阅读说明：本技术 易打浆性丙烯腈系纤维、浆粕状丙烯腈系纤维、含有该纤维的结构体和该纤维的制造方法 (Easy-beating acrylic fiber, pulp-like acrylic fiber, structure containing the fiber, and method for producing the fiber ) 是由 小见山拓三 于 2021-03-11 设计创作，主要内容包括：本发明涉及易打浆性丙烯腈系纤维、浆粕状丙烯腈系纤维、含有该纤维的结构体和该纤维的制造方法。浆粕状纤维被应用于制纸、包装材料、涂料、建筑材料、产业材料、美容、健康等各种领域中,对于丙烯腈系纤维也研究了浆粕化。然而,在一直以来的研究中,成为原料的丙烯腈系纤维的打浆速度慢、且难以获得低滤水度的制品,对于颗粒捕捉性、粘结性也未必能够满足。本发明是鉴于上述现有技术的现状而完成的,其目的在于提供打浆速度优异的丙烯腈系纤维及将该纤维打浆而得到的低滤水度的浆粕状丙烯腈系纤维。一种易打浆性丙烯腈系纤维,其特征在于,具有0.2～4.0mmol/g的羧基量,由实质上不具有基于共价键的交联结构的聚合物构成,且在纤维内部含有亲水性成分。(The present invention relates to an easy-beating acrylic fiber, a pulp-like acrylic fiber, a structure containing the fiber, and a method for producing the fiber. Pulp-like fibers are used in various fields such as paper making, packaging materials, paints, building materials, industrial materials, cosmetics, and health, and pulp formation has been studied for acrylic fibers. However, in the conventional studies, the beating speed of acrylic fibers as a raw material is slow, and it is difficult to obtain a product having a low degree of drainage, and the particle capturing property and the adhesive property are not necessarily satisfactory. The present invention has been made in view of the current state of the art, and an object thereof is to provide an acrylic fiber having an excellent beating speed and a pulp-like acrylic fiber having low drainage obtained by beating the fiber. An easy-beating acrylic fiber having a carboxyl group content of 0.2 to 4.0mmol/g, comprising a polymer substantially free from a crosslinked structure by a covalent bond, and containing a hydrophilic component in the fiber.)

1. An easy-beating acrylic fiber having a carboxyl group content of 0.2 to 4.0mmol/g, comprising a polymer substantially free from a crosslinked structure by a covalent bond, and containing a hydrophilic component in the fiber.

2. The easy-beating acrylic fiber according to claim 1, wherein the hydrophilic component is a polymer containing 30 to 90% by weight of a monomer represented by the following chemical formula 1 as a structural unit,chemical formula 1

Wherein R is a hydrogen atom or a lower alkyl group, R' is a hydrogen atom or an alkyl group having 18 or less carbon atoms, a phenyl group or a derivative thereof, l is 9. ltoreq. l <50, and m is 0. ltoreq. l.

3. A pulp-like acrylic fiber obtained by beating the easy-beating acrylic fiber according to claim 1 or 2.

4. The pulp-like acrylic fiber according to claim 3, wherein the drainage degree is 600ml or less.

5. A structure comprising the pulp-like acrylic fiber according to any one of claims 1 to 4.

6. A sanitary article, a filter, a carbon sheet for a diffusion membrane of a fuel cell, a friction material, a functional paper product, a permeable paper or a cell member, comprising the structure according to claim 5.

7. A method for producing a pulp-like acrylic fiber, comprising the steps of: the method comprises adding a hydrophilic component to a spinning dope in which an acrylonitrile polymer is dissolved, spinning the resultant from a nozzle, subjecting the resultant to coagulation, washing with water, and drawing to obtain undried fibers, hydrolyzing the undried fibers, and then subjecting the fibers to beating.

Technical Field

The present invention relates to an easy-beating acrylic fiber, a pulp-like acrylic fiber, a structure containing the fiber, and a method for producing the fiber.

Background

Pulp-like fibers are characterized by a multi-branched structure and a high specific surface area, and are excellent in adhesiveness, trapping properties of functional particles such as activated carbon, and cohesiveness, and therefore are used in various fields such as paper making, packaging materials, coatings, building materials, industrial materials, cosmetics, and health.

On the other hand, acrylic fibers are difficult to pulp even after a beating step, and therefore, studies have been made to enable pulping. For example, patent document 1 reports: the acrylic fiber can be imparted with beating properties by kneading a hydrophilic resin, and the fiber obtained by beating can be used to obtain a fibrillated acrylic fiber.

In addition, patent document 2 reports: the undried fibers in the middle of the acrylic fiber production process are subjected to hydrolysis treatment to impart beating properties, and the fibers obtained therefrom are beaten to obtain beaten acrylic fibers containing carboxyl groups.

