JPH08246341A - Method for producing water-absorbent cellulose material - Google Patents

Abstract

(57) [Abstract] [Purpose] Not only absorbs a large amount of water, but also exhibits extremely high water absorption capacity for aqueous solutions containing ions such as saline and urine. To provide a method for producing a water-absorbent cellulose material which is useful in the fields of food packaging materials, civil engineering and construction materials, and the like. [Composition] A method for producing a water-absorbent cellulose material, comprising:
A material containing cellulose is impregnated into a reaction solution consisting of a carboxyalkylating agent, an alkali metal hydroxide, a cross-linking agent, a high boiling water-soluble organic solvent and water, and then water is partially evaporated to impregnate the reaction solution. The proportion of water in the reaction solution is adjusted to 10 to 35% by weight based on the total weight of the reaction solution, and then heated to simultaneously carry out carboxyalkylation and cross-linking of cellulose to produce cross-linked carboxyalkyl cellulose. To do. The high boiling water-soluble organic solvent has 4 to 4 carbon atoms.
6 diol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbing cellulosic material having high absorption performance. More specifically, the present invention not only absorbs a large amount of water, but also exhibits an extremely high water-absorption capacity for an aqueous solution containing ions such as saline and urine, and various sanitary materials and agricultural materials. The present invention relates to a method for producing a water-absorbing cellulose material which is useful in a wide range of fields such as food packaging materials, civil engineering and construction materials.

[0002]

2. Description of the Related Art In recent years, as a water-absorbing material for an aqueous solution containing salts such as water or saline, a group of materials called super absorbent resins have been known and put into practical use. Basically, these resin materials have a chemical structure in which a water-soluble polymer is slightly crosslinked to make it insoluble in water. Examples of such a highly water-absorbing material include, for example, starch obtained by graft-polymerizing acrylonitrile and then hydrolyzed, and graft-polymerized acrylic acid metal salt,
A large number of crosslinked resins obtained by polymerizing acrylic acid with a copolymerizable crosslinker, hydrolysates of methyl methacrylate-vinyl acetate copolymers, and the like have been proposed, and some of these have been put into practical use.

Cotton, pulp, paper, cloth, sponge, etc., which are known as traditional water-absorbing materials, absorb water by a capillary phenomenon, whereas the above-mentioned superabsorbent resin has a principle of absorbing water. Because it is osmotic, it can absorb much more water than capillarity. Further, the highly water-absorbent resin has an excellent feature that it does not easily re-emit water even when pressure is applied in a water-absorbing state. Therefore, as a use of the super absorbent resin, disposable paper diapers, sanitary materials field such as sanitary products, soil water retention agents, agricultural material fields such as sheets for raising seedlings, food freshness-maintaining materials, dehydrating materials in the food field,
It is widely used as a civil engineering / building material such as a material for preventing sludge when excavating tunnels and a sheet for preventing condensation on buildings.

On the other hand, a highly water-absorbent material produced from a cellulose derivative is also known, and is biodegradable unlike the above-mentioned synthetic polymer-based water-absorbent resin, so that it is particularly suitable for the field of disposable sanitary materials. . Carboxymethyl cellulose is often used as a cellulose derivative, and is disclosed in JP-A-49-128987 and JP-A-50-8568.
No. 9, JP-A-54-52189, JP-A-54-52189
-163981, JP-A-56-28755, JP-A-58-1701, JP-A-60-944.
No. 01, Japanese Patent Application Laid-Open No. 61-89364, and the like. However, the drawbacks of the superabsorbent materials obtained by these methods are that the manufacturing process is complicated and the cost is high, and the water absorption amount of the superabsorbent material obtained is relatively low.

For example, in Japanese Patent Laid-Open No. Sho 60-71797, rayon long-fiber non-woven fabric which has been cross-linked in advance is wound around a core with a nozzle to be wound up, which is then transferred to a reaction vessel and isopropyl alcohol, methanol and water are used. Carboxymethyl cellulose is chlorinated by jetting from a nozzle while heating a treatment liquid in which sodium monochloroacetate and sodium hydroxide are dissolved in a mixed solvent, and allowing the non-woven fabric layer to pass through. Since this method uses a solvent containing alcohol as a main component, the fiber shape is maintained as it is even after carboxymethylation, and a characteristic is that a water-absorbent nonwoven fabric having flexibility and excellent texture can be obtained. However, since sodium monochloroacetate and sodium hydroxide are difficult to dissolve in an organic solvent, the concentration of these chemicals in the treatment liquid cannot be increased. Therefore, a large amount of treatment liquid must be brought into contact with the non-woven fabric in order to cause the non-woven fabric to be treated with a sufficient amount of water-absorbing chemicals, which requires a special device.

On the other hand, in JP-A-54-163981, a reaction of cellulose, a carboxyalkylating agent and a cross-linking agent in an aqueous alkaline medium is carried out to carry out alkalizing, etherification and cross-linking simultaneously in one reaction step. Further carried out with cellulose-based fibers, fibrous sheet materials or various sheet materials containing said fibers, first contacting these fibers or sheet materials with a sufficient amount of an aqueous alkaline reaction mixture, Characterized in that the reaction mixture is removed from the fiber or sheet material in contact therewith, leaving at least the amount necessary for the reaction, and treating the fiber or sheet material containing this residual aqueous alkaline reaction mixture with thermal energy. Disclosed is a method for producing a swellable cross-linked carboxyalkyl cellulose material. There.

[0007] This method is an excellent method that can relatively easily produce a water-absorbing material from a material containing cellulose, but this production method comprises an alkali, a carboxyalkylated etherifying agent and a crosslinking agent. Since a mixed aqueous solution is used, the ratio of the carboxyalkylating agent that decomposes by reacting with water is high before and during the reaction, and the ratio of the carboxyalkylating agent that effectively reacts with cellulose decreases accordingly. Therefore, it is difficult to obtain a high degree of substitution, and in order to increase the degree of substitution, the same reaction must be repeated at least twice, which complicates the process and increases the cost.

