JPS6262181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has a multilayer structure of an outer layer of a hydrophilic crosslinked polymer (hereinafter referred to as hydrogel) and an inner layer of an acrylonitrile polymer (hereinafter referred to as AN polymer) and/or another polymer, and has a highly The present invention relates to a method for producing a novel water-swellable fiber having water-swellability and high physical properties. In recent years, highly water-swellable polymers have attracted attention for their special functions and are being applied to a wide range of fields of use. For example, the ability of such polymers to instantly absorb large amounts of water can be used to make diapers, sanitary products, etc., the ability to retain moisture can be used to make soil conditioners, instant sandbags, etc., and the compatibility with human tissue can be used to develop polymers. Attempts have been made to apply it to soft contact lenses, artificial organs, surgical suture materials, etc., and some of these applications have already entered the stage of practical application. It is often preferable for water-swellable polymers (hydrogel), which have a wide range of potential applications, to be in the form of fibers depending on the intended use, and some such fibrous hydrogels are known. . However, although such existing natural or synthetic fibers have a certain degree of water swelling ability, their degree of water swelling is extremely low, or they are water soluble, and in any case, their own weight is low. It can absorb and retain up to several hundred times as much water and is far from the category of water-swellable fibers, which are water-insoluble. Also, special public service 52-42916
The publication describes a highly swellable fibrous structure obtained by introducing a specific crosslinked structure and a large amount of carboxyl groups in the form of salt into acrylic fibers. However, in such fibrous structures, extremely large amounts of carboxyl groups in the form of salts are introduced, and the entire inner and outer layers of the fibers are hydrogel-formed, so they certainly have a high degree of water swelling performance. However, it was extremely brittle and had physical properties far from the concept of fiber. That is,
The reality is that water-swellable fibers with satisfactory performance still do not exist, and imparting high water-swellability and maintaining fiber physical properties are contradictory issues. As a result of intensive studies to overcome the above-mentioned essential difficulties and provide a high degree of water swelling while retaining the physical properties of the fiber, the inventors of the present invention have discovered fibers made of AN-based polymers (hereinafter referred to as AN-based fibers). )
By applying a specific alkali metal hydroxide aqueous solution to selectively hydrophilically crosslink (hydrogel) only the outer layer of the fiber, water swelling performance is advantageously imparted without impairing the physical properties of the fiber. We have discovered the fact that this is possible, and have arrived at the present invention. That is, an object of the present invention is to provide a novel method for producing water-swellable fibers that have both high water-swellability and high physical properties. The water-swellable fiber according to the present invention to achieve the above purpose is an AN-based fiber containing 6.0 mol/1000 g.
The outer layer of the fiber is treated with a high concentration alkali metal hydroxide aqueous solution at a concentration higher than the solution or a low concentration alkali metal hydroxide aqueous solution coexisting with an electrolyte salt at a concentration higher than 0.5 mol/1000 g solution for less than 40 minutes. -COOX (X:
A fiber into which 0.5 to 4.0 mmol/g of a salt-type carboxyl group represented by an alkali metal or NH ₄ ) is introduced, and is composed of an outer layer made of hydrogel and an inner layer made of AN polymer and/or other polymers. It can be advantageously manufactured by forming it in the following manner. Therefore, the AN-based polymer according to the present invention is a general term for polymers containing AN as a copolymer component,
AN homopolymer or a copolymer of AN and one or more other ethylenically unsaturated compounds, or
AN and other polymers, such as starch, graft copolymers such as polyvinyl alcohol, AN polymers and other polymers, such as polyvinyl chloride, polyamide, polyolefin, polystyrene, polyvinyl alcohol, and cellulose. Examples include mixed polymers with the like. The content of AN in such an AN-based polymer is desirably 30% by weight or more, preferably 50% or more, and fibers made of a polymer with an AN content less than this recommended range are used as the starting material. In some cases, the alkaline hydrolysis treatment may not make the fiber sufficiently hydrophilic, or even if it can be made hydrophilic, it is difficult to form water-swellable fibers, which is not preferred. In addition, there are no particular restrictions on the polymer composition, such as the type of the ethylenically unsaturated compound that is the copolymerization component of the AN polymer or the molecular weight of the polymer, and the required performance of the final product and the monomer It can be arbitrarily selected depending on the copolymerizability and the like. Furthermore, regarding methods for producing these polymers and methods for forming fibers from the polymers,