Documents of the prior art

Patent document

Patent document 1: japanese patent application laid-open No. 2005-154958

Patent document 2: japanese patent No. 6656608

Disclosure of Invention

Problems to be solved by the invention

However, although the fibrillated acrylic fiber of patent document 1 and the pulped acrylic fiber containing a carboxyl group of patent document 2 have beating properties, the beating speed is slow, and it is difficult to obtain a product having low water permeability, and the particle capturing property and the adhesive property are not necessarily satisfactory.

The present invention has been made in view of the above-described current state of the art, and an object thereof is to provide: an acrylic fiber having an excellent beating speed and a pulp-like acrylic fiber having a low degree of drainage obtained by beating the acrylic fiber.

Means for solving the problems

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that: the present inventors have found that a beating speed of an obtained fiber is remarkably improved by adding a hydrophilic component to a spinning dope in advance at the stage of the spinning dope, and the present invention has been completed.

That is, the present invention can be realized by the following means.

(1) An easy-beating acrylic fiber having a carboxyl group content of 0.2 to 4.0mmol/g, comprising a polymer substantially free from a crosslinked structure by a covalent bond, and containing a hydrophilic component in the fiber.

(2) The easy-beating acrylic fiber according to (1), wherein the hydrophilic component is a polymer containing 30 to 90% by weight of a monomer represented by the following chemical formula 1 as a structural unit.

[ chemical formula 1]

(wherein R is a hydrogen atom or a lower alkyl group, R' is a hydrogen atom or an alkyl group having 18 or less carbon atoms, a phenyl group or a derivative thereof, and 9. ltoreq. l <50, 0. ltoreq. m < l.)

(3) A pulp-like acrylic fiber characterized by being obtained by beating the easy-beating acrylic fiber of (1) or (2).

(4) The pulp-like acrylic fiber according to the item (3), wherein the drainage degree is 600ml or less.

(5) A structure comprising the pulp-like acrylic fiber according to any one of (1) to (4).

(6) A sanitary article, a filter, a carbon sheet for a diffusion membrane of a fuel cell, a friction material, a functional paper product, a permeable paper or a cell member, comprising the structure of (5).

(7) A method for producing a pulp-like acrylic fiber, comprising the steps of: the method comprises adding a hydrophilic component to a spinning dope in which an acrylonitrile polymer is dissolved, spinning the resultant from a nozzle, subjecting the resultant to coagulation, washing with water, and drawing to obtain undried fibers, hydrolyzing the undried fibers, and then subjecting the fibers to beating.

ADVANTAGEOUS EFFECTS OF INVENTION

The easy-beating acrylic fiber of the present invention has an excellent beating speed and can easily obtain a pulp-like acrylic fiber having a low freeness. The pulp-like acrylic fiber is excellent in adhesiveness and particle capturing property, and therefore can be suitably used as a binder for supporting functional particles or the like in a filter or the like. Further, the pulp-like acrylic fiber of the present invention can also exhibit functions such as ion exchange property, moisture absorption, deodorization, antivirus, anti-allergen property, etc. derived from carboxyl groups, and therefore, can be used as a functional material for imparting these functions to paper and filters.

Drawings

Fig. 1 is a drawing showing an SEM photograph of the pulp-like acrylic fiber of example 3.

Fig. 2 is a drawing showing an SEM photograph of the pulp-like acrylic fiber of comparative example 4.

Detailed Description

The easy-beating acrylic fiber of the present invention contains a carboxyl group in an amount of 0.2 to 4.0mmol/g, preferably 0.4 to 3.0mmol/g, and more preferably 0.6 to 2.0mmol/g in the method described later. If the carboxyl group content is less than 0.2mmol/g, the pulp-like acrylic fiber obtained after beating may not be sufficiently provided with the properties of tackiness, particle-capturing property, etc., whereas if it exceeds 4.0mmol/g, the hydrophilicity of the fiber becomes too high and the fiber swells or dissolves in water, thereby adversely affecting the physical properties of the fiber. In addition, in order to obtain good beating properties, it is desirable that the easy-beating acrylic fiber also contains a carboxyl group in the above-described range.

In addition, in the easy-beating acrylic fiber of the present invention, since the polymers constituting the fiber are linked to each other and the beating property is lowered if there is a crosslinked structure by covalent bond, those having substantially no crosslinked structure by covalent bond are used. As a result, the pulp-like acrylic fiber of the present invention also has substantially no crosslinked structure by covalent bond. Here, "substantially not having a covalent bond-based crosslinked structure" means: the absence of a crosslinked structure intentionally formed by using a crosslinking agent or the like does not mean that a small amount of crosslinked structure which may be unintentionally by-produced in hydrolysis treatment or the like described later is absent.

