JP6656608B1 - Carboxyl group-containing beaten acrylonitrile fiber, method for producing the fiber, and structure containing the fiber - Google Patents

Abstract

A beaten acrylonitrile fiber having a carboxyl group has a property of having high swelling property in water, and is considered advantageous in terms of powder capturing property. However, this characteristic also causes an aspect that it is likely to shrink due to heating or drying, which causes a problem of poor morphological stability during processing. An object of the present invention is to provide a beaten acrylonitrile fiber containing a carboxyl group, which is excellent in morphological stability. A beaten acrylonitrile fiber composed of a polymer having a carboxyl group content of 0.2 to 4.0 mmol / g and having substantially no cross-linked structure by covalent bonds. A beaten acrylonitrile fiber having a shrinkage of 25% or less when formed into a paper shape having an amount of 50 g / m 2. [Selection diagram] None

Description

The present invention relates to a carboxyl group-containing beaten acrylonitrile-based fiber, a method for producing the fiber, and a structure containing the fiber.

The beaten fiber has a multi-branched structure and a high specific surface area, and is excellent in adhesiveness and ability to capture functional particles such as activated carbon, so that papermaking, packaging materials, paints, building materials, industrial materials, beauty, health, etc. It is applied in various fields.

Beating of acrylic fibers is also being studied, and Patent Document 1 reports that beaten acrylonitrile fibers having high adhesiveness can be obtained by beating raw material acrylic fibers having a carboxyl group. .

Since the fiber has a carboxyl group in addition to the above-described adhesiveness and the ability to capture functional particles, it has functions such as easy dispersibility, ion adsorption, moisture absorption, and deodorization, and is used for various applications. Applications can be expected.

JP-A-2003-166118

The beaten acrylonitrile-based fiber disclosed in Patent Document 1 has a property that it has a high swelling property with respect to water, and is considered to be advantageous in terms of powder capturing properties. However, this property also has the aspect of easily shrinking by heating and drying, and causes a problem of poor form stability during processing. Further, the beaten acrylonitrile-based fiber disclosed in Patent Document 1 has a property that once the fibrillated fiber is dried, the fibrils adhere to each other and do not swell again. For this reason, there is also a problem that once dried, the properties of the carboxyl group such as ion adsorption, moisture absorption and deodorization cannot be effectively used.

The present invention has been made in view of the state of the art, and an object of the present invention is to provide a carboxyl group-containing beaten acrylonitrile fiber having excellent form stability.

The present inventors have conducted intensive studies to achieve the above-mentioned object, and as a result, after spinning a spinning solution in which an acrylonitrile-based polymer was dissolved from a nozzle, the solution was obtained through coagulation, water washing, and stretching. By hydrolyzing the undried fibers, a portion having a carboxyl group is present throughout the fiber structure when viewed macroscopically, while constituting the fiber when viewed more microscopically. Fibers with a structure in which more carboxyl groups are present on the surface than inside each fibril can be obtained, and by beating this fiber, it has excellent form stability during processing and a function derived from carboxyl groups. It has been found that a carboxyl group-containing beaten acrylonitrile-based fiber capable of sufficiently exhibiting the above is obtained, and the present invention has been achieved.