Any method can be selected from known methods (for example, single-component spinning, sheath-single-core composite spinning, etc.). In other words, the AN-based fiber employed in the present invention is industrially preferably a fiber consisting of a single component of the above-mentioned AN-based polymer. The polymer may be used as a sheath component and an AN-based polymer that is difficult to hydrolyze as a core component, or the AN-based polymer may be used as a sheath component and another polymer (such as the above-mentioned polyamide-based, polyolefin-based, etc.) may be used as a core component. Examples include sheath-core type spun fibers such as the above. Note that as long as at least a part of the AN-based polymer has a cross-sectional structure exposed on the fiber surface, it can be used as the AN-based fiber, which is the starting material of the present invention. It does not deviate from the gist of the present invention to use special spun fibers such as composite spun fibers, sea-island type composite fibers, two-component bonded type composite fibers, or sand-Germany type composite fibers as starting materials. . The fibers produced in this way can be in any form such as short fibers, long fibers, fiber tows, threads, knitted fabrics, non-woven fabrics, etc., and can be subjected to subsequent hydrolysis treatment. It goes without saying that waste fibers produced in the process or intermediate products of the fiber manufacturing process (for example, fibers after hot drawing) can be used as the starting material. In order to obtain water-swellable fibers having high water-swellability and high physical properties using such AN-based fibers as a starting material, only the outer layer of the AN-based fibers is selectively hydrogelated, and the outer layer of the hydrogel and the AN-based polymer are combined. It is necessary to form a fiber having a multilayer structure with and/or other polymer inner layers. The degree of water swelling of the fiber having a two-layer structure or a multi-layer structure produced in this way is required to be within the range of 3 to 300 c.c./g, more preferably 5 to 200 c.c./g, In addition, in order to have such water swelling degree and maintain sufficient fiber physical properties, the proportion of the hydrogel outer layer is 55% or less, more preferably 5 to 40%, based on the total volume of the fiber when dry.
It is desirable to control the temperature within the range of . If the proportion of the hydrogel exceeds the upper limit of the recommended range of the present invention, sufficient fiber properties will not be maintained, and if it exceeds the lower limit of the preferred range, sufficient water swelling performance will not be exhibited. -COOX (X: alkali metal or
The amount of salt-type carboxyl group represented by NH ₄ ) is 0.5~
4.0mmol/g, more preferably 0.5-3.5mmol/g
It is necessary to adjust it within the range of . If the amount of the salt-type carboxyl group is outside the lower limit of the recommended range of the present invention, the water swelling performance will be insufficient, and if it exceeds the upper limit of the range, the physical properties of the fiber will deteriorate and the fiber will become brittle with poor flexibility. This is not desirable. The salt-type carboxyl group may be any one of alkali metals such as Li, K, and Na, or _NH4 , or a mixed salt of two or more thereof. Next, the method for hydrolyzing AN-based fibers will be described in detail. As long as water-swellable fibers consisting of an outer layer of hydrogel and an inner layer of AN-based polymer etc. can be finally obtained, there are no restrictions on the hydrolysis method;
In the present invention, as a one-step hydrolysis and crosslinking treatment method that selectively hydrogelizes only the outer layer of AN fibers and can easily control the ratio of the outer layer, the following method was adopted in the present invention. That is, the AN-based fiber is treated with a highly concentrated alkali metal hydroxide aqueous solution of 6.0 mol/1000 g or more (hereinafter referred to as method A), or
One of the methods (hereinafter abbreviated as method B) was adopted in which a low concentration alkali metal hydroxide aqueous solution coexisting with an electrolyte salt having a concentration of 0.5 mol/1000 g or more was applied. In addition, when employing the above method A, if an alkaline aqueous solution with a concentration of less than 6.0 mol/1000 g solution is applied, the AN-based fibers will be made hydrophilic by the hydrolysis reaction but will become water-soluble, which will not achieve the purpose of the present invention. It is not possible to form an outer hydrogel layer that is similar to the above. Also, from 6.25
8.85mol/1000g solution, further 6.25~8.50mol/1000
The present invention can be more effectively achieved by using an alkaline aqueous solution in the concentration range of g solution. Under conditions exceeding the upper limit of this preferred range, the activity of the alkali metal hydroxide decreases, requiring high-temperature treatment to increase the reaction rate, and making it difficult to remove residual alkali, which is not practical. do not have. In addition, when adopting method B, the amount of salt to coexist is 0.5 mol/1000 g.