In the present invention, it is desirable that the easy-beating acrylic fiber have a structure in which a portion having a carboxyl group is present throughout the entire structure of the fiber made of the acrylic polymer and is not uniformly mixed at a molecular level. Specific examples of the above structure include the following structures: the fibrils (so-called fibrils) constituting the acrylic fiber are formed of an aggregate of fibrils having a core-sheath structure in which a carboxyl group is present in the surface layer portion and no carboxyl group is present in the central portion, that is, a core-sheath structure in which a carboxyl group is present in the sheath portion. Here, the presence throughout the fiber as a whole means: the coefficient of variation CV of the content of magnesium element in the fiber cross section measured by the measurement method described later is 50% or less. The coefficient of variation CV is preferably 40% or less, more preferably 30% or less.

When the carboxyl groups are present unevenly or uniformly on a molecular level in the fiber structure, sufficient beating properties may not be obtained. In a structure in which the portions having carboxyl groups are present throughout the entire fiber and are not uniformly mixed at a molecular level, the portions having carboxyl groups swell with water and are easily torn, and thus fibrillation by beating becomes easy.

Further, the surface of each of the beaten fibrils is rich in carboxyl groups, and therefore hydrophilicity and water diffusibility are increased, and particle capturing property, adhesiveness, ion exchange property, and the like are easily exhibited. On the other hand, since the interior of each fibril is composed of an acrylonitrile polymer, it is less likely to shrink and contributes to form stability.

In addition, in order to further improve the beating properties of the easy-beating acrylic fiber, the counter ion of the carboxyl group is preferably a cation other than a hydrogen ion. More specifically, the proportion of the counter ion that is a cation other than the hydrogen ion, 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 the cation 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, NH₄And cations such as amines, and a plurality of cations may be present in combination. Among them, Li, Na, K, Mg, Ca, Zn and the like are suitable.

The easy-beating acrylic fiber of the present invention has a hydrophilic component in the fiber. The hydrophilic component is in a phase-separated state from the acrylonitrile polymer in the fiber, and easily forms a void, thereby contributing to improvement of beating properties. The content of the hydrophilic component is preferably 0.5 to 10.0% by weight, more preferably 1.0 to 5.0% by weight, based on the weight of the acrylonitrile polymer used as a raw material. If the content of the hydrophilic component is less than 0.5% by weight, the above-mentioned effect of improving beating properties may not be obtained, and if it exceeds 10.0% by weight, there may be a case where troubles such as frequent breakage of the fiber in the spinning step and deterioration of workability occur in the production of the fiber.

The hydrophilic component is not particularly limited, and examples of the organic material include: an organic polymer compound having a hydrophilic side chain such as a polyalkylene oxide chain, a polyether amide chain or a polyether ester chain, and a hydrophilic functional group such as a carboxyl group. In addition, as the inorganic material, metal oxide particles such as titanium oxide and tin oxide, carbon black having a hydrophilic group such as a hydroxyl group and a carboxyl group, carbon fine particles such as graphite, and the like can be used.

Among the hydrophilic components, particularly useful are acrylonitrile-based hydrophilic resins obtained by the following method: a method of copolymerizing the vinyl monomer having the above-mentioned hydrophilic chain with acrylonitrile (hereinafter referred to as method [ 1 "); a method in which a vinyl monomer having a reactive functional group is copolymerized with acrylonitrile and then subjected to a graft reaction with a reactive compound having a hydrophilic functional group (hereinafter referred to as method [ 2 ]).

The acrylonitrile-based hydrophilic resin is preferably bound to acrylonitrile in an amount of 10 to 70 wt%, more preferably 15 to 50 wt%, and still more preferably 15 to 30 wt%. When the content of acrylonitrile is in the range of 10 to 70% by weight, the acrylonitrile-based polymer may have a certain degree of affinity. That is, micropores are formed at the boundary between the acrylonitrile polymer and the acrylonitrile hydrophilic resin, and a structure in which each micropore is connected can be obtained. If the content is less than the lower limit of the above range, the affinity of the hydrophilic resin for the acrylonitrile polymer is too low, and the compatibility is high. Therefore, when the dispersed hydrophilic resin is aggregated, the hydrophilic resin area in the fiber is increased, and the fiber is frequently broken in the spinning step, thereby deteriorating the workability. In addition, it can be considered that: when the content exceeds the upper limit of the above range, the compatibility with the acrylonitrile polymer becomes too high, and sufficient beating properties cannot be obtained.

In the above-mentioned method [ 1], it is preferable to use the monomer represented by the above-mentioned chemical formula 1 as the vinyl monomer having a hydrophilic side chain from the viewpoint of further improving the affinity of the obtained hydrophilic resin with the acrylonitrile-based polymer. The bonding content of the monomer is preferably 30 to 90% by weight, more preferably 50 to 85% by weight, and further preferably 70 to 85% by weight, based on the weight of the copolymer obtained. In the chemical formula 1, the lower alkyl group means a group having 5 or less carbon atoms, and further 3 or less carbon atoms in practical use. In addition, when copolymerization with acrylonitrile is carried out, other vinyl compounds may be copolymerized in addition to the above vinyl monomers.