On the other hand, the inventors of the present invention impregnated a composite sheet composed of synthetic fibers and cellulosic fibers with a mixed solution composed of an alkali, a carboxymethylating agent and a crosslinking agent and then heated to crosslink the cellulose fibers. We proposed a water-absorbent nonwoven fabric obtained by using carboxymethyl cellulose (Japanese Patent Application No. 5-217912). As an improved method, a material containing cellulose is impregnated into an aqueous reaction solution consisting of a carboxyalkylating agent, an alkali metal hydroxide, a cross-linking agent, and water, and then water is partially evaporated to impregnate the impregnated aqueous reaction solution. The ratio of water in the solution is 20 per total weight of the reaction solution.
By adjusting the content to be 60% by weight and then heating, carboxyalkylation and cross-linking of cellulose are simultaneously performed, and a method for producing a water-absorbing cellulose material having a higher water-absorbing capacity than the above water-absorbing nonwoven fabric was proposed. (Japanese Patent Application No. 6-187303).

However, depending on the application, there is a case where a higher water absorption capacity and a lower price of the water absorbent material are required, and it is difficult to cope with the above-mentioned method for producing the water absorbent cellulose material. That is, water containing ions, for example, a water-absorbing material having a high water-absorbing ability for physiological saline is most in demand, but in order to impart a high water-absorbing ability for physiological saline to a material containing cellulose. Must have some degree of carboxyalkyl group substitution. Generally, in the case of carboxyalkylating cellulose with a carboxyalkylating agent and an alkali metal hydroxide, if water is used as a solvent, decomposition of the carboxyalkylating agent by water occurs during carboxyalkylation in a considerable proportion. It is known that this is the main cause of high cost.

This tendency becomes more remarkable as a high degree of substitution is achieved. Therefore, it is desirable that the amount of water is small, but since water is also one of the important reaction solvents, if it is reduced to a certain level or less, carboxyalkylation does not easily occur. In the above method proposed by the present inventors, a material containing cellulose is impregnated into an aqueous reaction liquid consisting of a carboxyalkylating agent, an alkali metal hydroxide, a crosslinking agent and water, and then water is partially evaporated to react. The reaction efficiency of the carboxyalkylating agent is increased by carrying out carboxyalkylation after adjusting the ratio of water in the liquid to the range of 20 to 60% by weight. As described above, there is an optimum range for the ratio of water after evaporation, and for example, if the ratio of water is less than 20% by weight, the value of the substitution degree of the carboxyalkyl group is rather lowered.

[0011]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention As a result of earnest studies to solve the drawbacks of the prior art, the present inventors have found that
It has been found that as long as water is used as the solvent for the carboxyalkylation, there is a limit to inhibiting the decomposition of the carboxyalkylating agent by water during the carboxyalkylation reaction. However, a mixture of water and a water-soluble organic solvent having a specific high boiling point is used as a solvent, and a reaction solution in which a carboxyalkylating agent, an alkali metal hydroxide and a crosslinking agent are dissolved is impregnated with a material containing cellulose. Then
Then, most of the water is evaporated and removed, and carboxyalkylation is carried out in an atmosphere rich in organic solvent, whereby the decomposition of the carboxyalkylating agent by water can be suppressed, and the high boiling water-soluble organic solvent is carboxyalkylated. Since it acts as a solvent for, a higher degree of substitution of the carboxyalkyl group can be easily obtained than that obtained by the above-mentioned production method, and the resulting cellulosic material, when compared at the same degree of substitution, does not contain ion-free water. Of course, it was found that extremely high water absorption was exhibited even in urine and saline containing ions, and the present invention was completed.

The object of the present invention is to solve the drawbacks of the conventional method for producing a cellulose-based water-absorbing material, and to make the water-absorbing cellulose excellent in water-absorbing ability of pure water and an aqueous solution containing ions such as urine and saline. It is to provide a method of manufacturing a material.

[0013]

The first aspect of the present invention is to impregnate a reaction solution containing a material containing cellulose with a carboxyalkylating agent, an alkali metal hydroxide, a crosslinking agent, a high boiling water-soluble organic solvent and water. Then, the water is partially evaporated, and the ratio of the water in the impregnated reaction solution is adjusted to 10 to the total weight of the reaction solution.
A method for producing a water-absorbent cellulose material, characterized in that after being adjusted to be 35% by weight, heating is carried out to simultaneously carry out carboxyalkylation and cross-linking of cellulose to produce cross-linked carboxyalkyl cellulose. is there. A second aspect of the present invention is the method for producing a water-absorbing cellulose material according to the first aspect of the present invention, wherein the high boiling water-soluble organic solvent is a diol having 4 to 6 carbon atoms. A third aspect of the present invention is the method for producing the water-absorbing cellulose material according to the first or second aspect of the present invention, in which the material containing cellulose is a composite sheet or a composite non-woven fabric composed of synthetic fibers and cellulosic fibers. The fourth aspect of the present invention is
The method for producing a water-absorbent cellulose material according to any one of the first to third aspects of the present invention, wherein the degree of substitution of the carboxyalkyl group of cellulose in the water-absorbent cellulose material is 0.65 to 0.8.

The cellulose-containing material of the present invention may be partially or wholly composed of cellulose, and examples thereof include fibrous, sheet-like, non-woven or sponge-like cellulose materials. Examples of the fibrous cellulose include pulp fibers produced from wood, non-wood pulp fibers produced from herbs, regenerated cellulose fibers and the like. As the pulp fiber produced from wood, for example, the softwood or hardwood wood is crafted, the sulfite method,
Chemical pulp obtained by digesting with soda method, polysulfide method, etc., mechanical pulp made by mechanical grinding force such as refiner, grinder, etc., semi-chemical made by mechanical grinding force after pretreatment with chemicals Pulp, newspaper, high-quality paper, deinked waste paper pulp regenerated from used office paper discharged from an office, and the like can be exemplified, and each can be used in an unbleached or bleached state.

