of 5 at 20°C x 65% RH, although they did not have a covalently crosslinked structure. % or more and a water swelling degree of 10 times or less. In addition, these fibers have a large temperature rise due to photothermal conversion. Furthermore, these fibers have high whiteness due to the use of titanium oxide as the metal oxide.

On the other hand, since the fibers of Comparative Examples 1 and 2 do not contain metal oxides, the light-to-heat conversion function due to metal oxides cannot be obtained. Also, the whiteness is lower than that of each example containing titanium oxide.

Since the conventional crosslinked acrylate fibers of Comparative Examples 3 and 4 have a crosslinked structure, they exhibit good properties in terms of saturated moisture absorption and degree of swelling in water. There is a big problem of falling off. Furthermore, as described above, the steps are complicated, and each step requires a high temperature and a long time. For this reason, it is difficult to manufacture the fibers by continuous processing, and there is no choice but to carry out batch processing with low productivity.

The acrylic fiber of Comparative Example 5 had a low saturated moisture absorption rate because the carboxyl groups were not neutralized. The fiber of Comparative Example 6 was obtained by neutralizing the acrylic fiber of Comparative Example 5, but the improvement in saturated moisture absorption rate was insufficient, while the degree of swelling in water increased greatly. In Comparative Example 7, since the neutralization reaction conditions were strengthened, the saturated moisture absorption rate was improved, but the water swelling degree was too high, resulting in gelation of the fibers.

Since the acrylic fiber of Comparative Example 9 contains titanium oxide, the temperature after light irradiation is higher than that of Comparative Example 8, but the temperature after light irradiation is higher in the examples of the present application. , it can be seen that there is a dramatic photothermal conversion effect in the present invention.

Claims (9)

A hygroscopic acrylonitrile-based fiber composed of a polymer that does not substantially have a covalently crosslinked structure, the fiber containing 0.2 to 4.5 mmol/g of carboxyl groups and 0.1 to 15 wt. % of a metal oxide having a photothermal conversion property , a saturated moisture absorption rate at 20° C.×65% RH of 5% by weight or more, and a water swelling degree of 10 times or less. Acrylonitrile fiber. 2. The hygroscopic acrylonitrile fiber according to claim 1, wherein the carboxyl groups are uniformly present throughout the fiber. 2. The hygroscopic acrylonitrile fiber according to claim 1, wherein the carboxyl groups are localized on the fiber surface layer . The hygroscopic acrylonitrile fiber according to any one of claims 1 to 3, characterized in that the degree of neutralization of carboxyl groups is 25% or more. The hygroscopic acrylonitrile fiber according to any one of claims 1 to 4, wherein the metal oxide is titanium oxide. 3. The method according to claim 2, characterized in that after spinning the dope containing the acrylonitrile-based polymer and the metal oxide through a nozzle, the undried fibers obtained through the steps of coagulation, washing with water, and drawing are hydrolyzed. A method for producing a hygroscopic acrylonitrile fiber. After spinning a spinning dope containing an acrylonitrile polymer and a metal oxide from a nozzle, the undried fiber obtained through each step of coagulation, washing, and drawing is heat-treated to densify the fiber or after densification 4. The method for producing a hygroscopic acrylonitrile-based fiber according to claim 3, further comprising hydrolyzing the relaxation-treated fiber. The method for producing a hygroscopic acrylonitrile fiber according to claim 6 or 7, wherein the undried fiber has a moisture content of 20 to 250%. A fiber structure containing the hygroscopic acrylonitrile fiber according to any one of claims 1 to 5.