Suitable examples of the vinyl monomer having a hydrophilic side chain include a reaction product of 2-methacryloyloxyethyl isocyanate and polyethylene glycol monomethyl ether, and suitable examples of the monomer represented by chemical formula 1 include methoxypolyethylene glycol (30 mol) methacrylate, methoxypolyethylene glycol (30 mol) acrylate, polyethylene glycol-2, 4, 6-tri-1-phenylethylphenyl ether methacrylate (number average molecular weight of about 1600), and the like.

Further, suitable examples of the vinyl monomer having a reactive functional group used in the above-mentioned method [ 2 ] include 2-hydroxyethyl methacrylate, acrylic acid, methacrylic acid, N-hydroxymethylacrylamide, N-dimethylaminoethyl methacrylate, glycidyl methacrylate, and 2-methacryloyloxyethyl isocyanate, and suitable examples of the reactive compound having a hydrophilic group include polyethylene glycol monomethyl ether and polyethylene glycol monomethacrylate.

The property of the acrylonitrile-based hydrophilic resin of the present invention is desirably as low as possible degree of water swelling. The upper limit is preferably 300g/g or less, more preferably 150g/g or less. If the amount exceeds 300g/g, troubles such as breakage tend to occur in the spinning step. The degree of swelling in water can be adjusted by various methods, for example, by copolymerizing a crosslinkable monomer or changing the size of l or m of the monomer represented by chemical formula 1.

Further, the acrylonitrile-based hydrophilic resin is soluble in water and a solvent for the acrylonitrile-based polymer, but it is preferable that the acrylonitrile-based hydrophilic resin has a property of being insoluble in water and a solvent for the acrylonitrile-based polymer and stably dispersing in the solvent. When the acrylic fiber is insoluble in water and a solvent for an acrylic polymer, the dissolution of the acrylic hydrophilic resin from the fiber is suppressed in the spinning step, and therefore, the beating property of the finally obtained acrylic fiber can be effectively improved. Further, the stable dispersion of such properties suppresses troubles such as nozzle clogging and breakage in the spinning step, and thus contributes to stable spinning.

As a method for synthesizing the above-mentioned acrylonitrile-based hydrophilic resin, a known polymerization method can be used as in the case of the acrylonitrile-based polymer, and in some cases, a graft reaction can be used for introducing the hydrophilic component as described above.

The easy-beating acrylic fiber of the present invention has a structure comprising an aggregate of fibrils having a core-sheath structure with a carboxyl group at the sheath portion, and has a structure in which an acrylic polymer and a hydrophilic component are in a phase-separated state. In the easy-beating acrylic fiber of the present invention having the above-described structure, the portion having the carboxyl group swells with water and is easily torn, and the portion having the phase separation portion formed of the hydrophilic component is easily beaten, so that the fibrillation can be remarkably performed with a shear force smaller than that of the conventional fibers. That is, by adding the effects of the 2 structures, finer fibrillation can be achieved, the beating speed is excellent, and low drainage is easily achieved. The above-described characteristics cannot be obtained by any of the 2 structures described above, and the effects of these structures are obtained as a result of synergistic effects.

The pulp-like acrylic fiber of the present invention is obtained by beating the above easily beatable acrylic fiber. The pulp-like acrylic fiber preferably has a drainage degree of 600ml or less, more preferably 400ml or less, and further preferably 200ml or less. When the drainage degree exceeds 600ml, the adhesiveness, particle-capturing property, and the like may not be exhibited remarkably. Further, since the easy-beating acrylic fiber of the present invention is excellent in beating speed, beating can be performed in a shorter time than in the conventional art, and further, a pulp-like acrylic fiber having a low drainage degree of 200ml or less, which has been difficult to achieve in the conventional art, can be easily obtained.

The pulp-like acrylic fiber of the present invention has functions such as ion exchange property derived from carboxyl groups, hygroscopicity, deodorization, and antiviral property, in addition to the binding property, particle capturing property, and reinforcing material function, and therefore can be used alone or in combination with other materials as a useful structure in various applications. In this structure, from the viewpoint of obtaining the effect of the pulp-like acrylic fiber of the present invention, it is desirable that the content of the pulp-like acrylic 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.

The appearance of the structure may be a paper-like material, a sheet-like material, a laminate, a spherical or cylindrical molded article, or the like. The pulp-like acrylic fiber of the present invention contained in the structure may be distributed substantially uniformly by mixing with other fibers, resin compositions, and other materials, and may have a structure of a plurality of layers, such as a form of being concentrated in an arbitrary layer (which may be singular or plural), a form of being distributed at a specific ratio in each layer, and the like.