Non-wood pulp fibers produced from herbs include, for example, cotton, Manila hemp, flax, straw, bamboo, bagasse,
Examples include fibers obtained by pulping kenaf, mulberry, sanpei, etc., in the same manner as wood pulp. As the regenerated cellulose fiber, viscose rayon, which is prepared by spinning cellulose in a solution in the form of viscose and then regenerating and spinning the cellulose in an acid,
Obtained by dissolving cellulose in a copper ammonia solution, dissolving in a non-aqueous cellulose solvent such as copper ammonia rayon, N-methylmorpholine-N-oxide regenerated and spun in an acid, and then spinning. Examples include regenerated cellulose fibers.

As the sheet-like cellulose material, paper, cellophane, rayon cloth, cotton cloth, linen cloth, cotton or a mixed cloth of hemp and synthetic fibers can be used. Examples of the non-woven cellulosic material include rayon long fiber non-woven fabric, cotton non-woven fabric produced by hydroentanglement method, wood pulp non-woven fabric by air ray method, rayon short fiber non-woven fabric by card method. Examples of the sponge-like material include those in which viscose is foamed and then washed with acid to regenerate cellulose to form a sponge-like material.

Further, in the present invention, a material containing cellulose is laminated with a synthetic fiber layer or a non-woven fabric composed of synthetic fibers and a cellulosic fiber layer or a sheet composed of cellulose fibers to form a hot melt adhesive or mechanical needling. It is also possible to use a composite sheet or a composite non-woven fabric that is compositely integrated by a method, a water jet entanglement method, or the like. As the synthetic fibers in this case, known fibers can be used as they are, and examples thereof include polyolefin fibers, polyester fibers, polyamide fibers, polyacrylate fibers, and polyurethane fibers. These may be used in the form of fibers, fiber webs, or fiber layers, but they can be preferably used in the form of sheets or non-woven fabrics. The fineness of the synthetic fiber is in the range of 0.3 to 10 denier. When the fineness exceeds 10 denier and becomes thicker, the flexibility of the nonwoven fabric decreases, and when incorporated into the composition of the water-absorbent material, the flexibility, texture, processability, etc. become poor.
Further, when the fineness is less than 0.3, the density of the nonwoven fabric tends to be high and tends to be paper-like, which makes it difficult to control the properties of the nonwoven fabric.

As a method for producing a composite sheet or a composite non-woven fabric composed of synthetic fibers and cellulosic fibers, known methods can be directly applied to the present invention. For example, "Research disclosure, 17060, June 1978", JP-A-5-253160, JP-A-5-277053.
Japanese Patent Laid-Open No. Hei 5-285083, Japanese Laid-Open Patent No. Hei 5-2
The composite sheet and the composite non-woven fabric obtained by the method of hydroentangling the synthetic fiber non-woven fabric and the paper sheet, which are described in Japanese Patent Publication No. 86100, JP-A-6-17365, etc., are excellent in texture and processability. Can be preferably used in the present invention. In this case, the synthetic fiber non-woven fabric needs to have strength to withstand the pressure of water flow, and a long fiber non-woven fabric composed of continuous filaments of the synthetic fiber is suitable.

In addition to the above-mentioned composite sheet or composite non-woven fabric, a composite sheet or composite non-woven fabric is prepared by previously mixing short fibers of synthetic fibers and cellulosic fibers to form a web by a dry or wet method. Is also good. In this case, it is desirable to partially bond the synthetic fibers to each other in order to maintain the wet tensile strength of the composite sheet or composite nonwoven fabric. The synthetic fibers may be partially bonded to each other by any known method, such as a method of spraying an adhesive and then heating and bonding, a method of mixing heat fusion fibers and bonding by heating. The method, the method using needle punch, the method using stitch bond, etc. can be used.

In the present invention, a composite sheet or a composite non-woven fabric which is preferably used is a spun bond obtained by stretching, opening and collecting a continuous filament filament group obtained by melt spinning a thermoplastic resin and subjecting it to thermocompression bonding. A paper sheet obtained by paper-making wood pulp as a cellulosic fiber with a known wet paper machine is placed on the non-woven fabric to form a laminate, and then a water column flow consisting of a high-pressure water jet penetrates from the paper sheet side to the non-woven fabric side. Is a composite sheet or composite non-woven fabric formed by intertwining pulp fibers and synthetic long fibers with each other.

In this case, the blending ratio of the synthetic continuous fiber and the cellulosic fiber is in the range of 1 to 19 cellulosic fiber to 1 synthetic fiber by weight. When the ratio of the cellulosic fibers to the synthetic fibers is less than 1, the amount of the cellulosic fibers to the synthetic long fibers is relatively small, and the water absorption amount of the resulting superabsorbent material is small. On the other hand, when the proportion of the cellulosic fibers exceeds 19 and increases, the entanglement of the synthetic long fibers and the cellulosic fibers becomes difficult to occur, and the cellulose swelled when the obtained composite sheet or non-woven fabric is made to absorb water. It is not suitable because the system fibers are likely to fall off and the wet tensile strength is further reduced.

In order to produce a water-absorbing material from the material containing cellulose of the present invention, first, the cellulose fiber contained in the material is treated with a carboxyalkylating agent, an alkali metal hydroxide, a cross-linking agent and a high-boiling point water-soluble material. It is impregnated with a reaction solution composed of an organic solvent. At this time, an alkali metal salt of halocarboxylic acid is used as the carboxyalkylating agent used in the reaction solution. As the halocarboxylic acid alkali metal salt, monochloroacetic acid alkali metal salt, monobromoacetic acid alkali metal salt, α-chloropropionic acid alkali metal salt, β-chloropropionic acid alkali metal salt, α-bromopropionic acid alkali metal salt, β-bromopropion An acid alkali metal salt or the like having a carbon number of 3 or less is preferable, and these are used alone or by appropriately selecting and mixing them. In terms of cost, sodium monochloroacetate is the cheapest and should be used.