That is, the present invention is achieved by the following means.
(1) Beating acrylonitrile-based fibers composed of a polymer having a carboxyl group content of 0.2 to 4.0 mmol / g and having substantially no covalent cross-linked structure, Beating acrylonitrile-based fibers having a shrinkage factor of 20 % or less when formed into a paper having a shape of 50 g / m ² .
(2) The beaten acrylonitrile fiber according to (1), wherein the degree of water swelling is 0.2 times or more.
(3) The beaten acrylonitrile fiber according to (1) or (2), wherein the freeness is 730 ml or less.
(4) A spinning solution in which an acrylonitrile-based polymer is dissolved is spun out from a nozzle, and then the undried fibers obtained through the steps of coagulation, washing and drawing are hydrolyzed, and then beating is performed. A method for producing beaten acrylonitrile-based fibers.
(5) The beating-like acrylonitrile system according to (4), wherein the hydrolysis treatment is performed by impregnating the undried fiber with a basic aqueous solution or an acidic aqueous solution, squeezing, and heating the wet fiber in a moist and hot atmosphere. Fiber manufacturing method.
(6) The method for producing beaten acrylonitrile-based fibers according to (5), wherein the heating temperature in a moist heat atmosphere is 105 to 140 ° C.
(7) The method for producing beaten acrylonitrile-based fibers according to any one of (4) to (6), wherein the moisture content of the undried fibers is 20 to 250%.
(8) The method for producing beaten acrylonitrile-based fibers according to any one of (4) to (7), wherein a beating treatment is performed after a drying step after the hydrolysis treatment.
(9) A structure containing the beaten acrylonitrile-based fiber according to any one of (1) to (3).
(10) The structure according to (9), which is selected from a filter, an absorption layer and a diffusion layer of a sanitary ware, a carbon sheet for a fuel cell diffusion membrane, and a paper product.

The beaten acrylonitrile fiber of the present invention has a carboxyl group and can achieve a low shrinkage of 25% or less in the method described later. The beaten acrylonitrile-based fiber of the present invention is excellent in adhesiveness and particle trapping property and also excellent in form stability, so that it can be suitably used as a binder for supporting functional particles in a filter or the like. . Furthermore, the beaten acrylonitrile-based fiber of the present invention can also exhibit functions such as ion exchange properties derived from carboxyl groups, moisture absorption, deodorization, antivirus, and antiallergenic properties. It is also useful as a functional material for providing

The beaten acrylonitrile-based fiber of the present invention contains a carboxyl group, and its content is 0.2 to 4.0 mmol / g, and preferably 0.4 to 3.0 mmol / g in the method described later. 0 mmol / g, more preferably 0.6 to 2.0 mmol / g. When the amount of carboxyl groups is less than 0.2 mmol / g, the adhesiveness, particle trapping property, ion exchange performance, etc. may not be sufficiently obtained. It becomes too hydrophilic and swells and dissolves violently in water, adversely affecting fiber properties. Further, in the acrylonitrile-based fiber before beating (hereinafter, also referred to as unbeaten fiber), which is a raw material of the beaten acrylonitrile-based fiber of the present invention, in order to obtain good beating properties, a carboxyl group in the above range is used. It is desirable to contain.

Further, in the unbeaten fiber, the presence of a crosslinked structure due to covalent bonds, each polymer constituting the fiber is connected to reduce the beating property, so that those that have substantially no crosslinked structure due to covalent bonds. adopt. As a result, the beaten acrylonitrile-based fibers of the present invention also have substantially no crosslinked structure due to covalent bonds. Here, "substantially does not have a crosslinked structure by a covalent bond" means that it does not have a crosslinked structure intentionally formed by using a crosslinking agent or the like, and is subjected to a hydrolysis treatment described later. However, this does not mean that there is no trace of a crosslinked structure that may be unintentionally produced as a by-product.

The beaten acrylonitrile fiber of the present invention has a shrinkage of 25% or less, preferably 20% or less, more preferably 15% or less when formed into a paper having a basis weight of 50 g / m ² . If the shrinkage exceeds 25%, there may be a problem in form stability during processing or actual use.

In addition, the beaten acrylonitrile-based fiber of the present invention preferably has a water swelling degree (hereinafter also referred to simply as “water swelling degree” in the present invention) of 0.2 times or more after being dried once from a wet state after beating treatment. , More preferably 0.4 times or more, further preferably 0.7 times or more, and most preferably 1 time or more. When the degree of water swelling is less than 0.2 times, for example, after being formed into a water purification filter and dried, it hardly swells in water during actual use, so that ions to be removed in water reach inside the fiber. In some cases, the ion-adsorbing property of the carboxyl group cannot be used effectively. On the other hand, if the degree of water swelling is too high, there is a risk that the water will stop due to swelling, or the fibers will become brittle and some of the fibers will fall off, so the upper limit is preferably 10 times, more preferably 8 times. It is twice.