Examples of applications of the structure of the present invention include functional paper products such as diffusion layers, absorption layers, filters such as activated carbon support sheets, water purification filters, deodorizing filters, and filters for filtration in sanitary goods such as diapers, urine absorbent pads, and sanitary napkins, friction materials such as carbon sheets for fuel cell diffusion membranes, clutch linings, and brake pads, functional paper products such as deodorizing wallpaper, moisture absorbing wallpaper, permeable paper, latent heat exchange sheets, and battery members such as separators and electrode reinforcements.

In the above-described applications, the properties of the pulp-like acrylic fiber of the present invention can be effectively utilized. For example, in the use of a diffusion layer in a sanitary material product, the diffusibility of urine or the like can be improved by the hydrophilicity of fibrils, and in the use of an absorption layer in a sanitary material product, the use of an activated carbon-supported sheet, or the like, a water-absorbent resin or activated carbon particles can be immobilized by utilizing the particle-capturing property.

The method for producing the easy-beating acrylic fiber of the present invention includes the following steps: after a hydrophilic component is added to a spinning dope in which an acrylonitrile polymer is dissolved and spun from a nozzle, undried fibers are obtained through respective steps of coagulation, washing with water, and drawing, and the undried fibers are hydrolyzed. The pulp-like acrylic fiber of the present invention can be produced by beating the fiber. The above-mentioned production method will be described in detail below.

First, the acrylonitrile polymer which is a raw material of the easy-beating acrylonitrile-based fiber preferably contains 40% by weight or more, more preferably 50% by weight or more, and further preferably 85% by weight or more of acrylonitrile as a polymerization composition. Therefore, as the acrylonitrile polymer, in addition to acrylonitrile homopolymer, a copolymer of acrylonitrile and another monomer may be used. The other monomers in the copolymer are not particularly limited, and examples thereof include vinyl halides and vinylidene halides; carboxyl group-containing monomers such as acrylic acid and methacrylic acid, and salts and ester derivatives thereof; sulfonic acid group-containing monomers such as methacrylic sulfonic acid and p-styrenesulfonic acid and salts thereof, acrylamide, styrene, vinyl acetate, and the like.

Next, the above-mentioned acrylonitrile polymer and hydrophilic component are used to fiberize by wet spinning, but the case of using an inorganic salt such as sodium thiocyanate as a solvent will be described below. First, the above-mentioned acrylonitrile polymer is dissolved in a solvent to prepare a spinning dope. After the hydrophilic component is added to the spinning dope and spun from a nozzle, the undried fiber (hereinafter also referred to as gel-like acrylic fiber) is subjected to respective steps of coagulation, washing with water and drawing, whereby the water content of the undried fiber (hereinafter also referred to as gel-like acrylic fiber) is 20 to 250 wt%, preferably 25 to 130 wt%, more preferably 30 to 100 wt%.

Here, although there are voids in the gel-like acrylic fiber, since the voids are small when the moisture content of the fiber is less than 20% by weight, the reagent in the hydrolysis treatment described later may not penetrate into the fiber, and the carboxyl group may not be formed throughout the entire fiber. When the amount exceeds 250% by weight, the fiber contains a large amount of water therein and the fiber strength becomes too low, so that the spinnability is undesirably reduced. When the fiber strength is further emphasized, it is desirable that the content is in the range of 25 to 130 wt%. Further, there are various methods for controlling the water content of the gel-like acrylic fiber within the above range, but for example, it is preferable that the coagulation bath temperature is-3 to 15 ℃, preferably-3 to 10 ℃, and the draw ratio is 5 to 20, preferably 7 to 15.

Then, the gel-like acrylic fiber is subjected to hydrolysis treatment. By this treatment, nitrile groups in the gel-like acrylic fiber are hydrolyzed to generate carboxyl groups.

Examples of the hydrolysis treatment include a method of heating the solution in a state of being impregnated or impregnated with an alkaline aqueous solution such as an alkali metal hydroxide, an alkali metal carbonate, or ammonia, or an aqueous solution such as nitric acid, sulfuric acid, or hydrochloric acid. The specific treatment conditions may be appropriately set in consideration of the above-mentioned range of the amount of carboxyl groups and other conditions such as the concentration of the treatment agent, the reaction temperature, and the reaction time, and it is also preferable from the industrial and physical properties of the fiber that the treatment agent is impregnated with the treatment agent in an amount of usually 0.5 to 20% by weight, preferably 1.0 to 15% by weight, and then the extruded treatment agent is treated at a temperature of 105 to 140 ℃, preferably 110 to 135 ℃ for 10 to 60 minutes in a hot and humid atmosphere. When the temperature is lower than 105 ℃, the coloration of the fiber may be intensified. The hot and humid atmosphere is an atmosphere filled with saturated steam or superheated steam.