Sodium hydroxide is most preferred as the alkali metal hydroxide, but other alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide can also be used. The cross-linking agent is a cross-linking agent that cross-links with cellulose in an alkaline reaction liquid, and has a boiling point as high as possible and is close to non-volatile. In the present invention, since a step of impregnating a material containing cellulose into a reaction solution and then removing the water by evaporating water is included, a crosslinking agent having a low boiling point that is volatilized during this step is disadvantageous. Examples of the crosslinking agent that can be used in the method of the present invention include ethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol diglycidyl ether, polyepoxy compounds such as diepoxybutane; divinyl sulfone, methylenebisacrylamide. Such as divinyl compounds; dichloropropanol, dibromopropanol, dichloroacetic acid and other polyvalent halogen compounds;
In addition, polyvalent aziridine compounds and the like can be mentioned, and at least one kind is used by appropriately selecting. Epichlorohydrin, which is often used for crosslinking a cellulose derivative and can impart excellent pure water absorption performance, is not suitable for the present invention because of its low boiling point.

As the high-boiling point water-soluble organic solvent, a solvent which is compatible with water, has a high solubility of the alkali metal hydroxide, has a boiling point as high as possible, and is near nonvolatile is used. Since the present invention includes a step of evaporating and removing water after impregnating the material containing cellulose into the reaction solution as described above, a low-boiling point water-soluble organic solvent that volatilizes during this step is disadvantageous. is there. As the solvent satisfying these conditions, an aliphatic diol having 4 to 6 carbon atoms is preferably used. When a diol having less than 4 carbon atoms is used,
It cannot be used because the phenomenon in which the degree of substitution of the carboxyalkyl group decreases conversely is observed. Further, when the carbon number exceeds 6 and becomes large, it becomes incompatible with water and cannot be used.

Specific examples of the high-boiling point water-soluble organic solvent that can be used in the present invention include 1,4-butanediol,
1,3-butanediol, 2,3-butanediol,
1,5-pentanediol, 1,2-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol and the like can be mentioned, which are appropriately selected from these. , Either alone or as a mixture. Regarding the hydroxyl group of the diol, the secondary or tertiary hydroxyl group tends to be more effective than the primary hydroxyl group. In this sense, 2,3-butanediol, 2,
4-Pentanediol and 2-methyl-2,4-pentanediol are most preferably used in the present invention.

The reaction solution of the present invention is prepared by dissolving the above-mentioned carboxyalkylating agent, alkali metal hydroxide, crosslinking agent and high boiling water-soluble organic solvent in water. The ratio of water to the total weight in the reaction solution varies depending on the kind of the carboxyalkylating agent or the alkali metal hydroxide used, and the solubility is also similar depending on the mixing ratio of the high-boiling point water-soluble organic solvent. Since it varies, it cannot be specified unambiguously, but if the proportion of water is low within the solubility range of the carboxyalkylating agent and the alkali metal hydroxide, the energy cost for evaporation of water following impregnation will be low, so it will be less. It is advantageous. However, if the concentration is too high, the reaction liquid becomes unstable and handling becomes difficult. Therefore, in the present invention, the ratio of water to the total weight of the reaction liquid is in the range of 40 to 60% by weight when sodium hydroxide is used. A carboxyalkylating agent, an alkali metal hydroxide, a cross-linking agent and a high boiling water-soluble organic solvent are dissolved in water so that The proportion of this water varies slightly depending on the type of the carboxyalkylating agent, the alkali, and the crosslinking agent used, and therefore the water content varies slightly.

The mixing molar ratio of the alkali metal hydroxide and the carboxyalkylating agent is adjusted in the range of 0.8 to 1.2 of alkali metal hydroxide / carboxyalkylating agent. The more outside this range, one of the chemicals remains unreacted, which is uneconomical. The mixing amount of the cross-linking agent varies depending on the type of the cross-linking agent or the reaction conditions, but is 0.1 to 30 wt% based on the weight of cellulose. The high boiling point water-soluble organic solvent is 5 to 4 per total weight of the reaction solution.
Used at 0% by weight. If this ratio is less than 5% by weight,
There is almost no effect of using a high-boiling point water-soluble organic solvent mixed, and when the ratio becomes 40%, the effect is saturated, so there is no meaning. On the other hand, if it exceeds 40% by weight, the carboxyalkylating agent and the alkali metal hydroxide are difficult to be dissolved, which is not suitable.

Thereafter, the reaction solution prepared as described above is impregnated with a material containing cellulose. The impregnation amount is such that the molar ratio of carboxyalkylating agent to glucose residue is 1 in carboxyalkylating agent / glucose residue. .0 to
It is adjusted to the range of 1.8 (mol / mol). When the molar ratio is less than 1.0, it becomes impossible to obtain a substitution degree higher than 0.65, so that a material having a high water absorption cannot be obtained. On the contrary, when the molar ratio exceeds 1.8, the substitution degree hardly increases even if a large amount of the carboxyalkylating agent is added, which is economically disadvantageous. Further, it is advantageous to increase the total molar ratio by repeating the reaction two or more times in terms of increasing the substitution degree, but it is disadvantageous in terms of cost.

There is no particular limitation on the method of impregnating the above-mentioned reaction solution into the material containing cellulose, but after immersing the material containing cellulose in an excess amount of the reaction solution, it is squeezed by a roll to remove the excess reaction solution. Alternatively, a sheet-shaped material may be coated with a previously calculated amount of the reaction liquid using a coater. Further, if the material is a short fibrous material, a predetermined amount of the reaction liquid may be added and mixed while stirring in a container equipped with a stirrer such as a kneader. The material after the impregnation is removed by evaporating a part of the water in the reaction solution contained in the material by heating with air blowing under the condition of 50 to 150 ° C. for ten to several seconds to 8 minutes, The ratio of water to the total weight of the reaction solution is adjusted to be 10 to 35% by weight.