The beaten acrylonitrile fiber of the present invention desirably has a freeness of 730 ml or less. If the freeness exceeds 730 ml, the binder properties, the particle-trapping properties, and the like may not be exhibited significantly.

Further, in the present invention, in the internal structure of the unbeaten fiber, a portion having a carboxyl group is present over the entire fiber structure made of an acrylonitrile-based polymer, but is not uniformly mixed at a molecular level. Is desirable. As a specific example of such a structure, the small fibers (so-called fibrils) constituting the acrylonitrile-based fiber have a core-sheath structure having a carboxyl group in the surface layer and having no carboxyl group in the center. In other words, there can be mentioned a structure composed of an aggregate of small fibers having a core-sheath structure having a carboxyl group in a sheath portion. Here, being present over the entire fiber means that the coefficient of variation CV of the magnesium element content ratio in the fiber cross section measured by the measurement method described below is 50% or less. Such a coefficient of variation CV is preferably 40% or less, more preferably 30% or less.

If the carboxyl groups are present unevenly in the fiber structure or are uniformly present at the molecular level, sufficient beating properties may not be obtained. In a structure in which a portion having a carboxyl group is present throughout the entire fiber and is not uniformly mixed at the molecular level, the portion having a carboxyl group is easily swollen by water and thus easily fibrillated by beating.

Further, since the surface of each beaten fibril is rich in carboxyl groups, the hydrophilicity and the diffusibility of water are increased, and the particle trapping property, adhesive property, ion exchange property and the like are easily exhibited. On the other hand, since the inside of each fibril is composed of an acrylonitrile-based polymer, it does not easily shrink and contributes to form stability.

In order to further improve the beating property of the unbeaten fiber, it is preferable that the counter ion of the carboxyl group is a cation other than a hydrogen ion. More specifically, the ratio of the counter ion being a cation other than a hydrogen ion, that is, the degree of neutralization is preferably 25% or more, more preferably 35% or more, and further preferably 50% or more.

Examples of the above cations include alkali metals such as Li, Na, and K; alkaline earth metals such as Mg, Ca, and Ba; metals such as Cu, Zn, Al, Mn, Ag, Fe, Co, and Ni; and NH. ₄ , cations such as amines, etc., and a plurality of types of cations may be mixed. Among them, Li, Na, K, Mg, Ca, Zn and the like are preferable.

As a method for producing the beaten acrylonitrile-based fiber of the present invention described above, a spinning solution in which an acrylonitrile-based polymer is dissolved is spun from a nozzle, and coagulated, washed with water, and the undried fiber obtained through each of the steps of drawing is obtained. A method of producing unbeaten fibers by hydrolysis and beaten the unbeaten fibers can be mentioned. Hereinafter, such a manufacturing method will be described in detail.

First, the acrylonitrile-based polymer as a raw material contains acrylonitrile as a polymerization composition, preferably at least 40% by weight, more preferably at least 50% by weight, further preferably at least 85% by weight. Accordingly, 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 (the notation of (meth) is given with or without the word of the meta) Sulfonic acid group-containing monomers such as methallyl sulfonic acid and p-styrene sulfonic acid and salts thereof, acrylamide, styrene, vinyl acetate and the like.

Next, fiberization is performed by wet spinning using such an acrylonitrile-based polymer, and the case where an inorganic salt such as sodium rhodanate is used as a solvent will be described below. First, the acrylonitrile-based polymer is dissolved in a solvent to prepare a spinning dope. After spinning the spinning dope from a nozzle, the coagulation, washing, and drawing steps are performed to reduce the moisture content of the undried fiber (hereinafter, also referred to as gel acrylonitrile-based fiber) to 20 to 250% by weight, preferably 25 to 130% by weight. % By weight, more preferably 30 to 100% by weight.