In the fibers subjected to the hydrolysis treatment as described above, salt-type carboxyl groups having cations such as alkali metals and ammonium as counter ions are generated depending on the types of alkali metal hydroxides, alkali metal carbonates, ammonia, and the like used in the hydrolysis treatment, but treatment for converting the counter ions of the carboxyl groups may be performed subsequently as necessary. When an ion exchange treatment is performed with an aqueous solution of a metal salt such as nitrate, sulfate, or hydrochloride, a salt-type carboxyl group can be produced with a desired metal ion as a counter ion. Further, by adjusting the pH of the aqueous solution and the concentration/kind of the metal salt, different counter ions can be mixed and present or the ratio thereof can be adjusted.

The easy-beating acrylic fiber of the present invention, which is the fiber having introduced carboxyl groups obtained as described above, can be obtained. The pulp-like acrylic fiber of the present invention can be obtained by beating the above-mentioned fibers. The method of the beating process is not particularly limited, and a beater such as a beater (ビータ) or a refiner can be used.

The acrylic fiber of the present invention can be obtained as described above, but the production of easy-beating acrylic fiber can be continuously carried out by following the existing continuous production facilities for acrylic fiber. In the above method, an inorganic salt such as sodium thiocyanate is used as a solvent, but the same conditions apply when an organic solvent is used. Among these, since the type of the solvent is different, the temperature suitable for the solvent is selected for the coagulation bath temperature, and the water content of the gel-like acrylic fiber is controlled within the above range.

In the above-described production method, since the gel-like acrylic fiber having a void structure is subjected to hydrolysis treatment, it is considered that the agent penetrates deep into the fiber along the void and hydrolyzes not sequentially from the fiber surface but from the entire fiber. Further, since the acrylic fiber is usually present as an assembly of microfibrils when viewed microscopically, it is estimated that: the reagent penetrates between fibrils, and the unhydrolyzed acrylonitrile polymer remains inside the fibrils as hydrolysis proceeds from the surface of the fibrils. That is, a structure in which the carboxyl group-containing portion exists over the entire fiber and is not uniformly mixed at a molecular level is realized, and fibrillation is easily realized with the carboxyl group-containing portion as a boundary. Further, it can be presumed that: after beating, the particle trapping property is improved by the carboxyl groups on the surface of each fibril, and the acrylonitrile polymer remaining inside exhibits low heat shrinkage.

In the above-described production method, when the gel-like acrylic fiber, that is, the undried fiber after drawing is not used and the dried acrylic fiber is subjected to the hydrolysis treatment, the reagents do not penetrate into the deep inside of the fiber and are sequentially hydrolyzed from the fiber surface, and therefore, a structure in which the surface layer portion of the fiber has a large number of carboxyl groups and the inside of the fiber has a small number of carboxyl groups can be induced. In such a structure, the beating property is remarkably deteriorated.

[ examples ]

The embodiments are described below to facilitate understanding of the present invention, but these are merely examples, and the gist of the present invention is not limited to these. In the examples, parts and percentages are on a weight basis unless otherwise specified. The measurement of each characteristic was performed by the following method.

< distribution of carboxyl groups in fiber Structure >

The sample before beating was immersed in an aqueous solution containing magnesium nitrate in an amount 2 times the amount of carboxyl groups contained in the sample at 50 ℃ for 1 hour to carry out ion exchange treatment, and then washed with water and dried, thereby converting the counter ions of the carboxyl groups to magnesium. For the sample prepared as the magnesium salt type, the content ratio of magnesium element was measured by using an energy dispersive X-ray spectrometer (EDS) when 10 measurement points were selected at substantially equal intervals from the outer edge to the center of the fiber cross section. Based on the obtained values of the respective measurement points, the coefficient of variation CV [% ] was calculated according to the following formula.

Coefficient of variation CV [% ] [ (standard deviation/average value) × 100 [% ]

< amount of carboxyl group >

About 1g of the sample before beating was weighed, immersed in 50ml of 1mol/l hydrochloric acid for 30 minutes, and then washed with water and mixed at a bath ratio of 1: 500 was immersed in pure water for 15 minutes. The washing with water was carried out until the bath pH became 4 or more, and then drying was carried out in a hot air dryer at 105 ℃ for 5 hours. About 0.2g (W1 g) of the dried sample was precisely weighed, and 100ml of water and 15ml of 0.1mol/l sodium hydroxide and 0.4g of sodium chloride were added thereto and stirred. The sample was then filtered using wire mesh and washed with water. 2 to 3 drops of phenolphthalein solution were added to the obtained filtrate (including water washing solution), and the solution was titrated with 0.1mol/l hydrochloric acid by a conventional method to determine the amount of hydrochloric acid consumed (V1[ ml ]), and the total carboxyl group amount was calculated according to the following formula.