The method of evaporating water is not particularly limited, but a method of evaporating water in the shortest possible time is desirable. Since the reaction rate of carboxyalkylation is considerably high, if evaporation time is too long, for example, 30 minutes or more, the carboxyalkylation will proceed or end during the evaporation of water. No effect. For such evaporation, a method of evaporating water in a dryer or a reaction vessel while applying hot air in the above temperature range is convenient. Under the above evaporation conditions of the present invention, carboxyalkylation hardly progresses (for example, the degree of substitution is 0.1 or less). Even when the content of water in the reaction solution contained in the material after evaporation is less than 10% by weight or higher than 35% by weight, a considerably high degree of substitution can be achieved in one reaction, It is difficult to obtain one with excellent water absorption.

In the present invention, immediately after the proportion of water in the reaction solution is adjusted in this manner, as described above, almost no carboxyalkylation has occurred. Therefore, the material is heated to carboxyalkylate. And cause the crosslinking reaction. In this case, even if water evaporates during heating and escapes to the outside of the system, the proportion of water in the reaction liquid contained in the material needs to be maintained within the above range. In this operation, the cellulosic material containing the reaction liquid in which the proportion of water is adjusted is continuously passed through a heating device or covered with a sheet to make a sealed state, and then the reaction temperature is 50 to 50 in a batch type. 1
It can be easily performed by heating at 10 ° C. When the reaction temperature is 50 ° C. or lower, it takes a long time to complete the reaction. On the contrary, when the reaction temperature is higher than 110 ° C., the degree of substitution of the water-absorbing material obtained is low, resulting in poor water absorption performance. In addition, the water-absorbent material often turns yellow, which is not suitable.

The heating may be carried out from the outside of the cellulosic material, but when the amount of the cellulosic material is large, the above temperature range is naturally reached by the reaction heat of the carboxyalkylation. The object can be achieved only by leaving it under a closed condition or under an open condition. The reaction time is
It cannot be determined regardless of the reaction temperature, but it is in the range of 10 minutes to 4 hours. If the reaction time is less than 10 minutes, the reaction will not be completed sufficiently even if the temperature is increased, and if the reaction time is longer than 4 hours, the reaction will be completed. .

The pure water absorption of a cellulosic material having crosslinks and carboxyalkyl groups is determined mainly by the degree of substitution of carboxyalkyl groups and the crosslink density, and the pure water absorption is theoretical as the degree of substitution of carboxyalkyl groups increases. However, in the present invention, the range of substitution degree of 0.65 to 0.8 that can be achieved by one reaction is suitable. When the substitution degree is within this range, the water absorbent material of the present invention has an extremely high water absorption of pure water and water containing ions such as saline. The reason for this has not been clarified so far, but the decomposition of the carboxyalkylating agent by water in the reaction solution is suppressed, the degree of substitution is increased, and the distribution state of the carboxyalkyl groups in the cellulose molecule is made uniform. It is supposed that Therefore, the water-absorbent material of the present invention shows a high water absorption amount of pure water and saline when compared with the same degree of substitution. The upper limit of the degree of substitution is about 1.2.
Even if the water content exceeds 1.2, the water absorption will be almost saturated. And a high degree of substitution exceeding 0.8 cannot be achieved unless the reaction is repeated twice or more,
Then, the process becomes extremely complicated and the cost of the resulting water-absorbing material becomes high, which is disadvantageous.

The substitution degree within the range of the present invention described above is such that the amount of the carboxyalkylating agent and the alkali metal hydroxide added to the cellulose, the amount of the high boiling water-soluble organic solvent added, and the reaction liquid after the water is evaporated. It is determined by the total effect of the water content, reaction temperature, reaction time, etc., and if necessary, these factors are appropriately selected, combined and adjusted, and adjusted to a suitable range of substitution degree. Further, the pure water absorption becomes higher as the crosslink density becomes smaller, but if it is too small, the gel strength upon absorption of water becomes weak and the water-soluble carboxyalkylcellulose salt remains, which is not preferable because it becomes sticky. On the contrary, if the crosslink density is too high, the amount of water absorption decreases, so it is necessary to set the optimum crosslink density depending on the application. In the present invention, the crosslinking density is adjusted by adjusting the addition rate of the crosslinking agent.

The cellulosic material which has undergone the carboxyalkylation and the cross-linking reaction contains a large amount of inorganic salts and decomposed products of the carboxyalkylating agent, and it is necessary to remove them for purification. Any method of For example, a method of removing impurities by washing with a mixture of water and an organic solvent compatible with water such as lower aliphatic alcohols such as methanol, ethanol and isopropyl alcohol can be preferably used.

The present invention is greatly different from the method described in Japanese Patent Application No. 6-187303 in that the reaction solution contains a water-soluble high-boiling point organic solvent. This water-soluble high-boiling organic solvent is
Since it acts as a solvent for carboxyalkylation and has a small effect of decomposing a carboxyalkylating agent unlike water, a carboxyalkylation reaction of cellulose can be efficiently obtained. That is, the water-soluble organic solvent alone has a small dissolving power for the carboxyalkylating agent and the alkali metal hydroxide, but when used as a mixed solvent with water, the carboxyalkylating agent and the alkali metal hydroxide are well dissolved. Therefore, a uniform reaction solution can be obtained. Therefore, by impregnating this uniform reaction solution having a high concentration of the carboxyalkylating agent with the material containing cellulose, the contact between the cellulose and the carboxyalkylating agent can be carried out uniformly and sufficiently. It is possible to obtain a higher water absorption performance by comparing the high substitution degree with the same substitution degree.