Here, when the water content of the gel-like acrylonitrile fiber is less than 20% by weight, the drug may not penetrate into the fiber in the hydrolysis treatment described later, and the carboxyl group may not be able to be generated over the entire fiber. is there. On the other hand, if the content exceeds 250% by weight, a large amount of water is contained inside the fiber, and the fiber strength becomes too low. When more emphasis is placed on the fiber strength, it is desirable to be 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 It is desirably about 5 to 20, preferably about 7 to 15 times.

The gel acrylonitrile fiber is then subjected to a hydrolysis treatment. By this treatment, the nitrile groups in the gel-like acrylonitrile fiber are hydrolyzed to generate carboxyl groups.

As a means for such a hydrolysis treatment, a basic aqueous solution such as an alkali metal hydroxide, an alkali metal carbonate, or ammonia, or a means for impregnating or immersing an aqueous solution such as nitric acid, sulfuric acid, or hydrochloric acid is used. No. As specific treatment conditions, various conditions such as the concentration of the treatment agent, the reaction temperature, and the reaction time may be appropriately set in consideration of the above-described range of the amount of the carboxyl group. After impregnating and squeezing 5 to 20% by weight, preferably 1.0 to 15% by weight of the treatment agent, the conditions for treatment at 105 to 140 ° C, preferably 110 to 135 ° C for 10 to 60 minutes in a moist heat atmosphere. It is preferable to set within the range of industrial and fiber properties. If the temperature is lower than 105 ° C., the coloring of the fiber may be increased. Note that the moist heat atmosphere refers to an atmosphere filled with saturated steam or superheated steam.

In the fiber subjected to the hydrolysis treatment as described above, cations such as alkali metal hydroxides, alkali metal carbonates, alkali metals and ammonium according to the type of ammonia used in the hydrolysis treatment are used. Although a salt-type carboxyl group serving as a counter ion has been generated, a treatment for converting the counter ion of the carboxyl group may be performed as needed. By performing ion exchange treatment with an aqueous solution of a metal salt such as a nitrate, a sulfate, or a hydrochloride, a salt-type carboxyl group having a desired metal ion as a counter ion can be obtained. Further, by adjusting the pH of the aqueous solution and the concentration and type of the metal salt, it is possible to mix different counter ions or to adjust the ratio thereof.

The fiber into which the carboxyl group has been introduced as described above, that is, the unbeaten fiber is washed with water, dried and cut as necessary, and then subjected to beating treatment, but the beating method is not limited, and beater And a refining machine such as a refiner.

As described above, the beaten acrylonitrile fiber according to the present invention can be obtained, but the production of unbeaten fiber can be continuously performed by diverting existing continuous production equipment for acrylic fiber. Further, in the above method, an inorganic salt such as sodium rhodanate is used as a solvent, but the above conditions are the same even when an organic solvent is used. However, since the type of the solvent is different, a temperature suitable for the solvent is selected for the coagulation bath temperature, and the water content of the gel acrylonitrile fiber is controlled within the above range.

Further, in the above-described production method, since the gel-like acrylonitrile-based fiber having a void structure is subjected to a hydrolysis treatment, the drug is not hydrolyzed sequentially from the fiber surface, but the drug is transmitted through the void to the inner part of the fiber. Also penetrate and hydrolyze throughout the fiber. Further microscopically, since acrylonitrile fibers generally exist as a collection of microfibrils, the drug penetrates between the fibrils, hydrolysis proceeds from the fibril surface, and the inside of the fibrils undergoes hydrolysis. It is expected that the original acrylonitrile-based polymer will remain. In other words, a structure in which a portion having a carboxyl group exists throughout the entire fiber and is not uniformly mixed at a molecular level is completed, and fibrillation is facilitated with the portion having a carboxyl group as a boundary. After beating, it is assumed that the carboxyl group on each fibril surface improves the particle trapping property, and the acrylonitrile polymer remaining inside exhibits low heat shrinkage.