When the concentration is low, below that of the solution, the AN-based fiber becomes hydrophilic through a hydrolysis reaction, but most of it becomes water-soluble, and the outer layer of the hydrogel can be formed in a single step using a low-concentration alkaline aqueous solution. I can't. Also, use an alkaline aqueous solution having a salt concentration of 1.0 mol/1000 g solution or more, or the salt concentration and an alkali metal hydroxide concentration of 0.25 to 6.0 mol/1000 g solution, more preferably 0.5 to 5.0 mol/1000 g solution. Accordingly, the present invention can be implemented more industrially advantageously. The method A is described in more detail in Japanese Patent Application No. 158423/1983 filed by the present applicant. Here, examples of the alkali metal hydroxide used in the present invention include hydroxides of alkali metals such as Na, K, and Li, and mixtures thereof; and examples of electrolyte salts include alkali metal hydroxides such as Na, K, and Li. Any salt can be used as long as it is stable under the processing conditions, and the cationic component constituting the salt is, for example, an alkali metal such as Na, K, Li;
Alkaline earth metals such as Be, Mg, Ca, Ba;
Other metals such as Cu, Zn, Al, Mn, Fe, Co, Ni; _NH4 , etc., and anionic components such as hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, chromic acid, dichromic acid, chloric acid, One or two types of salts composed of acid groups such as chlorous acid, organic carboxylic acid, organic sulfonic acid, etc.
Mention may be made of mixtures of more than one species. In addition, when using electrolyte salts in which the above-mentioned cationic component is an element with a valence of 2 or more, the outer layer of the generated hydrogel tends to aggregate and coalesce, and the degree of swelling decreases.
It is preferable to use salts containing alkali metals or NH ₄ as the cationic component. Furthermore, as a solvent in place of water, methanol, ethanol, propanol, 2
- An aqueous mixed solvent of water and a water-miscible organic solvent such as methoxyethanol, 2-ethoxyethanol, dimethylformamide, dimethylsulfoxide, etc. can be used, and if necessary, other inorganic substances or organic substances can be used. It is also possible to coexist. Here, although the alkaline hydrolysis treatment under the conditions of the known technology actually produces only a water-soluble polymer, the specific conditions of the above-mentioned method A or B recommended for the present invention are adopted. By this,
Hydrogels are produced in a single step and in high yields, which are significantly different from the results expected from reactions under known conditions. As for the mechanism of action, side reactions that form intermolecular cross-links or intramolecular cyclic structures, etc. accompanying the hydrolysis reaction of the nitrile groups in the outer layer of the fibers are unique under the above-mentioned specific conditions. This can be explained by the gradual progression of the disease, but the details have not yet been elucidated. In addition, as for the reaction conditions such as temperature conditions and treatment time when the aqueous alkali solution as mentioned above is applied, the preferable range of conditions varies depending on the form of the polymer, the fine structure of the polymer such as crystallinity, the alkali concentration, etc. Although it is impossible to define unequivocally, in general, the reaction rate increases as the reaction temperature increases and treatment effects can be advantageously achieved, so it is preferable to
The present invention can be effectively carried out by using a temperature condition of 50°C or higher, more preferably 80°C or higher. In addition, there is no strict limit on the amount of alkaline aqueous solution applied to AN fibers, but
It is desirable to use at least 3 parts by weight, preferably 4 parts by weight or more of the aqueous solution per 1 part by weight of the fibers, and under such conditions, the contact between the fibers and the aqueous solution is facilitated, and the hydrophilization reaction of the present invention is facilitated. In addition, the crosslinking reaction can proceed effectively. Furthermore, as a method for applying an alkaline aqueous solution to AN fibers, short fibers cut to a desired fiber length are suspended in an aqueous solution, and then cut into a shearing device such as a screw type stirring device, mixer, or a kneader. A method of stirring or kneading using a kneading device etc.