Further, the cellulosic material after impregnated with the reaction liquid has a water content of 10 to 10 by removing water by hot air or the like.
It is adjusted to 35% by weight. In this case, since the water-soluble high-boiling point solvent hardly evaporates, it remains in the material containing cellulose as it is, and serves as a reaction solvent for carboxyalkylation. , A side reaction in which carboxyalkylation can be efficiently carried out even if the proportion of water in the reaction solution is significantly reduced, and moreover, water reacts with the carboxyalkylating agent to decompose the carboxyalkylating agent. These synergistic effects make a very significant contribution to the carboxyalkylation reaction, since
In this way, an expensive carboxyalkylating agent can be effectively used, the cost can be kept low, and a high degree of substitution can be obtained in a single reaction. Therefore, the water-absorbing material thus obtained can be obtained. Shows a better water absorbency with respect to water and saline.

[0038]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples and comparative examples,% means% by weight.

Example 1 ^On a spunbonded non-woven fabric having a basis weight of 12 g / m ^{2 and made} of continuous filament polypropylene having a fineness of 2.5 denier, a softwood bleached kraft pulp was used as cellulose, and the paper was made by a known wet paper machine. Rice grammage 76g / m ²
After stacking the paper sheets of to form a laminated body, a water column flow composed of a high-pressure water jet is jetted from the paper sheet side of the laminated body toward the spunbond nonwoven fabric, and the synthetic long fibers and pulp fibers are hydroentangled, A nonwoven fabric and a paper sheet were integrated to prepare a composite nonwoven fabric having a rice basis weight of 80 g / m ² . This composite non-woven fabric was cut into a size of 20 cm × 30 cm (weight 4.8 g), and the non-woven fabric was treated with sodium hydroxide 7.09%, sodium monochloroacetate 20.64%, ethylene glycol diglycidyl ether 1.68%, 2 , 3-butanediol (4 carbon atoms, boiling point: 176.7 at 742 mmHg)
C) 14.29% and water 56.30% for 1 minute, then take out, sandwich between filter papers and press, 3.5 g of reaction solution (carboxyalkylated) per 1 g of absolutely dry composite nonwoven fabric. Agent / glucose residue = 1.3 mol / mol).

Next, an electrothermal hot air dryer equipped with an exhaust facility was maintained at 50 ° C., and while exhausting, the composite nonwoven fabric containing the reaction solution was placed in this dryer for 5 minutes to evaporate water.
The ratio of water in the reaction liquid contained in the composite nonwoven fabric is 23%
Met. The composite sheet in which the proportion of water was adjusted in this way was taken out of the dryer, immediately put in a polyethylene bag and sealed to prevent water from evaporating, and heated again in a dryer at 50 ° C. for 3 hours to react. The pulp fibers were carboxymethylated and crosslinked. Then, the composite non-woven fabric was immersed in a 70% aqueous methanol solution and then taken out,
The operation of sandwiching between filter papers and pressing was repeated 4 times to thoroughly wash the composite nonwoven fabric. Finally, 1
After soaking in 00% methanol, the product was taken out, sandwiched between filter papers, pressed, and then air-dried to obtain a water-absorbent cellulose material composed of a composite nonwoven fabric. The pure water absorption, the physiological saline absorption and the degree of substitution of the thus obtained cellulose material were measured by the test methods shown below, and their quality was evaluated.

Test method (1) A test sample having a pure water absorption of 1 g was used as a 250 cm 10 cm × 10 cm sample.
It is sealed in a mesh nylon net bag, and this is deionized through an ion-exchange resin to distill the water.
After dipping for a minute to absorb water, and then pulling it up and suspending it and draining it for 10 minutes, the weight of the test sample was measured, and the weight of pure water absorbed per g of the absolutely dry test sample (g ) Is used to indicate the amount of water absorption. (2) Absorption of physiological saline solution The measurement was performed in the same manner as (1) Absorption of pure water, except that a 0.9% NaCl aqueous solution was used instead of pure water.

(3) A test sample having a degree of substitution of 1 g was placed in a flask, and 50 ml of a methanol-hydrochloric acid solution (a mixed aqueous solution prepared by dissolving hydrogen chloride in a 70% aqueous methanol solution to a concentration of 1 mol / liter).
Was added, the mixture was allowed to stand for 1 hour, washed thoroughly with methanol to completely remove hydrochloric acid, and air-dried. Then, the air-dried sample was placed in a 300 ml Erlenmeyer flask, about 30 ml of 0.1N sodium hydroxide solution and 100 ml of pure water were added, and the mixture was slowly stirred for 1 hour, and then phenolphthalein was added with 0.1N hydrochloric acid solution. Was used as an indicator, and the substitution degree was calculated by the formulas (1) and (2). Y = 0.1A-0.1B (1) Substitution degree = 162Y / (1000W-80Y) (2) However, A: Amount of 0.1N sodium hydroxide solution (m
l) B: Amount of 0.1N hydrochloric acid (ml) Y: Amount of carboxymethyl group (milliequivalent) W: Weight of carboxymethyl cellulose (g) Note: Formula (2) is sodium carboxymethyl cellulose (Examples 1 to 7) In case of other alkali metal salt or other carboxyalkylating agent, the constant in the formula needs to be slightly changed.

Example 2 A composite non-woven fabric having a basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was used to prepare 7.09% sodium hydroxide and 2 monosodium monochloroacetate.
0.64%, ethylene glycol diglycidyl ether 1.68%, 2,4-pentanediol (carbon number 5, boiling point: 760 mmHg, 197.5 ° C.) 14.29%, water 56.30% A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the material was impregnated.
Pure water absorption of the cellulose material thus obtained,
The amount of absorbed physiological saline and the degree of substitution were measured in the same manner as in Example 1 to evaluate the quality.

Example 3 A composite non-woven fabric having a rice basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was used to prepare sodium hydroxide 7.09% and sodium monochloroacetate 2
0.64%, ethylene glycol diglycidyl ether 1.68%, 2-methylpentane-2,4-diol (carbon number 6, 198.3 ° C. at 760 mmHg) 14.2
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the reaction solution containing 9% and 56.30% water was impregnated. The water absorption of pure water, the water absorption of physiological saline, and the degree of substitution of the thus obtained cellulose material were measured in the same manner as in Example 1, and the quality was evaluated.