In the above-described production method, the gel-like acrylonitrile-based fiber, that is, without using the undried fiber after stretching, when the acrylonitrile-based fiber after drying is subjected to a hydrolysis treatment, the drug is in the inner part of the fiber Since the fibers are not permeated and are sequentially hydrolyzed from the fiber surface, a structure having many carboxyl groups in the fiber surface layer portion and few carboxyl groups in the inner portion of the fiber is induced. With such a structure, beating properties are significantly deteriorated.

The beaten acrylonitrile-based fiber of the present invention described above has, in addition to particle-capturing properties and a reinforcing material function, functions such as ion exchange properties derived from carboxyl groups, hygroscopicity, deodorant properties, and antiviral properties. Therefore, it can be used alone or in combination with other materials as a useful structure in many applications. In the structure, the content of the beaten acrylonitrile-based 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 acrylonitrile fiber.

Examples of the appearance of the structure include a paper-like material, a sheet-like material, a laminate, and a spherical or cylindrical molded product. As a content form of the fiber of the present invention in the structure, by mixing with a material such as another fiber or a resin composition, substantially uniformly distributed, in the case of a structure having a plurality of layers, There are ones that are concentrated in one of the layers (single or plural) and ones that are distributed at a specific ratio in each layer.

The appearance form and content form of the structure exemplified above, the other materials constituting the structure, and the other members to be combined with the structure are determined by the type of the final product (for example, (Diapers, urine absorption pads, sanitary napkins, etc.) depending on the diffusion layer or absorption layer, fuel cell diffusion membrane carbon sheet, water purification filter, activated carbon carrying sheet or filter, papermaking binder, papermaking products, wet friction material, etc. It is appropriately determined in consideration of the required functions, characteristics, shapes, and how the beaten acrylonitrile fiber of the present invention contributes to exhibiting such functions.

In each of the above applications, the characteristics of the beaten acrylonitrile fiber of the present invention can be effectively utilized. For example, the hydrophilicity of fibrils can improve the diffusibility of urine and the like in the use of a diffusion layer for sanitary ware, and the particle-capturing property in the use of absorbent layers and activated carbon-carrying sheets for sanitary ware. Utilizing water can fix the water-absorbing resin and activated carbon particles.

Examples are shown below to facilitate understanding of the present invention, but these are merely illustrative, and the gist of the present invention is not limited thereto. In the examples, parts and percentages are indicated by weight unless otherwise specified. The measurement of each characteristic was performed by the following method.

<Distribution of carboxyl groups in the fiber structure>
An ion exchange treatment is performed by immersing a sample of the unbeaten fiber in an aqueous solution in which magnesium nitrate corresponding to twice the amount of carboxyl groups contained in the fiber is dissolved at 50 ° C. for 1 hour, followed by washing with water and drying. Thereby, the counter ion of the carboxyl group is changed to magnesium. Using an energy dispersive X-ray spectrometer (EDS), the content ratio of the magnesium element at ten measurement points selected at substantially equal intervals from the outer edge to the center of the fiber cross section is measured for the fiber sample of the magnesium salt type. The coefficient of variation CV [%] is calculated from the numerical values of the obtained measurement points by the following equation.
Coefficient of variation CV [%] = (standard deviation / average value) × 100

<Amount of carboxyl group>
About 1 g of the beaten 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 with a hot air drier at 105 ° C. for 5 hours. About 0.2 g of the dried sample is precisely weighed (W1 [g]), and 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0.4 g of sodium chloride are added thereto and stirred. Next, the sample is strained using a wire mesh and washed with water. To the obtained filtrate (including the washing solution), 2 to 3 drops of phenolphthalein solution was added, and titration was carried out with 0.1 mol / l hydrochloric acid according to a conventional method to obtain the consumed hydrochloric acid amount (V1 [ml]). The total amount of carboxyl groups is calculated by the following equation.
Total carboxyl group content [mmol / g] = (0.1 × 15-0.1 × V1) / W1