A method in which continuous fibers such as long fibers, fiber tows, threads, knitted fabrics, non-woven fabrics, etc. are run under tension or under no tension in the aqueous solution, or the short fibers, long fibers, etc. are filled in a mesh container. A wide range of known heterogeneous treatment methods can be selected, such as a method of shaking the mixture in an aqueous solution. As mentioned above, when an aqueous alkaline solution is applied to AN-based fibers to produce a fiber having a multilayer structure of an outer hydrogel layer and an inner layer of AN-based polymer and/or other polymers, the final product obtained is It is important to control the volume ratio and/or the amount of salt-type carboxyl groups (-COOX) in the outer layer of the hydrogel, which have a particularly close relationship with the water swelling degree and physical properties of the fiber. The volume ratio and/or the outer layer of the hydrogel
Alternatively, as a means of controlling the amount of salt-type carboxyl groups, the type of AN fiber to be treated, ie, composition, crystallinity, single fiber fineness, etc., or the hydrolysis treatment conditions, ie, the use of alkali metal hydroxide and/or electrolyte salts, etc. It is possible to vary the concentration, the temperature during hydrolysis, the amount of alkaline aqueous solution treated with the fibers to be treated, the treatment time, etc., and it is difficult to define it unambiguously, but the hydrolysis treatment conditions, In particular, the object of the present invention can be easily achieved by adjusting the treatment time to less than 40 minutes, preferably within the range of 2 to 30 minutes. If a fiber consisting of a single AN polymer component is hydrolyzed for a long period of time exceeding the recommended range of the present invention, the AN polymer layer may disappear completely or the inner layer may remain. Even if it does, it is not desirable because the amount is small or the boundary between the outer layer and the inner layer becomes unclear, making it impossible to obtain water-swellable fibers with satisfactory physical properties. After removing the alkali metal hydroxide remaining in the thus obtained water-swellable fiber by washing with water or the like, if necessary, the salt-type carboxyl group is converted to an alkali metal or ammonium salt by a known method. etc., and then, if desired, subjected to a drying treatment to form a dry product. As a result, water-swellable fibers composed of an outer hydrogel layer and an inner layer of AN polymer and/or other polymers can be obtained, and surprisingly, the fibers have a
It has a water swelling degree of 300 c.c./g, preferably 5 to 200 c.c./g, and its physical properties such as wet and dry strength, wet and dry elongation, and knot strength are almost inferior to ordinary AN-based fibers for clothing. (e.g. dry strength 2.0)
g/d or higher and wet strength of 1.5 g/d or higher). Furthermore, since the fiber has an inner layer made of an AN-based polymer or the like, it also has the unique property of not undergoing dimensional change in the length direction even in a swollen state. In this way, there is no need to use fibers made of polymers with special compositions containing crosslinking monomers etc. as copolymerization components, and it is possible to use ordinary AN-based fibers or the waste discharged from the AN-based fiber manufacturing process. Using fibers as a starting material, fibers with high water swelling performance and excellent physical properties can be obtained by a one-step treatment process with an alkaline aqueous solution, and furthermore, by adjusting the hydrolysis treatment conditions, the water content of the resulting fibers can be reduced. A notable advantage of the present invention is that the degree of swelling and physical properties can be easily controlled. Another major feature of the present invention is that such water-swellable fibers have excellent physical properties such as strength, elongation, flexibility, and stiffness, and can be handled in exactly the same way as existing clothing fibers. It is. The water-swellable fiber of the present invention, which has such high water-swellability and excellent physical properties, can be used alone or blended with existing natural, semi-synthetic or synthetic fibers, etc.