Total carboxyl group amount [ mmol/g ] ═ 0.1 × 15-0.1 × V1/W1

< degree of neutralization >

The sample before beating was dried at 105 ℃ for 5 hours in a hot air dryer, about 0.2g (W2 g) was accurately weighed, and 100ml of water and 15ml of 0.1mol/l sodium hydroxide and 0.4g of sodium chloride were added thereto and stirred. The sample was then filtered using wire mesh and washed with water. 2 to 3 drops of phenolphthalein solution were added to the obtained filtrate (including water washing solution), and the solution was titrated with 0.1mol/l hydrochloric acid by a conventional method to determine the amount of hydrochloric acid consumed (V2[ ml ]). The amount of H-type carboxyl groups contained in the sample was calculated from the following formula, and the degree of neutralization was determined based on the result and the total amount of carboxyl groups described above.

Amount of H-type carboxyl group [ mmol/g ] ═ (0.1 × 15-0.1 × V2)/W2

Degree of neutralization [% ] [ (total amount of carboxyl groups-amount of H-type carboxyl groups)/total amount of carboxyl groups ] × 100

< drainage Capacity (CSF) >

According to JIS P8121-2: 2012 pulp-drainage test method-part 2: canadian standard freeness method. The drainage degree of 20 or less was used as a reference value, and the drainage amount was not corrected, and the drainage degree value was used as it is.

< paper power (sticky) >

An aqueous slurry was prepared at a weight ratio of 30/79 pulp-like acrylic fiber/acrylic short fiber (fineness: 0.4dtex, fiber length: 3.0mm), and a mass per unit area of 50g/m was obtained using a paper making machine manufactured by bear grain processor co²The paper was made by a hot calender to prepare a paper for evaluation. The obtained paper was cut into a size of 2cm (W). times.10 cm (L), and a tensile tester (A) was used&RTA500(U-1573) manufactured by D Company, Limited, was measured for the breaking strength at a drawing speed of 2 cm/min. The greater the breaking strength, the more excellent the adhesiveness was judged.

< amount of activated carbon captured >

1g of pulp-like acrylic fiber in terms of solid content was added to 1L of pure water and stirred. 6g of powdered activated carbon (Brocol B-labeled activated carbon manufactured by Taiping chemical industries, Ltd./average particle diameter: 90 μm) was added thereto and stirred for 30 minutes. Then, a sieve (area 200 cm) with 173 μm mesh openings was used²) The filtrate was filtered, and the weight (A [ g ]) of the filtrate after drying at 105 ℃ for 5 hours was measured]) The amount of active carbon captured per 1g of the sample was calculated by the following equation.

The active carbon trapping amount (g/g) is (A-1)/1

< Water content of gel-like acrylic fiber >

The gel-like acrylic fiber was immersed in pure water, and then dehydrated for 2 minutes by a centrifugal dehydrator (TYPE H-770A manufactured by Nippon Kagaku K.K.) at a centrifugal acceleration of 1100G (G represents a gravitational acceleration). The weight of the undried fiber after dewatering (W3 g) was measured, and the undried fiber was dried at 120 ℃ for 15 minutes and the weight (W4 g) was measured, and the weight was calculated according to the following formula.

The water content (%) of the gel-like acrylic fiber was (W3-W4)/W3X 100

< example 1>

Acrylonitrile-based hydrophilic resin was prepared by suspension polymerization of 27.5 parts by weight of acrylonitrile and 72.5 parts by weight of methoxypolyethylene glycol (30 mol) methacrylate. Next, 10 parts of an acrylonitrile polymer composed of 90% acrylonitrile and 10% methyl acrylate was dissolved in 90 parts of 44% sodium thiocyanate aqueous solution, and 0.3 part of the above-mentioned acrylonitrile hydrophilic resin was added to prepare a spinning dope. The spinning dope was spun into a coagulation bath at-2.5 ℃ and coagulated, washed with water, and drawn by 12 times to obtain a gel-like acrylic fiber having a water content of 35%. The fiber was immersed in a 1.5% aqueous sodium hydroxide solution and extruded, then hydrolyzed at 123 ℃ for 25 minutes in a humid and hot atmosphere, washed with water and dried at 105 ℃ for 1 hour to obtain an easy-beating acrylic fiber of the present invention. The fiber was cut into 3mm pieces to prepare a water slurry having a concentration of 3%, and then the slurry was subjected to beating treatment using a refiner (KRK type manufactured by Fugu processor Co., Ltd.) at the number of passes (パス) shown in Table 1 to obtain a pulp-like acrylic fiber of example 1. The freeness of easy-beating acrylic fiber cut into 3mm was 760 ml.