<Degree of neutralization>
The beaten sample was dried in a hot air drier at 105 ° C. for 5 hours, weighed accurately about 0.2 g (W2 [g]), and added thereto 100 ml of water, 15 ml of 0.1 mol / l sodium hydroxide, and 0 ml of sodium chloride. Add 0.4 g and stir. Next, the sample is strained using a wire mesh and washed with water. To the obtained filtrate (including the washing solution), 2-3 drops of a phenolphthalein solution are added, and titration is carried out with 0.1 mol / l hydrochloric acid according to a conventional method to determine the consumed hydrochloric acid amount (V2 [ml]). The amount of H-type carboxyl groups contained in the sample is calculated by the following equation, and the degree of neutralization is determined from the result and the above-mentioned total carboxyl group amount.
H-type carboxyl group amount [mmol / g] = (0.1 × 15-0.1 × V2) / W2
Neutralization degree [%] = [(total carboxyl group amount-H type carboxyl group amount) / total carboxyl group amount] × 100

<Freeness (CSF)>
JIS P 8121-2: 2012 Pulp-Freeness test method-Part 2: Measured according to Canadian standard freeness method.

<Shrinkage>
The beaten sample is used as a water slurry, and paper is made to have a basis weight of 50 g / m ² and a size of 25 cm × 25 cm using a square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd. Next, drying is performed at 105 ° C. × 1 hour, and the lengths of the four sides are measured. The average value (B [cm]) of the length of one side is obtained from the measured value, and the shrinkage ratio is calculated by the following equation.
Shrinkage (%) = (25−B) / 25 × 100

<Water swelling degree>
The beaten sample was converted into a water slurry, paper was formed using a square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd. so as to have a basis weight of 50 g / m ^2, and dried at 105 ° C. × 1 hour for evaluation. Is made, and the weight (W3 [g]) is measured. After immersing the evaluation paper in pure water, centrifugal dehydration is performed at 1200 rpm for 5 minutes. The weight (W4 [g]) after dehydration is measured, and the degree of water swelling is calculated by the following equation.
Water swelling degree [times] = (W4-W3) / W3
The centrifugal dehydration is performed by using a centrifugal dehydrator (KS-8000) manufactured by KUBOTA and using a universal swing rotor (RS3000 / 6) equipped with a stainless steel basket.

<Activated carbon capture amount>
A beaten sample equivalent to 1 g in terms of solid content is added to 1 L of pure water and stirred. 6 g of powdered activated carbon (Brocoll B mark activated carbon manufactured by Taihei Kagaku Sangyo / average particle diameter 90 μm) is added thereto, and the mixture is stirred for 30 minutes. Thereafter, the mixture was filtered through a sieve having an opening of 173 μm (area: 200 cm ² ), and the weight (A [g]) of the filtrate on the sieve after drying at 105 ° C. for 5 hours was measured. The amount was calculated.
Activated carbon capture amount (g / g) = (A-1) / 1

<Paper strength (adhesive)>
A water slurry was prepared at a weight ratio of beaten sample / acrylic short fiber (fineness: 0.4 dtex, fiber length: 3.0 mm) = 30/70, and the basis weight was calculated using a square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd. Paper was made at 50 g / m ² and dried with a hot calender to make paper for evaluation. The obtained paper was cut into a size of 2 cm (W) × 10 cm (L), and ruptured using a tensile tester (RTA500 (U-1573) manufactured by A & D Corporation) at a pulling speed of 2 cm / min. The strength was measured. It is judged that the higher the breaking strength, the better the adhesion.

<Lead adsorption (ion exchange)>
(Preparation of test solution)
0.5 L of distilled water was placed in a 1 L volumetric flask, and 84 mg of magnesium sulfate heptahydrate, 100 mg of hydrate of calcium chloride, 166 mg of sodium hydrogen carbonate and 10.5 mg of sodium hypochlorite (effective chlorine 6% or more) were added. In addition, completely dissolve. Next, 1.2 ml of a 9.3% aqueous solution of lead nitrate is added, distilled water is added up to just before the marked line, and then a 0.1N aqueous solution of sodium hydroxide is added to adjust the pH to a range of 8.3 to 8.8. After stirring sufficiently, add distilled water up to the marked line to make 1 L.
(Lead adsorption test)
To 200 g of the test solution prepared as described above, a beaten sample having a dry conversion weight of 0.2 g is added, and the mixture is allowed to stand in a thermostat at 20 ° C. for 5 hours. Next, filtration was performed, and lead in the filtrate was quantified by ICP mass spectrometry (JIS K0102: 2016 54.4). The lead concentration under blank conditions was 70 ppb, and it can be said that the lower the lead concentration in the filtrate, the better the adsorption performance.