By mixing paper, it has outstanding hygroscopicity, water absorption,
New fiber materials or textile products with water retention properties can be used in diapers, sanitary products, filter paper, etc., or as dehydration materials from organic solvents that are immiscible with water, sealing materials, cation exchange fibers, etc., as well as existing hydrogels. Like powder and granules, it can be applied to instant sandbags, artificial soil, water drains, heat and cold insulation materials, etc. In order to further facilitate understanding of the present invention, Examples are described below, but the gist of the present invention is not limited in any way by the description of these Examples.
It should be noted that all percentages and parts described in the Examples are based on weight unless otherwise specified. The degree of water swelling, the amount of salt-type carboxyl group (-COOX), and the volume ratio of the outer layer of the hydrogel described in the following examples were measured or calculated by the following method. (1) Degree of water swelling (cc/g) Approximately 0.1 g of sample fiber was immersed in pure water, kept at 25℃ for 24 hours, wrapped in nylon filter cloth (200 mesh), and placed in a centrifugal dehydrator (3G x 30 minutes). However, G is gravitational acceleration) to remove water between the fibers. Measure the weight of the sample prepared in this way (W ₁ g). The sample is then dried in a vacuum dryer at 80° C. to a constant weight and weighed (W ₂ g). From the above measurement results, it was calculated using the following formula. Therefore, the actual water swelling degree is a numerical value indicating how many times the weight of the fiber can absorb and retain water. (Water swelling degree) = W ₁ - W ₂ /W ₂ (2) -COOX group amount (mmol/g) Approximately 1 g of a sufficiently dried sample was accurately weighed (Xg), and 200 ml of water was added to it. While heating to 50℃, add 1N hydrochloric acid aqueous solution to adjust the pH to 2, then
A titration curve was determined using a 0.1N caustic soda aqueous solution according to a conventional method. The amount of caustic soda aqueous solution consumed by carboxyl groups (Yc.c.) was determined from the titration curve. From the above measurement results, it was calculated using the following formula. (-COOX group amount)=0.1Y/X In addition, when polyvalent cations are included, it is necessary to determine the amount of these cations by a conventional method and correct the above formula. (3) Volume ratio of the outer layer of the hydrogel (V:%) 20 water-swollen samples were magnified 100 to 1000 times (Z times) and micrographs were taken. The average value (l ₁ mm) of the measured diameter of the inner layer of the polymer was calculated using the following formula. V={1-(1000l ₁ /Zl) ² }×100 where l: Diameter of treated AN-based fiber (μ) Example 1 AN-based material consisting of 90% AN and 10% methyl acrylate (MA) 4 parts of fiber (single fiber fineness: 3d, fiber length: 50 mm, intrinsic viscosity in dimethylformamide (DMF) solution at 30°C: 1.3) at 30%
(7.5mol/1000g solution) A water-swellable fiber that is immersed in 96 parts of a caustic soda aqueous solution, boiled for 10 minutes while stirring, then washed to remove the residual alkali in the fiber, and then dried to give a white to slightly yellow color. Formed in (). The obtained fibers () do not dissolve in water,
Contains 2.8 mmol/g of -COONa groups and also contains 174
It was confirmed that it had a water swelling degree of cc/g. In addition, the results of measuring the physical properties of the fiber () and the volume ratio of the outer layer of the hydrogel () were
The physical properties of the AN-based fibers are listed in Table 1.

[Table] As is clear from the results in Table 1, the water-swellable fiber according to the present invention has both strength and elongation at reference values (treated
It can be seen that it maintains a level that is almost comparable to AN-based fibers). On the other hand, as a comparative example, treatment was performed according to the above recipe except that 10% (2.5 mol/1000 g solution) and 23% (5.75 mol/1000 g solution) caustic soda aqueous solutions were used.
AN-based fibers only dissolve in an aqueous solution to form a viscous solution, and when such a low-concentration aqueous solution of caustic soda alone is used, it is not possible to form them into the water-swellable fibers that are the object of the present invention. Ta. Also, 35% of caustic potash can be used instead of the above-mentioned caustic soda.