Example 4 A composite nonwoven fabric having a rice basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was impregnated with the reaction solution, and then the composite nonwoven fabric was placed in a dryer. A water-absorbent cellulose material was produced in the same manner as in Example 1 except that water was evaporated by heating for 3 minutes and the proportion of water in the reaction liquid contained in the composite nonwoven fabric was adjusted to 33%. The water absorption of pure water, the water absorption of physiological saline, and the degree of substitution of the thus obtained cellulose material were measured in the same manner as in Example 1, and the quality was evaluated.

Example 5 A synthetic nonwoven fabric having a basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was impregnated with the reaction solution, and the composite nonwoven fabric was then dried in a dryer. A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the water was evaporated by heating for 7 minutes to adjust the ratio of water in the reaction liquid contained in the composite nonwoven fabric to 12%. The pure water absorption, the physiological saline absorption and the degree of substitution of the thus obtained cellulose material were measured in the same manner as in Example 1,
The quality was evaluated.

Example 6 Softwood bleached kraft pulp (Hunter whiteness 84.5%)
Double-arm kneader (model: S1-
1, manufactured by Moriyama Seisakusho, rotation speed of arm: 60 rpm and 100
rpm) and sodium hydroxide 7.09
%, Sodium monochloroacetate 20.64%, ethylene glycol diglycidyl ether 1.68%, 2,3-butanediol 14.29%, water 56.30% 70 g of reaction liquid (carboxyalkylating agent / glucose residue = 1 0.1 mol / mol) was added and the mixture was stirred and mixed at a pulp solids concentration of 22.2% for 10 minutes. This mixture was ground with a household mixer to give a cotton-like material. Next, spread it thinly on a stainless steel vat, evaporate water for 3 minutes while evacuation at 60 ° C. in the same dryer as in Example 1, and adjust the ratio of water in the contained reaction liquid to 25%. did.

Subsequently, the cotton-like material was placed in a polyethylene bag and sealed to prevent water from evaporating further, and then reacted at 60 ° C. for 2 hours. After completion of the reaction, the obtained cotton-like material was put into 1000 ml of 70% methanol, stirred for 1 hour, and then filtered using a glass filter (2G). 70% more fiber on glass filter
It was thoroughly washed with 2000 ml of methanol, then washed with 500 ml of 100% methanol and then vacuum dried to prepare a fibrous water-absorbent cellulose material. The water absorption of pure water, the water absorption of physiological saline and the degree of substitution of the thus obtained cellulose material were measured in the same manner as in Example 1 to evaluate the quality.

Example 7 Hardwood bleached kraft pulp (Hunter whiteness 84.4%)
80% and bleached softwood kraft pulp (Hunter whiteness 8
4.5%) Rice basis weight 6 made from 20% mixed pulp
A 4 g / m ² paper sheet was cut into a size of 20 cm × 30 cm (weight absolutely dry 3.84 g), and this was cut with potassium hydroxide 1
1.94%, sodium monochloroacetate 24.83%,
Ethylene glycol diglycidyl ether 1.96%,
After soaking in a reaction liquid consisting of 16.34 of 2,3-butanediol and 44.93% of water for 1 minute, the product was taken out and pressed between filter papers, and 3.2 g of the reaction liquid (carbox Alkylating agent / glucose residue = 1.1 mol / mol) was adjusted.

Next, an electrothermal hot air drier equipped with the same exhaust equipment as in Example 1 was kept at 50 ° C., and while evacuation was performed, a paper sheet containing the reaction solution was placed in the drier and water was added for 5 minutes. Evaporated to adjust the proportion of water in the reaction liquid contained in the paper sheet to 25%. Then, the paper sheet was taken out from the dryer, put in a polyethylene bag and sealed, and the reaction was carried out again in a dryer at 50 ° C. for 3 hours to prevent water from evaporating, to carry out carboxymethylation and crosslinking. Then, the paper sheet is dipped in a 70% aqueous methanol solution, taken out, sandwiched between filter papers and pressed.
Repeated times to thoroughly wash the paper sheet. Finally, the paper sheet was immersed in 100% methanol and taken out, sandwiched between filter papers and pressed, and then air-dried to produce a sheet-shaped water-absorbent cellulose material. The pure water absorption, the physiological saline absorption and the degree of substitution of the thus obtained cellulose material were measured to evaluate the quality.

Comparative Example 1 A composite non-woven fabric having a rice basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was used to prepare sodium hydroxide 8.38% and sodium monochloroacetate 2
After soaking in a reaction liquid consisting of 4.40%, ethylene glycol diglycidyl ether 0.68% and water 66.54% for 1 minute, taken out, sandwiched between filter papers and pressed, 3 g per 1 g of absolutely dry composite nonwoven fabric. The reaction solution (carboxyalkylating agent / glucose residue = 1.3 mol / mol) was adjusted to be contained. Then, an electrothermal hot air dryer equipped with an exhaust facility was maintained at 50 ° C., and while exhausting, the composite sheet containing the reaction solution was placed in this dryer for 5 minutes to evaporate water. The proportion of water in the reaction liquid contained in the composite nonwoven fabric was 42%. The composite sheet in which the proportion of water was adjusted in this manner was taken out of the dryer, immediately put in a polyethylene bag and sealed to prevent water from evaporating, and then the water was removed again.
The pulp fibers were carboxymethylated and crosslinked by heating in a dryer at 0 ° C. for 3 hours for reaction. Then, this composite nonwoven fabric is immersed in a 70% aqueous methanol solution, taken out, sandwiched between filter papers and pressed, and this operation is repeated 4 times.
The composite sheet was thoroughly washed. Finally, 1
It was immersed in 00% methanol, taken out, sandwiched between filter papers, pressed, and then air-dried to obtain a non-woven fabric-like water-absorbent cellulose material. The pure water absorption of the cellulose material thus obtained, the physiological saline absorption and the degree of substitution were measured,
The quality was evaluated.