<Moisture content of gel acrylonitrile fiber>
After the gel-like acrylonitrile fiber is immersed in pure water, it is dehydrated with a centrifugal dehydrator (TYPE H-770A manufactured by Domestic Centrifuge Co., Ltd.) at a centrifugal acceleration of 1100 G (G indicates gravitational acceleration) for 2 minutes. After measuring the weight after dehydration (W5 [g]), the undried fiber is dried at 120 ° C. for 15 minutes, the weight is measured (W6 [g]), and calculated by the following equation.
Water content (%) of gel acrylonitrile fiber = (W5−W6) / W5 × 100

<Example 1>
A spinning stock solution obtained by dissolving 10 parts of an acrylonitrile-based polymer composed of 90% of acrylonitrile and 10% of methyl acrylate in 90 parts of a 44% aqueous solution of sodium thiocyanate is spun into a coagulation bath at −2.5 ° C., coagulated, washed with water, It was stretched 12 times to obtain a gel-like acrylonitrile fiber having a water content of 35%. The fiber was immersed in a 1.5% aqueous sodium hydroxide solution, squeezed, hydrolyzed in a moist heat atmosphere at 123 ° C. for 25 minutes, washed with water, dried at 105 ° C. for 1 hour, and unbeaten. Fiber was obtained. The unbeaten fiber was cut into 4 mm to make a 1% concentration water slurry, and then beaten with a Niagara beater (BE-23, manufactured by Kumagaya Riki Kogyo Co., Ltd.) at a weight of 2 kg for the beating time shown in Table 1. The treatment was performed to obtain a beaten acrylonitrile fiber of Example 1. In addition, the freeness of the unbeaten fiber cut to 4 mm was 760 ml.

<Examples 2 to 5>
In the formulation of Example 1, the beaten acrylonitrile of Examples 2 to 5 was prepared in the same manner except that the concentration of the aqueous sodium hydroxide solution was changed to 4.0% and the beating treatment was performed at the beating time shown in Table 1. A system fiber was obtained.

<Examples 6 to 8>
In the formulation of Example 1, the concentration of the aqueous sodium hydroxide solution was changed to 7.5% in Example 6, 10.0% in Example 7, and 20.0% in Example 8, and as described in Table 1. Except that the beating treatment was performed for the beating time, beaten acrylonitrile fibers of Examples 6 to 8 were obtained in the same manner.

<Example 9>
The procedure of Example 5 was repeated except that a step of adjusting the pH to 3.5 with nitric acid in pure water and holding the mixture at 60 ° C. for 30 minutes was performed between the hydrolysis treatment step and the water washing step. Thus, a beaten acrylonitrile fiber of Example 9 was obtained.

<Comparative Example 1>
A fiber of Comparative Example 1 was obtained in the same manner as in the formulation of Example 2, except that beating treatment was not performed.

<Comparative Examples 2 and 3>
A spinning solution prepared by dissolving 10 parts of an acrylonitrile-based polymer composed of 95% of acrylonitrile, 2% of methacrylic acid, and 3% of methyl acrylate in 90 parts of a 44% aqueous solution of sodium thiocyanate is spun out by a conventional method, coagulated, washed and stretched. After that, it was cut to 4 mm without drying, and beaten in the same manner as in Example 1 to obtain fibers of Comparative Examples 2 and 3.

<Comparative Example 4>
The same treatment as in Comparative Example 2 was carried out except that drying was performed at 105 ° C. × 1 hour after stretching to obtain a fiber of Comparative Example 4.