% (6.25 mol/1000 g solution) was treated according to the above recipe except that an aqueous solution was used, and as expected, fibers were obtained which were white to slightly yellow in color and were substantially water-insoluble and water-swellable. Example 2 5 parts of AN fiber (single fiber fineness: 6d, fiber length: 65 mm, intrinsic viscosity in DMF solution at 30°C: 1.3) consisting of 90% AN and 10% MA was mixed with 20% (3.45 mol/
10% (2.5 mol/
1000g solution) Soaked in 95 parts of caustic soda aqueous solution,
Water-swellable fibers () according to the formulation described in Example 1
was formed. The obtained fibers () do not dissolve in water, and the volume ratio of the outer hydrogel layer () is 25% and
Contains 1.9 mmol/g of -COONa groups and also contains 150
It was confirmed that it had a water swelling degree of cc/g. In addition, in the above method, when only the hydrolysis treatment time was extended to 1 hour, the obtained fiber () was
Contains 8.6 mmol/g of -COONa group, 318 c.c./g
Although it has an extremely high water swelling degree, it is extremely brittle, and when the fiber was squeezed in the water swollen state, it was confirmed that no AN polymer core remained at all. Example 3 In the formulation described in Example 2, sodium nitrate was used instead of 20% common salt, and the concentrations of the salt and caustic soda were varied as shown in Table 2.
The AN-based fibers described were treated. Table 2 also shows the results of measuring the degree of water swelling, the amount of -COONa groups, and the volume ratio () of the outer layer of the hydrogel of the 10 types of water-swellable fibers (XII) obtained.

[Table] From the results in Table 2, when the concentration of salt coexisting in the alkaline aqueous solution is less than the range recommended for the present invention (Sample No. XII), only fibers with a low water swelling degree can be obtained. Furthermore, since the amount of water-soluble polymer produced increased significantly, the yield of the desired water-swellable fiber was as low as about 40%. Further, in sample No., that is, when the alkali concentration was extremely low, fibers having the desired degree of water swelling could not be obtained. Furthermore, it is clear from Sample No. and above that even if the alkali concentration is constant, by changing the salt concentration, it is possible to produce fibers with various degrees of water swelling. Example 4 AN-based fiber consisting of 80% AN and 20% vinyl acetate (single fiber fineness: 15d, fiber length: 50mm, at 30℃
When a DMF solution with an intrinsic viscosity of 1.5) was treated according to the recipe described in Example 1 (however, the treatment time was 6 minutes), it exhibited a white to slightly yellow color and was 1.6 mmol/g.
A water-swellable fiber () containing -COON _a groups and having a water swelling degree of 143 c.c./g was obtained.

[Brief explanation of the drawing]

FIG. 1 is an optical micrograph of water-swellable fibers (degree of water swelling: 12 times) in a swollen state.

Claims (1)

[Claims] 1. A fiber made of an acrylonitrile polymer,
A high concentration alkali metal hydroxide aqueous solution with a concentration of 6.0 mol/1000 g or more or a low concentration alkali metal hydroxide aqueous solution coexisting with electrolyte salts with a concentration of 0.5 mol/1000 g or more was allowed to act for less than 40 minutes. By hydrophilically crosslinking the outer layer of the fiber,
A salt type carboxyl group represented by COOX (X: alkali metal or NH ₄ ) is introduced at 0.5 to 4.0 mmol/g, and the outer layer is made of a hydrophilic crosslinked polymer and an acrylonitrile polymer and/or other polymer. A method for producing a novel water-swellable fiber having a degree of water swelling of 3 to 300 c.c./g and high physical properties, the method comprising forming the fiber into a fiber composed of an inner layer portion. 2. A patent claim that uses an alkali metal hydroxide aqueous solution with a concentration of 0.25 to 6.0 mol/1000 g solution in which electrolyte salts with a concentration of 0.5 mol/1000 g solution or more are coexisting as the low concentration alkali metal hydroxide aqueous solution. The manufacturing method according to scope 1. 3. The manufacturing method according to claim 1, wherein 55% or less of the fiber outer layer is hydrophilically crosslinked based on the total fiber volume.