Comparative Example 2 A composite non-woven fabric having a basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was used to prepare sodium hydroxide 7.09% and sodium monochloroacetate 20.
64%, ethylene glycol diglycidyl ether 1.
68%, propylene glycol (carbon number 3, boiling point: 76
188.2 ° C at 0 mmHg) 14.29%, water 56.3
A water-absorbent cellulose material was produced in the same manner as in Example 1 except that the reaction liquid containing 0% was impregnated. The pure water absorption amount, the saline water absorption amount and the degree of substitution of the thus obtained cellulose material were measured and the quality thereof was evaluated.

Comparative Example 3 In the reaction solution having the same composition as used in Example 1, 2,2-diethyl-1,3-instead of 2,3-butanediol was used.
Propanediol (C7, boiling point: 1 at 13 mmHg
It was attempted to prepare a reaction solution using (31 ° C), but when the propanediol was mixed and used, 2,2-diethyl-
Since the 1,3-propanediol layer and the aqueous layer containing the alkali metal hydroxide were phase-separated, a uniformly mixed reaction solution could not be obtained and impregnation treatment could not be performed.

Comparative Example 4 A composite non-woven fabric having a basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was impregnated with the reaction solution, taken out, dried and then dried. A water-absorbent cellulose material was produced in the same manner as in Example 1 except that water was evaporated in the vessel for 2 minutes to adjust the proportion of water in the reaction liquid contained in the composite nonwoven fabric to 40%. The pure water absorption, the physiological saline absorption and the degree of substitution of the thus obtained cellulose material were measured to evaluate the quality.

Comparative Example 5 A composite non-woven fabric having a basis weight of 80 g / m ² obtained by hydroentangling the same synthetic long fibers and pulp fibers as in Example 1 was impregnated with the reaction solution, taken out, dewatered and dried. A water-absorbent cellulose material was produced in the same manner as in Example 1 except that water was evaporated in the vessel for 9 minutes to adjust the proportion of water in the reaction liquid contained in the composite nonwoven fabric to 8%. The pure water absorption, the physiological saline absorption and the degree of substitution of the thus obtained cellulose material were measured to evaluate the quality.

The results obtained in Examples 1 to 5 are shown in Table 1.
It was shown to.

[0057]

[Table 1]

As is apparent from Table 1, according to the present invention, the water absorbent cellulose material obtained has a pure water absorption of 5 or less.
5 to 65 g / g, water absorption of physiological saline is 23 to 28 g /
Since it is in the range of g and is extremely high, and a relatively high degree of substitution of 0.65 to 0.8 can be achieved in one carboxyalkylation reaction, a water-absorbing cellulose material can be efficiently produced (Examples 1 to 1). 7). On the other hand, Japanese Patent Application No. 6-1
When the reaction solution does not contain a water-soluble high-boiling-point organic solvent (Comparative Example 1) as in the method described in No. 87303, the degree of substitution that can be achieved is higher than that of the present invention (Examples 1 to 4). It is low and almost equal to the low one of the present invention (Examples 4 to 7), but pure water absorption (51 g / g) and saline water absorption (2
3 g / g) is low (comparison between Examples 1 to 7 and Comparative Example 1).

When a diol having 3 carbon atoms was used as the water-soluble high-boiling organic solvent (Comparative Example 2), a low degree of substitution (0.5
Only 2) is obtained, and the pure water absorption (40 g / g) and the salt water absorption (20 g / g) are also low. When a diol having 7 carbon atoms is used (Comparative Example 3), phase separation occurs when an organic solvent is mixed, and a uniform reaction liquid itself cannot be generated. On the other hand, even if the reaction material produced using an appropriate water-soluble high-boiling point organic solvent is contained in the cellulose material,
When the material is heated to evaporate and remove water, when the proportion of water in the reaction solution is high (40%) due to insufficient removal of water (Comparative Example 4) and vice versa, When too much water was removed and the proportion of water in the reaction solution was too low (8%) (Comparative Example 5), the degree of substitution was also less than 0.65, and the pure water absorption amount and the saline water absorption amount were a little. It will be low.

[0060]

INDUSTRIAL APPLICABILITY According to the present invention, a high degree of substitution of carboxyalkyl groups (0.6
5 to 0.8), the treatment cost is low, and it has an extremely excellent water absorption capability not only for pure water but also for aqueous solutions containing ions such as saline and urine. Widely used in the field of sanitary materials such as disposable paper diapers and sanitary products, fields of agricultural materials such as soil water retention agents, sheets for raising seedlings, food fields such as food freshness-retaining materials and dehydration materials, and building dew condensation prevention sheets for buildings. The effect of providing a method for producing a water-absorbing cellulose material that can be used for

Claims (4)

[Claims] 1. A material containing cellulose is impregnated into a reaction solution consisting of a carboxyalkylating agent, an alkali metal hydroxide, a cross-linking agent, a high-boiling point water-soluble organic solvent and water, and then the water is partially evaporated to impregnate it. After adjusting the ratio of water in the reaction solution to 10 to 35% by weight based on the total weight of the reaction solution, heating is performed to simultaneously carry out carboxyalkylation and cross-linking of the cellulose to form a cross-linked carboxyalkyl cellulose. A method for producing a water-absorbent cellulosic material, which comprises: 2. The high-boiling water-soluble organic solvent has 4 to 4 carbon atoms.
6. The method for producing a water-absorbing cellulose material according to claim 1, wherein the diol is No. 6. 3. The method for producing a water-absorbent cellulose material according to claim 1, wherein the material containing cellulose is a composite sheet or a composite non-woven fabric composed of synthetic fibers and cellulosic fibers. 4. The substitution degree of carboxyalkyl group of cellulose in the water-absorbent cellulose material is 0.65 to 0.8.
4. The method for producing a water-absorbing cellulose material according to claim 1, wherein