<Comparative Example 5>
In Example 1, a densified fiber obtained by alternately performing dry heat treatment (110 ° C.) and wet heat treatment (60 ° C.) twice on the fiber instead of the gel acrylonitrile fiber was used. The treatment after the hydrolysis treatment was performed in the same manner to obtain a fiber of Comparative Example 5. The CV value of the distribution state of the carboxyl group of the fiber before beating was large, and the fiber had a core-sheath structure in which the carboxyl group was introduced only into the surface layer of the fiber.

Table 1 shows the evaluation results of the fibers obtained in the above Examples and Comparative Examples. Note that "-" in the table indicates that measurement was not performed.

As shown in Table 1, in Examples 1 to 8, the beating properties of the unbeaten fibers were good, and the beaten acrylonitrile fibers obtained also had a low shrinkage rate, excellent shape stability, and lead. It can also be seen from the adsorptive properties that it has ion exchange capacity. In addition, in Example 9 in which the degree of neutralization of Example 5 was reduced, the freeness was reduced, and it was shown that the higher the degree of neutralization, the better the beating property.

On the other hand, Comparative Example 1 in which no beating treatment was performed was so weak that the paper strength could not be measured, the activated carbon trapping amount was low, and the practicality was low. On the other hand, in Example 2, which was slightly beaten, the paper had a paper strength, and in the present invention, it was shown that binder properties could be obtained even with a slight beat.

Further, in Comparative Examples 2 and 3 in which acrylonitrile fibers were prepared from a polymer obtained by copolymerizing a monomer containing a carboxyl group, the shrinkage was high, and there was a problem in form stability. Furthermore, when comparing Example 1 with the same freeness as Comparative Example 2, Example 1 of the present invention has better paper strength (adhesiveness) and activated carbon capture amount, However, it can be seen that they are also excellent in adhesion and particle trapping properties.

Further, Comparative Example 4 in which an acrylonitrile fiber obtained from a polymer obtained by copolymerizing a monomer having a carboxyl group was subjected to a drying treatment, and a portion having a carboxyl group was not present in the fiber structure (fiber surface layer portion). In Comparative Example 5 using a raw material fiber (in which only a carboxyl group was introduced), beating did not proceed, and paper could not be prepared.

Claims (10)

Beating acrylonitrile fiber composed of a polymer having a carboxyl group content of 0.2 to 4.0 mmol / g and having substantially no covalent crosslinked structure, and having a basis weight of 50 g / m ^2. A beaten acrylonitrile-based fiber having a shrinkage factor of 20 % or less when formed into the paper shape of No. 2.
The beaten acrylonitrile-based fiber according to claim 1, wherein the water swelling degree is 0.2 times or more. The beaten acrylonitrile-based fiber according to claim 1 or 2, wherein the freeness is 730 ml or less. Beating acrylonitrile characterized by applying a spinning solution in which an acrylonitrile-based polymer is dissolved from a nozzle, hydrolyzing the undried fibers obtained through coagulation, washing, and drawing steps and then subjecting the fibers to beating. Method for producing base fiber. The production of beating-like acrylonitrile-based fibers according to claim 4, wherein the hydrolysis treatment is performed by impregnating the undried fibers with a basic aqueous solution or an acidic aqueous solution, squeezing the fibers, and then heating the fibers in a moist heat atmosphere. Method. The method for producing beaten acrylonitrile-based fibers according to claim 5, wherein the heating temperature in a moist heat atmosphere is 105 to 140C. The method for producing beaten acrylonitrile-based fibers according to any one of claims 4 to 6, wherein the moisture content of the undried fibers is 20 to 250%. The method for producing beaten acrylonitrile-based fibers according to any one of claims 4 to 7, wherein a beating treatment is performed after a drying step after the hydrolysis treatment. A structure containing the beaten acrylonitrile-based fiber according to claim 1. The structure according to claim 9, wherein the structure is selected from a filter, an absorption layer and a diffusion layer of a sanitary article, a carbon sheet for a fuel cell diffusion membrane, and a paper product.