< examples 2 to 5>

Pulp-like acrylic fibers of examples 2 to 5 of the present invention were obtained in the same manner as in example 1 except that the concentration of the aqueous sodium hydroxide solution was changed to 4.0% and beating was performed at the number of passes described in table 1. Fig. 1 shows an SEM photograph of the pulp-like acrylic fiber of example 3.

< examples 6 to 8>

The easy-beating acrylic fiber of the present invention was obtained in the same manner as in example 1 except that 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. The pulp-like acrylic fibers of examples 6 to 8 were obtained by beating the fibers at the number of passes described in table 1.

< example 9>

Easy-to-pulp acrylic fibers were obtained in the same manner as in example 4, except that a step of adjusting the pH to 3.5 with nitric acid in pure water and holding the mixture at 60 ℃ for 30 minutes was interposed between the hydrolysis step and the water washing step. Further, the pulp-like acrylic fiber of example 9 of the present invention was obtained by beating the fibers in the number of passes shown in Table 1.

< comparative examples 1 to 4>

Acrylonitrile-based hydrophilic resin was prepared by suspension polymerization of 27.5 parts by weight of acrylonitrile and 72.5 parts by weight of methoxypolyethylene glycol (30 mol) methacrylate. Next, 10 parts of an acrylonitrile polymer composed of 90% acrylonitrile and 10% methyl acrylate was dissolved in 90 parts of 44% sodium thiocyanate aqueous solution, and 0.3 part of the above-mentioned acrylonitrile hydrophilic resin was added to prepare a spinning dope. The spinning dope was spun into a coagulation bath at-2.5 ℃ and coagulated, washed with water, and drawn by 12 times to obtain a gel-like acrylic fiber having a water content of 35%. The fiber was subjected to moist heat treatment at 123 ℃ x 25 minutes in a moist heat atmosphere, washed with water, and dried at 105 ℃ x 1 hour to obtain an acrylic fiber containing a hydrophilic resin but not containing a carboxyl group. This fiber was cut into 3mm pieces to prepare a water slurry having a concentration of 3%, and then the fibers were subjected to beating treatment using a refiner (KRK type manufactured by Fugu processor Co., Ltd.) at the number of passes described in Table 1 to obtain pulp-like acrylic fibers of comparative examples 1 to 4. Fig. 2 shows an SEM photograph of the pulp-like acrylic fiber of comparative example 4.

< comparative examples 5 to 7>

10 parts of an acrylonitrile polymer composed of 90% acrylonitrile and 10% methyl acrylate was dissolved in 90 parts of 44% sodium thiocyanate aqueous solution to prepare a spinning dope. The spinning dope was spun into a coagulation bath at-2.5 ℃ and coagulated, washed with water, and drawn by 12 times to obtain a gel-like acrylic fiber having a water content of 35%. This fiber was immersed in a 4.0% aqueous sodium hydroxide solution and extruded, then subjected to hydrolysis treatment at 123 ℃ for 25 minutes in a moist heat atmosphere, washed with water, and then dried at 105 ℃ for 1 hour to obtain an acrylic fiber containing no hydrophilic resin but containing a carboxyl group. This fiber was cut into 3mm pieces to prepare a water slurry having a concentration of 3%, and then the fibers were subjected to beating treatment using a refiner (KRK type manufactured by Fugu processor Co., Ltd.) at the number of passes described in Table 1 to obtain pulp-like acrylic fibers of comparative examples 5 to 7.

The evaluation results of the fibers obtained in the above examples and comparative examples are shown in table 1. In the table, "-" indicates that no measurement was performed.

[ Table 1]

As shown in table 1, it can be seen that: in examples 1 to 8, it is found that the beating speed is high and the paper strength (breaking strength) and activated carbon capturing property of the obtained pulp-like acrylic fiber are excellent from the drainage degree corresponding to the number of passes of the refiner. In example 9 in which the degree of neutralization of example 4 was reduced, the drainage degree was reduced, and the results show that: the higher the degree of neutralization, the faster the beating.

In addition, it is known that: in comparative examples 1 to 4 in which hydrolysis was not performed, as is clear from the drainage degree corresponding to the number of passes of the refiner, the beating speed was slow, and further, the paper strength (breaking strength) and the activated carbon capturing property were low, as compared with examples 2 to 5. Therefore, the following steps are carried out: similarly, the beating speed was slow as seen from the drainage according to the number of passes of the refiner in comparative examples 5 to 7 in which hydrolysis was performed but no hydrophilic resin was contained, as compared with examples 2 to 5.

As is clear from fig. 1, the pulp-like acrylic fiber of example 3 also has excellent beating properties because the fibril surface is smooth. On the other hand, it is known that: the pulp-like acrylonitrile fiber of comparative example 4 shown in FIG. 2 had a distorted fibril surface and thus had poor beating properties, and beating was barely performed by applying a shearing force by repeating the process several times.